Studies in Surface Science and Catalysis 131 CATALYTIC POLYMERIZATION OF CYCLOOLEFINS Ionic, Ziegler-Nwtta and ring-opening met~he~s polymerization
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Studies in Surface Science and Catalysis Advisory E d i t o r s :
B. D e l m o n
a n d J.T. Y a t e s
Vol. 131
CATALYTIC POLYMERIZATION OF CYCLOOLEFINS Ionic, Ziegler-Natta and ring-opening metathesis polymerization
Valerian Dragutan
Institute of Organic Chemistry of the Romanian Academy, Bucharest, Romania
Roland
Streck
H~ils AG, Marl, Germany
20O0
ELSEVIER Amsterdam
- - L a u s a n n e - - N e w York - - O x f o r d - - S h a n n o n J
Singapore -- Tokyo
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V
To the outstanding community of prominent scientists and researchers, who devoted their efforts and ingenuity to the development of this facinating field of polymer chemistry and greatly inspired us in our work.
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vii
PREFACE
Ring-opening metathesis polymerization (ROMP) of cycloolefins is one of the most remarkable findings in polymer chemistry since the discovery of Ziegler-Natta polymerization of olefins. The unprecedented development of the new catalytic process originates in the high levels of achievement in olefin metathesis as well as in the abundant data accumulated on Ziegler-Natta polymerization. The impressive development of both ROMP and Ziegler-Natta polymerization inspired us to also take a broader view backwards to the existing research conducted on the cationic polymerization of cycloolefins and on its anionic counterpart, in order to outline the apparent connections between these earlier catalytic processes and the new discovery. As a natural consequence of this spectacular evolution, an array of new cycloolefin derived products have made their way to industrial sc~e manufacture. Moreover, a larger range of licensed products with excellent chemical, electrical, mechanical, optical and thermal properties expect their turn to be commercialized. Research in the area of catalytic polymerization of cycloolefins is intensely continuing in various academic and industrial teams, and many practical applications are emerging and, at the same time, further thermodynamic, kinetic, mechanistic and stereochemical aspects of these reactions are being elucidated. It is significant to follow the strong increase of the number of patents and publications, especially on ring-opening metathesis polymerization (ROMP) and Ziegler-Natta copolymerization, during the last four decades, which have promoted a range of new commercial products and opened the way to potential other applications in the near future. The obvious interest in this area is manifested by the many outstanding contributions presented at various international conferences and symposia on catalysis, organometallics and polymer chemistry. The book "Catalytic Polymerization of Cycloolefins: Ionic, ZieglerNatta and Ring-Opening Metathesis Polymerization" highlights the major trends appeared in the field of cycloolefin polymerization over the last four decades. The book critically evaluates the two main pathways that cycloolefins can follow under the action of specific catalytic systems,
VIII namely vinyl and ring-opening metathesis polymerization, both allowing the manufacture of numerous products with wide applicability in modem technologies. Furthermore, related emerging synthetic procedures are also elaborately outlined emphasizing the unlimited possibilities of these catalytic reactions under a variety of conditions. The wealth of information is systematically and logically compiled according to the basic catalytic processes involved, the types of monomers and catalysts, the structure and properties of the produced polymers. A distinctive feature is an exhaustive literature survey, till the end of 1999, with special accent on published patents and industrial applications. In the first introductory chapter, the short presentation of some general aspects of cycloolefin polymerization is followed by essential definitions and a description of reaction types, the scope and limitations of these catalytic reactions are further presented. The next three chapters largely illustrate a wide range of monomers, catalytic systems and reaction conditions. Special attention is devoted to the versatility of cycloolefin monomers and minute synthesis of substituted monomers, to the recently developed, selective chiral metallocene catalysts, to well-defined, living metathesis catalytic systems, to catalysts tolerant toward functionlities or water soluble catalytic systems as well as to the main reaction parameters. Chapters 5 through 10 cover the broad area of the studied cationic, anionic, Ziegler-Natta and ring-opening metathesis polymerization reactions of cycloolefins. Treatment of these processes is essentially organized on monocyclic, bicyclic and polycyclic olefins. Functionalized or heteroatomcontaining monomers are also included. The next chapter deals with the vast field of cycloolefin copolymerization. Herein, the multiple reaction types are briefly presented, then the three oopolymerization modes (cationic, Ziegler-Natta and ringopening metathesis) are fully illustrated. Of special significance from a theoretical and practical point of view is Chapter 12 focusing on the structure and properties of poly(cycloolefin)s, as determined from solution and solid state investigations. Despite the fact that the difficult task of structure elucidation makes use of most sophisticated spectroscopic methods, sometimes particular properties of polymers, such as insolubility in common solvents or infusibility in normal conditions, can render them practically not r Chapters 13 through 16 thoroughly discuss the thermodynamics, kinetics, mechanisms and stereochemistry of catalytic cycloolefin polymerization. The fundamental thermodynamic and kinetic aspects of
IX vinyl and ring-opening metathesis polymerization are separately dealt with and conclusions on the reaction mechanisms are drawn therefrom. Stereochernistry topics are interpreted on the basis of the presently accepted reaction mechanisms. The most important related processes, such as Ziegler-Natta polymerization of olefins and dienes, olefin metathesis, ring-opening metathesis (ROM), ring closing metathesis (RCM), acyclic diene metathesis (ADMET) and polymerization of acetylenes are surveyed in the following chapter. The last chapter of the book offers the reader the ultimate result of decades of outstanding research in these areas - industrial applications of cycloolefin polymers, with some emerging strategies for new products. Herein, pertinent data about synthesis procedures, physical-mechanical and chemical properties, as well as economical aspects are made available. The monograph, a well-constructed and stimulating guide to the ever-growing area of catalytic polymerization of cycloolefins, is intended mainly for the specialist research audience but will be of great use to post graduates and teaching staff with an interest in current developments in this field. Since the book includes reference to more general aspects and related fundamental reviews, it addresses itself also to chemical engineers, researchers and advanced students working in catalysis, organicYorganometaUic chemistry, petrochemistry and macromolecular chemistry. At the same time, it is hoped that some parts of the work will be useful to specialists from areas applying specialty polymers, e.g. computer technology, telecommunications, optics, microelectronics, fine mechanics, medicine, transportation, construction, sports and agriculture. The authors take a great pleasure in gratefully acknowledging the generous assistance of many colleagues and collaborators and are especially indebted to Drs. H. Eleuterio (DuPont), N. Calderon (Goodyear Tire & Rubber Co.) and G.D. Benedikt (BFGoodrich Co.) and Professors A.J. Amass (University of Aston, Birmingham, UK), J.M. Basset (Villeurbanne, Fr), H.-H. Brintzinger (University of Konstanz), T.C. Chung (PennState University), M. Farona (UNC, Greensboro), W.J. Feast (Durham University, UK), R.H. Gmbbs (Caltech, Pasadena), H HOcker (RWTH, Aachen), K. Hummel (TU, Graz), W. Kaminsky (University of Hamburg), T.J. Katz (Columbia University), R.R. Schrock (MIT, Cambridge), F. Stelzer (TU, Graz), E. Thom-Csanyi (University of Hamburg) and K. Weiss (Bayreuth University) for kindly providing manuscripts or reprints of their extensive work. We are much obliged to Drs. K.-M. Diedrich (Htils AG), A.E. Martin (Hercules Co), H.-T. Land (Hoechst A.G.) for providing
X valuable information on properties and technological applications of commercial cycloolefin polymers. One of the authors (R.S.) thanks his former employers at Hials AG for permission to use their information facilities. The other author (V.D.) deeply thanks his wife, Dr. lleana Dragutan, for helpful discussions and relevant suggestions during the manuscript elaboration and his son, Matei Dragutan, for his generously offered expertise in producing the graphical material included in this work. Very special thanks are due to Elesevier Science, and particularly to Drs. A. van der Avoird and H. Manten-Werker, for their kind and stimulating support for the publication of this book.
Bucharest, Romania Marl, Germany March, 2000
Valerian Dragutan Roland Streak
X1
CONTENTS
PREFACE ......................................................................... Chapter 1. I.I. 1.2. 1.3. 1.4.
VII
INTRODUCTION .................................................... ~ e r a l Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Definitions and Reaction Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scope and Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 l 2 11 12
Chapter 2. C Y C L O O L E F I N M O N O M E R S . TYPES AND S Y N T H E S E S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2. I. Monomers for Cationic Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.2. Monomers for Anionic Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.3. Monomers for Ziegler-Natta Polymerization . . . . . . . . . . . . . . . . . . . . 19 2.4. Monomers for Ring-Opening Metathesis Polymerization ...... 21 2.4.1. Monocyclic Olefins for Ring-Opening Metathesis Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 l 2.4.2. Bicyclic and Polycyclic Olefins for Ring-Opening Metathesis Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.4.3. Monomers with Functional Groups . . . . . . . . . . . . . . . . . . . . . . . 27 2.4.4. Hetero~yclic Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.5. Synthesis of Cycloolefin Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 2.5. I. Synthesis of Monocyclic Olefins . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 2.5.2. Synthesis of Bicyclic and Polycyclic Olefins . . . . . . . . . . . . . . 5 l 2.5.3. Synthesis o f Functionalized Cycloolefins . . . . . . . . . . . . . . . . . 69 2.5.3.1. Halogen-Containing Monomers . . . . . . . . . . . . . . . . . . 69 2.5.3.2. Oxygen-Containing Monomers . . . . . . . . . . . . . . . . . . 77 2.5.3.3. Sulphur-Containing Monomers . . . . . . . . . . . . . . . . . . 8 l 2.5.3.4. Nitrogen-Containing Monomers . . . . . . . . . . . . . . . . . 82 2.5.3.5. Boron-Containing Monomers . . . . . . . . . . . . . . . . . . . . 83 2.5.3.6. Silicon-Containing Monomers . . . . . . . . . . . . . . . . . . . . 84 2.5.3.7. Metal-Containing Monomers . . . . . . . . . . . . . . . . . . . . . 85 2.5.3.8. Monomers for Side-Chain Liquid Crystalline Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 2.5.3.9. Synthesis of Heterocyclic Monomers ........... 90
XII 2.5.3.10. Synthesis of Macromonomers . . . . . . . . . . . . . . . . . . 99 2.6. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Chapter 3. CATALYTIC S Y S T E M S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 3.1. Cationic Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 3.1.1. BrOnsted Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 3.1.2. Lewis Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 3.1.2.1. One-Component Lewis Acid Catalysts ........ 117 3.1.2.2. Two-Component Lewis Acid Catalysts ........ 118 3.2. Anionic Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 3.3. Ziegler-Natta Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 3.3.1. One-Component Ziegler-Natta Catalysts . . . . . . . . . . . . . . . . 120 3.3.2. Two-Component Coordination Catalysts . . . . . . . . . . . . . . . 121 3.4. Ring-Opening Metathesis Polymerization (ROMP) Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 3.4.1. One-Component ROMP Catalysts . . . . . . . . . . . . . . . . . . . . . . . 128 3.4.2. Two-Component ROMP Catalysts . . . . . . . . . . . . . . . . . . . . . . . 140 3.4.3. Multicomponent ROMP Catalysts . . . . . . . . . . . . . . . . . . . . . . . . 146 3.4.4. Catalysts for R O M P in Water Systems . . . . . . . . . . . . . . . . . . 150 3.5. Synthesis of Catalysts for Cycloolefin Polymerization ........ 152 3.5.1. Synthesis of Cationic Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 3.5.2. Synthesis of Anionic Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 3.5.3. Synthesis of Two-Component Ziegler-Natta Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 3.5.4. Synthesis of Ring-Opening Metathesis Polymerization Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 3.5.4.1. One-Component Metathesis Catalysts ......... 162 3.5.4.2. Two-Component Metathesis Catalysts ........ 165 3.5.4.3. Three-Component Metathesis Catalysts ....... 165 3.5.4.4. WeU-Defined Metathesis Catalysts . . . . . . . . . . . . . 165 3.6. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 Chapter 4. REACTION C O N D I T I O N S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 4.1. Monomer Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 4.2. Catalyst Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202 4.3. Ratio of Reactants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 4.4. Premixing Time of Reaction Components. 9 ... 206 4.5. Addition of Reaction Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 4.6. Reaction Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
XlII
4.7. Reaction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 4.8. Reaction Medium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.1. Solvents for Homogeneous Catalysis . . . . . . . . . . . . . . . . . . . . 4.8.2. Solvents for Heterogeneous Catalysts . . . . . . . . . . . . . . . . . . . 4.9. Inhibitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.10. Activators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11. Reaction Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12. Effect of Agitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.13. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
220 220 224 225 226 230 232 233
Chapter 5. CATIONIC P O L Y M E R I Z A T I O N OF C Y C L O O L E F I N S . . . 2 3 7 5.1. Cationic Polymerization of Monocyclic Olefins . . . . . . . . . . . . 237 5. I. I. Four-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . 237 5.1.2. Five-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . 239 5. 1.3. Six-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . 253 5.1.4. Seven-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . 260 5.1.5. Eight-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . 26 l 5.2. Cationic Polymerization of Bicyclic Olefins . . . . . . . . . . . . . . . . 264 5.3. Cationic Polymerization of Polycyclic Olefins . . . . . . . . . . . . . . 303 5.4. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 Chapter 6. ANIONIC P O L Y M E R I Z A T I O N OF C Y C L O O L E F I N S ..... 319 6.1. General Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319 6.2. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325 Chapter 7. Z I E G L E R - N A T T A P O L Y M E R I Z A T I O N OF C Y C L O O L E F I N S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 7.1. Polymerization o f Monocyclic Olefins . . . . . . . . . . . . . . . . . . . . . . 327 7.1.1. Four-Membered Rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 7.1.2. Five-Membered Rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 7.1.3. Six-Membered Rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338 7.1.4. Seven-Membered Rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 7.1.5. Eight-Membered Rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340 7.2. Polymerization ofBicyclic Olefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343 7.3. Polymerization of Polycyclic Olr . . . . . . . . . . . . . . . . . . . . . . . . . . 355 7.4. Polymerization o f Functionalized Cycloolefins . . . . . . . . . . . . . . 363 7.5. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372
XIV Chapter 8. RING-OPENING METATHESIS POLYMERIZATION OF CYCLOOLEFINS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 75 8. I. Ring-Opening Polymerization of Monocyclic Olefins .... 375 8.1.1. Four-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . 375 8.1.2. Five-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . 383 8.1.3. Six-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . 394 8.1.4. Seven-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . 395 8. 1.5. Eight-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . 397 8.1.6. Nine-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . 413 8.1.7. Ten-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . 414 8.1.8. Twelve- and High-Membered Ring Monomers ..... 416 8.2. Ring-Opening Polymerization of Bicyclic Olefins ......... 421 8.3. Ring-Opening Polymerization of Polycyclic Monomers... 455 8.4. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492 Chapter 9. POLYMERIZATION OF FUNCTIONALIZED CYCLOOLEFINS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513 9.1. General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513 9.2. Four-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . 513 9.3. Five-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520 9.4. Six-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521 9.5. Eight-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . 523 9.6. Higher Monocyclic Olefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 530 9.7. Functionalized Bicyclic Olefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532 9.8. Functionalized Polycyclic Olefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . 631 9.9. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 639 Chapter 10. POLYMERIZATION OF HETEROCYCLIC OLEFINS... 651 l 0. I. Four-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . . . 651 10.2. Five-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . 65 l 10.3. Heteroatom-Containing Norbomenes and Norbomadienes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 656 l 0.4. Seven-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . . 683 10.5. High-Membered Ring Monomers . . . . . . . . . . . . . . . . . . . . . . . . . 683 l 0.6. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 684 Chapter 11. COPOLYMERIZATION REACTIONS OF CYCLOOLEFINS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687 11.1. Introduction. Reaction Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687
XV 11.2. Cationic Copolymerization of Cycloolefins . . . . . . . . . . . . . 690 11.2.1. Monocyclic Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . 690 11.2.2. Bicyclic and Polycyclic Monomers . . . . . . . . . . . . . . 698 11.3. Ziegler-Natta Copolymerization of Cycloolefins ....... 707 11.3.1. Monocyclic Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . 707 11.3.2. Bicyclic and Polycyclic Monomers . . . . . . . . . . . . . . 715 11.4. Ring-Opening Metathesis Copolymerization of Cycloolefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 774 11.4. I. Monocyclic Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 774 11.4.2. Bicyclic and Polycyclic Monomers . . . . . . . . . . . . . . . 782 11.4.3. Copolymers by ROMP of Functionalized Cycloolefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 801 I 1.4.4. Synthesis of Star Copolymers . . . . . . . . . . . . . . . . . . . . . 836 11.4.5. Synthesis of Graft Copolymers . . . . . . . . . . . . . . . . . . . . 842 11.4.6. Copolymers from Macromonomers . . . . . . . . . . . . . . 844 11.4.7. Copolymers from Cycloolefins and Unsaturated Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 846 11.4.8. Copolymers from Unsaturated Polymers ......... 849 11.4.9. Copolymers from Cycloolefins and Acetylenes..850 11.4.10. Copolymers from Heterocyclic Olefins .......... 854 11.4.11. Copolymers by Different Polymerization Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 857 11.5. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 862 Chapter 12. STRUCTURE AND PROPERTIES OF POY(CYCLOOLEFIN)S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.1. Structure of Poly(cycloolefin)s . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12. I. I. Cationic Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.1.2. Anionic Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.1.3. Ziegler-Natta Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.1.4. ROMP Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.2. Solution Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.3. Solid State Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.4. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
875 875 875 888 890 90 l 923 924 93 5
Chapter 13.THERMODYNAMIC ASPECTS OF C Y C L O O L E F I N P O L Y M E R I Z A T I O N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 943 13.1. Thermodynamic Stability of Cycloolefin Monomers .... 943 13.2. Thermodynamic Parameters of Cycloolefin
XVI Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 945 13.3. Thermodynamic Equilibrium in Ring-Opening Metathesis Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 949 13.4. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 964 Chapter 14. REACTION KINETICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 967 14.1. Kinetics of Cationic Polymerization . . . . . . . . . . . . . . . . . . . . . . 967 14.2. Kinetics of Ziegler-Natta Polymerization . . . . . . . . . . . . . . . . 973 14.3. Kinetics of Ring-Opening Metathesis Polymerization..980 14.3.1. Kinetics of Initiation and Propagation. Living Metathesis Polymerization . . . . . . . . . . . . . . . . 980 14.3.2. Kinetic Models for Mctathesis Polymerization.981 14.4. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 992 Chapter 15. ASPECTS OF REACTION MECHANISM . . . . . . . . . . . . . . . . . . . 995 15.1. Mechanism of Cationic Polymerization of Cycloolefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 995 15.1. I. Initiation Systems for Cationic Polymerization.996 15.1.2. Nature of Cationic Propagation Reactions ...... 997 15.1.3. Termination Reactions of Cationic Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1005 15.2. Mechanism of Anionic Polymerization of Cycloolefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1006 15.2.1. Initiation and Propagation. Living Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1007 15.2.2. Molecular Structure of Anionic Initiators ...... 1009 15.3. Mechanism of Ziegler-Natta Polymerization of Cycloolefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l 010 15.3. I. Structure of Active Species . . . . . . . . . . . . . . . . . . . . . . 101 l 15.3.2. Mechanism of Insertion Reactions .............. 1013 15.4. Mechanism of Ring-Opening Metathesis Polymerization of Cycloolefu~ . . . . . . . . . . . . . . . . . . . . . . . . . . . l 015 15.4. I. Survey of Proposed Mechanisms . . . . . . . . . . . . . . . . l 016 15.4.2. Features of Metallacarbene/ Metallacyclobutane Mechanism ................. 1020 15.4.2. I. Mechanism of Initiation Reaction .... 1020 15.4.2. I. 1. Initiation with WCI6/ Organoaluminium Compounds ..... 1023 15.4.2.1.2. Initiation with WCI6/
XVII Organotin Compounds ............... 1026 15.4.2.1.3. Initiation with WClgqNater .......... 1027 15.4.2.1.4. Initiation with Metallacarbene Complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1028 15.4.2.1.5. Evidence for Initiating Metallacarbene Complexes .......... 1029 15.4.2.2. Mechanism of Propagation Reaction. 1031 15.4.2.2.1. Features of Metallacarbene/ Metallacyclobutane Mechanism .... 1031 15.4.2.2.2. Detection of Reduced Paramagnetic Species in WCk Systems . . . . . . . . . . . . . . . . . . . . . 1038 15.4.2.2.3. Evidence for MetallacarbeneOlefin Complexes .................... 1040 15.4.2.2.4. Evidence for Propagating Metallacarbene Complexes .......... 1041 15.4.2.2.5. Evidence for Propagating MetaUacyclobutane Complexes ..... 1042 15.4.2.3. Mechanism of Termination Reaction.. 1043 15.5. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1044 Chapter 16. STEREOCHEMISTRY OF CYCLOOLEFIN POLYMERIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1051 16.1. Steric Efffects in Cationic Polymerization .............. 1051 16.2. Steric Configuration of Vinyl Polymers ................ 1053 16.3. Stereoselectivity in Ziegler-Natta Polymerization ..... 1055 16.4. Steric Configuration of Polyalkenamers ................ 1057 16.5. Stereoselectivity in Ring-Opening Metathesis Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1059 16.6. Tacticity of Polyalkenamers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1079 16.7. The Nature of Steric Interactions in ROMP ........... 1088 16.8. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1097 Chapter 17. RELATED PROCESSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1103 17.1. Catalytic Polymerization of Olefins and Dienes ....... 1103 17. I. I. Cationic Polymerization of Olefins and Dienes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1103
XVIIl 17.1.2. Anionic Polymerization of Olefins and Dienes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1104 17.1.3. Ziegler-Natta Polymerization of Olefins and Dienes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1105 17.2. Atom Transfer Radical Polymerization of Vinyl Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1108 17.3. Metathesis Reactions of Olefins and Acetylenes ....... 1109 17.3.1. Ring-Opening Metathesis (ROM) .............. 1111 17.3.2. Ring-Closin Metathesis (RCM) ................. 1112 17.3.2.1. Synthesis of Carbocycles ............. 1113 17.3.2.2. Synthesis of Unsaturated Heterocycles . . . . . . . . . . . . . . . . . . . . . . . . . . . 1115 17.3.2.3. Synthesis of Crown Ethers .......... 1117 17.3.2.4. Synthesis of Polycyclic Polymers... 1118 17.4. Acyclic Diene Metathesis (ADMET) and Acyclic Diyne Metathesis (ADIMET) Polymerization ......... 1118 17.5. Carbonyl Olefination Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . 1120 17.5.1. Synthesis of Olefins and Cycloolefins .......... 1121 17.5.2. Carbonyl-Olefin Exchange Polymerization... 1122 17.6. Metathesis Degradation of Unsaturated Polymers .... 1123 17.6.1. Intramolecular Degradation ..................... 1123 17.6.2. Intermolecular Degradation .................... 1124 17.6.3. Acyclic Diene Metathesis (ADMET) Depolymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1124 17.7. Catalytic Polymerization of Acetylenes ................ 1125 17.7.1. Cationic Polymerization of Acetylenes ........ 1125 17.7.2. Anionic Polymerization of Acetylenes ........ 1125 17.7.3. Ziegler-Natta Polymerization of Acetylenes.. 1126 17.7.4. Metathesis Polymerization of Acetylenes ..... 1126 17.8. Ring-Opening Polymerization of Heterocycles ......... 1128 17.8.1. Cationic Ring-Opening Polymerization of Heterocycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1128 17.8.2. Anionic Ring-Opening Polymerization of Heterocycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1129 17.9. Miscellaneous Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1129 17.9.1. Metathesis of Alkanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1130 17.9.2. Catalytic Isomerization of Olefins .............. 1130 17.9.2.1. Cationic Isomerization of Olefins .... 1131 17.9.2.2. Anionic Isomerization of Olefins .... 1131
XIX 17.9.2.3. Ziegler-Natta Isomefization of Olefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.9.2.4. Metathefieal Isomerization of Olefins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.9.3. Cyclopropanation of Olefins . . . . . . . . . . . . . . . . . . . . 17.9.4. Friedel-Crafis Alkylation Reactions ........... 17.10. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1132 1132 1134 1134
Chapter 18. P R A C T I C A L APPLICATIONS AND F U T U R E OUTLOOK ........................................................ 18.1. Commercial Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.1. I .Hydrocarbon Resins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.1.2. Polyalkenamers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18.1.2.1. trans-Polyoctenamer . . . . . . . . . . . . . . . . .
1141 1141 1141 1153 1153
1131
18.1.2.2. Polynorbornene . . . . . . . . . . . . . . . . . . . . . . . 1161 18.1.2.3. Poly(dicyclopentadiene) . . . . . . . . . . . . . . 1173 18.1.3. Cycloolefin Copolymers . . . . . . . . . . . . . . . . . . . . . . . . . 1179 18.1.3.1. Topas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1179 18.2. Products of Interest for Industry . . . . . . . . . . . . . . . . . . . . . . . 1181 18.2.1. trans-Polypentenamer . . . . . . . . . . . . . . . . . . . . . . . . . . 1181 18.2.2. cis-Polypentenamer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1200 18.2.3. cis-Polyoctenamer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1203 18.2.4. Cyclorene Rubber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1206 18.3. Potential Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1207 18.3.1. Synthesis of Monodispersed Polyethylene... 1207 18.3.2. Synthesis of 1,4-Polybutadiene . . . . . . . . . . . . . . . . 1207 18.3.3. Synthesis of 1,4-Polyisoprenr . . . . . . . . . . . . . . . . . 1208 18.3.4. Alternating Copolymers . . . . . . . . . . . . . . . . . . . . . . . . 1209 18.3.5. Block Copolymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1210 18.3.6. Comb and Star Copolymers . . . . . . . . . . . . . . . . . . . . 1214 18.3.7. Amphiphilic Star Block Copolymers ......... 1215 18.3.8. Macrocyclic Compounds . . . . . . . . . . . . . . . . . . . . . . . 1215 18.3.9. Conducting Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . 1216 18.3.10. Semiconductors and Metal Clusters ......... 1221 18.3.11 .Functionalized Polymers . . . . . . . . . . . . . . . . . . . . . . . 1227 18.3.12.Polymers from Heterocyclic Olefins ......... 1231 18.3.13.Telechelic Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1232 18.3.14.Liquid Crystalline Polymers . . . . . . . . . . . . . . . . . . . 1233
XX 18.3.15. Optically Active P o l y m e r s . . . . . . . . . . . . . . . . . . . . 1235 18.3.16. M i s c e l l a n e o u s Applications . . . . . . . . . . . . . . . . . . 1236 18.4. F u t u r e O u t l o o k . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 8 18.5. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1239
SUBJECT INDEX ..............................................................
1249
Chapter I
INTRODUCTION
1.1. General Aspects In the presence of some specific catalytic systems, the cycloolefms (cycloalkenes) undergo vinyl and ring-opening metathesis polymerization yielding poly(cycloalkene)s in the former and polyalkenamers in the latter case (Eq 1.1).
CI
(1.1)
The polyalkenamers produced by ring-opening metathesis polymerization are also named poly(1-alkenylene)s At present, the two types of polymerization reactions of cycloolefins are well documented for a large number of monomers and catalytic systems. ~'~ Generally, the vinyl polymerization of cycloolefins is initiated by cationic, anionic and Ziegler-Natta coordination catalysts while the ringopening polymerization is promoted by metathesis (ROMP) catalysts. Extensive kinetic and thermodynamic work as well as stereochemical and mechanistic studies are published by numerous research groups. ~,-z0 While vinyl polymerization has found various applications in the manufacture of hydrocarbon resinsz~ and recently in the production of copolymers of cycloolefins, zz ring-opening metathesis polymerization has become a versatile method for the synthesis of a large class of polymers having desired physical and chemical properties, particularly good mechanical, electrical and optical characteristics as well as a superior weathering and heat resistant behavior. ~
1.2. Definitions and Reaction Types
In the course of vinyl polymerization, the cycloolefin wig open the carbon-carbon double bond with formation of polymers containing cyclic moieties in their recurring units (F~. 1.2).
The carbon-carbon double bond will open formally by a 1,2-addition reaction involving a carbocationic, cmbanionic or Ziegler-Natta insertiontype mechanism, depending primarily on the nature of the catalyst employed. In the first case, the initiating and propagating species will consist of free or associated carbocations, in the second of free or associated carbanions and in the third one will possess single m e t a l - ~ n bonds as the active sites. Of these reaction pathways, the most encountered are the carbocationic and Ziegler-Natta type mechanisms which are commonly present in the reactions of a large number of monomers. By vinyl polymerization, the c a r b o n ~ o n double bond can be opened via a trans mode, resulting in threo polymers of diisotactic, disyndiotactic or atactic structure (F-xl. 1.3).
GI
trent
-9
(1.3)
or via a cis mode, to yield erythro polymers of diisotactic, disyncfiotactic or atactic configuration (Eq. 1.4).
(3'
ds
(1.4)
:
Depending on the structure of the monomer and reaction conditions, in ~ o e a t i o n i c polymerization the 1,2-~ldition of ~ n - c a r b o n double bond may be accompanied by some side addition reactions or skeleton rearrangements. For instance, in the case of cyclodienes, the 1,2-addition reaction will be currently accompanied by 1,4-addition reactions (Eq. 1.5).
r
(1.5) r
11,
Alternatively, the polycyclic olefins will give also polymers having 1,2recurring units beside rearranged units with a more complicated structure (Eq. 1.6).
(1.6)
When the recurring unit in the polymer chain has one or more unsaturated bonds, cross-linked structures may arise as result of some secondary intemmlecular reactions under the action of the catalytic system (Eq. 1.7).
n
L.
Vinyl copolymers can be obtained by the reaction of two or more different cycloolefins, working under adequate reaction conditions (Eq.
].8).
I
!1
!
(1.8)
These copolymers may have a random, alternating or block distribution of the monomer units, depending essentially on the monomer reactivity and the reaction conditions (Eq. 1.9-1.11).
/~
~
_ 1
ca2~~ --
II
II
II
1 (1.9)
| [ ((cHz~I '~~(( z~r (1"10) i
I
i
[
l
(1.11)
Starting from monocyclic or polycyclic diolefins or polyolefins, graft copolymers can be obtained by a rigorous control of the monomer selection and using appropriate catalytic systems and operating conditions (F~. 1.12).
n
~
=
(1.12)
m
By the ring-opening metathesis polymerization, the cycloolefin will open the ring at the carbon-carbon double bond with formation of unsaturated polymers in which the u~turation degree is preserved throughout the polymer chmn (F~. 1.13).
In this process, the polymer chain is growing by an insertion-type mechanism involving a metallacar~ne propagating species. Depending primarily on the reaction conditions and monomer structure, the ring-opening metathesis polymerization can result in the formation of trans or cis stereoconfigurations of the double bonds in the polymer chain (Eq. 1.14).
I
(1.14)
In the case of polycyclic olefins, the cycle incorporated into the polymer chain will give rise to structures in which the successive rings stand in isotactic (m) or syndiotactic (r) configurational relationship (Eq. 1.15).
=
0.1S)
Furthermore, when the cycloolefin has substimcnts in certain positions or is chiral, polymers with head-head (HH), head-tail (HT) or tailtail (TT) structures may arise, each one having m or r configurational relationships and containing cis or trans double bonds along the polymer chain (Eq. 1.16).
=
(1.1e) \
~ \
i
Cross-linked polymers can also form when the monomer has two or more orders of unsaturation (Eq. 1.17).
(1.17)
..--.------lit,.
1,
By ring-opening polymerization of cycloolefins, cyclic oligomers or macrocycles can form along with linear polymers, depending on the monomer nature, catalyticsystem and reaction parameters (Eq. I.18).
,=
OI
(1.18)
C:__IIIIIIIIIIIIIIIIIII-D
Formation of cyclic oligomers, ranging from simple dimers, trimers etc. to macr~-'Tclic structures, ~.~urs by several parallel prc~,esses, under the action of the catalytic systen~ when a more severe thermodynamic control exists. Formally, by metathesis oligomerizatio~, the cycl~lefm will lead to cyclic dimers or higher cyclic oligomers with a macrocyclic structure, having an advanced degree of' un~turation (F~. 1.19).
,0,. C:_D --
-C:IIIIIIIIIIIIIIIIIII-__D
,'.'~,
The macrocycles thus obtained can be cleaved by intramolecular metathesis reactions with forn~tion of lower macr~"~jcles and eyclooletns (Eq. 1.20).
C]iill
iiiiiiiiiiiii_=D
C: ...................~,-,0 :*~176
-
~,.~o)
****** * * ' " * " * 1
By a similar way, unsaturated linear polymers can be ring-closed through an intramolecular metathesis reaction leading to new macrocycles with structures dependent on the starting material employed (Eq. 1.21).
C-IIIIIIIIIIIIIII ....---
~'-= .................. i=l.
"~._.--.
..................
I
17
(121)
Such processes are currently encountered in the metathesis desradation reactions of polyalkenamers or of other unsaturated polymers If, during the oligomerization reaction of cycloolcfins via metathesis, the macrocyclic ring is twisted, it will lead to catenanes or knots, depending on the number of half-twists that the chain will perform Thus, the catenanes are formed when the macrocycles undergo n=2 hafttwists (Eq. 1.22).
and the knots when the macrocycles undergo n=3 half-twists (F-~I. 1.23).
(1.23)
When the number of half twists is zero (n=O), the macrocycle will cleave into two cycloolefins (Eq. 1.24).
In the same way, a degenerate metathesis reaction occurs for one half-twist, when the same starting macrocycle is formed (Eq. 1.25).
il
I
II
Catenanes and knots of higher order can arise through further intramolecular metathesis reactions of initially formed structures. By a similar process, metathesis reactions between unsaturated catenanes and knots will lead to more complex compounds having structures of polycatenanes, catenanes,-knots and polyknots. Metathesis reaction of unsaturated catenanes or other interlocked tings makes possible the synthesis of a new type of compounds from the class of rotaxanes. For instance, by the reaction of a catenane having the interlocking order 1 with a linear disubstimted olefin, a rotaxane of the order 1 will arise (Eq. 1.26).
By the same process, catenanes having a higher interlocking number will lead to rotaxanes of higher orders.
10 Copolymefizafion reactiom of two or more different cycloolefim in the presence of metathesis catalysts will give copolymers along with c,~ligomers by a metathesis pathway (F-Xl. 1.27 and 1.25).
-
~=c,..,J~~,..,~~
<"~>
=======================
(~.=8)
2 m
tin
As a function of the monomer reactivity and reaction conditions, random, alternate or block copolymers can be readily obtained by this process (Eq. 1.29-1.31).
(11.29)
Gratt copolymers will form from polyalkenamers beating unsaturation or other functionality as side chains by a reaction with a second monomer (Eq. I. 32).
+ ~
90 C
~
(11.32)
(CH-Dm
11 Depending on the nature of the functionality present in the side chain, an anionic, cationic, metathesis or other adequate process can be used to graft the initial polymer backbone to a wide variety of grafted copolymers (Eq. 1.33).
t"
"1
(1.33)
(CH2),.
1.3. Scope and Limitations
The aim of this book is to deal with the main aspects of the catalytic polymerization of unsubstituted and substituted cycloolefins covering the major part of the patent and open literature published up to now on this subject. Both types of cycloolefin polymerization, vinyl and ring-opening metatla~is, will be considered with formation of vinyl polymers and unsaturated polyalkenamers, respectively. Vinyl polymerization will comprise cationic, anionic and Ziegler-Natta polymerization. The monomers will be exhaustively treated starting with simple, unsubstituted monocyclic olefins, bearing alkyl or aryl groups as substituents, according to the ring size and structure, passing then to bicyclic and polycyclic olefins with or without alkyl or aryl substituents. Subsequently, monomers having functional groups attached at the cyclic or polycyclic moiety will be treated. The catalytic systems able to promote these polymerization reactions will be dealt with according to the reaction type which they promote, the catalyst nature and composition as well as the procedure they are applied in. These will include homogeneous and heterogeneous catalytic systems of the cationic, anionic, Ziegler-Natta and ring-opening metathesis polymerization (ROMP) type. The main reaction parameters such as polymerization temperature, time, monomer concentration, catalyst concentration, ratio of reactants and catalyst components will be discussed in connection with the process optimization and valorification. Kinetic and thermodynamic aspects will be detailed for each class of cycloolefin with emphasis on the process parameters relevant for the reaction mechanism and stereochemistry. The elementary steps of initiation, propagation, chain transfer and termination will be elaborated in terms of the generally acc, pted reaction mechanisms. A historical survey of other
12 reaction mechanisms will be also provided. Reaction stereochemistry will be discussed in relation to the mechanistic aspects, catalyst structure, product stereoselectivity and polyng~ microstructure. A special attention will be devoted to the application potential of both vinyl and ring-opening metathesis polymerization of cycloolefms. Industrial procedures for the synthesis of hydrocarbon resins by cationic polymerization of hydrocarbon monomers and for the manufacture of plastics and elastomers by Ziegler-Natta and ring-opening metathesis polymerization of cycloolefms will be highlighted. Products of commercial interest will be also discussed:--A future outlook about other potential applications of the vinyl and ring-opening metathesis polymerization of cycloolefins will be provided. The scope of the book is to provide a comprehensive survey of the literature published on the catalytic polymerization of cycloolefins up to the end of 1999, useful for advanced research chemists and chemic~ engil~eers in catalysis, organic and organometallic chemistry, petrochemistry and macromolecular chemistry as well as for advanced students and teaching staff in organic, organometallic and polymer chemistry. Another essential scope of the work is to help information of specialists from various scientific and industrial areas applying speciality polymers in fields such as microelectronics, computer technology, optics, telecommunic~ons, mechanics, medicine, agriculture, construction, transportation and sports. 1.4. References
1. a. J.P. Kennedy, "Cationic Polymerization of Olefu~: A Critical Inventory", John Wiley & Sons, New York, 1975; b. P.H. Plesch, Ed. '~rhe Chemistry of Cationic Polymerization", MacMilan, New York, 1963, c. H.L. Hsieh and R.P. Quirk, "Anionic Polymerization. Principles and Practical Applications", Marcel Dekker, New York, 1996, d. M. Szwarc and M.V. Beylen, "Ionic Polymerization and Living Polymers", Chapman & Hall, New York, 1993, e. M. Szwarc, "Carbanions, Living Polymerization and Electron Transfer Processes", Interscience, New York, 1968, 2. a.J. Boor, Jr., "Ziegler-Natta Catalysts and Polymerization", Academic Press, New York, 1979, b. T. Keii and K. Soga, Eds., "Catalytic Olefin Polymerization", Elsevier Science Publishers, Amsterdam, 1990, c. G. Fink, g. Muhllmupt, H.H. Brint~ger "Ziegler Catalysts" Recent Innovations and Developments", Springer-Verlag, Berlin, 1995.
13 a. K.J. Ivin and L C. Mol. "Olefin Metathesis and Mctathesis Polymerization", Academic Press, London, 1997; b. V. Dragutan, A.T. Balaban and M. Dimonie, "Olefm Metathesis and Ring-Opening Polymerization of Cycloolefins", John Wiley & Sons, Chichester, 1985 c. R.P. Quirk (Ed.), 'q'ransition Metal Catalyzed Polymerization: Ziegler-Natta and Metathesis Polymerization", Cambridge Press, New York, 1988. Y. Ymamoglu, B. Zumreoglu-Karan and KJ. Amass, Eds., '%)lefin Mctathesis and Polymerization Catalyt~ts: Synthesis, Mechanism and Utilization", Kluwer Academic Publishes, Dordrecht, 1990. W. Vredenburgh, K.F. Foley and A.N. Scarlatti, in "Encyclopedia of Polymer Science and Engineering", J.l. Kroschnitz, Ed., John Wiley & Sons, New York, 1987, Vol. 7, p. 758. I Pasquon, L. Porri and U. Giannini, in "Encyclopedia of Polymer Science and Engineering", John Wiley & Sons, New York, 1989, Vol. 15, p. 662. a. N. Calderon, J. Macromol. Sci.-Revs Macromol. Chem., C7, 105159 (1972); b. K.W. Scott, N. Calderon, E.A. Ofstead, W.A. Judy and J.P. Ward, Adv. Chem. Ser., 91,399 (1969). a. G. Natta and G. dall'Asta, in "Polymer Chemistry of Synthetic Elastomers", J.P. Kennody and E. Thomquist, Eds., Interscience Publishers, New York, 1969, Part 2, p. 703; b. G. Dall'Asta, Rubber Chem. Technol. 47, 515 (1974). R.H. Grubbs, in '~omprehensive Organometallic Chemistry", G. Wilkinson, F.G.A. Stone, E.W. Abel, Eds., Pergamon Press, New York, 1982, Vol. 8, pp. 499-551. 10. K.J. Ivin, in "Encyclopedia of Polymer Science and Engineering", John Wiley & Sons, New York, 1987, Vol. 9, p. 634. 11. K.J. Ivin, in "Olefin Metathesis and Polymerization Catalysts:Synthesis, Mechanism and Utilization", Y. Ymamoglu, B. Zumreoglu-Karan and A.J. Amass, Eds., Kluwer Academic Press, Dordrecht, 1990, pp. 1-43. 12. J. WiRe, in "Houben-Weyl Methoden der Organischen Chemie", 4th Edition, Thieme Verlag, Stuttgart, 1987, Vol. 20, p. 134. 13. E.A. Ofste~, in "Encyclopedia of Polymer Science and Engineering, John Wiley & Sons, New York, 1988, Vol. 11, p. 287. 14. E.A. Ofstead and K.B. Wagener, in "New Methods for Polymer Synthesis",, W.J. Mijs, Ed., Plenum Press, New York, 1992, pp. 237271.
.
o
.
.
~
.
.
14 15. R.R. Schrock, in "Ring-Opening Polymerization: Mechanisms, Catalysis, Structure, Utility", D.J. Bnmelle, Ed., Hanser Publishers, Munchen, 1993, pp. 129-156. 16. a.V. Dragutan and R. Streck, in "Handbook of Polyolefins", C. Vasile and R.B. Seymour, Eds., Marcel Dekker, New York, 1999, pp. 99-137, b. V. Dragutan and R. Streck, in "Handbook of Polyolefins", C. Vasile and R.B. Seymour, Eds., Marcel Dekker, New York, 1999, pp. 139159. 17. A.J. Amass, M. Lotfipour, B.J. Tighe, C.N. Tuck and J.A. Zurimendi, in "Olefin Metathesis and Polymerization Catalysts: Synthesis, Mechanism and Utilization", Y. Ynmmoglu, B. Zumreoglu-Karan and A.J. Amass, Eds., Kluwer Academic Publishers, Dordrecht, 1990, pp. 161-185. 18. E.A. Ofstead mad N. Calderon, Makromol. Chem., 154, 21 (1972). 19. K.J. Ivin, in "Olefm Metathesis and Polymerization Catalysts:Synthesis, Mechanism and Utilization", Y. Ymamoglu, B.Zumreoglu-Karan and A.J. Amass, Eds., Kluwer Academic Publishers, Dordreeht, 1990, pp. 187-207. 20. R.H. Grubbs and W. Tumas, Science, 243, 907 (1989). 21. J.F. Holohan, Jr., J.Y. Penn and W.A. Vredenburgh, in '~Eneyelopedia of Chemical Technology", Kirk-Othmer, Eds., John Wiley & Sons, New York, 1980, 3rd Ed., Vol. 12, pp. 852-869. 22. a. H.-T. Land, Future Special Science 1, 32 (1995); b.W. Kaminsky, A. Bark and I. Dake, in '~atalytie Olefin Polymerization", T. Keii and K. Soga, Eds., Elsevier Science Publishers, Amsterdam, 1990. 23. a. R. Streek, in "Olefin Metathesis and Polymerization Catalysts: Synthesis, Mechanism and Utiliz~on", Y. Ymamoglu, B. ZumreogluKaran and A.J. Amass, Eds., Kluwer Academic Publishers, Dordreeht, 1990, pp. 439-455; b. R. Streek, ibid., pp. 457-488; e. R. Streek, ibid., pp. 489-515.
15
Chapter 2 CYCLOOLEFIN MONOMERS. TYPES AND SYNTHESES
A great number of cycloolefms have been used as monomers in the vinyl and ring-opening metathesis polymerization reactions using different catalytic systems. They pertain to monocycfic, bicyclic and polycyclic olefins, with or without substituents. Whether a cycloolefin is prone to vinyl or ring-opening p o l ~ o n , this propensity is a matter determined primarily by the nature of the catalytic system employed. However, the nature of the monomer can be quite effective in directing the polymerization reaction towards the first or the second type of polymerization. In most ~ , hydr~n compounds have been employed as monomers in these reactions. Cycloolefins bearing functional groups constitute, however, a special class of the starring materials. As the nature of the catalytic system and the reaction conditions are essential for directing the process towards the vinyl or ring-opening polymerization of cycloolefins, these monomers will be presented separately for the two types of process. Cycloolefins suitable for cationic, anionic and Ziegler-Natta coordination polymerization will undergo addition p o l y m ~ o n yielding poly(cycloolefin)s by opening the cat.n-carbon double bond of the monomer. As the catalytic properties of the corresponding catalysts vary drastically, ranging from pure cationic to anionic systems, the nature of the cycloolefin has to be carefi~y considered so that the atfmity of the polymefizable ~ n - c a r b o n double bond towards the catalyst be good enough that the p r o s be initiated. Taking into ~ u n t the different types of catalyst that can be employed in the cycloolefin polymerization, the monomers will be grouped into the following c l ~ : (i) monomers for cationic polymerization, (ii) monomers for anionic polymerization, (iii) monomers for Ziegler-Natta coordination polymerization and (iv) monomers for ring-opening metathesis polymerization.
16 2.1. Monomers for Cationic Polymerization.
It is a requisite for the cationic polymerization that the monomer should possess carbon-carbon double bonds having enough nucleophilicity so as to interact with the cationic species and promote both the initiation and propagation processes by a cationic pathway. In order that this reaction to occur, the cycloolefin has to contain electron-rich double bonds having high affinity towards the cationic species from the system. In this category we shall find simple, unmbst~ted and substituted cycloolefins, cyclodienes, bicyclic and polycyclic olefms. The substituents are generally alkyl or aryl groups, having an electron donating character, but also some specific donating functional groups of a low nucleophilicity, which will not interact with the cationic species, will be appropriate. It is of interest to note that a large number of unsubstituted and substituted cycloolefins possessing various degrees of unsaturation and structures from monocyclic to polycyclic monoenes, dienes and polyenes, have been used as monomers in cationic polymerization. I Some of these monomers served as starting materials for extensive kinetic and mechanistic studies while others have been fruitfully employed for important applications like manufacture of hydrocarbon resins or other chemical products. 27 In Schemes 2.1-2.3 we shall compile several monomers for which the cationic polymerization reaction has been described' whereas certain particularities for the polymefizztion reactions will be presented in the next chapters. These
o,o ,o cp c / o cr p p-,Q
Scheme 2.1
17 monomers can be grouped into the class of monocyclic and bicyclic olefi~ stemming from petrochemical sources.
0 0,, 0 Cr. 0
10
Schen~ 2.2
I
Scheme 2.3
18 2.2. Monomers for Anionic Polymerization
Simple, unsubstituted cycloolefi~ will be reluctant towards the anionic catalysts due to the lack of reactivity of the nucleophilic carbon~n double bond under these conditions. However, if appropriate electron withdrawing substituents, particularly functional groups, will be attached to the cycloolefin so that the basicity or nucleophilicity of the carbon-carbon double bond be diminished, substituted cycloolefins might become proper monomers for anionic polymerization. Such monomers, in the presence of anionic initiators, will lead to ~ o n a l i z e d polymers having interesting properties, related to the current functionalized polyolefins. Functional groups such as nitrile, ester, ether, halogen, etc., attached to the cycloolefins in certain positions, will be able to render the carbon-carbon double bond anionically polymefiz~le and produce polymers by addition polymerization with specific stnJctures and properties (Scheme 2.4). CN
COOR
COR
CONHR
Scheme 2.4
A special class of monomers for anionic polymerization is formed by heteroatom-containing unsaturated cyclic compounds, e.g., sila~cloalkenesS" ~2(Scheme 2.5).
O<"CH3 ps C., O<:"' ~ xCH3 6H5
CS
i,-CSHs "CsHs
< Scheme 2.5
19
2.3. Monomers for Ziegler-Natta Polymerization Both cationic and anionic coordination r as well as conventional Ziegler-Natta ~ y s t s will promote r polymerization once the monomer is able to coordinate and polarization of the coordinated monomer will allow subsequent insertion into the metalcarbon bond. In the fu~ case, in order that the coordination to occur at these types of catalytic systems, it is important that the nucleophilicity or electrophilicity of the carbon-carbon double bond to be high enough in order that the interaction with the cationic or anionic species of the ~ y s t to be possible. However, these two affinity parameters of the ~ n - c a r b o n double bond will be substantially determined by the existing substituents on the cycloolefin through their electron donating or withdrawing propensity. In the case of non-ionic coordination catalysts, the coordination process will be governed by the coordination ability of the cattalyst as a fire.on of the nature of the metal involved in the formation of the active species. As the variety of coordination catalysts of the Ziegler-Natta type is rather vast at present, a wide number of cycloolefu~ have been used in such polym~on reactions, their study being of a particular ac~emic and industrial significance. Simple, unsubstituted cycloolefins like cyclobutene, cyclopentene, cyr cyr etc. have been employed as monomers in early studies carried out by Natta and coworkers on the polymerization reactions with catalytic systems based on the transition metal derivatives and organometallic compounds 13"~6(Scheme 2.6).
n O 0
0
OQ
0 Scheme 2.6
20 Bicyclic and polycyclic olefins, e.g., norbornene and dicyclopentadiene, form an interesting class of monomers that have been fruitfully employed with various coordination catalysts due to their pronounced reactivity and highly performant characteristics of the products o b t a i ~ (Scheme 2.7).
Scheme 2.7 Recently, such monomers have been extensively employed in the copolymerization reactions with unsubstituted or substituted olefins linear olefins to yield new products having excellent mechanical, optical and electrical properties. ~s~2~ Substituted cycloolefins afford another class of monomers with a high potential in the polymerization and copolymerization reactions induced by coordination catalysts due to the special properties that the substituents will impart to the products obtained. In order that the coordination of the cycloolefin at the active site to ocx~r, it is a prerequisite for the substituents to be attached at distant positions with respect to the carbon-carbon double bond. Moreover, it is necessary that the nature of the substituents be so that their comvlexation with the catalyst to favor the insertion process.
21 Hydrocarbon substituents like alkyl and aryl groups are generally the preferred substituents in monocyclic or polycyclic olefins but also mild functionality, that will not interact with the coordination center, will be possible. Examples of such substituted monomers are 3-methylcyclobutene, 4-~ylcyclopentene, 5-methylnorbornene, 7-methylnorbornene etc. and a large number of monocyclic and polycyclic olefins bearing linear or branched alkyl or awl groups as far as possible with respect to the ~ n carbon double bond. ~~ They are of a partic~ar utility in copolymerization reactions where the presence of substituents in the cyclic recurring unit impart special physical-chemical properties to the obtained products.
2.4. Monomers for Ring-Opening Metathesis Polymerization So far, a wide range of unmbstituted and substituted cycloolefms have been employed as monomers in the ring-opening metathesis polymerization. 6 The cycloolefins pertain generally to monocyclic structures, they possess one or more degrees of unsaturation or may be of a more complicated architecture of the bicyclic or polycyclic type. The substituents are primarily a hydrocarbon group such as alkyl, cycloalkyl or aryl radicals. Functional groups are also possible as substituents at the parent cycloolefin or attached to the h y d r ~ o n radical but only when appropriate tolerant catalysts are used. Taking into ~ n t the cyclic nature of the starting olefin and the type of the substituents, the monomers for ring-opening metathesis polymerization will be divided into the following three groups: (i) monocyclic olefins, (ii) bicyclic and polycyclic olefms and (iii) monomers with functional groups.
2.4.1. Monocyclic Olefms for Ring-Opening Metathesis Polymerization
Due to their easy availability, u n s u b ~ e d monocyclic olefu~ have been largely used as advantageous monomers for ring-opening metathesis polymerization in the presence of a wide range of catalytic systems. ~l'z3 Of these monomers, cyclobutene, cyclopentene, cyclooctene, cyclodecene and cyclododecene have been s u ~ y p o l ~ under various reaction conditions to prepare polymers that can be widely applied for their practic~ properties. By this procedure, valuable polymers like polybutenamer,
22 polypentenamer and polyoetenamer have been successfully manufactured, zt'zs Higher unsaturafion is also encountered in several monomers like 1,5-cyelooetadiene, 1,5,9-eyelododecatriene and cyelooctatetraene or other cyclic structures, ~'3~ the unsaturation degree having an influence on the catalytic system and the reaction conditions (Scheme 2.8).
n C> (-)
( }
( } ! C''O Scheme 2.8
Substitution of monocyelic olefins with linear or branched alkyl and aryl groups provides useful monomers for the ring-opened polymers with particular structures and properties. It is essential that the substituents have to be attached at distant position with respect to the ear.n-carbon double bond in order to diminish the steric hindrance during the initiation and propagation processes of the ring-opening polymerization. Interesting examples are 3-methylcyclobutene, 4-methylcyclopentene, 4isopropylcyclopentene and several other alkyl- and aryl-substituted cycloolefins that have been polymefz~ in the presence of specific ringopening metathesis catalysts to the respective ring-opened polymers 2~'3~ (Scheme 2.9). In these monomers the distant substituent will not interfere with the active site in such a way as to hinder the initiation or propagation reaction. Importantly, if these substituents are attached directly at or in the vicinity of the carbon-ca~on double bond of the monomer, the polymerization reaction is strongly inhibited.
23 Rx
!11
III
/
R
1
!1 I
R
/ R
il I\ R
O
~
/ Alkyl
Ph
Scheme 29 2.4.2. Bicyclic and Polycyclic Old'ms for Ring-Opening Metathesis Polymerization Due to their high reactivity in this type of reaction, norbomene and substituted norbornenes represent a large group of bicyclic olefi~ that have been extensively applied in ring-opening metathesis polynmrizalJon. 31"3s Different alkyl radicals, e.g., methyl, ethyl, propyl, butyl, etc., have been attached in various positions of the norbomene skeleton leading to polymers with different structures and properties, depending on the substituent (Scheme 2.10). The re,activity of the substituted norbomene will change substantially as a function of the nature and position of the substituent. ~u~ In the same way, norbomadiene and substituted norbomadienes 3~9 offer another group of monomers for ring-opening polymerization providing related polymers of a higher unsaturation
24 degree which can be further processed and transformed into new products having totally different physical properties (Scheme 2.10).
Scheme 2.10
Many monomers of interest are derived from a large series of bicyclic, tricyclic or polycyclic hydrocarbons such as bicycloheptene, bicycloheptadiene, bicyclooctene, bicydooctadiene, 4~ indene," bicyclononadiene, benzvalene, ~s deltacyclene, ~ barrelene, benzobarrelene, ~ paracyclophene, 47 fullerene and their derivatives a (Scheme 2.11). It is worth mentioning that one of these monomers, indene, ~ which was widely employed as a cationic substrate, will produce by ring-opening polymerization products with interesting electrical properties. Benzvalene (5 and cyclophene 47 will also produce by ring-opening polymerization good precursors for highly unsaturated polymers with special electrical properties. Several benzo derivatives of various bicyclic and polycyclic monomers will lead to polymers with benzene moieties in the
25
reoming units, what will afford special properties, e.g. heat resistance, to the products obtained. +9 Finally, a norbornene derivative of fidlerene" will be able to introduce this particular stmcaue as a recurring unit in the polynorbomene chain by ring-opening polymerization reaction."
Q
Scheme 2. l I
26 Dicyclopentadiene has been extensively employed as an attractive monomer for ring-opening metathesis p o l y m ~ o n to produce highly appreciated linear and cross-linked products s~ (Scheme 2.12). Important industrial procedures for manufacture of poly(dicyclopentadiene) have been developed starting from this monomerss. Dihydrodicyclopentadiene is also a suitable monomer for the ring-opening polymerization reaction to linear polymers. Due to the absence of unsaturation in the condensed cycle, cross, linking is not possible and linearity of the polymer chain can thus be conveniently controlled. The next higher oligomer of the series, tricyclopentadiene, presents also unsaturated functionality similar to dicyclopentadiene leading by ring-opening to poly(tricyclopentadiene), able to cross-link.
Scheme 2.12 A great number of norbomene-like monomers available for ring-opening metathesis polymerization can be obtained by Diels-Alder method from norbomadiene and various substituted or unsubstituted dienes. ~s Using this class of monomers, a wide range of special ring-opened polymers with excellent mechanical and optical properties have been prepared . ' ~
27 2.4.3. Monomers with Functional Groups
Functional groups, when present in the cycloolefins, provide new sites of a t ~ t y towards the catalysts so that under these circumstances only a limited number of c,s~ysts will allow the polymerization p r ~ to ocxa~. In early explorations of the ring-opening p o l y m ~ t i o n , the reaction has been successfully applied to many monomers bearing specific fiu~onal groups like esters, nitrile, halogen etc. Recently, the re,action has been extended to monomers bearing a wide range of functionalities 2 (Scheme 2.13).
COOR
CO
OOR
/ CO
[~COOR QOH
/ N-CH2Ph CO
[~Y--COOR OCOOR
~~
CO
.CI
~
t OR CN
,/BR2
OCN
O ~~
CH~C,
BEt2 ICF3 CONH2
,,o oo.
~ ~
--CN
CH2CN
sicl,
Scheme 2.13
~
Si(OCH3)3
28
Thus, norbomene monomers, substituted with ester groups, cyan or halogens in the 5- or 7-position, have been frequently used in the ringopening metathesis polymerization in the presence of various catalytic systems. At the same time, as it has been observed in monocyclic olefu~ containing fimctional groups in the distant positions with respect to the carbon-carbon double bond, these functionality wig not hinder the accx=ss of the polymerizable double bond at tl~ active center. In this way, monomers like cyclopentene, cyclooctene, cyclononene, cyclodecene and c y c l o d o d ~ e substituted with ester, nitrile, halogen groups in remote positions have been s u ~ f u l l y polymerized under the action of the catalysts that tolerate such fimctional groups. Polycyclic olefins bearing functional groups constitute a special class of monomers for ring-opening metathesis polymerization. The majority of this group of cycloolefi~ have a norbomene-like structure and, unless the presence of the functional group will affect the carbon-carbon double bond and the catalytic center, the polymerizability is rather high due to strain relief and relatively diminished steric hindrance. Thus, a wide series of fluorine substituted norbomenes and related cyclic olefins have been employed as monomers in the ring-opening polymerization reaotion 61'62 (Schemes 2.14 - 2.15).
F
C5F11
~CF3
C~CF F3
F3
C~F3 F
~ C
F 2F5
Cl~
F3 F3 CeFs
CF3 F3 Schen~ 2.14
C4F9
CF3 CF3
29 Fluorinated polymers with.good mechanical and physical properties can be obtained conveniently ,by this route and find interesting pra~cal applications. It is worth mentioning that the fluorine atom may be introduced directly in the bicyclic skeleton or in the attached substituent as can be seen from Scheme 15. Some rich fluorine containing monomers have the fluorine atoms in both positions. Of a special interest are the fluorine containing monomers for polyng~ precursors of polyacetylene prepared by the Durham route ~2 (Scheme 2.15).
i~
F F.F
F F F
F
F3C~
F3C~ F
Scheme 2.15 Chlorine substituted cycloolefins of various types have been used as monomers in many ring-opening polymerization reactions~3 (Scheme 2.16).
,,,C,c,
••••-C
I
k,~ ~Cl
()-c' ~~-CI Cl
I~ qlo
#'-.Z_/.-c. #J~o-'c o Scheme 2.16
c' Cl
c ~ ] ~ c ~lo
Cl
.S--'c0
30 As Scheme 2.16 illustrates the chlorine atoms are situated in a remote position with respoct to the reactive carbon-carbon double bond in order to maintain the monomer reactivity. A very wide range of oxygen-containing monomers have also been employed in the ring-opening polymerization reactions~ ~ (Scheme 2.17).
r ~ o"
~--OR
/~~f
f_i.cooa
i-[ -~
\~
~COs
,OM
i_[. c-(:x:~ ~COOI~
/~~~,ocOCOOR _1~ CO\
oo. f,L ,7-00 o,,O
R
~ , cCH2OCOCH3 H2OCOCH3
OMe OMe I
x---OMe Scheme 2.17
Among the sulphur-containing monomers, ~ alkylthiocyclooctenes and a number of norbornene derivatives appear to be well tolerated by specific metathesis catalysts (Scheme 2.18).
(y"
SI~
SMe
~ O C S _OCS--SI~ _ SIV~
Scheme 2.18 In the case of alkylthiocyclooctenes, the reactivity showed to be crucially influenced by the steric crowding at the heteroatom ( R = c-Hex, n-Hex, tert-Bu, n-Bu, Et).
31 Of a great interest are the nitrogen-c~ntaining monomers that have been fi'uiffuUy employed in a number of ring-opening metathesis polymerization reactions. ~ u This type of monomers can tolerate a wide range of met~e~is polymerization catalysts and provide polymers with good physical and mechanic~ properties. The products can be further transformed by appropriate chemical reactions to new polymers with desired properties. Some examples are illustrated in Scheme 2.19.
CON 0
'CH2--
~~CH3 0
0
0
0
0
0
0
Scheme 2.19
Monong~ containing boron, e.g., (5-cyclooctenyl)diethylborane and 5-norbomenyl-9-borabicyclononane (Scheme 2.20), have been s u ~ f u l l y used in the ring.~ning polymerization reason to produce functionalized polyalkenamers. ~
Schomo 2.20
32 The alkylborane group has been easily removed from the polyalkenamer by oxidation with alkaline H202 to the corresponding hydroxy polymer. Many silicon-containing monomers have been employed in the ringopening metathesis reactions to produce interesting polymers, having particular physical-chemic~ properties 7s'n (Scheme 2.21). slch
~OSIMe 3 ~SiMe
~Si(OMe)3 ~Si(OEt)3
~
3
~li--'-(CH2)n'
iMe2tBu
0 S i(tBu)M
-N
e 2
Scheme 2.21 Of a great potential is the use of metal-containing monomers to prepare metallated polyalkenamers by ring-opening polymerization reaction. A first series is that of cyclic monomers containing organotin moieties (Scheme 2.22). 79
sou,
~
,~.~--Sn~
SnBu, (
~~~ ,
Scheme 2.22
~
C
H
~
C
H
2
-
-
S
n
B
~
33 The monomer and the metal can be varied in a wide range to obtain polymers with good physicS-chemical properties, suitable for many applicationss~ (Scheme 2.23-2.24). /tl~
iMe~
~N? \l'b
\t~
N/
/tBu R N ~r \
Scheme 2.23
Scheme 2.24 The metals induce specific properties to the polymers which can not be attained with the conventional substituents. These speciality polymers could be applied in various electric and electronic devices. Monomers containing a nematic side group attached at the monocyclic and bicyclic olefim, e.g., cyclooctene and norbomene, have been successfully employed to prepare side-chain liquid crystalline polymers by the ring-opening metathesis polymerization re.action,wg~
34 With the discovery of quite tolerable metathesis catalysts, the side group can be widely varied and the nematic properties conveniently tuned. Several examples are offered by monosubstituted cyclooctene and norbomene with nitrile and ether containing mesogenic groups u4s (Scheme 2.25).
O0.CH2.,,O~-->l\-~_c,
~C ~~C~~OMe ~~~,CO2(C H2)~OMe
~cm
Scheme 2.25 Within a new class of norbomene derivatives reported recently,ts'.7 in contrast to their hydrocarbon analogs which lead by ring-opening
35 polymerization to nematic liquid crystalline polymers, monomers with fluorocarbon and siloxane segments will induce smectic layering in nematic liquid crystalline polymers obtained therefrom (Scheme 2.26).
CO I
.OH20
0
0
0
c~
F(CF2)m(CH2
C~--~D(CH2)n(CF2)mF
I
c~
ot3
"-"
o
~
o
~
a~
o~
Scheme 2.26
Also, dimbstituted norbornenes, bearing this class of mesogenic groups, showed to be proper monomers for side-chain liquid crystalline polymersu'=9 (Scheme 2.27).
36
CH~O_~__~O_(OH~~CO~C~~ o ~ o c ~ Scheme 2.27 Such side-chain liquid crystalline polymers are proper components for special applications in electronic devices, for optically anisotropic materials and in other related fields. Macromonomers constitute an interesting class of monomers for the synthesis of speciality polymers. Some examples include polystyryl and polybutadiene macromonomers containing a norbornene units u'ss (Scheme 2.28).
O0 OOC,~
O~ Schemo 2.28
37 The properties of the polymers obtained from ~ type of monomers are remarkable, this makes the manufacture of this kind of products very attractive for their practical applications. 2.4.4. Heterocyclic Monomers Of the class of heterocyclic o l e O , 2,3-dihydrofia~n and 2,3dihydropyran have been used as monomers for the synthesis of unsaturated l~lyethers by ring--ol~~ meta~esis polymerization (Scheme 2.29).
Scheme 2.29 The application has been extended to larger oxygen-containing heterocycles such as 7-acetoxy-4,5,6,7-tetrahydrooxepine and ambrettolide. Sila- and disilacycloalkenes are monomers of interest for the synthesis of silicon eomaining polymers (Scheme 2.30).
GC
0'. SI
Sl
|
.J
Sch~
2.30
38 These monomers are prone either for the ring-opening metathesis or for the anionic polymerization, leading to polymers containing the silicon atom along the chain or included in a cyclic recurring unit. A considerable number of bicyclic and polycyclic oxygen-containing heterocycloolefins have been used in the ring-opening metathesis polymerization to manufacture speciality polymers with a polyether structure (Scheme 2.31 ). O
O
0
R4 0
O
O
O
2 o
O
R
R2
O
OCH2OMo O CH2OMe ~OC(=CH2)Mo OC(=CH2)Me
R~ 0
O
O
CN
CN
Scheme 2.31 Some of these monomers contain additional functional groups in order to impart specific properties to the respective polymers. Oxa- and aza-benzonorbomene monomers, with or without substituents, will lead by ring-opening metathesis polymerization to heteropolymers bearing benzene rings in the recurring units. In addition, a number of monomers containing the nitrogen atom in other positions than at the bridgehead position in the norbornene moiety have been
39
succ~sfully employed in this type of reactions (Scheme 2.32).
O
N~R
0
R
0 NH
o
Scheme2.32
R ~ f l y , heterocyclic monomers with a monodenddtic substituent have been used tO prepare polymers with particular architectures 9''92 (Scheme 2.3 3).
/
~--o
O
\CH 2
/
OCH2"---~
~O(CH2)I2H
--< '>-O(CH2)12H
OCH 2
OCH~ ~ ~---O(CH~),~H \
,/
~OCH2-~__~ O(CH2)'2H ~OCH2---~ ~--O(CH2)12H Scheme 2.33
Due to the fact that such structures can self-organize into well-defined supramolecular architectures, both before and after polymerization, these products are of a great interest for new applications in the colloid and polymer chemistry.
40
2.5. Synthesis of Monomers There is a great variety of cycloolefms that have been polymerized by one or more of the above reaction mechanisms; due to the fact that only a limited number of cycloolefins are available from natural resources, at present a large number of synthetic methods for cycloolefin production have been developed.
2.5.1. Synthesis of Monocydic Olerms Cyclopropene and substituted cydopropene. Closs and Krantz9s treated aUyl chloride with sodium amide in refluxing tetrahydrofiaan and obtained cyclopropene in about 10% yield. Cyclopropene produced in this way reacts with cyclopentadiene at 0~ to give the Diels-Alder adduct, tricyclo[4.1.0, l~4]o~-3-ene, in 10 % yield (Fxl. 2.1-2.2).
~k
CI
NaNH 2 THF, n__10%~
[}~>
(2.1)
T =(T'C = (2.2) 11---10% Similarly, Fisher and Applequist9~ reacted methaJlyl chloride with sodium amide in refluxing tetrahydrofuran to produce ]-methylcyclopropane in reasonable yield. The reaction probably involves the intermediate formation and cyclization of vinylcarbene (Eq. 2.3). +
-Cl
NsNHz-.~
~
THF
(2.3)
Cydobutene and substituted r Cyclobutene can be prepared in high yield from butadiene by photochemical isomerization97''~176 (F_.q. 2.4).
%
f
h.~ =
IF.]
(2.4)
Depending on the reaction conditions and the nature of the starting material, bicyclo[ 1.1.0]butane forms as a side-product along with two other products of intermolecular cycloaddition, 1,2.
41 4-vinylcyclohexene. High c o ~ t r a t i o n of butadiene and irradiation of pure monomer will favor formation of 1,2-vinylcyclobutane and 4-vinyle y c l o h ~ by i n t ~ l e ~ l ~ eycloa~ldRion. By exmm~ in highly diluted solutions, in hydrocarbon or ether media, and in the gas-pha.~ the reaction proceeds preferentially by an intramolecular pathway to cyclobutene. For instance, irradiation of butadiene in ethyl ether provides a mixture of r and bicyclo[l 10]butane in 7:1 ratio whereas in 2,2,4trimethylpentane the ratio of products will be 14:1 under the same conditions. :~ (I) salts favor also intramolecular cyclization reaction to cyclobuteneg~176 1,2-Dimethylcyclobutene can be prepared in 71% yield by an analogous photochemical route from 2,3-dimethylbutadiene :~ (Eq. 2.5). /
\
q=71%'~
/
.
,
(25)
Cydopenteae and Cydopeatadieae. There are several routes for the production of cyclopentene, some of them of great economical importance. ~ g e amounts of cyclopentene are obtained from the Cs stream of the steam cracking of heavy hydrocat~ns (naphtha, gas oil) whereas small scale production is provided by cyclopentane dehydrogenation, piperylene isomerization and cyclopentanol dehydration. :~:0~ Steam cracking has attained great importance in Europe and Japan as the main source of ethylene and propylene so that it is an economical source also for cyclopentene. The amount of Cs cut from a steam cracker is about 20% of the ethylene stream and its composition varies according to the cracking conditions. This fraction contains minor recoverable amounts Table 2.1 Hydrocarbm compcnition of C, cut from a stzam cracker" Cyclopmtme Dicyclopmtadime + Cyclopmtadiene Isoprene Piperylme C~ olefms Cs alkanes C, + C6 9Data fixsn referencea
i
2.5 16.5 17.0 11.5 17.0 31.0 4.5 i
42 of cyclopentene, but the principal source of this monomer would be from hydrogenation of cyclopentadiene (Table 2.1). The process for cydopentene production fTom C5 cut is based on extractive distillation with selective solvents. The solvents N-methyl-2pyrrolidone, dimethylformamide, furfural, aniline, acetonitrile and formylmorpholine, used to isolate butadiene from the C4 cut, have been proposed for cyclopentene extraction and, in some pilot plants, also applied to the recovery of dimes from the C5 cut. Acoording to a procedure developed jointly by BASF and Erdolchemie, '~ which uses Nmethylpyrrolidone as solvent, production of cyclopentene is combined with that of isoprene and piperylene (Figure 2.1). In this process, cydopentadiene is first dimerized to dicydopentadiene by heating of the Cs feedstock and, after separation and selective hydrogenation to cyclopentene, fed back to the N-methylpyrrolidone (NMP) extracts containmg the conjugated dienes and the aliquots of cyclopentene originally present in the feedstock. A further extractive distillation with Nmethylpyrrolidone, followed by fractional distillation, yields polymerization grade cyclopentene and isoprene. This combined facility is one of the most non to both rubber monomers. I'h Waste g n
Isoprene
1
I Cs
11-
7
2
Cyetoper~r~
Diobtns NMP
Pipen~enes Higher con-r
NMP
Figure 2.1. Process for cyclopmtme and isoprene production fi'om Cs cuts (1 :Dimerization, 2 :N-Methytpyrrolidone Extraction, 3:Distillation, 4:DicyclopeRadiene Decomposition, 5-6: Cyclopm~diene Hydrogenation, 7: NMethytpyrrolidone Extraction, 8" Cyclopentene and Isoprene Separation)'~ However, also the separation of dicyclopentadiene without extraction of isoprene has been reported as an economically feasible process for cydopentene production. '~
43 By c o n ~ the method for cyclopentene synthesis from cyclopentane, which occurs usually in many petroleum fractions, by catalytic dehydrogenation is far less selective and would involve a cyclopentane facility (Eq. 2.6).
[~~
[Cat]
(2.6)
However, another route to cyclopentene, that could bocome economic under special circumstances, depending on the availability of raw material, is the gas-phase cyclization of piperylene catalyzed by hydrogen sulphide (Eq. 2.7).
[H2S]
(2.7)
Piperylene is in fact one of the major by-products of steam-cracking and of some processes for isoprene synthesis such as the propylene dimefization over methylpentene and its subsequent demethanafion. Cyclopentadiene is readily obtained by distillation of dicyclopentadiene in the presence of copper powder or iron. '~ A continuous process for the depolymerization of dicyclopentadiene was described in the patent literature. ,09 An important amount of cyclopentadiene is produced by high temperature pyrolysis of hydrocarbons. By this way, cyclopentadiene is formed in cracking gas, natural gas, oil distillates. Two synthetic methods are most largely applied for the manufacture of dicyclopentadiene: (i) ~ y t i c dehydrogenation of cyclopentene and (ii) cyclization of piperylene ''~ (Eq. 2.8-2.9). [cat]
_
9- H2 "-
••.
[Cat] - H2
,
I~
(2.8)
[~
(2.9)
The first method is a further step of the previously mentioned catalytic dehydrogenation of cyclopentane to cyclopentene (Eq. 2.10)
44
[Cat]
[Cat]
(2.10)
but, on the other hand, the catalytic dehydrogenation of cyclopentane could be conducted, under rigorous conditions, directly to the selective formation of cyclopentadiene (Eq. 2.11).
[Cat]
(2.11)
The second method starting from pyperilene involves also two steps, occurring with the intermediate formation of eyclopentene but, under the conditions employed, cyclopentene is not separated and the reaction is conducted to eyclopentadiene (Eq. 2.12).
C
[Cat] ~ )
[Cat]
-.2
(2.12)
The monomer cyelopentadiene is stable only by -80~ Over this temperature dicyclopentadiene forms by dimerization reaction. Because of the easy dimerizafion, fresh distilled cyclopentadiene is used. Cydohexene and substituted cydohexene. There are several techni~ proc~ures for the synthesis of cyelohexene and some of its substituted derivatives which can be found in the literature. ~ ' ~ Thus, cyclohexene can be manufactured by (i) catalytic dehydration of cyclohexanol 1~2 at 300400~ (ii) dehydrocldorination of ehlorocyclohexane on alumina-silica at 130-140~ (iii) deamination of cyclohexylamine on heating over several metal phosphates as catalysts, (iv) isomerization of cyelohexane to methylcyclopentane on the Friedel-Crafls catalysts with subsequent dehydrogenation over Cr203 to methyleyelopentene and further i~merization on AICI~-tCI to eyelohexene, t~4"~6 (v) dehydrogenation of eyelohexane on sulphur at 520~ and (vi) eycloaddition of ethylene and butadiene at temperatures of 150 to 350~ and 100 to 150 atm when 4vinylcyclohexene forms as a side-product. ~7 4-Vinylcyclohexene is produced n~nly by catalytic dimerization of but~ene in liquid phase over
45
Cu- or Cr-naph~enate at 163~ and high presmre, in gas phase over SiC at 425~ and 14 atm or over Ni at 400-500~ or by photodimerization with Hg-light at low pressure l is (Eq. 2.13).
+
\ / /
---.
(2.13)
By this reaction, 4-vinytcyclohexene is formed also as a side-product in the commercial installations for the manufacture of cyclododecatnene. C ~ d o h e ~ d i ~ e . 1,342ydohex~iene can be prepared m high yield from cyclohexene in two steps ~9"~2~(Eq. 2.14).
0
(CH3)3COCl 0- - _ . i ~ . 1177%
CsI"IsN(CH3)2; , . . ~081
C;
n Bow,
..._
(2.14)
The chlorination is done in excess refluxing cyclohexene with ten-butyl hypochlorite and d i ~ y l peroxide as a catalyst. The second step is carried out at a temperature such that cyclohexadiene distills as formed. On the other hand, 1,4-cyclohexadiene is readily available by the catalytic hydrogenation of benezene (F-xl. 2.15).
+H2 0
(2.15)
Cycloheptene and cydoheptadiene. Cycloheptene is obtained by the general procedure by dehydration of cycloheptanol under the influence of with [3-naphthylsulphonic acid121 (Eq. 2.1 6)
P~loH7S03 H 1180%
=
~
(2.16)
46 On applying the above two-step proc~ure used for cyclohexadiene manufacture, cycloheptene can be conveniently converted to 1,3cyclohe~adiene (Fxl. 2.17)
~P'~>(CH3)3C ,OCL i/C> CeHs~CH3)2 ~ C C
(2.17)
By a different procedure involving r i n g - ~ a r g ~ t of a copper intermediate, 1,3,5-cycloheptatriene can be prepared from benzene and diazomethane ~zz as shown in Eq. 2 18 9
(~ CH2N2 r C u BC~~~)uB r
.
-CuBr=_ C~
(2.18)
Other methods ~z3 imply pyrolysis of 7,7-dichloronorcarane at 500~ to 1,3,5-eycloheptatriene (yield 57%) and toluene ~~ or heating over CaO at 444~ to 1,3,5-cycloheptatriene (yield 63%) without toluene ~23b(Eq. 2.19).
CH3
A.4A.~ C a O
_ .._
(2.19)
Cyclooctene and cydooctadiene. Cyclooctene, TM an important monomer for polyoctenamer production, can be prepared by the general methods employed for cycloolefin synthesis such as dehydration of cyclooctanol, dehydrochlorination of cyclooctyl chloride, dehydrogenation of cyclooctane and halogen elimination reactions of dihalides of cyclooctane. Of these methods, the most convenient procedure seems to be cyclooctadiene hydrogenation in the presence of specific catalysts as will be shown below. Cyclooctadiene is formed by cyclodimerization reaction of butadiene under the action of nickel catalysts ~2s'~ (Eq. 2.20).
47 ~
+ ~
[Ni]=
0
(2.20)
This reaction occurs in the synthesis of cyclododecatriene using nickel complexes. Ir7 When donor ligands, e.g. phosphites, have been used, the synthesis is directed toward cyclooctadiene formation and this process is the basis for the commercial production of cyclooctadiene. V'mylcyclohexene, a coproduct of butadiene dimerizafion, acts as a molecular weight regulator in further polymerization reactions and should be removed by fractional distillation. Partial catalytic hydrogenation of cyclooctadiene affords cyclooctene in high yield (Eq. 2.21). (2.21)
[Cat]
Cydooe~tetraene. The most straightforward way to prepare cyclooctatetraene is tetramerization of acetylene by the Reppe proceduremZS (Eq. 2.22).
1It + tit
~ ~
.
.
.
.
(2.22)
The reaction occurs readily in high yield under the action of nickel cyanide at temperatures between 60~ and 70~ and pressure of 20 arm. Cydononene and eydononadiene. Cyclononene and cyclononadiene can be prepared on small scale amount by means of the general methods used for cycloalkene synthesis. Thus, cyclononene is prepared by elimination reactions from the corresponding cyclic alcohols, halides and dilmlides ff.q. 2.23-2.25). OH (2.23)
-HX ~
(2.24)
48
X
-2X ..--- ~
(2.25)
1,3-Cyclononadiene is prepared from cyclononene via chlorination and dehydrochlorination, by an analogous way to 1,3-cyclohexadiene t~9"~2~(Eq. 2.26-2.27).
{~
(CH3)3COCI.~ .- p j ~
(2.26)
C
C6HsN(CH3)2-~ [ ~ ,
(2.27)
C Cyclodecene. This monomer can be conveniently obtained from cyclodecanol by dehydration with common dehydrating agents, e.g., P2Os (Eq. 2.28) OH
~
-H20. ~
(2.28)
Cydodecadiene. Cyclodecadiene is commercially produced by cyclo-cx~ trimerization of two moles of butadiene with one mole of ethylene t29 (Eq. 2.29).
( . )
[Cat]
>
~
(2.29)
Cydododecene and cydododecadienr The main source of cyclododecene production is by the selective hydrogenation of cyclododecatriene, a commercial product obtained by cyclotrimefization of butadiene 125'126'13~(Eq. 2.30).
(gao)
49
C y c l o d o d ~ e n e is commercially produced by c y c l ~ l i g o m ~ o n two moles ofbutadiene with two moles of ethylene (Eq. 2.31).
+
---
,C
of
(2.31)
Cydododecatriene~ Cyclotrim~tion of butadiene to c y c l o d o d ~ e n e occurs conveniently under the influence of three camdytic systemslU'l~: (a) titanium tetrachloride/ethylaluminium sesquichlorie, Co) "nacked nickel" and (c) chromyl chloride/triethylaluminium. (Eq. 2.32).
(2.32)
)
Four stereoisomers can arise, i.e., all-cis-, cis, trans, trans-, cis, cis, trans-,
all-trans-cyclododecatriene, the amount of which depends essentially on the catalytic system and reaction conditions (Scheme 2.34).
0_0 all-cis
CO cts, trans, trans
cis, cis, trans
all-trans
Schen~ 2.34
50 The ratio of the stereoisomers can be altered by varying the reaction temperature, pressure and nature of the catalyst. With TiCI4/Et3AI2CI3 as the catalyst, the main reaction product is cis, trans, trwts-cyclododecatriene. "blacked" Ni will form t r ~ , t r ~ s , tr~ms-cyclododecatriene as the main product while the system CrOCl2~hAl will produce c~z 60~ trans, trans, trans- and 40% cis, trans, trans-cyclododecatriene. The technical product, commercialized by Htils AG, Shell and Du Pont, 124'130with overall production of 40.000-45.000 to/year, is obtained with over 90% yield in installation presented schematically in Figure 2.2. Cyclooctadiene (COD) and vinylcyclohexene (VCH) are formed as side-products by accompanying cyclodimerization reactions of butadiene in the presence of the catalytic system. (Eq. 2.33). [Cat]
(2.33)
As Figure 2.2 illustrates, the initial butadiene is purified in a first column then oligomerized in the reactor under the action of the catalyst. VCH COD
Solvent
CDT
NaOH
Catalyst Butadiene
Higher comp.
Figure 2.2. Production of c y c l ~ e (CDT) by butadiene cyclccximerization(side-products:cyclooctadime (COD) and vinylcyclohexene (VCH)) (Installation: l-Drying, 2-Reactor, 3-Catalyst l ~ i t i o n , 4-Solvent Recovery, 5-Separation Colunm, 6-Distillation Column)m
51 After monomer conversion, the catalyst is destroyed with aqueous NaOH solution and the organic phase is separated in the following three colunms: first, solvent recovery, second, separation of by-products, vinylcyclohexene and cyclooctadiene and third, distillation of cyclododecatriene. Selective hydrogenation of c y c l o d o d ~ e n e forms c y c l o d o d ~ e . This compound is an important intermediate in the manufacture of nylon-12 via the cyclododecane-lauryl lactam route. 2.5.2. Synthesis of Bicydic and Polycydic Olefins Norbornene and substituted norbornene. Norbomene and a wide range of substituted norbomenes are made directly by the Diels-Alder condensation of cyclopentadiene with ethylet~ or substituted ethylene. 131"13s Under high pressure and with a large excess of ethylene, good yields in norbomene are obtain~ from cyclopentadiene t~'13= (Eq. 2.34).
Q
=-
(2.34)
Substituted olef~ react easily with cyclopentadiene but the yields are largely dependent on the n a t u r e and bulkiness of the attached substituents 139q41(Eq. 2.3 5).
Q
(2.35)
Also, substituted cyclopentadiene takes part in reactions with olefins to produce norbomenes bearing multiple substituents in various positions ~42 (Eq. 2.36).
A large number of substituted norbornenes have been prepared by this versatile route. For instance, Alder and Ache ~42 prepared l-methyl-and
52 2-methylnorbomene by reaction of methylcyclopentadiene with ethylene (Eq. 2.37-2.38).
~9
(2.37)
(2.38) 2-Methylenenorbomane has been formed as a by-product in this reaction (Eq. 2.39). +
=
(2.39)
Starting from ethyl- or isopropylcyclopentadiene and ethylene, lethyl- and 2-ethylnorbomene as well as l-isopropyl- and 2isopropylnorbomene have been obtained by this reaction way t43 (Scheme 2.35).
Scheme 2.35 2-Ethylidene- and 2-isopropylidenenorbornane resulted also as by-products under these reaction conditions (Scheme 2.36).
Scheme 2.36
53 Special procedures have been applied for the manufacture of some substituted norbomene derivatives. Thus, J.D. Roberts et al. TM prepared 7methylnorbornene by the thermal reaction of 7-bromo-7-methylnorbomene with tributyltin hydride (Eq. 2.40).
BaSaH
H
.~
+
(2.40)
Starting from 1,3-cyclohexadiene, 7-bromo-7-methylnorbomene was obtained by debromination and rearrangement of the intermediate 7,7dibromo-bicyclo[4.1.0]hept-2-ene with methyllithium~45(Eq. 2.4 1).
~ ~ KOtBu~HB~[ ~ B I r CHIJ r
(2.41)
1,2-, 1,3- and 2,3-Dimethylnorbornene have been produced by Alder and Ache ~42 by cycloaddition reaction of dimethylcyclopentadiene with ethylene (Eq. 2.42-2.44).
(2.42) (2.43) (2.44) Codimefization of cyclopentadiene with butadiene accompanied by thermal Cope rearrangement of the adduct gives two hydrocarbon monomers of
54 interest, 5-vinylnorbomene and bicyclo[4.3.0]nona-3,7]diene TM (Eq. 2.45).
In a similar way, 5-cyclohexenylnorbornene can be prepared by condensation reaction of cyclopentadiene with vinylcyclohexene ~47 (Eq. 2.46).
/ ~
(2.46)
Ethylene bis(5-norbornene) will be easily prepared by the Diels-Alder reaction of cyclopentadiene with 1,5-hexadiene ~47(Eq. 2.47).
.O
(2.47)
Four aryl-substituted derivatives of norbornene have been obtained by EI-Saz~n and Feast ~48by more elaborated methods. For instance, endoand exo-5,6-benzonorborn-2-ene were prepared by two independent ways starting from two different disubstituted benzene derivatives (Eq. 2.482.49).
[~
CHBr2 CHBr z
N.,.
]
(2.48) endo
O
- [ ~ ~
(2.49)
exD
On the other hand, exo- and endo-5,6-acenaphthonorbom-2-ene were obtained by Diels-Alder addition of acenaphthene with dicyclopentadiene (Eq. 2.50).
55 + O
=
(2.50) enclo + exo
All the synthetic routes gave isomer mixtures which were rather complex and the required pure monomers were to be obtained by standard, albeit tedious, preparative chromatographic techniques. Benzo- and substituted benzobarrelene, monomers for highly conductive polymers, have been synthesized by two-step procedures starting from benzene derivatives ~49'~5~(Eq. 2.51-2.52). CI
CI
C ~ 1 ~ CI BuLi
C F ~ l "Cl C61"~-
I Ph
O
O
F
~
CI
Na
=
~
.~--R ~-R KOtBu .~ LiN(CHMez)z
(2.51)
(2.52)
A series of norbornene derivatives, available by Diels-Alder synthesis, were prepared by ShellTM to manufacture thermoset copolymers. Such a monomer, 5,8-methylene-5a, Sa-dihydrofluorene, was obtained by the diene synthesis from indene and a mole of cyclopentadiene (Eq. 2.53).
(2.53) Similar reaction of 1,4-divinylbenzene with two moles of cyclopentadiene gave rise to 1,4-dinorbomylbenzene (Eq. 2.54).
56 An interesting monomer for thermoset polymers, 1,4,4a,9,9a,10hexahydro-9,10(l',2')benzene- 1,4-methanoanthracene, obtained Shell by this procedure from dibenzobarrelene and cyclopentadiene~5~ (Eq. 2.5 5).
(2.5s)
Norbornadiene. Diels-Alder reaction of dicyclopentadiene with acetylene will produce efficiently norbornadiene, ~$2 a highly reactive and quite versatile monomer (Eq. 2.56).
1~
" III
"
~
/ ~
(2.56)
The reaction occurs readily with mono- and disubstituted acetylenes providing mono- and disubstituted norbornadienes, ~53 respectively (Eq. 2.57-2.58).
I~
+ Ill
= ~
(2.57)
i~
, iII
~
(2.s8)
When substituted cyclopentadienes are employed as dienophile, 7substituted norbornadienes can be readily prepared by this method TM (Eq. 2.59).
C>- + III
~
(2.59)
57
Benzenorbornadiene and higher aromatic homologs. EI-Saafin and Feast ma prepared benzonorbomadiene by trapping benzyne with cyclopentadiene in a Dials-Alder process. The benzyne was generated from ~~lic and in the reaction with ~nyl nitrite (Eq. 2.60).
(z6o) c(x~
cooe
By a similar procedure, Feast and Shahada.155 prepared 2,3naphthonorbomadiene and 2,3-anthracenonorbomadiene reacting cyclopentadiene or dimethylenenorbomene with the reaoive acetylenic intermediates obtained from benzene or naphthalene derivatives. For 2,3naphthonorbornadienr two independent routes have been applied tl~ first involving cyclopentadiene addition with the acctylenic intermediate from naphthalene (F-.~l.2.61).
(2.61)
while the second addition of dimethylenenorbomene to the reactive intermediate benzyne obtained by diazotization of anthranilic acid (Eq. 2.62).
==
[ox]
(2.62)
58 Synthesis of 2,3-anthracenonorbomadiene occurred analogously from the corresponding naphthalyne obtained from 3-amino-2-naphthoic acid via ~ene d i a z . o n i u m - 2 ~ x y l ~ e as illustrated below (Eq. 2.63).
(2.e3)
This procedure can be easily applied to higher arene homologs bearing norbomene end groups. Trit-ydononene. Tricyclononene or deltacyclene is readily available via cobalt-catalyzed [2+2+2] homo-Diels-Alder reaction of norbomadiene with acetylene ~s~(Eq. 2.64).
+ III Analogously, substituted deltacyclene bearing butyl, phenyl or trimethylsilyl groups have been prepared from norbomadiene and the corresponding substituted acetylenes (Eq. 2.65).
RIll
=
(2.es)
R R = B u , Ph, Me Si
Tricyclo [4.3.0. I z~]dec-3-ene or trimethylenenorbornene~ T rimethylenenorbomene can been prepared by two independent routes i.e. Diels-Alder condensation of cyclopentadiene with cyclopentene ~" or partial catalytic hydrogenation of dicyclopentadiene (Eq. 2.66-2.67).
59
O
9C} H
~~~
.266.
~..~~
.26,.
The choice of the method depends essentially on the availability of the raw materials Tricydo[4.3.0.1Z~]deca-3,7-diene or dicyr This important monomer is recovered directly from refinery streams after thermal dimerization of cyclopentadiene (Eq. 2.68).
The crude product is unsatisfactory for polymerization due to the large amount of residual cyclopentadiene and other C5 dienes which can act as a catalyst poisons. As the normal dicyclopentadiene contains two stereoisomers, endo and e x o (Eq. 2.69)
(2.69) exo
endo
the separation of these two stereoisomers can be carried out by special techniques. Tricydo[4.4.0.1Z~]undeca-3-ene. This hydrocarbon and the higher polycyclic homologs can be easily prepared by Diels-Alder reaction of cyclopentadiene with cyclohexene 157(Eq. 2.70).
O
. O
60 When two or more moles of cyclopentadiene are employed, polycycilc olefins having cyclohexane end can be produced (Scheme 2.37).
Scheme 2.37 Tricyclo[4.4.0.12,s] undeca-3,8~iene. Tricyclo[4.4.0.12"5]undecat-3,8-diene is readily available by the condensation reaction of cyclopentadiene with
1,4-cyclohexadiene (Eq. 2.71).
O
=
(2.71)
With two or more moles of cyclopentadiene, two series of polycyclic olefins will arise, this depending on which of the double bonds will take part in the diene synthesis (Scheme 2.3 8).
Scheme 2.38 Tricyclo[4.5.0.12"Sldodeca-3-ene. Diels-Alder reaction of cyclopentadiene with cycloheptene will form easily tricyclo[4.5.0.12'5]dodeca-3-ene ~57 (Eq. 2.72).
Higher homologs will be produced by further Diels-Alder reaction of trieyclo[4.5.0.12"5]dodeca-3-ene with r (Eq. 2.73).
61 Tricydol4.6.0.1Z~tridec~3-ene. This hydrocarbon is readily available by the Diels-Alder reaction of cyclooctene with dicyclopentadiene or by partial hydrogenation of tricyclo[4.6.0.1 z'S]trideca-3,9-diene (Eq. 2.74).
O + ()
"'"
,,
Further reactions of tricyclo[4.6.0.1 ~S]trideca-3-ene with dicyclopentadiene will form higher polycyclic monomers (Eq. 2.75).
>o ~
.
) (2.75)
Tricydol4.6.0.1z~ltridec~-3,9-diene. 1,5-Cyclooctadiene and cyclopentadiene will react readily to produce tricyclo[4.6.0, l Z'S]trideca-3,9diene (Eq. 2.76).
(2.76)
O+ ( )
Two series of higher polycyclic homologs will arise by further reaction of one of the t w o double bonds of tricyclo[4.6.0.12"S]trideca-3,9-diene with cyclopentadiene (Scheme 2.39).
Schen~ 2.39 Tetracyclo [4.4.0.1 ~s. 17't~ dodec-3-ene tetracyclo [4.4.0.1 ~s. 17't~ dodec-3-ene.
and substituted Tetracyclododecene or be easily prepared from
dimethanooctahydronaphthalene can dicyclopentadiene and ethylene. ~ss In a first step, dicyclopcntadicne is cracked at high temperature to make two equivalents of cyclopentadiene.
62 In a second step, addition of ethylene to cyclopentadiene yields norbomene. The norbomene acts as a dienophile in a third step for the liberated cyclopentadiene, resulting in a concerted [4+2] cycloaddition (Eq. 2.77-
2.78).
(l)
C + i,
=.
2. [ ~
(2.77)
3_C>
(2.78)
Addition of cyclopentadiene to norbomene can occur in four distinct ways to yield four distinct stereoisomers: endo, exo-, exo, exo-, endo, endoand exo, endo-tetracyclododecene (Scheme 2.40).
endo, exo
exv, exo
endo,endo
exo, endo
Scheme 2.40 Soloway Is9 showed by a synthetic procedure that the major isomeric component from the cycloaddition reaction of norbornene to cyclopentadiene was the endo, exo-tetracyclododecene. This result has been recently confirmed by an elegant method by Benedikt et al. ~6o using highresolution NMR spectroscopy. By a similar route substituted tetracyclododecene can be prepared using monosubstituted or disubstituted clienophiles in the Diels-Alder reactions with cyclopentadiene (F_,q. 2.79-2.80).
63
i~ + ( ~
I~
(2.80)
Diels-Alder reaction of norbomadiene with cyclopentadiene gives tetracyclo[4.4.0. I z'5.17'~~ ~6~(Eq. 2.81).
I~ + / ~
~ ~
The same product can be obtained in a two-step cyclopentadiene and acetylene (Eq. 2.82).
(2.81) process from
By a similar way to tetracyclododecene, four distinct stereoisomers: endo, exo..exo, exo-, endo, endo- and exo, endo-tetracyclododecadiene occur (Scheme 2.41 ).
e n d o , exo
exo, exo
endo, endo
Scheme 2.41
exo, e n d o
64 Substituted tetracyclo[4.4.0.12"~,l~'t~ can be conveniently prepared in one step by the Diels-Alder reaction of dicyclopentadiene with substituted norbomadienes or in a two-step process from cyclopentadiene and substituted acetylenes (Eq. 2.83-2.84).
E~
+ III ~
~
(2.83)
E~
+ iii ~
~
(2.84)
I
The presence of substitutent at one of the carbon-carbon double bonds of the monomer will prevent this bond from cross-linking reactions during polymerization but will give the possibility to further functionlize the polymer by certain chemical reactions. Pentacyclo[ 10.2.1.0xlm.0~'t=]pentadeca-2-ene. This monomer can be easily prepared from octahydronaphthalene and cyclopentadiene by the DielsAlder reaction (Eq. 2.8 5).
=
~
(2.85)
Pentacyclo[10.2.1.1xs.02"tt.0m'9]hexadeca-6-ene, When starting from tricyclo[4.4.0, l~]undeca-3,8-diene or methyleneoctahydronaphthalene and cyclopentadiene, pentacyclo[ 10.2.1.15'8.02"tt.04'9]hexadeca-6-ene is obtained (Eq. 2.86).
65 Hexacydoll0.2.1.13'tS.lS~.0z'tt.0~ Diels-Alder reaction of tetracydo[4.4.0.12,5.17,10]d~e~-3-ene with dicyclol~m~ene gives hexacyclo[ 10.2.1.13'1~ I s'S.o~lt.O4~hept~lee~-6-ene (F~. 2.$7).
(2.87) Hepts~ddo [ 14.2.1. I s,t2.1 ~'ts.0z'ts.0~ t3,0s'ts]doeicotm-i-ene, dicyclopentadiene with pentacyclo[ 10.2.1.1 s,s.02,11.04#]hexader reacted hepta~r 14.2.1.1 s,t2.17"l~ obtained (Eq. 2.88).
When is will be
(2.88) Octacyclo[ 14.2.1. l~'t4. I s't2.17'ts.0z'ts.04't3.06'tS]doeicosa-g-ene. Further reaction of hexacyclo[10.2.1.13,t~ lS'S.02'tt.04a]heptade~-6-ene with dicyclopentadiene gives a new norbomen~like monomer octacyclo[ 14.2.1.13,t4. I s,t2.17't~ (Eq. 2.89).
Other multieydk norbornene-like monomers. The Diels-Alder reaction of cyclopentadiene with a variety of cycloolefins will produce a large number of norbomene-like monomers having one or more norbornene moieties in the molecule. In this way, reaction of cyclopentadiene with cyclopropene, cyclobutene, cyclopentene, cyclohexene, cycloheptene, cyclooctene and higher cycloolefins will provide a full series of tricyclic monomers containing one norbomene moiety in the molecule (Eq. 290)
C +C(CH2)n
(2.90)
66 Reaction of various cyclic dienes and polyenes with cyclopentadiene e.g. cyclohexadiene, cyclooctadiene, cyclooctatetraene, cyclododecatriene, etc. will form penta- and multicyclic olefin~ containing two and more norbornene moieties as a function of the number of double bonds of the reacting cyclooletin (Eq. 2.91).
+
(2.91)
+
(c
(CH2)rr
Examples for cyclohexadiene, cyclooctadiene, cyclooctatetraene and cyclododec~triene are illustrated in Eq. 2.92 - 2.95.
(2.92) (2.93)
(2.94)
O.,C
(2.95)
Further Diels-Alder reactions of these monomers with cyclopentadiene at any available double bond of the first formed molecule will produce higher homologs of interest for the vinyl polymerization or ring-ol~ning metathesis polymerization (Scheme 2.42).
67
Schemo 2.42
A special class of interesting norbomen~like monomers is formed from the higher oligomers of cyclopentadiene e.g., tricyclopentadiene, tetracyclopentadiene, pentacyclopentadiene, etc. Thus, starting from dicyclopentadiene as dienophile in the reaction with cyclopentadiene two types of tricyclopentadiene monomers can arise: (i) first, by addition of the more reactive norbornene double bond to cyclopentadiene will form the cyclopentene ring terminated monomer (F-x1.2.96)
-
(296)
and (ii) second, by addition of the least reaofive cyclopentene double bond to cyclopentadiene will form the norbomene moiety terminated monomer (Eq. 2.97).
+
r
Similarly, tetra-, penta- and multicyclopentadiene monomers will be produced readily from cyclopentadiene by successive Diels-Alder reactions (Scheme 2.43).
68
Scheme 2.43
If the starting molecules is indene and cyclopentadiene is then reacted successively, several l~lycyclic norbomene-like monomers l~ving the indane end group can be obtained ~62 (Eq. 2.98).
The synthesis of a fullerene monomer, the C6o derivative of norbornene, has been successfully effected in 43 % yield by Prato et al. ~63 by the reaction of quadricyclane with C60 hydrocarbon in toluene at 80~ (Eq. 2.99).
A
(2.gg)
This highly strained monomer has been effectively employed in the metathesis copolymerization reaction with norbomene to produce high molecular weight polymers with interesting electronic and electrochemical properties.
69 2.5.3. Synthesis of Functionalized Cydoolefins A large number of substituted cycloolefins containing a variety of functional groups can be prepared either by conventional or specific methods. 2.5.3.1. Halogen-Containing Monomers Fluorinated compounds. Fluorinated bicyclo[2.2, l]heptenes were prepared by Feast and Wilson 's4 via Diels-Alder reaction of fluorinated alkenes as &enoplfiles, i.e., 3,3,3-trifluoropropene, perfluoropropene, perfluoro-2-butene and 2,3-dichlorohexafluorobut-2-ene, with cyclopentadiene (Eq. 2.100-2.103).
[~
[~
[~
+
.
+
CHCF3 II CH2
-'~
(2.100)
H F
CF2 II CFCF3 CFGF3 II CFCF 3
CF3
=
(2.101) CF3 CF3
.
~
(2.102) CF3
[~
+
CClCF3 II CClCF3
..-
CF3
CI
(2.103)
CF3 Fluorinated bicyclo[2.2.1]-hepta-2,5-dienes have been similarly prepared by the same authors through the reaction of fluorinated alkynes as dienophiles, e.g., hexafluorobut-2-yne and 3,3,3-trifluorobutyne, with cyclopentadiene (Eq. 2.104-2.105).
70
[~ [~
CCF3
+
III
.~
CCH3
cF3
(2.104)
CH3
CCF3 III CCF3
+
~
=
~
CF3
(2.105)
CF3
Reaction conditions and yields obtained in the synthesis of some fluorinated bicyclo[2.2, l]heptenes and bicyclo[2.2.1 ]-hepta-2,5-dienes are presented in Table 2.2. Table 2.2. Synthesis of fluorinated bicyclo[2.2, l]heptenes -2t5-dienes' Dienophile Reaction Ten~rature time~ hr ~ CF3CF--CFz 72 160 CF3CF=CFCF3 24 100 CF3CH---CH2 72 160 CF3CCI=CCICF3 72 160 100 CF3C=C=CF3 24 155 CF3C~CH 48
and
'Data~ n reference~
'
Yield % 85 90 65 35 90 82
Diels-Alder addition of fulvene and substituted fulvenes to hexafluorobut-2-yne as dienophile gives rise to a new series of fluorinated norbomadienes~S (Eq. 2.106-2.107).
[ ~
+
i
F3
CF3 CF3
CFa
~
F3 CF3
(2.106)
71 When perfluorinated cyclobutene and cyclopentene were used as dienophiles in Diels-Alder reaction with cyclopentadiene, highly fluorinated norl~mene derivatives have been obtained ~ (Fxi. 2.108-2.109). 9 F
IF. F
F•
[~+
(2.108)
F
F
---~
(2.109)
F dienophile,
Similarly, with N - C 6 F s - m a l ~ d r as cyclo~tadiene produced a new fluorinated norbomenederivativesuitablefor ring-opening metathesis polymerization '6v (Eq. 2.110). 0
~~)
N-CeF5
4-
0
=O N'--CeF5
(2.110)
By the reaction of tetrafluorobenzyne with cyclopentadiene or dimethylfulvene, fluorinated arenenorbomadienes can be obtained 16s'169 (Eq.
2.111-2.112).
.I
F
F
F
-1 F
(2.111)
F
tF F F
(2.112)
72 The reaction of 2,3-dimethylenebicyclo[2.2.1 ]hep-5-ene with a perfluorobut-2-yne provided bis(trifluoromethyl)methanotetrahydronaphthalene (Eq. 2.113). CF3
(2.113) CF3
3
Further dehydrogenation of bis(trifluoromethyl)methanotetrahydronaphthalene led to 9,10bis(trifluoromethyl)benzobicyclo[2.2.1 ]hepta-2,5-diene ~7o(Eq. 2.114).
//
CF 3
H =
CF3
3
(2.114)
3
By an alternate route, the bridgehead isopropylidene derivative of 9,10-bis(trifluoromethyl)benzobicyclo[2.2.1 ]hepta-2,5-diene could be prepared from dimethylfulvene and 4,5-bis(trifluoromethyl)benzyne ~'~ (Eq. 2.1 15).
"cFa
.=
r'-~",,,~CF3 (2.115)
~CF3
CF3
The monomer 7,8-bis(trifluorome~yl)tricyclo[4.2.2.02"5]deca-3,7,9-triene, used by Edwards and Feast ~7~ for the preparation of polyacetylene precursor polymers has been readily synthesiz~ in 80 % yield by the thermal reaction between hexafluorobut-2-yne and cyclooctatetraene'n'~n at 120~ (Eq. 2.116).
F3C + -
CF 3
F3C,)
#
(2.116)
73 Another fluorinated monomer, used in the "Durham" precursor route for polyacetylene synthesis, 3,6-bis(trifluoromethyl) pentacyclo [6.2.0.02'4.03"6.0s'~]dec-9-ene, can be conveniently prepared by the photoisomerization reaction of 7,8bis(trifluoromethyl)tricyclo[4.2.2.0~'S]deca-3,7,9-triene~7~ (Eq. 2.117).
F3C\ . . ~
F3C~
(2.117)
Chlorinated compounds. A wide range of chlorinated monomers with the potential of manufacturing flame retardant polymers have been prepared by chlorinating the cycloolefms and subsequently reacting these chlorinated products with new monomers. Cycloolefins of the monoene, diene or polyene type provide chlorinated monomers by direct chlorination or hydrochlorination, but the reaction has generally a low s r 175 Chlorinated cyclopropene can be prepared by the general methods used for this type of compounds such as dehydrochlorination reaction of dichlorocyclopropane in the presence of bases, leading to lchlorocyclopropene (Eq. 2.118).
+
HCI
(2.118)
or direct chlorination of cyclopropene in the presence of specific initiators, with formation of 3-chlorocyclopropene ~" (Eq. 2.119).
~> + CI2 ~
~-CI
+ HCI
(2.119)
Chlorinated cyclobutene can be manufactured by similar methods from cyclobutene by the selective chlorination in the allylic position or from dichlorocyclobutane by mild dehydrochlorination (Eq. 2. 120-2.121). /CI
§
oh
il !
+
NO,
(2 2o)
74 /CI
! !
\
"~
[
I
J
CI
+
HCI
(2.121)
cI
Using the above procedures, l-cldorocyclopentene can be obtained from 1,2-dichlorocyclopentane through dehydrochlorination while 3chlorocyclopentene from cyclopentene via direct chlorination of cyclopentene (F4.2.122-2.123). Cl
+
HCI
(2.122)
Cl
On the other hand, chlorinated bicyclic and polycyclic olefins can be prepared by several more specific methods. Thus, reaction of norbomadiene with dichlorocarbene, generated from chloroform under the action of aqueous alkali solution in the presence of a phase transfer catalyst, provides exo-3,4-dichlorobicyclo[3.2.1]octa-2,6-diene as the main product m76 (Eq. 2.124). (2.124) CI
Reaction of this compound with lithium aluminium hydride in dry ethyl ether produced 3-chlorobicyclo[3.2.1]octa-2,6-diene in high yield (Eq. 2.125).
C~CI LiAIH_._
(2.125)
I Tetrachlorocyclopropene, prepared from trichloroethylene and dichlorocarbene with subsequent dehydrochlorination, ~" reacts readily I
75 with excess cyclopentadiene at room temperature to form 2,3,4,4tetrachlorobicyclo[3.2.1 ]octa-2,6~ene ~76(Eq. 2.126).
+
C
I
25oc
c,
cs
(2.126)
C Reaction of tetrachlorocyclopropene with 6,6-dimethylfidvene under more severe conditions (reflux temperature for 24 hr) gives rise to 2,3,4,4tetrachloro-8-isopropylidenebicyclo[3.2, l]octa-2,6-diene~*S (Eq. 2.127). C +
c
CI I
CI
24h cch
-
CI cI
(2 127) "
Diels-Alder reaction of cis-3,4-dichlorocyclobutenem with dicyclopentadiene yields as the main product endo-cmti-3,4dicNorotricyclo[4.2.1.0~]non-7-ene of the fmH" possible isomers, endo, anti-, a~o, syn-, exo, anti-exo, syn-isomers 1~6(Eq. 2.128).
~ +
~
I
CI
endo-enli
"~CI cl$
exo-syn
CI endo4yn
(2.128)
exo4ntl
Chlorinated cyclopentadiene reacts with a wide range of dienophiles to produce chlorinated norbomene derivatives of high interest as monomers for ring-opening p o l y m ~ o n reactions. Thus, the Diels-Alder adduct of 5,5-dichlorocyclopentadiene with acetylene will readily produce 7,7dichloronorbomadiene (Eq. 2.129).
76 C
cl
CI
+ III
=
(2.129)
Reaction of dichlorocyclopentadiene with cyclooctadiene will form the corresponding chlorinated tricyclic and tetracyclic hydrocarbons (Eq. 2.130-2.131). C
I
+
( )
CI
~
(2.130)
8O
c c, (2.131)
Similar reactions of hexachlorocyclopentadiene (obtained by the exhaustive chlorination of cyclopentadiene) with various cyclodienes, including cyclooctadiene and norbomadiene, give rise to potential monomers for flame retardant polymers. With an excess of cyclooctadiene, the 11 Diels-Alder adduct of perchlorocyclopentadiene with cyclooctadiene was prepared in high yield~79(Eq. 2.132).
cK~Cl
CI
CI
(2.132)
i,...._
CI
C
This monomer is a crystalline product and is recovered by precipitation rather than by distillation. Elastomers derived from this compound have been explored in some detail. Analogously, the Diels-Alder reaction of perchlorocyclopentadiene with norbomadiene will form the 1"1 adduct, Aldrin, a potential monomer for flame retardant polymers ~s~(Eq. 2.133).
77 CI Cl
CI CI Cl
O
cK/cl C l ~ ~
+
(2 133)
Other cycloolefins can react in a similar way with chlorinated cyclopentadienes to produce a variety of chlorinated bicyclic and polycyclic monomers of interest for specialty polymers production. Isodrin~S~ obtained from cyclopentadiene and 1,2,3,7,7pentachloronorbomadiene, is another attractive monomer for highly chlorinated polymers (Eq. 2.134).
<3
CI
CI lb..-
(2.134)
I
I 2.5.3.2. Oxygen-Containing Monomen
Alcohoh. 5-Hydroxybicyclo[2.2.1]hept-2-ene was prepared from 5acetoxybicyclo[2.2.1]hept-2-cne by hydrolysis with sodium hydroxide in water at reflux for 8 hours '=~ (Eq. 2.135).
OAc
~~7,/
H O ~~~7,/OH , -'~ NaOH
(2.135)
On the other hand, 5-hydroxymethylbicyclo[2.2.1]hept-2-ene ~'~ could be obtained from 5-carbox~icyclo[2.2.1 ]hept-2-ene by reduction with LiAIH4 (Eq. 2.136).
LiAIH4 COON
Et20
(2.136) 20H
78 A dialcohol, 2,3-dihydroxybicyclo[2.2.1]hept-5-ene, was manufactured from bicyclo[2.2.1 ]h~t-2,5--diene by the selective oxidation of one double bond with OsOJN-methylmorpholine N-oxide ~z (Eq. 2.137).
o,o, oOH
(2.137)
Ketones. The 11 Diels-Alder adduct of cyclopentadiene with dichlorovinylene carbonate hydrolyzed readily in aqueous 1,4-dioxane to yield the ~-diketone, bicydo[2.2, l]hept-2-ene-2,3-dione ~ (F~. 2.138).
CI
0 0
(2.138)
0
This monomer has been used in metathesis copolymerization reactions with norbomene. Related monomers employed in similar copolymerization reactions were 3,3-dimethowbicyclo[2.2.1]hept-5~2-~ne and exo-3chlorobicyclo[2.2.1 ]hept-5-ene-2-one (Scheme 2.44).
.OMe Me
Scheme 2.44 Ethers.
5-Methoxymethylbicyclo[2.2.1]hept-2-ene was obtained in two
steps starting from 5-~xybicyclo[2.2.1 ]hept-2-ene via 5-hydroxymethyl compound as an intermediate ~*~(Eq. 2.139).
Et20 COOH
2.Mel/Me2SO CH2OH
CH2OMe
79 Another norbomene ether, 7-methoxybicyclo[2.2. l]hept-2-ene, was prepared from the corresponding acetate by basic hydrolysis and subsequent conversion of the potassium salt with methyl iodide ~ (Eq. 2.140). e
KOH
CH31
(2.140)
7-tert-Butoxybicyclo[2.2.1]hepta-2,5-diene can be directly prepared from norbomadiene using readily available reagents lss (Eq. 2.141).
U (2.141) This compound may in turn be converted into the whole range of 7substituted derivatives of norbomadiene (Eq. 2.142). U
(2.142) where X is alkyl, phenyl, OR, CI and COOK. Carboxylic acids. Bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid was obtained by hydrolysis of the Diels-Alder adduct of cyclopentadiene with maleic anhydride in warm water (Eq. 2.143).
~~C
c Q~
O/O
"---"~"
~ c
0 0H
COOH
(2.1 4 3 )
Esters. Bicyclo[2.2.1]hcpt-5-en-2-yl acetate was prepared by the DielsAlder reaction of cyclopentadiene with vinyl acetate TM (Eq. 2.144). ~
*
L
OCOCH3
COCH3
(2.144)
80 Both e ~ and exo-isomers are formed (75 % endo, 25% exo) which could be separated by distillation though a spinning band column at 45 mmHg. When acrylates and methacrylates are employed as dienophiles, 5carboalkoxy-bi~do[2.2.1 ]hept-2-ene can be produced (Eq. 2.145-2.146).
Q
+ ~
~
(2.145)
COOR
COOR (2.146)
Anhydrides, Both e x o and endo isomers of bicyclo[2.2.1 ]hept-5-cne-2,3dicarboxylic anhydride have been pre~ed by Diels-Alder reaction of dicyclopentadiene with maleic anhydride (Eq. 2.147).
C>
CO
+
co 0~0
/0 ~
CO
(2.147)
Whereas endo isomer is essentially inert in the presence of classical metathesis catalysts, the exo isomer undergoes smooth metathesis homopolymerization and copolymerization. 2,3-Dichlorobicyclo[2.2. l]hept-5-ene-2,3-
+ Cl~l cON0
Cl/Nco/
=
Cl
C JCOx
o/O
(2.148)
Shahada has shown that the endo stereoisomer readily polymerizes in the presence of metathesis catalysts.
81 Carbonate~ Norbom-5-ene-2,3-diyl bis(methyl carbonate) was prepared from norbom-5-ene-2,3-diol and methyl chloroformate at room temperature in the presence of pyridine (Eq. 2.149).
+ 2 HCOOMo ~
[ ~ OCOOMo ~OCOOMo
(2.149)
3a, Ta-Dichloro-3a,4,7,Ta-tetrahydro-4,7-methano..l,3- benzodioxol-2-one, another cyclic norbomene carbonate, was prepared by thermal Diels-Alder condensation of 1"1 dichlorovinylene carbonate and cyclopentadiene~n(Eq. 2.150).
Q§
c C
o,
o,C~
The endo isomer has been employed by Feast and Harper m in the ringopening polymerization with classicalmetathesis catalysts WCI6/Sn(CH3)4. 3a,9a-Dichloro-3 a,4,4a,5,8,8a,9,9a-octahydro-4,9: 5,8- dimethanonaphtho[2.3--d]-l,3-dioxol-2--one was obt~ed by Diels-Alder reaction of 1:2-dichlorovinylene carbonate with cyclopentadiene (Eq. 2.151).
ck o\ +clio c~
CI
\
(2.151) O
Again, the endo,endo isomer has been analogously used by Feast and Harper ts3 in the ring-opening polymerization with the metathesis catalyst WCts/Sn(CH3),. 2.5.3.3. Sulphur-Containing Monomers
Bicyclo[2.2.1]hept-5-cne-2,3-di(S-methyl dithiocarbonate) was manufactured staring from bicyclo[2.2.1 ]hept-5-2,3-diol reacted in a first step with caubon disulphide and then iodomethane ~95(Eq. 2.152-2.153).
82
OHH
SII I ~ /O-~C-S H ~O-(~-S H
CS2 ._ DMSO "-
S
(2.152)
S
CH31 O--(~-SH
NaOH
.._ fi,,,[~,/O-~ -SCH3 v
~,'--',.,,z.~ , .,,.. , O_,.~_SCH3 L, (2.153)
2.5.3.4. Nitrogen-Containing Monomers.
Nitriles. Diels-Alder reaction of cyclopentadiene with acrylonitrile produces readily bicyclo[2.2. ] ]hept-5-ene-2-nitrile i~mgs (F-xl. 2.154).
+
II,.
CN
_
(2.154)
CN When methacrylonitrile is employed in conjunction with cyclopentadiene, 2methyl-2-cyano-bicyclo[2.2.1 ]hept-2-ene will be formed (F_,q.2.155).
+
;L
CN
(2.155)
CN
Amides. Reaction of acrylamide and N-substituted acrylamide with cyclopentadiene gives rise to norbornene derivatives bearing amide and Nsubstituted amide group ~99(Eq. 2.156-2.157).
"-
CONH2 r
CONHR
/~CONH ~~,,CONHR
2
(2.156)
(2.157)
83
Imides. Cycloaddition reaction of cyclopentadiene with m a l ~ d e bicyclo[2.2, l ]hept-5-ene-2,3-dicarboximide z~176 (Eq. 2.158).
CO
H
forms
(2.158)
Similar reaction of N-alkyl maleinimides with cyclopentadiene will produce N-substituted bicyclo[2.2,l]hept-5-ene-2,3-di~xi~deslZ~176176 (Eq. 2.159).
2.5.3.5. Boron-Containing Monomers.
(5-Cyclooctenyl)diethylborane has been prepared statlfi~ from cyclooctadiene and catecholborane. The intermediate borinated compound treated with diethylaluminium chloride led to the final product" (Eq.
2.160).
Et.AI~ ( ~-BEt (2.160)
0 "
Norbomenyl-9-borabicyclononane was produced by hydroborinating norbomadiene with 9-borabicyclononane (Eq. 2.161). B
+ /"~"1
B
(2.161)
The ~H NMR spectrmn of the monomer was found to be in agreement with the expected structure for the exo form. This hydrobofination reaction was very selective, occurring by cis addition from the less hindered side of the double bond of norbomadiene.
84 2.5.3.6. Silicon-Containing Monomers.
2-Trimethylsilylbicyclo[2.2.1]hept-5-ene can be readily available by Diels Alder reaction of cyclopentadiene with vinyltrimethylsilane7~ (Eq. 2.162).
C
+ IL ' SiMe3
=- ~_J~SiMe3
(2.162)
In case that allyltrimethylsilane is employed as dienophile instead of vinyltrimethylsil~e, 5-methyl(trimethylsilyl)bieyr will be produced 2~ (Eq. 2.163).
(2.163)
/~SiMe3
§ II
'~ilVle3
Diallyldimethylsilane will form two different silylated addition products as a function of the reaction conditions. With 1 equivalent of diallyldimethylsilane cyelopentadiene gives rise to 5methylene(allyldimethylsilyl)bicyclo[2.2.1 ]hept-2-ene whereas two equivalents of diallyldimethylsilane lead to bis(5methylenebicyclo[2.2.1 ]hept-2-ene)dimethylsilane 2~ (Eq. 2.164-2.165).
C
2
[~
---N S i / / N
+
+
--- \
__
/
Si
'
/ N
~--
(2.164)
/ \
I
2-Dimethylsilylbicyclo[2.2.1 ]hepta-2,5-diene has been prepared using Schlosser method by metallation of bicyclo[2.2.1]hepta-2,5-diene and further reaction of the metallated intermediate with dimethylchlorosilane z~ (Eq. 2.166).
85
tBuONa THFI-50~
U
HSiMe2C/ j ~ 20-250C
iMe2H
"-
(2.166)
2.5.3.7. Metal-Confining Monomers. At present a large number of metals have been introduc~ as component parts of polymefizable monomers. Of these, tin and germanium form a first group that give rise to monomers used for specialty polymers. Cyclooctenyltributyltin is thus formed from cycloctadiene and tributyltin hydride2~ (F,q. 2.167).
( )
+ Bu3SnH ~
(
~Sn
Bu3
(2.167)
Similar reaction of norbornadiene with tributyltin hydride will produce 2tributyltinbicyclo[2.2.1]hept-5-ene (Eq. 2.168).
+
Bu3SnH
/ ~ S
nBu3
(2.168)
Analogously, the addition reaction of allyltrimethylgermanium with cyclopentadiene w i l l form a 5-substituted norbomene having trimethylgermanium attached at the side group ~~ ~ q . 2.169). I>,,, N / (2 169) + Ge ~ Ge 9 A series of substituted norbomenes containing Sn, Pb and Zn have been also prepared by Diels-Alder reaction of cyclopentadiene with the corresponding aza-metallacycles210-2 12(F,q. 2-170-2.172).
tBu
/tBu
N!
Nk/tBu
"SnCI 2
N\/ ~u
(2.170)
86
SiMe
+
Pb
'
~
~
,SiMe3
~~"'""~NXpb
SiMe3
SiMe3
tBu
0
(2.171)
tBu
+ C
"-
1~'n "R
\R
(2.172)
\tBuXR
They were used for synthesis of the block copolymer films that are static cast from benzene and contain the organometallic reagent distributed in lamellar, cylindrical, or spherical microdomains. Substituted norbornenes derived from metallocenes of lead are easily available by Diels-Alder reaction. 2~3-zm4These lead metallocenes may contain one or more dienophiles able to react with one or more equivalents of cyclopentadiene (Eq. 2.173).
+
'm-"--"
~
~
(2.173)
The same derivative of lead, Pb(CpN)2, could be prepared in 85% yield from LiCp~ and PbCI2 as a pure endo compound 213 (Eq. 2.174).
2
PbCI2
THF ..= 85%
+ 2 LiCl
(2.174)
Li
Ferrocene and c o b a l t ~ e derivatives are suitable dienophiles which form Diels-Aldcr adducts with cyclopentadiene2~s (Eq. 2.175-2.176).
87 C02Me
Fo
~t~
+
=
,~~
v
(2.175)
C02Me Co
+
~
~
v
(2.176)
Palladium-containing monomers having norbomene moiety were prepared from palladium complexes and cyclopentadiene by the Diels-Alder route2~6. 2~7(Eq. 2.177).
"0
"
,2,77,
Polymer films with small palladium clusters (<100A) whose sizes and size distributions vary with the size of the metal-c~ntaining spherical microdomains.
2.5.3.8. Monomers for Side-Chain Liquid Crystalline Polymers A novel synthesis of a 5-substituted cis-cyclooctene, cis-[1 l-(4'cyanobiphenyl-4-yloxy)undecyl]r used as a monomer to obtain a side-chain liquid crystafime poly(l-octenylene), reported S t e ~ and coworkers 2~s (Eq. 2.178). (2.1711)
Several monosubsfituted norbornene derivatives bearing different methoxyand cyanobiphenyl groups as mesogenic entities have prepared Schrock and coworkers z~9.~ (Eq. 2.179-2.182).
88
.... K2~MF
=-~~~CH20(CH*~nO'~~~~
(2.179)
=- ~~~wCO2(CH2~f~~~~)Me (2.180)
HO(CH2~CN
.
.
.
.
.
Ne~a,'rHr
: ~Oz(CH2~CN
=- ~
(2.181)
<xx~ ~ _ /
_,_ .,~)r~
(2.182)
The norbomene derivatives used as monomers for the synthesis of laterally attached side-chain liquid crystalline polynorbomenes were prep~'ed by Pugh and ex~workers224~ by two different methods. The first method was applied to prepare monomers bearing mesogenic groups with hydrocarbon and fluorocarbon segments (Eq. 2.183-2.184).
,CH2Br
K2CO3 DMF
~
O __/CH20 H(CH2)nOQO~~( _
cH 2 ~ H (F_x].2.IB3)
89
~ f ~ ,CH2Br F(CF2)rn(CH 2 ~ O ~ C O-~__/~OC ~ O ( C O O
K2co31 & DMF
H2)n(CF2)mF
OOH
CO
~ ~ ,CH20 O--~,__/~--O(~~ O ( C O O I
F(CF2)m(CH2)nO~ C
H2)n(Cg2)mF (Eq. 2.184)
The second method for the synthesis of monomers having mesogenic groups with oligosiloxane substituents (Eq. 2.185).
~, ~,
CHl--~l--(O-~l)m---~CHz)rtO~O CHz CHz
~~o~ (~
CHzCiz
c
,,. ~ ~
CHs CHs
~ ~ H~
Ha
(CHz)ct---( F,--O)m-- I,~CHI CHz Hz
OCI
~xo
~-C~,o..
CHzb
CHs
(~.2.1s5) Similar synthetic procedures have been employed by Stelzer and coworkersz~27 to prepare disubstituted norbornene derivatives with cyanoor methoxybiphenyl as mesogenic groups (Eq. 2.186-2.187).
mr
~.lss~
90
••,,COCl. COCl
2IPy, C H ~DMAP~ C O 0 ( C ~ ~ ~ ~ - C 2HO(CI~~~~~"C N
N
CO0(CH~~-~~N
(2.~sz)
Recently, such monomers have been successfully employed to manufacture a wide range of side-chain liquid crystagine polymers with an attractive thermal and especially thermotropic behavior.
2.5.3.9. Synthesis of Heterocydic Monomers Simple heterocyclic monomers can be prepared by conventional methods; for instance, 2,3-dihydrofur~ is obtained by the partial catalytic hydrogenation of furan, under controlled conditions, while 2,3-dihydro-7pyran, from ethylene and acrylic aldehyde, by Diels-Alder reaction 22s (Eq. 2.188-2.189). [Cat] "-
(2.1
In addition, dihydropyran can be readily prepared from furfuryl alcohol by dehydration over alumna at 3 50~ r~ (F-xl. 2.190)
'~
AI203,350~ CH2OH ' ' -H20
~ ~O
(2.190)
A variety of heterocyclic substituted and unsubstituted olefins can be efficiently obtained from heteroatom-containing dienes by ring-closing metathesis reactions, z3~These reactions are favored for the production of 5,6-, 7- and 8-membered tings in the presence of molybdenum or ruthenium catalysts that are tolerant toward heteroatom functionality. In one process, 1,4-dihydrofuran was readily obtained from diallyl ether in the presence of R~Os/Al203 or R~Os/Al20;/Bu4Sn as a catalyst (Eq. 2.191).
O~__~ ~
=
(-~'~
(2.191)
91 Similarly, substitutod 2,5-dihydrofuran and 2,3-
=
~,,:,~--- P h
(2.192)
and 2-phonyl-2,3-dihydro-~-pyran (Eq. 2.193).
~",T/ph -~~0
~ ~ o ph
=
(2.193)
Substituted oxopins are also roadily obtained from unsaturated monocthers by ring-closing metathesis in the presence of molybdenum or mthonium carbone initiators (Eq. 2.194-2.195).
Ph~,.~.~..
[Ru]
o-../'=
Ph
Ph (2.194)
.-
__••Et O ~
~O
[Mo]
"Me
"11= 92%"-
Ph
(2.195)
Similarly, substituted ac,c ~ s have been prepared from unsaturated diothors in the prosonce of molybdenum initiators (F.q. 2.196).
Me 0-...../
"Me
"-
11= 89%
Ph
(2.196)
92 Analogously, nitrogen-, sulphur- and phosphorus-containing heterocyclic olefi~ have been prepared from the linear heteroatomcontaining dienes by ring-closing metathesis under the action of adequate metathesis catalysts (Eq. 2.197-2.199).
[Mo]. =._
Ph--N
~~q~
(2.197)
I
~
Ph
[Mo] m
Ph-P
= [w]
/S-~ =
(2.198)
~'-p-~ I
(2.199)
Ph
Oxanorbornene derivatives. A large number of substituted and unsubstituted oxanorbomenes can be prepared by the Diels-Alder reaction of fiuml with a variety of dienophiles. Thus, the simplest representative of the series, 7-oxanorbornene, is readily available by condensation of furan with ethylene (Eq. 2.200). 0
When substituted furan and substituted olefins are employed, various substituted 7-oxanorbomenes can be produced by this reaction ~" (Eq. 2.201).
R
O + i1
0 (2.201)
93
On usingolefinswith functionalgroupsasa dienophile,Daubenand Krabbenhafl~s9prepared 7,-oxanorbomenebearing nitrile, ester, aldehyde and ether functionality (Eq. 2.202).
X
O =
~ X
(2.202)
When acetylene derivatives are used as dienophiles in association with furan compounds, oxanorbomadiene derivatives can be obtained by this way (Eq. 2.203). R
R
COOR'
+ III
0 R
=
COOR'
COOR'
R 'COOR'
(2.203)
Further reaction of oxanorbomadiene derivatives with furan will form the corresponding dioxahexahydronaphthalene derivatives (Eq. 2.204).
~CC oR zRO + R~O 02R' R
~
RCo /2RR
(2.204)
7-Oxabicyclo[2.2.1 ]hept-5-ene-2,3-di~xylic anhydride was prepared by Diels-Alder reaction of furan with maleic anhydride~9~ (Eq. 2.205).
Co+Coo,
,f co,
(2.205)
Hydrolysis of 7-oxabicyclo[2.2. l]hept-5-ene-2,3-dicarboxylic anhydride produced 7-oxabicyclo[2.2.1]hept-5-ene d i ~ x y l i c ~ d 191 (Eq. 2.206).
94 CO~k
0/0
"
H20
O
=-
I,,%,~ .COOH
~ l ~ C OOH
(2.206)
Reduction of 7-oxabicyclo[2.2. l]hept-5-ene-2,3-dicarboxylic acid with lithium aluminium hydride formed 7-oxabicyclo[2.2.1]hept-2-ene-2,3dimethano1192 (Eq. 2.207).
COOH LiAIH4 OOH
0
.~.I~CH2 OH //.~.~/..CH20H
(2.207)
3-Mcthoxymcthyl-7-oxabicyclo[2.2. l ]hcpt-2-cnc-2-mcthanol w a s prepared from 7-ox~i~clo[2.2. l]hept-2-ene-2,3-dimeth~mol by the reaction with sodium hydride and subsequent treatment with iodomethane '92 (Eq. 2.208).
~
a. 1 Nail
CH2OH b. 1 CH31 CH2OH
CH2OMe
CH2OH
'
(2.208)
Further on, 2,3-dimethoxymethyl-7-oxabicyclo[2.2. l]hept-5-ene was obtained from 7-oxabicyclo[2.2.1]hept-2-ene-2,3-dimethanol when two equivalents of sodium hydride and iodomethane were employed m~ (Eq. 2.209).
,~~fcC H2OH a. 2Nail H2OH b'2CH31 =
O
~..~.,CH2OMo ~ | 7"CH2OMe (2.209)
Alternatively, 7-oxabicyclo[2.2.1 ]hept-5-ene-2,3-dimethyl diacetate was prepared by esterification of 7-oxabicyclo[2.2.1]hept-2-ene-2,3dimethanol with acetyl chloride in the presence of pyridine ~ (F,q. 2.210).
~ . ~ C cH2OH 2 AcOCI "= ~ H0 2~ O A.CcH2OAc H2OH PY
(2.210)
95 Norbornene monomers for polydendritic polymers have been prepared by the condensation re,actions of 7-oxanorbomene-5,6-carbonate with suitable ben~lic alcohols ~ ' ~ (Eq. 2.211).
O
~~OC Hz'~~O(C Hz)I=H 92 HOCHz'~t~~OCH2.~~~)(CH2),zH \ OCH2~lCH2)lzH
O
7C Hz'~k~O(C Hz)IzH
>_oc.,_< >o,c.,,,,. CH2
O(CH2)12H
r
~//OC H2-~ /~'~O(CH2)lZH
o O
--H2
'~
__
"-
~OOH2"~ ~O(CH2),2H ~OCH2"~'.. ~O(C Hz),2H (Eq. 2.211)
Azanorbornene derivatives. When pyrrole is used instead of furan, a wide range of 7-azanorbornene derivatives can be obtained by the Diels-Alder reaction with various dienophiles (Eq. 2.212).
~NH
*
(2.212)
N-Substituted pyrrole will give also N-substituted 7-azanorbornene derivatives (Eq. 2.213).
96 R~ N
N--R
(2.213)
+
2-Methyl-2-azanorbomene was prepared by the reaction of methylamine hydrochlofide with formaldehyde and cyclopentadiene (Eq. 2.214).
-HCI ~
+ CH20 + I'K31H2N--CH3
H20=-
CH3
(2.214)
In a similar fashion, 2-benzyl-2-azanorbomene was prepared from benzylamine hydrochloride, formaldehyde and cyclopentadiene (Eq. 2.215).
C
__~ + C1"120+ HCI'I"I2NHzC
-HCI -I"~O
(2.215)
l,l-Dimethyl-l-silacyclobutene, ~ a very reactive monomer, was prepared by flash high vacuum pyrolysis of diaUyldimethylsilane at 750~ (Eq. 2.216). ' .
\Si//_ \
' 750"C~
EIsi/
(2.216)
\
Other substituted sila-monomers, e.g., l-alkyl- and l-aryl-silacyclopentene, have been obtained by treating all~l- and aryldichlorosilanes with butadiene and magnesium. On this line, l-methyl-l-silacyclopentene and l-methyl-lphenyl- 1-silacyclopent-3-ene were readily prepared from methyldichlorosilane and methylphenyldichlorosilane, respectively, with 1,3butadiene and magnesium in tetrahydrofuran 2~ (Eq. 2.217-2.218).
(
+
HSiMeCI2
+ SiMePhCI2
IVlg~HF c s ( Hi .~ M HF
..~
Me
i Xp h
(2.217)
(2.218)
97 Analogously, l,l-dimethyl- and 1, l-diphenyl-l-silacyclopent-3-ene were synthesized by the addition reaction of dimethyland diphenyldichlorosilane, respectively, with butadiene, under the same conditions (Eq. 2.219-2.220).
~
SiMe2CI2 Mg/THF C S i /Me = XMe
+
+ SiPh2CI2
Mgnf CS /eh =-
ixp h
(2.219)
(2.220)
Functionally-substituted silacyclopentenes have been prepared by Heinicke ~ from silylenes, e.g., MeSiCI, MeSiOMe, MeSiNMe2, and dienes such as butadiene, isoprene and 2,3-dimethylbutadiene. For instance, methylchlorosilylene gives rise by the cycloaddition reaction with the above dienes to 1-chloro- 1-methylsilacyclopent-3-enes (Eq. 2.221). c, L ~ S ( - Me ,'."-~"
(2221, \Me Similar reaction os mcthoxym~ylsilylcnewill produce l-methoxy-]methylsilacyclopent-3-ene(F_,q.2.222-2.:223).
+ [CIMeSi:]
--
+ [Me(MeO)Si:] ~
R~ R
"
"qt
+ [Me(NMe2)SI:] ~
R/~
Si
+
(2222)
I\M e
R~L.~~ /NMe2 RT'~,,~ NMe2 R~,..jSI\M e + R,~Sk~Me (2.223)
The silylenes used as dienophiles in these reactions can be readily generated in situ thermally from disilanes (Eq. 2.224).
Me
Me
c~
cl
Me
,Me
400-550oc
.~
[CIMeSi:]
(2.224)
98 Further reactions of l-chloro-l-methylsilacyclopentene can provide a range of substituted silacyclopemenes suitable as reactive monomers for ring~ opening polymerization (Scheme 2.45).
C$i fOR \Me
CSi
/NEt \Me
Eh
m,,'~
~
....
~ O'~
/--x
ixMe
\Me --"NS/Me i
/H
CSi
Lj Me\ s/ f ' l
\Me
Scheme 2.45 2,3-B~5-silaspiro[4.4]nona-2,7-diene was prepared from benzyl(chloromethyl)dichlorosilane by intramolecular Friedel-Crai~ cyclization and subsequent addition of the intermediate l,l-dichloro-3,4benzo-l-silacyclopent-3-ene with butadiene and magnesium in tetrahydrofuran 2~ (Eq. 2.225).
~
C1"12-.SiCh AICI3 ~]~SiCh (
~S0
(2225)
Further treatment of 2,3-benzo-5-silaspiro[4.4]nona-2,7-diene with catalytic amounts of n-butyllithium and fIMPA resulted in the formation of a dimer, 2,3 12,16-dibenzo-5,10-~siladispiro[4.4.4.4] octadeea-2,7,12,16-tetraene (Eq. 2.226).
~Si~
nBuU/I-MPA TPF/-78~
(2226)
99 Likewise, dimerization of 2,3-dimethyl-5-silaspiro[4.4]nona-2,7-diene in the presence of n-butyllithium and ItMPA gave 2,3:12,13-tetramethyl-5,10disiladispiro[4.4.4.4]octadeca-2,7,12,16-tetraene (F-4. 2.227). 2 ~Si~
nBuLilHMPA -THFI-78~
i:~
(2.227)
By the same route, l,l-divinyl-l-silacyclopent-3-ene yielded sil~cant amounts of the dimer, 1,1,6,6-tetravinyl- 1,C~:lisila-3,8-cyclodecadiene along with the ring-opened polymer2~ IF_4. 2.228).
2
THF/-78~
.~J
"
i X~.
(2.228)
Substituted gennana- and stanacyclopentene were prepared by ringclosing metathesis reactions of the corresponding Ge- and Sn-containing dienes under the action of adequate metathesis catalysts TM (Eq. 2.2292.230). Me\ /~,~ Re2Os/AI203/Bu4S n
\Me BU~sn/~ au/ ~
.
[VV]=CHCMe3= '
CSn/. Bu au
(2.230)
2.5.3.10. Synthesis of Macromonomers
a~-Norbornene-ended polystyrene macromonomers have been prepared from polystyryllithium capped with ethylene oxide and the resulting polystyrylethyloxide condensed with norbom-5-enyl-2-e.arbonyl chloridez3z~3 (Eq. 2.231-2.232). O ,B="1.= ,B= ~o~ ~ (2231) It
100
(2.232)
- UCI
Similarly, polybutadienyllithium treated with ethylene oxide and then condensed with norbom-5-enyl-2-carbonyl chloride gave rise to norbomene-ended polybutadiene macromonomersTM (F~. 2.233-2.234).
Toluene"- "
=---
"-
OeLJe
fJ•COCl ,
(2234)
=---
- LiCl
Several other (z- or r macromonomers, having as host polymer for instance l~lyethyleneoxideTM or Imlyethyleneoxide/polystyrene block copolymer, were also prepared by this way~ (Eq. 2.23 5-2.237).
~ L i
c6~
+ n+l~
11~ED~
~-Z
MeOH=
LP
PhzCH~
TI"IF ~
OK
(2235)
(2.236)
101
(2237)
Polystyrene macromonomers, containing a norbomene unit within the chain, suitable for ring-opening metathesis polymerization, have been prepared in three steps by anionic polymerization of styrene under the action ofsec-butyllithium, capping the basic polystyryl anion with propylene oxide to produce lithium 2-polystyrylisopropyl alkoxide and further condensation of two equivalents of lithium 2-polystyrylisopropyl alkoxide with bicyclo[2.2.1]hept-5-ene-2,3-dicarbonyl chloride 93 (Eq. 2.238-2.240).
(2.238)
oE)Ij~
I~
-2L~= '~T~--y
(2.239)
-'L'1--~1-'~' (2:~)
Such macromonomers have been successfully used to the manufacture of polymers with special architectures such as grafted, comb-like or other related structures.
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115
Chapter 3
CATALYTIC
SYSTEMS
There is a wide variety of homogeneous and heterogeneous catalytic systems employed for the polymerization of cycloolefins. These catalytic systems consist of one, two, three or more catalytic components and display a different type of catalytic activity, depending greatly on the nature of their components. They will be broadly classified in cationic, anionic, ZieglerNatta and ring-opening metathesis polymerization (ROMP) catalysts, though some other specific types are also active in the reactions of various monomers. As f~om these types of catalytic systems the cationic, ZieglerNatta and ring-opening metathesis polymerization catalysts have been extensively investigated in the cycloolefin polymerization reactions, in the present chapter we shall deal with these systems in more detail.
3.1. Cationic Catalysts Cationic catalysts constitute the first large class of catalysts explored in the polymerization reactions of cycloolefins. ~ These catalysts are generally BrOnsted or lewis acids, act in homogeneous or heterogeneous systems and consist of one, two or several catalytic components whose presence is essential for the catalytic activity. The BrOnsted acids are mainly reported for the polymerization reactions of a limited number of cycloolefins while a great deal of ~ s acids have been employed for the reactions of monocyclic and polycyclic olefins and parti~darly in the manufacture of hydrocarbon resins from terpene monomers. 24 Both types of cationic catalysts are theoretically and experimentally well documented in the related area of linear olefin polymerization ~ so that only specific aspects connected with the cycloolefin polymerization will be considered here while further details concerning their nature, characterization and structure will be found in several excellent reviews published on this topic. 5"7
116
3.1.1. Br6nsted Acids
In the classic~ studies on eycloolefm polymerization, various BrOnsted acids such as H2SO4, H3PO4, H3BO3, HF, HCI, HBr, HI, benzene sulphonic acid etc. have been employed to polymerize different monomers, m~ The reactions were mainly homogeneous and the process yield and product composition depended essentially on the nature and concentration of the acid used to promote the reaction. Generally, oligomers and low molecular weight polymers with undefined structures have been obtained, s Concentrated sulphurie acid has been initially employed for the dimerization and oligomerization of cyclic monoolefins such as eyclohexene or diolefins such as eyelopentadiene and later on for indene-coumarone fractions. ~4 Diluted sulphurie acid and benzenesulphonic acid have been further used for the polymerization of more active monomers like norbomene and dicyclopentadiene. In these reactions, monomer conversion and product yield or molecular mass depended greatly on the acid concentration and monomer nature as well as on other reaction parameters. Various compositions of acid initiators e o n ~ g sulphurie acid in association with phosphoric acid, boric acid, sulphonie acids or inorganic sulphates of the type M~(SO4)y (M=AI,Cr,Mg, Co,V) have also been reported for the polymerization of unsaturated alieyclic and cyclic fractions or heavy aromatic fractions in hydrocarbon resin synthesis. Heterogeneous catalytic systems consisting of organic hydrosulphates and formic acid deposited on bentonite or various aluminosilieates have also been found to be active in the polymerization reaction of hydrocarbon fractions. The product composition and reaction yields are largely dependent on the concentration of the acid and the nature of the support ranging generally from low oligomers to high molecular weight polymers of undefined structure and molecular mass. Related heterogeneous catalysts can also be obtained by acid treatment of various solid supports such as inorganic sulphates, phosphates, borates, silica, alumina, titania, aluminosilicates, aluminophosphates, etc. The nature and structure of the support are crucial in obtaining very active and selective catalytic systems and allowing operation conditions that direct the reaction pathway towards the formation of high or low molecular weight polymers.
117
3.1.2. Lewis Acids
Due to their wide accessibility and excellent catalytic properties, this type of catalysts have been extensively used in cycloolefm polym~on for several decades resulting in important industrial applications such as synthesis of the well-known hydrocarbon resins.~ They are mainly applied in homogeneous systems in adequate solvents but also heterogeneous catalysts are active and promote cycloolefm polymerization to different products, depending on the reaction conditions. Generally, they are one-component, two-component or multicomponent catalytic systems and their final composition is greatly dependent on the nature and quality of the solvent, the reaction conditions and the monomer structure.
3.1.2.1. One~omponent ~ i s
Acid Catalysts
Traditional Lewis acids have been employed extensively as onecomponent catalysts to polymerize cycloolefins by addition reaction in a proper solvent to ensure a homogeneous medium and good reaction conditions. ~'~'7These can be illustrated by AICI3, AIBr3, BF3, SnCh, TiCh, FeCI3, SbCIs, ZnCI2, organometallic compounds like AIEh, Et2AICI, EtAICI2 and several metallic salts having Lewis acid character. Of these catalysts, the most frequently encountered for the polymerization of simple and substituted cycloolefins are AICI3, BF3, SnCh, TiCh. AIBr3 is a more active catalyst than AICI3 and whereas the chloride is substantially insoluble in hydrocarbons, aluminium bromide is quite soluble. 7 This difference in solubility accounts for the fact that in physicochemical studies, aluminium bromide is necessarily used as catalyst. Heterogeneous, one-component Lewis acid catalysts for cycloolefin polymerization are also generated from different metallic oxides or salts having a significant acid character such as AIzO3, SiO2, SnOz, TiO2, aluminosilicates etc., but they work under special conditions and the control of the process is severely demanding. Some of the most widely employed cationic catalysts for common cycloolefins are listed in Table 3.1.
118 Table 3. I Cationic polymorizatioa of cycloolefms with Lewis acids*
Catalyst
AICI3
Monomer
Cyclopentme, Cyclopmtadiene Cyclohexene,Cyclooctene, Cyclooctadiene,Norbomene, Norbomadiene: Dicyclopentadiene Cyclopmtme, C y c ~ d i e n e BF3, BCI3 Dicycl~dienez Indene BF3/~20 Cyclepmtme, Cyclopentadiene AIBr3 Cyclopm~diene, Indene FeCI3 Cyclopentene, Cyclopmtadiene SnCI4 Norbomener Dicyc!opm~diene~ Norbomene, Norbomadiene TiCL Cyclooctadime~Dicyclopentadiene ZnCI2 . N0rbomene~Norbomadiene "Data from references~~176
References
10,11,15,16 10,11 12 17,18 12, 13, 14,15 18tl9:20 15,16 13~14t 20 13,14,15,16 18t19 12,13,14 18r19, 20, 15, 18 a
3.1.2.2. Two-Component Lewis Acid Catalysts Activation of Lewis acids by a protogenic or cationogenic compound such as water, hydrohalides ~ X -- CI, Br, I), alkyl halides, alcohols, phenols, organic acids, l~ohydri~ is a convenient way to produce highly efficient two-component cationic catalysts of a wide utility in cychxdefin polymerization. These " ~ y s t s " or more properly named "coinitiators" play a crucial role in generating the actually active species by providing a proton or a carbenium ion in the catalytic system, able to electrophilically attack in a complexed or free state the c a r b o n ~ o n double bond of the cycloolefin and start the initiation step of the polymerization process. Such systems are of the following type: AIC|~/H20, BF3/HF, Et2AICVBuCI, SnCI4/CCI3COOH, etc. Ethers and esters are frequently used in conjunction with the Lewis acids to promote cationic polymerization of different cycloole~. The traditional catalytic system of this type, BF3/Et20, has been extensively employed in reactions of numerous cyclic olefms such as cyclopentene, cyclohexene, norbomene, norbornadiene, cyclopentadiene,
119 dicyclopentadiene, pinene, etc., to produce polymers in high yield and having large molecular mass. These strongly complexing agents impart a higher stability and selectivity to the catalytic system as compared to the uncomplexed Lewis acid. Efficient cationic catalysts for cycloolefin polymerization are derived from binuclear compounds consisting of Lewis acids, associated with transition metal salts, essentially metal halides.
3.2. Anionic Catalysts There is a great variety of anionic catalytic systems employed in addition polymerization of olefins. They include primarily alkali metals like Li, K and Na as such or in various compounds as amides, hydroxides, alkoxides or organometllic compounds. Specifically, these systems have to provide a proper anion able to overcome the significant basicity of the monomer, to add at the carbon-carbon double bond of the cycloolefin and thus initiate the chain propagation reaction by a carbanionic pathway. A wide range of anionic catalysts comprise organometallic compounds of Li, K and Na. Organolithium compounds with their representative n-butyUithium are readily available and used on a large scale. Buyllithium is a commercially available compound marketed usually as a 15% solution in heptane which is stable enough if stored at low temperature in a refrigerator and can be readily used in cycloolefin polymerization in aliphatic or aromatic solvents. Phenyllithium and benzyllithium could also be used in special polymerizations. As the organolithium compounds occur usually in an associate state in different solvents, the nature of the solvent is of paramount importance in assuring the actual catalytic species. 2s~4 The degree of association of several alkyl- and aryl-lithium compounds, as determined in ether and in benzene solution, are summarized in Table 3.2. Amylsodium as obtained from amyl chloride and sodium in a benzine fraction can be employed in some reactions but more effective seem to be benzylsodium, phenylsodium and naphthylsodium prepared in a similar way. Of a special utility will be triphenylmethylsodium, Ph3C Na +, a sodium derivative of a particular reactivity. Grignard compounds, easily to be prepared by the slow addition of a solution of the halide to a stirred suspension of magnesium turnings, constitute another important class of anionic initiators which can be extensivley employed instead of alkali metal compounds. Of these derivatives, butylmagnesium bromide, phenylmagnesium bromide and
120 benzylmagnesium bromide a r e readily available from the corresponding alkyl or aryl bromide and magnesium and can be effectively employed immediately after their preparation. Table 3.2. Degree of association of organolithium compounds' Organolithium compound CH3Li C2H~Li n-C4H9Li n-C4H9Li C~-I~Li CffI~CH2Li 9Data from reference
l~ree'of association --2 --6 --5 ---7 -2 ---2
Solvent
"'
Boiling ether Freezing benzene Boiling ether Boiling benzene Boiling ether Boilm~ ether
Sodium and potassium in liquid ammonia are particularly effective initiators in cycloolefin polymerization. Initiation by these compounds may be rapid but polymers would be of low molecular weight clue to easy occurrence of termination reactions. Similar behavior may be encountered using metallic sodium and potassium in hydrocarbon solvents or as alkoxides to initiate polymerization reactions. 25
3.3. Ziegler-Natta Catalysts The class of coordination catalysts used for polymerization of olefins is extremely vast, it comprises the extensively explored binary and ternary Ziegler-Natta catalysts applied on a large scale in the polymerization of linear olefins 26'27 as well as the recently developed ring-opening metathesis polymerization (ROMP) catalysts 2s'3~ used for cycloolefin reactions which, for the sake of clarity, will be treated separately in the next section.
3.3.1. One-Component Ziegler-Natta Catalysts Various catalysts based on 7t complexes of transition metals from groups IV-VII of the Periodic System were found to be very active in the polymerization of a large number of cycloolefins like cyclobutene,
121 cyclopentene, cyclooctene, cyclooctadiene and norbomene. Some of these catalysts induce the polymerization of cycloolefin totally to vinyl polymers while otlgn" catalysts of this class give preferentially vinyl polymerization accompanied at a certain extent by the ring-opening polymerization reaction 3m(Table 3.3). Tablo 3.3 Polymerization of cyclooleCmswith x-allyl catalysts'
Catalytic (~-allyl)oT,r (~-allylhCr
(s-atlyt),Ni ( -aliylhCo (x.aUytPdXh (x-anymhX ,
gmg
vmy i
% 3O 3O 0 0 0 0
%
7o 70 100 100 100 100 i
is|
|
i
"Data from n~rmce 3~
3.3.2. Two-Component Coordination Catalysts A wide range of binary Ziegler-Natta catalysts derived from group IV-VII transition metal salts associated with organometallic compounds have been used in cycloolefin polymerization to obtain high molecular weight vinyl polymers. The activity and selectivity of these catalysts depends greatly on the nature of transition metal and structure of cycloolefin. The first binary catalytic system of this class that promoted addition polymerization of norbomene was reported by Anderson and Merckling. 32 This system consisted of TiCh associated with Gfignard reagents, metal alkyls or aryls, similar orgaometallic compounds, metal hydrides and alkali metals or alkaline earth metals. The product did not melt when heated to its decomposition temperature (ca. 300~ and films shaped from the polymer at that temperature were quite brittle. Later on, Truer et al. 33 stuc~ed the polymerization of norbornene with the binary catalytic system derived from TiCh and tetraheptyllithiumaluminium. The main observation of these studies was that for molar ratios organomet~c compound 9TiCLs under 1 the reaction led to saturated polynorbornene whereas at molar ratios greater than 1 the reaction gave unsaturated polymer.
122 Soon thereafter, Natta and coworkers 3*'35 reported a large number of binary catalytic systems used in polymerization of cyclobutene. In their study they found that titanium-, vanadium-, chromium- or tungsten-based catalysts are the most active ones, those based on molybdenum are less active while those ba.q~ on ytterbium, uranium, manganese, iron or cobalt are inactive. Among the catalysts of the first group, those with vanadium and chromium yielded preferentially vinyl polymer, i.e. poly(cyclobutylenamer), whereas those of titanium and tungsten ringopened polymer, namely l~lybutenamer (Table 3.4). Table 3.4 Polymerization of cyclobutene with binary Ziegler-Natta catalysts' |
Catalytic System TiCh.EhAI gel4. F.~3AI V(acac)3.Et2AICl Cr(acach.EhAICI MoCI3.Et:b~l MoCIs.EhAI MoO2(acach.EtzAICl WCk.EhAI 'Data from reference 3s
Conversion % 100 100 100 100 3 5 55
100
Poly(cyclo-
butylenamer) % 5 99 100 100 10 30 10 40
l/olybmamn~r % 95 1 0 0
90 70 90 60
It is noteworthy that molybdenum catalyst, that were less active, gave
mainly polybutenamer while the very active catalysts based on tungsten led to both polymers, that is to poly(cyclolmtylenamer) and polybutenamer, in considerable amount. A large variety of binary catalysts derived from transition metal derivatives and organometallic compounds employed Natta and coworkers 36~7 in the polymerization reaction of cyclopemene and higher cycloolefins. In cyclopentene polymerization, titanium, zirconium and vanadium systems proved to have a low catalytic activity, those derived from chromium, manganese, iron, cobalt and uranium to be inactive while systems formed from molybdenum and tungsten compounds to be the most active (Table 3.5). The product selectivity was also dependent on the nature
123 of the transition metal derivatives, catalysts containing vanadium compounds leading to vinyl polymers with cyclopentylene structure whereas those derived from titanium, zirconium, molybdenum and tungsten ring-opened polymers having pentenamer units. Table 3.5 Polymerizatkm of cyclc~mtene with binary Zie~ler-N~ Poly.n~ ~nlcture Catalytic System Polymeryield % P o l ~ TiCh.Et~kl 1 Polar TiBr4.Et3AI 2 Polypmtmamer ZrCh.EhAl 1 Poly(cyclope~flene) VCl4.Et3Ptl 1 Poly(cyclopeutylene) VOCI3.EtzAICI 3 Poly(cyclopentylene) V(acac)s.Et2AICI 1.5 Polypmtmamer MoCI~.EhAI 21 WCk.Et~M 39 "Data from reference ~ i
Similar results in cyclopentene polymerization with various binary catalytic systems have been reported by other authors. 37 A wide range of binary metallocene catalysts containing derivatives of Ti, Zr, Hf and V associated with aluminoxanes have been employed to polymerize cycloolefins and copolymerize them with linear olefins. A first group consists of mono or dicyclopentadienyls of Ti, Zr, HI', V associated with methylaluminoxane used for the polymerization of norbomene and norbornadiene. 3~4~
1
2
3
where M - Ti, Zr, Hf, V and n - 6-20 Very active and stereoselective catalysts, however, showed to be the chiral ~ y s t s derived from ethylene[bis(qS-indenyl)zirconium] dichloride (4) and ethylene[bis(TIS-tetrahydroindenyl)zirconium] dichloride (5) associated with methylaluminoxane. 4~
124
~,,CI
.. CI CI
4
S
The activities and melting points for the polymers prepared from cycloolefms in the presence of the chiral catalyst consisting of ethylene[bis(rlS-indenyl)zirconium] dichloride and methylaluminoxane are given in Table 3.6. Table 3.6 Polymerization of cycloalkenes with the chiral catalyst ethylene[bis(rl~-mdenyl)~irconium] dichloride/methylaluminoxane' '
Monomer
T~emperature ~
g polymer/mole Zr.hr
Melting point ~ 485 485 395 395 >6OO .
0 Cyclob~e Cyclobutene -10 Cycks~ntene 0 Cyclopemene 30 20 Norbomene L 'Data from reference ~9
350 180 120 480 150
By replacing the ethylene group of the C2-synunetric ligand with the more rigid dialkyl-, diaryl- or diaralkylsilylene groups, more active and stereoselective catalysts for olefm polymerization have been obtained 4~'42
(6,7).
zr .= 6
7
Similar chiral catalysts have been prepared with dialkyl- and/or d i a r y l ~ y l groups "~(8 and 9).
125
I~,,
,,,CI
,.
8
,.,, CI c'
9
Different C. symmetric ligand were also largely used in new chiral zircon~e catalysts like dimethylcarbyl(rl s-cyclopentadienyl)(TI3fluorenyl)TJrconium dichloride and diphenylcarbyl(rlS-cyclopentadienyl)(rl 3fluorenyl)zirconium dichloride42 (10-11).
P
10
11
Such catalysts employed extensively Kaminsky and coworkers 4~ to polymerize cyclobutene, cyclopentene, norbomene, substituted norbomene, dimethanooctahydronaphthalene, substituted dimethanooctahydronaphthalene to addition polymers and r New ansa-metaUocene chiral catalysts with mono or doubly bridged prochiral or chiral ligands, which are expected to induce higher activities and stereoselectivities in cycloolefin p o l y m ~ o n , have been designed and prepared recently by different research groups 4z'4s (12-23).
Me2Gi,~~ ..,,,C I .~~~ 12
13
,,CI ~ , , C I 14
126
,a
,ca .~~~',,,Cl
,
~-,c,
15
16
~_,~, ~,,c, 18
17
~,,c,
19
CI
Cl
20
CI
..,,
N-
21
CI
Cl
22
Cl
23
Most of these catalysts are derived from Ti and Zr metallocenes but other transition metals can also be effective in these complexes (24-27, M = Ti, Zr, Hf, V).
.,el ~ C l
24
25
.,Cl
26
,,CI
27
127 Of a special interest are several z i r c o n ~ e aromatic moieties as ligands (28-32).
complexes bearing particular
R
Me2Si
~12
R
Me2Si ~ h
Me
12
R
28
29
30
R
Me
h R
31
32
3.4. Ring-Opening Metathesis Polymerization (ROMP) Catalysts The first catalysts to be active in ring-opening polymerization of cycloolefins were disclosed by Eleuterio ~s in 1957. Since this discovery, the class of ring-opening catalysts developed rapidly during the last three decades due to their unprecedented potential to create new highly performant polymers having wide applications in modem technologies.
128 3.4.1. O n e - C o m p o n e n t R O M P Catalysts
The first observation that one-component homogeta~us ~ y t i c systems consisting of WCI6, WBr6 or WOCh were active in the ringopening polymerization of cycloolefins was made by DaU'Asta and Carella. 47 They obtained polyalkenamers by reaction of several cycloolefms like cyclobutene, cyclopentene, cyclooctene and cyclododecene in the presence of these compounds without any cocatalyst. The yields reported were low but the stereospecificity of the polymer was high. Later on, Oshika and Tabuchia used WCI6 and MoCls in the polymeti~tion reactions of norbomene, exo-trimethylenenorbomene and endo-~icyclopentadiene obtaining the corresponding polyalkenang~s in high yields. It is noteworthy that in the polymerization of norbomene with these one-component catalytic systems, Laverty et a/. 49 observed formation of dimers and oligomers along with polynorbornenamer. One-component catalysts consisting of complexes M(CO)3X2L2 (where M = Mo or W, X = CI or Br, L = PPh3 or AsPh3) were reported by Bencze 5~ to be active in the ring-opening metathesis polymerization of norbomene and norbomadiene (Table 3.7). Table 3.7. Polymerization of norbomene with ono-componentcatalysts M(CO)-~2L2~b Catalyst Mo(COhCIz(PPh3)2 Mo(CO)3Bre(PPh3)2 Mo(CO)3CIz(AsPh3)2 W(CO)3CI2(PPh3)2 W(CO)3Cl2(AsPh3)2 W(C0)3Br~(,AsPh3.,h
Reaction time
min 20 20 20 23 20 9
Polymer yield % 0.5 0
2 4
51 19
'Data from reference ~ ~M = Mo or W, X = CI or Br, L = PPh3 or AsPh3.
Of these complexes, tungsten derivatives displayed a higher activity as compared to the molybdenum complexes in norbomene polymerization. It is remarkable that the compounds W(CO)3CIz(AsPh3)2 and W(COhBr2(AsPh3h showed a rather high activity and the p o l y n o r b o m e n ~ had a moderately high cis stereocontiguration.
129 It is also very important to note that the catalytic activity of these complexes was maintained in the presence of air and moisture. An interesting category of one-component ROMP catalysts is represemed by the late transition metal halides such as RuCI3, OsCl3 and IrCI3. Thus, using RuCI3 in a strongly polar medium such as water or ethanol, Natta and Dall'Asta s~ p o l y m ~ cyclobutene and 3methylcyclobutene to polyalkenamers in high yield. It is remarkable that when ethanol has been used as the reaction medium the trans stereoselectivity of the polyalkenamer was higher than in the case of water. Another important finding reported by Michelotti and Keaveney52 is that the hydrates of RuCl3, OsCl3 and IrCI3 in ethanol are particularly active in norbornene polymerization. The catalytic activity decreased in the following order: ~ > Os 3§ > gu 3+. It is worth noting that the osmiumbased system yielded a polyalkenamer with a high content of cis stereoconfiguration while the iridium-based system afforded a polyalkenamer with a high trans stereoconfiguration. Several complexes of cycloolefins with mthenimn, osmiun and iridium salts are active and selective in ring-opening polymerization. These complexes are formed from a cycloolefin with one or two double bonds like cyclooctene, 1,3-cyclooctadiene, 1,5-cyclooctadiene, norbomadiene and a halide of the above transition metal. For this purpose, Porri and coworkers" employed di-I~-chlorochlorobis(cyclooctene)iridium for the polymerization of norbornene in high yield to polynorbomene. Various one-component catalysts consisting of ~ complexes of transition metals were used by Kormer et al. ~ to polymetize a large number of cycloolefins such as cyclobutene, cyclopentene cyclooctene, cyclooctadiene, cyclododecatriene and norbomene. These catalysts proved to be particularly active leading in very high yield either to poyalkenamers or to a mixture of polyalkenamers with vinyl polymers. It is noteworthy that 7t-allyl complexes of tungsten and molybdenum formed totally polyalkenamers by ring-opening while x-allyl complexes of chromium and zirconium led to both the ring-opened and vinyl polymers (Table 3.8). A quite active catalyst for ring-opening p o l y m ~ o n of cycloolefins showed to be an arylmngsten compound, phenyltungstentrichloride (CfflsWCl3) in the absence of cocatalyst. On employing this compound alone, Grahlert et a/ss reported appreciable polypentenamer yields in the polymerization of cyclopentene. Titanacyclobutanes and tantalacyclobutanes showed to promote
130 Table 3.8 Polymerization of cytloolofms with o n ~ e m ~=all~ic r Catalytic System
Vinyl polymer % 70 70 0
(~-allyl)4Zr
(~-allyl)3Cr (~-allyl)oMo
, -aUyg,W,
0 i
i
Ring-evened polymer % 30 30 100 100
i i
"Data from reference ~4 the ring-opening metathesis polymerization of strained cyclic olefins like norbornene and its derivatives. Gilliom and Grubbs ~s have demonstrated that titanacycles derived from Tebbe reagent and norbomene or 3,3-dimethylcyclopropene upon reaction with norbornene give monodisperse polynorbomene (PDI=I. 1) with virtually no chain transfer or termination.
33
34
35
The catalysts are active at higher temperatures (>65 ~ and upon cooling to room temperature the living polymer was stable for several days. If stored at room temperature under an inert atmosphere, these systems retain some activity even after several months. Rapid decomposition was observed, however, at the polymerization temperature in the absence of monomer. Block copolymers of norbomene with benzonorbomene, 6methylbenzonorbomadiene and eta/o- and exo~cyclopentadiene were prepared by Cannizzo and Grubbs 57 using the titanacycles derived from di(cycl~ complex and isobutene or 3,3dimethylcyclopropene. The living polymers were end-capped by Wittig-type si/-.
CP2Ti
CpzT 36
37
131 reaction with acetone. Low polydispersity indices were recorded in all cases. On the other hand, Schrock and coworkers s= employed two
tantalacyclobutanes derived from Ta(CH'Bu)(OR)3(THF) complexes (OR 2,6-diisopropylphenoxide or 2,6-dimethylphenoxide) for the living polymerization of norbornene. =
-4-
38
39
These catalysts mimic ring-opening polymerization of norbomene by the riving titanacycles discovered by Gmbbs. A significant class of well-defined one-component catalysts for the ring-opening polymerization of cycloolefins derives from metallacarbene complexes. As soon as the carbene mechanism has become more and more popular for the initiation and propagation steps of the olefm metathesis and ring-opening polymefiz~on of cycloolefins, metaflacarbenes proved as a new potential class of catalysts for this process.
(C O)sW
40
.
/,OMe ~'~1:~h
( c o ) s w
,
Ph ~Ph
-~/
41
In fact, Katz was the first to employ diphenyl-pentacarbonylmngstencarbene, (CsHs)2C=W(CO)s, as a very active and stereo selective onecomponent catalyst in the polymerization of l-methylcyclobutene, cycloheptene and norbomene, affording in high yield the corresponding polyalkenamers with considerable stereochemical purity, s9 Later on, the number of metallacarbenes as ring-opening metathesis catalysts increased substantially spreading out to a large number of transition metals and covering a wide range of activity and stereo selectivity in the polymet~tion reaction of numerous cycloolefins. This class of ring-opening polymerization catalysts became quite attractive due to the particular features they possess in contrast to the classical metathesis catalysts such
132
as: well-controlled metathesis activity and stereosclcctivity, good tolerance toward functionality, "living" character affording narrow and monomodal molecular weight distribution of polyalkenamers and the possibility to
produce block copolymers as well as easinessand simplicity in handling and application in polymerization processes. In their early work on aryloxide complexes of tungsten, Basset and coworkerss~ reported the synthesis and catalytic properties of two families of chloro-aryloxide carbene complexes (VI) (42-43). CI
CI
ArO I H ArO/~/~/==~ (OR2)
ArO,, I H ArO/7==~ (OR2) CI
CH2CMe 3 43
42
The complexes of type 43 proved to be active without any cocatalyst for metathesis of various kinds of cyclic and acyclic olefins with or without functional groups. Also, depending on the nature of the aryloxide ligand and the coordinated ether, they exhibit various degrees of activity and stereoselectivity with respect to a given olefin. Very active tungsten carbene catalysts, particularly when they are associated with gallium halides (GaX3, X = CI, Br), prepared Krcss and O s b o m 61 (44-46).
RO./
Br -
Br 44
/~'
Br
RO. I RO
Br 45
/~,
Br RO. I
RO
/-"X
Br 46
Using this class of initiators, Kress and Osl~m were the first to detect by means of elegant NMR measurements the occurrence of intermediate tungstene-carbene and tungsten-cyclobutane complexes during the polymerization reactions of norbomene and its derivatives. 62 The tungstencyclopentylidene complex, W[cyclopentylidene](OCHzCMe3)2Brz, was used in association with GaBr3 to initiate the metathesis polymerization of synand a~ti-7-methylbicydo[2.2.1]hept-2-ene to produce homolxdymers as well as block and tapered block copolymers of the two stereoisomers. 63 In this ease, the intermediate met~lacyclobutane could be detected during the
133 reaction of ant/-7-methylnorbomene, but not for that of syn-7methylnorbomene. Tungsten-e,arbene complexes of the type W(=CRR'XOR")2Xz, where CRR' = cyclohexylidene, cyclopentylidene, CH'Bu or CIT'Bu, have also been used by Kress as catalysts to initiate ringopening metathesis p o l y m ~ o n of cyclopentene, cycloheptene and cyclooctene to living polyalkenamers. Their CmBr3 adducts react similarly but much more rapidly. A wide range of well-defined pseudotetrahedral imido alkylidene complexes of the type M(=CHR)(=NAr)(OR')2 ( M = Mo, W, R = C(CH3)3, C(CH3)2Ph, Ar = 2,6-dimethylphenyl, 2,6-diisopropylphenyl, OR' = OC(CH3)3, OCMe-2(CF3), OCMe(CF3)2, OC(CF3)2(CF2CF2CF3X47),
R'O_ @N-Ar \M R'O/ %CHR 47
suitable for ring-opening polymerization of cycloole~ were prepared by Schrock and coworkers~ from an "universal precursor" M(::~HRX=NArXtriflate)-XI,2-dimethoxyethane) (48). TfO
\
~0 --M~
N-Ar
CO/I \~Ol'f CHR 48
Several examples of effective molybdenum alkylidene complexes are given below
(49-54).
N
CH(CH3)2
(CH3)3CO\ Moo// 3)2 / (CH3)3CO '~CHC(CH3)~ 49
CH(CH3)2 (CH3)3CO\IMo/N_,~H(CH3)2 (CH3)3CO ~CHC(CH3)2Ph 50
134
CH(CH3h
CH(CH3h
(CF3XCH3)2CO\ Mo/N~dH(cH3)2 (CF3XCH3)2CO~oJf NcNh / CHC(CH3)2Ph (CF3XCH3)2CO/~CHC(CH~h (CF3XCH3)2CO 51
52
CH(CH92
1CF3)2(CH3)CO~o/'N CHC(C~h 53
CH(CH3h
(CF3)2(CH3)COk.,/N-~ ~
(CF3)2(CH3)C O
CH(C~h
X
CHC(CH3hPh
54
The molybdenum neophylidcnr complexes Mo(=CHCMe2Ph)(=NAr)(O'Bu) and Mo(=CHCMe2Ph)(=NAr)(OC(CH3XCF3hh as well as their precursor Mo(=CHCMe2Ph)(=NAr)(TfO)2(DME) are all now commercially available from Strem Chemicals, Inc. Selected ~H and ~3C NMR data for molybdenum and tungsten alkylidene complexes are given in Table 3.9. Table 3.9. tH and ~3CNMR Data for Molybdenum (and Tungsten) Alkylidene Complexes~b Mo Alkylidme Complex
~(ca ppm 312.2(283.8) 326.2 288.2(253.9) 276.8(244.9) 265.8(236.5) 289.8(242.8)
Jc.
Hz ppm 115 12.91(9.97) Mo(=CH'BuX=NAr)(DME)CI2 124 14.10 [Mo(=CHtBuX=NAs)Clz], 11~ 12.06(8.87) Mo(=CHtBuX=NAr)[OCMe(CF3h]z 11~ 11.61(8.41) Mo(---CH'BuX=NAr)[OCMez(CF3)]z 11~ 11.23(8.05) Mo(--~H'Bu)(=NArXOCMe3)z 11": 13.86(9.97) Mo(--CHSiMe3X=NAr)[OCMe(CF3)z]z Mo(=CHFX~=NAr)[OCMo(CF3)2]z _ 12.44(9.22) 9Data from reference6~; s Values for the correspcmdmg tungsten complexes are shown in parentheses
135 The activity of tungsten complexes of the type W(=CI-I'BuX=NArXORh ( A r - 2,6-diisopropylphenyl; OR = O'Bu, OCMe2(CF3), OCMe(CF3)2, OC(CF3)2(CF2CF2CF3)) in the metathesis of olefins depends critically upon the nature of the OR group. For instance, the complex in which OR = OCMe(CF3)2 is an active catalyst for the metathesis of ordinary olefins at rates that may be as high as 103 turnovers per minute at 25~ in a hydrocarbon solvent, while analogous W(=CI-~Bu)(=NAr)(OtBuh complexes do not react readily with internal olefms but react with more reactive cyclic monomers such as norbomene, benzvalene, 7,8-bis(trifluoromethyl)tricyclo[4.2.2.0z'S]deca-3,7,9-triene, and acetylene, a circumstance that allows one to prepare essentially monodisperse living polymers and block copolymers. Analogous molybdenum alkylidene catalysts of the type Mo(=CHRX=NArXOtBuh (Ar=-2,6-Cd-13~Pr2; R= q3u, CMe2Ph) have been used to initiate living ringopening p o l y m ~ t i o n of funetionalized norbomenes, norbomadienes, and 7,8-bis(trifluoromethyl)trieyclo[4.2.2.02"S]deea-3,7,9-triene to give polymers with narrow molecular weight distributions (polydispersity of 1.05-1.10). In some eases, e.g. with 2,3-bis(trifluoromethyl)norbomadiene and 2,3-bis(c,arbomethoxy)norbornadiene), the resulting polymer was virtually all-trans and possibly also tactic. The tolerance of the M(=CI-I'BuX=NArXOR)z(M=W, Mo) catalysts for fim~onalities allowed them to be used to ring-open norbomene that contains metals like Pb, Sn, Zn, etc. Recently, Grubbs and eoworkers 67 described the living ring-opening polymerization of norbornene catalyzed by the discrete ruthenium earbene complex (55). Ph3/H
~
Cl"~u=CXRcl /
PPh3
Other highly r
55 cyclic oleos such as cyelobut~e and ~ ~ -
cyclooetene were also readily polymefized by this ruthenium earbene complex in a living fashion, however it was inactive for the polymerization of less-strained cyclic olefins and aeyelie metathesis. Modification of this complex by the exchange of the triphenylphosphine (PPh3) ligands with tricyclohexylphosphines (PCy3) or tricyclopentylphosphines(PCyp3)resulted in more active catalysts. ~s
136 Cl....~ cy3 H
P.CyP3 u Cl..,. l u = c / ' '
C I"'~u=C~ R PCY3
Cl'" I
56
"R PCyP3
57
New active and selective benzylidene and vinylidene ruthenium complexes are represented by compounds 58-61. IPh3 / Ph C~.....PR I
U
CI,., !Cy3 / Ph
-
"~ U
CI/pph3
-
CI//cy 3
58
59
C L....I~Ph3 / Ph Ru / - - - \ I Ph C~'PPh3
Ck.. P CY3 Ru ~/f I Cid, PCy 3
/ Ph \p h
61
6O
The new ruthenium carbene complexes were active for the polymerization of cyclopentene, cyclooctcne and 1,5-cyclooctadiene as well as the metathesis of acyclic olefins.69 In addition, the copolymedzation of both high- and low-strain cyclic olefins employing these ruthenium complexes as catalysts was performed. The effect of the ligand as well as the nature of the carbene on the copolym~tion reaction was particularly pointed out by the above authors. Water-soluble ruthenium complexes containing preformed aJkylidene fragments that initiate rapidly and quantitatively cycloolefin polymerization were also reported by Grubbs and coworkcrs 7~ Me... Me ~. N CI
~N(Me)3
9 C IE) C k...l .....Ph ~ , ~ C P"~ U ~ A H
C I,... ...,P h C I~FIu'~~ H c,
62
/eK CI Me Me
63
137 In the presence of a BrOnsted acid, these complexes showed to initiate the living polymerization of water-soluble monomers in the absence of surfactants or organic solvents. Synthesis of five-coordinate tungsten(Vl) alkylidene complexes containing a bidentate C,N-bonded arylamine ligand or a monoanionic O,Nchelating ligand has been reported by Van Koten and coworkers (6466).'I,~
~ CH~iMea
/'-~
1-12SiMea C1-12SiMe.s ~ / C O-W.~ II"~"CHSiMe3 N N
0
64
65
66
Such complexes are inert toward linear olefi~ but can polymerize strained cyclic olefins e.g. norbomene in a ring-opening metathesis reaction. The reactivity of some of these complexes toward norbomene will differ considerably (Table 3.10). Table 3.10 Polymerization of norbornene with amgstm-alkylidenes W(--CHSiMe3)(CHaSiMe3)(=NI~)(L)~ '
Ligand(L)
'
8-qumolmola~
oc~(2-Py)
OCH(CMB3X2-Py) 'Dam from ~ c e
n
T~-t ~ 25 25 70 25 70
Reaction Rate
Cis/Trans I00:0
88"12
88:12
90:10
As Table 3.10 illustrates, the complex W(=CHSiMe3XCH2SiMe3)(=NPhXS-quin) is very reactive and p o l y m ~ 250 equiv of norbornene within 1 min at room temperature, affording all-cis polynorbomene. In contrast, the tungsten alkylidene complexes W(=CHSiMe3XCH2SiMe3X=NPhXOCPh~2-Py)) and W(=CHSiMe3XCH2SiMe3X=NPh)(OCH(CMe3)(2-Py)) reacted slowly
138 with norbomene at room temperature: they gave <10~ conversion after 24
hr. Howover, when the temperature was raised to approximately 70~ again 250 equiv of norbomene was polymerized within l min. In these two cases, as with the complex W(=CHSiMe3)(CH2SiMe3)(=NPh)(8-quin), norbomene was p o l y m ~ in a ring-opening metathesis fashion yielding polynorbomene with >90~ cis double bonds. Several chiral molybdenum alkylidene catalysts containing Cxsy.anetric chiral diolate ligands, e.g. tartrate, binaphthyl and biphenol derivatives have been prepared and successfully employed by Schrock and coworkers" for synthesis of poly(2,3-bis(trifluoromethyl)norbomadiene) and poly(2,3-dioarbomethoxynorbornadiene) that are >99 % cis and >99 % tactic. The synthesis of these chiral molybdenum alkylidene catalysts proceeded readily in high yield from the appropriate alkoxide and the universal precursor Mo(=CH'Bu)(=NArXtriflate)-z(1,2-dimethoxyethane) (67-70). Me.
R R OTf6
O X~ ,tN~Ar
R~
O or-C
OTf6
67 StMezPh
on.
I~O,,MIo.....N_Ar SIMe2Ph 68
SlMezPh
t,~
o on.
X~o=l~b..Ar
SIMe2Ph 69
's"r"Y
tBu
OT,.
W~/I-O,l~--Ar
tB
tBu
70
More recently, using new chelating chiral diol ligands, Grubbs and coworkersTM synthesized chiral metal alkylidene complexes for ring-opening polymerization of both strained and less strained cycloolefins. When (lS,2S)and (lR,2R)- 1,2-bis-(2-hydroxy-2,2bis(trifluoromethyl)c~yl)cyclo~tane (L), 71, has been employed as a chiral ligand, the chiral molybdenum alkylidene complex Mo(=CHCMc2PhX=NArXL), 72, active in polymerization of 1,5cyclooctadiene, has been produced.
139 AF
I N
F3cCF3 H
F3C_CF3 II
...,,,X-O//H /
"OF 3
"Z
F3
71
72
Stable chiral tungsten oxo vinylalkylidene complexes and tungsten amide vinylalkylidene complexes have been also obtained from the above chiral d i o l ligands and W(clLPh~clopropene)Cl2(O)[P(OMe)~]2, and W(=CHCHCOCH2CH2CH2OXO)CIz[P(OMe)3] W(=CHCHCPh2X=NAr)CI2[P(OMe)3]2, which are effective in the polymerization of norbomene, cyclooctene, 1,5-cyclooctadiene and substituted cyclooctatetraenes (73..75). h" I 0 N 0 Orb
F~.7 3 II ~ P ( ~
-
91
"CF3 74
73
75
Asymmetric tungsten-aJkylidene complexes containing either one or two l,l'-bi-2-naphtholate (RzBINO) ligands prepared Heppert and coworkers7s (76-77).
R
R
o
I o11
OtB u
76
,R
77
140 Both (RzBINO)('BuO)2W(=CHPh) and (Mc~BINOhW(=CHPh) act as ring-opening metathesis catalysts for norbomene polymerization, although there are startling differences in their reactivity. While neither catalyst produces a quantitative conversion of norbomene in 15 min, (Me2BINO)2W(=CHPh) exhibits extremely low activity, generating only 35 % yields of polymer. The addition of GaBr3 as a Lewis acid cocatalyst markedly increased the activity of (~BINOX'BuO)2W(=CHPh), generating virtually instantaneous quantitative yields of polynorbornene at O~ This increased activity probably stems from the abstraction of a terminal 'BuO ligand by the Lewis acid gallium reagent, generating a highly active four-ea3ordinate polymerization catalyst [(R2BINO)(tBuO)W(~HPh)] *, rehted to Osbom's structurally characterized [(RO),~Br3~W(=CHR')+I[GaBr4"] complex. 76
3.4.2. Two-Component ROMP Catalysts Soon after the discovery of ring-opening polymefz~tion reaction of cycloolefins by Eleuterio ~ with heterogeneous molybdena-type catalysts, the process attracted an increased number of research groups due to the great potential offered by the new reaction. A first objective was to create new catalytic systems and apply them to a wide range of cycloolfins in order to obtain products with highly performant characteristics. This trend generated a large variety of now termed "classic~" catalysts that have been used extensively to study various aspects of ring-opening polymerization of cycloolefins such as reaction kinetics and thermodynamics, reaction mechanism and stereochemistry as well as the ways of industrial valorification. These catalytic systems are mainly two-component catalysts that contain a transition metal derivative of group IV-VII of the periodic table associated with a coc,alalyst. The latter may be an organometallic compound (Ziegler-Natta type catalysts), Lewis acid (Friedel-Crafls type catalysts), x-complex or carbene complex. Their activity is generally high depending on the nature of the transition metal, the number and nature of ligands attached at the transition metal, the nature of the coc,atalyst, the solvent and other reaction conditions. The reaction selectivity is quite variable depending primarily on the nature of the transition metal, ligands and coc~talyst but also on the structure and conformation of the monomer. They display low tolerance relative to the functional groups and their activity may be substantially diminished by a strong complexation of the active sites.
141
The first two-component cattalyst to ring-open polymerize norbomene reported by Truer et eL/.33 OOl~sted of TiCh and tetraheptyllithiumaluminium. These authors investigated the influence of the molar ratio AI:Ti on the two types of p o l y m ~ t i o n , vinyl and ringopened. It is noteworthy their finding that at molar ratio AI:Ti
I the reaction occurred through ring-opening polymerization. Soon afterwards, Natta and coworkers 34"36 used numerous binary catalytic systems in the ring-opening p o l y m ~ o n and copolymerization of a wide range of cyeloolefins. Depending essentially on the nature of the transition metal compound, some of these catalysts led to both vinyl and ring-opened polymerization reactions while others gave preferentially ringopened polyalkenamers. The activity and stereoselectivity of these catalytic systems were also strongly dependent on the nature of the transition metal, cocatalyst, cycloolefin and reaction conditions. In eyelobutene polymerization, Natta and eoworkers 35 studied various binary ~ y f i c systems consisting of transition metal salts from the groups IV-VII of the periodic table and organoaluminium compounds (Table 3.11). Table 3. I I
Polymerization of cyclobutene with two-component ROMP catalysts'
CatalyticSystem TiCh/EhAI VCh/EhAl MoCI~3AI MoCI~3AI MoOz(acac)7]Et2AICI WCId~AI
Cotlv.
% 100 100 3 5 55 100
pcB ,
% 5 99 10 30 10 40 ,
cis-PB %
trans-PB %
30
65
,
0
l
60
30 30
40 45
45
40 30 "Data frvm refermce" PC-Poly(cyclobutyiename0, PB=Polybmman~r
They found that titanium-, vanadium- and tungsten-based systems were the most active while those based on molybdenum the least active. Moreover, vanadium-based catalysts formed preponderently poly(cyclobutylenamer) while titanium-, molybdenum- and t u n g s t e n - b ~ catalysts led to polybutenamer or poly(1-butylenamer).
142 A greater number of two-component ROMP catalysts, both heterogeneous and homogeneous systems, have been investigated by several research groups in cyclopentene polymerization due to the ready accessibility of this monomer and the increased interest in its polyalkenamers. Early studies of Natta and coworkers ~s showed that the binary catalysts based on molybdenum pentachloride and tungsten hexachloride associated with EhAI or Et2AICI were the most active and selective in ring-opening polymerization whereas those derived from titanium tetrachloride in conjunction with the above organoaluminium compounds led to both types of polymers, vinyl and ring-opened. It is significant that molybdenum-based catalysts formed preferentially cispolypentenamer and tungsten-based catalysts ~ave trans-polypentenamer. Extensive studies of Cmnther et a/. 3 used a large range of twocomponent catalysts consisting of tungsten halides and organometallic compounds in cyclopentene polymerization. Though initially the activity of some of these catalysts was low or moderate, later on their activity and stability have been substantially improved on using adequate activators and additives in ternary systems (see below). It is noteworthy that the stereospecificity of several catalysts of this group is rather high being of interest for their industrial application into trans- or cis-polypentenamer production. Thus, catalysts derived from WCI~ and ~Bu3AI or HSnEh gave polypentenamers with more than 90% trans stereoconfiguration, the use of Table 3.12 Cyclopemene polymerization with two-conq~ent tungstm catalysts' Yield % Catalytic System 35 WC~Bu~d 34 WF6/Et3AI2C]3 5 WCl~a3~h5 8 WCI6/(HSiOCH3)4 II WCls/(HSiOCH3), 4 WCI~i3WF~ 6 WCls/(x-allyl)sCr 18 WCId(x-allyl),W~ 35 WCl~SnEh 62 WCIJPh3Cr 'Data from referelloe37 i
i
trans- Polypmtmmrm., 90.4 17.2 24.4 65.1 55
cts-Polypmtmmner" 9.6 82.8
75.6 34.9 45
88.2
11.8
27.4 60.3 90.2 45
72.6 39.7 9.8
55
143 tungsten hexafluoride in the catmlytic systems WF~hAI2CI3 or WFdEtaAICI produced polypentenamers with more than 82% cis stereoconfiguration. Binary ROMP catalysts of this type were extended also to other tungsten derivatives and to other transition metals. With catalytic systems consisting of W(PhO)4Cb and MeAICI2 it was possible to obtain polypentenamer in 69% yield containing 84% trans stereo~ntiguration at the carbon-carbon double bond. On studying the effect of r on the activity and selectivity of the binary WCts-ba.q~ ROMP catalysts in cyclopentene polymerization, Dimonie and Dragutan " ~ showed that the catalytic systems containing isobutylaluminoxane and tetraphenyltin as cocatalysts were highly cis stereoselective, especially at lower temperatures (Table 3.13). Table 3.13 Catalytic System WCIJBu2AIOAIiBu2 WCIJBu2AIOAItBuz WCloq~e2AllyizSi WCI~,Sn WCIs/Ph4Sn WCldMe~n WCIs/Et4Sn WCld13u4Sn 'Data from reference
WCl~-ba.uxl Temp trans-Pol~ntmamer c i s - P o ~ r ~ % % - 10
9.1
0
11.2
-20 -20 +10 -20 -20 -10
38.0 11.7 45.3 80.0 28.9 24.2
'
90.9
88.8 62.0 88.3 54.7 20.0 71.1 75.8
It was observed, however, that the effect of temperature on the catalyst activity and polymer stereo selectivity was considerable, parfic~arly for the catalyst WCI~.Ph4Sn. In the two-component catalytic systems the tungsten halide has been replaced by MoCIs, ReCI5 and TaCls thereby changing drasti~y the catalyst activity and stereo selectivity . On using MoCIs associated with ~Bu3AI inste~ of WCI6 in cyclopentene polymerization, Natta and coworkers st varied the polypentenamer stereostructure from over 90% warts to over 90% cis. Similarly, Gtmther et al. rz's3 employing a catalyst consisting of ReCl5 and 'Bu3AI obtained a polypentenamer containing 96% cis stereoconfiguration with special properties of natural rubber. A different class of two-component catalytic systems has been obtained by replacing
144 the organometaUic compound from the above Ziegler-Natta ROMP systems with a Lewis acid. This new catalysts of Friedel-Crat~ type proved to be highly active in the ring-opening polymerization of cycloolefins. Thus, DaU'Asta and Carella s~ used two-component tungsten-based catalysts consisting of WCI6, WOCI4, WCIz or WBrs in conjunction with AICI3 or AIBr3 in the polymerization of cyclopentene and higher cycloolefins to obtain polyalkenamer with high tra~ stereoconfiguration at the carboncarbon double bonds. Furthermore, Marshall and Ridgewell ss carried out the polymerization of several cycloolefms such as cyclopentene, cycloheptene, cyclooctene, c y c l o d o d ~ e , 1,5-r and 1,5,9cyclododecatriene with catalysts consisting of WCI6 or MoCIs and AIBr3. It was observed that when using AIBr3 instead of AICI3 in these catalysts the efficiency of the process increased. A large variety of heterogeneous two-component catalytic systems formed from inorganic compounds of tungsten, for instance, tungsten trioxide, tungstic acid, isopolyacids, heteropolyacids or salts of these acids associated with AICI3 or AIBr3 were used by Herisson and Chauvin ~s to polymerize cyclopentene. On employing chlorobenzene as a reaction medium, they obtained high yields in polymers though the structures of the products were not completely elucidated. Significant results in cyclopentene polymerization obtained NiRzel et al. g7 with a series of two-component catalysts formed from organic compounds of transition metals of groups IV-VI of the Periodic Table and several Lewis acids. They used mainly aryl derivatives of tungsten, molybdenum, chromium or vanadium and halides of boron, aluminium, tin, tungsten or molybdenum (Table 3.14). It can be seen that these twocomponent FriedeI-Crafls systems displayed a substantial activity and stereoselectivity in cyclopentene polymerization comparable to the above presented binary Ziegler-Natta systems. For instance, catalysts like Li3WPh6.BCI3 gave a high yield of polymer (52%) and a considerable content of trans polypentenamer (92%). Similarly, Judyu employed several two-component catalysts based on tungsten or molybdenum compounds and ~ s acids in polymerization and c o p o l y m ~ t i o n reactions of cyclopentene, cyclooctene, cyclooctadiene and cyclododecatriene. These catalytic systems were very active affording high yields in polyalkenamers and copolyalkenamers. With such a system consisting of KWCI6 and AICI3 or AIBr3 Judy obtained a polyoctenamer in 82% yield. Furthermore, on employing tungsten carbonyl compounds associated with Lewis acids, e.g., W(CO)~(o-phenanthroline)
145
and AIBr3, this author was able to attain a 86.3% yield of polyoctenamer Table 3.14 Cyclopmtene polymerization with two-compcment ROMP catalysts of FriedeI-CratLs type' Catalytic System
Yield % 45
tram-
cis-
Pol.ypm_tetmmer, % 80
Polypmtmanm, % 20
Li3VVPhJBCI3
52
92
8
Li~MoPhdBF3
43 20 62 32
62 92 45 32
38
WCt,/AIO3
Pr4W/SnCI4
Ph3Cr~Cl6 LizVPhdMoCls 'Data from
8
55 68
Remarkably, two-component catalysts, consisting of tungsten compounds in conjunction with alkali metals or alkaline earth metals, showed to be very active and stereoselective in cyclopentene polymerization. Such binary systems, containing Li or Ca associated with tungsten halides, used Cmnther e t al. t9 to obtain high yields of trcms polypentenamer(Table 3.15). Table 3.15 Cyclopentene polymerizationwith two-c,ong~ent tungsten-based catalysts'
Polymer yield Catalytic % System 38 WCldLi 21 WCldCa 66 WCIsOX/Ca 30 WBr~/Ca 19 'Data from reference
trans-
~$-
80 90 80 89
Polypmtammer % 2O 10 20 11
Polypemmmnor %
Tungsten and molybdenum ~-complexes, in combination with aluminium and gallium halidcs, formed very active two-~mponent ROMP catalysts. Thus, GOnther9~ and Ntitze191 carried out the p o l y m ~ t i o n of cyclopentene using binary catalysts consisting of WCI6 and 0t-allyl)3Cr or
146 (~-allyl)4Wz. They obtained both cls- and trans-polypentenamers but the yields were relatively low. Furthermore, Yufa et al. ~ performed the ringopening polymerization of 1,5-r with the system 0tallylhW/GaBr3 to obtain 1,4-polybutadiene in high yields. It is noteworthy that the resulting polybutadiene contained 60% cis and 40% trans stereoisomer. However, when the catalyst (~-r was used in polymerization of trans, trans, cis-l,5,9-cyclododecatriene, Yufa et al. ~z obtained polybutadiene with 40% cis and 60% trans content of stereoisomer. Interesting binary catalytic systems for the ring-opening polymerization of cycloolefins, consisting of metal-carbene complexes and organoaluminium compounds or Lewis acids, reported Chauvin et al. s~ Such systems are formed from RR'C=M(CO)s (where R = CffIsO or CH30; R' = CH3 or Cd-15; M = W or Mo) and EtAICI2 or AICI3. Using such a system in cyclopentene polymerization, they obtained in 70~ yield polypentenamer. Related catalysts were also prepared starting from CIAPh3P)Pd--C(OCH3)NHC~s and AICI3 or EtAICIz. It is noteworthy also that Commereuc et al. sa employed the tungsten-carbene (CO)sW=C(OCffls)R, associated with TiCh in the two-c~mponent catalytic systems for cycloolefm polymerization. A range of asymmetric alkylidene and oxo complexes of tungsten (VI) were prepared by Heppert and coworkers95 by incorporating Czsynunetric l,l'-bi-2-naphtholate and other chelating bisaryloxides ligands onto tungsten oxo and tungsten arylimido complexes. Using these asymmetric complexes as procatalysts in association with EhAICI, norbomene and 5,5'-dimethylnorbornene were polymerized to the corresponding ring-opened polymers. The microstrucu~es of the resulting polymers were correlated with the structure of the procatalyst and the nature of the Cz-synunetric naphtholate ligand.
3.4.3. Multicomponent ROMP Catalysts Starting from the binary ROMP catalysts, ternary, quaternary and multicomponent catalytic systems have been prepared by adding a special component to the parent systems which may act as an activator, promoter, stabilizer or inhibitor of side reactions. These substances are usually organic compounds containing oxygen, nitrogen, sulphur, phosphorus, halogen or other heteroatom, in some cases they may be also inorganic compounds
147 containmg these heteroatoms or having a particular role in ROMP catalysis. The first catalytic system employed by Eleuterio *s in the discovery of ring-opening metathesis polymerization was a heterogeneous ternary catalyst consisting of an oxide of chromium, molybdenmn, tungsten or uranium deposited on alumina, titania or zirconia associated with a third component such as alkali metal, alkaline earth metal, boron or aluminium hydride. This ~ y s t allowed unsaturated polymers with cis and trans configuration to be obtained from cyclopentene, cyclobutene, norbornene and dicyclopentadiene working under inert atmosphere in hydrocarbons as reaction medium. L~er on, DalrAsta and Carella9~ obtained a series of homogeneous ternary catalytic systems consisting of tungsten or molybdenum salts, organometallic compounds and oxygen-c~ntaining substances such as organic peroxides, hydroperoxides, alcohols, phenols, molecular oxygen or water. The transition metal salts employed were WCIs, WOCh or MoCls, the organometallic compounds were EhAICI, EhAI, 'Bu3AL Hexyl3Al or EtzBe, and the oxygen-c~ntaining compounds benzoyl peroxide, tertbutylperoxide, cumyl hydroperoxide, hydrogen peroxide, ethanol, phenol, molecular oxygen or water. The optimum molar ratios between the catalytic components were in the range W" AI" O of 1 90.5-100" 0.5-1. With such systems Dall'Asta et al. 9~ prepared highly trans polyalkenamers in the polymerization and copolymerization reactions of cyclopentene, cycloheptene, cyclooctene or cyclopentadiene. Soon aider reporting the olefin metathesis with the ternary catalyst WCIdEtOH/EtAICI2 in homogeneous phase, Calderon and coworkers sa carried out successfully the ring-opening polymerization of a large range of cycloole~ with this catalytic system. They obtained mainly trcmspolyalkenamers in high yields in the reactions of cyclooctene, 3methylcyclooctene, 3-phenylcyclooctene, 1,5-r and 1,5,9cyclododecatriene. Subsequently, instead of ethanol, Calderon and Judyss employed also methanol, aUyl alcohol, cumyl alcohol, glycol, phenol, thiophenol and cumyl hydroperoxide. In addition, Judy ~~176 reported very active and stereo selective catalysts consisting of WCI~ AICl3 and powdered aluminium for the polymerization of cyclopentene, cyclooctene, cyclooctadiene and cyclododecatriene. For example, with such a catalyst this author obtained a polyoctenamer in 74.5% yield. Instead of WCk, Judy employed also WF6, MoCls, MoF6, MoF4, WOF4, WCh and MoOCh. Particularly active ternary catalytic systems for the polymerization of cycloolefins to polyalkenamers obtained Ofstead ~~ by using tungsten or
148
molybdenum carbonyl complexes. Such catalytic systems consisting of (CO)~(1,5-COD)W or (CO),(NBD)Mo, EtAICI2 and oxygen, bromine, iodine or cyanogen bromide gave high yields of polyoctenamer by cyclooctene polymerization. Furthermore, Ofste~ ~~ prepared new ternary catalytic systems derived from WCh,, EtAICIz and a hydroxynitrile (cyanohydrin) such as HOCHzCH2CN or chlorosilane of the type CICHzCHzOSiMe very active in cyclopentene polymerization. A large number of ternary catalytic systems based on tungsten salts prepared Ganther et al. ~o3 to be employed particularly in cyclopentene polymerization to trans-polypentenamer. In these systems, they used mainly oxygen-containing compounds such as alcohols, epoxides, peroxides, hydroperoxides, acetates, phenols or ethers, nitrogen-containing compounds such as amides, amines or nitroderivatives, various halogenated compounds as well as inorganic peroxides such as sodium or barium peroxides. In addition, Pampus et a l ~~ employed chloroethane or epichlorohydrin in catalysts derived from WCI~ and EhAICI or ~Bu3AI. With such catalyticsystems, they obtained high yields of trtms-polypentenamer and copolymers of cyclopentene with butadiene as well as graft copolymers with good elastomericproperties. It is noteworthy that 2-cyclopentenehydroperoxide increased the activity of the binary catalytic systems consisting of WCts and 'Bu3AI or tungsten salts and ~ s acids. Using such a ternary catalyst, N0tzel et a l ~~ obtained h i g h yields in trans-polypentenamer by cyclopentene polymerization. The catalyst proved to be very stable and reproducible. Similar results were reported also for nitroaromatic compounds and inorganic peroxides such as Na202 and BaOz.~~ Interesting tungsten-based ternary catalytic systems prepared W'me et a l ~~ using halogenated alcohols or halogenatod phenols as the third component. On using these compounds, the above authors s u ~ e d to improve the stability of the catalytic systems derived from WCI6 and ~u3Al or Et2AICI. Examples of such halogenated alcohols are 2-chloroethanol, 2bromoethanol, 1,3-dichloro-2-isopropanol, 2-chlorocyclohexanol and 2iodocyclohexanol and as halogenated phenol is o-chlorophenol. With a catalytic systems consisting of WCI6, CICH2OH and 'Bu3AI, Witte et al. ~o6 obtained high yields of polypentenamer having around 94% trans stereoconfiguration at the carbon-carbon double bonds. Moreover, acetals such as CHz(OCH3)2, CH2(OCH2CH2CI)2, CHsCH(OC2Hs)2, CI3CCH(OCH3h or Cd-lsCH(OC2Hsh have also been employed by Sch6n et al. ~~ as good stabilizersfor the binary catalysts formed from WCI6
149 and EtzAICI for cyclopentene polymerization. It is worth mentioning that epoxides such as ethyleneoxide or l-butyleneoxide have been employed by the same authors to improve the activity and stability of the binary catalysts derived from WCI~ and 'Bu3AI. On using a catalyst consisting of equimolar amounts of WCls, Czl~O and 'Bu3Al, they prepared in 82% yield a polypentenamer containing 90.5% trans stereoconfiguration at the carboncarbon double bonds. Halogenated hydrocarbons such as vinyl chloride have been employed by OberkJrch et al. ~os for cyclopentene polymerization with the catalytic systems formed from WCIs or TaCls and organoaluminium compounds. It was observed that these halogenated hydrocarbons increase substantially the activity of the catalyst but, at the same time, they modify the molecular weight of the polyalkenamer. Thus, on employing the ternary system WCI6, 'Bu3AI, CH2--CHCI, these authors obtained in 78% yield a high trans-polypentenamer having an intrinsic viscosity [11] of 3.27 dl/g (toluene). A wide range of ternary ROMP catalysts consisting of WCI6, organoaluminium compounds and halogen-, oxygen- and nitrogencontaining comtx~nds reported Dimonie, Coca and Dragutan ~~ for cyclopentene polymerization. These catalysts proved to be substantially trans-stereoselective. As Table 3.16 illustrates, polypentenamers with trans contents varying from 72 to 83% are readily obtaining using various organic compounds. In some cases the added compound may slightly increase (e.g. epichlorohydrin) or decrease (e.g. chloranil) the trans content but no drastic change in the steric configuration was observed for the range of additives employed. On using oxygen-containing compounds as a third component in ROMP catalysts derived from WCts and EtAICIz, Streck and coworkers tt~ obtained very active and stereoselective ternary systems for cycloolefin polymerization. Such systems with organic acids or their salts have been employed in cyclooctene polymerization. In one example, cyclooctene gave polyoctenamer with 63% cis configuration at the c,arbon-carbon double bond in the presence of the catalyst WCk/CH3COOH/C2HsAICI2. Heterogeneous three-component catalytic systems derived from 7tallyltungsten complexes and aluminosilicates containing trichloroaex~c acid as a third component have been prepared by Oreshkin et al. ~ to polymerize trans, trans, cis- l ,5 ,9-cyclododecatriene to polybutadiene. Though the catalysts had a high degree of activity their stereospecificity was limited to the cis:trans ratio from the initial cycloolefin.
150 Table 3.16 Polymerization of cyclcTamtme with WCl6-based ternary catalytic systems"b
trans'-Poly-
Catalytic System
|
cis-Poly~ r , % pmtmamr r t % WC rSu P o 85.5 14.5 WCh,/'Bu3/CA 0 72.0 28.0 WC~3AI/EP 0 81.6 18.4 0 WCIe.Et3AI2CI3/EP 81.9 18.1 0 WCI6/Et2A]CI/EP 78.4 21.6 -15 WCI6/'Bu3AI/DBQ 83.0 17.0 WCId'Bu3AI/MANH 0 72.O 28.0 0 WCI~Bu3AI/SALD 80.4 19.6 0 WCIJBu3AI/CYAC 74.2 25.8 0 WCI~Bu3AI/CYCL 73.0 27.0 'Data from rofwmoet~; bEP = epichlorohydrm, CA = chloranil, DBQ = dibenzoquinone, MANH --maleicanhydride, SALD = salicyiicaldehyde, CYAC = cyanuric acid, CYCL = cyanuric chloride. ~
3.4.4. Catalysts for ROMP in Water Systems
Early publications reponod the use of iridium salts and complexes as initiators for the polymerization of exo-bicyclo[2.2.1]hept-5-ene-2carboxylic acid in aqueous and alcoholic solvents. ~2 Noteworthy, investigations by Ivin and Rooney ~3 revealed that the trichlorides of ruthenium, iridium and osmium were also effective as initiators for the ringopening metathesis polymerization of both exo- and endobicyclo[2.2.1 ]hept-5-ene derivatives in ethanolic medium. ~13 The applic~ility of ruthenium salts in the polymerization of certain heteropolycyclic alkenes in poorly aqueous media has also been demonstrated by Novak and Grubbs. ~~4 Detailed studies on the polymerization of exo, exo-5,6ruthc~mn, bis(methoxymethyl)-7-oxabicyclo[2.2.1 ]hept-2-ene using iridium and osmium chlorides as the precursors of the active ring-opening metathesis polymerization initiators were carried out by Feast and Harrison. t~s In general, the polymerization was performed by adding aqueous solutions of the metal halide to stirred emulsions of the monomer in either pure water or mixtures of water and a chain transfer agent such as cis-but-2-ene-l,4-diol or its dimethyl ether. The reactions tcx~k place at
151 55~ under normal atmosphere and were run for two days. The product polymers were white solids; exposure to air resulted in slow degradation as evidenced by a yellow/green coloration. Typical experimental conditions and polymer yields with RuCI3.3H20, IrCI3.3HzO and OsCI3.3H20 in water are illustrated in Table 3.17. Table 3.17 Polymerization of exo, exo-5,6-bis(methoxymethyl)-7-oxabicyclo[2.2.1 ]hept-2-me initiated by RuCI3.3HzO, IrCl3.3HzO and OsCIs.3HzO in watzr ' Parameter Monomer, g Catalyst, g Water, ml Temperature, ~ Yield, % M., K tram-Double bonds, %
RuCI.3.3H20 1.0 0.07 7.5 55 95 155
IxCi3.3H20 1.0 0.07 7.5 55 2.0 20
OsCl3'.3HzO 1.0 0.07 7.5 55 95 5
60
90
75 |
i
9Data from r ~ r m o e ~'.
data indicated that the polymerization of exo, exo-5,6bis(methoxymethyl)-7-oxabicyclo[2.2.1 ]hept-2-ene initiated by RuCIs.3H~3and OsCls.3H~3 in water cwocurred in high yields, the molecular weight of the polymers being varied between 155 K and 5 K. In all ca.~s the microstructure of the polymer was altered only by the catalyst and was not dependent on the molecular weight or solvent composition. A new class of well-defined ruthenium carbene complexes, e.g. (Cy3P)2CIzRu=CHCH=CPh2, (Cy3P)2CIzRu=CHPh, (Cy--cyclohexyl) were used by Cmabbs and ooworkers ll6'll' for living ring-opening metathesis polymerisation of functionalized norbomene and 7-oxanorbomene in aqueous media. Monomers were dispersed in water using a cationic surfactant, and polymerization was initiated by injection of a catalyst solution to yield a polymer latex. The polymerization of hydrophilic 7oxanorbornene and a hydrophobic norbomene monomer displayed similar behavior in aqueous media, with the resultant polymers having lower molecular weights relative to polymerization in anhydrous organic solution on a similar time sc~e. The polydispersity indices of polymers prepared form the hydrophilic monomer using the catalyst
152 (CysPhCI2Ru=CHCH=CPh2 in the presence of water (PDI=I.20) were narrower than those obtained by solution polymerization (PDI=2.11) while polydispersity for polymers prepared using the catalyst (Cy3PhCI2Ru~HPh remained low in both the presence of water and in anhydrous solution (PDI=I. 13). The linear relationship between molecular weight and monomer/catalyst ratios and the absence of chain transfer and termination processes indicated that these systems are living. This technique was shown to be an efficient method for the preparation of well-defined block copolymers.
3.5. Synthesis of Catalysts for Cydoolef'm Polymerization 3.5.1. Synthesis of Cationic Catalysts Aluminium chloride, AICh. Due to its importance in the petroleum industry as a cracking and a refining agent and in the chemical industry as an alkylating and polymerizing catalyst, much work has been done on the commercial manufacture of aluminium chloride from bauxite or other aluminiferous ores. 6 The common commercial process developed by Gulf Refining Company (Texas) involves reaction of chlorine with bauxite under specific conditions. 6 In the laboratory, aluminium chloride is most readily prepared by passage of chlorine or hydrogen chloride over heated aluminium filings tts (Eq. 3.1). AI + 3HCI = AICI3 + 3/2 H2
(3.1)
Besides aluminium and aluminiferous ores, various compounds of aluminium, such as aluminium sulphate, aluminium phosphate, aluminium nitride, or aluminium carbide, have been used for the synthesis of aluminium chloride. Chlorination has been effected with chlorine, hydrogen chloride, metal chlorides, or other chlorine compounds. Several commercial processes with information on the cost of raw materials and economic feasibility have been described in the literature. 6'~9 Hydrogen fluoride, IIF. Hydrogen fluoride is currently obtained ~z~ from fluorite (CaF2) or even better, from cryolite (Na3AIF6) by reaction with 97.5% As-free H2SO4. (Eq. 3.2-3.3). CaF2 + H2SO4 = 2HF + CaSO(
(3.2)
153 2Na3AIF6 + 6HzSO4 = 12HF + 3NazSO4 + AI2(SO4)3
(3.3)
For further purification, it is distilled from a NaF-c~ntaining Pt retort into a Pt re~ver, leaving behind the SO42 and SiFe2" ions. A little PbCO3 is added to remove the CI'; this yields PbCIF, which is insoluble in concentrated HF. An excess of PbCO3 does not harm, even in the presence of H2S04. Organic material is removed only when KMnO~ is added. Boron fluoride, BF3. Several proc~ures for the preparation of BF3 in high yield are known starting from B203 and alkali fluoroborates (Eq. 3.4-3.5) KBF4 + 2B203 = BF3 + KF.B406 6NaBF4 + B203 + 6H2SO4 = 8BF3 + 6NaHSO4 + 3H20
(3.4)
(3.5)
or from H~BO3and fluorosulphonie acid (Eq. 3.6). H3BO3 + 3HSO3F = BF3 + 3H2SO4
(3.6)
The older method for preparing BF3 from CaF2 is not recommended, since the yields are low and the product is contaminated with SiF4. BF3 is conveniently stored in glass containers over Hg or in steel cylinders. Boron fluoride.etherate BF3.EhO. The etherate of BF3 is easily obtained by the reaction of BF3 with ethyl ether (Eq. 3.7). BF3 + O(C2Hs)2 = BF3.O(C2Hs)2
(3.7)
The product distils readily at 38~ (6 mm) and can be used as such or in ether solution. Aluminium bromide, AIBr3. Very pure AIBr3 may be prepared from aluminium turnings and dry bromine at a temperature sufficient for refluxing (Eq. 3.8). AI + 3/2 Br2 = AIBr3
(3.8)
The product is readily soluble in many organic solvents, hydrolyzes in moist air and reacts violently with water. Gallium bromide, GaBr3. Gallium bromide is readily prepared from metallic Ga by bromination (Eq. 3.9).
154 Ga + 3/2 Br2 = CraBr3
(3.9)
Very pure GaBr3 can be produced by vacuum sublimation in quarz equipment. Titanium tetrachloride, TiCh. Titanium tetrachloride is prepared by chlorinating titanium dioxide (mille) in the presence of charcoal or carbon black (Eq. 3.10). TiO2 + 2C + 2C12 = TiCh + 2CO (3.10) The crude product is decolorized and contaminants such as FeCI3, VOCI3, etc., are removed by means of Cu powder, Na amalgam or Hg. Zirconium tetrachloride, ZrCh. Zirconium tetrachloride is prepared similarly to titanium chloride by chlorinating zirconium dioxide in the presence of carbon black or charcoal (Eq. 3.11). Zr02 + 2C + 2C12 = ZrCl4 + 2C0
(3.11)
Preferably, zirconium dioxide with no admixtures is chlorinated in a CI2CCh gas mixture produced by passing CI2 through CCLs. The industrial chlorination of ZrC prepared from ZrSiO4 is described by KroU e t al. ~zo Iron trichloride, FeO~. Iron trichloride is prepared by reaction of dry chlorine with pure iron wire at 250-400~ (Eq. 3.12). 2Fe + 3C12 = 2FeCI3
(3.12)
An excess of chlorine should always be present. In another process the reaction occurs between chlorine and Fe(Ol~. The product is very readily soluble in water, ethyl alcohol, ethyl ether and acetone. Tin tetrachloride, SnCI4. Tin tetracloride is readily prepared in quantitative yield by direct chlorination of pure tin metal (Eq. 3.13). Sn + 2C12 = SnCh
(3.13)
The product is fuming in air, taking up moisture and forming various hydrates. It is stable only when kept in hermetically closed vessels. Zinc dichloride, ZnCIz. Very pure, anhydrous zinc chloride is prepared by treating Zn with dry HCI at 700~ in a quartz boat placed in a tube of highmelting glass (Eq. 3.14). Zn + 2HCI = ZnCIz + He (3.14)
155 At this temperature, the formation and sublimation of zinc chloride p r ~ at sufficiently high rates. The sublimed chloride is collected in a section of the tube which is kept cool for this purpose. For additional purification, the chloride may be resublimed in a stream of HCI. An efficient method for preparing ZnClz is by electrolysis of an acetonitrile solution of CuCI at room temperature with a Pt cathode and a Zn anode (Eq. 3.15). Zn + 2CuCI = ZnCI~ + 2Cu
(3.15)
The product is highly hygroscopic, soluble in methanol, ethanol, ether, acetone and other organic solvents. Triethylaluminium, Et~Al. Several proc~ures for the synthesis of triethylaluminium are known. ~'~2~ Pure triethylaluminium is readily produced from diethylaluminium bromide and sodium (Eq. 3.16). AI(C2Hs)zBr + Na = AI(C2Hsh + NaBr + AI
(3.16)
The product is spontaneously flammable in air and immediately hydrolyzed by moisture to AI(OH~ and C~-I~. Pressure processes for aluminium dkyls starting with Al, hydrogen and olefms are described by Ziegler and coworkerslZZ (Eq. 3.17). Al + 3CHz--CH2 + 3/2Hz = AI(C2Hsh
(3.17)
Diethylaluminium chloride, (CzHshAICL The ether complex of diethylaluminium chloride is prepared by the reaction of AICI3 with AI(CzHs)3.O(C2Hs~h (Eq. 3.18). AICI3 + AI(CzHsh.O(C2Hsh = (CzHshAICI.O(CzHs)2
(3.18)
3.5.2. Synthesis of Anionic Catalysts Organolithium compounds, RLL The most widely employed anionic catslyst, n-butyllithium, is readily prepared by reaction of lithium with nbutyl chloride in ether or pentane in an inert atmosphere, z3 Since the concentration of n-butyllithium solution in ether drops to half its original value in about a week at 25~ it is advantageous to store the solution in ice or in a refrigerator. Ethyllithium is best obtained by the slow addition of ethyl bromide to a well-stirred mixture of lithium and pentane or pentene
156 (mixture of isomers). Good yields result only when the ethyl bromide is added steadily and slowly. The first product is a precipitate consisting of lithium bromide and ethyllithium, the latter being only moderately soluble. Since ethyllithium is about ten times as soluble in benzene as in pentane at room temperature, it is conveniently separated from lithium bromide by solution in benzene, removal of pentane or pentene by distillation followed by crystallization of the ethyUithium from benzene. When the isolation of the organolithium compound is desired, the preparation is more difficult than when the product is intended for more or less immediate use for synthetic purposes. In this ease the method of choice is the reaction between lithium and an organomercury compound. An excess of lithium is desirable, to drive the reaction to completion and thus to avoid the presence of any soluble material except the desired product. An inert solvent is necessary and this may be light petroleum or benzene; ether is sometimes used but the product must then be worked up without delay. Solid compounds, e.g., ethyllithium, phenyllithium, are crystallized from the reaction mixture after filtration from insoluble matter, while liquid products, e.g., n-propyllithium, must be obtained by evaporation of the solvent in vacuum and cannot readily be purified. Organosodium compounds, RNa. Amylsodium and phenytsodium are conveniently prepared by reaction of amyl chloride and ehorobenzene with fine dispersions of sodium in hydrocarbon solvents under stirring at low temperatures. ~ Thus, if amyl eldodde is added slowly to a well-stirred sodium dispersion in a hydrocarbon solvent at room temperature, reaction generally starts within about two minutes (a little amyl alcohol helps to start the reaction if it does not begin on its own within several minutes). When the reaction has started, and not before, the reaction vessel is cooled, and amyl chloride (diluted with a h y d r ~ o n solvent) slowly added at such a rate as to maintain a reaction temperature about 25-30~ By the same procedure, phenylsodium can be prepared from ehlorobenzene in hydrocarbon solvent at temperatures of 30-35~ When the organosodium compound must be isolated, the exchange reaction between an alkali metal and the appropriate mercury compound, g2Hg, is the only satisfactory method. The reaction is carried out in light petroleum, in an atmosphere of pure nitrogen. Phenyl derivatives are best prepared by stirring the alkali metal with a benzene solution of dimbutylmercury. Grignard compounds, RMgX. Grignard compounds are normally prepared by the reaction of an alkyl or aryl halides with magnesium in dry
157 ether. 23 Since the reagents are very sensitive to air and moisture it is desirable that air should be excluded and that both reactants and installation should be carefully dried. The induction period at the beginning of the synthesis is in part due to thepresence of moisture, and in fact it increases rapidly with water content. Addition of a small crystal of iodine without stirring until reaction is well started, or the use of some magnesium which has previously been heated in the presence of iodine, are favored method for starting reaction. A similar effect may be achieved by the use of a little methyl iodide, ethyl bromide or ethylene dibromide. The formation of the Grignard reagent is generally a strongly exothermic process and, though slow to begin with common halides, accelerates very markedly when an appreciable amount of reagent has been formed. Care is necessary to avoid adding too much halide before it has been established that the reaction is well started. Halide is then added at such a rate as to maintain steady boiling of the ether.
3.5.3. Synthesis of Two-Component Ziegler-Natta Catalysts Two component catalysts for Ziegler-Natta polymerization of cycloolefins containing a metal halide such as TiCI4, ZrCI4, HIEh, VCI5 and organometallic compounds e.g. organoaluminium or organotin compounds are generally prepared in situ by adding a solution of the metal halide to a solution of the organometallic compounds in the presence or absence of the monomer. Examples for such catalyst preparation, including the systems EhAI/TiCI4, 'Bu3AIfFiCI4, NaAmfFiCI4, EhAI/ZrCI4 and Et3AI/VCIs, can be found elsewhere. ~23-~25 Metal(acetylacetonate), catalysts. Binary catalysts were prepared from V(acac)3, Cr(acac)3, Ni(acac)2, Mn(acach, MoOz(acac)2 and organoaluminium compounds or methylaluminoxane for polymerization and copolymerization of several cycloolefins such as cyclobutene, cyclopentene, norbomene and norbomene-like monomers. 126,127 Metallocene catalysts. Several metallocene catalysts employed for cycloolefin polymerization have been prepared by reacting CpTiCI3, Cp2TiCl2, CpzZrCl2, Cp2HfUIz, CpzVCIz, CpNi(Tt-allyl) or CpzCr with organoaluminium compounds or methylaluminoxane. ~z8'~29 Chiral metallocene catalysts. Various prochiral and chiral ligands have been designed and attached to the transition metal to form chiral precatalysts which in conjunction with aluminoxane as cocatalyst afforded chiral catalysts with a high activity and stereoselectivity in acyclic and cyclic
158 olefin polymerization. ~3~ Thus, ansa-zirconocene complexes, 1,2ethylenebi s(q Lind enyl)zirconiu m dichloride and 1,2-ethylenebi s(rl s_ tetrahydroindenyl)zirconium dichloride were prepared by the reaction of sodium or lithium derivatives of the C2 symmetric ligands 1,2ethylenebis(inden-l-yl) or 1,2-ethylenebis(4,5,6,7-tetrahydroinden-l-yl) with zirconium tetrachloride (Eq. 3.19-3.20).
§
K)~
_---
,,CI
*Z~~
Zr
(3.19)
(3.20)
. ~~
When dimethyl-, diphenyl- and dibenzylbis(l-indenyl)silane or dimethyl-, diphenyl- and dibenzylbis(4,5,6,7-tetrahydroinden-l-yl)silane have been used as C2 symmetric ligands in reaction with zirconium tetrachloride, dialkyl-, diaryl- and diaralkylsilyl-bridged zirconocene dichloride were prepared 133(Eq. 3.21-3.22).
K)~
*Z~I4
R"
i
R,..%R
Na(K)~
R. S
,Z~I4
R,.~.j R',
...
Nc,
(3.21)
(3.22)
These chiral zirconocene complexes in association with methylaluminoxane produced very active and stereoselective catalysts for the cycloolefin Ziegler-Natta polymerization and copolymerization.
159 The activity and stereoselectivity of these chiral zirconocene catalysts were further improved by introducing substituents such as alkyl, phenyl, naphthyl, benzo, substituted benzo, etc. into either the five- or sixmembered ring of the indene or tetrahydroindene moiety (Eq. 3.23- 3.26).
*ZrCI4
i~
+ZrC
R..
(3.23)
R" ~R Na(K)Na(K)
=
(3.24)
R" ~'R R I~
(3.25)
R (3.26)
o
When cyclopentadienyl or other aromatic anions are used as building units of the C2 symmetric ligand, various complexes can be prepared (78-80).
160
M ~~,
~
78
P
79
80
By replacing the dialkyl-, diaryl- and diaralkylsilyl bridge with a dialkyl-, diaryl- and diaralkylcarbyl bridge, a new class of active and stereoselective chiral zirconoc~e precatalysts bearing C2 symmetric ligands have been obtained (Eq. 3.27-3.28).
+Z~I4
;,,cI
~
I~
~'~a
(3.27)
R (3.28)
R
R
Chiral zirconocene complexes bearing C,-synunetric ligands containing different aromatic entities have been prepared by reacting a dialkyl- or diarylc,arbyl bridged cyclopentadiene and fluorene ligand with zirconuim tetrachloride (Eq. 3.29).
lnBuLi
2.Zrci4
d
(3.29)
161 A wide range of candidates for metallocene precatalysts in olefin polymerization that retain the C2 symmetry and highly stereodifferentiated reactive sites of ethylenebis(inden-l-yl)- and ethylenebis(4,5,6,7tetrahydroinden-l-yl)zirconium complexes have been designed and prepared recently having various stereogenic spacers while preserving the bis(cyclopentadienyl) framework. TM A first series was prepared using biphenyl and binaphthyl groups attached directly to the cyclopentadiene ligands in bis(cyclopentadieneyl) and bis(inden-l-yl) complexes of Ti and Zr. (81-83).
,o
81
o
c,
82
83
Another series of complexes contain more rigid alicyclic moieties of cyclopentane-l,3-diyl and cyclohexane-l,4-diyl bridges in r dichlorides TM (Eq. 3.30-3.32)
1.nBuLi ~.~
(3.30)
a.HC~ir
-p
(3.31)
a. lnBLd_i 3HCI/air
(3.32)
162 and various double bridges between the coordinated cyclopentadienyl ligands, e.g. two ethanediyl bridges or two dialkyl- or diaryl-silyl bridges ~3s (Eq. 3.33-3.36).
nBLLi.. zrc
r
h
reut.
ch
TiCl3/'i'H~
Me 2
Me2
,•
Ph2Si SiPh2
nBulLi ZI~Us
.._
Me2S~
nBLs Ph2S~~I2
ZrCl4 ~
(3.33)
(3.34)
(3.35)
(3.36)
3.5.4. Synthesis of Ring-Opening Metathesis Polymerization Catalysts 3.5.4.1. One-Component Metathesis Catalysts Tungsten hexachloride,WCl~ The most convenient ways to prepare tungsten hexachloride are the direct chlorination of tungsten with chlorine gas and indirect chlorination of tungsten trioxide with carbon tetrachloride. ~36 According to the first procedure W powder is contacted with chlorine in a special Vycor tube at elevated temperatures (ca. 600~ to produce highly pure oxychloride-free almost black crystalline tungsten
163 hexachloride (F,q. 3.37). W
+ 3C12 = W C l 6
(3.37)
In the second procaxlure tungsten trioxide is reacted with excess caubon tetrachloride under anhydrous conditions to thorough completion of the reaction (Eq. 3.38). WO3 + 3CCLs = WCts + 3COCb (3.38) If these conditions are not observed, yellow-red by-product WOCh forms readily (Eq. 3.39). WC[6 + H 2 0 = WOC[4 + 2HCI
(3.39)
Moreover, the WOCh has the undesirable property of catalyzing the hydrolysis of WCI6 in most air. Under these conditions, the process advances to formation of yellow WOzCIz by further hydrolysis of WOCLs (Eq. 3.40). WOCh + H20 = WOOl2 + 2HCI (3.40) The proper method yields an almost black crystalline tungsten hexachloride with no red or yellow impurities of tungsten oxychlorides. The product is very readily soluble in alcohol (with yellow color), CHCI3, CCh (with red and dark-brown color, respectively), CS2, ether, benzene, ligroin and acetone. Molybdenum pentachloride, MoCIs. The common procedure for preparing molybdenum pentachloride consists of chlorination of molybdenum in a special apparatus ~36(Eq. 3.41). 2Mo
+ 5C12 =
2MOC15
(3.41)
The blue-black, extremely hygroscopic c r y ~ e product, dark-green if oxychloride is present, is soluble in water and alcohol with solvolysis. The pure product is soluble without decomposition in organic solvents such as ether, CHCI3, CCh and CS2. Rhenium pentachloride, ReOs. Rhenium pentachloride is prepared by chlorination of rhenium metal at 500~ in a proper installation in a stream ofCl2 (Eq. 3.42). Re + 5/202 = ReCI5
(3.42)
164 A deep, black-brown product, sensitive to air is formed. It hydrolyzes with water forming various products. Rhenium pentachloride is soluble in hydrochloric acid (green solution) with liberation of CIz. Ruthenium trichloride, RuCI3. Ruthenium trichloride is prepared by chlorination of ruthenium metal at 700-800~ in a special Vyoor tube m36 (Eq. 3.43). Ru + 3/2Ciz = RuCI3
(3.43)
Good crystals in the form of shiny black platelets, insoluble in water, are obtained. RuCla.HzO. A pure product corresponding to the formula RuCI3.HzO can be obtained from hydrochloric acid solutions of RuCI3 (which is not free of Ru(IV)) by electrolytic reduction. 136 The process is adjusted to produce red colored solutions of Ru(Ill), a blue color indicating the formation of the undesirable R(II) product. Iridium trichloride, IrCl~. Iridium trichloride can be prepared by various procedures depending on the starting materials. ~s The most convenient way is by chlorination of iridium metal at 600~ in a special combustion tube
(Eq. 3.44).
Ir + 3/2CI2 = IrCI3
(3.44)
Alternatively, IrO2.2H20 may be heated to 240~ in a stream of C12 and illuminated with sunlight or a burning magnesium ribbon (Eq. 3.45).
IrOz.2HzO + 7/202 - IrCl3 + 4HCIO
(3.45)
Finally, (Nl'hhlrClz may be decomposed in a stream of CIz at 440-550~ for several hours (Eq. 3.46).
(NI-hhlrCl6 = IrCI3 + 2NH4CI + 1/2CI2
(3.46)
A dark olive-green powder, stable up to 760~ under a CIz pressure, is obtained. At 700~ the color changes to bright yellow.
165 x-Allyl complexes. There are various methods for preparin~ ~-allyl complexes of group V-VII transition metals published elsewhere ~3
3.5.4.2. Two-Component Metathesis Catalysts Synthesis of two-c~mponent metathesis catalysts ~ r s m s/tu by contacting the catalyst components in solution of the monomer or by precomplexafion the reacting components before adding the monomer. Variants for such catalysts as WCI6/Et3AI, WCIjMe4Sn and MoCIs/Et3AI are found in the open or patent literature. ~3s
3.5.4.3. Three-Component Metathesis Catalysts In addition to the catalyst and coc~talyst components, a great number of metathesis catalytic systems contain a third component introduc~ to adjust the catalyst activity, selectivity and stability. Depending on the nature of the catalyst, the third component can be an electron donor or acceptor compound, with specific electronic and steric effect on the catalyst active species. 139
3.5.4.4. Well-Defined Metathe~is Catalysts Ttianacyclobutanes. A wide range of titanacyclobutanes have been synthesized and characterized by Grubbs and coworkers 14~starting from the Tebbe reagent, olefins and a Lewis base. For example, reaction of Tebbe reagent with 1 equiv of norbomene gave the corresponding titanacyclobutane (Eq. 3.47).
CP2"I]=CH2+ ~
~
CP2T~
(3.47)
Similarly, reaction of Tebbe reagent with 3 , 3 - d ~ y l c y c l o p r o p e n e and isobutene formed the respective titanacyclobutanes (Eq. 3.48-3.49).
CP2Ti=CH2 + ~:~
~ CP2T{~
(3.48)
166
Such titanacyclobutanes have been used in the first living polymerization systems for the ring-opening polymerisation of cyclic olefins. Tantalaeydobutanes. Two Tantalacyclobutanes prepared Wallace and Schrock TM by the reaction of tantalum-neopentylidene complexes, Ta(=~I-I~uXOKh(TItT) (OR = 2,6-diisopropylphenoxide or 2,6dimethylphenoxide) with 1 equiv of norbornene (Eq. 3.50-3.51).
(3.50)
(3.51)
The Ta neopentylidene complexes were obtained from TaCls and Zn(CH2'Bu) as described below. Tantalum- and niobium-alkylidene complexes. Ta(=CH'BuXOR)3(THF) (OR = 2,6-diisopropylphenoxide or 2,6-dimethylphenoxide) were prepared by Schrock and coworkers 14z from TaCI5 and Zn(CHztBu)z in three highyield steps (F-~I. 3.52-3.54).
TaCI 5 +
Zn(CH2tBu )2 -ZnCI2~ ' ~ Ta(CH2tBu )2CI3 (3 52)
Ta(CH2tBu)2CI3 + 3ROLi (RO)3Ta(CH2tBuh
-3LiCI
-CH3tBUTHF"=
-
(RO)3Ta(CH2tBu)2 ( R O ) 3 " ~ a ~H
(3.53)
(3.54)
THF Tuntalum- and niobium-neopentylidet~ complexes were also prepared by Schrock and coworkers 143 from the corresponding trialkyl metal dichloride by subsequent alkylation and elimination reactions (Eq. 3.5 5-3.57).
167
M(CH2CMo3hCI2 M(CH2CMe3)4CI
LiCH2CMe 3 .= - I_JCI
(3.55)
[(MeaCCH2~CIM=CHCMe 3]
- CMe4 .
[~CCH2hCN=CHCMe-.j
M(CH2CMe3hCI
13.56)
UCHzCM~ - UC~ = M(CHzCMe:~(CHCM~)
0.57)
where M is Ta or Nb. The key step showed to be the decomposition of the initially formed monochloride by loosing neopentane as result of ahydrogen abstraction to give mb~uently an u n . ~ l e complex which reacts further with LiCHzCMe3 to give the final metal-alkylidene product.
Tungsten-alkylidene
complexes.
A
series of tungsten-alkylidene
complexes of the type W(=CHCMe3XOAr)2CI2(OR'2) and W(=CHCMe3XCH2CMe3)(OAr)z(OR'2) were prepared by Basset and coworkers6~ by means of the reaction of W(OAr~hCh with 1 equiv and 1.5 equiv of Mg(neopentyl)~dioxane), respectively (Eq. 3.58-3.59).
IAX
cloxane) - - - , -
(ArOhWCh* 1.5 Mg(Cl'12CMe3h(dtoxane) ~
(ArOhCl(
H (3.59)
Very active ring-opening metathesis catalysts, W(=CHR)(OR')zBr2, particularly when they were associated with GaBr3, prepared Kress and O s l ~ m 61'145 by reaction of WO(OCHz'Bu)~CH2'Buh with AIX3 (Eq. 3.60).
H Four-coordinate, Lewis acid-flee complexes of the type W(=CHCMe3X=NArXORh prepared Schrock and coworkers ~ by the route shown in Eq. 3.61-3.63.
168
x^ CI ,.,, -Me3SiC=I .u,, I / ~ ' [O..~/,^ .. + ArNH(SiMe3) CI ~mu ~0
9
~ INHAr
~o'~V\%ctBu CI 9
CI
.0.. [ ~NA r
(~I.NHAr vu (~ICtBu
~3
(3.61)
CI
NEt3
~-O..[ ~ NAr
Et20
,U ~, CHtBu
(3.62)
AF
+ 2 MOR
- 2MCI ~
m '~ RO""'V~/==K,
(3.63)
I-~uc, M=Li or K and OR=OCMr OCMez(CF3), OCMc(CF3h, OR/'. The key step is the catalysis of a proton transfer in W(-=CCMe3)(NHAr)(DME)CI2 by triethylamine in diethyl ether at -40~ to give orange W(=CHCMe3)(=NAr)(DME)CI2. Addition of two r of LiOR to W(=CHCMc3X=NAr)(DME)CIz gives four-cx~ordinate dialkoxy alkylidene complexes, since a six-coordinate complex is too crowded to retain a relatively weakly bonding DME ligand. A more convment route to W(=CHCMe~X=NAr)(ORh complexes starts from WOCh when 2 equiv of the ncopcntyl Grignard rcagem are required t47(Eq. 3.64-3.67).
WOCI4 + ArNCO
Octane.=. .~
CI4W==NAr+ 2 LiOtBu THF/Et20
CI2(OtBu)2CrHF)W=NAr
C12(tBuO)2(ll"f)~r + 2 (tBuCHz)MgCl ~
(tBuO)2(tBuCl'~)2~r + PCls
CI4W_-NAr
DME
=
(3.64) (3.85)
(tBuO)2(lSuCH~~r (3.66) 9 CI NAr .O.~
[.,
(3.e7)
169 The proposed intermediate, W(=NArXCH2'Bu)2CI2 is unstable with respect to a-elimination, at least in the presence of a donor solvent such as dimethoxyethane. The simplest synthesis of a "versatile precursor" to a variety of tungsten alkylidene complexes, W(=CHR)(=NAr)(OT0z(DME), uses WO2C12 as a raw materialla(F~. 3.68-3.69). WO2Cl2 +2AtNH2-- ~)2Cl2(DME)*2RCH2MgCI= W(NAr)2(CH2R)2 (3.68) ~O ~OTf VV(NAr)2(CPhRh,
+ DME
,.
= - ArNPhOTf _RCH 3
( . ,,~NAr
LJIW' "R 4U OTf H
(3.69)
The intermediate in the last step is believed to be the unstable compound W(=NArXCH2R)2(OTfh formed readily from W(=NArh(CHzR~h. The success of this reaction is attributed to the fact that the product W(=CHRX=NArXOTfh(DME) is relatively stable to triflic acid, presumably because the DME is bound tightly and the metal is relatively ionic. The neophyl ligand (R=CMe2Ph) is much less expensive than the neopentyl ligand (R=CMe3). A wide variety of W(=CWBuX=NAr)Xz complexes could be prepared from W(=CHK)(=NAr)CI~ME) or W(=CHRX=NArXOTf)2(DME) where X = alkoxide, primarily with examples of X = thiolate, amide, or alkyl. In all cases the X groups must be bulky in order to stabilize the four-cx~rdinate species toward bimolecular decomposition, especially when the alkylidene ligand is small. In addition, a variety of alkylidene complexes can be prepared from CWBu complexes by metathetical reactions involving an internal or terminal olefin. A new five-coordinate tungsten-alkylidene complex in which a bidentate arylamine ligand is present was prepared by van Koten and oowork~l"$ 72'149 by t r a n s l a t i o n between the lithium salt of 2[(dimethylamino)methyl]phenyl and tris[(trimethylsilyl)methylphenylimidotungsten chloride (Me3SiCH2)3W(=NPh)CI (F_x].3.70-3.71). ~ W
~
~_ ?Li
NMe2
+ W(CH2SiMe3)3CI(=NPh).~,--p,
~Me2
~CH2SiMe3 ~'~'CHSiMe3
(5
(3.70)
170
NM~ OU + V~CH~~,j~C(-NPh)---,,.
CH~~
(3.71)
The analogous transmetallation reaction of natrium 8-quinolinolate with tris[(trimethylsilyl)methylphenylimidotungsten chloride produced readily the tungsten(VI) alkylidene complex containing O,N chelating ligand, 8-
quinolinolate (Eq. 3.72). N
+ V~CH2SiMe3)3CI(=NPh ) ~
CH2SiMe3
O- II ~CHSiU~ 3,,~ N
(3.72)
{3
ONa
This complex was very active and stereoselective in the ring-opening metathesis polymerization of norbomene. Reaction of Li salts of 2-pyridylmeth~ol derivatives R~RZC(OI~2 Py) with tris[(trimethylsilyl)methylphenylimidotungsten chloride afforded
similar O,N-chelated tungsten(Vl) alkylidene complexes active in ringopening metathesis polymerization. Thus, reaction of Li[OCPh2(2-Py)] with (Me3SiCH2)3W(=NPh)CI in THF gave W(=CHSiMe~)(CH2SiMe~X=NPh)[OCPh2(2-Py)] (Eq. 3.73).
U[OCPh~(2-Py)] * V~CI"I2SiMe3)3CK=NPh)
r~
~N. p C-O-
Ph...L , ~
N
/
.CH2Si~ (3.73)
171 The 'H NMR spectrum of W(=CHSiMe3XCHzSiMe3X=NPh)[OCPhz(2Py)] in benzcno-d~ showed to be a mixture of two rotamers, in an anti:syn ratio of approximately 1"10. In an analogous m ~ e r , reaction of Li[OCH(CMe3)(2-Py)] with (Me3SiCH2)3W(=NPh)CI provided W(=CHSiMe3)(CH2SiMe3X=NPh)[OCH(CMe3X2-Py)] (Eq. 3.74).
U[OCH(CMe3X2-Py)]
9VV(CH2SiMe3)3CI(=NPh )
"n-IF
. H..•
~. *~
/
.CH2SiMe3
,c-o-W*cHsi
Me3C
(3.74)
N
Both O,N-chelated tungsten alkylidenr complexes of 2-pyridylmethanol derivatives showed to be active in the ring-opening metathesis polymerization of norbomene.
Molybdenum-alkylidene complexes, Mo(=CHCR'3X=NArXOR")2 A wide range of four-coordinate molybdenum-alkylidene complexes of the type Mo(=CHCRIR2RSX=NAr)(OR4)2 prepared Schrock and coworkers 15~ in high yield from amn~nium dimolybdate. The first series of neopentylidene complexes, Mo(=CI-~BuX=NArXOR)2 (Ar=2,6 diisopropylphenyl; OR = O~Bu, OCMe2(CF3), OCMe(CF3)2, etc.), can be prepared from a "universal precursor", Mo(=CH'Bu)(=NAr)(triflate)ADME) which is obtained in three steps from ammonium dimolybdate (Eq. 3.75-3.76).
[NH412M0207 ---~ Mo(NAr)2CI2(DME)__.~ Mo(NAr)2(CH2tBu)2 (3.75) (I)
TfO NAr (I) '-ArNH30-TfCH3~Bu/~d t~.,HtBu - 2 l.iOTf I OTf
ROI~-Ar ''CHtBu
The second series of neophylidene complexes, Mo(=CHCMe~h)(=NAr)(ORh (~---2,6-diisopropylphenyl; OR = O'Bu, OCMe-z(CF3), OCMe(CF3)z, etc.), can be prepared from another
172 "universal precursor", Mo(=CHCMe2Ph)(=NAr)(triflate)z(DME), which is obtained analogously in three high-yield steps from ammonium dimolybdate tsl (Eq. 3.77-3.78).
[NH412M0207~
Mo(NAr)2CI2(DME)--~Mo(NAr)2(CH2CMe2Ph)2 (3.77)
(u) § 3 TTOH/DME
T~~NAr ,~)_
(II) -ArNH3OTf-CH3CMe2Ph%6
+2L.iOR
R.O ?-Ar
HCMe2Ph-zLiOTI7
HCMezPh
These complexes serve as initiators for the ring-opening metathesis polymerization of norbomene and substituted norbornene as well as for related olefin metathesis reaction. Some of the neophylidene molybdenum complexes, Mo(=CHCMe2Ph)(=NAr)(ORh, and their precursor, Mo(=CHCMezPhX=NArXtriflate)-z(DME), are available commercially. An universal catalyst precursor ~sz that contains a benzylidene ligand could be prepared directly in four steps from ammonium dimolylxlate, one of which involves an co-hydrogen-abstraction reaction in a dibenzyl complex. Mo(=NA(hCIffDME) reacts cleanly with 2 equiv of KCHzPh to give Mo(=NAr)z(CHzPhh. Treatment of this compound with 3 equiv of triflie acid afforded Mo(=CHPhX=NArXOTfh(DME), which is isolated as a mixture of isomers according to NMR spectra (Eq. 3.79-3.81).
Ar I Mo(NAr)2(CH2Ph)2 -ArNH3OTf -CH3Ph
Ar s
c.6 o
.o~Mo.. / v
(3.80)
Ar I
=
"W,M,o-" L
"
(3.81)
173 Five-coordinate molybdenum (VI) alkylidene hexafluoro-tertbutoxide complexes that are stabilized by internal Lewis base coordination were prepared by Schroc~ and coworkers ~" starting from tetrac,oordinate molybdenum (VI) alkylidene complexes. For instance, reaction of 4methoxy- 1-hexene with Mo(=CHCMerPhX=NArXOI~h or Mo(=CHCMe3X=NArXOI~)~ in pentane (O1~ = OCMe(CF3)2) afforded crystalline, red-orange Mo[CHCHzCH(OMe)CHzCH3 ](=NArXOILssh in good yield (Eq. 3.82). Ar
Ar
I
RfeO".Mo//N
I R~O.... NI
+
Rf6C)~AM~ (3.82)
_CHz=CHCMezPh =
~
A related difimctional Mo alkylidene complex could be prepared in a similar manner from Mo(=CHCMe2Ph)(=NAr)(OR~h and the appropriate r diene (Eq. 3.83). ,sat-- N
R~)~.. |
I~
N-At
~ ~
-
Ar--~"O1~ M R spectra of these complexes indicated that no plane of symmetry was present in either complex and the Jcrk, value (158 Hz) suggested that the alkylidene was the anti rotamer in each case. Six-coordinate molybdenum (VI) alkylidene hexafluoro-tertbutoxide complexes that are stabilized by external Lewis base coordination were also prepared by Schrock and coworkers ~" starting from tetracoordinate molybdenum (VI) alkylidene complexes. Thus, st~cn@ or reacts cleanly with Mo(=CHCMe2Ph)(=NAr)(OR~)2 orange Mo(=CHCMe3)(=NArXOR~h in DME to afford Mo(=CHPh)(=NAr)(OI~)2(DME) in good yield (Eq. 3.84).
N~Ar RI'eQ,II ;[r
.O" "C H C M e a
/~ + (~ ?
[
+ DME
At
~
- I'hC=CHCMe3
RfoQ --.~ x.II / ("~'~ X...O ORf6
i
0 (3.84)
174 4-(Dimethylamino)styrene and 2,4,6-trimethoxystyrene react also with Mo(=CHCM~PhX=NArXOI~h or Mo(=CHCMe3X=NArXORch to yield dark red Mo[CH-4-GH4-NM~](=NArXOI~s).z(DME) and red Mo[CH2,4,6-CtH2(OMe)~](=NArXOR~s)z(DME), respectively (Eq. 3.85-3.86). NMe2
afoO,
+ Me2N~ RfsO/I~cHCMe,
RfeO / f ':.M0 .
R~O
=_ ~.,.~\..11 -H2C=CHCMe2Ph ~ ~ O R f s
(3.85)
|
1 ,DME ..n .~ Mo----/~"~ + MeO--~~ j '~ r - zP':'C=CHCMe=--h l'h ~,,.O-" -\r~of OMe ~CHCMezPh xC)Me ' v"~e
/-~
13.86)
On the basis of the relatively low value for Jca~ in the first two sixcoordinate complexes, they are believed to be the syn rotamers with the structures shown in Eq. 3.85-3.86. In contrast, the alkylidene ligand in the last Mo complex is in the anti orientation in solution (Jca~ = 159 Hz), consistent with internal coordination of an o-methoxy group to the metal, probably in a five-coordinate species (Eq. 3.87).
AIr = ~ ~ O M e ~1
-O9 2Mo ( ~ q %Rfe
OMe
Ar
NI
-DME
~Q
|
+DME
RfsO~-M Me"
OMo
(3.87)
OMe
Dimethoxyethane could not be removed m vacuo from solid samples of this Mo complex, however, so it was presumed that DME was extemaUy coordinated to form a six-coordinate compound in the solid state. The metathesis reaction between Mo(--CHCMe2PhX=NArXORas:h or Mo(=CHCMe3)(=NAr)(OI~)~ and 0.5 equiv of octatctracne in DME afforded the difunctional Mo complex [(DME)(Rf~O)-z(=NAr)Mo]z(CH~
3.88).
175
Ar
Rf6q-~~-O~
9
(3.88)
It was observed that the solution changed from yellow to deep red as the reaction went to completion, consistent with formation of a conjugated alkylidene complex. The six-coordinate structure of the difi~ctional complex was proposed on the basis of the observed stoichiometry, the stability of the compound in solution and in the solid state, and the values from the ~H NMR spectra. However, it was inferred that the six-coordinate complex must be in equilibrium in solution with fie, DME and a fourcoordinate alkylidene complex, on the basis of the reactivity of the complex toward norbomene and norbomadiene, as well as the fact that the DME ligand could be replaced easily by diethyl ether or T t ~ to form
monoadducts (Eq. 3.89).
/--[Mo~(DME) S
(DME._. _~]tMoR5/'~
/~~/--[Mo]f~S)
'2DME-~ ( S ) [ M o ~ - '
(3.89)
S = Et20,THF
[Mo~ = MoKNkrXOR~h
The monoadduct with ether could be prepared directly from Mo(=CHCMe2Ph)(=NAr)(OP~)2 or Mo(=CHCMe3)(=NAr)(OR,s)2 and octatetraene in ether in 66 % yield while the monoadduct with THF could not be prepared directly in THF, because the initial metathesis step is too low under these circumstances. A l l these difimctional Mo complexes are isolable, crystalline species that are stable at 25~ in solution and in solid state. The value for Jca,, for DME complex (132 Hz) and ether complex (127 Hz) indicated them as syn rotamers while the value of Jc~ for THF complex (152 Hz) was more consistent with its being anti rotamer. Reaction of the DME adduct with 4 equiv of LiOtBu and 2 equiv of quinuclidine (quin) afforded the difunctional complex (quinX'BuOh(=NAr)Mo(CH)sMo(=NArXO'Bu)~(quin) (Eq. 3.90).
J
(DMEXMo~~ [Mo~ = Mo(NArXORfeh
[M~
2quin 9 ..~
/[MoXquin)
,4 LiO~u ( q u i n t ] - " [Mo] = Mo(NArXO~uh
(3.go)
176 This complex is less stable than its precursor in the solid state. Presumably, the quinuclidine ligand is not bound strongly because of the more electrondonating nature of the alkoxide ligands. 1,4-Divinylbenzene reacted with Mo(=CHCMe2PhX=NArXOR~)2 or Mo(=CHCMe~X=NArXOR~h to produce another difunctional alkylidene complex, 1,4-[(DME)0~F60)2(ArN=)MoCH]zCasH4 (Eq. 3.91). Ar
Rf8
_ ~1~-O,.
.o.,.,:v_.
+
HCMe3
A,
L,,,.O'OR/8
This complex could be isolated as a crystalline, bright orange solid which was soluble in DME and THF but was nearly insoluble in other common solvents. Proton and carbon NMR data suggested that the structure of the complex was analogous to that proposed for the six-coordinate benzylidene complex. The value for Jct~ (125 Hz) was consistent with a syn orientation of the alkylidene ligand with respect to the imido ligand. An isolable THF adduct could be prepared from 1 , 4 - [ ( D M E ) ( R F 6 0 ) 2 ( A r N = ) M o C H ] 2 ~ simply by dissolving this complex in THF (F-4.3.92). Ar i
9 N
0 ~
'M'o ORf8
Ar
I .~'_
i
M
L;
N-ORI~
(3.92)
B'6o ORb Mo(=CHCMe2PhX=NArXOR~)2 or of However, metathesis Mo=(CHCMe3X=NArXOR~h with divinylbenzene in THF proceeds to slowly to prepare 1,4-[(TtW)(RF60)2(ArN=)MoCH]2Cdh directly by this reaction. Tungsten oxo alkylidene c o m p l e x e s . The first successful synthesis of a tungsten oxo alkylidene complex of the type w(oX=CHCMe3)(PEt3)2CI2 was reported by Schrock and coworkers ~s4'~ss starting from a tantalum alkylidene complex (Eq. 3.93). Ta(CHCMe3XPEh)2CI3
* w~oXOCMe3)4
PEh ..._ C k , ~ O
"- cr. i .CHCMea
- Ta(OC Me3)4cl
PEt3
(3.93)
177 Analogous benzylidene, ethylidene, propylidene and methylene complexes were prepared by treating W(O)(=CHCMe3)(PEt3)2CI2 with RCH~2H2 (R = Ph, Me, Et, H) in the presence of AICI3(Eq. 3.94).
PEh PEh Ck.~~3 + H2C=CHR Ck IW~-_ CI,"I~'CHCMe3 -H2C=CHClVl% 3 CI" I"CHR PEt3 PEh
(3.94)
Furthermore, the five-ca3ordinate, tungsten oxo alkylidene complex W(O)(=CHCMe3)(PEh)CIz was prepared by adding transition metal complexes which will scavenge phosphine ligands (Eq. 3.95).
Ck.l~ + Pd(Pt~N)2CI2 =- Et31:x.'.~.V~HCMe3 CF I'CHCMe3 -Pd(PEh)2CI2 ~ ~1 PEt3
(3.95)
Interestingly, this five-ca3ordinate tungsten oxo complex can metathesize terminal and internal olefins in chlorobenzene in the absence of AICl3 at an initial rate which is at least equal to that of the hexaooordinate tungsten oxo complex W(O)(=CHCMe3)(PEh)2CIz plus AICI3. The oxo alkylidene complex syn-W(=CHtBu)(O)(OAr)2(PMe3) (Ar=-2,6-Ph2C6H3) was prepared by Schrock and coworkers Is6 by the reaction between W(=Cl-r'Bu)(O)(PMe~)zClz and 2 equiv of KO..2,6PhzC6H3 (Eq. 3.96).
PEt3 Ck..i ~.O
CI~~~CHCMe3 PEt3
+ 2 KOAr - 2 KCI-PMe3=-
PMo3 ArO, l O
AK~'VV~cHCMe3
(3.96)
The alkylidene I~ resonance was found at l 0.13 ppm and the C= resonance at 287.4 ppm. A Jcn value of 120 Hz suggested that the alkylidene has the syn orientation. 3~p M R data (0.35 p p ~ ~Jpw=333 Hz) suggested that the PMe3 ligand was bound to tungsten on the M R time sc~e. A strong absorbance a t - 960 cmm has been assigned to the metal-oxo stretch. An analogous PPh2Me complex, syn-W(~H~uXOXOAr)z(PPheMe) could be prepared by adding 2 equiv of KOAr to W(=CHfBu)(O)(PPheMe)~Br2 (x=l,2) (Eq. 3.97).
178
P,Ph2Me
Br,. I ~
+
P,Ph2Me
2 KOAr
ArO. l O
B~'I'*~CHCMe3Wr- 2KCl_pph2Me~ PPh2Me
ArO~'~CHCMe3
(3.97)
Only a single broad 31p NMR resonancewas observed at 11.6 ppm at 22~ but a sharp resonance was found upon cooling the sample (Jpw=305 Hz). The alkylidene Ha (10.37 ppm) and C= (287.2 ppm) resonances also did not show coupling to 3~p at room temperature. A Jca value of 118 Hz was consistent again with the syn rotamer being present. A neophylidene complex, W(=CHCMe2Ph)(OXOAr)~pPh2Me), was also prepared (Eq. 3.98).
PPh2Me Br,,.I ~
,PPh2Me
ArO... V~I,~O Br"!'CHCMe2Ph-2KCI-PPh2M~ ArO/ ~CHCMe2Ph PPh2Me +2 KOAr
(3.98)
All these tungsten oxo alkylidene complexes react readily with 2,3dicarbomethoxynorbomadiene and 2,3-bis-(trifluoromethyl)norbomadiene in dichloromethane or toluene to give polyng~s that are >95% cis and >95% isotactic. Tungsten oxo vinylalkylidene complexes. Synthesis of tungsten oxo vinylalkylidene complexes ~" involved two main steps starting from tungsten oxo precursors WCI2(OXPX3)3 (PX3=P(OMe)3, PMePh2); first, formation of rl2-cyclopropene complexes, W(q2-diphenylcyclopropene)Cl2(O)(PX3)2, by reaction with 3,3-diphenylcyclopropene and second, conversion of these complexes into tungsten oxo v i n y l alkylidene complexes, W(=CHCHCPhzXO)(ORI~)z(PX3), by reaction with LiOC(CH3)(CF3h (LiORf6) in benzene or toluene at 55-60~ (Eq. 3.99-3.100).
X3R.,0 ,px 3 Ph . .,, ph2Mep~ O ~ P h Cff,~l,PMePh2
Ph
2 LiORfs 6~C, 12h Benzene
..=
=-
X3R.'ii'..J~ Ph
Rfs(~
(3.99)
~Ph
Ph Rfs~ PMePh2
(3.100)
179 The products were isolated as a mixture of the two rotaries, syn and an#, based on the values of the Jan coupling constants observed in the 'H NMR $po~i~m. Reaction of W(=CH=CHCPh2)(O)(OAr)2(POMe)3 with an excess of Tt~ led to the corresponding THF adduct W(=CH=CHCPh2XOXOAr)2(THF) (F_,q. 3. l01).
_o, LPh
Rf60"~V~v xPh Rf60 P(OMe)3
THF-da
O -Ph RfsO,j ~ ~ V ~ p h Rf60 THF
I
Benzenede
(3.101)
The complex appeared as a mixture of syn and anti rotamers, in 1"1 ratio, probably due to the low ligand steric bulk. In this case, the ~H NMR spectrum presented two doublets for the resonances of the H~ and H0 in each rotamer, at/~=l 1.86 and 9.32 for the anti rotamer and at 8=10.25 and 9.28 for the syn rotamer. These complexes were active in the ring-opening metathesis polymerization of norbomene as well as for cyclic olefins such as cyclooctene, 1,5-cyclooctadiene and cyclooctatetraene derivatives. Ruthenium-alkylidene complexes, Ru(CHR)LL A series of RuCI2(CHR)(PPh3h complexes (R= Me, Et, At) were prepared by Grubbs and coworkers rossfrom RuCI2(PPI~)3 via alkylidene transfer reactions from diazoalkanes. When RuCI2(PPh3)3 was reacted with diazoetlmne, diazopropane and variously para-substituted aryldiazoalkanes, pC6tGXCI-iN2, a spontaneous Nz evolution at-78 ~ indicated formation of RuCI2(=CHR)(PPh3)3 (R=Me, Et) and RuCI2(=CH-p-Cd-hX)(PPh3h (X=H, NMez, OMe, Me, F, CI, NO2) complexes (Eq. 3.102-3.103). PP~ H P,PlM H ,
Cl'Ru-PPh3pPh3 + N2--"C,R |Ph3 P
Ck u._pp .
~
Cl/-I" 'PR113 P
(3.1
CL..,PPh3 ,.,-H
H
= cp.&=,.,
PPh3
X
02)
(3.103)
X
The m~um-alkylidene complexes were isolated in 80-900,6 yield as green air-stable compounds. The awl complexes polymefized
180 norbomene in methylene chloride at room temperature to give polynorbomene in quantitative yields. Ruthenium-vinylalkylideae complexes, RuCIz(CHCHCR'2). Several ruthenium vinylalkylidene complexes of the type RuCIz(=CH=CHCPh2)(PR3h (g=Ph, Cy, Cyp) were prepared by Cnubbs and coworkers ~59 by the reaction of RuClz(PPh3)3 with 3,3diphenylcyclopropene and fiulher substitution by the appropriate phosphine
ligand (Eq. 3.104). PPI~ p c ~ U - Ph3
Ck~
PPh3
PPh3 Ckl~~p
Ph
PPh3
,Ph h
Ph
pR3 / = , , ~ P h .~ C l ~ ~ Ph
(3.104)
PR3 R = Ph, Cy, Cyp
compounds showed a remarkable activity in ring-opening metathesis reactions and good stability toward functional groups and protic media. However, the multistep synthesis of the cyclopropene and the low initiation rates of the resultant diphenylvinyl alkylidenes are present limitations of these complexes. Chiral alkylidene complexes. A number of ehiral molybdenum complexes have been synthesized by Schrock and coworkers ~6~ using C2-symmetric chiral diolate ligands which were active in ring-opening metathesis polymerization of 2,3-bis(trifluoromethyl)norbomadiene and 2,3diearbomethoxynorbornadiene. Synthesis of Mo(=CHCMe2PhX=NAr)[(+) Ph4tart](S) was carried out by the reaction of (+)-Pl~tartH2 with Mo(=C HCMe2PhX=NArXOTf):4"I)ME) (DME=dimethoxyethane) in diethyl ether in the presence of triethylamine (Eq. 3.105) M M
~~hh
P,l~h
~ O'TT8..Ar
+ L~ (~"~o I~l~I 2
I ~-~-Ph o~
Ph Ph O'l'fA Ar Ph Ph OTrr
where S was a mixture of NEt3 and DME. In an analogous manner were synthesized Mo(=CHCMe2Ph)(=NAr)[(-)-Ph4tart](S) and Mo(=CHCMezPh)(=NAr)[(+)-Naph4tart](S) (Eq. 3.106).
181
O RR ~~X~
\ OTf, . r'~"~'~ ~~]
M
9
I~N..Ar ~o~
Me. O 1 ~
RR Olfe R~
Mo(=CH'Bu)(=NAr)[(:I:)-BINO(SiMezPh)2](THF) was obtainr in 70~ yield from Mo(=CH*Bu)(=NAr)(OTf)2(DME) by reaction with (+)BINO(SiM~Ph)K2 in tetr~ydrofuran as a solvent (F~. 3.107). SiMe2Ph OT~,
SiMe2Ph [~OH
\O OTfe ,,_
~SiMe2Ph /
KOH
~,,~~o.~,~N-~
(3.107)
SIMe2Ph
O'r~
Similarly, Mo(=CHCMe2Ph)(=NAr')[(+)-BINO(SiMe~h)x](THF) (Ar'=2,6-GH3Mr was prepared from (:I:)-BINO(SiM~Ph)K2 and Mo(--CHCMezPh)(=NArXOTOADME) (Eq. 3.108). SiMe2Ph OH \.. OTfs Ar
[~[~ OH
+
SiMe2Ph
/
SiMe2Ph
OT~, .o~N_A~
KOH
OTfe
(3.108)
SiMe2Ph
Chiral Mo(~WBu)(=NAr)[Bipheno(tBu)4] was obtained by adding Bipheno('Bu),K2 to Mo(=CH'Bu)(=NAr)(OTOADME)in tetrahydrofuran
(~. 3.]09). ,,,,.O.. I ~ N ~ , "
KOH
O.
tBu
tBu OTfe
Ar
(3.1o9)
182 Starting from a new chelating chiral diol (IS,2S)- and (IR,2R)-1,2bis(2-hydroxy-2,2-bis(trifluoromethyl)ethyl)cyclopentane (TBEC-H2), the chiral alkylidene complex Mo(=CHCMezPhX=NAr)(TBEC) was prepared by Gmbbs and coworkers ~ by reaction of the dilithium alkoxide of TBEC with Mo(--CHCMe2PhX=NArXOTf~(DME) (Eq. 3.110). Ar i TftQ,. ~ -..),
Fac-CF3 H ~ H "
F3 -CF3
LiOH
"/O'/M~--'ph 9
~...O
OTfe
~
Ar i N Fac-CFa 'I "J' /'L O.'/M~' = " "p h I~~,CFa t ~ / ~ ' - "CF3
(3.110)
The chiral alkylidene molybdenum complex could be isolated as a brown yellow solid in 85% yield and used in ring-opening metathesis polymerization of strained and less strained cycloolefins. In an analogous manner, chiral tungsten oxo vinylalkylidene and tungsten amide
vinylalkylidcne complexes have been prepared by the reaction of the dilithium alkoxide of TBEC with W(rl2diphenylcyclopropene)Clz(O)[P(OMr W(=CH=CHCOCH2CHzCHzOXO)CIz[P(OMeh] and W(--CH--CHCPh2X=NAr)CI2[P(OMeh]2 (Ar=-2,6.-('Pr)~Cd-I3) (F-xi. 3.1113.113).
F3c.CFaH
.~d H
~
CF3
-CFa
F3C.~3F3H
~
(MeO)~pi~.~:~~hh L i % i %P(OMeh CK'CI 0 .,P(OMe)3
C"F, "(~.o~P~, -CF3
FaGcFaO...P(OMeh ,~IL,~..W~-,,.j~ ~Ph : u I ~ ~'Ph CF3 CF3
o.
o~
(3.111)
F3C CF3 0 ,,P(OMe)3
~% ~ c ~ ,
t.../-- "CF3
o.j
(~"~)
k F3C....?F3H ~J
-CF3
Ar NI P(OMeh U/" "" CF-W=~ .,~ .Ph 9 / \ " ~ " ~'
I
LiOH =
F-C CF3N )~ W_,,~ ~"\ ] "" ~ _Ph :I"'O"/ ~ ~ P h ,...~ O.CF3 I x.__..~ t~/v "CF3
(3.11 3)
183 Though these chiral complexes are less active than the above molybdenum compound, they can polymerize norbomene, cyclooctene, cyclooctadiene and even the less strained cycloolefins such as cyclooctatetraene. Asymmetric tungsten alkylidene complexes synthesized Heppert and coworkers ~sz by the reaction of tungsten carbyne complexes ('BuO)3W(CR') with 1 equiv of l,l'-bi-2-naphthol (HzRzBINO, R=Me, Ph, Br) in toluene at room temperature (Eq. 3.114).
R "
(~uO)3W(CR,)Toluene ~ R ~-- ~ ' R
(~u ~4=C (~u HR'
(3.114)
The products were obtained as red-orange waxy crystals in yields varying from 50 to 80%. The complexes (Me2BINOX'BuO)2W(=~HR ') and (Ph~INO)('BuO)2W(~HR') were stable in the solid state for weeks at ambient temperature, while the complex (Br2BINOX'BuOhW(=CHR') decomposed over several days to uncharactefized materials even under rigorous exclusion of air and moisture. Reaction between 2 equiv of rac-HzMezBINO and ('BuO)3W(-=CR') generated (MezBINOhW(=CHR'), which were obtained as a pure orange solid alter repeated reerystallization (Eq. 3.115).
R R
2
OH OH
R
§ (~uO)3VV(C I~) Toluene
?
~. 0" I CHR' (3.115) 0 R
Attempts to prepare an analogous complex (Ph2BINO)2W(=CHR'), generated only (PhxBINOX~BuOhW(=CHPh) and unreaeted HzPhzBINO (Eq. 3.116).
184
(•U
9 (~uOhVV(CR.) Toluerl~
W=CHR'
(3.116)
Tetraphenylporphyrinatotungsten tetrachloride/isobutylaluminoxane, PPWCIJ(~BuAI)xOy. Tetraphenylporphyrinatotungsten tetracldoride is prepared by reacting equimolar amounts of WCI6 and tetraphenylporphyrin in CCI,, under ambient conditions ~3'~ (Eq. 3.117).
WCI6 CC14
CI-W-CI
,..._ v
(3.117)
Further treatment of tetraphenylporphydnatotungsten with isobutylaluminoxane will produce the metathesis active complex tungstencarbene (Eq. 3.118).
C~CH3h !
cN -~~ !
x
Tolum~
where R is CH(CH3)z
=.._
(3.118)
185 3.6. References
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194 146. a. C.J. Schaverien, R.R., and J.C. Dewan, J. Am. Chem. Sot:., 108, 2771 (1986); b. R.R. Schrock, D.T. DePue, J. Feldman, C.J. Schaverien, J.C. Dewan, and A.H. Liu, J. Am. Chem. Soc., 109, 1423 (1987). 147. R.R. Schrock, R.T. DePue, J. Feldman, K.P. Yap, D.C. Yang, W.M.Davis, L. Park, M. DiMare, M. Schofield, J. Anhaus, E. Walborsky, E. Evitt, C. Kruger, and P. Betz, Orgmum~etallics, 9, 2262 (1990). 148. J. Feldman and R.R. Schrock, Progress Inorg. Chem., 39, 1, (1991). 149. P.A. Van der Scha~, W.J.J. Smetes, A.L. Spek and G. Van Koten, J. Chem. Sot:., Chem. Commun., 1992, 717. 150. H.H. Fox, K.B. Yap, J. Robbins, S. Cai and R.R. Schrock, Inorg. Chem., 31, 2287 (1992). 151. a. R.R. Schrock, J.S. Murzdek, G.C. Bazan, J. Robbins, M. DiMare, M. O'Regan, J. Am. Chem. Soc., 112, 3875 (1990); b. R.R. Schrock, Macromol. Syrup., 98, 217 (1995); c. J. Oskmn, H.H. Fox, K.B. Yap, D.H. McConville, R, O'Dell, B.J. Lichtenstein and R.R. Schrock, J. Organomet. Chem., 459, 185 (1985). 152. R.R. Schrock, The Strem Chemiker, 14,1 (1992). 153. H.H.Fox, J.K. Lee, L.Y.Park, and R.R. Schrock, Organometallics, 12, 759(1993). 154. a. J.H. Wengrovius, R.R. Schrock, M.R. Churchill, J.R. Missert, W.J. Youngs, J. Am. Chem. Soc., 102, 4515 (1980); b. M.R. Churchill, A.L. Rheingold, W.J. Youngs and R.IL Schrock, J. Orgam~met. Chem., 204, C17 (1981). 155. a. J.H. Wengrovius and R.R. Schrock, Organometallics, 1, 148 (1982); b. ILIL Schrock, S.M. Rocklage, J.H. Wengrovius, G. Rupprecht and J. Feldman, J. Mol. Catal., 8, 73 (1980). 156. M.B. O'Donoghue, R.R.Schrock, A.M. LaPointe, and W.M. Davis, Organometallics, 15,1334 (1996). 157. J. De la Mata and R.H. Grubbs, Orgmu~metallics, 15, 577 (1996). 158. P. Schwab, R.H. Grubbs, and J.W. Ziller, J. Am. Chem. Soc., 118, 100 (1996). 159. a. S.T. Nguyen, L.K. Johnson, R.H. Cn'ubbs, J.W. Ziller, J. Am. Chem. Soc., 114, 3974 (1992), b.T. Nguyen, R.H. Gmbbs, J.W. Ziller, J. Am. Chem. Sot:., 115, 9858 (1993). 160. a. D.H.McConville, J.R. Wolf, and R.R. Schrock, J. Am. Chem. Soc., 115, 4413 (1993); b. R. O'Dell, D.H. McConville, G.H. Hofmeister,
195 and R.R. Schrock, J. Am. Chem. So,:., 116, 3414 (1994). 161. O. Fujimura, F.J. De la Mata, and R.H. Cn~bbs, Organometallics, 15, i s65 (1996).
162. J.A. Heppcrt, S.D. Dietz, N.W. Eilerts, R.W. Henning~ M.D. Morton, and F. Tagusagawa, Organometallics, 12, 2565 (1993) 163. V. Dargutan, S. Coca and M. Dimonie, Polymer Prepnnts (ACS, Division of Polymer Chemistry), 35, 698 (1994). 164. V. Dragutan, L. Popescu, S. Coca and M. Dimonie, in 'Wletathesis Polymerization of Olefins and Polymerization of Alkynes", (Y Imamoglu, Ed.), Kluwer Academic Publishers, Dordrecht, The. Netherlands, 1998, pp. 103-115.
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197
Chapter 4
REACTION
CONDITIONS
The process of catalytic polymerization of cycloolefms is sensitive to a wide range of reaction parameters. TM The reaction can occur either in heterogeneous phase, preferentially at high temperatures or in homogeneous phase, at low to moderate temperatures, using a solvent as the reaction medium. Along with the nature of the monomer and the catalyst, the purity of the solvent and the presence of other substances as activators or inhibitors will influence considerably the reaction course. Furthermore, the monomer concentration, reaction temperature, time, pressure, agitation, ratio of reactants are essential parameters that influence significantly the conversion and polymer yield. In order to explore the scope and limitations of the catalytic polymerization of cycloolefins, a great number of studies have been carried out under various reaction conditions by numerous research groups, m-4Due to the role that such parameters play in determining the process performances, the present chapter will deal with monomer concentration, catalyst nature and composition, reaction temperature and time, reaction medium, solvents and additives, ratio of reactants, manner of reactant addition, pressure and agitation as the essential factors of this process.
4.1. Monomer Concentration Monomer concentration is an important factor governing the rate of the cycloolefin polymerization, the structure and molecular weight of the polymer. Up to now, the influence of this parameter has been studied with a large number of cycloolefins as monomer. 1-4 In cyclopentene polymerization with the catalyst WCI6/'Bu3AI, Amass and Tuck 5 found that the reaction rate was first order with respect to the monomer concentration (Figure 4.1, Line A).
198 1~, x 103, mole.L ~s ~
i
-~ .5
m
1.6
1.7
1.8
1.9
[M], mole./L
Figure 4. l Effect of monomer concentration [M] on the rate of cyclopentene polymerization (!~) (Adapted from Ref.'). Starting from these results, it was possible to evaluate the kinetics of cyclopentene polymerization in the presence of the above catalytic system. In their studies, these authors observed a specific influence of the 1~ x 103, mole.L~s ~ 6~
1
5 4
2
/ i
""
3 4
'
I
2
,"
3
4
5
6
7
Time, nun Figure 4.2. Effect of cyclopentene concentration and premixing time of the catalyst components on the initial rate of polymerization (Adapted from Ref.').
199 monomer concentration on the initial rate of polymerization. These results are summarized in Figure 4.2 for a range of premixing times of the catalyst components. It can be seen that there is a dependence of t=~ in the initial monomer concentration. This dependence is shown in Figure 4.3 where a straight line was obtained for the plot of t.ffi as a function of monomer concentration in cyclopentene polymerization (Figure 4.3, Line B). t~ 5
,4
(B) 3
2
0.5~
0.60
0.65
[CP], mole/L Figure 4.3. Effect of mononter o o n ~ on the pmnixing time ( t . J required to attain maximum rote of cyclopeutme polymerization (Adapted from Ref.s) In cyclooctene polymerization, different reaction orders with respect to the monomer concentration have been obtained depending on the catalyst. 6 Thus, when WCIdMe4Sn was used as a catalyst (0.05< [IVI],,<0.5), the order in monomer concentration was found to be 1 while for the system WCI6/EtOH/EtAICIz the reaction order 2 was observed. Induction periods up to 5 rain were recorded for the tin catalyst and up to 5 sec for the aluminium catalyst (Figure 4.4). It is noteworthy that there are no polymers formed until the monomer c o ~ t r a t i o n e x ~ s 0.21 mole~, which is much higher than the equilibrium monomer concentration [M]. of 0.002 mole~. Since [M]. provided such a poor indicator of cyclooctene p o l ~ i l i t y , HOcker e t a/.7 proposed the concept of critical concentration [M]~, defined as the total amount of monomer per unit volume that forms cyclic products at ring-
200 Coav.,%
Cony% 20
20
IG
.2
1
15
10
10
5
1
10
2O
(A)
9
i
i
I
30
10
20
30
Time,s
03)
Time,ram
Figure 4.4. Time-cxmversion curves for cyclooctme (CO) polymerization with WCIdEtOH/EtAICI2 (A) (1" [CO] = 0.25M, 2: [CO]=O.16M) and W C ~ e 4 S n (B) (1 [CO]=0.3M, b: [CO]=O.IM) (Adapted from Ref.s) chain equilibrium. If the initial monomer concentration is less than [M],, only cyclic and linear oligomers are produced. After exceeding [M]~, the equilibrium cyclics concentration is almost constant, and linear polymer begins to appear. The critical concentrations of several cycloolefins, [M]~, have been predicted theoretically s'9 and determined experimentally ~~ and found to characterize the polymerizability of a given monomer. The rate of norbornene polymerization m5 with the catalyst W(CO)3CIz(AsPh3h was essentially independent of the monomer concentration in the range [M] = 0.25-3.0 mole/dm 3. There was a slight tendency for increase in the cis content (or = 0.52-0.58) with increasing monomer concentration while the increase in blockiness was much more definite (r~r, = 1.1-36). The rate of norbornene polymerization became diffusion controlled above a 2-5% polyngT content for the reaction mixture, and gelation set a practical limit to the monomer conversion (Figure 4.5, Curve C). It is obvious that a high monomer c o ~ t r a t i o n will favor a high reaction rate, depending on the value of the corresponding concentration. For this reason, the increase in monomer c o n ~ t i o n will be effective in polymerization of less reactive monomers. Polymerization in bulk systems will be the ideal case for these monomers.
201 Yield,% 80
O0
40
(C) 20
0
5
10
[NBE], mole/din 3 Figure 4.5. Effect of initial monomer conce~xat~ on the polymer yield in norbomme (NBE) polymerization with W(CO)3CIz(AsPh3)2(Adapted from Ref. '5) The polyn~r yield and molecular weight could be strongly affected by the monomer concentration as result of transfer re,a~ons. For polymerization in inert solvents, an optimum of ~cloolefm concentration should be considered in view of avoiding side transfer reactions and control the molecular weight of the polymer. Yield, % 80
/-
(A)
(B)
/
60
/
40
20
0
1
2
3
4
5
6
Time, hr Figure 4.6. Dependenceof oligon~r (Curve A) and polymer yield (Curve B) on monomer concmtration in endo-
202 As Figure 4.6 illustrates, the polymer yield in dicyclopentadiene polymerization with ReCldMe4Sn increases up to monomer concentrations of 4 mole~ then suddenly decreases. ~6 At the concentration of 7 mole~, a strong increase in the viscosity of the system was responsible for the decrease of the activity. This phenomenon was explained by a behavior similar to the gel effect, inhibiting the reactivity of the active species at that monomer concentration.
4.2. Catalyst Concentration Generally, the catalyst concentration ~11 determine the number of active centres and will influence the overall catalyst activity and monomer conversion. The nature of the solvents and the presence of inhibitors or activators will also be affected by the catalyst concentration. An increase in the catalyst concentration will lead to an increase of the reaction rate and at the same time to a decrease of the polymer molecular weight. Commonly, catalyst concentrations of 103-10 "6 mole/L are used depending largely on the catalyst activity and monomer reactivity. Amass and Tuck 5 determined the rate of cyclopentene polymerization with WCIJBu3AI at constant monomer concentration and various concentrations of WCI~ whilst the molar ratio of W:AI was maintaincd at 12, in order that the concentration of WC~(~Bu3AI)2 could be varied. Rpx I 0Z,_mole.L"Is"l
('s 9
....-" .......
- "
._... -""
0
!
o
m.
5
9
1o
,
.
15
~ C ~ ] x 104, mole.L"1 Figure 4.7. Dependence of the initial rate of cyclopentene polymerization on the concentration of tungsten hexachloride (Adapted from Ref.~)
203
As it can be seen from Figure 4.7 (Line D), there was a first order dependence of the initial rate of cyclopentene p o l y m ~ o n on the concentration of WCts.
The dependence of the rate of cyclopemene polymerization with the same catalyst on the 'Bu3AI concentration was studied by Amass and Tuck s at constant WChs and cyclopentene concentrations. A linear plot of the rate of cyclopentene polymerization against the square of the ~Bu3AI concentration has been found (Line E, Figure 4.8). R,x 103, mole.L "~s"~ I0
8 6 4 2
0
1
2
3
4
5
6
7
[~Bu3AI]Zx10~, mole~.L "~ Figure 4.8. Dependence of the rate of cyclopentene polyn~rization on concentration oftriisobutyt aluminium (Adapted from Ref.s) With the most active catalysts, concentrations as low as l O~S-lO"7 mole~ can be employed to obtain appreciable yields and reproducibility. For instance, norbomene copolymerization with ethylene in the presence of the active zirconocene/methylaluminoxane catalysts m7 occurred readily at concentrations of 1.6-1.7x 10.7 mole~ in toluene (Table 4.1). Table 4.1 Copol~on ofnorbomme (N) and ethylene (E) in toluene with zireonocene/m~ylalummoxane(MAO) catalysts"b
Et0nd~rCl~ Zirconocene Et(Ind~ZrCl~ Cp2ZrCl~ CI~ZrCI2 1.7x10"s 1.6x10 "I Mole 1.6x10"~ 1.7x10"~ 60 60 Temp. ~ 25 25 0.5 0.5 Time, hr 0.5 0.9 2.3 2.8 Yieldt g 1.9 . 0.23 'Data fi'om refe~ce~TibN=l.4 g, E=I ban', MAO=480-600 m8, Toluene= 1O0 'n~.
2O4 4.3. Ratio of Reactants
The ratio between the catalyst components is a crucial parameter for the catalyst activity and selectivity as well as for polymer structure and properties. In cyclopentene polymerization with WCIjBu3AI, for instance, Amass and Tuck s found that the reaction rate was maximum at a W:AI molar ratio of 1:2 and fia~er addition of 'Bu3AI served only to deactivate the catalyst species (Figure 4.9, Curve F). R ~ 103, mole.L"~s"*
10
0
(~
0
1
2
3
4
5
Molar ratio AI:W Figure 4.9. Dependence of the rate of cyclopmtme polymerization on the AI:W molar ratio (Adapted from Ref.~) This result indicated that the catalyst species might arise from one mole of tungsten and two moles of aluminium compound. In another example, the course of norbornene polymerization in the presence of the binary catalyst TiCI4/Hep,AILi depends essentially upon the ratio of catalyst components. On carrying out the polymerization at several molar ratios AI:Ti, Truett and coworkers n observed that the reaction takes place either by a 1,2-addition pathway or by ring-opening, depending essentially on the molar ratio of the two catalyst components (Eq 4.1). Thus, at molar ratios AI:TiI the ring-opening polymerization to polyalkenamer is predominant. In the last case,
205 AI/Ti
(4.1) w
AI/Ti>I the polyalkenamer displayed better elastomeric properties and a higher crystallinity as compared to the vinyl polymer. In the ternary catalytic systems, the ratio between catalyst, cocatalyst and the activator component will substantially influence the catalyst activity and stereoselectivity. For instance, the activity of the catalytic system WCl6/'Bu3Al/chloranil and WC16/13u3AVepichlorohydrin in cyclopentene polymerization ~9 is strongly influenced by the ratio of activator to WCI6/'Bu3AI. The effect of cocatalyst/catalyst ratio on the activity of ReCls/Me4Sn has been examined by Pacreau and Fontanille ~6 in dicyclopentadiene polymerization. The optimal value of the catalyst activity was obtained for a mole ratio Me4Sn~eCIs of 1.5 (Figure 4.10, Curve G). Based on this result, these authors proposed a three-step reaction scheme for the formation of active species to explain the maximum activity of the catalyst at the above mole ratio. Yield, % 75
50
25
0
0~5
1~0
1:5
2~0
2~5
Me4Sn/ReCI~ Figure 4.10. Effect of mole ratio cocatalyst/catalyst on the monomer ctmsumption in the polymerization of endo-tficyclopentadiene (DCP) with ReCls/Me~n (Reaction conditions: [ReCI~]/[DCP]o= 0.02, [DCP]=1 mole/L, Temp.=50~ Time=! mm) (Adapted from Ref ~6).
206 On studying the influence of catalyst/monomer ratio on the activity in dicyclopentadiene polymerization with ReCl~Vle4Sn system, Pacreau and Fontanille ~6 observed that the amount of polymers produced increased gradually with the catalyst/monomer ratio; in contrast, the monomer was almost completely consumed even at low values of this ratio (Figure 4.11) Yield, % 80 60 40 20
0
I
2.
3
4
5
I OZx[ReCI~]/[DCP] Figure 4.11. Effect of mole ratio catalyst/monomer on polymer yield in the polymerization of endo-DCP with ReCI~/Me4Sn catalyst. (Curve I-Monomer conversion; Curve 2-Polymer yield) ([Me4Sn]/[ReCI~] = 1, [DCP]=3 mole/L, Temp.=50~ Time=4 hr) (Adapted from Ref.~s). This behavior was explained by a partial deactivation of the catalytic sites during the polymerization reaction. 4.4. Premixing Time of Reaction Components
Amass and Tuck s observed that under apparently identical conditions, the rate of cyclopentene polymerization with WCI6/'Bu3AI varied by as much as a factor of 2 when the concentrations of catalyst and monomer were maintained constant. This irreproducibility was traced to the variation in time between the additions of WCI6 and 'Bu3AI to the monomer solution. The dependence of the rate of cyclopentene polymerization on the time delay between the additions of WCI6 and 'Bu3AI to the solution of cyclopentene is shown in Figure 4.12, Curve H.
207 1~ x 103, mole.L"is"t 9.0
(H)
8.0 7.0
6.0 5.0 4.0 3.0 2.0 1.0 0
0.5
1.0
1.5
2.0
2.5
P
3.0
xmg time, mm
Figure 4.12. Depmdmce of rate of cyclopmtme polyn~rizaticn (R~) on the premixing time of WCI6 and 'Bu3AI in toluene (Tm-~raOLre = 25~ [WCI6] 2x104 mole/L, [~Bu3AI]= 4x104 mole/L, W:AI:CP=1:2:10*) (CP = cyclopentme) (Aaapt from =
The rate of cyclopentene polymerization showed a marked dependence on the time between the additions of WCts and ~u3Al to the monomer solution. Under the above conditions, the maximum rate of polyn~rization was obtained with a delay time of 2 rain. In another example, Dimonie et a/. 2~ showed that the premixing time between the reaction components influenced markedly the induction period of cyclopentene polymerization with WCk~zCHCOOEt. Thus, the induction period d e c r ~ drasti~y when the premixing time between WCts and cyclopentene increa.ugt from zero to 12 min before d i a z o ~ c ester addition (Figure 4.13). Significantly, if the monomer is added to the system after 5 rain of contact time between WCts and diazoacetic ester, the reaction does not take place.
208 Yield,% 100
80
60
40
20
0
10
20
30
40
50
60
Time, mm Figure 4.13. Effect of premixing time between WCI, and cyclopemene on the polymerization rate (l-premixing time WCIdCP = 12 mm, 2-premixing WC~CP = 0 mm, Solvent toluene, Tenq3erature = 0~ [CP] = 3.43 mole/L, [WCI~] = 2x103 mole~, DAFJWCI~= I) (CP = cyclopentene, DAE = diazoacetic ester)z~
4.5. Addition of Reaction Components The sequence of addition of reaction components (i.e. monomer, catalyst components, activator or promoter, molecular weight regulator and inhibitor) has a crucial effect on the course of the polymerization reaoJon.. Generally, the sequence of addition of monomers and catalyst components has to be adjusted in every case in order that the polymerization to ovcur at optimum parameters. Commonly, the polymerization reactions take place in bulk or in solution and the catalyst is prepared either /n s/tu or by precomplexation. In both cases the sequence of addition of the catalyst
2O9 components and monomer is essential for the generation of the actual active centers. In cyclopentene polymerization with WCIJ~usAl/epichlorohydrin in toluene, it was u n e q u i v ~ y established that a certain sequence of reagent addition was necessary. 2e For instance, when cyclopentene was contacted with WCl6 in toluene followed by addition of the organoaluminium compound, a substantial conversion of monomer could be attained. If the organoaluminium compound was added before the monomer, the conversion decreased to a very small value. By contrast, on substituting ~/dohexene for toluene as a solvent, the sequence of addition of the catalyst components was not very significant; however, the polymerizatiuon rate in this case was rather low (Figure 4.14).
d[M]/dt x 103
mole.L'~mm"a
16
~A~
12 ~CI
(D)
t.BI r----I
Figure 4.14. Influence of sequence of reactant ackiition upon reaction rate for cyclopentme polymerization with WCld'Bu~td/ECH (A = Solvent toluene, Sequence of addition: l-solvent, 2-WCl,, 3-ECH, 4~P, 5-'BusAl; B = Solvent toluene, Sequence of addition: l-solvent, 2-WCI6, 3-ECH, 4-'BusAl, 5-CP; C = Solvent cyclohexene, Sequence of addition: l-solvent, 2-WCI~, 3-ECH, 4~P, 5'BusAl; D= Solvent cyclohexene, Sequence of addition: l - s o l ~ 2-WCIs, 3-ECH, 4YBusAl, 5-CP; Reaction conditions" CP = 3.43 nmlefL, WCts = 1.2xl0 "3molefL, tm~rature = 0~ AI/W = 1.3, ECH/WCI, = 2) (CP = cyclopemme, ECH =
epichiorohydrm)(Adaptedfrom aef.~
210 4.6. Reaction Time
Various kinetic studies on the cationic, Ziegler-Natta and ROMP of cycloolefins evidenced a characteristic dependence of the polymerization rate on the reaction time. A typic,al curve for the deter~~tion of the rate of cyclopentene polymerization with WCIjBu3AI is shown in Figure 4.15, Curve (I), from which it can be seen that the rate of polymerization decreased substantially as a function of conversion 2t (Figure 4.15).
'Lmm 12110
10
20
3o
40
50
Time, mm Figure 4.15. Conversion4in~ curve in cyclopmtme polymerization with WCI~Bu3AI determined by dgatomary (Adapted from Ref.u) The observed decrease in the rate of cyclopentene polymerization was ascribed to a decrease in the concentration of the monomer and of the active species for the polymerization. This behavior is further illustrated in the dependence of log[monomer] against time that deviate from linearity ~3 (Figure 4.16, Curve J). The deviation from linearity of log[monomer] with time is a typical curve for the polymerization reactions of cycloolefins with
these catalytic systems.
211 Log[Ml/[Ml0
0.05
I
(J)
0.04 0.03 0.02 0.01
I0
20
30
Time, mm Figure 4.16. Dependence of log[monomer] upon reaction time in cyclopemcne polymerization with WCh,/'BusAI (Adapted from Ref.ts). Examination of the conversion-time curves of a large number of polymerization reactions in the presence of different catalyst systems revealed more or less a S-shape correlation with different induction periods and degrees of conversion as a function of the catalyst activity, monomer reactivity, solvent nature, presence or absence of inhibitors and activators. Yield, %
(K)
y ;
(o
,;
~o Time, hr
Figure 4.17. Cyclobmme polymerization with r dichloride./methylaluminoxane catalyst at 0~ (Adapted from Ref.~?).
212 The conversion-time curve for cyclobutene polymerization induced by zirconocene/methylaluminoxane catalyst ~7 at 0~ is illustrated by curve (K) in Figure 4.17. It can be readily observed that the monomer conversion increased to ~20% after an induction period of S hr and approached 3540% beyond 20 hr reaction time. By contrast, cyclopentene polymerization in the presence of WCI6/'Bu3AI exhibited a monomer conversion of 45-50% even after a period of one hour of reaction, as it can be seen from Figure 4.18, Curve L. ~
Cony., % 5O
20 10
0
0
10
20
30
40
'
"
50
Time, nun
Figure 4.18. Conversion-time curve in cyclopentene polymerization with the catalyst WCld'Bu3Al(Adapted from Ref.n).
A significant dependence of the induction period in cyclopentene polymerization on the temperature and nature of the catalyst is shown in Figure 4.19. It is interesting to note that with WCI6/'Bu3AI/CA, a sharp increase in the polymer yield is obtained at 0~ as compared to the reaction at -30~ while with WCI6/Ph4Sn, on the contrary, a higher yield is obtained at -20~ and a lower yield at +20~
213 Yield, %
, ~ ~ 0~~ - ~ 0 ~ I /
//2
~/ 0
0
v
0
~~
~
4O
80
o--'-'-~-
120
160
Time, mm Figure 4.19. Time evolution of cydopmtme polymerization with WCts-based catalysts at various ~ r e s (I-WCI~Bu3AI/CA, -30~ 2-WCldl~,Sn, +20~ 3-WCIJPh4Sn,-20~ 4-WCId~u3AFCA, 0~ = chloranil)22 Kinetic studies carried out by H6cker and coworkers 6 on the cyclooctene polymerization with the catalysts WCIs/EtOH/EtAICI2 (A) and WCIo~4e4Sn (13) revealed induction periods of 5 sec for the fu~ catalyst and 5 rain for the second one (Figure 4.20). Moht/Lxl02
15'
/"
~'~"~'~""
,o~ /
f.
20
10
30
//
/
/I-
2
/ S/If'
.~.s ~
10
3
15
/~
~
0
20
= v ~ ~. ~- . \, : ~ .
0
~
lO
_
2o
(A) Time, sec (B) Time, mm Figure 4.20. Ccmversion-tinw curves for c y c l ~ e (M) polymerization with the r WCIJF-,tOH/EtA]CI2(A: I-[M] 0.043 mole, 2-[M] 0.066 mole, 3-[M] 0.16 mole, 4-[M] 0.25 mole) and W C ~ e 4 S n (B: I-[M] 0.05 mole, 2-[M] 0.1 mole, 3-[M] 0.3 mole)(Adapted from Ref.~)
214 An interesting behavior was observed when using small amounts of cyclopentene, cyclohexene or 1,5-cyclooctadiene in cyclooctene polymerization with the WCk/PksSn system; in these cases different conversion-time curves resulted depending on the nature of the added cycloolefin. 22 This behavior is illustrated for cyclooctene polymerization with the above mentioned catalyst in Figure 4.21.
Yield, % 35r
1
30
,/
25
2
20 15 10
0
4
8
12
16
20
24
Time, hr
Figure 4.21. Conversion-tin~ curves for c y c l ~ e p o i s o n with the WCIJPh4Sn catalyst in the presence of small amotmts of cyclopentene (1), 1,5cyclooctadiene (2) and cyclohexene (3): [cyclooctme] = 3.5 mole/dm3, [CP,CH, COD] = 0.3 mole/dm 3, [WCts] = 2 . l x l 0 "3 mole/dm 3, Ph4Sn:WCI~ =
2,Ten~rature = 20~ (Adapted from Ref.zz) The influence of the nature of monomer on time-conversion curves was evidenced by H6cker et al. 6 in the polymerization of cyclododecene and cyclopentadecene with the WCk/EtOH/EtAICIz catalyst. As Figure 4.22 illustrates, it can be observed that c i s - c y c l o d o d ~ e reacts faster than trans-isomer and a similar result is obtained with cis- and transcyclopentadec~ne.
215 Cony., %
o.~
2
1OO. 2
(A)
mm
Time, mm
0
i -s (B)
13~ Time,
Figure 4.22. Time conversion curves for the c~s- (1) and trans-isome~ (2) of cyclododecene (A) and cyclopmtzdecene (B) polymerization with WCl~ztOH/F.tAlCIz catalyst (Adapted from Ref.6) It is very interesting to note the evolution of the product nature in the course of dicyclopentadiene polymerization with different catalyst systems. Thus, Balcar et al., z3 working with WCIs(OCH(CH2CI)2), observed that, at low monomer conversion, soluble polymer was formed predominantly, while at high conversion, cross-linked polymer strongly prevailed (Figure 4.23). Yield, % 60
8O 40 ,....,-
2
..---
30 20 10 0
L
0
1
2
3
Time, hr
Figure 4.23. Time evol~on of dicyclopmtadiene (DCPD) p o l ~ initiated by WCIs(OCH(CH2CI)2)catalyst: l-Soluble p o l ~ fraction, 2-Insoluble polymer fraction (Reaction ccmditims: Room temperatare, molar ratio DCPD:W = 74:1) (Adapted Ref.
216 4.7. Reaction Temperature
The temperature of cycloolefin polymerization is an important parameter governed by the reaction enthalpy. It affects greatly the reaction rate and the polymer properties. An increase in the reaction temperature will increase the polymerization rate with a factor depending on the nature of catalyst and monomer or solvent. With increasing reaction temperature the polymer molecular weight will decrease as result of more pronounced side reactions such as transfer to monomer and solvent or depolymerization and degradation reactions. Cationic polymerization was carried out usually at low temperatures ranging from room temperature to below -IO0~ whereas Ziegler-Natta and ROMP polymerization allows the reaction to be conducted at room temperature toward somewhat below O~ Anionic polymerization generally prefers low temperatures but that depends strongly on the initiator activity, nature of monomer and solvent. With reactive monomers, e.g., 3-methylenecyclobutene, cyclopentadiene, norbomene and norbomadiene, in the presence of active cationic initiators such as BF3.EhO, EhAICI/ttBr, AICI3, etc. the polymerization reactions have been carried out preferentially at low temperatures, ranging from-60~ to-80~ The solvents were selected from aliphatic hydrocarbons such as heptane or chlorinated hydrocarbons e.g. methylene chloride and chloroform. Under these conditions the kinetics and thermodynamics of these reactions could be better controlled and higher molecular weight polymers could be obtained. In addition, monodisperse~ polymers with a better solubility could be easier prepared under these conditions. With less reactive monomers like cyclopentene, cyclohexene, 1-methylcyclopentene, 3-methylcyclohexene, in the presence of cationic initiators e.g., AICI3, BF~i:F, the polymerization reactions have been effected at relatively higher temperatures e.g. between -20~ and +20~ in both aliphatic and aromatic solvents. Nonetheless, even under these special conditions, often only dimers and lower oligomers could be obtained from the less reactive monomers. For instance, polymerization of 3-methylcyclohexene with AICI3 occurred slowly in ethyl chloride solution at-20~ and-78~ at-20~ an oily product consisting of mixtures of dimers and trimers was obtained whereas at -78~ a small amount of solid product was formed. Further examples of cycloolefins, polymerized at various temperatures under cationic conditions, are illustrated in Table 4.2.
217 Table 4.2 Cationic polymerization of cycloolefins at various temperatures'
Cycloolefin Cyclopemene 1 -Methylcyclopentene
3-Methylcyclohexene 4-Vmylcyclohexene 1-Methyl-3methylenecyclobutene Cyclopentadiene
1,3-Cycxlohexadiene
1-Methylenecyclohexene 1-Vmylcyclohexene
-20 0 -20 -78 -70 -78 -78 -70 -78 -78 -78 0 0 0 0 0 30 -78 -78 0 -78
2-Methylenenorbomene
40-45 -78 -78 -I00 -20 -78 40 0 -78
Norbomadiene
-123
1,3-Cyclooctadiene ct-Pmene
Norbomene
9
T, ~
Data from reference t
Catalyst
Solvent
AICI3 BF3 AICI3 AICI3 BF3 BF3.OEtz EtzAICI/HBr TiCI30"Bu TiC.CA AIBr3 SnCI4 TiCh~CA AIBr3,SnCI4 TiCI4 SnCh~CA BF3.EtzO TiCI4 BF3.EtzO TiCh AICI3 BF3.EtzO TiC.CA TiC.CA AIBr3,AICI3, BF3.TiCI4 EtAICIz EtAICI2 VCL,
E~yl chloride n-Hexane, Chloroform Ethyl chloride Ethyl chloride Methylene chloride n-Hexane Methylene chloride Methylene chloride Methylene chloride Methylene chloride Toluene Toluene Benzene Methylene chloride Methylene chloride Toluene Methylene chloride n-Hexane,Toluene
AIBr3,EtAIC AICI3 AICI3.AIBr3 EtAICIz AICI3
yy
Methylene chloride Toluene Methylene chloride Toluene F~yl chloride E~yl chloride n-Heptane n-Heptane Methylene chloride Propyl chloride n-Heptane n-Heptane E~yl chloride
218 It is interesting to note that in the cyclopentadiene polymerization the nature of the Lewis acid affects substantially the relative contribution of the two repeat units, 1,4- and 1,2-enchainments in the polymer chain, whereas the effect of temperature on the microstructure of the polymer is negligible in the range 0~ to -100~ However, the variation of temperature is sensitive in the norbomadiene polymerization with AICI3 as can be observed from Table 4.3.
Table 4.3 Norbomadiene polymerization with AICI3at various temperatures'
Reaction temperature, ~ Solvent [M], mole,rL Time, mm Yield, % Benzene soluble fraction,% M, of soluble fraction
-123
-78
C2H5C1
C2H5CI
1.39 37 17.2 100 5520
1.39
25 42.0 72.5 8680
0 C3H~CI 1.39 29 71.0 34.5 3680
40
CH2C12 0.69 4 30.0 59 2980
' Data from reference
The evolution of the polymer yield with variation of temperature is entirely unexpected, whereas the highest value of 71% was reached at 0~ it dropped substantially at 40~ toward 30~ On the other hand, only the polymer produced at -123~ was found to be completely soluble in benzene. In the polymerization of dicyclopentadiene with the geCls/Me4Sn system, Pacreau and Fontanille 8 observed that at -20~ the reaction did not occur while the yield in polymer increased linearly as the temperature was raised from 0~ to 50~ Probably, the structure of the polymer was also changed on varying the polymerization temperature. In the polymerization reactions of cyclobutene and cyclopentene with zirconocene/methylaluminoxane catalyst, Kaminsky and coworkers ~7 showed that the temperature changed considerably the reaction rate. The evolution of cyclobutene conversion is illustrated in Figure 4.24.
219 Yield, %
GO 40
30 20 tO
0
o
s
tO
IS
20
25
Time, hr Figure 4.24. Evolution of cyclobutme conversion mduc~ by edsylmebis(rtS-mdmyt)zin:mium dichloride/m~ylaluminoxane catalyst at varkxts tmq)eratures (Curve 1" 0~ Curve 2:-10~ (Adapted from Ref.~7)
Interestingly, though the temperature range is different for the two reactions, the effect of temperature is more pronounced in cyclopentene polymerization in the presence of zirconocene/methylaluminoxane catalyst
(Figure 4.25). Yield, % 80
!
GO 40 30 20 tO
o
0
5
I0
t5
20
25
Time, hr Figure 4.25. Evolution of cyclopentme conversion reduced by ethylenebis(rt'-indmyi)~ium dichloride/methyialuminoxanecatalyst at various tm~ramres (Curve 1" 22~ Curve 2: 0~ (Adapted from Ref.'7)
220 Of a particular interest is the effect of temperature on the reaction rate and polymer microstructure in the ring-opening polymerization of cycloolefins. In this case, the effect is specifically dependent on the catalytic system, the monomer and solvent. Studies on the cyclopentene polymerization with binary catalysts consisting of WCh,fBu3Al, WCLs/EhAI and WCh,/PI~Sn evidenced significant differences in respect to the influence of temperature on the reaction rate and polymer microstructure. Thus, data obtained by Comilescu, Dimonie and Dragutan z~, showed that WCI6 associated with organotin compounds yield catalytic systems that are highly sensitive to temperature variation whereas WCI6 associated with organoaluminium compounds provides catalysts that are less sensitive to temperature than the former. In addition, the polymer microstructure was largely dependent on temperature when the catalyst WCI6/PI~Sn was employed; under these conditions high cis-polypentenamer was obtained at low temperatures and drastic changes in polyna~ microstructure occurred with temperature increase whereas for WCIJBu3AI and WCk/EhAI catalysts microstructure alteration was gradual with temperature variation, s6
4.8. Reaction Medium In homogeneous catalysis, the reaction medium is essentially an inert solvent that solvates the catalytic system and dissolves both the cycloolefin and the polymer product. It is important that the reaction medium not to have traces of impurities such as water, polar organic compounds, oxygen-, sulphur- and nitrogen-containing compounds that may act as inhibitors for the catalytic system. In heterogeneous catalysis, the polymerization reaction is carried out mostly in biphasic systems, in the presence of solid catalysts, with the cycloolefin in liquid phase. The adequate solvents for the two type of catalysis used in cycloolefin polymerization will be highlighted in the next sections. 4.8.1. Solvents for Homogeneous Catalysis The catalytic polymerization of cycloolefins in homogeneous medium requires an appropriate solvent for the starting cycloolefin, catalytic complex, reaction intermediates and products. A broad class of aliphatic and aromatic compounds can be used for this purpose but their choice is limited by the specific solubility of the catalyst, of the reaction
221 intermediates and of the polymeric products. In addition, the solvents have to fulfd several conditions in order not to affect the course of the process. First, they should be quite~inert relative to the cycloolefin and the cattalyst, neither deactivating nor consuming them in side reactions; also, the solvent should not undergo any transformation in the presence of the c,slalytic system or cycloolefin. Second, it is necessary that the solvent should be carefidly purified from t r ~ of moisture, air, and other substances which might inhibit the catalyst. Third, the solvent should have a high solvating power for high molecular weight reaction intermediates and products taking into account that these may possess a limited solubility in many common solvents. Hence, the solvent should easily remove the reaction products from the region of the active cemers, avoiding the formation of deposits round the catalytic complex. The solvent thus plays an important part in maintaining high activity and selectivity of the catalyst for a long period of the reaction time. Most cationic polymerizations have been carried out in non-polar and weakly polar solvents of the class of aliphatic hydrocarbons and halogenated aliphatie hydrocarbons, t Depending on the nature of the cationic catalyst, hydrocarbons like heptane, hexane or cyclohexane or chlorinated hydrocarbons such as methylene chloride, methyl chloride, ethyl chloride or carbon tetrachloride have been employed. In the presence of the cationic catalyst these solvents should possess a high purity and dryness degree so that not to inhibit the active sites. In addition, the aliphatic hydrocarbons will have a diminished isomerization tendency induced by the catalyst and in this case a correlation between nature of the catalyst and that of solvent is to be taken into account. Aromatic hydrocarbons as such or halogenated are also adequate solvents for cationic polymerization due to their efficient solvating power relative to the high molecular reaction intermediates and products but in the presence of most common Lewis acid catalysts like AICI3 or BF3 secondary alk'ylation reactions of the aromatic moiety by the cycloolefm can occur. Accordingly, the use of aromatic compounds like benzene, toluene, etc. as solvents should be considered with care in cationic re,actions. The solvent employed in the anionic polymerization of c y c l o o l e ~ is a non-polar or slightly polar hydrocarbon compound whereto both anionic initiating and propagating species are stable enough to assure chain formation. These solvents have to possess a low acidity so t l ~ proton transfer to initiating or anionic propagating species to be diminished or eliminated. These solvents include inert hydrocarbons like heptane,
222 cyclohexane, benzene, toluene, xylene, chlorinated hydrocarbons like chloromethylene and carbon tetrachloride. As the important classes of the anionic initiators including alkali metal alkyls such as butyllithium ~ r generally as dimeric or oligomeric aggregates in hydrocarbon medium, the solvent should have a particular solvating capacity. Anionic reactions can be performed also in ammonia in the presence of alkali metals or even in ethers and esters of low acidity. Traces of moisture and acids have to be totally excluded in every case because these act as strong inhibitor for the active anionic species. Ziegler-Natta polyn~rization of cycloolefins has been mainly effected in nonpolar solvents from the class of aliphatic hydrocarbons such as heptane, hexane or cyclohexane and slightly polar aromatic solvents like toluene, xylene or chlorobenzene z. Again the dryness and purity are essential factors that allow a good activity and selectivity of the catalytic complex and high yield in the reaction product. The solubility of the catalytic complex and of polymer product in these solvents is also an important factor in selecting an appropriate reaction solvent. The main types of solvents employed in ring-opening metathesis polymerization of cycloolefins pertain to non-polar aliphatic and aromatic hydrocarbons, slightly polar aromatic hydrocarbons as well as to halogenated aliphatic and aromatic hydroc,arbons. 3'4 Examples of such solvents range from heptane, hexane, cyclohexane to benzene, toluene, xylene, mesitylene and methylene chloride, chloroforn~ carbon tetrachloride, trichloroethylene, tetrachloroethylene, monochlorobenzene, m- and p..dichlorobenzene, 1,2,3-trichlorobenzene etc. With some catalytic systems such as derivatives of the late transition metals, highly polar solvents like water and alcohols have also been used. Significant studies carried out by HOcker and Muschzs on the effect of the solvent on the nature of reaction products in ring-opening metatlg~is polymerization of several cycloolefins, indicated that the solvent is important in directing the reaction selectivity. For example, in cyclooctene polymerization in the presence of tungsten-based metathesis catalysts the use of chlorobenzene as the solvent instead of n-heptane led to a substantial increase of the amount of oligomers in the reaction product. Furthermore, HOcker and Jones 26 studied extensively the effect of a large number of
chlorinated solvents on the ring-opening polymerization of cyclooctene. It is worthy mentioning that among the aromatic solvents, chlorobcnzcnr favored the formation of FriedeI-Crafts products to a greater extent than benzene. In addition, it was observed that of the chlorinated aliphatic
223 compounds, carbon tetrachloride did not achieve complete solvation of the metathesis catalyst employed so that the reaction system remained partially heterogeneous. The reaction in methylene chloride proceeded differently according to the reaction conditions and proc~ure employed. Thus, when the catalyst was prepared in benzene and the reaction was performed in methylene chloride, high yield (94%) in polyoctenamer was obtained while, when methylene chloride was used as a medium for both preparing the catalyst and the polymerization reaction, side processes occurred that diminished the polyoctenamer yield below 60%. Polymerization of norbomene carried out by Bencze and coworkers ~5 with the one-component catalyst W(CO)3C12 (AsPh3h is strongly solvent dependent (Table 4.4). Table 4.4 Effect of solvent on norbomene (M) polymerization with the one-componem catalyst W(CO)3C12(AsPh3)2
Solvent
Polymer yield, %
Product
Benzene 42 Polynorbomene Polynorbomene 29 Toluene Chlorobenzene 24 Polynorbomene Polynorbomene n-Octane 19 Polynorbomene n-Octane 53 Saturated telomers Carbon tetrachloride Nitrobenzene 0 0 F~71 acrylate 'Data from referenceIs. b[M] = 0.46 Mole./dm3 [W(CO)3CIz (AsPh3)z] = 0.25x I 0" 3Mole/dm3,Reaction time =20 rain; Temperature = 353 K (75~ ;~Reaction temperature = 398 K (120~ Thus, benzene is an acceptable solvent for this polymerization: it dissolves readily the catalyst and the polymer, and is easy to remove from the product. The polymer yield in toluene is somewhat smaller. The solubility of the polymer in chlorobenzene is relatively small with the swollen polymer beads separating from the liquid phase at an early stage in the reaction. There was no polymerization at all in nitrobenzene. Aliphatic h y d r ~ o n s such as octane do not dissolve the catalyst, however, the polymerization occurs, and at higher temperatures the yield is rather good.
224 Of the various solvents tested by Bencze, carbon tetrachloride appeared as one of the extreme. The conversion of the monomer in carbon tetrachloride was very high, but the yield of solid polymer was not more than 10%. The polymer was soluble in CDCI3 but its double bond content was practically zero. The majority of the products obtained in this case were soluble in benzene/alcohol mixture and consisted mainly of 2-chloro3-trichloromethylbicyclo[2.2.1 ]heptane and its analogs. Recently water and protic solvents have been successfully employed as adequate solvents for ring-opening polymerization of cycloolefins in the presence of late transition metal salts. 27'28 It is noteworthy that such catalysts can tolerate a wide range of functional groups and can be used with many heterocyclic monomers that are unreactive toward the early transition metal catalysts, z9 Significantly, the polarity of the solvent has a significant influence on the polymerization of cycloolefins in the presence of such catalytic systems like those derived from ruthenium, osmium and iridium compounds. 3~ Thus, in the polymerization reaction of cyclobutene induced by RuCI3, the stereoselectivity of the resulting polybutenamer was totally different when the reaction was carried out in water or in ethanol. 32 On employing water as the reaction medium, an equal amount (50:50%) of cis- and trans-polybutenamer was obtained whereas on working in ethanol a polybutenamer with predominant trans stereoconfiguration resulted.
4.8.2. Solvents for Heterogeneous Catalysts Polymerization of cycloolefins in the presence of heterogeneous catalysts are conveniently carried out using solvents and adequate diluents as the reaction medium. 33 The solvents or diluents are generally inert compounds relative to the catalytic system, e.g. saturated hydrocarbons such as heptane, octane, cyclohexane, benzene, toluene, etc. Their role in the polymerization process is, however, multiple. First, they have the quality of solvating and efficiently removing the high molecular weight compounds and the polymers formed during the reaction and maintain the access of the reactant at the active sites for further reaction. Second, they moderate the thermal effects of the polymerization reaction and extend thus the lifetime of the catalyst. Third, they can remove coke or polymer deposits more easily from the surface of the catalyst and prevent the catalyst deactivation by a regenerating effect. It is very important that the solvents employed in heterogeneous catalysis should be carefully purified in order to remove totally impurities
225 like moisture, air, oxygen-, nitrogen- and sulphur-containing compounds which may act as inhibitors for the catalytic system.
4.9. Inhibitors
~ e r a l l y , heterogeneous and homogeneous catalytic systems used in the cycloolefin polymerization are strongly affected by a wide range of substances that may be present in the reaction medium and which act as efficient inhibitors. Most of these substances rapidly deactivate the catalytic system by complexation at the active site and stop the elementary steps of the initiation and propagation of the polymerization process. A first class of inhibitors for cationic, Ziegler-Natta and ringopening metathesis polymerization of cycloolefins are organic and inorganic compounds that contain donor n-electrons at heteroatoms like oxygen, nitrogen, phosphorus, sulphur. Examples of such compounds are alcohols, ethers, esters, acids, nitriles, thiols, amines, phosphines, etc. Another significant class of inhibitors for Ziegler-Natta and metathesis polymerization contain donor n-electron in the double or triple bonds like dienes, mono- and diacetylenes, and some aromatic derivatives. Strong inhibitors for anionic polymerization include acids, water, alcohols and various organic compounds with pronounced acidity. Solvents employed in such reactions have tO be totally inert and carefully purified. Even soft acidity of the solvent could lead to transfer reactions with initiating and propagating anionic species. Homogeneous catalytic systems, particularly those consisting of transition metal halides and organometallic compounds react vigorously with water and alcohols yielding hydrated compounds and alkoxides, respectively. These catalytic systems can be easily destroyed by traces of water, alcohols, acids or other similar substances present in the solvent or in the cycloolefin. Amines, phosphines, and organic compounds with strong nucleophilic character can form stable combinations with most of the homogeneous catalysts employed in cycloolefin polymerization. Similarly, stable compounds may easily arise between the transition metal complex and dienes, acetylenes and aromatic hydrocarbons that prevent the polymerization process. The presence of such inhibitors in solvents or raw materials, even in small traces, has to be carefully controlled before starting the polymerization reaction.
226 4.10. Activators
The activators or promoters play an important role in the binary and ternary catalysts used for cycloolefin polymerization. Their nature varies essentially from cationic to Ziegler-Natta and ring-opening metathesis catalysts. They are generally compounds that improve the catalyst activity and selectivity when introduced in a certain proportion either by precomplexation or during the polymerization reaction. The activity of the cationic catalysts derived from metal halides, e.g., AICI3, BF3, TiCI, and SnCI4, is substantially enhanced when protogenic compounds like hydrogen halides, water and alcohols are added in traces or in certain amounts, depending on the nature of the catalytic system. TM Thus, both the alkylation and polymerization activity of AICI3 is markedly increased by traces of water or HCI, its high activity being assigned to formation of the complexes I-C[AICI3OH]" and I~[AICLs]', the actual initiators of the reaction. HF and HBr added to BF3 and AIBr3 promote generation of the very active complexes W[BF~]" and H~[AIBr4]. Ethers like ethyl ether when associated with BF3, form an active complex, BF3.OEtz, used largely in the cationic olefin polymerization. Similarly, lower alcohols like methanol, ethanol, and n-butanol may form new active species of a higher or moderate activity, as for instance TiCI3(OCH3), TiCI3(OC~Hs), and TiCI3(O"C,H9). Carboxy acids such as acetic acid, dichloro- and trichloroacetic acids coupled with SnCLs produce new cationic initiators of a higher activity and efficiency in cycloolefin polymerization. Alkyl halides, e.g. 'BuCI, reacted with EtzAICI will provide the complex Et2AICI/~BuCI which is active in the polymerization of indene and its derivatives. A large number of activators have been employed in the ringopening metathesis polymerization catalysts. ~ Thus, addition of small amounts of water to the system cyclopentene/WCl6 induces the ringopening polymerization of cyclopentene. The process is essentially dependent on the molar ratio HzO:WCI6 and reaction time3s (Figure 4.26, Curve M). It was found that the optimum activity of the water promoted WCI6 in cyclopentene polymerization was attained after 20 rain of reaction. The best yields were obtained for HzO/WCIs molar ratios less than 0.1, the polymer yield decreasing drastically at higher molar ratios. Interestingly, it has been noted that water initiates the polymerization only when added after the appearance of W(III) paramagnetic species in the ESR spectrum of the reaction mixture, the higher the concentration of the W(m) species, the
227 higher the activity of the water induced system. Yield, % .'3020100
o
o;2
0"4
o."6
o'e
1;o
H20[WCI~, mole ratio Figure 4.26. Influenceof water on cyclopentene polymerization with WCIs (Adapted from Ref. 35) Numerous oxygen-containing compounds like alcohols, haloalcohols, phenols, peroxides, hydroperoxides, carboxy acids, halocarboxy acids, ethers, esters, and molecular oxygen have been employed to improve the activity and selectivity of catalysts derived from WCI6 or MoCls and organometallic compounds. 4 Several peroxides e.g. benzoyl peroxide, Bz202, tert-butyl peroxide, ~BuzO2,cumyl hydroperoxide, CumOOH, hydrogen peroxide, H202, have been used as activator of the ternary catalysts derived from WCI6, WOCh or MoCls associated with Et2AICI, Et3AI, ~Bu3AI, 'Bu2AICI, Hex3Al, and Et2Be by DaU'Asta and Carella. ~s Ethanol has been widely used by Calderon and coworkers37~8 as an essential component of the WCh/EtAICI2 catalyst for the p o l y m ~ o n of cyclopentene, cyclooctene, cyclooctadiene, cyclodecene and cyclododecene. The role of ethanol as activator of this system has been largely discussed and ultimately it was assigned to the formation of alkoxy compounds of tungsten of high activity and selectivity in the ring-opening metathesis reaction. G0nther and coworkers39 employed oxygen-containing compounds like epoxides, peroxides, hydroperoxides, ~ e s , phenols and ethers, nitrogen-containing compounds such as amines, amides, nitroderivatives, and even inorganic peroxides like sodium and barium peroxides, NazO2 and BaO2, to improve the catalyst activity in cyclopemene polymerization with WCh,-based systems. Pampus and coworkers40'4~ employed halogen-containing compounds such as chloroethane and
228 epichlorohydrin in systems consisting of WCI6 and Et2AICI or 'Bu3AI to promote cyclopentene polymerization and copolymerization to high trcmspolypentenamer. Chloranil and epichlorohydrin have been extensively used by Dimonie and Dragutan *z'*3 in catalysts derived from WCIs and 'Bu3AI to increase the catalyst activity and selectivity in polymerization of cyclopentene, cyclooctene, 1,5-r and cyclododecene. Kinetic measurements undertaken in cyclopentene polymerization with WCI6CBu3AI, WC~chloranil/'Bu3Al and WCk/epichlorohydrin/Bu3Al revealed the strong effect of chloranil or epichlorohydrin on the polymerization p r ~ . 3s As Figure 4.27 illustrates, the initial rate of cyclopentene polymerization decreases significantly with time in the presence of WCI6fBu3AI. The introduction of epichlorohydrin into this catalytic system has a substantial effect on the kinetics of the process, however, the use of chloranil as the third component is accompanied by a drastic increase in the initial reaction rate. Yield, % 100
5
I0
Time, mm 15
50
9
5
-
,
~..~0 ~ I ~ I
10
I.'--
15
Time, hr Figure 4.27. The influence of activator on the ring-opening polymerization of cyclopmtme with WCId~urAl (Adapted from Ref.3s) The use of activators has a significant influence on the molecular weight distribution. This effect is more pronounced when two or more donor compounds are used as activators in WCis-based catalytic systems. 3s As it can be seen from Figure 4.28, the ternary catalytic systems consisting of WCIj'Bu3Al/epichlorohydrin and WCIjBu3Al/chloranil give a narrow molecular weight distribution in cyclopentene polymerization whereas
229 the quaternary catalytic system WCIJBu3Al/epichlrohyddn/chloranil leads to a broader molecular weight distribution as a function of the molar ratio of the catalytic components. M,x 10"s 10
"t
I
0
0
a
9
I
1
8
,
i
2
"
3
Time, hr
Figure 4.28. Influence of activators on the molecular weight distribution in cyclopmtme polymerization with ternary catalysts WCIjBu~d/A (A--a~ves)" Ofstead*' obtained highly active ternary catalytic systems for cycloolefin polymerization derived from tungsten and molybdenum complexes. Thus, high yields in polyoctenamer were obtained in cyclooctene polymerization using systems such as W(CO)4(I,5cyclooctadiene) or Mo(CO)4(norbomadiene) in conjunction with EtAICI2 and oxygen, bromine, iodine or cyanogen bromide. In addition, Ofstead prepared ternary catalysts for cyclopentene polymerization from WC~ EtAICI2 and a hydroxynitrile4s such as HOCH~HzCN or a chlorosilane~ of the type CICH2CH2OSiMe. ~ t t e et al. 47 showed that a-halogenated alcohols and halophenols impart higher activity and stability to the catalytic systems WCIJBu3Al and WCIdEtzAICI employed in cyclopentene polymerization. Examples of such halogenated alcohols are 2-chloroethanol, 2-bromoethanol, 1,3dichloroisopropanol, 2-chlorocyclohexanol, 2-iodocyclohexanol and ochlorophenol. Remarkably, with a catalytic system conta~ng WCI6, 'Bu3AI a~l CICH2OH, these authors obtained trans-polypentenamer in very high yields and with 94% trans double bond configuration.
230 A~s such as CHz(OCH3~z, CH2(OCH2CH2CI~h, CH3CH(OC2Hs~h, CI3CCH(OCH3)z or Cd'IsCH(OC2Hs)2 employed by SchOn et o2. a proved to be good activators and stabilizers for the catalyst WCIJEt2AICI. The same authors also employed various epoxides such as ethylene oxide and l-butylene oxide for increasing the activity of the catalyst WCk/'Bu3AI in cyclopentene polymerization. On using a ternary catalyst derived from WCI6, 'Bu3AI and C~'hO, they produced transpolypentenamer in 82% yield with 90.5% trans configuration at the double bond. Oberkirch et a/.49 used halogenated unsaturated hydrocarbons such as vinyl chloride in the catalytic systems derived from WCI6 or TaCIs and organoaluminium compounds. These additives increased the activity of the catalytic system but, at the same time, allowed the control of the molecular weight of the polymer. Similarly, Streck and Weber~ used tungsten- and molybdenum-based catalytic systems containing a halide or an unsaturated ether to adjust the molecular weight of polypentenamer to a desired value. Ktipper and Streck 5~ obtained polymers with high cis configuration at the double bond by using organic acids and their salts in the catalytic systems derived from WCI6 and EtAICIz. Thus, cyclooctene gave polyoctenamer with 63% cis configuration at the double bond when WC~CH3COOH/EtAICI2 was used as a catalyst. 4.11. Reaction Pressure
It is significant that catalytic polymerization of cycloolefms in homogeneous systems takes place commonly at low pressures, essentially at atmospheric or under vacuum. As in most cases with the classical catalysts, the absence of moisture and oxygen is a necessary condition, the removal of traces of these impurities from the reaction medium can be achieved making use of an inert atmosphere at normal pressure or at high vacuum. Cationic and anionic polymerization of cycloole~ are carried out commonly in an inert atmosphere and under high vacuum. Similarly, the polymerization of cycloolefins in the presence of classical Ziegler-Natta catalysts are conveniently carried out in an inert medium at atmospheric pressure. Both the contacting of the reactants and the polymerization reactions are preferentially carried out in se~ed vials with the reactants being handled via a high-vacuum technique (10"L10.4 ton'). Similar techniques under inert atmosphere and high vacuum have been applied for ring-opening metathesis polymerization with classical and unicomponent metallacarbene catalysts. More recently, with the advent of late transition
231 metal metathesis catalysts which are tolerant toward air and moisture, convenient procedures have been developed at atmospheric pressure in aqueous media. Polymerization of norbomene using Ru(H20)6(Tos)2 as catalyst has been conducted in liquid C02 at high pressure to obtain stereoselectively lfighly cis syndiotactic polymers2 (Table 4.5).
Table 4.5 Polymerization of norbomene with Ru(H20)dTosh in liquid C02 at various pressures* cis-
Reaction conditions
Yield %
Polymer %
Mexl0 "3
COz 2500 psi CO2 4000 psi CO2 5000 psi CO2/MeOH 5000 psi CO2/MeOH 5000 psi
19 34 32 29 26
76 87 90 32 37
269 77 187 58
55
Tacticity
2.5 1.9
2.5 3.7 3.4
Syndio Syndio Syndio Atactic~ Atactic~
'Data from referenceS2; ~ield of polymer after 5 hr of reaction; ~Polymers have a syndiotactic bias.
It can be seen that the reactions conducted in pure CO2 were more cis stereospecific than those in CO2/methanol, and the former polymers had a blocky distribution of cis and trans double bonds as judged from t i e r ~3C NMR spectra, an effect also observed for high cis content polymers when using Os-based catalysts in p o l y m ~ o n s at atmospheric pressure." The most important observation from these experiments is that increasing the pressure at which both homogeneous and heterogeneous polymerizations are conducted resulted in an enhanced cis stereoselectivity. Such results show also that the stereoselectivity of the ROMP reactions can depend sensitively on the reaction conditions and catalyst ligation, and there are many instances where change in these factors can radically alter the cis/trans ratio in the resulting polymer, s4 This correlation has a particular relevance to the application of cycloolefin polymerization processes at an industrial scale.
232 4.12. Effect of Agitation Although quantitative studies on the effect of agitation on the reaction parameters have not been reported, it is generally accepted that adequate stirring of the reaction mixture produces a better and uniform contact of the catalyst and reactants, an optimum heat and mass transfer and increases the monomer conversion and the polymerization yield. Heat release must be freed from the heavy mass continuously as it is evolved, and this can be ensured only by very thorough agitation of the rapidly swelling reaction mixture. Moreover, this parameter has to be correlated with the particular morphology of the growing polymer chain which allows the access of the monomer to the active site during the polymerization process. In most cases, the optimum reaction time, the convenient addition of monomer and catalyst components and the better control of the temperature is effected by vigorous stirring. In reactions in which the catalyst complex is a solid, the stirrer must be of a proper choice to provide the efficient agitation of the reaction mass as it thickens. This parameter is important when working at both the laboratory and industrial sc~e. Common experiments of cyclopentene polymerization in benzene and toluene as solvents in the presence of catalysts derived from WCI6 and organometallic compounds indicated that optimum speed of agitation in the range of 600-1200 rpm ensures a fast rate of reactant addition, a good control of mass and heat transfer and an optimum reaction time. 5~ Lower speed will affect strongly the catalyst activity, reaction yield, molecular weight and polymer structure. Under these circumstances, the catalyst activity and polymer yield decrease significantly, the molecular weight distribution broadens and the structure of the polymer could be totally uncontrolled Industrial plant installations make use of the helical and propeller stirrers to ensure an optimum heat and mass transfer in all type of processes encountered in the catalytic polymerization of cycloolefins: bluk, solution, suspension and emulsion. The mode of agitation depends substantially on the type of surfactant and emulsifier employed in the last two processes. A special attention is devoted to stirring in the operations involved in the catalyst preparations by both proc~ures, m situ or precomplexation. In particular cases, variable speed of stirring has to be applied for catalyst preparation and polymerization process. In this connection, the influence of speed of stirring on the reaction rate of a number of unit processes can be pursued in the excellent work of Groggins. s6
233 4.13. References
J.P. Kennedy, "Cationic Polymerization of Olefms: A Critical Inventory", John Wiley & Sons, New York, 1975. J. Boor, Jr., "Ziegler-Natta Catalysts and Polymerization", Academic Press, New York, 1979. K.J.Ivin and J . C . Mol, "Olefm Metathesis and Metathesis Polymerization", Academic Press, London, 1997. V. Dragutan, A.T.Balaban and M.Dimonie, "Olefm Metathesis and Ring-Opening Polymerization of Cycloolefins", John Wiley & Sons, Chichester, 1985. A.J. Amass and C.N. Tuck, Eur.Polym.J., 14, 81%823 (1978) 6. H. H6cker, W. Reiman, L. Reif and K. l~ebel, J. Mol. Catal., 8, 191 (1980). L. Reif and H. H6cker, Macromolecules, 17, 952 (1984). 8. H. Jacobson and W.H. Stockmayer, J. Chem. Phys., 18, 12, 1600 .
.
.
.
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(1950). Z.R. Chert, J.P. Claverie, R.H. Grubbs and J.A. Kornfield, Macromolecules, 28, 2147 (1995). 10. U.W. Suter and H. H6cker, Mal~omol. Chem., 189, 1603 (1988). 11. K.J. Ivin, Makromol. Chem., Macromol. Symp., 42/43, 1 (1991). 12. K.W. Scott, N. Calderon, E.A. Ofstead, W.A. Judy and J.P. Ward, Adv. Chem. Set., 91,399 (1969). 13. E.A. Ofstead and N. Calderon, Malcromol. Chem., 154, 21 (1972). 14. E. Thom-Csanyi, J. Hammer, K.P. Pttug, J.U. Zilles, "35 s Intl. Symposium on Macromolecules", Akron, OH, 1994, Abstracts p. 241. 15. L. Benczr and A. Kraut-Vass, J. Mol. Catal., 28, 369 (1985). 16. A. Pacreau and M. Fontanille, Mal~omol. Chem., 188, 2585 (1987). 17. W. Kaminsky, A. Bark and I. Dake, in "Catalytic Olefin Polymerization", Elsevier, Amsterdam, 1990, pp. 425-438. 18. W. L.Tmett, D.R. Johnson, I.M. Robinson and B.A. Montague, J. Amer. Chem. Sot., 82, 233 7 (1960). 19. M. Dimonie, V. Dragutan, A. Cornilescu, E. Nicolescu, M. Popescu, S.Coca, M. Cuzmici, Re,,. Roumaine Chim., 34, 1293 (1989). 20. M. Dimonie, A. Cornilescu, M. Chipara, M. Gheorghiu, V. Dragutan, E. Nicolescu, M. Popescu, S. Coca, C. Belloiu and G. Hubca, J. Macromol. Sci.-Chem., A22, 849-876 (1985). .
234 21. A.J. Amass and J.A. Zurimendi, J. Mol. Catal., 8, 243-252 (1980) 22. A. Cornilescu, E. Nicolescu, M. Popescu, S. Coca, M. Cuzmici, C. Oprescu, M. Dimonie, G. Hubca, M. Teodoreseu, V. Dragutaa and M. Chipara, J. Mol. Catal., 46, 423-431 (1988). 23. H. Balcar, A. Dosedlova and L. Petrusova, J. Mol. Catal., 77, 289-295
(1992). 24. A. Comilestm, E. Nicolesr M. Popescu, S. Coca, M. Cuzmici, C. Oprescu, M. Dimonie, G. Hubca, M. Teodorescu, R. Grosescu, A. Vasilescu and V. Dragutan, J. ?viol. Catal., 36, 163-175 (1986). 25. H. HOcker and R. Musch, Makromol. Chem., 176, 3117 (1975). 26. H. H0~ker and F.R. Jones, Makromol. Chem., 161,251 (1972). 27. a. M.B. France, R.A. Paciello and R.H. Grubbs, Macromolecules, 26, 4739-4741 (1993), b. M.B. France, R.H. Cnubbs and D.V. M~jrath, Macromolecules, 26, 4742-4747 (1993), c. M.A. Hillmeyer, C. Lepettit, D.V. McC~ath, B.M. Novak and R.H. Caubbs, Macromolecules, 25, 3345-33 50 (1992). 28. a. B.M. Novak and R.H. Grubbs, J. Amer. Chem. Soc., 110, 960-961 (1988), b. B.M. Novak and R.H. Grubbs, J. Amer. Chem. Sot:., 110, 7542-7543 (198g), c. D.M. Lymt, S. Kanaoka, and l~H. Grubbs, ,1. Amer. Chem. Soc., 118, 784-790 (1996). 29. R.H. Grubbs, J.M.S.-Pure Appl. Chem., A31, 1829-1833 (1994), 30. a. F.W. Michelotti and J.H. Carter, Polymer Preprints (Am. Chem. Soc., Div. Polym. Chem.) 5, 224 (1965); b. R.E. Rinehart and H.P. Smith, J. Polym. Sci., Polym. Lett., 3, 1049-1052 (1965). 31. a. J.W. Feast and D.B. Harrison, J. Mol. Catal., 65, 63-72 (1991), b. J.W. Feast, D.B. Harrison, A.F. Gerard and D.R. Randell, Brit. Patent, 2,235,460 (1991). 32. G. Natta, G. Dall'Asta and L. Porri, Makromol. Chem., al, 253 (1965). 33. H.S. Eleuterio, U.S. Patent 3,074,918 (1957), H.S. Eleuterio, Get. Often. 1,072,811 (1960). 34. P.H. Plesch, Ed., "The Chemistry of Cationic Polymerization", MacMilan, New York, 1963. 35. A. Cornilescu, E. Nicolescu, M. Popescu, S. Coca, C. Belloiu, M. Dimonie, M. Gheorghiu, V. Dragutan and M. Chipara, J. Mol. Catal.,28, 337-349 (1985). 36. G. Dall'Asta and C. Carella, Brit. Patent 1,062,367 (1965); Chem. Abstr. 66, 19005q (1967). 37. N. Calderon, E.A. Ofstead and W.A. Judy, J. Polym. Sci., A I, 5, 2209
235 (1967). 38. N. Calderon and W.A Judy, Brit. Patent 1,124,456 (1968); Chem. Abstr., 69, 77970 (1968). 39. P. Chmther et al., Angew. Makromol. Chem., 14, 87 (1970), P. C.dmther et al., Angew. Mal~omol. Chem., 16/17, 27 (1971 ). 40. a. G. Pampus and J. WiRe, Get. Often., 1,770,143 (1968), b. G. Pampus, G. Lehnert and J. WiRe, Get. Often., 2,101,684 (1972). 41. a. G. Pampus, J. WiRe and M. Hoffmann, Get. Often. 2,016,471 (1971), b. G. Pampus, J. WiRe and M. Hoffinann, Get. Often. 2,016,840 (1971), 42. M. Dimonie, S. Coca and V. Dragutan, J. Mol. Catal., 76, 79-91 (1992). 43. M. Dimonie, S. Coca, M. Teodorescu, L. Popescu, M. Chipara and V. Dragutan, J. Mol. Catal., 90, 117-124 (1994). 44. E.A. Ofstead, U.S. Patent 3,597,403 (1969); Chem. Abstr., 75, 141671 (1971). 45. a. E.A. Ofstead, U.S. Patent 3,997,471 (1976), Chem. Abstr., 86, 56559 (1977); b. E.A. Ofstead, U.S. Patent 4,010,113 (1977), Chem. A bstr., 86, 140694 (1977). 46. E.A. Ofstead, U.S. Patent 4,020,254 (1977), Chem. Abstr., 87, 24528 (1977). 47. a. J. WiRe, N. SchOn and G. Pampus, Fr. Patent 2,014,139 (1970); b. J. WiRe, G. Pampus and D. Maertens, Get. Often. 2,203,303 (1973). 48. a. N. SehOn, G. Pampus, J. WiRe and D. Theisen, Ger. Often. 2,006,776 (1971); b. N. SchOn, G. Pampus and J. WiRe, Get. Often. 2,012,675 (1970). 49. a. W. Oberkirch, P. GOnther and G. Pampus, Belg. Patent 742,391 (1968); b. W. Oberkirch, P. Gtmther and G. Pampus, Get. Often. 1,811,53 (1970). 50. a. R. Streck and H. Weber, Get. Often. 2,028,716 (1971); b. R. Streck and H. Weber, Get. Often. 2,028,905 (1972); c. R. Streck and H. Weber, Get. Often. 2,028,935 (1972). 51. a. F.W. Ktipper, R. Streck and K. Hunm~l,. Get. Often. 2,051,798 (1972); b. F.W. KOpper, R. Streck H.T. Heims and H. Weber, Get. Often. 2,051,799 (1972); 52. J.G. Hamilton, J.J. Rooney, J.M. DeSimone and C. Mistele, Macromolecules, 31, 4387 (1998). 53. D.G. Gilheany, J.G. Hamilton, O.N.D. Mackey and J.J. Rooney, J.
236 Chem. Soc., Chem. Commun., 1990 (1600). 54. K.J. Ivin, "Olefin Metathesis", Academic Press, London, 1983. 55. a. V. Dragutan, S. Coca and M. Dimonie, in "Metathesis Polymerization of Olefins and Polymerization of Alkynes", (Y. Imamoglu, Ed.), Kluwer Academic Publishers, Dordrecht, Netherlands, 1988, pp. 89-102; b. M. Dimonie, S. Coca, M. Teodorescu, L. Popescu, M. Chipara and V. Dragutan, J. Mol. Cata/., 90, 117 (1994). 56. P.H. Groggins, "Unit Processes in Organic Synthesis", McGraw-Hill, New York, 1952, pp. 375-376.
237
Chapter 5 CATIONIC POLYMERIZATION OF CYCLOOLEFINS Due to the easy availability of the cationic initiators of the BrOnsted or Lewis acid type, the catalytic polymerization of cycloolefins induced by these types of initiators has been extensively explored with a large number of monomers having monocyclic and polycyclic structures.
5.1. Cationic Polymerization of Monocyclic Olefins The study of cationic polymerization of mono~clir olefins covered a considerable number of common monomers with small- and medium-ring size. Of these monomers, substituted and unsubstituted four-, five- and sixmcmbered rings are most interesting and will be dealt with in detail in the following sections.
5.1.1. Four-Membered Ring Monomers Both unsubstituted and substituted cyclobutene have been used as monomers to produce polymers with particular structures and properties by cationic polymerization. Cydobutene. In the presence of cationic initiators, cyclobutene polymerizes by a conventional 1,2-addition pathway to produce polycyclobutene or poly(1,2-cyclobutylene) (Eq. 5.1 ).
n I~
~--
,Jn
[U
(5.1)
However, under the action of the cationic initiators, formation of the 1,3r product seems to be also possible, i.e., poly(l,3cyclobutylene), as result of the 1,2-hydride shift reactions in the intermediate carbocation (Eq. 5.2). n
I--il
-
-9
L
V
J
n
(5.2)
238 To our knowledge, polymerization of cyclobutene under these conditions has not been studied systematically as in the case of Ziegler-Natta and ringopening metathesis polymerization processes, described later in the following sections. Some interesting data about the 1,2-addition polymerization of cyclobutene can be found in an extensive review of Hall and Ykman. ~ Substituted cyclobutene. Several substituted c y c l o b u t ~ have been polymerized using cationic initiators, some of these monomers giving rise to products with a quite interesting structure. l-Mehtylcydobutene. By cationic polymerization, l-methylcyclobutene forms poly(l-methylcyclobutene) or poly(l,2-(l-methyl)cyclobutylene) through the 1,2-addition reaction (Eq. 5.3).
BF3 9 =
n
rl
~
LI lj n
(5.3)
This reaction occurs in low yield in the presence of some cationic initiators such as BF3, AICI3, AIBr3. The nature of the reaction products is rather complex and yet undefined. 3-Methylenecyclobutene. Polymerization of this very active monomer has been reported by Applequist and Roberts z in the presence of BF3 to obtain a brittle material that was insoluble in common solvents and turned brown soon after its preparation. From the infrared spectra, it was concluded that the polymer chain arose by 1,5-addition of the two conjugated double bonds of the monomer (Eq. 5.4).
n
.-~
BF3"~ - ' ~ - ' ~ n
(5.4)
Later on, polymerization of 3-methylenecyclobutene, in the presence of several cationic and anionic initiators, has been effected by Wu and Lenz. 3 Though the reaction of this monomer occurred readily under the action of BF3, BF3.EtzO and EhAICI, the low molecular weight products ( M ~ 3000-3500) rapidly oxidized after synthesis. The structures of these low molecular weight polyng~s were also supposed to arise by 1,5-enchainment of the monomer units. In this connection, it is worthwhile to note that the anionic polymerization of this conjugated cyclic diene gives rise to a methylene substituted poly(l,2-cyclobutylene) by a normal 1,2-addition reaction.
239 3-Methylcydobutene. The reaction of 3-methylcyclobutene to poly(3methylcyclobutene) has to ocx~ur easier than that of the monomer substituted in the position I (Eq. 5.5).
n
!-i
BF3 N
~
[I [Jn
(5.5)
N
The structure corresponds to a 1,2-addition reaction but 1,3-addition polymer can also arise via 1,2-hydride migration in the cationic intermediate
(Eq. 5.6).
n r~
\
BF3=
~ n
(5.6)
l-Methyb3-methylenecyclobutene. Polymerization of l-methyl-3methylenecyclobutene has been studied by Wu and Lenz3 using both cationic and Ziegler-Natta initiators. In the presence of BF3 in bulk, of BF3.EhO in n-hexane or with EtzAICIMBr in toluene at -78~ these authors prepared in high yield (-70%) polymers of a fairly moderate molecular weight (Me = 3800-19200). The structure of the polymers corresponded to a 1,5-addition reaction of the conjugated monomer as determined by IR and ~ spectroscopy (Eq. 5.7).
n ~
BF3~ -'~~ n
(5.7)
5.1.2. Five-Membered Ring Monomers
Due to thek ready availability from petrochemical sources, fivemembered ring monomers have been employed in a large number of studies with various cationic initiators. Cyclopentenr In the presence of cationic initiators cyclopentene has to form poly(cyclopentene) or poly(l,2-cyclopentylene) by a normal 1,2addition reaction (Eq. 5.8). n
I"
(5.8)
240 Under the action of cationic catalysts, however, 1,3-addition enchainment could also occur as result of a 1,2-hydride shift reaction in the intermediate carbocation (Eq. 5.9).
n ~~
'
=-
r ~
L\
/ J-~n
(5.9)
Cationic polymerization of cyclopentene has been first reported by Hoffman4 in the presence of BF3 and HF to obtain dimers, trimers and tetramers as well as transparent amber solid polymers. Later on, the reaction has been carried out by Boor et al., 5 using AICI3 at low temperature (-20~ in EtCI as a solvent, but no polymer was obtained under these conditions. Substituted r Several substituted cyclopentenes have been polymerized with cationic initiators to provide products with interesting structuresandproperties. l-Methylcydopentene Polymerization of this substituted monomer, having the methyl group at the cau~n-carbon double bond, with cationic initiators occurs readily in contrast to other types of catalytic systems (Eq. 5.10). n
/
BF3
=
Jn
(5.10)
The reaction has been performed by Schmitt and Schuerich6 in the presence of BF3 and BF;/camphor complexes, in hexane and chloroform at 0~ to obtain viscous oily products. The structures of these mbstituted polymers, though of interest due to a particular position of the substituent, has not bccn carefully examined. 3-Methyleydopentene. It was found by Boor et al. 5 that, while the parent olefin, cyclopentene, is difficult to polymerize by conventional cationic techniques or gives dimers at best4, the 3-methyl derivative polymerizes slowly to give a polymer with 1,3 repeat unit (Eq. 5.11).
n ~~~.
AICI3
"~~n
(5.11)
Under these conditions, probably 1,2-addition polymer can also arise but this structure has not been identified at that time (Eq. 5.12).
241
n ~
BF3 =
.
.
t~,~m
§
(5.12)
The reaction is very slow and is thought to occur by an intramoleodar hydride shift. Since the hydride shift can occur at every propagation step, it is understandable that the ultimate yields are very low. 3-Vinyicydopentene. Polymerization of 3-vinylcyclopentene has been performed by Ohara, 7 using various alkylaluminium compounds, for instance EtAICI2, to obtain a partially soluble polymer of undefined structure. Investigations on the structure of the p o l ~ thus obtained indicated the presence of bicyclic repeat units, probably of bicycloheptanic nature (Eq. 5.13).
It seems that under the action of the above cationic initiator, intramolecular cyclialkylation and not hydride shifts has occurred. 3-Allykydopentene. Polymerization of the related allyl homolog, 3allylcyclopentene, has been studied also by Ohara~ with organoaluminium compounds as initiators, e.g., EtAICI2 or EtAICI2/PhCH2CI, to produce soluble polymers in common organic solvents. The structure of the polymer indicated the presence of several bicyclic repeat units, probably of bicycloheptanic and bicyclooctanic nature, such as the followings (Eq. 5.14).
n -J --~ ~
~
§
§
(5.14)
Again, under the reaction conditions, it seemed that intramoleodar cyclialkylation reactions prevailed as compared to the intramolec~lar hydride rearrangement. 3-Chlorocyclopentene. Polymerization of 3-chlorocyclopent-l-ene was investigated by Cerkasin eta/., 8 under thermal and catalytic conditions, to produce polymers of different molecular weights and structures. Working in benzene as a solvent with t r i c h l o r o ~ c acid at room temperature, products of medium moleodar weight have been prepared whose struca~es
242 have not been completely elucidated. Proposed structures contain either exocyclic unsaturation along the chain or endocyclic unsaturation in the cyclic repeat units (Eq. 5.15).
~
(5.15)
Cydopentadiene. Due to its large accessibility and high reactivity, the cationic polymerization of cyclopentadiene has been extensively studied by several research groups, providing valuable results for polymer chemistry. First, Staudinger and coworkers 9'~~reported fundamental investigations on the polymerization of this monomer as early as 1926. They used a large number of metal h~de~, e.g., TiCI4, BCI3, SnCl,, FeCI3, .~C13, at low temperatures, to produce moderate to high molecular weight poly(cyclopentadiene) (1-7 x 103). Under these conditions, they obtained a rubbery and vulcanizable product which readily absorbed oxygen with gelation while an insoluble product formed on prolonged standing on air. Structural investigation revealed that the polymer contained 1,2-addition repeat units along with 1,4-addition type enchainment (F-xl. 5.16). f
_
9
An interesting observation in this process was the intense color development associated with the rapid exothermic reaction as well as when the product is treated with acids. The same phenomenon was also noted by Wassermann and coworkers ~'~2 in cyclopentadiene polymerization with several cationic initiators and when treating the p o l ~ with strong acids, for instance trichloroacetic acid. To explain the strong brown-red color that appeared during this reaction, the formation of a conjugated unsaturated polymer bearing carbon-carbon double bonds inside or outside the cycle was proposed (Eq. 5.17).
243 More r ~ t l y , Sigwalt and Vairon ~3'~4 examined in detail cyclopentadiene polymerization in the presence of weak initiators that do not attack the second double bond of the monomer and allow linear propagation. In order to control better the polymerization p r ~ , they reduced the electrophilic character of TiCh by replacing one of the electron withdrawing chlorine atoms in the TiCh molecule by an electron releasing substituent -O~Bu. Thus, on using the initiator TiCI30~Bu at high rates, they prepared quite high molecular weight poly(cyclopentadiene) that was soluble in common aromatic and chlorinated solvents. These polymers were readily oxidizable in air and became insoluble. In addition, with t r i c h l o r o ~ c acid, they also obtained high molecular weight products but at much lower reaction rates. Interestingly, the presence of small amounts of dicyclopentadiene in the raw material was found to be a strong molecular weight depressor. Molec~ar weights were measured by intrinsic viscosity and light scattering but the relationship between [q] and molecular weight could not be established because the latter varied significantly with the polymerization temperature. Moreover, in detailed kinetic investigations on cyclopentadiene polymerization with TiCI30"Bu, under conditions of high purity and dryness, Sigwalt and Vairon ls'16 demonstrated the ac,oelerating effect of water and hydrochloric acid on the reaction rate. Further experiments with the TiCI30"Bu initiator in methylene chloride as a solvent at -70~ indicated that the number average degree of cyclopentadiene polymerization decreased with increasing initiator concentration and decreasing monomer concentration. On the other hand, the reaction rate increased with increasing initiator and monomer concentrations. Interestingly, kinetic results showed that the initial rates were first order in TiCI30~Bu, H20 and monomer and quasistationary for the active centres. It was observed that the initiation was slower than propagation and independent on the initial monomer concentration. The rate constant for the initiation reaction was found to be k , - 11.1 L/mole.sec at -70~ and the enthalpy of polymerization-AH = 14.1 kc~mole. From NMR spectroscopic measurements they concluded that the microstructure of the poly(cyclopentadiene) consisted of equal contributions of 1,2- and 1,4enchainments. Remarkable studies on the cyclopentadiene polymerization carried out Sigwalt and coworkers ~7'~s using as catalyst the stable c,arboc~on salt PhC+SbCts to obtain quite high molecular weight poly(cyclopentadiene), entirely soluble in methylene chloride as a solvent. The range of molecular weight was between 1 ~ and 120000 when working at temperatures
244 from +20~ tO -70~ Interestingly, they postulated for the initiation mechanism a direct addition of the trityl carbocation to the monomer in methylene chloride as will be shown in a f u ~ chapter. Important kinetic studies on the cyclopentadiene polymerization carried out Imanishi and Higashimura mg~ using the binary catalysts TiCh/CCI3COOH, SnCLs/CCI3COOH and BF3.EhO. When working in toluene and methylene chloride at -78~ they obtained only low molecular weight polymers, [11] = 0.1-0.5. It is noteworthy that the polymerization in the presence of TiCh/CCI3COOH was extrenady rapid and nonstationary and conversion decayed at low values, however, remarkably, on adding fresh TiCh to the "dorntant" system, another burst or rapid polymerization occurred. In fiu~er detailed studies on this reaction, Imanishiz~ found that the polymerization promoted by SnCh/CCI3COOH involves two stages: (i) at the beginning, the reaction is nonstationary and extremely rapid, characterized by an inverse [q] v s . initiator c o ~ t r a t i o n dependence and by the fact that water has practically no effect on [11] and (ii) afterwards, the rate slows down and becomes stationary. On the other hand, with BF3.OEtz, the rate is much slower and, except for the very beginning, it is stationary, [~] is unaffected by the initiator concentration and it is much depressed in the presence of water. In the p o l ~ i o n of cyclopentadiene, in the presence of cationic polymerization catalysts selected from acidic compounds of halogenated metals such as aluminium, titanium or stannic chloride and boron trifluoride, Mitsubishi Monsanto Chemical Co. zz reported that the improvement comprises limiting the concentration of the free acid in the polymerization zone to < 100 ppm. By this proc~ure, colorless, transparent, rubber-like polymers of high molecular weight, which were soluble in solvents, were obtained. Microstructure of poly(cyclopentadiene) obtained with cationic initiators has been investigated in detail by Aso and Kunitake. z3 First studies dealing with the oxidation z3 and bromination z4 of poly(cyclopentadiene) evidenced the occurrence of 1,4-enchainment in the polymer chain whereas subsequent investigation by NMR spectroscopy of polymers prepared with TiCh/CCI3COOH, AIBr3, SnCh, etc. demonstrated the presence of both 1,2- and 1,4-enchainments. Furthem~re, Aso and coworkers ~ p r i e d to investigate the effect of the reaction parameters on the structure of poly(cyclopentadiene) obtained under certain conditions. In general, they found intrinsic viscosity [~] in the range of 0.1-1.7 and higher
245 molecular weights when weaker Lewis acids at lowest temperatures were employed. They also observed that while the addition of CCI3COOH or H20 to TiCI4 or SnCI4 accelerated the reaction rates, the microstructure of the polymers remained largely unaffected. Furthermore, gel formation was more frequent in methylene chloride tlum in toluene. Also, very important, they found evidence from NMR spectra for some isomerization reactions in the polar solvents at higher temperatures, particularly with AIBr3and TiCLs as catalysts. A structure with 1,3-enchainment of the repeat unit was proposed for this isomerized portion and the authors inferred that the isomerization occurred during the propagation and not as a postpolymefization step under the influence of excess of the unr~cted Lewis acid. Further compelling evidence for this proposal came from independent experiments that indicated only a little change in the structure of a preformed poly(cyclopentadiene) upon treatment with TiCh under the same reaction conditions. It was also remarkably demonstrated by Aso and coworkers 2~ that the nature of the ~ s acid affects s i g n i f i ~ y the relative contribution of the two repeat units in poly(cyclopentadiene) and that the effect of temperature on the microstructure of the polymer is negligible in the range 0~ to -100~ It was found that the highest amount of 1,2-enchainment was produced with TiCh and progressively lesser amounts with AIBr3, SnCh and BF3.Et20. To explain these results, Aso and coworkers 2~ postulated that the propagation reaction is controlled by tight and loose ion pairs that direct the incoming monomer differently to 1,4- and 1,2enchainment, respectively (see details in a forthcoming secfon) (Eq. 5.18).
e A del~ (Eq. 5.19).
6O
(5.18)
aHyfic cation seems to be operative under these conditions
8~
~80 6~
246 S i g n i f i ~ correlation between the nature of the cationic catalyst and the re,action temperature with the intrinsic viscosities [11] in cyclopentadiene polymerization has also been made by Aso and coworkers 2~ (Figure 5.1).
[11]
2.0 3
1.0 0.5 0.4
J
0.3 0.2 0.1
((~)
~
(-so')
4x10 -3
,
i
(-78-)
i
(-loo-)
5x10 -3 icr
Figure 5.1. Depmdmce of intrinsic viscosity [q] with ten~rature and catalyst in cyclopmtadime polymerization: 1-TiCh, 2-AIBr3, 3-SnCh, 4-BF3.OEtz (Adapted from Ref.n). As it can be observed from Figure 5.1, the viscosity values are rather high that indicates that high molecular weight poly(r [r > 1.O, can readily be obtained under suitable reaction conditions with the conventional cationic initiators. It is noteworthy that under similar conditions, the h i g h e s t polymer was obtain~ with the weak catalyst BF3.EtzO and the lowest with the stronger AIBr3. Interesting results on the cyclopentadiene polymerization in the presence of several cationic initiators reported Schmidt and Kolb. zs For instance, they studied the effect of reaction variables on the molecular weight of poly(cyclopentadiene) produced with BF3.EtzO (I-120) in toluene in the range + 18~ to -78~ and were able to obtain polymers in good yield with intrinsic viscosity [rl]> 1.0. When used BF3/anisol and
247 BF3/2CHsCOOH, at -78~ intrinsic viscosities [11] as high as 2.0 and 1.6 were obta/ned, respectively. Oxidation of poly(cyclopentadiene) in the presence of oxidation
agents such as 12, SbCls, SbFs, AsFs, PFs provided a highly unsaturated conductive polymer with conjugated double bonds in the polymer chain. The structureof thisunsaturated polymer corresponded to several reou~ng units,however, the following structureprevailed(Eq. 5.20)
IOxlThe product was insoluble in common solvents and posses.q~ a specific conductivity of at least 10"7S x cm"1 Substituted cydopentadiene Similar to its unsubstimted analogs, in the polymerization of the alkyl substituted cyclopentadiene in the presence of cationic polymerization catalysts selected from acidic compounds of the halogenated metals such as aluminium, titanium or stannic chloride or boron trifluoride, a significant improvement consists of limiting the concentration of the free acid in the p o l y m ~ o n zone to < 100 ppm. This process allows colorless, transparent, robber-like polymers of high moleodar weight to be prepared, which are soluble in common solvents. l-Methylcydopentadiene. Reaction of l-~ylcyclopentadiene in the presence of cationic initiators will form by addition polymerization at the u n s u b ~ t e d double bond one of the vinyl polynmrs which may arise from this monomer (Eq. 5.21). n
=~
[~
in
(5.21)
As the separation of l-methylcyclopentadiet~ from its mixture with 2methylcyclopentadiene is very difficult, the investigations of the polymerization of this highly reactive monomer have been carried out with compositions of the two isomers. Thus, using various isomer ratios l-
methylcyclopentadiene " 2-methylcyclopentadiene (from 89:11 to 27:73), Aso and Ohara z9 studied this reaction in the presence of BF3.Et20, SnCh and TiCh under a variety of conditions (various solvents, monomer concentrations and reaction temperatures). Though medium to high
248 conversions of the monomers were readily attained under most conditions, the molecular weight of the resulted polymers remained relatively low. The products were soluble white powders with softening points of 120-160~ which readily oxidized on standing in air. It is noteworthy the lack of gelation that may be due to the presence of trisubstituted double bond in the polymer chain. 2-Methylcydopentadiene. By cationic polymerization, 2methylcyclopentadiene may undergo readily 1,4- and 3,4-addition reaction with formation of both 1,4- and 3,4-enchainment in the polymer chain (Eq. 5.22)
(5.22) As a matter of fact, the polymerization of this monomer was effocted by Aso and Ohara3~ in the presence of its position isomer, 1methylcyclopentadiene, due to the difficult separation of the two compounds. The reaction of this isomer mixture was performed, as mentioned above, in the presence of BF3.Et20, SnCLs and TiCL=, under various conditions, when relatively low molecular weight polymers have been obtained. Analysis by LK and ~ spectroscopy of the microstructure of the polymers thus prepared indicated the major presence of 1,4enchainment along with less contribution of the 3,4-enchainment at the unsubstituted double bond of the two monomers. Practically, no evidence for 1,2-enchainment at the substituted double bond at either monomer was found, probably due to the steric hindrance exerted by the methyl substituent. 1,2-Dimethylcydo pentad ien e. Cationic polymerization of 1,2dimethylcyclopentadiene was mentioned by Aso and Ohara3~ to proceed in the presence of the above initiators with formation of polymers having 3,4enchainment (Eq. 5.23).
n
(5.23)
It is obvious that the highly substituted double bond will avoid unfavorable sterir hindrance and will prefer the less hindered 3,4-addition pathway.
249 1,3-Dimethylcydopentadiene. The polymerization of 1,3dimethylcyclopentadiene in the presence of cationic ~ y s t s leads to addition polymers with 1,4- and 3,4-enchainment (Eq. 5.24).
~163
~'~m
+
p (5.24)
As this monomer is the most stable isomer among the seven possible disubstituted isomers of cyclopentadiene, it can be obtained in the pure state and easily monitored in the polymerization reaction. Thus, Aso and Ohara3~ followed the polymerization under the action of BF3.EhO, TiCLs and SnCh in toluene and methylene chloride at 0~ and 78~ to obtain high conversions and reasonable intrinsic viscosity ([11] = 0.1- 1.0). The products were soluble in the common solvents and benzene solutions could be cast to yield transparent films. As in the case of the p o l y m ~ o n of cyclopentadiene and its monosubstituted derivatives with cationic systems, the nature of the catalyst influences significantly the intrinsic viscosity, the highest values being obtained with BF3.EhO and in decreasing order with SnCh and TiCI4. It is noteworthy that lowering the temperature and using the less polar solvents also i n c r ~ the polymer viscosity. Furthermore, the softening points of 150-155~ were somewhat higher than those of poly(cyclopentadiene) (90-120~ and poly(methylcyclopentadiene) (120150~ Interestingly, the rates of oxidation and oxygen absorption upon exposure to air were found to be slower for this polymer than those for poly(methylcyclopentadiene) which in turn were slower than those of poly(cyclopentadiene). Aso and Ohara attributed this increased oxidation resistance to the decreasing number of tertiary aUylic hydrogen in this series of polymers. The microstmc~e of the p o l ~ obtained was analyzed by fit and ~H M R spectroscopy. While IR measurements indicated undoubtedly the presence of trisubstituted double bonds and two kinds of methyl groups in the polymer chain, the ~H NMR data revealed the same number of methyl protons on saturated and unsaturated carbons and a correct ratio of the total number of protons to the number of protons at an unsaturated position. It is noteworthy that these results indicated the absence of isomefization during and after polymerization under the influence of cationic initiator and confirmed the 1,4- and 3,4-enchainment of the repeat units in the polymer as illustrated above in Eq. 5.24 It is
250 remarkable that the steric hindrance exerted by the tertiary methyl substituents at the double bonds did not prohibit the chain propagation. Nonetheless, the mode of r was found to be affected to a certain extent by the nature of the catalyst employed. 2,3-Dimethylcydopentadiene. Cationic polymerization of 2,3dimethylcyclopentadiene was reported by Aso and Ohara3~ to proceed essentially to pure 1,4-e~hainment polymer (Eq. 5.25).
(5.25) It is obvious that the two substituents will direct the polymerization reaction by the least hindered route of 1,4-addition. Furthermore, it is noteworthy the absence of isomerization during the polymerization process. l-Methyl-3~thylcydopentadiene. Polymerization of 1-methyl-3ethylcyclopentadiene was effccted by Ohara and Aso 3~ using several FriedeI-Crafls catalysts to produce poly(1-methyl-3-ethylcyclopentadiene) (Eq. 5.26).
n~
"-----~ - t ' ~ n
(5.26)
l-Methyl-3-isopropylcydopentadiene. The cationic polymerization of disubstituted cyclopentadienes was extended by Ohara and Aso3~ to 1methyl-3-isopropylcyclopentadiene. Under the action of a series of FriedelCrafts catalysts, these authors prepared poly(l-methyl-3isopropylcyclopentadiene) starting from this monomer (Eq. 5.27).
L ----.-
(5.27)
The steric effect of the substituent attached to cyclopentadicne showed to be significant on the reaction course. In similar conditions, the above authors observed a decrease of the reaction rate in the following order CH3 > CH3-CH2 > CH(CH3h. Allylcydopentadiene. Aso and Ohara 3~ carried out the cationic polymerization of mixtures of allylcyclopentadiene isomers to produce
251
polymers consisting of equal amounts of 1,4- and 3,4-enchainments (Eq.
5.2s).
The reaction was first undertaken by these authors in the presence of BF3.EhO, AIBr3, TiCh and SnCI4 in toluene and methylene chloride at 0~ and -78~ when soluble polymers were prepared with intrinsic viscosity [11] of 0.1 to 0.3. It is worth mentioning that the propagation proceeded essentially by the cyclopentadiene ring and the much less reactive allyl group remained unchanged. The microstruc~e of the polymer was investigated by IR and NMR spectroscopy to confirm the above indicated 1,4- and 3,4-enchainments of the monomer units in the polyng'r chain. Later on, Mitchell et al. 3z carried out allylcyclopentadiene polymerization induced by BF3.EtzO, in chloroform at room temperature, to obtain polymers with intrinsicviscosity[11] of 0.19, whose mierostmcture indicted -53% 1,4a n d - 47% 1,2-enchainment of the repeat units. In this way the latter investigators confirmed the earlier findings of Aso and Ohara c o ~ n g the nonreactivity of the allyl group in contrast to the substituted cyclopentadiene moiety. Methallylcydopentadiene. Mitchell et al. 32 synthesized and subsequently p o l ~ a mixture of methallylcyclopentadiene isomers in the presence of BF3.Et20 to obtain poly(methallylcyclopentadiene) with 1,2- and 1,4enchainment of the repeat units in the polymer chain (Eq. 5.29).
(5.29) The reaction has been effected in chloroform at room temperature. Microstructure of the poly(methallylcyclopemadiene) has been examined by NMR spectroscopy to result i n - 35% 1,2- and --65% 1,4-enchaimn~t. Allylmethylcydopentadiene. Allylmethylcyclopentadiene was f i ~ synthesized by Mitchell and c o w o r k ~ ' $ 32 al~ employed in cationic polymerization to produce polymers with 1,2- and 1,4-enchainment of the repeat units (Eq. 5.30).
252
The reaction was carried out using an unresolved mixture of isomers in chloroform with BF3.EhO at room temperature. The NMR spectroscopy indicated a polymer having- 31% 1,2 linkages and -69% 1,4 linkages. Substituted fulvenes. Several substituted fulvenes have been polymerized with cationic initiators. The high reactivity and specific structure of these monomers will lead readily to products having particular structures and interesting properties. 6,6-Dimethylfulvene. Cationic polymerization of 6,6-
=
+
T-[
N~_~_ i,
P
(5.31)
After air oxidation the polymers became tan and insoluble. 6-Methyl-6-ethylfulvene. Mains and Day33 reported the polymerization of 6-methyl-6-ethylfidvet~ in the presence of the same cationic catalysts employed for 6,6-dimethylfidvene polymerization. Polymers with unresolved structure were indeed formed from 6-methyl-6-cthylfulvene, under the action of AICI3, FeCI3 or SnCh.5H20 in chloroform at room temperature (Eq. 5.32). n
+
"~
I1/"]p
(5.32)
Their structures corresponded to two recurring units involving different double bond systems.
253
5.1.3. Six-Membered Ring Monomers Substituted and unsubstituted six-membered ring monomers are prone for producing polymers with interesting structures and properties by cationic polymerization. Cydohexene. By conventional addition polymerization, cyclohexene will produce poly(cyclohexene) or poly(l,2-cyclohexylene) through normal opening of the carbon-carbon double bonds and subsequent 1,2-addition reactions (Eq. 5.33).
Cyclohexene polymerization under the action of cationic initiators, for instance, BF3 and HF, has been reported by Hoffman4 to lead to oligomers such as dimers, trimers and tetramers along with solid resins. In another work, Boor eta/. 5 showed that this monomer with AICI3 in ethyl chloride at low temperatures (-20~ did not give the expected polymer. From these discrepancies, it is obvious that the reaction temperature plays an essential role in promoting the propagation re,action of the initial formed carboc~ons in the presence of the acid catalyst. However, the structure of the polyng~ products may be more complex, taking into account that cyclohexyl c,arbocations can readily undergo intramolecular 1,2-, 1,3- and 1,4-hydride shifts under the action of the strong Le~s acids to generate more steric~y accessible carbooations for monomer enchainment during the propagation reaction. In this case, poly(cyclohexene) having 1,3- and 1,4-repeat units as in poly(1,3-cyclohexylene) and poly(1,4-cyclohexylene) may ocx~r along with poly(l,2-cyclohexylene) shown above (Eq. 5.34).
~
--
'=.=>
The stm~ures of such polymers, however, can be rather difli~dt to identify by standard methods. Substituted cydohexene. Several substituted cyclohexenes have been reacted with cationic initiators to produce polymers having quite different physical and chemical properties
254 l-Methylcydehexene. Cationic reaction of l-methylcyclohexene has been examined by Roberts and Day~4in the presence of AICI3 in benzene solution at 40-45~ Under these conditions, mixtures of oligomers of lmethylcyclohexene, mostly dimers, have been obtained (Eq. 5.3 5).
_/
/, (s.3s)
High polymers with this structure can be obtained only under more severe reaction conditions. ~Methyleyclohexene. In contrast to cyclohexene which did not polymerize with AICl3 in ethyl chloride (see above), 3-methylcyclohexene was found by Marek 35 to react very slowly in the presence of this catalyst in ethyl chloride solution at -20~ and -78~ At -20~ Marek obtained an oily product consisting of mixtures of dimers and trimers and at -78~ he prepared a soluble polymer which, interestingly, after fusion at 280~ developed birefringence at room temperature. 35 Furthermore, after annealing and heating, the birefringence disappeared a t - 250~ The product appeared to be crystalline showing two directions at 5.82 and 5.35A in its X-ray spectrum. Microstructure detemfination by IR and M R spectroscopy of the product thus obtained indicated 1 , 3 - r ~ t units, suggesting that the polymer corresponded to a poly(3-methyl-l,3cyclohexylene) structure (Eq. 5.36).
Notwithstanding, further confirmation of such a structure would be necessary for this type of polymer by more accurate methods. 3-Methylenecyclohexene. The cationic polymerization of 3methytenecyclohexene has been first described by Bailey and Grossens36 in the presence of BF3 to obtain poly(3-methylenecyclohexene) with rcoJrfing units resulted from 1,4-addition of the conjugated double bonds of the monomer (Eq. 5.37).
255 The reaction has been performed with neat monomer at 20~ for 2 days. Beside the major 1,4-enchainment of the repeat units in the polymer, a minor contribution of the 1,2 linkages has bccn observed. Later, Mabuchi, Saegusa and Furukawa37 reported on the polymct~tion of 3-mcthylenccyclohcxcne using several cationic initiators, for ingance, BF3.EtzO, AICI3, EtzAICI, TiCh and VCh, working in hcxane or toluene as solvents at -78~ Under these conditions, they obtained white powdery polymers that were amorphous, having a softening range of 80~ to 82~ The products were largely soluble in chloroform and benzene and could be easily cast from solutions into flexible films. Miorostructure determinations by IR and N M R spectroscopy indicated that the recurring units in the polymer chain were mainly 1,4-r l-Vinylcydohexene. The cationic polymerization of l-vinylcydohcxcne has bccn inve~gatcd by Imanishi et a/. 3s~9 using BF3.Et20 and SnCI4.CCI3COOH (TCA) in tohcnr and methylene chloride at 0~ In these conditions, they obtained white, soluble polymers of a low molecular weight, M , - 1200 ( D P - 11). Following the reaction kinetics, these authors observed that the process procc~ed initially by a very fast non.stationary phase, starting immediately after initiator supply and the final conversions being reached rapidly after this initial burst of p o l y m ~ o n . This behavior was noted with all initiators investigated, that is, with BF3.EhO in toluene and SnCh.TCA in toluene and in methylene chloride at a temperature of 0~ and contrasted to other cyclic diencs for which under certain conditions the first nonstation~ rapid polymerization is followed by a much slower stationary phase. It is interesting that an inverse relation between the initial monomer concentration, [M,], and polymer yield, Y, was found for l-vinylcyclohcxene polymerization with the above catalysts. The product [Mo]xY showed to be independent of [Mo] and had a value of ---0.55 mole~. Structure determination by bromination and IR and NMR spectroscopy of poly(l-vinylcyclohexene) indicated that the polymer arose essentially by 1,4-addition of the monomer accompanied by 1,2-addition reaction at the vinyl group in some special cases, e.g., with SnCh/TCA as a
cat yst (Eq. 5.3S).
n
.
~--
§
(5.38)
256 Interestingly, the polynuer obtained with BF3.Et20 provided evidence for the presence of methyl groups along the chain. To explain this phenomenon, these authors proposed a reaction scheme involving ismoerizafion accompanied by a hydrogen transfer from the cycle to the side chain as will be shown in a following chapter (see further). 4-Vinylcydohexene. 4-Vinylcyclohexene has been polymefized first by Marcorfi et al., 4~ using both cationic and anionic catalysts. In the presence of cationic initiators they obtained low molecular weight, amorphous polymers of ill-defined structure. Later, Butler and Miles4~ investigated the polymerization of 4vinylcyclohexene induced by cationic catalysts, for instance, BF3, BF3.EtzO and TiCh as well as with Ziegler-Natta catalysts. Thus, on using BF3 gas in methylene chloride at -70~ a conversion of 28% of monomer could be reached and the product was 85% soluble and had an intrinsic viscosity [TI] of 0.11. Microstructure examination of the polymer thus prepared by NMR spectroscopy indicated the occurrence of two major recurring units in about equal proportions in the chain (Eq. 5.39). m n
+
(5.39)
In contrast, polymerization of 4-vinylcyclohexene with the complex BF3.Et20 in methylene chloride at 0~ led to 35% conversion and to a completely soluble polymer of a very low molecular weight, [11] - 0.03. Structure investigation of this polymer by NMR spectroscopy indicated the presence of cyclic recurring units in the proportion of 80% in the chain. Poly(bicyclic) polymers used as heat resistant semiconductors were made by the catalytic cyclopolymerization of 4-vinylcyclohexene in an organic solvem4z (Eq. 5.40).
n )
(5.40)
The yield was increased, the degree of cyclization improved, reaction time curtailed and a wider ran=e of r secured by conductimz the ~rocess
257
at -l0 to -15~ in the presence of acetyl chloride. The catalyst consists of anhydrous AICI3 at an equimolar ratio of chloride and monomer. Preferably, the molar ratio of catalyst to monomer was 1.2-1.3 1. In one example, cyclopcntadiene polymerization in dichloroethane at -10~ produced a dark yellow polymer in 80% yield, having a cyclizafion degree of 99%. By optimizing the process parameters, production time of the polymer was reduced from 1-14 days to 3-4 hrs. l-Methyl-~isopropenylcydohexene (d-Limonene). Cationic p o l y m ~ o n of d-limonene has been examined by Roberts and Day~ in connection with polymer~tion of r Under the action of a series of ~s acids, for instance BF3, AICI3, AIBr3, and ZrCI4, in toluene at 4045~ r undergoes o l i g o m e ~ o n to produce mainly trimers that are similar to d-limonene oligomers. Accordingly, these authors concluded that in the presence of the above catalysts, ct-pinene readily isomerizes to dlimonene which subsequently leads to the trimers found as the reaction product. The structural studies showed that the recurring units of the oligomers were not formed by a simple 1,2-addition of the exocyclic double bond of d-limonene (Eq. 5.41).
(5.41)
but involved also the endocyclic double bond becamse ozone absorption resulted in only 0.4-0.5 double bond per repeat unit. At the same conclusion arrived also Marvel and coworkers 42"43 who reinvestigated this reaction later. 3-Methylene-6-isopropylcyclohexene(~-Phellandrene). The cationic polymenzmion of J$-phellandrene has been reported to occur in the presence of trichloroacefic acid~ to give low molecular weight polymers (DP = 9 - 10) having probably mainly 1,4-enchainments of the recurring units, acx~mpanied by some 1,5- and 1,6-enchainments resulted from intramolecular 1,2- and 1,3-hydride shifts in the propagating carbocation (Eq. 5.42).
(5.42)
I
258 Such intramolecular 1,2- and 1,3-hydride shifts can readily occur in sixmembered ring c,arbocations in the presence of acid catalysts. 1,3-Cydoheudime. Cationic polymerization of 1,3-cyclohexadiene in the presence of various initiators has been investigated by several research groups. Under these conditions, 1,3-cyclohcxadiene will give rise, by 1,2and 1,4-addition reactions at one and two double bonds, respectively, to poly(l,3-cyclohexadiene) having 1,2- and 1,4-enchainments in the polymer chain (F.q. 5.43).
n ~f~ .__._~ [~ ,~m + ~
(5.43)
The polymedz~on of 1,3-cyclohexadiene was first studied by Marvel and coworkers 4s who employed several catalysts, for instance, BF3, PFs, and TiCl4 under a variety of conditions to obtain white polymers, the soluble fractions of which had inherent viscosity between O.04 and 0.19. The microstmcture investigation indicated recurring units of 1,2- and 1,4enchainments. Thereafter, the polymerization of 1,3-cyclohexene was carried out by LeFebvre and Dawans~'4~ with several cationic initiators. On employing TiCI4 in benzene and toluene at 0~ and 30~ they obtained soluble, very low molecular weight polymers, having intrinsic viscosity 0.09. Microstructure examination suggested 1,2- and 1,4-enchainments in the polymer prepared. Interesting studies on 1,3-cyclohexene polymerization were performed by Imanishi and coworkers 4s under the action of cationic initiators. On using the catalytic systems BF3.Et20 and SnCI4/CCI3COOH(TCA) in methylene chloride or benzene at 0~ they produced soluble polymers having [rl] = 0.04-0.12 and a softening range between 114~ and 130~ Remarkably, the microstructure of the polymers prepared in this way did not seem to be affected by the nature of the catalyst. From NMR measurements, they found that ~-20% of the initial unsaturation was lost. These results were rationalized by a chain-branching of the linear unsaturated polymer. Important kinetic aspects of 1,3cyclohexadiene polymerization induced by BF3.EhO and SnCL/TCA in benzene and methylene chloride at 0~ have also been studied by Imanishi el a/. 49 They observed that the polymerization in benzene was entirely homogeneous whereas in methylene chloride the polymer precipitated during the reaction and both polymers were soluble in common solvents, having intrinsic viscosity between 0.04 and 0.12. It is essential for kinetic
259 evaluation of this process that the pob o, in the presence of SnCIdTCA was nonstationary and upon catalyst addition a fast reaction occurred, although polymerization did not go to completion and higher conversions were obtained only by the repeated addition of SnCLs. Furthermore, highest conversions were attained for lower monomer concentrations. It is interesting to note that this particular behavior of 1,3cyclohexadiene in the presence of SnCLs/TCA is not encountered with BF3.Et20, however, a similar phenomenon will be observed later with cis, cis-l,3-cyclooctadiene. To explain the difference between these two catalytic systems, Imamslu et al. 49 $ug~e~ed that SI1CLI forllls a stable complex by the interaction with 1,3-cyclooctadiene which may depress the final conversion at high monomer concentration. By contrast, with BF3.Et20, the conversion-time curves did not level off and reached expectedly 100% conversion (Figure 5.2).
Conv.,%
1
100
2
9
3
BO 60 40 2O
0
0
20
40
60
BO
100
Time, rain Figure 5.2. Time conversion curves for 1,3-cyclohexadiene polymerization in the presence of SnCI4/CCI3COOHm CH2CI2 at 0~ and varkms monomer ~ (1-0,53 Mole~; 2-1,05 Mole/L; 3-1,58 Mole~; 4-2,63 Mole/L)(Adapted from Ref.~.
In this case, 1,3-cyclohexadiene polymerization, except for the very early stages, was a stationm~ p r ~ .
260 Substituted r Substitution of 1,3- and 1,4-cyclohexadiene affords readily polymerizable monomers in the presence of several cationic initiators. p,p'-Dimethylene-l,4-cydohexadiene(p-Xylylene). Polymerization of this very reactive conjugated tetraene occurs readily in the presence of some cationic catalysts such as BF3, AICI3, TiCh, SbCIs, H2SO4, CCI3COOH, in inert solvents, for instance, hexane, at low temperatures, e.g., -78~ to give low molecular weight polymers with 1,6-enchainment of the recurring units '~ (Eq. 5.44).
(5.44) The polymers of p-xylylene provided translucent materials that were extremely brittle. l-Methyl-4-isopropyl-l,3-cydohexadiene (a-Phellandrene). Cationic polymerization of r like its 13-isomer has been reported in the presence of trichloroacefic acid to produce low moleoalar weight products. *~ Probably, polymers having 1,4-enchainments along with 1,5enchainments as result of intramolecular 1,2-hydride shift are formed (Eq.
s.45).
~ ) The detailed microstructure of such polymer was difficult to be d~~mined by standard methods 5.1.4. Seven-Membered Ring Monomers
Of the seven-membered ring monomers, only one has been reported to polymerize in the presence of cationic initiators to products with a particular structure. 1,3-Cydoheptadiene. 1,3-Cycloheptadiene will readily polymefize under the influence of cationic initiators to give poly(l,3-cycloheptadiene). Microstructure investigation by Kohjiya eta/. s~, by means of IR and NMR spectroscopy, indicated 1,2- and 1,4-addition recurring units to be
261 accompanied by rearranged monocyclic and bicyclic structures (Eq. 5.46). n
(5.46)
§
Similar reaction in the presence of anionic initiators gave polymers consisting mainly of 1,2- and 1,4-addition recurring units.
5.1.5. Eight-Membered Ring Monomers Due to theft particular structure and reactivity, several eightmembered ring monomers have been used in cationic polymerization. Depending on the starting cycloolefin, products with various properties can be produced in these reactions. l,~Cyclooctadiene. Cationic polymerization of cis, cis-cyclooctadiene has bccn investigated by Imanishi eta/. s2 in the presence of BF3, TiCL~, TiC~CCI3COOH(TCA) and SnC~CCI3COOH in methylene choride and toluene as solvents. Infrared and NMR spectroscopy indicated that the microstructure of the polymers obtained with these ~ y t i c systems were essentially the same, however, the nature of the solvent significantly influenced the enchainment. Thus, working in methylene chloride, polymers having almost exclusively 1,4-enchaimn~t have been obtained whereas those prepared in toluene a s u b ~ a l amount of branched structures, probably cross-linked, along with the linear 1,4-enchainmentwere contained (Eq. 5.47).
n
()
(s.47) p'
Nonetheless, the nature of these branched structures could not be precisely determine. The polymers prepared under these conditions were white, amorphous powders with low intrinsic viscosity, [q] - 0.10, and having a
262 softening range between 172~ and I g4~ The linear product prepared in toluene was soluble in aromatic solvents and chlorinated hydrocarbons while the branched polymer was insoluble, probably due to cross-linking. In their studies on cis, cis-cyclooctadiene polymerization with the above cationic initiators, Imanishi et a/. sz revealed interesting kinetic aspects which provide important data for evaluating the reaction mechanism. Thus, with TiCL,/TCA in methylene chloride at -78~ they observed initially a burst of polymerization on catalyst addition, however, the polymefz~tion rapidly stopped and levelled off at conversion levels determined by the amount of the catalyst added. They found a straight relation between the amount of monomer converted and the catalyst concentration, however, molecular weights were independent of catalyst concentration at all conversions. In contrast, on using toluene as a solvent, after catalyst addition and the first burst of p o l y m ~ o n , the rate did not level off but progressed steadily albeit more slowly to higher conversions. Remarkably, an inverse relationship between monomer conversion and catalyst concentration was found similarly to 1,3-cyclohexadiene reaction in the same conditions. These particular results were rationalized by assuming a two-step mechanism involving a complex of the monomer with the metal halide which either react with the monomer to give inactive species or with trichloroacetic acid tO form the growing cation (see in further chapter). Detailed studies on the cis, cis-l,3-cyclooctadiene polymerization reported subsequently Mondal and Young" using TiCI4.HzO as a catalyst. The polymer yield was essentially dependent upon catalyst and monomer concentration (Figure 5.3). These authors obtained also white, soluble polymers of low molecular weight (M~ > 10,000) with so/tening points o f 200~ The products were easily oxidizable in air. Spectroscopic measurements indicated some branched structures. Importantly, their kinetic results confirmed the observation that cis, cis-l,3-cyclooctadiene ;~olymerization with T i C L , - b ~ catalyst consists of two phases - a first rapid, nonstationary phase and a second slow, stationary phase. Furthermore, the ultimate yields were directly proportional to the concentration of active centers and inversely proportional to the monomer concentration. As will be seen in a further chapter, this behavior was explained by Mondal and Young by assuming an aUylic mechanism for the termination reaction involving a chain transfer with unreacted monomer. Further studies on the polymerization of 1,3-cyclooctadiene, under the influence of stannic chloride, reported Mondal and Young" using also water as the cocatalyst. These results were correlated with that obtained in
263 copolymerization reactions with styrene. Yield, % 90
~
/
60
30
0
0
0.2
0.4
0.6
[M],[Cat] Figure 5.3. Dependence of poly(l,3-cyclooc~diene) yield upon catalyst and monomer concentration (Curve 1 Temprature -78~ [TiCh] 0.227 mole/L, [HzO] 0.003 mole/L; Curve 2 Ten-q3rature-78~ [monomer] 6.7 mole/l, [HzO] 0.002 mole~ (Adapted from RelY3).
1,5-Cyclooctadiene.The catalytic effect of several Lewis acids on the transannular cationic polymerization of cis, cis-l,5-cyclooctadiene polymerization has been investigated by Yuan et al. 54 The highest activity was observed for EtAICIz and Et3AIzCI3 catalysts. The influence of several reaction parameters such as catalyst and monomer concentration, cocatalyst, solvent (CHzCI2/hexane) and reaction time on the polymer yield have been examined. Oligomers in 87% yield with M,= I 000-2000 and softening temperatures between 130~ and 160 ~ have been obtained. The polymer structure, as determined by NMR, IR and MS spectroscopy, involved bicyclo[3.3.0]octane-2,6-diyl recurring units (Eq. 5.48).
264
n~
~
~n
(5.48)
On the other hand, results on the cationic polymerization of 1,5cyclooctadiene in the presence of AIX3 (X=CI, Br) reported by Eastman Kodak Co 55 revealed that the polymer formed under these conditions contained mainly transannular recurring units, bicyclo[3.3.0]octane-2,6-diyl, along with low levels of non-transannular units, 1,2-cyclooctenylene (Eq. 5.49).
The polymerization was carried out under N2 at 120-160~ for 2-6 hr, using 0.01-20 wt.% aluminum chloride or bromide as a catalyst. Products with molecular weight of 500-2000, having softening points between 110150~ and containing 3-10wt.% non-transannular structures were obtained. These hydrocarbon resins had improved solubility and showed improved compatibility with other hydrocarbon materials, e.g., polyethylene and polypropylene. Such resins can be used more efficiently as wetting or bonding agents for coatings, adhesives, inks and paints.
5.2. Cationic Polymerization of Bicyclic Olefins Polymerization of bicyclic olefins by a cationic mechanism gives rise to polymers having an interesting structure due to their special reactivity. This fact stimulated many studies on the polymerization of norbornene and substituted norbornenes with various cationic initiators. Bicyclo[2.2.1]hept-2-ene (Norbornene). By cationic polymerization, norbornene will lead essentially to polynorbornene or poly(l,2norbornylene) by a 1,2-addition reaction at the carbon-carbon double bond. (Eq. 5.50).
n
(5.50)
265 However, under the action of the Lewis acids, in the norbomyl cation generated during the initiation and propagation reaction, hydride shifts and rearrangements of the bicyclic skeleton are frequently encountered phenomena. ~s Accordingly, along with the normal 2,3-enchainments of the recurring units formed by 1,2-addition reactions, 2,5-, 2,6-, 2,7- and other enchainments might occur in the polymer chain as result of 1,2- and 1,3hydride shifts or skeleton rearrangements of norbornyl cation. Of these recurring units, the most probable are 2,5- and 2,7-enchainments formed by 1,3-hydride shift in the intermediate carbocation as well as a 3,1, l-bicyclic structure generated by 1,2-migration of the bridgehead o-bond. (Eq. 5.51).
During the course of their investigations on the polymerization of norbomene with Ziegler Natta catalysts, Saegusa and coworkers s7 carried out the reaction of this monomer using several cationic initiators, for example, BF3.EhO, AICI3 and TiCh. They obtained low molecular weight polymers which they assumed contained recurring units of 2,3enchainments. Interesting studies on the norbornene polymerization reported also Kennedy and Makowski ss in the presence of EtAICI2 in ethyl chloride at low temperatures (-78~ and -100~ They obtained white, soluble polymers of low molecular weight (M~ = 1470 and 1940, respectively) but quite high softening points, 235~ and 260~ respectively. It is noteworthy that the products were found to be amorphous by X-ray spectroscopy. On the basis of infrared measurements, Kennedy and Makowski initially assumed that polynorbomene prepared contained 2,3-enchainments of the recurring units. Later on, Kennedy suggested that the structure of polynorbomene synthesized by conventional cationic catalysts is a mixture of various recurring units resulted by isomerization of the norbomyl skeleton prior to propagation, s9 A possible contributing structure of polynorbornene having 2,7-enchainments of the recurring units has also been proposed by Kennedy. 6~ Substituted norbornene. Several substituted norbomenes have been employed as monomers in the presence of cationic initiators. 5-Methylbicydo [2.2.1 ! hept-2-ene(S-Methylnorbornene). Cationic polymerization of 5-methylnorbomene has been reported by Takada et al., 6~ in the presence of BF3.EhO and AIBr3. They obtained very low yields of
266 colorless or yellowish powdery products having low molecular weight.
5-Methylenebicyclo[2.2.1 ] hept-2-ene
(5-Methylenenorbornene).
Polymerization of this very reactive monomer has been performed by Sartori et al., 62 using AIBr3, EtAICI2 and VCI4 as the cationic initiators. Interestingly, working in n-heptane at low temperatures, e.g., at -78~ with AIBr3 and EtAICI2 and at -20~ with VCh, they obtained crystalline, soluble polymers having intrinsic viscosity of-00.3 and sot~ening range between 150~ and 160~ On the basis of infrared spectroscopy, they assumed a nortricyclic structure with 2,8-enchainments of the recurring unit (Eq. 5.52).
n~
(5.52)
5-Ethylidenebicyclo[2.2.1]hept-2-ene (5-Ethylidenenorbornene). In a similar way, cationic polymerization of 5-ethylidenebicyclo[2,2,1]hept-2ene gives rise to a nortricyclic polymer with a 2,8-enchainment of the recurring units (Eq. 5.53).
(5.53) 5-Vinylbicyclol2.2.1]hept-2-ene
(S-Vinylnorbornene). Kennedy and Makowski s8 investigated the cationic polymerization of 5-vinylnorbomene in the presence of EtAICI2 in ethyl chloride at low temperatures between, e.g., -30~ and - 135~ Remarkably, when working at - 100~ and below, no polymer was obtained, but at -78~ and above the polymerizations readily occurred and white powdery products were formed. It is of interest that the polymers prepared at -78~ were largely soluble in toluene having M , - 4020 and those formed at -30~ were practically insoluble. Although from infrared spectroscopy they found the polymer to contain mainly 1,2enchainments of the recurring units, additional rearranged structures having 2,7-enchainments of the recurring units have also been proposed for poly(5vinylnorbomene) (Eq. 5.54).
267 The formation of insoluble polymers at higher temperatures suggested that cross-linking of the less reactive vinyl groups occurred under these conditions. 5-1sopropenylbicydo[2.2.11hept-2-ene (5-1sopropenylnorbornene). In the course of their studies on the cationic polymerization of bicyclic monomers, Kennedy and Makowski 5s examined also the reaction of 5isopropenylnorbornene induced by EtAICI2 in ethyl chloride at low temperatures (-30~ to -100~ In these conditions, polymerization occurred readily and, interestingly, insoluble products were obtained. These results were rationalized by assuming the reactivities of the two kinds of double bonds to be comparable in this case and accordingly cross-linked polymers to be formed even at low temperatures (-100~ (Eq. 5.55).
n
=
(5.55)
/
Bicydo[2.2.1lhepta-2,5-diene (Norbornadiene). Interesting studies on the cationic polymerization of norbornadiene in the presence of AICI3 have been performed by Kennedy and Hinlicky63. Thus, working under nitrogen atmosphere in ethyl chloride solutions at different temperatures from +40~ to -123~ (methylene chloride was the diluent at +40~ they obtained soluble and insoluble polymers, depending essentially on the reaction temperature (Table 5.1). Table 5.1. Cationic polymerization of norbomadiene with AICI3as c~lyst ~ Reaction Temp., oC -123
Solvent
CzH~CI C2H~CI 0 CzH~CI +40 CH2CI2 'Data from reference ~ -78
[M], mole~
T i m e , Yields, mm. %
M, (Soluble Fraction)
Soluble Fraction
(C,H,),% 1.39 1.39
1.39 0.69
37 25 29 4
i7.2 42.0 71.0 30.0
100 72.5 34.5 59
5520 8680
i
As Table 5.1 illustrates, only the polymers prepared at -123~
3680 2980
were found
268 to be entirely soluble in benzene. It is quite noteworthy that from IR and NMR spectroscopy these authors suggested that the mierostructure of polynorbomadiene prepared at lower temperatures contained essentially linear 2,6-enchainment of the nortricyclene recurring units (Eq. 5.56).
At high temperatures, however, cross-linked polynorbomadiene (insoluble) has been assumed to arise by further addition reactions of the second double bond from the monomer (Eq. 5.57).
13
..~
+
,,
.. , , O '
L
Jp-
(5.57)
It is also remarkable that working at -127~ for 1 hr, a linear polynorbomadiene has been prepared in 12.5% yield, having M, = 9850 and glass transition temperature, Tg = 325~ extremely high for a hydrocarbon addition polymer. Interestingly, the presence of a low temperature glassy state relaxation in the thermomechanical spectrum of this polymer at -180~ to +500~ indicated some energy dissipation at low temperature. The polymer was processable at high speeds in inert atmosphere but subject to environment degradation due to the presence of tertiary hydrogen in its structure. Terpenes. Terpene hydrocarbons are easily accessible from petrochemical resources. These monomers display a good reactivity toward cationic initiators and lead to polymers with valuable physical-chemical properties. a-Pinene. In the course of their studies on the cationic polymerization of bicyclic olefins, Roberts and Day 34 investigated extensively the reaction of both isomers of pinene, ~ and [3, in the presence of several Lewis acids such as BF3, AIBr3, AICI3 and ZrCI4 as catalysts. Working in toluene at 4045~ they obtained low molecular weight products having softening points in the range 67-85~ A correlation between the softening points and molecular weights of the polymers prepared from ~-pinene was observed likewise to d-limonene. In addition, a similarity for some other physical characteristics e.g., density and refractive index of the polymers prepared from the two monomers was found. It is highly probable that, as
269 shown in an earlier section, the polymers obtained from a-pinene and dlimonene are similar because prior to polymerization a-pinene may readily be transformed into d-limonene. Accordingly, the microstructures of the polymers obtained from ct-pinene, like those ofd-limonene, will not involve recurring units formed by a simple 1,2-addition reaction of the endocyclic double bond but also rearranged structures (Eq. 5.58).
n
~
(5.58)
n
3-Carene. Cationic p o l y m ~ o n of 3-carcne will form similar products like d-limonene and a-pinene due to the easy interconversion of these monomers under the reaction conditions (Eq. 5.59).
In
n
n
~
~
n
(5.59)
Other bieydie olefins. A substantial number of other bicyclic olefins have been used as monomers in the cationic polymerization. Of these monomers, 5-methylbicyclo[2.2.2]oct-2-ene, bicyclo[6.1.0]non-4-en~ bicyclo[4.3.0]nonatetraene (indene) and bicyclo[4.4.0]decatetra-l,3,5,7-ene (1,2-dihydronaphthalene) and their derivatives are of a special interest. 5-Methylbicydo[2.2.2]oct-2-~ne. Cationic polymerization of 5methylbicyclo[2,2,2]oct-2-ene has been briefly reported by Takada et al. 6~. On using the catalytic complex BF3.Et20, they obtained low yields of products at 0~ and -78~ Probably, linear polymers having essentially saturated recurring units formed by normal 1,2-addition reaction accompanied by rearranged structures have been formed (Eq. 5.60).
270 Bicyclo[6.1.0]non-4-ene. According to Pinazzi et al., 64 the cationic polymerization of bicyclo[6.1.0]non-4-ene ~ s by transannular reaction and yields the polymer with a methylbicyclo[3.3.0]octane r ~ r r i n g unit in the chain (Eq. 5.61).
o (--)>
--,
Bicydo[4.3.0lnonatetraene (lndene). Due to its high reactivity and ready availability, cationic polymerization of indene has been extensively studied and well documented for more than six decades. By 1,2-addition reaction, this monomer will form the vinyl polymer, polyindene, having 2,3enchainments of the recurring units (Fxl. 5.62). m
9
]J3
The first investigations on this monomer come from the early work of Whitby and Katz6s and Staudinger and coworkerss6 who reported fundamental results on the polymerization of indene in the presence of several cationic catalysts. Whitby and Katz, for instance, carried out indene polymerization in the presence of SnCh and SbCls in chloroform to obtain polymers having DPs in the range 15-15. On the other hand, Staudinger and coworkers explored several cationic catalysts among them SnCh, TiCLs, SbCls, SbCI3, FeCI3 and BF3 to produce high molecular weight polymers. Further work on this monomer was reported by Brown and Mathieson6~ to yield polyindenes using CCI3COOH as catalyst. Intensive investigations on some important aspects of indene polymerization have been performed by Sigwalt and coworkers, a Thus, pioneering kinetic work has been reported by Sigwalt69 and Marechal 7~ on the polymerization of indene and its derivatives under various conditions. On using several catalysts, for instance, BF3, TiCh, SnCI4 etc., in chloroform and methylene chloride, Sigwalt succeeded to produce high molecular weight polyindenes working at temperatures between 0~ and 90~ Noteworthy, these authors observed that the intrinsic viscosity
271 [rl] of polyindenes thus obtained increased with decreasing temperatures. In addition, important equations to calculate the molecular weights from intrinsic viscosity were deduced. In parallel work, Sigwalt's coworkers found that the high molecular weight polyindenes were branched polymers. Some of these polymers have particular properties; for instance, the softening point of a polyindene with [11] = 0.2 i s - 240~ and that with [rl] = 0.7 is 250-260~ Remarkably, above these temperatures the polymer has a tendency to yellow and can be molded into brittle films. Important mechanistic aspects on the cationic polymerization of indene have been subsequently explored by Sigwalt and coworkers. 7~78 In refined experiments using the "stopping" technique (i.e., working under the highest possible degree of purity) they evidenced the effect of cationogenic agents on the initiation reaction in the presence of TiCh, SnCh and Ph3C+SbCI6 catalysts. Based on these data, these authors could elegantly demonstrate that H20 and HCI are real initiators of indene polymerization in the presence of TiCh and SnCI4 in methylene chloride as a solvent. Significant findings in the work with SnCI4 were that indene polymerization occurred even under the highest degree of purity of solvent and catalyst and that the polymerization was nonterminating, that is, like a "living" system resumed the polymerization and reached complete conversion when new monomer was added. The first finding gave important information about the nature of the initiation reaction under the direct influence of the Lewis acid and the second about the nature and life of the propagating carboeation generated under the action of this catalyst. Further interesting thermodynamic data provided by Sigwalt and coworkers TM concern the enthalpy of indene polymerization initiated by TiCI3OBu in methylene chloride found to be 13.9 kcal/mole at temperatures between + 10~ and -70~ Recently, the polymerization of indene in methylene chloride solution initiated with the cumyl methyl ether/titanium tetraehloride and cumyl chloride/titanium tetrachloride systems has been thoroughly investigated by Sigwalt and coworkers 8~ as a possibly "living" system. In the first work in this series, it has been found that transfer does occur during the polymerization of indene initiated by cumyl methyl ether/titanium tetrachloride at -40~ and that it became undetectable only at -75~ From these results, it was considered that the experimental data could be accounted for by a "conventional" cationic mechanism, the "living" character depending on two ratios: the monomer to initiator ratio ([M]o/[l]o), which determines to what extent transfer can remain
272 undetected, and the propagation to initiation rate ratio (Rp/P,q). When this last ratio is low enough, initiation is quantitative and an increase of the M, proportional to conversion can be observed. For low enough values of these two ratios, the reaction has the main features of a living polymerization. Subsequent work using cumyl chloride/titanium tetrachloride as the catalytic system, provided further support for these conclusions. Polymerization of indene with cumyl chloride/titanium tetrachloride (CumCI/TiCI4) has been carried out in chloromethylene at -40~ -75~ and +5~ The effect of the reaction temperature on the process parameters was obvious. Table 5.2 summarizes below some results recorded, working with cumyl chloride and titanium tetrachloride at -40~ Table 5.2 Polymerization of mdene (M) with the CumCI/TiCI4 system in methylene chloride at -40~ ~b [M] [CumCl] Mn M,,q~, Mll IN] mole.L"~ mole.L'lx 103 (Expt) mole.L'lx 10 3 (Calc) 0.43 0 87000 2.3 0.6 0.107 3.0 6100 4150 4.5 2.0 3.0 0.215 13200 8300 4.8 1.9 0.430 3.0 25900 16600 4.9 1.9 3.0 0.650 27150 25000 4.2 2.8 0.860 3.0 38050 33200 3.7 2.6 1.0 0.43 40000 50000 3.6 1.2 3.0~ 0.43 26000 16600 4.2 1.9 0.434 3.0 27300 ! 6600 3.2 1.8 i 'Data from referencei~; 'b[TiCh]=2xl02 mole.Li., ~[TiCh]=10~ mole.L'~; dCH2CI2/C6HI4(60/40 V/V).
As Table 5.2 shows, initiation with titanium tetrachloride alone produced a polyindene with a high molecular weight, M~=87000 and, in this case, initiation probably resulted from the presence of adventitious cocatalyst present in the solution. In the presence of cumyl chloride, the molecular weights of the polymers were much lower, but still higher enough than the values calculated assuming quantitative initiation by the cumyl chloride, and they increased with the monomer concentration. This increase was practically linear for monomer to initiator ratios up to 150 ([M] = 0.43mole.L ~, [I] = 3x10 3 mole.L ~) (Figure 5.4), and there was a curvature for higher values of this ratio ([M]=0.86 mole.L "~, [M]/[I]=290).
273 Besides, for a value of[M]/[l] equal to 430, the experimental M, was lower than the calculated one. M.
4OOO
3OOO 2OOO
1000
0
I
0.2
i
0.4
&
0.6
|
0.8
"
1.0
[M]o, mole/l Figure 5.4. Polymerizationof mdene reduced by CumylCIfricI4 at -40~ (Adaptod from Ref '1) The curvature of the M~ v s [M] plot and the lower values of M~ than expected could be attributed to transfer reactions, which have been shown to take place in the case of initiation with cumyl methyl ether, also occurring in this system. Attempts to increase the initiation rate at higher TiCl4 concentrations (0.1 mole.L~ instead of 2xl0 2 mole.L~) did not significantly change the M, of the polyindene. Similarly, the use of a mixture of solvents to shift a possible ionization equilibrium toward the ion pairs, supposedly less reactive, and to decrease the propagation rate failed to achieve complete initiation. In all these experiments, the molecular weight distributions of the polymers were rather broad (M,~q~ from 3.6 to 4.9), broader than those observed without cumyl chloride. Consequently, the cumyl chloride/titanium tetrachloride initiating system alone did not yield a "living" polymer. It is well known that addition of electron-donating compounds in cationic polymerization initiated with alkyl chloride and titanium tetrachloride or boron trichloride, which would otherwise yield a "nonliving" polymer, may turn it into a "living" system. Accordingly, Sigwalt and coworkers s~ examined the influence of various electrondonating compounds used in the polymerization of indene induced by cumyl
274 chloride and titanium tetrachloride (Table 5.3). Table 5.3 Polymerization of mdene (M) with the CumCFTiCh system (I) in the presence of electron-donating; compounds [ED] "b Electron Donor [ED] lED] M. MII (~Calc) (Exit) Nolle 0 13200 8300 Dimethylsulphoxide 2.5 8600 8300 Dimethylfonnamide 2.5 15700 8300 Dimethylformamide 7.0 5300 8300 Dimethylacetamide 2.5 10800 8300 Ethyl acetate 2.5 13200 8300 2,4-Pentanedione 2.5 9000 8300 2,5-Di(t-Bu)-4-Me-pyridine 0.1 13500 8300 2,5-Di(t-Bu)-4-Me-pyridine 0.5 13800 8300 Tetrahydrothiopheae 2.5 5400 8300 'Data from reference st; b [M]=0.215 mole/L; [CumCl]=3xl0 .3 [TiCh]=2xl0 z mole/L; temperature = -40~ solvent= CHzCIz.
4.8 3.1 3.1 3.3 3.3 5.0 4.4 3.9 3.2 4.0 mole~,
Among the various compounds used, dimethyl sulfoxide (DMSO) alone yielded the expected M, and the narrower molecular weight distributions. Table 5.4 Influence of dimethyl sulphoxide (DMSO) on the polymerization of mdene ~ ! 1 with the CumCI/TiCL mitiatinl] sTstem'~b [cumcl] M,JM= MII [M] Mll IN] (Expt) mole.L'~xl03 mole.L ~ mole. L~x 103 (CalQ 0 0.8 65000 0.43 2.4 3.0 86OO 8300 2.9 0.215 3.1 3.2 3.0 15500 16600 0.43 3.1 2.7 3.0 27100 24500 3.7 0.63 ~ 3.3 3.0 30300 33200 3.2 0.86 1.7 1.5 29300 33200 2.8 0.43 1.0 1.0 25000 25000 2.8 0.215 1.1 1.0 43000 50000 2.5 0.43 1.4 100000 1.0 71200 2.1 0.86 'Data from reference s~. b[TiCI,]=2xl0 "z mole~;[DMSO]=2.5xl0"3mole/L; Solvent=CHzCIz,Temperature=-40~ 100%;~Incremental monomer addition. [M]o = 0.43 mole/L.
275 On the other hand, 2,5-di-tert-butyl-4-methylpyridine, which was used at various concentrations, had no apparent influence on the M~ of the resulting polyindene. Consequently, it was of interest to observe the effect exerted by dimethyl sulphoxide in conjunction with the CumCl/TiCh initiating system on the polymerization of indene. Some results obtained under these conditions are given in Table 5.4. As it can easily be observed, in the presence of dimethyl sulphoxide (2.5x10 3 mole.L'm), for [M]/[I] ratios lower than about 200, the M~ increased linearly with the weight of the polymer formed and was only slightly lower than the calculated value of M~ up to 30000 (Figure 5.5).
MII 1
8OOOO 60000 9
2
4O00O 20000 0
o
0.2
0.4
0.6
0.8
[M]o, mole/l Figure 5.5. Polymerization of mdene with the CumCFTiC~MSO initiating system (Adapted from Ref. '~) It was inferred that this result might arise from moderate transfer reactions whereas at higher values of the [M]/[I] ratios, transfer became clearly detectable. The linearity of the corresponding Mayo plot, even for lower values of 1/Dp.0, (i.e. [C]0/[M]0), showed that transfer reactions of zero order with respect to the monomer, if they take place at all, are negligible. The M,/M~ values in this case were obviously smaller than in the previous experiments, for instance 2.1-3.3 instead of 3.6-4.9. With the CumCVl'iCh initiating system, it appears that DMSO provides the appropriate characteristics of a "living" system. As known from the work of Higashimura et al. s2, addition of a common ion salt to a cationic initiating system yielding a bimodal molecular
276
weight distribution often suppresses one of the molecular weight peaks. This phenomenon has been attributed to a shift of a dissociation equilibrium suppressing the free ions, the remaining ion pairs being the only propagating species. Studying the effect of common ion salts in the polymerization reaction of indene, Sigwalt et al. 8~ observed that, addition of tetra-nbutylammonium chloride or of tetra-n-butylammonium pentachlorotitanate to the CumClffiCI4 initiating system, in the absence of DMSO, caused a lowering of the molecular weight, M,, from 26000 to 14000, which is near the calculated value for a living polymer (Table 5.5). Table 5.5 Cationic polymerization of mdene with TiCh-based catalysts in the presence of common ion salts (S)~b
[S] d Yield M, IN]mole M/ MB % mole.L'~xl03 (Calc) (Ex~) L'IxI0 3 M, 16600 25900 ] .9 4.9 100 TiCG/CumCI 0 3.7 2.4 n-Bu~CI 100 16600 13500 14450 3.4 2.4 n-Bu~TiCI~ 100 16600 10600 4.7 2.3 100 11100 TiCh/CumOMe 0 ~450 5.2 100 10100 n-Bu~Cl ,2.0 *Data from referencesI~ bSolvent=C'H2Clz; Temperature = -40"C; Reaction time=6 mm; 'CumCl=3xl0 3 mole/L; CumOMe = 4.5x10 "3mol~,ds = 8x103 mole/L,. Catalyst~
In addition, in all cases the molecular weight distribution was significantly narrower than in the absence of common ion salts (e.g., 2.4 instead of 4.9). It is obvious that the common ion salts have an similar effect to that of DMSO. This effect was rationalized by assuming that the salts shift a dissociation equilibrium toward the formation of the ion pairs and covalent species. In their absence, the broadening of the molecular weight distribution could result either from a higher reactivity of the free ions or only from their slower interconversion into ion pairs and covalent species, or from both (Eq. 5.63). ; ..... - - - ; - c - c ,
,
"nc,,
-,--'-
e
)
(s.63)
Comparative experiments carried out with the cumyl methyl ether/titanium chloride initiating system showed that tetra-n-butylammonium chloride had a little effect on the molecular weight distribution of polyindene. In this case
277 of initiation one might have thought that, although the counterion initially formed is the methoxytetrachlorotitanate (TiChOMe'), pentachlorotitanate ions (TiCls') would be rapidly formed through reactivation by the excess TiCI~ of the dormant chlorinated end groups (if it is assumed that reversible termination involves the addition of a chlorine atom from the TiChOMe anion). If this was the case, the propagation would involve mainly pentachlorotitanate counterions at the end of the polymerization, and a common ion effect would have been observed with ~Bu,NCI in the polymerizations initiated with cumyl methyl ether as has been found with cumyl chloride. The absence of a significant common ion effect was rationalized by inferring that the active centres present in the polymerization of indene with the CumOMe~iCh system were different from those formed with the CumCl/TiCh system and that they were presumably methoxytetrachlorotitanate anions. These ions may result either from reversible termination by preferential addition of a methoxy end group instead of a chlorine atom or from a relatively slow reactivation of the dormant chains, the main part of the polymerization involving the initially formed methoxytetrachlorotitanate anions. To check the behavior of a system in which both oounterions are present, polymerization of indene (0.43 mole~) using a mixture of cumyl chloride and cumyl methyl ether associated with titanium tetrachloride was performed by Sigwalt et al. st at -40~ without dimethyl sulphoxide (Table 5.6). Table 5.6 Polymerization of mdene (M) initiated with cumyl chloride (It) and cumyl nmhtyl ether (Iz) in conjunction with titanium tetrachloride at -40~ ~b
t-l,i mole/LxlO~
mole/LxlO3
Yield %
1.5
1.5
100
9r i m m,m
",
Mo (Exix)
16000
.
Mo (Calc)
MJM.
16600
3.2
= 0.43 mole~, [TiCh]=2xl0 "z mole/l, ReaSon tnne
= 6 min.
The molecular weight, M., of the resulting polyindene had the value calculated assuming quantitative initiation by both compounds (16000), while initiation by the equivalent amount of cumyl chloride was not
278 quantitative as noted earlier (Table 5.3).The moleoAar weight distribution was narrower than with cumyl chloride alone (3.2 instead of 4.9) but wider than in the case of initiation with cumyl methyl ether alone (2.3). These authors assumed that the presence of propagating species resulting from initiation by cumyl methyl ether slowed down the global propagation rate, thus allowing complete initiation by the cumyl chloride, even in the absence of dimethyl sulphoxide, but the presence of two different types of growing centres broadened the molecular weight distribution as compared to that observed with initiation by cumyl methyl ether alone. A number of reactions of indene were carried out by Sigwalt et al. s~ at -75~ at which temperature a "living" polyindene could be obtained using cumyl methyl ether and titanium tetrachloride as a catalyst. However, when cumyl chloride was used as initiator, the molecular weights, M,,, of the polymer were considerably higher than the calculated values in the presence of dimcthyl sulphoxide. They increased with the conc,entration of indene, but their graphic representation exhibited a curvature at high indene concentration (see Figure 5.5 and Table 5.7). Table 5.7 Polynmrization of mdene (M) with the sysmn cumyl chlorideffiCI4 in the pr~smce of din~thyl sulphc xi'de ([DMS()~)at -75~ "b [DMSO] M. M. M.I [M] mole/LxlO3 molo/Lxl03 (:Expt) (,Calc) MI mol/L 0.2 8300 3.1 0 124000 0.215 0.82 3.1 2.5 15100 4150 0.107 0.86 0.215 2.5 28800 8300 3.3 1.04 0.43 2.5 48000 16600 3.7 1.6 0.86 2.5 62400 332,00 4.4
'Data from reference ,t; b[TiCh]=2xl0-2 mole/l~, Solvmt=CH2Cl2. The high values of M, were the consequence of incomplete initiation, and the curvature might be attributed to a more efficient initiation at higher monomer concentration, to the incidence of transfer reactions, or to both. But, since the transfer has been found to be very low in these conditions with cumyl methyl ether, it seemed be much less important in the present case as compared with results obtained at -40~ These results indicated that the initiation to propagation rate ratio was less favorable in polymerizations with cumyl chloride than with cumyl methyl ether. Alternatively, at higher temperatures, initiation may be faster,
279 but transfer reactions must also be more important than at lower temperatures. On carrying out the polymerization of indene with cumyl chloride and titanium tetrachloride at +5~ without DMSO, Sigwalt e t al. s~ found that for [M]/[I] ratios up to 150 the molecular weights, M,, of the resulting polyindene had the values expected for a living polymer. The molecular weight distributions were narrower than those obtained at -40~ in the presence of dimethyl sulphoxide that is 1.7-1.9 instead of 2.2-3.3. As in the previous systems employed by these authors, at higher monomer to initiator ratios, the curvature of the plot of M, v s the amount of polymer formed showed the incidence of transfer reactions ( see Table 5.8 and Figures 5.6-5.7). Table 5.8 Polymerisation of mdene (M) with cumyl chloride (I0 and TiCI4 at +5~ with and without d i m ~ i sulphoxide, DMS0) "b [I,] [DMSO] M, M. MJ mole/Lxl03 mole/LxI03 Mm (Calc) (ExpO 3.0 4OOO 4150 0 1.8 3.0 83O0 8500 1.8 0 3.0 17000 16600 1.9 0 3.0 0.86 ' 16100 33250 2.4 0 170OO 3.0 0.86a 33250 2.4 0 25000 1.0 19O0O 0.215 1.7 0 50000 3O9OO 1.0 1.8 0.43 0 100000 1.0 0.86 44300 2.0 0 25000 1.0 1.7 16800 0.215 2.5 50000 1.0 0.43 28000 1.8 2.5 1.0 0.86 41000 100000 2.2 2.5 'Data from reference s~; b[TiCL,]=2xl0"z mole/L, Solvent=CHzCIz; qncremental monomer addition (0.43 mole/L) after 6 rain; aSew,ond incremental monomer addition (0.43 nmle~) aRer 45 s. [M]
mole/L 0.107 0.215 0.43
As transfer reactions take place also at -40~ they should be still more important at +5~ but the R r ~ ratio might be more favorable at this temperature and might allow complete initiation and the formation of a "living" polymer when the molecular weights are low enough. However, the possibility of a compensation between partial initiation and transfer could not be entirely ruled out. To investigate this aspect, a few experiments of indene polymerization were also carried out by Sigwalt e t al. s~ with the cumyl chloride~iCl4 system in the presence of dimethyl
280
MI 50000 40000 30000
10000 0
0.2
0.4
0.6
0.8
[M]0, mole/L Figure 5.6. Variation of M. in polymerization of mdene with CumClfriCh. Reaction conditions Temperature = +4~ [CumCl]= Curve 1 l xl0 3 mole/L (without DMSO), Curve 2" lxl0 "3 mole~, [DMSO] 2.5x10 "3 mole/L, Curve 3" 3x10 "3 mole/L (without DMSO) (Adapted from RefS~).
MB 80000 60000
.
!
40000 -
20000 0
0.2
0.4
0.6
0.8
-
2
1.0
[M]0, mole/L |
Figure 5.7. Variation of M. in polymerization of mdene with CumClfriCl3OBu initiating system. Reaction conditions: Solvent CHzCI2, Reaction time 6 mm, Temperature --40~ [TiCI3OBu] = 2x 10.2 n~le/L; Curve 1" [CumCl]= I x 10.3 mole./L(without DMSO), Curve 2" [CumCl] 3x10 "s mole/L(without DMSO) (Adapted from Ref.S~). --
281 sulphoxide at high monomer to catalyst ratios (Table 5.8). In this case, the initiation should be quantitative, since it was already so at -40~ and the difference between the calculated and measured values of the molecular weight should result exclusively from a transfer process. As Table 5.8 shows, the molecular weights of polyindene, M,, were not significantly lower than those obtained without dimethyl sulphoxide. This finding suggested that initiation was practic~ly quantitative at this temperature, even without dimethyl sulphoxide, and that the deviations from the calculated values are due to transfer reactions. This fact also showed that the addition of dimethyl sulphoxide to the initiating system did not suppress or decrease the transfer process. Significantly, the Mayo plot yielded a value of the transfer constant equal to 1.4x10 3 for this polymerization (Figure 5.8, Line A). 103/Dp,
2:5
(A)
20 15 10
O
0.5
I.O
1.5
2.0
2.5
103/DP0 Figure 5.8. Measunanmt of the transfer constant to the monomer in the polymerization of mdene with CumCFTiCh~MSO in CH2CI2 at +5~ Reaction conditions: [TiCU] = 2x10 "2mole~, [CumCl] = 3x10 "3nmle~, 2.5x 10.3 nmle~ and i x 10.3 nmle/L (Adapted from Ref.Sl). It is noteworthy that in the polymerization of indene with these TiCh-based initiating systems, reversible termination by collapse of the carbocationic pentachlorotitanate ion pair should yield a polyindene with a chlorinated end group. If this is the case, the model compound of the chlorinated end group, l-chloroindan, should be an initiator for this polymerization. The results of indene polymerization initiated with lchloroindan instead of cumyl chloride in the catalytic system are presented
282 in Table 5.9. Table 5.9 Polymeriz~on of mdene(M) usmg I-chloromdan (I,) and TiCI4 (12) in the presence of dina~yl sulphoxide (DMSO) at -40~ ~b
[1,] Mj M~ MII IN] mole,/Lx103 mole/Lxl 03 (Expt) M. (Calc) 3.0 0.215~ 15500 83O0 3.7 1.6 0.215 1.5 14300 16600 3.0 1.8 0.215 3.0 7800 83OO 3.0 3.2 0.43 3.0 13200 16600 3.6 3.8 0.86 3.0 24500 332OO 3.0 4.0i "Data from reference "; b[TiCh] = 2 x 10" mole~; [DMSO] = 2.5 x 10;~ mole~, Solvent = CH2C12;~[DMSO] = 0. [M]
molelL
As with cumyl chloride, the presence of dimethyl sulphoxide was necessary to obtain the expected molecular weights, M~. This result suggested the possibility of a reversible termination in the case of initiation by titanium tetrachloride (Eq 5.64).
-::::::::::-C-el
+ TiCl4
~---
The data were similar to those obtained in the polymerization reaction with cumyl chloride, but in this case some scatter of the molecular weight was observed while the Mayo plot had an intercept of 1.4x10 .3 instead of 6x10 4. As it has been showed above, the n-butoxytrichlorotitanium/cumyl methyl ether initiating system yielded polyindenes with molecular weights, M,, in good agreement with the calculated values, and it has been postulated that the initiating system producing alkoxytitanate counterions give better results than those involving pentachlorotitanate counterions. These results were confirmed in further studies on the indene polymerization performed by Sigwalt et al. s' with the initiating system derived from cumyl chloride/n-butoxytrichlorotitanium. On carrying out the polymerization of indene with this catalytic system in the absence of dimethyl sulphoxide, these authors obtained a fairly good agreement between the experimental and calculated molecular weights, M., although transfer was apparent at high monomer to initiator ratios, as in other systems (Table 5.10).
283 Table 5.10 Polynamza~on of mdme (M) with the CumCFTiCI3OBu initiating system without DMSO "b
[l~
tCumC'i
mole~
moloFLxlO3
0.215 0.43 0.63' 0.86 0.215 0.43 0.86
3.0 3.0 3.0 3.0 1.0 1.0 1.0
MII
(ExpO
M.
MJ
(CalQ
Mo
N moled.,x I (P
6450 13500 22100 27200 20000 43700 79000
8300 16600 24500 33200 25000 50000 10(0)00
2.4 2.0 2.1 1.9 1.8 1.6 2.0
3.6 3.7 3.8 3.7 1.2 1.1 1.2
'rim frm ref oe"; [TiCl3OBul=2xl0 "2 m o l ~ ,
Solvent = CHiCle, Ten~rature = -40~ qncrenamtal monomer addition; [M]0---0.43 mole~. As Table 5.10 shows, the polyindene obtained had the narrowest molecular weight distributions observed with cumyl chloride, i.e. from 1.6 to 2.4, which should be expected if the global polymerization rate was smaller with this weaker Lewis acid. Relevant data on the qiving" polymerization of indene obtained by Sigwalt et al. .~ using cumyl chloride or cumyl methyl ether associated with titanium tetrachlofide or n-~toxytitanium trichloride in methylene chloride at -40~ are presented in Table 5.11. Table 5.11 "Living" polymerization of indene induced by TICK- and BuOTiCI3-based mitia~g systems"b
Initiating System
MJ Assunaxl Cotmterion
Mo
Living Polymer
,
BuOTiCl3/CumOMe BuOTiCI3/CumCI TiCIdCumOMe TiCldCumCI TiCIdCumCFDMSO TiCIdl-Cl-lndan/DMSO "Data from refermce
1.6-1.7 TiCI3OBuOMe" 1.6-2.4 TiCI4OBu" 1.9-2.3 TiCI4OMe" + TiCI; 3.6-4.9 TiCI~2.1-3.2 TiCI~TiCI; 3.0-3.7 t'Temperamre = -40*C, Solvent = CHzCIz.
yes yes yes no
yes yes
284 As Table 5.11 shows, the initiating systems having an alkoxy group in one of the components (either cumyl methyl ether or BuOTiCI3) yielded "living" polyindene without the addition of dimethyl sulphoxide. A common feature of these systems is that the assumed counterion is an alkoxychlorotitanate (TiCIs.,(OR)," inste~ of TiCIf. From this observation, it was inferred that such counterions play an important part in "living" polymerization of indene with these initiating systems. A possible explanation offered by these authors are either that the propagation rate constant on the ion pairs might be lower with the alkoxytitanate counterions than with TiClf or that the ionization constant might be lower in the former system. This would decrease the propagation rate and increase the number of interoonversions between dormant and propagating species during the polymerization and would make the molecular weight distribution narrower. Expectedly, a reduction of the concentration of free ions if Ka is lower would have the same effect. Significant work on the relationship monomer structure/reactivity connected with cationic polymerization of indene carried out Higashimura and coworkers. 83 On using the catalytic complex BF3.Et20 in ethylene chloride at 30~ they found that the rate of indene polymerization was greater than that of styrene and thus indene showed to be more reactive than styrene. At the same time, the average polymerization degree of polyindene was much larger than that of polystyrene under the same conditions (DP~ = 250 and DPo = 40). In addition, the difference in reactivity between the two monomers has been evidenced also in the c o p o l y m ~ o n reacfons as it will be seen in a further chapter. These results suggested that the increased reactivity of indene above that of styrene was a measure of the ring grain in the five-membered ring of indene. Synthesis of optic~ly active polyindene by indene polymcr~tion induced by BF3 associated with optically active alcohols, e.g., l..ocmethylbenzyl alcohol, has been investigated by Schmidt and Schuerch. ~ When working in n-hexane and chloroform as solvents, they obtained polyindene in high yield but the product did not exhibit optical activity, birefringence and crystallinity even after stretching a cast film. Another interesting work on the polymerization of indene by stable caubenium ion salts has been reported by Ledwith and cowrokers, ss They used as catalysts tropylium hexachloroantimonate and xanthylium perchlorate in methylene chloride to produce polyindene having molecular weight about 10000. Of the two initiators, the tropylium compounds showed to be superior to
285
xanthylium salt. It is important to note that spectrophoto~c analysis indicated the tropylium moiety to be incorporated as a chain-end into the polymer. Polymerization of indene by methylethylketone peroxide in liquid SOz provides an efficient way to produce high molecular weight polyindene. This reaction has been carried out by Filho and Gomes=s'r7on bubbling 02 or N2 through a solution of indene into liquid SOz at -10~ or +25~ and subsequently adding methylethylketone peroxide when polymer precipitation ensued immediately. On working at -10~ molecular weights of polyindene ranged from 55000 to 66000. It is remarkable that the molecular weight distributions were rather low (MJM, = 1.6-1.8) and they seemed to increase with conversions between 17 and 47%. This finding is somehow contrasting with the molecular weight distributions of polyindene obtained with conventional Lewis acids such as AICI3 and TiCI4 in various solvents at 0 to -76~ (M,JM, = 3.2-4.6). Based on these results, the above authors assumed the formation of a charge complex, [indene]*SOz" as the initiating species in the indene polymerization induced by methylethylketone peroxide. Substituted indenes. A large number of monomer derived from substituted indene have been used in cationic polymerization to produce polymers with various structures and properties. I-Methylindene. Sigwalt and coworkers ss investigated the polymerization of l-methylindene in the presence of several cationic catalysts such as BF3, TiCI, and SnCL~ in methylene chloride at various temperatures. The products were low molecular weight polymers, probably having 2,3enchainments as result of the 1,2-addition reaction at the double bond (Eq. 5.65).
n
=
(5.65)
The catalysts employed displayed a range of activity, TiCk inducing a fa~er reaction rate while SnCL~ a slower polymerization. Of the above catalysts, BF3 produced the polymers having the highest viscosity at -72~ e.g., [11] = 0.17, corresponding to molecular weights o f - 30000.
286 2-Methylindene. Due to the presence of a methyl substituent at the double bond, cationic polymerization of 2-methylindene occurs with much lower rates and to lower molecular weights as compared to its l-methyl isomer. Thus, under the action of BF3 in methylene chloride at -72~ Sigwalt and coworkers ss obtained in 68% yield a polymer having intrinsic viscosity, [TI], of 0.042 (Eq. 5.66). 9
n
n
=
(5.66)
It is interesting that with TiCh, methanol insoluble polymers could be obtained only in the presence of relatively large amount of water. 3-Methylindene. In attempts to polymerize 3-methylindene in the presence of BF3 and TiCI4, Sigwalt and coworkers" obtained only dimers of this monomer. (Eq. 5.67). . I
n
in
(5.67)
Notwithstanding, 3-methylindene showed to copolymerize with indene and l-methylindene, under appropriate conditions. 5-Methylindene. The cationic polymerization of 5-methylindene has been investigated by Marechal and coworkers =9who used several catalysts such as AICI3, TiCLs, SnCh and BF3.Et20. On working with 0.224M and 0.01M concentrations in methylene chloride at -72~ they obtained 100% yields with the last three catalysts but the molecular weights were rather low (Eq. 5.68).
n (--~ /
[ )in ~
(5.68)
287 Intrinsic viscosity [rl] of 0.5 to 0.8 were reported. The decomposition temperatures of the polymers thus prepared were in the range 250-260~ In contrast to these results, in presence of AICI3 or HzSO4, practic~y no polymer was obtained. 6-Methylindene. Interesting investigations have been carried out by Marechal and coworkers t9 on the cationic polymerization of 6-methylindene at very low temperatures in the presence of different catalytic systems. Using, for instance, TiCl4 in CHFzCI or mixtures of CHFzCI/CzHsCI, polymerization of 6-methylindene readily ocA~rred in each of these solvents at-140~ and -170~ to -180~ respectively, and polymers in high yields (100%) were obtained having intrinsic viscosity [TI] = 0.4-0.6 (Eq. 5.69).
in n
.~ \
(5.69) \
On the other hand, at -100~ in pure ethyl chloride with the same catalyst, products of [TI] = 1 were prepared. At higher temperatures, however, using TiC~ BF3.Et20 and HzSO4 as catalysts in methylene chloride, polymers having intrinsic viscosities [11] in the range 2.2 to 4.5 were recorded. It is remarkable that these values are among the highest values of intrinsic viscosity ever attained for the polymers of indene or its substituted monomers. They correspond to a very high molecular weight, for instance, the [TI] = 4.5 to Mo = 2.5 x 106 and Mw ~ 7 x 106. Quite relevant is the effect of the temperature on the intrinsic viscosity for poly(6-methylindene) prepared with TiCh and BFs.Et20 as catalysts. In their studies on these parameters, the above authors found that the molecular weights of the polymers i n c r ~ significantly with decreasing temperature. For instance, at complete conversions of the monomer, with TiCh in the range +15~ to -80~ [11] of polymers increased from 0.31 to 2.35, whereas with BF3.EtzO in the range -40~ to 70~ [11] increased from 2.2 to 3.5, respectively. 7-Methylindene. 7-Methylindene was also found to readily polymerize under the influence of several cationic initiators by Marechal and coworkers, s9 They employed as catalysts BF3.MezO, BF3.Et20, and TiCI4. Working in methylene chloride at -72~ with 0.22M monomer and 0.01M catalyst, yields of 100% polymer were obtained but the intrinsic viscosities
288
[11] were in the range 0.48 to 0.82 (Eq. 5.70). (5.70)
Furthermore, significantly, the decomposition temperatures of these polymers were between 252~ and 258~ l,l-Dimethylindene. Marechal and coworkers 9~ investigated the cationic polymerization of this l,l-disubstituted indene with a variety of Lewis acids, for example, TiCL,, VCI4, SbCIs, SnCI4, and BF3.Et20. They worked in methylene chloride at different temperatures, e.g., 20~ and -65~ Low molecular weight products (1~ ~ 770) in low yields (~ 15%) were formed using TiCI4, VCI4 and SbCI5 at 20~ It is interesting that all the products prepared were white powders displaying strong fluorescence and yielding colored solutions. From NMR analysis these authors concluded that, under polymerization conditions, l, l-dimethylindene had a tendency to isomerize to 2,3-dimethylindene. 2,3-Dimethylindene. Cationic polymerization of this 2,3-disubstituted indene was carried out by Heilbrunn and Marechal 9~ using various ~ s acids as catalysts, such as BF3.EtzO, TiCl4 and SbCls. Working in methylene chloride at 20~ and -65~ they obtained in ~30% yield products having l ~ ~ 750 after 24 hr. From NMR investigation, these authors obtained evidence that, under the influence of TiCl4 as catalyst, 2,3-dimethylindene was partially transformed into 2,3-dimethylindane. This phenomenon can be explained by assuming intermolecular hydride transfer reactions in the presence of Lewis acids. 4,6-Dimethylindene. In the course of their investigations on the cationic polymerization of disubstituted indene, Marechal and coworkers 9t examined the effect of various Lewis acids on the yield and intrinsic viscosity of polymers prepared from 4,6-dimethylindene. On using BF3.Me20, BF3.Et20, AIBr3, TiCI4, SnCI4, and SbF5 as well as H2SO4 in methylene chloride at -30~ and -72~ they obtained poly(4,6~imethylindene) of varying viscosity and molecular weight (Eq. 5.71). n
15.71) \
289 Thus, with BF3.MezO they recorded the highest intrinsic viscosity of the polymers, [11] - 2.5. Interestingly, they noticed that the temperature did not greatly affect the intrinsic viscosity obtained with this ~ y s t . On tl~ other hand, relatively high molecular weight poly(4,6.dimethylindene) has been obtained using TiCh as catalyst. The highest values reported with this Lewis acid were [11] -I .0, M~- 120000 at-72~ and [r ~ 1.5 and Mo = 20000 at-30~ 4.7-Dimethylindene. Interesting studies on the influence of the reaction parameters on the yield and molecular weights in cationic polymerization of 4,7-dimethylindene have been tamed out by Marechal and coworkers 9~ using various c,atalysts. Thus, among the catalysts employed (BF3.Me20, BF3.EtzO, TiCI4, SnCh, HzSO4), BF3.Me20 and BF3.EtzO produced at 30~ poly(4,7-dimethylindene) with the highest intrinsic viscosity, [q] of 3.6 and 3.5, respectively (Eq. 5.72).
i
n
=
)In
(5.72)
By contrast, BF3.Me20 gave a much lower intrinsic viscosity at -72~ [11] = 1.5. Moreover, these authors observed that the lower temperature did not much affect the intrinsic viscosity obtained with BF3.EhO; for instance, [11] - 3.4 at -72~ Interestingly, according to independent measurements, these intrinsic viscosities are well above the 1.06 value on the number molecular weights sc~e, e.g., [11]- 3.5 is equivalent to Mo = 1200000. In parallel studies, Anton and Marechal r determined the effect of temperature on the intrinsic viscosity [11] of poly(4,7-dimethylindene) prepared with SnCh in methylene chloride at various temperatures. Thus, these authors found that in the range of +30~ to -70~ at practically complete monomer conversions, the intrinsic viscosity decreased fiom 2.36 to 1.90, displaying a minimum around -30~ In addition, the influence of solvents on the intrinsic viscosity [11] of poly(4,7-dimethylindene) has been investigated and substantially higher values have been found for 4,7dimethylindene polymerization in ethyl chloride than in methylene chloride. 5.6-Dimethylindene. In order to study the influence of various experimental parameters (nature of catalyst, monomer concentration,
290 reaction temperature) on the polymer yield and molecular weight, Marechal and coworkers 91 carried out the cationic polymerization of 5,6dimethylindene using different reaction conditions (Eq. 5.73). ,it
X>ln n
"~
(5.73)
/ ~x
For this purpose, they used several catalytic systems, such as BF3.M~O, BF3.Et20, TiCh and SnCI4 as well as H2SO4 and worked at various temperatures in methylene chloride as a solvent. It is noteworthy that the highest intrinsic viscosity in this reaction was attained with the complexes BF3.Me~O and BF3.EhO at 100% yield. The intrinsic viscosity, [13], the molecular weights, M,, and the fusion temperatures Tf, m obtained with the two catalytic complexes, at-30~ and -72~ respoctively, are given in Table 5.12.. Table 5.12. Intrinsic viscosity, [11], molecular weight, M,, and fusion temperature in cationic polyn~rizatkm of 5,6-dimcthylmdme~
'cataly c System
~ -30 BF3.MozO -72 -30 BF3.Et20 -72 'Data from r~rmc~ 9t
M.
[ n] |
~
0.46 3.3 0.45
64000 1000000
286-288
65000
286-288
3.4
1000000
288-290
L
288-290 _
It is quite evident from the above data that the reaction temperature exerts a drastic effect on both the intrinsic viscosity and molecular weight of poly(5,6-dimethylindene). At the same time, with another catalyst, i.e., TiCI4, the intrinsic viscosity and number average molecular weights increased from [TI] - 0 . 2 and M , - 70000 at 0~ to [13] - 2.0 and M. = 400000 at -72~ It was found that only under suitable conditions TiCI4 gives rise to poly(5,6~imethylindene) having [rl] = 2.5 and M , - 106. 5,7-Dimethylindene. 5,7-Dimethylindene was first synthesized and polymcrizod by Marechal and ooworkcr$91 in the presence of various Lewis
291 acids as catalysts. They worked in methylene chloride or 1,2-dichloroethane at-30~ and -72~ employing as catalysts BF3.Me20, BF3.Et20, AIBr3, TiCh, SnCh and SbCls. While the first two complexes gave no polyng'r in these conditions, the other four Lewis acids produced low molecular weight poly(5,7-dimethylindene) ([r = 0.07-0.17) in high yields (Eq. 5.74).
n
~
(5.74) /
It is interesting that among the Lewis acids, the relatively highest intrinsic viscosity at 100% yield were attained using AIBr3 in methylene chloride when [q] = 0.12 at -30~ and [q] = 0.17 at -72~ 6,7-Dimethylindeue. Marechal and coworkers 9~93 were the first to synthesize and polymefize 6 , 7 ~ y l i n d e n e in the presence of several cationic initiators. On using several catalytic systems such as BF3.EhO, TiCh and SnCL,, they prepared poly(6,7-
In n
= \
(5.75) \
It is worth mentioning that polymerization of 6,7-dimethylindene, induced by TiCI4 at -70~ in methylene chloride and ethyl chloride, gave polymers in 100~ yield having [q] = 0.37, softening temperature 288292~ and [11] = 0.53, softening temperature 288-289~ respectively. At the same time, by decreasing the polymerization temperature, the intrinsic viscosity increased from 0.29~ at +25~ to 0.37 at -70~ On the other hand, higher molecular weights were attained using BF3.EtzO and SnCh as catalytic systems. Thus, in the polymerization induced by SnCI~ in methylene chloride, the intrinsic viscosity increased readily from 0.29 at +25~ to 1.23 at -70~ Likewise, high molecular weight polymers were
292 recorded at -70~ with SnCI4 and BF3.EtzO (M, = 138000 and soRening temperature 287-306~ 4,6,7-Trimethylindene. Synthesis and cationic polymerization of this trisubstituted indene derivative under the action of cationic initiators has been performed first by Marechal and coworkers. 91 Working under various reaction conditions, they examined the influence of the catalytic system, solvent and temperature on the polymer yields and molecular weight. The polymerization of 4,6,7-trimethylindene has been carried out in the presence of BF3.MezO, BF3.EtzO, TiCI4, SnCI4, and HzSO4 in methylene chloride and ethyl chloride at -72~ (Eq. 5.76).
/~ (s.r
N
\
It is interesting that the highest intrinsic viscosity of poly(4,6,7trimethylindene), [~] = 1.73, was recorded for BF3.Et20 as a catalyst. Notwithstanding, appreciable intrinsic viscosities of the polymer, [q] = 0.60.9, were also obtained with the other catalysts. Furthermore, it is remarkable the influenc~ of temperature on the intrinsic viscosity of these polymers in the temperature range of +25~ to -70~ Thus, the results obtained in reactions c,atTied out in methylene chloride indicated a maximum ([rl] - 0.6) at -15~ with TiCI4 and another ([~] = 2.0) at 0~ with SnCI4 as catalysts. 4,5,6,7-Tetramethylindene~ The cationic polymerization of 4,5,6,7tetramethylindene has been investigated by Marechal and coworkers 94 who worked out also a new efficient synthesis for this tetrasubstituted indene. In their studies, these authors examined carefully the effect of reaction parameters such as the catalytic system, reaction temperature, monomer concentration and solvent on the intrinsic viscosity, number average molecular weight, and softening point of poly(4,5,6,7-tetramethylindene) and compared these data with those of polyindene. Thus, working in methylene chloride with 0.03M monomer concentration for 5 min at -75~ they obtained 100% yield in polymer with intrinsic viscosity [r = 0.22 (Eq. 5.77).
293
n
=
(5.77)
/
\
Interestingly, the temperature variation in the range 0~ to - 45~ did not much influence the intrinsic viscosity, [11] --0.25, and softening point of 317-320~ On the other hand, when using HzSO4 as a catalyst at -30~ poly(4,5,6,7-tetramethylindene) having intrinsic viscosity [11] = 0.38, molecular weight M. = 94,500 and softening range 317-320~ was prepared. It is quite remarkable that with unsubstituted indene, much lower molecular weight polyindene in lower yields is obtained using H2SO4 as catalyst as compared with the conventional ~ s acids SnCI4 and TiCI4. 3,4,5,6,7-Pentamethyfindene. This highly substituted indene derivative has been f i ~ prepared by Quere and Marechal 9s and further polymerized in the presence of cationic initiators. Though the addition p o i s o n of 3,4,5,6,7-pentamethylindene would provide important information on the polymefizability of this monomer, detailed results on this reaction have not become available. $-Vinylindene. The cationic polymerization of 5-vinylindene has been examined by Marechal and Quere95m under the action of BF3.EtzO and TiCh in methylene chloride at -70~ In these conditions, they produced in high yields totally insoluble and infusible polymers. Interestingly, by theoretical calculations they showed that the two double bonds in 5vinylindene are of about the same reactivity toward cations. Accordingly, under cationic conditions, the two double bonds may take part in two independent polymerization reactions which give rise to cross-linked polymers (Eq. 5.78).
m n
(5.78)
294 l-Phenyfindene~ In a brief investigation on the cationic polymerization of 1-phenylindene, Marechal and H a m y 97 reported that this monomer reacts under the influence of AICI3 at 15~ and BF3 and TiCh at -72~ These authors obtained in high yields (90-95%) insoluble polymers that exhibited good thermal stability (infusible at relatively high temperatures). It is interesting that gel formation was attributed to the possibilities of the growing carbocation to react either with the olefinic double bond or with the phenyl group, mainly in the para position. 1,3-Diphenylinden~ In attempts to polymerize 1,3-diphenylindene in the presence of various Lewis acids Marechal and Hamy97 did not succeed. They observed, nonetheless, the d i m ~ o n of this monomer in 80~ yield, under the action of TiCI4 at ambient temperature. 4-Methoxyindene. Synthesis of 4-methoxyindene was reported by Marechal and coworkers9~ who carried out also the cationic p o l y m ~ o n of this monomer in the presence of several catalysts such as BF3.EtzO, AIBr3, TiCh, TaCIs, and HzSO4. Experiments have been performed in methylene chloride at -78~ for 5 min to produce largely insoluble polymers with softening points of-260~ On the other hand, using TiCI4 in ethyl chloride, soluble polymers were obtained having intrinsic viscosity [11] = 1.05 (Eq. 5.79). n
n
------~
(5.79)
MeO
5-Methoxyindene~ The cationic polymerization of 5-methoxyindene has been investigated also by Marechal and coworkers9s using various acid catalysts. Under the action of BF3, TiCh and H2SO4, poly(5methoxyindene) has been prepared having intrinsic viscosity [11] - 0.1 and softening range of 216-220~ (Eq. 5.80). n
n
=
(5.80)
295 In c o n ~ when BF3.Me~, BF3.Et20 and SnCI4 in methylene chloride at temperatures between -30 and -50~ were employed, 4-methoxyindene did not polymerize. 6-Methoxyindene. In their studies on the cationic polymerization of methoxyindenes, Marechal and coworkers 9s examined extensively the activity of 6-methoxyindene in the presence of various Lewis acids. High yields in polymers were attain~ with this monomer when gaseous BF3, BF3.Et20 and TiCI4 were employed as catalysts in methylene chloride for 5 rain at -78~ (Eq. 5.81).
l)'n n
The polyng~s displayed a softening range of 240-250~ It is quite interesting that of the methoxyindenes investigated, 6-methoxyindene exhibited the highest reactivity in cationic polymerization. These authors found the following sequence of relative reactivity: 6-Methoxymdene(10)>4-Methoxymdene(6.7)>5-Methoxymdene(2.8)>Incline( 1) l-lndenylindene(l,l'-Biindenyl). The cationic polymerization of lindenylindene was first investigated by Sigwalt and coworkers ss using as catalysts TiCU, SnCI4 and BF3 in methylene chloride at -72~ Of these, TiCI4 produc~ high molecular weight soluble polymers having intrinsic viscosity, [q] = 1.2, SnCL, gave very low yields in polymers, whereas BF3 led in moderate yields to a cross-linked product (Eq. 5.82). 13
n
-~
(5.82)
Later on, Marechal and coworkers 99"m studied in detail the polymerization behavior of l-indenylindene and its derivatives. Working with TiCI4 as a catalyst, they obtained soluble high molecular weight poly(I-indenylindene).
296 Interestingly, the thermal stability of the polymers thus prepared was not very high (softening range of 325-330~ and the product underwent yellow discoloration at around 280~ 3..Indenylindene(3,3'-Biindenyl). It is quite probable that by cationic polymerization, 3-indenylindene will form via the 1,4-addition reaction of the conjugated double bonds poly(3-indenylindene) having unsaturation along the polymer chain (Eq. 5.83).
.
n
.
.
.
~
]13
(5.83)
Marechal and Sigwalt ~~176 carried out the synthesis of 3-indenylindene and then its cationic polymerization using TiCh as a catalyst. Working in methylene chloride for 5 min at -40~ they obtained in 30~ yield poly(3indenylindene) having intrinsic viscosity [r = 0.08. It is remarkable that the polymer displayed a nice blue fluorescence. This phenomenon was explained by admitting three possible structures in the polymer chain: two of them having trans-stilbene like units and one a highly conjugated endgroup. l,l'-Biindenyl- 1,2,-ethane~ Synthesis of 1,1 '-biindenyl- 1,2-ethane has been reported by Marechal and Lepert ~~ to give a mixture of two isomers, the major compound (I, 63%) being optically inactive while the other one (II, 37%) racemic. It is quite remarkable that the two isomers produced under the action of TiCh in methylene chloride at -70~ polymers with different physical properties. Thus, starting from monomer I, after 5 rain reaction time, a partially (70~ soluble polymer with [11] - 0.1-0.34, M~ = 360014000 and softening range = 235-255~ was produced that cross-linked on standing in benzene solution. In contrast, compound II gave polymers with lower intrinsic viscosity, [11] =0.07, M~ = 4,600 and softening range = 220242~ They observed that the residual double bond contem of this polymer was much higher than that of the polymer from isomer I. On the other hand, polymers obtained from compound II cross-linked on heating. Probably, the unsaturated polymer formed in a first step by polymerization of one of the double bonds of the monomer cross-linked by fin~er reaction at the available double bond (Eq. 5.84 )
297
.=
(5.84)
L
Jn
3,Y-Biindenyl-l,2-ethane. Marechal and Lepert m carried out also the synthesis and cationic polymerization of 3,3'-biindenyl-l,2-ethane to produce the corresponding addition polymer(Eq. 5.8 5).
& (5.85)
The polymerization has been effected in the presence of TiCI4 in methylene chloride at -30~ to yield after 5 rain 70% polymer, [11] = 0.044, M, = 1800. On heating, a cross-linked product was obtained having the softening range between 250~ and 260~ l,l'-Biindenyl-l,4-butane. 1, l'-Biindenyl-l,4-butane has been prepared and investigated in cationic polymerization by Marechal and Lepert. ~02They observed that under the action of TiCLs in methylene chloride at -72~ the polymerization was fast and cross-linked polymers have been produced after 5 rain (Eq. 5.86). n
n
(5.86)
Yields up to 100% were reported. The polymers thus obtained had intrinsic viscosity [11] = 0.13-0.2 I, M~ = 5000-14500, softening temperature starting from 240~ and readily cross-linked on heating.
298 3,3'-Biindenyl-l,4-butane. Synthesis and polymerization of 3,3'biindenyl-1,4-butane have been reported also by Marechal and Lepert. ~~ In the presence of TiCl4 as catalyst, these authors produced completely soluble polymers in benzene, working in methylene chloride for 5 min at -37~ (Eq. 5.87).
n
=
~]n
(5.87)
Interestingly, under these conditions the yields in polymers were rather low, about 5% and unsaturation determination showed that only one of the two available double bonds reacted. The polymers had intrinsic viscosity [q] = 0.09, softening range = 175-225~ and cross-linked upon heating. l,l'-Biindenyl-l,4-trans-2-butene. This very interesting biindenyl derivative with an exocyclic double bond in the aliphatic chain has been prepared and investigated under cationic conditions by Marechal and Lepert. ~~ Its polymerization has been effected in methylene chloride in the presence of TiCI4 for 5 rain at -72~ when conversions up to 97% were readily attained (Eq. 5.88). t
n
-----~..
In
(5.88)
Soluble polymers thus prepared had number average molecular weights between 6700 and 14500 and softening range from 137 to 315~ It is quite remarkable that infrared spectroscopy evidenced that the exocyclic double bond in these polymers remained unchanged and cross-linking occurs upon heating. This finding indicated that the exocyclic double bond was less reactive under these conditions than the two endocyclic bonds available.
299 5-Bromoindene. In the course of their studies on the cationic polymerization of indene derivatives, Quere and Marechal 9~ examined the reaction of 5-bromoindene in the presence of several Lewis acids as catalysts. Under these conditions, 5-bromoindene could not be polymerized. It was suggested that the lewis acids strongly complex with the bromine in the 5-position. Further details on this reaction have not been reported. 6-Bromoindenr In contrast to its 5-isomer, the monomer 6-bromoindene, synthesized and examined under cationic conditions by Quere and Marec,hal,9~ showed to be highly reactive. Using various catalytic systems such as BF3, BF3.Me~, BF3.EhO, TiCI~, SnCI4 and HzSO4 in methylene chloride and ethyl chloride as solvents and working for 5 min at temperatures from 0~ to -117~ these authors studied the influence of various reaction parameters (e.g., catalytic system, monomer concentration, solvent, temperature) on the polymer yield and intrinsic viscosity. The results obtained in these polymerization reactions are quite signifi~. Thus, with TiCh, the highest intrinsic viscosity obtained was [rl] = 0.4 while, with BF3, intrinsic viscosity close to [q] = 3.0 was reported at -80~ 0.2M monomer concentration in ethyl chloride. However, the intrinsic viscosity obtained with SnCL, and H2SO4 was substantially low. In contrast, the two boron complexes, BF3.Me~O and BF3.EhO, did not produce any methanol precipitable polymer. Notwithstanding, carbon disulphide was the only solvent able to dissolve this polymer. The softening range reported was between 275~ and 285~ 5-Bromopropybl-indene. The cationic polymerization of this bromcontaining indene derivative has been investigated by Marechal and Lepert ~~ in the presence of TiCh as a catalyst. On working in methylene chloride for 5 min at -72~ they obtained 80% yield of polymer having intrinsic viscosity [11] = 0.045, M, = 5,860 and softening range between 195~ and 210~ It is remarkable that no bromine loss ocx:urred during the polymerization and upon heating cross-linked polymer was obtained. 4-Bromobutyl-l-indme. Interesting investigation has been also reported by Marechal and Lepert ~~ on the synthesis and cationic polymerization of 4-bromobutyl-l-indene. Thus, on using TiCh in methylene chloride for 5 min at -72~ these authors obtained 20% yield of polymer having intrinsic viscosity [q] = 0.015, number average molecular weight M, = 5400 and softening range from 95~ to 130~ In contrast to its 3-bromopropyl-lindene homolog, this monomer lost some bromine during the polymerization. In addition, cross-linking occurred upon heating.
300 Benzofulvene. Cationic polymerization of this highly unsaturated monomer has been investigated by Marechal et al. t~ in the presence of TiCI4 as catalyst. On carrying out the polymerization for 5 min at -72~ they obtained a soluble yellow powdery product having intrinsic viscosity [rl] = 0.2 and sot~ening point 300~ Under these conditions, 80% monomer conversion has been attained. Interestingly, the polymer yellowed on heating at ---265~ Unsaturation determination by bromine analysis showed one double bond per repeat unit. This result can be rationalized by 1,4-type enchainment through conventional 1,4-addition reaction at the conjugated double bonds ofbenzofulvene (Eq. 5.89). n
n
(5.89)
Methylbenzofulvene. This methyl substituted benzofulvene was also examined by Marechal and coworkers t~ using TiCI4 as catalyst in methylene chloride as a solvent. Working at-72~ they readily attained high yields (p = 100%) of colorless polymer having intrinsic viscosity [rl] = 0.14 and softening point 250~ It was interesting that the polymer thus prepared discolored a t - 230~ Structural analysis indicated one double bond per recurring unit. Probably, poly(methylbenzofulvene) consists of 1,4-type enchainment, resulted by 1,4-addition reaction of the conjugated double bonds of the monomer (Eq. 5.90).
n
n
~
(5.90)
Ethylbenzofulvene. Ethylbenzofulvene has been p o l y m ~ by Marechal under the action of TiCh in methylene chloride at -72~ After 5 min reaction time, they obtained in 94% yield a colorless polymer having intrinsic viscosity [11] = O. 16 and soRening point = 250~ In contrast to poly(methylbenzofulvene), no yellow discoloration with l~ly(ethylbenzofulvene) ~ r r e d on heating. In a similar way to its
et al. ~~
301 lower homolog, the structural investigation indicated one double bond per repeat unit. This finding suggested that the polymer formed by 1,4-type enchainment via conventional 1,4-addition reaction of the conjugated double bonds of ethylbenzofulvene (Eq. 5.91).
13 rl
.
-
_
Benzalindene. This highly conjugated benzofulvene derivative has been investigated by Whitby and Katz ~~ using SbCIs in chloroform at ambient temperature. Under these conditions, they produced a precipitable yellow powdery polymer having polymerization degree DP = 6 and melting point Mp = 252-255~ It is highly probable that the polymer consist of major 1,4-type enchainments with minor contributions of 1,2-type recurring units (Eq. 5.92). m I1
p
*
(5.92)
Cinnamalindene. Whitby and Katz ~~ examined the polymerizability of this conjugated triene derived from indene, under the influence of SbCls and SnCI4. Remarkably, the reaction of cinnamalindene in the presence of SbCI5 was so vigorous that it led rapidly to charting. In contrast, the polymerization induced by SnCI4 in chloroform produced a solid polymer that was purified by reprecipitation to a yellow powdery product with a degree of polymerization DP = 4 and having the melting point Mp = 238242~ Isopropenylindene. Polymerization of this monomer has been described by Cesca et ol. ~os under mild conditions in the presence of a number of FriedelCrafts catalysts, e.g., BF3.Et20, SnCI4, TiCI4, EtAICI2, Et2AICIYBuCI, to obtain addition polymers with both 1,2- and 1,4-enchainments of the repeat units (Eq. 5.93).
302
n
=
+
~--~
(5.93)
l-lsopropylidene-3a,4,7,7a-tetrahydroindene. The synthesis and cationic polymerization of l-isopropylidene-3a,4,7,7a-tetrahydroindene have been investigated by Cesca et al. ~~ On employing various Lewis acids like BF3.EtzO, SnCI4, TiCI4, EtAICIz and the binary system EtzAICI/tBuCI, they succeeded in obtaining high yields in polymers. It is quite remarkable that using a premixing technique for the catalytic system EtzAICI/'BuCI in toluene, they obtained high conversions at relatively low monomer:EtzAICl ratios (---100) with moderate molecular weights. Noteworthy, the premixing of various BrOnsted acids like HCI, HzO, CCI3OH and CH3COOH with EtzAICI gave very low molecular weight polymers at low monomer conversions. The polymers of l-isopropylidene-3a,4,7,7a-tetrahydroindene prepared by Cesca et al. ~~ were white, soluble products having a softening range of 150-170~ Their results indicated that the intrinsic viscosity and molecular weights of the methanol insoluble polymers were rather low and the highest values recorded were [rl] = 0.176 and M, = 15700. It is interesting that in these conditions they obtained medium to low molecular weight dispersities, M,dM,--- 1.3-2-4. From IR and NMR spectroscopy and chemical analysis these authors evidenced that the major repeat unit of the polymer consisted of 1,4-type enchainment resulted through 1,4-addition at the conjugated double bonds (Eq. 5.94).
,I
n
'I
n
(5.94)
Soluble high molecular weight polymers with high reactivity and good solubility in organic solvents were produced by Snare Progetti
303 SpA ~~ from l-isopropylidene-3a,4,7,7a-tetrahydroindene, under the influence of cationic catalysts consisting of a halide of group III or VIII or an organoaluminium halide (Eq. 5.95). ,1 n
~
tl
rn
p +
(5.95)
These polymers have remarkable activity and can be easily grafted or crosslinked. In addition, polar groups e.g., CN, SO3OH, OH or halogen can be easily introduced into the polymer chain.
Bicyclo 14.4.01decatetra- 1,3,5,7-ene(l,2-Dihydronaphthalene).
By
cationic polymerization, 1,2-dihydronaphthalene will lead to the normal vinyl polymer, poly(l,2-dihydronaphthalene) by 1,2-additon reaction (Eq. 5.96).
The reaction of 1,2-dihydronaphthalene has been carried out by Higashimura and coworkers s3 using SnCIdCCI3COOH and BF3.Et20 as catalysts. With SnCIdCCI3COOH in dichloroethane for 30 min they obtained in 10% yield poly(1,2-dihydronaphthalene) 60*/, of which was soluble in methanol. The molecular weight of the methanol insoluble product corresponded to a tetramer. Interestingly, in additional comparative studies they observed that the rate of polymerization of 1,2dihydronaphthalene was much lower than the rate of indene and styrene.
5.3. Cationic Polymerization of Polycyclic Olefins A large number of polycyclic olefins has been polymerized under the influence of cationic initiators to produce polymers with particular structures and properties. Dicyclopentadiene. The cationic polymerization of exo- and e n d o dicyclopentadiene (DCP) has been extensively studied by several research groups using various catalytic systems. A first important remark of these studies made by Comer et al. ~o7 is that in the presence of the complex
304 BF3.Et20 at room temperature, two kinds of polymers can be obtained starting from the two isomers, thus, from exo-DCP a polymer having M. = 1450 whereas from endo-DCP a polymer with M~= 820 was produced. It is significant that examination by infrared spectroscopy of the microstructure of the two polymers indicated that the polymer prepared from e x o - D C P contained 2,3-enchainments of the recurring units formed by a normal 1,2addition reaction of the more reactive double bond of the norbomene moiety whereas the polymer produced from endo-DCP had 2,7enchainments of the recurring units resulted by a Meerwein-Wagner rearrangement (Eq. 5.97-5.98).
(5.97)
n
=
(5.98)
Further investigation on the cationic polymerization of endodicyclopentadiene has been carried out by Cesca et al. ~os using a variety of one-component and two-component catalytic systems such as BF3, AICI3, TiCh, SnCI4, EtAICI2, EtAICI/BuCI, Et2AICIfBuCI. The polymerization reactions have been effected mostly in methylene chloride at variable temperatures between +I0~ and -87~ Under these conditions, the polymerization occurred readily when amorphous, soluble white powdery polymers have been obtained. The molecular weights ranged from 1300 to 4450 and the softening points between-180~ and >320~ depending on the corresponding molecular weight. It is interesting that microstructure determinations by infrared and NMR spectroscopy of the polymers thus prepared indicated rearranged norbornane and nortricyclene units involving participation ofboth double bonds of the monomer into reaction (Eq. 5.99).
(5.99)
305 Cesca et al. ~0s suggested that the poly(dicyclopentadiene) is largely linear,
finding a high value of the a exponent in the Mark-Houwink relation, but some branched structures may not be ruled out. In addition, we should mention briefly the results reported by Takada et al. ~~ on the dicyclopentadiene cationic polymerization. On using TiCh as a catalysts, these authors prepared low molecular weight products consisting mainly of repeat units formed by 1,2-addition reactions of the double bonds of the norbomene moiety. Dehydrodicydopentadiene. Soluble polycyclic polyene polymers with high molecular weight were prepared by Sham Progetti SpA.11~ by polymerization of dehydrodicyclopentadiene in the presence of halides of group III or VIII or of an organoaluminium halide (F_,q. 5.100). n
=
n
(5.100)
The product had a high activity and could be easily grafted or cross-linked. Moreover, polar groups e.g., CN, SChOH, OH or halogen, could be easily introduced into the polymer chain. 3,4-Dihydrodicydopentadiene. In the course of their investigation on the cationic polymerization of dicyclopentadiene, Cesca et al. ~~ also carded out the polymerization of 3,4~hydrodicyclopentadiene under the conditions of cationic catalysis. The reaction has been performed in the presence of the catalytic system EtAICI2fBuCI in methylene chloride at -78~ Under these conditions, they obtained only very low molecular weight products having number average molecular weight M~ = 540 and softening point 85-95~ It is expected that the main polymer to consist of 1,2-recurring units (Eq.
5.1o]). (5.101)
However, spectroscopic investigation by IR and NMR methods indicated the occurrence of hydride migration in the imermediate propagating carbocations giving rise to rearranged structures with 1,3-recurring units and possibly higher homologs structures (Eq. 5.102).
306 n [ ~
~
(5.102)
8,9-Dihydrodicyclopentadiene. The cationic polymerization of 9,10dihydrodicyclopentadiene has been performed by Cesta et al. ~~176using the catalytic system EtAICI~uCI in methylene chloride at various temperatures. When working at -20~ and -78~ they obtained in ~50% yields white polymers having number average molecular weights of 1670 and 2150, respectively, and softening range 265-280~ It is obvious the effect of temperature on the molecular weight evolution; thus, on decreasing the temperature the molecular weight increased. Structure investigation by infrared spectroscopy showed no evidence for unsaturation and the presence of norbomane units were inferred. By cationic polymerization of 9,10-dihydrodicyclopentadiene under the above conditions, Cesta et a/. ~0s assumed that linear polymers by 1,2-addition reaction of the double bonds of the norbomene system are formed (Eq.
5.1o3). n
n
=
(5.103)
l-Isopropylidenedicydopentadiene. Cationic polymerization of this polycyclic conjugated monomer has been investigated by Cesta e t al. tos under the action of various Lewis acids. On using as catalysts BF3.Et20, TiCI4, EtAICI2, EhAICI and EhAlfBuCI in methylene chloride, n-heptane and toluene as solvent in the range of temperatures 0~ to -78~ they produced completely soluble linear high molecular weight polyng~s. Spectroscopic investigation of the microstructure of the polymers thus prepared indicated 1,4-type enchainment of the recurring units formed by 1,4-addition reaction of the conjugated double bonds from the monomer
(Eq. s. to4).
,1 tl
in (5.1o4)
307
Soluble high molecular weight polymers with high reactivity and good solubility in organic solvents have been produced by Snam Progetti SpA ~l~ using catalysts consisting of a metal halide from the group HI or VIII of the Periodic System or an alkylaluminium halide. The polymers have high activity and can be easily grafted and cross-linked. Furthermore, polar groups, e.g., CN, SO3OH, OH or halogen, can be easily introduced into the polymer chain. In one example, this monomer was polymerized at -80~ in chloromethylene with BF3/etherate for 2 hrs to produce 96% polymer with an intrinsic viscosity [TI] of 0.82 dl/g. Di-endo-m ethyleneoctahyd ton aph th alene (Tetracyclo [4.4.0.1 ~. 1~,te] dodeo.3-ene). Cationic homopolym~on of tetracyclo[4.4.0.1z'5.17'l~ was carried out by Sagane et al. ~t~ using the catalyst system EtAICId~uCI, at various temperatures, in chloromethylene and cyclohexane as a solvent. The effects of the temperature on the polymer yield, product solubility, molecular weight and glass transition temperature were investigated in this system. Relevant results are summarised in Table 5.13. Table 5.13 Cationic polyn~fizafion oftetracyelo[4.4.0.12,5.17't~ (TCD) using the EtAICIz/BuCI catalyst systemLb M~/ Yield Soluble DP Ts M. % wt.-% "C (5.'3)o 275 (1.9) ~ 43 (840)" CH2CI2 17.4 (6.7) (1.9) (1070) 24 CH2C2 10.9 6.6 269 1.8 1060 100 CH2CI2 5.3 4.1 1.7 +lO C~tl~ 4.9 100 660 "Data from reference '; ~.eaction conditions: [EtAICI2] ['BuCI] = 10.5 rnmole/L: 5.0 mmole~, Time = 60 mm; Walues in parentheses: taken from the soluble fraction.
Temp oC -50 -30 +10
Solvent
As Table 5.13 shows, the polymerization was relatively slow, reaching 520% polymer yields after 60 rain. The polymers o b t a i n e d at +I0~ were completely soluble in boring toluene but those at lower temperatures were partly insoluble. The molecular weights of the soluble polymer were in the range 700-1100 as determined from gel permeation chromatography. Solvent polarity did not affect the polymer yield but reduced substantially the molecular weight.
308 A cationic mechanism for polymerization of tetracyclo[4.4.0.12,s. 1~'~~ under the influence of EtAICI~q3uCI was proposed by Sagane el al. ~ including the initiation, propagation and termination (deprotonation) steps. According to this mechanism and as evidenced by the ~3C NMR spectral analysis, the poly(tetracyclo[4.4.0.12,s. 1~'~~ contained two types of repeat units in the polymer chain formed by 1,2-addition and 1,3-addition reaction, respectively, the last involving an intramolecular 1,3-hydride shift in the intermediate propagating carbocation (Eq. 5.105).
In addition, two types of termination ends by deprotonation of the carbocationic propagating species were evidenced (Eq. 5.106).
It is noteworthy that the glass transition temperatures of the polymer ranged between 260~ and 275~ whereas addition polymers of norbornene were known to have a softening point of 235~ (M, = 1470). Interestingly, the repeating units of tetracyclo[4.4.0.1 ~s. 17'm~ being bulkier and of more rigid structure than that of norbomene, they did not affect much the melting behavior of the polymer. This may be caused by their low molecular weights, where end-groups strongly affect the glass transition temperature.
Di-endo-methylenehexahydrona phth alene (Tetracyclo [4.4.0.1 ~s. 17,~0] dodeca-3,8-diene). Forster and Hepworth tt2 reported on the cationic polymerization of di-e~methylenehexahydronaphthalene in the presence of BF3.Et20 to produce a soluble and completely saturated polymer. When working in neat system, at room temperatures under dry nitrogen, they obtained i n - 50% yield polymers having number average molecular weight M~ = 1050. Microstructure determination by infrared spectroscopy indicated along the normal 1,2-addition product (Eq. 5.107)
309
[
in (5.107)
the presence of saturated half-cage reoming units arising by subsequent rearrangement and transannular reactions (Eq. 5.108).
n~
_•]n
~
[
(5.108)
Acenaphthylene. The ready availability of this monomer attracted the interest of many investigators on its ionic polymerization. Due to the particular reactivity of the aliphatir double bond, acenaphthylene will lead, by 1,2-addition polymerization in the presence of cationic initiators, to poly(acenapl~ylene) having 1,2-enchainments in the polyng~ chain (Eq.
s.109). n
=
(5.109)
The first ionic polymerization of acenaphthylene tO relatively low molecular weight polymers has been reported by Dziewonski and Stolyhow. ~3 Later on, Flowers and Miller ll4 obtained higher polymers by reacting acenaphthylene with BF3 gas in chlorobenzene at 0~ while Jones prepared low molecular weight products on using AICI3 in carbon disulphide at 50~ Interesting research on the kinetics and mechanism of acenaphthylene polymerization has been carried out by Imoto and Takemoto ~s in the presence of the catalyst BF3.Et20, working in benzene at temperatures between 20~ and 50~ In their studies they found the overall rate to be first order in monomer and catalyst and the overall activation energy of 1.5 kcal/mole. The number average molecular weights of polyng~ reprecipitated from benzene into methanol were found to be M, = 1250002(g)O(X), corresponding to a degree of p o l ~ t i o n , DP = 840-1300. Remarkably, the polyacenaphthylene has been stable on heating up to 280~
310 Interesting work on acenaphthylene cationic polymerization have reported Story and Canty ~6 using as catalyst BF3, working in chlorobcnzene at -5~ and -23~ It is noteworthy that from their results, they inferred that initiation reaction was attributed to the presence of either adventitious water or purposely added initiator (H20 or CH3OH). The intrinsic viscosity and number average molecular weights of the polymers thus prepared were rather low, i.e., [1"1] = 0.03 and M~ - 3000, corresponding to a degree of polymerization, DP - 20. The polymers were found to be crystalline by X-ray analysis. Based on this finding and other spectroscopic evidence, the authors proposed that the polymer prepared with solid hexafluoroboric acid [I-VBF3OH'] had predominantly trans syndiotactic configuration and that obtained with methoxyfluoroboric acid [H+BF3OCHf] had trans isotactic configuration. Significant kinetic studies on the cationic polymerization of acenaphthylene have been carried out by Justi et al. ~7"~2~ in the presence of BF3 gas as well as, by using dilatometry, on the iodine initiated polymerization in dichloroethane at temperatures between 0~ and 30~ In these interesting studies, they found the rate law to be v = k[M]x[l] 2 and the overall activation energy Eo = 7.0 kc~mole. It is noteworthy that based on the low reaction rates and low conductivity found during the polymerization reaction, these authors proposed a pseudocationic mechanism. Interestingly, for the chain carrier they suggested a liodoacenaphthylene derivative in which the iodine is activated by coordination with one or two molecules of iodine and is stabilized by monomer. Subsequent investigations on acenaphthylene polymerization with these catalysts in the presence of dc fields (electric field strength from 0.33 to 1.5 kV/cm) confirmed earlier conclusions concerning the pseudocationic mechanism. In contrast to the above data, on using BF3.EtzO in methylene chloride or dichloroethane for acenaph~ylene polymerization by the same technique, for instance, dilatometry in the presence of dc fields, a more complex picture resulted and no finn conclusions on the nature of the propagating species could be drawn in this case.
Polymerization of acenaphthylene under the influence of BF3.EhO in benzene at 80~ has been reported by Barrales-Rienda and Pepper ~zs'~ to produce polyacenaphthylene in 100% yields. The polymers thus obtained were soluble in benzene and precipitated into methanol. These authors examined the dilute solution properties of the highest molecular weight fraction having M~=23000, M~=33000, M~=31000 and M,dM~=I.44. It is
311 remarkably that on the basis of their results, they came to the unexpected conclusion that the unperturbed coil dimensions of polyacenaphthylene were smaller than those of polystyrene. Detailed studies on the cationic polymerization of ~ a p h t h y l e n e and its derivatives have been carried out by Belliard and Marecha1123 on using a variety of Lewis acids as catalysts (e.g., BF3, BF3.Et20, AICI3, TiCh, SnCh and SbCI3) under various reaction conditions. It is noteworthy to mention that they developed a new synthesis method for acenaphthylene based on dehydration of acenaphthol with anhydrous MgSO4 to produce a chromatographically pure monomer. Notwithstanding, though using TiCI4 in methylene chloride at -70~ they attained a high yield (-94%), the molecular weights of the polymers and the intrinsic viscosities were rather low. Finally, of great interest is also the polymerization reaction of acenaphthylene induced by stable carbenium ions, e.g., tropylium salts C~HT*SbCIs" and C~H~BF4", that has been reported by Bawn et al. 124 Moderate molecular weights and intrinsic viscosities have been obtained, however, using these carbenium salts as cationic initiators. Substituted acenaphthylene The cationic polymerization of a series of substituted acenaphthylenes has been reported in the presence of various catalytic systems. Of these compounds, the monomers bearing the alkyl groups in various positions in the acenapphthylene moieties produced polymers with interesting physical-chemical properties. l-Methylacenaphthylene. In their extensive work on the cationic polymerization of polycyclic olefins, Belliard and Marecha1123 examined the synthesis and polymer~tion behavior of l-methylacenaphthylene. For this reaction they employed several Lewis acids, such as BF3, BF3.Et20, TiCh and SnCI4. It is remarkable that working in methylene chloride at -72~ only SnCI4 provided low yields (--2-3%) of methanol precipitable polymer. In contrast, the other catalysts produced trimers as oily products which could be purified by recrystalliz~tion from pentane. The product probably corresponded to a 1,2-addition reaction (Eq. 5.110).
/ n
[ ~
'/]n (5.110)
It was assumed that considerable steric hindrance due to the methyl group prevented propagation beyond the trimer stage with this monomer.
312 3-Methylacenaphthylene. To determine the change in the reactivity with respect to the other isomers, Belliard and Marechal t23 prepared and polymerized under cationic conditions 3-methylacenaphthylene. On using SnCI4 in methylene chloride at -72~ they recorded high yields, I~ > 90%, large intrinsic viscosities, [11] = 0.36-0.47 and high molecular weights, M, = 56000-90000 of poly(3-methylacenaphthylene) (Eq. 5.111).
[ n
----~
]n (5.111)
Interestingly, they observed that to reach the highest molecular weights of the polymer large amounts of SnCI4 were necessary, practically equimol~ SnCl4:monomer ratio. In their studies, they examined the influence of temperature on the molecular weight to find that, as expected, the molecular weight increased with decreasing temperature. 5-Methylacenaphthylene. The cationic polymerization of 5methylacenaphthylene, of interest due to the new position of the methyl group with respect to the reactive double bond, has also been investigated by Bellied and M~eehal Iz3(FN. 5.112).
=
(5.112)
In the presence of the catalytic complex BF3.EtzO in methylene chloride at 72~ they prepared in 57% yield polymers having intrinsic viscosity [11] = 0.55. Preparation of light-colored resins by cationic polymerization of multicyclic olefins has been reported in a patented process by Nippon Oil Co. t2s Starting from non-conjugated dienes or polyenes of the norbomene type, the monomer is first selectively hydrogenated in the presence of Ziegler catalysts then the partially hydrogenated product is submitted to the action of cationic catalyst to form high molecular weight addition polymers (Eq. 5.113-5.114).
313
+H2
AlCl 3
n :
(5.114)
Examples are given for dicyclopentadiene hydrogenated with titanocene dichloride and triethylaluminium and subsequently polymerized with aluminium chloride. Interestingly, when Pd/C was used as the hydrogenation catalyst, the product could hardly be polymerized. 5.4. References
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319
Chapter 6 ANIONIC POLYMERIZATION OF CYCLOOLEFINS 6.1. General Aspects The literature referring to the anionic polymerization of cycloolefins is limited so that this topic will be briefly reviewed in the present chapter. It is reasonable to assume that simple cycloolefins in the presence of anionic initiators have a reduced polymerizability because under these conditions stable vinyl anions may readily arise by a proton transfer from the most reactive allylic positions of the cycloolefin (Eq. 6.1).
(6.1)
=
However, under favorable conditions, i.e., when some strong electronegative groups are attached to the cycloolefin like nitrile, carboxyl, c,arboalkoxy, etc., the 1,2-addition polymerization of cycloolefins with anionic initiators might occur with formation of the corresponding saturated vinyl polymers (Eq. 6.2).
There exists several publications on the anionic polymerization of cyclic dienes. As it will be shown later, more data available are reported on the anionic ring-opening polymerization of substituted silacycloalkenes. It is of interest that the anionic polymerization of a cyclic diene, methylenecyclobutene, with alkyllithium, reported by Wu and Lenz,~ gives rise to a 1,2-addition product by opening the endocyclic double bond (Eq. 6.3).
n
f
1-1
[1 ] In f
(6.3)
320 It is not ruled out that some 1,4-addition units may oexmr along 1,2-repeat units in the polymer chain but their presence has not been proved yet (F_,q. 6.4).
n~
~
!1 l ]n
[__/
(6.4)
Since a dramatic improvement of the thermal stability, chemical properties and mechanical strength is expected for the obtained polymers with directly connected alicyclic structures in the main chain, the polymerization of a series of cyclic conjugated dienes, e.g., 1,3cyclopentadiene, 1,3-cyclohexadiene and 1,3-cyclooctadiene has been carried out using the classical anionic initiator alkyllithium, z'~2 However, the obtained polymers were of low molecular weight, undefined microstructure and in a low yield. In the presence of anionic initiators, cyclopentadiene will form a poly(cyclopentadiene) having two recurring units in the polymer chain (Eq.
6.5).
(6.5) The contribution of these two structures will depend on the reaction conditions. Details on these types of structures from classic~ studies are scarce. Anionic polymerization of' 1,3-cyclohexadiene w i l l form poly(cyclohexadiene) with 1,2 and 1,4 recurring units in variable amounts, depending also on the reaction conditions (Eq. 6.6).
n(
~
~
+
(6.6)
For instance, low molecular weight poly(cyclohexadiene) was obtained in substantial yield in the polymerization of 1,3-cyclohexadiene initiated by butyllithium ("BuLi)using benzene, tetrahydrofuran, dioxane, diethyl ether, n-heptane and cyclohexane as solvent. 2"s By contrast, in the polymerization of 1,3-cyclohexadiene initiated by Li-naphthalene,
321 Na-naphthalene and K-naphthalene, higher polymers with a broad molecular weight distribution were obtained in low yield.4'+ It has been reported that the anionic polymerization of 1,3cyclohexadiene in the presence of alkyllithium and alkylsodium (e.g., nbutyllithium, Na-naphthalene, polystryryllithium) in nonpolar solvents (e.g., n-hexane, cyclohexane, benzene) at room temperature, leads to low molecular weight products, in low yields and broad molecular weight distributions of polymers due to the deactivation of the living ends. 2"~'8'9 Furthermore, in the polymerization of 1,3-cyclohexadiene initiated by alkyllithium, the formation of 1,4-cyclohexadiene and benzene was observed, due to the abstraction of the allylic hydrogen from 1,3cyclohexadiene by organolithium species competing with the propagation reaction (Eq. 6.7-6.8).
~
L~
---
Lie* G
(6.7)
~
~
(6.8)
+ LiH
The first successful example of the living anionic polymerization of 1,3-cyclohexadiene with the "BuLi/TMEDA (N,N,N',N'tetramethylethylenediamine) system was reported by Natori ~2 leading to homopolymer, poly(l,3-cyclohexadiene), as well as to block copolymers. In addition, these authors, reported the relative reactivity of 1,3cyclohexadiene in the copolymefization with styrene and isoprene and the relative reactivity of the propagating species of living poly(l,3cyclohexadiene) and living polystyrene. ~3 The relationships between the microstructure and properties of homopolymers, block copolymers and their hydrogenated derivatives are also reported. ~4 Detailed studies on the polymerization of 1,3-cyclohexadiene with various alkyllithium (RLi)/amine systems have been carried out by Natori and Inoue. ~ Conversion-time relationships of the polymerization of 1,3cyclohexadiene with some ~BuLi/TMEDA systems in cyclohexane at 40~ are illustrated in Figure 6. !.
322 Yield,% 100 O0 60 40 20
0
lO0
200
300
400
5OO
Time, min Figure 6.1. Conversion-time curves for 1,3-cyclohexadiene polymerization with "BuLifFMEDA catalytic systems in cyclohexane at 40~ ([ 1,3-CHD]J[Li]o = 250, I-"BuLi/TMEDA = 4/5; 2-"BuLi/TMEDA = 4/2; 3-"BuLiFrMEDA = 4/0.5; 4-~BuLi)(Adapted from Ref. ~s) Of several catalytic systems employed (RLi -- MeLi, "BuLi, "BuLi, 'BuLi, PhLi), they observed that the "BuLi~gtEDA catalyst (molar ratio TMEDA/'BuLi higher than 4/4) induced polymerization of this monomer in a "living" manner to polymers having narrow molecular weight distributions with well controlled chain lengths. The rate of polymerization and polymer yield increased with increasing the ratio of TMEDA to "BuLi (Table 6.1). Table 6.1 Polymerization of !,3-cycl.ohexadiane .with.:BuLl frMED A mm.a!mg ~ ' Initiator Yield M,,/M. 1 , 2 - u n i t 1,4-unit % % % 98 2 2.2"I 33 nBuLi 79 21 2.42 77 "BuLifFMEDA(4/0.5) 67 43 1.52 72 "BuLifrMEDA(4/2) 52 48 1.12 100 "BuLifrMEDA(4/3) 49 51 1.07 100 "BuLifFMEDA(4/4) 48 52 1.06 100 "BuLi;YMEDA(4/5) 46 54 1.08 100 "BuLifYMEDA(4/6) "BuLi/TM ED A(4/8) 100 1.07 54 46 'Data from reference~ ~ffMEDA = NiN,N',N'4etram~hylethylenodiamme.
323 As it can be seen from Table 6.1, the molecular weight distribution of poly(l,3-cyclohexadiene) became narrower with the ratio TMEDA/~uLi. The microstructure of the polymer, determined by 2D-NMR, indicated a higher content of 1,4-units in the polymerizations initiated with higher "BuLi/TMEDA ratios. It is interesting that higher contents of 1,4-units have been also obtained in the polymerization of 1,3-cyclohexene using ~ u L i associated with other amines as compared with tetramethylethylenediamine (Table 6.2).
Table 6.2 Polymerizauon of 1,3-cyclohexene with ~BuLi/amme initiating systems'
Initiator ~
Yield %
M,,~.
"BuLifFMEDA(4/5) "BuLifFMMDA(4/5) "BuLifFMPDA(4/5) "BuLi/TMHDA(4/5) "BuLi/TEEDA(4/5) "BuLi/DABCO(4/5)
100 70 33 67 16 100
1.06 1.75
1,2-unit %
1,4-unit
52 24
48
%
76
2.16 91
1.95
1.14 1.69
21
79
'Data from re.fence ~s', brMEDA = N,N,N',N'4etramethylethylenediamine, TMMDA = N,N,N',N'-tetramethylmethylenediamme, PMPDA = N,N,N',N'tetramethyl- 1,3-propanodiamine, TMHDA = N,N,N',N'-tetramethyl- 1,6hexanecliamme, TEEDA = N,N,N',N'-4etraethylethylenediamme, DABCO=-I,4diazabicyclo[2.2.2]octane
It has been also found that the polymerization of 1,3-cyclohexadiene with polystyryllithium/amine systems can give in some cases poly(1,3cyclohexadiene) with narrow molecular weight, having a high content of 1,2-units in the polymer chain (Table 6.3). The highest content of 1,4-units has been obtained using n-butyllithium associated with N,N,N',N'tetramethyl- 1,6-hexanediamine and 1,4-diazabicyclo[2.2.2]octane. However, even though these initiating systems were quite active and selective, the molecular weight distribution was not narrower than that obtained with the ~BuLiFFMEDA system.
324 Table 6.3 Polymenzation of 1,3-cyclohexene with polystyryllithium/amme mitiating., Initiatorb Yield Mw/M. 1,2-unit % % l . e m ~
PStLi PStLi/TMEDA(4/5) PStLifFMMDA(4/5) PStLifFMPDA(4/5) PStLi/TMHDA(4/5) PStLi/DABCO(4/5) PStLi~Et3(4/5)
15 100 39 84 98 100 23
It
1,4-und:
%
21 64 26 32 18 25 14
1.60 1.29
1.55 1.55 1.27
1.14 1.45
79 34 74 68 82 75 86
*Data from reference*~; ~PStLi = Polystyryllithimn, TMEDA = N,N,N',N'tetra~ylethylenediamine, TMMDA = N,N,N,,N,_tetramethylmethylenediamme, PMPDA = N,N,N',N'-tetramethyl-l,3-propanediamme, TMHDA = N,N,N',N'~methyl-l,6-hexanediamine, TEEDA - N,N,N',N'-tetraethylethylenodiamme, DABCO= 1,4-diazabicyclo[2.2.2]octane Anionic polymerization of cyclooctatetraene carried out by Ushakov and Solomon ~6 in the presence of Na initiator led to a high molecular weight polymer which was insoluble in methanol and acetone. Plausibly, the highly unsaturated 1,2-addition polymer formed from eyclooctatetraene under anionic conditions underwent further cross-linking reactions to a branched polymer (Eq. 6.9).
n
~
~
(6.9)
t
Jp
Polymerization of l-isopropylidene-3a,4,7,7a-tetrahydroindene with anionic initiators gave oligomers, probably by competitive 1,2- and 1,4addition reactions of the endocyclic and conjugated double bonds of the monomer ~7(Eq. 6.10).
n
~
I
m
§ [(
IF< ~]P
(e.lo)
325 The actual nature of the products obtained in this reaction has not been accurately determined. l-lsopropylidenedicyelopentadiene, a monomer easily polymerizable by cationic initiators, has produced in the presence of anionic initiators poly(l-isopropylidenedicyclopentadiene), probably by 1,2- and 1,4-addition reactions Is (Eq. 6.11). [ n
,
I
]
m
+
(6.11) (
Details about the mierostructure of these polymers, however, have not been reported. 6.2. References
C.C.Wu and R.W. Lenz, Polymer Preprlnts (Amer. Chem. Soc., Div. Polym. Chem.), 12, 209 (1971 ). G. Lefebvre and F. Dawans, J. Polym. Sci., Part A, 2 3277 (1964). 3. P.E. Cassidy and C.S. Marvel, J. Polym. Sci., Part A, 3 1533 (I 965). 4. H. Lussi and J. Barman, Helv. Chim. Acta, 50 1233 (!967). 5. L.A. Mango and R.W. Lenz, Polymer Preprints (Am. Chem. Soc., Div. Polym. Chem.), 12 402 (I 971 ). L.A. Mango and R.W. Lenz, Makromol. Chem., 163 13 (1973). 7. Z. Sharaby, J. Jagur-Grodzinsky, M. Maritan and D. Vofsi, J. Polym. Sci., Polym. Chem. Fwl., 20 901 (1982). X.F. Zhong and B. Francois, Makromol. Chem., 191 2735 (1990). 9. B. Francois and X.F. Zhong, Makromol. Chem., 191 2743 (1990). 10. Y. Imanishi, K. Matsuzaki, T. Yamane, S. Kohjiya and S. Okamura, J. Macromol. Sci., Chem. A3 249 (1969). 11. B.A. Dolgoplosk, S.I. Beilin, Yu. V. Korshak, G.M. Chernenko, L.M. Vardanyan and M.P. Teterina, Fur. Polym. J., 9 895 (1973). 12. I. Natori, Macromolecules, 30 3696 (1997). 13. I. Natori and S. Inoue, Macromolecules, 31 982 (1998). 14. I. Natori, K. Imaizumi, H. Yamagishi and M. Kazunori, J. Poym. Sci., Polym. Phys. Ed, cited after reference 13. .
.
~
326 15. I. Natori and S. Inoue, Macromolecules, 31 4687 (1998). 16. S.N. Ushakov and O.F. Solomon, USSR Patent 104,198 (1956). 17. S. Cesca, A. Roggero, N. PaUadino, and A. DeChirico, Makromol. Chem., 136 23 (1970). 18. S. Cesca, A. Priola, A. DeChirico, and G. Santi, Makromol. Chem., 143 211 (1971).
327
Chapter 7
ZIEGLER-NATTA POLYMERIZATION OF CYCLOOLEFINS
Taking advantage of the abundant results published on the ZieglerNatta polymerization of linear olefins and dienes, polymerization of cycloolefins with this type of catalysts has been successfully performed in order to manufacture polymers with new structures and properties. For this purpose, all the traditional catalysts as well as new ones have been employed to polymerize monocyclic and polycyclic olefins, uncovering unexpected details of this challenging process.
7.1. Polymerization of Monocyclic Olefins A substantial number of substituted and unsubstituted monocyclic olefins have been reacted under the conditions of Ziegler-Natta catalysis to form polymers with interesting properties.
7.1.1 Four-Membered Rings Vinyl polymerization of cyclobutene and substituted cyclobutene has been effected with various types of Ziegler-Natta. The product selectivity depended essentially on the type of catalyst and reaction conditions. Cyclobutene. The vinyl polymerization of cyclobutene leads to a saturated polymer, poly(l,2-cyclobutene)or poly(cyclobutylenamer), by opening of the carbon-carbon double bond of the monomer (Eq. 7.1).
n ~-]
~
[I
[ in
(7.1)
The reaction occurs under the influence of a variety of coordination catalytic systems derived from transition metal compounds with or without organometallic derivatives as the cocatalysts. Often, the addition
328 polymerization is accompanied by ring-opening polymerization forming along with saturated vinyl polymers, unsaturated polymers, known as polyalkenamers or poly(l-alkenylene)s (Eq. 7.2).
[I lira
or-il
(7.2)
Cyclobutene polymerization has been extensively studied by Natta and coworkers ~'2 using a wide variety of binary or ternary catalysts based on group IV-VI transition metal compounds. In the majority of these studies, the two type of polymers, addition and ring-opened, have been obtained. Typical examples are outlined in Table 7.1. Table 7.1.
Cyclobutene polymerization with transition metal based catalytic systems' Temp ~
Catalytic System
3TiCI3/AICI~3AI TiCIVEhAI VCI4/EhAI VCI4~ex3AI VCI3/Et3AI VOCI3/Et3AI
+45 -10 -20 -20 +45 -20
V(acac)3/Et2AICl
-50
Cr(acac)dEt2AICl CrO2CI2/Et2AICI MoO2(acac)z/Et2AICl MoCI~zt3AI WCI6/Et3AI 'Data from reference~
m
u
-20 -20 - 10 -20 -20
Conversion Poly(cyclobutylenamer) % % 40 100 5 100 99 100 99 100 80 100 90 100 I00 100 I00 100 I00 100 I0 55 30 5 40 100
Polybutenamer
% 60 95 1 traces
20 10 0 0 0 90 70 60
As can be seen from Table 7.1, vanadium- and chromium-based catalysts were very active and promoted preferentially the addition polymerization ofcyclobutene to form poly(cyclobutylenamer). It is quite
329 interesting that the other catalysts based on titanium, molybdenum and tungsten, some of them very active, direct cyclobutene polymerization by the two pathways, addition and ring-opening reaction to produce both types of polymers, vinyl and ring-opened, that is poly(cyclobutylenamer) and polybutenamer, respectively, in various amounts. Several other catalysts have been used to transform selectively cyclobutene to saturated poly(cyclobutene) for instance the following x-complexes of nickel xC3HsNiBr, (~-CffIT)Ni 0t-CffITNiCI)2 provided entirely the addition polymer poly(cyclobutylenamer). 3"s More recently, addition polymerization of cyclobutene has been investigated by Kaminsky and coworkers 6 using two-component catalysts consisting of chiral metallocenes and methylaluminoxane. The activity of cyclobutene polymerization in the presence of ethylenebis(vlsindenyl)zirconiumdichloride/methylaluminoxane in toluene was high and dependent on the reaction temperature (Table 7.2). Table 7.2 Polymerization of cyclobutene (M) reduced by ethylenebis(rl'-mdenyl)zirconiumdichloride/methylalummoxane' Reaction Tc~g~rature ~
Catalyst Activity
Melting Point in Vacuum ~
0
149
-10
50
485 485
.
_
kg Polymer
'Data from reference ~ Under these conditions, highly melting point poly(cyclobutene) (Me 485~ in vacuum) has been prepared; the decomposition temperature was in the same range. The monomer conversion in cyclobutene polymerization at 0 and -10~ v s time is represented in Figure 7.1. As this figure illustrates, following a rapid start, the rate of eyelobutene polymerization decreases to become linear after a few hours for a long period. At the same temperature, it was found that the activity for cyclobutene polymerization induced by the ethylenebis(rlS-indenyl)zirconiumdichloride/ methylaluminoxane catalyst was about five times that of cyclo~tene reaction in the presence of the same catalyst.
330 Yield, %
50
( A ) ~ 0~ (B) - -10~
40 :30 20 10
o
~
z
3
4
5
~o
~5
20
2s
Time, hr
Figure 7.1. Monomer conversion in cyclobutenepolymerization reduced by ethylenebis(qS-indenyl)zirconiumdichloride/methylalummoxanecatalyst (Adapted from Ref.6) Substituted cydobutene. Several alkyl substituted cyclobutenes have been explored in Ziegler-Natta polymerization with various catalytic systems. Of these monomers, 1- and 3-methylcyclobutene provided the most interesting results. l-Methylcyclobutene By addition polymerization in the presence of the binary Ziegler-Natta catalysts l-methylcyclobutene will form readily the vinyl product, poly(l-methylcyclobutene) (Eq. 7.3).
n [--
-"-
[I
1
I In
(7.3)
This reaction has been investigated by Dall'Asta and Manetti 7 in the presence of a wide variety of transition metal based catalysts. On using catalysts derived from titanium, vanadium, chromium and molybdenum salts and organometallic compounds they found the activity was very low and the product was mainly a saturated polymer probably of a vinyl structure as in Eq.7.3. Alternatively, when catalysts based on tungsten hexachloride and organoaluminium compounds have been employed, saturated polymers having polyisoprene skeleton were formed, probably involving in a first step ring-opening polymerization and further intramolecular cyelization. (See later in section 7.3)
331 3-Methylcyclobutene. Addition polymerization of 3-methylcyclobutene in the presence of some binary transition metal catalysts gives the saturated polymer, poly(3-methylcyclobutene) (Eq. 7.4). n
i-I
l In
\
(7.4)
\
A series of binary Ziegler-Natta systems consisting of vanadium tetrachloride and organometallic compounds have been investigated by Dall'Asta s in 3-methylcyclobutene polymerization (Table 7.3). Table 7.3. Polymerization of 3-methylcyclobutene in the presence of binary Ziegler-Natta c,atalysts" Catalytic System
Conversion % 37 25 17 14
VC~3AI VC~3Ga VC~zBe VCI4/EttMg "Data from reference *
vm4 Polymer % 90 90 85 94
Polyalkenamer % 10 10 15 6
As Table 7.3 illustrates, the catalysts containing Et3AI and Et3Ga were the most active and produced vinyl polymer in 90*,6 proportion. The other catalytic systems obtained from Et2Be and Et2Mg, though displayed a moderate activity, afforded at a high selectivity vinyl polymer. 7.1.2. Five-Membered Rings Of the five-membered ring monomer, cyclopentene has been
examined with several types of Ziegler-Natta catalysts affording interesting data on the product selectivity and reaction mechanism. Cydopentene. By vinyl polymerization cyclopentene gives rise to a saturated product, poly(1,2-cyclopentylene), as result of the opening of carbon-carbon double bond (Eq. 7.5).
n
[~,v~]n
(7.5)
332 The opening of the carbon-carbon double bond can take place in a cis or trans fashion, giving rise to two type of isomeric polymers, erythro and threo poly(l,2-r The erythro polymers formed by cis opening of the double bond from cyclopentene may have di-isotactic or disyndiotactic stereocontiguration (I and II, Eq. 7.6).
cis
(7.6)
The threo polymers produced by trans opening of the double bond from cyclopentene may also possess di-isotactic or di-syndiotactic stereoconfiguration (I and II, Eq. 7.7).
0
trans
(7.7)
In addition, the threo di-syndiotactic poly(1,2-cyclopentylene) is expected to show optical activity. Boor et al. 9'!~ have carried out a systematic study on the polymerization of cyclopentene in the presence of Ti- and V-based ZieglerNatta catalysts. This cycloolefin was polymerized very slowly by TiCI3/Me3AI, TiCIdEt3AI, VCIdMe3AI and VCIdMe2AICI to give a poly(cyclopentene) with ring-retention along with cis-/transpolypentenamer. More recently, cyclopentene was found to polymerize via the double bond opening by Farona and Tsonis ~t~3 under the action of the catalytic system Re(CO)~CI~tAICI2. The microstructure of the product indicated that the cyclic ring was prevailingly retained in the polymer chain and the final polymers were made up of repeating 1,2-unit, or a combination of 1,2 and isomerized structures. In contrast to Re(CO)sCI/EtAICI2 catalyst, when Mo(CO)sPy/EtAICI2/Bu4NCI has been employed, cyclopentene
333 polyme~ predominantly with ring-opening but also ring-retained poly(cyclopentene) has been obtained (Table 7.4). Table 7.4 Polymerization of cyclopentme in the presence of Mo(CO)sPy/FaAICIz/Bu4NCI~b Solvent
Temp. ~
Heptane Chlorobenzene
30 26
Yiel~ %
O:Aa
0.5 14.7
I "3.6 1:4.8
Vinyl Product %
ROMP" Product %
7
93
18
82
'Data from reference~2; bThe polymerizations have born carriod out' for 20-22 hours; Wield of methanol insoluble polymer; aO:A=olefm to aliphatic proton ratio in NMR spectrum; "ROMP=ring-opening metathesis polymerization product. As Table 7.4 illustrates, both the polymer )ield and polymer structure have been significantly influenced by the reaction conditions. Polymerization of cyclopentene has been investigated by Kaminsky and coworkers" in the presence of several metallocene complexes. Some data obtained, using the binary systems zirconocene/methylaluminoxane in toluene at various reaction temperatures, are presented in Table 7.5. Table 7.5 Addition polymerization of cyclopmtme (M) reduced by zirconocene(1)/methylaluminoxane(MAO) catalysts~b Catalyst
Temp. ~
Reaction Time~ hr
Cp2ZrCI2 F_,t(Ind)2ZrCl2 Et0ndhZrCl2
30 10 25 22
20 90 72 10
Et(IndH,hZrC]z
Yield g Polymer m
13.6 20.0 24.5
'Data fzom reference 14; bPamction conditions: [M] = lOOml, [I] = 104 molo/L,
MAO = 200 mg. As Table 7.5 shows, there was no activity when cyclopentadienylzkconium dichloride was used as a catalyst component. However, the chiral catalysts
334 derived from ethylenebis(~ 5-indenyl)zirconium dichloride and ethylenebis(TIS-tetrahydroindenyl)zirconium dichloride were quite active. Similar results were found with other cyclic olefins. The poly(cyclopentylene) produced under these conditions was highly crystalline and insoluble in common hydrocarbons. Examination by ~3C NMR spectroscopy indicated that no ring-opening of the monomer occurred. Particularly active in cyclopentene polymerization showed to be the catalyst consisting of ethylenebis(TI~-indenyl)zirconium dichloride and methylaluminoxane. However, the activity of this catalyst was strongly dependent on the reaction temperature (Table 7.6). Table 7.6 Polymeriza~on of cyclopentene reduced by ethy!enebis(q'-mdenyl)zirconium dichloride/methylalummoxane catalyst Lb Reaction Temperature, Catalyst Activity, Melting Point in ~ k~ Polymer Vacuum~ ~ 22 195 395 0 32 395 'Data from references ~14;bReaction solvent=Toluene i
The monomer conversion v s time in cyclopentene polymerization with this catalytic system at the two temperatures is plotted in Figure 7.2 Yield, % (A)
I---(A)- 22~---I
50
/
40 30 20 J 10
-
/
~)
f o
~
2
3
4
5
~o
~5
zo
Time, hr
Figure 7.2. Monomer conversion in cyclopentene polymerization reduced by ethylenebis(Q~-indenyl)zirconiumdichloride/methylalummoxane catalyst (Adapted from Ref.6)
335
As it can be observed, following a rapid start of cyclopentene reaction, the rate decreased to become linear for a long period. Interestingly, at the same temperature, the activity of this catalyst in cyclopentene polymerization was about five times lower than that of cyclobutene reaction. The melting point of poly(1,2-cyclopentylene), determined under vacuum to avoid oxidation, was found to be rather high, i.e., 395~ The decomposition temperature was in the same range. Since the vinyl homopolymers of cyclopentene were insoluble in common solvents, it was difficult to study accurately their structure. To circumvent this difficulty, lower oligomers, soluble in hydrocarbons, were prepared by changing the reaction conditions. Higher reaction temperatures, higher zirconocene concentration and lower monomer concentration allowed soluble oligomers of cyclopentene to be prepared. By comparing the ~3C NMR spectra of soluble oligomers of cyclopentene with the solid state spectrum of insoluble poly(cyclopentene), all peaks could be identified. Two different kinds of end groups in the polymer could also be observed (Eq. 7.8). n j~~.. _
~
n12
n/2
C
sH9
(7.8)
Similar investigations on cyclopentene polymerization were carried out by Okamoto et al. mSwithtransition metal complexes/methylaluminoxane catalysts. On using complexes of Zr, Hf and Ni in conjunction with methylaluminoxane in toluene at 25~ they obtained poly(cyclopentene) of low molecular weight. In all cases the structure of the polymer was of vinyl type. More recently, Collins et al. ~6"~7 examined the polymerization of cyclopentene induced by metallocene catalysts and provided new, interesting data on the reaction mechanism and poly(cyclopentene) structure. Using rac-ethylenebis(rlS-indenyl)zirconium dichloride in conjunction with methylaluminoxane in the polymerization of cyclopentene, poly(cis-l,3-cyclopentylene) has been produced in high yield ~6 (Table 7.7). The polymer microstructure of poly(cis-l,3-cyclopentylene), in which the individual monomer units are incorporated by cis-l,3-enchainment in an isotactic manner, was evidenced through independent synthesis of the single, stereoisomeric tetramer produced under hydro-oligomerization conditions ~6(Eq. 7.9). -
n
[~
= m
C~
§ p
' "
c~r
~
(7.9)
336 Table 7.7 Polymerization of cyclopentene(M) using the catalytic system rac-ethylenebis(v ILmdenyl)zirconium dichloride (1)/methylalummoxane(MAO) ~b [I], mM 0.36 0.33
[MAO], mM 96 105
[M], Yield~, Cis d, M|~ M g % O 3.79 2.7 i~ i 2.02 7.4 96.0 39O 'Data from reference~6; bReaction conditions: Solvent=Toluene, Temperature=250C, Reaction time=24 hr; Wield of unffactionated polymer; dDetermmed from ~3C NMR spectrum; 'Not determined due to insolubility of the polymer. On the other hand, polymerization and hydro-oligomerization of cyclopentene in the presence of rac- and (S)-ethylenebis(rlstetrahydroindenyl)zirconium dichloride associated with methylaluminoxane led to the production of poly(cyclopentene) in which the monomer was incorporated in both cis- and trans-l,3-manner ~7 (Eq. 7.10). n O
~
9p
I-I9 * P
~
(7.10)
The polymer yield and molecular weight were strongly dependent on the reaction conditions(Table 7.8). Table 7.8 Polymerization of cyclopentene(M) using the catalytic system r a c-eth y lene b i s ( vl ~-t et rah yd rom den y l) zi rcon iu m
dichloride ~/methylalummoxane ~IAO) ~b [MAO] [M] ~ Temp [ giel~ Cis d M, [I] % o C M mM mM s 1.46 I 25 I 0.80 60.5 1400 0.043 94 1.46 I 25 I 0.74 59.6 1200 0.043 31 1.46 ! 25 I 2.03 60.6 920 0.17 94 0.91 1.46 I 25 [ 60.4 810 0.17 31 1.13 [ 0 [ 1.74 68.0 900 0.20 100 1.13 I 25 I 2.73 62.0 600 0.20 100 1.13 / 50 I 1.8s" 50.0 350 0.20 100 3.73 l 25 1 6.1 63.0 390 0.47 74 bReaction conditions: Solvent = Toluene, Timr = 'Data from reference 24hr;~'ield of unfraetionated polymer; dDetermmed from the ~3C NMR spectrum; "The reduced yield of polymer at higher ten~ratures is due to the formation of large amounts of oligomers (i.e., dimer, trimer, tetramer, etc.).
337 In contrast to poly(cyclopentene) produced using the catalytic system racethylenebis(rl Lindenyl)zireonium diehloride/methylaluminoxane, the majority of the polymers prepared with the catalytic system racethylenebis(rls-tetrahydroindenyl)zirconium dichloride /methylaluminoxane were soluble in hot toluene or 1,2,4-trichlorobenzene. The cis content of the polymer was found to be unaffected by the catalyst or eocatalyst concentration but was higher at lower temperatures. It is noteworthy that the cis content in the poly(1,3-cyclopentylene) prepared with this catalytic system was somewhat lower than that found for the trimers or even the tetramers. The number-average molecular weight of these unfraetionated polymers was low and dependent on the polymerization temperature. These authors observed that the occurrence of competitive "trans insertion" in cyclopentene polymerization with rac-ethylenebis(rl s_ tetrahydroindenyl)zirconium dichloride led to the production of poly(cyclopentene) with significantly lower erystaUinity than that observed for polymers prepared using rac-ethylenebis(rlLindenyl)zirconium dichloride (Table 7.9). Table 7.9 Melting temperature range and crystallmity of poly(cyclopmtene) prepared with rac-ethylmebis(rl~-mdmyl)zircoaium dichloride00 and rac-eth yleneb is(rl Lt~ trahydromdenyl)zireomum Zirconocene Cis, M. T.~ C~llmit% % % ~ I! 140-350 i 60 i 9 6 d 34 d 390 d 50-160 d 11 68 900 160-285 25 62 600 125-250 19 12 50 70-190 350 4 12 63" 40-80~ 390" 2" 12 'Data fixan reference 17; ~-,eaetJon conditions: Solvent = toluene, Time = 24 hr; "Not determined due to insolubility of the polymer; eData reported are for the fraction soluble in toluene; "Data reported are for a fraction msoluble m acetone r
r
,m
but soluble m hexane.
As it is obvious from Table 7.9, the r and melting temperatures decrease with decreasing cis content and molecular weight. For similar degrees of polymerization, it is the cis content that most dramatically influenced the product crystallinity.
338 Cyclopentene polymerization has also been investigated by Natta and coworkers ~s2~ under the influence of several catalytic systems, in numerous cases the vinyl polymerization is accompanied by ring-opening metathesis polymerization when polypentenamer is formed beside poly(cyclopentenylene) (Eq. 7.11).
0
%1
(7.11)
7.1.3. Six-Membered Rings Cyclohexene and several substituted cyclohexenes have been polymerized with various Ziegler-Natta catalysts, the product selectivity being greatly dependent on the nature of monomer and catalyst. Cyr Although attempts to polymerize cyclohexene in the presence of TiCl~te3Al,, TiCIJEhAI, VCLjMe3AI and VCI~te2AICI have been made by Boor et al. 9'!~ they have not observed the monomer to polymerize under these conditions. The reason for this failure has been attributed to the high ring-stability of cyclohexene. More recently, Tsonis and Farona, 12 however, discovered that Re(CO)sCI/EtAICI2 system promoted the homopolymerization of cyclohexene via the double bond opening process (Eq. 7.12). n
0
=
n
(7.12)
The weight average molecular weight of poly(cyclohexene) was about and ~3C ~ on the 2500. Physical measurements by IlL ~H ~ poly(cyclohexene) thus prepared indicated that the cycle was retained in the polymer chain and that the final product was made up of repeating 1,2or a combination of 1,2- and isomerized single-bond units. Further support for ring retention was provided by pyrolysis and gas chromatographic studies of poly(cyclohexene). 4-Methylcydohexene. Tsonis and Farona ~2 noted that the methyl group attached to cyclohexene in position 4 with respect to double bond will not impede the polymerization of the corresponding monomer, 4methylcyclohexene, by opening of the double bond. On this line, the above
339 authors s u ~ e d to polymerize 4-methylcyclohexene under the influence of Re(CO)sCl~tAIClz to manufacture the saturated polymer, poly(4methylcyclohexene), by ring-retention (Eq. 7.13).
n ~/~\
=
[~]n
(7.13)
4,4-Dimethylcydohexenr Remarkably, introduction of two methyl groups in the remote position of cyclohexene with respect to the double bond allowed to polymerize this monomer via 1,2-~ldition reaction. In their studies on the polymerizability of cyclohexene tings under various conditions, Tsonis and Farona ~z found that 4,4-dimethylcyclohexene polymerize in the presence of the Re(CO)sCI/EtAICI2 system by opening of the double bond to produce poly(4,4..dimethylcyclohexene) with ringretention(Eq. 7.14).
7.1.4. Seven-Membered Rings Of the scven-membcred tings, cycloheptene has bccn carefully examined in the presence of Ziegler-Natta catalysts. Cydoheptene. On extending their investigations of cychxdefin polymerization under the action of Re(CO)sCl~tAIClz catalyst to higher cycloolefins, Tsonis and Farona ~z'~3 disclosed that cycloheptene can be polymerized by opening of the double bond with this catalyst to obtain poly(cycloheptene) or poly(cycloheptylene) with ring-retention (Eq. 7.15).
(7.15) The reaction has been effected at 110~ using a molar ratio Re:AI of 12. The product was analyzed by IIL ~H- and ~3C-NMR and displayed saturated cyclic structures in the polymer chain.
340
7.1.5. Eight-Membered Rings The easy availability of eight-membered ring monomers offered an appealing field of research for Ziegler-Natta polymerization with this class of monomers. Cyclooctene. Of a great interest is the polymerization of cyclooctene to produce a vinyl polymer, poly(cyclooctene) or poly(cyclooctylene), in the presence of appropriate catalysts (Eq. 7.16). n
~
(7.16)
This reaction has been reported by Tsonis and Farona t2"~3tO proceed under the action of the Re(CO)~CI/EtAICI2 system, with a molar ratio ge:Al of 1:2 at I I0~ Structural measurements by IlL ~H NMR and t3C NMR spectroscopy on the poly(cyclooctene) prepared in these conditions indicated that the ring was retained in the polymer and the final product was made up of repeating 1,2-units, or a combination of 1,2- and isomerized units. 1,5-Cyclooctadiene. Polymerization of 1,5-cyclooctadiene has been effected by Bokaris et al. z~ using several metallocene catalysts associated with alkylaluminium compounds. The monomer conversion and polymer Table 7.10 Polymerization of 1,5-cyclooctadiene (M) with bmary catalysts Cp2MtCI2/alkylalummiumcompounds in c h l o r ~ y l e n e at 25 *C~b Polymer Catalytic System Monet Yield, % Conwrsion~ % 73 100 Cp2TiCI2/Et3AI2CI3 64 75 Cp2TiCI~2AICI 36 50 Cp2TiCI~3AI 69 90 CpzZrCI2~3A]2CI3 32 50 Cp2ZrCIz/F_,t2AICI 10 Cp2ZrCI2/Et3AI 37 52 Cp2HfCI2/~3AI2CI3 25 42 Cp2HfCI2/Et2AICI _r 8 Cp2H~I2~3AI "Data from reference 21. bReaction conditions: [CpzMtCI2]=10"z Mole, [Mt]/[AI]= 1/6, [Mt]/[M]=1/200; ~No polymerization was observed. r
m
y
341 yield with a series of binary catalysts derived from m e t a l l ~ e s , Cp2MtCIz (Mt=Ti, Zr, H0 and Et3AI2CI3, EtzAICI or EhAI are presented in Table 7.10. The order of activityof these catalysts dependedon the metal and the r and was found to be Ti>Zr>Hf and Et3AI2CI3>Et2AICI>Et3AI. The molecular weights of the resulting oligomers were in the range of 8001800. The values of molecular weights, intrinsic viscosity and polydispersity for poly(l,5-cyclooctadiene) prepared under these conditions are given in Table 7.11. Table 7.11 Molecular weights, intrinsic viscosity and polydispersity for poly(l,5-cyclooo~diene) prepared with metallocene r Catalytic System
M.~ I M,~ !
M.'
M,/M,
s'b
[n]', ml/g 0.22 0.52 O.77 0.26 0.45
760 1.18 860 728 Cp2TiCIz/Et3AI2CI3 1.21 950 1068 884 CpzTiCI~2AICI 1.35 1350 1758 129[ Cp2TiCI~3AI 1.17 830 905 775 Cp2ZrCI2/Et3AI2CI3 1.24 870 1007 813 Cp2ZrCI2/EtzAICI Cp2ZrCl~3Al f 0.40 1.75 670 1106 630 CpIHt~I~3AIzCI3 0.58 1.64 920 1352 826 CpzHICI2/~IAICI C~2HfC|2/Et3AIf ~ from reference 2,: 'Reaction conditions as m Table 7.10; =By GPC in toluene at 25~ ~By vapour phase osmomctry; "In toluene at 25~ fNo polymerizauon was observed The main structure of this polymer, as concluded from l~ and ~H NMR spectra, seemed to contain saturated transannular recurring units formed by a cationic process (Eq. 7.17).
n~
"~ ~ n
(7.17)
The products obtained were soluble in benzene, chloroform, dichloromethane and other chlorinated compounds. Based on these results, vinyl polymers formed by 1,2-addition reaction of one of the two double bonds of the monomer (Eq. 7.18)
342
n~
~
~ )|m__
(7.18)
while cross-linked polymers arisen by subsequent cross-linking reaction of the remaining double bond (Eq. 7.19) were ruled out. p
(;,.19) t
]p
A more detailed study of the effect of the reaction conditions on monomer conversion in 1,5-cyclooctadiene polymerization with the binary catalyst Cp2TiCl2/EtzAICl was effected by Bokaris et al. z~. Thus, on employing various solvents such as toluene, chlorobenzene and dichloromethane at temperatures of-10~ and 25~ they observed that the best results can be obtained when working in dichloromethane at 25~ On varying the ratio catalyst/l,5-cyclooctadiene from 1/50 to 1/400, the highest monomer conversions were found at a catalyst/monomer ratio of 1/200 (Figure 7.3).
Cony.% , 80-
f
I
A
60-
40
20
v
f /
! i I
2
t'"
.-'-" 111.-
3
S /I 9
~/1t
t
11
7" Time, hr Figure 7.3. The effect of molar ratio catalyst/monomer on monomer conversion in 1,5-cyclooctadiene polymerization with the catalytic system CpzTiCIz/~2AICI: 11/50, 2-1/100, 3-1/200, 4-1/400 (Reaction conditions:[Ti] = 10ZMole, [Ti]/[AI] = I/6,T = 25~ Solv~nt=Dichloromethane) (Adapted from Ref.z*)
343 Of a particular interest is the effect of molar ratio eatalyst/eoeatalyst of the binary system Cp2TiCIdEtzAICI on the monomer conversion and polymer structure in 1 , 5 - e y e l ~ i e n e polymerization. On carrying out the reaction in toluene at 25~ they observed that the best efficiency for this binary catalyst is obtained working at molar ratios Ti/AI of 1/6 (Figure 7.4). Cony., % 15 4
10 / /
I
-,
/
~
5 i
0
!
8
2
Time, hr Figure 7.4. The effect of molar ra~o c a t a l y s t / ~ l y s t (Ti/AI) on monomer conversion in 1,5-cyclocx~diene polymerization with the catalytic system CpzTiCl~_,tzAICl: Ti/AI=I/I(1), I/3(2), I/4(3), I/6(4), 1/10(5)and 1/15(6) (Reaction conditions: rri] = 10"2Mole, [Ti]/[AI] = 1/6, T = 25~ Solvent = Toluene) (Adapted from Ref.z~) As shown in Figures 7.3 and 7.4, the monomer conversion increased considerably in the first stages of the reaction and then decreased. The incomplete conversion of the monomer was attributed to the reduction of the catalyst (Ti ~v to Tim). Related studies on the catalyst structure of the system Cp2TiCI~/Et2AICI in toluene as a solvent were performed by ESR spectroscopy but the results have not been discussed.
7.2. Polymerization of Bicyclic Olefins Due to their particular structure and reactivity, a great number of bicyclic olefins have been tested in Ziegler-Natta polymerization using various catalytic systems.
344
Bicyclo[2.2.1 ]hept-2-ene(Norbornene) Polymerization of bicyclo[2.2, l]hept-2-ene (norbomene)inducexl by coordination catalysts of the Ziegler-Natta type will normally p r o ~ by opening of the carboncarbon double bond and subsequent 1,2-addition to form poly(bicyclo[2.2. I ]hept-2-ene), containing 2,3-enchainments of the recurring units (Eq. 7.20). (7.20) This reaction has been extensively investigated by many research groups in the presence of a large variety of catalytic systems derived from transition metal salts and organometallic compounds. Under various reaction conditions, poly(bicyclo[2.2.1]hept-2-ene) having different structures and physical-chemical properties has been prepared, depending essentially on the nature of the catalytic system employed. In their early report, Anderson and Merckling z2 polymerized bicyclo[2.2, l]hept-2-ene under the action of coordination catalysts derived from titanium tetrachloride and a reducing agent such as Gfignard compounds, metal alkyls and aryls, metal hydrides and even alkali metals or earth alkaline metals. The activity and stability of the catalytic systems employed were relatively low and impurities like water, carbon dioxide or oxygen led to a rapid deactivation of the process. Interesting work on the polymerization of bicyclo[2.2.1]hept-2-ene reported later Truett et al. z3 in the presence of catalysts derived from LiAIILs and TiCI4. On using binary systems consisting of LiAl(Heptyl)4 and TiCI4, these authors proved that the polymerization ofbicyclo[2.2, l]hept-2ene takes place either by vinyl addition at the double yielding saturated polymers, poly(2,3-bicyclo[2.2.1 ]hept-2-ene) or via ring-opening yielding unsaturated polymers, poly( 1,3-cyciopentylenevinylene), containing cyclopentylene tings linked in a c i s - l , 3 fashion with trans double bonds (Eq. 7.21).
Jm (7.21) -P
345 An important observation was that the vinyl polymerization at the double bonds was favored by molar ratios AI:Ti < 1, whereas ratios AI:Ti > 1 led, via ring-opening reaction, preferentially to unsaturated polymers. Furthermore, the ring-opening polymerization occurred with high stereospecificity and provided polymer with high crystallinity and good elastomeric properties. Crystalline polymers of poly(bicyclo[2.2.1]hept-2-ene) containing exclusively recurring units formed by opening of the double bonds prepared Sartori et al. 24 with catalysts derived from aluminium alkyls and titanium tetrachloride. Structural examination by IR and NMR methods of the polymer thus produced showed no unsaturation in the polymer chain. Substitution of molybdenum pentachloride for titanium tetrachloride in these catalytic systems provided effectively stereoselective catalysts for ring-opening polymerization of bicyclo[2.2.1]hept-2-ene to highly cispoly(l,3-cyclopentylenevinylene). Similarly, binary catalysts derived from aluminium alkyls or lithium-aluminium alkyls and titanium tetrachloride have been employed by Saegusa et al. ~ to polymerize bicyclo[2.2.1 ]hept-2ene to poly(bicyclo[2.2.1]hept-2-ene) containing predominantly saturated or unsaturated recurring units, depending on the nature of the catalytic components and the ratio metal alkyl : transition metal compound. Interestingly, on employing some Lewis bases such as tertiary amines, dioxane, dibutyl sulphide or pyridines associated with these catalysts, ternary catalytic systems leading exclusively to unsaturated polymers with trans or cis double bonds have been produced. Farona and coworkers 26 carried out relevant studies on the bicyclo[2.2.1]hept-2-ene polymerization in the presence of Re- and Mobased catalysts. Generally, the polymers obtained at higher reaction temperatures were of ring-retained type whereas those formed at lower temperatures of ring-opened type. At intermediate temperatures, polymers which showed both ring-retained and ring-opened structures in the same chain were obtained. Thus, when Re(CO)sCI/CzHsAICI2 was used as the catalyst, bicyclo[2.2.1]hept-2-ene produced a polymer in 26.8% yield in chlorobenzene, at 100~ for 24 hr. The molecular weight of the polymer, as determined by gel permeation chromatography in THF and by osmometry in toluene, was M~--433,00, M,,=154,000 and the polydispersity 2.14. The olymer softens at 220~ and melts completely at 260~ Examination by NMR spectroscopy (by integration of olefinic to aliphatic proton signals) of the polymer microstructure indicated that poly(bicyclo[2.2.1]-hept-2erie) prepared under the above conditions contained 10 monomers units
346 with ring-retention for every monomer unit with ring-opening in the same polymer chain (Eq. 7.22).
Further studies on the polymerization of bicyclo[2.2.1 ]hept-2-ene at various temperatures in the presence of the systems Re(CO)sCI/EtAICI2 and Mo(CO)sPy/EtAICIz/~NCI evidenced the occurrence of the two types of monomer insertion in the polymer chain, by ring-retention and ringopening. 26 The extent of ring-retention and ring-opening was strongly influenced by the nature of the catalyst and reaction temperature (Table 7.12). Table 7.12 Polymerization of bicyclo[2.2, l]hept-2-cne reduced by Re- and Mo-basod catalysts at various temperatures' O:A b
Ring-reteation/ Rmg-oponmg %
1:4.07
0.7:99.3
Catalytic System
Reaction Temp. ~C
Polymer Yield %
Re(C)~CI/EtAICI2 Re(C)5CFEtAICIz Re(C)~CI/EtAICI2 Re(C)~CI/EtAICI2 Mo(CO),Py/EtAICIj
100 110 120 132 26
77.2 41.4 25.4 100
1:97.5 1:175 0:100 1:4.0
90.3:9.7 94.5:5.5 I00:0 0:I00
100
89.7
1:6
17:83
110
84.6
1"15
52:48
I0
(C4Hg)qCI Mo(CO)sPy/EtAICIz/ (C4H9)4NCI Mo(CO)~Py/EtAICIz/
(C,H9),NCI
;Data from reference u; tO:A=olefmic to aliphatic proton ratio in tH NMR spectrum. These results suggested that propagation in bicyclo[2.2.1]hept-2-ene polymerization, under the action of the Re(C)sCI/EtAICIz and Mo(CO)sPy/EtAICIz/(C4H9)4NCI catalysts, occurred by a 1,2 insertion
347 process with an ocx,asional ring-opening step in the same chain. Evidence for this behavior came from NMR measuremems, where DEPT spectra of the polymer showed the disappearance of some olefinie carbons that do not have hydrogen atoms attached to them. Ozonolysis of poly(bicyelo[2.2.1 ]hept-2-ene) supported the NMR findings. Selective catalysts for vinyl polymerization of bicyelo[2.2.1 ]hept-2ene derived from various transition metal compounds and methylaluminoxane reported recently Okamoto et al. ~s. Depending on the transition metal compounds, variable monomer conversions and polymer yields have been reported (Table 7.13). Table 7.13 Polymerization of bicyclo[2.2. I ]hept-2-ene (M) transition metal compounds 0) and methylalummoxane~ Transition Metal
Corr~ound
Monon~r
Polymer Yield,
Conversions%
g
0.02 0.08 1.7 0.10 2.0 1.21 25.7 2.41 51.3 2.60 55.3 bReaction conditions" [M]=50 mml, [I] Al:Metal=200, Temperature=25~ Reaction time=4 hr V(acac)3 Cr(acach Mn(acach CpNi(allyl) Ni(aeach Pd(~COD~)CIi~
MW~
103 3.0 402 188
194 = 2.5 nml,
As it can be seen from Table 7.13, Ni and Mn containing catalysts provided high molecular weight poly(bicyclo[2.2.1 ]heptene). A new class of coordination catalysts based on Pd(II) for vinyl polymerization of norbornene and norbornene derivatives have been described by several Schulz 27, Gaylord ~, Kinnemann ~ and Sen. 3~ The poor solubility of the polymer hindered, however, its full characterization. Union Carbide Corp. 3~ prepared a series of very active palladium catalysts for norbornene polymerization containing at least one Pd-C bond and at least one Pd-halogen bond. These catalysts were obtained by reaction of a preformed complex having zerovalent Pd and stabili~g the monodentate or bidentate ligands of the phosphine, phosphite or arsine type with an organic compound containing at least one halogen-carbon bond and an alkyl, aryl, aralkyl, cyeloalkyl, acyl or alkenyl group.
348 Such catalysts with methyl, phenyl, acetyl, methallyl, cyano and ethyl formate groups and I, CI or Br ligands were obtained from tetrakis (trihydrocarbylphosphine)Pd(0) or bis(trihydrocarbylphosphine)Pd(0) and phenyl iodide, methyl iodide, acetyl chloride, methaUyl chloride, cyanogen bromide or ethyl chloroformate. Starting from tetrakis(triphenylphosphine)palladium, [(C6Hs)3P],Pd, and methyl iodide, bis(triphenylphosphine)methylpalladium iodide, [(C6Hs)sP]2CH3Pdl, was prepared in high yield by this proc~ure (Eq. 7.23).
[(C6Hs)3P],
+
CH31
=
[(C6H,)3PI2(CH3)Pdl
(7.23)
These catalytic systems were also used in vinyl polymerization of substituted norbornene. Hojabri et al. 32 reported on the polymerization of norbornene under the influence of palladium/~-complexes to produce selectively poly(norbornene) at high reaction temperatures (Eq. 7.24).
n~
~
[~]n
(7.24)
Relevant studies on the addition polymerization of bicyclo[2.2.1]hept-2-ene in the presence of cationic Pd(ll) complexes with the structure [Pd(RCN)4I[BF4]2 (where R=CH3, C2H5 and (CH3hC) were camed out by Risse et al. "'36. The resulting polymer, poly(2,3bicyclo[2.2.1]hept-2-ene), was insoluble in most other common organic solvents like THF, toluene, chloroform, dichloromethane. The product was, however, soluble in a few unsaturated halogenated hydrocarbons such as trichloroethylene, tetrachloroethylene, chlorobenzenr 1,2-dichlorobenzene and bromobenzene. This allowed polymer characterization by gelpermeation chromatography, vapour phase osmometry, and solution viscosimetry. With [Pd(CH3CNh][BF4]2 as a catalyst, higher molecular weight polymers were formed when the ratio of norbornene to Pd 2+compound was increased. (Table 7.14).
349
Table 7.14 Polymerization of bicyclo[2.2, l]hept-2-ene (M) with the [Pd(CH3CN)4][BF4]z (1) catalyst' [M]'[I]
n ~ ,b
MIIr
M,,q~o
dL.g"l 20 100 200 333 1000
0.07 0.22 0.31 0.45 1.10
qsd
24000 38000 70000 d
d
1.41 1.45 1.36 d
'Data frofll i~rellc.e33; bIIlherellt visoosity l'lialt in chlorobenzene(25~ ~Numberaverage molecular weight determined by GPC in chlorobethzene (vs. polystyrene standards); ~Not determined.
The relationship between the molecular weight and initial mole ratio of monomer to initiator was approximately linear while polydispersities were distributed in the range from 1.3 to 1.5. Furthermore, chain growth was found to continue after renewed monomer addition. These results indicated relatively fast initiation of polymerization and rare chain transfer and termination. Noteworthy, the addition of free nitrile to the polymerization mixture caused limitation of the molecular weight by chain transfer reaction. The inherent viscosity dropped from 0.22 dL/g down to 0,09 dL/g when 20 equivalents of acetonitrile (respective to Pd z§ were used. No polymerization occurred when the reaction was carried out in pure acetonitrile. On the other hand, addition of 1 equivalent of triphenylphosphine resulted in a molecular weight increase, corresponding to deactivation of a half of the [Pd(CH3CN)4][BF~]2 used for polymerization. Poly(2,3-bicyclo[2.2.1]hept-2-ene) with a polydispersity, M , ~ ~ . as low as 1.07 was obtained when [Pd(CH3CH2CN)4][BF4]2 was used as the catalyst35 and the polymerization was carried out at a temperature of 0~ The relationship between the molecular weight and monomer conversion was approximately linear for molar ratios of monomer to Pd-c,atalyst ([M]:[I]) up to 500:1 (Table 7.15).
350
Table 7.15 Polymerization of bicyclo[2.2.1 ]hept-2-ene (M) with the [Pd(CH3CH2CN)4][BF4]20) catalyst' Monomer Conversion
M.(GPC)
M,.~.
35
11200 21400 29400
1.07 1.12 1.34
54
100 |
9Data from reference3~ However, the reaction medium has to be carefully selected as the polymer was soluble only in a few unsaturated halogenated solvents. In a solvent mixture of chlorobenzene with nitrobenzene (volume ratio 2:1) the reaction medium remained nearly homogeneous up to high monomer conversions. In addition, the product was soluble in dichloromethane, nitromethane and nitrobenzene as long as a sufficiently high concentration of unreacted norbomene was present. This also allowed the preparation of poly(2,3bicyclo[2.2.1]hept-2-ene) having M,,/M~ below 1.2 by the use of high concentrations of bicyclo[2.2, l]hept-2-ene (higher than 4 mole/L) in the above mentioned solvents. Materials with molecular weights below 10000 were obtained from reaction mixtures containing molar ratios [M]:[I] smaller than 100:1. Higher molecular weight polymers were prepared from larger mole ratios of monomer to initiator (Table 7.16). Table 7.16 Molecular weights of poly(2,3-bicyclo[2.2.1]hept-2-ene) otgamed with the [Pd(CH3CH2CN)4][BF4]2catalyst' [M]'[I]b
Mo(GPC)~
M.(GPC) r
M,,(LS)d
M.(GPC)/ M.~S)
200 600
32900 79500
35200 112300
22000 77500
1.6 1.5
"Data from reference3S;blnitial molar ratio of monomer to Pd-catalyst; ~.elative number and weight average molecular weights determined by GPC in chlorobenzene calibrated with polystyrene standards; dAbsolute weight average molecular weights determined by light scarring (LS) in trichloroe~ylene.
351 Absolute weight average molecular weights MalLS) smaller than relative MdGPC) indicated that poly(2,3-bicyclo[2.2.1]hept-2-ene) has a more rigid molecular structure than polystyrene. The values for absolute M,,(LS) was by a factor of 1.5 to 1.6 smaller than that of relative M~GPC) for the two samples presented in Table 7.16. A radius of gyration l/2 of 130A found for the polymer with a M~LS)=77500 suggested the presence of slightly expanded Gaussian coils. In these studies, Risse e t al. 36 observed that the palladium-carbon bond of the end group remained intact after the isolation of the polymer by precipitation. Subsequent reaction with NaBI-h resulted in cleavage of the Pd-C bond and precipitation of Pd(0). This finding evidenced that an insertion type mechanism into Pd-C bond was responsible for chain propagation. The Pal-catalyzed polymerization of bicyclo[2.2.1]hept-2-ene was unexpectedly insensitive toward water present in the monomer solution. For instance, polymerization of norbornene still ~ r r e d when 1000 equivalents of water (molar ratio of H20 to Pd(II) = 1000:1) was added to a monomer solution containing 200 equivalents of norbomene ([M]:[I] = 200) (Table 7.17).
[M]:[I]b 2OO 200 200 200 3000
Table 7.17 The influence of water on the Pd(ll)-catalyzed (I) l]hept-2-ene (M)' pol~anerization of bi~clo[ M~~ d Yield~ % [H20]:[Pd]r M,(GPC)d ,is
10 100 1000 200
33000 11100 7000 4100 62000
1.24
90
2.06 2.44 2.57 2.00
80
70 70 60
"Data from reference~;blnitial' molar ratio of bicyclo[2.2.1]hept-2-ene to Pd(ll)catalyst, ~Molar ratio of water to monomer in the reaction mixture; aM.(GPC) relative molecular weights by GPC, calibration with polystyrene standards, M,,/M, = polydispersity index determined by G PC. The polymer yield of 70% was relatively little affected at such a high water:Pd ratio employed in this reaction. However, the molecular weight of poly(2,3-bicyclo[2.2, l]hept-2-ene) was drastically reduced from M~(GPC) = 33000 to 1~ (GPC) = 4100 (M,,/M~ = 2.6) indicating that water acts as
352 a chain transfer agent. The chain transfer property could be specifically used for the synthesis of reduced molecular weight poly(2,3- bicyclo[2.2, l]hept2-ene) using very small amounts of the Pd-catalyst. Examination by X-ray spectroscopy of the poly(2,3bicyclo[2.2.1]hept-2-ene) prepared with Pd(II)-tetrakisnitrile catalysts revealed that this polymer is predominantly amorphous. Thermomechanical analysis (TMA) studies on polymers with M,(GPC) = 33000 indicated a softening temperature of 330-335~ However, at this temperature also the onset of thermal decomposition occurred. According to thermogravimetric analysis (TGA) under nitrogen, the polymer of bicyclo[2.2.1]hept-2-ene was reasonably stable up to 300~ to 320~ A weight loss of 5% was recorded at a temperature between 370~ and 380~ The glass transition temperatures determined by two indirect methods indicated T s of 320~ for a low molecular weight polymer and of 330~ for a high molecular weight polymer. Bicyclo[2.2.1 ]hepta-2,5-diene (Norbornadiene). In their extensive studies on the polymerization on the norbomene-like systems with palladium chloride, Schulz27 reported on the polymerization of norbomadiene induced by PdCI2 complexes. Using this type of compounds, products of low molecular weight were obtained in which one of the double bond of the monomer was retained (Eq. 7.25).
n
]n
(7.25)
The polymer was a solid product and had quite a high decomposition temperature. Hojabri e t al. 32 investigated the polymerization of norbomadiene induced by palladiumht-complexes under various reaction conditions. Working at 300~ these authors observed that in the presence of the above catalysts poly(norbornadiene) was formed having only one c a r b o n - ~ o n double bond of the diene system opened (Eq. 7.26).
(7.26)
353 Nickel complexes in association with alkylaluminium halides showed to be very active in norbornadiene polymerization. Such catalytic systems have been reported by Sun Oil Co. 37 to be produced starting from nickelacetylacetonate-bis(tri-n-butylphosphine) or niekeldiehoride-bis(tri-nbutylphosphine) and diethylaluminium chloride or ethylaluminium dichloride at AI:Ni molar ratios between 0.5-100. Norbomadiene polymerization was performed in bulk or solution at temperatures ranging from -40~ to 120~ to form poly(norbornadiene) usable as energy rich solid fuel. Efficient binary catalysts for v i n y l polymerization of bicyclo[2.2.1]hepta-2,5-diene prepared Okamoto e t al. ~5 from various transition metal compounds and methylaluminoxane. On working in toluene at 25~ high monomer conversions and polymer yields have been obtained, depending essentially on the nature of transition metal compound (Table 7.18). Table 7.18 Polymerization of bicyclo[2.2.1 ]hepta-2,5-diene (M) reduced b), transition metal compounds ~ and methylalummoxane~b Transition Metal Monomer PolymerYield, M,,
(xlo")
Conversion,
Compound
% 66 2 47 95 66 69
CpTiCI3 CpzVCI2
V(acac)3 Cr(acac)3 Cp2C3 Mn(acach
1.52
3.0
0.05 1.08
3.8
2.20 1.52
1.60
5.7
'Data from referencelS;b Reaction condition" [M]=25 mmole, [I]=5 mmole Al:catalyst=200, Temperature 25~ Reaction time=4 hr Significantly, among the transition metal compounds employed in these systems, Cr(acac)3 exhibited the highest activity leading to 95~ comonomer conversion. It is noteworthy that the structures of the polymers obtained with Ti, V, Cr and Mn compounds consist of both the vinyl and transannular recurring units (Eq. 7.27).
n . \
/
.
=
(7.27)
354 The ratio of the two structures was found to depend primarily on the nature of the transition metal compound. It is noteworthy that when Mn compound was used associated with methylaluminoxane, the proportion of the transannular structure was 97%. Palladium salts such as PdCI2 was reported by Schulz 27 to polymerize bicyclo[2.2, l]hepta-2,5-diene to vinyl polymers in which one of the double bonds was retained (Eq. 7.28). n
O
=
(7.28)
The products were of low molecular weight and had quite a high decomposition temperature. Addition polymerization of bicyclo[2.2, l]hepta-2,5-diene has also been investigated more recently by Risse et al. 35 using the Pd(II) coordination complex [Pd(CH3CH2CN)~][BF4]2. Under the influence of this catalyst, bicyclo[2.2.1]hepta-2,5-diene gave a soluble unsaturated polymer which consisted predominantly of the 1,2-addition repeating units. Subsequent thermal treatment of poly(bicyclo[2.2, l]hepta-2,5-diene) at 240~ resulted in the formation of polyacetylene accompanied by elimination of cyclopentadiene (Eq. 7.29). [~2~ n
=
in
=
[\--/]n +
o()
(7.29)
These authors observed that it is important to keep the monomer conversion in the synthesis of poly(bicyclo[2.2.1]hepta-2,5-diene) low to avoid gelation by cross-linking reaction. After 3 hr reaction time at 20~ a polymer yield of 20% was obtained from an initial molar ratio monomer to catalyst [M][I] = 100:1. Interestingly, the molecular weight distribution of the addition polymer was very broad, with M~(GPC) = 3700 and M,,(GPC) = 11800. Examination by ~H NMR spectroscopy of the poly(bicyclo[2.2.1 ]hepta-2,5-diene) thus prepared showed that the polymer was not perfectly free of defects. It contained slightly less than one olefin bond in each repeating unit, i.e., approximately 85 to 90% according to the
355 signal at/5 = 6 ppm. This result indicated the presence of a small amount of branches and nortricyclene units in poly(bicyclo[2.2.1]hepta-2,5-diene) prepared under the above conditions. Alternatively, at higher monomer conversions, i.e., 90% after 30 hr reaction time at a temperature of 20~ a highly cross-linked product was obtained. Bicyclo[4.3.0t'6]nona-l,3,5,7-tetraene (Indene). Vinyl polymerization of indene under the action of Ziegler-Natta catalysts will form by the 1,2addition reaction of the nonaromatic double bond a saturated polymer bearing side aromatic moieties attached along the chain (Eq. 7.30).
n
~--
(I'o
(7.30)
This reaction has been investigated by Farona and coworkers 3s using the catalytic system Mo(CO)sPy/EtAICI2/Bu4NCI. Working in chlorobenzene at 30~ for 20-22 hours, a polyindene in 92% yield has been obtained. Structure determinations by m3C ~ spectroscopy indicated that polyindene thus prepared contained 34% repeating units formed by double bond opening, i.e., 7,8-indenylene units, and 66 % repeating units formed by ring-opening i.e., 1,4-phenylene-l',3'-propenylene.
7.3. Polymerization of Polycyclic Olefins Up to now, a substantial number of polycyclic olefins have been polymerized with Ziegler-Natta catalysts giving rise to polymers with outstanding physical and mechanical properties. Dicyclopentadiene. Relevant results on the polymerization of exo- and endo-dicyclopentadiene under the action of Re- and Mo-based catalysts reported Farona and coworkers 3s in connection with their investigations on norbornene and related cycloolefins. On using Mo(CO)sPy/EtAICI2 as a catalyst, they found that the polymer yield and the ratio of ring-retention to ring-opening was essentially dependent on the reaction temperature and nature of the solvent (Table 7.19).
356
Table 7.19 Polymerization of dicyclopentadiene(M) with Mo(CO)sPy/EtAICl2 as a catalyst"b O/A d Temp. Yiel~ % ~ exo-M 100 Heptane 1:2.7 100 exo-M 1:4.0 Chlorobenzene 54.7 25 Chlorobenzene 44.7 1:3.8 50 exo-M 1:5.8 exo-M 100 100 Chlorobenzene 1:7.3 endo-M 46.8 26 Heptane 1:3.7 endo-M 26 Chlorobenzene 31.7 1:8.6 I00 45.5 endo-M Chlorobenzene 'Data from reference 31, hAl I polymerizations were carried out for 20-22 h~rs;Wield of methanol m~luble poly(dicyclopemadime); aOlefin to aliphatic proton ratio from NMR spectrum. Dicyclopentadiene
|
|
Solvent
,
=,
The major product from the polymerization of exo- and endodicyclopentadiene was an insoluble material, a gel from the former and a white powder from the latter. The molecular weights and polydispersities are given in Table 7.20. Table 7.20 Molecular weights and polydispersities of poly(dicyclopmtadiene) prepared with Mo(CO)~Py/EtAICI~as a catalyst~b Dicyclopentadiene
Solvent
Temp., ~C
MwCy 103
PDI
2.4 1.1 50 chlorc~zene 2.8 189 100 chlorobenzene 2.2 2.4 26 heptane 2.0 1.9 26 chlorobenzene 1.6 121 100 chlorobenzene 'Data fron~ reference 3t; bReaction condition as in Table 7.19; CMolecular w'eights of the soluble fraction of poly(dicyclopemadiene). exo-M exo-M endo-M endo-M endo-M
As Table 7.20 illustrates, the nature of the solvent and reaction temperature exert a significant influence on the molecular weight and polydispersity
357 of poly(dicyclopentadiene) prepared under these conditions. Vinyl polymerization of dicyclopentadiene to poly(dicyclopentadiene) was reported by Mitsui Toatsu Chemical Co. 39 to proceed in the presr162 of catalytic systems consisting of a transition metal compound from Group IVB, VB or VIB of the Periodic Table and aluminoxanes. The transition metal compound was that of titanium, zirconium, hafnium, vanadium or chromium (e. g. bis[ cyclopentadienyl] diethyltitanium, bis[ cyclopentadienyl]titanium difluorid e, bis[ cyclopentadienyl ]d imethylzirconiu m, bis[cyclopentadienyl]diethyl~rconium, bis[cyclopentadienyl]zirconium difluoride or dichloride) and the aluminoxane was derived from an organoaluminium compound (Eq. 7.31) 13 n
,.~
(7.31)
where R = hydrocarbon group, preferably methyl, ethyl, propyl or butyl. The polymerization was conducted in a h y d r ~ o n solvents such as butane, pentane, cyclohexane, benzene, toluene or xylene at temperatures ranging from -30~ to 200~ In one example, poly(dicyclo~tadiene) was prepared in toluene at 20~ for 6 hr with bis(cyclopentadienyl)titanium dichloride and methylaluminoxane as the catalyst. The poly(dicyclopentadiene) thus produced was useful for paint, adhesive and thermoplastic resins. During their studies on the polymerization of e x o - and e n d o dicyclopentadiene induced by the Pd(II) coordination complex [Pd(CH3CN)4][BF4]z, Rissr et al. 35~ observed a significant differetw,r on the reactivity of the two stereoisomers in the presence of this catalytic system. Under these conditions, the exo monomer produced the addition polymer, poly(exo-dicyclopentadiene), with l~(GPC) = 8300 in 80% yield after 30 rain reaction time at a temperature of 25~ (Eq. 7.32).
n~
=
(7.32)
358 By contrast, the endo monomer gave only a 13% yield of addition polymer with M,(GPC) = 700 after 24 hr reaction time at a temperature of 25~ (Eq. 7.33).
n
=
(7.33)
-,,,/ By means of ~H M R spectroscopy these authors found that the polymers thus prepared contained two unreacted olefinic protons, indicating that the double bond of the less strained five-membered ring of both dicyclopentadiene monomers remained intact. The presence of the additional double bond in exo-dicyclopentadiene resulted in a smaller reaction rate as compared with exo-l,2-dihydrodicyclopentadiene. No structural rearrangements were observed for poly(dicyclopentadiene) which is a further indication that these Pd(II)-catalyzed reactions proceed by an insertion mechanism. 6,7-Dihydro-exo-dicyclopentadiene. Addition polymerization of exo-6,7dihydrodicyclopentadiene to poly(exo-l,2-dihydrodicyclopentadiene) has been conducted by Risse et al.36 using Pd z§ coordination complexes such as [Pd(CH3CN)4] [BF4]2(Eq. 7.34).
~
n
(7.34)
When a molar ratio monomer to initiator of 100:1 was employed, saturated vinyl polymers having a molecular weight M,(GPC) = 22000 and polydispersity M,,/M~ = 1.3 were obtained. Most of the monomer (75%) was consumed within 15 min at a reaction temperature of 25~ 1,4,5,8-Dimethano-l,2,3,4,4a,5,8,8a-octahydronaphthalene. The steric effect of the endo geometry was substantial in the addition polymerization of endo, exo- 1,4,5,8-dimethano- 1,2,3,4,4a,5,8,Sa-octahydronaphthalene carried out by Risse et al. 36 in the presence of [Pd(CH3CN)4][BF4]z as a catalyst (Eq. 7.3 5).
359
~ [ ~ n
[
in
=
(7.35)
In this process, poly(erMo,exo-l,4,5,8-dimethano-l,2,3,4,4a,5,8,Saoctahydronaphthalene) with molecular weight M~(GPC) = 2000 in a 23% yield was formed after 24 hr reaction time at a temperature of 25~ Starting with a molar ratio monomer to catalyst [M]:[I] = 100:1, they observed that this reaction was a "non-living" polymerization which led to a broad molecular weight distribution. 1,4,5,8-. Dim eth a n o--1,4,4a,5,8,$a-h exa hyd rona phthalen e. The vinyl polymerization of 1,4,5,8-dimethano-l,4,4a,5,8,Sa-hexahydronaphthalene (endo,exo-isomer:er~,endo-isomer = 85" 15) has been effected by Rissr et a/=.~ using the Pd(ll) complex [Pd(CH3CHzC~4][BF4]z to produce poly(1,4,5,8-dimethano- 1,4,4a,5,8,8a-hexahydronaphthalene) (Eq. 7.36).
n
=
~.
in
(7.36)
Working in CHaCI2 at a molar ratio [M]'[I] of 100:1, reaction temperature of 20~ and reaction time of 10 min, a soluble polymer having a molecular weight M,,(GPC) = 9100 and M,,(GPC) = 59000 was obtained for a monomer conversion of 35%. This polycyclic monomer with two double bonds, one being part of an exo-subsfituted bicyclic system, the second belonging to an endo-substituted bicyr unit, was expected to be less likely to cross-link under these conditions, due to the difference in reactivity between the two olefin units. However, the polymer was actually found to become cross-linked when longer reaction times were employed. For instance, when the polymerization was conducted for 100 min at 20~ a cross-linked polymer in 85% yield was produced. Substituted 1,4,5,8-d im eth a n o- 1,2,3,4,4 a,5,8,8 aoctahydronaphthalene. Vinyl p o l y m ~ t i o n of norbornene-like monomers of the types I and II was reported by Mitsubishi Petrochemical Co. 4~ to proceed in the presence of Ziegler-Natta catalysts consisting of vanadium compounds and organoaluminium compounds
360 e.g., trialkylaluminium, dialkylaluminium halide (Eq. 7.37-7.38).
n
~
[
R'
]n
(7.37)
R"
(D
R '/
\R" in
n
(7.38)
~ )l
(ID
(''3
(OH2)
4,9,5,8-Dimethano-3a,4,4a,5,8,8a,9,9a-octahydro-
1H-benzoindene.
Polymers of 4,9, 5,8-dimethano-3 a,4,4a, 5,8,8a,9,9a-octahydro- 1Hbenzoindene were manufactured by Nippon Zeon Co. 4~ in the presence of Ziegler catalysts comprising transition metal compounds and organoaluminium compounds in hydrocarbon solvents (Eq. 7.39).
In
(7.39)
Thus, working in hexane or benzene at temperatures from -30~ to 200~ under a pressure of 0-20 kg/cm 2, polymers soluble in organic solvents with excellent heat resistance and transparency, good chemical and ageing behavior as well as excellent dielectric and mechanical properties were produced. The polymer was useful for the manufacture of mouldings, e.g., optical lens, photo discs, optical fibers and circuit base boards for high frequency.
361
1,4,5,8-Dimethano-l,2,3,4,4a,4b,5,8,8a,9-decahydro-9H-fluorene. New addition polymers were obtained by Nippon Zeon Co. '2 from 1,4,5,8dimet~o-l,2,3,4,4~,4b,5,8,8~9..dec~ydm-9H-fluorene by Ziegler-Natta polymerization in hydrocarbon solvents (Eq. 7.40). n
(7.40)
The reaction occurred in various solvents e.g., hexane, benzene, toluene, in the presence of catalytic systems derived from Ti or other transition metal compounds and reducing agents e.g., organoaluminJum compounds at temperatures between-30~ and 200~ and pressures of 0-20 kg/cm 2. The poly(1,4, 5,8-dimethano- 1,2,3,4,4a,4b,5,8,8a,9-decahydro-9H-fluorene) was soluble in common solvents and had good chemical stability, good solvent
resistance, high glass transition temperature, excellent heat resistance, excellent transparency, improved dielectric and mechanical properties. The product could be used for manufacture of optical lens, photo discs, base boards for crystalline liquids, printing base boards, electronic and electric devices (Eq. 7.41-7.42).
n
(7.41)
n
L v
m
(7.42)
362 Hexacyclo [9.2.1.02"to.03'8.04'6.0x9] tetradec- 12-enes (exo, exoand endo,endo-dinorbomadiene). Investigations ~ e d out on the polymerization of exo,exo- and endo, endo~inorbomadiene, carried out by Alonso and Farona 43, in the presence of the Re(CO)sCI/EtAICI2 system, are of a great practical and theoretical interest due to the particular structure of these highly strained polycydic olefins (Eq. 7.43).
(7.43) (0
(lO
Reaction of exo, exo-dinorbomadiene has been performed in chlorobenzene at I I0~ for 24 hours to produce in 47.6 % yield a vinyl polymer, poly(exo, exo-dinorbomadiene) (Eq. 7.44). n
(7.44)
n
Analysis of the ~H NMR spectrum of poly(exo, exo-dinorbomadiene) with an olefin to aliphatic proton ratio of 1:32 indicated a minor contribution of unsaturated ring-opened structures along with the saturated vinyl units in the polymer chain. The molecular weights and polydispersity, as determined by GPC in THF and by osmometry in toluene, were M,=462,300 and M,=lg0,000, respectively, and PDI=2.57. The polymer softened at 200~ and melted above 300~ Reaction of endo, endo-dinorbomadiene, under the same conditions as the exo,exo-isomer, gave also a vinyl polymer, poly(endo, endo-dinorbomadiene), in 60~ yield by a preponderant opening of the double bond with ring-retention (Eq. 7.45).
n
=
--"
-
(7.45)
363 Although the homopolymer was of the ring-retained type, a minor olefinic signal appeared also in the mHNMR spectrum. The product had molecular weight M~--55600 and M,=37300, respectively, and polydispersity, PDI=1.49.
7.4. Polymerization of Functionalized Cydoolefins During their early studies on the vinyl polymerization of norbomene-like systems with palladium chloride, PdCI2, Schulz et al. z7 disclosed that this catalyst was quite tolerant to hydroxyl groups attached to the norbornene derivatives. Thus, 2-hydroxymethylbicyclo[2.2.1 ]hept-5-ene was readily polymerized under the action of PdCIz in acetone at 25~ for 6 hr. The polymer obtained in 20% yield was insoluble in chloroform and benzene and dissolved in dimethylformamide, dimethylsulphoxide and ethanol. The product had a low molecular weight, M~=2130, and decomposed at temperatures of 320-330~ The transition metal catalysts derived from the Pd(ll) cooordination complexes, [Pd(RCH2CN)4CI2][BF4]2, were found by Risse et al. 35 to tolerate the ester functionalities attached to norbomene moieties. However the rate of polymerization was reduced in comparison to the polymerization of norbomene. It is important to note that polymers with appropriate substituents, synthesized by this way, were found to possess a better solubility in organic solvents and a lower glass transition temperature than the parent, unsubstituted polynorbomene. Aliphatic esters of bicyclo[2.2, l]hept-5-ene-2-methanol with methyl, n-butyl, n-heptyl, n-nonyl and n-undecyl groups were polymerized by Risse et al. 44 using [Pd(CH3CN)4][BF4]z in nitromethane at 25~ resulting in the corresponding vinyl addition polymers (Eq. 7.46).
n ~CH20R
=
[~]n \
CH2OR
(7.46)
The polymer yields were moderate, i.e., in the range of 22-32%, when norbomene derivatives with a low e x o / e n d o ratio of 20:80 were used for polymerization (Table 7.21).
364 Table 7.21 Polymerization of aliphatic esters of bicyclo[2.2.1 ]hept-5-ene-2-methanol (~endo/exo : 80/20) with the Pd~CH3CN~,][ BF4]z (1~)in nitromethane at 250C~b Ma c R [M]:[I] Mwr Yieldt % CH3 100: I 3900 6600 22 200: l 8200 15000 24 nC4H9 100:1 5900 11000 24 350:1 17000 32000 24 900:1 32000 78000 25 7200 "C7HI 5 100:1 12000 25 550:1 33000 66000 26 nC9HI9 100:1 6800 12000 22 170:1 8400 16000 25 700:1 25000 53000 24 7100 12000 28 "Ct IHz3 100:1 1000:1 42000 92000 32 'Data from reference44; bReaction conditions: 16 hr at 20~ " M., M,, = number and weight-average molecular weight, respectively, determined by gel permeation chromatography (calibrated with polystyrene). 9
|
The exo-isomer of the above mixture underwent predominantly the polymerization under the above conditions. An increase in the molecular weight was observed when higher ratios of monomer to Pd(ll) catalyst were used for polymer synthesis: e.g., the molecular weight M, of the polymer prepared from n-butyl ester increased from 5900 to 32000, upon increasing monomer to catalyst ratio from 100:1 to 900 1, whereas of the polymer prepared from n-nonyl ester increased from 6800 to 25000, upon increasing the monomer to catalyst ratio from 100:1 to 700:1. However, the molecular weight distributions M,JM, (in the range of 1.6 to 2.5) were considerably broader than those of the unsubstituted poly(2,3bicyclo[2.2.1 ]hept-2-ene) prepared under similar reaction conditions. Similarly, aromatic esters of bicyclo[2.2, l]hept-5-ene-2-methanol with phenyl, 4-chlorophenyl and 3-nitrophenyl groups were polymerized by Risse et al.44 using [Pd(CHaCN)4][BF4]z in nitromethane at 20~ resulting in the corresponding vinyl addition polymers (Eq. 7.47).
n ~CH20R
..~
[~v~]n \
cNor
(7.47)
365 The polymer yields were also moderate, i.e., in the range of 24-28 %, when norbomene derivatives with a low exo:endo ratio of 20:80 were used for polymerization (Table 7.22). Table 7.22 Polymerization of aromatic esters of bicyclo[2.2.1]hept-5-ene-2-methaaol (M) (endo/exo:80/20) with the [Pd(~CH3CN)d[BFd20) in nitromethane at 20~ Lb [Ml:[x] Yielr % MW Mi R 24 8800 4200 100:1 C~l~ 26 19000 7700 150:1 28 3800 1400 100:1 4.-CI-.C~h 27 4300 1600 100:1 3-NO2-CffI4 28 5700 2300 250:1 M., M,, = number 'Data from reference**; ~.eaction conditions: l6 hr at 20~ and weight-average molecular weight, respectively, determined by gel penneauon chronmtography (calibrated with polystyrene). Again, predominantly the exo isomer underwent the polymerization reaction. An increase in the molecular weight was also observed when higher mole ratios of monomer to catalyst were used for the polymer synthesis. The molecular weight distributions M j M , in the range of 1.6 to 2.5 were further considerably broader than those of unsubstituted poly(2,3bicyclo[2.2.1 ]hept-2-ene) prepared under the same reaction conditions. The thermal properties of aliphatic and aromatic poly(5,6bicyclo[2.2, l]hept-5-ene) derivatives were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) (Table 7.23). As it can be observed, a weight loss of 5 % (under N2) was recorded at temperatures of 340~ to 350~ for the aliphatic ester derivatives and at 285~ to 339~ for the aromatic ester derivatives. The glass transition temperatures, T s, of these poly(5,6-bicyclo[2.2.1 ]hept-5-ene) derivatives were in the range of-40~ to 268~ For comparison, T 8 of the parent polymer, poly(2,3-bicyclo[2.2, l]hept-2-ene), could not be recorded clue to the onset of thermal decomposition above 320~ It was found that linear long-chain substituents such as "CTHmsC(O)O-CH2- and nCgHIgC(O)-O-CH2-drastically reduced T s to values of-25~ and -40~ respectively. Polymers of bicyclo[2.2, l]hept-2-ene ester derivatives thus prepared were soluble in a wide range of organic solvents, e.g., chloroform, dichloromethane, tetrahydrofuran, toluene and chlorobenzene.
366 Table 7.23 Thermal properties of aliphatic and aronmtic poly(5,6-bicyclo[2.2.1 ]hept-2-ene) derivatives' R
T~(5 %)/~ 349 343 344 346 339 331 285
Ta/'C ~ CH3 268 124 "C4H9 "C7H1~ -25 -40 "C9HI9 Cd'l~ 193 172 4-CI-C~-14 144 3-NOz-CrH4 'Data fxom reference"; bTon-~mmrr corrospoadmg to 5 % weight loss, determined by thermogravimetry (TGA) under Nz; "Class transition ten~erature, determined by differential scanning calorimetry (DSC).
In contrast to the polymerization of endo/exo..nf~ures of bicyclo[2.2.1]hept-2-ene derivatives, yields in the range of 70-85% were obtained for the polymerization of the pure exo~monomers with Pd(ll)compounds (Table 7.24). Table 7.24 Polymerization of esters of exo-bicyclo[2.2. I ]hept-5-ene-2-methanol (M) with the [Pd(CH3CN)4][BF4]z (I) in n i t r ~ a n e at 20~ '
R
[M]-[I] b
M8
CH3
I00:I 170:1 I000:I I00:I 200:1 I000:I I00:I 200:1 I000:I
II000 19000 138000 14000 30000 163000 14000 24000 142000
nC4H9
C~,
MW
Yield, %
14000 30000 310000
79 85 81 79 85 82 70 72 70
18000
46000 359000 18000
41000 345000
'Data from reference*~; bReaction 'conditions: 16~hr at 20~ ~ M., M, - number and weight-avorage molecular weight, resp~vely, determined by gel permeation chromatography (calibrated with polystyrene).
367 A nearly linear dependence of molecular weight on the initial mole ratio of monomer to Pd(lI) catalyst ([M]'[I]) was found, even though the polydispersity, MJM~, was quite high for the high-molecular-weight polymers. For instance, the molecular weight M, (GPC) of the addition polymer resulted from exo methyl ester increased from 11000 to 138000, when mole ratios [M]/[I] of 100:1 and 1000:1, respectively, were used. Approximately linear relationships of molecular weight to monomer conversions were found for the polymerization of esters of exa-substituted bicyclo[2.2.1]hept-2-enes (Table 7.25). Table 7.25 Molecular weight to monomer conversion in polymerization of esters of exo-bicyclo[2.2, l]hept-5-ene-2-methanol (M) with the [Pd(CH3CN)4][BF4]2 (I) in nitromethane at 20~ ~b R
Time, hr
CH3
0.5 1
nC4H9
3 0.5
C~,
4 10 0.5
1
1
4 10
Conv., ~
39 51 70 22 28 48 70 15 29 58 68
M. d
Mw 4
5800 7100 8800 4100 5100 9100 13600 3000 5800 9700 12600
7600 9200 11600 5100 5900 10400 16300 3700 8000 14500 20200
'Data from reference~; b~lole ratio monomer to P(II)-complex = I00:I m nitromethane at 20~ ~ conversion corresponds to polymer yield (cxmfirmed by GC); aM, (GPC) and M, (GPC) = number- and weight-average molecular weight, respectively, detennmed by GPC (calibrated with polystyrene). These results indicated that chain transfer and chain termination reactions were rare in pd2"-catalyzed polymerization of esters of exo-substituted norbomene derivatives. Furthermore, the ester substituents of bicyclo[2.2.1]hept-5-ene-2-methanol induced a drastically reduced rate of polymerization compared to the rate of polymerization of unsubstituted
368 bicyclo[2.2, l]hept-2-ene (50 % monomer conversion within 1-2 min under similar reaction conditions). Aliphatic esters of bicyclo[2.2.1 ]hept-5-ene-2-methanol were polymerized by Risse and coworkers 45'~ using more active (1'13allyl)palladium catalysts, (rl3-allyl)Pd(BF4) and (rl3-allyl)Pd(SbF6). Results obtained for bicyclo[2.2, l]hept-5-en-2-ylmethyl decanoate with these two catalysts are given in Table 7.26. Table 7.26 Polymerization of bicyclo[2.2.1 ]he~-5-en-2-ylmethyl decanoate (M) with the catalysts (rl3-all~r )Pd(BF4) ; nd (rlLallyl) 'd(SbF~)~ Yield M,,/M, M. Time Catalyst [M]/[Pd] % ~GPC) hr [Pd(CH3CN)4][BF4]b (rlLallyl)Pd(BF4)r (l'lLaIlyl)Pd(B F4)r (rlLallyl)Pd(BF4)~ (q3-allyl)Pd(BF4)~ (q3-allyl)Pd(gbF6)~
50/1 50/1 50/1 50/1 150/1 50/1
16 6 18 48 48 18
3900 17800 9700 9600 8800
25000
1.56 1.68
2.18 2.40 2.46 2.19
22
39 74 97 100 99
"Data from reference ~S;bSolvent: nitromethane; "Solvent: chlorobenzene The difference in activity between the (rl3-allyl)palladium catalysts was attributed to a more intimate association of the (rlLallyl)palladium unit with the smaller tetrafluoroborate anion. The presence of the solvent (nitrometh~e or chlorobenzene) was important for the stability of the (1"13al!yl)palladium complexes. Both catalysts were stable in solution at 20~ for approximately one hour; the decomposition was only slightly accelerated in the presence of air. More recently, Safir and Novak 4~ expanded the scope of this reaction by incorporating functional groups in the monomers to yield highly reactive precursor polymers. To this end, they synthesized and examined the polymerizability of diethyl bicyclo[2.2.1 ]hepta-2,5--diene-2,3dicarboxylate and diethyl 7-oxabicyr ]hepta-2, 5-diene-2,3diearboxylate. During some preliminary tests they found that Pd(CH3CN)4(BF4)z, normally a highly reactive insertion catalyst, failed to polymerize these two monomers under all conditions. They found, however, that in rigorously anhydrous organic solvents Pd(OAc)~ catalyzed
369 the slow oligomerization of diethyl 7-oxabicyclo[2.2.1 ]hepta-2,5-diene-2,3d i ~ x y l a t e over the course of several days. Surprisingly, addition of water to the reaction mixture led to a subsequent increase in the activity of the catalyst, i.e., 4-5 fold increase in the polymer yield at comparable times. The exact role of water remained unknown; the possibilities included nucleophilic aRack by water on a Pd-bound monomer to yield a Pd-alkyl species similar to the Wacker process a or the water-induc~ break-up of the inactive palladium aggregates. 49 Because excess water did not act as an inhibitor, the most convenient reaction conditions involved a simple aqueous emulsion polymerization of diethyl bicyclo[2.2.1 ]hepta-2,5-diene2,3..di~xylate or diethyl 7.-o~icyclo [2.2. l]hepta-2,5-diene-2,3dicarboxylate initiated by PdCl2 (Eq. 7.48-7.49).
. . [ ~ .COOEt ~ . i ~ C OOEt _(~ .COOEt n/~~ /~COOEt
.~._
[~]n
/ EtOOC
=
x COOEt
[~]n
EtOOC COOEt
(7.48)
(7.49)
Both poly(diethyl bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate) and poly(diethyl 7-oxabicyclo[2.2. l]hepta-2,5-diene-2,3-dicarboxylate) were readily soluble in a variety of organic solvents. A typical p o l y m ~ o n with Pd(OAc)2, using a monomer to initiator ratio of 200:1, gave a polymer in 75% yield with a molecular weight (GPC, relative to polystyrene) of 28000 and a polydispersity of 1.8. The structures of poly(diethyl bicyclo[2.2, l]hepta-2,5-diene-2,3-dicmboxylate) and poly(diethyl 7oxabicyclo[2.2.1 ]hepta-2,5-diene-2,3-dicarboxylate) were confirmed by IR, IH NMR, and {IH} 13C NMR spectroscopic methods as well as by elemental analysis. Both the ~H NMR and ~3C NMR spectra of poly(diethyl bicyclo[2.2, l]hepta-2,5-&ene-2,3-dicarboxylate) and poly(diethyl 7oxabicyclo[2.2.1 ]hepta-2,5-diene-2,3-dicarboxylate) showed evidence of a particular microstmcture, the nature of which was to be elucidated. Interestingly, kinetic studies of the homogeneous polymerization of diethyl 7-oxabicyclo [2.2.1 ]hepta-2,5-diene-2,3-~carboxylate in wet chloroform-d
370 revealed a zero-order rate dependence on monomer, a first-order rate dependence on catalyst, and a ko~ of 4.2 x 10-4 s"l (i.e., -d[monomer]/dt = k~Pd2+]). This rate behavior suggested that propagation involved a monomer-independent, rate-determining insertion p r ~ . Poly(diethyl 7-oxabicyclo[2.2. l]hepta-2,5-diene-2,3.
[' " *
/-"--\
EtOOC
COOEt
in
nfO' EtOOC
(7.50)
COOEt
During the thermal transformation process these authors observed a gradual color change from clear to deep purple which they attributed to an increase in the average degree of conjugation along the polymer backbone. This color change could be monitored by UV/VIS spectroscopy: a precursor polymer with a molecular weight of 29100 (relative to polystyrene) displayed an absorbance that red-shifted over time and culminated in an ultimate wavelength of 549 nm. Three additional independent techniques were used to characterize the polyacetylene produced as well as to probe the level of conversion of the polymer precursor poly(diethyl 7oxabicyclo[2.2, l]hepta-2,5-
371 By a similar procedure polyacetylene was produced from poly(diethyl bicyclo[2.2.1 ]hepta-2,5-diene-2,3-dicarboxylate) (Eq. 7.51).
[•x
[
jn
EtOOC
|n
+
(7.51)
COOEt / EtOOC
\
COOEt
When poly(diethyl bicyclo[2.2, l]hepta-2,5-dieno-2,3-dicarboxylate) was heated at 165~ tr~-I~lyaee~lene and diethyl cyclopenta-l,4~iene-l,5dicarboxylate resulted in high yield by a retro [4+2] Diels-Alder reaction. Oislfi et a/. ~0 reported on the addition polymerization of eta/o-Ncyclohexyl-bicyclo[2.2, l]hept-2-ene-5,6-dicarboximide and N-cyclohexyl1,4,6,9-dimetha~'lo[ 1,4,5,6,7,8,9,1 O]oetahydronaphth~ene7,8-di~xamide in the presence of several Ziegler-Natta catalysts to produce poly(e~N-cyclohcxyl-bicyclo[2.2, l]hcpt-2-cne-5,6~ic, arboximide) and poly(N-cTclohexyl- 1,4,6,9-dimethano [ 1,4, 5,6,7,8,9,10]octahydronaphthalene-7,8-di~x~nide) (Eq. 7.52-7.53).
OC,N.CO
(7.52)
I
C6Hll
ec;O"NCoH11 O1
(7.53)
OC.N.CO
66H11
The thermal stability of these polymers was studied by means of thermogravimetry and DSC. Their decomposition was found to begin at 334-363~ and the glass transition temperatures ranged from 138~ to 180oc.
372 7.5. References
1. G. Natta, G. Dall'Asta, G. Mazzanti and G. Motroni, Makromol. Chem., 69 163 (1963). 2. G. DaU'Asta, G. Mazzanti, G. Natta and L. Porri, Makromol. Chem., 56 224 (1962). 3. L. Porri, G. Natta and N.C. Gallazzi, Chimica e l ~ t r i a (Mikmo), 46 428 (1964). 4. G. Natta, G. Dall'Asta and G. Motroni, J. Polym. Sci., B 2 349 (1964). 5. G. Natta, G. Dall'Asta and L. Porri, Mal~omol. Chem., 81 253 (1964). 6. W. Kaminsky, A. Bark and I. Dake, "Proceedings of the Intl. Symp. on Recent Developments in Polymerization Catalysts", Tokyo, Japan, October 23-25, 1989. 7. G. Dall'Asta and R. Manetti, A tti A cad Naz. Lincei, Rend, Classe Sci. fis. Mat. Nat., 41,351 (1966). 8. G. Dall'Asta, J. Polym. Sci., A-l, 6 2397 (1968). 9. J. Boor, E.A. Youngman, and M. Dimbat, Makromol. Chem., 90, 26 (1966). 10. J. Boor, "Ziegler-Natta Catalysts and Polymerizations", Aeedemic Press, New York, 1979, p. 523. 11. M. F. Farona and C. Tsonis, J. Chem. Soc., Chem. Commun., 1977, 363. 12. C. Tsonis and M.F.Farona, J. Polym. Sci., Polym. Chem. Ed., 17, 185 (1979). 13. C. Tsonis, J. Appl. Polym. Sci., 26, 3525 (1981 ). 14. W. Kaminsky, A. Bark and I. Dake, "Catalytic Olefin Polymerization" (Keii and Soga, Eds.), Elsevier, Amsterdam, 1990, pp. 426-438. 15. T. Okamoto, J. Hasumoto and H. Haezawa, Polymer Prepints., J ~ , 40, E 767 (1991). 16. S. Collins and W.M. KeUy, Macromolecules, 25, 233 (1992). 17. W.M. Kelly, N.J. Taylor and S. Collins, Macromolecules, 27, 4477 (1994). 18. G. Natta, G. Dall'Asta and G. M ~ t i , Angew. Chem., 76 765, (1964). 19. G. Dall'Asta and P. Scaglione, Rubber Chem. Technol., 42, 1235 (1969). 20. G. Natta, G. Dall'Asta and G. Mazzanti, French Patent 1,294,380 (1965), Chem. Abstr., 68 (1968) 3656h.
373 21. E.P. Bokaris, M.G. Siskos and A.K. Zarkadis, Eur. Polym. J. 28, 1441 (1992). 22. A.W. Anderson and N.C. Merekling, U.S. Patent, 2,721,189 (1995). 23. W.L. Tmett, D.R. Johnson, I.M. Robinson and B.A. Montagur s Amer. Chem. Soc., 82, 2337 (1960). 24. G. Sartori, F. Ciampr and M. Camr Chim. Ind (Mikmo), 45, 1478 (1963). 25. T. Tsunio, T. Saegusa, S. Kobayashi, and T. Furukawa, Kogvo Kagaku Za~hi, 67, 1961 (1964). 26. a.J.A. Johnston, P.L. Rinaldi and M. F. Farona, J. Mol. Catal., 76, 209 (1992); b. M.A. Alonso, K.E. Bower, J.K Johnston, and M.F. Farona, Polymer Bulletin, 19, 211 (1988). 27. R.G. Schulz, J. Polym. Sci., Polym. Lea., 4, 541 (1966). 28. N.G. Gaylord, A.B. Deshpande, B.M. Mandal, and M. Martm~ ,L Macromol. Sci., Chem., A 11, 1053 (1977). 29. C. Tanelian, A. Kinnemann and T. Osparpucu, Can. d. Chem., 57, 2022 (1979). 30. A. Sen, T.W. L~ and R.R. Thomas, J. Organomet. Chem., 358, 567 (1988). 3 I. Union Carbide Corp., U.S. Patent 3,632,824 (1968). 32. Hojabri et al., Polymer 17, 710 (1976). 33. C. Mchler and W. Risse, Makromol. Chem., Rapid Commun., 12, 255 (1991). 34. C. Mehler and W, Risse, Macromolecules, 25, 4226 (1992). 35. J. Melia, S. Rush, J.P. Mathew, E. Connor, C. Mehler, S. Breunig and W. Risse, Polymer Preprtnts (Am. Chem. Soc., Dry. Polym. Chem.), 35, 518 (1994). 36. J. Mdia, E. Connor, S. Rush, S. Breunig, C. Mchler, and W. Risse,
Makromol. Chem., Macromol. Syrup. 89, 433 ( 1995). 37. Sun Oil Comp. O f P ~ l v a n i a , U.S. Patent 4,100,338 (1978). 38. J.A. Johnston and M.F. Farona, Polymer Bulletin, 25, 625 (1991). 39. Mitsui Toatsu Chem. Inc. Japan Patent 1,282-214A(1988). 40. Mitsubishi PetrocMnn., Japan Patent 41,027 (1970). 41. Nippon Zeon KK, Japan Patent 3,243-111A (1987). 42. Nippon Zeon KK, Japan Patent 3,223-013 A (1987). 43. M.A. Alonso and M.F. Farona, Polymer Bulletin, 18, 193 (1987). 44. S. Breunig and W. Risse, Makromol. Chem., 193, 2915 (1992). 45. A. Reinmuth, J.P. Mathew, J. Mdia, and W. Risse, Makromol. Chem.
374
Rapid Commun., 17, 173 (1996). 46. J.P. Mathew, A. Reinmuth, J. Melia, N. Swords, and W. Risse, Macromolecules, 29, 2755 (1996). 47. A.L. Safir and B.M. Novak, Macromolecules, 26, 4072 (1993). 48. N. Gregor and P.Henry, J, Am. Chem. Soc., 103, 681 (1981). 49. A.D. Ketley, L.P. Fischer, A.J. Berlin, C.R. Morgan, E.H. Gorman and T.R. Steadman, lnorg. Chem., 6, 657 (1967). 50. T. Oishi et al., Polymer J., 21 287 (1989).
375
Chapter 8
RING-OPENING METATHESIS POLYMERIZATION OF CYCLOOLEFINS Ring-opening metathesis polymerization of cycloolefins has been one of the most attractive and productive area of polymer chemistry for more than three decades. The reaction has a considerable theoretical and practical significance for the knowledge and applications of double-bond chemistry. By this way, it is possible to manufacture a large class of homopolymers, block copolymers, graft and cross-linked polymers of large utility in various technologies. ~-3
8.1. Ring-Opening Polymerization of Monocyclic Olefins The ring-opening polymerization reaction has been applied to a large number of monocyclic olefins, substituted and unsubstituted ones, using various catalytic systems.
8.1.1. Four-Membered Ring Monomers Cydobutene. By ring-opening metathesis polymerization, cyclobutene leads to polybutenamer, a polyalkenamer identical with 1,4-polybutadiene, well-known for its valuable elastomeric properties, which has been earlier obtained by the conventional route of the polymerization of butadiene (Eq. 8.I).
Eleuterio 4 was the first to report that cyclobutene and its derivatives polymerize by ring-opening in the presence of heterogeneous catalysts based on oxides of chromium, molybdenum, tungsten and uranium deposited on alumina, titania or zirconia and treated after hydrogen reduction with alkali metals, alkaline earth metals, boron or aluminium hydrides. Later on, the ring-opening polymerization of cyclobutene was carried out by Natta and coworkers 5'6 using a wide range of catalytic
376 systems of the Ziegler-Natta type. These authors found that, as a function of the catalytic system employed, cyclobutene polymerizes either by an addition pathway leading to a vinyl polymer, poly(cyclobutylenamer), or through ring-opening giving polybutenamer or poly(l-butenylene), or finally through both pathways providing a mixture of the two polymers (Eq. 8.2).
nit
=
~
(8.2)
In their extensive studies Natta and coworkers 6 used a large series of binary and ternary catalytic systems consisting primarily of transition metal salts of group IV-VI of the Periodic System and organometallic compounds. Of the transition metal salts, they used especially chlorides or acetylacetonate of vanadium, titanium, chromium, molybdenum and tungsten and of organometallics, e.g., organoaluminium compounds. One important finding was that while vanadium and chromium catalysts produced vinyl polymers, the catalysts based on titanium, molybdenum and tungsten gave predominantly polybutenamer (Table 8.1). Table 8. l Rmg-openmg polymenza~on of cyclobutene w ~ binary and tema~ catalytic s~rstem$ 9 trans-
Catalytic Systems
Tempi Conv Polybutenamer, % ~ I % 20 TiCI3/AICI~3AI [+45 30 TiC~3AI -10 0 -20 100 VCI4/Et2AICI 4O -20 5 MoCI~_,t3AI 45 -IO 55 MoOz(acac)~zAICI 30 I00 WCI~t3AI -20 'Data from reference6 i
Polybutenamer, % 40 65 1
30 45 30
Poly(cyclobutylenameO,~ 40 5 99 3O lO 40
377
In this reaction, though some of the catalysts displayed reduced activity, cyclobutene showed to be highly reactive and gave in some instances quantitatively polymer. The polybutenamer obtained under these conditions consisted generally of a mixture of cis and trans stereoismoers. Further investigation on cyclobutene polymerization reported by Natta and coworkers v9 employed different transition metal salts in polar solvents as reaction medium. Of these, ruthenium salts gave in high yield polybutenamer when working in water or ethanol. Interestingly, by using ethanol as solvent, the content of trans configuration in the polybutenamer was substantially improved. Early efforts by Grubbs and coworkers ~~to polymerize cyclobutene with well-defined titanium and tungsten metathesis catalysts led to linear polybutadiene with broad polydispersities and high molecular weights, which were much greater than expected from the monomer-to-catalyst ratio. Under these circumstances, they noted that during cyclobutene polymerization, only a small amount of the catalyst was activated as determined by NMR spectroscopy, indicating that the rate of propagation was much greater than the rate of initiation ( k ~ - 103 at -60~ Interesting work on the living ring-opening metathesis polymerization of cyclobutene carried out Grubbs and coworkers ~ using the tungsten alkylidene complex W(--CH'BuX=NArXO'Buh (At = 2,6diisopropylphenyl). It is noteworthy that in the presence of PMe3, the tungsten alkylidene complex catalyzes the metathesis polymerization of cyclobutene to yield linear polybutadiene with a polydispersity index of 1.03 as determined by GPC. In addition, they found that the polymerization of cyclobutene in the presence of PMes is first order in monomer and catalyst concentrations with AAG*z,K = 19.8 kcal/mole, AAH*~,) = 20.8 kca~mole, and ~AS*~)= 4 eu. Furthermore, they observed that the rate of initiation of the polymerization was much greater than the rate of propagation. On the other hand, in the absence of PMes, the polydispersity of the polymer prepared with the tungsten alkylidene complex was broader (PDI>2) due to the rate of propagation being much greater than that of the initiation, and the existence of the chain termination. These results were rationalized by the fact that PMe3 binds more strongly to the propagating alkylidene species than to the more sterically hindered initiating neopentylidene complex. Important thermodynamic studies on cyclobutene/polybutadiene system reported recently Thorn and coworkers ~2 using Schrock-type molybdenum catalysts. Based on accurate determinations of the oligomeric
378 products formed in cyclobutene polymerization under thermodynamic control, Thorn and coworkers evidenced that the cyclic trimer trarts, trarts, trarts-cyclododecatriene forms predominantly in the reaction products of cyclobutene under rigorous thermodynamic control (Eq. 8.3).
n/3
_J
l
(8.3)
These very interesting data about the nature of the reaction products in cyclobutene polymerization obtained under accurate thermodynamic control provide new aspects on the thermodynamics and mechanism of metathesis oligomerization and polymerization of small tings with this type of catalytic systems. Substituted cyclobutene. The success reported on the metathesis polymerization of cyelobutene stimulated the application of this reaction to substituted cyclobutene in order to obtain new polymers of practical importance. For this purpose, several substituted cyclobutenes bearing alkyl groups have been polymerized with various metathesis catalysts. l-Methylcyclobutene. The ring-opening metathesis polymerization of lmethylcyclobutene will lead to 1,4-polyisoprene, one of the most challenging polymers for many research groups due to its outstanding physical-chemical properties (Eq. 8.4).
Although the presence of the methyl substituent at the double bond will considerably restrain the ring-opening reaction, this route would provide one of the most attractive ways for preparing 1,4-polyisoprene with structures and properties close to those of the natural rubber.
379 The first attempts to carry out the polymerization of lmethylcyclobutene were made by Dall'Asta and M a n ~ 13 using catalytic systems based on titanium, vanadium, chromium, molybdenum and tungsten. Of these catalytic systems, the most active and selective ones proved to be those derived from WCts associated with EhAl or EhAICI. However, the structures of the polymers obtained under these conditions were not so simple. It is quite interesting to note that these products had saturated structures and possessed a polyisoprenic skeleton. In order to explain these results, it was supposed that l-methylcyclobutene yields by ring-opening polymerization the polyisoprcnic intermediate (I) which by subsequent intramolecular cyclization, under the action of the catalytic system, affords the condensed cyclohexane structures (F.q. 8.5).
>
/
ol II (1)
Interesting remits in the polymerization of l-methylcyclobutene obtained Katz and coworkers ~4 using a series of catalysts active in metathesis of acyclic olefins (Table 8.2). Table 8.2 R m g ~ m g polymerization of l-n~ylcyclobutene catalysts" in presence of transition metal ~ e s i s Polyisoprenic Conversion, CatalyticSystem % product, % 20
MoC 12(NO)z(Ph~)2/Me3AIzCI3 WCI6/Ph3SnEt
67 74
WCld~uLi Ph2C=W(CO)~
83
75
91
94
58
'Data horn referencet4 A first catalyst that these authors employed in this reaction was prepared from MoCI2(NO)'z(Ph3P)2 and Me3A]2CI3, a well-known catalyst, active in olefin metathesis. As Table 8.2 shows, the monomer conversion and the isoprenic compound were low in this case.
380 On using highly active metathesis catalysts derived from WCI6 and organometaUic compounds, both the monomer conversion and the polyisoprenic content of the product were increased. The best catalytic system for this reaction, however, was the tungsten carbene complex Ph2C=W(CO)5. Using this catalyst, Katz and coworkers obtained form lmethylcyclobutene 94% polyisoprenic product having 84-87% cis and 1316% trans stereoconfiguration. It is noteworthy that the polymer had, along with 2-methyl-butene structural units, also 2-butene and 2,3-dimethyl-2butene units. It is probable that the latter units result by subsequent migration of the methyl groups in the polymer chain under the influence of the catalytic system after the ring-opening polymerization of lmethylcyclobutene occurred. Recent studies by Thorn and coworkers ~2 on the ring-chain equilibrium in I-methylcyclobutene ring-opening metathesis polymerization and polyisoprene degradation with the well-defined molybdenum carbene initiator Mo(=CHR)(=NAr)(OR')2 indicated that, under rigorous thermodynamic control, cyclic oligomers with ttt-trimer prevailing (m - 0), along with the polymer, are formed (Eq. 8.6).
n I~/"
._._~ ~
_.., ~
(8.6)
The same products arise also in the metathesis degradation of polyisoprene under similar conditions, using the above catalytic system. 3-Methylcyr The ring-opening polymerization of 3methylcyclobutene was effected first by Natta~ Dall'Asta and Porri~ with one-component catalyst RuCI3 in polar media and then by Dall'Asta ~s using two-component catalytic systems based on vanadium chloride and organometallic compounds. In all cases, the ring-opened product was a substituted polybutenamer bearing one methyl group in the monomer unit. It is noteworthy that no methyl group migration in the chain was observed (Eq. 8.7). n
! II
n
381 It is interesting to .note that when RuCI3 in polar media was used as a catalyst, the structure of the polyalkenamer was substantially influenced by the nature of the solvent. Thus, similarly to the reaction of unsubstituted cyclobutene, ethanol as a solvent led to an increase of the trans stereoconfiguration in the polyalkenamer whereas water to an increase of the cis stereoconfiguration. The polymer resulted had an amorphous structure which was assigned to a lack of stereoregularity due to the tertiary carbon atom in the chain. Significant studies on the activity and regioselectivity in the ringopening polymerization of 3-methylcyclobutene have been effected by Dall'Asta using a series of two-component catalytic systems based on VCI4 and organometallic compounds (Table 8.3). Table 8.3 Rmg-~ening polymerization of 3-methylcyclobutene wnh two~mponemca~l:c .s~ ' n a s .~ transcisCatalytic System Conversion, Vinyl Polyalken% Polymer, Polyalken% amer~% amer,% VC LI/Et3A ]
VC~3Ga VCI4/Et2Be VC~zMg VCI4./"BuLi
37 25 17 14 3
90 90 85 94 0
0 4
3 0 45
10 6 12 6 55
'Data from reference~ As Table 8.3 illustrates, the most active systems proved to be those consisting of VCL~ and EhAl but in this case the polyalkenamer was formed in a lower amount. By contrast, the least active system, VCL,/"BuLi, showed to be the most regioselective directing the reaction exclusively toward the ring-opening pathway. It is interesting that in this case, the stereoconfiguration of the polyalkenamer was 45% cis and 55% trans. Significantly, with Mo(-CHCMe3)(=NAr)(OCMe3h as initiator, the polymer obtained had 84% cis double bonds and the methyl substituents were randomly oriented with respect to both cis and trans double bonds, t6 3,3-Dimethyleyelobutene. In the presence the of molybdenum carbene initiator, Mo(=CHCMe3)(=NAr)(OCMe3h, 3,3-dimethylcyclobutene gives
382 an all-tram, alI-HT polymer ~6 (Eq.
8.8).
I! ~
~~n
<8.8)
3,3-Diisopropylcyclobutene. In the same way, the ring-opening metathesis polymerization of 3,3-dipropylcyclobutene initiated by Mo(=CHCMe2Ph)(=NAr)(OCMe3)2 gives an all-tram, aU-HT polymer ~6 (Eq. 8.9).
n
/
I II
~
n
(8.9)
On the other hand, the initiator Mo(=CHCMe2Ph)(=NAr)[OCMe(CF3)2]2 forms a largely cis HT polymer while catalysts such as WCIdEt3AI give polymers that are neither stereospecific nor regiospecifie. 3,4,.Diisopropylcyclobutene. Ring-opening polymerization of 3,4diisopropylcyclobutene has been effected by Brunthaler, Stelzer and Leising t7 under the influence of the WCIdMe4Sn catalyst to produce high molecular weight poly(3,4-diisopropylbutenylene) in 60% yield (Eq. 8.10).
,.,o,
-( Structural measurements by IR, ~H and ~3C NMR methods indicated the presence of 3,4-diisopropylbutenylene units and no evidence for the presence of conjugated double bonds or isopropyl group shift. Interestingly, all attempts to degrade the polymer by metathesis degradation with WCI6/Me4Sn as the catalyst in the presence of trans-4-octene failed. Ring-opening metathesis reaction of 3,4-diisopropylcyclobutene in the presence of trans-4-octene led only to low molecular linear oligomers, despite of using a large excess of olefin (Eq. 8.1 l).
IT)~
-f
+ " ~
=
~~lJ,m
(8.11)
383 This remit suggested that no equilibration occurred between monomer, oligomers and polymer if such disubstimted cyclobutene was used as the starting monomer. 3,4--Bis(dimethylene)cydobutene. This disubstimted cyclobutene undergoes ring-opening polymerization in the presence of the onecomponent ROMP catalyst, titanacyclobutane, to produce living, highly conjugated polymers (Eq. 8.12).
] I!
n
18,2
//
These living polymers could be also blocked with other polyalkenamers e.g., polynorbornene to prepare block-copolymers with particular physicalmechanical properties. 3,4-Diisopropylidenecydobutene. Ring-opening polymerization of 3,4diisopropylcyclobutene with the titanium catalyst [Ti(=CH2)CI~] gave a colorless, soluble, cross-conjugated polymer after quenching with methanol ls'19 (Eq. 8.13).
1 n
I!
.~
(813)
-f Conduetivities in the range of 10.3 to 10"4 were observed after doping the polymer with iodine. The doped product was black, brittle, and air sensitive, similar to the classical Shirakawa polyacetylene. In practice, this product might be useful for preparing a weakly conducting material after the precursor polymer has been deposited on a surface of the desired shape. 8.1.2. Five-Membered Ring Monomers Soon after its discovery, the ring-opening metathesis polymerization reaction has been thoroughly studied with five-membered ring monomers in order to elucidate the main aspects of the reaction mechanism and stereochemistry and to produce speciality polymers with valuable physicalchemical properties.
384 Cyclopentene. Cyclopentene polymerizes by ring-opening to yield polypentenamer or poly(1-pentenylene) in the presence of a large number of appropriate catalytic system (F_,q. 8.14).
=
(8.14)
The ring-opening polymerization of cyclopentene is a highly stereoselective reaction in the presence of certain catalysts leading preferentially to one of the two stereoisomers, cis- or trans-polypentenamer. The reaction has a practical importance because trans-polypentenamer is a general purpose elastomer having properties similar to the natural rubber while cispolypentenamer is a special elastomer with remarkable physical-mechanical properties at low temperatures. The ring-opening polymerization of cyclopentene was first reported by Eleuterio 4 using heterogeneous catalysts based on chromium, molybdenum, tungsten and uranium. The reaction was performed with a three-component system consisting of oxides of chromium, molybdenum, tungsten or uranium supported on alumina, titania or zirconia and alkali metals, alkaline earth metals, boron or aluminium hydrides dispersed in hydrocarbons to yield polypentenamer with both cis and trans stereoconfigurations. The polymer obtained was an amorphous elastomer which developed crystallinity on stretching. A large number of two-c~mponent homogeneous catalysts based on transition metal salts and organometallic compounds employed Natta and coworkers z~ to manufacture tfigh-cis and high-trans polypentenamer by cyclopentene polymerization (Table 8.4). These authors found that a series of Ziegler-Natta type systems derived from titanium, zirconium and vanadium that are highly active in cyclobutene polymerization displayed a low activity with respect to cyclopentene, leading to conversions of the monomer of 1-3%. Though, in contrast to cyclobutene polymerization, the reaction of cyclopentene showed to be quite stereoselective, under the above conditions, yielding mainly trans_polypentenamer. Notwithstanding, systems based on chromium, cobalt, manganese, iron, uranium and barium were completely inactive towards cyclopentene whereas catalysts containing tungsten and molybdenum displayed a high activity.
385 Table 8.4 Ring-~pening polymerization of cyclopentene with binary catalyti, systmm' Catalytic System Polymer Yield,% Polymer Structure trans TiCLd~3AI " 1 trans TiBrdF.I3AI 2 C5+C2 VCId~3AI 1 VOCIdEI2AICI 3 C5+C2 1.5 C5+C2 V(acac)d~2AICl ZrC~3AI trans 1 cis MoCI~3AI 21 trans 39 WCI6~3AI 'Data from referencez'
Polymer Properties crystalline crystalline crystalline crystalline crystalline crystalline amorphous crystalline
Of the latter systems, the binary catalysts consisting of tungsten chloride and triethylaluminium proved to be the most active leading to high-trans polypentenamer and those formed of molybdenum pentaehloride and triethylaluminium to be less active yielding high-cis polypentenamer. The two types of polypentenamer thus prepared displayed different physicalchemical properties: the trans-polypentenamer exhibited a high degree of crystallinity, its melting point being 23~ and possessed good elastomeric characteristics whereas the c i s - p o l y p e n t e n a m e r was an amorphous substance with good elastomer parameters at low temperatures. Gunther et al. ~ 3 and Ntitzel et al. 24 carried o u t extensive investigation on the ring-opening polymerization of cyclopentene in the presence of a large variety of binary catalytic systems. They employed mainly tungsten and molybdenum compounds, associated with various cocatalysts such as organometallic compounds, n-allyl complexes, alkali and alkaline earth metals or Lewis acids (Table 8.5). As Table 8.5 illustrates, very active catalysts for the ring-opening polymerization of cyclopentene are derived from tungsten hexachloride and organoaluminium compounds, alkali or alkaline earth metals and Lewis acids. The polypentenamer produced is mainly of trans stereoconfiguration, the nature of the transition metal compound and cocatalyst being, however, significant. Thus, they obtained, using WCl6-based catalysts, polypentenamer having more than 90% trans content but, remarkably, on substituting WF6 for WCI6 the stereoconfiguration of the polypentenamer changed drastically to over 82% cis content.
386
Catalytic System
WCI6/'BtI3AI
~/'F~3AI2CI3 WCI~a3~VPh5 WCI6/Li3WEts WCld(~-allyl)3Cr WCld(n-allyl)4Wz WCI6/(HSiOMe)4 WCld(l-ISiOMe)s WClJHSnEt3 WCI6/Li WC~Ca WBr~/Ca WCIdAI,AICI3 WCI~OX/Ca WCh~h3Cr MoCIs/Li2VPl~, LiWPIh/BCI3 LiMoP~F3 WCIs/AICI3 Ph4W/SnCI4
Table 8.5 Cyclopentne polymerization with various binary catalytic s]tst_~ms Polymer cistransYield,% Polypemenamer,% Polypentenamer, % 35 34 5 4 6 18 8 11 35 38 21 30 45 66 62 32 52 43 45 20
9.6 82.8 75.6 11.8 72.6 39.7 34.9 45.0 9.8 20.0 10.0 11.0 20.0 17.0 55.0 68.0 8.0 38.0 20.0 8.0
90.4 17.2 24.4 88.2 27.4 60.3 65.1 55.0 90.2 80.0 90.0 89.0 80.0 83.0 45.0 32.0 92.0 62.0 80.0 92.0
'Data from referencezz The activity and stereoselctivity of these binary catalysts for cyclopentene polymerization have been further heightened by choosing appropriate additives as will be seen later. Furthermore, on using molybdenum 2S or rhenium~s compounds instead of tungsten, e.g., MoCIs/R3AI or ReCIs/'Bu3AI, the content of cis stereoconfiguration in the polypentenamer has been increased providing thus new procedures to obtain high performance polymers useful for low temperatures. Several other cocatalysts have been employed in the binary systems derived from WCI6 and organometaUie compounds for cyelopentene polymerization, z~ Such cocatalysts include "BuLi, EhAl, EhAICI, 'Bu3Al,
387 Et4Sn, Ph3SnCI, Ph4Sn. Silicon-containing compounds like Me3SiCHN2, Me3SiCH2CH=CH2, Me2Si(CH2CH=CH2)2, Me3SiCH2Li and Et3SiH showed also to be selective cocatalysts in cyclopentene polymerization at 28 room or lower temperatures. Cyclic dienes like cis, trans-l,5-cyclooctadiene and diazo compounds e.g.. ethyl diazoacetate or PhCHN2, have been used, the last being strongly cis-directing at room temperature. 29 One interesting twocomponent system proved to be WCI6 associated with substituted acetylenes like phenylacetylene, 3~ l-hexyne, l-octyne, l-decyne, etc. 32 It is noteworthy that Weiss and coworkers 32 examined in detail the influence of mono- and disubstituted alkynes on the yield and stereochemistry of cyclopentene ring-opening polymerization (Table 8.6). Table 8.6 Rmg-openmg metathesis polymerization of cyclopentene with WCI~associated with substitutod alk~es' cistransYield Catalytic System % Polypentenamer Polypentenamer % % WCl~ WCldphenyl acetylene WCId l-hexyne WCId l-oayne WCld l-decyne WCId3,3-Me2- l-butene WCIdLi-phenylacetylide WCIddiphenylacetylene WCIdbis(Me3Si)acetylene WCId4-octyne
6 >90 85 80 70 60 25 0 0 0
0 80 80 70 70 65 65 0 0 0
0 20 20 30 30 35 35 0 0 0
|
'Data from reference 32 As it can be observed from Table 8.6, WCI6 without alkyne provided a low yield of poly(cyclopentene) whereas, associated with monosubstituted alkynes, the yields of polypentenamer varied from 60 to 90% and the trans content of the polymer from 80 to 65%. Increasing the chain length and steric bulk of the alkyne resulted in a substantial reduction of the polymer yield and trans configuration. Disubstituted alkynes inhibited the ringopening polymerization and no polypentenamer was obtained in this case.
388 In addition, when the acidic proton of phenylacetylene was substituted by lithium, the yield and trans content of the polyalkenamer decreased. That the coc~talyst and temperature are significant factors in controlling the cis content in WCl6-based binary catalysts has been demonstrated by several authors. 33"38 Thus, Dimonie, Coca and Dragutan, 37'3s on using organotin, organosilicon and aluminoxane as a cocatalysts associated with WCI6, lfigh-cis polypentenamers up to ca. 9 0 0 stereoconfiguration have obtained, particularly at low reaction temperatures (Table 8.7). Table 8.7 Cyclopemene polymerization using binary systems with or ancqn t ganosilicon or alummoxane as cocatalTst' ReaSon % cis% tramCatal~c System Temp .*C Polypemenamer Pol~ent~amer WCIdPh4Sn WCIdPlhSn WCl~Vle4Sn WCIdEt4Sn WCIdEt4Sn WCldBu4Sn WCIdMe2AIlyl2Si WCId'Bu:,AIOArBuz WCIjBu2AIOAI'Buz
-20 +10 -20 -20 -10 -10 -20 0 -10
88.3 54.7 20.0 71.1 63.3 75.8 62.0 88.8 90.9
11.7 45.3 80.0 28.9 36.7 24.2 38.0 11.2
9.1
'Data from reference3s The cis content of polypentenamer has been further increased using a third component in these catalysts; for instance, when adding chloranil and piperylene to WCI6/Bu4Sn, polypentenamer of 97.5% was obtained working at a temperature of-20~ Furthermore, with the ternary catalyst WCldMe2Allyl2Si~20 the stereoconfiguration of the polypentenamer has 39 been increased from 62.0% to 74.4% cis content. It is noteworthy that the nature of the alkyl radical in the organoaluminium cocatalyst influences the trans content of the polypentenamer. Thus, triethylaluminium when associated with WCI6 as a cocatalyst leads to a higher polymer yield and trans configuration of polypentenamer than triisopropylaluminium or triisobutyl~uminium. ~'4~
389 A number of tungsten oxy compounds in conjunction with usual cocatalysts are used in the binary tungsten catalysts for cyclopentene polymerization. Thus, WOCldBu4Sn and WOCLd(CH~---CHCH2)4Si are quite selective while WOCIdEtAICIz is rea.~nably stable.42 Some other binary systems43"z include WO(OPh)dEtAICIz, WCIz(OPh)dCH3AICIz WCI4(OCHzCHCICH2CI)2/EtAICI2, WCI4(OCH2CH2CI)~uzAICI, WCI4[OCH(CHzCI)2]2 etc. x-Allyl complexes of tungsten form quite active binary catalysts when associated with I . , ~ s acids e.g., AIBr3 will produce high-trans polypentenamer. 43 MeWCI5 with a number of cocatalysts will give also weakly active systems. Tungsten carbene complex, Ph2C=W(CO)5, employed by Katz3~ to polymerize selectively several cycloolefins, has been used as such or associated with phenylacetylene or TiCLs in cyclopentene polymerization. As mentioned earlier, ternary catalysts based on tungsten or molybdenum salts, organometallic compounds and a third component, commonly an oxygen-, halogen-, nitrogen-, sulphur- or phosphoruscontaining compound, provide a wide and versatile class of initiators for cyclopentene polymerization. These additives essentially improved the catalytic activity and reproducibility, altered the catalyst stability and stereoselectivity and i n c r ~ the polymer yield. Thus, Dall'Asta and Carella4~ polymerized cyclopentene to high-trans polypentenamer using a series of catalytic systems based on tungsten halides, organoaluminium compounds and several oxygen-containing compounds like benzoyl peroxide, t-butyl peroxide, cumyl hydroperoxide, hydrogen peroxide, ethanol, phenol, water and even molecular oxygen. Likewise, Pampus et al. a s ~ used epichlorohydrin and chloroethanol to increase the catalyst stability and improve the trans content of the polypentenamer. Furthermore, N0tzel e t a / . st'S2 obtained high conversions in cyclopentene polymerization using cyclopentene hydroperoxide, aromatic nitroderivatives or inorganic peroxides. Similarly, ot-halogenated alcohols such as 2-chloroethanol, 2bromoethanol, 1,3-dichloro-2-isopropanol, o-chlorophenol, 2chlorocyclohexanol or 2-iodocyclohexanol were employed by Witte et al. 53 to obtain some of the most active and stable ternary catalysts for cyclopentene polymerization. Acetals proved to be efficient stabilizers for two-component tungsten based catalysts whereas various epoxides e.g., ethylene oxide and butylene oxide, increased the activity of these catalytic systems without affecting their stability in cyclopentene polymerization, s4 Unsaturated halogenated compounds, esters and ethers added to
390 tungsten-based catalysts were found to adjust the molecular weight of polypentenamer and impart useful properties for polymer processing. For this purpose, Oberkireh et al. ss employed vinyl chloride and Streek and Weber 56 used halides, esters and ethers such as vinyl fluoride, vinyl acetate, allyl phenyl ether, etc. It is of interest that a series of ternary catalytic systems derived from WCI6 and organoaluminium compounds containing epichlorohydrin, chloranil, dibenzoquinone, maleic anhydride, salicylaldehyde, cyanuric acid and cyanuric chloride as a third component displayed good activity and stability in cyclopentene polymerization to produce high-trans polypentenamer. With such catalysts, Dragutan, Coea and Dimonie 57 obtained polypentenamer with a trans content ranging from 72% to 85.5% as a function of the heteroatom-containing component employed. As Table 8.8 shows, significant changes in the reaction temperatures do not alter drastically the polypentenamer stereoseleetivity with trans-direeting catalytic systems containing organoaluminium compounds in contrast to earlier presented cis-speeific catalysts derived from WCI6 and organotin compounds. However, a slight increase in the tratts content of polypentenamer is obtained on substituting the organoaluminium compound, for instance, on using Et3AI2CI3 instead of EtzAICI in WCl6-based catalysts, the trans content increased from 78,4% to 81,9~ It is noteworthy that when chloranil (CA) is used instead of epichlorohydrin (EP) a significant increase in the cis content is observed. (Table 8.8). Table 8.8 Cyclopentene polymerization with heteroatom-cxaetaming ternary catalytic % cis% transReaction Catalytic System Polypentenamer Polypmtmamer Temp.~ 14.5 85.5 0 WCId'Bu3AI/EP 28.0 72.0 0 WCId'Bu3AI/CA 18.4 81.6 0 WCIdEhAI/EP 18.1 81.9 0 WCId~3AIzCI3/EP 21.6 78.4 0 WCI~tzAICI/EP 17.0 83.0 -15 WCId'Bu3AUDBQ 28.0 72.0 0 WCId'Bu3AI/MANH 19.6 80.4 0 WCI6/'Bu3AI/SALD 25.8 74.2 0 WCh,/'Bu3AI/CYAC 27.0 73.0 0 WCIJBu3AI/CYCL 'Data from reference" i
391 Similar results gave also maleic anhydride (MANH), cyanuric acid (CYAC) and cyanuric chloride (CYCL), as compared to dibenzoquinone (DBQ) and salicylaldehyde (SALD), employed as catalyst activators or stabilizers Microstructure of the polypentenamer prepared with binary or ternary WCI6-bascd catalysts is strongly influenced by the nature of the catalyst, cocatalyst, temperature and procedure of catalyst preparation. A neat difference will be observed between WChs-bascd catalysts prepared from organoaluminium or organotin compounds when the cis contents (eye) and the double bond diad distribution (r,rr of polypentenamers are compared for the two types of catalystsss (Table 8.9). As Table 8.9 fully illustrates, catalysts derived from WChs and organotin compounds led predominantly to cis-polypcntenamers having blocky or slightly blocky distribution of cis/trans double bonds diads, while catalysts consisting of WCI6 and organoaluminium compounds produced mainly trans-polylg~tenamer with random or slightly blocky distribution of the double bond diads. The effect of temperature is remarkable, the lowest ones favoring the cis stereoconfiguration of the polypentenamer and the blocky distribution of the double bonds. Table 8.9
Microstructure of polypmtmanmrs prepared with WClr binary and ternary catalytic systems'
CatalyticSystem WClJPh4Sn WCIs/Ph4Sn WCI6/Ph4Sn WCI6/'Bu3AI.EP WCI~Bu3AI.EP WCk/'Bu~il.EP 'Data from referencess
Reaction
cis-
Temp. ~
Content
Double Bond Distribution
cyr
rcrz
0.82 0.54 0.24 0.15
8.87 1.32 1.29
0.995
0.28
1.06
0.31
1.47
-20 10 25 0 0 -40
Type of Distribution blocky slightly blocky slightly blocky random random
Polymerization reactions of cyclopentene with the binary catalysts tetraphcnylporphyrinatotungsten tetrachloride,/diisobutylaluminoxane s9 and (C~TH35COOhMoCI~/:t2AICI6~ behave as living systems providing a poly~ntenamer with n~"row molecular weight distribution (e.g., M,,/M, -1.2 with the first catalyst). Several other rutherfium complexes, such as
392 diruthenium(II,ll) tetrakis(~oxylate) and Ru(H20)6(OTs)2 are also effective for cyclopentene polymerization in the presence of diazoesters. 6m'6z Classical catalytic systems derived from other transition metals than tungsten for cyclopentene polymerization were reported for titanium, molybdenum, rhenium, ruthenium, iridium, niobium and tantalum. ~'2"63 Binary catalysts containing molybdenum and rhenium pentachloride and organoaluminium compounds will lead to a Ifigh-cis polypentenamer at lower temperatures while titanium tertachloride will give a high-trans polypentenamer, zm Niobium and tantalum pentachloride associated with organoaluminium compounds will form polypentenamers with special properties, especially low-gel content polymer. 64'65 For instance, such a gelfree polypentenamer was obtained in high yield using NbCI5 in conjunction with 'Bu3Al as a coc,atalyst. It is of interest that ruthenium and iridium compounds will be active in cyclopentene polymerization when treated with trifluoroacetic acid (TFA). Such an active catalyst, reported by Porri and coworkers, 6~ RuH2(PPh3)~FFA, to lead to polypentenamer at a 50% monomer conversion. Polymerization of cyclopentene with well-defined W, Mo and Ru carbene initiators can provide high molecular weight polypentenamers with narrow molecular weight distribution. Thus, Schrock and coworkers 67 polymerized cyclopentene (50 equiv.) with the tungsten carbene complex W(=CHCMe3)(=NAr)(OCMe3)2 (0.04 M in benzene) to obtain an equilibrium mixture containing about 5% monomer (0.1 M) at -60~ and about 95% monomer (1.9 M) at 60~ On stripping completely the monomer from the living polymer, the original initiator could be reformed. In order to make a polymer of narrow molecular weight distribution (M,jM~ - 1.08) with this system, it was necessary to work at -40~ and to terminate the reaction after 1 hr, so as to forestall the tendency towards a thermodynamic distribution. 6s Similarly, the ruthenium carbene complex, R(-CHCH=CPhz)(CI)2(PCy3)2 (Cy - cyclohexyl), brings about living ring opening metathesis polymerization of cyclopentene, the propagating species being quite stable and detectable by ~H NMR spectroscopy. 69 l-Methylcyr Ring-opening metathesis polymerization of 1methylcyclopentene would lead to a polyalkenamer, i.e., poly-1methylpentenamer, whose structural unit represents the next higher homolog of that of 1,4-polyisoprene ( . . .
(8.1S)
393 The physical-mechanical properties of poly(l-methylpentenamer) may be very close to elastomers. Actually, its structural relationship with polypentenamer is of the same kind as that between 1,4-polyisoprene and 1,4-polybutadiene. For this reason, ring-opening polymerization of lmethylcyclopentene has been for long a real challenge for polymer scientists. Early attempts by Ntitzel et al. 7~ to ring-open polymerize lmethylcyclopentene with a catalytic system based on WCI6 were unsatisfactory. L~er on, the reaction has been carried out by Katz ~4using a binary catalyst consisting of molybdenum complexes and organoaluminium compounds, e.g., MoCIANO)APh3P)z/Me~AIzCI3, but the conversion was low and the polymer obtained had undefined structure. 3-Methylcydopentene. In contrast to the above isomer, 3methylcyclopentene was readily polymerized to the corresponding polyalkenamer, poly(3-methylpentenamer), in the presence of WCl~-based catalytic systems. 7~ By this way, poly(-3-methylpolypentenamer) was formed having the methyl group in the monomer unit in the r position with respect to the double bond (Eq. 8.16).
= ~
(8.16)
Spectroscopic investigation of the polymer structure indicated that poly(3methylpentenamer) thus obtained contained over 90% trans stereoconfiguration at the carbon-carbon double bond. The product was amorphous and had different physical-mechanical properties as compared to parent polypentenamer. Individual enantiomers of 3-methylcyclopentene have been prepared by ring-closing metathesis and polymerized by Sita 7~ in the presence of molybdenum carbene complex Mo(=CHMezPhX=NAr)[OCMe(CF3)2]z at -30~ to give a 52% yield of a 74% trans polymer. 4-Methylcydopentene. A mixture of 3- and 4-methylcyclopentene (2:3) undergoes ring-opening polymerization in the presence of the metathesis initiator WCIs/PhC-~CH in toluene to form a 90% trans polymer, n The product was probably a mixture of the two isomeric substituted polyalkenamers, bearing the methyl group in the r and [3 positions with respect to the double bond. When 4-methylcyclopentene was reacted with
394 the molybdenum carbene complex Mo(=CHMezPhX=NAr)[OCMe(CF3)2]2 at -55~ a 51% yield of 60*,6 cis polymer was obtained, with a blocky cis/trans distribution of the double bonds (rert = 6.3) (Eq. 8.17)
The hydrogenated product was atactic as shown by its ~3C NMR spectrum 73 Cyclopentadiene. By ring-opening polymerization, cyclopentadiene will lead to polypentadienamer, or poly(pentadienylene), the analogous polymer with a higher unsaturation degree of polypentenamer (Eq. 8.18).
n~
~
.~~~~
(8.18)
Cyclopentadiene polymerization in the presence of the binary catalyst W C I s / A I C I 3 has been performed by Marshall 74 to obtain in high yield a powdery amorphous polymer. However, the structure of the polymer has not been examined in detail. As can be seen above, the monomer units may enter the growing chain in two ways to yield head-head, head-tail and tailtail structures. This configuration may undergo further side cyclization and elimination reactions to form polymers of undefined structures. With WCI6 as a catalyst,, in toluene, a soluble polymer of low molecular weight has been obtained. 75
8.1.3. Six-Membered Ring Monomers Due to the high stability of the six-membered cycle toward ringopening reaction, polymerization of this class of monomers stimulated a special interest for the metathesis scientists. For this reason, the reaction of cyclohexene and related monomers has been a challenging subject. Cyclohexene. Ring-opening polymerization of cyclohexene should form the higher homolog of polypentenamer, i.e., polyhexenamer or poly(lhexenylene) (Eq. 8.19).
nC)
---.
8,9,
395 Nonetheless, due to the high thermodynamic stability of the cyclohexene ring, the opening reaction occurs with difficulty under common circumstances. Eleuterio 4 in his pioneering work on cycloolefin polymerization with heterogeneous catalysts based on chromium, molybdenum, tungsten and uranium oxides attempted to polymerize cyclohexene in the presence of these catalytic systems. He found that under these conditions, cyclohexene scarcely reacted and only traces of oligomers could be obtained. Later on, A m a s s et al. 76 tried to react cyclohexene under the effect of homogeneous tungsten hexachloride based catalysts but undefined polymers in 4% yield were produced. More r ~ t l y , Patton and McCarthy" reported on the polymerization of cyclohexene in the presence of WCIdMe4Sn catalysts at 77~ to produce oligomers in the 2-6 DP range. However, the evidence for cycloolefin metathesis comes from gas and gel permeation chromatography of the reaction products as well as from infrared and ~H NMR spectra of the reaction mixtures without isolation and characterization of the oligomeric products. The most convincing structural evidence provided by the authors was the conversion of an isolated mixture of oligomers back to cyclohexene upon exposure to tungsten hexachloride/tetramenthyltin catalyst. Further studies were carried out by Patton and McCarthy on the copolymefization reaction of cyclohexene with norbornene in the presence of the same catalytic system (see chapter 11). 1,3-Cyclohexadiene. Ring-opening polymerization of 1,3-cyclohexadiene has been reported to occur under the influence of iridium salts in polar media complexed with cyclooctene or 1,5-cyclooctadiene~ (Eq. 8.20).
nQ
~
(8.20)
For instance, using a catalytic system consisting of IrCI3/I-120 and cyclooctene, low yields of ill-defined polymers have been produced in ethanol and water. With WCI6 1,3-cyclohexadiene has been polymerized but the structure of the polymer is unknown, w 8.1.4. Seven-Membered Ring Monomers
Extension of the ring-opening metathesis polymerization to sevenmembered ring monomers provided new polymers with interesting physicalmechanical properties.
396
Cycloheptene. By ring-opening polymerization, cycloheptene will lead to polyheptenamer, according to the following reaction (Eq. 8.21).
(8.21) Ring-opening polymerization of cycloheptene has been effected in the presence of several tungsten- and molybdenum based catalysts. Natta and coworkers s~ used binary catalytic systems consisting of WCI6 or MoCI5 and Et3AI or EhAICI to yield tfigh-trans polyheptenamer with over 85% trans stereoconfiguration at the double bond. The polymer had a crystalline structure as determined by X-ray analysis. A polyheptenamer having predominantly trans stereoconfiguration (65%) obtained also Porri and coworkers 6~ using Ir/ATF complex as catalyst. White tacky polymers with undefined structures have been obtained with WCI6/Bu4Sn as a catalyst, s~ By contrast, 95% cis polyheptenamer has been prepared by Katz s2 using the unicomponent tungsten carbene complex Ph2C=W(CO)5 and 80~ cis polyheptenamer with WCI6/PhC-=CH or W(CPh)CI(CO),/O2 as catalysts, s3.s4 Lower cis contents of polyheptenamer (20-50~ have been obtained by Kress s~'s6 and Dounis 87 using tungsten and molybdenum carbene complexes. It is remarkable that in the presence of the tungsten carbene complex [CH2],CH=WBr2(ORh/CmBr3 (R = -CH2CMe3) Kress and Osbom s~ succeeded to detect by ~3C NMR the corresponding intermediates, tungsten carbene cycloolefin and tungsten carbene metallacyclobutane, formed be the interaction of cycloheptene with the catalytic species. With heterogeneous catalysts based on rhenium oxide cycloheptene gave low oligomers, ss's9 For instance, under the action of RezOT/AI203, preferably pretreated with Me, Sn, a 68% yield of cyclic dimers was obtained, the proportions being close to the equilibrium values: tt 88%, tc 9 % and cc 3%. Cyr Ring-opening polymerization of cyclohepta-l,3diene will form the polyheptadienamer by opening of one carbon-carbon double bond of the cycle (Eq. 8.22).
(8.22)
397 Early studies on cyclohepta-l,3-diene polymerization in the presence of WCI6 catalysts have been camed out by Laverty79 but the reaction product was undefined.
8.1.5. Eight-Membered Ring Monomers The ready availability of eight-membered ring eycloolefins stimulated a thorough investigation of their ring-opening metathesis polymerization in order to apply it for commercial purposes. Of these monomers, cyclooctene has been successfully ring-open polymerized to give a valuable commercial product. Cyclooctene. Cyclooetene readily polymerize by ring-opening in the presence of appropriate catalytic systems to form polyoetenamer or poly(loctenylene) (Eq. 8.23).
The ring-opening polymerization of cyclooctene has been first reported by Eleuterio 4 in the presence of heterogeneous catalysts based on chromium, molybdenum, tungsten or uranium oxides. Later on, the reaction has been effected by several investigators in the presence of various catalytic systems for both theoretical and practic~ purposes. Thus, Natta and coworkers s~176 employed homogeneous catalysts derived from WCI6 or MoCIs and EhAI or EhAICI to polymefize cis-cyclooctene to highly trans polyoctenamer, the polymer was crystalline and displayed good elastomeric properties. trans-Cyclooctene did not polymerize under the above conditions. Subsequently, Calderon9t and Scott ~ polymerized cis-eyclooctene with the binary catalyst WCIdEtAICIz to crystalline polyoctenamer, having both cis and trans stereoconfiguration of the double bonds in the polymer chain. It is very interesting that in this reaction, Calderon and coworkers observed the formation of cyclic oligomers which were separated and characterized by physical-chemic~ methods. The formation of cyclic oligomers from cyclooctene in the presence of WCIdEtAICIz as a catalyst has been also reported by Wassernmn, 93 Wolovsky94 and H6cker;95 this process has had a great importance for practical applications and for the understanding of the reaction mechanism.
398 High conversions to cyclic oligomers containing a substantial proportion of dimers have been achieved from cis-cyclooctene with alumina-supported Mo, W, or Re catalysts, ss'9*'9* For instance, a 30% yield of cyclic dimers, in their equilibrium proportions (tt 16%, tc 58%, cc 26%), has been obtained by passing a 0.02 M solution of cis-cyclooctene in pentane through Re2OT/AlzO3 at 15-50~ HOcker and coworkers~ showed that, under certain conditions, the proportion of dimer initially formed can exceed the ultimate equilibrium value. They found that in the early stages of the reaction catalyzed by WCIdMe4Sn, the concentration of oligomers was kinetic,ally controlled and their final concentration was determined by the ring-chain equilibrium.99 Substitution of ethylaluminium compounds with other organometallic compounds in the tungsten-based catalytic systems allowed to create various catalysts able to produce polyoctenamer with different characteristics as a function of the reaction conditions. On this line, Calderon and Morris, t~176 prepared a polyoctenamer using the binary catalyst WCId'Bu3AI obtaining a trans-polyoctenamer whose stereoc~nfiguration varied with the reaction time. They observed that the melting point of this product ranged between 20~ and 60~ an increase of I~ occurring for each percent of trans double bond in the polymer chain. Likewise, Bradshaw t~ employed a binary catalyst consisting of WCI,, and BruSh, obtaining substantial yields of high molecular weight polyoctenamer with excellent elastomerie properties. Furthermore, catalytic systems free of organometallics have been reported; thus, Marshall and Ridgewell ~4 observed a high activity using WCI6 associated with AICI3 in the cyclooctene polymerization. High-tram polyoctenamer has been prepared with numerous other catalytic systems based on tungsten, molybdenum or iridium compounds. Of these catalysts, it is worth noting that activation of the iridium complexes by excess of trifluoroacetic acid will form efficient transdirecting catalysts for cyclooctene polymerization. ~s It was also found that catalysts based on WCId'Bu3AI or WCId'Bu2AICI, to which a third component such as chloranil or water has been added, give 75-90~ cis polyoctenamer in the early stages of reaction. Catalysts giving imermediate trans content, sometimes increasing with cyclooctene conversion, include WCId'Bu3AI/H20, WCId'BuzAICI/2,6-di-tert-butyl-4-methylphenol, (xallyl)~W/AIBr3, [PhOC =w(CO)~]'NMe4'/EtAICI2 and PhC=W(CO)4CI/TiCI4. Also, catalysts affording high cis polyoctenamer are formed from unicomponent tungsten ~ne complex
399 Ph2C=W(CO)5 or binary, ternary or quaternary tungsten-based catalysts such as WCIdEtAICI2, MoCIz(PPh3)-~'NO)dEtAICI2, WF6/Et3AI2CI3/CCI3CH2OH, WCI4(OCH2CH2CI)2/EtAICI2/BF3/Et20. During extensive studies, Streck ~~176 obtained polyoctenamer with 63% cis configuration by employing ternary catalytic systems consisting of WCI6, CzHsAICI2 and organic acids such as acetic acid. On using mineral salts of organic acids, e.g., lithium palmitate or alkoxides, e.g., aluminium secbutoxide, the trans content of the polymer increased substantially. For the binary catalytic systems, addition of divinyldiphenylsilane or certain phenols raised the cis content to quite high values. The trans monomer gave a 43% cis polyoetenamer ~~ in the presence of MoCk~'PPh3)-R'NO)z/EtAICI2 and was readily polymerized~~ by the ruthenium carbene complex Ru(=CHCH=CPhz)(CI)~(PPh3h. Cyclooctene polymerization in the presence of WCI6 and q3u3Al in conjunction with epichlorohydrin or chloranil yielded mainly cispolyoctenamer at both high and low reaction temperature ~~ (Table 8.10). Table 8.10 Cyclooctene polymenzation with WCl6.-based r Catalytic System WCId'Bu3AI/EP 1"1.8"1
WCId'Bu3AFEP 11.8:1
WCId'Bu3AFCA 1"1.8"1
Reaction Temp.~ +20 +20 +20 +20 +20 +20 -20 -20 -20 -20 +20 +20 +20
Conversion % 8.0 15.0 19.0 26.5 27.0 30.0 7.5 8.0 9.0 10.0 25.0 55.0 80.0
~
cis-
trans-
Polymers% 62.1 58.5 53.2 54.3 5o.1 42.0 65.1 60.1 55.3 45.5 58.0 47.0 45.5
Polymer,% 37.9 41.5 46.8 48.7 49.9 58.0 34.9 39.9 44.7 54.5 42.0 53.0 54.5
iData from referencet66
As it can be observed, the cis content of the polyoctenamer gradually changes as the conversion degree increases. Similar results have been recorded using the catalyst WCldq3uzAIOAlq3uz. ~~
400 It is noteworthy that cis-cyclooctene in the presence of the binary catalyst WCldPh4Sn, a highly cis-directing system for cyclo~tene polymerization, does not polymerize. However, addition of small amounts of cyclopentene, cyclohexene or 1,5-cyclooctadi~e allowed conversions of cyclooctene from 20 to 30% to be attained ~~ (see Figure 4.21). On the other hand, polyoctenamers with lfigh-cis stereocontiguration have been obtained using the catalytic system WCIdMezAllylzSi and traces of water as evidenced by t3C NMR spectroscopy." As it will be seen later, the same catalytic system promoted the ring-opening polymerization of 1,5-cyclooctadiene to polybutenamer with a high-cis configuration. l-Methylcyclooctene. While l-methyl-cis-cydooctene has not been polymerized, 1-methyl-trans-cyclooctene in the presence of W(=CPhz)(CO)s gave a perfect head-tail, methyl substituted polyoctenamer, poly(l-methyloctenylene) m~ (Eel. 8.24)
n ~---
.___.~ ~
(8.24)
The polymer microstructure has been determined by ~3C NMR spectroscopy. Data obtained on the polymer structure indicated that the methyl group attached at the double bond exerts a strong regioselectivity during the propagation reaction. 3-Methylcyclooctene. By ring-opening polymerization, 3methylcyclooctene will lead to poly-3-methyloctenamer or poly(3methyloctenylene) (Eq. 8.25).
n
~
~
(8.25)
The reaction 3-methyl-cis-cyclooctene has been carried out by Calderon and coworkers 9~ with the catalytic system WCl~tAICIz to obtain both cyclic oligomers and poly-3-methyloctenamer in low yield. Subsequent studies on the structure of the hydrogenated polymer carried out by Dall'Asta ~~ indicated 5% head-he~, 5% tail-tail and 90% head-tail configuration of the monomer units in the chain. The hydrogenated polymer
401 has quite a high rate of crystallization in spite of the head-head and tail-tail irregularity and the atacticity resulting from the racemic mixture of the two enantiomer structures. 3-Phenylcyclooctene. Ring-opening polymerization of 3-phenylcyclooctene in the presence of metathesis catalysts will give poly-3-phenyloctenamer or poly(3-phenyloctenylene) (Eq. 8.26). Ph
n(
.~=.. ~
Ph
(8.26)
The polymerization of 3-phenyl-cis-cyclooctene has been performed by Calderon and coworkers 9~ in the presence of WCIc,/EtAICI2 to obtain poly3-phenyloctenamer. Studies on the polymer structure by ~H NMR indicated that the resulting polyalkenamer had the phenyl group in the ~ position with respect to the carbon-carbon double bond, without any migration of the phenyl group during the polymerization reaction. 5-Methylcydooctene, The ring-opening metathesis polymerization of 5methyl-cis-cyclooctene will lead to a product with the structure of the ternary butadiene-ethene-propene copolymer (Eq. 8.27).
The polymerization of this monomer was first carried out by Calderon and coworkers 9~ with the catalytic system WCIs/EtAICI2 obtaining in high yield the methyl substituted polyalkenamer. The polyalkenamer had predominantly a t r a n s stereoconfiguration. It is noteworthy that the methyl substiment in the position 5 with respect to the c a r b o n ~ o n double bond did not significantly modify the monomer polymerizability. Related studies by Sato et al. ~ revealed that the t r a n s content falls to 32% if the polymerization is conducted at lower temperatures and at low AI:W molar ratio. In this case, probably, the methyl substituent is too far away from the double bond to influence the propagation reaction and it may be assumed that the polymer chain consists of randomly oriented units.
402
5-Phenylcydooctene.
By ring-opening polymerization, 5phenylcyclooctene will form the ternary copolymer butadiene-ethenestyrene (Eq. 8.28).
n Ph-~ ~
~
Ph
~
(8.28)
Calderon and coworkers 91 carried out the reaction of 5-phenyl-ciscyclooctene in the presence of WCI6 and EtAICI2 to obtain poly-5phenyloctenamer in a good yield. The monomer showed to be highly reactive in spite of the bulky phenyl group in the 5-position. The polyalkenamer had a well-defined structure and displayed interesting elastomeric properties. 4-Methyl-6-phenylcydooctene. Polymerization of 4-methyl-6-phenyl-ciscyclooctene has been effected in the presence of WCI4(OC6HrPhr 2,6)/EhPb as the catalyst ttz (Eq. 8.29).
Me
Me Ph
The polyalkenamer had a microstructure corresponding to the terpolymer propylene-styrene-butadiene. 4,6-Diphenylcyclooctene. 4,6-Diphenyl-cis-cyclooctene has been polymerized in the presence of WCI4(OC6HrPhz-2,6)/Et,Pb to the disubstituted polyoctenamer tt2 (Eq. 8.30). Ph
Ph
Ph
(8.3o)
The product displayed the microstructure of the well-known copolymer prepared from styrene and butadiene.
403 1,3-Cydooctadiene. Ring-opening polymerization of 1,3-cyclooctadiene will lead to the unsaturated polyalkenamer having two conjugated double bonds in the polymer chain (Eq. 8.31).
n
(-)
----D,.
~
(8.31)
This reaction has been effected by Korshak et a/. ~3 in the presence of WCI4[OCH(CH2CIh]2/Et2AICI as a catalyst, with or without an ether as the additive. The polymer obtained contained mainly 1,3-diene structures corresponding to head-tail addition, but isolated C=C bonds and 1,3,5trienes were also present, indicating some head-head and tail-tail addition reaction. The polymer was initially a rubber-like product, which rapidly became brittle on exposure to air. ~4 1,4-Cyelooctadiene. Unlike its above 1,3-parent monomer, ring-opening polymerization of 1,4-cyclooctadiene will provide a higher unsaturated polyalkenamer, having additional unconjugated double bonds along the polymer chain (Eq. 8.32).
First, Amass ~m5 tried to polymerize 1,4-cyclooctadiene using WCh, but undefined products were obtained. More recently, Streck and coworkers ~m6']]7carried out the polymerization of 1,4-cyclooctadiene in the presence of the ternary catalytic system WCIdEtAICI2/EtOH, sometimes activated by allyl-2,4,6-tribromophenylether. In these conditions conversions up to a 67% were attained, yielding a high molecular weight polybutadiene-like rubber with the structure of the alternating copolymer propenylene-pentenylene. It is worthwhile noting that employing acyclic olefins as molecular weight regulators, Streck and coworkers s u ~ e d in preparing low molecular weight products useful as oxidatively drying oils. 1,5-Cyclooctadiene. Ring-opening polymerization of cis, cis-l,5cyclooctadiene, a monomer readily obtained from butadiene by cyclodimerization or from cyclobutene via metathesis, will lead to polyocta1,5-dienamer or poly(octa-l,5-dienylene) which is identical to the wellknown polybutenamer or 1,4-polybutadiene rubber (Eq. 8.33).
404
(8.33)
For a long time this reaction was a real challenge to the polymer scientists as a neat route to prepare high-cis or high-trans polybutadiene. The polymerization of 1,5-cyclooctadiene has been successfully performed by Calderon and coworkers 9''~ with the binary catalyst WCIdEtAICIz. Conversions of over 60~ have been attained leading to both cis- and trans1,4-polybutadiene, the product possessed quite good elastomeric properties. In order to obtain 1,4-polybutadiene with higher steric purity, Calcleron et al. ~s investigated several other catalytic systems. It is noteworthy to outline that using the less active catalyst consisting of WCI6 and 'Bu3AI, they succeeded in obtaining 1,4-polybutadiene with more than 75% cis stereoconfiguration. Later on, a great number of tungsten-based catalytic systems have been employed in 1,5-cyclooctadiene polymerization. A series of catalysts contain WCI6 associated with various cocatalysts such as 'BuzAICI, PhCHNz, EtOCOCHNz, AIBrflthiophene. ~mg"mz~Most of them yielded a polymer of high cis stereoconfiguration, of the order of 80%, one of the cis double bond being already preformed in the monomer. The cis content in the polyalkenamer has been increased by several means. For instance, the system HzWO4/AICI3 gave at-20~ a 93% cis polymer. TM Good remits have been obtained employing WCI6 associated with certain cocatalysts such as acetylenes, ~zz cyclodienes, ~z~ PhCHN2, TM polyge nnanes~z~ or methylallylsilane in the presence of water, s7 With the latter catalytic system, cis, cis-l,5-cyclooctadiene gave a polybutenamer having over 83% cis stereoconfiguration s7 (Table 8.11). It is quite remarkable that with some catalytic systems, such as WCIdPI~Sn and WCIdBu4Sn, the cis content is high (-85%) and remains at this level, with no sign of the development of tt diads with increasing time. With other catalysts, for instance WCIdEtAICIz, both secondary cis-trans isomerization and double bond shift reactions were observed. ~s Interestingly, the ~H NMR spectra of the polyalkenamers produced with WCIc,/'BuzAIOAl'Buz as a catalyst show that the newly formed cis and trans double bonds are randomly disposed in the polymer
405 Table 8.11 R i n g ~ m g polymerization of cis, cis-l,5-cyclooctadiene in the presence of the ternary catalyst WCI~.Me2AIlyl2Si.H~O'
CatalyticSystem
Reaction
c/s-
Temp. ~
Polybutenamer %
trans-
Polybutcnamcr %
=
WC~e2Allyl2Si/H20 WC~e2Allyt2Si/H20
+20 -20
81.12 83.34
18.88 16.66
'Data from reference~7. chain and that addition to form a t r a n s double bond needs and activation energy 31 kJ/mole higher than that needed to form a cis double bond. ~27 Catalysts based on other transition metals are also effective for cyclooctadiene polymerization. Of these, those based on molybdenum, m2s'~29 rhenium ~3~ and ruthenium ~33~35are ofinterest. Early studies by Calderon and coworkers 9~'92on 1,5-cyclooctadiene polymerization with the WCI6/EtOH/EtAICI2 catalyst indicated that macrocyclic oligomers consisting of the "whole" multiples of monomer (CgHI2), and sesquioligomers (C4H6), were formed. Later on, Chauvin and coworkers ~36 showed that, at the thermodynamic equilibrium, the C m6, C20, C24 and C2s up to C40 oligomers and sesquioligomers prevailed in the reaction products of 1,5-cyclooctadiene when reacted with the catalyst (CO)sW=C(OEt)Ph~iCL,. Similar results were reported by Sato et al. ~3t More recently, Thorn and coworkers ~37found different data concerning the composition of the reaction products obtained in 1,5-cyclooctadiene polymerization in the presence of tungsten and molybdenum carbcne complexes M(=CHR')(=NAr)(OR '') (M=W,Mo), at thermodynamic equilibrium. In contrast to earlier results, the butadiene trimers (m=l) were greatly preferred from both 1,5-cyclooctadiene polymerization and 1,4polybutadiene metathesis degradation, on the expense of higher oligomers (Eq. 8.34).
406 Of the possible stereoisomers of the butadiene trimers, trans, trans, transcyclododecatriene was the main product, under these conditions. Similar results were obtained also with WCIdROR/Bu4Sn as a catalyst. ~38 As an interesting extension of 1,5-cyclooctadiene polymerization using well-defined tungsten and ruthenium carbene catalysts, W(=CHAr)(=NPh)[OCCH3(CF3)2]2(THF) (where Ar = o-methoxyphenyl) and Ru(PCy3)2(CI)2(=CHCH=CPh2), was reported by G~bbs and coworkers ~3S'~39 for the preparation of hydroxytelechelic polybutadiene from 1,5-cyclooctadiene and ot,to-difunctional olefins. Such endfunctionalized polybutadiene has entirely 1,4 repeat units and only one type ofhydroxy end-group in the polymer chain (Eq. 8.35).
0()
[W, Ru]
§
AeO~OAe
=
A - r/-,. ~ cO'[ ~
1.OAt
~J'2n+l
=
HO'~e~j~
(8.35)
Molecular weights (M,), polydispersities (PDI) and polymer yields obtained for telechelic polybutadiene using various molar ratios of tt,tJ~-difunctional olefin vs 1,5-cyclooctadiene are given in Table 8.12. Table 8.12 Synthesis of polybutadiene telechelomers from 1,5-cycloo~diene (COD) with well-defined metathesis tungsten carbene catalysts' Olefin 9COD
M, x 10 .3
PDI
47.4 41.7 37.1 5.49 9.31 26.9 21.3 12.7 14.1 18.5 'Data from reference~39
2.1 2.0 2.0 2.1 2.1 3.0
0
1.53
Polymer Yield, % 92 9O 71 62 51 40
As it can be observed, the employed cx,t~-difunctional olefin changed considerably both the molecular weight and the polymer yield of the polybutadiene but, for a wide range of values, the polydispersity index was not affected significantly. Remarkably, the functionality of the
407 hydroxytelechelic polybutadiene thus obtained was close to 2, what is very important for most practical applications. l-Methyl-l,5-cydooctadiene. It is quite interesting that the higher substituted homolog of 1,5-cycloocatdiene, l-methyl-l,5-cyclooctadiene, will form by ring-opening polymerization poly-(l-methyloctadienamer), which is an ~temating copolymer of isoprene and butadiene (Eq. $.36).
On using the ternary catalyst WCIdEtAICIz/EtOH, Calderon and coworkers ~4~carried out the ring-opening polymerization of l-methyl-l,5cyclooctadiene to produce in high y i e l d (~80%) poly(lmethyloctadienamer) with a structure of the alternating butadiene-isoprene copolymer. The product with T8 = -85~ displayed good elastomeric properties. At low monomer conversions, some oligomeric products with only traces of sesquioligomers were formed. On increasing the monomer conversion, the proportion of sesquioligomers gradually increased, indicating that the substituted double bonds are partially reactive. ~'~ I-Ethyl-l,5-cydooctadiene. Ring-opening metathesis polymerization of lethyl- 1,5-cyclooctadiene occurs at the unsubstituted double bond giving the substituted polyalkenamer (Eq. 8.37). Et
=
~
Et
(8.37)
Cyclic oligomers are also formed, which are made up of the whole units of monomer with little sign of the sesquioligomers, indicating the inhibiting effect of the ethyl substituent on the adjacent double bond. TM 3-Methyl-l,5-cydooctadiene. In the presence of WCl6-based catalysts, 3methyl-l,5-cyclooctadiene leads to the corresponding substituted polyalkenamer (Eq. 8.3 8).
408 Oligomers and sesquioligomers may also be formed due to a little influence of the methyl substituent on the reactivity of the two double bonds. 1,2-Dimethyl-l,5--cyclooctadiene. 1,2-Dimethyl- 1,5-cyclooctadiene will react at the unsubstituted double bond to give the corresponding disubstituted polyalkenamer, poly(l,2-dimethyl-l,5-cyclooctadiene) (Eq. 8.39).
n~
=
(8.39)
Due to the difference in reactivity of the two double bonds, oligomers of the starting monomer without sesquioligomers might also arise. 3,7-Dimethyl-l,5-eyclooetadiene. 3,7-Dimethyl-l,5-cyclooetadiene can polymerize to any of the unsubstituted double bonds to form the disubstituted polyalkenamer (Eq. 8.40).
n~
~
~
(8.4O)
I A significant amount of oligomers and sesquioligomers may arise taking into account the equivalent position of the substituents with respect to the double bonds. Cyclooctatetraene. Ring-opening polymerization of cyclooctatetraene provides a direct and efficient route to manufacture polyacetylenes (Eq. 8.41). n
~
~
L
Jn
(8.41)
Both classical and well-defined catalysts have been employed to polymerize cyclooctatetraene, in bulk or in solution, to produce in quantitative yield high molecular weight polyacetylenes. Early results on cyclooctatetraene ring-opening polymerization were reported by Korshak et al. ~2 using the binary systems W[OCH(CH2CI)~],CI6~ and Et2AICI (n = 2 or 3). Polymer
409 yields up to 40% were obtained depending on the polymerization procedure, solution or bulk. In the former ease, there was a much greater tendency towards formation of oligomers. In the second case, the nature of polyacetylene depended on the ratio AI/W from the catalyst. When AI/W = 1, the polyacetylene was a blue-black film containing 84% cis double bonds whereas when AI/W = 2 the polymer was golden and contained 39~ cis double bonds. A 50~ yield of polyaeetylene has also been obtained by Makovetsky ~zz from neat monomer using WCIdBuC---CH as a catalyst. More recently, Grubbs and coworkers ~3 effected the ring-opening polymerization of cyclooctatetraene in a more controllable fashion with the well-defined tungsten carbene catalysts such as W(=CH'BuXOP,)2(=NAr) and W(--CH'BuXOR'hBrz.GaBr3, where R=C(CH3)(CF3h and R'=CHzrBu. Polyacetylene was readily obtained in various yields and with interesting physical-mechanical and electrical properties depending on the catalyst employed and the applied polymerization technique. The properties of these polyacetylene films were nearly identical to those of polyaeetylene produced by the Shirakawa method ~" (Table 8.13). Table 8.13 Physical properties of polyacetylene prepared by ROMP of cyclooctatet~ene (COT)' and Shirakawa methodb Physical Property Appearance Surface
Surface area (mZ/g)
Density, bulk (g/cm3) Density, flotation (g/cm3) Conductivity, undoped (ohm'l/cm) Conductivity, iodine-doped
Poly-COT shiny, silver smooth surface 31 0.40 1.12 <104
Shirakawa PA shiny, silver fibrillar surface 66 0.4-0.5 1.13 10 "~(trans) l0 "9 (cis)
50-350
160 (trans) 550 (cis)
"Data from reference ~43;bData from reference ~44
In a common procedure, dissolution of the catalyst W(=CH'Bu)(ORh(=NAr) (R=C(CH3)(CF3h) in neat cyclooctatetraene and polymerization at ambient temperature and pressure, produces within a few seconds a high-quality lustrous silver film with smooth surface morphology. The polymer has a predominant cis structure. Heating induces cis-trans
410 isomerization to form long segments of trans-transoid structure within the polymer chain. When doped with iodine, the polymer acquires conductivities of 50 to 350 ohm~cm ~. Copolymers of varying conjugation length have been synthesized by inclusion of a second monomer such as 1,5-cyclooctadiene during the preparation of the film, displaying a wide range of conductivities in the doped copolymers. ~4S Substituted cyclooetatetraene~ Likewise, substituted cyclooctatetraene will lead by ring-opening metathesis polymerization to substituted polyacetylenes bearing the substituent in certain positions of the repeat unit (Eq. 8.42).
R
n
[VV]
(8.42)
where R = methyl, isopropyl, n-butyl, s-butyl, t-butyl, neopentyl, 2ethylhexyl, n-octyl, n-octadecyl, cyclopropyl, cyclopentyl, phenyl, methoxy and t-butoxy. On employing the well-defined tungsten-based carbene complexes, (RvO)2W(=CHCMe3)(=NC6H3'Pr2) and (RFO)2W(=CHC6H4OMe) (=NC6Hs) (THF) (where 1~O = O C ( C F 3 ) 2 C H 3 ) , Gnabbs and coworkers 1~ ~48 prepared a family of partially substituted polyacetylenes starting from a wide range of monosubstituted cyclooctatetraenes (R-COT). These polymers were highly conjugated, as evidenced by their visible absorption spectra. Most polymers of the family are soluble in the as-synthesized, predominantly cis form in tetrahydrofuran, chloroform and benzene. The products can be isomefized to the predominantly trans form using heat or light. They were of a high molecular weight and with a varying polydispersity as a function of the substituent (Table 8.14). Remarkably, most of these polyacetylenes are soluble in the as-synthesized, predominantly cis stereor the solubility varying with the conjugation length. More conjugated polymers tend to be less soluble. Substituted polyacetylenes containing secondary or tertiary groups immediately adjacent to the main chain remained soluble in the trans form and were, in most cases, still highly conjugated. In these substituted polyacetylenes, Grubbs and coworkers observed that there is a connection between the steric bulk of the side group, their effective conjugation length, and their solubility. The side group twists the main
411 Table 8.14. Molecular weights (M) and polydispersity indexes (PDI) of substitutod polyaoc~cncs prepared with tungsten-carbene con~lexes ~
Substituem
Mo(xl0"3)
M,(xl0 "3)
PDI
10.0 2.9 24.8 25.0 47.0 14.0 93.0 238.0 20.4 16.0 252.0 233.0
58.0 13.8 49.5 42.0
5.7 4.7 2.0 1.7 2.5 3.2 1.4 1.5 2.6 7.6 1.4 1.5
i-Propyl n-Butyl s-Butyl t-Butyl
n-Octyl n-Octadecyl Neopentyl 2-E~ylhexyl Cyclopropyl Cyclopentyl t-Butoxy Phenyl
111.0
46.0 132.0 360.0 52.4 121.7 341.0 345
*Data from reference 148
chain of the polymer and induces a preference for cis structures in the chain. Interestingly, from computer modelling and experimental evidence they suggested that the twisting arises from the steric bulk at only et carbon of the side chain. For example, the soluble polyalkenamer trans-poly(tbutylcyclooctatc~aene) was found to be substantially twisted as indicated by its orange-red color ( k ~ = 432 nm in THF). By contrast, tra~spoly(neo~tylcyclooctatetraene), in which the t-butyl group is displaced from the main chain by a methylene linkage, is almost completely insoluble. The small amount of this polymer that is soluble in THF is intensively blue, probably due to a highly conjugated main chain with very little twisting (k,,~ = 634 nm in THF). By exploring the trade off between conjugation and solubility in these polymers, they discovered highly conjugated polyacetylenes that are still soluble. The authors showed that these polymers can be isomerized to the predominantly trans form using heat or light, the rate of thermal isomerization being monitored by visible absorption spectroscopy. In the solid state, these polymers were found to be amorphous by wide-angle X-ray scattering and near infrared scattering.
412 The amorphous nature of these polymers were correlated with the relatively low temperature cis-trans isomerization in the solid state. Remarkably, upon iodine doping, these substituted polyacetylenes became eleetric~ly conductive, but their conductivities were smaller than those of the unsubstituted polyacetylene. In order to prepare thin films of SiMe3containing polyacetylene useful for conducting-polymer solar cells and layered structures, Grubbs and eoworkers~49 polymerized trimethylsilylcyclooctatetraene with tungsten carbene complex (Eq. 8.43).
SiMe3 n
[W] ~-
(8.43)
Me3S Substituted cis polyacetylene films of 10 4 molecular weight (GPC) soluble in tetrahydrofuran were obtained. The polymers was then photochemically converted into trans configuration and their solutions were cast into thin films by using conventional spin coating technique. Interesting soluble and highly conjugated polyacetylene derivatives bearing chiral side groups (g*) with a stereogenic center ~t to the main chain have been synthesized by Grubbs and coworkers l~~ by ring-opening metathesis polymerization of monosubstituted cyclooctatetraene (Eq. 8.44). R"
R In these syntheses they employed the well-defined tungsten alkylidene catalyst W(=CH-o-(OCH3)C6I~)(=NPh)(OCMe(CF3h)2(TttF) that allowed easily to control the polymerization rate and the formation of high-quality poly(alkylcyclooctatetraene) films. The authors observed that the backbone ~-~* transition of these chiral polyalkenamers showed substantial circular dichroism (CD) and, accordingly, suggested that the chiral side groups twist the main chain of the polymer in predominantly one sense rather than just electronically perturbing that chromophore. Interestingly, the ellipticity observed for these substituted polyacetylenes, having an u-branched substituent on only one of every eight backbone atoms was of the same order of magnitude found for chiral polyacetylenes
413 that have cx-branchcd substituents on every other backbone atom. In addition, these polyalkenamers offered the opportunity to examine both the cis and trans stereosiomers of the backbone. Studies on CD indicated that decreasing temperature had much more influence on the CD of the cis polymers than on the CD of the trans polymers in their respective ~-~* regions, cis-Polymers thus synthesized seem to be more conformationally flexible and may contain helical regions in the chain, although the CD data do not provide conclusive evidence of this conformation. Furthermore, the ~H NMR spectra of these polyalkenamers suggested that the olefinic regions were probably not entire cis or trans with respect to the main chain of the polymer, and this irregularity might prevent long-range helical conformation. 8.1.6. Nine-Membered Ring Monomers Studies on the ring-opening polymerization of monocyclic olefins have been emended to cyclononene and 1,5-cyclononadiene from ninemembered ring monomers. Cydononene. Ring-opening polymerization of cyclononene will give polynonenamer or poly(l-nonenylene), the higher homolog of polyoctenamer (Eq. 8.45).
n{~
~ ~
(8.45)
This reaction was carried out by Natta and coworkers s~ using binary catalysts consisting of tungsten or molybdenum salts and organoaluminium compounds. A trans-polynonenamer has been obtained which displayed good elastomerir properties. 1,5--Cydoaonadiene. It is noteworthy that by ring-operung metathesis polymerization, 1,5-cyclononene will form a polyalkenamer having the alternating structure with butenamer and pentenamer units (Eq. 8.46).
n~
~ ~
(8.46)
414 The reaction is of real interest because it may provide a valuable polymer having good elastomeric characteristics ranging between 1,4-polybutadiene and polypentenamer. On using a binary catalyst consisting of WCI6 and LiAlI-h, Rossi and GeorgitSI carried out the ring-opening polymerization of 1,5cyclononadiene to obtain a polyalkenamer with a higher content of butenylene units than pentenylene in the chain. This unexpected result was explained on assuming that secondary intramolecular metathesis occurs with elimination of cyclopentene by a back-biting mechanism (Eq. 8.47).
8.1.7. Ten-Membered Ring Monomers Several ten-membered ring monomers have been employed in the studies on the ring-opening metathesis polymerization aiming to obtain new polymers with interesting physical-mechanical properties. Cyclodecene. Ring-opening polymerization of cis-cyclodecxme in the presence of metathesis catalysts proceeds readily to give polydecenamer or poly( 1-decenylene) (Eq. 8.48).
(8.48) This reaction has been effected by Dall'Asta and Manetti m52using binary catalysts of WCl6 or w o e h associated with EhAICI. They obtained a hightrans polydecenamer, in some cases with over 85% t r a ~ configuration. It is worthwhile that the catalytic system displayed optimum activity at molar ratio AI:W between 2.5 and 5.0. Ternary catalytic systems derived from WCIr, EhAICI and cumyl peroxide were also very active leading to tram'polydecenamer with high conversions of the monomer. More recently, ciscyclodecene has been also polymerized with metal carbene complexes to give high-tram polydecenamer. ~
415 1,5-Cyr Ring-opening polymerization of cis, trans-cyclodeca1,5-diene gives the polyalkenamer corresponding to an alternating polybutenamer-polyhexenamer copolymer (Eq. 8.49).
~
(8.49)
Products of prevailing trans configuration have been obtained in the presence of WCI6 and EIAICI2, EIzAICI, or EhAI, the activity decreasing in this order. ~53 MoCls-based catalytic systems were much less active. However, it was observed that, after a longer time, substantial amounts of cyclohexene appeared in the product and the trans content of the polymer increased. TM At the same time, the spectrum of the polymer tended towards that of 1,4-trans-polybutadiene (Eq. 8.50).
(B.so) The ready elimination of cyclohexene from this polymer by a back-biting mechanism is to be expected, taking into account the high thermodynamic stability of cyclohexene. 1,6-Cyclodecadiene It is of interest that the ring-opening polymerization of 1,6-cyclodec~diene to polydec~dienamer or poly(1-decadienylene) should provide a new way to produce polypentenamer or poly(1pentenylene) (Eq. 8.51).
(8.51) However, it is remarkable that the reaction of cis, cis-cyclodeca-l,6-diene in the presence of WCIr,/EtOH/EtAICIz at -30~ gave no polymer but led to cyclopentene at 50-80 ~ with this catalyst ~55(Eq. 8.52). +
It is obvious that, under these conditions, a direct metathesis scission of the cyclodiene to cyclopentene is readily favored.
416
8.1.8. Twelve and High-Membered Ring Monomers The behavior of higher monocyclic olefins in the ring-opening metathesis polymerization and the structure and properties of the resulting polymers has been an attractive objective for many research groups. These studies afforded valuable thermodynamic and kinetic data for the general knowledge of the chemistry and mechanism of metathesis reaction and provided interesting polymers which might find utility in various technological areas. Cyelododecene. By ring-opening metathesis polymerization in the presence of suitable catalytic systems, cyclododeeene will lead to polydodecenamer or poly( 1-dodecenylene) (Eq. 8.5 3).
The reaction of cis/trans-cyclododecene has been performed by Natta and coworkers 8~ using catalysts derived from WCI6 or MoCls in conjunction with EtsAI or Et2AICI. They obtained mainly transpolydodecenamer as a crystalline product with melting point of 80~ It is interesting that the properties of this polyalkenamer situated between those of a vinyl polymer with a saturated chain and those of unsaturated polymers. A similar high-tra~s polydodecenamer obtained also Calderon and coworkers 91'92using the binary catalyst WCldEtAICI2, widely applied in ring-opening polymerization of cycloolefins. On changing the organoaluminium compound in the above system to 'Bu2AICI, Vardanyan et al. 157 prepared a polydodecenamer that contained a variable amount of cis and trans stereoconfiguration. In addition, they proved that an equilibrium establishes between the cis and trans structures in this monomer-polymer system in the presence of the catalyst. On the other hand, H6cker and coworkers 9S observed that, when cyclododecene containing 32% trans isomer is treated with WCIdEtAICI2/EtOH, the cis isomer undergoes ring-opening polymerization faster than the trm~s isomer, but, when treated with WCI~Ie4Sn, the reverse is the case. Other catalysts providing intermediate cis or trans l~ill content (a~ = 0.3-0.6) were the following: (n-allyl)4W/AIBr3 system, tetraphenylporphyrinatotungsten terachloride/diisobutylaluminoxane ~9 and WCldcyclic dienes.~Z3 Metal carbene complexes give high-trans polydodecenamer. 87
417 When WChs associated with diisobutylaluminoxane, tBu2AIOAltBu2, is used to polymerize cyclododecene, preferentially trans-polydodecenamer is obtained at room temperature 57 (Table 8.15). Table 8.15
Rmg-q~enmg polymerization of cyclododecene m the presence of WCI~BuzAIOAI'Bu2 as catalyst' Reaction Temp. ~
Conversion, %
transPolyalkenamerr%
Polyalkenamer,%
+20 +20 +20 +20 -20 -20 -20
24.0 42.0 68.0 78.0 8.0 10.0 12.0
57.5 61.5 66.7 68.8 49.8 54.6 55.6
42.5 38.5 33.3 31.2 50.2 45.4 44.4
cis-
'Data from reference 57
As it can be observed from Table 8.15, in the presence of WCI6 and diisobutylaluminoxane, the low temperatures and short reaction times favor formation of cis-polydodecenamer but it seems that the cis isomer is readily transformed into trans at longer reaction time and as the temperatures increase. Furthermore, it is worthwhile noting that the low temperatures influence drastically the conversion degree of cyclododecene. 3-Methybtrans-oddododecene. The ring-opening polymerization of the methyl substituted derivative, 3-methyl-trans-cyclododecene, will lead to poly(methyldod~amer) or poly(methyl-l-dodecenylene) (Eq. 8.54).
n~,~
-~
(8.54)
The reaction was carried out by Dall'Asta,~~ in the presence of a ternary catalytic system consisting of WCI6, EtAICI2 and benzoyl peroxide, to prepare trans-poly(3-methyldodecenamer). The infrared spectrum of the hydrogenated polymer indicated that it contained about 5% each of headhead and tail-tail structure.
418
9-Phenybl,5-cydododecadiene. Polymerization
of 9-phenyl- 1,5cyclododecadiene in the presence of WCI4(OC6H3-CIz-2,6)~t4Pb in chlorobenzene at 80~ gave 98% yield poly(9-phenyl- 1,5dodecadienamer) t6o (Eq. 8.5 5). Ph
1
Ph (8.ss)
1,5,9-Cyclododecatriene. Ring-opening polymerization of 1,5,9cyclododec~triene is a new route for the synthesis of polybutenamer or 1,4polybutadiene (Eq. 8.56).
nC:::
(8.so)
This reaction was first performed by Calderon and r 9~ in the presence of WCI6 and EtAIClz as a catalyst to produce in high yield polybutenamer. On using an initial mixture cis, trans, transand trans, trans, trans- 1,5,9-cyclododecatriene of 40:60, they obtained a polybutenamer or 1,4-polybutadiene having both cis and trans stereoconfigurations at the double bonds. A correlation between the steric configuration of the polymer thus formed and that of the starting monomer was noticed. The properties of the polyalkenamer obtained by this way were very similar to those of the polybutenamer prepared from 1,5cyclooctadiene. Several other binary and ternary catalytic systems have been employed in this reaction to prepare polybutenamer of higher steric purity at optimum conversions of monomer. Thus, two-component catalysts consisting of WCI6/AIBr3 or RezOT/AlzO3 used Marshall 7~ and Saito, ~3z respectively, while Scott 92 and Khodzhemirov TM polymerizcd 1,5,9cyclododecatriene in the presence of three-component catalysts WCI6/EtAICIz/EtOH and WCIs/EtAICIz/PhOH, respectively. Furthermore, homogeneous and heterogeneous ~-allyl-mngsten complexes were applied by Oreshkin 162 to improve the polyalkenamer yield such as (TtalIyl)4W/CCI3COOH and (n-allyl)4W/Al203/SiOz. Recent studies on the ring-opening metathesis polymerization of trans.trans.trans-l,5,9-cvclododecatriene bv Thorn and coworkers ~z with
419 the tungsten carbene catalyst W(=CH'BuX=NArXOCMe(CF3)2h showed that the reaction product consisted either of oligomers or of oligomers and 1,4-polybutadiene, depending on the feed concentration. Under thermodynamic control, the distribution of the cyclic oligomers was similar to that obtained starting from 1,5-cyclooctadiene or 1,4-polybutadiene, with the trans, trans, trans-l,5,9-cyclododecatriene prevailing among the oligomeric products (Eq. 8.57).
These results obtained under rigorous thermodynamic control are different from earlier data ~32"~36concerning the concentration at equilibrium of the oligomeric compounds formed in the 1,5-cyclooctadiene ring-opening polymerization with similar catalysts. Cydopentadecene. Ring-opening polymerization of cyclopcntadecene occurs readily in the presence of WCI6-based metathesis catalysts to form polypentadecenamer (Eq. 8.5 8).
(8.s8) On using a cis:trans mixture of isomers of 18:82, in the presence the ternary system WCIs~tAICI2/EtOH, a faster conversion of the cis isomer to polyalkenamer as compared to trans was observed. 95 By contrast, when WCIs/Me4Sn was employed as a catalyst, the trans isomer converted faster to produce polyalkenamer. 1,5,9,13--Cyclohexadecatetraene. Ring-opening polymerization of 1,5,9,13-r is a new route to prepare polybutenamer or 1,4-polybutadiene ~3z (Eq. 8.59). ~
- -
- - -
The reaction was carried out successfully in the presence of heterogeneous catalysts ~32 like Re2OT/AI203 or homogeneous catalytic systems ~36 e.g., Ph(MeO)C=W(CO)4(PPh3)/TiCI4. Interestingly, the reactivity of this
420
monomer in the presence of some of these catalysts was higher than that observed to the related monomer 1,5,9-cyclododecatriene, affording thus better yields in polybutenamer. ~32 1,5,9,13,17-Cydoeicosapentaene. Analogously to 1,5,9,13cyclohexadecatetreaene, 1,5,9,13,17-cycloeicosapentaene provides a new way to prepare polybutenamer or 1,4-polybutadiene by ring-opening polymerizationS32 (Eq. 8.60). (8.80)
----
The polymerization of this monomer has been effected under similar conditions employed with 1,5,9,13-cyclohexadecatetraene to produce polybutenamer at high conversions. In the presence of Re2OT/AI203 as catalyst a higher reactivity of 1,5,9,13,17-cycloeicosapentaene was observed as compared to that of 1,5,9-cydododecatriene. ~32 1,9,17-Cyclotetraeicosatriene. Ring-opening metathesis polymerization of 1,9,17-cyclotetraeicosatriene is a new route to prepare a valuable polyalkenamer, Le., polyoctenamer (Eq. 8.61).
n~
--~
...~. ~ : ~
(8.61)
Polymerization of this monomer was carried out by Ofstead and Calderon ~63 using the catalytic system derived from WCI6 and EtAICI2 to produce polyalkenamer in high yield. Interestingly, at short reaction time they obtained quite good conversion of 1,9,17-cyclotetraeicosatriene, even higher than that of cyclooctene in the presence of the same catalyst. [2.21Paraeydophan-l-ene. Ring-opening metathesis polymerization of [2.2]paracyclophan-l-ene has been carried out in the presence of Mo(=CHCMe~Ph)(=NC6H3'Pr-2,6)[OCMe(CF3)2]2 in toluene giving a living polyalkenamer ~ (Eq. 8.62).
n H2i~CH
[Mo]
=
=pHC.--~--~--CH 2
(8.62)
The product is a soluble polymer with 98% cis double bonds. On irradiation
421 or exposure to catalytic amounts of iodine, the double bonds undergo cistrans isomerization and the polymer becomes insoluble. Several other molybdenum and tungsten based metathesis catalysts are also effective but produce insoluble polymers, presumably because of a high trans configuration. [2.21Paracyclophane-l,9-diene. Ring-opening metathesis polymerization of [2.2]paracyclophane-l,9-diene in the presence of molybdenum carbene complexes yields poly(p-phenylenevinylene) (Eq. 8.63).
.c <-> c. .c_<
[Mo]
= ,.[=HG~CH=CH~CH=~n
(8.63)
The polymer is an insoluble product displaying a yellow fluorescence. However, soluble copolymers have been prepared with an excess of cyclopentene, ~6s cyclooctene~SS and 1,5-cyclooctadiene. ~67
8.2. Ring-Opening Polymerization of Bicyclic Olefins A significant progress has been achieved in the study of the ringopening metathesis polymerization of cycloolefins using bicyclic monomers as the reaction substrates. This type of monomers allowed unprecedented data to be obtained about the reaction mechanism and stereocherrfistry and to produce polymers with a special architecture and physical-mechanical properties. Bicydo[3.2.0]hept-2-ene. Due to the reactive double bond of the cyclobutene moiety, bicyclo[3.2.0]hept-2-ene reacts readily by ring-opening polymerization in the presence of metathesis catalysts to give the corresponding polyalkenamer (Eq. 8.64).
(8.64)
The repeat unit in the polymer has an erythro structure, corresponding to the cis relationship of the bonds which attach the cyclobutene ring to the rest of the ring system in the bicyclo[3.2.0]hcpt-2-ene system.
422 This monomer has been first polymerized with the classical catalyst ~26 WCIdEtAICIjEtOH and more recently with the well-defined molybdenum and ruthenium carbene complexes Mo(=CHtBu)(=NAr)('BuO)2 (At = 2,6-diisopropylphenyl) and Ru(=CHCH=CPh2)(CI)2(PPh3)2, respectively. ~6s With the latter initiator, the polymerization proceeds at a rate proportional to both initiator and monomer concentration with an apparent I% of0.183 M"~ min~. In this case, the system exhibits all the characteristics of a living polymerization and the polymer has 58% cis configuration as compared to 62% obtained with the catalyst WCIdEtAICIz/EtOH. On adding norbomene, block copolymers could be obtained from bicyclo[3.2.0]hept-2-ene with the ruthenium carbene initiator. Bicyclo[3.2.0]hepta-2,6-diene. Dall'Asta and Motrorfi 169 carried out the polymerization of bicyclo[3.2.0]hepta-2,6-diene in the presence of various Ziegler-Natta catalysts and transition metal salts in polar media. Depending on the catalyst employed and reaction conditions, they obtained polymers by ring-opening and/or vinyl reaction of the double bond from cyclobutene, the cyclopentene ring being unaffected (Eq. 8.65).
(8.65)
Thus, on employing vanadium-based catalysts, Dall'Asta and Motroni recorded the formation of the corresponding polyalkenamers along with vinyl polymers from this monomer, both products having the cyclopentene ring preserved in the polymer chain. The same authors attempted the polymerization of bicyclo[3.2.0]hepta-2,6-diene under the influence of guCl3 in ethanol. The products formed contained transannular bonds whose structures were not fully determined. Bicyclo[2.2.1]hept-2-ene (Norbornene). Ring-opening polymerization of norbomene under the influence of metathesis catalysts gives rise readily to polynorbornene or poly(l,3-cyclopentylenevinylene), a high molecular weight polymer, having 1,3-cyclopentylenevinylene as recurring units (Eq.8.66).
423
n~
~ '['~~n
(8.66)
Due to the easy accessibility and high reactivity of norbornene, this reaction has been investigated by a great number of researchers, using a wide variety of catalytic systems. Though the polymerization of norbomene to an amorphous polymer with plastic properties has been reported by Anderson and Merckling ~7~ as early as 1955 in the presence of HepyhAILi/TiCh catalyst, Eleuterio was the first to report that norbornene ring-opens in the presence of heterogeneous catalysts formed from chromium, molybdenum, tungsten or uranium oxides reduced with hydrogen and supported on alumina, titania or zirconia. 4 On employing a catalyst consisting of 7.5% molybdenum oxide deposited on y-alumina, reduced with hydrogen for 16 hours at 480"C, in conjunction with lithium aluminium hydride, Eleuterio prepared in hydrocarbon solvents at room temperature an amorphous ringopened polymer of polynorbornene which by X-ray and IR spectroscopy showed to contain cis and trans stereoconfiguration at the double bonds. Later on, Truett and coworkers, ~Tmresuming the investigation of norbomene polymerization with the catalytic system (CTH~s)4AILi~iCI4. demonstrated that the polymerization of norbomene under the influence of this catalyst takes place either by addition at the double bond, yielding saturated polymers through vinyl polymerization, or by ring-opening of the unsaturated cycle, yielding unsaturated polymers (Eq. 8.67).
nr__
~
n
(8.67)
It is of interest that they noted that the addition polymerization leading to saturated polymers occurred at molar ratios Al:Ti l
gave rise to unsaturated polymers via ring-opening polymerization. In addition, they observed that the unsaturated polymers had better elastomeric properties and a higher crystallinity as compared to saturated ones.
424 Unsaturated polymers of norbornene having cis stereoconfiguration at the double bond were soon obtained using catalytic systems consisting of MoCl5 and organoaluminium compounds. ~72 However, working under the same conditions but using catalytic systems based on TiCl4 and alkylaluminium compounds, only vinyl polymers resulted. With TiCl4/'Bu3Al (2: l) as a catalyst, the polymer formed showed little unsaturation while with 1:2 catalyst:cocatalyst ratio ring-opened polymer has been obtained. Moreover, with EhAl as a cocatalyst, the cationic side reactions have been suppressed by using a tertiary amine in the reaction mixture. ~73'~74 It is interesting to note that the polymerization of norbomene with catalysts consisting of late transition metal salts in polar media has been reported as early as 1965. Thus, Michelotti and Keaveney ~75 carried out polymerization of norbornene under the influence of chlorides of Ru, Os and Ir in ethanol to prepare polynorbornene in high yields. It is noteworthy that they found the following order of activity for these catalysts IrCI3 > OsCl3 > RuCl3. They observed that, although the catalytic systems were homogeneous at the beginning of the reaction, the system gradually turned heterogeneous, suddenly altering the catalyst activity and changing the reaction kinetics. Depending on the catalyst employed, polymers with totally different physical properties were produced, working under identical conditions. Representative conversions of norbornene and the softening range of the polymers obtained with these catalytic systems are given in Table 8.16.
Table 8.16 Polymerization of norbomene with transition metal salts m polar media' Catalyst
OsCI3 RuCI3 IrCl3
Time
Conversion %
SoRenmg Range oC
4 hr 6.5 hr 7min
55 60 73
58-90 72-90 90-I 15
Reaction
'Data from reference ~7~
Monomer
425 In these experiments the above authors observed that the polynorbomene obtained with osmium catalysts had the lowest softening range and the highest content of cis stereoconfiguration while the polymer formed with iridium catalyst displayed the highest softening range and content of trans stereoconfiguration. Similar catalytic systems based on iridium and osmium salts were employed by Rinehart and Smith m~6for norbornene polymerization in polar media. Working under specific conditions, they obtained polymers having a higher degree of saturation which did not possess an uniform structure. On the other hand, in the presence of ruthenium complexes with phosphine ligands, Hirald and coworkers ~" prepared both types of polymers from norbomene, polyalkenamers and vinyl polymers. It was found that RuCI3.3H20 in hexane as a solvent is only effective in ring-opening polymerization of norbomene if ethanol is present as a coc~talyst (EtOH 9RuCI3 ratio = 3 9 1). In alcoholic solvents, the reaction rate increases in the order EtOH < n-BuOH < t-BuOH. By contrast, addition of trace amounts of cyclopentadiene to the reacting system brings it to a dead stop within a few minutes. Furthermore, small amounts of Ph3P enhance the reaction rate, with maximum effect at a molar ratio RuCI3 : Ph3P = 1 : 1, when the molar ratio reaches 1 : 10, the polymerization rate is very slow. All these effects were rationalized by Tanielian ~78 in terms of different strengths of coordination of the additives to the metal center, leading to a change in the rate of initiation and/or a modified rate of propagation. Porri ~9'ms~examined the activity of several catalysts derived from iridium and ruthenium complexes such as [(Cuql4hlr(CO)Cl]2, [(CsH ~4)21r(OCOCF3)]2, H21rCI6.6H20, [IrC1(C~II4)212 and {Ru[C~-II0(CH3)2]X}2 (CsHl4 = cyclooctene, X = Cl or OCOCF3) in norbornene polymerization. The presence of cross-metathesis products of norbornene with but-2-ene, 2-methylpropene, pent-l-ene and pent-2-ene was evidenced. Other catalysts that were active in norbornene polymerization included (Ph3P)~RuH2, (Ph3P)3RuHCI, (Ph3P)3RuH(OCOCF3), (Ph3P)3Ru(OCOCF3h, [(C6H6hRuCI2]2, [(1,5CsHI2)RuC12]n, and (C~Hs)RuCI2, where CTHs = bicyclo[2.2, l]hepta-2,5diene. Linear polyalkenamers with high molecular weight and uniform structure have been obtained by Oshika et al. ~s~ by norbomene polymerization in the presence of one-component catalysts working in a variety of chlorinated solvents. For instance, good conversions were
426 attained using molybdenum pentachloride in carbon tetrachloride, monchlorobenzene and o-dichlorobenzene at normal temperature. Interestingly, they found that in oxygenated compounds such as dioxan and tetrahydrofuran or in saturated hydrocarbons such as n-heptane, no polymers were formed under the influence of the same catalytic system. However, low conversions of the monomer were reached under the same conditions working in toluene as a solvent. In all cases, the polynorbornene produced had a prevailing trans stereoconfiguration at the double bond. It is noteworthy that the authors observed a gelification phenomenon which could not be explained. During their investigation on the norbornene polymerization with transition metal halides, Oshika and Tabuchi ~82 found that tungsten, molybdenum and rhenium chlorides in solvents such as carbon tetrachloride and carbon disulphide were very active catalysts. Moreover, in most cases a high degree of stereospecificity was observed. Thus, molybdenum pentachloride yielded a polymer having predominantly trans stereostructure at the carbon-carbon double bond, rhenium pentachloride a polymer with a cis stereostructure while tungsten hexachloride produced a polymer with both cis and trans stereoconfigurations. It is of interest that on raising the temperature, both the monomer conversion and polymer yield increaseA. Moreover, the addition of tertiary amines such as triethylamine and tributylamine during the course of polymerization also increased the polymer yield. Remarkably, traces of water caused a substantial decrease of catalyst activity but did not affect the polymer microstructure. Furthermore, elemental analyzes pointed out chlorine atoms to be attached at the polymer chain obtained in the presence of molybdenum pentachloride as a catalyst. Several other molybdenum-based catalysts have been successfully used for norbornene polymerization consisting of 0r-allyl)~lo, ~83
MoCI2(PPh3)2(NO)2,184
Mo(CO)6,185'1s6
Mo(CO)5(Py), 187
(Bu4N)2(Mo6Ot9), 188 [Mo2(CH3CN)8](BF4)2 and related complexes, !s9 usually associated with a cocatalyst. A great number of very active tungsten catalysts have been used in norbornene polymerization. ~9~ A first group consists of unicomponent tungsten carbonyl complexes, TM tungsten aryloxy derivatives ~92 sometimes with a cocatalyst.~93 unicomponent tungsten c,arbene complexes W(=CPh2)(CO)~ and W(=C(COMe)Ph)(CO)5 with or without a r TM tungsten carbene complexes with monodentate ligands of which two are alkoxy o r al~loxy, 195"200 with bidentate ligands, 2~176 or with one tridentate ligand. ~ Another group widely applied for norbornene
427 polymerization consists of WCI6 associated with a variety of organometallic compounds as cocatalysts. 2~176 As mentioned earlier, homogeneous rhenium catalysts consist mainly of ReCI5 and give polymers of high cis content. ~s2"2~'2~3 The heterogeneous rhenium catalyst Re2OT/AI203 leads also to an all-cis polymer, but when pretreated with Me~Sn gives a polymer with comparable content of cis and trans configuration. 2~4 Detailed studies on the norbornene polymerization carded out Ivin and coworkers 2~'2~s using a series of catalysts derived from WCI6, MoCIs, ReCIs, IrCl3 and RuCI3. The microstructure of poly(l,3cyclopentylenevinylene) thus obtained was more accurately evaluated from ~3C NMR spectra and indicated a fraction of cis double bonds (or from 1,0 to 0,14, depending on the catalyst employed. MoCI5 in conjunction with EtAICI2 (molar ratio from 10:1 to 1:10) in chlorobenzene at -46~ to 50~ gave polymers having 35-47% cis content. TM Addition of substantial amounts of Michael acceptors such as ethyl acrylate, diethyl maleate, or diethyl fumarate in the reaction mixture increased the cis content of the polymer to 65% or even higher. It was assumed that these additives might coordinate to the metal site providing a more crowded environment for the approach of the monomer, thereby favoring the formation of cis double bonds. On using ReCls in benzene at high monomer concentration, Ivin and coworkers 2~ were able to obtain for the first time all-cis poly(1,3cyclopetylenevinylene) by norbomene ring-opening polymerization. Iridium-based catalysts provided polymers with cis content in the range 2145% with a random distribution of cis and trans double bonds. Remarkable work on norbornene polymerization reported Farona and coworkers 2~6 using soluble catalysts prepared from Mo(CO)Py and Re(CO)sCI associated with EtAICI2. Interestingly, microstructure investigation by NMR spectroscopy of polynorbomene thus obtained indicated that, depending on the catalyst employed and reaction temperature, vinyl and ring-opened units were present in the same polymer chain (Eq. 8.68).
For instance, under cenain reaction conditions, using Re(CO)sO catalyst system, norbomene was converted to high molecular weight
428 polynorbornene (M, = 154200; Mw = 443000; polydispersity = 2,9) and the composition of the polymer was determined to have, by integration of olefinic to aliphatic proton signals in the ~H M R spectrum, 10 vinyl units for every ring-opened monomer unit. Tungsten-based catalytic systems yield polynorbornene with cis stereoconfiguration ranging from 35% to nearly 100%. WCI6 alone will induce norbornene polymerizationS9~ but its activity is much enhanced in the presence of a coc~talyst such as BuLi, EtAICIz, (~-allyl)4Sn, Ph4Sn. In addition to these cocatalysts, several other organometallic compounds or metallic hydrides such as Et2AICI, 'Bu2AICI, 'Bu3AI, Bu4Sn or LiAlt-h, respectively, showed to be effective. 2~2 It was observed that in some cases, e.g., WCI6/PIhSn, the molar ratio of catalyst to cocatalyst has little effect on the proportion of cis content (or but in other cases, e.g., WCIdBuLi, there is a marked variation of the cis content with the catalyst composition. Additives such as ethyl acrylate, diethyl fumarate and diethyl maleate increased also the cis content of the polymer. TM Polynorbornene with high molecular weight was prepared by Katz and coworkers ~94 using one-component tungsten-carbene complexes PhzC=W(CO)5, Ph(MeO)C=W(CO)5 and PhzC=W(CO)4(Ph3P) in benzene, toluene or heptane at 20~ and 50~ Microstructure examination by t3C spectroscopic method indicated cis content ranging from 75% to over 90%. Kormer et al. ~83 employed a series of n-complexes of various transition metals to manufacture polynorbornene under various conditions. Thus, on using (~:-CJ-17)4Mo in benzene at 30~ they attained 18% monomer conversion in 16 hr, the polymer formed having 86% cis stereocontiguration. With the catalytic systems (n-C41-17)~lo/TiCh and (nCJ't7)4W/TiCI4 a much faster reaction has been recorded but a somewhat lower cis content in the polymer (64% and 51%, respectively) has been obtained. Of the other catalysts, WCId(n-C3Hs)3Cr, WCId(n-C3Hs)4Zr, though rather active, produced polynorbomene of moderate stereospecificity. Recently, a variety of well-defined transition metal complexes have been used as efficient initiators for the living ring-opening polymerization of norbornene. 2~7 Thus, a number of titanacyclobutane complexes have been prepared and used for the living polymerization of norbornene 2~8'2~9 and synthesis of block copolymers~ or star shaped polymers2z~. The living process initiated with these complexes allowed the synthesis of
429 polynorbornene with various end-functional groups ~ ~ Tantalum carbene complexesZ24 Ta(-CH'Bu)(OCc,I-13'Prz-2,6)3(THF) and Ta(=CHtBu)(SC6Hz~r3-2,4,6h(Py) proved to be effective under conditions which allow monomer coordination to metal center. A ditantalacyclobutadiene complex, (Me~SiCH2hTa2(~t-CSiMe3)2, was found to induce ring-opening polymerization of norbomene in the presence of an equivalent amount of oxygen. ~ Several molytxlenum carbene complexes of the type Mo(=CHR)(=NAR)(OCtBu)2 (R = tBu or CMe2Ph) have been prepared and used for living ring-opening polymerization of norbomene ~'227 and production of block copolymers and star shaped polymers from norbomene. 228"~ Moreover, polynorbomene with a variety of functionalized end-groups have been prepared with substituted benzaldehydes as terminating agents. 23~The molybdenum carbene complex bearing a tridentate ligand [tris(pyrazolyl)borate] proved to be effective in the polymerization of norbomene only when AICI3 has been added. TM A related rhenium carbene complex has been also reported to be active in norbomene polymerization. 23z Ruthenium carbene complexes, Ru(=CHR)(CI)2(PPh3)2 (R = Me, Et, Ph)233 and Ru(=CHCH=CPhz)(CI)2(PR3h (R = Ph, Cyclohexyl), TM showed to be very active and efficient in ring-opening polymerization of norbomene. The latter ruthenium complex was also active when supported on polystyrene. TM In addition, a binuclear ruthenium carbene complex, (RuCICp)2(--CHCH=CPh2), showed to be less active as compared to the other ruthenium complexes. TM Substituted bieyclo[2.2.1lhept-2-ene.Numerous mono- and disubstituted norbomene derivatives have been polymerized under the action of ringopening metathesis catalysts yielding a wide variety of substituted polynorbomene. The ready accessibility of these compounds by the DielsAlder reaction, the high reactivity of norbomene moiety bearing substituents and the special architecture, stereochemistry and properties of the resulting substituted polynorbomenes opened a challenging research area in the polymer chemistry. Monosubstituted bicyclo[2.2.1]hept-2-,ne Norbomene monosubstituted with alkyl or aryl groups and beating functional groups in various positions as well as monosubstituted heteroatom- or metal-containing norbomenes have been extensively investigated in the ring-opening polymerization reaction. Aikyl-, alkylidene- and arylnorbornene. Several alkyl-, alkylidene- and phenylsubstituted norbornenes have been employed as monomers
430 in the polymerization reaction under the influence of ring-opening metathesis catalysts to manufacture substituted polynorbomene. Methylnod~menes. The l-methyl, 2-methyl, exo-5-methyl, e~do-5methyl, syn-7-methyl and anti-7-methylnorbomene have been reacted under the action of various transition metal catalysts to produce unsaturated polynorbomene bearing the methyl substituent in the corresponding position. The tacticity and stereoconfiguration of the resulted substituted polynorbomene is essentially dependent on the initial position of the methyl group and catalytic system employed. l-Methylnorbornene Ring-opening polymerization of 1methylnorbomene has, except when prepared with certain catalysts, a strong head-tail bias~7'23s (F.q. 8.69).
n~
"~r
(8.69)
Interesting work has been reported by Hamilton et al. z~7 using a wide variety of transition metal-based catalysts. Polymer stereoconfiguration and tacticity have been minutely examined by m3C NMR spectroscopy and the data obtained were interpreted in terms of trans-trtms, trans-cis, cis-trtms, cis-cis geometries and tail-head, tail-tail, heM-head, head-tail sequences. Significant studies on the stere~selectivity and regioselectivity of polymerization reaction of 1-methylnorbomene with titanacyclobutane catalyst published Gilliom and Grubbs. 2ts They found that the olefinic linkages in the polymer were primarily trans (90-95%) and the regiochemistry of addition favored head-tail diads. These data allowed the most probable titanacyclobutane intermediate of the propagation reaction to be postulated. 2-Methylnorbornene, Polymerization of 2-methylnorbomene in the presence of a variety of transition metal-based catalysts gives rise preferentially to all-head-tail polymers (Eq. 8.70).
n
=
~~~~"n
(8.70)
For instance, on using the carbene complex Ph2C=W(CO)5, Katz and coworkers 239 prepared in 91% yield poly(2-methylnorbomene) having both cis and trans geometries at the double bonds.
431
5-Methylnorbornene. Ring-opening polymerization of
exo- and endo-5-
methylnorbomene in the presence of a wide range of metathesis catalysts has been investigated in detail by Ivin and coworkers 24~ It is significant that under these circumstances, starting from exo-5-methylnorbomene, polymers having cis double bond contents of 11-100~ while from endo-5methylnorbomene, polymers with cis double bond contents of 22-100~ have been produced (Eq. 8.71).
(8.71) / On studying the polymer microstructure by ~3C NMR spectroscopy, Ivin provided also a full interpretation of these results in terms of tail-head(TH), tail-tail(TT), head-head(HH), head-tail(HT) and trans-trans(tt), transcis(tc), cis-trans(ct) and cis-cis(cc) sequences. In the case of the exo monomer, the all-cis polymer prepared with ReCI5 had a fully syndiotactic ring sequence as revealed by the TT, HH structure, identified by the olefinic carbon resonances in the ~3C NMR spectrum. TM By contrast, polymers prepared with RuCl3-cycloocadiene complex had a high-trans atactic structure in which TT, HH, TH and HT occur to equal extents. In the case of the endo monomer, the fine structure of the olefinic region indicated that the cis/trans double bond distribution was blocky when the cis contents were more than 50%. However, with most catalysts based on Ru, It, W and Re used in the polymerization of exo- and endo-5-methylnorbomene, Ivin et aLZ4~ obtained polymers with randomly oriented methyl groups along the chain. Interestingly, in a related work, Takada, Otsu and Imoto 242 prepared an unsaturated polymer containing primarily trans configuration at the double bond from 5-methylnorbomene in the presence of TiCLt and Et3AI (molar ratio AI Ti = 2.5). 7-Methylnorbornene. Ring-opening polymerization of syn- and anti-7methylnorbomene to poly(l,3(2-methyl)cyclopentylenevinylene) (Eq. 8.72) has been studied by several groups, z43z~
(8.72)
432 On employing conventional ring-opening metathesis polymerization catalysts, such as those derived from RuCI3, WCI6/Me4Sn and ReCls, Hamilton, Ivin and Rooneyz43 showed that anti-7-methylnorbomene polymerized selectively from a mixture of the syn and anti isomers. Analysis of the ~3C ~ spectra of the polymers thus obtained, gave detailed information about their tacticity. Noteworthy, of the catalysts originally tested only that derived from (mes)W(CO)~/EtAICl2/norbomene epoxide polymerized syn-7-methylnorbornene. In a more recent work, Kress et al. TM evidenced that the metalcarbene W[C(CHz)3CHz](OCH2CMe3)2Br2 selectively polymerizes anti-7methylnorbornene from a mixture of syn and anti isomers, but the complex W[C(CH2)~CHz](OCHzCMe3hBr]'GaBrs is more reactive and yields a tapered block copolymer of the two isomers. It is of interest that by using the above metal-carbene to polymerize the anti isomer and then producing the complex on adding GaBr3 to the initial metal-c~:~e, it was possible to induce the formation of a true block copolymer of the anti and syn isomers. Block copolymers of the two isomers prepared also Feast et al. 24s by ringopening polymerization of syn- and anti-7-methylnorbomene under the influence of the well-defined molybdenum complex Mo(--CHCMe3)(=NC~3-2,6-'Pr2)(OCMe3)2. These authors found that the anti monomer polymerizes first, followed much more slowly by the syn monomer. The reaction was considerably faster in CD2CI2 where it proceeded to completion, than in C6D~. Significantly, in C6D6 kc,/ki, = 9, as determined from the proportion of residual initiator. In addition, the double bonds formed were mainly tra~s (80-90%) in both blc~ks and the diads embracing the trans double bonds in the cmti blocks have an isotactic bias, (a,n)~ = 0.69 in Cd~6, independent of monomer concentration; the di~s in the syn blocks have a slight tactic bias, probably isotactic. Further studies on the ring-~pening polymerization of 7-methylnorbomene induced by several Schrock-type complexes [Mo(--CHRIX=NC6H3-2,62Pr2XOR2h] [R~=rBu, CMe2Ph; OR2=OCMe~, OCMe(CF3h] revealed a zero-order dependence on the monomer concentration in some cases; syn-ami alkylidene conversion of the initiator was proposed as the rate-limiting step. Polymerization of the anti-7-methylnorbomene from the mixture of the two isomers were also reported by ~lliom and Grubbsz~s under the influence of a titanacyclobutane catalyst. In these circumstances, a 80:20 trans:cis ratio of double bonds in the chin and a 31 ratio of racemic (r) to meso (m) junctions at the trans double bonds have been observed. Interestingly, in the polymer produced by reaction of ant/-7-methvlnorbomene with the
433 titanacyclobutane catalyst, the trans double bonds were primarily associated with r diads, while the cis double bonds with m diads, in contrast to that observed by Hamilton et al. z43 using classical metathesis catalysts. 5-Methylenenorbornene. While cationic polymerization of 5methylenenorbornene leads to a saturated polymer having nortricyclic recurring units (A), ring-opening polymerization of this monomer forms an unsaturated polymer (B) (Eq. 8.73).
\,
(A)
Jn (8.73)
(B) The reaction has been effected in the presence of several catalytic systems, 24~ e.g., WCI6/Et3AI, WCIdMe4Sn, MoCIdEt3AI or IrCl3. The structure of he polymer is essentially dependent on the catalyst employed. For instance, in the presence of WCIdEt3AI 5-methylenenorbornene yielded the expected ring-opened polymer (B) characterized by its t3C NMR spectrum corresponding to TH, TT, HH and TT carbons in cis and trans double bonds. However, when WCI6/Me4Sn was used as the catalyst, the polymer was totally devoid of double bonds and its ~3C NMR spectrum was consistent with the rearranged structure (A). The formation of this polymer is attributed to a cationic mechanism. 5-1sopropylnorbornene. 5-1sopropylnorbomene has been reacted by Tenney et al. TM in the presence of MoCIdEt2AII to obtain substituted polynorbornene with isopropyl groups randomly distributed in the polymer chain (Eq. 8.74).
(8.74)
c"
434 As it can be observed, the isopropyl groups maintained their initial structure and their position in the resulted polymer. 5-Isopropylidenenorbornene. By ring-opening polymerization 5isopropylidenenorbomene gives the corresponding polyalkenamer having the isopropylidene moiety attached at the cyclopentane unit 24s (Eq. 8.75).
n
(8.75)
r
The reaction has been effected by Tenney eta/. 245 in the presence of MoCIs/Et2AII producing the expected unsaturated polyalkenamer. 5-(4-Butenyl)-norbornene. Dekking 249 observed that norbomene substituted in position 5 with butenyl groups yielded in the presence of the catalytic system consisting of TiCI4 and LiAI(C~0Hz3)4 a mixture of substituted polynorbomene with vinyl polymer (Eq. 8.76).
n~
(A) I
(8.76) I"
1
By spectroscopic measurements it was found that the products contained 41% polyalkenamer and 59~ vinyl polymer. Details about the exact structure of the saturated polymer were not available, probably, both saturated units were present in the vinyl polymer (B). Interestingly, the polymer had a softening temperature of 150~ and did not contain gel.
435 5-Octyl- and higher alkylnorbornene. In the course of their studies on the polymerization reactions of substituted norbomenes, Tenney et al. TM investigated the behavior of 5-substituted norbomene with octyl and higher C ~ , § groups (n = 9-12) in the presence of MoCI~/EtzAII. Under these conditions, they prepared unsaturated polymers beating the alkyl substituent in the corresponding position of the recurring unit (Eq. 8.77).
(8.77) R
where g = n-octyl and C.H2.+mgroups (n = 9-12). 5-Phenylnorbornene. Ring-opening polymerization of 5-phenylnorbornene gives rise usually to poly(5-phenylnorbomene) by a normal ring-opening reaction of the norbornyl moiety (Eq. 8.78).
n
...~_~ ~ n
(8.78)
\
Ph The reaction has been effected by Rinehart, TM Tanaka25z and Komatsu ~3 using catalytic systems based on W, Ru and Ir. Di- and Polysubstituted bieydo[2.2.1]hept-2-~ne. The interesting results obtained in the norbornene polymerization with metathesis catalysts allowed a rapid extension of this reaction to di- and polysubstituted norbomenes. Dialkylnorbornene Ring-opening polymerization of norbornene carrying two alkyl groups will form substituted polynorbomene or poly(1,3cyclopentylenevinylene) having usually the two alkyl groups in the initial position of the cyclopentylene recurring unit (Eq. 8.79).
436 The two alkyl groups may be situated in gemminal positions, e.g., 5,5- or 7,7-dialkylnorbomene, in vicinal positions, e.g., 1,2-, 1,6-, 1,7-, 2,3-, 5,6dialkylnorbomene or at distant positions e.g., 1,3-, 1,4-, 1,5-, 2,5-, 2,7-, 5,7-dialkylnorbornene. Of the dialkylnorbornenes, the dimethylnorbornenes are the most studied disubstituted compounds of this class in the ringopening metathesis polymerization. Depending on the position of the two methyl groups, the reactivity of the monomers is totally different and the structure and properties of the resulted polyalkenamers are strongly dependent on the substituents. 5,S-Dimethylnorbornene Ring-opened polymers of optically active 5,5dimethylnorbomene, having cis double bond contents of 0-100~ were prepared by Ivin and coworkers TM using various catalytic systems based on Mo, W, Re, Os, Ru and Ir compounds. The polymer microstructure and ring diad tacticity varied considerably as a function of the catalyst employed and reaction parameters (Eq. 8.80).
(8.80)
n
I The ring diad tacticities in these polymers, with respect to both cis and t r ~ s double bonds, were determined from ~3C NMR spectra. They found that cis double bonds were always associated with 50-100% r diads (syndiotacticity (o,)~ - 0.5-1.0), while trans double bonds were always associated with 50-100% m diads (isotacticity (o~)t = 0.5-1.0). According to their tacticity, the polymers obtained were divided into four groups: (1) those of high tacticity, with (o,)r -- (om)~ -- 1.0, (ii) those of intermediate tacticity, with (o,)~ - (o~h - 0.6-0.9, (iii) those with (o,)~ > (om)~ (o,)~ >(om~h and (iv) those of low tacticity, with (o,)~ - (o~)t ---0.5. They observed that there was no correlation between tacticity and cis content, but all-cis polymers were generally highly syndiotactic and all-trans polymers slightly isotactir when prepared from 3 M monomer at 20~ Interestingly, the tacticity falls with increasing preparation temperature but not always with decreasing monomer concentration. Taking these results into account, a complete mechanism for the ring-opening metathesis polymerization was developed in order to explain the general features of the reaction stereospeeificity and selectivity. Relevant results concerning the values of cis content, cis-trans blockiness, ring-diad tacticity and head-tail bias in 5,5-
437 dimethylnorbomene polymerization with tungsten-carbene complexes as determined from ~3C NMR spectra reported Kress 19s and Greene. TM 5,6-Dimethylnorbomene. In order to evaluate the microstructure of poly(5,6~imethylnorbomene), the ring-opening polymerization of endo, endo-5,6-~imethyl- and exo,exo-5,6-dimethylnorbomene has been investigated by Kress ~95in the presence of tungsten carbene complexes and by Greene TM with conventional metathesis catalysts. At the same time, ringopening polymerization of endo,exo-5,6~imethylnorbomene has been examined by Greene ~99 using a series of conventional initiators and by Schrock and coworkers zss in the presence of well-defined molytxienumcarbene complexes. Thus, ring-opened polymers of (+)-endo,exo-5,6.~imethyl- and (+)endo, exo-5,6-dimethylnorbornene having cis double bonds contents between 5 and 85% were prepared by Schrock 2" using Mo(=CH ~Bu)(=NArXORh (At = Cd-13-t'r-2,3, OR = OCMe3, OCMe2(CF3), OCMe(CF3h) complexes as initiators (Eq. 8.81). (8.81) f
/
\
The cis content of the polymer was correlated with the electronwithdrawing ability of the alkoxy ligands, maximizing for the most electronwithdrawing hexafluoro-tert-butoxide group of the initiator. Some of relevant data are given in Table 8.17. Table 8.17 Polymerization of (+)- and (+)-endo.exo-5,64unethylnorbomene (M) usm~ nmlybdmum-carbene congdexes as initiators" M [ Catalyst [Yield [ o,r [ M,,/ i T. % I I M, I ~ (+) (+) (+) (+) (+)
Mo(--CH~u)(=NAr)(OC Mesh Mo(=CH~u)(=NArXOCMe3)2 Mo(=CHtBuX=NAr)(OCMe2(CF3h Mo(--CH~u)(=NAr)(OCMe2(CF3)2 Mo(--CH~uX=NArXOCMe(CF3)2)2 Mo(--CHtBuX=NAr)(OCMe (CF3h)2
'Data from reference "~
94 91 96 93 97 95
0.05 0.05 0.58 0.44 0.85 0.85
1.03 1.03 I. 15 1.13 1.20 1.19
55 55 75 71 85 79
438 The microstructure of these polymers has been thoroughly evaluated from ~3C NMR spectra in terms of the various possible diad relationship. They found that lfigh-cis polymer made from 98% (+)-endo, exo-5,6dimethylnorbomene contained 78% m diads (isotactic bias, (Om)~ = 0.78) and displayed more than twice the optical rotatory power and a higher glass transition temperature (T s = 85~ than the Ifigh-trans polymer which contained 48% m diads (atactic, (om)~ ---0.48) and had glass transition temperature T 8 = 55~ 5,6- Oi met h ylen en o rbo rn en r Polymerization of 5,6dimethylenenorbomene has been carried out by Shahada and Feast 2s6 with the catalyst WCldMe4Sn. The polymer obtained was insoluble but its solidstate ~3C NMR spectrum indicated that the reaction occurred by ringopening (Eq. 8.82).
n
~
(8.82)
//
"%
Spiro[cyclopropane-7,1']norbornene, It is remarkable that ring-opening polymerization of spiro[cyclopropane-7,1']norbomene under the influence of metathesis catalysts proceeds readily at the monomer double bond, without affecting essentially the cyclopropane ring (Eq. 8.83).
(8.83) This reaction has been examined by Makovetsky et al. 257 using heterogeneous rhenium-based and homogeneous ruthenium- and tungstenbased catalysts. The best results were obtained with the homogeneous WCldphenylacetylene system which afforded a quantitative yield of poly(spiro[cyclopropane-7,1']norbornene) within a short reaction time (Table 8.18). According to IR and ~H NMR spectroscopic measurements, the main chain structure of poly(spiro[cyclopropane-7,1']norbomene) was usually formed via ring-opening. Significantly, in the IR spectrum of these polymers an intense absorption band at 1010 cm~ and two moderate bands at 840 and 3080 cm~ characteristic of cyclopropane ring were observed.
439 Table 8.18 Polymerization of spiro[cyclopropane-7,1 ']norbomene under the mfluence of maathesis catalysts' Catalytic System
Mollofllcr:
Catalyst, mole
Reaction Time, hr
Polymer Yield, %
[n] dlg-I
0.2 I0 7 0.7 20 53 40 4.0 1000 20 mm I00 WCk/PhC=CH d 'Data from reference'7; ~3 wt.% ~Bu4Sn, toluene, 45~ ~C6HsCI:EtOH 1"1, 60~ dWCl6:Phenylacctylene 1 1, toluene, 20~ Re2OdAlzO3/"Bu4Snb RuCI3.3H20'
350
Likewise, ~H NMR spectra of the polymers indicated the presence of cyclopropane protons (d 0.2-0.45 ppm) along the chain. On the other hand, IR data showed that the microstructure of poly(spiro[cyclopropane7,1']norbomene) thus prepared ranged from all-trans in the case of Rubased catalyst to ca. 85% cis with Re-based systems. Parallel studies on the polymerization of spiro[cyclopropane7,1']norbomene carried out Seehof and Risse25s with the WCIjPh4Sn and RuCI3 as catalysts. The polymers thus obtained had a predominant trans stereoconfiguration for the two catalysts The first catalyst resulted in a o~ = 0.15 and a diad configuration of m / r = 44/56 for trans centered diads of the polymer and the second in a or = 0.05 and a diad configuration of m/r = 38/62 for trans centered diads. It should be mentioned that the polymers obtained from spiro[cyclopropane-7,1']norbornene were completely soluble in hydrocarbon solvents. This fact indicated that the reactive spirocyclopropane group remained intact during the ring-opening polymerization of norbomene moieties and did not participate in the intermolecular cross-linking reactions. Polysubstituted norbornene. A substantial number of polysubstituted norbornene derivatives have been examined in ring-opening polymerization reactions with various catalytic systems. The majority of them bear alkyl or aryl substituents in different positions of the norbomene skeleton. 1,7,7-Trimethylnorbornene. By ring-opening metathesis polymerization of 1,7,7-trimethylnorbomene, a trisubstituted polynorbomene bearing the three methyl groups in the recurring units can arise (F-xl. 8.84).
440
n
n
=
(8.84)
The kinetics of this reaction has been followed by Feast and coworkers 259 by ~3C NMR technique under the influence of the complex Mo(=CHCMe2Ph)(=NC6H3-'Pr2-2,6)(OCMe(CF3)2) in CD2C12 at 20~ (Table 8.19). Table 8.19 R i n g ~ m g polymerization of 1,7,74fimethylnorbomene reduced by Mo(=CHCMeqPh)(=NCtJ-132Prz-2,6)(OCMe(CF3)2)~ Catalyst Concentration
kdl0 -~ s-~
10 [ll,
Monomer:Catalyst [M]./[I].
1.9 2.85 2.6 2.85
5.2 14 23 34
1.02 2.84 3.51 4.12 6.1
'Data from reference 259 Under these circumstances, Feast et al. observed that the reaction of 1,7,7trimethylnorbomene was very slow, a first-order decay of the initiator over 4 half-lives was found while monomer concentration remained almost constant in each experiment. It initially produced the first insertion metallacarbene intermediate and eventually an all-trans, all-head-tail polymer which was isotactic when made from (-)-monomer and atactic when made from (+)-monomer. Bicyclo[2.2.1 ]hepta-2,5-diene (Norbornadiene). Ring-opening polymerization of norbomadiene occurs readily under appropriate conditions to form polynorbornadiene or poly(1,3-cyclopentenylvinylene), a highly unsaturated polyalkenamer (Eq. 8.85).
441 This reaction has been carried out first by Sartori, Valvassori and Faina ~ in the presence of various V- and Ti-based catalysts. The polymer structure, determined by IR spectroscopy, indicated mostly trans stereoconfiguration at the double bonds. Subsequently, Calderon and coworkers ~s~ employed particularly active catalysts for norbornadiene polymerization consisting of WCI6 with or without organometallic compounds. However, the structure of the polymers could not be determined accurately because significant amounts of gel formed on the polymer particles. In another series of polymerization reactions, Schulz 262 used several Ziegler-Natta catalysts which showed to be very active. Notwithstanding, in most cases, both types of polymers, namely ring-opened and vinyl products, were formed by the two reaction pathways of one of the double bonds of the monomer. Significant work on the norbornadiene polymerization, under the influence of a variety of transition metal-based catalysts, was carried out more recently by Ivin~s3 and Rooney. 2~ A number of homopolymers of norbomadiene and copolymers with norbomene have been synthesized in various yields ranging from 15% to 95%. By employing hex-1-erie as chain transfer agent, the molecular weight of these polymers has been regulated to levels that permitted high solubilities in suitable solvents. As a results, they obtained high.quality ~SC and ~H NMR spectra of these polynorbomadienes, analogous to those of polynorbornenes reported earlier. It is important to note that these spectra have been fully assigned and the detailed microstructures of the homopolymers e.g., cis-trans configuration, o~, and m-r diads, have been unequivocally established. Some relevant data obtained with a number of catalysts are given in Table 8.20. As this Table obviously illustrates, the fraction of main-chain cis double bonds, o~, ranged from o~ = 0.9 to a minimum of just under o~ = 0.4, and no catalyst system tried produced polymer with a lower value of o~. It is quite remarkable that OsCl3 as a catalyst afforded essentially all-cis polymers of norbornadiene, in contrast to norbornene, where the cis content was <50~ Moreover, RuCI3, which gives high-trans polymer with many norbornene-type monomers, was completely inactive with norbomadiene. Like polymers of norbomene, the high cis polymers of norbomadiene tend to have a blocky cis-trans distribution. It was also observed that omission of hex-l-ene as a chain-transfer agent, except in the case of the OsCl3 catalyst, produced ring-opened polymer almost instantaneously and in higher yield than the cases shown in Table 8.20,
442
Table 8.20 Ring-opening polymerization ofnorbomadiene with various transition metal-based catalysts' Catalytic System
MoCI~/Bu4Sn TaCIs/Me4Sn IrCI3.SH20 TaCI~/Bu4Sn NbCIs/Bu4Sn WC~e4Sn (mes)W(CO)3~tAICI2 ReCI5 OsC|3.nH20
Monomer Concentration
Hex-l-ene Concentration
[Mo]
[Hex]
1.8 1.8
0.7 0.7 0.7 0.7 0.7 0.7 1.7 1.7 1.7
1.8 1.8 1.8 1.8 4.4 4.4 3.8
Or
Yield %
0.37 0.39 0.48 0.49 0.50 0.51 0.67 0.82 0.90
82 48 25 15 35 95 95 25 88
'Data from reference 264
but samples of polymer thus obtained were invariably insoluble, and although swollen in CDCI3 gave poorly resolved ~3C and ~H NMR spectra, in which no fine structure could be discerned. It is significant that if the monomer concentration exceeds a critical value in the presence of the system WCI6/Me4Sn, there is immediate formation of a gel as result of the cross-linking by opening of the second double bond. This process can be reversed by dilution. From the variation of this critical concentration with temperature, it was possible to determine the values of AH ~ = -4.6 kJ mole ~ and AS ~ = -2.9 J K~mole ~ for the opening of the second double bond. 265 Totally insoluble polymers have been obtained with [W](=CHSLMe3) complex as a catalyst. 266 Remarkably, if the polymer is partially oxidized, e.g., with 12/CCh at reflux, a black lustrous rigid product is obtained which is strongly paramagnetic (g = 2.0027), probably due to conjugated double bonds in the chain. 267 Substituted bicyclo[2.2.1lhepta-2,S-diene. The ring-opening metathesis polymerization of a number substituted bicyclo[2.2, l]hepta-2,5-dienes bearing alkyl and aryl groups in various positions of the bicyclic moiety has been reported. In this section we shall highlight the most relevant results obtained in some of the reactions carried out with these monomers.
443 7-Methylbicyclo[2.2.1 ]hepta-2,5-diene (7-Methylnorbornadiene). Ringopening metathesis polymerization of 7-methylnorbornadiene has been effected by Hamilton et al. z6s using OsCI3, RuCI3.xHzO, MoCls, WCI6, (mes)W(CO)3, ReCls and cocatalystsMe4Sn and EtAICI2 (Eq. 8.86).
n
=
~ n
(8.86)
Under these conditions, they prepared in various yields poly(7methylnorbomadiene) with cis main-chain double bond contents ranging from 20 to 97% (Table 8.21). Table 8.21 Ring-opening polymerization of 7-methylnorbomadiene using transition metal-based metathesis catalysts' Catalytic System
mollomor
Concentration [M]o/mole.L"1 OsCl3 OsCl3 (nm)W(COh/EtAIClz WCl~le4Sn MoCl~fl~e~Sn/F.tzO ReCI~ RuCl3.xHzO
3.15 3.37 2.90 3.10 2.95 3.40 3.30
Hex-l-ene Concentration [HexJ/mole.L"1
0'r
Yield %
0.56 0.74 1.34 0.74
0.97 0.97 0.76 0.42 0.20
40 32 66 34
-
0.80
29
48
Q
"Data from reference~ The microstructure of the polymers has been examined in detail by ~3C NMR spectroscopy. Noteworthy, the results thus obtained showed that polymerization from the anti-exo orientation is greatly favored over the syn-exo mode. A non-bonded repulsion energy of 6-8 Id.mole "~ between the syn-7-methyl group and the double bond was estimated. The mierostruetural features also resembled those for polymers of the anti- and syn-7-methylnorbornenes, in contrast to polynorbornadiene itself and to
444
polynorbornene, in that the splitting of a given resonance due to tacticity effects was of the same order of magnitude as splittings due to neighboring double bonds. It was also observed that the cis double bond content and tacticities using different catalysts agreed well with those expected from previous work with norbomadiene and several methyl substituted norbomenes, respectively, as monomers.
7-Phenylbicyclo[2.2.1 ]hepta-2,5-diene
(7-Phenylnorbornadiene).
Interesting work on the 7-phenylnorbomadiene polymerization published Hamilton et al. 269 in the presence of a variety of catalysts based on Ru, Os, lr, W and Mo chloride salts and complexes (Eq. 8.87).
Ph
(8.87)
Detailed ~3C and ~H NMR spectra of the polymers thus prepared and of their corresponding hydrogenated derivatives provided significant information concerning tacticities and fractions of cis double bonds (o~). Some data obtained by these authors are illustrated in Table 8.22. Table 8.22 Polymerization of 7-phenylnorbomadiene with several transition metal salts catalysts' Catalytic System
OsCI3 RuCI3 MoCls/Me4Sn/Et20 WCI6/Me4Sn (mes)W(CO)3/EtAlCl2
Hex-l-ene
Monomer Con~tion [M]o/mole.L"l
Concentration [Hex]/mole.L"i
O'c
Yield %
1.29
0.39
0.80
37
1.40 1.19
0.48
0.33
76
0.48
0.40
76
1.30 1.19
i
'Data from referencez69 As with other analogous diene monomers, extensive use was made of hexl-ene as a chain transfer agent in an attempt to lower molecular weight and reduce the possibility of cross-linking which can lead to insoluble products.
445 Noteworthy, the behavior of 7-phenylnorbornadiene was similar to that of 7-methylnorbomadiene in that a strong preference for the anti over the syn mode of monomer insertion was observed in contrast to 7-tertbutoxynorbornadiene which showed little or no regioselectivity under these circumstances. Furthermore, a pronounced effect on or was observed using OsCl3 as expected from previous results on ring-opening metathesis polymerization of systems containing chelating dienes such as norbornadiene and 7-methylnorbomadiene in the presence of this catalyst.
Benzol2,3] bicyclo[2.2.1 ]hepta-2,5-diene
(Benzol2,3]norbornadiene).
Analogously to norbomadiene, benzonorbomadiene readily ring-open polymerizes in the presence of binary metathesis catalysts WCI~,/PtuSn and WCIjMe4Sn to form poly(benzonorbomadiene) 27~(Eq. 8.88).
(8.88)
The polymer partially soluble in hydrocarbon solvents but readily soluble in chloroform was highly susceptible to air oxidation. Ring-opening metathesis polymerization of benzonorbornadiene has been investigated recently by Hamilton et al. 269 using a variety of catalysts based on Ru, Os, It, W, Mo and Re chloride salts and complexes. Detailed ~3C and ~H NMR spectra of these polymers and their corresponding hydrogenated derivatives have been recorded and analyzed for information concerning tacticities and fractions of cis double bonds (or Some results on polymer yield and fraction of cis double bonds are given in Table 8.23. It is interesting to note that whereas the fraction of cis content for RuCI3 (or = 0.22) is not quite zero which is usual for this catalyst and is significantly higher than normal using OsCl3 (or = 0.69) and (mes)W(CO)3 (or = 0.68). This effect of benzonorbornadiene on its own polymerization was compared to that of the presence of excess Michael acceptors (e.g., ethyl acrylate) on o~ values for norbornene polymerization using MoCI5 and WCl6-based catalysts. Living ring-opening polymerization of benzonorbornadiene under the influence of Grubbs-type titanacyclobutane initiatorTM and Schrock-type molybdenum carbene complex 272such as Mo(CH'Bu)(NAr)(O'Bu)2 has also been reported.
446 Table 8.23 Polymerization of benzonorbomadiene with various transition metal salts catalysts' Catalytic System
Monomer Concentration, [M]Jmole.L"1
0'r
Yield
OsCI3 RuCI3 IrCI3 MoCIs/Me4Sn/Et20
1.14 1.41
0.69 0.22 0.47 0.45 0.40 0.68
50 70 62 81 87 57 80
1.41 1.21 1.27
WCk/Me4Sn (mes)W(CO)3/EtAICI2
1.29
ReCI,
1.70
%
'Data from r e f e r e n c e 269 9-Methylbenzo[2,3]bicyclol2.2.1]hepta-2,5-diene. Polymerization of 9methylbenzo[2.3]norbomadiene has been effected by Cannizzo and Grubbs TM using titanacyclobutane as a catalyst (Eq. 8.89).
(8.89)
The product having M,=3590, M~--6330 and PDI=I.76 was only sparingly soluble in toluene or methylene chloride. To improve the polymer solubility, copolymers with norbomene have also been prepared. 7-1sopropylidenebenzo[2,3] bicyclo[2.2.1 ] hepta-2,5-diene. Interesting results have been obtained in the ring-opening polymerization of the dimethyl fulvene derivative ofbenzo[2.3 ]norbomadiene 273 (Eq. 8.90).
n
/~
~
(8.90)
447 This reaction has been carried out in the presence of the molybdenum carbene complexes Mo(=CH'BuX=NArXOtBu)2 and Mo(=CH'Bu)(=NAr)(OCMe(CF3hh (Ar=-2,6-isopropylphenyl) in toluene at 20~ The polymer contained 80% trans configuration independent of the catalyst. The product is susceptible to photoxidation but remains stable at low temperature in the absence of air and light. It can be also dehydrogenated to yield a conjugated polymer. 7-(1 '- P h enylet hylid en e) benzo [2,3 ! bicy do [2.2.1 ] h e pta-2,5- die n e. Interesting results have been obtained with the phenylmethyl fulvene derivative of benzo[2.3 ]norbornadiene, 7-( 1'phenylethylidene)benzo[2.3]norbomadiene, in the presence of the same molybdenum carbene initiators zn (Eq. 8.91).
Ph
n
~
Ph
=
(8.91)
The polymerization rate was lower due to enhanced steric hindrance but the
polymer had 100% trans configuration and displayed an alI-HT structure. 7-(Diphenylmethylidene)benzo[2,31bieydo[2.2.1]hepta-2,5.-diene. The polymerization of the diphenyl fulvene derivative of benzo [2.3 ] norbornadiene, 7-(diphenylmethylidene)benzo [2,3]norbornadiene, occurs readily in the same conditions as the corresponding methyl bearing fulvenes 2n (Eq. 8.92).
Ph~ Ph
Ph
n
/~
~
(8.92)
However, in contrast to the methyl derivatives, the diphenyl monomer leads to a 100% cis polymer with both molybdenum carbene complexes
448 Mo(=CH'BuX=NAr)(OtBu)2 and Mo(=CHtBuX=NAr)(OCMe(CF3hh (Ar=2,6-isoprpylphenyl). The reaction rate is also lower than that of the methyl containing monomers as result of a larger steric hindrance generated by the two phenyl tings. Benzol3,41buta[l,2]bicyclo[2.2.11hepta-2,f~.diene Both endo and exo isomers of this monomer have been polymerized in the presence of WCI6/Ph4Sn and WCI6/Me+Sn to produce polyalkenamers27~(Eq. 8.93).
n
---~.
(8.93)
Microstructure determination indicated that, under these conditions, both cis and trans stereoconfigurations of the double bonds were formed. Acenaphtho[2,3lbicyclo[2.2.1lhepta-2,5~iene. Similarly to the above monomer, the endo and exo isomers of acenaphthonorbomadiene have been polymerized in the presence of the same binary catalysts, WCI~PI~Sn and WCh,/Me4Sn to form ring-opened polymers bearing acenaphtho moiety in the recurring units 2~~(Eq. 8.94).
n
(8.94)
High yields of polymers were attained under the reaction conditions employed (Table 8.24). As it can be observed from the Table, both monomers showed a relatively high reactivity. The products exhibited a considerable susceptibility to oxidation similar to that observed for poly(benzonorbomadiene).
449 Table 8.24 Polymerization of endo and exo acenaphtho[2.3]norbomadiene with WCldMe~n and WCIdPh4Sn catalysts'
Monomer (lVl)
Catalyst
W:Sn:M
endo endo endo endo endo endo
WCldPl~n WCldMe,4Sn WCldPl~Sn WCIdM~Sn WCldPh~n WCIdMe,4Sn WCIdMe4Sn
1:2:60 1:2:60 1:2:139 1:2:139 1:2:35 1:2:35 1:2:~140
exo
|
Reaction
time, hr 5s 1.5 mira 20 20 20 20 10rain
Yield, % -100 82 100 100 100 100 -100
'Data from referencez~~
N aphtho[2,3] bicyclo[2.2.1 ]hepta-2,5-diene. Polymerization of naphtho[2,3]norbomadiene has been carried out in chloroform with WCIdMe4Sn to the corresponding ring-opened polymer274 (Eq. 8.95).
n
~
(8.95)
Elemental analysis, IK 'H and ~3C NMK spectra confirmed the assigned polymer structure. The product was partially soluble in common solvents and susceptible to oxidation like poly(benzonorbomadiene). Benzo [4,Sltricyclo[6.2.1.0='7l undeca-2(7),4,9-triene (1 '5'Dihydronaphtho[2,3]bicyclohepta-2,5-diene). Polymerization of dihydro derivative of naphtho[2,3]norbomadiene occurs readily in the presence of WCIdMe4Sn to the unsaturated polyalkenamerTM (Eq. 8.96).
(8 .ge) ~
m
450 The product was easily soluble in chloroform. ~H and ~3C NMR spectra indicated 40:60 distribution of cis and trans double bonds but details about the polymer tacticity could not be obtained. A n t h raceno [ 2,3 ] b icy clo h e pta-2,5-d ien e. Polymerization of anthraceno[2,3 ]norbomadiene has been effected with both WCIdMe4Sn and MoCIs/Me4Sn catalysts in chloroform. 27~ Structure determination by conventional methods was frustrated by the insolubility of the polymer in common solvents. Solid state spectral determinations indicated that the product corresponded to ring-opened polymer (Eq. 8.97).
-[~m
5
(8.97)
( The polymer was strongly susceptible to oxidation like poly(naphthonorbornadiene) and poly(benzonorbornadiene). Bicyclol4.2.01oct-7-ene. The polymerization of bicyclo[4.2.0]oct-7-ene was investigated by Dall'Asta and Motroni 2~ using a variety of catalytic systems based on transition metals, in hydrocarbon or polar solvents. As a function of the catalytic system, vinyl polymers, polyalkenamers or mixtures of these two type of polymers have been prepared (Eq. 8.98).
(8.98)
These authors used first a series of binary Ziegler-Natta systems derived form halides or acetylacetonates of titanium, vanadium, chromium, tungsten associated with organoaluminium compounds and then one-component
451 catalysts based on nickel, rhodium, ruthenium, iridium and palladium salts in water, ethanol, or dimethylsulphoxide as solvent. In these studies DaU'Asta and Motroni found that the catalytic systems containing vanadium, chromium, nickel, rhodium and palladium form predominantly vinyl polymers, those of titanium, ruthenium, and iridium to unsaturated polymers by opening the cyclobutene ring whereas the catalysts containing tungsten led to both types of polymers. In all cases the molecular weights of the polymers obtained with these catalysts were low. Bicyclo[5.1.0]oet-2-ene. King-opening polymerization of bicyclo[5.1.0]oct-2-ene has been effected in the presence of the tungsten carbene catalyst W(=C(OMe)Ph)(CO)dTiCh at 50~ to the corresponding polyalkenamer bearing a cyclopropane in the repeat unit 276 (8.99).
[vv]
= ~
(8.99)
The ~3C NMR spectrum of the polyalkenamer displayed eight lines in the olefinic region, probably stemming from cis/trans splittings of the tail-head, tail-tail, head-head and head-tail resonances. Bicyclo[2.2.2loct-2-ene. Bicyclo[2.2.2]oct-2-ene has been polymerized by Ofstead ~63 in the presence of the homogeneous ternary catalyst WCIdEtOH/EtAICIz obtaining the corresponding polyalkenamer (Eq.8.100).
n
~
L
.I n
9
Using a catalytic system with a molar composition W:O:AI of 1 1 1.4, a polymer with prevailingly trans structure at the double bond has been produced. It is noteworthy that this reaction represents one of the few examples in which the cyclohexene ring undergoes ring-opening polymerization. Taking into account the thermodynamic stability of the sixmembered ring, Ofstead made some considerations concerning the ringopening polymerization of this system. He concluded that the polymerizability of this monomer is mainly attributed to the conformational effects occurring in the six-membered ring containing the unsaturated
452 bridgehead of bicyclo[2.2.2]oct-2-ene. It is significant to point out that all three six-membered cycles of the monomer, i.e., one cyclohexane and two cyclohexene tings, exist in a very stable boat conformation. More recently, Hamilton et al. 2" carried out the ring-opening polymerization of bicyclo[2.2.2]oct-2-ene in chlorobenzene at 20~ with W(CO)3(mesytylene)/EtAICl2/2,3-epoxynorbomene containing a trace of norbomene and Me4Sn. The polymer structure was assigned by ~3C NMR spectroscopy. A product of 34% cis configuration was obtained with a somewhat blocky cis/trans distribution. Benzobicyclo[2.2.2loctatriene (Benzobarrelene). Benzobarrelene has been readily polymerized in the presence of Mo(=CHC(CH3)2Ph)(=NAr)(OC(CH3XCF3h)2 (At = 2,6diisopropylphenyl) in methylene chloride at room temperature to form the corresponding insoluble polyalkenamer 278 (Eq. 8. I 01).
n
[M~
~
I"
1 Jn
L
~
(8.101)
This behavior indicates a very rigid structure for the insoluble ring-opened polymer which is the precursor of poly(l,4-naphthylenevinylene) (PNV). However, the introduction of alkyl substituents to the backbone of the rigid, planar PNV structure rendered the polymer soluble in common organic solvent. This objective has been achieved by ring-opening polymerization of alkyl substituted benzobarrelene (R = C6HI3 and CIIH23) with Mo(=CHC(CH3)2Ph)(=NAr)(OC(CH3)2(CF3))2 (At = 2,6diisopropylphenyl) and further oxidation of the polymer precursor to alkyl substituted PNV (Eq. 8.102).
n
(8.1(]2)
R
\
R R where R = C6H~3 and C~H23. The polymer thus obtained could be characterized by routine spectroscopic methods such as ~H NMR, ~3C NMR
453 and UV/VIS. The product showed strong fluorescence and after doping polymer films exhibited excellent conductivity. Bicydo[4.3.01nona-l,3,5,7-tetraene (Indene). By ring-opening metathesis polymerization under appropriate conditions, indene produces a highly unsaturated polyalkenamer, through opening of the exocyclic double bond of the five-membered ring (Eq. 8.103).
Early attempts to ring-open polymerize indene under the influence of the WCL~PI~Sn catalyst, by Feast and coworkers ~7~ indicated only a limited extent of the corresponding polyalkenamer to be formed and mainly conventional vinyl polymer, but the results were nor quite conclusive. More recently, on using Mo(CO)sPy/EtAICI~/BLhNCI as the catalyst, Johnston and Farona ~s~ obtained polyindene in 92% yield in chlorobenzene at 30~ The main pathway was ring-opening reaction (66%), but also vinyl polymerization oc,c~rred under the above conditions. Bicydo [4.3.0]nou-3,7-diene (Tetrahydroindene). Dall'Asta and Motroni ~9 polymerized tetrahydroindene in the presence of several transition metal catalysts to produce the corresponding polyalkenamer (Eq.8.104).
(8.1o4)
The product had prevailingly t r a n s stereocontiguration at the double bond. Of the catalysts employed, tungsten- and molybdenum-based systems proved to be the most active, leading to ring-opened polymers in 40% and 50% yield, respectively. By contrast, titanium-, vanadium- and chromiumbased catalysts showed to be less active and the polymers formed had a random microstructure.
454 Later on, Ofstead and Calderon, ~63 employing the binary catalyst WCI6/EtAICI2 used earlier in cyclooctene polymerization, showed that this catalytic system is also rather active in tetrahydroindene polymerization. Structure examination of the reaction product by spectroscopic methods indicated that the reaction occurred exclusively by ring-opening of the fivemembered ring while the six-membered ring remained intact in the polymer chain. 5,8-Methylene-Sa,8a-dihydrofluorene. Polymerization of 5,8-methylene5a,8a-dihydrofluorene has been effected in the presence of tungsten-based catalysts to the corresponding polyalkenameff"8~(Eq. 8.105).
n~
=
~.~
(8.105)
The catalysts consist of a tungsten compound obtained from WCI6 and ptrihalomethylphenol associated with an organotin or organosilicon compound as a cocatalyst. Copolymers of 5,8-methylene-5a,8adihydrofluorene with bulky norbornene derivatives allowed the manufacture in high yields of products having tailored properties, particularly glass transition temperatures. Bicyclo[6.1.0]non-4-ene. Polymerization of bicyclo[6.1.0]non-4-ene occurs readily in the presence of WCh,-based catalysts when cyclooctene ring opens to a polyalkenamer bearing a cyclopropane ring in the repeat unit (Eq. 8.106).
With WCI6]('Bu2AI)20 as a catalyst, a polymer containing 62% cis double bonds is obtained at 63~ which gives a well-defined ~3C NMR spectrum for both olefinic and cyclopropylene regions. TM Other catalytic systems lead to polyalkenamers having from 19 and 75% cis configuration. 282
455
8.3. Ring-Opening Polymerization of Polycyclic Monomers The ring-opening metathesis polymerization has become a versatile way to prepare polymers with particular structures and valuable properties from polycyclic olefins. The reaction has been applied selectively, due to a wide range of effective metathesis catalysts prepared in the last decade. Benzvalene(Tricydohexene). Ring-opening polymerization of benzvalene, B, a valence isomer of benzene, is an interesting way to prepare polyacetylene. This reaction has been effected in the presence of tungstencarbene catalysts, W(=CH'Bu)(OCH2~Bu)-zBr2, W(=CHtBuX=NAI')[OCMe(CF3)2]2 and W(--CHrBuX=NArXOtBu)2, leading first to polyCoenzvalene), PB 2s3 (Eq. 8.107). n
Q [wl , ~ ~ ~
B
,~,~ HgX2~g ,X
(8.1o7)
-.~
PB
PA
Poly(benzvalene) has a tendency to cross-link and tO decompose spontaneously when isolated in dry form, on heating too rapidly or under high mechanical stress. It is best handled in solution, especially as the decomposition can be explosive. Subsequent isomerization of poly(benzvalene) under the action of heat, light or metal salts such as mercury or silver halides gives readily polyacetylene, PA. After rearrangement it is difficult to rid the polymer entirely of residual metal. Nevertheless, polyacetylene was obtained which had conductivities of 10.8 to 10"? before doping and 0.1 after heavy doping with iodine. Tricydo[4.2.0.0~octa-3,7-diene. Ring-opening polymerization of syntricyclo[4.2.0.0~]octa-3,7-diene is encountered in cross-linking of polyalkenamers and occurs readily in the presence of WCL/Me4Sn as a catalyst giving cross-linked units of the following type TM(Eq. 8.108).
II t I ll
/-I-
r/ L
I !
(8.,o8)
J
It was observed that both cyclobutene tings readily open and if sufficient tricydo[4.2.0.O~]octa-3,7-diene has been employed, the cyclobutane rings
456 which form the cross-links give rise to observable signals in the ~H NMR and ~3C NMR spectra. Tetracyr [2.2.2 ~'s.1t'4.03"Slnon-8-ene (Deltacydene). Deltacyclene, readily available via Diels-Alder reaction of norbomadiene with acetylene, has been polymerized by Lautens and coworkers 285'2s6 in the presence of ROMP catalysts consisting of RuCI3, ReCI5 and WCIdPh4Sn. Depending on the catalyst and reaction conditions employed (solvent, reaction temperature, monomer concentration) ring-opened polymers having variable c i s / t r a n s stereoconfiguration at the double bond have been obtained (Eq. 8.109).
n
=~'~n
(8.109)
The polymers prepared from this monomer provide a combination of rigidity and strain throughout the chain since they contain an inflexible carbon backbone, a cyclopropane ring, and a repeating sequence of olefin, which are held in close proximity due to the d i - e n d o orientation of the nortricyclane framework. The crude products thus obtained were dark brown solids that could be easily purified by precipitation and column chromatography on silica gel. The highest molecular weight polydeltacylenes, which were the least soluble in chloroform, were soluble in halogenated solvents, THF, cyclohexane, and aromatic solvents such as benzene and xylenes. When RuCI3.H20 was used in ethanol/water mixtures as a solvent at 60~ for 24 hr, the catalyst activity and product molecular weight were strongly dependent on the molar ratio ethanol/water (Table 8.25). Table 8.25 Polymerization of deltacyclene (M) with RuCI3.H20 (I) at various ethanol/water (~S~)ratios' M/FS EtOH/H20 M~ Polymer Yield, % 100/1/400 100/1/400 100/1/400
1/0 1/1 1/100
2000 b 103000~ 206000 d
31 72 90
100/I/400
0/I
207000 d
85
'Data from reference 2s~; bRatio of cis to trans isomers = 1/1.3; "Ratio of cJs to trans isomers 1/1, dRatio of cts to trans isomers = 1/1.5.
457 As Table 8.25 shows, a low molecular weight polymer was produced in anhydrous ethanol while addition of varying amounts of water to ethanol resulted in a dramatic increase (100-fold) in the molecular weight of the polymer. Polymerization of deltacyclene also ocs in water as the only solvent in spite of the insolubility of the monomer; however, no further increase in the molecular weight or polymer yield was recorded under these conditions. An increase in the polydispersity index as a function of increasing water content (2.04 in ethanol and 3.46 in water) was observed. The molecular weight of polydeltacyclene was also affected by changes in the catalyst to monomer ratio. Thus, decreasing the ratio of the catalyst to monomer from 1 mole % to 0.17 mole % resulted in a substantial increase in the molecular weight of poly(deltacyclene) (Table 8.26). Table 8.26 Effect of monomer (M) to catalyst (I) ratio in deltacyclenepol~'merization with RuCI3.HzO catalyst' M/I EtOH/HzO M, Polymer Yiel~ % 100/1 200/1 600/1
1/1 1/1 1/1
103000 447000 856000
72 78 85
'Data from referencoZ'~;~ d o of cis to tram isomors = 1/1. By this way, polydeltacyclenes with molecular weights approaching 10 6 were routinely isolated. As Table 8.27 illustrates, both cls and trans stereoconfigurations of the double bonds resulted under the action of the RuCI3.HzO catalyst. It is surprising to note that ruthenium catalysts, which are known to yield polymers containing predominantly trans stereoconfiguration at the double bond, produced from deltacyclene polydeltacyclenes of low stereoselectivity in the above conditions. Further attempts to change the stereoselectivity of deltacyclene polymerization by adding formamide to the reaction mixture were unsuccessful. As Table 8.27 indicates, increasing the proportion of formamide to ethanol did not result in any change in polydeltacyclene stereoconfiguration as measured by tH NMR; however, the polymer molecular weight did increase considerably with increasing amounts of formamide. This result is also intriguing as formamide has been reported to have such an effect by increasing the amount of trans isomer in the ring-opening polymerization of norbomene.
458 Table 8.27 Polymerization of deltacyclene (M) in fonnamide/ethanol (S) with RuCI3.H20 rst' Mwb M/FS EtOH/HCONH2 Polymer Yield7 % 100/1/400 100/l/400 100/l/400
5/1 1/1 1/7
86000 259000 929000
42 54 42
'Data from reference2t~; bRatio of cis to trans isomers = l / I. 8. However, it is noteworthy that increasing amounts of formamide increased the molecular weight of polydeltacyclene. Interestingly, further examination of the deltacyclene polymerization under conditions where the starting material and product would be completely soluble indicated that the reaction in benzene or THF in the presence of hydroxylic solvents caused the solution to become highly viscous during the course of reaction but remained as one phase. In this case, the polymer molecular weight was again strongly influenced by the nature and composition of the solvent mixture (Table 8.28). Table 8.28 Homogeneous polymerization of doltacycleao (M) w~h RuCI3.HzO :I) as a catalyst' M/I/S Solv ratio) M. Polymer Yield~ % 100/1/350 200/1/400 100/1/400
EtOH/PhH ( 1/3) EtOH/THF (l / l 0) H2OfI'HF (1/ ] 0)
5000 35000 992000
60 68 74
'Data from reference2SS;bRatio o f cis to trans isomers = 1/1-1.5. When the polymerization was carried out in a mixture of water/THF, a high molecular polydeltacyclene was isolated. No other changes in polymer structure were observed. Changing the catalyst from RuCl3 to WCI6/PIhSn resulted in a smooth polymerization of deltacyclene 285 and provided a white solid polymer in good yield (73%) and of moderate molecular weight (Mw = 20000). Analysis of the tH NMR spectrum of polydeltacyclene indicated a more selective reaction had taken place, yielding polymer with the c i s geometry of the double bond predominating ( c i s : t r a n s = 70:30).
459 Remarkably, ReCIs showed to be substantially more cis stereoselective than the tungsten or ruthenium catalysts. The reaction was most effectively carried out by addition of deltacyclene to the catalyst at room temperature in the absence of any solvent. Under these conditions, a solid polymer was isolated in moderate yield (48%), which, by ~H and ~3C NMR spectra indicated over 95% cis-polydeltacyclene (Eq. 8.110).
2n
The gel permeation chromatography indicated that the cis-polydeltacyclene thus prepared was of very high molecular weight (Mw- 986000). A low molecular weight material (Mw = 6000) was also obtained in ca. 20% yield. It is interesting to note that cis-poly(deltacyclene) is substantially less soluble in chloroform, Tiff, or benzene than the cis/trans polymer. Polymerization of deltacyclene was very facile with the Schrock molybdenum alkylidene catalyst, Mo(=CHCMezPhX=N-2,6 'PrzPh)(OtBuh, either neat or as solutions in toluene or chloroform ~ . High yields of polydeltacyclene were obtained (>90%) of a variable molecular weight depending on the reaction conditions (Table 8.29).
Table 8.29 Polymerization of deltacyclene (M) using the Schroc~ catalyst Mo(=CHCMe2PhX=N-2,6JPr2PhXO~u)2~ Solvent
Mw
Mn
DP
PDI
Neat Toluene Toluene
466000 74100 16200
295000 58190 14970
3950 630 138
1.58 1.27 1.09
9
Data fn~a reference216
As Table 8.29 illustrates, the polydispersity of the high molecular weight polymers was found to be 1.58 and 1.27, respectively. Upon decreasing the chain length, the polvdispersitv improved to 1.09. In addition, the
460 spectral data indicated the ratio of trmzs to cis double bonds varied from 2.7:1 to 1.9:1. Substituted deltaeyelene During their studies on the polymerisation of substituted deltacyclenes, Lautens et aL 2s6 examined the reaction of butyland phenyldeltacyclene in the presence of the above metathesis catalysts. These monomers, which have been easily prepared by the Diels-Alder reaction of norbornadiene with butylacetylene and phenylacetylene, respectively, were readily polymerized to form ring-opened polymers of deltacyclene with butyl and phenyl groups along the polymer chain (Eq. 8.11]-8.] 12). (8.111)
n
Bu (8.1 12)
n
Ph
As a function of the catalyst employed and nature of the substituent, various yields and structures of the polymers have been recorded. The products thus synthesized have C=C double bonds that are more rigidly held at defined distances due to the nortricyclane framework and substituent bulkiness. 1 z,s]-deca-3,7-diene (Dicyclopentadiene). By ring-opening Tricyr metathesis polymerization, dicyclopentadiene (endo- and exo-isomers) may form two different unsaturated polyalkenamers having as recurring units bicyclo[3.3.0]octenylenevinylene (A) and bicyclo[2.2.1 ]heptenyleneallylene (B) (Eq. 8.113).
(8.113) exDlendo
461 These polymers result through scission of two distinct double bonds of the monomer, that from norbornene moiety and cyclopentene ring, respectively. Due to the substantial difference in the reactivity of the double bond from the strained norbornene moiety as compared to that of cyclopentene ring, formation of the first polyalkenamer by opening of norbomene double bond is preferred. However, depending on the catalysts activity and selectivity, both pathways can be competitive giving either different polymer chains with the two structures or a polymer containing both structures in the same chain (Eq. 8.1 14).
(8.114)
In the early work of Eleuterio 4 on the cycloolefin polymerization under the action of heterogeneous catalysts derived from transition metal oxides deposited on alumina in hydrocarbon solvents it was reported that dicyclopentadiene polymerizes to give unsaturated polymers. Later, Oshika and Tabuchi ~82 showed that endo-dicyclopentadiene gives with catalytic systems formed from MoCls, ReCls and WCI6 in carbon tetrachloride or carbon disulphide polyalkenamers with a high stereospecificity by opening of the norbornene double bond. Thus, MoCls led preferentially to transpoly(dicyclopentadiene), geCls formed c/s-polymer (Eq. 8.1 15)
leo]
(8.11s)
[Re]
462 and WCh, produced both cis and trans stereoconfigurations of the double bonds (Eq. 8.116)
IV4
(8.116)
The catalysts showed to be less active than in the similar reaction of norbornene. In contrast to the above results, Dall'Asta and coworkers, 2s~ using various transition metal catalysts consisting of chromium, molybdenum or tungsten halides and organometallic compounds, obtained mixtures of ring-opened and vinyl polymers (Eq. 8.117).
It also is possible that both ring-opened and addition structures to occur in the same polymer chain as Farona and coworkers TM demonstrated for norbornene and dicyclopentadiene polymerization in the presence of Mo(CO)5(Py)/EtAICI2/Bu4NCI as a catalyst (Eq. 8.118).
3
y
(8.118)
463
Up to now, the ring-opening polymerization of dicyclopentadiene has been effected with a wide range of catalytic systems including those based on TiCI4,289 titanacyclobutane complexes, 29~ WCI6,2::294 WOCh, TM MoCIs, ~ PxeCl~,295'297 IrCl3, O s C l 3 , guCl3, 29s (mesytilene)W(COh, 29~ Mo(CO)5(Py), 288 various WCI~(OR)6~ compounds, 298"3~ organoammonium molybdates and tungstates, a~176 the molybdenum carbene complex Mo(=NArX=NC'Bu)(CH2'Bu)2 in conjunction with a phenolic activator, 3~ tungsten tetraphenylporphyrinates associated with aluminoxane 39':59 and various polymetallates. 3~ It is worthy noting that, in many cases, the polymer formed is only partially soluble in organic solvents while, in other cases, is totally soluble. This result depends on the reaction conditions and mainly on the nature of the catalyst, monomer concentration and if a chain-transfer agent has been used to restrict the molecular weight. Thus, catalysts consisting of chloroaryloxide complexes of tungsten, WCI6.~(OAr)~ (x = 2,3,4; OAr = substituted phenoxide), associated with alkyl-aluminium, alkyl-tin or alloyllead compounds as a cocatalyst, lead to a highly cross-linked insoluble polymer when alkyl-aluminium compounds are employed and to a soluble poly(dicyclopentadiene) when alkyl-tin or alkyl-lead are employed as cocatalysts. 3~176 Analysis by Ig and :H NMR spectroscopy of the soluble polymer indicated that only the norbornene ring was cleaved and that there was no C=C double bond loss during polymerization. The structure assigned to the soluble polymer was that of a linear poly(dicyclopentadiene) as depicted in Eq. 8.113 and 8.114, while the structure of the insoluble polymer that of a cross-linked poly(dicyclopentadiene) as illustrated in Eq. 8.119
r
(8.119)
464 where in the first step only norbornene tings open and then cyclopentene or that shown in Eq. 8.120
z=,,= r
(8.12o)
where in the first step both norbomene and cyclopentene tings may open and then cyclopentene cross-links. Of the two isomers of dicyclopentadiene, endo-dicyclopentadiene, a relatively inexpensive and available by-product of naphtha cracking, was found to readily polymerize in the absence of solvents with classical homogeneous catalysts based on tungsten hexachloride and organoaluminium compounds. 3~ In a typical example, addition of a small amount of Et2AICI to about 5 ml of endo-dicyclopentadiene, containing a pinch of tungsten hexachloride, at room temperature leads, after a brief induction period, to a rapid rise in temperature above 200~ and the formation of an insoluble, cross-linked polymer. The process is ideal for RIM (reaction injection molding) since the catalyst system consisted of two parts and the fluid monomer would allow the filling of large, complex moulds. 3~~Elastomers were added to adjust the polymer viscosity whereas comonomers have been employed to tailor the physical-mechanical properties. 3~ The most active catalyst in this system appears to be a mixture of WCI6 and WOCh, the latter being formed in situ by the addition of tert-butanol. 3~2 The tungsten compounds were reacted with nonylphenol to solubilize them in the monomer. Acetylacetone was also added to increase self-life; in its absence a slow polymerization of dicyclopentadiene occurs, perhaps induced by acid traces. In their extensive work on the use of titanacyclobutanes as ringopening metathesis catalysts, Grubbs and coworkers 2s~ showed that endodicyclopentadiene could be polymerized by these species, however, only
465 low-molecular-weight polymers and an uncharacterized insoluble material could be obtained. Interestingly, subsequent investigations revealed that the exo isomer, behaved in a much more controlled fashion. Thus, titanium metallacycles catalyzed the living polymerization of exo-dicyclopentadiene to produce monodispersed homopolymer or narrow dispersed block copolymers with norbornene. Consistent with these early findings for the titanium catalysts, selective polymerization of exo-dicyclopentadiene by the living molybdenum and tungsten alkylidene catalysts, M(=CHR~)(ORZ)~(=NArR3z), where M=Mo or W, R~=Rz=C(CH3)3, R3=CH(CH3)~, produced freely soluble poly(dicyclopentadiene). The polymer displayed a narrow molecular weight distribution characteristic of living polymerization systems (Table 8.30). Table 8.30 Polymerization of exo-dicyclopentadiene (M) using metal alkylidene con~lexes' Catalyst
exo-M equiv.
MII
MW
PDI
CpzTi[CJ-hC(CH3h] CpzTi[CJ-t4C(CH3)z] Cp2Ti[C3H4C(CH3h] W(--CH~Bu) (O'Buh(=NCJ-13-'Prz) W(=CH~Bu) (O'Buh(=NCd-13-'Pr2) W(=CH~u) (O'Bu)z(=NCffI32Pr2) Mo(=CHtBu) (O'Bu)z(=NCd-13-'Prz) Mo(=CHtBu) (O'Bu)2(=NCJ-13-'Prz)
48 75 98 50 100 195 50 100
9425 13500 18825 12700 25800 57200 13900 27500
10400 15000 20250 15300 29800 65300 15400 30000
1.10 b 1.11 b 1.08 b 1.20 r
1.15' 1.14~ 1.11r 1.10~
'Data from referenceZ~; ~Reaction conditions: Temperature = 70~ [Catalyst]=0.005 M in CTl'h, Yields > 80% (polymerization stopped a t - 9 0 % conversion), Turnovers per hour 4.9; r condition: Temperature = 25~ [Catalyst] = 0.005 M in CTHs, Yields > 85% (all monomer consumed). Working with the above well-defined metathesis catalysts in solution, under normal conditions, completely soluble linear poly(-exo-dicyclopentadiene) was obtained in good yield, with no residual monomer detectable by gas chromatography. As the concentration of the monomer was gradually increased, an insoluble material was produced in addition to poly(-exodicyclopentadiene). When the polymerization was conducted in
466 neat exo-dicyclopentadiene, the insoluble material could be isolated in 50% yield and the filtrate contained unreacted monomer which also contained 20-30% soluble poly(exo-dicyclol~ntadiene). Since the product was formed by a well-defined, single component, mctathesis catalyst, the authors supposed that the cross-linkages were formed by metathesis of the cyclopentene side groups of the polymer and not by a Lewis acid catalyzed reaction (Eq. 8.121). n
(8.121)
The tungsten alkylidene complex, W(=CHRIXORZh(=NArR3z), where RI = C(CH3)(CF3)2, g2 = o-(CH30)C61-h and R3 = H, was too reactive as a metathesis catalyst for precise molecular weight control, however, the metal centre was active throughout the polymerization and a soluble polymer was obtained. Polymerization of endo- and exo-dicyclopentadiene has been investigated by Hamilton, Ivin and RooneyTM using a variety of homogeneous catalytic systems derived from group V-VIII of the Periodic System in chlorobenzene as a solvent. When noble metal salts were employed as catalysts, ethanol/chlorobenzene (1"1) was the solvent. Depending on the catalytic system and reaction parameters, variable yields in poly(dicyclopentadiene) and microstructures of polymer have been obtained (Table 8.31). As Table 8.31 illustrates, endo-.dicyclopcntadiene gives tfigh-trans polymer in the presence of IrCl3, Ifigh-cis polymer under the action of ReCl5 and RuCI3.3HzO while W-, Nb- and Os-based catalysts form a fair proportion of both cis and trans double bonds in the main chain. In contrast, exo-dicyclopentadiene will produce a high-trans polymer with RuCI3.3HzO, a tfigh-cis polymer with ReCI~ and intermediate stereoselectivities with W- and Os-based catalysts. In a number of cases, the polymers, after isolation and drying, were found to be insoluble, or poorly swollen in deuterochloroform, the solvent used in the t3C NMR measurements. In particular, fully hydrogenated poly(dicyclopentadiene) were completely insoluble irrespective of the solubility of the precursor polymer. However, these authors found that poly(dicyclopentadiene) of lower molecular weight, obtained in the presence of a chain transfer
467 T a b l e 8.31
Polymerization of dicyclopentadiene(DCPD) (M) using various catalytic systems' Monomer
Catalytic System
[Mo]
[Hexl-enel
2.60 (Mes)W(CO)3/EtAICI2 1.96 OsCI3 2.60 NbCIs/Me4Sn 3.79 (Me$)W(CO)3/EtAICI2 0. l I WClo~e4Sn 1.95 WCIJMe4Sn 2.62 RuCI3.3H20 I 7.60 ReCI5 i 2.50 RuCI3.3H20 1.06
0.82 0.24 0.82 0.24 1.90 0.17 -
9
endo-DCPD endo-DCPD endo-DCPD endo-DCPD endo-DCPD endo-DCPD endo-DCPD endo-DCPD endo-DCPD exo-DCPD exo-DCPD exo~DCPD exo-DCPD
IrCl3
OsCI3
WC~e4Sn ReCI~
-
3.20 2.50
a~
Polymer . Yieldt %
0.19 0.35 0.36 0.46 !~ 0.56 0.73 0.73 1.0 1.0 0.10 0.39 1.0
10 96 12 50 86 40 40 6 33 64 13 8 30
'Data from reference agent, hex-1-ene, was soluble and could be hydrogenated to either soluble polymers or polymers well swollen in deuterochlorofom~ giving high quality m3C NMR spectra. Significantly, the one exception was the lugh-cis poly(dicyclopentadiene) which was always insoluble and the hydrogenated product unswollen even when prepared employing chain transfer agents. Polymerization of endo-dicyclopentadiene carried out by Pacreau and Fontanille 29~ with the binary catalyst ReCIs/Me4Sn gave a substantial amount of linear polymer with high molecular weight and high content of cis double bonds. Kinetic studies of the early stages of the reaction showed that the polymerization proceeds via an oligomerization reaction followed by the formation of polymer when an equilibrium between oligomers and polymer is established. The influence of temperature, monomer concentration, catalyst/cocatalyst ratio and catalyst/monomer ratio on the activity of the system and polymer yield were examined. Insoluble polymers were obtained also with ReCI5 and EtAICI2 and Et2AICI. A mechanistic scheme to explain the generation of the primary active species and the twostep polymerization process was proposed.
468 Extensive work has been conducted by several authors on the polymerization of endo- and exo-dicyclopentadiene with tungsten alkoxide or phenoxide complexes, as such or associated with organometallic compounds. 3~176176 The latter systems provided the most efficient binary catalysts for poly(dicyclopentadiene) manufacture by means of RIM processes. Some of WOC~(OAr)~ complexes, e.g., WOCI3(OAr), WOCIz(OAr)z, and WOCI(OAr)3, in combination with trialkyltin hydrides or triaryltin hydrides, showed to be quite stable and useful to polymerize dicyclopentadiene in bulk in high yield.3~176 The degree of dicyclopentadiene conversion could be related directly to the reduction potential of the WOCIz(OAr)2 complexes employed (e.g., electronic charge on the oxygen of the phenoxide). It was observed that the activity of a particular catalyst could be empirically related to the electron-withdrawing characteristics, e.g., Hammett constants. For the series of WOCI,~(OAr)~ procatalysts, Bell3~ was able to gauge the metal electrophilicity by measuring the reduction potentials associated with each procatalyst. Electron-withdrawing phenoxides, such as 2,6-dichlorophenoxide and 2,6dibromophenoxide, ensured that the polymerization reaction induced by the corresponding W-phenoxide complex occurred almost completely to give polymer possessing a residual dicyclopentadiene level of 0.1 wt%. When WOCIz(OC6H3-2,6-'Prz)2, prepared using the less-acidic 2,6diisopropylphenol, was activated by a trialkyltin hydride, a slightly less active catalyst was generated, since the residual monomer level in the poly(dicyclopentadiene) was close to 0.4 wt%. In order to understand the range of reactivity which might arise with WOCIz(OAr)2 complexes bearing 2,6-diisopropylphenoxide and 2,6dichlorophenoxide moieties, as proc~talysts for dicyclopentadiene polymerization, under molding conditions, the effect of varying reactant stoichiometries on residual monomer level was systematically studied by Bell et al. 3~ Relevant aspects on the effect of the following reaction variables were investigated for these catalysts: (i) monomer to catalyst ratio, (ii) cocatalyst to catalyst ratio, and (iii) Lewis base as rate moderator to catalyst ratio. Some results obtained on the effect of monomer to catalyst ratio and cocatalyst to catalyst ratio are depicted in Figure 8.1. As Figure 8.1 A illustrates, although both procatalysts polymerize dicyclopentadiene to very high conversions, even at the highest monomer to tungsten ratio, the procatalyst based on 2,6-dichlorophenol (curve 2) afforded slightly lower residual monomer levels. On the other hand, there is little effect of increasing the trialkyltin coc~talyst to tungsten ratio on the residual
469
MR (A)
!
MtW
(e)
Figure 8.1. The effect of reactant stoichiometry on the residual monomer (MR) in dicyclopentadiene (M) polymerization with the con~lex WOCI2(OAr)2 (A) M:W; (B) R3SnH:W (Curve 1 92,6-Pr2;Curve i 2 92,6-C1z) (B) (Adapted from Ref.3~ ~ monomer levels (MR) even at high R3SnH:W ratios (Figure 8.1 B). The slight difference in residual monomer levels ( M s ) was attributed to the substitution at the phenol group. In addition, Bell found that the onset of gelation and curing could be adjusted by altering the Lewis base used as moderator to tungsten ratio. Suitable rate moderators could be selected from the compounds typically used in ternary catalysts such as ethers, phosphines, phosphites, phosphonites, pyridines, pyrazines, and many other Lewis bases. Overall, the activated 2,6-~ichlorophenol procatalyst showed to be more effective at polymefizing dicyclopentadiene than the corresponding 2,6-diisopropylphenol proc~talyst. Balcar et al. 3~ found that the complexes WCIs(OR), where R = CH(CH2CIh or substituted phenyl, and WOCh initiate the ring-opening polymerization of dicyclopentadiene without any cocatalyst. Their activities were, however, lower than when they were associated with a reducing organometallic compound. Results of these experiments are summarized in Table 8.32.
470 Table 8.32 Polymerization of dicyclopentadiene (M) induced by unicomponent catalysts (I) derived from WCl6~b Catalyst
Temperature V Time oC II hr i I
Yield 1 %
Soluble ~ : : fraction '1 !'
%
WCI6 WCI6
room 24 25 40 70 1 66 10 WCI~[OCH(CHzCI)z] room 3 59 0 WCI4[OCH(CHzCI)z]z room 24 0 WCI~(O-2,62Buz-CJ'I3) room 24 3 100 WCI~(O-2,6-tBuz-CJ-13) 70 , 6 20 10 WCI~(O-4-tBu-CJ-14) room 24 6 80 WCI~(O-4-tBu-CJ-14) room 50 24 58 WCI~(O-42Bu-CcJ~) 70 2 51 9 WCI~(O-4-CI-CJ-14) room 24 29 33 WCI~(O-4-CI-Cd'h) 40 6 i 23 17 WCI~(O-4-CI-CJ'I4) 70 2 46 9 WCh(O-4-'Bu-Cd'hh 70 6 7 73 WOCI4~ room 3 21 20 WOCh' 70 1 67 3 '13ata from reference3~ bRea~on conditions: [W] = 20 mmole.L "!", molar ratio M/I = 74/1; c[w]= 10 mmole.L"~. The catalytic activity was evaluated by the polymer yield after a given time. The monomer conversion as determined by C~ was in some cases about several percent higher than the polymer yield, suggesting formation of a methanol-soluble low molecular weight product. It was observed that WCI6 after addition of dicyclopentadiene provides a black precipitate, which partially redissolves at later stages. The inhomogeneity of the reaction mixture led, however, to decreased reproducibility of data. Other catalysts listed in Table 8.32 provided homogeneous systems, and their activity at room temperature increased with g in the following series: 2,6- tBuz-C6H3 < 4-'Bu-C61-h < WCI6 < 4-CI-C6I-h < WOCh < CH(CHzCI)z. In all cases, a strong increase in activity occurred with increasing temperature. Modification of WCI6 by a twofold excess of phenol or epichlorohydrin led to a strong drop in catalytic activity. Polymer products were separated into benzene-soluble and benzene-insoluble fractions. These authors observed that the amount of soluble fraction depended on the dicyclopentadiene
471 conversion. At low monomer conversions, soluble polymer was formed predominantly, but at high monomer conversions, cross-linked polymer was strongly prevailing. This finding suggested that in the initial stages linear polymer was formed and this was later cross-linked by opening of the cyclopentene tings (Eq. 8.122).
n
(8.122)
In most cases, the above unicomponent catalysts gave rise to poly(dicyclopentadiene) with a higher content of cis double bonds in the main chain. Only WOCI4 and the complex with the bulky 2,6YBuz-phenoxo ligand formed polymers with a higher content of trans double bonds. It is noteworthy that the catalytic activity of the complexes WCIs(OR) and WCI4(ORh strongly increased when they were associated with Et2AICI and Bu4Sn (Table 8.33). Table 8.33 Polymerization of d i c y c l ~ d i e n e (M) using binary catalysts (I) derived from WCI~(OR) and WCI4(ORh~b Catalytic Syaem (O
WCI,(O-4-rBu-CsI~)/EtzAICI WCh[OCH(CH2CIh]z/Et2AICI WCI,(O-4-rBu-CsI~)/Bu4Sn
W/Cocatalyst mole/mole 1:4
1"3 1:4
'Data from reference~; bReaction c o n d i t i o n s : mmole.L"~"MB = 150: l ~
Tim% mm
Polymer Yieldt %
1 1
100 90
30
30
Reaction
Teng~raturo
=
room; [W]
=
lO
9
It was observed that systems containing EhAICl were very efficient and produced the hard, insoluble poly(dicydopentadiene) with a high content of trans double bonds. On the other hand, the system WCIs(O-4-rBu C61~)/Bu4Sn initiated a less rapid polymerization and the resulting poly(dicyclopentadiene) was soft, soluble and contained a low percentage of trans double bonds.
472 More recently, polymerization of exo-dicyclopentadiene has been carried out by Coca et aL ~59using binary catalysts derived from tungsten tetraphenylporphyrinates and aluminoxane or organotin compounds. Working under controlled condition, these authors obtained linear, high molecular weight poly(exo-dicyclopentadiene). A direct correlation between monomer conversion and molecular weight has been observed. The polymer was soluble in common solvents, displayed a monodisperse and narrow molecular weight distribution and had no tendency to cross-linking. The polymerization behaved in a "living" manner, allowing block copolymers with cyclopentene and cyclooctene to be prepared.
Tricyclo[5.2.1.0X9]dec-2-ene (7,8-Dihydrodicyclopentadiene, Trimethylenenorbornene). Polymerization of dihydrodicyclopentadiene was carried out first by Eleuterio 4 using heterogeneous catalysts based on alumina-supported transition metal oxides. Polymers with a polyalkenamer structure have been obtained but under the conditions employed the yields were low. Later, Oshika and Tabuchita2 polymerized dihydrodicyclopentadiene with MoCls, ReCI5 and WCI6 as catalysts. They obtained poly(dihydrodicyclopentadiene) by a ring-opening reaction (Eq.8.123). o
_ _ .
,8123,
The polyalkenamers obtained in the presence of these catalytic systems exhibited a high stereospecificity, similar to that observed in norbornene polymerization. Thus, MoCI5 gave trans polyalkenamer, ReCI5 cis polyalkenamer and WCI6 led to both cis and trans configurations. It is interesting that the catalysts proved to be particularly active in the reaction of dihydrodicyclopentadiene, even more active than that of norbornene. Based on these results, these authors established the following order of reactivity in this series of polycyclic olefins exodihydrodicyclopentadiene>>norbomene>endo-dicyclopentadiene. More recently, Hamilton, Ivin and Rooney TM studied also the reaction of endoand exo-7,8-dihydro derivatives of dicyclopentadiene in the presence of several transition metal-based catalysts. Using chlorobenzene and a mixture ethanol/chlorobenzene (11) as the solvent, they obtained different polymer yields and product stereoselectivities, as a function of the nature of the catalyst (Table 8.34).
473 Table 8.34
Polymerization of 7,8-dihydrodicyclopmtadiene (H2DCPD) in the presence of transition metal-based catalysts' Catalytic
Monomer
[M]o
system endo-H2DCPD endo-H2DCPD endo-H2DCPD exo-DCPD exo-DCPD exo-DCPD
RuCI3.3H20 WC~e4Sn ReCl~ RuCI3.3H20 WCIJMe4Sn ReCI~
[aex ~
Polymer Yield~ %
O'r
l-ene]
1.00
0.20
0.11 0.46
1.02 1.02
0.82 1.00
16
100 64 48 42 70
high 0.09 0.75 0.85
1.57
1.02
'Data fi'om reference ~ The fraction of cis double bonds, o~, and tacticity in the polymers were evaluated by ~3C NMR spectroscopy. As Table 8.34 shows, both endo- and exo-7,8-dihydrodicyclopentadiene produced high-trans polymers under the action of RuCI3.3H20, l~gh-cis polymers with ReCls and polymers containing a fair proportion of cis and trans double bonds in the main chain in the presence of WCl6-based catalysts. Tricyclo[4.2.2.0~] deca-3,7,9-triene. Polymerization of tricyclo[4.2.2.02"5]deca-3,7,9-triene, under the influence of metathesis catalysts, occurs readily by opening of the cyclobutene ring to produce poly(bicyclo[2.2.2]octadienylenevinylene). The polymer thus formed is thermally unstable and decomposes rapidly by a retro Diels-Alder reaction to polyacetylene with the elimination of benzene (Eq. 8.124). r"
-1.-
100%
d
~1
§
-JN
(8.124)
nO
This process was first ~ e d out by Edwards et al. 3~3 and represents an alternate way to synthesis of polyacetylene by '1~urham route". Kingopening polymerization of tricyclo[4.2.2.0~5]deca-3,7,9-triene was conducted in the presence of WCIJMe4Sn at 15~ to yield 100% the corresponding unsaturated polymer. Due to its low thermal stability, the
474 polymer thus obtained leads, in a temperature range from 20~ to 50~ to polyacetylene, with the elimination of benzene in a symmetry allowed process. Similar results have been using molybdenum carbene complexes, Mo(=C'Bu)(=NAr)(OtBu)2 as ROMP initiator. 3~4 7,8-Benzotricyclo[4.2.2.02"Sldeca-3,7,9-triene. In an analogous manner to that of the above parent hydrocarbon, 7,8-benzotricyclo[4.2.2.0ZS]deca3,7,9-triene undergoes easily ring-opening polymerization at the cyclobutene ring under the influence of the metathesis catalyst WCIJMe4Sn to form the corresponding poly(2,3 benzobicyclo[2.2.2]octadienylenevinylene) (Eq. 8.125).
n(~~~{~ V~le/Me4SnC ~ 90%
'~ 100-150~ ~ 1-
~n "1
§
(8.125)
Thermal decomposition by a subsequent retro Diels-Alder reaction through a sytmnetry allowed process will lead to polyacetylene with the elimination of naphthalene. This new way to prepare polyacetylene by "Durham route" from 7,8-benzotricyclo[4.2.2.02"~]deca-3,7,9-triene was carried out by Edwards et al. 3~3 in the presence of the above catalyst, in chlorobenzene at 20~ when polymer yield of 90% was recorded after reprecipitation of the product in methanol. The polymer thus obtained was rather stable and could be characterized by IR and ~3C NMR spectroscopy as well as by gel permeation chromatography. Further transformation to polyacetylene with the elimination of naphthalene took place at temperatures between 100~ and 150~ The eliminated naphthalene was identified by IR, NMR and mass spectroscopy while the thermal transformation could be monitored by differential scanning calorimetry. Ring-opening polymerization of 7,8benzotricyclo[4.2.2.02"5]deca-3,7,9-triene has also been reported more recently by Fischer. 3~5 7,8,9,10-Dibenzotricyclo[4.2.2.0~ldeca-3,7,9-triene. A new monomer that can be ring-open polymerized in the presence of metathesis catalysts to form an unsaturated polymer which will be subsequently transformed into polyacetylene via retro Diels-Alder reaction is 7,8,9,10dibenzotricyclo[4.2.2.02"5]deca-3,7,9-triene. Thus, in their studies on polyacetylene synthesis by "Durham route", Edwards et al.3~3 showed that the above monomer polymerizes under the action of the WCIdMe4Sn
475 catalyst, in chlorobenzene at 20~ to produce in 95% yield poly(2,3,5,6dibenzodicyclo[2.2.2]octadienylenevinylene) (F_,q. 8.126).
n
~
~
I
"-
9
n~
The thermal transformation of this polymer, in the range of temperatures from 175~ to 200~ leads to polyacetylene and anthracene. The characterization of poly( 2,3,5,6-dibenzobi cyclo [2.2.2]octadienylenevinylene) obtained in the first step has been performed by IR and ~3C NMR spectroscopy and gel permeation chromatography. However, identification of polyacetylene in the second step could be done by IR and solid state CPMAS ~3C NMR while that of anthracene by IR, NMR and mass spectroscopy. Though the manufacture of the above presented tricyclic monomers for the two-step "Durham route" involves a special synthesis technique, it is worthwhile mentioning several advantages of this new synthetic route to polyacetylene over conventional methods. Thus, a first significant advantage is the ability to remove catalyst residues from the polymer via conventional techniques, this allowing the production of catalyst free polyacetylene and hence recognition of the effect of residues on the electrical properties. Secondly, the precursor polymers are processable, that is, they can be cast as films from solutions, this providing the possibility of morphological control of the precursor polymer and hence the final polyacetylene. Furthermore, the polyacetylene produced by this route has a similar molecular structure to the material prepared by conventional methods, as shown by the fact that IlL Raman and m3C NMR spectra are essentially identical. The morphology produced by the conversion of a free standing film is, however, totally different and electron microscopy and Xray studies revealed no significant order. 3~6 In this way, the ability to produce a thin, coherent film of polyacetylene is a significant development of the field, since the material produced by direct polymerization of acetylene is a disordered fibrillar material. Polymers prepared by this route are, however, similar to the conventional polyacetylenes in that they can be doped to similar levels of conductivity. 3~6
476
Tet racyclo [4.4.0. I z,s.1~'t~ dodeca-3-ene. (Dimethanooctahydronaphthalene). Dimethanooctahydronaphthalene has been polymerized with a variety of transition metal-based catalysts to ring-opened polymers (Eq.8.127).
n~
.~
(8.127)
The monomer conversion and polymer yield as well as the structure and physical-mechanical properties of the product depend essentially on the catalyst and reaction conditions. High conversion rates and excellent properties of poly(dimethanooctahydronaphthalene) have been obtained by BFGoodrieh 3~7 using tungsten and molybdenum chlorides and oxychlorides associated with organoaluminium compounds, organoammonium tungstates and molydbates with silicon, tin, germanium, lead or aluminium compounds (e.g., siloxalane, stannoxalane, germoxalane, plumboxalane or aluminoxane). In a convenient process for preparing thermoset polymeric moulded products, Hercules 318 employed WCI6/WOCI4, Oct2AlI and a reaction rate moderator such as an alkyl or aryl posphine, phoshpite, phosphonate, posphinate or phosphate. Nippon Zeon 3~9 developed a process for polymerization of dimethanooctahydronaphthalene and norbornene monomers with catalysts based on tungsten hexachloride and tridodecylammonium molybdate associated with organoaluminium compounds. Japan Synthetic Rubber 32~ prepared thermoplastic resins compositions from dimethanooctahydronaphthalene with WCI6 and organoaluminium halides. Teijin32~ used a group of catalysts derived from WCl6 and organoaluminium compounds (e.g., Oct3Al or Oct2All) to obtain moulded products. A wide range of polymers and copolymers prepared Mitsui Petrochemical n2 with tungsten and molybdenum halides and organoaluminium compounds. The products were hydrogenated to be used in optical devices such as optical lenses, optical fibers, optical filters, etc. Showa Denko 323 polymerized dimethanooctahydronaphthalene and subsequently prepared its hydrogenated polymer with good transparency and optical uniformity, low birefringence and high resistance to heat and chemicals used for optical materials and in medical and chemical applications.
477 Methyltetracyclo[4.4.0.1~.l~'t~ Ring-opening metathesis polymerization of 8-methyltetracyclo[4 4 0 1~5 l~'t~ in the presence of metathesis catalysts leads readily to poly(methyl tetracyclo[4 4 0 12'~ l~'t~ 8 128)
(8.128)
=
\ Methyltetracyclo[4.4.0.12,5.17'm~ has been conveniently used in ring-opening polymerization and copolymerization with norbornene-like monomers by various research groups using a variety of metathesis catalysts. TM The products have good physical and mechanical properties useful for optical applications. Isobutyltetracyclo[4.4.0.12"S.l~'t~ In a similar way to the methyl derivative, 8-isobutyltetracyclo[4.4.0.12"5. l~'~~ gives rise to the corresponding polyalkenamer in the presence of metathesis catalysts325 (Eq. 8.129).
n. ~ ~ i B u
=
(8.129)
\.
iBu
This monomer has been employed with other norbornene-like monomers to prepare products with special physical-mechanical properties used for optical devices. Ethylidenetetracyclo [4.4.0.1 ~. 1~'t~ dodeca-3-ene. Ring-opening polymerization of 8-ethylidenetetracyclo[4.4.0.12,s. 17'~~ gives rise to an unsaturated polyalkenamer bearing cross-linkable ethylidene group in the repeat unit (Eq. 8.130).
478
=
~
(8.13o)
Polymers and copolymers with high glass transition temperatures have been manufactured from ethylidenetetracyclo[4.4.0.12"s. 17'~~ and 3~s other norbornene-like monomers. Dimethyltetracyclo [4.4.0. l z,s.l ~'ts]dodeca-3-ene. Tetracyclo [4.4.0.12,5._ 17'~~ bearing two methyl groups in positions 5,7, 5,9, 8,9 and l l, 12 have been polymerized by Mitsui Petrochem Ind.325 using Mo and W chlorides and organoaluminium compounds. Ring-opened polymers having the following probable structures have been prepared (Eq. 8.131).
-5 (8.131)
=
Hydrogenated products obtained from such ring-opened polymers exhibited high dimensional stability, excellent transparency and good resistance against heat. These polymers found various applications in optical devices. A variety of ring-opened polymers and copolymers have been obtained by the above procedure from 8,9-disubstituted tetracydo[4.4.0.12"s. 17'~~ bearing aliphatic, aromatic or alicyclic hydrocarbon groups, optionally R' and R" = 1-2012 alkyl, cyclohexyl and substituted pheny1325(Eq. 8.132).
n
R"
-[-~//-~
R'
/ R'
\ R"
(8.132)
479 By further hydrogenation with homogeneous or heterogeneous catalyst systems, products useful for optical applications have been manufactured. Trimethyltetracyr z.s.lT't~ Ring-opened polymers of the trisubstituted cycloolefin 2,7,9-trimethyltetracyclo [4.4.0.12"5. l~'~~ have been obtained by Mitsui Petrochem. Ind.325 in the presence of the binary metathesis catalysts consisting of Mo or W chlorides and organoaluminium compounds (Eq. 8.13 3).
(8.133)
\ Hydrogenation of these polymers gave products with good optical properties. Similar products have been obtained from 2,7,9triethyltetracyclo[4.4.0.12"~. 17'~~ and 2,7,9triisobutyltetracyclo[4.4.0.12"5.17'~~ by the same procedure (Eq. 8.134, R = Et, 'Bu). q
=
(8.134)
R \
R On substituting tetracyclo[4.4.0.12,5.17'~~ with alkyl, aryl or aralkyl groups in any of its available positions (R~-R~2), a range of monomers suitable for ring-opening polymerization have been obtained. By polymerization of these highly substituted tetracyclo[4.4.0.12,s. 17'~~ 3-enes, in the presence of metathesis catalysts consisting of Mo or W chlorides and organoaluminium compounds, ring-opened polymers of varying structures have been produced 32s (Eq. 8.13 5).
480
R~,y,R4 RTN/R6
n ~,I~,I,Io
Rso_.._~~ i~
v
Ro
"
I
(8"135)
fa,2
Rio RII
Further hydrogenation of the above obtained unsaturated polymers gave rise to products with excellent physical-mechanical properties. Tetracyclo[4.4.0.12"s. 17'~eidodeca-3,g-diene. Tetracyclo[4.4.0.12,5.17.~0]_ dodeca-3,8-diene, having two double bonds of essentially the same reactivity, has been used as a cross-linking agent in the ring-opening polymerization. In the presence of metathesis catalysts, both carbon-carbon double bonds will open to form a cross-linked structure (Eq. 8.136).
..=
,-
(8.136)
This compound has been used, for instance, to aid cross-linking during the polymerization of endo-dicyclopentadiene. 329 Pentacyclo[8.2.1.1 pentacyclo[8.2, l.
47
' .0
2,9
38
.0 ' ]tetradeca-5,1 l - d i e n e The exo-trans-exo] l-diene, the [2+2] cycloaddition
14'7.02"9.03's]tetradcv.~-5,
dimer of norbomadiene, has been used as a cross-linking agent, for instance, in the living norbomene polymerization with well-defined metathesis catalysts (Eq. 8.137).
(8.137)
481
Star-block copolymers could be obtained through the controlled use of exoin norbomene polymerization with titanacyclobutanes initiators TM or tungsten and molybdenum carbene complexes. TM Hexacyclo[ 10.2.1.02"t t.04'9.13't~ I s'8]heptadeca-6,13-diene (Trimethanodecadydroanthracene). Hexacyclo[ 10.2. I. 0TM .0 ~'9.13,~0.1s'S]heptadeca6,13-diene has been easily prepared and used as a cross-linking agent in the living ring-opening polymerization of norbomene derivatives with molybdenum carbene initiators 332 (Eq. 8.13 8).
trans-exo-pentacyclo[8.2.1.14'7.02"9.03'8]tetradeca-5,11-diene
u,l,,,
(8.138)
By this way, amphiphilic star block copolymers have been prepared from appropriately functionalized norbomene-type monomers. Synthesis of these amphiphilic star block copolymers allowed to investigate their behavior as model micelles in aqueous solution. Hexacyclo[ 10.2.1.0z't t.04'9.13't'. I s's]heptadeca-~ene. The partially hydrogenated monomer obtained from hexacyclo[ 10.2.1.02"tt.04'9.13'~~ 15'8]heptadeca-6,13-diene has been readily polymerized in the presence of WCI6 and MoCI5 associated with organoaluminium compounds 325 (Eq. 8.139)
(8.139)
The polymer has, after hydrogenation, excellent optical properties and is useful for optical applications.
482 Higher monomers derived from tetracyclo[4.4.0.1 ~. 17't~162 Numerous other monomers derived from tetracyelo[4.4.0.12,5. I z~~ 3-ene by cyclopentadiene addition have been used in the dng-oi~ning polymerization. Examples are oc~acyclo[ 14.2.1.02'15.04'13.06'll. 1TM.15.12.1z l 0 ] doeicosa-g, 17-diene (tetramethano-pentadecahydrotetracene) (m = 2) and decacyclo[ 18.2.1.02'19.04'17.06'15.011'13.13,18.1$,16.17,14.19,12] heptaeosa- 10,21diene (pentamethan~-nonadec~ydropentacene) (m = 3) which give with metathesis catalysts consisting of WCI6 or MoCI5 and organoaluminium compounds the corresponding polyalkenamers (Eq. 8.140).
n I
m
9
(8.140) A
~
@ m
By hydrogenation of these polymers, products with interesting properties for optical applications have been obtained. Higher monomers derived from 8-ethylidene tetracyclo[4.4.0.1r~s.17't~ Of the two double bonds of this series of monomers, that of norbornene unit will readily polymerize by ringopening in the presence of metathesis catalysts to give polymers with a side unsaturation in their repeat unit (Eq. 8.141).
~k
n
I
(a.141)
m
This side-chain unsaturation can be further cross-linked under thermal or catalytic influence to form thermoset cross-linked polymers similar to poly(dicyclopentadiene).
483 Higher monomers derived from tetracyclo[4.4.0.1~.l~'t~ diene. These polycyclic dienes easily react by ring-opening at any of their double bonds in the presence of adequate ROMP catalysts leading to the corresponding ring-opened polymers (Eq 8 142)
--
L
(8.142)
Due tO the high reactivity of both double bonds, these monomers can also be employed successfully as cross-linking agents in the living ring-opening polymerization. Pentacyclo [6.5.1.13'6.0~7.09'ta]pentadeca-4-ene. This monomer, manufactured by selective reduction of the cyclopentadiene trimer, pentacyclo[6.5.1.13'6.02"~.09'~3]pentadeca-4,11-diene, gives readily ringopened polymers at the norbornene moiety in the presence of metathesis catalysts32~(Eq. 8.143).
=
(8.143)
After further hydrogenation, the saturated polymers thus obtained will acquire good physical and mechanical properties of interest for various industrial applications. Pentacydo[6.5.1.13'6.0~'~.09'~a]pentadeca-4,11-diene. Polymerization of pentacyclo[6.5.1.13'6.02"7.09'~3]pentadeca-4,1 l-diene, the cyclopentadiene trimer obtained by Diels-Alder addition of cyclopentadiene to norbornene double bond of dicyclopentadiene, produced ring-opened polymers in the presence of W and Mo halides and organoaluminium compounds 325 (Eq.8.144).
484
n
----,,.
(8.144)
Polymerization with moulding and foaming of tricyclopentadiene in the presence of W-based metathesis catalysts provided ring-opened polymer moulding products with good shape and controlled gravity. Teijin Co. TM performed this reaction under the action of tungsten hexachloride and trioctylaluminium and dioctylaluminium iodide (85"15 mol. ratio) in toluene at room temperature and 3 kg/cm 2 in a moulding container to form moulded poly(tricyclopentadiene). In another procedure, Teijin Co 333 manufactured less defect in surface and with less heat deformation products prepared by RIM method poly(tricyclopentadiene) using catalysts derived from halides of tungsten, rhenium, tantalum and molybdenum. The materials are useful for vehicle parts and housing of electrical instruments. Under appropriate conditions, cross-linked polymers could be obtained from tricyclopentadiene in a similar process to cross-linked polymers manufactured from dicyclopentadiene. Pentacyclo[6.5.1.13'6.02"7.09'13]pentadeca-4,11-diene can be also used as cross-linking agent in the synthesis of star block copolymers in an analogous way to tetracyclo[4.4.0.12"5.17't~ dodeca-3,8-diene and hexacyclo[ 10.2.1.0Z'l i.O4'9.13.10.I s'8]heptadeca-6,13-diene.
Higher
monomers
derived
from
pentacyclo [6.5.1.13'6.02'7.09'13]
pentadeca-4-ene. Numerous other monomers of this series have been used to prepare ring-opened polymers with ROMP catalysts (Eq. 8.145).
n
=
(8.145)
485 Such a monomer is heptacyclo[6.9.1.13'6.02'7.1 ~~ (m = 2). This compound obtained by partial hydrogenation of the parent diene, heptacyclo[6.9.1.13'6.02"7.1~~ ~'~5]eicosa-4,13-diene was polymedzed by Mitsui Petrochem. Ind.325 in the presence of WCI6 and MoCI5 in conjunction with organoaluminium cocatalysts. Higher monomers derived from pentacyclo[6.5.1.1x6.0z'7.09'ta] pentadeca-4.11-diene Monomers obtained by successive addition of cyclopentadiene to dicyclopentadiene have been polymerized in the presence of WCI6 and MoCIs associated with organoaluminium compounds (Eq. 8.146).
=
n
ll~ll
(8.146)
In one example, heptacyclo[6.9.1.13'6.02'7.110'16.09'17.01~'~5]eicosa-4,13-diene, a cyclopentadiene tetramer, gave high molecular weight polymers under the influence of WCI6 and MoCI5 with organoaluminium compounds 325 This monomer is also suitable for preparing cross-linked polymers by intramolecular metathesis reaction Pentacyclo[4.7.0.1Ls.01~3.19'~Z]pentadeca-3-ene. This monomer, resulted by selective reduction of the cyclopentadiene trimer, pentacyclo[4.7.0.1~'5.0s'~3.19'~2]pentadeca-3,10-diene, gave ring-opened polymers at the norbornene moiety 325 (Eq. 8.147).
n
.=
(8.147)
After hydrogenation, the saturated polymer is interesting for its particular physical and mechanical properties.
486
Higher monomers derived from pentacyclo[4.7.0.1z's.0s'~3.19.~2] pentadeca-3-ene. Higher monomers obtained by successive Diels-Alder reactions of pentacyr 7 0 12"50s'~319'~2] pentadeca-3-ene with cyclopentadiene have been used in ROMP reactions with W and Mo chloride and organoaluminium compounds (Eq 8 148)
(8.148)
t
m
Polymers obtained by this way were further used in optical field, due to their excellent physical and particularly optical properties. Pentacyclo[4.7.0.1~'s.08"~3.19'~2]pentadeca-3,10-diene. Polymerization of pentacyclo[4.7.0.12"~.08'~3.19'~2]pentadeca-3,10-diene, the cyclopentadiene trimer, resulted by addition of cyclopentadiene to cyclopentene double bond of dicyclopentadiene, gave ring-opened polymers in the presence of W and Mo halides and organoaluminium compounds 325(Eq. 8.149).
~
(8.149)
This monomer is also a good cross-linking agent in living polymerization of norbornene-type monomers with well-defined metal-earbene initiators Heptacyclo[7.8.0.1x6.0z'7.1 t~ tz'~Sleicosa-4-ene~ Polymerization of this compound obtained by partial hydrogenation of the parent diene, heptacyclo[7.8.0.13'6.02"7.1 ~~ m2"~]eicosa-4,13-diene, led to the ringopened polymer in the presence of WCI6 or MoCIs and organoaluminium cocatalysts 325. Further hydrogenation of the unsaturated polymer gave products with excellent optical properties.
487 Higher monomers derived from pentacydo[4.7.0.1z's.0s't3.19't2] pentadeca-3,10-diene A number of cyclodienes of this series have been used in the ring-opening polymerization reactions induced by adequate metathesis catalysts to obtain highly unsaturated polyalkenamers (Eq. 8.150).
(8.150)
n
For
instance,
cyclopentadiene tetramer, lt2"tS]eicosa-4,13-diene (m = 2), has been polymerized by Mitsui Petrochem. Ind.32s with WCI6 and MoCI5 in conjunction with organoaluminium compounds to obtain poly(heptacyclo[7.8.0.13'6.02"7.1 ~~ ~2"~5]eicosa-4,13-diene). Further hydrogenation of the unsaturated polymer, poly(heptacyclo[7.8.0.13'6.02'~. 1~~ ~'16.1~2'15]eicosa-4,13-diene), gave new saturated products with good optical properties. Monomers of this series can also be used as cross-linking agents in the living metathesis polymerization of cycloolefins. Tricyclol4.4.0.1Z~lundeca-3-ene. This monomer available by Diels-Alder reaction of cyclopentadiene and cyclohexene is capable of ROMP in the presence of W and Mo based metathesis catalysts (Eq. 8.151).
heptacyclo[7.8.0.13'6.0 2'7.11~
the
Pentacyclo[8.4.0.12"Xl~'t4.0s't3]hexadeca-3-.ene. This compound, readily available by Diels-Alder reaction from tricyclo[4.4 0 12'S]undeca-3-ene, can be effectively polymerized with ROMP catalysts to ring-opened polymers (Eq. 8.152).
488
(8.152)
() h.
The polymers thus obtained acquire especially after further hydrogenation good mechanical and optical properties and are potential products for various applications. Higher monomers derived from tricyclo[4.4.0.1~S]undeca-3-en~ The whole series of monomers can be obtained by Diels-Alder reaction of tricyclo[4.4.0.1 zs.]u ndeca-3-ene with eyelopentadiene. All these monomers are excellent candidates for ring-opening polymerization reactions in the presence of appropriate metathesis catalysts (Eq. 8.153).
|
n
9
9
,C.3,
I
(8.153)
(
The products obtained have especially after hydrogenation many physical and mechanical properties suitable for various applications. Tricyclo[4.4.0.1Z'Slundeca-3,8-diene. The norbomene double bond of tricyclo[4.4.0.12"~]undeca-3,8-diene is by far more reactive than that of cyclohexene and can be easily ring-opened in the presence of various ROMP catalysts (Eq. 8.154).
n ~
=
(8.154)
Linear polymers can be obtained which can be further functionalized by specific chemical reactions at the cyclohexene double bond.
489
Pentacydo [8.4.0.1 ~.0 s't3.19't2]hexadeca-3,10~iene.
Ring-opening polymerization of pentacyclo[2.1.02"11.04'9, lS'S]hexadec-3,10-diene in the presence of tungsten-based metathesis catalysts affords poly(pentacyclo[2.1.02'11.04'9.1 s'S]hexadec-3,10-diene) (Eq. 8.155).
r
(8.155)
This monomer can be used also as a cross-linking agent in the living metathesis polymerization reactions due to the ready availability of both norbomene double bonds of the same reactivity. Further hydrogenation of poly(pentacyclo[2.1.0~'~.0 4'9. l s'S]hexadec-3, l 0-diene) gave polymers with good mechanical and optical properties which are suitable for applications in various fields. Pentacyclo[8.4.0.1 ~.01~3.19'tZlhexadeca-3-ene. This monomer of interest for its ready availability from pentacyclo[2.1.02'tt.04"9, lS'S]hexadec-3,10diene by Diels-Alder reaction can be easily polymerized under the influence of ROMP catalysts to poly(pentacyr 0.12's.0s'13.19'12]hexadeca-3-ene) (Eq. 8.156).
(8.156)
The homopolymer as well as its copolymers produced in reactions with various norbomene-type monomers excel in transparency, optical uniformity, low birefringence and resistance to heat and chemicals, rigidity and dimensional stability.
490 Substituted pentacyclo[10.2.1..02"tt.04,91~a]hexadec.6.ene. Polymers of substituted pentacyclo[2.1.0z1~.04'9.15'8]hexadec-6-ene bearing alkyl groups with up to 10C have been prepared by Showa Denko TM by ring-opening polymerization of the corresponding monomers in the presence of tungsten based metathesis catalysts (Eq. 8.157).
R2
R4
n
= R
R3
I
(8.157)
Rs
Homopolymers and copolymers derived from these monomers have good optical and mechanical characteristics as well as excellent chemical and weather resistance and are suitable for optical materials or in some chemical and medical applications. Higher monomers derived from tricyclo[4.4.0.1~'Slundeca-3,8-diene. A wide range of monomers have been prepared by Diels-Alder reactions of dicyclopentadiene with tricyclo[4.4.0.12"5]undeca-3,8-diene, all of these displaying a good reactivity in polymerization reactions with ROMP catalysts. Ring-opened polymers with varying lengths of the side branches have been obtained under normal ROMP conditions (Eq. 8.158).
(8.158)
491 Polymers and copolymers thus obtained, after hydrogenation, have good physical and chemical properties and particularly high weather and chemical resistance and excellent optical and mechanical characteristics. They are useful for various optical and medical applications. Multicyclic norbornene-type monomers. The ring-opening polymerization reactions of a wide range of multicyclic norbomene-type monomers of the general formula (I) (F_,q. 8.159)
~
(CR'R") x
(8.1s9)
(0 (CR'R") X where m = 0 or a positive number, x = at least 3 and R' and R" = alkyl, aryl or aralkyl groups, and of formula (II) (Eq. 8.160).
R2
.R6
R14.RIa R19R2o)x
RI
=
(8.160)
R13R17
(=)
where n = o or a positive number, x = at least 3 and R~-R2o = alkyl, aryl or aralkyl groups, have been reported in numerous patents. 335"356
492 8.4. References
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511 Patent 4,808,635 (1989). 342. a. Hercules Inc., U.S. Patent 4,918,138 (1990), b. Hercules Inc., Eur. Patent 376,198 (1990). 343. a. Nippon Zeon KK Japan. Patent 264,147 (1987); b. Nippon Zeon KK Japan. Patent 137,896 (1989), e. Nippon Zeon KK Japan. Patent 172,296 (1989), 344. a. Nippon Zeon KK, Japan. Patent 238,921 (1989), b. Nippon Zeon KK, Japan. Patent 63 285,879 (1989), 345. a. Nippon Zeon KK, Japan. Patent 178,261 (1990), b. Nippon Zeon KK, Japan. Patent 185,491 (1990), c. Nippon Zeon KK, 221,407 (1990), 346. a. Mitsui Petrochem. Ind. KK, Japan. Patent 053,126 (1990), b. Mitsui Petrochem. Ind. KK, Japan. Patent, 071,770 (1990); c. Mitsui Petrochem. Ind. KK, Japan. Patent 199,477 (1990), 347. a. Mitsui Petrochem. Ind. KK, Japan. Patent, 234,035 (1990), b. Mitsui Petrochem. Ind. KK, Japan. Patent, 234,036 (1990), c. Mitsui Petrochem. Ind. KK, Japan. Patent, 273,229 (1990), 348. a. Mitsui Petrochem. Ind. KK, Japan. Patent, 246,559 (1990), b. Mitsui Petrochem. Ind. KK, Japan. Patent 252,193 (1990); c. Mitsui Petrochem. Ind. KK, Japan. Patent, 265,883 (1990), d. Mitsui Petrochem. Ind. KK, Japan. Patent 137,711 (1991). 349. a. Japan Synthetic Rubber, Eur. Patent 113,639 (1989); b. Japan Synthetic Rubber, Japan. Patent 288,527 (1989), c. Japan Synthetic Rubber, Japan. Patent 288,528 (1989), 350. a. Japan Synthetic Rubber, Japan. Patent 202,505 (1991), b. Japan Synthetic Rubber, Japan. Patent 240,172 (1991). 351. a. Japan Synthetic Rubber, Japan. Patent 288,527 (1991), b. Japan Synthetic Rubber, Eur. Patent 409,291 (1991). 352. a. Shell Int. Res. Maatschappij B.V., Eur. Patent 372,600 (1990), b. Shell Int. ges. Maatschappij B.V., Eur. Patent 374,997 (1990). 353. a. Teijin KK, Japan. Patent 134,492 (1989), b. Teijin KK, Japan. Patent 078,639 (1990), c. Teijin KK, Japan. Patent 156,728 (1990), d. Teijin KK, Japan. Patent 307,718 (1990). 354. a. Showa Denko KK, Japan. Patent 252,965 (1990),b. Showa Denko KK, Japan. Patent 274,189 (1990). 355. a. Mitsubishi Petrochem. KK, Japan. Patent 322,789 (1990); b. Mitsubishi Petrochem. KK, Eur. Patent 376,599A (1990); c. Mitsubishi Petrochem. KK, Eur. Patent 386,896A (1990).
512 356. Charbonnages de France, Fr. Patent 1,535,460 (1968).
513
Chapter 9 POLYMERIZATION OF FUNCTIONALIZED CYCLOOLEFINS
9.1. General Considerations The incorporation of functional groups (e.g.,halogen, alcohol, ether, carboxyl, ester, nitrile) into the backbone of the polymers obtained by ringopening metathesis polymerization has rec~ved a special attention due to the interesting properties that the functional groups impart to these types of polymers. ~,2 Although several classical metathesis catalysts exhibit tolerance towards certain functionalities, the development of new, well-defined transition metal catalysts, with enhanced tolerance for a broader range of functionalities, helped the progress in this field.3'4 The presence of a functional group into a strained cycloolefin which contains a highly reactive double bond such as norbornene imposes the use of a less active catalyst which will be more tolerant toward functionalities. By contrast, the polymerization of less strained cyclic olefins requires the use of a more active catalyst and thus precludes the incorporation of functional groups into the monomer. For this reason, there are relatively fewer reports concerning the ring-opening metathesis polymerization of less strained monocyclie olefins which contain functional groups as compared to strained polycyclic olefins, t'2
9.2. Four-Membered Ring Monomers The promising results obtained in the polymerization reaction of cyclobutene and its alkyl derivatives using Ziegler-Natta and ROMP catalysts prompted the extension of this process to four-membered ring monomers beating functional groups in the presence of several catalytic systems tolerant toward functionalities. c/s-3,4-Dichlorocyclobutene. Polymerization of cis-3,4-dichlorocyr butene, in the presence of WCIdMe4Sn, gives a black insoluble powder in relatively low yield whose elemental analysis showed a reduced content of chlorine. IR and UV spectroscopic analyses and conductivity measurements before and after doping indicated that the product possesses similar properties to polyacetylene 5 (Eq. 9.1).
514 n
C
WCI6/Me4Sn 9 ~
(9.1)
cl
It was supposed that the ring-opened polymer lost HCI or Clz, during or immediately after the polymerization step, with development of a conjugated polymer (Eq. 9.2). -HCI CI
CI
~
(9.2) CI
---,-=-,---liD"
-C12
The cross-metathesis of cis-3,4-dichlorocyclobutene with E-4-oetene yielded only a small amount of the expected ring-opened product together with a very small amount of a dark polymer, probably the same as that obtained by direct polymerization. Living ring-opening metathesis polymerization of a number of 3functionalized cyclobutenes containing ether, ester, alcohol, amine, amide and carboxylic acid substituents was investigated by Maughon and Grubbs 6 with the initiators (PCy3)zCIzRu=CHCH=CPhz and (PCy3)zCIzRu=CHPh. On correlating the activity of the two Ru carbenes with the nature and distance of the functional group from the ring system, a series of functionalized polybutadienes were readily synthesized (Eq. 9.3). n
~
(9.3)
where X = OCH2Ph, OC(Ph)3, OC(O)Ph, N('Pr)2, OCH2COOMe, (CH2)3COOH, (CH2)4OH, (CH2)3CONHBu, (CHz)3COOMe. In probing the polymerization mechanism, coordination of these Lewis base functional groups to the propagating carbene was observed, resulting in the formation of a chelated propagating species with concomitant loss of one phosphine ligand from the metal center. Formation of this new mono(phosphine) propagating species in addition to the expected bis(phosphine) species resulted in the attenuation of the k~,/k~for these polymerizations. While this coordination led to lowered polydispersities using the first initiator, (PCy3)2CIzRu=CHCH=CPh2, propagation rates were significantly reduced in
515 these polymerization and often decomposition of the propagating species was evident. The combination of higher initiation employing the second initiator, (PCy3hCI2Ru=CHPh, and the removal of the functional group further from the ring system resulted in the living polymerization of functionalized cyclobutenes bearing carboxylic acid, alcohol, amide, and ester functionalities. Through polymerization of these substituted cyclobutens, a new group of polybutadiens b e i n g a wide range of functional groups have been prepared. Depending on the nature of the substituent, polymers in almost quantitative yields with 40 to 50% cis configuration at the double bond have been obtained. (Table 9.1). Table 9.1 Ring-opening polymerization of functionaliz~ cyclobtaancs (M=C4H~-CH2X) with ruthenium carbene catalysts" X
% Yield
% cis-Olefm
OCHzPh, OC(Phh, OC(O)Ph, N(iPrh, OCHzCOOMe,
87 91 95 79 84 93 95 92 96
40
(CHz)3COOH, (CHz)4OH, (CH2)3CONHBu, (CHz)3COOMe
50 40 50 50 50 50
T~ ~ -22.6 69.4 24.0 -15.8 -42.9 1.3 -37.1 0.1 -46.6
'Data from reference 6
Examination of the thermal properties of these polymers was undertaken using both differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The T s values for the polymers ranged from -46.6~ to +69.4~ demonstrating the striking effect of the side chains on the phase transitions of these polybutadienes; however, no melting transitions were observed for any of these materials. In order to investigate the effect of backbone flexibility on the mesomorphic behavior of side-chain liquid crystalline polymers, several cyclobutene monomers containing a p-nitrostilbene moiety as the mesogenic group have been ring-open polymerized by Cn'ubbs and coworkers 7 with the initiator (PCy3hCIzRu=CHPh to produce side-chain liquid crystalline
516 polymers with low polydispersities and defined molecular weight (Eq. 9.4).
n
[ ~ O~
OR o
RuCI2(PCy3)2(CHPh) "
(9.4)
CH2Ch, 4 s ' c
where
R = (CH2)mO ~
N
O
2
and m = 6, 8, 10 and 12. The reactions were performed in CH2C12 at 45~ for 24 hr resulting polymers with polydispersities of 1.11-1.38 in 82-97% isolated yields (Table 9.2). Table 9.2 Polymerization of cyclobutene derivatives M-m bearing p-nitrostilbene moiety (R) as the mesogenic group with (PCy3hCI2Ru=CHPh (1) in CHzCIz at 45~ ' M-m
[M]/[I] b
M, b
PDI
M-6
25 25 25 25 5 10 25 50 100
33 300 35 400 31 900 38 500 15 000 21 600 35 400 57 000 89 100
1.16 1.15 1.16 1.14 1.13 1.11 1.15
M-8 M-10
M-12 M-8 M-8 M-8 M-8 M-8
1.27
1.38
;Data from reference~. bVetermmod by GPC in CHzCIz relative to monodispersed polystyrene standards. The relatively flexible polybutadienes showed enantiotropic smectic A mesomorphism with glass transition temperatures from 14~ to 3 I~ and isotropization temperatures between 74~ and 11 I~ This behavior
517 indicated that the flexible polybutadiene backbone allowed a higher order of alignment of the mesogenic units, resulting in a more ordered liquid crystalline phase. The dependence of the degree of polymerization and flexible spacer length on the phase transitions of these polymers was determined, demonstrating stabilization of the mesophase by both increasing molecular weight and flexible spacer length. A diblock copolymer containing a 11 mixture of substituted polynorbomene and polybutadiene exhibited a smectic A mesophase, demonstrating the dominance of the polybutadiene backbone in the polymer. With the aim of preparing disex~tic side-chain liquid crystalline polymers, cyclobutene monomers bearing pentoxy- and decyloxysubstituted triphenylenes have been polymerized by Grubbs and coworkers 8 with the initiator (PCy3)2CI2Ru=CHPh (Eq. 9.5).
n~
0
"*VJxR' RuCl-z(PCY3)z(CHPh)= CH2Ch, 4soc
(9.5)
where RO R
0
O(CH2)120--
~.
OR
RO
/ RO
\
OR
and R = CsH~I and CloH21. The reactions were performed in CH2C12 at 45~ for 1.5 hr, well-defined polymers with low polydispersities of 1.111.19 were obtained in quantitative yields. To increase the backbone flexibility, the substituted polybutadienes were subsequently hydrogenated using Crabtree's catalyst [Ir(COD)(Cy3P)(Py)][PF6] to obtain polyethylenebased polymers (Eq. 9.6).
518
[Ir(COD)(Cy3P)(Py)I[PFd
CH C , ssoc,12o psi R'
(9.6)
...._
-
R'
and R = CsH~ and Ct0H21. The hydrogenation was performed in CH2C12at 55~ and 120 psi for 16 hr with 5-10 mole % catalyst to produce in quantitative yield low polydispersities substituted polyethylene (Table 9.3). Table 9.3 Alkoxytriphenylene-substituted polybutylenamers (PB-R) and hydrogenated polymers (PE-R) prepared from alkoxytriphenylene substituted cyclobutene monomers (M-R)' |
|
Polymer
M,
PDI
PB-C~HII PB-CIoH21
157 000 33 000 125 000 50 000
1.19 1.11 1.32 1.11
PB-C~Htt
PB-CIoH21
'Data from reference' bDetermined by GPC in CH2CI2 'relative to rnonodispersed polystyrene standards. The mesomorphic behavior of these polymers were investigated by differential scanning calorimetry (DSC) and powder diffraction X-ray scattering (WAXS). The polymers bearing a 2,3,6,7,19pentakis(decyloxy)triphenylene-based mesogenic unit exhibited enantiotropic discotic hexagonal mesophases, while the pentoxy analogs did not display liquid crystalline behavior. A series of functionalized cyclobutenes, attractive for the synthesis of polymers with a high density of pendant functional groups, were reacted by Perrott and N o v a k 9 in the presence of Schrock alkylidene complexes. For this purpose, starting from cyclobut-3-ene-l,2-dicarboxylic anhydride (I), which was made by photochemical cycloaddition of acetylene to maleic anhydride, the corresponding dimethyl ester (lla), diethyl ester (lib), dibenzyl ester(Ilc), dimethyl ether (llla), dibenzyl ether(lllb), benzyl imide
519 (IV) and the bicyclic tetrahydrofuran(V) have been synthesized (Scheme 9.1).
o~_O_~oROOC~COORRO~~rOR (@
(lla-c)
(k,b)
a. R=Me b. R=Et c. R=C H2Ph
a. R=Me b. R=CH2Ph
Sz I
N H
(Iv)
(v)
(V~-c) a. R'=R"=C(C H3)3 b. R'=C(CH3)2Ph, R"=C(CF3)2CH3 c. R'=C(CH3)2Ph, R"=C(CH3)3
Scheme 9.1 Initial studies showed that all these substituted cyclobutenes polymerized under the appropriate conditions using the Schrock alkylidene complexes Mo(=CHR')(=NAr)(OR '') (Via-c) to form highly functionalized polymers possessing an analogous structure with substituted 1,4polybutadiene (Eq. 9.7). X n
! I
X
X
(9.r X
With the exception of cyclobut-3-ene-l,2-dicarboxylic anhydride, polymerizations of all these substituted monomers were quantitative, regardless of the monomer:initiator ratio, giving monodisperse polymers (PDI = 1.04-1.1) with narrow molecular weight distributions. It is noteworthy that, under the above conditions, the polymerizations behaved
520 as living processes. On using appropriate initiators, stereoregular polymers with up to 93% cis double bonds have been synthesized. Functionalized copolymers from some of the above monomers have also been obtained. l-Trimethylsilylcyclobutene. Interesting work on the ring-opening polymerization of 1-trimet hylsilylcyclobutene to poly( 1trimethylsilylbutenylene) reported Katz ~~ using the initiator of Casey and Burkhardt, (diphenylcarbcne)pentacarbonyltungsten (Eq. 9.8).
SiMe3
Ph2C=W(C 0)5
SiMe3
(9.8)
80%
The polymer was prepared in 80% yield working in toluene at 39~ Structural analysis by ~3C NMR spectroscopy indicated that poly(ltrimethylsilylbutenylene) obtained by this way was highly cis and had perfectly head-tail enchainment. This product was one of the most perfectly translationally invariant polymer made by metathesis polymerization. The polymer was interesting for yet another reason. It provided an attractive method for making functionalized olefins by metathesis reaction. Thus, the trimethylsilyl group of poly(l-trimethylsilylbutenylene) could be substituted by other functional groups, e.g., sulphur-containing groups, which hardly tolerate metathesis catalysts (Eq. 9.9).
SiMe3
1) PhSCIK~H2CI2
-~
/
SPh
(9.9)
On substituting with other related functional groups, the process would become a versatile method for functionalizing translationally invariant polyenes. 9.3. Five-Membered Ring Monomers
Taking into account the good elastomeric properties of poly(lpentenylenes) and the well established thermal stability and solvent resistance of fluorinated polymers, Feast and Wilson ~ examined the reaction of 1H,2H-hexafluorocyclopentene in the presence of a range of metathesis catalysts based on tungsten hexachloride. All attempts to polymerize this monomer to the corresponding fluorinated polyalkenamer
521 in the presence of these catalysts failed (Eq. 9.10).
n F2
~ F2
[W]
(9.10)
H
An explanation for the failure of l H,2H-hexafluorocyclopentene to react in these conditions was that the strong electronegative fluorine substituents in the monomer reduced the 7r-donor capacity of the double bond of cyclopentene to the point where coordination to the metal centre was totally inhibited. Another plausible explanation was that the polymerization mechanism is blocked at a subsequent stage, for example, the rearrangement of the possible metal-carbene olefin complex to the corresponding metallacyclobutane intermediate. l-Ethoxycyclopentene reacts by ring-opening with the diphenylcarbene-tungstenpentacarbonyl, Ph2C=W(CO)5, to give the stable Fischer-type carbene, (ethoxy)diphenylhexenylidene-tungstenpentacarbonyl along with several by-products~2 (Eq. 9.11).
EtO\ Ph2C=CH(Cl-hh/c~cO)s (20%)
n~OEt+ Ph2C=~/~CO) s~
+
(9.11)
CPh2 O ~ ~LT/CHPh2.ph.zCH-COOH 4-
110%)
144%)
16.4%)
9.4. Six-Membered Ring Monomers
Attempts to polymerize 1-ethoxycyclohexene with the diphenyl~ne-tungstenpentacarbonyl, Ph2C=W(CO)5, to obtain the functionalized poly(1-hexenylene) failed, probably, because its free energy of polymerization is positive m2(Eq. 9.12).
n
~
OEt
Ph2C=W(CO)5 v,
OEt
(9.12)
522 Ziegler-Natta polymerization of cis-5,6-bis(trimethylsiloxy)- 1,3cyclohexadiene with bis[(allyl)trifluoroacetatonickel(ll)][(ANiTFA)2] led in high yield to poly(cis-5,6-bis(trimethylsiloxy)- 1,3-cyclohexadiene) 13 (Eq.9.13). n
Q
(ANiTFA)2 "
=
~ ...........
In
(9.13)
TMSO OTMS TMSO OTMS The reaction proceededin aromatic solvents,e.g., chlorobenzene,or with neat monomer at a temperature of 50~ or higher. The polymer was a white powder, soluble in nonpolar solvents. With a monomer to catalyst ratio of 80:1 and a monomer concentration of 1.5 M in chlorobenzene, poly(cis5,6-bis(trimethylsiloxy)-l,3-cyclohexadiene) with a number average molecular weight (M~) of 38000 (average degree of polymerization (DP) of 150) and a polydispersity index (PDI) of 1.64, as determined by GPC, was obtained. The yield of polymer increased asymptotically up to 93% with increasing monomer concentration, but below a critical monomer concentration (0.14 M), polymerization did not proceed. A plot of molecular weight vs % monomer conversion exhibited a nonlinear relationship and suggested a non-"living" kinetics. However, blocking experiments, performed by adding fresh aliquots of monomer to the propagating system resulted in molecular weight increase without broadening the polydispersity. Polymerization of cis-5,6bis(trimethylsiloxy)-l,3-cyclohexadiene in the presence of [(ANiTFA)2] proceeded stereospecifically to cis-substituted poly(cis-5,6bis(trimethylsiloxy)-l,3-cyclohexadiene) as determined by a combination of ~H NMR spectroscopy, molecular modelling, powder X-ray diffraction (PXRD) and scanning tunnelling microscopy (STM). It was inferred that the cis relationship of the bulky TMS groups allows the catalyst to coordinate only to the opposite face of the diene. Subsequent syn insertion of the monomer into the propagating nickel-allyl complex afforded the cis stereostructure. Pyrolysis of poly(cis-5,6-bis(trimethylsiloxy)- 1,3cyclohexadiene), however, did not yield poly(p-phenylene) (PPP) probably because the TMS ether moieties are poor leaving groups. Quantitative conversion of the TMS ether groups to more facile leaving groups such as esters was accomplished by deprotection of poly(cis-5,6bis(trimethylsiloxy)-l,3-cyclohexadiene) to the corresponding poly(cis-5,6bis(hydroxy)-l,3-cyclohexadiene), followed by acylation to poly(cis-5,6bis(acetoxy)-l,3-cyclohexadiene) ( >93% overall recovered yield over two
523 steps) (Eq. 9.14).
F~
(MeCOhO py, 80"C-~
IVleOH TMS
TIVIS
140
OH
. I:.....~
MeCO0
.....~n
(9.14)
OOCMe
Pyrolysis of poly(cis-5,6-bis(acetoxy)-l,3-cyclohexadiene) to high-quality PPP occurred at 310-340~ on NaCI crystals in high yield.(Eq. 9.15).
coc( 'ooc
(9.15)
-2n MeCOOH
The use of acyl derivatives of cis-5,6-bis(hydroxy)-l,3-cyclohexadiene resulted only in aromatization of the monomers and deactivation of the catalyst (Eq. 9.16). n
RCOd \ OOCR
(ANiTFA)2> -2n RCOOH
n <--~
(9.16)
9.5. Eight-Membered Ring Monomers Due to the easy availability of functionalized eight-membered ring monomers, synthesis of functional polymers from these monomers, using tolerant catalytic systems, became of interest for several applications. Substituted cyclooctene. Cyclooctene substituted with functional groups has been studied as a potential monomer in several ROMP reactions. Ringopening polymerization of this type of monomer would produce interesting functionlized terpolymers, having butadiene associated with substituted ethylene units in the chain. In one example, 5-chlorocyclooctene was polymerized with WCI~t2AICI, under mild conditions, to form a terpolymer ofbutadiene with ethylene and vinyl chloride ~4(Eq. 9.17). n
=
Toluene, 20~
(9.17)
524 Thus, working in toluene at 20~ poly(5-chlorooetenylene) in 58% yield has been readily obtained. When the functional group was attached directly at the carbon-carbon double bond, the monomer was generally inert. Attempts to polymerize 1-ethoxycyclooctene with the diphenylcarbenetungstenpentacarbonyl catalyst, Ph2C=W(CO)s, failed. ~z Under these conditions, ROMP of 1-ethoxycyclooetene gave no substituted polyoctenamer (Eq. 9.18).
n
( '~OEt Ph2C=W(CO)5 O E ~ . v =
(9.18)
Ring-opening polymerization of 5-substituted cyclooetene with "unprotected" pendant groups, using the well-defined ruthenium-based metathesis catalyst, (Cy3PhCIzRuCH=CHCPhz, has been recently reported by Cmabbs and coworkers ~5 (Eq. 9.19). n
~
(9.19)
where X = alcohol, carbonyl, bromine, acetate. The reaction rate was relatively slow compared to that of unsubstituted monomers. Relevant data are shown in Table 9.4. Table 9.4 Polymerization of substituted cyclooctene (~M.= C~I,3-X') with the (,Cy3P)zClzRuCHCHCPhz (~) initiator"b Time M,xl0 "3 PDI Temp. Yield [M]:[I] X % hr ~ 1.6 139 65 23 24 1044 -OH 1.8 97.9 47 23 72 1037 =O 1.9 82.4 92 23 144 1056 -Br 1.9 96.0 57 23 72 1044 -OCOCH; 2.4 85 138 47 25 1041 -OCOCH; 0 23 24 181 -CN 0 23 24 523 -0'Data from referencet~; bThe initiator was dissolved in a minimum amount of CHzCIz, the mixture was added to neat monomer, and the polymerizations were performed under argon; ~Determmed by GPC in THF using polystyrene standard. |l
525 Both the rate of polymerization and polymer yield were significantly increased with increased concentration of the monomer, best results being obtained when the polymerizations were run in the minimum amount of solvent. In the case of poly(octenyleneacetate), an increase in the polymerization temperature increased the yield and molecular weight of the polymer. However, attempts to polymerize cyclooctene bearing nitrile and epoxy groups failed. Coordination of the nitrile group in 5cyanocyclooctenr by the ruthenium catalyst is probable responsible for monomer deactivation. In the case of 5,6-epoxycyclooctene, the mechanism of catalyst deactivation is not well understood. Ring-opening polymerization of cyclooctene-5-methacrylate in the presence of the (Cy3PhCI2RuCH=CHCPh2 initiator led to cross-linkable poly(cyclooctene-5-methacrylate) (Eq. 9.19a).
o,,CO-<
n
~
Copolymers of this monomer with cyclooctadiene, at varying feed ratios, were produced that were cross-linked through the methacrylate side-chain, both thermally and photochemically, to form AB cross-linked systems. The successful ROMP of a number of 5-(alkylthio)cyclooctene by a well-defined aryloxo(chloro)neopentylidenetungsten complex has been reported by Basset and coworkers, ~6 the resulting polymers being terpolymers of butadiene, ethylene, and vinyl sulphides (Eq. 9.20). SR n
...-
(9.20)
Examination of the conversion-time curves for the polymerization of 5alkylthiocyclooctene with g=Et, n-Bu, t-Bu, n-Hex and c-Hex at 25~ showed a strong influence of the nature of the alkyl substituent at sulphur on the rate of polymerization. The most reactive monomers were those with branched alkyl substituents on the sulphur atom, namely with tert-butyl and cyclohexyl. Thus, the polymerization of 5-tert-butylttfiocyclooctene was roughly complete within 15 min, with an initial turnover rate higher than 1000 hr ~
526 Thiocyclooctenes with n-alkyl groups were less reactive. In this series, however, there was a significant effect of the chain length of the alkyl substituent on the reaction rate, for longer substituents the polymerization was faster. These results were interpreted on the basis of a coordination competition between the thioether functionality, the C=C double bond of the cyclooctene moiety and the molecule of diethyl ether present in the aryloxo(chloro)neopentylidenetungsten complex. Such a coordination of the thioether functionality will be impeded when the substituent is tert-butyl or cyclohexyl, allowing a higher concentration of the olefin coordinated species which is the precursor to the transition state that leads to insertion of monomer and further propagation. On the other hand, coordination of thioether functionality will be stronger with less bulky substituents such as ethyl group, what will diminish the concentration of the olefinic coordinated species leading to monomer insertion and polymerization. Ring-opening polymerization of (5-cyclooctenyl)diethylborane induced by W(=CH'Bu)(=NAr)(OCMe(CF3hh gave a diethylborane substituted poly(l-octenylene) in high yield '7 (Eq. 9.21).
n~
1BEt2
OH
Complete oxidation and hydrolysis of the corresponding borane-substituted polymer yielded a terpolymer of butadiene, ethylene, and vinyl alcohol, poly(5-hydroxyoctenylene). In the starting monomer, the hydroxyl group was masked as a trialkylboron since the tungsten-based metathesis catalyst used in the polymerization was known to be intolerant towards alcohols. The thermal stability of the terpolymer and of its saturated derivatives was significantly better than that of the conventional poly(vinyl alcohol). It is interesting that polymerization of 3-tributyltincyclooctene in the presence of WCl6-based metathesis catalysts failed whereas 5tributyltincyclooctene gave under these conditions polyoctenamer substituted with the tributyltin group in the repeat unit ~s (Eq. 9.22).
n
~[/SnBu3 [VV/AI]
.-- ~
SnBu3
(9.22)
527 This reaction can be conducted with other substituted cyclooctene bearing tributyltin moiety in a distant position with respect to the double bond (Eq.9.22a).
~
SnBu3 ROMP ~
(9.22a)
\ SnBu3
Synthesis of these organotin-containing polymers may be of interest for their potential biocidal properties. Substituted cyclooetadiene. In case that the chlorine atom is attached directly at the carbon-carbon double bond, this bond becomes inert in metathesis reaction. For instance, 1-chloro-l,5-cyclooctadiene reacts in the presence of WCl6-based catalysts at the unsubstituted carbon-carbon double bond to give the alternating copolymer of butadiene and chloroprene 19 (Eq.9.23).
CI V~I6/EtOH/Et2AICI ,
n
_ 1 _ ~ _
(9.23)
Under the reaction conditions, the configuration of the chlorine substituted carbon-carbon double bond remained unchanged. Substituted cydooctatetraene. Using the well-defined tungsten carbene initiator W(=CH-o-MeO-C61~)(=NPh)OC(CH3)(CF3)E)(THF), Grubbs and coworkers 2~polymerized a series of monosubstituted cyclooctatetraenes via ring-opening metathesis to substituted polyacetylenes. These polymers were highly conjugated, as evidenced by their visible absorption spectra. They were of high molecular weight, as evidenced by GPC, and most members of the series were soluble in the as-synthesized, predominantly cis form. The polymers could be isomerized to the predominantly trans form by heat or light. The rate of thermal isomerization could be monitored by visible absorption spectroscopy. Methoxycyclooctatetraene. This substituted cyclooctatetraene has been polymerized by Cnubbs and coworkers 2~with the above tungsten initiator to the methoxy bearing polyacetylene (Eq. 9.24). OMo
n
~OMe
[w]
~
(9.24)
528 The polymer had a low solubility in common solvents. From differential scanning calorimetry of the solid samples, a Ti.~ of 131~ has been recorded. tert-Butoxyeyclooctatetraene, tert-Butoxycyclooctatetraene has been polymerized with the tungsten carbene initiator W(=CH-o-MeOC61"L)(=NPh)OC(CH3)(CF3)2)(THF) to the corresponding substituted polyacetylene~ (Eq. 9.25). n
~OtBu
OtBu
[W]
(9.25)
Working with a monomer to catalyst ratio of ~150 to 1, a polyacetylene having M, = 252 x 103 Mw = 341 x 103 and PDI = 1 4 has been obtained Trimethylsilylcyclooctatetraene. Polymerization of trimethylsilylcyclooctatetraene in the presence of W(=CHC(CH,)3)(=NAr)(OC(CH3XCF3)2h (At 2,6-(CH(CH;h)2-Cd-13) produced polyacetylene substituted with SiMe3 side groups 2~ (Eq. 9.26). 9
.
=
n
=
=
(9.2s)
Me3
Substituted cis polyacetylene, of 104 molecular weight (GPC), that were soluble in tetrahydrofuran were obtained by this way. The polymer was then converted thermally or photochemically into the trans configuration and the THF solutions were cast into thin films by using conventional spin coating procedures. Thin transparent films cast onto n-doped silicon (n-Si) substrates were doped with iodine to form surface barrier solar cells. The devices produced photovoltages that were at the theoretical limit and that were much greater than could be obtained from n-Si contacts with conventional metals. Methods for forming layered polymeric materials were also designed. An organic polymer analog of a metal/insulator/metal capacitor has been constructed with such a method. Polymerization of trimethylstannylcyclooctatetraene has been performed with W(=CHC(CH3)3)(=NAr)(OC(CH3XCF3)2)2 (At = 2,6(CH(CH3)2)2-C6H3) to poly(trimethylstannylcyclooctatetraene) (Eq. 9.26a).
n 2D Me3Sn
W(C HtBu)(NAr)(Off3u~..~
(9.26a)
Me3Sn
529 This polymer in conjunction with poly(trimethylsilylcyclooctatetraene) produced multilayer electrically conductive laminar structures taking advantage of the insolubility of 12-doped polymers in THF. Sandwich structures with 1000A layers have been resolved in the SEM and single layers with thickness of 100A have been produced by spin-coating techniques. Such thin multilayered structures are of interest for their potential use as waveguides and eleetrooptic modulators. Chiral cyclooctatetraene monomers. Monosubstituted cyclooctatetraene derivatives with chiral side groups have been polymerized with tungsten carbene initiators to chiral polyacetylenes~ (Eq. 9.27). R' n
R"
~/~~CH
R"
3 [W]~
where R' = H and CH3 and R" = OCH3 and
R ' R '
1"t3 § ~ C
'
Pt3 (9.27)
oxy(tert-butyldimethylsilyl).
To
some extent, substituted benzene was produced by a back-biting mechanism in competition with the propagation reaction. The tungsten carbene catalyst employed in these syntheses, W(=CHAr)(=NPh)(OCMe(CFah)2(THF) (Ar = o-(OCH3)CffI4), similar to Schrock-type catalysts, was easily prepared and handled. It allowed a controlled, reproducible polymerization rate and the formation of high-quality polymer films. The optimum monomer to catalyst ratio used of 150:1 led to high monomer conversions and produced high molecular weight polyacetylenes (Table 9.5). Table 9.5. Rmg-~enmg polymerization of chiral cyclooctatetraene (RCOT) with W(=CHArX=NPhXOCMe(CF3)2)2(THF) (Ar = o-(OCH3)C61"14) ~
9
99
BackTime Temp Collv % biting, % rain ~ O(TgS) d 20 4.9 82 90 CH3 20 66 3.1 O(TgS) 60 CH3 6.6 20 65 12 OCH3 CH3 55 2.8 45 75 OCH3 CH3 55 4.1 25 93 OCH3 CH3 O(TBS) 20 7.9 H 60 93 H O(TBS) 60 20 83 <5 'Data from referencer; ~RCOT of formula from Eq. 8.180;'All polymerizations were performed with a monomer to catalyst ratio of 150:1,aO(TBS) = (tert-butyldimethylsilyl)oxy. R
R
530 The polymers were soluble and highly conjugated. It is noteworthy that the backbone rr-n* transition of these polymers showed substantial circular dichroism (CD), the magnitude of which was characteristic of a disymmetric chromophore. Decreasing temperature had much more influence on the CD of the cis polymers than on the CD of the trans polymers in their respective n-n* regions, cis-Polyacetylenes were much more conformationally flexible than trans and may contain helical regions. ~H NMR spectra suggested that the olefinic units were probably not entirely cis or trans with respect to the main chain of the polymer, and this irregularity might prevent long-range (helical) order.
9.6. Higher Monocyclic Olefins Several higher functionalized cycloolefins have been employed in the polymerization reactions with tolerant catalytic systems to provide the corresponding functionalized polymers. The most accessible of these were the derivatives of cyclodecadiene, cyclododecadiene and paracyclophanene which have been reacted with appropriate ROMP catalysts. l-Methylcarboxy-3,7-cyclodeeadiene. Polymerization of (Z,E or E,Z) lmethylcarboxy-3,7-cyclodeeadiene has been carried out by Cho and Bae 23 using WCIt,/Me4Sn and WCI4(o-2,6-C6H3X2)2/EhPb (X=Ph,Me,CI) as the catalysts. Substituted polydeeadienamers having an alternating structure of butadiene and methyl methacrylate units in a 2 to 1 ratio have been obtained (Eq. 9.28).
n~C02Me
[W]> ~
(9.28)
Of the two catalytic systems, only WCI4(o-2,6-C6H3Xe)-~/Et4Pb (X=Ph,Me,CI) showed to have a substantial activity. The monomer conversion varied considerably with the nature of the substituents of the phenyl group in the following order Me
531 Table
9.6 Polymerization of 1-methylcarboxy-3,7-cyclodecadiene with tun~ sten based cataly ~ICsyst~ITIS' hCial, Conversion Cocatalyst Catalyst % x 104 mole x 104 mole dl/g i
17 25 56
EhPb EUPb
WCh(O-2,6-Cd-13Mez WCh(O-2,6~d-13Clz WCh(O-2,6-Cffl3Ph~ WCI~
0.08
0.12 0.23
Me~Sn
'Data from' reference 23
l-Trichlorosilyl-5,9-cyclododecadiene. 1-Trichlorosilyl-5,9-dodeeadiene has been polymerized in the presence of WCl~-based catalysts to the trichlorosilyl substituted polydodecenamer24 (Eq. 9.29). n
[w]
~
~
(9.29)
sich 9-(tert-gutyldimethylsilyloxy)12.2]paracydophan-l-ene. Living ringopening polymerization of 9-(tert-butyldimethylsilyloxy) [2.2]paracyclophan-l-ene initiated by the Schrock-type complex Mo(=CHCMe2Ph)(=NAr)(OCMe(CF3)2) (At = 2,6-diisopropylphenyl) gave poly(9-(tert-butyldimethylsilyloxy)[2.2]paracyclophan- 1-ene), a novel poly(p-phenylene vinylene) (PPV) precursor 2S (Eq. 9.30).
n~
~
OS0 i 8u)Me2I-ICI
,[I
Films of poly(9-(tert-butyldimethylsilyloxy)[2.2]paracyclophan- 1-ene) could be converted to PPV by heating to 120-140~ in the presence of HCI (g) for a period of 30 min. Infrared spectra indicated that the initial cis form of poly(9-(tert-butyldimethylsilyloxy) [2.2]paracyclophan-l-ene) generated PPV containing exclusively trans polymer. Poly(9-(tertbutyldimethylsilyloxy)[2.2]paracyclophan- 1-ene) could be also
532 quantitatively converted to soluble poly(9-hydroxy[2.2]paracyclophan-1ene) using Bu4NF in tetrahydrofuran. Dehydration of the benzylic group on this polyalcohol proceeded at room temperature by addition of a catalytic amount of HCI (g). These reaction conditions provided PPV under extremely mild conditions. 9.7. Functionalized Bicyclic Olefins The high potential of bicyclic monomers to produce polymers having particular structures and properties stimulated the synthesis of functional polymers from various derivatives of this class of monomers. Functionalized norbornene. In the course of their studies on the polymerization of norbornene, Michelotti and Keaveney z6 showed that the substitution of the saturated ring in the position 5 of norbomene with functional groups influences substantially the polymerizability of this system. When the functional group is strongly polar, it forms a stable complex with the metal site from the catalyst. Notwithstanding, with less polar substituents unsaturated polymers will arise wherein the substituent is maintained in the initial position of the cyclopentane moiety (Eq. 9.31).
'
n
f yx
~
(9.31)
\
X where X = CI, CHzCI, OR, CN. For instance, when X=CN, it was not possible to produce polymers from 5-cyanonorbomene with the catalytic systems that arc active in norbornene polymerization such as RuCI3, OsCl3 or IrCl3 in ethanol but with the chloromethylene group as substituent in the same position unsaturated polymers having low molecular weight have been obtained under the action os IrCl3 as a catalyst However, a polymer of 5cyanonorbomene has been prepared if WCk-based catalysts were employed. The ring-opening polymerization of norbomene bearing various functional groups was carried out by numerous authors in the presence of binary and ternary catalytic systems which showed good activity in cyclopentene reaction. (Table 9.7). It is noteworthy that Hepworth 2~ prepared substituted polynorbomene from 5-substituted norbomene containing chlorine atoms in the presence of WCI6 associated with
533 Et2AICI or Et3AI2CI3 and acetal groups or with the ternary catalyst WCI6, CH2OH and Et3AI2CI3. Polynorbomene substituted with chlorine and bromine were also obtained by Kobayashi e t al. 2, under the action of WCI6 and Et2AICI on the corresponding substituted monomers. Moreover, Table 9.7. R m g ~ m g polymerization of 5 - s u b ~ norbomene bearing various functional groups (X) using naxathesis catalysts'
Functional Group
Catalytic System
References
CI Br
WCIdEt2AICI, WC~3AIzCI3
27,28
WCIdEtzAICI
28
CH2CI
IrC13.3H20
exo-CF3 OR exo- COOH endo-COOH
WCld~h4Sn
26 29
WCI6/EtzAICI
28
Ru- and Ir-based Ru- and Ir-based Mo-, W-, Re-, Ru-, Os- and Ir-based
30,31 30,31 32,33
COOC2H5 COOCsH2Br3 COCH3
WCld~t3Al2Cl3
CONH2
WCI6/Et3A].Et2A]CI
CON(CH3)2
Mo- and W-based W-based W-based Ru- and k-based Ru- and k-based Ir-based Ir-based WCI~.,tzAICI Mo- and W-based WCIdEhAI
27 34 32 35, 28 33 30,33 30,33 30,31 30,31 36 30 36 32,33 37 37
WC[6/F_,t3AI2C|3 WCI6/Et3A]2C]3
38 38
COOCH3
exo~N endo~N exo- CH2OH endo-CH2OH CHzOCOCH3 CH2OCOCH=CHz CHzCN OCOCH3 Si(CH3)CI2 SiCI3 SiCI3, Si(OCH3)3
WCIdEt3AI Ru- and Ir-based
WCl6/Et3Al
'Data from references 2"~-3|
534 Kobayashi e t al. 39 carried out the ring-opening polymerization of norbornene containing a large number of substituents such as cyano, ester, ether, amide, imide or anhydride in the presence of several catalytic systems based on tungsten, molybdenum, rhenium, tantalum or niobium salts associated with organometallic compounds from groups la-IVa and Ilb-IVb or inorganic compounds of these metals such as phosphates or phosphites. It is also significant that Ueshima et al. 4o and Nakamura et al. 4~ prepared polymers and copolymers from substituted norbornene, especially with cyano group in position 5, with special characteristics such as good mechanical strength and low gas permeability for practical application. Kanega et al. 42 reported good yields in the synthesis of thermoplastic resins from 5-cyanonorbomene by employing WCI6, Et2AICI and Ph3P, while Imaizumi et al. 34 prepared fireproof resins from tribromophenylester of 2norbornene-5-carboxylic acid using WCI6 and EhAI. Fireproof polymers with remarkable properties were also obtained by Arai et al. 43 from norbornene derivatives containing cyano, ester, ether, halogen or imide groups, under the action of ternary catalysts consisting of WCI6, Et2AICI and oxygenated compounds such as 1,1-diethoxyethane. A variety of ternary catalysts tolerant to functional groups consisting of tungsten or molybdenum salts, organometallic compounds and epoxides, peroxides, acetals, esters, organic halides or water have been employed by Kurosawa et a l . " to polymerize several 5-substituted norbomenes such as 5-(2-pyridyl)-norbomene or e x o - d i c a r b o x y l i c anhydride. Catalysts with very high activity in the polymerization of norbomene with functional groups were obtained by Ikeda et al. 4~ on employing other transition metals such as vanadium, chromium, manganese, in addition to tungsten, molybdenum, rhenium or tantalum compounds. For instance, they prepared in 80-90% yield polymers from norbornene esters using chromium acetylacetonate and triethylaluminium. Starting from 5-substituted norbomene, silicon-containing polynorbornene has been synthesized by Streck 38 and Zimmermann. 37 Thus, norbornene bearing SiCI3 and Si(OCH3) groups has been successfully polymerized by Streck 38 under the action of WCl6 in conjunction with Et3AIeCI3 while norbornene carrying Si(CH3)CI2 was reacted by Zimmermann 37 in the presence of WCl6 and EhAI. Difunctionalized norbornene. Numerous 5,5-disubstituted norbomenes bearing functional groups such as alcohol, carboxylic acid, ester, nitrile in conjunction with an alkyl group have been investigated in the presence of various ROMP catalysts (Eq. 9.32).
535
n
Y
.-.---~
(9.32)
Y
X
where X and Y are hydrogen, alkyl or aryl and CHzOH, COOH, COOK, CN, COIL CONH2, CONHR. (Table 9.8). Table 9.8. Ring-opening polymerization of 5,5-disubstitW,.~ norbomene cxa~mmg various functional~'oups ~endo-Xz e: :o-Y)' endo-X exo-Y CatalyticSystem References i
|
CH2OH CH3 COOH CH3 COOCH3
CH3 CHzOH CH3 COOH CH3
CH3
COOCH3
COOCzH5 CN CN
CH3 CH3 CN
RuCI3 RuCI3 RuCI3, OsCI3 RuCI3 Ir-based WC~3AI2CI~OH Mo- and W-based RuCI3 b-based WCIjEt3AI2CI~OH Mo- and W-based RuCI3 RuCI3 Mo- and W-based WC IJEt2AICI/(CHzOEt)2
46 46 46 46 31 27 36 46 31 27 36 46 46 36 47
'Data from references 3147 As it can be seen from the Table, RuCI3 catalyst is the most tolerant with different functional groups like alcohol, carboxylic acid, ester, whereas the classical W- and Mo-based catalysts tolerate ester and nitrile groups. A wide range of 5,6-disubstituted norbomenes, having the same or distinct functional groups in the two vicinal positions, have also been studied in the presence of ROMP catalysts. They give a variety of functionalized polynorbornenes carrying various functional groups in the polymer chain (Eq. 9.33).
536
n
r---
(9.33)
X X
Y
where X and Y may be the same or different from the following functionalities CHzOH, COOH, COOK, CN, COIL, CONH2, CONHR (Table 9.9). Table 9.9 Rmg-openmg polymerization of 5,6-disubstituted norbomene containing various functional groups, X and Y" X
Y
Catal~,dc System
Ref.
CH2CI CI CH2OCH3 COOH COOCH3 COOC2H~ COOSiMe3 OCOCH3 O(CO)OCH3 O(CS)SCH3 CH2SCH3 CH2NHC(CH3)3 CHzNHSi(CH3)3 CN CN PPh3
CH2CI CI CH2OCH3 COOH COOCH3 COOC2H5 COOSiMe3 OCOCH3 O(CO)OCH3 O(CS)SCH3 CHzSCH3 CHzNHC(CH3)3 CH2NHSi(CH3)3 CN Ph PPh3
WCl6-based IrCI3 Ru-based WCl6-based (NH4)2IrCI6 Ir-, Os-, Ru-based Mo-based Mo-based Mo-based Mo-based Mo-based Mo-based Mo-based Mo- and W-based Mo- and W-based Mo-based
48
31 49 50 31,32 51 52 53 54,55 54,55 56 57 57 36 36 58
'Data from references 31-57 Many polysubstituted norbomenes, particularly tri- and tetrasubstituted norbornenes, carrying different functionalities have been also used in the ring-opening polymerization reactions in the presence of transition metal metathesis catalysts. They give functionalized polymers having several functional groups, Y, in the same repeat unit (Eq. 9.33a)
537
where Y substituents may contain halogen, ester, ether, cyano groups, etc. and x = 3, 4 or a higher integral number. Funetionalized norbornadiene. There is a large series of mono- and disubstituted norbornadienes bearing various functional groups that have been used as monomers in ring-opening polymerization. They give highly unsaturated functionalized polynorbornadienes which are of a particular interest for their physical and chemical properties. Monosubstituted norbornadiene will give rise to polynorbornadiene bearing a functional group in the repeat unit, in the presence of appropriate ROMP catalysts (Eq. 9.34),
n ~
x
~
~
(9.34)
\
X
whereas, disubstituted norbomadiene will produce polynorbomadiene bearing two functional groups attached at the repeat unit under these conditions(Eq. 9.35), n
~~~'~Y X
=
(9.35)
X
Y
where X and Y substituents are various functional groups. In a similar way, polysubstituted norbornadiene will from highly substituted polynorbornadiene under the action of appropriate ROMP catalysts (Eq. 9.35a).
538
(9.35a) I
COx where Y substituents are functional groups. Typical examples of substituted norbornene or norbornadiene with functional groups, containing halogen, oxygen, sulphur, nitrogen, silicon, boron and various metals, used as monomer in ring-opening metathesis polymerization will be presented in the following sections. Fluorinated monomers. A wide range of fluorinated monomers was found by Feast and coworkers 59'6~to undergo, under appropriate conditions, ringopening metathesis polymerization to highly fluorinated polymers. This finding afforded a convenient way to produce thermally stable and solvent resistant polymers inaccessible by conventional routes. A first series of such polymerizable monomers consists of derivatives of norbornene substituted with various fluorine-containing substituents in the position 5 or/and 6, l-IX (Scheme 9.2).
/ cF3 ]ffffff~ /ffffff~ C7
CsF11
I
II
III
~_~TF F(CF3) (CF3) IV
V
~r
•••7C
CI(CF3) I(CF3)
VI
F(CsF11) F2
VII
Fls
VIII Scheme 9.2
IX
539 The majority of these unsaturated compounds were polymerized with the catalyst system WCIdPh4Sn to form the respective fluorinated polynorbornene by the ring-opening reaction, e.g., the polymer from 5trifluoromethylnorbomene s9 (Eq. 9.36).
n
CF3
WCl6/Ph4Sn ~
-,
-J-n
(9.36)
CF3 and that from 5,6-bis(trifluoromethyl)-5,6-difluoronorbomene (Eq. 9.37).
n
C/~~F F3
WCI6/Ph4Sn
~-x~~
"~
---]-n
(9.37)
(CF FF
CF3
The polymerization yield and polymer structure depended essentially on the monomer nature and reaction conditions (Table 9.10). Table 9.10 Polymerization of fluorinated norbomene with the WCIdPh4Sn catalyst system~b Monomer R e a c t i o n Reaction Yield % Time Temp. ~ (Scheme 9.2) hr
[rl]
dt/g
.=
I (exo CF3) IV (endo CF3) IV (exoCF3)
V Vl
22 22 20 20 22
2 4
3.5 27 65
93 64 20 63 37
0.96
5.8 .
2.46
'Data from reference ~,bSolv~=Toluene.
It can be observed the high yield (93%) of polymer obtained from exo-5trifluoromethylnorbornene with the above catalyst as compared with the other substituted monomers. Of some classical catalysts, OsCl3 forms with this monomer an all-trans polymer that is probably atactic, although the
540 spectrum did not indicate any tactic splitting of the olefinic carbons. By contrast, endo-5-trifluoromethylnorbomene, gives with both OsCl3 and MoCI~/Me4Sn catalysts 90% trans atactic polymers with no head-tail bias while ReCI5 forms 92% cis polymer, also unbiased, but probably tactic. 6~'62 On using the molybdenum-carbene initiator63 Mo(=CHtBu)(=NAr)(OtBu)2, 5-trifluoromethylnorbomene gave, in a living manner, a polymer with M,jM,, = 1.09. Interesting data recorded Feast and coworkers 6~'64 on the polymerization of fluorinated norbomadiene derivatives in the presence of a variety of metathesis catalysts. Thus, under appropriate conditions, they prepared fluorinated ring-opened polymers from 2trifluoromethylnorbomadiene (I), 2,3-bis(trifluoromethyl)norbomadiene (II) 2,3-bis(trifluoromethyl)isopropylidenenorbomadiene (III) and 2,3bis(trifluoromethyl)(7-(l'-phenyl)ethylidene)norbornadiene (IV) (Scheme 9.3). Ph
~CF3 I
,K-~CF3 ~CF 3 II
K , ~ C F3 ,K,'~g./CF3 /~,,-"...,..,.4~ CF3 //..M,,,.,.~ CF3 Ill
IV
Scheme 9.3 Of these monomers, 2-trifluoromethylnorbomadiene undergoes readily metathesis polymerization under the influence of several metathesis catalysts, e.g., WCI6/Me4Sn, MoCls/Me4Sn, OsCl3, RuCI3, IrCl3 and ReCIs, to form poly(3,5-(l-trifluoromethyl)cyclopentenylenevinylene) 64 (Eq. 9.38).
n
OF3
~
~
(9.38)
/
CF3 Some relevant data on the 2-trifluoromethylnorbomadiene polymerization are given in Table 9.1 1.
541
Table 9.11 Polymerization of 2-trifluoromethytnorbomadiene under the influence of metathesis catalysts' Catalyst
MoCl~e4Sn W C ~ e , Sn OsCl3 RuCI3 IrCI3.CF3COOH ReCI~
Solvent
Chlorobeazeae Chlorobenzme Chlor~eJEtOH Chlorobeazeae/EtOH Chlorobenzene/F.~OH Chlorobenzene
Temp. ~
Time hr
Yield %
Room Room 40 40 40 60
5 min 5 rain 2.5 65 48 48
50 90 25 5 25 7
|
'Data from reference~
Analysis of the infrared and high-field ~3C NMR spectra of the different polymers thus prepared revealed that the Mo based catalyst gave predominantly trans-vinylene units, the Re based catalyst showed the greatest tendency towards stereoregulation giving predominantly cisvinylene units while the other catalysts were unselective in this respect. As compared to its 2,3-bis(trifluoromethyl) analog, 2trifluoromethylnorbomadiene was more reactive, however, both monomers displayed no vinylene stereo selectivity with the very active W-based initiators, whereas with Mo and Ru based catalysts the disubstituted monomer displayed significantly greater trans-vinylene selectivity. Fluorinated polymers with different trtms/cis double bonds, T s and T~ have been prepared by Feast et al. 65 from 2,3bis(trifluoromethyl)norbomadiene using various ROMP catalysts (Eq.9.39).
i/~'~/cF3
n/j/,,,~~
C F3
=
(9.39)
Some interesting results obtained with this monomer are summarized in Table 9.12.
542 Table 9.12 Polymerization of 2,3-bis(trifluoromethyl)norbomadiene with rmg-c~ening metathesis catalysts'
Catalyst
WCIs/Me4Sn RuCI3/Me4Sn MoCI~/Me4Sn Mo(=CH'Bu)(:NAr)(O'Bu)z mn n
Trans
Cis
Ts
Till
%
%
~
~
54 70
46 30 13
125 117 104 97
2OO
87 98
2
an
'Data from reference63 It can be easily observed that there is a clear correlation between ratio of the vinylene units and glass transition temperature, T s, of the polymer. Interestingly, the ~3C NMR spectra revealed that the microstructure of the polymers became more simple as the Table is descended; thus, the polymer made with WCIdMe4Sn catalyst is ataetie whereas the polymer made with the well-defined Mo(=CH'Bu)(=NAr)(O'Bu)2 catalyst has virtually exclusively trans vinylene and is totally tactic. Furthermore, the polydispersities observed in the polymerization of 2,3-bis(trifluoromethyl)norbornadiene with the first three initiators varied typically in the range 1.3 to 3.5 whereas that made with the Schrock initiator had values in the range 1.03 to 1.06 for polymers with M, values from 10000 to 170000. All the polymers prepared with two component catalysts were amorphous and displayed no melting points in the DSC traces before decomposition whereas the tactic polymer displayed a melting point in the DSC and the magnitude of the melting endotherm could be varied by annealing. This new semi-crystalline thermoplastic fluoropolymer formed fibers which could be cold drawn to increase their crystallinity, and high clarity films could be east from solution. The polymers thus prepared had very stiff immobile chains as was observed in the DMTA curves of both atactic and tactic samples and the tactic sample had a low proportion of crystallinity. Further fluorinated polycyclic monomers investigated by Feast and coworkers 6~7 under the action of the metathesis catalysts are illustrated in Scheme 9.4.
trans/cis
543
F
F
F
F
0
2 I
CeFs I
II
III
Scheme 9.4 It is interesting to point out that in the reaction of exo- and endo-Npentatluorophenylnorbomene-2,3-dicarboxamide carried out in the presence of several metathesis catalysts, Blackmore and Feast66 found that only the exo isomer was readily polymerized to the corresponding polyalkenamer by WCIVMe4Sn and MoCI~/Me4Sn systems whereas attempts to polymerize the monomer with RuCI3 and OsCl3 proved unsuccessful. On the other hand, the endo isomer could not be polymerized under the same conditions. A mixture of exo and endo isomers, however, was polymerized using MoCIdMe4Sn as a catalyst, giving a relatively low yield of polymer. Analysis of the polyalkenamer microstructure by IR and ~3C NMR spectroscopy indicated that MoCI5 catalysts gave a high trans vinylene content (ca. 90%) which is probably atactic and WCI6 systems afforded a mixture (ca. 40:60) of cis and trans double bonds and the polymer is probably also atactic. The polymerization of a mixture of exo and endo isomers showed that the exo monomer is preferentially incorporated into the polymer chain. The GPC results indicated that the products formed were genuine high polymers, having a fairly large molecular weight distribution. Ring-opening metathesis polymerization of another series of partially fluorinated norbomene derivatives was reported by Risse and coworkers 687~ using the highly reactive metathesis catalyst WCIdPh4Sn. Thus, the exo/endo monomers 5-fluoro-5-pentafluoroethyl-6,6bis(trifluoromethyl)norbomene, 5,6-difluoro-5-heptafluoroisopropyl-6trifluoromethylnorbornene and 2,3,3,4,4,5,5,602,6~ octafluorotricyclo[5.2.1. ]aec-8-ene were easily prepared by Diels-Alder reaction of cyclopentadiene with the perfluorinated olefins and polymerized under the action of the WCIdPhaSn catalyst to the corresponding fluoroalkyl-substituted polynorbornene derivatives (Scheme 9.5).
544
F
F(CF3)2
~
CI2F5 FF
F
2
CF 3
I
II
III
4F 9
C5Fll
IV
F
F V
Scheme 9.5 As compared to the parent norbomene (e.g., complete conversion after 1-3 min at 25~ with WCIdPlhSn), polymerization of these fluorinated monomers proceeds more slowly, reaction times of 20 to 64 hr at 70~ being needed to convert them in moderate yields (from 33% to 52%) to the corresponding fluorinated polynorbornene. These reaction conditions reflect a drastic decrease of reactivity, resulting from the reduced electron density of the carbon-carbon double bond caused by fluorolakyl substitution. Similarly, 5,5,6-trifluoro-6-undecafluoropentylnorbomene and 5,6difluoro- 5-nonafluorobutyl-6-trifluoromethylnorbomene have been polymerized in the presence of WCI6/PthSn to the corresponding fluorinated polynorbomene. Yields and physical properties of the fluorinated polymers thus prepared are given in Table 9.13. The reactions have been carried out with exo/endo mixtures of monomers, the exosubstituted cyclic olefin being usually more reactive than the corresponding endo isomer. The products containing the highest amount of fluorine were insoluble in most organic solvents. Nonetheless, trifluoromethylbenzene and hexafluorobenzene showed to be good solvents while toluene, chlorobenzene and methanol were very poor. Interestingly, poly(2,3,3,4,4,5,5,6-octafluorotricyclo[5.2.1.02"6]dee-8-ene) was soluble in tetrahydrofuran and acetone. As Table 9.13 shows, an increase in the amount of fluorine content leads to a decrease in the refractive index.
545 Table 9.13 Yields and physical properties of fluorinated poly(norbomene)s made by ring-opa mg aagathcsis polymerization" Polymerb Yield, nDTM F, Ts", [V]iah r % wt.% .dlg-I ~ *C Poly(D 33 0.74 1.3860 62.3 161 357 PolyOl) 50 0.33 1.3845 62.3 182 396 Poly(llI) 52 0.66 1.4089 54.6 193 357 Poly(lV) 40 0.39 1.3792 63.9 100 367 Poly~ 43 0.44 1.3806 63.9 103 363 'Data from'reformce~; SFluormntodmonomer f r ~ Scheme 9.5. "Inhermt viseos~y in trifluoromethylbmzene at 250C; dRefractive index at 25~ "Glass transition temperature, determined by DSC; fDocornposition ten~erature, 5% weight loss, determined by TGA. It is relevant that all the fluorinated polymers thus prepared by Risse et al. 69 are amorphous products. As it can be readily observed, one fluorinated substituent on the polynorbornene backbone results in a moderate glass transition temperature (for instance T s = 100-103~ however, if a second fluoroalkyl substituent is sterically more demanding, a substantial increase in transition glass temperature is recorded (T s = 182~ for perfluoroisopropyl group). A further increase is effected by the presence of three perfluoroalkyl substituents (T s = 182~ or by a perfluorocyclopentyl ring fused to the cyclopentylene units (T s = 193~ This increase in T s was rationalized by considering a significantly greater rigidity of the polymer main chain by restricting the rotation about the carbon-carbon double bonds that link olefin units with five membered rings. A striking feature of the above fluorine containing polymers is their remarkably good oxidation stability. As Risse et al. ~ observed, these products can be kept under air for more than a year without any n o t i ~ l e change in color, solubility or solution viscosity. The oxidative stability appears to be a result of the electron-withdrawing nature of the fluoroalkyl substituents, which stabilize the polymer toward attack by oxygen. By contrast, the parent polynorbornene starts to cross-link in the presence of oxygen within 24 hours. Novel polymers have been obtained by Rissr et al.7~ by ROMP of spiro fluoro derivatives of norbornene and norbornadiene such as 5,5,6trifluoro-6-(trifluoromethyl)spiro[7,1'-r I and If, and bis(trifluoromethyl)spiro[7,1'-cyr Ill
546 illustrated in Scheme 9.6. F
F F
F
CF
F3 F
CF 3
I
II
CF3 III
Scheme 9.6 It is interesting that the steric bulk of the cyclopropane ring in the position 7 of the fluorinated derivative of norbomadiene, 2,3bis(trifluoromethyl)spiro[7,1'-cyclopropane]norbornadiene, Ill, will not prevent the polymerizability of this monomer under the influence of metathesis catalysts. Risse er al. 7~ found that this spironorbornadiene derivative underwent ring-opening polymerization quite readily in the presence of WCl6 and PI~Sn (Eq. 9.40).
n
CF3
CF3
~~"n
(9.40)
" \CF3 CF3
The corresponding poly(spironorbomadiene) derivative was formed in excellent yields (98-100~ after 1 hr at 70~ The inherent viscosity of the polymer was 0.73 dlxg"~ (trifluoromethylbenzene) when an initial monomer:WCl6 molar ratio of 5001 was used for this polymerization reaction. Furthermore, the ~3C ~ spectra of the product thus produced indicated a trans/cis ratio of 80/20 for vinylene units. The trans/cis ratio in this polymer was larger than the reported trans/cis ratio of 54/46 by Feast et al. 6~ for poly{bis-5,6-(trifluoromethyl)norbornadiene} prepared using the same catalyst. The preferential formation of trans double bonds in poly {2,3bis(trifluoromethyl)spiro[ 7,1 '-cyclopropane] norbomadiene } was rationalized by a steric effect of the three-membered ring of the monomer during propagation reaction. It is relevant also that the cyclopropane ring
547 has a favorable influence on the glass transition temperature, T s, of poly{2,3-bis(trifluoromethyl)spiro [7,1'-cyclopropane] norbomadiene}. Owing to the steric bulk of this three-membered ring, the flexibility of the polymer chain seems to be reduced, resulting in a T s of 164~ approximately 40~ higher than the T s value of the polymer containing two hydrogen atoms instead of the cyclic substituent. As compared with the above results, a T s range of 97-125~ was found for the related fluoropolymer poly {bis-5,6-(trifluoromethyl)norbomadiene. Fluorinated benzonorbomadienes l-III have been polymerized by ring-opening with both WCIdMe~Sn and MoCldMe4Sn catalysts62 (Scheme 9.7).
CF3
F
F
CF3
F I
F
II
Ill
Scheme 9.7
These monomers afford the convenient synthesis of highly fluorinated poly(benzonorbomene)s; for instance, tetraflurobenzonorbomadiene gives in the presence of WCIdMe4Sn or MoCIdMe4Sn the corresponding fluorinated polymer (Eq. 9.41 ). F
VVCIs/Me4Sn F
F
=
(9.41)
MoCI5/Me4Sn F
F
In these reactions, the steric effect induced by both the isopropylidene group and the nature of transition metal is relevant. Thus, while monomers I and II gave 40 to 50~ cis polymer with WCI6 catalyst and monomer Ill gave 70% cis polymer, with MoCI5 catalyst, monomers I and II formed 70 to 85% cis polymer while monomer III led to 95% cis polymer.
548 Chlorinated monomers. The ring-opening polymerization of 5chloronorbornene, under the influence of ruthenium and iridium chlorides in ethanol, has been first briefly reported by Michelotti and Keaveney 26 (Eq.9.42).
n~_~Cl RuCI3' IrCl3~ "=
(9.42) \
CI The reaction has been also described later in various patents by Hepworth 27 and Kobayashi. z8 More recently, Makovetsky e t al. ~ examined the polymerization of this monomer in the presence of heterogeneous rheniumbased and homogeneous tungsten-based metathesis catalysts. The relevant data are presented in Table 9.14. Table 9.14 Ring-opening polymerization of 5-chloronorbomene (M) under the action of rhenium and tungsten based metathesis catal~s" [n] Catalytic System [M] Monomer: Time Yield dlg-I mole.L"~ Catalyst hr % mole RezO3/AlzOdBu4Snb WCl~hC_~Cl-g
WC~hC~H'
7.8 2.5 2.5
200 1000 1000
72 1
4
50 65
gel 0.25
'Data from referenceT~; b3 wt % Bu4Sn, toluene, 45~ %VC~:phenytaeetylene 1 1, toluene, 20~ 6Tetraallylsilane added (l'l mole with WCI6). These authors observed that the polymerization of neat 5-chloronorbomene carried out at 45~ with the rhenium/alumina catalyst promoted by BtuSn gave only traces of an unidentified product. On the other hand, the reaction induced by WCldphenylacetylene gave poly(5-r in rather high yields. However, the polymers prepared turned out to be praetieally insoluble in aromatic solvents (toluene, chlorobenzene) even when heated. Interestingly, completely soluble polymers having intrinsic viscosities of 0.2-0.45 dl/g and microstructure of ca.50% trans units, were obtained by adding an equimolar amount of tetraallylsilane to WCI6 before the start
549 of the polymerization reaction. Interesting results obtained Makovetsky et al.7~ in the ring-opening polymerization of 5-(chloromethyl)norbomene in the presence of homogeneous metathesis catalysts. The reaction has been ~ e d out without difficulties with the RuCI3.3H20 and WCldphenylacetylene catalysts to obtain high yields of soluble polymers (Table 9.15). Table 9.15 Ring-opening polymerization of 5-(chloromethyl)norbomene (M) mducod by hc na~oous metmhesis catal, ~.s' Catalytic System [M] Monomer: Time Yield [n] mole L"t Catalyst hr % dl g" mole RuCI3.3H20b WCIdPhC=CW
3.0 2.0
40
500
11
41
1
100
'Data f r o m reference7t" bCJ'I~CI:EtOH 11, T~aperaturo %VCl~:Phenylacetylene 1 1, Solvent Toluene, Temperature 20~ y
3.6 0.79 60~
Significantly, the polymers obtained using the above two catalysts were distinguished by their microstructure: thus, the RuCI3 catalyst gave a polymer containing only trans double bonds (Eq. 9.43)
2n~
CH2CI
cH2cl
(9.43)
\
CH2Cl
whereas the WCl6/phenylacetylene system produced a predominantly cis polymer (Eq. 9.44).
2 n ~ ~ -CH2CI
VVCk/PA
(9.44)
CH2Cl
CH2Cl
550 On using several metathesis catalysts based on Ru, Ir, Mo and W in 5(chloromethyl)norbomene polymerization, Ivin et al. ~2 showed that the reaction proceeds readily to give unbiased polymers with a range of cis contents. By this way, exo-5-(chloromethyl)norbomene gave with ReCl~ an all-cis polymer but endo-5-(chloromethyl)norbomene did not react cleanly. Polymerization of 5,6-bis(chloromethyl)norbomene in the presence of WCI6/Et2AICI/CICH2CH(OEth at a temperature of 60~ gave poly(4,5bis[chloromethyl]- 1,3-cyclopenylenevinylene) in 97% yield48 (Eq. 9.45). n "'~///~CH2Cl "-- "x~c
H2CI
[VVCIs/Et2AICI] =
(9.45)
t = 60~ ,11 = 97% CIH2 C
CH2Cl
The polymer obtained after 0.5 hour possessed an intrinsic viscosity [11] 0.46 dl/g (DMF, 30~ More recent studies carried out by Shahada and Feast 73 showed that polymerization of 5,6-bis(ehloromethyl)norbomene to poly( 1,4-[2,3-bis(chloromethyl)eyelopentene]vinylene occurs with MoCIs/Me4Sn to give ataetir polymer with predominantly trans vinylene units, whereas the reaction with WCIdMe4Sn gives ataetir polymer with predominantly cis vinylene units. It was found that highly chlorinated norbornene and norbornadiene derivatives of the type shown below undergo ring-opening polymerization and copolymerization with r under the action of metathesis catalysts to produce chlorinated polymers. Of this class of monomers, a very reactive, highly chlorinated norbornene derivative, 1,8,9,10,11,11hexachlorotetraeyr [6. 2.1.13'6.02"7] dodeca-4,8-diene (Aldrin), reacts in the presence of various metathesis catalytic systems giving rise to poly(1,7,8,9,10,10-hexaehloro-3,5-trieyr dec-8-enylvinylene) by ring-opening of the unsubstituted norbornene moiety 3~ (Eq. 9.46).
CI
n~
C
C c, I
Cl
WC~aZtOHtEtA~
kCI3.3H20 =
~
(9.46)
\ / C~CI /
CI
\
CI
551 The reaction occurs with WCIjEtOH/EtAICI2 in chlorobenzene giving the polymer in 95% yield after 10 rain while with IrCI3.3H20 in ethanol/4methyl-pentan-2-one/ethyl acetate~ight petroleum at a 100:1:1:1 volume ratio produces 39~ yield of polymer after 18 hours. The product is insoluble in ethanol, dimethylformamide and benzene. Oxygen-containing monomers. Several types of bicyclic monomers containing oxygen groups as functionalities have been polymerized using proper tolerant catalytic systems. They afford a large group of functionalized polymers with interesting properties. Norbornene with hydroxy and ether functionlities. Polymerization of exo-5-hydroxymethylnorbomene occurs in the presence of IrCI3.3H20 in ethanol to poly(4-hydroxymethyl-l,3-cyclopentylenevinylene)3~(Eq. 9.47).
.• n
IrCI3 3 H20 C H2OH
(9.47)
t = 20~ q = 48% \
CH20H
Poly(4-hydroxymethyl-1,3-cyclopentylenevinylene) is obtained in 48% yield after 30 hours at 20~ The endo monomer is rather inert under these conditions but can be polymerized with IrCI3.3H20 working at 60~ Both stereo isomers, exo- and endo- 5-hydroxymethyl- 5methylnorbomene undergo ring-opening polymerization in the presence of RuCI3.3H20 in ethanol/chlorobenzene solution to form all-trans poly(4hydroxymethyl-4-methyl- 1,3-cyclopenylenevinylene)~s (Eq. 9.48).
n
CH20H
RuCI3 3H20
=
~
(9.48)
CH 3
OH
CH3 Interestingly, using IrCI3 as a catalyst, poly(4-hydroxymethyl-4-methyl-1,3cyclopenylenevinylene) having about 2 0 0 cis configuration was obtained. Polymerization of endo-5-methoxynorbomene has been carried out by Ivin, Lam and Rooney 75 using several metathesis catalysts based on Mo, Re, Ir, W and Ru salts (Eq. 9.49).
552
n
~
-[--~ - - ~
OCH3
(9.49) \
OCH3
Under these conditions, they prepared poly(endo-5-methoxynorbomene) in varying yields with cis contents ranging from 10~ to 48% (Table 9.16). Table 9.16 Polymerization of endo-5-methoxynorbomene induced by transition metal-based catalysts' Catalytic System
Reaction Time
Reaction Temperature
Polymer Yield %
Content of cis Double Bonds
~C MoCIs/Et3AI ReCIs/Et3AI IrCI3.3H20 WCh/Me, Sn RuCI3.3H20
4 days 4days 2 days 2 hours 2 days
60 20 60 20 50
O'c
25 24 42 26 44
0.48
0.47 0.33 0.30 <0.1
'Data from reference 7~
Polymer microstructure was determined by ~3C NMR spectroscopy. Noteworthy, no significant head-tail bias was observed and no splitting due to tacticity could be identified. 1-Ethoxynorbornene does not polymerize in the presence of diphenyl~ene-tungstenpentacarbonyl complex but reacts stoichiometrically by ring-opening to form a new tungsten-carbene complex~2 (Eq. 9.50). cr,2~
(9.5o) cr~
553 This new tungsten complex is rather stable and of low activity to continue further insertion in the propagation reaction. Ring-opening polymerization of 5-methoxymethylnorbomene has been investigated by Ivin et al. ~6 in the presence of Ru-, Ir-, Mo- and Rebased metathesis catalysts when polymers with cis contents ranging from 10~ to 90~ starting with endo monomer and from 23% to 60% starting with exo monomer were produced (Eq. 9.51).
n
----~
~
\
H2OCH3
/ ,~ CH2OCH3
(9.51 )
No significant head-tail bias was observed in these polymer. A high-trans atactic product was thus prepared from the optically active endo monomer, (-)endo-5-methoxymethylnorbomene, while the Ifigh-cis polymer was either atactic or biased towards syndiotactic, depending on the catalyst. endo, exo-5,6-Dimethoxymethylnorbomene was polymerized in a living fashion with Mo(=CHMe2Ph)(=NAr)(OtBu~h (At = 2,6-C~-13-'Pr2) to form poly(4,5-trans-dimethoxymethylcyclopenylenevinylene) in high yield77" ~9 (Eq. 9. 52).
n
/CH2OCH3 CH2OCH3
[IVlo]
=_
~ H3coNc
(9.52) /
.,
CH2OCH3
The polymer had a low polydispersity and T s of ca. 45~ Block copolymers with methyltetracyclododecene were also prepared from endo, exo-5,6-dimethoxymethylnorbomene. 'H NMR spectrum indicated that the block to block ratio of the repeat units was that expected of a wellbehaved living polymerization. These products were used to bind metals in a dative fashion, e.g., silver and gold, for the synthesis of semiconductor clusters or metal clusters of a predictable size within microdomains. The endo monomer of the methoxy diether derivative of 5ethoxymethylnorbomene has been polymerized in a living system using the above molybdenum carbene initiator 77 (Eq. 9.53)
554
C H20(CH2)2OCH3
\ C H2C)(CH2)20CH3
Block copolymers with methyltetracyclododecene are capable of binding zinc and cadmium compounds through the oxygen donors to form semiconductor clusters. Living ring-opening polymerization of a series of n-[((4'-methoxy4-biphenyl)yl)oxy]alkyl(nobron-2-en-5-yl)methylethers in which n = 4-6 produced side-chain liquid crystalline polymers containing an homologous mesogenic group to the former norbomene derivative 8~(Eq. 9.54).
c~:~o~~~~o~ These new polymers obtained in the presence of Mo(=CHtBu)(=NAr)(OtBu)2 (Ar=-I,6-CsH3-'Pr2) as initiator provided information concerning the influence of the alteration of the connecting group on the thermal behavior and liquid crystalline properties. The molecular weights and polydispersities obtained on varying the molar ratio monomer:catalyst between 1001 and 51 are listed in Table 9.17. The living nature of the polymerization was inferred from the linear relationship obtained for M~ versus [M]/[Cat] and narrow molecular weight distributions (PDI
555 Table 9.17 Polymerization of [((4'-methoxy-4-biphenyl)yl)oxy]alkyl(nobom-2-en-5-yl)methylether (M-n, n=4-6) with Mo(=CHrBu)(=NAr)(OrBu)z (At= 1,6-Cd'ir'Prz)'
4 4 4 4 4 5 5 5 5 5 6 6 6 6 6 6
[Mnl:[Mo]
MI
DP
PDI
100 50 20 10 5 100 50 20 10 5 200 100 50 20 10 5
44700 16600 7400 4800 3300 79500 20200 8500 5300 3700 139100 49400 22900 8400 5400 3800
118 44 19 13 9 202 51 22 13 9 342 122 56 21 13 9
1.15 1.19 1.25 1.31 1.27 1.14 1.19 1.16 1.15 1.19 1.13 1.12 l.ll 1.11 1.12 1.15
;Data from reference '~
Norbomene ended polystyrene macromonomers have been and polymerized using the metathesis catalysts WCldPl~Sn to polystyrene grafted Mo(--CHtBu)(=NAr)(OC(CH3)(CF3)2)2 polynorborneneS2 (Eq. 9.55). lUol
r
The reaction performed with molybdenum initiator gave quantitatively polymacromonomer. Copolymers with cyclooctene containing as high
556 content of macromonomer as 94% have also been prepared with this catalyst. Ring-opening polymerization of norbomene ended polyethylene oxide macromonomer with the molybdenum initiator Mo(=CHq3u)(=NAr)(OC(CH3)(CF3hh occurs quantitatively to polyethyleneoxide grafted polynorbomene" (Eq. 9. 56). 1~4oi
Under these conditions, polymacromonomers with high molecular mass and narrow polydispersities have been obtained. Because the oxygen atoms existing in the macromonomer are prone to interact with the metal carbene, the proportion of initiator really available for coordination with the olefinir unsaturation of the cycloolefin obviously decreases, entailing larger DPs values for the polymacromonomers than expected. Norbornene with r and ester functionality. A range of norbomene monomers containing carboxy and ester functionality's have been employed in the polymerization reactions using appropriate tolerant catalytic systems. 5-Carboxynorborn-2-ene. Polymerization of exo-5-~oxynorbom-2-ene occurs readily in the presence of IrCI3.3H20 in ethanol to form poly(4carboxy- 1,3-r162 5~(Eq. 9.57).
n ~,.COOH
K;h 3 89 11 = 5 4 . 5 % >
(9.57)
\
COOH
Under these conditions, the monomer conversion will reach 54.5% after 1 hour reaction time. Methyl substituted homologs of endo- and exo-5-carboxynorbom-2ene, endo-5-carboxy-exo-5-methylnorbom-2-ene and exo-5-carboxy-endo5-methylnorborn-2-ene have been also polymerized with RuCI3.3H20 catalyst to poly(4-carboxy-4-methyl- 1,3-cyclopentylenevinylene) u (Eq.9.58).
557
n
~J~
COOH
Me
RuCI33H20 ~ O O H ""
(9.58)
Me
5-Carboalkoxynorborn-2-enes. Both endoand exo-5carbomethoxynorbom-2-ene react in the presence of various metathesis catalysts to give poly(4-earbomethoxy-l,3-cyclopentylenevinylene) 8s (Eq.9.59).
~~Z-COOMe
[W,Mo]
n
~
(9.59)
k COOMe
High yields in poly(4-carbomethoxy-l,3-cyclopentylenevinylene), ranging from 80 to 100%, have been obtained using W-based catalysts in benzene at 70~ or toluene at 30~ (Table 9.18). Table 9.18 Polymerization of 5-carbomethoxynorbom-2-ene (M) with various transition metal metathesis catalysts (I)* Catalyst
M:I
WCldMeMgBr 200 WCIdEt3AI 200 WCl6/Et3Al/Acetone 1000 WCI6/Et3SiH 200 WCIdEhSn 200 WCldPh3Sb 200 W(OPh)dF~2AICI 200 Ph(EtO)W(CO)yTiCI4 5000 Ph(EtO)W(CO)YTiC LdPh3P 5000 MoCI~,tAICIz 200 'Data from reference ss
Solvent
T~
Time hr
Yield %
Benzene Benzene Toluene Benzene
70 70 30 70
Benzene
70
Benzene l~n~e
70 70 70 70 70
17 17 0,25 17 17 17 17 16 16 17
91 99 I00 85-97 I00 81 95 I00 I00 49
-
Benzene
558 The ring-opening metathesis polymerization of 5-endo- and 5-exocarbomethoxynorbornene initiated by the tungsten cyclopentylidene complex W[=C(CHz)aCH2](OCHzCMe3)2Br2 in CD2CIz has been followed at 27~ by ~H NMR. ~'s7 It was found that the initial metal-carbene adducts were usually distinguishable from the subsequent adducts and the initiation was generally faster than the propagation. 87 Methyl substituted derivatives of endoand exo-5carbomethoxynorborn-2-ene, endo-5-carbomethoxy-exo-5-methylnorbom2-ene and exo-5-carbomethoxy-endo-5-methylnorbom-2-ene have been also polymerized with RuCIa.3H20 catalyst to poly(4-carboxy-4-methyl1,3-cyclopentylenevinylene) u'88 (Eq. 9.59a).
,•
n
Me
COOMe
RuCI33H20 ~ 0 0 =
Me
(9.59a) Me
The related compounds, endo- and exo-5-carbethoxynorbom-2-ene give by ring-opening with the RuCI3 catalyst poly(4-carbethoxy-l,3cyclopentylenevinylene) 89 (Eq. 9.60).
n~
RuCh3H20 COOEt
q = 90%~
(9.60)
COOEt
The polymer obtained in 90% yield with RuCI3 in ethanol at 90~ had a Tg of 14~ Poly(4-carbethoxy-l,3-cyclopentylenevinylene) could also be produced directly from the carboxylic acid monomer by heating with IrCI3 in ethanol.9~ In a similar way, .9 5-carbopropyloxynorborn-2-ene will give, by ring-opening polymerization in the presence of platinum metal group catalysts, poly(4-carbopropyloxy-l,3-cyclopentylenevinylene) with a T s of 7~ and 5-carboctyloxynorborn-2-ene will form poly(4-carboctyloxy-l,3cyclopentylenevinylene) with a Ts of-53~ 5-Carbohexadecyloxynorbom2-ene gives rise to poly(4-carbohexadecyloxy-l,3-cyclopentylenevinylene) with a Tg of 10~ Both the monomer and polymer form monolayers, the polymer displaying a higher collapse pressure and reduced collapse area compared with the monomer. 91
559 Ring-opened polymers of a number of 5-norbomene-2-carboxylates that contain acetal-protected sugars such as 1,2 3,4-di-O-isopropylidene-ctD-galactopyranos-6-O-yl) 5-norbomene-2~oxylate (1), 2,3-0isopropylidene-D-ribonic G-lactonyl 5-norbomene-2-carboxylate (If) and 3,4:5,6-di-O-i sopropylidene-ct-D-mannofuranos- 1-O-yl 5-norbomene-2carboxylate (III) were prepared in high yield in toluene or THF with Mo(=CHCMeePh)(=NAr)(O'Bu)z (Ar=-2,6-C6H3-'Pr2) as the initiator9z (Eq.9.61).
Mo(CHCMe2Ph)(NArXOrBu)2
= ~O
C§
(9.61) I
OR where mo
I
CH 2
OR =
--0,,
Io
O'-.~F,-
~
I
1
OX/('O
The homopolymers exhibited narrow molecular weight distributions (PDI=I.06-1.23) and a molecular weight dependence on the amount of monomer employed (Table 9.19). Starting from these monomers, di-, tri- and tetrablock copolymers with methyltetracyclododecene and trans-5,6-bis(((trimethylsilyl)oxy) methyl)norborn-2-ene were prepared which had low polydispersities. The cyclic acetal in polymers from 1,2:3,4-di-O-isopropylidene-ot-Dgalactopyranos-6-O-yl) 5-norbornene-2-carboxylate could be removed using CF3COeH/H20 (9/1 v/v, 15 min, 22~ to afford the corresponding water-soluble polymers containing the parent sugar. Several 5-carbalkoxynorbom-2-enes bearing at the alkyl moiety laterally attached aryl or aryloxy substituents with nitro, cyano or alkoxy groups have been polymerized in a controlled fashion to form polyalkenamers, some of which have properties of liquid crystalline polymers.
560 Table 9.19 Polymerization of aoetal-protected sugars of 5-norbomene-2-carboxylates (M)' Mb
I 1
Solvent~
Equiv.
Time hr
M. xl0 a
PDI
Yield %
Tol
20
1
1.47
1.06
99
Tol Tol
30 50
1 1
1.67 2.77
1.06 1.06
I
Tol
100
1
6.31
1.10
II II II II II II
HI: THF Tol THF THF Tol
30 30 30 50 50 50
1 0.5 l 1 0.75 l
2.14 1.37 1.81 2.59 1.73 2.53
1.08 1.02 I. 14 1.04 1.03 1.23
92 99 94 99 99 99 98 99 99
II III III
THF THF Tol
I00 30 50
I I I
3.89 2.09 3.25
1.09 1.06 I.16
99 99 99
I
'Data from
For this purpose, 5-[[[n-[(4-nitrophenylyl)oxy]alkyl]oxy] carbonyl]norborn2-ene and 5-[[[n-[(4'-nitro-4-biphenylyl)oxy]alkyl] oxy]carbonyl]norborn2-erie have been polymerized by Laschewsky 9~ with RuCI3 under mild conditions to the respective polyalkenamers (Eq. 9.62-9.63).
n
~.~
RuCh CO0(CH2hl~~2
(9.62)
CO0(CH,z1h~ N O z ta~
C 0 ~ 0 ~ 2 ) 1 1 0 ~ ~ ~2 These products, however, did not form well-defined monolayers. On using the well-defined molybdenum initiator Mo(=CH'Bu)(=NAr)(O'Bu)2(Ar=2,6-C6H3-'Pr2), Komiya, Pugh and
561 polymerized 5-[[[n-[(4'-methoxy-4biphenylyl)oxy]alkyl]oxy]carbonyl] norbom-2-ene in high yield to narrow MWD side-chain liquid crystalline polymers (Eq. 9.64). Schrock 93
(9 64)
C00(C~~-~)~)-0r
CO0(CH2~~~
It is interesting to note that poly {4-[ [ [n-[(4"-methoxy-4'biphenylyl)oxy]alkyl] oxy]carbonyl]-1,3-cyclopenylenevinylene} with n = 28 showed a enantiotropic nematic mesophase whereas the polymer with n = 9-12 exhibited side-chain crystallization in addition to the nematic or smectic mesophase. 5-[[[n-[(4'-Methoxy-4-biphenylyl)oxy] alkyl]oxy]carbonyl]norbom-2-ene was quantitatively polymerized by Komiya in 1 hr in tetrahydrofuran (Tiff) at room temperature under the action of Mo(=CHtBu)(=NAr)(O'Bu)2(Ar=-2,6-CsHr'Pr2). The living polymer was quenched with benzaldehyde to give a benzylidene-terminated polymer upon reaction of the living alkylidene with benzaldehyde in a Wittig reaction. The molecular weight of the polymer was controlled by varying the molar ratio of the monomer to Mo initiator. The polymerization was quantitative, and the polymer was flee of unreacted monomer after a single precipitation. The molecular weights, polydispersities and polymerization degrees for polymers prepared from monomer with n=9 - 12 are given in Table 9.20. It is noteworthy that the polydispersities (M,JM,,) were lower than 1.20 in most cases but were as high as 1.28 for some of the higher molecular weight polymers, as a result of small double molecular weight fraction. Significantly, a linear relationship was obtained by plotting the number-average molecular weight (M~) of the polymer as a function of [monomer] :[initiator] for ratios up to 100. The low polydispersities and linear relationships were consistent with a living polymerization under the conditions employed. Furthermore, proton NMR spectra evidenced that the polymerization proceeded by a ring-opening pathway. Thermal characterization of poly(4-[ [ [n-[(4"-methoxy-4 '-biphenylyl)oxy] alkyl]oxy]carbonyl]-l,3-cyclopentylenevinylene) was carried out by combination of DSC and thermal polarized optical microscopy.
562 Table 9.20 Polymerization of 5-[[[n-[(4'-methoxy-4biphenylyl)oxy]alkyl]oxy]carbonyl]norbomene (n=9-12)with the Mo(CH'Bu)(NAr)(O'Buh (Ar=-2,6-C~'13-iPrz) catalyst'
m
Monomer~M-n
[Monomer]" [Mo]
M-9 M-9 M-9 M-9 M-9 M-10 M-10 M-10 M-10 M-10 M-II M-II M-II M-II M-11 M-12 M-12 M-12 M-12 M-12
100 50 20 10 5 100 50 20 10 5 100 50 20 10 5 100 50 20 10 5
'Data from
MI
47949 18997 8649 5114 3220 62683 24378 8137 4710 3230 35086 16272 7226 4683 3183 49568 20830 9022 5386 3421
PDI
DP
1.07 1.08
104 41 19 10 7 132 51 17 10 7 72 33 15 10 6 98 41 18 11 7
1.13 1.14 1.17 1.26
1.13 1.12 1.14 1.16 1.23
1.12 1.12 1.15 1.18 1.28 1.22
1.13 1.15 1.17
.J
l'efer~rlGe 93
It was observed that all DSC cooling scans and the second and subsequent heating scans were identical when the same rates were used. Analogously, 5-[[[ n-[ (4 '- cyano-4-biphenylyl) oxy ] alkyl ] oxy ] carbonyl]norborn-2-ene (n = 3-7, 9-12) was polymerized by Komyia and Schrock s~ with Mo(=CHR)(=NAr)(OtBu)z(Ar=-2,6-C6H3-~Prz, R = 'Bu) in a living manner to poly {4-[[[n-[(4"-cyano-4biphenylyl)oxy]alkyl]oxy]carbonyl]- 1,3-cyclopentylenevinylene} (Eq. 9.65).
563 By the usual procedure, on contacting the catalyst with the monomer in THF at room temperature, quantitative polymer yields have been obtained. The living nature of the polymerization was inferred from the linearity of M,, vs. [M][Cat] and the narrow molecular weight distributions (Table 9.21). Table 9.21 Polymerization of [((4'-cyano-4-biphenyl)yl)oxy]alkylnobom-2-ene-5-carboxylates ~M-n) with Mo(=CHR~ =NAr)(O'Bu)2 (~tS = 2z6-Csl'13-i Pr2~ R = 'Bu~)' PDI DP M, M-n [M-n]:[Mo] M-3 M-3 M-3 M-3 M-3 M-4 M-4 M-4 M-4 M-4 M-5 M-5 M-5 M-5 M-5 M-10 M-10 M-10 M-10 M-10 M-II M-II M-II M-II M-II M-12 M-12 M-12 M-12
I00 50 20 10 5 100 50 20 10 5 100 50 20 10 5 100 50 20 10 5 100 50 20 10 5 100 50 20 5
'Data from reference *~
65700 23900 7700 4500 3500 52000 25300 9300 4800 3400 42800 23900 7900 4500 3200 44800 20700 10700 5500 3800 99500 35900 11400 6100 4500 52900 21400 7600 3600
1.23 1.13 1.12 1.13 1.16 1.17 1.08 1.12 1.12 I.II 1.18 1.13 1.16 1.14 1.13 1.27 1.15 1.14 1.13 1.13 1.20 1.16
1.08 1.12 1.13 1.24 1.20 1.26 1.14
176 64 21 12 9 134 65 24 12 9 107 60 20 II 8 95 44 25 12 8 205 74 24 13 9 I06 43 15 7
564 It was noted that the molecular weights of the polymers obtained when 100 equiv of monomer was used tended to deviate more from theory than molecular weights of shorter polymers, because of the sensitivity of the catalyst to both extraneous substances and experimental error in measuring small amounts of catalyst. The highest molecular weight polymers sometimes showed a small amount of double molecular weight peak. However, the polydispersities of higher molecular weights were still less than 1.27. Poly{4-[[[n-[(4"-cyano-4-biphenylyl)oxy]alkyl]oxy] carbonyl]-l,3cyclopentylenevinylene} was characterized by a combination of differential scanning calorimetry (DSC) and thermal polarized optical microscopy. The first and subsequent DSC scans were essentially identical, and all heating and cooling scans were completely reproducible. It is quite interesting that the polymers in which n=3 were amorphous, whereas all other polymers (n=4-7,9-12) displayed enantiotropic nematic mesophases that were independent of the molecular weight. The transition temperatures increased with increasing molecular weight and levelled off at approximately 30-50 repeat units, regardless of the spacer length. It was also observed that the length of the spacer did not affect the molecular weight at which the phase transition became independent. Significantly, polymers with long spacers (e.g., n = 9o12) did n o t undergo side chain crystallization and did not show an odd-even effect, in contrast to analogous polymers containing ((4'-methoxy-4-biphenyl)-yl)oxy mesogens, which exhibited side-chain crystallization when n>8 and an oddeven effect when n<7. The lower tendency to form a more ordered phase and the absence of an odd-even effect were attributed to the dipole-dipole repulsion between ((4'-cyano-4-biphenyl)yl)oxy mesogens. Polymerization of 5-[[[2',5'-bis[(4"-n-alkoxyoxybenzoyl)oxy] benzyl] oxy]carbonyl]norborn-2-ene (n = 1-6) with Mo(=CH'Bu)(=NAr)(OtBu)z (Ar=-2,6-C6H3-'Prz) has been effected by Pugh and Schrock 94 to poly {4-[ [ [2 ', 5'-bis[(4"-n-alkoxybenzoyl)oxy] benzyl]oxy]carbonyl]- 1,3-cyclopentylenevinylene} (Eq. 9.66).
n
Mo(C HMe2Ph)(NAr)(OtBu) 2 COOR
n = 72-94%
(9.66)
~-_
COOR
565 where
\
o,,
,o, e-x
High yields (72-94%) of narrow MWD poly{5-[[[2',5'-bis[(4"-nalkoxyoxybenzoyl)oxy] benzyl] oxy] carbonyl]norbom-2-ene} or poly{4[[[2',5'-bis[(4"-n-alkoxybenzoyl)oxy] benzyl] oxy]carbonyl]- 1,3cyclopentylenevinylene} have been obtained at various reaction times and monomer to initiator ratios (Table 9.22). Table 9.22 Polymerization of 5-[[[2',5 '-bis [(4"-n-alkoxybenzoyl)oxy] benzyl]oxy]carb<myl]norbom-2-ene (M-n) (n = 1-6) with Mo(=CHq3u)(=NAr)(O'Bu)2 (Ar=-2,64~d'13-'Pr2) (I)* M-n
[M],/[I],
Time, hr
Yield,, %
MII
9.7 19.5 49.6 39 45.3 4.7 39.2 50.8 52.4
0.5 2.0 0.5 2.5 2.0 0.5 3.0 2.0 2.0
91 94 91 89 87
4320 7707 20773 20380 39378 5178 14316 34050 55780
89
86 72 78
1.20
1.18 1.13 2.36 2.74 1.16 1.17 2.20 2.36
*Data from reference ~ Although the polymerizations were quantitative, the polymers became more soluble as the length of the n-alkoxy group increased. The thermotropic behavior was determined by a combination of DSC and polarized optical microscopy. Poly {4-[[[ 2 ',5 '-bis[ (4"-n-alkoxybenzoyl)oxy] benzyl]oxy]carbonyl]- 1,3-cyclopentylenevinylene } displayed an enantiotropic nematic mesophase over the entire range of molecular weights and the transition temperatures decreased with increasing length of the nalkoxy substituent. Polymers with an even number of methylene units in the substituents displayed a higher isotropization temperature and more stable
566 mesophases than polymers with odd-membered substituents. Obviously, the polymer backbone has little effect on the transition temperatures of sidechain liquid crystalline polymers displaying nematic mesophases, even when the chemical structures of the backbones are substantially different. This behavior confirms that mesogens jacket the extended polymer chains. 5-[[[2 ',5 '-B is [(4"- n- p ertlu o roal koxyoxybenzoyl) oxy ] benzyl ] oxy]carbonyl]norbom-2-ene (n = 1-6) has been polymerized with Mo(=CHq3u)(=NArXOq3u)z (Ar=-2,6-C6H3-'Prz) by Pugh e t al. 95 to poly {4[[[2',5'-bis[(4"-n-perfluoroalkoxybenzoyl) o x y ] b ~ l ] o x y ] carbonyl]-l,3cyclopentylenevinylene }(Eq. 9.67).
n
Mo(CHMe2Ph)(NAr)(OtBu)2 ,
COOR
=
"-~ A
/'~
(9.67)
COOR where
\ o
/_~
CH2
o
Such polymers would induce smectic mesomorphism by the immiscibility of the hydrocarbon and fluorocarbon segments, rather than to a shape persistence of"mesogenic perfluoroalkyl rods". In order to further induce smectic layering in nematic liquid crystalline polymers, Pugh e t al. 96 prepared poly{5-[[[2',5'-bis[(4"-n((dimethylsiloxy)alkoxy)benzoyl)oxy] benzyl]oxy]carbonyl]norborn-2-ene } or poly {4-[[[ 2', 5 '-bis[ (4"-n(-(dimethyl siloxy)alkoxy)benzoyl)oxy] benzyl]oxy]carbonyl]- 1,3-cyclopenylenevinylene } by ring-opening polymerization of 5-[[[2',5'-bis[(4"-n(-(dimethylsiloxy)alkoxy)benzoyl) oxy]benzyl]oxy]carbonyl]norborn-2-ene in THF at room temperature using Mo(=CHCMezPh)(=NAr)(O'Bu)2 (Ar=-2,6-C6H3-'Pr2) as the initiator (Eq. 9.68).
Mo(CHMe2Ph)(NAr)(OtBu)2
n ~~--COOR
9
=
~
\ / COOR
(9.68)
567 where
\
CH~ CH3CH3 , = , O ,.=,/ O ,__,9 i i / \ , /--\ t I , . . ~ c - , ~ ( ~ ) ~ c . ~ ) ~ o - L . / - c - o - ~ ....k-~176176 CH3CH3
CH3CH3 a I
~-c",
CH~ CH3
The polymerization was performed using [M]o/[I]o ~ 50 in order for the polymers' thermotropic behavior to be independent of molecular weight (DP > 25). The polymer exhibited a smectic C mesophase. However, the temperature range over which the smectic C mesophase was observed was narrow and isotropization occurred at a temperature very close to the glass transition temperature. Ring-opening polymerization of 5-[[[2'-[[(4"-methoxybenzoyl) oxy]methylene]-4'-[(4"- methoxybenzoyl)oxy] phenyl]oxy] carbonyl] norborn-2-ene and 5-[[[2'-[[(4"-methoxy- benzoyl)oxy]methylene]-5'[(4"- methoxybenzoyl)oxy]phenyl] oxy] carbonyl]norbom-2-ene has been carded out by Pugh and Schrock 9~ with Mo(=CHMe2Ph)=(NArXO'Bu)2 (Ar=-2,6-C~H3-'Pr2) (Eq. 9.69-9.70).
~~_
COOR
M~ (CHMe2Ph)(NAr)(OtBu)2 '
'
=
-" ~ "~ y y ~ n COOR
where
O~OCH3
R ~
~~~-COOR where a
(9.69)
Mo (CHlVle2Ph)(NAr)(OtBu) 2 .....
=-
~
(9.70) COOR
,,_, o c.,o- i F-c-o-k_ k-CH
o -O-C
OC.,
568
Using various monomer to initiator ratios, poly{4-[[[2'-[[(4"methoxybenzoyl) oxy]methylene]-4'-[(4"methoxybenzoyl) oxy] phenyl]oxy]carbonyl]-l,3-cyclopentylenevinylene} and poly{4-[[[2'-[[(4"methoxybenzoyl) oxy]methylene]-5'-[(4"methoxybenzoyl) oxy] phenyl]oxy]carbonyl]-l,3-cyclopentylenevinylene were obtained in almost quantitative yields (Table 9.23). Table 9.23 Polymerization of 5-[[[2'-[[(4"-methoxybenzoyl)oxy]methylene]-4'-[(4"methoxybenzoyl) oxy] phenyl]oxy]carbonyl]norbom-2-ene (M l) and 5-[[[2'-[[(4"methoxy- benzoyl)oxy]methylene]-5'-[(4"- methoxy- benzoyl)oxy]phenyl] oxy] carbonyl]norbom-2-ene (M2) with Mo(=CHMe2Ph)(=NAr)(O'Bu)2 (Ar=-2,6-Cd-13-'Pr2) (1)~ Monomer
[M]J[I],
Time, hr
Yield~ %
MI
MJM,
Ml Ml M2 M2
30.2 50.7 51.2 158.6
2.5 2.5 2.5 2.0
95 97 96 92
15198 21235 20528 89008
1.20
1.14 1.15 1.20
'Data from reference97
Both polymers were amorphous. Tg of poly{4-[[[2'-[[(4"-methoxybenzoyl) oxy]methylene]-5'-[(4"- methoxybenzoyl) oxy] phenyl]oxy]carbonyl]-l,3cyclopentylenevinylene} was slightly higher than that of poly{4-[[[2'-[[(4"metho xybenzoyl) oxy ]methylene ]-4'-[ (4"methoxybenzoyl)oxy] phenyl] oxy] carbonyl ]- 1,3-cyclopentylenevin-ylene Polymerization of norbornene monomers containing a pnitrostilbene moiety as the mesogenic group in the presence of RuCI2(Cy3P)(=CHPh) initiator in CHECI2 at room temperature has been performed by Grubbs and coworkers 98 (Eq. 9.71).
c~,O OR
=
Ru(C H P h)CI2(C Y3P)2 0H2012 ; RT
~
(9.71) I
OR
569
where
(CH2)m0--{~'--/~
Polymers with narrow polydispersities between 1.08 and 1.11 and controlled molecular weights in 90-99~ yield have been obtained. The dependence of the flexible spacer length and the DP at varying monomerto-initiator ([M]/[I]) ratios have been examined (Table 9.24). Table 9.24 Polymerization of norbomene monomers (M-n) containing p-nitrostilbene moiety as the mesogenic group with RuCI2(Cy3P)(=CHPh) initiator m CHzCIzat room temperature' M-n
[M]/[I]
M{I
PDI
M-6
25 25 25 25 5 10 25 50 100
13 400 13 000 22 000 20 800 7 300 9 800 13 000 18 000 23 200
1.08
M-8
M-10 M-12 M-8 M-8 M-8 M-8 M-8
1.08 1.11 1.10 1.11 1.09 1.08 1.07 1.08
'Data from referencea The relatively rigid polynorbornene displayed enantiotropic nematic mesomorphism with glass transitions from 44~ to 31 ~ and isotropization temperatures between 108~ and 121 ~ Interestingly, a diblock copolymer containing a 11 mixture of the polynorbornene and polybutadiene exhibited a smectic A mesophase, demonstrating the dominance of the polybutadiene backbone over that of polynorbomene. norbornene containing alkoxy-substituted triphenylene mesogenic groups has been polymerized with RuCIz(Cy3PX=CHPh) initiator at room temperature in CHzCIz to the corresponding substituted polynorbornene 99 (Eq. 9.72).
570
Ru(CHPh)CI2(CY3P)2
,.c.O
.
.
.
.
I
OR'
CH2012 ;
(9.72)
RT !
OR'
where
O(CH2)12-
RO R
t
_.
RO
OR
RO/
\ OR
White solid polymers with narrow polydispersities between 1.09 and 1.17 have been obtained. All polynorbornenes containing a 2,3,6,7,19pentakis(decyloxy)triphenylene-based mesogenic unit exhibited enantiotropic discotic hexagonal mesophases, while the pentoxy analogs did not display liquid crystalline behavior. Polymerization of 5-(2,4,6-tdbromophenoxycarbonyl)norbom-2-ene has been effected in the presence of the ternary tungsten carbene catalyst Ph(EtO)C=W(CO)5/TiCIdPh3P as initiator ~~176 (Eq. 9.73).
(MeO)PhC=V~CO)5/~CIdPh3P ,
--O o
Br
(9.73)
~
c2~ch, t-- 7ooc \ C=O
8/
/
Br~]
0
"Br
Br
Poly(4-(2,4,6-tdbromophenoxycarbonyl)-l,3-cyclopentylenevinylene) was obtained in 64% yield working in dichloroethane, at molar ratios monomer to catalyst of 2000 and at a temperature of 70~ for 17 hours. Polymerization of norbomene-5-carboxylate ended polybutadiene macromonomer has been conducted in the presence of molybdenum
571 initiator Mo(=CH'Bu)(=NAr)(O'Bu)2 polynorbornene I~ (Eq. 9.74). 13
to
give polybutadiene
grafted
(9.r
m~p,
2g<-
Provided the vinyl content of the macromonomer is low, as well as its molar mass, the ring-opening polymerization occurs under controlled conditions and almost to complete conversion with the above mentioned molybdenum carbene complex. Ring-opening polymerization of norbomene-5-carboxylate ended polystyrene with molybdenum ~ene catalyst Mo(=CH'Bu)(=NAr)(OC(CH3)(CF3hh occurred quantitatively to the corresponding polymacromonomer 82 (Eq. 9.7 5). p,t,ol
.,.,..-
o,C-
o:C-
(9.75)
Copolymerization of this macromonomer with cyclooctene has also been effected with the aim of obtaining graft copolymers with well-defined structures and properties. 5,6-Dicarboalkoxynorborn-2-ene. Numerous 5,6-dicarboalkoxy- norborn2-ene monomers have been polymerized with classical Mo-, W-, and Rebased catalysts, platinum metal group catalysts or well-defined molybdenum and tungsten carbene complexes. Poly(4,5-dicarboalkoxy- 1,3cyclopentylenevinylene)s have been readily prepared from various monomers, under these conditions (Eq. 9.76).
C~C000R OR
m
~ ROOC COOR
(9.76)
572 where R is methyl, ethyl, propyl, butyl, heptyl, dodecyl and higher alkyl groups. 89 Polymers with different molecular weights and varying T s have been obtained depending essentially on the monomer, catalyst and reaction parameters. It was readily observed that exo, exo-, endo, endo-, and endo, exo-monomers display a totally different reactivity and optimum catalysts have to be found for each steric configuration of the monomer. Thus, while exo, endo-5,6-dicarbomethoxynorbom-2-ene reacts with the classical W- and Mo-based catalysts and platinum metal group catalysts, endo, endo- and exo, exo-isomers react with well-defined molybdenum and tungsten carbene complexes. Similarly, exo, endo-5,6-dicarboethoxy-, dicarbopropyloxy-, dicarbobutyloxy- and dicarboheptyloxynorborn-2-ene react in the presence of platinum metal group catalysts in substantial yields, depending on the monomer (Table 9.25). Table 9.25 Polymerization of exo, endo-5 ,6-dicarboalkoxynorbom-2-enes [5,6-NB(COORh] with the ruthenium catalyst RuCIs.3H20 ~
Monomer
Yield, %
R = ethyl R = propyl R = butyl R = heptyl
48 68 43.5 9.2
M,, ~mol
T~ ~
2.3x106 1.27x106
-35 0 -26 -85
'Data from referenceS9 Of a special interest is the reaction of 5,6-dicarbododecyloxynorborn-2-ene giving rise to a long side-chain branched polymer in the presence of the RuCI3 catalyst 1o2 (Eq. 9.77).
n
C(:~121~ 12H25
RuCl3 m
~
(9.77)
H~C~2OOC COOC~2H~
Highly fluorinated alkyl groups can be incorporated as pendant groups into polyalkenamers by means of 5,6-dicarboalkoxy functionalities of norbornene. Thus, fluorinated exo, exo-5,6-dicarboheptyloxynorborn-2-
573 ene reacts with ruthenium chloride catalyst to form fluorinated poly(4,5dicarboheptyloxy-l,3-cyclopentylenevinylene), bearing the fluorinated alkyls as laterally attached pendant groups ~~ (Eq. 9.77a).
RuC~
(9.77a) F(F2C)sH2CO:X~ CCXX:;H2(CF2)sF
2-Norbomene-5,6-dicarboxylates that contain acetal-protected sugars, e.g., bis(1,23,4-di-O-isopropylidene-ct-D-galactopyranos-6-O-yl)2norobmene-trans-5,6-dicarboxylate, were reacted in toluene using Mo(=CH'Bu)(=NAr)(O'Buh (Ar=-2,6-diisopropylphenyl) as initiator to form in high yield (99~ ring-opened homopolymers92 (Eq. 9.78).
n
/~
COOR
[Mo].~
~
COOR
(9.78)
ROOC
1
COOR
where I
O
CH 2 I
R I
----J 0
o~ \
These homopolymers showed narrow molecular weight distributions (PDI = 1.21-1.25) and a molecular weight dependent on the number of monomers employed. Di-, tri-, and tetrablock copolymers containing bis(1,2:3,4-di-Oisopropylidene-ot-D-galactopyranos-6-O-yl) 2-norobrn-ene-trans-5,6dicarboxylat e, methyltetracyclododecene, or trims- 5,6bis(((trimethylsilyl)oxy)methyl)norborn-2-ene were also prepared and found to have low polydispersities. The cyclic acetal could be removed using CF3CO2H/H20 (9/1 v/v, 15 min, 22~ to afford the corresponding watersoluble polymer containing the parent sugar. Synthesis of side-chain liquid crystalline polymers bearing two mesogenic moieties per repeat unit in the polymer chain has been performed
574 by Stelzer and coworkers ~~ by ring-opening metathesis polymerization of norbom- 5-erie-2,3 dicarboxylates under the action of the molybdenum carbene complex Mo(=CH'Bu)(=NArXO'Bu)2 (NAr=-2,6-diisopropylaniline) (Eq. 9.79).
exo, endo-bis[ (4' cyanobi phenyl-4-yl) oxy-n-al kyl ]
n
~
COO(CI'I~mR COO(CI'I2)m R
[Mo]..= "-
~
[ R(H2"C)mOOC
(9.79) COO(CH2)mR
where
R= - - - - O ~ C N
A full series of poly(exo, endo-bis[(4"cyanobiphenyl-4-yl)oxy-n-alkyl] norborn-5-ene-2,3-dicarboxylates), poly(M-m) (m = 2-12) has been synthesized in high yields and the products were characterized by IR, NMR, GPC, DSC and optical polarizing microscopy. The IR and NMR determinations evidenced that the polymerization of this monomer under the above conditions proceeded by ring-opening. Interestingly, at short reaction time, the polymers exhibited a monomodal distribution of the molecular weight in GPC whereas at longer reaction time a bimodal distribution was observed, the peak with the higher molecular weight corresponding exactly two times higher than the other peak indicating a doubling of the molecular weight by a coupling reaction. This "doubling effect" seems to be enhanced through the low activity of the initiator used, with the faster fluorinated analog of this initiator a similar doubling was not observed. The relevant data on the thermal behavior of poly(exo, endobis[(4'eyanobiphenyl-4-yl)oxy-n-alkyl] norbom-5-ene-2,3-diearboxylates (poly(M-m)) are given in Table 9.25a. As Table shows, a strong decrease of the glass transition temperature, T s, with increasing spacer length, m, was found. T s changed in an exponential manner within the range from about 90~ to 20~ by using spacers with lengths of 2 to 12 methylene units. A plausible reason for this was thought to be the dilution effect leading to a decreased density caused by the spacers.
575 Table 9.25a Phase transitions in ~ (corresponding All in Jxg"~) of poly(M-m) prepared with the Mo(C~Bu)(NAr)(O'Bu)~ catalyst' Pol~M-m)
2nd Heatin8
1st Coolinff
M-2 M-3 M-4 M-5 M-6 M-7 M-8 M-9 M-10 M-I1 M-12
g95.4n I 15.1(1.9)i g80.8n107.3(l.7)i g62.4n 114.0(1.8)i g56.7n109.5(2, l)i g52.7n I 18.4(2.2)i g46.5n I 12.9(2. l)i g39.0sA114.8(5.4)i g30.9sA116.3(4.8)i g27.2sA 114.9(5.9)i g25.7sA 118.0(7.2)i g24.9sA 116.1 (7.2)i
i 109. l(-2.0)n88.8g i104.2(-l.8)n77.9g i lll.4(-2.0)n60.4g i108.0(-1.5)n56, lg i116.3(-3.2)n48.3g i l l l.4(-2.2)n42.5g i110.8(-5.4)sA35.9g i111.4(-4.6)sA27.9g i l I 1.5(-6.8)sA29.0g il 13.7(-7. l)sA20.6g i I 13.5(-7.7)sA20.8g
'Data from reference I~ bk = crystalline, g = glassy, n = nematic, SA= smectJc, l = isotropic Furthermore, all polymers had endothermic transitions that were in the range from 107~ to 118~ as a function of the spacer length, m, indicating thus liquid crystalline to isotropic phase transitions. Significantly, polymers having m = 2-7 showed a single nematic phase, the others exhibited a smectic phase. This fact evidenced that the phase behavior of the polymers corresponded to that already known for the monomers but liquid crystalline phases were now thermodynamically stable due to the suppressed crystallization achieved through polymerization. An exception was, however, the polymer M-7 which had only a nematic phase whereas the corresponding monomer had both a nematic and a smectic phase. A similar behavior of this series of polymers has been seen in the changes of enthalpy, AH~, which are also listed in Table 9.25a. Thus, going from the polymer M-7 to M-8, a significant increase in enthalpy changes was observed. While nematic polymers showed an enthalpy change of about 2 Jxg ~, for smectic to isotropic transitions these polymers had values of enthalpy change up to 8 Jxg "l. Additionally, this phase behavior was also observed by optical polarizing microscopy. For instance, the polymer M-6 had a marbled nematic texture while the polymer M-11 showed a fan-like smectic texture.
576 Significantly, if compared the isotropization temperature of these polymers with those of monosubstituted analogs, a substantial increase in their values due to disubstitution of the monomer unit is obvious. This increase indicated a much higher stability of the liquid crystalline phase of the disubstituted polymers and, therefore, a higher state of order of the liquid crystalline phase. It was concluded that the ratio of the number of mesogenic groups to the number of atoms in the main chain was a limiting factor for transition phases of the polymer, the lower values of this ratio favoring a higher stability of the liquid crystalline phase and consequently, a higher isotropization temperature. With increasing spacer length all polymers exhibited smeetic phases while for monosubstituted polynorbornene only nematic phases for all spacer length were found. Furthermore, a clear odd-even effect of the isotropization temperatures was observed when spacer length was varied, in contrast to the monosubstituted analogs. The odd-even effect for the nematic polymers M-2 to M-7 was much stronger than that of the smectic polymers M-8 to M-12. This effect was also attributed to a different ratio of mesogens to atoms in the main chain as compared to the monosubstituted mesogenic polynorbomene. A number of phenothiazine-based redox-active polymers were prepared from the diphenothiazin-10-yl ethyl endo, exo-5,6-dicarboxylate derivative of norborn-2-ene by ring-opening polymerization with molybdenum initiators Mo(=CH'BuX=NArXO'Bu)2 (At=-2,6diisopropylphenyl)t~ (Eq. 9.80).
n
COOCH2CH2R [Mo] COOCH2CH2R
=
~
(9.80)
RH2CH2COOC COOCI-I~CI'I2R
where R =
Moreover, polymers and block copolymers containing specific functional end groups (e.g. pyridine, pyrene, fluorobenzene, dimethyl~filine) for
577 covalent attachment to surfaces have been prepared and characterized from the diphenothiazin-10-yl ethyl endo,exo-5,6-dicarboxylate derivative of norbom-2-ene. Such a functionalized polymer allows a controlled attachment of redox-active components on the electrode surfaces in order to modify its electrochemical properties. Bis(trimethylsilyl)-4,5-norbomenedicarboxylate has been polymerized with the living molybdenum carbene initiator Mo(=CHR)(=NAr)(O'Bu)2 (At = 2,6-C,H3-'Pr2) and readily hydrolyzed to the acid upon exposure to water t~ (Eq. 9.81).
=
=-
(9.81)
CO--Me3
The resulting deprotected poly(carboxylic acid) was water soluble. Using endo-cis-endo-hexacyclo[ 10.2.1.13.10. I s'8.02"1t.04'9]heptadeca-6,13-diene as the cross-linking agent, star polymers have been prepared from bis(trimethylsilyl)-4,5-norbornenedicarboxylate in the presence of the above molybdenum initiator (Eq. 9.82).
ea.a2) c,zx~t,~
Although the high molecular weight of the products corresponded to the star polymer, it was not possible to determine the number of arms per star molecule from the GPC data for poly(bis(trimethylsilyl)-4,5norbomenedic, arboxylate). Living diblock copolymers of bis(trimethylsilyl)4,5-norbomenedicarboxylate with norbomene or 4,5bis(methoxymethyl)norbomene were also prepared with the molybdenum initiator, converted to star copolymers using the above cross-linking agent,
578
endo-cis-endo-hexacyclo [ 10.2. I. 13,10.15,s.02,.11.04,9]heptadeca_6,13-diene, and after hydrolysis of the trimethylsilyl groups in water, amphiphilic star copolymers with poly(4,5-dicarboxynorbomene) as the hydrophilic block and polynorbornene or poly(4,5-bis(methoxymethyl)norbomene) as the hydrophobic block have been produced. Polystyrene macromonomers derived from exo, endo-5,6dicarboalkoxynorborn-2-ene have been polymerized with molybdenum initiators, Mo(=CH'Bu)(=NAr)(O'Bu)~ (Ar=-2,6-diisopropylphenyl), to form comb graft copolymers with polystyryl grafts having average degrees of polymerization (DPs) of 4, 7, and 9 (Eq. 9.83).
~,oo-~-saJ o.~ c ~
The graft copolymers thus obtained exhibited single mode molecular weight distributions and narrow polydispersities. ~06 Norbornene monomers functionalized with various monodendrons have been polymerized with well-defined ruthenium based initiators in order to manufacture supramoleeular systems. For this purpose, the monodendron monomer exo, exo-5,6-bis[G2]norbornenedicarboxylate, containing the second generation monodendron G2(OH), based on the conformationally flexible ABe mesogenic monomer, 13-hydroxy-l-(4-hydroxyphenyl)-2-(4hydroxy-4"-p-terphenylyl)trid~e building block, has been polymerized in the presence of RuCIz(=CHPh)(PCy3)z (Cy = cyclohexyl) in methylene chloride to obtain poly(bis[G2]norbornene-5,6-decarboxylate) ~~ (Eq. 9.84).
. ~ /COO[G2] [Ru] ..~ ~ n ~~:::COO[G2] 22~ 12-1101~ [G2]O0c
COOIG2]
where the second generation monodendron Gz[OH] is represented by:
(9.84)
579
~-~(o~
=
H3C~o
OH
Synthesis of such products will allow studying the effect of molecular weight on the thermal and solution behavior of side-chain dendritic polymers. The results obtained with the monodendron monomer exo, exo.. 5,6-bis[G2]norbornenedicarboxylate indicate that in spite of the formidable size of these dendrimers, they can be readily polymerized. However, very high molecular weight polymers obtained from this class of monomers remain a challenge, since at high DP's dif~sion of the dendrimeric monomer to the active chain limits the rate of polymerization. 5-Norborn-2-enyl esters.Hepworth 2~ first reported the ring-opening polymerization of e n d o / e x o mixtures of 5-acetoxynorbom-2-ene to poly(4acetoxy-1,3-cyclopentylenevinylene) using WCI6/Et3AI2CI3 (Eq 9.85).
n
~~.
WCIslEt3AI2CI3 "-
OCOCH 3
(9.85)
OCOCH3
The reaction with various catalysts has been subsequently reported by several other authors. 32"a3'~~ Interesting work on the polymerization of 5-acetox~orbornene (mixture of endo and e x o isomers) and its copolymerization with cyclopentene and 5-cyanonorbornene was carried out by Thorn-Csanyi and coworkers ~~ using the three-component catalytic system consisting of tungsten oxytetrachloride, methylaluminoxane and tetraisobutyldialuminoxane. Noteworthy, these authors found that the incorporation of acetoxycyclopentenyl units in the polymer chain was not
580 stereoselective. Microstructure examination by ~H and t3C M R spectroscopy of the polymer thus obtained indicated a cis/trans double bond ratio of 80/20 and GPC analyses revealed very high molecular mass (> 800000). It is very significant that it was possible to control the molecular weight of the polymer with ot-olefins, e.g. using l-pentene and to detect the presence of oligomers by GPC under these conditions. Related studies on the polymerization of endo-5-acetoxynorbomene under the action of conventional Re-, W-, Mo and Ru-based metathesis catalysts published more recently Ivin et aL ~o With these catalysts, they obtained polymers with cis double bond contents ranging from 76% to 16%. Examination of t3C NMR spectra of the products prepared allowed a complete assignment of the corresponding lines to be made. Interestingly, no significant head-tail bias was observed and no splitting due to tacticity was detected. Tungsten and molybdenum carbene complexes proved to be the most active and stereoselective in this reaction. Thus, the carbene complex W(=CH'Bu)CI(CH2tBuXOAr)2[O(CHMe2)2] induced polymerization of (+_)endo-5-acetoxynorbom-2-ene in high yield after 10 min at 25~ TM On using Mo(=CHCMe2PhX=NAr)(OtBuh as a catalyst, (-)-endo-5acetoxynorbom-2-ene gives 30% cis polymer which is nearly atactic with respect to cis- and trans-centered ring diads while, when initiated by Mo(=CHCMe2PhX=NAr)(OCMe(CF3)2)2, the polymer has a much higher cis content (87%) and the cis-centered diads are biased towards isotactic. ~2 Interestingly, the 87% cis polymer has nearly twice the specific rotation of the 30% cis polymer. Optically active polymers have also been obtained from the enantiomers of endo-5-butyroxynorbom-2-ene and endo-5benzoxynorbom-2-ene by ring-opening metathesis polymerization with the molybdenum carbene initiator Mo(=CH'Bu)(=NAr)(OR)2 (R = 'Bu or CMe(CF3)2) in chlorobenzene and with K2[RuCIs(H20)] in aqueous solvents tt3 (Eq. 9.86-9.87).
[Mo] [~]~
n OCOC3~
(9.86) \ OCOC3H~
581
n
j~
[Mo]
[Ru]>
OCO06H5
(9.87)
\ OCOCeH5
Polymers obtained with the molybdenum initiators showed a higher specific rotation compared to those obtained with the ruthenium catalyst. The molybdenum-catalyzed polymers were atactic and contained about 30~ cis double bonds; they had a lower average molar mass and a narrower distribution. The ruthenium-catalyzed polymers contained ca. 2 0 0 cis double bonds and were biased toward tactic with trans vinylenes occurring more in meso diads (60~ and cis vinylenes occurring in racemic diads. Polymerization of norbomene-5-methyl acrylate has been effected by Michelotti 3~ with IrCl3 catalyst to poly(norbornene-5-methyl acrylate)
(Eq. 9.88). n
CH20COC C 89
-- -.=~~ ~~:-
(9.88)
C 89189
The side-arm unsaturation of poly(norbomene-5-methyl acrylate) could be cross-linked with conventional cross-linking agents. Polymerization of exo, exo- and endo, endo-norbomene-2,3-dicetate occurred readily in the presence of the molybdenum initiators Mo(=CHRX=NArXO'Bu~h to poly(norbomene-2,3-diacetate) S3'~'4''ts (Eq. 9.89).
n~
OCOCH3 --,,.OCOCH3
[Mo]
(9.89)
H3COCd OCOCH3
The polymer of exo, exo-norbomene-2,3-diacetate is a white powder that can be cast from toluene as a flexible transparent film. On heating at 300~
582 the film becomes red-black and insoluble and acetic acid is eliminated (Eq.9.90). T = 3(X)*C H3COCO
+ 2nCH3COOH (9.90)
OCOCH 3
Hydrolysis of poly(norbomene-2,3-diacetate) gives quantitatively the corresponding polydiol, poly(norbomene-2,3-diol) (Eq. 9.91). NaOMe
(9.91)
MeOHEHF H3 0 0 0 0
OCOCH 3
Since hydroxyl groups are incompatible with the molybdenum initiator, this polymer cannot be made directly from the corresponding monomer. Poly(norbomene-2,3-diol) is insoluble in standard solvents (THF, chloroform, aromatics, methanol, or water), but it dissolves completely in acidic chloroform (CF3COOH/CDCI3). The norbomene derivative, exo, syn-2,7-norbomenediol diacetate, was polymerized quantitatively with Mo(=CH'Bu)(=NAr)(O'Bu)2 to yield poly(2,7-norbornene diacetate) with a PDI = 1.09 in THF and 2.17 in chlorobenzene 53 (Eq. 9.92).
I~OCOCH3
n~OCOCH3
M0 (C HtBu)(NAt)(OtBu)?=_ .-
~
OCOCH3
(9.92)
ococ Poly(2,7-norbornenediol diacetate) can be cast from toluene to give flexible, transparent thin films. Its tensile strength at the breaking point is 420 kg/cm 2. DSC analysis indicated that it is amorphous with a T 8 at 110~ and that it is stable up to 300~ Pyrolysis at this temperature gives probably a cross-conjugated polymer with loss of acetic acid (Eq. 9.93).
583
OCOCH3
T = 300"C ~9
OCOCH3
"=[='N A
/"~
+ 2n CH3COOH
"LT"'
(9.93)
Hydrolysis of poly(2,7-norbornenediol diacetate) yields the corresponding poly(2,7-norbomenediol) (Eq. 9.94).
NaOie
3
=
OH|. _=..
,,
MeOHffHF OCOCH3
(9.94)
OH
This polymer also is soluble in aqueous acidic media (CF3COOH/H20). Polymerization of exo, cis-O,O'-isopropylidene-2,3-norbornenediol in the presence of Mo(=CH'BuX=NArXOrBu)2 occurred readily in Tiff to give poly(cis-O,O'-isopropylidene-2,3-norbomenediol) s3 (Eq. 9.95).
Mo(CHtSu)(NAr)(Otauh
(9.95)
This polymer contained 60% trans configuration, had a Ts of I08~ and decomposed at 300~ Hydrolysis yielded the polydiol obtained by hydrolysis of poly(norbomene-2,3-diac~ate) mentioned earlier 5,6-Norborn-2-endiyl esters. Ring-opening metathesis polymerization of bicyclo[2 2 l]hept-5-ene-2,3-bis(mcthyl carbonate) has been performed by Schimetta and Stelzer54'55 with the well-defined molybdenum carbene complex Mo(=CH~Bu)(=NAr)(O'Bu)2 (Eq 996)
,,,~OCOOCH~ n ~~..OCOOCH3
Mo(CH~u)(NAr)(OtSuh '
=
O Oc C (~ / ~ O O ~
H3C
(9.96)
I'h
584 On employing different initiator concentrations, ring-opened polymers of various molecular weights in high yields have been produced. (Table 9.26). Table 9.26 Polymerization of exo. exo-bicyclo[2.2.1 ]hept-5-ene-2,3-bis(methyl carbonate) (M) with the molybdenum earbene complex Mo(CHtBu)(NAr)(O'Bu)z(1) ~ [M]:[I] b
Yield %
MW
M,,~,
100:1 200:1
94 93
80600 152000
1.08
1.09
*Data from reference~; bMolecular ratao of monomer and initiator; 'Calibrated against polystyrene standard. Examination of the polymer microstructure by IR and NMR spectroscopy indicated a prevailingly trans configuration of the double bonds in the chain. The narrow molecular weight distribution (1.08-1.09) and the evolution of molecular mass pointed out a living process under the influence of the molybdenum carbene complex used as initiator. Thermal behavior of poly(bicyclo[2.2.1]hept-5-ene-2,3-bis(methyl carbonate)) showed a partial elimination of methyl carbonate groups at high temperatures (270~ to form poly(cyclopentadienylenevinylene), whereas a glass transition temperature at 96.0~ was observed (Eq. 9.97). T = 270~
H3COOCO
(9.97)
OCOOC H3
IK spectroscopy of heated poly(bicyclo[2.2.1]hept-5-ene-2,3-bis(methyl carbonate)) (350~ evidenced a small amount of functional groups remaining in the dark and red insoluble film. Due to the insolubility often found with the conjugated polymers, no NMR measurements could be carried out for the heated product. Norbornene with anhydride groups. Polymerization of bicyclo[2.2, l]hept-5-ene-2,3-dicarboxylic anhydride, a mixture of both e x o and e n d o isomers, was initially carried out by Ueshima, 4~ Kurosawa 5~ and
585 Matsumoto s~ in the presence of the classical WCl6-based catalysts. On using WCIdMe3AI2CI3 as a catalyst, MatsumotoS5 prepared poly(bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride) in low yield (10",6) (Eq. 9.98).
n
/~
,.CO~
CO/0
~Io/Me3AhCI3
(9.98)
n = lo% OC\o/CO
The effect of isomeric composition on the polymerization process was addressed in the later work of Castner and Calderon ~6 when it was reported that no polymer was obtained from a 99% pure sample of the e n d o isomer with a WCl6-based catalyst. Conversely, when mixtures of e n d o and exo isomers were employed, they found that the e x o isomer was preferentially polymerized, although some endo units were also incorporated into the polymer. These findings were more recently confirmed by Watkins et al. ~ when they found that the 98% pure e n d o isomer was polymerized to only a low conversion (3.7%) by the WCl6fBuPhenol~t2AICl catalyst, whereas a pure sample of the e x o isomer was polymerized to high yields by the WCI6fBuPhenol catalyst activated by both EtzAICI and EhAI. Interestingly, a 45:55 e n d o : e x o mixture of bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride gave a 66% yield of polymer which was higher than the amount of the e x o isomer present, indicating that some incorporation of the endo isomer must have occurred. The polymer obtained from the e x o isomer was found to be insoluble in common organic solvents, whilst its glass transition temperature (321~ as determined by DSC, was in good agreement with the value reported earlier by Castner and Calderon. ram6A weak transition was also observed at a temperature of approximately 135~ the origin of which was unclear. A possible explanation was the presence of a small amount of residual isomer (Mp = 147~ although it was possible that the acidic catalyst could have initiated a process of ring-opening polymerization of the cyclic anhydride by a cationic mechanism. However, e n d o - i s o m e r was found to react slowly when tungsten-cyclopentylidene initiator W[=C(CH2)3CH2](OCHz'Bu)zBrz in CDzCIz at 25~ was employed. ~s
586 Ring-opening polymerization of the exo-isomer and esterification in one operation has been also effected using RuCI3 or OsCl3 at 70~ as catalyst ~9. Attempts to polymerize endo-3a,4,7,7a-tetrahydro-4,7-methano1,3-benzodioxol-2-one with WCI6/Me4Sn by Feast and Harper ~2~ failed but using more active tolerant ROMP catalysts it was possible that this monomer to be reacted to the corresponding ring-opened polymer (Eq.9.99).
n
/••"0--
CO
= ~
(9.99) o,o CO
This monomer, however, has been readily copolymerized with norbornene with WCIdMe4Sn in chlorobenzene at room temperature. Polymerization of endo-3a,7a-dichloro-3a,4,7,7a-tetrahydro-4,7methano-l,3-benzodioxol-2-one was carried out using WCIdMe4Sn (mole ratio WCldMe4Sn/monomer of 1:2:242) in chlorobenzene at 70~ to give poly(6,8-(l,5-dichloro-2,4-dioxa-3-keto)bicyclo[3.3.0]octylene vinylene) in 35% yield 12~(Eq. 9.100).
n
i'o,
.O--C O
WCl6/Me4Sn ~ rl = 35%
---r-~ ~ / - ~ _ c,
no
(9.100)
CO "['he product was characterized by elememal analysis, []~ t3C NMR and DEPT (Distortionless F.r~anccment by Po|adzadon Transfer) spectra which confirmed to be produced by ring-opening polymerization rather than vinyl polymerization. Furthermore, the data obtained suggested that the polymer was assembled in an essentially random manner. Analogously, endo,endo-3a,9a-dichloro-3a,4,4a,5,8,9a-octahydro4,9 5,8-dimethanonaphta[2,3-d]- 1,3-dioxol-2-one was ring-opened polymerized using WCIdMe4Sn (mole ratio WCldMe4Sn/monomer of 1:2:250) in chlorobenzene at room temperature to give poly(9,11-(2,6dichloro-3,5-dioxa-4-keto)tetracyclo[ 5.5.1.02"6.08'~2]tridecylene vinylene) in
587
49% yield ~2~(Eq. 9.101). WCls/Me4Sn n
q = 49%
0
(9.1oI)
0
The polymer structure was examined by IR and ~3C NMR spectroscopy and further characterized by CPC and elemental analysis. Significantly, the fine structure observed in the ~3C NMR spectrum of the polymer indicated the complexity of its microstructure and no direct comparison could be made with the ~3C NMR spectrum of the related polynorbornene. However, data recorded on the microstructure appeared to be consistent with a random rather than a highly stereoregular distribution. Norbornadiene derivatives. Ring-opening polymerization of 7-tertbutoxynorbornadiene has been effected with several classical catalysts to give high-cis tert-butoxy substituted polynorbornadiene ~z~(Eq. 9.102). (C H3)3 n
MoC Is/Me4Sn/Et20
osch
m
O C (C H3)3 ----~ . _ . . . . .,L .
/==~ _.n
(9.102)
It is interesting to note that there was no differentiation between the ease of syn and anti attack using MoCIs/Me4Sn~tzO as a catalyst. A similar result has been obtained with the well-defined Mo(=CHMe2Ph)(=NAr)(OCMe(CF3h)2 (Ar=-2,6-'Pr2-C6H3) as initiator. ~ However, on using OsCl3 as a catalyst, a polymer with 30% syn units has been produced. This trend was also observed to a lesser extent in the polymerization of 7-acetoxynorbornadiene using the above catalytic systems ~2~(Eq. 9.103).
n
~
OCH3
MoCls/Me4Sn/Et20 .. m osci 3
- ~, . ,
OCOCH3 ,..= .,L ./.-.,.~. .
(9.103)
588 2,3-Dicarbomethoxynorbomadiene has been polymerized with various classical or well-defined metathesis catalysts to give poly(4,5dicarbomethoxy- 1,3-cyclopentenylenevinylene) ~.~z~(Eq. 9.104).
n
/~
COOCH3
COOCH3
.
MoClyMe4Sn
(9.104)
Mo(C HC Mez R'X NArX OR :)2
H3C(:X:X:
COOCH3
The structures of the polymers prepared with classical catalysts were rarely regular. By contrast, polymerization of 2,3-dic,arbomethoxynorbomadiene with well-defined initiators of the type Mo(=CHCMe2R')(=NAr)(OR)2 (R'=Me, Ph; Ar=2,6-'Pr2-C6H3) gave highly tactic (>90%), high trans polymers when OR=OtBu and high cis polymers with a tactic bias of-75% ((Om),=0.75) when OR=OCMe(CF3h. TM Molybdenum initiators that contain a racemic biphenolate ligand polymerized 2,3dicarbomethoxynorbomadiene to polymers that are >99% cis and >99~ tactic. ~25 The all-cis polymers of the homologous series of 2,3dicarboalkoxynorbomadienes (R = Me, Et, 'Pr, 'Bu) have been obtained with M(=CHCMe2Ph)(=NAr)(OCMe(CF3)2h as the initiator. ~26 They have an isotactic bias ( o r 0.78, 0.84, 0.81, 0.97, respectively) as evaluated from maCNMR spectra. Chiral 2,3-dicarboalkoxynorbomadienes have been polymerized with well-defined molybdenum ROMP initiators in order to determine the tacticity of the highly regular polymers prepared from enantiomerically pure monomers. ~27 To this end, 2,3 -(CO2R* )2norbomadiene (M), where R* = (lR,2S,5R)-(-)menthyl (1) or (R)-(-)pantalactonyl (II), reacted with Mo(=CHCMe2Ph)(=NAr)(O~Bu)2 (At=2,6 'Pr2-C6H3) (1) to yield high trans, highly tactic polymers and with Mo(=CHCMe2Ph)(=NAr)[OC(CF3)3]2 (2), Mo(=CHCMe2Ph)(=NAr ') [BIPH(tBu)4] (3) and Mo(=CHCMe2Ph)(NAr')[(+) BINO(SiMe2Ph)E](THF) (4) (Ar'=2,6-Me2C6H3) to yield high cis, highly tactic polymers (Eq. 9.105).
n
~J~
COOR*
[Mo]
~
(9.105)
COOR* R*OOC
COOR*
589 where O OR" =
or __011
l'"
I
II
The yields were generally high and polydispersities were relatively low for all polymers, but not as low as it is often obtained for polymers prepared by living ROMP using well-defined molybdenum initiators. Significantly, the cis polymers were found to be isotactic while the trans polymers syndiotactic (Table 9.27). Table 9.27. Polymerization of chiral 2,3-dicarboalkoxynorbomadienes (M-I and M-II) with molybdenum carbene complexes (l-1 to I-4)' M
Ib
S
I
1
Tol
II
1
CH2CI2
I
2
Tol
II
2
I
3
I1 I II
3 4 4
CH2C12 Tol
CH2C12 THF
CH2C12
Equiv
100 100 100 50 100 75 85 85
Yield % 97 78 97 95 92 93 91 91
M.
16300 21000 17700 7400 22800 19500 21300 28200
PDI
1.03 1.28 1.28 1.15 1.09 1.05 1.19 1.13 !
Tact-
Cis
%
icity
6 9 99 99 99 99 99 99
syn syn iso
iso iso iso iso iso
!
'Data from reference ~2~ hi Mo(=CHCMe~Ph)(=NAr)(O Bu)z, (Ar=2,6- Prz-Cffl3); 2" Mo(=CHCMe2Ph)(=NAr)(OC(CF3)3)2, (Ar=-2,6-'Prz-Cffl3); 3" Mo(=CHC Me~Ph)(=NAr') [BIPH(rBu)4], (Ar'=2,6-Me2C6H3); 4" Mo(=CHCMe2Ph)(=NAr') [(_)BINO(SiMe~Ph)z], (Ar'=2,6-MezCJ'13), As Table 9.27 shows, the monomer and solvent exhibited a minor influence on the molecular weight and polymer yield whereas the catalyst had a crucial effect on the cis/trans stereoconfiguration and the polymer tacticity.
590 Diels-Alder adducts of dimethylfulvene, diphenylfulvene and methylphenylfulvene with dimethyl acetylenedicarboxylate form the corresponding ring-opened polymers in the presence of MoCls/Me4Sn as a catalyst~2s (Eq. 9.106). R
II
R'
C~H 3
n
MoCIs/Me4Sn
H3
~
(9.106)
H3COOC
COOCH3
where R' and R" are Me or Ph groups. On working in chlorobenzene at 70 ~ and monomer (M) to catalyst ratios M:Mo:Sn of 100"1:2, the methylphenyl adduct gave poly(4,5-dicarbomethoxy-2-( 1phenylethylidene)-l,3-cyclopentenylenevinylene) in 20% yield and the diphenyl adduct gave poly(4,5-dicarbomethoxy-2-diphenylmethylene-l,3cyclopentenylenevinylene) in 46% yield. Norbornenebenzobisketals. Methyl norbornenebenzobisketal reacts quantitatively with titanacyclobutane Cpffi[CH2CH(CH3:hCH2] or tungsten-carbene W(=CH'Bu)(=NAr)(OtBu)2 (Ar=-2,6-'Pr2-Cd'I3) to polybenzobisketal which is hydrolyzed by soaking films or powders in 15% HCI to the corresponding polybenzoquinone ~29(Eq. 9.106a).
n MeO /:)Me
['1"I],[~-~ Me
15%HCI = ~
o
(9.10~)
OMe
Tautomerization of polybenzoquinone by dilute acid or better by treatment with base gives the polyhydroquinone which reoxidized may undergo further tautomerization to produce polyacetylene backbone polymers (Eq.9.106b).
(9.106b)
591 Such conjugated polymers should display high conductivities. Similar results have been obtained starting from methyl norbomenenaphthobisketal with both titanacyclobutanc Cp2Ti[CH2CH(CH3hCH2] and tungstencarbene W(=CH'Bu)(=NAr)(O'Bu)2 (Ar=2,6-'Pr2-C6H3) initiators~29 (Eq.9.106c). ROMP [TiI,[WI>
n
_
15% HCl
_
=
(9.106(:)
C~
Tautomerization of the polynaphthoquinonc, under the above conditions, and reoxidation will produce similar polyacetylene backbone polymers (Eq.9.106d).
w D ,
=
(9.1o~)
monomers. Ring-opening polymerization of bis(thiomethyl) derivative of exo, endo-5,6-dimethylnorbornene occurred Sulphur-containing
with the molybdenum initiator Mo(=CHCMe2Ph)(=NAr)(OtBu)2, (At=-2,6'Pr2-C6H3) to give the corresponding polymer of a low polydispersity (PDI < I. l 0) and Tg value of ca. 45~ (Eq. 9.107).
~
CI'I2-SC H3
CH2-SCH3
Mo(CHC MezPhXNArXOtBu)z
(9.1o7)
H3CS-H2C CH2-SCH3
Copolymers with methyltetracyclododecene were also prepared by Schrock and coworkers ~3~ and used to bind metals, e.g., Zn and Cd, in a dative fashion. Interesting results reported Schimetta and Stelzer~4 on the ringopening polymerization of a norbomcncdixanthate, exo, exo-
592 bicyclo[2.2.1 ]hept-5-ene-2,3-bis(S-methyl dithiocarbonate), using the molybdenum carbene initiator Mo(=CHtBu)(=NArXOtBu)2 (Ar=-2,6-'Pr2C6H3).This monomer was readily polymefized with different initiator concentrations to form in high yields poly(bicyclo[2.2.1]hept-5-ene-2,3bis(S-methyl dithiocarbonate) (Eq. 9.108).
s II
Mo(CHtBu) (NAr) (OtBu) 2 OC,-SQ-I 3
= CS_~ "/-'~~O'~~nn ~ H3
s It
s N
(9.108)
-~;H 3
The typical molecular weight distribution was larger for the thia analog (MJM,=1.3) than for the corresponding oxa analog (M,~,K=1.09). However, the molecular weighs increased linearly with the monomer concentration (Table 9.28). Table 9.28 Polymenzauon of exo, exo-bicyclo[2.2.1 ]hept-5-ene-2,3-bis(S-methyl dithiocarbonate) (M) using the molybdenum carbene initiator Mo(=CHtBu)(=NAr)(OtBu)z (I)~
[M][I]
Yield,%
Uw
MJM,
50:1 100-1 200:1
80
30000 60000 114000
1.3 1.4 1.4
90 93
'Data from reference~, bMolecular ratao of monomer and initiator, r against polystyrene standard. Spectroscopic measurements by IR and NMR methods of poly(bicyclo[2.2, l]hept-5-ene-2,3-bis(S-methyl dithiocarbonate) indicated a highly stereoregular polymer with entirely trans stereoeoniiguration of the double bond connections. Thermal elimination of S-methyl dithiocarbonates from poly(bicyclo[2.2.1 ]hept-5-ene-2,3-bis(S- methyl dithiocarbonate) to form poly(cyclopentadienylenevinylene) (Eq. 9.109)
593 n
H3CSS
=
~
(9.109)
SCH3 S
occurred at a lower temperature as compared with the methyl carbonate
analog. Though the accurate structural analysis of the final product poly(cyclopentadienylenevinylene) by NMR method was not carried out due to its insolubility, the polyconjugated structure was based on UV spectra available. Nitrogen-containing monomers. The development of well-defined alkylidene compounds that are both tolerant of functional groups and provide a living initiator for polymerization of strained cycloolefins has spawned further growth in the field of nitrogen-containing polymers. Studies by Perrot and N o v a k 9 o n the highly functionalized N-benzyl cyclobut-3-ene-l,2-dicarboxylic imide showed that this monomer readily polymerized under the influence of the Mo Schrock initiators Mo(=CHR')(=NAr)(OR '') (where Ar = 2,6-'Pr2C6H3 and R ' = R'' = C(CH3)3; R' = C(CH3)2Ph, R' ' = C(CF3hCH3 or R' = C(CH3)2Ph, R' ' = C(CH3h) to produce a highly functionalized polymer, consisting of an imide substituted 1,4-polybutadiene. It is noteworthy that, under these conditions, the polymerizations were quatitative regardless of the monomer:initiator ratio and monodisperse polymers with narrow molecular weight distributions could be prepared. Norbornene substituted with CH2NHR groups in the position 5 has been polymerized using various ROMP catalysts. Ring-opened polymers of substituted norbornene bearing the amino groups in the cyclopentylenevinylene repeat unit have been thus prepared (Eq. 9. 110). n
~7~
CH2 NHR
ROMP
.---
(9.110)
\
CH2NHR When R is H, Me, or 'Pr, appropriate catalytic systems are W(=CPh2)(CO)~tAICI2/O2 and W(CO)3(mesitylene)/EtAICl2/O2 in chlorobenzene at 25~ working with a large excess of cocatalyst (W/AI = 1/140). These polymers have 50% cis double bonds and can be rendered
594 soluble in water by quatemization of the amine groups. TM They can also be made more soluble if pent-l-ene is used as a chain transfer agent. The monomer with R = C6H4NHC6Hs has been used efficiently in copolymers with dicyclopentadiene to act as a built-in antioxidant. ~32 N-Substituted 5,6-bis(methylamino)norbomene has been polymerized with molybdenum initiators to give poly(5,6bis(methylamino)norbomene) ~: (Eq. 9.111).
H2NHR CH2NHR
[Mo] .~
~ RHNH2C
(9.111) CH2NHR
where R is C(CH3)3 or Si(CH3h. These amino-containing polymers have been used to complex Sn(IV), Sn(II) or Pb(II) for manufacture of semiconductor clusters of a predictable size. ~33 Norbornene derivatives bearing the amide group or N-substituted amides have been polymerized with W-based catalysts. 2a~3"3S For instance, 5-dimethylamidonorbom-2-ene reacted for 17 hr under the influence of WCIdEt3Al (1:2) and W(OPh)dEt3Al in chlorobenzene at 70~ using a molar ratio monomer:W of 200, to produce in high yield poly(4dimethylamido- 1,3-cyclopentylenevinylene) 33 (Eq. 9.112).
V h/Et l
W(OPh)ejEt3A/
n
(9.112) \
CON(CH3)2 Glycopolymers were prepared by ring-opening metathesis polymerization of a series of N-sugar-substituted norbomene-5-amides using the ruthenium carbene initiators~34(R3P)3CI2Ru=CHCH=CPh2(R = Ph or Cy) (Eq. 9.113). O
n ]~~NHgluRR'
[Ru] =
~
(9.113) \
NHgluRR'
595 where NHgluRR' =
OR RO'7~OR ~ i I ~ ~O H
and RR ' = H (NBEglu(H)4,-COCH3 (NBEglu(Ac),,-CH2Ph (NBEgluBn),, -SiEh (NBEglu(SiEh)4 and R = H and R ' = -CPh3 (NBEglu(Tr)). The ring-opening polymerization of 2-((• carboxamido)-2-deoxy-D-glucopyranose (NBEglu(H)4) and the protected sugar derivatives based on this monomer, 2-((• carboxamido)-2-deoxy- 1,3,4,6-tetra-O-acetylD-glucopyranose (NBEglu(Ac)4), 2-((_)-exo- 5-norbomene-2-carboxamido)-2-deoxy- 1,3,4,6tetra-O-benzyl-D- glucopyranose (NBEglu(Bnh), 2-((+_)-exo-5-norbomene2-carboxamido)-2-deoxy- 1,3,4,6-tetra-O-triethylsilylD-glucopyranose (NBEglu(SiEh)4) and 2-((• 6-O-trityl-D-glucopyranose (NBEglu(Tr)) to produce high molecular weight polymers bearing carbohydrate moieties has been investigated by Fraser and Grubbs TM using the above mentioned ruthenium carbene initiators (R3P)2CI2Ru=CHCH=CPhz (R = cyclohexyl or phenyl). Under these conditions, these authors observed a totally different reactivity of the series of norbomene derivatives, depending on the nature of pendant sugar group. The unprotected sugar monomer, NBEglu(H)4, did not undergo efficient ring-opening metathesis polymerization in the presence of either catalyst in any of the solvent systems examined (Table 9.29). Table 9.29 Polymerization of 2-((f)-exo-5-norbomene-2-carboxamido)2-deoxy-D-glucopyranose (NBEglu(H)4 with (R3PhCIzRu=CHCH--CPhz (R = cyclohexyl (Cy)or phenyl (Ph))~ |
Catalyst
Solvent
Temp. Time [MI'[E]:[I] ~ days Ph 40 2:1 MeOH/CHzCIz 160:0:1 1 Ph 50 50:0:1 4:1 HzO/CHzCIz 4 Cy 50 3:2 MeOI'FCHzCIz 55:0:1 2 Cy 6:1 HzO/CH2CIz 50 35:3:1 1 9Data from reference~; bM = monomer, E = emulsifier, I = initiator
Yield % 0 0 trace 99
596 The very low reactivity of this monomer was attributed to its poor solubility in all of the solvents compatible with the metathesis catalysts. In addition, the poly[NBEglu(H)4] product was also insoluble in these solvents systems and precipitated from the reaction mixture. This difficulty was overcome by using a different polymerization technique, namely, polymerization in the presence of ammonium halide salts as emulsifiers in an aqueous system. Reaction of NBEglu(H)4 in H20 containing dodecyltrimethylammonium bromide with the ruthenium carbene initiator, dissolved in a small amount of CHzCI2, resulted in polymer product in essentially quantitative yield. Of all the sugar monomers investigated, only the acetate-protected sugar monomer was efficiently polymerized by the less active (Ph3P)zCI2Ru=CHCH=CPhz catalyst (Table 9.30). Table 9.30 PolymerizaUon of 2-((+ )-exo-5-norbomene-2-carboxamido)2-deoxy- 1,3,4,6-tetra-O-ace~l-D-glue~yranose (NBEglu(Ac)4) with (R3P)zCIzRu=CHCH=CPhz(R = cyclohexyl (Cy) or phenyl (1~))~b Catalyst
Yield %
[M][I]
20 hr 20 hr 1 day 1 hr 5min 15min 15mm
110:1a 35:1 50:1~ 40:1 30:1 50:1 20:1 f
Ph Ph Cy Cy Cy Cy Cy I
|
gel 50 gel 71 68 gel gel
M~I0 "~
M,,xI0"
PDI ~
4r
1.87
2.63
1.40
1.34
3.02 2.70
2.25 2.09
1.31
Io
Xion conditions: CHzCIz:50 C; [M] = 0.14-0.18 M; "Data from'referencel"; bReactir By GPC, polystyrene calibration; a [M] = 0.5 M; ~25~ [M] = 0.45 M; f Cd'k.
r
In these experiments it was observed that the acetate polymers were very prone to gelation. The gels swelled upon addition of organic solvents such as CHzCI2, but they did not dissolve in any of a number of common polar or nonpolar solvents that were tested. With both catalytic systems, soluble poly[NBEglu(Ac)4] was obtained for lower monomer to catalyst feed ratios (<40:1) when the reactions were conducted in CH2CIz at elevated temperature. These results suggested a possible explanation for acetate polymer gelation. Since the acetate-protected sugar monomer was very
597 reactive, propagation might be much faster than initiation at room temperature. In this ease, poorly soluble high molecular weight polymers could result. On the other hand, the benzyl ether monomer (NBEglu(Bn)4) reacted with the [Ph2PRu] catalyst to give only a small amount of polymer while in the presence of Cy3PRu catalyst the polymer yields were high to quantitative. These results are fully illustrated bellow in Tables 9.31 and 9.31a. Table 9.31 Polymerization of 2-((• 2-deoxy-l,3,4,64a.m43-benzyI-D-glucx~yranose (NBEglu(Bn)4) with (R3P)2CIzRu--~HCH=CPhz(R = cyclohexyl (Cy) or phenyl (Ph))"b i
Catalyst
Solvent
Temp., *C
[M]:[I]
Time, hr
Yield, %
Ph Cy Cy
CH2C12
45 45 50
451 351 20:1
24 5 10
traoe
CHzCIz Cd-k
53 91
'Data from refermeet34; b[M] = 0.13, [I] = 3.2-4.6 raM. Table 9.3 la Polymerization of 2-((+)-exo-5-norbomene-2-earboxamido)2-deoxy-l,3,4,6-tetra43-benzyI-D-glucopyranose (NBEglu(Bn)4) with (R3P)2CIzRu---CHCH=CPhz(R = eyelohexyl (Cy) or phenyl (Ph))Lb
Catalyst
Soiv~
Temp.,*C
Time, hr
M,xI0 "4
M,,xl0 4
Ph Cy Cy
CHzCIz CH2C12 C6H6
45 45 50
24 5 10
0.56 2.75 1.69
0.95 3.36 1.99
PDF
1.68 1.22 1.17
'Data from reference t 4; b[M] = 0.13, [I] = 3.2-4.6 raM; ~By GPC. The polymerization of the NBEglu(Bn)4 monomer occurred in either CHzCL2 or benzene to give products with narrow molecular weight distributions; however, better yields were obtained for reactions carried out in benzene solution. By contrast, the triethylsilyl ether derivative, NBEglu(Et3Si)3, could only be polymerized with the active catalyst (Cy3P)zCIeRu=CHCH=CPhe, at elevated temperature (Table 9.32).
598 Table 9.32 Polymenza~on of 2-((+)-exo-5-norbomene-2-carboxamido)2-deoxy- 1,3,4,6-tetra-O-triethylsilyI-D-glucopyranose (NBEglu(EhSi)4) with (R3P)zCIzRu=CHCH=CPhz(R = cyclohexyl (Cy) or phenyl (Ph)) ~b Catalyst
[M][I]
(R) Ph Cy Cy Cy Cy
35.1 a 40:ld 45.1 ~ 40:1 ~ 35.1 ~
Time, days
Yield, %
MII
Mw r
xl0 "4
xl0 "4
1 0.7 2 3 2
0 32 55 45 78
0.69 0.91 1.16 4.01
0.79 1.11 1.35 4.41
9Data from reference I ~; b R = Cy, CHzCI.a, 50 oC; calibration; d [M] = 45 mM; ~[M] = 90-120 mM; f Cd-k.
PDF
1.14 1.12 1.16 1.10
By GPC, polystyrene
Typically, when monomer or polymer solubility is not a factor, olefin metathesis catalyzed by the ruthenium carbene catalysts is faster in CHzCIz as compared with benzene. With the silyl ether monomer NBEglu(EhSi)4, however, the opposite is true. Number-average molecular weights greater than--12000 (--15-mer) could not be achieved in CHzCI2. The reaction proceeded slowly for 3 days, at~er which time there was no increase in either the molecular weight or polydispersity index. This fact suggested that the propagating species were deactivated. Polymers with PDIs of 1.10-1.16 were thus obtained. Similarly, the trityl ether monomer NBEglu(Tr)3 underwent ringopening metathesis polymerization with the more reactive initiator (Cy3P)zCIzRu=CHCH=CPhz (Table 9.33). Unlike the acetate monomer, the polymerization of trityl ether monomer was more efficient and controlled in benzene. In most cases heating was not required for the polymerization to occur when the more active initiator was used. However, it was observed that with these monomers, as well as with simpler functionalized norbornene derivatives, that monodisperse materials were obtained with the more active catalyst if the reactions were run at elevated temperatures (-50~ This was supposed to be due to differential effects of temperature on the rates of initiation and propagation. If inter- and intramolecular chaintransfer reactions were a factor at all, these processes might occur primarily once all or most of the monomer was consumed since PDIs could
599
Table 9.33 Polymerization of 2-((• 2-deoxy- 1,3,4,6-tetra-6-O-trityl -D-glucopyranose (NBEglu(Tr)4) with (R3P)2CIzRu=CHCH---CPh2 (R = cyclohexyl (Cy) or phenyl (Ph))~ Catalyst 9
Solvent
Temp *C
[M]:[I] b
Time
6:1CHzCL2/MeOH CH2C12 CH2C12
50 25 50 50
30:1 50:1 50:1 25.1 d
3 days 15h 3h 4h
(R)
Ph Cy Cy Cy
c,l-l,
Yield % 0 trace c trace c
60~
9Data from reference~34; b M = monomer, I = catalyst; r Monomer and polymer precipitate from the reaction solution; a [M]=0.11 M, Polymer was only soluble in the presence of DMF or DMSO.
increase for longer reaction times. For instance, with the acetate-protected sugar monomer NBEglu(Ac)4 very large PDIs (>5) were observed for reaction times longer than a few hours. These values became smaller and approached PDI = 2 as the reaction time was decreased. Even for very short reaction times (5 rain), the polymer products of this reactive monomer still exhibited somewhat broad molecular weight distributions. Among the various sugar derivatives polymerized in the presence of (R3P)2CI2Ru=CHCH=CPh2 (R = cyclohex3,1 (Cy) or phenyl (Ph)), the dramatic differences in reactivity are striking and are unprecedented in similarly substituted simple norbornene. Selected data for the different sugar monomers that were reacted under similar conditions are collected in Table 9.34 for comparison. As it can be seen from Table 9.34, ring-opening metathesis polymerization of the acetate monomer was complete in 5 rain or less, whereas the silyl ether monomer required several days under similar reaction conditions. The ether monomers, benzyl and silyl, which might be expected to exhibit similar reactivity also required vastly different reaction times. The unprotected sugar monomer with free hydroxyl groups was essentially unreactive under these conditions, even in mixed solvent systems selected for enhanced monomer solubility.
600 Table 9.34 Substituent (R) Effects on Reaction Rates in Polymerizauon of Sugar Norbomene D e r i v a t i v e s ='b Sugar
R
Solvent
[M]:[I]
Time
Yield %
M, r xl0 "4
M,,r xl0 "4
PDI r
Ac Tr Bn Bn SiEh SiEh H
CHzCIz C~'E CHzCIz CJ'E C~'16 CHzClz MeOH: CH~CIz
30:1 30:1 35:1 20:1 35:1 40:1 20:1
5min 4 hr 5 hr 10 hr 2 days 3 days 1 day
68 60 d 53 91 78 45
1.31
2.70
2.09
2.75 1.69 4.02 1.16
3.36 1.99 4.41 1.31
1.22 1.17 1.10 1.16
trace e
'Data from reference t: 4; b Reaction conditions: R = Cy, 500C, [M] = 0.10-0.14 M; r By GPC, polystyrene calibration; d Product only soluble in DMF- or DMSOcontaining solvent systems; ~Monomer and product were poorly soluble. Norbom-2-ene-5,6-dicarboxamide reacts in the presence of welldefined molybdenum and ruthenium catalysts to give poly(2,4-dioxo-3-aza6,8-bicyclo[3.3.0]octanylene- vinylene) 33'~35 (Eq. 9.114).
,,O
n ~ ~ c C , , ~NH 0
[Mo,Ru]
~
"~~--~
(9.114)
o~C,,N/C_,,,,O I
H This reaction has also been performed using N-substituted norbom-2-ene5,6-dicarboxamide with methyl, ~36 ethyl, 33 propy133 or phenyl s3'~3~ as the substituents (Eq. 9.115).
n ~ c C # . ~N--R O tl
0
RuCI3. ~ o..C,, C. 0 NI R
(9.115)
601 N-Phenylnorborn-2-ene-5,6-di~xamide with alkyl or halogen (F, Cl, Br) substituents at different positions (ortho, meta, para) in the aromatic ring has also been polymerized with WCl6-based catalysts ~3s'~39 (Eq. 9.116).
, c NC lo
T=60~
X
~
~
(9.116) o~CxN/C.~o
O
• where X is methyl, fluorine, chlorine, bromine. The properties of the resulting polymers were all affected by the nature and position of the substituent in the aromatic ring. The methyl-substituted polymers showed that with orlho substitution the temperature of the transition in dynamic modulus and the glass transition temperature raised while with mela substitution these temperatures lowered relative to unsubstituted Nphenylnorborn-2-ene-5,6-dicarboxamide. For halogen-substituted Nphenylnorbom-2-ene-5,6-dicarboxamide, mixtures of ortho and meta substituted monomers melt at considerably lower temperatures than either substituted or unsubstituted monomers. Lower melting of these monomer mixtures made it possible to produce copolymers with aromatic substituents by bulk polymerization methods. exo-N-Pentafluorophenylnorbom-2-ene-5,6-dicarboxamide readily undergoes ring-opening polymerization when contacted with MoClvtMe4Sn or WCIdMe4Sn but its endo isomer is not polymerized under these conditions ~ (Eq. 9.117).
0
'~0 F
F
F
F
MoCIs/Me4Sn
(9.117) O..C,,~C-O
602 However, copolymers of exo- and e n d o - N - p e n t a f l u o r o p h e n y l n o r b o m - 2 ene-5,6-dicarboxamide could readily be obtained and characterized. The MoCl5 derived initiator led to a polymer with ca. 9 0 % trans vinylene units which is probably atactic and WCI6 derived initiator gave rise to an atactic polymer with ca. 60% trans vinylene units. 33 In the presence of molybdenum initiator Mo(=CH'Bu)(=NAr)(O'Bu)2, (Ar=2,6-'PrE-C6H3) Npentafluorophenylnorborn-2-ene-5,6-dicarbox-amide 53 led to a narrow polydispersity polymer with M,~IVI, = 1.05. Ring-opening polymerization of several amino ester functionalized norbom-2-ene-5,6-dicarboxamides, using the molybdenum initiators Mo(=CHCMe2Ph)(=NAr)(OR)2, (Ar = 2,6-Pr2-C6H3), (R -- CMe3, CMe2CF3, CMe(CF3)2), gave the corresponding ester functionalized polymers m4~(Eq. 9.1 18)
n
c .o-*CHRCOOMe II
O
[Mo]
(9.118)
O,,,C,N,C~o I
*CHRCOOMe where R is H (Gly), Me (Ala) and CHMeEt (lie). Both exo and e n d o monomers containing alanine moiety gave readily 78-91% trans, optically active polymers of narrow molecular weight distribution. However, the polymers obtained from the exo monomers showed a cis-trans vinylene dependence upon the ancillary alkoxide ligands of the initiator, the alkoxide ligand OCMe3 giving high trans content and OCMe(CF3)2 leading to high cis content. The cis/trm~s content for the endo polymers showed relatively little or no dependence upon the initiator. The optically pure monomers derived from alanine and isoleucine afforded optically active polymers whose optical activities were independent on the cis content and molecular weight, indicating the absence of a cooperative effect between chiral centers along the chain. Remarkably, the polymer prepared from exo monomer containing alanine is exceptional in its ability to incorporate various hydrocarbons in the solid state, including methane and hexane. TM The chirality and molecular recognition capacity of the resulting polymers might ultimately be useful as a template for controlling the architecture of other functionalized polymers of biological relevance formed in their presence.
603 It is of interest that the spiro-imide derivative from norbomene, bicyclo [2.2.1] hept-5-ene-2-spiro-3'-exo-N-phenylsuccinimide, synthesized by the reaction of the corresponding dicarboxylic anhydride with aniline, polymerized in an essentially quantitative yield (97%) to poly(bicyclo [2.2.1] hept-5-ene-2-spiro-3'-exo-N-phenylsuccinimide) under the action of the WCl~BuPhenol/EhAl catalyst ~ (Eq. 9.119).
n
CO,,
5/VlArJ
(9.110)
/ \ OC-.N,,CO
0
In contrast to polymers derived from the parent anhydride monomers, poly(bicyclo [2.2.1] hept-5-ene-2-spiro-3'-exo-N-phenylsuccinimide) was found to be soluble in organic solvents such as THF and methylene chloride, which allowed its easy GPC and ~H NMR characterization. The GPC results indicated an M~ value of 19200 (DP=76) and a polydispersity of 1.90 for this polymer suggesting a living process with a rate of initiation slower compared with the rate of propagation. From DSC spectrum, a clear glass transition at 190~ was obtained with no lower temperature transition being observed over a wide range of temperatures. In addition, the polymer was found to be thermoplastic in nature as indicated by its solubility in organic solvents. By ~H NMR spectroscopy, it was confirmed that the poly(bicyclo [2.2. I] hept-5-ene-2-spiro-3'-exo-N-phenylsuccinimide) obtained under the above conditions was predominantly the ring-opening product. The novel related compound, bicyclo[2.2.1 ]hept-5-ene-2-spiro-3'exo-N-(3 ", 5"-bis(trifluoromethyl)phenyl)succinimide, a fluoromethylsubstituted analog of the above monomer, was also polymerized by Watkins et al. ~ in a moderately high yield (63%), using the WCld'BuPhenol/EhAl catalyst, to produce poly(bicyclo [2.2.1] hept-5-ene-2-spiro-3'-exo-N(3",5"-his (trifluoromethyl) phenyl) suceinimide) (Eq. 9.120).
604
0(5
n
OkN LcoJ
\
CF3
~
(9.120) XN,.CO
oc /
F3C,~CF3 Like the polymer obtained from its unsubstituted analog, poly(bicyclo [2.2.1] hept-5-ene-2-spiro-3 '-exo-N-(3", 5"-bis(trifluoromethyl)phenyl) succinimide) was soluble in organic solvents with a glass transition temperature of 159~ as determined by DSC. Reversible melting was observed to occur at 193-207~ while GPC analysis indicated a value of M, of 22500 (DP = 58) and polydispersity of 2.07. Two norbornene derivatives bearing diimide group, hexamethylenedi(bicyclo[2.2.1 ]hept-5-ene-2-spiro-3'-exo-succinimide) and dod~ethylene(bicyr [2.2.1 ]hept-5-ene-2-spiro-3'-exo-sueeinimide) were also prepared and polymerized by Watkins el al. ~ with the above WCl~-based catalysts to the corresponding substituted polyalkenamers. Their structures are represented in Eq. 9.121 and Eq. 9.122.
.
o ~ ~ Lco /
[w]
= ~
(9.121) -V',N..CO OC
This time the products were found to be swollen by organic solvents such as THF and methylene chloride, indicating that, as expected, some degree of cross-linking was present. (Eq. 9.122)
605 lwl
--r.c
=
"=~~'~~=-n
/ OC\I~CO
(9.122)
oc(co (C,~ho
The thermoset nature of the polymers was also evidenced by their failure to undergo melting at temperatures up to 350~ whilst no clear glass transition was observed in their DSC spectra, suggesting that the degree of cross-linking was relatively high. Ring-opening metathesis polymerization of 5cyanomethylnorbomene occurs readily in the presence of W-based initiators*8 (Eq. 9.123).
n/ ~
ROMP ~_~ ..~ -~CH2CN
[VV]
(9.123)
-,,,, CH2CN
Polymerization of endo/exo-5-cyanonorbom-2-ene has been effected with numerous classical tungsten-based catalysts such as WCh,/Me4Sn, WCI6/Et3AI and WCIEEt2AICI and WCIjBu3AI to poly(4-cyano-l,3cyclopentylenevinylene) 33'85'~42"~"(Eq. 9.124).
ROM..~P
n CN
[W]
-~-\
/~
/-~
(9.124)
-,,,.
CN
On using WCIdEt3Al/acetone (13:6) in 1,2-dichloroethane at 50~ 100% yield of polymer could be obtained after 4 hours for a molar ratio of monomer:catalyst of 10001. With WCl6/'Bu3Al/paraldhyde (131.5) in 1,2-
606 dichloroethane at 60~ 100% yield of polymer with [11] = 0.66 dug and T s = 140~ has been produced after 4 hours using the same molar ratio monomer:catalyst, sS The most effective catalyst WCIdEt2AIOEt allowed 92% cis poly(4-cyano-l,3-cyclopentylenevinylene) to be obtained. ~43'~ 111,145 Molybdenum and tungsten carbene complexes give living systems. Under these conditions star and block copolymers have been prepared, s3'~45 Poly(4-cyano-l,3-cyclopentylenevinylene) prepared by this way is a potential thermoplastic for which there are numerous patents. 3~'~'~5~ Ring-opening polymerization of 5-cyano-5-methylnorborn-2-ene has been performed with the ternary system WCld'Bu3Al/paraldhyde to poly( 4cyano-4-methyl- 1,3-cyclopentylene - vinylene) 33 (Eq. 9.125).
n
CH3 CN
~
~
~~ /._._~_3 (9.125) CN
On using a catalyst with a molar ratio WAlparaldehyde of 1 3 1.5 and a monomer to catalyst ratio of 1000 1, 100% yield of polymer with [11] = 0.54 dl/g and T 8 = 160~ has been produced in dichloroethane with 1% lhexene at 70 ~ after 4 hours. 5-Phenyl-6-cyanonorborn-2-ene gives rise readily to poly(4-phenyl5-cyano-l,3-cyclopentylenevinylene) in the presence of W-based ROMP catalysts 8s (Eq. 9.126).
n
Ph
N
=
-~
NC
(9.126)
Ph
5,6-Dicyanonorborn-2-ene has also been polymerized in the presence of WCIdEhAICI/EtOCffI4OEt to form poly(4,5-dicy~o-l,39 88 cyclopentylenevmylene) (Eq. 9.127).
607
CN
n
[Wl
=
= ~ ~ - ~ \ /
NC
/ \
(9.127)
CN
Using the binary catalyst WCIjEt3AI (1 3) in dichloroethane, 5-exo(2-pyridyl)norborn-2-ene gave readily poly(4-(2-pyridyl)- 1,3cyclopentylenevinylene) 33 (Eq. 9.128).
n
,~
C2H4Cl2, 70"C
=
~
(9.128)
\
/
The polymerization occurred at 70~ with a molar ratio monomer:catalyst of 300:1. An effective catalyst for he polymerization of this monomer was 151 also WCI6/Et2AICI having EhN as a third component. Phosphorus-containing norbornene 5,6Bis(diphenylphosphine)norbomene (NORPHOS) can be readily polymerized with Mo(=CHCMe2PH)(=NAr)(O'Bu)2 to give the diphenylphosphine-containing ring-opened polymer 13~(Eq. 9.129).
n
/PPh2 Mo(CHCMe2phXNAr)(OIBu)2 --
~
(9.129)
PP~
Block copolymers of this monomer with methyltetracyclododecene were also prepared in order to bind metals (e.g., Ag and Au) in a dative fashion for obtaining metal clusters of a predictable size. Moreover, octylphosphine and octylphosphine oxide-containing polymers have been prepared by Schrock and coworkers in order to manufacture CdSe nanoclusters useful for fabrication of quantum dot/polymer composites. First attempts to polymerize 5-(dimethylphosphinemethyl)norbomene with the molybdenum
608 carbene complex Mo(=CHCMezPh)(=NAr)(O'Bu)2 failed, probably due to strong coordination of the phosphine ligand to metal center of the initiator ~52(Eq. 9.129a).
cH2P(CsH'7)2M~
H17ClK H,TCs---~,P~~ R (9.129o) t Ar
However, the phosphine oxide-containing monomer reacted with this catalyst to give the corresponding ring-opened polymer (Eq. 9.129b). O
n
,, CH2P(C8H17)2
Mo(C HC Me2Ph)(NAr)(OtBu)2
=- ~
(9.129b) CH2P(CeH17)2
In a similar way, dioctylphosphine and dioctylphosphine oxide derivative of 5-methylethernorbornene reacted with the molybdenum carbene complex to give the phosphine-containing ring-opened polymers (Eq. 9.129c-9.129d).
n~~CH2)sP(C'sH,7)2 E N ~ ~ P h ~ ~
- ~
19.129c)
0
n~CHTO(CH~I~(CeH,7)2 Mo(CHCMe2Ph) (NA0(OIBup2 =~
o u
~.12ea3
C~:~CHgsP(Ca~7~,
Diblock copolymers of phosphine- or phosphine oxide-functionalized norbomene and methyltetracyclododecene were prepared and nearly monodisperse CdSe nanoclusters, surface passivated with a layer of trioctylphosphine and trioctylphosphine oxide have been sequestered within phosphine-containing domains of these diblock copolymers. Boron-containing monomers. Several boron-containing cycloolefins have been used as monomers in the ring-opening metathesis polymerization reactions with well-defined metathesis catalysts tolerant towards functionalities.
609
(5-Norborn-2-enyl)-9-borabicyclononane
exo-(5-Norbom-2-enyl)-9-
borabicyclononane was synthesized by Chung and coworkers ~53 via selective hydroboration of norborna-2,5-dienr with 9-borabicyclononane and further ring-open polymerized in the presence of various metathesis catalysts to the boron-containing polynorbornene (Eq. 9.130). I n
(9.130)
+n
n
"B B
The polymerization reactions were carried out in toluene, at room temperature, to produce in high yields (80-95%) polyborane of varying cis/trans stereoconfiguration as a function of the catalyst and reaction conditions (Table 9.3 5). Table 9.35 Polymerization of (5-norbom-2-enyl)-9-borabicyclononane under the mfluence of metathesis catalysts' |1
|
MJ M,
W(=CH'Bu)(=NAr)(OC Me[CF3])z
2
95
93
270204 34833
Bimodal
WCldMe4Sn W(=CI-I'Bu)(=NAr)(O'Bu)z W(=C~Bu)(=NAr)(OCMe[CF3])2
2 2 60
84
48
58198
95 80
26 90
63211 36535
2.3 1.6 1.8
'Data from reference~s3 The structural characterization of these polymers was done by using IIL ~H NMR and ~3C NMR spectroscopy and the molecular weight was determined by GPC. As it can be seen from Table 9.35, the WCIdMe4Sn catalyst gave a polymer with almost equal amounts of cis and trans double bonds. By contrast, a high cis polymer (93%) was obtained with the active tungsten-carbene complex W(=CH'Bu)(=NAr)(OCMe[CF3]z)z which gave
610 also a bimodal distribution while a high trans polymer (74%) with a monomodal distribution was formed with the less reactive, W(=CH'Bu)(=NAr)(OrBu)2. Interestingly, the conventional catalyst ReCIs, which has been used to synthesize cis-polynorbomene, failed to polymerize the present borane monomer. The borane polymer was further oxidized by using alkaline HzO2 to give the corresponding poly(exo-5hydrox~orbome).The thermal properties and molecular orientation of various isomeric structures were evaluated by DSC and two-dimensional surface studies at the air-water interface separately. DSC results indicated a single glass transition temperature (Tg) for all polymers. The values for the high cis (140~ and mainly trans (138~ polymers were significantly higher than that of the cis-trans polymer (118~ A lower value for the cistrans polymer was expected from its less regular microstructure compared with the other two polymers. The presence of only one T 8 in all stereoisomers again evidenced the absence of microscopic phase separation; both head-tail and cis-trans sequences were randomly distributed along all polymer backbones. Additionally, surface area measurements showed that the polymer backbone with cis structure had a significantly higher rigidity than that of the corresponding trans form. Silicon-containing monomers. Due to their ready availability by DielsAlder reaction, many silicon containing norbomene monomers have been used in ring-opening metathesis polymerization in the presence of W, Re or Ru-based catalytic systems38'1S4(Eq. 9.131).
n
~
R
ROMP -
~
[W], [Re], [Ru]
(9.131)
\ R
where R is an alkyl-, halogen-, oxygen-, and nitrogen-containing silyl group. 5-Trichlorosilylnorbornene. The surprisingly high tolerance of the metathesis active centres toward Si-CI bond from this silicon-containing monomer has been emphasized first by Streck 38 in copolymerization reactions with 1,5-cyclooctadiene in the presence of the WCI6/EtOH/EtAICIz catalyst. More recently, Makovetsky et al. 7~ investigated the polymerizability of 5-trichlorosilylnorbornene under the influence of the catalytic systems WCl6-phenylacetylene and WCId~Bu2AICI to poly(5-trichlorosilylnorbomene) (Eq. 9.132).
611
sicJ3
n
[w]
-t-r
~
(9.132) \
SiCI 3
Working in toluene at 20~ moderate yields of soluble polymers were obtained which became rapidly insoluble after exposure to air. Partial hydrolysis of the Si-CI bonds and subsequent formation of siloxane bridges seemed to account for the cross-linking of these polymers. The IR spectrum of poly(5-trichlorosilylnorbomene) showed that its structure did not differ from that of other related polynorbomenes but indicated the simultaneous appearance of Si-O-Si bonds. 5-Dichloro(methyl)silylnorbornene. 5-Dichloro(methyl)silylnorbomene is readily polymerized in the presence of WCI6/CIC2H4OH/Et3AI initiator at 30~ to dichloro(methyl)silyl-substituted polynorbomene 37'38(Eq. 9.132a). CI
I ,s,
WC Is/CIC2H4OH/Et3AI
Cl
(9.132a)
T = -30~
\
CI--Si-CI I c~
The polymer is of interest for its reactive silyl groups along the chain that can be chemically easily converted to other functional groups. 5-Trimethylsilylnorbornene. King-opening polymerization of both e x o and e n d o - 5 - t r i m e t h y l s i l y l n o r b o m e n e to poly(5-trimethylsilylnorbomene) has been extensively studied by Makovetsky et al. 7~ under the action of various heterogeneous and homogeneous metathesis catalysts (Eq. 9.13 3).
n
/ S iMe3
[Re],[VV] ...._
~
(9.133) \
SiMe 3
Thus, starting from an equal amount of the two isomers, in the presence of heterogeneous catalytic systems derived from Re2Ov/AI203 promoted with
612 "Bu4Sn or EhPb, the corresponding polymer in moderate yields, ranging from 30 to 50%, has been obtained. Gas liquid chromatography of the unreacted monomer showed an increase of the endo-isomer, indicating its lower polymerizability as compared to exo~isomer. On using homogeneous catalytic systems based on WCI6, polymer yields from 75 to 100% have been recorded (Table 9.36). Table 9.36
Polymerization of 5-trimethylsilylnorbomene in the presence of metathesis catalytic systems in toluene Lb Catalytic System
WCI6 WCIJPhC-CH WCIJPhC=CH WCIJPhC=_CHd WC 16~ e2S i(CJ'[6) S iMoz WCIJMozSi(CHzCH=CHz)z WCIgPluSn WCIJBu2AICI Re20~/AI203/"Bu4Sn" Ro2OT/AIzOx/EhPb~
~,Re mole
1000 1000 2000 1000 1000 1000 1000 1000 400 400
[M] molexL "~
Yield %
[11]~ dl g-i
1.5 1.5 2.0 1.5 1.5 1.5 1.5 1.5 3.5 3.5
43.3 86.5 75 100 99.9 92.3 1000 71.4 45.5 51.3
3.3 3.7 9.0 0.6 4.0 0.85 2.5 4.4 1.8 1.7
|,
9Data from reference~; b Re catalysts 5 hr at 40~ W catalysts 2 h at 20~ ~ Intrinsic viscosities in toluene at 30~ d Polymerization in the presence of lhexene(l mol compared to monomer); " 3 wt. % n-Bu4Sn, 1.4 wt. % F~Pb. Several observations are worth mentioning from analysis of data presented in Table 9.36. First, it is interesting to note that polymerization of 5trimethylsilylnorbornene took place even in the presence of WCI6 alone. According to spectral measurements, the polymer backbone had a poly(1,3cyclopentenylenevinylene) structure, showing that the polymerization of the monomer proceeded via ring-opening. This behavior is not quite unexpected, because the ring-opening polymerization of the unsubstituted norbornene by WCI6 without any cocatalyst has been known for a long time. It is reasonable to assume that the interaction of the highly strained monomer with WCI6 results in the reduction of tungsten and the formation of the initial tungsten-carbene species, active in the ring-opening metathesis
613 polymerization, but details of this transformation are not studied with this system yet. It is relevant that 5-trimethylsilylnorbomene polymerized under the influence of WCIe alone at higher rates and gave polymers of higher molecular weights as compared with norbornene, which may be attributed to the presence of the SiMe3 groups into the system. Furthermore, the addition of the cocatalysts such as phenylacetylene, tetraphenyltin, diisobutylaluminium or some organosilicon compounds to WCIe led to formation of very active catalytic systems, giving nearly quantitative yields of poly(5-trimethylsilylnorbornene) at room temperature. As it can be observed from the Table 9.36, the intrinsic visicosities of the polymers thus prepared could be controlled within a wide range by the proper choice of the catalyst and by adding small amounts of ot-olefins (e.g., l-hexene). Structural measurements indicated that the polymers prepared under these conditions retained the initial unsaturation of the parent norbomene: according to the ~3C NMR spectra, the double bonds in the chain were ---68% cis and ~32% trans. The glass transition temperature and the temperature of the onset of decomposition of these polymers were found to be I I0~ and 375~ respectively. These polymers are of a practical interest for their special gas permeability properties. ~55 Introduction of trimethylsilyl groups into the polymer chain of norbornene resulted in a sharp increase in the gas permeability coefficients for many conventional 7~ gases. 5-(1,1,3,3-Tetramethyl- 1,3-dbilabutyl)norbornene. In the course of their studies on the mass-transfer properties of silicon-containing polynorbornene as potential material for gas-separating membranes, Makovetsky et al. 7~ examined the ring-opening polymerization of 5-(1,1,3,3-tetramethyl-l,3disilabutyl)norbornene (Eq. 9.134). n
/~
SiMe2(CH2S IMe3)
IReI,P~ =
(9.134) \
SIMe2(Cl-lzSiMe3)
The reaction has been effected in the presence of the heterogeneous system Re2OT/Al203/n-BuSn and with the homogeneous system WCIJphenylacetylenr It is noteworthy that high yields of polymers were obtained with the homogeneous catalyst WCldphenylacetylene (Table 9.37). Although the IR and NMR spectra of the polymers thus prepared
614 were rather complicated, it was possible to conclude polymerization proceeded vm ring-opening process (Eq. 9.13 5).
/~
Cl'12Si Me3
[ReI,[W]
~
that
the
(9.135) \
CH2SiMe3
Table 9.37 Polymeriza~on of 5-(1,1,3,3-tetramethyl- 1,3-disilabutyl)norbomene in the presence of metathesis catalysts in toluene~b Catalytic System
Monomer: Catalyst mole
[Monomer] mole L~
Yield %
[q]~ dl g-i
Re2OdAl203/n-Bu4Snd WCh~hC~CH
350 750
3.0 2.5
30
1.7 2.0
81
'Data from referencr bRe catalyst 5 hr at 40~ W catalyst 2 hr at 20~ r Intrinsic viscosities in toluene at 30~ 9d3 wt.% n-BtuSn. 5-[(Methylsilacyclobutyl)methyl]norbornene. With the aim of obtaining polynorbornene capable of further chemical modification, Makovetsky et al. 7t investigated the ring-opening polymerization of 5[(methylsilacyclobutyl)methyl]norbornene, under the influence of metathesis catalysts (Eq. 9.136).
[Ru]
c n
Me
(9.1:36)
~
\
c.2s<5 Me
The reaction of this monomer has been effeeted using homogeneous Ruand W-based catalysts. High yields of rather high molecular weight polymers have been obtained in both cases (Table 9.38).
615 Table 9.38 Polymerization of 5-[(methylsilacyr m the presence of metathesis catalysts'
Catalytic System
Monomer: Catalyst mole
RuCI3.3H20b WCI~hC~_CI-F
1000 500
Time hr
Polymer Yield %
dlg-I
89
0.21
100
0.1
[111
,.,
6.5 24
'Data from reference71; bCffI~CI:EtOH 11, 60~ ; %VCI~:Phenylacetylene 1"1, toluene, 20~
Analysis by IR spectroscopic measurements of the structure of polymers indicated that apart from the usual set of absorption bands for poly(l,3cyclopentylenevinylene), a series of absorption bands, characteristic to the silacyclobutyl groups were present. This observation was also confirmed by ~H NMR spectroscopy. It is interesting that the polymers thus prepared were completely soluble in hydrocarbon solvents. This fact shows that the reactive substituent was left intact during the ring-opening polymerization of norbornene moiety and did not participate in the intermolecular crosslinking. ~(Trimethoxysilyl)norbornene. The strong influence exerted by the alkoxysilyl groups from 5-(trimethoxysilyl)norbomene on the metathesis activity of the WCIJEtAICI2 system in copolymerization reactions with cyclopentene was pointed out by Streck 38 in a series of early investigations. Remarkably, only at much higher AI:W ratios, when the concentration of EtAICI2 was nearly as great as that of 5-(trimethoxysilyl)norbornene, reasonable yields of copolymer were obtained. Subsequently, trialkoxysilylnorbornene monomers were found by Schrock ~s to be tolerant with well-defined molybdenum carbene complexes employed in block copolymer manufacture. Recent work by Makovetsky et al.7~ showed that 5(trimethoxysilyl)norbornene can polymerize under the influence of heterogeneous rhenium-based and homogeneous RuCI3.3H20 catalysts to produce insoluble polymers which, according to their IR spectra, possessed structures formed v/a ring-opening metathesis of the norbomene moiety (Eq. 9.137).
616
n
~
Si(OMe)3
[VV],[Mol,[Ru] =_
(9.137) \
Si(OMe)3
For instance, using RuCI3.3H20 as a catalyst, in chlorobenzene/ethanol (1/1) solution at 60~ Makovetsky et al. obtained in 70% yield poly(5(trimethylsilyl)norbornene) during 13 hours reaction time. They assumed that the insolubility of the polymer thus prepared was due to the formation of interchain Si-O-Si bonds via the interaction of Si-OMe and Si-CI groups of different polymer chains. The occurrence of Si-CI bonds was related to the exchange of OMe groups of the monomer for chlorine atoms of the of the catalyst. ~(Triethoxysilyl)norbornene. Similarly to its methoxy analog, 5(triethoxysilyl)norbornene was ring-open polymerized under the influence of W-, Re- and Ru-based catalysts 7~ (Eq. 9.138).
~
Si(OEt) 3
IW],IReI,IRul
- ~ ~
(9.138) \
Si(OEt)3
Moderate to high yields (12-63%) of insoluble, seemingly highly crosslinked polymers were obtained with heterogeneous rhenium-based and homogenous RuCI3.3H20 catalysts. (Table 9.39). Table 9.39 Polymerization of 5-(triethoxysilyl)norbomene with heterogeneous and homogeneous metathesis catalysts' Catalytic System Monomer: Time Polymer hr Yield~ % Catalystz mole RezOT/AlzO3/Bu4Sn b RuCI3.3H20 r WCI6/'iBuzAICI d
350
40
500
12 6 5min
9Data from referencen; b 3 wt. % Bu4Sn, toluene, 45~ W:AI 1:5, toluene, 20~
12 60 63 ~ C6H~CI:EtOH 1"1, d
617 Interestingly, very active in other cases, the WCl6/phenylacetylene catalytic system proved to be unsuitable for the polymerization of 5(triethoxysilyl)norbomene, addition of monomer to the catalyst caused complete discoloration and no polymerization could be observed. High yields of insoluble polymer were obtained, however, in the presence of WCI6 associated with 'Bu2AICI; this catalyst showed high activity even at moderate concentrations of the organoaluminium compound (mole ratio AI:W ca. 5). Likewise, it was assumed that the production of insoluble polymers was due to the formation of Si-O-Si bonds v ia the interaction of the Si-OEt and Si-CI groups of the different polymer chains. 5-(Trimethylsiloxy)methylnorbornene. Polymerization of 5(trimcthylsiloxy)methylnorbomene occurs readily with the Ru complex to substituted poly(methylnorbomene) having reactive siloxy groups. By subsequent acid hydrolysis of the trimethylsiloxy groups, high molecular weight polymers with hydroxymethyl groups can be prepared ~57(Eq.9.139).
n
/~C~iM~ [Ru] ~
H20 ~
T=60~C
He~
CH2OSM i e3
(9.~) C~OH
New polymers containing reactive trichlorosilyl groups attached at the aliphatic arms were reported by Streck 3s to form by the ring-opening polymerization of 5-trichloroethylnorbornene under the action of W-based catalysts (Eq. 9.140).
/C H2CH2SiCl3 n
[W] ~
(9.140)
\
CH2CH2SiCI3
Ring-opening polymerization of 5(3-(9~azolyl)propyl)dimethylsilylnorbornene with the Ru complex RuCI2(Ph3P)3 occurs readily to the 9carbazolyl-containing polymer ~Ss(Eq. 9.141).
618
IRu]
(9.141)
/
H3C-S~CH3 I
Similar results have also been obtained in the reaction of 5(3-(9carbazolyl)propyl)dimethylsilylmethylnorbornene with the same Ru complex (Eq. 9.142).
.•C
[Ru]
(9.142)
H2--Si--(CH2)3-N CH3
/
~H2 H3C-S~CH3 I
Norbornene monomers having vinyl unsaturation at the functional group able for further cross-linking, have been polymerized with the Ru complex 159(Eq. 9.143).
n~
-
Me
"~.IISL.../~
[Ru]
>
~
e
(9.143) Me
Such cross-linked polymers have been obtained from dinorbornenyl monomers readily available by the Diels-Alder reaction of diallyldimethylsilane with cyclopentadiene~S9(Eq. 9.144).
619
.
M. Me Me
These cross-linked polymers belong to a potential class of products with high gas permeable and permselective properties. Kawakami et al.'6~ prepared a series of polymers of 5-cyano-5(triorganosilyl)norbornenes in the presence of WCId~Bu3AI as a catalyst (Eq. 9.145). ,(,~N n
~9.145)
[WJ
SiMe20)n--R
T= 80oc 9 20).
where n = 0-2, R = Me3Si, Me3SiCH2, Me3Si-SiMe2. These polymers showed high gas permselectivity with respect to a number of gases: H2, He, Oz, Nz, etc. However, in spite of rather severe reaction conditions, in most cases, the yield of polymers did not exceed 30~ Norbomadiene monomers containing silyl groups have been found to give highly unsaturated polymers containing reactive silyl groups. Thus, ring-opening polymerization of 2-(trimethylsilyl)norbomadiene with WCh,/Me4Sn catalyst in toluene at 20~ gave poly(4-(trimethylsilyl)-l,3cyclopentylenevinylene) in 46% yield aRer 5 hr reaction time t6~ (Eq. 9.146). /SiMe3 n
VVCIs/Me4Sn
T = 20~ 11=46%
(9.146)
\
SiMe 3
Similarly, 2-dimethylsilylnorbornadiene gives rise to poly(4-(trimethylsilyl)1,3-cyclopentylenevinylene) under the same reaction conditions~6Z (Eq.9.146a).
620
VVCIs/Mo4Sn Toluene '=
n
(9.146a)
SiMo2H
\
SiMe2H
Noteworthy, this was the first example of a ROMP reaction with a monomer which contains a reactive Si-H bond. A norbomene monomer containing germyl group has been polymerized in the presence of a Ru complex to give a polymer with germyl functionalities ~59(Eq. 9.147).
n~CH2GeMe3
[Ru]= ~
(9.147) \
CH2GeMe3
This type of polymers is of interest as components of gas separation membranes or precursor of ceramics and thermosetting products. They are also potential compounds for desirable chemical modifications. Metal-containing monomers. Norbomene monomers with organotin functionalities have been readily polymerized in the presence of WCl6-based metathesis catalysts. 3s By this way, it was possible to prepare polyalkenamers with a high tin content along the chain. One first example is the ring-opening metathesis polymerization of 5(tributyltinmethyl)norbomene to the corresponding substituted polynorbomene (Eq. 9.148).
/~
CH2SnBu3
[vv]
=
~
(9.148) CH2SnBu3
Another interesting example is the polymerization of the higher homolog, 5(tributyltinethyl)norbomene, under similar conditions, to the corresponding substituted polymer38 (Eq. 9.149).
621
CH2CH2SnBu3
[VVJ ..._
n
~
(9 149)
~
9
\
CNCNSnBu3
Such polymers and copolymers with cycloolefins showed good biocidal properties and are of interest for special applications. The tolerance of the Schrock-type metallacarbene complexes M(=CH'Bu)(=NAr)(O'Bu)2 (where M = Mo,W) for functionalities allowed them to be used to ring-open polymerize norbornene that contains metals as functional groups. A type of monomer that potentially can be used to carry a variety of metals into microphase separated materials is a chelating bisamido ligand, 2,3-trans-bis(tert-butylanfidomethyl)norbom-5-ene (bTAN). The Sn(IV) complex, Sn(bTAN)CI2 has been polymerized with Mo(=CH'Bu)(=NAr)(O'Bu)2 in THF to give the tin-containing polymer ~63 (Eq. 9.150).
,CI -,~N/Snc I \
tBu
Mo(c u•
(9.150)
THF
u N.sn/N tBu ct '"cl
By this way, block copolymers containing norbomene have been prepared in which the ratio of norbornene to Sn(bTAN)CI2 has been varied to give lamellae, cylinders, and spheres of the Sn-containing derivative in polynorbornene, t64 Norbornene monomers that contain Sn(ll) and Pb(ll) and the bTAN ligand were found to be unstable toward decomposition to give metal, but analogous monomers in which trimethylsilyl groups replaced the tert-butyl groups, Sn(bSAN) and Pb(bSAN), were stable in solution at room temperature for days. Accordingly, Sn(bSAN) and Pb(bSAN) could be polymerized by the tungsten complex W(=CH'Bu)(=NAr)(O'Bu)2 to the corresponding metal-containing polymers ~33(Eq. 9.151-9.152).
622 N,,st
Me3
vv(c HtBuXNArXOSu)z
~
(9.151)
\
StMe3
Me3Sp"N',sn/N"SIMe3
/~N/'SiMe3 N/pb \ SIMe3
W(CHtBuXNArXOtBu)2
-v = ~ ~
(9.152)
Pb Another norbornene monomer containing lead, Pb(CpN)2 or Pb(NBECp)2, employed by Schrock and coworkers ~65 gave lead-containing polymers under the influence of the catalyst Mo(CH'Bu)(NAr)(O'Bu)~. (Eq. 9.153).
(9.153)
n
With this norbomene derivative, block copolymers with norbornene as a comonomer have been synthesized. Further treatment of the static cast films of such polymers with hydrogen sulphide allowed nanoclusters of the semiconductor PbS within the polynorbomene matrix to be manufactured. The presence of two norbomene double bonds per metal created, however, the possibility that the complex would behave as a cross-linking agent. However, block copolymer synthesis has been controlled to a much greater degree by other Pb-containing monomers as Pb(NBECp)Cp* (Eq. 9.154).
Mo(CHtBu)(NAr)(OtBu)2
.••
Pb
(9.1s4)
Pb
623 or better Pb(CpN)(OTf), in the presence of the molybdenum carbene complexes l~ (Eq. 9.15 5). ~:~
Mo(CHCMe2PhXNArXOtBu)2
= ~
=p
(9.155)
Pb(CF3S03)
Pb(CF3S03)
Block copolymers of Pb(CpS)(OTf) with methyltetracyclododecene in the presence of the above catalyst have also been prepared. A zinc-containing monomer, Zn2R2(bTAN), has also been prepared and polymerized with W(=CH'Bu)(--NAr)(O'Bu)2 as a catalyst 167 (Eq.9.156).
N'tBu
tBu
VV(CHtBuXNArXOtBu~ .=--
(9.156)
tsgN*/N',tSu I
R
where R is a ethyl or phenyl group. Copolymers containing this monomer (R = Ph) and methyltetracyclododecene (MTD) have been obtained with the above catalyst in benzene under mild conditions. Films of copolymer were first treated with hydrogen fluoride-pyridine complex (70~ HF) to form ZnF2 clusters which treated further with hydrogen sulphide at higher temperatures yielded ZnS clusters. The process is reversible on lowering the temperature. Remarkably, the zinc-containing phase appeared to contain molecular species and each domain can act as an isolated reactor for chemical conversions. Different kinds of clusters can be synthesized by this method from a given starting material. For example, PbS can be synthesized by treating PbF2 clusters with H2S at temperatures above 70~ and CdS clusters by conversion of CdF2 to CdS well below room temperature. This approach generated ZnS quantum clusters which were superior in quality to other techniques employed. Norbomene derivatives that contain ferrocenes, e.g., trans-
(exo, endo)-2-carbomethoxy-(endo, exo)-3-ferrocenyl-5-norbomene
and
624 (FeNBE), have been polymerized with Mo(=CHR)(=NAr)(O'Bu)2 (R = 'Bu or ferrocenyl, Ar = 2,6-'Pr2-C6H3) to form redox-active polymers having terminal groups for covalent attachment to surfaces. Thus, pyrene-capped polymers have been prepared in an attempt to bind the polymers to carbon electrodes via selective pyrene adsorption ~ (Eq. 9.157).
n
~~j~
Me
,
M~ HR)(NArXOtBu)2 e "-
~
(9.157)
Fe
Fe
Ferrocene-based polymers terminated with bromobenzyl groups reacted with electrodes pretreated with benzyl chloride to produce polymerderivatized surfaces. Block copolymers with norbornene and 5(triethoxysilyl)norbomene were also prepared to derivatize Pt, In2(Sn)O3, and n-Si electrodes. Significantly, the solution electrochemistry of these products showed to be well-defined and well-behaved. By the above procedure, cobalt-containing polymers have been prepared from 5-carbomethoxy-6-coblatocenyl-2-norbomene with the molybdenum carbene Mo(=CHR)(=NArXO'Bu)2 as initiator ~33(Eq. 9.158).
/,~~~
n
Me Mo(CHB t uXNArXOB t u)2 M e ~
(9.158)
Co co
Similar techniques were used by these authors to generate zero valent metals in microphase-separated block copolymer films. Thus, the organometallic derivative, Pd(NBECp)(allyl), which is relatively stable thermally, was polymerized with Mo(=CHCMe2Ph)(=NAr)(O'Buh to give block copolymers containing methyltetracyclododecene (MTD)t6s (Eq.9. .
MoC ( HCMe2PhXNAO ()rB tu2 )= ~
n
(9.159)
Pd
@Ph
Pd
@Ph
625 Cast films showed the expected morphologies and could be treated with hydrogen gas at 100~ to generate palladium clusters-25-50A in diameter within polyMTD. Benzonorbornadiene derivatives. Polymerization of 9,10bis(trifluoromethyl)benzonorbomadiene has been investigated with several metathesis catalysts the best results being obtained with WC]6/Me4Sn or MoCIs/Me4Sn as a catalyst 62'169 (Eq. 9.160).
n
F3
VVCI6/Me4Sn "~ MoCIs/Me4Sn
(9.160)
F3C
CF3
The polymer produced with WCldMe4Sn had 50 to 60~ trans vinylene units whereas MoCIgMe4Sn led to 15 to 30% trans content. Similar results have been obtained in the polymerization of dihydrogenated compound of 9,10-bis(trifluoromethyl)benzonorbomadiene under the above conditions
(Eq. 9.160a). n
3
WCIs/Me4Sn
(9.160a)
MoCIs/Me4Sn
F3C
CF3
Ring-opening polymerization of 8,9,1O,1l-tetrafluorobenzonorbomadiene has been most conveniently effected using both WCIdMe4Sn and MoCls/Me4Sn catalysts6z (Eq. 9.161). F n
WCts/Me4Sn
F
=
(9.161)
MoCIs/Me4Sn
F F
F
626 Again the polymer steric configuration was dependent on the nature of the catalyst employed: W-based catalyst produced 50-60% trans vinylene units and Mo-based catalyst afforded over 70% cis vinylene units. By contrast, the related fluorinated monomer with the isopropylidene bridging substituent was less reactive but more stereoselective in the presence of the catalysts explored. In this case, the W-derived catalyst gave rise to a polymer with 70% cis content while the Mo-based catalyst produced a polymer with more than 95% cis content 6z (Eq. 9.162).
F
n
F F
VVCI6/Me4Sn~ MoCIs/Me4Sn
(9.162)
F F
F
Bicyclo[3.2.1locta-2,6-diene. In their studies on the polymerizability of halogen-containing monomers, Feast and coworkers ~7~ examined the behavior of a series of chlorinated polyeyelic unsaturated compounds in the presence of ring-opening metathesis catalysts. Thus, starting from 3chlorobicyclo[3.2.1 ]octa-2,6-diene, the corresponding chlorinated polyalkenarner was readily prepared under the action of WCldMe4Sn as a catalyst (Eq. 9.163).
n
CI
VVCI6/Me4Sn ~
(9.163)
CI Similarly, 3,4-dichlorobicyclo[3.2.1 ]octa-2,6-diene was successfully polymerized with the WCI6/Me4Sn and MoClvq~e4Sn catalysts, and interestingly, this demonstrated that an allylic chlorine atom does not necessarily inhibit the ring-opening reaction, at least if it occupies an exo oosition (Eo.9.164].
627
CI CI
n
WCI6/Me4Sn.~ MoCI5/Me4Sn'-
(9.164)
CI Likewise, using MoCl~le4Sn as a catalyst, the isopropylidene bridging monomer, 2,3-dichloro-8-isopropylidenebicyclo[3.2.1]octa-2,6diene, was quite easily polymerized giving a very viscous solution within l/2 hr at room temperature (Eq. 9.165).
n
CI C
M~176
-~
(9.165)
CI Ring-opening polymerization of this monomer was confirmed by means of spectroscopic measurements and elemental analyses. Bicyclo[2.2.2] octa-2,5-diene. Ring-opening polymerization of bis(carboxylic ester) derivatives of bicyclo[2.2.2]octa-2,5-diene-cis-2,3-diol occurs with Mo(=NAr)(=CHCMe2PhXOCMe2(CF3))2 (At=-2,6 171 diisopropylphenyl) at ambient temperature (Eq. 9.166).
n~~.OC(O)R
JV~,,.~OC(O)R
Mo(CHCMe2PhXNArXOCMe2(CF3))2 R(O)C~OC(O)R(9.166)
where R = Me, OMe. Of these two ester derivatives, only the methoxy compound undergoes polymerization in high yield. Preliminary investigations indicated that the rate of polymerization in CH2CI2 was at least an order of magnitude faster than in THF and that the rate of initiation was slower than the rate of propagation in both cases. Relatively narrow molecular weight distributions (PDI = 1.2-1.2) of the polymers were obtained, consistent with a living polymerization with slow initiation. Ratios of monomer to catalyst as high as 250: l have been employed without
628 diminuation of the polymer yield or broadening of the molecular weight distribution. The ~H and ~3C NMR spectroscopic analyzes of the polymer containing methoxycarbonyl groups suggested a polymer structure consisting of alternating sequences of vinylene and 1,4-cyclohexenylene units. An approximately equal distribution of the cis and trans double bonds was inferred for this polymer. The syn orientation of the methoxycarbonyl groups and the ring-junction protons allowed a concerted elimination of the acid, which is supported by the facile thermolytic conversion to PPV (Eq.9.167). .....
1~
CH30(O)CO
OC(O)OCH3
-2n COz, CH3OH~
(9.167)
It is noteworthy that the living metathesis polymerization of bis(carboxylic ester) derivatives of bicyclo[2.2.2]octa-2,5-diene-cis-2,3-diol permits direct control over the structure of PPV, including the ability to narrowly define the degree of polymerization, the molecular weight distribution, the end group and the sequence structure of copolymers Bieyclo [2.2.2 ] octa-2,5,7-t rien e (Ba rrelen e). 2,3Dicarboxybicyclo[2 2 2]octa-2,5,7-triene monomers were polymerized by the ring-opening metathesis molybdenum initiator Mo(=NAr)(=CHCMe~Ph)(OCMe(CF3)2h (Ar=2,6-diisopropylphenyl) in the presence of hexafluoro-tert-butanol (HFB) to the corresponding dicarboxy-substituted polymers ~ (Eq. 9.168). 0,~c/OR
ROMP
._._
(9.168)
Mo(C HCMe2Ph)(NArXOC Me(CF3)2)2 I
RO
I
OR
where g = CH3, C(CH3)3. Complete initiation by molybdenum carbene catalyst and living polymerization of di-tert-butoxybicyclo[2.2.2]octa-2,5,7triene were achieved by tuning the activity of the catalyst with FWB and THF. mH and ~3C NMR spectra showed that both cis and trans double bonds were formed between the cyclohexadiene tings during the
629 polymerization and that poly(di-tert-butoxybicyclo[2.2.2]octa-2,5,7-triene) had a higher percentage of cis linkages than poly(dimethoxybicyclo[2.2.2]octa-2,5,7-triene). Test experiments by using different amounts of didert-butoxybicyclo[2.2.2]octa-2,5,7-triene with the same amount of initiator showed that the molecular weight of the polymer increased linearly with the monomer to initiator ratio, as it is expected for a living polymerization. These two precursor polymers were readily converted to diester-substituted poly(1,4-phenylenevinylene) (PPV) by aromatizing the cyclohexadiene tings using 2,3-dichloro-5,6-dicyano-l,4benzoquinone (DDQ) (Fxl. 9.169). o NC~.~CN NC" "~ "CN (9.169)
cNch ON,C I
RO
I
I
OR
RO
I
OR
where R = CH3 or C(CH3h. The resulting PPVs were highly luminescent, and the PPV bearing tert-butyl groups on its esters, was soluble in methylene chloride and chloroform. These authors found that partially oxidizing poly(di-tert-butoxybicyclo[2.2.2]octa-2,5,7-triene), so that only 80~ of the polymer units were aromatized, increased both the solubility and photoluminescence quantum yield of PPV. Deprotection of PPV bearing tert-butyl groups by acid catalyzed thermolysis followed by treatment with aqueous base produced a PPV dicarboxylate (Eq. 9.170).
(9.17o)
T= 125"C RO
OR
RO
OR
Na'O"
ONa~
This sodium salt of the PPV dicarboxylate was soluble in water and uniform, highly luminescent films of it could be formed by spin casting the polymer from aqueous solution. UV/visible absorbance measurements showed that, in solution, the PPVs are blue shifted relative to films of unsubstituted PPV.
630 9,9-Dichlorobicyclo[6.1.01 non-4-ene. 9,9-Dichlorobicyclo[6.1.0]non-4ene reacts in the presence of WCI6/EtAICI2 at 25~ to form the chlorinated ring-opened polymer having the 3,3-dichloro-l,2-cyclopropylene units in the polymer chain ~73(Eq. 9.171 ).
wc
n
I
o,,,
T = 25"C
"-
(9.171)
Side reactions such as cationic polymerization and Friedel-Cratts alkylation were suppressed by a proper choice of the reaction conditions (monomer: W ratio of 600:1, AI'W ratio of 8:1, room temperature). Cyclooctene ring can be readily opened in the bicyclic monomer bearing an ester functionality, 9-carbethoxybicyclo[6.1.0]non-4-ene, when using WCh,/Me4Sn in chlorobenzene at 90~ giving rise to the corresponding polyalkenamer with functionalized cyclopropane in the repeat unit ~74(Eq. 9.172). n
C(X3C21"15
T = 90"C > n= 79,7%
(9.172) C00C21-1~
Incorporation of an additional ether functionality via a methoxy group into the ester functionality of 9-carbethoxybicyclo[6.1.0]non-4-ene does not impede the ring-opening polymerization of the new functionalized monomer in the presence of WCI6/Me4Sn as a catalyst 17~(Eq. 9.173). n ~~--COOC2H4OCH
3
VVCI6/Me4Sn _,= ~ T 90=C
(9.173) COOC2H4OCH3
Also larger functionalized monomers like 13carbethoxybicyclo[ 10.1.0]trideca4,8-diene could be polymerized under the above conditions to the corresponding polyalkenamers b e i n g the functionalized cyclopropane moiety into the repeat unit ~4 (Eq. 9.174). n
(XX)C2~
T= 90"C "n=:~, 4
(9.~74)
631 9.8. Functionalized Polycyclic Olefins The ring-opening polymerization reaction using tolerant catalytic systems toward functionalities has been successfully applied to a substantial number of functionalized polycyclic olefins. 3-Carbethoxytricyclo[3.2.1.0~'4]oct-6-ene. This monomer has been readily polymerized with WCI6/Me4Sn in chlorobenzene at 90~ to the corresponding functionalized polymer, poly(3-carbethoxy- 1,5bicyclo[3.1 ]hexylenevinylene), by ring-opening reaction of the norbomene moiety iv4 (Eq. 9.175).
n
WCle/Mo4Sn ~COOCzHs
90"C" 3 hr Cony. = 99%
~
(9.175)
OOCzHs
The monomer conversion was nearly quantitative after 3 hours reaction time. A functionalized polymer with a bicyclic repeat unit, having M, = 45000 g/mole, has been obtained under the above conditions. 2,3,3,4,4,5--Hexafluorotricyclol4.2.1.0Z'Slnon-7-ene. Polymerization of this highly fluorinated monomer occurs in the presence of WCIjMe4Sn to poly(2,3,3,4,4, 5- hexaflu oro- 1,6-bicyclo [3.2] heptylenevinylene)62"67 (Eq.9.176). n
F
WCl6/Me4Sn
(9.176)
i=..._
F F " "F
F F
3,4--Dichlorotricyclo[4.2.1.0z'S]non-7-ene. This chlorinated monomer, 3,4dichlorotricyclo[4 2 1 02"5]non-7-ene, was found by Feast and coworkers tT~ to readily ring-open polymerize at 25~ under the action of WCl6/Me4Sn as a catalyst to form the chlorinated polyalkenamer (Eq 9 177) n
CI I
VVC Is/Me4S n =_ T = 25~
n
(9.177)
632 Though a detailed characterization of the resulted polyalkenamer has not been performed, the product had IR and ~H NMR spectra consistent with the expected ring-opened polymer. 3,3,4,4-Tet racya not ricyclo [4.2.1.02"5] n o n-7-ene. 3,3,4,4-Tet racyanotricyclo[4.2, l.OZS]non-7-ene can be ring-open polymerized to poly(3,3,4,4tetracyano- 1,6-bicyclo[3.2]heptylenevinylene) ~76(Eq. 9.178). n
NC" CN
WCI6/Me4Sn 9 =
~
\
/
,,
(9.178)
NC]I 1ICN NC CN
N
3,4-Bis(trifluoromethyl)tricyclo[4.2.1.0r~s] nona-3,7-diene. Ring-opening polymerization of 3,4-bis(trifluoromethyl)tricyclo[4.2.1.02"S]-nona-3,7-diene occurs readily to poly(3,4-bis(trifiuoromethyl)- 1,6bicyclo[3.2.0]heptenylenevinylene) ~77(Eq. 9.179). WCI6/Me4Sn
n
~C
(9.179)
F3
CF3 3,4-Dicarbomethoxytricyclo[4.2.1.02"s] nona-3,7-diene. Ring-opening polymerization of 3,4-dicarbomethoxytricyclo[4.2.1.02"S]-nona-3,7-diene occurs readily to poly(3,4-dicarbomethoxy- 1,6bicyclo[3.2.0]heptenylenevinylene) ~77(Eq. 9.180). V~,16/Me4Sn
n
(9.180)
H3 H3
H3r
H3
3,4- Dicy an ot ricy clo [4.2.1.02`s] n o n a-3,7-d ien e. Ring-opening polymerization of 3,4-dicyanotricyclo[4.2.1.02"S]-nona-3,7-diene occurs readily to poly(3,4-dicyano- 1,6-bicyclo[3.2.0]heptenylenevinylene) ~76
633
181) WC,16/Me4Sn n
-
(9.181)
.~
CN CN tert-Butyldimethylsiloxydeltacyclene (tert-Butyltetracydo [2.2.2 ~ . 11'(.03~l-no n-8-en e ). Polymerization of tertbutyldimethylsiloxydeltacyclene occurred readily under the influence of the Schrock molybdenum alkylidene catalyst, Mo(=CHCMe2Ph)(=N-2,6 iPr2Ph)(OtBu)2, to produce poly(tert-butyldimethylsiloxydeltacyclene) t~s (Eq. 9.182). ~e~Si
tB
M~ HCMe2PhXNArXOtBu~-----Toluene, chloroformor neat
n
(9.182)
The polymerization reaction of this monomer was carried out by Lautens et al., ~Ts either neat or as solutions in toluene or chloroform, under rigorous dry conditions. The polymer molecular weight and polydispersity were essentially dependent on the reaction conditions (Table 9.40). Table 9.40 Polymerization of tert-butyldim~ylsiloxydeltacycleae with Mo(CHCMe2Ph~I-2t6-iPrzPl ~OtBu)2 c ~ :lyst" , Solvent Mw(uncorr) M, DP PDI neat toluene
78200 13300
44300 9300
315 55
1.77 1.44
'Data from reference~n The process was found to be highly exothermic and the increase in selectivity observed may be due to a more controlled polymerization under higher dilution conditions. Poly(tert-butyldimethylsiloxydeltacyclene) showed improved solubility in common organic solvents such as benzene or
634 chloroform compared to polydeltacyclene. The product was characterized by GPC and ~H and ~3C NMR spectroscopy and displayed a complex microstructure consisting of head-head, tail-tail and head-tail isomers. The glass transition temperature, measured using capillary rheometry, increased from 88~ to 108~ for polydeltacyclene and poly(tertbutyldimethylsiloxydeltacyclene), respectively. 7,8-Bis(trifluoromethyl)tricyclo[4.2.2.0~'Sldeca-3,7,9-triene. In order to manufacture soluble, stable and well-characterized polymers which could be converted to polyacetylene, Feast and coworkers ~79 investigated the ringopening metathesis polymerization of 7,8bis(trifluoromethyl)tricyclo[4.2.2.02'~]deca-3,7,9-triene with WCI6/Me4Sn in chlorobenzene at room temperature (Eq. 9.183).
n
F3C~
V~16/Me4Sn ~ Chlorober~ene,RT
F3C
~..~
/-~_
F3C
CF 3
(9.183)
11= 90%
Polymer yields of over 90% have been reported under these conditions. Subsequent decomposition of this polymer at 50-120~ gave polyaeetylene with elimination of aromatic moieties (Eq. 9.184).
A
(9.184) +
F3C
CF3
F3
F3
This new, attractive and efficient way to prepare polyacetylenes is known as "Durham precursor route". Polymerization of 7,8bis(trifluoromethyl)tricyclo[4,2,2,02,5]deca-3,7,9-triene was first carried out by Edwards and Feast ~8~using both WCI6/Ph4Sn and TiCIVEhAI catalysts, the former catalyst giving roughly equal amounts of cis and trans main chain double bonds whereas the latter predominantly trans stereochemistry. The ring-opening polymerization of this monomer in the presence of the above catalysts occurred readily in toluene as a solvent. In both cases, a
635 fawn colored granular product was obtained which was soluble in acetone and chloroform. These authors observed that the product decomposed spontaneously on standing in the dark under an atmosphere of dry nitrogen and more rapidly in solution. The decomposition was accompanied by a sequence of color changes from yellow, through orange, red and brown to eventually yield a black material with a metallic lustre and a colorless liquid identified as 1,2-bis(trifluoromethyl)benzene. In their earlier work on Durham polyacetylene by "standard Durham route", Feast and coworkers ~s~ used mainly the WCIdPh4Sn and WCIdMe, Sn catalysts to produce trans- and cis-vinylene units which were statistically distributed in the polymer chain. The polymer formed under these conditions had a relatively broad molecular weight distribution. However, when a well-defined initiator of the kind introduced by Schrock was used, namely M(=CH'Bu)(NAr(OtBu~h, (M = W or Mo), living polymerization resulted and the molecular weight distribution of the product precursor was narrow and controlled simply by the ratio of the monomer to initiator, ts~'ts2 The polyacetylene made via this last route is known as "improved Durham Polyacetylene". ~s3 This improvement in the precision and control with which the synthesis of polymer precursor may be carried out was anticipated to have an effect on the control of the precursor film formation and the detailed structure of the final product, transpolyacetylene. ~ s 7 The precursor polymer prepared by "standard Durham route" can be readily handled in solvents such as butanone, and polyaeetylene films of very high quality can be obtained. These have been used for the construction of semiconductor devices including metal insulator semiconductor field transistors (MISFETs). ~ss Moreover, the kinetics of the transformation and cis-trans isomerization reactions have been extensively studied and various steps for trans-polyacetylene synthesis are well understood. ~s9 Though the "standard Durham route" is very convenient, the precursor polymer thus prepared is not stable at room temperature, as the elimination to form polyacetylene is a symmetry-allowed reaction and the polymer must be stored at low temperature. An alternative route to polyacetylene synthesis via polymer precursor, known as "photoisomer Durham route", involves first photoisomerization of 7,8-bis(trifluoromethyl)tricyclo[4.2.2 .02,~]deea-3,7,9triene to its photoisomer, 3,6bis(trifluoromethyl)pentacyelo[6.2.0.0~'4.03'6.05'7]dec-9-ene, then ringopening polymerization of this monomer to the corresponding precursor
636 polymer and eventually thermal decomposition of the precursor polymer to trans-polyacetylene ~ (Eq. 9.18 5).
4,
E~
cF3
The advantage of this procedure is that the conversion of the precursor polymer to polyacetylene is no longer symmetry-allowed so that the precursor is much more stable thermally, requiting temperatures in excess of 60~ to bring about conversion. In practice, polyacetylene films are usually generated by this procedure between 100~ and 120~ The disadvantage is that the elimination reaction is strongly exothermic and there is the risk of thermal runaway and explosion if bulk samples or thick films are converted. TM Dilute solutions and thin films of the precursor, however, could be handled safely, and structural and electronic properties of the polyacetylene prepared in this way could be evaluated. ~92 Dimethyl 2,s| deca-3,7,9-triene-7,g-diearboxylate. tricyr Another Durham monomer used successfully for polyacetylene synthesis through ROMP reaction is dimethyl tricyclo[4.2.2.02"~]deca-3,7,9-triene 7,8-dicarboxylate. ~79'~93 Initially, dimethyltricyclo [4.2.2.02"S]deca-3,7,9 triene-7,8-dicarboxylate was polymerized with WCI6/Me4Sn in chlorobenzene at 20~ for 1 hr to yield 95% poly(5,6-dicarbomethoxy-2,3bicycloocta[2.2.2]dienylenevinylene)~79 (Eq. 9.186).
H3C02C~
H3C02C'
WCIs/Me4Sn .._--Chlorobenzene, RT 11= 95%
..r.~
L~
H3C02C
/q="
'n
(9.186)
C02CH3
In a second step, poly(5,6-dicarbomethoxy-2,3-bicycloocta[2.2.2] dienylenevinylene) undergoes a thermal conversion at 50-120~ to polyacetylene with elimination of dimethylphthalate~84 (Eq. 9.187).
637 A +
H30020 0020H3
nC ~ C
Nco2
o2cN
More recently, dimethyl tricyclo[4.2.2.02"S]deca-3,7,9-triene-7,8dicarboxylate has been polymerized in a controlled fashion to polyacetylene precursor using well-defined Mo or W carbene initiators. The final product is analogous to conventional forms of polyacetylene and can be doped to similar levels of conductivity. Dim eth yl tricy clo [4.2.2.0 ~s ] deca-3,9-d ien e- 7,8-dicarbo xyla t~ Polymerization of dimethyl tricyclo[4.2.2.0~S]deca-3,9-diene-7,8 dicarboxylate occurs readily in the presence of various metathesis catalysts 193 (Eq. 9.188).
n H30020
V~Ie/Me4Sn
H3C02C
(9.188)
Chlorobenzec~e, RT
H..,jC C"
"C02CH3
Polymers of different cis contents (6-77%) have been obtained. The products are quite stable because the retro Diels-Alder reaction is less favored as compared to polymers formed from dimethyl tricyclo [4.2.2.02"5]deca-3,7,9-triene-7,8-dicarboxylate. p-Dimethoxy-3,4-benzotncyclo [4.2.2.0 ]deca-3,7,9-trlene. pDimethoxy-3,4-benzotricyclo[4.2.2.02"5]deca-3,7,9-triene has been used as an alternate Feast monomer to prepare polyacetylene by the "Durham route". This monomer has been polymerized in the presence the welldefined tungsten carbene catalyst W(=CH'Bu)(=NAr)(OrBu)2 to a precursor polymer (Eq. 9.189) 9
9
2,5
9
638
OMe n~
W(CHtBu)(NAr)(OtBu)2 =
MeO
(9.189)
MeO---~--~---OMe
which was convened to polyacetylene upon heating (Eq. 9.190).
nO
MeO-<>--OMe
o.o
Block copolymers of p--dimethoxy-3,4-benzotricyclo[4.2.2.02"5]deca-3,7,9triene and norbornene or 5-((trimethylsiloxy)methyl)norbornene were prepared to obtain copolymer films containing self-assembled polyaeetylene structures. 185 Functionalized tetracyclo[4.4.0.12"S.l~'t~ On substituting tetracyclo[4.4.0.12,s. 17'~~ with alkyl, aryl, aralkyl and functional groups in any of its available positions (R~-R~2), a range of functionalized monomers suitable for ring-opening polymerization have been prepared. By polymerization of these highly substituted tet racyc1o[4.4.0.1 z.~.1'7 l0]dodec3-enes in the presence of metathesis catalysts consisting of Mo or W chlorides and organoaluminium compounds, functionalized ring-opened polymers of varying structures have been produced~94 (Eq. 9.191).
R3,.R4R7,..Re n
,.
~ y y X
ROMP~
[W],[Mo]
R3,, ~,R4 __-,_
R('\ /'R2 RsX_.~yRB Y X
(9.191)
639 where R t-Rs are alkyl, aralkyl or aryl groups and X and Y are various functional groups Multicyclic norbornene-type monomers. Ring-opening polymerization reactions of a wide range of multicyelic norbomene-type monomers bearing functional groups of the general formula (Eq 9 192)
R2_ ,R8 R12rRI ~1o m
1.= R1
(CXY)x
R~
(9.192)
h._ v
RIr
iR13
(cxY)x where n is 0 or a positive number, x is at least 3, R~-R~s are alkyl, aryl or aralkyl groups and X and Y are various functional groups have been reported in numerous patents. ~95't96 9.9. References
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649 179. J.H. Edwards, W.J. Fast and D.C. Bott, Polymer, 25, 395 (1984). 180. J.H. Edwards and W.J. Feast, Polym. Commun., 21,595 (1980). 181. a. R.R. Schrock, S.A. Krouse, K. Knoll, J. Feldman, J.S. Murzdek and D.C. Yang, J. Mol. Catal., 46, 243 (1988); b. R.R. Schrock, Polym. Mater. Sci. Eng., 58, 92 (1988). 182. a. K. Knoll, S.A. Krouse, and R.R. Schrock, J. Am. Chem. Soc., 110, 4424 (1988); b. K. Knoll and R.R. Schrock, ,/. Am. Chem. Soc., 111, 7989 (1989). 183. J.H.F.Martens, K. Pichler, E.A. Marseglia, R.H. Friend, H. Cramail, E. Khosravi, D. Parker and W.J. Feast, Polymer, 35, 403 (1994). 184. a. L.Y. Park, R.R. Schrock, S.G. Stieglitz, and W.E. Crowe, Macromolecules, 24, 3489 (1991); b. L.Y. Park, D. Ofer, T.J. Gardner, R.R. Schrock, M.S. Wilton, Chem. Mater. 4, 1388 (1992). 185. R.S. Saunders, R.E. Cohen, and R.R. Schrock, Macromolecules, 24, 5599(1991). 186. M. Buchmeister and R.R. Schrock, Macromolecules, 28, 6642 (1995). 187. P. Dounis, W.J. Feast and G. Widawski, J. Mol. Catal. A. Chem., 115, 51 (1997). 188. J.H. Burroughes, C.A. Jones and R.H. Friend, Nature, 335, 136 (1988). 189. D.C. Butt, C.S. Brown, C.K. Chai, N.S. Walker, W.J. Feast, P.J.S. Foot, P.D. Calvert, N.C. Billingham and R.H. Friend, Synth. Met. 14, 245 (1986). 190. W.J. Feast and J.N. Winter, d. Chem. Soc., Chem. Commun., 202 (1985). 191. W.J. Feast, D. Parker, J.N. Winter, D.C. Bott and N.S. Walker, Springer Ser. Solid State Sci., 63, 45 (1985). 192. C.A. Jones, R.A. Lawrence, J. Martens, R.H. Friend, D. Parker, W.J. Feast, M. Logdlund and W.R. Salaneck, Polymer, 32, 1200 (1991). 193. W.J. Feast, M.J. Taylor and J.N. Wimter, Polymer, 25, 593 (1987). 194. a. Mitsui Petrochem Ind. KK, Japan. Patent 33 5,042 (1990); b. Mitsui Petrochem Ind. KK, Japan. Patent 038,453 (1990); c. Mitsui Petrochem Ind. KK, Eur. Patent 384,693 (1990). 195. a. BFGoodrich, U.S. Patent 4,138,448 (1979); b. BFGoodrich U.S. Patent 4,262,103 ( 1981 ); c. BFGoodrich U.S. Patent 4,357,449 (1981 ); 196. a. BFGoodrich, U.S. Patent 4,418,178 (1983); b. BFCax~rich, U.S. Patent 4,418,178 (1983); c. BFGoodrich, U.S. Patent, 4,571,375 (1983); d. BFGoodrich, Eur. Patent 140,319 (1983).
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651
Chapter 10
POLYMERIZATION
OF HETEROCYCLIC
OLEFINS
Although classical cationic, = anionic, z Ziegler-Natta 3 and ROMP 4'5 catalysts are very sensitive to heteroatom-containing compounds, to water and oxygen, advanced exploration of polymerization reactions of heterocyclic olefins showed that, under appropriate conditions, this class of monomers can be polymerized to heteroatom-containing polymers. In addition, with the advent of well-defined ROMP catalysts, tolerant of functional groups, disclosed by Grubbs 6 and Schrock, 7 the possibilities of polymerizing heterocyclic olefins have increased considerably.
10.1. Four-Membered Ring Monomers Of a great interest, the anionic ring-opening polymerization of substituted silacycloakenes with the formation of unsaturated linear poly(1sila~kenes) has been explored by Weber and coworkers, s One relevant example is the stereoselective polymerization of l,l-dimethyl-1silacyclobutene in the presence of butyllithium and hexamethylphosphoramide in THF at -78~ giving poly(l, l-dimethyl- 1-silacis-but-2-ene) in high yield (Eq. 10.1). Me
Me_S/~ Me
nBuL,.~ .,,(_,,,,,~~ i~ Me
(10.1)
The polymer thus prepared was stable thermally up to 225~ however, between 225~ and 300~ it lost 5% of the weight whereas above 300~ a rapid decomposition took place until 430~ when complete weight loss was recorded.
10.2. Five-Membered Ring Monomers Depending on the catalyst employed, polymerization of 2,3dihydrofuran could occur by vinyl or ring-opening mechanism. Thus,
652 when diphenylcarbene tungsten pentacarbonyl or methoxyphenylcarbene tungsten pentacarbonyl complexes are used as catalysts, 2,3-dihydrofuran forms the saturated vinyl polymer, especially after UV-irradiation, by a Ziegler-Natta mechanism 9'~~(Eq. 10.2).
Ph2C=W(CO)5 n /,,,O3
Ph(MoO)O=W(CO)540.0 =--
[/-,, ,~O In v
(10.2)
By contrast, with diphenylcarbene chromium pentacarbonyl or methoxyphenylcarbene chromium pentacarbonyl as a catalyst, 2,3dihydrofuran gives the unsaturated ring-opened polymer in a fully head to tail fashion~~ (Eq. 10.3).
Ph2C=Cr(CO)5 Ph(MeO)C=Cr(CO)5 40*C-50"C
(10.3)
The initiation of metathesis polymerization of dihydrofuran with chromium carbene complexes may be achieved thermally over the temperature range of 40-50~ or photochemically by irradiation at -10~ to -20~ This behavior indicated that the elimination of a CO ligand to provide a free coordination site for the cycloolefin played an important role. Noteworthy, the cis content of the polymer obtained photochemically at -20~ was 65% whereas that of the polymer obtained thermally at 40~ was around 55%. The yield in unsaturated polymer prepared with the first catalyst was 4050% and with the second one 30-40%. In the first case a high molecular weight polymer with a cis/trans ratio close to 1 was obtained while in the latter case a polymer with a lower molecular weight was produced. l,l-Dimethyl-l-silacyclopent-3-ene undergoes readily ring-opening polymerization in the presence of WCI6/Na202/'Bu3AI at 20~ to form poly(l, l-dimethyl- 1-sila-cis-pent-3-enes) t~,~2(Eq. 10.4).
WC16/Na202/iBu3AI-.--
n M~ "Me
nBuLi/HMPA
~ S
Me i~,-~ I
Me
(10.4)
653 In these conditions, conversions of the monomer of ca. 50~ have been attained. Remarkably, anionic polymerization of 1,1-dimethyl-1silacyclopent-3-enes is totally different from the similar reaction of cyclic dienes, leading by ring-opening to poly(l-sila-cis-pent-3-enes). ~3 The reaction is stereoselective, gives rise, in most cases, to high molecular weight polymers with most probable molecular weight distribution M,jM, ~2. For instance, treatment of l,l-dimethyl-l-silacyclopent-3-ene with catalytic amounts of butyllithium and HMPA or TMEDA in THF at low temperatures (-40~ to -78~ led to formation of poly(1, l-dimethyl- 1-silacis-pent-3-ene) of high molecular weight. Polymerization of l-methyl-l-phenyl-l-silacyclopent-3-ene with butyllithium and HMPA gave rise to poly(l-methyl-l-phenyl-l-sila-cispent-3-ene)14 (Eq. 10.5).
n
Sl
nSul.J
~
M~ "Ph
I ~=N /Si\~]= n
(10.5)
Ph
Further reduction of this polymer with diimide, which was generated in-situ by the thermal decomposition of p-toluenesulphonhydrazide in refluxing toluene, produced the saturated polymer, poly(l-methyl-l-phenyl-1silapentane) (Eq. 10.6). Me
Me
Ph
Ph
(lo.6)
The structure of this polymer was determined by multinuclear resonance spectroscopic technique, i.e., by the 'H-, '3C- and 29Si-NMR methods. Analogously, 1,l-diphenyl-l-silacyclopent-3-ene in the presence of butyllithium and HMPA in THF formed poly(1,1-diphenyl- 1-sila-cis-pent-3ene) ,~ (Eq. 10.7). nBuU
PI '' Ph
Ph I Ph
(10.7)
654 Furthermore, anionic polymerization of l,l,3-trimethyl-l-silacyclopent-3ene was found to be highly regioselective at -78~ to yield a polymer in which cis-l,4-isoprene units are joined to dimethylsililene units almost exclusively in a head to tail orientationS3 (Eq. 10.8). Me
n
nBuU= Me/ \ Me
Me
Me t
~ S i ~
(10.8)
Me
By contrast, reaction of 1-methyl-l-silacyclopent-3-ene yielded poly(lmethyl- 1-sila-cis-pent-3-ene) of low molecular weight~3 (Eq. 10.9).
I•le
n
(10.9)
Me The low molecular weight of the polymer allowed determination of the structure of the end groups by standard tH, t3C and 29Si NMR spectroscopy. Anionic polymerization of l,l-divinyl-l-silacyclopent-3-ene with butyllithium and HMPA in THF at low temperature (-78~ yielded a mixture of poly(l, l-divinyl-l-sila-cis-pent-3-ene) with the cyclic dimer, 1,1,6,6-tetravinyl- 1,6-disilacyclodeca-3,8-diene t6't7 (Eq. 10.10).
n ~ __/ \__
nBuLi THF
(10.10) n/2
The ratio of polymer to dimer was insensitive of temperature (-78 to -45~ but dependent upon monomer concentration. This carbosilane
655 polymer had a high degree of unsaturation and was converted on thermal decomposition to a high char yield. Interestingly, experiments on the effect of monomer concentration and temperature on the ratio of dimer to polymer provided additional understanding to the mechanism of this reaction. The observation that the pure polymer could be equilibrated to a mixture of dimer and polymer under the reaction conditions is particularly relevant for this process. Specifically, treatment of poly(1,l-divinyl-l-silacis-pent-3-ene) with catalytic amounts of monomer, n-butyllithium and HMPA in THF at -78~ resulted in the formation of significant amounts of dimer as well as polymer (Eq. 10.11).
nBuU
(Io.~I)
The ratio of dimer to polymer, however, was somewhat lower than that found in the polymerization of l,l-divinyl-l-silacyclopent-3-ene. The reason for this behavior was assigned to the function of the monomer to convert the n-butyllithium into a hypervalent siliconate intermediate which could catalyze the equilibration process. However, when pure poly(1,1divinyl- 1-sila-cis-pent-3-ene) was subjected to treatment with nbutyllithium and HMPA in THF at -78~ complete gelation occurred. This result was attributed to the reaction of n-butyllitium with the pendant vinyl groups of the polymer. It is interesting to note that the reaction of 3,4-dimethyl-lsilabicyclo[4.4]nona-3,7-diene in the presence of n-butyllithium gave rise to a metathetic cyclic dimer 18'19(Eq. 10.12).
n
nBuU/HMPA THF/-78~
,,0,2,
A similar dimer product has been obtained with 3,4-benzo-lsilabicyclo[4.4]nona-3,7-diene in the presence of n-butyllithium as a catalyst 19 (Eq. 10.13).
656
nBuLi/HMPA n
THF/-78~
=
rV2
(10.13)
However, on using WCldPh4Sn as the initiator, 3,4-benzo-lsilabicyclo[4.4]nona-3,7-diene gave rise to ring-opened polymer by the scission of the unsubstituted silacyclopentene ring ~9'~ (Eq. 10.14). m
n
WCle/Ph4Sn
=
(10.14)
10.3. Heteroatom-Containing Norbornene
Metathesis polymerization of heteroatom-containing norbornene with classical ROMP catalysts occurs with difficulty due primarily to side reactions between the heteroatom present in the monomer and the catalyst. This reaction occurs readily, however, with functional group tolerant welldefined catalysts leading to a new class of acyclic heteroatom-containing polymers. These polymers are capable of forming coil or helical structures with ion-binding cavities having special properties analogous to the cyclic crown ethers and cryptands. 7-Oxanorbornene and substituted derivatives. By ring-opening metathesis polymerization, 7-oxanorbomene gives rise to poly(2,5poly(ethyli dene-co-2, 5-t etrahydro furan )2~ furanylenevinylene) or (Eq. 10.15). O
(10.15)
The poly(7-oxanorbornene)s resulting from the selective metathesis polymerization of 7-oxanorbornene are of interest due to their potential
657 ionophoric properties. A series of 7-oxanorbomene derivatives has been reported by Novak and Grubbs 22 to undergo ring-opening polymerization in the presence of various transition metal catalysts to the corresponding substituted poly(7-oxanorbomene)s (Eq. 10.1 6).
0
2
[
R2
~"
R3
where R mis hydrogen or an alkyl group and R2 and R3 may be hydrogen or a hydroxymethyl and alkoxymethyl group (Scheme 10.1).
0
0
I
O
II
~L~CH2OTMS V
0
CH2~
0
Ill
O
VI
IV
.zOCH3 ~.,/CH2OCH3 X.~..CH2OCH3 CH2OCH3 ~~CH2OCH3 ~-..J/CH2OCH3 O
O
CH3
C2H~
VII
VIII
Scheme 10.1
The catalytic systems effective for the ring-opening metathesis polymerization of the 7-oxonorbomene derivatives investigated are selected in Table 10.1. The cis double bond content and ring diad tacticity of the polymers obtained as well as the molecular weight and polydispersity index depend essentially on the monomer, catalyst and reaction conditions.
658 Table 10.1 Rmg-~enmg metathesis polymenzauon of 7-oxanorbomene derivatives with various catalytic systems'
Compound
Catalytic System
(,Scheme I0.1~ Ib
((CH3)3CCHzO)2W(=CHtBu)Br2 ((C F3)2(CH3)CO)2W(=CHtBu)(C6H32,6(CH(CH3)2)N) RuCI3, Ru(I,5-COD)CI3, OsCl3
IIb
((CH3)3CCH20)2W(=CH'Bu)Br2 ((CF3)2(CH3)CO)2W(=CH~Bu)(Cd-132,6(CH(CH3)2)N) RuCI3, Ru(I,5-COD)CI3, OsCI3
IIIb
RuCI3, Ru(I,5-COD)Ci3, OsCl3
IV"
RuCI3, Ru(I,5-COD)CI3, OsCl3
V~
RuCI3, Ru(I,5-COD)CI3, OsCI3
VI
((CH3)3CCH20)2W(=CH'Bu)Br2 ((C F3)2(CH3)CO)2W(=CH'Bu)(Cd-132,6(CH(CH3)2)N) RuCI3, Ru(I,5--COD)CI3, OsCI3
9
VIF
((C F3)2(CH3)CO)2W(=CHtBu)(Cd-132,6(CH(CH3)2)N)
VIIF
((CF3)2(CH3)CO)2W(=CHtBuXC6H3-
2,6(CH(CH3)2)N) |
'Data from reference 22 bEndo/Exo = 3/1 r Greater than 95% exo isomer. It is important to note that the poly(2,5-furanylenevinylene)s, resulting from the selective metathesis polymerization of 7-oxanorbomene monomers, exhibit potential ionophoric properties. Molecular model studies indicated that these poly(7-oxanorbornene)s have the ability to form helical
659 structures with all the tetrahydrofuran oxygen atoms facing into the interior of the helix 22 (Eq. 10.17).
0 (10.17)
Noteworthy, this unique helical conformation may allow these polymers, when in solution, to act as useful acyr ionophores, much like their cyclic analogs, the cyclic crown ethers. Thus, preliminary liquid/liquid and solid/liquid ion extraction experiments carried out by Novak and Grubbs ~ indicated that these poly(7-oxanorbornene)s indeed coordinated various cations. For instance, po ly(2, 5-( 3,4bis(methoxymethyl)furanylene)vinylene) prepared under the above conditions coordinated Na', K +, and Cs § salts but not Li§ salts, as observed through solid/liquid extraction. Of greater interest, however, was the observation that the flexible binding cavities formed by poly(2,5-(3,4-bis(methoxymethyl)furanylene)vinylene) preferentially complexed large polyaromatic cationic dyes such as methylene blue and rhodamine 6G. This polymer displayed high selectivity by complexing only dyes formed of large organic cations and small anions (CI) whereas dyes consisting of Na § and large aromatic anions were not complexed. Remarkably, this selectivity was exactly opposite to that observed for ionic complexing by using 18-crown-6 ethers. It is also significant that thin films composed of the poly(7oxanorbomene)s thus prepared may possess oxygen rich ionophoric channels that would enable them to act as ion permeable membranes. Demonstration of ion transport through these ionophoric materials was obtained by placing solid membranes cast from the poly(7-oxanorbomene) polymers between two ion concentration cells and measuring the membrane potential resulting from diffusion of ions through the ionophoric membranes. From the measured membrane potentials, cation transport numbers for K § Na § and Li § (all CI salts) were calculated to be 0.84, 0.73,
660 and 0.73, respectively. Efforts by Grubbs and coworkers z3 were directed on the systematic structural modifications of the basic poly(7oxanorbornene) skeleton in order to enhance both their ion transport and ion selectivity properties. Polymerization of 5-methoxy-7-oxanorbomene has been effected in the presence RuCI3, OsCl3 and Ru(I,5-COD)CIz as catalysts ~24 (Eq. 10.17a).
O
, u ,3,osc,3
n
OMe
Ru[C OD]C 12"-
(10.17a) \
OMe
Poly(methoxynorbornene) has been readily available by this ring-opening metathesis reaction. The methyl ether derivative, 5-methoxymethyl-7-oxanorbomene, can be polymerized with a wide range of catalysts, leading to poly(5methoxymethylnorbornene) 21"22(Eq. 10.17b).
O
[W],[Ru] -_
CH2OMe
''0''0'
\ CH2OMe
The tungsten carbene initiator W(=CHtBu)(=NArXOCMe(CF3)2)2 gives rise to a polymer with very high cis content (--99%), [RuCl(la-Cl)(rl3:rl L C~0H~6)]z (C~0H~6=2,7-dimethyloctadienediyl) forms a polymer with high trans content (---96%) and [Ru(HzO)6](OTs)2 leads to a polymer with an intermediate (--45% cis) stereoconfiguration. While the tfigh-cis polymer, when made from enantiomeric monomer, has mainly HH, TT structure and is therefore largely syndiotactic, the tfigh-trans polymer has an HT structure and is therefore essentially isotactic. The tacticity with respect to each type of double bond of the polymer with an intermediate stereoconfiguration could not be determined accurately because of the overlap of the cis and trans olefinic bands in the ~3C NMR spectrum.
661 Important work on the ring-opening polymerization of a number of 7-oxanorbornene derivatives bearing carboxylic, carbomethoxy, dicarboxylic anhydride, hydroxymethyl, methoxymethyl and acetoxymethyl groups, catalyzed by platinum group metal compounds in aqueous ethanolic solvents, has been performed recently by many authors. These monomers, easily prepared by Diels-Alder reaction of furan with a functionalized dienophile and subsequent transformation of the functional groups, allowed to produce under the above conditions new oxygen-containing polymers of varying structures and properties. Polymerization of 2,3-bis(hydroxymethyl)-7-oxabicyclohept-5-ene (over 95% exo isomer) has been first carried out by Novak and Grubbs ~ s using RuCI3, OsCl3 and Ru(I,5-COD)CI3 as catalysts. Later on, Lu et al. 25 carried out the reaction of exo, exo isomer with RuCI3, employing various water:ethanol ratios as reaction medium. The polymer was significantly dependent on the water content and catalyst concentration (Table 10.2). Table 10.2 Polymerization of 2,3-exo, exo-bis(h ydroxymeth yl)-7-oxabicyclohept-5-ene (M) with RuCI3 (I) in water/ethanol'
if]
[Water]
mole.kg"~
mmole.ks"
vol.-%
Temp ~
Time hr
2.0 1.9 2.0
20 70 20
10 50 90
60 45 60
48
9
22 21
87
[M]
Yield %
66
'Data from reference 2~
In each case the rubbery polymer was insoluble in the solvents commonly used for GPC and NMR (THF, N,N-dimethylacetamide, acetone, chloroform). Presumably, the insolubility was a consequence of hydrogen bonding between polymer chain. However, the product was swollen to a considerable degree by DMSO-d6 and a reasonable ~3C NMR spectrum was obtained consistent with the expected structure (Eq. 10.18).
r,?.x..,,.~C H2OH
n j~,)~~.CH2OH
RuCI3-3H20 EtOH/H2 O~
HOH2c CH2OH
(10.18)
662 Microstructural analysis of this spectrum indicated that ca. 30% of the chain units were in the trans stereoconfiguration. Interestingly, polymerization of the monomethyl ether of the above monomer, 2-exo-hydroxymethyl-3-exo-methoxymethyl-7oxabicyclo[7.7.2]hept-5-ene, using RuCI3.3H20 in 10 vol.-% water in ethanol, effected by Lu et al. 25, occurred in excellent yields to form high molecular weight polymer (Table 10.3). Table 10.3 Polymerization of 2-exo-hydroxymethyl-3-exo-methoxymethyl-7oxabicyclo[7.7.2]hept-5-ene (M) with RuCI3 (I) in water/ethanol at 60 *C~ [I]
[M]
mole.ks"1
mmole.kB |
9 19
0.8 2.0
[Water] vol.-%
Time hr
Yield %
'" Mb , g.mole"1 '
10 10
48 48
1O0 100
200000 ~ -
d
'Data from reference'; bCalibrated with polystyrene standards:molecular weight as "polystyrene",~Soluble sample taken directly from the reaction flask. Polymer was insoluble when precipitated and dried; dlnsoluble in THF. It was noted that polymers which were precipitated and dried were incompletely soluble in the usual solvents (THF, N,N-dimethylacetamide, acetone and chloroform). A sample of polymer taken directly from the reaction mixture was soluble and was analyzed by GPC in the usual way to obtain a molecular weight of 200000 g mole t. The t3C NMR spectrum of the highly swollen polymer in CDCI3 was consistent with the expected ringopened structure (Eq. 10.19).
~~~,
CH2OH RuCI3.3H20 CH2OMe EtOH/H20=-
(10.19) HOH2C CH2OMe
Microstructural analysis based on the spectral data suggested an all-tram configuration of the polymer chain. The large extent of swelling of poly(2exo-hydroxymethyl-3-exo-methoxymethyl-7-oxabicyclo [7.7.2] hept-5-ene) in chloroform contrasted with the very limited swelling of poly(2,3-
663 in the same solvent. Possibly, this fact reflects a reduced propensity towards H-bonding when one of the hydroxymethyl groups is methylated. Ring-opening metathesis polymerization of bis(methoxymethyl)-7oxabicyclo[2.2.1 ]hept-5-ene to the corresponding polyalkenamer has been extensively investigated by Benedicto, zt Novak and Gnabbs, 22"26'27Feast and Harrison, 2s'29 France et al. 3~ and Lu et al. ~3~'33 using various catalytic systems (Eq. 10.20).
exo, e x o - b i s ( h y d r o x y m e t h y l ) - 7 - 0 x a b i c y c l o h e p t - 5 - e n e )
:?.,.,..,./CH2OMo RuCI3.3H20 n /.p~~CH2OM e EtOH/H20"-
(10.20) MeOH2C
CH2OMe
Some relevant data for the polymerization of 5,6bis(methoxymethyl)-7-oxanorbornene (greater than 95% exo isomer) with four catalytic systems are presented in Table 10.4.
Rmg~mg
Table 10.4 polymerization of 5,6-bis(methoxymethyl)-7-oxanorbomene using various catalytic systems (O'
Solvent A
Cd-k
B
C6HsCH3 CcJ'~C2HsOH CzHsOH CeH6/C2HsOH CH3OH
C C D
D
"Data from
Cis/ Trans %
42/58 93/7 7/93 34/64 18/82 30/70
reference22, bA is
Sy,e
MW
MII
Iso
(xl0 "3)
(xl0 "3)
PDI
55/45 28/72
5.80 29.5 338
3.20 19.4 172 973 77.6 792
1.81 1.52 1.97
50/50
1120
133 965
1.15 1.71 1.22
((CH3)3CCH20)zW(=CHrBu)Br2, B
IS
((CF3)2(CH3)CO)2W(=CH'Bu)(C6H3-2,6(CH(CH3)2)N),C is RuCI3, D is Ru(I,5COD)CI3 The microstructure of poly(2,5-(3,4-bis(methoxymethyl) furanylene) vinylene) was determined by ~H and ~3C NMR spectroscopy and the molecular weight by gel permeation chromatography relative to
664 polystyrene. It is obvious that the choice of the appropriate catalyst can offer significant synthetic control over polymer characteristics such as the cis/trans ratio of the double bonds and the ring diad tacticity. Interesting data on the polymer microstructure were also reported by Feast and Harrison 28"29 in the ring-opening polymerization of exo, exo-2,3bis(methoxymethyl)-7-oxanorborn-5-ene in aqueous media using trichlorides of ruthenium, iridium and osmium as the catalysts. The inclusion of cis-but-2-ene-l,4-diol or its dimethyl ether in the reaction medium had a marked effect on both induction times and reactivity, and allowed control of the molecular weight of the product polymers, poly {2,5[ 3,4-bi s(methoxymethyl)fu ranylene] vinylene) s. Selected results on the polymerization of 2,3-exo, exo- and 2-endo3-exo-bis(methoxymethyl)-7-oxabicyclo [2.2.1] hept-5-ene recorded by Lu et al. 25 using commercial RuCI3 in water/ethanol are shown in Table 10.5. Table 10.5 Polymerization of 2,3-exo, exo- (M~) and 2-endo-3-exo- bis(methoxymethyl)-7oxabicyclo[2.2, l]hept-5-ene (M2) with RuCI3 (I) in water/ethanol at 60 *C' ii
M~, b Time Yield[ Mb hr % g/mole vol.-% mole,/kg 1.7 20 86 I 260000 10 2.1 M! 2.0 4 88 I 700000 90 1.9 MI 2.0 5 98 650000 100 1.9 MI 1.9 24 28 97000 10 1.9 Mz 2.1 24 76 120000 10 4 2.0 Mz M~ 1.4 20 100 15 96 560000 2.1 'Data from reference", bDetermmed by GPC in THF, calibrated with polystyrene standards, molar weights as "if polystyrene".
M
[M]
[11 mmole~ 21 19 19 19
[Water]
As it can be seen from Table 10.5, the 2,3-exo, exo-isomer readily polymerized in l0 vol.-% water in ethanol, giving polymer of high molecular mass in good yield. An increase in water concentration in the solvent resulted in faster reaction to polymers of higher molecular weight. Microstructure determination by ~H and ~3C NMR spectroscopy indicated that ca. 30% of the repeat units had cis stereoconfiguration of the double bonds. Compared under similar conditions, the rates of polymerization for 2..endo-3..exo-isomer were lower than those of 2,3-exo, exo-isomer at both low and high water concentrations and the corresponding molecular
665 weights were also lower. It is probable that the endo,exo-methoxymethyl groups sterically affect addition of monomer at the propagating centers, without affecting the unimolecular termination reaction. Polymerization of this isomer in 10% ethanol in water at a monomer:catalyst ratio of 100 yielded a polymer with a cis fraction of 47% as evaluated from mH and m3C NMR spectroscopy. The ~H and t3C NMR spectra were consistent with the expected structure (Eq. 10.21).
n
EtOH~20 CH2OMe
- ~ MeOH2(~ CH2OMo
A number of exo, exo-5,6-bis(alkoxymethyl)-7-oxanorbomenes with long alkyl chains have been polymerized by Kapellen and Stadler 34 with RuCI3.3H20 at 55~ in ethanolic solution to obtain poly(5,6bis(alkoxymethyl)-7-oxanorbome)s (Eq. 10.22).
n
,•oO• R R
RuCI3.3H20 -'=
(10.22) / OO\ R R
where R = -(CH2)mCH3, m = 0,9,13,15,17,19 and 21. It is significant that, contrary to a helical conformation as predicted by a previous molecular model study, the poly(5,6-bis(alkoxymethyl)7-oxanorbomene)s synthesized from these monomers adopted a coil conformation in solution. Moreover, in bulk these polymers showed side-chain crystalline properties. Of interest, the ring-opening polymerization of a monomer with an ether-ester functionality occurs readily in the presence of metathesis catalysts 35 (Eq. 10.22a).
o n
CO2(CH2CH20)2CH3
\
CO2(CH2CH20~CH3
666
7-Oxanorbomene-exo, exo-2,3-dicarboxylic acid was polymerized by Feast and Harrison 36 using the trichlorides of ruthenium and osmium as precursors to the initiating and chain propagating species to yield poly(2,5[3,4-bis(carboxylir acid)furanylene]vinylene (Eq. 10.23).
O
n
~__,~
/H OH
RuCI3.3H20
OsCI3.3H20 =
(10.23)
O/
/ OO \
N
N
Ruthenium-derived initiators gave polymers with 60% of cis-vinylenes whereas polymerization initiated by osmium compounds was irreproducible, giving polymers with either 65% or 95% cis-vinylenes. The inclusion of acrylic acid or maleic acid as chain transfer agents caused a marked reduction in the time to precipitation of polymer and the ultimate yield, cis2-Butene-l,4-diol affected the time to precipitation of the polymer in a similar manner without a reduction in yield and allowed control of the polymer molecular weight over the range M, = 10~ to 7x 102 with respect to poly(ethylene oxide) standards. Similarly, 7-oxabicyclo[2.2. l]hept-5-ene-2,3-exo, exo-dicarboxylic acid monomethyl ester was polymerized by Lu et al. 2~ with RuCIa.3H20 in 10 vol.% water in methanol to produce polymer of fairly high molecular weight (M = 50000 g/mole)in moderate yield (Table 10.6). Table 10.6 Polymerization of 7-oxabicyclo[2.2.1 ]hept-5-ene-2,3-exo, exo-dicarboxylic acid monomethyl ester (M) with RuCI3 (I) m water/ethanol at 60 ~ ~ [M] mole/kg
[q mmol~
[Water] vol.-%
Time hr
Yield %
M~/ g.moleb
MJ M, b
2.0 2.0
20 20
10 90
44 4
50 97
50000
2.7
'Data from reference 25, bDeterminod by GPC m THF, calibration with polystyrene standards.
667 The polymer was soluble in common solvents, including THF. The reaction was 10 times faster in 10 vol.-% ethanol in water, the resulting polymer being insoluble in THF but soluble in alkaline D20. The ~H and ~3C NMR spectra in alkaline D20 were consistent with the expected structure, except for partial (ca. 25%) transesterification to the ethyl ester (Eq. 10.24).
O
O
'oOMO RuCI3"3H20 H
O
EtOH/H20-=
(10.24)
HO OMeHO OEt Microstructure examination by NMR measurements indicated that ca. 30% of chain units were in the cis form. The product was best described as an approximately 75"25 statistical copolymer of the monomethyl and monoethyl esters of the dicarboxylic acids. Because of the complexity of the spectra, the sequence distribution could not be investigated. Ring-opening polymerization of exo, exo-2,3-dicarbomethoxy-7oxanorbomene occurs readily in the presence of a wide range of catalysts 36" ('. The reaction product, poly(2,3-dicarbomethoxy-7-oxanorbomene), is obtained in varying yields, depending on the catalyst nature and reaction conditions (Eq. 10.24a).
x..y.coocH3 [WJ,Mo],[Ru] ~-~COOCH3 O
(10.24a) H3COOC
COOCH3
Appreciable yields in polymer are also obtained when the ester functionality is a bulkier group. For instance, ring-opening metathesis polymerization of 2,3-dica~ohexyloxy-7-oxanorbomene gives rise to the substituted polymer3s (Eq. 10.24b) O
n k l J ' ~ ICOO(CI'Iz)sH #,-~',,,,J~COO(CI'~)sH
[Ru]
=
- ~ O ~
) - - k
H0-~C)eOOC
COO(CHaR
(10.24b)
668 and 2,3-dicarbohexadecyloxy-7-oxanorbomene substituted polymer3S(Eq. 10.24c). O n k~'[~7 ICOO(CI'Iz)IsH //,''',,,/~ COO(CH2)16H
to
the
corresponding
[Ru] ._ .v
(1024c)
HCh6OOC
COO(CHaheH
Similarly, the reaction of 2,3-dicarbobenzyloxy-7-oxanorbomene occurs in the presence of metathesis catalysts to corresponding dicarbobenzyloxy polymer 3~ (Eq. 10.24d).
O X~/,/COOCH2 Ph
n ~ ~COOCH2P h
[Ru]
(10.24d)
PhH2COOC
COOCH2Ph
Diesters of 7-oxabicyclo[2.2.1 ]hept-5-ene-2,3-exo, exo-dicarboxylic acid in which the ester groups are COO(CH2)z(glu), COO(CH2)z(man) and COO(CH2h(fuc), where (glu) is or-glucose, (man) is ot-mannose and (fuc) is ot-fucose attached via a C- or O-glycoside linkage, have been polymerized with RuCI3 in water 4z (Eq. 10.25).
O
RuCI3, H20 O
O O\ /
R
O R
(10.25)
55~
O O\
/
R
R
where R groups are: o
OH
HO
669 For instance, ring-opening polymerization of 7-oxabicyclo[2.2.1]hept-5ene-2,3-exo, exo-dicarboxylic acid diester in which the ester groups are COO(CHz)2(glu) and the a-glucose is bound by a C-glycoside linkage occurs readily with RuCI3 in water at 55~ to form in 72% yield the corresponding glucose-substituted C-glycoside neoglycopolymer (Eq. 10.26).
auc~. ~ n
0
= 55"c. 72%
0
0
(10.26)
0
These neoglycopolymers are soluble in water and are several thousand times as effective as the monomer in inhibiting erythrocyte agglutination by concanavalin A. In this way, the application of metathesis polymerization to the synthesis of polyglycomers opens new opportunities for the design of materials for modulation of cell adhesion, immobilization of particular cell types and investigation of extracellular interactions. '3
Bis[l[(3,4,5-tris((4-(dodecyl-l-oxy) benzyl)oxy)] benzyl)oxy]carbonyl]7-oxanorbornene. Living ring-opening polymerization of the monodendron 7-oxanorbornene monomer exo,exo-bis[[[(3,4,5-tris((4-(dodecyl- l-oxy) benzyl)oxy) ]benzyl)oxy] carbonyl]-7-oxanorbornene [bis 12ABG)ON] occurs readily in the presence of the ruthenium carbene complex RuCI2(=CHPh)(PCy3)2 (Cy = cyclohexyl) to form poly{bis[[[(3,4,5-tris((4(dodecyl- l-oxy) benzyl)oxy)] benzyl)oxy] carbonyl]-7oxanorbornene} ~(Eq. 10.27). H{C..H~),20. _ ~
C~?,
~~o..(~ c~o.r,~ ~ o
~c.,M~o
[Ru] ...._ 22"C,5-24h
H(CHI)120,,,v.,~. H(CH2)'z O " ~ ~ C H 0 H(CH2)I2Oy~CHzO~ IL~"~CH~)"J"~kCHzo.~O~
,,,~.CHzO H(CH2)I2~CH2~ CH20 H(CHz),20 "" H(CH:z)IzO''~'" -
H[CH~],~(r " *
(lo.27)
CH2~.%~o 11
670 The molecular weight of the resulting polymer was controlled by manipulating the ratio of monomer to initiator. Polymers with degrees of polymerization from 6 to 120, molecular weight M, between 12600 and 252800 and polydispersities PDI's of 1.06-1.29 were prepared. The living character of the monodendron polymerization was evaluated by monitoring the monomer conversion vs time; a linear dependence of ln([M]o/[M] on time (kp = 2.03x10"2M'~s~) was found (Figure 10.1). Cony. %
" '~176
/
8ok
-]5
-! 4
/
2
/
"t 3 I 2
/ /
201-1
0
1
~
60l401-
ln([M]o/[M])
11
/
50
100
150
200
"-'0 250
Time, mm Figure 10.1 Conversion vs time curves for polymerization of monodendron monomer bis(12ABG)ON with RuCIz(=CHPh)(PCy3)z(Cy = cyclohexyl) catalyst (Curve 1= conversion; Curve 2 = ln([M]0/[M]))(Adaptod from Ref.**) It is noteworthy that the monodendron monomer exo,exobis[ [ [(3,4,5-tris((4-(dodecyl- 1-oxy) benzyl)oxy)]benzyl)oxy]carbonyl]-7oxanorbornene and the resulting polymer self-assembled into disk-like and cylindrical shapes which produced an enantiotropie hexagonal columnar (q>h) liquid crystalline (LC) phase. Interestingly, the analysis of the q>h phase of the monomer, oligomers, and polymers as a function of the DP revealed four regions and mechanisms for the generation of q~ phase i.e., below the DP which forms a disk-like molecule, below the DP which corresponds to the maximum length of a disk-like molecule (DP = 2 6 ) , up to the DP which corresponds to the persistence of the rod-like cylinder (DP = 64), and above this value.
671 The living ring-opening polymerization of another monodendron 7oxanorbomene monomer, exo, exo-bis[G2]-7-oxanorbomene, derived from G2(OH) monodendron, based on the AB2 flexible mesogenic group, the 13hydroxy- 1-(4-hydroxyphenyl)-2-(4-hydroxy-4"-p-terphenyl) tridecane building block, has been performed using RuCI2(=CHPh)(PCy3)2 (Cy = cyclohexyl) in methylene chloride to form poly{ 5,6-bis[G2]dicarboxylate-7oxanorbomene} ~s(Eq. 10.28),
n
22~
O(~G21
12-110h
[G~]OOC
COO[G2]
where monodendron Gz(OH) is represented in Eq. 10.29. 83C
G"z(OH)
1"t3
)10
By this procedure, polymers with molecular weights ranging from 21900 to 811100 and polydispersities PDI of 1.09 to 1.55 have been produced from the monodendron monomer exo, exo-bis[G2]-7-oxanorbomene. 2,3- Diacetoxy-7-o xa no rbornene. 2,3 ..endo,cis-Diacetoxy- 7-oxanorbo mene can be polymerized quantitatively with Mo(=CHCMe2RX=NAr)(O'Bu)2 (Ar=2,6-C~Ha-~Pr2; R=CH3, C6H5) to form poly(2,3-cis-diacetoxy-7oxanorbornene) ~ (Eq. 10.30). O
[Mo]
fl
(10.30)
r
CH3 OOCCH 3
H3CCOO
OOCCH 3
672 Under these conditions, polymers of high molecular weight and narrow polydispersity (PDl
n ~~.CH2OCOMe _ " C H2OCOIVle
RuCI3.3H20 EtOH/H20=-
MeOCOH2C CH2OCOMe
(10.31)
(or HOCH2) (or CH2OH)
With both isomers, high yields and molecular weights have been recorded working at 10 vol.-% water in ethanol at a temperature of 60~ (Table 10.7). Table 10.7 Polymerization of 2,3-exo, exo-(MI) and 2-endo-3-exobis(acetoxymethyl)-7-oxabicyclo[2.2.1 ]hept-5-ene (Mz) with RuCI3 (I) in water/ethanol at 60~ ' M
[M]
mole/kg MI MI MI Mz
0.5 1.1 0.6 0.7
[l] mmol~kg
[Water] vol.-%
Time hr
Yield %
18
40 10 I0 10
24 12 24 12
15 100 100 100
10 19 19
,
Mb
g/mole 1000000 145000r d
130000~
'Data from referenceZ~; bDetermmed by GPC in THF, calibrged with polystyrene standards, molar masses "as if polystyrene"; r in THF; eSoluble sample taken directly from the reaction mixture, polymer was insoluble when precipitated and dried. As Table 10.7 illustrates, 2,3-exo, exo-bis(acetoxymethyl)-7oxabicyclo[2.2.1]hept-5-ene was polymerized in 10 or 40 vol.-% water in ethanol to readily obtain high conversions of the monomer. The precipitated
673 polymer was insoluble in THF and other solvents such as N,Ndimethylacetamide and chloroform. High molecular weight soluble polymers were, however, obtained at low conversions or by sampling the reaction mixture without drying the polymer. ~H and ~3C ~ spectra of poly(2,3-exo, exo-bis(acetoxymethyl)-7-oxabicyelo[2.2.1 ]hept-5-ene) in CDCI3 showed that the polymerization of the monomer to the expected structure with acetoxymethyl groups was accompanied by considerable hydrolysis of the ester groups. Polymerization of 2-endo-3-exobis(acetoxymethyl)-7-oxabicyclo[2.2.1]hept-5-ene in 10 vol.-% water in ethanol to high conversion of the monomer yielded results similar to those described above for its exo, exo-isomer. ~H and ~3C NMP, spectra of the products were complicated by hydrolysis of the ester groups and by the asymmetry of the tetrahydrofuryl ring. Because of the complication of the ester hydrolysis, the effect of microstructure on the propagation rate and molecular weight could not be pursued for this pair of monomers. From data recorded it was assumed that the hydrolysis occurred to a large extent before polymerization. Presumably, the product of polymerization was a statistical copolymer of the three types of recurring units (Eq. 10.32).
MeOCOH2C CI-12OCOMe HOH2C CH2OCOMe HOH2C CH2OH The insolubility of the high conversion polymer probably resulted from an increase of the proportion of the hydroxymethyl groups in the polymer as conversion increased. Interestingly, the effectiveness of ruthenium trichloride as a catalyst for ester hydrolysis was demonstrated by heating isobutyl acetate (11 mmole) and guCl3 (0.37 mmole) dissolved in 5 cm 3 10 vol.-% water in ethanol for 16 hr at 60~ Gas-liquid chromatographic analysis of the reaction mixture indicated over 90% conversion to isobutanol and ethyl acetate. 2,3-Dicyano-7-oxanorbornene. 2,3-trans-Dicyano-7-oxanorbomene has been polymerized quantitatively in 2 hours by using the initiator Mo(=CHCMe2Ph)(=NAr) (OCMe2CF3)2 in terahydrofuran *s (Eq. 10.33).
n
o
N
CN
[Mo]
=
0
-~'-"~ y--~ l
NC
-
~-,N
(10.33)
674
Poly(2,3-trans-dicyano-7-oxanorbomene) has a Ts of 193~ (DSC) and begins to decompose at 240~ temperature of 240~
The glass transition is reversible below the
2,3 -endo-cis(Isopropylidenedioxy)-7-oxanorbornene has been polymerized smoothly by the molybdenum carbene complex Mo(=CH~Bu)(=NAr)(O'Bu)z (At=2,6C6H3-'Prz) in tetrahydrofuran to poly(2,3-cis-(isopropylidenedioxy)-7oxanorbornene) 46 (Eq. 10.34).
2,3-( Isopropylidenedio xy)- 7-o xanorbornene.
O
n
[Mo]=
-[-'x~'O,7//-'lJ~ (10.34)
,,xo
0
The polymer has a narrow molecular weight distribution, PDI = 1.09, for a 150-mer. DSC analysis revealed a Ts at 171~ while TGA showed the onset of decomposition at ~200~ 7-Oxanorborn-2-ene-5,6-dicarboxylic anhydride, l~ng-opening polymerization of 7-oxanorbom-2-ene-5,6-di~xylic anhydride, the Diels-Alder adduct of furan with maleic anhydride, occurs readily with RuCIdKzRuCIs in aqueous methanolic media to give poly(7-oxanorborn-2ene-5,6-dicarboxylic acid) 2s (Eq. 10.35).
, ~O . ~ n
O
O
RuCI31K2RuCb~" ~ ~ . = (10.35) MeOH/H20 HOOC COOH
With RuCI3 in 10 vol.-% water in ethanol, 7-oxabicyclo [2.2.1] hept-5-ene-2,3-exo, exo-dicarboxylic anhydride polymerizes in good yield to form polymer of a moderate molecular weight (Table 10.8).
675 Table 10.8 Polymerization of 7-oxabicyclo[2.2.1]hept-5-ene-2,3-exo,exo-dicarboxylic anhydride) with RuCI3 (I) in water/ethanol as a solvent at 60 *C"
[q
[M] mole~8
mrnole/kg
2.0
20
1.8
18
[Water] Time vol.-% hr 10 100
'D~r,~ from reference~;
48 24
Yield %
M~ /g.mole b
Mw/ Mn b
44 42
15000 700
2.3
'Determined by GPC in THF, calibration with
polystyrene standards. As Table 10.8 illustrates, polymerization in water alone was not successful, resulting in polymers of a low molecular weight. Furthermore, the polymerization was accompanied by opening of the anhydride ring to form a polymer with dicarboxylic acid monomethyl ester repeat units (Eq 10.36).
~ 0 n
0=~
RuC13.3H20 -[--x(_.~ -~n EtOH/H20 )=O
(10.36)
HO OEt
A side reaction yielded also furan and maleic acid methyl monoester. ~H and ~3C NMR spectra indicated a microstructure with ca. 25% double bonds in the c i s form. Copolymers of 7-oxanorbom-2-ene-5,6-dicarboxylic anhydride with dimethyl 7-oxanorbom-2-ene-5,6-dicarboxylate were prepared in 40% yield with RuCIdK2RuCI5 in aqueous media and characterized by IR, NMR and DSC methods. Structure examination indicated the copolymer composition to be 50:50 of each of the monomer when an equimolar mixture of RuCI3 and K2RuCIs was used as the catalyst 47 (Eq. 10.37). 0
0
0
0
55"C
HO2C CO2HMeO2C CO2Me
676 Noteworthy, the poly(7-oxanorbom-2-ene-5,6-dicarboxylic acid) portion had mainly cis configuration whereas poly(dimethyl 7-oxanorbom-2-ene5,6-dicarboxylate) displayed a trans configuration. 7-Oxanorbom-2-ene- 5,6-dicarboxylic anhydride has been successfully polymerized within a forming sol-gel glass by incorporation of small amounts (ca. 0.4%) of K2RuCls to the reaction mixture~ (Eq. 10.38).
O
n~ O
O
+ Si(OR)4 K2RuCI5 = ~ N ~
+ SiO2 (10.38)
H20,NaF
HO2C
CO2H
Under these reaction conditions, the anhydride moiety was hydrolyzed to the diacid, thereby improving the polymer compatibility with the inorganic phase. Once formed, the polymer remained homogeneously embedded within the sol-gel glass. It is significant that this preformed polyacid material will consistently phase separate from the SiO2 when it is placed in the traditional sol-gel solutions. Yet formed in situ, it remains homogeneously embedded into the composite. Polymer formation within these glasses can be verified by crushing the composite and extracting the powder with a proper solvent. Polymer yields of 89*,6 have been obtained in this fashion. 7-Oxanorborn-2-ene-5,6-dicarboximide. Ring-opening polymerization of 7-oxanorborn-2-ene-5,6-dicarboximide occurs readily in aqueous media with ruthenium chloride catalyst to poly(7-oxanorborn-2-ene-5,6dicarboximide)49 (Eq. 10.39). O
RuCh
o H O
=
(10.39) I
H
N-Methyl-7-oxanorborn-2-ene-5,6-dicarboximide. The N-methyl substituted monomer polymerized efficiently in a living fashion with welldefined ruthenium carbene initiators in aqueous media5~ (Eq. 10.40).
677
0
0
n 0
[Ru]
--Me
..~
%Oy--~
(10.40)
I Me
Polymerization of this monomer in the presence of emulsifier (suspension system) resulted in polymer latex, while polymerization in the absence of emulsifier phase separated without vigorous stirring. Polymer yields and molecular weights for the reactions catalyzed by ruthenium-benzylidene complex, in the presence of water, were typically lower than those obtained under anhydrous conditions on the same reaction time scale. The polydispersities were low in all cases (Table 10.9). Table 10.9 Polymerization of N-methyl-7-oxanorbom-2-ene-5,6-dicarboximide with Ru catalysts I~R=CHCH=CPh2 (1) and I~Ru=CHPh (2)' Catalyst
Pr~re sohrdon suspension emulsion solution suspension emulsion
[M]/[C] 155 147 144 100 100 100
9 Yieldr % 95 82 85 99 84 78
M,xlO 4
PDI
8.47 6.81 5.95 4.41 2.93 2.46
2.11 1.37 1.20
1.13 1.12 1.07
'Data from reference52 It can be seen that when ruthenium catalyst 1 was used to initiate the polymerization in the presence of water, polydispersities were narrower than those obtained by polymerization in anhydrous organic solvent. A linear relationship was observed for the polymerization reactions in the presence of water, as well as for reactions in anhydrous solution. N-(2-Trimethylammonium chloride) ethyl-7-oxanorborn-2-ene--5,6dicarboximide. Living ring-opening polymerization of N-(2trimethylammonium chloride) ethyl-7-oxanorbom-2-ene-5,6-dicarboximide occurs in entirely aqueous solution in the presence of water soluble
678 ruthenium alkylidene complexes 53 (Eq. 10.41). O
n~
N(CH3)3(BCE) l
IRul
O
(10.41)
?
E)
N(CH3)~CI
The polymerization takes place in water, in the absence of surfactants or organic solvents, quantitatively to form water soluble polymers. The catalyst is active in the presence of BrOnsted acids such as DCVDzO. Block copolymers of N-(2-trimethylammonium chloride) ethyl-7-oxanorborn-2ene- 5,6-dicarboximide with N-(2-trimethylammonium chloride) ethylnorborn-2-ene-5,6-dicarboximide have also been prepared in high yield with the above catalyst system. The process is of interest for synthesis of water soluble polymers of biomedical relevance. N-Octyl-7-oxanorborn-2-ene-5,6-dicarboximide. N-Octyl-7-oxanorborn2-ene-5,6-dicarboximide polymerizes in a living fashion under the action of the bimetallic ruthenium carbene complex, (Cyp3P)2CI2Ru(=CH-pC6H4C(H)=)RuCI2(Cyp3P)2 (Cyp = cyclopentyl), to give in high yield poly(N-octyl-7-oxanorborn-2-ene-5,6-dicarboximide) ~4 (Eq. 10.42). O
O
n
--C8H17 O
[Ru]
=-
(10.42) I C8H17
Working at a monomer to catalyst ratio of 62 for 30 min, 98% poly(Noctyl-7-oxanorborn-2-ene-5,6-dicarboximide) was obtained with Mw=l.70xl04, M,,=l.55x104 and polydispersity PDI = 1.10. Triblock copolymers with narrow molecular weight distribution (PDI = 1.11) of Noctyl-7-oxanorborn-2-ene-5,6-dicarboximide and N-methyl-7-oxanorborn2-ene-5,6-dicarboximide have also been produced with the above bimetallic ruthenium catalyst.
679 2,3-Bis(trifluoromethyl)-7-oxanorbornadiene. 2,3-Bis(trifluoromethyl)7-oxanorbornadiene has been polymerized quantitatively with Mo(=CHCMe2PhX=NAr)(OCMe2CF3)z (Ar=- Ar=-2,6-C6H3-'Pr2) in toluene at room temperature to poly(2,3-bis(trifluoromethyl)-7-oxanorbornadiene) 46 (Eq. 10.43). 0
~.,,,.CF3
.~9
CF3
/
\
F3C
(10.43) CF3
The polymer with M, = 18900, M,=18500 and PDI =1.04 contained 65% trans configuration and had glass transition Ts--95~ (DSC). The rate of polymerization of 2,3-bis(trifluoromethyl)-7-oxanorbomadienr with M(=CHCMe2R)(=NAr)(O'Bu)z (R=Me,Ph) has been determined qualitatively to be comparable to that of norbornene. It was observed that the metallacyclr that results from addition of 2,3-bis(trifluoromethyl)-7oxanorbornadiene to [Mo](=CHCMe2Ph) is square pyramidal with the imido ligand in the apical position. The MoC3 ring is a planar, trans metallacyclic ring with the CMezPh group pointed toward the imido ligand and the C7 frame of the monomer pointed away from it. The oxygen in the 7-position of the norbornene moiety is located 3.332A from the metal. Steric and electronic factors that influence first-order breakup of the metallacycle have also been studied. 2,3-Dicarbomethoxy-7-oxanorbornadiene. 2,3-Dicarbomethoxy-7oxanorbornadiene reacted readily with Mo(=CHCMe2Ph)(=NAr)(OCMezCF3h (Ar=-2,6-C6Hr'Pr2) in methylene chloride to give poly(2,3-dicarbomethoxy-7-oxanorbomadiene) in high yield~ (Eq. 10.44). 0
C02 Me n
[Mo]
-[=
C02ie
0 /
Mo02C
-~ \
(10.44)
C02Me
The resulting polymer, off-white and powdery, with M~--30700, M,-26600 and polydispersity of l. 15 had 70% cis double bonds and glass transition
680 temperature T 8 = 107~ Structural studies on the metallacycle formed by addition of 2,3-dicarbomethoxy-7-oxanorbomadiene to [Mo](=CHCMe2Ph) indicated an overall geometry similar to that obtained from 2,3-bis(trifluoromethyl)-7-oxanorbomadiene with the same molybdenum carbene complex. A competition experiment between 2,3d icarbo met hoxy- 7-oxano rbo mad iene and 2,3 dicarbomethoxynorbomadiene in reaction with [Mo](=CHCMe2Ph) showed that 7-oxanorbomadiene derivative was more reactive than that of norbomadiene. 2,3-Dicarboethoxy-7-oxanorbornadiene. The heterocyclic monomer diethyl 7-oxanorbomadiene-2,3-dicarboxylate undergoes slow vinylic oligomerization with Pd(OAc)2 in anhydrous organic solvents over the course of several days. 5S Addition of water to the reaction mixture led to a subsequent 4-5 fold increase in the catalyst activity. The exact role of water was, however, unknown, the possibilities include nucleophilic attack by water on a Pd-bound monomer to yield a Pd-alkyl species similar to Wacker process 56 or the water-induced breakup of inactive palladium aggregates. 57 Because excess water did not act as inhibitor, the most convenient reaction conditions involved aqueous emulsion polymerization of diethyl 7-oxanorbomadiene-2,3-dicarboxylate initiated by PdCI2 (Eq. 10.45). O
n/~/~
C/O2Et ~cco 2Et
Pd(II)H20
(10.45)
EtO2C CO2Et
The product was readily soluble in a variety of organic solvents. A typical polymerization with Pd(OAc)2 using a monomer to initiator ratio of 200 gave a polymer in 75% yield with a molecular weight (GPC) of 28000 and a polydispersity of 1.8. The structure of poly(diethyl 7-oxanorbomadiene-2,3dicarboxylate) was confirmed by IR, tH NMR, and {tH} 13C NMR spectroscopic methods as well as by elemental analysis. Poly(diethyl 7oxanorbomadiene-2,3-dicarboxylate) is stable at room temperature, however, when heated at 100~ either in solution or after being processed into thin films, this polymer was transformed into polyacetylene via a retro [4+2] Diels-Alder reaction with formation of 3,4-dicarbethoxy furan (Eq. 10.46).
681
100oc Et02C
C02Et
H
~
+
n
H
(10.46)
Et02C
C02Et
During the thermal transformation process a gradual color change from clear to deep purple was observed which was attributed to an increase in the average degree of conjugation along the polymer backbone. It was supposed that the originally formed cis isomer was rapidly converted to trans-polyacetylene at this temperature. 7-Oxabenzonorbornadiene. Reaction of 7-oxabenzonorbomadiene with Mo(=CH'BuX=NArXO'Buh (Ar=-2,6-C6H3-~r2) in tetrahydrofuran has readily led to poly(7-oxabenzonorbomacliene) 46 (Eq. 10.47). O
n ~"'~p
[Mo] ..~ .r
=~=%~0~ ~J~"
(10.47)
The polymer had 50% trans configuration, polydispersity 1.05 and glass
transition temperature Ts=167~ It is noteworthy that under similar condition benzonorbomadiene gave a polymer with a higher trans content, i.e., ca. 76% trans double bonds, possibly because the more reactive 7-oxa derivatives attack the metal to give a metaUacycle in several different ways. 2-Azsnorbornene Polymerization of 2-azanorbornene bearing a ~ n y l group in the position 3 has been effected with WCI6/EhAI (1/4) as a catalyst in chlorobenzene at a temperature of 60~ (Eq. 10.48). O n
PhCI, 60~ 11= 34%
=
(10.48)
-L-
0
In the presence of this catalyst, a polymer has been obtained in 34% yield, having NH-CO group in the repeat units. 5s The ~3C NMR spectrum of the polymer in CDCI3 solution showed only one line for each carbon, which
682 indicated that the polymer was alI-HT with one dominant double bond configuration. Ring-opening metathesis polymerization of a series of cyclic alkenes containing nitrogen atom substituted directly into a ring position has been investigated by Watkins et al.59 under the action of classical WCl6-based catalyst systems. A first monomer examined, 2-benzyl-2azabicyclo[2.2.1 ]hept-5-ene, gave low yields (10.8%) of poly(2-benzyl-2azabicyclo[2.2.1]hept-5-ene) in the presence of WCIcfBuPhO/EhAI (Eq. 10.49).
WC 16/tBuPhO/Et3AI
n
11 = 1 0 . 8 % 2
~
-=r=x ~ / , , ~ '- " ~ . _ N~ - ' n
-n
(10.49)
\
The low conversion of this monomer was attributed to either a deactivation of the intermediate metallacarbene through a strong interaction with the polar nitrogen atom or to some kind of side reaction of the monomer with the alkyl aluminium component of the catalyst. The final polymer obtained was soluble in chlorinated solvents such as chlorobenzene and chloroform and was found to exhibit a moderately high molecular weight (M~ = 5240) with a wide polydispersity ( M ~ , = 5.7).Gr permeation chromatography showed that the material ranged from dimers up to polymers with DP of approximately 1700. The ~H NMR spectrum of the polymer indicated that the product contained predominantly the ring-opening moieties since the resonances of the cycloalkenic protons observed in the monomer were absent and replaced by resonances (at 5.2 and 5.4 ppm) corresponding to open-chain alkenic protons. The glass transition temperature of poly(2benzyl-2-azabicyclo[2.2, l]hept-5-ene) was found by DSC to be rather low (71~ probably due to the high free volume contributed by the pendant benzyl group which more than cancels out any improvement due to the presence of polar species in the polymer chain. Interestingly, attempts to polymerize the N-methyl analog of the above monomer, 2-methyl-2-azabicyclo[2.2. l]hept-5-ene, under the same conditions, with the aim of producing a polymer with a lower free volume failed (Eq. 10.50).
683 ,,~
-~
(10.50)
N~CH 3
\
CH 3 Zero conversion was observed in this case, presumably due to an even greater degree of complexation with the metaUacarbene catalytic species.
10.4. Seven-Membered Ring Monomers Polymerization of 7-acetoxy-4,5,6,7-tetrahydrooxepin in the presence of diphenylcarbene-chromiumpentacarbonyl occurs at a temperature of 10~ by the ring-opening mechanism to poly(oxy-1acetoxy-5-hexenylene) ~~(Eq. 10.51).
c
o/occH3
co T = 10~
-~9
(10.51)
The molecular weight of poly(oxy-l-acetoxy-5-hexenylene) prepared with the above catalyst amounted to 18000 g/mole and the cis content to 73%. The complex methoxyphenylcarbene-chromiumpentacarbonyl showed to be inactive toward 7-acetoxy-4,5,6,7-tetrahydrooxepin.
10.5. High-Membered Ring Monomers Polymerization of the unsaturated cyclic lactone ambrettolide occurs readily in the presence of WCldMe4Sn at 90~ to form poly(8-oxo-9-oxa1-heptadecenylene)6~(Eq. 10.52).
n (H2C)7/-~~(CH2)5
LOgo
WCIs/Me4Sn
~[~(CH2~O~(CH2)5~
(10.52)
3, =
On working at the above temperature for 3 hours, poly(8-oxo-9-oxa-1heptadecenylene) with a molecular weight of 95000 g/mole has been prepared in an appreciable yield.
684 10.6. References
1. J.P. Kennedy, "Cationic Polymerization of Olefins: A Critical Inventory", John Wiley & Sons, New York, 1975. 2. a.J.C.W. Chien, "Coordination Polymerization", Academic Press, New York, 1975, b. J.P. Kennedy and E. Thornquist, "Polymer Chemistry of Synthetic Elastomers", Interscience Publishers, New York, 1969. 3. J. Boor, Jr, "Ziegler-Natta Catalysts and Polymerization", Academic Press, New York, 1979. V. Dragutan, A.T. Balaban and M. Dimonie, "Olefin Metathesis and Ring-Opening Polymerization of Cycloolefins", John Wiley & Sons, New York, 1985. 5. K.J. Ivin and J.C. Mol, "Olefin Metathesis and Metathesis Polymerization", Academic Press, London, 1997. 6. a. R.H. Cn'ubbs, J.M.S. Pure Appl. Chem., A31, 1829 (1994), b. B.M. Novak, W. Risse and R.H. Grubbs, Adv. Polym. Sci., 102, 47 (1992). 7. R.R. Schrock, Acc. Chem. Res., 23, 158 (1990). 8. M. Theuring and W.P. Weber, Polymer Bulletin, 28, 17 (1992). 9. C.T. Thu, T. Bastelberger and H. H6cker, Makromol. Chem., Rapid Commun., 2, 7 (1981) 10. C.T. Thu, T. Bastelberger and H. H6cker, J. Mol. Catal., 28, 279 (1985). I I. Farbenfabriken Bayer AG, Ger. Often. 1,770,366 91968), Chem. Abstr., 73, 46423 (1970). 12. H. Lammens, G. Sartori, J. Siffert and N. Sprecher, 3'. Polym. Sci., B9, 341 (1971). 13. W.P. Weber, Y. T. Park, S.Q. Zu, Makromol. Chem., Macromol. Symp., 42/43, 259 (1991 ). 14. X. Liao and W.P. Weber, Polymer Bulletin, 25, 621 9199 l). 15. D.A. Stonich and W.P. Weber, Polymer Bulletin, 25, 629 (1991). 16. S.J. Sargent, S . Q . Zhou, G. Manuel, and W.P. Weber, Macromolecules, 25, 2832 (1992). 17. S.J. Sargent, S.Q. Zhou, G. Manuel, and W.P. Weber, Polymer Preprints (Am. Chem. Soc., Div. Polym. Chem.), 33, 1052 (1992). 18. Y.T. Park, S.Q. Zhou, G. Zhao, G. Manuel, R. Bau and W.P. Weber, Organometallics, 9, 2811 (1990). 19. L. Wang, Y.-H. Ko and W.P. Weber, Macromolecules, 25, 2828 (1992). .
685 20. L. Wang, Y.-H. Ko and W.P. Weber, Polymer Preprints (Am. Chem. Soc., Div. Polym. Chem.), 33, 1050 (1992). 21. A.D. Benedicto, B.M. Novak and R.H. G~bbs, Macromolecules, 25, 5893 (1992). 22. B.M. Novak and R.H. Cmabbs, J. Am. Chem. Soc., 110, 960 (1988). 23. R.H. Gnabbs and W, Thumas, Science, 243, 907 (1989). 24. M.W. Ellsworth and B.M. Novak, J. Am. Chem. Soc., 113, 2756 (1991). 25. S.Y. Lu, J.M. Amass, N. Majid, D. Glermon, A. Byerley, F. Heatley, P. Quayle, C. Booth, S.G. Yeates, and J.C. Padget, Macromol. Chem. Phys., 195, 1273 (1994). 26. B.M. Novak and R.H. ~ b b s , Polymer Mater. Sci. Eng., 57, 651 (1987). 27. B.M. Novak and R.H. Gnabbs, J. Am. Chem. Soc., 110, 7542 (1988). 28. W.J. Feast and D.B. Harrison, J. Mol. Catal., 65, 63 (1991). 29. W.J. Feast and D.B. Harrison, Polymer Bull., 25, 243 (1991). 30. M.B. France, R.H. Grubbs, D.V. McGrath and R.A. Paciello, Macromolecules, 26, 4742 (1993). 31. S.Y. Lu,P. Quayle, F. Heatley, C. Booth, S.G. Yeates, and J.C. Padget, Macromolecules, 25, 2692 (1992). 32. S.Y. Lu,P. Quayle, F. Heatley, C. Booth, S.G. Yeates, and J.C. Padget, Eur. Polym. J., 29, 269 (1993). 33. S.Y. Lu,P. Quayle, C. Booth, S.G. Yeates, and J.C. Padget, Polymer Int., 32, I (1993). 34. K.K. Kapellen and R. Stadler, Polymer Bull. 32, 3 (1994). 35. B. Bell, J.G. Hamilton, E.e. Law and J.J. Rooney, Macromol. Chem. Rapid. Commun., 15, 543 (1994). 36. W.J. Feast and D.B. Harrison, Polymer, 32, 558 (1991). 37. M. Gilbert and l.g. Herbert, Polymer Bull., 30, 83 (1993). 38. T. Karlen, A. Ludi, A. Muhlebach, P. Bernhard and C. Pharisa, J. Polymer Sci., A, Polymer Chem., 33, 1665 (1995). 39. C.M. McArdie, J.G. Hamilton, E.E. Law and J.J. Rooney, Macromol. Chem. Rapid Commun., 16, 703 (1995). 40. A.W. Stumpf, E. Saive, A. Demonceau and A.F. Noels, J. Chem. Soc., Chem. Commun., 1995, 1127. 41. E. Zenld and F. Stelzer, J. Mol. Catal., 76, 1 (1992). 42. K.H. Mortell, M. Gingras, and L.L. Kiessling, J. Am. Chem. Soc., 116, 12053 (1994).
686 43. K.H. Mortell, R.V. Weatherman, and L.L. Kiessling, J. Am. Chem. Soc., 118, 2297 (1996). 44. V. Percec and D. Schlueter, Macromolecules, 30, 5783 (1997). 45. D. Schlueter, P. Chu, V. Percec, and G. Ungar, Polymer Preprints (Am. Chem. Soc., Div. Polym. Chem.), 77, 109 (1997). 46. G.C. Bazan, J.H. Oskam, H.N. Cho, L.Y. Park, and R.R. Schrock, J. Am. Chem. Soc., 113, 6899 (1991). 47. T. Viswanathan, J. Jethmalani, and A. Toland, J. Appl. Polymer Sci., 47, 1477 (1993). 48. B.M. Novak, M. Ellsworth, T. Wallow and C. Davies, Polymer Preprints (Am. Chem. Soc., Div. Polym. Sci.), 31,698 (1990). 49. T. Viswanathan, J. Jethmalani, ,I. Appl. Polymer Sci., 48, 1289 (1993). 50. M.A. Hillmyer, C. Lepetit, D.V. McGrath, and R.H. Grubbs, Polymer Preprmts (Am. Chem. Soc., Div. Polym. Chem.), 32, 162 (1991). 51. M.A. Hillmyer, C. Lepetit, D.V. McGrath, B.M. Novak, and R.H. Gnabbs, Macromolecules, 25, 3345 (1992). 52. D.M. Lynn, S. Kanaoka, and R.H. Grubbs, J. Am. Chem. Soc., 118, 784 (1996). 53. D.M. Lynn, B. Mohr, and R.H. Grubbs, ,I. Am. Chem. Soc., 120, 1627 (1998). 54. M. Week, P. Schwab, and R.H. Gnabbs, Macromolecules, 29, 1789 (1996). 55. A.L. Safir and B.M. Nova&, Macromolecules, 26, 4072 (1993). 56. N. Gragorand P. Henry, J. Am. Chem. Soc., 103, 681 (1981). 57. A.D. Ketley, L.P. Fischer, A.J. Berlin, C.R. Morgan, E.H. Gorman and T.R. Steadman, Inorg. Chem., 6, 657 (1967). 58. H.-N. Cho and S.-K. Choi, J.Polymer Sci., Polymer Chem., 23, 1469 (1985) 59. N. Watkins, P. Quigley and M. Ortort, Macromol. Chem. Phys., 195, 1147 (1994). 60. W. Ast, G. Rheinwald and R. Kerber, Makromol. Chem., 177, 1349 (1976).
687
Chapter 11 COPOLYMERIZATION REACTIONS OF CYCLOOLEFINS 11.1. Introduction. Reaction Types
Under the influence of suitable catalytic systems, two or more cycloolefins can undergo copolymerization reaction to yield copolymers containing recurring units which arise from the corresponding monomers. The copolymers obtained may have a random or blocky distribution of the monomer units as a function of the monomer nature and reactivity, catalytic system and polymerization procedure. These copolymers display totally different physical and mechanical properties as compared to the respective homopolymers. Depending primarily on the nature of the catalytic system, two major types of copolymers may arise from cycloolefins: vinyl and ringopened copolymers. Vinyl copolymers, named also copoly(cycloalkylene)s, result via addition polymerization by opening of the carbon-carbon double bonds of the cycloolefins under the action of the catalytic system, the tings being preserved throughout the chain. In this case, the polymer contains prevailingly saturated recurring units formed by 1,2-addition reaction at the double bond (Eq. 11.1).
p
\--I
(CH2)n
+
r \ / (Cl-12)m
=
[\
/~L\ /Jr (CH2)n (CH2)m "!
r
(11.1)
This process occurs in the presence of cationic, anionic and coordination catalysts of the Ziegler-Natta type, under normal reaction conditions. ~ Sometimes, depending on the monomer structure and catalyst nature, particularly under the influence of cationic initiators, rearranged polycyclic recurring units may appear in the polymer chain formed by hydride shill migration or skeleton rearrangement of the intermediate propagating species 2 (Eq. 11.2).
P!
(CH )n
C H2)m
CH2,)n '
C H2/)m
(11.2)
688 Ring-opened copolymers, known as copolyalkenamers or copoly(1alkenylene)s, are formed via metathetic copolymerization i.e. through scission of the carbon-carbon double bond of the cycloolefin and further insertion, under the action of the metathesis catalysts. 3'4 In this case, unsaturated copolymers will be formed containing different 1-alkenylene recurring units in the backbone (Eq. 11.3).
p\
/
+ r\--/
(Ct"lz)n
(CHz)m
=[=~ (Ci.iz)n/'~ (CH.x)m/~ (11.3)
v
By coupling vinyl with ring-opening copolymerization through a proper choice of the catalytic system, random or block copolymers having saturated along with unsaturated recurring units may arise by the two types of polymerization mechanisms ~ (Eq. 11.4).
P ~----/
(CH2)n
+ r \ "i
~
(CH2)m
[\
/]p [---\
(CH2)R
/~ (CH2)m
(11.4)
When an ct-olefin is a comonomer in conjunction with cycloolefins, vinyl copolymers or ring-opened/vinyl ones may be produced by a competition between addition and metathesis polymerization 6 (Eq. 11.5-11.6).
p \---/ + (CH2)n
r "---N
P \---7
r ~
(CH2)n
+
R R
~
[\
=
--[-\
I r IJpL (CH2)n
1 IJr R
/']i5" r
(CH2)n
(11.5)
lit R
(11.6)
Instead of a linear olefin, unsaturated polymers can be used as comonomers in vinyl or ring-opening metathesis polymerization of cycloolefins to form copolymers containing cycloalkylene or 1-alkenylene units linked with the former linear polymer7 (Eq. 11.7-11.8).
p V-/
(CH2)n
p
~---/
(CH2)n
*
§
=
[\
lip
(CH2)n
_____.
~
o~.7) (11.8)
(CH2)n
689 When unsaturation occurs in the side arms of the polymer (e.g., 1,2polybutadiene), graft copolymers can arise by vinyl or ring-opening metathesis copolymerization with cycloolefins8 (Eq. 11.9-11.10). CH2)m r \1
n \ / + R'[ (CH2)m
---R" ~
n \----~ + R'--[-- I - ~ - - R " I" (CH2)m
R'-[-
--
---R"
R~L---
(11.9)
(11.10)
Furthermore, block copolymers can be produced by coupling,various polymerization techniques such as condensation polymerization with ringopening metathesis polymerization of cyclooletins 9(Eq. 11.11)
(11.11)
or group transfer polymerization with polymerization of cycloolefins ~~(Eq. 11.12).
~H3m~C=CHOSiR3
= "~~n
ring-opening
metathesis
~ ,OSiR3.0SiRJ:?SIR3 ~--~~~~O H (11.12)
The versatility of cycloolefin copolymerization under the influence of various types of catalytic systems provides a powerful technique to produce new materials having totally different chemical and physical-mechanical properties as compared to the corresponding homopolymers.
690
11.2. Cationic Copolymerization of Cycloolefins Copolymerization of cycloolefins in the presence of cationic initiators ~ has been for long a significant technique to manufacture valuable copolymers with special physical-mechanical properties and a practical tool
to evaluate the relative re,activities of various cycloolefins under cationic catalysis. In the following sections the main aspects concerning the kinetics and mechanisms of cationic copolymerization of monocyclic, bicyclic and polycyclic monomers will be summarized with emphasis on the monomer reactivities and polymer microstructures.
11.2.1. Monocyclic Monomers Interesting copolymers of monocyclic cycloolefins with linear conjugated dienes have been prepared by Japan Synthetic Rubber Co. ~ by using AI halides and oxygen-containing organic compounds as catalysts. In one example, cyclopentene was copolymerized with 1,3-pentadiene under the action of AICI3 and monochloroacetic acid in methylene chloride at 40~ for 1 hour to give 88% copolymer with softening point 76~ and Gardner colour index 2. The copolymer had the two recurring units linked by 1,2 addition reaction (Eq. 11.13). n (' | + m ~
AICI-~/CICH2CO2H .
=
,,._
_rA
"i_.
~',/~1.1~"~11~
(11.13)
Of the five-membered ring monomers, cyclopentadiene proved to be highly reactive in cationic copolymerization with acyclic olefins. In their studies on cationic copolymerization, Heublein and coworkers ~2 examined the reaction of cyclopentadiene with isobutylene and a-methylstyrene under the action of several catalytic systems such as AICI3, AIBr3, TiCh/AIBr3, Et3AIflBuCI and Et2AICI. With both monomers, cyclopentadiene provided random copolymers having as repeat units 3,5-cyclopentenylene structures, linked to isobutylene and styrene entities, respectively (Eq. 11.14-11.15).
of)§
eC/
lll 111,,
691
[All
~
.
-1
(1 1 15)
For example, starting from cyclopentadiene and ct-methylstyrene in toluene and methylene chloride, random copolymers have been produced in high yields in the presence of the binary catalysts TiCI4/AIBr3 (molar ratio 60:1). The random distribution of the recurring units evidenced that the two monomers have comparable reactivities. Heublein et al. ~3 found that the catalytic activity in this reaction decreased in the following order : Et2AICI/BuCI > AICIa > AIBr3 > TiCI,/AIBr3. The cationic copolymerization of cyclopentadiene with 1methylcyclopentadiene has been reported by Aso and Ohara ~ to occur in toluene and methylene chloride under the influence of BF3/Et20, SnCI4 and TiCh. It is of interest that microstructure investigation of the copolymer indicated that 3,5-cyclopentenylene units resulted by 1,4-addition reaction of cyclopentadiene are linked to 3,4-(l-methylcyclopentenylene) units arisen by 1,2-addition reaction of the unsubstituted double bond of 1methylcyclopentadiene (Eq. 11.16).
It is obvious that the methyl substituent in the position 1 exerts both a steric and electronic effect on the monomer reactivity, directing the reaction toward 1,2-addition, as compared to unsubstituted cyclopentadiene. In contrast to its l-substituted isomer, 2-methylcyclopentadiene forms with cyclopentadiene copolymers having mainly 3,5-(2methylcyclopenenylene) units together with 3,5-cyclopentenylene, both of them resulting by 1,4-addition reaction of the two conjugated double bonds from the monomer (Eq. 11.17).
I
I
692 In this case, the position 2 of the methyl substituent perturbs less, by its steric and electronic effect, the 1,4 regioselectivity of the two conjugated double bonds of the monomer. The reactivity ratios, r~'r, were found to be markedly in the favor of the methyl-substituted monomer, depending on the solvent employed; for example, under certain conditions, r~,~/r was 8.5/0.36 in toluene and 14.9/0.42 in methylene chloride. It is noteworthy that the nature of the cationic initiator had little effect on the copolymer composition. The cationic copolymerization of cyclopentadiene with 1,3dimethylcyclopentadiene ,carried out by Aso and Ohara ~5 in the presence of the complex BF~/EtzO, gave rise to copolymers having probably 1,4- and 3,4-enchainments of the dimethylcyclopentadiene units along with 1,4enchainment of the unsubstituted cyclopentadiene (Eq. 11.18).
I The reaction has been conducted in toluene at -78~ to provide reactivity ratios of r~.3 - 6.85 and r = 0.30 for the two monomers, respectively. It is obvious that the 1,3-disubstituted isomer is much more reactive than the parent cyclodiene. Evidently, methyl substitution increased the stability of the cyclopentadienyl cation. Copolymerization reactions of 1- and 2-methylcyclopentadienes, under the action of various cationic catalysts, has been investigated by Aso and Ohara. ~4 In the course of these reactions, they prepared copolymers having mainly 1,4-enchainment of the repeat units along with less proportions of 3,4-enchainments (Eq. 11.19).
I Aso and Ohara employed a range of isomer ratios (l-isomer:2-isomer between 2773 and 89:11) as the starting material to be reacted in the presence of BFJEtzO, SnCI4 and TiCh under various conditions (monomer concentration, various solvents and temperatures). They readily obtained for medium to high monomer conversions relatively low molecular weight
693 copolymers, having intrinsic viscosities [11] > 0.8. The products were soluble, white powdery polymers, with softening range of 120-160~ The lack of gelation is of interest and may be due to the presence of substituted double bonds in the polymer chain as it could be seen above. It is noteworthy that the polymers readily oxidized on standing in air for some time. The reactivity ratios of the two isomers were found to be r~:r2 of 0.01:1.1, that is, the 2-methylcyclopentadiene was far more reactive than lmethylcyclopentadiene. It is remarkable that 1,4-enchainment was preferentially formed when SnCh and TiCh were used as the catalysts (~ 90% 1,4 structure) and much less with the complex BF~/Et20 (~76%). This finding is contrary to that with parent cyclopentadiene where 1,4enchainment was preferred when BF3/EteO was used as a catalyst. The explanation for this behavior involving specific steric effects of the substituents in the presence of different catalytic species will be given in a later chapter. Copolymerization of cyclopentadiene with 1-methyl-3ethylcyclopentadiene and 1-methyl-3-isopropylcyclopentadiene has been studied by Ohara and Aso m6under the action of a series of Friedel-Crafis catalysts (Eq. 11.20-11.21).
n
+ m
"~
-In L
~m
(11.21)
The reactivity ratios r~rz with respect to cyclopentadiene have been determined for the two comonomers. The influence of the steric effect was significant for both substituents in the position 3. Random copolymers prepared from cyclopentadiene and 2chloroethyl vinyl ether have been reported by Kohjiya e t al. ~7 Using BF3.Et20 as the catalyst, in various solvents at -78~ they obtained products whose structures have not been fully elucidated. Apparently, because of the difference in reactivity between the two monomers, the
694 repeat units arising from 1,4-enchainment of cyclopentadiene and 1,2enchainment of vinyl ether will not form a real random copolymer, under the conditions employed. (Eq. 11.22).
n~
+ m __jO~__./CI
0122)
Data concerning the reactivity ratios and physical-mechanical properties of the sulphur vulcanizates were also reported for this copolymer. Synthesis of ternary copolymers starting from 1-methyl, 2-methyl, and 5-methylcyclopentadiene has been conducted by Imanishi et aL ~8 using BF3/Et20, SnCIdCCI3COOH(TCA) and TiCIdCCI3COOH as catalysts. Working with an isomer mixture (1-2-:3-isomer = 4552:3) at -78~ they prepared white powdery polymers having the intrinsic viscosities [rl] = 0.10.5. Interestingly, the polymerizations with TiCIJTCA and SnCI~rCA were non-stationary: e.g., upon catalyst addition a fast polymerization occurred that was followed by a rapid termination. ~9 In this case, fresh catalyst addition was necessary to attain high conversions. In contrast, when BFjEt20 was used as a catalyst, after a rapid reaction, a stationary phase was reached that slowly progressed until the monomers were consumed. Noteworthy, the level of conversion did not affect the intrinsic viscosities, though the nature of the catalyst influenced these values significantly, that is, [11] - 0.15, --- 0.3, and -~ 0.15 with TiCIJTCA, SnCIJTCA, and BFjEhO, respectively. It is obvious that the reactivity ratios differed essentially with the position of the substituent, the 2-isomer being the most reactive. Accordingly, the polymer microstructure will contain mainly recurring units consisting of 1,4-enchainments of the 2substituted monomer along with less contributions of 3,4-enchainments arisen from l-methyl and 5-methyl isomers (Eq. 11.23).
n--f ).mr).
l r
Copolymers of variable structures formed from cyclopentene and cyclopentadiene with a-methylstyrene and piperylene are frequently encountered in the synthesis of Cs aliphatic petroleum resins using various catalysts such as AICI3, AIBr3, BFjEhO, SnCI4 and TiCI4.~ Furthermore,
695 mixtures of Cs stream containing cyclopentene and cyclopentadiene have been copolymerized with styrene and vinyltoluene to manufacture hydrocarbon resins that have different physical-mechanical properties, depending on the reaction conditions, for this purpose, EtzAICI, EhAIzCI3, and EtAICIz associated with 'BuCI have been used as catalysts. Moreover, it should be mentioned that terpene hydrocarbons like ot-pinene and dipentene are currently copolymerized with isobutylene, isoprene, styrene, and terpene oligomers under the influence of AICI3 or EtAICIz to produce useful resins with particular chemical and physical-mechanical properties. Carboxy-functionalized hydrocarbon resins were prepared at Fridrich-Schiller University Jenaz~ by the reaction of oxidation-stable, unsaturated copolymers of cyclopentadiene, o~-methylstyrene and other cationically polymerizable monomers with thioglycolic acid in the presence of a solvent. For instance, the copolymers of cyclopentadiene and ~methylstyrene with styrene or vinyltoluene gave the following functionalized copolymers (Eq. 10.24-10.25).
(11.24)
HSCH2COOH
~-,,., [
1...
(11.25)
~Ncs
In a similar way, the copolymer of cyclopentadiene and ot-methylstyrene with indene, isobutene or diisobutene gave the corresponding functionalized products (Eq. 11.26-11.28).
HSCH-zCOOH _ ~ HOOCH2CS
(112.6)
696
k.l. ~ , - L~L L
r
HSCH2C(X:)H Ii r I I'K)OCI-hCS -E~]n['l~n" ' " HSCH2COOH
"-
(1127)
(1128)
HOOCH2CS
The solvent was an aromatic hydrocarbon, e.g., benzene or toluene, a C~-2 chlorinated hydrocarbon, e.g., chloroform or dichloroethane or a cycloaliphatic hydrocarbon, e.g., cyclohexane. Carboxylation reaction of the copolymer was effected at 40-120~ preferentially at 60-80~ Interestingly, the copolymer may be reacted without previous isolation from the polymerization mixture after separation of the coinitiator. On varying the amount of COOH groups and residual C=C bonds, the reactive resins can be used in coatings and for production of ion-exchangers, hydrophilic membranes and polyelectrolytes. Cheap raw materials, which are to some extent under-utilized, can be used, replacing monomers such as isoprene and butadiene. The COOH-resins thus prepared are stable against oxidation, remaining soluble in organic solvents and with stable colors for years. Similarly, sulphonated hydrocarbon resins were prepared 22 by reacting the above stable, unsaturated copolymers of cyclopentadiene and other cationically polymerizable monomers with SO3 complexes or carboxysulphates in the presence of a solvent. The sulphonating agent was a complex of SO3 with tetrahydrofuran, 1,4-dioxan or trialkyl phosphates or a carboxylsulphate, preferably acetyl-sulphate prepared or formed in situ by sulphonation. Sulphonation of these copolymers occurred at -50-100~ preferably between -20~ and 30~ The sulphonated copolymers could be used in coatings and for the production of ion-exchangers, hydrophilic membranes, impregnants and adhesives. In their studies on the polymerization of 1,3-cyclooctadiene with TiCI4 and SnCI4 in the presence of some activators such as water, Mondal and Young 23 transferred the results obtained in homopolymerization reaction on the copolymerization of this cycloolefin with styrene. Copolymerization of 1,5-cyclooctadiene with one or more copolymerizable olefins having at least C2 to form hydrocarbon resins,
697 containing bicyclo[3.3.0]octane-2,6-diyl units along with hydrocarbon moieties, has been reported by Eastman Kodak Co. z4 As comonomers, acyclic olefins such as ethylene, propylene, isobutylene and hexenes up to 80 wt.% have been employed (Eq. 11.29 where P,,' and P,," may be one or both H, CH3, and Coqg).
n
()
+
m
R'
"~~
]n[
.,,l
(11.29)
1~m R'
The reaction has been effected with aluminium chloride or aluminium bromide as a catalyst, at temperatures between 30~ and 250~ Similarly, cyclic olefins such as cyclopropene, cyclobutene, cyclohexene, cyclooctene and norbomene have been used. Products with a wider range of properties than homopolymers, e.g., softening points ranging from lower temperatures to 180~ have been obtained in 40-90% yield. The structures of such ca)polymers of 1,5-cyclooctadiene with cyclic monomers are illustrated by the general formula of Eq. 11.30, where x is an integer greater than 2. /---X n ~
\
/
~
+ m ~
ICH)x
~)..
/]m
(11.30)
(CH2)x
These copolymers displayed improved solubility and exhibited improved compatibility with other hydrocarbon materials, e.g., polyethylene and polypropylene. They are useful as wetting or bonding agents for coatings, adhesives, inks and paints. Synthesis of interesting copolymers of 1,5-cydooctadiene with SOz in the presence of ammonium persulphate has been reported by Teijin Co. zs (Eq. 11.3l).
n
)
+ m 802
[NH412S208
"-
(11.31)
so
+ m
698 Microstructure examination showed alternating SO2 and alicyclic recurring units in the copolymer chain. The products were useful for membranes with high permeability toward oxygen and carbon dioxide.
11.2.2. Bicyclic and Polycyclic Monomers Copolymerization of norbomene with styrene in the presence of the cationic catalyst EtAICIz/BuCI has been investigated by Sagane and Minami 26 to produce unsaturated copolymers containing reactive double bonds in the polymer chain (Eq. 11.32).
+Q
Et~ICl2/tBuCl
= "'~
(11.32)
On varying the feed ratios norbomadiene:styrene, they observed that by increasing the incorporation of styrene units into norbomadiene polymer, the insoluble fraction formed by cross-linking reaction might decrease and that the T 8 values could be controlled easily by varying the norbomadiene: styrene ratio in the monomer feed. Hydrocarbon resins having excellent heat and weathering resistance have been manufactured from copolymers of C2-t0 unsaturated hydrocarbons, e.g., 1,3-pentadiene, or aromatic C,-t6 hydrocarbons, e.g., styrene, with dihydrodicyclopentadiene by Mitsui Petrochemical Industries, 27 in presence of AICI3 as a catalyst. Under cationic catalysis, dihydrodicyclopentadiene has formed by reacting with 1,3-pentadiene and styrene the corresponding 1,2- and 1,4-addition copolymers (Eq. 11.33). AICI3 >
"~
(11.33)
The reaction occurred readily in hydrocarbon solution (xyleneh~exane) at a moderate temperature to give high yields of random copolymers. The products were suitable for additives of clays and coatings. Graft copolymers were also prepared by Mitsui Petrochemical Industries z' by copolymerizing isobutylene by a cationic mechanism with
699 compounds having two or more double bonds of different ion-polymerizing characteristics e.g., norbornene derivatives such as 5-vinyl-2-norbomene or 5-ethylidene-2-norbomene and polyenes, e.g., 1,3,7-octatriene using organoaluminium compounds and then grafting the copolymer by a ZieglerNatta mechanism with ot-olefins, especially ethylene and propylene, without inactivating the catalyst, in the presence of halides of Ti or V and optionally adding organoaluminium compounds. Graft copolymers of the following structures have been thus prepared (Eq. 11.34-11.35).
n--<.
+ p j*~.j'~j'"~j
2. [Ti,V]
=
1. [R:~I]
(11.34)
(11.~)
2 [Ti,Vl
Reaction solvents fir these reactions are hexane, carbon tetrachloride, benzene and dichloroethane. The organoaluminium compounds are trialkylaluminium, dialkylaluminium chloride, alkylaluminium dichloride and alkylaluminium sesquichloride while the halides of Ti and V are TiCI4, TiCI3, (EtO)TiCI3, VCL, and VOCI3. The ratio of AI to Ti or V is preferably 0.5-5. The degree of polymerization of isobutylene copolymer is 10-10000, preferably 10-3000 and it should not contain insoluble portions. Addition of Ti or V compound was effected after removing isobutylene and diolefins. Step two was usually effected under Ziegler conditions at 0-100~ under 0-20 kg/cm z, using hydrocarbon solvents, e.g., hexane or heptane. This procedure is a time saving process to produce enhanced quality thermoplastic resins. Noteworthy, even if the olefin polymer is copolymerized with a much higher amount of isobutylene, compared to conventional methods, the eopolymers obtained did not show a decrease in the degree of crystallization and polymerizing activity. Interesting block copolymers of 5-chloronorbornene with isobutylene have been prepared by Sangalov et al. 29 in the presence of Lewis acids e.g., EtAICI2(Eq. 11.36).
700 n
+
m
=
\ CI
-[-
In
(11.36)
CI
The block copolymers thus obtained underwent readily hydrolysis of the chlorine groups to form hydroxy polymers which by further treatment with phenylmethyldiisocyanate were converted to polyamides (Eq. 11.37).
-[--~ (~
CH
(11.37) Ph
High molecular weight copolymers of 5-ethylidene-2-norbomene with SO2 have been obtained by DeSimone and McGrath 3~ under mild conditions (Eq. 11.3 8).
n~
+ n S02
=
[~
S02~--
(11.38)
Moreover, grafted copolymers of norbomene and SO2 with dimethylsiloxane as side arms have been also prepared. Due to their low decomposition temperature, these polysulphone are useful materials for manufacture of fotoresists Cationic copolymerization of dicyclopentadiene with several unsaturated hydrocarbons has been extensively investigated in order to manufacture hydrocarbon resins having improved chemical and physicalmechanical properties. Thus, the catalytic reaction of this monomer with styrene, indene, r and various hydrocarbon fractions has been effected in the presence of AICI3 to produce copolymers having various physical characteristics, depending essentially on the proportion of the two monomer units in the copolymer3~ (Eq. 11.39-11.41).
701
(11.39)
L~
I~
n
+ m
~
AICI3 "~
~
=I
r"
"I
(11.40)
L ] Jm (11.41)
In the production of reactive hydrocarbon resins, by-product hydrocarbon mixtures which contain dicyclopentadiene as the main component and other diolefins from the Diels-Alder reaction of unsaturated C5 hydrocarbons are converted to copolymers by continuous cationic copolymerization with other monomers which are also components of these hydrocarbon mixtures such as styrene and styrene derivatives or diisobutene and oligoisobutene mixtures with C4_Ct~ fractions. 32 Typical copolymers obtained from these raw materials contain dicyclopentadiene and styrene (Eq. 11.42) ,,=.= r
(11.42)
or dicyclopentadiene and diisobutene as the main structural units (Eq. 1 1.43). L v
(11.43)
702 These reactions were carried out in aromatic hydrocarbon solvents, optionally mixed with halogenated hydrocarbons, at 0~ to +80 ~ especially +20~ to +50 ~ The preferred cationic initiators are alkylaluminium halides of the R~AIX3., type, e.g., EbAI2CI3, aluminium halides, e.g., AICI3 and particularly liquid complexes of AICI3, other Lewis acids, with BrOnsted acids, especially water as co-initiators. The process is economical and the products thus prepared are useful for producing alkydic resins and printing inks, for adhesives and coatings and as ancillaries in the rubber industry. The cationic copolymerization of dehydrodicyclopentadiene with lisopropylid enedicyclopentadiene, 1-i sopro pylid ene-3 a, 4, 7, 7 atetrahydroindene or isoprene has been effected by Snam Progetti SpA 33 to produce high molecular weight polycyclic polyene copolymers with high reactivity and good solubility in organic solvents (Eq. 11.44-11.46).
n
§
~~
(11.44)
m
(11.45)
+ m
-----.w,.
(11.46)
These products could be easily grafted and polar groups e.g., CN, SO3OH, OH or halogen groups could be thus introduced into the polymer. Similar copolymers have been prepared from l-isopropylidenedicyclopentadiene and isopropylidene-3a,4,7,7a-tetrahydroindene or isoprene (Eq. 11.4711.48)
n
+ m
(11.47)
703
n
+ m ~
=
or from l-isopropylidene-3a,4,7,7a-tetrahydroindene and (Eq. 11.49).
n
§ m
~
(11.48)
isoprene
(11.49)
Interesting studies on the copolymerization reaction of tetracyclo[4.4.0.12"5.17'~~ (TCD) with styrene, in the presence of the binary catalyst EtAICI/BuCl, carried out Sagane e t al. 34 Copolymers having mainly two types of polycyclic repeat units, generated from tetracyclo[4.4.0.12"S.l~'m~ along with styrene units, have been produced under these conditions.(Eq. 1 1.50).
n
(11.50)
On varying the ratios of r (TCDSt), a wide range of polymer yields, molecular weights and polydispersities have been obtained working in chloromethylene at -50~ (Table I I. l).
704 Table 11.1 Copolymerization oftetracyclo[4.4.0.1 ~'~.17'~~ (TCD) with styrene (St) using the EtAICIz/q3uCI catalyst system TCDSt mole %
Yield %
MO
100:0 96:4 93:7 70:30 50:50 25:75 0:100
17.4 20.9 22.2 42.4 47.0 61.0 85.5
(840) r
780 780 790 870 1480 23500
Dp d
PDI
(1.9) ~ 1.7 2.0 1.7 2.0 2.4 4.3
(5.3) r
5.0 5.1 5.6 6.6 12.4 226
mole %
Tg *C
0 5.7 10.9 34.0 50.8 73.8 100
275 181 166 141 138 117 98
St
'Data from reference34; bReaction conditions" [TCD],+[St], = 1.0 mole/L, [EtAICI2],[t-BuCI]o = 10.5 mmole/L:5.0 mmole/L, for 60 min;"Numbers in parentheses are for the soluble fraction in boiling toluene; dCalculatod from M, and TCD/St composition. Surprisingly, the solubility of the polymer increased from 43% to 100% at the very small amount of styrene feed ratio of 4 mole %. The reason for this drastic solubility change was not clear, but, as expected, a soluble polymer containing units of tetracyclo[4.4.0.12"5.17't~ was indeed obtained by copolymerization with styrene under the above conditions. As Table 11.1 shows, the polymer yield increased from 17% to 86% with an increase in the monomer feed ratio of the more reactive styrene. The relationship between styrene content and styrene feed ratio indicated that the copolymer composition was almost equal to that of the feed ratio, in spite of the reactivity difference of the two monomers. Furthermore, as the amount of styrene in the feed ratio increased, the polymer yield continuously increased, and M, slowly increased up to the styrene feed ratio of 75 mole %. The molecular weights of the copolymers were much smaller than that of styrene homopolymer. As indicated in the equation 11.51, a transfer reaction by proton elimination from styrene-TCD cationic propagating end and the resultant formation of a less reactive buried tertiary cation might be the reason for the molecular weight drop (Eq. 11.51). St
~
St
(11.51)
705 It was found that a small amount of styrene units (caL 5 mole %) in the copolymer with tetracyclo[4.4.0.12"5.17'~~ drastically depressed the glass transition temperature, and beyond 10-20 mole % of styrene units, the glass transition temperature gradually decreased. This anomalous dependency of glass transition temperature on the copolymer composition was attributed to the lower molecular weight of the eopolymer than that of the styrene homopolymer and the absence of TCD/St random copolymers of polymerization degree of 5 with a content of styrene units below 20 mole %. Furthermore, it was pointed out that TCD/St copolymers with a controlled glass transition temperature in the range of 100~ to 260~ could be prepared by choosing the TCD: St composition. New copolymer compositions were manufactured by Mitsui Petrochemical Industriesss from random copolymers of norbornene type monomers and ethylene polymerized in a second step under the influence of cationic initiators with ct-olefin/diene copolymers, containing at least two ot-olefins and one nonconjugated diene (Eq. 11-52-11.53). n
~
\ - - /
+
m
~
+~,~~
(11.s2)
-----~
~
(11.53)
The cycloolefins included in the random copolymers would preferentially have the structures illustrated in the equation 11.53. Alternatively, cyclic olefin polymer compositions can be obtained by reaction of ring-opened polymers from cyclic olefins with the above ct-olefin/diene copolymers in the presence of cationic polymerization initiators (Eq. 11.54).
~
(11.54)
706 Significant advantages of these copolymer compositions are that they possess excellent heat resistance, heat ageing resistance, chemical, weathering and solvent resistance, good mechanical and dielectric properties, high rigidity and impact resistance, particular external appearance and lustre. They are used for the manufacture of printed bases, circuit bases for high frequency uses, camera bodies, housings for meters and appliances, films and helmets. Functionalized copolymers were obtained by Oishi et al. 36 by copolymerizing endo-N-cyclohexylbicyclo[ 2.2.1 ]hept-2-ene- 5,6dicarboximide with styrene under the influence of cationic and ZieglerNatta catalysts (Eq. 11.55).
% n
0
*
m~~l
~ ~
(11.55)
The endo-N-cyclohexylbicyclo[2.2.1 ]hept-2-ene-5,6-dicarboximide adduct could be readily synthesized by Diels-Alder reaction of cyclopentadiene with N-cyclohexylmaleinimide. Similar copolymers were also prepared from higher Diels-Alder homologs of cyclopentadiene and endo-Ncyclohexylbicyclo[2.2.1 ]hept-2-ene-5,6-dicarboximide by cationic or Ziegler-Natta copolymerization with styrene (Eq. 11.55a).
n
+ m
(11.55a)
0
The structure and properties of such copolymers are of interest due to their special characteristics, induced by the bulky and rigid functional groups incorporated into the polymer backbone. It is significant that the thermal degradation of these copolymers was in the range 334-363~ and the glass transition temperature varied from 180~ to 138~
707
11.3. Ziegler-Natta Copolymerization of Cycloolefins Copolymerization of cycloolefins in the presence of Ziegler-Natta coordination catalysts provides a powerful synthetic route to prepare a wide range of random and block copolymers. Moreover, copolymers can be prepared by this mechanism from cyclic monomers and acyclic olefins. Based on a solid documentation from the coordination polymerization of acyclic olefins, the reaction of cycloolefins with this type of catalysts has been rapidly expanded to a substantial number of cyclic and acyclic monomers. This chapter will focus on the copolymerization reactions of cyclic monomers including copolymers prepared from cyclic and acyclic olefins by the Ziegler-Natta procedure.
11.3.1. Monocyclic Monomers Early studies by Natta and coworkers 37 dealt with the copolymerization of several cycloolefins like cyclobutene, cyclopentene, cyclohexene, cycloheptene and cyclooctene with ethylene, propylene, isobutylene, and other lower, linear or branched olefins, under the influence of the catalytic systems consisting of transition metal salts of groups IV-VI and organometallic compounds of groups l-IIl of the Periodic System. By applying this procedure to a wide range of cycloolefins, linear thermoplastic copolymers containing up to 50% molar content of cycloolefin units, alternating with polyolefin fragments, were prepared and characterized using fractionation and extraction techniques, combined with infrared, NMR and X-ray spectroscopy or other adequate analytical methods. Detailed investigation has been conducted by Natta and coworkers 38'39 on the copolymerization of cyclobutene with ethylene and propylene induced by TiCI4- and V(acach-based catalytic systems. Copolymers having cyclic monomer units along with linear fragments have been obtained in these reactions (Eq. 11.56-1 1.56a).
n I--I
+ m I[
nl--']
+
TiC14/Hex3AI V(acac)2/Et;AIC/ "~ TiCI4/Hex3AI-.~. - ~ V(acac)2/Et2AICI
(11.56) [ ~
(11.56a)
708 To provide evidence on the structure of the products obtained, cyclobutene has been copolymerized with [~4C]ethylene in the presence of the V(acac)#Et2AICl catalyst to produce a cyclobutene-ethylene copolymer, containing cyclobutylene units linked to [~4C]ethylene in the polymer chain 39 (Eq. l 1.57).
H2?_CH
HzC--CH
14
CH.z
H2C--CH2
When the reaction was performed at a temperature of-60~ a powdery, white thermoplastic copolymer of the two olefins was obtained in 88% yield. Kaminsky and coworkers 4~2 carried out extensive work on the copolymerization of cycloolefins with ethylene and et-olefins in the presence of the metallocene/aluminoxane catalytic systems. The copolymerization process was found to lower the melting point of the products, thereby making possible the common processing operations of such copolymers. Thus, on using the binary catalytic system Et(IndhZrCI2/MAO, Kaminsky and Spiehl4~ succeeded in obtaining high yields of copolymers from cyclopentene and ethylene. The incorporation of the cyclopentylene and ethylene units into the copolymer chain followed a statistical distribution (Eq. 11.58).
Working under various reaction conditions, they observed that the content of cyclopentene in the copolymer varied from 0.3 to 37 mole %. A high concentration of cyclopentene led to formation of small blocks of cyclopentylene units in the polymer chain. Interestingly, this content decreased with increasing temperature and decreasing the catalyst concentration. Moreover, they found that the amount of the incorporated cyclopentene substantially affected the melting point and crystallinity of the copolymer. On the other hand, average molecular weights were slightly affected by the change of the amount of cyclopentylene units. Propylene was also copolymerized with cyclopentene by Kaminsky et al. 4~ using the catalyst Et(IndhZrCI2/MAO. In this case, they found that,
709 at a temperature of 0~ the catalyst activity reached 57.6 kg polymer/mole Zr.hr and at 30~ it was 13 5.4 kg polymer/mol Zr.hr (Table 11.2). Table 11.2 Copolymerization of cyclopeme~e (M~) with propylene (M2) reduced by Et(IndhZrCldMAO catalyst' Temp. oC
MI mole/L
Time hr
0 0 0 0 30 30 30
1.41 2.82 4.23 5.64 1.41 2.82 5.64
15.7 15.7 5 5 5 5 3.3
Activity kg polymer/mole Zr.hr 48.2 46.7 61.5 57.6 45.5 86.1 135.4
'Data from reference4'; bReaction conditions: [Et(IndhZrCl~] = 6.25x10"~ mole/L, [MAO] = 2. l xl0 3 mole/L, [Pr~ene] = 0.5 bar The activity was much higher than for the homopolymerization of cyclopentene but lower than for the homopolymerization of propylene. The molecular weights were low and ranged between 35000 (0~ and 17000 (30~ The copolymers obtained under these conditions contained between 2 and 5 wt. % cyclopentylene units in the polymer chain (Eq. 11.58a).
n
0
+
m
I
(11.58a) T=0-30~
"~
Remarkably, cyclohexene can not copolymerize with ethylene under the influence of Et(Ind)2ZrCI2/MAO as a catalyst in the same conditions as cyclopentene does. This fact was attributed to the higher stability and lower ring tension of the six-membered ring of cyclohexene. Larger cycloolefins like cycloheptene and cyclooctene will copolymerize with ethylene in the presence of Et(Ind)2ZrCI2/MAO to produce the corresponding copolymers in substantially higher yields as compared to cyclopentene 40 (Eq. 1 1.59-1 1.60).
710
t) n(
mH § H
Et(Ind)2ZrCI2/MAO --
~
(11.S9)
Et(Ind)2ZrCI2/MAO
(11.60)
Relevant data concerning the reaction conditions and polymer yields for these reactions are summarized in Table 11.3. Table 11.3. Copolymenzation of cycloolefins(M~)with ethylene(M2) in the presence of Et(Ind)2ZrCl~AO catalyst' Cycloolefm
M~M2 (mol)
Cyclopentene
3.85
Cycloheptene
2.3 5.85 11.7 2.3 5.85 11.7
Cyclooctene
10 10
Reaction Conditions
[Zr] = 6.4x 10"6 mole/L [MAO]=2.2xI0 "~ mole AI/L [Czl'h]=0.296 mole/L Time = 2h [Zr] = 7.4x 10"6 mole/L
[Zr] = 7.4x 10~s mole/L [Zr] = 7.4x 10"6 mole/L
Temp ~C
Yield kg /mole Zr/hr 0.01
30 30 30 50 50 50
5.9 2.8 2.2 12 I1 7
30 30
5.4 1.5
"Data from reference 4~ The effect of some of the reaction conditions such as the molar ratio between the two monomers, catalyst concentration and reaction
711 temperature on the polymer yield might be, however, significant. As it can be readily observed from the data presented in Table 11.3, for cyclopentene copolymerization the lowest yield of polymer was recorded at a temperature of 0~ while for the other cycloolefins a substantial yield was reported at 30~ Significant investigations were reported by Kaminsky and coworkers 4z on the copolymerization reaction of cyclopentene with allyltrimethylsilane in the presence of metaUocene/aluminoxane catalyst in toluene as a solvent (Eq. 11.61).
SiMe 3
In this work, they assumed that the bulky silyl side groups in combination with the cyclopentylene units would promote optical rotation. For this purpose, the S-enantiomeric form of the optically active component Et(Indl-h)2ZrCI2 was used in the catalytic system. Data concerning the catalyst activity in various reaction conditions are presented in Table l 1.4. Table 11.4 Copolymerization of cyclopentene(CP) with allyltrimethylsilane(ATS) m the presence of (S)Etz(IndH4)ZrCI~AO catalyst (800 mg/L)' Catalyst Conc. (mole/L)x 104
1.2 0.56 1.9 0.56 1.5 0.95
CP:ATS (mole/L)
Temp (~
3.7:0.12 3.5:0.19 6.1:0.86 5.6:0.01 5.6:0.01 2.2:0.12
28 20 19 17 16 15
Time Activity, Olr) kg product/ mole ZrXcMxhr 48 45 92 40 48 90
0.2 3.1 0.01 0.07 0.07 0.02
'Data from reference 42 These authors observed that the activity of the copolymerization reaction decreased drastically in the first 10 minutes by a factor of 20 to become
712 nearly constant after 30 minutes. The microstructure was examined by ~HNMR, ~3C-NMR and IR spectroscopy and the optical activity was determined at several wave lengths in decahydronaphthalene. Some of the data obtained are given in Table 11.5. Table 11.5 Physical properties and optical activity of cyclopentene(CP)/allyltnmethylsilane(ATS) copolymers' Copolymer CP:ATS(mole)
Reaction Temp. ~ 28 20 19 17 16
11:1 7:1 2:1 28:1 25:1 'Data from reference
Mill
14000 700 8400 8500 9500
Melting
Point ~
200 180
[ OL]3652~
(dr /dag) -4.4 -8.0 -17.6 -7.5
42
As Table 11.5 illustrates, the melting points are relatively high for these copolymers, that is, in the range 180-200~ The optical activity found was between -4.4 ~ and -17.6 ~ To explain the optical activity of the copolymer these authors assumed that the end-groups may affect the chiral cyclopentylene and allyltrimethylsilane units or that the cyclopentylene units in the di-syndiotactic configuration would be optically active. Interesting results reported Sumitomo Chemical Co. 43 on the copolymerization of cyclopentadiene and substituted cyclopentadiene (methylcyclopentadiene, ethylcyclopentadiene, dimethylcyclopentadiene) with a wide range of olefins (e.g., 1-butene, 2-butene, isobutylene, lpentene, 2-pentene, 1-hexene, 2-hexene, butadiene, isoprene, piperylene, styrene, a-methylstyrene, vinyltoluene, isopropylbenzene and indene) in the presence of catalysts consisting of organometallic compounds and transition metal salts. The catalyst comprises preferentially organoaluminium compounds, e.g., trialkylaluminium, dialkylaluminium halides, alkylaluminium sesquihalides, alkylaluminium dihalides, organotin compounds, e.g., tetraalkyltin, trialkyltin halides, associated with halides or oxyhalides of W (WCI6, WBr6), Mo (MoCls) or Re (ReCls) and optionally a third component, e.g., water, alcohols, ethers, esters, ketones, carboxylic
713 acids, 02, nitrogen-containing compounds, sulphur-containing compounds, halogen-containing compounds or Lewis acids. Possibly, the polymers have a statistical distribution, the real structure depending on the monomer reactivity and reaction conditions (Eq. 11.62).
= R'
R"
~
(11.62) R
!
where g ' is hydrogen or an alkyl group and g" is an alkyl or aryl group. The process occurred readily in hydrocarbon solvents at room temperature and provided cyclopentadiene copolymers which were not gelated at the polymerization temperature. The structures of these copolymers were not discussed. Copolymers of cyclopentadiene (M~) with indene (Mz) were produced by Nikolaev et al." with the catalyst CF3COOH/Co(OAc)2 in 1,2dichloroethane at 20~ The reaction occurred probably by 1,2- and 1,4addition pathway (Eq. 11.63).
(11.03)
Under these conditions, the reaction proceeded with monomer reactivities rm = 3.25 and r2 = 0.29. It was noted that the glass transition temperature, hardness and softening temperature of the copolymer increased with increasing indene content. On the other hand, copolymers with high cyclopentadiene content were readily susceptible to oxidation, but could be stabilized with 2% antioxidant, e.g., BHT. Novel solid copolymers of l-butene and 4-vinylcyclohexene were prepared by Shell Oil Co. 45 using titanium halide coordination catalysts
(Eq. 11.64).
714
The copolymers have broader molecular weight distribution, shorter crystallization half-time, greater isotacticity (~3C NMR) and greater X-ray diffraction crystallinity than l-butene homopolymers prepared with identical catalysts. The catalysts consist of TiCI3 and trialkylaluminium, especially Et3AI and Et2AICI, the ratio of TiCl3 to organoaluminium compound is 1/36. Hydrogen was present during polymerization. Various amounts of 1butene and 4-vinylcyclohexene were bulk copolymerized using TiClflEt3Al or TiCla/Et2AICI catalysts at 60~ for 90 min. Yields ranged from 700-2000 g polymer/g catalyst hr, decreasing with increased amounts of 4vinylcyclohexene. These copolymers are believed to have single 4vinylcyclohexene units distributed randomly over the polymer chain; they are capable of reaction on their unsaturated sites. Structural analysis of these products indicated that 0.1-1 mole % 4-vinylcyclohexene was present in the copolymer: this was achieved by having 5-15% 4-vinylcyclohexene in the reaction mixtures, in solution or slurry type systems, at temperatures from 40~ to 80~ Products thus obtained had improved strength without decrease in the desirable properties of the corresponding l-butene homopolymers. An ethylene-propylene-diene terpolymer, wherein the third monomer component was 4-ethylidenecyclohexene, was produced by Sun Research and Development Co. ~ using a conventional Ziegler-Natta catalyst (Eq. 11.65).
+
II
=
(11.65)
The terpolymer composition was 60-75 mole % ethylene, 20-30 mole % propylene and more than 10 wt. % 4-ethylidenecyclohexene and it had an inherent viscosity, [11] = 2.0-2.7 (tetralin at 37.8 ~ Surprisingly, the corresponding isomer, 3-ethylidenecyclohexene, did not polymerize to the corresponding terpolymer under the same conditions. The monomer 4ethylidenecyclohexene used in this reaction has been prepared by
715 isomerizing 4-vinylcyclohexene at 75~ with a Ziegler-Natta catalyst made of an organonickel compound, (R3PhNiX2 or (R3P)2NiX2/SnX3 (where R and R'=Cm.6 alkyl, Cs.7 cycloalkyl or aryl, X and X'=halogen) and an organoaluminium compound, R'zAIX', and separating the 3- and 4ethyliclene isomers. A stereospecific synthetic rubber was produced by Dolgoplosk et al. 47 by copolymerizing 1,3-butadiene with 1,3-cyclohexadiene in the presence of ~-allyl Ni complexes with electron acceptor compounds (Eq. 11.66).
For instance, using bis0t-crotyI-NiCl)/Ni(CCl3COOh as a catalyst, copolymerization of 1,3-butadiene with 1,3-cyclohexadiene for 6 min at 20~ gave poly(butadiene-co-cyclohexadiene) having a glass transition temperature of-91.7~ The microstructure examination of the product thus obtained indicated 8 mole % cyclic units in the polymer chain. The material exhibited improved low temperature properties and a better resistance to crystallization as compared to conventional butadiene rubbers. The reactivity of various cycloolefins in copolymerization reactions with ethylene and 2-methylbutene in the presence of V(acac)dEtzAICl and VCh/Hex3AI as catalysts has been examined in detail by Natta and coworkers. 4s In the course of their studies, they found that, while the catalytic system had little effect on the relative reactivity of the cycloolefin, the nature of the cyclic and acyclic monomer influenced substantially the reaction kinetics and stereochemistry. In this respect, cyclopentene and cycloheptene displayed high reactivity as compared to cyclohexene and cyclooctene whereas c i s - 2 - b u t e n e was more reactive than trans-2-butene. These findings were rationalized by Natta and coworkers 37 considering essentially steric factors induced by monomers rather than catalyst activity and stereospecificity.
11.3.2. Bicyclic and Polycyclic Monomers A great number of copolymers have been prepared from norbornene with linear olefins such as ethylene, propylene, butene, pentene and higher homologs in the presence of a large variety of coordination
716 catalysts, particularly of Ziegler-Natta type, which find useful applications in numerous modem technologies. They contain the two structural units, norbomylene and alkylene, corresponding to both monomers, norbornene and a-alkene, in a random or blocky distribution, as a function of the catalyst nature, monomer type and reaction conditions (Eq. 11.67).
(11.67) R
Catalytic systems based on titanium and vanadium salts and organometaUic compounds were claimed for this reaction but best results provided catalysts derived from TiCI4, TiCl,~(Og~)n or TiCI3 and VOCCI2(OR2), in conjunction with organoaluminium compounds of the type R'3AI or R'3. mAICl~. Depending on the microstructure of the polymer chain, these products exhibited improved physical-mechanical properties, particularly the optical and electrical parameters, suitable for applications in optics, electronics and fine mechanics. In their early report, Gladding, Fischer and Collette49 showed that ethylene and propylene readily polymerized with linear or cyclic nonconjugated dienes in the presence of vanadium oxychloride, VOCI3 and organoaluminium compounds, 'Bu3Al, to form new hydrocarbon elastomers in high yield. As cyclic non-conjugated dienes they used norbornene and norbornadiene derivatives, e.g., 2-methylenenorbornene, dicyclopentadiene, etc. By copolymerizing these cycloolefins with ethylene and propylene in tetrachloroethylene, under the influence of the catalyst VOCI3/'Bu3AI, new copolymers with elastomeric properties were produced, e.g., poly(ethyleneco-propylene-co-2-methylenenorbornene) (Eq. 11.68)
§
II
+
----,-
(11.68)
717 and poly(ethylene-co-propylene-co-dicyclopentadiene) (Eq. 11.69).
(11.69)
A new procedure for manufacturing these elastomeric terpolymers was also reported by Sun Oil Co. ~~ using binary catalysts derived from VO(OR)~X~ and R'pAIXs.p, where R and R' are hydrocarbyl groups, X is halogen and m, n and p are integers. According to several procedures for norbornene copolymerization with a-olefins in the presence of Ziegler-Natta titanium-based catalysts reported by VEB Leuna-Werke, 5~ the catalytic components are preferably added at temperatures from-30~ to +60~ the norbomene concentration during the catalyst formation is between 0.25 and 5.00 mole/L and the catalytic system is aged at 20 to 70~ for a period of 15 to 180 rain. Generally, the process takes place in a liquid inert medium (e.g., aliphatic hydrocarbons or benzines, poor in aromatics and cycloaliphatics), at temperatures and pressures required to control the desired monomer ratio in the copolymer and to improve the product physical-mechanical properties. The catalysts comprise Ti salts TiX~(OR), or TiXs where X=halogen, especially el, Br or mixtures of these, R=alkyl, cycloalkyl, alkylaryl and arylalkyl, n=O-4 and organoaluminium compounds, AIR ls-mX'm where R~=H, alkyl, cycloalkyl, arylalkyl, X'=halogen, especially CI, Br, I or a ligand (OR) and m=l or 2. The copolymers have improved purity and transparency, particularly useful for electrical, electronic, fine mechanical and optical applications in blends with polyethylene. 5z' Of these copolymers, norbornene-ethylene combinations, used as dielectric for capacitors in electrical and electronic engineering, impart better resistance to ageing, better constancy of electrical parameters, improved dielectric strength and low dielectric loss at high frequencies as well as high voltage m, resistance over a long range time and temperature. It is noteworthy that numerous blends of norbornene-ethylene copolymers with many elastomers form high impact compositions with high heat resistance, optional with fiber or particulate reinforcement and crosslinking. TM Some of these blends contain 95-70% norbornene-ethylene copolymer and 5-30% of butyl rubber, polyisoprene, ethylene-propylene
718 copolymer or mixtures of these elastomers as well as additives such as stabilizers and lubricants. They may also contain as rubber component silicone, polysulphide or chlorinated rubber, chlorosulphonated polyethylene, polyacrylate rubber, poly(chlorotrifluoroethylene), polychloroprene, carboxyl rubber, vinylidene fluoride-hexafluoropropylene copolymer, chlorotrifluoroethylene-vinylidene fluoride-pentafluoropentene terpolymer and/or trifluoronitromethane-tetrafluoroethylene copolymer. Other highly performant compositions contain 15-60% norborneneethylene copolymer associated with 85-40% elastomer and 0.1-2% crosslinking agent and/or 10-70% fiber forming or particulate reinforcing agent. The elastomeric components consist of natural rubber, elastomeric ethylene co- and terpolymers or graft copolymers, polybutadiene elastomeric butadiene co- and terpolymers or graR copolymers, chlorinated and sulphochlorinated polyethylene, polyisobutylene, polyisoprene, polychloroprene, chlorohydrin, butyl, silicone, polysulphide, f l u o r o ~ n , nitroso, carboxynitroso, polyacrylate or polyurethane rubbers. Cross-linking agents may include di-tert-butyl peroxide, cumyl hydroperoxide or tertbutyl hydroperoxide and as reinforcing agents glass- or mineral fibers or particulate materials e.g. chalk, silicates, wood flour or milled thermosetting resins. These polymer blends may be modified by "/or electron irradiation. Compositions with high heat resistance, stiffness and toughness are useful in precision engineering, electrotechnology and machinery, automobile and container industry. 53b Furthermore, multiple compositions having improved mechanical properties are prepared from norbornene-ethylene copolymers with aliphatic and/or aromatic polyamides, elastomers and various reinforcing agents. TM Novel copolymer compositions contain ethylene~ norbornene copolymers associated with thermoplastics (e.g., polyethylene, polyamides, polyethers) and particulate reinforcing materials (PRM), glass fibers, bonding agents, cross-linking agents, lubricants, stabilizers and pigments. 5~b Heat stable shaped articles of norbornene and ethylene copolymer with high resistance to radiation are useful in medical, nuclear, radiation and space-travel technologies and can withstand doses up to 15 MGy at 373 K without loss of strength. 55" Typical applications of such articles include manufacture of injection needles, canulae, infusion apparatus components, containers, casings, linings, etc. Fibers for production of technical textiles, especially filter cloths, comprise ethylene~ norbornene copolymers or blends of these copolymers with elastomers, other polymers and additives. ~Sb The fibres have good resistance to hot water, aqueous solutions of acids, bases and salts, polar organic solvents
719 and biodegradation. They can be used at temperatures up to 100~ and produce fabrics which are dimensionally stable and easy to clean. Such copolymers contain 25-90 (esp. 40-80) mole % norbomene and optionally 0.02-3 (esp. 0.05-1) wt.% stabilizers and has a melt index of 1-80 (esp. 220) g/10 min at 275 ~ and 2. l kg load. These copolymers can be blended with natural rubber, elastomefic ethylene copolymers, butadiene homo- or copolymers, chlorinated or chlorosulphonated polyethylene, polyisobutylene, polyisoprene, polychloroprene, chlorohydrin, butyl, silicone, polysulphide, fluorocarbon, nitroso, carboxynitroso, polyacrylate or polyurethane rubber, with polyolefin, ethylene/vinyl acetate copolymers, polyamides, thermoplastic polyesters, polystyrene, polyc,arbonates, polyphenylene oxides and/or polysulphones. The fibers can be melt-spun at 130-200~ or spun from a 3-40 wt.% solution in an organic solvent, especially dec~in, trichloroethane or norbomene, into a precipitant bath of hydrocarbon or alcohol solvent. Interesting moulding compositions contain norbomene-ethylene copolymer associated with ethylene vinyl acetate (EVA) copolymer or ethylene propylene diene terpolymer (EPDM). 56" They are used for dynamically stressed units in electrotechnique and machine construction. The units resist dynamic stress reversal and permanent temperatures above 373~ Surface hardness, modulus of elasticity and rigidity are not affected. New thermoplastic blends containing branched polyolefins, associated with norbornene-ethylene copolymer and optionally containing elastomer and reinforcing agent, are useful for the moulding of structural components in the electrical, electronic precision engineering, machine and vehicle construction and in the manufacture of containers. 56b These blends comprise 5-95% norbomene-ethylene copolymer (preferably 30-70%), 955% a branched polyolefin, 1-25% an elastomer and other thermoplastics and 1-50% a fibrous and particulate reinforcing agent and optionally stabilizers and lubricants. The branched polyolefin may be polypropylene, poly(1-butene), poly(4-methyl-l-pentene) and poly(l-hexene). The elastomer improves the impact strength of the composition and may be natural rubber, ethylene co- and terpolymer rubbers, polybutadiene, butadiene co- and terpolymers and graft polymers, chlorinated and chlorosulphonated polyethylene, polyisobutylene, polychloroprene, butyl rubber, silicone rubber or polyacrylate rubbers. The reinforcing agent is glass fibers, asbestos fibers, mineral fibers, organic high modulus fibers, CaCOs, silicates, metal powders, metal oxides, glass microspheres or modified regenerated thermoplastics. These materials have high heat
720 deformation resistance, solvent resistance, rigidity, toughness and good electrical properties and are useful for the moulding of structural components for use in electrical, electronic precision engineering, machine and vehicle construction and in the manufacture of containers. On the other hand, the surface properties of semi-finished goods and mouldings of ethylene-norbornene copolymers containing thermoplastics, fillers, reinforcing agents and other plastic adjuvants could be modified by chemical etching in an oxidizing medium such as fluorine, chlorine, sulphur dioxide, chromic acid and sulphurir acid solutions, nitric acid, fluorosulphonic acid or organic sulphonic acids. The surface etching treatment gave products with improved adhesion, printability, metaUizability and paintability. Thermoplastic combinations useful for electrical engineering, electronics, precision engineering, machine-, vehicle- and container construction contain 5-95% norbornene-ethylene copolymer, 95-5% polyethylene and optionally 1-25% elastomer and/or a further thermoplastic material and/or 1o50% fibrous and/or particulate strengthener. 5~" Stabilizers and lubricants are optionally added. The addition of polyethylene to norbomene-ethylene copolymer improved the resistance to chemicals and tenacity of the copolymer while the addition of the norbornene-ethylene copolymer to polyethylene increased the strength, modulus and hardness without lowering impact-flexure strength. Novel, filled thermoplastic compositions of ethylene-norbornene copolymer consist of 20-99% copolymer, 1-70~ particulate reinforcing material and 1-60~ of a further thermoplastic and 1-35% of a natural or synthetic elastomer. 57b These compositions may also contain stabilizers, bonding agents, cross-linking agents, glass fibers, lubricants and pigments. The particulate reinforcing materials may be inorganic compounds such as CaCO3, mica, kaolin, clays, silicates, SiO2, metal powders, metal oxides or salts or carbon black or organic materials e.g., duroplastic microspheres, wood flour or reclaimed thermoplastic. Interracial bonding between ethylene-norbornene copolymer and particulate reinforcing material was improved by addition of known bonding agents e.g., silanes or acrylic derivatives and by ultrasonic or other known pretreatment. They have good dielectric properties and other properties e.g., durability, thermal stability, mechanical properties, water- and solvent-uptake superior to those of priorart compositions based on polyamide, polyethylene or polyvinyl chloride. Increasing amounts of PRM gave higher flexural modulus, hardness, Vicat temperature and solvent resistance. Additional thermoplastics e.g.
721 polyethylene, polyamide, polyester, etc. provided further improvement of material properties. Thermoplastic hollow mouldings contain ethylenenorbomene copolymers or mixtures of ethylene-norbornene copolymer, elastomers, other polymers and additives, preferably mixtures of stabilizers, dyestuffs or pigments. The thermoplastic hollow bodies are useful as transparent, strong, lightweight, dimensionally stable liners for industrial or domestic liquid containers and in packaging for e.g., hot water, acids, alkalis, cosmetics, detergents, aggressive gases and suitably modified for petrol, oil and oil-containing media. The liners have a long-term service temperature of at least 100~ These ethylene-norbornene copolymers contain elastomers or other copolymers e.g., natural rubber, elastomeric ethylene co- and terpolymers or graft copolymers, polybutadiene, elastomeric butadiene co- and terpolymers or graft copolymers, chlorinated and chlorosulphonated polyethylene, polyisobutylene, polyisoprene, polychloroprene, r rubber, butyl rubber, silicone rubber, nitroso or carboxynitroso rubber, polyacrylate rubber, polyurethane rubber, polyethylene, polypropylene, poly(l-butene), EVA copolymer, polyamide, thermoplastic polyester, polystyrene, polycarbonate, polyphenoxide, polysulphone or mixtures of these polymers or copolymers. High impact norbornene-ethylene copolyrner compositions containing partly hydrolyzed olefin vinyl ester copolymer elastomer and additives such as stabilizers or lubricants were prepared by VEB LeunaWerk ~' for use as a material of construction for precision parts, containers and in electrical industry. Such a product consisting of 60-95 (70-85)% norbomene-ethylene eopolymer and 5-40 (15-30)% vinyl ester-olefin copolymer modified by reaction with metal alcoholates containing alcohol has high long-term thermal stability, good impact strength and high strength and elongation The vinyl ester-olefin copolymer has excellent dosing properties so that a high product quality could be guaranteed. Alternate compositions containing 0.05-20 (1-6)% co-, ter- or graft copolymer of maleic anhydride with C2-4 olefins, styrene or C4.~ acrylate esters produced materials with high long-term thermal stability, good impact strength, good processability and high strength and elongation. The vinyl ester-olefin copolymer had excellent dosing properties, so that a high product quality could be guaranteed. Moreover, when the above copolymer combination contained 0.1-10 (0.5-2)% modified polyolefin wax and optionally crosslinking agent, lubricant and stabilizers, good processability, good impact strength and high strength have been attained. The modified wax, particularly oxidized, was from low-molecular weight polyolefins e.g.
722 polyethylene, ethylene copolymers, polypropylene or polybutene, a lowmolecular weight co- or terpolymer of ethylene, propylene or butene with (meth)acrylic acid or esters and vinyl esters, a low- molecular weight polyolefin grafted with polar monomers such as maleic anhydride, (meth)acrylic acid or esters, vinyl esters or vinyl ethers. Efficient ethylenenorbomene copolymers bonded to metals or metal alloys with epoxy resin adhesive, containing aromatic or halohydrocarbon solvent, can be used in electrical and electronic engineering and in precision mechanics and optical instrument construction. The epoxy resin adhesive consists especially of low- and medium molecular weight resin and optional contains fillers. The metal components can consist of Fe, AI, Cu, Sn, Zn, Cd, Ag or Ni. Remarkably, strong bonds are formed at the metal surface, e.g., requiring a force of 1300-1500 N to destroy the adhesion surface area. Thin films of norbomene-ethylene copolymer were produced by casting polymer solutions in tetrachloroethylene and 1-30 (esp. 20) wt.% cyclohexane onto a carrier material, e.g., capacitor paper, which has been pretreated with polar organic compounds such as higher carboxylic acids or esters. ~Sb The films could be metallized under high vacuum. The resulting films were strong, with good dielectric properties and suitable for use as electrical insulation films, sterilizable packaging films or as a dielectric in wound capacitors. If desired, the metallized base layer could be coated with a layer of the same or other thermoplastic polymer. Self-lubricating polyamide compositions containing polyethylene, ethylene-norbomene copolymer and lubricating oil were prepared by VEB Leuna 59" for use in high load, permanent, self-lubricating glide elements, at low and high speed. These compositions contain 95-55 wt.% of a polyamide resin, 2-10% of a lubricating oil which is liquid at room temperature or at below the flow point of the organic oil-binding agent, 0.5-10% of low density polyethylene and ethylene-norbornene copolymer as oil binder, 2-20% of talc, active silicic acid or graphite, as reinforcing agent and optionally nucleating inorganic binder, and 0.5-5% of a dispersant based on oxidized low-molecular weight polyolefins and/or a metal salt of a fatty acid. The composition was easily prepared and processed and had very low frictional resistance and abrasion, and showed no stick-slip at varying loads and glide speeds. In another process, 5~' hard foam contains norbomene-ethylene copolymers or a mixture of 30-90% copolymers and 5-50% fibrous and/or particulate reinforcing materials and/or 2-40% of an elastomer or other thermoplastic and optionally stabilizers and lubricants. The foam had high heat distortion temperature and good dielectric
723 properties. Heat resistance was up to 400 ~ Pipes are resistant to aggressive, hot aqueous media. The composition is useful for electrical and electronic industries, in precision work, in machine and vehicle construction, in household technology and in protective linings. Its applications include high frequency or heat insulation units, switch parts, condensers, connecting sleeves, and insulated containers. New compositions containing norbornene-ethylene copolymer and vinyl aromatic polymers 59~ or vinyl halide polymers 59a with high heat distortion temperature were also prepared. The vinyl aromatic polymer may be polystyrene, polychlorostyrene, polydichlorostyrene, polymethylstyrene, polydimethylstyrene, polymethoxystyrene, polyvinylpyridine or polyvinylcarbazole or a co- or terpolymer e.g., of styrene-acrylonitrile or styrene-acrylonitrile-~-methylstyrene. The vinyl halide polymer is usually polyvinylchloride. These compositions can be used for long periods at high temperatures. Heat distortion temperature, rigidity and toughness, ball pressure hardness, flexing strength and rigidity are good. The polyvinylchloride compositions are transparent. They are usable in the electrical and electronic industry, in the precision work and machine construction as well as in the household goods and toys. Polymeric aldehyde compositions containing norbomene-ethylene copolymer with good heat-dimensional stability, stiffness and toughness were prepared from 5-95% polymeric aldehyde, 95-5% norborneneethylene copolymer and optionally 1-25% elastomer and/or other thermoplast and 1o50% fibrous or particulate reinforcement and optionally stabilizer and lubricant. 59~ The concentration of the norbornene units into the norbornene-ethylene copolymer was 30-70~ The polymeric aldehyde may be polyformaldehyde, polyacetaldehyde, polyglyoxal and polytrifluoroacetaldehyde or a formaldehyde-amide copolymer. The product can be used as a construction material, especially for mechanical engineering, vehicle construction, precision engineering. Several copolymers of l-butene with norbornene were obtained by Heublein and coworkers 6~by copolymerizing the two monomers with Tibased ternary catalysts (Eq. 11.70).
724 As catalysts they employed y-TiCI3, 13-TiCI3, TiCh, TiCI3/AICI3(I/3), Ti(ORhX2, Ti(OR)3X associated with Et2AICI, Et2AIBr, MezAICI and electron donors such as amines, ethers, carbonyl compounds, phosphorus compounds, sulphur compounds, cycloalkenes. In an economical procedure in the butadiene free C4 olefin fraction consisting of l-butene, isobutene, E2-butene and Z-2-butene, only l-butene reacted with norbomene under Ziegler-Natta conditions avoiding thus the purification of l-butene from the C4 fraction before use. On varying the reaction conditions, copolymers of lbutene with norbomene having various composition and properties (e.g. molecular weight and melting point) could be synthesized by this means. A series of copolymers of linear and cyclic dienes with more than two a-olefins were prepared by Japan Synthetic Rubber Co. 6~ in the presence of titanium halide compounds of formula TiX, (X=F, CI, Br or I) and organomagnesium compounds of formula MgR~R2 (R~ and Rz each = alkyl, cycloalkyl, aryl or alkoxy groups) in hydrocarbon solvents (e.g. hexane) at -80~ to 150~ and pressure of 60 kg/cm z. Of the cyclic monomers, 4-vinyl-cyclohexene, 1,4-cycloheptadiene, 1,5-cyclooctadiene, dicyclopentadiene, norbomadiene, 5-ethylidene-2-norbomene and 5propenyl-2-norbomene were preferred whereas the r were ethylene, propylene, l-butene, 1-pentene, l-hexene, 1-octene, l-decene or ldodecene. Various random copolymers with structures given in the equations 11.71-11.77 were thus prepared by this method.
(11.71)
k_ (11.72)
(11.73)
725 §
LR
=--
(11.74)
R
(11.76)
+ L
..~
~
(11.77)
R
By an alternate procedure, 6z' a rubbery copolymer was prepared by slurry polymerization of ethylene, an a-olefin and optionally a nonconjugated c y c l i c diene such as 5-ethylidene-2-norbornene, dicyclopentadiene, 5-propylidene-2-norbornene and 1,5-cyclooctadiene, under the action of a catalyst consisting of an organoaluminium compound or organomagnesium compound and a halogenated titanium compound, at temperatures of 0-90~ and pressures of 1-50 kg/cm 2. In this case, a polysiloxane compound was precoated on the inner wall of the reactor and the surface of other parts with which the reaction medium would contact. Since the polysiloxane compound is generally colorless and harmless, it does not contaminate the products. The slurry polymerization technique has been also used to prepare new rubbery copolymers from ethylene, ~-olefins and conjugated dienes under the action of binary catalysts consisting of vanadium compounds and organoaluminium compounds. The preferred monomer composition consisted of ethylene, propylene and 5-ethylidene-2norbomene forming mainly the corresponding random vinyl terpolymer (Eq. 11.78).
726 _...__.=,.
(11.78)
The polymerization occurs in hydrocarbon solvents e.g., hexane, benzene or toluene at -60-100~ and leads efficiently with increased reaction rates to rubbers of a high quality. The vanadium compounds include VCI4, VOCI3 and di-n-butoxide vanadate while the organoaluminium compounds consist of triethylaluminium, diethylaluminium monochloride, ethylaluminium sesquibromide and isobutylaluminium sesquichlodde. According to an improved procedure, 6~ synthetic rubbers were prepared from ethylene, propylene and 5-ethylene-2-norbornene in presence of transition metal compounds and organoaluminium compounds with controlled stirring and adding polymerization inhibitors. Polymerization terminators were added to the reaction liquid discharged from polymerization cells in the laminar flow zone and the reaction mixture was stirred at a given stirring velocity to continuously control the molecular weight distribution of the synthetic rubber formed. Products with desired molecular weight distribution were continuously obtained by this way. An early procedure, patented by Dunlop Rubber Co., 63 described copolymerization of ethylene and propylene with diolefins such as dicyclopentadiene using organometallic compounds and transition metal salts. The organometallic compound was mainly an organoaluminium halide, e.g., R2AIX and R3AI2X3 (R = Cz-8 alkyl group, X = Br or CI), and the transition metal compound vanadium oxytrichloride, VOCI3. In one example, ethylene, propylene and dicyclopentadiene were copolymerized to high molecular weight products containing the three monomer units in the polymer chain (Eq. 11.79). m,.= v
(11.79)
Naphthachimie Co. 64 produced elastomeric terpolymers containing ethylene, propylene and a diene, e.g., 5-ethylidene-2-norbornene by contacting a gaseous mixture of the monomers in the absence of a liquid
727 hydrocarbon with a catalyst consisting of a solid titanium compound and an organometallic compound of group II or Ill of the Periodic System (Eq. 11.80). +
[
+
k
"~
(11.80)
Preferably TiCh was reduced by an organoaluminium compound, e.g. EhAICI, at temperatures between -10~ and 80~ in the presence of an electron donor such as R'-O-R", where g ' and g" are Cz-~ alkyl groups. The terpolymer was obtained directly as a powder with grain size of 0.2-1 mm. Separation of the polymer from a hydrocarbon medium was thus avoided. Interesting elastomeric terpolymers from poly(cycloalkenyl) compounds and a-olefins were produced by Chemische Werke Htils65 using catalysts derived from vanadium compounds and organoaluminium compounds. Thus, starting from 3-chloro- 1-cyclopentene and cyclopentadiene reacted first with ZnClz (Eq. 11.81),
z-r h
n O~~~.--CI
(11.81)
Cl a copolymer was prepared with ethylene or a-olefins in hexane as a solvent, under the catalytic effect of VOCI3 and Et3AI2CI3 (Eq. 11.82). voch
CI +
,
Et3AIzCI3
~\
R
=
(11.82)
R
CI
In a specific process, a copolymer was prepared by reacting chlorodicyclopentyl with Mg and ether in tetrahydrofuran and
728 polymerizing with ethylene and propylene in the presence of the above catalytic system (Eq. 11.83). ~)~~CI
+
,, *
~~"
(I 1.83)
By a similar way, ss elastomeric terpolymer ethylene/propylene/5-(3'cyclohexenyl)-2-norbomene was synthesized under the influence of the vanadium oxytrihalide/organoaluminium halide ). +
,,
+
\
=
(11.84)
According to a new economical procedure, patented by Chemische Werke H01s,67 a number of copolymers are produced by copolymerization of ethylene with propylene and/or l-butene and optionally a polyene using a mixed catalyst of halo-orthotitanic ester and organoaluminium compounds. The copolymerization was carried out at 50-80~ in a solvent containing butane and/or propane and 2-butene besides 30-99 mole % propene and/or l-butene. The catalyst consists of dipropyl or dibutyl dichlorotitanate and Et3AI2CI3. Suitable polyenes are dicyclopentadiene, ethylidenenorbomene and hexa-l,4-diene. Copolymers of the following structure have been thus prepared (Eq. 11.85-11.87). (11.85)
(11.86) =~
(11.87)
729 One important advantage of the process is due to the use of C3-4 fractions rather than pure propylene and 1-butene. The products can be used in coating, sealing and casting applications and also to improve the soRening point, brittle point and weathering resistance of bituminous compositions. Another specific procedure, patented by Chemische Werke Htils,68 described high molecular weight, partially crystalline terpolymers with improved green strength to be prepared from ethylene, ~-olefins and norbomene in the presence of VOCl~/EhAlzCl3/methyl perchlorocrotonate. Thus, a copolymer containing 3.35% norbomene, 3.35% propylene and the remainder ethylene was prepared in 98% yield under the influence of the above catalytic system (Eq. 11.88).
~'
+ ~
+
= 1198%
(11.88)
The copolymer had green strength 138 kg/cm 2, elongation 586%, 100~ modulus 90 kg/cm 2 and Shore hardness 92 at 22~ compared with values of 87 kg/cm 2, 507%, 63 kg/cm z and 93, respectively, for a control ethylene/propylene rubber containing 10% propylene and no norbomene. They were superior to similar copolymers obtained by a radical mechanism.69 Moreover, in another improved procedure, ethylene/propylene/diene rubbers with excellent physical- and mechanical properties were prepared by Bunawerke HLils Co.,T~ using as catalysts vanadium compounds and organoaluminium halides in conjunction with ester, where the ester was a functional group of a polymer chain. In their early patent, Societe Nationale des Petroles d'Aquitaine, 7~ described the copolymerization of tz-olefins, e.g., ethylene and propylene, with tricycloalkenes, particularly unsubstituted and substituted tricyclodec8-enes, under the action of binary catalysts consisting of vanadium halides or vanadium oxyhalides and alkylaluminium halides. Preferred copolymers were obtained from tricyclo[5.2. I. 0~'6]dec-8-ene (Eq. I I. 89),
+/+
,~
.= " ~ ~
(11.89)
730 1'-methyl-6-ethenyltricyclo[5.2.1.02"6]decen-8-ene (Eq. 11.90)
+I
§
(11.90)
v
or l'-methyl-l',3'-butadienyltricyclo[5.2.1.0z'6]decen-8-ene and ethylene and propylene (Eq. 11.91 ).
"-~
(11.91)
The copolymers thus prepared contained usually 0.1-20% tricycloalkene units and 5-75% propylene units. At the same time, the proportion of tricycloalkene and propylene in the monomer feed was so chosen that the maximum amount of ethylene units in the polymer chain to be 75%. Further vulcanization of these copolymers provided materials with good elastomeric properties. Du Pont n reported on the copolymerization of ethylene with bicyclic and multicyclic non-conjugated dienes such as norbornadiene, dimethano-tetrahydronaphthalene, trimethano-decahydroanthracene, dinorbomenyl-alkylene and bis-norbornadiene (Eq. 11.92-11.96).
+
II
§
II
~
-~/,--,~~
(11.92) (11.93)
731
I n
* !
II
~
[-,v--""~
~
(11.95)
~
~
(11.96)
i
These reactions were conducted under the influence of several coordination catalysts consisting of vanadium compounds such as vanadium oxychloride and organoaluminium compounds such as EhAIzCI3, in the presence of oxygen-containing compounds, e.g., N-alkyltrichloroacetamide, trichloroacetic acid, using inert solvents at a pressure allowing the gaseous reactants to be in solution state. The products had a low unsaturation content and possessed good rheological characteristics. Hydrogenated dicyclopentadiene-ethylene copolymers were produced by Nippon Zeon Co. r~ by hydrogenating the unsaturated bonds of dicyclopentadiene-ethylene copolymer, preferably of 5000-700000 molecular weight, using H2 in the presence of hydrogenation catalysts such as Ni/silica or palladium/alumina at 20-120~ (Eq. 11.97). §
i
---
~"
(11.97)
732 The copolymer may contain the third component e.g., alkyl substituted dicyclopentadiene, olefin monomer, etc. The hydrogenation occurred in hydrocarbon solvents e.g., cyclohexane, benzene, toluene, at a concentration of 1-20 wt.% and under hydrogen pressures of 1-150 atm. The hydrogenated products had excellent thermal fusion mouldability, heat resistance, transparency, solvent resistance and mechanical properties and were used for manufacture of photodiscs, printing base boards, transparent conductive sheets, injectors, etc. Novel copolymers of 1,4,5,8-dimethano-l,2,3,4,4A,4B,5,8,gA, gAdecahydro-9H-fluorene with ethylene have been prepared by Nippon Zeon TM using Ziegler type catalysts containing Ti compounds, transition metal compounds and reducing agents e.g., organoaluminium compounds (Eq. 11.98). (11.98)
The reaction has been claimed for molar ratios ethylene to norbomene type monomer 0:100-95:5 at-50 to 300~ preferably-30 to 200~ under 0-50 kg/cm z, preferably 0-20 kg/cm z. Products with a limiting viscosity determined at 25~ in toluene of 0.005-20 dl/g have been obtained. The polymers had good chemical stability, high glass transition point, excellent heat resistance, excellent transparency, good chemical and solvent resistance, good dielectric and mechanical properties. They are useful for manufacture of optical lens, photodiscs, base boards for crystalline liquids, printing base boards etc. A number of copolymers of 4,9,5,8-dimethano-3a,4,4a,5,8,ga,9,9aoctahydro-lH-benzoindene and optionally ethylene in a molar ratio of 0 100-95:5 have been produced also by Nippon Zeon Co. 7~ in the presence of Ziegler catalysts in hydrocarbon solvents at -50 to 300~ (Eq. 11.99). The products were soluble in organic solvents and had excellent heat resistance and balanced transparency, good chemical resistance, good dielectric and mechanical properties, e.g., hardness and rigidity. They could be used for the manufacture of mouldings, e.g., optical lens, photodiscs, optical fibres and circuit base boards for high frequency.
733
(11.99)
Addition copolymers for optical and electric fields were also manufactured by Nippon Zeon 76 by polymerizing wax-like or oily products obtained form dicyclopentadiene and ethylene in the presence of Zieglertype catalysts. These copolymers and their hydrogenated products had high glass transition temperatures and excellent heat resistance. The polymerization process was performed in aliphatic or aromatic hydrocarbons at -50 to 300~ under 0-50 kg/cm 2, using binary catalytic systems derived from ethylaluminium sesquichloride and dichloroethoxyoxovanadium. Hydrogenation may be effected in organic solvents, in the presence of current hydrogenation catalysts, e.g., Ni and Pt compounds. ATO Chimie" patented gaseous phase copolymerization by contacting a monomer, which is a gas under the reaction conditions, with a heterogeneous catalyst, in an agitated polymerization zone defined by spherical walls, the agitation being effected with a rotating turbine assembly provided with vanes. The vanes scrape the wall over 10-60% of its surface and the solid catalyst particles and the growing polymer powder are dragged by the centrifugal force on at least a part of the spherical surface and fall back to the central part of the spherical zone, thus ensuring an energetic and uniform mixing and no dead zone. The process was used for the prepolymerization, polymerization and copolymerization of olefins and diolefins and resulted in homogeneous agitation. The monomers are gaseous or liquifiable, can be injected into the polymerization zone of the reactor and can be used together with inert gases and/or gases acting as chain regulators, e.g. H2. The reaction was effected under a pressure ranging from subatmospheric up to 500 atmospheres and at temperatures ranging from below room temperature up to 250~ or more. The catalyst may be in a granular or particulate form, e.g. a supported Ziegler-Natta type catalyst or a supported chromium type catalyst. Examples of preferred olefins are ethylene, propylene, C3-~8olefins such as l-butene, 1-pentene, 4methyl-l-pentene, l-heptene and 1-octene and of diolefins butadiene,
734 isoprene, vinylnorbornene and dicyclopentadiene. Copolymers having the following structures have been produced by this process (Eq. l l.lO0-
ll.lOl). R
O+
R
(11.1oo)
R
R
~
+
(11.101)
Copolymers of norbomene with l-butene, isobutene or 2-butene are preferably prepared employing TiCI3, TiCI4, Ti(OKhX2 or Ti(OR)3X in conjunction with Et2AICI, Et2AIBr or Me~AICI, in the presence of electrondonating compounds such as amines, ethers, esters, carbonyl-, phosphorusor sulphur-containing derivatives (Eq. 11.102-11.104).
~.~ +y----~, ~~,v.,~ (11.102) ,~
+
=
(11.103)
735 It was noted that the influence of the electron-donating components on the monomer reactivity and copolymer microstructure was essential. The physical and mechanical properties of these copolymers could be gradually modified by changing the composition of the catalytic system within desired limits. Elastomeric copolymers and terpolymers of ethylene and C3.~0 aolefins, optionally containing acyclic or multiring alicyclic, fused and bridged ring dienes, preferably alkylidene, cycloalkenyl or cycloalkylidene norbornenes, were produced by Exxon Research and Engineering Co. 78'~9 using Ziegler-Natta catalytic systems consisting of at least one transition metal component and an organoaluminium cocatalyst (Eq. 1 1.105-11.107). R
§247
(11.1o5)
) R + '~
§ ~'R
_
~~,~L,,~
~,
)
(11.1o6)
, R
§ /
)
(11.107)
+~R \
The reaction was performed by connecting two stirred reactors in series and then adding to the first reactor ethylene, a C3-~0 ~-olefin (and additionally the diolefin)and the Ziegler-Natta catalyst, polymerizin8 a portion of the
736 monomers at 0-100~ and 0-1000 psig to form a polymer, passing the polymer to the second reactor, adding ethylene, the C3-~0 Gt-olefin, additional acyclic or alicyclic diene and an organoaluminium sesquihalide to finish the monomer consumption. 8~ Preferred ct-olefin was 1-butene, lpentene, l-hexene, 1-octene, 3-methyl- l-butene, 4-methyl- l-pentene, 5,5dimethyl-l-hexene, vinylcyclopentane, vinylcyclohexane and especially propylene. The diene was 5-isopropylidenenorbomene, methyltetrahydroindene, dicyclopentadiene and especially 5-ethylidene-2norbornene. The transition metal component were VCI3, VOCI4, VO(OEt)3, VOCIz(OEt), VOCI2(OBu), V(acac)3, VO(acach and VOClz(acac), especially VOCI3 or VOCI3 associated with Ti(OBu)4 and VO(OEh). The cocatalyst added to the first reactor was 'Bu3AI, 'BuzAICI, ~Hex3Al or Et2AICI, especially EhAI and Et2AICI, and to the second EhAIzCI3. Hydrogen may be fed in at any stage to control the molecular weight of the polymer. When the reaction was carried out in the gas phase by contacting a gaseous mixture of ethylene and ot-olefin, in the absence of a liquid hydrocarbon solvent, on a fluidized bed of inert carrier which has been made active by superficial impregnation with the catalytic components, high activity and correct distribution of monomer units in the polymer chain were recorded. 8~ Such copolymers with density below 0.9 could be used e.g. for vehicle radiator and heater hose, vacuum pipes and draught strips. Sumitomo Chemical Co. ~ produced copolymers of ethylene, an otolefin CHz=CHR where R is C ~ alkyl, and optionally a linear or cyclic diene or polyene having non-conjugated double bonds by polymerization in the presence of a tri- to pentavalent vanadium compound, soluble in an inert organic solvent, organoaluminium compound, R'~AIX3~, where g' is C~-2o hydrocarbyl, X is a halogen or alkoxy, and an ester of a halogenated organic acid. The ot-olefin is preferably propylene, l-butene, 1-pentene, lhexene and/or 4-methyl-l-pentene and the diene is preferably 1,4hexadiene, dicyclopentadiene and/or 5-ethylidene-2-norbornene. Products having three or four different structural units in the polymer chain have been prepared under these conditions (Eq. 11.108-11.109). The process was performed in one or two reactors in series, which are at different temperatures. The preferred polymerization temperatures were 10-60~ in the first reactor and 50-100~ in the second reactor, with a difference of 540~ The vanadium component of the catalyst was selected from VCh, VOCI3, V(acac)3, vanadic acid triethoxide, vanadic acid diethoxymonochloride, vanadic acid ethoxydichloride, vanadic acid tributoxide,
737 vanadic acid dibutoxymonochloride and/or vanadic acid butoxydichloride. R'
R"
(11.108)
+/"8"
R
R'
The preferred organoaluminium compound was Et2AICI, EtAICI2, 'Bu2AICI, 'BuAICI2, Et3AI2CI3,'Bu3AI2CI3and/or Hex3Al and the halogenated organic acid was (re)ethyl trichloroacetate, (re)ethyl tribromoacetate, butyl perchlorocrotonate and/or an ester of ethylene glycol monoalkyl ether and trichloro- or tribromoacetic acid. Preferred solvents were hexane, heptane, cyclohexane, kerosene, benzene, chloroform, tri-or perchloroethylene or perchloroethane. The copolymers thus prepared had good processability and physical properties such as high creep resistance and low cold flow. Copolymer rubbers with a low content of gel components were produced which were useful for car materials, building materials, industrial materials or plastic blending materials. In another procedure, Sumitomo Chemical Co. 8a produced particulate rubber-like ethylene, tz-olefin and optionally non-conjugated cyclodiene copolymers in the presence of Ziegler-Natta catalysts using alkali metal salts of sulpho-carboxylic acid dialkyl ester as an adhesion preventing agent. The adhesion preventing agent was an alkali metal salt of dialkyl sulphosuccinate, especially Na or K salt of dioctyl or dihexyl sulphosuccinate. The process prevented agglomeration and adhesion of polymer particles to reactor walls or agitating blades and was specifically applied for slurry polymerization. An ethylene-propylene-diene terpolyrner prepared by Petrochemical Works Brazi u contains monomer units derived from ethylene, propylene and 5-propenyl-2-norbornene and dicyclopentadiene (Eq 11 1 I0-11 11 I)
738
) + ,/
+
(11.111)
The terpolymer was manufactured by polymerizing ethylene, propylene and a diene mixture produced during the synthesis of 5-propenyl-2-norbornene and containing 70-75% this hydrocarbon and 25-30% dicyclopentadiene. The reaction occurred in solvents such as aliphatic, naphthenic or aromatic hydrocarbons at -30~ to 30~ and 1-10 atmospheres, in the presence of a catalyst consisting of a solid vanadium component and a halogenated organoaluminium compound, optionally with modifiers. The vanadium catalyst was VCI4, VOCI3 or V(acac)3 and the organoaluminium compound EhAI2CIa or Et3AICI. Modifiers included Lewis acids or oxidation agents. The product was amorphous, curable with sulphur and had a high molecular weight and a degree of unsaturation of 3-15%. A significant advantage of the process was that the diene mixture polymerized rapidly and did not have to be purified prior to polymerization. Yokkaichi Polymer Co. 8S reported on the copolymerization of ethylene with ct-olefins and non-conjugated dienes in the presence of a transition metal solid catalyst containing a magnesium compound and an organoaluminium compound. The ot-olefin was 1-butene, 1-hexene, 4methyl-l-pentene or l-octene and non-conjugated diene was an endomethylene cyclic diene. The transition metal solid catalyst was produced by reacting magnesium metal or oxygen-containing organo(halo)magnesium compound with an oxygen-containing organo(halo) titanium, zirconium or vanadium compound, a silicon compound and organoaluminium compound. By this procedure, a number of copolymers with low density and improved transparency have been obtained in high yield.
739 Several copolymers of ethylene with norbomene, lmethylnorbomene, dicyclopentadiene and octahydrodimethanonaphthalene were synthesized by Wilson e t al. ~s using VOCI3 and ~u2AICI in heptane (Eq. 11.112-11.115). "
VOCI3/iBu2AICl
II
*
9 II
+ II
R.
=
i
VOCI3/IBu2AICl R~~_R" = VOCI3/iBu2AICI = VOCI3/iBu2AICI _-
(11.112)
(1 1.1 13)
R
R"
(11.114)
R
R"
(11.115)
The dynamicS-mechanical properties of the copolymers thus obtained were examined by an usual torsion apparatus. These authors observed that the 13relaxation temperatures of the copolymer depended essentially on the sequence of norbornene units, thus, for copolymer chain with isolated norbornene units values of Tp of ctt 10~ were found whereas for pairs of norbornene units separated by ethylene units Tp of ca. 55~ were determined. Furthermore, substitution of norbornene moiety with alkyl groups exerted a slight influence of the Tp, but this could also be evaluated. Cesta et al. 8~ prepared random ethylene-propylene-triene 2 terpolymers starting from tricydo[5.2.1, 02"6"' laeca-,5,8-triene as a third monomer (Eq. 11.116).
~,~
~//AI] ~
(11.116)
740 Using three catalytic systems based on Et2AICI and VCh, VO(O~Pr)3 and VO(acac)s, they examined the effect of AI:Ti ratio, catalyst and monomer concentration on the polymer yield. In their studies these authors observed that the above catalysts were active for opening the endo double bond of norbornene moiety but were inactive for the two conjugated exo double bonds. These conjugated double bonds could react, however, in the presence of cationic initiators. In a number of patents, Mitsui Petrochemical Ind.8s~~ reported production of random copolymers from ethylene and/or higher linear otolefins (C3-C2o) by copolymerization with multicyclic olefins having general formulas (1)-(VII) or more particular structures (VIII) and (IX) under the action of soluble catalysts consisting of vanadium compounds and organoaluminium compounds in aliphatic, alicyclic or aromatic hydrocarbon media (e.g., hexane, heptane, cyclohexane, benzene, toluene), at various temperatures (-50~ to 100~ and pressures (0-25 kg/cm2) (Scheme 11.1). R2
.Re
R2
T a ~ R10 T-in R9 Rs
R1
R2
R R1
(1)
(CRsRlo)X
R5
R1
(II)
R2
.R~
R1
Rs
R1
(CRgRlo)X
R~
(Vll)
R5
R9
(V)
~
R5
(Ill) .R~o
(IV)
R~
.Rs
~ (viii)
Scheme 11.1
R14 R~3
R2
.Re
R1
R5
(Vl)
RR12
(IX)
o
741 This process provides random copolymers in high yield, having excellent transparency, thermal resistance, aging resistance, chemical, weather and solvent resistance The products have good optical, electrical and mechanical characteristics and are suitable for these applications. In a significant work, 1,4,5,8-dimethano-l,2,3,4,4a,5,8,8aoctahydronaphthalene was copolymefized with ethylene in the presence of VO(OEt)CIz and EhAIzCI3 in cyclohexane solution at temperatures of 1013~ to obtain poly(ethylene-co-l,4,5,8-dimethano-l,2,3,4,4a,5,8,Saoctahydronaphthalene) in high yieldsU9 (Eq. 11.117). +
~
VO(OEt)CI-z/Et3,~Ch...
R"
(11.117)
Other interesting examples include copolymers of ethylene and ~z-olefins with pentacyr ~ (Eq. 11.118)
VO(OEt)Ch/Et3AI2Ch
R"
(11.118)
as well as of higher substituted and unsubstituted polycyclic homologs91"93"95 (Eq. 11.119).
vo(oEt)ChtEt~,hCh
(cN).
(11.119)
(c~.,~n
The products thus prepared have intrinsic viscosities of 0.05 to 10 dl/g ( d e . i n , 135 ~ and narrow molecular weight distributions and possess
742 good heat and ageing resistance, good chemical, weather and solvent behavior, mouldability, dielectric properties, rigidity and impact strength. Associated with amorphous or low-crystalline olefinic copolymers (ethylene/Ca.20 o~-olefins), olefin/non-conjugated diene copolymers (C3.20 ctolefins/ethylidenenorbomene), aromatic vinyl/diene random or block copolymers (styrene~sopprene, butadiene), divinylbenzene and organic peroxides, they provide useful compositions for printed circuit boards, camera bodies, housings of various measuring devices and instruments and various exterior and interior finishing parts of automobiles, t0~ Polyamide resin compositions of cycloolefin/ethylene copolymers derived from monomers I and II (Scheme 1 1.1) ~~ with good heat and chemical resistance, low absorption ratio and low moulding shrinkage, high mechanical strength (e.g. impact strength) are used for car interior parts (e.g., instrument panel, console box, etc.), car exterior parts (e.g., fender, bonnet, trunk, etc.), office machine, tool, housing of appliances. Alternatively, polyester resin compositions consisting of ethylene copolymers of monomers I and II and polyethylene or polybutylene terephthalate, having excellent resistance to heat and chemicals and low absorption and moulding shrinkage, were used in various car exterior and interior parts, housing of appliances and measuring devices, etc. Similar characteristics were provided by special compositions of ethylene/cycloolefin copolymers with polyester ~~ poly(phenylene ether) ~~ or polycarbonate resins. ~~ Other reaction products of cycloolefins I and II with ethylene and r were also used for manufacturing synthetic wax in candles, coating protecting agents and ceramic binders. ~~ In an economical procedure, Mitsui Petrochemical Ind. ~~ prepared cycloolefin random copolymers with low halogen content in the presence of vanadium and organoaluminium compounds and an absorbent containing at least one alkali or earth alkaline metal cation. These copolymers were synthesized from ethylene and optionally an r having more than C3 with cycloolefins of type 1 or II under the influence of soluble vanadium compounds and organoaluminium compounds, at least one of which contains halogen. The absorbent was in an amount of 5 wt.% and had maximum pore diameter at least 0.5 run and specific surface area 100-1000 m2/g. The resulting copolymer had a halogen content of no more than 200 ppm. They had good transparency, thermal resistance, chemical behavior, solvent resistance, dielectric and mechanical properties and was free of byproducts containing halogen thus avoiding causing corrosion of the moulding equipment. In another quite efficient procedure, ~~ this company
743
produced o~-olefin/cycloolefin copolymers by copolymerizing the monomers in hydrocarbon solvent in the presence of soluble vanadium compounds and organoaluminium halides and flash drying. According to this procedure, a first copolymer prepared from ethylene and cycloolefin and having intrinsic viscosity [11] of 0.05-10 and softening point of at least 70~ and a second copolymer prepared from propylene or 1-butene and cycloolefin and having intrinsic viscosity [11] of 0.05-10 and softening point of at least 70~ are mixed together and flash dried. Examples are provided for copolymers of tetracyclododecene with ethylene and propene or l-butene, respectively (Eq. 11.120-11.121). . ~, .
,~
+ ~' + ~X~
[V/AI].._ R
R"
(11.120)
IV/All
K~ (11.121)
The process is quite economical, continuous and stable running. The cycloolefin random copolymer products have excellent heat, chemical and solvent resistance and heat ageing, dielectric properties, rigidity and impact strength. The materials are used for optical products, particularly as optical memory discs. Thermoplastic resin compositions produced by Mitsui Petrochemical Ind.m~ for precision machine parts contain a random copolymer of ethylene with polycyclic olefins, glass fibers and potassium titanate fibers. The resins are injection molded to form precision pans, e.g. compact discs, floppy disc drives, printer carriages, optical fiber connectors and guide rollers of VTRs, because they possess good hygroscopic properties, heat resistance, surface gloss, low moulding contraction and low linear expansion coefficient. Optical recording material with substrates containing random copolymers of ethylene and cycloolefins and recording layer including tellurium were prepared by Mitsui Petrochemical Ind. ~~
744 using special cycloolefins of the following structure: 6ethylbicyr ]hept-2-ene, 8-chlorotetracyclo[4.4.0.1 z,5.17'~~ erie, 12-ethylhexacyclo[6.6.1.13'6. I l~ and heptacyclo[8.7.0.1 z'9.14'7.1 ~~'~.03's.0~z'~6]icos-5-ene (Eq. 11.122-11.125).
=
(11.122)
JJ =
(11.123)
\
CI
(11.124)
§ II
(11.125)
The cycloolefin copolymers preferably have a softening temperature of at least 70~ and the recording layer contained less than 40 atom % of C and 1-40 atom % of H. The products have good sensitivity and there is good adhesion between the recording layer and the substrate. Optical discs
745 structure including an air sandwich prepared by ultrasonic melt adhesion of discs and spacers composed of ethylenic and cycloolefinic copolymers with good flatness were manufactured by Mitsui Petrochemical Ind. ~~ The copolymers consisted mainly of tetracyclododecene monomers and ethylene at different ratios for spacers and discs. These discs had good thermal, moisture, water and chemical resistance, were moldable, had good dimensional accuracy and had good optical properties which were nor changed on ultrasonic melt-adhesion. New optical recording materials were produced from thin film recording layers containing Te, Cr, C and H and a substrate containing a copolymer of ethylene with the cycloolefin of the following type (Eq. 11.126).
\ R2. -R~2 RIo R,I
II
--
~
~
(11.126)
R2 /
Rio Rll
where R~.t2 = H, halogen or a hydrocarbon group, R9-12 may together form a mono- or polycyclic hydrocarbon ring which may optionally contain a double bond. These materials had good recording sensitivity and there was good adhesion between the recording layer and the substrate. Also, the copolymer evacuation time prior to sputtering was only half that required by polycarbonates. Photorecording medium consisting of a base material, a recording layer and a film was manufactured by Mitsui Petrochemicals Ind., ~ using specific ethylene/cycloolefin copolymers for the base material. The copolymer consisted of polymer units derived from ethylene and various polycyclic olefins of the type given above where R~-Rt2 = hydrogen, halogen or Cm-20alkyl, Re or Rt0 and Rtt or Rt2 may form 3- or 6membered ring by combination. The film provided on the recording layer contains an epoxy resin, a compound selected from sulphonium and cyclopentadienyl-Fe derivatives, a compound selected from acrylates, methacrylates and oligomers and an organic peroxide. The photorecording medium thus produced had excellent adhesion between the recording layer and the film as well as excellent water and moisture resistance. In another procedure,~ t2 ethylene/cycloolefin random copolymers containing inorganic
746 particles are useful as spacers which, welded by ultrasonic vibration, form information recording discs having reduced warp-angle. The copolymer comprise ethylene and at least one cycloolefin of formula I and II and contains 0.01-5 parts wt./100 parts wt. inorganic particles having a size of less than 300 n (Scheme 11.2). R2
~[~~(
Re
(i)
CR~%)
(Jl) Scheme 11.2
High frequency electric circuit board containing a conductive layer laminated on a polymer layer consisting of an ethylene cycloolefin copolymer were manufactures by Mitsui Petrochemical Ind.,~3 using classical catalysts derived from soluble vanadium compounds and organoaluminium compounds. The monomer was preferably 2-methyl1,4,5,8-di methano- 1,2,3,4,4a, 5,8,8 a-oct ahydronaphthalene, 1,4, 5,8dimethano- 1,2,3,4,4a, 5,8,8 a-octahydronaphthalene or 6ethylbicyclo[2.2.1 ]hept-2-ene (Eq. 11.127-11.129).
\
+
II
*
II
,Aq Rt..FL~ ~.R"
[V~Aq._~ R
R"
(11.127)
(11.128)
\ (11.129)
747 The conductive layer is mainly a metal such as Cu, AI, Ni, Au or Ag or a conductive polymer such as polyacctylene, polypyrrole or polypyridine. These circuit boards had a small dielectric constant and water absorbing property, an enhanced thermal resistance, soldering resistance and dimensional stability and were useful for fiat antenna, boards combined with chassis or flexible boards. Low dielectric laminates for high frequency insulating materials contain matrix resin of polyolefin and reinforcing material of ultrahigh molecular weight polyethylene cloth. The matrix resin was preferably a random copolymer of 40-90 mole % repeating units of ethylene and 60-10 mole % repeating units from polycyclic olefins of the following type (Eq. 11.130). §
II
(11.130)
=
(R ;CR2)
R~ ' ( CFR2)
where R~ and R2 are substituted or unsubstituted alkyl and aryl groups. The low dielectric laminates had high strength and were used for high-frequency insulating materials, particularly radar domes and parabolic antennas. Interestingly, functionalized copolymers of ethylene, ~-oletins with norbomene-type monomers bearing functional groups have been prepared by Mitsui Petrochemical Ind.~' using soluble vanadium and organo~uminium catalysts. Thus, cx~l~lymers having improved compatibility and adhesion with other polymers were prepared by polymerization of ethylene, C3-~8 r and functionalized norbomene derivatives (1) where Y and Z are O- or N-containing functional groups, in hydrocarbon solvents (Eq. 11.131). Y
Z
(i)
+ ~'
+ ~X,R
[VIAl]
=
R
111.131)
The reaction occurred with VO(OEt)CI2 and EhAI2CI3 in hex~e to form high yields of the corresponding functionalized copolymer. The functional
748 group could also be introduced by copolymerizing the cycloolefin of type I or II with an unsaturated linear derivative bearing various functional groups, CH2=CH-RX, where R is at least C2 hydrocarbon group and X is a N- or O-containing functional group *~=' (Eq. 11.132).
R4 /
~)--R2
~)--Ro
l R~2
[VIAl]
~RX
RX
(11.132)
=
R.Io R.
R2 R s ~ R o R e ~ R~n l~11
12
(II) In a similar procedure, ethylene, a C3-,s ct-olefins and at least one functional group-containing unsaturated linear monomer, CH2=CH-R'-X (R TM at least C2 hydrocarbon group, X= OR, COOR, CRO, NR2, CONR2, OCOR, CN, OH, COOH or NH2) were copolymerized with functionalized norbomene or tetracyclododecene derivatives (Eq. 11.133-11.134). R \
9~ '
R'X
§ ,4P'XR § ,~X.R,X
(11.133) \
Y
(I)
R
9~ '
Y
* "~R
* JNR'X
Y
R'X
~
(11.134)
,,=..._
Y
(II) Cross-link~ cycloolefin copolymers were prepared by Mitsui Petrochemical Ind. ramsby copolymerizing ethylene with cycloolefins of type I or II in the presence of vanadium compounds and organoaluminium halides and then cross-linking the copolymer with sulphur, an organic peroxide, an electron beam or a radiant ray. Examples are given for copolymers of
749 ethylene with 2-methyl- 1,4,5,8-dimethano- 1,2,3,4,4a, 5,8,8aoctahyd ronaphthalene, 1,4, 5,8-dimethano- 1,2,3,4,4a, 5,8,8aoctahydronaphthalene and 6-ethylbicyclo[2.2. l]heptene. The copolymers were synthesized in the presence of VO(OCzHOCI and EhAIzCI3 in toluene solution at 10~ and cross-linked with dicumyl peroxide by heating at 160~ The cross-linked copolymers had an enhanced thermal resistance and strength and were used in the manufacture of electrical circuit boards, electrical wire coating material, vibration preventing materials or software for an electronic range. Uniform addition copolymers of ethylene and norbomene-type monomers of formulas I and II were obtained by BFGoodrich Co. ~6'~7 by bulk copolymerization using binary catalysts based on vanadium compounds and alkylaluminium compounds (Eq. 11.135-11.136). 9 R2
R3
(11.135)
II / R2
\
R3
(1)
(11.13s) R2
R3
/
R:~
\
R3
(II) where R2 and R3=H, halogen or C~-2o alkyl groups, or combined from saturated and unsaturated C~.7 hydrocarbon cyclic groups, with the two ring C atoms connected. The vanadium compound was of the general formula V(O)o(OR')b(X)~ where X=halogen, R'=hydrocarbon portion of C~.z0 alkoxy group, a=0 or 1, b=0-3 and c=1-5, provided that when a=l then b+c=3 and when b=0 then c=5-3 and selected from VCIs, VOCI3 and VO(OC3H9)CI. The alkylaluminium compound was an alkylaluminium halide or an alkoxy alkylaluminium halide of formula (X),.AI(R")b.(OR)c, where R'=C~.6 alkyl, R=hydrocarbon portion of C~4 alkoxy, X=halogen, a TM 1-2, b TM 1-2 and c'=0 - 1, provided that a'+b'+c'=3. The reaction medium
750 was kept at -50~176 and the molar ratio of norbornene-type monomer to ethylene above 90:10. An additional olefinic monomer, selected from a non-conjugated acyclic ~-olefin which is liquid at reaction temperature, was also included in the reaction medium. Examples for addition copolymers prepared from ethylene and 5-methyl-2-norbomene and ethylene and 9methyltetracyclo[6.2.1.13'6.0~'7]dodec-4-ene are illustrated below (Eq. 11.136a- 11.136b).
(11.136a)
\ +
II
-
-E
\ The concentration of the norbomene-type monomer within the reaction medium was above 35 vol.%. The pressure of ethylene was kept constant during the reaction so that the molar ratio of ethylene to norbomene-type monomer in the copolymer to be 11. Ethylene was copolymerized with preferentially at least two norbornene-type monomers. Copolymers containing ethylene and 5-methyl-2-norbomene had a T s above 120~ and those containing ethylene and 9-methyltetracyclo[6.2.1.13'6.02"~]dodec-4-ene a Tg above 200~ These copolymers have a uniform composition, without significant crystallinity. They exhibited a constant high T s value and had good solvent and chemical resistance, transparency and dielectric properties. They could be shaped by conventional methods such as injection molding or laminating processes. Their uses include replacement for glass in optical lenses and discs, and as electrical insulators for wires or printed circuits boards. Random copolymers of improved fluidity, comprising ethylene, propylene and 5-alkenyl-2-norbomene units, adapted for articles with smooth surface, were prepared by Mitsui Petrochemical Ind. ~s with VO(OEt)CI2 and EtAICI2 in hydrocarbon solvents, working under specific conditions (Eq. 11.137).
751
R)
. ~
. ~
VO(OEt)CI24EtAICI2 .~
(11.137)
For a molar ratio os slkenyl groups to 5-alkenyl-2-norbomenr os 0.2-0.8, copolymers with intrinsic viscosity [TI] of 0.5-10 dl/g (decalin, 135 ~ and molecular weight distribution, MJM,, of 2-6 were obtained. The products have improved fluidity in the molten state and efficient molding processability as well as smooth surface and good glossiness. Special rubbery copolymers of ethylene, 1-butene and a cyclic diene, with high ethylene content, rapidly vulcanizable with sulphur and easily moulded, were also obtained by Mitsui Petrochemical Ind. ~9 using soluble vanadium catalysts. The preferred cyclic dienes were dicyclopentadiene, 5vinyl-2-norbomene and 5-ethylidene-2-norbomene (Eq. 11.138-11.140).
[V/A~
§ 2 4 7
) + /
+ ~
.
(11.138)
Iv/A!
-___ ~
[v/Aq
--
~,-~', (11.139)
(11.140)
The copolymerizations were performed in an inert hydrocarbon, at 40100~ (50-80~ using a catalyst containing VO(OR)~X3~ and R'.AIX'3~, where R and R' are hydrocarbon groups and X and X' are halogen. At a molar ratio of ethylene: butene of86:14-955 an iodine number of 2040, an
752 intrinsic viscosity, [rl], of 0.8-4 dl/g (decalin, 135~ and a molecular weight distribution, MdM, of 1.3 were recorded. The copolymers were preferably vulcanized with 0.1-10 wt.% S or with a peroxide, optionally with 0.1-20 wt.% of an accelerator. They have high tensile strength, can be easily moulded, have better surface properties, elongation at break of 2002000% and/IS hardness of 50-85. Strength is not affected by inclusion of large amounts of filler. The products obtained are suitable for insulation on high voltage cables, giving good AC breakdown voltage, automobile parts, hose, films (e.g. roofing) and sealing tings. Foams may be used as heat or electrical insulation, flotation material, cushioning and soundproofing. New synthetic waxes, having high glass transition temperatures, were manufactured by Mitsui Petrochemical Ind. ~z~ starting from 1,4,5,8,dimethano-l,2,3,4,4a,5,8,8a-octahydronaphthalene and its substituted derivatives. Homopolymers of 2-ethyl- 1,4,5,8,-dimethano1,2,3,4,4a,5,8,8a-octahydronaphthalene and its copolymers with ethylene, propylene, 1-pentene and styrene were prepared using dichloroethoxyoxyvanadium and ethylaluminium sesquichloride in toluene at 30~ (Scheme 11.3).
Scheme 11.3 The waxes produced by this way had glass transition temperatures of 80220~ and viscosities of 100 to 2x10 s cps. Significantly, the materials possessed excellent transparency and fluidized with a small amount of heat.
753 Novel random copolymers of cyclic olefins with linear olefins have been prepared by Mitsui Petrochemical Ind. ~z~ using very active catalysts derived from group IVB transition metals compounds and aluminoxane. Examples are given for copolymers of ethylene and propylene with tetracyclododecene obtained in toluene at 20~ for 2 hr under atmospheric pressure in the presence of ZrCI4 and methylaluminoxane as a catalyst (Eq.11.141).
ZrCh/MAO
(11.141)
7
Such products have excellent transparency, thermal stability, heat ageing, chemical and solvent resistance, dielectric and mechanical properties and a narrow molecular weight distribution. Several copolymers of dicyclopentadiene, ethylidenenorbornene and tetracyclododecene with ethylene have been prepared by Schnecko et al. ~ under the influence of VOCI~/EhAI2CI3 as a catalyst (Eq. 11.142a-11.142c).
vOCIL
§
I
Et~,12Cl3 VOCI3 ._
+
~
Et3AI2 C'[3
(11.142a)
(11.142b)
voch
When hydrogen was employed as molecular weight regulator, low molecular weight products were obtained with a wide range of
754 unsaturation. They observed that the amount and nature of cyclic diene influenced strongly the catalyst activity, copolymer composition and the product viscosity. The introduction of" diene monomer units resulted in decreasing the melting point of the copolymer. For dicyclopentadiene and ethylidenenorbornene as comonomers, they found that the product would be amorphous at 15-20 mole % diene and showed a minimum in glass transition temperature. Saturated terpolymers or multipolymers have been prepared from norbornene and other bicyclic or multicyclic olefins with ethylene and higher ix- or internal olefins containing at least three monomer units in the polymer chain (Eq. 11.143).
§ R1
R2
+ JXR
[V/AI]
~
'~'~...~
R
~]" /
R1
\
(11.143)
R2
High molecular weight, partially crystalline copolymers of this type, displaying improved green strength, have been manufactured by efficient procedures from norbornene and ethylene with C~.m0 ct-olefins in the presence of the ternary catalyst consisting of VOCI3, EhAIzCI3 and methyl perchlorocrotonate. ~23 In one example, the copolymer containing 3.35% norbornene, 93.3% ethylene and 3.35% propylene possessed a ~een strength of 138 kg/cmz, elongation 586%, 100~ modulus 90 kg/cm and Shore hardness 92 at 22~ as compared to the values of 87 kg/cmz, 507%, 63 kg/cmz and 93, respectively, for a control EPR copolymer containing 10% propylene. In another example, synthetic rubber was produced by copolymefization of ethylene, propylene and dicyclopentadiene in an inert hydrocarbon solvent at 20-50 ~ catalyzed by VCh or VOCI3 and 'Bu2AICI. The copolymer obtained had a viscosity of 2.24, a tensile strength of 370 kg/cmz, a relative elongation of 580%, residual 28% and elasticity 50%. It was 99.5% soluble in boiling heptane. Numerous other bicyclic, tricyclic and polycyclic monomers containing norbornene and norbornadiene structures have been used in efficient copolymerization procedures to prepare new products having improved physical-chemical properties. In one procedure, TM synthetic rubber with unsaturation in tricyclic recurring units has been manufactured by copolymerizing dicyclopentadiene with ethylene and propylene in inert
755 hydrocarbon solvents, using as catalysts VCh or VOCIs, in conjunction with R'zAICI or P,,'AICI2(Eq. 11.144). §
/
+/x,
VCI4/R2AICI--
(11.144)
On employing r of the class RCH=CHz, where R are Cz~ alkyl groups, copolymers having good processability and particular physicalmechanical properties such as high creep resistance and low cold flow have been obtained. (Eq. 11.145). +
//'
+ '/~'R'
VCI4/R2AICI
R
"
!
(11.145)
Other efficient procedures employ bicyclic and multicyclic dienes in copolymerization reactions with ethylene, propylene, various higher aolefins induced by conventional Ziegler-Natta catalytic systems. By these methods, copolymers having remarkable physical-mechanical properties are prepared starting from bicyclic and tetracyclic monomers such as 5ethylidenenorbomene, norbomadiene, dimeth~ohexahydronaphth~ene ~z~ (Eq. 11.146-11.147).
Q
+ 1 + J~'R' ----P" ~
+ /
R'
R
(11.146)
!
(11.147)
In their studies on the effect of diene third monomer on the physical-mechanical properties of EPDM terpolymers, Baranwal and
756 Lindsay~26, prepared several terpolymers derived from methyltetrahydroindene, ethylidenenorbomene and dicyclopentadiene in conjunction with ethylene and propylene (Eq. 11.148-1 I. 150) (11.148)
+H
+A
~- -~---[
~,~~
(11.149)
) ~~
+ I + A
-- -E---
I
(11.150)
and examined the influence exerted by these monomers on the properties of the corresponding copolymers. It is remarkable that the eX~l~lymer ethylenedpropylenes' ethylidenenorbomene vulcanized faster with sulphur as compared to the other terpolymers, whereas ethylene/propylene/dicyclopentadiene terpolymer vulcanized faster in this conditions than ethylene/propylene/l,4-hexadiene terpolymer. Showa Denko Co. ~27,~zs manufactured a series of random copolymers of ethylene with polycyclic monomers in the presence of catalysts comprising vanadium compounds soluble in hydrocarbon solvents and an organoaluminium compounds containing halogen (Scheme 11.4).
Scheme 11.4 Relevant examples are given for some copolymers of ethylene with pentacyclo[9.2.1. I s's.0a~~ 4'9 ]pentadec-6-ene 127 (Eq. 11.151),
757
[v~Arl
pentacyclo[9.2.1.14'7.02"~~
(11.151)
~2~(Eq. 11.152),
N/Arl
(11.152)
pentacyclo[ 10.2.1.15's.02'm~.04'9]hexadec-6-eneIz8 (Eq. 11.153)
[V/Arl
(11.153)
and pentacyclo[9.2.1.16'12.0s'13.07'll]pentadeca-2,8-diene (Eq. 11.154).
[v/Aq
(11.154)
758 The catalyst comprises vanadium compounds used in hydrocarbon medium at concentration 0.1-30 mmole~ selected from VCI4, VCI3 and compounds of formula VO(OR)tX3, (R=C~.t0 alkyl, X=halogen, t=0-3) e.g. VOCI3 or VO(OCzHz)CIz and organoaluminium compounds selected from compounds of formula RI=AIXI3.~ (Rl=Ct.10 alkyl, Xt=halogen, u<3), e.g. MezAICI, EtzAICI/'BuzAICI, used at molar ratio V/AI of 1-30, preferably 220. The copolymerizations were effected in hexane, cyclohexane or toluene at -60~ to + 100~ preferably at -30~ to +50~ and pressures of 0-50, preferably 0-30 bar, with hydrogen used to adjust the molecular weight to produce polymers having intrinsic viscosities [rl] of 0.5-8 dl/g and glass transition temperatures Tg of 80-230~ preferably 100-200~ The materials prepared had well-balanced transparency, good optical and mechanical properties, heat and chemical resistance and dimensional stability. They were mouldable to optical articles e.g., discs, filters and lenses as well as window panes. ~29 A variety of random copolymers comprising monomer units derived from 5-arylnorbornene, ethylene and an ot-olefins were produced by Nippon Oil Co. ~3~via organoaluminium and vanadium catalysis (Eq. 11.155).
~
R.R/ ' +~ ,X.
[VIAl]
R
" - - ~
(11.155) ]
Q R'
The arylnorbornene monomer contained as aryl group phenyl, o,m or p tolyl, o,m or p-ethylphenyl, p-isopropylphenyl, 1,4-methano-l,4,4a,9atetrahydrofluorene while the ~-olefin was selected from 1-butene, 3-methyll-butene, 1-pentene, 1-hexene, 1-decene, styrene, ~-methylstyrene, bicycloheptene, ethylbicycloheptene, 2,3,3a,4,7,7a-hexahydro-4,7-methanoI H-indene, 5-ethylidenebicyclo[2.2.1 ]heptene and mixtures thereof. The reaction was performed in hydrocarbon solvents, in the presence of VCI4, VBr4, VOCI3, VOBr3, VO(OR)3, V(OR),X3~ and R'=AIX'3.m, e.g., Me3Al, Et2AICI, EhAlzl3, at temperatures of-30~ to +800C and pressures of 0.150 kg/cm z. The solvent was selected from aliphatic hydrocarbons, e.g., hexane, heptane, octane, from cycloaliphatic hydrocarbons, e.g., cyclohexane or from aromatic hydrocarbons, e.g., benzene, toluene, xylene
759 or mixtures thereof. The process enabled plastics of improved light transmissability and dielectric properties, thermochemical resistance, mechanical workability, which were usable for optical products such as discs, fibers, windows, etc. as well as medical products such as syringes to be manufactured. An interesting procedure performed at the University of Akron TM produced graft terpolymers containing monomer units of ethylene, propylene and macromonomers derived from ethylidenenorbornene with polystyrene or polyisobutylene as pendant groups (Eq. 11.156-11.157). R !
R
i
R
+ ~ ___~ ~ ' ~ R
(11.157)
or from dicyclopentadiene with polystyrene or polyisobutylene as pendant groups (Eq. 11.15 8-11.15 9). R
~
~-I"~.
.~~ ~ ' ~ R
(11.158)
(11.159)
760 The catalyst was a combination of organoaluminium compounds and vanadium compounds, preferably Et3AI2CI3 and VOCI3, in molar ratio 3-5:1 and was used at 0.1-0.6 moles per mole macromonomer. The macromonomer was prepared by reacting a halo derivative of dicyclopentadiene or ethylidenenorbornene with styrene or isobutylene, under the action of Et2AICI. Ethylene and propylene were reacted with the macromonomer in the presence of Ziegler-Natta catalyst at 0-50~ preferably at 15-25~ The graft copolymer had a molecular weight of 5000 to 1 million, as determined by GPC. The copolymers thus obtained are vulcanizable, using conventional amounts of rubber curing chemicals such as S, ZnO, etc. They are effective for the compatibilization of ethylenepropylene rubbers and butyl rubbers. The products are useful as materials for roofing compounds, rubber blends, sealants, caulking agents, cements, etc. Both random and block copolymers of norbomene and e x o , e x o dinorbornadiene have been synthesized by Alonso and Farona ~32 using the Re(CO)sCI/EtAICI2 catalyst system. When norbomene and e x o , exo.. dinorbornadiene were reacted in chlorobenzene at 110~ for 24 hours, a random copolymer in 54% yield was obtained. ~H NMR spectra evidenced that both monomers were incorporated in the polymer chain with ringretention (Eq. I 1.160).
Re(CO)
CI
-,
The product had the molecular weight Mw=502300 and M,=325500, respectively, the polydispersity PDI=I.54 and melted in the range of 130160~ By changing the reaction technique, first polymerizing norbomene in chlorobenzene at 100~ in the presence of the same catalytic system Re(CO)sCI/EtAICI2 for 4 hours and then adding and polymerizing e x o , e x o dinorbomadiene at 100~ for 3.4 hours, a block copolymer of the two cycloolefins was produced in 15.5 % yield (Eq. 11.161).
761
n~
+ m~
Re(CO)5C/
(11.161)
The evolution of copolymefization process was monitored by ~H NMR spectroscopy. The block copolymer had the molecular weight, M~--262000 and Mo--95300, polydispersity PDI=2.75 and displayed a melting range of 220-240~ By GPC examination, the diblock microstructure of the copolymer could be predicted. The NMR spectra of the polymer indicated that the monomers were incorporated in the polymer with ring-retention. In addition, the M R spectra of the random and block copolymers evidenced significant difference in the region of aliphatic protons. Random copolymers of norbomene with 5-hexylnorbomene prepared Risse et al. ~33 in the presence of Pd(ll) cationic complexes such as [Pd(CH3CH2C~4][BF4]z (Eq. 11.162).
0
+
~
[Pd(CH3CH2CN)4][BF4]~ ~ v ~x] ~
C6Hll
(11.162)
C6H11
Extrapolation of the glass transition temperatures of these copolymers (T s between 413~ and 533~ to the T s corresponding to a composition of 0% 5-hexylnorbomene (i.e., 100 % norbomene) gave a value of Ts = 603~ (330~ for the addition polymer of norbomene. Very interesting results reported Kaminsky and coworkers ~z in the copolymerization reactions of ethylene with norbomene and dimethanooctahydronaphthalene (tetracyclododecene) in the presence of chiral zirconocene catalysts under various conditions (Eq. 11.163-11.164).
0
+ I CP2ZrCI2'Et(Ir~)2ZrC~MAO ._ ~
(11.163)
762
I
Cp2Z~ 12,Et(hd)2Z~ ~ MAO -
(11164)
In early studies using two different catalysts, Cp2ZrCI2/MAO and Et(IndhZrCl~L~O, Kaminsky found that the activity of the chiral catalyst was much higher, e.g. by a factor of 10 at 25~ and by a factor of 100 at 60~ than the aehiral bis(TiS-cyclopentadienyl)zirconium compound (Table 11.6). Table 11.6 Copolymerizafion of norbomene with ethylene in the presence of zirconocene./MAO catalysts~b
[i atalya]
Catalyst
Cp2ZrCIz/MAO Et0ndhZrClz/MAO Cp2ZrCI~AO Et(IndhZrClz/MAO l|
mole
Temp. ~
Time' hr
Yield g
1.7xlO"7 1.6x10"v 1.7xlO"7 1.6xlO"7
25 25 60 60
0.9 0.5 0.5 0.5
0.23 1.9 2.3 2.8
9
'Data from roferoflC, O42, bRoactiOIl r Norbomene (1.4 g), F~ylene (1 bar); Catalyst (480-600 rag); Toluene (100 ml). By ~3C NMR measurements, a random distribution of the norbornene units in the polymer chain was detected. Moreover, under comparable conditions, they revealed that the incorporation of the cyclic olefin is improved with the ehiral catalyst. When more than 14 wt.% of the cyclic monomer was incorporated into the copolymer, the product was amorphous. The copolymers thus obtained are highly resistant to chemicals and heat and exhibit very high glass transition temperatures, Ts, as well as desirable elastic modules, making them suitable for polymeric optical fibers. In subsequent investigations using as zirconoeenes two C2symmetric ([Me2Si(Indh]ZrCl2, [Ph2Si(Ind)2]ZrCl2) and two C,-symmetric ([Me2C(Fluo)(Cp)]ZrCI2 and [Ph2C(Fluo)(Cp)]ZrCI2) compounds associated with methylaluminoxane, Kaminsky ~34'~3S prepared ethylenenorbomene copolymers with various molecular weights and compositions
763 depending essentially on the catalyst nature and reaction parameters. Several data concerning the catalyst activity, molecular weight and norbomene content for various molar ratios of the monomers, when the most active catalyst based on zirconium complex [PhzC(Fluo)(Cp)]ZrClz was employed, are given in Table 1 1.7. Table 11.7 Copolynmrization of norbomene~0 with ethylene(M2) in the presence of [Ph2C(Fluo)(Cp)]ZrCIz/MAO catalyst' i
MI " M2
0 0.6 1.6 3.2 6.4 9.5 12.7 15.9
AcUv
M, (g/mole)
(mole %)
(kg polymer / mole Zr.bar.hr)
620000 322000 280000 191000 146000 132000 95000 97000
0 14 24 29 42 48 52 56
660 3780 2940 2810 2840 2760 2370 2335
MI
"Data from reference t "
As it can be noted from Table 11.7, even at high norbornene concentration, the copolymer yield attains a constant level of 2200 to 2400 kg copolymer per mole Zr, bar ethylene and hour, respectively. Thus, these authors found that the copolymerization activity with bulky cyclic olefins is approximately 4 to 5 times faster than ethylene homopolymerization. Furthermore, they observed that of the metallocenes employed, the Co symmetric complexes, display better steric conditions for the insertion of the bulky olefins than the C2 synm~etric ones, result attributed to the greater coordination space arising from the shorter isopropyl bridge. Significantly, the copolymers prepared with these catalytic systems possessed glass transition temperatures T s above 180~ molecular weights>lO0000 and narrow molecular weight distribution M j M , = 2. In the course of their work on the copolymerization of bicyclic olefms with cx-olefins in the presence of metallocene catalysts, Kaminsky et al.t36 examined also the reaction of dimethanooctahydronaphthalene or
764 tetracyclo[4.4.0.12"~.17'~~ with ethylene under various conditions. Using Cp2ZrCI2/MAO and Et(Ind)2ZrCI2/MAO as the catalytic systems in toluene, they prepared copolymers in varying yields containing up to 12.5% units of the cyclic monomer into the polymer chain. Relevant data are presented in Table 11.8. Table 11.8 Copolymerizauon oftetracyclo[4.4.0.1 ~'~.17'l~ with ethylene(M2)m the presence of metallocene/MAO catalysts~b Catalyst
Et(IndhZrClz/MAO Cp2ZrCI~AO Et(Ind)2H.~I2/MAO Et(Ind)2ZrClz/MAO Cp2ZrCI2/MAO
Mt ml
M, bar
5 10 10 3 3
3 3 1.5 1 1
Temp. Time ~ hr 25 25 10 25 25
0.3 0.8 3 0.5 0.5
Yield g
M~ mole
7.7 0.9 0.3 4.1 0.2
0 0 0 12.5 2
%
'Data from reference1~bl~letallocene (I0-6 mole), M A O (420 mg), Toluene (100 ml). Molecular weights of these copolymers between 50000 and 150000 have been obtained under these conditions. Of the various metallocene/aluminoxane catalytic systems employed, the Et(Ind)2ZrCIz/MAO catalyst showed to be the most active. With about 50 mole % of tetracyclododecene incorporated into the polymer chain, the glass transition temperature was 150~ This high glass transition temperature and the resistance to chemicals indicated good optical properties for the transparent copolymers. These products appear to be suitable for application in optical discs and fibers. Recently, quite active and stereoselective catalysts derived from several metallocenes, e.g., titanocenes, zirconocenes, vanadocenes and chromocenes and cyclic or linear aluminoxanes, have been successfully employed for copolymerization of bicyclic and polycyclic olefins with ctolefins, m37 The number of cycloolefins used as substrate in these copolymerization reactions is rather large including relatively simple monomers such as cyclopentene, cycloheptene going to norbomene and substituted norbornene, bicyclononene, dicyclopentadiene,
765 tetracyclodecene and hexacycloheptadecene (Scheme 11.5).
o 0 @ Scheme 11.5
In an efficient procedure, patented by Hoechst AG, ~3s copolymers are produced by polymerization of 0.1-100 wt.% bridged polycyclic cycloolefins (I), (II), (III) or (IV) , 0-99.9*6 monocyclic cycloolefins (V) and 0-99.9 % acyclic ct-olefins (VI), in solution, suspension or the gas phase at -60~ to 150~ and 0.5-64 bar, in the presence of catalysts consisting of a transition metal metallocene compound and a linear aluminoxane and/or cyclic aluminoxane (Scheme 11.6).
I
N
I
IV
V
VI
Scheme 11.6
The preferred metalloeene component is a zirconium compound, especially ethylene-bis(rlS-indenyl)zirconium dichloride and the aluminoxane is methylaluminoxane. The polycyclic olefin is 1,4,5,8-dimethano1,2,3,4,4a,5,8,8a-octahydronaphthalene or norbomene and the ct-olefin is ethylene or propylene. The monomer composition is within the triangle of comers defined by the polycyclic/monocyclic/ct-olefin molar ratios 93/5/2, 5/93/2 and 5/5/90. It is noteworthy that this catalytic system is very active and selective, thus small amounts of the catalyst giving high rates of largely uniform addition copolymers. The products obtained have a narrow polydispersity (M,g'M, in the range of 2.9-6.0) and a high stereoregularity,
766 making them especially suitable for injection moulding. These results allowed Hoeehst AG in conjunction with Mitsui Petrochemical Ind. to manufacture at an industrial scale Topas, 139a new commercial product with wide applications in optics, electronics, electrotechnical equipment, building materials, medical instruments, domestic articles, etc. On the other hand, Mitsui Petrochemicals Ind. m4~reported on the synthesis of random copolymers in high yields from ethylene or ct-olefins and norbomene-type cycloolefins, in the presence of coordination compounds of group IVB and aluminoxane. Examples are given for copolymerization of propylene with tetracyclododecene in the presence of ethylenebis(rlLindenyl)zirconium dichloride and methylaluminoxane in toluene at 20~ under atmospheric pressure, to yield a copolymer having 75 mole % propylene units in the polymer chain along with tetracyclododecene units (Eq. 1 1.165).
+ (
Et(Ind)2Z~12
(11.16.5)
~O
The product had the intrinsic viscosity [11] of 0.09 dl/g, a molecular weight distribution of 1.48 and a glass transition temperature T s of 78 ~ The reader may find abundant literature describing various copolymerization reactions of ethylene or propylene with norbomene, 2-methylnorbomene, dicyclopentadiene, dimethanooct~ydronaphthalene and 2methyldimethanooctahydronnaphthalene. ~4~~43 Remarkably, when chiral catalysts are employed, e.g. ethylenebis01Lindenyl)zirconium dichloride associated with methylaluminoxane, the activity in the copolymerization reactions was much higher than that of the achiral catalyst. Furthermore, the chiral catalyst increased the polymer stereoselectivity and the amount of cyclic monomer incorporated into the copolymer. 5-Vinylnorbom-2-ene was found by Marathe and Sivaran t " to undergo facile copolymerization with ethylene in the presence of the zirconocene/methylaluminoxane catalyst to produce high yields of poly(ethylene-co-5-vinyl-2-norbomene) (Eq. 11.166).
767
§
II
(11.166)
me
k_ By adjusting the feed ratios in this reaction, copolymers containing as high as 15 mole % 5-vinylnorbom-2-ene have been synthesized under these conditions (Table 11.9).
Table 11.9 Copolymerizau~ of 5-vinylnorbom-2-ene (M~) with ethylene (M2)
m the presence of zirconocene/methylalummoxane as catalyst ~b
[M,]'[M2] mole:mole
Time mm
Yield %
Couv. %
0:0.11 0.28:0.11 0.28:0.11 0.28:0.11
20 120 65 45
0.53 0.56 0.42 0.61
0.22:0. I I 0.33:0.I I 0.39:0. l I 0.44:0.11
45 45 45 45
0.79 0.35 0.39 0.30
100 48 37 49 70 29 28 20
kg pol3aner /g Zr 14.0 4.9 3.4 7.1 9.3 4.1 4.6 3.5
Mira copolymr mole % 0 8 6.5 6 11 10 14
[11]' dug
2.38 0.41 0.37 0.50 0.75 0.37 0.32 0.29
'Data from reference *; bReaction conditions: tea'q~rature = 35 ~ toluene = 25 mL; ethylene pressure = 1 atm; r from ~H NMR spectra; 4In 1,2,4trichlorobenzene at 135~ Copolymers with high 5-vinylnorbomene were completely soluble in toluene at 50~ indicating that they were gel-free. As expected, the products containing under 5 mole % 5-vinylnorbornene were soluble only at 135~ in 1,2,4-trichlorobenzene. Catalyst activity in the copolymefization reaction as well as the copolymer imrinsic viscosity [11] decreased with increasing comonomer content in the feed. The best results were obtained at an [AI]:[Zr] ratio of 1500. Reactivity ratios of the two comonomers were found to be r~(vinylnorbornene) = 0.3, r2(ethylene) = 18.6, and r~r2 = 5.5. The copolymers were generally amorphous or showed a melting
768 temperature, T=, in the range 80-110~ depending on the composition. These properties are similar to those known for the copolymer poly(norbornene-co-ethylene) of a similar composition. Interesting studies on the copolymefization of tetracyclo[4.4.0.12,5.17'l~ -ene and methyltetracyclo[4.4.0.12,5.1 z~~ with ethylene reported Benedikt et al. ~45 using 1,2-ethylenebis(rlLindenyl)zirconium dichloride in conjunction with methylaluminoxane (Eq. 11.167-11.168).
Et(i'~:l)2Z~ ~
(11.167)
Et(17d)2ZrC~
(11.168)
\
\
On working in toluene at temperatures between 0~ and 65~ these authors observed a positive influence of the temperature on the catalyst activity (Table 11.10). Table 11.10. Copolymefization oftetracyclo[4.4.0.1 z,s.I z~~ with ethylene(M ~)induced by t2-ethylenebis(rl'-i~ lenyi~)zirconocenedichloride/MAO ~ MI [ Activity MwxlO3 M~xlO3 M,,:M, Temp. g/mmole (mole ~ Zr/hr %) i 0 0 20 20 65
250 300 540 750 4,650
'Data from reference ~4~
29
127
216
141
1.53
33 31
149 145
375 479
230 253
1.63 1.89
769 The microstructures of the copolymers have been examined by using I D and 2D NMR spectroscopic technique. It is noteworthy that these authors found an increase of the glass transition temperature, T s, with the incorporation of the cyclic monomer into the polymer chain. Interestingly, they also evidenced that the glass transition temperature increased as the stereoisomeric content of tetracyclo[4.4.0.12,~. 17'~~ went from 95:5 endo, exo:exo, exo to 80:20 endo, exo:exo, exo. A great number of papers and patents describe a large variety of procedures for the manufacture of copolymers from multicyelie olefins and ethylene or ot-olefins in the presence of different Ziegler-Natta catalysts. ~ ~50The multicyclic monomers employed are mostly of norbornene type and can be easily prepared by the Diels-Alder route from norbornene, norbornadiene, dicyclopentadiene or various bieyclir and polycyr unsaturated hydrocarbons. As a function of the reactivity of the starting materials used for their synthesis and the reaction conditions, these monomers will cover a wide range of structures going from those of the usual medium and high molecular weight monomers to macromonomers. In copolymerization reaction with ethylene and cz-olefins, these substrates will produce random or blocky distributions of the structural units in the polymer chain depending on the monomer reactivity, nature of the catalyst and reaction parameters. Illustrative examples are given for tricyclic olefins (Eq. 11.169)
nn
(CH2)m
R
R
(~
and for polyeyelir olefins (Eq. 11.170).
(11.189)
770
n
+ n~
(CH2),.
+ n j',, R
(11.170) R
(C~),.
(CH2).,
It is quite significant that these copolymers are claimed to possess remarkable physical-chemical properties as evidenced by excellent transparency, good moldability, high glass transition point, high resistance to heat, ageing, solvents and weathering good electrical and mechanical parameters. In addition, they are compatible with different polymers including polyesters, polycarbonates, polyamides and polyolefins, and find potential applications in manufacture of optical devices, photo disks, circuit boards for crystalline liquids, printed circuit boards, special electrical and electronic devices, etc. Interesting copolymers containing functional groups are prepared by copolymefization of ethylene or C3.~8 ~-olefins with functionalized monomers of the general type X, where X - OH, OR, COOK, CKO, NH2, CONH2, CN (Eq. 11.171). R
\ In a selected procedure, TM the monomer is preferentially contacted with at least an equimolar amount of the organometallic compound and/or a halogen-containing metal salt then it is fed into the reaction system comprising a soluble vanadium compound, e.g., VO(OEt)CIz, and an organoaluminium compound, e.g., EhAI2CI3. Due to the presence of special functionalities, the products thus obtained have excellent resistance against ozone, weathering and heat as well as high adhesion to metals and good compatibility with other resins and elastomers. They find application as modifiers for resins and adhesives, as additives to lubricating oils.
771 in the manufacture of paint or inks, and in other related areas. A large variety of functional group-containing copolymers were produced by Mitsui Petrochemicals Ind. ]52 by copolymerization of ethylene with a C3.~8 ct-olefin and at least one functional-group containing monomer of formula CHz=CH-R~-X or norbomene-like derivative (Eq. 11.172).
q X
§
9
,##XR,
R
= ~
x
X
111.172)
z where R~= at least Cz hydrocarbon group, X = OR, COOK, CRO, NKz, CONR2, CN, OH, COOH or NHz (R=H or a hydrocarbon group) and Z=X. The monomer is contacted preliminary with at least exluimolar amount of" an organometallic compound and/or a halogen-containing metal compound and fed to the reaction system in the presence of" a catalyst containing a soluble vanadium compound and an organoalumJnium compound. The soluble vanadium compound is VO(OR)aXb where R=a hydrocarbon group and a and b are each 0-3 or its adduct with an electron donor. The aluminium compound is of the type R~mAl(OR2)nHpXq where R~ and R2 are each independently a C~.~5 hydrocarbon group, m,n,p and q are each 0-3 or of formula MAIR~ where M=Li, Na or K. The process effectively provides copolymers having high resistance against ozone, weathering and heat, high adhesion with metals and high compatibility with other resins and elastomers. These copolymers are usable as modifiers for resins, modifying aids, adhesives, additives to lubricating oil, etc. or for manufacturing paint compositions, primers, etc. Examples are illustrated for copolymers prepared from ethylene, propylene and 10-undecen-l-ol in hexane, in the presence of VO(OEt)Cl2 and EhAl2Cl3 as the catalyst. New functionalized copolymers were obtained by Oishi et al. 36 by copolymerizing endo-N-cyclohexylbicyclo[2.2.1 ]hept-2-ene-5,6dicarboximide with styrene under the influence of the cationic or ZieglerNatta catalysts (Eq. 11.173). ---"
co
N
,,,,73,
OCx/
co
772 The endo-N-cyclohexylbicyclo[2.2.1]hept-2-ene-5,6-dicarboximide adduct could be readily synthesized by Diels-Alder reaction of cyclopentadiene with N-cyclohexylmaleinimide. Similar copolymers were also prepared from higher Diels-Alder homologs of cyclopentadiene and endo-Ncyclohexylbicyclo[2.2.1 ]hept-2-ene-5,6-dicarboximide by cationic or Ziegler-Natta copolymerization with styrene (Eq. 11.174).
(11.174) oc
\ /
co
N
oc
\ /c o N
It is noteworthy that the thermal degradation of such eopolymers began around 334-363~ and glass transition temperatures Ts ranged from 180~ to 138~ The synthesis of functionalized AB-diblock copolymers from esters of bicyclo[2.2.1]hept-5-ene-2-methanol has been effeeted by Breunig and Risse ~$3using cationic Pd(II) complexes with weakly coordinating ligands. To this end, reaction of bicyclo[2.2.1]hept-5-ene-2-methyl benzoate (50 equiv.) with [Pd(CH3CN)4][BF4]2 followed by the addition of bicyclo[2.2.1]hept-5-ene-2-methyl pentanoate (200 equiv.) produced the corresponding copolymer (Eq. 11.175).
n ~ § m~
pd(C
o
6
CO
CO
'
'
'
'
C
3F
~ [~Jn ~Jm 0
, C, O
(11.175)
0
, C, O
The molecular weight, as determined by GPC, increased readily from 6500 to 21000 at~er 64 % of the second monomer was consumed. The ratio of
773 pentanoate to benzoate substituents incorporated in block copolymer measured by ~H ~ spectroscopy was 2.7 to 1. Copolymerization of norbornene derivatives containing silicon groups with ethylene and/or C3-z0 monoolefins and polyolefins have produced useful copolymers for various applications. Thus, starting from 7isopropylidenyl-5-trichlorosilyl-2-norbornene, ethylene and propylene, a terpolymer having a silyl derivative of norbomane as structural unit has been prepared by Copolymer Rubber Chem.TM in high yields, in the presence of VOCI3 and EhAI2CI3 as a catalyst (Eq. 11.176).
voch/EhAhCh
sich
*
/
(11.176)
*
\
S~Ch
The copolymefization reaction occurred in hexane at 35~ for one hour with continuous addition of ethylene and propylene. It is noteworthy that such a copolymer could be cured or subjected to sulphur vulcanization and possessed particular elastomeric properties. Organometallic copolymers have also been prepared by copolymerizing a cyclic olefin metal alkoxide Q(Rl)mOnMp(R2)q (where Q is a cyclic hydrocarbon residue having at least one unsaturated bond, P,,~ is alkylene or alkylidene, M is metal, Rz is hydrogen, halogen, alkyl or aryl) with one or more a-olefins under the influence of TiCI4 and organoaluminium compounds. ~5 Such a copolymer obtained from ethylene and the r derivative of 5-methyl-2-norbomene (Eq. 11.177)
\
CH=-O-AI--C=~ i cl
= ~
(11.177) X
CH=-O-AJ--C2~ I
Cl
provided a pressed sheet with a greater adhesion than the conventional polyethylene. Infrared spectra indicated the presence of hydroxy groups in the polymer chain.
774
11.4. Ring-Opening Metathesis Copolymerization of Cycloolefins By ring-opening metathesis copolymerization the cycloolefins will form linear unsaturated copolymers named copolyalkenamers or copoly(1alkenylene)s (Eq. 1I. 178). n
~~::(Cl-l.z)x
§
m
~(Cl-l.z)y (CH2)x (CH2)y
This type of copolymers contains different recurring units in the polymer chain as a function of the starting cycloolefins. Ring-opening metathesis copolymerization of cycloolefins has recently become an attractive area of large interest for production of copolymers of unprecedented architecture that are useful for many applications in modem technologies. In addition, ring-opening copolymerization of cycloolefins has provided an efficient means to elucidate the mechanism and stereochemistry of the extensively investigated metathesis polymerization. Accordingly, this chapter will survey the main aspects of the ring-opening copolymerization reactions of monocyclic, bicyclic and polycyclic monomers and will address the possibilities of producing copolymers by combining ring-opening metathesis polymerization with other types of polymerization reactions.
11.4.1. Monocyclic Monomers In the course of their studies on the mechanism of ring-opening polymerization of cycloolefins induced by the transition metal catalysts, Dall'Asta and coworkers ~$6 investigated the copolymerization reaction of ['4C]labelled cyclobutene with 3-methylcyclobutene. On starting from cyclobutene labelled at the double bond, in conjunction with 3methylcyclobutene, these authors succeeded to point out that during the copolymerization process the ring opens at the carbon-carbon double bond and the methyl group preserves the initial position in the recurring unit (Eq. 11.179). ,4
/
(11.179)
775 The yields and composition of the resulting copolymers differed significantly as a function of the catalytic system employed (Table 11.11). Table 11.11 Copolymerization of cyclobutene (Mr) with 3-methylcyclobutene (M2) in the presence of transition metal catalysts' Catalytic System
TiCL~3AI WCIdEt3AI
MoO2(acac)2/EtzAICl RuCI3/H20/EtOH
MI:Mz mole
Time hr
Yield %
26:74 30:70 35:65 35:65
2 24 14 100
100 38 47 20
'Data from reference ~
Copolyn~r Con'q3osition (M,:Mz) 25:75 50:50 40:60 45:55
As it can be seen from Table 11.11, the catalytic system TiCI4/EhAI proved to be the most active providing readily a 100% copolymer yield after two hours whereas the catalyst RuCI3/HzO/EtOH was the less active, going up to 20% copolymer yield in a hundred hours. Furthermore, the composition of the copolymer was substantially dependent on the catalytic system, 3methylcyclobutene being more reactive than the unsubstituted cyclobutene. Interesting results have been recorded on the structure of the copolymers prepared from cyclobutene and 3-methylcyclobutene in the presence of the above catalytic systems. Relevant data are presented in Table 11.12. Table 11.12. Structure of ~ l y m e r s of cyclobutene and methylcyclobutene prepared with transition metal catalytic systems' Catalytic System TiC~3AI WCE/Et3AI MoOz(acac)2/EtzAICl RuCI3/HzO/F_XOH 'Data from reference ~
trans-
Polyalkmamer % 55 25 25 80
cis-
Polyalkman~r % 30 60 70
traces
Poly(cycloalkylene) % 15 15 5 2O
776 As Table 11.12 illustrates, the structure of copolymers is primarily of a polyalkenamer type accompanied up to 20~ of poly(cycloalkylene) units. It is also noteworthy that the tungsten and molybdenum catalytic systems provided a high cis-content of polyalkenamer while ruthenium catalysts gave preferentially trans-polyalkenamer. Cyclopentene has been reported to copolymerize with cyclopentadiene, ~s7 cyclohexene, ~$8 cycloheptene, ~9,~6~ cyclooctene, ~59-~6~ 1,5-cycloctadiene ~61 and cyclododecene, m59'm6~under the influence of ringopening metathesis catalysts. The structure of these copolymers is strongly dependent on the nature of the reacting cycloolefin. In the reaction of cyclopentene with cyclohexene, in the presence of WCIc,/EtAICI2 catalysts, copolyalkenamers having a limited amount of hexenamer (1-hexenylene) units along pentenamer (1-pentenylene) in the polymer chain have been observed IS8 (Eq. 11.180).
Under these conditions, the maximum proportion of hexenamer units was about 25%. Noteworthy, the ratio of cocatalyst to catalyst, EtAICI2:WCI6, of 131 seemed to be crucial for copolymer composition. On decreasing this ratio to 41, homopolymers of cyclopentene are already formed. Copolymerization of cyclopentene with cycloheptene in the presence of WCI6- or WOCl4-based catalytic systems yields copolymers having pentenamer and heptenamer (l-heptenylene) units of mainly trans stereoconfiguration of the double bonds in the chain~$9'~6~(Eq. 11.181).
+
(11.181)
The copolymer composition and steric configuration varied, however, with the molar ratio of the reactants. Using a ternary catalyst consisting of WOCI4, Et2AICI and benzoyl peroxide, 1-heptenylene units up to 82 mole % have been incorporated into the copolymer, having 80% trans stereoconfiguration (Table 11.13).
777 Table 11.13. Copolymerization of cyclopm~o(M,) with cyr in the presence of WCI6/BzzO~zAICI as catalyst" Mollomor
Food
Conversion %
Mr'M,
Polymer Composition Mt:Mz mole 72:28 44:56 18:82
45 50:50 25"75 37 44 10:90 'Data from reference t60
Polymer Structure t r a n s :c i s
Inherent
Viscosity dlJg
75:25 80:20 80:20
1.4 1.0 1.1
As Table 1 1.13 illustrates, the polymer composition is greatly dependent on the monomer feed but the copolymer stereostrueture and molecular weight are less affected. Copolymerization of cyclopentene with cyclooetene in the presence of tungsten-based catalytic systems will afford eopolyalkenamers having prevailingly l-pentenylene units along with l-octenylene units ~s9~6~ (Eq. 11.182). +
~
~
(11.182)
The copolymer composition and structure is also influenced by the molar ratio and the reactivity of the monomers; products of varying structure and properties can be obtained by changing these parameters (Table 1 1.14). Table I I. 14.
Copolymerization of cyclopemene (Mr) with c y c l ~ e ( M 2 ) in the presence of WOCI~z2Oz/EtzAICI catalyst~ Motlomor
Feed Mt:Mz 50:50 25:75
10:90
Conversion %
13 10 13
'Data from reference t6~
Polymer Composition Mt:Mz (mole)
Polymer Structure t r a n s :c t s
Viscosity dlJg
97:3 53:47 13:87
70:30 65:35 75:25
2.5 3.1 3.0
Inherent
778 From the data presented in Table 11.14, it is obvious that, due to a substantial difference in the reactivity of the two monomers, under the above conditions, the copolymer structure and composition can be affected considerably. Thus, at equimolar ratios cyclopentene:cyclooctene, copolymers of 3 mole % 1-octenylene content were produced while, at molar ratios of 10:90, the copolymer composition moved to 87 mole % of 1-octenylene. In addition, a high cis content and a high inherent viscosity [rl] of the copolymer was obtained in the last case. The reactivity ratio for cyclopentene/cyclooctene copolymerization, ~6~ in the presence of WCI6/Et2AICI as a catalyst, was found to be r~:r2 = 1.07:0.45 (Table 11.15). Table 11.15 Reactivity ratios (rdrz) in copolymerization of cycloolefins (Mi-Mz) reduced by WC~2AICI as the catalyst' Copolymerization System MI-Mz Cyclopentene-Cyclooaene Cyclopentenr 1,5-Cyclooetadiene Cyclopentene-Cyclododecene Cyclooctenr 1,5-Cyclooctadiene Cyclooctene-Cyclododecene 1~5-Cyclooctadienr yclododecene 'Data from reference ~6~
r2
1.07 0.89 3.94
0.18 1.24
3.58
0.45 0.45 0.33 2.42 4.19 0.39
On employing cyclopentene isotopically labelled with ~4C at the double bond in the copolymerization reaction with cyclooctene, induced by WOCLdEt2AICI/Bz202, Dall'Asta and Motroni t6z were able to prove that the ring-opening reaction occurred by splitting the carbon-carbon double bond (Eq. 11.182a). (11.182a)
By copolymerization of cyclopentene with cyclododecene, ~6~ in the presence of WCI6- and WOCl4-based catalytic systems, copolyalkenamers of varying composition have been prepared, depending largely on the catalyst and reaction conditions (Eq. 11.183).
779 01.183)
Thus, on using WCI6/Et2AICI as a catalyst, a reactivity ratio of r~'r2 = 3.94:0.33 was found. ~6~The copolymer composition and trans/cis structure obtained with the catalytic system WOCL,/Bz2Oz/Et2AICI are given in Table 11.16. Table 11.16 Cr of cyclopentene(M~) with cyclododeoene(M2) using the catalytic system WOCL~z20~2AICI' Polymer Composition
PolYmer Structure
MI"Mz
MI"Mz
t r a n s :c i s
mole
mole 85"15 69:31 14:86
80:20 80:20 70:30
Monomer
Feed
80:20 50:50 5:95
Conversion %
23 12 17
Inherent
Viscosity dug 1.4 1.3
1.6
"Data from reference ~60
It is noteworthy that only at higher cyclododec,ene concentration in the feed a high proportion of this monomer, dodecenamer (1-dodecenylene), will be incorporated into the polymer. Furthermore, again an increased trans stereoconfiguration of the double bonds in the copolymers are produced like in the cycloheptene copolymerization (see above). A thorough comparison of the data obtained on the cyclopentene copolymerization with CT-C~z cycloolefins, in the presence of WOCL,/BzzO2/EtzAICI, indicates that lower cycloolefins possess a substantially higher reactivity in these conditions. Though the trans content of the copolymers is not in all cases as high as in the homopolymers made with the same catalyst, all copolymers prepared, even those amorphous in the unstretched state at room temperature, showed to be crystallizable upon stretching and annealing. The molecular weights of the above copolymers are as high as those of the corresponding homopolymers what will not significantly influence the melting temperature of the crystal structure. It was noted that the crystallization temperatures are generally 20~ to 30~ below the melting temperature and, accordingly, the rate of crystallization is low if compared with that of the corresponding homopolymers. This phenomenon suggests that the copolymerization technique is of interest
780 for manufacturing elastomeric copolymers of cycloolefins, the homopolymers of which are thermoplastic materials. Investigation by X-ray spectroscopy of the above copolymers ~6~ revealed that in the range of composition where one component is predominant, the structure of the copolymer is the same as in the corresponding homopolymer in its more stable modification. Structure examination showed that in the C~/C7 copolymer orthorhombic geometry characterizes all composition range whereas in the Cs/Cs copolymers the product has an orthorhombic symmetry in the range of prevalence of the C5 units and a triclinic symmetry when C8 units prevail. Furthermore, in the C8C t2 copolymer the product has triclinic symmetry in the region where C8 units predominate while the structure is monoclinic when C t2 units prevail. In the intermediate composition range of 50: 50, the degree of crystallinity is comparatively low and the X-ray pattern resembles that of the orthorhombic polyethylene. Copolymerization of cyclopentene with 1,5-cyclooctadiene has been effected with WCIdEt2AICI catalyst to form a copolyalkenamer with prevailingly l-pentenylene units t6~ (Eq. 11.184).
n
+
m
~
[VVIAI] =
(11.184)
The reactivity ratio r~r2 for this system was found to be 0.890.45 (Table 11.15). Cyclooctene has been polymerized with cycloheptene in the presence of WCI6- and WOCl4-based catalysts to poly(l-octenylene-co-1heptenylene) 159(Eq. 11.185). n
~/~ + Q m
[VWAI]~
(11.185)
Copolymerization of cyclooctene with cyclododecene has been effected with various tungsten based catalysts such as WCIc,/Et2AICI, WOCI,/Et2AICI, with or without Bz202 or Cum202 as a ternary component. 159'~6~ Interestingly, in the reaction of cyclooctene with cyclododecene in the presence of WCI~t2AICI a copolymer having a
781 higher content of l-dodecenylene units in the chain has been obtained ~6~
(Eq. 11.186).
The reactivity ratio, r~r2, was found to be of 3.58"0.39 for the two monomers. Copolymerization of cyclooctene with 1,5-cyclooctadiene has been carded out with WCIdEhAICI catalyst to a copolyalkenamer with prevailingly octadienylene units ~6~(Eq. 11.187).
(11.187)
1,5-Cyclooctadiene showed to be more reactive than cyclooctene, the reactivity ratio of the two monomers, rt:r2, being of 0.18"2.42 under these conditions. Copolymerization of 1,5-cyclooctadiene (COD) with cyclooctatetraene (COT) in presence of ring-opening metathesis catalysts ~63 has been carried out to produce random copolyalkenamers displaying good electrical and optical properties (Eq. 11.188).
o( )'m0
(11.188)
It is obvious that, as 1,5-cyclooctadiene and cyclooctatetraene have similar molecular structures and ring strain, and consequently similar re,activities, they undergo metathesis polymerization at close rates. Using molybdenum carbene as initiator, a random copolymer was formed in which the conjugated units of COT are interrupted by insertion of COD units. By controlling the molar ratio 1,5-cyclooctadiene 9 cyclooctatetraene, unsaturated copolymers with varying conjugation length and variable electrical parameters were prepared. 1,5-Cyclooctadiene reacts readily with 1,5,9-cyclododecatriene in the presence of WCh,/'Bu2AICI to form a copolymer with a random
782 to blocky structure, depending on the reaction conditions (Eq. 11.189).
nO.-c
(11.180)
The polymer thus obtained has a different structure imposed by the initial structure of the two monomers as compared to the conventional 1,4polybutadiene.
11.4.2. Bicyclic and Polycyclic Monomers Recently, a great number of copolymers of bicyclic and polycyclic olefins have been synthesized, under the influence of ring-opening metathesis catalysts, providing products of interest for their plastic and elastomeric properties. Depending on the monomer structure and reaction conditions, these copolymers may have a random or blocky distribution of the monomer units and may be grafted or have a particular architecture. Furthermore, copolymers bearing different functional groups or heteroatom-containing recurring units have been prepared widening the area of application. Norbornene and norbornadiene and their substituted derivatives have been largely explored in copolymerization reactions with a variety of cycloolefins due to their easy accessibility and particular reactivity. In addition, valuable information concerning the reaction mechanism and stereochemistry has been obtained by selecting specifically substituted or unsubstituted cycloolefins and/or norbornene and norbornadiene monomers. Copolymerization of both reactive monomers, norbomene and cyclobutene, has been conducted in a living fashion with the well-defined tungsten carbene initiator W(=CtBu)(=NAR)(OtBu)2 to the dibloek copolymer formed from the two recurring units ~65(Eq. 1 1.190).
n .m
VWCH~BuXNArXCXBuh
A substituted cyclobutene, diisopropylidenecyclobutene, has also been easily copolymerized with norbomene using a titanaeyelobutane complex as
783 initiator, generated in situ from the Tebbe reagent "CI~Ti=CH2'' norbomene166 (Eq. 11.191).
m
+
n
ROM:)
"-
and
(11 191)
The product is a robbery material with more desirable mechanical properties than the homopolymer but conductivities, upon doping, are similar to that of the homopolymer. Norbomene has been reacted with cyclopentene in the presence of metathesis catalysts to provide random or block copolymers having 1pentenylene and l-vinylene-1,3-cyclopentylene units (Eq. 11.192).
(11.192)
Depending on the microstructure of the copolymers thus prepared, the products have more elastomerir or plastic properties. It is remarkable that these properties can be readily modelled by changing the copolymer compositions when varying the reaction conditions such as monomer feed ratio, monomer concentration, nature and composition of the catalyst and cocatalyst, reaction temperature and solvent, t67,16s Interesting studies carried out by Ivin and coworkers 169 on the cyclopentene-norbornene copolymerization induced by several metathesis catalytic systems revealed that the copolyrner compositions and microstructures are strongly influenced by the nature of the catalyst and sometimes by the method of mixing. The reactivity ratios for cyclopentene and norbornene, rl and r2, (determined by these authors from monomer diads in the t3C NMR spectra of the copolymer) and the cis content, oc, for copolymers prepared in the presence of various catalytic systems in chlorobenzene at 20~ are given in Table 11.17.
784 Table 11.17 Copolymerization of cyclopentene (M~) with norbomene (M2) in the presence of various catalytic systems' Catalytic System (MzMz)b 0.11 0.33 0.44
gut~i/l,5-COD 48 IrCI3/I,5-COD 0.07 5.6 MoCIs/EtAICIz 56 (Mes)W(CO)3/AICI3 41 0.45 WCIdEtAICIz 0.32 13 0.48 WCldPh4Sn 0.55 2.6 0.53 WCldBu~n 0.27 12 0.60 70 WCld(allylhSn 0.68 WCIdPh4Sn/EAc 0.62 2.2 0.72 ReCI~ 18 0.73 'Data from referencet69; bl~raction of cis double bond in the MzM2 diads; eEA = ethyl acrylate
It is obvious from the reactivity ratios of cyclopentene and norbornene, r~ and r2, that at the two extremes of high-c/s copolymer (geCI5 catalyst) and high-trans copolymer (RuCI3/I,5-COD), both catalysts discriminate strongly in favor of norbornene. At the same time, for catalysts giving intermediate cis content, the least discriminating is WCI6/PIhSn and the system behaves approximately ideally at 20~ as shown by the proximity of the r~r2 value to unity. Furthermore, in their studies, Ivin and coworkers 169 observed that in the case of the WCIdPIh system, the composition of the copolymer is not sensitive to the proportions of the catalyst and cocatalyst or to the method of mixing, suggesting that there is basically one initiating species in this system. By contrast, this is not so for the system WCIdEtAICI2 which is strongly discriminating in favor of norbornene, but to an extent that depends largely on the proportions and on whether EtAICI2 or the monomer mixture is added last. Based on these results, Ivin suggested the presence of at least two types of initiating species, one of which may dominate under certain conditions. Copolymerization of cyclooctene with norbomene in the presence of ring-opening metathesis catalysts formed also random or block copolyalkenamers, having l-octenylene and 1-vinylene- 1,3-cyelopentylene units in the polymer chain ~~ (Eq. I I. 193).
785
(11.193)
The product microstructure depends essentially on the catalytic systems and reaction conditions. Thus, using WCIdEtAICI2 (1/4) with EtAICI2 added last, the structure corresponded to a homopolymer of norbomene while for WCIjEtAICI2 (I/10), with monomer mixture added last, significant proportions of cyclooctene-norbornene diads were noted. Similar to the cyclopentene-norbomene copolymerization, such results suggested the presence of at least two types of initiating species, one of which may dominate under some conditions. Another important observation was the fact that the cis content of the different copositional diads was not always the same. Thus, for the copolyrnerization of cyclooctene (M~) with norbomene (Me) in the presence of WCldPh4Sn at 20~ Ivin et al. Iv~ found that the cis content of the double bonds contained in the M~M~, M~M2, and M2M2 diads was about 85%, 65%, and 50%, respectively, regardless of the overall composition of the copolymer. By ring-opening copolymerization of 1,5-cyclooctadiene with norbomene in the presence of metathesis catalysts, polymers having as structural units 1-butenylene and 1-vinylene-l,3-cyclopentylene, similar to those encountered in cyclobutene-norbornene copolyalkenamer, can be formed (Eq. 11.194).
(11.194)
The copolymer compositions also depend on the catalyst nature and reaction parameters, as it was found for the other related monomers. The apparent reactivity of 1,5-cyclooctadiene has been in the same range as those of cyclopentene and cyclooctene, under the same conditions (Table 11.18).
786 Table 11.18 Reactivity ratios for norbomene (M2) copolymerization with cycloolefms (M,) mducod by W C l ~ h 4 S n a'b i
Cycl0oiefm Cyclopentene Cyclooctene 1,5-Cyclooctadiene
rl
r2
rlr2
0.50 0.51 0.48
2.6 8.9 12.4
1.3 4.5 6.0
' Data from reference t~0 bTeng)erature = 20oc, Solvent = chlorobenzene. Though the monomers employed, norbomene and cyclooctatetraene (COT), had different reactivities, they could be copolymerized under the influence of tungsten carbene ROMP initiators ~ (Eq. 11.195).
(11.195)
m0
Norbomene, due to a greater ring-strain, polymerizes nearinstantaneously in a mixture with cyclooctatetraene to a block polymer (repeat length n) and when its concentration tapers off, cyclooctatetraene begins to polymerize producing the final block (repeat length m) of consecutive COT units. Even at high norbomene:cyclooctatetraene ratios in the monomer mixture, the great difference in rates of polymerization of the two monomers ensures that a long block of consecutive COT units will be formed. Ruthenium carbene initiator RuCI2(PPh3h(=CHCH=CPh2) was found to readily copolymerize norbomene with bicyclo[3.2.0]heptene in a living fashion in dichloromethane at 40~ to diblock and triblock copolymers by sequential addition technique t~ (Eq. 11.195a).
_R'O2(PPt T=4O' ~)z(~O. .C' izCI2--; ~
(11.1cjsa)
The progress of the copolymerization was followed by ~H NMR spectroscopy. ~z3 Noteworthy, it was observed that when a 50/50
787 mixture ofbicyclo[3.2.0]heptene and norbomene was added to a solution of ruthenium catalyst in methylene chloride, polymerization of norbomene did not initiate until the polymerization of bicyclo[3.2.0]heptene was complete. This result has been attributed to a less hindered double bond in bicyclo[3.2.0]heptene than in norbornene. Copolymerization of norbomene with anti-7-methylnorbomene (M,) was first reported by Ardill et al. ~74using conventional tungsten-based catalysts. The polymer structure was inferred from ~H and ~3C NMR spectra. New experiments concerning the eopolymerization of norbornene with syn-7-methylnorbomene (M,) induced by the (mesitylene)W(CO)jEtAICl2/norbomene epoxide catalyst were conducted by Hamilton, Ivin and Rooney ~75(Eq. l 1.196).
(11.198)
Thus, after contacting syn-7-methylnorbomene for 2 days with the W-based catalyst, a small amount of norbornene was added resulting immediately in copolymer formation. From ~3C NMR spectrum, its microstructure indicated 34% norbomene units flanked by 58% cis, 42% trans double bonds, and 66% syn monomer units flanked by about 85% trans and 15% cis double bonds. Unfortunately, it was not possible to decide between a true copolymer, a block copolymer or just a mixture of homopolymers. In another experiment, using four parts syn-7-methylnorbornene and one part norbornene and the same catalyst, a eopolymer containing more than 90% norbornene units were prepared. Thereafter, Greene et al., ~76 explored the possibility of making block copolymers at room temperature from syn- and anti-7-methylnorbomene with norbornene using tungsten carbene initiator W(cyclopentylidene)(OCH2tBu)2Br2 in CD2C12. The reaction of successive small amounts of the monomers with the catalyst was followed by ~H NMR to determine the rate of the reaction and the stability of the m e t a l - ~ n e propagating species. AB and ABA type copolymers were then prepared from 7-methylnorbomene and norbornene and analyzed by GPC. The ~3C NMR spectrum of the final product did not show any significant difference from that recovered 2.5 hr after the second addition of 7-methylnorbornene so that there were no marked secondary metathesis reactions affecting the compositional distribution, nor any sign of incorporation of the syn isomer.
788 This spectrum, however, indicated that the fraction of cis-double bonds in the A block was 0.40 and the B block 0.44. The B block had a random cks/trans double bond distribution and the A block had atactic ring sequences. Reaction of syn- with anti-7-methylnorbornene, has been examined by Hamilton, Ivin and Rooney ~S in order to obtain further details on the reaction mechanism and stereochemistry (Eq. 11.197).
(11.197)
In a series of experiments, a 5149 mixture of syn- and anti-7methylnorbornene was subjected to a number of Ru-, Os-, Ir-, W- and Rebased catalysts, and the structure of the polymers and their hydrogenated analogs determined by ~3C NMR spectroscopy. Except in the case of the (mesitylene)W(CO)3/EtAICl2/norbomene epoxide catalyst, the polymer consisted exclusively of ring-opened units of the anti isomer, the syn-7methylnorbomene could be recovered in good yield. This confirmed that the exo face of the norbornene moiety is normally highly reactive whereas the exo face is relatively inert towards metathesis. On using the highly reactive (mesitylene)W(CO)~/;tAICl2/ norbomene epoxide (1"1"1) catalyst at 20~ a copolymer of syn- and anti7-methylnorbornene was produced from the above mixture of monomers having the cis content, o~=0.45, and the proportions of the double-bond pairs rr and rt=2.6. The greater value of r~rt than unity indicated a certain degree of cis/trans blockiness. Starting from 7-methylnorbornene rich in syn isomer, under the action of the same catalyst, a copolymer containing 83% syn units flanked by 80% trans and 20% cis double bonds, and 17% anti units flanked by 60% cis and 40% trans double bonds has been produced. Significantly, a predominance of trans double bonds associated with syn units was also observed in the solution fraction of the polymer containing mainly anti units. Furthermore, there was no sign of m/r splitting of any peak associated with syn units in the ~3C NMR spectrum, so that here too the polymer was likely to be tactic (c r, t m). Since the much more reactive anti isomer polymerizes first, followed more slowly by the syn isomer, the products obtained under these conditions consist,
789 at least in part, of a block copolymer. Kress e t aL ~77 used W(cyclopentylidene)(OCHz'Bu)zBr2/CraBr3 to initiate polymerization and copolymerization of syn- (M,) and anti-7-methylnorbomene (M,). Block and tapered block copolymers of san- and anti-7-methylnorbornene were prepared. The early stages of the reaction could be readily followed by ~H NMR at 220-250~ the intermediate metallacyclobutane could be detected during the reaction of anti-7-methylnorbornene, but not for that of syn-7methylnorbornene. The syn monomer was less reactive than the anti monomer but reacted in due course when a mixture of monomers was employed. Related studies on the polymerization of syn- and anti-7methylnorbornenes have been conducted by Feast et aL, ~Ts using the molybdenum initiator Mo(=CH'Bu)(=NAr)(O'Bu)z. On following the reaction course by ~H and ~3C NMR in C6D6 and CDzCIz, they observed that the anti monomer M, polymerizes first, then more slowly the syn monomer M,, leading to a block copolymer. A solvent effect was observed, the reaction taking place considerably faster in CDzCIz, where it proceeded to completion, than in C6D6. In C6D6 the ratio of propagation to initiation of the anti monomer, k ~ i , , was 9, as determined from the proportion of residual initiator. The double bonds formed were mainly trans (80-90~ in both blocks and the diads embracing the trans double bonds in the M, blocks had an isotactic bias: (Om)t = 0.69 in C6D6, independent of monomer concentration, the diads in the M, blocks had a slight tactic bias, probably isotactic. The tacticity was interpreted in terms of a control of the addition reaction of monomer by the configuration of the chiral carbons in the Cs ring nearest to the molybdenum center in the propagating metal-carbene complex. Copolymerization of norbornene with spiro[cyclopropyl7,1']norbornene has been examined by Makovetsky et al. ~9 under the influence of homogeneous gu and W catalytic systems (Eq 11.198).
n
+
m
=
(11.198)
Despite of the steric restraints imposed by the substituent in the position 7 of the norbornene moiety, high yields have been recorded using the RuCI3.3HzO catalyst (Table 11.19).
790 Table 11.19 Copolymerization of norbomene (MI) with spiro[cyclopropyl-7,1 '] norbomene (M2)under the influence of metathesis catalysts' Catalytic System
MI" Me mole
M2:Catalyst mole
Reaction Time
Poly~rYield % 100 32
[11] dl gq
1000 9:1 5 hr 1.0 1000 30s WC~hC-CH r 9:1 1000 50s 2.0 14 WCIflPhC-CW 3"1 'Da& from referenc~"~; bC~I,:EtOH 11, 60~ 'WCl~:phenylacctylene 11, toluene, 20~ RuCI3.3H20 b
Analysis of the copolymer composition showed norbornene to be more active than spiro[cyelopropyl-7,1']norbomene. It should be noted that spiro-cyclopropane group seemed to be left intact during the ring-opening polymerization and did not participate in the intermolecular cross-linking. In order to attain special properties to the copolymer, bicyclo[2.2.1]heptadiene (norbomadiene) has been copolymerized with eyclopentene using various homogeneous ~s~and heterogeneous TM catalysts. The product has a higher unsaturation as compared to the corresponding norbornene copolymer (Eq. 11.199).
0
(11.199)
Effective homogeneous catalysts for this reaction were derived from WCI6 and Et2AICI or 'BuaAI associated with epiehlorohydrin or 2chloroethanol. ~8~ Heterogeneous catalysts were based on WO3/AI203 (TiO2,ZrO2), MoO3/AI203, Cr203/AI203 and UO2/AI203 in inert hydrocarbons as reaction media. TM A variety of norbornadiene copolymers with norbornene have been synthesized by Bell et al. ~82 using a range of olefin metathesis catalysts. By employing hex-1-ene as chain transfer agent, the molecular weight of these copolymers has been regulated to levels that permit high solubilities in suitable solvents. As a result, high-quality ~3C and ~H NMR spectra of these products have been obtained. Their spectra have been fully assigned and the detailed microstructure of norbornadiene/norbomene copolymers
791 accurately established (Eq. 11.200).
n
+ m
~
(11.200)
One of the most significant observations was that OsCl3 as catalyst afforded essentially high-cis and compositionally random copolymers, a result which indicated that the metallacarbene propagating complex holds one norbornadiene molecule as a di-endo chelating ligand, which remains intact as a spectator species throughout the reaction. The steric bulk of this extra ligand then constrains the incoming norbornene or norbornadiene molecule to form metallacyclobutanes in the cis mode. With some catalysts, for example RuCI3, this chelating effect is so dramatic that it effectively renders the catalyst almost inert. With the expansion of poly(dicyclopentadiene) production and applications, synthesis of a range of copolymers of dicyclopentadiene with various cycloolefins has became a particular challenge for various research groups. Of the traditional ROMP monomers, cyclopentene and cyclooctene have been tested in copolymer manufacture with dicyclopentadiene. Block copolymers of cyclopentene with dicyclopentadiene have been prepared by Coca, Dimonie and Dragutan ~s~ in 40% yield using tetraphenylporphyrinate tungstenchloride/diisobutyl aluminoxane as a catalyst (Eq. 11.201). (11.201)
The IR and m3C NMR spectrum of the copolymer indicated a prevailingly trims configuration of the double bonds. In addition, the polymer showed a narrow molecular weight distribution as determined by GPC. Similar block copolymers were obtained by the same authors from dicyclopentadiene and cyclooctene with tetraphenylporphyrinate tungstenchloride/diisobutyl aluminoxane as a catalyst in 30~ yield ~s~(Eq. 11.202). n
§
m
~
(11.202)
792 The polymer, as characterized by IR and ~3C NMR spectroscopy, had also a predominantly trans configuration and displayed a narrow molecular weight distribution. Block copolymers (A-B and A-B-A) containing segments of narrow molecular weight distribution from endo- or exo-dicyclopentadiene and norbornene have been synthesized by Cannizzo and Gnabbs ~85 by living ring-opening metathesis polymerization using a titanacyclobutane complex as the catalyst (Eq. 11.203).
n~
§ m~
ROMP =-
(11.203)
Thus, diblocks of" exo-dicyclopentadicne (DCP) with norborncne (NBE), e.g. X-(NBE)45(xDCP)~-Y and X-(xDCP)48(NBE)45-Y, having polydispersity indices (PDI's) of 1.08 and 1,14, respectively, and a triblock X-(xDCP)44(NBE)4~(xDCP)2a-Y with PDI of 1.14 have been prepared under the above conditions. Analysis by differential scanning calorimetry (DSC) showed a single T s for these block copolymers indicating that polynorbornene and poly(-exo~icyclopentadiene) are compatible. Copolymers of different architectures can be prepared from two or more norbomene-like polycyclic olefins 185'1~ (e.g. norbornene and its substituted derivatives, dicyclopentadiene, tetracyclododecene, alkyltetracyclododecene, etc.) in the presence of various well-defined molybdenum- and tungsten-carbene complexes, working under appropriate reaction conditions. For instance, starting from norbornene and dicyclopentadiene first a linear copolymer can be obtained then a crosslinked one, under more severe conditions (Eq. 11.204).
.J
(11.204)
793 When norbornadiene is used instead of norbornene, unsaturated crosslinked copolymers which can be further derivatized with appropriate functionalities will be produced (Eq. 11.205).
.j
,.-
(11.205)
A special class of cross-linkable copolymers have been obtained by ring-opening polymerization of dicyclopentadiene with substituted norbornene-like dienes. An interesting example is the copolymerization reaction of dicyclopentadiene with ethylidenenorbornene, under the action of ROMP catalysts consisting of ammonium molybdate and organoaluminium compounds ~s~(Eq. 11.206). n
9 rn
~
(11206)
The process can be adapted for application in reaction injection moulding (RIM). The product can be further cross-linked or derivatized with appropriate agents to attain desired properties. Copolymerization reactions of dicyclopentadiene with a great number of polycyclic olefins containing norbornene moiety as a structural unit, under the action of tungsten-based metathesis catalysts, provided a versatile way to manufacture new polymers useful as raw materials in RIM process. ~ss The ratio between the two comonomers and the structure of the second polycyclic olefin will determine considerably the cross-linking ability of the products prepared. A first copolymer was obtained from dicyclopentadiene and 1,4-dinorbomylbenzene in the presence of tungsten phenoxides and organotin or organosilicium compounds ~ss (Eq. 11.207).
794
6
Tungsten phenoxides were prepared through the reaction of tungsten hexachloride or tungsten oxytetrachloride with a monocyclic phenol (e.g. 2trichloromethylphenol, 3-chlorofluoromethylphenol) while the organotin compounds were selected from trialkyl- or triaryltinhydride (e.g. tripropyltinhydride, tributyltinhydride, triphenyltinhydride) and the organosilicon compounds from a dialkyl-, trialkyl- or diarylsilan (e.g., dibutylsilan, triethylsilan, diphenylsilan). By the same procedure, a copolymer of dicyclopentadiene with 5,8methylene-5a,8a-dihydrofluorene was easily prepared under similar working conditions t89 (Eq. 11.208). (11~)
The comonomer was readily available by Diels-Alder reaction of cyclopentadiene with indene. In this case, the cross-linking ability was controlled by the ratio of comonomers and reaction parameters. Copolymerization of dicyclopentadiene with 5,6acenaphthonorbornene, under the influence of the above catalysts, gave rise to new products containing aromatic moieties along the polymer chain ~89 (Eq. 11.209). n
~
(11208)
The new copolymer was manufactured by the Diels-Alder pathway from cyclopentadiene and acenaphthene. The properties of the copolymer
795 thus prepared were essentially dependent on the proportion of 5,6acenaphthonorbornene units in the final product. A new copolymer of dicyclopentadiene with 1,4,4a,9,9a,10hexahydro-9,10(1 ',2')benzene- 1,4-methanoanthracene was prepared in the presence of tungsten phenoxides and organotin or organosilicon compoundslS9 (Eq. 11.210).
n
~
(11.210)
.m
1,4,4a,9,9a, 10-Hexahydro-9,10( 1',2')benzene- 1,4-methanoanthracene is readily available by the Diels-Alder reaction of dicyclopentadiene with dibenzobicyclo [2.2.2 ]octatriene. Of interest, benzonorbomadiene gives rise, by living ring-opening metathesis copolymerization with norbomene, under the influence of bis(cyclopetnadienyl)titanacyclobutanes complexes as initiators, to A-B and A-B-A block copolymers ~s5 (Eq. I 1.21 l). ROMP
(11.211)
The copolymers obtained under these conditions have a single T s and display a narrow molecular weight distribution. Similar block copolymers have been synthesized also from 6-mehtylbenzonorbomadiene and norbomene with the same bis(cyclopetnadienyl)titanacyclobutanes initiators ~ss (Eq. 11.212). n
9m
ROMP >
(11.212)
796 These copolymers had again a single T 8 and displayed a narrow molecular weight distribution. However, despite of the expectations concerning an improved solubility of the methyl-substituted polymer, the products remained still insoluble in common solvents. With the aim of modifying the thermal and mechanical properties of the highly rigid and strained polymers obtained by ring-opening metathesis polymerization of deltacyclene, Lautens ~9~ prepared copolymers from deltacyclene and norbomene in the presence of molybdenum initiators Mo(=CHCMezR)(=NAr)(O/Bu~h (R = Me, Ph) (Eq. 11.213). [Mo]
(11.213)
In these conditions, copolymers with high molecular weight and narrow polydispersities were produced. With the same purpose of modifying the polymer properties, copolymers of methyldeltacyclene and norbornene have been obtained using the above molybdenum carbene initiators (Eq. 11.214).
n
+
m
=-
(11.214)
The high molecular weight copolymers have been characterized by ~H and ~3C M R spectroscopy and GPC. In a similar way to the unsubstituted polymer, they displayed a narrow molecular weight distribution. Taking advantage of the living ring-opening polymerization of [2.2]paracyclophan-l-ene with Schrock molybdenum carbene initiators, Miao and B a z a n TM prepared random and block copolymers of this monomer with norbornene, in the presence of the carbene complex Mo(=CHCMezPh)(=NAr)(OCMe(CF3)2)2 (Eq. 11.215).
n
9 m
=
(11215)
GPC analysis of the block copolymer indicated a narrow molecular weight
797 distribution (PDI 1.1). Interestingly, fluorescence measurements of the block copolymer gave a spectrum similar to that of poly([2.2]paracyclophanol-ene) or cJs-stilbene whereas the fluorescence spectrum of the random copolymer resembled that of traz~-stilbene. Block copolymers of benzotricyclo[4.2.2.02"~]deca-3,7,9-trienr a "Durham" polyacetylene precursor, with norbomene have been prepared in a controlled fashion by living ring-opening polymerization with weU-defined titanium-, tungsten- or molybdenum-based initiators ~92"~ (Eq. 11.216). =
,~
+ m
j~
rn~~t~ .=
(11216)
Both, A-B diblock and A-B-A triblock copolymers showed microphase separation by small-angle X-ray scattering (SAXS) or transmission electron microscopy (TEM). By subsequent thermal treatment of these polymer precursors, block copolymers of polyacetylene with polynorbornene have been obtained (Eq. 11.217).
(11217)
Except for the lowest molecular weight samples, all the block copolymers retained their microphase separation after thermal treatment as seen by SAXS or TEM measurements, thus creating serf-assembled structures of polyacetylene dispersed throughout the polynorbornene matrix. To modify the physical and mechanical properties of a class of polymers of technical interest, a wide range of copolymers have been prepared by ring-opening copolymefization of norbornene with various norbornene-like monomers. For this purpose, tetracyclododecene (TCD) and methyltetracyclododecene (MTCD) have been largely used as comonomers along with norbomene and substituted norbornenes ~95 (Eq. 11.218-11.219).
798
n
13
9 m
9
m
(11.218)
~
ROMP
(11.219)
/ is significant to mention that of the substituted norbomenes, vinylnorbornene associated with tetracyclododecene or methyltetracyclododecene gave rise to cross-linkable copolymers ~96 (Eq. 1 1.2 19a). It
n
+
m
ROMP
Moreover, ternary copolymers or higher interpolymers may be made on combining three or more norbomene-like monomers in the above procedures. One interesting example is the efficient synthesis of ternary copolymers containing recurring units arising from norbomene, dicyclopentadiene and tetracyclododecene under the influence of classical or well-defined Mo- and W-based catalysts mg~(Eq. 11.220).
Likewise, substituted norbomene and substituted tetracyclododecene will give the ternary substituted copolymers in the presence of the above mentioned catalytic systems ~ (Eq. 11.221).
799
(11221) R
These speciality copolymers are highly appreciated for their improved thermoplastic characteristics or large profile of elastomer properties. According to Mitsui Petrochemical Ind., ~99 hydrogenated ringopened copolymers for optical uses were prepared by hydrogenating ringopened copolymers obtained from cyclic olefins of formulae I-Ill in the presence of a metal halide (e.g.,. Ru, Rh, Pd, Os, Ir, Pt, Mo or W, V or Zr halide) or acetylacctonate (e.g., V or Zr acetylac~onate) and organoaluminium compounds (Scheme 11.7).
R2
Rltl
Re
I
II
III
Scheme 11.7
The hydrogenated products were obtained in the presence of a homogeneous catalyst system (e.g., Ni, Pd or Pt supported on a carrier) or homogeneous catalyst (e.g., Ni naphthenoate/triethyl aluminium or Co octenoate/n-butyl Li). The monomer of formula I can be any cycloolefin from Scheme 11.8. Those of formula II can be cyclobutene, cyclopentene, cycloheptene to cyclododecene, methylcyclobutene, methylcyclopentene, methylcycloheptene, methylcyclooctene, dimethylcyclopentene or trimethylcyclodecene. The monomer of formula Ill can be cycloolefins from Scheme 11.9.
800
Me
Et
Me
Me
Me
Et
iBu
Scheme 11.8 Copolymers thus prepared provided moulded products having high dimensional stability, no change in their optical activity due to strain, high
@ CY""
Me
CY''
Scheme 11.9 transparency, high resistance against heat, solvents, chemicals, water and impact, high thermoplasticity and low glass transition temperatures. Due to their high dimensional, heat and impact resistance, they can be used for automobile parts such as instrument panels, column corners, bonnets, radiator grills and electronic tools as well as for business machine castings, cameras and domestic appliances, films and helmets. Their good optical
801 characteristics made them suitable for moulding plastic lenses such as spherical lens, Fresnel lens, optical fibers and optical filters. Taking into account the peculiar features that fullerene possesses, polymeric fullerene materials are expected to display the same electronic, optical and catalytic properties of the parent C60. In addition, C60 polymers can be easily handled, whereas C60 and its derivatives give films with much difficulty. To fulfil this objective, Prato et al. 2oo prepared and characterized high molecular weight copolymers containing C60 via ring-opening metathesis copolymerization of such monomers with norbornene ~ q . 11.222).
rn~ [ ~
+
n
[Mo]_
(11.222)
The product was soluble in chloroform and a free-standing film could be obtained on a glass substrate. The cis/trans isomer ratio increased with the relative amount of C60 monomer present in the polymerization process. Raising the amount of C60 monomer up to 1 mole % resulted in an increase of cis/trans ratio to 6:1. Thermogravimetric analysis showed that the Crocontaining polymer is a robust material which degraded at 470~ but of lower thermal stability than polynorbomene. When the copolymer was heated to 80~ for 72 hr in the solid state, cross-linking occurred. The resulting product was insoluble in all organic solvents, exhibiting the swelling and solvent sorption, typical of cross-linked materials. Proeessable films containing 1% C60 derivative exhibited electronic and electrochemical properties which are typical of the carbon cluster.
11.4.3. Copolymers by ROMP of Functionalized Cycloolefins The development of well-defined alkylidene initiators that are both tolerant of a wide variety of functional groups and provide a living initiation and propagation of polymerization of strained cycloolefins has spawned further research in copolymerization of functional cycloolefins. The living behavior of the polymerization of 3,4-difunctional cyclobutene in the presence of the Schrock molybdenum complexes prompted Perrott and
802 Novak 2~ to synthesize block copolymers of dimethyl and diethyl 3,4cyclobutene dicarboxylates (Eq. 11.223).
n ~ "C02Me ~C02Me
§ m~ "
C02Et ~'C02Et
[Mo] ~=,.
C02Me
C02Et
(11.223)
The reaction readily occurred in the presence of the molybdenum initiator Mo(---CHCMe2Ph)(=NAr)(OC (CF3hCH3 h. Sequential addition of monomers to a solution of initiator resulted in the expected block copolymer, although care must be taken to add the second monomer exactly at the correct time: too early resulted in a tapered block copolymer while too late resulted in the decomposition of the living end group with contamination by the homopolymer of the first monomer. Cyclopentene has been copolymerized with trifluoromethylnorbomadiene and bis(trifluoromethyl)norbomadiene by Feast and Wilson 2~ in the presence of WCI~Me4Sn in toluene at 20~ Working with equimolar amounts of monomers, yields of copolymers of 61% and 76%, respectively, have been reported for the two fluorinated monomers after 2.5 hr reaction time. Details about the copolymer structures were not given. Copolymers of fluorinated norbomene or norbomadiene have been prepared by Feast 2~ using the well-defined Schrock-type molybdenum initiators (Eq. 11.224-11.225).
n
Fx+ m Fx
n ~ ~ ~ - Fx
9m/ ~
Fy [M~
~
(11"225) Fx
Fy
Highly chlorinated norbomene and norbomene derivatives have been reported 2~ to undergo metathesis polymerization and copolymerization with cyclopentene in the presence of tungsten hexachloride and either organoaluminium or organotin compounds to form highly chlorinated copolymers. The products obtained display special properties, they are thermally stable and particularly flame and oil-resistant. The diether derivative of 5-methylnorbornene (M) has been
803 copolymerized by Schrock 2~ with methyltetracyclododeeene (MTD) in the presence of the well-defined molybdenum complex initiator Mo(=CHCMe2PhX=NAr)(OtBu)2 (At = 2,6-C6H3-'Pr2) to form block copolymers (Eq. 11.226). [uD] n
9 m
~
(11.228)
Interestingly, a well-defined lamellar morphology was observed in a film of (M)~MTD)220 that had been static cast from benzene in the presence of 80 equiv of ZnF2 or Cd[3,5-C6H3(CF3)2]. The latter samples, after treatment with HzS, afforded (ZnS)~ and (CdS)~, respectively, within the lamellar microdomains. The procedure opened a new way toward the synthesis of semiconductor clusters or metal clusters of a predictable size within microdomains in films of block copolymers prepared via ring-opening polymerization. By a similar method, block copolymers of the dimethoxy derivative of 5,6-dimethylnorbornene with methyltetracyclododecene have been prepared with the above molybdenum carbene initiator2~ (Eq. 11.227).
n
9 rn
~
(11.227)
Likewise, these products were suitable for binding metals in a dative fashion through oxygen with applicability in metal and semiconductor cluster synthesis. Block copolymers of norbornene with 2,3-diacetoxynorbomene have been prepared by Stelzer et al. ~6 in high yield using the well-defined Schrock initiator Mo(=CHCMezR)(=NAr)(O'Buh (Ar = 2,6-C6H3JPr2) (R = Me, Ph) (Eq. 11.228).
804
= ~
(11.228)
The high molecular weight copolymers were characterized by GPC and ~H and ~3C NMR spectroscopy. Similar block copolymers have been reported also by S c h r o c k 2~ from 2,3-dicarbomethoxynorbomene and norbomene with the same molybdenum initiator Mo(=CHCMezPhX=NArXOtBu)2 (At = 2,6-C6H3-'Pr2) (R = Me, Ph) (Eq. 11.229).
n
, m
=
(11229)
Significant results obtained Tlenkopatchiev2~ in the copolymerization reaction of 5- {[(3,5-di-tert-butyl-4hydroxybenzoyl)oxy]methyl}-norbom-2-ene with norbomene in the presence of Ru- and Os-based catalysts, tH- and ~3C NMR data of the copolymers thus obtained revealed that both monomers were incorporated randomly and with the same reactivity in the polymer chain (Eq. 11.230).
OC=O
tB
tBu
Despite the bulky substituent attached at the norbornene moiety, these results indicated that 5-{[(3,5-di-tert-butyl-4-hydroxybenzoyl)oxy]methyl norbom-2-ene exerts a small steric effect during insertion reaction. The Rubased catalyst produced polymers with mainly trans double bonds whereas Os-based catalyst gave rise to both cis and trans configurations. The
805 molecular weights were found to be of the order 3xl05, with a polydispersity index of 2. The products exhibited a single T s of 76~ Syntheses of carbohydrate-based polymers, especially with wellcontrolled low-polydispersity, are particularly interesting for applications in biology such as cell surface recognition or protein stabilization. To this end, a series of diblock and triblock "sugar-coated" copolymers have been prepared by Nomura and Schrock 2~ by Mo-catalyzed living ring-opening polymerization using as the initiator the complex Mo(=CHCMe2Ph)(=NArXO'Bu)z. A first example is the synthesis of the diblock copolymer of 1,23,4-di-O-isopropylidenc-a-galactopyranos-6-O-yl 5-norbornene-carboxylate with trans-2,3-bis(((trimethylsilyl)oxy)methyl)norborn-5-ene (F-x1. 11.231).
n
c//O
+ m
(11.231)
iMe3 ----~
\
O,SIMe.3
OR
i
00 SIMe 3
where
~0 OR
I
CH2
=
I0
The copolymer was obtained nearly quantitatively (yield 98%) and had a low polydispersity index, PDI = 1.08. Under similar conditions, copolymers of methyltetracyclododecene with 1,2:3,4-di-O-isopropylidener 5-norbornene-carboxylate or 3,4:5,6-di-Oisopropylidene-a-D-mannofuranos- 1-O-yl 5-norbornene-2-carboxylate have been prepared (Eq. 11.232).
.my" \ OR
where
[~].~
(11.232) C-=O
806 ---o
I
o~.
~~
CH2
o~
or
I0 o-~
Polymer yields of 94-99% and polydispersity indexes of 1.03-1.18 have been recorded in these reactions. By the same procedure, block copolymers of 1,23,4-di-Oisopropylidene-ct-galactopyranos-6-O-yl 5-norbomene-carboxylate with 5norbomene-2-carboxylic acid ester containing 2,3-O-isopropylidene-Dribonic 7-1actone or 3,4:5,6-di-O-isopropylidene-(t-D-mannofuranos- 1-O-yl 5-norbornene-2-carboxylate have been prepared (Eq. 11.233).
n
,~O
* m
\ OR
=
(11.233)
\OR'
C=O = OR
C=O I OR'
where --0
OR=
I
C.H2 ) ~ O ' ~ O)l
--O"c H2,., OR'= I~u")'O I
1
or
o_
High yields in polymers (>99%) and low polydispersity indexes, PDI 1.10 and 1.13, respectively, have also been obtained. Also, triblock copolymers of methyltetracyclododeccne with 1,2:3,4-di-O-isopropylidene-ctgalactopyranos-6-O-yl 5-norbomene-carboxylate and 3,4"5,6-di-Oisopropylidene-ct-D-mannofuranos- l-O-yl 5-norbomene-2-caxboxylate (Eq. 11.234) =
(117-114)
OR
where
(:~
807 ~O
I
CH 2 OR:,
~_~
O~
or
I0
or with 1,2:3,4-di-O-isopropylidene-ct-galactopyranos-6-O-yl 5norbomene-carboxylate and bis( 1,2:3,4-di-O-isopropylidene-ct-Dgalactopyranos-6-O-yl)5-norbomene-trans-2,3-dicarboxylate have be~n prepared (Eq. 11.235). 0! 0§
n
(11.235)
p
c 9
bR bR A triblock copolymer from methyltetracyclododecene and trans-2,3bis(((trimcthylsilyl)oxy)methyl)-norborn-5-ene with bis(l,2:3,4-di-Oisopropylidene~-D-galactopyranos-6-O-yl) -5-norbornene-trans-2,3dicarboxylate with PDI = 1.16 in 97% yield has been obtained (Eq. 11.236). 0
~
!
(11.2~
Moreover, tetrablock copolymers of 1,2:3,4-di-O-isopropylidene-ctgalactopyranos-6-O-yl-5-norbornene-~oxylate (M~) and bis(1,2:3,4-diO-isopropylidene-ct-D-galactopyranos-6-O-yl)5-norbomene-trans-2,3dicarboxylate (M2) with trans-2,3-bis(((trimethylsilyl)oxy)methyl)-norbom5-ene (M3) and methyltetracyclododecene (M4) have been prepared (Eq. 11.237). n~
+ mM2 + pM 3 § rMI
=
(11237)
I
I
808 In order to examine the effect of backbone flexibility on the mesomorphic behavior of side-chain liquid crystalline polymers, Grubbs and coworkers 2~~ synthesized copolymers from norbornene and cyclobutene monomers bearing a p-nitrostilbene moiety as the mesogenic group (Eq. 11.238).
n~C.,OR . 0
§ p ~.
Ov C(~"C) [Ru] OR
=P~~c~ 0~~- (11.238) o.C-oR O,,C) bR
where R = (CH2)m O
~
N
O
2
Using Ru(=CI-IPh)CI2(PCy3)2 as the catalyst, side-chain liquid crystalline copolymers with polydispersity index of" 1.12 have been obtained in high yield (96%). ~H and ~3C NMR spectra indicated a 11 mixture of polybutadiene and polynorbomene backbone. Related AB type block copolymers that contain a side-chain liquid crystalline polymer block and an amorphous polymer block have been synthesized by Komiya and Schrock TM by living ring-opening copolymerization of m-[((4'-methoxy-4-biphenyl)yl)oxy]alkyl norbom-2ene-5-carboxylates (m = 3,6) with norbornene, 5-cyanonorbornene or methyltetracyclododecene employing Mo(=CH'BuX=NAr)(O'Buh (At = 2,6-C6H3-'Pr2) as initiator. The amorphous polymer block consisted of polynorbornene, poly(5-cyano-2-norbornene) and poly(methyltetracyclododecene). For the synthesis of such copolymers, the non-mesogenic monomer, e.g. norbornene, has been added to the molybdenum initiator in Tiff to give a living polymer that subsequently was treated with the mesogenic monomer to form the final block copolymer (Eq. 11.239). n
c,.OR
6
, p
~
(11.239) ,C-oR
809 where R = (CH2) m
O
~
O
M
e
Yields were quantitative and the polymer was free of unreacted monomers according to GPC studies. The molecular weight distribution was relatively narrow and polydispersities were less than 1.2. DSC analyzes showed that the block copolymer with the mesogen group m = 6 had one T s at 38-42~ regardless of the ratio of the two monomers. Relevant studies on norbomene copolymerization with norbomene derivatives bearing carbonates and chlorocarbonates carried out Feast and Harper 2~z using the conventional catalyst WCIc/Me4Sn. With the aim of examining the structure and properties of the new copolymers of norbomene with functionalities, these authors employed in their studies as comonomers endo-3a,4,7,7a-tetrahydro-4,7-methano-l,3-benzodioxol-2one (norbomene-5,6-carbonate), endo-3a,7a-dichloro-3a,4,7,7a-tetrahydro4,7-methano- 1,3-benzodioxol-2-one (5,6-dichloronorbomenr 5,6carbonate) and endo, endo-3a,9a-dichloro-3a,4,4a,5,8,Sa,9,9a-octahydro4,9: 5,8-dimethanonaphto[2.3-d]- 1,3-dioxol-2-one (7,8-dichlorooctahydrodimethanonaphtalene- 7, 8-diearbonate). As a first pair of comonomers, norbomene and norbomene-5,6carbonate were reacted under the influence of WCIdMe4Sn in chlorobenzene at room temperature (mole ratio WCl6:Me4Sn:comonomer:norbomene, 12:16:85) to give ca. 1 12 poly(6,8(2,4-dioxa-3-keto)bicyclo[3.3. O]octylene vinylene)/ polynorbomene copolymer (A, Table 11.20) in 40 wt.% yield, based on the combined masses of comonomers (Eq. 11.240). CO
d'o n
CO , m
CIC6H5,R'I;
The polymer thus produced was characterized by elemental analysis, IR and ~3C M R spectroscopy and gel permeation chromatography. A new pair of comonomers employed by Feast and Harper, 2~2 norbornene with 5,6-dichloronorbornene-5,6-c.arbonate, were copolymerized in the presence of WClcqVle4Sn in chlorobenzene at room
810 temperature (mole ratio WCI6:Me4Sn:comonomer: norbomene, 1:2:125:143) to produce a 1:5 poly(6,8-(l,5-dichloro-2,4-dioxa-3keto)bicyclo[3.3.0]octylene vinylene)/polynorbomene (B, Table 11.20) copolymer in 33 wt.% yield, based on the combined masses of the starting olefins (Eq. 11.241). CO
d'o " /o.-CO
nij,~
VVCIs/Me4Sn
. m
CIC6H5, R-Ip
CI
(11.241)
The polymer structure was evaluated from IR and ~3C NMR spectra in conjunction with elemental analyses whereas data on molecular weight and polydispersity (PDI) from gel permeation chromatography. Another related copolymer was prepared by Feast and Harper2~2 starting from norbomene and 7, 8-dichlorooctahydrodimethanonaphthalene-7,8-dicarbonate using WCIcrMe4Sn in chlorobenzene at room temperature (mole ratio WCI6:Me4Sn:comonomer:norbomene, 1276:174) (Eq. 11.242).
n
~
O
~CO
9m
CIC6H5, R.I~
(11.242)
CI
Under these conditions a 12.4 poly(9,1l-(2,6-dichloro-3,5-dioxa-4keto)tetracyclo[5.5.1.0 2,6 .0'$12 ]tridecylene vinylene)/polynerbemene copolymer (C, Table 11.20) in 92% yield, based on the combined masses of the comonomers was obtained. Data on its structure and composition are based on IR and ~3C NMR evaluation and elemental analyses and values of molecular weights and polydispersity (PDI) were determined by gel permeation chromatography (GPC).
811
Table 11.20 Copolymerization ofnorbomene with cycloalkenes bearing carbonate and chlorocarbonate substituents' Copolymer
Ten'tp. ~
Time hr
Yield %
MI
MW
PDI
A
20 20 20
0.75 0.75 0.75
40 33 93
40800 5800 16800
94400 451500 169200
2.3 78.6
B
C
10.1
'Data from reference2t2. It is noteworthy to outline the very wide molecular weight distribution of copolymer formed from norbomene and 5,6-dichloronorbomene-5,6carbonate, 78.6, as compared to the other copolymcrs of norbomene produced usually under the same conditions. That this product was a true copolymer and not a mixture of homopolymers was evidenced by Feast and Harper~t2 on examining its behavior in solution in THF and chloroform in contrast to the homopolymer of 5,6-dichloronorbomene-5,6-caubonate which is insoluble in these solvents. Castner and Calderon 2~3 investigated the copolymerization of cyclopentene with exo-5-norbornene-2,3-dicarboxylic anhydride to obtain the corresponding copolymers (Eq. I 1.243).
,.l co.o
n~ C O
oc,~ + m [~
--
(11.243)
The reaction has been effected in c h l o r o ~ e n e at 50-60~ in the presence of the binary catalysts consisting of WCI6 (or its complexes with PhOH or Ph3SiOH) and organoaluminium compounds. Alternatively, oopolymers of cyclopentene with exo-5-norbomene-2,3
812 Table 11.21
Copolymerization of cyclopentene (Mr) with exo-5-norbomene-2,3-diearboxylic anhydride (Mff Mt:Mz mole
Reaction
Time, hr
Yield %
3.5:0.000 3.5:0.175 2.0:0.200
3 3 24
65 62 63.5
Functionality %
[n]
dl g-t 1.65
2.1 7.0
2.30 4.00
'Data from reference~
These authors observed that the presence of exo-5-norbomene-2,3dicarboxylic anhydride in the monomer mixture at concentrations as low as 5 mole % did not disturb the polymerization of cyclopentene, while at higher concentrations it caused a decrease in the reaction rate. From these data, they inferred that the apparent enrichment of eopolymer by functionalized units did not reflect the higher relative reactivity of the polar comonomer, but was related only to the equilibrium propensity of the cyclopentene polymerization. Copolymerization of norbomene with exo-5-norbornene-2,3dicarboxylic anhydride, induced by WCldphenylacetylene as a catalyst in toluene at 20~ gave copolymer in 30% yield after 0.5 hr reaction time, containing 2.25% functional units per chain (Eq. 11.244). OC n #,'~.,~CO
, m
=
,o
CO ( 11.244)
These functional groups can be easily converted into carboxyl, ester or amide groups, if desired. Such small mnounts of functional groups into polynorbornene seem to be sufficient for improving the adhesive and other properties of the polymer. Dicyclopentadiene showed also to be reactive in the ring-opening copolymerization reaction with exo- 5-norbomene-2,3-dica~oxylic anhydride induced by tungsten-based catalysts to give high yields of copolymer214 (Eq. 11.245).
813
n
O+
[vv.~!
m
(11.245)
Fast polymerization rates and high conversions were observed in all reactions featuring dieyclopentadiene with rapid gelation of the reaction mixture occurring (Table 11.22). Table 11.22 Solution copolyn~rization of exo-norbomene..2,3-~carboxylic anhydride (M~) with di(cyclopmtadiene) (DCPD) ~b
mole
Temp. ~
Gelation time~s
Yield %
0:100 8:92 17:83 45:55 76:24 100:0
23 23 23 65 65 65
17 22 20 2 5 60
97 96 97 99 94 86
[M~I'[DCPD]
T$ ~ 153 173 174 188 210 231
"Data from reference2~4; SReacuon conditions: solvent = chlorobemzene, [total monomers] = 20% w/v, molar [W]:[Al]'[dibutyl ether]' [total monomers] = 17:28:200, reaction temperature = 65~ reaction time = 40 ram.
The glass transition temperatures of the eopolymers of exo-5-norbomene2,3-dicarboxylic anhydride with dicyclopentadiene were found to be intermediate between those of the respective homopolymers. Both block and random copolymers have been prepared from norbomene and 2-((+)-exo-5-norbomene-2-carboxamido)-2-deoxy-l,3,4,6tetra-O-aeetyl-D-glucopyranose (NBEglu(Ac)4) by ring-opening metathesis polymerization with the ruthenium earbene complex initiator Ru(=CHCH-CPhz)CI2(Ph3P)z to demonstrate their accessibility and to see what the effect of copolymerization would have on the properties of the resultant materials 2~ (Eq. 11.246).
814 ,~C/NHglu(COC H3)4 n
\
+ m
111.246)
NHg~(COCH3)4
where .OCOCH3
NHglu(COC Ha)4 =
CHaCOO~OCOCH3 NH~-
[ CHACO0
--
It was readily observed that the molecular weight distribution was lower in the block copolymer than in the random copolymer. In addition, gelation was suppressed in both the random and block copolymers, and soluble high molecular weight materials were obtained under these reaction conditions (Table 11.23). Table 11.23
Copolyn~rization of norbomene (M0 with (NBEglu(Ac)4) (M2) induced by Ru(=CHCH=CPhz)CIz(Ph3P)z~ Polymer Random b
Homopolyme: Blocka
[Md/[Mz]/[l]
M.x'lO4
M,,xlO4
PDI
50/50/1 67/0/1 67/67/1
2.91 1.11 2.05
4.53
1.55 1.23 1.35
1.36
2.77
'Data from referenceZ~; sCHzCIz, 25~ 1 day and then 50~ 1 day; r 25~ 1 day;~First block as in c, Secxmd block 25~ 1,5 days and then 50~ 6 hr. In order to produce new functionalized polyalkenamers, Makovetsky et al. ~ carried out the eopolymerization of cyclopentene with exo-5-norbomene-2,3-dicarboxy-N-phenylinude (Eq. 11.247). It is significant that in this case the steric conditions appeared to be less important as compared to exo- and endo-5-norbomene-2,3-dicarboxylic anhydride. Both exo- and e n d o - 5 - n o r b o m e n e - 2 , 3 - d i ~ x y - N - p h e n y l i n f i d e could participate in the copolymerization reaction with cyclopentene under the effect of the WCldphenylacetylene catalyst. It is of great interest that by copolymerization of cyclopentene with derivatives of norbomene
815
0 N
oc" 'co
co,
(11247) %
dicarboxylic acids, it is possible to introduce ca. 1-2 mole anhydride or imide groups into the chain with polypentenamer. These groups may be easily converted into carboxyl, ester or amide groups. Such small amounts of functional groups seem to be sufficient for improving the adhesive and other properties of polypentenamer. Copolymers of norbornene with exo-5-norbomene-2,3-dicarboxylic anhydride and e n d o - and exo-5-norbomene-2,3-dicarboxy-N-phenylimide prepared Makovetsky et al. 179 using WCIdphenylacetylene as a catalyst (Eq. 11.248).
0 N
n~+
m~'cCo-O'N-~ WCle~A._ ~
m
' 'co
01.248)
The polymer yields and functional group contents in the polymer chain, as evaluated from IR spectra, are given in Table 11.24. Table 1!.24 Copol3anerization of norbomenetM0 with 5-norbomene-2,3-diearboxy anhydride(M2) and N-pheny[imide(M3)lb MI:M2, MI:M3 mole
Time hr
Yield %
M~:M=2 2:0 Mr:Mr=2.5:0.125 M~:M2=2.5:0.125 M~:M3=2.5:0.125
2 0.5 1.5 72
93 30 56.5 18
Functional Group, % o
2.25 1.1 0.9
[n]
dlg-i 8.0 5.0 6.0 2.4
'Data from referenceI"~ bReaetio. conditions" catalyst WCl~:phenylaeaxylene 1"1, solvent toluene, reaction temperature 20~
816 As Table 11.24 illustrates, in the case of 5-norbornene-2,3-dicarboxy-Nphenylimide as a polar comonomer, steric conditions appeared to be less important than with 5-norbomene-2,3-dicarboxy anhydride. However, it is remarkable that addition of 5 mole % of exo-5-norbomene-2,3-dicarboxyN-phenylimide to a monomer mixture did not influence substantially either the rate of polymerization of norbomene or the intrinsic viscosity of the polymer while both polymer yield and intrinsic viscosity decreased considerably in the presence of the same amount of endo isomer. It is significant that by copolymerizing norbornene with derivatives of 5-norbomene-2,3-dicarboxylic acid as anhydride or N-phenylimide, it is possible to introduce ca. 1-2 mole % of these groups into the polynorbornene chain. These groups may be easily further converted into carboxyl, ester or amide groups, if desired. Such small amounts of functional groups seem to be sufficient for improving the adhesive and other properties of polynorbornene. The performance of a bulky spiro-imide, 5-norbornene-2-spiro-3'exo-N-phenylsuccinimide, in the ring-opening copolymerization with dicyclopentadiene (DCPD), was examined by Watkins et al. 2~+, in the presence of WCI6 and organoaluminium compounds as catalysts (Eq. 11.249).
O
+
(1124,9)
m
N-Ph 0 Ph
The relevant data obtained in these reactions are summarized in Table 11.25. Quantitative yields of copolymers were obtained in this case whilst the DSC curves of the product revealed that the glass transitions were broadened and moved to lower temperatures as the dicyclopentadiene content increased. In order to improve some performances of polypentenamer, copolymers of cyclopentene with 5-cyanonorbomene have been prepared by ring-opening metathesis polymerization in the presence of various tungsten-based classical catalysts 2~6"2~(Eq. 11.250).
817 Table 11.25 Solution ccv~lymerization of 5-norbomeno-2-spiro-3'-exo-N-phenylsuccmimide (MI) with di(cyclopentadiene) (DCPD)~b
[M,]'[DCPD] mole
Gelation time~ s
Yield %
Tg
0:100 6:94 12:88 35:65 68:32 100:0
2 60 115 230
98 98 97 98 98 97
162 155 156 165 178 187
840
~
'Data from re~ll~c,~2|4; bR.ea~..IOl'] c~ditiolls: solvent = chlorobenzene, [total monomers] = 20% w/v, molar [W][Al]:[total monomers] = 1"3"50, reaction temperature = 70~ reaction time = 120 rain.
n
+
m
-
.~
(11.250)
C2q Depending on the catalyst employed, the products can be random or block copolymers. It is important that such copolymers can be easily functionalized by subsequent chemical conversion of the cyano groups. Interesting diblock copolymers of 5-cyanonorbornene with norbornene prepared Schrock 2~8 by the living ring-opening metathesis polymerization, in the presence of the well-defined molybdenum complex Mo(=CH'Bu)(=NAr(O'Buh as an initiator (Eq. 11.251).
nj~CN +mj~
[Mo]
(11.251)
/ NC Under these conditions, high molecular weight copolymers with narrow polydispersities (PDI = 1.03) have been obtained almost quantitatively.
818 Because of their interesting thermoplastic properties, a large number of copolymers have been prepared from norbomene derivatives bearing different substituents. For this purpose, Tanaka and coworkers 2t9 prepared a copolymer from 5-cyano-2-norbomene and 5-phenyl-2-norbomene in the presence of classical catalysts derived from WCI6 and organoaluminium compounds (Eq. 11.252).
n~~.CN + m ~ p
= ~
(11.252)
WCh/Et2mcl
Furthermore, Asrar22~ copolymerized 5-cyano-2-norbomene with dicyclopentadiene in order to modify the reaction injection moulding (RIM) parameters for dicyclopentadiene polymerization. The ring-opening copolymerization of the two monomers has been carried out in toluene solution using WCIdEt2AICI as the catalyst (Eq. 11.253). n
CN
+
m
>
(11.2S3)
It was found that the metathesis polymerization of dicyclopentadiene, which is very fast and exothermic in these conditions, can be controlled by the addition of 5-cyano-2-norbomene. Though the cyano monomer delayed the polymerization at room temperature, at high temperatures the process was accomplished in reaction injection moulding time. The effect of incorporation of nitrile monomer onto the physical and mechanical properties of the copolymer was clearly outlined. The similar effect of 5cyanonorbomene has been encountered in the copolymerization reaction with methyltetracyclododecene carried out in the presence of W-based catalytic systems (Eq. 11.253a). n
f.~
CN
§ m
~
tCaAq "-
(11.253a)
819 Copolyalkenamers from 5-cyano-2-norbomene and a variety of substituted norbornenes have been prepared using classical W- and Mbased catalysts as well as more tolerant well-defined W and Mo alkylidene initiators ~ ' ~ (Eq. 11.254).
n
9rn
.=
(11.254) CN
R
where g is an alkyl, aryl, ester, amide, imide, halogen or anhydride group. With the aim of studying the influence that 5-cyano-2-norbornene will exert on the thermal and mechanical properties of the final product, copolymers of exo-5-norbomene-2,3-dicarboxy-N-phenylinfide and 5-cyano-2norbomene have been prepared by Asrar 22a with the classical tungsten/alkyl aluminium catalyst (Eq. 1 1.255).
/
n~CN+
J~ -COx m/.~co~N ~
[W/AIL ..~
N\
O(3 CO (11.255)
NC The glass transition temperatures, T s, of these copolymers ranged between those of the two homopolymers, increasing linearly with the N-phenylimJde content. The thermograms showed a change in the specific heat only at one temperature, indicating that random copolymers were produced which form a single-phase system. Block copolymers of mcthyltetracyclododecenr with methyl dithioether of trans 5,6-dimethyl-2-norbomcne were prepared by Schrock by living ring-opening metathesis polymerization in the presence of the molybdenum initiator Mo(=CHCMe2Ph)(--NAr)(O'Bu)2 (Ar = 2,6-C6Hr 'Pr2)2~ (Eq. I 1.256). e
+
m
~
~]
=
(11.256)
820 The products, characterized by GPC and tH NMR and TEM, exhibited a low polydispersity (PDI
~PPhz
+
PPh2
111
~
[v,ol
(11.257)
Ph2P
~H NMR analysis of the block copolymer in C6D6showed the composition to be that expected while GPC yielded a polydispersity index of 1.08. Further addition of Ag(COD)(Hfacae) (Hfacac=[CF3C(O)CHC(O)CF3] ") or Au(PMe3)Me and thermal treatment of the Ag- or Au-containing films allowed silver (20 to 100A) and gold clusters (15 to 40A) to be manufactured. A new series of block copolymers of methyltetracyclododecene with phosphine- or phosphine oxide-functionalized norbomenes have been obtained by S c h r o c k :z?'6 in a living fashion by ring-opening metathesis copolymerization in the presence of the molybdenum initiator Mo(=CHCMeePh)(=NArXO'Bu)2 (Ar = 2,6-C6H3-'Pr2) (Eq. 11.258). R n
(11258)
9m
\
where R =-CHzP(O)(oet)z,-CHzO(CHz),P(o~)z,-CHzO(CHz),P(OXoct)z.Low polydispersities (PDI<1.06) resulted under these conditions but an unexpected bimodality was observed for these block copolymers by contrast to the unimodal block copolymers prepared from MTD and NORPHOS. The origin of the bimodal molecular weight distribution
821 remained unclear despite considerable effort was directed at its elucidation. Under suitable conditions, these copolymers underwent microphase separation, and the metal chalcogenide clusters were predominantly sequestered within the phosphine-containing microdomains. Phenothiazine-based redox-active block copolymers containing Si(OEth groups for surface attachment have been manufactured by living ring-opening metathesis polymerization using Mo initiators of the Schrock type, Mo(=CHR)(=NAr)(OtBuh (R = ferrocenyl, Ar = 2,6-Cc,H3-'Pr2)zz7 (Eq. 11.259).
(•)'S n
9m
(~S
Si(OEt)3
(11.259)
~0
(CH2)2
O,
(CH2)2
These copolymers were successfully used to derivatize Pt, In2(Sn)Os, and nSi electrodes, whereas analogs of those same copolymers lacking Si(OEt)3 groups did not bind to these surfaces. Attaching molecules to electrode surfaces in order to modify electrochemical properties is an area of wide interest. In addition, new developments in catalysis and chromatography have led to processes involving adsorbing or covalently bonding discrete molecules to surfaces. In this way, living ring-opening metathesis copolymerization of the above type of functionalized monomers affords products suitable to attach them to electrode surfaces with a degree of orientation of the polymer with respect to the polymer/surface interface. By copolymerizing two monosubstituted cyclooctatetraene (COT) derivatives, one which homopolymerizes to give a soluble polymer and one which homopolymerizes to give an insoluble polymer (both in the trans form), it would be possible to tailor the effective conjugation length of the resulting copolymer by adjusting the ratio of the two monomers. Through the copolymerization of (trimethylsilyl)COT with n-butylCOT or noctyICOT, CmJbbs and coworkers z~ synthesized a family of copolymers in which the effective conjugation length of the resulting copolymer increased monotonically with the amount of the n-butylCOT or n-octylCOT in the monomer feed. The copolymefization reactions were carried out in the
822 presence of the well-defined tungsten carbene initiators W(=CH'Bu)(=NAr)(OCMe(CF3h)2 (At = 2,6-C6H3-'Pr2) and W(=CH(oMeOPh)(=NPh)(OCMe(CF3h)dTHF. Subsequent cis/trans isomerization was accomplished either thermally (heating the sample in benzene or THF at 60-80~ or photochemically (at 0~ by exposure of the sample dissolved in benzene or Tiff to light from a medium-pressure mercury lamp approx. 6-12 hr for an-1 mg/mL sample) to produce the trans copolymer (Eq. 11.260-11.261). n
n
+m OSiMe30nOcd:~] 9m
huorA
~
h~orA.~
(11.260) ~
(11.261)
For both families of copolymers, as the absorption maximum of the copolymer reaches approximately 580 nm, the polymer becomes insoluble. While copolymers derived from 40% or 50% trimethylsilylCOT were completely soluble in concentrated solutions in both the cis and trans forms, copolymers synthesized with a smaller ratio of this monomer might be aggregated in the trans form, much like trans-poly(n-butylCOT) or transpoly(n-octylCOT). 5-Trichlorosilyl-2-norbomene gives readily with 1,5-cyclooctadiene a trichlorosilyl-containing ring-opened copolymer in the presence of metathesis catalysts based on tungsten chloride and organoaluminium compounds 229 (Eq. 11.262).
= C
~
(11.262)
A practical example is the copolymer made from 1,5-cyclooctadiene with 10 mole % 5-trichloro-2-norbornene and about 15 mole % 1-vinyl-3cyclohexene. An oily product with M , - 1000 was obtained which can be used as a very efficient adhesion promoter for the coupling of rubber (especially EPDM) to siliceous fillers such as silica or China clay.
823 Copolymerization
of
5-trimethylsilyl-2-norbomene e t al. 179 at 20~ WCIJphenylacetylene catalytic system (Eq. 11.263).
cyclopentene was carried out by Makovetsky
SiMe a
9m
=
with using
111.263) Me3Sr/
The reaction has been terminated before the monomer conversion reached 15%. On this way, it was possible to modify the hydrocarbon chain of polynorbornene/polypentenamer by introducing small amounts of trimethylsilyl groups into it. The reactivity ratios of the two monomers, 5trimethylsilyl-2-norbornene (M l) and cyclopentene (Mz), determined from the data obtained, were r~rz = 1.40:0.30. Similar results have been obtained in the copolymerization reaction of 5-trimethylsilyl-2-norbomene with 1,5cyclooctadiene, working under the same conditions (Eq. 11.264). SiMo3
9m
~
(11.264)
The reactivity ratios of the two monomers, 5-trimethylsilyl-2-norbornene (M~) and 1,5-cyclooctadiene (Mz), determined from the data obtained, were r~'rz = 8.0:0.25. A slight change in reactivity ratios was observed in the copolymerization of 5-trimethylsilyl-2-norbomene (M~) with norbornene (Mz) using the above catalytic system, WCl6/phenylacetylene (Eq. 11.265).
~SiMe
3
9m
wc~/PA
(11.265)
=
Me3S'r /
The values determined in this case, r~:rz = 0.19:0.80, indicated that the copolymer was always enriched by trimethylsilyl groups, even though a significant difference in the reactivity of the two monomers existed. The distribution of the comonomer units in the polymer chain had a random
824 distribution, with a slight trend toward alternation. As could be expected, norbomene proved to be the more active comonomer in the copolymerization reactions of 5-trimethylsilyl-2-norbornene with cyclopentene and 1,5-cyclooctadiene, under the influence of the catalytic system WCIdphenylacetylene. Interesting results obtained Finkel'stein et al.23~ in the copolymerization of norbomene with 5-(trimethoxy)- and 5-(triethoxy)-2norbomene to the corresponding copolymers in the presence of homogeneous gu-based and W-based catalysts (Eq. 1 1.266-11.267).
n~si(OMe)
3+ m
[RuCI2(PPh3)3]_ T =60"C ~
(MoOhS('
[RuCI2(PPh3)3]
(11.266)
(11.267)
T = 60"C (EtO)3Sr/
The products can be used as high reactive thermo- and chemosetting materials, starting materials for preparation of membranes, charge transfer complexes, adhesives. 5-(Trimethylsiloxy)methyl-2-norbomene can be readily copolymerized with norbomene under the action of the ruthenium complex RuCI2(Ph3P)3 to form polynorbomene b ~ n g (trimethylsiloxy)methyl groups 23~(Eq. 11.268). [Rul
T --60=C
0~.2~) Me3SiO
These copolymers can be readily further convened to high molecular mass polyalcohols. Monodisperse diblock copolymers of 5-((trimethylsiloxy)methyl)-2norbomene with a "Durham" polyacetylene precursor, pdimethoxybenzotricyclo[4.2.2.02"5]deca-3,7,9-triene, have been prepared by Schrock~92 using a tungsten alkylidene complex as initiator (Eq. 11.269).
825
(11.289)
OSiMe3
Narrow polydispersities have been recorded with the majority of these copolymers. Spin cast samples of these diblocks have been characterized by NMR, DSC, SAXS, TEM and STEM (Table 11.26). Table 11.26 Molecular characterization of diblock copolyn~rs of 5-((trimethylsiloxy)~yl)-2-norbomene with p-dimethoxybenzc~cyclo [4.2.2.0~]deca-3,7,94xiene' Molecular weight 48 48 48 48
Stoichi~cwt%
000 000 000 000
35 000 20000 10 000
8
15 28
50 50 50 50
PDI Average wt % (DSC and NMR~) (GPC) 8.2 16.8
27.4 52.2 51.0
1.74 1.23 1.07
1.04
49.1
1.04 1.06
51.0
1.10
Morphology
(sAxs) spherical cylindrical cylindrical lamellar lamellar lamellar
'Data from reference~92 Six of the diblock copolymers showed microphase separation by SAXS, with morphologies ranging from spherical to cylindrical to lamellar. These diblocks were heat treated (130~ for 10 rain) to thermally eliminate dimethoxynaphthalene and form block copolymers of 5((trimethylsiloxy)methyl)-2-norbomene and polyacetylene (Eq. 11.269a). Except for the lowest molecular weight sample, all the block copolymers retained their mierophase separation as seen by SAXS and TEM, thus creating self-assembled structures of polyacetylene dispersed throughout the derivatized poly(5-((trimethylsiloxy)methyl)-2-norbomene) matrix. The diblocks possessing self-assembled polyacetylene structures could be
826 Orb 111 §
l~rrin
(11.~
IV'e3,90
M~O
chemically doped to render them electrically conductive and thus create materials with potentially interesting electrical properties. An alkylsiloxy derivative of norbomene, 5,6-bis((tertbutyldimethylsiloxy)methyl)-2-norbomene, undergoes readily ring-opening copolymerization with norbornene, under the influence of ruthenium carbene R(=CHCH=CPhz)CIz(Ph3P)z, to form polynorbomene bearing tertbutyldimethylsiloxy moieties as pendant groups TM (Eq. 11.270).
n~ ' ~ O
SIMe2tBu
+ rn ~ J ~
~[Ru]
OSiMe2tBu
(11.270) OO
tBuMe2S( 'SiMe2~u By further chemical conversion of the tert-butyldimethylsiloxy pendant groups, new derivatized block copolymers of norbornene and substituted norbomene could be manufactured by this method. Interesting copolymers of 5-(l'-methylsilacyclobutnane)methyl-2norbornene (Mr) with norbornene (M2) have been prepared in the presence of RuCI3.3H20 as a catalyst z3z (Eq. 11.271).
60"C"-
(11.271)
Me, Si
When a monomer to catalyst ratio of 18401 has been employed, quantitative yields (100%) of copolymers were attained at 60~ for 5 hr,
827 starting from a feed ratio MtMz of 9:91. Subsequent thermal treatment of these copolymers at 180-220~ afforded thermoset eopolymers by crosslinking. Another norbomene derivative containing two silicon atoms into the functional group, 5-( 2 '-methyl- 5 ', 5 '- dimethyl- 1', 4 'disilapentyl)norbomene, has been copolymerized with norbomene under the action of WCIdPhC---CH (11) as a catalystz33 (Eq. 11.272).
n~SiMe2CH2SiMe3+ m ~
WC~hC=CH
~
111272) SiMe2CH2SiM3e
It was found that the incorporation of a second silyl atom into the pendant group did not lead to a further increase in the permeability. However, the values obtained for the permeability coefficients and the separation factors of these copolymers showed that these compounds belong to the class of the most permeable and sufficiently permseleetive polymers used in the membrane applications. Of a special interest are copolymers prepared from 5(trimethylgermyl)methyl-2-norbomene and norbomene in the presence of the ruthenium complex RuCIz(Ph3P)3 as catalyst TM (Eq. 11.273).
n
•
~
GeMe3
§
m
[Rul=-
~
(11273) GeMe3
Such eopolymers possess selective permeability coefficients for light gases and are promising for applications in membrane technology. Starting from the promising results obtained in the polymerization of cycloolefins in the presence of ~organostanyl-ct-olefins z~9, Zerpner and Streek T M carried out the ring-opening copolymerization of a number of cycloolefins bearing organostannyl substituent with several cycloolefins. The products were expected to be polymeric bioeides with possible applications to marine anti-fouling coatings, wood preservatives or similar uses. The catalyst employed was the classical system WCIdEtOH/EtAICI2 with or without additional components. Two examples of this series are the copolymerizations of 3-tributylstannyl- and 5-tributylstannylcyclooctene
828 with cyclooctene, in the presence of the above catalyst, to form the substituted polyoctenamer containing tributyltin as the pendant groups in different positions (Eq. 11.274-11.275). $rlBu3
mo n
§m
[W/All
(112.74) SnBu3
~Aq Sre~
The content of tributyltin in the copolymer was then gradually modified as accomplished by copolymerizing two cycloolefins with different reactivities, 5-tributylstannylcyclooctene with cyclododecene (Eq. 11.276).
The effect of incorporating the more rigid and steric demanding norbornane skeleton into both monomer and polymer has also been examined in the copolymerization reaction of cyclooctene with 11tributylstannyltricyclo[8 29 . 1.02,9]triclec-5-ene (Eq. 11.277).
sn 'O
[W/A~ ~
(11~77) Bu~Sn/
In a preliminary test of biocidal activity, a glass plate coated with the with copolymer of ll-tributylstannyltricyclo[8.2.1 .02,9]tndec-5-ene 9 cyclooctene (Sn content 11%) was placed in a biologically very aggressive environment, i.e., in a fiver just downstream of a water sewage outlet. When inspected after two weeks, it was nearly completely free of the slimy greenish-black growth which had accumulated on the control plate coated with tin-free polyoctenamer. New examples of combining two monomers with totally different re,activities are the copolymerization reactions of 5tributylstannylmethylnorbomene with cyclopentene and cyclododecene in the presence of the WCh,/EtAICI2 catalyst TM (Eq. 11.278-11.279).
829
nl:
"~ 9m
c ~
(11.278)
Bu3SnCH2/
CHzSnau3
n
~
(1127g)
It was already mentioned in an earlier section that a type of monomer that has been used to carry a variety of metals into microphaseseparated materials is a chelating bisamido ligand, 2,3-trans-bis(tertbutylamidomethyl)norbom-5-ene (bTAN). On using Mo(=CHtBu)(=NAr)(OtBu)~ in THF, copolymers of the Sn(IV) complex, Sn(bTAN)CIz, with norbomene have been prepared by Schrock and coworkers, TM in which the ratio of norbomene to Sn(bTAN)CI2 has been varied to give lamellae, cylinders, and spheres of the Sn-containing derivative in polynorbomene z37 (Eq. 1 1.280). ~u n
9 m
[Mo]= ~
(11.280)
t
~u
Monomers that contain Sn(ll) and the bTAN ligand were found to be unstable toward decomposition to give metal, but analogous monomers in which trimethylsilyl groups replace the tert-butyl groups, Sn(bSAN), were stable in solution at room temperature for days. Copolymers of SnCoSAN) with methyltetracyclododecene have been prepared under the action of W(=CH'Bu)(=NAr)(OtBu)~, although the control of morphology has not been established z36'238(Eq. 1 1.281).
~l~~--N"siMO3 ~
n~'J"~
~SR
+m
lvvl
I
SiMe3 Me
(11281)
830 Block copolymers of (CTH9CH2CsI'I4)2Pb, Pb(CpN)2, with norbornene have been prepared by sequential addition of norbomene and lead-containing monomer to Mo(=CH'Bu)(=NArXO'Buh (At = 2,6-C6H3'Pr2), followed by quenching with benzaldehyde~39(Eq. 11.282).
n
Pb
(11.282)
+ m
Pb
Small particles of lead sulphide have been prepared by further treatment of block copolymer films wherein aggregates of poly[(CTHgCH2CsH4)2Pb] reside as microdomains distributed throughout the polynorbornene matrix. The interdomain spacing of 320-480 A, before and after H2S treatment, were determined by small-angle X-ray scattering (SAXS) and average cluster diameters of 20-40 A by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The PbS clusters in these copolymers were identified by X-ray fluorescence analysis performed on the STEM and by wide-angle X-ray powder diffraction. As the disadvantage of the above approach is the potential for the leadcontaining monomer, Pb(CpNh, to behave as a cross-linking agent, other lead-containing monomers have been used to prepare copolymers with a more controlled morphology. Block copolymer synthesis could be better controlled using Pb(CpS)Cp*, since although scrambling to give Pb(CpN)2 and PbCp*2 occurs, the equilibrium lies toward Pb(CpN)Cp* under the condition employed. To this end, block copolymers of Pb(CpS)Cp * with norbomene have been prepared in a living fashion, using the above molybdenum initiator Mo(=CHtBuX=NAr)(OtBu)2 (At = 2,6-C6H3-'Pr2)TM (Eq. 11.282a). n
+
p"
rn
~
(11.282a)
831 Microphase separation in static cast films of these block copolymers have been observed. For the same purpose, another lead-containing monomer, CpNPbOTf, has been copolymerized with methyltetracyclododecene (MTD) in a living fashion in the presence of Mo(=CHCMe~PhX=NAr)(O'Buh (At = 2,6-C6H3-'Prz)Z~(Eq. 11.283). n
9
[Mo]
(11.283)
Pb(CF3S03)
Pb(CF3S03)
The living copolymer was capped in a chain-transfer reaction by adding 1,3pentadiene to yield a polymer terminated with a methylene group and a vinylakylidene complex. Polydispersities for the MTD block of 1.02-1.11 have been obtained. Films of the block copolymers that were static cast from benzene contained lead in microphase-separated domains. Treatment of these films with hydrogen sulphide produced nanoclusters of PbS within the microdomains that were characterized by TEM and X-ray powder diffraction. By an alternate way, copolymers of Pb(bSAN) with methyltetracyclododecene have been prepared under the action of W(=CH'Bu)(=NAr)(O'Bu)2, although the control of morphology has not been established 238 (Eq. 11.284). .SiMe3 (11.284) I
SiMe3 Me
With the goal of making block copolymers that produce stable clusters which subsequently allow to interconvert reversibly between one type of cluster and another, Schrock and coworkers T M copolymerized a zinc-containing monomer, bTAN(ZnPh)z, with methyltetracyclododecene (MTD), using W(-~HrBu)(=NAr)(OrBu)z as the initiator (Eq. 11.285). (11.285) v
--,<,~N / I
tBu t
I
R
832 The reaction has been conducted in benzene by sequential addition of the monomers with MTD added first and bTAN(ZnPhh second. 236 Films of copolymer were exposed to hydrogen fluoride-pyridine (HF-Py) complex containing 70*,6 HF to produce ZnF2 clusters within the spherical microdomains. By treating the ZnF2 clusters with H2S at a high temperature (140~ for 12 hr, it was possible to synthesize ZnS clusters. Further treatment of the same film with HF-Py at room temperature resulted in the conversion of ZnS to ZnF2 clusters. Noteworthy, this approach has generated ZnS quantum clusters which are superior in quality (WAXS) to other techniques for their generation. To produce redox-active copolymers able to attach to surfaces, ferrocene-containing block copolymers were prepared from a 5-ferrocenyl6-carbomethoxynorbomene (Mr), norbomene (M2), and with or without 5(triethoxysilyl)norbornene (M3), in the presence of the molybdenum initiator Mo(=CHtBuX=NArXO'Bu)2 (Ar = 2,6-C6H3-'Pr2)227(Eq. 11.286).
. ~J~o
9m Fo
9p
(11.2B8)
i { o e t ~- - ~ "
Fo
I
OMo
To observe the influence on the binding propensity to surfaces, the positions of the ferr~.ene-containing block [M l]. and the block of norbomene [M2]min relation to the Si(OEt)3 block [M3]pin triblocks were reversed. Pretreated Pt electrodes with these triblock copolymers, examined by cyclic voltarnetry, showed no significant differences in the electrochemical behavior, this result suggesting that the polymer conformation at the surface is flexible enough for all ferrocene sites to communicate with the electrode. On the other hand, pretreated Pt electrodes with diblocks of 5-ferrocenyl-6w,arbomethoxynorbomene and norbomene, l:mly(M2)/poly(Mt), showed no surface-bound active material by cyclic voltametry for these polymers which did not contain Si(OEt)~ groups. Palladium nanoclusters within polymer films that display a spherical morphology have been prepared by blending a palladium-containing diblock copolymer [Pd(Ca,~XPA)].[MTD]= (CpN = endo-2(cyclopentadienylmethyl)norborn-5-ene, PA = TI3-1-phenylallyl, MTD = methyltetracyclododecene) with polyMTD homopolymer. The diblock
833 copolymer has been prepared by living ring-opening metathesis copolymerization of Pd(Cps)(PA) with methyltetracyelododecene in the presence of molybdenum initiator Mo(=CHCMe2PhX=NAr)(O'Buh (At = 2,6-C6H3-'Pr2)z4z (Eq. 11.287).
n
9
(11 ~.s7)
m
Ph
Palladium clusters have been generated by treating the copolymer film with hydrogen (5 bar) at mild elevated temperatures (90~ for three days. The cluster sizes and size distributions varied with the size of the metalcontaining spherical microdomains. Related platinum clusters have been manufactured from platinum-containing diblock copolymers; these diblock copolymers have been p,repared by living ring-opening metathesis copolymerization of Pt(Cp")(Me~) with methyltetracyclododeeene in the presence of the molybdenum initiator Mo(=CHCMezPhX=NAr)(OtBu~h (Ar = 2,6-C6H3-'Prz)z43 (Eq. 11.288).
n
+m
----~
Interesting monodisperse diblock copolymers of norbornene with a "Durham" polyacetylene precursor, 7,8-bis(trifluoromethyl)tricyclo [4.2.2.02"5]deca-3,7,9-triene, have been prepared by living ring-opening metathesis copolymerization in the presence of the well-defined Mo or W carbene initiators, Mo(=CHCMe2PhX=NAr)(O'Buh or W(=CHtBuX=NArXO'Bu)z(Ar=-2,6-C6H3-'Prz) ~gzz~ (Eq. 11.289). n
+ m
"=
(11.289)
CF3 F3C
CF3
834
These diblocks contain one sequence of polynorbomene and one sequence of a precursor polymer which converts to polyacetylene via a retro-DielsAlder reaction with elimination of o-di(trifluoromethyl)benzene, upon heating (Eq. 11.290). A
F3C
CF 3
(11.290) n F3C
CF 3
Though monodisperse copolymers can be obtained by this method, as the polymer of the precursor monomer 7,8-bis(trifluoromethyl)tricyclo [4.2.2.02"S]dec~-3,7,9-triene is thermally unstable and converts substantially to polyacetylene over 24 hr at room temperature, ca.qing uniform films from these copolymers becomes difficult. Sequential ring-opening metathesis polymerization of either norbomene or methyltetracyclododecene (MTD) and 7, 8bis(tdfluoromethyl)tdcyclo [4.2.2.02"5]deca-3,7,9-tdene (TCDT) with Mo(=CWBu)(=NAr)(OtBu)~ (At = 2,6-C~H3-'Pr2) followed by linking termination with a conjugated dialdehyde, hexadienedial or octatdenedial, allowed Schrock and coworkers TM to prepare highly soluble A-B-A triblock copolymers containing a precursor to "Durham" polyacetylene as the central block. Thus, a series of precursor copolymers of norbomene and MTD that contained from 10 to 200 equiv of TCDT have been synthesized by this method ~45'2~ (Eq. 11.29 l-11.292).
(11291)
835
The precursor triblock copolymers from both norbornene and MTD with TCDT have been spin coated into thin films, and the polyacetylene precursor blocks in the copolymer films have been converted into "Durham" polyacetylene (Eq. 11.293-11.294).
---~~
(
1
1
~
2
9
3
)
c~3
(11~H)
1C0'
0:3
In some cases, the converted copolymers have been thermally isomerized. The products have been characterized with GPC and UV/visible spectroscopy. The nonlinear optical properties have been analyzed with third harmonic generation (THG) and degenerate four-wave mixing (DFWM) techniques. It was observed that g(3)increased with increasing equivalents of TCDT. In all cases, the copolymers made with norbornene had larger X(3) values than the copolymers made with MTD. The living polymerization of 9-(tert-butyldimethylsilyloxy[2.2] paracyclophan-2-ene by Mo(=CHCMe2Ph)(=NArXOCMe(CF3h (Ar = 2,6CsH3-'Prz) allowed well-behaved monodisperse block copolymers with norbornene (NBE) to be prepared 247(Eq. 11.295).
+m
(11.295)
This block copolymer has been converted to poly(para-phenylene vinylene)-polynorbomene (PPV-PNBE) first by treatment with Bu2qF and then with HCI (g) at 25~ (Eq. 11.296).
836 1 .Bu4NF lib
2.HCI
(11.2~)
Noteworthy, this new approach is an efficient way to synthesize block copolymers containing extended PPV fragments.
11.4.4. Synthesis of Star Copolymers The development of well-defined transition-metal catalysts for controlled living ring-opening polymerization of mono- and polycyclic olefins influenced considerably the production of particular macromolecular structures and architectures such as stereoregular functionalized polymers, block copolymers, graR and star copolymers, etc. A first strategy applied by Bazan and Schrock z48 to prepare star-shaped copolymers starts from living ring-opening metathesis polymerization of norbornene and its derivatives initiated with the metal-carbene complexes, M(-CHR)(=NAr)(O'Bu)z (M = W or Mo) ( A t - 2,6-CsH3-~Prz), and employs the norbornadiene dimer, exo, trans, exo-pentacyclo[8.2.1.14'7.02"9.03"8]tetradeca-5,1 l-diene, as a crosslinking reagent. This reagent contains two reactive norbornene-like double bonds, its rigid backbone prevents metathesis of both olefins by the same metal centre and it is readily available by the catalytic dimerization of norbornadiene. By a similar living process, functionalized star polymers and copolymers have been prepared by Bazan and Schrock z4s from 2,3dicarbomethoxynorbornadiene and the same cross-linking agent, exo, trans, exo-pentacyclo[8.2.1.14"7.02"9.0xs]tetradeca-5,1 l-diene, in the presence of the catalyst Mo(=CHR)(=NArXO'Buh. Thus, addition of 25 equiv of 2,3-dicarbomethoxynorbornadiene to the Mo catalyst completely consumed the catalyst and produced oligomers with a narrow molecular weight distribution (PDI = 1.08). Reaction of 6 equiv of the cross-linking agent with these living 25-mers resulted in the formation of the star polymer. Unexpectedly, some 25-mer unreacted oligomers remained (1020%). This result contrasted with living polynorbornene, where only 3 equiv of cross-linking agent were needed for complete consumption of the linear precursor, and was attributed to the lower reactivity of the corresponding metallacarbene propagating species relative to that from norbornene.
837 In order to circumvent it, 25 equiv of norbomene was added to the living poly(2,3-dicarbomethoxynorbomadiene) followed by 6 equiv of crosslinking agent. This approach allowed soluble star copolymers of norbomene and 2,3--dic~omethoxynorbomadiene to be prepared (Eq. 11.297).
cX~t
:-
(11.297)
The final structure of this star copolymer was interesting since it contained a more polar "shell" around a less polar interior. At the same time, this example illustrated the importance of reactivity of the living alkylidene in determining the monomer conversion. In case that the propagating alkylidene is not reactive enough, then the initiator remains and homopolymer is found in the final product. A cross-linking agent that has a low rate of propagation would be ideal but that would mean that it also would not efficiently cross-link living oligomers. Using the same cross-linking agent, star polymers and copolymers were further prepared by Bazan and S c h r o c k 24s from 5-cyanonorbomene and bis(trifluoromethyl)norbomadiene. In one experiment, the polymerization of 50 equiv of 5-cyanonorbomene followed by quenching with excess p-(trimethylsilyl)benzaldehyde yielded a polymer with a polydispersity of 1.06. Reaction of this living 50-mer with 5 equiv of exo, trans, exo-pentacyr followed by termination with p-(trimethylsilyl)benzaldehyde, resulted in quantitative formation of a star polymer. The structure of the star polymer thus prepared was evaluated by proton ~ spectroscopy. When the above living poly(5-cyanonorbomene) star was treated with 50 equiv of 2,3bis(trifluoromethyl)norbomadiene then quenched with (trimethylsilyl)benzaldehyde, a new "heterostar" block copolymer poly(5cyanonorbomene)/poly(2,3-bis(trifluoromethyl)norbomadiene) has been produced. A similar heterostar copolymer could be also obtained starting from the parent copolymer 5-cyanonorbomene/2,3bis(trifluoromethyl)norbomadiene by the reaction with
838
exo, trans, exo-pentacyclo[ 8.2.1.14'7.02"9.03'8]tetradeca_5,1 l-diene 11.298).
~m~_ CF3 9 R CN
F3~
~:3
C~t
~
F3~
(Eq.
0:3
CF3
(11,29e)
=
§
R
m 0:3
Gel permeation chromatography showed that the molecular weight has increased from that of the original poly(5-cyanonorbomene) star, and the molecular weight distribution was monomodal. Integration of the allylir proton resonances in the polymer backbone versus the total olefin resonance area in the :H M R spectrum of the final product indicated that the stoichiometry was that expected. This result was also confirmed by :3C NMR determinations. It is noteworthy that the synthesis of "heterostar" copolymers has not been previously reported using anionic polymerization systems, in part because of gelation of the reaction medium and possibly also in part because of the relatively low tolerance of the anionic catalysts for many common unsaturated polar functionalities. In another approach Schrock and coworkers 249 employed a new cross-linking agent, endo-cis-endo-hexacyclo[ 10.2.1.13,:0.15':.02"::.04'9] heptadeca-6,13-diene (HCHD), to prepare star homo- and copolymers by living ring-opening metathesis polymerization of norbomene and its derivatives in the presence of the appropriate ROMP initiators. This new cross-linking agent, HCHD, is also obtained in a relatively low yield from norbomadiene with two moles of cyclopentadiene but, in contrast to PCTD, requires no catalyst preparation and is easily purified. Several amphiphilic star copolymers have been produced by Schrock and coworkers z49 from norbomene, 5,6-bis(methoxymethyl)norbomene and 5,6bis(trimethylsilylcarboxy)norbomene using as a cross-linking agent endocis-endo-hexacyclo [ 10.2.1.13.:0.15'8.02'::.04'9] heptadeca-6,13-diene (Eq. 11.299-11.300).
839
4n
~4m
~o]
D-
(11.299)
M,O
OM.
04~
P.~s4q q,sJ~s
9
Q, ~
-
_
(11.300)
_
IMH
~s8~o os~Mss
os~
For this purpose, 5,6-bis(trimethylsilyl~xy)norbomene was first added to the initiator, and after its consumption, norbomene or 5,6bis(methoxymethyl)norbornene was added in order to make the hydrophilic block. Further on, these living diblocks were treated with 5-6 equiv of cross-linking agent to form the star copolymer (Eq. 11.301).
9
v
01:3Ol)
In order to convert the trimethylsilyl ester groups to car~xylic acids, the copolymers thus prepared were treated with water. The data
840 obtained for four different amphiphilic star copolymers, two that contain polynorbomene as the hydrophobic block and two that contain poly(5,6bis(methoxymethyl)norbomene) as the hydrophobic block are presented in Table 11.27. Table 11.27 Hydrophobic star polymers of norbomene(Mt), 5,6-bis(methoxymethyl)norbomene (Mz) and 5,6-bis(trimethylsilyl-carboxy) norbomene (M3) prepared using endo-cisendo-hexacyclo- [ 10.2.1.13.10.I s's.0z'11.04~Jheptadeca-6,13Miene' Star copolymer
Mb
Hydrophobid
PDI of star
core, %
Poly(M0/Poly(M3) Poly(Mi)/Poly(M3) Poly(M2)/PolyOVI3) Poly(M2)Poly(M3)
7000/10000 2000/23000 2000123000 2000/25000
43 17 17 14
1.41 2.63 1.76 1.86
'Data from referenceZ49;bAll molecular weights are in units of grams )er mole and are based on stoichiomotry; ~Including the tetrafunctional cross-linking agent as well as the hydrophobic block. It is interesting to note that GPC data of these star block copolymers indicated some linear and slightly branched chains present that are not coupled to the star, similar to the observations for other star systems. This phenomenon was least prominent in star poly(M~)/poly(M3), which contained 43% of the hydrophobic portion and most prominent in stars poly(Mt)/poly(M3) and poly(M2)/poly(M3) containing 14-17% of the hydrophobic portion. The existence of these uncoupled chains was assigned to a resistance to linking that could arise from two sources (i) a steric hindrance caused by the increased segment density at the core of the star, preventing the living ends from adding onto any remaining active site, and (ii) a diffusion barrier created by the outer hydrophilic shell of the alreadyformed stars. In the last case, the living diblock chain ends, which are attached to the hydrophobic section of the molecule, might prefer to remain in solution rather than diffuse through the hydrophilic shell to find the core. For instance, the star of polynorbornene (poly(Mt)) contained a small amount of uncoupled chains. Since this star was made from homopolymer branches, there was no hydrophilic shell to create a diffusion barrier, and
841 thus the relatively small resistance to coupling was most likely caused by steric hindrance. The star poly(M~)/poly(M3) contained a significant amount of uncoupled chains. This star was made from branches of molecular weights similar to those of star poly(M~) and should therefore encounter similar steric hindrance, however, this star actually contained diblock copolymer branches and therefore had a hydrophilic shell that could create a diffusion barrier and thus would increase the resistance to coupling. The solubility of amphiphilic star polymers is relevant to illustrate their behavior as model micelles in aqueous solution. As Table 11.28 shows, only star poly(M3), containing just the cross-linking agent as its hydrophobic portion at 7 wt.%, was completely water soluble. On the other hand, the star copolymer poly(M2)/poly(M3), even as its potassium salt, was not completely solubilized (Table 11.28). Table 11.28 Solubility of amphiphilic star copolymers in different solventsLb
Star
Poly(M3) PolytMI)/ Poly(M3) Poly(M,)/ Poly(M3)
H20
MeOH
THF
MeCOMe
M~
H20:THF 50:50
pa
'Data from n~erence29;bi=msolul~le,p=partially soluble, s=soluble; ~Pol3nner swellod a small amom~ in this solvent; dPol)nner swelled significantly in this solvent. On the basis of the data thus recorded, it was concluded that for these systems it was necessm~ to maintain the hydrophobic portion of the amphiphilic star copolymers to percentages below a value in the range of 7-17% in order to maintain water solubility. In view of this goal two competing factors were evident" more uniform, monodispersr stars could be made by lowering the percentage of the hydrophilic portion, but water solubility requires increasing the hydrophilic portion. To obtain high molecular weight water-soluble stars free of uncoupled linear chains, the monomers or aspects of the polymerization process needed to be changed.
842
11.4.5. Synthesis of Graft Copolymers When unsaturation occurs in the side chain of the unsaturated polymer, e.g. 1,2-polybutadiene, 1,2-polyisoprene, butadiene-styrene copolymers or EPDM terpolymers, graft copolymers bearing polyalkenamers in the side chain will arise by cross-metathesis polymerization with cycloolefins in the presence of ring-opening metathesis catalysts. Thus, the reaction of 1,2-polybutadiene with cyclobutene under the action of WCIdEtzAICI or WCI6/EtAICIz catalysts will produce graft copolymers derived from 1,2-polybutadiene, beating side arms of polybutenamer or 1,4-polybutadiene (Eq. 11.302).
n[F-~
+ R
=
R
(11.302) R
Instead of cyclobutene, other monomers such as cyclopentene, cyclooetene, 1,5-eyclooctadiene or norbornene derivatives can be used along with 1,2polybutadiene, 1,2-polyisoprene or EPDM terpolymers to produce, under the action of WCl6-based catalysts, grafted copolymers having polypentenamer, polyoctenamer, polyoctadienamer and polynorbomenes as the side chains. Cyclopentene has been reacted with 1,2-polybutadiene in the presence of WCl6/epichlorohydrin~tzAICl as a catalyst2~~ (Eq. 11.303)
R_ R
[Wl L
R
~
(11.303)
as well as with butadiene-styrene copolymers or ethylene-propylenedicyclopentadiene terpolymers. Polypentenamer has also been galled onto 1,2-polybutadiene to produce similar copolymers. ~2 According to Medema and coworkers, 2~3 cyclooctene was galled onto the unsaturated side group of the natural rubber by the action of the ReCI~JEhAI catalyst (Eq. 11.304).
843
= R
(11.304)
Graft copolymers have also been obtained from 1,5-cyclooctadiene with 1,2-1~lybutadiene TM (Fxt. 11.305)
n
,
R
=9
.~
(11.305)
or with ethylene-propylene-diene terpolymers. 2s5 On using the same technique, cyclododecene produced valuable graft and block copolymers with 1,2-polybutadiene and EPDM terpolymers. ~4'256 Norbornene and various norbornene derivatives (X = CN, COOMe, CI) can be grafted and copolymerized with 1,2-polybutadiene 2s7 (Eq. 11.306)
n
+
R
R
"=
~
(11.306)
R
or with isoprene-isobutene copolymers, polychloroprene and polypentenamer. ~s Novel comb graft copolymers with a high density of grafts have been reported by Feast and coworkers 259 by polymerization of bicyclo[2.2.1] hept-2-ene-2,3-trans-bis(polystyrylcarboxylate) macromonomers via living ring-opening metathesis, using the weU-defined Schrock initiators, namely Mo(=CHR)(=NAr)(OR'h, where R is (CH3)3Cor C6HsC(CH3)2-, Ar is 2,6-diisopropylphenyl and R' is (CH3)3C- group (Eq. 11.307).
844
,.o,
(11.307) "
Thus, on coupling living anionic polymerization with living ring-opening metathesis polymerization, first well-characterized macromonomers of the above mentioned structure were prepared and then comb-graft copolymers with polystyryl gratis, having average degree of polymerization of 4, 7, and 9, were produced from these macromonomers, in the presence of molybdenum-based carbene complex. The polymerization reactions were carried out in benzene or a tolueneffHF mixture (80/20, v/v) as solvent. The graft copolymers obtained in this way exhibited single mode molecular weight distributions and narrow polydispersities. It is noteworthy that further attempts by Feast and coworkers to prepare eopolymers with longer polystyryl gratis (e.g., DPs 14, 24 and 46) gave products which exhibited bimodal molecular weight distributions in which one component of the distribution displayed the same retention time as that of the macromonomer. This observation was rationalized by these authors in terms of steric inhibition of the ring-opening metathesis polymerization of such macromonomers with increased lengths of the polystyrene block. 11.4.6. Copolymers from Macromonomers A series of graft copolymers of cyclooctene with o-norbomenyl macromonomers bearing polystyryl side chains connected through ether, carbonyl or carboxy groups have been prepared by Fontanine and coworkers 26~ using both classical WCIjPI~Sn and well-defined Schrock catalyst Mo(=CH'Bu)(=NAr)(OCCH3(CF3h)2 (Eq. 11.308-11.311).
n0
, m~
~JL~
CH-z~ "- [Wl ~ Sn]
(11.308)
845
4~~~~~C~ c
n0 .
(11~308)
[W~n] [uo]
=
(11.310)
0
no.
~n] ~ ~ ~ ~ ~ C coo(cH~ ~]
~C~y(11.311)
In the presence of transfer agents, e.g., l-hexene, the incorporation of the macromonomer in the growing polyoctenamer chain was greatly improved. Prolonged reaction time led to still better incorporation of the macromonomer which amounted to 60~ in the copolymer The classical catalyst was stable only for a limited time and subsequent introduction of additional catalyst was necessary. The use of the living polymerization system allowed prolonged reaction time due to a higher stability and a better tolerance of the catalyst toward functional groups of the macromonomer. Interesting comb-graR copolymers with polystyryl in the side arm of a polynorbomene unit prepared Norton and McCarthy~ by ring-opening copolymerization of a mixture of a bicyclo[2.2, l]hept-5-ene-2polystyrylcarboxylate macromonomer, norbomene and 1-octene, in the presence of WCIc/Me4Sn as catalyst (Eq. 11.312).
n .m
. R
V~ls/Me4Sn
(11.312)
846 The acyclic olefin has been used as a chain transfer agent to limit the polymer molecular weight and minimize the tendency to gelation often observed in polymerization of norbornene with such catalysts. The grafted copolymer thus obtained carried one polystyryl graft on each grafted cyclopentane unit and the grafted tings were statistically distributed along the polynorbornene backbone. Bis(trifluoromethyl)norbomadiene has been copolymerized in a living fashion with bicyclo[2.2.1 ]hept-2-ene-2,3-transbis(polystyrylcarboxylate) macromonomers (R = COOCH(CH3)2), using the molybdenum alkylidene initiator Mo(=CH'BuX=NAr)(O'Bu)2 ~2 (Eq. 11.312a).
n~ ~ "cF3
The block copolymers obtained exhibited single mode molecular weight distribution and narrow polydispersities in GPC. Interestingly, the incorporation of the fluorinated monomer in the chain eliminated the steric hindrance effects and hence the unreacted macromonomer in the mixture participated in further polymerization, resulting in the formation of tapered block copolymers.
11.4.7. Copolymers from Cycloolefins and Unsaturated Polymers A versatile route to manufacture block copolymers from cycloolefins consists of ring-opening metathesis polymerization of these monomers in the presence of unsaturated polymers containing ~ n carbon double bonds in the chain. In this process, the unsaturated polymer will first provide, under the action of metathesis catalysts, polymer-being catalytic species able to initiate and propagate the cycloolefin polymerization by further insertion of the monomer. In this way, diblock copolymers containing the initial unsaturated polymer and the newly grown polyalkenamer will be obtained. The products thus prepared have superior mechanical properties as compared to the random copolymers or blends of homopolymers of the same overall composition.
847 Starting from 1,4-polybutadiene, several block copolymers have been synthesized by the reaction with cycloolefins in the presence of metathesis catalytic systems. Thus, reaction of 1,4-polybutadiene with cyclopentene under the influence of WCl6-based catalysts gave the diblock copolymer polybutadiene-polypentenamer 2s4"263(Eq. 11.313)
nO
+ t - - - - - - - ~ . ~ --~..~. ~ ~ - - - - - . ~
(11.313)
whereas reaction of 1,4-polybutadiene with cyclooctene gave the diblock copolymer polybutadiene-polyoctename~ 5 (Eq. 11.313a).
n[~
9=[.,--
~ ~
--"~m (11.313a)
~ = ~
Noteworthy, 1,5-cyclooctadiene afforded a particular diblock copolymer, 1,4-polybutadiene-polyoctadienamer, consisting actually of two blocks of 1,4-polybutadienes TM (Eq. 11.314).
nO
+~
~'~m
~
~
~
-----'I'm(11.314)
Likewise, interesting diblock copolymers were prepared from 1,4polybutadiene and cyclododecene 2s6(Eq. 1 1.315) nL
l
§
(11.315)
as well as from 1,4-polybutadiene and substituted norbomenes presence of tungsten-based metathesis catalysts (Eq. 11.316).
257 258
'
in the
---'=~m (11.316)
R where R is CN, COOMe, CI.
848 It is quite remarkable that in order to attain high performance in chemical and physical-mechanical characteristics, numerous diblock copolymers have been prepared by ring-opening polymerization of several norbomene derivatives in the presence of polyisoprene, polychloroprene, polypentenamer and butyl rubber. 258 These new block copolymers containing fragments of both polymers, i.e., the initial rubber associated with the newly formed derivatized polynorbomene chain, will combine in the final product the excellent properties of the former polymer with those of the latter (Eq. 1 1.317-320). R
~R
n
+ =[="-------I=~m --D,. ==[=~~~T/J=r~ R
Cl + =~
J'~m ~
"["~~t,/~
J==]=m(11.317) Cl
J-']'m (11.318)
R ~~/R
n
§ "{'='x"~'~=m ~
=~=~,]/~m
--~
(11.319)
R (11.320)
R On using this synthetic procedure, triblock copolymers have also been prepared by ring-opening polymerization of cycloolefins in the presence of styrene-butadiene copolymers. In this way, copolymerization of cyclopentene with styrene-butadiene rubber, under the action of WCI6based metathesis catalysts, produced terpolymers consisting of polystyrene-polybutadiene fragments in conjunction with polypentenamer units in the chain263 (Eq. I 1.321).
849
(11.321)
Similarly, polymerization of norbomene derivatives in the presence of styrene-butadiene rubber, under the influence of ring-opening metathesis catalysts, gave rise to triblock copolymers containing styrene-butadiene copolymer linked to derivatized polynorbornene ~'z~ (Eq. 11.322). n
/~
R + (11.322)
\
R
Again, the high quality of the styrene-butadiene rubber will be associated by this approach with the high performance of the functionalized polynorbomene. 11.4.8. Copolymers from Unsaturated Polymers Cross-metathesis between polyalkenamers and unsaturated polymers contmning c~on-carbon double bonds affords another efficient method to prepare block copolymers from cycloolefins. By this procedure, for example, polydodecenamer will react with 1,4-cis-polybutadiene under the influence of WCI6/EhAI2CI3to produce a diblock copolymer consisting of segments of polydodecenamer linked to 1,4-cis-polybutadiene254'256 (Eq. 11.323). 2_
9
~=x__/-+ m
~-
(11.323)
850 It was shown that by careful control of the reaction conditions, the amount of simultaneous degradation of polybutadiene has been diminished to minimum proportions. Interestingly, the technological characteristics of these block copolymers were comparable to those of blends from the corresponding homopolymers. Block copolymers were obtained by Scott and Calderon ~-67 by the same procedure from polyoctenamer and polydodecenamer or other unsaturated rubbers. Polybutadiene, butadiene-styrene copolymers and ethylenepropylene-diene terpolymers have been reacted among themselves or with polypentenamer and polyoctenamer leading to block copolymers with interesting elastomeric properties. Thus, Pampus and coworkers 268 synthesized several diblock copolymers by cometathesis reaction of polybutadiene with butadiene-styrene rubbers or polypentenamer.
11.4.9. Copolymers from Cycloolefins and Acetylenes Synthesis of block copolymers containing varying polyacetylene segments has become a challenging research area due to the particular electrical properties of these materials and their easy incorporation into the special electrical devices in modern technologies. At present, two of the most efficient techniques employ "living" ring-opening metathesis catalysts for their manufacture. The first one makes use of the direct copolymerization reaction of acetylene with other cycloolefins to form diblock and triblock copolymers with polyacetylene~s9 while the second one, known also as "Durham route", consists of production of block copolymers containing one precursor polymer which converts subsequently to polyacetylene via a retro Diels-Alder reaction. 27~ In the first process, acetylene is polymerized in the presence of metallacarbene complex M(=CH~Bu)(=NArXO'Bu), where M = Mo or W, and then with norbomene under the action of the same catalyst to yield diblock and triblock copolymers, respectively TM (Eq. 11.324-11.325). n
+
m
m
~
~--
IMo],b'r
~
'=~
~
-..,n ft.
.lm'~
(11.324)
851 The polymers prepared by this proc~ure display a narrow molecular weight distribution. The products with high-trans content exhibit a greater insolubility and a pronounced tendency to cross-link, especially when the polyene is present as the center block in the triblock copolymers with polynorbomene. By this method, triblocks polynorbomene,/polyacetylene/ polynorbornene (50:x:50) were synthesized by Schrock and coworkers z~ by adding 50 equiv of norbornene to a mixture of Mo(=CH'Bu)(=NAr)(O'Bu)~ and quinuclidine, followed by x equiv of acetylene, 50 equiv of norbornene, and finally excess pivaldehyde. It is noteworthy that when up to 11 equiv of acetylene were used, gel permeation chromatography indicated a distribution of the triblocks with a low polydispersity and the expected molecular weight. However, when more than 11 equiv of acetylene were used, a bimodal distribution was obtained. The lower molecular weight was approximately the same as that resulted with 11 equiv of acetylene. The higher molecular weight polymer was at least twice the molecular weight of the first and thought to arise from cross-linking or aggregation of the individual chains in the triblocks. In addition, as the number of equivalents of acetylene used was increased, the percentage of the higher molecular weight polymer increased relative to the polymer with the expected molecular weight (Table 11.29). Table I 1.29 Polydispersity oftriblocks copolyn~rs prepared from norbomene (M~) and acetylene (M2) with Mo(=CH~u)(=NAr)(OtBuh in toluene~b MI"M2:MI, equiv
MW
MII
50:5:50 50:7:50 50:9:50 50: I 1:50 50:13:50 50:15:50 50:20:50 50:25:50
21220 17671 20904 21899 18709 79609 141493 214334
19826 16780 19938 20856 17506
23907 26106 31627
'Data from reference~n;~4o(=CH'BuX=NArXO'Buh c o n ~ o n 0.025 M
PDI
1.07 1.05 1.05 1.05 1.07 3.33 5.42 6.78
in toluene,
852 The analogous tungsten system, W(=CH'Bu)(=NAr)(O'Bu)2, was less well-behaved, as determined by analysis of similar 50-x-50 triblock copolymers. In this case, when greater than 9 equiv of acetylene were used, a trimodal distribution of molecular weights was obtained. The middle molecular weight product corresponded to the expected polymer; the highest molecular weight product corresponded to the cross-linked material described above. Formation of a polymer with a molecular weight approximately half that of the expected product suggested that the third block of polynorbomene did not form for a significant fraction of the chains; i.e., some chain termination took place during the acetylene polymerization step. By contrast, in the molybdenum system there was no evidence for an analogous chain termination. Phenylacetylene was found to readily copolymerize with norbomene and tetracyclododecene in the presence of tungsten-based catalysts, e.g. WCIdPh4Sn and W(CO)6-hv (CCh), to produce copolymers having phenylethylidene repeat units along with cyclopentylenevinylene or tricyclodecylenevinylene in the polymer chainz73 (Eq. 11.326-1 1.327).
~ n
+ m
~ , m
n
WCldPI~Sn W(CO)~CC~
111.326)
WCIs/PI~Sn W(CO~~4
(11.327)
Moreover, ring-substituted phenylacetylene has been reacted with norbomene in the presence of WCl6-based catalytic system to form copolymers containing the corresponding ring-substituted phenylethylidene repeat units along with cyclopentylenevinylene 274"275(Eq. 11.328-11.330). n
.
m R
.
-.~
111.328)
R
853
n 'mC
[WChl
(11.329)
9- - -
R
R
(11.330)
----
R
R R
A fluorine substituted phenylacetylene, o,m-tetrafluoro-p-nbutylphenylacetylene, has been readily copolymcfized with norbornene in the presence of WCl+-based catalysts to produce fluorinated copolymers with the fluorine atoms in the aromatic ringzT+(Eq. 11.331). E
F
+ mnBu
> F
(11.331)
,
nBu
Alternatively, l-chloro-l-octyne and l-cldorophenylacetylene can copolymerize with norbomene under the influence of WCIJ'Bu4Sn and MoCI~'Bu4Sn to form unimodal copolymers having the chlorine atoms
attached directly to the polymer chain2/6(Eq. 11.332-] 1.333). ~
n
+ m H13Cs~CI
+m
~
WCle/nSu4Sn
MoCIraJnBuaSn~
C6H13
WCls/nBu4Sn CI M~ ~ _
(11.332)
(11.3,33) CI
854
Uniform films of these copolymers were cast from toluene solution, indicating that the two monomer units were present in the same polymer chain and the products were not mixtures of the corresponding homopolymers.
11.4.10. Copolymers from Heterocyclic Olefins The discovery of well-defined m e t a l - ~ e n e initiators, tolerant toward functionalities, allowed synthesis of block copolymers from cycloolefins and heterocyclic olefins, bearing e.g., oxygen or nitrogen atoms in the molecule. 27z278The synthesis of such copolymers is of actual interest because the heteroatoms incorporated into the polymer chain impart new physical and chemical properties to the products. The first example of such copolymers is that prepared from 1,5-cyclooctadiene and 4,7-dihydro-l,3dioxepin with the ruthenium carbene initiator (Cy3P)2CI2Ru=CHR279 (R = Ph or CHPh2) (Eq. 11.334).
n
9
o~o
2m ~
IRu]
~
~-0/-0~~~~.~-.3~0..0.~
(11.334)
The product can be degraded at the acetal groups in acidic media to 1,4hydroxytelechelic polybutadiene. Similarly, 2-phenyl4,7-dihydroxy-l,3dioxepin reacts with 1,5-cyclooctadiene under the influence of the above ruthenium initiator to from the phenyl-substituted copolymer28~ (Eq. 11.335). n
O
Ph
O~k'O [Ru] Ph + 2m ~ ) ---~ ~ O - J " o ~ O , u
Ph
(11.335)
This product can be also converted to 1,4-hydroxytelechelic polybutadiene by degradation under different acidic conditions. Block copolymers of 5,6-dimethoxymethylnorbomene with 7oxanorbomene-2,3-dicarboxylic acid N-methyl imide have been prepared in a living fashion, by subsequent monomer addition, using the monometallic ruthenium carbene initiator (Cy3P)~CI2Ru-CHPh, in aqueous mediaTM (Eq. 11.336).
855
n
,m
O
O
N-Me ~
O
(11.336)
I
Me
Under these conditions, M. increased from 25200 for the homopolymer of' imide monomer to ]45300 for the block copol~er after the addition of' 5,6~imethoxymethylnorbomene. The polydispersity increased from 1.06 to 1.32. Besides, triblock copolymers of 5,6-dimethyl-tertbutylsiloxymethylnorbomene and 7-oxanorbornene-2,3-dic~oxylic acid Nmethyl imide have been obtained by the above technique, using the bimetallic ruthenium initiator (R3PhCIzRu(=CH-p-Cd-hCH=)RuCIz(PR3h, R = Cy (cyclohexyl) or Cyp (cyclopentyl)m (Eq. 11. 337).
OSIIBuMe2+m ~P',,J,~OSItB~ 2
N-Me ~
O
(11.337)
I
MezSItButBuSIMe2 The resulting block copolymers had high molecular weights and polydispersities ranging from 1.26 to 1.28. Of a great interest, synthesis of water soluble block copolymers derived from norbomeneand 7-oxanorbomene-2,3-dicarboxylic Nsubstituted imides has been achieved with water soluble ruthenium alkylidene complexes (Cy2(CH2CH2N(Meh +CI'hCI2Ru=CHPh and (Cy~Mc2Pipcridinium+Cl'hCl2Ru=CHPh in acidic medium, in the absence of suffactants or organic solvents2~ (Eq. I 1.338). 0
n ~ N _ +RO
0
0
m~N-Ro
[Ru_~]~
(11.338) R I
R I
where g is CHzCHzN(Meh'CI group. By sequential monomer addition, quantitative conversions of the two monomers have been attained. GPC analysis indicated a symmetric, monomodal peak and polydispersities as low as 1.3.
856 To modify the physical properties and the morphologies of such polymers, ABA triblock copolymers from 7-oxanorbomene-2,3dicarboxylic acid N-alkyl imides having different alkyl groups have been also prepared using the bimetallic ruthenium initiator (R3P)2CI2Ru(=CH-pC6FhCH=)RuCI2(PR3)2, R = Cy (cyclohexyl) or Cyp (cyclopentyl). In one example, 7-oxanorbomene-2,3-dicarboxylic acid N-oetyl imide has been reacted with 7-oxanorbomene-2,3-dicarboxylic acid N-methyl imide in the presence of the above bimetallic ruthenium initiator to give block copolymers having low polydispersities (the PDIs varied from 1.10 to 1.11)2s2 (Eq. 11.339). 0
0
0
0
I
Oct
I
Me
Interestingly, while RuCI3 and K2RuCI5 exhibited a low activity in the copolymerization reaction of 7-oxanorbomene-2,3-dicarboxilic anhydride with 2,3-dicarbomethoxy-7-oxanorbomadiene, an equimolar mixture of the two initiators in methanol/water was able to initiate at 55~ the copolymerization of the two monomers more readily and produced copolymers in relatively high yields (40%) TM (Eq. 11.340).
O + m O
~:~o O
=
(11.340)
T - ~"C HOOH
MeO C:I~
Hydrolysis of the anhydride group, during the polymerization reaction, led directly to a copolymer with both carboxylir acid and ester functionalities. Microstructure analysis by ~3C NMR indicated the copolymer composition to be 50 50 for each monomer units, with the cis form predominant for the acidic functionality and the trans form predominant for the ester functionality. The DSC of the copolymer showed two major extremes close to each other, one at 370~ and the other at 415~ Analysis, after heating the polymers above the exotherm temperature, showed that the products were degraded or cross-linked as indicated by their insolubility in common
857 solvents. Of practical interest, the acidic and ester functionalities of these copolymers would lend itself to be both blendable and selectively extractable with petroleum-based acrylate polymers.
11.4.11. Copolymers by Different Polymerization Mechanisms By combining various polymerization mechanisms such as anionic, cationic, coordination, condensation and group transfer polymerization with ring-opening metathesis polymerization, new block copolymers can be prepared from cycloolefins. This challenging technique has been applied to produce speciality copolymers with unprecedented architectures and remarkable properties. One interesting procedure starts from anionic polymerization of styrene initiated by n-butyllithium to combine then this process with ringopening metathesis polymerization of cyclopentene induced by the intermediacy of a styryltungsten catalyst. 2s5 Thus, in a first step, a living polystyrene is prepared by polymerizing styrene with n-butyUithium as a catalyst, the polystyryllithium active species is then treated with WCI6 to form polystyryltungsten chlorides. In a second step, cyclopentene reacted with the thus formed polystyryltungsten system undergoes ring-opening metathesis polymerization to produce a diblock copolymer consisting of polystyrene and polypentenamer segments (Eq. 11.341).
(11.341)
If the living titanocene-carbene chain carrier, generated in norbornene ring-opening polymerization with titanocene initiators, is converted into titanocene alkoxide complex via alcohol treatment, a new titanium Ziegler-Natta catalyst is obtained, having a saturated titanium-alkyl bond, able to initiate olefin polymerization. When ethylene is added to this complex, a diblock copolymer of norbornene with ethylene is obtained by changing the mechanism from ROMP to Ziegler-Natta polymerization m (Eq. 11.342).
~
lCl~'l'i]
~
m C,21~ OR
858 Another convenient procedure for the synthesis of block tripolymers links condensation polymerization of aromatic diols with living polymerization of norbornene to produce aromatic polyethers into polynorbornene matrix. According to a process elaborated by Risse et al., 287 in a first step, aromatic polyethers having carbonyl containing end groups are prepared from aromatic diols by polycondensation reaction under the action of an appropriate conventional catalyst and, in a second step, living polynorbornene is attached at the both ends of the aromatic polyether by a normal Wittig reaction of two equivalents of titanacycleended polynorbomene with the existing carbonyl groups of the preformed aromatic polyether to form AB A-triblock copolymers polynorbomene/poly(phenylene ether)/polynorbornene. (Eq. 11.343).
(11.343)
The new block tripolymer thus produced possesses totally different properties as compared to the corresponding homopolymers, polynorbornene and poly(phenylene ether). When instead of titanacycle-ended polynorbornene, a titanacycleended poly(exo-dicyclopentadiene) was employed in the above Wittig reaction with the carbonyl groups of the aromatic polyether, then ABAtriblock copolymers poly(exo-dicyclopentadiene)lpoly(phenylene ether)/poly(exo-dicyclopentadiene) could be prepared (Eq. 11.344).
859
+ 2CP2
-R
(11.344)
1
An efficient way to prepare block copolymers combines ringopening metathesis polymerization with group transfer polymerization technique. Such a procedure has been applied successfully by Risse and Grubbs 2ss to manufacture block copolymers consisting of polynorbornene or poly(dicyclopentadiene) linked to vinyl polya~te. In this process, polynorbornene with one aldehyde end group is first synthesized by living ring-opening metathesis polymerization of norbornene and subsequent reaction of the polyalkenamer with terephthalaldehyde. The aldehyde end group served further as an initiator for allyl silyl aldol condensation polymerization of tert-butyldimethylsilyl vinyl ether to produce diblock polynorbomene-poly(silyl vinyl ether) copolymer with narrow molecular weight distribution (Eq. 11.345).
[CP2Ti] ZnCI2 /CH2=CHOSiR 3
(11.345)
SiR3 SiR3 SiR3
\__/
Lv
v
j~..- "H
Further cleavage of the silyl groups led to hydrophobic-hydrophilic block eopolymer having poly(vinyl alcohol) as the second segment.(Eq. 11.345a).
860 SiR3 SiR 3 SiR3 I I
I 1.NaBH4 2.Bu4NF
(11.345a)
These block copolymers could potentially be applied as emulsifiers, flocculants, wetting agents, foam stabilizers and as polymeric dispersants for the stabilization of polymer blends. By esterification of the alcohol groups from poly(vinyl alcohol), diblock copolymers consisting of polynorbomene linked to poly(vinyl acetate) will be produced (Eq. 11.345b).
(11.a45b)
The phase behavior of norbornene/(tert-butyldimethylsilyl vinyl ether) and norbomene./(vinyl alcohol) block copolymers was studied by Risse et al. ~o by means of differential scanning calorimetry. They could not observe any phase separation for the norbomene/(silyl vinyl ether) system, when the degree of polymerization of the (silyl vinyl ether) block was as small as 30. Though, a degree of polymerization of 123 was large enough for phase separation to occur. Significantly, two glass transition temperatures of the corresponding block copolymer were detected: Tg = 37~ and T s = 63~ However, polynorbomene-block-poly(vinyl alcohol) formed two separate phases at smaller block length of poly(vinyl alcohol), due to its high polarity. By a similar reaction sequence, poly(exo-dicyclopentadiene) with one aldehyde end group was prepared and used in group transfer
861
polymerization reaction with tert-butyldimethylsilyl vinyl ether to produce the diblock ~polymer poly(exo-dicyclopentadiene)/poly(silyl vinyl ether) 2"'2~ (Eq. l 1.346). n
~
[CP2Ti] OHCOCH ~
CHO
ZnC I2 / c H2=CHOSiR3
(11.346)
SiR 3 SiR 3 SiR3
This copolymer led to poly(exo-dicyclopentadiene)/poly(vinyl acetate) diblock copolymer by further hydrolysis and esterification of the polyether fragment (Scheme 11.10). SIR 3 SIR~ SIR 3
6 "
6
6
o
~ 2-Bu4N F
~
AcOH
'•__i
L-V
Scheme
v
j-~ i~i - H
l l. l 0
The last two copolymers can be useful for various practical applications.
862 11.5. References
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875
Chapter 12 STRUCTURE AND PROPERTIES
OF POLY(CYCLOOLEFIN)S The structure of polymers obtained from cycloolefins varies largely with the nature of the monomer, catalyst and reaction conditions. This fact will impart different physical and mechanical properties to the resulting polymers. Due to the correlation existing between the structure and properties of poly(cycloolefin)s, these two characteristics will be dealt with in this chapter.
12.1. Structure of Poly(cydoolefin)s Taking into account that the structure of poly(cycloolefin)s is substantially sensitive to the nature of the catalyst employed, the present chapter will examine a number of polymers obtained using the most known cationic, anionic, Ziegler-Natta and ROMP initiators.
12.1.1. Cationic Polymers The relationship between the nature of the catalyst or monomer and the polymer properties has been fully illustrated in the cationic polymerization of cycloolefins when using different cationic initiators. This behavior is mostly encountered in the cationic reactions of monocyclic dienes and bicyclic and polycyclic olefins. Cationic polymerization of simple cycloolefins induced by common cationic initiators gives primarily dimers, trimers and tetramers along with transparent amber solid resins, whose structures have not been fully elucidated. It is possible that with BF3, at a temperature higher than -20~ cyclopentene gives unsaturated trimers of the following type z (Scheme 12.1).
Scheme 12.1
876 When 3-methylcyclopentene was polymerized with AICI3, a completely soluble polymer, with a softening point below 50~ having 1,3enchainment resulted 3 (Eq. 12.1). n
CH3
E ~ ~
CH3
(12.1)
Large amounts of bicyclic repeat units were observed in the polymers prepared from 3-vinyl- and 3-allylcyclopentene in the presence of various alkylaluminium compounds (EtAICI2, EtAICIz/PhCHzCI, EhAl). 4 These might be of bicycloheptane structure, as seen in the polymerization of 3-vinylcyclopentene with EtAICl2 (Eq. 12.2)
EtAICI2 . =
n
(12.2)
or both bicycloheptane and bicyclooctane structures, as detected in the polymerization of 3-allylcyclopentene with EtAICI2 and EtAICI2/PhCH2CI initiators (Scheme 12.2).
-[-CH2
'
Scheme 12.2 In their early work on the cationic polymerization of cyclopentadiene with BCI3, TiCI4, SnCh and FeCI3, Staudinger and coworkers 5 suggested a polymer structure corresponding to two unsaturated cyclopentenylene units (Eq. 12.3)
nO
[Cat]
(12.3)
r
\_I
877 from the fact that one mole of polymer consumed one mole-equivalent of bromine. Later work by Wassermann and coworkers6, concerning the color changes occurred during cyclopentadiene polymerization and when poly(cyclopentadiene) was treated with strong acid (e.g., trichloroacetic acid), attributed these phenomena to conjugated double bonds formed by hydrogen migration in the polymer under these conditions (Scheme 12.3).
E Scheme 12.3 Poly(cyclopentadiene) obtained by Vairon and Sigwaltv with the milder catalyst TiCl30~u was readily soluble in aromatic and chlorinated solvents, but it rapidly oxidized in air and became insoluble. Molecular weights were characterized by intrinsic viscosity [11] and by light scattering, however, the relationship between [11] and Mw could not be established because M, varied with the polymerization temperature. This fact was attributed to diminished branching at increasingly low temperatures. Convincing work on the structure of poly(cyclopentadiene) carried out Aso et al., s using TiCh/CI3CCOOH, AIBr3, SnCh etc. in toluene and methylene chloride at -78 ~ and 0~ Their basic approach was to synthesize two model compounds (Scheme 12.4)
H3C
H3
H3C~CH3
Scheme 12.4 for the recurring units in poly(cyclopentadiene) and to investigate their NMR spectra and compare them with those of high polymers. Methods were developed to determine the relative quantities of methine, methylene, and olefinic protons in the polymer. From the data obtained they concluded that poly(cyclopentadiene) prepared in the above conditions contained both 1,2- and 1,4-enchainments. Related work on the influence of reaction conditions on the poly(cyclopentadiene) structure carried out Aso and coworkers 9 using
878 various cationic initiators. In general, these authors found intrinsic visicosities in the range [1]] = 0.1-1.7 and higher molecular weights with weaker Lewis acids at lowest temperatures. While the addition of tricholoroacetic acid or water to TiCI4 or SnCI4 accelerated the rates, the structure of poly(cyclopentadiene) remained unaffected. Gel formation was more frequent in methylene chloride than in toluene solvent. Also, there was evidence for some isomerization in the polar diluent as revealed by the ratio of the olefinic protons to the sum of methine and methylene protons. While this ratio was in general 0.5, a closer examination of the data suggested isomerization to occur, particularly with AIBr3 and TiCLs, that is, with stronger initiators in polar solvents at higher temperatures. Detailed analysis indicated that the most likely structure formed by isomerization contained 1,3-cyclopent- l-enylene units
and that isomerization occurred during propagation and not as a postpolymerization step under the influence of excess or unreacted Lewis acid. Evidence for this proposal came from independent experiments that showed only little change in structure of a preformed poly(cyclopentadiene) upon treatment with TiCh under simulated polymerization conditions (in methylene chloride or in toluene at 0~ It was also shown that the effect of temperature on the polymer structure was negligible in the range 0~ to 100~ but the nature of the Lewis acid affected substantially the relative contribution of the two repeat units, 1,2- and 1,4-enchainments, in poly(cyclopentadiene) (Figure 12.1). 1,2 Content, % 60
OO
9 /
CXo
:
/
.-
511
40 4
-1~ 9
,
.
9
9
&
A
4x10"3 5x10"3 (l/T) Figure 12.1. Influence of intitator on poly(cyclopentadiene) structure (I-TiCI4; 2-AIBr3; 3-SnCI4; 4-BF3.OEt2) (Adapted from Ref.9)
879 The structure and properties of polymers prepared from 1- and 2methylcyclopentadiene with various catalysts (BF3.OEh, SnCh, TiCL) have been examined in detail by Aso and Ohara. ~~ The polymers were soluble white powders, with softening points of 120-160~ The lack of gelation is of interest and may be due to the presence of trisubstituted double bonds in the polymer chain. The microstmctures were analyzed by comparing the infrared and NMR spectra of the polymers with the model compounds 1and 3-methylcyclopentane. Structure analysis indicated that the most important contributing repeat unit was I, with less important contributions by II and Ill and practically no evidence for IV (Scheme 12.5).
CH3
L\ /J
/ H3C
OH3 OH3
I
II
III
IV
Scheme 12.5 At the same time, polymers prepared from 1,3dimethylcyclopentadiene with cationic initiators ~ were readily soluble in benzene, had softening points of 150-155~ somewhat higher than those of poly(methylcyclopentadiene) and poly(cyclopentadiene). The rate of oxidation or oxygen absorption upon exposure to air was found to be slower with these polymers than with poly(methylcyclopentadiene) and poly(cyclopentadiene). This enhanced oxidation resistance was assigned to the decreasing number of tertiary allylic hydrogens in this series of polymers. Analysis of polymer microstructure indicated trisubstituted double bonds and two kinds of methyl groups. Sharp NMR absorption revealed the same number of methyl protons on saturated and unsaturated carbons (CH3-C at 0.96 ppm and CH3-C=C at 1.66 ppm) and a nearly theoretical ratio of 10 for the total number of protons to the number of protons at an unsaturated position. These results indicated the absence of isomerization during or after the polymerization step. While cyclohexene gives low molecular weight oligomers with cationic initiators, z 1,3-cyclohexadiene forms readily white polymers with
880
BF3, PF6, and TiCG as catalysts, ~2 the soluble fraction of which showed intrinsic viscosity [11] in the range 0.04-0.19. The structure corresponded to 1,2-and 1,4-enchainments (Eq. 12.4).
-->
[BF3]'['I'iCI4]
(12.4)
structure
The of poly(1,3-cyclohexadiene) synthesized with SnCIJCCI3COOH or BF3.OEt2 initiators in methylene chloride and benzene as solvents at 0~ has been more thoroughly examined by Imanishi and coworkers. ~3 The polymers were soluble with intrinsic viscosity [11] - 0.040.12 and softening range of 104-130~ The microstructure did not seem to be influenced by the nature of the initiator. According to NMR spectra, about 20% of the unsaturation was lost. The authors suggested that chainbranching might be responsible for this result. While there was strong evidence for 1,4- and 1,2-enchainmnents, no quantitative analysis as to the relative amounts of these structures was given. Polymerization of l-methylene-2-cyclohexene with various cationic initiators (BF3, BF3.EteO, TiCh, AICI3, EteAICI and VCh) gives rise to polymers with essentially 1,4-enchainments, accompanied by minor amounts of 1,2-1inkages~4'~s (Eq. 12. 5).
n H2C-----~--~
[Cat]
,E-cH2,~~.~
(12.5) chloroform
The white, powdery products were largely soluble in and benzene and could be solution cast to flexible films. The polymers were amorphous, with a softening range between 80-82~ Polymerization of 1vinylcyclohexene induced by BF3.EteO and SnCIVCCI3COOH (TCA) in toluene and methylene chloride at 0~ produced soluble, white, low molecular weight polymers, M,-- 1200 (DP--- 11) ~6. These properties remained almost unaffected by the reaction conditions. The structure of poly(l-vinylcyclohexene) was investigated by bromination, IR and NMR methods. The spectra indicated a preponderance of 1,4-enchainment accompanied by some 1,2-1inkages in the polymer prepared by SnCIdTCA
881 (Eq. 12.6).
SnCI4/TCA .._
+
(12.6)
Somewhat different occurred the polymerization of 4vinylcyclohexene in the presence of cationic initiators, for example, BF3, BF3.OEtz, and TiCh. The polymerization with BF3 gas in methylene chloride at -70~ led to 28% conversion of product, of which 85% was soluble and had an intrinsic viscosity [11] = 0.11. NMR spectroscopy indicated a polymer structure with at least two repeat units in about equal amounts ~v(Eq. 12.7). BF3
..=
[ §
~.~
(12.7)
Alternatively, the polymerization of 4-vinylcyclohexene with BF3.OEtz in methylene chloride at 0~ led to 35% conversion and to a completely soluble product of very low molecular weight (intrinsic viscosity [11] = 0.03). NMR spectra indicated c a . 80% cyclization.. The structure of oligomers obtained from d-limonene and tz-pinene in the presence of AICI3 probably corresponded to vinyl-type recurring units and equal amounts having bicycloheptane skeleton (Eq. 12.8)
y
i r
l
§
(12.8)
882 because ozone absorption indicated only 0.4-0.5 double bonds per repeat unit. ~8 The microstructure of polymers prepared from 1,3-cyr with TiCL~, TiCIdTCA, SnCIdTCA and BF3 initiators in methylene chloride and toluene as solvents at -78~ have been investigated by Imanishi et al. ~9 by infrared and NMR spectroscopy. The structures obtained with different initiator systems were essentially the same, however, the nature of the solvent significantly affected the enchainment. Thus, in methylene chloride, polymerization gives almost exclusively linear 1,4-enchainment and no branching (Eq. 12.9)
while in toluene there was 1,4-enchainment accompanied by branched polymer. Whether the branch sites were 1,2 or 1,4 units, that could not be determined. The products were white, amorphous powders of low intrinsic viscosity, [11] = 0.10 and softening range of 172-184~ The linear polymers obtained in toluene solvent were soluble in aromatic and chlorinated hydrocarbons, however, the branchy materials were insoluble, indicating cross-linking. The structure of polymers prepared from bicyclic and polycyclic olefins with cationic initiators is more complex due to the secondary reactions induced by the initiator on these type of monomers. Of such reactions, hydrogen migrations and skeleton rearrangements, under the influence of cationic initiators, are the most significant. A first example is the polymerization of u-pinene in the presence of various FriedeI-Crafis catalysts such as BF3, AICI3, AIBr3, ZrCL in toluene at 40-45~ leading to different polymers as a function of the catalyst employed. ~8 The oligomeric products resulted from ~-pinene in the presence of AICI3 at 40~ have similar properties (e.g. density and refractive index) to those obtained from d-limonene, it was suggested that they are limonene oligomers because prior to oligomerization, r is isomerized to d-limonene (Eq. 12.10).
883
AIC ~...~
AlCh
40oc v
.
40~
(12.10)
Norbornene gives readily polymers with cationic initiators having different bicyclic recurring units, depending on the initiator employed. In the presence of EtAICIz in ethyl chloride at o78~ and o100~ white, soluble solids were obtained (M~ = 1470 and 1940 and softening points 235~ and 260~ respectively) which were found to be amorphous by x-rays. It was inferred that the structure of polynorbornene was a mixture of bicyclic recurring units formed by isomerization of the norbornyl skeleton prior to propagation, e.g., syn, exo-norbornane along with normal 1,2-addition product 2~(Eq. 12.11).
[Cat]=
(12.11)
,
In contrast, polymerization of methylenenorbornene by the use of EtAICI2 and AIBr3 as catalysts at -78~ and VCh at -20~ in n-heptane gave a soluble, crystalline (by X-rays) polymer ([q] = 0.3, softening range 150160~ whose structure (by infrared spectra) corresponded to nortricyclic recurring units 2~ (Eq. 12.12).
n
%•
EtAICI2 -~
[ ,~~,., ~-]-n
(1212) "
The structure and physical properties of polynorbornadiene obtained with AICI3 in ethyl chloride and methylene chloride at various temperatures (+40~ to -123~ are sensitive to the polymerization temperature of norbornadiene. ~ The dependence of the benzene soluble fraction and molecular weights on the reaction temperatures can be observed in Table 12.1.
884 Table 12.1 Polymerization of norbomadiene with AICI3 at various temperatures' 9Ten~erature~ ~
Solvent Time, mm Yield, % Benzene soluble fraction, % Mn of soluble fraction Melting behavior Crystallmity (x-ray) Ts,~
+40
-123
-78
C2H~CI 37 17,2
C2H~CI 25 42.0 72.5 8680
C2H5C1 29 71.0 34.5 3680
Dec.
Dec.
100
5520 9850b Dec. Amorphous 320
CHzCI2 4 30.0 59 2980
'Data from reference 22;bPrcpar~ at - 12 7~
Only the polymer prepared at -123~ was completely soluble in benzene. The structure of the polymer was investigated by infrared and NMR spectroscopy and from these data it was concluded that linear polynorbornadiene essentially consisted of 2,6-disubstituted nortricyclene repeat units (Eq. 12. 13). AICI3 .~ "-
r
"l j
L
(12.13)
-1230C These authors suggested that cross-linked polymer, which is insoluble in common solvents, will arise at high temperatures by "2,3-type" reactions (Eq. 12.14).
[
AK~j +40~
] (12.14)
[
The physical transitions of the linear polynorbornadiene of M. = 9850 have been examined by torsion braid analysis, z3 The thermomechanical spectrum of this polymer, determined at less than 1 r in the range -180~
885 to +500~ revealed the glass transition temperature to be 320~ which is one of the highest known Ts for a hydrocarbon vinyl polymer. 5-Vinylnorbomene reacts at -78~ with EtAICI2 to form white powdery product with M~ ~ 4020, largely soluble (78%) in toluene. Analysis by infrared spectroscopy indicated the presence of 1,2 recurring units in the polymer but also a rearranged structure might be present, formed by the isomerization of the norbomene skeleton 2~(Eq. 12. 15).
m
(1215)
+
-71~C
]
At higher temperatures (-30~ predominantly insoluble polymer was produced with the above catalyst, indicating that a cross-linking reaction of the vinyl groups occurred under these conditions (Eq. 12.16). --
t
]
~--
E (1216)
+ ]
Likewise, polymerization of 5-isopropenylnorbomene with EtAICI2 in ethyl chloride in the range of temperatures-30~ to -100~ gave readily insoluble products, having a cross-linked structure (Eq. 12.17).
-
E\
I ~
-100"C
x]
§
]
(1217)
Evidently, in this molecule the reactivities of the two kinds of double bonds are comparable so that cross-linked polymer is formed even at a temperature of- 100~ Very low molecular weight oligomers (M~ - 540, softening point 85-95~ were obtained from 2,3-dihydro-era/o~icyclopentadiene with EtAICI/BuCI (11) initiator in methylene chloride at -78~ Infrared and
886 NMR spectroscopy indicated that polymerization occurred through hydride migration z4 (Eq. 12.18).
-78~
]~~~__ ] ,
,,,=
(12.18)
[
At the same time, white products with M~ of 1670 and 2150 and sottening points 265-280~ have been obtained from 5,6-dihydro-endodicyclopentadiene with EtAICI2/'BuCI (1"1) initiator in methylene chloride at-20~ and -78~ respectively. Infrared analysis showed no evidence for double bonds occurrence in the polymer chain and consequently the polymer structure seemed to involve double bond opening of the norbomene ring system with possible rearranged norbomyl repeat units (Eq. 12.19).
~
E~.~
-7s'c
§ [
[
[
(12.19)
Interestingly, cationic polymerization of exo- and endodicyclopentadiene in neat system with BF3.OEh at room temperature leads 25 to distinct poly(dicyclopentadiene)s as a function of the starting monomer. Thus, reaction of exo-dicyclopentadiene in the above conditions gives rise to poly(dicyclopentadiene) with 2,3-enchainment of the norbornene ring
(Eq. 12.20)
/~~
BF3/Et20 RT
.~~
(12.20)
[
whereas that of endo-dicyclopentadiene forms polymer with 2,7enchainment of the norbomene ring resulted by a Wagner-Meerwein rearrangement of the norbornene skeleton (Eq. 12.2 1).
B F 3/E t20
RT ~
[
3
(12.21)
887 By contrast, reaction of endo-dicyclopentadiene in methylene chloride diluent in the range of temperatures + 10~ to -78~ by the use of a variety of cationic initiators (e.g. AICI3, EtAICIz, EtAICI~BuCI, BF3, TiC~ SnCL~, EtzAIC~BuCI), gave white powdery, soluble polymers whose structures (by infrared and NMR spectroscopy) indicated norbomane and nortricyclene structures as repeat units z4(Eq. 12.22). "~'I~3"I~'~ [ (1222) +10to-l(XT13 The products have molecular weights in the range of ]300-4450 and softening points between 180~ and 320~ Tetracyclo[4.4.0.12,5. l ~ ~~ (di-endo-methylene octahydronaphthalene) has been polymerized with the catalyst EtAICI/BuCI in neat system at various temperatures (+ 10~ to -50~ to form white, powdery, low molecular weight polymers, M~ = 660-1070, having glass transition temperatures between 260~ and 275~ Structural analysis by ~3C NMR (see Figure 12.2, full spectrum (A) and olefinic region =v
C-7, C-IO PTCD
Qleltnic carbon
]
I
~H2 tn
1
C_H3
65 60 6 in p p m
55
50
t. 5
~.0
3.5
30
25
Z0
Figure 12.2. ~3CNMR spoctra ofpoly(tetracyclo[4.4.0.1~'5.1~.~o]dodec-3-ene) (PTCD) obtained with EtAICI~BuCI as catalyst (Adapted from Ref.~) (B)), revealed the presence of both 3,4- and 3,1 l-addition repeat units in the polymer chain (Eq. 12.23).
888
= +10t0-50~
*
(12.23)
[
Somewhat different occurred the reaction of tetracyclo[4.4.0.1 z,s. 1~~~ 2v (di-endo-methylene hexahydronaphthalene) with BF3.OEt2 in neat system at room temperature. It led to a completely soluble and saturated polymer of M~ = 1050, whose structure involved a half-cage recurring unit formed by a transannular reaction (Eq. 12.24).
n
BF31Et20 ~ RT
(12.24)
In
Indene and its derivatives are readily polymerized by a variety of cationic initiators (BF3, TiCh, SnCh, SbCI~, Ph3C+SbClf) to linear and branchy high molecular weight polymers whose structure corresponded mainly to a 1,2-addition reaction z8 (Eq. 12.25).
n [ ~ ~
BF3'TiCl4'SnCh'SbCI5
[
~n
(1225)
The softening points of such products were in the range 240-260~ Above these temperatures, the polymers exhibited a tendency to yellow and oxidize and could be molded into brittle films.
12.1.2. Anionic Polymers The structure of polymers obtained from cycloolefins by anionic polymerization is more well-defined as compared to the cationic polymers. The nature of anionic catalysts and of monomers prevent secondary isomerization or rearrangement reactions that would affect the polymer structure. As a results of these features, vinyl polymers formed by 1,2-
889 enchainment are normally produced from cycloolefins with one or more non-conjugated double bonds in the presence of anionic catalysts (Eq. 12.26).
[An] .~
n (C
[ /,,~. ~Jn "1
(12.26)
(CH2)x By contrast, polymers obtained from conjugated cyclic dienes with anionic initiators consist mainly of 1,4 recurring units (Eq. 12.27)
n (CH2~/
[An]
=---
rL/~- -/ \ Jn ~ (CH2)x
(12.27)
accompanied, in many cases, by a certain amount of 1,2 recurring units (Eq. 12.28). (CH2)~x
[An]
~
] [/ \] (CH2)x (CH2)~
(12.28)
Examples of such anionic polymers are those prepared from cyclopentadiene, 1,3-cyclohexadiene and 1,3-cyclooctadiene, under the action ofn-butyllithium ~ (Eq. 12.29). ~
n
nB uLi
..~
r ~
I
(12.29)
Of a particular interest is the structure of polymers produced from substituted and unsubstituted silacycloalkenes in the presence of anionic initiators. Thus, l,l-dimethyl-l-silacyclobutene gives with n-butyllithium and hexamethylphosphoramide as initiator a ring-opened polymer poly(1,1dimethyl-sila-cis-but-2-ene) 3~(Eq. 12.30). Me I
n
Me--S! I] [
nBuLtlHMPA=_THF,-78~
Me
[
sli~='w'~ i I Me
Jn
(12.30)
890 l-Silacyclopent-3-ene forms also poly(l-sila-cis-pent-3-ene) in the presence of methyllithium and hexamethylphosphoramide in tetrahydrofuran at a temperature of-78~ as evidenced by ~H-, ~3C- and ~Si-NMR spectroscopy sl (Eq. 12.31).
n
M
%H/O
L
EA
THF,-78~
~
[
HI H
-1
-In
(12.31)
Similar ring-opened polymers have been prepared from 1,l-dimethyl-1silacyclopent-3-ene 32 and l-methyl- 1-phenyl- l-silacyclopent-3-ene 33 under the action of n-butyllithium and hexamethylphosphoramide as a catalyst (Eq. 12.32-12.33).
n
Me /
]'1"1=, -78~
Me~s.~
nBuLi/HMPA ~ THF,-78~
ph/ ~
(12.32) Me Me
-'[---i--/---
.~
(12.33)
Ph
12.1.3. Ziegler-Natta Polymers It is expected that cycloolefins will form polymers by addition reaction in the presence of Ziegler-Natta catalysts. The structure of these polymers would generally correspond to a 1,2-type and 2,1-type cis insertion. Such structures have been found in the polymerization reactions of the majority of mono- and polycyclic cycloolefins with the classical Ziegler-Natta systems based on the transition metal salts and organometallic compounds. 4 Though with special Ziegler-Natta catalysts, e.g. metallocenebased systems or particular monomers, other polymer structures (by 1,3- to l,~addition reactions and with rearranged recurring units) can result. Using a large range of classical catalysts based on transition metal compounds and organometallic compounds, Natta and coworkers 35 found that cyclobutene can form poly(cyclobutylenamer) by vinyl
891 polymerization, polybutenamer by ring-opening reaction or both structures by the two competitive pathways, depending on the catalyst employed (Eq. 12.34).
VCI~HexaAI T~CL~E~I
nl il
=
r
I
-~
q
~
(12.34)
TiC~JEhAI
The vinyl and ring-opened structures of these poly(cyclobutene)s have been evaluated from infrared and NMR spectroscopy. More recent work on the structure of poly(cyclobutene) obtained with metallocene catalysts reported Kaminsky and coworkers. ~s For instance, poly(cydobutene) prepared with ethylenebis(TILindenyl)zirconium dichloride/ methylaluminoxane in toluene is a crystalline product as evidenced by the two peaks 1 and 2 of curve (A) in the X-ray spectrum (Figure 12.3)
(A)
10
16
22
2e o
28
Figure 12.3. X-ray spectrum of poly(cyclobutene) (PCB) powder prepared with the ethylmebis(rlLmdmyl)zir~ium di~loride/methylalummox~e eatalys't
(A~~
from gef.~
and exhibits a high melting point, Mp = 485~ The solid state ~3C NMR spectrum (B) displays also two characteristic peaks, 1 and 2, at/5 = 27 and 40 ppm, respectively, resulting from the CHz and CH groups of the fourmembered ring (Figure 12.4).
892 2
140
120
100
80
(~0
40
20
0
PS~
Figure 12.4. Solid state ~3CNMR spectnun (75 MHz) of poly(cyclobutene) (PCB) prepared with the ethylenebis(rlS-mdenyl)zirccmium dichloride/methylaluminoxane catalyst (Adapted from Ref.~. In a similar way, Natta and coworkers 37 showed that cyclopentene forms, in the presence of various classical transition metal catalysts, poly(cyclopentylenamer) by vinyl polymerization, polypentenamer by ringopening reaction or both structures by the two pathways, as a function of the catalyst employed (Eq. 12.3 5).
V~4/Et~,I
=
~
(12.35)
~CI4/EhJ~,I
The polymers were either amorphous or crystalline products, depending on the catalyst and reaction conditions. More recently, Kaminsky and
893 coworkers 38, using the chiral catalyst ethylenebis(TiS-indenyl)zirconium dichloride,/methylaluminoxane, prepared highly crystalline isotactic poly(cyclopentene) with a fairly high melting point (395~ (Figure 12.5, zone (A) and (B)). (A) (l) I~P
(B) (20)
(s~:, ~
~000 50"
jl-~tl~~
700 355" 600 570 3SO'"
.~
' 0 0 J' 0"9~ 320 2 22O 25O'-
100 200"
(~) (~
~9".5
~
(28)
Figure 12.5. X-ray diagram using synchrotron radiation of poly(cyclopmtme) (PCP) prepared with ethylenebis(rls-mdenyl)zirconium dichloride/methylaluminoxane (Adapted from Ref.3s). The product is insoluble in common hydrocarbons. Based on the infrared spectra, Debye-Sherrer photographs and ~3C NMR spectra in the solid state, these authors concluded that poly(cyclopentene) can be described by two distinct structures, I and II (Scheme 12.6).
j I
II
Scheme 12.6
894 The assignments of these two structures in the solid state ~3C NMR spectrum ofpoly(cyclopentene) can be observed in Figure 12.6 (A) and (B). C13 - S - NMR
l:~P C13 - AP.T,
- NMR
H -"fH
I
(B)
ii I
'
,
I"
,i
""1
iiii:........ "
""~'." "~ "e
"~~ ~176
(A)
180
140
100
60
20
-20
ppm
Figure 12.6. Solid state ~SCNMR spectrum (A) and (B) ofpoly(cyclopcntcne)~s In contrast to these data, Collins and coworkers 39 showed that cyclopentene in the presence of rac- ethylenebis(rlS-indenyl)zirconium dichloride/methylaluminoxane system forms oligomers and polymers by cis1,3 insertion of the monomer (Eq. 12.36)
~~
Et(Ind)2ZrCI2/MAO .~
(12.36)
whereas using the catalyst system rac-ethylenebis(clstetrahydroindenyl)zirconium dichloride./methylaluminoxane both cis- and trans-l,3 insertion structures can arise (Eq. 12.37).
895 (12.37)
Interestingly, this was the first report of a trans "insertion" product being formed in cycloolefin polymerization using homogeneous Ziegler-Natta catalysts. To reduce the melting point of poly(cyclopentene), copolymers with ethylene have been synthesized using ethylenebis(rlS-indenyl)zirconium dichloride/methylaluminoxane, Et(IndhZrCl2/MAO, as the catalyst 4~ (Eq. 12.37a). +
~
II
(12.37a)
Sequence analysis by ~3C NMR spectroscopy indicated the presence of 1,2cyclopentylene-cthylene units. In the spectra of copolymers with 28% mole cyclopentene monomer units, minor amounts of short blocks can be observed, consisting of two cyclopentene moieties (Figure 12.7). S
S
T
T
S
-CH)-CH)~CHz-CH C S ~ C :m C+
_
S
oh.,o
i Pc
+,l
l-
Slhl /SILO
br onc hk~g
Tu \+ 11 T ~
,,5
s
4o
3~
3o
2"5
porn
Figure 12.7. S3CNMR spectrum of c~olymer of cyclopentene (CP)
with ethylene (ET) prepared with ethylenebis0lS-mdenyl)zirconium dichloride/m~ylalummoxane (Adapted from Ref.4~
896 The fact that the polymer structure results from a transannular rearrangement of the monomer in the Ziegler-Natta polymerization was reported by Bokaris, Siskos and Zarkadis 4~ in the reaction of 1,5cyclooctadiene induced by cationic metaUocene catalysts CpzMCI~q~t3AI,EtzAICI, Et3AIzCI3 (M=Ti,Zr, Ht). By the use of infrared and ~H NMR spectroscopy, these authors showed that poly(1,5cyclooctadiene), obtained in the above conditions, contained bicyclo[3.3.0]octane or bicyclo[4.2.0]octane as repeat units (Eq. 12.38).
n
)
cp2uc~t~ =
or
(12.38)
The structure of polymers prepared from bicyclic and polycyclic olefins with the Ziegler-Natta systems depends largely on the catalyst employed. Relevant work has been conducted with norbomene and norbornene-like monomers in the presence of various Ziegler-Natta catalysts. Thus, in their early report, Anderson and Merckling 42 showed that norbornene under the action of TiCldLiHepdd gives rise to a mixture of saturated and unsaturated polymers whose structure was not fully elucidated at that time. Later on, Truett e t al. 43 proved that norbornene yields, with the above catalyst, saturated polynorbornene by vinyl polymerization and unsaturated polynorbornene by ring-opening polymerization (Eq. 12.39).
AI:Ti
(12.39) AI:Ti>I
The vinyl polymerization occurred when the molar ratio AI:Ti <1 and ringopening polymerization at molar ratios AI:Ti >1. Significantly, the unsaturated polymer displayed better elastomeric properties and a higher
897 crystallinity than the saturated polymer. More recent work on the polymerization and copolymerization reactions of bicyclic and polycyclic olefins using various Ziegler-Natta systems evidenced formation of vinyl polymers and copolymers by 1,2insertion mechanism ~ (Eq. 12.40)
C
(CH2)x
Z-N =
(CH2)x
(12.4o)
where n may be zero and an integer and x is an integer greater than 1. The copolymers with ethylene are amorphous and transparent with a glass transition temperature between 120~ and 160~ and they can be used as proper materials for optical discs and fibers. The structure of the norbornene-ethylene copolymers can be readily evaluated from the characteristic chemical shifts displayed in the ~3C NMR spectra (Figure 12.8). CH
2
-- C h a i n
r
!
3
Figure 12.8. ~3CNMR spectnun of norbomme-cthylene (NB/ET) copolymer prepared with ethylenebis(rls-mdmyl)zirconiumdichloride/methylalummoxane (Adapted from Ref.~
898 The variable content of norbornene incorporated into the copolymer norbomene/ethylene prepared with different metallocene catalysts is clearly illustrated by the splitting of each of the four characteristic norbomene ~3Csignals ~ (Figure 12.9).
P0qB/ET)
60
55
So
~
4o
3S
3o
2
1
55
So
~,
40
X~
~
ZS pore
Figure 12.9. ~3CNMR spectra ofnorbomene-ethylene (NB/ET) copolymers prepared with two zirconocene catalysts (l-MezSi[Ind]zZrCIzand 2PhzC[Fluo][Cp]ZrClz) (Adapted from Ref +6) The splitting of each norbomene ~3C signal in these spectra is due to the formation of short blocks of norbomene in the copolymer. For the copolymer 2 additional peaks in the range of 36-40 ppm can be observed. Based on the t3C NMR results of norbornene dimers and trimers it can be shown that these additional signals are a consequence of the formation of longer norbomene blocks. Further investigations by WAXS and differential scanning calorimetry confirmed the above results. The WAXS diagrams for polynorbomene and copolymers of norbomene with ethylene are
899 illustrated in Figures 12.10 and 12.11. Countrate, [a.u.]
./~'~176 9 !
Angle 2| Figure 12.10. WAXS diagrams for polynorbomene prepared with various zirconocene catalysts (I-Ph2C[Fluo][Cp]ZrCI2, 2-Me2Si0nd]2[Cp]ZrCl2)
(Adapted from Ref.") It can be observed that the copolymer prepared with Ph2C[Fluo][Cp]ZrCl2 as a catalyst, which exhibits only a glass transition temperature, has the WAXS pattern of an amorphous halo compound. In contrast to this Countrate [a.u.] !
o
~,
Io
15
2o
2-5
s-o
35
40
Angle 20 Figure 12.11. WAXS diagrams of norbomene,,ethylene copolymers prepared with various zirconocme catalysts (1-Me2Si[Ind]2ZrCl2; 2-Ph2C[Fluo][Cp]ZrCl2) (Adapted from Ref.46)
900 product, the WAXS diagrams of the copolymers prepared with Me2Si[Ind]2ZrCl2 and of polynorbomene prepared with Ph2C[Fluo][Cp]ZrCl2 and Me2Si(Fluo][Cp]ZrCl2 as catalysts, show two patterns due to the existence of the amorphous polynorbomene region. The formation of distinct blocks in these eopolymers has also been confirmed by DSC experiments. The structure of the copolymers prepared from dimethanooctahydronaphthalene and ethylene, in the presence of ethylenebis(rlLindenyl)zirconium dichloride/methylaluminoxane as the catalyst, 36 have been also evaluated by t3C NMR spectroscopy. The t3C chemical shifts assigned to dimethanooctahydronaphthalene skeleton in a copolymer with 7% mole of this monomer incorporated into the polymer chain are illustrated by spectrum (A) in Figure 12.12. f
P(DMON/ET) CH2
2
(A) i
sO
- 7o
LI
I
S 7
,i
!
eo
i
IJL
.
.
.
.
sO
.
.
!
40
3o
' "
pp,.
Figure 12.12.13C NMR spectrum of ~anooctahydronaphthaleneethylene (DMON/ET) copolymerprepared with ethylenebis(qLmdenyl)zirconium dichloride/methylalummoxaneas the catalyst (Adapted from Ref.
901 The copolymerization products are amorphous at room temperature, insoluble in hydrocarbons and display a high glass transition temperature. These materials have excellent transparency, thermal stability and chemical resistance and are suitable for optical applications.
12.1.4. ROMP Polymers The structure of polymers prepared by ring-opening metathesis polymerization (ROMP) commonly known as polyalkenamers concerns the position, steric nature, ratio and distribution (random or blocky) of the ~ o n - c a r b o n double bonds as well as the polymer tacticity (isotactic, syndiotactic, atactic and head-head, head-tail, tail-head enchainment). Ozonolysis. Of the chemical methods suitable to examine the structure of polyalkenamers, ozonolysis is one of the most convenient and precise methods for the determination of the double bonds in the polymer chain. Two approaches of this method have been widely employed i.e. total and partial ozonolysis. The first approach allowed Eleuterio 4~ to isolate cyclopentane-cis-l,3-dicarboxylic acid by the oxidative degradation of polynorbornene prepared with heterogeneous catalysts (Eq. 12.41).
[o]
n
(12.41)
This result unequivocally demonstrated for the first time that norbornene polymerization, under the action of heterogeneous molybdena catalysts, occurred by ring-opening at the C=C double bond of the monomer. By the same approach, Natta and coworkers 4s isolated the monomer units in the form of ot,co-di~xylic acids, e.g., glutaric acid in the case of polypentenamer (Eq. 12.42).
4-vv
[o]
n
I-IOs
(12. 42)
However, the oxidative ozonide cleavage used to obtain such acids was accompanied by undesired side reactions, which can be avoided by the reductive cleavage with NaBH4. This more convenient method was therefore preferred in succeeding work on the chemical degradation of
902 polyalkenamers. It is significant to note that the exclusive presence of ozonolysis products, having the same methylene sequence length as the starting cycloolefin, showed that no appreciable shift of double bonds accompanied the ring-opening polymerization reaction. Similar results obtained in the polymerization of alkyl substituted cycloolefins are also of particular relevance. The presence of ozonolysis products, having a methylene sequence length different from that of the starting cycloolefins, should indicate double bond migration, especially as a consequence of irradiation of polymers, stored over long period of time. Using the ozonization and reductive degradation, Dall'Asta and coworkers 49 demonstrated that the structure of copolymers prepared from isotopically labeled cyclopentene and cyclooctene was formed by ringopening polymerization. Thus, the nature of the final glycols resulted after ozonization and reduction indicated the positions of the carbon-carbon double bonds in the copolymer (Eq. 12.43).
(1Z43)
By a similar way, the products obtained by oxidative degradation of the copolymers prepared from t4C-labelled cyclobutene and 3methylcyclobutene indicated that the structure of the copolymer corresponded to ring-opening copolymerization.(Eq. 12.44).
.~j~.~
[CII~II = n~ , . ~ ~
,n ~
~
(12.44)
The second approach used by DaU'Asta and coworkers 5~ for structure determination of cycloolefin polymers is based on a partial ozonization technique. In this case, in addition to the normal ozonolysis products, dimeric and trimeric compounds will be formed, in which two or three monomer units are linked together by non-ozonized polyalkenamer double bonds. Examination of the nature of such dimeric and trimerir cz,r~ diols, resulted from copolyalkenamers, is an important method for the determination of the degree of randomness of copolyalkenamers. This method, applied to homo- and copolyalkenamers containing alioyl
903 substituents, allowed Dall'Asta and coworkers 5~ to draw important conclusions about the tacticity of substituted copolyalkenamers. Chemical degradation. An efficient chemical method for the structure determination is the polymer degradation induced by metathesis catalysts in the presence or in the absence of an acyclic olefin. Unsaturated polymers can be converted metathetically to fragments of low molecular weight by a controlled reaction with olefms. Since the scission of the polymer backbone occurs at the double bonds, analysis of the degradation products enables establishing the structure of the polymer. This technique has been first applied by Michailov and Harwood 52 to structure evaluation of 1,4-polybutadiene and styrene-l,4-polybutadiene copolymers, which were fragmented with excess 2-butene in the presence of WCIdEtOH/EtAICI2. The amount of 2,6-octadiene provided a measure of the 1,4-butadiene units (Eq. 12.45) ....
I
I
I
I
!
(12_45)
w--
! !
I
I
!
'
I
whereas the amount of 5-phenyl-2,8-decadiene and 4-phenylcyclohexene a measure of 1,4-butadiene-styrene-1,4-butadiene triads (Eq. 12.46).
.--
~
/5 / ,
!
r
....~
9~
.... 0246)
/X/ ii
At the same time, Hummel and coworkers 53 used an analogous technique to determine the possible double bond migration in the vulcanized polybutadiene and polypentenamer during vulcanization process or to measure the rate of penetration of swollen polymer gels by a solvent. A more selective approach has been applied by Thorn and coworkers s~ in the quantitative metathetic degradation of rubbers and sulphur cross-linked rubbers, including tires. These authors used Grubbs and Schrock tungsten alkylidene catalysts and 3-hexene as a scission agent. Metathetic
904 degradation of cis- and trans-1,4-polybutadiene showed that the fragments were not affected by the steric configuration of the polybutadiene sample. In both eases, the same ratio of the three possible isomers of deca-3,7-diene was observed after thermodynamic equilibrium was reached (Eq. 12.47). I I
....
I I
[W=O'F~
I
...." - , , ~ x j
=
§ ~
/
I
....
(12.47)
/
, I
'
I
The structure of the cyclic isoprene trimer (ttt-(CsHsh) obtained from polyisoprene degradation under the action of tungsten-carbene initiator W(=CHPh~ in the absence of acyclic olefins (Eq. 12.47a) ..
[
.
~
~
"
..
[V~O~ =
(12.47a)
n
has been determined using a combination of analytical methods such as gas chromatography/m~s spectrometry (C_~B~tS) and ~3C NMR spectroscopy (see spectrum (A) in Figure 12.13). 55
5 3
2
5
u
leo
14o
.q_
12o
1oo
8o
60
zo
o pcm
Figure 12.13. ~3CNMR spectnun ofttt-(C~'l=)3 isomer obtained by melmhetic degradation of 1,4-polyisoprene with tungsten carbene catalysts"
905 The ~3C NMR spectrum shows five distinct lines due to two olefinic carbons and three different aliphatic carbons which evidenced the structure of ttt-(CsI'h)3 isomer. Oligomer analysis. An efficient method for the determination of the chemical structure of the fraction of oligomers obtained from cycloolefins and polyalkenamers consists of gel-permeation-chromatography (GPC) and combined techniques of gas chromatography and mass spectrometry (C~MS). In some cases, IH- and n3C-NMR spectroscopy give unambiguous data about the structure of the oligomeric compounds. This group of compounds may be of linear or macrocyclic nature and are normal coproducts in cycloolefin polymerization. The GPC evolution of the homologous series of cyclic oligomers obtained in the polymerization of cyclooctene and cyclododecene, ~s using WCIdMe4Sn as a catalyst, is illustrated by the chromatogram (A) and (B), respectively (Figures 12.14 and 12.15).
2 5
35
40
45
50
55
4
60
!
3
65
70
75
80
85
90
95
Figure 12.14. GPC of the homologous series of cyclic oligomers and polymer obtained from cyclooctcne (CO) using WCIdMe4Sn as a catalyst (Adapted from Ref.~s) It can be seen that all oligomers of cyclododecene up to nonamer are kinetically enhanced, while the polymer is only formed at the end of the reaction, at the expense of oligomers.
906
n
I /x II
9 - -
m
~
vg/n Figure 12.15. GPC of the homologous series of cyclic oligomers and polymer obtained from cyelododecene (CDD) using WCIdMe4Sn as a catalyst (Adapted from Ref. The cyclic nature of these oligomers can be evidenced by GC-MS from single components. For instance, the trimer of cyclododecene shows a molecular ion peak in the mass spectrum corresponding to 498 (m/e). The high intensity as compared with that of lower fragments is a first indication for the cyclic structure of the compound. Though the peak is not very characteristic as these values are typical for fragments of polyolefins. When the trimer is hydrogenated, the C36-product shows the molecular ion peak at 504 (m/e), corresponding to the formula C,H2,.~+, typical for a cycloalkane. Research on this line by the above techniques, carried out by Calderon and coworkers, s7 revealed the existence of butenamer units (Coils) in the macrocyclic oligomer fraction of polymers from 1,5cyclooctadiene. Also, by analysis of the oligomer fraction separated from polymers of l-substituted 1,5-cyclooctadienes, these authors found that the structures of these polymers were equivalent to an alternating copolymer of butadiene with isoprene (Eq. 12.48).
!
(1248)
i
Infrared spectroscopy. Infrared spectroscopy has been widely applied during early studies on the structure of polyalkenamers in order to reveal the presence of ring-opened structures and to determine the cis and trans vinylene content in these polymers. For several years the method was
907 based on absorptivity values previously established for cis- and trans-l,4polybutadiene without controlling their transferability to higher homologs. However, in a more detailed IR and NMR spectroscopic investigation of the structural units occurring in polyalkenamers, Tosi, Ciampelli and Dall'Asta st" determined more accurately the molar infrared absorptivities for several polyalkenamers (Table 12.2). Table 12.2 Molar absorptivities of infrared bands due to trans and cis double bonds in polyalkenamers'
Polyalkman~r
E~,(7.12 (mole.cm)"1
Polybtaman~r Polypmtmamcr Polyhoptcnamer Polyoctcnamcr Polydecenamer Polyd~amer 9Data from reference ~s
132 152 137 135 134 133
~m) (rnole.cm) "! 5.0 9.4 8.7 8.6
Inspection of the values from Table 12.2 surprisingly shows that the molar absorptivities vary considerably, depending on the length of the methylene sequence occurring between two successive double bonds. Analysis by this method of the structure of trans-polypentenamer, prepared by ring-opening polymerization of cyclopentene under the influence of the three-component catalyst WCl6/peroxide/EtAICl2 indicated that the amount of non-alkenamer units did not exceed 2-3%. Vinyl end groups were shown by infrared spectroscopy to be virtually absent in the high molecular weight polyalkenamers and to be present in the low molecular weight products only in amounts corresponding to the end groups, in accordance with the metathesis mechanism of ring-opening polymerization. The trans vinylene double bonds from polyalkenamers were generally determined by using infrared absorption band at 10.3 5 p whereas the cis vinylene double bonds either by using the infrared bands at 7.1 or at 13.7 p, or by assigning the complement to 100 per cent of the trans double bonds to the cis vinylene ones. Comparative examples with IR spectra of cis and trans polypentenamers obtained by Natta and coworkers 37 with Mo-and W-
908 based catalysts, respectively, are given in Figures 12.16 and 12.17.
x La) ~t| ~ .... 3...3~..~..~ zr
so
.... 5~ .... 6....6~...?...?~5...L.~...?.2~o. ~. ~L,~.m,~.~,5
---~
dO
40
cis-PPM
20 I
4000 ~
I
i
i=
3200 ~
I
*
2400 2000
"
9
IgO0
i
9
1600
9
t
9
1400
t
9
1200
t
9
1000
9
800
650
Wavenumber, cmt Figure 12.16. IR spectrum of cis-polypentenamer (PPM) prepared with MoCl~-based catalysts (Adapted from Ref.37) It is obvious that a clear distinction between the cis and trans structures of the two isomers can be observed by a rapid inspection of the two spectra.
x (~t) %
,d 5 . . . .
{,,, 33
a 45 $
5.5
6
6.5
7
7.5 8 83 99.510
II 12 131415
W 60 40 trlms--PPM
20 9
l
/
4000 3600 32(}0~
l
g
2400 ~
9
9
9
ISO0
t
9
I~
&
it
1400
it
9
1200
9
9
I000
9
t
900
9
~I~
Wavenumber, cm~ Figure 12.17. IR Spectrum of trans-polypentenamer (PPM) prepared with WCl~-basod catalysts (Adapted from Ref.37) The cis-polypentenamer displays the characteristic absorption bands at 7.1 2 and 13.8-13.9 g while the trans-polypentenamer at 10.35 g. Absorption bands in the region 8 and 8.5 It, characteristic of cyclopentane structures, are absent indicating the occurrence of a ring-opened polymer.
909 Investigation by infrared spectroscopy of the crystalline polyalkenamers showed a series of IR bands that are characteristic of crystallinity. This fact is illustrated for trans-polypentenamer in the wavenumber region of 400-2000 cm~ (Figure 12.18). 60 % G |._a__
6 l_
i
_l_
l
L
la__l
I
7 l
l
1
l
1 i
i
i
i
i I I lllllllt
8
9
lllllJllll
l
l
10 1.
I
A
l,
1G I
l
20 A
A
~
I
2G
l ~ t l ~
100
i. o
2ooo
t~
~o
~)o
I~
~obo
~o
~
,toe
Wavenumber, cm"t Figure 12.18. IR spoetrum of trans-polypentenarner (PPM) in the 400-2000 cm"~ region (-amorphous and "crystalline modification) (Adapted from Ref.~r*) Interestingly, some of these bands were found to be indicative of the specific type of crystalline modification present in the polymer. The structure of polyoctenamer with 62% trams content can be estimated from the FTIR spectrum of this polymer shown in Figure 12.19. 59 The absorption bands at 960 cm t (trans =C-H bending) and at 715 cm t (cis =C-H bending) give the ratio trans/cis using a factor of 0.10 for the trans band and 0.16 for the cis band. The FTIR spectrum of hydrogenated 62% polyoctenamer is comparable with that of polyethylene. In particular, the absorption bands at 3000 cm t (ethylenic C-H stretching) and at 960 cm" (the trans olefinic C-H bending), originally present in polyoctenamer, are completely eliminated by hydrogenation and the cis olefinic bending at 715 cm"~ is replaced by the CH2 rocking at 730 cm"t and 720 cm "t. From the ratio of the band at 730 cmt (assigned to the crystalline portion of the macromolecule) to that at 720 cm ~ (assigned to the amorphous portion of the macromolecule) it was possible to estimate the crystaUinity of the hydrogenated polyoctenamer.
910 Transmittance -/
ir \
/
..! !
POM ,,ooo
~oo
2obo
,~o
,oho
5o0
Wavenumbcr, cm" Figure 12.19. FTIR spoctrum of polyo~amcr (POM) with 62% trans conte~t and of its hydrogenated product (Adapted from Ref.59) The FTIR spectrum of polynorbornene ~9 with 80% trans content is given in Figure 12.20. The microstructure of polynorbornene can be roughly estimated by using the absorption band at 960 cm ~ due to trans out of plane =C-H bending and the cis in-plane =Coil bending at 1404 cm ~. Further estimation of the trans and cis content of polynorbornene can be clone by comparing the trans absorption band at 960 cm ~ with the cis absorption at 740 cm~. After hydrogenation, the FTIR spectrum of polynorbornene shows a complete absence of the cis band at 1400 cm~ and a very strong reduction of absorption band in the 740 cm ~ region also due to cis double bond while the trans absorption band at 960 cm "~ remains, but is strongly attenuated. This means that the cis portion of polynorbornene is more readily hydrogenated than the trans portion.
911 Tran~__~rn~ancr
'
w
I
9
9
l
!
:316O0
~0OO
2~OO
2OOO
lfl~o
mooo
ooo
Wavmumber, cm"t Figure 12.20. FTIR spectnnn of polynorbomenamer (PNB) with 80% t r a n s content and of its hydrogenated product (Adapted from Ref.'9)
tH NMR and t3C NMR spectroscopy. With the rapid advance in NMR spectroscopy, this technique has become one the principal methods for structural characterization of polyalkenamers. As early as 1965, Michelotti and Keaveney6~ reported the first ~H M R spectrum of polynorbornene, but some structural features were not discerned at that time with the available instrumentation. Subsequently, ~H NMR spectroscopy has been widely applied for evaluating the structure of polyalkenamers, namely to determine the number and types of protons present in the polymer chain. A first example is the ~H M R spectrum of polybutenamer where the CH2 and CH protons can be easily identified6~ (Figure 12.21). ...
--
t.4 2 -
.=.
mIND
pg~rn
Figure 12.21. ~H NMR spoctrum ofpolybutenamer (PBM) (Adaptod from Ref.6~).
912 In a similar way, the tH NMR spectrum of polypentenamer gives the type and amount of CH2 and CH protons in the polymer chain (Figure 12.22). Pr'M 1 I
-Cl-I--
planr~
Figure 12.22. ~H NMR spectnnn of polypent~amer (PPM) (Adapted from Ref.6~) Wide-line H NMR spectra, obtained at low temperatures provided a measure of the T s for several polyalkenamers. The apparent Tss of higher polyalkenamers were between those for polyethylene and polypentenamer, indicating Tss to be slightly below -100~ for these type of polymers. As ~3C NMR spectroscopy became readily available, more detailed information regarding the microstructure and tacticity of poly(cycloolefin)s was possible. Thus, chemical-shift additivity parameters for carbons in polypentenamer at various distances from the double bond were first reported by Chen 62 (Figure 12.23). m
_
|
..__.._...
1
,~o
,]o
,~o"
2
do
io pll~'n
Figure 12.23.13C NMR spectrum of polypentenamer (PPM) (Adapted from Ref.62)
913 From the characteristic ~3C NMR chemical shifts, the microstructure of a series of polyalkenamers can be accurately evaluated. Accordingly, the ~3C NMR chemical shifts of cis-polyalkenamers in CDCI3 at 60~ in ppm relative to tetramethylchlorosilane are given in Table 12.3. Table 12.3
~3CNMR Chemical Shifts of cis-Polyalkenamers in ppm relative to TMS"b
Polyalkenaater
Ct
C2
129.66
27.52
129.91
27.01
29.96
"129.88
27.25
29.72
29.02
129.88
27.33
29.85
29.29
133.95
38.70
33.32
42.77
Structure
Polybutenamer
1
C3
C4
2 Polypentenamer
1
3
1
3
Polyheptenamer
"0~'~
Polyoctenamer
~
1
4 v ~ ' ~ 3
] 2 1
4
~
4
Polynorbomene
'Data from reference
Solvent CDCI3 at 60~
The essential feature from these data is that the trans olefinic bonds are characterized by aUylic carbon resonances at ca. 5.0 ppm higher frequency than cis olefmic ones. For a more detailed information, the methylenic region of the ~3C NMR spectrum of 85.5% trans polypentenamer obtained with the catalytic system WC~epichlorohydrinfBu3Al, in toluene at a temperature of 0~ is illustrated in Figure 12.24 and that of 81.98% cis polypentenamer obtained with the catalytic system WCIdPI~Sn, in toluene at a temperature of-20~ in Figure 12.25. 64
914
trans-PPM
.{.- c N
1
2
2~
3"3
i2
i,
s'o
z~
2"8
i?
2"6
i5
Figure 12.24. Expanded ~3C NMR spectrum (methylene region, 25<(ppm)<33) of trans-polyp~tenamer (trans-PPM) (85.5%) obtained with the catalytic system WCldepichlorohydrin/iBu3Al in toluene at 0~ from Ref.~ cis-PPM
1
--[-- C H " ~ C H - - C N 2 -
Z
1
Cl, I 2 -- C H 2 --}--
2cc
ttr
2~t(tc)
211
3~
3'0
2"9
~
~7 pl~nn
Figure 12.25. Expanded ~3CNMR spectrum (methylene region, 25<(ppm)<33) of cis-polypentenamer (cis-PPM) (81.98%) obtained with the catalytic system WCl~h4Sn in toluene at -20~ (Adapted from Ref.~)
915 The above spectral results allow a quantitative evaluation of the cis and trans stereoc~niiguration of polypentenamer to be done. Moreover, from the data presented in Table 12.4, a comparison of the relevant chemical shifts in ppm relative to TMS for the cis and trans configurations of a number of polymers, I-VI (Scheme 12.7), can be readily done .6~ Table 12.4
13CNMR Chemical shills of cis- and trans-polyalkmana~rs I-VI (Scheme 12.7) in ppm relative to TMS ~ cis-Polymer
trans-Polymer C2 C3
CI
C2
C3
c'
CI
I
133.88
II III IV V VI
130.9 130.9 129.66 129.72 129.98
38.70 42.16 37.8 27.52 27.66 27.36
42.77 32.5 30.3
33.32 23.30 23.6
28.88
15.52 29.35
133.10 131.2 132.4 130.11 130.20 130.46
29.87
43.15 47.46 43.5 32.84 33.06 32.71
c
41.40 31.5 30.3
32.20 23.30 23.6
28.88 29.74
15.52 29.18
'Data from reference 6~ The accurate record of these values is extremely useful for a rapid evaluation of the stereoconfiguration and steric~ purity obtained for this class of ring-opened polymers.
4 I
4
II
Ill
IV
5
V
VI
Scheme 12.7
916 The study of the structure of polymers obtained from norbornene and its derivatives played a particular role in the development of a correlation with the properties of such products and the mechanism of their formation. A first indication for the stereoconfiguration of polynorbomene obtained by ring-opening metathesis polymerization is obtained from its ~H NMR spectrum ~ (Figure 12.26).
/
t
~-
f)
/ H
-.J
I ~__/ 2
1
0
Figure 12.26. ~H NMR spectrum ofpolynorbomene (PNB) (Adapted from Ref.~') Abundant data, however, on the structure of polymers prepared via ring-opening metathesis polymerization of norbornene or norbornadiene and their derivatives come from the detailed structural analysis effected by Ivin and coworkers 6~ as well as by other authors by ~3C M R spectroscopy. 6. Furthermore, Ivin69 and Rooney7~ characterized many subtle structural features in the polymerization of substituted norbornene such as head-to-head and head-to-tail linkages, tacticity of adjacent ring structures, and distributions of cis and trans double bonds in the polymers.
917 A first example reported by Ivin and coworkers 67" consists of the '3C NMR spectra for three samples of l~lynorbomene, A, B, and C, prepared using ReCIs, WCldEtAICI2 and a ruthenium complex generated from RuCI3.xH20, ethanol and cis, cis- 1.5-r (Figure. 12.27). PNB I
KN..c. $
if,
. C; "~ iCt
,b
~"
'~
,~,-..
]"
5!m
T,
:
9
3
?
9
i
1EtK)
i
i
140
9
9
120
i
,
i
100
i
i
80
i
"
60
i
i
410
*
i
20
Figure 12.27.~3CNMR spectnan ofpolynorbomene (PNB) (C~ualyst: ReCI~ (A), W C ~ C I 2 (B) and Ru complex (C)) (Adapted from Ref.67") The sc~e refers to the spectrum of the sample C obtained with ruthenium complex while the spectra of samples A and B are offset by 20 ppm and 40 ppm, respectively. The spectrum of sample A is strikingly simple compared with those of samples B and C and the four lines could be easily assigned to the carbons in an all-cis structure on the basis of the IR spectrum. Taking into account that the peak 11 is the trans C4 counterpart of peak 12 pertaining to cis C 4, the steric configuration of samples B and C can be readily determined from the relative intensities of peaks 11 and 12 giving o~ = 1.0, 0.51 and 0.16 for the three samples, A, B and C, of polynorbornene. The structure of ring-opened polymers obtained from substituted norbornene has been intensively studied in order to get more information about the reaction mechanism and stereochemistry. Significant evidence
918 about the microstructure of such polymers is based on the t3C M R spectra of 1-, 2-, 5- and 7-methylnorbomene prepared with ROMP catalysts. Figure 12.25 illustrates the ~3C M R spectrum of a l~gh..cis, all head-to-tail, fully 9
b
y
14141
1~
3S
134
Figure 12.28.125 MHz t3C NMR spocttmn of poly(l-methylnorbomene) [P(I-MeNB)] obtained with ReCI~ catalyst (Adapted from Ref.6~') syndiotactic polymer obtained from 1-methylnorbomene with ReCls as a catalyst. 6r~'r Analogously, the F./Z structure of poly(2-methylnorbomene) 7E,Z
12. t.
V
I P(2"MeNB)I
I
"11
8E
C0CII1[3 Figure 12.29.25 MHz m3CNMR spectrum of poly(2-methylnorbomene)a
919 can be easily inferred from the :3C NMR spectrum of this polymer in CDCI3. The arrow of the spectrum points to the region where trans- and cis-polynorbornenamer have their olefin resonances, at 133,1 and 134,1 ppm68 (Figure 12.29). The fine structure of the ring-carbon region of the :3C NMR spectrum of poly(5-methylnorbomene) prepared with ReCI5 as catalyst (o~ = 1.0)is given in Figure 12.30. The two inserts(A)and 03)
(A)
Figure 12.30.:SC NMR spectnan of poly(5-methylnorbomene) [P(5-MeNB)] (Adapted from Ref.*~) represent the resonances of the carbon atoms of the five-membered ring of substituted norbornene. The :3C NMR spectrum of poly(7methylnorbomene) represented in Figure 12.31 illustrates the more CZ,3
9
1
cS.Q
~
P ( 7 - M e l q 13)
.
!
ca r
1
13S
9
I
1
132
SO
9
1
40
II
1
30
9
1
~PO
Figure 12.31.:3C NMR spoctrum of poly(7~ylnorbomcne) [P(7-MeNB)] (Adapted from Rcf.~
v
11:9~
920 simple structure for the polymer resulted from a symmetrically substituted monomer. The structure of polyalkenamers, in some cases, needed a further examination of the ~H/t3C heteronuclear correlation spectrum. By this method, for instance, the structure of a tfigh-cis polynorbomadiene obtained with OsCl3 (its ~3C NMR spectrum shown in Figure 12.32, region (A) and region (B)), has been accurately determined. cG
C~,6 r
"" C Iu$
ee
i
cc
d
C~.3
er
c~ e,e
O3)
(A) te ppm
,is
' ,"3 3
is
,/o
pp,,,,,
Figure 12.32. ~3CNMR spectnun of polynorbomadiene (PNBD) (Adapted from Ref.7~ Also, a variety of copolymers of norbomene and norbornadiene have been prepared and their structures elucidated by means of ~3C NMR spectra. One example, illustrated in Figure 12.33 by spectra (A) and (B), is the copolymer obtained with OsCl3, having the various homodiad units of
03)
4"5
40
35
ppm
Figure 12.33.~3CNMR spectrum ofnorbomene-norbomadiene [P(NB-NBD)]copolymer (Adapted from Ref.X~)
30
921
configuration. The method showed to be successful in structure determination of many similar copolymers. Full information about the tacticities and fractions of cis double bonds (o~) of polymers prepared from phenyl- and benzonorbomadiene have been obtained directly from their ~3C NMR spectra. The assignments for these structures reported by Hamilton et al. ~ are illustrated in Figures 12.34 and 12.35. all-cis
P(7-PhNBD) 9
t
~ 2 1
4
Io ~
1o' 11
c
144
142
~a~
~3..~
Figure ]2.34.~3C NMR ~
t2g
~;z7
oo
58
5e
~,~
~2
pp.m
ofpoly(7~hmylnorbomadiene) [P(7-1~NBD)] (Adapted from Ref.TM)
I
I ttm/r)
I ctm/rl
ou #t~mjr~l
cU
mm/mr/rr
147
145
135
133
128
126
124
122
48
46
44
42
pDcn
Figure 12.35.~3C NMR spectnun ofpoly(benzonorbomadiene) [P(5,6-BzNBD)]
(Adapt fromRef.
J
922
Of a special interest is the study of the microstructure of poly(dicyclopentadiene) (Figure 12.36, spectra (A) and (B)) and some of r
TH.T T
C 3 TH.TT C 4' HT. HH
Cs C
P(DCPD)
] C7
7
Cs
(A)
135
13o
125
,
~
pr
(1~)
135
125
Figure 12.36.m3CNMR spectrum of trans-poly(dicyclopentadiene)(A) and cis-poly(dicycl~maafftene) (B) (Adapted from Ref.a~) its copolymers, e.g., poly(dicyclopentadiene)-poly(cyclopentene)(Figure 12.37), due to their increased potential for industrial applications. 130.97 130.45 1 29.93
J:J'I)-4U P )
42.50 4 1 .OO
55.58 .55.32
47.26 45.70 4d.92
35.04 2.44
\
.
.
.
.
.
13o-12o-~io-16o-
~
-
6o
-
7-o-
r~o
" s~o
" 4"0 "
3"0
"
2 0 " - 1()
&. p p m
Figure 12.37.~3C NMR spectnun of copolymer dicyclopentadiene-cyclopentene [P(DCPD-CP)] (Adapted from Ref.n)
923 12.2. Solution Properties
Solubility. Amorphous as well as crystalline poly(cycloolefin)s are generally soluble in many organic solvents at room temperature, except the higher melting crystalline poly(cycloolefin)s obtained with Ziegler-Natta catalysts and some trans polyalkenamers which are dissolved by the same solvents only at higher temperatures. Such solvents consist of aliphatic, cycloaliphatic, aromatic and chlorinated hydrocarbons and various polar compounds, except low boiling alcohols and ketones, which are currently employed to coagulate polyalkenamers from their solutions. Acetone dissolves only low molecular weight polymers. Polyalkenamers from polar monomers like 5-norbornenecarbonitrile require highly polar solvents, and chlorinated solvents are oRen employed for polymerization since they provide polarity without affecting catalyst activity. Viscosity. The effect of molecular weight on the dilute solution properties of polypentenamer has been examined by Gianotti et. al.72 for narrow molecular weight distribution of polymer fractions with 80-85% trans structure (see Table 12.5). Table 12.5 Viscosimetric properties of polyalkenamers~b |
Polymer
Temp. ~
Solvent
Trans %
KxI0 4
[11]
Polypentenmner Polypentenamer Polypentenamer Polyoctenamer~
30 30 38 30
Toluene Cyclohexane lsoamyl acetate Toluene
85 85 85 40-50
5.21 5.69 23.4 8.0
0.69 0.68 0.50 0.63
9Data from reference n, b Mark-Houwink relationship [q] = KM "; ~Data from reference. 73 Osmotic measurements showed the usual linear relation between the second osmotic virial coefficient and the molecular weights. Higher [rl]/M values were found for trans than for cis polypentenamer of approximately the same molecular weight suggesting a stifler, more extended structure for trans polypentenamer. 74 This observation was in agreement with the finding that Mooney viscosity/solution viscosity ratio is considerably higher for
924 polypentenamer than for cis polybutadiene. 7s The viscosity/molecular weight relationship for polyoctenamer with ca. 45% trans content was obtained from a correlation between GPC data and intrinsic viscosities. 73 Molecular weight. A wide range of molecular weights (Mw and M,) of poly(cycloolefin)s can be obtained depending on the mechanism of polymerization. It varies from low oligomers (M~=IOL103) to very high molecular weight polymers (M~=-105-107) as a function of monomer, catalyst, transfer agent and reaction conditions. The molecular weight distribution can be rather broad or very narrow, the last being available by the use of living catalyst systems. The most convenient method for the determination of molecular weights consists of size exclusion (gel-permeation) chromatography (GPC) calibrated with polystyrene standards. 76 The molecular weight distributions (M,u~,) of poly(eyeloolefin)s are evaluated by polydispersity indexes (PDIs); these values determine their potential use. The living systems allow a rigorous control of molecular weight distributions giving in the ideal case values of 1.0 for PDls. Polydispersities indexes between 1.00 and 1.15 have been frequently recorded for living ring-opening polymerization of cycloolefins with well-defined titanacyclobutaner~ and tantalacyclobutane78 or with molybdenum29, tungsten -s~ and ruthenium-alkylidene initiators. 8~ A substantial number of solvent-nonsolvent fraetionations of poly(cycloolefin)s which allow a good characterization of the polymers can be found elsewhere. 82"84 trans
12.3 Solid State Properties The linear polyalkenamers with low glass-transition temperatures (Tgs) display elastomeric properties whereas polyalkenamers from substituted cycloolefins and polycyclic olefins with Tss above room temperature have thermoplastic properties. However, the thermoplastic propensity of some stereoregular polyalkenamers may also be the result of crystallization. Since many polyalkenamers prepared from simple cycloolefins exhibit crystallinity, a property that plays an important role in most applications, this phenomenon has been widely investigated for the homologous series of linear polyalkenamers. Glass transition. The glass transition temperatures (T s) of the majority of cis and trans polyalkenamers are well below those of practical rubber applications. Differential scanning calorimetry (DSC) showed second-order transition temperatures near to-100~ for the linear
925 polyalkenamers. It was observed that the T s is increased by various substituents on the polymer such as alkyl groups or incorporation of a rigid cyclic structure within the chain, such as in polynorbomene (Table 12.6). Table 12.6 Glass Transition Temperatures of Polyalkenamers'
Polymer or Monomer
cis-Polyp~enamer t r a n s - P o ly p e n t e n a m e r
cts-Polyoctmamer trans-Pol~r
cis-Polybutmamer Poly( 1-methyl- 1,5-cyckxx~diene) Poly( 1-ethyl- 1,5-cyclooctadiene) Poly( 1-chloro- 1,5-cyclooctadiene) Polynorbomene Poly(dicyclopentadiene)
Ts ~ -114 -II0 -97 -90 -95 -93 -91 -108 -65 -I04 -85 -84 -6O 35 130
Method
DTA TBA DTA DTA DSC TBA DSC DSC DSC DTA DSC DSC DSC DSC TMA
/
'Data from referenceSS As can be noted from Table 12.6, cis-polypentenamer exhibits the lowest T s of all known hydrocarbon polymers and has been recommended for cryogenic applications. It is interesting to compare the T s values of different c i s polyalkenamers with those of the trans stereoisomers. From the data shown in Table 12.7 it is obvious that the c i s stereoisomers always show considerably lower Tss than the corresponding trans stereoisomers. However, the T s values of polyalkenamers also depend on the vibration frequency of the method employed for the measurement and on the degree of crystaUinity of the polyalkenamer. Thus, for cis-polypentenamer, which has the lowest T s value, three different T s values were reported s~
926 Table 12.7 Values of Ts, T, and Trrl'., ratio of polyalkenamers' Polyalkenamer
Steric purity %
Ts ~
T., ~
T/T. ~
cis-Polybutenamer
98 98 99 85 93 90
-95 "1~
2 76 41 18 18 62
0.63 0.55 0.69 0.61 0.57
trans-Polybutenamer
cis-Polypentenamer tra n s - P o l y p e n t e n a m e r
cis-Polyoctenamer tr a n s - P o ly o c t e n a m e r
-
-9"~ -10: -65
9Data from reference ~s - 105~ (shear modulus), - 114~ (DTA) and - 135~ (flexural modulus, forced vibrations). Generally, the TerI'~ relation is in the expected 0.6 range, thus following Boyer's rule. Lower T s values have also been observed by Ofstead ss for some substituted polyalkenamers prepared from l-methyl- (-85~ l-ethyl- (-84~ 1,2-dimethyl- (-59~ and 1-chloro1,5-cyclooctadiene (-60~ Second-order transitions of a series of polyalkenamers ranging from trans polybutenamer to trans polydodecenamer were determined also by using the method of NMR linewidth as a function of temperature. 89 The temperature at which the characteristic transitions occur decreases with decreasing methylene sequence in the polyalkenamer. Glass transition temperatures have also been determined for several copolyalkenamers of cyclopentene copolymerized with cyclooctadiene, 9~ 5norbomene-2,3-dicarboxylic anhydride 9t and dicyclopentadiene92; the values are between those of the respective homopolymers. In general, the T s of the copolyalkenamers can be adequately estimated by using the following equation, where T A and TB are the Tss of the respective homopolymers and WA and WB are the weight fractions of components A and B, respectively ss (Eq 12.49). lfrg = (w
fr^) + (WdTB)
(12.49)
Crystalline Transformations. Up to now, crystalline melting points Tm have been reported for a series of polyalkenamers that varied in
927 monomer composition, cis-trans isomer content and procedure of preparation (catalyst, reaction time, temperature). It was easily observed that, the melting temperatures of stereoregular homopolyalkenamers depend on the microstructure of the double bonds, length of the methylene sequence of the monomer units, and crystalline modification of polymer. The experimentally determined melting points increase with increasing the methylene sequence length. According to Natta and Dall'Asta, 93 in the series of trans-polyalkenamers (containing ca. 80-90*,6 trans double bonds) an approximately linear relationship exists between melting temperatures of polymers crystallized in orthorhombic and monoclinic forms and the reciprocal value of the length of the monomer unit. The melting temperature of several polyalkenamers are given in Table 12.8. It can be observed that most polyalkenamers included are considered to possess 74-85% trans structure or 95-100*,6 cis structure. Table 12.8 Crystalline meltm~ points ~T~) ofpolyalkenamers' Polyalkmamcr Trans Tm AH ~t %
Polybutenamer Polypentenamer
Polyheptenan~r Polyoctenamer
1 1 85
-
44 51 17 62 77 73 60 72 80 80 82 84 202
(trans)
11
100 100
87 100
(trans)
96 100 Polynorbomene
(trans)
j/gb
-5 -41 18
100
100
Polydodecenamer
o c
100
(trans)
Poly~amer
_
176.6
37.6 220.1 136.4 185.8 241.5
251.1
9Data from reference "'; ~To convert J to cal, divide by 4.184
Method
_
DSC DTA DTA Diluent DSC X-ray DSC X-ray Diluent Dilatome~ Diluent DSC Diluent X-ray DSC Diluent X-ray
928 As Table 12.8 shows, trans-polypentenamer exhibits the lowest melting temperature of the series ( 18~ for 85% trans and -4 I~ for 99~ cis), very close to that of natural rubber. This property seems to be an optimum range of melting temperature from the point of view of the elastomeric properties. However, trans-polybutenamer, which melts much higher, has an abnormal behavior, which is likely to be related to the different chain packing and to the vicinity of the double bonds. It may be pointed out that the triclinic forms of even trans-polyalkenamers exhibit higher melting temperatures than the monoclinic forms and that this behavior appears to be related to trans-polybutenamer. The influence of microstructure on melting temperature has been investigated in detail for trans-polypentenamer, trans-polyoctenamer, transpolydecenamer, trans-polydodecenamer and cis-polyoctenamer. 85 Notwithstanding, the control of microstructure in polypentenamer has received special attention because of the commercial interest of this elastomer, and the technological importance of this crystallization phenomenon. These properties refer particularly to the processability in rubber-mixing equipment, tensile properties of cured and uncured polymers, and to cured characteristics such as the tear and abrasion resistance and low temperature flexibility. The higher trans-polyalkenamers possess melting points that are too high to have good elastomeric properties at conventional temperatures. On the contrary, stereoregular cis-polyalkenamers exhibit much lower melting temperatures than the corresponding trans isomers (e.g., cispolypentenamer melts at -41~ If one assumes, also for the cispolyalkenamer series, that the melting point increases with increasing length of the methylene sequence, one could expect melting points shortly below room temperature for a cis-polyalkenamer having a methylene sequence between 4-10 units. This situation is fully met in the case of cispolyoctenamer prepared by DaU'Asta and Manetti. 94 For instance, polyoctenamer of 90~ cis configuration showed an experimental melting point of 18~ i.e., the same as that of trans-polypentenamer of 85% trans content. It is significant that the melting temperatures of polyalkenamers not only depend on the type of double bonds but also on their steric purity. On this line, Calderon and Morris 95 investigated the dependence of the Tm values on the trans content of polyoctenamer. For this purpose, the Tm values were measured dilatometrically on bulk and on benzene-diluted polymers, after assuming the validity of the Flory equation, by considering
929 the cis octenamer groups as randomly distributed, non crystallizable units. By extrapolating the T J c i s content plot for 100~ cis to transpolyoctenamer a melting temperature of 73~ was found. Surprisingly, cis , contents of polyoctenamer up to 50~ did not prevent crystallization. This finding, as well as the discrepancies of the heat and entropy of fusion values observed between bulk and diluted polymer measurements were assigned, at least in part, to a non-ideal random distribution of the cis double bonds in the polymer. Gianotti and Capizzi ~ employed an analogous approach for the determination of thermodynamic quantities of trans-polyoctenamer, transpolydecenamer, and trans-polydodecenamer. The meRing point depression method of Flory (r diluent), used to polyalkenamers of widely different trans content, allowed these authors to calculate T.. values for 100% trans polymers. The above authors also determined the fusion enthalpies and entropies for trans polypentenamer by using the meltin~ point depression method for polypentenamer of 85% trans configuration. ~' Values of T,,, fusion enthalpy and entropies for different transpolyalkenamers are presented in Table 12.9 Table 12.9 Values ofthemmdynamic parameters of fusion of some trans-polyalkenamers ~
Polyalkcnamcr
Crystalline modification
T~, ~
td-l. cal/mole
AS~,eal/ mole.deg
aS/boad, cal/
mole.dog Polyethyleneb orthorhombic 411 1,4-Polybutadieneb monoclmic 370 Polypemenamer~ orthorhombic 300 Polyoctenamerb triclinic 350 unknown 346 Polyoctenamer' Polydecenamerb monoclmic 353 Polydodecenamerb monoclinic 357
1920 3300 2870 5680 4800 7850 9840
4.68
8.90 9.36 16.20 14.4 22.20 27.60
2.34 2.90 2.34 2.32 2.06 2.47 2.50
9Data from reference 95.~; b Extrapolated values; Non extrapolated exp. values.
The decrease of the melting temperature with decreasing steric purity has been observed by G. Dall'Asta and coworkers n also for cis-
930 polyoctenamer. In this case, the T~ values linearly decrease from 18~ down to -8~ for polyoctenamer containing from 93 to 60% cis double bonds. A polyoctenamer with 60~ cJs and 40~ trans double bonds can be prepared not only employing a normally cis-specific catalyst, but also by using a normally trans-specific catalyst under specific conditions. However, the two polyoctenamers have different melting temperatures: the former exhibits Tm= - 8~ whereas the latter T~ = +I0~ This finding suggested the occurrence of some heterogeneity of the double bond distribution in the polymer chain. It was supposed that limited regions of predominantly cis double bonds in the former, and limited regions of trans double bonds, in the latter, should coexist with other regions in which both types of double bonds are randomly distributed and mutually prevent crystallization. Crystallization rate. Crystallization rate is a very important characteristic for rubber processing and elastomer applications. A high quality rubber should be substantially amorphous at room temperature and somewhat below, but should rapidly crystallize under stress. Two of the polyalkenamers which meet the Tm and T s requirements, i.e., transpolypentenamer and cis-polyoctenamer, have been studied with the aim of evaluating theircrystallizationrates. Normally, both polyalkenamers do not crystallize at room temperature in the unstretched state within reasonable times. However, under stress, trans-polypentenamer rapidly crystallizes thus improving the building tack of rubber mixes and causing self-reinforcement resulting in high green strength and consequently in good processability. In their studies on the rate of crystallization, in the unstretched state, of polypentenamers having different trans contents, Haas and Theisen99 showed that the crystallization half-times may be strongly increased even by small decreases of the trans content of polypentenamer. The effect of microstructure of trans-polypentenamer on the crystallization half-time is illustrated in Table 12.10 and compared with similar data of other general purpose rubbers. As it can be seen from these results, it was necessary to reduce the trans content of polypentenamer below the equilibrium value in order to duplicate the properties of natural rubber. The kinetics of crystallization of an unstretched 85% transpolypentenamer has been examined by Capizzi and Gianotti 9~ dilatometrically at different temperatures in the range of 0~ to 14~ Data obtained on the crystallization half-times as a function of temperature indicated fast crystallization rate in the region of 0~ to -8~ By comparing this behavior of trans-polypentenamer with that of natural
931 Table 12.10 Crystallization half-times (tt~) of polyalkman~rs and rubbers ~b
Polymer
tt~ at 0~
Trans/CJs"
cis- 1,4-Pelybutadiene cis- 1,4-Polyisoprene Natural rubber
5/95 2/98
t rans- P ol ypemenamer t rans- P ol y p m t m a r ~ r tra ns-p o lyp entenamer t r a ns-po ly p e m en a me r
93/7(85/15) 90/10(82/18) 89/11(81/19) 87/13(79/21)
hr
weeks >>100 50 0.3 0.8 13 45
i
9Data from referencegS; i, Results obtained at 0~ ~ Values in parentheses are estimates based on r e f m e ~ in infrared analysis method t~176 rubber under analogous conditions, one can observe how much faster transpolypentenamer crystallizes than the natural rubber (Figure 12.38).
log ttn 2
9
-30
-20
9
-I0
a
0
9
+10
9
+20
Ten~., ~ Figure 12.38. Crystallization half-times(log tt~) of trans-polypentenamer (1) and natural rubber (2) at various temperatures (Adapted from Ref.~7)
932 Interesting studies, carried out by Dall'Asta and coworkers, 9s on the rate of crystallization of cis-polyoctenamer (90%cis), trans-polypentenamer (85% trans) and natural rubber as a function of the degree of undercooling (T~.q>-T~) showed cis-polyoctenamer to be the fastest crystallizing of the three polymers (Figure 12.39). log ttrz (mm)
10
20
30
40
50
Tmoq- Tx (~ Figure 12.39. Crystallization half-times of cis-polyoetenamer (COR-1,2,3,4), trans-polypentenamer(l'P-5)and natural rubber (NR-6) as a function of the degree of undercoolmg (T~,,0-T,,) (Adapted from Ref.9') This data are quite surprising if one considers that cis-polypentenamer (T~=-41~ has a very low crystallization rate in the whole range between 41~ and -78~ Furthermore, Calderon ~~ determined the rate of crystallization of unstretched trans polyoctenamer at a temperature 17.9~
933 below melting temperature. Thus, polyoctenamer containing 78, 74, and 41% trans double bonds indicated tv2 values of 16, 32, and 3000 min, respectively. These results showed that trans-polyoctenamers, under comparable undercooling conditions, are slower crystallizing than cispolyoctenamer having the same steric content. In an analogous manner to natural rubber and other elastomers under stress, trans-polypentenamer showed an increase in melting temperature when stress was applied in cured samples. Thus, stress-induced crystallization occurred at test temperatures above the normal melting point of the unstressed polymer, resulting in strengthening. Crystallization kinetics and melting points of peroxide-cured trans-polypentenamer as a function of elongation have been examined by birefringence technique. ~~ It was observed that melting points increased from ca 17~ to 38~ as elongation increased to 300%. The effect of strain rate on stress-strain properties of trans-polypentenamer is presented in Figure 12.40. Stress, MPa 16,
Break
14 12 10 Break
), (Upturn) 1
2
3
4
5
6
7
8
9
Figure 12.40. The mflumce of strata rata on stress-gram properties of trans-polypomenamer at 10~ 9l-R=0.002s'~; 2-R=300s "~ (To convert Mpa to kgf/cmz, multiply by 10) (Adapted from Ref. ~0z)
934 In a similar study applying stress-decay measurements, ~~ it was found that melting temperature of trans-polypentenamer was much less dependent on elongation than in natural rubber because polypentenamer possesses a much higher heat of fusion. Crystallographic characterization. In their systematic crystallographic studies on polyalkenamers, Natta and coworkers ~~ provide the basic crystallographic parameters for most trans-polyalkenamers, from polypentenamer to polydodecenamer. The polyalkenamers obtained from cyclopentene and cycloheptene exhibited crystallinity analogous to that of polyethylene: two types of behavior were observed, depending on whether the cycloolefin possessed an odd or an even number of carbon atoms. Thus the "odd" polyalkenamers exhibited a single crystallographic form, which was orthorhombic whereas the "even" polyalkenamers presented polymorphism, with two distinct crystalline forms, monoclinic and triclinic. Relevant data concerning the crystalline form, number of monomer units in the identity period, and length of the identity period are summarized in Table 12.11. Table 12.11 Crystalline form and crystallographic identity periods for trans-polyalkenamers" Polyalkenamer
trans-Polypentenamer trans-Pol yheptenamer trans-Polyoctenamer trans- Po lyoctenamer trans-Polydecenamer trans-Polydecenamer trans-P ol ydodecenamer trans-P ol ydodecenamer t rans- Pol ynorbomenamer
Crystalline form
orthorhombic orthorhombic monoclinic triclinic monoclinic triclinic monoclmic triclinic
Monomer units in unit cell
Identity period 1.19 1.71 0.99 0.97 1.24 1.23 1.485 1.478 1.18
Data from reference ~o4 Generally, the homologous trans-polyalkenamers possess similar chain conformations in the crystal lattice; however, copolymers with high trcms content exhibit isomorphism. Random trans copolymers of
935 cyclopentene-cycloheptene, cyclopentene-cyclooctene, and cyclooctenecyclododecene show crystallinity over the entire copolymer composition range. These copolymers may be considered as possessing a linear polyethylene frame that contains trans vinylene units that cause only minimal distortion of the crystal lattice and thus are able to crystallize. Because of the irregularity of the trans vinylene units, these crystalline copolymers possess only bidirectional order, in contrast to the three dimensional order of the homopolymers. For copolymers, also, the melting points and degrees of crystallinity are lower than for the corresponding homopolymers. The morphology of solution-grown single crystals of transpolyoctenamer, trans-polydecenamer and trans-polydodecenamer have been examined by Martuscelli et al. ~~176 In these studies they observed that the lamellar single crystals exhibited chain fold whose length varied, depending on crystallization temperature and trans content. Interestingly, low degree of crystallinity was attributed to the presence of cis alkenamer defects incorporated into the crystals. Density, apparent fusion enthalpy, degree of crystallinity, and end surface free energy of crystallites were investigated for polydodecenamers having different trans content as a function of annealing temperature and thickness of the crystallites. Moreover, the above authors ~~ investigated the effects of oxidative attack by ozone or nitric acid upon trans-polydecenamer and transpolydodecenamer single crystals. Results on the changes of double bond concentration and molecular length distribution revealed that the unsaturations were attacked deep within the crystals without clear distinction between fold surface and crystal interior. These authors found that the attack of the oxidant does not follow a random pattern, but preferentially leads to dimeric residues, which appear highly resistant in spite of the double bond. Apparently, crystallographic studies for the cis-polyalkenamers have been carried out on a reduced scale because of the very low melting points of some members of the series and because of the unavailability of polymers possessing sufficient structural purity. 12.4. References
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939 1545 (1977); b. J.G. Hamilton, K.J. Ivin and J.J. gooney, Brit. Polym. ,/., 16, 21 (1984); c. J.G. Hamilton, K.J. Ivin, G.M. McCann and J.J. Rooney, Makromol. Chem., 186, 1477 (1985). 68. T.J. Katz, S.J. Lee and M.A. Sheppey, J. MoL Catal., 8, 219 (1980). 69. a. K.J. Ivin, G. Lapienis and J.J. Rooney, Polymer, 21,436 (1980); b. K.J. Ivin, L.M. Lam and J.J. Rooney, MakromoL Chem., 182, 1847 (1981). c. J.G. Hamilton. K.J. Ivin and J.J. Rooney, J. Mol. Catal., 28, 255(1985). 70. a. B. Bell, J.G. Hamilton, O.N.D. Mackey and J.J. Rooney, J. Mol. Catal., 77, 61 (1992); b. J. Hamilton, J.J. Rooney and D.G. Snowdert, Makromol. Chem. Phys., 196, 1031 (1995); c. J. Hamilton, K.J. Ivin and J.J. Rooney, J. Mol. Catal., 36, l 15 (1986). 71. V. Dragutan, L. Popescu, S. Coca and M. Dimonie, in "Metathesis Polymerization of Olefins and Polymerization of Alkynes"(Y. Imamoglu, Ed.), pp. 103-II 5, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1998. 72. G. Gianotti, U. Bonicelli and D. Borghi, Makromol. Chem., 166, 235 (1973). 73. W. Glenz, W. Holtrup, F.W. KOpper and H.H. Meyer, Angew. Makromol. Chem., 37, 97 (1974). 74. G.Dall'Asta, P. Meneghini, and U. Genaro, Makromol. Chem., 154, 279 (1972). 75. P. Gunther, F. Haas, G. Marwede, K. Niatzel, W. Oberkirch, G. Pampus, N. SchOn and J. Witte, Rubber Chem. Technol. 43, l116 (1970). 76. a. G. Odian, "Principles of Polymerization", 3'd Ed., John Wiley & Sons, New York, 1991; b. W. Kern and R.C. Schulz, in "Methoden de Organischen Chemie" (E. M011er, Ed.), 4~ Ed. Vol. 14/l, Thieme Verlag, Stuttgart, 1961. 77. a.L.F. Cannizzo and R.H. Gnabbs, Macromolecules, 20, 1488 (1987); b.L.F. Cannizzo and R.H. Grubbs, Macromolecules, 21, 1961 (1988); 78. a.K.C. Wallace and R.R. Schrock, Macromolecules, 20, 450 (1987); b. K.C. Wallace, A.H.Liu, J.C. Dewan and R.R. Schrock, J. Am. Chem. Soc., 110, 4964 (1988). 79. a. G.C. Bazan, R.R. Schrock, H.N. Cho and V.C. Gibson, Macromolecules, 24, 4495 (1991); b. G.C. Bazan, J.H. Oskam, H. Cho, L.Y. Park and R.R. Schrock, J. Am. Chem. Soc., 113, 6899 (199 l). 80. B.M. Novak, W. Risse and R.H. Grubbs, Adv. Polym. Sci., 102, 47
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943
Chapter 13
THERMODYNAMIC ASPECTS OF CYCLOOLEFIN POLYMERIZATION
The thermodynamics of the cycloolefm polymerization possess a series of specific features, distinct from those of linear olefins. These features are determined by the thermodynamic stability of the cycloolefins, the free energy of reaction and the corresponding reaction enthalpy and entropy, the polymerization equilibrium and the thermodynamic stability of the product poly(cycloolefin)s. Based on the existing studies carried out on the catalytic polymerization of cycloolefins, the present chapter focuses mainly on the thermodynamic stability of the cycloolefin monomers, the relevant thermodynamic parameters of the polymerization reaction and the types of thermodynamic equilibrium occurring particularly in the ringopening metathesis polymerization of cycloolefins.
13.1. Thermodynamic Stability of Cycloolefin Monomers The thermodynamic stability of the cycloolefins is an major parameter which will determine greatly both the enthalpy and flee energy of the reaction and consequently the polymerizability of these monomers. Taking into account that the double bond of the cycloolefin makes a minor contribution to the stability of the ring, at least for medium and large tings, the thermodynamic stability can be easily followed along the entire range of cycloolefins by comparison to the corresponding cycloalkanes. The thermodynamic stability of cycloalkanes was evaluated by Eliel ~ on the basis of the heats of combustion for these compounds. It is obvious, as it can be seen from Table 13.1, that the small tings of three or four carbon atoms, with the highest heats of combustion, will have the lowest stability as a consequence of a considerable deviation of the ring angles from the normal tetrahedral angle of the sp3-hybridized carbon atoms, 109~ '. Cyclopentane and medium or large rings (but not cyclohexane) present slight deviations from the normal value, as result of eclipsed conformations and of the interaction between the methylene groups, cyclohexane, however, which has a normal heat of combustion, possesses a strainless
944 chair conformation and has the highest stability of the ring (Table 13.1). Table 13.1 Heats of combustion for n-memberod cycloalkanes~ i
n-Membcred cycloalkane
Heat of combustion b
Ring stratar kcal/mole
3 4 5 6 7
9.2 6.55 1.3 0.0 0.9 1.2 1.4 1.2 1.0 0.3 0.4 0.0 0.1 0.2
27.5 26.1 6.1 0.1 6.1 9.7 12.5
8
9 10 11 12 13 14 15 16
kcal/mole
9Increment per CHz group to the value of 157.4 kcal/mole for the CHz group of alkanes or cyclohexane; bData from reference~Data from referencezd To convert kcal to Id, multiply by 4.184.
Due to their structural relationship, cycloolefins exhibit a thermodynamic behavior akin to that of cycloalkanes. Since the two sp zhybridized carbon atoms of the double bond have the normal valence angle of 120 ~ the steric strain of n-membered cycloolefins is slightly larger than that of the corresponding n-membered cycloalkanes. It was observed that in many polymerization reactions, the cycloolefins have several peculiarities closely related to the stability of the ring. Thus, small tings, such as cyclobutene and cyclopentene, are easily polymerizable3'4 while cyclohexene has not been polymerized by ring-opening under usual conditions 5 and the polymerizability of larger tings decreases with increasing the ring size6. The non-polymerizability of cyclohexene under usual conditions is attributed to the high stability of the six-membered ring. Cyclohexene
945 occurs primarily in the chair form. According to published data, 7 this conformation is with 29.2 kJ/mole more stable than the boat form. The stability of the chair conformer considerably restrains its mobility and decreases the probability of its conversion into other conformations (boat and twist form), which would allow the access to the reaction centre. Estimation of the barrier of pseudorotation from the chair form into another, involving a boat form as intermediate, gave values of 22.2 and 26.7 kJ/mole. 8'9 Attempts to polymerize cyclohexene with metathesis catalysts, under normal conditions, actually led to vinyl polymers which contain even the more stable cyclohexane ring in the chain. ~0 The stability of cyclohexene relative to the polyhexenamer was revealed by Hocks et al. ~ through the elimination reaction of cyclohexene from the polymer chains containing [=CH(CH2)4CH =] units when treating this polymer with WCIdEtAICI2 as a catalyst (Eq. 13.1).
It is well-known that cyclohexene adopts the less stable boat conformation in a series of bridged, highly strained bicyclic and polycyclic compounds such as norbomene, dicyclopentadiene, tricyclodecene and bicyclo[2.2.2]octene. The lower stability of the boat form in these compounds will favor their ring-opening polymerization. In this case, the polymerization reaction of these strained structures is possible because of the release of the ring strain as the driving force. In their extensive thermodynamic studies on the polymerization of small and medium tings, Natta and Dall'Asta ~z established the dependence of the polymerizability of cycloolefins on the ring strain. They demonstrated that the polymerizability of small ring cycloolefins can be directly correlated with the ring strain while for medium tings, where the strain energy is relatively low, the polymerizability is related to the entropy change during the reaction.
13.2. Thermodynamic Parameters of Cycloolefin Polymerization It is important to outline that the thermodynamic parameters of conventional vinyl polymerization are different from those of the ring~ opening polymerization. This behavior can be readily inferred from the
946 nature of the chemical bonds involved in both vinyl and ring-opening polymerization processes and the stability of the final products. First, in the vinyl polymerization the carbon-carbon double bond of the monomer is transformed into two carbon-carbon single bonds whereas in the ringopening metathesis polymerization the overall number of carbon-carbon single and double bonds of the monomer are preserved into the polymer. Moreover, the stability of the final products, poly(cycloalkylene) and polyalkenamers is totally different. Consequently, the vinyl polymerization will be strongly favored by enthalpy and weakly influenced by entropy while the ring-opening polymerization will be mainly favored either by enthalpy or by entropy. Furthermore, in the ring-opening metathesis polymerization the enthalpy factor is strongly influenced by the release of ring-strain as compared to vinyl polymerization. This parameter is particularly large in four- and five-membered tings; cyclohexene, which is almost a strain-free ring, is an exception, the equilibrium favors the monomer. Taking into account that the polymerization of cycloolefins is an equilibrium process, the main thermodynamic parameters of the reaction can be estimated by Eq. 13.2 AG = All- TAS
(13.2)
where AG represents the free energy change during the polymerization reaction, z~H the enthalpy change and AS the entropy change, respectively. It is significant to note that in their early work, Dainton and coworkers ~3'~4employed a semiempiric~ method to calculate the enthalpy, entropy and free energy changes in the hypothetical polymerization of cycloalkanes to the corresponding polymers (polyethylene or polymethylene). As it can be observed from Table 13.2, the lowest values of the free energy of polymerization were found for cyclopropane and cyclobutane (-22.1 and -21.2 kcal/mole, respectively) whereas the highest value was found for cyclohexane. For small tings, though the reaction entropy is negative, it can be seen that the reaction enthalpy greatly determines the value of the free energy and, accordingly, makes the polymerization of these tings possible. Cyclohexane, with a positive reaction enthalpy will have a positive free energy as well; the polymerization of cyclohexane ring is thus thermodynamically unfavorable. However, the larger tings possess negative free energies for polymerization reaction, what render them polymerizable. Besides the reaction enth~py, the entroov has a significant contribution to the free ener~ for these rintzs.
947 Table 13.2. Reaction ~halpy, entropy and free energy in the hypothetical polymerization of cycloalkanes' i
Cycloalkane (CH2h
kcal/mole
cal/mole.de8
AGo kcal/mole
n=3 n=4 n=5 n=6 n=7 n=8
-27.0 -25.1 -5.2 +0.7 -5.1 -8.3
-16.5 -13.2 -10.2 -2.5 -0.7 +8.9
-22.1 -21.2 -2.2 +1.4 -4.9 -11.0
/~iS ~
9Data from reference~3; b To convert cal to J, multiply by 4.184. In some case, e.g. for cyclooctane, the reaction entropy is positive. It was observed that cycloolefins have a similar trend to that found for cycloalkanes. Semiempirical thermodynamic parameters for the polymerization of cyclopentene and larger cycloolefins are given in Table 13.3. As Table 13.3 illustrates, cyclobutene, cyclopentene, cycloheptene and cyclooctene have a considerable negative value of the reaction enthalpy, resulting in a negative value of the free energy of reaction. By analogy to the hypothetical reaction of cycloalkanes, though the reaction entropy of these cycloolefins is negative, the reaction enthalpy greatly determines the value of the free energy change and, accordingly, makes the polymerization of these tings possible. In contrast, cyclohexene with a positive reaction enthalpy will have a positive free energy as well and, consequently, the polymerization of cyclohexene ring is thermodynamically unfavorable. However, it was observed that between -45~ and -84~ where AG is less positive, up to 14% of cyclohexene can be converted to oligomeric products (DP<6) in the presence of WCI6/(CH3)4Sn. These cyclic oligomers revert to monomer when warmed at room temperature in the presence of the same catalyst. ~s The thermodynamic parameters determined for vinyl polymerization of cycloolefins are scarcely reported. Sigwalt and coworkers ~9 found the enthalpy of reaction for cyclopentadiene polymerization under the influence of TiCI30'Bu to be -14.1 kcal/mole (-59 kJ/mole). The same authors obtained for indene polymerization, under the
948 influence ofTiCl30'Bu, a value of-13.9 kcal/mole (-58.15 kJ/mole) for the reaction enthalpy. Table 13.3. Semien~irical thermodynamical parameters for the r m g ~ m g metathesis polymerization of cycloolefins at 25 ~ .AH o
Monomer
Polymer
kJ/moleb (kcal/mole)
.AS~ J/K.moleb (cal/K.mole)
Cyclobutene Cyclopentene
cis
121 16 (3.82) 20(4.46) -2(-0.48) 2(0.48) 16(3.82) 20(4.8) 20(4.8) 22(5.26) 25 33 62.2
52 46(10.99) 46(10.99) 31(7.41) 28(6.7) 20(4.8) 17(4.06) 2(0.48) 2(0.48) 5 5 50
r trans
Cyclohexene
cis trans
Cycloheptene
cis trans
Cyclooctene (Z)
ci$ trans
1,5-Cyclooctadiene
ci$ trans
Norbomene
45% trans
_AGo kJ/moleb (kcal/molr 105 2.3(0.55) 6.3(1.5) -6.2(-1.48) -7.3(-1.74) 8.0(1.91) 14.0(3.35) 19.0(4.54) 20.0(4.8) 19 24 47
~'Data from references tS~7;b'l'o convert J to cal, divicie by 4.184.
Estimation of the thermodynamic parameters for the ring-opening polymerization of cyeloolefins comes from the reports of Natta and Dall'Asta, 12 Calderon, 2~ Hocker, 21 Teyssie ~ and other authors. ~ Based on an empirical method analogous to that employed by Dainton for the hypothetical polymerization of cycloalkanes, Teyssie and r ~ calculated the thermodynamic parameters for a series of r with the monomers in the liquid state and polymers in the condensed state. They found that for small and highly strained tings, polymerization was allowed because of the high value of the reaction enthalpy. They observed that, generally, for these tings the enthalpy change was negative and it determined to a great extent the free energy of polymerization. Alternatively, Natta and Dall'Asta ~2 showed that the reaction enthalpy for small tings depends mainly on ring strain, this factor being the driving force for the polymerization of these cycloolefins. For instance, in the case
949 of cyclobutene, a cycloolefin with large ring strain, the high negative value of the enthalpy favors ring-opening polymerization, whereas, by contrast, its negative entropy contributes with a positive value to the free energy.
13.3. Thermodynamic Equilibrium in Ring-Opening Metathesis Polymerization There are four types of equilibrium in the ring-opening metathesis polymerization of cycloolefins: (i) monomer-polymer equilibrium, (ii) ringchain equilibrium, (iii) cis-trans equilibrium and (iv) equilibrium between chains of different lengths. (i) Monomer-polymer equilibrium. The ring-opening metathesis polymerization of cycloolefins is a reversible process, consequently, under given conditions the equilibrium conversion of the monomer and polymer is reached (Eq. 13.3). nM
_..
"-
Pn
(13.3)
It is significant to note that this equilibrium is determined by the relative stability of the monomer and polymer, by the characteristic thermodynamic parameters such as the reaction enthalpy and entropy or the overall free energy as well as by the reaction conditions such as monomer concentration, reaction temperature and solvent. The equilibrium concentration of the monomer is given by the relationship (Eq. 13.4) In [M], = AHdRT - AS~
(13.4)
where [M], represents the equilibrium concentration of the monomer, AH0 the enthalpy change during the polymerization reaction, AS~ the standard entropy change, T the reaction temperature, and R the ideal gas constant. The free energy of ring-opening metathesis polymerization is negative for three-, four-, eight, and larger-membered tings which completely polymerize at normal temperatures and monomer concentrations. With five-, six-, and seven-membered tings, the low strain energy of the ring results in a rather low or even negative enthalpy of polymerization (-AH), consequently, the decrease in the free energy (-AG) will also be small and either positive or negative, depending on the monomer concentration, reaction temperature, monomer and polymer structure. Whether or not the cycloolefin will polymerize at all and to what
950 extent that will depend very much on the reaction conditions. Thus, cyclopentene will polymerize only if the equilibrium monomer concentration [M], is exceeded; this concentration is higher for the formation of cispolypentenamer than for trans-polypentenamer and increases with increasing temperature (Figure 13.1). In[M]. (
cp - - r,cp )
2
'
3.4
3.6
3.8
,,'o
4.2 '
10-3-VI/K-I Figure 13.1. Equilibrium monomer concentration for cyclopentene (CP) polymerizationz~ (1) cis-catalyst WCIdAllyl4Si; (2) trans-catalyst WCIJEtAICI2 (Adapted from Ref.z3) The values of [M], at 263 ~ are 0.4 and 3.2 mole~ for cis- and transpolypentenamer, respectively. This fact indicates that the cis polymer has a free energy of ca. 5 kJ/mole greater than the trans polymer. Ofstead and Calderon 2~ quantitatively determined the equilibrium monomer concentration in the reaction of cyclopentene at various temperatures in the presence of the ternary catalytic system WCIdEtOH/EtAICI2. On carrying out the reaction at temperatures of 0, 10, 20 and 30~ they found a characteristic dependence of cyclopentene concentration on temperature. The minimum equilibrium concentration of 0.51 molefL was obtained at 0~ what corresponded to a maximum concentration of monomer of 78%. On the contrary, the maximum equilibrium concentration of 1.19 molefL was reached at 30~ corresponding to a value of the conversion under 50% (Table 13.4).
951 Table 13.4 Equilibrium concentration of cyclopentene polymerization with the ternary catalytic system W C I 6 / E t O ~ C I 2 at various temperatures~b Reaction Temperature ~
Equilibrium Concentration, [M], mole~
0
0.51 0.70 0.88 1.19
10 20 30 'Data from reference2~ [Monomer]'[WCle] = 4.5 x 10 3
bReaetio,
eo, ditiom: [M],=2.2[M].
Thus, by this way, from the equilibrium concentration of the monomer at various temperatures, the thermodynamic parameters of the reaction could be estimated. (ii)Ring-chainequilibrium.Jacobson and Stockmayer24 developed a theory of ring-chain equilibrium based on the consideration of the set of reaction equilibrium (Eq. 13.5) Pn
:..
~
~
+
Cm
(13.5)
where P, and P~.~ are linear polymer chains of degree of polymerization n and n-m, respectively and Cm is a cyclic oligomer of m degree of oligomerization. The Jacobson-Stockmayer theory includes the following four assumptions: (a) all tings are strainless and there is no heat of cyclization, (b) the end-to-end distances of linear chains obey Gaussian statistics, (c) the probability of ring formation is governed by the fraction of all configurations for which the ends coincide, and (d) the reactivity of each terminal functional group is independent of chain length. It follows from the first assumption that only the entropic term contributes to the equilibrium constant as there is no heat of cyclization for strainless tings. There are two contributions to the entropy change: a positive one due to the dissociation of one molecule of polymer into two molecules of polymer and cyclic oligomer, respectively, and a negative one due to the decreased number of configurations on going from a linear chain to a linear and a cyclic product.
952 The reduction in configurational entropy increases with ring size m but is independent of n. According to Jacobson and Stockmayer, the equilibrium constant K~, for the resulting oligomer C~, depends only on m and is given by Eq. 13.6.
I~= (3/27t)ar2xl/NAx(l/v12~)3r2m'Sr2
(Eq. 13.6)
where NA is Avogadro's number, v is the number of bonds in the monomer unit, I is the average bond length, Cm = /vml is the constant characteristic ratio. If is substituted by the characteristic ratio c~ and if c,, is assumed to be constant, which is generally valid for molecules, the number of bonds of which is > 50, K. is proportional to m "zS. When the logarithm of the equilibrium constant, Kin, was plotted v e r s u s the logarithm of degree of polymerization for cyclobutene, cyclooctene, cyclododecene and cyclopentadecene, straight lines with the slope -5/2 were obtained (Figure 13.2). log K. 1
-2.0
-2.5
2
3
9
v
0
4
5
9
X
10 .
9
.
.
9
9
v
9
v
.
9
0
-
4 -3.0 -
-3.5
0.2
0.4
0.6
0.8
1.0
1.2
log m Figure 13.2. Plot of log K., versus log m for various cycloolefins (lcyclooctadiene; 2 - c y c l ~ e ; 3-cyclododecene and 4-cyclopentadocene)
953 As it may be seen from Figure 13.2, K~ decreases with increasing m. Significant deviations have been observed for the oligomers with m<4. Moreover, the smaller the degree of unsaturation, the lower is the position of the straight line; this is equivalent with a higher c,, value and consequently a stiffer chain. Although the original theory gives the correct form of dependence of K~ on m, generally, the calculated values of Ks are too high. This originates from the fact that Jacobson-Stockmayer theory requires an accurate value of O in order to predict K~. This need has been refined by using the rotational isomeric state model (tLIS) to calculate the end-to-end distances of chain molecules." The results of RIS model for K,, agree very well with the experimental data for macrocycles having more than 30 backbone atoms, but the predicted values of Ks for smaller cycles are still too high. To remedy the failure of these models to agree with the experimental values of K~, another approach has been developed ~ taking into account the enthalpic contribution to the change in free energy of reaction 13.5. For this purpose, the strain energy has been estimated by means of a Monte Carlo configurational search using molecular mechanics (MM3) and the equilibrium constants, K,,, have been calculated from both the enthalpic and entropic contributions to the free energy (Eq. 13.7). (13.7)
In K,, =-AH.,/RT + In[ l/2iN^(3/2n) 3r~]
This approach led to a better agreement between the calculated and experimental values of K,, for cyclobutene, even for small m (Figure 13.3). log(K,,) |-".... !
O
L
[ cB
q. """""
---
PCB
]
1
r ~176
-2
-
1
,b q.
o
~'~'Jhk
~ ""
10 m
Figure 13.3. E x p e ~ l and calculated rmg-c,ham equilibrium constants K= for cyclobutene reaction (CB --~ PCB) (1" J-R theory; 2" JS-RIS model; 3 Chert model'S; 4:Exp.) (Adapted from Ref.~
954 The existence of the thermodynamic equilibrium in the ring-opening polymerization of cycloolefins has been first observed by Calderon and coworkers. 27 These authors evidenced the equilibrium that has been established between the monomer and growing tings and the equilibrium between the macrocycles formed in the previous process and the linear polyalkenamer (Eq. 13.8). m
/ - - . _ .......
R,,,,,,R
0 An important finding is the constant oligomer distribution which can be attained starting from monomer, a single oligomer or a fraction of higher oligomers, or from the polymer. The absolute concentration of cyclic oligomers was found to be constant above a minimum monomer concentration, and independent of the catalyst concentration or temperature in a certain range between 0~ and 100~ Up to a minimum monomer concentration named cut-off point, the monomer is generally converted into cyclic oligomers, while above this concentration linear polymers are formed. It is noteworthy that higher monomer concentrations will result in higher polymer/oligomer ratios. The equilibrium monomer concentration, [M]~, is a measure of the polymerizability of cycloolefins. Depending on the size and nature of the cycloolefin, the terms of Eq. 13.7 make different contributions to the value of the equilibrium monomer concentration, i.e. of the polymerizability. Thus, Natta and Dall'Asta ~2showed that for small tings the polymerizability is determined mainly by the strain energy. On the other hand, the polymerizability of larger tings is determined principally by the entropy of the ring. Generally, the equilibrium monomer concentration decreases with increasing of the ring size. The value of the equilibrium monomer concentration, [M]~, was related directly to the entropy of formation, AS~ by the relationship from the equation 13.9. R ln[M], = AS~
(13.9)
Noteworthy, it was found that the plot of the entropy per carbon atom v e r s u s the number of carbon atoms for cyclobutene, cyclooctene, cyclododecene and cyclopentadecene resulted in a common curve (Figure 13.4).
955 (~/~
0.8 0.7 0.6 0.5
0.4
"/
9 cydobutone
el
o
o
cydodo<::lecene
c ~ n t a d ~
" "~- |,x, ~ 8 e',~ All
0.3
IIJ-._.t.__ e-
0.2 0.1
2o
3O
40
50
60
70
80
90
1O0
110
Temp., ~ Figure 13.4. Standard entropy of formation per carbon atom as a function of ring size for cyclic oligomers from diffcrmt cycloolefms (Adapted from Ref.21) Consequently, the number of double bonds has no effect on the entropy of formation for these cycloolefins. Detailed studies on the ring-chain equilibrium for the polymerization of cyclooctene have been reported by Scott 2s and Hocker. 29 Scott found that the polymer obtained in the absence of acyclic olefin consisted of 1520% cyclic and 80-85% linear product. 2s However, HOcker et al. 29 correlated the product distribution with the initial monomer concentration, they showed that below an initial monomer concentration of 0.1 mole/L practically no monomer was present while at higher concentrations the presence of cyclic oligomers and linear polymer was evidenced. Moreover, in the ROMP of cyclooctene, HOcker et al. ~ pointed out that there are no polymers formed until the monomer concentration exceeds 0.21 mole~, which is much higher than the equilibrium monomer concentration of 0.1 mole~. Since [M], provided such a poor indicator of polymerizability in this case, HOcker proposed the concept of critical monomer concentration [M]r defined as the total amount of monomer per unit volume that forms cyclic products at ring-chain equilibrium. If the initial monomer concentration is less than [M]r only cyclic and eventually linear oligomers are formed. After exceeding [M]~, the equilibrium cyclics concentration is
956 almost constant and linear polymers begin to appear. The critical concentrations of a number of cycloolefins have been predicted theoretically 26 and determined experimentally. 3~ The oligomer-polymer equilibrium in the reaction of 1,5cyclooctadiene has been investigated by Scott, 27 Calderon, 3z Chauvin, 33 Hocker, 29 Thom-Csanyi 3~ and other authors. 3~ On usin~ (CO)4(PPh3)W=C(OMe)PhffiCh as a catalyst, Chauvin and coworkers 3 found that the molecular weight distribution in both oligomer and polymer is constant whatever the starting material (l,5-cyclooctadiene, polymer, oligomer or a mixture oligomer-monomer). The monomer/oligomer/polymer compositions at various times have been represented on a triangular diagram (Figure 13.5). [ 1,5-COD
(A).
(
.
/
-.
P(1,5-COD) ]
/~/(B)
_
_v
b
~
Figure 13.5. Metathetic interconversion of 1,5-cyelooctadiene-oligomer-polymer with (CO)4(PPh3)W=C(OMe)Ph/TiCI4 catalyst system (Adapted from Ref. 33) In this case, the equilibrium concentration of monomer is rather small and the equilibrium mixture reached by route (1) is represented by a point (A) very close to the polymer-oligomer line. The same polymer/oligomer ratio has been obtained starting from polymer, oligomer or a mixture of oligomer/monomer, point (B). These authors concluded that a true equilibrium between cyclic oligomers and high molecular weight polymer
957 without participation of monomer in detectable amounts was attained in this case n
(Eq.
13.10). =
~.
~
113.10)
The existence of such an equilibrium which supported the backbiting mechanism, was ascribed, in part, to the conformational effects in the macromolecules. In addition, no significant variations in the composition of the equilibrium mixture or in the molecular weight of the polymer with temperature were observed at high conversions. The absence of such a variation of equilibrium oligomer composition at low monomer concentration was attributed to the strainless nature of cyclooctadiene oligomers. The enthalpic term in Eq. 13.11 is negligible (AH = 0) and the entropic term is the only parameter governing the equilibrium 0Eq. 13.11). In [Oligomer]= = ~ T -
AS/R
(13. 1)
Furthermore, Chauvin et ol. 33 found that the equilibrium oligomer concentration increased with increasing concentration of 1,5-cyclooetadiene when chlorobenzene was used as solvent (Figure 13.6). [ 1,5-COD
-- P ( 1 , 5 - C O D )
]
| . OLI~ERS
.
. . . e/,,, P O L Y M E R
2 \ 3 4
7 6 .
POLYMER
.
1.5-COD
Figure 13.6. Effect of monomer concentration on the reaction pathway in 1,5cyckxxcadiene polymerization with (CO)4(PPh3)W--C(OMe)Ph~iCI4 catalyst system:[M]0= 0.65 (1), 0.9 (2),1.3 (3),1.8 (4), 2,1 (5),2.2 (6),3.4 (7) and 4.7 (8) (Adapted from Ref. 33)
958 This result was ascribed to the increasing "aliphatic" character of the reaction medium, the effect of which is similar in nature to the use of heptane as a solvent. Of a particular relevance are the results obtained by Thom-Csanyi and coworkers 34 in the metathesis polymerization of cyclobutene/l,5cycloctadiene system (cyclobutene, cyclooctadiene, cyclododecatriene, 1,4polybutadiene) using several stable tungsten and molybdenum carbene complexes as well as classical metathesis catalysts. In contrast to earlier data, under these conditions, significant amounts of butadiene cyclic trimers were observed (Table 13.5).
Table 13.5 Distribution of cyclic oligomers obtained in r m g ~ m g metathesis polymerization of 1,5-cyclooctadiene~b Oligomer Fraction' % mole
Oligomer Fraction b % mole
2 3
2
81.4
4
28
5 6 7
21 15 12 7.8 6.9 5 2 0.3
5.4 6.3 4.0 2.0
Degree of Oligomerization
8
9 10 11 12
0.8
not. det. not. det. not. det. not. dot.
'Data from reference 33; bData from reference
In these butadiene trimers the trans configuration predominated at the thermodynamic equilibrium (Table 13.6). The trans content, however, decreased with increasing ring size. Moreover, cyclic butadiene dimers were not detected, under these conditions. Significantly, these data gave strong evidence that the product spectrum is thermodynamically controlled.
959 Table 13.6 Relative proportion of c i s / t r a n s isomers of butadiene trimers and tetramers obtained m 1,5-cyclooctadiene polymerization with W(=CHAr~ ArM~ Mo(CF3h)z/TH~ CDT b
Relative proportion
CHTE"
Relative pmportioa
ttt
100.0 9.9 0.24
tttt tttc
100.0 51.2 12.1 12.1 6.4
ttc tcc
ttcc tctc tccc
"Data from reference34; bCDT=l,5,9-Cyelododecatriene; 'CHTE=i,5,9,13Cyclohexad~ene Similar results have been obtained by the same authors in the study of metathesis ring-chain equilibrium of l-methylcyclobutene/1,4polyisoprene system. 36 As an interesting application, the intramolecular metathetic degradation of 1,4-polyisoprene with the tungsten carbene complexes to the preferred all-trans cyclic isoprene trimer has been performed (Eq. 13.12).
(13.12)
W 86.4% tlc 11.6% tcc 1.9%
These type of compounds are of interest for the synthesis of fragrances and pheromone derivatives. (iii) c/s-trans Equilibrium. There are two types of cis-trans equilibrium in the ring-opening polymerization of cycloolefins: (a) cis-trans equilibrium in the cyclic oligomers and Co) cis-trans equilibrium in the linear polymers.
960 (a) The first type of configuration equilibrium has been readily observed between the ttc-ttt-tcc C4-trimers (C~2) and tttt-tttc-ttcc-tccc C~tetramers (C~6) formed in the ring-opening metathesis polymerization of 1,5-cyclooctadiene. For the smaller tings, the probability of ring closure is evidently higher when there is a greater proportion of cis double bonds in the ring to be formed z5'35 (Figure 13.7).
cis % 80
7O
[ 1,5-COD --- P(1,5-COD) ]
60 50
II
1
1t
9
!
40
30
3
5
7
9
11
13
Ring size Figure 13.7. Evolution of cis contents of cyclic oligomers as a function of ring size in 1,5-cyclooctadiene (I,5-COD) polymerization (1- WCl~-based catalyst; 2-Re20~/AlzO3 catalyst) (Adapted from Ref.Z~3s) Thus, at the early stages of the reaction, the average cis content was found to fall from 70% for the C~6 fraction to about 40% for C~ and higher fractions. However, when the thermodynamic equilibrium establishes, the proportions of the cyclic isomers are changed in favor of the more stable trans configurations. This process has been successfully illustrated by Thorn and coworkers 36 in the ring-opening metathesis polymerization of 1,5cyclooctadiene with the tungsten complex W(=CHAr~ as initiator at room temperature in cyclohexane (Figure 13.8). It can be easily seen that, although at early stages of the reaction the content of ttc- and tcc-C4trimers prevailed over ttt-isomer, at the equilibrium the content of ttt-isomer
961 was predominant. Yield, mg [ 1.5-COD
15
---. P ( I , 5 - C O D )
]
COD t tt-CD T
(C'HI)s k
{CI.HllJt. ttc-COT
tcc-CDT
0
1
2
3
4
5
6
7
8
9
10
Time, hr Figure 13.8. Evolution of cyclic oligomers in 1,5-cyclooctadiene(I,5-COD) polymerization with W(=CHAr~ (Adapted from Ref.~ A similar trend has been observed for C4-tetramers. The equilibrium between the steric isomers of low molecular weight oligomers occurs in the favor of the trans stereoconfigurations (Eq. 13.13 ).
(13.13)
At equilibrium, the C4-trimers showed an overall trans-content of 97% and C4-tetramers of 84%. The actual composition of C4-oligomers at thermodynamically controlled equilibrium is given in Table 13.7. A similar distribution of the steric isomers of C4-oligomers has been obtained in the ring-opening polymerization of ttt-l,5,9-cyclododecatriene, the ADMET reaction of 1,5-hexadiene and the metathesis degradation of 1,4-polybutadiene using as a catalyst the tungsten alkylidene complex W(=CHAr~
962 Table 13.7 Distribution of steric isomers of C4-thn~rs and C44etramers in 1,5-cyclooctadienepolymerization with W(=CHAr~ b
C4-Oligomer
Steric structure
%
1,5,9-Cy c l o d o d ~ e n e
ttt Re tee
1,5,9,13-Cyclohexad~ene
tttt tttc ttcc
90.8 9.0 0.2 97 55.0 28.2 6.7 6.7 3.5 84
~t
tctc tccc ~t |
'Data from reference~; bReaction conditions: Solvent cyclohexane; Room temperature. (b) The second type of cis-trans configuration equilibrium, namely the cis-trans equilibrium in the polymer, has been observed in polybutenamer and polypentenamer, provided that the catalyst is not too stereoselective. This type of equilibrium is sensitive to temperature and favors the more stable trans configuration (Eq. 13.14). .
.
.
.
.
.
.
.
In the 1,4-polybutadiene system, under the precipitation temperature (PT), the equilibrium is shifted towards trans polymer which precipitates in the solid area. 37 On increasing the temperature, the reverse process takes place. The Gibbs-Helmholtz plot for the configuration equilibrium of the polymeric chain is illustrated in Figure 13.9.
963 ln(trans/c~s) 18
1.7
1.6
1.5
{ m.P(I,5.COD) - - t n ~ P(I~COD) i
14
1.3
305
310
315
320
3~i
330
335
340
345
I/T [ l/K] x 10"z Figure 13.9. Gibbs-Helmholtz plot (y = 590.66x -0.3381; R z = 0.9951) for cispolymerization with W(=CHAr~ (Adapted from Ref.3~)
trans ison~rization of the polymer fraction in 1,5-r
The thermodynamic data obtained are in good agreement with the results for low molecular weight olefins. For the trans-cis isomerization a small amount of entropic change was found experimentally. The enthalpic value of 4.9 J/mole is very near to the one known for olefinic double bond in the gas phase (4.2 J/mole), independent of their substitution. In addition, the ratio of different diads was in accordance with a random distribution of the cis and trans double bonds, which is an evidence that the equilibrium has been achieved within the polymeric chain fraction. (iv) Equilibrium between chains of different lengths. The existence of an equilibrium between chains of different lengths has been evidence~ in metathesis degradation of various unsaturated polymers (Eq. 13.15).
Such studies have been performed with polybutenamer (1,4-polybutadiene), polypentenamer, polyoctenamer and polydodecenamer.
13.4. References
1. E.Eliel, "Stereoehemistry of Carbon Compounds", MacGraw Hill, New York, 1995. 2. J.D. Cox, Tetrahedron, 19, 1175 (1963). 3. G. Natta, G. Dall'Asta, G. Mazzanti and G. Motroni, Makromol. Chem., 69, 163 (1963). 4. G. Natta, G. Dall'Asta, G. Mazzanti, Angew. Chem., 76, 765 (1964). 5. N. Calderon, J. Macromol. Sci., Macromol. Chem. C7, 111 (1972). 6. G. Natta, G. Dall'Asta, I.W. Bassi and G. Carella, Makromol. Chem., 91, 87 (1966). 7. R. Bucourt and D. Hainaut, Bull. Soc. Chim. France, 1366 (1965). 8. F.A.L. Anet and M. Z. Haq, d. Am. Chem. Soc., 87, 3147 (1965). 9. N.L. Allinger and J.T. Sprague, 9'. Am. Chem. Soc., 94, 5734 (1972). 10. M.F. Farona and C. Tsonis, d. Chem. Soc., Chem. Commun., 1977, 363. 11. L. Hocks, D. Berck, A.J. Hubert and Ph. Teyssie, J. Polym. Sci., Polymer Letters, 13, 391 ( 1975). 12. G. Natta and G. DaU'Asta, in "Polymer Chemistry of Synthetic Elastomers", (J.P. Kennedy and E. Thornquist, Eds.), Interscience Publishers, New York, 1969, p. 703. 13. F.S. Dainton, T.R.E. Delvin and P.P. Smith, Trans. Faraday Soc., 51, 1570(1955). 14. F.S. Dainton and K.J. Ivin, Quart. Rev., 12, 61 (1958). 15. a. B.Lebedev, N. Smimova, Y. Kiparisova and K. Makovetsloy, Makromol. (;hem., 193, 1399 (1992); b. B.Lebedev and N. Smimova, Macromol. Chem. Phys., 195, 35 (1994). 16. D. Kranz and M. Beck, Angew. Makromol. Chem., 27, 29 (1972). 17. V.M. Cherednichenko, Polymer Sci. USSR, 20, 1225 (1979). 18. P.A. Patton, C.P. Lillya and T.J. McCarthy, Macromolecules, 19, 1266 (1986). 19. H. Cheradame, J.P. Vairon and P. Sigwalt, Eur. Polym. J., 4, 13 (1968). 20. E.A. Ofstead and N. Calderon, Makromol. Chem., 154, 21 (1972). 21. H. HOcker, W. Reimann, L. Reif and K. Riebel, d. Mol. Catal., 8, 191 (1980). 22. K. Ntitzel and V. Henze, cited after reference 16. 23. K.L. Makovetsky and L.I. Red'kina, Dokl. Akad Nauk SSSR, 231, 143
965 (1976). 24. H. Jacobson and W.H. Stockmayer, J. Chem. Phys., 18, 1600 (1950). 25. U.W. Suter and H. HOcker, Makromol. Chem., 189, 1603 (1988). 26. Zh.-R. Chen, J.P. Claverie, R.H. Grubbs and J.A. Kornfield, Macromolecules, 28, 2147 (1995). 27. K.W. Scott, N. Calderon, E.A. Ofstead, W.A. Judy and J.P. Ward, Adv. Chem. Set., 91,399 (1969). 28. K.W. Scott, N. Calderon, E.A. Ofstead, W.A. Judy and J.P. Ward, Rubber Chem. Technol., 44, 1342 (1971 ). 29. H. HOcker, L. Reif, W. Reimarm, and K. Riebel, Rec. Trav. Chim. Pays Bas, 96, M47 (1977). 30. L. Reif and H. HOcker, Macromolecules, 17, 952 (1984). 31. K.J. Ivin, Makromol. Chem., Macromol. Syrup., 42/43, 1 (1991). 32. N. Calderort, E.A. Ofstead and W.A. Judy, J. Polym. Sci., A I, 5, 2209 (1967). 33. Y. Chauvin, D. Commereuc and G. Zaborowski, Rec. l'rav. Chim. Pays Bas, 96, M131 (1977). 34. E. Thom-Csanyi, J. Hammer, K.P.Pflug and J.P. Zilles, Macromol. Chem. Phys., 196, 1043 (1995). 35. H. Sato, Y. Tanaka and T. Taketomi, Makromol. Chem., 178, 1993 (1977). 36. E. Thom-Csanyi, in "Metathesis Polymerization of Olefins and Polymerization of Alkynes", (Y. Imamoglu, Ed.), Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 117-137, 1998. 37. E. Thom-Csanyi and K. Ruhland, Macromol. Phys. Chem. 200, (1999).
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967
Chapter 14
REACTION
KINETICS
Whereas studies on the kinetics of cationic ~ and anionic 2 polymerization of cycloolefins are limited, the kinetics of Ziegler-Natta 3 and particularly of ring-opening metathesis polymerization 4'5 have been thoroughly investigated. Data obtained in these kinetic investigations have brought a more real picture of these processes and led to a better understanding of the reaction mechanism and product selectivity.
14.1. Kinetics of Cationic Polymerization The most relevant studies on the kinetics of cycloolefin polymerization with cationic initiators have been reported on the reactions of cyclopentadiene, cyclohexadiene, cyclooctadiene and indene. Vairon and Sigwalt investigated the kinetics of the polymerization of cyclopentadiene initiated by TiCI30~Bu under conditions of highest purity and dryness. 6'7 Efforts were made to dry the system and to determine the effect of water on the polymerization rate. While the polymerization could not be completely stopped even after most rigorous drying, the accelerating effect of water and hydrochloric acid on the reaction rate was unambiguously demonstrated. Careful investigations with the TiCI30~Bu initiator in methylene chloride as solvent at a temperature of-70~ showed that the number average degree of polymerization decreased with increasing initiator concentration and decreasing monomer concentration. At the same time, the reaction rates increased with the monomer and initiator concentration. The initial rate was found to be first order in TiCI30"Bu, water and cyclopentadiene. Calculations of the number of active centers indicated a quasistationary concentration. Significantly, in this case, the initiation was slower than propagation and was independent of the initial monomer concentration. The rate constant for the initiation reaction was found to be k~ = 11.1 L/mole.sec at a temperature of-70~ The enthalpy of cyclopentadiene polymerization was determined independently and was found to be-AH = 58.99 kJ/mole s (14.1 kcal/mole).
968 The kinetics of cyclopentadiene polymerization with TiCIdCCI3COOH(TCA), SnCLdCCI3COOH(TCA) and BF3.OEt2 have been thoroughly investigated by Imanishi and Higashimura9 in toluene and methylene chloride at a temperature of-78~ These authors found that the polymerization with TiCIdTCA was extremely rapid and nonstationary and conversions stopped at low values (Figure 14.1, Curve A); however, when fresh TiCh was added to such a "dormant" system, another burst of rapid polymerization occurred. ~~ Conv., %
~oo
CPD -~ P(CPD) Conv., % ~O0
,/(A)
50
0
(B)
50
0
'
1
"
0
2
Time, hr
0
1
2
Time, hr
Figure 14.1. Time-cxmversion curves for cyclopentadiene (CPD) polymerization with TiCh~CA (A) and SnCIdTCA (B) (Adapted from Ref.t0.tl) On the other hand, polymerization of cyclopentadiene induced by SnCIdTCA involved two stages; at the beginning the polymerization was nonstationary and extremely rapid, characterized by an inverse [1"1] v s [I] dependence and by the fact that water had practically no effect on [rl]. During the next stages the rate slowed down and became stationary. With BF3.OEtz the rate was much slower and, except for the very beginning, it was stationary, [rl] was unaffected by the initiator concentration and it was 11 much depressed in the presence of water. New kinetic studies on the cyclopentadiene polymerization were carried out with the TiCIdTCA system in toluene at temperatures of-69~ to -77~ under high vacuum anhydrous conditions. The exothermicity of the polymerization was followed accurately by determining the change in resistance by means of an oscilloscope of a platinum wire submerged directly into the liquid reaction mixture. The theoretical treatment followed the model developed by Hayes and Pepper ~z for styrene polymerization assuming fast initiation and a non-steady state with diminishing concentration of active species. The rate constant for propagation was determined to be k2 = 3500-~71 L/mole.see and that for termination kt =
969 0.11i-0.06 sec ~. Notably, this propagation constant is very high considering various vinyl polymerizations, however, it is at least five to six orders of magnitude less than that obtained by the y-radiation induced polymerization of cyclopentadiene. ~3 Polymerization of l-methyl- and 2-methylcyclopentadiene with TiCIdTCA and SnCIdTCA are typically non-stationary: upon initiator addition a burst of polymerization ensued that was followed by rapid termination (Figure 14.2, Curve C). ~4'~ Fresh initiator addition was needed to give high conversions. In contrast, with BF3.OEtz, after the rapid polymerization, a stationary phase was obtained that slowly progressed to 100% conversion (Figure 14.2, Curve D) ~6. 100
Conv., %
(C)
Me4~PD -~ P(Me~PD) Conv., % 100
5O 0
5O
0
1
2 Time, hr
0
0
-
1
2
Time, hr
Figure 14.2. Conversion-time curves for methylcyclopentadiene polymerization with TiCLdTCA (C) or S n C ~ C A and BF3.EtzO (D) (Adapted from Ref.~s) Noteworthy, the level of conversion did not influence intrinsic viscosities, however, the nature of the catalyst did affect these values, i.e., [11] -0.4, ---0.3, and ---0.15 with BF3.OEtz, SnCIdTCA, and TiCIdTCA, respectively. Copolymerization of methylcyclopentadiene with cyclopentadiene indicated a higher reactivity of the substituted monomer. The reactivity ratios of methylcyclopentadiene (rM=) and cyclopentadiene (r) were r ~ = 8.5+3.5 and r = 0.36-x-0.26 in toluene and r ~ = 14.9-a=5.6 and r = 0.42~0.23 in methylene chloride. The enhanced reactivity of methylcyclopentadiene over that of cyclopentadiene was explained by the inductive effect of the methyl group and, particularly, the 2-methyl substituent. Rapid initiation and propagation of cyclopentadiene and its derivatives are conceivably due to the ease of formation and high stability of the cyclopentyl cation. The nature of the initiator had little effect on the reactivity. Copolymerization of 1,3-dimethylcyclopentadiene with cyclopentadiene with B F3.OEtz in toluene
970 at a temperature of-78~ gave the reactivity ratios r~=6.85+1.10 and r=0.30-~0.10 for these two monomers, respectively. ~s Accordingly, the 1,3 isomer is much more reactive than the parent cyclodiene. Also, methyl substitution enhanced the stability of the cyclopentyl cation. Interesting kinetic studies ~7 on the polymerization of 1,3cyclohexadiene have been performed with BF3.OEt2 and SnCldtrichloroacetic (TCA) acid, in benzene and methylene chloride as solvents, at a temperature of 0~ Polymerization in benzene was completely homogeneous while in methylene chloride the polymer precipitated during the reaction. It was observed that the polymerizations with SnCIdTCA were non-stationary, i.e., upon initiator addition a fast reaction commenced, although polymerization did not go to completion and high conversions were attained only by the repeated addition of SnCI4. Noteworthy, the highest conversions of cyclohexadiene were obtained with lower monomer concentrations (Figure 14.3). Conv., % 1,3-CHD -+ P(I,3-CHD) 100 r
50
0
1
2
Time, hr Figure 14.3.Variation of 1,3-cyclohexadiene conversion with time in presence of SnCL~CA at 0~ m methylene chloride as solvent (Adapted from Res ~7) This unusual behavior has not been observed when BF3.OEt2 was used as initiator, however, an identical phenomenon was obtained with cis, cis-l,3cyclooctadiene (see below). The above authors proposed that 1,3cyclohexadiene and SnCl4 form an inactive complex. With larger amounts of 1,3-cyclohexadiene larger quantities of SnCI4 are converted into the active species which explains depressed final conversions at higher monomer concentration. By contrast, with BF3.OEt2 as catalyst, the conversion-time curves did not level off as with SnCIETCA and reached 100% conversion. In this case, except for the very early stages, the polymerization was stationary. The overall rate law was that given by the
971 following relationship (Eq. 14.1) Rp = k [M] [I]
(Eq. 14.1)
where [M] and [I] are monomer and initiator concentrations, respectively, and k = 0.2-~.5 L/mole.min in methylene chloride at 0~ and k = 0.03i-0.003 L/mole.min in benzene at 0~ Kinetic studies on the cationic polymerization of 1-vinylcyclohexene in the presence of various initiators indicated that the reaction proceeded by a very fast non-stationary phase ~s (Figure 14.4). Conv., %
I-VCH -~ P(1-VCH)
100
50
0
0
1
2
Time, hr Figure 14.4.Conversion-time curve for 1-vinylcyclohexenepolymerization(0~ SnCh~CA and BF3.EhO in methylene chloride and toluene (Adapted from Ref.~s) The reaction started immediately after initiator addition and final conversions were reached rapidly after the initial burst of polymerization. This phenomenon was observed with all initiators employed, namely, SnCh/TCA in toluene and methylene chloride and BF3.Et20 in toluene at a temperature of 0~ Similar to 1,3-cyclohexadiene and 1,3-~clooctadiene, an inverse relation between the initial monomer concentration, [M]o, and ultimate polymer yield, Y, exists with l-vinylcyclohexene. The yield was found to be independent of [M]o and was --0.55 mole~ Very interesting kinetic results have been obtained in the polymerization of cis, cis-l,3-cyclooctadiene with TiCLdTCA in methylene chloride or toluene at a temperature of-78~ Thus, in methylene chloride a burst of polymerization ensued on initiator addition, however, the reaction rapidly stopped and levelled off at conversion levels determined by the amount of initiator added 19(Figure 14.5).
972 Conv., %
Conv., %
~oo
1oo
(E)
50
0
50
0
1
2
0
Time, hr
0
,
1
"
2
Time, hr
Figure 14.5. Conversion-time curve for cis, cis-1,3-cyclooctadiene polymerization with TiCh~CA (E) and TiCldl'IzO (F) in methylene chloride and toluene (Adapted from Ref 19) In this process there was a straight relation between the amount of monomer converted and the initiator concentration, however, molecular weights of the polymer were independent of 1,3-cyclooctadiene concentration. In toluene, the behavior was somewhat different; after addition of initiator and the first burst of polymerization, the rate did not level off but progressed steadily albeit more slowly to higher conversions. Notably, an inverse relationship between conversion and initiator concentration was found by Imanishi and coworkers, ~9 like in cationic polymerization of 1,3-cyclohexadiene. This phenomenon was explained by these authors by assuming a two-step mechanism involving both the rapid, non-stationary and slow, stationary phase. When TiCLdI-120 has been employed as a catalyst, the polymerization consists also of two phases, a rapid one, non-stationary, whose initial rate follows the law:
Rate = k [TiCI4] [H20] [Monomer]
(14.2)
and a slow one, stationary. The ultimate yields were found to be directly proportional to the concentration of active chains but inversely proportional to the monomer concentration. The second, stationary phase was much slower in this case. Mondal and Young 2~ explained these results by postulating an allylic (suicide) termination mechanism. The key equation derived from the above assumption is: Yield = (kp/k~t)x([P+]o/[M]0)
(14.3)
973 where !~ and k~ are the rate constants for propagation and chain transfer with monomer and [P+]0 and [M]0 are the initial concentrations of active chain ends and monomer, respectively. Polymerization of.indene in methylene chloride solution initiated by cumyl chloride and TiCh has been investigated by Sigwalt e t al. 2~ as a possibly "living" system. They found that at the temperature of-40~ the initiation reaction is quantitative only in the presence of dimethyl sulphoxide as an electron donating compound. Linear growth of the M, with the amount of monomer converted was observed for monomer to initiator ratios lower than 200, although transfer did take place ( ~ = 6 x 10 4). At a temperature of +5~ linear growth was observed only up to M~ = 15000, when initiation was quantitative without dimethyl sulphoxide, and this compound did not reduce transfer ( ~ + 5 . c = 1.4 x 103 in both cases). At a temperature of-75~ the initiation was not quantitative, even in the presence of dimethyl sulphoxide. Common ion salts had the same effect as dimethyl sulphoxide on the molecular weight distribution and on the "living" character, and this fact was attributed to a shiR of equilibrium between "dormant" covalent species, ion pairs, and free ions, favoring the exchanges between active and "dormant" species. This process implies the existence of a reversible termination, which was confirmed by initiation with a model of the chain end (1-chloroindan). A slow exchange between the active and "dormant" species was supposed to explain the relatively broad molecular weight distributions observed (MJM~ = 2-3). Better results (M,~r = 1.6-2) were obtained using n-butoxytrichlorotitanium as coinitiator at the temperature of-40~ without dimethyl sulphoxide. The two parameters allowing the observation of a "living" polymerization of indene were the propagation to initiation rate ratio, which has to be low enough to give quantitative initiation, and the monomer to initiator ratio, which has to be low enough to yield low molecular weight polymers, for which transfer is undetectable. In addition, as expected, the transfer reaction was reduced at low temperatures. All these results have been easily accommodated in terms of the classical carbocationic polymerization mechanism.
14.2. Kinetics of Ziegler-Natta Polymerization Although kinetics of Ziegler-Natta polymerization in acyclic series of olefins is well documented, z2 investigations on the kinetics of cycloolefin reactions with this type of catalyst are described for a certain number of monomers. The firs kinetic data on this process have been reported by
974 Natta and coworkers 23 in reactions of monocycloolefins such as cyclobutene, cyclopentene, cycloheptene and cyclooctene with a number of classical Ti- and V-based catalysts. Subsequently, Kaminsky and coworkers z4 published new kinetic data on the polymerization of cyclobutene, cyclopentene and norbomene, using chiral metallocene/aluminoxane catalysts, particularly ethylidenebis(Tlsindenyl)zirconium dichlodde./methylaluminoxane and Collins et al.25 on the polymerization of cyclopentene with the above zirconocene catalyst. More recent work on the kinetics of norbornenc/ethylene copolymerization using homogeneous metallocenes and some half-sandwich catalysts comes from Ruchatz and Fink 26 and provides quantitative data on the reaction orders and rate constants. The time evolution of cyclobutene polymerization in the presence of ethylidenebis(TIS-indenyl)zirconium dichloride/methylaluminoxane as catalyst at the temperatures of 0~ and -10~ is given in Figure 14.6. Conv., %
CB
-~
P(CB) I /
/
50
/
/
/ /
40
/
30
/
j j l
z
20 10 0
'
0
i
5
10
15
20
25
Time, hr Figure 14.6. Conversion4.ime curve for cyclobtmme (CB) polymerization with ~ghylidenebis(rl~-mdcnyl)zirctmium dichlorideim~hylalummoxane (1 Temperature 0~ 2 Temperature - 10~ (Adapted from Ref. As it can be seen from Figure 14.6, following a rapid start, the polymerization rate decreases to become linear after a few hours. The conversion is substantially affected by the reaction temperature, decreasing several times on going from 0~ to -10~ A similar behavior can be
975 observed in the polymerization of cyclopentene in the presence of ethylidenebis(~S-indenyl)zirconium dichloride/methylaluminoxane~ (Figure 14.7). Conv., % CP
--~ P(CP)
60 !
50 40 30 20 10 0
0
5
10
15
20
25
Time, hr Figure 14.7. Conversion-time curve for cyclopentene (CP) polymerization with ethylidenebis(vls-mdenyl)zirconium dichloride/methylaluminoxane (1 Temperature 22~ 2" Ten~rature 0~ (Adapted from Ref. It can be observed that, at a reaction temperature of 0~ the rate of cyclopentene polymerization was four times lower than that of cyclobutene. The kinetics of cyclopentene polymerization with 1,2-ethylenebis(rl 5tetrahydroindenyl)zirconium dichloride have been thoroughly studied by GC of quenched aliquots in the presence of n-decane as an internal standard. 25 Interestingly, the consumption of monomer does not obey first order kinetics as is typically encountered in such reactions. 27 Plots of 1/[M]1/[M]0 v s time were found to be linear, indicating a second-order dependence of the rate of polymerization on monomer concentration (Figure 14.8). Kinetic experiments at higher monomer concentrations also confirmed these data. These results suggested that 1,2-insertion of r does not occur in the conventional way (i.e., rate-limiting insertion from an olefin alkyl complex) but is triggered by coordination of additional monomer. 2s
976 30.0
2 40.0
r'1 @ 30.0 r-~
20.0
keff'(D)[Zr"]
[CSDS l = 0. ! 3 M [CSHSl = 0.13 M [ C S H S ] -- 0 . 2 6 M -- 2 . 4 4 x I O - 4 ( M - I s - I )
lid
!
I0.0
) 0.0 0.0e*0
1.0e§
2.0e-,-5
3.0e§
Figure 14.8. Reciprocal monomer conversion vs. time for polymerization of cyclopentene (1) and cyclopentene-d= (2) with 1,2-r t~-ahydromdenyl)zircomum dichloride (Adapted from Ref.~) However, according to this concept, it is not clear whether this unusual 1,2insertion mechanism impacts on the cis-/trans-l,3 insertion process; possibly, the latter two processes occur subsequently to the first rate limiting step. In spite of the above ambiguities, these kinetic results provide an attractive explanation for the stereochemical control observed in polymerization of cyclopentene with the chiral catalyst 1,2-ethylenebis(rl 5tetrahydroindenyl)zirconium dichloride that incorporates cyclopentene in a cis- 1,3 fashion (Scheme 14.1).29
o
--~
~
L,z
-'-
[~L/
--k'o
R Scheme
14.1
R
977 where -d[M]/dt = K~',ki[Zr*][M] 2 = k~Zr*][M] 2
(14.4)
and L is tetrahydroindenyl ligand and R is (Cd-h)~. As it can be seen from Scheme 14.1, two molecules of cyclopentene can coordinate to the metal center via the same enantiotopic face of the catalyst so as to favor insertion of either monomer unit into the metal-carbon bond. Kinetic investigations on the copolymerization of norbomene with ethylene using 'Pr[IndCp]ZrCI2/MAO as a catalyst showed that ethylene reaction rate vpr decreases linearly with increasing norbomene concentration 26 (Figure 14.9).
Vp~ x 104, mole/L.s 20 [
ET
+ NB
: P(ET-NB)
]
16
12
o
mole/L Figure 14.9. F~ylene (ET) reaction rate as function ofnorbomene (NB) concentration in copolymefization reaction in the presence of 'Pr[IndCp]ZrClz/MAO as a catalyst (Adapted from Ref.~ However, it was observed that in the ethylene concentration interval from 0 to 3.5 mole~ (0-26 bar), vpE increased linearly with increasing ethylene concentration whereas further increasing the ethylene concentration to 11 mole~ (60 bar) caused no further increase of vpE. The norbomene reaction rate could not be directly measured but has been calculated by measuring the norbomene content in the copolymer by
978
'3C NMR after a short polymerization time and determination of the copolymer yield. The calculated values for the reaction rate of norbornene are shown in Figure 14.10.
Vp~E x 104, mole~.s [ E T + NB
o P(ET-NB) ]
g
mole/L Figure 14.10. Norbomene reaction rate as function of norbomene (NB) concemration in copol)anerization with ethylene (ET) in the presence of iPr[IndCp]ZrClz~AO as a catalyst (Adapted from Ref.~ From the slope of the first four points and the rate law VN = kN [ Z r ]
[norbomene]
(14.4a)
the value ks = 80 L/mole.sec for the norbomene rate constant and 0.5 for reaction order of polymerization have been determined. The norbomene rate constant of copolymerization, kNc~ was larger than the norbornene rate constant of norbomene homopolymerization, ks H~176ks c~ > ks H~176 In contrast, the ethylene rate constant of copolymerization, kEc~ was smaller than the ethylene rate constant of ethylene homopolymerization, k HOMO co k HOMO E
,kE
<
E
9
The reaction orders determined for cthylene-norbomene copolymefization and ethylene and norbomenr homopolymerization with 'Pr[IndCp]ZrCI2/MAO as a catalyst at a temperature of 70~ are
979 summarized in Table 14.1. Table 14.1 Reaction orders for ethylene-norbomene copolymerization and ethylene and norbomene homopolymerization with 'Pr[IndCp]ZrCl2/MAO as a catalyst at 70~ ' Reaction
Copol3anenzation
F.~ylene Polymerization
Norbomene Polymerization
1
1
1
Component Zr
0.5(50~
AI
Ethylene
1
Norbomene
0.5
1(25~ I. 1,1.5 (35~
0.85 0.5-0.7
'Data from referenceu Based on the results obtained in the homo- and copolymerization reactions
of ethylene and norbomene with ~Pr[IndCp]ZrCI2/MAO as a catalyst, the rate constants, the copolymefization parameters and the activation energies have been further evaluated. Their values are illustrated in Table 14.2. Table 14.2 Rate constants, copolyrnerization parameters and activation energies for ethylenenorbomene copolymerization and ethylene and norbomene homopolymehzahon with 'Pr[IndCp]ZrCldMAO as a catalyst' Component
Copolymerization
E~ylene Polymerization
I~ (L/mole.sec) ks(L/mole.see) rl;r2 E^~(kJ/mole)
30-34b 80b 0.88;0.05 b 155(60-70~ 128(60-70~
160 b
EAN (kJ/mole)
'Data from refermcr
Norbomene Polymerization 1.5 b
73(20-80~ 63(10-100~
bAt a temperature of 70~
As it can be readily observed, the rate constants for copolymerization reactions, kE and ks, lie between those of homopolymerization of norbomene and ethylene while the activation energies, E ~ and Eft,
980 are higher than that of homopolymerization reactions within similar ranges of temperatures
14.3. Kinetics of Ring-Opening Metathesis Polymerization The kinetics of ring-opening polymerization of cycloolefins display a range of common features with the kinetics of metathesis reaction of acyclic olefins. However, the complex nature of the polymerization process has to accommodate the well-known diNculties of the related Ziegler-Natta systems. So far, a number of kinetic studies concerning the polymerization rates, the nature of the main kinetic species, the determination of the concentration of the active centres and the catalytic activity have been published. The main kinetic data rely on the homogeneous catalysis involving the ring-opening polymerization of cyclopentene, cyclooctene, cyclooctadiene and norbornene. 4'S
14.3.1. Kinetics of Initiation and Propagation. Living Metathesis Polymerization In the ring-opening polymerization of cycloolefins, mctal-carbene complexes used as initiators (1) are not always totally consumed before the monomer (M) has been completely polymerizecl. This is the case when the propagating rate constant, kp, is greater than the initiation rate constant, k~. The expression of k ~ in terms of the fraction of initiator remaining is obtained by dividing the rate of reaction of the monomer by that of the initiator, substituting [P] = [I]o-[I], and integrating between the limits [M]=[M]o and 0, and Ill = [I]o and [I]., where [I]. is the final concentration of initiator. In this way, we can obtain the following equations for d[M]/d[I] and kp/ki, respectively (Eq. 14.5-14.5 a). d[Ml/d[l] = 1 + (kp/k~)([P]/[l]) = [ l - (kp/k,}] + (k~)([l]o/[l])
(14.5)
kp/k~ = {([M]o/[l]o) + ([I]../[I]o) - 1}/{ln([l]o/[l].) + ([I]../[I]o)- 1}(14.5a) The values of kp/k~ can de determined experimentally from this relationship and directly from the value of [l]/[P~] at the maximum concentration of [P~] in the ~H and ~3C NMR spectrum, since at this point the rate of formation of P~ is equal to its rate of disappearance.
981 Living systems are obtained when the rate of initiation is greater or at least equal with that of propagation. This depends essentially on the efficiency of initiator and the polymerizability of monomer. It is better to choose an initiator which is consumed before too much monomer is used up in the reaction. A Poisson distribution for the molecular weight is obtained with narrow M,,/M~ values. Provided that [M]o/[I]o > 100, values of k ~ i up to about 10 are admitted. A large number of living systems have been obtained with Mo-, W-, and gu-carbene initiators leading to high molecular weight polymers with narrow molecular weight distribution (PDI - 1.001.05). Block copolymers can be obtained by subsequent addition of another monomer. Numerous examples have been described in special chapters of this book. Living polymers obtained with Mo and W initiators are best terminated by reaction with an aldehyde while those derived from Ru initiators have to be quenched by use of a transfer agent like unsaturated ethers.
14.3.2. Kinetic Models for Metathesis Polymerization In early investigations by Hodjemirov et aL 3~ on the ring-opening polymerization of cyclopentene induce~ by WCl6-based catalytic systems the reaction kinetics displayed a first-order rate equation. The following expression has been found for the rate of monomer consumption (Eq. 14.6).
In {[M-M0] / [M-Me] }= k~x t
(14.6)
where M, M0, M~ represent the concentration of the monomer at a certain time, at the initial time and at equilibrium, respectively, l~ is the rate constant and t the time. Significant studies on the kinetics of cyclopentene polymerization with WC~Bu3AI were published by Amass and Tuck. 3~ A first order dependence of the reaction rate on the catalyst concentration was found whereas the order with respect to the monomer concentration was more complex. The initial reaction rate showed to be of first order with respect to cyclopentene concentration but the rate rapidly decreased as the reaction proceeded (Figure 14.11, Curve G)). The results obtained by Amass and Tuck indicate the presence of two active species in cyclopentene polymerization with WCl6fBu3Al. A first species was supposed to arise by the reaction of a complex of cyclopentene with WCl6 and 'Bu3AI. This species was partially convened by further
982
Cony., % CP
~
PPM
50 40 30 20
10
0
0
10
20
30
40
50
Time, min Figure 14.11. Variation of monomer conversion with reaction time in cyclopentene (CP) polymerization with WCIJBu3AI (Adapted from Ref.31) reaction with cyclopentene into a second species with much lower activity. The above authors suggested a simple kinetic scheme, illustrating the generation of two distinct active species, W* and W**, with the constant rates k~ and k2, respectively (Eq. 14.7-14.8).
V~16 +
W*
+
(~
kl
C>
k2 ,._
W* "~
VV~
iBu3AI
=
iBu3AI ,._~
W"/AI
(14.7)
W**IAI
(14.8)
In this scheme, the second species W** has unknown activity and exhibits a more complex behavior. An interesting finding was that the rate of polymerization under a given set of conditions depended upon the time that elapsed between the addition of the two catalyst components (WCI6 and 'Bu3Al) to the monomer. The premixing time of WCI6 before adding ~Bu3Al, that gave the highest polymerization rate, was defined by the equation (Eq. 14.9).
983 t,~ = { l/(k~-k2)[M]o} x In k~/k2
(14.9)
where [M]0 represents the initial concentration of cyclopentene. They found that the optimum premixing time, t,~, was inversely proportional to the monomer concentration. Accordingly, in the above scheme, the initial rate of polymerization, 1~, was represented by the following kinetic equation (Eq. 14. lO). R~ = kp[W*/Al]0[M]0
(14.10)
Where [W*/AI]0 was estimated to be equal to [I]. Thus, the initial rate of polymerization was used to measure the concentration of the first active species, [W*/AI], at any time of the reaction. Subsequent investigations of Amass and Zurimendi, 3z by dilatometric measurements, showed that, during the polymerization of cyclopentene, the rate of propagation decreased faster than could be accounted for by the consumption of monomer. These authors concluded that the decrease of the rate of polymerization was second-order with respect to the concentration of the active species. In agreement with such a statement was the observation that the reciprocal rate of polymerization, equivalent to the concentration of the propagating species, was a linear function with time. Furthermore, the above authors found that the catalyst formed from WCI6 and 'Bu3AI, during the cyclopentene polymerization, was not a living system. They demonstrated that the deactivation of the catalytic system occurred in the course of polymerization. Moreover, the kinetic behavior of this system suggested the existence of a termination reaction of the second order with respect to the active species W*, similar to the bimoleeular termination reaction that occurs in the Ziegler-Natta polymerization of linear olefins (Eq. 14.1 I). W* + W*
= Polymer
(14.11)
The kinetics of ring-opening metathesis polymerization of norbomene catalyzed by several Ru complexes have been investigated by Tanielian et al.33 but these authors erroneously concluded that the reaction kinetics were zero order in monomer, whereas the results clearly showed that they were first order. Based on the kinetic model of Hughes, 34 elaborated for metmhesis of acyclic olefin, a Michaelis-Menten type equation for the rate of propagation has been derived (Eq. 14.12).
984 Rr = Iq,K[M][cat]/(1 +K[M])
(14.12)
where [M] is the concentration of monomer. Unfortunately, an equilibrium constant, K, for the complexation of monomer was used instead of the correct Michaelis-Menten constant. A detailed kinetic approach on the cycloolefin polymerization was developed by Ivin35 and Rooney 36 in the course of their extensive investigations of the mechanism and stereochemistry of ring-opening metathesis polymerization of cyclopentene, norbomene, norbomadiene and their substituted derivatives. The variation with temperature of the fraction of cis and trans double bonds of the polymers, o= and or, respectively, were correlated with the rate constant of interconversion or relaxation of the intermediate metallacarbenes, k, and those of propagation to the corresponding metallacyclobutanes, k~, k2~ and k2t (Scheme 14.2) 1(3)
+M
2
§
~
kl
k2t
4(cis)
~-
5(trans)
~
3(1)
.~
2
Scheme 14.2 where 1,2 and 3 represent the intermediate metallacarbenes, 4 and 5 the corresponding metallacyclobutanes and M the monomer (Scheme 14.3).
P~CH
PNC
H
H P
9
C
/I
/I 1
/I 2
3
R \
P. M
,%
R
5(trans)
4(cis)
Scheme 14.3
985 A steady-state treatment of Scheme 14.2 led to the following equation: odot
- k2J k2t = kzJ k2t x kl/k x [M]
(14.13)
If at high temperature k~[M] < k, then from the Eq. 14.2 one obtains for o J o, the following relationship" o J o, = k2flka
(14.14)
The fall in or with increasing temperature will thus be governed by the rate of conversion of 2 to 5 trans. At low temperatures, kin[M] < k, and the equation 14.14 will become o J o , = k ~ tkax k , / k x [ M ]
(14.15)
In this case, or is high and should decrease as [M] is decreasing, as was observed experimentally. The effect of initial monomer concentration on or values for norbomene polymerization catalyzed by WCIt:Me4Sn and WCld~h4Sn at a temperature of 20~ and IrCl3 at a temperature of 75~ is illustrated in Figure 14.12, Curve H. O'r 0.6
/.
(H)
0.4
V
O
0
1
2
3
4
5
6
[M]., mole/rim 3
Figure 14.12. Influence of initial monomer concentration on o, for norbomene polymerization with WCk/Me4Sn, WCh/Ph4Sn and IrCl3 as catalysts (Adapted from Ref.3~)
986 It can be observed that in the higher range, 1-4 mole/dm 3, o= is independent of [M] but in the lower range, 0.26-0.1 mole/dm 3, o= decreases rapidly with dilution for the WCl6-based catalysts. The value of o= ~ 0.5 is obviously a limit since it also remained essentially constant for WCIdPthSn in the range70~ to +130~ Similar values (o= ~ 0.5) have been obtained using a variety of other catalyst systems at a temperature of 15~ To explain these kinetic results, gooney and coworkers 37 advanced a metallaearbene mechanism suggesting that the metallacyclobutane is present as a transition state and that for the highly reactive olefin, e.g. norbomene, the appropriate orbitals of M=C and C=C are already engaging each other to form a quasi-metallacyclobutane in the monomer complexation step (Scheme 14.4).
P~ICH II [Mg 6
7
8
9
6"
Scheme 14.4
For any given catalyst system they considered three kinetically distinct propagating species P~, P and P,, and two relaxation processes, P= ~ P and P ~ P, (Scheme 14.5). Pc
+
M
p
+
M
P=
+
M
k2c
3t
~
Pc
"--
Pt
e..
P=
k4
Scheme 14.5
987 Since each catalytic cycle consists of a series of steps, the rate constants in Scheme 14.3 were regarded as rate constants for monomercomplexation step. The kinetics of propagation have been treated in terms of Michaelis-Menten theory leading to three distinct limits: Type (a): Step of conversion of 7 into 6 and monomer (Eq. 14.16)
[Mr]
7
+
(14.16)
6
is negligible compared with conversion of 7 into $ (Eq. 14.17)
(14.17) 7
8
which is the rate controlling step, so polymerization is zero order in [M]. Type (b)" Step of conversion of 7 into 6 and [M] (Eq. 14.18)
_. 7
oc. Q,.,., .
(14.18)
6
is also negligible compared with conversion of 7 into 8 (Eq. 14.19)
P
::G 7
Poc
(14.19)
8
but with dilution the conversion of 6 with monomer into 7 (Eq. 14.20)
988
PoOH 0 II
[Mt]
+
--..
PoC. I,
[Mt]---
'
(14.20)
6 7 becomes slower than conversion of 7 into 8 (Eq. 14.21)
P
(14.21)
7
8
and first order behavior in [M] is eventually obtained. Type (r Step of conversion of 7 into 6 and monomer (Eq. 14.22)
PoC. [i~]----
.
P~ O . [~1
(14.22)
7 6 is always significant and in the limit it is at equilibrium with the complexation step, such that the rate of polymerization is first order with respect to monomer. Significant contribution to the kinetics of cyclopentene polymerization in the presence of WCh,-based catalytic systems was reported by Bittman et al. 3s From the experimental data a second-order rate with respect to the concentration of active centres for the termination reaction was obtained (Eq. 14.23). In {[Mo-M~]/Mo-M]} = (1 + k,C'0t)kJk,
(14.23)
where h represents the rate constant for the termination reaction, M0, M and Me represent the monomer concentration at the initial time, at a given time and at equilibrium, and Co is the concentration of the active species. The kinetics thus found for the termination reaction of the ring-opening polymerization of cyclopentene showed analogy to the known bimolecular
989 termination reaction which occurs in the Ziegler-Natta polymerization of linear olefins. 39 Relevant kinetic studies have been carried out in the ring-opening polymerization of higher cycloolefins like cyclooctene, 1,5-cyclooctadiene, cyclododecene and cyclopentadecene. Thus, HOcker '~ and Reimann 4~ investigated the kinetics of cyclooctene polymerization in the presence of various catalytic systems when typical conversion curves were recorded for different reaction times. With WCI6/EtOH/EtAICI2 as a catalyst, the reaction proved to be first order with respect to the catalyst concentration and second order with respect to the monomer (catalyst concentration 1-5 x 104 M). (Figure 14.13). Mole/L x 103
co
P(CO)
20-
15-
10-
3
5
0
0
10
20
30
Time, mm Figure 14.13. Time/conversion curves for cyclooctene (CO) polymerization with WC~OH/EtAICIz ([W] - 2.5 x 10"4mole/L) as a catalyst (Curve l-[CO]0 = 0.25M; Curve 2-[CO]0 = 0.16M]; Curve 3-[CO]0 = 0.086; Curve 4-[CO]0 = 0.043) (Adapted from Ref.~ In contrast tO this catalytic system, with (Ph3P)z(NOhMoClz/EtAICl2 and WCIdMe~Sn as catalysts first order kinetics were found with respect to the monomer concentration. For WCh/Me4Sn the typical conversion curves of cyclooctene are represented in Figure 14.14.
990 M o l e / L x 10 3
CO
15-
/
10
P(CO)
/
2
.5
,, /.
0
0
10
20
30
Time, mm Figure 14.14. Tin.conversion curves for cyclooctene (CO) polymerization with W C ~ e 4 S n (1:5) [W]=l.25x10 "3mole/L ( Curve I-[CO]0=0.3M, Curve 2-[CO]0=0. I M, Curve 3-[CO]0 = 0.05) (Adapted from Ref.40)
The activation energy for the polymerization of cyclooctene was determined to be 21.7 kJ/mole and the activation entropy-55 e.u. The above authors observed a pronounced kinetic control of the reaction products during the early stages of the reaction, at high initial monomer concentration immediate formation of polymer occurs whereas at low monomer concentration the homologous series of oligomers is formed and eventually the polymer. The concentration of oligomers increased as the reaction progressed, reached a maximum as the reaction progressed and then decreased as the polymer was formed. Interesting kinetic investigation on the polymerization of 1,5cyclooctadiene with WCI6:Bu3AI reported Korshak et al. ~2 T h e s e authors showed that significant similarities to the reaction of cyclopentene with the same catalyst exist although the reaction for 1,5-cyclooctadiene is substantially lower. An important observation is that the polymerization of 1,5-cyclooctadiene did not proceed at the equilibrium concentration of the monomer; upon addition of new catalyst during the polymerization stage the reaction proceeded at a higher rate as can be seen from Figure 14.15.
991
1,5-COD
Ccmv., % 100
--+ P(I,5-COD)
-
2
J
80-
/
(304020
0
." 0
.'50
1O0
Time, mm Figure 14.15. Time conversion curve for 1,5-cyclooctadiene (I,5-COD) polymerization with WCI6/~Bu3AI;[COD] = 1 mole~ (Curve l-initial addition of catalyst; Curve 2-new addition of catalyst) (Adapted from Ref. 42) The decrease in the reaction rate was assigned to the significant consumption of the active species. This behavior suggested a bimolecular termination reaction similar to that found in the cyclopentene reaction in the presence of the same catalytic system. Interestingly, it was found that the kinetics of cycloolefin polymerization depends on the cycloolefin stereoisomer and the type of catalyst employed. Thus, in the reaction of cyclododecene induced by WCI6/EtOH/EtAICI2 Reibel observed that cis-cyclododecene reacts at a higher rate than the trans-isomer 43 (Figure 14.16). Cony., %
cis-/trans-CDD --~ P(CDD)
100 1
0
0
60
120
Time, sec
Figure 14.16. Thne/conversion curves for cis- and trans-cyclododecene (cis-/trans-CDD) polymerizauon with WC~OH/EtAICIz as catalyst (Adapted from Ref.43)
992 Similar results have been recorded by Reif~ in the ring-opening metathesis polymerization of cyclopentadecene in the presence of the catalytic system WCI~tOH/EtAICIz (Figure 14.17).
Co.v., %
cis-/trans-CPD -~ P(CPD) 100, .i
I
50
=
o;
a;"
|
6;
"
I
9
8"
Time (sec, mm) Figure 14.17. Time/conversion curves for cis- and t r a n s - c y c l o p e n t a ~ e (cis-/trans-CPD) polymerization with WCh/EtOH/EtAICI2 (Adapted from Ref. 44) When WCIJMe4Sn was used as the catalyst, the reactivity of the two stereoisomers was reversed, i.e. the trans-isomer reacted faster than the cisisomer. This result indicated that the nature of the active centers was different for the two catalysts.
14.4. References
1. a. J.P. Kennedy, "Cationic Polymerization of Cycloolefins: A Critical Inventory", John Wiley & Sons, New York, 1975; b. P.H. Plesch (Ed.), "The Chemistry of Cationic Polymerization", MacMillan, New York, 1963; c. P.H. Plesch (Ed.), "Cationic Polymerization and Related Processes", Heifer & Sons, Cambridge, 1953; d. J.P. Kennedy and E.G.M. Tomquist (Eds.), "Polymer Chemistry of Synthetic Elastomers", Interscience, New York, 1968. 2. a. M. Szwarc, "Carbanions, Living Polymers and Electron Transfer Processes", Interscience, New York, 1968; b. M. Szwarc and M.V. Beylen, "Ionic Polymerization and Living Polymers", Chapman & Hall, New York, 1993.
993 a. J. Boor, Jr., "Ziegler-Natta Catalysts and Polymerizations", Academic Press, New York, 1979; b. G. Fink, R. Mtihlhaupt and H.H. Brintzinger, "Ziegler Catalysts: Recent Innovations and Developments", Springer-Verlag, Berlin, 1995. K.J. Ivin and J.C. Mol, "Olefin Metathesis and Metathesis Polymerization", Academic Press, London, 1987. V. Dragutan, A.T. Balaban and M. Dimonie, "Olefin Metathesis and Ring-Opening Polymerization of Cycloolefins", John Wiley & Sons, Chichester, 1985. J.P. Vairon and P. Sigwalt, Bull. Soc. Chim. France, 569 (1971). 7. J.P. Vairon and P. Sigwalt, Bull. Soc. Chim. France, 569 (1971). 8. H. Cheradame, J.P. Vairon and P. Sigwalt, Eur. Polym. J., 4, 13 (1968). Z. Momiyama, Y. Imanishi, and H. Higashimura, Kobunshi Kogaku, 23, 56 (1966). 10. Y. Imanishi, S. Kohjiya, Z. Momiyama, and T, Higashimura, Kobunshi Kogaku, 23, 119 (1966). 11. Y. Imanishi, S. Kohjiya and S. Okamura, J. Macromol. Sci. Chem.,A2, 471 (1968). 12. M.J. Hayes and D.C. Pepper, Proc. Roy. Soc. (London), Ser. A, 263, 63 (1961). 13. M.A. Bonin, W.R. Busier, and F. Williams, J.Am. Chem. Soc., 87, 199 (1965). 14. C. Aso and O. O'Hara, Makromol. Chem., 109, 161 (1967). 15. C. Aso and O. O'Hara, Makromol. Chem., 127, 78 (1967). 16. S. Kohjiya, Y. Imanishi, and S. Okamura, J. Polymer Sci., A-l, 6, 809 (1968). 17. Y. Imanishi, T Yamane, S. Kohjiya, and S. Okamura, J. Macromol. Sci. Chem. ,A 3, 223 (1969). 18. K. Hara, Y. Imanishi, T. Higashimura, and M. Kamachi, J. Polymer Sci., A-l, 9, 2933 (1971). 19. Y. Imanishi, K. Matsuzaki, S. Kohjiya, and S. Okamura, J. Macromol. Sci. Chem.,A3, 237 (1969). 20. M.A.S. Mondal and R.N. Young, Eur. Polym. J., 7, 523 (1971). 21. L. Thomas, M. Tardi, A. Polton, and P. Sigwalt, Macromolecules, 26, 4075 (1993). 22. a.T. Keii, "Kinetics of Ziegler-Natta Polymerization", Chapman & Hall, London, 1972; b.G.E. Ham (Ed.), "Kinetics and Mechanism of .
.
.
.
.
994 Polymerization Series", Vol. I, Part I and II, M. Dekker, New York, 1969. 23. G. Natta, G. Dall'Asta, G. Mazzanti and G. Motroni, Makromol. Chem., 69, 163 (1963). 24. W. Kaminsky, A. Bark, I. Dake, in 'Catalytic Olefin Polymerization", (T. Keii and K. Soga, Eds.), Elsevier, New York, 1990. 25. W.M. Kelly, Sh. Wang, and S. Collins, Macromolecules, 30, 3157 (1997). 26. D. Ruchatz and G. Fink, Macromolecules, 31, 4669 (1998). 27. J.A. Ewen, J. Am. Chem. Soc., 106, 6355 (1984). 28. M. Ystenes, J. Mol. Catal., 129, 383 (1991). 29. S. Collins, W.M. Kelly, Macromolecules, 2S, 233 (1992). 30. V.A. Hodjemirov, V.A. Evdokimova and V.M. Cherebnichenko, Vysokomol. Soedin., B 14, 727 (1972). 31. A.J. Amass and C.N. Tuck, Eur. Polym. J., 14, 817 (1978). 32. Amass and Zurimentdi, J. Mol. Catal., 8, 243 (1980). 33. C. Tanielian, A. Kinnemann and T. Osparpueu, Can. J. Chem., 58, 2813 (1977). 34. W.B. Hughes, d. Am. Chem. Soc., 92, 532 (1970). 35. K.J. Ivin, D.T. Laverty, J.H.O'Donnell, J.J. Rooney and C.D. Stewart, Makromol. Chem., 180, 1989 (1979). 36. K.J. Ivin, G. Lapienis, J.J. Rooney, and C.D. Stewart, J. Mol. Catal., 8, 203 (1980). 37. B.H.H. Thoi, B.S.R. Reddy and J.J. Rooney, J. Chem. Soc., Faraday Trans. I, 78, 3307 (1982). 38. S. Bittman, M. Dimonie, A. Comilescu, C. Cincu, E. Nicolescu, M. Popescu, S. Coca, "1 't National Congress on Chemistry", Bucharest, Sep. 11, 1978. 39. P. Pino and R. Muhlhaupt, Angew. Chem. Int. FM. Engl., 19, 857 (1980). 40. H. HOcker, W. Reimann, L. Reif and K. Riebel, d. Mol. Catal., 8, 191 (1980). 41. W. Reimann, Ph.D. Thesis, Mainz, 1977. 42. Yu.V. Korshak, B.A. Dolgoplosk and M.A. Tlenkopatchev, Rec. Trav. Chim. 96, M64 (1977). 43. K. Riebel, Ph.D. Thesis, Mainz, 1976. 44. L. Reif, cited after reference 40.
995
Chapter 15
ASPECTS OF REACTION
MECHANISM
The reaction pathway in cycloolefin polymerization depends essentially on the nature of the monomer and catalyst and its mode of their interaction. A certain influence exerts also the nature of the reaction medium and other reaction parameters. Taking into account the cationic, anionic and coordination nature of the catalysts employed in these reactions, in this chapter the mechanisms of cycloolefin polymerization will be addressed for these type of catalyst systems. 15.1. Mechanism of Cationic Polymerization of Cycloolefins In the presence of cationic initiators, the polymerization of cycloolefins proceeds via a carbocationic pathway in which the initiation, propagation, chain transfer, and termination steps involve the well documented processes related to carbocation chemistry ~'2 (Eq. 15.1).
0s.1)
Initiation occurs by the addition of a proton or a cationic species to the carbon-carbon double bond from cycloolefin, generating a c a ~ n i u m ion as a free ion or as an ion pair with the counterion from the catalytic complex. 3 Propagation proceeds by successive additions of newly formed carbocations to the monomer, while chain transfer and termination steps take place by the usual deactivating reactions known for carbocations. 4 Intensive studies on the carbocation mechanism revealed interesting aspects concerning the mode of generating the active species, the identification and characterization of the initiating and propagating species, the nature of the chain transfer and termination steps, and other reaction parameters. 5
996 15. 1.1. Initiation Systems for Cationic Polymerization There is a great variety of initiating systems consisting of BrOnsted acids, Lewis acids and carbenium ions salts. Initiation by BrOnsted acids occurs through protonation of the cycloolefin with formation of a carbenium ion, the first propagation species (Eq. 15.2).
There is a strong evidence for the formation of a carbenium ion as a first initiating species in this reaction from infrared and NMR spectroscopic studies. When the initiator is a Lewis acid, this may act as a cocatalyst in association with a Bronsted acid, water or alkyl halide to form a complex acid or salt which is the real initiator of polymerization (Eq. 15.3-15.5).
BF3 + HF AICI3 + i..120 acl
-,, ..- HS[BF4]e ~
+AICh
~
(15.3)
H~)AI[(OH)Cl3]G
(15.4)
-.-R~[AICh] e
(15.5)
This complex acid or salt can act as a protogen or cationogen able to induce the formation of the first propagating species by the reaction with cycloolefin (Eq. 15.6-15.7).
I~ [BF4] + C(Cl-12)x
H(
R~[AICl4] + C(Cl.-h)x
"/,
f
(C 89
(CH2)x
[BF4]e
(15.6)
t,,c ,P
(15.7)
997 Formation of a carbocationic initiating species from cycloolefin and Lewis acid by self-ionization is also possible without the intervention of a Br6nsted acid, water or alkyl halide (Eq. 15.8). (is.0)
This type of initiation has been demonstrated in cationic polymerization of olefins with Lewis acids under severe dry conditions. 6 Another possibility is the generation of cationic initiating species by autoionization of the Lewis acid (Eq. 15.9).
2 AICh
[AICI2]| [AlCl4]E)
(15.9)
In some cases, solvents or promoters may play an important role during the initiation reaction favoring formation of eationogenic species 6 (Eq. 15.10).
(15.1o)
(CHgx The influence of tight and loose ions pairs on the re.activities of the initiating complexes may be significant in acting as generators of the active species, for example, the opening of the AlzMe6 dimer by a stoichiometric reaction leading to AIMe3, the real cationic initiator of the polymerization process (Eq. 15.11).
~
2AIV~
(15.11)
15.1.2. Nature of Cationic Propagation Reaction
There is good evidence that during the propagation reaction the intermediate carbenium ion may suffer hydrogen, double bond or o-bond rearrangement with formation of new structures incorporated in the
998 polymer chain. The type of rearrangement depends essentially on the nature of the monomer and catalyst. For instance, the cationic polymerization of cyclopentene can proceed through 1,2- and 1,3-enchainment due to the occurrence of 1,2-hydrogen migration in the intermediate cyclopentyl carbocation under the influence of cationic initiator (Eq. 15.12).
__~
(15.12)
0
.
The extent of 1,2- and 1,3-addition will depend on the type of catalyst employed. The highest amount of 1,2-enchainment in cyclopentadiene polymerization was obtained with TiCh and progressively lesser amounts with AIBr3, SnCI4 and BF3.OEtz as initiators. 7 To explain these results, Aso and coworkers 7 suggested that the propagation is controlled by the distance between the counterion and the carbenium ion in the propagating species and that "tight" ion pairs preferentially direct the incoming monomer toward 1,4-enchainment (Eq. 15.13)
0
lb.._
~
[MXn] e
(15.13)
whereas "loose" ion pairs are less selective and allow both 1,2- and 14enchainment (Eq. 15.14).
(15.14) /
999 These authors argued that tightly associated counterions from strong Lewis acids localize the positive charge in the 4 position (e.g., BF3.OEh), whereas the charge is delocalized with "looser" ion pairs obtained from weaker acids (e.g., TiCh). It is noteworthy that in the polymerization of 2methylcyclopentadiene, 1,4-enchainment is preferentially obtained by the use of SnCh and TiCh (~90% 1,4-structure) and much less with BF3.OEtz (--76%). This result is contrary to that with cyclopentadiene, where 1,4enchainment was preferred with BF3.OEt2. Aso and Ohara s explained this finding by assuming that in the presence of a propagating "loose" ion pair (SnCh or TiCh) the sterically less hindered and more reactive secondary allylic position will propagate preferentially by attacking the more negative 1 position of the incoming monomer (Eq. 15.15).
3
(15. 5)
Accordingly, when steric restriction is minimum, attack will occur preferentially on the 1 position leading to 1,4-enchainment. With a "tight" propagating ion (e.g., BF3.OEh) steric compression directs the approach of the monomer so as to have the methyl substituent from cyclopentadiene away from the growing site, that is, the monomer approaches the active site with its 4 position (Eq. 15.16).
(15.16)
On the basis of microstructure results and some theoretical arguments concerning the charge distribution in 1,3dimethylcyclopentadiene, Aso and Ohara s showed that the polymerization of this monomer p r o s predominantly by 1,2- and 1,4-route (Eq. 15.17).
1000
CH 3 ~ ~ R
cH3 ,
R 9 CH3~R
~CH3
NCH3
(15.17)
CH3 The steric hindrance exerted by the methyl substituents does not prohibit the propagation step. In this reaction, the mode of enchainment was affected to a certain extent by the particular initiator employed. It is interesting to compare the fast propagation reaction of this monomer with that of 3-methylcyclopentene which is slower. 9 Thus, due to the difference in the reaction rate, the latter polymerization proceeds readily by intramolecular hydride migration (Eq. 15.18).
c83
(15.18)
cn3
The rapid propagation of the cyclodiene is probably due to the higher stability of the substituted allylic cation as compared with the much less stable initial secondary ion formed in the cyclic monoolefin. In addition, the nucleophilicity of the cyclodiene is much higher than that of the monoolefin. The slow polymerization of cyclohexene in the presence of cationic initiators ~~ is probably accompanied by 1,2- and 1,3-hydride shills in the intermediate cyclohexyl cation due to the easiness these migration occur in the cyclohexyl system under the influence of the Lewis acids ~ (Eq. 15.19). R
a,
=
~,, R
(15.19)
R \
1001 The structure of these polymers could not be identified yet. However, the polymerization of 2-vinylcyclohexene showed some peculiar behavior in the presence of different catalytic systems.~2 Thus, while with SnCIVtrichloroacetic acid the polymerization followed a normal 1,2- and 1,4-addition reaction (Eq. 15.20)
S
9,, nCI4/TCA
(15.20)
by using BF3.OEt2 as a catalyst, the presence of side methyl groups in the polymer chain has been explained by assuming the rearrangement of the intermediate allylic cation by a 1,4-hydride shift pathway (Eq. 15.21).
BF3.CE~
R
",
R
R
R ---D.
(1521)
In addition, the fast termination reaction and the inverse monomer concentration v s . conversion relationship were assigned to the allylic ("suicide") termination mechanism ~3 similar to that for 1,3-cyclooctadiene ~4 (Eq. 15.22). G4" "~
_,p~
+ I" x'l
%/
=
--,PH +
G+.
+
(15.22)
The newly formed highly stabilized allylir ion is unable to sustain even a slow reinitiation process. While the cationic polymerization of 1,3-cyclooctadiene occurs with numerous initiators by a 1,4-addition mechanism ~ (Eq. 15.23),
1002
) R~~
R
@
--~
,__C)_-
~
(15.23)
the peculiar kinetic behavior of this monomer with TiCh as a catalyst was explained by an allylic ("suicide") termination with unreacted monomer ~4 (Eq. 15.24).
- ' '
()
-
"
C)
Of a particular interest is the mechanism of the cationic polymerization of bicyclic and polycyclic olefins due to the multiple rearrangement possibilities in these carbocations, prior or during the propagation reaction. Thus, it has been shown in chapter 12 that the cationic polymerization of norbomene leads to a mixture of various recurring units that have been formed by isomerization of norbornyl skeleton prior to propagation. ~6 The presence of syn, exo-norbomane structures along with 1,2-norbomyl unit has been explained by a ready 1,2rearrangement process occurring in the intermediate norbornyl cation during the propagation reaction (Eq. 15.25).
Formation of nortricyclic recurring units in the cationic polymerization of 5methylenenorbornene with AIBr3 and EtAICI2 as catalysts ~v'~8could be also explained by rearrangements occurring in the norbomenyl moiety (Eq. 15.26).
|
1003 The initially formed tertiary carbenium ion is unable to propagate the polymerization because of prohibitively large steric compression. However, isomerization to the crowded secondary ion which is more reactive, provides a possible pathway for propagation to high polymer. Polymerization of norbornadiene with AICI3 leads mainly to a linear, soluble polymer consisting essentially of 2,6-disubstituted nortricyclene repeat units. 19 Such structures can arise by intramolecular rearrangements of the homoallylic cation during the propagation reaction (Eq. 15.27). =
(152.7)
2-Vinylnorbomene forms readily 1,2-addition polymer in the presence of EtAICIz but also rearrangement of the norbornyl cation prior to each propagation step can occur leading to 1,7-addition product ~7(Eq. 15.28).
~= ~
(15.28)
The formation of insoluble polymer has been explained by participation of the vinyl groups in the cross-linking reaction. Depending on the nature of the starting isomer, exo- and endodicyclopentadiene lead to polymers with different structures in the presence of BF3.OEtz as initiator.2~ Thus, exo~icyclopentadiene gives by 1,2addition mechanism poly(dicyclopentadiene) having 1,2-repeat units in the polymer chain (Eq. 15.29).
+1
(15.29)
1004 Alternatively, endo~icyclopentadiene forms poly(dicyclopentadiene) containing 1,10-repeat units in the polymer chain as result of WagnerMeerwein rearrangement of the intermediate norbornyl moiety during the propagation step (Eq. 15.30).
(ls.3o)
Evidence for these structures is based mainly on the analysis by infrared spectroscopy of the two polymers. The driving force for the Wagner-Meerwein rearrangement occurring during this process seems to be provided by the endo -~ exo isomerization reaction. In contrast, with a variety of cationic initiators (e.g., AICI3, EtAICI2, EtAICI~/fBuCI, BF3, TiCI4, SnCI4), poly(dicyclopentadiene) with a more complicated structure, containing nortricyclene repeat units, has been obtained, as evidenced by infrared and ~ spectroscopic measurements. 2~ Taking into account these results, a polymerization mechanism has been postulated involving a rearrangement of both double bonds of the monomer via intramolecular hydride shift and subsequent cyclization (Eq. 15.31). (15.31) R
R
R
Though the polymer showed to be largely linear, some branches were also present. In a similar way, endo-dihydrodicyclopentadiene, when polymerized with EtAICI~uCI, gives polymer by a 1,2-addition mechanism accompanied by hydride shift and Wagner-Meerwein rearrangement. The cationic polymerization of tetracyclo[4.4.0.12"5.17'~~ 3,8-diene, induced by BF3.OEh at room temperature, yields a soluble polymer with a half-cage recurring unit, resulting by a Wagner-Meerwein rearrangement of the intermediate tetracyclic carbocation formed in the initiation step ~ (Eq. 15.32).
1005 In contrast, tetracyclo[4.4.0.12"5.17'l~ gives by cationic polymerization with Et~CISBuCI a polymer containing both 3,4- and 3,1 l-enchainment of the repeat units 23 (Eq. 15.33).
(15.33) ,/' A competition between the 1,2-addition reaction and Wagner-Meerwein rearrangement of the intermediate carbocation along with termination by a deprotonation mechanism, similar to that encountered in norbomene polymerization, explained better the structure of the polymer, as determined by infrared and ~3C NMR spectroscopy. 15. 1.3. Termination Reactions of Cationic Polymerization
The common termination reactions in cationic polymerization of cycloolefins are deprotonations of the carbocationic propagating species under the action of the Lewis acid complex, R § [AIX]4. According to this mechanism, the chain termination results in unsaturated chain-end of the type (II) and (III) from the propagating species (I) (Eq. 15.34)
(CH2)~ +ROA[X4~ (CH~~
R _
HOA[X4e<
(ID
R
(15.34)
(0 {iO
Such a mechanism for termination reaction has been observed by spectroscopic measurements in the cationic polymerization of norbomene giving rise to chain-ends with structures (II) and (III) ~6 (Scheme 15.1)
1006
~~7
,9 ~AIx4r-+R~AIX4 e F ~ ~ ~ ~ 7 _H e
R ~
@
(i)
"--R~~ Scheme 15.1
(ll)
-HeAIX~e (ill)
In a similar way, by means of ~3C NMR spectroscopic measurements, the chain-end groups in the cationic polymerization of tetracyclo[4.4.0 91Z'Sl 7,~0 . . . ]dodeca-3,8-&ene, reduced by BF3.OEh, have been identified as having structures (If) and (Ill) (Scheme 15.2)
:3.CEh (0
(I)
Scheme 15.2
15.2. Mechanism of Anionic Polymerization of Cycloolefins The mechanism of anionic polymerization of cycloolefins has the common features of anionic polymerization of linear olefins or heterocyr As the literature about the mechanism of anionic polymerization of linear olefins is abundant, in the present section only the differences coming from the structure and reactivity connected with cyclic olefins will be dealt with.
1007
15.2.1. Initiation and Propagation. Living Polymerization Anionic polymerization of cycloolefins occurs via earbanions generated in the initiation step by the interaction of the monomer with organometallic catalyst followed by consecutive insertions of the monomer into the propagating organometaUic species 3 (Eq. 15.35). U n
The initiating and propagating complex may have a o - or n-allylic structure depending on the nature of the cycloolefin and solvent. In hydrocarbon solvents, the reaction pathway prefers a-allylic intermediates but when complexation agents such as Tiff are used in the polymerization of conjugated r e.g., cyr 1,3-cyclohexadiene and 1,3cyclooctadiene, the reaction pathway preferably involves g-allylir complexes 24 (Eq. 15.36).
r~~l (15.38)
~u
9r
1
H
The process may also involve chain transfer or termination by reaction with the solvent or any electrophilic species present in the reaction medium. In case that such an electrophilic agent is absent from the reaction medium, the polymerization goes to completion and continues when further monomer is added. The reaction has the characteristics of a "living" polymerization and can be efficiently employed to prepare block copolymers. 3 Of a particular significance is the mechanism of anionic polymerization of heterocyclic olefins containing silicon as a heteroatom. 25 28 Thus, it is supposed that the mechanism of stereospecifir polymerization of l,l-dimethyl-l-silacyclobutene, under the action of n-butyllithium, proceeds by the nucleophilic attack of the anionic species to the silyl center
1008 to form a pentacoordinate anionic silicon intermediate. 2s Ring-opening of this intermediate leads to a cis-allyl anion which reacts rapidly with another molecule of 1,l-dimethyl-l-silacyclobutene. This process leads to a new pentacoordinate silicon species (Scheme 15.3).
~-CH3 I CH3
~c
[r c'a,s/-
I~.,,c~ -,.
H3qS/
Ue
u*
h c .c~
~'"
-CN CH3
1
,o,
CH3 Scheme 15.3
This reaction must occur faster than the isomerization of the cis-allyl anion into a trans-aUyl anion by rotation about the partial c a r b o n - ~ o n double bond to account for the predominant cis stereospecificity observed. This is not unreasonable at low temperatures utilized for the polymerization (e.g., at -78~ since the energy of activation for such isomerization process is known to be between 10 and 17 kcal/mole. 29 Similar mechanisms have been proposed for the anionic ringopening polymerization of 1-silacyclopent-3-ene, 26 l,l-dimethyl-1silacyclopent-3-ene 26 and other substituted l-silacyclpentenes. 2~ In the case of l-methyl-l-silacyclopent-3-ene, the l-silacyelopent-3-ene end-groups have been identified whose formation was accounted for by the loss of hydride ions from the chain propagating anionic pentacoordinate silicon species. The rationalization of this mechanism is represented by the pathway shown in Scheme 15.4.
1009
Ie
H
Scheme 15.4 15.2.2. Molecular Structure of Anionic Initiators
The nature of the initiating species generated from the organometallic compounds, particularly organolithium compounds, is rather complicated. 3~ It is well-known that organolithium compounds, the frequently used anionic initiators, occur as oligomers; the degree of association is greatly influenced by the solvent, temperature and reaction conditions. The nature of bonding in these associations of organolithium compounds is likely to be the same type of half-bonding as that known for the associations of the alkyls of beryllium and aluminium. It is also very likely that in its covalent organic compounds lithium expands its covalency above unity by p or even higher orbital participation. This electronic particularity of organolithium compounds makes possible monomer coordination before generation of the first carbanionic propagating species. Further coordination of the monomer at the lithium metal during the propagation steps is also very likely. Organosodium and organopotassium compounds generate carbanions of a high reactivity which find applications in many anionic polymerizations. They are ionic in structure and display a high instability.
1010 Some of them, e.g. sodium-naphthalene, can be used to prepare polymers and block copolymers in a "living" fashion. Due to their high reactivity, this class of compounds may promote easily side reactions with the solvent or impurities resulting in a diminished efficiency. Organoberyllium and organomagnesium compounds are essentially covalent and highly reactive, they resemble organolithium compounds in many respects. Organoberyllium compounds, however, may occur as dimers and oligomers, having similar bridging structures to organoaluminium compounds. The special place occupied by the organomagnesium compounds is due to their reactivity and the comparative ease of preparation from metallic magnesium. Grignard compounds have the great advantage over organic derivatives of alkali metals in their exceptional stability in ether solution. Their structures imply a complex equilibrium between monomer and dimer species. Organozinc compounds have a definite monomer structure, are less reactive than Grignard compounds and have a special utility in organic and polymer synthesis. In contrast, organoaluminium compounds find broad applications as anionic initiators in polymerization reactions. The nature of the aluminium-carbon bond and the molecular structure of the dimeric compounds of organoaluminium compounds are well-documented. Their ease of preparation and manipulation made them suitable for large scale industrial applications. 15.3. Mechanism of Ziegler-Natta Polymerization of Cycloolefins The polymerization of cycloolefins in the presence of Ziegler-Natta catalysts generally involves the main steps known for this type of reaction from the well-documented Ziegler-Natta polymerization of acyclic olefins3' (e.g., cycloolefin coordination at the metal center, monomer insertion into the metal-carbon bond, chain termination, and transfer reactions) (Eq. 15.37). R
ff-x~./(o.h)x (O-h)x
+RCH (Oh)<
(O-h~
Coordination of linear olefins at the transition metal compound with formation of ~ complexes is a common process occurring in transition metal catalyzed polymerizations, well-documented theoretically and exoerimentallv. 32 However. whether a t)articular cvcloolefin will first
1011 coordinate and then insert into the metal-carbon bond, or will insert directly, depends on the steric environment imposed on the cycloolefin by complexation; in addition, the reactivity of the cycloolefin plays a determinat role. This latter characteristic also influences the opening of the double bond during the insertion process. Since both the structure and reactivity of the monomer extend over a wide range from small to large and from mono to poly(cycloolefin)s, the borderline between complexation and direct insertion is difficult to define. Furthermore, because of the marked differences in polymer structure compared to polymers obtained from simple or- and linear olefins, the polymerization of cycloolefins may involve specific chain transfer or termination processes. 15.3.1. Structure of Active Species There exists a wealth of information about the nature of active species generated from conventional Ziegler-Natta catalysts consisting of transition metal halide/organometaUic compounds." The interaction between the organometallic compound (e.g., organoaluminium, organozinc) and transition metal halide (e.g., TiCh, TiCI3, VCh), leading to the reactive transition metal-alkyl bonds, has been largely studied by means of various spectroscopic techniques. 3436 Several monometallic37"39 and dimetallic~ models have been proposed for the structure and configuration of the active centers. Addition reactions of olefins to organometallic compounds, which are the simplest models for the polymerization of cz-olefins, were early described. They involve, in general, organometaUic compounds of the metals of the first three groups of the Periodic System, in all these cases, a planar four-center intermediate for the addition of lithium alkyls to olefins has been postulated. 4S Subsequently, a non-planar intermediate complex has also been proposed. ~ An interaction between the olefin and the alkylmetal compound prec~ing the formation of the cyclic transition state and activating the olefinic double bond has also been proposed. In the case of alkylaluminium compounds, an interaction between double bond and the aluminium atom has been proved by infrared spectroscopy. ~7 To explain the much higher activity of Ziegler catalysts containing transition metal atoms, the activation of the olefinic double bond by chemical adsorption on the surface of the transition metal salt has been postulated by Natta. 48 Subsequently, Natta, ~ as well as Ludlum 5~and Carrick, 5~ proposed that the polymerization takes place through the coordination of the monomer to the metal followed by an insertion of the coordinated monomer into the metal-
1012 carbon bond (Eq. 15.38). R'
H2C,~C H--R' 1-12C,=~=,(:f:;H R' I § ~ , ~ [Mt]--C Hz--C H--R (15.38) [Mt}---R [I~]--R Cossee 37 proposed that the olefin forms a ~-complex with hexacoordinated transition metal species having a vacancy in its coordination sphere and then is inserted into one of its bonds with alkyl group (Eq. 15.39). ~ c~
.
cF' ,
~ cJ
IL.,
Ce'c,
~c~
R'
C cl,
- - "
(15.39)
Olefin coordination and the insertion of the first monomer unit into metalalkyl bond have also been widely investigated by ~3C NMR spectroscopy. TM Models in which the 1,2-insetion of olefin is triggered by coordination of additional monomer have also been advanced. 5~ The mechanism of propagation and termination steps are well documented in the polymerization of linear olefins with Ziegler-Natta catalytic systems. Migration of the growing chain-end to the complexed monomer in the monometallic or dimetallic centers have been extensively considered by many authors. 37'3s'~44 1,2-Type insertion of monomer has been evidenced for the synthesis of isotactic polymers and 2,1-type insertion for the synthesis of syndiotactic polymers. In addition, growing chain-end bound by a double bond to the metal atom (carbene complex) and insertion reaction through a metallacyclobutane intermediate have also been proposed 39 (Scheme 15.5). R
R
R H
C
R
R
/C H 2"~"
[MI t ]/~ \C j c H2 J H
H
[M t]---C H R --C H 2 --C H R --C H 2
"~ Scheme 15.5
1013 This type of mechanism has an apparent relationship with the well-known metalla~ne/metallacyclobutane mechanism operating in the metathesis ring-opening polymerization of cycloolefins. At present, the fundamental processes observed in the polymerization of simple olefins using metallocene,/aluminoxane catalysts are firmly established. ~3"5S The chain initiation process involves cis-l,2insertion of the monomer into M-H (generated by J3-hydride elimination) so as to give saturated n-alkyl end groups. With cz-olefins, the propagation process consists of repetitive cis-l,2 migratory insertion, and to a much lesser extent, both cis-2,1 and cis-l,3-enchafinment of the monomer. Chain transfer reactions are dominated by 13-hydride elimination so as to give terminal unsaturation (i.e. vinylidene end groups), whereas [3-alkyl elimination has been observed with sterically demanding catalysts. ~s'57 Under starved feed conditions, metallocenes can also act as epimerization catalysts via a reversible [3-H elimination/insertion mechanism. Moreover, remote C-H activation processes have been involved in the polymerization of branched olefins (e.g. 4-methylpentene) using sterically hindered metallocene catalysts. 57 15.3.2. Mechanism of Insertion Reactions
Results obtained by Natta and coworkers ~s in the cycloolefin polymerization with conventional Ziegler-Natta catalysts were interpreted in terms of the classical coordination mechanism involving first a coordination of the cycloolefin at the vacant site of the transition metal and then insertion of the coordinated cycloolefin into the metal-carbon bond by a 1,2- and 2,1-addition type process (Eq. 15.40).
+ [Mt]--R
=
I [l~t]-R
=
[Mt]
R
(15.40)
This reaction pathway leads to vinyl polymers with a poly(l,2cycloalkylene) structure. Such a mechanism has subsequently been generalized for copolymefization of cycloolefins with linear olefins. The same reaction pathway was admitted by Kaminsky and coworkers 59'6~in the polymerization and copolymerization of cycloolefins using metallocene-
1014 based catalysts where poly(l,2-cycloalkylene) structures for products have been admitted. However, more recently, Collins et al. 6~ demonstrated that in hydrooligomerization and polymerization of cyclopentene using racemic 1,2-ethylenebis(rlLindenyl)zirconium dichloride and methylaluminoxane poly(cis-l,3-cyclopentylene) is formed. Analogous reactions using 1,2ethylenebis(rlLtetrahydroindenyl)zirconium dichloride led to the production of oligomers in which cyclopentene was incorporated in a cis- or trams-1,3 manner. Two plausible mechanisms for trans-l,3 insertion were proposed by Collins62 which involve reversible 13-hydrogen elimination reactions of the unsaturated oligomers or direct interconversion of olefin hydride complexes via the intermediacy of a o-CH complex. According to the first mechanism, an olefin hydride complex of zirconium produced via ll-hydride elimination could undergo a displacement reaction by monomer (Scheme 15.6).
O
.
.
,
,
,
a
R
L/ Scheme 15.6 This process would initiate a new polymer chain producing an oligomer with terminal unsaturation. If the latter product recoordinates to another metal center via its opposite face and inserts, the resulting stereochemical relationship between the metal and the penultimate cyclopentane ring is trans-1,3. The process of trans-l,3 insertion would then involve reversible chain transfer, which has been postulated to occur in olefin polymerizations. 63 The second mechanism involves indirect isomerization of the hydride complex of zirconium via the intermediacy of a o-CH complex (Scheme 15.7).
1015
~
L N ~ .....H ,R
~L/L~/ ( ,....~,H .,
:
,,R
1L
LN ~...,,H
L \ .~....,'H
z -.CT,R
R
Scheme 15.7
A similar process has been advanced to explain the observed isomerization of diastereomeric ge-olefin complexes without prior olefin dissociation 64 and the isomerization reactions of cationic o>-0t-alkenyl)alkoxyzirconocene complexes. ~5 Polymerization of cyclopentene-d8 led to significantly different ratios of cis and trans trimers compared with that observed during polymerization of cyclopentene. The observed deuterium isotope effect on the stereochemistry of cyclopentene polymerization with 1,2ethylenebis(tlS-tetrahydroindenyl)zirconium dichloride could be interpreted in terms of trans-l,3 insertion occurring predominantly via the second mechanism.
15.4. Mechanism of Ring-Opening Metathesis Polymerizationof Cycloolefins Though at present it is unanimously accepted that the ring-opening metathesis polymerization of cycloolefins occurs by a metathetic scission of the carbon-carbon double bond from the cycle, it is of interest in the context of the present work to mention the most relevant proposals for the mechanism of this reaction. Initially it was believed that the ring-opening polymerization of cycloolefins occurred by scission of the ~ n - c a r b o n obond situated in the cz or 13 position with respect to the double bond. Subsequently, when more data concerning the mechanism of acyclic alkene metathesis have been accumulated, it was undoubtedly recognized that the ring-opening polymerization of cycloolefins p r o s by a metathetic scission of the carbon-carbon double bond.
1016
15.4.1. Survey of Proposed Mechanisms As early as 1960, Truett and coworkers 6~ proposed a mechanism involving scission of the C-C o-bond, situated in the ,x-position relative to the double bond, for the polymerization reaction of norbornene with the catalytic system consisting of tetraheptyllithiumaluminium and titanium tetrachloride. These authors showed that the active catalyst is titanium in a valence state lower than IV, bearing the alkyl group as a ligand. This valence state of titanium was electrophilic enough to coordinate the double bond of norbomene. In the complex thus formed electron redistribution with the rupture of the single C-C bond in the ,x-position was supposed to occur and form two new bonds, one between titanium and the olefinic carbon and another between the alkyl group of titanium and the carbon atom situated in the ,x-position (Eq. 15.41).
(15.41) --TiXn In this process titanium atom regains its initial valence state and is ready for further coordination of a new molecule of monomer. The newly formed alkyl group contains the monomer unit from norbomene cleaved at the double bond. Growth of the macromolecular chain will occur by repeating the same process with new monomer molecules. A similar pathway for the polymerization of norbomene induced by transition metal salts in polar media was proposed later by Michelotti and Keaveney. 67 In addition, these authors showed that the solvent takes a direct part in the initial step of the reaction, its nucleophilic character weakening the carbon-carbon single bond situated in the or-position. This type of mechanism was also initially considered by Natta 68 and Dall'Asta 69 for the ring-opening polymerization of small cycloolefins such as cyclobutene and cyclopentene and then generalized to the polymerization of larger cycloolefins such as cycloheptene, cyclooctene and cyclododecene. 7~ By the scission of the C-C single bond situated in the a-position with respect to the double bond, Oshika and Tabuchi 7~ explained the structure of ring-opened polymers
1017 prepared from norbomene, endo~icyclopentadiene and exotrimethylenenorbornene. A different mechanism involving n-allyl complexes formed by cycloolefins through scission of the C-C single bond situated in the 13position with respect to the double bond was suggested by Kormer e t al. ~ (Eq. 15.42). ,
According to these authors, the polymerization may also proceed v i a a chelate intermediate of the ~-allylic type generated from the dimer and oligomers of the cycloolefins and the active site of the catalytic system. Calderon and coworkers 73 were the first to suggest a metathesis route for cycloolefin ring-opening polymerization that involved the cleavage of the C=C double bond of the cycloolefin but the detailed mechanism has not been elaborated. According to this concept, the cycloolefin reacts with the catalytic system at the C=C double bond to form dimers and progressively oligomers of cyclic nature. These macrocycles eventually will lead to linear polymers either by a cleavage reaction at the double bond with an acyclic olefin or by another termination reaction (Scheme 15.8).
,
-
( xC...~.../CCSz)"
....... ~ " " ~ ( 0 ~
''x~
-.... .--_.~/( C t ~
......... R
Scheme 15.8 The metathesis mechanism proposed by Calderon and coworkers was essentially a stepwise mechanism. A special merit of this mechanism was that it explained for the first time the formation of macrocyclic compounds along with polyalkenamers in the ring-opening polymerization of cycloolefins.
1018 Herisson and Chauvin TM proposed for the first time a metallacarbene mechanism for the ring-opening polymerization of cycloolefins in the presence of tungsten-based catalysts (Eq. 15.43). (
* H W
According to this approach, which is at the origin of the present accepted metallacarbene mechanism for olefin metathesis, the propagation step involved a metallacyclobutane intermediate formed by [2+2]cycloaddition reaction of the cycloolefin with metallacarbene. Their proposal was based on the kinetic results obtained in the telomerization reaction of cyclopentene with 2-pentene in the presence of tungsten catalysts. For the telomerization the reaction pathway involves metallacarbene addition at the monomer double bond with formation of the intermediate metallacyclobutane and subsequent reversion and addition reactions with further molecules of monomer (Scheme 15.9).
C•
(
/ CHR W
"1
1L
/
RH~<~HR"
~(O'~2-CH=C~R , ,
Hc.~
W~. IC~(~2-O-~O-R ----~ RI-C CHR'
w ~+(O-b,,.2-C~CHR
------~ l~J +CH~
~c cH
Scheme 15.9 This mechanism successfully explained the formation of polyalkenamers by ring-opening polymerization of cycloolefins, the degradation of polyalkenamers to macrocycles and the distribution of telomers formed in the cometathesis reaction of cycloolefins with internal unsymmetrical olefins. However, at that time, the mode of generation of the metallacarbene species and the product distribution in the telomerization reaction of cycloolefins with cz-olefins remained still unexplained.
.
1019 In the course of their extensive studies on the polymerization of isotopicaUy labelled cycloolefins, Dall'Asta and coworkers 75 provided convincing evidence in favor of the metathetic mechanism. Thus, on using cyclopentene labelled at the carbon atoms of the C=C double bond in the copolymerization reaction with cyclooctene, they demonstrated that the structure of the copolymer corresponded to mission of cyclopentene at the C=C double bond and not at the C-C single bond. This fact can be seen by a straightforward examination of the reaction scheme outlined by Dall'Asta for the two modes of ring cleavage of the two above cycloolefins. (i) In case that ring-opening occurs at the C=C double bond of the two cycloolefins, the following glycols should be obtained after oxidative degradation of the double bond from the copolymers, as was experimentally found (Eq. 15.44). .
.
.
---
.
~
+
05.44)
(ii) In case that ring-opening occurs at the C-C single bond situated in the a-position, the following glycols would have been obtained after oxidative degradation of the copolymer, what actually were not found (Eq. 15.45).
[o1 .
.
.
.
.
.
.
.
Furthermore, through isotopic labelling technique, Dall'Asta and coworkers ~6 proved that the copolymerization of cyclobutene with 3methylcyclobutene proceeds via metathesis. Thus, after oxidative degradation of the copolymer prepared from ~4C-labelled cyclobutene at the double bond and unlabelled methylcyclooctene, these authors obtained diols with a radioactivity distribution corresponding only to the ring-opening at the C=C double bond. Based on further investigations of the polymerization and copolymerization reactions of a large number of cycloolefins, using a
1020 variety of catalytic systems derived from molybdenum, tungsten, titanium and ruthenium, Dall'Asta was able to generalize the metathetic mechanism for ring-opening polymerization of cycloolefins to polyalkenamers. 15.4.2. Features of Metallacarbene/Metallacyclobutane Mechanism
There are some particularities which characterize the metallacarbene/metallacyclobutane mechanism proposed for the ringopening polymerization of cycloolefins. These regard the nature of the of the initiation reaction, that of the intermediate metallacarbene/ metallacyclobutane species, the nature of transfer and termination reactions. 15.4.2.1. Mechanism of Initiation Reaction
A chain initiation mechanism for the ring-opening polymerization of cycloolefins involving metallacarbenes was suggested by Dolgoplosk and coworkers, 77 based on extensive studies on the cycloolefin polymerization promoted by carbene precursors. These authors advanced a proposal for the generation of metallacarbene species in the initial step by the reaction of the olefin with the catalytic system followed by an intramolecular migration of the hydrogen atom within the olefin complex (Eq. 15.46).
+
[Mt]
,
R
K, c / =[Mt]
(15.46)
R Relevant experimental results reported by Dolgoplosk and coworkers 78 provided convincing evidence that the chain process of ring-opening metathesis polymerization was initiated by carbene species. For instance, they observed that the decomposition of phenyldiazomethane, ethyldiazoacetate and trimethylsilyldiazomethane initiated the reaction of cyclopentene and 1,5-cyclooctadiene under the influence of tungsten chlorides. In the case of phenyldiazomethane, the reaction proceeded practically instantaneously at room temperature. Furthermore, the formation of high molecular weight products with a low content of oligomers even in the earliest stages of the reaction indicated a chain process and the generation of some highly reactive centres in the system.
1021 Significant work of Rooney e t al. ~9 showed that metal-hydride complexes could be largely responsible for the ring-opening polymerization of norbomene. Such hydrides, whose concentration is increased for WCI6 by a little water and diminished by LiC,Hg, could arise from the reaction of H20 and/or HCI with W(IV) species subsequent to reduction of W(VI) by norbomene. These metal-hydrides seem to generate the metallacarbenes which initiate the polymerization process (Scheme 15.10).
H
H
Scheme 15.10 Such hydrides of the transition metal complexes, for instance hydrated complexes of IrCl3 with 1,5-cyclooctadiene, which are active in norbornene polymerization, have been detected using infrared spectroscopy by means of their characteristic absorption of the M-H bond. To account for the role of oxygen as an activator in the initiation of cyclopentene polymerization induced by WCI6, Amass and McGourtey 8~ suggested the occurrence of an oxygen ligand at the tungsten active species which assist the generation of the carbenic chain-carrier (F-xt. 15.47).
/I
/I
/I
Analysis of the polymer structure by infrared spectroscopy indicated the presence of the carbonyl groups in the polymer chain. The oxygen ligand seemed to be essential in the initiation step with this activated catalyst but
1022 not directly involved in the propagation step. Katz and coworkers 8~ explained the mechanism of the polyalkenamer formation from cycloolefins in the presence of the metaUacarbenes Ph2C=W(CO)5 and Ph(MeO)C=W(CO)5 by a chain process where the initiation and propagation reactions are attributed to a carbene species (Eq. 15.48).
(5 where X = Ph or MeO. In addition, Katz and coworkers 82 demonstrated how alkynes can induce cycloolefin polymerization with stabilized metallacarbenes. Thus, they assumed that alkynes combine first with stabilized m a t a U a ~ e n e s of the type Ph(MeO)C=W(CO)~ producing a more reactive metallacarbene vm an insertion process which then initiates cycloolefin polymerization like the conventional metallacarbenes (Scheme 15.11).
HsCe~ H3CO/C =W(C O)5 + R
---.---li,.
HsCo\
H3CO
W(C O)5
HsCe\
/c=w(co)s
L
HsCe
Scheme 15.11 These authors 83 also pointed out that alkynes can also quench the polymerization process by the same insertion-type mechanism (Eq. 15.49).
R~ (1s.49)
(~
(CH~
(cugx
1023
15.4.2.1.1. Initiation with WCIs/Organoaluminium Compounds Extensive investigations on the ring-opening polymerization of cycloolefins (e.g., cyclopentene, cyclooctene, 1,5-cyclooctadiene, cyclododecene) with the ternary catalysts based on WCI6 and organometallic compounds (e.g., 'Bu3AI, Et2AICI, EhAIzCI3, EtAICIz) and activators (e.g., epichlorohydrin, chloranil) by Cornilescu et al. v'~s pointed out that the initiation step depended markedly on the alkylating and reducing power of the organometallic compound, the electron-accepting or donating ability of the activator and the nature of the cycloolefin. Examination of the time-conversion curves for cyclopentene polymerization during the first stages of the reaction indicated that 'Bu3AI, EhAI and Et2AICI lead to a rapid initiation while EhAI2CI3 and EtAICI2 exhibit a slow initiation. Similar results have been obtained for cyclooctene, 1,5cyclooctadiene and cyclododecene. Of the two activators employed, chloranil and epichlorohydrin, the first promoted a high reaction rate as compared to the second for both initiation and propagation steps. These data were explained by two possible mechanisms for the initiation step under the above conditions. The first mechanism involves the generation of the metallacarbene species through prior alkylation of WCI6 by the organoaluminium compound and subsequent a-hydrogen migration to form a tungstacarbene complex (Eq. 15.50).
vvc
,-.
RCH2 I
X
RCH tl
RCH II
+.x
(15.50)
X
This carbene complex leads via reductive elimination to a new tungstacarbene in a reduced state able to coordinate the cycloolefin and initiate the polymerization reaction (Eq. 15.51).
[V',F-CH
4q
=Ct'R
(15.51)
This reductive elimination step, assisted by a Lewis acid, seems to be essential for the initiation process.
1024 The second mechanism, distinct from that shown above, implies the direct intervention of the cycloolefin in the initiation step. ESR spectroscopic measurements carried out on the system WCldcycloolefin indicated that W(VI)is readily reduced by cyclopentene to W(V) and W(III) paramagnetic species ~ (Figure 15.1). /./1
S I
g.1.680 i
Figure 15.1. ESR Spectra of WCldcyclopemene system (Adapted from Ref.u') while in the presence of cyclooctene and cyclododecene W(VI) is reduced slowly to W(V) paramagnetic species. Moreover, when organometallie compounds are used as cocatalysts, the reduction rate depends markedly on the order of contacting the cycloolefin with WCI6 and the organometallic compound, this being higher when the cycloolefin was added first. In this case, it was supposed that the generation of the metallacarbene species may involve the prior interaction of the cycloolefin with the tungsten compound in a low oxidation state to form a coordination complex which, via 1,2hydrogen migration, leads to a tungsten-cycloalkylidene complex able to further initiate the polymerization reaction (Scheme. 15.12).
tO
WC le
X
X
X
Scheme 15.12
1025 The presence of cyclopentylidene chain ends in the polypentenamer was unambiguously evidenced by mass-spectroscopic measurements, ss Similar results have also been obtained in the ring-opening polymerization of cyclooctene and cyclododecene. There is a strong evidence from ESR spectroscopy that tungsten atom in the WCl~-based system is reduc~ to lower oxidation states by the organoaluminium compound in the presence of cycloolefins, s6 Some relevant ESR spectral data and the assigned oxidation state of the tungsten atom are summarized in Table 15.1 for the system WCl6/organoalumium compound/cycloolefin, s7 Table 15.1 g-Factors in ElLS spectra and formal oxidauoa states of catalytic systems WCij'Bu3Al/cycloolefin Catalytic System
g-Factor
Oxidation State
WCI6/'Bu3AI
g1=1.950 g2=1.850 gs= 1.806
wOO wOO
WCl6/Cyclopeat~e/' Bu3AI WC 16/Cyclohexene,/'Bu3Al
g4=1.740 gi=1.9555 g2- 1.740
gt=l.830
W(V) or W(III) W(III) (WV) W(III)
w(v) W(III)
WC 16/Cyclooctene/Et2AIC1
g2 = 1.740 gi=1.920
W(III)
WCI6/1,5-Cyclooctadiene/Et2AIC1
g3 = 1.740 gt=l.920
g~=1.830
g2= 1.830 g3=1.740
wOO wOO wOO w(v) W(III)
'Data from reference s7 It can be seen that the higher reducing power was encountered for the system WCld'Bu3Al. It is interesting to note that this system provided the higher content of trans-polypentenamer in the ring-opening polymerization of cyclopentene.
1026
15.4.2.1.2. Initiation with WCI6/Organotin Compounds The catalytic systems derived from WCldorganotin compounds displayed generally a lower activity in cycloolefin polymerization as compared to the WCl#organoalumium systems. In the aliphatic series of organotin compounds, the initiating rate in the cyclopentene polymerization decreases in the following order C2Hs>>C~-Ig>CH3. It is noteworthy that WCld(CH3)4Sn is also active in the metathesis of unsaturated compounds bearing certain functionalities. On the other hand, tetraphenyltin associated with WCI6 provides a highly active binary catalytic system for the polymerization of cyclopentene and cyclooctadiene. Higher cycl~lefins such as cyclooctene and cyclododecene were practically inactive under these conditions. However, these two r could be l~lymerized when small amounts of cyclepentene, cyclohexene or 1,5-cyclooctadiene were added to the catalyst (see Figure 4.21). Two alternate mechanisms for the generation of the initiating species have been envisaged for the two types of catalytic systems. The first mechanism, occurring with the alkyltin compounds, involves initially an alkylation step and subsequent ~-hydrogen elimination from the alkylated tungsten compound by one of the path (a) or (b), leading to metallacarbene species ~ (Scheme 15.13). WCl6 + (RCH2)4Sn
RCH WCI RCH=VVCI4
-~ RCH2WCIs + (RCH2)3SnCI RCH=WCl4
(b)
(RC H2)2VVC[4
O
=
-RCH 3
RCH=WCI4
c,,vvtc : .4
Scheme 15.13 The metallacarbene thus formed is able to initiate the polymerization process by subsequent coordination and insertion of cyclopentene. A similar mechanistic scheme for the generation of mngstac,arbene species by the interaction of WCI6 with (CH3)~Me has also been advanced by Thorn and coworkers. 88 In contrast to the tetraalkyltin compounds, tetraphenyltin can
1027 not generate directly m e t a l l a ~ n e species by the above reaction sequence since the phenylated derivative that would arise is devoid of hydrogen atoms in the cz position. The high activity of this system is rationalized by a reaction pathway in which the tungstaearbene species can arise directly from the cycloolefin and the phenylated tungsten compound as a result of the reductive elimination assisted by the cycloolefin ~ (Scheme 15.14).
WCl6 + (CsH5)4Sn~
C6H5WCI5 + (C6H5)3SnCI
C6H5WCI5 ~C61"15WCl5"0
0+<3
'C6H5C/CIxW=~
nO Scheme 15.14
The reduced activity of higher cycloolefins (e.g., cyclooetene, cyclododecene) in this polymerization reaction can be assigned to a high aerie barrier encountered in the first step of the interaction between the cycloolefin and the tungsten compound responsible for the generation of the initiating metal-carbene complex. However, when catalytic amounts of small-ring eycloolefins are added such as cyclopentene, cyclohexene or even 1,5-cyclooetadiene which can coordinate at the tungsten atom and consequently assist the reductive elimination step, then polymerization of higher cycloolefins can be initiated as shown above. 15.4.2.1.3. Initiation with WCI6/Water
As mentioned previously in Chapter 4, addition of small amounts of water to the cyclopentene-WCl6 mixture initiated the ring-opening polymerization of cycloolefins to high molecular weight polymers in the absence of organometallic compounds. 89 The highest reaction rates were obtained at a pre-contacting time of cycloolefin with WCI6 of several hours. The molar ratios water:WCl6 were found to influence considerably the yield in polypentenamer (see Figure 4.26). Thus, while yields of over 20% polymer have been obtained at molar ratios water:WCl6 < 0.2, on increasing this molar ratio the polymer yield decreased rapidly. Moreover, water
1028 initiated the cyclopentene polymerization only when W(III) paramagnetic species were observed by ESR spectroscopy in the system and the activity increased with the concentration of the W(III) species. Taking into account these data, a plausible mechanism for the generation of the initiating m e t a l l a ~ e n e species, under these conditions, has been proposed (Scheme 15.15).
0
WCI6 ~
0 "---LxW(IV)
LxW(V)
O
LxW(lll )
LxW(III)
..
0 0
0 0
0
0
H20 ~ "- LxW OH
-,-x-,
LxVV(III)
0
~
W Lx-lll 0
0
0
Scheme 15.15
As it can be seen, a first metallacarbene species may arise through the interaction of cyclopentene with the tungsten compound in a reduced state but this metallacarbene initially has a low activity and only aRer interaction with water its activity increases so as to be able to propagate the polymerization reaction. 15.4.2.1.4. Initiation with Metallacarbene Complexes There is at present a great number of metal-carbene complexes that initiate the ring-opening polymerization of cycloolefins. They are divided into two broad classes, Fischer-type and Schrock-type. Fischer-type carbene complexes are low-valent and generally characterized by the presence of one or two heteroatoms (O, N or S) bonded to the carbene carbon while Schrock-type carbene complexes do not have a heteroatom (other than Si) bonded to the carbene carbon. The first type of complexes do not normally initiate the ring-opening metathesis polymerization of
1029 cycloolefins since they are both coordinatively and electronically (18e) saturated, however, they can sometimes be activated for ring-opening polymerization by heating, by use of a cocatalyst or photochemically (Table 15.2).
Table 15.2 Fischer~e carbene initiators for ROMP of cycloolefms
Carbene Complex
(CO),W=C(OEt)Bu (CO)sW=CPh2
(CO),W=C(OMe)Ph (CO),W=C(OMe)Ph (CO),W=C(OMe)Ph (CO),W=C(OMe)Ph
(CO)4W~C,(OMo)
Activator
TiCI4 Heat (38~ Heat(50~ Heat (50~ PhC~H hv
Heat (60~ Et3AI AICI3
Monomer
Cyclopentene cis-Cycloalkenes Cyclobutene Norbomene Cyclopentene 1,5-Cyclooctadiene Norbomene Norbomene Norbomene
*Data from reference9~
The second type of complexes are of the general formula Mt(=CR'R")(L),, where R' and R"= H, alkyl, aryl and L = different ligands (Table 15.3). These carbene complexes are effective in metathesis and ringopening polymerization, but their effectiveness significantly depends on the transition metal and solvent. Ethers, such as tetrahydrofuran and dimethoxyethane, may be strongly bound to these complexes and have a moderate or strong retarding effect on the reaction. 15.4.2.1.5. Evidence for Initiating Metallacarbene Complexes Strong evidence for the initiation of the ring-opening polymerization by metallacarbene species has come from the ~H and ~3C NMR studies on the polymerization of norbomene or norbornadiene and their derivatives effected by Kress, 91 Feast, 92 Ivin93 and Schrock. 94
1030 Table 15.3 Schrock-type Carbene Initiators for ROMP of Cycloolefins~
Carbene Complex
Ta (=C HC Me3)(OAt)3(THF) Ta(=CHCMe3)(TIPT) Mo(=CHC Me3)(=NAr)(OCMe3)2 Mo(=CHC Me3)(=NAr)[OCMe(CF3)2]2 Mo(=CHCMeePh)(=NAr)[OCMe(CF3)z]2 W(=C HC Me3)(Br)2(ONp)2 W(=C HC Me3)(Cl)(Np)(OAr)z(O-ipr2) [W]=CHCMe3
W[=CHCd-14(OMe)z](=NAr)[OCMe(CF3)2]2 W(=C HS iMe3)(=NPh)(C H2SiMe3)L Re(=CHC Me3)(-CCMe3)[OC Me(CF3)2]2 Ru(=CHCH=CPhz)(CI)2(PPh3)2 Ru(=CHCH=CPh2)(CI)2(PCy3)z Ru(=CHR)(CI)2(PR'3)z R = H, Me, Et,Ph~-CIC~; R'=Ph,Cy
Electron Count
Monomerb
12 10 12 12 12 12 14 14 12 14 14 16 16 16
NB NB NB, ONB NB, ONB NB, ONB NB, DCPD NB, DCPD NB, DCPD NB, NBD, DCPD ND, DCPD NB, ONB NB, ONB NB, ONB NB, ONB
'Data from reference~; ~B--norbomene, ONB=oxanorbomadiene, DCPD=dicyclopentadiene
NBD--norbomadiene,
When the reaction is sufficiently slow, signals for the first addition product of initiator with monomer and subsequent addition products can be observed, either for the carbene proton resonance or elsewhere in the spectrum. By this means, it was found that the concentration of the first addition product (P~) passes through a maximum with increasing time when the rates of formation and disappearance of P~ are equal. At this point k.,/kp = [P~]/[I], where [I] is the momentary concentration of initiator. The relative reactivities of syn and anti rotamers of the Mo(=CHCMe2Ph)(=NAr)(OI%6) initiator with 2,3bis(trifluoromethyl)norbomadiene have been evaluated qualitatively by means of ~H NMR spectra when initiating the polymerization of this monomer with a mixture of syn and anti rotamers generated by photolysis at-80~ The I-~ resonance for the anti rotamer was replaced by an Ha resonance for the syn "first insertion product" downfield from the I-~
1031 resonance for unreacted syn rotamer. The C=C double bond in the "first insertion product" was found to be trans (Jm~ = 15.4 Hz) (Eq. 15.52). N~r H RID, tl I
CF 3
=N~N"
cCF3 CF, \
9
CF3
(15.5,2)
H
After 1 hr at a temperature of-40~ all monomer was consumed by syn rotamer of the molybdenum alkylidene complex to give other "living alkylidenes" of syn configuration. A reactivity ratio of anti to syn rotamers of the initiating metallacarbene in toluene was estimated to be at least 2 orders of magnitude.
15.4.2.2. Mechanism of Propagation Reaction At present it is unanimously accepted that the ring-opening metathesis polymerization of cycloolefins is a chain process occurring through a metaUacarbene,/metallacyclobutane mechanism.
15.4.2.2.1. Features of MetaHacarbene/Met~acyclobutane Mechanism The carbene mechanism advanced for the first time by Herisson and Chauvin TM assumed a metallacarbene/metallacyclobutane pathway for the propagation step in the cycloolefin ring-opening polymerization. Following a [2+2] cycloaddition reaction of cycloolefin with a metallacarbene initiating species, the metallacyclobutane thus formed accomplishes the monomer insertion into the metal-carbene bond and generates a new metallacarbene able to funher coordinate a new molecule of cycloolefin, resuming the catalytic cycle metallacarbene,/metallacyclobutane (Eq. 15.53).
(15.53) :
,
(cN Though the occurrence of metallacarbene and metallacyclobutane was invoked from the results obtained in telomerization reaction of cyclopentene
1032 with 2-pentene in the presence of classical tungsten catalysts, the validity of this concept was fully confirmed by refined spectroscopic techniques more than ten years later. According to a chain mechanism proposed by Dolgoplosk and coworkers, 9~ the propagation step involves the reversible monomer coordination to the metal species followed by monomer insertion into the polymer growing chain(Scheme 15.16).
___---
m __.
__.
Scheme 15.16 Investigations carried out by this group with cyclopentene, 1,5cyclooctadiene and norbornene showed that polymers of high molecular weight have been formed in the early stages of the reaction. Significantly, these polymers were characterized by a narrow molecular weight distribution that gradually broadened at high conversions. The amount of oligomers at low conversions was found to be small and their formation was associated with polymer cyclodestruction. This process was interpreted in terms of reversible polymer-oligomer equilibrium promoted by the reaction of the active centers with the nearest double bond of the polymer chain (Eq. 15.54).
The mechanism of the ring-opening metathesis polymerization of cyclopentene with cis-stereospecific and non-stereospecific catalysts was rationalized by Calderon and coworkers 96 in terms of a dentate chelating concept involving a chelated growing chain for cis-specific catalysts (I) and a non-chelated growing chain for non-specific catalysts (II) (Scheme 15.17).
1033
(CH2)x
(C
(
Mt
I
II
Scheme 15.17 In the first case, the propagation reaction involved a "three-ligand sequence", implying a simultaneous coordination of the carbene, monomer and polymer chain to the metal center while in the second case, a "twoligand sequence" with coordination of the carbene and monomer only (Scheme 15.18).
QY Scheme 15.18 Based on the microstructure of the polyalkenamers, Ivin and coworkers 9v postulated the presence of two kinetically active species, not in equilibrium with one another, to explain the mechanism of ring-opening polymerization of cycloolefins. Taking into account these distinct kinetic species, Ivin and coworkers 98 interpreted this process within the limits of the carbene concept as involving metallaca~nes which first coordinate and then add olefin to give a transient metallacyclobutane which subsequently ruptures to yield a new metallacarbene and a newly formed double bond (Scheme 15.1 9).
1034
[Mt] +
(C H2)x
~--
PnCH [~t]I~-IL~(c H2)x
PnCH---~'%
,
3
PnCH~ [Mt]z,,~,/(cH2)x
[Mt]=CHPn. 1
4
1'
Scheme 15.19 It was assumed that the metallacarbene 1 has approximately octahedral geometry and one vacant position for coordination of the olefin. In this case, four possible orientations of the carbene ligand with respect to the vacant site were considered, A,B,C and D (Scheme 15.20).
P----H i I
H----P
,Y._ L
,-;M t-i~]
-'-Mt '-[]
/_J_J
"1,r I
A
I~
, I
i
.,'4,
,--Mt--~
:,; I~tj-I]
/_!_J
B
,,,i
C
D
Scheme 15.20 where P represents the polymer chain and Mt the metal centre. According to this concept, in the ring-opening polymerization of norbomene only two types of metallacyclobutane structures 3 are possible, E and F, which were termed cis and trans, respectively ~ (Scheme 15.21)
M
~'N \H
M
E(cis)
~,
F(trans) Scheme 15.21
R
1035 If it is admitted that the cycloolefin attacks the metallacarbene with its less hindered e x o side, the coupling of the monomer to the metallacarbene may occur in one of the four possible ways according to which of the two olefinir carbons becomes attached to the carbenecarbon. 99 The polymer chain may also have one of the four possible positions (Scheme 15.22)
'
, I,
I~ I,J'-N
~"
L'"
,.~_,~1
I," I
t-Mt.H:I l/i, i I,"
j
#
#
--
I
I/I,IL~ I,, # #
,J l #
-- -- ~,H
,
#
I,' "
"'1 I
--In
""
i/I,i~--~
#
"
L"
'"
i/I,I
I,"
'
~
I
I
I
----i,,
-"9 /! I//
,
'H'
d--_
#
Scheme 15.22 By a detailed analysis of all possible modes of rupture of the intermediate metallacydobutanes, Ivin concluded that the most likely pathways for reaction are those represented by the full lines in the Scheme 15.23, together with some contribution from the pathways with broken linesm~ (Scheme 15.23).
1036
C +M
B (D)
+M
=rE
s
(cis)""',,,~ B (B)
j
......w C
+M
C f
S
s
(tra ns) -- ,,
'~D (B)
Scheme 15.23 To explain the results obtained in ring-opening metathesis polymerization of optically active 5,5,-dimethylnorbomene with various catalysts based on transition metal (i.e., Mo, W, Re, Os, Ru and Ir) compounds, Ivin and coworkers m~ considered further a sequential formation of a metallacarbene-monomer complex, 2, a metallacyclobutane, 3, a metallacarbene with the newly-formed double bond first coordinated to, 4, and then decoordinated from, 3, the metal site (Scheme 15.24).
(C
H2)~
*
Pn'ICH-~ X(CH2)x [Mt]---...J 11
[Mt] +
PnCH ~ 11_4"il :(CH2)x ~
(CH2)x
PnC H--~-'X [l~lt]._J~(C H2)x
[Mt] ~....j
PnCH-~'
[Mt~
X(CH2)x
4
[Mt]==CHPn.1 1'
Scheme 15.24 Two types of metallacycle rupture were postulated, one w a a parallel mode of orbital separation to give a mirror-image form of 4, the other via a disrotatory mode resulting in an achiral "symmetrical" form of 4, there are
1037 also corresponding mirror-image and symmetrical forms of 1. The first type of rupture accounted for the cases of high tacticity or tacticity which falls with monomer dilution, the second one explained how the tacticity can be independent of monomer dilution. Propagation was assumed to occur either by addition of monomer to l to form a cis or trana double bond, or by displacement of coordinated cis double bond from 4 by monomer to form a new cis double bond. Based on these assumptions, Ivin et aL ]0~ developed a complete mechanism to explain the more general features of the olefin metathesis and ring-opening polymerization of cycloolefins, especially stereospecificity and stereoselectivity in r reactions (Scheme 15.25).
! !
I Pl(r~ Pi(r)Psc Ps I I I
,, ,, ! I i I I
'
J
I
=r C~O/r)r ~ ;
Pst
IL - IP,,ol
Scheme 15.25
In the Scheme 15.25 it is assumed that the boxes enclose species that are capable of adding monomer. Subscript (t/r) means that the product C may have either I or r configuration and subscript l(r) means that the product has the configuration appropriate to the reactant. The dashed paths were considered improbable. This mechanism could explain all types of observed tacticity and blockiness behavior in polyalkenamers. ~~176 A different insertion=type mechanism for cycloolefin polymerization involving a bimetallic propagation center was proposed by Levisalles and coworkers ~~ (Scheme 15.26).
1038
(CO)sMt--Mt(CO)4
=_
-CO
(
(C O)4Mt-Mt(C 0),I
(C
(CO)4Mt-Mt(C 0)4
+
(C O)4Mt--Mt(C0)4
C(
CH2)x
(CH2)x
Scheme 15.26 Evidence for this mechanism was based on the isolation and characterization of the bimetallic complexes of tungsten which are active in alkene metathesis and alkyne polymerization.
15.4.2.2.2. Detection of Reduced Paramagnetic Species in WCI6/Organoaluminium Systems The ring-opening polymerization of cyclopentene initiated by the catalyst WCk,/epichlorohydrin/'Bu3Al has been followed by ESR spectroscopy at room temperature, either under dry argon or in high vacuum (10-3 torr). 86 Under dry argon, only one ESR signal was recorded with a g-factor of 2.0048, All = 13G. The occurrence of this signal has been reported also by other authors, m~ In high vacuum, the ESR spectra showed three distinct paramagnetic signals (Figure 15.2).
1
a
,
', ~.~.,ss
g-2 019
i
g',,1 73
Figure 15.2. ESR spectra recorded during the rmg-q3enmg polymerization of cyclopentene initiated by WCldepichlorohydrinfBu3Al (Adapted from Ref.~
1039 The signals with g-factors of 1.055+0.005 and 1.730-a:0.03 were assigned to W(V) and W(III) species, respectively, the signal connected with the W(V) species exhibited a weak hyperfine structure. The signal with a g-factor of 2.019a:0.002 was associated with a hydrocarbon radical. The time variation of the amplitude of these three ESR signals in cyclopentene polymerization is illustrated in Figure 15.3.
I, r.u.
l
1.0
!
0.5
&
0
20
40
60
80
Time, mm Figure 15.3. Time evolution of the amplitude of ESR signals rocordod during rmg-opcnmg polymerization of cyclopmtcne with WCldcpichlorohydrin/'Bu3Al (1" signal associated with W(lll) species; 2: signal associated with W(V) species; 3 signal associated with hydrocarbon radical (Adapted from Ref.~ It can be observed that, during the first 20 min, the amplitude of the W(III) signal increased rapidly and then decreased as the cyclopentene polymerization progressed. The evolution of this signal was correlated with the monomer conversion and catalyst activity. The mode of time variation of the amplitude of the signal assigned to W(V) species evidenced the rapid reduction of the W(V) species to W(III) effected by the organoaluminium compound. Interestingly, the third signal with a g-factor of 2.019-~.002, assigned to a hydrocarbon radical, increased significantly as the polymerization reaction progressed.
1040
15.4.2.2.3. Evidence for Metallacarbene-Olefin Complexes
The presence of metallacarbene-olefin complexes in the metathesis catalytic systems has been evidenced by Kress and Osborn m~ by t3C NMR spectroscopy during the interaction of tungsten cycloalkylidene complexes with cycloolefins. Thus, following the interaction of cycloheptene with the tungsten-cyclopentylidene complex (I) in CD2C12 at a temperature of-73~ additional resonances assigned to tungsten-carbene-olefin complex have been observed in the ~3C NMR spectrum: a signal at/5 355.3 (mJwc = 142 Hz) assigned to the carbene carbon of the cyclopentylidene unit and two signals at ~5 124.4 and 107.8 ( I j wc = 165 Hz) corresponding to two nonequivalent olefinic carbons, upfield from the olefinic carbon signal of cycloheptene at /5 132.4 (mJwc = 154 Hz). It was concluded that cycloheptene was coordinated at the tungsten atom in the cyclopentylidene complex (II) (Eq. 15.55).
RID (I)
i
-7"313
(
T>-I (II)
The equilibrium constant for the formation of this complex was estimated to 4.5 M ~, the temperature variation gave AH~ - - 5 7 kJ/mole and AS~ - -230 J/K.mole. When raising the temperature above -18~ polymerization of cycloheptene begins to occur, indicating that the complex can be considered a true intermediate in this reaction. Similar results have been obtained during the interaction of cyclooctene with tungsten-cyclohexylidene complex. No interaction was found, however, between cyclohexene and these tungsten complexes and no polymerization occurred, suggesting that ring-strain relief is involved in the formation of the cycloolefin-tungsten complex as well as in its polymerization.
1041 15.4.2.2.4. Evidence for Propagating Metallacatrbene Complexes
The occurrence of propagating metallacarbene complexes in the ring-opening polymerization of cycloolefins can be easily followed by ~H and ~3C NMK spectroscopy. The first-formed metal-carbene complex P~ can often be distinguished from the subsequent carbene complexes P~ (n> 1) formed by further addition of the monomer. A convincing evidence comes from the ~H NMR spectroscopic studies on the reaction of norbornene and its substituted derivatives in the presence of W(=CHrBu)(OCH2tBu)BrJGaBr3 carried out by Kress et al. l~ during the course of reaction the proton resonances corresponding to each propagating species has been followed and identified. In the case of 1methylnorbornene, both the head propagating species (sing,let), (1) and the tail propagating species, (II) have been observed (Eq. 15.56).
...= w.--
CH3
[WJ----C~CH-CHP H3C H (0
[WI=CHtBu L
w
(15.56)
[W}=CH-~-CH=CHP H CH3 (")
It was the more hindered head species, (I), having the tertiary alkyl substituent, that is present in higher concentration and therefore less reactive in the propagation reaction, as expected. Stable propagating carbene complexes may also be detected when certain carbene initiators of W, Mo, Re or Ru are used without a Lewis acid. Moreover, it was observed that the propagating species are "living" in character and addition of successive amounts of different monomers can be used to make block copolymers. In such copolymerization reactions the conversion of the living polymer derived from the first monomer into the propagating species of the second monomer could be readily followed by memas of ~H NMR spectroscopy.
1042
15.4.2.2.5. Evidence for Propagating Metallacyclobutane Complexes Observation of metallacyclobutane complexes in the ring-opening polymerization of cycloolefins initiated with metal carbene complexes has been performed by ~H and ~3C NMR spectroscopy. Thus, a series of transoid tungstacyclobutanes, (I), formed from norbornene or its substituted derivatives and W(=CHq3uXOCH2'Bu)Br2/GaBr3 have been detected by their ~H and ~3C ~ resonances at low temperatures ~~176 (Eq. 15.57).
-78"0-53~
(1557) R
R
R
(1) Their structures correspond to a [2+2] cycloaddition product of tungstacarbene to the e x o face of the norbornene double bond. The resonances for tungstacyclobutane complexes disappeared when the temperature was raised to 20~ and were replaced by those identified for tungstacarbene complexes. Also, the intermediate molybdenacyclobutane complexes of type (II) have been detected in the reactions of Mo(=CHCMe2R)(=NAr)(OtBu)2 (Ar = 2,6-'Pr2-C6H3, R=Me,Ph) with some 7-oxanorbomene and 7-oxanorbornadiene derivatives ~~ (Eq. 15.58).
~R
0
~ ~ C F
3
(15.58)
0:3 (II)
The molybdenacyclobutanes derived from 7-oxanorbomene-5,6-dinitrile and 7-oxanorbornadiene-2,3-bis(trifluoromethyl) have been isolated and their crystal structures determined
1043 15.4.2.3. Mechanism of Termination Reaction
Based on analogies with carbene chemistry in solution, Dolgoplosk and coworkers ~ advanced several hypotheses for the termination reaction in ring-opening polymerization of cycloolefins. Thus, one possibility for termination would be the formation of cyclopropane groups by the reaction of the propagating metallacarbene species with the C=C double bonds and subsequent isomerization to the corresponding unsaturated products (Eq. 15.59). R
-c
-cmo-
Oss
R'
Another way of termination mechanism would involve formation of a more stable carbene complex by the reaction of the propagating metallacaxbenes with impurities of unsaturated character like olefms, dienes, acetylenes or similar compounds. Thus, these authors observed that in the polymerization of cycloolefins with (CH3)~SiCHzLi~CI6 and CzH~AICI~VCI6 small amounts of trimethylvinylsilane completely inhibited the reaction. This fact was assigned to the formation of the more stable metallacarbene complex (CH3)3SiCH=WX~. A further hypothesis assumed the migration of a hydrogen atom in the carbene complex with the formation of unsaturated chain endsliZ (Eq. 15.60).
,--,CH2CH=MtX.
=
--CH=CH2
+
(15.60)
Evidence for the bimolecular termination reaction was obtained in cyclopentene polymerization with the catalytic systems WCIdEtzAICI and WCI6/'Bu3AI by Bittman e t al. ~3 The bimolecular termination step was assumed to occur by a disproportionation pathway common to organometallic compounds. This assumption was supported by the data recorded concerning the molecular weight change during the polymerization with the above catalytic systems. It seems that deactivation of the tungsten active species by disproportionation is corroborated with the reduction of the valence state of the tungsten atom observed by ESR spectroscopy and ceriometry. ~4
1044 Taking into account a second order kinetics for the termination reaction in cyclopentene polymerization induced by tungsten catalysts, Amass and coworkers ~5 proposed a bimolecular mechanism for the termination step involving an intermolecular hydrogen transfer. In addition, these authors inferred the probability that the termination reaction would involve a lower oxidation state of the transition metal compound because the catalyst species can be regenerated upon treatment with oxygen.
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1047 57. L. Resconi, F. Pietmontesi, G. Franciscono, L. Abis and T. Fiorani, J. Am. Chem. Soc., 114, 1025 (1992). 58. G. Natta, G. DaU'Asta, G. Mazzanti and G. Motroni, Makromol. Chem., 69, 163 (1963). 59. a. W. Kaminsky, A. Bark and I. Dake, in "Catalytic Olefin Polymerization", (T. Keii and K. Soga, Eds.), Elsevier, New York, 1990; b. W. Kaminsky, M. Arndt and A. Bark, Polymer Preprints (Am. Chem. Soc., Div. Polymer Chem.), 32, 467 (1991), 60. W. Kaminsky, K Bark, R. Spiehl, N. Moller-Lindenhof and S. Niedoba, in "Transition Metals and Organometallics as Catalysts for Olefin Polymerization" (W. Kaminsky and H. Sinn, Eds.), Springer-Verlag, Berlin, 1988. 61. W.M. Kelly, N.J. Taylor and S. Collins, Macromolecules, 27, 4477 (1994). 62. W.M. Kelly, S. Wang and S. Collins, Macromolecules, 30, 3151 (1997). 63. G.H. Llinas, R.O. Day, M.D. Rausch and J.C.W. Chien, Organometallics, 12, 1283 (1993). 64. T.S. Peng and J.A. Gladysz, J. Am. Chem. Soc., 114, 4174 (1992). 65. a. R.F. Jordan, cited atter reference 62; b. R.F. Jordan, Adv. Organomet. Chem., 32, 352 (1991). 66. W.L. Truett, D.R. Johnson, I.M. Robinson and B.A. Montague, J. Am. Chem. Soc., 82, 2337 (1960). 67. F.W. Michelotti and W.P. Keavney, J. Polymer Sci., A, 3, 895 (1965). 68. G. Natta, G. Dall,Asta and L. Porri, Makromol. Chem., 81,253 (1965). 69. a. G. Dall'Asta, J. Polymer Sci., A-l, 6, 2397 (1968); b. G. Dall'Asta and G. Motroni, J. Polymer Sci., A-l, 6, 2405 (1968). 70. G. Natta, G. Dall'Asta, I.W. Bassi and G. Carella, Mal~omol. Chem., 91, 87 (1966). 71. T. Oshika and H. Tabuchi, Bull. Chem. Soc. J ~ , 41, 211 (1968). 72. V.A. Kormer, I.A. Poletayeva and T.L. Yufa, J. Polymer Sci., A-l, 10, 251 (1972). 73. K.W. Scott, N. Calderon, E.A. Ofstead, W.A. Judy and J.P. Ward, ,Adv. Chem. Ser., 91, 399 (1969). 74. J.L. Herisson and Y. Chauvin, Makromol. Chem., 141, 161 (1970). 75. a. G. Dall'Asta, Makromol. Chem., 154, 1 (1972); b. G. Dall'Asta and G. Motroni, Eur. Polym. J., 7, 707 (1971); c. G. Dall'Asta and G. Motroni, Angew. Makomol. Chem., 17/15, 51 (1971 ).
1048 76. G. Dall'Asta, G. Motroni and L. Motta, ,I. Polym. Sci., 10, 1601 (1972). 77. B.A. Dolgoplosk, K.L. Makovetsky, T.G. Golenko, Yu. V. Korshak and E.I. Tinyakova, Eur. Polym. J., 10, 905 (1974). 78. B.A. Dolgoplosk, I.A. Oreshkin and S.A. Smimov, Eur. Polym. J., IS, 23 7 (1980) 79. D.T. Laveny, M.A. McKervey, J.J. Rooney and A. Stewart, J. Chem. Soc., Chem. Commun., 1976, 193. 80. A.J. Amass and T.A. McGouney, Eur. Polym. J., 16, 235 (1980). 81. a.T.J. Katz and N. Acton, Tetrahedron Lett., 1976, 425 l, b. T.J. Katz, S.J. Lee and M.A. Shippey, J. Mol. Catal., 8, 219 (1980). 82. T.J.Katz, S.J. Lee, M. Nair and E.B. Savage, J. Am. Chem. Soc., 102, 7940 (1980). 83. T.J. Katz, E.B. Savage, S.J. Lee and M. Nail J. Am. Chem. Soc., 102, 7942 (1980). 84. A. Comi.'lescu, E. Nicolescu, M. Popescu, S. Coca, M. Cuzmici, M.Dimonie and V. Dragutan, J. Mol. Catal., 46, 415 (1988). 85. M. Dimonie, A. Comilescu, M. Chipara, M. Gheorghiu, V. Dragutan, E. Nicolescu, M. Popescu, S. Coca, C. Belloiu, C. Oprescu, G. Hubca, J. Macromol. Sci., Chem. Phys. Revs. Macromol. Chem. Phys., A22, 849 (1985). 86. A. Cornilescu, E. Nicolescu, M. Popescu, S. Coca, C. Belloiu, C. Oprescu, M.Dimonie, G. Hubca, V. Dragutan, M. Chipara, J. Mol. Catal., 211, 351 (1985). 87. M. Dimonie, S. Coca and V. Dragutan, J. Mol. Catal., 76, 79 (1982). 88. E.Thorn-Csanyi and H. Timm, J. Mol. Catal., 7,8, 37 (1985) 89. A. Cornilescu, E. Nicolescu, M. Popescu, S. Coea, C. Belloiu, M. Dimonie, M. Gheorghiu, V. Dragutan, M. Chipara, J. Mol. Catal., 28, 337(1985). 90. K.J. Ivin and J.C. Mol, "Olefin Metathesis and Metathesis Polymerization", Academic Press, London, 1997. 91. J. Kress, J.A. Osborn, K.J. Ivin and J.J. Rooney, NA TO ASI Series, C 215, 363 (1987). 92. W.J. Feast, V.C. Gibson, K.J. Ivin, A.M. Kenwright and E. Khosravi, J. Mol. Catal., 90, 87 (1994). 93. K.J. Ivin, J. Kress and J.A. Osborn, ,I. Mol. Catal., 46, 3 51 (1988). 94. J.H. Oskam and R.R. Schrock, ,I. Am. Chem. Soc., 114, 7588 (1992). 95. B.A. Dolgoplosk, ,I. Polym. Sci., Polymer Symposia, 67, 99 (1980).
1049 96. N. Calderon, J.P. Lawrence and E.A. Ofstead, Adv. Organomet. Chem., 17,449(1979). 97. K.J. Ivin, D.T. Laverty, J.H. O'Donnell, J. J. Rooney and C.D. Stewart, Makromol. Chem., 180, 1989 (1979). 98. K.J. Ivin, G. Lapienis, J.J. Rooney and C.D. Stewart, J. Mol. Catal., 8, 203 (1980). 99. K.J. Ivin, Pure Appl. Chem., 52, 1907 (1980). 100. H.T.Ho, K.J. Ivin and J.J. Rooney, Makromol. Chem., 183, 1629 (1982). 101. H.T.Ho, K.J. Ivin and J.J. Rooney, J. Mol. Catal., 15, 245 (1982). 102. J.G. Hamilton, K.J. Ivin and J.J. Rooney, ,]. Mol. Catal., 28, 255 (1985). 103. K.J. Ivin, in "Olefin Metathesis and Polymerization Catalysts: Synthesis, Mechanism and Utilization" (Y. Imamoglu, B.ZumreogluKaran and A.J. Amass, Eds.), Vol. C 326, 187, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1990. 104. J. Levisalles, F. Rose-Munch, H. Rudler, J.C. Daran, Y. Dromzee and Y. Jantfin, J. Chem. Soc., Chem. Commun., 1981, 152. 105. A.M. Shapiro, Yu.V. Korshak, M.A. Tlenkopatchev and B.A. Dolgoplosk, Dokl. Akad. Nauk SSSR, /,48, 1173 (1979). 106. J. loess and J.A. Osbom, Angew. Chem. Int. F~ Engl., 31, 1585 (1992). 107. J. Kress, J.A. Osbom, R.M.E. Greene, K,J, Ivin and J.J. Rooney, J. Chem. Soc., Chem. Commun., 1985, 874. 108. a. J. Kress, J.A. Osborn, R.M.E. Greene, K.J. Ivin and J.J. Rooney, J. Am. Chem. Soc., 109, 899 (1987); b. J. Kress, J.A. Osborn and K.J. Ivin, J. Chem. Soc., Chem. Commun., 1989, 1234. 109. a. J. Kress, J.A. Osborn, V. Amir-Ebrahimi, K,J, Ivin and J.J. Rooney, J. Chem. Soc., Chem. Commun., 1988, 1164; b. J. Kress, K.J. Ivin, V. Amir-Ebrahimi and P. Weber, Makromol. Chem., 191,2237 (1990). 110. G.C. Bazan, J.H. Oskam, H.N. Cho, L.Y. Park and R.R. Schrock, J. Am. Chem. Sot:., 113, 6899 (1991). 111. E.N. Kropacheva, B.A. Dolgoplosk, D.E. Sterenzat and Yu.A. Patrushin, Dokl. Akad. Nauk SSSR, 195, 1383 (1970). 112. S.A. Smirnov, I.A. Oreshkin, I.A. Kopieva, B.A. Dolgoplosk and E.I. Tinyakova, Dokl. Akad. Nauk SSSR, 239, 392 (1978). 113. S. Bittmann, M. Dimonie, A. Cornilescu, C. Cineu, E. Nicolescu, M. Popescu, S. Coca, C. Boghina and G. Hubca, ,,l,t National Congress of
1050
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1051
Chapter 16
STEREOCHEMISTRY OF CYCLOOLEFIN POLYMERZATION Steric effects are generally weak and rare in the cationic polymerization of cycloolefins, ~ whereas they are more strong and frequent in the Ziegler-Natta z and ROMP polymerizations. 3'4 In contrast to the cationic polymerization where the alkyl and aryl substituents on the cycloolefins essentially enhance the reaction rate by their prevailing electronic effect, in the Ziegler-Natta and metathesis polymerization these substituents significantly affect the reaction kinetics, mechanism and stereochemistry by their interaction with the bulky ligands of the active centers.
16.1. Steric Effects in Cationic Polymerization Substitution of cycloolefins with the alkyl or aryl groups has not a significant influence on the steric course of the cationic polymerization but rather has an electronic effect increasing generally the reaction rate, except the reactions occurring in tight ion pairs where the steric effect is more pronounced. However, in many cases, the alkyl substituent of the cycloolefin affects the regioselectivity of the polymerization reaction with conventional catalysts. For instance, while the parent olefin, cyclopentene, is difficult to polymerize by the conventional cationic techniques or gives oligomers at best, its 3-methyl derivative polymerizes slowly to give a polymer of the unusual recurring unit ~ (Eq. 16.1).
I--~ n \~/--CH3
A]Ch
._ "-
CH3
r/"',J a L\ /JR
(16.1)
The very low yield is probably due to an isomerization of the first formed cm~nium ion through a 1,2-hydride shift, yielding a "buried" carbenium ion (Eq. 16.2).
1052 This hydride shift is competitive with every propagation step and leads finally to a 1,3 repeat unit in the polymer. A similar regioselective effect of the methyl group has been encountered in the cationic polymerization of 3methylcyclohexene with AICI3 as a catalyst S (Eq. 16.3).
n (--~-CH3
AICI3
=
~
CH3
(16.3)
Structure analysis of the solid polymer, carried out by infrared and NMR spectroscopy, indicated the presence of 1,3 repeat units in the polymer. Of a special interest is the steric effect exerted by the methyl group in 1- and 2-methylcyclopentadiene on the reaction rate and product selectivity. The copolymer obtained in the presence of some cationic catalysts has been derived mainly from the 2-isomer, giving rise, preferentially, to the sterically least hindered 1,4 recurring units 6 (Eq. 16.4).
C
C
H~
(16.4) V
The other two recurring units, 1,2 and 3,4, for which spectroscopic evidence is available, would appear to form under sterically much less favorable conditions. It is worth noting that 1,4-enc~nment is preferentially obtained (---90%) with SnCl4 or TiCI4 and much less (---76%) with BF3.OEh. This behavior was explained by assuming that, in the presence of a propagating "loose" ion pair (SnCl4 or TiCI4), the sterically less hindered and more reactive secondary allylic position will propagate preferentially by attacking the more negative 1 position of the incoming monomer. 7 Thus, when the steric compression is minimum, like in propagating "loose" ion pairs, the attack will occur preferentially on the 1 position leading to 1,4-enchainment. By contrast, with a "tight" propagating ion pair (BF3.OEtz) the steric compression will direct the approach of the monomer so as to have the methyl substituent away from the growing site, that is, the monomer approaches the active site with its 4 position, giving rise also to 1,2-enchainments beside the 1,4-enchainments (Eq. 16.5).
1053 io-h
o~
An important steric hindrance is encountered in the homopolymerization of 1,2-dihydronaphthalene with cationic catalysts. This behavior has been evidenced in comparative studies with indene and styrene, s Thus, while the homopolymerization of 1,2-dihydronaphthalene using BF3.OEt2 occurs at a lower rate than that of indene or styrene, in copolymerization reactions with styrene the relative re,activities of these two monomers are not too different and the product of the reactivity ratios is less than unity, i.e. 0.4. This may be due to the removal of the steric compression of 1,2-dihydronaphthalene during the propagation step of the copolymerization reaction.
16.2. Steric Configuration of Vinyl Polymers The opening of the double bond of cycloolefins in the 1,2-addition step of polymerization may occur in a cis fashion leading to an erythro polymer (Eq. 16.6)
(16.@
-~
/
--
alactJc
or in a trans fashion leading to a threo polymer (Eq. 16.7).
1054
di-imta:lic
P'ar~
.~
-
~
c
(16.7)
Each of these polymers may arise in a di-isotactic, di-syndiotactic or atactic configuration. The threo di-syndiotactic form is expected to show optical activity. Sequence distribution of the monomer units in the polymer chain can be evaluated by means of the ~H and ~3C NMR spectroscopy. A similar situation happens if cycloolefin polymerization occurs through a cis-l,3- and trans-l,3-insertion process leading to erythro and r polymers with 1,3-enchainments (Eq. 16.8-16.9).
(o+z)x ds
dvis01a~
~
c
(16.8)
alaelie
Each of these polymers will be formed in a di-isotactic, di-syndiotactic or atactic configuration, as a function of the catalyst stereoselectivity.
1055
di-ismclic
06.9) alal~C
16.3. Stereoselectivity in Ziegler-Natta Polymerization Initially, based on the m3C NMR spectroscopic measurements, Kaminsky et al.9 assigned 1,2-enchainment structures to polymers obtained from a series of cycloolefins, e.g., cyclobutene, cyclopentene, cycloheptene, norbornene, tetracyclododeccne with metalloc,ene catalysts such as bis(qScyclopentadienyl)zirconium dichloride [Cp2ZrCI2], 1,2-ethylenebis(q 5indenyl)zirconium dichloride [Et(Ind)2ZrCl2] and 1,2-ethylenebis0q 5tetrahydroindenyl)zirconium dichloride [Et(IndH4)2ZrCl2] associated with methylaluminoxane. The possible steric configurations and tacticity of these polymers would be those mentioned above for cis and trans insertions of the monomer. Thus, cyclopentene would form poly(cis-l,2-cyclopentane) and poly(trans- 1,2-cyclopentane), respectively (Eq. 16.10).
(16.10)
/j
-
However, more recently, Collins et al. ~o showed that hydro-oligomerization or polymerization of cyclopentene using racemic 1,2-ethylenebis(T15-
1056 indenyl)zirconium dichloride and methylaluminoxane formed poly(cis-l,3r in which the individual monomer units are incorporated in an isotactic manner (Eq. 16.11).
(16.11) This result has been verified through independent synthesis of the single, stereoisomeric tetramer produced under hydro-oligomerization conditions. In contrast to these results, hydro-oligomerization and polymerization of cyclopentene with racemic 1,2-ethylenebis(rl 5tetrahydroindenyl)zirconium dichloride and methylaluminoxane led to the production of oligomers in which cyclopentane is incorporated in a cis- and trans- 1,3-manner ~ (Eq. 16.12). (16.12)
These findings were also confirmed through independent syntheses of some of these oligomers. ~2 Polymerization of norbomene, with metallocene catalysts, seems, however, to occur by cis- and trans-l,2-insertion reaction leading to poly(cis-l,2-norbomane) and poly(trans-l,2-norbomane) structures~3 (Eq. 16.13).
(16.13')
Higher norbornene-like monomers provide probably analogous stereoseleetivities in the presence of metallocene/aluminoxane catalytic systems.
1057
16.4. Steric Configuration of Polyalkenamers Polyalkenamers prepared by ring-opening polymerization of cycloolefins, in the presence of metathesis catalysts, may have various stereoconfigurations and tacticities, depending essentially on the nature of the catalytic system and cycloolefin. These refer to the cis-trans geometry and the random or non-random distribution of the double bonds in the polymer chain, to the stereoconfiguration of the chiral or achiral monomer units and their arrangement in atactic and tactic relationship as well as to the geometry and conformation of the polymer chain or network in the macromolecular or supramolecular assemblies. The steric configuration of the double bonds in polyalkenamer may be of cis (or Z) and trans (or E) geometry. These configurations may occur exclusively in all-cis (Z) or all-trans (E) distributions, may be predominant or in a fair amount in a random, alternate or blocky distribution (7_/E) (Eq. 16.14).
L7 [~]
(al-Z)
(aN-E)
(16.14)
(CHz)x (ql"E)x
The cis and trans geometry of the polyalkenamers can be evaluated
by means of IR and NMR spectroscopy. ~ The diad configuration can be more accurately determined from the fine structure measured by m3CNMR spectroscopy. ~5 These data provide significant information about the reaction mechanism and stereochemistry. ~6 When the polyalkenamer possesses chiral centers, the monomer units may have an isotactic, syndiotactic or atactic relationship (Eq. 16.15).
1058
f
R e---HT
I
R
HT
~,
R
HT
I
R
syndiotac~ R
R
~---HT
+
R HT
/ R R
(16.15)
R
;
HT
t
TT----~
fJf
:
R
P---I-H---t--TH,,
In fully isotactic and syndiotactic polyalkenamers the diad relationship may be of the HH or TH type (H = head, T = tail) whereas in atactic polyalkenamers the diad sequence may be of the HH, TH, HT, and TT type. The tacticity of chiral polyalkenamers can be also quite accurately determined by the use of ~3C NMR spectroscopy. ~ If the substituent on the cycloolefin is situated at the unsaturated carbon, the all-cis polyalkenamer formed will have a translationally invariant structure ~8(Eq. 16.16). R
R
R
R
R
[Mt]
R (1 6.1 6)
In this polyalkenamer, the diad relationship will be of the HT or TH type, analogous to the isotactic and syndiotactic configurations. In polyalkenamers obtained from bicyclic and polycyclic olefins, adjacent tings may have an isotactic (m), syndiotactic (r) or atactic (m/r) relationship. In the case of polynorbomenamer, these configurations are illustrated in equation 16.17.
I
~
m
',
m
:
l
r
i
r
l
r,
I
I
m
I
r
I
r
;
1059 Polyalkenamers prepared from non-synunetfically substituted bicycloolefins, such as 5-alkylnorbornene, may have the monomer diad in a HH, TT or TH sequence (F.q. 16.18). M \
t
R'
R/ I~,I
\
\1~ :
"n"
l
(16.18) R'
FIT
In this case, regioselectivity relationships connected with the orientation of the double bonds in the monomer units (cis/transXtrans/cis) arise in addition to the stereoselectivity encountered at the unsubstituted monomers.
16.5. Stereoselectivity in Ring-Opening Metathesis Polymerization There exists at present a great deal of evidence that the ring-opening metathesis polymerization of cycloolefms is a highly stereoselective process and affords the synthesis of polyalkenamers with a wide range of stereoconfiguration, going from all-cis polyalkenamers to all-trans polyalkenamers, having a blocky to random distribution of the c,arboncarbon double bond diads along the polymer chain. Furthermore, if the cycloolefin is a chiral or prochiral monomer, pure enantioselective polyalkenamers can be obtained in which isotactic or syndiotactic structures are fully connected by head-tail or tail-head relationship. The nature of the catalytic system is crucial in directing the stereoselectivity of polymerization towards cis or trans polyalkenamers with a high degree of tacticity. Definite classes of highly enantioselective, cis and trans stereospecific catalysts are known today. Different transition metals and non-transition metals allow catalysts and cocatalysts with particular stereospecificity to be created and for the same binary or ternary catalyst system, the cis or trans stereocontiguration of the polymer can be varied by appropriate change in the molar ratio of the components. Also, well-defined, highly stereoselective one-component catalysts have been prepared by an adequate choice of the transition metal or ligand that promoted the stereocontrolled synthesis of pure enantiomeric polymers. In addition, operating conditions such as temperature or solvent may change substantially the steric course of the reaction.
1060 The stereoselective ring-opening metathesis polymerization has been effected with nearly all common unsubstituted cycloolefins as well as with many substituted ones. Except polyhexenamers, polyalkenamers of predominantly trans structure have been prepared from cyclobutene to cyclododecene and polyalkenamers of predominantly cis structure from cyclobutene to cyclooctene. Furthermore, polyalkenamers of high tacticity and enantiomeric purity have been obtained from some unsubstituted or substituted bicyclic and polycyclic olefins, beating one or more chiral or prochiral centers in the molecule. Of a great interest is the stereoselective polymerization of cyclobutene to high cis- or trans-polybutenamer, due to the fact that these polyalkenamers are the well known cis- and trans-l,4-polybutadiene, polymers of considerable industrial importance. Detailed studies on cyclobutene ring-opening polymerization with one-component catalyst RuCI3 and two-component catalytic system TiCh/EhAI led to 1,4polybutadiene having predominantly cis stereoconfiguration at the carboncarbon double bond. ~9 By contrast, catalytic systems based on TiCI3 and EhAI provided polybutenamer with prevailingly trans configuration at the c a r b o n - ~ o n double bond. z~ When catalytic systems derived from WCI6 and EhAI or MoOz(acach and EhAICI were employed, the polybutenamer had a random distribution of cis and trans stereoconfiguration at the double bonds. 2~ It is worth noting that cis-polybutenamer of high steric purity (93% cis) has been obtained by cyclobutene plymerization~ in the presence of the one-component carbenic system (C6HshC=W(CO)s. High stereoselectivity has also been reported in the ring-opening metathesis polymerization of l-methylcyclobutene. 23 Thus, on using the above one-component carbenic system, (Cd-ls)C=W(CO)s, a polymer having essentially a polyisoprene structure of 84 to 87% cis stereoconfiguration was prepared whereas with the two-component catalyst WCI6/n-BuLi a substituted polybutenamer of about 83% cis stereoconfiguration was obtained, having additional 2-butene and 2,3dimethyl-2-butene units in the polymer chain as result of the methyl group migration under the influence of the catalyst. The stereoselective ring-opening polymerization of cyclopentene to lfigh trans- and cis-polypentenamers is important clue to the distinct physical-mechanical properties of the two polyalkenamers as special elastomers. For this purpose, the stereospecific polymerization of cyclopentene has been widely studied with classical binary and ternary catalytic systems as well as with non-classical well-defined one-component
1061 metal-carbene catalysts. Early studies z4 using binary and ternary catalysts derived from WCI6 or TiCh and organoaluminium compounds or boron halides with or without a third component, respectively, such as alcohols, peroxides, hydroperoxides, chlorinated compounds, nitro compounds, etc. showed that high tra~-polypentenamers (90-95% trtms content) are generally formed. Subsequently, cis-polypemenamer with high cis stereoc~nfiguration (>9(Y%) was obtained using two-component catalytic systems formed from WF6, MoCls or ReCI5 and organoaluminium compounds 25 or the one-c~mponent metal-carbene catalyst mentioned above (C6H02C=W(CO)5. 22 Interestingly, cis-polypentenamers having more than 99/6 cis stereoconfiguration have been prepared using the binary catalytic systems WCId(CHz=CHCH2)4Si and MoCIs.Et3A126. Of a particular interest is the stereoselectivity of cyclopentene polymerization induced by WCI6 associated with monosubstituted acetylenes. On using the binary system WCldphenylacetylene as a catalyst in cyclopentene polymerization, Weiss and coworkers 27 obtained polypentenamer with over 80% trans stereoconfiguration which remained near constant during the course of the reaction. However, on using several monosubstituted acetylenes associated with WCI, as binary catalysts for the cyclopentene polymerization, a significant effect of the substituted acetylene on the polypentenamer stereoselectivity was observed (Table 16.1). Table 16.1
Effect of monosubstituted acetylene on polypentenamer stereoselectivity in cyclopentene r m g ~ m g polymerization'
CatalyticSystem
D'arts
Polypemenan~r %
cis-
=
Polypentenanter % .=
WCldphenylacetylene WCId I -hexyne WCld 1-ocxyne WCldl-decyne WCId3,3 Mimethyl-l-butyne WCldlithium phenylacetytide
80 80
70 70 65 65
20 20 30 30 35 35
'Data from reference z7
It is obvious from the above data that on increasing the steric bulk of the
1062 monosubstituted acetylene, the trans content of polypentenamer decreases substantially. The highest trans content of the polyalkenamer was obtained with the system WCl6/phenylacetylene while WCI6/3,3-dimethyl-l-butene and WCl6/lithium phenylaeetylide gave the highest cis content. These results suggested that the alkyne substituents are associated with the active centers of the catalyst throughout the reaction at the tungsten atom and not far away on the other end of the polymer chain. This finding was further supported by using disubstituted acetylenes in conjunction with WCI6 when the ring-opening metathesis reaction of cyclopentene was inhibited, probably, due to stable tungsten r complexes. In stereochemieal studies on the cyclopentene polymerization with binary and ternary WCl~-based catalysts,2s it was observed that the steric configuration of the polypentenamer is readily altered by changing the nature and composition of the catalytic system as well as the reaction temperature. For instance, in cyclopentene polymerization with binary catalysts derived from WCI6 and organotin, organosilicon or aluminoxanes as the cocatalyst, the cis and trans stereocordiguration of the polypentenamer varied drastically by changing the cocatalyst (Table 16.2). Table 16.2 Polymerization of cyclopmtme with binary catalysts derived from WCI6'
Catalytic System WCldPh4Sn WCl~e4Sn WCI6/EUSn WCI6/EUSn WCldBu4Sn WClflMe2allylzSi WCI6/'Bu2AIOAI'Bu2 WCIJBu2AIOArBu2
Temp. ~
-20 -20 -20 -I0 -I0 -20 0 -I0
cis-
trans-
%
Polypmtmamer %
Polyp~amer 88.3
20.0 71.1 63.3 75.8 62.0 88.8
90.9
11.7 80.0 28.9 36.7 24.2 38.0 11.2 9.1
'Data from reference 2=
An important factor in determining the reaction stereoselectivity in the ring-opening metathesis polymerization of r induced by
1063 tungsten-based catalysts is the molar ratio between the catalytic components. 2s The change of the molar ratio between the catalyst components may give readily polymers of different stereoconfigurations. For instance, in the reaction of cyclopentene with the catalytic system consisting of WCI~ and Et3AI2CI3, a range of polypentenamers having from 85% cis stereoconfiguration t o 95% trans stereoconfiguration were formed on varying the molar ratio AI" W between 1 and 7. By contrast, with the cis-specific catalysts derived from MoCI5 and EhAI, the variation of the molar ratio AI:Mo between 0.25 and 10 promoted only small changes in the steric configuration of the polypentenamer (Table 16.3). Table 16.3 Polymerization of cyclopentene with the binary catalyst M o C I s / ~ 3 A I ~
Molar Ratio Al:Mo
Polypentenamer %
Pol~ntmarr~r %
Polymer Yield %
0.25 0.5 1.0 1.5 2.0 2.5 3.5 5.0 10.0
90.1 98.0 99.4 99.1 99.4 99.3 99.4 98.9 99.0
9.9 2.0 0.6 0.9 0.6 0.7 0.6 1.1 1.0
1.0 10.7 41.4 49.2 45.3 47.2 7.4 3.0 2.3
cis-
/'gc/g/s-
'Data from reference ~
This finding is very important for obtaining polypentenamers with an established stereoconfiguration and determined physical-mechanical properties. It was also observed that in ternary catalytic systems employed in the cyclopentene polymerization, the heteroatom-containing component may influence substantially the cis and trans stereoconfiguration of the polypentenamer (Table 16.4).
1064 Table 16.4 Stereoselectivity of cyclopentene polymerization in the presence of temary WCl6-based catalytic systems *'b
Catalytic System
WCh,/'Bu3AI/EP WCId'Bu3AI/CA WCIa~3AI/EP WCId~zAICI/EP WCIc~3AIzCIdEP WCId'Bu3AI/DBQ WCh,/'Bu3AI/MANH WCI6/'Bu3AI/SALD WCId'Bu3AI/CYAC WCI6/'Bu3AUCYCL WC~e2AUyl2Si/H20 WCIdBu4Sn/CA~P
Reaction Temp. ~
0 0 0 0 0 -15 0 0 0 0 -20 -20
trans-
P o l a r %
85.5 72.0 81.6 78.4 81.9 83.0 72.0 80.4 74.2 73.0 25.6 2.5
cis-
Polypentenarner %
14.5 28.0 18.4 21.6 18.1 17.0 28.0 19.6 25.8 27.0 74.4 97.5
a
'Data from reference~; bEP=epichlorohydrm, CA=~loranil, DBQ=dibenzoqumone, MANH= maleic anhydride, SALD=salicylic aldehyde, CYAC=cyanuric acid, CYCL=cyanuric chloride, PP=piperilene Thus, substitution of chloranil for epichlorohydrin in the three-component catalytic systems based on WCk, and organoaluminium compounds used in the ring-opening polymerization of cyclopentene increased the content of cis stereoconfiguration in the polypentenamer. A similar behavior displayed maleic anhydride, cyanuric acid and cyanuric chloride. By contrast, dibenzoquinone and salicylic aldehyde favor a high trans content in the polypentenamer. It is remarkable that piperilene, added to the ternary catalyst WCldBu4Sn/chloranil, increased the cis stereoconfiguration of the polypentenamer to 97.5%. The nature of the catalytic system strongly influences the polypentenamer microstructure. In this respect, catalysts based on WCI6 and organoaluminium compounds form mainly a random distribution of the double bond diads in the polymer chain while catalysts based on WCI6 and
1065 organotin compounds produce blocky or slightly blocky distribution of the double bond diads (Table 16.5). Table 16.5
Microstructure of polypmtmamer obtained with WCl~-based catalyst'
Catalytic System
Temp. ~
o~
r~
WCId'Bu3AI/EP WCId'Bu3AI/CA WCK/'Bu3AI/CA WCldPh4Sn WCldPh4Sn WCldPh4Sn
0 0 -40 -20 10 25
0.15 0.28 0.31 0.82 0.54 0.24
0.18 0.413 0.581 8.375 1.38 0.379
r~r,
;.5 .58 .53 .06 .96 .43
0.995 1.06 1.47 8.87 1.32 1.29
Type of Distribution random random slightly blocky blocky slightly blocky slightly blocky
'Data from reference30 It is of interest that a correlation between the steric configuration of the polypentenamers and the oxidation state of the tungsten atom has been observed for the catalytic systems based on WCI6 and organometallic compounds. 3~ Thus, in a series of investigations, it was found that the catalysts with a high oxidation state of the W atom afford polypentenamers with a high cis content and those with a low oxidation state give polypentenamers with a high trans content of the double bonds (Table 16.6). In these studies, the oxidation state of the W atom has been thoroughly determined by means of ESR spectroscopy and ceriometric methods while the polypentenamer stereoconfiguration by use of ~3C NMR spectroscopy. The temperature of initiation and polymerization is also a determinant factor for the polymer microstructure, even when a highly stereospecific catalyst is employed. Thus, it was found that temperatures below -10~ favor a high cis content of the polypentenamer, particularly when binary cis-specific catalysts derived from WCI6 and Ph4Sn or MoCI5 and Et3AI are employed. With the system MoCIs/Et3AI as catalyst, polypentenamers of 97.7 to 99.4% cis content were obtained at temperatures from -10~ to -80~ while above this temperature a sharp fall in the cis stereoconfiguration was observed (Table 16.7).
1066 Table 16.6 Correlation between the oxidation state of the W atom and steric configuration of polypentenamers obtained with WCl~-based catalysts ~
Temp.
Catalytic System
WCIJBu3AI/EP WC~h4Sn WCI6~h4Sn WCI6/Ph4Sn WC~e2AIlyl2Si WC~ezAllyl2Si
WC~o2AIIyl2Si/H20 WC~ezAllylzSi~20 WCI6/'BuzAIOAI'Bu2 WCI6/'Bu2AIOAI'Bu2 WCIs/'BuzAIOAIiBu2 WC IJBu2 AIO Al' Bu 2
~C
Oxidation State of W
0 +20 -20 -30 +20 -20 +20 -20 -20 -10 0 +20
III IV V-VI V-VI IV-V V VI VI V-VI V-VI V-VI V-VI
cis-
trQrls-
Polymer %
Polymer %
72.0 45.3 11.7 15.0 58.0 38.0 67.85 25.6 11.33 9.1 11.16 16.0
28.0 54.7 88.3 85.0 42.0 62.0 32.15 74.4 88.67 90.9 88.84 84.0
'Data from reference 3~
Table 16.7 Effect of temperature on the stereoconfiguration of polypemenamer obtained with MoCI~3AI' Reaction Temp. ~C
Polymer Yield %
Polypmtmamer %
Polypentenamer %
-80.0 -55.0 -40.0 -30.0 -I0.0 +I0.0 +30.0
3.3 14.6 40.8 27.0 13.3 2.0 0.3
99.4 98.1 99.3 98.8 97.7 91.9 85.4
0.6 1.9 0.7 1.2 2.3 8.1 14.6
'Data from reference29
CiS-
trolT$-
1067 It is noteworthy that when using the catalytic system WCld(allyl)4Si, cyclopentene gave a polypentenamer having over 99~ cis stereoconfiguration at temperatures between-30~ and -80~ while at 30~ a polypentenamer with 30~ cls stereoconfiguration has been obtained.3~ Ring-opening polymerization of cycloheptene showed a certain degree of stereoselectively in the presence of binary and ternary catalytic systems consisting of WCh, or MoCI5 and organometallie compounds. 3~ By this way, polyheptenamers of high trans or cis stereoconfigurations at the c a r b o n - ~ n double bonds can be prepared just selecting an appropriate stereoselective catalyst. It was noted that the two-component catalytic systems derived from WCI6 or MoCI5 and organoaluminium compounds give polyheptenamers with high trans configuration. It is surprising that even the binary catalyst consisting of MoCI5 and EhAI, that polymerizes cyclopentene preferentially to cis-polypentenamer, forms trtmspolyheptenamer. On the other hand, cis-polyheptenamer can be obtained using the well-known cis-stereoselective carbene complex (CsHshC=W(CO)5. 22 It is noteworthy that the proportion of cis stereoconfiguration in polyheptenamer was as high as 98%. Due to its practical importance, the stereoselective ring-opening polymerization of cyelooctene is also of a great interest. In studies on ciscyclooctene polymerization in the presence of the catalytic systems derived from WCI6 and EhAI, EtAICI2 or other organoaluminium compounds it was observed that trtms-polyoctenamer is preferentially formed. 3~ However, a significant dependence of the content of trans stereoconfiguration with conversion and reaction time was reported with the binary catalyst WCI6~u3AI. 32 Moreover, it was found that addition of electron donors or acgeptors to the binary catalyst WCId'Bu3AI changes substantially both the catalytic activity and the steric configuration of the polyoctenamer. As Table 16.8 fully illustrates, when using epichlorohydrin as a third component in the catalytic system WCld13u3Al, at low conversions of the monomer, the cis stereoconfiguration prevails and gradually decreases as the conversion increases. It was also observed that the reaction temperature does not alter substantially the steric configuration of the polyoctenamer. However, on adding chloranil, high conversions of cis-cyclooctene are easily reached but the polymer has a fair amount of both structures with bias towards trans stereoconfiguration. Similar results have also been obtained with the catalyst WCId'Bu2AIOAI'Bu2 in cyclooctene polymerization. 3~ Remarkably, high-cis polyoctenamers have been obtained
1068 using the catalyst WCI6.Me2AIIyI2Si and traces of water as evidenced by means of the ~3C NMR spectroscopy, zs
Table 16.8 Steric configuration ofpolyoctenamer obtamod with ternary catalytic systems based on Wcl~'
System
WCI6/'Bu3AI/EP (l'l.S:l)
WCId'Bu3AI/EP (ll.Sl)
WCId'Bu3AI/CA (l-l.8l)
Temp. ~
Conversion %
transPolymer %
cis Polymer %
+20 +20 +20 +20 +20 +20 -20 -20 -20 -20 +20 +20 +20
8.0 15.0 19.0 26.5 27.0 30.0 7.5 8.0 9.0 10.0 25.0 55.0 80.0
37.9 41.5 46.8 48.7 49.9 58.0 34.9 39.9 44.7 54.5 42.0 53.0 54.5
62.1 58.5 53.2 54.3 50.1 42.0 65.1 60.1 55.3 45.5 58.0 47.0 45.5
'Data from reference n. b EP 9
ichlorohydrin CA=chloranil Y
"
High-cis polyoctenamers have been prepared by the ring-opening metathesis polymerization of cis-cyclooctene in the presence of the wellknown cis-directing ROMP catalysts WF6/EtAICI2 and (C6H~)zC=W(CO)5. ~ With the binary catalytic system WFdEtAICI2, cis polyoctenamer h a v i n g - 9 7 % cis stereoconfiguration has been obtained whereas the latter one-component tungstacarbene complex, (C6Hs~hC=W(CO)5, gave 97% cis stereoconfiguration. It is further noteworthy that whereas in the ring-opening polymerization of cyclooctene the cis stereoisomer is reactive, the trans monomer remains inert in the presence of the above catalytic systems. Analogously, in the ring-opening polymerization of cis-cyclodecene, in the presence of the binary or ternary catalytic systems derived from WCI6
1069 and organoaluminiumcompoundse.g., WCIr/EtAICIz, WCh,/EtOH/EtAICI2, WOCh/Cum2Oz/Et2AICI, trans-polydeccnamer is preferentially formed. 33 It is important to note that when an initial mixture of cis-/trans-cyclodeccne is used in the presence of WCk/EtzAICI, trans-polydecenamer results while the residual monomer contains less cis stereoisomer than the initial ratio of stereoisomers. This observation indicated that of the two stereoisomers, cis-cyclodecene reacts faster than trans-cyclodecene. Polydodec~namer having trans stereoconfiguration has been obtained in the ring-opening polymerization of cyclododecene under the action of WCI6 in conjunction with 'BuzAlOAl'Buz as a catalyst (Table 16.9). Table 16.9 Stercoscloctivity in cyclodod~e polymerization using the catalytic system WCIJBuzAIOAI'Bu~~ Reaction
Monomer
trans-
cis-
Temp. ~
Conversion %
Polymer %
Polymer %
+20 +20 +20 +20 -20 -20 -20
24.0 42.0 68.0 78.0 8.0 10.0 12.0
57.5 61.5 66.7 68.8 49.8 54.6 55.6
42.5 38.5 33.3 31.2 50.2 45.4 44.4
9Data from reference 28 Under these conditions, it was observed that only at low temperatures and short reaction times the tfigh-cis polydodecenamer can be produced and it was readily converted to the trans stereoisomer during the course of the reaction. Of the studies about higher cycloolefins bearing two and more carbon-carbon double bonds in the cycle, the ring-opening metathesis polymerization of cis, cis- l , 5-cyclooctadiene, cis, trans, trans- l , 5 , 9cyclododccatriene and trans, trans, trans-l,5,9-cyclododccatriene will be mentioned, due to their significance for the synthesis of highly
1070 stereospecific 1,4-polybutadiene. Thus, it was found that in the presence of the catalytic systems WCI6/EtAICI2, WCIdEtOH/EtAICI2 and WCI6/Et2AICI, these monomers lead mainly to high-trans polybutenamer. 34 Interestingly, in the presence of the ternary catalyst derived from WCIdMe2Allyl2Si, 1,5-cycloctadiene produced Ifigh-cis polybutenamer 28 (Table 16.10). Table 16.10 Stereoselectivity in 1,5-cyclooctadienepolymerization with the catalytic system WCIdMe2AllylzSi~zO' Reaction Temp.
trans-
CiS"
Polybutenamer %
Polybutenamer %
18.88
81.12 83.34
~C
+20 -20
16.66
9Data from reference 2,
In the ring-opening metathesis polymerization of substituted cycloolefins, high stereoselectivity has been reported using several tungsten-based catalytic systems. It is noteworthy that, when the substituent is located at the double bond in the monomer, translationally invariant polyalkenamers are readily formed in the presence of the carbenic system (C6Hs)2C=W(CO)5. For instance, high stereoselectivity in the ring-opening polymerization of l-methylcyclobutene was obtained, leading essentially to 1,4-polyisoprene of Z stereostructure, t8'23 Likewise, 1trimethylsilylcyclobutene produced the most perfectly translationally invariant polymer made by ring-opening metathesis polymerization till now which has essentially 100% cis stereostructure at the double bond. 3S It was found that 1-methylcyclopentene failed to polymerize with the above tungsten-carbene complex t8 or with other tungsten catalysts36 whereas 3-methylcyclopentene, like unsubstituted cyclopentene, gave with catalysts based on WCI6 polyalkenamers having over 90% trans stereoconfiguration. 36 Also remarkably, the polymerization of 1-methyltrans-cyclooctene, induced by the tungsten-carbene complex (C6Hs)2C=W(CO)s, yielded a perfectly alternating polyalkenamer with predominantly trans stereoconfiguration while 1-methyl-cis-cyclooctene failed to polymerize under the same conditions. 37
1071 A high stereospecificity was observed in the ring-opening metathesis polymerization of bicyclic and polycyclic olefins using various catalytic systems. 38 In the presence of metathesis catalysts, norbomene and substituted norbomenes afford a wide range of stereoselectivities ranging from high-trans to high-cis contents of the double bonds in the polymer chain. The polymers possess various degrees of tacticities (isotactic, syndiotactic and atactic) and contain certain head-head (HH), tail-tail (TT) or tail-head (TH) sequences of the cyclopentane unit when the monomer bears substituents. The microstructure of these polyalkenamers has been accurately examined making use of high-quality ~C and ~H NMR spectroscopy. 39 Thus, it was found that MoCls or RuCI3 form preferentially trans-polynorbomenamer, 4~ geCI5 or certain metal-carbenes like (C6HshC=W(CO)5 provide cis-polynorbornenamer, ~ while binary and ternary catalytic systems based on WCI6 or other transition metals (Ir,Rh, Os) lead to mixtures of cis- and trans-polyalkenamer. 4~ In many cases, a blocky distribution of the cis double bond diads in the polymer chain has been observed for polynorbornene. As the cis content decreased from 100% to 3 5%, a trend from fully syndiotactic to atactic ring diads has been observed. 4~ Ivin and Rooney 42 extensively investigated cis contents (or cis/trans blockiness (hl~) and tacticities of the ring-opened polymers of norbornene and substituted norbornenes prepared with numerous metathesis catalysts under a variety of reaction conditions. On studying the effect of initial concentration of the monomer on the cis content (o~) in the norbornene polymerization catalyzed by WCIdPI~Sn and WCIdMe4Sn at 20~ and by IrCl3 at 75~ they observed that in the higher range, i.e. at values of 1-4 mole/dm 3, or is independent of monomer concentration, [M], but in the lower range of 0.26-0.1 mole/dm 3, o~ decreases rapidly with dilution for the WClr-based systems. The value of o~ - 0.5 was shown to be a limit since it also remained essentially constant for WClr/Ph4Sn in the range 20-220~ Similar results 43 for the cis contents (or - 0.5) were found using a variety of other catalytic systems at a temperature of 115~ as illustrated in Table 16.1 1. Polymerization of norbornene with Ru(HzO)6(Tosh, under different conditions (solvent, pressure), showed that the reactions carried out with bulk monomer or in pure COz are more cis stereospecific than those in methanol or COz/methanol and the former polymers have a blocky distribution ofcis and trans double bonds as judged from their m3CNMR
1072 Table 16.11 Content of cis double bonds in polymers of norbomene made using various ROMP catalysts at 115~ ~ Catalytic System WCI6 WCIdPlhSn WCldMe4Sn WCIJEtAICIz MoCI~ MoCls/Me4Sn MoCls/Ph4Sn Ph (M eO)C =W(C O)5b MesW(CO)~/EtAICIz/E ~ MesMo(CO)dEtAICIz/E MesCr(CO)3/EtAICIz/E MesW(CO)3/AICI3 ReCIs/EtAICIz
o~
r,r,
0.55 0.55 0.56 0.50 0.45 0.46 0.47 0.60 0.46 0.42 0.52 0.42 0.55
1.7 2.0 2.1 1.4 1.2 1.6 1.6 1.5 -
' Data from reference 43; bThe temperature was 80~ M e s = mesitylene and E = norbomene epoxide. spectra, an effect also observed for the polymers with high cis content when using Os-based catalysts in the polymerization reactions at atmospheric pressure ~ (Table 16.12). Table 16.12 Polymerization of norbomene with Ru(HzO)6(Tos)z using various reaction media" Reaction Medium Bulk
COz, 2500 psi COz, 4000 psi COz, 5000 psi MeOH COz/MeOH, 5000 psi COz/MeOH, 5000 psi
Yieldb % 20 19 34 32 92 29 26
clsContent %
M,x 10.3
MWD
Tacticity
77 76 87 90 26 32 37
272 269 77 187 nc 58 55
2.7 2.5 1.9 2.5 nc 3.7 3.4
Syndio Syndio Syndio Syndio Atactic r Atactic~ Atactic~
'Data from reference 44; hfield of polymer after 5 hr of reason; "Polymers have a syndiotactic bias.
1073 In this case, it is remarkable that increasing the pressure at which both homogeneous and heterogeneous reactions are carried out results in enhanced cis stereospecificity. The dramatic fall in the cis content, on introduction of methanol to the reaction medium, was assigned to the propagation reaction by a species in which one or more of the H20 ligands are displaced by methanol, although it is not obvious why such a species would be less stereoselective. It is interesting that the addition of methanol has the effect of solubilizing the catalyst, and an alternative explanation may be that the change in the cis content may be due to the change in the physical state of the propagating species. The ring-opening polymerization of l-methylnorbomene, induced by ReCI5 as a catalyst, leads to all-cis, all-head-tail and syndiotactic polyalkenamer. That geCl5 is a tfigh-cis directing catalyst in norbornene and substituted norbornenes will be encountered in further examples. However, that this polyalkenamer has an all-head-tail structure can be related to the fact that the cis head-head structures can not arise in polymers from 1methylnorbornene, such structures being precluded by steric hindrance. ~5 Furthermore, the syndiotactic configuration of this polymer indicates that it is an alternating copolymer of its two enantiomers. With RuCI3.3H20 in EtOH~hCI an all-trans polymer has been obtained without any significant 46 bias toward the head-tail structure. It is very interesting for the mechanism of ring-opening metathesis polymerization of bicyclic olefins that highly tactic polyalkenamers have been prepared from 5-substituted norbornene such as endo- and exo-5methylnorbornene ~v or 5,5-dimethylnorbomene~8 in the presence of several transition metal catalysts. The content of cis double bonds as well as the blocky or random distribution of cis and trans double bond diads in the polymer changed significantly with the nature of the transition metal, the presence or absence of the electron acr,eptors or donors, other reaction parameters and particularly the reaction temperature. A direct comparison of the contents of cis double bonds obtained in the polymers of norbornene and 5,5-dimethylnorbornene using several ROMP catalysts is presented in Table 16.13. As it can be remarked from these data, in the polymerization reactions of norbornene having substituents in the position 5, the cis content may increase (e.g., with WCIdMe4Sn, WCIjPI~Sn, and RuCI3/COD) or decrease (e.g., with WCl6/BthSn, Ph(MeO)C=W(CO)~, Ph2C-W(CO)5, IrCI3 and OsCl3), or may remain unchanged (e.g., with WCI6/EtAICI2, ReCIs and guCl3). It is noteworthy that using ReCI5 as a catalyst, all-cis polymers have been
1074 Table 16.13 Contents of cis double bonds in polymers of norbomene and 5,5-dimethylnorbomene using ROMP catalysts'
Catalytic System
WCh,fEtAICI2 WCIdBu4Sn WCI6~e4Sn WCldPh4Sn Ph(CH30)C=W(COh Ph2C=W(CO)5 ReCI~ RuCI3 RuCI3.CODb IrCl3 OsCl3
Polynorbomene,
Poly(5,5-dimethylnorbomene),
0'r
0'r
0.55 0.70 0.55 0.55 0.75
0.55 0.60 0.69 0.69 0.70 0.92 1.0 0.05 0.35--0.65 0.30 0.41
1.0 1.0 0.05 0.2 0.45 0.50
9Data from reference "', ~ COD = 1,5-cyclooctadiene
obtained from both norbomene and 5,5-dimethylnorbomene, characterized by a high syndiotacticity of the structural units while RuCl3-based catalysts formed polymers, having predominantly trans double bonds with a different degree of tacticity. The polymerization of anti-7-methylnorbomene in the presence of ReCIs provides an all-cis, syndiotactic polyalkenamer. 49 By contrast, the polymerization of this monomer with MesW(CO)3/EtAICI2 leads to a hightrans, essentially isotactic polymer while RuCI3 forms an all-trans, atactic polymer, having equal proportions of m and r diads. Norbomadiene gives a wide range of stereoselectivities in the presence of various transition metal-based metathesis catalysts. ~~ The fraction of the main-chain cis double bonds, or which was determined from the ~3C NMR spectra, ranged from or = 0.9 to a minimum of just under or = 0.4, and no catalyst system tried produced polymer with a lower value of or for instance, RuCI3, which gives lfigh-trans polymer with many norbomene-type monomers was completely inactive with norbomadiene (Table 16.14).
1075 Table 16.14
Sterooseloctivities and yields in norbomadiene [M] polymerization with various melathesis catalysts'
Catalytic System
[Mo]
O'r
Yield, %
OsCl3.nHzO ReCI~ (Mes)W(CO)s/EtAICIz WCldMe~n NbCI~/Bu4Sn TaCls/Bu4Sn IrCl3.5HzO TaCls/Me~n MoCls/Bu4Sn
3.8 4.4 4.4 1.8 1.8 1.8 1.8 1.8 1.8
0.90 0.82 0.67 0.51 0.50 0.49 0.48 0.39 0.37
88 25 95 95 35 15 25 4g 82
'Data from reference so One of the most significant observation is that OsCl3 affords essentially allcis polymers of norbornadiene, in contrast to norbornene, where the cis content is <50*6. Furthermore, the copolymer of norbornene with norbornadiene is also tfigh-cis and compositionally random, a result which indicates that the metallacarbene propagating species holds one norbornadiene molecule as a di-endo chelating ligand, which remains intact as a spectator entity throughout the reaction. The steric bulk of this extra ligand then constrains the incoming monoene or diene monomer to form metallacyclobutanes in the cis mode. For some catalysts, e.g. with guCl3, this chelating effect is so dramatic that it effectively renders the catalyst almost inert. The stereoselectivity in the ring-opening polymerization of endoand exo-trimethylenenorbomene and endo- and exo-dicyclopentadiene, in the presence of various metathesis catalysts, has also been studied extensively due to its significance to the reaction mechanism. From endoand exo-trimethylenenorbomene, lflgh-cis and high-trtms polymers were made as a function of the type of catalyst and the reaction conditions 5~ (Table 16.15). It is obvious from these results that while W-based catalysts lead to a fair amount of cis and trans stereocontigurations in the polymer chain starting from both endo- and exo-trimethylenenorbornene,
1076 Table 16.15 Polymerization of endo- and exo-trimethylmenorbomme (TMN) with one- and two-componem ROMP catalysts' Catalytic System
WCldMe4Sn RuCI/3H20 ReCl~ WCldMe4Sn RuCI3/3H20 ReCl~
Monomer
Polymer Yield, %
cis-FraetJont o,
endo-TMN endo-TMN endo-TMN exo~TMN exo-TMN exo-TMN
100 16 64 42 48 70
0.46 0.11
high 0.75 0.09 0.85
'Data from reference ~
RuCI3/3H20 forms a high-trans polymer and ReCls a Ifigh-cis polymer, respectively. Analogously, high-trans and Ifigh-cis polymers have been prepared from endo- and exo-dicyclopentadiene using a wide range of one- and twocomponent ROMP catalysts 5~ (Table 16.16). Table 16.16 Polymerization of endo- and exo-dicyclopentadiene (DCPD) with one- and two-component ROMP catalysts' Catalytic System
(Mes)W(CO)JEtAICI2 WCldMe4Sn NbCIYMe4Sn RuCI3/3HzO ReCI~ IrCl3
OsCI3 WCldMe~Sn RuCI3/3H20 ReCI~
OsCI3 'Data from reference~
Monomer
endo-DCPD endo-DCPD endo-DCPD endo-DCPD endo-DCPD endo-DCPD endo-DCPD exo-DCPD exo-DCPD exo-DCPD exo-DCPD
Yield %
cis-Fraction,
96.0
0.35 0.73 0.46 1.O l.O
40.0 50.0 6.0 33.0 lO.O 12.0 8.0 64.0 30.0 13.0
Oc
0.19
0.36 O.lO 1.O 0.39
1077 As Table 16.15 illustrates, polymers formed from endo- and e x o dicyclopentadiene using W-, Nb- and Os-based catalysts contain a fair proportion of both cis and trans double bonds in the main chain. By contrast, ReCls produces an all-cis polymer from both endo and e x o monomers while RuCIfl3H20 produces polymers containing almost exclusively trans-double bonds from exo-dicyclopentadiene and an essentially all-cis polymer from endo-dicyclopentadiene. When classical binary and ternary ring-opening metathesis catalysts were employed, copolymerizations of cycloolefins were less stereoselective as compared to the homopolymerization of the respective monomers. For instance, in the copolymerization reactions cyelopentene-eycloheptene, cyclopentene-cyclooctene and cyclooctene-cyclododecene in the presence of the ternary catalyst WCIdEhAICI/Bz,O2, random distributions of the monomer units and mainly t r a n s stereoconfigurations at the double bonds were obtained 52 (Table 16.17). Table 16.1 7 Stereoselectivity in copolymerization of cycloolefms using the temary catalyst WC~zAICI/BzzO2 ~
r (molar ratio)
Copolymer cxanposition (molar ratio)
50:50 25:75 10:90 50:50 25:75 10:90 80:20 50:50 5:95
72:28 44:56 18:82 97:3 53:47 13:87 85:15 69:31 14:86
Monomer Monomers
CyclopemeneCycloheptene CyclopenteneCyclooctene CycloocteneCyclododecene
t r a m "cis
75:25 80:20 80:20 70:30 65:35 75:25 80:20 80:20
70:30
9Data from reference52 Taking into account that the above monomers yield homopolymers with over 80% trans stereoconfiguration under the same conditions, it is obvious that the stereoselectivity of the copolymerization reactions were less than that obtained in the homopolymerization reactions.
1078 It is of interest that when various transition metal salts were employed as catalysts in the copolymerization of cyclobutene and 3methylcyclobutene, a dependence of the reaction stereoselectivity on the nature of the transition metal was clearly recorded." In this context, the alkenamer units in the copolyalkenamer were predominantly of trans stereoconfiguration when the catalysts based on titanium and ruthenium compounds were employed and of cis stereoconfiguration for the catalysts derived from tungsten and molybdenum compounds. Such examples are given in Table 16.18.
Table 16.18 Microstructure of copolyalkenamers of 3-methylcyclobutene (M~)cyclobutene (Me) prepared with various ring-opening meta~esis catalysts'
Catalytic System
WCk/Fa3AI MoO2(acac)~zAICI TiC~t3AI RuCIs.xH20/EtOH
M2:Mt (molar ratio)
M2:M~ (molarratio)
30:70 35:65 26:74 35:65
50:50 40:60 25:75 45:55
trans-
cis-
Polymer Polymer % % 25 25 55 ---80
15 5 15 20
9Data from reference~3
The stereoselectivity in the copolymerization reactions of cyclopentene with norbomene promoted by a range of ring-opening metathesis catalysts has been thoroughly investigated by Ivin and coworkers. ~6'~4'55 The relevant data concerning the fraction of cis double bonds for the norbornene-norbornene diads in the copolymer are represented in Table 16.19. It can be easily observed that going from ReCIs through WCI6- and IrCI3-based catalysts to RuCIJCOD, the content of the cis stereoconfiguration decreases significantly in the norbornenenorbomene diads. At the same time, a slight trend towards lowering the cis content in the copolymer, as compared to the homopolymer, may be observed. ~6
1079
Table 16.19 Cormmts of cis double bonds in the copolymers cyclopentene(Mt)-norbomene(M2) made with ROMP catalysts' Catalytic System b
Monomer Feed (mole fraction of Mr)
Polymer Composition (mole fraction of Mr)
0.67 0.66 0.73 0.61 0.66 0.68 0.68
0.04 0.51 0.04 0.13 0.46 0.23 0.04
R~I~
WCldPktSn/EA WCld(allyt)4Sn WCldn-Bu4Sn WCldPh4Sn IrCI3/COD RuCh/COD
( MzM2 diads) 0.86 0.71 0.68 0.60 0.53 0.33 0. II
'Data from roferencet6; b EA = F~yl acrylate, COD = 1,5-cyclooctadiene
16.6. Tacticity of Polyalkenamers The study of tacticity in the ring-opening metathesis polymerization is based mainly on the polymers obtained either from norbomene or other norbomene-type monomers. ~s On ring-opening metathesis, these monomers form the cyclopentylenevinylene repeating units and the tacticity arises as result of the relative orientation in which the neighboring cyclopentylene tings are enchained. Thus, meso (m) and racemic (r) junctions may arise and the tacticity of a particular diad unit is defined as reference to the relative configuration of the neighboring allylic carbon atoms in the adjacent cyclopentylene tings (Eq. 16.19). "
].
I
RCt~
rn
t
r
t (16.19)
H
H t
H r
H f
H m
H ;
1080 The methodology which has been developed and applied by Ivin and Rooney tr'tT'48 as well as by other authors 22~ to the determination of tacticity of numerous polymers produced by ring-opening metathesis polymerization is based mainly on the ~3C NMR spectroscopy. Depending on the monomer/catalyst system, a full range of tacticity of polymers has been obtained in the ring-opening metathesis polymerization of cycloolefins: from all-cis syndiotactic to all-trans isotactic and atactic polymers. Data on the tacticity in the ring-opened polymers of the symmetrically substituted, unsymmetrically substituted and other norbomene derivatives have been examined in detail by Ivin et al. 48 When these monomers react with the propagating metallacarbene species, either C-2 or C-3 atom of the norbomene molecule may become attached to the carbene-carbon, so that in the final polymer each enchained cyclopentane ring may have one of two possible configurations, as represented in Eq. 16.19a. 7
3~6
5
34/
1/~74 1~47
12 7 t
7 m
r
r
r
m
;
The two bonds attaching the C-1 and C-4 atoms in cyclopentane to the olefinic carbons C-2 and C-3, respectively, have a cis relationship, as would be expected from the structure of the monomer and confirmed by the oxidative degradation of the polymer leading to cyclopentane-cis-l,3dicarboxylic acid. The dots on the C-I and C-4 atoms serve to remind us of a cis relationship, which also means that the atoms C-1 and C-4 are always of an opposite chirality. Thus, for two successive tings the chiralities may be (RS)(RS), corresponding to an m diad, or (RS)(SR) corresponding to an r diad. Each diad may pertain to a cis or trans double bond so that in all there are four possible diad structures, designated c/r, c/m, t/r, t/m. The following symbols have been used to characterize the tacticity and the cis content o, - fraction of double bonds having cis configuration, (ore)= = fraction of cis double bonds associated with m diads, (o=)t = fraction of trans double bonds associated with m diads, Om = overall m diad tacticity defined by equation 16.19b.
1081
o= = or162
+ Ot(Om)t
(16.19b)
where ot = I-o~, (o,)~ = 1-(o=)~ and (o,~h = 1-(o=)t. If polynorbornene is hydrogenated, the fraction of m diads will be identical with o=. This result is useful since the ~3C chemical shifts in the hydrogenated polymers of norbornene derivatives are often more sensitive to tacticity than are the chemical shifts in their unsaturated precursors. For the polyalkenamers made from a symmetrically substituted norbomene, or norbomene itself, there may be two kinds of microstructure: (a) m,r diads, ram, mr, rr triads etc., (b) cc, ct, tt diads, ccc, ctc, tct, ttt triads etc. In case that the polymer is all-cis or all-trans, or the polymer is hydrogenated, then only m/r isomerism is possible and it is therefore better to examine first the ~3C NMR spectra for these three types of polymer. A good example is the microstructure of polymers made from 7methylnorbornene with various catalysts as evidenced by t3C NMP, spectroscopic studies on these polymers. Thus, the atactic nature of hightrans poly(7-methylnorbomene) obtained using RuCI3 catalyst is recognized in an unprecedented degree of m/r diad splitting and triad tacticity, ram, mr, rm and rr, on several of the ~3C NMR signals. 49 The atactic nature of this polymer and the syndiotactic nature of the high-cis polymer formed using the ReCI5 catalyst, where only five sharp lines are observed in its Z3C NMR spectrum, are entirely consistent with the behavior of these catalysts in polymerization of other substituted norbornenes. Polymers of intermediate cis content were also examined and the resolution observed in their t3C ~ spectra allowed to determine the tacticity of both cis and trans junctions. This can be seen in the contrasting cases of polymers prepared with two tungsten-based catalysts of different oxidation state and ligation, i.e., W C I ~ u 4 S n and (mesitylene)W(CO)3, and a Ru(trifluoroacetate) system with hard ligands. Each of these catalysts produces a polymer with a similar cis/trans ratio but distinctly different tacticity. The WCl6-based catalyst forms an atactic polymer in which cis and trans double bonds are associated with both m and r diad units, whereas a tactic polymer, cis/r and trans/m, is formed from the (mesitylene)W(CO)3based catalyst. An intermediate case of a semi-tactic polymer is obtained with the Ru(trifluoroacetate) catalyst in which cis/r junctions are present and trans junctions appear as m and r in equal proportion. It may be calculated from these spectra that there is a blocky distribution of the cis and trans double bonds which is expressed in numerical terms by the product cc/ct x tt/tc = 6.
1082 Both the blockiness and the tacticity observed are in accord with the mechanism outlined in Chapter 15 which views the polymerization in terms of propagation of two kinetically distinct metallacarbene species, Pc and P, which are distinguished by the nature of the last formed double bond (Scheme 16.1 ).
C
II/ c
--/Mt~-~
.-
Pn
Pc
IIJ c
~-
--Mt-~-II/iC
C
II..--
--Mt/I
CH=CH*-Pn
Pn
Pt
P
Scheme 16.1 For the case of a totally tactic polymer, prepared using the (mesitylene)W(CO)a catalyst, it was envisaged that the species P and P~, which are self-regenerating and, as such, lead to blocks of cis and trans double bonds, are responsible for the formation of trans (m) and cis (r) junctions, respectively. The cis/trans distribution is blocky and this leads to a stereoblocky polymer (blocks of m and r diads) when the double bonds are removed by hydrogenation. Semi-tactic polymer produced with gu(trifluoroacetate) catalyst, which contains both trans (r) and trans(m) junctions, arises when the trans forming species P is symmetrical or epimerizes at a rate which is faster than propagation. The chiral identity of P~ is maintained by the coordinated cis double bond, leading to the formation of only cis (r) junctions. Epimerization at the metal center or relaxation to a different geometry of both P and P~ would lead to formation of totally atactic polymer, in which each type of junction, cis or trans, is associated with both r and tn units. It is noteworthy the effects that the substituents with different steric requirements have on the degree of m/r splitting in the ~3C NMR spectra. The bulkier anti-7-ethyl derivative in substituted norbornene, 57 and its spiro analog, ~8 both yield high trans polymers with the RuCI3 catalyst and each shows greater m/r resolution than in the case of the methyl derivative. The m/r splitting in the spectra of poly(7-ethylnorbornene), for the sterically
1083 more demanding cis diads, is up to three times greater than in the methyl case, but this is compensated by a general decrease in the m/r splitting for the trans diad units. In contrast, in the polymer made from the spiro analog, the comparative splitting is increased for both types of diad. Studies on the microstructure of the polymers made from norbomadiene are frequently hampered by their insolubility, although this difficulty could be overcome by employing chain transfer agents such as lhexene which lower the molecular weight. The ~3C NMR spectra of the polymers made by this proc~ure have shown some interesting microstructural features. For instance, a tendency to give high cis polymers has been noted and is explained to be the result of propagation by the catalyst sites sterically crowded by the monomer molecules which also act as chelating, spectator ligands. As with polynorbomene, there are no well defined tacticity splittings in the ~3C M R spectra. Polymers made from 7substituted norbomadienes, 59 e.g., 7-methylnorbornadiene and 7phenylnorbomadiene, have exhibited levels of tacticity resolution comparable to that observed in poly(7-methylnorbomene). The appearance of the ~3C NMR signal for the syrmnetrically positioned C-7 carbon atom in the case of poly(7-methylnorbomadiene) shows that it is the tt signal which exhibits a well-defined tacticity triplet whereas the cc signal is only poorly resolved; the exact opposite is for poly(7-methylnorbomene). It was observed that the hydrogenated polymers of norbomene give no fine structure for any carbon, regardless of the cis content of the precursor polymer. Hydrogenated cis/trans polymers contain both m and r diads so the absence of fine structure must be taken to indicate insensitivity of the chemical shifts to m/r diads rather than any stereoregularity. The allcis polynorbomene (obtained with ReCI5 catalyst) and high-trans polynorbornene (obtained with RuCI3 catalyst) also give no fine structure assignable to m/r splitting but it is not possible to attribute this to insensitivity (i.e. unresolved m/r splitting) or stereoregularity (i.e. m or r) only. In contrast to the results obtained in the norbornene polymerization, the hydrogenated cis/trans polymers of ant/-7-methylnorbornene showed m/r fine structure for every carbon atom except C-7, and with triad sensitivity for C-1,4, C-5,6 and C-8 atoms. The hydrogenated l~gh-cis polymer made with ReCls as catalyst gave essentially a single set of lines in the ~3C NMR spectrum, as also did the I~gh-cis polymer itself. This indicated it to be stereoregular and syndiotactic. The hydrogenated all-trans polymer prepared with RuCI3 gave a spectrum characteristic of an atactic
1084 polymer (ore = 0.5) as also did the all-trans polymer itself. This result indicated that with this catalyst the metal center of the propagating metalcarbene complex was either achiral, or chiral but epimerizing completely between each propagating step. Interestingly, unexpected results have been obtained in the polymerization of anti-7-methylnorbomene with the titanacyclobutane initiator. These results were explained in terms of a mechanism in which the electrophilic titanium-carbene complex trends to retain coordination of the previously formed double bond and in these circumstances the incoming monomer must attack from the other side, with trans attack leading to an r diad. If decoordination takes place first, then there may be an equal chance of forming m and r diads for both cis and trans double bonds. Different results were obtained for syn-7methylnorbornene which is much less reactive than its anti-isomer towards ROMP catalysts. It was inferred that the syn-7-methyl substituent not only reduced the rate of attack at the exo face of the monomer but also introduced a restriction to epimerization of the propagating metal-carbene complex. Two other symmetrically substituted norbornenes, studied by Ivin and coworkers, 6~ were exo, exo-5,6-dimethylnorbomene and its endo, endoisomer. These authors observed that the hydrogenated cis/trans polymers of the both monomers showed m/r splitting for some nuclei. High-cis polymers of the endo, endo-isomer could be made using either ReCI5 (o~ = 1.0) or WCI6/Bu4Sn (o~ = 0.94) but whereas the former gave a ~3C M R spectrum with five sharp lines as expected for a syndiotactic polymer, the latter gave a spectrum in which the C-5,6 signal was split into two, with one line corresponding to that in the spectrum of the ReCIs-initiated polymer. The polymer prepared with WCIs/BthSn was atactic and this was confirmed by the spectrum of the hydrogenated polymer which showed splitting for C-1,4 and C-7. The high-trans polymer of the endo, endo-isomer, made with RuCI3, was also atactic with splitting of the C-2,3 and C-5,6 signals. However, for the exo, exo-isomer no m/r fine structure was found for any polymer, whatever the cis content, but the hydrogenated polymers showed m/r splittings for C-1,4, C-7, C-2,3 and C-8,9 except for the ReCls-initiated polymer (or = 0.95) which gave only a single set of lines in the spectrum. The ring-opening polymerization of enantiomerically pure dicarboalkoxynorbornadienes (2,3-(COzg*)z-norbornadiene, where R* is (1R,2S, 5R)-(-)-menthyl or (R)-(-)-pantalactonyl)) with Mo(=CHCMe2PhX=NAr)(O'Bu)2 (At = 2,6-diisopropylphenyl) yielded high
1085 trans, highly tactic polymers. 6~ The ring-opening polymerization of these chiral monomers with the following Mo initiators Mo(=CHCMe2)(=NArXOC(CF3 )3)2, Mo(=CHCMe2PhX=NAr ' XB IPH(tBu)4) and Mo(=CHCMezPhX=NAr')[(+)-BINO(SiMe2Phh](THF) (At' 2,6diisomethylphenyl) yielded high cis, highly tactic polymers. Tacticities could be determined by homonuclear (proton/proton) correlation spectroscopy and decoupling experiments. The cis polymers were found to be isotactic, the trans polymers syndiotactic. Related experiments employing enantiomerically pure disubstituted norbomenes, e.g., 2,3dicarbomethoxynorborn-5-ene, 2,3-dimethoxymethylnorborn-5-ene and 5,6-dimethylnorborn-2-ene, allowed to prepare high trans atactic polymers and l~gh cis isotactic polymers. Significantly, unsymmetrically substituted norbomenes have one key feature that enables them to be used to make absolute assigmnents of tacticity, namely that each such compound exists in enantiomeric forms, for instance exo-5-methylnorbornene (Scheme 16.2).
Me (+) M
(-) M Scheme 16.2
In this case, if a single enantiomer is polymerized, an isotactic polymer must have the alI-HT structure while a syndiotactic polymer must have the tR-t, TT structure (Eq. 16.20). Me
Me
HT
R(~P r
Me
t
HT
t
(162o)
Me
t
Me
HH
~
1"1"
t
1086 Accordingly, if the chirality of the propagating m e t a l ~ e n e complex is preserved between propagation steps, an all-trans polymer of a single enantiomer will be isotactic and therefore alI-HT, while and all-cis polymer will be syndiotactic and therefore alternating HH, TT. A consideration of the substitution effects of the methyl groups in the polymers of exo-5-methylnorbomene showed that a symmetrical pattern of four lines could be expected for cis-centered diads, with the line order TH, TT, HH, HT and another four for trans-centered diads. The tacticities of five ring-opened polymers prepared from unsymmetrical methyl-substituted norbornenes, i.e., exo-5methylnorbo rnene, ~7 endo- 5-methylnorbomene, 62 5,5dimethylnorbomene, 38 1-methylnorbomene63 and endo, exo-5,6dimethylnorbornene64 have been examined in detail by Ivin and coworkers. Of these monomers, exo-5-methylnorbornene, 5,5-dimethylnorbomene and l-methylnorbornene have been prepared in optically resolved form and polymerized with different catalytic systems. On using ReCI5 as a initiator, a high cis polymer of 5,5-dimethylnorbomene was made from the raeemie monomer and an optically active monomer resulted (86% optical purity). As expected, the intensity patterns of the olefinic region in the ~3C NMR spectrum were symmetrical and the TT,HH peaks predominated for the polymer made from optically active monomer. The relatively weak TH, HT peaks were due to the presence of units derived from 7% of the minor enantiomer in the monomer and the intensities comformed with a fully syndiotactic polymer, as predicted for an all-cis polymer. The equal intensities showed that there was no enantiomeric selection in the propagation reaction. Interestingly, with (mesitylene)W(CO)-flEtAIClz/exo-2,3epoxybicyclo [2.2.1]heptanes as the catalyst, optically active 5,5dimethylnorbornene gave a polymer with a moderately high trans double bond content (o, = 0.33). Its ~3C NMR spectrum showed that the transcentered diads were mainly HT(TH) while the cis-centered diads were mainly HH,TT. The additional fine structure was attributed to cc/ct and tt/tc splittings. A different situation was found with RuCI3 as a catalyst; the polymer was high-trans but essentially atactic, as indicated by the splitting of the HH resonances of the polymer made from the racemic monomer and by the nearly equal TH,TT,HH,HT intensities in the spectrum of the polymer made from the optically active monomer. In the latter polymer the r diads were necessarily HH or TT, and the m diads HT, as can be seen in Eq. 16.21.
1087 I
m
IVle
~
H
r
H
I
IV'e
IV~
Me
(16.21) H
H
H
H
Ire I
I-IT
I
~|',
i
The monomer 1-methylnorbornene behaved somewhat differently in that its polymers made from racemic monomer frequently showed a marked HT bias, depending on the catalyst. 63 It was found that all-trans polymer could be unbiased (RuCI3, or = 0.0) or strongly biased (OsCl3, o~ = 0.0) depending on the catalyst, while tfigh-cis polymers were always strongly biased (WCIC'Me4Sn, o~ = 0.8) and all-cis polymers were completely biased (ReCIs, or = 1.0). Analysis of the ~3C NMR spectra of the whole range of these polymers showed that cis HH diads were completely absent and models showed that steric interactions of the methyl groups would make it very difficult to form such structures. All-cis polymer was therefore compelled to be alI-HT and to be an alternating copolymer of the two enantiomers, (-) and (+) 1-methylnorbomene (Eq. 16.22). Me
Me
IV~
Me
(+)or(-)
I
HT
I
I-IT
I
This result was a combined consequence of the chirality of the metal center and the inability to form cis HH diads. On the other hand, the variable bias with respect to the trans-centered diads was probably governed by a combination of steric and electronic effects. Tacticity parameters of polymers prepared from 7-oxanorbornene derivatives with various catalysts have also been evaluated by Grubbs 65 and Ivin and coworkers ss (Table 16.20).
1088 Table 16.20 Tacticity parameters for poly(4,5-dimethylmethoxy-7-oxanorbomene) and its hy~ogenated pol~cmermade with different catal~,sts ~g` Catalyst
O'r
O'm
(o.)o
W(=CH'Bu)(=NAr)(OCMe(CF3)z)z RuCI3 Ru(COD)CI3
0.93 0.07 0.18
0.45 0.72 0.50
0.45 0.74 0.50
'Data from reference6~; bO,, (Om)r and (om)t of unsaturated polymer, O' m of hydrogenated polymer; '(om)~ and (Om)~values were estimated by use of equation o . = o~(o.)0 + o,(o.O,
As it can be seen from Table 16.19, the first and third catalysts gave atactic polymers, while the second (RuCI3) gave a polymer of intermediate tacticity, corresponding to some epimerization between the propagation steps. 16.7. The Nature of Steric Interactions in ROMP
The range of stereoselectivities and tacticities encountered in the ring-opening metathesis polymerization of cycloolefins with various catalytic systems indicate that significant steric interactions occur throughout the reaction. Although several interpretations of reaction stereoselectivity and polymer tacticity have been advanced, these do not fully explain some particular features of the reaction stereochemistry. Taking into account the metallacarbene/metallacyclobutane mech~sm discussed in the previous chapter, the following factors can be considered to rationalize the sterir course of the reaction: (a) the mode of cycloolefin approach to the coordination site; (b) the nature of coordination of cycloolefin at the m e t a l l a ~ e n e species; (c) the geometric configuration of the intermediate metallac~ene; (d) the steric environment around the transition metal: (e) the rotation of the metal-carbene bond; (f) the mode of addition and insertion of the coordinated cycloolefin to m e t a l l a ~ e n e ; (g) the steric interactions arising in the transition state or metallacyclobutane intermediate; (h) the mode of decoordination of the newly formed double bond of the polymer chain; (i) the mode of rupture of the intervening cyclic
1089 intermediate and (j) the nature of the transition metal. The mode of cycloolefin approach to the coordination site, e.g., parallel or orthogonal, is significantly determined by two main factors: (i) the geometry of cycloolefin and the steric environment around the transition metal. The cis or trans geometry of the cycloolefin determines primarily the orientation of the cycloolefin approach for larger tings, for substituted cycloolefins and for bicyclic or polycyclic olefins. For these particular cases, strong interactions of the cycloolefin with ligands around the metal arise which may direct the parallel or orthogonal mode of approach (Scheme 16.3). H P
H P
H2,x
Y
A
Mt%H2) x B
Scheme 16.3 It is possible that finally the parallel mode of approach prevails this being required for a positive overlap of the molecular orbitals. Rotation of the cycloolefin around the c a r b o n ~ o n double bond during the coordination process is another requisite for the positive overlap of the molecular orbitals (Scheme 16.4).
NYR~
H .P~r
H2)x
N t N - - - ~ C H2)x
C
D Scheme 16.4
The restriction imposed by the steric interaction of the cycloolefin with the other ligands of the metal on the barrier to rotation around the carboncarbon double bond may render substituted cycloolefins such as l-methyl-
1090 cis-cyclooctene nonpolymerizable. For this particular case, the rotation
around the carbon-carbon double bond, necessary for a positive orbital overlap, seems to be restricted on the ground of steric interactions with the ligands. On the contrary, for trans cyclooctene, the distorted geometry obviates the necessity of further rotation around the double bond for an effective overlap. Presently, it is supposed that the configuration of the metallaca~ene species for some catalysts is octahedral, having one vacant position cis to the carbene ligand available for olefin coordination t6 (Scheme 16.5). H
P
H
P
H
/l(--a
P
M
E
F
G
Scheme 16.5 This type of coordination is possible in higher oxidation states of the transition metal and imposes a definite steric course of the reaction. However, other configurations of the transition metal are possible, for instance trigonal-bipyramidal and square pyramidal in which the cycloolefin may attach to the metallacarbene directly without requiring a vacancy. These configurations may appear in lower oxidation states or in more electropositiv e transition metals and particularly in homogeneous systems. The octahedral metallac,arbene species may coordinate and add the cycloolefin in one of the four conformations, depending on the relative orientation of the polymer chain and of the hydrogen attached to the carbenic c a r b o n 16 (Scheme 16.6). P H H~/,
Ic ,
.',., L"
.
H
"" -"
,-c' ' .
..__
_
P
.
" ~
I,"
1
r, .-'
Mf~]
i . __
J
Scheme 16.6
-'
I----M i"--[=] L_
_J
K
1091 The first two non-synunetrical conformations (H and I) are mirror images to each other when the four additional ligands are identical and are considered to be of a chiral type. They have approximately the same energy and reactivity, and are kinetically indistinguishable. The last two symmetrical conformations (J and K) of achiral type are kinetically distinct species. A feature of the metallac.arbene species, and perhaps of the classical metathesis also, is the presence of syn and anti alkylidene rotamers 6z6s that may, or may not, interconvert readily (AG + = 16-18 kcal/mole) 69 compared to the rate of copolymerization (Eq. 16.23). Ar
Ar
I
N II H R 0 ......M O ~ c / RO4 ' I R' anti
I
ka,, ~"
k 9
=
N II R' R 0 ....../MO ~ c / RO a H
(16.23)
syn
The syn and anti rotamers of complexes of this type play a major role in determining whether ROMP polymers prepared from norbomenes and norbomadienes contain cis or trans double bonds. 7~ The re,activities of several ~ n and anti rotamers have been evaluated (e.g. OR = OCMe(CF3h) and were found to differ considerably. The two rotamers interconvert at rates that differ by up to 6 orders of magnitude and relatively rapidly (1~, = L s"~ at 25~ when OR = OrBu but relatively slowly (1~, = 10-5s"~ at 25~ when OR = OCMe(CF3h. In most cases, I ~ was found to be >103. The rate of rotamer interconversion was found to be faster by approximately three orders of magnitude in ortho~monosubstituted phenylimido complexes such as Mo(=N-2-tBuC61-h)(=CHtBu)[OCMe(CF3h]2 than in 2,6disubstituted phenylimido complexes. ~~ The single bulky substituent in the ortho position was supposed to promote bending of the imido ligand and therefore a lowering of the barrier to rotamer interconversion by making the orbital that lies in the N-Mo-C plane more accessible. On the basis of detailed NMR studies, it was proposed that synMo(=CH~BuX=NAr)[OCMe(CF3)2]2 (Ar = 2,6-'Pr2C~3) reacts with 2,3bis(trifluoromethyl)norbomadiene (NBDF6) by coordinating to the exo face of the unsubstituted double bond to generate a syn first insertion product having a cis double bond (syn+ 1~, Eq. 16.24),
1092
F 3 C ~ CF3 ArN~ =C .... RO / I ~ ~H OR
Arl N MIIo--C
----~"
RO/'
(16.24)
[
OR
syn
syn + 1 c
while the anti rotamer reacts at least 100 times more rapidly to give a syn first insertion product having a trans double bond (syn + l t, Eq. 16.25).
F3
F3
ArN~Mo_C=..,'H RO//RO anti
~P
._ "~
Ar NI IMoI = C ~
RO~IoR
H
anti
+
P
(16.25)
1t
trans-PolyNBDF6 prepared from Mo(=CHCMezPhX=NAr)(O'Bu)2 was thought to arise from reactions involving only anti rotamers, since the anti rotamer is kinetically accessible at room temperature ( k r L s~). Alternatively, with Mo(=CHCMe2Ph)(=NAr)[OCMe(CF3)2]z as the initiator, c i s - p o l y N B D F 6 is preferably obtained. In this case, synMo(=CHCMe2Ph)(=NAr)[OCMe(CF3)z]z, the predominant species present in solution at 25~ is reactive enough to react with NBDF6. Since a syn insertion product that contains a cis double bond is formed at each step, the polymer continues to grow from syn rotamers to give all-cis polyalkenamer. The anti rotamers of the alkylidene intermediates, even though they are much more reactive, are simply inaccessible on the time sc~e of the polymerization reaction initiated by the Mo(=CHCMe~Ph)(=NAr)[OCMe(CF3h]2 complex. There are four possible modes of parallel approach of cycloolefin to the metallacarbene to form the intermediate metallacyclobutane. These have been suggestively illustrated by Ivin and coworkers 63 for the ring-opening metathesis polymerization of norbomene and its derivatives. In the polymerization of norbomene, the monomerir units may approach the metallacarbene bond preferentially by the exo side so as to bring the polymer chain either to the left- or to the right-hand side (Scheme 16.7).
1093 C M
§
/I
p.c
cis
9 M
M
/I
",.? Y A
M
""
P
,=
*
/I
M
/I
H
H
/I'Id-~ M
+
,P
H
"~"
"1 P
%
H
S c h e m e 16.7
Two distinct metallacyclobutane intermediates may arise, cis or trans, which lead to the formation of a new cis or trans double bond in the growing chain. In the case of molybdenum alkylidene complexes, it is believed that a molybdenacyclobutane is formed when the monomer approaches one of the two CNO faces of the pseudotetrahedral catalyst (Eq. 16.24 and Eq. 16.25). The two faces correspond to the two sides of the M=C bond. If the monomer approaches the same CNO face in each step, an isotactic polymer is formed while if the monomer approaches alternate CNO faces sequentially, a syndiotactic polymer is formed. If a polymerization process yields all-trans or all-cis polyalkenamer, then it is possible in some cases to determine the degree of tacticity in a relatively simple manner from its ~3C NMR spectrum 3. It has become possible to prepare highly tactic all-cis polyalkenamers with molybdenum initiators that contain a racemic binaphtholate ligand ~ and to prove that related all-cis polyalkenamers that contain chiral groups in the ester of a bis(~oalkoxy)norbomadiene are isotactic while all-trans polyakenamers that contain chiral groups in the ester of a bis(carboalkoxy)norbornadiene are syndiotactic. It also has been shown that all-cis polyalkenamers prepared from several enantiomerically pure 2,3-disubstituted norbornenes
1094 employing molybdenum binaphtholate initiators are isotactic. 72 The formation of cis and trans double bonds in the polymer was suggested to arise via intermediate cis and t r ~ met~lacyclobut~es in a planar or puckered form 16(Scheme 16.8). R
R
\ R
R
Scheme 16.8 Ivin et al. ~6 argued that under severe steric crowding, norbomene adds to the metaUacarbene in such a way leading mainly to a cis metallacycle. This metallacycle prefers the puckered conformation rather than a planar which has unfavorable 1,3-diaxial interactions. On the contrary, in conditions of less severe steric crowding, norbomene can add the metallacarbene with the formation of a trans metallacycle. The two puckered forms appear to be energetically equivalent, imposing similar steric interactions. The fact that the steric interactions arising in the transient metallacyclobutane are determinant for stereoselectivity has been outlined by Katz et al. 37 in rationalizing the product stereoselectivity in the polymerization of 1methylcyclooctene. In this case, the predominant formation of the cis stereoisomer in the polymerization of 1-methyl-trans-cyclooctene has been assigned to a lesser 1,3-diaxial interaction between the methyl groups in the intermediate metallacyclobutane structure as compared to the metallacyclobutane where the methyl groups interact more strongly with the polymer chain. Two interesting concepts have been advanced for the interpretation of cis and trans stereospecificity in the cycloolefin ring-opening polymerization. First, Calderon and coworkers ~ proposed a chelating concept to explain the high stereospecificity of cyclopentene polymerization with tungsten-based catalysts. According to this concept, a "three ligand"
1095 sequence involving simultaneous coordination of the metallaearbene, cycloolefin and polymer chain leads in the presence of cis-specific catalysts to a highly cis polyalkenarner, whereas a "two-ligand" sequence, involving simultaneous coordination of the metallaearbene and cycloolefin in the presence of trans-directing catalysts, leads to trans polyalkenamer (Scheme 16.9). P cis-Polymer
P W
.~
W
.~.~.
~rans-Polymer
Scheme 16.9 The ligand chelating concept has firmly been supported by the results obtained by Calderon and coworkers in the cyclopentene polymerization with molecular weight regulators. 25 The second concept based on the special steric interactions arising at the metal site was proposed by Ivin and Rooney. ~6 According to this proposal, the steric crowding at the metal center during coordination and addition reaction exerts a direct effect on the monomer influencing the formation of a cis and trans metallacyclobutane. Thus regardless of the tacticity behavior, two kinetically distinct propagating metallacarbene species have been postulated. In the first, the more strongly complexing cis unit (which possesses a dipole moment) may remain within the coordination sphere until the next monomer enters, and, because of steric compression, forces the next junction to be again largely cis. Within the second, when the last formed unit is trans, it is likely to be less strongly complexing (no net dipole moment) and to detach completely from the metal center before the next monomer complexes, which it does in a largely trans mode, in order to minimize steric repulsion on the developing metallacyclobutane. Provided that both species are chiral, and do not epimerize or become achiral by some relaxation processes between propagation steps, the stereoselectivity is accounted for by complexes X and Y and their mirrorimage forms (Scheme 16.10).
1096
/'--(C H2)x
.,Pn+l
....-
/I
H1C,,..p n
/I
Scheme 16. l 0 The mechanism discussed in the previous chapter then envisages the direct suprafacial [2+2] cycloaddition and cycloreversion involving the Mt=C double bond in these complexes and the C=C double bonds in monomers and polymer chain, respectively. 49 It is possible that a kinetically symmetrical agostic-type alkylidene complex TM to be a better description of the above complex in the high-c/s-directing W-based systems. 75 Such a complex, which will propagate atactic polymer formation, has also a possible counterpart in another agostic-type structure (Scheme 16.1 1).
/--(CH2)x P
H"~C" ., n+l /I
i..~,C,,,,pn
/I
Scheme 16.11 These species probably have not much significance for the noble metal catalysts where the t28 set of d orbitals is filled, such that the tendency to form a carbyne complex from a carbene complex by an agostic-type interaction is greatly diminished. Two modes of rupture of the intermediate metallacyclobutane have been postulated to rationalize the stereoselectivity in cycloolefin polymerization (a) conrotatory or parallel and (b) disrotatory or orthogona148 (Scheme 16.12).
1097
(
(CH~x
CII c (''H
(CH
Mt l .,,H
(
Y
C---C
fC
Np
II C .....H M t.~--// P"CScheme 16.12
H
According to the first mode of rupture, the ring opens in such a way that the 7t~ orbitals of the unsaturated carbons in the product separate in a parallel alignment. This mode of rupture leads to the formation of chiral conformations of the intermediate metallacarbene and seems to be characteristic of the more electronegative transition metals. In this case, racemization of the resulting chiral conformations may occur only after the propagation step. This mode of rupture leads preferentially to highly tactic polymers. In the second mode of rupture, the ring opens so that the ~" orbitals rotate into orthogonal planes as they separate one of the other. This mode of rupture leads to the formation of achiral "symmetrical" conformations of metallacarbene and seems to prevail for less electronegative metals. Racemization may also occur during the propagation step. This type of rupture rationalized the independence of tacticity on monomer dilution and the fall in tacticity with increasing temperature in the polymerization of norbornene derivatives. 4s
16.8. References
1. J. Kennedy, "Cationic Polymerization of Olefins, A Critical Inventory", John Wiley & Sons, New York, 1975. 2. a. G. Fink, R. Mtihlhaupt, H.H. Brintzinger "Ziegler Catalysts: Recent Innovations and Developments", Springer-Verlag, Berlin, 1995, b. J. Boor, Jr., "Ziegler-Natta Catalysts and Polymerizations", Academic
1098 Press, New York, 1979. K.J. Ivin and J.C. Mol, "Olefin Metathesis and Metathesis Polymerization", Academic Press, London, 1997. V. Dragutan, A.T. Balaban and M. Dimonie, "Olefin Metathesis and Ring-Opening Polymerization of Cycloolefins", John Wiley & Sons, Chichester, 1985. J. Boor, Jr., E.A. Youngman and M. Dimbat, Makromol. Chem., 90, 26 (1966). C. Aso and O. O'Hara, Makromol. Chem., 109, 161 (1967). 7 C. Aso and O. O'Hara, Makromol. Chem., 127, 78 (1969). 8 A. Mizoe, T. Tanaka, T. Higashimura, and S. Okamura, J. Polymer ScL, A 1, 4, 869 (1966). W. Kaminsky, A. Bark and I. Dake, in "Catalytic Olefin Polymerization" (T. Keii and K. Soga, Eds.), Elsevier, Amsterdam, 1990. 10 S. Collins and W.M. Kelly, Macromolecules, 25, 233 (1992). 11 W.M. Kelly, N.J. Taylor and S. Collins, Macromolecules, 27, 4477 (1994). 12. W.M. Kelly, S. Wang and S. Collins, Macromolecules, 30, 3151 (1997). 13. W. Kaminsky, Catalysis Today, 20, 257 (1994). 14. a. M.A. Golub, d. Polymer Sci., Polymer Left. Ed., 12, 295 (1971); b. M.A. Golub, S.A. Fuqua and N.S. Bhacca, d. Am. Chem. Soc., 84, 4981 (1962). 15. K.J. Ivin, D.T. Laveny and J.J. Rooney, Makromol. Chem., 178, 1545 (1977). 16. K.J. Ivin, G. Lapienis, J.J. Rooney and C.D. Stewart, J. Mol. Catal., 8, 203 (1980). 17. K.J. Ivin, G. Lapienis and J.J. Rooney, Polymer, 21,436 (1980). 18. T.J. Katz, J. McGinnis and C. Altus, J. Am. Chem. Soc., 98, 606 (1976). 19. G. Dall'Asta, G. Mazzanti, G. Natta and L. Porri, Makromol. Chem., 56, 224 (1962). 20. G. Natta, G. Dall'Asta, G. Mazzanti and G. Motroni, Makromol. Chem., 69, 163 (1963). 21. G. Natta, G. Dall'Asta and L. Porri, Makromol. Chem., 81,253 (1965). 22. T.J. Katz, J. McGinnis, S.J. Lee and N. Acton, Tetrahedron Len., 47, 4247 (1976). .
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1099 23. T.J. Katz and N. Acton, Tetrahedron Lett., 47, 4251 (1976). 24. a. G. Natta, G. Dall'Asta and G. Mazzanti, Angew. Chem., 75, 765 (1964), b. P. C~nther, F. Haas, G. Marwede, K. Ntitzel, W. Oberkirch, G. Pampus, N. SchOn and H. Witte, Angew. Makromol. Chem., 16/17, 27 (1971), c. P. Gimther, F. Haas, G. Marwede, K. Ntitzel, W. Oberkirch, G. Pampus, N. Sch6n and H. WiRe, Angew. Makromol. Chem., 14, 87 (1970). 25. E.A. Ofstead, J.P. Lawrence, M.L. Senyek and N. Calderon, J. Mol. Catal., 8, 227 (1980). 26. I.A. Oreshkin, L.I. Rednina, T.L. Kershenbaum, G.M. Chernenko, K.L. Makovetsky, E.I. Tinyakova and B.A. Dolgoplosk, Eur. Polymer J., 13, 447 (1977). 27. K. Weiss and R. Goller, J. Mol. Catal., 36, 39 (1986). 28. M. Dimonie, S. Coca, M. Teodorescu, L. Popescu, M. Chipara and V. Dragutan, J. Mol. Catal., 90, I 17 (1994). 29. G. Dall'Asta and G. Motroni, Angew. Makromol. Chem., 16/17, 51 91971). 30. M. Dimonie, S. Coca and V. Dragutan, J. Mol. Catal., 76, 79 (1992). 31. G. Natta, G. DaU'Asta and I.W. Bassi and G. Carella, Makromol. Chem., 91, 87 (1966). 32. N. Calderon and M.G. Morris, J. Polymer Sci., A2, 5, 1283 91967). 33. G. Dall' Asta and R. Manetti, Eur. Polymer J., 4, 145 (1968). 34. N. Calderon, E.A. Ofstead and W.A. Judy, J. Polymer Sci., A 1, 5, 2209 (1967). 35. T.J. Katz, S.J. Lee and M.A. Shippey, J. Mol. Catal., 8, 219 (1980). 36. G. Pampus, J. Witte and M. Hoffmarm, Rev. Gen. Caoutch. Plast., 47, 1343 (1970). 37. S.J. Lee, J. McGinnis and T.J. Katz, J. Am. Chem. Soc., 98, 7818 (1976). 38. K.J. Ivin, D.T. Laveny and J.J. Rooney, Makromol. Chem., 178, 1545 (1977). 39. K.J. Ivin, J.J. Rooney, L. Bencze, J.G. Hamilton, L.M. Lum, G.. Lapienis, B.S.R. Reddy, H.T. Ho, Pure Appl. Chem. 54, 447 (1982). 40. T. Oshika and H. Tabuchi, Bull. Chem. Soc. Jatxm , 411, 211 91968). 41. K.J. Ivin, D.T. Laverty and J.J. Rooney, Makromol. Chem., 179, 253 (1978). 42. a. K.J. Ivin, D.T. Laveny, J.H. O'Donnell, J.J. Rooney and C.D. Stewart, Makromol. Chem., 180, 1989 (1979), b. H.E. Ardill,
1100
R.M.E.Greene, J.G. Hamilton, H.T.Ho, K.J. Ivin, G. Lapienis, G.M. McCann and J.J. Rooney, Am. Chem. Soc., Syrup. Ser., 286, 257 (1985). 43. K.J. Ivin, "Olefin Metathesis", Academic Press, London, 1983. 44. J.G. Hamilton, J.J. Rooney, J.M. DeSimone and C. Mistele, Macromolecules, 31, 4387 (1998). 45. J.G. Hamilton, K.J. Ivin and J.J. Rooney, Brit. Polym. J., 16, 21 (1984). 46. J.G. Hamilton, K.J. Ivin, G.M. McCann and J.J. Rooney, Makromol. Chem., 186, 1477 (1985). 47. K.J. Ivin, D.T. Laverty, J.J. Rooney and P. Watt, Recl. Trav. Chim., 96, M54 (1977) 48. a. H.T. Ho, K.J. Ivin and J.J. Rooney, d'. Mol. Catal.,15, 245 (1982).b. H.T. Ho, K.J. Ivin and J.J. Rooney, Makromol. Chem., 183, 1629 (1982). 49. J.G. Hamilton, K.J. Ivin and J.J. Rooney, ,/. Mol. Catal., 28, 255 (1985). 50. B. Bell, J.G. Hamilton, O.N.D. Mackey and J.J. Rooney, ,I. Mol. Catal., 77, 61 (1992). 51. J.G. Hamilton, K.J. Ivin and J.J.Rooney, ,I. Mol. Catal., 36, 115 (1986). 52. G. Motroni, G. Dall'Asta and I.W. Bassi, Eur. Polym. jr., 9, 257 (1973). 53. G. Dall'Asta, G. Motroni and L. Motta, ,/. Polym. Sci., A1, 10, 160 (1972). 54. K.J. Ivin, J.H. O'Donnell, J.J. Rooney and C.D. Stewart, MakromoL (?hem., 180, 1975 (1979). 55. K.J. Ivin, "Olefin Metathesis", Academic Press, New York, 1983. 56. J. Hamilton, Polymer, 39, 1669 (1998). 57. R.M.E. Greene, K.J. Ivin, D.B. Milligan and J.J. Rooney, Brit. Polym. ,/., 19, 339 (1987). 58. N. Seehof and W. Risse, Macromolecules, 26, 5971 (1993). 59. J.G. Hamilton, J.J. Rooney and D.G. Snowden, MakromoL Chem., 194, 2907 (1993). 60. H.T. Ho, K.J. Ivin and J.J. Rooney, MakromoL Chem., 183, 1629 91982). 61. R.O'DelI, D.H. McConville, G.E. Hofmeister and R.R. Schrock, ,I. Am. Chem. Soc., 116, 3414 (1994). 62. K.J. Ivin, L.M. Lam and J.J. Rooney, MakromoL Chem., 182, 1847 (1981). 63. J.G. Hamilton, K.J. Ivin, G.M. Mr and J.J. Rooney, Makromol.
1101
Chem., 186, 1477 (1985). 64. T. Sunaga, K.J. Ivin, G.E. Hofmeister, J.H. Oskam and R.R. Schrock, Macromolecules, 27, 4043 (1994). 65. B.M. Novak and R.H. Grubbs, J. Am. Chem. Soc., 110, 960 (1988). 66. K.J. Ivin, in "Olefin Metathesis and Polymerization Catalysts" (Y. Imamogly, B. Zumreoglu-Karan and A.J. Amass, Eds.), Kluwer Academic Publishers, Dordrecht, 1990, K.J. Ivin, Pure Appl. Chem., 52, 1907 (1980). 67. R.R. Schrock, J.K. Lee, R. O'Dell and J. H. Oskam, Macromolecules, 28, 5933 (1995). 68. J.H. Oskam and R.R. Schrock, J. Am. Chem. Soc., 114, 7588 (1992). 69. a. R.R. Schrock, W.E. Crowe, G.C. Bazan, M. DiMare, M.B. O'Regan and M.H. Schofield, Organometallics, 10, 1832 (1991), b. R.R. Schrock, J.S. Murdzek, G.C. Bazan, J. Robbins, M. DiMare and M. O'Regan, J. Am. Chem. Soc., 112, 3875 (1990). 70. J.H. Oskam and R.R. SchrocL J. Am. Chem. Soc., 115, 11831 (1993). 71. D.H. McConville, J.R. Wolf and R.R. Schrock, J. Am. Chem. Soc., 115, 4413 (1993). 72. R.O'DelI, D.H. McConville, G.E. Hofmaister and R.R. Schrock, J. Am. Chem. Soc., 116, 3414 (1994). 73. N. Calderon, J.P. Lawrence and E.A. Ofstead, Adv. Organomet. Chem., 17, 449 (1979). 74. M. Brookhart and M.L.H. Green, J. Organomet. Chem., 250, 395 (1983). 75. S.J. Holmes, D.N. Clark, H.W. Turner and R.R. Schrock, J. Am. Chem. Soc., 104, 6322 (1982).
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1103
Chapter 17
RELATED PROCESSES
There are numerous processes related to the catalytic polymerization of cycloolefins, many of them being of academic or commercial importance. Some of these are essentially connected with the mechanism and stereochemistry of the catalytic polymerization of cycloolefins or are related with the nature of the monomers and catalysts and have common features with the processes described in this book.
17.1 Catalytic Polymerization of Olefins and Dienes The field of catalytic polymerization of olefins and dienes has been rapidly expanded during the last three decades covering a large amount of readily available monomers and catalytic systems. The process has stimulated an intensive academic and industrial research and led to a considerable number of commercial products suitable for applications in various domains. The rich information accumulated in this area has greatly helped the scientific community to better understand the mechanisms underlying these catalytic processes and design and apply new related processes. The literature is covered by several excellent books and monographs on this subject, mS The essential aspects of the catalytic polymerization of olefins and dienes will be summarized according to the nature of the catalysts employed in this process, i.e., cationic, anionic and Ziegler-Natta systems.
17.1.1. Cationic Polymerization of Olefins and Dienes The cationic polymerizations of olefins and dienes are polyaddition reactions of these monomers under the influence of the cationic initiators. The reaction has been applied to a large number of olefins and dienes comprising straight-chain aliphatic olefins, branched cz-olefins, aromatic olefins, alicyclic olefins, straight and branched dienes. The catalysts for such a process include homogeneous and heterogeneous BrOnsted acids and Lewis acids or complex compounds with strong electrophilic properties 2
1104
(Eq. 17.1).
R~ CH2=CHR'
AIX3
9 ~
c82=c~'
R-CH2--CHR' ~
~
~
--CH2-CHR'--
(17.1)
The most common example is the well-known cationic polymerization of isobutene to high molecular weight polyisobutene in the presence of Lewis acids and traces of water (Eq. 17.2).
CH2= " o h
~
c~
--,,,. __,,.._,,.
--cl..h-tc-,. o-h
(172)
Considerable research work has been conducted on this and other linear olefins resulting in valuable data on the kinetics and mechanism of the process. The reaction has been explored with a large number of conventional cationic initiators such as AICI3, AIBr3, BF3, TiCh, TiCIdCCI3COOH, SnCIdCCI3COOH. The carbocationic mechanism of initiation, propagation and termination reactions is well-documented. Of the linear dienes, isoprene has been used as monomer in various reaction conditions with conventional Lewis acids (e.g., AICI3, AIBr3, BF3, SnCh) to produce low or high molecular weight polyisoprene, having 1,4-, 1,2- and 3,4-enchainment (Eq. 17.3).
+
(17.3)
17.1.2. Anionic Polymerization of Olefin and Dienes
Anionic polymerization of olefins, e.g., styrene and particularly of conjugated dienes, e.g., butadiene and isoprene, has been intensively studied for their application in industrial scale preparations of valuable polymers 3 (Eq. 17:4).
1105
n
nSut.i
nB
ki (17.4)
By anionic initiation, cis or trans 1,4-polybutadiene and 1,4polyisoprene or 1,2-polybutadiene and 1,2-polyisoprene can be prepared, as a function of the reaction conditions (Eq. 17.5).
n ~
nBuLi
~
R~ILIC~~~
Li
(17.5)
Depending on the catalyst and reaction parameters, the reaction pathway may involve a carbanion with a o-allyl or 7t-allyl bond 4 (Scheme 17.1).
u 1,4ds-or1 , ~
= 12~'ct~m
P Scheme 17.1
17.1.3. Ziegler-Natta Polymerization of Olefins and Dienes (z-Olefins are readily polymerized in the presence of a wide range of Ziegler-Natta catalysts consisting of transition metal salts and organometallic compounds 5'6 (Eq. 17.6)
n ~R
~
TiCI4/Et3AI
~
R
(17.6)
Polymers such as polypropylene (R = Me) or polystyrene (R = Ph) have a chiral center at each methine carbon (Eq. 17.6a).
1106
CI'r
[ZN cat] =
R
R
H
I I I --CH2--C-C H2--C-C H2--C-C H2--I I I H
H
t
R
,t
rn
(17.6a)
r
Adjacent chiral centers may have the same configuration, in which ease one refers to the pair of repeat units as a meso (m) diad, or they have opposite configuration in which case one has a racemic (r) diad. If this symbolism is extended to any number of successive chiral centers, one observes three tactic triads (ram, mr, rr) and six tetrads (mmm, mmr, rmr, mrm, rrm, rrr). The two types of completely stereoregular polymers, isotactic and syndiotactic, correspond to the one in which every chiral center has the same configuration (mmmm...) and to the one in which the chiral centers have alternating configuration (rrrrr...). Polymers which do not conform to one of these two extremes are termed atactic. With the design of new Ziegler-Natta catalysts, it has been possible to make stereoregular vinyl polymers (isotactic and syndiotactic) in high yield by polymerization of (xolefins 7 (Eq. 17.7)
R
~ R
R
R
R
R (17.7)
R R
R
and cis-l,4-, trans-l,4- or 1,2-polymers by polymerization of conjugated dienes (Eq. 17.8).
n ~
VCI3/R3AI
..-"-
CoC /Et --120 i,-..-
~
(17.8)
1107 Several monometallic and bimetallic mechanisms have been proposed for the Ziegler-Natta polymerization of ot-olefins with various catalysts, some of which accommodate satisfactorily the reaction kinetics and stereochemistry. 8~ The monometaUic mechanisms rationalize the insertion reaction via migration of the growing chain end to the complexed monomer 8~~ whereas the bimetallic mechanisms ~ imply the growing chain end bound to two metal atoms with insertion of the complexed monomer into one of the metal-to-carbon bond followed by 1-3 migration of the other metal atom and of a hydrogen atom. Generally, a two-step mechanism is admitted for the stereospecific polymerization of cz-olefins in the presence of transition metal salts/organometallic catalysts (Scheme 17.2). H H I I [MI~--CH2- IC-CH2-(~-- Pn.,
CH3
7 Pn C
[l~--Pn
J
CH2
c~
H
c~
CH2 _1
,
H (~H3 I [MI:I-- (~-CH2--(~--CH2- Pn.,
,C,H2
C~ c~
c~
~CI"~-C-CH2-(~--P.. H H
H
H I
~C-CI'~--(~--CH2-P.. H Cl"l3
,
Scheme 17.2 According to this mechanism, the position of diastereomeric and rotameric equilibrium in the ~-complexes and the activation energy for the insertion reaction of the ~-complexed olefin could cause the large regioselectivity and enantioface discrimination necessary for the synthesis of stereoregular polyolefins. Of keen interest for its connection with the metathesis polymerization process is the monometallic metallacarbene/metallacyclobutane mechanism proposed by Ivin et al. ~2 involving the growing chain end bound by as a carbene ligand to the metal atom and the insertion reaction occurring through a metallacyclobutane intermediate (Scheme 17.3).
1108 R
H I
I
[M t ] - - C H --C H 2 " * "
H
=,,...-
R I
[M t]=C
R fC H 2 . . . , ~"
[MI
--C H 2 ~
R
I
v
C H 2 = C HR
R
I
[M t]--C H--C H 2 - C H - - C H 2 .....
4\ N R
Scheme 17.3 This mechanism could not explain, however, the synthesis of isotactic polymers which was found to occur by a "1-2" insertion reaction and not according to a "2-1" insertion. ~3 The occurrence of a back-biting process in the stereospecific polymerization of dienes leading to cis and trans polymers with transition metal catalysts has been postulated by Furukawa (Scheme 17.4). ~4
nj
f
"L
Scheme 17.4
17.2 Atom Transfer Radical Polymerization of Vinyl Compounds Atom transfer radical polymerization (ATRP) of vinyl monomers using catalytic systems based on ruthenium and copper complexes has been reported recently ~5(Eq. 17.9).
1109
n
ATRP = [R u],[C u] .r
~R
. ~
(17.9)
where R is phenyl, vinyl, carboxylate and other substituents. The copperbased complexes contain nitrogen ligands, e.g., bipyridine, multidentate amines and Schiff bases whereas the ruthenium complex, RuCI2(PPh3)2, requires the addition of a Lewis acid such as Al(O'Pr)3 or MeAl(2,6-di-tertbutylphenoxideh to become active. New efficient ruthenium catalysts, e.g. RuCl~-cymene)(PR3), have also been used in this reaction. ~6 It is quite remarkable that the best catalysts system for ATRP were also the most active ones for the ring-opening polymerization of cycloolefins. On this line, the Grubbs' mthenium-carbene complex, RuCI2(=CHPh)(PCy3)2, commonly used for olefin metathesis, was found to be also highly efficient for ATRP. ATRP of various vinyl monomers such as styrene, dienes, (meth)acrylates in the presence of redox active transition metal compounds provides polymers with high molecular weights (M,>100000) and low polydispersities (M,JM, < 1.05). A wide variety of polymers with new topologies, compositions and functionalities have been prepared by this method. ~7 17.3. Metathesb Reactions of Olefins and Acetylenes
Olefin metathesis is the reaction that interchange the alkylidene fragments existing at the carbon-carbon double bond in the starting olefin with formation of higher and lower members of this series of compounds~S'm9(Eq. 17.10).
+ _
R1/
~.
--~
+
(17.10)
_
\R2
R1
R2
The process takes place in the presence of a wide range of heterogeneous and homogeneous catalysts derived from group IV-VII transition metal salts, preferably in association with organometallic compounds. In addition, efficient catalysts for this type of reaction proved to be specific metallacarbenes derived from W, Mo and Ru and certain compounds of
1110 platinum group metals such as of Rh, Ir, Os and Ru. The reaction may occur between two different olefins, giving rise to other two new olefins, when it is termed cross-metathesis (Eq. 17.11).
Rx',- -/R2
[cat]
R2
+(
+
R3/=="I~
R3
(17.11)
R4
Applied in the class of cycloolefins, the metathesis reaction provides an unique route for the synthesis of polyalkenamers by the ring-opening polymerization. :8 It is firmly established that the reaction occurs through a metallacarbene-metallacyclobutane mechanism involving a [2+2] cycloaddition of the m e t a l l a ~ n e to the olefin to form the intermediate metallacyclobutane :9 (Eq. 17.12).
(17.12)
The intermediate species can either revert to starting material or open in a productive manner via a retrocycloaddition reaction to generate the metallacarbene and produce a new olefin. Metathesis of acetylenes occurs by interchanging the alkylidyne fragments of the c a r b o n - ~ o n triple bond with formation of new, higher and lower acetylenes:8 (Eq. 17.13).
RI~R2 R1
+
[cat] --R2
-
R1
-
R2
,I, +,1,
R1
(17.13)
R2
This reaction is catalyzed by various heterogeneous and homogeneous catalysts derived mainly from W or Mo compounds, a special class of appropriate catalysts for this reaction consists of m e t a l l a ~ y n e s prepared from the W or Mo derivatives. It is supposed that the reaction involves a
1111 metallacarbyne mechanism through a [2+2] cycloaddition to a metallacyclic intermediateS8 (Eq. 17.14).
I~l Rf•R2 Rr~--M
R,,
R,,
The intermediacy of metallacarbyne species in this type of reaction has been evidenced by synthesis of several carbyne complexes which are active in the acetylene metathesis.
17.3.1. Ring-Opening Metathesis (ROM) The cleavage of cycloolefins by ring-opening metathesis (ROM) with acyclic olefins in the presence of appropriate metathesis catalysts constitutes an elegant method to manufacture linear dienes from cycloolefins~8 (Eq. 17.15).
R2 This reaction termed also alkenolysis has been applied successfully to prepare 1,6-heptadiene from cyclopentene and ethylene (Eq. 17.16)
and of 1,9-decadiene from cyclooctene and ethylene by ethenolysis using W-based catalysts (Eq. 17.17).
+
II
-
-
(,71
1112 The process has to be conducted under controlled conditions, i.e., catalyst, monomer or product concentration and temperature, because two competitive processes, ring-opening metathesis polymerization (ROMP) of the monomer and acyclic diene metathesis polymerization (ADMET) of the product can also occur ~ (Eq. 17.18).
R I ~ R ~ R
2
It is noteworthy, the intervention of the ruthenium carbene initiator in the cleavage of the double bond in the ROM of compound (I) has been evidenced recently by isolation and characterization of the intermediate ruthenium olefin complex (II) 2t (Eq. 17.1 9). cy3
oi III O
(l)
CDCI3
e
Ph
e
(n) 17.3.2. Ring-Closing Metathesis (RCM)
The ring-closing metathesis reaction has recently become a versatile route for the synthesis of cyclic compounds in the organic and polymer chemistry. 22 The reaction can be applied in two variations, one to linear unconjugated dienes forming carbocyclic compounds ~ and the other to heteroatom-containing dienes leading to heterocyclic compounds. 24 Whereas the former process is promoted by some classical and well defined carbene initiators, the latter can be induced only by functional group tolerant catalysts. Besides the general class of molybdenum initiators of the Schrock-type, the ruthenium carbene initiators disclosed by Grubbs are convenient catalysts particularly for the ring-closing metathesis of functional group containing dienes. By this procedure, oxygen-, nitrogen-
1113 or even phosphorous-containing heterocycles can be easily prepared from the corresponding heteroatom-containing dienes using tungsten, molybdenum or ruthenium carbene initiators as catalysts 24 (Eq. 17.20).
(17.20)
-C2H4, X = O,N,C~
Two competing pathways are available to the intermediate metallacarbene: (a) the intramolecular ring-closing metathesis (RCM) leading to the cyclic product and (b) the intermolecular acyclic diene metathesis (ADMET) forming the polymeric product (Eq. 17.21).
l (c)
(17.21)
The process is further complicated by the possibility of the ring-opening metathesis polymerization (ROMP) of the unsaturated cyclic compound in the presence of the metathesis catalyst, path (c). ns
17.3.2. 1. Synthesis of Carbocycles
Ring-closing metathesis reactions of acyclic cz,0~-dienes, induced by metathesis catalysts, give rise to cycloolefins with ethylene evolution ~ (Eq. 17.2e).
1114 The reaction occurs readily when the cycloolefins have a pronounced thermodynamic stability to shift the equilibrium toward the cyclic product. One interesting example is the ring-closing metathesis of 1,7-octadiene when cyclohexene is easily formed ~s (Eq. 17.23).
--"
O
+
II
This process is frequently encountered in the ring-opening metathesis polymerization of r where large unsaturated linear oligomers give carbocycles by a back-biting mechanism (Eq. 17.24). R
R
(17.24)
[MI] )x-
- -
--(CH2)x-
- -
Such carbocycles having up to 120 carbon atoms are known to arise in the metathesis of cyclooctene under mild conditions in the presence of WCI6/EtOH/EtAICI2 as a catalytst. 25 The ruthenium carbene initiator RuCI2(=CHCH=CPh2)(PR3)2 (R = Cy) was found to be extremely efficient in the synthesis of cycloalkenes bearing functional groups such as carboxylic acids, alcohols and aldehydes which readily destroy the classical or well-defined tungsten or molybdenum initiators 23(Eq. 17.25).
~~~,.R
Ru(=CHCH=CPh2)CI 11=87%' 2(PCYL~R=CO2H "CH2OH
CHO
R
(17.25)
88%
82%
The yields are substantial and such compounds can be easily handled and separated from the reaction mixture. A new procedure for the diastereoselective synthesis of bicyclic derivatives such as substituted dec~ins, makes use of readily available acyclic tetraenes which can be closed using the transition metal catalyzed olefin metathesis approach 26 (Eq. 17.26).
1115 H OR
H
OR
OR
The resulting decalins are symmetrical and afford the opportunity to perform enantioselective desymmetrization reactions to yield non-racemic compounds. Enantioselective sigmatropic rearrangements can lead to bicyclic structures reminiscent of the dec~in moiety of a number of HMG CoA reductase inhibitors used to lower cholesterol levels. The remarkable activity of the W-carbene catalysts in metathesis reactions set the stage for their application in tandem reactions employing alkynes as olefin metathesis relays. Interesting examples of these reactions is the synthesis of bicyclic and tricyclic compounds from enynes by ringclosing metathesis involve the two types of unsaturated carbon-ca~on bonds27(Eq. 17.27).
[~
~
(CO)5W=PCh(MeO) Mo
3o-5o%
,
e
(17.27)
17. 3. 2. 2. Synthesis of Unsaturated Heterocycles
A great number of unsaturated heterocycles containing endocyclic oxygen, nitrogen, phosphorous and other heteroatoms have been now available by using the widely tolerant ruthenium carbene initiators in the ring-closing metathesis reactions. A first group of unsaturated heterocyclic compounds consists of five-, six- and seven-membered oxygen-containing tings prepared by using ruthenium vinylidene complexes as catalysts 2~ (Eq. 17.28).
m%
C
(17.28)
1116 This procedure has been also applied for the synthesis of unsaturated heterocycles containing two oxygen atoms such as seven-membered cyclic acetals 24 (Eq. 17.29).
.~~..~O~Ph
-C~, ,1=B7% =
Ph
(1729)
Interestingly, the unsaturated C~8 and C2o macrolides have been obtained by ring-closing metathesis of the corresponding unsaturated lactones with the tolerant classical WCl6-based catalyst 28 WCIdCp2TiMe2 (Eq. 17.30). O
(CH~o,,(CH97
/L o "-
L,,/(CH2)7
% -
\R
(17.~)
Nitrogen-containing heterocycles have been readily available in high yield by ring closing metathesis of amino dienes. Significantly, ruthenium vinylalkylidene complexes tolerates common protecting groups, e.g., trifluoracetyl, tert-butoxycarbonyl and benzy126(Eq. 17.31).
~...,,N,I,o
Ru(=CFC_2-1=CPh2)CI2(PCy3)2CN,Io" - C2H4, TI = 91%
.~~
=
~
(17.31)
It is interesting to note that cyclization of dienes bearing benzyl groups can not be effected using molybdenum-based initiators z9 (F_xl. 17.32).
Ph~
0
Ru(=CHC 2 CH=CPh2)Ci 2H41,1- = 93% 2(PCy3) "-'-
0
PhAI~~)
(17.32)
Ring closing metathesis of vinyl- and allylphosphonamides using the ruthenium carbene initiators is an interesting way for the synthesis of five-
1117 or six-membered P-heterocycles, as a function of the starting vinyl- or allylphosphon~nide (n = 0 or 1)~(Eq. 17.33). n=O
Iol (17.33)
R3 By the same technique, on applying the reaction to the diallyl vinylphosphonates, unsaturated heterocycles with both oxygen and phosphorous atoms in the cycle can be obtained z9 (Eq. 17.34).
0 I
I~=CHPh)CI2(PCYa)2 O1~,~O = Pt'I,,.j',,~O,, rl=30%
(17.34)
17. 3. 2. 3. Synthesis of Crown Ethers A large number of compounds, potentially important for the organic synthesis like crown ethers, became available in high yields through the ring closing metathesis of unsaturated polyethers, due to the tolerance of benzylidene ruthenium carbene complexes toward oxygen functionalities. One interesting example is the synthesis of unsaturated 17-membered crown ether in 90% yield,3~ from the corresponding polyether diene under the influence of the benzylidene ruthenium complex (Eq. 17.35).
O
(o
~ Ru{=CHPh)Ch(PCY3)20 ~
(o
(17.35)
1118 In the same way, synthesis of 17-, 20- and 26-membered ring dibenzo crown ethers has been carried out in good yield with the above benzylidene ruthenium complex, even at moderate substrate concentrations (0.35 M), at room temperature 3~(Eq. 17.36).
0
n=1.80%
"~
0
n =4,72%
17. 3. 2. 4. Synthesis of Polycyclic Polymers By the use of the ruthenium-carbene complex, Ru(=CHz)CI2(PCy3)2 (Cy = cyclohexyl), the highly selective and quantitative cyclization of neighboring vinyl groups in the 1,2-polydienes has become possible 31 (Eq. 17.37).
(w.3z)
Thus, 1,2-polybutadiene underwent more than 97% cyclization of the vinyl side-groups, in the presence of the same ruthenium complex, leading selectively to poly(cyr Hydrogenation of this product yielded a saturated polymer with NMR spectra identical to those of atactic poly(cyclopentylenemethylene).
17.4. Acyclic Diene Metathesis (ADMET) and Acyclic Diyne Metathesis (ADIMET) Polymerization Acyclic diene metathesis (ADMET) polymerization has proven to be a viable synthetic route to high molecular weight polymers. By this method, a wide variety of unsaturated polymers and copolymers can be prepared from the linear ct,0r-dienes by a step propagation condensation reaction in the presence of metathesis catalysts3z34 (Eq. 17.38).
1119
,~',,,,~R~7~.
~
,.~',v,,~R,~
+ n CH2-Cl.-I2 (17.38)
The catalysts employed efficiently for ADMET polymerization are Lewis acid free Schrock catalysts 35z6 of the type Mt(=CHR')(=NArXOR}2 where Mt = W or Mo, Ar = 2,6-Prz-C6H3, ' R' = CMe2Pr and R = CMe(CF3)2. The ability of these transition metal catalysts to initiate diene condensation under mild conditions makes ADMET polymerization a particularly versatile process for the synthesis of perfectly linear unsaturated polymers. For example, poly(1-butenylene) or 1,4-polybutadiene has been prepared easily by the metathetic condensation polymerization of 1,5-hexadiene to perfectly linear polybutadiene 37 (Eq. 17.39).
[cat] ~
~
.
nCH2.=CH 2
(17.39)
Similarly, poly(1-octenylene) or polyoctenamer has been conveniently obtained by ADMET polymerization of 1,9-decadiene in the presence of Mo carbene initiators 3s'39 (Eq. 17.40).
[eat]
+ nCH2--CH2
(17.40)
The product has been further hydrogenated to polyethylene having a molecular weight distribution in the range M,dM, = 2.0-2.6. The final polymer displayed a high degree of crystallinity which varied with the molecular weight. Up to now, by the use of well-defined metathesis catalysts, aliphatic and conjugated aliphatic dienes as well as a multitude of functionalized dienes including ether, ketone, ester, carbonate, thioether and aromatic amine functionalities have been shown to polymerize and eopolymerize by this process ~42 (Eq. 17.41).
S.,,vX,,/~
~[call
~,,,,,, X [ , , / % / ~ ) ~ ~ ~
. n C,l_t2_CH2
(17.41)
where X is O, CO, COO, S, N, Si, B, etc. More recently, 43the reaction has been successfully extended to un~njugated dienes containing various
metals in their structure such as Sn, Cu, Ag, Fe, etc.
1120
Of interest, the ADMET reaction of divinylsilanes and divinylsiloxanes was realized in the presence of homogeneous Ru- and Rhcontaining systems in combination with cocatalysts of the HSi- type. The use of ruthenium hydride complexes, in particular RuHCI(CO)(PPh3)3, as catalysts in the ADMET reaction of vinylsilanes, turned out to be quite useful 44(Eq. 17.42). Ph
Ph
Ph
Ph I
+
n CH2=CH2
(17.42)
Ph
The analogous reaction, acyclic diyne metathesis polymerization (ADIMET), carried out in the presence of metallacarbyne complexes, provides a unique way for the synthesis oflinear polyalkynes 4~(Eq. 17.43). H~C --
n--
O-h
=
-t- .'~' _1. -~ 0 t 3 + n-1 H ~ c - - O"h H~C _r_
(17.43)
The position of the triple bonds can be varied inside the linear chain without affecting the reaction pathway (Eq. 17.44) (E3U~WCtI~
R---~C~
.9~ I H ~ - - - - C ~
(17.44)
The process has been applied successfully to conjugated diynes, e.g. diynes containing aromatic moieties in their structure, leading to fully conjugated polymers (Eq. 17.45).
O'h " n-11"hc'-'=-o'h
(17.45)
17.5. Carbonyl Olefination Reactions
Several approaches to the formation of unsaturated carbocycles involving the cyclization of some specific reactive functionalities such as carbonyl groups are known.
1121 17.5.1. Synthesis of Olefins and Cycloolefins
Carbonyl olefination is a route for the synthesis of olefins from carbonyl compounds via transition metal alkylidene intermediates46 (Eq. 17.46).
R1/~0
+ [~11] O
RI
(17.46)
By this way, synthesis of cycloalkenes from olefinic ketones in the presence of molybdenum or tungsten carbene catalysts is possible4~ (Eq. 17.47).
(CH2~~_O
[Mt]=CHR
--
-[Mt]=O
"-
(C
(17.47)
This reaction has similarities to the ring-closing metathesis reaction (RCM) known for unconjugated dienes. It can be accompanied by ring-opening metathesis polymerization (ROMP) of the cycloalkene in the presence of the catalyst leading to polyalkenamer ~8(Eq. 17.48).
/'~_
[Mt]=CI-R
(17.48)
The carbonyl olefination can also occur by an intermolecular carbonyl-olefin exchange mechanism, leading directly to linear polyalkenamer (Eq. 17.49).
o
~]=CHR - [Mq=O
(17.49)
1122
17.5.2. CarbonyI-Olefin Exchange Polymerization Polymerization of conjugated unsaturated ketones under the influence of WCI6 as a catalyst, termed carbonyl-olefin exchange reaction, leads to substituted polyacetylenes. ~s Thus, reaction of benzylideneacetophenone in the presence of WCI6 leads readily to polyphenylacetylene 49 (Eq. 17.50).
CH=CH-C=O
v~
t
(17.5o)
In a similar way, from 4-methyl-3-penten-2-one (mesityl oxide), polymethylacetylene can be obtained by the use of WCI6 as a catalyst 5~ (Eq. 17.51).
H~C=C~C=O
CH-
~
-[-C=(~
(17.51)
c~
Reaction of 2-benzylideneacenaphthen-l-one gives, under the similar conditions, a substituted polyacetylene containing acenaphthylidene recurring units4S (Eq. 17.52).
~
CI-I=C----C=O
-C6H~H6
----
(17.52)
The carbonyl-olefin exchange polymerization of conjugated unsaturated carbonyl compounds can be considered a particular case of intermolecular carbonyl-olefination reaction occurring through a tungstacarbene/tungstaoxacvclobutane mechanism (Scheme 17.5).
1 123 0
-C
H
...._ v
Scheme 17.5 The process displays many similarities to the ADMET polymerization of unconjugated dienes.
17. 6. Metathesis Degradation of Unsaturated Polymers
There are two classical ways for the degradation of unsaturated polymers by metathesis reaction (a) the degradation of polymers by intramolecular cyclization to macrocyclic compounds and (b) the intermolecular degradation of polymers to low molecular weight oligomers by metathesis with linear olefins.5~'52A third method for the degradation of unsaturated polymers involves ADMET depolymerization in the presence of well-defined metathesis catalysts. ~3 17. 6. 1. Intramolecular Degradation
Intramolecular degradation of the linear unsaturated polymers to macrocyclie oligomers, induced by WCl6-based catalysts, has been first observed by Calderon and coworkers. 54 Typical examples are the degradation of 1,4-polybutadiene and 1,4-polyisoprene, in the presence of the metathesis catalytic system WCh,/EtOH/EtAICI2. By imramolecular metathesis, 1,4-polybutadiene affords a series of unsaturated maerocyeles with the number of repeat units, n, ranging from 3 to 8 (Eq. 17.53).
1124
x=3,8 Detailed studies on the degradation of 1,4-polybutadiene and 1,4polyisoprene with classical and well-defined metathesis catalysts showed that the composition and structure of the cyclic oligomers depends greatly on the catalyst and reaction conditions. While many authors reported on the nature of cyclic oligomers form 1,4-polybutadiene and 1,4-polyisoprene under kinetic control, the real composition at thermodynamic equilibrium has been established by Thorn, 52 using well-defined metathesis catalysts as the degradation agents. 17. 6. 2. Intermolecular Degradation By intermolecular degradation of the unsaturated polymers in crossmetathesis reactions with linear olefins, low molecular weight products are obtained by the controlled scission of the double bonds from the polymer. Both internal and terminal olefins can be used as scission agents 5~ (Eq. 17.54). [cat]
R
The reaction occurs readily in the presence of classical and non-classical, well-defined metathesis catalysts. The products obtained are routinely separated by gas-chromatography and analyzed by mass spectrometry. The procedure became an efficient method for the structural analysis of the unsaturated polymers, copolymers and particularly polyalkenamers. 17. 6. 3. Acyclic Diene Metathesis (ADMET) Depolymerization Taking into account that ADMET polymerization to high molecular weight unsaturated polymers is an equilibrium process, it is possible that, under suitable conditions, the reaction to be reversed toward starting materials. By this way, the degradation of ADMET polymers to low molecular weight oligomers of the starting dienes became accesible 53 (Eq. 17.55).
1125
-c2
"-9 n
"~,,,-~~
(17.55)
[cat] Thus, in the presence of W- and Mo-carbene catalysts, employed in the ADMET chemistry, polymers can be degraded to low molecular weight products in a controlled manner.
17. 7. Catalytic Polymerization of Acetylenes Due to the special role that they play in the hydrocarbon chemistry, acetylenes have been polymerized by various mechanisms. Of these ways, we shall focus on the cationic, anionic, Ziegler-Natta and metathetical polymerizations. 17. 7. 1. Cationic Polymerization of Acetylenes Acetylenes can be easily polymerized by the use of cationic initiators, products of low molecular weight are generally obtained 55 (Eq. 17.56). n HC =C--P h
AICI3
=
-~C H=C --~ I -1'3
(17.56)
Ph
For instance, phenylacetylene produces, under the action of AICI3 as a catalyst, polymers of a few thousand number-average molecular weight.
17. 7. 2. Anionic Polymerization of Acetylenes In the presence of anionic initiators, acetylenes polymerize t o polyacetylenes of low molecular weight. 5s One example is the polymerization of phenylacetylene by n-butyllithium to form poly(phenylacetylene) with number-average molecular weight of ~ 1000 (Eq. 17.57). n HC=C--Ph
nBu~ _~CH=C% Ph
(17.57)
1126 17. 7. 3. Ziegler-Natta Polymerization of Acetylenes
Polymerization of acetylenes occurs readily under the influence of various Ziegler-Natta catalytic systems5~(Eq. 17.58).
n HC-C-R
---,.
-[-cH=C,-~ R
(17.58)
Polymers obtained in this way have alternating double bonds along the main chain and often show the following unique properties: geometric~ isomerism, electrical conductivity, paramagnetism, chain stiffness and a particular color. Acetylene selectively polymerizes in the presence of Ziegler-Natta catalysts whose components have low Lewis acidity. Thus, cis-polyacetylene can be obtained at low temperatures, in the presence of Ti(O"Bu)dEhAl as a catalyst, while trans-polyacetylene forms at high temperatures 56 (Eq. 17.59).
n c t .Jcl
HC=CH
n(Orau)4 t J -7ff'C
~_/,'~~
(17.59)
-n(C u)4 t:
150=C Similarly, phenylacetylene can polymerize with several Ziegler-Natta catalytic systems (e.g., TiCIVEhAI, VO(sal)2~hAl and Fe(acac)3~hAl) leading to high molecular weight oligomers, containing a large fraction of insoluble products. 17.6.4. Metathesis Polymerization of Acetylenes
A great number of acetylenes have been polymerized using metathesis catalysts based on group V and VI transition metal compounds (Nb, Ta, Mo, W) to produce high molecular weight polyacetylenes. 57 The polymerization reaction has been successfully applied to unsubstituted acetylene and to monosubstituted acetylenes having alkyl and aryl groups as
1127
substituents (Eq. 17.60)
n
=
R
[I~],[W]
r
"1
L
1 -In
R ~
(17.60)
H
where R is H, alkyl or aryl group as well as to disubstituted acetylenes (Eq. 17.61)
n RI
--
R2
.[Mo],[W]
[I
fin
(17.61)
RI R2
where R~ and R2 are different alkyl and aryl groups. With the discovery of well-defined metathesis catalysts which are tolerant toward functional groups, the controlled polymerization of acetylenes bearing a variety of functionalities has become possible (Eq. 17.62-17.63). n
---
n XI
--
X
X2
[Mo],[Wl
~
[Mo],[W]=
r
"1
L
IJn
(17.62)
X
rL [
I In X1 X2
(17.63)
Of a particular interest are polymers obtained from acetylenes bearing silicon, nitrile, carboxyl, ester, ether, and halogens as substituents. Unlike polyacetylene, these substituted polyacetylenes are generally colorless, soluble, amorphous, air-stable, electrically insulating, and nonparamagnetic. Some of these polymers have been found to be useful as membranes for separation of gases and liquids, thus constituting a new class of specialty polymers. As in the case of olefns and cycloolefns, metathesis polymerization of acetylenes involves a metallacarbene initiation but propagation is supposed to occur through an intermediate metallacyclobutene, as a key step for acetylene insertion into the metallacarbene bond 5s (Scheme 17.6).
1128 R R
+•R Ntl
R
tR
[Mtl
R
R
IR
R
i-"
R R--~
lMt I
\R
R .... ~
R
R
R
R
R Scheme 17.6
This mechanism can explain the results obtained in the polymerization of various acetylenes using the tungsten-carbenes Ph(MeO)C=W(CO)5 and Ph2C=W(CO)5 as catalysts.
17.8. Ring-Opening Polymerization of Heterocycles
The ring-opening polymerization of heterocycles with various types of catalytic systems has been for long a challenging area of research of a fundamental significance and with many useful applications. 17.8.1. Cationic Ring-Opening Polymerization of Heterocycles
Polymerization of heterocycles under the action of cationic initiators is a widespread process applied to a large variety of monomers. 59"62These include cyclic ethers, cyclic acetals, lactones, sulphides, lactams, imines and other N-containing tings. Good initiators for such reactions are BrOnsted acids, complex salts and Lewis acids generating complex salts (Eq. 17.64).
nO)
1129 Two mechanisms for the cationic ring-opening polymerization of cyclic ethers and acetals have been considered. The first in which the active species is located at the end of the growing macromolecule, named the "active chain end" mechanism and the other in which the charge is located on the monomer itself called the "active monomer" mechanism.
17.8.2. Anionic Ring-Opening Polymerization of Heterocycles Heterocyclic monomers such as cyclic ethers, lactones, episulphides, dimethylsiloxanes, lactames and N-carboxy~-amino acid anhydrides have been polymerized with anionic initiators from the class of organometallic compounds. 63"~7One interesting example is the ring-opening polymerization of 2,2-dimethyltrimethylene carbonate with sec-butyUitlfium resulting in high molecular weight polymer in the domain of kinetic control. This process was achieved in apolar solvents and at low temperatures (0~ to 25~ (Eq. 17.65)
n 0~
sBuLisBu~O~%Li
0
(17.65)
0
Under thermodynamic control, a ring-chain equilibrium was obtained, which followed the concentration dependence of the cyclic oligomers predicted by the Jacobson-Stockmayer theory (Eq. 17.66).
"%0-o
o
0
17.9. Miscellaneous Processes There are several catalytic processes related to the polymerization of cycloolefins, some of them having common features regarding the monomers or catalytic systems employed, others displaying certain resemblance concerning the kinetics or mechanism of the process. The following section briefly selects the most representative processes of this category.
1130 17.9.1. Metathesis of Alkanes
Metathesis of linear and branched alkanes in the presence silicasupported transition metal hydrides (SiOSi)(SiO)2Ta-H and (SiO)xM-H (M = Cr or W) into the next higher and lower alkanes at moderate temperatures (25~ to 200~ is an unprecedented catalytic reaction in this class of compounds 6s (Eq. 17.67).
CnH2n+ 2
[Ta] - H =
Cn+iH2(n+i)+2
+ C n.i H2(n.i),2
(17.67)
A o-bond metathesis mechanism, involving a four-centered transition state with the presence of an sp 3 carbon in the middle of the metallacycle, was assumed to be operative in this process. For example, the formation of butane/isobutane and ethane from propane occurs by alkylation of [Ta],-H species in a first step, followed by C-C bond formation via a four-centered transition state in a second step, and evolution of butane/isobutane and then ethane with regeneration of the active tantalum hydride species in a final step (Eq. 17.68).
\
I
[1"~ -H
s
rral---/X - 89
+
~ 1 ~
~
[~a 1 "
J
-(
00 Formation of both n-butane and isobutane in this process implies two distinct surface species, tantalum-n-propyl and tantalum-isopropyl surface complexes, generating two distinct four-centered transition states (I) and (II). 17.9.2. Catalytic Isomerization of Olefins
There are several catalytic processes in which linear or cyclic olefins undergo isomerization reactions wherein their structure, steric configuration or position of the double bond can be affected. These processes are summarized as cationic, anionic, Ziegler-Natta and metathesis isomerization
1131 reactions, depending on the type of catalyst. 17.9.2.1. Cationic lsomerization of Olefins
Acyclic and cyclic olefins can readily isomerize by a cationic mechanism under the action of Friedel-Crafls catalysts. 69 For instance, apinene in the presence of AICI3 rapidly isomerizes to d-limonene 7~ (Eq. 17.69).
~~ AICI~
(17.09)
This process occurs during polymerization of a-pinene in the presence of Lewis acid catalysts, when the products obtained (trimers) are in fact oligomers of d-limonene. In addition, isomerization of alkanes and cycloalkanes, under the action of Friedel-Crafis catalysts and particularly AICI3, is a widespread process applied in petrochemistry. 17.9.2.2. Anionic Isomerization of Olefins
In the presence of anionic initiators internal olefins can isomerize to terminal olefins by an anionic mechanism involving hydrogen abstraction from the allylic position of the initial olefin accompanied by double bond migrationT' (Eq. 17.70). NaM"I2
~
+ ~
(17.70)
17.9.2.3. Ziegler-Natta Isomerization of Olefins
Under certain conditions, linear and cyclic olefins can isomerize in the presence of the Ziegler-Natta catalytic systems leading to a mixture of isomers. ~ For instance, l-butene isomerizes under the influence of a number of transition metal catalysts to form a mixture of 1- and 2-butene (Eq. 17.71).
1132
H3C-HC=CH-C~
89
(17.71)
The selectivity of the isomerization product depends to a large extent on the nature of the transition metal compounds. 17.9.2.4. Metathetical Isomerization of Olefins
Acyclic and cyclic olefins may undergo easily geometrical isomerization under the action of the metathesis catalysts via a metathesis pathway. Thus, the isomerization of cis-2-pentene to trans-2-pentene occurs during its metathesis reaction to 2-butene and 3-hexene" (Eq. 17.72).
(17.72) The reaction takes place in the presence of heterogeneous catalysts derived from WO3 or MoO3 and homogeneous catalysts based on WC[6 and organometallic compounds. Similarly, cis-2-butene undergoes isomerization to trans-2-butene during its degenerate metathesis under the influence of the above catalytic systems t8 (Eq. 17.73).
[~
_. [cat] ._
/
(17.73)
17.9. 3. Cyclopropanation of Olefins
The addition reaction of carbenes to olefins, catalyzed by the transition metal compounds, is a well-known route for the preparation of substituted cyclopropanes" (Eq. 17.74).
R
,
[:CR~C2]
[cat]=
R\C/R2 /\ \R
(17.74)
1133 The reaction takes place readily in the presence of a variety of late transition metal complexes such as that of Ni, Co, Pd, Rh, Os and Ru. Of these catalytic systems, ruthenium-based catalysts mediate both the olefin metathesis and cyclopropanation reaction, as evidenced in the ROMP of cyclooctene~ (Eq. 17.75).
n
+ n N..,CHR
(17.75)
It is supposed that cyclopropanation reaction of olefins involves a metaUacarbene/metallacyclobutane mechanism commonly occurring in the metathesis reaction. The polarization of the metal-c.arbon bond plays a crucial role in directing the metallacyclobutane conversion toward cyclopropanation or metathesis products. This can be readily observed in the reaction of diphenylcarbene-tungstenpentacarbonyl with isobutene ~ (Scheme 17.7).
Ph
\
1L \
l
1l N
Scheme 17.7
1134 17.9.4. Friedel Crafts Alkylation Reactions
The alkylation reactions of olefins with appropriate alkylating agents such as alkyl halides occur readily under the action of the cationic initiators of the Friedel-Crafis type. 69 The reaction involves first the addition of a carbocation at the carbon-carbon double bond and then of an appropriate nucleophile with formation of the alkylated product (Eq. 17.76).
r-/vH3 CH2=C\ C H3
RX
CH3 J R-CH2-C-XI
AIX3
CH 3
~
(17.76)
In the series of aromatic compounds, Friedel-Crafts alkylation will lead to mono- and polyalkylated compounds 69 (Eq. 17.77).
(17.77) AICI3"~ ( C ~
This type of reactions are frequently encountered in the cationic polymerization of olefins and cycloolefins carried out with FriedeI-Cratts catalysts. 2-69 17.10. References
1. a.H.R. Allcock and F.W. Lampe, "Contemporary Polymer Chemistry", Prentice-Hall, Englewood Cliffs, N J, 1981; b. H.P. Plesch (Ed.), "The Chemistry of Cationic Polymerization", Mac Millan, New York, 1963. 2. J.P. Kennedy, "Cationic Polymerization of Olefins: A Critical Inventory", John Wiley & Sons, New York, 1975. 3. a. H.L. Hsieh and R.P. Quirk, "Anionic Polymerization. Principles and Practical Applications", Marcel Dekker, New York, 1996; b. M. Szwarc and M.V. Beylen, "Ionic Polymerization and Living Polymers", Chapman & Hall, New York, 1993; c. M. Szwarc, "Carbanions, Living Polymerization and Electron Transfer Processes", Interscience, New York, 1968; d. M. Szwarc(Ed.), "Ions and Ion Pairs in Organic
1135 Reactions", John Wiley & Sons, New York, 1972. 4. a. T. Matsumoto and J. Fumkawa, J. Polymer Sci., Part B, 5, 935 (1967); b. T. Matsumoto and J. Fumkawa, J. Polymer Sci., Part B, 6, 869 (1968); c. T. Matsumoto and J. Furukawa, d. Polymer Sci., Part B, 7, 541 (1969). 5. a. J. Boor, Jr., "Ziegler-Natta Catalysts and Polymerizations", Academic Press, New York, 1979; b. W. Kaminsky and H. Sinn, "Transition Metal Compounds in Polymerization and Catalysis", Springer-Verlag, Berlin, 1988; c. G. Fink, R. Miihlhaupt, H.H. Brintzinger "Ziegler Catalysts: Recent Innovations and Developments", Springer-Verlag, Berlin, 1995; d. R.P. Quirk (Ed.), "Transition Metal Catalyzed Polymerization: Ziegler-Natta and Metathesis Polymerization", Cambridge Press, New York, 1988; e. J.A. Ewen, L. Haspeslagh, J.L. Atood and H. Zhang J. Am. Chem. Soc., 109, 6544 (1987); f. J.A. Ewen, R.L. Jones, A. Razavi and J.D. Ferrara, J. Am. Chem. Soc., 110, 6255 (1988); g. W. Kaminsky, K. Kupler, H.H. Brintzinger and F.R.W.P. Wild, Angew. Chem., Int. Ed Engl., 24, 507 (1985). 6. a. P.L. Watson, .1. Am. Chem. Soc., 104, 337 (1982); b. P.L.Watson and D.C. Roe, J. Am. Chem. Soc., 107, 6471 (1985); c. J.J. Eisch, A.M. Piotrowski, S.K. Brownstein, E.J. Gabe and F.L. Lee, J. Am. Chem. Soc., 107, 7219 (1985); d. R.F. Jordan, W.E. Dasher and S.F. Echols, J. Am. Chem. Soc., 108, 1718 (1986); e. R.F. Jordan, C.S. Bajgur, R. Willett and B.J. Scott, J. Am. Chem. Soc., 108, 7410 (1986); f. G. Jeske, H. Lauke, H. Mauermann, P.N. Swepston, H. Schumann and T.J. Marks, J. Am. Chem. Soc., 107, 8091 (1985); g. J. Soto, M.L. Steigerwald and R.H. Gmbbs, J. Am. Chem. Soc., 104, 4479 (1982); h. L. Calwson, J. Soto, S.L. Buchwald, M. Steigerwald and R.H. Grubbs, J. Am. Chem. Soc., 107, 3377 (1985); i. B.J. Burger, M. E. Thompson, W.D. Cotter and J.E. Bereaw, J. Am. Chem. Soc., 112, 1566 (1990); j. J.A. Ewen, J. Am. Chem. Soc., 106, 6355 (1984). 7. a. P. Pino and R. Mtihlhaupt, Angew. Chem. Int. Ed Engl.,19, 857 (1980); b. B. gegier, J.C.W. Chien, Polymer Bull., 21, 159 (1989; c. B. gegier, X. Mu, D.T. Malin, M.D. Rausch, J.C.W. Chein, Macromolecules, 23, 3559 (1990); d. J.C.W. Chien, R. Sugimoto, J. Polymer Sci., Part A, 29, 459 (1991); e. J.C.W. Chien, G.H. Llinas, M.D. Rausch, G.Y. Lin and H.H. Winter, J. Am. Chem. Soc., 113, 8569 (1991).
1136 8. a.P. Cossee, J. CataL, 3, 80 (1964); b. E.J. Adman and P. Cossee, 3'. Catal., 3, 99 (1964). 9. a.D.G.H. Ballard, Adv. Catal., 23, 203 (1973); b. P. Patat and H. Sinn, Angew. Chem., 70, 496 (1957). 10. a. G. Henrir and S. Olive, Angew. Chem., 79, 764 (1967), b. G. Henrici-Olive and S. Olive, Angew. Chem. Int. Ed Engl., 6, 790 (1967). 11. a. P. Pino, Adv. Polym. Sci., 4, 193 (1965), b. P. Pino, G. Consiglio and H. Rinnger, Ann., 509 (1975). 12. K.J. Ivin, J.J. Rooney, C.D. Stewart, M.L.H. Green and R. Mahtab, 3,. Chem. So,:., Chem. Commun., 1978, 604. 13. a. A. Zambelli, G. Gatti, M.C. Sacchi, W.O. Crain and J.D. Roberts, Macromolecules, 4, 475 (1971); b. A. Zambelli, P. Locatelli, M.C. Sacchi and E. Rigamonti, Macromolecules, cited after reference 7a. 14. a. J Furukawa, Pure Appl. Chem., 42, 495 (1975), b. J. Furukawa, Acc. Chem. Res., 13, 1 (1980). 15. K. Matyjaszewski, "Controlled Radical Polymerization", ACS, Vol. 685, Washington D.C., 1998. 16. A. Demonceau, F. Simal, L. Delaude, and A.F. Nods, "'13'* International Symposium on Olefin Metathesis and Related Chemistry", Rolduc, Kerkrade, The Netherlands, July 11-15, 1999, Abstracts, p. 25. 17. K. Matyjaszewski, "'13th International Symposium on Olefin Metathesis and Related Chemistry", Rolduc, Kerkrade, The Netherlands, July 1115, 1999, Abstracts, p. 21. 18. V. Dragutan, A.T. Balaban and M. Dimonie, "Olefin Metathesis and Ring-Opening Polymerization of Cycloolefins", John Wiley & Sons, Chichester, 1985. 19. K.J. Ivin and J.C. Mol, "Olefin Metathesis and Metathesis Polymerization", Academic Press, London, 1997. 20. K.B. Wagener, J.G. Nel, R.P. Duttweiler, M.A. Hillmyer, J.M. Boncella, J. Konzelman, D.W. Smith, Jr., R. Puts, and L. Willoughby, Rubber Chem. Technol., 64, 83 (1990). 21. J.A. Tallarico, P.J. Bonetatebus, Jr., and M.L. Snapper, ,I. Am. Chem. Soc., 119, 7157 (1997). 22. R.H. C_mabbsand S. Chang, Tetrahedron, 54, 4413 (1998). 23. G.C. Fu and R.H. Grubbs, J. Am. Chem. Soc., 115, 3800 (1993). 24. G. C. Fu, S.T. Nguyen, R.H. Ca~bbs, J. Am. Chem. Soc., 11, 9856 (1993).
1137 25. E. Wassermann, D.A. Ben-Eft'aim and R.Wolovsky, ,1. Am. Chem. Soc., 90, 3286 (1968). 26. M. Lautens and G. Hughes, "13th International Symposium on Olefin Metathesis and Related Chemistry", Rolduc, Kerkrade, The Netherlands, July 11-15, 1999, Abstracts, p. 9. 27. T.J. Katz and T.M. Sivared, J. Am. Chem. Soc., 107, 737 (1985). 28. J.Tsuji and S. Higashiguchi, Tetrahedron Lett., 21, 2955 (1980). 29. Y.-J. Hu and R. Roy, Tetrahedron Lett., 40, 3305 (1999). 30. B. Konig and C. Horn, Synthlett, 1996, 1013. 31. G.W. Coates and R.H. Grubbs, J. Am. Chem. Soc., 118, 229 (1996). 32. K.B. Wagener, J.M. Bone,ella, J.G. Nel, R.P. Duttweiler and M.A. Hillmyer, Makromol. Chem., 191,365 (1990). 33. K.B. Wagener, J.M. Boncella, J.G. Nel, Macromolecules, 24, 2649 (1991). 34. J.E. O'Crara, J.D. Ponmess and K.B. Wagener, Macromolecules, 26, 2831 (1993). 35. R.T. Depue, R.R. Schrock, J. Feldman, K. Yap, D.C. Yang, W.M. Davis, L. Park, M. DiMare, M. Schofield, J. Anhaus, E. Walborsky, E. Evitt, C. Kruger, P. Betz, Organometallics, 9, 2262 (1990). 36. R.R. Schrock, J.S. Murdzek, G.C. Bazan, J. Robbins, M. DiMare, M. O'Regan, J. Am. Chem. Soc., 112, 3875 (1990). 37. P.O. Nubel, C.A. Lutman and H. Yokelson, Macromolecules, 27, 7000 (1994). 38. J.E. O'Gara and K.B. Wagener, Makromol. Chem. Rapid Commun., 14,657(1993). 39. F.J. Gomez and K.B. Wagener, Macromol. Chem. Phys., 199, 1581 (1998). 40. K. Bmezinska, P.K. Wolfe, M.D. Watson and K.B. Wagener, Makromol. Chem. Phys., 197, 2065 (1996). 41. J.T. Patton, J.M. Boncella and K.B. Wagener, Macromolecules, 25, 3862 (1992). 42. P.S. Wolfe and K.B. Wagener, Polymer Preprints (Am. Chem. Soc., Div. Polymer Chem.), 37, 439 (1996). 43. P.S. Wolfe, F.J. Gomez amd K.B. Wagener, Macromolecules, 30, 714 (1997). 44. B. Marcinec, "Organosilicon Chemistry" (H.Sakurai, Ed.), Ellis Horwood, New York, 1985. 45. K. Weiss, "NATO ASI Studies", Akcay, Balikesir, Turkey, Sep 3-16,
1138 1995. 46. R.H. Grubbs and S.H. Pine, in "Comprehensive Organic Synthesis" (B.M. Trost, Ed.), Vol. 5, Ch. 9.3, Pergamon Press, New York, 1991. 47. G.C. Fu and R.H. Cnubbs, J. Am. Chem. Soc., 115, 3800 (1993). 48. I. Schopov and C.Jossifov, Malcromol. Chem., Rapid Commun., 4, 659 (1983). 49. C. Jossifov and I. Schopov, Malcromol. Chem., 192, 857 (1991). 50. C. Jossifov and I. Schopov, Eur. Polym. J., 29, 621 (1993). 51. K. Hummel, Pure Appl. Chem., 54, 351 (1982). 52. E.Thom-Csanyi, J. Hammer, K.P. Pflug and J.U. Zilles, Malcomol. Chem. Phys., 196, 1043 (1995). 53. K.B. Wagener, Rubber Chem. Technol., 70, 519 (1997). 54. K.W. Scott, N. Calderon, E.A. Ofstead, W.A. Judy, and J.P. Ward, Adv. Chem. Ser., 91,399 (1969). 55. M.G. Chauser, Yu.M. Rodinov, V.M. Misin, M.I. Cherkasin, Usp. Khim., 45, 695 (1976). 56. C. Simionescu and V. Percec, Progr. Polym. Sci., 8, 133 (1982). 57. T. Masuda and T. Higashimura, Adv. Polym. Sci., 81, 122 (1987). 58. T.J. Katz and S.J. Lee, J. Am. Chem. Sot., 102, 422 (1980). 59. S. Penczek, P. Kubisha and K. Matyjaszewski, Adv. Polym. Sci., 37, 1 (1980), 68/69, 1 (1993). 60. S. Inoue and T. Aida in "Ring-Opening Polymerization" (K.J. Ivin and T. Saegusa, Eds.) Elsevier, New York, 1984. 61. E.J. Goethals, in "Comprehensive Polymer Science", (G. Allen and J.C. Bevington, Eds. ), Vol. 3, Ch. 51, Pergamon, Oxford, 1989. 62. R.C. Schulz, W. Hellermann and J. Nienburg, in "Ring-Opening Polymerization" (K.J. Ivin and T. Saegusa, Eds.) Elsevier, New York, 1984. 63. R. Jerome and P. Teyssie, in "Comprehensive Polymer Science", (G. Allen and J.C. Bevington, Eds.), Vol. 3, Ch. 34, Pergamon, Oxford, 1989. 64. S. Boileau, in "Comprehensive Polymer Science", (G. Allen and J.C. Bevington, Eds. ), Vol. 3, Ch. 32, Pergamon, Oxford, 1989. 65. T. Tsuruta, in "Comprehensive Polymer Science", (G. Allen and J.C. Bevington, Eds.), Vol. 3, Ch. 33, Pergamon, Oxford, 1989. 66. J. Sebenda, in "Comprehensive Polymer Science", (G. Allen and J.C. Bevington, Eds. ), Vol. 3, Ch. 35, Pergamon, Oxford, 1989. 67. P.V. Wright, in "Ring-Opening Polymerization" (K.J. Ivin and T.
1139 Saegusa, Eds.) Elsevier, New York, 1984. 68. V. Vidal, A. Theolier, J. Thivolle-Cazat and J.M. Basset, Science, 276, 99 (1997). 69. G. A. Olah, "Friedel-Craits and Related Reactions", Vol. 1-4, Interscience, New York, 1964. 70. W.J. Roberts and A.R. Day, J. ,4m. Chem. Soc., 72, 1226 (1950). 71. a. J. March, "Advanced Organic Chemistry: Reactions, Mechanisms and Structure", 3'd, John Wiley & Sons, New York, 1985, b. S. Patai, "The Chemistry of Alkenes", Interscience, New York, 1964. 72. M.B. France, J. Feldman and R.H. Grubbs, 3. Chem. Soc., Chem. Commun., 1994, 1307. 73. C. Kirmse, "Carbene Chemistry", 2~a Ed, Academic Press, New York, 1971. 74. A.F. Noels and A. D e m o n ~ , in "Metathesis Polymerization of Olefins and Polymerization of Alkynes" (Y. Imamoglu, Ed.), NA TO ASI Series, Vol. C ~16, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1998.
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1141
Chapter 18
PRACTICAL
APPLICATIONS
The progress made in the catalytic polymerization of cycloolefins stimulated a variety of applications for both commercial and technological purposes. These applications range from commercial products to small scale manufacture of speciality polymers suitable for top technologies like automotive industry, computer science, microelectronics, fine mechanics, electrotechnique, constructions, optics, etc. In addition, the process opened the way for the synthesis of new compounds with unprecedented structure and architecture which cannot be prepared by conventional methods.
18.1. Commercial Products Whereas hydrocarbon resins dominated the plastics production for several decades, only recently a family of new polymers with remarkable physical-mechanical properties entered successfully the market. These products are suitable to a wide variety of applications in many areas. In the following section the most important representatives of this class will be highlighted.
18.1.1. Hydrocarbon Resins The products commonly known as hydrocarbon resins t are low molecular weight, thermoplastic polymers obtained from cracked petroleum distillates, turpentine fractions, coal tar and various pure hydrocarbon monomers. This class of compounds is used extensively in several industrial fields such as adhesives, rubbers, printing inks, hot-melt coatings, protective coatings, paint, flooring and other areas, z They generally are employed to modify existing materials and are rarely used alone. The average molecular weights of these resins are usually below 2000 and they range from viscous liquids to hard, brittle solids. Hard resins are commercialized in flake or solid form or in solutions according to customer demand. Some of the hydrocarbon resins are also available in the form of cationic, anionic or nonionic aqueous emulsions. The colors range from water-white for resins
1142 produced from pure aromatic vinyl monomers prepared with boron trifluoride to pale yellow and amber, and to very dark brown in the case of some inexpensive petroleum by-product resins. The first hydrocarbon resins to be manufactured on a commercial scale before 1920 were coumarone-indene or coal-tar resins. The next to be produced on the market since the mid-1930s are terpene resins used mostly in adhesives. They are mainly polymers prepared from ot-pinene, [3-pinene, and d-limonene of citrus origin, or dipentene mixtures obtained from sulphate turpentine. Due to the increasing demand for resins, petroleum resins were manufactured as a new type and distributed as commercial products by the mid-1940s. A wide range of petroleum resins is currently available. They have a varying degree of unsaturation and aromatic content and may be used in various fields of application. Resins from pure monomers have been developed and produced from styrene, otmethylstyrene, vinyltoluene, isobutylene, dicyclopentadiene, and other compounds with related structures. 3 These products are very light in color, frequently water-white compounds. Resins prepared from dicyclopentadiene, an important monomer obtained from cracked petroleum stream, have been recently available. Coumarone-indene resins. This type of hydrocarbon resins named also coal-tar resins is derived mainly from coumarone (1) and indene (2) where indene is the major component of the monomer feed. 2
1
2
The feedstock originated from coal-tar contains several other lower and higher boiling components such as styrene, o-, m-, p-methylstyrene, 2methylcoumarone, 2-methylindene, naphthalene which contribute as be resin-formers. The polymerization process of the monomer feed occurred first under the action of sulphurir acid but higher melting, lighter-colored products were obtained with aluminium chloride or boron fluoride and their complexes as catalysts. Though these feedstocks are mixtures of monomers exhibiting fairly wide boiling ranges, product softening points up to 150~
1143 and even higher could be obtained. Usually, the crude feedstock is diluted before polymerization with an aromatic naphtha solvent so that the final resin solution to contain about 30-35% solid products. As the heat of polymerization of indene is ca. 63 kJ/mole (15 kcal/mole), the heat removal is easier from a more diluted and less viscous polymer solution. The catalyst is frequently added to the indene-containing mixture, although the order of reactant addition may be reversed as in the case of other h y d r ~ o n resin processes. When the polymerization reaction is completed, the catalyst may be removed by means of alkaline washing or lime treatment. Subsequently, the solvent is removed from the resin by distillation. Coumarone-indene resins with a softening point of 100~ and higher have been employed extensively in coatings together with filmforming materials such as drying oils. They have also been widely used as process aids and pigment-dispersing agents in the compounding of the natural and synthetic rubber. Terpolymers of indene, cx-methylstyrene and vinyltoluene produced with BF3 have been applied in alkyd-based coatings because of improved compatibility compared with resins derived only from cx-methylstyrene and vinyltoluene. Indene resins have also been used as components of printing inks, adhesives and flooring. Importantly, the polyindene resins reportedly improve the flexural modulus and processability of high molecular weight poly(vinylchloride), polystyrene and other commercially available thermoplastic resins. Terpene resins. Terpene resins are manufactured by cationic polymerization of various terpene hydrocarbons, most of which occur naturally. The most important terpene resins are those prepared from otpinene (3), 13-pinene (4), and limonene or dipentene (5) (Scheme 18.1).
3
6
4
7
5
8
Scheme 18.1
9
1144
Less important resins include those obtained from [}-phellandrene (6), myrcene (7), 3-carene (8), camphene (9), terpinolene, and various other terpinene isomers. Optically active d-limonene is a product derived from citrus-fruit industry, d,l-Limonene or dipentene is sometimes obtained as crude distillate fraction from pulp-mill liquor. It has the same physical properties as d-limonene with the exception of optical activity, d, l-Limonene is formed in addition to other terpenes in the processing of sulphate liquor from kraftpaper production. Polymerization reaction of these monomers has been effected by means of high-energy radiation, Ziegler-Natta 4 catalysts and Friedel-Crafis 5 type catalysts. Of the latter class, wide range of catalysts were evaluated in the following decreasing order of effectiveness: AICI3 = AIBr3, ZrCL, AICI3.OEtz, BF3.OEtz, SnCLs, BiCI3, SbCI3 and ZnCI2. The terpene resins are solids with fairly light colors, ranging from Gardner 1 to Gardner 5. When the polymerization reaction is carried out in solution in the presence of AICI3, 13-pinene and limonene give better polymer yields than r However, dibutyltin dichloride as a cocatalysts in conjunction with AICI3 substantially improves the yield of solid resins from ot-pinene.6 Also, trialkylsilicon halides are effective cocatalysts. 7 Moreover, organogermanium halides and organoantimony halides were reported to produce high yields of terpene resins from otpinene s when used in association with AICI3. The structure and properties of r resins are somewhat different from those of 13-pinene resins. Neither the structure nor the mechanism of ot-pinene resins are completely elucidated. Although ot-pinene can initially form the same carbenium ion as 13-pinene under the influence of cationic initiators, the final products have different molecular weight distributions and infrared spectra and display a distinct behavior in tackifying natural and synthetic rubbers. Significantly, in a comparison of products with a softening temperature of 115~ r resins possess a narrower molecular weight distribution than 13-pinene resins. Relevant differences in solubility profiles and tackifying efficiencies for natural rubber and styrene-butadiene rubber were also reported. 9 Limonene and sulphate dipentene were polymerized with AICI3 to produce high yields of light-colored terpene resins. The structure of these polymers has been thoroughly examined and found to contain two types of repeat units (Eq. 18.1).
1145
2n
+~ n
(18.1)
The polymerization of dipentene is usually conducted in a combination of toluene and high boiling aliphatic naphtha to improve the catalyst effectiveness. In this process the dipentene is gradually added to an agitated slurry of aluminium chloride in the diluent. It was observed that though terpenes may be polymerized by gradual addition of the catalyst to the monomer, the reverse addition procedure afforded a better control of the reaction temperature and usually resulted in higher yields of cleaner products. In the batch process for dipentene polymerization, the reaction mixture is conveniently stirred for an additional 30 min following monomer addition; sometimes, an hour or longer was needed to complete the reaction. Generally, the polymerization temperature is between 30~ and 55~ preferably of 40-50~ For some reactions, the temperature may be as low as 15~ to 20~ and the process can be run continuously. The catalytic system is deactivated with lime and clay at the end of the polymerization. Following the complete removal of toluene by distillation, the mixture of polymer, naphtha, lime and clay is heated for 4 hr at reflux to remove chlorine eliminated as hydrogen chloride. In the polymerization of dipentene and d-limonene the catalyst concentration is of 4-8% AICI3 whereas ]3-pinene requires less catalyst. Following catalyst removal, the final polymer is recovered by distillation of the solvent, the finished product is commercialized in drums containing approximately 182 kg or flaked and packaged in multiwall paper bags containing 22.7 kg. Copolymers of terpenes have been manufactured by copolymerization reaction of a variety of terpene monomers or with other nonterpene monomers. ~~ An efficient process for the preparation of terpene resins with low softening points (0-40~ using AICI3 as a catalyst starts from J3-pinene, dipentene and terpene oligomers (dimers and trimers) as the raw materials. Copolymerization of ]3-pinene with styrene and otmethylstyrene in the presence of AICI3 has been largely explored, the products obtained were true copolymers as evidenced by NMP, and GPC analyses. ~2 Several patents apply resin production from 13-pinene and styrene, from dipentene and styrene and ot-pinene and isoprene. ~3 13-Pinene-
1146
styrene-isobutylene terpolymers with softening points--IO0~ were manufactured in hexane solutions under the influence of ethylaluminium chloride as a catalyst. ~ These resins are successfully applied as tackifiers for pressure-sensitive adhesives and as components of hot-melt coatings or adhesives, m5 Petroleum resins. Petroleum resins are low molecular weight, thermoplastic hydrocarbon polymers manufactured from cracked petroleum fractions. Initially, the petroleum resins were soft, unstable and darkcolored products, but improvements in the methods of preparation have provided products with acceptable color, better stability and higher melting points. Nowadays, petroleum resin colors vary from pale yellow to dark brown. They have practically replaced eoumarone-indene resins in all areas. Large volume applications of petroleum resins are in the rubber industry, printing inks, adhesives and coatings. The raw materials for petroleum resins come from the deep cracking of petroleum distillates and usually exhibit wide boiling range. Three main streams from cracking of petroleum distillates are employed as crude feeds for the resin production namely C4-C6 aliphatic stream, Cs-C~0 aromatic stream and dicyclopentadiene stream. The C~-C6 aliphatic stream contains varying amounts of piperylene, isoprene and various linear and cyclic mono and diolefins in addition to not polymerizable paraflinic compounds. Examples of unsaturated monomers of the C4-C6 aliphatic stream are illustrated in Table 18.1. Table 18.1 Unsaturated monomers of the C4-C6 aliphatic stream from petroleum cracking' Monomer Pentenes Hexenes Heptenes Pentadienes Hexadienes Cyclopentene Cyclopentadiene Cyclohexene Cyclohexadienes Methylcyclopetaadime Data from reference.~
Boiling range, ~ 20-40 41-73 72-98.5 34-38 59-80 44 41.5 83 81.5-88.5
73
1147 The Cs-C~0 aromatic stream contains indene, vinyltoluene isomers, styrene, c~-methylstyrene and dicyclopentadiene in varying amounts in addition to ethyl- and polymethylbenzenes. The unsaturated monomers and boiling range of these compounds are listed in Table 18.2. Table 18.2 Unsaturated nsmomers of the Cs-C~0aromatic stream from petroleum cracking' Monomer Dicyclopentadiene Methylcyclopentadiene dimer Styrene ct-Methylstyrene Vinyttoluenes Indene Methylindenes
Boiling range, ~ 170 200 145.2 164 166-170 182.6 15%199
9Data from reference. The dicyclopentadiene stream contains 45-75% dicyclopentadiene in addition to other substituted monomers, streams of over 90~ dicyclopentadiene are also employed. The manufacture of petroleum resins from crude streams occurred in the presence of boron trifluoride and aluminium trichloride as catalysts. In early procedures H2SO4 has also been employed to initiate the polymerization reaction. With these catalysts, the reaction temperature varied from below 0~ to ~IO0~ depending on the type of the product prepared and the polymerization conditions. After the reaction time needed to achieve a complete conversion of the monomer, the catalyst was deactivated and removed with water, aqueous alkalies, ammonia, or lime. The polymer product was recovered by distilling the solvent from the "polymerized oil" or polymer solution. Petroleum resins range from liquids with softening points below 10~ to hard, brittle products with softening points up to 180-190 ~ Oicyclopentadiene resins. 1,3-Cyclopentadiene which is formed along with many other hydrocarbon compounds in the cracking of petroleum is removed from C4-C6 fraction by thermal dimerization to dicyclopentadiene (Eq. 18.2).
1148
(18.2)
Dicyclopentadiene feedstocks obtained from petroleum cracking may vary in purity from high (90-95%) to medium (78-80%) and to low purity mixtures of varying dicyclopentadiene content (45-70%). Codimers of cyclopentadiene with other linear dienes, e.g., butadiene or isoprene, and cyclic dienes, e.g., methylcyclopentadiene, are also present in the feedstock. Hydrocarbon resins were prepared from dicyclopentadiene by catalytic and thermal polymerization. ~6 The catalytic polymerization occurred mainly with AICI3 in solution. In this case, the process was conducted at 30~ by adding dicyclopentadiene slowly to half its weight of toluene in which 1% of AICI3 was suspended. After neutralization with aqueous alkali and removal of the solvent, a polymer with a softening point of 152~ bromine number 47 and Gardner color 13 was manufactured. Interestingly, a similar product, also with softening point of 152~ was obtained by the polymerization of the distillation bottoms from isoprene purification, under the same conditions. ~ This finding indicates that cyclopentadiene can increase the softening point when added to Cs monomers polymerized in the presence of AICI3 as catalyst. Hydrocarbon resins with lower softening points may be produced from dicyclopentadiene by an alkylation-polymerization process in mixed xylenes under the action of AICI3. The structure of these products involves aromatic xylyl groups attached to dicyclopentadiene recurring units ~8(10)
,C 10
1
Usually polymers with softening points between 30~ and 130~ are obtained. The lower softening point products are mainly employed as plasticizers.
1149
Applications. The main types of hydrocarbon resin are used widely as component parts in a great number of materials such as adhesives, rubber articles, printing inks, hot-melt coatings, floor coverings, textiles, paints and varnishes, caulks and sealants, and plastics. They are generally compounded with elastomers, plastics, alkyds, waxes and oils to confer special properties for a certain use. Sometimes, they are employed as the sole component in a particular application. For convenience of handling and transportation, hydrocarbon resins are commercialized in several physical forms including solid, bead, flake, crushed, powder or molten as well as water emulsions or dispersions, and solutions in adequate solvents or oils. The largest application of hydrocarbon resins is in the adhesive production. ~ As the conventional elastomers used in the adhesive compositions do not possess all of the desired properties for good adhesive performance, the hydrocarbon resins are incorporated into the formulation to modify the properties of the base elastomer and create the needed characteristics such as tack, resistance to creep, and viscosity control in hot-melt adhesives. The type of resin employed, e.g., indene, terpene or petroleum resin is determined, among other parameters, by the compatibility of the resin with the base elastomer. The main adhesive composition which contain resins are the following types industrial, construction, packaging, transportation, pressure-sensitive and consumer. Of all these types of adhesive, pressure-sensitive adhesives are one of the fastest growing area of the adhesive industry. This adhesive can be produced by resin modification of a large number of elastomers such as natural rubber, styrene-butadiene rubber, butyl rubber, chloroprene rubber, silicone rubber, acrylics, vinyl ether copolymers and ethylene-vinyl acetate copolymer. Terpene resins, particularly the [3-pinene resins, aliphatic C5 resins, and low molecular weight aromatic resins are widely employed for manufacturing pressure-sensitive adhesives from natural rubber. In adhesives based on styrene-butadiene rubber, ~-pinene resins, low molecular weight aromatic resins and aromatic-modified aliphatic hydrocarbon resins are suitable tackifiers. In addition to elastomer and tackifying resin, the adhesive includes plasticizer, filler, pigment, curing resin or cross-linker, and antioxidant. Hydrocarbon resins have also been extensively applied in hot-melt adhesives for markets such as packaging, disposable products, product assembly, bookbinding, and kraft-paper laminating to confer improved adhesion, enhanced hot tack, controlled viscosity and improved heat stability.These adhesives are formulated from polymers or copolymers e.g.,
1150 low molecular weight polyethylene, amorphous polypropylene, ethylenevinyl acetate (EVA) and ethylene-ethyl acetate(EEA). In the hot-melt adhesives derived from EVA copolymers the type of tackifying resin depends on the amount of vinyl acetate in the copolymer. Resins such as terpenes, pure and modified aromatics, and aliphatics have been effectively employed. In addition to the pressure-sensitive and hot-melt adhesives, large quantities of various hydrocarbon resins have been employed in special compositions of caulks, mastics and sealants. These adhesives are primarily solvent-applied or water based, but hot-melt caulks and sealant have been also developed. Polymers suitable for such compositions include neoprene, butyl rubber, natural rubber, polyisoprene, polyisobutylene, styrene-butadiene rubber, acrylics, polyesters, polyamides, amorphous polypropylene and block copolymers. The hydrocarbon resins are widely applied in the production of a variety of rubber-based products such as auto and truck tires, shoe soles and heels, hoses, industrial belting, mats, electric wire insulation, and roll covering. In this production they serve as processing aids, tackifiers and reinforcing agents. For instance, the coumarone-indene and aromatic resins reinforce mineral-loaded styrene-butadiene rubber stock and increase the tensile strength, elongation, and resistance to flex cracking. Also, aliphatir and terpene resins are useful as tackifiers for natural rubber and natural rubber/styrene butadiene rubber compositions used in the formulations of tires and molded goods. In this case, aliphatir resins impart good tack to unvulcanized carcass plies prior to tire building. In addition, resins may be involved in many other applications in tire manufacturing. A great amount of hydrocarbon resins are used in printing inks providing excellent pigment wetting, compatibility with many ink components, good resistance to water and alkali and good solvent release. Significantly, adequate selection of the feedstreams, careful control of the manufacturing processes, and continued quality assurance proc~ures ensure the supply of useful resin products to the printing industry. Thus, hydrocarbon resins with softening point of at least 140~ are usually desired as they provide higher solution viscosity, better solvent release, and improved hardness after drying. The resin may also behave as solubilizer or solid plasticizer when applied in conjunction with certain higher softening rosin ester resin in ink vehicles. Hydrocarbon resins are used extensively in letter press, lithographic and gravure inks. At a reduc~ sere the resins are used in flexographic inks because they are poorly soluble in the more polar flexo solvents. However, the hydrocarbon resins find some use in
1151 publication gravure and packaging gravure inks. In these applications, the resin contributes essentially to good pigment wetting as well as solvent release. Attempts have also been made to develop functional hydrocarbon resins with controlled solubility to preserve low ink-solution viscosity while providing fast ink setting for high-speed printing. A large number of paints and varnishes as protective coatings for industrial and trade-sale applications contain hydrocarbon resins as solid or solutions. Thus, petroleum resins are applied in air-dry and low bake industrial primers containing medium or long oil alkyds, gloss and semigloss industrial and trade-sale enamels to speed up drying, leafing aluminium paints to improve leafing properties and speed dry time, and oil and varnish stains to improve penetrating parameters and impart water resistance. Also, dieyr resins acting as oxidizing resins improve solvent resistance in aged films. Due to their unsaturation, these resins undergo copolymerization in drying oils used in cooked varnishes and alkyds to reduce the dry time in traffic paints. Furthermore, pure monomer resins are used in aerosol can paints where they retain pigments in excellent condition and promote high gloss and fast solvent release. In addition, the low solution viscosity of the resin is helpful in formulating these low solids coatings. Used in 20-30% as component part of the binder portion, the coumarone-indene and styrene modified aromatic resins are applied in the manufacture of light-colored asphalt floor tile. On their turn, some terpene resins are used as tackifiers for the natural rubber and synthetic gum bases employed in the manufacture of chewing gum due to their low odor and acceptable clearance. Block copolymer elastomers of styrene-butadienestyrene modified with parts of styrene or styrene copolymer resins are injection-molded to produce tennis shoes and tubing. Also, poly(vinyl chloride) compounded with styrene or styrene copolymer resins as processing aids is extruded into underground drain pipes. Furthermore, corrugated containers for shipping i c ~ or frozen poultry, fish, and meat are coated or impregnated with certain hot-melt blends composed of aliphatic or terpene resins, ethylene-vinyl acetate resin, and paraffin or microcrystalline waxes. In building technology, in order to control the degree of moisture evaporation and setting time, freshly poured concrete is sprayed with solutions of aromatic, dicyr or aliphatir resins. Economic aspects. Estimation of the total worldwide annual h y d r ~ o n resin production capacity indicated the value of ~1.04 million tons in the year of 1985. The main hydrocarbon resin producers are grouped in the
1152 United States, Japan, France, Netherlands, United Kingdom and Germany. (Table 18.3).
Table 18.3 Hydrocarbon resin manufacturers groupod by country'
United States Amoco Chemicals Corp. Arizona Chemical Co. Beatrice Companies, Inc., Chemfax, Inc. Eastman Chemical Products, Inc. Exxon Chemical Co. Goodyear Chemicals Co Hercules Inc. Hooker Chemical Corp., S.C. Jolmson & Son, Inc.
Lawter Chemicals, Inc. Neville Chemical Co. Polymer Applications, Inc. Reichhold Chemicals, Inc. Resmall Corp. Saturn Chemicals, Inc. Schenectady Chemicals, Inc.
Japan Arakawa Forest Chemical Hitachi Chemical Co. Mitsui Petrochemical Co. Maruzen Co. Mitsubishi Co., Ltd. Nippon Oil Co. Nippon Zeon Nisseki Plastic Chemical Co. Sanyo Toho Chemical Co. Torten Petrochemical Co. Yasuhara Zyushi Kogyo Co. I ~ . Netherlands AKZO Hercules B.V.
Neville Cindu Synthese Germany France Charbonnage de France (CdF) Chimie Ho~Alst AG Verkaufsveremigung fur Derive Resines Terpeniques (DRT) Teererzeugnisse Esso Chimie Others Granel Camphor and Allied Products, L~. Le Monde Chemicals, Inc. (India) Rousellot S.A. Faime (Italy) DSM, Sheby Hercules do Brazil (Brazil) United Kingdom Kolon Petrochemical Co., Ltd. (Korea) British Steel Corp. Quimica Demieres S.A. (Spare) Imperial Chemical Industries St Lawrence Resin Products, Ltd. (Canada)
' Data from reference. ~
1153
18.1.2. Polyalkenamers At present there are several industrial processes for the synthesis of poly~kenamers with elastomeric or thermoplastic properties. ~9"~ They supply a significant amount of products suitable for important applications in various scientific and technological areas.
18.1.2.1. trans-Polyoctenamer Though at first the research on polyoctenamers concentrated on the polymers rich in cis structure, for economic reasons an industrial breakthrough was achieved only with trans-polyoctenamer. This polymer was introduced as under the trade name Vestenamer by Chemische Werke Htils in 1980 and is at present commercialized as different types of products, depending on the molecular weight and trans contents. 2~23 Production of cyclooctene.The monomer, cyclooctene, is manufactured by partial hydrogenation of 1,5-cyclooctadiene. The latter was formed as a byproduct in the synthesis of 1,5,9-cyclododecatriene or from butadiene via dimerization in the presence of modified Ziegler-Natta catalysts with zerovalent nickel compound 24(Eq. 18.3).
(.)
()
Under these conditions, complete conversion of the starting material and high selectivity at elevated temperatures can be attuned. The crude product in the first step is separated from by-products and catalyst residues by flash evaporation. Purity of >99% can be easily reached. The selectivity of the hydrogenation step to cyclooctene is slightly less than 100% when commercial heterogeneous catalysts are employed. With rigorous temperature control and hydrogen metering a specially developed hydrogenation catalyst gives complete selectivity. However, a small degree of overhydrogenation to cyclooctane must be admitted, otherwise, traces of 1,5-cyclooctadiene can remain in the product that may hinder the sensitive polymerization process as results of its isomerization to 1,3-cyclooctadiene. The latter acts especially as a strong catalyst poison. The monomer with the purity necessary for polymerization contains 95-97% cyclooctene, the remaining being essentially cyclooctane. Synthesis of trans-polyoctenamer. On the industrial scale, polymerization of cyclooctene is performed in hexane as a solvent in the presence of a
1154 WCI6-based metathesis catalyst. 24 High purity monomer and anhydrous conditions are essential. The reaction is carried out adiabatically to complete conversion of monomer in almost 100% yield. The workup involves flash evaporation of the solvent with subsequent recycling. The final product is filtered in the melt, pelletized after cooling, and packed at a purity of >99.5% in bags. The content of impurities and low mass oligomers is very small. Properties of trans-polyoetenamer. Polyoctenamer has been produced over a wide range of molecular weights and cis:trans ratios of the double bonds. 24 The products exhibit bimodal molecular weight distribution with the first maximum corresponding to the low molecular weight oligomers. Depending on the reaction conditions, linear, unbranched polyoctenamers with an ideal poly(l-octenylene) structure in addition to macrocycles are formed in the polymerization process. As one double bond occurs at every eighth carbon atom of the chain or macrocycle, polymers with high chain mobility and low glass transition temperature will result. The crystallinity of the polyalkenamers depends strongly on their microstructure i.e., the ratio of cis:trans double bonds. The double bonds can be arranged in sequences and crystallites with defined melting temperatures will be formed. The crystallinity is thermally completely reversible and has a beneficial effect in blends of Vestenamer and other rubbers. During the mixing and extrusion the temperatures exceeds 50~ and the molten polyoctenamer improves the flow properties of the blend. After cooling the polymer recrystallizes and increases the green strength and shape stability. It was observed that the influence of the trans double bonds on the crystallinity is more pronounced than that of the cis double bonds. It is significant that recrystallization from the melt occurs within seconds; this property is very important in certain applications involving rubber processing. Several polyoctenamer grades are available commercially from Hials AG under the trade name Vestenamer. z5"3~The low molecular weight and crystallinity are chosen specifically so that they provide advantages in rubber processing due to their low melt viscosity. Typical properties of Vestenamer 8012 and Vestenamer 6213 are given in Table 18.4. In addition to these two types, a low molecular weight polyoctenamer has been offered to the coatings industry as Vestenamer L. The molecular weight of Vestenamer is kept intentionally low for a rubber. Due to its thermoplasticity, the viscosity in the molten state is unusually low compared to other solid rubbers. The Mooney viscosity ML
1155 Table 18.4. Properties of Vestezmmer 8012 and 6213' Property
Molecular mass, g/mol Glass transition temperature Tg, ~ Crystallmity (at 23 ~ % Melting point, ~ Startof d~osition, ~ Ratio trans:cisdouble bonds, % Mooney viscosityM L (l+4)(at I00 ~ Viscositynumber J(at23 ~ mL/g
Density,g/cm 3
Vestenamer
Vestenamer
8012
6213
100000 -65 30 54 275 80:20 <10 120 0.91
120000 -75 12 <36 250 60:40 <10 130 0.89
' Data from reference.24 (1+4) at I O0~ is between 5 and 8. Interestingly, it was found that polyoctenamer with 55% trans content and rather low viscosity exhibited surprisingly high elastomeric characteristics when compared with a cispolybutadiene of the same viscosity (e.g., tear strength 120 vs. 60 kp/cm 2, rebound elasticity at 22~ 43 vs. 30 %, modulus at 300% elongation 105 vs. 50). In contrast to common baled rubbers, the handling of polyoctenamers is simplified because they are delivered as pellets. Vulcanization and processing. ~3. Vestenamer can be vulcanized with all the cross-linking agents commonly used in the rubber industry such as sulphur, sulphur donors and accelerators, peroxides and vulcanization resins. Its cure rate with sulphur is comparable to that of a slow curing styrene-butadiene rubber. In blends with faster curing rubbers like natural rubber, isoprene rubber, butadiene rubber the accelerator level can be slightly increased. Blends of EPDM with Vestenamer are normally cured with peroxides since sulphur curing can deteriorate the vulcanizate properties. Vestenamer has two important functions when used as a blend component in 5 to 20 parts in the rubber compounds; first, due to its low viscosity, Vestenamer acts as a plasticizer or processing agent in compounding and molding and second, after vulcanization it is cross-linked like all other rubbers, completely incorporated into the network, and can no longer be extracted. It is interesting to note that the ring molecules in
1156 Vestenamer permit good rubber properties at low molecular weight. In vulcanizates the same amount of cross-linking agent (e.g., sulphur) binds long polymer chains as well as medium-sized tings (Figure 18. l, A, B and C) to an effective polymer network but fails to do so with short or medium length chains. (A)
(B)
(c)
S-bridges
S-bridges
S-bridges
\
Figure 18.1. Different network types in rubber vulcanizates (Adapted from Ref.23). These network types can explain the good elastic and thermodynamic properties of vulcanizates from a polymer with low molecular weight. Addition of Vestenamer in rubber compounds affords a series of significant advantages. These imply a lower overall energy consumption for the mixing process, easier filler incorporation, better filler dispersion and a smaller temperature increase during mixing. In the extrusion process the mass pressure and die swell are decreased and the surface finish of the extrudates, e.g., profiles and tubing, is improved. Furthermore, the high rate of crystallization of Vestenamer leads to a significantly higher green strength of the compounds. Examples on the improvement in the green
1157 strength of the natural rubber and of polybutadiene or polyisoprene rubber in rimstrip compounds or carcass compounds in tire building are illustrated in Figures 18.2 and 18.3. Green Strength, Mp. 10 1
06
/ 06
,X,,..~...X,,--'X.~,~o,,~ '" ' ' ' ~ ' ' ' ' ~ ' ' ' ' ~ ' ~ ' ' " .... ~''" "'~''''~ 2
ts S
04
.~. o*
' O " "" ~* ' ' ~ ~ ' " 0 ' " ' ~ "" ~
' ' 0 ' ' ' ~* ~ ~ * "" 0 ~* ' "' " 0 "' ' ' 3
02
Elongation, % Figure 182 lnfluen~ of Vestenamer on green strength m rimstrip compounds (Curve 1 NR/BR/TOR = 10/70/20 ; Curve 2 NR/BR/TOR = 20/70/10; Curve 3 NR/BR/TOR = 70/70/0) (Adapted from Ref3~ As it can be seen, the replacement of natural rubber by small amounts of Vestenamer 8012 improved the green strength considerably what helps to avoid overstretching during the tire building operations. Significantly, such effects can be obtained with the more crystalline Vestenamer 8012 and not with Vestenamer 6213. It was also found that the rigidity and dimensional stability of extrudates, which are stored before vulcanization, are increased markedly; examples are tire bead and apex compounds, profiles and braided hoses. Due to the improved flow properties of these compounds, the mold-filling process can be improved and shortened in the production of molded articles
1158 Green Strength, MPo ! /
4.5
9
J
3 /
/
t
/
t/"
3.0
.,.--
1.5
/
/
7
0
2
4
6
8
10
12
Elongation, % Figure 18.3.. Influence of Vestenamer (TOR) on green strength in carcass compounds (Curve 1 NRfTOR = 50/50; Curve 2: NRfFOR = 80/20; Curve 3" NRfrOR 90/10; Curve 4" NR = 100; Curve 5" IRfI'OR = 80/20; Curve 6" IRfFOR = 90/10, Curve 7" TOR = 100) (Adapted from Ref.3~ and complicated mold geometries are cleanly manufactured. As result of the rapid recrystallization of Vestenamer 8012, the anisotropy of the calender shrinkage is considerably reduced; even very thin sheets can be calendered without defects. Moreover, the tack of the compounds is reduced due to the completely unbranched polyoctenamer molecules in conjunction with their crystallinity.
1159 The vulcanizate properties of rubber-polyoctenamer blends are barely affected compared to compounds without Vestenamer. Tensile strength and tear resistance are decreased somewhat as a consequence of the low molecular weight of the polyoctenamer. The elongation at break decreases while the modulus increases. The hardness is also increased because the crystallinity is substantial after cross-linking. In addition, the ozone resistance is not changed. It was also observed that in blends of polar and nonpolar (NBR-EPDM) rubbers or emulsion and solution rubbers (NRBR), the use of small amounts of Vestenamer (5-10 phr) increased dispersion of the otherwise mutually not very compatible rubbers and processing can thus be improved. The dynamic properties of the natural rubber compounds are improved on blending with Vestenamer and reversion is suppressed at the same time. These results open up new possibilities for tire compounding and manufacture. Applications and economic aspects. Vestenamer has been used in all areas of rubber industry, z;'z4 At present it is predominantly used in blends with the following rubbers: NR, SBIL EPDM, NBR, CIL CSM and precross-linked rubbers. Thus, the improved flow with Vestenamer often provides smoother extrudates and higher output, while the swell is diminished. This allows the extrusion of the very hard compounds which otherwise could not be achieved by conventional ways. Moreover, by improving the flowability of the compounds, Vestenamer facilitates mold filling by decreasing the pressure build-up and affords a better shape precision. In this way, even poorly flowing hard compounds may be injection molded by the addition of Vestenamer. During calendering process Vestenamer decreases the shrinkage and improves the surface quality particularly of coated fabrics. In many cases, in the hose production, the improved green strength of the uncured hose core enables savings by eliminating the costly cooling operation, usually necessary before braiding the core. It was found that covering of the metal rolls with unvulcanized rubber sheets is made easier by the improved green strength given by Vestenamer. The good compatibility and covulcanization properties of Vestenamer with other rubbers improves the peel strength between the layers. Vestenamer also improves the processing of very hard roll coverings making thus the injection molding of e.g., type-writer rolls and rice hulling rolls possible. It allows to manufacture rolls consisting of natural rubber and EPDM mixtures which are otherwise incompatible. The pronounced thermoplasticity and low melting point of
1160
Vestenamer permit the use as a carrier material for filler batches. In this case, the filler incorporation is high and the rapid recrystallization from the melt allows granulation of the batches. Of interest are uses of Vestenamer as carrier material in combination with dyes, accelerators, peroxides and very fine powders. Vestenamer is mainly used in the bead area and in the sidewall of passenger and truck tires. This facilitates the building process by increased green strength which also contributes to a better tire uniformity. At the same time, the processing is improved especially for highly filled compounds. Unlike other processing aids, Vestenamer is used to replace the base rubber, normally at 5-20 phr. Interest is also increasing in the use of Vestenamer as the only rubber component for the manufacture of extremely hard but readily processible tire apex compounds and golf balls. Vibration damping sheets for steel plates based on butyl rubberpolyoctenamer blend have been developed and commercialized. Recent development is the application of Vestenamer-oil mixtures as coating and binding agents for ground rubber waste powder. This technique can be employed for recycling rubber waste, which is technically rather difficult. Vestenamer production began at Hills Company in a pilot plant in 1980 and in 1989 a large plant with a capacity of c a . 12000 to/year was put in operation. Of interest, in 1991 the following quantities of Vestenamer were consumed in different areas of the rubber industry (Table 18.5).
Table 18.5. Uses of Vestenamer in the rubber industry'
Industrial Area
Tires Profiles Molded articles Tubing Calendered articles Roll covers Other ' Data from reference.~
Vestenamer amount % 34 27 15 3 2 1 18
1161 Toxicology. ~ trans-Polyoetenamer and its precursors have been thoroughly investigated with regard to their toxic properties. Toxicology studies on 1,5-cyclooetadiene indicated that this precursor has an LDs0 (oral) of 1900 mg/k 8 in rats and LDs0 (dermal) of >10000 mg/k 8 in rabbits. This compound shows a slight irritant effect on the skin but has no sensitizing effect in the corresponding test according to Magnusson and Kligrnan. It has no irritating effect on the eyes or mucous membranes. Cyelooctene has an LDs0 (oral) of 4550 mg/kg in rats and an LDs0 (dermal) of >10000 mg/kg in rabbits. This compound exhibits a slight irritant effect on the skin but has no sensitizing effect in the corresponding test according to Magnusson and Kligman. It shows no irritating effect to the eyes and mucous membranes. Studies on trans-polyoctenamer indicated an LDs0 (oral) of > 12500 mg/kg in rats. The product exhibits no irritating effect on the skin or on rabbit eyes. Experiments on rats showed that a 90-d oral administration at concentrations up to 4000 mg/kg did not result in any toxic effect. The polymer showed no mutagenic effect in the Ames test (m vitro) on Salmonella typhimurium and the micronucleus test (in vivo) on mice.
18.1.2.2. Polynorbornene Polynorbornene is the frequently used name for poly(1,3cyclopentylenevinylene) obtained by the ring-opening polymerization of bicyclo[2.2.1]hept-2-ene (norbornene) though polynorbornene designates also the product obtained by vinyl polymerization of norbornene. Since 1940 this highly strained reactive monomer has been subjected to numerous polymerization investigation using various types of catalytic systems. As result of intensive studies on the polymerization of norbornene, the polymer has been produced in France by CdF Chimie under the trade name of Norsorex since 1976. The final products are copolymers of norbomene with ethylene and propylene and possess the structure of a trans-poly(l,3cyclopentylene-l-vinylene) with ethylene and propylene units. They are characterized by an unusual high molecular weight (>3x106 g/mole) and a glass transition temperature T s of 37~ being intermediate between elastomers and thermoplastics. The materials are compatible with plasticizers and acquire elastomeric properties by incorporation of these substances. At present, the worldwide production capacity of polynorbomene is 5000 to/year (Norsorex)in the French plant of Elf Atochem (Carling).
1162 Consumption of pure polynorbomene was about 1000 to in 1991, corresponding to 5000 to of compounded elastomer. Norsorex product was introduced in North America by American Cyanamid in 1977 and in Japan by Nippon Zeon in 1978; the product price was of $3.00-4.00/kg in 1987. Production of 2-norbornene. The monomer, 2-norbornene, is synthesized by Diels-Alder reaction of cyclopentadiene with ethylene. Cyclopentadiene is itself obtained by cracking of dicyclopentadiene at a temperature higher than 160~ (Eq. 18.4).
,,0.c.
o §
-~
(18.4)
II
Dicyclopentadiene is extracted from the Cs streams from naphtha steam cracking. The addition reaction occurs without catalyst at a high temperature and a high pressure. The impurities contained in the commercial dicyclopentadiene (about 5%) and the by-products formed by reaction of 2-norbomene with the raw materials are removed by a thorough purification of 2-norbomene after the synthesis step. The polymefizable monomer has 99.7% purity. Pure 2-norbomene is solid at room temperature (Mp = 47~ and has to be protected from air oxidation. Manufacture of polynorbornene. Commercial polynorbomene (Norsorex) is produced by ring-opening polymerization of norborrlerle 31'32 in the presence of RuCI3 in butanol~C131'32 (Eq. 18.5).
n
i~~
RuCI3 C41..IoOH/HC ~-
(18.5)
The chemical structure of the polymer corresponds to poly(1,3cyclopentylenevinylene) preserving one double bond per repeat unit with mainly t r a n s configuration. The polymerization reaction is extremely rapid and highly exothermic. A special technology provides a polynorbomene with a convoluted and porous structure. After cooling and drying, the polymer appears as a white, free flowing and easily processible amorphous powder, with an irregular surface area having a grain size of <0.8 mm and an apparent density of 0.3 g/cm. 3 It rapidly absorbs oils typically employed
1163 in compounding formulations. The porous structure and the presence of double bonds render polynorbornene very sensitive to air oxidation; therefore, a non-staining antioxidant is added during its manufacture. Several grades of Norsorex are produced which contain various concentrations of aromatic and naphthenic processing oils; these products are available in slab form. Properties and processing. Polynorbomene possesses remarkable properties due to its particular chemical structure, uncommonly high molecular weight and unusual transition temperature. Relevant physical properties of the pure polymer are given in Table l8.6. Table 18.6. Physical properties of polynorbomene ~
Property
Value
Microstructure, % t r a n s Appearance Molecular weight, g/mole Glass transition, T s, ~
80 white amorphous powder >3x10 s 37 ~ 0.96 1.534 19.8 2.09 218 0.285 2.5 10.4 7x1016
Dens y, g/cm3
Refractive mdex Solubility parameter, Mpa 1/2 Heat capacity, J/(g.K) Heat of formation, J/g Thermal conductivity, W/(m.K) Dielectric constant (1 MHz) Dissipation factor (l MHz) Volume resistivity f2.cm 9Data from reference. 33"35
The thermal behavior of pure polynorbomene classifies it as a thermoplastic product with a very low transition temperature. Because of its high molecular weight, polynorbornene does not melt under usual conditions and decomposes at >200~ without real fluidization. Interestingly, the polymer exhibits a "shape memory effect": when heated to more than 37~ it recovers its memorized shape. The pure product is used
1164 in only a few minor applications. The pure polymer has a very high attinity for liquid hydrocarbons promoted by its extremely porous structure. Due to its ability to absorb and gel about ten times its weight of common hydrocarbons, pure polynorbomene is considered a highly efficient antipolluant. Because of the compatibility of polynorbomene with various extension oils that act as plasticizers, the transition temperature of the polynorbornene-oil mixture is lowered thus converting the plasticized polymer into an elastomer (Figure lS.3). Ts, ~ 10
-10
-20
-30
-40 0
I 5O
i IO0
i 150
I 2OO
Oil, phr Figure 18.4. Influence of various plasticiz~rs on Ts of polynorbomene (Curve l aromatic, Curve 2, naphthenic; Curve 3, paraf~ic) (Adapted from Ref.S~). Moreover, the presence of double bonds in the structural unit allows further vulcanization of the polymer with common peroxides or various sulphur vulcanization compounds. Pure polynorbornene has good aging and heat resistance (up to 90~ excellent mechanical strength, low compression set, and high compatibility with most other rubbers. When unprotected, polynorbornene rubbers exhibit poor ozone resistance, however, efficient protection is obtained by addition of antiozonants or small amounts of EPDM rubber.
1165 Polynorbornene rubbers allow a high level of palsticizers and filler to be incorporated. Plasticizers can be applied at up to 500 parts per 100 parts of polymer while fillers up to 200 parts. Most usual polynorbornene rubbers contain on average 20~ pure polynorbomene so that the properties of the resulting vulcanizates will vary over a wide range depending on the formulation. The amount of plasticizer incorporated in the polymer determines the soRness of the vulcanizates, usually low hardness values of products clown to 10 Shore A can be reached in combination with good mechanical properties. The type of plasticizer affects substantially the cold resistance, energy absorption capability and compatibility with other rubbers. The dependence of the cold resistance (brittle point) of the polynorbornene v u l ~ t e s on the type and level of plasticizer is illustrated in Table 18.7. Table 18.7. Influence of plasticizer on the brittle point of polynorbomene vulcanizat~~ Plasticizer type
Aromatic oil Naphthenic oil Paraifmc oil Dioctyl adipate Brittle point, ~
Plasticizer level, ph'r
160
180
180
180 180
20 40
-30
-42
-49
-38
-52
9Data from reference.2' As Table 18.6 shows a wide range of brittle points result for various groups of plasticizer and different levels of incorporation. Several types of mineral fillers and carbon blacks can be used with polynorbornene rubber. The type of filler will influence mainly physical properties such as strength resistance, abrasion and tear resistance, electrical properties and dynamic damping parameters. The degree of their effect depends essentially on their concentration in the rubber compound. Values of the mechanical properties of a given polynorbornene rubber compound containing 200 parts of naphthenic oil and 200 parts of various fillers are listed in Table 18.8.
1166
Table 18.8 Effect of filler type on polynorbomene rubber' Property ~itin B
MT
sal
Type of filler GPF
FEF
HAF
28 l 0.5 525 55
35 l I. 8 507 56
43 14.r 369 45
57 15. l 276 34
61 16.9 268 22.5
Hardness, Shore A Tensile strength, Mpa Elongation, % Rebound at 20 ~ %
53 14.8 322 35
9Data from reference,z4 Highly filled polynorbomene vulcanizates can be employed where the ability to accept ultrahigh Ioadings provides excellent damping characteristics, which are little affected by the temperature. It was observed that the glass transition T s of the polynorbomene rubber is determined by the oil selection and the damping above 20~ can be adjusted by the type and amount of filler. Remarkably, small-particle-size carbon blacks provide both reinforcement and damping. Two formulations of low and high damping are presented in Table 18.9. Table 18.9 High and low dampmg formulations for polynorbomene' Ingredient
Low damping, parts
High darnpmg, parts
Norsorex polynorbomene Mediun viscosity napl~enic oil Dioctyl adipate N-990 thermal black N-774 furnace black N-220 fumace black N-octyl diphenylamme Zinc oxide Stearic acid N-Isopropylbenzothiazole-2-sulphenamide Sulphur
100 150 50 100 100
100 250 50
Data from reference. ;a
2 5
2OO 2 5
I
1
5 1.5
5 1.5
1167 The effect of temperature on the damping parameter (tan ~i) for the two polynorbornene formulations for low and high damping characteristics is illustrated in Figure 18.5. Tan 8 1.00
0.30
0.25
0.10 -40
9 -20
, 0
9
9
t
t
t
20
40
SO
80
100
Temp., ~ Figure 18.5. Effect of ten'~rature on damping parameter (tan 6) for polynorbomene formulations (Curve 1" high damping characteristics; Curve 2" low damping characteristics) (Frequency 110 Hz, Stram amplitude 3%) (Adapted from Ref.35). It is relevant that formulations with good aging characteristics include a microcrystalline wax with a p-phenylenediamine antiozonant for ozone resistance. For non-staining applications, blends of polynorbornene with EPDM rubber are employed. The best results are recorded with high unsaturation, oil-extended EPDM rubbers. These formulations give better dispersions in the high molecular weight polynorbomene and provide a better match of cure rates for the respective compounds. Matching of the cure rates will give satisfactory ozone resistance with a 25:75 blend of polynorbornene-EPDM rubber. Interesting results on the effect of various compounding ingredients such as oil, filler, curative, antioxidant on hot-air aging of polynorbornene vulcanizates have also been reported. It is noteworthy that, because of its high molecular weight, polynorbornene rubbers can be blended with large amounts of extenders and fillers without affecting their processability or mechanical properties. For instance, compounds that contain 100-400 parts each of oil and carbon
1168 black varied in 200% modulus from <2 to >20 MN/m z (2900 psi) (Figure
18.6). Oil, phr
Oil, phr 5004Oo
0
200
100
300
30O
300
/'~3o.o as.o t
100
|
2OO (a}
200
loo I
'
100
30O
2"04.0
7.0
300
10.0
12.0 150
i
3OO
3OO 2OO
100
I00
200
!
2OO Co)
30 4050
200
100
,
300
(c)
6O
i
i
I
100
2OO
30O
(d)
Carbon black, phr Figure 18.6. Effect ofoil and carbon black on properties ofpolynorbomene
vulcanizates (a) Tensile strength, M N / m 2, Co) Elongation at break, %; (c) 200% Modulus, MN/mZ; (d) Shore A hardness (1 MN/m z = 145 psi) (Adapted from Ref.').
Other properties such as tensile strength and Shore A hardness changed correspondingly. As Figure 18.6 shows, modulus was also affected greatly by the type of reinforcing carbon black, thus, high surface carbon blacks provide the greatest increase. Significantly, high concentrations of nonreinforcing fillers (qv), e.g., mineral fillers, afford low cost compounds that
1169 are remarkably soft, yet possess low permanent set under compression. Processing of polynorbornene rubber ~ r s in common equipment used for rubbers under usual conditions. Both internal mixers and open mills can be employed for polynorbomene rubber compounding. Preferably, the equipment must be preheated at c~z 80~ to avoid possible degradation of the long polymeric chains at lower temperature due to mechanical rupture. The process always involves a preliminary absorption of oil (i.e. plasticizer) by the powdered polynorbornene, so that it becomes an elastomcric material that can be submitted to she~ng. For the manufacture of very soft compounds, a masterbatch with a limited amount of oil (150 parts) is mixed first and then the additional ingredients are introduc~ in a second mixing step. Further processing is carried out with common equipment in the rubber industry. In addition, the polynorbornene compounds can be produc~ as free-flowing dry blends in a high-speed powder blender. Moreover, the dry blend may be extruded or injection molded. Applications and economic aspects, polynorbornene rubber is a specialty elastomer which is used widely in areas where its unique properties are in demand. The most important applications are in the field of low-hardness solid parts and elastomers with tailore~ damping properties. These properties are exploited in very different industries such as automotive, appliance, office equipment and leisure industries for the production of moldext or extruded goods. Thus, high density sheet material is used for noise control under the hood in Diesel-powered cars, and body mounts based on polynorbornene provide a smooth fide. Other automotive applications, e.g., gaskets and seals, require soft, durable and moisture resistant products. Special nonautomotive vibration-isolation applications include railway cushions and seismic equipment pads as well as audio Ioudspe~er seals and cushioninserts for running shoes. The ability of polynorbornene to absorb great amounts of oil rapidly is applied to control oil spills. The advantage is that the polymer floats on water and soaks up the spill in a few minutes. The resulting product may form a cohesive, continuous sheet, which will be easily removed and dispose~ of. Toxicology and explosion hazard, z4 Polynorbornene powder is non-toxic and non-mutagenic to Salmonella (Ames test). Acute oral toxicity for rats is 11 g/kg. However, the product is flammable and can create a potential explosion hazard as an airborne dust. The high concentration of allylic,
1170 tertiary hydrogen atoms in the polymer requires that products be stabilized against oxidative aging. Polynorbornene is currently supplied with a protective antioxidant, but, because of the high surface area, antioxidant depletion and subsequent autoxidation can pose some problems. The storage of the powder beyond one year is not recommended. The main photooxidative degradation behavior is similar to that observed with polydienes, however, there are other possible degradation pathways. Zeonex 280. Since 1991 Nippon Zeon commercialized a hydrogenated ROMP polymer from norbornene-like polycyclic monomers under the trade name of Zeonex. A new commercial product manufactured by Nippon Zeon Co. by ring-opening metathesis polymerization of norbornene monomers and subsequent hydrogenation is Zeonex 280. The product has remarkable physical and chemical properties what makes it of interest for many applications in optical, electrical and medical fields. Some of its properties compared to traditional resins for optical uses such as polycarbonate (PC) and polymethylmethacrylate (PMMA) are given in Table 18.10. Zeonex 280 is an amorphous, colorless and transparent polymer. For its application potential, it is remarkable that the transmittance of Zeonex 280 is comparable to polymethylmethacrylate in the visible light region, but is superior to polycarbonate and polymethylmethacrylate in the near ultraviolet region. This behavior is illustrated in Figure 18.7. Transmittance, % 100 I
~ ' -
.....
2
80 3
60 40 20
0
y; L.at
200
400
600
800
Wavelength, run
Figure 18.7. Transmittance curves for Zeonex 280, PC and PMMA (8 mm thick; l-Zeonex; 2-PC; 3-PMMA) (Adapted from Ref.~).
1171 Table 18.10. Physical properties of Zeonex 280 con~ared with polycarbonate (PC) and polymethy~acrylate (PMMA) ~b
Property
Unit
Specific gravity % Water absorption % Moisture absorption 8/m2.24hr Water permeability % Transmittance 25 nd Refractive index r Photoelastic coefficient nlTI Retardation of birefrmgence of disk ~ Glass transition temp. ~ Heat defloction tenq3. cal/sec.cm Thermal conductivity .~C Lmear expansion ~ c i e n t deg"1 Solubility parameter Melt-flow index
Bending modulus
Bending strength Tensile modulus Tensile strength Elongation Impaa strmgth Pencil hardness
~/10min k~cm z kgfcm ~ k~crn 2 k~cm 2 %
kgf.cm/cm
Zeonex 280
PC
PMMA
1.01 <0.01 <0.01 <0.01 91
1.20
1.19 0.30 0.50 1.14 91
0.20 0.24 1.53
90
1.53
1.59
1.49
6.3.10"13 <25
72.10 "13 <60
6.0.10 "13
140 123 4.7.104 7.0.I0 "s
140 121 4.5.104 7.0.10 "~
105 90 4.6.104
6.2 15
57
24,000 1,010 24,000 643 10 3,0 H
24,000 930 24,000 640 90 6.0 B
8.0.10 "~
30,000 1,150 31,000 730 5 1.6 3H
|
'Data from reference.3~
In addition to this behavior, it is noteworthy that Zeonex is an optically stable polymer and shows a minimal thermal dependency of the refractive index. The dependency of the refractive index with the temperature is illustrated in Figure 18.8.
1172 Refractive index, nk
1 ! .535
1.530
1.525
"~X.......~x
1.520
1.515
0
I
l
10
20
,
l
&
30
40
~ 5--L~~.,~_..~ ~x~'~X
,,
9
50
&
60
X
m
70
9
80
Temp., ~ Figure 18.8. Thermal dependencyof refractive index of Zeonex 280 (Adapted from Ref~S). Interestingly, Zeonex 280 shows one tenth less optical elasticity than polycarbonate and is nearly equal to polymethylmethacrylate. Thus, when molded into optical disks, for instance, this polymer provides extremely small retardation and minimal sub-retraction difference on any incident beam angle. Because Zeonex has no polar groups, it provides extremely low water absorption and moisture permeability. Disks made from this polymer show good durability under high humidity. Zeonex 280 is easy to mold and provides good groove transfer rate. In addition, its thermal decomposition temperature is 420~ approximately 100~ above its molding temperature. Consequently, there is a considerable less risk of thermal decomposition during the molding process for Zeonex as compared to polymethylmethacrylate. Likewise, Zeonex 280 has excellent electric properties such as low dielectric constant, low dielectric loss tan/5 and high dielectric breakdown strength. Furthermore, the polymer dissolves completely in aromatic or cyclic hydrocarbons but exhibits a high resistance to alcohols, ketones and cellosolves.
1173 Due to its outstanding properties including dimensional stability, low water absorption, high transmittance and low retardation as well as high heat resistance, Zeonex 280 is efficiently employed in various areas and particularly for optical lenses and prisms of cameras, CD and CD-ROM players, laser beam printers, and optical link modules, etc. It can be a proper substitute of the traditional resins applied in optics such as polycarbonate (PC), polymethylmethacrylate (PMMA), and regular polyolefins. In medical field Zeonex is used for prefilled syringes, vials and cells for blood analysis systems because of high purity, low adsorption of medicines, low water permeability and high tolerance to steam sterilization. In electrical field, due to its low tan/5 and dielectric constant, Zeonex 280 is used for the insulator of coaxial connectors
18.1.2.3. Poly(dicyclopentadiene) Recently, poly(dicyclopentadiene) prepared by ring-opening metathesis polymerization of dicyclopentadiene gained an important role on the market of thermoset polymers due to its wide range of valuable physical-mechanic~ properties. The product is manufactured mainly by reaction injection molding (RIM) process and commercialized under various trade names. Manufacture of poly(dieyclopentadiene) ~. In the currently applied RIM process for the manufacture of poly(dicyclopentadiene), the monomer is split into two parts which serve as carriers for catalyst components. The two solutions are stable enough to be mixed in the mixing head of the RIM machine and react after their injection into the mold. The first composition contains the transition metal compounds, typically WCI6 whereas the second part contains a cocatalyst such as an organoaluminium compound. The second composition can also contain esters or ethers, which control reaction rate and induction time. Modification of the first part with oxygenated compounds such as phenols is beneficial for increased catalyst solubility and activity. As with most metathesis reactions, strict exclusion of air and moisture is necessary. In addition, the purified dicyclopentadiene has to be free of traces of conjugated dienes and polar impurities which are strong catalyst poisons. The monomer portions may contain additives that facilitate the reaction or modify the product properties. Certain dissolved polymers, for instance, increase the viscosity of reactant streams, improve pumping characteristics, and may increase the impact resistance of the polymer.
1174 Reinforcing fillers such as glass, mica, carbon black, and talc increase hardness and reduce mold shrinkage, whereas chopped fibers improve dimensional stability, flexural modulus and heat-distortion temperature. Usually dicyclopentadiene is polymerized in conventional urethane RIM equipment. Since the process effected at a low pressure, molds can be of light weight constmctiort, allowing low cost, short production runs. The low viscosities of the two monomer solutions permit filling of rather complex shapes and allow molding of large parts. Articles up to several tens kg could be manufactured by this efficient technology. The polymerization reaction of dicyclopentadiene in the presence of these catalytic systems is exothermie, with an estimated heat of reaction of about 41.85 kJ/mole (10 kcal/mole). As a result, the temperature increases about 170-190~ under adiabatic conditions. This temperature increase will promote cross-linking as well as complete reaction of dicyclopentadiene. These factors, in turn, will influence hardness, glass transition temperature and heat distortion temperature as well. In actual practice, the temperature rise will vary with mold geometry and part thickness, and process conditions have to be carefully controlled. Polymerization of dicyclopentadiene by the RIM process leads to gel formation at a very early stage, although soluble polymers are readily attainable with other catalyst systems. It is well documented that, under these conditions, dicyclopentadiene reacts as a difunctional monomer, leading first to linear and then to cross-linked structures (Scheme 18.1). RIM
~
Scheme 18.1
RIM
1175 However, in view of the fact that norbomene also yields gelled polymers with this procedure, it is likely that cationic side reactions are involved in the gelation process. In addition, the high reaction temperatures encountered in dicyclopentadiene polymerization might favor reversible formation of low strained tings rather than ring-opening reaction. Properties of poly(dicyclopentadiene), as Poly(dicyclopentadiene) as manufactured in the Metton RIM process has several remarkable properties what makes the polymer of a wide use in many industrial fields. Some of the most relevant physical properties of the polymer are listed in Table 18. l I.
Table 18.11 Physical properties of poly(dicyclopentadiene)' Physical property
Flexural modulus, MPa b Flexural strength, MPab Tensile modulus, MPab Tensile strength, Mpab Tensile elongation, % Plate impact strength, J at 23 ~ at -29~ Glass transition, Ts, ~ Coefficient of linear expansion Mold shrinkage, cm/cm
Orientation
parallel perpendicular parallel perpendicular parallel parallel
parallel parallel perpendicular
Unfilled polymer 1790 62 1620 34 80 13-16 11-13 90,119,127 37 0.035
.
Mi Milled glass (20%) 2620-2900 2480 62-76 62 31 25 11-13 11-13 127 17 0.008-0.014 0.012-0.021
'Data from reference 3,; hi,o convert Mpa to psi, multiply by 145.
As it can be easily observed, the combination of high modulus and high impact strength, even at -30~ affords outstanding properties for poly(dicyclopentadiene). In addition, the polymer has excellent creep resistance. As Figure 18.9 illustrates, after 105 hours under equal loads, poly(dicyclopentadiene) creeps 1/5 as much at 38~ as nylon-6 at 23~
1176 Stram, % 3
m
1
2 3
0
iL
9
1
0.1
I
10
"
"
100
9
1000
10000
9
100000
Figure 18.9. Creep behavior of Metton (100~ vs. Nylon-6 (75~ (1- Nylon 6, 1000 psi; 2-Metton, 2000 psi, 3-Metton 1500 psi; 4-Metton 100 psi, 5 Nylon 6, 435 psi) (Adapted from Ref.3=). Surprisingly, unlike most polymers, the impact strength of poly(dicyclopentadiene) increases as the square of the thickness, rather than linearly (Figure 18.10). Plate impact strength, J 180 r 160 140 120 100 80 60 40 20 0
Ik.
0
2
4
6
8
10
12
Thickness, mm Figure l 8. l O. Plate impact strength of poly(dicyclopemadiene)
as a function of thickness (Adapted from Ref.3=).
1177 Another significant property, considering the polymer's high degree of unsaturation, is the high resistance to oxidation, it appears to undergo surface oxidation to form a oxygen-impermeable film at air exposure. This characteristic improves the product paintability. Paint adhesion was reported to be excellent, with no need for priming. Outstanding properties were also reported for the poly(dicyclopentadiene) products Telene RIM or RTM. These specialty polymers provide an excellent combination of stiffness, impact strength and heat deflection temperature with a low specific gravity. They have superior hydrolysis resistance to water, acids and bases, remarkable electrical insulating properties and give paintable products with good painting adhesion. The formulations can be easily processed on high pressure impingement mixing gIM or low pressure RTM type equipment. A wide range of viscosity values, between 50 and 1000 cps is provided at room temperature. Some physical properties of the standard formulation of Telene are included in Table 18.12.
Table 18.12. Physical properties of standard Telene formulation*
Physical Property
Value
Specific gravity Tensile yield strength, MPa Flexural modulus, MPa Notched Izod impact, J/cm +25 ~
1.03 45 1850
load 18.5 kg/cm2 Coefficient of thermal expansion, cm/cm.~ Weight change after 7-d, % 100~ in water Dielectric constant, 1 MHz Dissipation factor, 1MHz
110
-40 ~ Heat deflection temperature, ~
9Data from reference. 39
5 1.6
8.2x10 "~
+0.75 2.66 8.15x10 "3
1178 Insolubility of poly(dicyclopentadiene) has hindered for some time the accurate determination of the chemical structure. Infrared methods have indicated a high concentration of open-chain cis vinylene units, as well as the retention of most of the fused cyclopentene tings present in the monomer. Also, it is estimated that in the polymer prepared under RIM conditions one cross-link occurs for every five monomer units. The double bond geometry is about 60:40 cis:trans. Traces of norbornene units also survive under some conditions, probably due to the presence of unreacted monomer or reaction of fused cyclopentene ring. Applications and economic aspects. Poly(dieyclopentadiene) has been produced since 1982 by BF Goodrich under the trade name of Telene and since 1984 by Hercules Inc. under the trade name of Metton. Telene RIM/RTM products include a standard formulation, an FR grade and a fiberglass reinforced glass mat to service a variety of applications. 39 These specialty polymer finds wide uses in leisure vehicles, automotive and truck industry, industrial and agricultural equipment, lawn and garden equipment, marine and aerospace equipment. Leisure vehicle applications concern golf carts, jet skis, snowmobile hoods, motorcycle and moped fenders and cowlings whereas automotive and truck areas refer to truck wind deflectors, fairings and shields, van conversion parts-running boards, cargo box for pick-up trucks. Industrial and agricultural equipment will comprise corrosion resistant blowers and fans, photographical chemical tanks, underground electrical junction boxes, material handling pallets and containers, tractor fenders and hoods, seed and fertilizer hoppers. Lawn and garden equipment implies lawn tractors and tiding mowers, fenders and hoods, clipping containers and snow blowers. Interesting applications in the marine and aerospace fields will produce marine propellers, small boats, water intake strainer grates and jet skis. The first reported use of Metton was for snowmobile hoods, where good low temperature impact resistance is very important. 4~ Other applications of Metton product include golf carts, water crafts, one-piece cabs for farm machines, satellite receiver dishes, seamless plastic pipes. Seamless pipe could be manufactured in situ since the RIM technology is not energy-intensive and could be portable. Automotive industry will benefit by the polymer's high impact strength for the production of car bumpers, hoods and other car parts. Especially good chances seem to be in the molding of very large parts (up to 700 lb. presently) as well as in various composites. 4t
1179
18.1.3. Cycloolefin Copolymers A great number of copolymers derived from ot-olefins e.g., ethylene and propylene with norbornene-like cycloolefins e.g., norbomene, dieyclopentadiene, tricyclopentadiene etc. have been manufactured using binary Ziegler-Natta type catalysts such as TiCldorganoaluminium compounds, VOClflorganoaluminium compounds, metalloeene/methylaluminoxane. '2 Of these products, copolymers under the trade name of Topas have found interesting applications in various areas.
18.1.3.1. Topas Copolymers of ethylene with norbomene-type cycloolefins produced with metalloeene/methylaluminoxane catalysts are commercialized under the trade name of Topas (Thermoplastic Olefin Polymers of Amorphous Structure) by HOchst Company in conjunction w i t h Mistui Petrochemicals. 43 Starting materials. The main starting monomers for Topas production include ot-olefins such as ethylene and propene and bieyclie olefins such as norbornene and substituted norbornenes. The standard catalysts used derive from metallocenes and methylaluminoxane. Polymerization procedures. The copolymerization reaction is carried out under the standard conditions of Ziegler-Natta polymerization using metallocene catalysts. Several patents published by H0chst Company describe the main procedure applied for the synthesis of copolymers. Specific data of Topas technology are proprietary. Structure and properties. The structure of Topas products corresponds to olefin/cycloolefin copolymers of the following general formula (11)
Rl/
\R2
11 where R, R~ and R2 call be hydrogen or alkyl groups. The physical and mechanical properties of these products vary as a function of the composition of the copolymers. Due to the random
1180
distribution of ethylene and norbornene units, Topas is an amorphous compound in which the crystallization is suppressed. The high transparency in the visible and near ultraviolet regions (transmission above 90% up to 300 nm) is coupled with low optical anisotropy and an inherently low birefringence. Generally, the products display a low density, extremely low water absorption, a thermal stability up to 170~ good resistance toward acids, bases and hydrolysis, high electric insulating propensity, high hardness and weathering. Due to the aliphatic character, Topas is resistant to polar solvents such as methanol and acetone but non-polar solvents like toluene do attack the polymer. The product is water-repellent and exhibits negligible swelling when immersed in water. Water uptake is only 0.01% after 24 hr at a temperature of 23~ Besides that, water vapor permeability is extremely low, giving excellent water vapor barrier properties, even superior to polyolefins like polypropylene. It is noteworthy that the glass transition temperature of Topas can be shifted in a wide range by simply adjusting the ratio between the two comonomers. As the amount of norbornene component increases, the polymer chain is stiffened and thus mobility decreased. Therefore, glass transition temperature will be increased. The influence of norbornene content on the glass transition temperature of Topas, Ts, can be observed in Figure 18.11. Tg,~ 250 200
150 100 50 a
10
l
l
9
20
9
30
,
9
40
9
a
,50
9
9
6O
9
a
70
9
J
80
Norbomene, mole % Figure 18.11. Influence of the norbomene content on the glass transition temperature m Topas polymers (Adapted from Ref.43). Glass transition temperatures well above 200~ are available but currently grades with T s between 80~ and 180~ are preferred.
1181
The products can be easily processed under normal conditions. As flowability is correlated to the molecular weight, flow behavior can be tailored to the customer's requirements for any given T 8. Interestingly, the mechanical properties are retained over a wide temperature range from 50~ to near glass transition temperature. This behavior is usually observed for an amorphous thermoplastic polymer. Topas is a plastic material with high modulus and high stif~ess. Tensile modulus is about 3 Gpa, tensile strength varies from 40 to 70 Mpa. Elongation at break is in the range from 3% up to 10%. The behavior under long-term stress is excellent. Stress relaxation test revealed the very low creep tendency; even after several hundreds of hours, flexural creep modulus is decreased by a small amount only. Applications and economic aspects. ~ Four types of commercial products are at present available on the market: Topas 8007, 5013, 6015 and 6017, the first two numbers indicating the product viscosity and the last two indicating the thermal stability. A global output of 3000 t/year Topas products has been foreseen for 1996 to be manufactured in an industrial plant in Japan by H6chst Company (Germany) in conjunction with Mitsui Petrochemicals (Mitsui Sekka). Topas products find direct application in several modern technologies such as data processing machines, optical devices, as parts of elements in construction, electronics, electrotechnique, illuminating devices etc. Special applications are particularly for production of optical lenses, optical storage media such as compact discs and CD-ROMs, films for capacitors. The chemical purity of Topas products allows them to be also used for medical articles, for steam- and gamma-sterilization techniques. 18.2. Products of Interest for Industry
Though not applied on an industrial scale, many polyakenamers have been developed due to their easy availability and attractive physicalchemical properties. Some of these are potential products for interesting applications in various fields. 18.2.1. trans-Polypentenamer
Due to the easy accessibility of cyclopentene and the excellent properties of trans-polypentenamer as a general purpose rubber, the synthesis and properties of this polyalkenamer have been extensivley
1182 studied by many research groups. The abundant results obtained in these studies constitutes a valuable reference source for the vast ring-opening metathesis polymerization chemistry. Starting materials. Significant amounts of cyclopentene are obtained from refinery C5 fractions. Cyclopentene itself is a minor recoverable component of these streams, but larger amounts can be obtained by hydrogenation of the more abundant component eyclopentadiene. Several routes are known for the hydrogenation of eyclopentadiene. Of these, two particularly attractive procedures utilize titanium- or nickel-based catalysts. "'~5 These methods appear to be over 97% selective for the production of cyclopentene at quantitative conversion of cyclopentadiene. According to a process developed jointly by BASF and Erdolchemie, cyclopentadiene is first isolated as dicyclopentadiene, this is then cracked, hydrogenated and recombined with the initially separated C5 fraction which contains some cyclopentene. Ultimate separation and recovery of monomers consists of extractive distillation. ~ Cyclopentene is a colorless, pungent liquid product under normal conditions. It is quite volatile and highly flammable. In contact with air for extended periods forms a relatively stable hydroperoxide. Importantly, samples that have not been treated to remove peroxides should not be distilled to dryness. The oral LD50 is 2.14 g/kg in rats. The relevant physical properties of cyclopentene are summarized in Table 18.13. Table. 18.13 Ph~!cal properties of cyclcl~ntene* ' Physical Property
Value
Molecular weight Freezing point Boilmg point rla2O d2~ g/mL
68.11 -135.076 44.242 1.42246 0.77199 1.837 233/4.79 20.5,28.5 d
Cp20, J(g.oC)b
Critical temperature, ~ Ring strata, kJ/mole b
~
9Data from reference47, b To convert Id to cal, divide by 4.184, ~To convert MPa to atm, divide by O.101 ~ Different data from reference,a
1183
Polymerization procedures. Cyclopentene polymerization has been carried out in bulk and more conveniently in solution where the control of the reaction exotherm of ca. 4.5 kcal/mole (19 kJ/mole) is better accomplished. Suitable inert solvents include aromatic and aliphatic compounds such as benzene, toluene, chlorobenzene and methylene chloride. Usually, the polymerizations have been conducted at room temperature or below, because polymer yields decrease substantially at elevated temperatures. This is a consequence of the rather low ceiling temperature of cyclopentene polymerization. As the majority of p r ~ u r e s employed classical metathesis catalysts derived from metal halides e.g., WCI6, MoCI5 and organometaUic compounds, e.g., organoaluminium compounds, organotin compounds, strict precautions for the control of monomer and solvent purity are required to maintain the catalyst activity. Usually, allenes, conjugated dienes and acetylenes which may be present as impurities in the starting material must be removed. Moreover, polar impurities such as oxygenated compounds have also be removed. On the other hand, adventitious traces of some polar contaminants such as water, or the easily formed cyclopentene hydroperoxide, can serve rather to enhance reaction rate as catalyst modifiers. A wide range of binary homogeneous catalytic systems have been developed for cyclopentene polymerization including a large variety of transition metals ranging from zero-valent coordination complexes to salts of the metals in their highest oxidation states. In association with the transition metal compound, a great number of coc,atalysts have been employed that are typically organometallic compounds or Lewis acids. The activity of binary catalyst systems has been often substantially enhanced by the addition of a third component known as promoter, activator or modifier. The three-component catalysts form the basis for many excellent catalytic systems which are well suited for economically commercial polymerization processes. Oxygen-compounds such as alcohols, phenols, haloalcohols, ethers, peroxides, hydroperoxides, epoxides, c,arboxylic acids, esters, molecular oxygen, and water have been preferably employed as catalyst modifiers. Generally, the catalytic systems were prepared by precomplexation of catalyst components or in situ in the presence of the monomer. It was observed that addition of catalyst components is crucial for the optimum activity; particularly, the reaction of promoter or activator with the transition metal component should ~ r prior to the addition of the organometallic cocatalyst. Reaction termination and catalyst deactivation were carried out by quenching with alcohols or adequate
1184 oxygen-containing compounds. Polymer separation and characrterization were performed by standard methods known from polymer chemistry. Structure and properties, trans-Polypentenamer has a fairly low melting point (18~ very close to that of the natural rubber. The low glass transition temperature (-97 ~ close to that of 1,4-polybutadiene, imparts good processability and elastomeric properties. Practically, transpolypentenamer does not crystallize at room temperature within a limited period of time. However, under strain it will crystallize readily and the polymer acquires good processing qualities. Polypentenamers with a high trans content, ranging normally from 75 to 85%, as determined by IR and NMR spectroscopy, were usually obtained using trans-specific catalytic systems. The content of trans structure varied markedly with catalyst, reaction temperature, solvent and reaction time. The steric content has also been obtained by variation of the ratio transition metal/organometallic compound or other catalyst components in the base system, trans-Polypentenamer appears to exhibit higher intrinsic viscosities than cis polymers of comparable molecular weight, suggesting stiffer, more extended chains.~s Compounding and processing. Due to its special structure and properties, trans-polypentenamer exhibits a good compounding and processing behavior. 49 This refers to mill banding, filler and ingredient dispersion, extrusion, calendering, tire building, and other operations with compositions of any Mooney range between 30 and >150. These outstanding properties were attributed not only to the chemical structure, but also to a wide molecular weight distribution of a special type. The presence of low molecular weight fractions imparts to transpolypentenamer the plasticity needed for easy processing whereas high molecular weight fractions provide good vulcanizate properties and the steep shear gradient necessary for ready filler and ingredient dispersion. Such a compromise is generally unfavorable in view of the mechanical properties of the v u l ~ z a t e s , however, solution polymerization of cyclopentene leads to a large molecular weight distribution of a special type due to the particular polymerization mechanism and to the use of special catalytic systems. From a comparative examination of the molecular weight distribution of trans-polypentenamer, polybutadiene and polyisoprene, it is obvious that trcms-polypentenamer is essentially characterized by a large fraction of high molecular weight polymer and by small fractions of products ranging down to very low molecular weights. (Figure 18.12).
1185
[~], % lO0-
1
50-
/
lOII
0.I
0.5
II
II
5
1.0
9
I0
log [11],toluene, 25~ Figure 18.12. Molecular weight distributions of trans-polypentenamer (1), cis-polybutadiene (2) and cis-polyisoprene (3) (Adapted from Ref.*9). Extensive studies carried out by Haas and Theisen s~ showed that the processability of trans-polypentenamer is equivalent to that of the natural rubber, as indicated by the Mooney viscosity/temperature relationship (Figure 18.13). Mooney viscosity, ML-4' 120 1
100
M &
80 6O
20-
60
8O
100
12.0
140
160
Temp., ~ Figure 18.13. Mooney viscosity/temperature dependence for trans-polypentenamer and diene rubbers (Adapted from Ref.S~
1186
As it can be seen, trcms-polypentenamer exhibits the highly desired strong viscosity as a function of the temperature gradient, which at room temperature provides low cold flow while at the processing temperature (80-130~ combines sufficient plasticity for extrusion with mechanical strength for rapid filler and ingredient dispersion. It was found that transpolypentenamer can be easily compounded on the open mill and in Banbury without premastication, the mix is rapidly blended to a smooth and compact band. The favorable compounding behavior of trans-polypentenamer evidenced by the energy absorption and temperature profiles during filler incorporation has been illustrated by G0nther and coworkers 5~ for tire tread formulations of different elastomers. It is worth noting that trans-polypentenamer may be loaded with exceptionally large amounts of carbon black and oil. Black Ioadings of 110125 phr and oil levels of 75-90 phr are tolerated by trans-polypentenamer without extensive drop in mechanical properties. Taking tensile strength as a criterion for comparing the response of trans-polypentenamer and natural rubber to heavy Ioadings, it may be inferred that even at 160 phr black and 100 phr oil loading good mechanical properties are retained. Interestingly, microscopic examination of the trans-polypentenamer mixes revealed that black dispersion in the polymer is at least as perfect as in the natural rubber and definitely superior to that in polybutadiene rubber and styrenebutadiene copolymer. It is relevant that the extrusion behavior of trans-polypentenamer is substantially better than that of polybutadiene rubber and close to that of styrene-butadiene rubber (Table 18.14). Also remarkably, trans-polypentenamer mixtures display a very high building tack, much higher than that of any other general purpose rubber. This is another highly desired processing property of trans-polypentenamer which was ascribed to the rapid stress crystallization of the polymer. This property is reflected in the excellent rubber-to-fabric adhesion of highly loaded trans-polypentenamer stocks as compared to natural rubber. One of the most important properties of trans-polypentenamer is the rapid stress crystallization of the unvulcanized polymer, resulting in strong self-reinforcement or green strength of the product. This outstanding property is a significant advantage of the polymer for all processing operations, including carcass build up. Haas and Theisen s~ showed that tire tread stocks of trans-polypentenamer exhibit exceptionally high green strength, even higher than that of natural rubber (Figure 18.14).
1187 Table 18.14. Garvey Die extrusion radices for trans-polypentenamer cJs-poly~utadiene~) _and ,st~'ene--butadiene rubber ~ Rate, Rate Rating ElasWn~r m/mm g/min t ra ns- P o l ypentename r
ML 1+4 (100~ = 30 40 phr IS AF black t rans-P ol ypentenamer
ML 1+4 (100~ = 70 65 phr ISAF black, 40 phr Paraflux oil cis-Poly(butadiene) ML 1+4 (100~ = 40-50 40 phr IS AF black Styrene-Butadiene Rubber ML 1+4 (100~ = 50 65 phr ISAF black 40 phr Paraflux oil
38.5
113
2434
37
102
3433
27
I00
1342
35
80
3444
9Data f r o m reference. 49
Stress, kg/cm z 4O
1
30
20
2
10
0 0
100
200
300
400
500
eO0
700
Elongation, % Figure 18.14. Green strengthof uncured 50 phr HAl: black loaded tiretread stocks (at 23~ l_trans.polypentenamer; 2-natural rubber; 3-styrene-butadiene rubber (Adapted from Ref.S~
1188
Vulcanization and vulcanizate properties, trm~-Polypentenamer can be easily vulcanized with sulphur and sulphur donors. Compared to other highly unsaturated hydrocarbon polymers, the vulcanized products show substantial cross-linking structures and consequently require low vulcanizing agent and accelerator consumption to attain high tensile and modulus values. Interesting studies carried out by Dall'Asta and coworkers 49 on the black and oil loaded trans-polypentenamer mixes using conventional sulphur and accelerator or sulphur donor and accelerator formulations showed high cure rate up to a pronounced plateau with only very low reversion (Figure 18.15). in/lb J| r
m/lb I
~
/
3_
/ |
o
Tm~e,
(A)
~o
~
30
18
~0
Time, mm
(B)
Figure 18.15. Rheometer curves for sulphur cured (A) and sulphur donor cured (B) carbon black and oil loaded trans-polypentenamer at d~fferent temperatures (Adapted from Ref.*9).
1189
Relevant data on the reversion in trans-polypentenamer have been recorded by Jahn. ~z Some of these results together with comparative data obtained with natural and polyisoprene rubber are given in Table 18. I 5. Table 18.15 Reversion (R) in trans-polypentmamer~PR), natural rubber(NR) and polyisoprene rubber(IR)'
NR
IR "rPR ISAF black Oil Sulfur CBS b
100
100 100
50 6 2.3 0.7
50 6 2.3 0.7
100 100 50 12 1.8 0.3
MOW TMTD ~ R' 160~ 180~
52.8 58.8
46.5 57.3
16.0 16.8
50 6
50 6
100 50 12
I
I
1
2 0.1 21.5 39.4
2 0.1 16.2 34.0
2 0.1 9.3 13.2
'Data from reference s2; ~'N-Cyclohexyl-2-benzothiazole sulphenamide;'~lMorpholmyl-2-benzc~iazole sulphenanude; d~retramethylthiuram disulphide; "R=[ I - o ~.,o'.,6o o, ,,ooclo 3oo ~
,,~.c].
It may be noted that both at 160~ and 180~ the reversion in the transpolypentenamer cure was much smaller than for natural and polyisoprene rubber. On the other hand, Dall'Asta ~3 found that special formulations containing very low sulphur and accelerator levels induced rapid cure without appreciable reversion and simultaneously yielded vulcanizates characterized by high tensiles and moduli and low heat buildup (Table 18.16). Even lower heat build up have been recorded by employing low levels of sulphur donor/accelerator formulations with the same carbon black and oil load (Table 18.17). Using a computed regression analysis method, Haas and Theisen ~~ examined the influence of different vulcanization parameters on the vulcanizate properties of the tire tread stocks. In the course of their studies they calculated the tensile strength, the elongation at break, the compression set, and the abrasion resistance as functions of the dosage of
1190 Table 18.16 Physical-nmdmnical and dynamic propertiesof trans-polypemenamer rubber (TPR) v u l c a n ~ at different times of cure ~b Time of cure t min
20
40
60
80
12(
TS, kg/cm 2 EB, % 200% Mod., kg/cm 2 300% Mod., kg/cm 2 H(IRHD) Tear strength, kg/cm H B U AT, ~ (I00~
188 460 47 103 62 43 22
178 400 50 108 64 40 20
180 420 50 108 64 40 22
170 380 50 114 64 42 22
17( 40( 50 11( 64 38 22
9Dat~a from reference"; b Recipe: TPR 100, PBNA 1.5, Stearic acid 2, ZnO 5, Circosol 4240 oil 30, ISAF black 50, MBTS 0.7, TMTD 0.7, S 0.75, ML 1+4 (100~ 72, cure at 140 ~
Table 18.17 Physical-mechanical and dynamic properties of trans-polypentenamer rubber (TPR) vulcanizates at different times of cure ~b Time of cure~ mm
20
40
60
80
120
TS, kg/cm 2 EB, % 200% Mod., kg/cm~ 300% Meal., kg/cm ~ H(IRHD) Tear strength, kg/on HBU AT, ~ (100~
77 540 16 31 39 21
179 360 61 132 65 44 19
178 360 60 134 64 42 21
183 360 65 139 64 44 19
175 360 62 128 64 44 19
==
9Data from reference53, ff Recipe: TPR 100, PBNA 1.5, Stearic acid 2, ZnO 5, Circosol 4240 oil 30, ISAF black 50, MBTS 0.5, TMTD 0.5, Sulphasan R 1.5, ML 1+4 (100~ 72, cure at 140 ~ zinc oxide and stearic acid on the vulcanization temperature, at constant sulphur and accelerator levels. The above authors calculated simultaneously these properties as a function of the dosage of sulphur and CBS accelerator
1191 on the vulcanization temperature, both at constant zinc oxide and stearic acid content. The most important result deduced from this approach was that the optimum properties for trans-polypentenamer vulcanizates are obtained at a high vulcanization temperature (170~ with low zinc oxide, stearic acid, and accelerator, and medium (2 phr) sulphur content. By studying the vulcanizate properties, Meissner 5~ observed that trans-polypentenamer cured with dicumyl peroxide exhibited very high cross-linking efficiency, as compared to other elastomers. This result is in agreement with previously reported data on the sulphur cure of transpolypentenamer. He ascribed the high efficiency to an exceptionally high content of physical bonds in the polymer. Accordingly, Meissner found also a very high Mooney-Rivlin (C2) constant. Significant kinetic results on the strain-induced crystallization of a dicumyl peroxide cured trans-polypentenamer as a function of temperature and strain were published by Kraus and Gruver. ~5 Interestingly, they employed a combined birefringence and stress relaxation technique which showed to be more reliable for rapidly crystallizing materials than the stress relaxation technique alone. From their data the above authors confirmed the high crystallization rate of trans-polypentenamer already observed for unvulcanized material. They found that both the rate and degree of crystallization strongly depend on temperature, on the strain rate, and on the degree of undercooling. Elevated tensile strength results to be a consequence of the strain induced crystallization. Typical stress-strain curves at different strain rates are given in Figure 18.16. kg/~:rn2
1
140
\
120
~
"'-,,, \,,
I O0
3
\
80
B
~
60 4O 2O ~
T
0 I
2
3
*
il
4
5
9 6
9
7
9
8
&
9
Figure 18.16. Influence of strata rate (a) on stress-strata curves (~.) for trans-polypentenamer(at 10~ (1- R = 0.002 sot"; 2 - R= 300 sec"~) (Adapted from Ref.~).
1192 It was inferred that the degree of crystallization does not exceed 10 per cent and, consequently, the tensile strength is not as high as that of natural rubber. This result was assigned to the relatively low trans content of the polymer. Also, the Avrami indices found by Kraus and Gruver were generally low, thus indicating prevalence of linear crystallite growth from pre-existing nuclei. Measurements on the stress-temperature dependence were carried out by Flisi et al.56 in their studies of the stress-induced crystallization of trwLs-polypentenamer vulcanizates. In addition to gums, also reinforced and pigment-filled materials have been investigated. In these studies, dicumyl peroxide or two different conventional sulphur formulations characterized by mono- and polysulphide cross-links, respectively, have been employed. Interestingly, the plot of melting points as a function of elongation and the thermodynamic parameters (fusion enthalpy and entropy) were found to be independent of the curing formulation and of the presence of fillers. Also, it Stress,kg/cm2 2
200 .~ . . . . . . -
...
.o....-~
100
i
.....-
...~
50
1
2
3
4
~5
6
7
e
....
9
(I
Figure 18.17. Stress-strain curves of peroxide cured 85% trans-polypmtenamer gum at various temperatures (Adapted from Ref.~.
1193 was observed that high crystallization tendency confers an undesired stiffness to trans-polypentenamer at low temperatures. This fact is dearly pointed out by the stress-strain curves at various temperatures illustrated in Figure 18.17. It was outlined that the upturn of the stress-strain curves at high elongations, characteristic of stress-crystallizing elastomers, was in the reported ease much weaker than for natural rubber at the same temperature. This finding was attributed to the relatively low trans content of the polypentenamer and consequently to the low degree of crystallization. In similar studies, carried out by Natta, Dall'Asta and Mazzanti, s7 it was found that trans-polypentenamer gum vulcanizates show steep upturns of the stress-strain curve and high tensile strength provided that very high trans content is present in the polymer (Figure 18.18). Stress, k ~ c m 2
250 -
200
I
-
/ t
150
-
J
t
I
I / /
2
/
/
f
I
'
/
IOO
/ ~ J ft i/ /
jf /
f/
!
50 ~d O I~
2~
3~
4~
500
~0
7~
8~
~10
2
Figure 18.18. Stress-strata curves of sulphur vulcanized 90% trans-polypmtenamer (1) and vulcanizate reinforced with 50 phr HAF black (2) (Adapted from Ref.~7). However, such a strong crystallization tendency is not always desired because of the resulting stiffness below room temperature. Therefore, a compromise is necessary to conciliate good mechanical and processing properties with acceptable low temperature characteristics. To solve this
1194
problem three approaches have been proposed by Haas and Theisen s~ (i) an intermediate trans content of the polymer, (ii) use of the crystallizationhindering plasticizers and (iii) high trans content of the unvulcanized polymer to be used in the compounding and processing operations where rapid stress crystallization is necessary followed by lowering of the trans content by any way during the vulcanization process. In this connection, Gunther and coworkers s~ showed that trans to cis isomerization of the double bonds in the polymer occurred to a certain extent when zinc stearate was employed as the activator in sulphur vulcanization. The strong reinforcing effect induced by carbon black on the transpolypentenamer vulcanizates can be readily pointed out if stress-strain values of pure 90~ trans-polypentenamer gum and filled vulcanizates are compared. It is significant that even at high oil and carbon black loads a set of remarkable physical-mechanical and dynamic properties of the transpolypentenamer rubber are retained as illustrated in Table 18.18. Table 18.18 Influence of oil and carbon black loadmgs on the physical and mechanical properties of trans-polypentmamer vulcanizates ~b
Values
Component/Property
Circosol 4240, phr ISAF black, phr Sulphur, phr MLMB 1+4 at 100~ TS, kg/cmz EB, % M~oo, kg/cmz M~3o, kg/cm2 H, IRHD HBU at 100~ At, ~
25 50 0.75 82 194 380 48 122 70 25
25 50 1.0 82 185 380 52 138 71 24
50 75 0.75 63 176 390 47 l l6 74 37
50 75 1.0 63 181 380 5g 133 74 32
75 100 0.75 57 146 410 43 92 60 36
75 100 1.0 57 154 400 48 lOl 60 30 |
9Data from reference ~; b Recipe: Polymer (ML 1+4 = 72) 100, PBNA 1.5, Stearic acid 2, Zinc oxide 5, Circosol 4240 oil and ISAF black as indicated, MBTS 0.7, TMTD 0.7, Sulphur as mdic,atod, cure 40 mm at 140~ As already mentioned
above, tram-polypentenamer vulcanizates
1195 undergo a certain amount of static crystallization when stored at low temperatures. In order to evaluate how far this phenomenon could affect the low temperature performances of trans-polypentenamer, Jahn 52 investigated the behavior of several rubbers at low temperature. Data recorded on the variation of the Shore hardness of tire tread formulations of trans-polypentenamer, butadiene rubber and styrene-butadiene rubber with temperature are illustrated in Figure 18.19. Shore A
1oo1"~'hx', 9~ 1
~176
70 ,,,.m
o
~
~
~
~
Q'O e O B 0 0
-60
-40
-20
0
20
40
60
80
!00
120
,
o
BIP
~
~
9O O O O l l ,
140
160
Temp., ~ Figure 18.19. Variation of Shore hardness with ten'~mture for trans-polypentenamer(1), cis-polybutac~me(2) and styreno-butadiene rubber (3). Recipe polymer 100, ISAF 75, aromatic oil 40 (Adapted from Ref.S2). As it can be noted, the increase of hardness below O~ was much stronger for trans-polypentenamer than for cis-polybutadiene but similar to that of styrene-butadiene rubber. Analogous results were recorded on the dependence of rebound and compression set on the temperature for trans-polypentenamer and butadiene and styrene-butadiene rubbers. The variations of rebound resilience with temperature for trans-polypentenamer, cis-polybutadiene and styrene-butadiene rubber are represented in Figure 18.20 whereas the dependence of the compression set with temperature for these three polymers in Figure 18.21.
1196
% 50
40
30 20 10
-40
40
O
80
120
160
Temp., ~ Figure 18.20 Variation of rebound resilience with temperature for trans-polypemenamer (1), cis-polybutadieae (2) and styrene-butadiene rubber (3). Recipe: polymer 100, ISAF 75, aromatic oil 40 (Adaptod from Ref.n).
% 100 -
2
/
I
,r
.
9
f
10"'k
-60
-40
-20
0
"
m'
20
9
40
9
60
9
80
i
9
l
100 120 140
9 --
180
Temp., ~ Figure 18.21. Compression set as a function of te~erature for transpolypentenamer (1), styrene-butadiene rubber (2) and cas-polybutadiene (3)
(Adapted from Ref.S2).
1197
From inspection of Figures 18.20 and 18.21, it is obvious that these properties are better for trtms-polypentenamer than for butadiene and styrene-butadiene rubbers above 10~ It is important for its application in tire building that transpolypentenamer is a highly abrasion resistant rubber. On comparing tire tread stocks for several rubbers, trans-polypentenamer appears definitely superior to natural rubber, isoprene robber, or styrene-butadiene rubber, similar to styrene-butadiene~utadiene rubber (1:1) and somewhat inferior to butadiene rubber. Conversely, the wet skid resistance of transpolypentenamer tire treads is inferior to that of natural rubber, isoprene rubber, and styrene-butadiene rubber, but exceeds that of butadiene rubber or styrene-butadiene/styrene rubber (1:1). Surprisingly, trans-polypentenamer exhibits a low air permeability as compared to other rubbers. However, according to Jahn, 52 air permeability of trtms-polypentenarner decreases considerably with increasing filler content. Thus, at very high extension degrees, the value of air permeability for trans-polypentenamer are lower than those of ethylenepropylene-diene rubber, isoprene rubber, and butadiene rubber and approaches that of butyl rubber. Another remarkable property of trans-polypentenamer is the fairly good aging resistance. Relevant data on the variation of tensile strength and elongation at break of trans-polypentenamer at prolonged heating under air were reported by Dall'Asta 49 (Table 18.19). Table 18.19 Tensile strength (TS) and elongation at break (EB) during air aging of t r a n s pol~~Jmamer butadiene rubber and styrene-butadiene rubber vuleanizates~~ Polymer S phr Initialvalue 2 Days ~ 4 Days~ 8 Days' 20Daysd TS EB TS EB TS EB TS EB TS EB TPR 1.0 204 480 103 71 105 63 108 62 101 50 1.4 210 400 105 75 99 67 84 52 93 50 BR 1.0 190 520 83 63 83 58 83 52 49 27 1.4 220 500 77 60 78 54 73 44 50 24 SBR 1.4 295 590 103 78 100 68 93 61 92 51 2.0 320 480 90 73 83 60 81 56 74 42 'Data from rerfOl'~ee49, bAt 100~162 Polymer 100, Flectol H 1.5, Stearic acid 2, Zinc oxide 5, HAl: black 50, CBS 1.0, Sulphur as m d i ~ , Cure: TPR and BR 40 mm at 150~ SBR 60 min at 150~ as percent of initial value.
1198
It is noteworthy that comparison of the black reinforced transpolypentenamer, butadiene rubber and styrene-butadiene rubber stocks, vulcanized with two sulphur amounts, revealed a much better behavior of trans-polypentenamer with respect to butadiene rubber and at least equivalent to styrene-butadiene rubber. This behavior was assigned to the trans structure of the double bonds rather than to the lower content of double bonds if compared to butadiene rubber. Also, of great significance is the considerable stability of transpolypentenamer to UV irradiation. 5s In contrast to 1,4-polybutadiene, which undergoes trans/cis isomerization as well as chain mission under the action of UV irradiation, trans-polypentenamer shows only trans/cJs isomerization, but no appreciable chain mission. This particular behavior was attributed to the fact that the mission of the bond between two ormethylene groups yields two allylic radicals in the case of 1,4polybutadiene, but only one in that of polypentenamer, thus conferring higher bond strength to the latter. Most interestingly, trans-polypentenamer exhibits ozone and weathering resistance, both of which are exceptionally high for a largely unsaturated polymer. It is remarkable that crack formation under static ozone attack or under outdoor weathering, in the presence or in the absence of antiozonants and antioxidants respectively, occurs in transpolypentenamer after very much longer times than in natural rubber and nearly at as long times as for chloroprene rubber. Significantly, the resistance of trans-polypentenamer rubber to dynamic crack formation under ozone attack (De Mattia dynamic flex cracking) obviously turns out best as compared to natural rubber, butadiene rubber, natural~utadiene rubber, styrene-butadiene rubber or styrene-butadiene/butadiene rubber, in the presence as well as in the absence of anitozonant compounds. Of particular significance for its application, trans-polypentenamer is compatible and covulcanizable with several other diene rubbers, including natural rubber, isoprene rubber, butadiene rubber and styrene-butadiene rubber, as well as even with ethylene-propylene-diene terpolymer. Using light scattering combined with diffiasion techniques, H o f f m a n n s9 examined the compatibility of trans-polypentenamer with cis-l,4-polybutadiene whereas Schnecko and Caspary~ applied a viscosimetric method for this study. Despite the different configurations of the double bonds in these polymers, both methods revealed a high compatibility between the two rubbers. Of a special interest are trans-polypentenamer/isoprene rubber and trans-polypentenamer/ethylene-propylene-diene rubber blends. In the first
1199
of these two blends, trans-polypentenamer confers green strength to isoprene rubber which is lacking to the latter, whereas, conversely, isoprene rubber improves the tear strength of the trtms-polypentenamer blend. On the other hand, trans-polypentenamer in the second blend may solve some difficult problems which still hinder the application of ethylene-propylenediene terpolymer in the tire field. Thus, it was found that small amounts of trans-polypentenamer in ethylene-propylene~ene terpolymer improve building tack of the latter, this effect being markedly more than additive in the blend. However, a proper adjustment of the vulcanization formulation is needed to achieve good covulcanizability of transpolypentenamer/ethylene-propylene-diene rubber blends. This propensity has been evidenced by following the reciprocal equilibrium swelling of the two components as a function of the blend composition. Applications and economic lspects. Due to the excellent properties of trtms-polypentenamer, this product has a large area of applications as general purpose rubber, including tires and rubber articles. Here the polymer displays a high tack, green strength and abrasion resistance as well as good processability and extendability. trans-Polypentenamer can be applied in compositions with various diene rubbers exhibiting good compatibility and co-vulcanizability. Thus, it is compatible with natural rubber, polyisoprene, polybutadiene and butadiene-styrene copolymer as well as ethylene-propylene--diene terpolymer yielding various compositions suitable for tire and rubber industry, trat~-Polypentenamer confers to these blends high abrasion and aging resistance, superior elasticity and low air permeability. Reversion and aging resistance make it a good candidate for various applications at higher temperatures. Its characteristics open a very promising field of application as a rubber basis for high impact polymers such as polystyrene, ABS copolymers and poly(vinyl chloride). Several companies pursued development programs at pilot and semiindustrial plant level aimed toward tire applications but changes in petroleum feedstock availability and costs resulted in the discontinuation of these programs. Notwithstanding, at present, studies for improving the costs and technologies for cyclopentene production are in course in many research groups. Moreover, the wealth of information about the synthesis, structure and properties of trans-polypentenamer renders this polyalkenamer of a special interest for its application in various technologies in the near future.
1200 18.2.2. c/s-Polypentenamer
The compounding and processing properties of cis-polypentenamer considerably differ from those of trans-polypentenamer, but markedly resemble that of cis-polybutadiene and of cis-polyoctenamer. Thus, cispolypentenamer is not easily compounded at room temperature. The bank is largely tacky and lacy with tearing edges. At slightly higher temperature it becomes dry and brittle. It was found that only when operating at 80-100~ are common fillers and ingredients incorporated and homogeneously dispersed. This compounding and processing behavior was ascribed to the conformations around the cis double bonds and the adjacent single bonds rather than related to glass and melting temperatures. 6~ Analogously, the vulcanization behavior and vulcanizate properties of cis-polypentenamer rubber differ substantially from those of transpolypentenamer. The absence of stress crystallization at room temperature, owing to the low melting point (-41~ and to the slow crystallization kinetics, fails to confer to cis-polypentenamer adequate properties, like green strength and tack, characteristic of trans-polypentenamer. For this reason, the green properties have not been investigated in detail. Vulcanization of cis-polypentenamer occurs with conventional sulphur and sulphur donor compounds. It was observed that the rubber is fast curing and, even with small amounts of sulphur, it reaches a pronounced level in reasonable times (Table 18.20).
Time min
Table 18.20 Cure rate of ci.s, ,olyoctenamer~b 3OO% 200% Elongation Tensile % Modulus Modulus streagth kg/cm 2
kg/gm 2
10 20 40 60 80 120 180
1040 530 490 490 520 510 560
113 147 144 149 154 147 164 9
22 66 71 72 72 68 65
15 37 37 38 38 37 35 |
Hardness
IRHD
49 63 63 63 63 63 62
|J
' Data from reference6'; b Recipe: Poi ner ]oo, PBNA 1.5, 'Stearie acid 2, Zinc oxide 5, ISAF black 50, C i r r i 4240, 40 CBTS 0.8, S 1.25, Cured at 1500C.
1201 Examination of the physical-mechani~l properties of cispolypentenamer revealed that, generally, the polymer properties are not as good as those of trans-polypentenamer at room temperature. However, Minchak and Tucker 6z showed that cis-polypentenamer of high molecular weight exhibits good physical properties when extended with high levels of oil dilution and of carbon black reinforcement. The best performances are usually attained by cis-polypentenamer at low temperatures. Some relevant physical-mechanical properties of carbon black reinforced cispolypentenamer vulcanizates are compared in Table 18.21 for various temperatures in the range from +23~ to -90~ 6z
Table 18.21
Physical properties of cis-polypentmamer vulcanizate at various teng>eratures*
Temperature, ~
Tensile, kg/cm2 Elongation, % 100% Modulus, kg/cm2 200% Modulus, kg/cm2 300% Modulus, kg/cm2 Tear strength, kg/cm
+23
-20
-50
-70
-90
168 500 24
148 420 25 53 93 50
225 490 32 64 113 53
284 490 37 79 142 82
392 495 61 126 213 133
48 88
51
9 Data f r o m reference. 6z
It is noteworthy that the strong increase of the tensile strength and moduli is not accompanied by appreciable variation of the elongation at break, this fact indicating high elastomeric performances rather than stiffening of the material. The excellent properties of cis-polypentenamer at low temperatures are fully illustrated when comparing the dependence of the 100% modulus (Figure 18.22), the compression set (Figure 18.23), and the plot of hardness (Figure 18.24) as a function of temperature for various rubbers (e.g., transpolypentenamer, styrene~utadiene rubber 1500, polypropylene oxide,/allyl glycidyl ether and cis-1,4-polybutadiene). 63
1202 M ,oo, kg/cm2
200
/ t ./
100
4
5O
-70
-40
-20
-0
20
Temp., ~ Figure 18.22. Variation of 100% modulus with temperature for various elastomers (1-trans-Polypentenamer; 2- Styrene~utadiene Rubber 1500; 3-Polypropylene Oxide/Allyl Glycidyl F~er; cis-l,4-Polybutadiene; 5-cis-Polypentenamer) (Adapted from Ref.63). Compression, % 4
loo
80
60
I
1 / "
40 I
I
20
O
/
9
-80
9
-70
9
-60
a
-50-40
9
a
-30
f
9
-20
9
-10
9
0
,,
9
!0
20
A
30
Temp., ~ Figure ] 8.23. Dependence of compression set as a function of temperature for different rubbers (]-cis-Polypentenamer; 2-cis-Po]~outadiene 80%; 3-Smok~
Sheet; 4-Styrene/Butadiene Rubber). Conditioning 22 hr, Relaxation 30 mm (Adapted from Ref.63).
1203 Shore A 100
4
90
80
2
7O 6O
50 -80-70
-60-50-40-30
-20 -10
0
10
20
30
Ten~., ~ Figure 18.24. Variation of Shore A hardness with temperature for various rubbers
(l-cis-Polypemenamer; 2-cis-Polybutadiene; 3-Smoked Sheet; 4-StyreneJButadiene Rubber); Conditioning 70 hr (Adapted from Ref.63). It is obvious that cis-polypentenamer exhibits a much better low temperature behavior than general purpose rubbers, like natural rubber, styrene-butadiene rubber, or trans-polypentenamer, and displays even superior properties to the known low temperature rubbers, like cis-l,4polybutadiene and propylene oxide/allylglycidyl ether copolymer. 18.2.3. c/s-Polyoctenamer
cis-Polyoctenamer displays a series of particular physical properties. Thus, high cis-polyoctenamer has the same melting temperature as transpolypentenamer but exhibits a considerably higher crystallization rate at room temperature." To diminish the excess crystallization at room temperature, it is preferable to reduce the proportion of cis configuration to about 75-80%. Furthermore, the glass transition temperature (T o is lower (- 108~ than that of the trans-polypentenamer. cis-Polyoctenamer has poor processing properties, especially at temperatures below 100~ In these conditions, and particularly when the
1204 intrinsic viscosity of the polymer markedly exceeds [11] = 2, the material is dry and brittle and it is difficult to be processed. However, at temperatures between 100~ and 120~ it can be compounded with fillers, ingredients
and oil and the mixes are quite homogeneous. Significantly, sulphur cure is fast even at low sulphur doses. The influence of different oil loading on the vulcanization behavior and on some of the physical and dynamic properties of cis-polyoctenamer is illustrated in Table 18.22.
Table 18.22 Influence of oil loadmg on the cure behavior and physical-mechanical properties of cis-polyoctenamer '~b
Parameter
Sundex 790, phr Compound ML 1+4 at 100~ T2, mm T90, mm AL, m.lb Tensile, kg/cm2 Elongation, % M~0, kg/cm2 M3oo, kg/cm~ D1,% HIRHD HBU at 100~ A~
Value
72 7.5 32.5 95 182 340 77 160 5 75 26
5 62 10 37.5 90 189 370 76 152
I0 54 10 28.5 84 172 370 61 131
20 41 12.7 32.5 74 165 400 45 100
4
4
4
74 23
71 20
68 19
'Data from reference~9; I' Recipe: Polymer i00, SWC 0.5, ~;tearic acid'2, zinc oxide 5, ISAF black 50, Sundex 790 as indicated, Santocurr 0.8, Sulphur 1.0, Monsanto rheometer at 150~ Vulcanization 40 mm at 150~
Examination of the physical and dynamical properties of the reinforced cispolyoctenamer shows that the performances are similar to those of the conventional general purpose rubbers. The dependence of the elastomeric properties of cis-polyoctenamer with temperature is illustrated in Table 18.23.
1205 Table 18.23 Variation of physical properties of cis-polyoctenamer vulcanizates with temperature ~b Temperature ~
Tensile strength kg/cm2
Elongation %
M200 k~n 2
M200
M300
kgcm
kg/. 2
70 50 23 0 -10 -20 -40 -50
117 139 161 157 192 207 300 310
360 360 360 360 360 370 380 360
24 25 23 22 27 41 115 135
57 59 60 70 93 123 200 218
104 107 119 136 168 193 256 283
'Data from refermce~ b Recipe:Polymer 100, SWC 0.5, Stearic acid 2, Zinc oxide 5, Nocton 10, I S , ~ 50, Sant~ure 0.8, Sulphur 1.0, Vulcanization 40 ~ at 150~ It is relevant to note that like cis-polypentenamer, cis-polyoctenamer does not exhibit significant variation of the elongation at break with temperature in the range of +70~ to -50~ However, unlike cis-polypentenamer, as it can be noted from the above data, the 100% modulus of cis-polyoctenamer considerably increases below -10~ this fact indicating rubber stiffening. Also, it is of interest to compare the aging resistance of cispolyoctenamer with that of several rubbers such as trans-polypentenamer, cis-1,4-polybutadiene and styrene-butadiene copolymer (Table 18.24). Table 18.24 Aging resistance of cis-polyoctenamer(COR)and several rubbers L~' |
Aging
TPR
COR
BR
SBR 15O0
days TS 4 8 16
93 86 83
69
TS
E
105 108 96
63 63 50
TS
E
TS
E
83 58 114 72 50 83 52 110 63 45 66 38 108 60 ' Aging resistance m air at 100~ ' Values of TS
' Data from reference' (tensile) and E (elongation) are percent of the original values.
1206 It is obvious that the behavior of cis-polyoctenamer is intermediate between that of cis-l,4-polybutadiene, on one hand, and trans-polypentenamer and styrene-butadiene copolymer, on the other hand. The higher aging resistance of cis-polyoctenamer compared to that of butadiene rubber was attributed to the lower content of double bonds in the former polymer while the lower aging resistance compared to that of trans-polypentenamer was assigned to the different configurations of the double bonds of the two polymers. From careful examination of the physical-mechanical properties of cis-polyoctenamer, it may be concluded that this rubber is to be considered as a special purpose rubber of the butadiene rubber type. However, in comparison to butadiene rubber, it displays poorer low temperature performances, but better aging resistance and stress crystallization (green strength).
18.2.4. Cyclorene Rubber A new flame resistant chlorine-containing elastomer that can be readily vulcanized with sulphur-based curatives has been developed since 1973 using as a monomer the Diels-Alder product of hexachlorocyclopentadiene with 1,5-cyclooctadiene. 65 This compound was copolymerized with additional 1,5-cyclooctadiene to give a family of copolymers with variable microstructures, chlorine content, melting points and glass transition temperatures as well as with a high solvent resistance (Eq 18.6). O
Due to its good solvent and weathering resistance, this product appeared to be capable of replacing polychloroprene (Neoprene) in many applications. Importantly, the copolymers thus manufactured showed to be compatible with conventional diene elastomers and could be vulcanized by sulphur and common sulphur donor curatives.
1207
18.3. Potential Applications Conventional and new polymers have become more and more accessible with the development of the versatile processes of ring-opening metathesis polymerization of cycloolefins.
18.3.1. Synthesis of Monodispersed Polyethylene Linear, monodispersed polyethylene is an extremely important practical and synthetic goal and provides the challenge of preparing essentially monodispersed, linear 1,4-polybutadiene. At present low polydispersity polyethylene is produced by the hydrogenation of 1,4polybutadiene prepared by the anionic polymerization of butadiene. However, this approach results in a somewhat branched polyethylene, since the 1,4-polybutadiene prepared by anionic polymerization generally contains C2 branches as a result of low levels of 1,2-polymerization of butadiene. With the advent of well-defined transition metal alkylider~e and metallacyclobutane complexes for living ring-opening metathesis polymerization (ROMP) of cycloolefins, synthesis of monodispersed, linear 1,4-polybutadiene by ring-opening metathesis polymerization of cyclobutene became feasible. Interesting studies by GnJbbs and coworkers ss showed that 1,4-polybutadiene with a polydispersity index of 1.03 can be manufactured by ring-opening polymerization of cyclobutene under the action of the alkylidene complex W(=CH'Bu)(=NAr)(O~Bu)2 (Ar=2,6diisopropylphenyl) in the presence of PMe3. Further hydrogenation of 1,4polybutadiene in the presence of appropriate hydrogenation catalysts will produce linear, low polydispersity polyethylene (Eq. 18.7).
18.3.2. Synthesis of 1,4-Polybutadiene 1,4-Polybutadiene is produced on a large industrial scale by anionic polymerization of 1,3-butadiene, under various conditions. The polymer obtained by this procedure contains generally a low level of C2 branched as a result of 1,2-polymerization of the monomer. An alternative, efficient route to prepare linear, monodispersed 1,4-polybutadiene, with a high steric
1208 purity, is available by ring-opening metathesis polymerization of cyclobutene, 1,5-cyclooctadiene and 1,5,9-cyclododecatriene 67 (Eq. 18.8). - -
(18.8)
The reaction is promoted selectively to cis-l,4-polybutadiene by TiCI,/Et3AI. 6~" Other catalysts such as TiCI4/(~-C,HT)4Mo, 6~ V(acac)3fEt3Al, 67c Cr(acac)3/Et3Al, 67c MoCI3/Et3AI,67c VCI4/BuLi, 67d MoCIs/(Tt-CaHT)4W,67e MoCIs/(Tt-C4H7)2Mo,67e WCl6/(~-c4n7)4W, 67e RuCI3,6?f Ph(MeO)C=W(CO) 5,67g Ph2C=W(CO)56"th and Mt(=CH'Bu)(=NAr)(O'Bu)2 (Mt = Mo or W, Ar=-2,6-diisopropylphenyl) 67iJ may give trans- or cis-l,4-pelybutadiene, depending on the catalyst and reaction conditions. With the availability of 1,5-cyclooctadiene and 1,5,9cyclododecatriene on the industrial sc~e by cyclodimerization and cyclotrimerization of butadiene, respectively, this method becomes of a great commercial interest.
18.3.3. Synthesis of 1,4-Polyisoprene Due to its outstanding elastomeric properties, synthesis of 1,4polyisoprene has stimulated intensive research work for a long period of time. Recent developments in the ring-opening metathesis polymerization catalysts prompted interesting studies for the synthesis of 1,4-polyisoprene by ring-opening metathesis polymerization of l-methylcyclobutene 68 and 1,5-dimethyl- 1,5-r 69 (Eq. 18.9).
(18.9)
1209 Polymerization of l-methylcyclobutene in the presence of the tungstencarbene catalyst Ph2C=W(CO)5 has been conducted by Katz and coworkers 6t" to appreciable yields of 1,4-polyisoprene having cis configuration at double bonds of ca. 90%. More recently, Wu and Cn'ubbs6~' prepared polyisoprene having an exclusively cis and head-to-tail structure by polymerization of l-methylcyclobutene with the well-defined alkylidene complexes of the type Mt(=CH(CH3)2R)(=NAr)(OC(CH3)n(CF3)3.~)2 (At = 2,6-diisopropylphenyl, Mt = Mo, R - Ph, n = 2). The polymer thus prepared showed properties similar to natural rubber. Unfortunately, at present the manufacture of 1,4polyisoprene through this procedure is limited by the availability of the starting materials, 1-methylcyclobutene and 1,5-dimethyl-1,5cyclooctadiene.
18.3.4. Alternating Copolymers Ring-opening metathesis polymerization of substituted cycloolefins afford a unique method for the synthesis of perfectly alternating copolymers of olefins. Starting from a substituted cyclobutene, a substituted polybutenamer can be prepared in a first step which by subsequent hydrogenation will provide the corresponding copolymer of the linear olefins. Thus, by ring-opening polymerization of 3-methylcyclobutene, in the presence of classical WCl6-based catalysts, poly(3-methylbutenamer) is obtained which by subsequent hydrogenation in the presence of Pd/C catalysts will form the alternating copolymer of ethylene and propylene 7~ (Eq. 18.10).
\ n U
[V l "-
~"-
(18.1@
Similar reactions of 3-ethylcyclobutene will produce the alternating copolymer of ethylene and l-butene whereas those of 3-propylcyclobutene will give rise to the alternating copolymer of ethylene and l-pentene. Alternating diene copolymers have been readily prepared by ringopening polymerization of monosubstituted 1,5-cyclooctadienes (R= CH3, C2H5, CI) in the presence of the ternary metathesis catalysts based on WCIffEtOH/EtAICI2.69 Interestingly, when the substituent was a CH3 group, the alternating copolymer of butadiene and isoprene was formed
1210 (Eq. 18.1 l) n
=
(18.11)
whereas when it was a chlorine atom, the alternating copolymer of butadiene and chloroprene was produce~ (Eq. 18.12). n
Cl
ROMP
(18.12)
If the starting material is 1,2-disubstituted 1,5-cyclooctadiene, an alternating copolymer of butadiene and disubstituted butadiene can be prepared. Obviously, the ring-opening reaction occurs at the more reactive, unsubstituted double bond of the cycle, due to the strong steric hindrance exerted by the substituents at other double bond.
18.3.5. Block Copolymers There are at present several experimental techniques which can be used to produce block copolymers from cycloolefins. The most straightforward synthesis that uses living systems derived from well-defined transition metal alkylidene and metallacyclobutane complexes involves growing the homopolymer with a desired molecular weight of one monomer and continuing the process with a second monomer until a final structure and molecular weight of the copolymer is obtained. A large number of diblock and triblock copolymers with very low polydispersities have been prepared by this method. Some examples are selected from the extensive work by GnJbbs and coworkers 7~ on the synthesis of diblock and triblock copolymers of norbornene with exo-dicyclopentadiene and benzonorbornadiene under the action of titanacyclobutane catalysts (Eq. 18.13-18.14). [ri]
...-~..--~
(18.13)
1211
[Til
"-----.--!~
(18.14)
as well as by Schrock and coworkers ~ on the synthesis of diblock and triblock copolymers of norbornene with substituted norbomene or polycyclic olefins in the presence of Ta, W and Mo catalysts (Eq. 18.15).
nf .m t
(1815)
l
Of a special interest are the block copolymers from halogen-n or ferrocene-containing monomers 74 in the presence of the Mo-alkylidene complex Mo(---CH'BuX=NAr)(OtBuh (Eq. 18.16-18.17).
n
+
[Mo]
m
--
F3C
(18.16)
CF3 F3C
9rn
Fe
, p
CF3
(1817)
1212 By this procedure, copolymerization of norbomene-like monomers having transition metals or main group metals, electroactive groups, etc. leads to products of potential use. Thus, block copolymers prepared from 5(ferrocenyl)-norbornene and 5-(trialkoxysilyl)norbomene were attached to electrode surfaces; redox-active materials with specific morphologies and prescribed dimensions were manufactured by this way. Block copolymers could be prepared by grafting living ring-opened polymers onto polymers that contain carbonyl groups, a method that takes advantage of the Wittig-like alkylidene transfer reactions 75 (Eq. 18.18).
According to several procedures, blocks that are not prepared by ring-opening metathesis polymerization could be added to ring opened polymers to provide a wide range of block copolymers with varying properties. Relevant examples reported GnJbbs and Risse, ~6 for instance, by growing a second block on a ring-opened polymer of norbornene by the use of group transfer polymerization (Eq. 18.19). (18,10) I
I
-2,-2
The silyl vinyl ether block can be modified by cleaving off the silyl groups. Treatment with tetrabutylammonium fluoride results in the formation of the hydrophobic-hydrophilic AB-diblock copolymer with poly(vinyl alcohol) as hydrophilic segment (Eq. 18.20). H
H
-S-
-S-
H
H
CH
O-t
1213 These block copolymers can potentially be applied as emulsifiers, flocculants, wetting agents, foam stabilizers and as polymeric dispersants for the stabilization of polymer blends. On coupling the anionic polymerization with ring-opening metathesis polymerization, Amass and coworkers ~ prepared block copolymers of styrene and cyclopentene (Eq. 18.21)
n
euLi
.=
Bu
"
mo
B
WCl6=
'[VV] (18.21)
and Feast and coworkers 7s grafted block copolymers of norbornene dicarboxylate with styrene (Eq. 18.22). o~ng:n,johcn~og~
Furthermore, changing the reaction mechanism from Ziegler-Natta polymerization to ring-opening metathesis polymerization, Cmabbs and coworkers ~9 prepared block copolymers of norbornene with ot-olefins in the presence of modified titanium catalysts (Eq. 18.23).
--- Cp2Tt-
,. yc.2H4
(
08.23)
CIMa
Graft copolymers of practical interest could be readily produced by the ring-opening metathesis polymerization of cycloolefins in the presence of unsaturated polymers bearing unsaturation in the side chains (Eq 18.24).
rn x +
P,,~tl
(182,4)
1214 Thus, Medema e t al. so grafted cyclooctene on the unsaturated branches of the natural rubber in the presence of ReCIs/EhAI, Pampus and coworkers s~ obtained graft copolymers by ring-opening polymerization of cyclopentene with 1,2-polybutadiene, butadiene, styrene-butadiene copolymer and ethylene-propylene-dicyclopentadiene terpolymer whereas, Scott and Calderon 82 prepared graft copolymers from ethylene-propylene-diene terpolymer and 1,5-cyclooctadiene. 18.3.6. Comb and Star Copolymers
Comb copolymers can be produced by ring-opening polymerization of mono- and disubstituted cycloolefins with moderate to long side chainss3 (Eq. 18.25).
coA
n
lc
M
~D.
~
(18.2b~
Icth H3C,(O42I
CO2(O4 I OH3
Such products behave like hydrogels and can take up a moderate amount of water. Synthesis of a large number of star copolymers s4 is possible by ringopening metathesis polymerization using well-defined metathesis initiators and a cross-linking agent (Eq. 18.26) p
p
P
Reactive alkylidenes such as living poly(5-cyanonorbomene) can be quantitatively converted into living star polymers, which upon treatment with relatively unreactive monomers like 2,3bis(trifluoromethyl)norbornadiene give "heterostar" copolymers, since all the sites in the star core serve as initiators.
1215
18.3.7. Amphiphilic Star Block Copolymers Synthesis of amphiphilic star copolymers that consist of a hydrophobic polynorbornene "core" and hydrophilic functionalized polynorbomene "shell" has been effected by Schrock and coworkers s5 (Eq. 18.27). p.
P
[MI
A variety of star copolymers can be made by this procedure with functional groups in the shell, in the core, or in both, to suit whatever application is desired. Such amphiphilic star copolymers behave as model micelles in aqueous solution.
18.3.8. Macrocyclic Compounds Ring-opening metathesis polymerization affords an elegant and simple way to prepare macrocyclic compounds of the carbocyclic type from cycloolefins. This method has several advantages as compared to multi-step conventional methods. In the presence of metathesis catalysts cycloolefins produce macrocyclic compounds of various size as a function of the nature of the cycloolefin, catalytic system and reaction conditions ~~ (Eq. 18.2S). R
(
- (~~. -~
R .... ._~ ,,
F [1~
R = ( ~ _ . ~ . .......
. . _ /(CH2)x (18.28)
(CH2)x
Thus, starting from cyclooctene, Wassermann and coworkers ~s prepared unsaturated carbocycles having up to 120 carbon atoms in the molecule. The reaction proceeded under mild metathesis conditions, in the presence of the catalytic system WCIdEtAICIJEtOH at 5-20~ in benzene as a solvent. By subsequent catalytic hydrogenation, the corresponding saturated
1216 carbocycles were synthesized. Carbocyclic oligomerization products were also obtained by Calderon and coworkers s~ in the ring-opening metathesis polymerization of cyclooctene with the WCIdEtAICI2 catalyst under special conditions. Interestingly, the higher unsaturation degree in 1,5-cyclooctene and 1,5,9-cyclododecatriene as compared to cyclooetene led to a higher amount of carbocyclic compounds. Significantly, the carbocyclic nature of the oliogomeric compounds produced in cyclooctene metathesis was elegantly demonstrated by Hocker and Musch ss by detailed chromatographic and spectrometric investigation of the reaction products. A wide range of unsaturated carbocycles were also produced by Wolovsky and Nirs9 by the metathesis reaction of cyclododeeene in the presence of WCl6-based catalysts. The unsaturated oligomers separated in the first stage were subsequently reduced to the corresponding monoolefins which were further subjected to oligomerization in the presence of the same catalytic system. Carbocycles with 24, 36, or 48 carbon atoms were readily synthesized by this procedure.
18.3.9. Conducting Polymers Synthesis of poly(p-phenylene) (PPP), a remarkable material with good thermal stability, chemical resistance and electrical conductivity when doped, has been reported by Caubbs and coworkers 9~ to occur from stereoregular precursors made by transition metal catalyzed polymerization. Thus, cis-5,6-bis(trimethylsiloxy)-l,3-cyclohexadiene was polymerized by the Ziegler-Natta-type catalyst bis[(allyl)trifluoroacetatonickel(ll)] to give exclusively 1,4-poly(cis-5,6-bis(trimethylsiloxy)-l,3-cyr which after deprotection to the corresponding hydroxy polymer, followed by acylation to the acetoxy polymer, produced high-quality poly(p-phenylene) by the pyrolysis of the acetoxy compound (Eq. 18.29). (18.29) TMSO ~
TM~
OTt~
HO
CH
/k~
O~
As ring-opening metathesis polymerization of cycloolefins produces directly polymers with carbon-carbon double bonds in the backbone, this reaction is an attractive and powerful synthetic route for the preparation of materials with desired electrical and optical properties. One interesting example is the synthesis of the new product poly(diisopropylideneeyclobutene), a cross-
1217 conjugated polymer, by ring-opening metathesis polymerization of 3,4diisopropylidenecyclobutene 9~ (Eq 18.30).
n
--•
rri] ._ MeOH'-
(18 30)
The polymer could be spin-cast, formed flexible films, and, upon doping, exhibited moderate conductivities (10 .3 S cm~). The doped material was brittle and insoluble, but these undesirable properties could be altered by forming block copolymers. It is of interest that blocking this product with polynorbornene yielded a rubbery material with more desirable mechanical properties, though the electrical properties after doping were similar to the homopolymer (Eq. 18.31). t~'li +
m--~
65=C
(18.31)
Two major approaches were developed for the synthesis of polyacetylenes by ring-opening metathesis polymerization of cycloolefins. A first approach is the ring-opening polymerization of suitable monomers such as cyclooctatetraene and substituted cyclooctatetraenes in the presence of the tungsten alkylidene complex W(=CHtBu)(-NAr)[OCMe(CF3h]2, reported by Grubbs and coworkers 92 (Eq. 18.32). R n
R ~
These reactions, especially that from substituted cyclooctatetraene, produced interesting and potentially useful materials, which might have valuable applications.
1218 Another important route, discovered by Feast and coworkers, 93 involves the preparation of a "precursor polymer" in a first step followed by "polyacetylene" synthesis upon thermal treatment in a second one. For instance, 7, 8-hi s(tri fluoromet hyl)t ricyclo [4.2.2.02"s]dec.a-3,7, 9-t riene (TCDT-F6] could be ring-opened by classical olefin metathesis catalysts to give a precursor polymer from which hexafluoro-o-xylene was eliminated upon heating to produce polyacetylene (Eq. 18.33).
n
CFa
[Mr]
CF3
A
F3
(18.33)
CF3
n F3C
CFa
Of a significant synthetic value is the finding of Schrock and coworkers 94~ who demonstrated that it is possible, by using the tungsten and molybdenum alkylidene metathesis catalysts, to prepare a homologous series of polyenes that contain up to 15 double bonds by the ring-opening polymerization of TCDT-F6 in a controlled manner (Scheme 18. l). n
F3
[Mt]
[Mt]
F3 I
r
F3C
CF 3
F3C
nQ F3C
CF 3
nQ
CF3
F3C
Scheme 18.1
CF3
1219 The first double bond was trans, and warts propagation mechanism dominated (~75%). When pivaldehyde was used in the Wittig-like reaction, a series of "odd" polyenes containing 2x+ 1 double bonds resulted. If 4,4dimethyl-trans-2-pentanal was employed, then the resulting polyenes contain 2x+2 double bonds. Since evidence was accruing that relatively short conjugated sequences could sustain a soliton and could have significant third-order nonlinear optical properties, it was of fundamental interest to produce well-defined unsubstituted polyenes. Interesting variations have been imagined, including capping with para-substituted benzaldehydes, and di-or trialdehydes. Polyenes can be manufactured in diblock or triblock copolymers combined with polynorbomene or similar polymers. For example, Stelzer et al. 97 prepared a block copolymer of polyacetylene and polynorbomene from benzotricyclo[4.2.2.02"5]deca-3,7,9-triene (benzoTCDT) and norbornene using a titanacycle catalyst (Scheme 18.2).
011
Schen~ 18.2
The living polymer obtained from the Feast monomer could be further blocked with polynorbomene. Thermolysis of this product eliminated naphthalene to give rise controllable block lengths of polyacetylene within a polynorbornene matrix. Schrock and coworkers 98 prepared triblock copolymers by adding norbornene to W(=CH'Bu)(=Nar)(OtBu)2, followed by TCDT-F6, and norbornene again. Further heating generated the polynorbornene/polyene/polynorbomene triblock. Interestingly, between 10
1220 and 30 of these macromolecules "aggregated" when the polyene block contained more than approximately 20 double bonds, a phenomenon that was ascribed to cross-linking of polyene chains. When enough TCDT-F6 monomer was employed to generate a 50-ene in the triblock, then all of the macromolecules cross-link to yield dichloromethane-soluble red polymers with molecular weights approaching 500000 (vs. polystyrene). This process opened the possibility to control the size of the cross-linked portion of such copolymers and to prepare polyenes in the block copolymers that contain a wide variety of functionalities, redox centers (for self-doping), etc. Another application of living TCDT-F6 technique could be the generation of isolated polyenes diluted in a host polymer. 99 For this purpose, low concentration of polyTCDT-F6 in homopolymer should be homogeneously dispersed, as should the polyene chains generated from polyTCDT-F6 if the retro-Diels-Alder reaction is carried out in the solid state. If such films can be oriented by stretching before the retro-DielsAlder reaction is carried out, then an anisotropic distribution of polyenes with a known distribution of chain length could be produced. Such products would be valuable in the fundamental and applied third-order nonlinear optical fields. An alternate polymeric precursor route to polyaeetylene that did not involve elimination of molecular fragments was developed through the ringopening metathesis polymerization of the highly strained monomer, benzvalene (a valence isomer of benzene). The polymer precursor which was prepared from benzvalene using the tungsten alkylidene complex W(=CH'Bu)(=NAr)(O'Bu)2 formed soluble, tastable films and could be isomerized to polyacetylene upon treatment with mercury salts ~~176 (Eq. 18.34).
--~D. ~
(18.34)
A new interesting precursor route to high-quality poly(l,4phenylenevinylene) (PPV) by ring-opening metathesis polymerization of substituted bicyclo[2.2.2]octadienes reported recently C~ubbs and coworkers. ~~ Thus, starting from the bis(~xylic ester) of bicyclo[2.2.2]octa-5,8-diene-cis-diol, the precursor polymer was prepared by living ring-opening polymerization under the action of the molybdenum
1221 alkylidene complex Mo(=CHCMe2Ph)(=NArXOCMe2(CF3)h which by subsequent pyrolytic acid elimination provided poly(l,4-phenylenevinylene)
(Eq 18.35).
~OC(O)OO'l.sROMP O ) ~ H3CO(
A -~~
(18.35)
OC(O)OO'h
Significantly, the living metathesis polymerization of the starting bis(carboxylic ester) of bicyclo[2.2.2]octa-5,8-diene-cis-diol permitted direct control over the structure of poly(1,4-phenylenevinylene), and particularly the degree of polymerization, the narrow molecular weight distribution, the end group, and the sequence structure of the final copolymer. By a similar route poly(cyclopentadienylenevinylene) has been prepared by ring-opening metathesis polymerization of bis(carboxylic esters) of bicyclo[2.2.1 ]hept-5-ene-l,2-diol and subsequent thermal elimination reaction from the precursor polymers ~~ (Eq. 18.36).
n
~
A v-~ ~
(18.36)
The temperature needed for thermal elimination was reasonably reduced to <100~ by using organic acids as catalysts. An efficient procedure of high technological value would be the use of photo-acid generators to catalyze the elimination reaction because this seems to enable not only low conversion temperatures but also the production of structures via photoresist technology. 18.3.10. Semiconductors and Metal Ousters.
At present, the manufacture of small semiconductor microstructures and microcrystallites (nanoclusters or nanoparticles) is of considerable importance because of the potential exploitation of quantization effects for the production of optical signal processors and switches. ~~ Several
1222 techniques have been devised to synthesize semiconductor clusters or metal clusters of a predictable size. The manufacture of stable semiconductor clusters of controllable sizes in amorphous polymer films seems to be the most desirable in terms of device fabrication. Recently, one elegant and sophisticated approach involving living ring-opening metathesis polymerization of metal-containing monomers to produce nanoparticles within microphase-separated diblock copolymers has been disclosed by Schrock and coworkers. ~~ The monomers are mainly metal norbornene derivatives that contain metals bound to a cyclopentadienyl group. The initiators suitable for these polymerizations have been the wellcharacterized molybdenum ~~ and tungsten ~~ alkylidene complexes used in the living ring-opening polymerization of cycloolefins. The molybdenum complexes appeared to be more useful as they tolerate functionalities to a greater extent than the tungsten catalysts. This approach took advantage of the ability of block copolymers to self-assemble to form lamellae, cylinders, and spheres with dimensions of the order of 50-200A. !~ Ultimately, the nature of the morphology and to some degree the domain size could be altered by varying the amount and ratio of monomer in each copolymer block. A significant application concerns the manufacture of lead sulphide semiconductors, a material that exbibits a high dielectric constant and a large exciton radius. It has a narrow-bandgap semiconductor with an infrared bandgap (0.41 eV) and an ionic crystal structure (cubic rock salt). According to a procaxlure, small particles of PbS have been obtained by H2S treatment of block copolymer films wherein aggregates of poly[(C~HgCH2CsI'~)-zPb] reside as microdomains distributed throughout a polynorbornene matrix. The block copolymer was prepared by sequential addition of norbomene and (CTH9CH2CsI-L)2Pb to Mo(=CH'Bu)(=NArXO'Bu)z followed by quenching with benzaldehyde l~ (Eq. 18.37).
[Col
(18.37)
The interdomain spacings (320-480A) before and after HzS treatment were determined by small-angle X-ray scattering (SAXS)technique.
1223 Average cluster diameters (20-40A) were measured by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) methods. The clusters were identified as PbS by X-ray fluorescence analysis performed on the STEM and by wideqmgle X-ray powder diffraction. In another procedure, m a lead(II) norbomene derivative, Pb(CpN)OTf (Cp N = 2-(cyclopentadienylmethyl)norbom-5-ene) (OTf = CF3S(h) has been employed along with methyltetracyclododecene (MTD) to produce diblock copolymers via living ring-opening metathesis polymerization with Mo(=CHCMe2PhX=NAr(O'Bu)~_ (Eq. 18.38).
(18.38) ~ c ~ ~
The living copolymer was capped in a chain-transfer reaction by adding 1,3pentadiene (a mixture of isomers) to yield a ~polymer terminated with a methylene group and the corresponding vinylalkylidene complex. Films of these block copolymers were prepared from benzene solutions which upon treatment with H2S under nitrogen atmosphere at a temperature of 100~ provided PbS clusters in lamellar/wormlike and regular spherical morphologies. In one case the PbS dusters ranged in size from 16A to 25A. A new approach for the synthesis of metal clusters makes use of block copolymers to first produce stable clusters and subsequently to interconvert reversibly between one type of cluster and another. The clusters were synthesized in poly[bTAN] domains within poly[MTD] matrix, where bTAN = 2,3-trans-bis(tert-butylanfidomethyl)norbom-5-ene and MTD = methyltetracyclod~tecene. In one ex~unple, Zn clusters were manufactured by sequential addition of monomers to W(=CH'BuX=NArXO'Buh initiator in benzene with MTD added first and [bTAN(ZnPh)2] second ''~ (Eq. 18.39).
n
+m
(18.:3e)
~
4-
,
1224 The benzene solution of the copolymer was dried slowly in a nitrogen atmosphere resulting in thick films. Zinc fluoride clusters were produced by exposing the films to hydrogen fluoride-pyridine (HF-Py) complex containing 70% HF. Further analysis by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) indicated the formation of ZnFz clusters within spherical domains in the copolymer film. Wide-angle X-ray scattering (WAXS) showed the formation of crystalline ZnF2, the peaks in the spectra corresponded to those expected for bulk ZnF2 in the futile form. Interconversion of ZnF2 cluster to ZnS cluster is ready possible by reaction with HzS within the nanoscale domain of the copolymer with the equilibrium shifted toward ZnS at higher temperatures (above ~ 120~ and toward ZnF2 at lower temperatures (at room temperature) (Eq. 18.40). ZrkS
+
2HF
_..
~
ZrhC2
+
H2S
(18.40)
Several kinds of clusters can be produced by this general approach from a given starting material. For instance, thermodynamic data indicate that PbS clusters can be synthesized by treating PbF2 clusters with HzS at temperatures above 70~ while for the interconversion CdF2/CdS this process can be accomplished well below room temperature. ~ Significantly, this approach has generated ZnS quantum clusters which are superior in quality (WAXS) to other available techniques. Metal nanoclusters in lamellar or cylindrical microphase-separated precursor diblock copolymer films in which metal complexes initially were attached to the monomer comprising one block of the block copolymer have been synthesized with silver, ~2 gold, ~2 platinum ~3 and palladium. ~ The organometallic palladium derivative, Pd(NBECpXaUyl), which is relatively stable thermally, but which reacts with hydrogen gas to give Pd(0), could be polymerized smoothly to give block copolymers containing MTD. Cast films showed the expected morphologies and could be treated with hydrogen gas at 100~ to generate palladium clusters having ~25 to 50A diameter in polyMTD matrix. However, the greatest control over the number of atoms or molecules in clusters is possible in spherical microdomains. Synthesis of metal clusters in spherical microdomains is connected to production of metal and metal sulphide (semiconductor) clusters in solution within micelles ~4 and vesicles.~5 Work on this line by Schrock and coworkers ~6 showed that polymer films containing evenly-dispersed silver spherical microdomains can be prepared, and that upon heating these films a single
1225 silver cluster (diameter
n
,
m
(18.41)
-------~
/ The diblock was dissolved in benzene, and the copolymer reacted with Ag(HfacacXCOD) (Hfacac=[CF3C(O)CHC(O)CF3]; COD= 1,5cyclooctadiene). Poly[MTD] was then added to form a polymer mixture and films were cast by evaporating the solvent under nitrogen. Analysis by TEM showed silver-containing microdomains of ca. 180A diameter while X-ray fluorescence on a scanning transmission electron microscope(STEM) indicated the presence of silver and phosphine within the spherical microdomains only. Upon heating to 90~ spherical silver clusters having mean diameters of 55A with a standard deviation of ca 20% were produced. Palladium nanoclusters ~7 within polymer film that display a spherical morphology have been manufactured in polymer films prepared by blending a palladium-containing diblock copolymer of the general formula [Pd(C pN)(P A)] ~-[MTD ]m (CpN = endo- 2(cyclopentadienylmethyl)norbom-5-ene, PA = TI3-l-phenylallyl, and MTD = methyltetracyclododecene) with polyMTD homopolymer (Eq. 18.42).
§ m
~ ~
(18.42)
1226 Small palladium clusters (
1227 method (Eq. 18.43).
n
+ m
.~
(18.43)
All polydispersities were low (<1.10) and ~H NMR spectra confirmed that the block-to-block ratio of repeat units was that expected of a well-behaved living polymerization. Copolymers from M-S monomer and MTD were thus prepared and micrograph of a section of a film showed lamellar morphology. Zn nanoclusters were manufactured by adding diphenylzinr to the (M-S)(MTD) copolymer and then treating the film with HzS in order to convert the ZnPhz to [ZnS]x and benzene. Analysis by TEM indicated the expected lamellar microstructure with interdomains spacing similar to those observed for the film of (S-M)(MTD) alone. Furthermore, X-ray fluorescence in a STEM measurement showed that the ratio of zinc to sulphur in the lamellae was that expected. Similar results were reported by Schrock and coworkers ~s employing block copolymers containing M-O monomers. A well-defined lamellar morphology was found in a film of (MO)(MTD) that had been static cast from benzene in the presence of ZnPh2 as well as of Cd[3,5-(CF3hC6H3]2. The latter products had been treated with H2S to afford (ZnS)x and (CdS)x, respectively, within the lamellar microdomains.
18.3.11. Functionalized Polymers Nowadays, there is a great variety of functionalized polymers prepared by ring-opening metathesis polymerization of r bearing functional groups. Generally, the functional group is situated into a remote position with respect to the double bond, rarely it is in an adjacent position. With the discovery of well-defined transition metal alkylidene and metallacyclobutane catalysts largely tolerable to functional groups, the number of functionalized polymers increased considerably. ~9 The polymers thus prepared possess totally different properties and can be used in a variety of fields depending on their structure and the nature of the functional group.
1228 Polymers containing halogen are of practical importance owing to their particular elastomeric properties that make them to be used as special rubbers. Usually, monomers bearing halogen at the double bond deactivate strongly the catalytic system and the reaction is practically suppressed. Thus, l-chlorocycloolefins are found to be inert in the ring-opening polymerization reactions with classical catalysts. However, it was observed that metathesis polymerization would readily occur under these conditions if halogen atoms are present in a remote position. For instance, l-chloro1,5-cyclooctadiene polymerizes by opening of the unsubstituted double bond to give poly(5-chloro-l,5-octadienamer) which is the perfectly alternating copolymer ofbutadiene with chloroprene. 69 Synthesis of a great number of chlorinated and fluorinated polyalkenamers has been effected by Feast and coworkers re~ using both classical and well-defined metathesis catalysts. These products were derived from several series of substituted bicyclic and tricyclic olefins such as norbomene, norbomadiene, benzonorbomadiene, dimethanohexahydronaphthalene, bicyclo[3.2.1 ]octa-2,6-diene, tricyclo[4.2.2.02"5]deca-3,7,9-triene. Such highly chlorinated and fluorinated products are of major technical importance since they display high thermal stability associated with good mechanical properties. Halogen-containing polyalkenamers have been manufactured that seem to be suitable flameretardant and solvent-resistant materials. Several polymerization procedures have been reported that made use of norbornene derivatives containing halogen, hydroxyl, ester, ether, amide, acid, anhydride and nitrile substituents. TM Polymers manufactured from adducts of cyclopentadiene with vinyl acetate, methyl methacrylate, and dimethyl fumaratr are hard, brittle plastics with low heat-distortion temperatures. Re, Ru, Ir and Rb salts have been employed as catalysts with or without reducing agents in polar media such as water and alcohol, which are normally poison for classical catalysts. Polar norbomene monomers have been widely evaluated in a variety of applications. By reaction of polar monomers, including ester and nitrile derivatives of norbomene, polymers of 5-cyanonorbomene have been manufactured with a desirable balance of chemical and mechanical properties. Some of them have been successfully compounded with various vinyl polymers. These amorphous, solventresistant products possess good heat, weathering and solvent resistance as well as excellent impact and shock resistance, properties that suggested valuable applications in pipes, automotive parts, bottles, food wrap films, and other materials.
1229 Development of.new, well-defined ROMP catalysts, tolerant to functional groups, allowed ring-opening polymerization of less grained cycloolefins bearing .various functional groups. Thus, the tricyclohexylphosphine complex of the stable vinylcarbene complex of ruthenium can polymerize cyclooctene and its derivatives ~z2(Eq. 18.44).
X
a,.~m
x
x
This reaction opened a new way to manufacture the interesting class of terpolymers of butadiene, ethylene and vinyl monomers. Polymerization of organoborane monomers, e.g., (5cyclooctenyl)diethylborane or norbomenyl-9-borabicyclononane and further conversion of novel organoborane polymers to hydroxyl-containing materials with different structural parameters and particular physical properties were reported by Chung and coworkers ~23(Eq. 18.45).
n
>
(~
(18.45)
v
B
OH
It is noteworthy that some of these polymers were thermally stable and began to lose weight only at temperatures above 400~ compared to poly(vinyl alcohol), which undergoes weight loss at temperatures as low as 300~ Interesting polymers have been produced by polymerization of cycloolefins with pendant silane or stannane functionalities, these products showed promise for special applications. An attractive example is the metathesis polymerization of 1-trimethylsilyleyclobutene to a perfectly invariant substituted cis polyalkenamer reported by Katz and coworkers TM (Eq. 18.46).
1230 The reaction occurred readily in the presence of the tungsten carbene complex W(CO)s(=CPh2) to produce a perfect head-tail structure which was unaffected by the catalyst. The pendant trimethylsilyl groups could be easily replaced by other functional groups which otherwise are not tolerated by the catalyst. For instance, a sulphur-containing polymer was obtained via substitution of the silyl groups by thio groups. Related examples include norbornene and norbomadiene monomers bearing silane groups such as trimethylsilyl-norbornene or dimethylsilyl-norbornadiene. ~zs The last type of carbosilane polymers containing Si-H bonds in the backbone appear to facilitate the formation of silicon carbide. This probably results from the ability of these polymers to undergo cross-linking via thermal hydrosilylation. Cross-linking by such Si-bonds seems to be an essential requirement for the high yield conversion of linear preeeramic polymers to ceramic materials. Also, polymers containing Si-H bonds appear to crosslink giving rise to films and gels via hydrosilylation. Several polymers have also been produced from cycloolefins possessing trichlorosilyl substituents. Suitable monomers are 5-trichlorosilylnorbomene, 5trimethyloxysilylnorbornene, 10-trichlorosilyl-l,5-cyclododec~diene. When associated with unsubstituted cycloolefins, the silicon-containing monomers confer new properties to the copolymers. Thus, the copolymer manufactured from cis, cis-l,5-cyclooctadiene with 10 mole % 5trichlorosilylnorbornene and 15 mole % 4-vinylcyclohexene is an efficient adhesion promoter for coupling rubber to siliceous fillers. Furthermore, silicas and other mineral fillers may serve as reinforcing agents for these materials because of specific chemical interactions with these type of polymers. Polymers with biocidal properties were prepared from cycloolefins bearing stannyl groups in a remote position with respect to the double bond. ~26 For instance, cyclooctene, norbornene and tricyclo[8.2, l]tridecene substituted with tributylstannyl were found to be suitable monomers (Eq. 18.47). ROMP
(18.47)
n
Bu3Sn
Products thus prepared find applications as marine antifouling coatings, in wood preservation, etc.
1231
18.3.12. Polymers from Heterocyclic Olefins A new class of acyclic polymeric ionophores prepared by polymerization of oxygen-containing monomers was reported by Novak and Grubbs. ~z7 Thus, poly(ethenylidenetetrahydrofuran) compounds were synthesized by ring-opening metathesis polymerization of 7-oxanorbomene derivatives (Eq. 18.48).
0
These materials are capable of forming helical structures with ion-binding cavities, analogous to the cyclic crown ethers and cryptands. Such products which can be cast into thin films might find potential applications as ion-selective permeable membranes. Metathesis polymerization of unsaturated lactones afforded unsaturated polyesters having interesting properties. Ast and coworkers ~28 synthesized a rubber-like polyester by the polymerization of the lactone of 16-hydroxy-6-hexadecenoic acid in the presence of WCldMe~Sn catalyst (Eq. 18.49). n II
I
--
CH(CH CO0(
(18.49)
The product was a fibrous, non-tacky polymer having an average molecular weight of about 95000. Likewise, polymerization of 2,3-dihydrofuran in the presence of tungsten and chromium carbene complexes, as reported by H6cker and coworkers, ~29 gave rise to a polyether structure having a c J s : t r a n s configuration of the double bonds of ca. 1 (Eq. 18.50).
1232 n
-~ O
ROMP
~--
=[=C H-O-CH2CH2--C H==~ I
I
(18.50)
The availability of the new class of tolerant, well-defined metathesis catalysts allowed ring-opening metathesis polymerization of a wide range of heterocyclic olefins. ~30
18.3.13. Telechelic Polymers Ring-opening metathesis polymerization of cycloolefins provides a new, efficient route for the manufacture of telechelic polymers, macromolecules with one or more reactive end-groups which are useful materials for chain extension processes, block copolymer synthesis, reaction injection molding and network formation. Several applications for the production of this class of compounds by cross-metathesis of cycloolefins with a,~difunctional olefins in the presence of metathesis catalysts have been described. TM An interesting example consists of synthesis of hydroxytelechelic polybutadiene by ring-opening polymerization of 1,5cyclooctadiene in the presence of protected cis-l,4-butenediol as the bis(tert-butyldimethylsilyl)(TBS) ether with W(=CHAr)(-NPh)[OCCHs(CFs)2](THF) as the catalyst t32 (Eq. 18.51).
0 Removal of the TBS end-groups from the polymer was performed by the reaction with excess tetra_nobutylammonium fluoride in tetrahydrofuran. The hydroxytelechelic polybutadiene obtained by this procedure has entirely 1,4 repeat units and only one type of hydroxy end-groups. The functionality of the hydroxytelechelic polybutadiene thus prepared is close to 2.0. The synthesis of hydroxytelechelic oligomers of norbornene has been also performed by the reaction of norbornene with u,~difunctional olefins bearing ester groups in the presence of WCL/Me4Sn catalyst ~33 (Eq. 18.52).
1233
R3M~ YX=/_ Y Y=(33C~
Reduction of the ester groups to hydroxytelechelic oli80mers were carried out quantitatively with LiAIH4. The functionality of the hydroxytelechelic product was found to be-~ 1.9.
18.3.14. Liquid Crystalline Polymers An important application of the ring-opening metathesis polymerization of cycloolefins is the synthesis of side-chain liquid crystalline polymers (SCLCPs), products of interest for modem technologies in electronics and optics. Several norbornene derivatives with mesogenic groups have been polymerized during the last six years. A first series of SCLCPs was manufactured by Schrock and coworkers TM from monosubstituted norbornenes by living ring-opening metathesis polymerization under the action of Mo alkylidene complexes of the type Mo(=CH~Bu)(=NAr)(O'Buh (Ar=2,6-C6H/Pr~). Thus, reactions of norbomene derivatives containing laterally attached mesogens, e.g., [(4'methoxy-4-biphenylyl)oxy] and 2,5-bis[(4'-n-alkoxybenzoyl)oxy] and various spacers produced in high yield SCLCPs with variable molecular weight and narrow molecular weight distribution. Variation in the mesogenic group allowed nematic (parallel) and smectic (perpendicular) mesophases to be obtained. Furthermore, AB type copolymers that contain a side-chain liquid crystalline block and an amorphous polymer block were also prepared from n-[((4'-methoxy-4-biphenyl)yl)oxy)]alkyl bicyclo[2.2.1 ]hept-2-ene-5-carboxylates (n=3,6) and norbomene, 5-cyano2-norbomene, and methyltetracyclododeccne ~35(Eq. 18.53). n
9m
RDIVP Not =
(18.53)
X
1234 Another series of SCLCPs with a high density of mesogenic groups per monomer unit prepared Stelzer and coworkers m36 starting from 2,3disubstituted norbornenes in the presence of Mo alkylidene complexes (Eq.
18.54).
m
oo(c8. ,r
[uo] ROMP
(18.54)
~ ~ , .
CoO(CH
mCH ).O0(#
89
In this case, the increase of the number of mesogenic groups brought some remarkable differences in the structure of the liquid crystal phases. Significantly, the liquid crystal phases changed from nematic to smectic with spacer length of n - 6 or 7, also depending on the Mo catalyst employed. Through copolymerization with norbornene esters of a , ~ i o l s , the above authors were able to produce liquid crystalline elastomers by "m situ" cross-linking during the ROMP reaction. Significantly, the crosslinking yield depended greatly on the spacer unit ~37Y (Eq. 18.55).
m
.,. n
O~u
~
(la56)
/
0
X0
They observed that these liquid crystalline polymers were weakly crosslinked in the first step during polymerization, but oriented in a second step by mechanical drawing and finally fixed by a second cross-linking step, e.g., by peroxides or irradiation. By this procedure, materials with anisotropies in their physical properties could be obtained. When such materials are optically clear, they may be employed for the production of biofocal contact lenses.
1235
18.3.15. Optically Active Polymers. Synthesis of optically active polymers became an area of large practical interest over the last decade for several reasons. First, these polymers find special applications as chiral phases in liquid or gas chromatography. Second, synthesis of optically active polymers would mimic the synthesis of enantiomericaUy pure natural compounds of relevance in biochemistry. Third, such polymers are of great importance in the investigation of reaction mechanisms and stereochemistry. However, presently, the main disadvantage of many chiral stationary phases prepared for liquid or gas chromatography is their limited stability towards certain solvents as results of the lack of cross-linking. In order to circumvent some of the existing disadvantages and, primarily, to improve their stability toward solvents, optically active polymers with unsaturation in the main chain, suitable to provide crosslinking, would be suitable for desired applications. Such polymers can be easily manufactured by stereoselective ring-opening polymerization of chiral cycloolefins in the presence of well-defined metathesis catalysts. Polymerization of 2-substituted chiral bicycloalkenes affords such polymers where the ring is embedded between two cross-linkable vinylene groups. A first example is the synthesis of optically active polymers prepared by the ring-opening metathesis polymerization of enantiomerically pure 2acyloxybicyclo[2.2, l]hept-5-enes with Mo(-~H~Bu)(=NAr)(O'Buh in chorobenzene or K2[RuCIs(H20)] in aqueous solvents reported by Stelzer and coworkers m3s(Eq. 18.56).
m
ROMP
OCCI-U
o
._
OCCH3 II 0
The acyl substituent was selected from acetyl, butyryl or benzoyl groups. These optically active polymers could provide appropriate double bonds in the chain for further cross-linking.
1236 Another interesting example is the polymerization of N-(amethylbenzyl)-2-azanorbom-5-ene-3-carbowlates having two chir~ substituents with different Mo alkylidene initiators ~39(Eq. 18.57).
m
~
COOCH3
ROMP __ [Mo]
' '
w
~
.
.
.
..N~'"
.
(18.57)
.
~;OOCH3
The resulting polymer, poly(vinylene-N-(ct-methylbenzyl)pyrrolidine-3,5ylene-2-methylcarboxylate), is a derivative of a poly(ct-amionoacid). Further hydrolysis gives free poly(aminoacid). The formation of helices was expected for highly ordered polymers of this type, for e.g., all-cis, isotactic polymer, the amino acid groups are to point toward the outer surface of the helix. Olefinic bonds could be used for further derivatizing or cross-linking reactions, so the stereoregular optically active polymers may be useful for analytical and chiral inducing purposes. Significantly, for such optically active polymers a high separation power for use in the separation of enantiomers is expected.
18.3.16. Miscellaneous Applications A significant application of the ring-opening polymerization of cycloolefins is the synthesis of a new type of blue-light-emitting electroluminiscent polymer from a norbomene monomer that contains a phenylenevinylene oligomer unit as a side-chain, NBTPV-C~ (Eq. 18.58). ONe
OMe OMe
MeO
[Mo]
0 ~ 0 . ~ ~OMe
(18.58)
1237 Using Mo(=NAr)(=CHCMe~PhXOtBuh as the initiator, Schrock and coworkers ~4~ prepared a polymer of NBTPV-Cs in 95% yield. Electroluminiscent devices were manufactured with single layers of polyNBTPV-C5 with ITO as the anode and Ca as the cathode, both by itself and in blends containing the electron transport material, biphenyl-tertbutylphenyloxadiazole. Interesting applications w i l l f i n d ring-opening metathesis polymerization of cycloolefins in the redox chemistry. Thus, monomers that contain redox-active frrocenes, e.g. FeNBE, have been polymerized along with monomers that contain other redox-active groups such as phenothiazine to give small block copolymers74 (Eq. 18.59).
§
[IV
~
(18.59)
The solution chemistry of these materials showed them to be well-defined and well-behaved. Analogously, more elaborate polymers that contain several redoxactive groups along with several equivalents of trialkoxysilylmethylnorbornene have been obtained and shown to derivatize Pt electrodes with well-defined monolayers. In one example, the molybdenum complex M(=CHFcX=NArXO'Buh (Fc = ferrocenyl) has been employed as the initiator and octamethylferrocenylaldehyde as the capping agent TM (Eq. 18.60).
F~
1238 Polymers terminated with pyridyl or bromobenzyl groups, introduced in the capping reaction employing the appropriate aldehydes, reacted with electrodes pretreated with benzyl chloride or pyridine groups, respectively, to produce special polymer-derivatized surfaces. Appealing well-defined redox chemistry was observed for all redox-active groups in the polymer, both in solution and bound to an electrode surface.
18.4. Future Outlook
Catalytic polymerization of eycloolefins has proved to be an efficient method for the synthesis of a wide variety of polymers. The broad class of catalysts allow the successful application of this process to various monomers, under different conditions, from high vacuum technique to high pressure, in the presence or absence of oxygen and water, in aprotic and protic solvents and sometimes under the influence of Lewis and BrOnsted acids as initiators. Monomers of different structures and re,activities will enable synthesis of new block copolymers, graft and star copolymers as well as dendritic polymers with particular shapes and architectures, of relevance in supramolecular chemistry. A promising trend in the near future is the polymerization of metal-and heteroatom-containing monomers which opens new ways to create and manufacture specialty polymers of interest for semiconductor technology. Polymers and copolymers prepared by this way will find broad applications to refined technologies for many areas such as automotive, construction, fine mechanics, electronics, computer science, optics, telecommunications, etc. A special attention for the future work deserves the design of water soluble ruthenium with quaternary amine groups that creates the possibility for living polymerization in aqueous solution and the synthesis of water soluble polymers in the absence of surfactants or organic solvents. Moreover, the synthesis of functionalized polymers bearing biological entities as pendant groups with potential applications in medicine and biology is a challenging subject for future studies. An area of interest for macromolecular and biological chemistry is the synthesis of macrocyclics, e.g., carbocyclic and heterocyclic compounds, by means of back-biting metathesis reactions of appropriate monomers. Combination of the living polymerization processes with other type of polymerization mechanisms will open the possibility to synthesize copolymers of unprecedented structures with useful applications.
1239 18.5. References
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1249
SUBJECT INDEX
Aeenaph~o[2.3]bieydo[2.2. l ]hepta2,5-diene, 448 Acenaphthonorbomene endo-5,6-, 54 exo-5,6-, 54 Aemaphthylene, 309 l-Methyl-, 31 l 3-Methyl-, 312 5-Methyl-, 312 7-Acetoxy-4,5,6,7-tetrahyflrooxepm, 683 A c e t y l a ~ a t e , 157 Acetylenes, 850 Anionic polymerization, 1125 Catalytic polymerization, 1125 Cationic polymerization, 1125 Metathesis of, 1109 Metathetical polymerization, 1126 Ziegler-Natta polymerization, 1126 Activators, 226 ADIMET, 1118 ADMET, 1118 A g o s t i c ~ structure, 1096 Alcohols, 77 Aldrin, 76 Alkylation reaction, 1134 Alkylidenenorbomene, 429 Alkylnorbomene, 429 Allylcyclopentadiene, 250 x-Allylic catalysts, 130 ~-Allylic complexes, 165 Allylmethylcyclopentadiene, 25 l Aluminium bromide, 153 Aluminium chloride, 152 Ambrettolide, 37,683
Amides, 82 Anhy des, 80 Anionic catalysts, 119 Anionic mechanism, 857 Anionic polymerization, 319 of 1,3-r 320 of cyclooctatetraene, 324 of cyclopm~diene, 320 of isopropylidene-, 325 of methyleneeyclobutene,320 Anthra camo[2.3 ]b ieyclohepta-2,5 -dime, 450 2,3-Anthracenonorbomadiene, 57 Arylnorbomene, 429 ATRP of vinyl compomlds, I 108 Azanorbomene, 95,68 l Boron fluoride, 153 Boron fluoride.etherate, 153 Back-biting, 957 Barrelene, 24,628 Benzalmdene, 30 l Benzobarrelene, 24,55,452 Benzo[2.3]bicyclo[2.2. l ]hepta-2,5dime, 445 7-(Dipheny~ylene)-, 447 7-1sopropylidene-, 446 9-Methyl-, 446 7-( 1'-Phenylethylidene)-,44 7 Benzobieyclo[2.2.2]~ene, 452 Benzo[3.4]buta[ 1.2]bieydo[2.2. l ]he-
pta-2,5-.diene,448
Benzo~cyclo[4.2.2.02'~]deca - 3,7,9triene, 797 Benzofulvene, 300 Benzonorbomadiene, 57 Benzoaorbomadiene derivatives, 625 Benzonorbomene, 38
1250 aza-, 38
endo-5,6-, 54 exo-5, 6-, 54 oxa-, 38 3,4-Benzo- l-silabicyclo[4.4]nona-3,7-diene, 656 Benzo-5-silaspiro[4.4]nonadiene, 98 Benzo[4.5 ]tricyclo[6.2.1.0~7]undeca triene, 449 Benzvalene, 24,455 Bicyclo[ 4.4.0] decatetra- 1,3,5,7erie, 303 Bicyclo[2.2.1 ]hepta-2,5-diene, 24, 267, 440 Bicycloheptene, 24 Bicyclo[2.2.1 ]hept-2-ene, 264,422 5-Ethylidene-, 266 5-1sopropenyl-, 267 5-Methyl-, 265 5-Methylene-, 266 5-Vinyl-, 266 Bicyclo[3.2.0]hept-2-ene, 421 Bicyclononadiene, 24,54 B icyclo [4.3.0 ]nona- 1,3,5,7 -tetra erie, 270,453 Bicyclo[6.1.0]non-4-ene, 270 9,9-Dichloro-, 630 Bicyclooctadiene, 24 Bicyclo[2.2.2]octa-2,5-diene, 627 Bicyclo[3.2.1 ]octa-2,6-diene, 626 Bicyclo[2.2.2]octa-2,5,74~ene, 628 Bicyclooctene, 24,269 Bicyclo[4.2.0]oct-7-ene, 450 Bicyclo[5.1.0]oct-2-ene, 451 Bicyclo[2.2.2]oct-2-ene, 451 1,1 '-Biindenyl, 295 3,3'-Biindenyl, 296 1,1 '-Bimdenyl- 1,4-butane, 297 3,3'-Bimdenyl-1,4-butane, 298 1,1 '-Bimdenyl- 1,4-trans-butene, 298 I, 1 '-Biindenyl- 1,2-ethane, 296 3,3'-Biindenyl- 1,2-r 297
7,8-Bis(trifluoromethyl)tricyclo[4.2.2.02"~]deca-3,7,9-triene, 634 3,4-Bis(trifluoro~yl)tricyclo[4.2 91. 0 2,~]nona-3,7-dime,632 Blockiness, cis-trans, 1071,1082 Blue-light-emitting polymers, 1236 Br6nsted acids, 116 5-(4-Btaanyl)-norbomene, 434
tert-Butyldimcthylsiloxydeltacyclene, 633 n-Butyllithium, 155
tert.Buty~cyclo[2.2.22.~. 11.4.03.~]ntm-8-ene, 633 3-Carbethoxytricyclo[ 3.2.1.02"4]oct 6-ene, 631 Carbocycles, 1113 Synthesis of, 1113 Carbon dioxide, 231 Carbonates, 8 l Carbonyl-olefm exchange, I 122 Carboayl olefination, 1120 Carboxylic acids, 79 3-Carene, 269 Catalysts, I 15 Catenanes, 8,9 Cationic catalysts, 115,152 Cationic polymerization, 237 Cationic polymers, 875 Chemical degradation, 903 Chiral alkylidene complexes, 180 Chiral catalysts, 124,157 Chiral m e t a l l ~ e catalysts, 157 Chlorinated con~aounds, 73 Cinnamalmdene, 301 Condensation polymerization, 858 Con~tion Catalyst, 202 Critical, 200 Cyclopentene, 198 Monomer, 197 Conducting polymers, 1216
1251 Contmt (a~ of polynorbomene, 1071,1072 Conversion, 219 Cyclobutene, 219 Cyclopentene, 219 Copolymerizafion reactions, 687 Cationic, 690 Rmg~ing ~esis,774 Ziegler-Natta, 707 Copolymers, 687 ARemating, 1209 Block, 1210 Comb, 1214 Cyano-cxmtammg, 818 Fluorine-comammg, 833,834 Germanium-cxa~ming, 827 Graft, 842 H a l o g e n ~ m m g , 802 Iron-cxmtainmg, 832 Lead-ctmtaining, 831 Metal.c<mtammg, 830 Nitrogen.ccmammg, 815 Oxygen-cxx~ming, 802 Palladium-comaming, 833 Phosphorous-comaming, 820 Redox-active, 82 l Siliccm~ining, 826 Star, 836,1214 T i n - - r u i n g , 827 Coumarone, 1142 Comnarone-mdene resins, 1142 Copolyn~rs, l0 Cross-lmked polymers, 6,463, l 174 Crown ethers, I I 17 Synthesis of, I 117 Crystallographic characterization, 934 Crystalline transformations, 926 Crystallization rate, 930 Cycloalkenes, 1 Cyclobutene, 40,237,327,375,707, 774
cis
cis-3,4-Dichloro-, 513 3,3-Dimethyl-, 381 Functionalized, 514 l-Methyl-,378 3-Methyl-, 239,380,774 1-Methyl-3~ylene, 239 l-Trimethylsilyl, 520 Cyclodecadiene, 48,415 1,5-Cyclodecadiene, 415 1,6-Cyclododecadiene, 415 Cyclodecene, 48,414 Cyclododeoadiene, 48 Cyclododecene, 416 1,5,9-Cyclododecatriene, 22,49,50, 418 Cyclododecene, 48 1,5,9,13,17-Cycloeicosapentaene, 420 1,3-Cycloheptadiene, 45,260,396 1,4-Cycloheptadiene, 724 Cycloheptene, 45,396,710 1,5,9,13-Cyclohexad~ene, 419 1,3-Cyclohexadiene, 45,258,395 l-Methyl-4-isopropyl-, 260 1,4-Cyclohexadiene, 260 p,p '-Dinmthylene-, 260 Cyclohexene, 44,253,394 l-Methyl-, 254 3-Methylene-, 254 3-Methylene6-isopropyl, 257 1-Methyl-4-isopropenyl-,257
IVinyl-,255 5-(3'-Cyclohexmyl)-2-norbomene, 728 Cyclononadiene,47,413 Cyclononene,47,413 1,3-Cyclooctadiene,261,403 1,4-Cyclooctadiene, 403 1,5-Cyclooctadiene, 22,47,263,403, 724,780 Cyclooctat~'aene,22,47,408,781 tert-Butoxy-,528
1252 Chiral, 529 Methoxy-, 527 Trimethylsilyl-, 528 Cyclooctene, 46,397,710,777,781, 1153 Production of, 1153 Cycloolefins, 774,1121,8501 Synthesis of, 1121 Cyclopentadecene, 419 Cyclopentadiene, 41,43,242,690 Allyl-, 250 Allylmethyl-, 251 1,2-Dimethyi-, 248 1,3-Dimethyl-, 249 2,3-Dimethyl-, 250 l-Methyl-, 247 2-Methyl, 248 1-Methyl-3-isopropyl-, 250 l-Methyl-3~yl-, 250 Substituted, 247,692 Cyclopentene, 41,42,239,384,709, 776 3-Allyl-, 241 3-Chloro-, 241 I-C 14labeled, 778 l-Methyl-, 240,392 3-Methyl-, 240,393 4-Methyl-, 21,393 3-Vinyl-, 241 Cyclopropanation, 1132 of olefins, 1132 Cyclopropene, 40 Cyclorene rubber, 1206 1,9,17-Cyclotetraeicosatriene, 420 Degradation, 1123 ADMET, 1124 Intermolecular, 1124 Intramolecular, 1123 Metathetical, 1123 Dehydrodicyclopentadiene, 305 Deltacyclene, 24,58,456 te rt-Butyldimeth yls iloxy,633
Depolymerization, ADMET, 1124 . 3,4-Dicarbomethoxytricyclo[4.2. l.O~'~]nona-3,7-diene, 632 3,4-DichlorcCncyclo[4.2.1.0~]non-7 -one, 631 3,4-Dicyanotricyclo[4.2.1.0~5]nona-3,7-diene, 632 Dicyclopentadiene, 20,26,41,59,303, 717,725,731,791,1147 resins, 1147 Diels-Alder reaction, 26,51,55,56 Dienes, 1103 Anionic polymerizationof, 1104 Catalytic polymerization of, 1103 Cationic polymerization of, 1103 Ziegler-Natta polymerization of, 1105 Diethylalummium chloride, 155 3,4-Dihydrodieyclopentadiene, 305 8,9-Dihydrodieyclopetnadime, 306 2,3-Dihydrofuran, 37,652 1,2-Dihydronaphthalene, 303 2,3-Dihydropyran, 37 Dimethanooctahydro- 1H- benzomdene, 732 D~an~ydronaphthalene,476 741 Di-endo-methytenehexahydronaphthalene, 308 p-Dimethoxy-3,4-ben~eyclo[4.2.2.0~"~]deca-3,7,9-trien e, 637 5,6-Dimethylenenorbomene, 438 Di-endo-methylenooetahydronaphthalene, 307 6,6-Dimethylfulvene, 252 1,2-Dimethylnorbomene, 53 1,3-Dimethylnorbomene, 53
1253 2,3-Dimethylnorbomene, 53 5,5-Dimethylnorbomene, 436 5,6-Dimethylnorbomene, 437 3,4-Dimethyl- 1-silabicyclo[4.4 ]nona-3,7-diene, 655 1, l-Dimethyl- 1-silacyclobutene, 96, 651 1, l-Dimethyl- l-silacyclopentene,652 1,4-Dmorbomylbenzene, 55 Dipentene, 1143 1,1 -Diphenyl- 1-silacyclopent-3-ene, 653 1,4-Divinylbcnzene, 55 1, l-Divinyl- l-silacyclopent-3-ene, 654 Durham route, 29 Effect of agRation, 232 Esters, 79 E~ylbenzofulvene, 300 l-F~yl- 1,5-cyckxx~diene, 407 E~ylene, 41 E~ylene[bis(mdenyl)zirconium], 123 E~ylene[bis(tetrahydromdenyl)zirco mum], 123 2-E~ylidenenorbomene, 725,735 l-Ethylnorbomene, 52 2-Ethylnorbomene, 52 N-Ethyl-7-oxanorbom-2-ene-5,6-dicarboximide, 677 (2-Trimethylammonium chloride}-, 677 Fischer-type catalysts, 131 Fluorinated bicycloheptadienes, 69 Fluorinated bicycloheptenes, 69 Fluorinated confounds, 69 Fluorinated polymers, 29 Friedel-CraRs catalysts, 1134 Friedcl-CratL~ reaction, 1134 Fullerenr 24,68,801 Functional groups, 27,513, 801 Functionalized cycloolefins, 513,638, 801
Functionalized polymers, 1227 Gallium bromide, 153 Glass transition, 924 Glycopolymers, 805 Grat~ copolymers, 5,10,842 Grignard compounds, 156 Group transfer polymerization, 859 Grubbs-type catalysts, 130,135,165 Heptacyclodoeicosa-8-ene, 65 Heterocycles, I 115 Anionic ring-opening polymerizaUon, 1129 Cationic ring-q~enmg polymerization, 1128 Ring-opening polymerization 1128 Synthesis of, 1115 Heterocyclic olefins, 651,854,123 l Hexacycloheptadeca-6,13-diene, 48 l Hexacycloheptadec,a-6-ene, 65,48 l 2,3,3,4,4,5-Hexa fluorc~sicyclo[4.2.1.0ZS]non-7-ene, 63 l Hydrocarbon resins, 1,695, l 14 l Hydrofluoric acid, 152 Hydrogen fluoride, 152 Hydroxybenzylbenzalindene, 302 Imides, 83 Indene, 24,270,453,1142 l-lndenylmdene, 295 Influence of activator, 228 Influence of water, 227 Initiators, 225,996 Molecular structure of, 1009 Iron trichloride, 154 Isobutylaluminoxane, 184 lsomerization of olefms, 1130 Anionic, 1131 Catalytic, 1130 Cationic, 1131 Metathetical, 1132 Ziegler-Natta, 1131 Isoprene, 41
1254 4-1sopropylcyclopentene, 22 1-Isop ropylidene-3a,4, 7, 7a4etrahydromdene, 301,302 Isoptop ylidenedicyclopentadiene, 306 5-1sopropylidenenorbomene, 434 I -Isopropylnorbomene, 52 2-1sopropylnorbomene, 52 5-1sopropylnorbomene, 433 Ketones, 78 Kinetic models, 981 Kinetics, 967 of cationic polymerization, 967 of initiation, 980 of propagation, 980 of ROMP, 980 of Ziegler-Natta polymerization, 973 Knots, 8,9 Lewis acids, 117 One-component, 117 Two-component, 118 d-Limonene, 1143 Liquid crystalline polymers, 33,1233 Nematic, 35 Side-chain, 36 Living polymerization, 980,1007 Macrocycles, 7,8,1215 Macromonomers, 36,99,844 Polystyryl, 36 Polybutadiene, 36 Mechanism, 995 of anionic polymerization, I006 of cationic polymerization, 995 of initiation, 1007,1020 of insertion reactions, 1013 of propagation, 997,1007, 1031,1041 of ROMP, 1015 of termination, 1005,1043
of Ziegler-Natta polymerization, 1010 Mesogenic groups, 34 Metal-carbene complex, 1041 Metal-carbene-olefin complex, 1040 Metal clusters, 1221 Metallaearbenr 1020,1028,1031 Metallacyclobutanr 1020,1031,1042 Metallocene catalysts, 123,157 Mctathesis reaction, 1 of acetylenes, 1109 of alkanes, I 130 of olefms, 1109 Metathesis catalysts, 162 One-component, 162 Three-component, 165 Two-component, 165 Well-defined, 165 Metathetical degradation, 1123 Methallylcyclopentadiene, 251 1,4-Methanoanthracene Hexahydro-9,10-b~azenr Methylahanmoxane, 123,333,334 2-Methyl-2-azanorbomene, 96 Methyl~zofulvene, 300 5-Methylbicyclo[2.2.2]oct-2-ene,269 3-Methylcyclobtaene, 21,239 l-Methylcyclohexene, 254 Methylenecyclobtaene, 319 3-Methylcyclododecene, 417 1-Methylcyclopentadiene, 247 1-Methylcyclopentene, 240 3-Methyleyel~ene, 240 4-Methylcyclopentene, 21 l-Methyl- 1,5-cyclooctadiene, 407 3-Methyl- 1,5-cyclooctadiene, 407 3-Methylenocyclohexene, 254 5,8-Methylenc-5aSa-dihydrofluorene, 454 5-Methylenenorbomene, 52, 433,726 6-Methyl-6~ylfulvene, 252 l-Methylmdene, 285
1255 2-Methylmdene, 286 5-Methylmdene, 286 6-Methylmdene, 287 7-Methylmdene, 287 1-Methyl-3~ y l e n e c y c l o b ~ e , 239 l-Methylnorbomene, 430 2-Methylnorbomene, 52,430 5-Methylnorbomene, 21,430 7-Methylnorbomene, 21,430 Methylnorbomenes, 430 N-Methyl-7-oxanorbom-2-ene-5,6dicarboximide, 676 1-Methyl- 1-phenyl- 1-silacyclopent3-erie, 653 l-Methyl- l-silacyclopmt-3-ene, 96, 654 Methy~cyclododecene, 746 805 Metton, 1175 Microstructure of copolyalkenamers, 1079 of polypentenamer, 1064 Miscellaneous processes, 1129 Molecular weight, 924 Molybdenum-alkylidene, 171 Molybdenum pentachloridr 163 Monodendritic, 39 Monomer concentration, 197 Monomers, 15 B o r o n ~ m i n g , 31,83 H a l o g e n ~ m i n g , 69 Heterocyclic, 37,90,651 Metal-examining, 32, 85,620 Monodendritic, 39 Nitrogen-containing, 31, 77, 82, 593 O x y g e n ~ m i n g , 30 S i l i c o n ~ m i n g , 32, 84, 610 Sulphur'c'~ 30,81, 591 Multicyclic norbomene-type
491,639 Naphtho[2.3]bicyclo[2.2.1 ]hepta-2,5 -dime, 449 2,3-Naphthonorbomadiene, 57 Niobium-alkylidene, 166 Nitriles, 82 Norbomadiene, 23,56,267,440,725, 730,791 Norbomene, 20,23,51,264,422,715, 734,782, l 162 5-(3'-Cyclohexenyl)-, 728 5-Dichloro(methyl)silyl-,61 l 5-Ethylidene-, 266,735,737 Heteroatom-containing, 656 5-1sopropenyl-, 267 5-Methyl-, 265 7-Methyl-, 788 5-Methylene-, 266 5-[(Methylsilacyclobutyl)methyl]-, 614 Production of, 1162 Spiro[cyclopropyl-7,1 ']-,789 5-( 1,1,3,3-Tetramethyl- 1,3disilabutyl)-, 613 5-(Triethoxysilyl)-, 616 5-(Trimethoxysilyl)-, 615 5-(Trimethylsiloxy)methyl-, 617 5 - T ~ y l s i l y l - , 611 5-Vinyl-, 266 Norbomenebenzobisketals, 590 (5-Norbomenyl)-9-borabicyclononane, 609 Norsorex, 1161 Octacyclodoeicosa-g-ene, 65 5-Octylnorbomene, 435 N-Octyl-7-oxanorbom-2-ene-5,6-dicarboximide, 678 Olefmation reaction, 1120 Carbonyl, 1120 Olefms, 1103 Anionic polymerization of, 1104
1256 Catalytic polymerization of, 1103 Cationic polymerization of, 1103 Metathesis of, 1109 Synthesis of, 1121 Ziegler-Natta polymerizaUon of, 1105 Oligomers, 905 Optically active polymers, 1235 Organolithium compounds, 155 Organosodium compounds, 156 7-Oxabenzonorbomadiene, 681 7-Oxanorbomadiene, 679 2,3-Bis(trifluoromethyl)-, 679 2,3-Dicarboethoxy-, 680 2,3-Dicarbomethoxy-, 679 7-Oxanorbomene, 92,656 2,3-Diacetoxy-, 671 -5,6-dicarboximide, 676 -5,6-dicarboxylic anhydride, 674 2,3-Dicyano-, 673 2,3-(Isopropylidenedioxy)-, 674 Monodendron-, 669 Ozonolysis, 901 [2.2]Paracyclophene, 24, [2.2]Paracyclophan-l-ene, 420 9-tert-Butyldimethylsilyloxy, 531 [2.2]Paracyclophane-l,9-diene, 421 Paramagnetic species, 1038 Pentacyclohexadec~-3, I 0-dime, 489 Pentacyclohexadeca-3-ene, 487,489 Pentacyclohexadeca-6-ene, 64,490 Pentacyclopentadeca-3,10-diene, 486 487 Pentacyclopentadec.a-2-ene, 64 Pentacyclopentadeca-3-ene, 485,486 Pentacyciopentadeca-4-ene, 484 Pentacycl~dec.a-5,1 l-dime, 480, 485
Petroleum resins, 1146 a-Phellandrene, 260 13-Phellandrene, 257 Phenylacetylene, 1125 7-Phenylnorbomadiene, 444 5-Phenylnorbomene, 435 ct-Pmene, 268, l 143 13-Pinene, 1143 Piperylene, 4 l Poly(l-alkenylene)s, l 1,2-Polybutadiene, 842,843 1,4-Polybutadiene,403,418,842,1207 Polybutenamer, 375,376 Polycyclic polymers, I 118 Polydecadienamer, 415 Polydecenamer, 414 Poly(dicyclopentadiene), 26, l 173 Applications of, 1178 ~ o m i c aspects of, 1178 Manufacture of, I 173 Metton, 1175 Properties of, 1175 Telene, 1177 Polydodecenamer, 416 Polyethylene, 1207 Polyheptenamer, 396 Polyhexenamer, 394 1,4-Polyisoprene, 959,1208 Polymerization ADIMET, 1118 ADMET, 1118 Anionic, 319 Carb~yl-olefm exchange 1122
Cationic, 217,237 of cyclobutene, 237 of cyclooctene, 200 of cyclopentene, 198,227 of dicyclopentadiene, 201 of heterocyclic olefins, 651 of norbomadiene, 218,268
1257 of norbomene, 200,223,231 Rmg~mg ~esis,375 Ziegler-Natta, 327 Poly(methyldodeeenamer), 417 Polynonenamer, 413 Polynorbomadiene, 218,268,440 Polynorbomene, 264,344,422,1161 Applications of, 1169 Ecxmomic asper of, 1169 Explosion hazards of, 1169 Manufacture of, 1162 Prcxressmg of, 1163 Properties of, 1163 Toxicology of, 1169 cis-Polyoctenamer, 397,1203 trans-Pol~amer, 397,1153 Applica~ons of, 1159 Ecxmomie aspects of, 1159 Processing of, 1155 Properties of, 1154 Synthesis of, 1153 Toxicology of, 1161 Vulcanization of, 1155 cis-Polypentenamer, 1200
trans-Polypentenamer, 1181 Applications of, 1199 Compounding of, 1184 Economic aspects of, 1199 Polymerization proc~ures of, 1183 Processmg of, 1184 Properties of, 1184 Starting materials of, 1182 Structure of, 1184 Vulcanizate properties, 1188 Vulcanization of, 1188 Polystyryllithium, 857 Polysubstituted norbomene, 439 Premixing time, 199,206 Properties, 875 Solid state, 924 Solution, 923
Reactants, 204 Ratio of, 204 Reaction ~ e n t s , 208 - conditions, 197 - enthalpy, 947 - entropy, 947 - froe energy, 946,947 - medium, 220 - pressure, 230 - temperature, 216 -time, 210 Redox-active polymers, 1237 Resins, I 1 4 l Rhenium pentachloride, 163 RIM process, I 174 Ring-closing metathesis (RCM), 1123
Ring-opening metathesis (ROM), llll R m g ~ m g polymerization of acenaphtho[2.3]bicyclo.[2.2.1 ]hepta-diene, 448 of 7-acetoxy-4,5,6, 7-tetrahydrooxepm, 683 of ambrettolide, 683 of anthraceno[2.3] bicyclohepta-2,5-diene,450 of 2-azanorbomene, 681 of barrelene, 628 of benzobarrelene, 452 of benzo[2.3]bicyclo[2.2.1 ] hepta-2,5-diene, 445 of benzo[3.4]buta[ 1.2] bicyclo[2.2, l ]hepta-2,5diene, 448 of benzonorbomadiene derivatives, 625 of benzvalene, 455 of bicyclic olefms, 42 l of bicyclo[3.2.0]hepta-2,6diene, 422
1258
of bicyclo[2.2.I]hept-2-ene, 422 of bicyclo[3.2.O]hept-2-ene, 421 of b icyclo[4.3.0]nona-3,7diene, 453 of bicyclo[6.1.0]non-4-ene, 454 of bicyclo[3.2.1 ]octa-2,6-diene, 626 of bicyclo[2.2.2]octa-2,5-dime, 627 of bicyclo[2.2.2]octa-2,5,7triene, 628 of bicyclo[4.2. O]oct-7-ene, 450 of bicyclo [2.2.2 ]oct-2 -ene, 451 of bicyclo[5.1 .O]oct-2-ene, 451 of bicyclo [4.3.0] nona1,3,5,7- tetraene, 453 of bis(dimethylene)cyclobutene, 383 of boron-containing monomers, 608 of 5-(4-butenylO-norbomene, 434 of tert-butoxycyckxx~tetraerie, 528 of tert-butyldimethylsiloxydeltacyclene, 633 of 3-carbethoxytricyclo[3.2.1.0~*]oct-6-~e, 631 of 5-carboalkoxynorbom-2erie, 557 of 5-carboxynorbom-2-ene, 556 of chlorinatedmonomers,548 of cyclobutene, 375 of 1,5-cyclodecadiene, 415
of 1 , 6 - c y c l ~ d i e n e , 415 of cyclododocatriene, 418 of cyclodocene, 414 of cyclododocene, 416 of 1,5,9,13,17-cycloeicosapentaene, 420 of 1,3-cycloheptadiene, 396 of cycloheptene, 396 of 1,5,9,13-cyclohexadecatetraene, 419 of 1,3-cyclohexadiene, 395 of cyclohe• 394 of 1,5-cyclononadiene, 413 of cyclononene, 413 of 1,3-cyclooctadiene, 403 of 1,4-cyclooctadiene, 403 of 1,5-cyclooctadiene, 403 of cyclooctatetraene, 408 of cyclooctene, 397 of cyclopentadocene, 419 of cyclopentene, 384 of deltacyclene, 456 of dialkylnorbomene, 435 of 5,6-dicarboalko• n-2-ene, 57 l of 9,9-dichlorobicyclo[6. l.O] non-4-ene, 630 of 3,4-dichlorotricyclo[4.2.1. O~'~]non-7-ene, 631 of dicyclopmtadiene, 460 of difimctionalized norbornerie, 534 of 7,8-dihydrodicyclopentadime, 472 of 3,3-diisopropylcyclobuterie, 382 of 3,4-diisopropylcyclobuterie, 382 of 3,4-diisopropylidenecyclobutene, 383 of dimethanooctahydronaph_ thalene, 476
1259 of 3,3-dim~ylcyclobutene, 381 of 1,2-dime~yl- 1,5-cyclooctadiene, 408 of 3,7-dimethyl- 1,5-cyclooctadiene, 408 of 5,6-dime~ylenenorbomerie, 438 of 5,5-dimethylnorbomene, 436 of 5,6-dimethylnorbomene, 437 of 4,6-diphenylcyclooctene 402 of l-ethyl-l,5- cyclooctadime, 407 of fluorinated monomers,538 of functionalized cycloolefms, 513 of functionalized norbomadierie, 537 of functionalizod norbomerie, 532 of heteroatom-cxa~ ining norbomene, 65 6 of heterocyclie olefins, 651 of 2,3,3,4,4,5-hexafluomtficyclo[4.2.1.02"~]non7-r 631 of mdene, 453 of 5-isop ropylidmenorbomene, 434 of 5-isopropylnorbomene, 433 of m e t a l ~ m i n g monomers, 620 of methoxycyclooctatetraene, 527 of l-methylcyclobutene, 378 of 3-methylcyclobutene, 380 of l-methyl-l,5-cyclooctadiene, 407
of 3-methyl- 1,5-cyclooctadime, 407 of l-methylcyclooctene, 400 of 3~ylcyclooctene, 400 of 5~ylcyclooctene, 401 of 1~ylcyclopentene,392 of 3-methylcyclopentene,393 of 4-methylcyclopentene,393 of 7-methylnorbomadiene, 443 of 1~ y l n o r b o m e n e , 430 of 2 ~ y l n o r b o m e n e , 430 of 5-methylnorbomene, 431 of 7-naghylnorbomene, 431 of 4-methyl-6-phenylcyclooctene, 402 of n i t r o g e n ~ m i n g monomers, 593 of norbomadiene derivatives, 587 of norbomene, 422 of norbomenebenzobisketals, 590 of 5,6-norbom-2-endiyl esters, 583 of (5-norbom-2-enyl)-9-borabicyr 609 ofnorbom-2-enyl esters, 579 of 5-octylnorbomene, 435 of 7-oxabenzonorbomadiene, 681 of 7-oxanorbomene, 656 of o x y g e n ~ i n i n g monomers, 551 of [2.2]paracyclophan- 1-erie, 420 of [2.2]paracyclophane- 1,9dime, 421 of l-phenyl- 1,5-cyclododecadiene, 418 of 3-phenylcyclooctene, 401 of 5-phenylcyclooctene, 402
1260 of 7-phenylnorbomadiene, 444 of 5-phenylnorbomene, 435 of phosphorus-ctmtaining norbomene, 607 of polysubstituted norbomerie, 439 of silicon-comammg monomers, 610 of substituted bicyclo[2.2, l ]hept-2-ene, 429 of substituted bicyclo[2.2, l ]hepta-2,5-dieae, 442 of substituted cyclooctadiene 527 of substituted cyclooctatetraerie, 410,527 of substituted cyclooctene, 523 s u l p h u r ~ i n i n g monomers, 591 of tetrahydromdene, 453 of tricyr 3,7,9-triene, 473 of tricyclo[4.2.0.O~S]octa 3,7-diene, 455 of 5-(triethoxysilyl)norbomerie, 616 of 5-(trimethoxysilyl)norbornene, 615 of 1,7,7-tfimethylnorbomene 439 of 5-(trimethylsiloxy)methylnorbomene, 617 of trimethyisilylcyclooctatetraeae, 528 ROMP catalysts, 127,385 Fischer-type, 13 l One-cx)mponent, 128,162 Multicomponent, 146 Schrock-type, 133 Two-component, 140
Rotaxanes, 9 RTM process, 1177 Ruthenium-alkytidene, 179 Ruthenium trichloride, 164 Ruthenium-vinylalkylidene, 180 Schrock-type catalysts, 133 Semiconductors, 1221 Side-chain liquid crystalline polymers, 87,808 Monomers for, 87 Silacycloalkenes, 18 l-Silacyclobutene, 96 1, l-Dimethyl-, 96 l-Silacyclopentene, 96 l-Chloro- l-methyl-, 98 1, l-Dimethyl-, 97 1, l-Diphenyl-, 97 l-Methyl-, 96 l-Methyl- l-phenyl-, 96 Solubility, 923 Solvents, 220 Spiro[cyclopropyl-7,1 ']norbomene, 789 Star copolymers, 836,1214 Amphiphilic, 841,1215 Stereochemistry, 1051 Stereoselectivity, 1055 in copolymerization, 1077 of 1,5-cyclooctadiene polymerization, 1070 of cyclopemene polymerization, 106 l of dicyclopemadiene polymerization, 1076 of norbomadiene polymerization, 1075 ofnorbomeae polymerization, 107 l in ROMP, 1059 in Ziegler-Natta polymerization, 1055 Steric configuration, 1053
1261 of polyalkenamers, 1057 of polydodecenamer, 1069 of polyoctenamer, 1068 of polypentenamer, 1066 Steric effocts, 1051 in cationic polymerizations, 1051 Steric interactions, 1088 Structure, 875 of active species, 1011 of anionic polymers, 888 of cationic polymers, 875 of ROMP polymers, 901 of Ziegler-Natta polymers, 890 Substituted acenaphthylene, 311 l-Methylacenaphthylene,311 3-Methylacenaphthylene,312 5-Methylacenaphthylene,312 Substituted bieyelo[2.2.1]hept-2-ene, 429 Substituted bieyelo[2.2.1]hept-2,5-di erie, 442 Substituted cyclohexene, 253 l-Methylcyclohexene, 254 3-Methyleneeyelohexene,254 l-Vmylcyelohexene, 255 4-Vinylcyclohexene, 256 Substituted cyclooctatetraene, 410 Substituted cyclopentadiene, 247 Substittaed deltacyclene, 460 Substituted fulvenes, 252 Substittaed mdenes, 285 5-Bromomdene, 299 6-Bromomdene, 299 4-Bromobutyl-I-mdene,299 3-Bromopropyl-l-mdene,299 I,l-Dimethylmdene,288 2,3-Dimethylindene,288 4,6-D~ylmdene, 288 4,7-Dimethylmdene, 289 5,6-Dimethylmdene, 289
5,7-Dimethylmdene, 290 6,7-D~ylindene, 291 1,3-Diphmyl- 294 l-lndenylmdene, 295 3-1ndenylmdene, 296 4-Methoxymdene, 294 5-Methoxymdene, 294 6-Methoxymdene, 295 l-Methylindene, 285 2-Methylmdene, 286 5-Methylindene, 286 6-Methylindene, 287 7-Methylmdene, 287 3,4,5,6,7-PmtanaXhylindene, 293 l-Phenylmdene, 294 4,5,6,7-Tetramethylindene, 292 4,6,7-Trimethytindene, 292 5-Vinylindene, 293 Substituted norbomene, 265 Taetieity, 1071, 1079 of polyalkenan~rs, 1079 of polynorbomene, 1071,1081 of substituted polynorbomene, 1071 Tantalacyclobutanes, 166 Tantalum-alkylidene, 166 Tebbe reagent, 165 Telechelic polymers, 1232 Telene, 1177 Terpene resins, 1143 Terpenes, 268,1143 3,3,4,4-Tetracyanotricyclo[4.2.1.0 ~'s] non-7-ene, 632 Tetracyclo[4.4.O. 12,s.17'1~ -diene,308,480,483 Tetracyclo[4.4.0.12"517'~~ me, 61,476,482 Dimethyl-,478 Ethylidene,477,482 Functionalized, 638
1262 Isobutyl-, 477 Methyl-, 477 Trimcthyl-, 479 Tetracyclo[2.2.2 ~. 11'4.03.~]non-8-ene see Deltacyclene 4,5,6,7-Tetrahydrooxepme, 37 7-Acetoxy-, 37 Tetraphenylporphyrmat~ungsten, 184 Thermodynamic, 943 Equilibrium, 949 Parameters, 945 Stability, 943 Thermodynamic equilibrium, Monomer-polymer, 949 Ring-chain, 951 cis-trans, 959 between chains, 963 Tm tetrachloride, 154 Titanacyclobutanes, 165 Titanium tetrachloride, 154 Topas, 1179 Applications of, ! 181 ~ o m i c aspects of, 1181 Polymerization procedures of, 1179 Properties of, II 79 Starting materials of, 1179 Structure of, 1179 l-Trichlorosilyl-5,9- cyclododecadierie, 531 Tricyclo[4.3.0. I ~]deca-3,7-diene,59, 460, see Dicyclopentadiene Tricyclo[4.2.2 .0~ ]deca-3,9-diene-7,8-dicarboxylate, 63 7 Dimethyl, 637 Tricyclo [4.2.2.0~ ]deca-3,7,9-triene, 473 7,8-Benzo-, 474 7,8,9, I 0-Dibenzo-, 474 7,8-dicarboxylate, 636 Dimethyl-, 636
Tncyclo[5.2.I.0z'6]deca-2,5,8-triene, 739 Tricyclo[4.3.0.12"~]doc-3-ene,58 Tricyclo[5.2.1.02"~]doc-3-ene,472 Tricyclo[4.5.0.12"5]dodoca-3-ene,60 Tricyciohexene, see benzvalene Tricyclononene, 58 T ricyclo[4.2.0.0z'5]octa-3,7-dime, 455 Tricyclopentadiene,26 Tricyclo[4.6.0.12"~]~decadiene,61 Tricyclo[4.6.0.12"~]tridoca-3-ene, 61 Tricyclo[4.4.0.12"S]undeca-3,8-~ene, 488,490 Tricyclo[4.4.0.12"S]undeca-3-ene,59, 487,488 Triethylaluminium, 155 Trimethanodecahydroanthracene,481 N-(2-Trimethylammonium chloride)ethyl-7-oxanorbom-2-enc~ 5,6-dicarboximide,677 Trimethylenenorbomene, 58,472 I,7,7-Trimethylnorbomene, 439 I,1,3-Trimethyl-I-silacyclopent-3ene, 654 Tungsten-alkylidene,167 Tungsten hexachloride, 162 Tungsten oxo-alkylidene,176 Tungsten oxo-vinylalkylidene,178 Unsaturatod polymers, 846,849 Vestenamer, I 154,I159 4-Vmylcyclohexme, 255,724 5-Vmylnorbomene, 54 Viscosity,923 Water soluble ruthenium, 136 Water systems, 150,1027 WCIdwater, 1027 Well-defined catalysts, 131,132 p-Xylylene, 260 Zeonex, 1170 Ziegler-Natta catalysts, 120 On~ent, 120
1263 Two-component, 121,157 Ziegler-Natta polymerization, 327, 707, 857 of cyclobtmme, 327 of cycloheptene, 339 of cyclohexene, 338 of 1,5-cyclooctadiene, 340 of cyclooctene, 340 of cyclopentene, 331 of dicyclopentadiene, 355 of dihydrodicyclopentadime, 358 of dimothanodecahydro-9Hfluorene,361 of dimethanohexahydronaphthalene,359
of d i m e t h a n ~ y d r o - I,Hbenzoindene, 360 of dimethanooctahydronaphthalene, 358 of dimethylcyclohexene, 339 of mdene, 355 of hexacyclotetradecene, 362 of functionalized cyr 363 of l-methylcyclob~e, 330 of 3-me~ylcyclobutene, 33 l of norbomadiene, 352 of norbomene, 344 Zinc dichloride, 154 Zirconium tetrachloride, 154 Z i r c o n ~ e , 124,125, 329,330,333
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1265 STUDIES IN SURFACE SCIENCE AND CATALYSIS Advisory Editors: B. Delmon, Universit~ Catholique de Louvain, Louvain-la-Neuve, Belgium J.T. Yates, University of Pittsburgh, Pittsburgh, PA, U.S.A. Volume 1
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Prepacetion of Catalysts I.Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the First International Symposium, Brussels, October 14-17,1975 edited by B. Delmon, P.A.Jacoba and G. Poncelet The Control of the Reactivity of Solids. A Critical Survey of the Factors that Influence the Reactivity of Solids, with Special Emphasis on the Control of the Chemical Processes in Relation to Practical Applications by V.V. Boldyrev, M. Bulen$ and B. Delmon Preparation of Catalysts I1.Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Second International Symposium, Louvain-la-Neuve, September 4-7, 1978 edited by B. Delmon, P.Grange, P.Jacob= and G. Poncelet Growth and Properties of Metal Clusters. Applications to Catalysis and the Photographic Process. Proceedings of the 32nd International Meeting of the Societe de Chimie Physique, Villeurbanne, September 24-28, 1979 edited by J. Bourdon Catalysis by Zeolites. Proceedings of an International Symposium, Ecully (Lyon), September 9-11, 1980 edited by B. Imelik, C. Naccache, Y. Ben Taarit, J.C. Vedrine, G. Coudurier and H. Praliaud Catalyst Deactivation. Proceedings of an International Symposium, Antwerp, October 13-15,1980 edited by B. Delmon and G.F. Froment New Horizons in Catalysis. Proceedings of the 7th International Congress on Catalysis, Tokyo, June 30--July4, 1980. Parts A and B edited by T. Selyama and K. Tanabe Catalysis by Supported Complexes by Yu.I. Yermakov, B.N. Kuznetsov and V.A. Zakharov Physics of Solid Surfaces. Proceedings of a Symposium, Bechyi~e, September 29-October 3,1980 edited by M. Lbzni~ka Adsorption at the Gas-Solid and Uquld-Solid Interface. Proceedings of an International Symposium, Aix-en-Provence, September 21-23, 1981 edited by J. Rouquerol and K.S.W. Sing Metal-Support and Metal-Additive Effects in Catalysis. Proceedings of an International Symposium, Ecully (Lyon), September 14-16, 1982 edited by B. Imelik, C. Naccache, G. Coudurier, H. Praliaud, P. Meriaudeau, P. Gallezot, G.A. Martin and J.C. Vedrine Metal Microstructures in Zeolites. Preparation- Properties - Applications. Proceedings of a Workshop, Bremen, September 22-24, 1982 edited by P.A.Jacobs, N.I. Jaeger, P.JiK= and G. SchuIz-Ekloff Adsorption on Metal Surfaces. An Integrated Approach edited by J. B&nard Vibrations at Surfaces. Proceedings of the Third International Conference, Asilomar, CA, September 1-4, 1982 edited by C.R. Brundle and H. Morawitz Heterogeneous Catalytic Reactions Involving Molecular Oxygen by G.I. Golodets
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Preparation of Catalysts III. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Third International Symposium, Louvain-la-Neuve, September 6-9, 1982 edited by G. Poncelat, P. Grange and P.A. Jacob= Spillover of Adsorbed Species. Proceedings of an International Symposium, Lyon-Villeurbanne, September 12-16, 1983 edited by G.M. Pajonk, S.J. Teichner and J.E. Germain Structure and Reactivity of Modified Zeolite=. Proceedings of an International Conference, Prague, July 9-13, 1984 edited by P.A.Jacobs, N.I. Jaeger, P.Jim, V.B. Kazansky and G. Schulz-Ekloff Catalysis on the Energy Scene. Proceedings of the 9th Canadian Symposium on Catalysis, Quebec, P.Q., September 30-October 3, 1984 edited by S. Kaliaguine and A. Mahay Catalysis by Acids and Bases. Proceedings of an International Symposium, Villeurbanne (Lyon), September 25-27, 1984 edited by B. Imelik, C. Naccache, G. Coudurier, Y. Ben Taartt and J.C. Vedrine Adsorption and Catalysis on Oxide Surface=. Proceedings of a Symposium, Uxbridge, June 28-29, 1984 edited by M. Che and G.C. Bond Unsteady Processes in Catalytic Reactors by Yu.Sh. Matros Physics of Solid Surfaces 1984 edited by J. Koukal Zeolites: Synthesis, Structure, Technology and Application. Proceedings of an International Symposium, Portoro~-Portorose, September 3-8, 1984 edited by B. Dr'2aj, S. Ho~evar and S. Pejovnik Catalytic Potymedzatlon of Oleflns. Proceedings of the International Symposium on Future Aspects of Olefin Polymerization, Tokyo, July 4-6, 1985 edited by T. Keii and K. Soga Vibrations at Surfaces 1985. Proceedings of the Fourth International Conference, Bowness-on-Windermere, September 15-19, 1985 edited by D.A. King, N.V. Richardson and S. Holloway Catalytic Hydrogenation edited by L. Cerven'~ New Developments in Zeolite Science and Technology. Proceedings of the 7th International Zeolite Conference, Tokyo, August 17-22, 1986 edited by Y. Murakami, A. lijima and J.W. Ward Metal Clusters in Catalysis edited by B.C. Gates. L. Guczi and H. Kn6zinger Catalysis and Automotive Pollution Control. Proceedings of the First International Symposium, Brussels, September 8-11, 1986 edited by A. Crucq and A. Frennet Preparation of Catalysts IV. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Fourth International Symposium, Louvain-laNeuve, September 1-4, 1986 edited by B. Delmon, P. Grange, P.A. Jacobs and G. Poncelet Thin Metal Films and Gas Chemisorption edited by P.Wissmann Synthesis of High-silica Aluminosilicate Zeolites edited by P.A. Jacob= and J.A. Martens Catalyst Deactivation 1987. Proceedings of the 4th International Symposium, Antwerp, September 29-October 1, 1987 edited by B. Delmon and G.F. Froment Keynotes in Energy-Related Catalysis edited by S. Kaliaguine
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Methane C o n ~ . Proceedingsof a Symposium on the Production of Fuelsand Chemicals from Natural Gas, Auckland, April 27-30, 1987 edited by D.M. Bibby, C.D. Chang, R.F. Howe and S. Yurchak Innovation in Zeolite Materials Science. Proceedings of an International Symposium, Nieuwpoort, September 13-17, 1987 edited by P.J. Grobat, W.J. Mortler, E.F.Vansant and G. Schulz-Ekloff Catalysis 1987. Proceedings of the 10th North American Meeting of the Catalysis Society, San Diego, CA, May 17-22, 1987 edited by J.W. Ward Characterization of Porous Solids. Proceedings of the IUPAC Symposium (COPS I), Bad Soden a. Ts., April 26-29,1987 edited by K.K. Unger, J. Rouquerol, K.S.W. Sing and H. Kral Physics of Solid Surfaces 1987. Proceedings of the Fourth Symposium on Surface Physics, Bechyne Castle, September 7-11, 1987 edited by J. Koukal Heterogeneous Catalysis and Fine Chemicals. Proceedings of an International Symposium, Poitiers, March 15-17, 1988 edited by M. Gutsnat, J. Barrault, C. Bouchoule, D. Duprez, C. Montissler and G. Pkrot Laboratory Studies of Heterogeneous Catalytic Processes by E.G. Christoffei, revised and edited by Z. Pail Catalytic Processes under Unsteady-State Conditions by Yu. Sh. Matros Successful Design of Catalysts. Future Requirements and Development. Proceedings of the Worldwide Catalysis Seminars, July, 1988, on the Occasion of the 30th Anniversary of the Catalysis Society of Japan edited by T. Inui Transition Metal Oxide=. Surface Chemistry and Catalysis by H.H. Kung Zeolite= as Catalysts, Sorbents and Detergent Builders. Applications and Innovations. Proceedings of an International Symposium, W0rzburg, September 4-8,1988 edited by H.G. Karge and J. Weltkarnp Photochemistry on Solid Surface= edited by M. Anpo and T. Matsuura Structure and Reactivity of Surfaces. Proceedings of a European Conference, Trieste, September 13-16, 1988 edited by C. Morterra, A. Zacchina and G. Costa Zeolite=: Facts, Figures, Future. Proceedings of the 8th International Zeolite Conference, Amsterdam, July 10-14, 1989. Parts A and B edited by P.A. Jacobs and R.A. van Santen Hydrotreating Catalysts. Preparation, Characterization and Performance. Proceedings of the Annual International AIChE Meeting, Washington, DC, November 27-December 2, 1988 edited by M.L. Occelli and R.G. Anthony New Solid Acids and Bases. Their Catalytic Properties by K. Tanabe, M. Misono, Y. Ono and H. Hattort Recent Advances in Zeolite Science. Proceedings of the 1989 Meeting of the British Zeolite Association, Cambridge, April 17-19, 1989 edited by J. Klinowsky and P.J. Barrie Catalyst in Petroleum Refining 1989. Proceedings of the First International Conference on Catalysts in Petroleum Refining, Kuwait, March 5-8, 1989 edited by D.L. Trimm, S. Akashah, M. Absi-Halabi and A. Bishera Future Opportunities in Catalytic and Separation Technology edited by M. Misono, Y. Moro-oka and S. Kimura
1268 New Developments in Selective Oxidation. Proceedings of an International Symposium, Rimini, Italy, September 18-22, 1989 edited by G. Centi and F.Trifiro Volume 56 Olefln Polymerization Catalysts. Proceedings of the International Symposium on Recent Developments in Olefin Polymerization Catalysts, Tokyo, October 23-25, 1989 edited by T. Keii and K. Soga Volume 57A Spectroscopic Analysis of Heterogeneous Catalysts. Part A: Methods of Surface Analysis edited by J.L.G. Rerro Volume 57B Spectroscopic Analysis of Heterogeneous Catalysts. Part B: Chemisorptlon of Probe Molecules edited by J.LG. Rerro Volume 58 Introduction to Zeolite Science and Practice edited by H. van Bekkum, E.M. Ranigen and J.C. Jansen Volume 59 Heterogeneous Catalysis and Fine Chemicals II. Proceedings of the 2nd International Symposium, Poitiers, October 2-6, 1990 edited by M. Guismet, J. Barrault, C. Bouchoule, D. Duprez, G. Pkrot, R. Maurel and C. Montassier Volume 60 Chemistry of Microporous Crystals. Proceedings of the International Symposium on Chemistry of Microporous Crystals, Tokyo, June 26-29, 1990 edited by T. Inui, S. Namba and T. Tetsumi Natural Gas Conversion. Proceedings of the Symposium on Natural Gas Volume 61 Conversion, Oslo, August 12-17, 1990 edited by A. Holmen, K.-J. Jens and S. Kolboe Characterization of Porous Solids II. Proceedings of the IUPAC Symposium Volume 62 (COPS II), Alicante, May 6-9, 1990 edited by E Rodriguez-Reinoso, J. Rouquerol, K.S.W. Sing and K.K. Unger Preparation of Catalysts V. Scientific Bases for the Preparation of Heterogeneous Volume 63 Catalysts. Proceedings of the Fifth International Symposium, Louvain-la-Neuve, September 3-6, 1990 edited by G. Poncelet, P.A. Jacobs, P. Grange and B. Delmon Volume 64 New Trends in CO Activation edited by L Guczi Catalysis and Adsorption by Zeolttes. Proceedings of ZEOCAT 90, Leipzig, Volume 65 August 20-23, 1990 edited by G. Ohlmann, H. Pfeifer and R. Frlcke Dioxygen Activation and Homogeneous Catalytic Oxidation. Proceedings of the Volume 66 Fourth International Symposium on Dioxygen Activation and Homogeneous Catalytic Oxidation, BalatonfOred, September 10-14, 1990 edited by LI. Sim&ndi Structure-Activity and Selectivity Relationships in Heterogeneous Catalysis. Volume 67 Proceedings of the ACS Symposium on Structure-Activity Relationships in Heterogeneous Catalysis, Boston, MA, April 22-27, 1990 edited by R.K. Grasselli end A.W. Sleight Catalyst Deactivation 1991. Proceedings of the Fifth International Symposium, Volume 68 Evanston, IL, June 24-26, 1991 edited by C.H. Bartholomew end J.B. Butt Zeolite Chemistry and Catalysis. Proceedings of an International Symposium, Volume 69 Prague, Czechoslovakia, September 8-13, 1991 edited by P.A.Jacobs, N.I. Jaeger, L. Kubelkov~ and B. Wichtertov~i Poisoning and Promotion in Catalysis based on Surface Science Concepts and Volume 70 Experiments by M. Kiskinova
Volume 55
1269 Volume 71 Volume 72
Volume 73 Volume 74 Volume 75 Volume 76 Volume 77
Volume 78
Volume 79 Volume 80 Volume81 Volume82
Volume 83 Volume 84
Volume 85 Volume 86 Volume 87
Catalysis and Automotive Pollution Control II. Proceedings of the 2nd International Symposium (CAPoC 2), Brussels, Belgium, September 10-13, 1990 edited by A. Crucq New Developments in Selective Oxidation by Heterogeneous Catalysis. Proceedings of the 3rd European Workshop Meeting on New Developments in Selective Oxidation by Heterogeneous Catalysis, Louvain-la-Neuve, Belgium, April 8-10, 1991 edited by P. Rulz and B. Delmon Progress in Catalysis. Proceedings of the 12th Canadian Symposium on Catalysis, Banff, Alberta, Canada, May 25-28, 1992 edited by K.J. Smith and E.C. Sanford Angle-Resolved Photoemission. Theory and Current Applications edited by S.D. Kevan New Frontiers in Catalysis, Parts A-C. Proceedings of the 10th International Congress on Catalysis, Budapest, Hungary, 19-24 July, 1992 edited by L Guczi, F. Solymosi and P.T4~knyi Ruid Catalytic Cracking: Science and Technology edited by J.S. Magee and M.M. Mitchell, Jr. New Aspects of Spillover Effect in Catalysis. For Development of Highly Active Catalysts. Proceedings of the Third International Conference on Spillover, Kyoto, Japan, August 17-20, 1993 edited by 1".Inul, K. Fujimoto, T. Uchijima and M. Masal Heterogeneous Catalysis and Rne Chemicals III. Proceedings of the 3rd International Symposium, Poitiers, April 5- 8, 1993 edited by M. Guisnet, J. Barbier, J. Barrault, C. Bouchoule, D. Duprez, G. P6rot and C. Montassier Catalysis: An Integrated Approach to Homogeneous, Heterogeneous and Industrial Catalysis edited by J.A. Moulijn, P.W.N.M. van Leeuwen and R.A. van Santen Fundamentals of Adsorption. Proceedings of the Fourth International Conference on Fundamentals of Adsorption, Kyoto, Japan, May 17-22, 1992 edited by M. Suzuki Natural Gas Conversion II. Proceedings of the Third Natural Gas Conversion Symposium, Sydney, July 4-9, 1993 edited by H.E. Curry-Hyde and R.F. Howe New Developments in Selective Oxidation II. Proceedings of the Second World Congress and Fourth European Workshop Meeting, Benalm~dena, Spain, September 20-24, 1993 edited by V. Cort~ Corber&n and S. Vic Bellbn Zeolites end Microporous Crystals. Proceedings of the International Symposium on Zeolites and Microporous Crystals, Nagoya, Japan, August 22-25, 1993 edited by T. Hattori and 11.Yashlma Zeolttes and Related Microporous Materials: State of the Art 1994. Proceedings of the 10th International Zeolite Conference, Garmisch-Partenkirchen, Germany, July 17-22, 1994 edited by J. Weitkamp, H.G. Karge, H. Pfelfer and W. H61derich Advanced Zeolite Science and Applications edited by J.C. Jansen, M. St(~:ker, H.G. Karge and J.Weltkamp Oscillating Heterogeneous Catalytic Systems by M.M. Slin'ko and N.I. Jaeger Characterization of Porous Solids III. Proceedings of the IUPAC Symposium (COPS III), Marseille, France, May 9--12, 1993 edited by J.Rouquerol, F. Rodriguez-Reinoso, K.S.W. Sing and K.K. Unger
1270 Volume 88 Volume 89
Volume90 Volume91
Volume92
Volume 93 Volume 94 Volume95 Volume96
Volume97 Volume98
Volume99 Volume 100
Volume 101 Volume 102 Volume 103 Volume 104 Volume 105
Catalyst Deactivation 1994. Proceedings of the 6th International Symposium, Ostend, Belgium, October 3-5, 1994 edited by B. Detmon and G.F. Froment Catalyst Design for Tailor-made Polyoleflns. Proceedings of the International Symposium on Catalyst Design for Tailor-made Polyolefins, Kanazawa, Japan, March 10-12, 1994 edited by K. Sogs and M. Terano Acid-Base Catalysis II. Proceedings of the International Symposium on Acid-Base Catalysis II, Sapporo, Japan, December 2-4, 1993 edited by H. Hattori, M. Misono and Y. Ono Preparation of Catalysts VI. Scientific Bases for the Preparation of Heterogeneous Catalysts. Proceedings of the Sixth International Symposium, Louvain-La-Neuve, September 5-8, 1994 edited by G. Poncelet, J. Martens, B. Delmon, P.A.Jacobs and P.Grange Science and Technology in Catalysis 1994. Proceedings of the Second Tokyo Conference on Advanced Catalytic Science and Technology, Tokyo, August 21-26, 1994 edited by Y. Izumi, H. Arai and M. hNamoto Characterization and Chemical Modif~,ation of the Silica Surface by E.F. Vansant, P.Van Der Voort and K.C. Vrancken Catalysis by Microporous Materials. Proceedings of ZEOCAT'95, Szombathely, Hungary, July 9-13, 1995 edited by H.K. Bayer, H.G.Kerge, I. Kiricsi and J.B. Nagy Catalysis by Metals and Alloys by V. Ponec and G.C. Bond Catalysis and Automotive Pollution Control III. Proceedings of the Third International Symposium (CAPoC3), Brussels, Belgium, April 20-22, 1994 edited by A. Frennet and J.-M. Bestin Zeolites: A Refined Tool for Designing Catalytic Sites. Proceedings of the International Symposium, Qu(~bec, Canada, October 15-20, 1995 edited by L. Bonneviot and S. Kalisguine Zeolite Science 1994: Recent Progress and Discussions. Supplementary Materials to the 10th International Zeolite Conference, Garmisch-Partenkirchen, Germany, July 17-22, 1994 edited by H.G. Karge and J. Weitkamp Adsorption on New and Modified Inorganic Sorbents edited by A. Dqbrowski and V.A. Tertykh Catalysts in Petroleum Refining and Petrochemical Industries 1995. Proceedings of the 2nd International Conference on Catalysts in Petroleum Refining and Petrochemical Industries, Kuwait, April 22-26, 1995 edited by M. AI)si-Halabi, J. Bashara, H. Qabazerd and A. Stanisiaus 1l t h International Congress on Catalysis - 40th Anniversary. Proceedings of the 1lth ICC, Baltimore, MD, USA, June 30-July 5, 1996 edited by J. W. Hightower, W.N. Delgass, E. Iglesia and A.T. Bell Recent Advances and New Horizons in Zeolite Science and Technology edited by H. Chon, S.I. Woo and S. -E. Park Semiconductor Nanoclusters - Physical, Chemical, and Catalytic Aspects edited by P.V. Kamet and D. Meisel Equilibria and Dynamics of Gas Adsorption on Heterogeneous Solid Surfaces edited by W. Rudzifiski, W.A. Steele and G. Zgrsblich Progress in Zeolite and Microporous Materials Proceedings of the 1lth International Zeolite Conference, Seoul, Korea, August 12-17, 1996 edited by H. Chon, S.-K. Ihm and Y.S. Uh
1271 Volume 106
Hydrotreatment and Hydrocracking of Oil Fractions Proceedings of the 1st International Symposium / 6th European Workshop, Oostende, Belgium, February 17-19, 1997 edited by G.F. Froment, B. Detmon and P.Grange Volume 107 Natural Gas Conversion IV Proceedings of the 4th International Natural Gas Conversion Symposium, Kruger Park, South Africa, November 19-23, 1995 edited by M. de Pontes, R.L. Espinoza, C.P. NJcolaides, J.H. Scholtz and M.S. Scurretl Volume 108 Heterogeneous Catalysis and Rne Chemicals IV Proceedings of the 4th International Symposium on Heterogeneous Catalysis and Fine Chemicals, Basel, Switzerland, September 8-12, 1996 edited by H.U. Blaser, A. b i k e r and R. Prins Volume 109 Dynamics of Surfaces and Reaction Kinetics in Heterogeneous Catalysis. Proceedings of the International Symposium, Antwerp, Belgium, September 15-17, 1997 edited by G.F. Froment and K.C. Waugh Volume 110 Third World Congress on Oxidation Catalysis. Proceedings of the Third World Congress on Oxidation Catalysis, San Diego, CA, U.S.A., 21-26 September 1997 edited by R.K. Grassetlt, S.T. Oyama, A.M. Gaffney and J.E. Lyons Volume 111 Catalyst Deactivation 1997. Proceedings of the 7th International Symposium, Cancun, Mexico, October 5-8, 1997 edited by C.H. Bartholomew and G.A. Fuentes Volume 112 Spillover and Migration of Surface Species on Catalysts. Proceedings of the 4th International Conference on Spillover, Dalian, China, September 15-18, 1997 edited by Can U and Qin Xin Volume 113 Recent Advances in Basic and Applied Aspects of Industrial Catalysis. Proceedings of the 13th National Symposium and Silver Jubilee Symposium of Catalysis of India, Dehradun, India, April 2-4, 1997 edited by T.S.R. Presade Rao and G. Murali Dhar Volume 114 Advances in Chemical Conversions for Mitigating Carbon Dioxide. Proceedings of the 4th International Conference on Carbon Dioxide Utilization, Kyoto, Japan, September 7-11, 1997 edited by 1".Inui, M. Anpo, K. Izui, S. Yanagida and T. Yamaguchi Volume 115 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters. A patent-oriented survey by M. Siderls Volume 116 Catalysis and Automotive Pollution Control IV. Proceedings of the 4th International Symposium (CAPoC4), Brussels, Belgium, April 9-11, 1997 edited by N. Krmm, A. Frennst and J.-M. Bastin Volume 117 Mesoporous Molecular Sieves 1998 Proceedings of the 1st International Symposium, Baltimore, MD, U.S.A., July 10-12, 1998 edited by LBonneviot, F. B61and, C. Danumah, S. Giasson and S. Kaliaguine Volume 118 Preparation of Catalysts VU Proceedings of the 7th International Symposium on Scientific Bases for the Preparation of Heterogeneous Catalysts, Louvain-la-Neuve, Belgium, September 1-4, 1998 edited by B. Delmon, P.A.Jacobs, R. Maggi, J.A. Martens, P.Grange and G. Poncelat Volume 119 Natural Gas Conversion V Proceedings of the 5th International Gas Conversion Symposium, Giardini-Naxos, Taormina, Italy, September 20-25, 1998 edited by A. Parmaliana, D. Sanfilippo, E Frusteri, A. Vaccari and E Arena Volume 120A Adsorption and its Applications in Industry end Environmental Protection. Vol I: Applications in Industry edited by A. Debrowski
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Volume 120B Adsorption and its Applic~ions in Industry and Environmental Protection. Vol II: Applications in Environmental Protection edited by A. Debrow~ki Volume 121 Science and Technology in Cataly~s 1998 Proceedings of the Third Tokyo Conference in Advanced Catalytic Science and Technology, Tokyo, July 19-24, 1998 edited by H. Ha~ori and K. O1s~uka Volume 122 Reaction Kinstlcs and the Development of Catalytic Procesm Proceedings of the International Symposium, Brugge, Belgium, April 19-21, 1999 edited by G.F Froment and K.C. Waugh Volume 123 Catalysis: An Integrated Approach Second, Revised and Enlarged Edition edited by R.A. van Santen, P.W.N.M. van Leeuwen, J.A. Moulijn and B.A. Averill Volume 124 Experiments in Catalytic Reaction EngineIDring by J.M. Berry Volume 125 Porous Materials in Environmentally Friendly Processes Proceed,ngs of the 1st International FEZA Conference. Eger. Hungary. September 1.4. 1999 edited by I. Kiricsl. G. PiiI-Borb~ly. J.B. Nagy and H.G. Karge Volume 126 Catalyst Deactivation 1999 Proceedings of the 8th International Symposium. Brugge. Belgium. October 10-13. 1999 edited by B. Delmon and G.F Froment Volume 127 Hydrotreatment and Hydrocracking of Oil Fractions Proceedings of the 2nd International Symposium/7th European Workshop. Anl~,verpen. Belgium. November 14-17. 1999 ed,ted by B. Delmon. G.F Froment and P. Grange Volume 128 Characterisation of Porous Solids V Proceedings of the 5th International Symposium on the Characterisation of Porous Solids (COPS.V). Heidelberg. Germany. May 30- June 2. 1999 edited by K.K. Unger. G. KreyM and J.P. Bas~elt Volume 129 Nanoporous Materials II Proceedings of the 2nd Conference on Access in Nanoporous Materials. Banff. Alberta. Canada. May 25-30. 2000 edited by A. Sayari. M. Jaroniec and T.J. Pinnavaia Volume 130 12th International Congress on Cataly~ts Proceedings of the 12th ICC. Granada. Spain. July 9-14. 2000 edited by A. Corma. F.V. Melo. S. Mendtoroz and J.L.G. Fierro Volume 131 Catalytic Polymerization of Cycloolefins Ionic. Z,egler-Narla and Ring.Opening Metathesis Polymerizat,on by V. Dragutan and R. Streck
