Polymer Synthesis, Volume 3, Second Edition (Organic Chemistry, a Series of Monographs)

PREFACE TO SECOND EDITION This volume continues in the same format as the first edition with updates on the syntheses o...

Author: Stanley R. Sandler | Wolf Karo

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PREFACE TO SECOND EDITION

This volume continues in the same format as the first edition with updates on the syntheses of various types of polymers, including olefin-sulfur dioxide copolymers, polythioesters, sulfide polymers, polyisocyanates, polyoxyalkylhydroxy compounds, polyvinyl carbazole, polyvinyl acetate, polyallyl esters, polyvinyl fluoride, and miscellaneous polymer preparations. The book should be useful to academic and industrial chemists who desire typical synthetic procedures for preparing the polymers described herein. In addition to reviewing the latest journals, we survey the patent literature and give numerous additional references. Safety in carrying out the preparations is essential to experimenters and their co-workers. The Material Safety Data Sheets (MSDS) for all chemicals to be used must be reviewed for hazards and safe handling procedures. When in doubt about any matter in the MSDS, please consult the manufacturer or supplier. Also, seek the advice of an experienced chemist on any questions that you may have concerning safety. Be sure to follow the recommendations for personal protective equipment and always operate in a well-ventilated hood with proper shielding. We again express our appreciation to our wives for their understanding and encouragement during the preparation of the manuscript for this second edition. We also thank the staff of Academic Press for guiding the publication of the manuscript to its final book form.

Stanley R. Sandler Wolf Karo

ix

PREFACE TO FIRST EDITION

In a manner similar to Volumes I and II, detailed laboratory instructions are presented for the preparation of various types of polymers such as olefin-sulfur dioxide copolymers, polythioesters, sulfide polymers, polyisocyanates, polyoxyalkylhydroxy compounds, polyvinyl carbazole, polyvinyl acetate, polyallyl esters, polyvinyl fluoride, and miscellaneous polymer preparations. The latest journal articles and the patent literature have been reviewed and tabulated in each chapter. In some cases, the major literature sources used were patents. As in our earlier volumes, the procedures were selected both on the basis of safety and as representative of the general polymer preparation in question. Each chapter should be considered a good preparative introduction to the subject but not a final, definitive work. This book should be especially useful to both industrial chemists and students of polymer chemistry by providing a ready source of preparative procedures for various polymer syntheses. We have omitted many details of the mechanisms and kinetics of these polymerizations and have concentrated only on the synthetic details. Safety hazards and precautions are stressed in all chapters and the reader is urged not only to observe these but constantly to seek up-to-date information on a given monomer from both the literature and the chemical manufacturer. This book is only designed to provide useful polymer synthesis information and not to override the question of patentability or to suggest allowable industrial use. The toxicological properties of the reagents have in most cases not been completely evaluated, and the reader is urged to exercise care in their use and professional judgments before undertaking a procedure. We assume no liability for injuries, damages, or penalties resulting from the use of the chemical procedures described. We express our appreciation to our wives and children for their understanding and encouragement during the preparation of this manuscript. Special thanks are xi

xii

Preface to First Edition

due to Miss Emma Moesta for typing our manuscript in a most professional fashion. Finally, we thank the staff of Academic Press for guiding the publication of the manuscript to its final book form.

Stanley R. Sandler Wolf Karo

CONTENTS OF VOLUME 1, SECOND EDITION Chapter 1. Polymerization of Olefinic and Diolefinic Hydrocarbons Chapter 2. Polyesters Chapter 3. Polycarbonates Chapter 4. Polyamides Chapter 5. Polymerization of Aldehydes Chapter 6. Polymerization of Epoxides and Cyclic Ethers Chapter 7. Polyureas Chapter 8. Polyurethanes Chapter 9. Thermally Stable Polymers Chapter 10. Polymerization of Acrylate and Methacrylate Esters Chapter 11. Polymerization of Nitrile Monomers Chapter 12. Polyacrylamide and Related Amides Chapter 13. Organophosphorus Polymers Chapter 14. Free-Radical Initiation of Vinyl and Related Monomers Appendix Subject Index

CONTENTS OF VOLUME II, SECOND EDITION Chapter 1.

Urea,Melamine, Benzoguanamine-Aldehyde Resins (Amino Resins or Aminoplasts) Chapter 2. Phenol-Aldehyde Condensations Chapter 3. Epoxy Resins Chapter 4. Silicone Resins (Polyorganosiloxanes or Silicones) Chapter 5. Alkyd Resins Chapter 6. Polyacetals and Poly(vinyl acetals) Chapter 7. Poly(vinyl ethers) Chapter 8. Poly (N-vinylpyrrolidone) Chapter 9. Polymerization of Acrylic Acids and Related Compounds Chapter 10. Poly(vinyl chloride) Subject Index

xiii

Chapter 1

Olefin-Sulfur Dioxide Copolymers 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Conditions of Copolymerization of Sulfur Dioxide with Unsaturated Compounds . . . . . . . 3. Polysulfones by the Reaction of Olefins (Linear, Cyclic, and Branched) with Sulfur Dioxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1. General Procedures for Copolymerization of Olefins and Sulfur Dioxide . . . . . . . . . 3-2. Sulfur Dioxide-Butene Copolymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3. Preparation of a Copolymer of Ethylene and Sulfur Dioxide . . . . . . . . . . . . . . . . . 3-4. Preparation of Propylene-Sulfur Dioxide Copolymer . . . . . . . . . . . . . . . . . . . . . . 3-5. Preparation of Octene-Sulfur Dioxide Copolymer . . . . . . . . . . . . . . . . . . . . . . . . 3-6. Preparation of Cyclohexene-Sulfur Dioxide Copolymer . . . . . . . . . . . . . . . . . . . . . 3-7. Emulsion Copolymerization of 1-Butene and Sulfur Dioxide . . . . . . . . . . . . . . . . . . 4. Polysulfones from the Reaction of Dienes (Conjugated and Unconjugated) with Sulfur Dioxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1. Copolymerization of 1,3-Butadiene with Sulfur Dioxide . . . . . . . . . . . . . . . . . . . . . 4-2. Terpolymerization of 1,3-Butadiene, Cyclopentadiene, and Sulfur Dioxide . . . . . . . . 4-3. Copolymerization of Sulfur Dioxide with 1,5-Cyclooctadiene--General Method . . . . 4-4. Terpolymerization of Butadiene, trans-Piperylene with Sulfur Dioxide . . . . . . . . . . . 5. Polysulfones by the Reaction of Acetylene with Sulfur Dioxide . . . . . . . . . . . . . . . . . . . 5-1. General Procedure for the Preparation of Polysulfones from Acetylenes . . . . . . . . . 6. Polysulfones by the Reaction of Vinyl Monomers (CH2 -- CH -- R) with Sulfur D i o x i d e . . 6-1. Preparation of a Propylene-Methyl Methacrylate-Sulfur Dioxide Terpolymer . . . . . 6-2. Preparation of Propylene-Methyl Acrylate-Sulfur Dioxide Terpolymer . . . . . . . . . . 6-3. Preparation of Bicyclo[2.2.1]hept-2-ene-Ethyl Acrylate-Sulfur Dioxide Terpolymer 7. Polysulfones by the Reaction of Allylic Compounds with Sulfur Dioxide . . . . . . . . . . . . 7-1. Preparation of Allyl Chloride-Sulfur Dioxide Copolymer . . . . . . . . . . . . . . . . . . . 7-2. Terpolymerization of Allyl Alcohol, Acrylic Acid, and Sulfur Dioxide . . . . . . . . . . . 8. Miscellaneous Preparations and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 3 6 10 16 17 18 19 19 19 22 23 25 25 27 27 28 31 32 34 34 37 37 39 41 42

2

1.

1. Olefln--Sulfur Dioxide Copolymers

INTRODUCTION

It was early recognized that amorphous products were formed by the reaction of olefins and sulfur dioxide [1-1 d]. The elucidation of the products formed was first reported by Marvel [2] and Staudinger [3, 3a] in the early 1930s. Marvel reported that propylene and cyclohexene react with sulfur dioxide to form alternating copolymers of olefin and sulfur dioxide in a head-to-tail arrangement [2, 4]. Staudinger reported that 1,3-butadiene reacts with sulfur dioxide to form a cyclic sulfone and an amorphouse linear polysulfone [3, 3a, 5]. C--C

/

+ 802

-~

\

- - S O 2 - - C - - I -I

CH2 = CH-- C H = CH2 + SO2

,

so

- cI-I - ci-i= c i - i - cii

(1)

/

-), + t.

/

J

(2)

SO2 Sulfolene m.p. 65~

Fitch [6] at Phillips Petrolium Co. was issued a patent in 1936 that was followed by many others on the formation of polymeric sulfones from the reaction of olefins and sulfur dioxide. A patent to Frey and Snow of Phillips Petroleum Co. also describes some of the prior literature [7]. The olefin-sulfur dioxide polysulfone compositons are usually light-colored, thermoplastic, amorphous products that are moldable and extrudable. The polymers are not very resistant to alkaline solutions. The only olefin-sulfur dioxide product sold commercially is sulfolene by Phillips Petroleum Co. The linear polymers remain to be commercially produced. It is imeresting to note that a polysulfone, i.e., poly(phenylene sulfone), has been sold commercially since 1966 [8]. For more detailed discussions and historical background several earlier reviews are worth consulting [9, 9a]. The ceiling temperature of polymerization (T~) of the SO2/olefin polymers are between 25 to 100~ NMR analysis has indicated [9b] that the olefin used does not isomerize during copolymerization. Various vinyl monomers copolymerize with SO2 such as vinyl chloride, styrene, acrylamide, and chloroprene. However, methyl methacrylate is reported [9b] to homopolymerize in SO2 when used as a solvent (cationially or radically) but not to form polysulfones (sulfur dioxide copolymers). Acetylene and disubstituted acetylene (such as 2-butyne) do not form copolymers with SO2. However, n-alkyl acetylenes and phenylacetylene reaction to give a copolymer.

3

2. Conditionsof Copolymerization of Sulfur Dioxide

Polysulfones have found use as resists in the area of microlithography since the polysulfones are unstable toward radiation and heat below their melting points and the SO2 and olefin degradation products are volatile. It is interesting to note that some olefins undergo isomerization during the radiation induced degradation step [9c]. The structure of the olefin SO2 polymers has been investigated by NMR [9d] and a helical structure has been reported for these polymers via transmission electron microscopy.

0

CONDITIONS OF COPOLYMERIZATION OF SULFUR DIOXIDE WITH UNSATURATED COMPOUNDS

Sulfur dioxide does not homopolymerize, but on reaction with olefins it yields copolymers.Terminal olefins react more readily than those with an internal double bond. The presence of various substituents affects the rate of polymerization. Conjugated dienes copolymerize with sulfur dioxide to give linear polymers comaining residual double bonds. The copolymerization reaction is free radical in nature and is catalyzed by such initiators as peroxides [10], oxygen, azo compounds [11, 1 l a], and light [9a, 12]. Styrene dissolved in liquid sulfur dioxide and catalyzed by stannic chloride (cationic catalyst) gives only polystyrene whereas the use of azobisisobutyronitrile gives poly(styrene sulfone). Sulfur dioxide is a gas at ordinary temperatures and has the following physical properties. m.p.

- 75.46~

b.p.

- 10.02~

vapor pressure

( d e n s i t y o f liquid at - 10~

-

1.46 g r n / m l )

28.5 c m H g at - 3 0 ~ 53.1 c m H g at - 2 0 ~

115 171 2456

cmHgat0~ cmHgat

10~

c m H g at 2 0 ~

Reactions with sulfur dioxide are carried out in pressure vessels constructed of glass or stainless steel. Caution should be used and all reactions should be done under a hood and behind a barrier for protection. Copoiymerization is usually carried out in solution or emulsion [13-13b], but not in the vapor phase [14]. The reaction in the gaseous phase usually gives sulfinic acids. A solid state copolymerization has been reported for vinyl acetate with sulfur dioxide initiated by radiation [15].

1. Olefin-Sulfur Dioxide Copolymers

4

\

Liquid phase"

S O 2 -~-

/

\

/ C=C

9~

\ \ /

Gas phase"

802

-+-

C=C

\

/

\

/

EC--CSO2--1n \

/ C--C

\

/

502

\

/

/ "C--C--S02

- -~

/

/ C=C

(4)

\ SO2H

A ceiling temperature [16] (temperature at which rate of propagation and depropagation are equal) is independent of the kind of initiator, but depends on the given olefin. The polymerization is not always accelerated by heat and in fact in some cases slows as it approaches the ceiling temperature. The ceiling temperature for the copolymerization of sulfur dioxide with various vinyl compounds is shown in Table I [17] and is said to follow the relationship: T~ = A H I S

where AH is the heat change and S is the entropy change. Olefins with electron withdrawing substituents (--CN, --COOH, --COOR) cannot enter into copolymerization with sulfur dioxide. The reactivities of the olefins with sulfur dioxide is obtained by using cyclohexene as a standard at -20~ far below the ceiling temperature where depropagation is negligible [18]. Charge transfer complexes of the monomers were studied in the terpolymerization of neutral monomers (N) with electron-donor (D) and electron-acceptor (A) monomers [18a]. For example, norbornene as (D) monomer, SO2 as (A) monomer, and acrylonitrile as (N) molecules were studied. Thus acrylonitrile may not be effective in copolymerization but can be terpolymerized with SO2 [18a]. The NMR spectra have been reported for a variety of polyalkylene sulfones [ 18b]. All the polymers were prepared by radical copolymerization of a mixture of sulfur dioxide and alkene (mw 104-107). The NMR spectra were determined in DMSO or CDC13 solutions. Acrylamide has also been reported to be effective in producing copolymer using AIBN or ),-ray irradiation, as described by Bell Labs (R. E. Cais and G. J. Stute [ 18c]). Other catalysts have been reported by Shell [18d] to effect SO2/olefin polymerization, which involves Group VIII metal compounds, a bidentate ligand of P, As, or Sb, and an anion of nonhydrohalogenic acid having pK of approximately 6 (for example, the catalyst Pd(OAc)2"4-MeC6HaSO3H, and Ph2P(CHz)3PPh2).

2.

Conditions o f Copolymerization o f Sulfur Dioxide

TABLE I

Ceiling Temperatures for Polysulfone Formation a

Olefin Straight-chain 1-olefins Ethylene Propylene 1-Butene 1-Pentene 1-Hexene 1-Hexadecene Branched 1-olefins Isobutene

5

Structural skeleton

C=C C--C--C C2--C=C C3--C--C C4--C--C C 14 ~ C - - C

T~, ~

<95 62.5 63.5 44.5 60 48.5

C--C--C I C

6.5 - 3.5

2-Methyl- 1-pentene

C3--C=C I C

32.5

3-Methyl- 1-butene

C--C--C--C I C

36.5

4,4-Dimethyl- 1-pentene

2-Ethyl- 1-butene

2-Ethyl- 1-hexene

2,4,4-Trimethyl- 1pentene

(obs)

C I C--C--C--C--C I C C2--C-- C I C2

14.7 13.0 Completely miscible. No polymer formed on irradiation at any temp. down to - 80~ Upper soln. temp. at about - 3 1 o. No polymer formed on irradiation at any temp. down to - 80~

C4--C=C I C2 C I C-- C-- C-- C--C CI CI

Upper soln. temp. at about - 3 0 ~ No polymer formed on irradiation at any temp. down to - 80~

2-Olefins and cycloolefins /

trans-2-Butene

/

C

C= C

33.0 33.0

cis-2-Butene

C C

C

36.1

2-Butene (50% cis) 2-Pentene (---50% cis) 2-Heptene (---88% cis)

C--C=C--C C2--C=C--C C4--C=C--C

34.6 8.5 -38

Cyclopentene

C

N

/ C=C

/

C=C

\

/

N C

73

C

(continues)

6

1. Olefin-Sulfur Dioxide Copolymers

TABLE I Olefin

Structural skeleton /

Cyclohexene

(continued)

C

C=C

\

/

\

2-Methyl-2-butene

/ C--C

C

C

/ C

4-Methyl-2-pentene

Allyl compounds Allyl alcohol Allyl ethyl ether Diallyl ether Allyl formate Allyl acetate

\

\

/ C=C

27.3 25.5

C

C

2,3-Dimethyl-2-butene

(obs)

\

C--C C

Tc, ~

Completely miscible. No polymer formed on irradiation at any temp. down to - 80~

C

\ C

C-- C-- C - C-- C I C

HO--C--C=C

C2--O--C--C=C (C=C--C)20 O=C--O--C--C=C O=C--O--C--C--C I C

Allylacetic acid

O--C--C--C--C=C I O

Allyl chloride

C1--C--C--C

Allyl bromide

Br--C--C=C

Completely miscible. No polymer formed on irradiation at any temp. down to - 6 3 ~ (m.p.) Completely miscible. No polymer formed on irradiation at any temp. down to - 80~

66 66.5 >85 46 45

66___4

Trace of gummy material formed after 3 hr irradiation at - 8 0 ~ No polymer formed after 3 hr irradiation at - 80~

a Reprinted in part from R. E. Cook, F. S. Dainton, and K. J. Ivin, J. Polym. Sci. 26, 351 (1957). Copyright 1957 by the Journal of Polymer Science. Reprinted by permission of the copyright owner.

0

POLYSULFONES BY THE REACTION OF OLEFINS (LINEAR, CYCLIC, AND BRANCHED) WITH SULFUR DIOXIDE In 1910 B a d i s c h e A n i l i n e u n d S o d a - F a b r i k A k t i e n - G e s e l l s c h a f t ( B A S F ) [ 1 a]

o b t a i n e d a p a t e n t on the p r o d u c t ( p o l y s u l f o n e ) o b t a i n e d b y the a c t i o n o f s u n l i g h t o n a s o l u t i o n o f e t h y l e n e in s u l f u r d i o x i d e in a s e a l e d tube. T h e s a m e p a t e n t

3. Polysulfones by the Reaction of Olefins

7

noted that the polymerization was slower than that obtained with 2-butene or propylene with sulfur dioxide. In 1914, Matthews and Elder [1 c] described the sunlight or ultraviolet light initiated copolymerization of either 2-butene, propylene, or amylene with sulfur dioxide. Matthews and Elder [lc] also noted that the butene sulfone polymer was soluble in chloroform and tetrachloroethane. They reported that the polymer softens without dissolving in acetone and that it may be useful as an additive in films, varnishes, and ornamental articles. Staudinger and Ritzenthaler [3] reinvestigated the copolymerization of ethylene or propylene with sulfur dioxide but described very little of the polymer characteristics. Dainton and co-workers [19] described the kinetics and thermodynamics of the polymerization of butene [20]. In 1955 Dainton and Bristow [20] found that cis-2-butene and trans-2-butene gave the same polymeric product. In 1957 Skell and co-workers [21] confirmed the nonstereospecificity of the copolymerization reaction. Copolymers have also been prepared using mixtures of olefins with sulfur dioxide. Olefin pairs studied were butene with propylene [22-22b], butene with pentene [13], butene with isobutene [13b], butene with acrylonitrile [13,23], butene with vinyl acetate [24], butene with methacrylate esters [25], butene with acrylic esters [25], and butene with butadiene [24]. Sulfur dioxide reacts with pentenes [26, 26a], higher olefins (1-hexene [22], 1-nonene [27]), cyclopentene [17], and cyclohexene [2, 14]. Marvel and Weil have presented evidence to support a head-to-tail structure in the propylene sulfur dioxide copolymer [4] [see Eq. (5)].

CH3CH--CH2 + SO2

-~ -- CH -- CH2 -- SO2 -- ,,

(5)

Some examples of olefin-sulfur dioxide copolymers are shown in Table II. Initiation of the olefin-sulfur dioxide copolymerization is radical in nature and a variety of radical initiators are shown in Table III. The use of certain metal salts to initiate copolymerization has also been reported and the mechanism of initiation is the subject of some controversy. For example, Ivin [28] has suggested that metal nitrate reacts with sulfur dioxide to yield nitro radicals and sulfite anion radicals. M+NO~ - +

SO2

~

M + + NO2 ~ +

SO3 ~

(6)

The effect of various metal salt catalysts [29-33] on the production of olefinsulfur dioxide copolymers was studied earlier by Frey, Snow, and Schulze [33]. It was found that the soluble catalysts (silver nitrate, lithium nitrate, ammonium nitrate, and dilute alcoholic nitric acid) are much more effective than insoluble salts (barium nitrate, zirconium nitrate, titanium nitrate, strontium nitrate, and mercuric nitrate) which usually have long induction periods for reactions as shown in Table III [33].

8

1.

TABLE II

Olefin--Sulfur Dioxide Copolymers

Sulfur Dioxide-Olefin Copolymers Polymer properties

Initiator

Olefin Ethylene Pyropylene 1 -Butene

2-Butene (cis, trans) 1 -Pentene 1-Octene

Cyclopentene Cyclohexene Bicyclo[2.2.1 ] Hept-2-ene cis-cis- l ,5Cyclooctadiene

Peroxide Azobisisobutyronitrile Peroxide Azobisisobutyronitrile Peroxide Azobisisobutyronitrile Benzoyl peroxide Azobisisobutyronitrile light H202-paraldehyde light H202-paraldehyde H202 H202 None Peroxide

m.p. (~

Solubility

300-310 d

H2SO4(conc)

250-270 d

H2SO4(conc) HNO3 (conc) DMSO THF, CHC13, SO2 Acetone, MEK, DMSO THF, CHC13, SO2 or DMSO

---

340 175-200 d -200 d

CHCI3, DMSO, SO2 Toluene, Benzene, CHC13, SO2

-250 d

Ref. a b a b c d c b e d f g h i j

DMSO, Tetramethylene sulfone

k

H. Staudinger and B. Ritzenthalen, Ber. Dtsch. Chem. Ges. B. 68, 455 (1935). b M. A. Naylor, Jr. and A. W. Anderson, J. Am. Chem. Soc. 76, 3962 (1954). r Z. Kuri and M. Ito, Kogyu Kaqaku Zasshi 69, 1066 (1966). aM. A. Jobald, J. Polym. Sci. 29, 275 (1958). ep. S. Skell, R. C. Woodworth, and J. H. McNamara, J. Am. Chem. Soc. 79, 1253 (1959); J. Harmon, U.S. Patent 2,190,836 (1940). fC. S. Marvel and W. H. Sharkey, J. Am. Chem. Soc. 61, 1603 (1939). gF. J. Glavis, L. L. Ryden, and C. S. Marvel, J. Am. Chem. Soc. 59, 707 (1937). h O. Pipik, Bull. Acad. Sci. URSS, CI. Sci. Math., Ser. Chim. 1097 (1938). i D. S. Frederick, H. D. Cogan, and C. S. Marvel, J. Am. Chem. Soc. 56, 1815 (1934). iN. L. Zutty, C. W. Wilson, III, G. H. Potter, D. C. Priest, and C. J. Whitmore, J. Polym. Sci., Part A 3, 2781 (1965). kA. H. Frazer and W. P. O'Neill, d. Am. Chem. Soc. 85, 2613 (1963); A. H. Frazer, J. Polym. Sci., Part A 2, 4031 (1964); U.S. Patent 3,133,903 (1964); Chem. Abstr. 61, 12168 (1964). a

Some characteristic infrared absorption frequencies in the 7.5-9.5 micron range are shown for several olefin polysulfones in Fig. 1. Two strong absorption bands, one at 7.7 microns and the other at 8.75-9.0 microns, are characteristic stretching vibrations of the sulfone group as shown in Fig. 1. The olefin-sulfur dioxide copolymers are thermoplastic and colorless; transparent coherent moldings can be prepared. The properties of the polymers vary from that of ethylene-sulfur dioxide, which is very interactable, to 1-decenesulfur dioxide, which is soft, rubbery, and soluble in many organic solvents. The

FABLE III

Percentage Conversion of 2-Butene and Sulfur Dioxide to Polysulfone [29] a Time

Catalyst b ~0.5-1% by wt)

4 (hr)

Dilute nitric acid Lithium nitrate Ammonium nitrate Ethyl nitrite Beryllium nitrate Postassium nitrate Magnesium perchlorate Perchloric acid Thallium nitrate Calcium nitrate Sodium nitroprusside Phenyl mercuric nitrate Mercuric nitrate. Triphenyl bismuthine Tetraethyllead Mercury diethyl Mercury di-n-butyl Zirconium nitrate Titanium nitrate Sodium nitrite Uranyl acetate Barium nitrate Strontium nitrate Lead nitrate Cobalt nitrate Isoamyl nitrite Sodium chlorate

100

6 (hr)

1 (day)

2 (day)

3 (day)

4 (day)

5 (day)

7 (day)

9 (day)

15 (day)

21 (day)

26 (day)

35 (day)

45 (day)

r 100 100

1

a

10 10

100 60 20

e~

100 80 95 75 45

5 0 10 12

5

100 100 90 55 65

10 20

90 90

50 2 30

5

0

50

m

15 75 50

70 20 25

75 30 30

10

15 --

25

0

0

20

30 0 0 0 0 30

a Equal volumes of liquid sulfur dioxide and 2-butene. bData from F. E. Frey, R. D. Snow, and W. A. Schulze, U.S. Patent 2,280,818 (1942).

-~ 20

95 80 40 40 17 10

0 0 0 0 -35

100 100 100 100 95 99 80 70 60 75 50 10 60 3 15 0 15 40

r~

100 80 100 90 95

12 25 10

65

100 100 80 65 20 40 20 20 85 65

I I I I

100 70 40 40 40 40

75 50 45

,D

10

1. Olefln--SulfurDioxide Copolymers '

'

I

'

I

'

I

'

I

'

I

'9

pBUntte1en: r~. 2.Methyl_~l /~!~ Hexene'l~~f~%~P ~ ~ penetene t I~J~rl~ IHeec;1/~ ne."~

"~--

~~("~ ,

3-MethI'y t /

' 8 ' 19 • -- JJ/~/

ether

j~II

/ ~ butene"l l ' / j J K,,,~ thy~l~V~q ! 4~4ntDinm.~

L-Cvc,o- ^I

hexene/~ Pentene-2~ Heptene-2 ~

;ii i e

Diisobut~ N ~/~D'~et"~ A (liq.) ?~ sulfoneDi~/// ethyl~ / \ A/k sulfone

,

8I

,

9 sulfone 87 ~

,

,

acid

9~

8

i~

,

I ,

,

8

,

9#ml

Fig. 1 Infrared absorption spectra of some olefin polysulfones and some aliphatic sulfones. Absorption increasing upward. [Reprinted from R. E. Cook, F. S. Dainton, and K. J. Ivin, J. Polymer Sci. 26, 351 (1957). Copyright 1957by The J. Polymer Sci. Reprintedby permission of the copyright owner.]

resins prepared from the olefin have higher softening points, are less soluble in organic solvents, and are more resistant to alkali. Although all the olefin-sulfur dioxide resins decompose by heating well above their softening points, they can be satisfactorily molded within a fairly wide temperature range [22a]. For example, propylene-sulfur dioxide copolymers can be molded at 180~176 Some properties of the molded resins are shown in Table IV [9a]. Some other examples of olefin-sulfur dioxide copolymers and their polymerization conditions are shown in Tables V-IX.

3-1.

General Procedures for Copolymerization of Olefins and Sulfur Dioxide [9a]*

C--C -~- SO2 ~ C - - C - - SO2-(7) / \ \ n * Reprinted from R. D. Snow and F. E. Frey, Ind. Eng. Chem. 30, 176 (1938). Copyright 1938 by the American Chemical Society. Reprinted by permission of the copyright owner.

3. Polysulfones by the Reaction of Olefins

11

Most of the small-scale, resin-forming reactions shown in Table IV are carried out in Pyrex glass tubes sealed at the bottom and beating a tube with a 3-5 mm-diameter neck at the top, which could be readily sealed by a flame after filling. The tubes are 15-30 cm long to facilitate cooling in a Dewar flask filled with liquid nitrogen or solid carbon dioxide, and vary from a few millimeters to 6 cm in diameter, depending upon the quantity of product desired and the vapor pressure to be withstood. When a catalyst is used, it is introduced first. The tube is then connected by a manifold-beating connection to a vacuum pump, closed manometer, and cylinders of olefins and of sulfur dioxide. Usually the tube is cooled in liquid nitrogen while being evacuated. Approximately equal liquid volumes of olefin and sulfur dioxide are then condensed in the tube, which is again evacuated and sealed with a torch. Equal volumes of solidified olefin and sulfur dioxide* correspond to approximately 2 moles of sulfur dioxide to 1 mole of a simple olefin. This excess of sulfur dioxide is found desirable because most of the resins that are insoluble in the reaction mixture tend to carry down dissolved sulfur dioxide, thereby depleting the olefin-sulfur dioxide liquid phase in which the reaction takes place. In the case of the more soluble resins, excess of sulfur dioxide maintains a fluid condition throughout the reaction. After being sealed, the tubes are allowed to warm in the dark. As soon as the contents of the tube have melted, they are thoroughly mixed and are then brought to the desired conditions of the experiment. At the end of the reaction the tubes are cooled to approximately - 10~ opened, and allowed to warm to room temperature so that the unreacted olefin and sulfur dioxide can escape (use a hood). Experiments on a larger scale are carried out in cylindrical stainless steel bombs holding 1-4 gal. To facilitate the removal of solid resin, both ends of the bomb are closed with blind flanges lined with stainless steel plates drawn against lead gaskets. The top flange is fitted with one or two filling tubes closed by Hoke valves. The bomb is evacuated and cooled in an ice water bath to facilitate filling. The olefins and sulfur dioxide are then passed in as liquids and thoroughly mixed by tumbling the bomb on a shaft in the manner of an oldfashioned chum. The required amount of catalyst, usually in the form of an alcoholic solution, is then forced into the bomb, and the contents are again mixed by tumbling. For the rapid propylene reaction which is quite exothermic, it is advantageous to keep the bomb in the cooling bath for approximately an hour after filling. In many cases higher conversions can be obtained by adding the catalyst in two or more portions at intervals than can be obtained by adding the same total quantity at the start of the reaction. At the end of the experiment the valves are opened, and unreacted olefin and sulfur dioxide are allowed to escape before dissembling the bomb to remove resin (use a hood). * When filling at liquid nitrogen temperature, at least 30% of the volume of the tube is left to provide for expansion of the charge in coming to room temperature.

TABLE IV

Specific gravity

Tensile strength

Compressive strength

Transverse strength

(lb.~in. 2)

(lb.~in. z)

(lb./in. z)

20,400-23,650

2000-5000 4100-6720 5285 5380

Propylene Propylene Propylene Propylene 2 parts SO2 to 1 propylene 5 parts SO2 to 1 propylene 10 parts SO2 to 1 propylene 92% Propylene, 8% 1-butene 84% Propylene, 16% 1-butene 75% Propylene, 25% 1-butene

1.49-1.51 2000-3200 3200-3685 1800-3950 1800-2575 3488 3733 3343 3780-4300 3820-4260 5615

50% Propylene, 50% 1-butene

5929 4330--4415 3820--4080 4070--4200

87.5% Propylene, 12.5% 2-butene 75% Propylene, 25% 2-butene 50% Propylene, 50% 2-butene

Properties of Molded Resins a

Impact strength energy

(ft. lb for an in. 2) 1.43-1.72 1.84-1.96

Dielectric strength (instantaneous) per mil thickness

Hardness

Moisture absorption in 48 hr

(volts)

(Brinell No.)

(%)

338-381

40

0.262-0.285

I

23,400-24,250 21,250-21,850 22,150-23,100 {14'850-18'350l 11,850-17,350J 22,400-22,650 21,850-22,400 19,350-19,650

5330-5474 4080-6195 6000-7150 7100-7980 6570-8450

k

h

1.42-1.76 1.50-1.92 1.42-1.83

389-393

0.279-0.297

7210-8050

1.68-1.79

347-381

0.347-0.378

5910-7000 4900-5290 4800-6900

1.74-1.98 1.77-1.82 1.73-1.77

372-417 361-401

0.357-0.372 0.477-0490

I

75% Propylene, 25% isobutylene 75% Propylene, 25% 1-pentene 50% Propylene, 50% l-pentene Mixed preformed resin (25% butene, 75% propylene) 2-Butene 2-Butene 2-Butene 50% 2-Butene, 50% 1-butene 1-Butene 1-Butene

1-Butene from n-butyl chloride Allyl alcohol Allyl alcohol 1-Pentene 1-Pentene

3360-4370 2792-3715 2800-3820 2465

22,850-24,350 12,350-12,850 12,350-18,350

1.30-1.36 2800--4200 3100-4000 2300--4460 3820 1.35-1.40 3200--4100 3113 4298 2400-4100 2355 1.31 2100-2350 2100-3190

16,350-20,550

6530-6720 3650-4960 4235-5700

t~

5135-5520 4730-6025 4845-5150 4730 4800-6000 4100--4250

1.47-1.73 1.69-1.83

3745-7050

1.16-1.26

12,350-13,350 12,350-15,350

3600-4300 3190-4295

12,350-15,100

4600-5280 3550-4375

0.665-1.26 0.95-1.32 1.12-1.20 1.08-1.11

15,600 12,050-16,350

1-Pentene

Treated refinery butene Acid-regenerated refinery butene 1-Pentene (with paper pulp filler) Mixed butene (with paper pulp filler)

3200-3450 3330-3955 6408 5550

1.49-1.81 1.37-1.54 1.78-1.88

1.85 1.14-1.18

346-358

25-30

0.695-0.748

329-360

20-23

0.371-0.398 t~

35-40 355-369

18-19

0.315-0.345

3.94 4.57

~Reprinted from R. D. Snow and F. E. Frey, Ind. Eng. Chem. 30, 176 (1938). Copyright 1938 by the American Chemical Society. Reprinted by permission of the copyright owner.

ta~

TABLE V

Representative Polysulfone Preparations Reaction conditions m.p.

Sulfur dioxide

Olefin 10ml

10 ml

10.5 gm 2.8 gm

24 gm

1-Butene

36gin

1O0 g m

2-Pentene

36 gm 36 gm 36 gm 36 gm 36grn 20 ml

1O0 1O0 1O0 1O0 1O0

Methyl propene 1 Propylene 1- and 2-Butenes

1-Pentene 1-Nonene

3-Cyclohexylpropene 3-Methylcyclohexene Cyclohexene

gm gm gm gm gm

20 ml

Catalyst 1 ml Paraldehyde 1.0 ml 3% H202 50 gm Abs ethanol 0.1 gm Benzoyl peroxide 0.1 grn Ascaridole 0.32 gm Benzoyl peroxide 10 gm Abs ethanol 10 gm Abs ethanol 10 gm Abs ethanol 10 gm Abs ethanol 10 gm Abs ethanol 10 grn Abs ethanol 5.0 ml 95% CzHsOH 3.0 ml 2% aq H202

Time (hr)

(oc)

Temp (~

Yield

(decomp.)

12

25

75-90%

340

120

25

25.2 gm

72

25-30

49grn

72 72 72 72 72 24

25-30 25-30 25-30 25-30 25-30 25-30

75% 80-90% 78-80% 75% 5-10% 93-100%

290-300 340 300 330 270

Ref.

Pentene Styrene

5 ml 10 ml

5 ml 10 ml

Octene

10 ml

10 ml

Octene C6 --C 18 olefins C9 ----C14 olefins

C20

150 ml 28 ml

300 ml 20 ml

UV lamp 2 ml Ethyl alcohol 2 drops 30% H202 5 ml paraldehyde (old) 2 ml Ethyl alcohol 2 ml 3.0% H202 5 ml Paraldehyde (old) Co 60 y-rays 1% tert-butyl hydroperoxide based on olefin 7_rays Co60 MEK hydroperoxide

24 12-18

25 25

5-5.2 gm 0.4-2.5 gm

-185-190

d e

12-18

25

2-4 gm

175-200

e f

20 1 1

25 25 0-20

g

31 gm

h i

aL. L. Ryden and C. S. Marvel, J. Am. Chem. Soc. 57, 2311 (1935). b j. Harmon, U.S. Patent 2,190,836 (1940). CD. S. Frederick, H. D. Cogan, and C. S. Marvel, J. Am. Chem. Soc. 56, 1815 (1934); C. S. Marvel and D. S. Frederick, U.S. Patent 2,136,389 (1938). d C. S. Marvel and W. H. Sharkey, J. Am. Chem. Soc. 61, 1603 (1939). e F. J. Glavis, L. L. Ryden, and C. S. Marvel, J. Am. Chem. Soc. 59, 707 (1937). fM. A. Jobard, J. Polym. Sci. 29, 275 (1958). g J. E. Crawford and D. N. Gray, J. Appl. Polym. Sci. 15, 1881 (1971). h B. G. Harper and C. F. Smith, U.S. Patent 3,409,548 (1968). ill. G. Burkard, R. O. Henselman, H. N. Miller, and N. Tunkel, U.S. Patent 3,442,790 (1969).

~~

16

1.

TABLE VI

Olefln--Sulfur Dioxide Copolymers

Preparation of Olefin-Sulfur Dioxide Copolymers Using cqt~'-azobisisobutyronitrile Initiator (0.2 gm) a Conditions

Olefin

(gm)

Ethylene Propylene Propylene Propylene Propylene 2-Butene Isobutene Isobutene Butadiene Propylene 2-Butene Propylene 2-Butene Propylene Ethylene

26 120 33 110 40 120 80 120 50 42 56 42 56 42 28

Sulfur dioxide (gm) 32 32 126 40 150 40 35 30 40 40 40 30

Solvent (gm) Benzene 80 Propylene Sulfur dioxide Toluene 100 Sulfur dioxide 2-Butene Toluene 130 Isobutene Toluene 130 Propylene 2-Butene Propylene 2-Butene Benzene 90

Synthesis temp (~ 70 70 70 -40 - 50 - 25 - 20 - 20 - 20 70 - 40 70

Time (h) 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2

Yield (gin)

Type Thermal Thermal UV (3500-3600 UV (3500-3600 UV (3500-3600 UV (3500-3600 UV (3500-3600 UV (3500-3600 UV (3500-3600 Thermal Thermal UV UV Thermal Thermal

A) ,~) A) A) A) ,~) ,~)

41 40-50 83 10 37 10 8.6 9.5 34 31

34

a Reprinted in part from M. A. Naylor and A. W. Anderson, J. Am. Chem. Soc. 76, 3962 (1954). Copyright 1954 by the American Chemical Society. Reprinted by permission of the copyright owner.

3-2.

Sulfur Dioxide-Butene Copolymers [21]* CH3CH--CHCH3

+ S02

~

( - - C H ( C H 3 ) - - C H ( C H 3 ) - - SO2 - - )n

(8)

A nitrogen atmosphere is maintained. Pyrex containers are used in all photopolymerizations. Silver nitrate catalyzed polymerizations are carried out in the dark. Close pairing of experiments is maintained for concentrations of reactants, distance from light source, and procedure for polymer isolation. Samples of unreacted olefins are isolated by pumpting the gases in v a c u o through a tower of diethanolamine. In all experiments the infrared spectrum of the residual olefin (gas, 100-200 mm, 10-cm path) is indistinguishable from the spectrum of the starting olefin. See Table IX for conditions used. For examination of infrared spectra of the copolymers a sample (1 mg) is ground with KBr (0.2 gm) and compressed to a transparent disk at 16,000 lb/in 2. A similar blank is used in the reference beam. Although quantitative work is not feasible in examination of the spectra, particular attention is given to relative * Reprinted from P. S. Skell, R. C. Woodworth, and J. H. McNamara, J. Am. Chem. Soc. 29, 1253 (1957). Copyright 1957 by the American Chemical Society. Reprinted by permission of the copyright owner.

3.

17

Polysulfones by the Reaction o f Olefins

TABLE VII

Reaction of Olefins with Sulfur Dioxide

Monoolefins Ethylene Propylene 1-Butene 2-Butenes Isobutene (2-methylpropene) 1-Pentene 2-Pentene Isopropylethylene 1-Hexene 1-Octene 1-Nonene Cyclohexene 2- Methylcyclohexene Styrene 2- Cyclohexylpropene

Yield

Melting point (~

Ref. a, a, a, a,

75-90 80-90 75

340 340 290-300

Small 75-80

175-200

Small 75

<200 330 185-190 330

b, c c, d, e b b

d, b e, f d, e, f a a g f e, h, i f e f

a L. H. Fitch, U.S. Patent 2,045,592 (1936). bF. E. Matthews and H. M. Elder, British Patent 11,635 (1914). CH. Staudinger and B. Ritzenthaler, Ber. Dtsch. Chem. Ges. B 68, 455 (1935). aM. Hunt and C. S. Marvel, J. Am. Chem. Soc. 57, 1691 (1935). eL. L. Ryden, F. J. Glavis, and C. S. Marvel, J. Am. Chem. Soc. 59, 1014 (1937). fL. L. Ryden and C. S. Marvel, J. Am. Chem. Soc. 57, 2311 (1935). gD. N. Gray, U.S. Patent 3,728,185 (1973). h D. S. Frederick, H. D. Cogen, and C. S. Marvel, J. Am. Chem. Soc. 56, 1815 (1934). iw. F. Sayer and E. G. King, J. Am. Chem. Soc. 55, 3140 (1933).

peak heights in an effort to detect relative exaltations. The spectra of all copolymers appears to be identical. The characteristic absorption bands for sulfur dioxide-2-butene copolymers are 3.37 (w), 3.42 (mw), 6.85 (m), 6.90 (m), 7.18 (w), 7.67 (s), 7.92 (m), 8.20 (mw), 8,76 (s), 9.00 (ms), 9.53 (ms), 10.47 (w), 12.00 (mw), 13.63 (ms, broad) microns.

3-3.

Preparation of a Copolymer of Ethylene and Sulfur Dioxide [34] C H 2 - - C H 2 + SO2

) ( - - CH2 - - CH2 - - SO2 - - )n

(9)

To a 450 ml stainless steel autoclave is added 0.05 gm azobisisobutyronitrile in 2.0 ml of ethyl acetate followed by 168 ml of water containing 58 gm (0.56 mole) sodium bisulfite and 50 gm (0.40 mole) sodium sulfite. The reaction mixture is heated to 65~ and the autoclave is pressurized with ethylene to

18

1.

TABLE VIII

Olefin-Sulfur Dioxide Copolymers via Catalysis with Ascaridole Catalyst (ml)

Unsaturated compound

Used (ml)

SO2 (ml)

Propylene 1-Pentene 2-Pentene Cyclohexene Styrene Undecylenyl alcohol Undecylenic acid Methyl undecylenate

100 5 5 5 5 5 5 5

100 5 5 5 5 5 5 5

7

10

Trimethyl ethylene

Olefin--Sulfur Dioxide Copolymers

EtOH

Ascaridole

Time of standing (hr)

Yield of polymers (gm)

m.p. of polymers (~

20 1 1 1 1 2 5 5 Hbr 3

3 0.2 0.2 0.2 0.2 0.1 0.2 0.2

24 5 5 5 5 7 1 10

100 4 0.1 0.2 0.5 7 5.5 5

300 d 340 290-300 Above 200 185-190 Above 330 255-275

0.2

12

6

Ref.

125-160

C. S. Marvel and E. D. Weil, J. Am. Chem. Soc. 76, 61 (1954). bL. L. Ryden, F. J. Glavis, and C. S. Marvel, J. Am. Chem. Soc. 59, 1014 (1937). c M. S. Kharasch and E. Steinfeld, J. Am. Chem. Soc. 62, 2559 (1940).

a

1800-2000 atm. The reaction is maintained for 2 hr, cooled, vented, and the polymer removed by filtration. The polymer is dried to afford 7.5 gm of a polymer containing 42% sulfur dioxide. The polymer is rich in ethylene and can be molded at 210~ for 2 min under pressure.

3-4.

Preparation of Propylene-Sulfur Dioxide Copolymer [35] CHz--CH--CH3 + SOz

~ --CH--CHz--SOz-- ,,

(10)

To a l-liter, stainless steel pressure rocker bomb cooled with dry ice-acetone is added 33 ml (0.41 mole) of liquid propylene followed by 33 ml (0.75 mole) of liquid sulfur dioxide. Then 4 ml of paraldehyde is added and the bomb sealed. The bottle is rocked without cooling for approximately 2-3 hr. The bomb is cooled and opened to afford a solid. The solid is ground finely in a mortar, washed with two 50-ml portions of ethyl ether and dried to give 40 gm (83%) of the white amorphous polymer, PMT)approximately 250~176 (decomp). The polymer is insoluble in chloroform, carbon tetrachloride, dioxane, ether, ethyl acetate, benzene, acetone, and acetyl chloride. The polymer dissolves in concentrated sulfuric acid without change. The use of 1 ml of ascaridole and 7 ml of absolute ethanol can also initiate the polymerization which requires 24 hr at 25~176 [4].

3. Polysulfonesby the

3-5.

Reaction

19

of Olefins

Preparation of Octene-Sulfur Dioxide Copolymers [36] C 6 H 1 3 - - C H = C H 2 + 802

,

(11)

mC--CH2--SO2--

I

H To a cooled, glass pressure vessel are added 40 gm (0.62 mole) of liquid sulfur dioxide, 30 gm (0.27 mole) of octene, and 0.3 gm tert-butyl hydroperoxide. The vessel is sealed and the contents agitated and warmed to room temperature. After 50 hr, the container is vented and the polymer placed in a vacuum oven to strip off excess sulfur dioxide and unreacted olefin. The polymer yield is 45.6 gm (95%).

3-6.

Preparation of Cyclohexene-Sulfur Dioxide Copolymer [37]

]so . To a pressure vessel are added 200 ml (2.0 mole) of cyclohexene, 50 ml of 95% ethanol, and 0.30 ml of 2% aqueous hydrogen peroxide. Then 200 ml (4.6 mole) of liquid sulfur dioxide is added; the vessel is sealed and kept at 25~176 for 24 hr. The container is cooled to - 2 0 ~ vented, and opened. The polymer is a viscous mass which is then dissolved in 500 ml chloroform and precipitated by adding 3 liters diethyl ether. The filtered polymer is a solid and is obtained in 270-290 gm (91-98%) and contains 21.5% sulfur. 3- 7,

Emulsion Copolymerization of 1-Butene and Sulfur Dioxide [9, 38-40] C2H5

I

C 2 H s - - C H - - C H 2 + SO2

(13)

--CmCHzmSO2 -

I

H

n

To a cooled, glass-lined autoclave are charged 46.7 gm (0.83 mole) 1-butene, 88.3 gm (1.38 mole) sulfur dioxide, 1.0 gm Maprofix MM (60% solid sodium lauryl sulfate emulsifier supplied by Onyx Oil and Chemical Co.), 0.5 gm ammonium nitrate and 180 gm water. The autoclave is stirred at 100~ for 4 to 6 hr. After a short induction period the reaction proceeds with a considerable

TABLE IX

Preparation of 2-Butene-Sulfur Dioxide Copolymers a Polymeric product

Run

2-Butene (mmoles)

Sulfur dioxide (mmoles) 148 148 77.9 71.5 80.0 71.3 164 171

lb 2a 2b 2c 2d 3a 3b

25.1 26.2 81.4 74.7 84.2 75.0 18.6 19.3

3c

22.4 trans

198

3d 3e

25.1 cis 20.0 cis

216 172

la

trans cis trans trans cis cis trans trans

Other reactants

0.31, Benzoyl peroxide 0.32, Benzoyl peroxide 23.3, Bromotrichloromethane 24.2, Bromotichloromethane 0.074, Potassium nitrate 28.1, Bromotrichloromethane 0.061, Silver nitrate 23.8, Bromotrichloromethane 23.8, Bromotrichloromethane 0.061, Potassium nitrate

Time (hr)

Initiation

Bath temp

(~ <0 <0 - 78 - 78 - 78 - 78 0 0

Wt

Conversion

(grn)

(%)

2.39 g 3.37 g

79.0 107 8.9 12.6 16.2 22.5 72.5

Light b'c Light b'r Light b Light b Light b Light b Light b Light b

0.5 b + 3 e 0.5 b + 3 c 3.0 3.0 1.1 1.1 5.0 5.0

Ag +

4.0 i

0

1.42 h

63.4

Light b Light b

5.0 5.0

0 0

1.64 h 2.20 h

54.4 91.6

0.83 g'h

1.08 g'h 1.56 g'h 2.14 g'h 1.62 h f

3f

18.8 cis

162

4a 4b

23.9 trans 20.4 trans

246 209

4c

20.8 trans

214

4d

24.5 trans

251

22.4, Bromotichloromethane 0.051, Silver nitrate 5.3 ml, Anhydrous ether d 0.24, Hydroquinone 4.6 ml, Anhydrous ether d 0.031, Silver nitrate 4.5 ml, Anhydrous ether a 0.28, Hydroquinone 0.032, Silver nitrate 5.4 ml, Anhydrous ether d

Ag +

4.0 i

0

1.91 h

84.6

Light b

2.7

0

0.84 g

29

Light b Ag +

2.7 43

0 0

0.25 e'g 0.38 g

9.8 15

Ag +

43

0

0.10 g

3.4 i:l r~

aReprinted from P. S. Skell, R. C. Woodworth, and J. H. McNamara, J. Am. Chem. Soc. 79, 1253 (1957). Copyright 1957 by the American Chemical Society. Reprinted by permission of the copyright owner. b General Electric AH-6 high pressure mercury arc lamp. c Direct sunlight. d Solvent for hydroquinone. e Viscous liquid. fSolid. g Reaction mixture pumped at 2 mm to constant weight. h Polymer precipitated from filtered reaction mixture with absolute methanol, benzene* or ether dissolved in liquid sulfur dioxide, reprecipitated, dissolved in sulfur dioxide, frozen and then lyophilized from the frozen sulfur dioxide. i Days. * Caution: Benzene has been shown to be carcinogenic--handle with great care in a hood.

1',,9

22

1.

Olefin-Sulfur Dioxide Copolymers

exotherm. The conversion is 95-100% and the reaction pressure gauge drops from 75 to 30 psi during the course of the polymerization. At the end, the reactor is vented to remove excess sulfur dioxide and the latex has approximately 35% resin content. The latex is coagulated with magnesium sulfate solution, filtered, washed with water, and dried in a forced air oven at 140~ to yield a finely powdered, white, thermoplastic resin. Earlier references to these terpolymers (SO2/olefin/carbon monoxide) are known. For example, U.S. Patent 2,634,254 discloses the terpolymer prepared by polymerization in the presence of a free radical catalyst such as an azo compound. Also, U.S. Patent 4,251,340 discloses similar terpolymers prepared using irradiation as the initiator. These terpolymers are generally high melting (m.p. about 280~ and show good structural durability for high temperature applications. The Drent catalyst [ 18d] can also be used to prepare alternating terpolymers of sulfur dioxide/ethylene/propylene that have melting points above 300~ NMR (13C) has been run to confirm the structure, -- (SO2-- C2H4)-- (SO2-- C3H6)--

4.

POLYSULFONES FROM THE REACTION OF DIENES (CONJUGATED AND UNCONJUGATED) WITH SULFUR DIOXIDE

BASF [la] reported that dienes react with sulfurous acid or sulfur dioxide generating agents to give novel products. De Bruin [41 ] reported that isoprene reacts with sulfur dioxide (equal volumes) in sealed tubes at room temperature to give a crystalline product, m.p. 62.5~ The elemental analysis and molecular weight (138) suggested that it had the structure: CH3

Matthews and Strange [42] reported a similar reaction of isoprene with sulfur dioxide in the presence of hydrogen chloride. Seyer and King [1 d] reported that 1,3-cyclohexadiene reacted with sulfur dioxide to give a white amorphous compound, as earlier reported by Hofmann and Damm [43]. 2-Methyl- and 4-methyl-l,3-pentadiene were reported by Morris and Van Winkle [44] to react with sulfur dioxide to yield a cyclic sulfone and some hydrocarbon polymer. Starkweather [45] in 1945 reported that chloroprene (2-chloro-l,3-butadiene) reacted with sulfur dioxide in an emulsion system to give a copolymer. Polysulfone is the major product when radical initiators are used. Cyclic products predominate when radical inhibitors (hydroquinone) or temperatures in excess of the ceiling temperature are used. For example:

4.

23

Polysulfones from the Reaction of Dienes

C H 2 - - C H - - C H = C H 2 + SO2 . [ - - C H 2 - - C H : C H - - C H 2 - - S O 2 - - ] n or <SO2"j

(14)

Surprisingly allene gave no polymer on reaction with sulfur dioxide [46] but a polymer was prepared from diallyl (1,5-hexadiene) [47]. Some typical dienesulfur dioxide copolymers are shown in Table X. The pyrolysis products of 1,3-diene-sulfur dioxide copolymers were analyzed in a field-ion mass spectrometer and the fragmentation results suggest an alternating 1:1 copolymer for poly(butadiene sulfone), poly(isoprene sulfone) and poly(2,3-dimethylbutadiene sulfone) [48]. Recently [48a] it was reported that Diels-Alder adducts of butadiene with acrylonitrile, acrylamide, methyl methacrylate, acrylic acid, acrolein, and Nphenylmaleimide formed alternating copolymers with SO2. No copolymers were formed from butadiene/maleic anhydride adducts. As the temperature increased the yield decreased. The group on the cyclohexane ring had a considerable effect on the reactivity. Copolymers of SO2 and alpha-olefins have also been reported to have been prepared as liquid-crystalline polysulfones with mesogenic units [48b]. In the case of solvents, increased electron donating capacity (C6H6, PhCH3, o-xylene, mesitylene) decreased the yield of the altemating copolymer due to increased stabilization of the SO2 terminated acceptor radicals [48c]. Electrochemically induced copolymerizations of sulfur dioxide and impregnated dienes in liquid SO2 have been carried out using 0.1 M benzyl trimethylammonium perchlorate as a background electrolyte. A Pt or vitreous carbon electrode was used and potential cycles of 0 and 2.8 V for butadiene and isoprene (0.6 to 1.0 M) gave a precipitate in a few minutes [48d]. The product from isoprene was identified as

(--CH2-- C-- CH--CH2-- SO2--)x I

CH3 % S Found 23.10

4-1.

% S Calc. 24.22

Copolymerization of 1,3-Butadiene with Sulfur Dioxide [49]

SO2 -~- CH2--CH--CH--CH2

~ ( -- CH2 -- CH -- CH -- CH2 -- SO2 -- )n (15)

To an 8.0 ounce pressure polymerization bottle or Hoke cylinder are added 160 ml of water, 1.0 gm sodium lauryl sulfate, 0.25 gm ammonium nitrate, and 50 gm (0.78 mole) of liquid sulfur dioxide. The temperature is lowered to

TABLE X

Sulfur Dioxide-Diene Copolymers Polymer properties

Diene Butadiene Isoprene 1,5-Hexadiene Cyclopentadiene Bicyclo[2.2.1 ]hepta-2,5-diene

cis,cis-l,5-Cyclooctadiene cis,cis- 1,3-Cyclooctadiene cis,trans- 1,5-Cyclodecadiene Chloroprene Dicyclopentadiene

Initiator Peroxide Azobisisobutyronitrile Peroxide

m.p. (~ >200 d --

H202-paraldehyde Benzoyl peroxide

307-328

H202 tert-Butyl hydroperoxide MEK peroxide AgNO3/Aq H202 tert-Butyl hydroperoxide Cumene hydroperoxide H202, AgNO3, or azobisiobutyronitrile

->250 a 160a >255 ~ -~

Solubility conc H2504 conc HNO3 ~. conc H2504 conc HNO3 Partly soluble in conc H2504 MEK

DMSO, tetramethylene sulfone C H C 1 3 ,DMSO --

Ref. a b a c c d e f g h i j k

all. Staudinger and B. Ritzenthaler, Ber. Dtsch. Chem. Ges. B 68, 455 (1935). b Z. Kuri and M. Ito, Kogyo Kagaku Zasshi 69, 1066 (1966). cj. K. Stille and D. W. Thomson,,/. Polym. Sci. 62, 5118 (1962). aT. Yamaguchi and T. Ono, Chem. Ind. (London) No. 24, p. 769 (1968); L. de Vries, U.S. Patent 3,476,716 (1969). R. J. Alexander and J. R. Doyle, J. Polym. Sci., Part B 1, 625 (1963). fG. Vanhaeven, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem. 6(2), 709 (1965). gA. H. Frazer and W. P. O'Neill, J. Am. Chem. Soc. 85, 2613 (1963); A. H. Frazer, J. Polym. Sci., Part A 2, 4031 (1964); U.S. Patent 3,133,903 (1964); Chem. Abstr. 61, 12168 (1964). hT. Yamaguchi and K. Nagai, Kobunshi Kagaku 26, 809 (1968). iF. L. Ramp, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem. 7(2), 582 (1966). YF. Hrabak, J. Weber, and J. Blazek, Czech. Patent 122,050 (1967). kT. Yamaguchi and T. Ono, Chem. Ind. (London) No. 24, p. 769 (1968). e

25

4. Polysulfonesfrom the Reaction of Dienes

11 ~ and 15 gm (0.28 mole) of butadiene is added. The bottle is sealed and thoroughly agitated for 16 hr at 10~ The insoluble, white polymer is separated by filtration, washed with methanol, and dried. The polymer decomposes at 225~ without melting. On hydrogenation the polymer is shown to have the composition (--CHE--CHECHECH2SO2--)n by elemental analysis and melted without decomposition at 282~ (intrinsic viscosity of 2.0dl/gm in 1:1 p-chlorophenol-m-cresol at 25~ Similar reactions were reported for isoprene and piperylene [49]. Terpolymers of 1,3-butadiene, sulfur dioxide, and norbornene-styrene or cyclopentene were also reported [50]. An example of terpolymerization is illustrated in preparation 4-2. -

4-2.

Terpolymerization of 1,3-Butadiene, Cyclopentadiene, and Sulfur Dioxide [51] CHE=CH--CH=CH2 + ~ ' ~

+

SO2

Terpolymer

~

(16)

To a 4-liter, stirred reactor at 8~ are added 2 liters of deaerated water, 8 ml of Triton X-100, 300 gm (5.6 mole) 1,3-butadiene, 67.0 gm (1.0 mole) of cyclopentadiene, and 80 gm (1.25 mole) of sulfur dioxide. The reaction is polymerized at 80~ after adding 2 ml of 20% aqueous ammonium persulfate solution. During the polymerization additional initiator and reactants are cautiously metered into the reactor 0.18 gm/min (initiator), 1.0 gm/min (cyclopentadiene), and 1.7 gm/min (sulfur dioxide). The temperature of the polymerization is approximately 8~176 for the 50 min polymerization period. The reaction is stopped by discharging the reactor into 8 liters of methanol. The product is filtered, washed with water several times to remove emulsifier, and then washed with methanol to give 207 gm of a white polymer having 36 mole% cyclopentadiene derived units in the polymer and having an inherent viscosity of 0.75 dl/gm in 1 : 1 p-chlorophenol : m-cresol at 25~

4-3.

Copolymerization of Sulfur Dioxide with 1, 5-Cyclooctadiene--General Method [52]

+ SO2

~

SO2

(17)

i

/x

All polymerizations are carded out in round-bottom flasks fitted with a dry ice

26

1.

Olefin--Sulfur Dioxide Copolymers

condenser, thermometer, and magnetic stirrer. Provisions are made so that the polymerization can be carried out under an intert atmosphere, open to the air, or with a gas bubbling through the reaction mixture. After cis,cis-l,5-cyclooctadiene, b.p. 67~176 (46 mm) (+99.8% pure VPC), and the distilled solvents are added, the flask is chilled to - 7 0 ~ and anhydrous sulfur dioxide, as a liquid, is transferred under nitrogen to the flask. With the flask still at - 70 ~ the catalyst is added and the reaction mixture allowed to rise to the reflux temperature of the given mixture. The time of reaction noted in Table XI refers to elapsed time from the addition of the catalyst to the precipitation of the reaction mixture. For those mixtures in which such polymer solvents as dimethyl sulfoxide and tetramethylene sulfone are used, the polymer remains in solution and is precipitated by the addition of methanol. For nonsolvents the polymer is precipitated by the addition of methanol. For non-solvents the polymer is precipitated during the polymerization. In all cases, the isolated

TABLE XI Infrared Absorption Bands of cis,cis-l,5-Cyclooctadiene and I a Wave length (~m)

3.30 3.45 6.00 6.15 6.70 6.98 7.36

Wave length (l.tm)

Intensity

(A) cis,cis- l,5-Cyclooctadiene Strong 7.90 Strong 8.10 Strong 8.27 Weak 9.22 Strong 9.95 Strong 11.05 Weak 12.53

Intensity

Weak Weak Medium Medium Medium Weak Strong

(B) Copolymer of sulfur dioxide and cis,cis- 1,5-cyclooctadieneb (I) 3.30 3.45 6.70 6.98 7.45 7.60

Medium Medium Medium Medium Strong Strong

7.80 8.40 8.85 9.22 11.05 12.53

Strong Strong Strong Weak Weak Strong

Reprinted from A. H. Frazer and W. P. O'Neill, J. Am. Chem. Soc. 85, 2613 (1963). Copyright 1963 by the American Chemical Society. Reprinted by permission of the copyright owner. b Unsaturation in the copolymer was determined using thin film (less than 1 mil) cast from dimethyl sulfoxide solutions by examination of the infrared absorption in the 6.0 and 6.2 la region. a

5. Polysulfones by the Reaction of Acetylene with Sulfur Dioxide

27

products are repeatedly washed with methanol to remove all traces of monomers and solvents. The dried polymer is analyzed for sulfur; the inherent viscosities are determined in dimethyl sulfoxide. Unsaturation is determined by catalytic hydrogenation in tetramethylene sulfone and examination of the infrared absorption in the 6.0 and 6.2 micron range. a. Viscosity Determinations

Inherent viscosity, r/, for 0.5 gm of polymer per 1O0 ml of dimethyl sulfoxide solution is determined at 30~ using an Ostwald-Fenske viscometer. b. Determination of Residual Unsaturation

Catalytic hydrogenation of copolymers was performed in a volumetric microhydrogenation apparatus. Tetramethylene sulfone is used as solvent and 10% palladium-on-charcoal is the catalyst. In each case the reaction is allowed to run for 18 hr to ensure complete reaction. The infrared spectrum of I showed the pertinent peak as listed in Table XI. For comparison, significant peaks of cis,cis1,5-cyclooctadiene are also listed in Table XI. The co-polymerization of sulfur dioxide and 1,5-cyclo-octadiene is shown in Table XII.

4-4.

Terpolymerization of Butadiene, trans-Piperylene with Sulfur Dioxide [53]

C H 2 = C H - - C H = C H 2 + C H 3 - - C H = C - - C H = C H 2 + 802 ' Terpolymer (18) To a 1-quart pressure vessel containing 500 ml of a mixture of 80% water, 20% methanol, 0.5 gm ammonium nitrate initiator, and 4.0 gm sodium lauryl sulfate is added 67.8 gm (1.06 mole) of liquid sulfur dioxide. The vessel is cooled to - 11 ~ and a mixture of 33.4 gm (0.62 mole) butadiene and 27.0 gm (0.40 mole) of trans-piperylene is then added. The reaction is allowed to proceed at room temperature for approximately 16 hr while being vigorously agitated. The insoluble polysulfone is washed with ethanol and dried to afford 119 gm (93%) which contains 25.1 wt% S. The hydrocarbon portion contains 45 wt% piperylene and 55 wt% butadiene. The product is soluble in solfolane, p-chlorophenol and m-cresol at 100~ 0

POLYSULFONES BY THE REACTION OF ACETYLENE WITH SULFUR DIOXIDE

Ryden and Marvel have reported that sulfur dioxide reacts with monosubstituted acetylenes in a 1:1 ratio to yield a polymeric product [54]. No satisfactory yields of polymers were obtained from either of the following type

28

1. Olefin--Sulfur Dioxide Copolymers

of disubstituted acetylenes: RC----CR or R2CHC--CH [55]. Peroxides such as hydrogen peroxide or ascaridole, a naturally occurring terpene peroxide and tertamine oxides act as catalysts for the acetylene-sulfur dioxide reaction. The structure of the polymer contains one double bond for each hydrocarbon residue in the polymer since oxidation gives the carboxylic derived from the substituted acetylene as shown [54]. RC=CH +

502

~-- ( - - C - ' C H m S O 2 - - ) n

oxidation

I

,

RCOOH

(19)

R

Some typical polymerization reactions are shown in Table XIII.

5-1.

General Procedure for the Preparation of Polysulfones from Acetylenes [54]

Ten milliliters each of liquid sulfur dioxide and the substituted acetylene are placed in a pressure bottle, and 5 ml of ethyl alcohol is added. The bottles are sealed and allowed to stand overnight, then cooled and opened to permit the TABLE XII Reaction medium Diethyl ether DMSO b TMS c TMS c TMS c TMS c DMSO b TMS c TMS c TMS ~

Representative Copolymerizations of Sulfur Dioxide and 1,5-Cyclooctadienea

Initators d A B A A A A C C C C

Temp (~

Time (hr)

Atmosphere

Yield g (%)

?]inhh

S (%)

15 - 5 22 25 25 25 25 22 25 25 -4

2 10 8 16 16 16 16 16 16 16 2

N2 N2 N2 N2 Air e Airy Air f N2 N2 Air e N2

37 23 84 83 89 93 50 88 80 98 15

0.62 0.90 0.21 1.55 1.95 2.10 1.20 0.21 1.40 2.20 1.13

26.42 26.93 26.51 26.94 26.85 26.93 26.84 26.43 26.86 26.76 26.87

a Reprinted from A. H. Frazer and W. P. O'Neill, J. Am. Chem. Soc. 85, 2613 (1963). Copyright 1963 by the American Chemical Society. Reprinted by permission of the publisher. All reactions carried out with 10% wt concn of monomers; Mso2/Mc~H,2 = 0.25/0.10. b DMSO, dimethyl sulfoxide. c TMS, tetramethylene sulfone. d A initiator, 5 drops of ascaridole and 5 drops of concd HC1; B initiator, 1 drop of ascaridole and 400 ml of HC1 (gas); C initiator, 5 drops of methyl ethyl ketone peroxide. e Reaction mixture opened to air. fAir bubbled through reaction mixture. g Yield, per cent based on 1,5-cyclooctadiene. h r/inh, inherent viscosity (In r/rel/C) for 0.5 gm polymer/100 ml of dimethyl sulfoxide solution.

TABLE XIII

Acetylenic compound Acetylene 1-Pentyne Phenylacetylene 1-Nonyne Cyclohexylpropane 1-Pentadecyne 1-Pentyne

Methylacetylene Ethyl acetylene n-Propyl acetylene n-Butyl acetylene n-Amyl acetylene 1-Heptyne

502

(ml) ,a

10 5 6 10 5 10 10 10 10 10 10

,a 10 5 5 10 5 10 10 10 10 10 10

Solvent (ml/EtOH) *~ 5 3 1 2 1 5 5 5 5 5

Acetylene-Sulfur Dioxide Polymers Reaction time (hr)

Catalyst Ascaridole (*~) Ascaridole (0.2 ml) Ascaridole (1.0 ml) Ascaridole (0.2 ml) Ascaridole (0.2 ml) Ascaridole (0.2 ml) Me2NO (0.5 cm) Paraldehyde-Peroxide Paraldehyde-Peroxide Paraldehyde-Peroxide Paraldehyde-Peroxide Paraldehyde-Peroxide 3% H202

10 1

(1-5 (1-5 (1-5 (1-5 (1-5

ml) ml) ml) ml) ml)

3 3 5 18 3--5 3-5 3--5 3-5 3-5 72

Polymer yield (gm or %) 0 8 5 2.4 15 3.5 13.4 40 30 60 90 75 50--60

r

m.p.

polymer (~

Ref.

203-208 250--275 160-169

110-145 120-140 250-260 210-215 203--208 195--205 164--170 160-169

a ,, Used but amounts not specified.

b C. S. Marvel and W. W. Williams, J. Am. Chem. Soc. 61, 2710 (1939). c L. L. Ryden, F. J. Glavis, and C. S. Marvel, J. Am. Chem. Soc. 59, 1014 (1937). d C. S. Marvel, L. F. Audrieth, and W. H. Sharkey, J. Am. Chem. Soc. 64, 1229 (1942). e L. L. Ryden and C. S. Marvel, d. Am. Chem. Soc. 58, 2047 (1936). fL. L. Ryden and C. S. Marvel, J. Am. Chem. Soc. 57, 2311 (1935). t~

30

1.

Olefin-~Xulfur Dioxide Copolymers

addition of 1 to 5 ml of paraldehyde which contains peroxides. The amount of paraldehyde to be added varies roughly with various samples. Fresh paraldehyde is inert, but older samples which have been exposed to the air are very effective catalysts for the addition reaction. The flasks are sealed and allowed to come to room temperature. The contents of the flask is usually solid at this time. With 1-pentyne and 1-hexyne, the reactions is distinctly exothermic. The reaction mixtures are poured into water and the products collected on a filter. The excess of sulfur dioxide and paraldehyde is removed by triturating with alcohol and ether several times. The polymer from 1-pentyne is further purified by dissolution in dioxane and reprecipitating by the addition of water. The products from 1-hexyne and 1-heptyne are purified similarly with acetone as the solvent. The polysulfones from methyl-, ethyl-, and propylacetylene are white, powdery amorphous substances. The butyl- and amylacetylene derivatives are more flaky and are not easily ground to powder. The products which have been prepared are listed in Table XIV. Under the same experimental conditions that gave addition products when the monosubstituted acetylenes were used, no polysulfones could be obtained from dimethylacetylene, 2-hexyne, methylphenylacetylene, diethyl acetylenedicarboxylate, or allene and sulfur dioxide. Acetylene itself was not investigated. TABLE XIV Sulfur Dioxide-Acetylene Copolymers Polymer properties

Monomers

Initiator

CH=--CH C6HsC~CH/CHE=-CHC1 mole ratio 5:13 C6H5C~CH/CH2=CH--C3H7 mole ratio 1 :l 3:2 1:3 CH~C--CH=CH2 CH2=C--C=C--CH=CH2 CH3C=C--CH=CH2

Ascaridole Ascaridole

M.P.D. (decomposition) No polymer 280~176

Solubility --

Ascaridole

Ref. a b c

210~176 270~176 210~176

sol dioxane insol dioxane sol dioxane

m

m

a C. S. Marvel and W. W. Williams, J. Am. Chem. Soc. 61, 2710 (1939). bC. S. Marvel and F. J. Glavis, J. Am. Chem. Soc. 60, 2622 (1938). c C. S. Marvel, S. J. Davis, and F. J. Glavis, J. Am. Chem. Soc. 60, 1450 (1938). dA. Gulyaeva and T. Dauguleva, Caoutch. Rubber (Moscow) No. 1, p. 53 (1937); Chem. Abstr. 32, 3754 (1938). F. E. Frey, R. D. Snow, and L. H. Fitch, U.S. Patent 2,225,266 (1940). fM. Ya. Slobodin, J. Gen. Chem. USSR (Engl. Transl.) 16, 1831 (1946). e

31

6. Polysulfones by the Reaction of Vinyl Monomers (CH2=CH--R)

In an attempt to elucidate the structure of 1-pentynepolysulfone, Marvel and Williams [56] found that heating of this polymer gave a crystalline solid of composition C10H16SO2 that was tentatively assigned the structure of di-npropylthiophene (II, Ill, or IV) n-C3H7--C ~

II HC

\

HC ~

C--C3H7-n

/ SO2

II CH

CH

II n-C3H7--C

II \

II

/ SO2

C--C3H7-n

III HC ~ II n-CaH7--C

C--C3H7-n

II

\

/

CH

$02

IV Recently, purified terminal aliphatic acetylenes were copolymerized with liquid SO2 in the presence of t-BuOOH at low temperature [54a]. The use of benzoyl peroxide, hydrogen peroxide, and p-chloroperbenzoic acid initiators was ineffective. Aged (impure) aliphatic alkynes could be copolymerized without the need to add hydroperoxides. All the resulting alkyne/SO2 copolymers were altemating with a 100% t r a n s configuration regardless of the alkyne, temperature, or solvent used. Infrared spectroscopy and NMR were used to characterize the polymers. In the case of phenylacetylene the use of t-butylperoxide was an effective catalyst. However, aged phenylacetylene was ineffective in causing copolymerization to occur [54b]. Some examples of alkynes copolymerized with SO2 are shown in Table XIVa.

6.

POLYSULFONES BY THE REACTION OF VINYL MONOMERS (CH2--CH--R) WITH SULFUR DIOXIDE

Vinyl monomers such as styrene, vinyl halides, and vinyl esters react with sulfur dioxide to give polysulfones. Barb [57] found that no more than 1 mole of sulfur dioxide reacted with 2 moles of styrene to give a polysulfone soluble in many solvents (chloroform, sulfuric acid, dimethylformamide, and mixtures of benzene and acetone). Marvel and Glavis [1 l a] reported that both vinyl chloride and vinyl bromide react with sulfur dioxide in the presence of acidic paraldehyde containing

32

1.

TABLE XIVa

Copolymers

Copolymers of Alkynes with SO2 Catalyzed by t-Butyl Hydroperoxide [54c] a Reaction temp [7] (~

Alkyne

Olefln--Sulfur Dioxide

1-pentyne 1-Hexyne 1-Heptyne 1-Nonyne 1-Decyne 3-Hexyne

-

37 37 37 37 37 25

Yield (%) 25 50 60 51 68 0

Tm (~ 185-195 115-125 125-135 140-150 135-145 -

-- [C---~CH-- SO2]hR

trans a Conditions used: 15 ml liquid no solvent.

SO2, 1.0 ml t-BuOOH, 1.5 hr,

peroxide. However, higher molecular weight vinyl halides such as 1-bromo1-heptene do not react with sulfur dioxide [ 11a]. Vinyl acetate in the presence of other olefins reacts with sulfur dioxide to give copolymers [24]. For example 20-30% vinyl acetate in the presence of propylene or butene reacts with sulfur dioxide. Acrylic esters do not copolymerize with sulfur dioxide unless olefins such as propylene or butene are present [9, 24, 58]. Vinyl ethers also react with sulfur dioxide to give polysulfone copolymers [59]. Some representative vinyl monomer-sulfur dioxide copolymers and their conditions of polymerization are shown in Table XV. Using Preparation 3-7, a series of emulsion polysulfone latexes were prepared from butene with either ethyl acrylate, acrylonitrile, or methyl methacrylate as shown below in Table XVI.

6-1.

Preparation of a Propylene-Methyl Methacrylate-Sulfur Dioxide Terpolymer [24] CHa--CH=CH2 + CH3-C--COOCH3 + 5 0 2 I

~

Terpolymer

(20)

CH3

To a pressure vessel at - 8 0 ~ is added a solution of 0.1 part benzoyl peroxide and 0.1 part of ascaridol in 50 parts absolute alcohol. Then 10.5 gm (0.13 mole) propylene, 24 gm (0.375 mole) sulfur dioxide, and 5.0 gm (0.05 mole) methyl methacrylate is added. The vessel is sealed, packed in ice, and

TABLE XV

Monomer (amt)

Amount of sulfur dioxide

Polysulfones by the Reaction of Vinyl Monomer and Sulfur Dioxide

Solvent

Catalyst

Vinyl chloride (10 ml)

10 ml

95% EtOH (2 ml)

Paraldehyde (5 ml)

Vinyl chloride (10 ml) Vinyl chloride (10 ml) Vinyl bromide (10 ml) Styrene (5.0 ml) Divinyl ether (1.0)ml) Vinyl ether (1.0 ml) Propylene (50 gm), methacrylate (13.2 gm) Bicyclo[2.2.1 ]hept-2-ene (18.8 gm), ethyl acrylate (10 gm) 1-Butene (82 gm, 95%), acrylonitrile (18.6 gm)

10 ml 10 ml 10 ml 5.0 ml 1 ml 1 ml 20 gm

95% EtOH (2 ml) 95% EtOH (2 ml) 95% EtOH (2 ml) 95% EtOH (1.0 ml) Ether EtOH Benzene (150 ml)

Peracetic acid (15 ml) Benzoylperox or ascaridole Paraldehyde (5 ml) Ascaridole (0.2 ml)

12.8 gm

Azobisisobutyronitrile (0.2 g)

Benzene (100 ml)

T (~

Time (hr)

25 1-2 (pressure bottle) 25 1-24 25 1-24 - 2 0 - 2 5 ~ 1-2 25 5 0-25 1-2 0-25 1-2 70 2 60

1

Yield 5-30% 30% 0 1-2.5 gm 0.5 gm

13 gm 33.9 gm

m.p. (~ or viscosity (r/) 135-140 250-275 250-275 250-275 200-225 180-190

dark melts melts melts

Ref. t~

~inh = 0.48 (in conc H2SO4) ~inh -- 0.51 (in DMF) i,a

II 152 gm

H20 (300 ml)

0.721 grn NH4NO3, 9.05 gm NH4 alkane sulfonate, 3.7 grn dodecylmercaptan

a C. S. Marvel and F. J. Glavis, 3". Am. Chem. Soc. 60, 2622 (1938). bL. L. Ryden, F. J. Glavis, and C. S. Marvel, J. Am. Chem. Soc. 59, 1014 (1937). c A. Gulyaeva and T. Dauguleva, Caoutch. Rubber (Moscow) No. 1, p. 49 (1937). aM. A. Naylor, Jr., U.S. Patent 2,703,793 (1955). eN. L. Zutty, U.S. Patent 3,313,785 (1967). fG. Steinbach van Gover, French Patent 1,390,384 (1965); Chem. Abstr. 62, 14898 (1965).

48

6

163 gm

I

34

1. Olefln--Sulfur Dioxide Copolymers

TABLE XVI Polysulfone Emulsion Polymerization Preparationsa [39] Formulation (parts by wt)

1

2

3

4

5

1-Butene Ethyl acrylate Acrylonitrile Methyl methacrylate Sulfur dioxide Water Ammonium nitrate 60% Sodium lauryl sulfate

42.0 4.67 n ~ 88.3 220 0.5 1.0

36.4 9.34 __ ~ 88.3 220 0.5 1.0

42.0

43.9 __ 2.8

42.0 w

4.67 88.3 220 0.5 1.0

88.3 220 0.5 1.0

4.67 88.3 220 0.5 1.0

a The polysulfones are prepared at about 100~ at 75-90 psig pressure. After the excess sulfur dioxide is vented the latex is coagulated with methanol to give the polymer. The polymer is washed with water and dried for 72 hr at 140~ allowed to w a r m to r o o m temperature (25~ over a 3-hr period. The reaction is then left at r o o m temperature for 7 days, cooled, vented, and the p o l y m e r filtered and dried to afford 19.8 g m (analysis: 22.05% S). In a similar manner propylene-n-butene polysulfone, 1-butene polysulfone, and 2-butene polysulfone are prepared [60].

6-2. Preparation of Propylene-Methyl AcrylateSulfur Dioxide Terpolymer [58] C H 2 - - C H - - C H 3 + C H 2 - - C H - - C O O C H 3 + SO2

"~

(C3H6)(502)0.77 + (Methyl Acrylate)o.s3

(21)

To an evacuated 500-ml pressure resisting vessel containing 0.2 g m o f azobisisobutyronitrile are added 120 gm (2.86 mole) propylene, 20 g m (0.31 mole) sulfur dioxide, and 26.8 gm (0.31 mole) o f methyl acrylate. After 1 hr o f heating at 75~ the p o w d e r y p o l y m e r is isolated and 20.7 gm (12%) is obtained. The p o l y m e r loses 3.3% o f its weight on heating at 226~ for 1 hr.

6-3. Preparation of Bicyclo[2.2.1]hept-2-ene-Ethyl Acrylate-Sulfur Dioxide Terpolymer [61] + C H 2 - - C H C O O C 2 H 5 + SO2

Terpolymer

(22)

To a 300-ml Crown-capped polymerization bottle at -80~ are charged 12 gm (0.125 mole) of bicyclo[2.2.1]hept-2-ene, 15.0 gm (0.230 mole) sulfur dioxide, 3.0 gm (0.03 mole) of ethyl acrylate, and 30 gm of methanol. The bottle is sealed and rotated end-over-end in a glycol water bath maintained at 0~ The

35

6. Polysulfones by the Reaction of Vinyl Monomers ( C H z = C H - - R )

contents become slightly hazy after 5 min, milky white after 10 min and solid after 20 min. The bottle is opened and the contents added to methanol. The polymer is filtered, washed with methanol and dried to afford 20 gm (67%) polymer having a reduced viscosity of 0.68 in cyclohexanone. The terpolymer contains 42.4 mol% of polymerized bicyclo[2.2.1]hept-2-ene, 45.0 mol% polymerized sulfur dioxide, and 12.6 mol% polymerized ethyl acrylate. Other bicyclo[2.2.1]hept-2-ene and derivative sulfur dioxide polymers were prepared by a similar method and are shown in Table XVII. Vinyl acetate copolymerizes with SO2 at - 7 0 ~ using t-butylhydroperoxide as the initiator to give a 1:1 copolymer of molecular weight 100,000 [61a]. More recently it has been shown that the temperature has a great effect on the amount of copolymerization taking place [6 l b]. Some of the data are shown in Table XVIIa. At 110~ VAc and SO2 form two separate layers and copolymerization does not take place. The nature of the solvent also has an effect on the copolymerization. The best conditions imply no solvent and use only an excess of SO2. Polar solvents such as DMF or DMSO give no copolymerization. The use of toluene and methylene chloride allows copolymerization to take place. The molar ratio of the copolymer is about 1.0 (VAc/SO2) if excess SO2 is used. TABLE XVII

Polysulfones Based on Bicyclo[2.2.1]hept-2-ene and Derivativesa

Monomer (gm) Bicyclo[2.2.1 ]hept-2-ene 5.0 5.0 5.0

Solvent (gm) CH3OH 10 10

Sulfur dioxide 6 (gm)

Temp (~

Time (hr)

% Yield

5.0 5.0 5.0

0 50 0

1/6 1/30 1/6

6.1 6.8 4.9

2.0

0

1/20

3.8

6.4

50

1.5

3.2

50

8

4.7

19.8

25

6

70 c

Cyclohexane 3.0 Bicyclo [2.2.1 ]hept-2-ene5-carboxylic acid 13.8 Bicyclo[2.2.1 ]hept-2-ene5,6-dicarboxylic anhydride 8.2 Bicyclo[2.2.1 ]hept-2-ene 28.2 Butyl acrylate 450

17

14

Acetonitrile 15

Toluene 300

aData taken from N. L. Zutty, U.S. Patent 3,313,785 (1967). b No external source of free radicals were required. c Copolymer.

36

I. TABLE XVIIa

Temp

(oc)

Copolymerization of Vinyl Acetate with Effect of Temperature [61 b] a

% Yield copolymer

-

20 ~ 40 ~ 60 ~ 70 ~ 80 ~ - 100 ~ -110 ~

Olefin--Sulfur Dioxide Copolymers

0 38.4 63.7 79.0 64.2 9.2 0

M,,

SO2~

Analysis of copolymer

Mole ratio VA/SO2 in copolymer

% S

% VAc

-1.42 1.02 1.08 1.15 1.19 ~

17.6 20.8 20.1 19.3 18.9 --

68.8 58.5 58.8 61.4 62.3

43,900 26,900 31,400 29,700 32,500

a Conditions used for copolymerization were 1.00 g VAc, 10 ml 0.15 ml t-BuOOH, reaction time 1 hr.

SO2,

In a similar manner vinyl t-butyl carbonate copolymerizes with S O 2 [61b]. Vinyl t-butyl carbonate and vinyl acetate have the same ceiling temperature (-20~ as was observed in the VAc/SO2 copolymerization. No polymer is obtained above this temperature and the yield of polymers increases as the temperature is lowered to -80~ (85% yield). + SO2

t-BuOOH

O~x,T/O

~.~SO2

~)L n

O~O ~~.~SO2

~--~

O~x,T/O O

+

+ SO2

t-BuOOH

")'n

O~O O

+

The structures of the copolymers were examined also by NMR and IR. Vinyl acetate and 3-methylcyclopentene-SO2 terpolymers have also been reported to be useful as electron beam resist mediums [61c]. The polymer obtained is a VAc/3-methylcyclopentene/SO2 terpolymer. This terpolymerization was reported to occur at -60~ using t-BuOOH as the initiator. The difficulties in forming copolymers of certain olefins with SO2 have been discussed in a number of papers [61 d]. The highest copolymerization rates were found in systems containing an electron-donor monomer with low resonance stabilization and gave altemating copolymer compositions. Monomers with high resonance stabilization with electron-acceptor groups result mainly in homopolymerization under normal conditions. For example, styrene forms only a

37

7. Polysulfones by the Reaction of Allylic Compounds

trace of the copolymer and acrylic acid only undergoes homopolymerization under standard conditions. The case of a-methylstyrene led to only homopolymer. Vinyl chloride does not give an alternating 1:1 copolymer but was found to give a 2:1 copolymer [61e].

@

POLYSULFONES BY THE REACTION OF ALLYLIC COMPOUNDS WITH SULFUR DIOXIDE

In 1898 Solomina [1] reported that sulfur dioxide reacted with allyl alcohol, allyl methyl ether, and allyl ethyl ether [1]. Solomina reported that carboxyl, halide, and ester groups inhibited the reaction [1]. In 1935 Ryden and Marvel [26] reported that sulfur dioxide did not copolymerize with allyl cyanide or 2-allyl-~t-cresol when peroxide-paraldehyde was used but did polymerize when ascaridole was added [62]. In a later publication Kharasch and Steinfeld reported that allyl chloride copolymerized with sulfur dioxide in the presence of ascaridole and aqueous hydrochloric acid [63]. Representative allyl monomer-sulfur dioxide copolymers and their conditions for polymerization are shown in Table XVIII.

7-1.

Preparation of Allyl Chloride-Sulfur Dioxide Copolymer [63] CH2--CH--CH2C1 + 802

-~ [--CH2--CH--SO2--] I

CH2CL

n

(23)

To 10 ml (0.23 mole) of liquid sulfur dioxide in a flask are added 5.0 gm (0.066 mole) of allyl chloride, a drop of ascaridole, and a few drops of aqueous hydrochloric acid. While agitating (magnetic stirrer) the polysulfone began to precipitate in a few seconds as a white, viscous polymer which hardened in a few minutes. The total reaction time is less than 5 min. The polysulfone is isolated by adding ether, breaking up the mass, filtering, powdering, washing thoroughly with ether, and then drying to afford 6.5-9.0 gm (70-100%). The polysulfone does not melt when heated up to 210-235~ but is soluble only in acetone and chloroform. Under the above conditions allyl bromide did not react with sulfur dioxide to yield any polymer [63]. Using a similar procedure some additional data on the polymerization of allyl compounds is shown in Table XIX.

38

1.

TABLE XVIII

Olefin-Sulfur Dioxide Copolymers

Copolymerization of Allyl Compounds with Sulfur Dioxide ii

Polymer Allyl compound Allyl alcohol

Allyl alcohol-Acrylic acid Methallyl alcohol-Isobutene Methallyl alcohol-allyl chloride Methallyl alcohol Allyl chloride Allyl chloride Allyl chloride Allyl chloride Allyl bromide Cinnamyl bromide Allyl cyanide 2-Allyl-p-cresol Allyl acetate Diallyl formal Diallyl acetal Allyl acetic acid Allyl phenol Allyl chloride-Isobutene Methallyl alcohol-Isobutene Allyl acetate Diallylammonium chloride Allyl chloride-Ethyl acrylateButyl acrylate Diallyl tolyl phosphate t~-Olefins-Alkyl chloride Diallyl sulfide Allyl pheny ether Diallyl phosphonate Allyl chloroformate-~-Olefin

Initiator

Yes

LiNO3 AgNO3 NH4NO3 (NH4)28207 H202, - 30~ H202, - 3 0 ~ tert-Butyl hydroperoxide Irradiation Ascaridole-HC1 CHaCOOH "Active" paraldehyde

x x x x x x x x x x x

-- 30~ -30~ ),-rays Azobisisobutyronitrile or tert-butyl-hydroperoxide ~

tert-Butyl peroxypivalate

"

Ref.

x x x x x x x x x

a b c d e c e b f f g g f h h i j j k k l e, l m n

x

o

x x x x x x

p q r s t u

x x x x

-Paraldehyde-H202 Paraldehyde-HEO2 -AgNO3 AgNO3

~ Cumene hydroperoxide AgNO3 (NH4)2S208

No

aF. E. Frey, R. D. Snow, and W. A. Schulze, U.S. Patent 2,280,818 (1942). bF. E. Frey, L. H. Fitch, Jr., and R. D. Snow, U.S. Patent 2,114,292 (1938). c C. C. Allen and D. M. Leslie, Canadian Patent 412,461 (1943). d R. R. Dreisbach and J. F. Mulloy, U.S. Patent 2,794,014 (1957). e S. E. Ross and H. D. Noether, U.S. Patent 2,698,317 (1954). fM. S. Kharasch and E. Steinfeld, J. Am. Chem. Soc. 62, 2559 (1940). g C. S. Marvel and F. J. Glavis, J. Am. Chem. Soc. 60, 2662 (1938). hL. L. Ryden and C. S. Marvel, J. Am. Chem. Soc. 57, 2311 (1935). i D. S. Frederick and C. S. Marvel, U.S. Patent 2,201,544 (1940). J S. N. Ushakov, I. A. Arbuzova, and N. N. Efremova, Izv. Akad. Nauk SSSR, Otd. Khim. Nauk p. 551 (1949); Chem. Abstr. 44, 1746 (1950).

39

7. Polysulfones by the Reaction of Allylic Compounds

7-2. Terpolymerization of Allyl Alcohol, Acrylic Acid, and Sulfur Dioxide [64] CH2=CH--CH2OH + CH2--CHCOOH + SO2

'

Terpolymer

(24)

Into a pressure polymerization vessel are added 150 gm water, 3 gm ammonium persulfate, and 24 gm (0.415 mole) allyl alcohol. The mixture is cooled to 15~ and then 50 gm (0.695 mole) of acrylic acid is added. The mixture is further cooled to - 2 0 ~ and 26 gm (0.406 mole) of sulfuric dioxide is added. The vessel is sealed and polymerization is initiated by raising the temperature to 40~ with initial agitation. Polymerization is continued for 16 hr and then the reaction mixture is cooled, water added, and the mixture steam distilled at 200 mm pressure. The steam distillation is continued until 100 gm water is collected. The polymer is soluble in hot water and when the solution is cooled no polymer settles. The solution has little odor and can be used to cast clear film on glass plates, or used as spinning dope to prepare fibers which are insolubilized by heat. The polymer analyzes as follows: 27% sulfur dioxide, 50% acrylic acid, and 23% allyl alcohol. Recently the copolymerization of allyl-2-phenylcyclopropane-l-carboxylate with SO2 to give an alternating copolymer prepared in 87% yield at - 30~ was reported [61 f]. Poly(diallylammonium halide-sulfone) prepared from methyl dodecyldialkyl ammonium halide and SO2 to give an alternating copolymer for bactericidal applications was reported in [61 g]. Alkylphenyl ether, allyl-p-nitrophenyl ether, N-allylbenzamide, N-allyl-pnitrobenzamide, allyl cinnamate, and allyl-o-benzoylbenzoate were each copolymerized with SO2 to give an alternating copolymer that absorbed UV light. The conditions of reaction were - 7 8 ~ with t-BuOOH as the initiator [61h].

kL. L. Ryden, F. J. Glavis, and C. S. Marvel, J. Am. Chem. Soc. 59, 1014 (1937). tW. W. Crouch and L. D. Jurrens, U.S. Patent 2,531,403 (1950). mS. Fujioka, Y. Shinohara, and K. Hayashi, Kyogo Kagaku Zasshi 69, 334 (1966). "S. Harada and M. Katayama, Makromol. Chem. 90, 177 (1966); Nitto Boeski Co. Ltd., Belgian Patent 664,427 (1965); Chem. Abstr. 65, 2374 (1966). ~ Ito, T. Saegusa, and J. Furukawa, Kogyo Kagaku Zasshi 65, 1878 (1962). P I. N. Faizullin, T. M. Maksudova, I. F. Gabitova, A. V. Dyul'deva, and D. A. Faizulline, Vysokomol. Soedin., Ser. B 13(2), 147 (1971). qI. Ito, H. Hayaski, T. Saigusa, and J. Furukawa, Makromol. Chem. 55, 15 (1962). r C. D. Wright and W. S. Friedlander, U.S. Patent 3,072,616 (1963). ST. Harada and M. Katayama, Japanese Patent 14,587 (1963). t I. N. Faizullin, I. Lazareva, E. M. Shagiakhmetov, and E. V. Kuznetsov, Vysokomol. Soedin., Ser. B 13(1), 9 (1971). u W. S. Pickle and N. B. Lorette, U.S. Patent 3,563,961 (971).

TABLE XIX

Allyl compound (ml) o-Allylanisoleb o-Allylphenolc p-Bromoallylbenzened Allylacetic acid e Allyl cyanider

(5) (5) (10) (5) (10)

Allyl Compounds-Sulfur Dioxide Copolymers a

SO2 (ml)

C2HsOH (ml)

Ascaridole (gm)

Time (hr)

Polymer yield (grn)

m.p. of Polymer (~

5 5 10 5 10

5 5 2 5 2

0.2 0.2 0.2 0.4g 0.2g

8 4 12 4 12

7 4 16.5 5 1

150-160 120-160 255 180-230 222

Analysis S (%) Experimental formula

CloHl203S C9HloO38 C9H9BrOES C5H804S CaHsNO2S

Calc

Found

15.1 16.1 12.2 19.5 24.45

14.7 15.8 12.0 18.8 h 24.57

aReprinted in part (footnotes included) from L. L. Ryden, F. J. Glavis, and C. S. Marvel, J. Am. Chem. Soc. 59, 1014 (1937). Copyright 1937 by the American Chemical Society. Reprinted by permission of the copyright owner. bAllylanisole polysulfone is soluble in dioxane, and was purified by dissolving it in this solvent and reprecipitating with water. The compound melted to a clear, glassy substance, and did not decompose below 200~ Co-Allylphenol polysulfone is soluble in acetone, ether, ethyl acetate, ethyl alcohol and 0.1 N socium hydroxide solution. It could be reprecipitated from the alkaline solution by addition of acid. ap-Bromoallylbenzene polysulfone is insoluble in all common organic solvents. It was purified by washing with alcohol and ether. eAllylacetic acid polysulfone separated as a white, rubbery polymer in the reaction flask. It was purified by removing some impurities by steam distillation and then dissolving in dioxane and precipitating it by adding water. This polymer is soluble in ethyl alcohol. It can be dissolved in alkali and reprecipitated. fAllyl cyanide polysulfone separated in the reaction flask as a white, insoluble powder. It was purified by washing with alcohol and ether. It was insoluble in all of the common organic solvents which were tried. g Ascaridole (0.2 ml) was added when the reaction mixture was made up and after 2 hr, a second portion of 0.2 ml was added. h Calculated for C, H: C, 36.6, H, 5.9. Found: C, 37.5, 37.7; H, 4.86, 4.91.

8.

41

Miscellaneous Preparations and Methods

The cyclo-copolymerization of diallyl compounds with SO2 has also been reported [61i]. For example, 4-substituted 1,6-heptadiene derivatives with SO2 of the following structure were also studied [61j]: CH2 -- CH--CH2 R -+

X-

CH

\ CH2 -- CH-'CH2

1,6-Heptadiene and SO2 also yield cyclocopolymers. The radical polymerization of diallyl ether with sulfur dioxide produced soluble copolymers whose composition was between 1:1 and 2:1 on SO2. Formation of tings made of diallyl ether and SO2 and 3,4-disubstituted tetrahydrofuran tings by the cyclized diallyl ether units was proposed on the basis of 1H NMR data [61k].

8.

MISCELLANEOUS PREPARATIONS AND METHODS

1. Polysulfone copolymer by the reaction of 5-hexene-2-one with sulfur dioxide [65]. 2. Polysulfone by the reaction of polyisobutene, norbornene with sulfur dioxide [66]. 3. Polysulfone terpolymer from monoolefinic materials, liquid polymer of a conjugated diene and sulfur dioxide [67]. 4. Polysulfone resins from unsaturated hydrocarbons of greater than 3 carbon atoms with acrylonitrile and sulfur dioxide [68]. 5. One step synthesis of sulfones using formic acids (not polymers but may be useful technique for application to polymer forming reactions) [69]. 6. Polysulfones by the reaction of diolefin polymers with sulfur dioxide [70,71]. 7. Stabilization of polysulfones [72, 73]. 8. Reaction of undecylenic acid with sulfur dioxide when initiated by ascaridole [62]. 9. Polysulfone from p-xlylene with sulfur dioxide at -78~ [54]. 10. Reaction of sulfur dioxide with fl-butoxyvinyl phosphonic acid ester [74]. 11. Terpolymer of styrene-vinyl acetate-sulfur dioxide [75]. 12. Terpolymer of cis,cis- 1,5-cyclooctadiene-carbon monoxide-sulfur dioxide [76]. 13. Polysulfone from the reaction of tetrafluoroethylene with sulfur dioxide in the presence of peroxide [77]. 14. Copolymerization of diallylphosphoramidic dichloride with SO2 [78].

42 15. 16. 17. 18. 19. 20. 21. 22. 23.

1.

Olefin-Sulfur Dioxide Copolymers

Benzoguinone for inhibition of radical alternating copolymerization [79]. Poly(vinyl trimethyl) silane sulfone [80]. Copolymerization of p-benzoquinone with sulfur dioxide [81 ]. Copolymerization of 5-ethylidene-2-norbomene with SO2 [82]. Copolymers prepared from pentamethyldisilylstyrene and SO2 using t-butylhydroperoxide for use in resists [83]. Copolymerization of alkenoic acids with SO2. The alkenoic acids used were acrylic, 3-butenoic, 4-pentenoic, and 10-undecenoic [84]. Alternating copolymers of linear and cyclic alkenyldisilanes and silylated styrenes with SO2 [85]. p-Trimethylgermylstyrene/SO2 copolymer for resists [86]. Copolymerization of olefinic zwitterionic sulfobetaine surfactants with SO2 [87].

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44

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61e.

61 f.

1.

Olefin--Sulfur Dioxide

Copolymers

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References

45

61g. W. Shun and D. Zhao, Gongneng Gaofenzi Yuebao 2(4), 294 (1989). 61h. Z. Florjanczyk and E. Zygadlo, Makromol. Chem. 192 (1991); Chem Abstr. 115, 159901j (1991). 61 i. Y. Ameniya, M. Katayama, and S. Harada, Makromol. Chem. 178, 289 (1977). 6 lj. Y. Ameniya, M. Katayama, and S. Harada, Makromol. Chem. 178, 2499 (1977). 61k. K. Fujimori, J. Polym. Sci. Polym. Chem. Ed. 21, 25 (1983). 62. L.L. Ryden, F. J. Glavis, and C. S. Marvel, J. Am. Chem. Soc. 59, 1014 (1937). 63. M.S. Kharasch and E. Steinfeld, J. Am. Chem. Soc. 62, 2559 (1940). 64. R.R. Dreisbach and J. F. Mulloy, U.S. Patent 2,794,014 (1957). 65. R.J. Himics, S. O. Graham, and D. L. Ross, U.S. Patent 3,964,909 (1976). 66. G. Sartori and R. D. Lundberg, U.S. Patent 3,932,369 (1976). 67. C.S. Lynch, U.S. Patent 2,625,525 (1953). 68. Produits Chimiques Pechiney-Saint Gobain, Netherlands Appl. Patent 6,601,057 (1966). 69. H.W. Gibson and D. A. McKenzie, J. Org. Chem. 35, 2994 (1970). 70. C.S. Lynch, U.S. Patent 2,770,603 (1956). 71. L.S. Pitts, Fr. Addn. 87,949 (1966); Chem. Abstr. 67, 44781 (1967). 72. J.M. Goppel, U.S. Patent, 2,647,887 (1953). 73. J.M. Goppel and G. E. Rumscheidt, U.S. Patent 2,583,527 (1952). 74. E.V. Kuznetsov and J. N. Faizullin, Vysokomol. Soedin. 5, 347 (1963); Chem. Abstr. 59, 12935 (1963). 75. Research Institute for Synthetic Fibers, Japanese Patent 6,642 (1963); Chem. Abstr. 61, 1972 (1964). 76. A.H. Frazer, J. Polym. Sci., Part A 3, 3699 (1965). 77. J. Harmon and R. M. Joyce, Jr., U.S. Patent 2,411,722 (1946); Chem. Abstr. 41, 2275e (1947). 78. M. Haruta, S. Harada, K. Kageno, T. Ueda, and T. Hashimoto, Japan, Kokai 75-12,177 (2/7/75); Chem. Abstr. 84(12), 74852K (1976). 79. V.B. Golubev, I. V. Semonikhina, M. B. Gurtovaya, I. L. Stoyachenko, and V. P. Zubov, Deposited Doc., VINITI 3930-84 (1984); Chem. Abstr. 103, 160883 (1988). 80. A. S. Gozdz and M. J. Bowden, Polym. Commun. 27(2), 34 (1986); Chem. Abstr. 104, 149536C (1986). 81. A.Y. Nagiev, A. V. Ragimov, S. G. Mirsalieva, A. I. Kuzaev, and B. I. Liogon'kii, Vysokomol Soedin. Ser. A 30(1), 154 (1988); Chem. Abstr. 108, 1324022 (1988). 82. J.M. DeSimone, J. E. McGrath, and S. D. Smith, Polym. Prepr. (Am. Chem. Soc. Div. Polym. Chem.) 29(2), 345 (1988). 83. M. Matsuda, S. Ito, and H. Ono, Jpn. Kokai Tokkyo Koho JP 01131246A2 5/24/89; Chem. Abstr. 111, 1842189 (1989). 84. A.P. Tsonis, S. A. Ali, M. I. M. Wazeer, and A. M. Abdennabi, J. Appl. Polym. Sci. 38, 1899 (1989); Chem. Abstr. 112, 78058a (1989). 85. A.S. Gozdz, J. S. Shelburne, M. J. Bowden, S. Ito, and M. Matsuda, Polym. Mater. Sci. Eng. 64, 23 (1991); Chem. Abstr. 115, 60647a (1991). 86. S.J. Kim, B. S. Park, and H. Lee, Proc. SPIE Int. Soc. Opt. Eng. 1672, 477 (1992); Chem. Abstr. 117, 201690h (1992). 87. D. Anton and A. Laschewsky, Makromol. Chem. Rapid Commun. 12, 189 (1991); Chem. Abstr. 114, 207936c (1991).

Chapter 2

Polythioesters 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Condensation of Diolefins with Dithiocarboxylic Acids . . . . . . . . . . . . . . . . . . . . . . . . .

2-1. 2-2. 2-3. 2-4. 2-5.

Bulk Polymerization of Dithioadipic Acid with Biallyl (1,5-Hexadiene) . . . . . . . . . . Solution Polymerization of Dithioadipic Acid and Biallyl . . . . . . . . . . . . . . . . . . . . General Procedure for Solution Polymerization of Dibasic Thioacids and Biallyl. . . Solution Polymerization of Dithioadipic Acid and Biallyl . . . . . . . . . . . . . . . . . . . . Emulsion Polymerization of Dithioacids and Biallyl . . . . . . . . . . . . . . . . . . . . . . .

3. Free Radical Polymerization of Unsaturated Thioesters . . . . . . . . . . . . . . . . . . . . . . . . .

3-1. Homopolymerization and Copolymerization of Alkyl Thioacrylates . . . . . . . . . . . . . 3-2. Preparation of tert-Butyl Thiomethacrylate Polymers . . . . . . . . . . . . . . . . . . . . . . 3-3. Bulk Polymerization of 1,2-Bis(methacryloylthio)ethane in a Glass Mold . . . . . . . . . 4. Condensation of Dimercaptans with Dibasic Acid Derivatives . . . . . . . . . . . . . . . . . . . .

4-1. Preparation of a Polythioester by the Condensation of Sebacyl Chloride with Hexamethylenedimercaptan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2. Preparation of a Polythioester by the Interfacial Condensation of Ethanedithiol and Terephthaloyl Chloride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3. Preparation of a Polythioester by the Reaction of Diphenyl trans-Cyclohexane1,4-dicarboxylate and 1,6-Hexanedithiol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4. Preparation of Polythioesters by the Reaction of Adipoyl Chloride-Pyridine Complex with Hexanedithiol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Miscellaneous Preparations and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1.

46 47 48 48 49

51 53 56 57 59

61 62 63 64 65 68 71 71

INTRODUCTION

Polythioesters are a relatively new class of polymers analogous to polyesters. Marvel and co-workers [1 ] were among the first to report their preparation [2]. In general, polythioesters are more difficult to prepare in high molecular weight 46

2.

Condensation of Diolefins with Dithiocarboxylic Acids

47

compared to polyesters. The most common methods of preparation involve: (1) condensation of diolefins with dithiocarboxylic acids [1]; (2) free radical polymerization of unsaturated thioesters such as alkyl thioacrylates [3, 3a]; (3) condensation of dimercaptans with dibasic acids or adic chloride derivatives [ 1-3a]. Other routes to preparing polythioglycolates are: (1) from thioglycolic acid (TGA), (2) from the methyl ester of TGA, (3) from the cyclic dimeric anhydride to TGA, (4) from 2,5-dioxo-l,3-oxathiolane, and (5) from S-trimethylsilyl TGA. These routes are discussed in a recent review [3b]. The interfacial polymerization of dithiols with dicarboxylic acid dichlorides gives polythioesters of high molecular weight [3b]. The use of S-vinylthioacetate gives a polymer which could give another polymer useful for obtaining polythiols [3b]: O

II nCH2=CH--S--C--CH3

'

(-- CH2 -- CH -- )n

I

S

~"

(-- CH2 -- CH-- )n

I

SH

I

C=O

I CH3 Other polythioesters are mentioned in the above referenced review [3b]. Polythioesters are generally soluble in chloroform or benzene, but the solubilities of the dithioterephthalates are very low. None of the thioesters was soluble in water or hydrolyzed at 30~ over a 4-day period. The thioesters readily hydrolyzed with 5% alcoholic sodium hydroxide solution [1]. The polythioesters have little odor, but the residual thiolodors, if any, are difficult to remove. Although attempts to prepare high-molecular-weight resins for fibers [4] have been reported, no commercial use of polythioesters for this or any other applications is known.

1

CONDENSATION OF DIOLEFINS DITHIOCARBOXYLIC ACIDS

WITH

Marvel and Kotch [5] have reported that polythioesters can be obtained by the UV-catalyzed addition of dithioacids to unconjugated diolefins in hydrocarbon solvents. The polymers are of low molecular weight as determined by measurement of their inherent viscosity. In order to prepare higher-molecular-weight polymer emulsions UV polymerizations of dithioacids with diolefins were carried out and the results are shown in Tables III and IV and Preparation 2-5.

2. Polythioesters

48

2-1. 0

Bulk Polymerization o f Dithioadipic Acid with BiaUyl (1,5-Hexadiene) [6] 0

II II HSC(CH2)4CSH + CH2--CH--CH2--CHz--CH--CH2

Io

o

-

]

II II --C(CHE)a--CSCHz--CHE--CHE--CHE--CHE--CHES-- ,~ (1)

To a quartz test tube were added equimolar amounts of dithioadipic acid and biallyl. The tube was stoppered, agitated, and placed under a UV lamp for several hours to give a solid product. The product was isolated by dissolution in chloroform and reprecipitation in methanol. The polymer was filtered, washed with fresh methanol, and dried under reduced pressure to give a 6.3% yield of polymer with inherent viscosity (in chloroform at 25~ of 0.22

2-2.

Solution Polymerization o f Dithioadipic Acid and Biallyl*

a. In Cyclohexane Solution [51 In a 100-ml quartz flask are placed 1.76 gm of crude dithioadipic acid, 0.82 gm of biallyl, and approximately 40 ml of purified cyclohexane. All of the acid did not dissolve in the cyclohexane. The flask was stoppered with a cork and placed under the UV lamp (at a distance of about 6 in from a polychromatic source of UV light, Hanovia Type 7420). After 3 hr of exposure, a solid began to form on the wall of the flask. The flask was removed after a total exposure time of 15 hr. When the solid was filtered and dried, it weighed 0.69 gm, a yield of 26.8%. The solid was dissolved in chloroform, the solution was filtered, and the polymer reprecipitated with methanol. The melting point was 91-95~ and the inherent viscosity 0.13.

b. In Benzene Solution

CAUTION: Benzene is a known carcinogen. In a 50-ml quartz flask are placed 3.08 gm of crude dithioadipic acid, 1.43 gm of biallyl and 20 ml of dry, thiophene-free benzene. After an exposure time of approximately 18 hr under the UV lamp, a solid weighing 1.74 gm is filtered from the solution. An additional 1.51 gm is obtained by diluting the filtrate with methanol. The total weight of solid polymer is 2.50 gm, a yield of 72%. Both * Reprinted from C. S. Marvel and A. Kotch,J. Am. Chem.Soc.73, 1100(1951). Copyright1951 by the American Chemical Society. Reprinted by permission of the copyrightowner.

2.

49

Condensation o f Diolefins with Dithiocarboxylic Acids ,

,

v

w

, i , , , , 1 , , , , 1 , , , , 1

75 50 ,"_ 25 .o ._= 0

A

,.,...

~

T

f

L)

~ so 25 0

,I,,,,I

700

900

11 O0

1300

1500

2500

3500

Wave number (cm -l)

Fig. 1 (A) Polymer from adipoyl chloride and hexamethylenedithiol; (B) polymer from biallyl and dithioadipic acid. [Reprinted from C. S. Marvel and A. Kotch, J. Am. Chem. Soc. 73, 1100 (1951). Copyright by the American Chemical Society. Reproduced by permission of the copyright owner.]

samples are reprecipitated by dissolving them in chloroform, filtering with chloroform solution, and pouting the solution into excess methanol. The first fraction has a melting point of 99~176 and an inherent viscosity of 0.16, while the second fraction has a melting point of 92~176 and an inherent viscosity of 0.12. (See Fig. 1).

2-3.

General Procedure for Solution Polymerization of Dibasic rhioacids and aiaUyl [5] *

CAUTION: Benzene is a known carcinogen. Other polymers from dibasic thioacids and biallyl are made and isolated according to the following general procedure. Approximately 0.01 or 0.02 mole of each monomer and 200 ml of dry, thiophene-free benzene are placed in a quartz flask under the UV lamp. Except in the case of dithioterephthalic acid where some of the polymer comes out of solution, the polymers remain in solution with that amount of benzene. After approximately a day of irradiation, the polymers are isolated by evaporating the benzene solution at the pressure of the water aspirator to a volume of about 50 ml and then pouting the solution into approximately 200 ml of methanol. The solid polymer thus obtained is filtered, dried, and weighed. It is then dissolved in reagent-grade chloroform, and the solution filtered through a sintered-glass funnel into about four volumes of methanol which has also been filtered. The reprecipitated polymer is filtered and dried. All inherent viscosities are taken in chloroform. The data on the polymers * Reprinted from C. S. Marvel and A. Kotch, J. Am. Chem. Soc. 73, 1100 (1951). Copyright 1951 by the American Chemical Society. Reprinted by permission of the copyright owner.

TABLE I

Polythioesters from Dibasic Thioacids and Biallyl a Analyses (%) Sulfur

Formula

Inherent viscosity in CHCI3

Yield

Calc

Found

Calc

Found

Calc

Found

Diathioadipate

O O II II -- S-- C(CH2)4-- C - - 5(CH2)6--

99-102

0.16

72

55.35

55.37

7.74

7.86

24.62

24.90

Dithiopimelate

O O II II -- SC(CH2)5-- CS(CH2)6--

61-64

0.19

61

56.89

56.62

8.08

7.94

23.37

23.63

Dithiosuberate

O O II II -- SC(CH2)6--CS(CH2)6--

82-85

0.12

69

58.29

58.16

8.39

8.66

22.23

21.94

Dithioazelate

-- SC(CH2)7CS(CH2)6--

68-72

0.21

75

59.56

59.79

8.66

8.83

21.20

20.95

Dithiosebacate

O O II II -- SC(CH2)8CS(CH2)6--

68-80

0.17

65

60.71

60.58

8.92

8.89

20.26

19.92

Dithioterephthalate

-- S C - - ~

160-200

0.07

92

59.97

60.14

5.75

5.94

22.87

22.98

Dithioisophthalate

II -- SC ~ - a , ~ L -

75-82

0.07

22

59.97

60.23

5.75

6.00

22.87

22.59

O II

O II

O

Carbon

Hydrogen

m.p. (~

Polyhepamethylene polymer

O

ii ~

II

~--- CS(CH2)6--

o

o

II C S - - (CH2)6 -

a Reprinted from C. S. Marvel and A. Kotch, J. Am. Chem. Soc. 73, 1100 (1951). Copyright 1951 by the American Chemical Society. Reprinted by permission of the copyright owner.

2.

51

Condensation o f Diolefins with Dithiocarboxylic Acids

obtained by this method are recorded in Table I. The yields vary from 22% to 92% depending on the purity of the dibasic thioacid.

2-4.

Solution Polymerization of Dithioadipic Acid and Biallyl [6]*

To a quartz flask containing tetrahydrofuran are added equimolar amounts of dithioadipic acid and biallyl. The flask is stoppered and irradiated with a UV lamp (Hanovia type 7420) for 50 hr to give a solid that separates from the solution. The polymer is filtered, washed with fresh tetrahydrofuran, and dried to give 24% of the theoretical amount of polymer with an inherent viscosity of 0.36 in chloroform at 25~ Low-molecular-weight products (inherent viscosity of 0.07 in chloroform) are also isolated from the filtrate and washing solution by concentration and precipitation of the chloroform solution with methanol. The analogous solution polymerization of dithioterephthalic acid and dithioisophthalic acid does not take place but gives degradation products of the dithiol acids. The capillary melting points of some polythioesters are shown in Table II. TABLE II

Capillary Melting Points of Some Polythioesters a

Hexamethylenedithio ester of Adipic acid Adipic acid Pimelic acid Pimelic acid Suberic acid Suberic acid Azelaic acid Azelic acid Sebacic acid Sebacic acid Sebacic acid Sebacic acid p-Benzenediacetic acid

Homoterephthalic acid

Inherent viscosity b

m.p. (~

0.16 0.50 0.19 0.31 0.12 0.92 0.21 1.00 0.17 0.65 1.3 2.0 0.71 0.11

99-102 100 61-64 70 82-85 110 68-72 105 68-80 95 140 250 d. 105 Gummy

Ref.

a Reprinted from C. S. Marvel and E. A. Kraiman, ,I. Org. Chem. 18, 707 (1953). Copyright 1953 by the American Chemical Society. Reprinted by

permission of copyright owner. b The polythioesters with inherent viscosities above 0.5 were fibrous in character as they were precipitated from chloroform solution. * Reprinted from C. S. Marvel and A. Kotch, J. Am. Chem. Soc. 73, 1100 (1951). Copyright 1951 by the American Chemical Society. Reprinted by permission of the copyright holder.

2. Polythioesters

52

TABLE III

Emulsion Polymerization of Dithioacids and Biallyl: Persulfate-Bisulfite Initiated a

Dithiol acid

Emulsifier concentration b

Initial pH

Volume of initiator, (ml c)

Temp (~

Time (days)

Yield (%)

Inherent viscosity

Terephthalic

5 5d 4e 4e 5 5 5 5 5 5 5 5 5 10 5g 5h 5 10 20 i 4j 4k 4t 4m 4n 10 20 10 20 10 20 10 10 20

2.0 2.0 5~ 5 1.0 1.5 2.0 2.5 3.0 4.0 5.0 6.0 7.0 "4 "5 ---5 2.0 2.0 2.0 ---5 "--5 ----5 --5 "--5 2.0 2.0 2.0 2.0 2.0 2.0 ---4 2.0 2.0

1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.5 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0

30 30 30 50 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30

5 5 5 5 4 4 4 4 4 4 4 4 4 5 4 5 5 5 4 3 5 5 5 5 5 4 5 4 5 4 5 5 4

3.5 8.4 0 26 88 97 92 94 87 90 78 74 58 86 81 84 100 94 98 99 65 77 62 62 89 84 89 93 90 99 100 96 99

0.01 0.01

Adipic p

Pimelic Suberic Azelaic Sebacic

m f 0.19 0.28 0.32 0.30 0.21 0.16 0.10 0.10 0.07 0.15 0.22 0.16 0.32 0.28 0.17 0.24 0.07 0.08 0.07 0.07 0.24 0.35 0.29 0.33 0.43 0.52 0.44 0.52 0.49

a Reprinted from C. S. Marvel and E. A. Kraiman, J. Org. Chem. 18, 707 (1953). Copyright 1953 by the American Chemical Society. Reprinted by permission of the copyright owner. bNumber of ml of 50% MP 635 S solution per 100 ml of distilled water. c Number of ml of each of ammonium persulfate solution (1.46 gm/20 ml of water) and sodium metabisulfite solution (0.37 grn/10 ml of water). d Five milliliters of benzene added. e Ten milliliters of benzene added. fDried polymer no longer soluble in chloroform. g One gram of (anal. reagent) sodium chloride added. h Two grams of (anal. reagent) sodium chloride added.

2.

Condensation of Diolefins with Dithiocarboxylic Acids

2-5.

53

Emulsion Polymerization of Dithioacids and Biallyl [6] *

The freshly prepared dithioacid was weighed into a 4-ounce screw-cap, polyethylene bottle (used for its light weight) on an analytical balance. The corresponding weight of biallyl was accurately weighed into a glass-stoppered weighing bottle which could fit through the neck of the polyethylene polymerization bottle. An emulsifier solution was prepared by diluting a 50% MP 635 S solution and adjusting the pH with acid or base using a Beckman pH meter. Then 50 ml of this solution was added to the bottle followed by the initiator. In rapid succession, the glass stopper of the weighing bottle was loosened; the weighing bottle followed by the stopper was dropped into the polyethylene bottle that was then tightly stoppered, thoroughly shaken, and placed in a constant temperature bath to be tumbled end-over-end. After the indicated lenth of time, the polymerization was stopped by pouting the contents of the bottle into 100 ml of a coagulant solution (100 gm of hydrated aluminum potassium sulfate and 100 ml of glacial acetic acid diluted to 2.5 liters with distilled water). The coagulated polymer was collected, washed with water, and dissolved in 150 ml of chloroform. Filtering this solution into 300 ml of methanol precipitated the polymer which was then separated by filtration, washed with methanol, and dried under reduced pressure. Inherent viscosities were determined in chloroform at 25~ Tables III and IV contain the experimental data. Emulsion polymerization (UV-catalyzed) of dithioacids with 1-hexyne was reported by Marvel and Kraiman, but gave inferior results to biallyl, as shown in Table V. * Reprinted from C. S. Marvel and E. A. Kraiman,J. Org. Chem. 18, 707 (1953). Copyright 1953 by the American Chemical Society. Reprinted by permission of the copyright owner.

/Fifteen grams of dithioacid used. J Five percent excess dithioacid used. kTwo percent excess dithioacid used. tan excess of 2.5% dithioacid used. " Three percent excess dithioacid used. "Four percent excess dithioacid used. oWhere an approximate pH is indicated, it is that of the emulsifier solution without anything added. PThe infrared spectrum of this emulsion polymer was the same as that found previously for the corresponding solution polymer.

~b

0

0

0

0

0

~ . . o

o.~u~

0

0

0

o o o

0

0

o

0

o

0

o

0

o o

0

0

0

0

0

0

0

0

0

u~

0

o c ~ c ~ o o o o o o o

0

u~

0

o

0

o

0

o o

0

0

o

0

o o

~.,.

0

0

0

0

o o o o

0

0

o o

~

0

0

I l l l

0

0

o o o o

0

0

I

0

o o o

0

~...

o

t:L~

~

._.. ~.~.

o

o

o

n~

:s

g~

:n ,,<

~176

,..~~

t:L

o

~.~~ o

N

o

o

.....,

rn

rn

2.

Condensation of Diolefins with Dithiocarboxylic Acids

(continued)

TABLE IV

Initial Emulsifier concentration b pH

Dithiol acid Azelaic

Suberic Pimelic p-Benzenediacetic Homoterephthalic 2,5-Dimethoxyterephthalic

10 10 10 10 10 10 10 10 10

55

4.2 4.4 4.6 4.2 4.4 4.2 4.4 4.4 4.4

Volume of 3% H202, Temp (ml (~ 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5

30 30 30 30 30 30 30 30 30

Time (days)

Yield (%)

Inherent viscosity

1 1 1 1 1 1 1 1 1

79 79 85 91 94 74 96 38 0

1.0 1.0 0.70 0.92 0.62 0.31 0.71 0.16

a Reprinted from C. S. Marvel and E. A. Kraiman, J. Org. Chem. 18, 707 (1953). Copyright 1953 by the American Chemical Society. Reprinted by permission of the copyright owner. bNumber of ml of 5% MP 635 S solution per 100 ml of distilled water. c Used 99.50% of required dithioacid. dUsed 99.75% of required dithioacid. e Used 100.00% of required dithioacid. fUsed 100.25% of required dithioacid. g Used 100.50% of required dithioacid. h Where approximate pH is indicated, it is that of the emulsifier solution without anything added.

TABLE V

Emulsion Polymerizations a

Dithioacid

trans-Hexahydrodithioterephthalic cis-Hexahydrodithioterephthalic Hexamethylene bis(dithiohydrogen adipate) Dithioadipic Dithiosebacic

Unsaturated monomer

Initial pH

Yield (%)

Inherent viscosity b

Biallyl Biallyl Biallyl Biallyl 1-Hexyne 1-Hexyne Biallyl f 1-Hexyne f

4.2 4.2 4.2 4.1 4.2 4.2 4.2 4.2

c 99 85 87 61 60 90 49

d e 0.48 0.33 0.29 0.33 0.27 0.15

a Reprinted from C. S. Marvel and E. A. Kraiman, J. Org. Chem. 18, 1664 (1953). Copyright 1953 by the American Chemical Society. Reprinted by permission of the copyright owner. b In chloroform at 25~ r Insoluble in chloroform; not precipitated; crude material in excess of theoretical yield. d Insoluble in both chloroform and m-cresol. e Precipitated polymer no longer soluble in chloroform; insoluble in m-cresol. fUltraviolet light-initiated.

56

0

2. Polythioesters

FREE RADICAL POLYMERIZATION UNSATURATED THIOESTERS

OF

Marvel and co-workers [7] were one of the first groups to study in detail the preparation and polymerization of alkyl thioacrylates. Mikeska [8] earlier prepared thioacrylic esters by the reaction of chloropropionyl chloride and the mercaptan followed by dehydrohalogenation with diethylaniline. Marvel prepared alkyl thioacrylates by the reaction of a,fl-dibromopropionyl chloride with mercaptan followed by the reaction with sodium iodide to eliminate the bromine atoms to give the acrylate ester. O II CH2--CH--C--C1 + RSH I I Br Br

--HC1

O II CH2--CH--C--SR

I Br

I Br O

Nal --2Br-

}l

CH2=CH--C--SR

(2)

Marvel reported that the reaction of acrylyl chloride with the mercaptan led only to the Michael addition product. Hauptschein, Hager, and Allen [9] reported the preparation of

/

o /

II RfCH2CH2SC--C--CH2 I R

perfluoroalkyl thiomethacrylates and acrylates by the reaction of the acid chloride with the mercaptan using pyridine at 30~ in benzene solution. For example: O II CllF23CH2CH2SH + CH2=C--C--C1 I CH3

O II

Pyridine Benzene 30~

C 11F23CH2CH2S-- C - - X - - C H 2

I CH3

Free radical

' Polymers

(3)

They [9] also reported the homopolymerization and copolymerization of these monomers. Kydonieus and Sandier [10] reported that mercaptans, especially fluorinated mercaptans, can react with acrylyl chloride or methacrylyl chloride in the presence of ferric chloride catalyst using a methylene chloride solution to yield

3.

Free Radical Polymerization of Unsaturated Thioesters

57

the aft-unsaturated thioesters directly with very little Michael addition product being formed. The reaction of aft-unsaturated carboxylic anhydride with mercaptans under similar conditions also gives the thioesters in good yields.

RfCH2CH2SH + CH2=C--COC1

] CH3

0 FeC13 11 CH2CI2~ RfCH2CH2SC--C=CH2 [ CH3

(4)

The stereospecific polymerization of alkyl thioacrylates has also been reported using n-butyllithium [ 11 ]. More recently there have been a large number of reports on the preparation and polymerization of alkyl thiocrylates [ 11 a]. The activity in this area is a result of the interest of these compounds for optical lenses because of the high refractive index of the resulting plastics. For example, some monomers used are: R R I I CH2=C--C--S--R1--S--C--C=CH2 II II O O

(for example, where R - - H or CH3 and R1 = - - C H 2 C H 2 - - , --(CH2)--4, mC6H4-- , or--CHz--C6H4--CH2--). The above thioesters can be prepared by the reaction of methacryloyl chloride with the thiol in toluene in the presence of hydroquinone as an inhibitor and aqueous sodium hydroxide as an acid acceptor (at about 0~

3-1. Homopolymerization and Copolymerization of AIkyl Thioacrylates [3a] CAUTION:

Carbon tetrachloride is a known carcinogen.

Polymerization reactions performed in bulk were carried out in heavy-walled sealed tubes ~1 to g5 in. in diameter and 8 to 10 in. in length at 70~ Catalyst and monomers were added to the tubes and air was displaced by dry, oxygen-free nitrogen. The tubes were sealed while cooled in a dry ice-chloroform-carbon tetrachloride mixture. After polymerization for the desired length of time, the tubes were cooled with running water, then placed in a dry-ice bath, and opened. The time required for each polymerization reaction was determined by observing the increase in the viscosity of the monomer charge. Where possible, the viscous polymer-monomer mixture was poured from the opened tubes into 50 to 100 ml of methanol for precipitation. Methanol was then added to the tubes to precipitate any remaining polymer which could then be easily removed. Occasionally it was necessary to add benzene to the tubes before the polymer could be poured from the tube. Polymer was then precipitated from the benzene solution by methanol as above. The products were thoroughly washed with

58

2. Polythioesters TABLE VI

Bulk Copolymerizations of Alkyl Thioacrylates with Vinyl Monomers at 70~ a

Co-monomer

Polymerization time Conversion (hr) (%)

Inherent viscosity (benzene)

Sulfur (%)

Thioester incorp Appearance (wt%) of solid

n-Propyl thioacrylate Styrene Acrylonitrile Vinyl acetate

2.25 1.0 5.1

43.3 38.4 45.0

0.60 0.18 0.51

12.43 17.35 20.70

50.5 70.5 84.0

Tough Tough Rubbery

Isopropyl thioacrylate Styrene Acrylonitrile Vinyl acetate Maleic anhydride

2.25 1.0 5.1 1.5

38.4 21.7 45.0 35.0

0.89 -0.49 0.43

12.56 16.06 21.67 21.45

51.0 65.2 88.2 87.3

Brittle Brittle Tough Brittle

Methyl thioacrylate Styrene Acrylonitrile Methyl acrylate Maleic anhydride Isobutyl vinyl ether Vinyl acetate

1.0 0.33 0.1 0.1 0.17 0.33

25.0 11.7 61.7 38.4 30.0 45.0

1.18 -0.85 0.35 1.21 0.90

15.40 20.86 18.30 23.22 22.84 24.58

49.2 66.6 58.4 74.2 73.0 78.5

Brittle Brittle Tough Powdery Tough Tough

Isobutyl thioacrylate Styrene Acrylonitrile Methyl acrylate Isobutyl vinyl ether

1.67 0.6 0.1 6.33

36.7 0.78 18.3 0.16 23.4 1.26 No polymer obtained

12.53 15.38 14.61

56.5 69.3 65.8

Tough Brittle Rubbery

Ethyl thioacrylate Styrene Acrylonitrile Vinyl acetate Methyl acrylate Maleic anhydride

1.5 0.45 0.33 0.1 0.13

30.0 18.3 35.0 65.0 45.0

1.38 -1.47 0.79 0.37

14.25 18.33 24.10 16.90 23.76

51.7 66.5 87.4 61.4 86.2

Brittle Brittle Rubbery Rubbery Brittle

n-Butyl thioacrylate Styrene Acrylonitrile

1.5 0.25

35.0 20.0

2.43 0.40

11.97 12.02

53.8 54.1

Tough Brittle

53.6 71.1 89.1 66.1 88.8

Brittle Brittle Brittle Powdery Brittle

tert-Butyl thioacrylate Styrene Acrylonitrile Vinyl acetate Methyl acrylate Maleic anhydride Isobutyl vinyl ether

1.75 0.75 5.1 0.13 0.67 5.1

33.3 0.96 11.90 25.0 0.25 15.80 43.3 0.31 19.85 18.4 0.41 14.68 11.7 0.26 19.72 Negligible polymer obtained

a Reprinted by C. S. Marvel, S. L. Jacobs, W. K. Taft and B. G. Labbe, J. Polym. Sci. 19, 59 (1956). Copyright 1956 by the Journal of Polymer Science. Reproduced by permission of the copyright owner.

3.

59

Free Radical Polymerization o f Unsaturated Thioesters

TABLE VII

Thioacrylate Methyl Ethyl n-Propyl Isopropyl n-Butyl Isobutyl tert-Butyl

Homopolymerizations of Alkyl Thioacrylates in Bulk at 70~ a

Polymerization time (hr)

Conversion (%)

Inherentb viscosity in benzene

Sulfur (%) Calcd

Found

Appearance

0.03 0.07 0.50 0.50 0.05 0.10 0.33

70.0 73.4 50.0 50.0 70.0 63.4 33.3

0.53 0.63 0.67 0.81 0.58 0.54 0.24

31.37 27.59 24.60 24.60 22.21 22.21 22.21

30.73 26.94 24.53 24.92 22.32 22.31 21.73

Tough Tough Rubbery, tacky Tough Semifluid, tacky Rubber, tacky Brittle

a Reprinted from C. S. Marvel, S. L. Jacobs, W. K. Taft, and B. G. Labbr, J. Polym. Sci. 19, 59 (1956). Copyright 1956 by the Journal of Polymer Science. Reprinted by permission of the copyright owner. b All polymers were soluble in benzene.

methanol and dried for approximately 20 hr in tared vials at room temperature and a pressure of 0.03 to 0.05 mm. For analytical purposes, a portion of each polymer was reprecipitated twice successively from a small amount of redistilled reagent grade benzene by about 50 ml of reagent grade methanol. Drying of the polymers was effected as above. In preparing samples of acrylonitrilecontaining polymers for anlaysis, it was necessary to substitute N,N-dimethylformamide for benzene as the solvent. Homopolymers of the thioacrylates (Table VI) were prepared using 3 gm of the monomer and 0.015 gm of benzoyl peroxide. For the copolymers (Table VII), 3 gm of each co-monomer and 0.020 grn of benzoyl peroxide were used. The constants for relating viscosity to molecular weight in this series have not been determined but it is estimated these products have molecular weights in excess of 35,000 and in some cases up to several hundred thousand.

3-2. Preparation of tert-Butyl Thiomethacrylate Polymers* [3] a. Polymerizations and Processing of Polymers The liquid monomers were stored with a trace of iodine (0.01-0.1%) to prevent polymerization. When such a monomer was used to prepare a polymer, the charge of monomer or mixed monomers was washed with a few drops of concentrated aqueous sodium thiosulfate to remove the iodine. Then a small amount of sodium sulfate was added and the monomer charge was decanted. Polymerizations were carried out in screw-cap vials or bottles of sufficient size that the monomer charge filled them one-half to three-fourths full. * Procedure 3-2 and Tables VIII and IX are reprinted from G. Sumrell, J. Briskin, G. E. Ham, and C. H. Schramm, J. Am. Chem. Soc. 81, 4308 (1959). Copyright 1959 by the American Chemical Society. Reprinted by permission of the copyright owner.

60

2. Polythioesters

Aluminum foil was placed between the cap and the vial or bottle. After the monomer charge and catalyst were added, the container was flushed with nitrogen before capping. The polymerizations were carded out as described. The resulting polymers were dissolved in enough chloroform to give approximately a 5% solution. The latter was poured with stirring into 5 volumes of methanol. The precipitated polymer was filtered, washed thoroughly with methanol, and dried. The softening points (s.p.) were determined on a Parr melting point apparatus. The intrinsic viscosities were determined in the usual way using dioxane as a solvent and constant temperature bath regulated to 20 +_ 0.02 ~

b. tert-Butyl Thiomethacrylate Polymers A sample of 62 gm of tert-butyl thiomethacrylate was heated at 60~ for 4 days with 0.1% of azobisisobutyronitrile. Gelation occurred in 12 hr. The material dissolved readily in 1200 ml of chloroform. Precipitation from 6000 ml of methanol gave 41 gm (66%) of white, odorless powder. This material had an intrinsic viscosity of 0.24 and s.p. 193~ Compression molding gave a clear brittle specimen which did not exhibit surface flow when heated in steam as 121~ This monomer copolymerized readily with methyl methacrylate giving clear copolymers up to approximately 40 wt% of the thioester. Larger amounts of thioester gave hazy and increasingly brittle materials. On one run, a mixture of 5 gm tert-butyl thiomethacrylate and 45 gm of methyl methacrylate was heated at 60~ for 5 days without a catalyst. Precipitation gave 36.7 gm (73%) of copolymer which had an intrinsic viscosity of 1.63 and s.p. 154~ Compression molding gave a clear, tough bar which had an ASTM heat distortion of 112~ Table VIII lists the softening points of homopolymers of methacrylate and thioacrylate-type esters. Table IX describes the polymerization conditions for new homopolymers. TABLE VIII SofteningPoints of Homopolymers of Methacrylate and Thioacrylic-Type Esters (~ R group in ester Methyl Ethyl i-Propyl t-Butyl Phenyl 4-Chlorophenyl Pentachlorophenyl

Thiocrylate Methacrylate

Thiomethacrylate

144 65a 95 a

98 101

152b 154b >250

Data from Anonymous, Ind. Eng. Chem. 28, 1161 (1936). bUnpublished data from our laboratories. a

152 127 140 193 169 172 >250

3.

61

Free Radical Polymerization of Unsaturated Thioesters

TABLE IX Polymerization Conditions for New Homopolymers

Monomera

Grams

AIBN (wt%)

Temp (~

Time (hr)

Conversion (%)

[r/]

Me TMa Et TM i-Pr TM t-Bu TM Ph TM 4-C1Ph TM C6C15 TMf tert-Bu TAd Ph TAa

32 10 15 62 40b 6 10 11 28

None None None 0.1 None None 0.5 None None

60 60 60 60 60 60 105 60 60

14 12c 12 96 24 24 48 24 24

25 20 20 66 52 37

1.03 0.52 0.54 0.24 0.32 0.23

e

e

23 64

0.28 0.29

a Became viscous from polymerization on standing several hours at room temperature prior to heating. b Sample partially gelled on storage ovemight at 5~ c Another similar sample which was maintained at 60~ for 6 days gave an insoluble polymer; above sample was soluble in 50 ml in chloroform. a TM = thiomethacrylate, TA = thioacrylate. See Experimental. fPentachlorophenylthioacrylate and pentachlorophenylthiomethacrylate polymerizations are described by A. Arman and R. E. Gentry, U.S. Patent 2,945,843 (1960). e

3-3.

Bulk Polymerization of 1,2-Bis(methacryloylthio)ethane in a Glass Mold [1 l b] CH3

I

CH2--C--C-II O

CH3

I

SCH2CH2S--C--C----CH2 II O

~ Polymer /x Free radical Initiator

A mixture o f 100 parts by weight o f 1,2-bis(methacryloylthio)ethane and 0.5 part by weight o f 2,2-azobis (2,4-dimethylvaleronitrile) was placed in a m o l d having two glass plates and a silicone rubber gasket. The m o l d was heated at 50~ for 6 hr, at 60~ for 16 hr, and at 90~ for 2 hr to prepare the polymer. The r e s u l t i n g r e s i n was clear and had a high refractive index (1.608), an Abb6 n u m b e r o f 34.5, and gave 92% light transmission. For comparative purposes m e t h y l methacrylate p o l y m e r i z e d with the same initiator under the same conditions gave a resin with a refractive index o f 1.491 and an Abb6 n u m b e r o f 57.8. In addition, diethyleneglycol bisallyl carbonate (ADC) was p o l y m e r i z e d using 2.5 parts by w t % diisopropyl peroxycarbonate under similar conditions to that in the above preparation. This gave a resin with a refractive index o f 1.500 and an Abb6 n u m b e r of 58.8.

62

2. Polythioesters TABLE IXa

Copolymers of BMTEa

Parts by wt Monomer (BMTE) 70.0 60.0 50.0

Comonomers

Initiator b

Additive C

Refractive Index

Styrene (20) Benzylmethacrylate (10) Benzylmethacrylate (20) 2,4,6-Tibromophenyl methacrylate (20) Benzylmethacrylate (20) 2,2-bis(3,5-dibromo-4methacryloxyethoxyphenyl) propane (30)

0.02

0.02

1.6801

0.20

0.02

1.6803

0.2

0.2

1.5950

aData from [lib]. b 2,2-Azobis (2,4-dimethylvaleronitrile). c 2-(2-Hydroxy-3-methylphenyl) benzotriazole.

The copolymerization of 1,2-bis(methacryloylthio)ethane (BMTE) with comonomers is shown in Table IXa. Other references to these preparations are found in Table IXb.

4.

CONDENSATION OF DIMERCAPTANS WITH DIBASIC ACID DERIVATIVES

Polythioesters have been prepared by the condensation of dimercaptans with either dicarboxylic acids or ester derivatives [12, 13], the ester interchange of phenyl esters of dicarboxylic acids [ 14], or by their reaction with acid chlorides of dibasic carboxylic acids [ 15, 16] TABLE IXb Thioacrylate/Methacrylate Monomers and Their Resulting Polymers Monomers

Reference

Thiophenyl(thioacrylate) and thiomethacrylate

D. P. Warren, U.S. Patents 4,606,864 (1986) and 4,710,557 (1987)

Copolymerization of thioarylalkylacrylates with acrylic monomers

C. D. Deboer, Japanese Patent JP93005873 (1993), and G. W. Lucken and C. D. Deboer, U.S. Patent 4,733,090 (1988).

Homopolymerization of triphenylmethyl thiomethacrylate and its copolymerization with methylmethacrylate

Daicel Chem. Ind. KK, Japanese Patents 91057893 (1991) and JP59134776 (1984).

Polymerization of aryl thiomethylmethacrylates

S. Hayakawa, T. Isuka, F. Watari, and Y. Zanka, U.S. Patent 5,191,061 (1993).

4.

63

Condensation o f Dimercaptans with Dibasic Acid Derivatives

/

0 0 II R' II RO--C-- --C--OR'

HS--R--SH \

[ ",~ /

[

o

o

II II S--C--R'-- C--S--R

] ,

(5)

0 0 II II C1--C--R'--C--C1 where R = X, C6H5. The use of the acid chloride route has the disadvantage of liberating corrosive hydrochloric acid but the advantage of being carried out by either a [12, 13] solution [15] or a low-temperature interfacial process [16]. A variety of engineering polymers and copolymers can be prepared by reacting an aromatic ether dithiol (HS--C6H4OC6H4SH) which has just been stannylated [by reaction with bis(tri-n-butyltin)oxide] with isophthaloyl chloride in dry chloroform. The polymer is precipitated from methanol and the infrared spectrum is consistent with the structure of the polymer [ 16a] as ~S~C6H4~O~C6H4~S~C~C6H4~C~I II II O O

n

Thermoplastic polymers were also earlier reported to have been prepared by heating tricyclodecane dithiol with terephthaloyl chloride in a chlorinated solvent [16b]. Additional examples are cited for polythioesters based on bisphenol A and random other polythioesters derived from bicyclic thiols. The starting diolefins for the dithols are prepared by the Diels-Alder synthesis using cyclopentadiene, acetylene, butadiene, etc.

4-1.

Preparation of a Polythioester by the Condensation of Sebacyl Chloride with Hexamethylenedimercaptan [15]

0 0 II !1 C1--C--(CH2)8--C--C1 + HS(CH2)6SH [

OII OII 1 -- C -- (CHz)8 -- C -- S -- (CH2)6 -- S -- n (6)

TO a small resin flask (equipped with a glass tube for conducting nitrogen gas to the bottom, condenser, and gas exit tube) is added 5.78 gm (0.024 mole) sebacyl chloride. The flask is cooled in an ice bath to approximately 0~ and then 3.71 gm (0.025 mole) hexamethylene dimercaptan is slowly added. The reaction does not start until the flask is warmed to room temperature and above. The reaction starts with the evolution of hydrogen chloride and the nitrogen bubbles are used for agitation. In a few minutes the reaction becomes vigorous

64

2. Polythioesters TABLE X

Condensation of Dimercaptans with Diacid Chlorides to Give Polythioesters [ 15] Product

HS--R--SH Dimercaptan (mole) Xylyl (CH2) 10 (CH2)4 (CH2)4 (CH2)4

R(COC1)2 Acid chloride (mole)

Reaction temp (~

m.p. (~

Viscosity (poises)

Isophthaloyl Terephthaloyl --(CH2)4-Terephthaloyl Isophthaloyl

237 210 210 340 210

200-210 200-201 120-128 310 162-165

785 3290 19,000 198

and after 10 min of reaction time the contents solidify. The temperature is raised to 218~ in about 10 min and maintained at this temperature for 1 hr to complete the condensation reaction while a nitrogen stream passes through the polymer melt. The melt viscosity at 218~ is 216 poises. The flask is cooled and the hard white opaque polymer removed (polymer melt temperature = 107 ~ 109~ The polymer is capable of being extruded in the form of fibers. Other dimercaptans and diacid chlorides undergo this condensation by a similar procedure and are shown in Table X.

4-2.

Preparation of a Polythioester by the Interfacial Condensation of Ethanedithiol and TerephthaIoyl Chloride [16]

HS--CHECH2--SH

+

O

O

II

II

C1--C--C6H4--C--C1

[

o II

o] II

-- S -- CH2CH2 -- S -- C -- C6H4 -- C --

n

(7)

To a l-liter flask equipped with a high-speed stirrer are added 150 ml water, 4.7 gm (0.05 mole) ethanedithiol, 1.0 gm Duponol ME, and 4.2 gm (0.105 mole) sodium hydroxide. The aqueous phase is cooled at 5~ and a solution of 10.1 gm (0.05 mole) terephthaloyl chloride in 150 ml benzene is added all at once with vigorous agitation. A white, solid polymer begins to separate at once and the temperature rises to approximately 15~ over a period of 10 min. The resulting polydimethylene thioterephthalate is filtered, washed three times with water, twice with acetone, and dried to give 11.8 gm (100%) product. The polymer is reported to have a sticking temperature of 340~ and is insoluble in most organic solvents. Other polythioesters prepared by a similar procedure are shown in Table XI.

4.

65

Condensationof Dimercaptans with Dibasic Acid Derivatives

TABLE XI Polythioesters by Interfacial Condensation Method [16]

Dimercaptan HS--R--SH (gm)

Reaction Polymer preparation temp (~ Viscosity Temp (~

Yield

30-55

0.41 b

260-270

100%

50

0.35b

185

4.3 grn

CC14 (140 gm)

0.57C

175

78%

Hexene (100 gm)

0.5 c

100

Acetone (100 gm) Kerosene (200 gm)

0.4r

Diacid chloride

R(COC1)2(gm)

(--CH2--)6 (0.0263)a

Solvent

C6H6 (50

ml)

(0.025)"

(--CH2--)6 (2.5) ~ (0.0263)a

Cyclohexane (40 ml) C6H6 (10 ml)

(51)

(0.025)a

(--CH2--)5 (2.5) (3.74)a (--CH2--)4 (5)

(--CH2--)4 (10)

(--CH2--)2 (4.7) (--CH2--)8 (12)

0.5c

(--CH2--)2 (4.7) (--CH2--)4 (9.15)

9 gm 125

8.1 gm

a Moles.

b In CHC12CHC1/C6HsOH(40/60). c In m-cresol.

4-3.

Preparation of a Polythioester by the Reaction of Diphenyl trans-Cyclohexane-l,4-dicarboxylate and 1, 6-Hexanedithiol [ 14] 0

[

H S C H 2 - - (CH2)4-- CH2SH + C6H5-- O [C[- ~

o< >F]

~--COOC6H5-

2C6H'~

- - S - - C H 2 - - (CH2)4 - - C H 2 S - C n

To a resin kettle equipped with a short distillation column, stirrer, and inlet for dry, purified nitrogen is added 9.7 gm (0.03 mole) of diphenyl transcyclohexane-l,4-dicarboxylate, 4.5 gm (0.03 mole) of 1,6-hexanedithiol, and a

o~ o~

TABLE XII

Polythioesters by Procedure 4-3 [14] Polymerization conditions

Diaryl ester

Dimercaptan

Temp (~

Inherent viscosity a

m.p. (~

LiH

0.53

168-174

Call and Sodium aluminate

0.83

280-300

Reaction time (hr)

} 2} 89 2}

Polymer properties

Catalyst

Diphenyl isophthalate

1,4-Tetramethylenedithiol

200 250

Diphenyl terephthalate

1,6-Hexamethylenedithiol

200 250

Di(2,6-dichlorophenyl)-adipate

4,4'-Isopropylene bisthiophenol

Same as above

LiH

185-198

Di-o-tolyl-trans-cyclo-

1,4-Cyclohexane di(methylmercaptan)

Same as above

LiH

240-255

Diphenyl succinate

HS---~ /v-- SH k......../

Same as for prep. except 250

Di-o-chlorophenyl 4,4'-sulfonyl dibenzoate

HSCH2--CH--(CH2)4SH

hexane- 1,4-dicarboxylate

C2H5

230

0.68

291-302

0.56

200-208

r~

Di-p-tolyl-4,4-methylene dibenzoate

HS-- C H 2 - ~

Diphenyl-p-phenylene diacetate

HS-- c H E H ~ 3 c H 2 S H H3C ICOOH

Diphenyl ester of ( S ~ \ / ~COOH

_ _

CH2SH

240

0.89

268-274

265

0.61

257-262

260

0.51

205-224

CH3 CH3 CH3

70 Mol% diphenyl terephthalate 20 Mol% diphenyl adipate

HS-- C H 2 ~ C H 2 S H

240

0.93

257-264

Diphenyl terephthalate

[80 mol% HS(CH2)4SH 20 mol% HS(CH2)IoSH]

240

1.02

263-270

a

Phenol/tetrachloroethane (60/40).

r~

2. Polythioesters

68

toluene suspension containing 0.0005 gm of lithium hydride ester interchange catalyst. The mixture is melted down in an atmosphere of nitrogen and heated at 1 1 200~ for i hr and at 250~ for another i hr. The phenol formed on transesterification is removed under reduced pressure (30 mm Hg-0.5 mm Hg). Stirring is continued for 2 hr at 250~ under 0.5 mm Hg to complete the polymerization. The light yellow polymer is crystalline and turns opaque on cooling. The polymer melting range is 188~176 Additional examples of polymers prepared by the Procedure 4-1 are shown in Table XII.

4-4. Preparation of Polythioesters by the Reaction of Adipoyl Chloride-Pyridine Complex with Hexanedithiol O II CIC--

O II (CH2)4--CC1 + 2

[5]

+ HS--

(CH2)6--SH

[_o II

o II

C - - (CH2)4-- C - - S - - ( C H 2 ) 6 - - S - -

CAUTION:

] n

(9)

Benzene is a known carcinogen.

In a three-necked, 250-ml, round-bottom flask equipped with a mechanical stirrer, dropping funnel, and condenser are placed 5 ml of reagent grade pyridine and about 50 ml of dry distilled benzene. The mixture is stirred and cooled in an ice-water bath while 3.66 gm (0.02 mole) of adipoyl ' chloride in 10 ml of benzene is added dropwise. The white complex immediately forms. To this reaction mixture is added 3.01 gm (0.02 mole) of hexanedithiol dissolved in 10 ml benzene. Another 5 ml of pyridine is added and the mixture refluxed for 24 hr with stirring. The mixture is cooled, the solids filtered, washed with water, and the remaining solid dissolved in chloroform. The product is isolated by precipitation in methanol, filtering, and drying to give 0.27 gm polymer which has an inherent viscosity of 0.15 and a m.p. range of 97~176 More polymer is isolated from the benzene filtrate by concentration to 25 ml and then addition to 100 ml methanol. The polymer is filtered, reprecipitated, and dried to give 2.10 gm (m.p. range 87~176 and has an inherent viscosity of 0.08. An additional 0.32 gm of polymer is isolated from the filtrate in the reprecipitation step to give a total of 2.69 gm or 52% yield. Using the same procedure other dibasic and chlorides are reacted with dithiols to give polythioesters as shown in Tables XIII and XIV.

TABLE XlII

Polythioesters from Adipyl Chloride and Dithiols a Analyses b (%)

Dithioadipate

Formula

Polyethylene

-- SCO(CH2)4--COS(CH2)2--

Polytetramethylene

-- SCO(CH2)4COS(CH2)4--

Polyhexamethylene

-- SCO(CH2)aCOS(CH2)4--

Polydecamethylene

-- SCO(CHz)aCOS(CH2)I 0--

Polydiethylenesulfide

-- SCO(CH2)aCOS(CH2)2S(CH3)2--

m.p. (~

Inherent viscosity in CHC13

Yield

Carbon

Hydrogen

Sulfur

(%)

Calc

Found

Calc

Found

Calc

Found

111-125 95-100 97-104 70-75 67-70

0.13 0.13 0.15 0.10 0.12

62 50 51 57 47

47.03 51.69 55.35 60.71 45.42

47.78 51.52 55.37 60.74 46.25

5.92 6.94 7.74 8.92 6.10

6.13 7.00 7.86 9.07 6.20

31.39 27.60 24.62 20.26 36.38

31.08 27.82 24.90 19.98 36.10

a From C. S. Marvel and A. Kotch, J. Am. Chem. Soc. 73, 1100 (1951). Copyright 1951 by the American Chemical Society. Reprinted by permission of the copyright owner. b Microanalyses reported in this paper were performed by Miss Emily Davis, Miss Rachel Kopel, and by the Clark Microanalytical Laboratories, Urbana, Illinois.

TABLE XIV

Polythioesters from Terephthalyl Chloride and Dithiols a Analyses b (%) Carbon

Dithioterephthalate

Formula Oii

Polyethylene

O --S--C---~ \

Polydecamethylene

--S--C---~ \

Polydiethylenesulfide

--S--C

O

Calc

Found

Calc

Found

Calc

Found

335-340

68

53.55

53.62

3.59

3.74

29.59

28.83

230-260

70

57.11

57.03

4.79

4.78

25.41

25.18

136-144

71

64.24

63.43

7.19

7.34

19.06

18.77

140-146

73

50.67

50.73

4.25

4.21

33.82

33.53

O

Polytetramethylene

ii

Sulfur

Yield (%)

Oal

,r

-- S-- C---~z \ _ _ /\)---C-- S-- (CH2)2--

O

Hydrogen

m.p. (~

~/v---C--S-- (CH2)4-/ O

,r

ii

/

~---C-- S-- (CH2)10-O -- S-- (CH2)2-- S-- (CH2)2--

a From C. S. Marvel and A. Kotch, ,I. Am. Chem. Soc. 73, 1100 (1951). Copyright 1951 by the American Chemical Society. Reprinted by permission of the copyright owner. b Microanalyses reported in this paper were performed by Miss Emily Davis, Miss Rachel Kopel, and by the Clark Microanalytical Laboratories, Urbana, Illinois.

References

1;

71

MISCELLANEOUS

PREPARATIONS

AND

METHODS 1. Preparation of asymmetric polythioesters [ 17]. 2. Polymerization of thiepan-2-one to a linear polythioester [18]. 3. Preparation of polythioglycolides from cyclic dithioglycolides from cyclic dithioglycolide [ 19]. 4. Amine ring opening polymerization of thiolactone to polythioesters [20]. 5. Polythiolesters by reaction of certain unsaturated thioacids [21 ]. 6. Polythiolactones [22]. 7. Thiolactone polymerization and catalysts [23]. 8. Preparation of a polythioester by the reaction of ketene with 2-methyl1,3-semithiodioxolane in the presence of catalytic amounts of hexafluorophosphoric acid in a methylene chloride solution [ -- C O -- CH2 -- CIH -- O -- C H 2 C H 2 -- S-- ] CH3

9. 10. 11. 12. 13. 14.

n

[24]. Preparation of tetrathiooxalate polymers [25]. Preparation of polythiocarbonates [3b]. Reaction of maleic anhydride with thioalcohols and hydroxythioether to give thioesters which are copolymerized with vinyl monomers [26]. Epoxythioester polymers [27]. Resins for high refractive lens containing a sulfur-containing aromatic methyacrylate and a mercapto compound [28]. Preparation of polymers with a thioester pendant group [3b].

References 1. 2. 3.

C.S. Marvel and A. Kotch, d. Am. Chem. Soc. 73, 1100 (1951). Wingfoot Corp., British Patent 630.625 (1949); Chem. Abstr. 44, 3741 (1950). G. Sumrell, J. Brisken, G. E. Ham, and C. H. Schramm, J. Am. Chem. Soc. 81, 4308 (1959); G. Braude, J. Org. Chem. 22, 1675 (1957); W. Reppe, Justus Liebigs Ann. Chem. 582, 13 (1953); M. M. Koton, T. M. Kiselyev, and K. S. Podgoskagar, Zh. Obshch. Khim. 26, 475 (1956); Chem. Abstr. 50, 13815 (1956). 3a. C. S. Marvel, S. L. Jacobs, W. K. Taft, and B. G. Labbr, J. Polym. Sci. 19, 59 (1956). 3b. A. Duda and S. Penczek, in "Encyclopedia of Polymer Science and Engineering," Vol. 16, p. 304, 1989. 4. W.A. Murphy, U.S. Patent 2,870,126 (1959). 5. C.S. Marvel and A. Kotch, J. Am. Chem. Soc. 73, 1100 (1951). 6. C.S. Marvel and E. A. Kraiman, J. Org. Chem. 18, 707 (1953). 7. C.S. Marvel, S. L. Jacobs, W. K. Taft, and B. G. Labbr, J. Polym. Sci. 19, 59 (1956). 8. L.A. Mikeska, U.S. Patent 2,474,246 (1949). 9. M. Hauptschein, R. B. Hager, and T. C. Allen, U.S. Patent 3,544,663 (1970). 10. N. Kydonieus and S. R. Sandler, U.S. Patent 3,929,852 (1975).

72 11. 1la. 1lb. 12. 13. 14. 15. 16. 16a. 16b. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28.

2.

Polythioesters

Y. Nakayama, T. Tsuruta, J. Furukawa, A. Kawasaki, and G. Wasai, Makromol. Chem. 43, 76 (1961). Y. Iguchi, M. Kimura, and K. Oka, U.S. Patent 5,247,041 (1993); T. Matsuda, Y. Fumono, and M. Yoshido, U.S. Patent 4,931,521 (1990). T. Matsuda, Y. Funao, M. Yoshida, and T. Takaya, U.S. Patent 4,931,521 (1990). W. Carother, U.S. Patents 2,071,250 and 2,071,251 (1937); J. T. Dickson, U.S. Patent 2,465,150 (1949); J. R. Whinfield and J. T. Dickson, U.S. Patent 2,465,319 (1949). J.C. Patrick and H. R. Ferguson, U.S. Patent 2,563,133 (1951). J.C. Martin and R. Gilkey, U.S. Patent 3,254,061 (1966). P.J. Flory, U.S. Patent 2,510,567 (1950). W.A. Murphey, U.S. Patent 2,870,126 (1959). I. D. H. Towie and P. J. Homer, U.S. Patents 4,999,411 (1991), 4,960,835 (1990), and 4,845,175 (1989). G. L. Brode and T. L. Picketing, U.S. Patent 3,640,965 (1972). C.G. Overberger and J. K. Weise, J. Am. Chem. Soc. 90, 3538 (1968). C.G. Overberger and J. K. Weise, J. Am. Chem. Soc. 90, 3533 (1968). A. Sch6bert, Makromol. Chem. 37, 64 (1960). C.G. Overberger and J. K. Weise, J. Am. Chem. Soc. 90, 3533 (1968). F. Korte and H. Christoph, Chem. Ber. 94, 1966 (1961). M. Matzner, J. E. McGrath, and S.-W. Chow, U.S. Patent 3,631,223 (1971). P.E. Fritze, U.S. Patent 3,755,268 (1973); A. C. Pierce, U.S. Patent 3,520,903 (1970). H. Eck, J. Heckmaier, and H. Prigge, U.S. Patent 3,519,683 (1970). H.D. Hartzler, U.S. Patent 3,717,619 (1973). Atlantic Richfield Co., U.S. Patent 3,650,978 (1972). J. Emert and R. D. Lundberg, U.S. Patent 5,205,947 (1993). Z. Yukihito, S. Hayakawa, T. Isaka, and F. Watari, U.S. Patent 5,191,061 (1993).

Chapter 3

Sulfide Polymers 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Polysulfides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Condensation Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-1. Preparation of Polyethylenetetrasulfide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2. Preparation of Polysulfide Latex Polymer . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Oxidation Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-3. Preparation of Polydisulfides by Oxidation of Dimercaptans . . . . . . . . . . . . . . . 2-4. Preparation of a Polydisulfide by the Oxidation of Hexamethylenedithiol with Bromine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5. Polysulfide Formation by the Dimethyl Sulfoxide Oxidation of Dimercaptop-xylene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Poly(alkylene sulfides) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Polymerization of Episulfides (Thiiranes) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-1. Polymerization of Ethylene Sulfide Using Diethyl Zinc-Water Catalyst . . . . . . . . 3-2. Polymerization of Ethylene Sulfide Using Acetone-Sodium Catalyst . . . . . . . . . . B. Poly(alkylene sulfides) by the Reaction of Dimercaptans and Dihalides . . . . . . . . . . .

3-3. Preparation of Poly(alkylene sulfide) by the Condensation of the Disodium Salt of Hexamethylenedithiol (1,6-Hexanedithiol) and Tetramethylenedibromide . . . . . . 3-4. Preparation of a Poly(alkylene sulfide)from the Disodium Salt of Hexamethylenedithiol and 1,6-Dibromohexane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5. Preparation of the Poly(alkylene sulfide)from the Disodium Salt of Hexamethylenedithiol and meso-2,5-Dibromohexane . . . . . . . . . . . . . . . . . . . . . . . . C. Poly(alkylene sulfide) by the Addition of Thiols to Olefins . . . . . . . . . . . . . . . . . . . .

3-6. Poly(alkylene sulfide) by the Reaction of Hexamethylenedithiol and 1,5-Hexadiene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7. Addition of Trimethylenedithiol (1,3-Propanedithiol) to Allene at Ambient Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Poly(alkylene sulfides) by the Addition of Thiols to Carbonyl Compounds . . . . . . . . .

3-8. General Procedure for the Preparation of Polymercaptols Shown in Table IX. .. E. Poly(alkylene sulfides) by the Dehydration of Mercaptoalkanols . . . . . . . . . . . . . . . .

3-9. Cocondensation of Mercaptoethanol and Mercaptopropanol . . . . . . . . . . . . . . .

74 75 75 76 78 80 83 84 86 86 88 88 89 92 92 93 95 95 96 98 99 99 102 102

73

74

3. SulfidePolymers

4. Poly(arylene sulfides) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1. Preparation of Poly(phenylene disulfide). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2. Preparation of Poly(phenylene sulfide) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

103 105 107

4-3. Preparation of Poly(phenylene sulfide) by the Reaction of p-Dichlorobenzene and Sodium Sulfide in N-Methyl-2-pyrrolidone. . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 5. Miscellaneous Preparations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1.

113 114

INTRODUCTION

The sulfide polymers covered in this chapter are those based on the polysulfides derived from the reaction of dihalides and sodium di- or polysulfides; polyphenylene sulfides generated from aryl dihalides and sodium sulfide; polyalkylene sulfides generated from ethylene episulfide or dimercaptan-olefin or diolefin-diketone reactions, all of which are outlined in Scheme 1. The sulfide polymers are used because of their resistance to oils and solvents, and they are used as specialty plastics [poly(phenyl sulfides)] or as gaskets, hoses, printing rolls, etc. (polysulfides). Polymers based on ethylene sulfide (thiirane, ethylene episulfide) have not been developed into commercial products yet. Polysulfides are used in synthetic rubber compositions [1], epoxy resin modifiers [2], coatings [3], adhesives [4], sealants [5], and many other products as described in recent Chemical Abstract issues. For additional background material up to about 1960 one should consult available reviews [6-9]. Several additional reviews [9a, 9b] which cover the literature to 1986 are also worth consulting. This text covers the literature to 1994. Poly(ethylene sulfide) differs greatly from poly(ethylene oxide) in being insoluble in water and melting at a much higher temperature [9a]. Na2S + ArX2

Na2S + RX2

R ( - - SI-1)2+ R(CH =CH2)2

/ CH2

R(SH), + R(C =oh

'

(-- S--R--)n

"~

s,, I

CHR

(--S~--R--)~

1

Na2S~ + RX2

Scheme 1

Preparation of sulfide polymers.

75

2. Polysulfides

Progress has been made on the synthesis of polysulfide polymers by the ring opening polymerization of cyclic polysulfides as well as by addition/condensation copolymerization using elemental sulfur [9a]. The poly(alkylene sulfides) can be deodorized by treatment with aqueous acetaldehyde [9c]. Poly(propylene sulfide) has also found applications in photo and radiation sensitive resins for use in resists [9d]. The thermal properties of poly(ethylene sulfide) and poly(isobutylene sulfide) and copolymers have been reported via DSC (differential scanning calorimetry) [9e]. 2.

POLYSULFIDES

Earlier accounts of the reaction of halogenated products with potassium sulfide did not report useful polymeric products [10]. Patrick and Mnookin [ 11] were the first to report useful polysulfide products that were to become the early basis of the Thiokol Chemical Corp. business. Polysulfides generated interest before and after World War II because natural rubber was difficult to obtain at times and was also high in price [12]. The polysulfides derived from ethylene dichloride were not as elastomeric as natural rubber. It was found that increasing the spacing between reactive terminal groups improved the properties. Better products derived from bis(2chloroethyl) ether were soon developed in the United States by the Thiokol Chemical Corp. The presently used commercial polysulfides are based on bis(2-chloroethyl)formal and possess excellent solvent resistance. The elastomeric products are used in such applications as lacquers, hoses, priming rolls, diaphragms, and gaskets. The chemistry of the polysulfides is described in many reviews which should be consulted for additional details [9a, 9b, 13].

A.

Condensation Reactions

The raw materials for the preparation of the polysulfides are sodium polysulfide and dichloroalkane. Sodium polysulfide is prepared by reacting sulfur with aqueous caustic to give sodium polysulfides of various ranks (values ofx in the empirical formula NaxSx) 6NaOH + (2x + 2)S

' 2Na2Sx + Na2S203 + 3H20

(1)

Heating for 1 hr gives a rank of 4 and heating for 6 hr gives a rank of 2. The sodium thiosulfate is not removed since it does not interfere in the subsequent reaction with organic dihalides. The latter reaction is rapid and is complete in 1 hr at 120~

3.

76

Sulfide Polymers

The organic dihalides most often used are those that are commercially available such as methylene chloride, ethylene dichloride, propylene di-chloride, glycerol dichlorohydrin, dichloroethyl ether, dichloroethylformal, and triglycol dichloride. The most reactive chloro-compounds are the primary ones and these are the most commonly used. Dichloroethylformal can be prepared by reacting ethylene chlorohydrin for formaldhyde and the water of reaction is removed either by azeotropic distillation with solvent (ethylene dichloride) or by vacuum distillation. 2C1--CHECHEOH + HEC--O

--H20

~ (C1--CHECHEO)ECH2

(2)

The polymerization can be carried out with or without dispersing agents, but the latter is a more commonly used process in which magensium hydroxide [ 14] from magnesium chloride and sodium hydroxide is used in the presence of surfactants and/or wetting agents. The reaction of formaldehyde (paraformaldehyde) and hydrogen chloride (anhydrous) with tetrahydrofuran has been used to produce 6-chlorobutyl chlorornethyl ether [15] a halide useful for preparing polysulfides [Eq. (3)].

~

+ H 2 C - - O + HC1

, C I - - ( C H 2 ) 4 - - O - - C H 2 C 1 + H20

and/or C1 -- (CH2)4-- OCH20 - - (CH2)4C1 + H20

(3)

CAUTION: The reaction of formaldehyde with hydrogen chloride has been reported to yield the known carcinogen bis(chloromethyl) ether [16].

2-1.

Preparation of Polyethylenetetrasulfide [17] Na2S-9H20 + S Na2S4 + C1--CH2CH2C1

H20

~ NaES4

H20 70oc ~ (--CH2CH2S4--)n

(4) (5)

(s.p. 130~176 To a three-necked flask equipped with a reflux condenser, mechanical stirrer, and thermometer is added 750 gm (9.6 moles) Na2S- 9H20 dissolved in 1 liter of water, and 300 gm (9.4 gm atom) sulfur. The mixture is boiled for 1 hr to form sodium tetrasulfide Na2S4. At 70~ approximately 200 gm of water is added to make a solution that has a specific gravity at 70~ equal to ethylene dichloride. Then 300 gm (3.0 mole) of ethylene dichloride is added and the mixture is

2. Polysulfides

77

heated to about 70~ and held at this temperature for 1-2 hr. The mixture is cooled and the aqueous solution is decanted from the yellow polymer. The polymer is purified by heating several times with water to remove soluble salts, and then dried. The polymer can be molded and rolled into sheets at 130~176 Related polymers have been reported by Patrick [18, 19] and Spielberger [20]. Sodium tetrasulfide used in Preparation 2-1 may also be produced by the reaction of sulfur and sodium hydroxide. 9S

+ 6NaOH

(6)

~ 2Na2S4 + Na2SO3 + 3H20

This method requires that the reaction be run at 140~ so that the water is boiled off. Then the reaction mixture is heated for 4-8 hr. The reaction mixture is filtered while hot to remove the insoluble sodium sulfite [21]. The following tabulation [21 ] shows how the mole ratio of sulfur and sodium hydroxide will affect the rank of the sodium sulfide. Alkaline hydroxide (moles) 6 6 6 6 6 6

NaOH Na0H NaOH NaOH NaOH NaOH

3Ca(OH)2 3Ca(OH)2 3Ca(OH)2 3Ca(OH)2

Sulfur (gm atoms)

Product Sulfide (moles)

Rank of sulfide

Sulfite (moles)

3 5 7 9 10 11

2 2 2 2 2 2

1 2 3 4.5 5

1 1 1 1 1 1

3 5 7 9

2 2 2 2

1 2 3 4

1 1 1 1

Low-molecular-weight polymers can be further reacted with 0.2 mole sodium polysulfide per mole polymer in an aqueous dispersion at 82~ for 1-2 hr to give polymers of higher molecular weights. Polymers of too high a molecular weight can be reduced to smaller segments by reduction of the disulfide-thiol linkages with aqueous sodium hydrosulfide and sodium sulfite [22] at 82~ for lhr. (-- R-- S-- S-- R--). + NaSH + Na2SO3 --RSNa + --RSH +

Na2S203

(7)

Controlled concentrations of sodium hydrosulfide-sodium sulfite give specific molecular weight ranges. The polymer is coagulated by the addition of acetic or sulfuric acid, washed, and dried.

78

3. SuifidePolymers

2-2. Preparation of Polysulfide Latex Polymer [22] H20 (C1--CH2CH20)2CH2 + some CH2--CH--CH2 + Na2S4 - - - - *

I

c1

I

c1

(--CHECHEO--CHE--OCHECH2--SS--)~

I

c1 NaSH Na2SO3

~

(8)

NaS(-- CHECH20-- CHEOCHECH2-- SS--)CEH4OCHEOCEH4SNa

H* ~ HS(--CEH40--CHE--OCEH4--SS--)CEH4OCHEOCEH4SH

Method A [22]: To an agitated and jacketed stainless steel reactor are added 9.6 lb moles of NaES4, 560 gal of water, 15 lb of NaOH, and 48 lb of MgC12" 6H20 [23]. The reactor is closed and heated at 180~ and then a mixture of 8 lb moles dichloroethyl formal and 0.04 lb moles 1,2,3-trichloroethane is added over a 1-hr period. The solution is heated at 180~ for 30 min and then heated for 15 min at 212~ The latex suspension (the polymer particles have a density of 1.2 and settle rapidly) that is formed is washed with water several times, then with 8 lb of sodium hydroxide (50% solution) at 170~ for 1 hr to remove labile sulfur and then twice with water. The latex suspension is heated at 180~ for 30 min with 0.9 lb mole of Na2S4, then washed free of unreacted sodium sulfide. The polymer at this point, if obtained by coagulation of the latex, has properties similar to cured rubber. A more thermoplastic polymer is obtained by heating the latex with 2.6 lb mole of Na2SO3 and 0.24 lb mole of NaSH at 180~ for 30 min. The polymer is coagulated with acid, washed, and dried. The process can also be used to give liquid polymers. Swaab and Sutker [24] reported a modification of the foregoing procedure in which a solid, particulate, polysulfide polymer mixture is formed that is free flowing, insensitive to moisture, and redispersible in water to form a stable latex. The process involves the reaction of a Bunte salt (reaction product of sodium thiosulfate and bis(chloroethyl) ether with calcium sulfide in the presence of 5-30% of a dispersing agent [Mg(OH)2 or the sodium salt of a polyalkylnaphthalenesulfonic acid]. Method B [25]: To a round-bottom flask is added 900 ml of freshly prepared 2 M solution of sodium tetrasulfide, 8 drops of sulfonated ricinoleic acid, and 4.8 gm (0.12 mole) of sodium hydroxide. To this mixture is added 12.18 gm (0.06 mole) of magnesium chloride (MgC1E'6H20) and the flask is heated to 75~ To this mixture is added dropwise a solution of 254.4 gm (2.0 mole) of bis(2-chloroethyl)formal and 4.41 gm (0.03 mole) of 1,2,3-trichloropropane. When the addition is complete the reaction mixture is heated at 98~176 with vigorous stirring and kept at this condition for approximately 1 hr. During this time a finely dispersed high-molecular-weight polysulfide polymer forms. When

79

2. Polysulfides

the reaction is complete the polymer dispersion settles and the polymer is washed to eliminate inorganic salts. A 150 gm portion of a 50% solution of carbonate-free sodium hydroxide is added at 75~ and the mixture is heated again to 90~176 to eliminate the labile sulfur from the polymer. The polymer is washed with water, filtered, and dried. Polysulfide rubber manufacturing processes are described in more detail by Bertozzi [26]. Briefly, the processes involve preparation of sodium polysulfide (S + NaOH), and reaction with bis(2-chloroethyl)formal along with 2% of a branching agent such as 1,2,3-trichloropropane to give a mercaptan terminated polymer of MW approximately 80,000 similar to that described in Preparation 2-2, Method A. The polysulfide rubbers containing terminal mercaptan groups are vulcanized by oxidation of these groups to polysulfide groups. This condensation reaction involves splitting out a small amount of water. The oxidizing agents are selected from metallic peroxides in the presence ofp-quinone dioxime [27]. The liquid polysulfides (LP) were first commercially available in 1943. These polymers have terminal thiol groups and only 6 types are available (LP-31, LP-2, LP-32, LP-12, LP-3, LP-33) [28]. These polymers HS(C2H4OCH2OC2H4SS)xC2H4OCH2OC2H4SH can be cured either by oxidation [29] [Eq. (9)] reaction with epoxy resins [Eq. (10)] or by reaction with aromatic amines [30, 31 ]. 2RSH + (O) \

/ O

+ HS--R--SH

, - - R - - S - - S - - R - - + H20 ; --C--C--S--R--S--C--C-I I OH OH

(9) (10)

The LP-liquid polysulfides are manufactured by the condensation of organic dihalides and sodium polysulfide at elevated temperature. A controlled amount of a trifunctional organic halide is also coreacted in this process. Some examples of commercial liquid polymers are reported in Tables I and II. The liquid polymers can be formulated into caulking compounds, adhesives, air-drying paints, and epoxy resin systems [32, 33]. The kinetics of the reaction of dichloroethane, dibromoethane, dichloropropane, and dichloroisobutane with KaS, Na2S, and (NH4)2S were reported by Dobrikov and co-workers in 1976 [33a]. The effects of temperature, concentration, and the nature of the monomers on the course of the polymerization kinetics are described. Related methods for preparing polyarylene sulfides are discussed in Section 4.

3. Sulfide Polymers

80 TABLE I CommercialLiquid Polysulfide Polymersa Polysulfide resin Property

LP-31

LP-2

LP-3

Average molecular weight Viscosity (poises at 25~ pH (water extract) Specific gravity (20/20) Refractive index n2~ Pour point (~ ~ Mol% trifunctional

8000 950-1550 6-8 1.31 1.57 10" 50 0.5

4000 410-525 6-8 1.29 1.56 7" 15 2

1000 9.4-14.4 5-6 1.27 1.56 - 26" - 15 2

Data from J. S. Jovezak and E. M. Fettes [Ind. Eng. Chem. 43(2), 324 (1951)], E. R. Bertozzi and W. D. Helmer [Chem. Eng. Prog. 57(6), 96 (1961)], and "An Engineering Guide to LP Polysulfide Polymers," Tech. Bull. No. TD 1251b 5M, 2-76. Thiokol Chemical Corp., Trenton, New Jersey, 1976. a

B.

Oxidation

Reactions

Martin and Patrick [34] reported that the ethylene disulfide polymer prepared from ethylene dichloride and sodium disulfide is practically identical to the polymer prepared by the sodium hypobromate oxidation of alkaline solutions of ethylene mercaptan. The resulting polymer can be converted to the tetrasulfide [35] by combination with 2 gm atoms of sulfur. In addition the tetrasulfide can be reconverted to the disulfide polymer by treatment with sodium hydroxide. HS--CH2--CH2--SH C1--CH2--CH2C1 + Na2S2

[o]

l

; (--CH2CH2--SS--)n

1

2S

C1--CH2CH2--C1 + Na2S4

TNao. ) | -2S

' /--CH2--CH2--S--S-II II S S

(11)

n

These polysulfides are usually powdery or rubber-like. Some examples are shown in Table III. Marvel and Olson [36] further developed the oxidation polymerization technique that was earlier reported by Patrick [37] to give polydisulfides. When a dimercaptan was dispersed in an aqueous soap solution and air was passed through the mixture, oxidation to a polydisulfide readily occurred and a stable polymer latex was produced. Foaming was troublesome, but the addition

2. Polysulfides

81

TABLE II

Solubility of Solvents in Thiokol Liquid Polymersa

Solvent Acids, organic Formic acid Acetic acid, glacial Alcohols Methanol Ethanol 1 -Butanol Ethylene glycol Furfuryl alcohol Glycerol Aldehydes Benzaldehyde Furfural Ethers Diethyl ether Dioxane Ketones Acetone Methyl ethyl ketone Methyl isobutyl ketone Cyclohexanone Esters Methyl acetate Ethyl acetate Butyl acetate Dibutyl phthalate Tricresyl phosphate Aromatic hydrocarbons Bezene Toluene Xylene Chlorinated hydrocarbons Carbon tetrachloride Ethylene dichloride Ethylene chlorohydrin Chlorobenzene Nitro paraffins Nitromethane Nitroethane 1 -Nitropropane 2-Nitropropane

LP-2b

LP-36

20 0

20 0

0 0 0 0 90 0

0 0 0 0 M 0

M M

M M

0 M

40 M

50 70 30 M

80 M 80 M

60 50 50 M M

M M M M M

M M 50

M M M

70 M 90 M

M M M M

60 90 90 80

M M M M

a Reprinted in part from J. S. Jorczak and E. M. Fettes, Ind. Eng. Chem. 43(2), 324 (1951). Copyright 1951 by the American Chemical Society. Reprinted by permission of the copyright owner. Solvent in liquid polymer is given as wt%. b M signifies miscible in all proportions.

82

3. Sulfide Polymers TABLE III Unit Polymers of Sulfides a

Unit

Approximate physical state

--CS2S --CH2SS --CHESS-IIII SS

Powder Powder Rubber-like

--CH2CH2S---CH2CH2SS---CHECHESS--

Powder Powder Rubber-like

IIII

SS

--CH2CH2CH2S---CH2CH2CH2SS---CHECHECHESS--

IIII

Powder Powder Rubber-like

SS

--C2H4OC2H4S---C2H4OC2H4SS---CEH4OCEH4SS--

IIII

Powder Rubber-like Rubber-like

SS

--C2H4OC2H4OC2H4S-C2H4OC2H4OC2H4SS---C2H4OC2H4OC2H4SS-IIII SS

Powder Rubber-like Rubber-like

--CH2CH2CH2CH2CH2SS---CH2CH2SCH2CH2SS--

Rubber-like Rubber-like

-

-

a Reprinted from S. M. Martin, Jr. and J. C. Patrick, Ind. Eng. Chem. 28(10), 1144 (1936). Copryight by the American Chemical Society, 1936. Reprinted by permission of the copyright owner.

of a little silicone antifoam agent (Dow Coming Antifoam A was used) controlled it. It was also necessary to add water to the reaction mixture from time to time to maintain the volume. The reaction at room temperature was slow and required 4--10 days to yield a polymer with an inherent viscosity of 0.2 to 0.3. The addition of a little selenious acid [37a] to the reaction mixture speed up the oxidation so that high-molecular-weight polymers could be prepared in a shorter time. The limiting factors on the molecular size appeared to be the purity of the dimercaptan and the time of oxidation. Tough, plastic, odorless polydisulfides with inherent viscosities as high as 1 have been obtained. The polydisulfide derived from the dimercaptan that was prepared by adding 2 moles of thiolacetic acid to 4-vinyl-1-cyclohexene with hydrolysis was heated

2. Polysulfides

83

with sulfur at 150~ for 3 hr. This reaction yielded a more rubber-like polymer that was far less soluble in organic solvents than the untreated polymer. Analysis of the new polymer showed that approximately 0.7 atom of sulfur had been added for each disulfide link in the original material. Some experiments were conducted to determine whether such oxidizing agents as halogen, nitric acid, or ferric chloride could be used in place of air, but none of these worked as satisfactorily as air in emulsion systems. One experiment on the oxidation of hexamethylene dimercaptan with bromine is described in Preparation 2-4. The oxidative polymerization of diphenyl disulfides with quinones to form ultrapure poly(1-p-phenylene sulfide)s is discussed in Section 4 [37b]. In the presence of SO2 the alkylene dithiols produce alkylene polysulfides as well as a complex mixture of disulfides, trisulfides, and dithiosulfate linkages. The redox copolycondensation is catalyzed by the following: (C2Hs)3N, BF3 etherate, MnO2, PbO2, and P205 [37c]. The use of free sulfur ($8) in place of air and catalyzed by triethylamine leads to the polycondensation of ethanedithiol [37d]. nHSCH2CH2SH

S8

' --~-CH2CH2S--)-n TEA--H2S

The oxidative polymerization of diphenyl disulfides or of thiophenal with quinones at room temperature has been reported to produce pure poly(pphenylene sulfides) [37c]. This will be described in more detail in Section 4.

2-3.

P r e p a r a t i o n o f P o l y d i s u l f i d e s by O x i d a t i o n o f Dimercaptans [36] *

A typical oxidation polymerization was carried out as follows. In a 4-ounce, wide-mouth bottle were placed 50 ml of distilled water, 1.5 gm of lauric acid, 4 gm of potassium hydroxide, and 5 ml of dimercaptan. When these ingredients were dissolved, 1 drop of Antifoam A was added. Filtered compressed air was bubbled through the mixture by a piece of 6-mm glass tubing at a rate of about two bubbles per second for four to ten days. More Antifoam A was added as needed to control foaming and the volume of the mixture was maintained by adding distilled water as needed. At the end of the oxidation period the Antifoam A was removed by skimming it off the surface and the polymer lattices were coagulated. Polymers coagulated with 20 ml of alum coagulant (prepared by dissolving 100 gm of aluminum potassium sulfate in a mixture of 100 ml of concentrated hydrochloric acid and 1 liter of distilled water) had up to * Reprinted from C. S. Marvel and L. E. Olson, J. Am. Chem.Soc. 79, 3089 (1957). Copyright 1957 by the American Chemical Society. Reprinted by permission of the copyright owner.

3. SulfidePolymers

84

TABLE IV Air Oxidation of Dimercaptans in Emulsion without Catalysta

Mercaptan 1-fl-Mercaptoethyl-3 (or 4)mercaptocyclohexane

1-(tx-Methyl-fl-mercaptoethyl)-3mercapto-4-methylcyclohexane

Time of oxidation (hr)

Yield of polymer (%)

Inherent viscosityin chloroform

24 48 72 144 92b 236b 236c 236d

13 46 61 76 47 92 77 94

0.09 0.27 0.50 0.59 0.14 0.46 0.24 0.33

a Reprinted from C. S. Marvel and L. E. Olson, J. Am. Chem.Soc. 79, 3089 (1957). Copyright 1957 by the American Chemical Society. Reprinted by permission of the copyright owner. bThree grams of potassium hydroxide was used in this run. c Two grams of potassium hydroxide was used in this run. dFour grams of potassium hydroxide was used in this run. 20% ash as residue after combustion. The ash could be diminished, but not eliminated, by repeated reprecipitations of the polymer from benzene or chloroform into methanol. Polymers coagulated by pouting the emulsion into methanol containing some hydrochloric acid, followed by reprecipitation, gave satisfactory analyses. The polymers were dried in a vacuum desiccator, then dissolved in 50 ml of chloroform, and reprecipitated by pouting these solutions into 400 ml of methanol. In later runs approximately 5-20 mg of selenious acid was introduced in the emulsion as a catalyst. When 20 mg of this catalyst was used, the polymer obtained by breaking the emulsions varied in color from pink to red. This color could be removed by adding a small amount of sodium hydroxide to the methanol (about 1 gm per 400 ml) used in the reprecipitation of the polymer from chloroform solution. Some of the oxidation polymerization experiments are recorded in Tables IV and V.

2-4.

P r e p a r a t i o n o f a P o l y d i s u l f i d e by the O x i d a t i o n o f H e x a m e t h y l e n e d i t h i o l with B r o m i n e [36]* H S - - ( C H 2 ) 6 - - S H + Br2 ----* H [ - - S - - ( C H 2 ) 6 - - S - - ] n H

(12)

Five milliliters of hexamethylenedithiol was added to 50 ml of 2% MP-635-S solution in a 4-ounce polymerization bottle. Three grams of sodium hydroxide * Reprinted from C. S. Marvel and L. E. Olson, J. Am. Chem.Soc. 79, 3089 (1957). Copyright 1957 by the American Chemical Society. Reprinted by permission of the copyright owner.

TABLE V

Polydisulfides Prepared by Air Oxidation in the Presence of Selenious Acid a Analyses (%)

Oxidation time (hr)

Mercaptan

1-fl-Mercaptoethyl-3(or

Yield (%)c

Inherent viscosity d

Softening temp (~

C

H

S

Formula polymer unit

Calc

Found

Calc

Found

Calc

Found

C8H14S2

55.12

55.19

8.10

8.09

36.79

36.68

C~0H18S2 59.35

58.95

8.97

9.16

31.69

31.58

C6H1252 C7H14S2 C9H18S2 C~0H20S2

48.55 51.97 56.42 59.08

8.10 8.68 9.53 9.86

8.28 8.44 9.47 9.92

39.51 33.69 31.38

39.17 33.64 31.14

4)-

mercaptocyclohexane

144

80

0.23

83

76

0.14

240 90 90 90

50 92 92 100

0.226 0.59 f 0.39 0.30

110

1-(tx-Methyl-fl-mercaptoethyl)-3mercapto-4-methylcyclohexane Dithiol Hexamethylene -e HeptamethyleneNonamethyleneDecamethylene-

40 b 57 130 55 45

48.70 51.80 56.78 58.76

a Reprinted from C. S. Marvel and L. E. Olson, J. Am. Chem. Soc. 79, 3089 (1957). Copyright 1957 by the American Chemical Society. Reprinted by permission of the copyright owner. bpolymer [tx]2SD + 19.5 ~ C 2 in chloroform. c Calculated after one reprecipitation from chloroform by methanol. d Measured in chloroform after one reprecipitation. e This polymer was prepared by Eugene D. Vessel. fFractionation of the polymers by repeated reprecipitation from chloroform and methanol gave a rubber-like material with an inherent viscosity of 0.95.

OO

86

3.

SulfidePolymers

was added and the mixture shaken until solution was complete. Then, 6 gm of bromine was added and the bottle was capped and sh~rken on a mechanical shaker for 3 hr. Some polymer formed almost immediately and separated as precoagulum. At the end of the shaking period alum coagulant [37e] was added to break the emulsion and the polymer was collected on a filter. The precipitate contained a great deal of inorganic material. By extracting with chloroform and evaporating this solution, about 60% of the theoretical yield of polymer was obtained as a white powder with an inherent viscosity of 0.21. Analysis Calculation for (C6H12S2): C, 62.00; H, 10.41; S, 27.59 Found: C, 61.62; H, 9.98; S, 28.11 More recently, the oxidation of mono- and dimercaptans to disulfides has been reported [38, 39]. The dimercaptans afford polydisulfides whereas the monomercaptans give disulfides [39].

2-5.

Polysulfide Formation by the Dimethyl Sulfoxide Oxidation of Dimercapto-p-xylene [39]

HS -- C H 2 - ~

CH2SH + (CH3)2S-- O

[ -- S - - C H 2 - ~

CH2-- S ~ n + H20 + (CH3)28 (13)

To a 125-ml, two-necked flask equipped with a water condenser through a Stark trap for collection of low boiling sulfides generated in the reaction are added 13.8 gm (0.081 mole) of dimercapto-p-xylene and 100 ml of dimethyl sulfoxide. A magnetic stirring bar is used along with a thermometer and the reaction heated in an oil bath at 100~ for 2 hr. Within 45 min dimethyl sulfide starts to distil at 34~ while crystals separate in the flask. The reaction mixture is cooled and after standing overnight the polymer is filtered and dried in air to give 135 gm (98%), m.p. 185~176 MW in DMSO is 929 ___3%: DP is about 7.

3. POLY(ALKYLENESULFIDES) The poly(alkylene sulfides) are aliphatic polymers with a single sulfur atom as a repeat group (--RS--)n in contrast to the polysulfides which have one or more sulfur atom repeat-group combinations (--R--Sx--)n where x is 2 or more units. The poly(alkylene sulfides) have quite different properties in comparison

87

3. Poly(alkylenesuifides)

to their oxygen analogues. For example, high molecular-weight poly(ethylene oxide) is water-soluble and has a relatively low melting point (less than 100~ whereas the high-molecular-weight poly(alkylene sulfides) are insoluble in water and most known solvents at room temperature and melt at temperatures above 200~ The earliest preparation of the poly(alkylene sulfides) was by polycondensation of a divalent metal sulfide or bis-mercaptide with alkylene dihalides. Poly(ethylene sulfide) was first prepared in 1839 by Loewig and Weidmann [40] and the polymer was later studied by Crafts [41] and Meyer [42]. The latter polymer was prepared from ethylene dibromide and potassium sulfide as shown in Eq. (14). Br--CHECHz--Br + KzS

~ (--CH2CHzS--),, + 2KBr

(14)

These poly(ethylene sulfide) polymers had very low molecular weights (m.p. 113~176 and were thermally unstable. The presence of unreacted halogens as acid catalysts caused the polymers to decompose into 1,4-dithiane. More recently poly(ethylene sulfide) has been prepared by the polymerization of ethylene sulfide or thiirane. H2C ~ CH2 N / S

~ (--CH2CH2-- S--)n

(15)

The major methods of preparing poly(alkylene sulfides) are shown in Scheme 2. The four major methods of preparation of poly(alkylene sulfides) involves the polymerization of episulfides (thiiranes), addition of dithiols to olefins, reactions of dithiols with carbonyl compounds, and reaction of dithiols with dihalides and these will be discussed in this section. Other methods will be mentioned in Section 5 (Miscellaneous Preparations). R(CH = CH2)2 + R(SH)2

R I

1 1

R I

H C\~ C/ H S

'

R(C =

(--R--S--),

0)2

'

R(SH)2 + RX2

-~- (HS)2R(SH)2

Scheme 2 Preparationof poly(alkylene sulfides) [43-46].

3. Sulfide Polymers

88 H2C

-

-

N

/

C1--CH2CH2-- SCN

CH2

I

Na2S, H20

CH2-- O N

I

/C=O

H2C

KSCN

'

CH2-- O

~

N /

H2C ~ N

/

CH2

~ K S C N or O NH2CSNH2

CH2

s

aq Na2CO3

CH3COOCH2CH2SH

b.p. 55~176 pressure

CH2 "-" CH2 + (C2H5)2S4 Scheme 3 Preparation of ethylene sulfide (episulfide, thiirane) [47-52].

A.

Polymerization of Episulfides ( T h i i r a n e s )

Ethylene sulfide was first prepared by Dele'pine [47] by the action of aqueous sodium sulfide with 2-chloroethyl thiocyanate. The best laboratory method involves the reaction of epoxides with either thiourea or potassium thiocyanate [48]. These and more recent methods are described in Scheme 3. Culvenor, Davies, and Pausacker extended the alkylene oxide-thiourea, thiocyanate, or thiocarbamide synthesis to prepare the higher alkylene sulfide monomers [53 ]. Ethylene sulfide is polymerized by catalyzed ring-opening reactions involving either cationic (mineral acid, boron trifluoride [54], triethyl aluminum [55], phosphorus pentafluoride [56]) or anionic catalysts [57] (sodium hydroxide, sodium alkoxide, ammonia, amines, and alkali metals). Gobran and Osbom [58, 58a] at Thiokol Chemical Corp. introduced the diethylzinc-water complex catalyst to prepare high-molecular-weight polymers that melted at 208~176 Besides water, a variety of other co-catalysts can be used such as water, alcohols, glycols, oxygen, hydrogen sulfide, mercaptan, and sulfur [58, 58a]. A typical polymerization is shown in Preparation 3-1.

3-1. Polymerization of Ethylene Sulfide Using Diethyl Zinc-Water Catalyst [58] HEC~ \

/

CH2

(C2Hs)2Zn, H20 C6H6

~ ( - - CHECH2 - - S - - ) n

(16)

S C A U T I O N : Ethylene sulfide is toxic and should be handled only in a hood, while wearing the proper protective garments and gloves. The monomer is capable of penetrating rubber gloves and clothing.

89

3. Poly(alkylene sulfides)

A 30-ounce, stainless steel, polymerization cylinder is sequentially charged by mixing under a blanket of nitrogen gas 400ml of dried benzene, approximately 100 gm (100 ml) of dried ethylene sulfide monomer, 0.0011 mole (0.02 ml) of water, and 0.58 ml of a benzene solution containing 0.0011 mole of diethyl zinc. The vessel is sealed and the contents raised to and maintained at 80~ for 2 hr with agitation. The cylinder is cooled, vented, and emptied to give a white polymer. The polymer is dried at <10 mm Hg in a vacuum oven at 60~176 for 24 hr to give 97.6 gm of dry, white, powdery polymer with a melt index average flow at 215~ (flow 0.00 gm/min for the first 5 min). Other examples of the polymerization of cyclic alkylene sulfide monomers to polymers are shown in Table VI.

CAUTION: Handle all ethylene sulfides with great care in a hood. These compounds are known to be toxic.

3-2. Polymerization of Ethylene Sulfide Using Acetone-Sodium Catalyst [59] H2C~ \ / S

O II CH2 + Na + CH3--C--CH3

~- ( -- CH2CH2 -- S -- ),

(17)

Catalyst

To a glass flask equipped with a mechanical stirrer, reflux condenser, and thermometer is added 75 ml of acetone and 0.1 ml of a 10% by weight sodium dispersion in toluene. When acetone/sodium precipitates as a white compound, then 25.0 gm (0.41 mole) ethylene sulfide is added. The exothermic polymerization starts immediately and the polymer precipitates as a fine powder while the temperature rises to cause refluxing of acetone. In 10 min the polymerization is complete and 200 ml of 10% HC1 is added followed by a 15 min agitation period. The polymer is filtered, washed with water, and dried under reduced pressure at 50~ to give 24.8 gm (99%) of poly(ethylene sulfide) as a colorless powder, m.p. 211 ~ The specific viscosity of a 0.5% DMSO solution at 175~ is 1.30 corresponding to a reduced viscosity of 60 ml/gm. The flexural strengths of test specimens of the polymer are 9,000-197,000 lb/in 2. Poly(ethylene sulfide) requires the use of polyamine stabilizer in order to permit processing in standard injection-molding equipment [60]. Stille and Empen [61] reported on ring-opening polymerization of other cyclic sulfides to give poly(alkylene sulfide). Stille and Empen [61] found that

TABLE VI

Polymerization of Cyclic Alkylene Sulfides (Thiiranes) Reaction conditions

Alkylene sulfide (gm)

Catalyst

Solvent (ml)

Temp (~

Time (hr)

Yield (%)

m.p.

Viscosity

(oc)

Rel Visc 1.3 cm 0.5% soln of DMSO at 175~

211

Ethylene sulfide (25)

0.1 ml of 10% by wt sodium dispersion in toluene

Acetone 75

25-56

0.25

99

Ethylene sulfide (25)

16 mg potassium metal suspended in toluene 10 mg lithium dispersion in toluene 0.023 Bu3P as 1% soln in anhydr THF ZnC03, 1.0 gm ZnS, 2.40 gm

Acetone 75

25-26

0.25

97

209-210

Acetone 75

25

20

76

211

- 26

120

55

80 80

20 20

88 94

Ethylene sulfide (10) Ethylene sulfide (6.8) Ethylene sulfide (200.8) Ethylene sulfide (25.1)

THF 20 C6H6 200 C6H6 100

100,000 (poises) 209-214 203-207

Ref.

Ethylene sulfide (50) and propylene sulfide (50)

Propylene sulfide (10) Propylene sulfide (47.3) Propylene sulfide (50) Isobutylene sulfide (11.0)

3-Phenoxypropene sulfide- 1 (5)

(CzHs)2Zn 2 ml 5.8 • 10 -3 mole/ml + 0.15 ml H20 (8.3 • 10 -3 mole) 16 mg sodium as 10% suspension in toluene 0.2 gm Cd(OAc)2"2HzO EtzZn (55.8% in C6H6) 17.6 ml (CzHs)2Zn 4.7 ml of 1.5 ml (CzHs)2Zn/C6H6 soln in 50 ml THF Sodium metal 1 mol%

C6H6 100

27

C6H6 50

56

C6H6 90 C6H6 150

65 65

C6H6 11

25

C6H6 20

50

a M. Sander, U.S. Patent 3,317,489 (1967). b B. E. Jennings, British Patent 1,077,958 (1967). c S. W. Osborn, T. F. Wells, III, and E. L. Kutch, U.S. Patent 3,359,248 (1967). a R. H. Gobran and S. W. Osborn, U.S. Patent 3,504,050 (1970). eE. L. Kutch, S. W. Osborn, and T. F. Wells, U.S. Patent 3,337,513 (1967). fR. H. Gobran and S. W. Osborn, French Patent 1,444,664 (1966). gR. H. Gobran, U.S. Patents 3,329,659 (1967); 3,365,431 (1968).

24

95

145-184

88 16 14 5.5

82 90-700 38

92

-185

r~

92

&

Sulfide Polymers

tetrahydrothiopene and 7-thiobicyclo[2.2.1 ]heptane do not polymerize with any of the initiators used. [PFs, BF3"(C2Hs)20, (C2Hs)3A1-H20, BF40(CH3)3].

BO Poly(alkylene sulfides) by the Reaction of

Dimercaptans and Dihalides Meyer [62] in 1886 and Ray [63] in 1929 reported that high-boiling liquids were formed in their preparation of ethylene mercaptan. Tucker and Reid [64] studied the reaction of the sodium salt of 1,2-ethanedithiol with various a,og-dibromides and found both cyclic products as well as amorphous polymers were produced. Additional cyclic products and polymers were reported by Meadow and Reid [65] in later investigations. Carothers [66] in a patent briefly mentions that polyhexamethylene sulfide can be made by the reaction of hexamethylenedithiol with 1,6-dibromohexane. Marvel and Chambers [67, 67a] prepared these low-molecular-weight polymers as suggested by Carothers. More recently Lal and Trick [68] using the procedures of Marvel and Kotch extended this work to prepare various polymers and copolymers as shown in Table VII and compared their properties to the analogous polyethylene oxides.

3-3.

Preparation of a Poly(alkylene sulfide) by the Condensation of the Disodium Salt of Hexamethylenedithiol (1, 6-Hexanedithiol) and Tetramethylenedibromide [69]

NaS(CH2)6SNa + Br--(CH2)4--Br

C6H6

' [--S(CH2)6S(CH2)4--]n

(18)

To a dry flask containing 15 ml of absolute ethanol is added 0.46 gm (0.02 gm atom) of sodium metal. After the metal dissolves 1.5 gm (0.01 mole) of hexamethylenedithiol is added. The disodium salt of the dithiol precipitates and is then redissolved when the mixture is heated. To the hot solution is added 25 ml of dry thiophene-free benzene followed immediately by 2.15 gm (0.01 mole) of tetramethylene dibromide. An immediate vigorous reaction is initiated and the solvent begins to reflux. When the reaction subsides, another 25 ml of benzene is added and the mixture refluxed overnight. The polymer is isolated by pouting the reaction mixture into methanol. The polymer yield is 1.08 gm (50%) (m.p., 63~176 inherent viscosity, 0.36 dl/gm).

3.

Poly(alkylenesulfides)

TABLE VII

93

A Comparison of Melting Temperatures and Rates of Crystallization of Polymethylene Sulfide and Polymethylene Oxide Polymers ~ Melting temperatures (~

Structure of repeat unit

Inherent d viscosity (dl/gm)

Polarizing microscope

0.048 b 0.05 c

220-245 187-190

--

0.31 0.45 0.15

66-67 79-79.5 90-91.5

67

0.14 0.17 0.2 0.2 0.21 0.32

72-73 88-89 62-64 65-67 73-75 84-86

Polymethylene sulfides --CH2--S--- (CH2)2-- S--- (CHz)3 -- S --- (CH2)4 -- 5 --- (CH2)6 -- S ---(CH2)Io--S-Polymethylene sulfide copolymers -- CH2S-- (CH2)4-- S--- (CH2)2S-- (CH2)4S---(CH2)aS--(CH2)4-- S-(CH2)5-- S-- (CH2)4-- S--- CH2)6-- S-- (CH2)4-- S--- (CH2) 1oS-- (CH2)4S-Polymethylene oxides --CH2--O--- (CH2)2 -- O ---(CH2)3--O . --(CH2)4--O---(CH2)6--O---(CH2)1o--O--

-

.

-

-

. 1.35 0.13 0.2

Dilatometric

64 67 74 85.5

-

. 36 55-58 74-79

80

a Reprinted in part from J. Lal and G. S. Trick, J. Polym. Sci. 50, 13-19 (1961). Copyright 1961 by the Journal of Polymer Science. Reprinted by permission of the copyright owner. b Tetrachlorobiphenyl (Monsanto "Arachlor 1254") solvent at 230~ c Trichlorobenzene at 150~ d In most cases determined by 30~ in 0.2% solutions of the sulfide polymers in CHC13 and of the oxide polymers in C6H 6. For very low MW polymers 0.5% solutions were used.

3-4.

Preparation of a Poly(alkylene sulfide)from the Disodium Salt of Hexamethylenedithiol and 1,6-Dibromohexane [66, 70] Na

HS--(CH2)6--SH

+ Br--(CH2)6--Br

;

HS[(CH2)6-- S-- (CH2)6-- ]nBr (19)

94

Sulfide Polymers

3. so/

I ,

I '

, '

I ,

, '

I ,

~

'

,

'

~

'

,

I 1300

I

I 1400

=

i 1500

I

I 1600

60 4O

0 8O

A

o~

60 . _

E ~:

1

20

40

0

I 700

I

I 800

I

I 900

I

I 1000

I

I 11 O0

I

I 1200

J

Wave number (cm - l )

Fig. 1 Polymers A, B, and C were obtained by the following reactions. HS(CHE)6SH + CHE~--CH(CHE)ECH~-CH2 HS(CHE)rSH + Br(CH2)rBr

NaOR

~ Polymer A

~ [--(CHE)rS--(CHE)6--S--]x

HS(CHE)rSH + CHaCHBr(CHE)ECHBrCH3

Polymer B

NaOR CH3

CH3

[--(CH2)6S--CH(CH2)2CH--S--)x

Polymer C

[Reprinted from C. S. Marvel and R. R. Chambers, J. Am. Chem. Soc. 70, 993 (1948). Copyright 1948 by the American Chemical Society. Reprinted by permission of the copyright owners.]

To a 50-ml Erlenmeyer flask containing a solution of 0.26 gm of sodium in 20 ml of absolute ethanol is added 1.5 gm (1 mole) of hexamethylenedithiol, followed by the dropwise addition of 2.44 gm (0.01 mole) of hexamethylene dibromide. The reaction proceeds rapidly and the solid polymer separates. The polymer is filtered and the filtrate diluted with water to recover more polymer that separates out. The combined crude polymer precipitates are dissolved in benzene and the polymer is precipitated with methanol. This is repeated again to afford a final 0.26 gm (10%) of polysulfide product (m.p. 71~176 (for infrared spectrum see Fig. 1, Polymer B). This polymer is linear and similar to that obtained by the reaction of hexamethylene dimercaptan and 1,5-hexadiene but not similar to that for the reaction of hexamethylene dimercaptan and 2,5-dibromohexane (see methyl deformational frequencies at 1375 cm -1, 1225 cm -1, and 1300 cm -1 in Fig. 1).

95

3. Poly(alkylene sulfides)

3-5.

Preparation of the Poly(alkylene sulfide)from the Disodium Salt of Hexamethylenedithiol and meso-2,5-Dibromohexane [67]

HS(CH2)6SH + CH3--CH--(CH2)2--CH--CH3

I

I

Br

Br CH3

CH3

I

I

H[-- S-- (CH2)6-- S-- CH-- (CH2)2-- CH-- ]nBr (20) To a 50-ml Erlenmeyer flask are added 15 ml of absolute ethanol and 0.24 gm sodium hydride. To the resulting solution is added 1.5 gm (0.01 mole) hexamethylenedithiol followed by 2.44 gm (0.01 ml) of meso-2,5-dibromohexane (m.p. 37~176 [71] dissolved in 15 ml of absolute alcohol. The reaction mixture is refluxed for about 4 hr and cooled. Then 50 ml of water and 20 ml of ether is added. The ether solution is separated and solvent evaporated. The residual liquid product is treated with methanol to dissolve about one-half of it and then the methanol solution is separated. The remaining one-half of the product is dissolved in low-boiling petroleum ether, decolorized with Norite, filtered, concentrated, and heated to 100~ for 2 hr to remove traces of solvent yielding a yellow, mobile liquid containing 6.45% bromine by analysis. The infrared spectrum of the product is shown in Fig. 1 as Polymer C.

C.

Poly(alkylene sulfide) by the Addition of Thiols to Olefins

Posner [72] in 1905 described the reaction of thiols with olefins to produce monosulfides. In more recent work it was established that two modes of thiol addition to olefins are possible and involve either normal addition or abnormal (non-Markovnikov) addition [73]. CHa--CH--CH3

CH3CH

--

erie + RSH

~

/~No~al (acidor base)

[ SR (21)

Abno~a~'~l (free radical) CH3CH2CH2SR The normal addition is catalyzed by acids or bases and yields branched products, whereas the abnormal addition is free radical catalyzed and gives linear products. Activated double bonds as in the case of methyl acrylate give the same product by both routes, but different mechanisms are said to be operative [74].

3.

96

SulfidePolymers

Braun and Murjahn [75] reported that attempts to distill allyl mercaptan gave the pure product and a nondistillable residue. Braun and Plate [76] later reported that several other unsaturated mercaptans gave liquid polymers. Vaughan and Rust [77] obtained low-molecular-weight (less than 300) poly(alkylene sulfide) by the reaction of hydrogen sulfide and diallyl or diallyl ether. Coffman [78] reported that polymeric alkylene sulfide of molecular weights to about 1300 were obtained by the reaction of dithiols with diolefins. Langkammerer [79] and then Marvel and co-workers [80, 80a] followed with a series of investigations which is the basis of much of the information today in this area. Marvel and Chambers [80, 80a] extended Coffman's work and obtained polymers up to MW 14,000 using UV irradiation of a dimercaptan/diene solution in cyclohexane, in a closed quartz test tube. The results of Marvel and Chambers work is summarized in Table VIII. Marvel and Chambers [80] also demonstrated that the UV, free-radical catalyzed polymerization of hexamethylenedithiol and 1,5-hexadiene (Preparation 3-3) gave a linear product (non-Markovnikov addition) that had the infrared spectrum similar to that of the condensation polymer from hexamethylenedithiol and 1,6-dibromohexane (Preparation 3-4) under alkaline conditions, but not similar to that of the product from the alkali condensation of hexamethylenedithiol and 2,5- dibromohexane (Preparation 3-5).

3-6.

Poly(alkylene sulfide) by the Reaction of Hexamethylenedithiol and 1,5-Hexadiene [80]

HS--(CH2)6--SH + CH2--CH--(CH2)2--CH--CH2 [-- S(CH2)6-- S-- (CH2)6-- ]n (22) To a quartz test tube are added 1.5 gm (0.01 mole) of hexamethylenedithiol, 0.82 gm (0.01 mole) of 1,5-hexadiene, and 10 ml of cyclohexane. The tube is tightly stoppered and irradiated for 1 to 2 hr with a UV lamp and during this period some white solid begins to precipitate. After the reaction, the white polymer is filtered and dried to afford 1.69 gm (74%) with s.p. 70~ (liquid at 74~ and intrinsic viscosity in benzene of 0.4188. Other polymers were similarly made that had an intrinsic viscosity of 0.293 (12,000-14,000 MW, approximately) and s.p. 74~176 Marvel and Cripps [81] reported that 1,3-butadiene does not react with hexamethylenedithiol to give polymeric products, rather 1,6-dicrotylmercaptohexane is formed in 46% yield [see Eq. (22)]. This was also said to be true of other conjugated dienes.

? TABLE VIII

Polyalkylene Sulfides from Diolefins and Dimercaptans a

Monomers

Calculated (%)

Found (%)

t~

m.p.

Dithiol Ethanedithiol Tetramethylenedithiol Pentamethylenedithiol Hexamethylenedithiol Decamethylenedithiol Hexamethylenedithiol Decamethylenedithiol bis(p-fl-Mercaptoethylphenyl)methane Hexamethylenedithiol bis(p-fl-Mercaptoethylphenyl)methane Hexamethylenedithiol Hexamethylenedithiol 2-Methyl- 1,4-butanedithiol

Diolefin 1,5-Hexadiene 1,5-Hexadiene 1,5-Hexadiene 1,5-Hexadiene 1,5-Hexadiene 1,10-Undecadiene 1,10-Undecadiene 1,5-Hexadiene

(~ 82-86 65-67 64-65 71-76 76-78 72-78 74-78 84-88

(I'/)

0.256 0.206 0.238 0.217 0.143

C

H

S

C

H

S

54.49 58.76 60.49 62.00 66.60 67.48 70.32 74.54

9.15 9.86 10.15 10.41 11.18 11.33 11.80 8.16

36.36 31.37 29.36 27.59 22.22 21.19 17.88 17.30

54.65 58.91 60.32 62.29 66.76 65.91 69.58 74.05

9.06 10.05 10.10 9.98 11.41 11.03 11.69 7.96

36.56 31.28 29.30 27.88 21.99 22.89 18.31 17.85 16.27 16.05 12.66

Bis(p-vinylphenyl)-methane

gel b

74.54

8.16

17.30

74.19

8.10

Bis(p-vinylphenyl)-methane

105-108

80.26

7.13

12.60

80.40

7.22

3,4-Dimethyl- 1,5-hexadiene Vinyl-3-cyclohexene 1,5-Hexadiene

Liquid Liquid Liquid

64.55 65.05 60.49

10.83 10.14 10.15

24.62 24.81 29.36

63.62 63.86 59.99

10.68 9.75 10.16

0.097 0.072

25.46 29.75

i

a Reprinted from C. S. Marvel and R. R. Chambers, J. Am. Chem. Soc. 70, 993 (1948). Copyright 1948 by the American Chemical Society. Reprinted by permission of the copyright owner. b This gel did not melt or otherwise change at 220~

98

3. SulfidePolymers

HS(CH2)6SH + CHE=CH--CH=CH2

CH3--CH=CH--CH2S

I (CH2)6

CH3 --CH = CH-- CH2S

(231 Marvel and Cripps also reported that diallyl sulfide does not polymerize with hexamethylenedithiol, but polymers may be obtained with diallyl ether. More recently Oswald, Griesbaum, and Hall [82] reported that allene can be reacted with aliphatic and aromatic dithiols in a free-radical process to give thiol- or allyl-terminated difunctional polythioethylenedithiols useful for elastomers, mastics, or adhesive applications. C H 2 = C - C H a + HS--R--SH

(24)

[-- (CHECHECHES-- R-- S)x(CHa-- CH-I S--R-- S)y]

CH3

n

where x > y; x + y = n; y--- 1; and x = - 2 5 . An excess of dithiol gives a polymer terminated by thiol groups, as described in Preparation 3-7.

3 - 7,

Addition of Trimethylenedithiol (1,3-Propanedithiol) to Allene at Ambient Temperature [82]

HS--CH2CH2CH2--SH + CH2--C-CH2 HS--R--S--(CHzCHECHE--S--(CHE)aS)x (CHzCH--S--(CH2)3

I

\

CH3

]?

(25)

y

Under UV irradiation, allene (16 gm, 0.4 mole) was bubbled for 11 hr into 54 gm (0.5 mole) of trimethylenedithiol contained in a quartz tube at 15~ At the end of this time 0.4 mole of allene was absorbed and the reaction mixture solidified to yield the raw polytrimethylenesulfidedithiol. The polymer was repeatedly dissolved in benzene and reprecipitated with methanol to give 50 gm (84.5%) of a polymer with MW 837 by potentiometric titration assuming a dithiol structure.

Analysis [H(SCH2CH2CH2)9SH, MW 701.5] Calculated for (C27H50S10)" C, 46.24; H, 8.04; S, 45.72 Found: C, 45.33; H, 7.06; S, 45.05

99

3. Poly(alkylene sulfides)

D.

P o l y ( a l k y l e n e sulfides) by t h e A d d i t i o n o f T h i o l s t o Carbonyl Compounds

Baumann was the first to report the reaction of a mercaptan with either an aldehyde or a ketone to give a high yield of the corresponding mercaptal or mecaptol [83]. O

SR'

li

RCH + 2R'SH

HC1

/

-~ R--CH \

+ H20

(26)

+ H20

(27)

SR' SR'

R

RCR + 2R'SH II

HC1

\

~

/

O

C

/

\

R

SR'

Autenrieth and Geyer [84] later reported crystalline cyclic mercaptols with acetone and diethyl ketone by the reaction of pentamethylenedithiol. They also reported that noncrystalline products were obtainedusing benzaldehyde, benzophenone, and acetaldehyde. The latter were probably polymeric but were not further characterized. Fisher and Wiley [85] prepared polymercaptols of the spirane type by the reaction of the tetramercaptan derived from pentaerythritol and 1,4-cyclohexandione. HSCH2

X / /

HSCH2

c

CHESH

\

+o< >o

CHESH CHzS /

H

SCH2

C\

(28) CHzS

Marvel and co-workers [86] described the preparation of linear type polymercaptals and polymercaptols. The reactions were carried out between a wide variety of carbonyl compounds and dimercaptans in the presence of dry hydrogen chloride with or without solvent (dioxane) present. The reactions are summarized in Table IX.

3-8.

General Procedure for the Preparation of Polymercaptols Shown in Table IX [86]

The carbonyl compound and an equivalent amount of the dithiol were placed in 10 ml of freshly distilled dioxane. The solution was cooled in an ice bath

TABLE IX

Dithiol Decamethylene Hexamethylene Decamethylene Hexamethylene Decamethylene Decamethylene Hexamethylene The above polymer after a Hexamethylene The above polymer after a

gm

Properties of Polymercaptals and Polymercaptols a

Carbonyl compound

0.9444 Acetaldehyde 0.9800 Acetaldehyde 0.9370 Butyraldehyde 0.9700 Butyraldehyde 0.9800 Benzaldehyde 0.9800 Benzaldehyde 0.9700 Benzaldehyde month in corked tube 0.9700 Benzaldehyde month in vacuum

gm

Time (min) passing HC1

% Reaction detd by unused -- SH

0.2078 0.3685 0.4587 0.8170 1.0504 1.0504 1.0504

30 1189 17 15 12 (hr) b 15c 7

95.39 --

35 60

m ---

40 135 120 115

1.0504

10

--

110

m.p. (~

Inherent viscosity

MW (Calc)

0.042 0.146 0.102 0.049 0.428 0.452 1.374 0.864 0.98 0.93

1100 5100 3300 1400 18600 19900 76000 43000 50000 47000

Eqv wt by amperometric titration w

3930

25030 29500 480

r t~ t~

Hexamethylene Hexamethylene Hexamethylene Decamethylene Hexamethylene Hexamethylene Hexamethylene Hexamethylene Hexamethylene Hexamethylene Hexamethylene Hexamethylene Decamethylene

1.5329 0.9810 0.9840 1.8847 0.9872 0.9818 0.9823 0.9886 0.9779 0.9920 0.9797 0.9815 0.9502

Vanillin Vanillin Anisaldehyde m-Nitrobenzaldehyde p-Nitrobenzaldehyde p-Bromobenzaldehyde 2-Butanone 3-Methyl-2-pentanone 4-Methyl-2-pentanone Acetophenone Cyclohexanone Cyclohexanone Vanillin

1.0178 0.9950 0.9278 1.3842 1.0005 1.2253 0.5023 0.6653 0.6649 0.8013 0.7345 0.6662 0.7042

25 10 10 60 22 17 188 (hr) 60 60 12 10 10d 10

--99.80 99.75 99.71 99.16 70.87 45.83 48.45 71.40 90.00 95.93 97.18

40 150 130 75 80 e 72 Low Low Low 30

0.065 Insoluble 0.440 0.160 Insoluble 0.067 0.088 0.048 0.053 0.088

75 140

0.340 Insoluble

1900

528

19000 5700 2000 2700 1300 1500 2700

2380 1360

14300

a Reprinted in part from C. S. Marvel, W. H. H. Shen, and R. R. Chambers, J. Am. Chem. Soc. 72, 2106 (1950). Copyright 1950 by the American Chemical Society. Reprinted by permission of the copyright owner. b Hydrogen chloride gas was passed very slowly into the reaction mixture. This reaction was carried out without solvent. r After passing hydrogen chloride into the mixture for 15 min, the reaction mixture was left in contact with air for 6 hr. This reaction was carried out in dioxane solution (10 ml). d The polymer solution was exposed to air for 10 hr before precipitating by methanol. e Calc: N, 4.90; Found: N, 4.87.

3.

102

SulfidePolymers

while dry hydrogen chloride was bubbled imo the mixture for varying lengths of time as indicated. In all cases the reaction was exothermic and usually developed a pink color. The mixture was cooled and the polymer precipitated by the addition of 20 ml of cold methanol. The polymer was filtered, washed with cold methanol, and dried in a desiccator under reduced pressure to give yields as shown in Table IX. E.

P o l y ( a l k y l e n e sulfides) by t h e D e h y d r a t i o n o f Mercaptoalkanols

The acid-catalyzed polycondensation of certain mercaptoalcohols represents a method for the preparation of polyalkylene sulfides [87-90]. HOCH2CHzSH

H--H20

' (-- CHzCH2 -- S -- )n

(29)

Acids which are particularly effective in catalyzing this condensation are p-toluenesulfonic acid, sulfuric acid, zinc chloride, boron trifluoride-ether complexes, and acid clays [88]. The preferred catalyst (0.5 to 10 parts per 100 parts monomer) is p-toluenesulfonic acid and it is important that the catalyst be nonoxidizing relative to the mercaptan group present. The pure alkylene sulfides can also be prepared first by the dehydration of 2-mercaptoethanol using a catalyst consisting of an alkali or alkaline earth with metal along with compounds of A1, B, Si, P, lanthanides, etc., with metals according to a disclosed procedure [86a]. These alkylene sulfides can then be subsequently polymerized.

3-9.

Cocondensation of Mercaptoethanol and Mercaptopropanol [88]

HS--CH2CH2OH + HSCH2 -- CH -- OH

I CH3 H(-- S-- CH2CH2)x(S-- CH2CH--)yOH CH3 I

(30)

To a 5-liter reactor, which is equipped with a mechanical stirrer, thermometer, nitrogen bubbler tube, condenser, and Barrett trap, are added 39.0 gm (0.5 mole) of mercaptoethanol, 46 gm (0.5 mole) of mercaptopropanol, 4 gm p-toluenesulfonic acid (PTSA), 75 ml of benzene (see note of caution), and 75 ml of toluene. Nitrogen is bubbled through the reaction mixture and a small nitrogen pressure is maintained. The reaction mixture is refluxed for 3 hr at 90~176 and 17.5 ml of water is collected. Then 250 ml of toluene is added to dilute the

103

4. Poly(arylene sulfides)

reaction mixture and the mixture is further heated for a short time to insure complete reaction (no more water collected in Barrett trap). The reaction mixture is cooled to 80~ then 5 gm Filtrol No. 13 and a few grams of Celite Super-Cel is added, and stirring is continued. The hot mixture is filtered through a stream-jacketed Buchner funnel and the clear, hot filtrate collected. The filtrate is placed into Pyrex trays and the solvent evaporated first in a hood and then in a vacuum oven at 80~ (also in a hood). The polymer obtained weighs 62.5 gm and is a thermoplastic, rubbery material.

CAUTION: Benzene is known to be toxic and carcinogenic. It can be substituted with toluene in this preparation. 4.

POLY(ARYLENE SULFIDES)

The search for a thermally stable thermoplastic polymer led to the recent developments in poly(phenylene sulfides). The latter polymers are analogous to the poly(phenylene ethers) described in an earlier volume of this series [91]. Poly(p-phenylene sulfide) was first reported in 1897 by Genvresse [92] who reported an insoluble resin prepared by the reaction of benzene with sulfur in the presence of aluminum chloride. A variety of other procedures were reported to yield similar resins. Macallum [93] in 1948 reported a novel procedure that yielded an improved resin. Lenz and co-workers [94-96] modified the procedure and Edmonds and Hill [97] of the Phillips Petroleum Co. developed a commercially successful process. The material is now marketed under the trade name Ryton [98]. The crystallinity of the polymer has recently been reported [99-101]. Earlier suggested syntheses for poly(arylene sulfides) are shown in Scheme 4. Most of these syntheses involve either electrophilic or thermal reactions. ~--OH+SC12

~-OH+S

~

8-/1

HS ~ Scheme

SH

~~

+S+AICI3

~

+S

-SH + A1C13or H2SO4or

8OC12

4 Earlierpreparations of Poly(arylene sulfides) [92, 102-109].

104

3. Sulfide Polymers

Macallum [93, 110] reported a more convenient poly(phenylene sulfide) syntheses by the reaction of p-dichlorobenzene in a dry state using a mixture of sulfur and sodium carbonate at 300~176 Macallum reported that if sodium sulfide were used in place of sodium carbonate and sulfur then a small amount of sulfur was still required to catalyze the reaction (Eq. 31). C I - ~

(31)

C1 + Na2CO3 + S

The reaction of sulfur and sodium carbonate gives the nascent metal sulfide as earlier described by Pearson and Robinson [ 111 ]. 3Na2CO3 + (2n + 2)S

' 2Na2Sn + Na2S203 + 3CO2

(32)

The poly(phenylene sulfides) are light-colored, cream to canary yellow, in the solid state having good thermal stability. The addition of sulfur acts as a plasticizer to give a poly(phenylene sulfide) with rubber-like properties. In the presence of metallic lithium thereaction of $8 with 1,4-dichlorobenzene yields a linear poly(1,4-phenylene polysulfide) in which the sulfur content could be 3 sulfur atoms per phenylene unit (Mn as high as 12,000) [11 l a]. CI-~C1

+ $8 + Li

THF 25~

~ S x

~n + 2LiC1 + Li2S

where x = 3 In more recent developments poly(p-phenylene sulfides) have been reported to have been prepared by the oxidative polymerization of diphenyl disulfides or thiophenol with quinones at room temperature [37b, 11 l b]. C1

C1

n SS- + nO@O C1

,

C1 C1

el

C1

el

The advantage of this process is that no salt is produced as a by-product and the resins are obtained with improved electrical performance and moldability properties as seen in Table IXa.

105

4. Poly(arylene sulfides) TABLE IXa Metal Content of PPS Produced by Various Methodsa

Method

Monomer

Na (ppm)

C1 (ppm)

Cu (wt%)

Br (wt%)

Oxidative polym. Oxidative polym. Polycondensation Polycondensation

Diphenyldisulfide (3,5-Dimethylphenyl)disulfide Sodium sulfide + p-Dichlorobenzene Copper p-Bromothiophenoxide

7 5 1500 4700

125 85 4700 3500

0 0 0 >1

0 0 0 1.7

a

Data taken from [37b].

Diphenyldisulfide can also be polymerized to poly(p-phenylene sulfide)s using Lewis acids such as SbC15 at room temperature [11 l c]. However, these resins may be slightly contaminated by residual metal catalyst impurities. Poly(phenylene sulfide)s are highly stable and have a high melting point. The presence of sulfur atoms between the aromatic tings provide flexibility and the resins can be used for fibers, and thermoplastics. Polyphenylene sulfides doped with AsFs, I2, or SO3 could also provide electrically conductive materials [111d].

4-1. Preparation of Poly(phenylene disulfide) [93] C1 ~~

S + S + Na2CO3

,

+ NaC1 +

Na2SO4

+

CO2 (33)

C1 To a heavy-walled, glass-polymer tube is added a prepulverized mixture of 3.0 gm of sulfur and 3.9 gm of low-density sodium carbonate (prepared by heating sodium bicarbonate at 200~176 Then 3.3 gm ofp-dichlorobenzene is added and the tube is evacuated and sealed. The tube is now heated for 20 hr at 300~176 in a nearly horizontal position. On cooling the tube is cautiously opened and vented under a hood and the contents are pulverized. The product is extracted with water and the residue dried to give 4.1 gm of a sulfur-colored resin containing 56.2% total S (modified Liebig method) and 9-10% labile S (by Parker's method). The crude product is purified by continuous extraction with acetone and then toluene. It is dried at 140~176 under reduced pressure to give 2.0 gm of product. The product is straw-colored, brittle when cold, resilient at 80~176 and plastic from 180~ to above 350~ Analyses indicate it corresponds to (C6H4S2.3).

o~

TABLE X

Acid-Catalyzed Polycondensation of Mercaptoethanol and Mercaptopropanol a Reaction conditions

Mercaptoethanol (moles)

Mercaptopropanol (moles)

Solvent (ml)

0.5

0.5

Toluene 75 Benzene 200 Toluene 150 Benzene 800 Benzene 2000 Toluene:Benzene 150:150 Benzene: Toluene 125:125 Benzene: Toluene 125:125

10

10

0.5

0.5

5

5

10

10

1.9

0.1

1.0

1.02

1.02

1.0

PTSA catalyst (gm)

Temp (~

Time (hr)

Yield

4

90-95

3-4

62.5 grn

32

80

18

4

100-110

1.5-2

16

90

10-11

32

80

15

8

90-95

7.5

6

90-95

4.5

120 gm

Elastomer

6

90-95

4

119 gm

Rubbery thermoplastic

aData taken from M. B. Berenbaum, E. Broderick, and R. C. Christena, U.S. Patent 3,317,486 (1967).

m.p.

(oc)

60.g gm 91% 678 gm 100%

169-174

107

4. Poly(arylene sulfides)

4-2. Preparation of Poly(phenylene sulfide) [93] C1 + S + Na2CO3 C1

s_] +

aCl + a,_SO4 +

Using a procedure similar to Preparation 4-1 a mixture of 1.2 gm of sulfur. 4.0 gm of anhydrous sodium carbonate, and 3.3 gm of p-dichlorobenzene was heated in a similar manner to give 2.4 gm of a pale-yellow, crude resin which is purified in a similar fashion. After drying the recovery amounts to 87-88% of the crude which is a white powder, brittle when cold, and fuses sharply at 255~ The polymer corresponds to the empirical composition of (C6H4S1.2) with MW 35,000-70,000. Macallum observed that the addition of 1,2,4-trichlorobenzene to the monomer mixture gave a polymer which was moldable at 280~176 under low pressure to yield a tough plastic [11 le] (Eq. 35). C1 x

C1 + y

C1

+ S + Na2CO3

'

C1

, S

S

+ NaC1 + Na2SO4 + CO2

(35)

Y

x

where x >>y. Lenz and Carrington [ 11 l f] reinvestigated the Macallum polymerization and extended our polymerization data on these systems. Some typical polymerizations are shown in Table XI. The infrared spectra of phenylene sulfide polymers are chosen in Fig. 2. Linear poly(phenylene sulfides) prepared by the condensation polymerization of alkali metal salts ofp-halothiophenols have been reported [112]. The reaction can be carried out in the absence of solvent at 10~176 below the melting point or in pyridine at 250~ The rate constants for the reaction in pyridine is shown

oo

TABLE XI Conditions Polymer No.

Time (hr)

Temp. (~

I II III IV V VI

20 20 20 24 20 6 48 48 6 48 6 96

350 300 300 300 300 200 350 350 200 350 200 350

VII VIII IX

Conversions and Yields in the Macallum Polymerizationa Mole ratio of reactants

p-C6H4CI2

1,2,4-C6H3C13

Yields (gm)

S

Na2CO3

% cony b

Dol C polymer

Insol polymer

Total

1 1 1 1 1

0.1 0.042 0.1

1.5 1.53 1.63 1.84 1.73

1.5 1.53 1.56 1.84 1.73

98.4 80.5 93.0 99.0 99.0

24.8 m

45.4 m

70.2 77.5 100.4 94.9 94.2

83.3 73.6

11.6 20.6

1 1

-0.15

1.5 2.0

1.5 2.0

90.7 93.4

62 49

25 46

87 95

1

0.15

2.0

2.0

93.6

58

28

86

1

0.15

2.0

2.0

92.7

36

56

92

aReprinted from R. W. Lenz and W. K. Carrington, J. Polym. Sci. 41, 333 (1959). Copyright 1959 by Joumal of Polymer Science. Reprinted by permission of the copyright owner. b Conversion based on chloride ion. c Soluble in boiling toluene and/or boiling diphenyl ether, insoluble in methanol.

109

4. Poly(arylene sulfides)

? A

t

1

I

1

I

I

1

I

1

I

1

I

1600 1500 1400 1300 1200

1

I

1

I

I

1

1

i

I

I

1100

1000

900

800

1

I 700 600

Wave number (cm -l)

Fig. 2 Infrared spectra of phenylene sulfide polymers: (A) linear polymer, (B) Macallum homopolymer, (C) Macallum copolymer (Nujol mulls). [Reprinted from R. W. Lenz and Handlovits, J. Polymer Sci. 43, 167 (1960). Copyright 1960 by the Journal of Polymer Science. Reprinted by permission of the copyright owner.]

in Table XII for the reaction:

110

3. Sulfide Polymers

TABLE XII OverallRate Constants for the Polymerizationof a Series of Alkali p-Halothiophenoxides in Pyridine at 2 5 ~ a

x- sM X

M

Second-order rate constants k (liter mole- 1min- 1)

F C1 Br I Br Br Br

Na Na Na Na Li Na K

0.026 0.011 0.13 0.86 2.6 0.13 0.096

a Reprinted from R. W. Lenz, C. E. Handlovits, and H. A. Smith, J. Polym. Sci. 58, 351 (1962). Copyright 1962 by the Journal of Polymer Science. Reprinted by permission of the copyright owner. where M = Na, Li, K; X = F, C1, Br, I. The percent conversions are 91.5% when X = F, M = Na; 75.76% when X = C1, M = Na; 82-93% when X = Br, M = K; and 74-77% when X = I, M = Na. Handlovits [113] reported that poly(phenylene sulfide) can also be prepared by the polymerization of copper p-bromothiophenoxide in the solid state or in pyridine

CuS

r

37,

Recently, Price [114] reported that poly(phenylene sulfides) can be obtained with the use of the analogous silver salts. Poly(phenylene sulfides) have also been prepared by metal salts of m-halothiophenoxides [ 115] as well as by a two-component system using metal salts of dithiohydroquinone and dihalobenzene [116]. Poly(phenylene sulfide) may also be prepared starting with mercaptobenzenediazonium salts [ 117]. Edmonds and Hill of Phillips Petroleum Co. reported that poly(phenylene sulfides) may be prepared by the reaction of p-dihalobenzene with sodium sulfide in N-methylpyrrolidone or dimethylformamide [118, 119]. Copper metal or cuprous chloride was also shown by Edmonds and Hill to give improved yields [118]. Table XIII lists examples of various poly(phenylene sulfides) and the conditions used for their preparation. Philllips Petroleum Co. is now producing poly(phenylene sulfides) under the name Ryton (trademark of Phillips Petroleum Co.) [98].

TABLE XIII

Na2S'9H20 (gm) 73.4 73.4 240.2 240.2 240.2 240.2 240.2 240.2 240.2 240.2 240.2 240.2 27.75 (anhydrous) 73.2

p-Dichlorobenzene (or other, as specified) (gm) 45 45 147 147 147 147 147 147 147 147 147 73.5 80.5 50.7 100

Preparation of Polyphenylsulfides Using Procedure 3-3 a Reaction

Additive (gm)

CuE1 (2) CuE1 (4) Cu (tubing) CuE1 (8) p-dichlorobenzene, 2,4-dichlorotoluene p-dichlorobenzene bis(p-bromophenyl)-ether

Volume of solvent (ml)

Temp (~

Time (hr)

Polymer (gm)

Yield

m.p.

(%)

(oc)

200 b 200 b 1,000 b 1,200 c 1,000 b 1,000 b 1,0006 1,000 b 1,000 b 1,000 b 1,000 b 100 b

260-265 260 250 250 250 250 250 250 250 250 250 250

41.5 91 17 16 17 17 17 17 17 17 17 17

26 20 96.3 59.9 91.0 90.7 91.2 92.8 92.6 98.8 89.6 100.3

79 60.5

89.5

275 248.5-252 275 240 282.5-285 28i5-291 284-287 282.5-286.5 285.5-286.5 276-280 282.5-288.5 <100

76.5

280-285

400 d

250

21

28.5

400 b

250

17

47.1

aData from J. T. Edmonds, Jr. and H. W. Hill, Jr., U.S. Patent 3,354,129 (1967). 6 N-Methylpyrrolidone. c DMF. d Tetramethylurea.

84.2 84.0 84.5

195-200.5

Low shear visc. at 303~ Poises 8.8

40 37.3 37.8 18.5 52.4 56.3 12.4

3. SulfidePolymers

112

The mechanism of polymerization of dihalo aromatics with sodium sulfide has been proposed to be either anion-radical or cation-radical depending on how the reaction is carried out [ 111 d].

4-3.

Preparation of Poly(phenylene sulfide) by the Reaction of p-Dichlorobenzene and Sodium Sulfide in N-Methyl-2-pyrrolidone [ 118, 119]

In a stainless steel bomb located behind a safety shield in a hood is added 60 grn Na2S" 9H20 in 100 ml N-methyl-2-pyrrolidone. The mixture is heated to 160~176 while flushing with nitrogen, to remove water of hydration from the sodium sulfide. To the resulting solution is added 36.7 gm (0.25 mole) of p-dichlorobenzene and the resulting mixture is sealed and heated at 231 ~ for 44 hr. Then the mixture was heated for 20 hr at 225~ followed by heating for 24 hr at 260~ The bomb is cooled, opened cautiously, and then the polymer is removed, washed with water, acetone, and dried. The polymer melting point is 275~176 and it can be molded at 290~ to a hard film. Some typical reaction conditions, polymer yield, and the effect of copper or copper salts are shown in Table XIII. Recently, Vidaurd [120] reported a batch process for increasing the production capacity of the poly(phenylene sulfide) wherein incremental quantities of the aryl dihalide are added to an alkali metal sulfide in the presence of a polar organic compound (N-methyl-2-pyrrolidone). These conditions allow the reaction to be carried out with good control of the temperature and without excessive build-up of pressure in a closed reactor system. Vidaurri prefers the use of sodium sulfide monohydrate [120]. Alkyl- and halogen (fluoro)-substituted poly(phenylene sulfides) have also been reported. For example, Robson et al. [121] reported that hexafluorobenzene reacts with fresh sodium sulfide to give a yellow amorphous material, m.p. > 300~ F

F

F - ~ F + H2S + Nail / \ F F

)

(38)

--S

F

F J.

The naphthalene, anthracene, and phenanthrene polysulfide polymers have been prepared using $2C12 [122]. Poly(phenylene sulfides) find use in coating compositions [123, 123a], plastics [118, 124], and fibers with nonburning properties (limiting oxygen index of 44-46) [98, 123, 123a, 124a]. The thermogravimetric analysis of

5. Miscellaneous Preparations

113

poly(phenylene sulfide) shows no weight loss at 400~176 in air or nitrogen indicating good thermal stability [98, 125]. For more details, the brief review by Smith [126] should be consulted.

5.

MISCELLANEOUS PREPARATIONS

Preparation and polymerization of thiocarbonyl fluoride [ 127]. 2. Preparation of methylol derivatives of polythiols [ 128]. 3. Reaction of sulfur and olefins to yield polysulfides [129]. 4. Preparation of sulfur-containing polymers by the reaction of unsaturated compounds simultaneously and continuously with H2S and SO2 in a mole ratio of from 1:1 to 3:1 [130]. Reaction of polyalkylene polysulfide with a polyfunctional aziridine ring [131]. Preparation of phenol polysulfides [132]. 7. Ketone polysulfides by the reaction of ketones with $2C12 [ 133]. 8. Preparation of poly(chlorophenyl sulfides) [134]. 9. Reaction of sulfur with phenol or aniline [ 135]. 10. Preparation of allyl thioglycidyl ether-l,2-butylene sulfide copolymer [136]. 11. Liquid polymercaptopolysulfide polymers 137]. 12. Halogen terminated polysulfides [138, 139]. 13. Thiosulfate process for making organic polysulfides [140]. 14. The reaction of aliphatic dithiols with dichlorosulfones gives polymeric alkylene polysulfides [ 141, 142]. 15. The reaction of thionyl chloride with aliphatic dithiols gives polymeric disulfides [ 141 ]. 16. Crystalline poly(methylene sulfide) [ 143]. 17. Polysulfide elastomers from the reaction of 1,5-pentanedithiol with thionyl chloride [ 144]. 18. gem-Dithiols [ 145]. 19. Polysulfide-urethane compositions [ 146]. 20. Polysulfide-polyester compositions [ 147]. 21. Polysulfide-conjugated diene rubber compositions [148]. 22. Polysulfide sealant composition [149]. 23. Polysulfides prepared heavy residues from vinyl chloride production [150]. 24. Copolymerization of ethylene sulfide and carbon disulfide [151 ]. 25. Reaction of furfural with thiol-terminated polysulfides [152]. 26. Toluene diisocyanate polysulfide reaction products [ 153]. 27. Phenol-formaldehyde polysulfide condensation polymers [154]. o

.

,

114

3. Sulfide Polymers

28. 29. 30. 31. 32. 33. 34. 35. 36. 37.

Reaction of hydroxy-terminated polysulfides with dicarboxylic acids [155]. Condensation of thiodiglycols [156]. Poly(chlorophenyl sulfides) [157]. Sulfur and olefins to give polysulfides [158]. Ketone polysulfides by the reaction of ketones with $2C12 [159]. Polysulfide foams [160]. Polysulfides from p-aminothiophenol and maleic anhydride [ 161 ]. Aminothiol poly(alkylene sulfide) oligomers [162]. Epoxy polyalkylene sulfide resin with polyisocyanate hardener [163]. Interpenetrating networks of poly(alkylene sulfide)-polydiisocyanate system [ 164]. Graft polymerization for polyalkylene sulfides [165]. CS2 was polymerized with ethylene sulfide or propylene sulfide in the presence of diethyl zinc to give poly(trithiocarbonate) [ 166]. Block copolymers of hydrogenated chorostyrene with polymerized alkylene oxide and alkylene sulfide [167]. Copolymers of epichlorohydrin and ethylene sulfide [168]. Phosphazene polymer with alkylenesulfide side chains [169]. Anionic copolymerization of sulfur with cyclic mono- or polysulfides [ 170]. Thermal (230~176 polymerization of halo substituted diaryl disulfides in the presence of KI to yield poly(arylene sulfide)s [171]. Preparation of poly(arylene sulfide) with low metal contamination by the process involving contacting a dihaloaromatic compound, a sulfur source, and organic amide, alkali metal carboxylate, and water in a reaction vessel made of titanium [ 172]. Preparation of polyarylene thioether ketones [173]. Poly(arylene thioether) block copolymer with units of (mC6Ha--CO--C6H4--Sm) and ( m C 6 H a m S m ) as one example [174]. Poly(arylene sulfide) polymer containing sulfone, ether, and biphenyl groups [ 175].

38. 39. 40. 41. 42. 43. 44. 45.

46. 47. 48.

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174. 175.

119

E.R. Bertozzi, Fr. Demande 2,218,355 (1974). E.R. Bertozzi, Ger. Often. 2,404,749 (1974). K.C. Tsou, U.S. Patent 3,054,781 (1962). R.M. Fitch and D. C. Helgeson, Macromol. Syth. 4, 171 (1972). B.D. Stone, M. L. Nielsen, and R. L. Jenkins, J. Polym. Sci. 47, 526 (1960). J. Harmon, U.S. Patent 3,070,580 (1962). B.S. Stone, M. L. Nielsen, and R. L. Jenkins, J. Polym. Sci. 47, 149 (1960). T.L. Cairns, G. L. Evans, A. W. Larcher, and B. C. McKusick, J. Am. Chem. Soc. 74, 3982 (1952). C.R. Morgan, U.S. Patent 3,945,982 (1976). D.R. Leonard and L. H. Davis, Def. Publ. U.S. Pat. Off. T 943,007 (1976). K. Moriguchi and T. Fukui, Japan Kokai 75 10,888 (1976). H. Imaki, T. Nakayama, K. Kono, and S. Sasatani, Japanese Patent 75/31,886 (1975). F. Peerts and Y. Delaunois, Ger. Often. 2,531,107 (1976). K. Soga, H. Imamura, M. Sato, and S. Ikeda, J. Polym. Sci., Polym. Chem. Ed. 14(3), 677 (1967). E.M. Fettes, U.S. Patent 2,606,173 (1952). M.H. Malootian, Electron. Equip. Eng. 4(7), 2 (1956). T.C. Patrick and H. R. Ferguson, U.S. Patent 2,646,415 (1953). Dunlop Rubber Co., Ltd. and M. Goldstaub, British Patent 618,449 (1949). F.P. Richter and E. E. Reid, U.S. Patent 2,582,605 (1952). M.E. DeGeorges and Y. Bourgau, U.S.S.R. Patent 176,533 (1965). L. Bateman, R. W. Glazebrook, C. G. Moore, M. Porter, G. W. Ross, and R. W. Saville, J. Chem. Soc. p. 2838 (1958). L.E. Foreman, U.S. Patent 3,038,883 (1962). G.L. Woo, Ger. Often. 2,504,113 (1975). T. Asahara, Kobunshi Ronbunshu 32(7), 452 (1975). R.T. Woodhams and S. Adamek, J. Appl. Polym. Sci. 14(5), 1253 (1970); Chem. Abstr. 73(6), 26185w (1970). N.A. Suvorovskaya and co-workers, Russian Patent Su 410,071 (1974); Chem. Abstr. 82, 45235q (1974). V.I. Klenin and co-worker, Vysokomol. Soedin Ser. A 19(5), 1138 (1977); Chem. Abstr. 87, 24048h (1977). N. Moszner and M. Hartmann, Acta Polym. 37(5), 304 (1986); Chem. Abstr. 105, 68705 (1986). S. Ikeda, Japanese Patent JP51038393 (1976); Chem. Abstr. 85, 47316c (1976). F.C. Schwab and I. J. Heilweil, U.S. Patent 3,954,915 (1976). A. Maeda, T. Senda, and H. Seya, Japanese Patent JP63081157A2 (1988); Chem. Abstr. 109, 130655x (1988). Y. Kuraki and S. Yasunami, Japanese Patent JP02301749A2 (1990); Chem. Abstr. 115, 243836z (1990). T. Baran, A. Duda, and S. Penczek, Polish Patent PL 14248513 (1988); Chem. Abstr. 111, 40109j (1988). E. Tsuchida, K. Yamamoto, M. Jikei, and K. Miyatake, Macromolecules 26, 4413 (1993). J.F. Geibel and H. D. Yelton, U.S. Patent 5,235,032 (1993). H. Endo, T. Kaneko, K. Kashiwadat, T. Katto, T. Mizuno, Y. Satake, Z. Shiiki, M. Tada, S. Yamamoto, and K. Kashiwadati, U.S. Patent 5,153,279 (1992) and U.S. Patent 5,153,264 (1992). Y. Satake, S. Yamamoto, T. Kaneko, M. Tada, K. Kashiwadati, T. Mizuho, H. Endo, T. Katto, and Z. Shiiki, U.S. Patent 4,960,806 (1990) and U.S. Patent 5,120,808 (1992). R.L. Bobseln, J. F. Geibel, and H. F. Efner, U.S. Patent 5,245,000 (1993).

Chapter 4

Polymerization Reactions of Mono- and Diisocyanates 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Homopolymerization of Monoisocyanates to 1-Nylon . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1. General Method for the Preparation of 1-Nylon . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Polymerization of Diisocyanates to Give Polycarbodiimides . . . . . . . . . . . . . . . . . . . . .

3-1. Polymerization of 2,4-Toluene Diisocyanate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Poly-2-oxazolidone by the Reaction of Isocyanates with Epoxides . . . . . . . . . . . . . . . . .

120 121 122 129 130 136

4-1. Preparation of the Poly-2-oxazolidone from the Reaction of 2, 4- Toluene Diisocyanate and the Diglycidyl Ether of 2,2-Bis(4-hydroxyphenyl)propane . . . . . . . . . . . . . . . . 138 5. Polymerization of Polyisocyanates to Polyisocyanurates . . . . . . . . . . . . . . . . . . . . . . . .

5-1. 5-2. 5-3. 5-4.

Preparation Preparation Preparation Preparation

of a of a of a of a

6. M i s c e l l a n e o u s M e t h o d s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References ........................................................

1.

138

Polyisocyanurate Foam from 4,4'-Diphenylmethanediisocyanate . . 145 Polyisocyanurate from Diisocyanates . . . . . . . . . . . . . . . . . . . . . 145 Polyisocyanurate Foam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 Polyisocyanurate from a TDI-Modified Polyester . . . . . . . . . . . . . 146 147 148

INTRODUCTION

The purpose of this chapter is to outline some selected polymerization reactions of mono- and diisocyanates. In a previous volume (this series, Vol. I) we described the preparation of polyurethanes and, therefore, we will not deal with this aspect in this chapter. The major homopolymerizations reactions of isocyanates are shown in Scheme 1. These reactions are discussed in this chapter. A good review of the Chain structure, polymerization, and conformations of polyisocyanates should be consuited for further details on the 1-nylon-type polymers [ 1]. 120

121

2. Homopolymerization of Monoisocyanates to 1-Nylon

O II --N--C-I R

-- R-- NCO

f

-.... 0

[--R-- N = C = N - - ] .

_R_N I~-N_R _

o2 2o I R I

Scheme 1

In most cases, especially in the presence of catalysts, it is possible that more than one of the isocyanate reactions shown in Scheme 1 takes place simultaneously. Some typical examples of these reactions are described in Section 6 (Miscellaneous Methods). Some of the major copolymerization reactions of isocyanates are shown in Scheme 2. Only the reaction with epoxides is discussed in this chapter. The reaction with polyols to give polyurethanes and with amines to give polyureas is discussed in Vol. I of this series [2]. Ulrich [2a] has briefly reviewed these and other reactions and this review should be consulted for additional material and references. New monomers have been introduced which combine both unsaturation in with isocyanate groups. For example, 2-isocyanatoethyl methacrylate (Dow) has been reported to give a mixture of trimer and polymers using titanium complexes (Tyzor DC from DuPont) which still has unsaturation [2b]. The resulting polymer can possibly be crosslinked via the unsaturated part of the molecule.

CAUTION: Handle all isocyanates with great care. Isocyanates are known carcinogens.

0

HOMOPOLYMERIZATION OF MONOISOCYANATES TO 1-NYLON

Shashona [3, 3a] reported that the anionic-catalyzed polymerization of monoisocyanates at - 2 0 ~ to - 1 0 0 ~ gave linear high-molecular-weight polymers

122

4. Polymerization Reactions of Mono- and Diisocyanates

(see Table I). The reaction takes place with both aliphatic and aromatic isocyanates and the polymers are classified as 1-nylons:

R--N--C--O

,

0 II --N--C--

(1)

I R

Suitable catalysts are shown in Table II, where the solvent is generally DMF, and some typical polymer preparations are shown in Tables II and III. Table II illustrates the use of different solvents and catalysts to effect the polymerization which is thought to take place as follows" 0 R--N--C--O + XO

,

O

II

II

RN=C=O

R--N--CX

II

II

X--C--N--C--N-

I

I

R

R

Low Tempt

X--C--

--

\R

--N-

I

/, R

linear polymer High temp

l~CO land high cone

~of initiator

l

Sk ation Sto (isolation of polymer)

R

I

(2)

o

,,

R--N~c..N--R

X--C--

II 0 Trimer

2-1.

General Method for the Preparation of 1-Nylon [3]

To a 250-ml, 3-necked flask (thoroughly dried by flame) equipped with a stirrer, two side-adapters (one for calcium chloride and a low-temperature thermometer, the other with a nitrogen bubbler and rubber, hypodermic-syringe cap) is added 30 ml DMF, and the contents are cooled to - 58~ A hypodermic needle is used to pierce the rubber cap and deliver the catalyst dropwise over a 2- to 3-min period while the reaction mixture is stirred vigorously. The polymer precipitates rapidly, and after 15 min of stirring at - 5 8 ~ 50 ml methanol is

123

2. Homopolymerization of Monoisocyanates to I-Nylon

--R--N

CH--R'--J, Copolymer

Poly(parabamic acid)

-.-Vo //" Aldehyde

Polyhydantoins

Polyurea

Amines

,

Polyurylene *" Hydrazide/ / / Polysemicarbazide /

-- RNCO

/

/

Olefin (AnionicCat)

Polyol

~Dicarboxylicacid ~~arthydride

_

Polyurethane . Polyt ae Dioximes

Polyamides or Polyimide or Polyamide-imides

/ Poly(o-acyloximes) Scheme

, Copolymer

2

added. The polymer is filtered and washed with 300 ml methanol, dried at 40~ under vacuum, and isolated. Typical preparations are described in Table II, using DMF as a solvent. Other solvents were evaluated as described in Table III. Heating 1-nylon at elevated temperatures converts it to trimers (isocyanurates). Diisocyanates on homopolymerization produce cross-linked polymers. The reaction is usually carried out in DMF with sodium cyanide initiator at low temperature [3b]. Cyclopolymerization can also occur with 1,2-[3b, 3c] and 1,3-diisocyanates [3b] as well as 1,2,3-triisocyanates [3c, 3d] to give cyclic ureas.

I NCO NCO

i

i

'

O-

O

ii

II

--I N ~ C ~ N ~ C ~

Li

I

n

Recently polyisocyanates or 1-nylons have received more attention due to their chiral helical [3e] structure and their liquid crystalline properties [3t]. The older methods of polymerization involve anionic polymerization and generally the yields and molecular weights are low.

124

4.

Polymerization Reactions of Mono- and Diisocyanates

TABLE I 1-NylonPolymers and Their Properties R

Softening tempb (~ Ethyl n-Propyl n-Butyl Isobutyl n-Amyl n-Hexyl n-Heptyl n-Undecyl n-Octadecyl Allyl 9-n-Decenyl

180 180 173 145 120 100 45 40 180 75

Benzyl Phenyl m-Methylphenyl p-Methoxyphenyl

m

0

J.

Meltingc or decompositiontemp (~ 250 250 209 210-220 209 195 180 155 94 260-290 180-240

250 197 200 212-214

Soluble in H2504, CF3CO2H H2SO4, CF3CO2H Aromatic and chlorinated hydrocarbons Same Same Same Same Same H2SO4, CFaCOEH Aromatic and chlorinated hydrocarbons H2504, CFaCOEH H2SO4 N,N-Dimethylformamide N,N-Dimethylformamide

Reprinted from V. E. Shashona, W. Sweeney and R. F. Tietz, J. Am. Chem. Soc. 82, 866 (1960). Copyright 1960 by the American Chemical Society. Reprinted by permission of the copyright owners. bTemperature at which the polymer first became plastic without sticking on a metal temperature gradient bar. c Temperature at which the polymer first left a clear molten trail on a metal temperature gradient bar. a

Patten and Novak [3d] reported in 1991 that the use of the following two catalysts separately give quantitive yields of polymers from the alkylisocyanates with no trace of trimers: TiC13(OCH2CH3) TiC13(OCH2CF 3)(THF)2. Experimental evidence suggests that these polymerizations involve "living" type polymers which allow one to control the molecular weight and to form block copolymers. More recently Patten and Novak [3h] reported that cyclopentadienyl titanium compounds were also effective catalysts. For example: CpTiC12X

where X = - - O R , --NR2, or mCR3

Polymerizations with CpTiC12X were found to tolerate a wide variety of Lewis bases. The process of polymerization of n-hexyl isocyanate is

125

2. Homopolymerization of Monoisocyanates to 1-Nylon

CI~ TI'1/C1 I

OCH2CF3

NCO

H CF3CH20

R where R = n-hexyl. The presence of the CF3CH20-end group was identified by 19F NMR (~ = 74.8 ppm). The polymerization mechanism proposed involves a coordination of the isocyanate with the titanium catalyst and its insertion to form a titaniumamidate end group species. The titanium end group stays active until quenched by the addition of a protonic source. The addition of other monoalkyl isocyanates gives a block copolymer.

(o)

Catalyst

n-C6H13NCO

'

/J~N

I

n

n-C6H13 MW 46,400

n-C6H13NCO I

n

n-C6H13

I

n-e6H13

MW 193,300 The latter type of catalysts (Cp-TiC13) are very tolerant toward the polymerization of isocyanates with other functional groups such as unsaturation. For example, 2-isocyanatoethylmethacrylate give an unsaturated polymer. O ~O/~/NCO

RCOOR

Cp-TiC12X ' ( ~ J)n whereX = NCCH3)2 N 24hr,25~ O~ ~ o

O/.~,,.O/~/NCO Lns 9

=

190~ (22% wt loss) 335~ (reminder)

The side chains can be polymerized further to give a crosslinked polymer.

126

o r~

.<

r~

c..) o

g

g

<

I

I

"~~z

,/

~"

I

I

I

I

I

'~~'~"

I ~~'~'~'*

I

I

-I-

I

I I

I

I~ ~

I

z

I

z

I

I

I N ~ N N N N~ N~~ ~ ~ I ~I ~ N ~

4. Polymerization Reactions of Mono- and Diisocyanates

~

I

~ e "~.~

~ o o o - o o - o o o o o ~ o o ~

<m~oo

18 19 20 21 22 23 24 25 26 27 28

m-Tolyl p-Tolyl m-Chlorophenyl p-Chlorophenyl o-Methoxyphenyl p-Methoxyphenyl Benzyl Benzoyl a-Naphthyl a-(3-Isocyanatoethyl)-phenyl 2,4-Toluene di-

10 ml 5 ml 10 ml 10 ml 10 gm 35 ml 12.5 ml 10 ml 10 ml 10 ml 10 ml

29

Trimethylsilyl

10 ml

30 50 30 30 30 100 30 30 30 45 30 c 30

8g

1g 8g 4g 4g 12g 1g 3g 3g 2.25 g 3g 4g

-

58 50 20 30 40 58 40 40 40 58 - 100

60 25 None None None 35 50 None None 11 30

- 40

None

--

0.3 1.1 h

DMF r ~

0.7 h

Benzene

0.04 h

H2S04

a Repreinted from V. E. Shashona, W. Sweeney, and R. F. Tietz, J. Am. Chem. Soc. 82, 866 (1960). Copyright 1960 by the American Chemical Society. Reprinted by permission of the copyright owner. b D M F = N,N-dimethylformamide, D M A = N,N-diemthylacetamide, T F A = trifluoroacetic acid. c Triethylamine used as solvent. d D M F / D M A (70/30 by vol) used as solvent. e Sodium in DMF. f Sodium benzophenone ketyl. g N a C N in DMF. h At 0.5% concn. i At 0.1% concn.

J sym-Tetrachloroethane-phenol (66 : 100 by wt).

t,~

1',9

TABLE III

Expt.

Monomeric isocyanate (ml)

30 31 32 33 34 35 36 37 38 39 40

(8) Hexyl (7.5) Hexyl (8) Hexyl (8) Hexyl (8) Hexyl (7.5) Heptyl (8) Decenyl (8) Propyl (25) p-Tolyl (25) p-Tolyl (25) Phenyl

Polymerizations Illustrating the Use of Different Solvents and Catalysts"

Solvent (ml) 30 30 30 30 30 30 35 30 25 7 25

Acetonitrile Triethylamine Methylene chloride DMA C Toluene Hexane DMF/DMA (7/3) DMF/DMA (7/3) Methylene chloride Glycol dimethyl ether DMF a

Initial temp (~ -58 -70 -58 -20 -30 -70 -70 -70 - 50 -50 -40

/Tinh

Yield

(0.5%)

Catalyst

(%)

benzene

4 ml NaCN soln in DMF 3 drops triethylphosphine 4 ml NaCN soln in DMF 4 ml NaCN soln in DMF 4 ml NaCN soln in DMF 3 ml 0.1 M lithium butyl in decalin 10 ml of 3 M EtMgBr in ether 0.05 gm sodamide 2 ml NaCN in DMF 2.5 ml sodium naphthalene soln 3 ml sodium naphthalene soln

0 0 10 30 0 0 0 0 30 20 60

0.3 1.1

0.45 b 0.97 b

a Reprinted from V. E. Shashona, W. Sweeney, and R. T. Tietz, J. Am. Chem. Soc. 82, 866 (1960). Copyright 1960 by the American Chemical Society. Reprinted by permission of the copyright owner. b This was measured in sym-tetrachloroethane-phenol (66"100 by wt). c DMA = N,N-dimethylacetamide. d DMF = N,N-dimethylformamide.

t~

129

3. Polymerization of Diisocyanates to Give Polycarbodiimides

The chemistry and synthesis of poly(alkyl isocyanates) have earlier been reviewed [3i]. The glass transition temperature (tg) of the polymers can be lowered by introducing ethyleneoxy groups in the backbone such as by polyethylene glycols or polypropylene oxides. The adhesive properties of these materials with respect to steel, glass, and paper are outstanding [3j]. The catalyst used for the latter was NaCN in DMF and the molecular weights (Mn) were in the range of 36,000 to 1,000,000 depending on the monomer used. Liou et al. [3j] prepared 1-nylon polymers from alkoxyalkyl isocyanates. ROCH2NCO

NaCNcatalyst 5oC ~ ( O j) n inDMF(dry)~ N I CH2OR

The isocyanates were prepared as follows: C1CH2COONa + RONa

',

ROCH2COOH

ROCH2COC1

I NaN3 ROCH2CO + N2 '

Curtius Rearrangement

ROCH2CON3

Okamoto et al. reported recently that using chiral anionic initiators (such as the lithium salt of ( - ) menthol) for the polymerization of butyl and 4-phenylbutyl. Isocyanate gave 1-nylons which showed optical activity [3k]. The 1-nylons or poly(alkyl isocyanates) give liquid crystalline polymers which may make them useful for electrical applications. These polymers are characterized as main-chain mesogenic polymers having a semirigid structure. The polymerization and characterization of liquid crystalline poly(hexyl isocyanate/styrene solutions) have been reported by Kozakiewicz [3m]. 3.

POLYMERIZATION OF DIISOCYANATES TO GIVE POLYCARBODIIMIDES

Campbell and co-workers [4-5a] reported that certain phospholenes and phosphalene oxides [5a] are useful in converting diisocyanates to polycarbodiimides of high molecular weight [Eq. (3)]. The polymers were reported to be molded into tough, clear, nylon-like films having good tensile strength and electrical properties. The carbodiimide reaction has also been used in the preparation of special urethane elastomer [6] and rigid forms [7]. Polycarbodiimides have been reported to be useful for fire retarding film applications [7a]. In addition, carbodiimide polymers also find use in electrode plate applications where plasma etching is involved [7b]. More recently,

130

4.

Polymerization Reactions o f Mono- and Diisocyanates

carbodiimides have also been reported to be used for carbon fiber composite materials [7c]. Surprisingly the polymers were inert to boiling acid and alkali as well as certain organic solvents. However amines were reported to convert the carbodiimides to guanidines as shown in Eq. (4). /CH3

C2H5

OCN--R--NCO [--R--N=C=N--],,

O

+ nR'NH2

, [ - - R - - N = C - - N - - ] ~ + CO2

,

(3)

1 NHR'

J~

Since the high-molecular-weight polycarbodiimides are insoluble and thus difficult to process, techniques to overcome this problem have been studied. One such approach involves adding given amounts of monofunctional isocyanates to give lower-molecular-weight polymers [8]. The rate of reaction was followed by carbon dioxide evolution with an American Meter Co. gas meter, and by infrared measurements of the isocyanate absorption at 2270 cm -1 and the carbodiimide peak at 2130 cm-1 [8]. After the polymer was dried, the DTA and TGA thermograms were obtained (DuPont 9N Thermal Analyzer) [8] . The number average molecular weights were determined using a Hewlett-Packard vapor-phase osmometer [8]. The melt-processing viscosities were determined used a Brabender Plasti-Corder [8]. A recent review of this reaction is worth consulting for additional details [8a]. The preparation of some typical polycarbodiimides is shown in Table IV.

3-1. Polymerization of 2,4-Toluene Diisocyanate [5b]* a.

Preparation of Catalyst: 1-Ethyl-3-methyl-3-phospholene 1-Oxide CH2. CEHsPC12 +

"~

CH2

CH3

CI\ /~CH3 ~ CEHs--P

C1/ \

II

(5)

II

o;G c 3 C2H5 * Reprinted from T. W. Campbell, J. J. Monagle, and V. S. Foldi, J. Am. Chem. Soc. 84, 3673 (1962). Copyright by the American Chemical Society. Reprinted by permission of the copyright owner.

3. Polymerization of Diisocyanates to Give Polycarbodiimides

CAUTION:

131

Phosphorus compounds are highly toxic and may be

carcinogenic. A 3-liter, four-necked flask is fitted with a spiral condenser topped with a dryice condenser, thermometer, l-liter dropping funnel with pressure equalizing side arm, and a magnetic stirrer. To this flask are added 1 gm of copper stearate, 780 gm (5.96 moles) of dichloroethylphosphine, and by the dropping funnel 447 gm (6.50 moles) of freshly distilled isoprene. The reaction mixture is stirred and refluxed under nitrogen for 42 hr, cooled and allowed to stand for 2 days and then refluxed without stirring for 5 days. Excess isoprene is distilled from the mixture and 850 ml of water is added dropwise with stirring to the reaction flask, which is cooled in an ice bath. The dark-brown, aqueous solution is transferred to a 5-liter flask and 1250 ml of 30% sodium hydroxide solution is added gradually to make the solution slightly alkaline (pH 8). The mixture is filtered and the aqueous solution is extracted continuously with chloroform for 12 days. The chloroform is distilled and the residue vacuum distilled through a 25-cm Vigreux column to give 435 gm (51%) of water-white liquid with a slight odor of phosphine. The product is further purified by oxidation at 50~ with excess 3% hydrogen peroxide for 6 hr. The aqueous mixture is extracted continuously with benzene and the oxide is recovered by distillation, b.p. 115 o_ 119~ (1.2-1.3 mm), n2D51.5050. Analysis Calculated for C7H12OP: C, 58.4; H, 9.0; P, 21.5. Found: C, 58.3; H, 8.8; P, 21.6

b.

Polymerization of 2,4-Toluene Diisocyanate [5]*

/CH3 NCO CH3

o ~p, ~ NCO

-2CO2

I C II N C H 3 @ N =

I N C--N-~CH3

(6)

* Reprinted fromT. W. Campbelland K. C. Smeltz,J. Org. Chem. 27, 2069 (1962). Copyrightby the AmericanChemical Society, 1962. Reprintedby permissionof the copyrightowner.

bO

TABLE IV Preparation of Polycarbodiimidesa

Diisocyanate (gm) Methylenebis(4-phenyl isocyanate), 20 3,3-Dimethyoxy-4,4'-biphenylene diisocyanate, 10 3,3-Dimethyl-4,4'biphenylene diisocyanate, 20 Propane-2,2-bis(4-phenyl isocyanate), 10 m-Phenylate diisocyanate, 8 4,4'-Biphenylene diisocyanate, 15 Mesitylene diisocyanate, 15 3,3 '-Dimethoxy-4,4-bisphenylene diisocyanate, 10 3,3-Dimethyl-4,4'-biphenylene diisocyanate, 20 Hexamethylene diisocyanate, 15 2,4,4'-Triisocyanato-diphenyl ether, 10 2,4-Toluene diisocyanate (TDI), 54

Catalyst (1-Ethyl-3-methyl3-phospholene 1-oxide) (gm)

Solvent (xylene) (ml)

Reaction conditions Temp (~

Time (hr)

Polymer Yield (gm)

5

8.5

3 4 24 5

6.5

150 100

0.03 0.04

Reflux Reflux

200

1 Drop

Reflux

75

1 Drop

Reflux

75 150 150 100

0.03 0.03 0.15 0.04

Reflux Reflux Reflux Reflux

200

1 Drop

Reflux

25 68 C2C14, 500

0.15 0.03 1-Phenyl-3-methyl-phospholene oxide, 0.13

140 Reflux 120

8.5

Ref.

e~

r~

TDI, 10, + 4,4'-diphenyl ether diisocyanate, - Isophorone diisocyanate, 187.1

THF, 680 C2C14, 850

MDI, 675, + Phenylisocyanate, 71.4

C2C14

Methylenebis (4-isocyanato-cyclohexane), 71.23, and cyclohexylisocyanate, 0.87 Isophorone diisocyanate, 231.2, and butyl isocyanate, 68.8 2,4-TDI, 36

Xylene, 273.7

Amylacetate, 270 MEK, 25, and xylene, 35

3-Methyl- 1-phenylphospholene 1-oxide, 0.075 3-Methyl-l-phenyl-2-phospholene 1-oxide, 1.87 3-Methyl- 1-phenyl-2-phospholene 1-oxide, 1.87 Ph3AsO, 0.2168

1-Phenyl-3-methyl-2-phospholene oxide, 30 g of 10% soln in xylene 1-Phenyl-3-methyl-2-phospholene-1oxide, 0.3

67

70

120

48 (See also Figs. 1 and 2)

120

4

Reflux

3

140

26

60

2

aData taken from T. W. Campbell and K. C. Smeltz, J. Org. Chem. 27, 2069 (1963). b S. Amano and Y. Imashiro, European Patent Application EP 398069A2 (1990); Chem. Abstr. 114, 229661 (1991). c S. Amano, Japanese Patent JP 04279618A2 (1992); Chem. Abstr. 118, 235147 (1993). ay. Imashiro and I. Takahashi, European Patent Application EP 548816A2 (1993); Chem. Abstr. 120, 55309 (1993). ey. Imashiro and I. Takahashi, Japanese Patent JP 05239223A2 (1993); Chem. Abstr. 120, 136613 (1994). UM. M. J. West, WO Patent 9322282A2 (1993); Chem. Abstr. 120, 299581 (1994). gR. Takehara, H. Tanda, Y. Nunokawa, and T. Ishibashi, Japanese Patent JP 06016988A2 (1994); Chem. Abstr. 121, 11967 (1994). h T. Shiomura, N. Inoe, Y. Sonde, and N. Yamatani, Japanese Patent JP 02202906A2 (1994); Chem. Abstr. 113, 232308 (1990).

-t

134

4. Polymerization Reactions of Mono- and Diisocyanates

9990-

r O 09

09 72 E 09 t"

I--

63" 54" 4536

4000 36"00 32"00 2800 2z100 2600 1600 1200 800

400

Wavenumber cm -1

99.0 94.4 89.0 t"0

09 83.6 E

o'} .m 09 t'-

i,..,. !..-.

78.2

o--e 72.8 67.4 62.(

4000 3600 3200 2800 24'00 2()00 1600 1200 800

400

Wavenumber cm -1

Figs. 1 and 2 From Y. Imashiro and I. Takahashi, European Patent Application EP 548816A2 (1993); Chem. Abstr. 120, 55309 (1993). 2,4-Toluene diisocyanate was distilled through a spinning band column. After a small forecut, distillation proceeded smoothly at 80~ (1.3 mm Hg). Polymerization of a 10% solution in boiling decahydronaphthalene was carried out with catalytic quantities of 1-ethyl-3-methyl-3-phospholene oxide. The reaction was

3. Polymerization of Diisocyanates to Give Polycarbodiimides

135

complete in less than 1 hr, and the polymer was obtained in small, fluffy particles very reminiscent of puffed cereal in appearance and texture. These little particles were white and gave very tough, clear, nearly colorless film when pressed at 275~ Strips of this film could be cold drawn; however, the film strips relaxed in boiling water and exhibited no crystallinity and extremely low X-ray orientation. Analysis Calculated for (C8H6N2)x: C, 73.8; H, 4.61; N, 21.4 Found: C, 73.4; H, 4.4; N, 21.0 73.5 4.2 21.0 Some typical properties of polycarbodiimides are shown in Tables V-VIII. Ulrich [2a] described various carbodiimide catalysts in the order of their relative reactivity as being CH3 CH3N\

/N--CH3

> [(CH3)2N]3--P--O > (C2HsO)3--P--O

O// NR where R = alkyl > aryl > CH2C1 > OC2H5 > N(CH3)2. With aryl isocyanates in general pentavalent phosphorus compounds could act as carbodiimide formation catalysts. In addition trivalent phosphorus compounds such as triethyl phosphine are also efficient carbodiimide catalysts [8b]. TABLE V Properties of Films of Poly(3,3'dimethoxy-4,4'-biphenylene carbodiimide) a'b Initial modulus (p.s.i.) % Elongation Tenacity (p.s.i.) Dielectric constant (102-105 c.p.s.) Dissipation factor (102-105 c.p.s.) Volume resistivity

1,183,500 6.2 39,800 3.4 (25~ 3.8 (170~ 0.002-0.003 (25~ 0.006-0.02 (170~ > 1 x 1014 (25~ 2.2 • l0 ll (200~

a Reprinted from T. W. Campbell and K. C. Smeltz, J. Org. Chem. 27, 2069 (1963). Copyright 1963 by the American Chemical Society. Reprinted by permission of the copyright owner. b Film was molded at 300~ and drawn 4.5 times at 115~

136

4. Polymerization Reactions of Mono- and Diisocyanates

TABLE VI

Physical Test Data on Poly(toluene carbodiimide) Film Stripsa

Temp. ~

Tenacity g.p.d.

Elongation, %

Initial modulus, g.p.d.

Denier

25 110

3.2 0.3

52 121

38 0.19

467 449

a Reprinted from T. W. Campbell and K. C. Smeltz, J. Arg. Chem. 27, 2069 (1963). Copyright 1963 by the American Chemical Society. Reprinted by permission of the copyright owner.

0

POLY-2-OXAZOLIDONE BY THE REACTION OF ISOCYANATES WITH EPOXIDES +-

(CH3)4NI OCN--R--NCO

+ CH2--CH--CH20--R'--OCH2CH--CH2 \ / \ /

0

DMF

0

/CH2--CH

~ c

I

O--CH2

~ "

N--R--N~

I

CH-- CH20--R'--

II o TABLE VII Equivalents N = C - - N per Mole for Polycarbodiimides Derived from Toluene 2,4-Diisocyanate a

Alcohol used

CO2 (gm)

MW calc. from CO 2 data

Ethanol Ethanol Isopropyl alcohol Isopropyl alcohol Benzyl alcohol Ethanol Ethanol

7.3 6.7 7.0 7.8 6.9 8.2 7.3

902 670 794 1334 855 2114 1332

Total wt

Equiv N--C=N/mole 4.89 3.11 3.85 8.00 3.58 14.22 4.86 b

a Reprinted from T. W. Campbell and K. C. Smeltz, J. Org. Chem. 27, 2069 (1963). Copyright 1963 by the American Chemical Society. Reprinted by permission of the copyright owner. b Polycarbodiimide derived from methylenebis(4-phenyl isocyanate).

OCH2--

4. Poly-2-oxazolidone by the Reaction of Isocyanates with Epoxides

137

TABLE VIII Comparisonof Molecular Weight for Stabilized Polycarbodiimides Using Titration Data and CO2 Dataa

Diisocyanate u s e d 2,4-TDIb 2,4-TDI MDIc 2,6-TDIa MDI

Alcoholused

Total wt CO2 (grn)

MW calcd from CO2 data

MW from titration data

Ethanol Isopropyl alcohol Ethanol Ethanol Ethanol

6.7 7.0 7.3 6.6 8.1

670 794 1332 642 2752

664 803 3700 1176 2771

a Reprinted from T. W. Campbell and K. C. Smeltz, J. Org. Chem. 27, 2069 (1963). Copyright 1963 by the American Chemical Society. Reprinted by permission of the copyright owner. bToluene 2,4-diisocyanate. cMethylenebis(4-phenyl isocyanate). a Toluene 2,6-diisocyanate.

Sandier, Berg, and Kitazawa [9] reported that 2,4-toluene diisocyanate reacts with diglycidyl ethers to give poly-2-oxazolidones. A similar reaction was also reported for monoisocyanates reacting with monoepoxides [9, 10]. The reaction takes place in DMF as a solvent and is catalyzed by tetramethyl-ammonium iodide at 160~ for 6 hr. A recent review of this reaction is worth consulting for additional background material [ 10a]. Since the earlier work by Sandier, Berg, and Kitazawa [9] numerous studies [10b-f] and patents [10g-i] have appeared and a few are cited here. This area continues to be an active area for research and applications. Among catalyst studies [ 10b, c] it has been reported that 2-ethyl-4-methylimdazole (EMI) is preferred since it is soluble in the reaction medium and was very effective. The use of N-methyl-pyrrolidone (NMP) in these studies gave a polyoxazolidones with little or no isocyanurate trimer seen in the infrared spectrum of the product (reaction of MDI with DGEBA using 0.17 EMI at 180-185~ in NMP) [ 10C]. Other studies [ 10d-f] report on numerous other catalysts and in some cases on the use of aliphatic isocyanates. Most of the structural evidence is based on infrared spectral data (IR) and no reports appear using nuclear magnetic resonance (NMR) to confirm structures. These polyoxazolidones represent a new generation of isocyanate derived polymers which have characteristic thermal stability properties. They are useful in adhesives, elastomers, coatings, foams, and electrical applications. Numerous other applications will no doubt be found for them.

138

4. Polymerization Reactions of Mono- and Diisocyanates

4-1. Preparation of the Poly-2-oxazolidone from the Reaction of 2,4-Toluene Diisocyanate and the Diglycidyl Ether of 2,2-Bis(4-hydroxyphenyl)propane [9] CH3

+-

I

CH2 - C H - CH2 - C6I-L- C - C6H4- OCH2CH - CH2

N /

\ /

/

O

CH3 H2-CH

I N

(CH3)4NI

DMF

O

/O-CH2 H3C,~~] O=C, I

CH3,

N - CH- CH20- C6H40- C-I C6FL- OCH2

,

CH3

_

To a flask is added 0.1 mole of 2,4-toluene diisocyanate, 50 ml DMF, and 0.1 mole of the diglycidyl ether of 2,2-bis(4-hydroxyphenyl)propane. Then 0.2 gm tetramethylammonium iodide is added and the reaction mixture heated with stirring for 6 hr to give a 91% yield of the polymer, m.p. range 175~176 IR strong absorptions at 5.65 and 7.10 microns, with no absorption at 4.25-4.60 microns for the free NCO groups. Sandler [11] also reported that poly-2-oxazolidones can be prepared by the reaction oftrimerized isocyanates, i.e., isocyanurates on reaction with diepoxides. A variety ofpoly-2-oxazolidones have been reported (see Table IX). The reactions can be used to cure diisocyanate prepolymers as an alternate cure method to the diamines. Some typical preparations are reported in Table IX. Sandler [ 12] and later Ashida and Frisch [ 13] reported that poly-2-oxazolidones can be converted to polyisocyanurates.

0

POLYMERIZATION OF POLYISOCYANATES TO POLYISOCYANURATES

Hofmann [ 14] in 1858 was the first to report the trimerization of isocyanates to isocyanurates. Hofmann used triethylphosphine as a catalyst to trimerize phenylisocyanate to triphenylisocyanurate. NCO 3

O

C6H5~ N"~ N/C6H5 (C2Hs'3P O~... N ~ O I

C6H5

(9)

TABLE IX

Preparation of Monomeric and Polymeric Substituted 2-Oxazolidones from 1,2-Epoxides and Isocyanates a Reaction conditions

Experiment No.

Epoxide (moles)

Isocyanates (moles)

Catalyst (gm)

Solvent

Time (hr)

Temp (~

2-Oxazolidone

m.p. (~

Yield (%)

Characteristic infrared spectral bands and commentsd

TMAI b 0.2

DMF

6

160

3-Phenyl5-phenoxymethyl

137-8

28

0.10 Phenyl

Pyridine

DMF

6

160

136-7

144

0.10 Phenyl

0.2 ZnBr2

DMF

6

160

136-7

33

Same as above

0.10 Phenyl

0.2 None

DMF

6

160

136-7

15

Same as above

0.10 2,4-Toluenedi-

TMAI

DMF

6

160

0.10

0.20

3-Phenyl5-phenoxymethyl 3-Phenyl5-phenoxymethyl 3-Phenyl5-phenoxymethyl 2,4-di[3-(5phenoxymethyl-2-oxazolidonyl)] toluene

5.60 (w) 5.65 (w) 5.68 (mw) 5.70 (m) 5.72 (m) 5.72 (ms) 5.75 (m) 5.78 (ms) 5.80 (m) 5.81 (ms) 7.08 (s) Same as above

3-Phenoxy1,2-propylene

Phenyl

0.10 3-Phenoxy1,2-propylene 0.10 3-Phenoxy1,2-propylene 0.10 3-Phenoxy1,2-propylene 0.10 2-Phenoxy1,2-propylene

0.20

60-63

78

5.50 (w) 5.57 (m) 5.62-5.72 5.75 (s) 5.90 (m)

5.55 (mw) 5.60 (s) (vs) 5.85 (s) 7.10 (vs)

(continues)

k~

TABLE IX

(continued)

Reaction conditions Experiment No.

Epoxide (moles)

Isocyanates (moles)

Catalyst (gm)

Solvent

Time (hr)

Temp (~

DGBA C

Phenyl

TMAI

DMF

6

160

0.050 DGBA

0.10 2,4-Toluenedi-

0.20 TMAI

None

2

120

0.025

0.50

0.20

DGBA

2,4-Toluenedi0.050 2,4-Toluenedi-

None

None

2

120

TMAI

DMF

20

160

0.050

0.050

0.20

DGBA

1,6-Hexa-

TMAI

0.050

methylenedi0.050

0.20

2-Oxazolidone 2,2-bis(3-phenyl-5phenoxymethyl 2-oxaolidone)propane Polymere (brittle)

0.025 DGBA

Polymer MW

m.p.

Yield

Characteristic infrared spectral bands and comments d

(oc)

(%)

(u)

40

Softens 70-80 m.p. >300

Softens 175-185

93

5.55 5.70 5.77 7.10

(w) (s) (s) (s)

100

5.60 5.68 5.72 5.80 7.10

(w) 5.65 (w) (mw) 5.70 (m) (ms) 5.75 (s) (vs) 5.85 (vs) (vs) No reaction

91

2880

10

DMF

6

160

Polymer gelled

79

5.65 (s) 5.75 (s) 5.85 (s)

5.52 (w) 5.75 (m) 5.60 (ms) 5.63 (ms) 5.65 (vs) 5.84 (ms) 7.10 (vs) (No absorption at 4.25-4.60/t) 5.68 (m) 5.90 (vs) 6.80 (m) 12.0 (m)

8.05 (m) (No absorption at 4.25-4.60/~)

i:l r~

11

DGBA

12

0.050 Epon 828

13

0.050 Epon 828

14

0.050 DGBA

15

0.050 0.050

16

DGBA

17

0.050 DGBA (3.4 g)

Softens 170 190-5

120

Polymer MW g 2870 m.p. Polymer (soft)

6

160

Polymer (hard)

Softens 90-100

None

2

120

Polymer (hard)

0.4 0.4

None

6

160

Polymer (hard)

None

None

6

160

Liquid (viscous)

TMAI

None

2

120

Polymer

4,4'-diphenylmethane-di0.050 2,4-Toluenedi0.050 2,4-Toluenedi0.050 2,4-Toluenedi0.050 0.050

TMAI

None

6

160

0.20 TMAI

None

2

0.4 TMA

None

0.4 TMAI

2,4-Toluenedi0.050 Adiprene L-315f (17.8 g)

(0.06)

100

5.55 (mw) 5.70 (s) 5.80(m) 7.10(s)

100

100

4.38 (m) 5.75 (s) 5.82 (vs) 7.10

100

Softens 170-180 m.p. <300 m

100

5.68 (vs) 5.83 (vs) 7.15 (vs)

100

4.43 (vs) 5.75 (w) 5.77 (m)

Softens 65-70 m.p. <300

100

5.60 (w) 5.63 (w) 5.68 (m) 5.75 (s) 5.80 (s) 5.85 (s)

"Reprinted from S. R. Sandier, J. Polym. Sci., Part A-1 5, 1481 (1967). Copyright 1967 by the Journal of Polymer Science. Reprinted by permission of the copyright owner. b Tetramethylammonium iodide (Eastman Chemical Co.). c Diglycidyl ether of Bisphenol A: (Dow Chemical Co.). d 2-Oxazolidone (Allied Chem. Co.) has a broad maximum between 5.75-5.80/1. e When Epon 828 was used in its place similar results were obtained. This polymer and that from DGBA had residual isocyanate groups because of the stoichiometry of this reaction. This experiment was first performed by Speranza and Peppel. 1~ fPolyurethane prepolymer terminated with free isocyanate groups. NCO = 9.5% (E. I. du Pont de Nemours & Co., Inc.). g The molecular weights were determined at Galbraith Labs in Knoxville, Tenn using vapor-phase osmometry in DMF.

a,

142

4. Polymerization Reactions of Mono- and Diisocyanates

Other trimerization catalysts that have been reported are amines [ 15, 15a], salts of weak acids [ 16], potassium acetate, sodium carbonate [ 17], soluble compounds of K, Mg, Zn, Hg, Cu, Ni, Cr, Sn, A1, V, Ti [18], and epoxides in the presence of tertiary amines [19] such as triethylene diamine-propylene oxide [20]. Sandier [21 ] employed a variety of catalysts including calcium naphthenate, amines, and organometallics. Burkus [22] was one of the first to report the preparation of isocyanuratecontaining urethanes from polyester urethane prepolymers reacted with a triethylamine propylene oxide trimerization catalyst. Burkus [ 15, 15a] also reported the preparation of rigid foamsby a similar trimerization process. More recently Nicholas and Gmitter [23] prepared heat-resistant, rigid polyisocyanurate foams and Sandier [24] reported on a similar process to prepare heatresistant adhesives for aluminum. The trimerization agents reported by Sandier [24] were various metal salts and organometallic compounds such as trin-butylantimony oxide [25] as shown in Table X.

OCN - ~ C H 2 - ~

NCO

O II --CH2

O II N

0 ~C\N/

CH2

I

I C

CH2

%0

CH2--

N

0

~C\

N

/C

I

%0

CH2

I

(10)

Additional references for preparing isocyanurate trimers [26] and polytrimerization [27] of diisocyanates to polyisocyanurates should also be consulted for further examples of this process. More recent reports on the preparation of polyisocyanurates by the trimerization of isocyanates are shown in Table Xa. Frisch, Patel, and Marsh [28] also reported on the preparation of isocyanurateurethane foams and briefly reviewed the early developments in the field of polyisocyanurates. Reymore et al. [29] reviewed the chemistry and processing of isocyanurate foams. These authors also presented a general mechanism for isocyanurate trimerization and suggested an explanation for the role of the catalyst.

143

5. Polymerization of Polyisocyanates to Polyisocyanurates

TABLE X

Trimerization of Phenyl Isocyanate (0.005 M) by Various Catalysts (0.0001 M) a Trimer observed b

Catalyst

23~

50~

Triphenylarsine Bis(tri-n-butylin) oxide Dibutyltin oxide Tricresyl phosphate Antimony chloride Bismuth trioxide Bismuth oxychloride Triphenyltin hydroxide Tributyltin chloride Triethylamine Calcium naphthenate Dibutyltin dilaurate Stannous octoate Aluminum isopropylate Sodium methoxide Calcium oxide Tri-n-butylantimony oxide

N.R. C 24 hr 24 hr N.R. N.R. N.R. N.R. N.R. N.R. N.R. N.R. N.R. 24 hr N.R. 48 hr N.R. 15 min

N.R. 7 hr -N.R. N.R. N.R. N.R. N.R. N.R. N.R. 24 hr 7 hr 5 hr 24 hr

m.p. a (~

275-81

270-75 275-81 275-81 272-78

N.R. 265-75

a Reprinted from S. R. Sandier., J. Appl. Polym. Sci. 11, 811 (1967). Copyright 1967 by the Journal of Applied Polymer Science. Reprinted by permission of the copyright owner. b The times listed are the times for complete solidification of the triphenyl isocyanate. c No reaction. d Literature value for the m.p. of triphenyl isocyanurate is 280~ ~

Isocyanurates are usually more thermally stable than urethanes since they contain no labile hydrogen in the isocyanurate ring system. Hipchen [32a] reported the comparative thermogravimetric analysis of pure polyisocyanurate, pure urethane, and urethane-modified polyisocyanurates. The modified isocyanurate showed a total wt loss at 300~ of 9% versus 25-30% for the urethane and 7% for the pure isocyanurate. The incorporation of polyether groups into the polyisocyanurates gave increasing strength and less brittleness at low temperatures [21 ]. Recently cocatalysts for the polytrimerization of toluene diisocyanate have been reported to be phenols as shown in Table XI Recently Haggis [30] and later Hipchen [31] reported on methods to prepare polyisocyanurate structural laminates. Recent reviews on the subject of isocyanurate foams are worth consulting for additional references [32, 32a].

144

4.

TABLE Xa

Polymerization Reactions o f Mono- and Diisocyanates

Catalysts for the Trimerization of Isocyanates

Catalyst

Isocyanate

Aliphatic amines Oxalic acid Calcium naphthenate Mn naphthenate Zr Octanoate Co Octanoate N-2-hydroxypropyl-N,N,N-tributyl ammonium 2,2-diemthylpentanoate Tetraethylammonium capriate Tetraethylammonium capriate Potassium caprylate Tetiary amines and epoxides 2,4,6-tris(dimethylaminomethyl)phenol Phosphorus triamides

TDI TDI TDI TDI TDI TDI 1,12-dodecamethylenediisocyanate alicyclic types aliphatic types TDI TDI TDI TDI

Reference a a a

a a a

b c d e f

g h

aM. Pavlova and M. Draganova, Polym. Commun. 32, 446 (1991); Chem. Abstr. 115, 233030 (1991). bM. Kise, Y. Kawasaki, and N. Ogoshi, Japanese Patent JP 03244623A2 (1991); Chem. Abstr. 116, 176275 (1991). cY. Asahina, Japanese Patent JP 02107615A2 (1990); Chem. Abstr. 113, 153316 (1990). ay. Asahina and K. Kamiyanagi, Japanese Patent JP 02107615A2 (1990); Chem. Abstr. 113, 79776 (1990). eT. Ota and T. Ogawa, Japanese Patent JP 01272652A2 (1989); Chem. Abstr. 112, 140654 (1989). fK. Hayashi, R. Haseyama, and K. Sasagawa, Japanese Patent JP 63160915A2 (1988); Chem. Abstr. 110, 115513 (1988). g v. G. Golov, T. K. Sorokina, E. S. Barkina, and A. M. Bondarenko, Lakokras. Mater. Ikh Primen. (2), 11 (1988); Chem. Abstr. 108, 223138 (1988). A. M. Fainleib and Y. N. Nizelskii, Ukr. Khim. Zh. 53(8), 877 (1987); Chem. Abstr. 108, 22355 (1987). hN. K. Emel'yanova, M. I. Bakhitov and E. V. Kuznetsov, Vysokomol. Soedin Ser. A 27(7), 1434 (1985); Chem Abstr. 103, 196442 (1985).

Hipchen [32a] also outlined the preparation of urethane-modified isocyanurate foams and gave the following recipe for one giving 19.6% isocyanurate groups: Ingredient

wt%

Crude MDI of eq. wt 134 Hydroxyl component (polyol-derived) from polyether or polyester, eq. wt. 31 Propylene oxide modifier to increase trimer formation Silicone surfactant Refrigerant 11 (CFCL3) Tris(2,4,6-dimethylaminoethylphenol ) N-2-hydroxyethyl aziridine

80.5

The cream time is 18 sec and the firm time is 45 sec.

6.1 1.43 0.86 10.0 0.58 0.58

145

5. Polymerization of Polyisocyanates to Polyisocyanurates TABLE XI Polytrimerization of 80"20 2,4- and 2,6-Toluene Diisocyanatea'b 0.1 Part cocatalyst (25~ None Phenol m-Chlorophenol p-Chlorophenol o-Chlorophenol Hydroquinone

Gelation time (sec) 6,300 30 15 15 30 20

Five parts TDI in 5 parts butyl acetate solvent, 0.05 part by volume of a 10% cellosolve acetate solution containing 0.005 part by wt of trimethylbenzylammonium hydroxide. b Data from Y. M. Hyogo and J. Gotu, U.S. Patent 3,487,080 (1969). a

5-1. Preparation of a Polyisocyanurate Foam from 4, 4 '-Diphen ylmethanediisocyanate [30] To a resin flask are added 30 parts of distilled diisocyanate, 7 parts of ethylene dichloride, 0.2 part siloxane oxyalkylene copolymer, and 0.5 part tris(3-dimethylaminopropyl)hexahydro-s-triazine. The mixture reacts to form a hard, coarse foam of low flammability.

5-2.

Preparation of a Polyisocyanurate from Diisocyanates [21 ] *

a. Polymerization

Sample compositions shown below were heated for 2 hr at 165~ to give a hard, resinous product useful as adhesives for aluminum. Compositions used a.

b.

Catalyst

7 drops 0.5% soln of calcium naphthenate in petroleum ether (Harshaw) 0.05 ml Calcium naphthenate Prepolymer I (0.5 part) solution (see above) diphenylmethane diisocyanate (2.5 part)

Diphenylmethane diisocyanate (1.0 part)

* Prepolymer Preparation reprinted from S. R. Sandier, J. Appl. Polym. Sci. 11, 811 (1967). Copyright 1967 by the Journal of Applied Polymer Science. Reprinted by permission of the copyright owner.

146

4. Polymerization Reactions of Mono- and Diisocyanates

b. Preparation of Prepolymer I A 500-ml resin kettle equipped with stirrer, condenser, thermometer, and a 250-ml dropping funnel was purged with nitrogen for 10 min. Diphenylmethane diisocyanate (Nacconate 300, National Aniline, 0.24 m, 60 mg) and 0.6 ml o-chlorobenzoyl chloride were placed in the kettle and heated with stirring to 45~ Polytetramethylene ether glycol (Quaker Oats PTMEG, MW 1103, 0.12 m, 132 gm) was placed in the funnel and added dropwise during a 2-hr period while the pot temperature was maintained at 50-60~ Stirring was continued for 1 hr after final addition while the pot reached room temperature. Fifty grams of the product and 2.1 gm toluene diisocyanate (Du Pont, Hylene T) were mixed together in an atmosphere of nitrogen for 15 min (% NCO calculated = 7.0).

5-3.

Preparation of a Polyisocyanurate Foam [33]

In a glass vessel 560 gm (4.2 gm equiv) Mondur MR (Mobay), poly(phenyl isocyanate) is mixed with 70 gm CFC13 (isotron 11, Pennwalt) at 15~ In another vessel 42 gm (1.35 equiv) ethylene glycol, 10 gm propylene oxide, and 6 gm Dow Coming DC 193 Silicone surfactant is mixed at 15~ In a third vessel is mixed at 15~ 4 gm tris(2,4,6-dimethylaminoethyl)phenol and N(2hydroxyethyl)aziridine. The contents of the first and second vessels are then thoroughly combined with mixing and then the content of the third vessel is mixed in. An exothermic reaction starts and eventually produces a foam. The cream time is 18 see and the firm or gel time is 45 sec to give a 1.9 lb/ft 3 density foam. The oxygen index of the foam is 24.9. References should be consulted for additional examples of this type of preparation and for details on the properties of the foam.

5-4.

Preparation of a Polyisocyanurate from a TDIModified Polyester [ 15a]

a. Preparation of TDI-Modified Polyester A polyester of MW approximately 2000 having hydroxy end-groups was made by known procedures from the reaction of adipic acid with a mixture of glycols containing a 80:20 wt% ratio of ethylene glycol-propylene glycol. The polyester is then reacted with 2.2 mole TDI to one mole of polyester.

b. Preparation of Polyisocyanurate To a cooled resin flask are added 25.0 gm of the TDI-modified polyester, 1 ml of triethylamine, and 1 ml of propylene oxide. The flask is sealed shut and

6.

147

Miscellaneous Methods

allowed to stand at room temperature for several hours or until solidification takes place. The polyisocyanurate is insoluble in DMF, benzene, and toluene. Burkus [ 15a] found that triethylamine and propylene oxide trimerized phenylisocyanate to yield the crystalline trimer, m.p. 268~ (uncorr). 0.046 mole (5.5 grn) C6Hs--NCO + 0.046 mole (C2Hs)3N + 0.046 mole \ O/

15 ml ether 20 hr room temp ~

CH3

oy .yo

In the absence of propylene oxide only traces of trimer were isolated. However [15] in the presence of N,N'-N"-tris(3-dimethylaminopropyl)symhexahydrotriazine trimerization took place in the absence of propylene oxide.

6.

MISCELLANEOUS METHODS

1. Reaction of diisocyanate with dianhydrides to give polyimides [1, 34]. 2. Polycarbodiimide polyester [35]. 3. Two component catalyst composition for trimerizing isocyanate to isocyanurates [36]. 4. Polyurethane molding compositions containing isocyanurate groups [37]. 5. Polyisocyanurate-poly(propylene sulfide) compositions [38]. 6. Carbodiimide polyurethanes [39]. 7. Urethane-polyisocyanurate foam [40]. 8. Three-part catalyst for trimerizing isocyanates to polyisocyanurates [41 ]. 9. p-Toluenesulfonic acid as an inhibitor for polyisocyanurate formation from TDI [42]. 10. Polyisocyanurate-polycarbodiimide molding compositions [43]. 11. Alkali metal tertiary amines dithiocarbamate salt catalysts for the preparation of polyisocyanurates [44]. 12. Water glass-polyisocyanurate foams [45]. 13. Preparation of polyoxazolidinediones by the reaction of a-hydroxy acids or a-hydroxy acid esters and diisocyanates [46]. 14. Preparation of polyhydrouracils by the reaction of aromatic diisocyanates with N,N'-bis(2-carbomethoxyethyl)-l,6-hexanediamine in chloroformDMF solution followed by cyclization with polyphosphoric acid [47].

148

4. Polymerization Reactions of Mono- and Diisocyanates

15. Preparation of polybenzoxyazinediones by reaction of di-o-hydroxy dicarboxylates with diisocyanates in DMSO in the presence of tertiary amine catalysts [48]. 16. Preparation of polyquinazolinediones by the reaction of diisocyanates with bisanthranilic acids and subsequent cyclization of the poly(urea acids) [49]. 17. Crosslinked polycarbodiimide by the polymerization of hexanethylene diisocyanate and poly(phenylenemethane carbodiimide) [50]. 18. Reaction of polycarbodiimides with terminal isocyanate groups with saturated or unsaturated monomers having active hydrogens [51 ]. 19. Low temperature plasma polymerization of toluene diisocyanates [52]. 20. Surface active polycarbodiimides [53]. 21. Cationic polymerization of aromatic isocyanates and their copolymerization with unsaturated monomers [54]. 22. Polycatenanes based on diisocyanates [55]. 23. Ruthenium catalyzed spirocyclization of isocyanates [56]. 24. Interaction of oligocarbodiimides with oligoepoxides [57]. 25. Novel polyether-urethane ureas--chain extension with tertiary alcohols

[58].

References 1. 2. 2a. 2b. 3. 3a. 3b. 3c. 3d. 3e. 3f. 3g. 3h. 3i. 3j. 3k. 31.

A.J. Bur and L. J. Fetters, Chem. Rev. 76, 727 (1976). S . R . Sandler and W. Karo, "Polymer Syntheses," Vol. 1. Academic Press, New York, 1974. H. Ulrich, J. Polym. Sci., Macromol. Rev. 11, 93 (1976). S. C. Graham, X. Xu, L. Jones, and M. Orticochea, J. Polym. Sci. Part A Polym. Chem. 28, 1179 (1990). V.E. Shashona, W. Sweeney, and R. F. Tietz, J. Am. Chem. Soc. 82, 866 (1960). V. E. Shashona, Macromol. Synth. 1, 63 (1963). Y. Iwakura, K. Uno, and K. Ichikawa, J. Polym. Sci., Part A-1 2, 3387 (1964); 6, 793, 1087, and 2611 (1968). C. King, J. Am. Chem. Soc. 86, 437 (1963); W. L. Miller and W. B. Black, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem. 3(2), 345 (1962). R. G. Beaman, U.S. Patent 3,048,566 (1962). M. Goodman and S. Chen, Macromelecules 3, 398 (1970). S.A. Ahoroni, Macromolecules 12, 94 (1979). T. E. Patten and B. M. Novak, J. Am. Chem. Soc. 113, 5065 (1991). T. E. Patten and B. M. Novak, Macromolecules 26, 436 (1993). A.J. Bur and L. J. Fetters, Chem. Rev. 76, 727 (1976). K. Liou, K. C. Khemani, and F. Wyndl, Macromolecules 24(9), 2217 (1991). Y. Okamoto, M. Matsuda, T. Nakano, and E. Yashima, Polym. Sci., Part A Polym. Chem. 32(2), 309 (1994). J.J. Kozukiewicz, Polym. Prepr. 26(1), 114 (1985); B. Duroiraj, E. T. Samulski, and M. T. Shaw, Macromolecules 23(5), 1229 (1990), and references therin to Aharoni and co-workers (1979-1980).

References

14 9

3m. J. J. Kozakiewicz, Macromolecules 19, 1262 (1986). 4. T.W. Campbell, U.S. Patent 2,941,966 (1960); T. W. Campbell and J. J. Verbanc, U.S. Patent 2,853,473 (1958). 5. T.W. Campbell and K. C. Smeltz, J. Org. Chem. 27, 2069 (1963); T. W. Campbell, J. J. Monagle, and V. S. Foldi, J. Am. Chem. Soc. 84, 3673 (1962). 5a. W. B. McCormack, Org. Synth., Collect. Vol. 5, 787 (1973). 6. P. Fischer, W. Kallert, H. Holtschmidt, and E. Meisert, German Patent 1,145,353 (1963); A. Reischl, H. Holtschmidt, and P. Fischer, German Patent 1,143,018 (1963); General Tire & Rubber, British Patent 1,332,607 (1973). 7. H. None, R. Platz, and E. Wegner, Belgian Patent 657,835 (1964); P. Kan, C. Moses, and T. Narayan, U.S. Patent 3,772,217 (1973). 7a. K. Saito, S. Amano, and Y. Imashiro, Japanese Patent JP04268343A2 (1992); Chem. Abstr. 118, 193226 (1993). 7b. K. Saito and T. Ishimatsu, European Patent Application EP 573915A1 (1993); Chem. Abstr. 120, 336841 (1994). 7c. F. Ichikawa, H. Takayonagi, and H. Nakamo, Japanese Patent JP06016829A2 (1994); Chem. Abstr. 121, 59330 (1994). 8. L.M. Alberino, W. J. Farrissey, Jr., and A. A. R. Sayigh, J. Appl. Polym. Sci. 21, 1999 (1977). 8a. R. J. Cotter and M. Matzner, "Ring-Forming Polymerizations," Part B, Vol. 1, pp. 14, 18, and 71-76. Academic Press, New York, 1972. 8b. C. Brown, R. F. Hudson, V. T. Rice, and A. R. Thompson, Chem. Commun. p. 1255 (1971). 9. S.R. Sandier, F. Berg, and G. Kitazawa, J. AppL Polym. Sci. 9, 1994 (1965). 10. B.F. Speranza and W. J. Peppel, J. Org. Chem. 23, 1922 (1958). 10a. R. J. Cotter and M. Matzner, "Ring-Forming Polymerizations," Part B, Vol. 1, pp. 194 and 262-275. Academic Press, New York, 1972. 10b. J. S. Senger, I. Yilgor, J. E. McGrath, and R. A. Patsiga, Am. Chem. Soc. Polym. Prepr. 26(1), 244 (1985). 10c. J. S. Senger, I. Yilgor, J. E. McGrath, and R. A. Patsiga, J. Appl. Polym. Sci. 38, 373 (1989). 10d. A. Sendijarevic, V. Sendijarevic, and K. C. Frisch, J. Polym. Sci. Part A Polym. Chem. 25, 151 (1987). 10e. H. Sehovic, A. Sendijarevic, V. Sendijarevic, and K. C. Frisch, J. Polym. Sci. Part A Polym. Chem. 25, 2729 (1987). 10f. A. Sendijarevic, V. Sendijarevic, K. C. Frisch, M. Maljanovic, and H. Sehovic, J. Polym. Sci. Part C Polym. Lett. 28, 119 (1990). 10g. S. Fuzesi and R. W. Brown, U.S. Patent 4,699,931 (1987). 10h. T. O. Murdock and B. W. Carlson, WO Patent 9,211,304A (1992); Chem. Abstr. 118, 82058 (1992). 10i. R.A. Koenig and J. Gen, WO Patent 90150089 (1990); Chem. Abstr. 115, 72937 (1990). 11. S.R. Sandier, J. Polym. Sci., Part A-1 5, 1481 (1967). 12. S.R. Sandier, J. Appl. Polym. Sci. 11, 811 (1967). 13. K. Ashida and K. C. Frisch, J. Cell. Plast. 8, 194 (1972). 14. A.W. Hofmann, Jahresber. Fortschr. Agrikulturchem. 1, 349 (1858). 15. J. Burkus, U.S. Patent 2,993,870 (1961). 15a. J. Burkus, U.S. Patent 2,979,485 (1961). 16. W. Frentzel, Ber. Dtsch. Chem. Ges. 21, 411 (1888). 17. A.W. Hofmann, Ber. Dtsch. Chem. Ges. 18, 764 (1885). 18. H. Havekoss, "Polymerization of Diisocyanates," O.P.B. Rep. 73894. France, 1942.

150

19.

4.

Polymerization Reactions of Mono- and Diisocyanates

I.I. Jones and N. G. Savill, J. Chem. Soc. p. 4392 (1957); E. K. Moss, U.S. Patent 3,799,896 (1974). 20. B.D. Beitchman, Rubber Age 98, No. 2, 65 (1966). 21. S.R. Sandler, J. Appl. Polym. Sci. 11, 811 (1967). 22. J. Burkus, U.S. Patent 2,979,485 (1961). 23. L. Nicholas and G. T. Gmitter, J. Cell. Plast. 1, 85 (1965). 24. S.R. Sandier, J. Polym. Sci. 5, 1482 (1967); S. R. Sandier, F. Berg, and G. Kitazawa, J. Appl. Polym. Sci. 9, 1994 (1965). 25. S. Herbstman, J. Org. Chem. 30, 1259 (1965). 26. A.G. Davies, U.S. Patents 3,396,167(1968); 3,450,701 (1969). 27. Y.M. Hyogo and J. Goto, U.S. Patent 3,487,080 (1969); D. L. Bernard, J. K. Backus, and W. C. Darr, U.S. Patent 3,644,232 (1972). 28. K.C. Frisch, K. J. Patel, and R. D. Marsh, J. Cell. Plast. 6, 203 (1970). 29. H.E. Reymore, Jr., P. S. Carleton, R. A. Kolakowski, and A. A. R. Sayigh, 3". Cell. Plast. 11, 328 (1975). 30. G.A. Haggis, U.S. Patent 3,516,950 (1970). 31. A. DeLeon, D. E. Hipchen, and M. J. Skowronski, U.S. Patent 3,903,346 (1975). 32. K . C . Frisch and J. E. Kresta, in "International Progress in Urethanes" (K. C. Frisch and A. Hernandez, eds.), Vol. 1, pp. 191-232. Technonic Pub. Co., Inc., Westport, Connecticut, 1977. 32a. D. E. Hipchen, Proc. SPI Int. Cell. Plast. Conf., 4th, 1976, pp. 23-29 (1976). 33. E.K. Moss, U.S. Patent 3,799,896 (1974). 34. V.B.K. Kaisha, British Patent 1,155,768 (1969); R. L. Grieve, Belgian Patent 745,003 (1969); D. L. Bernard and A. J. Dobeny, Belgian Patent 723,151 (1967); B. A. Bolton, U.S. Patent 3,592,789 (1971). 35. F.M. Berardinelli and R. Edelman, Ger. Often. 2,642,513 (1977); Chem. Abstr. 86, 19091t (1977). 36. M. and T. Chemicals, Inc., Ger. Often. 2,641,734 (1977). 37. G. Behrendt and D. Joel, German Patent (East) 122,182 (1976). 38. Z.D. Chemova, K. Kalmins, and G. A. Belonovskaya, Vysokomol. Soedin., Ser. B 19(1), 61 (1977). 39. S . N . Starosol'skaya, E. N. Sotnikova, N. I. Mysin, and Y. I. Dergunov, Sint. Svoistva Uretanovykh Elastomerov, pp. 102-105 and 176-179 (1976). 40. G. Falkenstein, G. Fahrbach, and H. Wulff, Ger. Often. 2,525,017 (1976). 41. H.E. Reymore, Jr. and J. K. Zano, U.S. Patent 4,003,859 (1977). 42. S. Nagahisa, Y. Tajima, and T. Kawabata, Japan Kokai 77/14,692 (1977). 43. G. Behrendt and D. Joel, German Patent (East) 121,460 (1976); G. Behrendt, German Patent (East) 121,461 (1976). 44. R.L. Zimmerman, T. H. Austin, and H. Schulze, U.S. Patent 4,009,130 (1977). 45. K.H. Hilterhaus and F. G. Teuter, Ger. Offen. 2,528,215 (1977). 46. R. Merton, Angew. Chem. 83, 339 (1971). 47. E. Dyer and J. Hartzler, J. Polym. Sci., Part A 17, 833 (1969). 48. R.J. Angelo, U.S. Patent 3,244,675 (1966); L. Bottenbruch, Angew. Chem. 81, 911 (1969); Angew. Makromol. Chem. 13, 109 (1970). 49. N. Yoda, R. Nakanishi, M. Kurihara, Y. Bamba, S. Tohyama, and K. Ikeda, J. Polym. Sci., Part B 4, 11 (1966). 50. Y. Lipatov andY. Nizek'sky, NewJ. Chem. 17(10-11), 715(1993); Chem. Abstr. 1211, 108641 (1993). 51. H. Nava, R. D. Lake, and R. B. Makepeace, U.S. Patent 5,115,072 (1992).

References 52. 53. 54. 55. 56. 57. 58.

151

S. Cai, X. Yu, and J. Fang, Yingyong Huaxue 4(6), 76 (1987); Chem. Abstr. 108, 95040 (1987). J.W. Taylor, European Patent EP 241805A2 (1987); Chem. Abstr. 108, 133501 (1987). V. G. Matyushova, T. E. Lipatova, Y. S. Lipatov, T. S. Kramova, and T. D. Ignatova, Vysokomol. Soedin. Ser. A 31(9), 1938 (1989); Chem. Abstr. 112, 99285 (1989). Y. LipatovandY. Nizel'sky, NewJ. Chem. 17(10-11), 715(1993); Chem. Abstr. 120, 108641 (1993). G. Herrmann and G. Suess-Fink, Chem. Ber. 118(10), 3959 (1985); Chem. Abstr. 104, 129867 (1985). V.A. Pankratov, T. M. Frenkel, A. M. Fainleib, and V. V. Korshak, in "Crosslinked Epoxies," Proc. Discuss. Conf. 9th Meeting, 1986, pp. 41-46; Chem. Abstr. 107, 116072 (1987). B. Lee, J. E. McGrath, G. L. Wilkes, and D. Tyagi, in "Sagamore Army Mater. Res. Conf. Proc., 1985," 1-28; Chem. Abstr. 107, 116709 (1987).

Chapter 5

Polyoxyalkylation of Hydroxy Compounds 1. I n t r o d u c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.

3.

158

2-1. 2-2. 2-3. 2-4. 2-5. 2-6. 2- 7. 2-8. 2-9. 2-10. 2-11. 2-12. 2-13.

159

Polyoxypropylation of Methanol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preparation of Ethyleneglycol Monoethyl Ether . . . . . . . . . . . . . . . . . . . . . . . . . Polyoxyethylation of 2-Butyl-l-octanol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polyoxyethylation of Clo-C13 Straight-Chain, Secondary Alcohols . . . . . . . . . . . . Preparation of the Triethylene Glycol of 2,6,8-Trimethyl-4-nonanol . . . . . . . . . . . Polyoxypropylation and Polyoxyethylation of 2, 6,8-Trimethyl-8-nonanol . . . . . . . . Polyoxyethylation of 2-Methyl- 7-ethyl-4-undecanol . . . . . . . . . . . . . . . . . . . . . . . Polyoxyethylation of tert-Butyl Alcohol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preparation of Polyoxypropylated Stearyl Alcohol . . . . . . . . . . . . . . . . . . . . . . . Polyoxyethylation of n-Octanol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preparation of Polyoxypropylene Glycol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preparation of Polyoxyethylene Glycol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reaction of Dipropylene Glycol with Propylene Oxide . . . . . . . . . . . . . . . . . . . .

Polyoxyalkylation of Polyhydroxy Compounds

3-1. 3-2. 3-3. 3-4. 3-5. 3-6. 3-7. 3-8. 4.

153

Polyoxyalkylation of Alcohols and Diols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

..............................

Polyoxypropylation of Sucrose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polyoxypropylation of Sucrose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polyoxyethylation of Sorbitol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polyoxyethylation of Sorbitol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polyoxypropylation of Trimethylolethane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polyoxypropylation of Pentaerythritol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preparation of Polyoxyethylated Pentaerythritol . . . . . . . . . . . . . . . . . . . . . . . . . Reaction of 2,4,4,4-Tetrachlorobutylglycidyl Ether with Glycerol . . . . . . . . . . . . .

162 162 163 163 164 164 165 165 166 166 166 167 169 170

171 172 172 172 173 173 174

Polyoxyalkylation of Phenols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

174

4-1. 4-2. 4-3.

175 176

152

Preparation of Polyoxypropylenephenol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preparation of Polyoxyethylene Nonylphenol . . . . . . . . . . . . . . . . . . . . . . . . . . . Preparation of Polyoxypropylene Nonylphenol . . . . . . . . . . . . . . . . . . . . . . . . . .

175

1.

Introduction

4-4. Polyoxypropylation of p-tert-Butylphenol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. M i s c e l l a n e o u s P o l y o x y a l k y l a t i o n P r e p a r a t i o n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References ........................................................

1.

153 177 178 179

INTRODUCTION

The purpose of this chapter is to describe the polyoxyalkylation of various alcohols and phenols. These compositions are used as polyurethane starting materials (polyols), as surfactants, and as textile aids. The polymerization of various oxiranes to give polyoxyalkylenes has been described in Volume 1 and is not the subject of this chapter.

a. Safety Precautions

Ethylene oxide is a low boiling, flammable liquid, whose vapors easily form explosive mixtures in air [1]. It is to be labeled as a cancer hazard and a reproductive hazard [2]. It is prudent to handle propylene oxide and other threemembered ring organic oxides with safety precautions similar to those used for ethylene oxide. The permissible 8 hr time weighted average exposure limit is 1 part per million parts of air [3]. Even at concentrations as "high" as 50 ppm, full-face respirators with EO-approved canister are required [4]. Work should be carried out in well-ventilated hood areas behind safety shields. Full protection against explosive hazard associated with this compound is not achieved by this. It also should be kept in mind that the density of ethylene oxide is greater than that of air and therefore, may not necessarily be carried up and out of the hood. Also, the problem of air pollution downwind from the hood's vent needs to be addressed. Special precautions must also be taken for the problems that may arise should there be a release of high levels of ethylene oxide as a result of an explosion. Since ethylene oxide is flammable, care must be used in handling it near heating mantles. Reactions that may be carried out under pressure require additional safety precautions. Several companies have published descriptive bulletins for the safe handling of ethylene oxide, propylene oxide, and butylene oxide. Typical glassware and technical reviews are given in [5, 6]. Some physical properties of ethylene and propylene oxides are given in Table I. Despite its widespread use in consumer products, ethylene glycol, which is formed from ethylene oxide, is considered to be toxic. On the other hand, propylene glycol derivatives are thought to be of low or no toxicity.

154

S. Polyoxyalkylation of Hydroxy Compounds

TABLE I Physical Properties of Ethylene and Propylene Oxides Property MW b.p. (~ at 60 mm Hg) Vapour pressure (mm Hg at 25~ Freezing point (~ Specific gravity Explosive limits (%, by volume in air) Auto ignition temp (~ in air at 1 atm)

Ethylene oxide Propyleneoxide 44.05 10.4 1292 - 112.5 0.896 3-100 804

58.08 34.2 569 - 112 0.826 3.1-27.5 869

The physiological properties of polymers of ethylene oxide or propylene oxide or their derivatives are not well known. Presumably their solvent and/or surfactant properties may lead to unanticipated effects. For example, a compound of one mole of nonylphenol that has been reacted with nine moles of ethylene oxide is a human spermicide used in certain contraceptives ("Nonaxanol"). Under other trade names, this compound finds application as a nonionic surfactant. Its analogue with 10 ethylene oxide units is the well-known "Triton X-100." The use of a dry-ice condenser is essential when setting up glassware for nonpressure-type reactions with ethylene oxide. The slow addition of ethylene oxide is controlled by monitoring the reflux in the dry-ice condenser. Small laboratory cylinders of ethylene oxide are available and addition may be controlled by means of a needle valve. With propylene oxide an ordinary watercooled condenser may be used and addition may be made from a glass dropping funnel. The disadvantage of this technique is that only low concentrations of the oxide can be maintained in the reaction zone and thus the rate may be too low to be practical. Sealed autoclaves or bombs capable of withstanding pressure greater than 1 atm can also be used. In this case, the reactants, catalyst, and solvent are added to the bomb. The reactor is heated to the desired temperature and the alkylene oxide is metered in to maintain a pressure of approximately 10-15 psig. As the alkylene oxide reacts, the pressure drops and then additional alkylene oxide can be added from a steel cylinder connected by flexible tubing to the bomb with appropriate valving. The bomb can either be heated or cooled as desired and agitation may be provided by either a rocking mechanism or a sealed mechanical stirrer.

b. Chemistry In general, most active hydrogen-containing compounds can be made to react with ethylene oxide (or propylene oxide) to give hydroxyethyl (or propyl)

1.

Introduction

155

derivatives and on further reaction to give substituted polyoxyalkylene ethers as described in Eq. (1). R

RZH + ~ 0 /

R'

t

I RZCH2--CH--OH

(

R' )

~--/---R' I o } RZ CH2--CH--O ,,H

(1)

where Z = O [7], S [8], COO [9], NH [10]; R' = H or CH3; R = alkyl [11], aryl [11], H [12]. As a result of this reaction a mixture (n = 1-100) of polyglycol ethers may be obtained. The oxyalkylation reaction can be catalyzed by either acids or bases. Some common catalysts are alkali and alkaline earth oxides, hydroxides and alkoxides, amines, tertiary amines, sodamide, zinc oxide, boron trifluoride, stannic chloride, and sulfuric acid. The reactions can be carried out at atmospheric pressure or at 10-50 psig in order to shorten reaction times. The usual temperatures employed are 100~176 for base-catalyzed reactions and 50~176 when Lewis acids are used. The reaction is exothermic involving about 20 kcal/mole of ethylene oxide reacted, therefore adequate cooling capacity is essential to maintain reproducible (not runaway) reactions. At the end of the reaction the catalyst is neutralized and the product is isolated. The reactivity of alcohols and phenols with ethylene oxide varies in the order primary > alkyl phenol > secondary >> tertiary [ 13]. However, tertiary alcohols can be made to react with ethylene oxide [ 14]. Some linear secondary alcohols have been reacted with ethylene oxide to give nonionic surfactants (Union Carbide) [15]. Some typical alcohols used to give the nonionic surfactants (polyoxyethylenealkyl ethanols) are allyl, lauryl, cetyl, stearyl, tridecyl, myristyl, C~2-C15 primary linear, tallow, and trimethylnonyl [16]. Propylene oxide reacts with water using basic catalysts to give polyoxypropylene glycols [ 17]. In the case of primary and secondary aliphatic alcohols propylene oxide reacts to give monoalkyl ethers of polyoxypropylene glycol [18]. Propylene glycol reacts with propylene oxide to give polyoxypropylene glycol as reported by Lundsted [19]. The use of triols give polyoxypropylene triols and pentaerythritol gives polyoxypropylene tetrols [20]. In a similar manner sucrose [19, 21] may be reacted with propylene oxide to give polyoxypropyl derivatives of sucrose. These liquid polyoxyalkylated alcohols are widely used as starting materials for the preparation of polyurethane foams and elastomers. For example, polypropylene polyols having two to three hydroxy groups are useful for flexible polyurethanes and those having four or more hydroxyl groups are used in rigid polyurethane foams.

156

5.

Polyoxyalkylationof Hydroxy Compounds

A special group of polyoxyalkylene ethers are used as nonionic surfactants. These surfactants were introduced around 1940 and are made up of a hydrophobic end and hydrophilic end (polyoxyalkylene ether) comprising about 60-75 wt% of the molecule [approximately 1CH2CH20 unit for 1CH2 group]. Particularly interesting block-copolymers are available commercially from the reactions of ethylene oxide (monomer or polymers) with propylene oxide (monomer or polymers) or of 1,2-diaminoethane with ethylene oxide and/or propylene oxide. The series of surfactants in which a central polypropylene oxide is attached to polyethylene oxide polymeric chains are called Pluronic; the series with a central polyethylene oxide surrounded by polypropylene oxides are called Pluronic R. Products of diaminoethane reacted first with propylene oxide and terminated with ethylene oxide polymers are Tetronics. In the Tetronic R series the arrangement of the oxides is reversed--the four terminal groups are polypropylene oxides while polymeric ethylene oxides are used to replace the four reactive hydrogens of 1,2-diaminoethane. The ethylene oxide portions of the products confer hydrophilic characteristics on the molecules, the propylene oxide units are considered hydrophobic. By control of the molecular weights of the polymeric oxides, liquids, semisolids, and powders are formed. By the use of appropriate proportions of oxides, products with a wide range of application are available. Among these are uses that require defoaming/antifoaming properties. There are applications in cleaning; formation of foams, emulsions, and gels; solubilization; lubrication; wetting; thickening; and controlled dissolution [22]. In addition, phenols and naphthols are oxyalkylated to give products with varying units of either ethylene oxide or propylene oxide. The compositions are commercially available as nonionic detergents. An interesting property of dodecylphenol condensed with 6 moles of ethylene oxide is that it has a negative temperature coefficient of solubility in water, i.e., becomes less soluble at higher temperatures. Several reviews are worth consulting for additional information on the various aspects of the preparation and uses of polyoxyalkylene compounds [23]. Most preparative information is found in the patent literature. The products resulting from the reaction of ethylene oxide with water or alcohols (or diols, etc.) are variously called poly(ethylene oxide) resins, poly(ethylene glycols), polyoxyethylene resins, PEOs, PEGs. The reaction products involving propylene oxide are the higher homologues known as poly(propylene oxide)resins, etc. The very high molecular weights PEGs have been called "POLYOX." The reaction products of mono-hydroxyalcohols are really tx-alkoxypoly(ethylene oxides); however, we are treating all of these various products as one general class from the preparative standpoint. With ordinary reaction catalysts such as conventional acids or bases, the products of the alkoxylation reactions are mixtures with a considerable range of

1.

157

Introduction

molecular weights. By the appropriate adjustment of reactant ratios and reaction conditions, some control over the molecular weight of these products may be exercised. By this method, molecular weights from approximately 200 to 20,000 are obtained. By use of coordinate anionic initiator systems such as some involving ferric chloride, for example, high molecular weights from about 100,000 to 4,000,000 have been obtained. Since iron salts may be present in the pressure equipment used in handling ethylene oxide, it is not surprising that high molecular weight residues are frequently detected. With fluorinated Lewis acids, such as boron trifluoride, crown ethers rather than linear polymers may be formed [24]. On some catalyst surfaces, such as solid potassium hydroxide or alkaline earth compounds, PEGs or PPGs form. Since the molecular weight of the products from these reactions do not increase with conversion, it has been postulated that here we are dealing with a chain reaction rather than a polycondensation [25]. The determination of the molecular weights of the PEGs and PPGs is complex. First of all, these products are hygroscopic to some extent. They probably also form complexes with alcohols and/or glycols from the synthetic procedures used. Many salts are soluble in the PEGs and may also form complexes. The high molecular weight products form stringy solutions even at fairly low concentrations. Some solutions are reputed to "creep" out of the beaker in which they have been prepared. There are also problems of oxidative and shear degradation that contribute to difficulties in these determinations. Even so, intrinsic viscosity measurements have been used to determine molecular weights. A possible solvent for these may be benzene. For such systems, the constants relating intrinsic viscosity, [/~], to molecular weight in the Mark-Houwink equation [/2] = k(Mol.Wt) a are at 25~ K = 39.7 x 10-5,

a = 0.686

at 30~ K = 61.4 X 10- 5,

a = 0.64

[26].

Other methods of determining the molecular weights of these compounds include freezing point depression measurements in acetophenone [27]: vaporpressure osmometry along with end group analysis (OH groups using their cerium(IV) complexes), light-scattering, and sedimentation equilibria [28]; infrared spectroscopy in carbon tetrachloride [29]; refractive index measurements [30]; reversed-phase HPLC [31, 32]; and supercritical fluid chromatography [33, 34]. The heterogeneity of poly(oxyethylenes) has been examined using light diffusion. In this connection it was found that microcrystals formed when the solutions were passed through fine filter paper. This interfered with the determination of molecular weight distributions. The aggregates could be

5o Polyoxyalkylationof Hydroxy Compounds

158

separated if the objective was the determination of the high molecular weight fractions of the material [35].

0

POLYOXYALKYLATION OF ALCOHOLS AND DIOLS

Mono- and dihydroxy compounds can be polyoxyalkylated with either ethylene oxide, propylene oxide, ethylene carbonate, or propylene carbonate. Emphasis will be placed on the use of ethylene oxide and propylene oxide. R'

R O H + \0 /

R,

v

0

ROCH2CH-- OH

II

..C..

(

, RO\CH2CH--

o)

nH

J R'

(2)

In most cases the reaction rate is increased by the use of an acidic or basic catalyst. The advantage of alkylene carbonates is that the reaction can be run at atmospheric pressure. In general, alcohols are reported to react faster than phenols and these in turn are reported to react faster than carboxylic acids [36]. Polymerization continues until all the ethylene oxide is reacted. The effectiveness of the catalyst is proportional to its basicity. In most cases 0.005-0.05 mole base (KOH, NaOH, or NaOCH3) per mole of alcohol is used at temperatures varying from 100 ~ to 200~ In the absence of basic catalyst and in the presence of anhydrous excess alcohol the mono adducts are obtained in good yields [37, 38]. For example, ethanol is reacted with ethylene oxide to give ethylene glycol monoethyl ether [37, 38]. The mono adducts are also obtained by the use of acid catalysts such as BF3 etherate in the addition of ethylene oxide to primary, secondary, and tertiary alcohols [39]. Some typical examples are described in Table II. A large variety of catalyst systems for the polymerization of alkylene oxides have been described. Mention has already been made of the use of acids and bases and examples are to be found below. Metal alkyls, particularly when used in binary systems, lead to high molecular weights and high conversions. While alumina or compositions of alumina and silica have been used, binary compositions of such compounds as diethylzinc, diethylcadmium, triethylaluminum, and butyllithium lead to higher molecular weight polymers at higher conversions [40].

159

2, Polyoxyalkylation of Alcohols and Diols

Solutions of tris(acetylacetonato)zirconium chloride, bis(acetylacetonato)zirconium dichloride, tetrakis(acetylacetonato)zirconium, zirconium tetraacetate, or zirconium tetranitrate, all reduced with triethylaluminum in hexamethylphosphoramide, are said to lead to high molecular weight products [41]. Unfortunately, the solvent is no longer available because of its carcinogenicity. Perhaps such alternate solvents as formamide, dimethylformamide, dimethylsulfoxide, and acetonitrile should be investigated. The initiation of the polymerization of alkylene oxides with iron has been known for some time. A recent patent extends this concept to the alkoxylation of many active hydrogen compounds. The catalyst for this process is a polycrystalline iron oxide (a-iron(III)oxide). For example, in an autoclave, under nitrogen, n-decanol and 2 wt% of the iron catalyst are treated with ethylene oxide at a pressure of less than 6 bars for 4 hr. The resulting liquid had a degree of polymerization of 5 [42]. An extraordinary patented process deals with the polyoxyethylation of esters of fatty acids. In the resulting product, several ethylene oxide units are inserted between the carboxylic acid moiety and the original alkyl group. In effect, the product is a polyoxyalkylene ether ester of the carboxylic acid. The catalyst system consists of magnesium oxide treated with one or more ions selected from metals such as aluminum, gallium, indium, thalium, cobalt, scandium, lanthanum, or manganese. In one example, a mixture of 750 g of methyl laurate was treated with 22.5 g of magnesium oxide containing aluminum(III) ions in an autoclave with 772 g of ethylene oxide at 160 ~ and a pressure of 3 atmospheres for 1 hr. The average composition of the product may be represented by

Cll H23C(O)O(C2H4O)nCH3, where n ~ 5 [43]. With boron trifluoride etherate as catalyst, the reaction of ethylene oxide with diethyl phosphate may produce products with a degree of polymerization in the range of 50 to 60 ethylene oxide units. With chloroacetic acid, the product contained between 65 and 85 ethylene oxide units [44].

2-1.

Polyoxypropylation of Methanol [5] CH3

I CH3OH + CH2--CH \ / O

cn3 CH30--CH2CH-- O - - ) l l H

(3)

To a 2-gal stainless steel autoclave, which is equipped with a stirrer, thermocouple, pressure gauge, and reactant inlet tube with its outlet under the stirrer, are added 96 gm (3.0 mole) of methanol and 12.0 gm (0.30 mole) of sodium

TABLE II

Polyoxyalkylation of Alcohols and Diols Reaction Conditions

Alcohol

Oxylkylating agent

CH3OH

Propylene oxide

C2HsOH

Ethylene oxide

C3H7OH

Ethylene oxide or Propylene oxide Cyclohexane oxide Ethylene oxide

CaH9OH HOCH2CH2OH (HOCH2CH2)20 HOCH2CH2OH CH3 I (HOCH2CH -- )20 C4H9OH t-Butyl alcohol Lauryl alcohol C12C14 Alcohol (MW 200) 2,6,8-tri-methyl-4-nonanol 2-Butyl- 1-octanol 2-Butyl- 1-octanol 2 -Methyl -7 -ethyl-4-undecanol 5-Ethyl-2-nonanol

Ethylene oxide Ethylene oxide or Propylene oxide Propylene oxide Ethylene oxide Ethylene oxide Ethylene oxide Ethylene oxide Ethylene oxide Ethylene oxide Ethylene oxide Ethylene oxide Ethylene oxide

Solvent

H20 H20

Temp (~

pressure (lb/in 2)

NaOH or Hexamethylenetetramine None or Hexamethylenetetramine NaOH

100--400

85-100

100-300

100-600

NaOH KOH (or Na2CO3 or NaOH) NaOH NaOH

135-185 150-160

35-40

150-160 50-135

35-40 1-90

NaOH NaOH Tropylium Fluoroborate NaOH BF3 KOH KOH BF3 BF3 KOH

140-150

60

151 75-83 135-150 70 130-150 120-150 10-50 10-50 155-160

atm 50 5 kg/cm 2 atm atm atm atm

Catalyst

50-140 .

Yield

(%)

Ref.

70

60-90

a,

w

N

m

c

C 12H15OH Sec Alcohols

2-n-Propylheptanol 7-Ethyl-2-methyl-4-undecanol

Ethylene Ethylene Ethylene Ethylene

oxide oxide oxide oxide

KOH NaOH KOH KOH

160 100-180 150-160 120-150

---

l m n o, p

aD. R. Jackson and L. G. Lundsted, U.S. Patent 2,677,700 (1954); H. M. Stanley, T. Eaglesfield, and P. Eaglesfield, U.S. Patent 2,276,597 (1942). b C. O. Young, U.S. Patent 1,696,874 (1928); G. Cocuzza, B. Calcagno, and G. Torreggiani, U.S. Patent 3,935,279 (1976); H. M. Stanley, T. Eaglesfield, and P. Eaglesfield, U.S. Patent 2,276,597 (1942). c j. T. Patton, Jr., U.S. Patent 3,101,374 (1963). a W. P. Krause, U.S. Patent 2,983,763 (1961). eF. H. Roberts and H. R. Fife, U.S. Patent 2,425,755 (1947). fW. Umbach and W. Stein, U.S. Patent 3,651,152 (1972). g J. T. Patton, Jr. and W. T. Schulz, U.S. Patent 3,190,927 (1965); N. Kuratu, K. Koshida, T. Fujii, K. Matsuhiro, and Y. Okuda, U.S. Patent 3,959,389 (1976). hM. Kosmin, U.S. Patent 2,671,116 (1954); C. A. Carter, U.S. Patent 2,870,220 (1959). ;M. Kosmin, U.S. Patent 2,671,115 (1954). J C. A. Carter, U.S. Patent 2,870,220 (1959). kM. Kosmin, U.S. Patent 2,508,035 (1950). CH3(CH2)2-- CH2-- CH-- (CH2)2-- CH-- CH3 I I C2H5 OC2H4(OC2H4)3C2H4OH t C. Schoeller and J. Nuesslein, U.S. Patent 2,133,480 (1938). inF. Schlegel, U.S. Patent 2,355,823 (1944); J. R. Riddle, U.S. Patent 4,064,182 (1972). n M. Kosmin, U.S. Patent 2,508,036 (1950).

~ Kosmin, U.S. Patent 2,617,830 (1952). P Pentaethylene glycol deriv.

CH3(CH2)4-- CH-- CH20(CHzCH20) 1oH I C3H7

162

Polyoxyalkylation of Hydroxy Compounds

s.

hydroxide. The autoclave is pressurized to 100 psi with dry nitrogen and vented three times to expel all oxygen from the system. The methanol and sodium hydroxide are then heated to 100~ with stirring. Then a total of 4520 gm (78 moles) of propylene oxide is added to the reaction over a period of 2 hr while maintaining the reaction temperature at 140~ At the start, the operating pressure is 100 psi. As the reaction proceeds the operating pressure falls to 85 psi. At the end of the reaction 50% sulfuric acid is added to neutralize the catalyst. Then 4565 gm of product (MW 678 by OH number) is recovered.

2-2. Preparation of Ethyleneglycol Monoethyl Ether [37] /

0

N

C2H5OH + CH2--CH2 (excess)

' C2H50--CH2--CH2OH

(4)

To an ice-cooled autoclave are added 10-30 moles of absolute alcohol and 2.0 mole of ethylene oxide. The autoclave is sealed and heated to 150~ for 12 hr or to 200~ for 3-4 hr. The autoclave is cooled and opened. The product is fractionally distilled to give 70% of ethylene glycol monoethyl ether, b.p. 134~ A more recent process [38] uses sodium methoxide as catalyst and the weight ratio of methanol to ethylene oxide is 9:1 to give 91.5% yield of ethylene glycol monomethyl ether.

2-3.

Polyoxyethylation of 2-Butyl-l-octanol [44a] C4H9

I

CH3(CH2)sCH--CH2--OH + CH2--CH2 \ / O

KOH

C4H9

I

CH3(CH2)5-- CH-- CH2-- O-- (CH2CH20)sH

(5)

To a flask containing 141.0 gm (0.756 mole) of 2-butyl-l-octanol is added 2.6 gm powdered KOH. The contents are heated to 120~ while a stream of ethylene oxide is passed into the alcohol by a gas dispersing tube. The addition is continued until 167.0 gm of ethylene oxide has been absorbed. The reaction is exothermic and the temperature of the reaction is maintained at approximately 150~ by application of cold water. The product obtained corresponds to the pentaethylene glycol ether of 2-butyl-l-octanol.

2.

163

Polyoxyalkylation of Alcohols and Diols

2-4. Polyoxyethylation of Clo-Cla Straight-Chain, Secondary Alcohols [45] BF3-Ether R2CHOH + \ / ' R2CHO(CH2CH20)3H (6) O To an autoclave is added 462 gm of a mixture of C10--C13 straight-chain, secondary alkanols with an average MW of 173. Then 0.075 wt% of 48% BF3 in ethyl ether is added followed by 255 gm of ethylene oxide. The addition is done with stirring, while the maximum pressure is kept at 10 psig. The reaction mixture is stirred and the temperature kept at 60~ for 2 hr. After another 30 min at 60~ the reaction product is neutralized with 20 wt% of NaOCH3 in methanol. The resulting product is partially purified by fractional distillation to remove the unreacted alcohols. The residue of crude polyethylene glycol monoethers has an average MW of 313.5.

2-5. Preparation of the Triethylene Glycol of 2,6,8-Trimethyl-4-nonanol [46] CH3 CH3 CH3 I I I CH3--CH--CH2--CH--CH2--CH--CH2--CHCH3 + CH2--CH2 I OH

\

/ O

CH3 CH3 CH3 I I I CH3--CH--CH2--CH--CH2--CH--CH2--CH2--CH--CH3 (7) I O(CH2CH20)3H To a flask containing 1042 gm (5.60 mole) of 2,6,8-trimethyl-4-nonanol is added 10.4 gm of powdered KOH and the contents are heated to 120~ A stream of gaseous ethylene oxide is passed into the reaction mixture by means of a gas-dispersing tube until 735 gm (16.8 mole) of ethylene oxide has combined. The reaction is exothermic and the temperature (150~ is maintained by cooling the flask with cold water. The product obtained corresponds to the triethylene glycol of 2,6,8-trimethyl-4-nonanol. In a similar manner 2,6,8-trimethyl-4-nonanol is reacted with ethylene oxide to give the pentaethylene glycol ether [47] CH3--CH--CH2--CH--CH2CH--CH2--CH--CH3 + ~ - 7 I I I I O CH3 OH CH3 CH3

CH3 I CH3CH--CH2--CH--CH2--CH--CH2--CH--CH3 I I I CH3 O(CH2CH20)sH CH3

(8)

164

2-6.

s. Polyoxyalkylation of Hydroxy Compounds

Polyoxypropylation and Polyoxyethylation of 2,6,8-Trimethyl-8-nonanol [48]

CH3 CH3 CH3 CH3 I I I ___.__/ \ / CH3--CH--CH2--CH--CH2--CH--CH2--CH--CH3 + I O OH

BF3

CH3 CH3 CH3 I I I O ,~ CH3 ~ C H ~ C H 2 - - C H ~ C H 2 - - C H ~ C H 2 - - C H ~ C H 3 NaOH I O(CH2 -- CHO -- )x( -- CH2CH20)yH I CH3

(9)

To a l-liter, four-necked flask equipped with an agitator, thermometer, addition funnel, and condenser are added 186 gm (1.0 mole) of 2,6,8-trimethyl4-nonanol, and 0.55 gm (0.03 mole) of boron trifluoride. The reaction mixture is purged with nitrogen and then 116 gm (2.0 moles) propylene oxide; is added over a 1-hr period at 75~176 with constant agitation. The acid catalyst is neutralized with methanolic caustic to pH 8.5. Then 0.3 gm sodium hydroxide is added and the temperature raised to 150~176 ethylene oxide is added (369 gm = 8.4 mole) at 0-15 lb pressure to a cloud point (1% in water) at 36~ The final product has surfactant properties. A similar two-stage ethoxylation of secondary alcohols of 10-17 carbon atoms has been described earlier by Carter [49].

2-7.

Polyoxyethylation of 2-Methyl-7-ethyl-4undecano! [49]

CH3--CH--CH2--CH--CH2--CH2--CH--CH2--CH2--CH2--CH3 + CH2-~CH2 I I I CH3 OH C2H5 O C2H5 I CH3-- CH-- CH2--CH--CH2CH2CH(CH2)3CH3 etc. (10) I I CH3 O(CH2CH20)nH To a reaction flask equipped with a mechanical stirrer, dry-ice condenser, and thermometer is added 1200 gm (6.0 mole) of 2-methyl-7-ethyl-4-undecanol containing 0.05 wt% boron trifluoride. The mixture was cooled to 10~ Then 264 gm (6.0 mole) of ethylene oxide is added rapidly and the mixture is slowly heated to 50~ at atmospheric pressure over a 2-hr period. The mixture is heated at 50~ until all the ethylene oxide has reacted.

165

2. Polyoxyalkylation of Alcohols and Diols

The reaction mixture is neutralized with methanolic caustic soda until the phenolphthalein indicator just turns pink. The reaction mixture is distilled to remove volatiles at 10 mm Hg and temperatures up to 158~ The residue consists of 2.6 moles of a mixture of monotetradecyl ethers of ethylene glycol, and polyethylene glycols having an average MW of 315 (avg 2.3 moles of ethylene oxide per mole of the mixed ethers). The latter product can be made to react further with ethylene oxide by first adding 1 gm sodium metal to 315 gm of the above product. Then ethylene oxide is added to the reaction at 165~ at atmospheric pressure. Approximately 7.4 moles of ethylene oxide is added to give a cloud point of 0.5 wt% aqueous solution of the mixture at 35~

2-8. Polyoxyethylation of tert-Butyl Alcohol [14] R+(BF4)(CH3)3~C--OH + CH2--CH \ /

O

75~176

~ (CH3)3C--O~(CH2--CH20)2H

(11)

To a three-necked flask equipped with a mechanical stirrer, thermometer, gas inlet, and gas outlet device is added 112 gm (1.5 mole) of tert-butanol. Then 0.5 gm (0.45 wt%) of tropylium fluoroborate is added and the temperature rises to 75-83~ Then 132 gm (3.0 mole) of ethylene oxide is added over a 1-hr reaction time. The final product is obtained by neutralizing with sodium hydroxide, filtering the salts, and stripping the resulting liquid under reduced pressure. The unreacted alcohol amounted to only 10%.

2-9.

Preparation of Polyoxypropylated Stearyl Alcohol [50] CH3

I

C18H37OH + C H 2 ~ C H \ / O

(c.3)

' C18H370 C H z - - C H - - O

5H

(12)

To a l-liter stainless steel autoclave are added 230 gm (0.8 mole) of stearyl alcohol and 0.9 gm of sodium methoxide powder. The reactor is purged with nitrogen. Then 408 gm (7.0 mole) of propylene oxide is added over a 16-hr period while the temperature is kept at 130~176 After the reaction is complete the mixture is cooled and the volatiles are eliminated by heating on a water bath for 15-20 min. Then dilute sulfuric acid is added to neutralize the catalyst and the product is washed with 1 liter of water at 60~ followed by two washings with 500 ml of water at 60~ The product is dried under reduced pressure to give 548 gm (99%) of a light-yellow product having a hydroxyl number of 94.

166

s. Polyoxyalkylationof Hydroxy Compounds

In a similar manner ethylene oxide can be further reacted with the product to give a hydroxyethyl terminated product.

2-10.

Polyoxyethylation of n-Octanol [14]

CHs(CH2)6CH2OH + CH2--CH2 \ / O CH3(CH2)6-- C H 2 0 - - (CH2-- CH20)nH

(13)

To an autoclave equipped with a stirrer, thermometer, gas inlet, and gas outlet device are added 130 gm (1.0 mole) of n-octanol and 0.3 gm (0.24 wt%) of triphenylmethylcarbonium fluoroborate. The mixture is heated to 740-78 ~ then 44 gm (1.0 mole) of ethylene oxide is added within the pressure range of 0.7-13.5 atm. The reaction takes approximately 5-6 hr and approximately 24% n-octanol remains unreacted as determined by gas chromatography. The polyethylene glycol content is about 1%.

2-11. Preparation of Polyoxypropylene Glycol [19] CH3

CH3--CH--CH2 I i OH OH

NaOH

~ HO -- CH2 -- CH -- O -- nH

(14)

To a l-liter, three-necked, round-botton flask equipped with a mechanical stirrer, reflux condenser, thermometer, and addition funnel is added 57 gm (0.75 mole) of propylene glycol and 7.5 gm (0.19 mole) of sodium hydroxide. The flask is purged with nitrogen to remove air and heated to 120~ with stirring to dissolve the sodium hydroxide. Then propylene oxide is added (40-45 mole). The reaction mixture is cooled under nitrogen, neutralized with dilute sulfuric acid, filtered, and dried under reduced pressure to give a water-insoluble product with MW 1620 as determined by hydroxyl number or acetylation analytical procedures.

2-12. Preparation of Polyoxyethylene Glycol [51] HOCHzCH2OCH2CHzOH + \

O

/

NaOH

~ HO(CHzCHzO)9H

(15)

To a pressure reactor are charged 665 gm of diethylene glycol and 150 gm of sodium hydroxide catalyst dissolved in 300 gm of water. Ethylene oxide 1860 gm is reacted over a 5.2 hr period at 150~176 and a reactor pressure of

2.

167

Polyoxyalkylation of Alcohols and Diols

35-45 psig. The crude product is pale yellow. To this is added 225 gm of 85% orthophosphoric acid without omitting air (1.5 parts acid to 1 part NaOH used). Then air is admitted to the reactor and the product is heated for 1 hr at 120~176 The reactor is opened and the product is filtered to remove phosphate salts. The product is colorless and has MW approximately 400.

2-13. Reaction of Dipropylene Glycol with Propylene Oxide [51] CH3

CH3

CH3

I I HOCH2--CH--O--CH--CHaOH + \ /J O

[

CH3

~

| / ) NaOH ~ HO\CH2CH--O 4H (16)

To a pressure reactor are added 8.0 lb of dipropylene glycol, 4.0 gm sodium hydroxide catalyst, and then 5.15 lb of propylene oxide. The temperature is raised to 140~176 at 60 psig and kept there for 2.5 hr. A portion of the product is treated with 85% orthophosphoric acid (1.5 parts acid to 1 part catalyst). Air is bubbled through the product for 30 min at 110 ~ 130~ and then the product is filtered [pH 6.8 (5% aq); ash content 0.0036 wt%]. So-called "amorphous poly(ethylene oxide)" [a-PEO] is a material which is formed by linking fairly large poly(ethylene oxide) molecules with --CH2 u bridges. In this procedure, to a suspension of finely ground potassium hydroxide in PEG 400 (e.g., Carbowax 400), which is assumed to consist primarily of chains of eight ethylene oxide units, dry dichloromethane is added, with stirring, under nitrogen, over a 30 min period, until the mixture becomes too viscous to stir. Then an excess of dichloromethane is added and the mixture is allowed to react overnight. After the excess solvent is evaporated off, the crude product is dialyzed against distilled water for 10 days. For this process, Spectrum cellulose tubing with a molecular weight cutoff of 3000 is suggested. The excess water is removed from the dialysate under reduced pressure at room temperature and finally by heating under reduced pressure. The product is a tacky, slightly yellow resin with degrees of polymerization ranging from 15 to 150 (presumably by varying the ratio of the reactants [52]. By the judicious selection of diols or glycols for reaction with ethylene oxide, propylene oxide, or higher alkylene oxides (or other 1,2-epoxides) as well as mixtures of such reactants, a large variety of polymers may be formed. A solution of dipropylene glycol containing aqueous potassium hydroxide was dewatered on a rotary evaporator. The resulting composition was then heated in an autoclave at 100 ~ while a mixture of propylene oxide and ethylene oxide was gradually added. This reaction stage was followed by the addition of further quantities of ethylene oxide. The product was isolated after neutralization with dilute hydrochloric acid, followed by dewatering and filtration. A

TABLE III

Polyoxyalkylation of Polyhydroxy Compounds o~ oo

Reaction Conditions

Alcohol

Oxyalkylating agent

Pentaerythritol Sorbitol Sorbitol Cornstarch Trimethylolethane Sucrose Sucrose Sucrose Glycerol Glycerol and methyl glucoside Glucose Glucose Cellulose

Propylene oxide Propylene oxide Ethylene oxide Ethylene oxide Propylene oxide Propylene oxide Propylene oxide Propylene oxide Propylene oxide Propylene oxide Butylene oxide Ethylene oxide Ethylene oxide

Solvent

Catalyst

Temp (~

Pressure (lb/in 2)

Yield (%)

-~ H20 H20 N

NaOH NaOCH3 NaOCH3 NaOH Tetramethylethylenediamine 1,2,4-Trimethylpiperazine (C2Hs)3N (nC3H7)3N (C2Hs)3N KOH NaOCH3 Boric acid NaOH

135-150 150-180 90-140 120-130~ 124-126 115 105-110 140 180 160 135-150 115 45-100

50 ~ 100-120 N

~

-H20 Xylene H20 --

~ 30-107 30-107 70 70 50 100 --

100 100 ~ 100 100

~

Ref. a, j b c d d d e e e f g h i

a j. T. Patton, Jr. and W. F. Schulz, U.S. Patent 3,190,927 (1965); A. W. Anderson, U.S. Patent 2,902,478 (1959); P. T. Bowman, R. H. Barth, and H. Burrell, U.S. Patent 2,401,743 (1946). bM. DeGroote, U.S. Patent 2,552,528 (1951); J. T. Patton, Jr. and W. F. Schulz, U.S. Patent 3,346,557 (1967); A. W. Anderson, U.S. Patent 2,927,918 (1960). r O. Schmidt and E. Meyer, U.S. Patent 1,922,459 (1933); K. R. Brown, U.S. Patent 2,450,079 (1948). d j. T. Patton, Jr. and W. F. Schulz, U.S. Patent 3,346,557 (1967); C. C. Kesler and E. T. Hjermstad, U.S. Patent 2,516,633 (1950); C. C. Kesler and E. T. Hjermstad, U.S. Patent 2,516,632 (1950); R. W. Kerr and W. A. Faucette, U.S. Patent 2,733,238 (1956); S. Fuzesi and L. Klahs, U.S. Patent 3,402,170 (1968). e A. W. Anderson, U.S. Patent 2,927,918 (1960); M. DeGroote and O. H. Pettingill, U.S. Patent 2,945,023 (1960); M. DeGroote, U.S. Patent 2,652,394 (1953). fD. W. Kaiser and S. Fuzesi, U.S. Patent 3,167,538 (1965). g M. DeGroote and O. H. Pettingill, U.S. Patent 2,945,024 (1960). hK. R. Brown, U.S. Patent 2,450,079 (1948); W. C. Griffin, U.S. Patent 2,407,003 (1946). i A. W. Schorger and C. F. Burgess, U.S. Patent 1,863,208 (1932); P. W. Kersnar, U.S. Patent 2,833,614 (1958). J cfY. Hara, S. Izukawa, H. Kawakami, and T. Takayoshi, Jpn. Koka: Tokkyo Koho JP 03 12,421 [91, 12,421], June 12, 1989 for use of KOH in a slurry system.

r

169

3. Polyoxyalkylation of Polyhydroxy Compounds

product with a hydroxyl number of 50.6, an iodine number of 0.24, a number average molecular weight of 2100, and a weight average molecular weight of 2250 was isolated after such a reaction [53]. Among new initiators for the polymerization of propylene oxide, ethylene oxide, 1-butene oxide, and isobutylene oxide are zinc hexacyanocobaltate [54] and aluminum porphyrin [55]. It is of interest that when aluminum porphyrin is used, oligomers or polymers of controlled molecular weight distribution can be produced by using bisphenol A or related bisphenol-type compounds as chain transfer agents. Living cationic polymerizations of propylene oxide and of epichlorohydrin have been reported. The procedure is carried out in an alcohol with a strong acid catalyst such as fluoroboric acid. Interestingly enough, the procedure is not applicable to the polymerization of ethylene oxide [56].

0

POLYOXYALKYLATION OF POLYHYDROXY COMPOUNDS

The polyoxyalkylation of polyhydroxy compounds is usually carried out using basic catalysts in high-pressure reactors. The starting polyols are in most cases solids and are reacted with either ethylene or propylene oxide with or without a solvent (e.g., water, xylene, DMSO), under about 100 psig pressure at temperatures ranging from 100~ to 150~ In most cases the reaction is run under anhydrous conditions. When water is used, a low-molecular-weight polyoxyalkylene derivative is observed and this is used again as the solvent for subsequent polyoxyalkylation reactions of the solid polyol. The use of ethylene carbonate has the advantage of allowing the reaction to be carried out at atmospheric pressure in typical laboratory glassware. The products described in this section find wide use as starting polyols for the preparation of rigid polyurethane foams. (For polyoxyalkylations see Tables III-V.) TABLE IV Polyoxyalkylation of Polypentaerythritols Reaction conditions

Alcohol

No. OH groups

Oxyalkylating agent

Solvent

Catalyst

Temp (~

Pressure (psi)

Ref.

Dipentaerythritol Tripentaerythritol Tetrapentaerythritol Heptapentaerythritol

6 8 10 16

Propylene oxide Ethylene oxide Ethylene oxide Ethylene oxide

Xylene Xylene Xylene Xylene

NaOCH3 NaOCH3 NaOCH3 NaOCH3

150-180 150-180 150-180 150-180

15-100 15-100 15-180 15-100

a b b b

aM. DeGroote, U.S. Patent 2,254,667 (1951). bM. DeGroote, U.S. Patent 2,552,532 (1951).

170

5. Polyoxyalkylationof Hydroxy Compounds

3-1. Polyoxypropylation of Sucrose H

CH2OH

no-- _yZ2o H

[57]

O ~ H --~

CH3

H CH2OH ~ O

Base

H

CH2OH HO

H

H CH2OROH HORO ~ / - ~ O HORO ~ ~ H

u~~-~ CH2OROH ~rl~.,

~O~H

Ox..~

~HOR~/ HORO

H

(17)

CH2OROH

H

where R = --CH2CH(CH3)--. To a steam-heated autoclave are added 950 gm (28.00 moles) of sucrose, 3 gm of 1,2,4-trimethylpiperazine catalyst, and 60 ml of distilled water. The autoclave is purged three times with nitrogen gas and heated to 100~ Then the addition of 1550 gm (27.0 mole) of propylene oxide is started. After 1 hr the temperature is raised to 115~ At this temperature the addition is carried out at approximately 90 psig. The addition of the remaining propylene oxide requires about 10.25 hr. The reactants are then heated to 120~ for another 45 min. The reaction mixture is cooled to 60~ and the liquid product is blown into a clean vessel. The volatiles are removed under reduced pressure varying from 80 mm Hg to a final 2 mm Hg over a 5-hr period. The product has MW 839. This product can be used again in a second stage of polyoxypropylation wherein it acts as a solvent for fresh sucrose. The reaction conditions are basically as described before. Using this procedure 670 gm (0.8 mole) of sucrose-propylene oxide product is used for 670 gm (1.95 mole) of fresh sucrose. A similar procedure is reported by Patton for the polyoxypropylation of pentaerythritol [58]; and Table III, Ref. a].

3. Polyoxyalkylation of Polyhydroxy Compounds

171

TABLE V Oxyalkylation of Pentaerythritols with Alkylene Carbonates or Alkylene Oxidesa Alcohol (gm) Pentaerythritol Dipentaerythritol Tripentaerythritol Pentaerythritol

Pentaerythritol 408 Dipentaerythrital 381 Tripentaerythritol 272 Pentaerythritol 406 Dipentaerythritol 381 Tripentaerythritol 372 Pentaerythritol 408

Oxyalkylation reagent

Catalyst (gm)

Temp (~

Time (hr)

Ethylene carbonate Ethylene carbonate Ethylene carbonate Propylene carbonate Ethylene Oxide Propylene oxide Ethylene carbonate 508 528

K2CO3 K2CO3 K2CO3 K2CO3 NaOH

155-200 170-180 150-190 160-195 140

6 6

K2CO3 10 10

155-200

6

170-180

6

528 Propylene carbonate 612

10

150-190

6

10

160-195

8

612

8.5

165

6

612 Butylene carbonate 696

l0

160-190

8

10

155-200

6

6

8 8

a L. T. Monson and W. J. Dickson, U.S. Patent 2,766,292 (1956).

3-2.

Polyoxypropylation of Sucrose [59, 60]

To a jacketed autoclave were charged 3600 gm of propylene oxide, 2400 gm of sucrose, and 21 gm of trimethylamine. The mixture was stirred and heated to 105~176 for 3 hr and then heated for 2 hr at 110~176 Finally the mixture was stirred and heated for 1 hr at 105~ The pressure observed varied from 107 psig to 30 psig at the end. Once the pressure was approximately 0 psig for some time, the reaction was terminated, and volatiles, if any, were completely removed by stripping under reduced pressure. The residue was a syrupy liquid, [n] 25 = 1.4860, [d]~ = 1.187. The yield is reported to be 5925 gm (8.66 hydroxypropyl groups per sucrose molecule). A similar procedure can be used to polyoxypropylate glycerol, sorbitol, or pentaerythritol. Anderson [60] described similar procedures for the oxyethylation of sucrose, the oxyphenylation of sucrose, and the oxybutylation of pentaerythritol.

5. Polyoxyalkylationof Hydroxy Compounds

172

3-3. Polyoxyethylation of Sorbitol [61] CH2OH

CH20(cH2CH20)nH

I

I

(CH--OH)4 + CHz--CH2 I

CHzOH

\

/

O

~ (CH--O(CHzCHzO)nH)4

/

(18)

CH20(CHzCHzO)n H

To 200 gm sorbital in an autoclave is added 350 gm ethylene oxide. The mixture is stirred and heated for 12 hr at 140~ The reaction mixture is cooled and the excess ethylene oxide removed to give a viscous water-white liquid. The authors of the foregoing procedure report that boric or sulfuric acid facilitate the polyoxyethylation reaction. However, other researchers report that basic catalysts such as sodium methoxide are preferred [62-64].

3-4.

Polyoxyethylation of Sorbitol [65]

To 134 lb of an aqueous solution of sorbitol (contains 5% water) in an autoclave is added 225 gm sodium methylate catalyst and the mixture is heated to 70~ Then 200 lb of ethylene oxide is added over a 2- to 4-hr period, holding the reaction temperature at 90~ and the pressure at a maximum of 110-120 psi. At the conclusion of the reaction the pressure drops to 0 psi. The reaction mixture is cooled, vented, and neutralized. Concentration followed by filtering of the salt affords a viscous, water-white liquid. The same reaction can be carried out using anhydrous sorbitol. In addition, the polyoxypropylation reaction has been reported [66].

3-5.

Polyoxypropylation of Trimethylolethane [63] CH3

I

CHa--C(CHEOH)3 + CHE--CH \ / O

/1 (19) To an autoclave are added 648 gm (5.4 moles) of trimethylolethane, 400 gm of distilled water, and 12.0 gm (1.9 mol%) of tetramethylethylenediamine catalyst. Then 870 gm (15 moles) of propylene oxide is introduced over a 3.25-hr period at 124~176 The reaction mixture is cooled and stripped under reduced pressure to give a yellow, liquid product having a MW 210. In a second stage of the reaction 506 gm of the foregoing product is charged to an autoclave along with 108 gm (0.9 mole) of trimethylolethane. The product

3. Polyoxyalkylationof PolyhydroxyCompounds

173

from the first portion of the reaction is a solvent for the added trimethylolethane. Then 20 gm of tetramethylenediamine is added followed by 1636 gm (28.2 moles) of propylene oxide introduced over a 6.25-hr period at 124~176 The reaction mixture is cooled and stripped of residual propylene oxide to afford a liquid having MW 684. The product contained a small amount of diols.

3-6.

Polyoxypropylation of Pentaerythritol [65]

HOCH2--C--CH2OH + CH2--CH I

\

CH2OH

/

i

~ C --CH20

(

CH2--CH--O/nHJ4

O

(20)

To a thoroughly dried stainless steel reaction vessel equipped with a mechanical stirrer, pressure gauge, cooling coil, and thermocouple are added 136 gm (1.0 mole) pentaerythritol, 250 gm dimethyl sulfoxide, and 9 gm powdered potassium hydroxide. The reaction mixture is heated to 100~ and stirred for 1 hr at 30 mm Hg pressure while nitrogen is added. Then 1410 gm (24.3 moles) propylene oxide is added over a 4-hr period at 100~176 The reaction product is obtained by stripping off the dimethyl sulfoxide at 150~ at 30 mm Hg. Approximately 9 gm adipic acid is added to neutralize the potassium hydroxide catalyst. Further stipping at 30 mm Hg in a stream of nitrogen for 1 hr at 100~ gives 1400 gm of product (OH % - 5.4; viscosity at 25~ = 290 centistokes). The color of the product can be removed using a dilute solution of hydrogen peroxide. A similar procedure is used to polyoxypropylate sucrose.

3-7.

Preparation o f Polyoxyethylated Pentaerythritol [67] 0 II

c

/ \ CH2OH O O I I I H O ~ C H 2 ~ C ~ C H 2 O H + CH2~CH2

K2CO3

I

CH2OH C[--CH20(CH2--CH20)nH]4

(21)

To a glass resin-flask equipped with a stirrer and condenser are added 408 gm of pentaerythritol, 528 gm ethylene carbonate, and 10 gm of potassium carbonate. The temperature is slowly raised to 155~ at which point the mixture begins to evolve carbon dioxide and become homogeneous. Heating and stirring is continued for 6 hr and the temperature is slowly raised to 200~ The product is a dark, viscous liquid that is soluble in water or in a xylene-methanol mixture.

174

5. Polyoxyalkylationof Hydroxy Compounds

The polymerization of ethylene oxide and propylene oxide with various active hydrogen compounds is the primary thrust of the present chapter. However, other epoxy compounds also undergo this type of reaction as is detailed in the chapter "Polymerization of Epoxides and Cyclic Ethers" of this series [5]. An example of the polycondensation of a complex glycidyl ether with a polyol, taken from the patent literature, is cited here for reference only.

3-8.

Reaction of 2,4,4,4-Tetrachlorobutylglycidyl Ether with Glycerol [68] CH2--OH

i 2C13C-- CH2-- CH--CH2--O--CH--CH2 +CH--OH i \ / I C1 O CH2--OH

OH I

C1 I

CH2 -- O - - CH2 - - C H - - O - - C H 2 - C H - - CH2 --CC13

I , HO--CH I

(22)

CH2 -- O - - CH2-- C H - - O - - CH2 -- C H - - CH2-- CC13

I OH

I C1

In a 2-liter four-necked round-bottomed flask equipped with a mechanical stirrer, a condenser, a heating mantle with temperature controller, an addition funnel, and a nitrogen inlet tube, 128.8 g (1.4 moles) of glycerol and 7.5 g (0.053 moles) of boron trifluoride etherate are stirred under a nitrogen atmosphere and heated to 90-100 ~ Then 750.4 g (approximately 2.8 moles) of 2,4,4,4-tetrachlorobutylglycidyl ether is added over a 35 min period without external heating. (The preparation of this reactant from carbon tetrachloride and allyl glycidyl ether in the presence of 2-tert-butylazo-2-cyanobutane (Luprazo 82 from Atochem) is given in Ref. [68].) The ensuing reaction is exothermic and the temperature in the apparatus rises to approximately 106~ After the temperature rise ceases, the reaction mixture is maintained, with stirring and external controlled heating, for 3.5 hr. The reaction mixture may be used as is for thepreparation of polyurethane foams with appropriate diisocyanates. 4.

POLYOXYALKYLATION OF PHENOLS

Phenol and its O-alkyl derivatives (from propylene dimers, trimers, or tetramers) are oxyalkylated usually at atmospheric pressure or under moderate pressure conditions using basic catalysts at approximately 50~176 in the absence of solvents. Glass reaction flasks are the typical labware, thus the

175

4. Polyoxyalkylation of Phenols

reaction can be carried out conveniently in the laboratory. In the absence of catalysts the reactions require high temperatures and pressures [69-72]. The products have been used since the early 1940s as nonionic surfactants and appear under a variety of trade names. The reactivity of the various phenols depends on the substituent present. Reactivity is increased if the substituent decreases the acidity of the phenol (electron-donating groups) and is decreased if the acidity is increased (electronwithdrawing groups) [70]. (See Table VI for polyoxyalkylation of some phenols.) The molecular weight distribution of the polyoxyalkylated products has been shown to follow a Poisson distribution [71]. The reaction of ethylene oxide with phenol in the presence of sulfuric acid gives o-vinylphenol [72].

4-1.

Preparation of Polyoxypropylenephenol

C>

OH

C?_O--

, NaOH(Cat)

[73]

,

CH2-- CH-- O 7H

(23)

To a l-liter, three-necked, round-bottom flask equipped with a mechanical stirrer, reflux condenser, thermometer, and propylene oxide feed inlet are added 94 gm (1.0 mole) of phenol and 5 gm (0.13 mole) of sodium hydroxide. The reaction mixture is heated to 125~ and 590 gm (10.2 mole) of propylene oxide is added to the reaction mixture over a 54-hr period. The catalyst is neutralized with sulfuric acid and then filtered from the salts. The residue is stripped under reduced pressure at room temperature to remove any remaining volatiles. The product weighs 684 gm and has a MW of 495 (by OH number), which corresponds to about 7 moles of propylene oxide-phenol molecule.

4-2. Preparation of Polyoxyethylene Nonylphenol [74] C9H19--~/ \

~ /

OH + CH2 ~ CH2 \

/

NaOH}

O

C9H19--~ \

~ /

0 ~ (CH2CHzO)loH (24)

To a reactor are charged 890 lb of monononylphenol and 404 gm filtered sodium hydroxide. The reaction mixture is heated to 140~ and then 1630 lb ethylene oxide is added over a 6-hr period at 140~176 while the pressure remains at 40 psig. At the end of the reaction 350 gm of 85% H3PO4 is added

5. Polyoxyalkylationof Hydroxy Compounds

176

TABLE VI

Polyoxyalkylation of Phenols Reaction conditions

Phenol

Alkylene oxide

Catalyst

Temp (~

Time (hr)

Pressure (psi)

Ref.

Nonylphenol Nonylphenol Nonylphenol Nonylphenol Isooctylphenol Tetramethylbutylphenol Diisobutylphenol Phenol

Ethylene oxide Ethylene oxide Propylene oxide Propylene oxide Propylene oxide Ethylene oxide Ethylene oxide Styrene oxide Propylene oxide

NaOH NaOH Na (metal) NaOCH3 NaOH NaOH NaOH NaOH NaOH

140-180 160-190 150 239-301 160-180 50-82 160-180 120 150-225

6 -33 ~ -~ ~

40 ----~ ~ ~ --

a b c d e f e, g c h

p-tert-Butylphenol

--

a W. P. Krause, U.S. Patent 2,983,763 (1961). Product corresponds to 9.5 moles of ethylene oxide combined with nonlyphenol. bE. M. Stoltz, U.S. Patent 2,778,854 (1957). Product corresponds to 11 ethylene oxide groups/ mole nonylphenol. c D. R. Jackson and L. G. Lundsted, U.S. Patent 2,677,700 (1954). Product corresponds to about 11.0 propylene oxide groups/mole of nonylphenol. d W. Stein and W. Umbach, U.S. Patent 3,436,425 (1969). e A. Steindorff, G. Balle, and R. Michel, U.S. Patent 2,213,477 (1940). fH. A. Bruson and O. Stein, U.S. Patent 2,075,018 (1937). g C. R. Enyeart, U.S. Patent 2,496,582 (1950). hW. D. Harris and J. W. Zukel, U.S. Patent 2,820,808 (1958).

(0.87 parts acid per 1 part NaOH). Then air is bubbled through the product at 120~176 over a 1-hr period. The product is filtered to remove sodium phosphate and is stripped of volatiles under reduced pressure at room temperature to give the final product. The product corresponds to nonylphenol reacted with about 10 moles of ethylene oxide.

4-3. Preparation of Polyoxypropylene Nonylphenol [73] CH3 C9H19

OH + CH

H

C9H19 ~

Na

O (ca2--

!n3-- O)11a

(25)

To a l-liter, three-necked, round-bottom flask equipped with a thermometer, mechanical stirrer, reflux condenser, and propylene oxide feed inlet are added

177

4. Polyoxyalkylation of Phenols

61 gm (0.28 mole) of nonylphenol and 0.7 gm metallic sodium. The reaction mixture is heated to 150~ and then 303 gm (5.2 mole) of propylene oxide is added to the reaction mixture while the reaction temperature is kept at 150~ over a 33-hr period. The product obtained has MW 875 (OH number) and corresponds to about 11 moles propylene oxide reacted with the starting phenol.

4-4.

Polyoxypropylation of p-tert-Butylphenol [74]

(CH3)3C

_

CH3 [ OH + CH2-- CH No /

~

NaOH

(CH3)3C - - ~

,

O-- (CH2-- ;H3-- O)2_5H (26)

To a 2-liter, three-necked, glass, round-bottom flask equipped with a mechanical stirrer, thermometer, addition funnel, and dry-ice-acetone condenser is added 600 gm (4.0 mole) of p-tert-butylphenol. The flask is heated in order to melt the latter phenol and then 8.0 gm (0.2 mole) of sodium hydroxide is added. The temperature is raised to 150~ and then 929 gm (16 moles) of propylene oxide is added in 50-ml increments over a 7.5-hr period while slowly raising the temperature to 225~ during this period. Heating is continued. After cooling to room temperature the product is neutralized with a solution of 20.8 gm conc HC1 in 150 ml water. The organic layer is separated and washed with 500 ml saturated salt solution. This product is filtered, dried and distilled under reduced pressure to give 4 products:

(ca2a O)m" \

b.p. (~ 2 3 4 5

p (mm Hg)

121-137 0.15-0.45 153-168 0.2-0.6 181-196 0.2-0.4 198-222 0.25-0.65

CH3

Specific gravity

[n]aD~

0.9924 0.9929 0.9970 0.9967

1.4968 1.4888 1.4819 1.4752

178

5. Polyoxyalkylation of Hydroxy Compounds

MISCELLANEOUS POLYOXYALKYLATION PREPARATIONS

0

o

2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.

22. 23. 24. 25. 26. 27. 28.

Reaction of ethylene oxide with dehydrogenated rosin [75]. Polyoxypropylation of benzenesulfonamides [76]. Polyoxyethylation of octadecylamine [77]. Polyoxyethylation of ricinoleic acid [77]. Polyoxyethylation of stearylamine [78]. Polyoxyethylation of ethylenediamine [79]. Polyoxypropylation of ethylenediamine [80]. Polyoxyethylation of oleylamine [81 ]. Preparation of nonionic detergent by oxyethylation reactions [82]. Polyoxypropylation of oleic acid [7]. Process for making hydroxyalkylated polyvinyl alcohol [83]. Reaction of ethylene oxide with hydrazine [84]. Reaction of ethylene oxide and urea [85]. Reaction of ethylene oxide with alkylol amides [86]. Reaction of ethylene oxide with dimethyl- or diethylamines [87]. Reaction of ethylene glycol with epoxydodecane in the presence of BF3 etherate [88]. Preparation of carboxyalkylated alkyl ether surfactants with a narrow polyethoxy chain distribution [89]. Polyoxypropylation of polymethylolphenols [90]. Preparation of sucrose-ethylenediamine polyols [91 ]. Polymerization of epoxides initiated by tertiary amines and the effect on the molecular weight distribution [92]. Preparation of polyether polyols dispersions with high solids content and low viscosity from sucrose and propylene oxide with triethanolamine and tributylamine initiation [93]. Ethoxylation of 1,1,1,3,3,3-hexafluoro-2-propanol [94]. Polysulfide synthesis based on the reaction of malononitrile, carbon disulfide, and a,a'-dichloro-p-xylene [95]. Polyether-thioether polymers from bisacrylate ethers [96]. Poly(phenylene oxides), synthesis and properties of carboxylated derivatives [97]. Molecular weight determination of PEG and PPG by laser mass spectroscopy [98]. Purification of glycols: by extractive distillation [99]; by steam distillation under nitrogen [ 100]. Cationic polymerization of 1,2-epoxy-3-nitropropane with ethylene oxide [1011.

References

179

29. Molecular weight limiting step in alkalene oxide polymerization initiated by bis(diisobutylaluminum)oxide [ 102]. 30. Manufacture of high molecular weight polyethers [ 103]. 31. Functionalized poly(ethylene oxide) preparation [ 104]. 32. Polystyrene-poly(ethylene oxide) block copolymers [105]. 33. Chitosan-PEG hydrogel preparation [106]. 34. Preparation of PEG-dendritic block copolymers [107]. 35. Polyblend of PEG/poly(2-vinylpyridine) and lithium perchlorate [108]. 36. Synthesis of block copolymers of tert-butyl methacrylate and ethylene oxide [109]. 37. Poly(oxybutylene/oxyethylene) diblock preparation [110].. 38. New syntheses of segmented tri-block copolyether [ 111 ]. 39. Poly(L-lactic acid)/Pluronic blends [112]. 40. Thermal oxidation of PEG/poly(methyl methacrylate) blends [113]. 41. Manufacture of oxymethylene copolymers [ 114]. 42. Graft copolymers of ethylene with hydrocarbons [115]. 43. Molecular weight determination of Pluronic F 68 and of Brij 35 [116].

References 1. 2. 3. 4. 5. 6.

7.

8. 9. 10. 11.

12. 13. 14. 15. 16.

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180

5.

Polyoxyalkylation o f Hydroxy Compounds

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References

181

39. C. A. Carter, U.S. Patent 2,870,220 (1959); W. Umbach and W. Stein, U.S. Patent 3,651,152 (1972). 40. J. Furukawa, T. Saigusa, T. Tsuruta, and G. Kakogawa, Makromol. Chem. 36, 25 (1959). 41. P. Guenther and W. Oberkirch, Ger. Often. 1,804,528 (1968). 42. W. Hoelderich, J. Houben, G. Wolf, and M. G. Kinnaird, U.S. Patent 5,126,493 (1992). 43. H. Nakamura, I. Hama, Y. Fujimori, and Y. Nakamoto, Japanese Patent 04,279, 552[92,279,552] (1992). 44. T. M. Moshkina and A. N. Pudovik, Vysokomol. Soedin. 5, 1106 (1963). 44a. M. Kosmin, U.S. Patent 2,671,115 (1954). 45. R. C. Myerly, J. M. Rector, E. C. Steinle, and H. T. Zika, U.S. Patent 3,393,219 (1968). 46. M. Kosmin, U.S. Patent 2,637,740 (1953). 47. M. Kosmin, U.S. Patent 2,671,116 (1954). 48. R. E. Leary, L. T. Nehmsmann, III, and L. M. Schenck, U.S. Patent 3,350,462 (1967). 49. C. H. Carter, U.S. Patent 2,870,220 (1959). 50. F. Lachampt and G. Vanderberghe, U.S. Patent 3,489,690 (1970). 51. W. P. Krause, U.S. Patent 2,983,763 (1961). 52. J. P. Lemmon and M. M. Lerner, Macromolecules 25, 2907 (1992). 53. G. Behrendt, H. Becker, B. Guettes, W. Lehmann, and P. Bischoff, Ger. (East) DD 237,438 (1982). 54. H. Takeyasu, Y. Matsumoto, and O. Shigayuki, Japanese Patent 64,268,329192,268,329], Feb. 25, 1991; S. L. Aggarwal, I. G. Hargis, and R. A. Livigni, U.S. Patent 4,279,798 (1980). 55. J. E. McGrath, Chemtech, May 1991, 310, and Refs. 28 and 29 therein. 56. O. W. Webster, Science 251, 887 (1991). 57. J. T. Patton, Jr. and W. F. Schulz, U.S. Patent 3,346,557 (1967). 58. J. T. Patton, Jr. and W. F. Schulz, U.S. Patent 3,190,927 (1965). 59. A. W. Anderson, U.S. Patent 2,927,918 (1960). 60. A. W. Anderson, U.S. Patent 2,902,478 (1959). 61. O. Schmidt and E. Moyer, U.S. Patent 1,922,459 (1933). 62. M. DeGroote, U.S. Patent 2,552,528 (1951). 63. J. T. Patton, Jr. and W. F. Schulz, U.S. Patent 3,346,557 (1967). 64. A. W. Anderson, U.S. Patent 2,927,918 (1960). 65. K. R. Brown, U.S. Patent 2,450,079 (1948). 66. R. P. Genties, U.S. Patent 3,042,666 (1962). 67. L. T. Monson and W. J. Dickson, U.S. Patent 2,766,292 (1956). 68. S. R. Sandier and J. M. Boben, U.S. Patent 4,393,248 (1983). 69. R. A. Smith, J. Am. Chem. Soc. 62, 994 (1940); H. M. Stanley, J. E. Youell, and G. Minkoff, U.S. Patent 2,141,443 (1938); Chem. Abstr. 33, 2536 (1939). 70. D. R. Boyd and E. R. Marle, J. Chem. Soc. 105, 2117 (1914); J. M. Cloney and R. L. Mayhew, Soap Chem. Spec. 33, No. 8, 52, 109, and 111 (1957). 71. R. L. Mayhew and R. C. Hyatt, J. Oil Colour Chem. Soc. 29, 357 (1952); S. A. Miller, B. Bann, and R. D. Thrower, J. Chem. Soc. p. 3623 (1950). 72. R. A. Smith and J. B. Niederl, J. Am. Chem. Soc. 53, 806 (1931). 73. D. R. Jackson and L. G. Lunsted, U.S. Patent 2,677,700 (1954). 74. W. D. Harris and J. W. Zukel, U.S. Patent 2,820,808 (1958). 75. J. B. Batdorf, U.S. Patent 2,662,881 (1953). 76. L. G. Lundsted, U.S. Patent 2,577,256 (1951). 77. C. Schoeller and M. Wittower, U.S. Patent 1,970,578 (1934). 78. C. Schoeller, H. Ulrich, and E. Ploetz, U.S. Patent 2,214,352 (1940). 79. C. Schoeller, H. Ulrich, and E. Ploetz, U.S. Patent 2,214,352 (1940). 80. L. G. Lundsted and W. F. Schulz, U.S. Patent 2,697,113 (1954).

182

5. Polyoxyalkylation of Hydroxy Compounds

81. 82. 83. 84.

P. M. T. Matell, U.S. Patent 3,168,569 (1965). C. N. Winnick, U.S. Patent 3,475,499 (1969). L. C. Lukman, P. L. Gordon, and D. E. Dean,, U.S. Patent 3,125,556 (1964). E. deB. Barnett, Proc. Chem. Soc., London 28, 259 (1912); G. Benoit, Bull. Soc. Chim. Fr. [5] 6, 708 (1939). H. L. Piggott, U.S. Patent 2,059,273 (1936); W. F. Tousignant and A. W. Baker, J. Org. Chem. 22, 166 (1957). J. J. Cames, U.S. Patent 2,520,381 (1950). A. J. W. Headlee, A. R. Collett, and C. L. Lazzell, J. Am. Chem. Soc. 55, 1066 (1933); E. J. Schwoegler, U.S. Patent 2,337,004 (1943). W. Rupilius, U.S. Patent 3,931,338 (1976). H. K. Krummel and R. M. Wise, U.S. Patent 4,098,818 (1978). K. D. Longley, R. Herke, and R. J. Kufrin, U.S. Patent 4,110,268 (1978). W. R. Fijal, U.S. Patent 3,640,997 (1972). A. Vasquez, R. Deza, and R. J. J. Williams, Polym. Bull. (Berlin) 28, 459 (1992). R. Mendieta, Ger. Often. DE 4,030,831 (1992). H. H. Greve and W. Obrecht, Ger. Often. DE 4,107,647 (1992). D. H. Suh, J. C. Won, D. K. Kim, and J. C. Jung, J. Polym. Sci. Part C Polym. Lett. 26, 83 (1988). L. J. Mathias and A. O. Kress, Polym. Prepr. Am. Chem. Soc. Div. Polym. Chem. 29(1), 331 (1988). M. E. Denker and F. W. Harris, Polym. Prepr. Am. Chem. Soc. Div. Polym. Chem. 35(1), 521, (1994). D. F. Mattem and D. M. Hercules, Anal. Chem. 57, 2041 (1985). E. T. Marquis, G. P. Speranza, Y. H. E. Sheu, W. K. Culbreth III, and D. G. Pottratz, U.S. Patent 5,154,803 (1992). D. K. V. Steel, British Patent 927,809 (1960). L. Reibel and E. Franta, Makromol. Chem. 193(5), 1099 (1992). P. P. Nicholas, J. Polym. Sci. Part A 30, 1123 (1992). T. Morimoto and N. Yoshida, Japanese Patent 02,227,426 (1989). R. P. Quirk and J.-J. Ma, J. Polym. Sci. Part A Polym. Chem. 26, 2031 (1988). M. A. Winnick and R. Xu, Polym. Prepr. Am. Chem. Soc. Div. Polym. Chem. 32(3), 659 (1991). M. M. Amiji and V. R. Patel, Polym. Prepr. Am. Chem. Soc. Div. Polym. Chem. 3(2), 403 (1994). I. Schipor and J. M. J. Fr6chet, Polym. Prepr. Am. Chem. Soc. Div. Polym. Chem. 3(2), 480 (1994). J. Li and I. M. Khan, Polym. Prepr. Am. Chem. Soc. Div. Polym. Chem. 34(2), 777 (1994). J. Wang, S. K. Varshney, R. Jerome, and P. Teyssie, J. Polym. Sci. Part A Polym. Chem. 30, 2251 (1992). W. B. Sun, J. F. Ding, R. H. Hobbs, F. Heatley, D. Attwood, and C. Booth, Colloids Surf. 54(1-2), 103 (1991). O. Sangen, S. Matsuda, H. Nakano, K. Yamana, K. Sasaki, and N. Ikeda, J. Polym. Sci. Part A Polym. Chem. 30, 1171 (1992). T. G. Park, S. Cohen, and R. Langer, Macromolecules 25, 116 (1992). S. Makhija, E. M. Pearce, and T. K. Kwei, J. Polym. Sci. Part A Polym. Chem. 30, 2693 (1992). S. Okita, T. Hatsu, and Y. Yamamoto, Japanese Patent JP 01 69,616 (1987). R. P. Foss and H. W. Jacobson, U.S. Patent 4,254,238 (1981). F. Guay and S. Bisaillon, J. Pharm. Sci. 73(3), 392 (1984).

85. 86. 87. 88. 89. 90. 91. 92. 93. 94. 95. 96. 97. 98. 99. 100. 101. 102. 103. 104. 105. 106. 107. 108. 109. 110. 111. 112. 113. 114. 115. 116.

Chapter 6

Polymeriz ation Reactions of N-Viuylcarbazole and Related Monomers 1.

Introduction

2.

Polymerization

to N - V i n y l c a r b a z o l e

A. Free-Radical

2-1. 2-2. 2-3. 2-4. 2-5. 2-6. 2- 7. 2-8.

Reactions Process

........................................

of N-Vinylcarbazoles

184

..............................

185

185

..............................................

Bulk Polymerization of N-Vinylcarbazole . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 Bulk Polymerization of N-Vinylcarbazole . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 Continuous Bulk Polymerization of N- Vinylcarbazole . . . . . . . . . . . . . . . . . . . 187 Suspension Polymerization of N-Vinylcarbazole Using Hydrolyzed Poly(vinyl acetate) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 Suspension Polymerization of N- Vinylcarbazole Using Wheat Starch . . . . . . . . 187 Suspension Polymerization of N-Vinylcarbazole Using Sodium Polyacrylate. . . 188 Emulsion Polymerization of N- Vinylcarbazole . . . . . . . . . . . . . . . . . . . . . . . . 188 Solution Copolymerization of Methyl Acrylate and N-Vinylcarbazole . . . . . . . . 188

B. Anionic

189 189

Process ..................................................

C. C a t i o n i c P o l y m e r i z a t i o n

............................................

2-9. Polymerization of N-Vinylcarbazole Using BF3"Et20 . . . . . . . . . . . . . . . . . . . 2-10. Polymerization of N-Vinylcarbazole Using Aqueous Perchloric Acid . . . . . . . . 2-11. Cationic Polymerization of N-Vinylcarbazole in Toluene . . . . . . . . . . . . . . . . D. Charge-Transfer

Polymerization .......................................

E. O r g a n o m e t a l l i c - C a t a l y z e d

Polymerization

................................

2-12. Polymerization of N- Vinylcarbazole Using Triisobutylaluminum Catalyst 3.

N-Vinylamides

3-1. 3-2. 3-3. 3-4. 4.

Polymerization of N- Vinvl-N-propylacetamide . . . . . . . . . . . . . . . . . . . . . . . . Polymerization of N- Vinylacetamide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polymerization of N- Vinyl-N-methylpropionamide . . . . . . . . . . . . . . . . . . . . . Copolymerization of N- Vinyl-N-methylacetamide with Acrylonitrile

Miscellaneous

.....

.....................................................

Preparations

............................................

References ........................................................

190 190 190

191 192 192 193 194

195 196 .........

196

196 197

183

184

1.

6.

PolymerizationReactions of N-Vinylcarbazole

I N T R O D U C T I O N TO N - V I N Y L C A R B A Z O L E

N-vinylcarbazole (also known as 9-vinylcarbazole) is usually prepared by the reaction of acetylene with carbazole in the presence of an alkali hydroxide [1 ] or by the reaction of acetylene with alkali salts [2] of carbazole. (1) N

I

H

N

I

CH---CH2 m.p. 64~176

Other procedures involving dehydration of N-(2-hydroxyethyl)carbazole [3] and dehydrochlorination of N-(2-chloroethyl)carbazole [4] are less preferred. The former procedure gives low yields. N-vinylcarbazole has also been prepared by transvinylation with vinyl ethers [5]. The polymerization of N-vinyl carbazole may be initiated by free radicals, by cations, by organometallic catalysts, by charge-transfer processes, or by electrochemical methods. Since the monomer is a solid at room temperature (m.p. 64-66~ b.p. 154-155~ mm), solid state polymerizations have been carried out both on powdered monomer and on the surfaces of larger crystals. In this process, the reactive species propagates into the interior of the solid. N-vinylcarbazole and its polymers and copolymers are unusual materials with potentially interesting applications. For example, poly(N-vinylcarbazole) [PVK] is a charge-transporting polymer. This is of interest in the development of photorefractive materials. These have potential applications in optical storage devices [5a]. The electrophotographic characteristics of the purified polymer and of "doped" PVK has been studied [6]. PVK-based materials have been suggested for blue and green emitting diodes

[7, 8]. The use of these polymers in electrophotographic photoreceptors has been patented [9, 10]. In another patent, a material consisting of poly(vinyl chloride), a plasticizer, an ion-conductive additive, and poly(vinylcarbazole), among other components, was suggested as a thermosensor in thermistor materials [ 11]. The monomer can sublime. The polymer may be vacuum deposited as a film. The characteristics of such a film are similar to those of films formed from solutions [ 12]. The polymers are glassy and of good thermal stability. Their dielectric properties remain substantially constant over a wide range of temperatures. They are suitable for electrical applications. They have been used as capacitors [13], insulators, and foams [14], and in image recording systems [15].

Polymerization Reactions of N-Vinylcarbazoles

2.

185

The polymers are brittle. They melt above 200~ The polymerization of polyvinylcarbazole has been reviewed in several sources which should be consulted for more information [ 16-19].

CAUTION: Vinylcarbazole is a suspected carcinogen and should be handled appropriately. The monomer has been reported to be a mutagen and to have allergenic effects. Even small residue of the monomer in the polymer may lead to serious health problems [18]. The major manufacturer of the monomer ceased production some time ago. Specialty chemical suppliers also may no longer make this material available in the U.S. However, it is available from laboratory chemical suppliers in small quantities. 0

POLYMERIZATION REACTIONS OF N-VINYLCARBAZOLES

N-Vinylcarbazole polymerizes by means of either free-radical or cationic catalysts but not by means of anionic catalysts. Polyvinylcarbazole is a hard, brittle polymer. The polymer was made accidentally by Reppe and co-workers when attempting to oxidize vinylcarbazole to N-carboxycarbazole using sodium chromate (NazCrO4) [20]. This polymer was marketed in Germany as Luvican M-150 and in the United States as Polection. The polymer has good dielectric properties at random frequencies and a softening range above those of polystyrene, polyurethanes, and polyethylene [20]. Cornish [21], Ellenger [22], and Tazuke and Okamura [23] have reviewed the polymerization reactions.

A.

Free-Radical Process

N-Vinylcarbazole polymerizes faster than styrene. At 70~ using 0.1 mole azobisisobutyronitrile in cyclohexanone as solvent [23] the rate constant is k = 2.303-t log(Mo/M) = 945 _+ 2.4 see

(2)

where t = reaction time and M0 and M are monomer concentrations at time t. The kinetics of polymerization of N-vinylcarbazole using azobisisobutyronitrile and benzoyl peroxide has been reported [24]. For styrene under similar conditions k = 9.4 _+ 0.4/sec. The absolute rate constants have been determined by the rotating sector method [25]. N-Vinylcarbazole can be polymerized in the solid state to partially crystalline polymers by cationic C12, Br2, and I2, and by Friedel-Crafts catalysts SnC14, A1C13, A1Br3 [26]. The polymers usually have a low molecular weight [27, 28]. Higashimura et al. [28] studied the solid-state polymerization of N-vinylcarbazole using various catalysts and determined the molecular weight distribution of the polymer by gel permeation chromatography (GPC). The polymers

186

6. Polymerization Reactions of N-Vinylcarbazole

obtained by cationic or radical catalysts had low molecular weights in the range of 400-600, whereas radiation from Co 6~ gave high-molecular-weight polymers [28,29]. Free-radical catalysts can also induce solid-stage polymerization. A typical catalyst is azobisisobutyronitrile [30,31]. The polymer obtained is also crystalline. Other catalysts, such as high-energy radiation [32], are also effective in promoting solid-state polymerization. Suspension [33-35] and emulsion [36, 37] polymerization of N-vinylcarbazole has also been reported. Sulfur contamination in the monomer must be removed to avoid inhibition [38]. N-Vinylcarbazole undergoes free-radical copolymerization with various co-monomers at 30~ in the presence of 10 -2 mole/liter azobisisobutyronitrile or of 102 mole/liter tert-butyl peroxide dissolved in tetrahydrofuran (THF). The following reactions by ratios were obtained [39]:

CAUTION: Handle azo compounds and peroxides with great caution. Co-monomer (M2)

rl

rE

CH2 = C H - - C N CH2=CH--COOCH3 p-CI--C6H4CH =CH2 CHE--C--COOCH3

0.04 0.11 0.023 0.07

0.28 0.43 a 7.0 2.7

3.9

0.13

I

CH3 CHE--CHOAc

a Cf Ref. [41 ] and Preparation 2-8.

2-1.

Bulk Polymerization of N-Vinylcarbazole

[34]

To an open autoclave is added N-vinylcarbazole which is then melted at 65~ Then 0.02% di-tert-butyl peroxide and 0.01% azobisisobutyronitrile is added with stirring. The vessel is sealed, pured with nitrogen, and pressured to 40 atm with nitrogen. The autoclave is heated to 80~176 to initiate polymerization as evidenced by a rapid increase in temperature. After the maximum temperature has been reached the polymerization reaction mixture is cooled under pressure. The autoclave is vented and the glassy polymer removed.

2-2.

Bulk Polymerization of N-Vinylcarbazole [36]

To a vessel was added fused N-vinylcarbazole which was then mixed with 0.01% tert-butyl peroxide. The vessel was closed and air was removed. Upon heating polymerization took place starting at 120~ aiter which the temperature

2. Polymerization Reactions of N-Vinylcarbazoles

187

rose to 300~ The polymer softened at >200~ Similarly N-vinylcarbazole polymerized in the presence of 0.02% tert-butyl peroxide and 0.01% azobisisobutyronitrile (polymerization starts at 80~ in the absence of air).

2-3.

ContinuousBulk Polymerization of N-Vinylcarbazole [30]

A mixture of 29 lb of N-vinylcarbazole and 0.145 lb of azobisisobutyronitrile was spread in a 3/8-inch layer on a stainless steel conveyor belt moving at 68 ft/min. The material was passed under a bank of three 6,000 watt infrared heaters (approximately 20.4 sec of heat) whereupon the mixture melted and polymerized. The mixture was passed under a hood and then over a cold water bath to aid solidification. The polymer was broken and pulverized. A 20% solution in toluene gave a Gardner viscosity of Y.

2-4. Suspension Polymerization of N-Vinylcarbazole Using Hydrolyzed Poly(vinyl acetate) [33] To a three-necked flask equipped with a stirrer, condenser, and dropping funnel are added 1700 gm of water, 500 gm (2.6 mole) of N-vinylcarbazole, 3 ml of a 3% solution of 86-89% hydrolyzed poly(vinyl acetate), and 0.5 gm sodium acetate. The mixture is stirred at 80~ while 5 grn of azobisisobutyronitrile is added. In 2 min the temperature rises to 97~ and after 5-10 min it drops. The polymer suspension is cooled and filtered. The residue is washed with methanol and acetone, and then extracted for several hours with acetone in a Soxhlet extractor. The polymer weighs 400 gm (80%).

2-5. Suspension Polymerization of N-Vinylcarbazole Using Wheat Starch [33] To a 5-liter polymerization flask equipped with a stirrer, condenser, nitrogen inlet tube, and dropping funnel are added 21 kg water, 0.5 kg (2.6 mole) N-vinylcarbazole, and 5 gm wheat starch. The reaction mixture is heated to 70~ at which temperature the monomeric vinylcarbazole becomes molten. Then 50 ml of an o-dichlorobenzene solution containing 0.5 gm of dissolved azobisisobutyronitrile is added all at once. The reaction mixture is stirred slowly until a uniform mixture is obtained consisting of a dispersion of 9-vinylcarbazole in wheat starch suspension and a droplet phase of catalyst containing dissolved monomer. The temperature is now raised to 90~ with stirring continued at 300 rpm for 5 hr while a stream of nitrogen gas is introduced. A transparent, bead-like polymer particle of approximately 2 mm diameter is

6.

188

PolymerizationReactions of N-Vinylcarbazole

obtained. The polymer can be isolated by dissolving the beads in chlorobenzene and precipitating in methanol. On drying a 97% yield of polymer is obtained. (Critical visc. at 30~ in chlorobenzene = 1.31.)

2-6.

Suspension Polymerization of N-Vinylcarbazole Using Sodium Polyacrylate [40]

To a three-necked, round-bottom flask equipped with a condenser, mechanical stirrer, addition funnel, and nitrogen inlet were added 1.0 liter water (pH 9.2 by the addition of 0.48 gm NaOH, 1.55 gm H3BO3, and 1.86 gm KC1), 500 gm N-vinylcarbazole, 2.5 gm sodium polyacrylate, 0.5 gm azobisisobutyronitrile, and 1.0 gm di-tert-butylperoxide. The mixture was stirred at 75~ for 24 hr and then poured into an autoclave that had been preheated at 90~ The autoclave was sealed and then heated to 130~ for 2 hr with stirring. (The polymer at this stage can be isolated and used as a suspension type polymer, in order to obtain yield data and purified polymer it becomes necessary to obtain a solution, then precipitation is carried out from methanol.) The charge was cooled and then dissolved in monochlorobenzene followed by precipitation from methanol to give 90% yield of polymer.

2-7. Emulsion Polymerization of N-Vinylcarbazole [36] To a glass flask equipped with a stirrer, condenser, dropping funnel, and nitrogen inlet were added 1000 parts of fused, powdered N-vinylcarbazole, 2,000 parts water, 5.0 parts of a protective colloid, 2.0 parts tert-butylperoxide, and 1.0 part azobisisobutyronitrile (pH 7.5-10). The stirred mixture was heated at 70~176 for 24 hr. Then the mixture was stirred at 120~176 to give an emulsion polymer. The polymer had a softening point > 190~ A study of the microstructure of copolymers made use of a simple solution procedure for the copolymerization of methyl acrylate (MA) with N-vinylcarbazole (NVK). The ratio of the feed composition ranged from (0.1429 moles of MA to 1.00 of NVK) to (7 moles of 1 of NVK)--a 49-fold range in composition. The experiments were carried out to high conversions [41 ]. Preparation 2-8 is based on this work. The reactivity ratios calculated from this series were approximately rMA = 0.90,

2-8.

rNWr = 0.18.

Solution Copolymerization of Methyl Acrylate and N-Vinylcarbazole [41]

In a suitably sized polymerization ampoule, a solution of 5.1 gm (0.06 moles) of methyl acrylate and 16.7 gm (0.10 moles) of N-vinylcarbazole in 100 ml of

2. Polymerization Reactions of N-Vinylcarbazoles

189

toluene was treated with 0.22 gm of 2,2'-azobisisobutyronitrile (AIBN). The air was replaced with nitrogen. Then the ampoule was sealed and heated at 60~ for 21.5 hr. After the vessel had been cooled and cautiously opened, the polymer was isolated by pouting the solution into methanol. The product was reprecipitated by dissolving it in tetrahydrofuran and precipitating the product by addition to fresh methanol. The product was then dried. Conversion was 84.2%. The ratio of MA to NVK in the copolymer was 0.72 to 1. It is interesting to note that a copolymer with a composition of approximately 3.3 moles of MA to 1 mole of NVK could be reacted with mercury(II) trifluoroacetate to give a stable material with approximately one mercury atom per carbazole unit. Upon treatment with iodine, the copolymer apparently loses the mercury trifluoroacetyl group and forms iodinated carbazole moieties along the polymer chains [42].

B.

Anionic Process

An anionic initiator such as n-butyllithium failed to initiate the polymerization of N-vinylcarbazole. Evidently, the production of NVK-anion radicals when the monomer was treated with sodium in THF led to decomposition to carbazole and ethylene rather than to polymerization. Interestingly, the anion of N-vinylcarbazole does not dimerize, if it is formed, but seems to be capable of initiating the polymerization of other monomers such as styrene. (It is of course conceivable that just the presence of any anionic species will initiate the polymerization of styrene. The presence of NVK would then not be significant.) It has been suggested that the failure of the anionic process with NVK may be the result of the high concentration of negative charges around the vinyl group [43].

C.

Cationic Polymerization

N-Vinylcarbazole polymerizes readily to give a low-molecular-weight polymer when trace amounts of protonic acids such as trichloroacetic acid are used. Sulfuric acid has been reported to give 90-93% yield of polyvinylcarbazole by the heterogeneous polymerization of N-vinylcarbazole in benzene [44, 45]. Certain oxidizing metal salts [46], perchlorates [47], boron trifluoride chelated compounds [48], boron trichlorides [49], and stable oxonium compounds initiate the polymerization [50]. The electron-releasing nitrogen groups help to increase nucleophilicity of N-vinylcarbazole. This aids in its attraction to weak cationic groups. Some catalysts are suspected of inducing an electron transfer reaction. Scott and Labes [51 ] reported that N-vinylcarbazole polymerizes by a cationic mechanism in carbon tetrachloride. The have shown that traces of chlorine are the active catalyst and that the polymerization can be initiated by removal of

190

6. Polymerization Reactions of N-Vinylcarbazole

free chlorine. Breitenbach and Sma [52] have shown that the use of methyl methacrylate in the presence of N-vinylcarbazole and carbon tetrachloride gives a homopolymer of N-vinylcarbazole which they suggest is an indication of a cationic mechanism. Biswis and co-workers [53] have shown that POC13 and SOC12 initiate a cationic polymerization of N-vinylcarbazole. In the latter case, the mechanism is thought to involve the formation of a cation by the direct interaction on the monomer with the thionyl chloride [54]. The solid state cationic polymerization process has also been reported [55].

2-9.

Polymerization of N-Vinylcarbazole Using BF3 . EteO [56]

To a flask containing 180 ml of cyclohexane cooled to 5~176 is added 20 gm of N-vinylcarbazole. Then 1 ml of 2.5% BF3" Et20 in THF is added while stirring. After 1 hr the polymer suspension is filtered and dried at 90~ to give 19 gm (95%) of product having a relative viscosity of 1.148 (1% in benzene at 25 ~

2-10.

Polymerization of N-Vinylcarbazole Using Aqueous Perchloric Acid [57]

To a solution of N-vinylcarbazole in ethyl acetate is added 0.1-1% aqueous solution of perchloric acid. A yellow-orange color develops immediately and the polymer spontaneously precipitates to give a polymer of MW 600-2000 (cryoscopically in C6H6).

CAUTION: Handle perchloric acid with great care. 2-11.

Cationic Polymerization of N-Vinylcarbazole in Toluene [58]

To a flask equipped with a stirrer, a thermometer, and a reflux condenser are added 10 gm (0.06 mole) of N-vinylcarbazole, 30 ml of toluene, 3.42 ml of paraldehyde, and 3.75 ml of acetaldehyde. To the stirred mixture is added 0.6 ml of a mixture of hydrochloric acid and perchloric acid (10:1 volume ratio). The reaction mixture is heated to 55~ and stirring is continued for 1 hr. The solution is washed with aqueous alkali, then with water, and poured with stirring into 150 ml of petroleum ether. The precipitated polymer is separated by filtration, washed with alcohol then water, and dried to give 8.8 gm (70.5%) of

2. Polymerization Reactions of N-Vinylcarbazoles

191

a white polymer (softening point 130~176 7.19% N; MW 600-1500). For a related publication see a patent from the Tomsk Polytechnic Institute [59]. In a heterogeneous system, powdered biosynthesized ?-poly(glutamic acid), in the free acid form, has been used to initiate the polymerization of N-vinylcarbazole as well as N-vinyl-2-pyrrolidone. The rate of polymerization in nitrobenzene was greater than in toluene. In the process, there was no significant grafting onto the surface of the ~,-poly(glutamic acid). It has been proposed that initiation involves proton addition from the surface of the carboxylic acid to the monomer. The propagation proceeds with carboxylate anions on the surface of a counter ion [60]. In a solution of 1,2-dichloroethane at 60~ N-vinylcarbazole has been cationically polymerized with ethyl 1-cyano-2-(p-methoxyphenyl)cyclopropanecarboxylate as initiator. The polymers obtained had a bimodal distibution of their molecular weights. It was postulated that the propagation steps of the process proceeded by both free-ion and an ion-pair steps. At low temperatures, low monomer concentrations, higher initiator concentrations, lower conversion, and in more polar solvents, the free-ion propagation was favored [61 ].

D. Charge-Transfer Polymerization Metal salts are good initiators of the charge-transfer polymerization of N-vinylcarbazole. Some oxidizing metal salts have been shown by ESR spectroscopy to be involved in an electron-transfer mechanism [62, 63]. Polynitro compounds are also reported to be involved in a charge-transfer initiation process of the polymerization of N-vinylcarbazole [64]. Aromatic nitro compounds have similar properties [65]. The polymerization reaction has been reviewed [66]. The mechanism of charge-transfer polymerization and the detection of ionradical intermediates in the photosensitized reaction of N-vinylcarbazole in the presence of chloranil have been reported [67]. Hydrogen halides also form charge-transfer complexes which then initiate polymerization [68]. These charge-transfer polymerization and cationic polymerization mechanisms are related. However, charge-transfer polymerization may also involve radical processes as in the alternating copolymers of N-vinylcarbazole with fumaronitrile or diethyl fumarate [69]. The photopolymerization mechanism for the polymerization of NVK in the presence of 2,4,7-trifluorene postulates the formation of a dimer radical cation by a charge-transfer reaction. The dimer radical cation may then form cyclodimers, form cationic polymers, or polymerize by a free radical process [70]. Ledwith and co-workers have reviewed molecular complexes and fluorescent properties of poly(vinylcarbazole) and of optically active derivatives of NVK [71, 72].

6.

192

Polymerization Reactions

ofN-Vinylcarbazole

Complexes of poly(N-vinylcarbazole) and tetracyanoquinodimethane (TCNQ) have been prepared by treating PVK with TCNQ in dioxane solution followed by rapid evaporation of the solvent. A second method used a mixture of chloroform and methanol to prepare the complexes. In the latter case, the products precipitated as sticky materials which were separated and then dried. The electrical conductivities of complexes prepared with different ratios of reagents and by the two different methods were then evaluated [73].

E. Organometallic-Catalyzed Polymerization N-Vinylcarbazole undergoes stereospecific polymerization in the presence of diethyl aluminum chloride catalysts [(C2Hs)2A1C1] [74, 75]. By means of X-ray diffraction analysis the crystallinity of the polymer was found to be 30-50%. The polymer is reported to be stable at 250~ [75]. Other catalysts that are also reported to be effective for initiating this polymerization are (C2Hs)2A1C1/VOC13 in toluene at -20~ [76], (C2Hs)A1C12 [77], (C2Hs)2A1C1 [77], Ti(OC4H9)2C12 [77], Ti(OAc)2CI2 [77], Fe(OAc)2C1 [77], Sn(OAc)2C12 [77], and TiCla-SiO2(C4H9)3A1 [78, 79].

2-12.

Polymerization of N-Vinylcarbazole Using Triisobutylaluminum Catalyst [78]

a. Preparation of Catalyst

To a l-liter, three-necked, round-bottom glass flask is added 10 gm "Alon" (a pyrogenic alumina from Deutsche Gold- und Silber-Scheidenstalt Vermals Roessler, 10--40/~m diameter: OH equiv 0.7 mEq/gm). The reaction flask is put in a vacuum drying over at 110~ for 15 hr. To the sealed cooled flask is charged 5 mmole of TiF4 dissolved in 500 ml of n-heptane. The mixture is refluxed for 10 hr while being swept with a dry nitrogen stream to remove the HF that is formed. (The TiF4 and A1203 are reacted in this way and aluminum has 5 milliatoms of Ti chemically bound to it.) This is a catalyst to be used in the polymerization reaction as described below.

b. Polymerization

To a dry, 500-ml, three-necked round-bottom flask, which has a nitrogen blanket, is added 100 ml of the catalyst slurry from the above catalyst preparation (contains approximately 1 milliatom Ti bound to the surface of about 2.0 gm A1203). Then 1.0 mmole triisobutylaluminum is added followed by 200

193

3. N-Vinylamides

millimoles of N-vinylcarbazole monomer. The flask is stirred at room temperature for 48 hr to give poly(N-vinylcarbazole).

3.

N-VINYLAMIDES

The N-vinyl compounds may be prepared by one of the methods shown in Scheme 1. The use of acetylene is the most direct route; the other methods are of secondary importance. The acetylene route is also used to prepare N-vinylcarbazole [88]. The properties of some representative N-vinyl compounds are shown in Table I. The N-vinylamides are liquids or low-melting solids which are soluble in organic solvents. Some typical compositions are shown in Table I along with the physical properties. N-Vinylamides homopolymerize and copolymerize with various vinyl monomers as shown in Table II. The homopolymers are generally water soluble and because of this property are used in adhesives, cosmetics, toiletries, detergents, and pharmaceuticals. The N-vinylamides are readily hydrolyzed to acetaldehyde and free amide in the presence of dilute aqueous acid. Aqueous solutions of either poly(N-vinylcaprolactam) or polyvinylpiperidine precipitate from water on raising the temperature [89, 90]. Polyvinylcaprolactam precipitates at 35~ whereas polyvinylpiperidine precipitates at 64~176 The water solubility of polyvinylcaprolactam was found to increase with an increase in its molecular weight [90]. The latter polymer is also soluble in organic solvents as are the open-chain N-vinylamides.

RCONH -- CH2CHEC1

RCONHCH2CH2OAc

o II RC -- NHCH = CH2

CH2=CH--NCO ~ + RMgl

H20

CH3-- CH(NHCOR)2 Scheme 1

RCONH2

(where

RCONH2

R' = OCCH2CH3)

f

CH2--CH2 + RCONH I R Preparative methods of N-vinylamides [80-87].

194

6. Polymerization Reactions of N-Vinylcarbazole TABLE I N-Vinylamides R10 I II CH2=CH--N--C--R 2 R1

R2

CH3 C2H5 CH3 C2H5 CH3

CH3 CH3 C2H5 C2H5 C6H5

b.p. (mm Hg)/m.p. 70~ (25) 101~ (3)/52~ 69~ (13) 74~ (12) 137~176 (14)

n2o~

Ref.

1.4806 1.4797 1.4737 1.5670

a a b b b

1.5057

c, d e d, f

O II / C -'--I CH2=CH --N (CH2),

~~'

n= 3 n= 4 n= 5

96~ (14)/13.5~ 109~176 (12)/42.5~ 11.0.8~176 (10)/34.5~

W. E. Hanford and H. B. Stevenson, U.S. Patent 2,231,905 (1941); Chem. Abstr. 35, 3267 (1941). bH. Bestian and H. Jenson, U.S. Patent 3,324,177 (1967). c,,Vinyl Pyrrolidone," Bull. 7543-037. GAF Corp. d W. Reppe, H. Krizkalla, O. Doraheim, and R. Saurbier, U.S. Patent 2,317,804 (1943); Chem. Abstr. 37, 6057 (1943). eFarbwerke Hoechst A. G., French Patent 1,340,350 (1963). f o . F. Solomon, M. Corciovei, and C. Boghing, J. Appl. Polym. Sci. 12, 1843 (1968). a

3-1. Polymerization of N-VinyI-N-propylacetamide [91] O II CH3--C--N--CH=CH2

I C3H7

-"

- - CH2 - - C H - -

I C3H7--N--C--CH3

(3)

II O To a polymerization bottle containing 3.0 gm N-vinyl-N-propylacetamide and 6.0 gm C6H6 is added 0.009 gm azobisisobutyronitrile catalyst. The bottle is flushed with nitrogen, sealed, and placed in a 75~ water bath for 24 hr. The bottle is cooled to room temperature and a benzene solution of 2,6-di-tert-butylp-cresol is added. The contents of the bottle are transferred to a beaker containing 50 ml of distilled water. The solvent and unreacted monomer are removed under reduced pressure to give a 44% conversion to polymer (softening point

3. N- Vinylamides

195

TABLE II Copolymerization of N-Vinylamides

N-Vinylamide N-Vinylacetamide N-Vinyl-N-methylpropionamide N-Vinyl-Nmethylacetamide N-Vinyl-Npropylacetamide N-Vinylformamide N-Vinylpiperidone

N-Vinyl-Nmethylacetamide N-Vinylphthalimide N-Vinyl-Nmethylacetamide

Co-monomer

Acrylonitrile

Solvent

Catalyst

Temp (~

Time (hr)

Yield (%)

Ref.

Water Water

H202 H202

50 50

15 12

Water

50

1-2

C6H6

H202 NH4OH AIBN

75

24

t-BuOH Water

AIBN H202

65 90-100

18 1/2

c d

Ethylene

t-Bu202

180

--

e

50

24

f g

Ethylene N-Methylol Acrylamide Butyl acrylate

Vinyl acetate

Azobisisobutyronitrile

a a

44

b

a H. Bastian and D. Ulmschneider, U.S. Patent 3,316,224 (1967). b R. B. Blanc and S. M. Cohen, British Patents 1,031,269 (1966), 1,082,018 (1967). CR. Resz and H. Barth, British Patent 1,158,539 (1969). d V. Jasinsko and M. M. Fein, U.S. Patent 3, 536, 650 (1970). eB. O. Baum, R. K. Walton, and R. E. Raynolds, Belgian Patent 633,689 (1963). f A. F. Nikolaev, N. V. Daniel, and T. B. Drozdova Karbotsepnye Vysokomol, Soedin. p. 114 (1963). gF. E. Bailey, Jr., U.S. Patent 3,212,972 (1965).

115~ [r/] = 0.17 dl/gm, a[r/] ~ 0.04 dl/gm has MW 5,000). The product is useful in adhesive and hair spray applications.

3-2. Polymerization of N-Vinylacetamide [92]

CHaCONH--CH--CH2

~ --CH2--CH--

-]

I NH--C--CH3

II O

J

(4)

n

To a reaction flask is added 20 gm of N-vinylacetamide in 47 ml water. Then 0.12 ml of hydrogen peroxide (30%) and 0.3 ml ammonia (20%) are added slowly. The hydrogen peroxide is added in 4 equal portions over a 3-hr period while the reaction temperature is kept at 50~ After 15 hr a clear, colorless solution of a polymer is obtained which has a K value of 88.5 and a reduced viscosity of 3.0 (det of a 1% aq soln at 25~

196

3-3.

6. Polymerization Reactions of N-Vinylcarbazole

Polymerization of N-Vinyi-N-methylpropionamide [92] C2HsCO--N--CH:CH2

I

~

--CH2--CH--

-

I

CH3

N--COC2H5

(5)

I

CH3

n

To 40 gm of N-vinyl-N-methylpropionamide in 70 ml water is added 0.5 ml of ammonia. The reaction mixture is stirred and heated at 50~ while hydrogen peroxide (30%) is added in 6 increments of 0.1 ml each. As the polymerization proceeds the separated organic phase becomes solubilized in the aqueous phase to give a clear polymer solution having a K value of 41.7.

3-4.

Copolymerization of N-Vinyl-N-methylacetamide with Acrylonitrile [92]

CH3--CON--CH=CH2 + CH2--CH--CN

I

CH3

I C2CHII -cH2-c-cN NCOCH31 (6)

x

CH3

x

To a flask are added 30 gm of N-vinyl-N-methylacetamide and 5.0 gm acrylonitrile dissolved in 70 ml water. Then 0.5 ml ammonia (20%) is added and the flask is flushed with nitrogen. The reaction mixture is heated at 50~ and 0.3 ml of hydrogen peroxide (30%) is added. The reaction mixture thickens and finally becomes a gel. The polymer is isolated by vacuum stripping the water for 8 hr.

4. 1. 2. 3. 4.

MISCELLANEOUS

PREPARATIONS

Preparation and polymerization of N(1-alkenyl)piperazines [93, 94]. Poly(aminoalkyl)vinyl ethers [94]. Vinylpyridines and vinylquinolines [95]. Copolymerization of N-vinylcarbazole with acrylic and methacrylic acid esters [96]. 5. Poly(N-ethynylcarbazole) [97]. 6. Modifying polyvinylcarbazole by reaction with an aromatic nitro compound [98]. 7. Poly(N-vinylamines) [99].

References

8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.

197

Copolymerization of isobutylene and N-vinylcarbazole [ 100]. Copolymerization of N-vinylcarbazole and other N-vinyl monomers [ 101 ]. Cationic polymerization of N-ethyl-3-vinylcarbazole [ 102]. Copolymerization of N-ethyl-N-vinylacetamide with vinyl propionate [103]. Purification of N-alkyl-N-vinylacetamides [ 104]. Cyclodimerization, polymerization, and copolymerization of N-vinylcarbazole photoinduced by Rhodamine [ 105]. Polyvinylcarbazole as a photosensitive material [106]. Polyvinyl carbazole as an organic electrophotographic material [107]. Oxygen-catalyzed photodimerization of N-vinylcarbazole in donor solvents [108]. Radiochemical polymerization of N-vinylcarbazole in liquid and solid phase [109]. Radical bulk polymerization of N-vinylcaprolactam [ 110]. Mechanism of the charge-transfer polymerization of NVK-maleic anhydride when exposed to light of wavelength greater than 360 nm [ 111 ]. Structural effects on the properties of polymeric charge-transfer complexes containing carbazolyl groups [112]. Electrochemical polymerization of NVK to form electrochromic films [113]. Films of poly(2-[9-carbazolyl]ethyl methacrylate-co-isobutyl methacrylate) [114]. Light-responsive microgels containing N-vinylcarbazole copolymers [115].

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198

6. Polymerization Reactions of N-Vinylcarbazole

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200

6. Polymerization Reactions of N- Vinylcarbazole

79. J. Heller, D. O. Tieszen, and D. B. Parkinson, J. Polym. Sci., Part A 1, 125 (1963). 80. H. Bestian and H. Jensen, U.S. Patent 3,324,177 (1967); W. Reppe, H. Krizkalla, A. Dornheim, and R. Sauerbier, U.S. Patent 2,317,804 (1943); Chem. Abstr. 37, 60571 (1943); W. E. Hanford and D. L. Fuller, Ind. Eng. Chem. 40, 1171 (1948); C. E. Schildknecht, "Vinyl and Related Polymers," p. 662. Wiley, New York, 1952; J. E. McKean and P. S. Stauber, U.S. Patent 3,318,906 (1967). 81. W. E. Walles, W. F. Tousignant, and T. Hortman, Jr., U.S. Patent 2,891,058 (1959); Chem. Abstr. 54, 2359 (1960); W. J. Peprel and J. D. Watkins, U.S. Patent 3,019,231 (1962); Chem. Abstr. 54, 23591 (1960). 82. J. W. Lyan and B. D. Ash, U.S. Patent 3,144,396 (1964); W. E. Hanford and H. B. Stevenson, U.S. Patent 2,231,905 (1941); Chem. Abstr. 35, 3667 (1941). 83. R. Bacskai and L. Halmos, Magy. Kem. Foly. 60, 8 (1954); Chem. Abstr. 52, 3396 (1958). 84. R. Bacskai, Acta Chim. Acad. Sci. Hung. 19, 1 (1959); Chem. Abstr. 54, 13047 (1960). 85. E. Husemann, German Patent 1,088,479 (1960); Chem. Abstr. 55, 15353 (1961). 86. D. Ben-Ishai and R. Giger, Tetrahedron Lett. 50, 4523 (1965). 87. H. Hirai, H. Sawai, and S. Makijima, Japanese Patent 71/05,128 (1971); Chem. Abstr. 75, 6612w (1971). 88. S. R. Sandier, U.S. Patent 3,679,700 (1972); Abstr., 164th Nat. Meet., Am. Chem. Soc., 1972 Paper 168 ORGN. 89. M. F. Shostakovski and F. B. Sydelkovskaya, Vestn. Akad. Nauk SSSR 7, 1957 (Refs. 1-55). 90. O. F. Solomon, M. Corciovel, I. CiutL and C. BoghinL J. Appl. Polym. Sci. 12, 1835 (1968). 91. R. B. Blanc and S. M. Cohen, British Patent 1,031,269 (1966). 92. H. Bestian and D. Ulmschneider, U.S. Patent 3,316,224 (1967). 93. S. R. Sandier and M. Delgado, U.S. Patent 3,738,986 (1973). 94. S. Melamed, U.S. Patent 2,871,203 (1959). 95. J. P. Schroeder and D. C. Schroeder, High Polym. 24, 1357 (1971). 96. L. N. Fedorova, L. I. Nyun'ko, V. Ya. Pochinok, E. D. Korotkaya, T. D. Butmerchuk, V. P. Nardenov, and I. Vapsinskaite, Sposoby Zapisi Inf. Besserebryanykh Nositelyakh. 7, 69 (1976); Chem. Abstr. 86, 122101 (1977). 97. Y. Okamoto and S. K. Kundu, J. Org. Chem. 35, 4250 (1970). 98. Y. I. Vasilenok, B. E. Davydov, B. A. Krentsel, and B. I. Sazhin, U.S.S.R. Patent 208,930 (1968); Chem. Abstr. 69, 3319w (1968). 99. E. E. Sirotkina, V. P. Lopatinsky, V. D. Filimonov, R. N. Kogan, V. D. Pirogov, S. I. Kudinova, and G. I. Rybalko, British Patent 1,436,204 (1976); Chem. Abstr. 85, 143784z (1976). 100. Compagnie Franqaise de Raffinage, Fr. Demande, 2,258,405 (1975); Chem. Abstr. 84, 90767s (1976). 101. R. Hart, Makromol. Chem. 47, 143 (1961); Chem. Abstr. 56, 10387 (1962). 102. A. H. DeMola, A. Ledwith, J. F. Yanus, W. W. Limburg, and J. M. Pearson, J. Polym. Sci., Polym. Chem. Ed. 16, 761 (1978). 103. F. E. Bailey, Jr., U.S. Patent 3,212,972 (1965). 104. J. W. Lynn and B. D. Ash, U.S. Patent 3,144,396 (1964). 105. R. A. Crellin and A. Ledwith, Macromolecules 8(2), 93 (1975); Chem. Abstr. 83, 2868p (1975). 106. Xerox Corp., British Patent 1,188,376 (1970); Chem. Abstr. 73, 26753 (1970). 107. Y. Murakami and K. Morimoto, British Patent 1,125,548 (1968); Chem. Abstr. 71, 3277x (1969). 108. Y. Shiroto, K. Tada, M. Shimizu, S. Kusabayashi, and H. Mikawa, J. Chem. Soc. D No. 17, p. 1110 (1970); Chem. Abstr. 73, 98723t (1970).

References 109. 110. 111. 112. 113. 115.

H. Chapiro and G. Hardy, J. Chim. Phys. 59, 993 (1962). O. F. Solomon, M. Corciovei, and C. Boghina, J. Polym. Sci. 12, 1843 (1968). Y. Shirota and Y. Yoshida, J. Photopolym. Sci. Technol. 5(3), 475 (1992). A. V. Tkachev, V. A. Tverskoi, and V. P. Zubov, New Polym. Mater. 3(3), 187 (1992). U. Geissler, M. L. Hallensleben, and L. Toppare, Synth. Met. 55, 1662 (1992). M. Shiotani, Japanese Patent JP 05/78,592 [93/78,592] (1993).

201

Chapter 7

Polymerization of Vinyl Acetate and Other Vinyl Esters 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Physical Properties of Vinyl Acetate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Monomer Purification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-1. 1-2.

Vinyl Acetate Purification with Aqueous Alkali Extraction . . . . . . . . . . . . . . . Vinyl Acetate Purification with Aldehyde Reagents . . . . . . . . . . . . . . . . . . . . .

C. Initiation, Inhibition, and Retardation of Polymerization . . . . . . . . . . . . . . . . . . . . . . D. Polymer Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Polymer Fractionation and Molecular-Weight Constants . . . . . . . . . . . . . . . . . . . . . .

1-3.

Fractionation of Poly(vinyl acetate) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

F. Inhibitors of Vinyl Acetate Polymerizations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Bulk Polymerizations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-1. 2-2.

Sealed-Tube, Bulk Polymerization of Vinyl Acetate . . . . . . . . . . . . . . . . . . . . Bulk Polymerization of Vinyl Acetate (Reflux Apparatus) . . . . . . . . . . . . . . . .

3. Solution Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-1. 3-2. 3-3.

4-2. 4-3. 4-4.

Suspension Polymerization of Vinyl Acetate (Control of Molecular Weight by Variation in Initiator Level) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Suspension Polymerization of Vinyl Pivalate . . . . . . . . . . . . . . . . . . . . . . . . . Suspension Polymerization of Vinyl Acetate in the Presence of Hydrogen Peroxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preparation of a Stable Poly(vinyl acetate) Dispersion . . . . . . . . . . . . . . . . . .

5. Emulsion Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5-1. 202

211 211 214 219 220 223 223 225 226 232 233 235

Polymerization of Vinyl Acetate in Ethylene Dichloride . . . . . . . . . . . . . . . . . Polymerization of Vinyl Acetate in tert-Butyl Alcohol . . . . . . . . . . . . . . . . . . . Formation of Low-Molecular-Weight Poly(vinyl acetate) (Gradual Addition Procedure) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237

4. Suspension Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4-1.

203 205 206 210

Emulsion Bottle Polymerization of Vinyl Acetate at 70~ . . . . . . . . . . . . . . . .

239 242 244 245 246 248 259

1. Introduction Emulsion Bottle Polymerization of Vinyl Acetate from Aqueous Solution at 40~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3. Emulsion Polymerization of Vinyl Acetate with Poly(vinyl alcohol) as Emusifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4. Emulsion Polymerization of Vinyl Acetate-Potassium Persulfate-Sodium Lauryl Sulfate Systen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5. High Percent Solids Continuous Addition Emulsion Polymerization of Vinyl Acetate: Potassium Persulfate Initiated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6. Continuous Addition Emulsion Polymerization of Vinyl Acetate: Hydrogen Peroxide-Tartaric Acid Initiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7. Emulsion Polymerization of Vinyl Acetate with Preemulsification . . . . . . . . . . 5-8. Emulsion Polymerization of Vinyl Acetate without Surfactant . . . . . . . . . . . . . 5-9. Emulsion Polymerization of Vinyl Pivalate . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10. Emulsion Ter-polymerization of Vinyl Acetate, Butyl Acrylate, and Vinyl Neodecanoate (Seeded Process with Gradual Monomer and Initiator Additions) . . . .

203

5-2.

6. Nonaqueous Dispersion Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6-1.

Preparation of Poly(vinyl acetate) in Nonaqueous Dispersion . . . . . . . . . . . . .

7. Radiation-Initiated Polymerizations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8. Polymerizations Initiated by Ionic, Coordination Complexes, and Other Mechanisms . . . . 9. Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1.

259 260 261 261 262 262 263 266 266 268 268 269 270 271 273

INTRODUCTION

In this chapter we mainly discuss the polymerization of vinyl acetate; other vinyl esters will only be mentioned briefly. While the major industrial applications of vinyl acetate produce copolymers with such monomers as vinyl chloride or ethylene, substantial amounts of the homopolymers of vinyl acetate are also used. Poly(vinyl acetate) is used in floor tile, chewing gum bases, paper coatings, latex paints, adhesives, and in textile treatments. In the textile field the polymer goes into bodying and stiffening agents, binders for pigments, fabric sizes, bonding agents for nonwoven textiles, and as a material which improves the abrasion resistance of the substrate. Its durability, transparency, flexibility, and stability to weathering and sunlight are attributes that contribute to its industrial acceptance. A major fraction of the industrial homopolymer of vinyl acetate is converted to poly(vinyl alcohol). Since the monomer vinyl alcohol does not exist, poly(vinyl alcohol) must be produced by hydrolysis or alcoholysis of a polymeric vinyl ester. The equilibrium between acetaldehyde and vinyl alcohol is overwhelmingly in the direction of acetaldehyde. In fact, monomeric vinyl alcohol evidently has not been isolated. Yet poly(vinyl alcohol) is an important item of commerce. It is manufactured by the controlled hydrolysis of polymeric vinyl esters. In fact, a major fraction of the industrial homopolymer of poly(vinyl acetate) is used to

204

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

produce poly(vinyl alcohol). The technology of the saponification is quite complex and shrouded in company "secrecy" files. The process appears to be autocatalytic. The degree of hydrolysis is difficult to control unless the approximately 98% hydrolyzed product is wanted. Suffice it to state that many varieties of poly(vinyl alcohol) (PVA) are available commercially. These differ from each other in the degree of hydrolysis and molecular weight of the starting poly(vinyl acetate), its degree of branching or cross-linking, the distribution of the monomeric units along the polymer chain, residues from the saponification reagents, etc. Most industrial grades of partially hydrolyzed poly(vinyl acetates) are, in effect, block copolymers of poly(vinyl acetate) and poly(vinyl alcohol). Interestingly, a grade of poly(vinyl alcohol) which still contains approximately 20% vinyl acetate is more easily dispersed in water than "100%" poly(vinyl alcohol). Reasonably random copolymers of vinyl acetate and vinyl alcohol can only be produced by reacetylation of completely hydrolyzed poly(vinyl acetate). While the vinyl esters of a large variety of acids have been studied, few have found significant industrial applications. For example, during the 1950s, vinyl stearate was produced in the United States. The intended application for this compound was as a polymerizable internal plasticizer for poly(vinyl acetate). However, the cost of production included not only that of the vinylation of stearic acid, but also that of separating inhibiting oleic acid from the starting material. Consequently, this monomer could not compete either on the basis of cost or of plasticizing efficiency with ethylene or with the 2-ethylhexyl esters of maleic or acrylic acids. Vinyl propionate, whose polymerization characteristics are somewhat unique among the vinyl esters of fatty acids, and vinyl esters of mixed, branched acids in the C9- and Cl0-range ("Versatic Acids") have commercial applications [1, 2]. Quite recently, Union Carbide Corp. introduced "Vinate" monomers. These are vinyl pivalate, vinyl neodecanoate, vinyl neononanoate, vinyl propionate, and vinyl 2-ethylhexanoate. These monomers are said to improve the hydrolytic stability and water resistance of emulsion copolymers [3]. The literature on vinyl esters and their polymers is quite extensive albeit somewhat sketchy from the preparative standpoint. Among the leading reviews are Lindemann [1 (which cites 33 general references in its bibliography), 2], Bartl [4], Tromsdorff and Schildknecht [5], E1-Aasser and Vanderhoff [6], Daniels [7, 8], and Rohde [9] . Two reviews about poly(vinyl alcohol) are by Cincera [ 10] and Marten [ 11].

SAFETY NOTE: Traditionally, vinyl acetate monomer has been considered a flammable liquid which is also an irritant. At the present time, in the U.S., the toxicity status of all chemical intermediates is in a constant state of flux, and any statement made here may very well be out of date by the time this work reaches

1.

205

Introduction

the reader. We therefore recommend that prior to handling the monomer, the current manufacturer's safety data sheet (MSDS) be consulted. In March 1993, an explosion, resulting in one fatality, occurred in a German plant which produced poly(vinyl acetate) and PVA. The exact cause of the explosion was not reported. However, the news article in Chemical and Engineering News stated that, at least in Germany, vinyl acetate is "under justified suspicion" for being a potential carcinogen [12]. In the light of this statement, prudence dictates the use of due precautions in the handling of vinyl acetate and other vinyl esters. Naturally precautions must also be taken to protect personnel and equipment against fires and explosions. By the way, the related polymers are considered relatively innocuous. Poly(vinyl alcohol) is thought to be harmless. The toy "Slime" is obtained by mixing a solution of poly(vinyl alcohol) with a borax solution [13]; some grades of poly(vinyl acetate) have been used inchewing gum bases.

A.

Physical Properties

of Vinyl Acetate

The physical properties of vinyl acetate are outlined in Table I [13a-18]. In particular note the water solubility of the monomer. This property appears to go through a minimum of 2.2 wt% at 29~ The solubility data above 66~ are probably somewhat uncertain since these data are taken above the boiling point of the water-vinyl acetate azeotrope and are, therefore, pressure dependent. The fact that the water-vinyl acetate azeotrope boils at 66~ may affect the reproducibility of suspension and emulsion polymerizations which are frequently said to be carried out at about 70~ It would appear self-evident that operations carried out at reflux temperatures would encounter difficulties resulting from the problem of returning the monomer to the sites of polymerization in the reaction medium. In part, this problem may be overcome by returning the refluxing distillate well beneath the surface of the dispersion rather than to the top of the medium. Generally, the monomer is sufficiently stable that it may be stored without any inhibitor, provided it is not subjected to excessively warm temperatures [22]. For this reason, commercial monomers are supplied with surprisingly low levels of inhibitor (e.g., 3-5 ppm or 12-15 ppm of hydroquinone) [19]. The monomer inhibited with only 3-5 ppm of hydroquinone, should be checked for inhibitor content every 2 months and reinhibited to maintain the concentration at 3-5 ppm. Commercially produced vinyl acetate is generally of high purity. The nature of the impurities which may be present varies considerably with the method of manufacture.

206

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

TABLE I Physical Properties of Vinyl Acetate Property Boiling point -

Melting point

72.7~ 9~ 18~

Value

Ref.

mm Hg mm Hg mm Hg

[ 13a] [ 13a] [13a]

- 92.8~

Density, d 2~ (grn/ml)

0.9312

Solubility in water at 10~ 20~ 29~ 65~ 70~ 80~ 90~

3.1 wt% 2.3 wt% 2.2 wt% 2.6 wt% 2.7, 3.5 wt% 3.0 wt% 3.3 wt% 3.5 wt%

100~

[ 13a] [14] [ 13a] [ 13a] [ 13a] [ 13a] [13a, 15] [ 13a] [ 13a] [ 13a]

Solubility of water in vinyl acetate at 20~

1.0 wt%

[ 13a]

Refractive index, n2D~

1.3953

[ 13a]

Absolute viscosity, 20~

0.41 cP

[ 13a]

Specific heat, 20~

0.460 cal/gm/~

[ 13a]

Azeotrope with water Boiling point of azeotrope Composition Upper layer Lower layer

66~ 92.7% vinyl acetate, 7.3% water 98.97% vinyl acetate, 1.03% water 2.0% vinyl acetate, 98% water

Monomer also forms azeotropes with cyclohexane, heptane, isopropanol, and methanol Heat of combustion (kcal/mole) Heat of vaporization (kcal/mole) Heat of polymerization (kcal/mole)

[ 13a]

[ 13a]

495 7.8 21.0 ___0.5

[ 16] [ 16] [17, 18]

Vinyl acetate also may contain dissolved oxygen which acts as a polymerization inhibitor. Table II [20, 21] illustrates the actions on the polymerization process of a variety of typical impurities found in vinyl acetate.

B.

Monomer Purification

T h e purification p r o c e d u r e s o f vinyl acetate for precise kinetic studies are not entirely satisfactory. M a n y o f the impurities m e n t i o n e d in T a b l e II, for e x a m p l e , m a y f o r m a z e o t r o p i c c o m p o s i t i o n s with the m o n o m e r . D i s s o l v e d o x y g e n s e e m s

1.

Introauction

TABLE II

207

Effects of Typical Impurities on the Polymerization of Vinyl Acetate [20]

Inhibitors Oxygen Hydroquinone, other phenolic compounds Phenothiazine Diphenylamine Retarders Crotaldehyde (also acts as chain-transfer agent) Divinylacetylene Vinylacetylene Crotonic acid (also copolymerizes) Butadienylacetylene Isopropenyl acetate (also copolymerizes) Vinyl crotonate (also copolymerizes) Copper acetate Chain-Transfer Agents Oxygenated products from the action of oxygen on vinyl acetate Acetic acid Acetaldehyde Acetone Crotonaldehyde (also acts as retarder) Methanol Methyl acetate Aromatic solvents such as benzene and toluene Copolymerizing Impurities Methyl vinyl ketone Crotonic acid (also acts as a retarder) Isopropenyl acetate (also acts as a retarder) Vinyl crotonate (also acts as a retarder) Impurities with no Significant Effect Water (up to 5%) Ethylidene diacetate (up to 5%) a a In a polymerization study of vinyl benzoate, a definite inhibiting effect was attributed to ethylidene diacetate (1,1-diacetoxyethane) [21].

to be difficult to remove even on repeated degassing. Acetaldehyde, which is a significant chain-transfer agent, is particular troublesome since it forms readily by hydrolysis of vinyl acetate. The separation of inhibitors by distillation is said to be difficult [22]. The techniques of purification consist of three procedures: (a) washing with appropriate reagents, (b) fractional distillation in an atmosphere from which oxygen has been rigorously excluded, and (c) partial bulk polymerization

208

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

followed by distillation, or various combinations of these three methods. These procedures may then be followed by repeated careful degassing. The effect of oxygen on the polymerization characteristics of the monomer is quite dramatic. In bulk polymerization of reasonably purified vinyl acetate, the process is autoaccelerated from the start and goes nearly to completion with a residual monomer content of 2-4%. When the monomer distillation is carried out in contact with air, inhibiting impurities form quite rapidly. These lead to dead-end polymerizations with 30-40% unreacted monomer left in the product [17]. The difficulty of removing acetaldehyde completely by distillation is indicated by the fact that a sample, presumably purified by Nozaki and Bartlett's [22] best techniques still contained about 3 x 10 -4 Macetaldehyde as estimated by UV spectroscopy at 290 nm (the absorption maximum for acetaldehyde) [13]. Using as a criterion the conversion after 4 hr when the purified monomer is warmed at 45~ with benzoyl peroxide (conc" 8.27 x 10 -3 moles/ liter), after two degassing cycles at oil pump pressure of 30 rain each, in sealed ampoules, the most satisfactory procedure used by them consisted of fractional distillation through a distillation column of at least 50 theoretical plates (cf. Table III). A number of variations of the distillation procedure have been mentioned. For example, the monomer has been fractionally distilled through a 25-theoretical plate column and polymerized to approximately 10% conversion. Then the residue has been distilled directly into a dilatometer [24], the monomer has been distilled and percolated through a silica gel column prior to use [25]. In another procedure, the monomer was distilled at 300 mm Hg in an oxygen-free nitrogen atmosphere through a 2 cm X 60 cm glass-helix-filled column, retaining only middle fractions boiling within 0.1 ~ of each other [26]. Inhibitor-free monomer was distilled three times at 300-400 mm Hg under nitrogen through a 25theoretical plate column, a process during which partial polymerization contributed to the elimination of impurities [27]. A reduced pressure distillation under argon using a 15-theoretical plate glass column has also been reported [28]. Purification procedures which depend primarily on the removal of interfering materials by partial polymerization of the monomer are usually not described in detail [22]. It appears that the monomer is generally warmed with a typical freeradical initiator until a slight increase in viscosity is observed. Then the unpolymerized monomer is distilled off in an inert atmosphere through a fractionating column. The monomer may be predried with a zeolite such as Linde 4A prior to partial polymerization and fractional distillation [29]. Gunesch and Schneider [30] prepolymerized a distilled sample of vinyl acetate in the presence of as much as 5-8% of lauroyl peroxide. When the extent of the polymerization had been judged to be sufficient, the process was "shortstopped" by the addition of 2,4-dinitrophenylhydrazine. This step, it seems to us,

1.

209

tntroauction

may also assist in the removal of traces of acetaldehyde. The monomer was then fractionally distilled in the usual manner through a column of 10 theoretical plates. Those methods of purifying vinyl acetate which involve washing of the monomer usually seem to be concerned with the removal of hydroquinone, acetic acid, and acetaldehyde. The use of aqueous solutions for these procedures actually is somewhat questionable in view of the ease of hydrolysis of vinyl acetate (comparable in rate to the hydrolysis of ethyl acetate). In aqueous alkali, the hydrolysis rate of this monomer is said to be 370 times as fast as in water [2]. Nevertheless, such procedures have been suggested and are given here for information only as a typical example of this method. The percolation of the monomer through a short column packed with an aluminum oxide such as Alcoa Alumina CG20 should be evaluated as a means TABLE III

Effect of Purification Procedure on Conversion of Vinyl Acetate [22] a

Purification method

Condition of polymerization

Polymer formation

(%)

1. Fractionation through Widmer column, use middle fractions of constant boiling point and constant refractive index

Sealed in soft glass ampoule

0.77

2. Monomer heated with benzoyl peroxide till moderately viscous, unreacted monomer distilled off under reduced pressure

Saturated with oxygen, then sealed in ampoules

0.63

2. Prepolymerized as above

One drop of water added, ampoule sealed under reduced pressure

5.7

2. Prepolymerized as above

Sealed in ampule after 2 day exposure to air

8.5

2. Prepolymerized as above

Sealed under reduced pressure in either soft glass or Pyrex ampoules

9.6

3. Distillation (under oxygen-free nitrogen) through 50 theoretical plate column (b.p. 72.3~ mm Hg, n 25 1.3934). Only the sixth fraction used.

Sealed under reduced pressure in either soft glass or Pyrex ampoules

23.3

(Similar results were obtained with the sixth fraction from a 100-120 theoretical plate column) a Polymerization conditions: Samples (8.27 x 10-3 M in benzoyl peroxide) were degassed and heated for 4 hr at 45~

210

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

of removing not only phenolic inhibitors, but also of their oxidation products. This approach has been successful in styrene and acrylic ester deinhibition. It also has the virtue of reducing the water content of the monomer and the possibility of uncontrolled hydrolysis. The older literature generally recommends the use of purified nitrogen to create an inert atmosphere in a reaction system. Since the density of nitrogen is close to that of air, nitrogen has to be bubbled into a reactor constantly to prevent oxygen from entering. On the other hand, argon is sufficiently high in density that it can form a much more satisfactory inert blanket in the system.

1-1.

Vinyl Acetate Purification with Aqueous Alkali Extraction [31]

A sample of vinyl acetate is extracted rapidly with two portions of a 10% aqueous sodium hydroxide solution followed by several washes with distilled water. The monomer is then rapidly dried with anhydrous sodium sulfate and filtered. To the dried monomer is added 0.5% of recrystallized dibenzoyl peroxide. The solution is transferred to a boiling flask attached to high-vacuum distillation column and blanketed with oxygen-free nitrogen. The monomer is warmed at 45~ until the increase in viscosity is judged to represent a conversion to approximately 10% of polymer. The flask is then cooled, and the pressure in the apparatus is lowered to 0.1 mm Hg. At this pressure, the monomer is fractionally distilled and a center-cut is retained as purified monomer. In a variation of this procedure, the monomer is extracted twice with dilute aqueous sodium hydroxide, twice with water, then dried over calcium chloride, refluxed with calcium hydride, and distilled from this drying agent [32]. According to one patent, the higher vinyl esters have been treated with the hypochlorites of the alkali metals or with 1,3-dichloro-5,5-dimethylhydantoin in the presence of water. This procedure was said to increase the polymerizability of the monomer [33]. Another procedure makes use of successive washes with 5% aqueous sodium thiosulfate and with dilute aqueous sodium hydroxide. After drying over calcium chloride, the monomer is distilled under oxygen-free nitrogen in the presence of 2% of 2,2'-azobisisobutyronitrile [34]. In Procedure 1-2, the general procedure of Nazakura, Morishima, and Murahashi [35] is combined with the drying procedure of Chen [32]. This method seems to make a particularly determined effort to remove aldehydes from the monomer, but does not come to grips with the problem of preventing the hydrolysis of vinyl acetate in aqueous media.

1.

Introduction

/-2.

211

Vinyl Acetate Purification with Aldehyde Reagents [32, 35]

Commercial vinyl acetate is rapidly extracted in turn with a 5% aqueous solution of sodium bisulfite, a 5% aqueous solution of hydroxylamine hydrochloride, and water. The monomer is dried with calcium chloride and transferred to a distillation flask. Calcium hydride is added and the flask is attached to an efficient helixpacked distillation column. The monomer is refluxed under oxygen-flee nitrogen through the column and then fractionally distilled. The fraction boiling between 72~ and 73~ is retained. This distillation cut is redistilled through a distillation column two more times. The monomer is then degassed, treated with a small quantity of AIBN and polymerized to approximately 10% conversion. The residual monomer is then distilled under an inert atmosphere. The purified monomer is stored at - 78~ until required. Prior to use, this monomer may be distilled into reaction ampoules.

NOTE: The original procedure [35] calls for the use of a Widmer column for the fractional distillation step. Since this piece of equipment is no longer generally available and discredited by some experts in laboratory fractional distillations, we suggest the use of a single-turn, glass-helix packed distillation column or its equivalent with a total-reflux, partial-take-off distillation head. In the purification of vinyl acetate, particular attention has to be paid to the removal of oxygen. Frequently, sufficient dissolved oxygen remains in routinely degassed samples to enter into an autoxidation process initiated by the free radicals generated from the initiator. This step, in effect, inhibits polymerization until all of the oxygen has been consumed. It is recommended that for precision polymerization studies, vinyl acetate be distilled repeatedly at a pressure less than 0.001 mm Hg directly into the reaction vessel. At these pressures, the monomer is conveniently condensed in the apparatus using liquid oxygen. Monomer which has been carefully freed of oxygen polymerizes without an induction period by zero-order kinetics at least up to 10% conversion [36].

Co Initiation, Inhibition, and Retardation of

Polymerization The role of aromatic moieties in the polymerization of vinyl acetate is interesting since benzene, for example, may be considered a natural solvent for the solution of polymerization of vinyl esters. Yet, in the presence of oxygen, cumene (isopropylbenze) inhibits the autoxidation process which may use up oxygen. Thus, the onset of polymerization may be delayed. On the other hand,

212

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

when oxygen has been stringently excluded from the system, cumene (isopropylbenzene) acts as a simple retarder. All aromatic solvents, including those without alkyl side chains such as chlorobenzene, ethyl benzoate, and benzene, retard the polymerization of vinyl acetate [37]. It has been postulated that the very reactive free radical formed from vinyl acetate reacts with an aromatic nucleus to form a less reactive free radical capable of adding more monomer [Equation 1]. R(-- CH2 -- CH -- )~ -- CH2 -- CH. + ~ \ I I O O

I

C=O

I CH3

/

)

I

C=O

I CH3 CH=CH / \ R(-- CH2-- CH --)~ --CH2 -- CH-- CH CH.

I

I

O

O

I

I

C=O

I

CH3

\

(1)

/

CH--CH

C=O

I

CH3

In a study using ~4C-labeled benzene, it was found that at a degree of polymerization of 700, the average polymer molecule contained about 20 benzene units [37]. Thus there is evidence of retardation attributable to a degradative chain-transfer process [37, 38]. In addition, there is evidence that actual copolymerization of vinyl acetate and benzene takes place. As a matter of fact, there may be controversy whether the observations discussed here are a result of chain transfer or of copolymerization. The point in question may be rather subtle [39]. The facts, regardless of theoretical interpretation, are that aromatic solvents retard the polymerization of vinyl acetate, and the polymer contains substantial quantities of covalently bound solvent. Related to these observations are studies on the polymerization of vinyl benzoate [40]. The monomer is an example of a self-inhibiting reactant. During polymerization, aromatic radical adducts form which are sufficiently stable to result in a retardation of the rate of polymerization as the copolymer with the benzene ring forms. During the process, it is also possible for the aromatic radical adduct to react with monomer to re-form the aromatic nucleus as well as form vinyl radicals. With increasing temperatures, there is evidence that the mechanism of the polymerization gradually changes from a rate of polymerization proportional (as

1.

Introduction

213

is conventional) to the square root of the initiator concentration at 60~ (using AIBN as initiator) to a rate directly proportional to the first power of the AIBN concentration at 95~ Changes in the termination steps with temperature may explain these transitions [40]. Once the above observations have been made, questions naturally arise concerning the influence of the aromatic nuclei of such initiators as benzoyl peroxide on the polymerization process. Indeed chain transfer between benzoyl peroxide and poly(vinyl acetate) free radicals has been observed [41]. The copolymerization of benzoyloxy radicals with vinyl formate, vinyl propionate, vinyl butyrate, vinyl benzoate, and vinyl phenylacetate has been studied in considerable detail [42, 43]. Additional Notes on Laboratory Procedures

Throughout this series, the laboratory procedures closely follow those of the cited authors. As a result, many solvents are suggested that are either considered hazardous for one reason or another (e.g., benzene and aliphatic chlorinated solvents) or are no longer commercially available (e.g., carbon tetrachloride). The procedures described are believed to be reasonably reliable as given. The user will have to determine experimentally what modifications will be suitable for his purposes. In many emulsion polymerization procedures, the original authors call for the use of ammonium persulfate as the water-soluble initiator. The shelf-life of this salt is quite limited and the concentration of available persulfate ions is quite variable from experiment to experiment. We therefore suggest, on the basis of our own experience, that either potassium persulfate or sodium persulfate be substituted for the initiation process, on a molar equivalent basis. Of these two latter salts, the sodium salt dissolves rapidly in water and usually may be added directly to the reaction flask. The potassium salt exhibits surprisingly low watersolubility. As a result, if potassium persulfate needs to be used, an aqueous solution of it should be prepared separately. Then this initiator solution is added to the emulsion polymerization system. Particularly for emulsion polymerizations, we have found several pieces of relatively modem equipment useful. Instead of the tradition mercury-sealed stirrer beating, a Bunsen beating (a short length of rubber tubing, lightly lubricated with petroleum jelly, sealing the stirrer shaft to a glass tube that holds the stirrer in place), or ground glass stirrer beatings are useful. Teflon stirrer beatings such as the Ace TRUBORE Teflon stirrer beating (e.g., Aldrich Z 15,440-7), while expensive, are quite effective, provided a stirrer shaft that fits properly has been selected and the internal O-ring is kept in proper repair. From bitter and messy experience, we suggest that a rubber stopper be drilled to fit tightly on the stirrer shaft. This is then attached strategically between the

214

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

top of the stirrer beating and the motor at such a point that the stirrer blade cannot touch the bottom of the flask. This will help to prevent the stirrer from dropping into (and through) the flask. There is a tendency to select stirring motors for polymerization that can stir at tremendous rotational speeds. Steady and reliable power rather than speed is the important factor. Usually a speed of 150 to 250 rpm is quite sufficient for emulsion polymerizations in a 12-liter flask with a stirrer blade that is approximately 10 cm wide. The power is needed in case of unforeseen increases in viscosity or lump formation. The constant speed is useful when uniformity of the size of latex particles is desired. To control the heating cycles of polymerizations, we have found that electrically actuated pneumatic jacks are very useful. In conjunction with temperature controller that monitors the temperature inside the reaction flask, the heating mantle for the flask is raised or lowered as required with such jacks. The temperature history may be recorded simultaneously with a suitable fiat-bed recorder. There is also equipment to monitor and record the stirring speed [44]. For the gradual and continuous additions of liquids to the reaction mixture, FMI Lab Pumps [44a] are very useful. The volumes which these pumps deliver are readily adjusted over a wide range. The use of these pumps for delivery of latices is not recommended. Traces of a latex left in the pump head may dry and jam the mechanism. Repair service by the manufacturer is prompt and very accommodating. In emulsion polymerizations, in which the film-forming characteristics of the product are important, silicone-based greases must be avoided. Petroleum jelly or, if appropriate, the Teflon tapes used by plumbers may be used.

D.

Polymer Structure

The nature of the end groups of high-molecular-weight polymers is a general problem in polymer chemistry. The analytical determination of a functional group with a molecular weight on the order of 102 in a molecule with a molecular weight in the range of 105 is complicated by the fact that ordinary polymers consist of chains with a wide distribution of molecular weights. The two ends of each chain probably have different compositions and the nature of the end groups vary with the nature of initiators, solvents, chain-transfer agents, surfactants, incidental impurities, etc. The chemical reactions of functional groups attached to polymer chains are not always well understood, e.g., conformational factors and shielding effects due to a coiling of a polymer chain around a potentially reactive site are two obvious matters that may interfere with conventional chemical procedures. For these and many other related reasons, end-group analyses for all polymeric systems must be viewed with considerable skepticism.

1.

Introduction

215

In the field of poly(vinyl acetate) research, it was noted early that hydrolysis of the polymer to poly(vinyl alcohol) followed by reacetylation visually led to the production of poly(vinyl acetates) of lower average-molecular-weight distribution than that of the original polymer [45]. The influence of the conditions of polymerization and of repeated hydrolysis and reacetylation will be discussed further. To be noted here is that Marvel and Inskeep [45] at that time, postulated that the observations were somehow related to aldehyde end-groups in poly(vinyl acetate) and/or in poly(vinyl alcohol) which, in turn, could form acetals with hydroxyl groups of poly(vinyl alcohol). This concept was extended to the possibility that ketals also might form [46]. Wheeler and co-workers [47] insisted that there seems to be no way for acetals or acetal linkages to form during the polymerization of vinyl acetate. Unless such linkages were initially present, the hydrolytic degradation of the polymer cannot be attributed to hydrolysis of these gem-diethers. The claimed isolation of 2,4-dinitrophenylhydrazones from low-molecular-weight poly(vinyl alcohols) in Marvel and Inskeep [45] has been overlooked in subsequent discussions. It is conceivable that aldehydes had been used as chain-transfer agents in the preparation of the poly(vinyl acetate) under study. In subsequent stages of work these reagents might have reacted with 2,4-dinitrophenylhydrazine. It is also possible that residual ester groups had reacted with the substituted phenylhydrazine to form the corresponding phenylhydrazides. This would be difficult to differentiate from 2,4-dinitrophenylhydrazones, particularly in polymeric systems. Flory and Leutner [48, 49] have hydrolyzed poly(vinyl acetate) to the corresponding poly(vinyl alcohol) and then treated the product with periodic acid and other reagents which attack 1,2-diols. The expected head-to-tail sequence of monomer units leads only to 1,3-diols which would not be attacked. Occasional head-to-head, tail-to-tail sequences could be expected to be attacked by periodic acid with rupture of polymeric chains. From the changes in molecular weight as a result of such reaction, a measure of the number of 1,2-diol units that were present is obtained. From this, the percentage of head-to-head, tail-to-tail sequences in the chain can be calculated. The temperature at which poly(vinyl acetate) is formed seems to determine the mole percentage (based on the structural units --CHe--CHOH--) of the 1,2-diol units corresponding to the unusual structural sequence. At a polymerization temperature of 25~ the mole percentage of 1,2-diol structures is 1.15; at 110~ it is 1.86 [49]. Table IV presents additional data about the amount of head-to-head, tailto-tail sequencing not only for the case of poly(vinyl acetate) but also for polymers of vinyl formate and of vinyl trifluoroacetate. The amount of the "abnormal" sequence in these vinyl esters is said to be related to the inductive effect of the acid portion of the ester [50].

216

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

The variation in the water resistance of the polymers, also shown in Table IV, was attributed to the degree of syndiotacticity of the poly(vinyl esters) and the derived poly(vinyl alcohols). It was concluded that poly(vinyl formate) produced at low temperatures by free-radical means was similar to poly(vinyl trifluoroacetate) in regard to a high percentage of syndiotactic sequencing. This conformation is retained upon hydrolysis to the poly(vinyl alcohol). The stereoregularity in the case of poly(vinyl acetate) produced by free-radical initiation is quite low. It was proposed that the inductive effect of the acid portion of the monomer has a greater influence on stereoregularity during free-radical propagation than steric effects [50]. Commercial poly(vinyl acetate), as is well known, may be subjected either to acid or basic hydrolysis to form a completely hydrolized poly(vinyl alcohol). Upon reacetylation of this poly(vinyl alcohol), the regenerated poly(vinyl acetate) usually exhibits a reduction in molecular weight [47]. Poly(vinyl acetates) produced at low conversion or at low temperatures may be subjected to this process without significant changes in the molecular weight distribution. As indicated before, Marvel and Inskeep [45] had postulated that acetal (or ketal) linkages were ruptured during hydrolysis. The existence of acetal bonding in poly(vinyl acetate) is, however, difficult to visualize. TABLE IV Structural Parameters of Poly(vinyl alcohols) Derived from Various Poly(vinyl esters) [50]

Poly(vinyl ester) Poly(vinyl formate)

Polymerization temp. (~

Intrinsic viscosity, [r/] of derived poly(vinyl alcohol) (dl/gm)

- 35 20 - 10 0 10 20 30 38 - 30 60 10 60

1.09 0.46 0.78 0.95 1.16 1.34 1.39 0.88 0.66 0.97 0.47 1.25

-

Poly(vinyl acetate) Poly(vinyl trifluoroacetate)

`"Based on the method of Flory and Leutner [48, 49]. b Solubility of a film in water after 1 hr at 70~ c Measured in water at 30~

1.2 Diol content, mol% in Water poly(vinyl solubleb alcohol)" (%) 0.31 0.46 n 0.53 0.67 -0.78 ~ 0.50 1.25 0.48 0.94

Swelling indexr

n 4 5 6 13 32

1.14 1.18 1.25 1.30 1.80

100 100 ~ 5

2.60 2.90 1.60

217

1. Introduction

TABLE V

Change in Viscosity of Poly(vinyl acetate) upon Alcoholysis and Reacetylation [47]

Initial intrinsic viscosity of PVAc samples

Approximately MW (x 10-6)a

Viscosity of PVAc after alcoholysis and reacetylation

Approximately MW (X 10-6)a

0.146 0.496 1.286 1.956 2.116 3.296 4.10 c 4.30 d

0.021 0.14 0.585 1.10 1.24 2.41 3.35 3.60

0.14 0.42 0.84 1.03 1.08 1.16 1.13 1.17

0.021 0.11 0.31 0.422 0.453 0.505 0.485 0.511

,

a Estimated by simplifying the equation of A. Berensniewicz [J. Polym. Sci. 35, 321 (1959) [r/] = 1.83 x 10 -4 M 0"65, to read [r/] = 1.83 x 10 -4 x 3M 2. b Suspension polymers. c Bulk polymers produced from purified monomer by photopolymerization. d Bulk polymers produced from purified monomers initial with benzoyl peroxide.

Table V illustrates the changes in viscosity of a series of polymers produced at high conversion of monomer with different average-molecular-weight distribution upon alkaline alcoholysis and reacetylation. To be noted first is that low-molecular-weight polymers are not degraded by the processing under consideration. This implies that low-molecular-weight polymers are not significantly branched. At high molecular weights it should be noted that there is a trend toward degradation to a "maximum" molecular weight average of approximately 500,000. Even a polymer of molecular weight 3,600,000 is degraded into the equivalent of approximately seven equal segments. Studies of the effect of conversion on degradation indicate that the extent of degradability increases with increased conversions. Polymerizations carried out to high conversion at - 30~ with highly purified monomers gave insoluble resins which, after alcoholysis and reacetylation, gave products with intrinsic viscosities as high as 3.65. This intrinsic viscosity is significantly higher than that obtained from polymers produced at 67~176 [47]. Hydrolysis under acidic conditions leads to degradation which is frequently not as extensive as that found with alkaline hydrolysis. In fact, there may be increases in the viscosity as a result of the reaction under acid conditions. This aspect of the observations has not been adequately explained. Most of the chemical facts described have been attributed to branching of the polymer primarily through an ester bond. The ester linkages presumably form by a chain-transfer reaction with the carbon-hydrogen bonds of the acetate grouping both in the polymer and in the monomer.

218

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

In Structure I, 1, 2, and 3 indicate the position of hydrogens which may conceivably be involved in chain-transfer reactions leading to branching: 3

2

--CH2--CH-I o I c=o I ICH3

Structure I

Branches at positions 2 or 3 would, of course, not be degradable under the conditions discussed here. A kinetic analysis indicated that branching at position 1, leading to a polymeric ester branch, was of primary importance in developing branched polymers [51 ]. The chain-transfer constant of the poly(vinyl acetate) is larger than that of most other monomers. Consequently branching is very significant in these polymerizations. Chain transfer takes place 40 times more frequently at position 1 than at position 2 [52]. Branching at position 3 is negligible. The number of branch points per polymer molecules may be computed as a function of the degree of conversion [53]. as well as a function of temperature [27]. Emulsion polymerization of vinyl acetate at 5~ gave a polymer with very little branching. On the other hand, polymers, whether produced in emulsion, suspension, or solution at 65~ gave rise to approximately one branch for each polymer chain. At high temperatures and higher conversions, the molecular weight of poly(vinyl acetate) passes through a maximum. This effect is thought to be related to chain branching at approximately 0.15 branches per polymer molecule. The result is independent of the technique used in producing the polymer [54]. These observations are at variance with the data given in Table V where it would appear that (assuming that [r/] is a measure of single long chains) a polymer with MW 3.6 x 106 is made up, on the average, of approximately seven long branches of MW 5.1 X 105 joined together through position 1 (the acetoxy unit) in Structure I. To indicate that the nature of the branching in poly(vinyl acetate) is far from understood reference is made to the papers ofNozakura et al. [35, 55-57]. These workers proposed to study branching in poly(vinyl alcohol). Obviously, if most of the branching in poly(vinyl acetate) occurs through the acetoxy linkage, the poly(vinyl alcohols) isolated from its hydrolysis should be essentially unbranched. Such a poly(vinyl alcohol) is reacetylated to give linear poly(vinyl acetate). In this work the possible low level of branches grafted onto position 2 of Structure I, was ignored. The linear poly(vinyl acetate) was now only partially hydrolyzed. Through the resulting hydroxyl groups, the polymer was cross-linked with distilled commercial toluene diisocyanate (TDI) [55].

1.

Introduction

219

This cross-link has the interesting property that it may be cleaved quantitatively with 3 N aqueous hydrobromic acid to produce the starting, partially hydrolyzed, poly(vinyl acetate) without further hydrolysis of the acetate groupings. The cross-linked poly(vinyl acetate) was treated with laC-labeled vinyl acetate under polymerization conditions at 60~ or at 0~ The resulting homopolymer was separated readily from the cross-linked graft copolymer. The grafted cross-linked copolymer was cleaved. The degree of grafting onto the acetoxy-group (position 1) and onto the main chain (position 2) was estimated. It was found at 60~ that the chain transfer to the polymer main chain (position 2 in Structure I) was 2-4 times as frequent as at position 1 and that this ratio rose to 4.8:1 at 0~ [56]. In a study of chain-transfer constants of the monomeric vinyl acetate it was found that the formation of nonhydrolyzable branches is virtually negligible while hydrolyzable branches are formed at position 1 of Structure I by a terminal double-bond reaction rather than by a polymer-transfer reaction. The long nonhydrolyzable branches in poly(vinyl alcohol) are, presumably formed almost exclusively by a polymer transfer mechanism [35]. A study involving the grafting of 1,2-[lac]vinyl trimethylacetate (V*TMAc) to crosslinked poly(vinyl acetate) also demonstrated that grafting to the main chain of poly(vinyl acetate) takes place 2.8 times as readily as grafting to the acetoxy group [57].

EO Polymer Fractionation and Molecular-Weight

Constants Before the advent of gel permeation chromatography, the molecular-weight distribution of polymers was determined by fractional precipitation techniques. As a nonsolvent is added to a solution of a polymer, the highest molecular weight portion of the polymer will tend to precipitate out first. As more and more precipitant is added, lower and lower molecular weight polymers separate. Polymer fractionation is quite tedious. Careful control of precipitation temperatures, concentrations, solvents, and agitation rates are required. The fractions isolated may have to be refractionated to obtain more carefully defined molecular-weight ranges. One early publication advocated the precipitation of poly(vinyl acetate) from toluene solution with a methanol-water mixture or from an acetone solution with 50% water in methanol at 25~ [58]. A rapid fractionation method for poly(vinyl alcohol) and poly(vinyl acetate) is the method of Fuchs which was advocated by Berensniewicz [59]. The procedure consists of depositing films of the polymer on stainless steel screens. The

220

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

films are then extracted with solvent-nonsolvent mixtures with increasing solvent power. By use of this method, the highest molecular-weight fraction is dissolved away from the film last, and in some cases may even remain as a film on the screen before it is completely dissolved. The method is said to give relatively homogeneous fractions. In the case of poly(vinyl alcohol), this method is complicated because of the crystallinity of the polymer. Therefore poly(vinyl alcohol) should be reacetylated and fractionated as poly(vinyl acetate). Upon hydrolysis of the fractionated polymer, no further degradation was observed, since the polymer branches had already been degraded during the initial preparation of poly(vinyl alcohol). Procedure 1-3 is a typical example of a fractional precipitation method.

1-3. Fractionation of Poly(vinyl acetate) [55] A solution of 2 gm of poly(vinyl acetate) in 98 ml of purified acetone is well stirred at 30~ From a buret, measured amounts of water are added dropwise until the mixture becomes cloudy. To purify the polymer, the mixture is warmed to 32~ to dissolve the polymer. The solution is then allowed to return slowly to 30~ to reprecipitate the polymer. After allowing the polymer to settle overnight, the gelled polymer is isolated; the mother liquor is preserved. The polymer is dissolved in benzene (CAUTION: Carcinogen) and removed by freeze-drying. The procedure is repeated with the mother liquor to isolate the remaining fractions of polymer. The data on the weight of the fraction and the volume of water used to precipitate the fractions is valuable in evaluating the molecular weight distribution of the polymer. An alternative solvent system for the fractionation of poly(vinyl acetate) consists of the precipitation of an acetone solution of the polymer with petroleum ether [60]. Since the volumes of solvents and nonsolvents become quite large during fractional precipitation, a change in the composition of the precipitant may be desirable. Wagner, for example, precipitates a solution of 150 gm of poly(vinyl acetate) in 2300 ml of acetone with up to 3900 ml of 1 : 1 (v/v) methanol-water. Further fractions were isolated by the gradual addition of up to 800 ml of a 1 : 2 (v/v) methanol-water mixture at 30~ [61]. Routinely, molecular weights of polymers are conveniently estimated from intrinsic viscosity measurements using the Staudinger (also known as the Mark-Houwink-Sakurada) equation [~] = z a 3 a

(2)

1.

221

Introduction

TABLE VI Mark-Houwink-SakuradaParameters for Number Average Molecular Weights of Poly(vinyl acetate) It/] = kM~ (dl/gm) Temperature (~

Solvent

k x 104

a

MW Range (M X 10-4)

Acetone

30

1.76 1.318

0.63 0.74

Toluene

25 25

3.86 3.86 3.273

0.65 0.53 0.60

1.549

0.72

60

1.862 1.259 4.699 9.440 11.350

0.70 0.74 0.595 0.50 0.50

60 60 60 60 60

Benzene Ethyl methyl ketone Ethyl acetate Butyl acetate n-Butyl ethyl ketone Carbon tetrachloride

29 (theta solvent) 46.4 (theta solvent)

2-163

Ref.

4-15

61-64 60 65 65 60

where [r/], the intrinsic viscosity, has units of dl/gm. Usually this equation is used to calculate the "viscosity" molecular weight, Mv. However, by correlation of the viscosity data with other types of molecular-weight determinations, parameters may be developed to permit calculation of the number-average molecular weight, ~Qn, or the weight-average molecular weight, Mw, from viscosity measurements. In the case of vinyl acetate, the parameters for the Mark-Houwink-Sakurada equation vary considerably with investigator, molecular-weight range of the sample, narrowness of the molecular-weight range of a fraction, nature of"good solvents" used, nature of "theta solvents" used, and the temperature of the determination. The fact that the changes in K in equation 2 may, in part at least, be compensated for by changes in a has not been considered. We also suspect that the number of significant figures usually reported are not justified by the precision of the observations and calculations. Tables VI, VII, and VIII list a selection of parameters for calculating numberaverage, weight-average, and viscosity-average molecular weights from intrinsic viscosity measurements. Table VI, in particular, shows the great variations in the parameters with changes of "good" solvents. It is interesting to note that D'Amelia and Jacin [65] mention variations in the exponent, a, as the molecular weight range of the polymer changes. They noted that toluene, a good solvent for low-molecular-weight poly(vinyl acetate) is a poor solvent for the highmolecular-weight material.

222

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

TABLE VII Mark-Houwink-Sakurada Parameters for Weight Average Molecular Weight of Poly(vinyl acetate) [r/] = kMa (dl/gm) Temperature (~

k X 104

a

(M X 10 -4)

Ref.

Acetone

30 30 25 25 56.9 (them solvent) 26.9 (them solvent) 6 (theta solvent)

0.74 0.65 0.73 0.65 0.53 0.50 0.50 0.50

8-66

Acetone Toluene Toluene Ethanol 3-Heptanone Methanol

0.86 1.7 1.01 2.15 2.15 9.0 8.2 10.1

63-66 59 63, 64, 67 65 65 63, 64, 67 63, 64, 67 63, 64, 67

Solvent

MW Range

6-150 4-15 4-150 4-150 0.3-150

The ratio of the number-average molecular weight to weight-average molecular weight is given as almost exactly 1 : 2 in unfractionated samples by Berensniewicz [59] and as 1.02 to 1.05 by Ueda and Kajitani [67]. Assuming that the molecular weight distribution is random, Lee and Turner [68] have stated that the ratio of the viscosity molecular weight to the number-average molecular weight is 1.8 : 1. If we were to accept the ratio of Berensniewicz along with that o f Lee and Turner, the viscosity-average molecular weight would be virtually equal to the weight-average molecular weight. However, because of the profound effects attributable to branching, these relationships must not be taken too seriously. For example, in the of weight-average molecular weights from approximately 1 x 106 to 3.8 x 106, the ratio of/~w 9a~tn varies from 2.2 to 5.1, according to Graessley and Mittelhauser [28].

TABLE VIII Mark-Houwink-Sakurada Parameters for "Viscosity" Molecular Weight of Poly(vinyl acetate) [r/] = kMa (dl/gm)

Solvent

Temp (~

k x 104

a

Ref.

Acetone

20

5.6

0.625

29

2.

E

Bulk Polymerizations

223

l n h i b i t o r s o f Vinyl A c e t a t e P o l y m e r i z a t i o n s

In Table II, mention was made of oxygen, hydroquinone and other phenolic compounds, phenothiazine, and diphenylamine as inhibitors of the polymerization of vinyl acetate. In connection with a study of a number of anticancer compounds which, presumably also act as inhibitors of free-radical polymerization, eight classes of compounds were studied as to their inhibitory properties. The classes studied were unsaturated hydrocarbons, phenolic compounds, quinones, amines, stable free-radicals, sulfur compounds, carbonyl compounds, and metallic salts. The most effective inhibitors, of those evaluated, were cupric acetate and cupric resinate, followed by trans-l,3,5-hexatriene, hydroquinone, benzoquinone, and diphenylamine as modest inhibitors. Among the low-activity inhibitors were 2,2-diphenyl-l-picrylhydrazyl, benzene thiol, and crotonaldehyde [70]. Diphenylamine has also been suggested as a "short stop" for vinyl acetate polymerizations [47, 62].

2.

BULK POLYMERIZATIONS

The bulk polymerization of vinyl acetate is primarily of interest for laboratory studies, although a few large-scale procedures have been reported. Since the heat of polymerization is quite high (21 kcal/mole) and the boiling point of the monomer is relatively low (72.7~ (Table I), not only must the reaction temperature be monitored closely, but the reaction temperature must be kept low, unless pressure equipment is used. The low temperatures mean that the usual initiators of free-radical polymerization will act rather slowly. To further complicate bulk polymerizations, the polymerization process is strongly autocatalytic [ 17, 68]. Among the initiators which have been used in the bulk polymerization of vinyl acetate are dibenzoyl peroxide (BPO) [48, 71, 72], benzoyl steroyl peroxide [71], disteroyl peroxide [71], dialiphatic acyl peroxides in general [71], 2,2'-azobisisobutyronitrile [37, 69, 72], pinacols [73], dilauroyl peroxide (LPO) [74], and difuroyl peroxide [74, 75]. Bulk polymerizations of vinyl acetate, on a laboratory scale, have been carried out in sealed tubes or ampoules, in dilatometers, and at atmospheric pressure at reflux. A representative selection of data on the effects of reaction temperatures, initiators, and reaction times on the percent conversion when polymerizations were carried out in sealed tubes is given in Table IX. It is interesting to note that in one set of preparations by Flory and Leutner [48] which appear to be duplicates in regard to reaction temperature and initiator concentration, the same degree of conversion is achieved at considerably different polymerization times.

224

0

0

>~ 0

< ~

0

0

0

I I I I I I

r

0

0

.,-

r 0

0

,-'~

-~ o ~ = =

""

0

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

I I I I I~~l

? •

I I

I I I I I I I I I I I I

I I t I I ~ - ~

I~l

•

7 •

~b

~Z

~176176

I I I I I I I I~176

I ~

2.

Bulk Polymerizations

225

It should also be noted that at least one group of investigators [77] observed an induction period for the process. Few if any of the other workers in the field have mentioned this. The induction period is said to be variable, decreasing as the polymerization temperature increases. The cause for this induction period was not further explored. It could not reasonably be attributed to residual inhibitor since the experimemal description specifically indicated that an effort was made to remove the inhibitor first; then the monomer was partially polymerized. Only then was the unpolymerized monomer distilled under reduced pressure in a nitrogen atmosphere. When we combine this observation with the autoaccelerating tendencies of the system, the chain-transfer reactions to both the monomer and the polymer on one of the several positions which leads to branched-chain formation, and the possible reactivation of "dead" polymer molecules by hydrogen abstraction with monomeric free radicals [78], the complexity of the kinetics of vinyl acetate polymerization may be appreciated. Similar factors may be involved not only in the polymerization of other vinyl esters, but also in the free-radical polymerization of other types of monomers. In devising experimental procedures for the polymerization of vinyl esters, the elimination of oxygen is extremely important. Joshi [ 17] has shown that the bulk polymerization of vinyl acetate and vinyl propionate exhibited autoacceleration from the start and proceeded nearly to completion with only 2-4% unreacted monomer within 200 min in one case. When, however, the monomer had come in contact with air, inhibiting impurities developed and even after hours of heating, "dead-end polymerization" had taken place with 30--40% of unreacted monomer remaining. As we have memioned in previous volumes in this series, we consider bulk polymerizations in sealed ampoules or even sealed heavy-walled tubes not merely unsafe, but dangerous. The procedure, in some respects is so trivial, that it is rarely described in any detail. Yet, so much polymer chemistry has been studied by sealed-tube polymerization that the procedure has to be described. Procedure 2-1 is a composite of those described elsewhere [28, 34, 35, 75, 76]. Safety procedures will have to be designed to conform to OSHA regulations.

2-1.

Sealed-Tube, Bulk Polymerization of Vinyl Acetate

In a heavy-walled Pyrex ampoule with a constriction near its upper opening is placed a dispersion of 10 ml of purified vinyl acetate and 0.0004 gm of 2,2'-azobisisobutyronitrile. The content is sparged with oxygen-free nitrogen or argon and attached to high-vacuum line. The monomer is chilled with a dry iceacetone mixture. The tube is evacuated on the high-vacuum line while the

226

7.

Polymerization of Vinyl Acetate and Other Vinyl Esters

monomer remains frozen. By conventional techniques, the monomer is then degassed repeatedly. Finally the tube is sealed under reduced pressure. After the seal has cooled, the tube is placed in a suitable, protective sleeve and slowly tumbled, end-over-end, in a constant temperature bath at 50 ___0.2~ with suitable safety precautions. Conversion, after 3 hr, is approximately 35.6%. To isolate the product, the ampoule is cooled in dry ice-acetone, appropriately wrapped, and with suitable safety precautions, the ampoule is opened. The polymer may be dissolved in such solvents as acetone, benzene, or tetrahydrofuran (THF) and precipitated with petroleum ether or with redistilled hexane. The polymer may also be isolated from benzene solution by freezedrying. Bulk polymerizations have also been carried out in a conventional reflux apparatus. While, in principle, this procedure permits the preparation of larger quantities of polymer than is possible in sealed tubes, the control of the reaction temperature presents problems. The polymerization is autoaccelerating. As the viscosity of the medium increases, as the molecular weight increases, heat transfer from the interior of the reacting mass becomes increasingly difficult. The heat of polymerization is quite high so that great care is required. Naturally, a means of removing the polymer mass from the equipment also needs to be provided. The pneumatic jack and temperature controller mentioned in Ref. [44] will be useful for bulk processes. Procedure 2-2 is an adaptation of the procedure of Braun et al. [79].

2-2.

Bulk Polymerization of Vinyl Acetate (Reflux Apparatus) [79]

A 500-ml glass resin kettle is fitted with a reflux condenser, addition funnel, a nitrogen inlet tube extending to the bottom of the reactor, a means of evacuating the apparatus, and a thermometer. The gas exhaust, through the reflux condenser, is fitted with a Bunsen valve which prevents oxygen and moisture from entering the equipment. The equipment is flamed out under oxygen-free nitrogen and then is evacuated and flushed with oxygen-free nitrogen three times. While a slow stream of oxygen-free nitrogen passes through the equipment, 20 gm of a solution of highly purified vinyl acetate containing 0.14 gm of recrystallized dibenzoyl peroxide is added to the apparatus. The mixture is warmed with a water bath held at 80~ Once the polymerization has been initiated, the temperature of the water bath is lowered to maintain a gentle reflux. The reaction is maintained at a gentle reflux by the dropwise addition of further quantities of vinyl acetate solution containing 0.7% of dibenzoyl peroxide. After the desired quantity of monomer has been added, the reaction

2.

227

Bulk Polymerizations

temperature is continued at 80~ for 30 min, followed by heating for 60 min at 90~ The residual monomer is removed by distilling it out of the equipment at 90~ under reduced pressure. Air is now allowed to enter the apparatus. The overhead equipment (condenser, thermometer, gas inlet tubes, etc.) is removed. The resin kettle itself is heated to 170~ and the viscous vinyl acetate is poured out of the kettle. A porcelain spatula may be useful in removing the polymer from the equipment. The equipment may be cleaned by refluxing methanol in the kettle (approximately 20 ml of methanol are required to dissolve 1 gm of polymer). The polymer may be recovered from its methanol solution by precipitation with an eight-fold excess of water. This portion of the product may be dried under reduced pressure at 50~ Unreacted vinyl acetate may be separated from the polymer, which has been precipitated in an aqueous system, by steam distillation. This procedure is also thought to decompose excess initiators [80]. The method used in Procedure 2-2, in a sense, is an adaptation of an old patented process for the commercial preparation of poly(vinyl acetate). In that procedure, as a stream of monomer is added to a polymerizing reaction mixture, an equal volume of the partially polymerized mixture is withdrawn to a finishing vessel where the reaction is allowed to go to completion at reflux [81]. On a commercial scale, a variation of this procedure, involves the extrusion of the finished product onto a moving belt. The molecular weight may be maintained within fairly narrow limits by this procedure, particularly when propionaldehyde is used as a chain-transfer agent. In a typical formulation, 3140 lb of vinyl acetate, 27 lb of dibenzoyl peroxide, and 11.8 lb of propionaldehyde give rise to a product with an average molecular weight of about 40,000 [82]. Pinacols are unique polymerization initiators. At temperatures below 100~ where the usual free-radical initiators such as the peroxides, are effective, pinacols are only of limited value. However, at temperatures above 100~ diaryl hydroxymethyl radicals form that initiate polymerization by hydrogen transfer [Eqs. (3, 4, 5)]. Ar Ar I I Ar--C--C--Ar

lOOOC

Ar I , 2. C - - O H

I I OH OH ar

I C H 2 = C - - R + .C--OH I I X Ar

(3)

I Ar ar

I } C--O + CH3--C--R I I Ar X

(4)

228

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

C H 3 - - C - - R + monomer

polymeric free radicals, etc.

(5)

I X Note that it is hydrogen abstraction which brings about initiation with pinacols rather than the addition of initiator radicals, as is the case with dibenzoyl peroxide, for example. Such high-temperature initiation may find specialized applications [73]. The bulk polymerization of vinyl acetate in dilatometers has been described [31, 72, 74, inter alia]. As the carboxylate moieties of vinyl esters increase in length, the degree of branching due to chain transfer to both monomer and polymer increases. The relationship between the chain-transfer constant (C.T.) and the number of carbon atoms in the carboxylate portion of a fatty acid vinyl ester in the presence of vinyl acetate is given by the expression C.T. = 4.0 X 10 -3 + n X 0.7 • 10 -3

(6)

where n is the number of non-a-methylene groups in the carboxylic acid chain beyond the propionate group. While the polymerization kinetics of vinyl propionate is normal in the sense that the rate is first order in monomer and 0.5 order in initiator, the rate of polymerization is much lower than that of vinyl acetate and the chain-transfer constant to monomer is greater than expected (C.T. = 4.9 X 10 -3) [83]. Table X lists chain-transfer constants of a number of ethyl esters reacting with vinyl acetate. According to Buselli et al. [83], the chain-transfer behavior of vinyl esters toward vinyl acetate is similar, except, of course, for the inexplicably anomalous vinyl propionate. The heat of polymerization of vinyl esters exhibits essentially no dependence on the length of the carboxylic acid. Generally the range of the heats of polymerization is between 20.5 and 21 kcal/mole. Steric strain is thought to reduce this value in the case of vinyl benzoate and the plasticizing effect of the side chains is believed to raise the value slightly in the case of vinyl 2-ethylhexanoate [ 17, 18]. In the bulk polymerization of vinyl propionate, up to a conversion of 25%, the average degree of polymerization remains constant. Beyond this point, the molecular weight increases as the conversion increases [78]. Table XI illustrates the effect of the increase in molecular weight with increasing conversion of vinyl butyrate [84]. As has been observed before, as the length of the acyl group increases from the n-butyrate to the n-caproate, the chain transfer to monomer tends to increase. Also, as the molecular weight of the polymer increases the polymer tends to assume a coiled configuration [84].

2.

229

Bulk Polymerizations

TABLE X

Representative Chain-Transfer Constants for Vinyl Acetate [83] ~

Chain-transfer agent

Chain-transfer constant b (XlO 2)

Ethyl stearate Ethyl laurate Ethyl pelargonate Ethyl octanoate Ethyl butyrate Ethyl propionate Ethyl acetate Ethyl formate Ethyl 2-ethylhexanoate Ethyl isobutyrate Ethyl trifluoroacetate Toluene (BPO initiated) Toluene (AIBN initiated) Vinyl propionate

1.40 1.05 0.80 0.70 0.45 0.40 0.12 0.22 0.65 1.60 0.30 1.00 1.23 0.49

a Polymerization conditions: The bulk polymerization was conducted using 0.24 gm of dibenzoyl peroxide per 100 gm of monomer at 50~ to 10% conversion. b Constants for the ethyl ester are said to be comparable to those of the vinyl esters [83].

The reactivities of various vinyl esters in copolymerizations are generally very similar. The sampling of reactivity ratios given in Table XII indicates this quite clearly. The somewhat unique behavior of vinyl benzoate is indicated in the Table XII. The copolymerization of various substituted vinyl benzoates has been studied. It was found, first of all, that there was no polymerization with vinyl pnitrobenzoate. A plot of the relative reaction rates of vinyl benzoates with TABLE XI

The Effect of Conversion on the Intrinsic Viscosity of Poly(vinyl butyrate) [84] a

Benzoyl peroxide used (moles/liter x 103)

Reaction time (min)

Conversion (%)

Intrinsic viscosity (dl/gm)

2.611 4.975 2.611 4.975

19 20 50 240

20.5 45.5 61.5 94.5

0.288 0.307 0.381 0.840

a Polymerization temperature was 79.6~

230

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

TABLE XII

Reactivity Ratios of Selected Vinyl Esters

M2

rl

r2

Ref.

Copolymers of various monomers (M2) with vinyl acetate (M~) Vinyl formate Vinyl propionate Vinyl butyrate Vinyl trimethylacetate ("Vinyl pivalate") Vinyl 2-ethylhexanoate Vinyl neonanoate Vinyl neodecanoate Vinyl phenylacetate Vinyl benzoate Vinyl ethyl oxalate Vinyl thioformate Acrylic acid Behenyl acrylate Butyl acrylate Crotonic acid Ethyl acrylate Ethylene Maleic anhydride Methyl methacrylate Phenyl acrylate Vinyl chloride

0.94 0.98, 1.06 1.00 0.79

0.95 0.98, 0.76 0.97 0.96

85 85, 3a 85 3

1.19 0.93 0.99 0.96 0.70 0.30 0.05 0.02 0.021 0.05, 0.05 0.21 0.62 0.02 1.00 0.01 0.03, 0.03 0.22 0.60

1.90 0.90 0.92 0.92 1.13 3.00 5.50 20.64 1.76 5.89, 5.50 3.3 0.27 7.20 1.00 0.01 26.0, 22.21 2.48 1.40

3b 3 3 85 85 86 87 c 113 c. 170 171 c c 3 c 85, 3 114 c

Copolymers of vinyl esters (M2) with methyl methacrylate (M~) Vinyl Vinyl Vinyl Vinyl Vinyl Vinyl Vinyl

formate acetate propionate butyrate phenylacetate benzoate ethyl oxalate

28.6 26.0, 22.21 24.0 25.0 26.4 20.3 6.0

0.05 0.03, 0.03 0.03 0.03 0.03 0.07 0.10

85 85, 3 85 85 85 85 86

a All the data from Ref. [3] are said to be calculated values (see c below). b private communication of E. L. Kitzmiller, Lehigh University to Union Carbide Chemicals and Plastics Co., South Charleston, WV, in Ref. [3]. c Calculated data from "Vynate, Vinyl Ester Monomers," Technical Bulletin F-60848 10/93-3M, Union Carbide Corporation, Danbury, CT, 1993, and D. Lee, Am. Paint Coatings J. Oct. 18, 1993, reprinted in Technical Bulletin F-60889 11/93-1M, Union Carbide Corp.

2.

Bulk Polymerizations

231

para-substituents such as hydrogen, methoxy, methyl, chloro, bromo, and cyano groups against HammeR's a-values gave a straight line. A small Hammer p-value indicated that, in this case, a small polar effect operates on the vinyl group [88]. The radical copolymerization of vinyl thioacetate and vinyl thiobenzoate has also been investigated. Overall, the polymerization rate of vinyl thioacetate was smaller than that of vinyl acetate, but its reactivity in copolymers was larger. This has been attributed to the participation of a d - n interaction of the sulfur groupings with the vinyl moiety [87]. Dialkyl vinylphosphonates, where the alkyl groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, and n-pentyl have been studied. The polymerization kinetics of these monomers indicate that chain termination may be by chain transfer through the alkyl groups of the monomer and that this chain transfer takes place in the later stages of polymerization [89]. The tacticity of the polymers of vinyl acetate and other vinyl esters has been studied for some time. Increasing stereoregularity of polymers was noted as esters of halogenated acids with increasing amounts of chlorine were polymerized. The sequence of increasing degree of stereoregularity was in the order: vinyl acetate < monochloroacetate < polychloroacetate < trifluoroacetate. Even in the most stereoregular poly(vinyl trifluoroacetate) ester, the sequence of regularly oriented units was relatively short [75]. Fordham and co-workers [75] observed that syndiotactic propagation may be preferred for free-radical polymerization in general. In other words, it was proposed that free-radical polymers may be significantly more regular in conformation than had previously been realized. They believed that the polymerization process was characterized by syndiotactic propagation, with frequent interruptions by isotactic propagation steps. It has been stated that at a conversion of 15%, the free-radical polymerization of vinyl acetate with AIBN and 2.4% triethylamine at 27~ produced an atactic poly(vinyl acetate) with a number-average molecular weight of 166,000. When chloroform was added to this initiator system, chain-transfer activity was sufficient to reduce the molecular weight of an atactic poly(vinyl acetate) to 1894 [90]. The vinyl esters of perfluorinated acids give rise to polymers which tend to be unstable to moisture. In fact, both the monomers and the polymers hydrolyze readily [91]. Interestingly enough, unlike the corresponding vinyl acetate system, poly(vinyl trifluoroacetate) is insoluble in its monomer. Substitution of fluorines for the hydrogens of the acetate portion of the monomer is thought to reduce chain transfer and branching. The poly(vinyl alcohols) derived from the hydrolysis of stretched poly(vinyl trifluoroacetate) were found to be highly ordered and birefringent [92]. Even in the presence of such aldehydes as acetaldehyde, propionaldehyde, butyraldehyde, and heptanol (all conventional chain-transfer agents for vinyl

232

7. Polymerization of Vinyl Acetate and Other Vinyl Esters TABLE XlII BulkPolymerization of Vinyl 1-Adamantanecarboxylateand Vinyl Trialkylacetates [94]a Polymerization Monomer

Vinyl 1-adamantane' carboxylate Vinyl trimethylacetate Vinyl tri-ethylacetate Vinyl tri-n-propylacetate Vinyl tri-n-butylacetate

Temp (~

Time (hr)

Yield (%)

Softening point (~

0.2

60

5

89

220-225

53

0.2 0.1 0.05 0.1

60 45 60 60

22 24 6 24

80 96 87 84

73-78 80-83 51-55 68-70

56 61 62 64

Initiator (moles)

Syndiotacticity (%)

a polymerization conditions: The monomer concentration was 20 moles. Polymerization was conducted using 2.2'-azobisisobutyronitrileas the initiator in degassed sealed ampoules. Times and temperatures are given for each monomer in the body of the table. esters) in the temperature range from - 4 0 ~ to 60~ the free-radical polymerization of vinyl trifluoroacetate gives rise to a polymer in which syndiotactic and isotactic diads are found in up to 56% concentration [93]. Bulky substituents on the acid portion of vinyl ester evidently affect the stereoregularity of the polymer obtained either by free-radical or cationic mechanisms. To study this matter further, vinyl 1-adamantanecarboxylate vinyl 1-adamentyl ether, and, as open-chain analogs of the adamentyl group, various vinyl trialkylacetates and vinyl tri-n-propylcarbinyl ethers were prepared and polymerized. The admantanecarboxylate ester exhibited a syndiotactic propagation stage much like the trialkylacetates. Syndiotacticity of the polymers seems to increase as the molecular weight of the trialkylacetate moeity increases up to a limiting value of approximately 65% syndiotacticity for vinyl tri-n-butylacetate as is indicated in Table XIII. Table XIII also lists the general conditions for the preparation of these polymers by bulk polymerization in degassed, sealed ampoules. The final purification of the polymers was by reprecipitation from benzene solutions with methanol. These polymers have also been prepared by irradiation with a low-pressure mercury lamp and with a tri-n-butylborane-air initiation system [94]. The exceptionally high softening point of poly(vinyl 1-adamantanecarboxylate) as compared with those of the vinyl trialkylacetates is noteworthy. 3.

SOLUTION

POLYMERIZATION

The polymerization of vinyl acetate in solution may be carried out to produce lacquers, chewing gum bases, and adhesives. Usually the polymers are used

3. Solution Polymerization

233

directly in the solvents in which they are formed. A few applications may call for the recovery of the solid polymer from solution. This may be accomplished by addition of a nonsolvent of the polymer or, where applicable, by removal of the solvent by steam distillation [95]. Most of the solvents that have been studied act as chain-transfer agents in the polymerization of vinyl acetate. The fact that the monomer itself acts as a chaintransfer agent for its own radicals has already been discussed, tert-Butyl alcohol is exceptional in that it is one of the few common solvents with minimal, if any, chain-transfer activity [96, 97]. Among the solvents which have been used in the polymerization of vinyl acetate are ethyl acetate [62, 82, 95, 96, 98, 99], butyl acetate [95], dimethylcarbitol [62], acetic acid [95], acetic acid-water mixtures [100], dimethylformamide [ 101 ], acetone [95], benzene [25.95, 98, 99, 102], various alcohols [25, 67, 95, 96, 99, 103, 104], toluene [95, 104], dichloromethane (methylene chloride) [ 104], and 1,2-dichloroethane (ethylene dichloride) [ 105]. An azeotropic mixture of methyl acetate and methanol is a common coproduct from the manufacture of poly(vinyl alcohol) from poly(vinyl acetate) in the presence of methanol and sodium methoxide. The polymerization of vinyl acetate in this azeotropic solution, with the total removal of oxygen from the system, and using conventional free radical initiators is said to afford highmolecular weight poly(vinyl acetate) [ 106]. The solution polymerization may be carried out conveniently in a typical reflux apparatus. If samples are to be taken during the course of the reaction, a sampling tube leading downward through a short condenser to a receiving flask may be incorporated. Although the reactions are usually carried out under a nitrogen atmosphere, the careful degassing of the reactants, which is possible in sealed ampoules or enclosed dilatometer polymerizations is normally not achieved. Consequently, induction periods must be anticipated. Procedure 3-1 is based on directions given in a study of the retarding and inhibiting effects of low levels of acrylonitrile on the polymerization of vinyl acetate [ 105].

3-1.

Polymerization of Vinyl Acetate in Ethylene Dichloride [105]

In a 3-liter, three-necked flask fitted with a propeller-type agitator, thermometer, reflux condenser, and inlet and outlet tubes for purified nitrogen which are fitted with bubble counters, a solution of 600 gm of purified vinyl acetate and 900 gm of ethylene dichloride is heated to reflux with stirring while a nitrogen flow of 7 ml/min is maintained. The heat is adjusted to maintain a reaction temperature of 70~ At that temperature, 1.5 gm of dibenzoyl peroxide is added and the nitrogen flow is reduced to 5 ml/min. Within approximately 5.5 hr, approximately 85% of the monomer is converted to polymer.

234

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

A sample of the polymer may be isolated by evaporating an aliquot of the product solution under reduced pressure, dissolving the residue in approximately 20 volumes of methanol, and precipitating the polymer with water. The filtered product is then dried under reduced pressure at a modest temperature. The polymerization of vinyl acetate in various alcohols has been suggested by many workers. Certainly when methanol is used as a solvent, the solvent concentration has a profound influence on the molecular weight of the polymer [67, 99, 103]. This effect has been attributed to the formation of acetaldehyde, a well-known chain-transfer agent, by a transesterification reaction involving the monomer [103]: O II CH2---CHOC--CH3 + CH3OH

O O II II ~ CH3COCH3 + CH3CH

(7)

Table XIV indicates the effect of methanol and dibenzoyl peroxide concentration on the percent conversion of the monomer and on the degree of polymerization of the polymer. Of t h e common solvents, tert-butyl alcohol because of its very low chaintransfer constant, may be used to produce polymers of relatively high molecular weight. If we concede that single-point measurements of specific viscosity and inherent viscosity may be considered indications of the general trend of molecular weights, then the effect of various solvents on the molecular weights of the poly(vinyl acetate) produced may be seen in Table XV. Procedure 3-2 outlines the method for polymerizing vinyl acetate in tert-butyl alcohol. Particular attention is directed to the method for removing excess monomer and solvent. TABLE XIV The Polymerization of Vinyl Acetate in Methanol Solution [103] Concentration of methanol (%)

Dibenzoyl peroxide (% on monomer)

15 15 30a 33 33 33 33 50 50

0.025 0.050 0.10 0.017 0.066 0.23 0.46 0.23 0.92

a Based on data from Horn [99].

Polymerization time (hr) 18 16 -46 45 17 15 26 26

Conversion (%) 64 96 92 96 97 97 98 98

Degree of polymerization of poly(vinyl acetate) 1800 1900 850 640 760 670 600 360 300

3.

235

Solution Polymerization

TABLE XV

The Effect of Solvents on the Polymerization of Vinyl Acetate [96] ~

Diluent

Yield of polymer (%)

Specific viscosity

Inherent viscosity (dl/gm)

(None) Isopropyl alcohol n-Propyl alcohol Acetic acid Ethyl acetate tert-Butyl alcohol

92.4 75.4 50.0 34.0 73.2 84.2

0.210 0.023 0.031 0.047 0.080 0.186

1.89 0.22 0.29 0.44 0.75 1.69

a polymerization conditions: Polymerization was conducted using 50 gm of vinyl acetate, 30 ml of diluent, and 0.05 gm of dibenzoyl peroxides. The solution was heated for 22 hr at reflux.

3-2.

Polymerization of Vinyl Acetate in tert-Butyl Alcohol [96]

In reflux equipment similar to that described in Procedure 3-1, but scaled down to a 500-ml flask, 50 gm of freshly distilled vinyl acetate is dissolved in 30 ml of tert-butyl alcohol. To this solution is added 0.05 gm of dibenzoyl peroxide. The mixture is heated under nitrogen on a steam bath for 22 hr. The warm viscous solution is diluted with 200 ml of acetone. The solution is transferred to a 3-liter flask containing l-liter of hot, distilled water to precipitate the polymer. The equipment is set up for steam distillation, steam is passed through the suspension to distill out unreacted vinyl acetate and tert-butyl alcohol. After the steam distillation is completed, the polymer is filtered off and dried to constant weight at 80~ and 8 mm Hg pressure (yield, 42.1 gm or 84.2%; specific viscosity, 0.186; inherent viscosity in benzene, 1.69 dl/gm). By using greater levels of tert-butyl alcohol, polymers with somewhat lower molecular weights are produced. As indicated in Table XV, the chain-transfer activity of this solvent is substantially less than that of many other common solvents. This solvent has also been suggested for continuous polymerization or copolymerization processes [97]. Benzene, in small quantities, reduces the rate of polymerization of vinyl acetate. In effect it acts as an inhibitor for this polymerization [86]. Actually, the function of benzene in the polymerization of vinyl acetate is quite complex and has been discussed above. Benzene may form a complex with the monomer, it may act as a chain-transfer agent, or it may actually copolymerize [cf. 37-43]. A solution of 70% vinyl acetate in benzene with 0.1% dibenzoyl peroxide produces a polymer with a degree of polymerization of 850 [99]. The procedure for the polymerization in benzene given by Sorensen and Campbell [102] is

236

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

completed in approximately 2 hr and yields a polymer with an inherent viscosity greater than 1 (concentration in chloroform: 0.5% at 25~ One of the advantages of the use of benzene as a reaction solvent is the ease of its separation from the polymer by steam distillation. This procedure also removes unreacted monomer, of course. In a suitable solvent, solution polymerization involving the delayed addition of the monomer may be carried out. In this procedure, all of the solvent and 10-25% of the monomer are heated to reflux in the presence of an initiator. As the polymerization proceeds, additional monomer is gradually added. To complete the polymerization, the reaction solution is heated for a prolonged period after the monomer addition has been completed. Even so, the residual monomer content may be as high as 2% [95]. The determinination of the rate of polymerization of vinyl acetate in solution has been carried out in a mercury recording dilatometer. In this procedure, the solution of the monomer and 2,2'-azobis(2,4-dimethylvaleronitrile) is placed in the dilatometer, degassed, and sealed at a pressure of approximately 1 0 - 4 m m Hg. The dilatometer is maintained at 50.0 ___0.02~ The total shrinkage is calculated using 0.892 gm/ml as the density of the monomer and 1.166 gm/ml as that of the polymer. The rate of polymerization is usually determined from the rate of shrinkage in the conversion range of 5-7% [62]. A continuous solution-polymerization process using ethyl acetate as solvent and a range of propionaldehyde as chain-transfer agent has been described. In this process, a solution of dibenzoyl peroxide in ethyl acetate is gradually added to a reactor along with the solution of propionaldehyde in vinyl acetate at 80~ The ratio of the monomer solution to the initiator solution is given as 7 : 3. The solution leaving the reactor contains 5-8% of residual monomer. Its level is reduced by reacting the product solution for several hours in a separate reactor at

80oc [52]. In the polymerization of vinyl esters of perfluorinated acids, ordinary organic solvents are not suitable because of the low solubility, particularly of the higher esters. Therefore, fluorinated solvents have been suggested. Methyl perfluorobutyrate is considered satisfactory. While benzotrifluoride may be used, the polymers produced in this solvent are low molecular weight [91 ]. The polymerization of vinyl formate is of considerable interest since its polymer is particularly readily hydrolyzed to poly(vinyl alcohol). For example, according to one patent, a solution of 70% vinyl formate in methyl formate containing 0.2% of 2.2'-azobisisobutyronitrile was polymerized in a sealed tube under nitrogen for 10 hr at 30~ The reaction product was hydrolyzed to give a poly(vinyl alcohol) with a degree of polymerization of 2110 [107]. In a 1955 patent, a polymerization procedure is discussed which may be considered a transition stage between solution and suspension polymerizations, i.e., the processes which will be discussed in Section 4. The polymerization is

3.

Solution Polymerization

237

carried out in a water and ketone solution. The product, because of its low molecular weight and the presence of a solvent separates as an oil rather than as beads usually associated with suspension polymers. In this procedure, the molecular weight of the polymer is controlled by the use of the ketone. Generally ketones are not considered as effective as chaintransfer agents for the polymerization of vinyl acetate as aldehydes of approximately the same molecular weight. However, the products are thought to be heat resistant and odor free. In the example cited from the patent, the product is said to be useful as a chewing gum base. Considering the fact that methyl ethyl ketone is used in the procedure, current views on toxicity raise serious questions about the suitability of this product for use in chewing gums [ 108].

3-3. Formation of Low-Molecular-Weight Poly(vinyl acetate) (Gradual Addition Procedure) [108] In a 2-liter reaction kettle equipped with a mechanical stirrer, addition funnel, reflux condenser, and a thermometer are placed 100 gm of vinyl acetate, 200 gm of methyl ethyl ketone, 20 gm of water, 0.50 gm of sodium bicarbonate, and 0.62 gm of 30% hydrogen peroxide (CAUTION: Strong oxidizing agent, must be handled by personnel using protective gloves, face shield, and other appropriate safety clothing). The mixture is heated at the reflux temperature with agitation. After the polymerization has been initiated and requires no external heating, 300 gm of vinyl acetate is added gradually over a 3-hr period while moderate refluxing is maintained. After the addition has been completed, heating is continued at the reflux temperature for an additional 4 hr. At this point approximately 75% of the monomer has been converted. The polymer mixture may be separated and dried at reduced pressure for 5 hr at 60~ Alternatively, the reaction temperature may be raised gradually while more water is added to the reaction mixture. During this process, the polymer separates as a soft semisolid from the aqueous system. The excess monomer and the methyl ethyl ketone is then separated by steam distillation. The water is separated from the polymer by decantation. The product is then dried under reduced pressure at 60~ A molar solution of the product in benzene has a viscosity of 1.5 cp at 20~ In this process, with increasing levels of hydrogen peroxide, the molecular weight of the product decreases. According to the patent, at least 0.01 mole of sodium bicarbonate per mole of hydrogen peroxide is required for the process to be operative. In organic solutions, polyethylene oxides of molecular weight less than 1000 or copolymers of PEO may act as molecular weight regulators of the polymerization of vinyl acetate. For 100 gm of the monomer, from 0.5 to 20 gm of the

238

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

molecular weight regulator have been used along with conventional initiators [109]. Trialkyl phosphites have been used in the presence of dibenzoyl peroxide (BPO) for the radical polymerization of vinyl acetate. In the presence of tris(2,2,2-trifluoroethyl)phosphite, there appears to be no significant change in molecular weight and polydispersity with increasing conversion. Lower molecular weights are formed with higher concentrations of BPO, regardless of the ratio of initiator to phosphite. There is an effect of the structure of the alkyl groups of the phosphite. With increased size, the rate is reduced. Yet the fastest rate was observed with the trifluoroethyl substituent. Pentavalent phosphates lead to increased rates of polymerization, greater polydispersity, and molecular weight results similar to those obtained with BPO alone. With initial conditions of a ratio of [P(trifluoroethoxy)]3 to BPO of 1.5 to 1; a concentration of BPO of 0.025 mol/liter of benzene; and 7 moles/liter of vinyl acetate in benzene, a polymerization was carried out at 60~ for 6 hr. At a conversion of 86%, the number average molecular weight of the polymer was 63,000, and the polydispersity was 1.39 [110]. Control of the molecular weight of poly(vinyl acetate) has also been accomplished in one recent example by an extension of what appears to be a "redox" polymerization in nonaqueous solutions. In this work, the reducing component is an organochromium(II) complex, the oxidizing agent is dibenzoyl peroxide (BPO), and the solvent is tetrahydrofuran (THF). Specifically, 1 liter of a THF solution containing 5 mole of vinyl acetate, 0.25 mole of BPO, and a composition of 0.25 mole of Cr 2+ ions and 0.25 mole of 1,4,7,10,13,16-hexaazacyclooctadecane trisulfate was maintained for 30 hr at 20~ After this period, the conversion to polymer was up to 90%. There was evidence that the concentration of the active species was constant throughout the experiment. The number average molecular weight of the isolated product was reported to be 15,000. In general, with increasing conversion, the molecular weight increased from approximately 5,000 at 18% conversion to 15,000 at 90% conversion. The polydispersity ranged from 1.54 to 1.63 [111 ]. This procedure is of considerable theoretical interest. The use of heavy metal ions, however, will present problems. Chromium ions are thought to be carcinogenic. The removal of such species to below the one part per billion level from the final product will be problematical. Consequently, a polymer produced with a heavy metal ion as part of the initiator system probably will have difficulties as a commercially viable product. A variety of copolymers of vinyl esters have been prepared in solution. For example, vinyl 2-ethylhexanoate and 2-ethylhexyl acrylate have been copolymerized in feed ratios ranging from 1 to 1 to 1 to 3 (on a molar basis). The acrylic monomer was said to have a greater reactivity than the vinyl ester. The product was studied as a possible viscosity index improver [112].

4. Suspension Polymerization

239

The reactivity ratios for the copolymerization of vinyl acetate and behenyl acrylate were determined by polymerization with BPO in toluene solution at 70~ They were found to be 0.021 for vinyl acetate and 1.76 for behenyl acrylate [113]. The copolymerization of vinyl acetate (ml) and phenyl acrylate (m2) led to a copolymer with a greater tendency to forming an alternating product than a copolymer of vinyl acetate and vinyl benzoate. The reactivity ratio for vinyl acetate was 0.22, that of phenyl acrylate was 2.48 [ 114].

4.

SUSPENSION POLYMERIZATION

In general, in previous discussions of free-radical polymerizations, we have attempted to draw a sharp distinction between suspension- and emulsionpolymerization processes. This distinction is quite readily apparent in the case of monomers which are quite insoluble in water, such as styrene. In that case, by use of monomer-soluble initiators and a variety of suspending agents, the suspension-polymerization process leads to the formation of spherical particles which can be separated by filtration. When water-soluble initiators and surface-active agents are used, relatively stable latices are formed from which the polymer cannot be separated by filtration. In the case of vinyl acetate, the distinctions are more blurred. Our description of Procedure 3-3 above represents a transitional situation between a solution and a suspension process since the product separated from the reaction medium. Between the true suspension and the true emulsion polymerization, we find, according to Bartl [4], the processes for formation of reasonably stable dispersion of fine particles of poly(vinyl acetate) using reagents which are normally associated with suspension polymerization. The product is described as "creme-like." The well-known white, poly(vinyl acetate), household adhesives may very well be examples of these creamy dispersions. The true latices are characterized by low viscosities and particles of 0.005-1 ~tm diameter. The creme-like dispersions exhibit higher viscosities and particle diameters of 0.5-15/tm. Probably most industrial homopolymerizations of vinyl acetate are carried out by suspension processes, since the resulting beads are readily converted to poly(vinyl alcohol). This is the major reason for producing the homopolymer. Surprisingly little has been published about the suspension polymerization of vinyl acetate, despite the fact that Lindemann [ 1] cites nearly 1100 references on the subject of vinyl acetate and approximately 200 references on the higher vinyl esters. While there have been many patents issued which deal with peripheral matters such as suspending agents and initiators, much of the published technology has advanced a little beyond that known by the end of World War II. As in the case of poly(vinyl chloride) technology, the chemistry of poly(vinyl

240

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

acetate) consists of seemingly closely guarded industrial know-how. However, enough information is available to develop useful laboratory procedures. As has been discussed in other cases of free-radical suspension polymerizations, the process may be considered as consisting of bulk polymerizations of small droplets cooled by the surrounding aqueous media. This similarity of the kinetics of suspension and bulk polymerizations of vinyl acetate has been demonstrated [115]. The fact that vinyl acetate is moderately soluble in water may be a cause for the tendency for coalescence of the suspended particles unless care is taken in the proper selection of initiator concentration, suspending agents, and stirring rate. Table XVI indicates that at a low stirring rate, particles tend to coalesce. The reactions tabulated were carried out in air. Under nitrogen a somewhat faster rate and polymers with reduced branching were observed. In Table XVI, we have included data from Wagner [61] to show that the suspension process may be carried out for prolonged reaction periods, at a low rate, and still produce products of high molecular weight. From the preparative standpoint several points should be considered. The need for an inert atmosphere over the reaction system appears to be secondary. Sakurada et al. [ 115] indicate that the polymerization is somewhat more rapid under nitrogen than under air. The difference in the molecular weight of poly(vinyl acetate) produced under these two conditions is not great. However, when the polymers are hydrolyzed to poly(vinyl alcohol), the polymer produced under nitrogen gives rise to a substantially higher degree of polymerization of the poly(vinyl alcohol) than the polymer formed in air. This seems to indicate a

TABLE XVI Effectof the Stirring Rate on the Suspension Polymerization of Vinyl Acetate [ 115]a Initiator concentration (% on the monomer)

Stirring rate (rpm)

0.1 0.3 1.0 0.3 0.4 (25~ 50~ b (water to monomer ratio not given)

500 900 500 350 not given

Polymerization State time Conversion of Degree of (hr) (%) particles polymerization 4.0 2.5 4.0 1.5 22

85 82 92 67 not given

good good good poor presumed good

4650 1650 6100C

a Polymerization conditions: The water to monomer ratio was 2 to 1 by volume. Polymerization was conducted at 65~ using 1 gm poly(vinyl alcohol) per 100 ml water with dibenzoyl peroxide as the initiator. Considering the high conversion within relatively short reaction times, we suspect that the data refers to the use of 2,2'-azobisisobutyronitrile at 65~ rather than dibenzoyl peroxide. bFor comparison. c Data from Wagner [61].

4. Suspension Polymerization

241

substantial difference in the degree and nature of the branches in the poly(vinyl acetate). The polymerization of vinyl acetate is best carried out in a pH range in which the hydrolysis of the monomer is minimized. Since this hydrolysis leads to the formation of acetaldehyde, a notorious chain-transfer agent, careful control of the pH is important, albeit the available literature rarely considers this. The pH range of 4-5 is considered optimum for minimizing vinyl ester hydrolysis. Formic acid, at a level of 0.15-0.25% of the monomer has been suggested for this purpose [4]. In connection with this it should be kept in mind that formic acid does have an aldehydic structure and may, therefore act as a chain-transfer agent. It is also a potent reducing agent and may create a redox system with BPO or other oxidizing initiators. In this connection, two points should be investigated further. 1. To what extent are the modifications of polymerization characteristics the result of formic acid acting as the reducing agent in a redox system which is being compared with a simple case of thermal initiation? 2. Since formic acid is toxic, can this material be removed sufficiently well from the final product to permit use of poly(vinyl acetate) or poly(vinyl alcohol) in situations where toxicity factors come into play (e.g., adhesives for food packaging, household adhesives)? Factors which influence the particle size formed during suspension polymerization are the ratio of monomer to water, the viscosity of the aqueous medium as modified by suspending agents or protective colloids, the rate of agitation, the diameter and shape of the reaction vessel, and the relationship of agitation rate to agitator shape and diameter, to mention only a few [ 116]. The reproducibility of suspension polymers is thought to be improved if, instead of allowing the monomer reflux to drop back to the surface of the reaction medium, the reflux is returned to the bottom of the reactor. The suspension polymer has a tendency to be soft and tacky. Several techniques have been proposed to overcome this problem. These include coating the polymer beads prior to filtration or hardening the beads by cooling the reaction mixture to below 10~ prior to filtration. The polymer isolated may contain substantial quantities of water and must, therefore, be carefully dried [95]. Typical suspending agents for the vinyl acetate polymerization are poly(vinyl alcohol) [particularly a grade represented as approximately 88% hydrolyzed poly(vinyl acetate)], gum arabic, hydroxyethyl cellulose, methyl cellulose, starches, sodium polyacrylate or sodium polymethacrylate, gelatin, and an equimolar copolymer of styrene and maleic anhydride neutralized with either sodium hydroxide or aqueous ammonia. Water-insoluble dispersing agents or

242

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

high concentrations of electrolyte to reduce water solubility are not usually used in the suspension polymerization of vinyl acetate. The usual initiators are monomer-soluble ones such as dibenzoyl peroxide, lauroyl peroxide, and di-o-toluyl peroxide. Hydrogen peroxide and a few other water-soluble initiators usually associated with emulsion polymerizations have also been used. The molecular weight of the polymer may be controlled by variations in the concentration of the initiator. This effect is illustrated in Procedure 4-1. It is interesting to note that this procedure which goes back to FIAT Final Report 1102, i.e., a report compiled toward the end of World War II [4], was still used in 1974 according to Bravar et al. [117]. We have adapted these procedures to a laboratory scale.

4-1.

Suspension Polymerization of Vinyl Acetate (Control of Molecular Weight by Variation in Initiator Level) ( B a s e d o n B a r t l [4] a n d B r a v a r et al. [117])

a. Preparation of Low-Molecular-Weight Poly(vinyl acetate) In a 3-liter reaction kettle fitted with a mechanical stirrer, reflux condenser, thermometer, and an addition funnel, 800 ml of distilled water and 0.8 gm of the sodium salt of an equimolar copolymer of styrene and maleic anhydride (German trade name Styromal) are heated to 80~ with agitation. Meanwhile a solution of 600 gm of vinyl acetate, 5.4 gm of dibenzoyl peroxide, and 3 gm of ethyl acetate is prepared. To the warm aqueous suspending agent is added 100 gm of the vinyl acetate solution. The stirred mixture is brought up to 80~ by external heating. Once the polymerization has started, heating and cooling is applied as required while the remainder of the monomer solution is added over a 5-hr period. After the addition has been completed, heating is continued for an additional 3-hr period. The residual monomer is removed by steam distillation with agitation. The aqueous dispersion is cooled with agitation to 4~ The polymer beads are filtered off or centrifuged and washed repeatedly with water at 5~ to remove the suspending agent. The polymer is then dried under reduced pressure at 30~ The dry product is glass clear. The product is reported to have MW 110,000.

b. Preparation of an Intermediate-Molecular-Weight Poly(vinyl acetate) For this preparation, the procedure used is the same as that given in Section a except that the reactants used are 800 ml of distilled water and 0.8 gm of Styromal (sodium salt) to which is added by the described gradual addition

4. SuspensionPolymerization

243

technique a solution of 600 gm of vinyl acetate and 1.2 gm of dibenzoyl peroxide. The final product has MW on the order of 1,000,000.

c. Preparation of a High-Molecular-Weight Poly(vinyl acetate) For this preparation, the procedure used is the same as that given in Section a except that the reactants used are 800 ml of distilled water and 1.2 gm of Styromal (sodium salt) to which is added by the described gradual addition technique a solution of 600 gm of vinyl acetate and 0.18 gm of di-o-toluyl peroxide. The final product has MW on the order of 1,500,000. A patented procedure for the suspension polymerization of vinyl acetate which is claimed to produce a nonsticky bead polymer [118] uses an aqueous phase consisting of 537 gm of distilled water, 0.25 gm gum tragacanth, and 0.10 gm sodium dioctylsulfosuccinate (Aerosol OT). The monomer charged consists of 690 gm of vinyl acetate and 0.69 gm of dibenzoyl peroxide. In a complex apparatus, Gunesch and Schneider [30, 119] studied the suspension polymerization of vinyl acetate. Their procedure involved equipment which automatically added tempered water to the reacting system as heat was evolved as a result of the polymerization process. Thus they maintained isothermal reaction conditions. The rate of reaction could be followed by recording the water uptake of the equipment with time. The heat of polymerization was also determined (found to be 23 kcal/mole which was considered a satisfactory check of the literature value which is scattered around 21.4 kcal/mole). From this work, a somewhat different mechanism of the suspension polymerization process emerges than the widely accepted concept of the "water-cooled bulk polymerization of small particles." It was noted that with an increase in the initiator concentration, there was the expected increase in polymerization rate. With increasing stirring rate, the rate of polymerization decreased. Along with the suspension polymerization, there was always a certain amount of undesirable emulsion polymerization. It was postulated that in the process, free radicals, formed in a monomer drop may be extracted into the aqueous phase where they may act on dissolved vinyl acetate by kinetic processes Unique to this system and different from the conventional mechanism of suspension polymerization. Sodium thiosulfate interfered with the polymerization in the aqueous phase. This manifested itself in a decrease in the overall rate of polymerization (cf. Table XVII). In this work, substantial additions of sodium chloride were made to the aqueous phase to reduce further the unwanted emulsion polymerization. The suspending agent used in these experiments was a partially saponified poly(vinyl acetate) whose trade designation is Rhodoviol HS 100. This poly(vinyl alcohol) was normally added to the reaction system as a 6% aqueous

244

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

solution. Table XVII primarily shows the effect of the rate of agitation on the bead size and the yield of polymer. The amount of water added during the polymerization was 1430 ml of 20~ water. Unfortunately the report did not define very precisely the quantities of initiators used. The polymerization of vinyl pivalate by the suspension procedure gives a product of very high molecular weight. The molecular weight seems to be independent of the extent of the conversion. This has been attributed to the fact that the pivalate moiety has no a-hydrogens and hence cannot act as a chaintransfer agent in a manner analogous to an acetate. It is interesting to note that the suspension polymer of vinyl pivalate has a higher molecular weight than its emulsion polymer [116]. Procedure 4-2 details the suspension process.

4-2.

Suspension Polymerization of Vinyl Pivalate [116]

In a 2-liter reaction kettle equipped with a mechanical stirrer, thermometer, nitrogen inlet and outlet tubes, reflux condenser, and an addition funnel, under nitrogen a solution of 500 ml of distilled water containing 7.5 gm of Mowiol 70/88 [a grade of poly(vinyl alcohol), probably consisting of 88% hydrolyzed TABLE XVlI The Effect of the Agitation Rate on Yield and Bead Size in the Suspension Polymerization of Vinyl Acetate [30] a Rate of agitation (rprn/min)

Yield (%)

Average diameter of beads (mm)

Lauroyl peroxide (only)

120 240 480

98 95 93

0.9 0.5 0.2

Lauroyl peroxide with sodium thiosulfate

120

89

0.8

240 480

85 76

0.4 0.2

120

77

0.6

240 480

61 58

0.2 0.1

Initiator

Dibenzoyl peroxide with sodium thiosulfate

a Polymerization conditions: Polymerization was conducted using 250 ml vinyl acetate (233 gm, carefully purified), 500 ml distilled water containing 50 gm sodium thiosulfate (when indicated), and 6 ml of 6% solution of poly(vinyl alcohol) (Rhodoviol HS 100). To control the reaction temperature at 63.5~ under nitrogen, water was gradually added. The water temperature was 20~ During the preparation a total of 1430 ml of water was added. The initiator used was lauroyl peroxide or AIBN. On 250 ml of vinyl acetate, 0.5-3 gm of initiator was used.

4. Suspension Polymerization

245

poly(vinyl acetate) of high molecular weight] is stirred at 60~ while a solution of 0.118 gm of dibenzoyl peroxide in 250 gm of vinyl pivalate is added all at once. The reaction mixture is heated for 5.5 hr. Then the reaction temperature is raised to 80~ and maintained at that temperature for 22 hr. The reaction mixture is then cooled to 4~ The polymer is filtered off and washed repeatedly with water at 5~ The product is dried under reduced pressure at 30~ (yield 236 gm or 94.3%; MW, 3.58 • 106). It should be noted that if the reaction temperature is raised to 80~ earlier than indicated in this procedure, the degree of polymerization will be reduced. To return to the matter of increased molecular weights of suspension polymers, it seems that the incorporation of a small amount of hydrogen peroxide along with an organic peroxide in a suspension-polymerization procedure increases the molecular weight of the polymer substantially. It also reduces the induction period [ 120]. It is interesting to speculate whether the small amount of hydrogen peroxide used is sufficient to initiate polymerization of a seed polymer in the aqueous phase about which the suspension polymer forms. Procedure 4-3 illustrates the use of hydrogen peroxide to form a relatively high-molecularweight polymer.

4-3.

Suspension Polymerization of Vinyl Acetate in the Presence of Hydrogen Peroxide [120]

In equipment similar to that indicated in Procedure 4-2, into 500 ml of a 2% solution of poly(vinyl alcohol) (viscosity and degree of hydrolysis not specified in the original patent) is added a solution of 500 gm of vinyl acetate containing 0.25 gm of dibenzoyl peroxide along with 5 ml of a 1.0% aqueous solution of hydrogen peroxide. With agitation, the mixture is heated for 6 hr at 70~ The reaction mixture is then cooled to 4~ filtered, and washed repeatedly with water at 5~ The polymer is dried under reduced pressure at moderate temperatures (yield, 85% of theory). The viscosity of a 1 "molar" solution of this polymer in benzene is reported to be 150 cP. When the polymerization is carried out without hydrogen peroxide, the viscosity of a solution of comparable concentration is only 92 cP. The technique described above may be modified by use of gradual addition of the monomer. Methyl cellulose may be substituted for poly(vinyl alcohol). A novel method of producing suspension polymers of poly(vinyl acetate) with a closely controlled molecular weight distribution involves the solution polymerization of vinyl acetate in methanol. By varying the ratio of monomer to methanol, a variety of molecular weight distributions may be prepared. The solution polymer is then added with agitation to an aqueous system containing poly(vinyl alcohol). The methanol is then distilled off to give a bead polymer [121].

246

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

One interesting aspect of this method of producing a suspension polymer is the fact that this method produces beads of poly(vinyl acetate) which may be loosely coated with poly(vinyl alcohol). This coating may be removed much more readily than the poly(vinyl alcohol) used in a conventional polymerization procedure. In the conventional process, a fair amount of the suspending agent probably forms a graft copolymer with vinyl acetate and is, therefore, permanently bound to the polymer bead. The properties of the two types of bead polymers are expected to be somewhat different since the graft copolymer with poly(vinyl alcohol) is present only in one and not the other polymer. When substantial quantities of a suspending agent are used in a typical suspension polymerization (i.e., 2-5% by weight of suspending agent based on the weight of the monomer) instead of beads which settle out of the aqueous medium, a stable dispersion of creme-like consistency is formed. The product consists of particles with average diameters in the range of 0.5-15 pm, which are somewhat larger than the diameters associated with latex particles (0.005 to 1/zm) dispersed in the aqueous medium. Poly(vinyl alcohol) and the partially hydrolyzed poly(vinyl acetates) are particularly suitable suspensing agents for these creme-like dispersions. Just as in the case of latex polymers of vinyl acetate, these dispersions tend to exhibit better freeze-thaw stability when partially hydrolyzed poly(vinyl acetate) is used rather than the fully hydrolyzed poly(vinyl acetate), i.e., 100% poly(vinyl alcohol). When ammonium persulfate is used as an initiator, the rate of polymerization is said to be increased if a mild alkali such as sodium carbonate is added. In fact, the high pH thus achieved may have an additional effect, since in the absence of the buffer, substantial coagulation takes place. The addition of a neutral salt such as sodium chloride (at a level of 0.05-1% of the reaction charge) is said to increase the molecular weight to very high levels [122]. Procedure 4-4 is an example of the preparation of a stable dispersion by this procedure.

4-4.

Preparation of a Stable Poly(vinyl acetate)

Dispersion [122] In a l-liter reaction kettle fitted with two addition funnels, reflux condenser, mechanical stirrer, and a thermometer, 14 gm of a 87% hydrolyzed poly(vinyl acetate) and 1.5 gm of sodium carbonate are dispersed in 190 ml of water. The aqueous phase is heated to 68~ with agitation. Over a 5.5-hr period, with agitation, 274 gm of vinyl acetate and a solution of 1 gm of potassium persulfate in 20 ml of water are added simultaneously from separate addition funnels. The rates of addition are controlled so that the ratio of monomer to initiator is maintained constant in the reaction mixture. During the addition stage, the reaction temperature is permitted to rise to reflux at 80~ After the addition has been completed, the reaction temperature is raised over a 1-hr period to 90~

247

4. Suspension Polymerization

Then, if necessary, the residual monomer may be stripped out by steam distillation. The resulting product is a smooth, creamy dispersion with particle diameters between 2 and 6 r The nonvolatile content of the dispersion is approximately 58%. Ordinarily the use of hydrogen peroxide as the only initiator is not satisfactory for the suspension polymerization of vinyl acetate. Incomplete conversion of the monomer is usual. By introducing additional hydrogen peroxide after a substantial amount of polymer has formed, this problem may be overcome. A typical reaction charge would be Reagent

Amount (gm)

Water Gum arabic Sodium dioctylsulfosuccinate Ferric chloride hexahydrate Vinyl acetate Hydrogen peroxide (as a 0.3% aqueous dispersion)

440 25 1.50 0.02 530 0.20

In the preparation, 10% of the monomer and 25% of the hydrogen peroxide are heated in the aqueous phase containing the gum arabic, sodium dioctylsulfosuccinate, and ferric chloride hexahydrate at 75~176 with agitation. The remaining monomer and the hydrogen peroxide are added gradually over a 2- to 3-hour period [ 123]. The control of particle size from 0.5 to 15/zm is possible by adding varying amounts of a protective colloid such as hydroxyethyl cellulose, an alkali salt of a maleate half ester, sodium phenyl phenolate, and/or a phosphate buffer at pH 6.9 [124]. It should be noted again that in the procedure attributed to Wilson [ 123], as in many other suspension polymerization procedures mentioned above and in many procedures for emulsion polymerizations to be described later, reaction temperatures are given which are above the boiling point of the monomer (72.7~ at 760 mm Hg), not to mention, above the boiling point of the vinyl acetate-water azeotrope (66~ (composition, 92.7% vinyl acetate, 7.3% water, cf. Table I). For reactions carried out in sealed ampoules or closed bottles, this reaction temperature is readily explained. How such reaction temperatures are reached in a reflux apparatus open to the atmosphere is in question. It is hardly likely that the rate of polymerization is so rapid that no free monomer exists when it is added with conventional initiators to hot water. We presume that most of the polymerizations reported to proceed at about 66~ in an aqueous medium are simply run at reflux. At such a temperature, initiation by dibenzoyl peroxide is rather slow. If the suspension polymerization is to be forced at higher temperatures, provisions will have to be made to force the monomer into the

248

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

reaction system. Simply to depend on condensing vinyl acetate dripping from a condenser to the surface of the water is not a very satisfactory procedure. It is best to introduce the refluxing monomer well under the surface of the reaction system or to operate in an appropriate autoclave. Mixtures of methyl acrylate and vinyl acetate, in various proportions, have been grafted to starch. To a stirred dispersion of 20 gm of starch, under nitrogen, was added 30 grn of the monomer composition. After 5 min of stirring, a solution of 0.676 gm of ceric ammonium nitrate in 6 ml on 0.1 N nitric acid was added. The mixture was stirred at room temperature for 3 hr. The crude product was filtered off, resuspended in water. The aqueous supematent layer was neutralized with 0.1 N sodium hydroxide. The graft copolymer was again separated by filtration, washed with methanol, and then air dried. To separate homopolymers from this product, 5 gm of this polymer was dispersed in 100 ml of acetone containing 2% of water. The solid graft copolymer was isolated by centrifugation and dried under reduced pressure. The product could be extruded into ribbons [125]. 5.

EMULSION

POLYMERIZATION

From the industrial standpoint, the suspension polymerization of vinyl acetate is of primary interest for the production of poly(vinyl acetate) homopolymer beads. Most of these beads are converted to poly(vinyl alcohol) with a variety of degrees of hydrolysis and in a number of different molecular weight ranges. On a laboratory scale, suspension copolymerizations of vinyl acetate with other monomers may have an advantage in terms of ease of handling and ease of developing a suitable suspension medium. Industrially emulsion polymerizations, both homo- and copolymerizations, are of great importance, particularly in the development of adhesives, paints, paper coatings, and textile finishes. The production of vinyl acetate monomer by the current top ~four U.S. producers (H6chst-Celanese, Union Carbide, DuPont, and Quantum Chemical) in 1989 was about 1.25 x 109 kg [8], compared to 1.14 x 109 kg reported for 1980 [7] and 0.89 x 109 kg for 1977 [126]. Since there are major producers of poly(vinyl acetate) not only in the U.S. but also in Japan, the United Kingdom, Germany, Switzerland, Canada, France, and Italy, one may assume that the total annual production of the monomer is well above the figure given here for the U.S. production. Although more than one third of all the monomer is used to produce latices in the form of paints and adhesives, published information on the emulsion polymerization of vinyl acetate is limited. References [1, 4, 7, 8] are general references. Bacon [127] reviews the redox initiation of the polymerization. Shapiro [128] deals with the applications of vinyl acetate to the paper industry.

5. Emulsion Polymerization

249

The emulsion polymerization of vinyl acetate may be unique among polymerization processes in that true latices have been formed with anionic surfactants, cationic surfactants, nonionic surfactants, or protective colloids, and with combinations of two or more such reagents, as well as without any added emulsifier. According to O'Donnell et al. [130], the emulsion polymerization of vinyl acetate follows the Smith-Ewart theory of emulsion polymerization [131] because the rate of polymerization is independent of the total amount of monomer present, the rate is a function of the 0.6th power of the emulsifer concentration, and the rate of emulsion polymerization is a function of the 0.7th power of the initiator concentration instead of the expected 0.4th power. In this work poly(vinyl alcohol), 88% hydrolyzed with a medium molecular weight (i.e., Du Pont's Elvanol 52-22), was used as the only externally added emulsifier. Light-scattering studies indicated that this emulsifier formed no aggregates in the aqueous solution. These latter observations may, however, have been made at room temperature and not at the reaction temperature [ 1]. The conversion versus time curve was essentially linear up to 80% conversion. Since the solubility of vinyl acetate is 2.1% at 50~ and 3.5% at 70~ [15], deviations from the Smith-Ewart treatment are not entirely surprising. The water solubility of vinyl acetate was one of the significant factors in the deviation from the conventional theory of emulsion polymerization. Another factor is the reactivity of the vinyl acetate radicals toward other materials present in the system such as the surfactants. Okamura and Motoyama [132] showed that the emulsion polymerization of vinyl caproate, a monomer of low water-solubility, followed the same pattern as styrene did as far as the Smith-Ewart theory is concerned. During the emulsion polymerization of vinyl acetate, unlike the case of the styrene polymerization, emulsion particles form up to a conversion of 80%. The reaction also appears to be dependent on the rate of agitation; the more vigorous the stirring, the slower the rate. It is also reported that the effect of the initiator concentration (i.e., the concentration of a persulfate) is complicated by the formation of free sulfuric acid during the reaction. This leads to the hydrolysis of some of the monomer to acetaldehyde which, aside from its chain-transfer activity, also retards the rate [132]. These observations again point up the importance of pH control during the polymerization of vinyl acetatewa matter already mentioned in connection with suspension polymerizations. As a matter of fact, the rate of emulsion polymerization of vinyl acetate is said to be at a maximum at a pH of 7 [ 133]. This is higher than the range of pH 4-5 which is the one most desirable from the standpoint of minimal hydrolysis of vinyl esters [4]. An additional factor which may not have been considered adequately in the theoretical treatment of the emulsion polymerization of vinyl acetate arises from the work of Dunn and Taylor [134]. These researchers noted that in their

250

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

dilatometric study of the emulsion polymerizations, the contraction of the monomer in an aqueous system was only 15.7 ___0.4%, whereas the bulk polymerization contraction was reported to be 26-28% [135]. The difference was attributed to the solvation of the monomer in the aqueous medium. If this is indeed so, it is not inconceivable that under the conditions of both suspension and emulsion processes, not the monomer vinyl acetate, but new monomers, of variable composition and conceivably of distinctly different chemical properties, are involved; vinyl acetate hydrates. Among the observable facts it was found that there is no significant effect of the concentration of emulsifier on this system. Therefore, the implication is that the polymerization initially takes place exclusively in the aqueous phase [ 136]. The resulting polymer particle "precipitates" as it forms [ 134]. In this case we may assume, that only a microscopic phase-separation takes place. The polymer particles which form adsorb emulsifier from the aqueous environment and remain dispersed. Then the particles may absorb more monomer somewhat in the manner called for by the Smith-Ewart theory. Of course, other dissolved vinyl acetate monomer molecules may continue to be polymerized in aqueous solution, thus accounting for the increase in the number of particles as the polymerization proceeds to high conversion. The classical Smith-Ewart treatment states that the number of particles is determined by the surfactant to monomer ratio and, in effect remains constant throughout the process. When neutral salts are added to an emulsion-polymerization system for vinyl acetate, the monomer, in effect, is salted out. The process then takes place at a much higher rate in the monomer-polymer particles than before. This is generally expected for ordinary emulsion polymerizations [ 136]. When reviewing the published literature on the emulsion polymerization of vinyl acetate, one is struck with seemingly contradictory data presented by many reputable research teams. Some of these results published may not be strictly comparable because of variations in the polymerization recipes used. For example, the effect of the emulsifiers on the rate of polymerization may have a profound effect on the course of the reaction. In a persulfate-initiated system using no other surfactant, it has been postulated that the free radicals formed from the decomposition of the initiator combine with the monomer in solution. As polymer forms, aggregates develop which absorb more monomer and the number of particles increases up to a constant value (at about 5% conversion). Then, while the number of particles remains constant at 1.7 • 1012 per ml, the reaction rate increases. Ultimately, as a last stage of the reaction, the rate begins to drop off. The latex formed in this process is said to consist of particles of great uniformity with a diameter of 0.26/~m [137]. In the case of polymerizations in the presence of seed latices, there is evidence that polymerization of additional monomer occurs exclusively in polymer particles which have been swollen by the available monomer [138].

251

5. Emulsion Polymerization

This observation seems to be in line with the Smith-Ewart concepts. The adsorption of surfactants on the surfaces of latex particles influences the capture by the particles of low-molecular-weight polymers formed in the aqueous solution. This in turn affects the reaction kinetics and the formation of new particles. The number of free radicals per particle, which is usually considered to be constant during the major phases of an emulsion polymerization, seems to vary considerably during the polymerization of vinyl acetate [139]. The effect of the ionic strength in the aqueous system on the emulsion polymerization has been investigated in some detail [140, 141]. According to this work, the rate of polymerization of vinyl acetate at low ionic strength is directly proportional to the first power of the initiator concentration and is independent of the surfactant concentration. In seeded polymerization procedures with media of low ionic concentration, the rate of polymerization is given by Rp oc [I]~176

(8)

0"33

where Rp is the rate of emulsion polymerization of a seeded system; [I], the concentration of initiator (potassium persulfate); [N], the concentration of polymer particles; [ V], the monomer volume. In all cases, the rate is reported to be almost independent of the monomer concentration in the particles up to 85-90% conversion [ 140]. With increasing ionic strength, the solubility of the monomer increases. At constant temperature, this is attributed entirely to a decrease in interfacial tension. The temperature effect is on both the monomer-water interaction and on the interfacial tension [ 141 ]. Stannett and co-workers [ 190] postulate that in aqueous media, water soluble polymers of the structure indicated in Eq. (9) are formed. O II (n + 1) C H 2 = C H - - O - - C - - C H 3 / H2C

I C~ // O

CH2 \ CH

I 0

(9)

CH2--CH

J O--C--CH3 II O

n

where 0 < n < 10. In the proposed mechanism, the butyrolactonyl group is formed by chain transfer to the acetyl group of the monomer followed by cyclization [Eq. (10)].

252

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

O II CHz--CH--O--C--CH2"

CH2 \ ~ HzC CH" I I C~O II O /

(10)

The butyrolactonyl free-radical, then reinitiates polymerization in aqueous solution. In general initiation is postulated to take place in the aqueous phase followed by stabilization due to the adsorption of surfactants on the growing polymer chain. Under the conditions of preparation, when the growing polymer reaches a degree of polymerization between 50 and 200, it is captured by the seed particles. Growth continues in these particles. The main termination step is the reaction of a butyrolactonyl radical with a growing aqueous polymer radical. At low ionic strength, a secondary termination step consists of the capture of an aqueous radical by a particle which already contains a radical. At high ionic strength, this may be the major termination step. It was observed in this work that the rate of polymerization was increased somewhat when potassium sulfate was added to the system. However, the rate was greatly increased when a phosphate buffer was added. This buffer adjusts the pH of the system to 7. Evidently Stannett and co-workers [ 140] overlooked the pH effect noted already by Naidus [ 133] as operating here. Also to be noted is that although the rate increased with increasing ionic strength of the medium, the dependence of the rate on the initiator concentration decreased. At high salt concentrations, the particle diameter increased. The effect of a fourfold increase in the surfactant concentration had no significant affects on the rate of polymerization, nor had a doubling of the ratio of monomer to water [ 140]. The average number of free radicals per emulsion particle has been estimated to be between 0.01 and 0.5. This represents an unusually low concentration of active free radicals. One proposal to explain this phenomenon is that monomeric radicals are rapidly lost by chain-transfer reactions in the polymer particles [142]. For the emulsion polymerization of vinyl acetate without seed polymer under purified nitrogen, using sodium lauryl sulfate as surfactant and potassium persulfate as initiator, at 50~ with agitation at 400 rpm in a resin kettle of 500 ml capacity, the same research group made the following observations [143]. 1. When the initial emulsifier concentration is low, the number of particles is constant regardless of initiator concentration. As the initial emulsifier concentration is increased, the percent conversion of the monomer at which the number of particles becomes constant also rises.

5.

Emulsion Polymerization

253

2. The rate of polymerization is essentially linear between 15 and 80% conversion and increases with emulsifier concentration, there is an abrupt change in the slope near the critical micelle concentration (CMC). 3. The initial monomer concentration has no effect on the number of particles. The reaction order with respect to the monomer concentration is about 0.36. 4. The number of polymer particles is independent of the initiator concentration. The order of the reaction with respect to the initiator concentration is approximately 0.5. It was also concluded that since there is a sharp break in the plot of the number of particles versus the emulsifier concentration and since this discontinuity is near the CMC of sodium lauryl sulfate, it seems reasonable to conclude that the polymer particles are generated from the emulsifier micelles [143]. The following additional observations were also made about the same time [144]. 5. The reaction order with respect to the number of particles is small, between 0.05 and 0.2. 6. The average number of free radicals in each particle is small, usually between 0.001 and 0.01. 7. The molecular weight of the polymer produced is independent of the number of particles, the particle size, and the initiator concentration. With increasing conversion, the molecular weight distribution broadens and the average molecular weight increases. The branching reactions contribute to the broadening of the molecular weight distibution with conversion. At high conversion, the emulsion exhibits a broader range in the molecular weight distribution than that obtained in bulk polymerizations [ 144]. That there is no generally acceptable model for the emulsion polymerization was emphasized by Min and Ray in their extensive discussion of mathematical modeling of emulsion polymerizations [145]. They list five deviations of the emulsion polymerization of vinyl acetate from the Smith-Ewart theory, which may be a bit different from the points made by Nomura and co-workers [ 143] and by Friis and Hamielec [144]. These points are as follows: 1. The rate of polymerization is not linearly related to the number of particles. It shows a 0.14-0.12 power dependence. 2. The rate of polymerization is independent of the emulsifier concentration while the number of particles increases with emulsifier concentration. 3. The rate of polymerization is directly proportional to the monomer concentration dissolved in the aqueous phase.

254

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

4. The number of particles increases to a maximum at about 10% conversion and then decreases continuously during the period of constant reaction rate. A large number of particles is formed even in the absence of micelles. 5. The conversion versus time curve is sigmoidal in shape [145]. To explain some of these phenomena, it is postulated that radicals may grow in the aqueous phase to a degree of polymerization between 50-200. These oligomers form new particles by precipitation from the aqueous phase or in micelles. Small particles may coalesce readily to form larger particles. There is an appreciable migration, or desorption, of free radicals out of the particles back into the aqueous phase. Termination reactions may take place in the aqueous phase as well as within the polymer particles. The number of end-groups increases on the surface of the polymer particle as the conversion proceeds. These end-groups, in effect, augment the quantity of available emulsifier in the system [145]. Despite the difficulties in developing a universal theory for the emulsion polymerization of vinyl acetates, large quantities of usable latices are being produced throughout the world every day. Considerable quantities of poly(vinyl acetate) emulsions are produced with anionic surfactants along with various colloidal materials which are thought to prevent the coagulation of the latex (hence the name "protective colloid"). The nature of the surfactants and of the protective colloid and their concentrations have profound effects on the properties and applications of a latex. For example, if poly(vinyl alcohol) is used as the sole protective colloid, emulsions of large particle size (2-10/lm) may be formed. Films produced from such latices tend to be hazy. They are usually sufficiently sensitive to water to be redispersible. The latices may be coagulated with electrolytes such as borax. On the other hand, they are highly stable to agitation and mechanical shear, the addition of solvents, and to freeze-thaw cycling. In the presence of surfactant along with poly(vinyl alcohol) finer particlesized latices are formed. The emulsions form clear, glossy films. On addition of borax, such latices may be coagulated. Combinations of synthetic colloids with surfactants may produce fine-particle emulsions stable to borax and other additives such as starches, dextrines, and salt. Many natural gums have been used as protective colloids along with surfactants to produce fine-particle, waterresistant, borax-stable emulsions [128]. The degree of hydrolysis of poly(vinyl alcohol) influences the emulsion polymerization of vinyl acetate. The lower the degree of hydrolysis, the better the emulsifying action of the protective colloid and the faster the rate of polymerization [146]. In connection with this statement we must point out that the terminology "a poly(vinyl alcohol) of low degree of hydrolysis" is widely

5.

Emulsion Polymerization

255

used but confusing. The term refers to a poly(vinyl acetate) of which only a few acetate moieties have been saponified to alcohol units. All poly(vinyl alcohols) may be considered to be block copolymers of vinyl acetate and the hypothetical vinyl alcohol. A poly(vinyl alcohol) of low degree of hydrolysis is a block copolymer consisting primarily of poly(vinyl acetate) blockswith only a few poly(vinyl alcohol) units. The distribution of the blocks of poly(vinyl acetate) and poly(vinyl alcohol) in a particular poly(vinyl alcohol) may effect emulsion properties. For example, a poly(vinyl alcohol) with a "blocky" intramolecular distribution of residual acetate groups produces latices of greater viscosity and stability toward electrolytes than a more randomly distributed structure [147]. The blocky nature of these products vary considerably with the manufacturer of the polymer. Therefore it is quite important that the description of a grade of poly(vinyl alcohol) used in a process specify not only the degree of hydrolysis of the base poly(vinyl acetate) and the viscosity of a 4% solution in water at 20~ (an indication of the molecular weight), but also the actual manufacturer of the product. By the way, it is interesting to note that the type of poly(vinyl alcohol) most conveniently dissolvable in cold water contains 10-30% residual poly(vinyl acetate). The compatibility of the poly(vinyl acetate) blocks with latex particles may explain the suitability of these grades of poly(vinyl alcohol) in vinyl acetate emulsion polymerizations [ 145]. In their review of the effects of poly(vinyl alcohol) on the polymerization of vinyl acetate. Dunn and co-workers [145] point out that because of the variations in the distribution of vinyl acetate blocks in poly(vinyl alcohol), similar grades from different manufacturers differ in effect on emulsion polymerizations. For example Elvanol (product of Du Pont Co.) has a retarding effect when compared to Gehsenol (product of Nippon Gosei Co.). The difference in structure may also affect the ease with which micelles may form in poly(vinyl alcohol) solutions. Among the effects that poly(vinyl alcohol) may have in emulsion polymerization systems are adsorption on the poly(vinyl acetate) latex, chain-transfer reactions, enhancement of the initiation rate since it increases the rate of decomposition of potassium persulfate, the oxidation of poly(vinyl alcohol) by the initiator, solubilization of monomer and polymer [ 148]. An interesting interaction of poly(vinyl alcohol) on the initiator system was reported by Hayashi and co-workers [149]. Using poly(vinyl alcohol) NO-05 from Nippon Synthetic Chemical Industry Co., Ltd., freed of low-molecularweight polymer and of sodium acetate by dialysis, they found that stable latices could be formed using a hydrogen peroxide-ascorbic acid redox initiator. When this initiator was used in the absence of the protective colloid, the latex coagulated. On the other hand, even without any protective colloid, a very stable poly(vinyl acetate) latex was formed when the initiator consisted of potassium

256

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

persulfate and ascorbic acid. It is also interesting to note that the rate of polymerization was virtually constant over a six-fold increase in the concentration of poly(vinyl alcohol). In the presence of a poly(vinyl alcohol) emulsifier, the emulsion polymerization of vinyl acetate initiated by potassium persulfate is said to be seriously inhibited by dissolved air. The rate of polymerization is enhanced by the addition of triethanolamine. At a concentration of 5 x 10 -3 moles/liter of potassium persulfate up to 0.03 moles/liter of triethanolamine enhanced the polymerization rate. Beyond this concentration of the amine, the rate decreases but the induction period in air is eliminated [150]. Nonionic surfactants such as polyoxyethylated fatty alcohols (such as Emulphor ON-870 from GAF), alkyl phenyl polyethylene glycol ethers (such as the Tergitols from Union Carbide) and polyoxyethylated octylphenol may be used as protective colloids along with anionic surfactants or, in some cases, as emulsifiers in their own fight. The block copolymers of polyoxyethylene and polyoxypropylene (Pluronics) solubilized vinyl acetate. Polymerization takes place at the interface of the surfactant-monomer droplet and the aqueous phase [151]. In a study of the use of Pluronic F68 in the emulsion polymerization of vinyl acetate, it was found that the particle surface area per unit weight of emulsion was directly proportional to the ratio of the surfactant to the monomer. The viscosity of the latex was also directly proportional to the ratio of the surfactant to the monomer. The number of particles per unit volume, at a constant ratio of the weight of the polymer to the emulsion weight, was directly proportional to the cube of the surfactant concentration [152]. Most commonly, in the emulsion polymerization of vinyl acetate, anionic surfactants are used either alone or in combination with a protective colloid. Typical examples of surfactants which have found application are Aerosol OT (sodium dioctylsulfosuccinate), alkyl aryl sulfonate salts (e.g., Santomerse-3), sodium lauryl sulfate, etc. A study of the kinetics of the vinyl acetate polymerization in the presence of sodium lauryl sulfate indicated that the rate of polymerization was proportional to the square root of the initiator concentration and the 0.25th power of the number of particles. The number of particles were proportional to the 0.5th_ 0.05 power of the surfactant concentration but independent of the level of potassium persulfate. The intrinsic viscosity of the final polymer was said to be independent of the initiator concentration and of the number of polymer particles. These observations were said to suggest that the mechanism of the vinyl acetate polymerization in emulsion resembles that of vinyl chloride [153]. Cationic emulsifiers have been used to prepare positively charged poly(vinyl acetate) emulsions. The method of preparation is said to be similar to that used in conventional anionic latex preparations except that a cationic surfactant is

5. Emulsion Polymerization

257

used. Unfortunately details were not published since they were subject to patent applications. It is unfortunate that reputable journals permit the publication of such incomplete data [154]. The rate of polymer formation in the presence of cationic surfactants (cetyltrimethylammonium or dedecyltrimethylammonium bromide) is slower than the rate in the absence of any surfactant, at least until the 20% conversion level. Thereafter it is comparable to the rate found for systems with no surfactants or with non-ionic surfactants. With anionic surfactants, the rate of conversion is fastest. The square root of the percent conversion is linear with time up to approximately 50% conversion [155]. To be noted here is that these observations contradict the observations of Patsiga [ 136], who stated that there was no dependence of the system on the emulsifier concentration. Cationic surfactants, in contrast to anionic surfactants, usually reduce both the number of particles involved in the polymerization and the rate of polymerization. The nature of the stabilizing emulsifier has a marked effect on the polymerization kinetics. For example, addition of a non-ionic stabilizer [e.g., poly(vinyl alcohol), a block copolymer of carbowax 6000 and vinyl acetate, or ethylene oxide-alkyl phenol condensates] to a seed polymer stabilized by an anionic surfactant decreased the rate of polymerization to 25% of the original rate. The effect was as if the nonionic stabilizer (or protective colloid) acted as a barrier around the seed particles to alter the over-all kinetics. It may be that the viscosity of the medium in the neighborhood of the nonionic surfactant coating of the polymer particle is sufficiently different from that of an anionic layer to interfere with the diffusion of monomer or free radicals. There may also be a change in the chain-transfer characteristics of the system [ 156]. In the preparation of emulsion polymers, particularly when copolymer systems are involved, several methods of adding the monomer to the reacting system are available. Obviously, one may add all of the monomer at once to the aqueous phase. Alternatively, the monomers may be added gradually stepwide. Finally, the monomers may be added gradually and continuously. The first two methods lead to more or less heterogeneous copolymers while the continuous addition method affords homogeneous copolymers. The best adhesive properties are achieved from homogeneous copolymer systems; other properties may vary considerably with the degree of heterogeneity of the polymer [157]. There are, of course, procedures which also call for the gradual addition of initiator solutions, additional surfactant, plasticizer, etc. The manipulation of various emulsion polymerization techniques assists in developing poly(vinyl acetate) latices with specific characteristics needed for certain end-uses. Some of these are summarized in Table XVIII. In preparing emulsion polymers, some procedures have been developed which are carried out under an atmosphere of nitrogen while others are carried out in

258

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

TABLE XVIII Effect of Polymerization Technique Modification on Latex Characteristics Technique modification Increasing the concentration of surfactant and protective colloid Decreasing the concentration of surfactant and protective colloid Delayed addition of surfactant and protective colloid Delayed addition of monomer Increasing the initial monomer charge 15-20% Reducing the rate of delayed monomer addition Use of water-soluble initiators Use of monomer-soluble initiators Increasing initiator concentration Decreasing initiator concentration Delayed addition of initiator Use of a redox initiator Increasing the temperature of polymerization Decreasing the temperature of polymerization Increasing the potential solids contraction of the latex Decreasing or eliminating materials with chain-transfer activity

Effect Latex viscosity increases: particle size decreases Particle size increases Increases particle size Reduces particle size Increases MW Reduces particle size Reduces particle size Increases particle size Reduces particle size: effect on MW is minimal Increases particle size Increases particle size May increase MW Increases latex viscosity: reduces particle size Increases particle size: increases MW Increases latex viscosity Increases MW

air. Atmospheric oxygen does cause some induction of the polymerization. Low levels of triethanolamine are said to reduce this induction period [150]. Presumably many redox systems are not seriously affected by air. In reducing the air in the system, many processes call for bubbling purified nitrogen through the aqueous solutions. Obviously, in the case when anionic surfactants are present, a serious foaming problem will result. We therefore suggest that freshly boiled deionized water is flushed with the nitrogen before adding emulsifiers. Then, while the surfactant is being added, nitrogen is bled in over the liquid surface. During the polymerization itself, the nitrogen is also kept just over the surface of the liquid to minimize foaming.

CAUTION" The simplest emulsion polymerizations have been carried out in closed bottles or sealed ampoules [130, 138, 139]. We generally do not consider these procedures safe. They are also of questionable value if the nature of the latex particles is to be studied. Two examples are given here only to illustrate the techniques used.

5.

Emulsion Polymerization

5-1.

259

Emulsion Bottle Polymerization of Vinyl Acetate at 70~

[130]

In a 4-oz bottle equipped with a cap lined with Mylar are placed 25 gm of distilled water. 0.0050 gm of potassium persulfate, 0.51 gm of poly(vinyl alcohol) [Elvanol 52-22, a Du Pont product, 86-89% hydrolyzed poly(vinyl acetate) of medium molecular weight with a viscosity of a 4% aqueous solution at 20~ of 20-25 cP], and 5.00 gm of vinyl acetate. Prior to capping the bottle, oxygen-free nitrogen is bubbled through the contents. The bottle is closed, placed in a steel protective sleeve, and placed on a suitable rack which permits end-over-end rotation of several such bottles in a constant temperature bath at 70 ~ + 0.lOG. Bottles are withdrawn periodically to study the progress of the reaction. After an induction period of 30 min, the polymerization proceeds rapidly. After another 30 min, conversion is approximately 80%. With decreasing levels of poly(vinyl alcohol) the rate decreases. Upon removal of each bottle and cooling of it, a small quantity of styrene is added to the contents to inhibit the polymerization. The conversion is evaluated by determining the total solids of the latex. Procedure 5-2 illustrates the formation of a latex from an aqueous solution of vinyl acetate.

5-2.

Emulsion Bottle Polymerization of Vinyl Acetate from Aqueous Solution at 40~ [138, 139]

With suitable safety precautions in a 100-ml volumetric flask is placed 47 ml of distilled water, 3.75 mmoles of potassium persulfate, 0.5 mmoles of sodium hexadecyl suflate, and 3 gm of vinyl acetate. The volumetric flask is stoppered and placed in a constant temperature bath at 40~ After seven days conversion is 100%. The resulting latex may be freed of initiator and surfactant by dialysis. If the undialyzed latex is to be coagulated, the addition of 0.5 mg of a cationic surfactant such as hexadecyltrimethylammonium bromide is suggested. For kinetic studies, emulsion polymerizations have been carried out in a variety of dilatometers [134, 139, 148, 149]. Perhaps, most interesting is the work of Litt et al. [139], who used a large stirred dilatometer. Typically, they used a recipe consisting of 180.0 gm of distilled water, 60.0 gm of distilled vinyl acetate, 1.2 gm of sodium lauryl sulfate, and 0.04 gm of potassium persulfate. The polymerization was carried out under oxygen-free nitrogen with suitable nitrogen purging prior to the filling of the dilatometer. Agitation was at 150-200 rpm with a reaction temperature of 60 +__0.03~ In general, approximately 85% conversion had taken place after approximately 1 hr with an

260

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

induction period of 5-10 min, depending on the concentration of potassium persulfate and the extent of the nitrogen purge prior to the ran. The total volume contraction anticipated in these experiments ranged from 8 to 10 ml. In discussing experimental techniques, Dunn and Taylor [134] mention that while dilatometric studies with degassed materials eliminated the induction period, the start of the reaction was difficult to observe since the initiation of the polymerization takes place during the thermal expansion period as the equipment was thermostated. Most emulsion polymerizations are, of course, carried out in conventional stirred reactors. There are procedures in which all of the monomer is charged at once to the reactor; procedures wherein the monomer is gradually added, possibly with gradual addition of surfactant solutions, initiator solutions, and other modifying agents; procedures using redox initiation or thermal initiation; and procedures using preemulsified monomers. Procedure 5-3 uses poly(vinyl alcohol) only as an emulsifier. Its level is rather high (7.5% on the monomer). The percent solids of the resulting latex is moderately high. To be noted is the use of formic acid both to adjust the pH of the system and to act as a reducing agent.

5-3.

Emulsion Polymerization of Vinyl Acetate with Poly(vinyl alcohol) as Emulsifier [158]

In a l-liter, four-necked resin kettle fitted with a mechanical stirrer, a reflux condenser, a pressure-equalizing addition funnel, and a thermometer is heated (using a water bath which has been arranged for convenient and safe raising and lowering) 285 ml of deionized water with agitation at 60-70~ Into this water is sifted 15 gm of poly(vinyl alcohol) [Lemol 42-88, a Borden product, 88% hydrolyzed poly(vinyl acetate), high-molecular-weight product with a viscosity of a 4% aqueous solution at 20~ of 42 cP]. Warming and stirring is continued until the emulsifying agent is completely dissolved. This may require 1 hr or more. Then 300 gm of vinyl acetate is added from the addition funnel. Through the condenser, are added, in turn, 0.2 gm of 30% hydrogen peroxide [CAUTION: strong oxidizing agent; face mask, gloves, and protective clothing must be worn when handling 30% hydrogen peroxide; severe skin burns may be caused upon contact] and 0.6 gm of formic acid [CAUTION: toxic reagent]. The mixture is stirred and heated to 70~ and maintained at that temperature for 5 hr by raising or lowering the water bath as required. Then the latex is cooled to room temperature. This latex contains approximately 43% nonvolatiles. The study of Nomura et al. [143] is perhaps one of the most detailed investigations on the kinetics and mechanism of the emulsion polymerization of vinyl acetate published. The work presents a detailed evaluation of the interactions of monomer, surfactant, and initiator concentration in the course of the

5. Emulsion Polymerization

261

reaction. Procedure 5-4 illustrates the use of potassium persulfate and sodium lauryl sulfate in one emulsion procedure developed for these data.

5-4.

Emulsion Polymerization of Vinyl AcetatePotassium Persulfate-Sodium Lauryl Sulfate System [143]

To a 500-ml, resin kettle with a bottom stopcock, equipped with a pressureequalizing addition funnel, reflux condenser (topped with a pressure regulator permitting exhausting of nitrogen but preventing air from entering the system), a thermometer, a 4-bladed paddle, 3.75 cm in diameter with blades set at 90 ~ to each other in the reaction chamber with inside diameter of 7.5 cm, 4 baffle plates approximately 0.75-cm wide, and a nitrogen inlet, were added 250ml of distilled water, 50 gm of vinyl acetate, and 0.25 gm of sodium lauryl sulfate. The mixture was freed of oxygen by bubbling nitrogen through it for at least 0.5 hr. Then 0.3125 gm of potassium persulfate was added (possibly in aqueous solution which had been deoxygenated separately). The agitator was operated at 400 rpm and the reaction is maintained at 50 ___0.5~ Within 40 min, nearly 100% conversion was observed. Many variations on the "delayed addition" or gradual addition procedures are possible. Procedure 5-5 is a relatively simple example of the technique which produces a latex of high solids content with a low level of anionic surfactant and a modest level of protective colloid.

5-5.

High Percent Solids Continuous Addition Emulsion Polymerization of Vinyl Acetate: Potassium Persulfate Initiated [ 159]

In equipment similar to that used in Procedure 5-3 with provisions for maintaining a nitrogen atmosphere in the system, 210.75 gm of deionized water, 0.75 gm of Tergitol-7 (sodium heptadecyl sulfate, an anionic surfactant from Union Carbide), 12.5 gm of Cellosize WP-09 (a protective colloid from Union Carbide) and 1 gm of potassium persulfate is blended under nitrogen with agitation. Then 25 gm of vinyl acetate is added and the mixture is heated to 70~ When the polymerization has started, with stirring, over a 2- to 3-hr period, 250 gm of vinyl acetate is added. The temperature is maintained at 70~176 After the addition has been completed, heating at 70~176 is continued for an additional 30 min. The residual monomer content of this latex is less than 1%. More complex gradual addition procedures have been reported. For example, in Vona et al. [95], a procedure for the gradual addition of monomer and

262

7. Polymerizationof VinylAcetate and OtherVinylEsters

initiator is given. In Gulberkian [152], three ingredients are added simultaneously at a steady rate: a monomer-surfactant solution, the persulfate initiator solution, and a sodium hydroxide solution. Procedure 5-6 is an example of a redox-initiated system involving the use of three separate streams to add monomer, oxidizer, and reducer.

5-6.

Continuous Addition Emulsion Polymerization o f Vinyl Acetate: Hydrogen Peroxide-Tartaric Acid Initiation [160]

In a reactor equipped much like that used in Procedure 5-3 except that provision is made for additions from two burets, 30 gm of poly(vinyl alcohol) (such as Lemol 42-88) is dissolved in 260 ml of water at 70~ Once the emulsifier has been dissolved completely, 26 gm of vinyl acetate, 4 ml of 2% aqueous hydrogen peroxide, and 4 ml of a 3% aqueous tartaric acid solution are added. The mixture is heated, with agitation at 70~ for 1 hr. Then over a 3-hr period, there are added continuously from separate streams 240 gm of vinyl acetate, 4 ml of 2% aqueous hydrogen peroxide, and 8 ml of a 3% aqueous tartaric acid solution. After the addition has been completed, the reaction mixture is heated at 80~ for 1 hr. Bouchard [161] developed a poly(vinyl acetate) adhesive formulation using hydrogen peroxide-zinc formaldehyde sulfoxylate as the initiator system, poly(vinyl alcohol) and sodium decylbenzene sulfonate as the emulsification system, and lauryl peroxide dissolved in the seed monomer to reduce the viscosity of the final latex (see Table XVIII). To this, from separate streams, a hydrogen peroxide solution, a sodium bicarbonate solution, and vinyl acetat e are added. The final latex had a pH of 4.5 and a viscosity of 7 cP at 25~ Many different redox systems have been used in the emulsion polymerization of vinyl acetate. Further investigations on the use of persulfate-bisulfite, hydrogen peroxide-ascorbic acid, tert-butyl hydroperoxide with various water-soluble as well as monomer-soluble reducing agents, etc., should be carried out. In an effort to develop "high solids" latices, one early approach has been to preemulsify the monomer in a distinctly separate step from the polymerization step. While the example in Procedure 5-7 goes back to a patent of 1951 [162], a more recent example of a somewhat complex copolymer system will be found in Vegter [ 163].

5-7.

Emulsion Polymerization o f Vinyl Acetate with Preemulsification [162]

An aqueous phase is prepared by dissolving 0.5 gm of sodium dioctylsulfosuccinate (Aerosol OT), 0.6 gm of sodium cetyl sulfate, and 1.4 gm of ethyl

5.

Emulsion Polymerization

263

alcohol in 200 ml of distilled water. After dissolution is complete, 1.5 gm of ammonium persulfate and 0.01 gm of sodium bicarbonate are added. This aqueous phase, along with 200 ml of vinyl acetate, is emulsified in a hand operated emulsifying machine. The monomer emulsion is placed in a l-liter flask fitted with a mechanical stirrer and a reflux condenser. The reaction mixture is heated with agitation at 60~ for 6 hr. After this time, the reaction is judged to be complete. A freeflowing latex with pH 4.8 and 47.8% nonvolatiles is isolated. In a study of the polymerization of vinyl compounds initiated by sulfite radicals, Sully [164] showed that in styrene polymerizations in emulsion with radicals generated by the oxidation of sodium sulfite, the polymer molecules formed have sulfonic acid end-groups. It is, therefore, not entirely unanticipated that monomers polymerized in the presence of persulfate have end-groups characteristic of anionic surfactants. Indeed, mention has been made of stable latices of poly(vinyl acetate) prepared without external surfactants [137]. More recently, it was pointed out that with persulfate initiated polymerizations, both hydroxyl and sulfate groups become part of the polymer systems at the particle surface. Whereas a surfactant like sodium lauryl sulfate can be removed from latex particles by dialysis and slight hydrolysis of poly(vinyl acetate) favors the desorption of anionic surfactants, sulfate groups attached to the polymer, obviously are not removable. Therefore, stable latices are formed [ 165]. Before this explanation was offered, a patent had been issued for the preparation of stable latices of high solids content which were free of emulsifier. To achieve additional stability, a protective electrolyte was added. These electrolytes are salts of organic or inorganic acids containing two or more oxygens. The nature of the action of these salts is obscure, but it should be pointed out that with the exception of bisulfates (which were not cited in the examples), all of them have a buffeting action. The patent in question goes into considerable detail about the ratio of electrolyte to initiator, reaction temperatures, and other factors. A detailed discussion and critique of this is beyond the scope of this chapter. Table XIX gives typical reaction conditions. Procedure 5-8 is an adaptation of an example found in the patent [ 166].

5-8.

Emulsion Polymerization of Vinyl Acetate without Surfactant [166]

In a 3-liter reaction vessel equipped with pressure-equalizing addition funnel, reflux condenser, thermometer, and mechanical stirrer, 3.5 gm of potassium persulfate and 5.5 gm of potassium citrate monohydrate are dissolved in 80 gm of water maintained at 82~ To this solution, with agitation, 100 gm of vinyl acetate is added continuously over a 3-hr 20-min period. During the addition period the reaction temperature is maintained between 82 and 85~ After the

TABLE xIX

Reactions Conditions for the Polymerization of Vinyl Ester Homo- and Copolymers without Surfactant [ 166] Reaction temperatures

Initiator (gm)

Protective electrolyte (gm)

Water gm (Solution temperature (~

Monomer(s) (gm)

K citrate monohydrate (0.55) Na acetate trihydrate (0.178) Na bicarbonate (0.89) Disodium phosphate tetrahydrate (0.48) K citrate monohydrate (0.42) Na succinate hexahydrate (0.5)

80 (82) 71 (-)

Vinyl acetate (100) Vinyl acetate (100)

80 (82) 80 (-) 86 (-)

(0.5)

K citrate monohydrate (0.35)

80 (-)

K2S208 (0.4)

K citrate monohydrate (0.42)

80 (-)

Vinyl propionate (100) Vinyl butyrate (100) Vinyl acetate/(35) Vinyl pelargonate (65) Vinyl acetate/(35) Vinyl 2-ethylhexanoate (65) Vinyl acetate/(33) Vinyl butyrate (67)

K2S208 (0.35) K2S208 (0.444) K2S208 (0.625) K2S208 (0.4) Na2S208 (0.44) K25208

Particle size 0.3 ___0.1. b Reported in Reference 166.

a

Addition period (hr)

Addition stage (~

Finished stage (~

3.3

82-85

5.75

79.5-8.5

1 hr 55 min

82-85

Yield (%)

Nonvolatiles

90 (20 min) 89 (0.25 hr)

91.6

53a

94.1

59.6

95

58.4

88.8

82

89.6

53.4

(%f

.',,I

5.75

74-85

95 (20 min) 77 (1 hr) (1.3 hr)

6.5

76-85

(1.5 hr)

95

54.3

4.3

69-78

(10 min)

90.6

52.0

15

70-75

5.

265

Emulsion Polymerization

addition is complete, the temperature is allowed to rise and is maintained at 90~ for 20 min. Upon cooling, the yield of latex is 91.6%, the solids content 53%, and the particle size 0.3 ___0.1/tm with remarkable uniformity of size. By conventional procedures, the expected particle size distribution would have been between 0.5 and 2/tm. In Section 4 on the preparation of poly(vinyl acetate) suspension polymers, mention was made of the preparation of polymer beads by adding a methanol solution of that polymer to an aqueous solution of poly(vinyl alcohol). By varying the concentration of emulsifying agent and the rate at which solvents are distilled off, it is possible to develop conditions for the generation of emulsions with polymer particles of diameter between 1 and 3/zm [ 121 ]. The emulsion polymerization of vinyl esters of the high carboxylic acids is somewhat difficult since stable emulsification before and during polymerization is difficult to achieve with the common soaps of the alkylaryl sulfonate salts. Best results are said to be achieved when a mixture of a nonionic surfactant such as esters of anhydrosorbitol or anhydromannitol (e.g., Span 20) and a branchedchain alcohol sulfate [e.g., Tergitol Paste 4 (50%)] are used. These emulsifers do not produce emulsion polymers with vinyl acetate but do so with vinyl palmitate. The usual procedure for polymerization consists of weighing monomer and emulsifiers into a flask through which oxygen-free nitrogen is passed. With swirling and warming, a uniform mixture is produced which is transferred to a mechanical blender containing oxygen-free distilled water. In the blender, during agitation, nitrogen is continuously passed through. The resultant emulsion is then polymerized in conventional equipment after 7 hr at 55~176 A typical recipe consists of Reagent

Amount

Vinyl palmitate Span 20 Tergitol Paste 4 (50%) Water, distilled Potassium persulfate

0.20 moles 2.8 gm 5.7 gm 113 gm 0.27 gm (0.001 moles)

,,

Within 7 hr at 55~176 a conversion greater than 80% was achieved. To isolate the polymer, the latex may be coagulated by pouting it into a warm aqueous sodium chloride solution. The polymer may be purified by dissolving it in benzene and then, at - 5 ~ pouting the solution while swirling by hand into acetone. The poly(vinyl palmitate) could be isolated as discrete particles [167]. The monomer vinyl pivalate polymerizes readily. Unlike most common monomers, this monomer yields polymers of high molecular weight by the suspension procedures and modest molecular weights in an emulsion polymerization. This has been attributed to its lower capability of diffusing through the

266

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

aqueous system as compared to vinyl acetate. This monomer is quite resistant to saponification and exhibits little chain-transfer activity [116]. Procedure 5-9 illustrates a redox procedure using a persulfate-bisulfite redox system.

5-9.

Emulsion Polymerization of Vinyl Pivalate [116]

In a 2-liter, reaction kettle provided with a reflux condenser, mechanical stirrer, thermometer, pressure-equalizing addition funnel, and provision for passing oxygen-free nitrogen through the system, to a solution of 0.52 gm of ammonium persulfate, 50 ml of a 15% solution of sodium hydroxyoctadecylsulfonate (Amphoseife-18) in 450 ml of distilled water is added 1.05 gm of potassium bisulfite followed by 250 gm of vinyl pivalate. The mixture is agitated under nitrogen at 40~ for 24 hr. During this time, the pH of the latex is adjusted to 3.5 by additions of formic acid. If desired, the polymer may be isolated by coagulation with a 10% aqueous aluminum sulfate solution. Procedure 5-10 is an adaption of a ter-polymerization that starts with the formation of a seed latex followed by the gradual addition of both a monomer composition and an initiator solution at separate rates. The resulting latex has a high percentage of non-volatiles. It is said to be suitable for formulating good emulsion paints. In connection with this preparation, care must be taken that the initiating ammonium persulfate is indeed active.

5-10.

Emulsion Ter-polymerization of Vinyl Acetate, Butyl Acrylate, and Vinyl Neodecanoate (Seeded Process with Gradual Monomer and Initiator Additions) [ 168]

To a l-liter resin kettle equipped with a reflux condenser, an explosion-proof stirrer, a thermometer and temperature controller, and a nitrogen inlet is charged 204.00 grn of deionized water. Then 6.00 gm of Cellosize hydroxyethyl cellulose WP-300, 3.00 gm of Tergitol NP-40, 3.90 gm of Tergitol NP-15 (two nonionic surfactants), 3.3 gm of Siponate DS-4 (an anionic sufactant), and 0.6 gm of ammonium bicarbonate are added and the stirred mixture is blanketed with nitrogen and warmed to 55~ This temperature is maintained for 20 min. A mixture of 18.00 gm of vinyl acetate, 4.50 gm of butyl acrylate, and 7.5 gm of vinyl neodecanoate is added, followed by 0.24 gm of ammonium persulfate. The reaction mixture is heated to 75~ and maintained at that temperature for 15 min to form the seed latex. The reaction temperature is then raised to 78~ and the gradual addition of monomers and initiator solution is begun. The monomer solution, consisting of 162 gm of vinyl acetate, 41.4 gm of butyl acrylate, and 66.6 grn of vinyl neodecanoate, is added over a 2-hr period. The initiator solution of 0.60 gm of

5.

Emulsion Polymerization

267

ammonium persulfate dissolved in 60.00 gm of deionized water is added over a period of 2.5 hr. All the while, the reaction temperature is maintained at 78 ~. After the last of the initiator solution has been added, heating and good stirring is continued for another hour. The latex is cooled and filtered though a 200 mesh stainless steel screen. The % nonvolatiles of the latex is 53.2%. Coagulum is 0.01%. Vinyl acetate is fairly water soluble and somewhat deficient in hydrolytic stability. The incorporation of a vinyl ester of the higher branched carboxylic acids into a copolymer system improves the resistance of the product to hydrolysis. Thus the latex formed in Preparation 5-10 has been used in formulating exterior paints. Copolymers of vinyl acetate with increasing concentrations of vinyl 2-ethylhexanoate (VEH) were prepared by a procedure similar to that of Preparation 5-10, except that the initiator system consisted of tert-butyl hydroperoxide and sodium formaldehyde sulfoxylate, and the buffer was sodium acetate. As the level of VEH increased, the hydrolytic stability of the copolymer increased significantly [ 169]. The emulsion copolymerization of vinyl acetate and butyl acrylate has received considerable attention. The butyl acrylate confers improved film forming characteristics to the polymer. The disparities in their water solubilities and of their individual polymerization rates may help to explain the variations in reactivity ratios that have been reported [ 170, 171]. The variation in reactivity ratios may also by related to the following observations: The reaction method has an effect on the morphology of the polymer particles. In a batch emulsion process, a butyl acrylate--rich core is formed which is surrounded by a vinyl acetate-rich shell, in a process in which the monomers are fed into the reactor in a semicontinuous manner, particles form with a more uniform distribution of the monomers [172]. The kinetics for a batch process indicates that the initially formed polymer is indeed high in butyl acrylate. As this monomer is used up, eventually a copolymer high in vinyl acetate develops. It is this latter polymer which forms the final shell around the particles. When a copolymer seed is preformed and then a preemulsified mixture of vinyl acetate and butyl acrylate in water (using sodium dodecylbenzenesulfonate, Siponate DS-10, as surfactant) is added slowly, the composition of the product approaches that calculated from the reactivity ratios. The particle size and the size distribution is related to the ionic strength of the medium. With low levels of initiator and buffer, the particle size tends to be small and the size distribution narrow. As ionic strength increases, the particle size increases. At low monomer addition rates, the particle size increases. Typically, particle sizes range from 0.206 to 1.05/tm with coefficients of variation ranging from 10.5 (for the smaller particles) to 5.9 (for the larger ones) [173, 174]. To a latex of poly(vinyl acetate) that had been freed of surfactant by prolonged dialysis, more monomer and more potassium persulfate, but no

268

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

further surfactant, were added. The rate of polymerization was found to be [I]~176176176 where [I] is the initiator concentration. With the addition of fresh monomer, a significant increase in the diameter of the particles took place provided the weight ratio of monomer to initial particles was kept below approximately 10 to 1. When the monomer level was raised above this, new particles formed, albeit without affecting the polymerization rate [175]. 6.

NONAQUEOUS DISPERSION

POLYMERIZATION

The preparation of polymers as dispersions in nonaqueous systems has not been discussed very extensively. Even so, an interesting book has been published [ 176]. Stable dispersions in organic liquids are usually formed by using graft copolymers to stabilize the system. According to one patent, the copolymer "emulsifier" is selected so that its polymer chains contain groups of differing polarities; some of which may be solvated by the organic solvent and other groups which may become associated with the particles of the dispersed polymer [177]. These stable dispersions have found application in baked-on finishes. In Procedure 6-1, a remarkably high solids dispersion of poly(vinyl acetate) in cyclohexane is prepared. Since this procedure has been patented, it is given here only to illustrate the techniques used in preparing nonaqueous polymer dispersions.

6-1. Preparation of Poly(vinyl acetate) in Nonaqueous Dispersion [178] In a resin kettle equipped with a mechanical stirrer, reflux condenser, thermometer, and provisions for passing oxygen-free nitrogen through the system, with agitation, under a nitrogen atmosphere, 240 gm of vinyl acetate, 160 gm of cyclohexane, and 1.4007 gm of an ethylene-vinyl acetate copolymer (DQDA 3267, a copolymer containing 28 wt% vinyl acetate and having a melt index of 23.8 dg/min) are heated to 70~ for approximately 1 hr to bring about complete solution. Then 0.1514 gm of dibenzoyl peroxide is rapidly added. After stirring and heating for about 1.5 hr a milky dispersion begins to form. The polymerization is continued for 22 hr. The product is a dispersion with solids content of 58% at 97% conversion of the monomer to polymer. The poly(vinyl acetate) exhibited an inherent viscosity (0.2% solution in cyclohexane at 30~ of 45. The particle size of the polymer is between 0.3 and 5/zm. This dispersion can be used to produce a dispersion of poly(vinyl alcohol) [albeit only about 75% hydrolyzed poly(vinyl acetate)] by hydrolyzing it with a solution of sodium methylate in methanol at 30~

7.

Radiation-Initiated

269

Polymerizations

Dispersions of poly(vinyl acetate) in n-alkanes have been prepared using a diblock copolymer of poly(styrene-b-[ethylene-co-propylene]) as the stabilizer for the colloidal PVAc. The dispersing agent contained 38.5% styrene and was used at a concentration of 1-5 wt%. The monomer concentration ranged from 10 to 30 wt% in the various experiments. A typical initiator was 2,2'-azobisisobutyronitrile. The particle diameters were in the range of 0.10 to 0.31/lm [179]. 7.

RADIATION-INITIATED

POLYMERIZATIONS

Many details of the complex steps in the formation of polymers of high molecular weight beginning with the initiation step have been studied by UV-radiation-initiated polymerization. By a technique which interposed a rotating sector between a source of UV radiation and a dilatometer beating a monomer, variations in the rotational speed of the sector and size of the opening, controlled bursts of radiation strike the monomer and induce polymerization. From the frequency of exposure and the effect on the polymerization many of the kinetic constants were evaluated. In this connection it should be noted that vinyl acetate exhibits virtually no absorption of UV radiation at 290-300 nm. On the other hand, acetaldehyde has an extinction coefficient of 14 at 290 nm and an extinction coefficient of 15 at 300 nm. Therefore acetaldehyde can act as a photo-sensitizer for the polymerization of vinyl acetate at wavelengths above 299.8 nm [23]. At 366 nm, 2,2'-azobisisobutyronitrile has been used as a sensitizer [29, 180]. Azobicyclohexane carbonitrile is a UV sensitizer suitable for use with a 124 watt mercury arc at 25~ which does not produce a dark reaction in rotating-sector experiments. Its absorption peak is at 350 nm with an extinction coefficient of 16 [181]. The UV-initiated polymerization of vinyl acetate, sensitized with various quantities of AIBN at - 19~ gives polymeric products which, upon saponification and reacetylation, produce polymers with substantially the same molecular weight as that initially observed. These observations contribute to the postulate that at low temperatures, polymerizations proceed essentially with the formation of branched chains [26]. A composition of vinyl acetate, ethylene dimethacrylate, benzil (a UV sensitizer), and finely ground vinyl acetate-ethylene dimethacrylate popcom copolymer on exposure to radiation at 365 nm gave rise to a proliferating polymerization which continued after the source of radiation had been tumed off. It has been postulated that in this case most of the growing radicals are formed by chain scission during polymerization [182]. Vinyl acetate, frozen to a glassy state or a crystallized form, has been subjected to solid-state polymerization with UV radiation. The rate of polymerization was found to vary with the physical state [183]. On the other hand at -195~ vinyl acetate did not polymerize when exposed to a dosage rate of

270

7, Polymerization of Vinyl Acetate and Other Vinyl Esters

7.8 • 105rad (),-radiation). It has been postulated that solid-state vinyl polymerizations proceed by an anionic mechanism [184]. At 20~ the rate of polymerization of vinyl acetate initiated by ),-radiation is substantially greater than that of many common monomers [ 1]. Emulsion polymerizations initiated by ),-radiation have been carried out [141,185]. For example, compositions of 10 ml of a 3.75 gm per 100 ml aqueous solution of sodium dioctylsulfosuccinate (Aerosol OT or Manoxol OT) and 1.25 ml of vinyl acetate with small additions of sodium dihydrogen phosphate, after exclusion of oxygen by at least four degassings, were sealed in glass ampoules. The samples were exposed, at 15~ to a 6~ source (100 curie): Conversion was nearly 75% after 30 rain. Polymers of MW as high as 106 were formed. The polymers contained trapped free radicals capable of initiating graft polymerization with methyl methacrylate after removal from the radiation source [ 185]. By ),-radiation a latex was also prepared from a composition of 151.4 gm of vinyl acetate and 10.9 gm of sodium lauryl sulfate in 300 gm of distilled water (irradiation was 26.5 hr at 6 • 104 rad/hr) [142].

go

POLYMERIZATIONS INITIATED BY IONIC, COORDINATION COMPLEXES, AND OTHER MECHANISMS

The copolymerization of styrene and vinyl acetate affords an example of the significant differences in the effects of the initiation system on the monomer composition. The copolymerization ratios for the three processes may be used as a guide to the effect under study. For M1 as styrene and M2 as vinyl acetate, in the cationic copolymerization, rl is 8.25 and 1"2 is 0.1, while for the free-radical polymerization, r~ is 55 and r2 is 0.01. The cationic copolymerization was carried out in air at 25~ in a nitrobenzene solution using stannic bromide as catalyst, while the anionic polymerization was studied in air with sodium dissolved in ammonia [ 186]. Although many monomers may be polymerized by quaternary ammonium salts, vinyl acetate does not produce any polymer on treatment with dimethylphenylbenzylammonium chloride [ 187]. The polymerization of vinyl esters in the presence of alkali metals, particularly lithium, was characterized by lengthy induction periods. It was not possible to verify whether a nonfree-radical mechanism was involved in the polymerization process [ 188]. Ziegler-Natta type polymerizations of vinyl esters with trialkyl aluminum and metal halides have been discussed [189-193]. The "living" radical polymerization of vinyl acetate and subsequent use of the "living" polymer to form block copolymers, makes use of an initiating system

9.

Miscellaneous

271

consisting of triisobutyl aluminum, 2,2'dipyridyl, and the 2,2,6,6-tetramethyl1-piperidinyloxy free radical ("TEMPO"). The molar ratio of the trialkyl aluminum to Tempo was 3 to 2; that of the trialky aluminum to dipyridyl was 1 to 1. At room temperature, 90% conversion of the monomer was achieved in 1 day. The molecular weight of the product, Mn, was 50,000, with polydispersity ranging from 1.25 to 1.5. As more monomer was added to the system, the molecular weight increased. When other monomers, such as methyl methacrylate or styrene, were added, block copolymers formed. This was considered a characteristic of "living" polymerization. The authors claim that this work represented the first cases of block-copolymer formation with poly(vinyl acetate) as one of the blocks [194]. The use of trialkylboron and related initiators is discussed in references [195-197]. The polymerization of vinyl esters with trialkylaluminum and organic peroxide was patented in 1974 [ 198]. Zinc chloride has been used in a variety of polymerization systems. References to its use and to charge transfer complex polymerizations are Nikolayev et al. [29], Imoto et al. [34], Semiuk and Thomas [199], and Seymour et al. [200].

9.

MISCELLANEOUS

Hydrolysis of PVAc, Hydrogels, Poly(vinyl alcohol) [PVA] 1. Poly(vinyl acetals) from polyvinyl alcohol and 2,6-dichlorobenzaldehyde [201]. 2. Poly(pyrrole)-poly(vinyl alcohol) composite films which are conducting and transparent [202]. 3. Preparation of concentrated PVA solutions [203]. 4. Stretched PVA-methyl acrylate graft copolymers for moisture-shrinkable films [204]. 5. Properties of PVA-hydroxypropylmethylcellulose-water systems as dispersants in suspension polymerizations [205]. 6. Hydrogel preparation by grafting 2-hydroxyethyl acrylate onto PVA [206]. 7. Prediction of concentration, conversion, particle size for the emulsion polymerization of PVAc stabilized by PVA using mathematical modeling [207]. 8. A "smart" material based on PVA-borate gelation [ 13]. 9. Protein deposition on PVAc-poly(methyl methacrylate) contact lens type hydrogels [208]. 10. pH-sensitive hydrogels based on block-copolymers of poly(hydroxethyl methacrylate) with PVA esterified with maleic anhydride or acryloyl chloride [209].

272

7. Polymerization of Vinyl Acetate and Other Vinyl Esters

11. Isotactic poly(propylene)-PVA graft copolymers [210]. 12. Hydrolysis of methyl tributyltin maleate-vinyl acetate copolymers [211]. 13. Biodegradability of poly(vinyl alcohol) [212]. Complexes and Polyblends 14. Formation of binary complexes of PVAc with poly(acrylonitrile), poly(methyl methacrylate), or poly(methacrylic acid) [213]. 15. Polyblends of cellulose with PVA [214]. 16. Interpenetrating polymer networks of epoxy novolac-based vinyl ester in polyurethane systems [215]. 17. Blends of [poly(vinyl acetate)-co-poly(vinyl alcohol)] with poly(4-vinylpyridine) [216]. 18. Synthesis and polymerization of metal-vinyl acetate colloids [217]. General 19. Thermal and dilute solution properties of low molecular weight poly(vinyl acetate) [218]. 20. Emulsion polymerization of vinyl acetate with a polymerizable surfactant, sodium dodecyl allylsulfosuccinate [219]. 21. Fluorescence of pyrene derivatives in low molecular weight copolymers of vinyl acetate and sodium methallylsulfonate [220]. 22. Microemulsions of vinyl acetate polymerization [221]. 23. Method of fractionation of PVAc [222]. 24. Effect of retardation by ethyl formate on the latex polymerization of vinyl acetate [223]. 25. Use of ultrasound in latex polymerization of vinyl acetate copolymers [224]. 26. Polyisobutylene-polyoxyethylene-polyisobutylene triblock copolymers as stabilizers in the aqueous polymerization of vinyl acetate [225]. 27. Organic sulfide-terminated poly(styrene) as photoinitiator for the polymerization of vinyl acetate [226]. 28. Cyclopolymerization of vinyl cinnamate [227]. 29. Cyclopolymerization of vinyl methacrylate [228]. 30. Precipitation copolymerization of vinyl esters [229]. 31. Terpolymers of vinyl chloride, vinyl acetate, and vinyl alcohol [230]. 32. Polymerization at subzero temperatures initiated by methyl chlorosulfite and hydroperoxide [231 ]. 33. Polymerization in DMF with 2,2'-azobisisobutyronitrile and dissolved salts [ 101 ]. 34. Solution copolymerization of vinyl acetate and ethylene [232].

References

273

35. Preparation of syndiotactic polymers of vinyl esters of fluorinated acids [233]. 36. Kinetics of emulsion polymerization of vinyl stearate [234]. 37. Redox emulsion copolymerization of vinyl acetate and vinyl propionate

[235]. 38. 39. 40. 41.

Continuous emulsion polymerization of vinyl acetate [236]. Polymerization of vinyl acetate initiated by metal chelate [237, 238]. Carbanionic copolymerizations with vinyl butyl sulfone [239]. Preparation of monomeric vinyl alcohol from acetals, by rearrangement of allyl alcohols (to 1-propene-l-ols) and polymerization thereof

[240, 241]. 42. Free radical copolymerization of vinyl acetate with N-substituted maleimides and bismaleimides [242]. 43. Vinyl acetate-co-vinyl pyrrolidone: A study of the solution behavior of various copolymer compositions in aqueous and in alcoholic systems [243].

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Chapter 8

Polymerization of Allyl Esters 1. 2. 3. 4.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chain Transfer in Allyl Polymerizations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cyclopolymerization of Diallyl Esters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polymerization of Allyl Acetate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4-1. 4-2.

Bulk Polymerization of Allyl Acetate in Sealed Tubes . . . . . . . . . . . . . . . . . . Solution Polymerization of Allyl Acetate . . . . . . . . . . . . . . . . . . . . . . . . . . .

5. Polymerization of Allyl Esters of Higher Monoearboxylic Acids . . . . . . . . . . . . . . . . .

5-1.

Copolymerization of Vinyl Chloride and Allyl 1 O,11-Dibromo-undecanoate and Fractionation of the Copolymer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303

6. Polymerization of Allyl Acrylate and Methacrylate . . . . . . . . . . . . . . . . . . . . . . . . . . .

6-1. 6-2. 6-3.

Solution Polymerization of Diethylene Glycol Bis(allyl carbonate) . . . . . . . . . Preparation of Diethylene Glycol Bis(allyl carbonate) Cast Sheet . . . . . . . . .

8. Polymerization of Diallyl Esters of Phthalic Acids . . . . . . . . . . . . . . . . . . . . . . . . . . .

8-1. 8-2. 8-3. 8-4. 8-5.

Bulk Polymerization of Diallyl o-Phthalate with High-Temperature Initiator.. Sealed-Tube Bulk Polymerization of Diallyl o-Phthalate . . . . . . . . . . . . . . . . Bulk Polymerization of Diallyl o-Phthalate at 200~ . . . . . . . . . . . . . . . . . . Solution Polymerization of Diallyl o-Phthalate . . . . . . . . . . . . . . . . . . . . . . "'Suspension Polymerization" of Diallyl o-Phthalate . . . . . . . . . . . . . . . . . .

9. Polymerization of Allyl Esters of Other Polyfunctional Acids . . . . . . . . . . . . . . . . . . .

9-1. 9-2.

305

Solution Polymerization of Allyl Methacrylate . . . . . . . . . . . . . . . . . . . . . . . 306 Ultraviolet-Initiated Polymerization of Allyl Methacrylate with Benzoyl Peroxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 Ultraviolet-Initiated Polymerization of Allyl Methacrylate with Biacetyl . . . . . 309

7. Polymerization of Diallyl Carbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7-1. 7-2.

282 283 287 295 298 299 301

Preparation of Diallyl Brassylate Prepolymer in a Stirred Reactor . . . . . . . . Copolymerization of an Unsaturated Polyester and Diallyl Adipate . . . . . . . .

10. Miscellaneous Preparations and Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

311 312 313 314

316 316 317 320 321 322 323 324 326 327 281

282

1.

8. Polymerization of Allyl Esters

INTRODUCTION

The 2-propene group is commonly referred to as the "allyl group." The term is derived from the Latin allium meaning garlic. Many natural and artificial flavoring agents contain allyl derivatives. For example, oil of garlic contains diallyl sulfide, other allyl sulfur derivatives are components of oil of mustard, dill, wasabi, horseradish, and onion. Allyl esters are found in many perfumes [1]. Since allyl compounds are capable of free-radical polymerization (albeit sluggishly) they are used in a number of copolymer systems. Only four allyl esters are of significant industrial importance as monomers for the production of homopolymers: diethylene glycol bis(allyl carbonate), which, as "CR-39," is widely used as a plastic spectacle lens material of exceptional clarity, scratch, abrasion, and impact resistance, and diallyl o- and m-phthalates, supplied commercially as soluble low-molecular-weight prepolymers. These prepolymers may be molded and subsequently cross-linked to give rigid plastic objects. The prepolymer of o-diallyl phthalate (DAP) copolymerized with unsaturated polyesters and reinforced with either glass fibers or glass roving find application in high impact resistant molding compounds for electronic molded parts, decorative panels, and nonwoven glass fabrics, to mention only a few applications. The prepolymer of meta-isomer (DAIP) copolymerizes more rapidly than DAP and produces materials with higher heat resistance than the analogous DAP derivative. It is used in molting powders. Because of its high refractive index, DAIP is of interest in the manufacture of lenses. Other monomers which find large-scale applications are diallyl chlorendate (I), diallyl maleate, diallyl fumarate, allyl methacrylate, and allyl acrylate. C1

I

i ~ C H - - oCII -- O-- CH2-- C H = CH2 Ilel-Celf.

C1-- C / C1-- C

| _ _ C H - - C -- O-- CH2-- CH-- CH2

II

I

O

C1 Diallyl Chlorendate (I) The high level of chlorine in diallyl chlorendate contributes to the flame retarding properties of polymers containing this monomer. The free-radical polymerization process with allyl esters resembles that of vinyl and acrylic esters in that there are similar initiation, propagation, and

2.

Chain Transfer in Allyl Polymerizations

283

termination steps. Of particular importance in the case of allyl compounds is the chain-transfer process. It is this chain-transfer reaction which constitutes the predominant characteristic differences between allylic and vinyl polymerization reactions. In the case of allyl esters both "effective" and "degradative" chaintransfer seem to occur side by side. Some investigations indicate that free radicals generated from allylic compounds may be either "head radicals" or "tail radicals." The polymerization of allyl methacrylate and acrylate is of more than academic interest. The reactivities of allyl and acrylic moieties are so different that the acrylic portion of the monomer essentially may homopolymerize while the allylic groups are unaffected. At a latter stage, perhaps by increasing the reaction temperature or by incorporating additional initiator, the allyl groups may be used to crosslink the polymer. Such a two-stage system permits ready molding or extrusion of an acrylic copolymer which can be rendered thermosetting at a later time. The polymerization of diallyl o-phthalate as well as of other a-, r esters is characterized by the formation of cyclic structures along the lowmolecular-weight chains. At approximately 25% conversion to a low-molecularweight polymer, the mass rapidly gels. The ease of ring formation of diallyl esters decreases with increases in the separation between the two allyl groups. Interestingly enough, the cyclic reagents involved in diallyl o-phthalate prepolymers form quite readily even though the tings probably consist of 11- or 12-member tings, sizes thought to be difficult to establish, at least in the case of cyclic polymethylene derivatives. In this chapter, procedures for the polymerization of allyl acetate and related monocarboxylates of diallyl carbonate types, of diallyl phthalates, and of diallyl esters of other dicarboxylic acids are discussed. References [1-13] are a selection of review articles and books dealing with the chemistry of allyl compounds.

2.

CHAIN TRANSFER

IN ALLYL

POLYMERIZATIONS The free-radical polymerization of allyl esters exhibits several unique characteristics. In this respect they differ materially from the polymerization characteristics of vinyl esters. Litt and Eirich [14] note the following unique factors for the peroxide initiated process: 1. In any one experiment, the rate of decomposition of the peroxide is first order. 2. Yet there is a concentration dependence of the rate constant.

284

& Polymerization of Allyl Esters

3. The rate of monomer disappearance with respect to the initiator concentration is constant during any one experiment. 4. With increasing peroxide concentration, the rate of disappearance of monomer with respect to peroxide, d[M]/d[P], decreases. 5. Over a fivefold variation of the peroxide concentration, at a constant polymerization temperature, the MW of poly(allyl acetate) remains virtually constant at 1300 (i.e., DP = 13) (Litt and Eirich found the degree of polymerization to be 20-25 in their work). 6. Upon substituting deuterium for the two allylic hydrogens in allyl acetate (cf. Structure II) as the polymerizing monomer, both the molecular weight and the disappearance of the monomer with respect to peroxide, d[M]/d[P], increased [ 15]. O II

CH2--CH--CD2--O--C--CH3 Allyl-1, 1-dideutero Acetate or Allyl-l-d2 Acetate (II) The rates of polymerization of the deuterated analog of allyl acetate were from 1.93 to 2.09 times those of the undeuterated compound while the average MW of deuterium-containing polymer was 2.38 times greater than that produced from ordinary allyl acetate. The kinetic chain length of a free-radical polymerization process is the ratio of kp/kr, where kp is the rate of propagation and kr is the rate of termination. Since allylic hydrogens are not involved in the propagation step, substitution of deuterium for these hydrogens was expected to affect the termination process. When this indeed was found to be the case, as evinced by the increase in the kinetic chain length and the MW of the polymer, it was considered reasonable evidence that the allylic hydrogens were the cause of the characteristic behavior of allyl esters [ 15]. In their pioneering studies of the free-radical polymerization of allyl acetate, Bartlett and Altschul [ 16, 17] found that the average MW of poly(allyl acetate) produced by bulk polymerization with benzoyl peroxide or di(p-chlorobenzoyl)peroxide was generally about 1300 (DP = 13). While oxygen is capable of retarding the polymerization, the low molecular weight of the polymer had to be attributed to other causes. The work with di(p-chlorobenzoyl)peroxide showed that 72.5% of the peroxide fragments were bound to the polymers and 16.8% were converted to free p-chlorobenzoic acid (an additional 10.7% was not accounted for). The peroxide fragments which were not effective in initiating polymerization must have abstracted hydrogen from the monomer to form p-chlorobenzoic acid. At least 72% (but not all) of the polymer molecules produced had a p-chlorobenzoate end group; the remainder did not. This

2.

285

Chain Transfer in Allyl Polymerizations

observation indicates that while most of the polymer was formed from free radicals generated from the peroxides, a substantial quantity was initiated by a chain-transfer process. The abstraction of an allylic hydrogen from allyl acetate, either by benzoyloxy radicals or by other free radicals, such as growing, polymeric free radicals, yields a radical capable of resonance stabilization (Structure III): O II CH2=CH--CHOCCH3

-~

O II -~-CH2--CH--CHOCCH3

(III) Since such radicals react less rapidly than radicals not stabilized by resonance, the observable polymerization rate decreases. For this reason, the process is termed "degradative chain-transfer." In degradative chain-transfer, growing, polymeric free radicals collide with a monomer molecule to form a new, stable free radical which propagates only with difficulty. The allylic radical may terminate growing radicals, dimerize, cause the decomposition of peroxidic initiators, or initiate the formation of new polymerizing species. The first of these possible processes has been termed "cross termination" [14]. Along with degradative chain-transfer, there is evidence, as already mentioned above, that some new chains are initiated by allylic radicals. This has been termed "effective chain-transfer." In the polymerization of vinyl acetate, chain transfer to the acetate portion of the monomer is an important aspect of the process (see Chapter 7 of this volume). In the case of the allyl acetate polymerization, chain transfer to the acetate moiety is considered negligible as compared to the degradative chaintransfer process [ 14, 15]. Very much as in the case of vinyl acetate, the solution polymerization of allyl acetate in benzene leads to the addition of the growing radical chains to benzene to produce stable aromatic adducts with a tendency to terminate by combination. This explains the retention of the degree of polymerization in the expected range ( D P = 14.3-14.9) and the fact that a polymer chain may contain more than one aromatic group [ 14]. The preceding indicates that in bulk and in benzene solution, the polymerization of allyl acetate leads to polymers of relatively low molecular weight. It had been expected that in emulsion processes, a higher-molecular-weight polymer would be formed. However, with a persulfate initiator, the emulsion polymerization of this monomer led to a product with the same molecular weight as was found upon bulk polymerization [18]. The ratio of the rate constant for degradative chain-transfer to that of effective chain-transfer has been derived as a function of the ratio of the rate of monomer consumption, the rate of initiator consumption, and the degree of polymerization

286

8. Polymerization of Allyl Esters

[19]. This ratio may also be estimated from a determination of the amount of initiator residues found in the monomer. From such data the significance of degradative chain-transfer in an allyl ester polymerization can be judged. For example, it was found that in the allyl ethyl carbonate polymerization, degradative chain-transfer predominates, whereas in the polymerization of allyl laurate and allyl benzoate, effective chain-transfer predominates [ 19]. The order of decreasing degradative chain-transfer constants for a series of allyl esters has been given as allyl ethyl carbonate > allyl acetate > allyl propionate > allyl laurate > allyl trimethylacetate [20]. Effective chain-transfer also predominates for allyl benzoate, allyl chloroacetate, and allyl chloride [20]. It is interesting to note that measurement of the rate of decomposition of dibenzoyl peroxide in various allyl esters showed that the decomposition rate decreased in the same order as the degradative chaintransfer constants decreased [21 ]. This indicates that the radicals formed during the initiation stage not only propagate and attack the allylic hydrogens as expected, but also the acyl portion of the ester group. The degree of polymerization of the isolated polymers increases as the degradative chain-transfer decreases [22]. However, a generalization that degradative chain-transfer decreases with increasing chain length of the carboxylic acid portion of the ester is a gross oversimplification. Thus, the allyl esters of undecanoic; 10- and 11-phenylundecanoic; 10,11-dibromoundecanoic; 11-iodounde-canoic; 12-hydroxystearic; and 12-ketostearic acid did not homopolymerize at all in either bulk or emulsion. Copolymers were not formed readily with either styrene or methyl methacrylate. However, with vinyl chloride, fairly homogeneous copolymers were formed. For M1 as allyl iodoundecanoate and M2 as vinyl chloride, at 60~ in benzene, rl was estimated to be 0.42 and r2 was 1.64 [23]. Chow and Marvel [23] attribute the fact that allyl esters copolymerized readily with vinyl chloride and not with liquid monomers to the pressure under which the vinyl chloride polymerizations were carried out (approximately 8 atm). They pointed out that Walling and Pelion [24, 25] had shown that a high pressure (e.g., at 8500 atm [85 MPa]) the overall rate of polymerization of allyl acetate had increased 50-fold yet the MW of the polymer had not changed materially over that formed at atmospheric pressure. This indicates that chain transfer is no longer degradative. Therefore, Chow and Marvel seem to reason, even at a pressure of 8 atm the pressure is sufficiently high that degradative chain-transfer can no longer interfere with copolymerization. The addition of zinc chloride to allyl acetate in equivalent amounts lead to increased polymerization rates upon exposure to 6~ radiation. The viscosity MW of the poly(allyl acetate) produced increases with increased levels of zinc chloride [24]. The zinc chloride may assist in activating allylic-free radicals and in developing an organized array of monomers for effective polymerization. In the presence of zinc chloride it has also been proposed that the probability of

287

3. Cyclopolymerization of Diallyl Esters

degradative chain-transfer taking place has been reduced while the initiation rate has increased. [27]. Even though monomers like allyl acetate do not polymerize rapidly nor produce products of high molecular weight, with active chain-transfer agents good yields of addition products may be isolated [28]. Among the chain-transfer agents proposed for such systems are chloroform and carbon tetrachloride. Sakurada and Takahashi [29], formulated the reaction as follows: "~CH2--CH" + CC14

I

; 'w'CH2--CHC1 + "CC13

I

CH2

CH2

O

O

I

I

I

I

C=O

(1)

C=O

I

I

CH3

CH3

Equation (1) represents a termination step for one particular chain with the simultaneous formation of a new free radical with considerable reactivity. This trichloromethyl radical is capable of initiating a new chain leading to further propagation if the initial concentration of carbon tetrachloride is low. This step is shown as 9CC13 + CH2=CH

} C13C--CH2--CH.

I

I

CH2

CH2

I

I

O

O

I

I

C=O

(2)

C--O

I

I

CH3

CH3

Thus, the chain length of polymers is shortened while the reaction itself is not terminated. Experimentally it was found that each polymer molecule contained between two and three chlorine atoms. With decreasing concentrations of allyl acetate in carbon tetrachloride, the MW of the polymer decreased [28, 29]. Another factor contributing to the formation of low-molecular-weight polymers of allyl ethers of dibasic acids is the tendency of some of these to cyclize. This process is discussed in greater detail in the next section.

3.

CYCLOPOLYMERIZATION

OF DIALLYL

ESTERS

The polymerization of allyl esters may suffer from the standpoint of practical applications because the resins formed usually have a low molecular weight, and are slow to form even in the presence of excesses of initiator at advanced temperatures. On the other hand, these same shortcomings make allyl ester polymers uniquely suitable for the study of the fine structure of the polymer. The

288

8. Polymerization of Allyl Esters

slow rates of polymerization permit studies involving changes that take place with increasing conversion. The requirement for high levels of initiator has been used to evaluate the effects and nature of end groups by conventional wetanalytical techniques [ 16]. The molecular weights of allylic polymers tend to be low (frequently their degree of polymerization is in the range of 20 mer units). This readily permits the use of colligative property measurements to establish molecular weights with a reasonable degree of assurance. Such determinations may then be correlated with molecular weight determinations based on viscosity measurements. The study of unconjugated diolefin polymerizations is usually considered quite difficult because complex, three-dimensional networks are set up at very low conversion. Such cross-linked materials are generally intractable. The situation is quite different in the case of diallyl esters, especially in the case of diallyl phthalates. Both diallyl o-phthalate and diallyl m-phthalate may be converted to "prepolymers," which are soluble in a variety of solvents. These two prepolymers are commercially availabe. When dissolved in their respective monomers and heated in the presence of typical initiators, such solutions are converted to cross-linked resins. Most of the shrinkage related to the conversion of monomers to polymers has taken place when the pre-polymer was formed originally. Therefore solutions containing relatively high levels of diallyl o-phthalate prepolymer shrink little on polymerization. It was observed that up to about 25% conversion, the polymerization of diallyl o-phthalate is linear with time and initiator concentration. As the process continues, a cross-linked gel forms. The polymer formed up to 25% conversion has a melting point of about 90~ is soluble, and is less unsaturated than would be expected for a linear polymer. Therefore, it was presumed that the prepolymers consisted of a main chain with a number of short branches [30]. In 1950, Haward [31 ] postulated that in these polymerizations the concentration of free radicals normally is low. In the reaction with diallyl o-phthalate, for example, intramolecular crosslinking is more likely than intermolecular reactions. The collisions between segments of the same molecule would lead to cyclic structural features. Regardless of conversion, up to the gel point, the soluble prepolymer (or "fl "-polymer to use the nomenclature of Simpson and co-workers) exhibited a degree of unsaturation corresponding to 25% of the unsaturation of monomeric diallyl o-phthalate. This observation, along with measurements of the degree of polymerization of poly(diallyl o-phthalate) at various conversions and the degree of polymerization determinations of poly(allyl acetate) produced by saponifying the diallyl o-phthalate prepolymer followed by reactylation of the isolated poly(allyl alcohol) by conventional methods, permitted Simpson and co-workers to develop considerable detail about the fine structure of this polymer [32].

3.

Cyclopolymerization of Diailyl Esters

289

It should be noted that in this work, Simpson and co-workers [32] report their viscosities in units of ml/gm (i.e., cm3/gm) rather than in units of dl/gm (i.e., dm3/gm) which we have used conventionally in this series. For their molecular weight-viscosity relationship, they make use of the expression LVN = 2.35 X 10-3M where LVN is the limiting viscosity number in cm3/gm and M is the molecular weight. To be noted is that the exponent of M is 1. In Table 1 this bulk polymerization data and certain calculated values are presented. The experiments used covered a range of conversions, including one preparation carried to a highly crosslinked state. If we consider the results given in Table I for Experiment No. 1, we find that the polymer molecule consists of chains with a DP of 19.4, joined by o-phthalate units. Each of these chains bears 5.8 tings per chain, leaving 13.6 monomer units as a linear array. It has been suggested that the formation of cyclic units is, in part, responsible for the difficulty in predicting the degree of conversion at which gelation takes place. In the case of diallyl o-phthalate, gelation takes place at a much higher degree of conversion than can be calculated on the basis of the modified Stockmayer equation [33]. The probability of cyclopolymerization by diallyl o-phthalate by various possible ring closures was calculated by Haward [34]. He predicted that 31% of the monomer units in the soluble polymer were cyclized. Experimentally, Simpson and co-workers [32] found that 41% were involved. This was considered excellent agreement between calculated predictions and empirical observations. Haward based his calculations on the assumption that the cyclic structures formed contained 11 or 13 members. Ziegler [35], Stoll and Rouve [36], and Prelog and co-workers [37], among others, had concluded long ago that 10- to 13-membered carbon tings have a low probability of forming stable structures, compared to 15- to 20-membered tings. Haward, however, indicated that this only had the effect of overestimating the contribution of the ring formation of this size compared to the probability of large tings forming. He implied that various other limitations of this proposal would affect his estimates in reverse order. In sum, all the simplifying assumptions would tend to balance each other. The fact is that experimental data confirmed his predictions. Considering various possible ring-closure reactions involving the action of one allyl radical on the other of a single diallyl o-phthalate monomer, Haward proposes four possible structures. Figures 1, 2, 3, and 4 give the skeletons of these cyclic structures with the points of attachment to a polymer chain (indicated in the figures by AN') and the location of the odd electron of the propagating free radical (indicated by ~). The structural designation x, y, z, and w are those used by Haward.

t~

TABLE I

Exp No 1 2 3 4

Reaction time (min) 65 155 245 2880 (48 hr)

Conversion (%)

No avg degree of polymerization of diallyl o-phthalate b

6.7 15.6 22.2 86

15.9 32.0 55.2 d

Polymerization of Diallyl o-Phthalate [32] a

Residual unsaturation (%) 28.01 26.64 26.02

No avg degree of polymerization of derived acetate C 19.4 19.6 19.8 (20.8)

n No of branches in polymer

R No of rings per polymer molecule

R/n No of rings per chain

1.17 2.40 4.12

6.8 13.6 23.3

5.8 5.6 5.8

a Polymerization conditions: Polymerization using benzoyl peroxide (11,200 grn/dm 3 of monomer, i.e., 1 wt%, 0.0463 moles dm 3) was conducted at 80 __+0.25~ with a variable reaction time under reduced pressure in sealed ampoules. b It is interesting to note that the increase in molecular weight per unit time for the first three polymers is essentially constant, 60, 50.7 and 55.4 Daltons/ min, with a mean of 55.4 Daltons/min. The values in this column represent the DP's for the total polymer. c See Procedure 8-2, p. 316, as to method of preparation. The DP's show the chain lengths of poly(allylic segments) which had been joined originally by the phthalate moieties. d Cross-linked polymer.

3. Cyclopolymerization of Diallyl Esters

*--C

C I C --C --C --C - - O - - C O

C

f

291

C O - - O - - C --C = C

I C

C

I

I

C

c

I

I

co

co

Fig. 1

f

Structure x.

C I C --C--C --O--CO

C

C *-C

C O - - O - - C --C = C

C

I

I

CO

CO

Fig. 2

IC\

Structure y.

t C --C--C--C--O--CO

'w'C - - C

I

I

c

c

I

I

o

0

I

I

co

co

Fig. 3

Structure z.

~ccc-o-co "" C --C

I C

CO--O--C --C--C

C O - - O - - C --C = C

C

I C-*

I

I

0

0

I

I

CO

CO

Fig. 4

Structure w.

292

s. Polymerization of AUyl Esters TABLE II Proportion of Cyclic Structures Found in Diallyl o-Phthalate Prepolymers [34]

Structure

Figure

Cyclic structures (%)

x y z w

1 2 3 4

53.9 16.2 22.7 7.2

The proportions of these structures in the cyclized prepolymers were computed as shown in Table II. Using only one of these cyclic configurations, for purposes of illustration an approximate structure of a diallyl o-phthalate prepolymer near the gel point is given in Fig. 5. The cyclic units may be one or more of those shown in Figs. 1-4. The various monomeric units are probably more randomly distributed. It will be noted that in Fig. 5, the low-molecular-weight polymer chains are based, substantially, on the polymerization of only one of the two ally groups of each monomer with one allyl group of an adjacent monomer molecule. This mechanism of the polymer formation has been treated mathematically by employing "cascade formalism" [38, 39]. Hence, we may term the process a "cascade polymerization." The pendant allyl groups may occasionally form tings if they are at the free-radical end of a propagating chain ("incestuous polymerization" [40]) or participate in crosslinking reactions, making use of"spanning tree

t

~ C H

CO I O \ CH2 I CH

CO I O \ CHv I CH

CH2

CH2

//

I CH21

CH / I ~H2

O I CO

O I CO

CH I CH2 / O I CO

CO I O \ CH2 I

ctt //

//

/t/

CH2

Fig. 5 Approximate structure of diallyl o-phthalate prepolymer near the gel point. At the gel point: m, approximately 7-8; and m + n, approximately 17-18.

3. Cyclopolymerization of Diallyl Esters

293

approximations" [38, 39]. These picturesque mixed metaphors are useful in visualizing the course of the cross-linking polymerization. Of course, also to be included in this list of reactions is degradative chain-transfer along with the usual initiation, termination, and more ordinary propagation steps. It will be noted, on examining Fig. 5, that the cyclic portions of the polymer are incapable of cross-linking. In other words, approximately 40% of the polymer cannot undergo this reaction. This fact contributes to the deviation from the theoretical gel point calculation in the direction of gelation taking place at an unusually high degree of conversion [40]. When the conversion at gel-formation was studied for the diallyl esters of isophthalic, terephthalic, oxalic, and sebacic acid, it was found that all systems gelled at approximately 25% conversion of the monomer to the polymer. All polymers, on saponification and reacetylation of the resultant poly(allyl alcohol) gave rise to chains with DPn in the range 18.6 to 20.6. These chain lengths appear to be independent of the degree of conversion of the polymer under investigation. Whereas the extent of residual unsaturation of poly(diallyl o-phthalate) was approximately 26%, for the other four polymers in this series, the unsaturation value was approximately 40%. With increasing conversion, the unsaturation of poly(diallyl terephthalate) decreased considerably while that of poly(diallyl o-phthalate) and of the other three monomers decreased only slightly as the conversion increased [41 ]. From these observations it was concluded that, of these diallyl esters, only diallyl o-phthalate gave rise to highly cyclized structures, although the extent of cyclization in the other systems is not negligible. The chain length, when expressed in terms of the number of reacted double bonds is significantly less for poly(diallyl o-phthalate) than the other polymers. All systems gel at the same degree of conversion regardless of monomer. Cyclization does not seem to affect gelation as expected from theory. The satisfactory correlation to the gelation of diallyl o-phthalate is considered fortuitous [41 ]. It should be noted here, that a prepolymer of diallyl isophthalate is commercially available. Its use is similar to that of the ortho-isomer although the properties of the final crosslinked resin are somewhat different. This may be the result of the fact that only the poly(o-phthalate) is markedly cyclized [42]. The terephthalate has not been studied very extensively. However, it has been found that diallyl terephthalate initially does not cyclize, as the conversion increases, more than one crosslink per chain is formed [42, 43]. The termination step of the polymerization of diallyl o-phthalate involves degradative chain-transfer to fresh monomer, yet a significant fraction of the radicals so produced are capable of reinitiating chain-propagation steps [42]. By studying the changes in the infrared absorption band at 1645 cm-1 (an olefinic double bond stretching band) with time, the rate, order of initial polymerization reaction, activation energy, and the extent of the reaction could

294

8. Polymerization of Allyl Esters TABLE III Initial Degrees of Polymerization of Diallyl Esters of Aliphatic Dicarboxylic Acids [46] a Diallyl ester of Oxalic acid Malonic acid Succinic acid Adipic acid Sebacic acid

DP~ 85 70 71 61 54

a Polymerization conditions: bulk polymerization using dibenzoyl peroxide as the initiator. The polymerization was conducted under reduced pressure in sealed ampoules.

be studied well beyond the gelation [44]. It has been stated that the gel point of diallyl o-phthalate could be predicted with a reasonable degree of certainty by taking into account the relative rates of entry of the doubly unsaturated and the singly unsaturated monomer units along with those units in which two reacted allyl groups exist in the same polymer chain [44]. In dilute solution, it was found that even diallyl terephthalate was capable of undergoing intramolecular cyclization. In general, with decreasing monomer concentration in a solvent, such as benzene, the possibility of cyclopolymerization increases [45]. Because of the ease of synthesis and industrial importance of diallyl esters much of the research has dealt with the behavior of the isomeric phthalates. Some other dicarboxylic acid esters have been studied by Simpson and Holt [41 ]. The kinetics of the polymerization of the diallyl esters of oxalic, malonic, succinic, adipic, and sebacic acid have also been considered. In previous kinetic studies, no differentiation was made between the behavior of the uncyclized monomer (or its free radical) and of the cyclic free-radicals. A priori, differences should have been presumed, but evidently Matsumoto and Oiwa [46] were the first seriously to attempt a kinetic analysis based on the concept that the linear and the cyclic units are two different species. In effect, these two species copolymerize with each other. However, the analysis has not been carried so far as to determine reactivity ratios. In the bulk polymerization of the diallyl esters of the aliphatic dicarboxylic acids, the initial degrees of polymerization are quite large (Table III). In these data, it should be emphasized that the degree of polymerization___was determined by osmometry and refers to the total polymer and not to the DPn of chains obtained upon saponification of such polymers. The ratio of the unimolecular rate-constant of the cyclization to that of the bimolecular propagation-reaction of the linear free-radical has been given the

295

4. Polymerization of Allyl Acetate TABLE IV Ratio of Rate of Cyclization to Rate of Bimolecular Propagation, Kc, and Overall Activation Energies of Polymerization of Diallyl Esters of Aliphatic Dicarboxylic Acids [46]a

Diallyl ester of Oxalic acid Malonic acid Succinic acid Adipic acid Sebacic acid

Kc (moles/liter)

Overall activation energy of polymerization (kcal/mole)

3.6 3.2 2.8 2.5 1.2

21.1 24.2 21.7 22.0 22.2

a Polymerization conditions: bulk polymerization using dibenzoyl peroxide as initiator. The polymerization was conducted under reduced pressure in sealed ampoules.

symbol Kc. This term is a measure of the tendency of the molecule to cyclize. It was found (cf., Table IV) that with increasing separation between the carboxylic acid groups of the dicarboxylic acid, Kc decrease and, therefore, the tendency to cyclize decreases. Table IV also lists the overall activation energies of polymerization [46]. In attempts to copolymerize various diallyl esters with styrene it was found that the reactivity was quite low. Further, the rate and degree of copolymerization was roughly inversely related to the concentration of diallyl ester. With increasing styrene levels, the tendency toward cyclopolymerization decreased [47]. In effect, the diallyl esters act as chain-transfer agents for the polymerization of styrene. Table V gives the chain-transfer constants and the reactivity ratios for the copolymerization with styrene. It is noteworthy that the formation of cyclic structures is not confined to diallyl esters. For example, Haward and Simpson found evidence for cyclopolymerizations at low conversion of solutions of divinylbenzene in styrene [48]. Diallyl ammonium halides were among early examples of cyclopolymerizations [49]. Two reviews of interest are Marvel [50] and Butler [51]. In their highly mathematical treatment of cyclization in cross-linking polymerizations, it is interesting to note that Du~ek and Ilavsk~ [38, 39] found that the data of Simpson and Holt [41], gathered 20 years earlier, were quite consistent with their analysis.

4.

POLYMERIZATION OF ALLYL ACETATE

The polymerization of acrylic and vinyl esters generally proceeds quite rapidly, with relatively low levels of initiators, to form products of considerable molecular weight. By contrast, allyl esters polymerize slowly with high levels of

296

8. Polymerization of AUyl Esters

TABLE V Chain-TransferConstants, Cs, and Copolymerization Reactivity Ratios of Diallyl Esters with Styrene (M1) [7] Reactivity ratiosa Diallyl ester of (M2) Carbonic acid Oxalic acid Malonic acid Succinic acid Adipic acid Sebacic acid o-Phthalic acid Isophthalic acid Terephthalic acid

G (X 104)

rI

r2

6.2 4.2 5.2 5.4 6.0 4.8 6.3 3.5 4.5

55.0 59.6 71.8 71.0 70.0 65.6 53.4 53.0

0.052 0.050 0.053 0.044 0.052 0.029 0.046 0.034

a Determined for only one functional group of the diallyl ester. initiators to give polymers of low molecular weight. When one considers the difficulties involved in the synthesis of vinyl esters as compared to the ease with which allyl esters may be prepared, this is a rather unfortunate circumstance. As a result, very few allyl esters have any industrial uses as polymers or copolymers. The polymerization of allyl acetate has been studied reasonably extensively in the effort to elucidate the mechanisms of the polymerization process. The utility of poly(allyl acetate) as a resin is believed to be negligible. Nevertheless, this compound has been polymerized in bulk, in solution, and in emulsion. There is mention of a cationic polymerization process and of radiation-induced chargetransfer processes. The ordinary, free-radical induced bulk polymerization of this monomer appears to be only modestly affected by the presence of atmospheric oxygen (cf. Table VI). Despite these observations, Bartlett and Altschul [ 16] routinely used degassing (Procedure 4-2) for their experiments. Additives such as water, dilute hydrochloric acid, or a trace of pyridine appear to have no effect on the rate of polymerization of allyl acetate [16]. As expected, at a constant polymerization temperature and constant time, with increasing percentages of initiator, the conversion of monomer to polymer increases. In Table VII this effect of the concentration of benzoyl peroxide on the polymer formation is shown. The reaction times, given in this table vary slightly. The data are taken from a more extensive study [ 17]. In connection with Table VII it should be noted that at 80~ 48 hr represents approximately 12 half-life periods for dibenzoyl peroxide and 45 hr is approximately 9 half-life periods for di(p-chlorobenzoyl)peroxide. This means that in

4. Polymerization of Allyl Acetate

TABLE VI

297

Effect of Supernatent Oxygen on the Formation of Poly(allyl acetate) [16] a Conversion (after 12 hours)

(%)

Degassing procedure 1. Air in ampule, no agitation 2. Ice-cooled monomer was evacuated at the water pump five times at approximately 20 mm Hg; with purified nitrogen flushing between evacuation. Monomer finally sealed under purified nitrogen 3. Procedure similar to 2 except that cooling was with dry ice-ethanol and evacuation was with an oil pump at approximately 2 mm Hg 4. Procedure similar to 3 except that thawing and refreezing step followed each evacuation 5. Procedure similar to 4 except that monomer was cooled with liquid nitrogen and evacuation was with a diffusion pump to less than 1 0 - 4 m m Hg

11.2

12.5 12.2 12.4 12.5

~ Polymerization conditions: Polymerization using dibenzoyl peroxide as initiator (1.12% of the monomer system) was conducted at 80.0 ~ • 0.2~ in sealed ampoules for 12 hr with degassing procedure as indicated.

both cases, the initiator has been essentially completely destroyed at the indicated time. The bulk polymerization of allyl acetate using 2,2'-azobisisobutyro-nitrile proceeds in the same manner at 80~ as similar polymerizations involving the use of diacyl peroxides [52]. CAUTION" care.

Allyl compounds are toxic and should be handled with great

TABLE VII

Effect of Peroxide Concentration on the Conversion of Allyl Acetate to Polymer [ 17] a

Concentration of dibenzoyl peroxide (%)

Polymerization time (hr)

1.01 2.14 6.10 9.95 Avg

5.906

tpol =

Polymer formed (%)

49.0 47.5 48.0 45.1

12.0 25.2 49.0 70.9

47.4 46.5

50.3

a Polymerization conditions: Polymerization using dibenzoyl peroxide (concentration given in first column) was conducted at 80.0 ~ _+ 0.3~ in sealed tubes degassed by Procedure 2 of Table VI. b Di(p-chlorobenzoyl)peroxide instead of dibenzoyl peroxide.

298

8. Polymerization of Allyl Esters

In the example of bulk polymerizations cited here, the polymer isolation procedure follows that of Litt and Eirich [14] since they maintain that the original procedures of Bartlett and co-workers did not adequately remove volatile, low-molecular-weight components from the polymers. Consequently, the MW determinations by Bartlett and co-workers are thought to be low.

4-1.

Bulk Polymerization of Allyl Acetate in Sealed Tubes [16, 17]

In a constricted test tube is placed a solution of 0.603 gm of di(p-chlorobenzoyl)peroxide in 9.61 gm of allyl acetate. The sample is degassed five times at ice temperature with a water aspirator at 15-20 mm Hg. The tube is flushed with highly purifed nitrogen between each degassing step. The tube is sealed under nitrogen pressure. After placing the sealed tube in a protective metal sleeve, the assembly is heated in an oil bath at 80 ~ for 46.5 hr. After this period, the tube is cooled to room temperature, then chilled in an ice bath, and cautiously opened. The reaction product is dissolved in 40 ml of reagent-grade benzene and extracted with four portions of a 35% ice-cold aqueous potassium carbonate solution. The last aqueous extract gives no precipitate upon acidification. The benzene layer is neutral. The organic layer is separated and, if necessary, filtered. The benzene is evaporated off in a slow stream of clean dry air at room temperature. The residue is dried for at least three days at 60~ at a pressure of 0.3 mm Hg to constant weight. To follow the polymerization of allyl acetate dilatometrically, Bartlett and Tate [15] made use of Adams brand Wintrobe hemacrit tubes which are fitted into a vapor thermostat. The hemacrit tube was calibrated in millimeters and had a total capacity of 1 ml. Degassed monomer solutions were transferred to the Wintrobe hemacrit tube (which had been degassed and prepared with a nitrogen atmosphere) by means of syringes. The apparatus permitted observation of the volume shrinkage and hence the progress of a polymerization. Use of a hemacrit tube as a low-capacity dilatometer may be of interest in other studies involving the polymerization of many monomer systems. Presumably hermacrit tubes are relatively inexpensive compared to precision-bored glass capillary tubes frequently used in the construction of dilatometers. The solution polymerization of allyl acetate was studied in an effort to determine the effect of monomer concentrations on the reaction kinetics [14]. These studies were limited to the use of benzene. The growing allyl acetate radicals formed stable adducts with the solvent much as vinyl acetate does. The stabilized adduct is terminated by combination with a growing radical. The twinning reaction is said to account for the relatively high molecular weight of the polymer despite the fact that the reaction with benzene is a chain-transfer reaction. Ethyl acetate, on the other hand, would have been a preferable solvent

4. Polymerization of Allyl Acetate

299

since chain transfer occurs only slowly and the growing chains are re-initiated relatively rapidly in this solvent. Procedure 4-2 outlines one technique used in the solution polymerization of allyl acetate.

4-2.

Solution Polymerization of Allyl Acetate [14]

In a stirred apparatus which allowed material to be degassed and polymerized (as well as permitting the removal of samples from time to time without exposure to the atmosphere) is placed a solution of 1.17 gm (0.00826 mole) of dibenzoyl peroxide and 50 grn (0.5 mole) of allyl acetate in 48.8 gm of benzene. The solution is cooled to - 8 0 ~ with dry ice-acetone and degassed to 0.3 mm Hg. The monomer solution is allowed to thaw. The pressure is then brought up to atmospheric pressure with nitrogen which had been prepurified by passage through Fieser's Solution. A mercury safety valve is used to regulate the gas pressure. The monomer solution is then refrozen and degassed three more times. The apparatus containing the degassed solution, at atmospheric pressure, under nitrogen, is then placed in a water bath and stirred. For kinetic measurements, the starting time for the reaction is considered to be 3 min after placement in the bath at 65~ 4 min at 80~ and 5 min at 90~ Samples of the reaction mixture are withdrawn at appropriate intervals. The reaction solution is heated for at least 6 half-life periods of the initiator. The polymer solution is diluted to a workable viscosity with benzene and extracted three times with 5% aqueous potassium hydroxide solution, so that a sample of the next to the last aqueous extract gives no precipitate upon acidification. The benzene solution is then repeatedly washed with deionized water until the washings have the same (near neutral) pH as the fresh, deionized water being used. The benzene solution is carefully separated and filtered into a tared beaker. The solvent and monomer is allowed to evaporate at room temperature. The residue is dried to constant weight for 3 days at 60~ and 0.3 mm Hg. In the polymerization of typical vinyl and acrylic esters, the molecular weights of polymers produced by emulsion-polymerization processes are generally substantially greater than those produced in bulk or in solution. The bulk polymers produced by treating allyl acetate with peroxides or with 2,2'-azobisisobutyronitrile have molecular weights in the range of only 1400-3000. It was therefore important to study emulsion polymerization of this monomer in an effort to produce a substantially higher-molecular-weight resin. The results show that even by this procedure, the degree of polymerization remained in the range of 13.6-14.3 (i.e., MW 1360-1430). The polymers contained sulfate end-groups, presumably from the persulfate initiator used [18]. Unfortunately, the experimental details for this work are not very clear. The work was done by shaking

300

8.

Polymerization of Allyl Esters

the emulsion recipe in sealed tubes in an oil thermostat at 80~ Bartlett and Nozaki [18] tabulated data for two experiments. In Experiment 1, 9.28 moles of allyl acetate per liter of latex was emulsified with 0.087 mole of sodium lauryl sulfate, buffered with 0.45 mole of sodium pyrophosphate, and initiated with 0.0920 mole/liter of potassium persulfate. In experiment 2, again 9.28 moles of allyl acetate per liter of latex was polymerized in the presence of 0.087 mole of sodium lauryl sulfate, 0.45 mole of sodium pyrophosphate, and 0.366 mole/liter of potassium persulfate. Since the MW of allyl acetate is 100, the above information implies that the basic monomer to water ratio is an unlikely 928 gm of monomer to approximately 70 gm of water. If indeed these are the experimental facts, then the fact that the polymers produced resembled those produced in bulk or in solution is not surprising. A reaction mixture consisting of nearly 93% pure monomer, naturally would be expected to produce a polymer similar to one produced from a pure (i.e., bulk) monomer and not one similar to an emulsion polymer. Compositions of less than 60% monomer in water would ordinarily be expected to produce latices. Perhaps the data in question refer to a ratio of 9.28 moles of monomer to one liter of water. By the way, it should be noted that Barlett and Nozaki included sodium pyrophosphate in their formulation to counteract the decrease in pH as a persulfate-initiated polymerization proceeds. At a low pH, the monomer is said to be susceptible to hydrolysis [18]. Work by R~.nby and co-workers has indicated that the nature of the addition of free radicals such as HEN- and OH. is profoundly influenced by changes in the pH of the medium from 1.4 to approximately 7.8 [53-55]. The radicals formed from persulfate in emulsion systems may be expected to be influenced by pH variations also. One patent reports the use of a "seed"-polymerization technique to produce an allyl acetate-ethyl acrylate copolymer [56]. In a typical example, to 305 gm of a 3.28% solution of poly(vinyl alcohol) (DP 1000) is added 10 gm of allyl acetate and 0.8 gm of potassium persulfate. The mixture is heated to 75~ followed by the addition of 190 gm of ethyl acrylate with heating for 2.25 hr at 80~176 After stirring for an additional hour and cooling to room temperature, the resultant latex is claimed to exhibit 99.6% conversion of all of the monomer to polymer. The pH of the latex is said to be 2.5. Cationic polymerizations of allyl esters require further investigation. Schildknecht [7] mentions the polymerization of allyl acetate and of allyl formate in benzene solution upon heating the solution with 6% of benzenediazonium fluoroborate under nitrogen at 200~ in sealed tubes. The solid products melt at about 190~ (d) and are soluble in benzene and insoluble in methanol. A 10% solution of allyl acetate in petroleum ether treated in a dry ice-acetone bath with gaseous boron trifluoride for several hours gave rise to a solid polymer with m.p. approxiamtely 145~ The product exhibited a certain amount of

5. Polymerization of Allyl Esters of Higher Monocarboxylic Acids

301

crystallinity. A poly(allyl trichloroacetate) formed under similar conditions had m.p. 330~ without decomposition [57]. The slowness of these polymerizations is rather surprising for cationically initiated processes. Zubov and co-workers observed that photo-induced polymerizations of a number of monomers were accelerated by certain metallic compounds. Allyl acetate, for example, exhibited an increased rate of polymerization in the presence of zinc chloride. It was postulated that a mobile, organized assemblage of monomers was involved in activating the allyl radicals. This may well be an example of a charge-transfer process [58]. In another paper, Zubov and co-workers [59] observed that ordinarily, radiation-initiated polymerizations of allyl acetate proceed sluggishly to low-molecular-weight products. However, upon the addition of phosphoric acid to the system, the rate of polymerization increases and solid polymers can be isolated. The proposed mechanism for this process involves the postulation of the formation of oligomers of allyl acetate with residual double bonds to which the phosphoric acid adds. This is thought to activate the polymerization of the oligomer. Other possible hypotheses for the activation by phosphoric acid involves chain-transfer reactions or the formation of complexes of phosphoric acid with allyl acetate monomer and allyl acetate free radicals [59]. 5.

POLYMERIZATION

OF ALLYL ESTERS OF

HIGHER MONOCARBOXYLIC A C I D S The synthesis of vinyl esters of the higher monocarboxylic acids is troublesome and costly. The preparation may involve transvinylation with vinyl acetate and the higher carboxylic acid with a costly mercuric salt as a catalyst. In this procedure, the equilibrium situation is unfavorable and yields of product usually are low. Altematively, a similar catalyst may be used for the addition of acetylene to the carboxylic acid. This procedure requires pressure equipment not usually available in a synthesis laboratory. The allyl esters, on the other hand are readily prepared by conventional esterification procedures. Therefore, they are of potential interest as plasticizers which might copolymerize with resins such as vinyl acetate that normally give rise to hard resins. Unfortunately, allyl esters of more ordinary carboxylic acids homopolymerize sluggishly. Their ability to enter into copolymer systems also seems to be marginal. Swem and Jordan [60] prepared the allyl esters of caproic, caprylic, pelargonic, capric, lauric, myristic, palmitic, and stearic acids. Attempts to bulk polymerize the compounds with 0.5% of dibenzoyl peroxide resulted in only a slight lowering of the monomers' iodine numbers, indicating very limited polymer formation. Copolymers with diallyl o-phthalate seemed to form with 1-20% of allyl esters. These copolymers were insoluble in acetone, amyl acetate, benzene, and acetic acid.

302

S. Polymerization of Allyl Esters

If the initiator concentration is reasonably high and heating is carried out for a sufficiently long time, allyl esters of fairly long-chain carboxylic acids have produced polymers. For example, after 24 hr at 80~ with 2% dibenzoyl peroxide, a 52% conversion of allyl stearate to its polymer is obtained [61]. Under similar conditions, conversion of allyl oleate is only 19%, allyl linoleate 5%, and allyl 10,12-octadecadienoate 3%. When allyl linoleate was heated with di-tert-butyl peroxide at 130~ for 24 hr, 21% of the monomer was converted to a polymer which was found to be partially soluble in methanol. It was postulated that under the reaction conditions, copolymerization of the allyl group of one molecule with a double bond of the acid portion of another molecule has taken place [61 ]. With a high-temperature initiator such as di-tert-butyl peroxide, copolymers of 1-octene with allyl propionate or allyl butyrate have been prepared in sealed tubes. The reaction conditions included methyl ethyl ketone as a solvent, 0.05% di-tert-butyl peroxide heated in sealed ampoules at 200~ for 4 hr. The molecular weights of the product were in the range of 600 _ 200 [62]. Allyl esters of long-chain carboxylic acids such as undecanoic: 10- and 11-phenylundecanoic; 10,11-dibromoundecanoic; 11-iodoundecanoic; 12-hydroxystearic; and 12-ketostearic acids do not copolymerize significantly with either styrene or methyl methacrylate. On the other hand, reasonably high conversions with significant concentrations of the ester in the copolymer are formed when these allyl esters are copolymerized with vinyl chloride [23]. Since the pressure inside the copolymerization apparatus is estimated to reach 8 atm or more at 60~ when vinyl chloride is the co-monomer, it is postulated that the effect observed by Walling and Pellon [24, 25] (that degradative chain-transfer is reduced at high pressure) comes into play here. While we believe that the pressure generated may be rather low for this Walling effect, the observed copolymerization is an experimental fact of significance. Generally, as expected, the rates of copolymerization are slow and conversions are low. Procedure 5-1 details the preparation of a copolymer of vinyl chloride and allyl 10,11-dibromoundecanoate. It should be noted that the directions are based on Chow and Marvel [23] which goes back to 1968, before the hazards of vinyl chloride monomer were appreciated. Therefore, no safety precautions which would be meaningful today are given. In fact, the whole concept of heating a sealed bottle containing vinyl chloride under pressure ~should be considered unsafe. On the positive side, the procedure does give details on a fractionation procedure for the copolymer. It is interesting to note that the fractions isolated by this procedure varies in composition~approximately 70% of the polymer (i.e., the high-molecular-weight fractions) was reasonably constant in composition while the low-molecular-weight fractions were richer in vinyl chloride.

5. Polymerization of Allyl Esters of Higher Monocarboxylic Acids

5-1.

303

Copolymerization of Vinyl Chloride and AUyl lO,11-Dibromo-undecanoate and Fractionation of the Copolymer [23]

NOTE: The directions given here are for reference only and require modification to conform with applicable safety regulations for the handling of the known carcinogens, vinyl chloride monomer and benzene. Read the MSDS for each chemical. In a tared pressure bottle of approximately l l0-ml capacity (i.d. 1.5 in. x length 7 in.) are placed 5 ml of benzene, 5.0 gm of allyl 10,11-dibromoundecanoate, and 0.10 gm of 2,2'-azobisisobutyronitrile. With proper safety precautions about 6 gm of vinyl chloride is charged to the bottle. This mixture is degassed three times to approximately 1 mm Hg and then filled with prepurified nitrogen. Then the excess of vinyl chloride is distilled off to leave 5.0 gm of vinyl chloride in the composition. The bottle is capped and placed in a protective metal sleeve. The polymerization bottle is tumbled end-over-end in a water bath at 60~ for 44 hr (approximately 2 half-life periods). The bottle is then cooled in a dry ice-acetone bath, opened, and carefully vented as the content warms to room temperature (precautions against exposure of personnel and the environment to the carcinogen vinyl chloride must be taken). The product is precipitated by the addition of methanol. The polymer is dried to constant weight under reduced pressure. Conversion is 57%, inherent viscosity 0.24 (in 0.2% solution in THF at 30~ 47.3% ester in polymer.

Polymer Fractionation A 4.465-gm sample of the polymer is dissolved in 70 ml of THF in a 200-ml beaker. To the solution is added 70 ml of methanol and 2 drops of concentrated sulfuric acid. After allowing the mixture to settle for 24 hr at room temperature, the first fraction is isolated by decanting the solvent into another beaker. The polymer in the first beaker is dried to constant weight. The solvent in the second beaker is treated with 30 ml of methanol and again allowed to settle for 24 hr to produce a second fraction of the polymer. This polymer fraction is isolated as the previous fraction and dried. To the filtrate is added 70 ml of methanol to yield a third fraction. The last fraction is obtained by adding 100 ml of methanol to the filtrate. Thus, 4.465 gm of polymer is dissolved in 70 ml of THF and precipitated with a total of 270 ml of methanol. Table VIII gives details of the properties of these fractions. With vinyl chloride (caution: known carcinogen) as the major component, copolymers of allyl laurate and vinyl chloride have been prepared by a suspension-polymerization procedure. In a typical formulation, 2.5 gm of allyl laurate,

8. Polymerizationof Allyl Esters

304

TABLE VIII Fractionation of a Vinyl Chloride-Allyl 10,11-Dibromoundecanoate Copolymer [23]

Fraction No.

Cumulative volumes (ml) of methanol added to 4,465 gm of Copolymer in 70 ml of THF

1 2 3 4

70 100 170 270

a

Polymer recovered (%)

Inherent viscosity of fraction (at 30~

Allyl ester content (%)

0.26 0.21 0.13 0.07

54.4 53.8 45.3 44.9

11.4 60.1 16.8 5.0a

93.3% recovery of polymer from the fractionation.

200 gm of water containing 0.05 gm of poly(vinyl alcohol), and 97.5 gm of vinyl chloride are heated with 0.07 gm of lauryl peroxide at 65~ [63]. In copolymerizations involving allyl esters, chain transfer between the allylic portion of the comonomer and the growing chain leads to termination of the growing polymer and, consequently, to low molecular weight products. To reduced the possibility of chain transfer by abstraction of the allylic hydrogen during copolymerization with vinyl acetate, the effect of varying the electron density around the alpha carbon atom was studied. This involved the copolymerization of vinyl acetate with a variety of allyl esters. In Table IXa the esters are listed with their reactivity ratios and the Alfrey-Price Q - e parameters for the copolymerization of these monomers with vinyl acetate. The polymerizations were carded out by a bulk process in sealed, heat resistant bottles at monomer ratios ranging from equi-molar to 9 mol of the allyl monomer to one of vinyl acetate with 0.1% by weight of dibenzoyl peroxide at 60~ for up to 168 hr in some cases. Even so, the polymer yields were less than 5% [64]. The molecular weights of the copolymers ranged from 10,000 to 150,000. It is to be noted that in every case, the product of rl r2 is less than unity. Therefore each monomer pair can copolymerize easily. However, at mole percentages of TABLE IXa ReactivityRatios and Q-e Parameters for Copolymerization of Allyl Esters (MI) with Vinyl Acetate (M2) [64] Allyl monomer

rl

r2

rl r2

Allyl acetate Allyl propionate Allyl butyrate Allyl isobutyrate Allyl trimethylacetate Allyl valerate

0.70 0.42 0.64 0.51 0.34 0.58

1.00 1.29 0.97 1.04 1.15 1.07

0.70 0.54 0.62 0.53 0.39 0.62

e -

1.48 1.66 1.57 1.68 1.85 1.57

Q 0.044 0.040 0.049 0.050 0.053 0.045

305

6. Polymerization of Allyl Acrylate and Methacrylate TABLE IXb Reactivity Ratios Allyl Acetate (M~) with Other Monomers (M2) [65] M2

rl

r2

El r2

Methyl methacrylate

0.024 +_0.009 0.04 +__0.04 0.021 _0.001

41 6 11.7 1 66 4

0.98

Butyl acrylate Styrene

0.47

75 or more of allyl valerate, little copolymerization took place. In the case of the allyl trimethylacetate-vinyl acetate copolymerization, deviations from ideal random copolymerization were noted. Some recent NMR studies on the copolymerization of allyl acetate with methyl methacrylate, butyl acrylate, and styrene reported their reactivity ratios (cf. Table IXb) [65]. The reported error terms, if we assume them to be standard deviations, are quite large with respect to the rl term. Therefore it is problematic whether these numbers are really meaningful. It would seem to us that the large r2 terms imply that substantially only homopolymers of these three "vinyl" monomers form. This situation is modified in the case of allyl methacrylate or allyl acrylate copolymers, as will be mentioned below. With these acrylic derivatives, copolymerization depends on the acrylic bonds primarily with modifications due to the allylic hydrogen. Subsequently, the allylic units in a copolymer of allyl methacrylate with butyl methacrylate, for example, will be the sites for crosslinking. 6.

POLYMERIZATION METHACRYLATE

OF ALLYL ACRYLATE AND

Allyl acrylate and methacrylate are reasonably simple to synthesize. In fact, allyl methacrylate is manufactured in bulk quantities. Since each of these monomers contains two double bonds of distinctly different susceptibility to polymerization when considered individually, these monomers are interesting both from the practical as well as the theoretical standpoint. Early interest in allyl methacrylate arose from the concept that it was possible that this monomer would copolymerize with methyl methacrylate through its methacrylate bonds. The resulting resin could then be shaped, for example by injection molding, since it was still thermoplastic. After the molding had been completed, a separate heating cycle would bring about crosslinking through the allyl bonds to produce hard thermoset materials. Early applications in the production of plastic dental prostheses were visualized.

306

& Polymerization of AIlyl Esters

The use of these monomers for radiation cross-linking of polyethylene has been suggested [66]. With benzophenone as a photosensitizer, atactic as well as isotactic polypropylene is crosslinked with allyl acrylate by UV radiation. In this process both types of double bonds react [67]. Elastomers such as ethylenevinyl acetate copolymer have been cross-linked with this monomer on a roller mill at 150~ using dicumyl peroxide as the initiator. Such cross-linked elastomers exhibit little or no swelling with aromatic solvents or chloroform after 24 hr at 30~ conditions under which the uncured elastomers ordinarily dissolve [68]. Despite these interesting applications for such monomers, the bulk of the commercially produced allyl methacrylate finds application as a synthetic intermediate rather than as a monomer. One of the early theoretical studies of the polymerization of allyl acrylate considered the "homopolymerization" of this monomer to be an "intramolecular copolymerization" of the allyl and the acrylic double bonds. In this process it was calculated that only about 3% of the allyl groups participated in the process. Upon extended heating, the residual allyl groups served as cross-linking sites [69]. An examination of the earlier allyl methacrylate literature by Butler [51] indicated to him that the results reported by earlier investigators may be explained, in part, by assuming that cyclization of allyl acrylate or methacrylate takes place to some extent before gelation takes over. Blout and co-workers [70, 71] studied the initiation of allyl methacrylate using biacetyl and UV radiation at low temperatures and using benzoyl peroxide at higher temperatures. At I~ gelation occured only after 39% conversion, whereas gelation at higher temperatures took place at 6% conversion. Data on the unsaturation of the soluble prepolymers might be used to postulate cyclization polymerizations. At the time of this work, however, this concept had not yet been established, hence this factor was not considered. The bulk polymerization of allyl acrylate with benzoyl peroxide as initiator to 10% conversion gave a brittle, glassy polymer which was considered partially cyclized with a Kc (ratio of rate of cyclization to the rate of bimolecular propagation, cf., Table IV) of 0.41 moles/liter [72]. The polymer was described as soluble in both toluene and in carbon tetrachloride. Two possible structure of the cyclic radicals which may be involved in the polymerization of allyl methacrylate are given in Fig. 6. Procedure 6-1 is an example of the solution polymerization of allyl methacrylate using benzoyl peroxide as initiator. The polymer is said to be thermoplastic.

6-1. Solution Polymerization of Allyl Methacrylate

[74]

In a 100-ml, round-bottom flask fitted with a reflux condenser, a solution of 10 gm of allyl methacrylate and 0.7 gm of recrystallized benzoyl peroxide in

307

6. Polymerization of Allyl Acrylate and Methacrylate

Ha/cH_.2 R --CH2-- C CHI I O --C ~ O / C H 2

CH3 I R --CH2-- C ~ C H --CH2" I I O - - C ~O ./CH2

(a)

(b)

Fig. 6 Structures of cyclic allyl methacrylate free radicals [73]. (a) cLlactone unit with carbonyl stretch frequency at 1740 cm-l and 1230 cm-i. (b) y-lactone unit with carbonyl stretch frequency at 1775 cm -1 and 1275 cm - l

56 gm of dry acetone is heated at reflux for 1.5 hr. The solution is then cooled and carefully poured with vigorous stirring into 1 liter of methanol. The precipitated polymer is collected on a filter, dried under reduced pressure at room temperature. The product is fusible and soluble in acetone. Upon heating under a slight pressure at 90~ the polymer fuses and converts to an insoluble, infusible material. By conventional emulsion polymerization procedures, a crosslinked copolymer of butyl acrylate and 1% allyl methacrylate was formed in the presence of methyl methacrylate. Then additional methyl methacrylate is polymerized in the system. The resultant product was a poly(methyl methacrylate) with improved impact resistance [75]. In toluene solution, syndiotactic block copolymers of methyl methacrylate (PMMA) and allyl methacrylate were formed using triphenylphosphine and triethylaluminum as initiator [76]. In acetone solution, syndiotactic poly(methyl methacrylate) forms a stereocomplex with other syndiotactic polymers. The complex formed with syndiotactic poly(allyl methacrylate), upon separation from the reaction mixture and drying had a melting point of 141.5~ by DSC thermogram. From X-ray powder patterns of this and related complexes of PMMA with other polymethacrylates, the authors postulate that a doublestranded helix may represent a model of the structure of these complexes [77]. Oligomerization of allyl methacrylate apparently takes place when the initiator is either triethylaluminum or chlorodiethylaluminum. If dichloroethylaluminum was used as a catalyst, only Friedel-Crafts type alkylations took place [78]. Copolymers containing allyl methacrylate have found application as an additive to other resin to enhance the properties of the system. For example, in one patent disclosure, an aqueous emulsion polymer was formed in water using 0.03 gm of sodium carbonate, 50 gm of methyl methacrylate, 2.0 gm of ethyl acrylate, and 0.1 gm of allyl methacrylate, and 0.40 gm of the sodium salt of an allyl C13-alkyl ester of sulfosuccinic acid. The polymerization was initiated with sodium persulfate and heated at 83~ for 1 hr. To this latex, 40 gm of butyl acrylate, 10 gm of styrene, 1.0 gm of allyl methacrylate, and another 0.40 gm of the above surfactant were added while polymerization continued. In a third

308

& Polymerizationof Allyl Esters

stage, more methyl methacrylate and ethyl acrylate were added. The resultant latex was dried, ground to a fine powder and with melting and kneading combined with a methyl methacrylate-co-ethyl acrylate resin. The final composition was said to exhibit improved physical properties [79]. While this patent is somewhat overly complex, our main point is that evidently allyl methacrylate may be incorporated readily in a conventional latex copolymerization process. For the manufacture of a resin that is to be used for soft, water-containing contact lenses with high oxygen permeability, good mechanical strength, and heat resistance, a copolymer of 2-hydroxypropyl isopropyl fumarate and allyl methacrylate has been the subject of a Japanese patent disclosure [80]. Presumably these polymers were formed by a bulk polymerization process. Allyl a-(hydroxymethyl)acrylate and ethyl tx-[(allyloxy)methyl]acrylate have been synthesized. Their polymerization behaviors were studied in bulk and in benzene solution. The bulk polymerizations were carried out with 0.5-1% AIBN at 50~176 The solution polymerization of the (allyloxymethyl)acrylate was carried out for five days at 70~176 using as initiator 2-[(carbamoyl)azo]isobutyronitrile. The typical yield was 90%, the intrinsic viscosity taken in chloroform was 0.18 dl/gm. The allyl tx-(hydroxymethyl)acrylate polymerized to a product that was insoluble but slightly swellable. It exhibited considerable residual unsaturation. Presumably, a typical acrylic polymerization had taken place. The product formed from ethyl ~x-[(allyloxy)methyl]acrylate was more complex. After initiation, during the propagation step, 5-membered, tetrahydrofuran-structures form by an intramolecular addition step. Figure 7 shows the proposed structure of this polymer [80a]. With UV radiation, it is possible to interrupt the polymerization process before gelation takes place, at 25-27% conversion. In Procedure 6-2, it should be noted that the reaction mixture must be cooled to prevent premature gelation. Details about the apparatus to be used are given in Procedure 6-3.

6-2.

Ultraviolet-Initiated Polymerization of Ailyl Methacrylate with Benzoyl Peroxide ['/0]

In a 500-ml Vycor flask is placed 200 grn of allyl methacrylate and 0.6 grn of benzoyl peroxide. While stirring vigorously and while continuously maintaining a nitrogen atmosphere over the monomer, the flask is cooled by running water to 10~ • 5~ The mixture is exposed to a Hanovia Luxor L UV arc with all due safety precautions. The polymerization is continued for 1 to 2 hr. Before the mixture gels, it is removed from the source of radiation (25-27% conversion). This point may also be determined by following the change in refractive index of the reacting mixture or by precipitating the polymer.

6. Polymerization of Allyl Acrylate and Methacrylate

309

I

Et Fig. 7 Proposedstructure of poly{ethyl a-[(allyloxy)methyl]acrylate}[80a]. When a similar reaction mixture is polymerized thermally at 75~ gel forms after only 6% conversion [71]. Below 25~ visible light (photoflood lamps) or UV radiation may induce the decomposition of benzoyl peroxide or of biacetyl. These decompositions, in turn, bring about polymerization of the monomer. Biacetyl is activated by visible radiation in the range of 400--460 nm. Benzoyl peroxide is activated in the long UV wavelength range of 350-380 nm. The increase in the extent of conversion at the gel point at lower temperatures is accompanied by a reduction of the product's molecular weight. Since the rate of initiation under radiation remains high and the rate of termination is not affected because of its low activation energy, the decrease in molecular weight has been attributed to a decreased rate of chain growth. This may also be attributed to cyclization taking place under these conditions. The extent of polymerization at the gel point is more dependent on the rate of polymerization when biacetyl is used to initiate the process than when benzoyl peroxide is used. Procedure 6-3 illustrates the use of biacetyl as an initiator for the polymerization of allyl methacrylate at a low temperature. It should be noted that after 200 min the gel point is reached at 30% conversion.

6-3.

Ultraviolet-Initiated Polymerization of Allyl Methacrylate with Biacetyl [71]

a. E q u i p m e n t

The UV-initiated polymerization of allyl methacrylate is carried out in a 500-ml Pyrex or Vycor Erlenmeyer flask with a side arm. The front of the flask is painted black except for an area of 4 x 11 cm which assures that a constant area is exposed to the radiation source. The back and bottom of the flask is covered with aluminum foil. The side arm is used for withdrawing samples periodically. The charged flask is kept in a stirred, water thermostat controlled to +__1~ Preparations are run under a slight positive pressure of purified nitrogen. An ordinary R-2 photoflood lamp is used as a source of visible radiation. As a source of UV radiation, a quartz Hanovia Luxor L arc is used. This source had an aluminum reflector. It is placed approximately 2.5 cm from the nearest part of

310

8. Polymerization of Allyl Esters

the clear area of the Vycor flask. The source requires a minimum of 12 min to reach maximum intensity. It is the usual practice to shield the reaction mixture for a full 20 min before exposure to the radiation source. This assures constancy of the radiation.

b. Polymerization To the equipment described in Section a, with suitable protection of personnel against radiation, is charged 200 ml of allyl methacrylate and 0.6 gm of biacetyl. The monomer solution is cooled to I~ and, after the radiation source has reached constant intensity (about 20 min), the monomer mixture is exposed to the radiation at 1~ Samples of the mixture may be withdrawn from time to time and studied. The samples are treated with a small quantity of pyrogallol and then added to an excess of methanol. The methanol mixture is cooled to -50~ The polymer is isolated by centrifugation. The polymer may be dissolved in a minimum amount of acetone, reprecipitated with methanol, and dried under reduced pressure at room temperature. After 200 min of exposure, approximately 30% conversion is achieved. Before gelation sets in, the irradiation is terminated. Table X outlines the results of a number of polymerizations of allyl methacrylate carried out using Procedure 6-3. The reduced viscosities of the isolated polymers are given in Table X. In several cases the reduced viscosities are given for polymer samples taken as the preparation proceeded but before the gel point had been reached. Printing plates have been prepared which depend on the photopolymerization of allyl esters to generate an image [81 ]. As an etch resist for printed circuits, a solution of a prepolymer of allyl methacrylate, benzil, and 4,4'-bis(dimethylamino)benzophenone in methyl isobutyl ketone-cellosolve acetate was coated on a substrate. After exposure to UV, the image was developed with methyl ethyl ketone [81 ]. Among the UV sensitizers, some of which may accelerate the crosslinking rate by 100-200 times that of ordinary free-radical initiated processes, are ethers of benzoin, benzophenones, anthrone, benzil, and Michler's ketone [81]. Anion-initiated polymerizations of allyl methacrylate have been studied. For example, Walling and Snyder produced a polymer using finely divided sodium in benzene, under nitrogen, at 25~ for 22 hr [82]. The widely quoted article by Donati and Farina [83] detailed the use of either butyl lithium or phenylmagnesium bromide to produce solution polymers of allyl acrylate at 50~ in toluene without gel formation even at conversions greater than 70%. The resulting polymers are noncyclic, stereoregular, crystalline polyacrylates. Evidently only the acrylate group polymerizes in their process [83].

7. Polymerization of Diallyl Carbonates

311

TABLE X Polymerization of Allyl Methacrylate: Rates, Gel Points, Viscosities [71] Gel point Initiator (gm/1O0 ml)

Activator

Temp (~

Reaction (%)

Time (min)

0.3

Biacetyl

UV

1

36

200

3.0

Biacetyl

UV

1

39

420

0.3 0.3

Biacetyl Biacetyl

UV UV

15 15

33 33

95 78

0.3

Biacetyl

UV

25

31

41

0.3

Biacetyl

Photoflood

15

29

70

0.3 2.0 0.3 0.3

Biacetyl Bz202 Bz202 Bz2026 + 0.1 Biacetyl Bz202

Photoflooda UV UV UV

15 15 15 15

19 22 19 29

95 53 90 82

Heat

75

6

8

0.3

Reduced viscosity of polymer,

[Y/]sp/C 0.12 0.32 0.25 0.33 0.30 0.21 0.37 0.22 0.41 0.22 0.70

0.79

2.0

a Light source 15 cm from the reaction. Normally the source of radiation was kept at 2.5 cm from the reactor. bAn early preparation run under a stream of nitrogen in an unmasked flask.

Lithium dispersions have also been used to prepare soluble p o l y m e r s high conversions [84]. The pendant allyl groups m a y be used to cross-link the p o l y m e r with sulfur and sulfur m o n o c h l o r i d e [84]. A brief review o f the radical and anionic polymerization o f allyl acrylate and allyl acrylamides has appeared in Spanish [85].

7.

POLYMERIZATION OF DIALLYL CARBONATES The m o n o m e r diethylene glycol bis(allyl carbonate) (Structure IV) 0 0 II II CH2-- CH-- CH2-- O-- C-- O-- CH2-- CH2-- O-- CH2-- CH2-- O-- C-- O-- CH2-- CH =CH2 (w)

has considerable commercial value as a highly transparent, hard, scratchresistant resin for use in high-quality, plastic lenses. Both the m o n o m e r and p o l y m e r have been designated by the tradename "CR-39." The m o n o m e r is also

312

8. PolymerizationofAUylEsters

referred to as "allyl diglycol carbonate." While other diallyl carbonate derivatives have been studied [86], the primary interest has been in CR-39-monomer and its polymerization. Like most allyl esters, diethylene glycol bis(allyl carbonate) requires high concentrations of initiators for conversion. Even then, to complete the process, extensive postcures are required. Since the monomer is reasonably nonreactive, solutions of up to 5% of benzoyl peroxide in CR-39-monomer may be stored at 10~ or lower. If diisopropyl peroxydicarbonate is used, monomer solutions of this material must be stored below - 5 ~ The polymerization is air inhibited. With care a noncross-linked syrup can be prepared which finds application as an optical cement. Whether this material is a cyclic prepolymer seems not to have been considered. Such structures would have tings with 16 members. Procedure 7-1 is an early example of the preparation of a thermoplastic resin in solution.

7-1.

Solution Polymerization o f Diethylene Glycol Bis(atty! carbonate) [86]

In a four-necked, 500-ml flask fitted with a reflux condenser, mechanical stirrer, thermometer, and a means of maintaining a nitrogen atmosphere, are placed 100 gm of diethylene glycol bis(allyl carbonate), 100 gm of dioxane, and 4 gm of dibenzoyl peroxide. The mixture is stirred and the air is displaced with nitrogen. Then the reaction solution is heated between 80 ~ and 85~ until a noticeable increase in viscosity is observed. The reaction mixture is then cooled to room temperature. Methanol is added until the solution becomes slightly turbid. Then the turbid mixture is added with vigorous stirring to five times its volume of methanol. The polymer is filtered off and dried under reduced pressure. This granular, white product, on mixing with 5 wt% of dibenzoyl peroxide, at 145~ and with the application of a pressure of 13.79 MPa (2000 psi), produces a transparent, infusible sheet. To prepare glazing, transparent sheets are cast in cells made of plate glass with flexible gaskets used as spacers (cf., Sandier and Karo [87], Procedure 4-2 for a detailed description of a glass casting cell). Control of the polymerization temperature used with such cells varies considerably with the thickness of the polymer sheet to be produced. For example, a sheet 3- to 5-mm thick can be prepared at 70~ with a monomer solution containing 3% of dibenzoyl peroxide over a period of 60-72 hr in a circulating air oven. After the sheet is removed from the cell, it is postcured at 115~ for an additional 2 hr. With thicker sheets, lower initial temperatures are required to permit proper dissipation of the heat of polymerization. If diisopropyl peroxydicarbonate (also known as isopropyl percarbonate or DIPP) is used in a single temperature process, the polymerization may be carried

313

7. Polymerization of Diallyl Carbonates

out at 45~ for about the same length of time (60-70 hr) [88] . At a constant initial polymerization temperature, the process starts rapidly. As the initiator level decreases with time, the rate of polymerization also levels off. Therefore, the prolonged heating cycles indicated above are necessary to produce good castings by a single temperature process. The process can be substantially sped up by increasing the reaction temperature as the process progresses. Dial et al. [88] go into considerable detail about the method of determining a heating schedule for a CR-39 casting process in which the rising processing temperature approximately maintains a constant rate of initiator decomposition along with a constant rate of polymerization. It was found that the kinetics of the polymerization of diethylene glycol bis(allyl carbonate) differed substantially from that of allyl acetate. This was attributed to the early establishment of a three-dimensional, crosslinked network in the case of the diallyl ester. 1 9 Procedure 7-2 outlines a procedure for the preparation of a 3-1n. cast sheet using a temperature schedule based on data found in Dial et al. [88].

7-2.

Preparation o f Diethylene Glycol Bis(allyl carbonate) Cast Sheet [88] 1

9

In a glass casting cell [cf. 76a] prepared from ~-m. plate glass with a spacer 1 9 sufficient to give a ~-ln. thick final sheet, cooled to 20~ is placed a cool (20~ solution of diethylene glycol bis(allyl carbonate) containing 4 wt% based on the monomer of diisopropyl peroxydicarbonate (DIPP). With appropriate safety precautions the cell is placed vertically in an explosion-proof, air oven and heated according to the following heating cycle. Time (hr) Initial 1

2 3 4 5

Temperature (~ 56 58 64 72 90 90 (end of cycle, cool to room temperatures)

The cell is then disassembled. By the use of temperature schedules of this sort, satisfactory, clear sheets can be prepared in between one-eighth to one-fourth the time normally required for a single temperature process. The effect of sheet thickness on the required temperature cycles is given in detail in Dial et al. [88]. Here we give the range of temperatures and times for comparative purposes.

& Polymerization of Allyl Esters

314

Sheet thickness (in.) 1

l-g 1 1 16-8 1 3 8-8 1

Total process time (hr)

Temperature (~ Initial

Final

12 15 17 24

45 46 44 39

90 105 105 105

It will be recalled that monoallyl esters undergo degradative chain-transfer during polymerization. This process results from the abstraction of a hydrogen atom adjacent to a double bond by one free radical to form a stabilized allylic radical. Beyond the gel point of the polymerization of diallyl esters, however, degradative chain-transfer is less significant. Thus, during the polymerization process there is a gradual shift from degradative chain-transfer to effective chaintransfer. In fact, even before the gel point is reached, effective chain-transfer is said to play a significant role in the polymerization of diallyl esters, presumably because more than a single, physical chain is involved per kinetic chain. To visualize the process, it should be considered that early in the polymerization, allylic radicals are mobile and combine rapidly with each other. As the process proceeds, the allylic radicals formed by degradative chain-transfer are confined by their attachment to the crosslinked polymer network. Their ability to combine with each other is reduced whereas their ability to add to double bonds becomes somewhat more favored. The local rate of polymerization will increase as the degree of crosslinking increases. This could lead to uneven contraction of the resin, particularly if the initiator concentration is low. Greater uniformity of the polymer is achieved with higher levels of initiator [89]. Incidentally, it was discovered that heating the monomer for prolonged periods prior to adding initiator, increases the rate of polymerization without changing the time required to reach the gel point [89]. The preparation of poly(allyl carbonates) from preformed poly(allyl alcohol) has been discussed. In this preparation, a poly(allyl alcohol) of MW approximately 13,000 is treated in a solution of dimethyl sulfoxide, triethylamine, and dioxane with ethyl chloroformate. The resultant polymer is insoluble, contains a high proportion of carbonate units and some eight-membered ring structures [90].

8.

POLYMERIZATION OF DIALLYL ESTERS OF PHTHALIC ACIDS

The diallyl esters of o-phthalic and of isophthalic acids are commercially available both as monomers and as low-molecular-weight prepolymers. Diallyl terephthalate has been studied only occasionally. Diallyl chlorendate is of

8. Polymerization of Diallyl Esters of Phthalic Acids

315

interest in copolymer systems since its high chlorine content is thought to contribute to the flame resistance of organic materials. The most extensive research and development activity has involved diallyl o-phthalate. The studies on the cyclopolymerization of this monomer have already been discussed at length in Section 3 of this chapter. Diallyl isophthalate polymerizes more rapidly than the the ortho-isomer. It cyclizes less during the early stages of polymerization. Consequently the prepolymer of the isophthalate has more reactive double bonds available for further reaction than the o-phthalate and the final resin produced from it is more highly cross-linked [91]. The methods of polymerization of the diallyl phthalates deal with control of the process to permit isolation of the thermoplastic prepolymer before the fully cured, crosslinked resin is formed. Simply heating diallyl o-phthalate with benzoyl peroxide at 115~176 produced a highly cross-linked thermoset resin [92]. The usual methods of producing "prepolymers" involve the interruption of the polymerization process before gelation sets in (at about 25% conversion). One novel method of polymerization without the use of any peroxide initiator involves heating diallyl o-phthalate under nitrogen in the presence of metallic copper. Below 205~ copper acts as a retarder of the polymerization. However, above 225~ it accelerates the process (at about 215~ it neither inhibits nor accelerates) [93]. Shokal and Bent [93] pointed out that the course of the polymerization may be monitored by taking the refractive index of the solution of the prepolymer in the monomer. The refractive index of the pure monomer is n2o5 1.5185. For each 1% of soluble polymer formed, the refractive index increases by 0.0005 units. Thus, at 25% conversion the refractive index of the solution is approximately n2D5 1.531. The isolation of the prepolymer from the reaction mixture usually involves its precipitation with an alcohol or some other nonsolvent. Two Japanese patents are based on this well-known phenomenon. In one, 100 gm of a prepolymer solution containing 25% of the prepolymer is treated at 40~ with 200 gm of ethanol in an extractor operating at 200 rpm for 5 min. After a second extraction at 65~ for 5 min with 240 gm of ethanol, 25 gm of the white prepolymer is isolated. Propanol, isobutanol, and isopropanol may also be used. The process is also applicable to poly(diallyl isophthalate) [94]. For poly(diallyl terephthalate) the use of methanol at 40~ followed by a second extraction with methanol at 65~ is patented [95]. Using high-temperature initiators such as dicumyl peroxide or tert-butyl perbenzoate at high temperature, the expected oxygen inhibition from the environment is substantially reduced and the polymerization proceeds at a reasonable rate [96].

316

&

Polymerizationof Allyl Esters

The use of a high-temperature initiator actually goes back to a 1947 patent. In that patent, di(tert-butyl)peroxideis used as an initiator at 65~ This is curious since the half life of this peroxide at 100~ is over one week! We wonder whether this may not be a typographical error. At 135~ for example, the half life would be about 4 hr, which would be much more reasonable. However, in Procedure 8-1 we follow the original directions [97].

8-1.

Bulk Polymerization of Diallyl o-Phthalate with High-Temperature Initiator [97]

In a l-liter flask fitted with mechanical stirrer, a nitrogen bleed, a means of withdrawing samples, and a thermometer is placed 100 gm of diallyl o-phthalate and 2 gm of di(tert-butyl)peroxide. The mixture is heated with stirring under nitrogen at 65~ (see note in preceding text) until the refractive index of the solution reached n2D5 1.5313. Then the reaction mixture is slowly poured, with stirring, into 600 ml of methanol. The semisolid prepolymer is filtered off and dried under reduced pressure. The product is soluble in a mixture of 3 parts of toluene and 1 part of xylene. This solution may be used as a bake-on coating on steel at 150~ for 1 hr. A hard, flexible, transparent, water-white film forms. The prepolymer has also been prepared in two stages at two different temperatures using two initiators which operate at two distinctly different temperatures like tert-butyl hydroperoxide and di-tert-butyl peroxide [98]. In a strictly thermal process, diallyl o-phthalate has been polymerized at 200~176 The conversion of monomer to polymer was followed by checking the change in refractive index with time. The process was "short stopped" before the gel point was reached by adding a solvent which separated unreacted monomer from the polymer [99]. The classical work by Simpson and co-workers on the cyclization of diallyl o-phthalate during polymerization was carried out in sealed ampoules [32, 41 ]. Procedure 8-2 outlines their method.

8-2.

Sealed-Tube Bulk Polymerization of Diallyl o-Phthalate [32, 41]

A solution of 11.200 gm of recrystallized dibenzoyl peroxide in 1 liter of redistilled diallyl o-phthalate at 20~ is prepared. This solution contains 1 wt% of initiator [0.0463 mole/liter]. Twenty-gram portions of this solution are placed in Pyrex ampoules which are degassed several times and sealed under reduced pressure. The ampoules are places in protective sleeves and heated in a bath thermostated at 80 ~ +__0.25~ At intervals ampoules are removed to establish kinetic data points (cf. Table I).

8. Polymerization of Diailyl Esters of Phthalic Acids

317

The ampoules are cooled and opened. The contents of the ampoules are precipitated by addition to redistilled ethanol which has been denatured with methanol. The polymer is then dissolved in a minimal quantity of acetaone and again precipitated with denatured ethanol. This process is repeated another time. Then the polymer is dried to constant weight under reduced pressure. The filtrates are checked for dissolved low-molecular-weight products by dilution with water. In no case is such material found to be present. For molecular weight determinations, approximately 5 gm of the polymer is dissolved in benzene. The benzene solution is cooled to 0~ and, while maintaining a temperature of 0~ the benzene is sublimed off under reduced pressure for 24 hr. The polymer is finally maintained at 2 mm Hg at room temperature for 14 days. The residual benzene in no case was more than 1.5%. The polymer treated in this manner is used for molecular weight determinations and to determine the degree of unsaturation. The conversion of the monomer to polymer may be determined simply by precipitating aliquots of the reacting solution with methanol, washing the polymer with a 1% solution of hydroquinone in methanol, and finally drying the polymer to constant weight at 100~ In connection with bulk polymerization experiments of diallyl o-phthalate, it should be pointed out that this monomer behaves quite differently from vinyltype monomers in that its rate of polymerization increases linearly with initiator concentration. This phenomenon is conveniently studied by use of a gel-time meter [ 100]. This instrument also is used to demonstrate that hydroquinone is a more effective inhibitor of the polymerization of a 1% solution of dibenzoyl peroxide in diallyl o-phthalate at 100~ than t-butyl catechol [ 100]. While Procedure 8-1 purports to illustrate the use of a high-temperature initiator to bring about polymerization at the relatively modest temperature of 65~ a more recent patent details the use of a high-temperature initiator at a high temperature (200~ At that temperature the half life of the initiator tertbutyl hydroperoxide is approximately 60 min in an aromatic solvent. The polymerization is carried out for 780 min (13 hr). It is noted that the process is quite rapid during the first 20 min. Thereafter the process is said to be quite slow. Since the initial initiator concentration is deliberately kept quite low, it is possible that the reduction of the polymerization rate is related to the destruction of a substantial portion of the hydroperoxide relatively early in the process [101]. Procedure 8-3 is given here only for purposes of illustration since the procedure is patented.

8-3.

Bulk Polymerization of Diallyl o-Phthalate at 200~ [ 101 ].

In a 22-liter, four-necked flask fitted with mechanical stirrer, a sampling and addition line, a thermometer and means of maintaining a nitrogen atmosphere

318

8. Polymerization of AIlyl Esters

over the monomer is placed 11.6 kg of diallyl o-phthalate (haD5 1.5181). The equipment is flushed with nitrogen and a slow stream of nitrogen is maintained in the flask throughout the preparation. The monomer is heated with stirring to 200~ and is maintained at 200~ throughout the process. The time required to reach 200~ is approximately 75 min. Then a solution of 150 mg of tert-butyl hydroperoxide (i.e., 13 ppm on the monomer) is added rapidly. Stirring and heating is continued for 13 hr. From time to time, samples are withdrawn and refractive index and viscosity determinations are made. These observations are as follows: Time (min) sample was taken (after initiator addition)

Refractive index of cooled sample, n2D5

Viscosity of sample cPs at 25~

0 20 40 120 190 250 280 310 370 430 490 550 610 650 690 720 750 770 780

1.5185 1.5209 1.5224 1.5235 1.5248 1.5255 1.5260 1.5265 1.5275 1.5282 1.5290 1.5300 1.5310 1.5316 1.5324 1.5329 1.5332 1.5335 1.5339

50 65 75 100 145 180 255 285 340 400 450

The product solution from several runs is then fed into a wiped still at a rate of 6 kg/hr at 195~176 at 80 p. With a residence time of 2 min, 72 parts of distilled monomer and 28 parts of polymer are isolated. A variety of techniques have been used to monitor the course of the polymerization of diallyl o-phthalate. The traditional methods of precipitating the polymer from the polymerizing solutions lend themselves only to that portion of the process in which gelation has not yet taken place. Methods of studying postgelation kinetics are few. Generally such studies are made on bulk polymers. Starkweather and Eirich [89] determined the refractive index of the crosslinked polymer by floating cylindrical samples on solvent mixtures which were adjusted until the composition had the same refractive index as the polymer. Then the refractive index of solution was measured with an Abbe

8. Polymerization of Diallyl Esters of Phthalic Acids

319

refractometer. For resins of diallyl o-phthalate, mixtures of bromobenzene and carbon disulfide were used. We presume that today with chemical microscopic technique more widely known than in 1955, the refractive indices of polymer samples would conveniently be taken under an optical microscope using standardized, commercially available refractive index fluids. In any case, using the refractive indices of polymer samples isolated at given time intervals after initiation and the densities of each polymer sample, the unit refraction R was calculated with the Lorenz-Lorentz equation:

[R]

=

2

+ 2

where [R], unit refraction; n, refractive index of a given polymer sample; M, MW of the monomer; p, density of the polymer sample under consideration. The unit refraction may be predicted from the sum of the molar refraction equivalents for the atomic units and for structural features such as double bonds. The unit refraction may be correlated to percent conversion. In the case of diallyl o-phthalate, it was found that the ultimate conversion reached about 60% regardless of initiator concentration. In another procedure, a special cell was constructed to fit an infrared spectrophotometer. This absorption cell was electrically heated. As the polymerization in this apparatus proceeded, it was scanned by the spectrophotometer. The absorption band at 1598 cm -1 was attributed to the aromatic double bond vibration which did not change in intensity during the process. On the other hand the allylic double bond stretching at 1645 cm -~ changed with time. Therefore, the ratio of the percent transmission at 1645 cm -1 to that at 1598 cm-1 was considered a measure of the disappearance of the allylic double bond concentration even beyond the gel point [44]. The isothermal bulk polymerization of diallyl o-phthalate was also measured by following the change in electrical resistivity as the polymerization took place. With increasing conversion, the resistivity increased [ 102]. Unfortunately, these methods do not seem to have a means of detecting the gel point. When the individual measurements made by any of these techniques were plotted against time, smooth curves resulted. There were no significant changes in curvature at the gel point. The exception to this generalization was the technique of Cass and Burner [ 100], which depends on a simple stirring device which stops when the viscosity of a polymerizing system reaches a certain high value. Otherwise the gel points were determined visually or by poking at the polymer. The control of the molecular weight of the prepolymer of diallyl o-phthalate has led to several processes which may be considered solution polymerizations in which the solvent serves also as a chain-transfer agent. Procedure 8-4 is an adaptation from a patented process given here to illustrate the process. In this

320

& Polymerization of Allyl Esters

procedure, the initiator has a considerable effect on the conversion and on the molecular weight of the product as indicated by viscosity measurements of 25% solution of the polymer in its monomer [ 103]. In Procedure 8-4, the initiator is 50.4% hydrogen peroxide. This compound is quite hazardous. While its appearance is similar to plain water, spills on the skin cause severe bums. Spills on paper, etc., may cause fires. While the author of the patent, which we present here, ran the polymerization under a nitrogen atmosphere, we question the need of eliminating atmospheric oxygen by this method, or by any method, in view of the fact that the initiator--hydrogen peroxide--is capable of furnishing oxygen to the system in its own fight.

8-4.

Solution Polymerization of Diallyl o-Phthalate

[103]

In a 2-liter, resin kettle equipped with a mechanical stirrer, reflux condenser, thermometer, and a means of maintaining the reaction mixture under a nitrogen atmosphere, a solution of 886 gm of diallyl o-phthalate, 62.2 gm of anhydrous isopropanol, and 7.5 gm of 50.4% hydrogen peroxide is heated with stirring, under nitrogen at reflux (104~176 for 10 hr. At the end of this time, the viscosity of the reaction mixture, at 106~ is 27 cPs. The reaction mixture is cooled to 25~ whereupon the viscosity of the solution is found to be 425 cPs. The reaction mixture is added with cooling to 5 liters of anhydrous isopropanol which has been cooled to 0~ The prepolymer, which precipitates, is filtered off and dried under reduced pressure (yield: 245 gm 27.6%). The unreacted monomer may be recovered from the filtrates. The product had a softening range of 80~176 a specific gravity (ASTM D792-50) of 1.267 at 25~ and an iodine number of 55. It is soluble in ketones, benzene, ethyl acetate. When cured in the presence of 2% tert-butylperbenzoate (15 min at 175~ under 6000 p.s.i, of pressure), a thermset resin is formed with a Rockwell hardness of 114-116 (M-scale), flexural strength of 9000 p.s.i., and a heat distortion point at 264 p.s.i, of 155~ [103]. Table XI indicates the effect of hydrogen peroxide on the conversion and the viscosity of the propolymer solution. When chloroalkanes or ketones are used as regulators of the molecular weight of diallyl o-phthalate polymers, telemerization has been observed [ 104]. According to another patent, heating 100 parts of diallyl o-phthalate with 2 parts of methanol, 2 parts of carbon tetrachloride, and 0.4 parts of dibenzoyl peroxide for 3.5 hr at 110~ results in the isolation of 27 gm of a prepolymer by precipitation with an excess of methanol [105]. After heating 30 gm of the monomer with 10 gm of hexachloroethane for 18 hr with 0.3 gm of dibenzoyl peroxide at 80~ 12.3 gm of a prepolymer is isolated which could readily be molded. This process affords a greater than 30% yield of prepolymer [106]. Evidently by using a rather large quantity of chain-transfer agent, substantial

321

8. Polymerization of Diallyl Esters of Phthalic Acids

TABLE XI

Effect of Hydrogen Peroxide Level on the Viscosity of Prepolymer [ 103]a

H202

Conversion

Viscosity of a 25% prepolymer solution in monomer at 25~

(%)

(%)

(cPs)

0.11 0.27 0.43 0.51 0.54

24.5 25.8 27.6 28.0 29.3

550 390 354 220 179

Polymerization conditions: As given in Procedure 8-4 except for indicated changes in percentage of H202.

yields of the prepolymer are readily formed. The patents are not clear as to the composition of these prepolymers. It may be presumed that a reaction mixture containing 25% of a perhalogenated chain-transfer agent such as hexachloroethane will produce a low-molecular-weight polymer replete with highly halogenated segments. Usually, suspension polymerizations consist of a process in which droplets of a monomer (or monomers) containing an initiator in solution are polymerized while being dispersed in an aqueous medium containing a suspending agent. Attempts are usually made to carry the process to high conversion and to isolate the product as rigid beads. The foregoing discussion of the polymerization of the diallyl phthalates has indicated that any process which leads to essentially complete conversion will result in cross-linked beads which will have virtually no uses. Therefore a suspension process for the present monomers would have to be carried out to a modest conversion and isolation of the prepolymer would have to be from the solution of the polymer in its monomer. With dimethylbenzyl alcohol as a polymerization regulator which prevents cross-linking and using animal glue as a suspending agent, a "suspension" polymer has been prepared. This material gave clear solutions in acetone and could be molded as 85~ and 5000 psi within 10 min. Procedure 8-5 illustrates the polymerization process of this patented process [ 107].

8-5.

"Suspension Polymerization" of Diallyl o-Phthalate [107]

In a 2-liter resin kettle fitted with an addition funnel, reflux condenser, mechanical stirrer, thermometer, and a means of maintaining an inert atmosphere, to 600 gm of water heated, with stirring, under a nitrogen atmosphere at 80~ are added 2 gm of animal glue and 35 gm of dimethylbenzyl alcohol. While maintaining a temperature of 80~ a solution of 15 gm of recrystallized

322

8. Polymerization of Allyl Esters

dibenzoyl peroxide in 150 gm of diallyl o-phthalate is added from the addition funnel while stirring vigorously. After heating for 21 hr, the mixture is cooled to 30~ and transferred to a separatory funnel. The lower organic layer is added dropwise with vigorous stirring to 500 ml of methanol. The precipitated prepolymer is separated, resuspended in fresh methanol, filtered, and dried under reduced pressure. The yield is 76 gm with a saponification number of 428, an iodine number of 58, and a viscosity, in a 5% solution in benzene, of 0.82 cPs. The use of magnesium carbonate at levels of 2-5% based on diallyl o-phthalate has been suggested as a suspending agent. Since the abstract indicates that polymer conversions of greater than 94% are achieved, we presume that this suspending agent was only of use when rigid polymer beads were to be isolated. At that level of conversion, the polymer may be expected to be thoroughly crosslinked. The same suspending agent had also been suggested for the polymerization of tiallyl citrate [108]. Aqueous emulsions containing between 30% and 70% of the prepolymer or of mixtures of monomer and prepolymer have been suggested for application in textiles and paper making. The emulsion is said to be formulated with 1% of tert-butyl perbenzoate. The composition is cured under pressure at 140~176 Details on the preparation of a true latex are not available [ 109]. There appears to have been little interest in ionic polymerization of the diallyl phthalates. In one patent, it is implied that the initiation of diallyl o-phthalate by boron alkyls in the presence of oxygen probably involves a free-radical process [110]. The soluble prepolymers of diallyl isophthalate may be cured not only by conventional thermal methods but also by photocross-linking techniques. The use of aryl diazides as photoinitiator of solutions of poly(diallyl isophthalate) in aryl ketones has been suggested. With synergistically active sensitizers such as benzil or benzophenone with Michler's ketone curing is possible at 300--400 nm [111]. Studies of the pre-gel stage of free radical polymerizing diallyl isophthalate as well as of diallyl sebacate have been shown to involve significant intramolecular cyclization. On the average six to eight monomer units appear to be involved in each cycle [ 112, 113].

11

POLYMERIZATION OF ALLYL ESTERS OF OTHER POLYFUNCTIONAL ACIDS

Many esters of polyfunctional acids have been prepared. For example, triallyl citrate was mentioned in Chia and Chao [108]. Simpson and Holt [41, 42] studied the oxalate and sebacate. Matsumoto and Oiwa [46, 47] worked with the carbonate, oxalate, malonate, succinate, adipate, and sebacate. Early works with

9. Polymerization of Allyl Esters of Other Polyfunctional Acids

323

the suberate, the fumarate, and the maleate were mentioned in Kardashev et aL [ 114]. The preparation and polymerization of diallyl tartrate along with several other esters was described in Araki and Iida [115]. The formation of prepolymers from diallyl brassylate, a novel monomer, and from diallyl azelate were described in [116]. The bulk-copolymerization procedure for the diallyl esters of the dicarboxylic acids from the carbonate to the sebacate in sealed ampoules uses Procedure 8-2 with substitution of the appropriate diallyl ester for the diallyl phthalate indicated in that procedure. Gelation generally takes place at approximately 25% conversion. Hence the process is generally stopped before cross-linking begins. Diallyl oxalate and diallyl sebacate frequently form semisolids which are difficult to filter. Therefore they may be isolated by centrifugation from methanolic dispersions [41, 42]. The degree of polymerization of the bulk polymers produced are quite large: the initial degree of polymerization of poly(diallyl oxalate) is 85, of poly(diallyl malonate) 70, of poly(diallyl succinate) 71, of poly(diallyl adipate) 61, and of poly(diallyl sebacate) 54 [46]. The tendency of these monomers to cyclize decreases as the separation between the two allyl groups on a given molecule increases (but cf. [112, 113]). The polymerizations of diallyl brassylate and of diallyl azelate in a stirred reactor to soluble prepolymers are given in Procedure 9-1.

9-1.

Preparation o f Diallyl Brassylate Prepolymer in a Stirred Reactor [116]

In a l-liter, three-necked flask fitted with a mechanical stirrer, thermometer, and a means of introducing nitrogen and maintaining a nitrogen atmosphere, 240 gm of a solution consisting of 98 mol% of distilled diallyl brassylate (MW 324) and 2 mol% of dibenzoyl peroxide is heated at 76~ until the refractive index reaches n 25 1.4630. The reaction mixture is cooled in a refrigerator to stop the polymerization. The reaction mixture is then warmed to 25~ and equally divided among four 250-ml centrifuge bottles. To each bottle, 150 ml of methanol is added and stirred for 0.5 hr. The supernatant liquids are discarded. The residues are worked up with methanol four times to remove unreacted monomer. The combined residue is dried under reduced pressure. The polymer is dissolved in acetone. The acetone solution is filtered to separate the cross-linked polymer. The prepolymer is recovered by evaporating most of the acetone on a rotating evaporator at ambient temperature. The remaining solvent is removed by freezedrying at - 2 5 ~ at 0.02 mm Hg pressure. The mother liquors from the work-ups were found to contain oligomers along with unreacted comonomer. Table XII gives properties of the prepolymers of diallyl brassylate and of diallyl azelate prepared by this procedure.

324

8.

Polymerization of Allyl Esters

TABLE XII Properties of Poly(diallyl brassylate) and Poly(diallyl azelate) Prepolymers [116]

a

Prepolymer Property

Diallyl brassylate

Diallyl azelate

Glass transition temperature M.P., C Refractive index, n~5 Density, ml/gm, 25~ MW, number average Degree of polymerization, DPn Apparent MW, weight avgb Apparent polydispersity ratio, Mw/M,,b Viscosity, 25~ cPs Solubilityc Partially soluble in: Completely soluble in:

- 63 21 1.4839 1.0269 28,000 86 716,000 25.6 9.6

- 70 1.4882 1.0767 40,000 149 739,000 18.5 39

acetonitrile dimethyl sulfoxide

diemthyl sulfoxide acetonitrile

a Polymerization conditions are as given in Procedure 9-1. bThe property is designated as apparent because of the great difference in three-dimensional structure between the prepolymers and the polystyrene used as standards in gel permeation chromatography. r Both polymers exhibit these common characteristics: Soluble in acetone, benzene, tetrachloride, chloroform, dioxane, ethyl acetate, diethyl ether, and THF. Insoluble in cyclohexane, dimethyl formamide, methanol, and water. A rapid copolymerization of diallyl adipate with an unsaturated polyester using a small quantity of lauryl mercaptan and stannous chloride along with dibenzoyl peroxide has been described. This patented procedure is of particular interest in the manufacture of flexible coatings or textiles. Procedure 9-2 may be investigated as a general method of accelerating conventional peroxide-initiated polymerizations provided the patent does not impose restrictions on such work.

9-2.

Copolymerization of an Unsaturated Polyester and Diallyl Adipate [ 117]

A mixture of 65 gm of an unsaturated polyester, 35 gm of diallyl adipate, 2 gm of recrystallized dibenzoyl peroxide, and 0.4 ml of lauryl mercaptan (CAUTION: stench), and 0.7 ml of a saturated solution of stannous chloride in DMF is prepared at room temperature. A fibrous substrate is impregnated with this mixture, heated for 5 min at 70~ and cooled to 22~ The resultant impregnated material has slightly tacky faces. By passing the sheet between felt rollers saturated with an accelerator such as dimethylaniline, a smooth, nonsticky skin is formed on the sheet.

9. Polymerization of Allyl Esters of Other Polyfunctional Acids

325

At 70~ this sheet may be stored for 3 weeks. The sheet may be shaped by stamping and may then be cured by heating at 150~ for 15 sec. The diallyl esters of maleic and fumaric acid have found application primarily in copolymer systems. Considering that the distance between the two allyl groups of the maleate ester is similar to those of the o-phthalate, and that of the fumarate is geometrically quite different, it is unfortunate that there seems to have been no study of the cyclopolymerization possibilities of these monomers. In addition there are the problems associated with the copolymerization of an allyl grouping with the double bond of the maleic or fumaric moieties within the same molecule. Highly purified diallyl maleate and fumarate in an inert atmosphere, are said to polymerize very rapidly [118]. However, trace impurities and atmospheric oxygen substantially reduce the polymerization rate under ordinary circumstances. Naturally with the double bond between the two carboxylate groups and the two allylic double bonds, crosslinking takes place at very low conversion. Even so, in copolymer systems such as in poly(vinyl acetate) emulsion copolymers, the cross-linking of a fumarate or maleate within the latex particles appears not to interfere significantly with film formation properties. As a matter of fact these monomers are incorporated in poly(vinyl acetate) latices used in adhesives and in water-based paints. Prepolymers of diallyl maleate have been prepared although not as readily as the prepolymers of the diallyl phthalates. A composition of 80% diallyl maleate prepolymer and 20% monomeric diallyl monomer with 3% dibenzoyl peroxide forms a hard transparent resin when subjected to 90~ at 2000 psi for 20 min [119]. Stereoregular, crystalline polymers are said to form from allyl esters of unsaturated acids in hydrocarbons or ether with such catalysts as butyl lithium, phenyl magnesium bromide, or lithium diethylamide [107]. Typically, these polymerizations were carried out between - 70~ and + 20~ According to the patent, films and fibers are readily formed from these polymers. The properties of these articles can be greatly modified by cross-linking [ 120]. Using differential scanning calorimetry, studies on the isothermal bulk polymerization of diallyl fumarate, diallyl maleate, and diallyl succinate were carried out. At a concentration of 2,2'-azobisisobutyronitrile of 0.0225 mole/liter of diallyl fumarate, the heat of isothermal bulk polymerization at 75~ was found to be - 6 3 . 6 kJ/mole ( - 15.2 kcal/mole). At 96~ it was - 87.9 kJ/mole ( - 2 1 . 0 kcal/mole). Similar decreases in the heat of polymerization were also noted at high levels of initiator over the same temperature range. The overall activation energy for the bulk polymerization of diallyl fumate was determined to be 100.4 kJ/mole (24.0 kcal/mole). At low conversions, the initial rates were a function of the square root of the initiator concentration.

326

8. Polymerization of Allyl Esters

At constant initiator concentration and using a programmed heating cycle, the heats of polymerization for diallyl fumarate was found to be -126.4 kJ/mole ( - 30.2 kcal/mole); for diallyl maleate -82.9 kJ/mole ( - 19.8 kcal/mole); and for diallyl succinate - 90.8 kJ/mole ( - 21.7 kcal/mole) [ 121 ]. 10.

MISCELLANEOUS PREPARATIONS INFORMATION

AND

1. Polymerization of diallyl chlorendate (diallyl 1,4,5,6,77-hexachlorobicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate) by heating for 4 hr at 80~ with 0.5% dibenzoyl peroxide [122]. 2. Application of diallyl terephthalate as an accelerator for curing fluorinated polymers such as a terpolymer of tetrafluoroethylene, vinylidene fluoride, and perfluoropropylene [ 123]. 3. Reactivities of allyl esters in the radiation-induced telomerization with carbon tetrachloride. Inter alia, it was found that substituted benzoates react more rapidly than substituted phenylacetates. Esters of stronger acids reacted more slowly that those of weaker acids. It was postulated that a C--H"-n interaction prevents allyl esters from interaction with "CC13 radicals [ 124]. 4. Formation of diallyl phthalate prepolymers from preformed poly(monoallyl phthalates) by esterification with allyl alcohol in benzene solution, catalyzed by p-toluenesulfonic acid [125]. 5. Polymerization of bis[p-(allyloxycarbonyl)phenyl] esters of aliphatic and aromatic dicarboxylic acids to produce highly cross-linked polymers with good optico-mechanical properties [126]. This study should be compared with the more recent work of Ref. [80a] on the polymerization of ethyl a-[(allyloxy)methyl]acrylate. 6. Synthesis and graft copolymerization of poly(diallyl dimethylammonium chloride) with acrylamide [127]. 7. Electrochemical reductive dimerization and Claisen rearrangement of allyl acrylate [128]. 8. Anisotropy of side group motion of poly(fluoroalkyl acrylates) crosslinked with allyl methacrylate and ethylene dimethacrylate [129]. 9. Improved impact and heat resistance of an engineering plastic such as ABS by blending with a copolymer of allyl methacrylate and ethylene as well as a EPDM rubber [130]. 10. Highly hydrous contact lenses produced from copolymers of 2-(methacryloxy)ethyl-2'-(trimethylammonio)ethyl phosphate, 2-hydroxyethyl methacrylate, and allyl methacrylate [ 131 ]. 11. Radical branching polymerization of diallyl isophthalate in bulk and in benzene solutions [132].

References

327

12. A study o f the copolymerization o f the three diallyl phthalates with N-vinylpyrrolidone. Reactivity ratios, Q - e values, and intramolecular cyclization factors were evaluated [133]. 13. A study o f compatible simultaneous interpenetrating p o l y m e r networks (SINs) o f diallyl phthalate and (diglycidyl ether o f bisphenol A)-based epoxy resin [134]. 14. Use o f diallyl phthalate and diallyl maleate copolymers with vinyl chloride as rubbery sealams [ 135]. 15. Paper coating latex binder based on the copolymerization o f pre-emulsified vinyl acetate and diallyl maleate with ethylene under pressure [136]. 16. UV-curable coating composition based on diallyl maleate, tetraethylene glycol diacrylate, and a photoinitiator [137].

References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24.

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8.

Polymerization of Allyl Esters

W. E. Cass and R. E. Bumett, Ind. Eng. Chem. 46, 1619 (1954). S. A. Mednick, L. Seglin, and W. B. Tuemmler, U.S. Patent 3,385,836 (1968). R. W. Warfield and M. C. Petree, J. Polym. Sci. 37, 305 (1959). C. A. Heiberger, U.S. Patent 3,096,310 (1963). D. Porret and L. Leumann, U.S. Patent 3,366,667 (1965). A. Neri and L. Capitano, U.S. Patent 3,474,127 (1966); Chem. Abstr. 65, 9053 (1966). H. Inoue, H. Inukai, and H. Ito, Japan Kokai 72/22,992 (1972); Chem. Abstr. 78, 73083 (1973). C. A. Heiberger and J. L. Thomas, U.S. Patent 2,832,758 (1958). K.-S. Chia and F.-Y. Chao, Chemistry (Taiwan) p. 31 (1956); Chem. Abstr. 51, 1645 (1957). W. Festag, German Patent 1,163,774 (1964); Chem. Abstr. 60, 1345z (1964). Solvay, Belgian Patent 562,701 (1959); Chem. Abstr. 53, 10845 (1959). M. N. Gilano and M. A. Lipson, Tech. Pap., Reg. Tech. Conf., Soc. Plast. Eng., Mid Hudson Sect. p. 30 (1970); Chem. Abstr. 74, 4077f (1971). I. I. Romantsova, Int. Polym. Mater. 19(1-2), 51 (1993). I. I. Romantsova, Polym. Mater. Sci. Eng. 66, 121 (1992). D. A. Kardashev, N. S. Leznov, and V. P. Nuzhdina, Khim. Promst. No. 2, p. 5 (1945); Chem. Abstr. 40, 45594 (1946). T. Araki and H. Iida, Rep. Gov. Chem. Ind. Res. Inst., Tokyo 47, 95 (1952); Chem. Abstr. 47, 108899 (1953). S.-P. Chang, T. K. Miwa, and W. H. Tallent, d. Appl. Polym. Sci. 18, 319 (1974). P. P. W. Varlet, U.S. Patent 3,133,826 (1964). C. E. Schildknecht, "Allyl Compounds and Their Polymers (Including Polyolefins)," p. 638. Wiley (Interscience), New York, 1973. M. A. Pollack, I. E. Muskat, and F. Strain, U.S. Patent 2,370,578 (1945). J. Natta, M. Donati, and M. Farina, Belgian Patents 620,901 and 621,007 (1963); Chem. Abstr. 59, 1777c (1963). F. Cernec, U. Osredker, A. Moze, I. Vizovisek, and S. Lapanje, Makromol. Chem. 178(8), 2197 (1977). C. F. Baranaukas, U.S. Patents 2,810,712 and 2,903,463 (1962). J. F. Smith, U.S. Patent 3,011,995 (1963). M. Okubo, Nippon Kagaku Zasshi 87(11), 1196 (1966); Chem. Abstr. 66, 90113d (1967). Y. Umezu and B. Kobayashi, Japanese Patent 67/26,698 (1967); Chem. Abstr. 68, 9636 (1968). B. M. Zuev, A. P. Filippova, and Z. I. Validov, U.S.S.R. Patent 394,681 (1973); Chem. Abstr. 81, 50460c (1974). Y. Q. Lin, H. Pledger, Jr., and G. B. Butler, d. Macromol. Sci. Chem. A 25(8), 999 (1988). T. Troll and J. Wiedermann, Tetrahedron Lett. 33(27), 3847 (1992). E. R. Basilova, V. A. Shevelev, L. D. Budavskaya, and V. N. Ivanova, Polym. Mater. Sci. Eng. 66, 115 (1992). F. Hirofumi and S. Katsufumi, European Patent Application EP 472,898 (1990). N. Nakabayashi, K. Ishihara, Y. Murata, N. Nakada, T. Matsumoto, and Y. Koinuma, European Patent Application EP 537,972, Oct. 14 (1991). V. I. Kolegov, M. I. Khramushina, and I. N. Yudina, Vysokomol. Soedin. Ser. B 34(11), 9 (1992). A. V. Safronov, L. B. Zubakova, L. Ya. Nikiforova, and I. Yu. Pilina, Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 36(3), 81 (1993). M. S. Lin and C. C. Yeh, J. Polym. Sci., Part A: Polym. Chem. 31(8), 2093 (1993). O. Matsumoto and S. Arima, Japanese Patent Application JP 05/25,346 [93/25,346] (1991). Y. J. Shin, U.S. Patent US 5,219,924 (1993). B. Gupta, U.S. Patent US 5,143,947 (1989).

Chapter 9

Polymerization of Vinyl Fluoride 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

331

2. C h e m i c a l l y Initiated P o l y m e r i z a t i o n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

336

A. Bulk P o l y m e r i z a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-1. Bulk Polymerization of Vinyl Fluoride: Benzoyl Peroxide Initiated. . . . . . . . . . . B. Solution P o l y m e r i z a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-2. Solution Polymerization of Vinyl Fluoride in tert-Butyl Alcohol . . . . . . . . . . . . . 2-3. Solution Polymerization of Vinyl Fluoride in Aqueous Methanol . . . . . . . . . . . . C. S u s p e n s i o n P o l y m e r i z a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-4. Suspension Polymerization of Vinyl Fluoride, Benzoyl Peroxide Initiated . . . . . . D. E m u l s i o n P o l y m e r i z a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-5. Emulsion Polymerization of Vinyl Fluoride . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6. Emulsion Polymerization of Vinyl Fluoride in the Presence of Ammonium Iodide E. O r g a n o m e t a l l i c and Related Initiator Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2-7. Solution Polymerization of Vinyl Fluoride with Oxygen-tri-n-Propylborane Initiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Radiation-Initiated P o l y m e r i z a t i o n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-1. Photopolymerization of Vinyl Fluoride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

336 338 338 338 339 339 341 343 344 344 345 347 347 348

4. Health A s p e c t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

349

5. M i s c e l l a n e o u s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

350

References ........................................................

1.

350

INTRODUCTION

The monomer vinyl fluoride has been known since the beginning of the 20th century. The compound is a gas at ordinary temperatures and pressures with a boiling point of - 72.2~ at 1 atm, a critical temperature of 54.7~ and a critical pressure of 760 psi (5.21 MPA) [ 1]. These properties along with the lack of purity 331

332

9. Polymerizationof Vinyl Fluoride

of early samples and the limited understanding of the techniques of flee-radical polymerizations delayed preparation of the polymer well into the 1930s. It was not until after World War II, when the interest in fluoride-containing compounds increased, that developments in the preparation of poly(vinyl fluoride) of high molecular weights were patented, reported, and commercialized. Among early patents dealing with the polymerization of vinyl fluoride are those of Coffman and Ford [2-4]. An early patent that used organic azo initiators was that of Johnston and Pease [5]. Poly(vinyl fluoride) has been formed as a transparent film which is tough, flexible, and capable of orientation by cold drawing. Its primary applications are as weather- and stain-resistant films and coatings. The resin is remarkably transparent to radiation from 230 nm to 1.4/zm. However, below 200 nm light transmission drops off rapidly [6]. Thus it is used in greenhouse windows that block out harmful short-wavelength UV radiation (below 200 nm), but transmit light of wavelengths above 300 nm, which is thought to be beneficial for plant growth [7]. The polymer also exhibits good chemical stability, insolubility in most ordinary solvents, and abrasion resistance. This combination of properties has led to a variety of applications in building materials, packaging, coil coatings, and protective coatings for steel containers. Other applications include the use of films for protective coatings of fiberglass-reinforced polyester panels and preformed plastic parts [8]. Films are also suggested for use as release films in the production of printed circuit laminates and multilayer printed circuit boards [9]. Compositions of aromatic polyether-polyketones, a fluoropolymer, and aluminum borate whiskers have been patented for the production of parts with low coefficients of friction [10]. Another patent uses fluoropolymers in the manufacture of optical fibers constructed of several fibers in a unitary fiber-drawing apparatus [11]. Panels that could be embossed were prepared by laminating poly(vinyl fluoride) over polyaryletherketoneketone with a poly(methyl methacrylate) adhesive over Nomex core paper and in turn adhering such composites to glass fiber reinforced resins [12]. As mentioned before, the monomer has a low boiling point ( - 72.2~ and a relatively low critical temperature (54.7~ For comparison, vinyl chloride has a boiling point of - 13.8~ and a critical temperature of 147~ (cf. this series, Vol. 11, 2nd ed., p. 358). Therefore the polymerization of vinyl fluoride is usually carried out under high-pressure conditions which probably resemble the polymerization of ethylene more than that of the other vinyl halides. The monomer is soluble in a variety of solvents. At room temperature, the homopolymer is insoluble. Therefore the neat subdivision of polymerization techniques into bulk, solution, suspension, and emulsion procedures which we have used in many other sections in this series becomes blurred. Most procedures seem to lead to blocks of polymer or some sort of dispersions from which

1.

Introduction

333

polymeric powders may be isolated. The emulsion polymerization procedures also frequently lead to the isolation of powders. We presume that the high density of the polymer (ranging from 1.37 to 1.72 gm/ml [8], as well as the electronic configuration of the fluorinated monomer and/or polymer, interferes with real latex formation. In one series of experiments on the polymerization of vinyl fluoride in bulk and in solution using tributylborane monoperoxide as the initiator, a difference between the two polymerization techniques was illustrated. In the bulk polymerization, the reaction order was 0.61 with respect to the initiator. In the solution polymerization, the reaction order with respect to the initiator was 1.24. The activation energy for the bulk polymerization of vinyl fluoride was found to be 10.1 kcal/mole [ 13]. The initiation processes used have included various forms of radiation as well as chemical initiators. In connection with chemical initiators, it is interesting to note that among these are water-soluble amidine salts derived from such "oilsoluble" initiators as 2,2'-azobisisobutyronitrile. These water-soluble initiators tend to produce polymer latices in the presence of appropriate surfactants in the way more conventional water-soluble initiators do in the case of other vinyl monomer types. The purification of the monomer is evidently extremely important. Early samples were sufficiently low in quality that satisfactory polymers could not be produced. Consequently the important properties of the resin were not observed until relatively recently. The purification procedure described by Kalb et al. [ 1] includes the following sequence of steps: 1. Distillation to separate the vinyl fluoride from 1,1-difluoroethane, hydrogen fluoride, and other impurities; 2. Removal of last traces of hydrogen fluoride by percolation through soda-lime towers; 3. Separation of acetylene from the monomer by scrubbing with ammoniacal cuprous chloride (CAUTION: This procedure may lead to the formation of metal acetylides among the reaction products. Acetylides of heavy metals are said to be explosive, especially when dry. Partially dried acetylides may present similar hazards); 4. Separation of oxygen by another fractional distillation between - 5 0 ~ and - 2 5 ~ at 40-100 psi (0.25-0.69 MPa) pressure. Monomers with less than 5 ppm of acetylene and less than 20 ppm of oxygen were used for polymerization studies [ 1]. The purification of vinyl fluoride has been monitored by gas-liquid chromatography. Levels of impurities lower than 1 ppm by weight have been observed [14].

9. Polymerizationof Vinyl Fluoride

334

Vinyl fluoride monomer from a commercial supplier of specialty gases has been purified by passing the gas through silica gel. Then the compound was freed of air by conventional degassing procedures using liquid air to freeze the monomer [ 15]. The homopolymer poly(vinyl fluoride) is not soluble in ordinary solvents at temperatures below 100~176 At more elevated temperatures, dimethylformamide and tetramethylurea are particularly suitable solvents for the polymer. Other solvents are dinitriles, ketones, and tetramethylene sulfone [ 1]. Solution characteristics of the polymer have been studied particularly in dimethylformamide that was made 0.1 N in anhydrous lithium bromide to suppress an apparent polyelectrolyte effect occasionally observed [16]. In this system the Mark-Houwink relation for the intrinsic viscosity at 90~ was found to be [r/] = 6.42 • 10- 5M~176 (1) where Ms is the molecular weight derived from sedimentation studies in the ultracentrifuge and the weight average molecular weight, Mw, is given by

Mw

Ms~(0.90).

(2)

In a series of nine unfractionated polymers, prepared by free-radical polymerizations, the degree of polydispersity, Mw/Mn, ranges from 2.47 to 5.59. The deviation from a normal distribution where Mw/Mn is 2.0, is attributed to chain branching [ 16]. The glass transition temperature of poly(vinyl fluoride) was determined to be 43~ The transition is independent of the molecular weight of the polymer. Polymers, for this study, were prepared in the presence of a variety of initiators such as 2,2'-azobisisobutyronitrile, tributylborane monoperoxide, or diisopropyl diperoxycarbonate [ 17]. Poly(vinyl fluoride) is a somewhat unusual polymer from the structural standpoint. It was found that the telemerization of vinyl fluoride in the presence of trifluoromethyl iodide gave rise to products formed by the addition of trifluoromethyl radical to either the methylene or the CHF end of the monomer. The rate of addition to the methylene group was found to be nearly 11 times greater than the CHF group. The propagating radical CF3(CH2CHF)2 adds to the methylene group only twice as rapidly as it does to a CHF group [ 18]. In other words, the propagation stage has a high probability of forming head-to-headtail-to-tail chain segments along with the more common head-to-tail structures. If the polymerization is carried out at lower temperatures, chains of greater regularity are formed with a more substantial fraction of head-to-tail structures. This leads to greater crystallinity of the polymer [6, 19, 20]. In a flow reactor in which vinyl fluoride is continuously polymerized by photochemical initiation, the polymer formed has a higher proportion of head-to-tail sequences than the commercial product [21 ].

1. Introduction

TABLE I

335 Reactivity Ratios of Vinyl Fluoride (MI) with Co-monomers (M2) at 30~ ,

M2 Vinyl chloride Vinylidene fluoride Hexafluoropropene Ethylene Tetrafluoroethylene 1,1,2-Trifluoro-2-chloroethylene cis- 1,2,3,3,3-Pentafluoropropene Hexafluorocyclobutene Methyl acrylate Acrylonitrile Methyl methacrylate

rl 0.07 + 0.02 0.05 + 0.005 4.2 + 0.4 5.5 + 0.5 1.1 + 0.05 1.01 + 0.01 0.3 + 0.03 0.4 (at 0~ 0.27 + 0.03 0.18 + 0.02 0.09 4- 0.05 3 4- 0.6 0.16 4- 0.01 --~10- 3 0.0030 4- 0.003 (temp not specified)

rE

Ref.

+ 1 + 1 + 0.02 + 0.3 0 0 1.7 + 0.1 3.0 (at 0~ 0.05 + 0.02 0.06 + 0.02 0 0 2.9 4- 0.2 24 4- 2 51.5 + 2 (temp not specified)

19, 20

9 11.0 0.18 0.17

19, 20 19, 20 19, 12 23 19, 20 19, 20 19, 20 19, 20 19, 20 19, 20 22

The matter of the head-to-head, tail-to-tail polymerization of vinyl fluoride, vinylidene fluoride, and trifluoroethylene and the copolymerization of vinyl fluoride with vinylidene chlorofluoride and 1-chloro-2-fluoroethylene has been extensively studied by Cais and Kometani [24-27] and by Bmch, Bovey, and Cais [28]. The synthesis of pure head-to-tail poly(trifluoroethylenes) is described in Ref. [25]. Isomers of poly(vinyl fluoride) with controlled regiosequence microstructure are discussed in Ref. [27]. The copolymerization of vinyl fluoride has been studied systematically only with a few co-monomers. Table I [19, 20, 22, 23] lists some of the reactivity ratios which have been reported. The meaning of the error terms given in the table is, as is so often the case in the chemical literature, not at all clear. It is interesting to note that the same authors, in the same paper, using two different initiator systems now and again report two sets of reactivity ratios which do not always agree with each other even when the error term is added or subtracted. The Q - e values for vinyl fluoride copolymerizations have been reported as Q = 0.010 + 0.005; e = - 0 . 8 +_ 0.2 [10] or Q = 0.0084; e = 0.97 [22]. Generally useful reviews of the polymerization of vinyl fluoride are Kalb et al. [1] and Cohen and Kraft [6]. Kalb et al. [1] is particularly useful for a discussion of the effect of various reaction parameters on the polymerization process when it is chemically initiated. Other reviews are by Trappe and other authors [29-33]. Among more recent reviews are those of Brasure and Ebnesajjad [34] and of Ebnesajjad and Snow [35].

9. Polymerizationof Vinyl Fluoride

336

2.

CHEMICALLY

INITIATED

POLYMERIZATIONS

For the sake of classifying the methods of polymerization of vinyl fluoride, we use two broad categorizations in this chapter. 1. Chemically initiated processes, i.e., processes in which free radicals are

generated chemically or thermally from typical free-radical initiators such as the organic peroxides, azo compounds, etc. Ziegler-Natta catalysts, metalloorganic systems, and donor-acceptor complex polymerizations are also included in this category. 2. Radiation-initiated processes which include the use of ultraviolet radiation, ?-rays, glow-discharges, etc. Processes, if any, in which chemical initiators are used in conjunction with radiation would also be part of the second category. We believe that such a process may be primarily one in which the radiation initiates the formation of free radicals by the decomposition of the initiator rather than the direct generation of free radicals from the monomer. In either situation, it would be the radiation which actually initiates the polymerization process. A.

Bulk Polymerization

With chemical initiators, examples of true bulk or solution polymerizations are rare. This may simply be a reflection of practical considerations. The monomer is a gas at ordinary temperatures and pressures, therefore work has to be carried out in some sort of pressure vessel. Bulk polymers generally are difficult to remove from reactors. They usually do not exhibit the optimum properties of the polymer. Poly(vinyl fluoride) is quite insoluble in most solvents at temperatures below approximately 100~ It probably is also insoluble in its liquified monomer. Therefore, bulk polymerization processes would probably be strongly influenced by the precipitation of polymer from liquified monomer. A similar difficulty is found in attempts to prepare solution polymers. While the monomer may be soluble in many solvents, the polymer is not. As a result solution processes usually lead to precipitation or dispersion polymers, or some sort of swollen particles or gels. For classification purposes only, we are listing preparations carried out in the presence of a solvent (other than water or monomer) as "solution polymerizations" despite the indicated limitations. In this connection it should also be pointed out that many solvents act as chain-transfer agents for vinyl fluoride polymerizations and are therefore of interest in controlling the molecular weight distribution of the product. Solvents are also significant in the effort to develop processes which may be carried out at lower pressures than those involving nonsolvent systems. Because of the solubility of vinyl fluoride in a given solvent, the weight of monomer which can be compressed into a pressure vessel

2.

Chemically Initiated Polymerizations

337

at any given pressure is greater in the presence of a solvent than in its absence. Suspension and emulsion polymers have been prepared. In the case of emulsion polymers, the choice of surfactant is particularly critical. Salts of perfluorinated heptanoic or octanoic acids have been found suitable [6], although the products frequently are somewhat off-white. Higher yields of polymer and excellent color were obtained when salts of perfluoroalkylpropylamines served as emulsifiers. Even these materials, the patent implies, lead to slumes of polymer in the aqueous medium rather than to reasonably stable latices [36]. In our description of the polymerization processes we do not give detailed descriptions of the equipment and methods necessary for handling gases under pressure. We only mention that careful engineering is mandatory even though the older literature seems to indicate the use of rather haphazardly designed vessels. Procedure 2-1 is an example of a bulk polymerization of vinyl fluoride. It should be noted that the conversion is quite low. At 62~ benzoyl peroxide has a half-life of approximately 35 hr. Consequently heating the reaction mixture for 112 hr represents only a little over 3 half-life periods. From the literature [37] no estimate of the pressure inside the reactor could be made. Table II does indicate that in the presence of acetone or of aqueous acetone the conversion increased substantially. In fact, the procedure of the sixth experiment was found to be highly reproducible. Acetone was thought to enhance the solubility of the initiator in the monomer [37].

C A U T I O N : Vinyl fluoride is very toxic and should be handled with great care (see p. 349). TABLE II Bulk Polymermization Experiments on Vinyl Fluoride (Procedure 2-1)a Exp No.

Initiator (1% concentration of)

Solvent

Temp (~

1 2 3 4 5 6 7 8

Benzoylperoxide Benzoylperoxide Benzoylperoxide Benzoylperoxide Benzoylperoxide Benzoylperoxide Lauroylperoxide Acetyl peroxide

None None None Acetone Acetone 10% H20 in acetone 10% H20 in acetone None

51 62 85 64 72 71 71 43

T i m e Conversion Half life (hr) (%) (hr)b 37 112 89 23.5 23.5 23.5 23.5 117.5

0.5 4.0 1.7 38.4 17.8 35 44 15

150 35 2.3 29 9 10.3 3 >400

Based on Newkirk [37]. bAn estimate of the half life of the indicated initiator at the stated temperature based on the nomograph given in Vol. I of this series. a

338

2-1.

9. Polymerization of Vinyl Fluoride

Bulk Polymerization of Vinyl Fluoride: Benzoyl Peroxide Initiated [37]

With suitable safety precautions, in a small steel bomb is placed liquid vinyl fluoride containing 1% dibenzoyl peroxide. The bomb is sealed and heated at 62~ for 112 hr. Then the bomb is cooled in a dry-ice bath and cautiously opened. The excess monomer is vented off and the polymer is isolated. The yield is 4.0% of the charged monomer. In the case of bulk polymerizations, reaction mechanism seems to depend on the nature of the initiator. Thus, the same research group reports that with respect to the monoperoxide of tributylborane as the initiator, the bulk polymerization is of the 0.61st order with an activation energy of 10.1 kcal/mole [13]. With diisopropyl peroxydicarbonate, while the reaction order was of the 0.58th order with respect to the initiator, the overall activation energy of the bulk polymerization was 16.9 kcal/mole [38]. The conversion with the latter initiator was as high as 90% at a reaction temperature of 40~ [38]. Copolymers of vinyl fluoride with such monomers as vinylidene fluoride or 1-chloro-2-fluoroethylene were prepared in the presence of trichloroacetyl peroxide at 0~ in sealed tubes. The chlorine-containing copolymers were then reductively dechlorinated at 60~ in tetrahydrofuran with tri-n-butyltin hydride in the presence of 2,2'-azobis(isobutyronitrile) for up to 40 hr. This general procedure led to the formation of polymers with a reasonable control of the level of head-to-head, tail-to-tail linkages in the product [27].

B.

Solution Polymerization

Vinyl fluoride monomer exhibits solubility in a variety of organic solvents, e.g., the lower alcohols, ethers, mono- and dinitriles, butyrolactone, liquid amides such as diethylformamide [6], and heptane [38]. As mentioned before, the polymer is generally quite insoluble at ordinary temperatures. At temperatures in the range of 100~ some of these compounds dissolve the polymer. During the polymerization of vinyl fluoride, one would, therefore, expect to find that the polymer precipitates as it forms. Solvents also tend to act as chaintransfer agents which yield products of lower molecular weights than those formed in the absence of solvents. Procedure 2-2 shows the effect of a solvent on the intrinsic viscosity and on the overall conversion. Since the procedure is patented it is given here only to illustrate the procedure.

2-2.

Solution Polymerization of Vinyl Fluoride in tert-Butyl Alcohol [39]

With appropriate safety precautions, a 40-ml autoclave is charged with 9.5 gm of vinyl fluoride, 0.05 gm of 2,2'-azobisisobutyronitrile, and 10 ml of tert-butyl

2.

Chemically Initiated Polymerizations

339

alcohol. The autoclave is heated with agitation at 50~ for 16 hr. The autoclave is then cooled and cautiously vented. The product isolated represented a 76% conversion of monomer to polymer with an intrinsic viscosity of 2.25 dl/gm (DMF, 100~ When 10 ml of water is substituted for the tert-butyl alcohol, conversion drops to 39% while the intrinsic viscosity rises to 5.34 dl/gm (DMF, 100~ The polymerization has been carried out in heptane [38]. The reaction was again 0.60th order with respect to the initiator, diisopropyl peroxydicarbonate. The polymer produced had MW in the range of 44,300 to 358,600. It did not swell in either heptane or chloroform. It swelled more in carbon tetrachloride than in dioxane [38]. Solvents containing water have also been used in solution polymerizations. The resulting products are said to be film-forming polymers. Procedure 2-3, which is based on a patent process, is given here only to illustrate the general procedure used.

2-3.

Solution Polymerization of Vinyl Fluoride in Aqueous Methanol [40]

With suitable safety precautions, in an autoclave is placed at 0~ 150 gm of a deaerated solution consisting of 37.5 gm of water and 112.5 gm of methanol, 0.15 gm of diisopropyl peroxydicarbonate, and 97 gm of vinyl fluoride. The apparatus is sealed and heated at 45~ for 12 hr. During this period the pressure varies between 26.6 and 43.5 kg/cm 2 (0.266 and 0.435 MPa). The reactor is then cooled and cautiously vented. The product is isolated. Conversion is 89.7%. The inherent viscosity of the product is 2.22. When 10% aqueous dimethylformamide is substituted for the 25% aqueous methanol in Procedure 2-3, the conversion is 75% and the inherent viscosity of the product is 1.2.

C.

Suspension Polymerization

Probably a major fraction of commercially-produced poly(vinyl fluoride) is manufactured by suspension polymerization. The various reaction parameters associated with the process have been studied in considerable detail. Below is a brief summary of the paper by Kalb et al. [1 ].

a. Effect of Initiators The nature of the initiators used, despite the low level of initator fragments in the final polymer, affects the final thermal stability and wettability of the product. Furthermore, as generally anticipated, the molecular weight was found

340

9. Polymerization of Vinyl Fluoride

to decrease with increasing concentration of initiator. The initiator efficiency also decreases with increasing initiator concentration. Polymers prepared at higher temperatures had, as expected, lower molecular weights than those produced at lower temperatures. The "high-temperature polymers" appeared to be more highly branched and were more easily compression molded. One interesting set of experiments was reported [ 1]. In this case, heavy, glasswalled, liquid level gauges were used as specially designed reactors instead of the usual steel autoclaves. When vinyl fluoride was polymerized in the presence of water while using a water-soluble initiator (2,2'-azobisisobutyramidine hydrochloride or ammonium persulfate), initiation took place in the water phase. The initially clear solution changed appearance from clear, to red, to red-orange, to orange, and finally to opaque. These colors (judging from the description in Kalb et al. [1]) were not due to the formation of chromophoric groups. The colors were those associated with light-dispersion on passing through colloidal particles. The changes in the color are associated with changes in particle size. In this experiment, the polymer was isolated as a dispersion [1 ]. When solvent-soluble initiators were used, polymerization took place above the surface of the water. The polymer chains formed in the gas phase. They were described as "webs." As their sizes increased, they dropped and floated on the surface of the water [ 1]. b. Effect of Temperature

As the temperature is raised, the efficiency of an initiator goes through a maximum in the polymerization of vinyl fluoride. In the case of 2,2'-azobisisobutyronitrile, this temperature of maximum initiator efficiency appears to be independent of pressure, at least in the range from 100 atm (10 MPa) to 250 atm (25 MPa), at approximately 70~ With increasing polymerization temperature, the melt viscosity of the product decreases. The product has a reduced molecular weight and increased chain branching. c. Effect of Pressure

Higher pressures increased the rate of polymerization, favored formation of polymers of higher molecular weight, and enhanced efficiency in the utilization of the initiator. d. Effect of Impurities

In the presence of 0.2% benzoyl peroxide, during the polymerization of vinyl fluoride at 900 atm (90 MPa) and 80~176 the process is slightly inhibited by

2.

Chemically Initiated Polymerizations

341

500 ppm of oxygen. On the other hand, 135 ppm of oxygen seems to promote the process, particularly at the lower temperature ranges. As much as 2% of acetylene strongly inhibits the polymerization to a conversion of 3% of a readily soluble, brittle product. However, when the acetylene concentration is only 1000 ppm, the polymerization is accelerated almost to the point of being uncontrollable. Conversions run to 99%. The product is reported to be insoluble and highly cross-linked. Monomer free of oxygen and acetylene, but containing as much as 2.5% of 1,1-difluoroethane in a 40% methanol-60% water medium, gave rise to a polymer with normal conversion and normal film and molding properties. e. Effect of C h a i n - T r a n s f e r Agents

Among the chain-transfer agents evaluated, are methanol, isopropanol, and 1,3-dioxolane. Of these, methanol has the most modest effect on the molecular weight of the product. A medium containing 30% methanol affords a polymer with an intrinsic viscosity of 1.3 dl/gm whereas the product produced in a methanol-free reaction medium has an intrinsic viscosity of 4.5 dl/gm. Isopropanol and 1,3-dioxolane had much more profound effects on the molecular weight. For example, only 5% of isopropanol in the medium produces a polymer with an inherent viscosity of approximately 0.8, whereas 5% of 1,3-dioxolane in the medium gives a product with an intrinsic viscosity of approximately 0.25 dl/gm. fi Effect of M edi a Other Than W a t e r

Most organic solvents substituted for water in the polymerization of vinyl fluoride exhibit chain-transfer characteristics. Benzene gives rise to lowmolecular-weight products in poor conversion. Procedure 2-4 is a typical suspension polymerization process in which 52% conversion is achieved within 8 hr.

2-4.

Suspension Polymerization of Vinyl Fluoride, Benzoyl Peroxide Initiated [1]

With appropriate safety precautions, 0.4 gm of dibenzoyl peroxide is placed in a 1300-ml stainless steel pressure vessel. The vessel is closed and repeatedly pressured with nitrogen and evacuated until the air has been removed from the reactor. The apparatus is placed on its rocking agitator. Into the evacuated vessel is pumped 400 ml of deoxygenated water and 500 gm of vinyl fluoride. Heating and agitation is begun. During the heating-up period, additional vinyl fluoride is forced into the autoclave so that the 300 atm (30 MPa) of pressure and 85~

TABLE III

Weight, vinyl fluoride (gm)

Weight, water (gm)

Weight, initiator (gm)

120 242 100 15 ml 11.2 and 15.1 Hexafluoropropylene 11.2 and 15.1 Hexafluoropropylene

200 480 275 g 75 66

0.3 ~ 2.42 ~'c 0.75 a 0.0963 a 0.263 ~

100 12.7 22

Suspension Polymerization Conditions for Vinyl Fluoride Weight, suspending agent (gm) 0.4 b 0.48 a

Reaction Pressure (MPa)

Time (hr)

Temp (~

Conversion (%)

0.40

15 18 20

40 40 40 55 50

83.3 86.5 e 100

h 0.06 a 0.2 a

80

Intrinsic viscosity (dl/gm)

Ref.

220 e 1.44 0.94 f 0.34

[42] [43] [44] [45] [46]

0.1 i

3j 65

400 quantity not given 60

0.263 ~

0.1 i

0.151

0.2 a 4* 0.05 m b,o

0.1 ~

0.02 a 3.@

a Diisopropyl peroxydicarbonate. b Poly(vinyl alcohol). c 50 wt% of heptane. d Methyl Cellulose. r Compared to only 23.9% conversion with inherent viscosity of 0.93 when dimethyl phthalate was used instead of heptane. flnherent viscosity. g Containing 25 ml of t e r t - b u t y l acetate. , In a 500 ml autoclave.

8

50

67

7

55

98 72.5

4

40

74

0.31

77"

[47]

[48] [49]

2.0 q

[50]

; Sodium perfluorooctanesulfonate. J FCCI3. * Toluene. 12,2'-azobisisobutyramidine hydrochloride. m t r a n s - 1,2-dichloroethylene. "Fikentscher K value. o 5 ml C2F3C13 or CF3CI, hexane, chloroform, or C2C14F2. P Gaseous ethylene oxide. q Without ethylene oxide, intrinsic viscosity was found to be 2.5 dl/gm.

r ~

2.

Chemically Initiated Polymerizations

343

temperature are reached simultaneously within 1.25 hr. During the polymerization, the pressure is maintained at 30 MPa by repressuring as required. After 8 hr the polymerization comes to a stop. The reactor is cooled, the excess monomer is bled off cautiously and the polymer is isolated (yield: 200 Gm or 52%). Interestingly, when 2,2'-azobisisobutyronitrile is substituted for dibenzoyl peroxide in Procedure 2-4, the reaction can be carried out at 70~ with a pressure of only 70 atm (7.0 MPa) for 19 hr. A 90% conversion of a high molecular-weight-polymer is obtained [1, 5]. There are examples of suspension polymerizations of vinyl fluoride making use of suspending agents. A French patent [41] held by Kureha Chemical Industry Co. reports a reaction that is interesting because of three features: (a) the use of dipropyl peroxydicarbonate as an initiator, (b) the use of methyl cellulose as the suspending agent with sodium phosphate as a buffer, and (c) a two-stage heating cycle at two different temperatures and pressures. This process was said to reduce the over-all processing time. Unfortunately, the Chemical Abstracts write-up of this French patent gives details for the polymerization of vinylidene fluoride rather than of vinyl fluoride. We presume that the examples for the polymerization of vinyl fluoride in the original patent are very similar [41 ]. Table Ill outlines the conditions used for a number of suspension polymerization processes of vinyl fluoride [42-50]. Attention is directed in particular to a number of additives which have been used as chain-transfer reagents to control the molecular weights of the polymers.

D.

Emulsion Polymerization

The work of Kalb et al. [ 1] indicates that the polymerization of vinyl fluoride in the presence of water with a water-soluble initiator may give rise to a polymer dispersed in the water phase and having the small particle diameter associated with latices. However, there is no particular discussion of the properties of poly(vinyl fluoride) latices in this article. The surfactants usually used in the emulsion polymerizations of nonfluorinecontaining monomers appear to be unsatisfactory in the case of vinyl fluoride polymerizations [6]. Salts of the higher perfluorinated carboxylic acids are more suitable emulsifiers. Cationic surfactants based on perfluoroalkylpropylamines are used in a recent patent for the emulsion polymerization of vinyl fluoride [36]. Procedure 2-5 is a patented process outlined here for reference purposes only. In this preparation, the patentee [51] claims that the incorporation of sodium orthosilicate raised the polymer yield to 95%. Without this component, the yield was only 65%. Even when the emulsifier was doubled, the yield of poly(vinyl fluoride), in the absence of sodium orthosilicate, only rose to 70%. In the

344

9. Polymerization of Vinyl Fluoride

procedure, Emulsifier L 1159 is believed to be a perfluorinated carboxylated emulsifier from 3M Corp.

2-5.

Emulsion Polymerization of Vinyl Fluoride [51]

In a suitable autoclave, to a solution of 3 gm of sodium orthosilicate, 0.2 gm of ammonium persulfate, and 0.6 gm of Emulsifier L 1159 (3M Corp.) in 200 gm of distilled water is added 100 gm of vinyl fluoride. The autoclave is sealed and heated at 46~ at 42.5 atm (4.25 MPa) for 8 hr. The conversion to poly(vinyl fluoride) by this procedure is 95%. Without sodium orthosilicate the conversion is 65%. When 1.2 gm of Emulsifier L 1159 is used in the absence of the orthosilicate, conversion is 70%. Redox initiators such as potassium persulfate-sodium metabisulfite or ammonium persulfate-sodium sulfite have been patented for use in poly(vinyl fluoride) emulsion polymerizations [52]. In another patent [53], a seeded emulsion polymerization is described. The "seed" polymer is prepared by emulsion polymerization of vinyl fluoride using tert-butyl peroxypivalate as initiator and ammonium co-hydroperfluorononanoate as emulsifier. The process required 9 hr at 40 kg/cm 2 (0.4 MPa). The resultant particles were described as having an average diameter of 18 pm (which we would consider a a bit large for emulsion particles) and are said to be present in a concentration of 2.26 • 1016 particles/dm 3. In the second stage of the process, this seed latex (400 ml in a total volume of 1.8 dm 3) was subjected to the same reaction conditions a second time. By use of between 0.1% and 1% of a non-ionic surfactant of HLB-value between 8 and 15 and surface tension less than 30 dyne/cm, poly(vinyl fluoride) emulsions with particle diameter less than 5 pm have been prepared at 30~176 [54]. Procedure 2-6 is a patented process given here for reference only. It is of interest because the incorporation of an iodine-containing compound such as ammonium iodide, 2,2'-azobisisobutyramidine hydroiodide, potassium iodide, iodine in isopropanol, isopropyl iodide, tetraiodoethylene in tert-butanol, iodobenzene, 2-iodothiophene, or ethyl iodide give rise to polymers of improved thermal stability and resistance to color deterioration [55]. The process does not seem to involve the use of an emulsifying agent.

2-6.

Emulsion Polymerization of Vinyl Fluoride in the Presence of Ammonium lodide [55]

In a suitable stirred autoclave equipped for the addition of aqueous solutions while under pressure to 1.3 dm 3 of water at 75~ and stirred at 180 rpm is added 350 gm of vinyl fluoride. The free space is purged with some of the monomer. Then the pressure in the autoclave is raised to 200 kg/cm 2 (2 MPa). Under

Z

345

Chemically Initiated Polymerizations

pressure a solution of 2,2'-azobisisobutyramidine hydrochloride in 50 ml of water is added followed in turn by 50 ml of rinse water, 25 ml of an aqueous solution of 25 mg of ammonium iodide, and 25 ml of water. After 150 min, the internal pressure of the autoclave drops to 30 kg/cm 2 (0.3 MPa). The reaction mixture is cooled and stirred at 5000 rpm to coagulate the latex. Conversion is 86%. The polymer is said to have a Fikentscher K-value of 89 (at 120~ in a 1% cyclohexanone solution). By careful removal of oxygen and other impurities from the system by passing the monomer over finely divided copper at 50~ prior to use, another patent claims the production of a 13% nonvolatile latex with particle diameter of 0.36/tm using a water-soluble azo compound as initiator at 60~176 and 40-60 kg/cm 2 (0.4-0.6 MPa) of pressure [56]. With 2,2'-azobisisobutyramidine hydrochloride as an initiator for the emulsion polymerization of vinyl fluoride, the use of an anionic surfactant in the dispersing medium leads to ineffective initiator systems. Nonionic surfactants, while compatible with the initiator, generally lead to low yields and low molecular weights of the polymer. Similarly, ordinary cationic emulsifiers lead to colored products of low degree of polymerization [36]. Uschold's patent [36] makes use of fluorinated amine salts as surfactant. In one example, in a stainless steel shaker tube, to 200 ml of deionized water are added 0.10 gm of 2,2'-azobis(isobutyroamidine) dihydrochloride and 0.400 gm of C6Fla(CH2)aNHaC1.The mixture is frozen. The tube is then evacuated and purged with nitrogen. This procedure is repeated three times. The tube is again evacuated and 100 gm of vinyl fluoride is pumped in. After the apparatus is sealed, it is placed on a shaker and heated at 90~ for 3 hr. Then the reactor is cooled, and under environmentally appropriate conditions, the tube is vented. The product is isolated either by filtration or by use of a high speed centrifuge. The polymer is dried in a circulating air oven at 90~ to 100~ The yield of polymer was said to be 27.5 gm [36].

E.

Organometallic

and Related

Initiator Systems

The usual initiators such as 2,2'-azobisisobutyronitrile, benzoyl peroxide, and lauroyl peroxide have to be decomposed to generate the free radicals which bring about the polymerization process. While there are methods which involve the use of radiation to accomplish this, these are rarely advocated; it is more common to use thermal means to generate the initiating species. In order that the product be formed in a reasonable time interval, it is usual to attempt the use of these initiators at temperatures in the range of 60 ~ to 80~ (with the notable exception of diisopropyl peroxydicarbonate which may be used in the range of 25~ to 50~ Such temperatures are above the critical temperature of vinyl fluoride (54.7~ Consequently, regardless of applied pressure, the monomer cannot be liquified above 54.7~ the temperatures at which the initiators are

346

9.

Polymerization of Vinyl Fluoride

most effective. Processing, therefore, suffers from the fact that only relatively low concentrations of monomer can be reacted even at high pressures. For this reason, low-temperature processes are desirable. Low-pressure procedures are also of interest for other reasons, not the least of which are the enhanced safety of the process and the reduction in the complexity of the technology required when switching from a high- to a low-pressure method. The use of ZieglerNatta catalysts or of boron trialkyl systems was explored since these materials frequently are effective at modest temperatures and at low pressures. The effectiveness of Ziegler-Natta catalysts of the triethylaluminum-titanium tetrachloride type seems to be the subject of some controversy. One patent describes the formation of poly(vinyl fluoride) with such a catalytic system in THF in a bottle polymerization at 30~ and autogenous pressure for 6 hr [57]. A complex of triisobutylaluminum, vanadium oxytrichloride, and THF is said to be particularly effective at 30~ both for the homo- and copolymerizations of vinyl fluoride [58, 59]. The processes are said to resemble typical Ziegler-Natta systems and are independent of the THF concentration when the mole ratio of THF to VOC13 was greater than 2.3:1. The use of triisobutylaluminum with tetraisopropoxytitanium at 30~ for 15 min is said to lead to a process with an ionic-coordination mechanism [60]. On the other hand, Usmanov et al. [17] and Sianesi and Caporiccio [20] imply that Ziegler-Natta catalysts of the trialkylaluminum-titanium (or vanadium) tetrachloride type are ineffective because the rate of polymerization is slow and the degree of polymerization of the product is also low [ 19, 20]. Vanadium compounds such as vanadyl acetylacetonate with aluminum compounds of the type AIR(OR)C1 form effective Ziegler-Natta catalysts [19, 20]. The polymers produced by these catalysts are of rather low molecular weight. However, they have crystalline melting points in the range 220~176 substantially higher than those for poly(vinyl fluoride) produced under high pressure by conventional initiators. The polymers are not stereo-regular. The reaction rates and intrinsic viscosities of polymers produced by a vanadyl tris(acetylacetonate)-RAl(OR')C1 (where R and R' may be either methyl, ethyl, or isobutyl groups) catalysts showed little change with variations in the aluminum to vanadium ratios. Trialkylboranes activated by oxygen, strongly increase the rate of polymerization of vinyl fluoride and bring about high degrees of polymerization. While the oxygen-trialkylborane initiators are the most effective ones of the group, complexes of oxygen with dialkylzinc, oxygen with dialkylcadmium, and oxygen with dialkylberyllium also catalyze the polymerization of vinyl fluoride. Oxygen also enhances the activity of the ammonium addition complex of triethylborane, which is reactive even without oxygen. With these initiators, at conversions above approximately 30%, the rates of polymerization decreased. Maximum conversions achieved were on the order of

3.

347

Radiation-Initiated Polymerizations

70%. This phenomenon has been attributed to catalyst depletion during the initiation of a very rapid reaction and to the heterogeneity of the system brought about by the insolubility of the polymer [20]. Procedure 2-7 is an outline of the method used in the polymerization of vinyl fluoride with oxygen-tri-n-propylborane in ethyl acetate as an indifferent solvent.

2-7.

Solution Polymerization of Vinyl Fluoride with Oxygen-tri-n-Propylborane Initiation [20]

With proper safety precautions, to a 50-ml stainless steel bomb filled with dry nitrogen is charged 2 ml of ethyl acetate and 0.028 gm (0.2 x 10-3 mole) of trin-propylborane. The bomb is cooled at liquid air temperature and 15 gm of vinyl fluoride is distilled into the bomb under reduced pressure. The bomb content is then deaerated by repeated freezing and thawing under reduced pressure. Then, to the frozen and evacuated vessel is added from a small calibrated buret 0.0016 gm (0.1 x 10- 3 mole) of oxygen. The bomb is sealed and heated in a constant temperature bath at 30~ for 5 hr. Then the polymerization is stopped by freezing at liquid-air temperature. The bomb is cautiously vented to permit unreacted monomer to escape and residual polymer is washed repeatedly with boiling methanol and dried at 100~ under reduced pressure (yield, 7.5 gm or 50% conversion; intrinsic viscosity, [r/] = 2.8 dl/gm). In general, these reactions were found to have polymerization rates which are first order in the monomer and 0.5 order in the catalyst and oxygen. Activation energies vary with the catalysts used from 6 kcal/mole in the case of triethylborane initiation to 25 kcal/mole for the case of triethylborane-ammonia complex [61]. These initiators are also effective in the preparation of copolymers of vinyl fluoride [20, 62]. Instead of introducing gaseous oxygen into the system to form the oxygentrialkylborane initiator, a patent relates the use of hydrogen peroxides with trialkylborane in aqueous media [63]. Other organometallic initiators which have been mentioned include tetramethyllead (or tetramethyltin) in tert-butanol dispersed in an aqueous solution of ammonium persulfate and borax [64] and silver compounds such as silver nitrate with organic lead or tin compounds and organic promoters such as acetone, dimethyl sulfoxide, ethanol, or tert-butanol [65]. 3.

RADIATION-INITIATED

POLYMERIZATIONS

Early polymerization experiments on vinyl fluoride which yield a reasonable quantity of the polymer involved the use of ultraviolet radiation [37]. This work was carried out in quartz capillary tubes. Sources which emitted ultraviolet

348

9. Polymerizationof VinylFluoride

radiation at less than 280 nm such as a General Electric Type H-4 lamp, without the outer glass bulb, were used. A 4-watt germicidal lamp whose emission was over 90% at 253.7 nm converted 0.6203 gm of the monomer to 0.22 gm of polymer within 2 days at 27~ Low-pressure polymerizations were initiated by ultraviolet radiation in the presence of di-tert-butyl peroxide in bulk, dimethyl sulfoxide, or tert-butanol solution at - 2 0 ~ to + 30~ While the polymer precipitated out of solution at low conversion, in dimethyl sulfoxide, this precipitate was a gel which was partially transparent to light. At low conversions, the reaction kinetics were treated as pseudohomogeneous processes [15]. The growing vinyl fluoride free radical is not resonance stabilized. Therefore it is quite reactive and capable of abstracting a hydrogen atom from active hydrogen compounds such as isopropanol or acetonitrile with consequent chain termination by a chain-transfer mechanism. In the case of a solvent such as dimethyl sulfoxide, such processes do not take place. As a result, the precipitating polymer has difficulties finding appropriate radicals for termination reactions. As in other examples of the gel or Trommsdorff effect, an acceleration in rate is observed because the free radical propagation is not terminated while the viscosity of the product increases and the rate of the transfer of the released heat to the outside is severely limited. In UV-initiated bulk polymerizations at 25~ the polymerization proceeds to a conversion of 90% in 8 hr. The product was described as a white, soft, porous solid with a density of approximately 0.5 gm/cm 3 from a monomer with a density of 0.6 grn/cm 3. The polymer seems to consist of open pores. When a preparation was carried out in which only the bottom of an ampoule containing the monomer is irradiated, the cellular structure forms near the bottom. The liquid monomer then diffuses into the pores and reacts. The result is the gradual formation of a uniform block of transparent, slightly yellow, solid [75]. Procedure 3-1 outlines the procedure for the photopolymerization of vinyl fluoride.

3-1.

P h o t o p o l y m e r i z a t i o n o f Vinyl F l u o r i d e [15]

With suitable safety precautions, purified vinyl fluoride is frozen in an ampoule by immersion in liquid air. The monomer is degassed several times to remove dissolved air. In the meantime, in a thick-walled glass ampoule (wall thickness, 4 mm, i.d. 12 mm, capacity approximately 12 ml) containing di-tertbutylperoxide (concentration: 0.6 • 10 -2 moles per liter of liquid monomer) and dimethyl sulfoxide (50% by volume of the total liquid monomer composition) is attached to a high-vacuum system so that a measured quantity of vinyl fluoride can be transferred to the ampoule beating the solvent and photoinitiator. The solvent is thoroughly degassed and the monomer is transferred to the

4.

Health Aspects

349

ampoule containing the solvent. The ampoule is sealed off and placed in a constant-temperature bath at 25~ From a distance of 8 cm, the ampoule is irradiated with a Hanau Q81, 1.4 .~ mercury lamp. After 30 min, the ampoule is frozen in liquid air and cautiously opened. The content of the ampoule is allowed to warm up gradually while the unreacted monomer is evaporated off. The product is washed repeatedly with methanol and dried under reduced pressure at 60~ (yield, 23.5%). At comparable concentrations of photoinitiator, reaction temperature, and time, solvents such as dimethyl sulfoxide and tert-butanol enhance the conversion while ethyl acetate, hexane, dimethylformamide, isopropanol, acetone, acetonitrile, and hexamethylphosphoramide reduce the conversion. Sulfalone has no solvent effect. The photochemically-initiated polymerization of vinyl fluoride has also been carried out in a continuous-flow, cylindrical reactor at pressures up to 30 atm (30 Pa). The polymers produced by this method had a higher proportion of a head-to-tail arrangement than commercial polymer [21 ]. Considerable work has been done on the initiation of the vinyl fluoride by ionizing radiation much as ),-radiation from a 6~ source. A selection of references on this research includes Usmanov and other authors [4, 48-62]. Of these, Usmanov et al. [4] deal with the graft copolymerization of vinyl fluoride to some natural and synthetic polymers. Usmanov et al. [53] discuss the formation of branched polymers during radiation-induced polymerization. Gubareva et al. [54] deal with solution polymerizations. Nakamura et al. [58, 59, 61] deal with emulsion polymerizations of vinyl fluoride by radiation initiations. Usmanov et al. [60, 61 ] discuss the effects of chain-transfer agents during radiation-initiated polymerization. Some copolymerization studies are described in Usmanov et al. [55]. The polymerization of vinyl fluoride in a glow-discharge or plasma polymerization is reported in Westwood [63] and Kobayashi et al. [64].

4.

HEALTH ASPECTS

Vinyl chloride was once considered to possess a relatively low toxic character. In fact, at one time it was used as a propellant in spray cans used in the home. Only very recently has the carcenogenic nature of this monomer been discovered. In view of this experience it is difficult to evaluate the toxicity of other compounds such as that of vinyl fluoride. One of the most recent studies is dated 1950 [65]--long before the vinyl chloride toxicity had surfaced. In this study, the maximum allowable concentration for a single short exposure of human beings for vinyl fluoride is given as a concentration of 20% by volume. The effects of long-term exposure or the effect of a single exposure after 20 to 30 yr

350

9. Polymerizationof Vinyl Fluoride

were not considered then and may very well not have been studied more recently. Therefore we recommend extreme caution in handling vinyl fluoride until such time as reliable medical studies on the toxicology of this monomer have been made.

5.

MISCELLANEOUS

1. 2. 3. 4. 5.

Copolymerization studies [22, 73, 84, 85]. Copolymerization with fluoroketones [86]. Donor-acceptor complex polymerization [87]. Vinyl fluoride polymerization with azobisisobutyramidines [88]. Preparation of head-to-head, tail-to-tail poly(vinyl chloride) and poly(vinyl bromide) by halogenation of 1,4-cis-poly(butadiene) [89]. 6. Synthesis of 3-fluoroacrylic acid by hydrolysis of the reaction product from the reaction of vinyl fluoride and carbon tetrabromide [90]. 7. X-ray diffraction pole figure measurements on a poly(vinyl fluoride) film [91].

References 1. G. H. Kalb, D. D. Coffman, T. A. Ford, and F. L. Johnston, J. Appl. Polym. Sci. 4, 55 (1960). 2. D. D. Coffman and T. A. Ford, U.S. Patent 2,419,008 (1947). 3. D. D. Coffman and T. A. Ford, U.S. Patent 2,419,009 (1947). 4. D. D. Coffman and T. A. Ford, U.S. Patent 2,419,010 (1947). 5. F. L. Johnston and D. D. Pease, U.S. Patent 2,510,738 (1950). 6. F. S. Cohen and P. Kraft, Encycl. Polym. Sci. Technol. 14, 522 (1971). 7. DuPont Co. "Tedlar, Technical Information," 234444A, Reorder No. H-49719 (6/93). 8. DuPont Co. "Tedlar, Technical Information," 234427A, Reorder No. H-49725 (6/93). 9. DuPont Co. "Tedlar, Technical Information," 243343A, Reorder No. H-59002 (10/94). 10. M. Amano, Y. Goto, T. Toshiaki, and H. Ochi, Japanese Patent JP 04/258,663 [92/258,663] (1992). 11. F. Suzuki, T. Sumi, and M. Okamoto, Japanese Patent JP 04/141,605 [92/141,605] (1992). 12. R. Davis and S. Ebnesajjad, U.S. Patent 5,137,775 (1992). 13. A. Kh. Gafurov, Nauchn. Tr. Tashk. Gos. Univ. 403. 98 (1971); Chem. Abstr. 78, 72707u (1973). 14. Kh. U. Usmanov, A. A. Yul'chibaev, M. K. Asamov, and A. Valiev, J. Polym. Sci., Part A-1 9, 1459 (1970). 15. D. Raucher and M. Levy, J. Polym. Sci., Polym. Chem. Ed. 13, 1339 (1975). 16. M. L. Wallace and M. A. Kabayama, J. Polym. Sci., Part A-1 4, 2667 (1966). 17. Kh. U. Usmanov, A. A. Yul'chibaev, and A. Kh. Gafurov, Dokl. Akad. Nauk. Uzb. SSR 29, 41 (1972); Chem. Abstr. 78, 98142 (1973). 18. T. J. Dougherty, J. Am. Chem. Soc. 86, 460 (1964). 19. D. Sianesi and G. Caporiccio, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem. 7(2), 1104 (1966).

References

3 51

20. D. Sianesi and G. Caporiccio, dr. Polym. Sci., Part A-1 6, 335 (1968). 21. A. Korin, M. Levy, and D. Vefsi, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem. 20(1), 672 (1979). 22. Kh. U. Usmanov, A. A. Yul'chibaev, A. A. Mat'yakabov, Kh. Kuzieva, and S. Masharipov, Dokl. Akad. Nauk Uzb. SSR 29(12), 24 (1972); Chem. Abstr. 79, 5695 (1973). 23. A. D. Sorokin, E. V. Volkova, and R. A. Naberezhnykh, Radiats. Khim. 2, 295 (1972); from Ref. Zh. Kim. 1973, Abstr. No. 15177 Chem. Abstr. 81, 106152 (1974). 24. R. E. Cais and J. M. Kometani, Macromolecules 17, 1887 (1984). 25. R. E. Cais and J. M. Kometani, Macromolecules 17, 1932 (1984). 26. R. E. Cais and J. M. Kometani, Macromolecules 18, 1354 (1985). 27. R. E. Cais and J. M. Kometani, Polymer 29, 168 (1988). 28. M. D. Bruch, F. A. Bovey, and R. E. Cais, Macromolecules 17, 2547 (1984). 29. G. Trappe, in "Vinyl and Allied Polymers" (P. D. Ritchie, ed.), Vol. 1, p. 260. Iliffe, London, 1968. 30. J. D. Delorme, Rev. Gen. Caoutch. Plast., Ed. Plast. 5(4), 216 (1968). 31. V. A. Korin'ko, M. I. Levinskii, E. A. Chaika, and A. L. Englin, Usp. Khim. 39(1), 94 (1970); Chem. Abstr. 72, 111827 (1970). 32. Kh. U. Usmanov, A. A. Yul'chibaev, G. S. Dorkin, M. K. Asamov, A. Valier, Kh. Kuzieva, and S. G. Yul'chibaev, Nauchn. Tr., Tachk. Gos. Univ. 399, 64 (1970); Chem. Abstr. 77, 152810 (1972). 33. A. A. Yul'chibaev, M. K. Asamov, S. G. Yul'chibaev, A. Valiev, T. Latypov, K. R. Khalikov, Kh. Kuzieva, A. Matyakubov, R. Aslanova et al., Proc. Tihany Syrup. Radiat. Chem., 3rd 1971, Vol. 1, p. 1025 (1972); Chem. Abstr. 78, 137698 (1973). 34. D. Brasure and S. Ebnesajjad, in "Concise Encyclopedia of Polymer Science and Technology" (J. I. Kroschwitz, ed.), pp. 1273ff. Wiley, New York, 1990. 35. S. Ebnesajjad and L. G. Snow, "Kirk-Othmer Encyclopedia of Chemical Technology," 4th ed., Vol. 11, p. 683. Wiley, New York, 1994. 36. R. E. Uschold, U.S. Patent 5,229,480 (1993). 37. A. E. Newkirk, J. Am. Chem. Soc. 68, 2467 (1946). 38. Kh. U. Usamanov, A. A. Yul'chibaev, A. Kh. Gafurov, and V. G. Kolyodin, Vysokomol. Soedin., Ser. B 15(2), 124 (1973); Chem. Abstr. 79, 19188 (1973). 39. T. Nishida and K. Itoi, Japanese Patent 70/18,463 (1970); Chem. Abstr. 73, 99406 (1970). 40. Pittsburgh Plate Glass Co., Netherlands Patent Appl. 6,607,093 (1966); Chem. Abstr. 66, 86116 (1967). 41. Kureha Chemical Industry Co., Ltd., French Patent 1,566,920 (1969); Chem. ,4bstr. 71, 125237 (1969). 42. R. Iwa and Y. Adachi, Japanese Patent 74/27,108 (1974); Chem. Abstr. 82, 86877 (1975). 43. B. Tatsuya, A. Tanaka, and K. Yamashita, Japanese Patent 74/28,670 (1974); Chem. Abstr. 82, 73661 (1975). 44. T. Kawai, M. Ootsuka, and K. Matsuoka, Japan Kokai 74/104,985 (1974); Chem. Abstr. 83, 79961 (1975). 45. Y. Tamura, Y. Shishido, and S. Negishi, Japan Kokai 72/34,785 (1972); Chem. Abstr. 78, 137022 (1973). 46. Y. Tamura and Y. Shishido, Japan Kokai 73/30,787 (1973); Chem. Abstr. 79, 67068 (1973). 47. Y. Tamura and Y. Shishido, Japan Kokai 73/29,883 (1973); Chem. Abstr..79, 67069 (1973). 48. G. Bier, W. Trautvetter, and G. Weisgerber, Fr. Demande 2,004,908 (1969); Chem. Abstr. 72, 122445f (1970). 49. S. Negishi, A. Yonemura, and J. Tamura, Japanese Patent 71/09,261 (1971); Chem. Abstr. 75, 21444 (1971). 50. T. Nishida and Y. Iikubo, Japanese Patent 73/32,579 (1973); Chem. Abstr. 81, 26268 (1974).

352

9. Polymerization of Vinyl Fluoride

51. Deutsche Solvay-Werke, G.m.b.H. French Patent 1,560,029 (1969); Chem. Abstr. 71, 81896 (1969). 52. L. E. Scoggins, U.S. Patent 3,573,242 (1971); Chem. Abstr. 75, 6639 (1971). 53. M. Tatemoto and S. Sakata, Japanese Patent 74/43,386 (1974); Chem. Abstr. 82, 157053 (1975). 54. S. Yoshida, T. Masui, and Y. Matsunaga, Japanese Patent 74/28,669 (1974); Chem. Abstr. 82, 73874 (1975). 55. Dynamit Nobel A.-G., Fr. Demande 2,004,758 (1969); Chem. Abstr. 72, 112058 (1970). 56. F. Engl~inder and G. Meyer, Ger. Often. 2,321,121 (1974); Chem. Abstr. 82, 86864 (1975). 57. G. F. Helfrich and E. J. Rothermel, Jr., U.S. Patent 3,380,977 (1968); Chem. Abstr. 68, 115212 (1968). 58. R. N. Haszeldine, T. G. Hyde, and P. J. T. Tait, Polymer 14(5), 221 (1973). 59. R. N. Haszeldine, T. G. Hyde, and P. J. T. Tait, Polymer 14(5), 224 (1973). 60. G. Caporiccio and D. Sianesi, Chim. Ind. (Milan) 52(2), 139 (1970). 61. G. Caporiccio, E. Strepparola, and D. Sianesi, Chim. Ind. (Milan) 52(1), 28 (1970). 62. G. Caporiccio and D. Sianesi, Chim. Ind. (Milan) 52(1), 37 (1970). 63. Y. Iikubo, T. Nishida, and Y. Furukawa, U.S. Patent 3,645,998 (1972); Chem. Abstr. 76, 154464 (1972). 64. D. Sianesi and G. Caporiccio, French Patent 1,464,332 (1966); Chem. Abstr. 67, 54590 (1967). 65. A. Damiel, M. Levy, and D. Vovsi, Ger. Often. 2,227,914 (1973); Chem. Abstr. 78, 98285 (1973). 66. L. A. Bulygina and E. V. Volkova, Radiats. Khim. Polym., Mater. Simp. 1964, p. 122 (1966); Chem. Abstr. 66, 95567 (1967). 67. E. V. Volkova, P. V. Zimakov, A. V. Fokin, A. D. Sorokin, V. M. Belikov, L. A. Bulygina, A. I. Skobina, and L. A. Krasnousov, Radiats. Khim. Polym., Mater. Simp., 1964, p. 109 (1966); Chem. Abstr. 67, 22304 (1967). 68. Kh. U. Usmanov, A. A. Yul'chibaev, G. S. Dordzhin, and Kh. Yuldasheva, Proc. Tihany Symp. Radiat. Chem., 2nd, 1966, p. 511 (1967); Chem. Abstr. 68, 30135 (1968). 69. E. V. Volkova, P. V. Zimakov, and A. V. Fokin, At. Energ. 26(3), 240 (1969); Chem. Abstr. 71, 3891 (1969). 70. S. S. Dubov, M. A. Landau, E. V. Volkova, and L. A. Bulygina, Zh. Fiz. Khim. 43(6), 1574 (1969); Chem. Abstr. 71, 102274 (1969). 71. Kh. U. Usmanov, A. A. Yul'chibaev, and T. Sirlibaev, J. Polym. Sci., Part A-1 9, 1779 (1971). 72. L. L. Gubareva, G. S. Dordzin, A. A. Yulchibaev and Kh. U. Usmanov, Izv. Yyssh. Ucheb. Zaved., Khim. Khim. Tekhnol. 14(8), 1252 (1971); Chem. Abstr. 76, 25659 (1972). 73. Kh. U. Usmanov, A. A. Yul'chibaev, A. A. Mat'yakubov, Kh. Kuzieva, and S. Kazakov, Dokl. Akad. Nauk Uzb SSR 29(6), 37 (1972); Chem. Abstr. 79, 44039 (1973). 74. A. M. Zaozerov, A. D. Sorokin, L. A. Bulygina, E. V. Vokova, and A. V. Fokin, Dokl. Akad. Nauk SSSR 210(2), 349 (1973); Chem. Abstr. 79, 79285 (1973). 75. N. Nakamura and M. Yoneya, Japanese Patent 73/01,830 (1973); Chem. Abstr. 80, 27677 (1974). 76. K. Nakamura, M. Ichimura, and Y. Fukushima, Japanese Patent 73/08,755 (1973); Chem. Abstr. 80, 109244 (1974). 77. K. Nakamura, M. Ichimura, and K. Fukushima, Japanese Patent 73/37,754 (1973); Chem. Abstr. 81, 38346 (1974). 78. Kh. Usmanov, A. A. Yul'chibaev, G. S. Dordzhin, and L. L. Gubareva, Deposited Publ. 1973, VINITI 5785; Chem. Abstr. 85, 21954 (1976). 79. T. S. Sirlibaev, A. A. Yul'chibaev, Kh. U. Usmanov, and V. G. Kalyadin, Uzb. Khim. Zh. No. 2, p. 37 (1976); Chem. Abstr. 85, 63586 (1976).

References

353

80. L. L. Gubareva, T. S. Sirlibaev, A. A. Yul'chibaev, and Kh. U. Usmanov, Uzb. Khim. Zh. No. 4, p. 39 (1976); Chem. Abstr. 85, 178255 (1976). 81. A. R. Westwood, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem. 10(1), 433 (1969). 82. H. Kobayashi, M. Shen, and A. T. Bell, U.S.N.T.I.S. AD Rep. AD778682/SGA (1974); Chem. Abstr. 81, 152780 (1974). 83. D. Lester and L. A. Greenberg, Ind. Hyg. Occup. Med. 2, 335 (1950). 84. J. R. Semancik and W. A. Gallup, U.S. Patent 3,325,344 (1967); Chem. Abstr. 67, 65029 (1967). 85. A. A. Mat'yakubov, A. A. Yul'chibaev, Kh. Kuzieva, and Kh. Ya. Usmanov, Izv. Vyssh. Uchebn. Zaved., Khim. Khim. Teknol. 15(8), 1265 (1972); Chem. Abstr. 77, 115154 (1972). 86. E. G. Howard and P. B. Sargeant, J. Macromol. Sci., Chem. Al(6), 1011 (1967). 87. Kh. U. Usmanov, Kh. Kuzieva, A. A. Yul'chibaev, and M. Zh. Akimdzhanova, Izv. Vyssh. Uchebn. Zaved., Khim. Khim. Tekhnol. 16(6), 948 (1973). 88. J. E. Cook and O. L. Marrs, U.S. Patent 3,428,618 (1969); Chem. Abstr. 70, 78753 (1969). 89. M. Oin, F. Tudos, and O. Vogl, Am. Chem. Soc. Polym. Prepr. 35(1), 484 (1994). 90. T. Nguyen, J. Leroy, and C. Wakselman, J. Org. Chem. 58, 3772 (1993). 91. R. Large, W. P. Maddams, and J. E. Preedy, J. Appl. Polym. Sci. 22, 3031 (1978).

Chapter 10

Miscellaneous Polymer Preparations 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Preparation of Miscellaneous Organometallic and Metal-Containing Polymers . . . . . . . .

2-1. 2-2. 2-3. 2-4.

Preparation and Polymerization of p-Trimethylleadstyrene . . . . . . . . . . . . . . Preparation of Polyvinylferrocene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preparation of Polymeric Metal Phthalocyanines . . . . . . . . . . . . . . . . . . . . . Polyaddition of Diphenyltin Dihydride and N,N'-Ethylene Bis-acrylamide . . .

3. Poly(metal phosphinate)s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-1. Preparation of Poly[zinc(II)diphenylphosphinate] . . . . . . . . . . . . . . . . . . . . 3-2. Preparation of Poly[zinc(II)methylphenylphosphinate] . . . . . . . . . . . . . . . . 4. Modification of Existing Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Chlorination of Poly(vinyl chloride) (PVC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4-1. Preparation of Chlorinated Poly(vinyl chloride) . . . . . . . . . . . . . . . . . . . . . . B. Diels-Alder Reaction of Triene Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4-2. Preparation of 1,6-Poly(1,3,5-hexatriene)-Tetracyanoethylene Adduct . . . . . . 4-3. Preparation of Dibromocarbene-Modified Polybutadiene Rubber. i . . . . . . . . 5. Miscellaneous Polymer-Forming Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5-1. 5-2. 5-3. 5-4. 5-5. 5-6. 5-7.

Preparation of Poly(diallyldiethylammonium bromide) . . . . . . . . . . . . . . . . . Preparation of Polyimidate Resins from Ethylene Cyanohydrin . . . . . . . . . . . Preparation of Polyamidine from Bisketenimines and Diamine . . . . . . . . . . . Preparation and Polymerization of Vinylene Carbonate . . . . . . . . . . . . . . . . Preparation ofAliphatic Poly-l,3,4-oxadiazoles . . . . . . . . . . . . . . . . . . . . . . Polymerization of m-Diethylnylbenzene . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preparation of Poly-p-xylylene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6. Preparation of Polymers from Propargyl-Terminated Monomers . . . . . . . . . . . . . . . . . .

355 356 356

357 358 359 359 360 360 360 361 361 362 362 364 365 366 367 367 370 373 374 376 376

6-1. Preparation of Dipropargyloxy Ether of Sulfonyldiphenol (4,41-Dihydroxydiphenyl Sulfone) and Its Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . 377 6-2. Preparation of the Dipropargyl Ether of Bisphenol A . . . . . . . . . . . . . . . . . . 378 354

1.

Introduction

7. Recent Polymers Based on Fullerenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8. Polycyanurates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9. Starburst Dendrimers or Star-Shaped Dendritic Macromolecules . . . . . . . . . . . . . . . . . .

355 380 381 382

9.1. Preparation of a Third Generation Polyamine Dendrimer Starting from Methyl Acrylate, Ammonia, and Ethylenediamine Using Various Reaction Sequences. 383 10. Polymerizations in Supercritical Fluids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10-1 Polymerization of Styrene in Supercritical Carbon Dioxide . . . . . . . . . . . . . . 11. Metal-Containing Polymers as Polymeric Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . .

386 387 388

11-1. Preparation of Anthranilic Acid Anchored to Polystyrene and Complexed with RhC13.3HeO Useful for the Hydrogenation of Olefins . . . . . . . . . . . . . . . . . 391 12. Polymer Particles of Uniform Size Distribution (Monodisperse Latices) . . . . . . . . . . . .

12-1. Preparation of Monodispersed Styrene-co-p-Sodium Styrenesulfonate Latex . . 12-2. Preparation of a Styrene-co-Acrylamide Latex . . . . . . . . . . . . . . . . . . . . . . . 12-3. Chemical Modification of the Functionalities of Poly(styrene-co-Acrylamide) Latices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-4. Monodispersed Crosslinked Microspheres by Dispersion Polymerization . . . . 12-5 Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13. Optically Active Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Naturally Occurring Chiral Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Introduction of Optical Activity into Inactive Polymers . . . . . . . . . . . . . . . . . . . . .

13-1. Reaction of Chloromethylated Polystyrene with a Tertiary Amine . . . . . . . . . 13-2. Preparation of (+)-Poly-[4-(2-hydroxyethyl)styrene by Asymmetric Reduction C. Polymerization of Optically Active Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13-3. 13-4. 13-5. 13-6.

Low Temperature Cationic Polymerization of ( + )-3-Methyl-l-pentene . . . . . . Polymerization of l-tx-Methylbenzyl Methacrylate . . . . . . . . . . . . . . . . . . . . . Polymerization of o-Vinylbenzyl D-sec-Butyl Sulfide . . . . . . . . . . . . . . . . . . . Polymerization of l-Propylene Oxide with Potassium Hydroxide . . . . . . . . . .

D. Separation and Polymerization of Racemic Monomers . . . . . . . . . . . . . . . . . . . . . . E. Cationically Induced Polymerizations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

392 396 397 398 401 401 401 402 402 403 404 404 405 406 408 408 409 410

13-7. Summary of the Polymerization Procedure for the Production of a Poly (benzofuran) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410 F. Polyisocyanates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13-8. Polymerization of (R)-2, 6-Dimethylheptyl Isocyanate . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1.

410

411 411

INTRODUCTION

Several areas of polymer preparations that extend the general scope of the materials covered in Vols. I-III of this series are discussed. The main areas covered are organometallic polymers and modification of existing polymers. In addition a variety of miscellaneous polymers are presented that are of general interest.

356

10. Miscellaneous Polymer Preparations

PREPARATION OF MISCELLANEOUS ORGANOMETALLIC AND METAL-CONTAINING POLYMERS

0

The preparations of several organometallic polymers are given here for reference to some more common types of polymers. They are the vinyl type, complex metal phthalocyanines, organotin hydride-olefin condensations, and the poly(metal phosphinates). More detailed reviews on organometallic polymers should be consulted for additional information [1, 2]. CAUTION: All of these monomers are extremely toxic.

2-1.

Preparation and Polymerization of p-TrimethyUeadstyrene [3]

a. Preparation ofp-Trimethyneadstyrene

CH2 -- CH-~---~?MgCI + (CHa)aPbBr THF CH2-- CH - ~ - - - / ~ Pb(CH3)3

(1)

To a 250-ml, three-necked, round-bottom flask, equipped with a stirrer, dropping funnel, and condenser is added a solution of 0.1 mole of p-vinylphenylmagnesium chloride in 50 ml THF (THF is distilled to remove peroxides before use). A solution of 24.9 gm (0.07 mole) of trimethyllead bromide in 75 ml THF is added and the reaction is exothermic. The temperature of the reaction is kept below 30~ by cooling and when the exothermic reaction ceases the reaction mixture is kept at 35~ for 8 hr. Then 100 mg p-tert-butylcatecholis added and the mixture is added carefully to an ice-cold saturated ammonium chloride solution. The organic layer is separated and the aqueous layer extracted with ether. The combined organic layer is dried over magnesium sulfate. The solvent is removed under reduced pressure and the product distilled to give 22 gm crude product (b.p. 77.5~ at 0.0003 mm Hg; 86~ at 0.01 mm Hg). This fraction is redistilled from a 30-in. Vigreux column to give 17.9 gm (67%) of a slightly yellow oil (b.p. 60~ ~ at 0.0015 mm Hg, n 2~ 1.6070, and d 2~ 1.7278).

b.

Polymerization ofp-Trimethylleadstyrene CH-- CH2

--CH--CH2-(2)

Pb(CH3)3

Pb(CH3)3

~

2. MiscellaneousOrganometallicand Metal-ContainingPolymers

357

One to two grams of 0.1 mol% of 2,2'-azobisisobutyronitrile in p-trimethylleadstyrene is sealed in a glass ampoule. The ampoule is repeatedly evacuated and flushed with oxygen-free nitrogen before sealing under vacuum. The ampoule is heated at 70~ for 24 hr, cooled, and opened. The contents are dissolved in 20 ml benzene and the polymer isolated by precipitation in 400 ml methanol. The polymer is isolated as a white powder after filtration, washing in methanol, and drying at 60~ in a vacuum oven to constant weight. Similarly p-triphenylleadstyrene can be prepared and homo-or copolymerized (with vinyltoluene) [4]. In addition, other [p-(CH3)3M(IV)C6H4CH--CH2] trimethylmetalstyrenes have been prepared and polymerized using a procedure similar to the foregoing one (M = Ge, Sn) [5].

2-2.

P r e p a r a t i o n o f P o l y v i n y l f e r r o c e n e [6] CH2=CH

" --CH2--CH--"

ii:.F,'e:il

(3)

.

To 5 gm vinylferrocene in 5 ml benzene in Fischer-Porter aerosol compatibility tubes equipped with valves is added 2.52 wt% of azobisisobutyronitrile, based on vinylferrocene. (Caution: benzene is extremely toxic.) The tubes are degassed by three alternate freeze-thaw cycles and then filled with nitrogen to slightly above ambient pressure and placed in a 80~ constant-temperature bath. After 2 hr, another portion (2.48 wt%) of azobisisobutyronitrile is added and the heating continued for a total of 20 hr. The tube is cooled, vented, and the polymer is precipitated in methanol. The polymer is purified by two more precipitations and then dried at 70~176 under vacuum to give 3.1 gm (62.4% yield), m.p. 281 ~176 (yellow powder). The MW of the polymer from gel permeation chromatography (GPC) is 4,000-280,000 (37/w). The UV spectrum in methylene chloride exhibits/].max at 440, 323, 260 and 232 nm with extinction coefficients of 109, 4960, 6660, and 6460, respectively. The IR in KBr exhibits bands at 3095, 2860-2990, 1360, 1218, 1103, 1038, 1020, 997, and 670 cm-1 and resembled spectra for monoalkyl ferrocenes. The glass transition temperature was estimated to be 190~ from the broad curves obtained from differential-scanning calorimetry (DSC).

358

10.

Miscellaneous

Polymer Preparations

2-3. Preparation of Polymeric Metal Phthalocyanines [7] O II

,c~c,

O II

O\C~c/O

II O

o II + CuC12 + H2N-- C--NH2

II O

HO

OH

I

I

O=C

o II

o

C=O

N=C.wC--N I II _

HO--C~C II

CuCI2

II

/

0il

u

I

C~"-~C--OH I II

N-c"N'c-N

o

(4) O II HO--C~C II 0

N-- C\N~C-- N

I

II

/ ~

l c~N\c

C'~-~"C--OH I II --N 0

--

O=C

I HO

O II

C=O

I OH

To 20 gm (0.092 mole) of pyromellitic dianhydride, 8.0 gm (0.06 mole) of anhydrous copper chloride, and 108 gm (1.8 mole) of urea is added 0.1-0.4 gm ammonium molybdate catalyst. The reaction mixture is heated at 160~ for 30 min. The final product is washed with 6 N HC1, dissolved in 200 ml conc H2SO4 and reprecipitated by dilution with water. The precipitate is washed with water (24 liter), filtered, and dried to give a product with MW approximately 1500 (dimer). The highest molecular weight obtained is 4,000 (6 repeat units)

359

3. Poly(metal phosphinate)s

using 16.0 gm (0.28 mole) CuC12 and 5.0 gm (0.023 mole) of pyromellitic dianhydride at a reaction temperature of 180~

2-4. Polyaddition of Diphenyltin Dihydride and N,N 'Ethylene Bis-acrylamide [8] O

O

II

II

C H 2 - - C H - - C - - H N C H 2 C H 2 - - N H C - - C H - - C H 2 + (C6Hs)2SnH2 C6H5

I

O

II

Cat

O

II

-

(5)

-- Sn-- CH2-- CH2C--NHCH2NHC--CH2--CH2--

I

C6H5

n

a. Preparation ofN, N'-Ethylene Bis-acrylamide The product was obtained in 83% yield by the reaction of acryoyl chloride and ethylenediamine by an interfacial condensation in a chloroform water system. Crystallization from acetone gave a 64% yield of colorless material (m.p. 142~176

b. Condensation Polymerization with Diphenyltin Dihydride

CAUTION"

Benzene is a known carcinogen and must be handled with great

care.

To a flask containing 5.28 gm (0.0314 mole) of N,N'-ethylene bis-acrylamide in 40 ml benzene is added 8.63 gm (0.0314 mole) of diphenyltin dihydride and the mixture is heated to reflux. After 5-hr refluxing the benzene is removed under reduced pressure and the residue heated at 95~ for 4 hr. The infrared spectrum of the solid indicated no free Sn--H absorption. The product is extracted with acetone for 6 hr to remove low-molecular-weight species and then the residue is dissolved in DMF. The DMF solution is centrifuged and then evaporated to dryness to afford 8.3 gm (60%) of polymer (m.p. 110~176 The related additives of diphenyltin dihydride with ethylene glycol dimethacrylate gave a Mw of 150,000. The addition of diphenyltin dihydride to diacetylenic compounds is also reported to give polymers.

3.

POLY(METAL PHOSPHINATE)S

The work in this field was earlier reviewed by Block who summarized the work through 1968 [9]. The interest in these materials is partly due to their

360

10.

Miscellaneous

Polymer Preparations

thermal stability and the fact that some polymers may also have interesting high-temperature film or coating applications. Several other references to these materials should be consulted for additional details [10-11 ].

3-1.

Preparation of Poly[zinc(ll)diphenyl phosphinate] [11] O II (CH3COO)2Zn + (C6Hs)2P -- OH

,

--Zn~OP--O-\

(6)

C6H5

n

To 20 mmoles of diphenyl phosphinic acid in 300 ml of 95% ethanol is added 10 mmole zinc acetate dihydrate dissolved in 100 ml water. Then 19.7 mmole of aqueous sodium hydroxide is added and a precipitate forms. The white precipitate is filtered, washed several times with water and acetone, and dried in a vacuum oven at 110~ to give 4.2 gm (85%). The polymer is insoluble in water and common organic solvents and is infusible to above 450~

3-2.

Preparation of Poly[zinc(ll)methylphenyl phosphinate] [11]

O

(CH3COO)zZn + 2CH3 -- P -- OH

I

C6H5

~

II

I i OH3 --Zn - - O - - P - - O - -

I

C6H5

(7)

n

To a stirred solution of 11.09 gm (71.0 mmole) of methylphenyl phosphinic acid in 600 ml of ethanol is added 7.72 gm (35.5 mmole) of finely divided zinc acetate dihydrate. A white precipitate results and the mixture is stirred for another 2 hr at room temperature. The precipitate is filtered and washed twice with ethanol to give 11.8 gm (95%) after drying at 60~ in a vacuum oven. The TGA of the polymer indicates it is stable to about 400~ in nitrogen without weight loss. Weight loss starts at 425~ The polymer softens below 100~ and is soluble in benzene and chloroform. The molecular weight of the polymer varies between 2500 and 10,000 (colligative methods).

4.

M O D I F I C A T I O N OF E X I S T I N G P O L Y M E R S

The modification of the polymer backbone by selective reactions (halogenation, esterification, etherification, oxidation, reduction, Diels-Alder reactions, dehydrations, dehalogenations, cyclization, grafting [12], etc.) further extend the usefulness of a particular polymer.

4. Modification of Existing Polymers

361

The chlorination of poly(vinyl chloride) (PVC) and the use of unsaturated polymers for further reaction is presented in this section only as an example of some common techniques used. The use of unsaturated polyesters is described in Vol. II of this series [13]. The reaction of polyvinyl alcohol to give polyacetals or polyketals has been already described in Vol. II of this series. In addition the conversion of polyhydrazides to polyoxadiazoles, and polymeric acids to polyimides is also described in Vol. I of this series [ 14] and in Section 5 of this chapter.

A.

Chlorination of Poly(vinyl chloride) (PVC)

PVC was first chlorinated in Germany to 65% chlorine content to give a polymer more soluble than PVC. The soluble polymer was used as a lacquer for the manufacture of fibers by the wet-spinning process. Renewed interest was started in 1962 by B. F. Goodrich [15], which promoted the resin for hightemperature, water-pipe applications in which PVC was not suitable. Other references to preparations are described in several reviews [ 16]. More thermally stable chlorination products are reported to be obtained by introducing chlorine gas containing chlorinated hydrocarbon vapors to PVC suspended in an aqueous system and irradiating without light in the visible and or short wavelength spectrum as described further on.

4-1.

Preparation of Chlorinated Poly(vinyi chloride) [17]

C12

CH2--CH-+i-I C1

--CH-C1

H-- ----CH2--C-- ----CH2--CH-I I C1

C1

(8)

C1

In a 4-liter, glass-lined vessel equipped with a mechanical stirrer, light source (70 watt UV lamp), and chlorine gas inlet and outlet tubes is added 425 gm of PVC (suspension type have a K value of 68 (see [17a]) of 24% water content (fresh from filtered PVC polymerization). Then 900 ml of conc HC1 and 300 ml water are added. The flask is warmed to 35~ and then 20 liter of chlorine is passed over free space to remove air. The UV lamp is turned on and chlorine is

362

10. Miscellaneous Polymer Preparations

passed through a chloroform saturator at 40~ to the reaction flask. After 56 liter of chlorine is fed into the system over a 85-min period. The UV lamp is turned off and then nitrogen is passed through the mixture to remove free chlorine. A total of 185 gm of chloroform is absorbed by the chlorine gas in circulation. The product is washed with water until neutral and purified by steam distillation. The dried product has a 66.9% chlorine content. The Vicat heat is 119.5~

B.

Diels-Alder Reaction of Triene Polymers

Polytrienes undergo the Diels-Alder reaction With strong dieneophiles and tetracyanoethylene, sulfur dioxide, maleic anhydride, etc., as shown in Eq. (9) and Table I [18]. --CH--CH2

CN

CN

['--CH--CH2--

/ C--C \ CN CN

(9)

n

4.2.

Preparation of 1,6-Poly(1,3,5-hexatriene)Tetracyanoethylene Adduct

CAUTION:

Benzene is carcinogenic and must be handled with great care.

a. Preparation of 1,6-Polyhexatriene (Amorphous) [ 19] To a cooled ( - 25~ 100-ml flask previously flame-dried and blanketed with nitrogen is added via a syringe a solution of 0.17 gm (0.4 mmole) of tetraphenyl titanate and 0.02 ml (0.2 mmole) vanadyl trichloride in 55 ml of chlorobenzene. Then a 3-ml portion (3.0 mmole) of a 1 M solution of di-ethylaluminum chloride in heptane to which a molar equivalent of anisole has been added is injected into the flask. Then 5 ml (0.045 mole) hexatriene is added via a syringe and stirred at - 2 5 ~ for 24 hr. The resulting viscous solution is carefully quenched by pouting into cold, acidified (3% HC1) ethanol to precipitate the polymer. The polymer is washed with cold, acidified ethanol, absolute ethanol, and then dissolved in benzene to remove insolubles. The polymer (2.75 gm 78%) is stable in the benzene solution ([/~]inh 0.5% in benzene at 30~ of 0.61). The polymer on drying becomes crosslinked but is stable in solution. The infrared spectrum of 1,6-polyhexatriene is shown in Fig. 1.

TABLE I

Typical Postreactions of Polytrienes a

Polymer

Time (hr)

Temp (~

Adduct r/inhc

TCNE

4

25

0.52

Benzene d

TCNE

24

25

0.62

0.99

THF

TCNE

24

25

0.64

Anionic polyhexatriene

1.15

THF

TCNE

4

25

0.98

1,6-Polyhexatriene

0.61

THF

CN(CF3)C = C - - CN(CF3)

5

65

0.63

1,6-Polyhexatriene

0.61

Toluene

Maleic anhydride

72

25

1,6-Polyhexatriene

0.61

Toluene

Sulfur dioxide

5

65

1,6-Polyhexatriene

0.61

Benzene d

Dimethyl acetylenedicarboxylate

5.5

80

Base polymer

qinhb

Solvent

1,6-Polyhexatriene

0.61

Benzene d THF

1,6-Polyheptatriene

0.88

2,7-Polyoctatriene

Dienophile

Remarks 45% reaction of trans, trans-diene units 50% reaction of trans, trans-units 43% reaction of trans, trans-dienes 38% reaction of trans, trans- and trans-vinyl dienes 45% reaction of trans, trans-units; C-F bands in infrared 55-60% reaction of trans, trans-units; infrared bands at 1820, 1765, and 1240 - 1 < 10% reaction of trans, trans-units; sulfone bands at 1300 -1 and 1125 cm > 75% reaction of trans, trans-dienes; infrared bands at -1 1750-1700 and 1250 cm

a Reprinted from V. L. Bell, J. Polym. Sci., Part A 2, 5305 (1964). Copyright 1964 by the American Chemical Society. Reprinted by permission of the copyright owner. b 0.5% in benzene at 30~ c 0.5% in THF at 30~ d Caution." Benzene is carcinogenic and must be handled with great care.

ta~ O~

364

10.

Miscellaneous

Polymer Preparations

0.0

0.1

o C

0.2

=. 0.3

a ,12

<

0.4 0.5

1.0 oo

I I

,

3000

I

i

i

i

i

I

i

i

i

i

I

1000

2000 Wave

~

900

]

800

number (cm -~ )

Fig. 1 Infraredspectrum of amorphous 1,6-polyhexatriene. Reprinted from V. L. Bell, J. Polym. Sci. 2A, 5291 (1964). Copyright 1964by the Journal of Polymer Science. Reprinted by permission of the copyrightowner.

b. Preparation of 1,6-Polyhexatriene-Tetracyanethylene To a solution of 2.0 gm (0.025 equiv) of 1,6-polyhexatriene ([/~]inh 0.59 in C6H6 at 30~ = 0.61) in 25 ml benzene is added 3.2 gm (0.02 mole) tetracyanoethylene in 15 ml of THF. The initial red color of the solution turns to a pale yellow-green in 4 hr whereupon the precipitated polymer is filtered. The polymer is washed with methanol and dried under vacuum at room temperature to yield 3.0 gm of a colorless polymer that is insoluble in benzene but soluble in THF. The polymer gives clear films when cast from THF, and at 0.5% in THF at 30~ has a [/~]inh -- 0.52. The nitrogen analyses of 18.2% indicates about 45% of the diene is reacted with tetracyanoethylene. The IR spectra is shown in Fig. 2. The IR indicates that the trans, trans-diene absorption band at 985 cm-] is removed while the 970 cm-] shoulder for cis, trans-diene group is unchanged. The cyano absorption appears weakly at 2220 cm-~.

4-3. Preparation of Dibromocarbene-Modified Polybutadiene Rubber [20] ( - - C H 2 - - C H : C H - - C H 2 - - ) n + CHBr3 + KOt--Bu --CH2--CH--CH--CH2 \ /

I

C /

Br

\

Br

tn

365

5. Miscellaneous Polymer-Forming Reactions 0.0

0.1

0.2

!

.a 0.3

I I I

~ O.4 0.5

!

1.0 =

3000

II

2000

I

I

=

I

=

I

I

1500 Wave

I

I

1000

I

I

900

=

1

800

number (cm -~ )

Fig. 2 Infrared spectrum of amorphous 1,6-polyhexatriene. (. . . . ) Unreacted polymer: ( ~ ) polymer adduct with tetracyanoethylene. Reprinted from V. L. Bell, J. Polym. Sci., Part A 2, 5305 (1964). Copyright 1964 by the Journal of Polymer Science. Reprinted by permission of the copyright owner.

To a 2-liter, round-bottom, glass flask equipped with a reflux condenser, drying tube, dropping funnel, thermometer, and stirrer, is added 300 ml of tert-butyl alcohol. While stirring, 10 gm (0.25 mole) of potassium metal (as small pieces) is slowly added at a rate to keep the reaction under control. The excess alcohol is removed under reduced pressure and to the residual cake of potassium tert-butoxide is added 300 ml of dry n-pentane. Then a solution of 60 gm of stereospecific polybutadiene rubber in 800 ml cyclohexane is added. The resulting mixture is cooled to 0~ while 63 gm (0.25 mole) of bromoform is added dropwise and when complete the temperature is allowed to rise to 25~ Then 2,6-di-tert-butyl-4-methyl phenol (5 ppm of rubber product) is added and then the mixture poured into methanol to precipitate the product. The solid is filtered, washed with alcohol, water, alcohol, and then dried at 50~ under reduced pressure. The product on analyses showed 2 wt% of chemically bound bromine.

1

MISCELLANEOUS POLYMER-FORMING REACTIONS

This section presents examples of less typical polymer preparations that may be of general interest due to their interesting properties. For example, the polymerization of alkynes is a topic of increased interest in recent years.

10. Miscellaneous Polymer Preparations

366

5-1.

Preparation of Poly(diallyldiethylammonium bromide) [21]* CH2 CH2 II II CH CH I

Z" -k CH2

\

R

(1)

I

ZCH2--CH ,

cn2

I

initiation

/ N+ / \Br

CH2 II CH I

CH2

\

R

R

/

/ N+

CH2

I

CH2 CH2 N / N / +\Br-

R /

\

CH--CH2--CH

I

I

CH2

\

/

CH2

/ + \BrR

CH2 % CH

I

I

CH2

\

N

R

lr(3) (CH2= CHCH2)2NI~2

propagationby intramoleculargrowth

R

CH2

Z--CH2--CH

growth

\BrR

CH2 / \ ZCH2--CH CH" I

(2) propagation ) by intramolecular

/

CH2

Alternate repetition of steps (2) and (3)

'

Polymers (11)

N

R

/ + \BrR

where R = C2H5 radical, Z = Free radical. a. P r e p a r a t i o n

of Diallyldiethylammonium

Bromide

Allyl bromide, 60.5 gm (0.5 mole), is added to 50.0 gm (0.44 mole) of N,N-diethylallylamine dissolved in 100 ml of acetone; the N,N-diethylallylamine has a b.p. of 110~ and n 22 1.4198; Libermann and Paal [21a] report the boiling point as l l 0 ~ 1 7 6 Upon addition of the bromide, the mixture becomes cloudy and crystals begin to form. The product is washed and decanted several times with cold acetone, filtered, and dried in a vacuum desiccator. White, hygroscopic crystals, 87 gm (84% yield), m.p. 155~ (closed capillary) are formed and are recrystallized from acetone-absolute alcohol. Analysis Calculated for (C10HEoNBr): Found

Br, 34.15 Br, 34.12

b. P o l y m e r i z a t i o n

Twenty drops of 60% tert-butyl hydroperoxide (approximately 0.012 gm/drop) is added to a solution of 8.0 gm of diallyldiethylammonium * Reprinted from G. B. Butler and R. J. Angelo. J. Am. Chem. Soc. 79, 3128 (1957). Copyright 1957 by the American Chemical Society. Reprinted by permission of the copyright owner.

5.

367

Miscellaneous Polymer-Forming Reactions

bromide and 4.0 ml of water. The mixture is allowed to remain open to the atmosphere in an oven at 60~ for 48 hr. The resulting white hygroscopic product is ground to a fine powder and dried for several days in a vacuum desiccator. Eight grams of product, melting with considerable decomposition at 346~176 is obtained. The product is quite soluble in water and ethanol and gives an immediate halogen test when treated with- AgNO3 solution. The avg MW is approximately 7,000-11,000. Analysis Calculated for (C10H2oNBr): C, 51.30 H, 8.20 N, 5.98 Br, 34.15 Found C, 51.35 H, 8.32 N, 5.50 Br, 33.90 Analogously, this intramolecular-intermolecular polymerization also occurs when the nitrogen alone is substituted by phosphorus, silicon, and tin. These reactions have been briefly reviewed by Marvel [22].

5-2.

Preparation of Polyimidate Resins from Ethylene Cyanohydrin [23] nHOCH2CH2--CN

NaOCH3,

[

-- O -- CH2CH2 -- C -- _I,,

(12)

Ethylene cyanohydrin alone or in a solvent polymerizes with the aid of basic catalysts to give a low-molecular-weight polymer that is soluble in water. The details of the reaction are shown in Table II and analogous reactions of ethylene cyanohydrin with alcohols is described in Table III.

5-3.

Preparation of Polyamidine from Bisketenimines and Diamine [24] 0 II

H2N--CrH4--NH2 + 2(CrHs)2CH--CC1

Base

O O II II (CrHs)2CH-- C--NHCrH4--NH-- C-- CH(CrHs)2

azo~

A (C 6H 5) 2C - - C - - N - - C6H4 - - N - - C - - C (C6H 5)2

H2N(CH2)6NH2

B --C = N - - C 6 H 4 - - N = C - - N H - - (CH2)6--NH-- ] I I C H ( C 6H 5)2 C H(C6H 5)2 ,,

(13)

oo

TABLE II

Homopolymerization of Ethylene Cyanohydrin (EC) a

Reaction conditions Base EC (mole)

Type

Mole

2.0 2.0 2.0 2.0 12.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 1.0 1.0 1.0

NaOCH3 NaOCH3 NaOCH3 NaOCH3 NaOCH3 NaOCH3 NaOCH3 NaOCH3 NaOCH3 NaOCH3 NaOCH3 NaOH NaOCH3 KO-t-Bu KO-t-Bu

0.185 0.185 0.185 0.074 1.13 0.185 0.185 0.185 0.185 0.185 0.25 0.037 0.02 0.01

Solvent (150 ml)

H20 CH3CN DMSO THF

Temp (~

Time (hr)

Yield (%)

25 25-90 76 82-160 25 50-70 76 76 58 58 58 25 25 25 25

18 0.75 0.25 1 24 3.5 1 1 2 0.5 0.25 18 384 456

100 100 100 100 100 0 0 100 100 100 100 100 100 100

Softening point (~ 100-110

Calcd (%)

Found (%)

MW

Degree of polymerization

C

H

N

492

7

50.70

7.05

19.70

Violent polymerization 575 8 Violent polymerization

C

H

N

51.60

7.25

18.6

52.38

7.15

Violent polymerization Violent polymerization 330 5 300 4

aReprinted from S. R. Sandier, J. Polym. Sci. 11, 2373 (1973). Copyright 1973 by the Journal of Polymer Science. Reprinted by permission of the copyright owner.

r~

TABLE III

Reaction of Ethylene Cyanohydrin (EC) with Alcohols a

Reaction conditions ROH EC (mole)

2.0

Type

C2HsOH

Mole

6.9

Base (NaOCH3) (mole)

0.2

Analysis (%) Temp (~

78-80

Time (hr)

3.5

Yield (%)

Product structure

b.p. (~ mm)

25.1

NH II HOCHzCHC--OC2H5

125-3.2

13.7 17.0

10.3

C2H5OH

34.3

1.0

78-80

3.5

22.3

Polymer before distillation Polymer after distillation NH II HOCH2CHE--C--OC2H5

np

(~

2.0

(CH3)2CHOH

5.3

0.1

38-83

3.5

18.5

131-132/9

\

N

Calc Found Found Found

51.30 51.02 39.92 51.67

9.40 11.95 8.89 11.85 6.12 7.00 5 . 7 1 15.14

Calc. Found

51.30 51.22

9.40 9.54

11.95 11.71

Calc Found

55.00 53.45

9.93 9.76

10.70 11.06

1.4580 (26)

m.p. 30-31 NH CH3 II / HOCH2CH2--C--OCH

H

1.4580 (24.5)

m.p. 23.0

134-135/9

C

1.4505 (40)

CH3

m.p. 38

aReprinted from S. R. Sandier, J. Polym. Sci. 11, 2373 (1973). Copyright 1973 by the Journal of Polymer Science. Reprinted by permission of the copyright owner.

370

10. MiscellaneousPolymerPreparations

a. Preparation of A: N,N'-Bis(diphenylacetyl)-p-phenylenediamine To a solution of 0.56 gm (5.1 mole) of p-phenylenediamine and 1.0 gm (10.3 mole) of triethylamine in 100 ml of dry ether is added dropwise a solution of 2.37 gm (10.3 mole) of diphenylacetyl chloride in 20ml of dry ether (diphenylacetylchloride is prepared from diphenylacetic acid and thionyl chloride) [25]. Fine, white crystals immediately appear and the reaction mixture is continuously stirred for 18 hr. The resulting solid is filtered, washed with cold water and dried to give, after recrystallization from DMF-water, 1.67 gm (66%), m.p. 333~176

b. Preparation of B: N,N'-Bis(diphenylvinylidene)p-phenylenediamine To a stirred solution of 14 gm (0.028 mole) of (A) in 600 ml of dry pyridine is added 100 gm of alumina and 60 gm (0.42 mole) of P205. The mixture is refluxed for 10 hr and the solid is filtered and extracted with n-hexene in a Soxhlet extractor. The combined filtrate and extract on evaporation give 9.1 gm (71%) (m.p. 178~176 (See also Barker and Wierengo [25a] who reported m.p. 180~176 e. Polymerization of B A solution of both hexamethylenediamine and (B) at 0.12 mole/liter each in dioxane is refluxed for 24 hr to give 64.1 gm (93%) yield, [/]]inh dl/gm (0.2% soln in DMAc at 25~ of 0.31. The polymer is isolated from water and gives a fiber-like material.

5-4.

Preparation and Polymerization C a r b o n a t e [26]*

CH2--CH2 + C12 ~ I I O\ / O

C1 I Base CH2--CH ~ CH--CH ~ I I I I O\ / O O\ / O

C

C

C

0"

0"

0"

of

Vinylene

r--CH--CH-1 t / l1 \/OcO

l

(14)

n

* Reprinted in part from M. S. Newman and R. W. Addor, J. Am. Chem. Soc. 75, 1263 (1953). Copyright 1953 by the American Chemical Society. Reprinted by permission of the copyright owner.

5. Miscellaneous Polymer-Forming Reactions

371

a. Preparation of Vinylene Carbonate (a) Chlorination of Ethylene Carbonate. A stream of chlorine is passed through 303 gm (3.44 moles) of freshly distilled ethylene carbonate at 63~176 in the presence of a UV light. After 24 hr the weight gain is 119 gm (3.44 moles for monochloro substitution). Vacuum rectification yielded 28.0 gm (5.2%) of 1,2-dichloroethylene carbonate and 291 gm (69.0%) of monochloroethylene carbonate. Further rectification afforded pure 1,2-dichloroethylene carbonate [b.p. 78~176 at 19-20 mm Hg, 178~ at 730 mm Hg; n~5 1.4610; d 25 1.5900; MRo calculated (Eisenlohr) for C3H203C12; 26.9. Found: 27.2. Analysis, calculated for C3H203C12 : C, 22.9; H, 1.3; C1, 45.2. Found: C, 22.9; H, 1.2; C1, 45.3. Strong strained-ring carbonyl absorption at 5.40 pm]; pure monochloroethylene carbonate [b.p. 106~176 at 10-11 mm Hg, 212~ at 735 mm Hg, n 25 1.4530, d 25 1.5082, MRo calculated for C3H303C1" Found: 22.0. Analysis, calculated for C3H303C1: C, 29.4; H, 2.5; C1, 29.0. Found: C, 29.6; H, 2.5; C1, 29.2. Strong strained-ring carbonyl absorption at 5.45 pm]. (b) Vinylene Carbonate. To 30.0 gm of monochloroethylene carbonate in 100 ml of dry ether at reflux temperature is added dropwise over over a 7-hr period 25.3 gm of triethylamine in 50 ml of ether. Following refluxing and stirring ovemight, the solids were removed and washed with ether. The remaining ether was removed and distillation yielded 12.4 gm (59~ of colorless liquid (b.p. 76~176 at 37 mm Hg). Further rectification afforded pure vinylene 25 carbonate (b.p. 73~176 at 32 mm Hg, 162~ at 735 mm Hg; m.p. 22~ nD 1.4190; d 25 1.3541. MRo calculated for C3H203" 16.7. Found: 16.1. Analysis, calculated for C3H203: C, 41.9; H, 2.3. Found: C, 42.1; H, 2.4). Infrared analysis showed carbon-hydrogen absorption at 3.12 pm and strained-ring carbonyl absorption at 5.48 pm. This procedure has been modified by the use of carbon tetrachloride solvent [27]. The procedure of Newman and Addor is followed, but the addition of di-tertbutyl-p-cresol is suggested as a polymerization inhibitor. The resulting monomer is further purified by refluxing (64~ the monomer with 1-2% sodium borohydride at 35 mm Hg and then distilling through a short Vigreaux column.

b. Preparation of Poly(vinylene carbonate) The polymerization can be carried out in bulk using initiator or in solution under vacuum in a sealed tube. Monomer, initiator and solvent are added to the glass tubes which are successively flushed with nitrogen and evacuated to 30--40 mm Hg pressure several times and sealed in vacuo. After the polymerization the tubes are broken, the contents dissolved in DMF, and the polymer isolated by precipitation in methanol as described in Tables IV and V. The infrared spectrum of the polymer is shown in Fig. 3.

372

10. Miscellaneous Polymer Preparations

TABLE IV Effect of Initiator (Azobisisobutyrontrile) Concentration on Polymerization at 60~ for 18 hr of Vinylene Carbonate in Bulk a Initiator conc gm 100 ml

Yield (%)

/']inh

0.1 0.1 0.2 0.3 0.3 0.3 0.5 1.0

62 62 67 68(62) --(87) e 69 67

1.36 c 3.86 3.34 3.22(2.42) 0.89 d 2.5 r 2.64 2.16

b

Reprinted from N. D. Field and J. R. Schaefgen, J. Polym. Sci. 58, 533 (1962). Copyright 1962 by the Journal of Polymer Science. Reprinted by permission of the copyright owner. b Inherent viscosity at 30~ in N,N-dimethylformamide solution at 0.5 % concentration. r Vinylene carbonate made by the procedure of Newman and Addor, and fractionally distilled. a Monomer recovered from several polymerizations and fractionally distilled. It had at a much earlier date been treated with NaBH4. e Monomer described in footnote c treated with NaBH4 and distilled. This polymerization was carried out at 56~ for 3 days. fConcentration 0.1% in DMF.

TABLE V

Polymerization of Vinylene Carbonate in Solution at 60~ for 18 hr a

Solvent b None Dimethyl sulfoxide Ethylene carbonate Ethylene carbonate

Initiator (AIBN) conc (grn/100 ml monomer) 0.1 0.1 0.1 0.3

Yield (%)

/~inhc

62 68 69 80

3.86 2.21 1.01 0.95

a Reprinted from N. D. Field and J. R. Schaefgen, J. Polym. Sci. 58, 533 (1962). Copyright 1962 by the Journal of Polymer Science. Reprinted by permission of the copyright owner. b 100 ml of monomer per 100 ml of solvent. c Inherent viscosity at 30~ in N,N-dimethylformamide solution at a concentration of 0.05%.

5.

373

Miscellaneous Polymer-Forming Reactions

0.1 0.2

8E 0

<

0.3 0.4

0.6 0.8 1.0 1.5 1 3

2

1 4

1 6

1 5

1 7

I 8

I 9

1 10

I 11

1 12

1 13

1 14

15

Wavelength (microns)

Fig. 3 Infrared spectrum of (A) poly(vinylene carbonate). This spectrum as a thin film was recorded using a Model-21 Perkin-Elmer spectrometer. Reprinted from N. D. Field and J. R. Schaefgen, J. Polym. Sci. 58, 533 (1962). Copyright 1962 by the Journal of Polymer Science. Reprinted by permission of the copyright owner.

5-5. Preparation of Aliphatic Poly-l,3,4-oxadiazoles A review of the preparation of the aromatic poly-l,3,4-oxadiazole appears in Vol. I of this series [28]. The aliphatic poly-l,3,4-oxadiazoles are made by a similar process by the thermal reaction of the polyhydrazides.

a. Preparation of Polyhydrazides [29] 0 II

0 II

C6H5OC--R--COC6H5

DMF + NH2NH2

110~176

2-5 hr C6H50 \C /

IO I

N H - - NH \ C--R--C II li O O

/

N H - - NH \ C II O

OC6H5

(15)

n

where n = 3-5. The diphenyl ester of the dicarboxylic acid was heated with anhydrous hydrazine in DMF at 110~176 for 2-5 hr. The product precipitates during the reaction as a white solid and is isolated by removal of the solvent and by-product phenol under reduced pressure. Approximately 80-90% of the

374

10. MiscellaneousPolymerPreparations

theoretical phenol is eliminated. Data on some typical preparations is shown in Table VI.

b. Preparation of Polyoxadiazoles [29] / C6H5~O

N H - NH \

C

/

N H - NH \

C~ R~C II II O O

'o'

C~ II O

OC6H5

//

N--N

%

R--C

C

(16) n

The polyhydrazide was converted to the polyoxadiazole by heating at the m.p. for approximately 30 min or until the melting temperature of the product corresponded to the polyoxadiazole in TableVII. The polyoxadiazoles were soluble at room temperature in m-cresol, 1,2-dichloroethane, and chloroform. The IR spectra of the polymers are shown in Fig. 4.

5-6.

P o l y m e r i z a t i o n o f m - D i e t h y n y l b e n z e n e [30]

In 1960 Hay [30] reported that various diacetylenic compounds undergo oxidative coupling with the aid of copper(I) chloride-amine complexes and oxygen to give polymeric products. TABLE VI Preparationof Polyhydrazides Reaction conditions No.

Diphenyl ester O II

I.

II.

III.

Temp (~

Product (m.p. ~

Yield (%)

69-70

2

110-120

280-285

90

62-63

4

110-120

257-263

80

76-76.5

5

110-120

265-270

85

O II

C6Hs--OC(CH2)9--COC6H5

O II

Time (hr)

O II

C6HsOC(CH2)8--COC6H5

O II

m.p. (~

O II

C6H5-- OC(CH2) 1o-- COC6H5

5.

375

Miscellaneous Polymer-Forming Reactions

TABLE VII

Polyoxadiazoles

Polyhydrazides

Intrinsic viscosity (30~ m-cresol)

Specific gravity (gm/cm 2)

m.p. (~

I. II. Ill.

0.45 0.40 0.41

1.21 1.28 1.22

90-110 66-82 64-100

HC--=C--R--C=CH

' [--C--=C--R--C--=C--],,

(17)

An example of this preparation is given in Eq. (18).

'/'- C ~ CH

,

~~--

C=C

C----C-- .

(18)

--C=C

To a 500-ml Erlenmeyer flask is added 250 ml of pyridine, 20 gm of copper(I) chloride, and 61.7 gm (0.49 mole) of m-diethynylbenzene. Oxygen is bubbled through the vigorously stirred reaction mixture which is kept in a bath at 30~

-"-U A

e-

.o etO i_

I

3500

I

I

2500

I

I

1900

I

1

1700

I

I

1500

I

I

1300

I

I

11 O0

I

I

900

I

I

700

Wave n u m b e r (cm -~ )

Fig. 4 Infrared spectra of (I) poly[1,8-octamethylene-2,5-(1,3,4-oxadiazole)]; (II) poly[ 1,9-nonamethylene-2,5-(1,3,4-oxadiazole)]; (Ill) poly[ 1,10-decamethylene-2,5-(1,3,4-oxadiazole); and (IV) 2,5-dipropyl-(1,3,4-oxadiazole). Reprinted from T. Unishi and M. Hasegawa, J. Polym. Sci., Part A 3, 3191 (1965). Copyright 1965 by the Journal of Polymer Science. Reprinted by permission of the copyright owner.

376

10. Miscellaneous Polymer Preparations

A vigorous reaction ensues and the temperature rapidly rises to 40~ After 40 min the reaction subsides and approximately 50-56 gm of polymer is isolated. The polymer is soluble in solvents such as chlorobenzene and nitrobenzene above 100~ Evaporation of the solvent leaves a transparent flexible film (IR, -----CH stretching, 3290 cm -1) of MW approximately 7,000, intrinsic viscosity (nitrobenzene at 150~ of 0.25 dl/gm. The polymer is stable at room temperature but an explosive reaction takes place upon ignition at room temperature. Sondheimer and co-workers [31] have reported that copper(II) acetate in methanolic pyridine has been used to prepare large ring polyacetylenes.

Preparation of Poly-p-xylylene [321

5-7. C1CH2 -

~

CH2C1

Na naphthalene 60~

(_

+ 2NaC1

(19)

To a dark-green solution of sodium naphthalene (prepared under nitrogen from 5.5 gm naphthalene and 3 mI of 50% sodium dispersion in p-xylene) in 70 ml ethylene glycol dimethyl ether at -60~ is added dropwise a solution of 2.6 gm of p-xylylene dichloride in ethylene glycol dimethyl ether. After the addition the mixture is refluxed for 2 hr, the reaction product filtered, washed with water, then acetone, and dried to yield 1.2 gm (77% yield). The X-ray analysis of the product compares well to the product prepared by pyrolysis of p-xylene at 850~176 This polymer is soluble in high-boiling solvents indicating that no cross-linking is present. Poly-p-xylylene has also been made by the pyrolysis of p-xylene at 700~176 in a quartz tube [32].

1t

PREPARATION OF POLYMERS FROM PROPARGYL-TERMINATED MONOMERS

Propargyl ethers of aromatic bis and polyphenols produce precursor candidates for preparing hydrophobic thermoset resins which have more stability in the presence of water than similar resins obtained from diepoxy compounds.

6. Preparationof Polymersfrom Propargyl-Terminated Monomers

377

The dipropargyl ether of bisphenol A undergoes oxidative polymerization in which the two terminal acetylenic hydrogen atoms react to form a high molecular weight linear polymer with two conjugated triple bonds in their main chain. The propargyl monomers are easily prepared in almost quantitative yield by reaction of propargyl chloride with bisphenols or polyphenols in the presence of aqueous sodium hydroxide. The monomers can be purified by recrystallization when they are crystalline. In addition the propargyl monomers were reported to have a lower toxicity than the epoxies and isocyanates [33].

6-1. Preparation of Dipropargyloxy Ether of Sulfonyldiphenol (4, 4Z-Dihydroxydiphen yl Sulfone) and Its Polymerization [33a1 H O - ~

S O 2 - ~

OH + 2HC = C-- CHEBr

Aq. NaOH

O--CHEC~CH (A) Desired Product Ho HC----CCH2

oH

(20)

CH2C----CH

(B) By-product (sol. in aq. NaOH) To a reaction flask fitted with a mechanical stirrer, dropping funnel, reflux condenser and heating mantle is added 8.0 g sodium hydroxide (0.2 mole) and 25.0 gm (0.1 mole) of 4,4-dihydroxydiphenylsulfone dissolved in 200 ml water. While the solution is at room temperature is added dropwise 26.2 gm (0.2 mole) of propargyl bromide over a 30 min period. The reaction mixture is stored for 2 hr at room temperature with little product separating out. Then the mixture is heated rapidly to 90~ (at about 70~ white product is seen separating). The reaction is heated for 30 min at 90~ and the aqueous phase tested neutral indicating the completion of the reaction. The product is separated by filtrations from any (B) and weighed 30.8 gm (99.4% yield) after drying. The melting point after recrystallization from acetone is 185-186~ [330]. The preparations can be improved by the addition of a phase transfer catalyst (PTC) such as tetrabutylamonmonium bromide which also allows one to use propargyl chloride at room temperature [34]. This latter process also leads to less by-product (B) which is the undesired C-alkylated product (probably

37 8

10. Miscellaneous Polymer Preparations

formed by rearrangement of the O-alkylated product at the higher temperature of reaction).

6-2.

Preparation of the Dipropargyl Ether of Bisphenol A [34] CH3

2HC = C - - CH2C1 + HO

OH CH3

"' 20oc 20% NaOH (-2NaC1)

CH3 (21)

I

CH3 To a flask equipped as in the latter preparation (no heating mantle) is added 45.6 gm (0.2 mole) of bisphenol A, 200 ml of 20% aq NaOH (1.0 mole) and 3.22 gm of tetrabutylammonium bromide (0.01 mole). The mixture is stored at 20~ while 34.7 gm (0.46 mole) of propargyl chloride is added over a 10 min period. Then the mixture is stored for 16 hr at 20~ and filtered to yield 57.9 g (95.2%) of white crystals of the desired bipropargyl ether of bisphenol A, m.p. 83~ (99.7% by GC), which did not require recrystallization.

NOTE: Other phase transfer catalysts were evaluated and all were approximately equally as effective (PT-catalysts ranged from tetraalkylammonium halides to polyethylene glycols). In the same manner the bispropargyl ether of 4,4~-dihydroxydiphenyl sulfone (same as from preparation 6.2) gave a 96.2% yield, m.p. 184-186~ of light tan colored crystals. The NMR was consistent with its structure. In a similar manner several other monomers shown in Table VIII were prepared. The product is thermally polymerized by heating at 210~ for a period of 12 hr to yield a hard, black polymer with no evolution of any volatile by-products. If desired, the propargyl-terminated monomers can be B-staged without a catalyst at 185~ for 16-25 hr. This prepolymerization leads to the formation of liquid oligomers below the gel point. It also helps to eliminate shrinkage during the final curing stage, which takes place at 205-210~ for 4 hr without a catalyst allowed by 260~ for 6 hr to improve physiomechanical properties. The thermogravimetric analyses (TGA) indicate that these resins do not lose weight in air or in nitrogen until about 380~ Some dipropargyl ethers are stable to about 420~ (from hexafluorobisphenol A) (see S. K. Dirlikov [33]).

TABLE VIII

Preparation of Bispropargyl Ethers of Substituted Diphenols

Moles Bisphenol H O - ~

(X),,-~

where X = mC(CH3)2 (0.2) mC(CH3)2 (0.2) mSO2 m (0.2) - - C - - (0.2) --CHz m (0.2) m S - - (0.2) C(CF3)2 (0.2) - - O - - (0.2) where n = 0 (0.2)

OH

%

NaOH (20%)

HC--CCH2CI

Bu4N+Br -

Temp (~

Time (hr)

yield

0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4

0.46 0.46 0.46 0.46 0.46 0.46 0.46 0.46 0.46

0.01 0.02-0.05 0.01 0.01 0.01 0.01 0.01 0.01 0.01

20 50 20 20 20 20 20 20 20

16 4 16 16 16 16 16 16 16

95.2 85-97 96.2 95.6 98.7 96.0 94.8 97.0 98.0

m.p.

(~

83 83 184-186

79-81 Oil (98.2% by GC) Oil (98% by GC) Oil (98.6% by GC) Oil (97.1% by GC) Powder (97% by GC)

" Data taken from M. N. Inbasekaran and S. K. Dirlikov, U.S. Patent 4,885,403 (1989).

--.O

380

10. Miscellaneous Polymer Preparations

Bisphenol A propargyl ethers rearrange to chromenes (I) on heating in the range from 150~176 [35]. This is normally carried out in a solvent such as diethylbenzene (Dowtherm J). These chromene-propargyl ether monomer mixtures are of the structure

where X = 502, S, CO, O, C(CH3)2, C(CF3)2, or nothing, and can be polymerized to a resin. Triethylenetetramine can be used to improve the cure of this resin (2 hr at 205~ and 2 hr at 250~ [35]. Propargyl ethers of bisphenol A can also be polymerized by an oxidative polymerization using aqueous cuprous chloride in a mixture of pyridine, and DMF, and oxygen [33]. CH3 HC ~ C-- C H 2 0 ~

C[~ O C H 2 C

~ CH

I

CuC12,DMF1021pyridine 25~

CH3

n C--C--Cn20

CH3

ocn2c--c

n

(22)

CH3 M.W. 15,000-25,000

7.

RECENT POLYMERS BASED ON FULLERENES

Polymers involving C60 are of considerable research interest since they can add properties involving electrical, optical or catalytic properties. In a recent article summarizing this area, A. Hirsch [36] describes the following three possible prototypes of polymers or solids containing the C60 moiety: (1) polymers with a pendant C60 group, (2) polymers in which C60 is an integral part as a dendritic polymer, and (3) polymers with C60 in chain or polymer backbones. The first examples of all these possible cases have already been synthesized. The commercial uses of fullerenes are being explored by many groups but actual commercialization has been slow [37]. Other areas being

381

8. Polycyanurates

explored are superconductors, drug delivery vehicles, and improved batteries. Concerning the commercial state of the art, reference [37] is worth consulting.

8.

POLYCYANURATES

Difunctional cyanate ester monomers were reported about 30 years ago by E. Grigat. The synthesis of these cyanates is reviewed by us in a previous volume [38]. Grigat reported at a recent [39] American Chemical Society meeting that the key synthesis feature involves the use of gaseous cyanogen chloride and phenols rather than aliphatic alcohols. Grigat, who was earlier at Bayer, found that the dicyanate ester of hydroquinone (p-phenylene dicyanate) polymerized on standing at room temperature. The Bayer technology was licensed to Celanese and Mitsubishi Gas Chemical Co. The Celanese technology was later passed on to Ciba-Geigy. The major companies fully involved in cyanate monomers are Ciba-Geigy, Mitsubishi Gas Chemical, Allied Signal and Dow Chemical Co. Ciba and Allied Signal both have cyanated phenolic novolacs as part of their product lines. NCO

OCN

OCN

Allied-Signal (Primeset PT) Ciba-Geigy (REX-371) All the cyanated phenols polymerize by a trimerization mechanism to give cyanurate ring systems as shown below for the polymerization of p-phenylene dicyanate.

NCO OCN ~176 N~N 0

382

10. Miscellaneous Polymer Preparations

Other monomers ofvarious types are also available. For example:

Available from X = C(CH3)2

Ciba-Geigy (and Mitsubishi)

CH2

Ciba-Geigy

C(CF3)2

Ciba-Geigy

C(H)CH3

Ciba-Geigy Ciba-Geigy

NCO

NCO

OCN

OCN

Dow Chemical

CAUTION" Cyanates are toxic and should be handled with great care.

9.

STARBURST [40] DENDRIMERS OR STARSHAPED DENDRITIC MACROMOLECULES

Starburst dendrimers [40] are three-dimensional highly ordered polymers formed by reiterative reaction sequences starting from smaller molecules such as initiator cores. These polymers, also referred to as Star polymers, are formed by a cascade of reactions. Dendrimer (from the Greek for tree-like) is a term that refers to this type of branched and functionalized macromolecules. The ideal of "cascade synthesis" was first introduced in 1978 by Vogtle [41 ] et al., who reported reactions involving Michael additions of an amine to acrylonitrile, followed by reduction of the nitrile group to an amino group. In 1979 [40] a Dow research group reported that a variety of amines could be added to methyl acrylate and the products subsequently amidated with ~x, o~-diaminoalkane to give "cascade products". Further work by the Dow group has expanded this area to produce the Starburst system [40]. An in depth review by Tomalia [40] et al. should be consulted. In a typical example, Tomalia [42] etal. describes a system involving Michael addition of methyl acrylate to ammonia to give the initiator core and then reaction with ethylenediamine. Then again methyl acrylate addition followed by reaction with ethylenediamine. This is repeated many times to finally give the Starburst oligomer or "dendrimers" shown below in the preparation which follows.

9.

383

Starburst Dendrimers or Star-Shaped Dendritic Macromolecules

NH3 + 3CH2--CH--COOCH3

Step A

Step B

' N(CH2CH2COOCH3)3

excess

H2NCH2CH2NH2

NH2(CHE)ENH-- C//O

O%C__NH(CHE)ENH2 NL / ~ / NH(CHE)ENH2

=y

NH2 NH2

c II

NH2

O (Generation O) Repeated (StepsA and B manytimes

NH2

NH2

NH2

N

N

NH2 ~ N

"~, g ' y ' ~ ,

Starlike Shapes to Sequences

,'

NH2

N NH2 NH2 ,,,,,,N

Nr

NH2

g" N

N

(24) NH2

N ,,,,,,NH2

NH2 NH2 Starburst oligomer or "Dendrimer" (Generation 2)

These starburst oligomers may have important implications for the synthesis of biocatalytic mimics, membranes, electronic devices, ion-exchange resins (especially for removing metal ions from solution), photographic imaging, etc. A variety of reagents can be used to produce these starburst oligomers by various reactions, as described in the review by Tomalia et al. [43].

9-1. Preparation of a Third Generation Polyamine Dendrimer Starting from Methyl Acrylate, Ammonia, and Ethylenediamine Using Various Reaction Sequences [43] a. Polyamidoamine Dendrimer--by Michael Condensation of Ammonia with Methyl Acrylate

To a l-liter, 3-necked flask equippped with a mechanical stirrer addition funnel, condenser, and thermowell with thermometer is added 296.5 gm

10. Miscellaneous Polymer Preparations

384

(3.45 mole) of methyl acrylate at room temperature. Then 8.7 gm ammonia (0.58 mole) dissolved in 102.2 gm methanol is added dropwise over a 6 hr period while stirring. The reaction mixture is allowed to stand at room temperature for 48 hr and then excess methyl acrylate is removed by vacuum distillation at 1.0 mm Hg at 22~ to yield 156 gm (97.8% yield) of the product (analyzed by C13 NMR and liquid chromatography).

b. Preparation of the First Generation Adduct To a 3-liter flask equipped with a mechanical stirrer, condenser, and thermowell and thermometer is added 505.8 gm (8.43 mole) of ethylenediamine dissolved in 215.4 gm methanol. Then 28.1 gm (0.1022 mole) of the product of A above is added and the reaction mixture is allowed to stand at room temperature for 55 hr. The resulting reaction mixture (747.6 gm) is vacuum distilled at 2.0 mm Hg at 72~ to remove excess ethylenediamine and methanol. The product obtained amounts to 35.4 gm (98.6% yield) which by analysis is shown to have the amide structure shown below. O 0 II II H2N-- CH2CH2--NH-- C-- CH2CH2--N-- CH2CH2--C--NH-- CH2CHz--NH2

CH2 CH2 C=O NH

CH2 CH2 NH2

c. Preparation of the Second Generation Polyester Dendrimer To a l-liter flask equipped with a condenser, an addition funnel, a mechanical stirrer, and a thermowell-thermometer assembly is added 93.2 gm (1.08 mole) of the methyl acrylate and then heated to 32~ Then 18.0 gm (0.050 mole) of the product of B above dissolved in 58.1 gm methanol is added over a 1.5 hr period. The resulting reaction mixture is kept at 32~ for an additional 5 hr and then allowed to stand at room temperature for 18 hr. Then the reaction mixture (165.7 gm) is subjected to vacuum distillation (2.0 mm Hg at 50~ in order to remove the excess methyl acrylate and methanol to give 43.1 gm (98.4% yield)

9.

385

Starburst Dendrimers or Star-Shaped Dendritic Macromolecules

of product of the following formula: O O I II N - - CH2CH2-- NH-- C-- CH2CH2-- N-- CH2CH2-- C-- NH-- CH2CH2-- N / \ / \ CH2 CH2 CH2 CH2 CH2

I

I

I

I

CH2

CH2

CH2

CH2

CH2

C=O

C=O

C=O

C=O

C=O

I

I

I

I

I

I

l

l

0

0

NH

I CH3

l CH3

o

o

CH2

CH3

CH3

I

I

CH2 N / \ CH2 CH2

I

CH2

I

I

CH2

I

C=O C=O I

I

OCH3 OCH3 d. P r e p a r a t i o n

of the S e c o n d G e n e r a t i o n

Polyamine

Dendrimer

To a l-liter flask as in C above and containing 328.8 gm of ethylenediamine (5.48 mole) dissolved in 210.2 gm of methanol at room temperature is added with stirring 34.9 gm (0.0398 mole) of the second generation polyester dendrimer prepared in C above dissolved in 45.3 gm of methanol. The resulting reaction mixture is allowed to stand for 66 hr at room temperature and then the excess ethylene-diamine and methanol are removed under reduced pressure (2.0 mm Hg and 72~ to yield 41.1 gm of product (99.0% yield). e. P r e p a r a t i o n

of the T h i r d G e n e r a t i o n

Polyester

Dendrimer

To a l-liter flask equipped as in C above and containing 65.1 gm (0.757 mole) of methyl acrylate is added 28.4 gm (0.0272 mole) of the second generation polyamine dendrimer of D above dissolved in 84.6 gm of methanol over a 1.25 hr period. The resulting mixture is allowed to stand for 18 hr at room temperature (25~ and then the excess methyl acrylate and methanol are removed under reduced pressure (2.0 mm Hg at 50~ to yield 56.3 gm product (100% yield). f. P r e p a r a t i o n

of the T h i r d G e n e r a t i o n

Polyamine

Dendrimer

To a 3-1iter flask equipped as in B above and containing 437.6 grn (7.29 mole) of ethylenediamine dissolved in 192.0 gm of methanol is added 44.9 gm (0.0216 mole) of the product of E above dissolved in 69.7 gm of methanol over a period of 48 hr at 25~ while stirring. The resulting reaction mixture is

386

10. Miscellaneous Polymer Preparations

allowed to stand for 19 hr at 25~ after which the excess ethylenediamine and methanol are removed under reduced pressure by vacuum distillation (2.0 mm Hg and 72~ to yield 51.2 gm of product (85.3% yield). The resulting dendrimer has three core branches with four terminal primary amine moieties per core branch, which provides 12 terminal primary amine moieties per molecule of dendrimer. The dendrimer calculated molecular volume is 50,000-97,000cubic A and its density of terminal amine moiety is 1-3 (x 10 -4) moieties/cubic A. The reader should also examine References [44-51] for more examples of starburst molecules. The additional references cited therein are also valuable. Dendrimers can be reacted with a variety of compounds to further functionalize them to give them unique characteristics. For example, amine-terminated dendrimer can be reacted with unsaturated nitriles to give a polynitrile dendrimer. In another case the polyamine dendrimer can be reacted with r-unsaturated amides to give amide-terminated dendrimer. A whole host of possibilities can be visualized based on the reactivity of the amino group [43]. 10.

POLYMERIZATIONS

IN SUPERCRITICAL

FLUIDS

In the last three years, reviews and publications by DeSimone and co-workers [52-59] have shown that free-radical polymerizations can be carried out with ease in supercritical fluids such as carbon dioxide. Since there is a dependence of supercritical fluid density on pressure, a range of densities ranging from vapor-like to liquid-like can be obtained by varying the pressure while holding the temperature constant. At conditions near the critical point of the supercritical fluid, small changes in pressure or temperature result in large changes not only in density but also in viscosity, dielectric constant, and solvent strength. It is this ability to vary the solvent properties of supercritical fluids that provides a good opportunity to investigate the effects of solvents on the outcome of the polymerizations of various monomers without the problems associated with changing the chemical composition of the solvent [60]. Until very recently, there have been few reports on the use of supercritical fluids as the inert reaction solvent in polymer syntheses. The solvent power of supercritical fluids varies with density and pressure. Recently, it has been reported that low density polyethylene has been prepared in supercritical CO2 [61]. The latter is also reported to be a good solvent for fluoropolymers and siloxanes. Earlier work by researchers at Sumitomo Chemical reported polymerizations of vinyl chloride to PVC in supercritical CO2 [62]. Other monomers, such as styrene, methyl methacrylate, and vinyl acetate, were also found to be polymerized under these conditions. This area is receiving increased interest because of environmental conceres with volatile organic compounds (VOCs). Common solvents such as

387

10. Polymerizations in Supercritical Fluids

TABLE IX

Polymerizations of Some Selected Vinyl Monomers in SCF Conditions

Monomer

SCF

Initiator

Ethylene Acrylic acid Acrylic acid Vinyl carboxylic acids with divinyl or polyvinyl monomers Styrene Alpha olefins (C2, C8, C10)

CO2 CO2

Ionizing radiation Peroxy or azo AIBN

C02 CO2 CO2

Free-radical AIBN Benzoyl

CO 2

Temp (~

Pressure (bars)

Ref.

20-45 85-140

392 < 310 110-140

a b c

d 50 71

e

96-130

f

aM. Hagiwara, H. Mitsui, S. Mechi and T. Kagiya, J. Polym. Sci., Part A-1 6, 603 (1968). b W. G. Sertage, Jr., P. Davis, H. U. Schenck, W. Denzinger, and H. Hartmann, Canadian Patent 1,274,942 (1986). CT. J. Romack, E. E. Maury, and J. M. DeSimone, Macromolecules 28, 912 (1995). all. Hartmann and W. Denzinger, U.S. Patent 4,748,220 (1988). e K. Fukui, Y. Kaglya, H. Yokota, Y. Torluchi, and K. Fujii, U.S. Patent 3,522,228 (1970). UR. E. Terry, A. Zaid, C. Angelos, and D. L. Whitman, Energy Prog. 8, 48 (1988).

chlorofluorocarbons and aqueous waste streams from plants will both become increasingly regulated by environmental authorities. In fact, CFC production and importation ceased as of January 1, 1996 (Montreal Protocol). Supercritical CO2 now offers a low-cost, environmentally clean alternative to the common organic solvents currently used in industry.

10-1.

Polymerization o f Styrene in Supercritical Carbon Dioxide [62]

To a stainless steel autoclave having an inner capacity of 30.0 ml was charged 0.2 ml of a benzene solution of 2,2'-azobisiosobutyronitrile (AIBN) (cone. 0.205 gm/5 ml benzene). (Caution: Benzene is a known carcinogen.) The autoclave was tightly closed and then exhausted by means of a vacuum pump while being cooled with liquid nitrogen. Then 5.2 gm (0.05 mole) of styrene monomer was charged followed by 4.4 gm of carbon dioxide. The autoclave temperature was raised to 50~ while stirring and the polymerization continued for 20.0 hr. At this time a transparent liquid remained in the autoclave. The polystyrene was precipitated by the addition of methanol to give a white solid. After washing and drying there was isolated 1.2 gm (24% yield) of polystyrene with molecular weight 12,000. Other reports on the polymerization of styrene in supercritical fluids using AIBN as the initiator have also been reported. Kumar and co-workers in 1986 and 1987 [63] reported polymerizations in supercritical ethane at different

388

10. Miscellaneous Polymer Preparations

pressures and temperatures. On working up the polymerization reaction they found that the precipitated and dissolved polystyrene had different molecular weights. These researchers reported that the polystyrene obtained not only had a lower average molecular weight but also had a narrower molecular weight distribution than could be obtained by precipitation polymerization conducted in conventional liquid solvents. The advantage of conducting the precipitation polymerization in supercritical fluids is the ease with which the unreacted monomer can be recovered from the reaction medium and the ease of recovering the produced polymer from the solvent. Free-radical polymerization in SCF hydrocarbon solvents makes use of the relationship between solvent power and SCF density to alter the threshold of precipitation of the polymer chains and also to minimize the swelling of the precipitate. This process produces polymers with controlled molecular weight with a narrow molecular weight distribution. In 1990, Saraf and Kiran [64] reported on more extensive studies of the freeradical precipitation polymerization of styrene in several SCF solvents (ethane, propane, and n-butane). For each solvent, a free-radical initiator was chosen to make sure that a significant amount of polymerization took place once the critical temperature was reached. Saraf and Kiran reported that the molecular weight increased at higher reaction pressures. As the temperature increased, the molecular weight decreased. This latter effect may be due solely to an increase in radical concentration from the initiator. DeSimone reported, in 1992, the first homogeneous polymerization in supercritical CO2 with free-radical initiation methods using, for example, a fluoroalkylacrylate ester (CH2=CH--COOCH2(CF2)6CF3 [65]. Copolymers of the latter were also prepared with methyl methacrylate, styrene, butyl acrylate, and ethylene. The papers by J. M. DeSimone should be consulted for further details as to experimental conditions. It is interesting to note that AIBN was found to decompose 2.5 times more slowly in CO2 than in benzene, but the radicals produced had higher initiator efficiencies [65]. Table X gives a variety of monomers polymerized in SCF CO2 using either free radical or cationic initiation as reported by DeSimone and co-workers.

11.

METAL-CONTAINING POLYMERS AS POLYMERIC CATALYSTS

Since Merrifield's first disclosure in 1963 [66] that his "solid phase" technique was useful for preparing peptides (Nobel Prize awarded to Merrifield in 1984), there has been an explosion of publications on the use of polymers as polymeric-supported catalysts for various reactions [67].

11.

389

Metal-Containing Polymers as Polymeric Catalysts

TABLE X

Polymerizations or Telermerizations in Supercritical CO2 Reported by DeSimone Conditions

Monomers

Initiators

Temp. (~

Pressure (bars)

Time

CH2 = CH-- COOCH2(CF2)6CF3 (FOA) + CH2 = C - - COOCH3

AIBN

59.4

345

48

AIBN AIBN AIBN

59.4 59.4 59.4

345 345 345

48 48 48

AIBN AIBN EtA1C12 BF3

60 62 40 - 10

205-345 125-345 345 290

24 4 12 4

(hr)

Ref.

I CH3 FOA + styrene FOA + butyl acrylate FOA + ethylene CH2=CH2 + CF3CFaCFaCFaI

Acrylic acid Isobutylvinyl ether Bis(ethoxymethyl) oxetane

j. M. DeSimone, Z. Guan, and C. S. Elsbend, Science 257, 945 (1992). b j. R. Combes, Z. Guan, and J. M. DeSimone, Macromolecules 27, 865 (1994). CT. R. Romack, E. E. Maury, and J. M. DeSimone, Macromolecules 28, 912 (1995). d M. R. Clark and J. M. DeSimone, Macromolecules 28, 3002 (1995). a

The immobilization of a reactive species on a polymer has the potential benefit of easy separation of the catalyst from the reaction to simplify purification of the product. It also has the advantage that the polymer catalyst can be recycled for the next reaction. In addition, corrosive or toxic species are rendered less toxic because they are nonvolatile or skin absorption is decreased. Furthermore, there may be increased selectivity in the reaction. The polymer-supported catalysts must be prepared so that they do not leach (by cleavage from the support) into the product. This is a serious problem in the case of immobilized metal complex catalysts. Another problem results when the resin catalyst offers a diffusional barrier to the reactants and products. This will then adversely effect the rate of the reaction and is a serious problem. These metal-containing polymers are still very expensive because only a few are commercially available. Styrene-divinyl benzene resins have been used as typical support for the metal containing catalysts bound to them. The synthesis of these polymeric reagents has involved several approaches depending on the application which they are intended. The immobilization of transition metals on polymer supports involves using polymers containing ligands which can complex with the metal such that the coordination sphere of the metal remains essentially the same as in

390

to.

Miscellaneous Polymer Preparations

the homogeneous complex. For example, Wilkinson's alkene hydrogenation catalyst [(C6Hs)3P]3RhC1 was one of the earliest to be supported in a polymer matrix using a phosphine bound to the polystyrene [68]. The catalyst was active but it was less than the unbound or homogeneous catalyst. A drawback of this bound catalyst was that it showed a decrease in activity which is thought to be due to the leaching of the metal center from the polymer support. In another development, a stable oxidative metal catalyst which was polymer bound has been developed which showed good recyclability [69]. Recently Dobson, Venter, McDade, and Mirabelli [70] of Rohm & Haas reported in a European patent application that to overcome metal leaching in a transesterification catalyst they used a metal coordinated to one or more pendant ligands to provide three or more chelate bonds to the metal. The polymer is derived from a monovinyl monomer containing units derived from vinyl benzylacetylacetonate and 2-(meth)acrylamidomethyl 1,3-diketone. The polymer catalyst was reported to contain not less than 0.1% metal catalyst. The comonomers used were styrene, vinyl toluene, vinyl naphthalene, ethyl vinylbenzene, and various acrylates, as well as some divinyl benzene to act as a crosslinking agent to form an insoluble copolymer. The preferred catalyst was described as having the formula i

i,

R1

\ / C - - 0 ,,,

R2 --C

M(OR)y

%C ~ 0 pSS / R3

where M is a metal selected from the group A1, Sb, Cu, Cr, Hf, Ru, Pd, Pb, Ni, Sn, Ti, Vd, Zr, and where x is either greater than or equal to 2 and y + 2x = coordination number of the metal. The R groups are either alkyl, alkenyl, or phenyl substituted or unsubstituted groups and OR is alkoxide with a carbon content higher than the alcohol being transesterified. Another preferred polydentate ligand was prepared from 3-vinylbenzyl acetylacetonate or 2-[(meth)acrylamidomethyl]-l,3-deketone as disclosed in European Patent EP A0345573. R R I

0 II

\ C--O

R I

/

CH2=C--C--N--CH2--CH \ / R

C--O

11. Metal-Containing Polymers as Polymeric Catalysts

3 91

Catalysts prepared from these polymeric ligands were said to be useful for the production of methacrylic esters as well as acetates by the transesterification process. The reader is referred to European Patent EP 05557131A2 for details of the preparation of polymeric metal containing catalysts of the latter type. A wide variety of polymers have been used to prepare polymer supported transition metal complexes for a variety of applications, as shown in Table I.

11-1.

Preparation of Anthranilic Acid Anchored to Polystyrene and Complexed with RhCI3. 31120 Useful for the Hydrogenation of Olefins [71 ] COOH

NH2

~

-CH2C1 + @ , C O O H

I RhC13"3H20 CEHsOH O

Rh 4

99%

H2,25oC 0

CH2N

/

~

\o

I C--O

Amberlite XAD-4 polystyrene was supplied by Rohm & Haas (20-50 mesh spheres) and was dried in a rotary evaporator at 50~ for 12 hr before being chloromethylated by the procedure of Pepper et al. [71a], to give a chlorine content of 10-11% (Aldrich also supplies a chloromethylated polystyrene which is a 1 and 2% crosslinked copolymer--called Merrifield's peptide resin and containing 1 meq C1/gm resin [72]. Anthranilic acid was anchored to the polystyrene beads by stirring the beads with an excess of anthranilic acid in ethyl ether or DMF. For example, to 1.00 gm of chloromethylated beads suspended in 50 ml of ethyl ether was added to 0.5 gm of anthranilic acid. This was stirred for 20 hr, filtered, and washed with 200 ml of absolute ethanol. To 1.00 gm of the anthranilic acid anchored beads was added 0.10 gm RhC13"3H20 in 5 ml absolute ethanol. The mixture was stirred for 24 hr, and then filtered, washed with 200 ml of absolute ethanol and treated with 0.1 gm of sodium borohydride. The color of the polymer changed to a dark brown. The

392

lO. Miscellaneous Polymer Preparations

beads were dried under vacuum for 1 hr and analyzed as Rh, 0.96%; N, 0.40%. The low pressure hydrogenation of 2-cyclohexenone was carried out in a Parr catalytic hydrogenator model #3911. In a typical run, in a 500 ml reactor was charged 3.00 ml catalyst. The system was sealed, purged 3 hr with hydrogen, and then pressurized to 50 psig and shaken for 18 hr at room temperature. The product was shown to be cyclohexanone and was obtained in 99% yield. Other chloromethylated polystyrene-divinylbenzene (Merrifield's peptide resin) polymers have also been reacted with other ligands such as lithiated phosphines (for example, t-Bu-PH-Li) and then reacted with transition metal complexes such as [Rh(CO)2C1]2 to give a transition metal bound polymeric catalyst also useful for hydrogenation [73].

CH2

[

/ t-Bu

P

\

Rh(CO)2

In catalysis involving transition metal complexes supported on polymers it is recognized that the chemical and physical structure of the polymeric matrix can have a large effect on the performance of the catalyst. Table XI presents several different polymeric matrixes that are used for this application. A search of the recent literature via Chemical Abstracts also indicates there is much activity in the area of metal containing polymers as polymeric catalysts. Some selected references to these applications are shown in Table XII.

12.

POLYMER PARTICLES OF UNIFORM SIZE DISTRIBUTION (MONODISPERSE LATICES)

A priori, latices formed by the polymerization of dispersions of a waterinsoluble monomer in aqueous media are expected to exhibit a wide distribution of particle sizes. In the 1950's, chemists at the Dow Chemical Company discovered that a batch of polystyrene latex consisted of spherical particles that were uniform in diameter. At the time, this was considered a laboratory curiosity. Nowadays, monodisperse latices have found a wide variety of applications [74]. An early application was in pregnancy testing kits. Other uses are in diagnostic tests for various ailments and for the presence of illegal drugs. These microparticles are available in a variety of colors and with various functionalities along the polymer chains. They may be prepared as porous particles and as

12.

393

Polymer Particles of Uniform Size Distribution

TABLE XI

Polymer Supported Metal Complexes as Catalysts for a Variety of Organic Reactions and Polymerizations

Polymer type metal complexes Crosslinked polystyrene with units of 3-vinylbenzyl acetophenone using Zr and other metals for complexation Organosilicon polymer complexed with transition metals Naton 511 polymer containing Cr(III) or Ce(IV) Shift base functional polymers containing Mn(III) Chloromethylated resins reacted with lithiodiphenyl phosphine and then reacted with RhC13 Polyamides with pyridine moiety in repeat units

Reaction Transesteritication

Ref. a

Polymerization of alpha oletins Oxidation of alcohols Epoxidation of olefins Hydrogenation, also hydrosilation and hydroformylation of olefins Hydrosilation of oletins

c d e

f

a j. C. Dobson, J. J. Venter, C. McDade, and M. G. Mirabelli, European Patent EP 0557131A2 (1995). b K. C. Benton, J. R. Mooney, and R. Weinert, U.S. Patent 4,289,651 (1981). r S. Kanemoto, H. Saimoto, K. Oshima, and Nozaki, Tetrahedron Lett. 25(31), 3317 (1984). aB. B. De, B. B. Lohray, and P. K. Dhal, Tetrahedron Lett. 34(14), 2371 (1993). eM. Capka, P. Svoboda, M. Ceray, and Hetfleja Tetrahedron Lett. 50, 4707 (1971). fz. M. Michalska, B. Ostaszenski, and K. Strzelec, J. Organometallic Chem. 496, 19 (1995).

bearers of microscopic magnetizable components. As a matter of fact, magnetizable polystyrene particles, about 3 pm in diameter, have been used in the removal of neuroblastoma cells from bone marrow. In effect the patient was cured of her cancer by the use of these particles [70]. We understand that the technique has been used successfully quite a few times in Great Britain. Since so many of the applications of monodisperse particles are in biochemical fields, it is a fortunate circumstance that most of the syntheses may be carried out with little or no surfactant or other additives. While the early work was usually carried out with conventional surfactants, today many latices with uniform particle size polymers are simply initiated with an inorganic persulfate. Buffers and some other water-soluble electrolytes may be added mainly to modify the particle size distribution. The few water-soluble components that may be present are subsequently removed by such techniques as ion exchange using a mixed bed of ion-exchange resins, centrifugation, dialysis, or water-replacement using suitable membranes or hollow fiber equipment. In the pioneering work of Krieger and co-workers, monodisperse latices were prepared with mixtures of anionic and nonionic surfactants in the aqueous phase. Their mixtures of styrene (or vinyltoluene), water, surfactants, and initiator were stirred in a resin flask using a very large, specially designed stainless steel paddle. Stirring was at a very modest rate [76].

394

10.

TABLE XII

Miscellaneous Polymer Preparations

Some Selected Applications of Polymer Supported Metal Catalysts from the Recent Literature

Polymer system Acrylic copolymer/Ziegler-Natta catalyst Microporous polydimethylacrylamide-p-styrylsulfonatemethylene bis-(acrylamide)-Pd catalyst Polymer supported crown ether/metal salt Polymer supported transition metal catalysts Polymer supported Fe-Co-Cu clusters Polysilanes coordinated with transition metals Transition metal complexes of Rh, Pt, Pd bound to macroporous resins with nitrile groups Polymer with immobilized metal clusters of Pt or Rh Polymeric metal-containing catalysts Porous polyethylene with Ziegler-Natta impregnated catalyst Poly(4-vinylpyridine)-Cu(II) complex

Application

Ref.

Polymerization of ethylene Hydrogenation of cyclohexene

Prep. of cyclic carbonates from epoxides and CO2 Asymmetric hydroformylation or oxidation reactions Hydroformylation of olefins Polymerization of olefins

c

f

Hydrosilation

g

d e

Hydrogenation of olefins or dienes Various applications Polymerization of olefins Oxidation of thio salts by molecular

i J 02

C. C. Hsu and L. Sun, World Patent WO 9420545A1 (1994). b A. Biffis, B. Corain, Z. Cvengosova, M. Hronec, K. Jerabek, and M. Kralik, Appl. Catal. A124(2), 355 (1995); Chem. Abstr. 123, 94374 (1995). c j. Yamashita, A. Kameyama, T. Nishikubo, W. Fukuda, and M. Tomoi, Kobunshi Ronbunshu 50(7), 577 (1993); Chem. Abstr. 120, 8418 (1994). d j. K. Stille, React. Polym. 10(2-3), 165 (1988); Chem. Abstr. 112, 54669 (1990). e C. Jia, Y. Wang, and H. Feng, React. Polym. 18(3), 203 (1992); Chem. Abstr. 118, 191996 (1992). fT. Shinozaki, K. Kawakita, and M. Kicha, Japanese Patent JP 04202506A2 (1992), Chem. Abstr. 118, 39602 (1992). g Z. M. Michalska, B. Ostaszewski, and J. Zientarska, React. Polym. 16, 213 (1992); Chem. Abstr. 116, 195758 (1992). hN. Toshima, M. Ohtaki, and T. Teranishi, React. Polym. 15, 115 (1991). iF. Ciaralelli, C. Carlini, P. Pertici, and G. Valentini, J. Macromol. Sci. Chem. A26(2-3), 327 (1989). J C. Brun and J. L. Lacombe, European Patent Applic. EP 168317A1 (1980), to Elf Atochem SA; Chem. Abstr. 104, 149625 (1986). kM. Chanda, K. F. O'Driscoll, and G. L. Rempel, J. Mol. Catal. 11(1), 9 (1981); Chem. Abstr. 95, 13457 (1981). a

The use of an ordinary "half moon" stainless steel stirrer to agitate the reaction mixture in a resin kettle of 2-L capacity or in larger round bottom flasks is quite satisfactory. Stirring speeds of about 150 rpm are suggested. Much higher rates of agitation may bring about the formation of a second generation of particles with different, usually smaller diameters. Considerable coagulum may also form.

12. PolymerParticles of Uniform Size Distribution

395

To obtain reproducible results, the proper support of the reactor is important. With ordinary ring stands and clamps that hold the equipment from the rear there is a strong tendency to sway or vibrate during the reaction. A rack that is attached directly to the support beams of the building has been suggested as the primary support. Also, an additional ring stand which holds the reactor from the front reduces the vibration. A stirring motor with constant torque is highly desirable. Even so, after a certain stage of the polymerization, stirring is not important. In fact, there is one report which states that after the conversion has reached about 45%, reducing the impeller speed led to a narrow size distribution [77]. This indicates that after the polymerization has run for a reasonable time, accidental stoppage of the stirrer during the night may actually lead to a latex with a particularly uniform size distribution. The literature references cited here usually call for the use of potassium persulfate as the initiator. We suggest the use of the corresponding sodium salt, mainly because sodium persulfate dissolves much more rapidly in a small amount of water than the potassium salt. This can be a significant factor in setting the reaction up. Many writers recommend running the polymerizations in a nitrogen atmosphere while an additional slow stream of nitrogen is bled into the reactor during the reaction. We are not convinced of the need for an inert atmosphere at all; but, if such is desired, argon, because its specific gravity is greater than that of either nitrogen or air, is much to be preferred. On a laboratory scale, it is traditional to heat the reaction flask with a water bath. With some experience, electric heating mantles can be used and maintained at a reasonably constant temperature. The IR Company fumishes a laboratory jack, "Jack-O-Matic," which raises or lowers a heating mantle, while the reactor is held from its necks. With an appropriate temperature sensor, such as their "Therm-O-Watch," the heating of the flask is well controlled as needed. This method of controlling the polymerization temperature has much to recommend it. There are a number of procedures for determining the particle size of the latex polymer. Transmission electron microscopy (TEM) has been used for some time. The method is necessary to confirm the sphericity of the particles. Since a microscopist selects the images for further study, and the number of slides to be taken is limited for practical reasons, the statistical randomization of the measurements is somewhat questionable. Results, by the latter technique have actually been surprisingly good. The use of scanning electron microscopy (SEM) is not as satisfactory. Other methods of measuring particle size are somewhat indirect and actually derive their calibi'ation from electron microscopy. In effect, measurements with instruments such as a Coulter Electronics Multisizer or a disc centrifuge average the diameters of a great many particles. In the case of the disc centrifuge, the

396

lO.

Miscellaneous

Polymer Preparations

data is presented in the form of curves that represent the statistical distribution of the particles. If a latex has a bimodal distribution of diameters, two curves a r e displayed. With appropriate computer software, the calculation of the needed statistics is easily performed by the software. The procedure given here for the preparation of a copolymer of styrene and p-sodium styrenesulfonate may be extended to the preparation of a monodispersed latex of styrene alone or other co-polymers involving styrene. Usually, in those cases, the use of a phosphate buffer or of an alkali is not necessary. In general, the concentration (or more correctly, the activity) of added electrolytes has an effect on particle diameter. Even increasing the level of the persulfate initiator may act as an increase in the electrolyte concentration and increase the particle diameter.

12-1.

Preparation of Monodispersed Styrene-co-pSodium Styrenesulfonate Latex [78]

In a 2-liter resin flask equipped with a stainless steel stirrer, a thermometer, a nitrogen inlet, a reflux condenser, and an addition funnel were placed 952.4 ml of deionized water, 100 ml of a 0.075 M solution of potassium monobasic phosphate (KH2PO4), 60 ml of 0.1 N potassium hydroxide, and 237.6 ml of inhibitor-free styrene. The reaction mixture was stirred at 150-160 rpm, heated until the reaction mixture was at 65~ and purged with nitrogen for 45 min. Then 100 ml of a 1.125% solution of sodium p-styrene sulfonate was added, followed by 50 ml of a 2.3% solution of potassium persulfate. Stirring and heating at 65~ under a slow stream of nitrogen, was continued for 4-6 hr. Then the temperature was slowly raised to 70-75~ The reaction was run for a total of 24 hr. Then the latex that had formed was filtered through a 100-mesh cheesecloth to remove coagulum. The latex was finished by placing it in an oven for 24 hr at 65-70~ The particle diameter (by electron microscopy) was reported as 0.251/lm. A more recent study of the course of the polymerization used 50 gm of inhibitor-free styrene, 0.5 gm of potassium persulfate dispersed in 400 ml of deionized water heated in a 500 ml four-necked flask and using a Tefloncoated steel shaft with a dual-bladed mixing paddle at 70 ~ 0.5~ under nitrogen with a rate of stirring of 200 +_ 20 rpm. It was found that there was a "limited conversion" phenomenon to the process. After conversion between 89 and 95%, the process came to a stop. After prolonged heating conversion barely reached 100%. (In this particular preparation, the particle diameter was 0.54/zm [79]. Since monodisperse latex particles are frequently coupled to proteins, it may be desirable to produce particles with functional groups on their surfaces that

12. Polymer Particles of Uniform Size Distribution

397

are capable of covalently reacting with appropriate sites on the proteins. Perhaps the most important functionality is the carboxyl group. The introduction into the monomer system of a polymerizable carboxylic acid such as methacrylic acid is an obvious approach. The number of carboxyl groups that can be introduced into the copolymer chains of the particles is quite low. First of all, the partition coefficient of, for example, methacrylic acid between an excessive amount of water and styrene probably leaves most of the acid in the water phase initially. The acid may also homopolymerize rapidly to produce a water-soluble product while the polystyrene-based particles form. Further, either the monomer or the poly(methacrylic acid) may be either trapped in or block copolymerized with the styrenic system. The fact is that some carboxylation of the polymer particles takes place. The level is low. This, it turns out, is an advantage when the application of a latex involves the binding of proteins to the particles. In effect, the low concentration of carboxyl groups tends to prevent the bonding of more than one reactive site of a protein such as a monoclonal antibody to the polymer. Multiple bindings are thought to interfere with the biological activity of the protein. Consequently limited carboxylation of latex particles is desirable. The preparation of surfactant-free latices of styrene with a water-soluble monomer such as acrylamide and its derivatives illustrates the complexities that may be encountered generally when an aqueous solution of one monomer is reacted with a relatively hydrophobic monomer such as styrene [80a, b, c]. According to Kawaguchi and co-workers, the copolymerization of acrylamide and styrene in water and in the absence of an external surfactant takes place in three stages: 1. The substantial preferential homopolymerization of acrylamide to form particles which are low in co-polymerized styrene. During this period, the oligomeric poly(acrylamide) imbibes additional monomeric styrene. 2. In the second stage, the styrene polymerizes exclusively until about 50% of the available styrene has been converted. 3. In the third stage, the concentration of styrene being low, the polymerization process returns to the aqueous solution phase and the remaining monomers react. When the ratio of acrylamide to styrene low, and the polymerization is run at a pH of 9, reasonably monodispersed latex particles may be obtained.

12-2.

Preparation of a Styrene-co-Acrylamide Latex

[80a, b, c] In a 250 ml reaction flask, equipped substantially as in Preparation 12-1, were placed 18 gm of de-inhibited styrene, 2 g of acrylamide, and 150ml of deionized water whose pH had been adjusted to pH 9. With stirring and under a stream of nitrogen, the mixture was heated to and maintained at 70~ Then a

398

to. MiscellaneousPolymerPreparations

solution of 0.28 gm (equivalent to 5 mmole/liter of the total reaction mixture) of potassium persulfate in 10 ml of deionized water was added and the polymerization proceeded. Conversion up to approximately 80% took place within 3 hr. The diameter of the latex particles that had formed was 0.31/zm. With increasing initial concentrations of acrylamide, the particle size decreased. At a low pH, the particle size of the product is larger, but the monodispersivity is less satisfactory. Other related co-monomers were also studied. These included N-(hydroxymethyl)acrylamide (HMA), methacrylamide, and N,N-dimethylacrylamide. The copolymerization of styrene with HMA led to less water-soluble polymer in the serum than in the case of copolymers of acrylamide and styrene. This may be attributable to differences in the hydrophilic-hydrophobic properties of acrylamide and HMA. Some monodisperse latices were prepared from styrene-HMAwater systems by procedures similar to Procedure 12-2. At a ratio of HMA to styrene of 0.2 to 1.0 the reported particle diameter was 0.3 pm with good size uniformity. It was projected that even better uniformity would be obtained when the ratio of HMA to styrene is 0.09 to 1.0. Either potassium persulfate or N,N'-azobisisopropylamidine hydrochloride has been used as initiators with similar results. Latices were generally purified by repetitive centrifugationdecantation-redispersion cycles. The latex copolymerization of styrene with N-methylacrylamide does not follow the three stage process observed with the other acrylamide derivatives. The styrene-acrylamide latices lend themselves particularly well to modification of the functional groups on the particle surfaces without significantly affecting the particle diameters [8 l a, b].

12-3.

Chemical Modification o f the Functionalities o f Poly(styrene-co-Acrylamide) Latices [81a, b]

a. Hydrolysis to Carboxylates

- - [ -- CONH2] + H20

' --[--CO2H] + NH3

(25)

(For clarity, only the reactions of the appropriate functional groups are shown in Eqs. 25-29 of this section.) At 30~ treatment of 50 gm of a 20% solids styrene-acrylamide latex with 10 gm of 20% aqueous sodium hydroxide for various time periods (up to 5 hr) converted the amido groups to carboxyl groups. The reaction was stopped by neutralizing the latex with dilute hydrochloric acid. Then the latex was, in turn, dialyzed, centrifuged, decanted, and redispersed repeatedly. Depending somewhat on the level of acrylamide present in the original co-polymer, the carboxyl groups tended to be on the particle surface.

399

12. Polymer Particles of Uniform Size Distribution

b. Hydroxymethylation

--[--CONH2] + CH20

, --[--CHNHCH2OH2]

(26)

Treatment of a styrene-acrylamide latex similar to the one mentioned immediately above with 0.34 gm of 35% formaldehyde at various pH's for 1 hr at 50~ introduced N-hydroxymethyl groups on the amido-nitrogens. The highest surface density of N-hydroxymethyl groups was obtained when the reaction was run at pH 12.1. The product work-up was similar to that described above.

CAUTION: Formaldehyde is known to be a carcinogen. c. Hofmann Reaction

--[--CONH2] + (NaOC1/NaOH)

' --[--NH2]

(27)

The conversion of the amido-group of a poly(styrene-co-acrylamide) latex to amino groups by use of the Hofmann rearrangement is particularly interesting. The reaction is, of necessity, accompanied by the hydrolysis reaction described above. This side reaction is reduced by running the process at a low temperature. Typically, to a 30% solids styrene-acrylamide latex sodium hypochloride is added in a mole ratio of 0.74 hypochloride to 1 amido unit and the mixture is cooled to 4~ After 5 min, 20 molar equivalents to the amido groups of sodium hydroxide is added. The reaction was carried on for 6 hr. The reaction temperature of 4~ led to a product with 2.27 amino groups and 0.66 carboxyl groups per 100 square Angstroms of particle surface. d. Mannich Reaction

- - [ -- CONHz] + (CH20/R2NH) - - [ -- CONHCH2NR2] + R'X

, - - [ -- CONHCHzNR2]

, --[(--CONHCH2NR2R'+)X-]

(28) (29)

With formaldehyde and amines such as dimethylamine, diethylamine, or pentaethylenehexamine, Mannich reactions have been carried out on poly(styrene-co-acrylamide) latex particles. The expected tertiary amines were accompanied by hydrolysis products. Thus both the Hofmann rearrangement and the Mannich reactions led to amphoteric latex particles. When attempts were made to alkylate the Mannich reaction product, soluble products (presumably quarternary ammonium salts) were formed. Treatment of acrylamide-containing co-polymers with sodium bisulfite (NaHSO3) is said to introduce SO3 moieties into the polymer system [82]. The various applications of monodisperse poly(styrene) latex particles require different particle diameters. For example, we have mentioned above the use of 3/zm magnetizable particles.

400

lO. Miscellaneous Polymer Preparations

Strictly speaking, dispersions of particles that settle out of the serum should not be referred to as "latices," yet it is a general practice to refer to them as latex particles, if they have been prepared by a process that resembles an emulsion polymerization. Generally, the emulsion processes described above lead to particle diameters in the range of 0.1 to 0.7 pm. The methods of increasing the diameter of existing particles are somewhat troublesome. If the diameter of a particle is to be doubled, for example, geometry shows that the volume increase will be by a factor of 8. Allowing for the volume shrinkage of fresh monomer due to polymerization, to double the diameter the volume of monomer to be added will have to be 7 + approximately (0.15 x 7) of the particle volume. While one would question the feasibility of adding such a large volume of styrene to polystyrene without destroying the particles, the experience has been that properly prepared latices will tolerate the addition of surprisingly large volumes of fresh monomer. Some workers add stabilizers to mixtures of latex particles and monomer [83]. Ugelstad, in several patents, makes use of a twostep process. The first step involves treating the monodisperse latex particles with oligomeric swelling agents. Then the particles were said to be capable of safely absorbing huge quantities of monomer prior to polymerization [84]. This approach is difficult to reproduce [85]. It may be that the preparation of the initial monodisperse latex required microspheres of a porous structure with special characteristics. The polymerization of styrene to produce uniform microspheres with diameters of 1/lm or larger in a single step has been a challenge. The use of conventional suspension polymerization techniques are unsatisfactory since they invariably lead to a very broad size distribution. The use of dispersion polymerization methods, i.e., polymerizations in media with little or no water, is promising, albeit many interrelated factors have to be controlled for success. Reference [85] reviewed this field and cites at least 16 leading references. Rudin and co-workers [85] make use of a clear solution of ethanol, styrene, poly(vinyl pyrrolidone) [PVP], and AIBN. Upon initiation at 70~ a homopolymer of styrene and a graft copolymer of polystyrene and PVP form along side of each other. As the polystyrene chains grow initially, they gradually reach their solubility limit in the ethanol solution. Several chains then coalesce to form unstable nuclei. Along with this step, some of the graft copolymer chain are also adsorbed until the graft copolymer stops further adsorption of polystyrene chains and a fixed number of stable nuclei form. This nucleation step is short in duration and is followed by a relatively lengthy growth stage to form monodispersed particles. Since the objective of this work was the production of microspheres for peptide syntheses, some commercial divinylbenzene was incorporated in the preparative procedure. The resulting particles were said to be resistant to the solvent systems used in peptide synthesis. The uniformity of

13.

Optically Active Polymers

401

particle diameters produced by this method, as evidenced by the large standard deviations, is not up to the quality usually associated with monodispersed microspheres.

12-4.

Monodispersed Crosslinked Microspheres by Dispersion Polymerization [85]

To a 1 liter glass resin flask equipped with a stainless steel stirrer which was sealed with a Teflon gasket, nitrogen inlet, addition funnel, condenser, and thermometer and maintained at 70~ with a water bath, was charged, with stirring at approximately 100 rpm, 270.436 gm of ethanol, 7.2 gm of PVP (mol wt 40,000), 0.364 gm of uninhibited divinylbenzene (derived from a commercial 55% solution of the mixed meta and para isomers), and 75 gm of uninhibited styrene. The reaction mixture was stirred under nitrogen for 30 min. Then a solution of 2 gm of AIBN in 25 gm of styrene and 20 gm of ethanol was added. Heating and stirring was continued for 18 hr. After cooling, the product was filtered through cheese cloth to remove some coagula. From the Coulter Multisizer, the particle size (reported as a ds0) was 4.57/lm with a "geometric standard deviation" (calculated a s (dg4/d16)1/2)of 1.02. Reference [85] gives many details of the effect of reaction variables such as the temperature at which the AIBN is added; the effects of different levels of AIBN, PVP, and styrene on particle size; the effect of adding either toluene or water to the reaction medium; the addition of water initially or after nucleation; and the effect of the level of divinylbenzene and the method of its addition.

12-5.

Miscellaneous

1. Preparation of porous, monodisperse microspheres of poly(2,3)-epoxypropylvinylbenzyl ether-co-divinylbenzene) [86]. 2. Preparation of micrometer-sized microspheres of poly(styrene-co-butyl methacrylate) by dispersion polymerization in the presence of dyes such as Nigrosin, Sudan red 7B, Sudan black B, rhodamine B base, ethyl eosin, phenolphthalein, Disperse orange 13, and Disperse blue [87]. 3. Synthesis of monodispersed poly(divinylbenzene) by precipitation polymerization in acetonitrile [88]. 13.

OPTICALLY

ACTIVE POLYMERS

It has been known for some time that the biochemical activities of related enantiomorphs may differ significantly. In effect, the pharmacological behavior of a racemic mixture of a compound may be as if one of the enantiomorphs were a diluent for the other. Furthermore, while one compound may be beneficial, its

402

10. Miscellaneous Polymer Preparations

mirror-image may have a deleterious effect. So the drive is on to produce "enantiopure" drugs. Among the techniques for the separation of racemic compositions is the use of chromatography with chiral column packing [89]. This may well turn out to be the most important application of optically active polymers today, although the use of such polymers as chiral reagents in general or as catalysts for asymmetric syntheses should not be overlooked. The basic research on chiral polymers in its own fight is also of interest.

A.

Naturally Occurring Chiral Polymers

Many optically active polymers exist in nature. Polysaccarides, proteins, enzymes, nucleic acids, polypeptides are some examples. Derivatives of such materials may also exhibit optical activity. This activity is usually preserved throughout the derivatization reactions, provided the reactions do not change the nature of the asymmetric carbon atoms that conferred the chirality to the molecule. Optical activity of natural products may depend on chemical factors such as asymmetric carbon atoms, restricted rotation, etc. These may be termed primary structural features. There are also secondary structures, e.g., helices or random coils, that may confer chirality to a natural product. Optical rotatory dispersion (ORD, i.e., rotation of plane-polarized radiation over a range of wave-lengths usually from approximately 200 to approximately 500/zm) has been used in studies of the conformations of many different molecules, including polymers, proteins, and polypeptides [90]. Poly(L-lactide) has been derivatized by such straightforward reactions as esterification, acetylation, and etherification. Often, the optical rotation of a monomeric analog or of some other small, related molecule is similar to that of a polymer after making due allowances for the concentration of the asymmetric unit in a polymer chain. The monomeric lactide was not considered a satisfactory model for the ORD of the polymeric lactide. However, the derivatives mentioned above, did have ORDs that were similar to each other and to the poly(lactide) [91 ].

BO Introduction of Optical Activity into Inactive

Polymers The presence of an asymmetric carbon in the polymer backbone does not necessarily lead to a polymer with optical activity. For example, polymerization of propene may form atactic, syndiotactic, or isotactic poly(isopropylene). In the atactic polymer, the chirality of the asymmetric carbons is such that the D-configuration balances the L-configuration. This results in an optically inactive material.

13. Optically Active Polymers

403

The isotactic polymers have a plane of symmetry and therefore cannot exhibit optical activity. If the syndiotactic poly(propylene) chains consist of an odd number of carbon atoms in the backbone, the product has a plane of symmetry and is inactive optically. In principle, if the polymer chain consists of an even number of carbons, it is optically active. However, the contribution of a single asymmetric carbon to the optical activity of a long polymeric chain is expected to be too low to be significant. When a polymer has reactive functional groups along its backbone, these may be reacted with appropriate enantiomorphic reagents, the resulting product will be optically active by virtue of the chiral side chains that have been introduced. For example, poly(acrylic acid) may be converted to the corresponding acid chloride with thionyl chloride. Then the poly(acrylyl chloride) may be reacted with resolved reagents such as quinine [92] or ethyl L-leucinate [93]. The products of these types of reaction are optically active. The degree of activity is probably modulated by the degree of crosslinking of the substrate polymer, the extent to which every available site has been functionalized for the condensation reaction, and the completeness of the reaction with the optically active reagent. It is conceivable that in some cases only the surfaces of a polymer coil have been reacted. In other experiments the interiors of the coils (or helices) have been affected. In the preparation given here, chloromethylated, crosslinked, polystyrene was reacted with resolved L ( - )-N,N-dimethyl-t~-phenethylamine to produce an optically active strong-base anion-exchange resin. Since the resin was crosslinked, it was insoluble. Therefore the optical rotation of the product could not be measured directly. The evidence for the optical activity of this resin is indirect and is deduced from the following observations: 1. The recovered excess amine had the same optical rotation as the starting amine. This showed that no racemization had taken place during the reaction. Presumably the amine that had reacted also had remained in the L-(--) form or at least had not racemized during the process. 2. The resulting ion exchange resin was capable of resolving a racemic mixture.

13-1.

Reaction of Chloromethylated Polystyrene with a Tertiary Amine [94]

In a glass flask, 90gm of chlormethylated styrene (2% crosslinked, 200-400 mesh) was stirred with 200 gm of L-(-)-N,N-dimethyl-a-phenethylamine ([tRE6D- 70.3~ at room temperature for 1 hr. Then the mixture was heated in a thermostated oil bath at 100~ for 2 hr. After allowing the mixture to remain at room temperature for 24 hr, the resin was separated on a dry, sinteredglass funnel. The excess amine in the filtrate had [a]25D -- 70.7 ~ The resin was

404

10. Miscellaneous Polymer Preparations

washed in turn with 500 ml of 1.0 N hydrochloric acid, 1 liter of ethanol, and 2 litre of deionized water. This washing procedure was repeated until the wash water gave a negative test for chloride ions with silver nitrate. The reduction of poly(vinylacetophenone) with lithium aluminum hydride (LiA1H4) and quinine led to a product which was estimated to contain about 9% of (+)-poly-[4-(2-hydroxyethyl)styrene. This asymmetric reduction is described in Preparation 13-2.

13-2. Preparation of (+)-Poly-[4-(2-hydroxyethyl)styrene by Asymmetric Reduction [95] The preparation of the starting material, poly(vinylacetophenone), may be carried out by a Friedel-Krafts reaction of polystyrene in carbon disulfide with acetyl chloride and aluminum chloride by the method of Kenyon and Waugh [95a]. In a 500 ml four-necked reaction flask equipped with a reflux condenser, stirrer, addition funnel, and argon gas inlet, to a suspension of 2.112 gm (0.0553 mole) of LiA1H4 in anhydrous 250 ml of tetrahydrofuran was added 16.2 gm (0.05 mole) of quinine ([a]D = --172~ The mixture was heated at reflux with stirring for 10 min. Then, over a 10 min period, a solution of 4 gm (0.0274 unit mole) of poly(vinylacetophenone) in 50 ml of tetrahydrofuran was added dropwise. The reaction mixture was then refluxed for 6 hr. The product was precipitated by pouring the reaction mixture into 3% sulfuric acid. The precipitated polymer was filtered off, redisbursed in tetrahydrofuran, and reprecipitated by pouting the solution into 3% sulfuric acid. After this, the product was again taken up in tetrahydrofuran and precipitated by pouting the solution into a saturated solution of sodium bicarbonate. After repeated washing with deionized water and drying, 2.5 gm of product were isolated, [a]589 = + 3.86 ~ [a]500 = + 5.92 ~ (c = 3,000 in THF). These data represent ~- 9% of the optical activity expected from consideration of the related (+)-a-methylbenzyl alcohol. When poly(vinyl alcohol) [PVA] was reacted with the acid chloride of (+)-2-methyl-6-nitrodiphenyl-2'-carboxylic acid in dioxane at 20~ potentially optically active structures were formed with restricted rotation about the carboncarbon bonds of the PVAlc (atropisomerism) [96].

C.

Polymerization of Optically Active Monomers

Such a-olefins as (+)-(S)-3-mcthyl-l-pemene, (-)(S)-4-(mcthyl-l-hcxene, and (+)(S)-5-methyl-heptene have been polymerized with a titanium trichloride/tri-isobutylaluminum catalyst without solvents. From the product mix, by solvent extraction crystalline and amorphous fractions were isolated. Both forms

13.

OpticallyActive Polymers

405

of the polymer, at least of (S)-4-methyl-l-hexene, are isotactic and highly optically active. This activity has been attributed not only to the asymmetric carbon atom in the monomer, but also to the helical structure of the polymer chains [97]. It is of interest that polymerizations carried out with a typical coordinated anionic Ziegler-Natta catalyst, as in the work of Pino and coworkers [97] referred to above, lead to unrearranged polymers. The stiuation is more complex when cationic or free radical initiators are used. Depending on the reaction temperature, intramolecular hydride shift may take place with the formation of rearranged products. During this rearrangement, the asymmetry of the number 2 carbon atom of the monomer may be lost [98]. The following preparation is an example of a low temperature cationic polymerization of an a-olefin to an optically active polymer.

13-3. Low Temperature Cationic Polymerization of (+)-3-Methyl-l-pentene [98] The polymerization was carried out with the exclusion of atmospheric moisture in well flamed-out glass equipment. A 20 ml glass tube equipped with a 24/40 standard taper female joint was fitted a 24/40 standard taper adapter that accommodated a thermometer (held by a rubber stopper), a drying tube filled with anhydrous calcium sulfate, and a side arm beating a rubber cap for the addition of reactants by means of a syringe. This reaction vessel was flamed out with a Bunsen burner and cooled to room temperature. Using a syringe, to this apparatus was added, in turn, 4 ml of methylene chloride and 1 ml of a 5% solution of anhydrous aluminum chloride in ethyl bromide. (CAUTION: Both of these alkyl halides are cancer-suspect agents. They may also have effects on the ozone layer.) The tube was cooled to - 7 5 ~ and, by means of another hypodermic syringe, 0.73 gm of( + )-3-methyl1-pentene was added drop-wise over a period of approximately 13 min. The polymerization reaction was exothermic. The polymer precipitated as it formed. During this period, the reaction mixture was stirred with the thermometer. The maximum temperature reached in this preparation was -55~ Meanwhile a quantity of methanol was cooled in dry ice-acetone. To the reaction tube, 10 ml of the precooled methanol was added. This terminated the polymerization. The precipitated polymer was collected on a sintered glass filter and washed with additional quantities of methanol. The product was dried under reduced pressure at 80~ Yield was 0.70 gm (95.8% of theory). The polymer was purified by dissolution in n-pentane and precipitation of the product by the dropwise addition of this solution to methanol. Then the polymer was again dried under reduced pressure. The product was used for the measurement 25 of intrinsic viscosities and specific rotation; [a]589 = +0.05~ intrinsic viscosity = 0.20 dl/gm.

406

10. Miscellaneous Polymer Preparations

When a similar polymerization was carried out between - 3 and + 9~ the polymer that was isolated had no optical activity. Free-radical homopolymerizations of this and related monomers led to inactive polymers, presumably because of the loss of asymmetry during possible hydrogen shifts when free radicals started to propagate. The same author prepared alternating copolymers of a-olefins with sulfur dioxide since here the possibility of a hydrogen shift is evidently eliminated. These processes usually were initiated spontaneously when the components were stirred in sealed pressure bottles at room temperature. Sluggishly initiating systems were accelerated by the addition of a few drops of cumene hydroperoxide. These processes were free-radical polymerizations. The effect of cumene hydroperoxide on the initiation is interesting in view of the very low half life of this reagent at room temperature. The products from these polymerizations were optically active. In a recent paper, a study of optically active isotactic alternating copolymers of a-olefins with carbon monoxide showed that it was possible to discriminate on the basis of both chirality and steric structural features. It appears that a copolymer with one chiral configuration in its main chain can select a copolymer chain of the other configuration for racemic complex formation, even if the pendant alkyl groups of the two polymer chains are different. A system can also distinguish the case of two chains with the same chirality but different chain lengths of their pendant substituents [99]. The complexation of a pair of polymers of the same configuration was preferential over the formation of complexes formed between backbone chains of different configurations. This ability of polymer recognition on the basis of both the asymmetry of the carbons in the chains and the steric factors is thought to be without precedent. Esters of acrylic and methacrylic acids may, of course, be polymerized by the conventional free-radical techniques that have been described at length in this series of PolymerSyntheses.If the carbinol portions of these esters are optically active and these groups are not involved in the free radical process, the products will be optically active. The distance of the asymmetric carbon atom from the poly(vinyl) backbone may be expected to influence the amount of rotation [ 100]. Many naturally occurring carbinols, already being optically resolved, have been converted to the appropriate asymmetric esters. Among the starting materials described for this were menthol, bomeol, various carbohydrates, and resolved synthetic carbinols such as 1-a-methylbenzyl alcohol [ 101, 102].

13.4. Polymerization of I-a-Methylbenzyl Methacrylate [ 102] In a 50 ml flask protected against implosions, fitted with a sidearm for a thermometer well and a tube leading to a high vacuum system, was placed

13.

Optically Active Polymers

407

0.687 gm of 1-a-methylbenzyl methacrylate (3.6 • 10-3mole; b.p. 92~ 3-4 mm; [a]25D -- --41.48 ~ and a solution of 0.040 gm (2.44 • 10 -4 mole) of 2,2'-azobisisobutyronitrile i n 3 ml of dioxane. The solution was frozen, degassed three times under reduced pressure, and sealed at a pressure of 10-5 mm. The polymerization was photoinitiated by illuminating the flask from a shielded AH4 Hanovia mercury lamp. The light from this bulb was directed at the flask through a black-walled 15 cm long tube with a 4 cm diameter. The reaction temperature measured by the thermometer ranged between 30 and 35~ The polymerization was carried out for 8 hr of continuous irradiation. Then the flask was cautiously opened. The product solution was poured into petroleum ether (b.p. 35.5-50~ and the polymer was thus precipitated. This product was purified three times by uptake in dioxane and precipitation into petroleum ether. The polymer was freeze-dried for 24--48 hr and finally dried under reduced pressure to constant weight at 60~ The product had a melting range of 136-139~ yield 0.456 gm (67%), [a]25D = --77.4 ~ As anticipated, upon reaction of this polymeric ester under hydrogen with phosphonium iodide, the poly(methacrylic acid) which had formed in an 84% yield showed no optical activity. When the same ester was copolymerized with three molar equivalents of maleic anhydride, the resulting ester-anhydride copolymer had an optical rotation of [a]25D = --50.2 ~ When this resin was reacted under hydrogen with phosphonium iodide, the resulting polymethacrylic acid had an optical rotation of [a]250 = + 23~ (Note the reversal of the optical rotation in this case.) This appears to have been the first demonstration of a case of asymmetric induction during vinyl polymerization. The copolymerization of an optically active monomer with a monomer that is not optically active generally leads to resins with "induced optical activity." Such activity may be assumed to depend on the structures of the monomers involved, on stereoregularity, and on the distribution of the compositional sequences. Ciardelli and co-workers have reviewed this matter in considerable detail [ 103 ]. Many other vinyl compounds that have an asymmetric carbon atom attached to the monomer at some point other than at the vinyl group itself have been polymerized. The monomers have included vinyl ethers, vinyl esters, vinyl acetals, vinyl ketones, N-vinylureas, N-vinylurethanes, N-vinylurethanes, etc. [ 104]. In general, the further the resolved asymmetric atom is from the polymerizing vinyl group, the lower the optical activity of the final resin. The polymerization of o-vinylbenzyl D-sec-butyl sulfide is another example of the straightforward polymerization of a simple vinyl moiety in the presence of a chiral substituent. This particular preparation had been carried out in an attempt to induce asymmetry in the polymeric backbone by means of that chiral side chain. Unfortunately, upon removal of the D-sec-butyl sulfide group, the remaining polymer had no optically active character [ 105].

408

10.

Miscellaneous

Polymer Preparations

13-5. Polymerization of o-Vinylbenzyl o-sec-Butyl

Sulfide [105] CAUTION:

Benzene is a known carcinogen.

A suitable glass tube containing 4 gm of o-vinylbenzyl D-sec-butyl sulfide (b.p. 90~ m m . , [ ~ ] 2 4 7 D "- + 13.92 ~ and 58 mg of 2,2'azo-bis-isobutyronitrile (AIBN) was evacuated and sealed. The polymerization was carried out by heating the sealed tube for 13 hr at 76~ After cooling the reaction product was dissolved in 20 ml of benzene. The solution was added dropwise to 200 ml of methanol. The polymer was reprecipitated twice more by the same technique. After drying, the product weighed 3.4 gm (85% yield), [0(]24"7D = +9.57 ~ (ca. 6.67 gm in benzene). The desulfurization of this polymer was carried out in a bomb by heating the polymer with Raney nickel W-2 catalyst at 1800 lb of hydrogen pressure for 13 hr at 150~ The isolated product exhibited no optical rotation. A copolymerization of the same monomer with a molar equivalent of methyl methacrylate with AIBN produced a polymer with optical rotation [~]247D "-- + 6.89 ~ (ca. 6.67 gm in benzene). Desulfurization of this copolymer also resulted in an optically inactive polymer. When the asymmetric carbon is a part of a heterocyclic monomeric system, the polymerization of such a compound may lead to optically active products. For example, in the case of the polymerization of 1-propylene oxide with potassium hydroxide as catalyst, a low molecular weight crystalline optically active polymer formed. When the same monomer was polymerized by use of a ferric chloride-propylene oxide complex catalyst, a high molecular weight product was formed. This polymer could be separated into an amorphous form with little or no optical activity and a crystalline resin with optical rotation similar to that observed for the potassium hydroxide-catalyzed process [106].

13-6. Polymerization of l-Propylene Oxide with Potassium Hydroxide [ 106] CAUTION: Benzene is a known carcinogen. In a Pyrex tube, 2.5 gm of 1-propylene oxide and 0.5 gm of powdered potassium hydroxide were mixed under nitrogen. The tube was sealed. Then the mixture was shaken at room temperature for 50 hr. During this time, the mixture solidified to a waxy material. After the tube was opened the contents were dispersed in 250 ml of benzene. The benzene solution was washed in turn with water, dilute aqueous sulfuric acid, aqueous sodium bicarbonate solution, and distilled water until the water was neutral. The benzene solution of the product was filtered. The solution was frozen and evaporated under reduced pressure.

13.

Optically Active Polymers

409

The residue was freeze dried in a high vacuum system for 12 hr. Yield: 2.2 gm (88%); m.p. 55.5-56.5~ [a]2~ = -- 16 _ 5 ~ (1% in benzene); + 25 _+ 5~ (1% in chloroform). When D,L-propylene oxide was used in a similar preparation, an optically inactive product formed. When the polymerizations was carried out with a separately prepared ferric chloride-propylene oxide catalyst, the 1-monomer formed a high molecular weight polymer which could be separated into an amorphous fraction with low optical rotation and a crystalline form with the same optical rotation as had been obtained with potassium hydroxide initiation.

D@ Separation and Polymerization of Racemic

Monomers From the economic point of view it would be highly desirable to polymerize a racemic monomer mixture followed by the resolution of the products. However, for this to be practical, one would expect the two enantiomorphs to polymerize at different rates and, in order for optically active products to be isolated, conversion in the process would have to be only partial. If the reaction rates were the same, the two polymers would have to be resolved. To be resolvable the two enantiomorphs should not copolymerize with each other but should substantially homopolymerize to separate polymers. Linear polymers of (R)(S)-4-methyl-l-hexene have been resolved using as a chromatographic support of an optically active poly(cx-olefin) which was selected for its insolubility in eluting solvents. For the resolution of poly(4-methyl1-hexene), the column packing consisted of crystalline (+)-poly-(S)-3methyl-l-pentene. By using a range of eluding solvents, fractions ranging in optical rotation f r o m [~]4~ = - - 2 3 . 0 ~ to [o(]4~ -- § 47.7 ~ have been separated [107]. Evidently, the conformation of the polymers that are to be resolved is significant in resolving macromolecular racemic mixtures. The molecules with the same conformation as that of the column packing are more strongly held by it than polymers with a different conformation. Much of the work on the conformation of polymers concerns itself with reactions of the lower olefins. By the use of certain catalytic systems, crystalline syndiotactic polypropylene may be formed exclusively, rather than as a co-product in the formation of the isotactic macromolecule. To accomplish this, rather specific reaction conditions are required. For example, a catalytic system of approximately five molar equivalents of aluminum dialkylmonochloride to one of vanadium triacetylaceonate at less than 0~ initiates the stereospecific polymerization of propylene to a syndiotactic resin. Other catalytic systems have also been described [ 108]. As discussed above, these polymers are not expected to be optically active.

410

10. Miscellaneous Polymer Preparations

With a chiral anionic initiator such as (+)-(S)-2-(1-pyrrolidinylmethyl)pyrrolidine, a 1-handed helical polymer with a narrow molecular weight distribution has been produced from diphenyl-2-pyridylmethyl methacrylate. This helixsense selectivity by an initiator should be explored further [109].

E.

CationicaUy Induced Polymerizations

A compound such as benzofuran is a monomer with no asymmetric center. In a formal sense, its oxygen-containing five-membered ring may be considered as a vinyl ether. Upon polymerization two asymmetric centers form from the two "vinyl" carbon atoms. The product is optically active although its exact structure and its optical purity is not known. Sorensen and Campbell [110] indicate that, depending on the nature of the initiator that has been used, either an erythro-diisotactic or a threo-diisotactic polymer forms. The catalyst is formed from aluminum chloride and either (+)-fl-phenylalanine (to produce a polymer with ( + ) rotation) or (-)-flphenylalanine (to produce a ( - ) rotating polymer) in toluene. Other initiators include aluminum chloride with ( - )-menthoxytriethyltin, -germanium, or -silicon [111]. The following preparation is a brief summary of the detailed procedure given in Ref. [ 110].

13-7.

Summary of the Polymerization Procedure for the Production of a Poly(benzofuran) [110]

Catalyst preparation: To 100 ml of toluene is added 0.405 mole of the fl-phenylalanine selected. Then 2.43 mole of anhydrous aluminum chloride is added. The mixture is agitated for 1 hr at room temperature. Then the insolubles are allowed to settle, and the clear supernatant is used as a catalyst solution. The catalyst solution is removed to the dried polymerization flask and cooled in a dry ice-acetone bath. A solution of 4 gm of benzofuran in 100 ml of dry toluene (which is also maintained at the dry ice-acetone temperature) is added with stirring. The polymer which forms early in the process has a higher optical rotation than the resin that forms as the process continues. The process may be terminated by quenching with methanol after 30 min. The optical rotation of the product, depending on the fl-phenylalanine used, is either + or - ~ 50 ~

F. Polyisocyanates Alkyl and related isocyanates have been polymerized with sodium cyanide in N,N-dimethylformamide solution. The products were considered 1-Nylons [112]. The polymers are considered stable extended, worm-like molecules. Extensive work on the stereochemistry of these macromolecules are currently under investigation by M. M. Green and co-workers at Polytechnic University [113].

References 13-8.

411

Polymerization of (R)-2,6-Dimethylheptyl Isocyanate [ 113e]

In a suitable glass ampoule, under a nitrogen atmosphere, in a dry box, to a solution of 0.207 gm of Call-dried (R)-2,6-dimethylheptyl isocyanate (DMHI) in 20 ml of toluene was added a solution of 0.12 mg of dried sodium cyanide (Caution) in 2 ml of freshly distilled dimethylformamide. The ampoule was sealed and maintained at - 7 8 ~ for several hours. The mixture gradually increased in viscosity during this time. To isolate the product, the reaction mixture was poured into an excess of methanol. The precipitated polymer was purified by repeatedly precipitating its chloroform solution in methanol. Chiral chromatography was conducted on a cellulose tris[3,5-(dimethylphenyl)carbamate HPLC column using a 90/10 mixture of n-hexane and 2-propanol as eluent. Yield: 99%, [cx]D = - 4 8 3 ~ (EDITOR'S NOTE: The optical rotation given here was taken directly from the cited reference.)

References 1. M. C. Henry and W. E. Davidson, Ann. N. Y. Acad. Sci. 125(1), 172 (1965). 2. E. W. Neuse, Encycl. Polym. Sci. Technol. 8, 667 (1968). 3. J. G. Noltes, H. A. Budding, and G. J. M. Van der Kerk, Recl. Trav. Chim. Pays-Bas 79, 1076 (1960). 4. S. R. Sandier and K. C. Tsou, J. Phys. Chem 68, 300 (1964). 5. J. G. Noltes, H. A. Budding, and G. J. M. Van der Kerk, Rec. Trav. Chim. Pays-Bas 79, 1076 (1960). 6. Y. Sasaki, L. L. Walker, E. L. Hurst, and C. U. Pittman, Jr., J. Polym. Sci. 11, 1213 (1973). 7. W. C. Drinkard and J. C. Bailar, Jr., J. Am. Chem. Soc. 81, 4795 (1959). 8. A. J. Leusink, J. G. Noltes, H. A. Budding, and G. J. M. Van der Kerk, Recl. Trav. Chim. PaysBas 83, 609 (1964). 9. B. P. Block, Inorg. Macromol. Rev. 1, 115-125 (1970). 10. B. P. Block, J. Simkin, E. S. Roth, and S. H. Rose, U.S. Patent 3,255,125 (1966). 11. S. H. Rose and B. P. Block, J. Polym. Sci., Part A-1 4, 573 (1966). 1la. S. H. Rose and B. P. Block, J. Am. Chem. Soc. 87, 2076 (1965); J. Polym. Sci., Part A-1 4, 583 (1966); S. H. Rose, B. P. Block, amd J. E. Davis, Inorg. Chem. 3, 1258 (1964); A. J. Saraceno, U.S. Patents 3,275,574 (1966); 3,328,296 (1967); A. J. Saraceno and R. B. Block, J. Am. Chem. Soc. 85, 2018 (1963); Inorg. Chem. 2, 864 (1963); 3, 1699 (1964); B. P. Block, U.S.C.F.S.T.I., AD Rep. AD-678324 (1968); B. P. Block, S. W. Rose, K. D. Maguire, J. P. King, and A. J. Saraceno, Am. Chem. Soc., Org. Coat. Plast. Chem., Pap. 25(2), 294-297 (1965); B. P. Block, H. D. Gilman, P. Nannelli, and P. T. Grzymalo, U.S.N.T.I.S., AD Rep AD-744962 (1972); J. K. Gillham, J. Appl. Polym. Sci. 16, 917 (1972); P. Nannelli, H. D. Gillman, and B. P. Block, J. Polym. Sci. 13, 2849 (1975). 12. W. J. Burlant and A. S. Hoffman, "Block and Graft Copolymers," Van Nostrand-Reinhold, Princeton, New Jersey, 1960; see also R. J. Ceresa, Encycl. Polym. Sci. Technol. 2,485 (1965); G. Smets and M. Claesen, J. Polym. Sci. 8, 289 (1952). 13. S. R. Sandier and W. Karo, "Polymer Syntheses," Vol. 2, Academic Press, New York, 1977. 14. S. R. Sandier and W. Karo, "Polymer Syntheses," Vol. 1, Academic Press, New York, 1974. 15. B. F. Goodrich Chem. Co., British Patent 893,288 (1962).

412

10.

Miscellaneous Polymer Preparations

16. C. A. Brighton, EncycL Polym. Sci. Technol. 14, 460 (1971); M. L. Dannis and F. L. Ramp, in "Encyclopedia of PVC" (L. I. Nass, ed.), pp. 227-232. Dekker, New York, 1976. 17. G. Bier and H. E. Konermann, U.S. Patent 3,362,896 (1966). 17a. H. Fikentscher, Cell. Chem. 13, 58 (1932). 18. V. L. Bell, J. Polym. Sci., Part A 2, 53.05 (1964). 19. V. L. Bell, J. Polym. Sci., Part A 2, 5291 (1964). 20. M. Narayana, H. Keskkula, and J. E. Mason, U.S. Patent 3,639,522 (1972). 21. G. B. Butler and R. J. Angelo, J. Am. Chem. Soc. 79, 3128 (1957). 21a. C. Libermann and C. Paal, Ber. 16, 526 (1883). 22. C. S. Marvel, J. Polym. Sci. 58, 101 (1960). 23. S. R. Sandier, J. Polym. Sci. 11, 2373 (1973). 24. K. Kurita, Y. Kusayama, and Y. Iwakura, J. Polym. Sci. 15, 2163 (1977). 25. O. Mitsunobu, K. Kato, and M. Wada, Bull. Chem. Soc. Jpn, 44, 1362 (1971). 25a. M. W. Barker and C. J. Wierengo, J. Heterocycl. Chem. 11, 633 (1974). 26. M. S. Newman and R. W. Addor, J. Am. Chem. Soc. 75, 1263 (1953). 27. N. D. Field and J. R. Schaefgen, J. Polym Sci. 58, 533 (1962). 28. S. R. Sandler and W. Karo, "Polymer Syntheses," Vol. 1, pp. 249-250. Academic Press, New York, 1974. 29. T. Unishi and M. Hasegawa, J. Polym. Sci., Part A 3, 3191 (1965). 30. A. S. Hay, J. Org. Chem. 25, 1275 (1960). 31. F. Sondheimer, R. Wolovsky, and Y. Gaoni, J. Am. Chem. Soc. 82, 755 (1960). 32. L. A. Auspos, L. A. R. Hall, J. K. Hubbard, W. Kirk, Jr., J. R. Schaefgen, and S. B. Speck, jr. Polym. Sci. 15, 9 (1955). 33. S. K. Dirlikov, Chemtech, 32-37 (October 1993). 33a. L. G. Picklesimer, U.S. Patent 4,226,800 (1980). 34. M. N. Inbasekaran and S. K. Dirlikov, U.S. Patent 4,885,403 (1989). 35. G. C. Kolb, S. M. Scheck, S. Dirlikov, M. Inbasekaran, and J. P. Godschalx, U.S. Patent 5,155,196 (1992); W. Anderson and E. LaVoie, J. Org. Chem. 38, 3822 (1973); and M. Harfenist and E. Thorn, J. Org. Chem. 37, 841 (1972). 36. A. Hirsch, Adv. Mater. 5, 859 (1993). 37. R. M. Baum, Chem. Eng. News, 8-18 (Nov. 22, 1993). 38. S. R. Sandier and W. Karo, Organic Functional Group Preparations, 2nd ed. pp. 362-363, Academic Press, San Diego, 1983. 39. Papers 368-374, 405-410, and 432-444 presented at 208th ACS National Meeting, Washington, D.C., August 21-25, 1994, Division of Polymeric Materials Science and Engineering. 40. "Starburst" is a registered trademark of the Dow Chemical Company. See D. A. Tomalia, A. M. Naylor, and W. A. Goodard, III, Angew. Chem. Int. Ed. Engl. 29, 138 (1990). 41. E. Behlein, W. Wehner, and F. Vogtle, Synthesis 155 (1978). 42. D. A. Tomalia, H. Baker, J. Dewald, H. Hall, G. Kallos, S. Martin, J. Roeck, J. Ryder, and P. Smith, Macromolecules 19, 2467 (1986). 43. D. A. Tomalia and R. Dewald, U.S. Patent 4,587,329 (1986). 44. D. A. Tomalia and R. Dewald, U.S. Patent 4,568,737 (1986). 45. G. R. Killat and D. A. Tomalia, U.S. Patent 4,871,779 (1989). 46. D. A. Tomalia and J. R. Stahlbush, U.S. Patent 4,857,599 (1989). 47. D. A. Tomalia, U.S. Patent 4,737,550 (1988). 48. D. A. Tomalia and P. M. Kirchoff, U.S. Patent 4,694,064 (1987). 49. D. A. Tomalia and J. R. Dewald, U.S. Patent 4,507,466 (1985). 50. D. A. Tomalia and R. Dewald, U.S. Patent 4,558,120 (1985). 51. D. A. Tomalia, Aldrichimica Acta 26(4), 91 (1993).

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SUBJECT INDEX

Acetophenone, EP. depression in, 157 Acetylene-sulfur dioxide copolymers, 25 general procedure for copolymerization, 26 Acetylides, hazards, 333 Acrylonitrile, 196 Acrylyl chloride, 56 reaction with mercaptans, 56-57 reaction with fluorinated mercaptans, 56 1-Alkylpiperazines, 196 Alkyl thioacrylates, 56-57 stereospecific polymerization, 57 homopolymerization and copolymerization, 57, 59 bulk copolymerization with vinyl monomers, 58 Allyl acetate bulk polymerization, 298-299 cationic polymerization, 300 emulsion polymerization, 299 molecular weight of bulk polymer, 284 polymerization of, 295-301 radiation-initiated polymerization, 301 solution polymerization, 299 zinc chloride-accelerated radiation initiated polymerization, 301 Allyl alcohol-acrylic acid-sulfur dioxide terpolymer, 39 Allyl acrylate, 305-311 Allyl bromide, 366 Allyl chloride-sulfur dioxide copolymer, 39 Allyl compounds, 37, s e e a l s o Allyl esters copolymerization with sulfur dioxide, 37-41

Allyl esters of higher monocarboxylic acids, 301-310 of higher polycarboxylic acids, 322-326 molecular weights, 287-294, s e e a l s o Allyl acetate, molecular weight of bulk polymer polymerization of, 281-330 reactivity ratios, 304, 305, 327 stereoregular polymers, 325 Allyl formate, cationic polymerization, 300 Allyl hydroxymethylacrylate, 308 Allyl linoleate, polymerization, 302 Allyl methacrylate, 305-311 solution polymerization, 306 syndiotactic, 307 ultraviolet-initiated polymerization, 306, 308-311 Allyl trichloroacetate, polymerization, 301 Aluminum porphyrin, 169 Anionic polymerization with sodium, 310 Anionic surfactants for vinyl acetate emulsion polymerizations, 256 Aqueous phase, polymerization of vinyl acetate in, 243, 245,249-250 Aromatic solvents, as retarders of vinyl acetate polymerization, 212 Ascorbic acid-hydrogen peroxide, s e e Hydrogen peroxide-ascorbic acid redox initiator, 262 Autoaccelerated polymerization of vinyl acetate, 210, 225 B Benzene addition to allyl acetate, 285

415

416 as comonomer, 189 in vinyl acetate polymerization, 235 Benzoquinone inhibitor, 223 Bicyclo[2.2.1 ]hept-2-ene-ethyl acrylate-sulfur dioxide terpolymer, 34-35 B is(2-chloroethyl)ether, 76 Bis(2-chloroethyl)formal, 76, 78 Bis(methacryloylthio)ethene, 61 Branching, effect of emulsion polymerization on, 218 effect of nitrogen on, 240 1,3-Butadiene-cyclopentadiene-sulfur dioxide terpolymer, 24 Butadiene-trans-piperylene-sulfur dioxide terpolymer, 25 1,3-Butadiene-sulfur dioxide copolymer, 23 1-Butene-sulfur dioxide copolymer, 17 emulsion copolymerization, 19, 34 2-Butene-sulfur dioxide copolymers, 18-19 2-Butene-sulfur dioxide copolymer, catalyst and percentage conversions, 16-17 tert-Butyl alcohol low chain-transfer activity, 234, 235 as solvent in vinyl fluoride polymerization, 338 Butyllithium, 192 tert-Butylthiomethacrylate polymers, 59 polymerization and processing conditions, 59-61 Butyrolactonyl groups in vinyl acetate polymers, 251-252

Carbodiimides, 129 catalysts, 135 Cascade polymerization, 292, 382-388 Cationic polymerizations of benzofuran, 402 Cationic surfactants, for vinyl acetate emulsion polymerizations, 256-257 Chain transfer agents for vinyl acetate, 228-229 agents for vinyl fluoride, 338, 341,348 constants for vinyl acetate, 229 degradative, 212, 283, 285, 286, 293, 314 effective, 283, 286 in allyl and vinyl acetates, 286 in allyl polymerizations, 284-288 order of decreasing degradative, 286 Charge-transfer polymerization, 191 Chromium complexes, 238 Complexes of poly(vinyl esters), 272

Subject Index

Contact lenses, 308, 326 Copolymerization ratios, see Reactivity ratios Copper, in diallyl o-phthalate polymerization, 315 Copper p-bromothiophenoxide, 107 Copper(I) chloride-amine complexes, 338 CR-39, see Diethylene glycol bis(allyl carbonate) Cross termination, 285 Crotonaldehyde, 223 Cumene, 212 Cupric acetate, 223 Cupric resinate, 223 Cyclic alkylene sulfides, 88-91 polymerization, 88-91 Cyclic urea, 123 Cyclohexene-sulfur dioxide copolymer, 19 1,5-Cyclooctadiene-sulfur dioxide copolymer, 24-27 determination of residual unsaturation, 27 viscosity determination, 27 Cyclopolymerization of allyl acrylate and methacrylate, 305 of diallylammonium halides, 295 of diallyl esters, 287-295 of diallyl terephthalate, 293 of divinylbenzene, 285 of vinyl esters, 272

Dead-end polymerization, of vinyl acetate, 207, 225 Dendrimer macromolecules, 382-386 preparation, 391 Degradative chain transfer, see Chain transfer Diallyl adipate, 322-324 Diallyl azelate, 323 Diallyl brassylate, 323-324 Diallyl carbonate, 322 polymerization, 311-314 see also Diethylene glycol bis(allyl carbonate) Diallyl chlorendate, 282 Diallyldiethylammonium bromide, 366 Diallyl esters, as chain-transfer agents, 295 copolymerization with styrene, 295 Diallyl fumarate, 323, 325 heat of polymerization, 325 Diallyl isophthalate, polymerization, 280 Diallyl isophthalate prepolymer, UV-crosslinking, 322

Subject Index

Diallyl maleate, 322, 327, 328 Diallyl malonate, 322 Diallyl oxalate, 322 Diallyl phthalate ester polymerization, 314- 322, see also Cyclopolymerization of diallyl esters Diallyl o-phthalate, bulk polymerization, 315, 321 polymerization, 314-322 solution polymerization, 320-321 suspension polymerization, 321 Diallyl o-phthalate prepolymer, in emulsion, 322 Diallyl sebacate, 322 Diallyl suberate, 322 Diallyl succinate, 322 Diallyl tartrate, 322 Dialkyl vinylphosphonates, 231 Dibasic thioacids, 47 emulsion polymerization with biallyl, 53 solution polymerization with biallyl, 51 Dibromocarbene, 364 p-Dichlorobenzene, 103-112 1,3-Dichloro-5,5-dimethylhydantoin, in vinyl acetate purification, 210 Dichloroethylformal, 76 Diels-Alder reaction, 360 Diethylcadmium, 158 Diethylene glycol bis(allyl carbonate), 310-314 cast sheet preparation, 312-314 solution polymerization, 312 Diethylzinc, 158 m-Diethynylbenzene, 374 Differential-scanning calorimetry, 357 Diisocyanates, 129-138 polymerization to give polycarbodiimides, 129-136 polymerization reactions, 129-136 trimerization to isocyanurates, 138-147 Dilatometers, use of hematocrit tubes as, 298 Dimercaptans, 83-86, 92-95 condensation with adipoyl chloride, 68 condensation with diacid chlorides, 62-70 condensation with dibasic acid derivatives, 62-70 condensation with terephthaloyl chloride, 64 Dimercapto-p-xylene, 86 2,4-Dinitrophenylhydrazine, 210 1,3-Dioxolane, 341 Diphenylamine, 223 Diphenyltin dihydride, 359 polyaddition to N,N'-ethylene bisacrylamide, 359 Diphenyl phosphinic acid, 360

417

2,2-Diphenyl- 1-picrylhydrazyl, 223 Dipropylene glycol, reaction with propylene oxide, 167 2,5-Dipropyl-(1,3,4-oxadiazole), 337 2,2-Dipyridyl, 271 Dithioacids, 47-55 emulsion polymerization with biallyl, 53 Dithioadipic acid bulk polymerization with biallyl(1,5hexadiene), 51 solution polymerization with biallyl, 51-52

Effective chain transfer, see Chain transfer Electrophotographic receptors, 184 Emulsion polymerization, without external surfactants, 263 End-group analysis, 214 Ethanedithiol, 64 interfacial condensation with terephthaloyl chloride, 64 Ethyl esters, as chain-transfer agents, 228-229 N,N'-Ethylene bisacrylamide, 359 Ethylene carbonate, 158, 370 Ethylene chlorohydrin, 76 Ethylene cyanohydrin, 367 Epoxydodecane, 178 Ethyl allyloxymethylacrylate, 308 Ethylene episulfide, 74 polymers, 74, 87-91 Ethylene glycol monoethyl ether, 162 Ethylene oxide, 152-153 physical properties, 154 reaction with urea, 178 safety precautions, 153 Ethylene sulfide, see Ethylene episulfide polymerization, 87-91 polymerization using acetone-sodium catalyst, 89 polymerization using diethylzinc-water catalyst, 88 Ethylene-sulfur dioxide copolymer, 17 1-Ethyl-3-methyl-3-phospholene oxide, 130

Formaldehyde, 76 Fractionation, of poly(vinyl acetate), 219 Freeze-thaw stability, 246 Friction, low coefficient of, 332

418 Fuchs fractionation method, 220 Fullerenes, 380

Gamma radiation initiation, of vinyl acetate, 270 Gel permeation chromatography, 357 Guanidines, 130 Gel-time meter, 317, 319

p-Halothiophenols, 107 condensation of metal salt compounds, 107-110 Hammett sigma and rho values, effect on reactivity ratios of vinyl benzoate, 231 Head-to-head, tail-to-tail sequences in poly(vinyl acetate), 215 in poly(vinyl fluoride), 334 Health and Safety Notes, acetylides, 333 ethylene glycol, 153 ethylene oxide, 153 metal acetylides, 333 Nonaxanol, 154 polyoxyalkylation, 153 propylene glycol, 153 propylene oxide, 153 vinyl acetate, 205 N-vinyl carbazole, 185 vinyl fluoride, 349 Heat of polymerization of vinyl acetate, 206, 223, 243 of vinyl esters, 228 Heavy metal ion removal from resin, 238 Hematocrit tubes as dilatometers, 298 Hexafluorobenzene, 112 reaction with sodium sulfide, 112 Hexamethylene dimercaptan, 63 condensation with sebacyl chloride, 63 oxidation, 84 1.6-Hexanedithiol, see Hexamethylene dimercaptan reaction with adipoyl chloride-pyridine complex, 68 reaction with diphenyl trans-cyclohexane 1,4-dicarboxylate, 65 trans-1,3,5-Hexatriene inhibitor, 223 High-solids latices, 261 Hydrogels, 271 Hydrogen abstraction, 228

Subject I n d e x

Hydrogen peroxide, effect on molecular weight of poly(vinyl acetate), 245 as suspension polymerization initiator, 245 Hydrogen peroxide-ascorbic acid redox initiator, 262 Hydrogen peroxide-tartaric acid redox initiator, 262 Hydrolytic degradation, 215 Hydroquinone inhibitor, 223 Hydroxy compounds, 153-182 polyoxyalkylation, 153-182

Induction period, of vinyl acetate polymerization, 225 Inhibition of vinyl acetate polymerization, see Vinyl acetate, inhibition of Initiators, for vinyl acetate bulk polymerizations, 223 Initiation of vinyl acetate polymerization, 211 Intramolecular copolymerization of allyl acrylate, 306 Intramolecular cross-linking, 288 Ionic strength, effect on emulsion polymerization, 251 Isocyanates, polymerization catalysts, 135 Isocyanurate foams, 146 Isocyanurate-urethanes, 147 Isocyanates, 120-151 polymerization, 120-151 Isopropanol, as chain-transfer agent, 241

Laboratory procedure notes, 211, 213 Latex characteristics, effect of polymerization technique, 258 Living radical polymerization, 270 Lorenz-Lorentz equation, 319 M

Macallum polymerization, 107 Mark-Houwink-Sakurada equation, 157, 221, 334 Mark-Houwink-Sakurada parameters, for poly(vinyl acetate), 221 Markovnikov addition, 95 Mercaptoethanol co-condensation with mercaptopropanol, 102 Mercaptols, 98

Subject Index Mercaptopropanol, co-condensation with mercaptoethanol, 102 Metal-containing polymers, 356- 360 preparation, 391 Methacrylyl chloride, 56-57 reaction with fluorinated mercaptans, 56-57 reaction with mercaptans, 56-57 Methanol (aqueous), as solvent in vinyl fluoride polymerization, 339 Methylene diisocyanate, 132-133 diphenylmethane diisocyanate, 132 MDI, 133 poly(phenyl isocyanate), 132-133 Methylphenyl phosphinic acid, 360 Michael addition, 56 Monochloroethylene carbonate, 370 dehydrochlorination, 370 preparation, 370-371 Monodisperse latices, 395-400 preparation of chemically modified functionalities, 398 preparation of crosslinked, 400 preparation of styrene-co-acrylamide, 397 preparation of styrene-co-p-sodium styrenesulfonate, 395 Monoisocyanates, 121-129 homopolymerization to 1-Nylons, 121 - 129 polymerization reactions, 121-129 trimerization to isocyanurates, 138

Nonaqueous dispersion polymerization, 268 Nonaxanol, 154 Nonionic surfactants, for vinyl acetate emulsion polymerizations, 256 1-Nylons, 121 - 129 preparation, 121-129 properties, 129

Olefins, 45 reaction with sulfur dioxide, 1-45 yields of reaction with sulfur dioxide, 15 Olefin-sulfur dioxide copolymers, 1-45 catalysis with ascaridole, 14, 33, 44 general procedure for copolymerization, 10 initiation by o~,oL'-azobisisobutyronitrile, 8 initiation of copolymerization, 7-8 nonstereospecificity of copolymerization, 7 properties of copolymers, 12-13 properties of molded resins, 12-13

419 Octene-sulfur dioxide copolymer, 19 Optical storage devices, 184 Optically active polymers, 401-408 naturally occurring, 401 preparation of optically active monomers, 401-408 preparation of styrene based derivatives, 403 Organometallic initiators, 158, 159, 169, 192 Organometallic polymers, 356-359 Oxidative coupling, 374 Oxygen inhibition, of vinyl acetate polymerization, 207, 223 Oxymethylene copolymers, 179

Paraformaldehyde, 76 reaction with tetrahydrofuran and hydrogen chloride, 76 Particle size, factors influencing, control of, 241, 247 Perfluoroalkyl thioacrylates, 56-57 Perfluoroalkyl thiomethacrylates, 56-57 pH in vinyl acetate polymerization, 241,249, 252 Phenol polysulfides, 103 Phenyl acrylate, 239 Phenylene sulfide polymers, 102-112 infrared spectra, 109 Phospholenes, 130-131 Phospholene oxides, 131,135 Photo-initiators, 310, 312, 322 Phthalocyanines, 358 Pinacols, as high-temperature initiators, 227 Polyacetylenes, 374 Poly(alkylene sulfides), 74, 86-95 by the addition of thiols to carbonyl compounds, 87, 89, 98-99 addition of thiols to olefins, 87, 95-98 by condensation of alkylene dihalides with bis-mercaptides, 92-95 by condensation of 1,6-dibromohexane with the disodium salt of hexamethylenedithiol, 92 by the condensation of diolefins and dimercaptans, 87, 95-98 by the condensation of meso-2,5dibromohexane and the disodium salt of hexamethylenedithiol, 94 by the condensation of tetramethylene dibromide with disodium salt of hexamethylenedithiol, 92

420 by the reaction of hexamethylenedithiol and 1,5-hexadiene, 97 dehydration of mercaptoalkanols, 99 methods of preparation, 102-112 Poly(allyl carbonate), from poly(allyl alcohol), 314 Poly(arylene sulfides), 102-112 Polyblends with poly(vinyl esters), 272 Polybutadiene rubber, 364 stereospecific, 364 Poly(butadiene sulfone), 23-24 Polycarbodiimides, molecular weight, 129 Polycyanurates, 381 Poly[1,10-decamethylene-2,5'(1,3,4oxadiazole)], 375 Poly(diallyldiethylammoniumbromide), 366 Poly(3,3'-dimethoxy-4,4'-biphenylene carbodiimide), 132 Poly(2,3-dimethylbutadiene sulfone), 23 Poly(ethylene oxide), amorphous, 167 Poly(ethylene sulfide), 87 1,6-Polyhexatriene (amorphous), 362 Polyhydrazides, 373 Polyimidate resins, 367 Polyisocyanates, 410 preparation of (R)-2,6-dimethylheptyl isocyanate, 410 Poly(isoprene sulfone), 23 Polymercaptals, 98 Polymercaptols, 98 general procedure for the preparation of, 99 Poly(metal phosphinate)s, 359-360 Poly 1-ot-Methylbenzyl methacrylate, 406 Poly (+)-3-methyl- 1-pentene, 404 Polymeric metal phthalocyanines, 358 Poly[ 1,9-nonamethylene-2,5- ( 1,3,4oxadiazole)], 375 Poly[1,8-octamethylene-2,5-(1,3,4-oxadiazole)], 375 Poly-1,3,4 oxadiazoles, 373 Poly-2-oxazolidones, 136-138 by the reaction of isocyanates with epoxides, 136-138 Polyoxyalkylation, 153-182 of alcohols and diols, 158-169 catalysts, 155 chemistry, 154-158 with MgO, 159 of polyhydroxy compounds, 169 of phenols, 174 of poly(vinyl alcohol), 178

Subject Index reaction of ten-butyl alcohol with ethylene oxide, 165 reaction of ethylene oxide with 2-butyl-1octanol, 162 reaction of propylene oxide with methanol, 159 reaction of ethylene oxide with 2-methyl-7ethyl-4-undecanol, 164 reaction of ethylene oxide with 2,6,8trimethyl-4-nonanol, 164 reaction of n-octanol with ethylene oxide, 166 reaction of propylene oxide and ethylene oxide with 2,6,8-trimethyl-4-nonanol, 163-164 reaction of propylene oxide with stearyl alcohol, 165 of straight-chain secondary alcohols, 163 Polyoxyethylation, 153-169 of alkylol amides, 178 of ten-butyl alcohol, 165 of 2-butyl- 1-octanol, 162 of C~0-C~3 straight-chain secondary alcohols, 163 of ethyl alcohol, 162 of 2-methyl-7-ethyl-4-undecanol, 164 of nonylphenol, 175-176 of octadecylamine, 178 of n-octanol, 166 of phenols, 174-177 of sorbitol, 172 of triethylene glycol, 163 of 2,6,8-trimethyl-4-nonanol, 164 using ethylene carbonate, 173 Polyoxyethylene glycol, 166 Polyoxypropylation, 153-169 of tert-butylphenol, 177 of dipropylene glycol, 160, 167 of methanol, 159 of nonylphenol, 175-176 of pentaerythritol, 168, 171, 173 of phenols, 174-177 of propylene glycol, 160, 166 of stearyl alcohol, 165 of sucrose, 168, 170 of 2,6,8-trimethyl-4-nonanol, 164 of trimethylolethane, 172 Polyoxypropylene glycol, 166 Poly-o-vinylbenzyl D-sec butylsulfide, 407 Poly(parabamic acid), 123 Poly(phenylene disulfide), 106 Poly(phenylene sulfide), 102

Subject In dex

by the reaction of p-dichlorobenzene, and sodium sulfide, 110 Polypropylene, cross-linked with allyl acrylate, 306 Poly 1-propylene oxide, 408 Polysemicarbazide, 123 Poly(styrene sulfone), 2 Polysulfides, 74-119 by oxidation of hexamethylenedithiol with bromine, 84 by oxidation using selenious acid, 85 infrared spectra of polymers, 94 oxidation of dimercaptans, 80-86 by the dimethyl sulfoxide oxidation of dimercapto-p-xylene, 86 Polysulfide latex polymer, 78 Polysulfide rubber, 74-75 Polysulfones, 1-45 by reactions of allylic compounds with sulfur dioxide, 37-40 by reaction of acetylene with sulfur dioxide, 25-31 by reaction of dienes with sulfur dioxide, 22-25 by reaction of vinyl monomers with sulfur dioxide, 31-36 emulsion preparations, 19, 22 from the reaction of olefins with sulfur dioxide, 1-45 infrared absorption spectra of olefin polysulfones, 8, 10 representative preparations, 1-45 Polythioesters, 46-72 by condensation of diolefins with dithiocarboxylic acids, 47-55 preparation methods, 46-72 Polyurea, 123 Polyurethane, 123 Poly(vinyl acetate), 203-280 atactic polymer, 231 branched structure, 217 chain-transfer branching, 218 cross-linking with toluene diisocyanate, 219 dispersions, 269 head-to-tail vs head-to-head, tail-to-tail, sequences, 215 high-molecular-weight, 242 hydrolytic degradation, 215, 271 syndiotacticity, 216, 231 intermediate-molecular-weight, 242 low-molecular-weight, 242 molecular weight determination, 220

421 partially hydrolyzed, 204, 271, see also Poly(vinyl alcohol) polymer structure, 214 uses, 203 Poly(vinyl acetate)-poly(vinyl alcohol) block copolymers, 204 random copolymers, 204 Poly(vinyl alcohol), 271 as block copolymer, 255 degree of hydrolysis, 254 from poly(vinyl acetate), 204 reacetylation, 215-217 stability in water, 204 Polyvinylcarbazole, 183-193 uses, 184, 197 Poly(vinyl chloride), 361 chlorination, 361 Poly(vinylene carbonate), 370 infrared spectrum, 373 Polyvinylferrocene, 357 Poly(vinyl formate), syndiotacticity, 216 Poly(vinyl fluoride), degree of polydispersity, 334 intrinsic viscosity, 334 properties, 332 structural features, 334 Poly(vinyl pivalate), molecular weights of suspension and emulsion polymers, 244, 266 Poly(vinyl trifluoroacetate), 216, 231 isotactic diads, 231 syndiotacticity, 216, 231 Poly-p-xylene, 376 Poly[zinc(II) methylphenylphosphinate], 360 Poly[zinc(II) diphenylphosphinate], 360 Preemulsification of monomers, 262 Prepolymers of diallyl phthalates, 282, 314 Propargyl monomers, 376-380 preparation of dipropargyl ether of bisphenol A, 378 preparation of dipropargyl ether of sulfonyl diphenol, 377 Propionaldehyde, as a chain-transfer agent, 227 Propylene carbonate, 141-142 Propylene-methyl methacrylate-sulfur dioxide terpolymer, 32 Propylene oxide, 152-182 physical properties, 154 safety precautions, 153 Propylene-sulfur dioxide copolymer, 18 Protective colloids, in vinyl acetate emulsion polymerization, 254

422 PVC, s e e Poly(vinyl chloride) Pyromellitic dianhydride, 358

Racemic monomers, 408-409 polymerization, 408 separation, 409 Rate of polymerization, effect of high pressure, 286, 301 effect of zinc chloride on radiation-initiated allyl acetate polymerization, 268, 286 Reactivity ratios of vinyl esters, 229-230 of vinyl fluoride, 335 Retardation of vinyl acetate polymerization, 207, 212-213, s e e a l s o Vinyl acetate, retarders of Ryton, 103

Short-stop, for vinyl acetate polymerizations, 209, 223 Significant figures of Mark-Houwink-Sakurada parameters, 221 Smith-Ewart theory, deviation from, 249, 251 - 254 Sodium polysulfide, 75-76 Sodium tetrasulfide, 76-79 Solvation of vinyl acetate, 249-250 Spanning tree approximations, 292 Staudinger equation, s e e Mark-HouwinkSakurada equation Sulfide polymers, 73-119 oxidation, 80 uses, 74-75 Sulfones, 1-45 one step synthesis, 31 Sulfur dioxide ceiling temperature for copolymerization with vinyl compounds, 4-6 conditions of copolymerization with unsaturated compounds, 3-6 gas-phase reaction with olefins, 3 liquid-phase reaction with olefins, 3 olefin copolymers, 1-45 physical properties, 3 reaction with olefins, 1-45 Sulfur dioxide-butene copolymers, 11-17 Sulfur dioxide-diene copolymers, 22 Supercritical fluid polymerization media for styrene and other monomers, 386-387

Subject Index Surfactant type, effect on rate of emulsion polymerization, 250-251 Suspending agents for vinyl acetate polymerization, 241 Suspension polymer from polymer solution, 245 Syndiotactic propagation, in free-radical polymerizations, 231,232 T Tacticity, of poly(vinyl esters), 231 TCNQ, 192 TDI, 140, 144 modified polyester-polyisocyanurate, 146 Telomerization of diallyl o-phthalate, 320 of vinyl fluoride, 334 2,4,4,4-Tetrachlorobutylglycidyl ether, 174 Tetracyanoethylene, 324 adduct with 1,6-polyhextriene, 324-326 Tetrafluoroethylene-sulfur dioxide copolymer, 41 Thiirane, s e e Ethylene episulfide Thiocarbonyl fluoride, 112 Thioesters, 46-72 perfluoroalkyl thiomethacrylates and acrylates, 56-57 thioacrylates, polymerization, 57-62 thioacrylates, preparation, 56-62 unsaturated, free-radical polymerization, 56-62 Thiolactones, 71 Toluene diisocyanate, 130-136 polymerization, 130-136 reaction with diglycidyl ether of 2-2-bis(4-hydroxyphenyl) propane, 136-138 trimerization, 130-136 Trialkylaluminum, 158, 192, 271,307 Trialkylboron, as initiator, 271 Trialkylborane-oxygen, in vinyl fluoride polymerization initiations, 346-347, s e e a l s o Tributylborane monoperoxide Triallyl citrate, 322 Tri-n-butylantimony oxide, 142-143 Tributylborane-air, s e e Tributylborane monoperoxide Tributylborane monoperoxide in vinyl acetate polymerization, 232, 270 in vinyl fluoride polymerization imitation, 333, 334, 338, 346-348 Triene polymers, 362 Trimerization catalysts, 143 Trimethylenedithiol, 98 addition to allene, 98

Subject Index

p-Trimethyllead styrene, 356 polymerization, 356 preparation, 356 p-Trimethyllead bromide, 356 Trimethylmetal styrenes, 356 Tri-n-propylborane-oxygen, see Trialkylborane-oxygen Triphenylphosphine, as initiator, 307 Trommsdorff effect, during vinyl fluoride polymerization, 348 Two-stage polymerization, 283

Urethane-polyisocyanurate, 142-143 UV-initiated polymerization of vinyl acetate, 269

Versatic acids, 205 N-Vinylacetamide, 195 Vinyl acetate azeotrope with water, 205-206 chain-transferring impurities, 207 emulsion polymerization, 248 creme-like dispersions, 239, 246 impurities in, 207 inhibition of, 205-207, 211 ionic, coordination complex, and other initiation systems, 270 nonaqueous dispersion polymerization, 268 oxygen removal from, 207 physical properties, 205 polymerization of, 203-280 purification, 207-211 retarders of, 207, 212-213 radiation-initiated polymerization, 269 solid-state polymerization, 269 solution polymerization, 232 suspension polymerization, 239-248 water solubility, 206 water solubility, effect on emulsion polymerization, 248 Ziegler-Natta polymerization, 270 Vinyl acetate hydrates, 249 Vinyl acetate polymerization in alcoholic solutions, 233-235 in aqueous phase, 243,245,250 benzene, effect of, 235 tert-butyl alcohol as solvent in, 233 inhibitors for, 207, 211 pH effect, 241,245,252 Vinyl 1-adamantyl ether, 232

423 Vinyl 1-adamantane carboxylate, 232 N-Vinyl amides, 193-196 examples of copolymers and conditions for copolymerization, 195 physical properties, 194 preparation by various methods, 194 Vinyl butyrate, polymerization, 228-229 Vinyl caproate, in emulsion polymerizations, 248 Vinyl carbazole, 183-201 anionic process, 189 bulk polymerization, 186 cationic polymerization, 189, 191 charge-transfer polymerization, 191 emulsion polymerization, 188 free-radical processes, 185 organometallic-catalyzed polymerization, 192 polymerization reactions, 185-193 polymerization using aqueous perchloric acid, 190 polymerization using BF3oEt2O, 190 suspension polymerization, 187 triisobutylaluminum-catalyzed polymerization, 192 Vinylene carbonate, 370 polymerization, 370 preparation, 370 Vinyl esters of perfluorinated acids, 231,232 Vinyl esters polymerization of, 202-280 reactivity ratios, 230, 239, 270, 304 Vinyl ferrocene, 357 Vinyl fluoride, bulk polymerization, 336-338 effect of solvents on polymerization, 336, 338 emulsion polymerization, 343- 345 health aspects, 349 polymerization, 331-353 chemically initiated, 336 initiated with Ziegler-Natta catalysts, 346 radiation-initiated, 347 solution, 338 suspension, 339 purification, 333 use of organometallic and related initiators, 345 Vinyl formate, polymerization of, 216, 236 N-Vinyl-N-methylpropionamide, 196 Vinyl neodeconoate in a terpolymer, 366 Vinyl palmitate, emulsion polymerization, 265 p-Vinylphenylmagnesium chloride, 356 Vinyl pivalate, emulsion polymerization, 266 N-Vinyl-N-propylacetamide, 194 Vinyl propionate, 204

424 bulk polymerization, 228 Vinyl pyrrolidone copolymer, 273 Vinyl stearate, 204 Vinyl thioacetate, 231 Vinyl thiobenzoate, 231 Vinyl trialkylacetate, 232 Vinyl tri-n-butyl acetate, 232 1,2-[14C]Vinyl trimethyl acetate, 219

Subject Index

Xylylene dichloride, 376

Zinc chloride, in charge transfers, 271 Zinc hexacyanocobaltate, 169