Ring-opening polymerization

Ring-Opening Polymerization Takeo Saegusa, EDITOR Kyoto University Eric Goethals, EDITOR University of Ghent

An international symposium sponsored by the Division of Polymer Chemistry, Inc. at the 173rd Meeting of the American Chemical Society, New Orleans, La., March 21-23, 1977

ACS

SYMPOSIUM

SERIES

AMERICAN CHEMICAL SOCIETY WASHINGTON D. C. 1977 In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

59

Library of Congress

Data

Ring-opening polymerization. (ACS symposia series; 59 ISSN 0097-6156) Includes bibliographical references and index. 1. Polymers and polymerization—Congresses. 2. Cyclic compounds—Congresses. I. Saegusa, Takeo, 1927- . II. Gœthals, Bric. III. American Chemical Society. Division of Polymer Chemistry. IV. Series: American Chemical Society. ACS symposium series; 59. QD281.P6R56 ISBN 0-8412-0392-X

547'.28 77-13631 ACSMC8 59 1-352 1977

Copyright © 1977 American Chemical Society All Rights Reserved. No part of this book may be reproduced or transmitted in any form or by any means—graphic, electronic, including photocopying, recording, taping, or information storage and retrieval systems—without written permission from the American Chemical Society. PRINTED IN T H E UNITED STATES O F AMERICA

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

ACS Symposium Series Robert F . G o u l d , Editor

Advisory Board

Jeremiah P. Freeman E. Desmond Goddard Robert A . Hofstader John L. Margrave Nina I. McClelland John B. Pfeiffer Joseph V . Rodricks Alan C. Sartorelli Raymond B. Seymour Roy L. Whistler Aaron Wold

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

FOREWORD The A C S SYMPOSIU a medium for publishing symposia quickly in book form. T h e format of the SERIES parallels that of its predecessor, ADVANCES IN CHEMISTRY SERIES, except that in order to save time the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form.

As a further

means of saving time, the papers are not edited or reviewed except by the symposium chairman, who becomes editor of the book.

Papers published in the A C S SYMPOSIUM SERIES

are original contributions not published elsewhere in whole or major part and include reports of research as well as reviews since symposia may embrace both types of presentation.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

PREFACE he international symposium on which this volume is based consisted of invited lectures from the United States, Europe, and Japan and honors W . H . Bailey, of the University of Maryland, who received the ACS Witco Award in polymer chemistry. The full papers corresponding to all of the invited lectures cover a great variety of important aspects of ring-opening polymerization l

A

In polymer chemistry and in the associated industrial processes, polycondensation and vinyl polymerization have long played prominent roles. Ring-opening polymerization does not have a long history, but it has been extensively studied in the past two decades. Monomers suitable for ring-opening polymerization show a great variety of functional groups and ring sizes. Therefore the patterns of polymerization reactions are very diversified. Various polymerization catalysts with specific activities were discovered, and several of the polymerizations are now important to industry. Some of the commercially produced polymers obtained by ring-opening polymerization are nylon-6, polyacetal, poly (ethylene oxide), poly (propylene oxide) and their copolymers, poly(epichlorohydrin), poly(ethylenimine), poly(tetrahydrofuran), and poly(caprolactone). The back-bone units of polymers made by ring-opening polymerization may contain one, two, or even three heteroatoms or no heteroatoms at all. These polymers exhibit a wide variety of properties. We believe that ring-opening polymerization has great possibilities for further progress, and we hope that this book will contribute to the understanding and the significance of this field. At the symposium, we received a grant from the American Chemical Society (ACS-PRF Special Education Opportunities Grant) and donations from the following companies: Allied Chemical Co., Dow Chemical Co., Ethyl Corp., General Electric Co., Minnesota Mining and Manufacturing Co., Phillips Petroleum Co., and Tennessee Eastman Co. These funds were used mostly to subsidize the travel expenses of the speakers from the academic institutions outside the United States. We wish to express our hearty thanks to the American Chemical Society and to the above-named companies. We also thank W . J. Bailey and the other vii In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

contributors for their excellent papers and for their cooperation in organizing, presenting, and publishing this symposium. Kyoto University Kyoto, Japan

T A K E O SAEGUSA

University of Ghent Ghent, Belgium July 21, 1977

ERIC GOETHALS

viii In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1 Cationic Polymerization of Cyclic Amines E. J. GOETHALS, E. H . SCHACHT, P. BRUGGEMAN, and P. BOSSAER Institute of Organic Chemistry, Rijksuniversiteit Gent, B-9000 Ghent, Belgium

It is now generall accepted that th propagatio reactio in the cationic ring-openin nucleophilic attack o e monome nitroge o strained cyclic ammonium salt which is the active species of the growing macromolecule. The driving force of the polymerization is the relief of strain associated with the ring-opening of the active chain end. The resultant polymer molecules, however, also contain nucleophilic amino functions and therefore the polymer competes with monomer to react with the active species. This results in the formation of a (linear or cyclic) non-strained and therefore non-reactive ammonium salt.

With secondary cyclic amines (R=H), the proton on the terminated ammonium salt as well as the proton on the active species can be transferred to other amino groups present in the mixture including monomer. Dimers and other low oligomers are therefore the initial products, and the final products are branched polymers containing a distribution of primary, secondary and tertiary amino functions (1, 2). With cyclic tertiary amines (R = alkyl), the formation of a non-strained ammonium salt is a real termination reaction. If the rate of this termination reaction is not negligably small compared with the rate of the propagation, in other words if the ratio kp/kt is not very high, the polymerization will stop before 1 In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2

RING-OPENING

POLYMERIZATION

a l l monomer i s consumed and low molecular weight polymers w i l l be obtained. Therefore, i t i s i n t e r e s t i n g to know the f a c t o r s which i n f l u e n c e t h i s t e r m i n a t i o n . The main purpose of the i n v e s ­ t i g a t i o n s presented i n t h i s paper i s to determine the r e l a t i o n between monomer s t r u c t u r e and the r a t i o k / k . The i n i t i a t o r f o r a l l p o l y m e r i z a t i o n s was t r i e t h y l o x o n i u m t e t r a f l u o r o b o r a t e . This substance r e a c t s very r a p i d l y w i t h amines so that i t may be assu­ med t h a t i n i t i a t i o n i s f a s t compared w i t h propagation. A l s o , the counter i o n B F ^ i s s t a b l e and has a low n u c l e o p h i l i c i t y so that t e r m i n a t i o n r e a c t i o n s w i t h counter i o n may be neglected. p

Methods f o r the Determination

t

of k / k f p

For f a s t p o l y m e r i z a t i o n s w i t h values of k / k method based on the maxima i n i t i a t o r concentration i s given by : p

Rp - -dm/dt = k

p

up to 100, a

t

m[p£]

[l]

where m • monomer concn. and [pj] = concn. of growing c h a i n s . I f t e r m i n a t i o n i s a f i r s t order r e a c t i o n the r a t e R i s g i ­ ven by : t

R

t - - Φ η Ί / d t - k [p+]

[2]

t

I f t e r m i n a t i o n occurs by r e a c t i o n of the growing chains w i t h any of the amino f u n c t i o n s of polymer the r a t e R i s given by the se­ cond order eqn. : t

R

t "

_ d

p

[ nl /

d t

k

P

( m

3

= t t nJ o

[]

where tOq = i n i t i a l monomer concn. D i v i d i n g eqn. [ l ] by eqn. [2] or [3] leads to : dm _ ^£ dbnJ t k

m

dm d[pj]

0 Γ

=

k

t

m (m -m) 0

I n t e g r a t i o n of these equations between the l i m i t s m = m , f c and m = mf, [p£] = 0 leads to : 0

Q

mo k l n - = J i f c m k f

0

[4]

t

f o r a f i r s t order t e r m i n a t i o n and to :

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

[p+] =

1. GOETHALS ET AL.

Cationic

Polymerization

of Cyclic

3

Amines

f o r a second order t e r m i n a t i o n where f = e f f i c i e n c y f a c t o r of i n i t i a t i o n ; c = i n i t i a t o r c o n c e n t r a t i o n , and m£ = monomer con­ c e n t r a t i o n a t the end of the p o l y m e r i z a t i o n . With t r i e t h y l o x o n i u m t e t r a f l u o r o b o r a t e , the i n i t i a t i o n r e a c ­ t i o n i s f a s t compared w i t h propagation, so that f ^ 1. The type of t e r m i n a t i o n r e a c t i o n d e f i n e s the f u n c t i o n a l form o f m , m^ and c , i . e . eqn. [4] or [ 5 ] . Consequently the ( g r a f i c a l ) s o l u t i o n of these equations permits to d i s t i n g u i s h between f i r s t order and second order t e r m i n a t i o n r e a c t i o n and t o determine the values of k /k . For slow p o l y m e r i z a t i o n s , separate values f o r k and k can be d e r i v e d from time-conversion curves by u s i n g eq. [β] or eq. [7] depending on whether t e r m i n a t i o n occurs by a f i r s t order o r a second order r e a c t i o n . 0

Q

0

p

t

p

t

m i

In

In k mc

r

t

- k / (m -m)dt ο t

0

[7]

Rp can be measured from the tangent a t the time-conversion curves and ^ ( m - m ) d t i s the area under a time-conversion curve up to time t when (mQ-m) i s used as the o r d i n a t e ( 3 ) . I f termina­ t i o n i s slow compared w i t h propagation, i n other words i f the r a t i o k p / k has a high v a l u e , the kp can be d e r i v e d d i r e c t l y from f i r s t order p l o t s of the p o l y m e r i z a t i o n . I n that case the t e r m i ­ n a t i o n becomes s i g n i f i c a n t only a t n e a r l y q u a n t i t a t i v e conversions and k can then be d e r i v e d from experiments i n which "dying" p o l y ­ mer s o l u t i o n s are used t o i n i t i a t e new p o l y m e r i z a t i o n s a t r e g u l a r i n t e r v a l s . These second p o l y m e r i z a t i o n s become slower as the i n i ­ t i a t i n g s o l u t i o n s become o l d e r . F i r s t order p l o t s o f these new p o l y m e r i z a t i o n s g i v e s t r a i g h t l i n e s the slopes o f which are equal to kp[Pn]« Since kp i s known, t h i s method allows to measure the decrease o f [F£] i n the i n i t i a t i n g polymer s o l u t i o n and hence t o calculate k . t

)

0

t

t

t

R e s u l t s and D i s c u s s i o n . 1) N-Substituted Ethylenimines. These monomers polymerize very r a p i d l y a t 0°C and i t was not p o s s i b l e t o evaluate separate values f o r kp and k a t t h i s temperature. G e n e r a l l y the polyme­ r i z a t i o n s stop a t l i m i t e d conversions. I t was found t h a t eqn. [4] (and not eqn. [ 5 ] ) leads t o s t r a i g h t l i n e s the slopes o f which are equal t o f . k / k f Some examples are shown i n F i g u r e 1. Conse­ quently the t e r m i n a t i o n r e a c t i o n s occur according t o f i r s t order k i n e t i c s . This can be explained by assuming that the t e r m i n a t i o n r e a c t i o n i s predominantly i n t r a m o l e c u l a r which means that the t e r ­ minated ammonium s a l t s are c y c l i c . This i s i n agreement w i t h the o b s e r v a t i o n that a number of N - s u b s t i t u t e d a z i r i d i n e s form not t

p

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4

RING-OPENING POLYMERIZATION

only polymer but a l s o the c y c l i c dimer ( d i s u b s t i t u t e d p i p e r a z i n e ) or c y c l i c tetramer (4>5). These c y c l i c oligomers are formed by degradation of the polymer. This i s supported by the f a c t that these oligomers are formed mainly a f t e r the p o l y m e r i z a t i o n . Gel permeation chromatography a n a l y s i s of the mixture shows t h a t du­ r i n g the time oligomer i s formed, polymer c o n c e n t r a t i o n decreases whereas r e s i d u a l monomer c o n c e n t r a t i o n remains unchanged. I t thus seems that a r e a c t i o n s i m i l a r to t e r m i n a t i o n continues to oc­ cur at the terminated c h a i n ends; f o r example :

Table 1 g i v e s a survey of values of f . k / k f o r d i f f e r e n t Ns u b s t i t u t e d ethylenimines together w i t h the pKfc values of the mo­ nomers. I t i s c l e a r t h a t there i s no simple r e l a t i o n s h i p between k p / k and the pR^ v a l u e s . On the other hand, the trend f o r e t h y l , i s o p r o p y l and t e r t . b u t y l a z i r i d i n e s t r o n g l y i n d i c a t e s that s t e r i c hindrance p l a y s an important r o l e . p

t

t

Table 1:

Values of f . k p / k f o r the p o l y m e r i z a t i o n of N - s u b s t i t u ted e t h y l e n i m i n e s , Ç 2 (a) I V R CH t

H

V

2

N-substituent

f.k /k p

b

<>

t

1

(l.mol- )

(R)

max.yield f o r m = 1 and c • 0.01 m o l . l Q

of monomer

0

-C H -CH(CH ) -C(CH ) ~ 2 6 5 —CH2CH2C gHij -CH CH CN 2

6 21

5

3

3

C H

C

2

2

2 15 100 55 12 55

3

85 14 82

H

2

(a) In CH C1 a t 0°C w i t h E t 0 B F ^ as (b) E f f i c i e n c y f a c t o r f £ 1. 2

2

3

6.09 6.23 5.44 7.24 6.75 8.67 initiator.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1.

Cationic

GOETHALS ET AL.

Polymerization

of Cyclic

5

Amines

Of a l l monomers l i s t e d i n Table 1 only t e r t . b u t y l a z i r i d i n e showed no evidence of a t e r m i n a t i o n r e a c t i o n . Even w i t h small i n i t i a t o r concentrations (e.g. 10"" 3 mol.l"^-) d i d the polymeriza­ t i o n go t o completion. The absence o f t e r m i n a t i o n was f u r t h e r i n ­ d i c a t e d by k i n e t i c s t u d i e s a t low temperatures (-40 t o -20°). As shown i n F i g u r e 2, the f i r s t order p l o t s of the r e a c t i o n gave per­ f e c t s t r a i g h t l i n e s up to h i g h conversion. The v i s c o s i t y data given i n Table 2, show that the molecular weight o f the polymer can be c o n t r o l l e d by the m / c r a t i o . This i n d i c a t e s that a l s o t r a n s f e r r e a c t i o n s a r e unimportant and i s i n agreement w i t h the high l i v i n g c h a r a c t e r f o r t h i s p o l y m e r i z a t i o n . 0

0

Table 2: I n t r i n s i c v i s c o s i t i e s of poly(t.BA.HCl), as a f u n c t i o n of mo/c . 0

ο Co"

1

(mol.l" )

(mol.l" )

1.0 1.0 1.0 2.0 1.0 1.0 1.0 1.0

0.05 0.03 0.02 0.04 0.01 0.006 0.002 0.00Γ

1

1

(dl.g" ) 0.035 0.066 0.078 0.078 0.12 0.18 0.43 0.84

20 33 50 50 100 167 500 1000

(a) i n aqueous 0.4 N.KC1 a t 25°C. The absence of t r a n s f e r r e a c t i o n s i s confirmed by the p o s s i ­ b i l i t y t o produce block-copolymers o f t e r t . b u t y l a z i r i d i n e by u s i n g " l i v i n g " c a t i o n i c polymers as i n i t i a t o r . This has been achieved w i t h l i v i n g p o l y ( t e t r a h y d r o f u r a n e ) a t 0°C (6) and w i t h l i v i n g po­ l y s t y r e n e p e r c h l o r a t e , a t -60°C 07). I n both cases the formation of block-copolymers was demonstrated by the s o l u b i l i t y p r o p e r t i e s of the obtained polymers which were d i f f e r e n t from those o f homo p o l y - ( t e r t . b u t y l a z i r i d i n e ) , and by g e l permeation chromatography.

V7

0°C

BF/,

θ^ι * /S^O^N/VN^J

Ν I R

poly(THF-baziridine)

R

9

* w C H -CH C10? 2 ι 4

ν I R

-60°C >

20°C β 4

>poly(styrene-b-aziridine)

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6

RING-OPENING POLYMERIZATION

Figure 1. Determination of f · k /k , according to for the polymerization of 1-benzyl aziridine (Φ), ethyl)aziridine (O), and l- 2-phenylethyl)aziridine Cl at 0°C with triethyloxonium tetrafluoroborate m = 1.0 mol · r p

t

{

2

Equation 4, l-(2-cyano(*) in CH as initiator, 2

1

0

Timelmin)

Figure 2. First-order plots of the polymerization of J-tertbutyhziridine with triethyloxonium tetrafluoroborate at differ­ ent temperatures. (1) -40°C; c = 0.020 mol · I' . (2) -30°C; Co = 0.025 mol · l . (3) -20°C; c = 0.018 mol · IK m = 1.0 mol · l . 1

0

1

0

0

1

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1

GOETHALS ET AL.

Cationic

Polymerization

of Cyclic

Amines

7

When i n i t i a t i o n i s q u a n t i t a t i v e and i n the absence of t r a n s ­ f e r and t e r m i n a t i o n , the molecular weight a t q u a n t i t a t i v e conver­ s i o n i s given by Mmo/c (M = molecular weight of monomer). Ac­ c o r d i n g l y , the l a s t polymer i n Table 2 (with [η] = 0.84) has a molecular weight of 100,000. The absence of a t e r m i n a t i o n r e a c t i o n i n the p o l y m e r i z a t i o n of 1 - t e r t . b u t y l a z i r i d i n e i s explained by the high s t e r i c hindrance caused by the t e r t . b u t y l groups around the n i t r o g e n atoms o f the polymer c h a i n . As a consequence a n u c l e o p h i l i c a t t a c k by these n i t r o g e n atoms on the a c t i v e species i s no more p o s s i b l e . P o l y ( t e r t . b u t y l a z i r i d i n e ) i s a h i g h l y c r y s t a l l i n e polymer w i t h a m.p. of 142°C. 0

2) N - s u b s t i t u t e d Propylenimines. These monomers polymerize r a t h e r s l o w l y a t temperature high conversions. As a curves f o r d i f f e r e n t monomers a t 10°C. F i r s t order p l o t s o f these p o l y m e r i z a t i o n s g e n e r a l l y give s t r a i g h t l i n e s up t o high conver­ sions which i n d i c a t e s that t e r m i n a t i o n r e a c t i o n s are not impor­ tant d u r i n g the course of p o l y m e r i z a t i o n . Values of kp ( d e r i v e d from the f i r s t order p l o t s ) and of k (derived from second mono­ mer a d d i t i o n s as d e s c r i b e d above) a r e l i s t e d i n Table 3. For these p o l y m e r i z a t i o n s propagation i s c l e a r l y much slower than i n i ­ t i a t i o n and t h e r e f o r e the e f f i c i e n c y f a c t o r f o r i n i t i a t i o n f , may be assumed to be equal t o 1. t

Table 3; Values of k and k f o r the p o l y m e r i z a t i o n of N - s u b s t i ­ tuted propylenimines, CI^-CH^ ( ) p

t

a

I »-* C&2

N-substituent

2

6

χ 10

2

k

(l.mol ^ s e c " ) 5

—CK^CI^C^Hcj -CH CH CN 2

p

1

(R) -CH C H

k

2

1.27 1.55 2.5-1.7

t

χ 10

k /k

6

p

pK

t

1

(sec *)

(l.mol" )

11.6(b) 1.6 4.5

1100 < > 10,000 5,500-3,800

b

of

monomer 7.00 5.93 8.00

b

(a) I n CH C1 a t 10°C w i t h Et 0BF4 as i n i t i a t o r . (b) Values obtained f o r p o l y m e r i z a t i o n s w i t h m / c up t o 40. For higher r a t i o s k seems to i n c r e a s e markedly. 2

2

3

0

0

t

Comparison of the k / k values l i s t e d i n Tables 1 and 3 c l e a r l y shows t h a t the i n t r o d u c t i o n o f a methyl group i n 2 - p o s i t i o n of the a z i r i d i n e r i n g r e s u l t s i n a dramatic increase o f the l i v i n g character o f the p o l y m e r i z a t i o n s . With these monomers i t i s p o s s i b l e t o prepare l i n e a r polyamines w i t h a d e s i r e d molecular weight by u s i n g the a p p r o p r i a t e m /c r a t i o . I n t h i s way polymers w i t h molecular weights up to 20.000 were obtained. I f c i s f u r p

t

0

0

Q

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

Figure 3. Time-conversion curves for the polymerization of l-(2-cyanoethyl)-2-methyl aziridine (CEMA), l-(2-phenylethyl)-2-methyl aziridine (ΡΕΜΑ), and l-benzyl-2-methyl aziri­ dine (BMA) inCH Cl at 10°C with triethyloxonium tetra­ fluoroborate. c = 0.015 and m = 0.80 mol · l . 2

2

0

0

1

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1. GOETHALS ET AL.

Cationic

Polymerization

of Cyclic

Amines

9

ther decreased,the maximum y i e l d s become lower i n accordance w i t h eqn. [4] and consequently a l s o the molecular weights l e v e l o f f . The d i f f e r e n t behaviour as f a r as t e r m i n a t i o n i s concerned between the a z i r i d i n e monomers and t h e i r 2-methyl analogues i s a l s o w e l l i l l u s t r a t e d by the observation that a polymerized s o l u t i o n o f 1benzyl-2-methyl a z i r i d i n e (BMA) i s capable of i n i t i a t i n g the p o l y ­ m e r i z a t i o n of 1-benzyl a z i r i d i n e (BA) but the reverse i s not pos­ s i b l e . This again proves that the former polymer ( i f not too o l d ) s t i l l contains a c t i v e chain-ends capable to i n i t i a t e the polymeri­ z a t i o n of BA, whereas poly-ΒΑ i s "dead" d i r e c t l y a f t e r the polyme­ rization. Even more s t r i k i n g i s the behaviour o f l-benzyl-2,2-dimethyl a z i r i d i n e (BDMA)

BA

BMA

BDMA

I t was not p o s s i b l e t o polymerise t h i s monomer a t temperatures be­ tween 0° and 120°C, i n bulk or i n s o l u t i o n . BDMA does r e a c t w i t h t r i e t h y l o x o n i u m t e t r a f l u o r o b o r a t e t o form the expected a z i r i d i n i u m s a l t b u t t h i s s a l t does not give a ring-opening r e a c t i o n w i t h BDMA monomer. I t i s however an e x c e l l e n t i n i t i a t o r f o r the polymeriza­ t i o n o f BA : + BDMA

A l s o , BDMA does copolymer!se w i t h BA although the amount o f BDMA incorporated i n the copolymer i s s m a l l . These observations lead to the c o n c l u s i o n that a propagation r e a c t i o n between a h i g h l y s u b s t i t u t e d a z i r i d i n i u m s a l t and a h i g h l y s u b s t i t u t e d a z i r i d i n e monomer i s not p o s s i b l e , b u t that r e a c t i o n between the h i g h l y s t e r i c a l l y s u b s t i t u t e d a z i r i d i n i u m w i t h a n o n - s t e r i c a l l y hindered mo­ nomer or v i c e v e r s a , i s p o s s i b l e . 3) A z e t i d i n e s . The p o l y m e r i z a t i o n s o f these monomers a r e c h a r a c t e r i z e d by low r a t e constants o f p o l y m e r i z a t i o n and by a h i g h l i v i n g c h a r a c t e r . Values o f kp and k f o r two a z e t i d i n e s a r e l i s t e d i n Table 4. 1,3,3-Trimethylazetidine i s a very s l u g g i s h t

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

10

RING-OPENING POLYMERIZATION

monomer even a t 80°C. With t h i s monomer, the a c t i v e species f o r the p o l y m e r i z a t i o n can be seen i n the NMR spectrum ( 8 ) . The ob­ served s i g n a l s a r e i n complete agreement w i t h the a z e t i d i n i u m i o n s t r u c t u r e and they remain unchanged d u r i n g and a f t e r the polyme­ r i z a t i o n . A t 80°C, 90% conversion i s reached i n a few hours but no t e r m i n a t i o n could be observed a f t e r 10 days so that t h i s system may be considered as a l i v i n g p o l y m e r i z a t i o n ( 9 ) . 1-Methylazetidine i s more r e a c t i v e than the t r i m e t h y l d e r i v a t i v e but the is s t i l l s m a l l compared w i t h k and t h e r e f o r e , p o l y m e r i z a t i o n leads to h i g h conversions. p

Table 4:

Rate constants i n the p o l y m e r i z a t i o n o f a z e t i d i n e s . C H

3

/ \

Monomer CH CH C1

Solvent

2

Temp. (°C) k

p

χ 10

2

3

C H N0 6

5

20

78

47

1.4

0. 18

Of 0

2

4

( l . m o l ^sec 4

k χ 10 (l.mol'^sec" ) t

1

k

k

p / t

00

250

The p o l y m e r i z a t i o n of another a z e t i d i n e , c o n i d i n e , has been des­ c r i b e d by Razvodoyskii and coworkers ( 1 0 ) .

conidine

The p o l y m e r i z a t i o n of t h i s monomer i n i t i a t e d w i t h b o r o n t r i f l u o r i de i n methanol a l s o proceeds v i a a l i v i n g polymer mechanism. In c o n t r a s t w i t h the a z i r i d i n e s , the t e r m i n a t i o n r e a c t i o n i n the p o l y m e r i z a t i o n of 1-methylazetidine i s of second order. This c o n c l u s i o n i s based on the f a c t that eqn. [ 7 ] , and not eqn. [β], leads t o s t r a i g h t l i n e s . A l s o , the v i s c o s i t y of the polymeriza­ t i o n mixture continues to i n c r e a s e when most of the monomer has been consumed. This i s i n accordance w i t h the occurrence of a slow i n t e r m o l e c u l a r t e r m i n a t i o n r e a c t i o n l e a d i n g to branched

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1. GOETHALS ET AL.

Cationic

Polymerization

of Cyclic

Amines

11

s t r u c t u r e s . An analogous d i f f e r e n c e i n t e r m i n a t i o n behaviour be­ tween three- and four-membered h e t e r o c y c l i c monomers has been found w i t h the s u l f u r analogues ( t h i i r a n e s and t h i e t a n e s ) ( 1 1 ) . I t has been p o s t u l a t e d e a r l i e r (9) that the h i g h l i v i n g cha­ r a c t e r of the p o l y m e r i z a t i o n of 1 , 3 , 3 - t r i m e t h y l a z e t i d i n e i s due to the high b a s i c i t y of t h i s amine (pK =2.7) compared t o l i n e a r t e r t i a r y amines (pK^ = 3,5-4,0). Assuming t h a t the b a s i c i t y o f the polymeric amino groups i s comparable to that of l i n e a r t e r t i ­ ary amines, t h i s would r e s u l t i n a high preference of the monomer to r e a c t w i t h the growing species compared w i t h the polymer, which would lead t o a high k p / k r a t i o . I n the case o f 1 - m e t h y l a z e t i d i ne, the b a s i c i t y o f the monomer ( p K = 3.6) i s c l o s e t o the b a s i ­ c i t y of l i n e a r t e r t i a r y amines and s t i l l k i s 250 times higher than k . This leads t o the c o n c l u s i o n that b a s i c i t y i s not the major f a c t o r that determines the r a t e s of propagation and termina t i o n (although i t may hav drance around the amin t o r . Due t o the c y c l i c s t r u c t u r e of the monomers, the monomeric amino f u n c t i o n s are r e l a t i v e l y l e s s hindered compared w i t h the polymeric ones. I n a d d i t i o n , amino groups i n the polymer have twice the amount o f s u b s t i t u e n t s as the monomeric ones. b

t

D

p

t

Experimental. The a z e t i d i n e s were prepared by r i n g c l o s u r e of the c o r r e s ­ ponding 3-amino propanol s u l f a t e s (14). N - s u b s t i t u t e d a z i r i d i n e s were synthesized from the correspon­ d i n g u n s u b s t i t u t e d a z i r i d i n e (12) or by r i n g c l o s u r e of the c o r ­ responding 2-amino a l c o h o l s u l f a t e (13). The monomers were d i s t i l ­ led from calcium hydride j u s t before use. Triethyloxonium t e t r a ­ f l u o r o b o r a t e was synthesized as described by Meerwein (15) and was p u r i f i e d by s e v e r a l r e p r e c i p i t a t i o n s w i t h e t h e r , from i t s methy­ lene c h l o r i d e . Time-conversion curves f o r the p o l y m e r i z a t i o n o f the propylenimine monomers and 1-methylazetidine were obtained by d i l a t o m e t r y , those f o r 1 , 3 , 3 - t r i m e t h y l a z e t i d i n e by NMR spectrosco­ py. P o l y m e r i z a t i o n s were c a r r i e d out i n such a way that the r e a c ­ t i o n mixture was always under an atmosphere of d r y n i t r o g e n .

Literature cited. (1) Dick C. and Ham G., J . Macromol.Sci.-Chem., (1970), 4, 1301. (2) Schacht E.H. and Goethals E.J., Makromol.Chem., (1974), 175, 3447. (3) Goethals E.J. and Drijvers W., Makromol.Chem., (1970), 136, 73. (4) Schacht E.H., Bruggeman P. and Goethals E.J., Paper presented at the Int.Symp. on Cationic Polymerization, Rouen, 1973. (5) Goethals E.J., Adv. Polym. Sci., (1977), 23, 121. (6) Bucquoye M. and Goethals E.J., unpublished results (1976). (7) Bossaer P.K., Goethals E., Hackett P., Pepper D.C., Europ.Polymer J., (1976), 12, in press.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12

RING-OPENING POLYMERIZATION

(8) Goethals E.J. and Schacht E.H., J.Polym.Sci., Pol.Letters Edn. (1973), 11, 497. (9) Schacht E.H. and Goethals E . J . , Makromol.Chem., (1973), 167, 155. (10) Razvodovskii E.F., Berlin Α.Α., Nekrazov A.V., Pushchaeva L.M., Puchkova N.G. and Enikolopyan N.S., Vysokomol.Soedin., Ser. A, (1973), 15, 2219 and 2233. (11) Goethals E . J . , Makromol. Chem., (1975), 175, 1309. (12) Bestian H., Ann.Chem., (1950), 566, 210. (13) Bottini A. and Roberts J.D., J.Am.Chem.Soc., (1952), 80, 5203. (14) Anderson A.G. and Wills M.T., J.Org.Chem., (1968), 33, 2133. (15) Meerwein H., Bottenburg Ε., Gold H., Pfeil E . , Willfang G., J.Prakt.Chem., (1939), 154, 38; Org.Synth., (1973), Coll. Vol. V, 1080.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2 New Aspects of the Chemistry of Living Tetrahydrofuran Polymers Initiated by Trifluoromethane Sulfonic Anhydride SAMUEL SMITH, WILLIAM J. SCHULTZ, and RICHARD A. NEWMARK Central Research Laboratories, 3M Co., 3M Center, St. Paul, MN 55101

Smith and Hubin hav t e t r a h y d r o f u r a n (THF) u s i n as i n i t i a t o r s ( 1 ) . These anhydrides o f tne s o - c a l l e d "super" a c i d s were found t o y i e l d l i v i n g polymers o f THF i n which the end groups c o n s i s t e d o f oxonium i o n s i n e q u i l i b r i u m w i t h c o v a l e n t l y bonded e s t e r s . The nature o f the r e a c t i o n s i n the case o f t r i f l i e anhydride i n i t i a t i o n was p o s t u l a t e d t o be as f o l l o w s ( 1 ) .

l 19 S e v e r a l papers have r e c e n t l y appeared i n which n, F and C nmr s p e c t r a l analyses were used t o i n v e s t i g a t e the nature of the macroester-macroion e q u i l i b r i u m which r e s u l t s when a l k y l e s t e r s o f the super a c i d s are used as THF p o l y m e r i z a t i o n i n i t i a ­ t o r s (2-7), The exact determination o f these e q u i l i b r i u m constants i n v a r i o u s r e a c t i o n s o l v e n t s has been an e s p e c i a l l y noteworthy r e s u l t (2b, 3 ) . Very r e c e n t l y , the s u r p r i s i n g l y dramatic e f f e c t of the o v e r a l l c o n c e n t r a t i o n o f poly-THF l i v i n g end groups on the macroester-macroion e q u i l i b r i u m has been r e ­ ported and a t t r i b u t e d t o i o n aggregation e f f e c t s which a c t t o i n c r e a s e the i o n / e s t e r r a t i o ( 8 ) . Two important f e a t u r e s d i s t i n g u i s h THF p o l y m e r i z a t i o n i n i t i a t e d w i t h super a c i d anhydrides from t h a t i n i t i a t e d w i t h the corresponding e s t e r s which have r e c e i v e d so much study. Anhydride i n i t i a t i o n i s much more r a p i d than e s t e r i n i t i a t i o n and i t leads t o a polymer capable o f growing a t both ends, where­ as e s t e r i n i t i a t i o n produces polymer growing a t only one end.

^

3

13

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14

RING-OPENING POLYMERIZATION

These d i s t i n c t i o n s prompted us then to study i n some d e t a i l the exact nature of the r e a c t i o n of ( C F S 0 ) 0 w i t h THF. 3

2

2

EXPERIMENTAL NMR s p e c t r a were obtained w i t h a V a r i a n XL-100 spectrometer. ChemicaJgShifts were measured from t e t r a m e t h y l s i l a n e ( h) and CFClg ( F) reference i n t e r n a l standards and s h i f t s are r e ­ corded here as p o s i t i v e when^they are downfield from the r e ­ ference. Samples used f o r F nmr s p e c t r a were withdrawn by s y r i n g e through a septum cap c l o s u r e from a r e a c t i o n v e s s e l which had been maintained at 0 ° d u r i n g the mixing of r e a c t a n t s . A l l r e a c t a n t s had been d i s t i l l e d and great care was e x e r c i s e d to avoid moisture contamination. The ^ F nmr spectrum of the (CF S 0 ) 0 i n i t i a t o r used i n t h i s work i n d i c a t e d at l e a s t 95% p u r i t y , w i t h CF^SOgH and C F S 0 C F c o n s t i t u t i n g the major i m ­ p u r i t i e s and being presen nmr s p e c t r a were determined at 2 5 ° , w i t h the f i r s t spectrum obtained 3 minutes a f t e r i n i t i a t i o n of the r e a c t i o n . Mass s p e c t r a were obtained w i t h a CEC 21-110C mass spectrometer and values are reported as molecular mass per u n i t charge, m/e. Molecular weight d i s t r i b u t i o n s were obtained by g e l p e r ­ meation chromatography (GPC) (Waters A s s o c i a t e s Chromatograph) using a set of s i x S t y r a g e l columns, each 122 χ 0.63 cm, which were s e l e c t e d to achieve h i g h r e s o l u t i o n of low molecular weight f r a c t i o n s . The gels £ a d rated pore s i z e s of 10 (3 columns), 1 0 , 10*, and 1 0 A . The molecular weight d i s t r i b ­ u t i o n s were determined i n e i t h e r chloroform or THF s o l u t i o n s at 2 5 ° u s i n g both standard d i f f e r e n t i a l r e f r a c t i v e index and U.V. detectors. The l a t t e r was employed at a wave length of 2540 Â to detect the phenyl end groups of s p e c i a l l y terminated polymeric i n t e r m e d i a t e s . The phenyl groups were appended to r e a c t i v e intermediates by terminating r e a c t i o n s w i t h the a d d i t i o n of a 3-molar excess of sodium phenoxide i n THF s o l u t i o n . Excess NaOC^H5 was o r d i n a r i l y not removed s i n c e i t d i d not i n t e r f e r e with either H nmr or GPC s p e c t r a . 2

2

R

3

6

DISCUSSION OF RESULTS 19 F nmr. The a d d i t i o n of ( C F S 0 ) 0 to a cyclohexane s o l u t i o n of THF immediately gave r i s e to the appearance of 3 d i s t i n c t f l u o r i n e a b s o r p t i o n peaks, as shown i n F i g u r e l a . It i s noteworthy that i n every case s t u d i e d the * F nmr i n d i c a t e d that the anhydride, which gives a sharp s i n g l e t peak at -73.2 ppm i n cyclohexane s o l u t i o n , r e a c t s e s s e n t i a l l y i n s t a n t l y on mixing w i t h THF at 2 5 ° . (In one instance a known amount of r e f e r e n c e t r i f l u o r o m e t h y l benzene was added to the r e a c t a n t s o l u t i o n and the l ^ F nmr spectrum was i n t e g r a t e d to prove that these three peaks accounted f o r a l l the f l u o r i n e s d e r i v e d from the anhydride). The F nmr a b s o r p t i o n peaks at - 7 5 . 7 , - 7 5 . 8 , and -78.6 ppm ( u p f i e l d from C F C I 3 ) were assigned to tetramethylene b i s ( t r i f l a t e ) (V) ( i . e . C F S 0 f C H - } 0 S C F ) , macro-triflate 3

2

2

9

3

3

2

4

3

3

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2.

SMITH ET AL.

Living

Tetrahydrofuran

Polymers

15

e s t e r IV and m a c r o - t r i f l a t e i o n I I I , r e s p e c t i v e l y , by the f o l l o w i n g c o n s i d e r a t i o n s . ( S t r i c t l y speaking, ^ F nmr observes o n l y the macroester and macroion end groups and does not d i s ­ t i n g u i s h between e i t h e r I I and I I I o r I I and IV, s i n c e I I c o n t r i b u t e s e q u a l l y t o the macroion and macroester peaks.) The assignment o f the peak a t -78.6 ppm to macroion I I I was f a c i l i t a t e d by s t u d y i n g the * F nmr s p e c t r a o f s o l u t i o n s c o n t a i n i n g s o l u b l e t r i f l a t e s a l t s , e.g. NH4O3SCF3 (chemical s h i f t = -78.8 ppm). The assignments o f the peaks a t -75.7 and -75.8 ppm t o V and macroester IV, r e s p e c t i v e l y were made i n a separate study i n which an a u t h e n t i c sample o f V, prepared u s i n g the procedure o f r e f e r e n c e ( 1 ) , was added t o a 10.2 molar s o l u t i o n o f THF i n cyclohexane and an i n i t i a l l y s t r o n g peak a t -75.7 ppm was observed. T h i s peak s l o w l y disappeared to give i n c r e a s i n g l y stronge IV as the slow p o l y m e r i z a t i o (These l ^ F nmr assignments f o r I I I and IV agree v e r y w e l l w i t h the v a l u e s p r e v i o u s l y r e p o r t e d f o r the corresponding l i v i n g t r i f l a t e end groups which had been c h a r a c t e r i z e d under v e r y s i m i l a r experimental c o n d i t i o n s ) (j6). As the p o l y m e r i z a t i o n r e a c t i o n i n i t i a t e d by (CF^SO^^O progressed a t 25° the peak a t t r i b u t e d t o V s l o w l y and s t e a d i l y decreased, w h i l e the c o n c e n t r a t i o n s o f both macroester and macroion i n c r e a s e d , as i l l u s t r a t e d i n the k i n e t i c data o f Table I . 19 TABLE I . R e l a t i v e C o n c e n t r a t i o n s o f Products by F nmr Versus P o l y m e r i z a t i o n Time a t 25°. Reactant C o n c e n t r a t i o n s : (CF SO£) 0 - 0.079 M; THF i n Cyclohexane = 10.2 M. Reaction Time (min.) CF^SO^CH^^O^SCF^ Macroester Macroion 3 ^36 58 7 10 33 59 8 30 16 70 11 74 10 77 13 280 3 79 18 3

2

J

I t i s i n t e r e s t i n g t o note t h a t the macroion/macroester r a t i o increased as V was d e p l e t e d , a f i n d i n g which seems t o accord w i t h the r e p o r t t h a t the e q u i l i b r i u m shown i n Equation (3) s h i f t s t o produce more macroion as a consequence o f the o v e r a l l i n c r e a s e i n the c o n c e n t r a t i o n o f poly-THF l i v i n g end groups Ç8). An otherwise i d e n t i c a l experiment t o t h a t shown i n Table I was performed i n which the v e r y p o l a r s o l v e n t , nitromethane, was s u b s t i t u t e d f o r the non-polar cyclohexane. I n t h i s case V was formed i n almost the same p r o p o r t i o n (32% a f t e r 4 minutes a t 25°), but macroion c o n c e n t r a t i o n predominated over macroester, I I I - 47% and IV - 21% a f t e r 4 minutes. (This spectrum i s shown i n F i g u r e l b . ) The i n c r e a s e i n the d i e l e c t r i c constant o f the medium would, o f course, be expected t o s h i f t t h e e q u i l i b r i u m i n the d i r e c t i o n o f macroion f o r m a t i o n , a s i t u a t i o n which had indeed been found p r e v i o u s l y ( 3 ) .

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

16

RING-OPENING POLYMERIZATION

Other s o l v e n t s were i n v e s t i g a t e d as d i l u e n t s i n the r e a c t i o n of (CF3S02>20 w i t h THF. These i n c l u d e d methylene c h l o r i d e , carbon t e t r a c h l o r i d e , nitrobenzene, toluene and o-dichlorobenzene. In each i n s t a n c e l ^ F ^ showed t h a t V formed t o account f o r a t l e a s t 30% of the t o t a l products formed e a r l y i n the r e a c t i o n . The e f f e c t of THF c o n c e n t r a t i o n on the formation of V was exam­ ined i n one case. At THF c o n c e n t r a t i o n s of 10.2 and 5.6 molar i n cyclohexane, V c o n s t i t u t e d 36% and 68%, r e s p e c t i v e l y , of the t o t a l r e a c t i o n products formed a f t e r 3 minutes at 25°. GPC. The d i s c o v e r y t h a t V was being formed and was a c t i n g as a v e r y slow THF p o l y m e r i z a t i o n i n i t i a t o r , as i n d i c a t e d above and i n r e f e r e n c e ( 1 ) , i m p l i e d t h a t f u r t h e r i n f o r m a t i o n concerning the progress of the p o l y m e r i z a t i o n could be gained by i n v e s t i g a t ­ i n g the molecular weigh the course of the r e a c t i o to those d e s c r i b e d i n Table 1. Toward t h a t end, a f l a s k r e a c t i o n was run i n which a l i q u o t samples were terminated a t v a r i o u s r e a c t i o n stages by quenching w i t h sodium phenoxide. This r e a c t i o n i s known to convert oxonium i o n end groups to phenyl ethers (9) and we e s t a b l i s h e d i n model r e a c t i o n s t h a t i t a l s o converted t r i f l a t e e s t e r s to phenyl e t h e r s . The f i r s t sample quenched a f t e r 3 minutes of r e a c t i o n (8.4% THF conversion) showed a bimodal molecular weight d i s t r i b u t i o n by GPC w i t h w e l l r e s o l v e d peaks a t 21.5 Â and 75 Â end-to-end d i s t a n c e , as shown i n F i g u r e 2. A sample of the e l u e n t at 21.5 1 was separated and d r i e d and the mass spectrum of the product was run. One major peak was found a t m/e 242, corresponding t o the molecular i o n of C6H 0-(CH2>40C6H5 ( V I ) , and t r a c e peaks were observed a t m/e 314 and 386, corresponding t o the THF-dimer and t r i m e r d i phenyl ether molecular i o n s , r e s p e c t i v e l y . The U.V. t r a c e of the GPC, which i s i n d i c a t i v e of the number-average molecular weight (M ) , showed t h a t the 21.5 Â peak c o n s t i t u t e d 35 mole % of the t o t a l product, i n good agreement w i t h the corresponding data shown f o r V i n Table I . As the r e a c t i o n progressed, GPC analyses showed t h a t the d i s t r i b u t i o n became i n c r e a s i n g l y u n i modal. The polymer peak moved up-scale w i t h the simultaneous appearance of a d i s t i n c t i v e , i n c r e a s i n g l y low molecular weight t a i l , as V s l o w l y disappeared by i n i t i a t i n g new polymer chains growing a t both ends. When e q u i l i b r i u m c o n v e r s i o n of THF (69%) was reached a f t e r 90 minutes, the 21.5 Â peak was no longer d i s c e r n i b l e and the and v a l u e s were 13,000 and 19,000, r e s p e c t i v e l y ( p o l y d i s p e r s i t y • 1.5). (The Q f a c t o r f o r c o n v e r t i n g A end-to-end d i s t a n c e t o molecular weight f o r our c a l i b r a t e d column system was 29). (The d i s t r i b u t i o n curve f o r the 90 minute r e a c t i o n product i s a l s o shown i n F i g u r e 2 ) . P r o l o n g a t i o n of the r e a c t i o n f o r an a d d i t i o n a l 3 hours caused the p o l y d i s p e r s i t y to i n c r e a s e to 2.6, f o r reasons which have been i n v e s t i g a t e d independently (10,11). 5

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

SMITH ET AL.

Living

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Polymers

Macro—Triflate Ester

C

Ï 3 3< 2 4 3 9f3 S0

CH

,

0

S

Ij

'ι

"

PPM

7 7

—3 3

"

7

8

w Figure 1. F NMR spectrum of products of reaction of 10.2M THF with 0.079U (CF S0 ) 0. Conditions: 3 min at 25°. (a) in cyclohex­ ane, (b) in nitromethane. 19

s

2

2

End-to-End D i s t a n c e (Â)

Figure 2. Mol wt distribution of phenyl ether-terminated products. [THF] in cyclohexane — 10.2M; [(CF S0 ) 0] = 0.079M. ( ; Product of 3-min reaction (8.4% THF conversion); ( ) product of 90-min reaction (69% THF conversion). s

2

2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

18

The f i r s t order dependence of THF p o l y m e r i z a t i o n r a t e on (CF3S02)2° c o n c e n t r a t i o n has been r e p o r t e d ( 1 ) . However, i n the course of continued s t u d i e s we have observed t h a t as the r e l a t i v e c o n c e n t r a t i o n of anhydride i s i n c r e a s e d beyond about 2 mole p e r ­ cent of the THF c o n c e n t r a t i o n , then a p r e c i p i t a t e occurs e a r l y i n the r e a c t i o n and lower than expected p o l y m e r i z a t i o n r a t e s are observed. We i n v e s t i g a t e d such a r e a c t i o n a t 25° i n which THF c o n c e n t r a t i o n i n cyclohexane was 9.4 M and anhydride concenteationi was 0.47 M. A w h i t e p r e c i p i t a t e was observed to form a t the be­ g i n n i n g of the r e a c t i o n . A l i q u o t samples of the s t i r r e d r e a c t i o n m i x t u r e were withdrawn a f t e r 5, 15, and 120 minutes of r e a c t i o n , quenched w i t h sodium phenoxide and the r e s u l t i n g , now homogeneous s o l u t i o n s were examined by GPC. A l l molecular weight d i s t r i b u ­ t i o n s were found to be t r i m o d a l as shown by the simultaneous U.V. and d i f f e r e n t i a l r e f r a c t i v the 15-minute r e a c t i o n d r i e d t o t a l sample removed a f t e r 15 minutes of r e a c t i o n was obtained and t h i s i s shown i n F i g u r e 4. Strong fragmentation peaks are seen a t m/e v a l u e s of 55, 77, 94, 107, 149 and 221, corresponding t o the r e s p e c t i v e r a d i c a l or molecular i o n s d e r i v e d from the o l i g o m e r i c d i p h e n y l e t h e r s : C4H7, C6H5, C6H5OH, C H50CH , C6H50C4H and C H ( O C 4 H ) . The h i g h mass p o r t i o n of the spectrum depended on the i n l e t temperature as expected f o r a mixture of o l i g o m e r s . At r e l a t i v e l y low temper­ a t u r e a s i g n i f i c a n t peak a t m/e 242 i s d e t e c t e d f o r V I . A t h i g h e r temperature a much s t r o n g e r peak a t m/e 386 i s observed, corresponding to the t r i m e r molecular i o n C ^ ^ O - f C 4 ^ 0 ) 3 0 ^ 5 ( V I I ) . Only t r a c e peaks were d e t e c t e d f o r m/e v a l u e s c o r r ­ esponding t o o t h e r o l i g o m e r i c poly-THF d i p h e n y l e t h e r s . On t h i s b a s i s , assignments were made f o r the GPC peaks: 21.5 A • V I ; 35 Â = V I I . The t r i m e r (VII) assignment was confirmed by an experiment i n which the elu«iit of the GPC peak a t 35 Â was c o l l e c t e d and d r i e d . The mass spectrum of t h i s sample showed the expected i n t e n s e molecular i o n peak a t m/e 386. I n f r a r e d a n a l y s i s f o r hydroxy groups proved n e g a t i v e . The % nmr spectrum showed the expected 1.5 tetramethylene oxide groups/phenoxy group. T h i s spectrum and the v a r i o u s s p e c i f i c p r o t o n a b s o r p t i o n assignments are shown i n F i g u r e 5. The k i n e t i c data of t h i s r e a c t i o n , based on the a n a l y s i s of the UV t r a c e s of the GPC s p e c t r a , are summarized i n Table I I . 6

2

8

6

5

8

2

TABLE I I . Product D i s t r i b u t i o n by GPC A n a l y s i s of the P o l y m e r i z ­ a t i o n R e a c t i o n a t 25°. Reactant C o n c e n t r a t i o n s : (CF3S02)2° 0.47 M; THF i n Cyclohexane - 9.4 M. R e l a t i v e Molar Concns. R e a c t i o n Time (min.) of D i p h e n y l E t h e r s Polymer Mol. Wt. VI VII Polymer Mri ^ 5 24 40 36 1,900 4,400 15 15 50 35 2,000 8,400 120 5 40 55 2,100 22,000 =

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

SMITH ET AL.

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21.5

3

19

Polymers

End-to-End Distance (A)

Figure 3. Mol wt distribution of phenyl etherterminated products. Reaction conditions: 15 min at 25°. THF in cyclohexane = 9.4M; (CF S0 ) 0 - 0.47U. 3

2 2

X50 75H +

M (YH) 50H

55

386 +

M (5I)

25H

242

lull

η100

Figure 4.

1

^-•p'T'-VT 'ΤΓ "Τ Τ""Τ'Τ "J" "Τ'

200

m/e

300

400

Mass spectrum of the total product, identical to that shown in Figure 3.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

20

Figure 5.

Proton NMR of the GPC eluent at 35 A (see Figure 3).

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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21

I t can be seen t h a t V (the a c t i v e intermediate which gives r i s e to VI) disappeared a t a r a t e which i s c o n s i s t e n t w i t h the p r e v i o u s l y discussed r e s u l t s . On the other hand, the r e a c t i v e intermediate which gives r i s e to V I I remained a t a r e l a t i v e l y constant c o n c e n t r a t i o n f o r the f i r s t 2 hours o f r e a c t i o n . These combined e f f e c t s accounted f o r the unusually l a r g e d i s ­ p a r i t y between ^ and shown i n Table I I . An a u t h e n t i c sample o f V I I was made i n which 0.25 mole THF was added s l o w l y a t -30° t o a s o l u t i o n o f 0.05 mole (CF3S02)20 i n 20 ml. CH Cl2 w h i l e s t i r r i n g , and then warmed t o 25° a f t e r the a d d i t i o n was completed. The r e s u l t i n g d i s p e r s i o n was then d i l u t e d w i t h 50 ml CH2CI2, f i l t e r e d and washed s u c c e s s i v e l y w i t h CH2CI2 and then THF. A white c r y s t a l l i n e product, now known to be the THF-trimer bisoxonium s a l t , 2

0*

C H 2 ) l

was obtained i n q u a n t i t a t i v e y i e l d , based on the s t a r t i n g an­ hydride. This s a l t was converted t o the d i p h e n y l ether V I I by adding 5 g. t o a s o l u t i o n o f 10 g NaOCfc^ i n a mixture o f THF and e t h a n o l , and then separated by p r e c i p i t a t i n g i t i n water and p u r i f i e d by repeated water washing. Proton nmr and mass s p e c t r a l analyses proved t h a t the f i n a l product was V I I i n t h a t they were i d e n t i c a l t o the s p e c t r a o f the product separated by GPC, as discussed above. The bisoxonium i o n s a l t V I I I decomposes on m e l t i n g t o g i v e 1 mole o f b i s e s t e r V and 2 moles o f THF (12). V I I I i s s p a r i n g l y s o l u b l e i n THF a t 25° and very s l o w l y disappears over s e v e r a l hours by i n i t i a t i n g p o l y m e r i z a t i o n . I t i s very s o l u b l e i n nitromethane, i n which s o l v e n t i t has been found to polymerize THF as r a p i d l y as (CF3S02)20 i n i t i a t i o n . Mechanisms o f Formation o f Monomer B i s e s t e r V and Trimer B i s ­ oxonium S a l t V I I I . The i n i t i a t i o n r e a c t i o n shown i n Equation (1) has been p o s t u l a t e d t o g i v e r i s e t o the oxonium i o n s a l t I . (High e l e c t r i c a l c o n d u c t i v i t y i s manifest immediately f o l l o w i n g the a d d i t i o n o f the anhydride t o THF a t 25°). I t i s now b e l i e v e d t h a t I disappears r a p i d l y by f o l l o w i n g e i t h e r o f two r e a c t i o n pathways having q u i t e competitive r a t e s . One i n v o l v e s nucleo­ p h i l i c a d d i t i o n o f THF t o I (Equation 2) and t h i s r a p i d l y leads to the formation o f higher polymers. The a l t e r n a t i v e pathway i s a cage r e a c t i o n i n which the CF3SO3 anion n u c l e o p h i l i c a l l y a t t a c k s the oxonium i o n t o open the r i n g t o form V. This view i s c o n s i s t e n t w i t h the f a c t s t h a t s o l v e n t p o l a r i t y does not a f f e c t the r e l a t i v e y i e l d o f V (suggesting a cage r e a c t i o n o f the contact i o n p a i r ) , and the r e l a t i v e y i e l d o f V i n c r e a s e s as THF c o n c e n t r a t i o n i s decreased, as discussed p r e v i o u s l y . V i s a s t a b l e compound and l ^ F nmr shows t h a t i t i s not i n e q u i l i b ­ rium w i t h I ( 1 ) . V then disappears s l o w l y as i t i n i t i a t e s THF p o l y m e r i z a t i o n a t a r a t e which appears to be s i m i l a r t o t h a t o f e t h y l t r i f l a t e (4).

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

22

The f a c t t h a t V appears t o form under a l l c o n d i t i o n s o f r e a c t i n g (CF3S02>20 w i t h THF and then behaves as a slow p o l y ­ m e r i z a t i o n i n i t i a t o r i n d i c a t e s t h a t the p r e v i o u s l y reported narrow molecular weight d i s t r i b u t i o n ( p o l y d i s p e r s i t y o f 1.08) f o r a poly-THF prepared a t -10° was probably i n e r r o r ( 1 ) . I t i s l i k e l y that the e r r o r might be a t t r i b u t e d t o the use o f GPC columns i n the e a r l i e r work which were not s u i t e d to r e s o l v e low molecular weight f r a c t i o n s . As s t a t e d p r e v i o u s l y , V I I I forms as a d i s t i n c t species only when a r e l a t i v e l y h i g h c o n c e n t r a t i o n o f anhydride i s employedI t i s important to note that the t r i m e r i s the lowest oligomer b i s ( t r i f l a t e ) which i s capable o f e x i s t i n g as a bisoxonium s a l t . Thus, i n Equation (3) the e q u i l i b r a t i o n between macrodication I I I and macrodiester IV can come i n t o p l a y only a t the t r i m e r stage. I f V I I I forms a low s a t u r a t i o n c o n c e n t r a t i o n the e q u i l i b r i u m e s s e n t i a l l y a l l the way toward bisoxonium i o n t r i f l a t e s a l t . As higher oligomer b i s ( t r i f l a t e s ) s l o w l y form, these are very s o l u b l e i n THF and the normal e q u i l i b r i u m be­ tween macroester and macroion i s r e - e s t a b l i s h e d .

ABSTRACT A detailed examination of the reaction of THF with (CF S0 ) has been carried out and two prominently distinct oligomeric species have been found to be produced as intermed­ iates during the polymerization which yields living products whose end groups consist of ions and esters in equilibrium. First, the ring-opened tetramethylene bis(triflate) ester is produced in all cases studied and its behavior as a relatively sluggish THF polymerization initiator causes the otherwise narrow molecular weight distribution to skew toward the low end. Second, at relatively high initial anhydride concentrations, 3

2

2

the bisoxonium ion salt,

•2CF SO , forms and 3

3

separates as a pure crystalline precipitate. Reaction mech­ anisms are postulated to account for the surprising formation of these compounds during THF polymerization. ACKNOWLEDGEMENT We are indebted to Dr. Peter F. Cullen for providing the GPC analyses. LITERATURE CITED Smith, S., and Hubin, A.J., J. Macromol. Sci. - Chem., (1973), A7, 1399. 2. Kobayashi, S., Danda, Η., and Saegusa, T., (a) Bull. Chem. Soc. of Japan (1973), 46, 3214, (b) Macromol., (1974), 7., 415. 3. Matyjaszewski, K., and Penczek, S., J. Polym. Sci. - Chem. Ed., (1974) 12, 1905. 1.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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4. Matyjaszewski, Κ., Kubisa, P., and Penczek, S., J. Polym. Sci. Chem. Ed., (1975), 13, 763. 5. Matyjaszewski, Κ., Buyle, A.M., and Penczek, S., J. Polym. Sci. - Letters Ed., (1976), 14, 125. 6. Wu, T.K., and Pruckmayr, G., Macromol., (1975), 8, 77. 7. Pruckmayr, G., and Wu, T.K., Macromol., (1975) 8, 954. 8. Matyjaszewski, K. and Penczek, S., J . Polym. Sci. - Chem. Ed. (1977), 15, 247. 9. Saegusa, T., and Matsumoto, S., J. Polym Sci., (1968), A6, 1559. 10. Rosenberg, B.A., Ludvig, E.B., Gantmakher, A.R., and Medvedev, S.S., J. Polym. Sci., (1967), C16, 1917. 11. Croucher, T.G., and Wetton, R.E., Polymer, 17, (1976), 205. 12. Cash, D.J., personal communication

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

3 New Developments in Graft Copolymerization by Oxonium Ion Mechanism Κ. I. L E E and P. DREYFUSS Institute of Polymer Science, The University of Akron, Akron, OH 44325

One importan has been to find genera polymers comprising hydrocarbon backbones with polar branches derived from cationically polymerizable heterocyclic monomers. Hitherto such polymers have not been available generally and are of interest be­ cause of the unique combination of properties that are potentially attainable. We recently reported a new efficient method for the preparation of this type of graft copolymer (1). Our new method consists of i n i t i a t i n g polymerization of the heterocycle from a hydrocarbon backbone con­ taining a reactive halogen by adding a suitable salt as shown i n equation 1, where X = halogen, Ζ = O, S, and MY is a salt of a metal (M) with a counter­ ion (y) capable of supporting onium ion polymeriza­ tions .

Not every halide, salt, and heterocycle can be used in our synthesis. We recently overviewed the scope of our discovery using studies with model halides, various heterocycles, a variety of salts, and numer­ ous backbones to help define the limitations (2). Our model halide studies showed that reactive halides include allylic, tertiary, and benzylic chlorides, bromides, and iodides. Soluble silver salts with anions such as SO CF , BF PF , AsF , SbF , and ClO are most suitable but LiPF and NaClO can also -

3

-

3

-

4

6

-

-

6

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24 In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

3. LEE AND DREYFUSS

Graft

Copolymerization

25

be used. We c o n c l u d e d t h a t a s u i t a b l e s a l t i s one t h a t i s s o l u b l e i n t h e p o l y m e r i z a t i o n medium, has an a n i o n t h a t l e a d s t o a s t a b l e onium s a l t , and l e a d s t o a product t h a t i s l e s s s o l u b l e than the o r i g i n a l s a l t . So f a r n i n e h e t e r o c y c l e s have b e e n p o l y m e r i z e d b y t h i s method. These i n c l u d e t e t r a h y d r o f u r a n , 7 - o x a b i c y c l o [2,2,1]heptane, oxetane, p r o p y l e n e o x i d e , s t y r e n e oxi d e , d i o x o l a n e , t r i o x a n e , e - c a p r o l a c t o n e , and t h i e tane. E f f o r t s t o optimize conditions f o r selected monomers a r e i n t h e i r e a r l y s t a g e s , and t h e p r e l i m i n ary d a t a s u g g e s t t h a t many o f t h e e x p e c t e d s i d e r e a c t i o n s a r e o p e r a t i v e (3) . G r a f t copolymers have been p r e p a r e d from seve backbones poly(vinyl chloride) polychloroprene, chlorinate b r o m o b u t y l r u b b e r , c h l o r i n a t e d p o l y ( b u t a d i e n e ) , and c h l o r i n a t e d b u t a d i e n e - s t y r e n e copolymer. I n t h e most t h o r o u g h l y examined c a s e s w i t h p o l y t e t r a h y d r o f u r a n as t h e g r a f t e d copolymer and s i l v e r t r i f l a t e as t h e i n o r g a n i c s a l t , c u r r e n t d a t a i n d i c a t e t h a t no u n r e a c t e d backbone remains and no homopolymer forms. W i t h some o f t h e o t h e r monomers, s t u d i e d o n l y w i t h A g P F as t h e s a l t , homopolymer i s formed i n a d d i t i o n t o g r a f t . No e v i d e n c e f o r c y c l i c o l i g o m e r f o r m a t i o n was o b t a i n e d w i t h any o f t h e monomers. 6

Efficiency of Initiation Our g o a l i s t o p r e p a r e w e l l - d e f i n e d g r a f t c o polymers. The method d e s c r i b e d i n t h i s p a p e r has t h e p o t e n t i a l o f l e a d i n g t o g r a f t s w i t h a c o n t r o l l e d numb e r o f b r a n c h e s o f known l e n g t h . "Living" polymeriz a t i o n s o f many o f t h e h e t e r o c y c l e s b e i n g s t u d i e d a r e known and t h e i r r a t e s o f p o l y m e r i z a t i o n have been c a r e f u l l y d e t e r m i n e d (3.,4) . Thus p r e p a r a t i o n o f g r a f t copolymers w i t h a p r e d i c t a b l e number and l e n g t h o f b r a n c h e s c a n be a c h i e v e d i f t h e e f f i c i e n c y o f t h e i n i t i a t i o n p r o c e s s i s known and r e p r o d u c i b l e . I d e a l l y the i n i t i a t i o n s h o u l d be i n s t a n t a n e o u s and 1 0 0 % e f f i cient. We t h e r e f o r e s e l e c t e d t h e s t u d y o f t h e i n i t i a t i o n p r o c e s s as o u r f i r s t i n d e p t h e x a m i n a t i o n o f o u r new p r o c e s s . I n t h i s p a p e r we r e p o r t d a t a from t h e f o l l o w i n g experiments: 1. Nmr s t u d i e s o f t h e p r o d u c t s o f r e a c t i o n s o f model h a l i d e s and s i l v e r s a l t s i n t h e p r e s e n c e o f

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

26

RING-OPENING

POLYMERIZATION

the nonpolymerizable h e t e r o c y c l e s , 2-methyltetrah y d r o f u r a n and t e t r a h y d r o p y r a n . 2. Studies o f the r a t e o f formation o f s i l v e r h a l i d e w i t h model h a l i d e s , d i f f e r e n t s i l v e r s a l t s , and n o n p o l y m e r i z a b l e h e t e r o c y c l e s . 3. Comparison o f t h e r a t e s o f s i l v e r h a l i d e f o r mation w i t h r a t e s o f t e t r a h y d r o f u r a n polymerizat i o n s u s i n g model h a l i d e s and d i f f e r e n t s i l v e r salts. 4. A p p l i c a t i o n o f t h e s i l v e r h a l i d e p r e c i p i t a t i o n method t o h a l o g e n a t e d b u t y l r u b b e r s i n c y c l i c e t h e r and c o m p a r i s o n w i t h r e s u l t s o f g r a f t c o p o l y m e r i z a t i o n s t u d i e fro th backbones Possible Reaction

Paths

One c a n imagine s e v e r a l d i f f e r e n t pathways t h a t r e a c t i o n o f a l l y l h a l i d e , s i l v e r s a l t , and a h e t e r o c y c l i c e t h e r might t a k e . These a r e i l l u s t r a t e d i n t h e s e r i e s o f e q u a t i o n s 2 where t h e r e a c t a n t s a r e a l l y l c h l o r i d e , 2 - m e t h y l t e t r a h y d r o f u r a n and s i l v e r hexafluorophosphate. The d e s i r e d pathway i s t h e addi t i o n o f t h e a l l y l group t o t h e h e t e r o c y c l e t o form an oxonium i o n (2-1) . However, we know from p r e v i o u s work t h a t when carbenium i o n s a r e p o s s i b l e i n t e r m e d i a t e s , h y d r o g e n a b s t r a c t i o n (2-2) and e l i m i n a t i o n r e a c t i o n s (2-3) have t o be c o n s i d e r e d (5_,6) . R e a c t i o n o f t h e carbenium i o n w i t h t h e c o u n t e r i o n t o form a l l y l f l u o r i d e i s a p o s s i b i l i t y ( 2 - 4 ) . R e a c t i o n s (2-2) t o (2-3) a r e u n d e s i r a b l e because t h e H ® P F formed would i n i t i a t e homopolymerization o f the c y c l i c e t h e r and p u r e g r a f t copolymer would n o t be formed. Finall y , as w i l l b e s e e n below, o u r d a t a s u g g e s t s t h a t some t y p e o f c o u p l i n g r e a c t i o n may a l s o be o c c u r r i n g o c c a s i o n a l l y and we i n c l u d e r e a c t i o n (2-5) as a p o s sibility. I n a n a l y z i n g o u r r e s u l t s , we l o o k e d f o r e v i d e n c e o f each o f t h e s e pathways because we needed an e x p l a n a t i o n f o r some unexpected r e s u l t s . e

6

Nmr S t u d i e s We began o u r s t u d i e s b y examining t h e s i l v e r s a l t a s s i s t e d r e a c t i o n o f 2-methyltetrahydrofuran with a l l y l c h l o r i d e , a l l y l bromide, and a l l y l i o d i d e .

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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E q u a t i o n 2 - P o s s i b l e Pathways CH =CHCH Cl 2

1

+ /

2

\

+

AgPP

>

6

Products

Initiation

6

I

CH CH=CH 2

2

2

Hydrogen a b s t r a c t i o »

/

I

+

CH =CHCH 2

+

3

Φ

Η ΡΡ

Θ 6

+ AqCl

i polymeric products 3

I

4

(black tar?)

E l i m i n a t i o n o f HX from a l l y l h a l i d e X

+

CH =C=CH 2

2

9

+

H PF

+

AqCl

9 6

+ AqCl

Reaction with counterion +

>

CH =CHCH F 2

2

PF 5

black t a r 5

C o u p l i n g w i t h CH =CHCH 2

+

3

C H =CHCH C H 8HCH 2

2

2

3

+ H°PF

E 6

+ AqCl

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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RING-OPENING POLYMERIZATION

I n i t i a l l y we had hoped t o i s o l a t e b o t h p r o d u c t s o f r e a c t i o n 2-1. We found t h a t a l t h o u g h the s i l v e r h a l i d e p r e c i p i t a t e c o u l d r e a d i l y be i s o l a t e d , attempts t o i s o l a t e the oxonium i o n s a l t gave o n l y b l a c k t a r and a gaseous p r o d u c t . This i s c o n s i s t e n t with the e l u s i v e c h a r a c t e r o f a l l y l carbenium i o n s p r e v i o u s l y r e p o r t e d by O l a h and Camisarov (7) . The b l a c k t a r c o u l d have b e e n formed e i t h e r from t h e f u r a n i n (2-2) o r from t h e adduct o f 2 - m e t h y l t e t r a h y d r o f u r a n and P F , w h i c h i s known t o be u n s t a b l e (8) . Nmr s p e c t r a t a k e n a t v a r i o u s times on a T-60 V a r i a n ftmr S p e c t r o m e t e r a f t e r r e a c t i o n s c a r r i e d o u t a t room temperature showed a f a r d o w n f i e l d p r o t o n t h a t s h i f t e d u p f i e l d w i t h time as would be e x p e c t e found no e v i d e n c e f o r e i t h e r p r o p y l e n e o r aliène, a l though we d i d demonstrate t h a t under t h e c o n d i t i o n s o f our experiments t h e s o l u b i l i t y o f p r o p y l e n e w o u l d be s o low i n 2 - m e t h y l t e t r a h y d r o f u r a n t h a t i t might w e l l d i s a p p e a r b e f o r e a spectrum c o u l d be t a k e n . There was no e v i d e n c e o f a s h i f t i n t h e peaks c o r r e s p o n d i n g t o 2 - m e t h y l t e t r a h y d r o f u r a n as would be e x p e c t e d i f the oxonium i o n had formed. The f o r m a t i o n o f a l l y l f l u o r i d e cannot be r u l e d o u t because a l l y l peaks p e r s i s t e d a l o n g w i t h t h o s e o f t h e 2 - m e t h y l t e t r a h y d r o f u r a n even a f t e r a l l t h e s i l v e r c h l o r i d e had p r e c i p i t a t e d . I f t h e r e a c t i o n was c a r r i e d out i n l i q u i d S0 at -78°C, i t was p o s s i b l e t o o b s e r v e a s h i f t o f t h e a l l y l and 2 - m e t h y l t e t r a h y d r o f u r a n p r o t o n s i n an nmr s p e c trum t a k e n on a HR300 V a r i a n nmr S p e c t r o m e t e r b u t t h e r e a c t i o n was v e r y slow. T h i s r e s u l t i s c o n s i s t e n t w i t h t h e f o r m a t i o n o f t h e e x p e c t e d oxonium s a l t . No o t h e r p r o d u c t s were a p p a r e n t . However, t h e spectrum was q u i t e c o m p l i c a t e d b e c a u s e o f t h e many a b s o r p t i o n s due t o p r o d u c t s and s t a r t i n g m a t e r i a l s and we d i d n o t attempt t o i n t e r p r e t i t c o m p l e t e l y . Lambert and Johnson made s i m i l a r comments about t h e i r nmr s p e c trum from a r e a c t i o n o f i s o p r o p y l bromide, t e t r a h y d r o f u r a n , and s i l v e r t e t r a f l u o r o b o r a t e (9)· We were more s u c c e s s f u l i n d e m o n s t r a t i n g t h e f o r m a t i o n o f t h e a d d i t i o n p r o d u c t of i n i t i a t i o n i n an experiment u s i n g u n s u b s t i t u t e d t e t r a h y d r o f u r a n and c a r r y i n g out the p o l y m e r i z a t i o n w i t h h i g h a l l y l b r o mide-AgSbF c o n c e n t r a t i o n and low enough c o n v e r s i o n so t h a t an o i l y p r o d u c t was formed. The nmr spectrum 5

2

1

6

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o f a c a r e f u l l y p u r i f i e d sample o f t h i s polymer c l e a r l y showed t h e p r e s e n c e o f a l l y l groups and t h e c h e m i c a l s h i f t s were c o n s i s t e n t w i t h t h e p r e s e n c e o f an a l l y l e t h e r l i n k a g e . Our p r e v i o u s g r a f t c o p o l y m e r i z a t i o n s t u d i e s a l s o i n d i c a t e a d d i t i o n o f t h e a l l y l group, s i n c e no homopolymer was formed d u r i n g g r a f t i n g . Appar­ e n t l y t h e a l l y l oxonium i o n i s u n s t a b l e and decomposes rapidly. Side r e a c t i o n s occur i f the h e t e r o c y c l e i s n o t p o l y m e r i z a b l e b u t p o l y m e r i z a t i o n o c c u r s when p o s ­ sible. O v e r a l l , we c o n c l u d e d t h a t i n o u r case nmr s t u d i e s a r e n o t a good method f o r s t u d y i n g t h e k i n e t i c s o f t h e i n i t i a t i o n p r o c e s s a t room temperature They were u s e f u l f o r g a i n i n t h a t might be formed. I s o l a t i o n o f S i l v e r H a l i d e from Model S t u d i e s P r e l i m i n a r y a n a l y s i s o f t e t r a h y d r o f u r a n polymer­ i z a t i o n s t e r m i n a t e d b y sodium phenoxide (jLO) i n d i c a t e s t h a t t h e r a t e o f f o r m a t i o n o f oxonium i o n p a r a l l e l s t h e r a t e o f p r e c i p i t a t i o n o f s i l v e r h a l i d e (11) . Thus i n ­ f o r m a t i o n about t h e r a t e and e f f i c i e n c y o f f o r m a t i o n o f oxonium i o n s from s i l v e r s a l t s , a l l y l h a l i d e s and a c y c l i c e t h e r was o b t a i n e d b y m e a s u r i n g t h e r a t e o f f o r ­ m a t i o n o f s i l v e r h a l i d e . I f t h e e t h e r was 2-methylt e t r a h y d r o f u r a n and t h e c o n c e n t r a t i o n s o f a l l y l h a l i d e s and A g P F were 2 χ 1 0 " m o l e s i n 2 ml o f c y c l i c e t h e r (6.7 χ 10~ M) , t h e f o r m a t i o n o f A g i and AgBr were much f a s t e r than t h a t o f AgCl. A f t e r 1 hr., the s h o r t e s t time o f o b s e r v a t i o n , t h e p e r c e n t s o f h a l i d e i s o l a t e d were 3, 76 and 88 f o r A g C l , AgBr, and A g i , r e s p e c t i v e ­ l y ( T a b l e I , F i g u r e 1) . A f t e r 6 h r s , p r e c i p i t a t i o n s o f A g C l , AgBr, and A g i were 10,83, and 9 1 % complete, r e ­ s p e c t i v e l y . A t s u f f i c i e n t l y l o n g times 1 0 0 % h a l i d e , w i t h i n e x p e r i m e n t a l e r r o r , was o b t a i n e d i n some c a s e s . To see i f t h e r e i s any i n f l u e n c e o f c o u n t e r i o n other than P F , the r a t e o f formation o f s i l v e r h a l i d e p r e c i p i t a t i o n was measured u s i n g AgSbF i n s t e a d o f A g P F . F i g u r e 2 i n d i c a t e s t h a t t h e r e i s no e s s e n t i a l d i f f e r e n c e between P F and S b F . The f a s t e r i n i t i a t i o n b y t h e bromide compared t o the c h l o r i d e i n t h e p o l y m e r i z a t i o n o f c y c l i c e t h e r s was a l s o demonstrated from t h e model r e a c t i o n s o f a l l y l 4

6

2

e

6

6

6

e

6

e

6

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

30

Table I Comparison Salt AgPF

Halide

6

AgSbF

6

b

a o f Rates o f AgX P r e c i p i t a t i o n c % AgX a f t e r 1 h r

Monomer

CI Br I

2-MeTHF 2-Me THF 2-Me THF

CI Br

2-MeTHF 2-MeTH

CI Br

ΤΗΡ THP

d

3 76 89 2

β

3 74

C o m p a r i s o n s a r e made a t 1 h r because even though t h e r a t e o f p r e c i p i t a t i o n o f AgCl had not y e t reached a s t e a d y s t a t e , b y t h i s time p r e c i p i t a t i o n o f A g i was e s s e n t i a l l y complete. No measurements were made a t l e s s t h a n 1 h r . R d a t a was n o t c a l c u l a t e d because under t h e s e c i r c u m s t a n c e s t h e numbers c o u l d n o t be compared. p

b A l l unsubstituted a l l y l halides. Halide concentra­ t i o n was a p p r o x i m a t e l y 10"" moles i n 2 ml c y c l i c e t h e r i n each case. 4

% AgX = t h e a c t u a l amount o f AgX i s o l a t e d / t h e e x p e c t e d amount o f AgX b a s e d on t h e t o t a l amount o f a l l y l h a l i d e charged. d

2-Methyltetrahydrofuran. Tetrahydropyran.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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h a l i d e s and s i l v e r s a l t s i n t h e p r e s e n c e o f t e t r a h y d r o p y r a n ( F i g u r e 3) . A f t e r 1 h r , about 7 4 % o f the e x p e c t e d amount o f AgBr had p r e c i p i t a t e d whereas o n l y 3 % A g C l was i s o l a t e d . A f t e r 6 hrs p r e c i p i t a t i o n s of AgBr and A g C l were 8 9 % and 1 4 % complete, r e s p e c t i v e l y . These r e s u l t s i n d i c a t e t h a t the f a s t e r f o r m a t i o n o f oxonium i o n from t h e bromide compared t o the c h l o r i d e i s independent o f t h e c y c l i c e t h e r . These r e s u l t s a r e i n c o n f o r m i t y w i t h o u r expect a t i o n from t h e o r g a n i c c h e m i s t r y o f s m a l l m o l e c u l e s . The e a s i e r d e p a r t u r e o f bromide compared t o c h l o r i d e by e l e c t r o p h i l i c a s s i s t a n c e o f t h e Ag^ would l e a d t o more r a p i d f o r m a t i o n o f oxonium i o n and hence more rapid conversion t R e l a t i v e Rates o f T e t r a h y d r o f u r a n

Polymerizations

F u r t h e r e v i d e n c e f o r the more r a p i d f o r m a t i o n o f a c t i v e c e n t e r s from t h e bromide compared t o the c h l o r i d e , f o r example, was o b t a i n e d by e x a m i n i n g t h e % c o n v e r s i o n o f t e t r a h y d r o f u r a n t o polymer ( F i g u r e 4) . A f t e r 1 h r the p o l y m e r i z a t i o n w i t h a l l y l c h l o r i d e had r e a c h e d 2 % c o n v e r s i o n , w h i l e 6 5 % c o n v e r s i o n was obt a i n e d w i t h a l l y l bromide i n t h e same time i n t e r v a l . C o n c e n t r a t i o n s o f a l l y l h a l i d e and s i l v e r s a l t were comparable and a l l r e a c t i o n s were c a r r i e d o u t a t room t e m p e r a t u r e , where 7 5 % i s t h e t h e r m o d y n a m i c a l l y exp e c t e d maximum c o n v e r s i o n . A l s o a sigmoidal convers i o n - t i m e p l o t i n d i c a t i v e o f slow i n i t i a t i o n was obt a i n e d w i t h a l l y l c h l o r i d e whereas a s i m i l a r p l o t from a l l y l bromide was l i n e a r i n t h e e a r l y s t a g e s . Again d i f f e r e n t c o u n t e r i o n s , S b F , P F , o r S 0 C F , made no g r e a t d i f f e r e n c e i n the c o n c l u s i o n s about r e l a t i v e r a t e s o f i n i t i a t i o n w i t h c h l o r i d e , bromide, o r i o d i d e . Osmotic m o l e c u l a r w e i g h t s o f the r e s u l t i n g p o l y t e t r a h y d r o f u r a n s a t e q u i l i b r i u m c o n v e r s i o n were near t h o s e c a l c u l a t e d from the amounts o f h a l i d e s and s i l v e r s a l t s charged. e

6

e

6

e

3

3

I s o l a t i o n of S i l v e r Halide a f t e r Reaction of Halogena t e d Polymers

cial

These e x p e r i m e n t s were c a r r i e d o u t u s i n g commerc h l o r o b u t y l and b r o m o b u t y l r u b b e r s d i s s o l v e d i n

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

ιοσ

andAgPFc

andAgSbF

6

Figure 3. Effect of halide on formation rate of silver halide in reactions of tetrahydropyran with allyl halides and AgSbF 6

TIME (HRS)

TIME (HRS)

TIME (HRS)

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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Copolymerization

33

2 - m e t h y l t e t r a h y d r o f u r a n and t r e a t e d w i t h A g P F . Samp l e s c o n t a i n i n g a p p r o x i m a t e l y t h e same t o t a l p e r c e n tage o f h a l o g e n were used. The most p r o b a b l e s t r u c t u r e and t h e p e r c e n t a g e o f a l l y l i c h a l o g e n i n c h l o r o b u t y l r u b b e r , whose s t r u c t u r e i s b e t t e r known t h a n t h a t o f b r o m o b u t y l r u b b e r a r e shown below (12) : 6

ÎCH C(CH ) 2

3

^ Œ C = Œ C H - 3 - £ o r {CH C ( CH ) 4 t C H CCHClCH -3

2

2

2

2

3

2

2

I

CH C l

CH

2

98%

2

II

2%

98%

2

2%

As shown i n T a b l e I I , a g a i n the r a t e o f p r e c i p i t a t i o n o f AgBr was f a s t e r t h a n t h a t o f A g C l The amount o f silver halide precipitate and was c o n s i d e r a b l y l e s s t h a n t h e t o t a l p e r c e n t a g e o f h a l o g e n i n t h e polymer. T h i s s u g g e s t s t h a t o n l y about 1 6 % o f t h e h a l o g e n i s a c t i v e toward p r e c i p i t a t i o n by o u r method and t h a t e i t h e r t h e s e h a l o g e n s have a d i f f e r e n t , more r e a c t i v e s t r u c t u r e t h a n t h a t g i v e n above o r t h a t t h e p e r c e n t a g e o f h a l o g e n s o f t h e above s t r u c t u r e i s lower t h a n p r e v i o u s l y supposed. Table I I % Halide

P r e c i p i t a t e d from H a l o g e n a t e d

Rubber Chlorobutyl

Time (hrs) rubber

Bromobutyl r u b b e r

Butyl %

Rubbers Halide

1 6 12 24

1.9 7.6 15.2 15.2

1 6 12 24

10 16.7 16.7 16.7

3

% h a l i d e = t h e a c t u a l amount o f AgX i s o l a t e d / t h e e x p e c t e d amount o f AgX b a s e d on the t o t a l amount o f h a l i d e i n the rubber. U n l e s s t h e r e a c t i o n w i t h b r o m o b u t y l was c a r r i e d o u t a t h i g h d i l u t i o n ( 0 . 7 5 % ) compared t o c h l o r o b u t y l r u b b e r ( 2 . 3 5 % ) , i t was n o t p o s s i b l e t o i s o l a t e t h e AgBr because t h e polymer g e l l e d and t r a p p e d t h e s a l t . We

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

34

RING-OPENING POLYMERIZATION

s u g g e s t t h a t a s i d e r e a c t i o n s u c h as t h a t i l l u s t r a t e d i n 2-5 o c c u r s a t h i g h e r c o n c e n t r a t i o n s . Alternately, s i n c e a r e a c t i o n such as 2-3 c o u l d produce a polymer containing D i e l s - A l d e r a c t i v e conjugated dienes ( r a t h e r t h a n the aliène shown) , the t r e a t e d polymer might be s e l f - c u r i n g by d i m e r i z a t i o n o f t h e s e u n i t s . Data on t h i s p o i n t was o b t a i n e d by t a k i n g uv measurements o f the o r i g i n a l polymers d i s s o l v e d i n i s o o c t a n e . The c h l o r o b u t y l r u b b e r c o n t a i n e d o n l y an a b s o r p t i o n a t about 210 πιμ, w h i c h c o u l d be a s s o c i a t e d w i t h the o l e ­ f i n i n the s t r u c t u r e above, b u t the b r o m o b u t y l r u b b e r a l s o had a d d i t i o n a l a b s o r p t i o n s between 220 and 240 πιμ t h a t would i n d i c a t multiplicit f conjugated d i e n e s even i n the o r i g i n a G r a f t i n g from H a l o g e n a t e d B u t y l

Rubbers

F u r t h e r i n f o r m a t i o n about the r e l a t i v e r e a c t i v ­ i t i e s o f c h l o r o b u t y l and b r o m o b u t y l r u b b e r s was ob­ t a i n e d from g r a f t i n g s t u d i e s w i t h p o l y t e t r a h y d r o f u r a n as t h e b r a n c h . The r e s u l t s are summarized i n T a b l e I I I . Table I I I P o l y t e t r a h y d r o f u r a n G r a f t s from C h l o r o b u t y l and Bromobutyl Rubber Backbones Halide

Salt

CI CI Br Br

AgBF AgPF AgBF AgPF

PTHF C o n v e r s i o n a f t e r 24 h r s - % 3 13 0 5

4

6

4

6

I t i s noteworthy t h a t a f t e r 24 h o u r s the conversions t o p o l y t e t r a h y d r o f u r a n were a l l v e r y low and t h a t t h o s e from the b r o m o b u t y l r u b b e r were l o w e r t h a n t h o s e from t h e c h l o r o b u t y l r u b b e r . The d i f f e r e n c e s between the r e s u l t s w i t h AgBF and A g P F c a n be e x p l a i n e d , s i n c e t e r m i n a t i o n r e a c t i o n s a r e known t o o c c u r more readily with B F than w i t h P F (4) . The d i f f e r ­ ences between the c h l o r i d e and the bromide can be r a t i o n a l i z e d by assuming t h a t r e a c t i o n s ( 2 - 2 ) and(2-3) 4

6

e

4

e

6

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

LEÉ AND DREYFUSS

24

Graft

48

TIME (HRS)

Copolymerization

Figure 4. Effect of halide on conversion (%)to polytetrahydrofuran (PTHF) in reactions of tetrahydrofuran with allyl halides and AgPF G

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

36

RING-OPENING POLYMERIZATION

o r the D i e l s A l d e r d i m e r i z a t i o n a r e more i m p o r t a n t w i t h the bromide t h a n w i t h t h e c h l o r i d e , b u t t h a t t h e y can o c c u r i n b o t h c a s e s . E v i d e n c e t h a t t h e y do o c c u r was o b t a i n e d from uv s p e c t r o s c o p y . Figure 5 shows the uv s p e c t r a f o r t r e a t e d and u n t r e a t e d c h l o r o ­ b u t y l r u b b e r s . A s h o u l d e r from 220 t o 240 πιμ appears i n the polymer i s o l a t e d a f t e r the g r a f t i n g r e a c t i o n . This shoulder i s c o n s i s t e n t w i t h but not proof t h a t d i e n e s a r e b e i n g formed. Because the b r o m o b u t y l r u b ­ b e r uv spectrum a l r e a d y c o n t a i n e d a s i m i l a r a b s o r p t i o n b e f o r e the a t t e m p t e d g r a f t i n g , i t was d i f f i c u l t t o ob­ t a i n c o n v i n c i n g e v i d e n c e f o r an i n c r e a s e d d i e n e c o n ­ tent a f t e r grafting T h i s was e s p e c i a l l y d i f f i c u l t s i n c e a f t e r the g r a f t i n m a r k e d l y i n c r e a s e d t e n d e n c y t o g e l and samples r e p r e s e n t a t i v e o f the whole were n o t p o s s i b l e t o o b t a i n . The i n c r e a s e d t e n d e n c y t o g e l i s c o n s i s t e n t w i t h i n ­ creased diene content. On the b a s i s o f our g r a f t i n g s t u d i e s w i t h h a l o g e n a t e d b u t y l r u b b e r s we must c o n c l u d e t h a t a l t h o u g h the bromide i s more e a s i l y d i s p l a c e d t o form AgX, as e x p e c t e d from o r g a n i c c h e m i s t r y , the c h l o r i d e i s more s u i t a b l e f o r making g r a f t s . Summary New i n s i g h t i n t o the c h e m i s t r y o f g r a f t i n g p o l a r b r a n c h e s s u c h as p o l y t e t r a h y d r o f u r a n from h y d r o c a r b o n backbones c o n t a i n i n g a l l y l i c h a l o g e n s by a d d i n g s u i t ­ able s i l v e r s a l t s i s reported. Model s t u d i e s show t h a t t h e r a t e o f f o r m a t i o n o f s i l v e r h a l i d e can be used as an i n d i c a t i o n o f the r a t e o f f o r m a t i o n o f ox­ onium i o n s and t h a t the r a t e s o f p r e c i p i t a t i o n o f AgX a r e i n the e x p e c t e d o r d e r AgI>AgBr>AgCl. The r e s u l t s a r e independent o f c o u n t e r i o n and o f h e t e r o c y c l e . S i d e r e a c t i o n s such as h y d r o g e n a b s t r a c t i o n , e l i m i n ­ a t i o n o f HX, and r e a c t i o n w i t h c o u n t e r i o n a r e p r o b a b l e . I t i s concluded t h a t although i t i s p o s s i b l e to p r e ­ p a r e p u r e g r a f t s by t h i s method, p r e c i s e c o n t r o l o f the number and l e n g t h o f the b r a n c h e s may be d i f f i c u l t .

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

3. LEE AND DREYFUSS

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37

Literature Cited

1.

Dreyfuss, P., and Kennedy, J. P., J. Polym. S c i . , Polym. Letters Ed. (1976) 14, 135. 2. Dreyfuss, P., and Kennedy, J. P., paper presented at 4th International Symposium on Cationic Poly­ merization, Akron, Ohio, June (1976). J. Polym. S c i . , Polymer Symposia (in press). 3. Frisch, K. C . , and Reegen, S. L., Eds., "Kinetics and Mechanisms of Polymerization Reactions, Vol 2, Ring-Opening Polymerization", Marcel Dekker, New York, N.Y., 1969. 4. Dreyfuss, P., and Dreyfuss M P. Chapter 4 in "Comprehensive Bamford, C. H . , and Tipper, C. F. H . , Eds., Else vier Scientific Publishing Co., Amsterdam - W., Netherlands, 1976. 5. Dreyfuss, M. P., Westfahl, J. C . , and Dreyfuss, P., Macromolecules, (1968) 1, 437. 6. Pocker, Y. and Wong, W. H . , J. Am. Chem. Soc. (1975) 97, 7097. 7. Olah, G . , Comisarov, M. B., J. Am. Chem. Soc. (1964) 86, 5682. 8. Muetterties, L., Butler, T. Α., Farlow, M. W., and Coffman, D. D., J. Inorg. Nucl. Chem. (1960) 16, 52. 9. Lambert, J. B., and Johnson, D. H . , J. Am. Chem. Soc. (1968) 90, 1349. 10. Saegusa, T . , and Matsumoto, S., J. Polym. Sci. (1968) A l , 6, 1559. 11. Quirk, R. and Dreyfuss, P., unpublished results. 12. Baldwin, F. P., Gardner, I. J., Malatesta, Α., and Rae, J. Α., Paper No. 1 presented at 108th meeting Rubber Division of ACS, New Orleans, LA., Oct. 7, 1975. Acknowledgment Acknowledgment is made to the donors of the Pet­ roleum Research Fund, administered by the American Chemical Society, for support of this research.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4 Ring-Opening Polymerization with Expansion in Volume WILLIAM J. BAILEY, ROBERT L. SUN, HIROKAZU KATSUKI, TAKESHI ENDO, HIDEAKI IWAMA, RIKIO TSUSHIMA, KAZUHIDE SAIGOU, and MICHEL M. BITRITTO Department of Chemistry, University of Maryland, College Park, MD 20742

For a number of industrial applications h strain-fre composites, potting resins propellants, and impression materials, it appeared highly desir able to have monomers that will polymerize with near zero shrinkage. For other applications, such as precision castings, high strength adhesives, prestressed plastics, rock-cracking materials, elastomeric sealants, and dental fillings, it appeared highly desirable to have monomers that would undergo positive expansion on polymerization. For example, many composites involving high strength fibers in a polymeric matrix fail because of either poor adhesion between the matrix and the fibers or because of voids and microcracks in the matrix. Both of these problems are at least partially related to the fact that when available materials polymerize or cure, a pronounced shrinkage takes place. Examples are available from other fields to suggest that monomers that expand on polymerization would indeed produce strong adhesives. For example, when water freezes, it expands by 4%, and as a result ice will adhere to almost any surface, including Teflon which it does not even wet, by expanding into the various valleys and crevices of the irregular surface to promote strong micromechanical adhesion. For these reasons a research program was initiated to find monomers that would undergo either zero shrinkage or expansion upon polymerization. Shrinkage that occurs during polymerization arises from a number of factors. One of the most important, however, is the fact that the monomer molecules are located at a van der Waals' distance from one another, while in the corresponding polymer the monomeric units move to within a covalent distance of one another. Thus, the atoms are much closer to one another in the polymer than they were in the original monomer. Smaller, but yet significant factors, are the change in entropy in going from monomer to the polymer, free volume in amorphous polymers, and how well the monomer and polymer pack if crystals are present in either phase. In a condensation polymerization, in which a small molecule is eliminated, the shrinkage is partially related to the size of 38 In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4. BAILEY ET AL.

Polymerization

with Expansion

in

Volume

39

the molecule that i s e l i m i n a t e d . For example, the shrinkage that takes p l a c e d u r i n g the s y n t h e s i s o f nylon 6,6 can vary from 22% when hexamethylenediamine i s condensed w i t h a d i p i c a c i d w i t h the e l i m i n a t i o n o f water t o 66% when hexamethylenediamine i s condensed w i t h d i o c t y l adipate w i t h the e l i m i n a t i o n o f o c t y l a l c o h o l . During a d d i t i o n p o l y m e r i z a t i o n , where no molecule i s e l i m i n a t e d , the shrinkage, as i n d i c a t e d i n Table I , can vary from 66% f o r the p o l y m e r i z a t i o n o f ethylene t o 6% f o r the p o l y m e r i z a t i o n o f v i n y l pyrene. The shrinkage appears t o c o r r e l a t e t o a f i r s t approximat­ i o n t o the number o f monomer molecules that are converted t o p o l y ­ mer per u n i t volume. For example, styrene, which has approximately four times the molecular weight o f ethylene, undergoes approximate­ l y o n l y one-fourth the shrinkage that occurs during the polymer­ i z a t i o n o f ethylene. TABLE I .

C a l c u l a t e d Shrinkage

Monomer

Shrinkage, % 66.0 39.0 36.0 34.4 31.0 21.2 20.9 14.5 11.8 7.5 6.0

Ethylene Propylene Butadiene Vinyl chloride Acrylnitrile Methyl methacrylate V i n y l acetate Styrene D i a l l y l phthalate N-Vinylcarbazole 1-Vinylpyrene

Ring-opening p o l y m e r i z a t i o n u s u a l l y i n v o l v e s l e s s shrinkage than simple a d d i t i o n p o l y m e r i z a t i o n . For example, Table I I g i v e s the c a l c u l a t e d shrinkages f o r a s e l e c t e d number o f ring-opening p o l y m e r i z a t i o n s . Ethylene o x i d e , which has a shrinkage o f 23%, on the b a s i s o f i t s r e l a t i v e molecular weight w i t h ethylene might have been expected t o undergo a 40% shrinkage. One can r a t i o n a l i z e the reduced shrinkage by n o t i n g that two processes are t a k i n g p l a c e during the p o l y m e r i z a t i o n o f t h i s monomer. F i r s t , the monomer u n i t s are moving from a van der Waals' d i s t a n c e t o a covalent d i s ­ tance during p o l y m e r i z a t i o n , which should have r e s u l t e d i n a shrinkage o f 40%, but a t the same time the r i n g i s opened and the oxygen atom moves from a covalent d i s t a n c e , w i t h respect t o t h e carbon atom, t o a near van der W a a l s d i s t a n c e w i t h the recovery o f about 17% o f the shrinkage that occurred i n the previous process. I t i s obvious from Table I I , that the bigger the r i n g the c l o s e r to a t r u e van der Waals' d i s t a n c e i s approached during ring-opening and the s m a l l e r the shrinkage. One would p r e d i c t t h a t i f the r i n g were l a r g e enough no shrinkage would be i n v o l v e d i n the polymer­ i z a t i o n but the d r i v i n g f o r c e f o r the p o l y m e r i z a t i o n would be q u i t e 1

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

40 small. TABLE

II.

C a l c u l a t e d Shrinkages f o r Ring-Opening P o l y m e r i z a t i o n

Monomer

Shrinkage,

Ethylene oxide Isobutylene oxide Cyclobutene Propylene oxide Cyclopentene Cyclopentane Tetrahydrofuran Cyclohexane Styrene oxide Cycloheptane Cyclooctene Bisphenol-A d i g l y c i d y l ether and d iethylaminopropylamine Cyclooctadiene Cyclododecatriene 5-0xa-l,2-dithiacycloheptane D i m e t h y l s i l a n e oxide c y c l i c tetramer Cyclooctane

%

23 20 18 17 15 12 10 9 9 5 5 5 3 3 3 2 2

I t was reasoned from t h i s study that i f monomers were a v a i l ­ a b l e i n which a t l e a s t two r i n g s were opened f o r every new bond that was formed i n the backbone, m a t e r i a l s w i t h e i t h e r no change i n volume during p o l y m e r i z a t i o n or s l i g h t expansion would be pos­ s i b l e . I t should be emphasized that t h i s concept would e l i m i n a t e from c o n s i d e r a t i o n the p o l y m e r i z a t i o n of a monomer, such as a d i epoxide or a d i a n h y d r i d e , because, although two r i n g s are opened during the p o l y m e r i z a t i o n , two new bonds are a l s o formed at the same time. I t was shown that a v a r i e t y of monomers would undergo such a polymerization. One of the f i r s t c l a s s e s of compounds s t u d i e d was the s p i r o ortho e s t e r s , of which the simplest example was 1,4,6-trioxaspiro[4.4]nonane ( I ) , which can be prepared from the con­ densation of b u t y r o l a c t o n e w i t h ethylene oxide i n the presence of boron t r i f l u o r i d e i n a 33% y i e l d (1-3). CH

0

- CH

+

0

CH -CH 0

BF

0

^

1

CH -CH2

13% Shrinkage

2

j20 d. 4

Λ

. 0.869 0

n

CH -CH

0

,20 d. 1.11 4 Λ Λ

> ι

0

0-CH

0

I

χ

2

CH -0 '

x

2

,20 d, 4

0-CH

o

2

- -, /» 1.16

From a comparison of the d e n s i t i e s of the m a t e r i a l s i n v o l v e d , i t i s obvious that the s p i r o compound i s a very compact monomer. When

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4. BAILEY ET AL.

Polymerization

with Expansion

in

Volume

41

t h i s monomer was polymerized i n the d i l a t o m e t e r , placed i n a con­ stant temperature bath a t 25°, i n the presence o f boron t r i f l u o r i d e , p o l y m e r i z a t i o n occurred over a 24-hr. p e r i o d . During the polymer­ i z a t i o n the meniscus remained e s s e n t i a l l y a t a constant l e v e l and i n d i c a t e d a s l i g h t i n c r e a s e i n volume o f 0.1%. P u r i f i c a t i o n o f t h e polymer by r e p r e c i p i t a t i o n gave a 94% y i e l d o f a v i s c o u s l i q u i d w i t h a molecular weight of about 25,000. Although the polymer was d i f f i c u l t t o p u r i f y i t s d e n s i t y i n d i c a t e d that the p u r i f i e d polymer i s s l i g h t l y more dense than the monomer ( l e s s than 0.1%). The mechanism o f the p o l y m e r i z a t i o n undoubtedly i n v o l v e s an oxonium i o n and a s t a b i l i z e d carbonium i o n :

CH -CH

CH

2

_

n

CH -CH 0

AT*

0

C CH -0

CH -0

0-CH„

2

X

2

0 CH

n

CH -CH

J

N

9

0.

0

CH -0 ^

+

f 2

\>- CH

monomer C H — CH

2

^CH

+ /

C H

0

0—CH

2

n

R-£o- •CH -CH -CH -C-0-CH -CH2-

repeat

2

2

2

2

Since the monomer c o n t a i n s two d i f f e r e n t types o f oxygen atoms, a t t a c k can a l s o occur a t the other oxygen: R CH.-O CH - CH 2

C

\ I 2

H

2 - ° \

r

CH -CH^ 2

CH

/ ° - f 2 .

^0-CH

2

. ^ 0-CH

CH -CH

0-CH„

2

2

0-CH

R

I

monomer

C

•»

V °

ι

2

Κ

ÇH— ηϊ

(fe^

ι

repeat

X

CH -CH 0 - C H 2

2

2

R—£-0-
2

2

2

2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

9

2

0

RING-OPENING POLYMERIZATION

42

On t h i s b a s i s one would p r e d i c t the formation of a p o l y e s t e r - e t h e r c o n t a i n i n g both h e a d - t o - t a i l and head-to-head u n i t s . T h i s f a c t was v e r i f i e d by t h e s y n t h e s i s o f t h e h e a d - t o - t a i l polymer by a d i r e c t t r a n s e s t e r i f i c a t i o n procedure: i? HO-CH -CH -0-CH -CH -CH -C-OEt — » — 0- •CH -CH -•0-CH„ -CH -CH 2

2

2

2

2

2

2

2

2

χ Comparison o f the NMR s p e c t r a o f the two polymers gave strong e v i ­ dence f o r the presence o f head-to-head u n i t s (10 t o 20%) i n t h e ring-opened polymer. The reason f o r t h i s low shrinkage d u r i n g p o l y m e r i z a t i o n can be r a t i o n a l i z e d by comparing the o r i g i n a l monomer w i t h the f i n a l etherc o n t a i n i n g p o l y e s t e r . There a r e two processes which would l e a d t o some c o n t r a c t i o n ; one bon covalent d i s t a n c e , and bond. For s m a l l atoms the covalent d i s t a n c e i s o n l y o n e - t h i r d the van der Waals d i s t a n c e and t h i s t r a n s f o r m a t i o n , t h e r e f o r e , i s much l a r g e r than the change from a s i n g l e bond t o a double bond. T h i s shrinkage i s counterbalanced by the two bonds that go from a covalent d i s t a n c e t o a near van der Waals' d i s t a n c e i n t h e f i n a l polymer. I n t h i s p a r t i c u l a r case, these processes seem t o j u s t about c a n c e l one another. 1

Covalent CH,r-CH ^ 2N

Near van der Waals' CKU CH V

van der Waals' 2

V

8

Covalent f 0ii — Ç H „

-

Double bond Near van der Waals' Since t h i s e t h e r - c o n t a i n i n g p o l y e s t e r i s a l i q u i d , i t i s of l i t t l e i n t e r e s t i n i t s own r i g h t . However, i f one d e s i r e s a higher m e l t i n g polymer from a s p i r o ortho e s t e r , the i n t r o d u c t i o n of c y c l o hexane r i n g s g i v e s a f a i r l y l a r g e i n c r e a s e i n the s o f t e n i n g p o i n t . The i n t r o d u c t i o n of one cyclohexane r i n g produces a monomer t h a t g i v e s a s l i g h t i n c r e a s e i n volume upon p o l y m e r i z a t i o n ( 1 % ) . The i n t r o d u c t i o n of two cyclohexane r i n g s g i v e s a m a t e r i a l w i t h a s o f t e n ­ ing p o i n t o f over 100°C, but there i s e s s e n t i a l l y no change i n volume. Covalent

S i n g l e bond

j

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4.

BAILEY ET AL.

Polymerization

with Expansion

in

Volume

43

ΓΟΟΙ I t was reasoned, t h e r e f o r e , t h a t i f a b i f u n c t i o n a l s p i r o ortho e s t e r could be prepared and a s m a l l amount o f t h i s b i f u n c t i o n a l m a t e r i a l were t o be copolymerized w i t h the l , 4 , 6 - t r i o x a s p i r o [ 4 . 4 ] nonane ( I ) , a l i g h t l y c r o s s - l i n k e d e l a s t o m e r i c m a t e r i a l could be produced w i t h e s s e n t i a l l y no change i n volume. Model compounds showed that phenyl g l y c i d y l ether would condense w i t h γ-butyrol a c t o n e t o produce a s u b s t i t u t e and t h a t t h i s m a t e r i a l sence o f boron t r i f l u o r i d e e t h e r a t e . 0 II BF *OEt 0-CH -CH—CH CH,-C. 3

o

2

2

0

V

2

I

>

CH -CH2 2

cci

4

5-10° 2 hr.

By analogy w i t h t h i s s y n t h e s i s a b i f u n c t i o n a l s p i r o ortho e s t e r was prepared by the condensation o f hydroquinone d i g l y c i d y l ether and b u t y r o l a c t o n e t o produce i n 30% y i e l d a c r y s t a l l i n e mat e r i a l w i t h a m e l t i n g p o i n t o f 176°. The s y n t h e s i s was enhanced by the f a c t that the s o l i d c r y s t a l l i z e d from the r e a c t i o n m i x t u r e and was c o n v e n i e n t l y i s o l a t e d by f i l t r a t i o n ( 4 ) . On p o l y m e r i z a t i o n w i t h boron t r i f l u o r i d e t h i s monomer gave an i n s o l u b l e , h i g h l y c r o s s ^ l i n k e d r e s i n . When a m i x t u r e o f the t r i - * oxaspirononane I c o n t a i n i n g 10% o f the b i f u n c t i o n a l s p i r o ortho e s t e r I I was polymerized a t 1 0 0 w i t h boron t r i f l u o r i d e , a l i g h t l y c r o s s - l i n k e d elastomer r e s u l t e d . The h i g h temperature was u t i l i z e d to make sure t h a t the m i x t u r e was homogeneous. The r e s u l t i n g e l a s t omer had a s w e l l i n g index of 12, A more t i g h t l y c r o s s ^ l i n k e d σ

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

44

RING-OPENING POLYMERIZATION

elastomer was produce ture c o n t a i n i n g 30% o w i t h e s s e n t i a l l y no change i n volume that had a s w e l l i n g index of 5 but was s t i l l somewhat elastomeric.

Although the adduct between an epoxy r e s i n (bisphenol-A d i g l y c i d y l ether) and the butyrolactone d i d not give a m a t e r i a l that

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4.

BAILEY ET AL.

Polymerization

with Expansion

in

Volume

45

could be i s o l a t e d i n the pure s t a t e , i t was p o s s i b l e t o use t h i s r e a c t i o n t o prepare prepolymers which had a l a r g e shrinkage during the i n i t i a l p o r t i o n of the r e a c t i o n when the m a t e r i a l was l i q u i d . When the prepolymer was f u r t h e r polymerized w i t h boron t r i f l u o r i d e , a c r o s s - l i n k e d m a t e r i a l r e s u l t e d w i t h e s s e n t i a l l y no change i n volume near the l a s t p a r t o f the p o l y m e r i z a t i o n where the m a t e r i a l becomes v i s c o u s and g e l s . T h i s technique should a l l o w the product­ i o n of s t r a i n - f r e e m a t e r i a l s a t a reasonable c o s t .

I n order t o demonstrate t h a t expansion i n volume would take p l a c e w i t h b i c y c l i c m a t e r i a l s other than s p i r o d e r i v a t i v e s , a k e t a l l a c t o n e was prepared by the method of Lange, Wamhoff, and Korte ( 5 ) . P o l y m e r i z a t i o n o f t h i s m a t e r i a l w i t h e i t h e r boron t r i f l u o r i d e o r a base produced the k e t o - c o n t a i n i n g p o l y e s t e r w i t h e s s e n t i a l l y no change i n volume. 0 II 0 - C H - C H - : H - C H -cBF 2

2

n

c=o I

CH

3

S t i l l another c l a s s o f b i c y c l i c m a t e r i a l s t h a t w i l l polymerize w i t h an i n c r e a s e i n volume, are the 2 , 6 , 7 - t r i o x a b i c y c l o [ 2 . 2 . 2 ] o c t a n e s . For example, the monoethyl d e r i v a t i v e I I I , w h i c h i s a s o l i d , w i l l polymerize a t 70° i n the presence o f boron t r i f l u o r i d e i n about 10 minutes t o produce the v i s c o u s l i q u i d polymer IV w i t h an i n ­ crease i n volume o f 1.3% (6»). When the p o l y m e r i z a t i o n was c a r r i e d out from 0-5°, evidence was obtained from the i n f r a r e d s p e c t r a (appearance o f a strong t r a n s i e n t band a t 1600 cm ) t h a t t h e p o l y m e r i z a t i o n took p l a c e stepwise t o produce a s t a b i l i z e d carbenium i o n which was converted t o the f i n a l polymer. I n t r o d u c t i o n o f l

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

46

RING-OPENING POLYMERIZATION

^CH -0

BF -OEt

2

E t

3

- -CH -0-p-H C

2

N

2

7 Q %

CH -0 2

III bulky s i d e groups gave s i m i l a r b i c y c l o monomers, which produced h i g h m e l t i n g t h e r m o p l a s t i c m a t e r i a l s . H a l l , DeBlauwe, and P y r i a d i (7 ) had p r e v i o u s l y reported the p o l y m e r i z a t i o n o f a 2,6,7 - t r i o x a b i c y c l o [ 2 . 2 . 2 ] o c t a n e a t low temperatures under c o n d i t i o n s t h a t o n l y one of the r i n g s was opened. We have demonstrated t h e r e f o r e t h a t p o l y m e r i z a t i o n w i t h no change i n volume o r w i t p o s s i b l e w i t h a wide v a r i e t b i c y c l i c monomers. Another v e r y i n t e r e s t i n g c l a s s o f compounds appeared t o be the s p i r o ortho carbonates (8) . S a k a i , Kobayashi, and I s h i i (9) r e ­ c e n t l y d e s c r i b e d a method f o r s y n t h e s i z i n g ortho carbonates u s i n g t i n compounds w i t h carbon d i s u l f i d e . Using t h e i r method, we were a b l e t o s y n t h e s i z e a s e r i e s of s p i r o ortho carbonates by the f o l ­ lowing set o f r e a c t i o n s . T h i s method worked w e l l f o r 1,2-,1,3-, o r 1,4g l y c o l s t o produce c r y s t a l l i n e monomers (10).

CH 0H 2

Bu Sn=0

C H

2

CH 0H 2

CS,

2-°\

CH,

^ C H -0

SnBu^rV

50%

CH -0^

CH -(T 2

2

CH -0 92%

CH. 2

BF -OEt

0-CH

3

^CH. ^CH -0^ \)-CH ^ 2

2

2

142°

2

mp 141°

{

9

0-CH -CH -CH -0-C-0-CH -CH -CHJ 2

2

2

2

2

Since the s p i r o ortho carbonate was a h i g h l y c r y s t a l l i n e mat­ e r i a l , i n i t i a l p o l y m e r i z a t i o n s t u d i e s were c a r r i e d out above i t s m e l t i n g p o i n t a t 142°C. Although t h e p o l y m e r i z a t i o n could be c a r ­ r i e d out w i t h a v a r i e t y of c a t i o n i c c a t a l y s t s , such as boron t r i ­ f l u o r i d e gas, boron t r i f l u o r i d e e t h e r a t e , and aluminum c h l o r i d e , boron t r i f l u o r i d e e t h e r a t e proved t o be the most convenient. Thus, when the p o l y m e r i z a t i o n o f molten s p i r o ortho carbonate was c a r r i e d out i n bulk w i t h boron t r i f l u o r i d e etherate a t 142°C, a q u a n t i t a t i v e y i e l d o f polymer was obtained a f t e r s e v e r a l hours. [When p o l y m e r i z a t i o n was c a r r i e d out a t higher temperatures, the e v o l u t i o n o f a gas (C0 ) was observed.] The polymer was p u r i f i e d 2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4.

BAILEY ET AL.

Polymerization

with Expansion

in

47

Volume

by d i s s o l u t i o n i n chloroform f o l l o w e d by e x t r a c t i o n o f the s o l ­ u t i o n w i t h water. The s t r u c t u r e of the polymeric m a t e r i a l was proven not o n l y by elemental a n a l y s i s , but a l s o by NMR and IR s p e c t r a . The polymer had an i n t r i n s i c v i s c o s i t y o f 0.26 i n c h l o r o ­ form a t 25°C. Although the r e l a t i o n s h i p between molecular weight and i n t r i n s i c v i s c o s i t y i s unknown f o r t h i s s e r i e s o f polymers, a reasonable assumption of the constants would i n d i c a t e a molecular weight i n excess o f 100,000. These r e s u l t s tend t o i n d i c a t e that the s t r a i n inherent i n the ortho carbonate s t r u c t u r e provides a strong d r i v i n g f o r c e f o r the p o l y m e r i z a t i o n . A v e r y s i m i l a r p o l y ­ m e r i z a t i o n could be c a r r i e d out a t 100°C by a d d i t i o n o f c a t a l y s t to the s o l i d monomer. When the p o l y m e r i z a t i o n was c a r r i e d out i n a d i l a t o m e t e r i n which the bath was held a t a constant temperature (142°C), t h e meniscus, i n s t e a d o f f a l l i n i z a t i o n , a c t u a l l y rose extent o f change i n volume i n d i c a t e s an expansion i n excess o f 2%. This compares very f a v o r a b l y w i t h the very s l i g h t i n c r e a s e (0.14%) i n volume reported e a r l i e r f o r the p o l y m e r i z a t i o n o f a s p i r o ortho e s t e r . This example, then, represents the f i r s t reported case i n which a s u b s t a n t i a l amount o f expansion i n volume occurs during polymerization. An even more remarkable r e l a t i o n s h i p was discovered when the d e n s i t i e s o f the monomer and polymer were determined as a f u n c t i o n of temperature. Table I I I l i s t s the d e n s i t i e s o f the two m a t e r i a l s at 25, 100, 130 and 142°C. TABLE

I I I . C a l c u l a t i o n o f Expansion During P o l y m e r i z a t i o n

Temperature

25 100 130 142

Density o f monomer, g/cc 1.31 1.30 1.30 1.12

Density o f polymer, g/cc 1.20 1.14 1.11 1.10

Expansion i n volume, % 9 14 17 2

The d e n s i t y o f the amorphous l i q u i d polycarbonate v a r i e d q u i t e r e g u l a r l y and smoothly w i t h changes i n temperature from 1.20 g/cc at 25°C t o 1.10 g/cc a t 142°C. The d e n s i t y o f the monomer, however, changed q u i t e a b r u p t l y when i t went from the molten monomer a t 142°C to the c r y s t a l l i n e monomer a t temperatures below i t s m e l t i n g p o i n t . Obviously, t h i s data shows t h a t the c r y s t a l l i n e monomer i s c o n s i d e r ­ a b l y more dense than the molten monomer. S i m i l a r l y , the c r y s t a l l i n e monomer was much more dense than the l i q u i d polycarbonate. Thus, when the expansion i n volume i s c a l c u l a t e d from the d e n s i t y of t h e c r y s t a l l i n e monomer, the expansion was 9% a t 25°C up t o 17% a t 130°C. Under i d e a l c o n d i t i o n s the expansion might even be somewhat l a r g e r s i n c e the d e n s i t y o f the c r y s t a l l i n e monomer was determined by

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

48

measuring the volume o f a given weight o f a s o l i d i f i e d molten mono­ mer. Under these c o n d i t i o n s i t i s almost Impossible t o avoid t h e presence o f some v o i d s o r the i n c l u s i o n o f a s m a l l amount o f amorph­ ous m a t e r i a l . By c o i n c i d e n c e , however, the 17% expansion i s q u i t e c l o s e t o the expansion a l r e a d y c a l c u l a t e d f o r the conversion o f adamantane t o polycyclopentenomer (2). F i g u r e 1 g i v e s the p l o t o f the d e n s i t i e s o f the monomer and polymer v s temperature. I t i s obvious from the data that the conversion o f a c r y s t a l ­ l i n e monomer t o an amorphous polymer represents the i d e a l case f o r the l a r g e expansion i n volume s i n c e i n most cases the c r y s t a l l i n e monomer would be expected t o be c o n s i d e r a b l y more dense than the corresponding l i q u i d monomer. T h i s i s j u s t the opposite o f t h e case i n which a l i q u i d monomer i s converted t o a c r y s t a l l i n e polym­ e r . For example, when l i q u i d ethylene monomer i s converted t o c r y s t a l l i n e polyethylen appears t h a t the conversio polymer represents the i d e a l case t o get the l a r g e s t shrinkage during p o l y m e r i z a t i o n (3) ·

1.00·· 1

—'

20

»

40

1——ι

1

ι

60 80 100 120 TEMPERATURE, "C

1

1—

140

160

Figure 1. Densities of the monomeric spiro ortho carbonate and related polyoxycarbonate vs. temperature

An i n s p e c t i o n of F i g . 1 i n d i c a t e s that the d e n s i t i e s o f t h e monomeric s p i r o ortho carbonate and the polymer appear t o c r o s s above 200°. A t t h a t p o i n t , one would expect no change i n volume during p o l y m e r i z a t i o n s i n c e the two m a t e r i a l s have the same d e n s i t y . Above t h i s c r i t i c a l temperature, one would expect t o get shrinkage d u r i n g the p o l y m e r i z a t i o n . U n f o r t u n a t e l y , the p o l y m e r i z a t i o n can­ not be c a r r i e d out c o n v e n i e n t l y i n t h i s temperature range w i t h the c a t a l y s t s now a v a i l a b l e s i n c e carbon d i o x i d e i s l i b e r a t e d and the polycarbonate i s not obtained i n a pure form. A t the lower end o f the temperature s c a l e the two l i n e s appear t o i n t e r s e c t a g a i n , but one would expect below the g l a s s t r a n s i t i o n o f the polymer t h a t t h e d e n s i t y l i n e would become more n e a r l y h o r i z o n t a l and become essent­ i a l l y p a r a l l e l t o the l i n e o f the d e n s i t y o f the monomer. While a t f i r s t i t appeared d i f f i c u l t t o f i n d a p o l y m e r i z a t i o n

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4.

BAILEY ET AL.

Polymerization

with Expansion

in

Volume

49

procedure that would take f u l l advantage o f t h i s l a r g e expansion, s i n c e the s o l i d monomer i s hard t o i n t r o d u c e j.nto a mold o r a comp­ o s i t e , i t was found p o s s i b l e to make a s l u r r y o f t h i s c r y s t a l l i n e m a t e r i a l i n l i q u i d epoxy monomer and copolymerize the two w i t h c o n t r o l l e d shrinkage. Expansion, c o n t r a c t i o n , o r zero change i n volume could be obtained depending on the c o n c e n t r a t i o n o f t h e c r y s t a l l i n e monomer i n the s l u r r y . The l a r g e volume i n c r e a s e a l s o suggests t h a t the p o l y m e r i z a t i o n may be used t o r e p l a c e e x p l o s i v e s i n c r a c k i n g rocks i n a quarry o r f o r excavations. A v a r i e t y o f analogs o f t h i s s p i r o ortho carbonate can be prepared and polymerized. For example, a higher s o f t e n i n g polymer i n t h i s same s e r i e s could be prepared from the t r i s p i r o analog, which has a m e l t i n g p o i n t o f 112 C. P o l y m e r i z a t i o n a t room temp­ e r a t u r e produced a m a t e r i a l w i t h an i n c r e a s e i n volume o f 4%. J u s t below the m e l t i n g p o i n t pansion o f 7%. The s p i r v e r s a t i l e c l a s s o f compounds f o r p o l y m e r i z a t i o n w i t h expansion i n volume.

Although the l i t e r a t u r e c o n t a i n s a l a r g e number o f examples of ring-opening p o l y m e r i z a t i o n s i n v o l v i n g i o n i c i n t e r m e d i a t e s , there are v e r y few examples i n v o l v i n g r a d i c a l ring-opening p o l y m e r i z a t i o n s . The few examples that e x i s t i n the l i t e r a t u r e i n v o l v e the polymer­ i z a t i o n o f v i n y l c y c l o p r o p a n e d e r i v a t i v e s , such as l , l - d i c h l o r o - 2 v i n y l c y c l o p r o p a n e and l-carbethoxy-2-vinylcyclopropane, o r s p i r o o - x y l y l e n e . Since these examples a l l c o n t a i n a h i g h l y s t r a i n e d r i n g , i t appeared p o s s i b l e t h a t a number o f other s t r a i n e d r i n g systems c o n t a i n i n g u n s a t u r a t i o n e i t h e r i n o r adjacent t o the r i n g could a l s o undergo ring-opening o r double ring-opening p o l y m e r i z a t ­ i o n by a r a d i c a l mechanism. For t h i s reason we undertook the syn­ t h e s i s of 3,9-dimethylene-l,5,7,ll-tetraoxaspiro[5.5]undecane (VI) by the f o l l o w i n g set o f r e a c t i o n s (11).

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

50

450°

^0Η 0Η

n-Bu Sn=0

2

CH -0

2

9 3 / o

2

V

x

CH =C'

»

0

CH 0H 2

% S

CH -0

S n - n -Bu

0

/ /

2

C S

2^ / > CH =C

2

,CH„-0. /~ Λ CH =C.

62%

\

0

/

2

C=S

1,2

0

O-CH;

VI

0

H

C=CH

\CH -0 A . /

2

2

C

0-CH„

mp 8 2

c

U2 H

0-CH -C-CH O

d i - t e r t - b u t y l peroxide 130" (stopped below 30% conversion) VI BF -OEt, 100° (stopped below 30% conversion) 0 il II * ϋ"2 - 0-CH -C -CH -0-C-CH -C -CHj2

2

2

2

I t was found when t h i s monomer was t r e a t e d w i t h d i - t e r t - b u t y l per­ oxide a t 130° and the r e a c t i o n was stopped below 30% c o n v e r s i o n , a s o l u b l e polymer was obtained having a s t r u c t u r e of a polycarbonate w i t h pendant methylene groups. The s t r u c t u r e of the polymer was e s t a b l i s h e d by elemental a n a l y s i s as w e l l as i n f r a r e d and NMR spectroscopy. A v e r y s i m i l a r polymer could be a t t a i n e d by t r e a t ­ ment of the monomer w i t h boron t r i f l u o r i d e e t h e r a t e a t low conver­ s i o n s . The mechanism of the p o l y m e r i z a t i o n appeared to i n v o l v e a r a d i c a l double ring-opening according t o the f o l l o w i n g mechansim (12): CH-0 R0- + CH =C'

1

x

x

C

CH -0 2

>CH *0

V

X

CH„-0 O-CH > R0-CH -C >C C=CH 2 νCH -0' \0-CHJ

0-CH v 2

X

C=CH 2

l

0

X

0-CH

x 2

o

0

2

0-CH

O-CH,

n

R0-CH -Ct

!C=CH„

2

CH. - < -0

/ V C H -

0-CH

2

c

=

c

h

2 — - >

2

r

o

-

c

h

2

2

- <

\

y C

H

^

. _ CH; 0

(

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4. BAILEY ET AL.

repeat

Polymerization

with Expansion

0

CH

II

I!

in

Volume

51

0

2

RO+CH -C- -CH -0-C-0- •CH - C - -CH„-0The d r i v i n g f o r c e f o r the double ring-opening p o l y m e r i z a t i o n ap­ p a r e n t l y i s the r e l i e f o f the s t r a i n a t the c e n t r a l s p i r o atom. At h i g h conversions t h i s monomer produced a h i g h l y c r o s s l i n k e d r e s i n , v e r y s i m i l a r i n appearance t o the m a t e r i a l produced from the p o l y m e r i z a t i o n o f d i a l l y l carbonate. Furthermore, i t was shown that t h i s unsaturated s p i r o ortho carbonate would r e a d i l y copolym­ er i z e w i t h s t y r e n e , methyl methacrylate, and d i a l l y l carbonate, but w i t h s l i g h t l y lower r e a c t i v i t y than these other monomers. As i n d i c a t e d i n F i g u r e 2 the volume change t h a t occurred d u r i n g homop o l y m e r i z a t i o n was q u i t pansion i n volume occurred 70°, a 7% expansion i n volume occurred; a t 85 a 2% expansion took p l a c e and the expansion decreased u n t i l a t 115° no change i n volume took p l a c e d u r i n g p o l y m e r i z a t i o n ; above 115° a s l i g h t shrinkage occurred. I t i s obvious from these data t h a t the l a r g e expansion i n volume t h a t occurs below the m e l t i n g p o i n t i n v o l v e s not o n l y the i n c r e a s e i n volume due t o the double ring-opening, but a l s o a change i n volume o f 3-6% due t o the process o f going from a c r y s ­ t a l l i n e monomer t o a l i q u i d monomer. Since the monomer i s a c r y s ­ t a l l i n e s o l i d , i t i s d i f f i c u l t t o f i n d examples o f homopolymerizati o n i n which the f u l l 7% expansion i n volume can be u t i l i z e d . How­ ever, i n copolymerizations i t i s p o s s i b l e t o use a s l u r r y o f the c r y s t a l l i n e monomer i n a l i q u i d monomer so t h a t as c o p o l y m e r i z a t i o n progresses, the c r y s t a l l i n e monomer d i s s o l v e s w i t h some expansion and a l s o polymerizes w i t h expansion. A p o t e n t i a l use o f t h i s monomer i s i n the area o f d e n t a l f i l l i n g s i n which a s l u r r y c o n t a i n i n g 20% o f v e r y f i n e c r y s t a l s o f the unsaturated s p i r o ortho carbonate V I i n 60% o f the adduct o f m e t h a c r y l i c a c i d t o bisphenol-A d i g l y c i d y l ether (Bis-GMA) p l u s 20% t r i m e t h y l o l p r o p a n e t r i m e t h a c r y l a t e produces on p o l y m e r i z a t i o n a m a t e r i a l w i t h e s s e n t i a l l y no change i n volume. An i n v e s t i g a t i o n of a bubble t e s t on t o o t h enamel showed t h a t t h i s copolymer had n e a r l y double the adhesion t o the t o o t h s t r u c t u r e t h a t the base r e s i n had without the a d d i t i o n o f the unsaturated s p i r o ortho c a r ­ bonate. The copolymer a l s o had improved impact s t r e n g t h but y e t e s s e n t i a l l y the same modulus, and f i l l e d composites appeared t o have somewhat improved a b r a s i o n r e s i s t a n c e . Since the s y n t h e s i s o f the s p i r o ortho carbonates through the t i n compounds could be m o d i f i e d t o produce unsymmetrical m a t e r i a l s , we undertook the s y n t h e s i s o f the unsymmetrical 2-methylene-l,5,7, l l - t e t r a o x a s p i r o [ 5 . 5 ] u n d e c a n e by the f o l l o w i n g s e t o f r e a c t i o n s :

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

'

0

Figure 2.

20

40

60 80 100 120 TEMPERATURE,°C

140 160 180

Densities of the monomeric unsaturated spiro ortho carbonate and related polyoxycarbonate vs. temperature

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

BAILEY ET AL.

4.

Polymerization

with Expansion

in

53

Volume

^CH -OH 2

CH =C;

HO-CH -CH -CH -OH

2

2

NSv

2

2

CH -OH 2

(η-Bu) Sn=0

(1) (2)

2

Na (n-Bu) SnCl 3

(η-Bu)«-Sn-0-CH -CH -CH -0-Sn(n-Bu), 2 2 2 o

o

o

1 X

CH =(T Sn(n-Bu) ^CH^O^ 0

CH

2

CS„

C=S

0

2

τ

ÏÏ65?

CH -0 0-CH^ CH =C^ ^ C ^ CH ^CH -0^ ^O-CH^ Z

Z

9

2

mp 61-62° VII The r e s u l t i n g monomer was a c r y s t a l l i n e s o l i d w i t h a m e l t i n g p o i n t o f 61-62°. When the p o l y m e r i z a t i o n was c a r r i e d out i n the presence o f d i - t e r t - b u t y l p e r o x i d e and the r e a c t i o n was stopped a t low conversion, a l i n e a r polycarbonate c o n t a i n i n g pendant methylene groups was obtained. υ 130° -CH,-, -C —CH -0-C-0-CH -CH -CH VII[η] = 0.11 2 h 2 h 2 2 CHC1 ι CH„ 0 J χ di-tert-butyl peroxide 43% 2 5

0

o

o

o

0

The s t r u c t u r e o f the polymer was e s t a b l i s h e d by elemental a n a l y s i s as w e l l as i n f r a r e d and NMR spectroscopy. The s t r u c t u r e o f t h i s m a t e r i a l was v e r y s i m i l a r t o the polymer that could be obtained by the i o n i c p o l y m e r i z a t i o n o f t h i s same monomer a t low conversions. Bulk p o l y m e r i z a t i o n of V I I w i t h peroxide c a t a l y s t gave a m a t e r i a l at 25 w i t h an expansion of 4.5% and a t 60° an expansion 5.5%; above the m e l t i n g p o i n t o f V I I (61-62°) the expansion decreased u n t i l a t 111°, the d e n s i t y o f the monomer and the d e n s i t y o f t h e polymer were the same. When the 3-methylene d e r i v a t i v e was mixed w i t h an equal amount of styrene i n the presence o f d i - t e r t - b u t y l peroxide and the r e a c t -

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

54

RING-OPENING POLYMERIZATION

i o n was stopped a t below 30% c o n v e r s i o n , a s o l u b l e copolymer was obtained c o n t a i n i n g 79% styrene and 21% of the l i n e a r polycarbon­ ate u n i t s . H

CH -CH-

CH -C—CH -0-C-0

2

2

2

CH

- C H

2

- CH -CH -02

2

0

2

x=0.79 y=0.21 J y

By a v e r y s i m i l a r s y n t h e t i c scheme, other unsaturated s p i r o ortho carbonates were prepared.

CH -0' 2

CH =C

CH =C

Sn(n-Bu)

2

2

^ C H ^ O ^

63%

\

A

I

CH 0-C

CH -0' o

N

bp 61-62° (0.33 mm) CH -CH -0 9

, 2

2

o

74%

N

*C=S

CH -CH -02

2

120-130° di-tert-butyl peroxide, 41% 0

£o-

II •CH -CH„-0-C-0-CH,

C H

-Ï

A

CH

2 C =C

X

C H - 0 2

/< X

0-CH -CH

bp 60-61° (0.01 mm) 0-(CH

1 - C H J -

Jx

120-130°

I

2

2

di-tert-butyl peroxide 40%

2

CH

0

I!

0

11

2'4 ),-0-C-0-CH -C O

CH*

Bulk p o l y m e r i z a t i o n or s o l u t i o n p o l y m e r i z a t i o n i n chlorobenzene gave s o l u b l e polymer i f the r e a c t i o n was stopped a t low conversion. Both monomers gave c r o s s - l i n k e d r e s i n s a t h i g h conversions. Since s e v e r a l of the p r e v i o u s l y d e s c r i b e d e t h e r - c o n t a i n i n g polycarbonates were low m e l t i n g m a t e r i a l s w i t h a Tg below room

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4. BAILEY ET AL.

Polymerization

with Expansion

in

55

Volume

temperature, i t appeared h i g h l y d e s i r a b l e to s y n t h e s i z e a b i s s p i r o ortho carbonate t o be u t i l i z e d as a c r o s s - l i n k i n g agent t o convert these l i n e a r polymers i n t o elastomers. By the method o f I s h i i (9) ethylene thiocarbonate was prepared i n a 48% y i e l d from ethylene carbonate through the use o f t r i b u t y l t i n oxide and carbon disulfide. The intermediate thiocarbonate^which i s a s o l i d m e l t i n g at 53°, was shown t o be an e x c e l l e n t intermediate f o r producing a wide v a r i e t y o f s p i r o ortho carbonates. For example, when pentae r y t h r i t o l was t r e a t e d w i t h the thiocarbonate i n the presence o f t r i b u t y l t i n o x i d e , a 20% y i e l d o f the b i s s p i r o ortho carbonate, 1,4,6,10,12,15,16,19-octaoxatrispiro[4.2.2.4.2.2] nonadecane ( V I I I ) m e l t i n g p o i n t 215°, was obtained. j;H -0-Sn(n-Bu)

(n-Bu) Sn-0-Sn(n-Bu) + 3

3

2

CH -0

HOCH^ /CH OH

CH -0

H0Ctf£

2

2

(η-Bu) Sn-0-Sn(η-Bu) 3

CH 0H 2

3

CS„

3

20%

mp 53°

CH--CL ^0-CH .CH -0. I 2 Ν* «^ 2\ S 2 S o

o

Γ

CH -0 2

^ ) - C H ^ ^CH -0"^ 2

^0-CH / ι2 o

0-CH

2

VIII mp 215° When t h i s m a t e r i a l was t r e a t e d w i t h boron t r i f l u o r i d e a t 150°, a hard, h i g h l y c r o s s e d - l i n k e d , i n s o l u b l e r e s i n , was obtained. On the other hand, when a homogeneous mixture c o n t a i n i n g 90% o f the s p i r o ortho carbonate V and 10% o f the b i s s p i r o ortho carbonate V I I I was t r e a t e d w i t h boron t r i f l u o r i d e a t 145°, a 3% expansion occurred t o produce a c l e a r , s o l i d elastomer w i t h a s w e l l i n g index of 10. When o n l y 5% o f the b i s s p i r o ortho carbonate was used, a s o l u b l e polymer c o n t a i n i n g o n l y a s m a l l amount o f i n s o l u b l e mater­ i a l was obtained. T h i s would i n d i c a t e t h a t the r e a c t i v i t y o f the b i s s p i r o compound i s l e s s than t h a t o f V, so t h a t a l a r g e r amount of V I I I i s r e q u i r e d i n order t o produce an e f f e c t i v e c r o s s - l i n k e d network.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

56

RING-OPENING POLYMERIZATION

,CH -0

O-CH

»

2

CH-0

O-CH

.c

CH, v

^ CH -0

/

c'

+

^ Η , - O

;c

O-ÇH,,

\f

N^-CH^ Ν » - 0 ^ ^ 0 - C H

<3BLj-f/

7)-CH^

2

O-CH

2

C H .

2

2

V 90% 145°, B F , 3

3% expansion

8

0-(CH ) -0-C-0-(CH ) 2

2

3

- i -

II

3

0

0-CH -CH -0-C-0-CH„

CH

•0-CH -CH -0-C-0-CH2

C H

2

2

^(CH ) -0- -(CH )j2

3

C

2

2

2

2

I t was reasoned that i f a b i c y c l i c monomer could be prepared c o n t a i n i n g a f u n c t i o n a l group, that a l a r g e number o f prepolymers could be u t i l i z e d i n producing m a t e r i a l s w i t h no change i n volume on c u r i n g . Thus, i n the s y n t h e s i s o f the b i s s p i r o ortho carbon­ ate j u s t d i s c u s s e d , a s m a l l amount o f a dihydroxy d e r i v a t i v e was i s o l a t e d . By o p t i m i z i n g the c o n d i t i o n s a 16% y i e l d o f the d i ­ hydroxy s p i r o ortho carbonate was prepared. CH -0

O-CH

o

CH -0 2

X

CH -OH

O - C H /

CH -0H 2

mp 155° A more v e r s a t i l e s y n t h e s i s was developed according t o the f o l l o w ­ ing equation: r e f l u x i n toluene CH -CH -C(CH -OH) + ( B u S n ) 0 > 12 h r 3

H0-CH

n

CH -CH 3

2

/

/ 2

H

2

2

3

3

-0-SnBu„

2

H0-CH

yCH -0

o

.0-CH

o

,CH -0H o

CS„

\ H - 0 - ! SnBu„

CH -CH

2

3

2

CH -0^ 2

Λ

0-ϋΗ

100° 18 hr 78%

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2

>CH -CH 2

3

Polymerization

BAILEY ET AL.

4.

with Expansion

in

57

Volume

By a similar reaction with ethylene thiocarbonate i n place of carbon disulfide, a monohydroxy derivative was prepared. HO-CH .

CH -O-SnBu.

CH -0.

CH -CH^ ^CH^O-SnBu,

CH^O^

I

c 3

22°,48 hr, CHC1

Q

c=s

**

y

14%

CH -0.

Ό-CH.CH -OH C^ C CH -0^ ^ O - C H ^ C H - C H

J

V

V

2

2

mp

3

66°

These materials could b produc polyurethane change i n volume on curing. For example, the dihydroxy spiro ortho carbonate can be allowed to react with hexamethylene d i i s o cyanate at room temperature to produce a linear polymer which on treatment with boron t r i f l u o r i d e gives a cross^-linked resin with essentially no change i n volume. H0-CH

CH -0 0-CH,. ^CQ J,^C CH -CH CH - O / ^ O - C H ^ ?

CH -0H 9

+

1

3

2

CH

0=C=N-(CH ).-N=C=0 9

-CH

3

CHC1 , 30 hr. 22° 3

' °- V^ V x.^ C

C

CH -CH 3

2

0

0

CH -0^ 2

C H

2N.^

0-CH^

H

C

2

- H

3 r

CH -0-C-NH-(CH ) -NH-C 2

2

6

BF 3—^

cross-linked resin

I,

Since rings are more compact than open chain analogs, i t appeared possible to use thermal ring-opening to control shrink­ age during polymerization. For example, cyclobutene i s about 20% more dense than butadiene. While the polymerization of butadiene involves a shrinkage of 36%, i f i t were possible to convert cyclo­ butene to this same material, the process would involve a shrink­ age of only 18%. Furthermore, most of the c r i t i c a l or damaging shrinkage that takes place during polymerization i s that which occurs after the gel point i n cross-linked materials or when the monomer-polymer mixture approaches the glass transition point i n linear thermoplastic materials. When the monomer-polymer mixture i s quite f l u i d , no strains are built up and the effect of the shrinkage can be p a r t i a l l y overcome by the introduction of add-

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

58

RING-OPENING POLYMERIZATION

itional monomer. However, the shrinkage t h a t takes p l a c e near the end o f the p o l y m e r i z a t i o n r e s u l t s i n the b u i l d up o f s t r a i n s , the formation o f m i c r o c r a c k s , and the i n t r o d u c t i o n o f poor adhesion. I t was reasoned t h e r e f o r e , t h a t i f a polymeric m a t e r i a l could be prepared c o n t a i n i n g r i n g s t h a t would open t h e r m a l l y during t h e c r i t i c a l p o r t i o n o f the p o l y m e r i z a t i o n , the e f f e c t o f the s h r i n k ­ age could be minimized. One o f the m a t e r i a l s t h a t appears to meet t h i s c r i t e r i a i s dimethyl cyclobutene-1,2-dicarboxylate ( I X ) . When t h i s m a t e r i a l i s mixed w i t h methyl methacrylâte and the mix­ t u r e i s t r e a t e d w i t h a peroxide c a t a l y s t , the double bond i n the r i n g i s f a i r l y i n e r t and doesn't take p a r t t o any l a r g e extent i n the p o l y m e r i z a t i o n . However, i f near the end o f the p o l y m e r i z a t ­ ion the temperature i s i n c r e a s e d t o 150°, the cyclobutene r i n g opens t o produce a diene X w i t h an i n c r e a s e i n volume of 5% (17). CH 0 -Ç 3

Ç0 CH

2

2

C = C

!

CH^

3

150°

, C-C

I

CH -CH 2

S

> r 2

IX

CH

\ v

CH

2

2

X

Since the double bonds i n t h i s compound are now r e a c t i v e , p a r t o f the double bonds are i n c o r p o r a t e d i n t o the polymer n e t ­ work to g i v e a c r o s s - l i n k e d m a t e r i a l . The volume change can be c o n t r o l l e d t o some extent by the r a t i o o f the c y c l i c e s t e r added and the extent of p o l y m e r i z a t i o n t h a t has taken p l a c e when the temperature i s r a i s e d t o 150°. T h e o r e t i c a l l y a l a r g e number o f r i n g compounds and polymers could be used t o c o n t r o l shrinkage o r to promote expansion o f polymers on ring-opening. A v a r i e t y o f r i n g systems c o n t a i n i n g s u l f u r , n i t r o g e n and carbon are being i n v e s t i g a t e d t o produce m u l t i p l e ring-openings t o g i v e polymers c o n t a i n i n g a v a r i e t y o f chemical s t r u c t u r a l u n i t s . I t i s hoped t h a t these m a t e r i a l s w i l l f i n d wide u t i l i t y f o r t h e uses d i s c u s s e d e a r l i e r and w i l l prove t o be a v e r y general s o l u t ­ ion t o the problem o f shrinkage d u r i n g p o l y m e r i z a t i o n . The authors are g r a t e f u l t o the Naval A i r Systems Command and to the N a t i o n a l I n s t i t u t e o f Dental Research f o r support o f t h i s research.

Literature Cited 1. 2. 3. 4.

Bailey, W.J., and Sun, R.L., Amer. Chem. Soc., Div. Polym. Chem. Prepr., (1972), 13 (1), 400. Bailey, W.J., J. Elastoplast., (1973), 5, 142. Bailey, W.J., J. Macrolmol. Sci.-Chem., (1975),A9(5), 849. Bailey, W.J., Iwama, Η., and Tsushima, R., J- Polymer Sci., Polym. Symposia Edition, in press; Abstracts of the 4th Internation­ al Symposium on Cationic Polymerization, Akron, Ohio, June

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4.

BAILEY ET AL.

5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.

Polymerization

with Expansion

in

Volume

59

20-23 (1976). Lange, C., Wamhoff, Η., and Korte, T., Chem. Ber., (1967), 100, 2312. Bailey, W.J.,and Saigou, K., J. Polym. Sci., Polym. Letters Ed., in press. Hall, H.K., Jr., DeBlauwe, Fr. , and Pyriadi, T., J. Am. Chem. Soc., (1975), 97, 3854. Bailey, W.J., and Katsuki, H., Amer. Chem. Soc., Div. Polym. Chem., Prepr., (1973), 14, 1679. Sakai, S., Kobayashi, Y., and Ishii, Y., J. Org. Chem., (1971), 36, 1176. Bailey, W.J., Katsuki, H.,and Endo, T., Amer. Chem. Soc., Div. Polym. Chem., Prepr., (1973), 14, 1976. Bailey, W.J., Katsuki H., and Endo T. Amer Chem Soc. Div. Polym. Chem. Endo, T.,and Bailey, , Polym , Polym Ed., (1975), 13, 193. Endo, T.,and Bailey, W.J., Makromol. Chem., (1975), 176, 2897. Endo, T., and Bailey, W.J., J. Polym. Sci., Polym. Chem. Ed., (1975), 13, 2525. Bailey, W.J.,and Endo, T.,J. Polym. Sci., Polym. Chem. Ed. (1976), 14, 1735. Bailey, W.J., and Tsushima, R., J. Polymer Sci., in press. Bailey, W.J., and Bitritto, M., J. Polymer Sci., in press.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

5 Progress i n Polymerization of C y c l i c Acetals

STANISŁAW PENCZEK and PRZEMYSŁAW KUBISA Polish Academy of Science, 90-362-Łodz, Poland

In our previous review paper presented at the Rouen Symposium on Cationi some of the major difference lymerization of c y c l i c ethers and c y c l i c acetals |1|. These differences are mainly caused by the much larger b a s i c i t y ( n u c l e o p h i l i c i t y ) of c y c l i c ethers, than that of c y c l i c a c e t a l s ; moreover, c y c l i c ethers are more basic (nucleophilic) than t h e i r polymers, whilst poly­ acetals seem to be more basic than t h e i r corresponding monomers. Thus, i n polymerization of c y c l i c ethers (or,at least i n polymerization of T H F ) , t e r t i a r y oxonium ions 1. are the only growing species |2| | 3 | |4|:

whereas i n the polymerization of c y c l i c a c e t a l s , i n c l u ­ ding 1,3-dioxolan (Diox), the equilibrium between the macroalkoxycarbenium ions 2 with t h e i r t e r t i a r y oxo ­ nium 2 counterparts i s i n our opinion the best represen­ of the active snecies : t a t i o n

Unfortunately, our knowledge of the carbenium-oxo­ nium ion e q u i l i b r i a i s very l i m i t e d ; some f i r s t 60

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

5.

PENCZEK AND KUBisA

Polymerization

of

Cyclic

Acetals

61

q u a n t i t a t i v e d a t a from our l a b o r a t o r y |5j were d i s c u s s e d i n the Rouen paper |1|, P r o p e r t i e s o f 2""and 3^ ^ e q u i l i b r i u m (1) may depend v e r y much on tïïe p o l y m e r i z a t i o n c o n d i t i o n s and s t r u c t u r e o f the c y c l i c a c e t a l . At the s u f f i c i e n t l y l a r ge excess o f a p o l y a c e t a l , £ can become the predominant structure. The o t h e r t o p i c , which w i l l be c o v e r e d i n t h i s pap e r , was p r e v i o u s l y r e v i e w e d by P l e s c h a t the IUPAC Symposium i n Budapest |6|, and more r e c e n t l y a t the I - s t IUPAC Symposium on"~Ring-Opening P o l y m e r i z a t i o n h e l d i n J a b l o n n a (1975) | 7 j . In t h i s p a r t o f our paper the s t r u c t u r e o f the end-groups i n p o l y - D i o x i s d e s c r i bed, and the m e c h a n i s t i c consequences o f the a l l e g e d m a c r o c y c l i c or l i n e a macromolecules i s d i s c u s s e d In 1975 Rosenberg, Irzhakh and E n i k o l o p i a n p u b l i s hed a book e n t i t l e d " I n t e r c h a i n exchange i n p o l y m e r s " I 8 j , summarizing r e s u l t s o f the Moscow group on the p o l y m e r i z a t i o n o f c y c l i c a c e t a l s . A l t h o u g h some o f the conc l u s i o n s o f t h i s book would c e r t a i n l y be p r e s e n t e d today d i f f e r e n t l y i n l i g h t of the new e x p e r i m e n t a l data, the r e a d e r may f i n d t h e r e an unorthodox s o l u t i o n o f the m a j o r i t y o f k i n e t i c problems p e r t i n e n t to the n o n s t a t i o n a r y polymerizations, i n c l u d i n g polymerization of cyclic acetals. We s h a l l s t a r t , however, t h i s r e v i e w o f the p r o g r e s s i n the p o l y m e r i z a t i o n o f c y c l i c a c e t a l s from a b r i e f d e s c r i p t i o n o f the new p o l y a c e t a l s p r e p a r e d , and from summarizing o f the new d a t a on the thermodynamics o f polymerization of substituted 1,3-dioxolans. n

Thermodynamics o f P o l y m e r i z a t i o n .

New

Polyacetals.

I v i n and Leonard |9| extended the thermodynamic t r e a t m e n t o f the polymer-monomer e q u i l i b r i u m to the non i d e a l systems, a c c o u n t i n g f o r the polymer-monomer i n t e r a c t i o n d e s c r i b e d by the F l o r y parameter x p « b u l k p r o c e s s , the f o l l o w i n g e x p r e s s i o n was o b t a i n e d f o r the f r e e energy change upon the c o n v e r s i o n o f one mole o f pure monomer i n t o one base-mole o f amorphous polymer ( A G ) : F

o

r

a

m

l c

A

G

il ^c = RT [ i n mΦ • lm+pX ^pU -Φ™)] (2) m/ where φ ( = 1 - Φ ) i s the e q u i l i b r i u m monomer volume f r a c ­ tion, ^computed from the e x p e r i m e n t a l l y d e t e r m i ­ ned e q u i l i b r i u m monomer c o n c e n t r a t i o n a t the g i v e n tem­ p e r a t u r e T. In t h i s method the F l o r y parameter χ is a r b i t r a r l y chosen (e.g. 0.4 f o r D i o x - p o l y - D i o x i n t e r a c t i o n ) and assumed to be independent on temperatu­ r e . L i n e a r i t y o f the p l o t o f AG /RT as a f u n c t i o n o f 1

T

A

V Y

Y

J

Ό

p

1

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

62

RING-OPENING POLYMERIZATION

1/T i n d i c a t e s t h e r e l i a b i l i t y o f these s i m p l i f i c a t i o n s . More r e c e n t l y i t has been o b s e r v e d | K)|, t h a t i n t r o d u c ­ t i o n o f a term i n c l u d i n g t h e monomer-solvent and p o l y ­ m e r - s o l v e n t i n t e r a c t i o n s a l l o w s t h e polymer-monomer e q u i l i b r i a i n s o l u t i o n t o be u n i f o r m l y t r e a t e d . T h i s term i s r e l a t e d t o t h e heat o f m i x i n g o f t h e s o l v e n t used w i t h monomer and polymer. I t does not depend, however, v e r y much on t h e s o l v e n t s t r u c t u r e f o r Diox, and. t h e r e f o r e , I D i o x I i s almost s o l v e n t independent \l±\ (although, only C H C 1 , C H r C l and C,H, were s t u d i e d ) . I t i s worth * noting, t h a t i n c o n t r a s t t o Diox, d i f f e r e n c e s between t h e e q u i ­ l i b r i u m monomer c o n c e n t r a t i o n s a r e much more pronounced i n the p o l y m e r i z a t i o n o f THF |1j2J . Indeed, |THFl =5.5 mole»l"' i n CH-,N0 s o l v e n t d onl 3.5 mole»l-1 i CC1 s o l v e n t (fTHF| =7. These l a r g e d i f f e r e n c e highe t y o f THF and much s t r o n g e r a c i d - b a s e i n t e r a c t i o n s between s o l v e n t s and THF, than s o l v e n t s and D i o x . The thermodynamic n o n - i d e a l i t y o f these systems are s t r e s s e d , because some a u t h o r s a r e s t i l l t e n d i n g to determine what they a r e c a l l i n g t h e thermodynamic q u a n t i t i e s ( l i k e ΔΗ° and AS*?) on t h e b a s i s o f s i m p l e r r e l a t i o n s h i p s , h o l d i n g o n l y * r o r t h e i d e a l systems. On t h e o t h e r hand, i t has t o be remembered, t h a t i n the p o l y m e r i z a t i o n k i n e t i c s , the proper value o f |monomerl has t o be used, and t h a t i t changes w i t h b o t h jmonomer I and s o l v e n t s t r u c t u r e . The combined r e s u l t s of bulk |l_3| and s o l u t i o n p o l y m e r i z a t i o n o f Diox (taken l a r g e l y from R e f e r e n c e |1J_|) a l l o w e d Leonard t o c a l c u l a t e ΔΗ, = -4.0±0.1 k c a l - m o l e " and A S =-11 ,0±0.3 cal*mole"1·deg~1, These r e s u l t s agree w e l l with v a l u e s o b t a i n e d from an e q u i l i b r i u m between gaseous monomer and amorphous polymer |14|. F o l l o w i n g t h e Ivin-Leonara "? method, Okada d e t e r m i ­ ned r e c e n t l y the thermodynamic f u n c t i o n s f o r the p o l y ­ m e r i z a t i o n o f 4-methyl-Diox |15| and, (assuming X . 0.3) found ΔΗ, =-3.2±0,2 k c a l / m o l e and AS° = - 1 2 . 7 ± 0 . 8 cal*mole~'»deg-1 , Another work, performed i n C H C l 2 s o l v e n t f o r t h e some monomer, and not a c c o u n ­ ting f o r t h e d i s c u s s e d above i n t e r a c t i o n s , g a v e t h e apparent v a l u e s ( ΔΗ P P and AS P P ) d e p e n d i n g , as i t c o u l d be e x p e c t e d , on the s t a r t i n g monomer c o n c e n t r a ­ t i o n 116 I , 9

z

9

z

9

z

0

0

9

4

e

o

1

X

1

mr

=

m p

9

a

of

Theoretical Dioxolans.

a

I n t e r p r e t a t i o n o f the P o l y m e r i z a b i l i t y

T h e o r e t i c a l i n t e r p r e t a t i o n o f the r i n g - c h a i n e q u i ­ l i b r i a , p u b l i s h e d by Jacobson and Stockmayer i n 1950 117 I c a n o n l y be a p p l i e d t o t h e case when c h a i n s o r

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

9

5.

PENCZEK AND KUBisA

Polymerization

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63

r i n g s a r e so l a r g e t h a t the c o n f i g u r a t i o n a l e n t r o p y i s governed by the G a u s s i a n f u n c t i o n and the energy d i f f e ­ rence between the c h a i n and r i n g forms i s n e g l i g i b l e . F o r a s m a l l r i n g , such as the five-membered r i n g o f Diox, Jacobson-Stockmayer e q u a t i o n cannot be a p p l i e d . In such c a s e , as shown i n many works, summarized r e c e n ­ t l y by H a l l f o r v a r i o u s c y c l i c monomers I l 8 j l l ? . | > s t a b i l i t y o f the r i n g i s c o n n e c t e d o n l y w i t h the s t r a i n i n the r i n g , caused m o s t l y by the d e v i a t i o n i n v a l e n c y a n g l e s . H a l l e x p l i c i t l y showed t h a t the d i f f e r e n c e i n s t r a i n energy between monomer and polymer e q u a l s the e n t h a l p y o f p o l y m e r i z a t i o n , p r o v i d e d t h a t no s u b s t i tuents are p r e s e n t , or e l s e c o n f o r m a t i o n a l s t r a i n s i n the polymer may outweigh the s t r a i n i n the r i n g . I t has a l r e a d y o f s u b s t i t u t e d ε-caprolactams t u t i o n o f hydrogen atoms d e c r e a s e s the p o l y m e r i z a b i l i t y o f monomers. The same phenomena were o b s e r v e d i n the p o l y m e r i z a t i o n o f 4 , 4 - d i m e t h y l - , c i s - 4 , 5 - d i m e t h y l and t r a n s - 4 ,5-dimethyl-Diox |lj>| . These d i f f e r e n c e s were i n t e r p r e t e d i n the p o l y m e r i ­ z a t i o n o f ε-caprolactams |20| from the change o f thermodynamical p r o p e r t i e s caused by the e x i s t e n c e o f r o t a t i o n a l isomers. In a n a l y s i n g p o l y m e r i z a t i o n o f s u b s t i t u t e d d i o x o l a n s Okada took a s l i g h t l y m o d i f i e d approach, comparing e n e r g e t i c a l d i f f e r e n c e s between d i o x o l a n s and t h e i r p o l y m e r s . Low - m o l e c u l a r weight a c e t a l s , e.g. dimethoxymethane and i t s homologues exist p r e d o m i n a n t l y i n the gauche form to a v o i d the r a b b i t -ear e f f e c t s i n the a n t i - f o r m 122|:

gauche

anti

P o l y d i o x o l a n s a r e a l s o assumed to e x i s t i n the gauche form, because the r a b b i t - e a r e f f e c t i n the a n t i form i s l a r g e r (1 k c a l m o l e ~ 1 ) t h a n the gauche i n t e r a c ­ t i o n o f the methyl groups { u s u a l l y c o n s i d e r e d to be from 0.6 to 0.9 k c a l * m o l e " ' ) . S u b s t i t u t i o n o f the H atoms by CH., groups d e s t a b i ­ l i z e s monomers by r e p l a c i n g the c i s - geminal C^-H and C -H bonds o p p o s i t i o n w i t h a g r e a t e r C^-H and C - C H opposition. e

5

5

3

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

64

RING-OPENING POLYMERIZATION

A l l o f the Okada's c a l c u l a t i o n s were based on the assumption, t h a t the s t a b l e c o n f o r m a t i o n o f Diox i s the " e n v e l o p e " form, i n which one o f the c a r b o n atoms o f the e t h y l e n e group i s l o c a t e d a t the t i p o f the f l a p , g i v i n g the d i h e d r a l angle o f the c i s - n e i g h b o r i n g hy­ drogens o f the e t h y l e n e group e q u a l to 35 degree. S u b s t i t u t i o n i n a polymer c h a i n l e a d s to the i n c r e a s e d energy o f the g a u c h e - i n t e r a c t i o n s and the d i f ­ f e r e n c e between these two e f f e c t s g i v e s e v e n t u a l l y a d e v i a t i o n i n ΔΗ, (ΔΔΗ, ) f o r a s u b s t i t u t e d Diox from unsubstituted monomer. These c a l c u l a t i o n s l e d Okada to the f o l l o w i n g e s t i m a t e d v a l u e s o f - ΔΗ- ( g i ­ ven below i n kcal»mole~1) f o r v a r i o u s methyl s u o S t i t u t e d Diox :

For 4-methyl-Diox t h e r e i s a good agreement w i t h the v a l u e determined e x p e r i m e n t a l l y (3.2 k c a l - m o l e " ) . Thus, these f i n d i n g a r e i n accordance w i t h a gene­ r a l o b s e r v a t i o n t h a t i n the p o l y m e r i z a t i o n o f h e t e r o c y c l i c monomers s u b s t i t u t i o n l e a d s to d e c r e a s e d probabi­ l i t y o f c h a i n f o r m a t i o n . The e x t e n t o f s e n s i t i v i t y o f a g i v e n c l a s s o f monomers t o s u b s t i t u t i o n i s g i v e n by the r i n g s t r a i n o f the p a r e n t , u n s u b s t i t u t e d monomer. Thus, even f o r h i g h l y s u b s t i t u t e d o x i r a n e s ( e . g . t e t r a ­ me t h y l o x i r a n e ) complete p o l y m e r i z a t i o n c a n be a c h i e ved, because the r i n g s t r a i n overshadows any o t h e r effect. J e d l i n s k i a n a l y s e d i n a s e r i e s o f papers the H-NMR s p e c t r a o f v a r i o u s s u b s t i t u t e d 1,3-dioxolans i n o r d e r to u n d e r s t a n d the s t e r e o c h e m i s t r y o f these monomers. Then, f o l l o w i n g e a r l i e r work, d e s c r i b e d p r e v i o u s l y f o r the u n s u b s t i t u t e d d i o x o l e n i u m s a l t s , s t u d i e d the k i n e ­ t i c s o f H" t r a n s f e r from these monomers t o the t r i p h e n y l m e t h y l i u m c a t i o n |23|, as the f i r s t r e a c t i o n , p r e c e ­ d i n g the t r u e i n i t i a t i o n . T h i s approach, i s complemen­ t a r y t o t h a t o f Okada,which g i v e s a thermodynamic i n f o r m a t i o n about the p o l y m e r i z a b i l i t y , w h i l e J e d l i n s k i tends t o c h a r a c t e r i z e the i n f l u e n c e o f s t r u c t u r e ( s t e ­ r e o c h e m i s t r y ) on the r a t e o f reactions pertinent to elementary r e a c t i o n s . There a r e t i l l now, however,no 1

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

5. PENCZEK AND KUBisA

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65

q u a n t i t a t i v e i n f o r m a t i o n s a v a i l a b l e about t h e r e a c t i o n s related to the a c t u a l polymerization process (initiat i o n , c h a i n g r o w t h ) . Recently,Kops r e p o r t e d on t h e pol y m e r i z a t i o n o f b i c y c l i c d i o x o l a n s , c y c l i c formais o f t r a n s - and c i s - c y c l o h e x a n e d i o l s :

cis-

Only the t r a n s - monomer p o l y m e r i z e d , g i v i n g h i g h molec u l a r weight, s o l i d polymer |24j . T h i s r e s u l t i s i n accordance w i t h a more g e n e r a l phenomenon o f t h e i n c r e a s e d s t r a i n i n t h e t r a n s - j o i n e d r i n g s , due t o t h e enhanced a n g u l a r s t r a i n In t h e p r e v i o u t i o n o f 1,3-dioxolans s u b s t i t u t e d a t C and C . I n f o r m a t i o n on t h e p o l y m e r i z a t i o n o f d i o x o l a n s s u b s t i t u t e d at C i s v e r y l i m i t e d ; we s h a l l c o n f i n e o u r s e l v e s t o the p o l y m e r i z a t i o n o f 2 - v i n y l - d i o x o l a n s and 2 - v i n y l -dioxans. 4

5

2

Polymerization

o f the Unsaturated

Cyclic Acetals.

Polymerization o f 2-vinyl-1 ,3-dioxolan (4) I 25| |26| 2-vinyl-1,3-dioxane (5) |27j |2J31 |29j and relatecT mono mers, s u b s t i t u t e d a t C : 2

/CH

I

2

J

, 2

9

2

CH

XH

CH -CH 4

CH -CH 5

2

I

2

2

have been i n v e s t i g a t e d d u r i n g t h e l a s t f i f t e e n y e a r s i n a t l e a s t f i v e l a b o r a t o r i e s , A f t e r the o r i g i n a l d i s c o v e r y o f Mukaiyama 125j|, who found t h a t 4 p o l y m e r i z e s , at l e a s t p a r t i a l l y , t o the l i n e a r p o l y e s t e r : {CH CH CH COCH > 2

2

2

2

Tada, Saegusa, and Furukawa |26| i n t e r p r e t e d t h i s result as a consequence o f t h e hydri3ê-shift p o l y m e r i z a t i o n , s i m i l a r t o t h a t e l a b o r a t e d e x t e n s i v e l y by Kennedy |30| f o r branched α-olefins :

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

66

RING-OPENING POLYMERIZATION

CH =CH-CHC' 7

0-CH I 0-CH

ù

^ (RCH CH-C-H

9

R

-

L

9

^ 0 - C H

L 2

o~ çU^r*

O-QL |

+

+

)

S

"

N

I

I

X

~

2

(3) + .0-CH, •RCH-CH-C 2

I

2

Z

^ - O - C H , +

CH-=CH-CH 2

^ O - C H ,

I

\ 0 - C H

Z

+

L

—

RΠCH C-0-ΠCH,CH 0

2 7

9

9

2

II

1

2

2

9

2

-CH j

0

.CH

0

0 1

I

CH CH 2

A l t h o u g h the mos 4 are r a t h e r the oxygen atoms, but, t i o n a t e d 4, e.g.: CH.

R - C H

2

C H

2

C O C H

2

C H ^ — 0

C H

2

J

I

2

the

ca

9

2

,0

χ

CH =CH'

apparently

2

N

H

or i t s o p e n - c h a i n isomer, s t a b i l i z e d by the f o r m a t i o n o f the a l l y l i c - type carbenium i o n , are not s u f f i c i e n ­ t l y r e a c t i v e i n the c h a i n growth to compete w i t h the H " ion t r a n s f e r processes. More d e t a i l e d a n a l y s i s o f p o l y m e r i z a t i o n o f £, and p a r t i c u l a r l y an a n a l y s i s o f the ^H-NMR s p e c t r a o f p o l y -5 r e v e a l e d |j27| , t h a t the complete s t r u c t u r e o f p o l y ­ mers i s much more complex. Almost a l l o f the r e p e a t i n g u n i t s t h a t one c o u l d imagine were found, the most im­ p o r t a n t ones b e i n g ( f o r p o l y - 5 ) as shown below:

• · · —CH ~CH—.. · , 2

. . . —OCH CH CH OCH— · · · , 2

2

2

CH

q

ρ

<s>

%· · —CH CH COCH CH CH — · . 2

2

2

2

2

·,

0

il C H 2

The two f i r s t s t r u c t u r e s c o n t a i n groups s t i l l r e a c ­ t i v e i n the c h a i n , and t h i s i s why these polymers are o f i n t e r e s t f o r polymer chemists working i n the polymer s y n t h e s e s , The two-stage p o l y m e r i z a t i o n o f these e a s i l y a v a i l a b l e monomers has been expected to p r o v i d e a new group o f r e a c t i v e p o l y m e r s . F r e e - r a d i c a l p o l y m e r i z a t i o n , f o l l o w e d by the c a t i o n i c f o r m a t i o n o f the network (and,

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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67

i n p r i n c i p l e , v i c e v e r s a ) was a l s o s u c c e s s f u l l y a p p l i e d by Minato t o ( 1 , 3 - d i o x o l a n - 4 - y l ) methyl a c r y l a t e |31 I. End-Groups i n P o l y a c e t a l s . P o l y - 1 , 3 , 5 - t r i o x a n i s known t o c o n t a i n h e m i a c e t a l -OH groups; some o f t h e s e are formed because o f the c h a i n t r a n s f e r t o water |32|, A c e t y l a t i o n o f the -OH groups g r e a t l y enhances tEermal s t a b i l i t y o f the p o l y oxymethylene polymers,and i s a t the base o f the com m e r c i a l i z a t i o n o f the f i r s t p o l y a c e t a l (a homopolymer o f CH 0) 132a| known, i n fact»many y e a r s ago from the c l a s s i c a l works o f S t a u d i n g e r and Kern. Jaacks a.o. d i s c o v e r e d |32| f o r m a t i o n o f the meth o x y l end groups i the Z e i s e l method, an from the H" i o n s h i f t ( i n t r a m o l e c u l a r l y ) o r t r a n s f e r (intermolecularly). S i m i l a r r e a c t i o n was proposed by us more r e c e n t l y i n the p o l y m e r i z a t i o n o f Diox, conducted above 0 ° , t o account f o r the methoxyl end-groups o b s e r v e d i n the 'H-NMR s p e c t r a |33|. 2

End-Groups i n P o l y - 1 , 3 - d i o x o l a n . Gresham p o l y m e r i z e d Diox w i t h m i n e r a l and Lewis a c i d s and was unable t o d e t e c t any end-groups |34j . P l e s c h c o n f i r m e d Gresham s o b s e r v a t i o n |35|, assumed t h a t p o l y - D i o x are m o s t l y c y c l i c and on tïïis b a s i s proposed a mechanism o f p r o p a g a t i o n w i t h p r o t o n i c a c i d s ( r i n g - e x p a n s i o n ) . J a a c k s , i n a p p a r e n t l y s i m i l a r cond i t i o n s (HC10 , C H C 1 s o l v e n t ) found e a r l i e r , t h a t polymers are r a t h e r l i n e a r , and q u a n t i t a t i v e l y d e t e r m i ned e t h y l a l c o h o l from the h y d r o l y z e d end-groups, formed when a l i v i n g - l i n e a r (on h i s o p i n i o n ) p o l y c a t i o n was k i l l e d w i t h sodium e t h y l a t e |36|. These r e s u l t s were r e c e n t l y c h a l l e n g e d by P l e s c h T ^ I · In the p o l y m e r i z a t i o n o f Diox i n i t i a t e d w i t h triethyloxoniumhexafluorophosphate ((C H )^0 PF7) W o r s f o l d |38| c l a i m e d t h a t he c o u l d not f i n e any end-groups i n p o l y - D i o x formed, a l t h o u g h a t r i p l e t from a CH^CH 0 group i s seen i n the 'H-NMR spectrum g i v e n i n n i s paper. Ponomarenko a.o. |39|, by u s i n g ( C H ) - 0 S b C l , l a b e l l e d w i t h 14c i n tïïe e t h y l group, c o n c l u d e d , t h a t the number o f moles o f Co^S groups, i n c o r p o r a t e d i n t o the macromolecules, i s c l o s e t o t h e number o f moles o f the used i n i t i a t o r , Okada |40| i n h i s study o f oligomers i s o l a t e d a t low c o n v e r s i o n ( p o l y m e r i z a t i o n o f Diox i n i t i a t e d w i t h w i t h ( C H ) 0 + BF" and k i l l e d w i t h CH^ONa) o b s e r v e d l i n e a r o l i g o m e r s w i t h e t h y l a t e and m e t h y l a t e end-groups, 1

ff

n

4

2

2

7

+

2

q

2

+

2

5

6

2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

5

3

68

RING-OPENING

POLYMERIZATION

Semlyen |4jJ i n a r e p o r t d e s c r i b i n g p o l y m e r i z a t i o n i n i t i a t e d w i t h BF^ ° ( 2 5 ) ? t h a t gc-ms method ga­ ve e v i d e n c e f o r tile e x i s t a n c e o f c y c l i c o l i g o m e r s formed i n the p r o c e s s , which l e d to the m i x t u r e o f l i n e a r and c y c l i c p r o d u c t s w i t h a d i s t r i b u t i o n governed f o r l a r g e r m a c r o c y c l i c s by the Jacobson-Stockmayer theory. T h i s i s an i m p o r t a n t r e s u l t , because an agreement between the o b s e r v e d d i s t r i b u t i o n o f the c y c l i c oligomers w i t h a d i s t r i b u t i o n p r e d i c t e d by the Jacobson-Stockmayer t h e o r y (a s l o p e e q u a l to 2.5 f o r the p l o t o f l o g Κ on l o g x, where Κ i s the molar c y c l i z a t i o n - e q u i l i b r i u m c o n s t a n t f o r m a c r o c y c l e s w i t h a p o l y m e r i z a t i o n degree e q u a l to x) s t r o n g l y i n d i c a t e s t h a t p o l y m e r i z a t i o n p r o ­ ceeds w i t h a l i n e a r a c t i v e s p e c i e s , f o r m i n g m a c r o c y c l e s by b a c k - b i t i n g and end-to-en Thus, because o and when p o l y - D i o x c o n t a i n the end-groups, and because of the f a r r e a c h i n g c o n c l u s i o n s based on e i t h e r macroc y c l i c o r l i n e a r s t r u c t u r e s o f the i s o l a t e d p o l y - D i o x , we r e i n v e s t i g a t e d r e c e n t l y t h i s problem. F i r s t o f a l l we d e c i d e d to use methods which would not i n v o l v e d e s t r u c t i o n o f the end-groups ( l i k e hydro­ l y s i s used by J a a c k s |36| and then by P l e s c h |37j as a p o s s i b l e s o u r c e o f a m i F T g u i t y . S e c o n d l y , we assumed, t h a t b o t h end-groups s h o u l d be o b s e r v e d ; the i n i t i a l one, formed from an i n i t i a t o r , and the t e r m i n a l one, coming from the k i l l i n g agent. Thus, we i n i t i a t e d p o l y ­ m e r i z a t i o n e i t h e r by b e n z o i l i u m h e x a f l u o r o a n t i m o n a t e ( C ^ H r C 0 S b F 7 ) , assuming t h a t the benzoate end-groups s h o u l d be o D s e r v a b l e i n UV, o r w i t h ( C H c ) ^ 0 S b F 7 , a s ­ suming, t h a t i n the FPT-^H-NMR s p e c t r a ; CH^C^O t r i p l e t from the end-group s h o u l d be seen. C H ONa, N(CH-)- and P ( C , H r ) - k i l l i n g agents were used a f t d ^ s t u d i e d i l l * * F P T - 1 H - N M R . The benzonoate end-groups absorb a t * 0 ( l i k e the low m o l e c u l a r - w e i g h t b e n z o a t e s ) ; thus as suming t h a t ε f o r e t h y l benzoate i s e q u a l to ε of the benzoate end-groups the DP of poly-Diox were c a l c u l a t e d . T a b l e 1 summarizes some o f these results where DP ( c a l c d . ) are compared w i t h DP (UV) and DP (osm.). The former v a l u e s were c a l c u l a t e d assuming, t h a t tne p o l y m e r i z a t i o n i s a l i v i n g one, i . e . t h a t e v e r y molecul e o f i n i t i a t o r g i v e s one macromolecule w i t h no t r a n s f e r , DP (UV) was c a l c u l a t e d as d e s c r i b e d above, and DP (osm.) was measured by h i g h - s p e e d osmometry. S i n c e polymers taken f o r measurements were i s o l a t e d and p u r i f i e d by s e v e r a l d i s s o l u t i o n / p r e c i p i t a t i o n c y c l e s , some amount of the lower m o l e c u l a r - w e i g h t m a t e r i a l c o u l d be l o s t . P o l y m e r i z a t i o n was conducted i n CH-NO- o r i n Cï^Cl? solvents at -15 i n o r d e r to minimize the H" i o n t r a n s f e r ( i t has been shown i n our l a b o r a t o r y t h a t below -20° C

H

s

h

o

w

e

d

+

+

7

9

q

0

= 2 3

n

m a x

m

a

x

m

n

n

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

a

m

5.

PENCZEK AND KUBisA

Polymerization

of Cyclic

Acetals

69

the H~ion t r a n s f e r f r o c e.g^ dimethoxymethane to methoxycarbenium i o n -CH^OCH^bF^- becomes immeasurably slow) T a b l e 1 |42| _ Comparison o f DP ( c a l c d . ) DP (UV) and DP (osm-l o f p o l y - 1 , 3 - d i o x o l a n s p r e p a r e d w i t h C H -UO SbF i n CH-N0 o r C H C 1 s o l v e n t s a t - 1 5 ° , and « t e r m i n a t e d w i t h C H ONa. | D i o x | =5.4 m o l e - l +

6

2

2

+

6

χ 10,πκ>1β·Γ

5

n

lF (calcd.)

5

n

Ί

6

2

2

|C H CO SbF-|

t

|Diox| -|Diox| 0

DP (UV)

lF (osm.)

10-3

10-3

n

e

i o

_

3

n

|C 4.05

I

1.15

1.30

1.39

2.75

i

1.69

1 .73

1 .77

2.70

1.72

•

2.07

1 .88

2.65

1.41

I

1.23

1 .33

1.10

4.19

5.24

4.35

0.95

4.81

3.69

4.00

The second end-group, i n t r o d u c e d upon a t e r m i n a t i o n r e ­ a c t i o n , was o b s e r v e d by FPT-1H-NMR f o r samples o f p o l y -Diox, p r e p a r e d from a p e r d e u t e r a t e d Diox(Diox-dg).This approach d e c r e s a s e s an o v e r - a l l number o f p r o t o n s i n the sample and i n c r e a s e s p r o p o r t i o n o f p r o t o n s i n the end-groups. A p p l i c a t i o n o f the F o u r i e r - P u l s e - T r a n s f o r m method f o r a c c u m u l a t i o n o f the s p e c t r a enhanced the s i g n a l to n o i s e r a t i o s u f f i c i e n t l y to observe s t r u c t u r e and c o n c e n t r a t i o n o f the end-groups by FPT-'H-NMR. Some o f the p e r t i n e n t r e s u l t s are shown i n T a b l e 2. An agreement ( w i t h i n 20-251) between DP c a l c u l a t e d and measured by UV and/or ^H-NMR methods i n d i c a t e s t h a t p r a c t i c a l l y a l l o f the i n i t i a t o r used i s p r e s e n t i n the macromolecules. An agreement between DP found from the end-groups and DP measured o s m o m e t r i c a l l y means, t h a t the p r o p o r t i o n o f c y c l i c macromolecules i s low, as i t c o u l d be p r e d i c t e d , f o r i n s t a n c e , from the Jacobson-Stockmayer t h e o r y . T h i s p r o p o r t i o n , i n p r i n c i ­ p l e , _ c o u l d be d e t e c t e d by comparing DP (end groups) and DP '(osmometry) but our a c c u r a c y o f measurements i s ,

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

70

RING-OPENING POLYMERIZATION

at l e a s t a t p r e s e n t , comparisons.

not s u f f i c i e n t l y

high

f o r these

Table 2 Comparison o f DP ( c a l c d . ) and DP (NMR) o f p o l y -1,3-Diox, p r e p a r e d from p e r d e u t e r a t e d Diox(-d^). P o l y m e r i z a t i o n c o n d i t i o n s : C H N 0 s o l v e n t , -15®, 12 h r s . 7

9

6

Starting concn. of i n i t i a t o r 103 mole*1 1

|Diox-d | 6

n

IDioxI -IDioxI

mole*l ^

0

n

€

I initiator|

+

|C H CO SbF-| 6

5

4.05

o

Initia-

6

5

2

4.75

+

0

750

C

H

2 5°1000

5.2

5

575

650

; Kc^jP3p aF-|

Termi-

C H C(0)0 -OC H

700

4.7

I

DP„ found 1 from H-NMR

T3F (calcd.)

Q

-

-

L

-P(C H )5 6

5

920

Thus, we c a n c o n c l u d e , t h a t p o l y - D i o x , prepared with C HrCO SbF7 or ( C ^ H r ) 3 6 are m o s t l y l i n e a r , and macromoleculës c o n t a i n an i n i t i a l end-group coming from an i n i t i a t o r and the t e r m i n a l end-group coming from the t e r m i n a t i n g agent, e.g.: +

0 + s b F

i

n

i

t

i

a

t

o

r

s

6

C H CfOCH CH OCH > OCH CH 6

5

2

2

2

n

2

3

(4) CH CH iOCH CH OCH > P(C H ) 3

2

2

2

2

n

6

5

3

P o l y m e r i z a t i o n degrees measured i n d i c a t e a l s o , t h a t p o l y m e r i z a t i o n ( a t l e a s t i n c o n d i t i o n s g i v e n i n Table 1 and 2) p r o c e e d s w i t h o u t an a p p r e c i a b l e t r a n s f e r a f f e c t i n g the p o l y m e r i z a t i o n degree. S t r u c t u r e o f P o l y - D i o x ( c y c l i c vs l i n e a r ) and Mechanism o f P o l y m e r i z a t i o n |43|. As i t w i l l be shown i n t h i s p a r a g r a p h , n e i t h e r predominantly l i n e a r nor predominantly c y c l i c s t r u c t u r e s o f the i s o l a t e d , k i l l e d macromoleculës a r e the s t r a i g h t f o r w a r d arguments by themselves f o r the l i n e a r or c y c l i c growth o f the l i v i n g macromoleculës. Indeed, l e t us c o n s i d e r an assumed e q u i l i b r i u m between l i v i n g

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

5.

PENCZEK AND KUBISA

cyclic

Polymerization

and l i v i n g

linear

of Cyclic

71

Acetals

poly-Diox: (5)

X

^linear living "^macromolecule

—• 0 0 ( bl ^ CH —Oww 2

7A 7C E q u i l i b r i u m (5) , d e s c r i b i n g the instantaneous state,should a l s o be supplemented w i t h the t e m p o r a r i l y dead c y c l i c and l i n e a r ( h o l d i n g two ends coming from an i n i t i a t o r X) macromolecules. C y c l i c l i v i n g macromolecules 7A and 7B a r e r e s u l t s o f the b a c k - b i t i n g l e a d i n g to the end-to-end c l o s u r e (7A oxygen atoms i n tïï mer p r o c e s s i s enhanced v e r y much, p a r t i c u l a r l y a t the e a r l y s t a g e s o f p o l y m e r i z a t i o n , when the oxygen atom i n the i n i t i a l end-group ( e . g . oxygen atom i n the ether end-group) i s much more n u c l e o p h i l i c than the oxygen atoms i n the a c e t a l bonds a l o n g the c h a i n . L e t us now examine r e a c t i o n o f a k i l l i n g agent with these l i v i n g macromolecules. The l i n e a r l i v i n g macro m o l e c u l e s w i l l g i v e t h e i r l i n e a r dead r e p l i c a / b u t the c y c l i c - l i v i n g ones may g i v e e i t h e r c y c l i c - d e a d o r l i n e a r - d e a d macromolecules, depending on the i n i t i a t o r used, and t h e r e f o r e on a s t r u c t u r e o f Χ i n 7A. In t h i s s t r u c t u r e t h e r e a r e t h r e e n o n e q u i v a l e n t boncTs: a, b, and c, t h a t can be b r o k e n upon an a t t a c k o f the k i l l i n g agent. I f X=e.g. CH- o r C H r , ^ th i IA r a t h e r s t a b l e bonds a and c, and one much l e s s s t a b l e a c e t a l bond b. Thus, even i f c y c l i c 7A were a predomi­ nant s t r u c t u r e a t some s t a g e o f p o l y m e r i z a t i o n , then t h e i r r e a c t i o n w i t h k i l l i n g agent would g i v e m o s t l y l i n e a r dead macromolecules. Thus, a l t h o u g h i t has been shown i n the p r e v i o u s p a r a g r a p h , t h a t p o l y - D i o x p r e p a r e d w i t h C.HrC0 SbF7 and ( C H ) ~0 SbF""are l i n e a r , t h i s i s not s u f f i c i e n t to argue t h a t - t h e c h a i n growth proceeds w i t h a l i n e a r m a c r o c a t i o n 7C. In o r d e r to d i s t i n g u i s h between the extreme s t r u c 7Λ ^ predominant d u r i n g the c h a i n growth, i t i s , t h e r e f o r e , n e c e s s a r y to o b s e r v e d i r e c t l y the p o s i t i o n o f X; i n 7A i t i s a d j a c e n t to the p o s i t i v e l y c h a r g e d oxygen atom, i n 7_C i t i s a p a r t o f the e t h e r c h a i n end. I f X=C Hr, t h e n the d i f f e r e n c e s between the chemical s h i f t s i n ^H-NMR are as f o l l o w s : Θ

η

e r e

a

r

e

R

2

+

+

2

t

u

r

e

s

a n

a

5

s

2

+

6 1.75(t)

δ 1 .15(t)

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

t

w

o

72

RING-OPENING POLYMERIZATION

t h u s , the difference between c h e m i c a l s h i f t s i s s u f f i ­ c i e n t l y l a r g e and both s t r u c t u r e s can be i n d e p e n d e n t l y observed by ^H-NMR. T h i s i s shown i n F i g u r e 1, t a k e n from R e f e r e n c e |43|, and i l l u s t r a t i n g the change o f the p o s i t i o n o f a t r i p l e t o f the CH^CH^-protons d i r e c t l y i n the l i v i n g p o l y m e r i z a t i o n system, c o n s i s t i n g o f a d e u t e r a t e d D i o x ( - d ) and ( C H ) - 0 S b F " i n i t i a t o r i n CD^CK s o l v e n t . At the b e g i n n i n g o f p o l y m e r i z a t i o n o n l y tne 61.75 t r i p l e t i s seen, w h i l e a t e q u i l i b r i u m o n l y the 61.15 t r i p l e t ; i n the i n t e r m e d i a t e s t a g e s b o t h t r i p l e t s are o b s e r v e d . A d d i t i o n a l s p l i t t i n g o f the 61.15 t r i p l e t i n ­ to two t r i p l e t s w i t h a d i f f e r e n c e i n c h e m i c a l s h i f t s e q u a l l i n g o n l y 13 Hz (300 MHz spectrum) and the r a t i o o f i n t e g r a t i o n s 1:2 taneous p r e s e n c e o f one from the polymer end-group, and the second one from e t h y l e t h e r , l i b e r a t e d from the i n i t i a t i n g t e r t i a r y oxonium s a l t . E v a c u a t i o n o f the sample i n high-vacuum removes c o m p l e t e l y e t h y l e t h e r , as i t can be judged from the d i s a p p e a r a n c e o f i t s t r i p l e t from the spectrum. A d d i t i o n o f the N ( C H ) k i l l i n g agent to the l i v i n g system does not change the p o s i t i o n o f the 61.15 t r i p l e t . The f i n a l spectrum o f the k i l l e d system i s shown i n F i g u r e 2 ( a l s o t a k e n from R e f e r e n c e 143j . In t h i s spectrum two s i n g l e t s due to the (CH-r) N and (CH-)-N p r o t o n s are o b s e r v e d , the r a t i o |CH CH 0-|/|-N (CH )-| (from the c o r r e s p o n d i n g i n t e g r a ­ t i o n s ) i s e q u a l to 1:1.1. R e s u l t s r e p o r t e d i n t h i s pa­ r a g r a p h , and based on the r e c e n t work from our l a b o r a ­ t o r y , s t r o n g l y i n d i c a t e t h a t p o l y m e r i z a t i o n o f Diox, i n i t i a t e d by ( C H r ) 0 S b F 7 p r o c e e d s , a t l e a s t i n C H N 0 s o l v e n t , on the l i n e a r a c t i v e s p e c i e s . Systems w i t h p r o t o n i c a c i d s i n i t i a t o r s may behave d i f f e r e n t l y , because i f X=H i n 7A, then the bond a (Η-δ<) i n the secondary oxonium i o n becomes the weakest one and t h i s system i s t h e r e f o r e much more s u s c e p t i b l e to t r a n s f e r (by t r a n s f e r r i n g H " from 7A) than systems i n i t i a t e d by s t a b l e c a t i o n s . However, the thermodynamic a l l y c o n t r o l l e d d i s t r i b u t i o n o f the p o l y m e r i z a t i o n degrees s h o u l d be s i m i l a r f o r b o t h systems. This is,never­ t h e l e s s n o t so; f o r ( C H r ) 0 S b F 7 and C H C 0 S b F 7 i n i t i a t i n g systems d e s c r i b e d i n R e f e r e n c e s |42| |43|, DP ( c a l c d . ) i s e q u a l to DP (found) ( w i t h i n < 2 5 l j w h i l e i n hands o f P l e s c h |351 , working w i t h HC10initiator, DP found e x p e r i m e n t a l l y were always much lower than DPjJ(calcd.) . +

6

2

5

3

3

3

+

+

3

2

3

+

2

3

3

2

f,

+

+

?

2

3

+

6

5

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

PENCZEK AND KUBisA

Polymerization

of Cyclic

Acetah

equilibrium

a III! i

Mil,

•I,

start

A

ι 2

1 0

1

1

8

1 6

1

ppmtf

1

U

1

I

2

1

0

Figure 1. 300 MHz gion from 1.0 to 2.0 δ ppm (CH CH O groups, in ionic and covalent species) of the polymerization of Diox-d (\Diox\ = 4.0 mol · Y ) initiated wtih (C H ) O SbF (3.10~ mol · Y ) in CDsNOg solvent at 25° (43) 3

s

6

1

s

5 s

+

1 j uuu

20

6

1

i

4

3

1

1

ppmcf

V—Λ_ l 2

· 1

Figure 2. H-NMR spectrum showing both end groups in poly (Diox-d ): ÇHsCH 0- at δ 1.15 and -N+(CH )s at δ 3.05 (CH ) N added in five-fold excess over growing species. Polymenzation conditions as in Figure 1 (43) 1

6

2

s

S S

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING

74

POLYMERIZATION

S t r u c t u r e o f the A c t i v e S p e c i e s i n the P o l y m e r i z a tion of Cyclic Acetals. Kinetics of Propagation. In the p r e v i o u s p a r a g r a p h a d i r e c t s p e c t r o s c o p i c e v i d e n c e e l i m i n a t e d the " r i n g - e x p a n s i o n " assumption as the supposed mechanism of p r o p a g a t i o n i n the p o l y m e r i z a t i o n o f Diox i n i t i a t e d w i t h s t a b l e c a t i o n s . T h i s mechanism r e q u i r e s i n f a c t , t h a t the bond b i n 7A i s so s t r o n g , t h a t d u r i n g the whole p o l y m e r i z a t i o n p r o c e s s i t does n o t brake i n any o t h e r p r o c e s s b u t f o u r - c e n t e r i n c l u s i o n o f a monomer. The s t a b i l i t y o f bond b c a n be s t u d i e d on the model compounds, f o r i n s t a n c e 8a b e a r i n g c l o s e resemblance to 7A : + CH OCH z

3

7

CH OC _ CH,

+

2

-

CH--0-CHb| CH

K

3

(6)

3

2

( w i t h SbF^ anion)

| 0-CH

3

Szymanski |44_| has shown r e c e n t l y i n o u r l a b o r a t o r y , t h a t i n r e a c t i o n o f 8^ ( a t l e a s t i n SO, s o l v e n t ) w i t h an excess o f d i m e t h y l e t h e r : X

CH -0-CH 3

3

+

0^

I

—1£ C H

~CH-

CH

3

% C H

CH 3

)

3

0

+

(7)

3

+ (CH 0) CH 3

2

2

2

0-CH

3

o n l y bond b, b r a k e s , as shown i n eq.7. T h i s exchange r e a c t i o n i s v e r y f a s t (as judged by l i n e b r o a d e n i n g i n NMR) i n i d i c a t i n g , t h a t bond b i s v e r y weak. Two e q u i v a l e n t bonds a and c a r e much more s t a b l e . T h i s l a t t e r c o n c l u s i o n _ i s based on the f a c t , t h a t the a d d i t i o n o f ( C H - ) 0 S b F 7 to the r e a c t i o n m i x t u r e c o n s i s t i n g o f 8 and (CH-)~0 g i v e s a s e p a r a t e s i n g l e t of ( C H - ) 0 (because o f tfie slow (on the NMR t i m e - s c a l e ) exchange w i t h (CH-) 0 ) )which was n o t o b s e r v e d i n th|3 r e a c t i o n m i x t u r e w i t h o u t i n t e n t i o n a l l y added ((H-) 0 SbF^. Thus, the t r i m e t h y l o x o n i u m s a l t i s n o t formed i n a system d e s c r i b e d by eq.7. We p r e v i o u s l y proposed, t h a t the l i n e a r growing m a c r o c a t i o n i n the p o l y m e r i z a t i o n o f Diox i s b e s t desc r i b e d by the e q u i l i b r i u m between the macroalkoxycarbenium i o n 2 w i t h i t s t e r t i a r y oxonium c o u n t e r p a r t _3, +

3

+

3

2

3

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

5.

PENCZEK AND KUBisA

Polymerization

of Cyclic

75

Acetals

which, a t the h i g h r a t i o o f a polymer to a c t i v e s p e c i e s , becomes a predominant s t r u c t u r e . Our r e c e n t d a t a |45| on the r a t e c o n s t a n t o f p r o p a g a t i o n f o r Diox i n i t i a t e d by C H r C O S b F 7 , a r e i n agreement w i t h p r e v i o u s l y r e p o r t e d k ~ 1 0 2 l«mole~1 s"1 a t 250 i n C H C 1 s o l v e n t . T h i s i s h i g h e r than k report e d f o r p o l y m e r i z a t i o n i n i t i a t e d by H C 1 0 , | 3J> | . Perhaps, i n the p o l y m e r i z a t i o n o f c y c l i c a c e t a l s the m a c r o e s t e r - m a c r o i o n - p a i r e q u i l i b r i u m , d e s c r i b e d f o r the p o l y m e r i z a t i o n o f THF, a l s o takes p l a c e , as p r o p o s e d r e c e n t l y f o r the C I O 4 a n i o n |46 |. +

6

e

P

2

2

p

REFERENCES : 1. S.Penczek, Makromol.Chem 2. B.A.Rosenberg, E.B.Ludvig, A.R.Gantmacher and S.S. Miedwiediew, Vysokomol. Soed. 6, 2035 (1964) 3. K.Matyjaszewski, P.Kubisa and S.Penczek, J.Polymer Sci. A12, 1333 (1974) 4. T.K.Wu and G.Prukmayr , Macromolecules 7, 136 (1974) 5. S.Slomkowski and S.Penczek, J.Chem.Soc.Perkin II (1974), 1718 6. P.H.Plesch IUPAC International Symposium on Macromolecules Budapest 1969, Plenary Lecture, p.213 7. P.H.Plesch, I-st IUPAC International Symposium on Rings-Opening Polymerization, Jablonna (Poland), 1975, Plenary Lecture, Pure & Appl.Chem., in press 8. B.A.Rosenberg, W.I.Irzak and W.S.Enikolopian "Interchain exchange in polymers" Chimia, Moscow, 1975 (in Russian) 9. K.Ivin and J.Leonard, European Pol.J. 6, 331 (1970) 10. J.Leonard, Macromolecules 2, 661 (1969) 11. L.I.Kozub, M.A.Markevich, A.A.Berlin and N.S. Enikolopian Vysokomol.Soed. 10, 2007 (1968) 12. S.Penczek and K.Matyjaszewski, submitted for publication 13. R.Binet and J.Leonard, Polymer 14, 355 (1973) 14. W.K.Busfield, R.M.Lee and D.Merigold, Makromol.Chem. 156, 183 (1972) 15. M.Okada, K.Mita and H.Sumimoto, Makromol.Chem. 176, 859 (1975) 16. Y.Firat and P.H.Plesch, Makromol.Chem. 176, 1179 (1975) 17. H.Jacobson and W.H.Stockmayer, J.Chem.Phys. 18, 1600 (1950) 18. H.K.Hall J r . , M.K.Brandt and R.M.Mason, J.Amer.Chem. Soc. 80, 6420 (1958) 19. H.K.Hall Jr. and J.H.Baldt, J.Amer.Chem.Soc. 93, 140 (1971)

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

76

RING-OPENING POLYMERIZATION

20. Y.Yumoto, J.Chem.Phys. 29, 1234 (1958) 21. J.Sebenda, I-st IUPAC International Symposium on Ring-Opening Polymerization, Jablonna (Poland), 1975, Plenary Lecture, Pure & Appl.Chem., in press 22. K.Pihlaja, Acta Chem.Scand. 25, 451 (1971) 23. Z.Jedlinski, J.Lukaszczyk, J.Dudek, and M.Gibas, Macromolecules 9, 622 (1976) and references cited thereof 24. J.Kops and Spanggaard, Makromol.Chem. 175, 3077 (1974) 25. T.Mukaiyama, T.Fujisawa, H.Nohira,and T.Hyngaji, J.Org.Chem. 27, 3337 )1962) 26. K.Tada, T.Saegusa.and J.Furukawa, Makromol.Chem. 95, 168 (1966) 27. M.Sumitomo, M.Okada,an 3182 (1968) 28. J.Martinez-Madrid and J.L.Mateo, Makromol.Chem. 136, 113 (1970) 29. Z.Jedlinski, J.Maslinska-Solich, J.Polymer Sci.A1, 6, 3182 (1968) 30. J.P.Kennedy and A.L.Langer, Fortschr, Hochpolym. Forsch. 3, 508 (1964) 31. H.Minato and N.Muramatsu, Bull.Chem.Soc.Japan 42, 1146 (1969) 32. W.Kern, H.Deibing, A.Giefer, and V.Jaacks, Pure & Appl.Chem.12, 37 (1966) 32a.C.E.Schweitzer, R.N.Mc Donald, and J.O.Punderson, J.Appl.Polymer Sci. 1, 185 (1959) 33. A.Stolarczyk, P.Kubisa and S.Penczek, submitted for publication 34. W.S.Gresham, U.S.P. 2394910 (1946) 35. P.H.Plesch and P.H.Westermann, J.Polymer Sci C16 , 3837 (1968) 36. V.Jaacks, K.Boehlke, and E.Eberius, Makromol.Chem. 118, 354 (1968) 37. Y.Firat, F.R.Jones, P.H.Plesch, and P.H.Westermann, Makromol.Chem.Suppl. 1, 203 (1975) 38. E.J.Black and D.J.Worsfold, J.Macromol.Sci. A9, 1523 (1975) 39. Z.N.Nysenko, E.L.Berman, E.B.Ludvig, A.P.Klimow, W.A.Ponomarenko, and G.W.Isagulanz, Vysokomol. Soed. 18, 1696 (1976) 40. Y.Yamashita, M.Okada,and H.Kasahara, Makromol.Chem. 117, 256 (1968) 41. J.M.Andrews and J.A.Semlyen, Polymer 13, 142 (1972) 42. P.Kubisa and S.Penczek, submitted for publication 43. R.Szymanski in preparation 44. P.Kubisa, Bull.Acad.Pol.Sci.,in press

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6 Ring-Opening Polymerization of Macrocyclic Acetals ROLF C. SCHULZ, K. ALBRECHT, C. RENTSCH, and Q. V. TRAN THI Institute of Organic Chemistry, University of Mainz, D-65 Mainz, West Germany

Numerous oxacyclic polymers in the presenc this way polyethers and polyacetals are obtained (1)(11). Besides the parent compounds, listed in Table 1 many substituted oxacycles, furthermore bicyclic (12)-

Table I. Some polymerizable oxacyclic compounds

77

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

78

RING-OPENING

POLYMERIZATION

(15) as w e l l as spirocyclic oxygen c o n t a i n i n g compounds (16);(17) a r e p o l y m e r i z a b l e . The p o l y m e r i z a t i o n mechanism does n o t o n l y depend on the monomer, b u t a l s o on the initiator and the e x p e r i m e n t a l c o n d i t i o n s . In particular the p o l y m e r i z a t i o n o f 1.2.- and 1.3-epoxides ( 1 ) - ( 5 ) ; ( 1 8 ) ; ( 1 9 ) ; t e t r a h y d r o f u r a n e ( 1 ) ( 4 ) ; ( 6 ) ; ( 2 0 ) ; d i o x o l a n e (21);(22) and t r i o x a n e ( 1 1 ) ; (23)-(26) was t h o r o u g h l y i n v e s t i g a t e d . F o r reviews see ( 4 ) ; ( 8 ) ; ( 2 7 ) ; ( 2 8 ) ; ( 3 0 ) . I t s h o u l d be emphasized, t h a t different o x a c y c l i c monomers c a n a l s o be c o p o l y m e r i zed by cationic catalysts. Of g r e a t practical importance is e.g. the c o p o l y m e r i z a t i o n o f t r i o x a n e w i t h e t h y l e n e o x i d e o r d i o x o l a n e ( 3 1 ) . Macromolecules w i t h a statistic distribution o f oxymethylene- and oxyethylene-units are hand, however, t h e y i e l d s a polymer c o n s i s t i n g o f s t r i c t l y a l t e r n a t i n g oxymethylene- and o x y e t h y l e n e u n i t s ( 2 1 ) ; ( 3 2 ) ; t h e r e f o r e i t can f o r m a l l y be c o n s i d e r e d as an a l t e r n a t i n g copolymer ( e q . i ) .

- C H O - •CH CH 0M E a

2

2

(i)

I t i s not formed by a normal c o p o l y m e r i z a t i o n s t a r t i n g from 2 d i f f e r e n t monomers, b u t s i n c e t h e monomer i t s e l f a l r e a d y c o n t a i n s both u n i t s i n the r a t i o o f 1 t o 1. We wanted t o i n v e s t i g a t e , whether i t would be poss i b l e t o p r e p a r e copolymers w i t h o t h e r sequences from analogous monomers by h o m o p o l y m e r i z a t i o n . F o r t h i s purpose one needs c y c l i c a c e t a l s , which c o n t a i n the oxymethylene- and o x y e t h y l e n e - u n i t s i n the d e s i r e d molar r a t i o . Of course d u r i n g t h e p o l y m e r i z a t i o n o f these monomers no e l i m i n a t i o n o f formaldehyde o r r e arrangement may o c c u r , s i n c e o t h e r w i s e the r e g u l a r sequence i n t h e polymer i s d i s t u r b e d . Monomers, which s h o u l d be a b l e t o form sequenced copolymers a c c o r d i n g t o t h e d e s c r i b e d p r i n c i p l e , a r e the compounds /1/-/6/. In t h e f o l l o w i n g , p r e p a r a t i o n and p r o p e r t i e s o f these monomers and the c o r r e s p o n d i n g polymers w i l l be described.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6.

SCHULZ ET AL.

Polymerization

of Macrocyclic

Acetals

79

1.3.5-trioxacycloheptane *(trioxepane)/!/ T r i o x e p a n e / l / i s formed as a b y - p r o d u c t d u r i n g t h e copolymerization o f trioxane or tetroxane with e t h y l e n e oxide o r d i o x o l a n e ( 3 3 ) - ( 3 5 ) . F o r i t s p r e p a r a t i o n a mixture o f d i o x o l a n e , paraformaldehyde and s u l p h u r i c a c i d as c a t a l y s t i s h e a t e d up t o 100°C f o r 5 h. A f t e r w a r d s one d i s t i l s a t 12 t o r r and 50°C ( 3 6 ) . A f t e r r e p e a t e d f r a c t i o n a t i o n a l d i s t i l l a t i o n s from lithium-aluminium hydride a gaschromatographically pure monomer i s o b t a i n e d (b.p. 1 3 0 ° C ) . I n t h e H-NMR spectrum o n l y two sharp s i n g l e t s appear (see F i g . l ) . The s i g n a l a t B = 4.92 ppm i s a s s i g n e d t o the methyl e n e p r o t o n s (M) and the s i g n a l a t S = 3.8 2 ppm t o the e t h y l e n e p r o t o n s ( E ) . The peak r a t i o i s e x a c t l y 1 t o 1. An a d d i t i o n o f s h i f t r e a g e n t s (Eu(F0D)3) l e a d s to a s h i f t w i t h o u t s p l i t t i n g o f t h e s i g n a l s ( 3 7 ) . The monomer i s e a s i l y p o l y m e r i z a b l e by c a t i o n i c c a t a l y s t s i n s o l u t i o n and i n b u l k . C o l o u r l e s s , w a x l i k e polymers a r e o b t a i n e d . At the p o l y m e r i z a t i o n o f / l / , e i t h e r the bond between 01 and C2 o r the bond between C2 and 03 can be c l e a v e d . In b o t h cases polymers w i t h the same t r i a d - s e q u e n c e c o n s i s t i n g o f 2 oxymethylene and 1 o x y e t h y l e n e - u n i t s (MME) would o c c u r .

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

80

A change o f the r i n g opening mechanism o r a t r a n s a c e t a l i z a t i o n would o f c o u r s e l e a d to o t h e r sequences. Whereas Gresham and B a l l (36) assume, t h a t the polymers o f t r i o x e p a n e have a r e g u l a r s t r u c t u r e w i t h a r a t i o o f 2 M to I E , Duke (38) c o n c l u d e d from IRand NMR-measurements, t h a t l o n g e r M-sequences must e x i s t . In our own NMR-spectroscopic i n v e s t i g a t i o n s we a l s o found, t h a t i n the homopolymers o f t r i o x e p a n e also MMM-triads ( S = 4,89 ppm) and E M E - t r i a d s ( 6 = 4,77 ppm) o c c u r b e s i d e the e x p e c t e d MME-triads (see F i g . l ) . Furthermore from the 13C-NMR-spectra we were a b l e t o determine pentad-sequences (see F i g . 2 ) and a f t e r a d d i t i o n o f Eu(F0D)3 even heptad-sequences (37). B e s i d e t h i s we c o n f i r m e d , t h a t i n the polymer the mole f r a c t i o n o than the c a l c u l a t e polymer made from / l / has n e i t h e r the r i g h t o v e r a l l c o m p o s i t i o n nor the e x p e c t e d r e g u l a r s t r u c t u r e . In o r d e r t o c l e a r up t h e s e anomalies the p r o g r e s s o f the p o l y m e r i z a t i o n i n d i c h l o r o e t h a n e w i t h boront r i f l u o r i d e a t d i f f e r e n t temperatures was i n v e s t i ­ g a t e d . H e r e t o the d e c r e a s e o f the monomer has been d e t e r m i n e d by gas chromatography ( 3 9 ) . An example o f a t i m e - c o n v e r s i o n curve i s shown i n F i g . 3 . The p o l y ­ m e r i z a t i o n proceeds r a t h e r q u i c k l y ; the monomer con­ c e n t r a t i o n reaches a f i n a l s t a t e , which does not change o v e r s e v e r a l h o u r s . T h i s c o n c e n t r a t i o n i n ­ c r e a s e s w i t h i n c r e a s i n g p o l y m e r i z a t i o n temperature (see T a b l e 2 ) . These f a c t s l e a d us to c o n c l u d e t h a t i t i s an e q u i l i b r i u m p o l y m e r i z a t i o n . The p l o t o f In (M) a g a i n s t 1/T f o r temperatures between 0° and 60°C i s shown i n F i g . 4 . We c a l c u l a t e d Δ S • -18,9 J/Mol*K and H = -6,6 k J / M o l . By e x t r a p o l a t i o n t o a monomer c o n c e n t r a t i o n o f (M) = 1 Mol/1 i n e q u i l i b r i u m , a f o r m a l c e i l i n g temperature o f 80°C r e s u l t s . In f a c t a t 80°C and w i t h a monomer concen­ t r a t i o n o f 1 Mol/1 no p o l y m e r i z a t i o n t a k e s p l a c e . But as we found, i n the gas chromatogramm o f the r e a c t i o n m i x t u r e , d i o x o l a n e too i s formed d u r i n g p o l y ­ m e r i z a t i o n (see F i g . 3 ) . T h i s f a c t e x p l a i n s the NMRs p e c t r o s c o p i c s t a t e m e n t , t h a t the polymer does not have the same c o m p o s i t i o n as the monomer, but c o n t a i n s an excess o f M - u n i t s . The c o n c e n t r a t i o n o f d i o x o l a n e a l s o reaches a f i n a l v a l u e , which i n c r e a s e s w i t h r i s i n g p o l y m e r i z a t i o n temperature (see T a b l e 2 ) . But t h i s means, t h a t the c o m p o s i t i o n o f polymer depends on temperature and approaches the t h e o r e t i c a l v a l u e o n l y at low p o l y m e r i z a t i o n t e m p e r a t u r e . The d e s c r i b e d r e s u l t s show, t h a t i n the p o l y m e r i z a t i o n o f t r i o x e p a n e s s

A

S

S

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6.

Polymerization

SCHULZ ET AL.

of Macrocyclic

Acetals

Figure 1. H-NMR spectra of trioxepane / l / and the polymer

ι

2

Figure 2. C-NMR spectrum of a polymer of trioxepane (CDCU; 25, 2 MHz). (1) MEMEM; (2) MMMEM; (3) EMMEM; (4) MMMMM; (5) EMMMM; (6) EMMME; (7) MMEMM; (8) ΎΜΕΜΕ, EMEMM. 13

Γ92.35 89.06!88,27 67.41 66.79 95,45 91.99 88.68

6 in ppm

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

81

82

RING-OPENING POLYMERIZATION Polymerization of trioxepane at 20°C with BF .Et 0 in CH-pCHfl 3

2

Figure 3. Time-conversion curve for the consumption of monomer (χ) and forma­ tion of dioxolane (O) during the polymeri­ zation of trioxepane /!/

*

*

11-

rit-

Table II· E q u i l i b r i u Dioxolane £DOlJ o f t r i o x e p a n e / l / w i t h BF^-etherate i n dichloroethane [m£ (Mol/1)

temp.(°C)

JDOLj

Q

5,55

0

5,72

20

0,50

5,82

30

0,60

5,50

45

1,01

5,71

60

1,36

(Mol/1)

0,23

Polymerization of

0

in Cf^CICH a 2

-0J

mth BF .Et 0 3

2

-0.3

-05 -Q6 Ό.7 -0.6 Figure 4. Monomer concentration at equilibrium in the polymerization of trioxepane /!/

3.5 eo

30

0

I VTtK .1(P] 4

X

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2Ch

6.

SCHULZ ET AL.

Polymerization

of Macrocyclic

Acetals

83

s e v e r a l r e a c t i o n s o c c u r s i m u l t a n e o u s l y and d i f f e r e n t polymers and monomers are formed s i d e by s i d e . The f o l l o w i n g scheme comprises the o b s e r v a t i o n s .

stst. copolymer

(iii)

J polymer +X


R e a c t i o n ( i i i ) d e s c r i b e s the s y n t h e s e s o f t r i o x e p a n e from d i o x o l a n e and formaldehyde; d u r i n g p o l y m e r i z a t i o n , o f c o u r s e , a c l e a v a g e i n t o the components c o u l d o c c u r a g a i n . But under the same c o n d i t i o n s a c o p o l y m e r i z a t i o n o f d i o x o l a n e and formaldehyde i s a l s o p o s s i b l e ( i v ) , l e a d i n g to a s t a t i s t i c copolymer. P o l y m e r i z a t i o n o f t r i o x e p a n e (V) l e a d s t o a polymer whereby, however, a c e r t a i n p a r t "x" o f d i o x o l a n e i s formed. T h e r e f o r e the polymer c o n t a i n s somewhat more than the c a l c u l a t e d q u a n t i t y o f M - u n i t s . Only a t low temperature, when "x" becomes z e r o , do monomer and polymer have the same over a l l c o m p o s i t i o n and one can suppose a r e a l p o l y mer i z a t i o n - d e p o l y m e r i z a t i o n - e q u i l i b r i u m . Whether the sequence i s hereby r e t a i n e d , depends on the p o s s i b i l i t i e s o f r i n g opening and t r a n s a c e t a l i s a t i o n , d i s c u s s e d above. R e a c t i o n ( v i ) d e s c r i b e s the above mentioned f o r m a t i o n o f t r i o x e p a n e as a b y - p r o d u c t d u r i n g c o p o l y m e r i z a t i o n o f t r i o x a n e and d i o x o l a n e ( 3 3 ) - ( 3 5 ) . 1.3.6-trioxacyclooctane

(trioxocane)

/2/

A c c o r d i n g to A s t l e (4o) e t a l . t r i o x o c a n e can be obt a i n e d by c o n d e n s a t i o n o f d i e t h y l e n e g l y c o l w i t h p a r a formaldehyde; i t i s e a s i l y p o l y m e r i z a b l e by c a t i o n i c c a t a l y s t s o r by e l e c t r o c h e m i c a l i n i t i a t i o n ( 4 1 ) . Cop o l y m e r i z a t i o n w i t h e.g. t r i o x a n e o r d i o x o l a n e are p o s s i b l e , too (41). K i n e t i c s , thermodynamics and mechanism o f h o m o p o l y m e r i z a t i o n have been s t u d i e d i n d e t a i l by s e v e r a l a u t h o r s . A c c o r d i n g t o the a n a l y t i c r e s u l t s o f W e i c h e r t (42) the s t r u c t u r e o f the polymers o f 121

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

84

RING-OPENING POLYMERIZATION

can o n l y be e x p l a i n e d by a r i n g opening mechanism between oxygen and carbon o f the f o r m a l group. L a t e r , Yamashita e t a l . (43) s t u d i e d the k i n e t i c s o f the p o l y ­ m e r i z a t i o n o f 12/ i n d i c h l o r o e t h a n e u s i n g t r i e t h y l oxonium t e t r a f l u o r o b o r a t e . They found t h a t the number average m o l e c u l a r weight o f the polymer remains almost c o n s t a n t throughout the p o l y m e r i z a t i o n (DP ^v>3o) i n ­ d i c a t i n g t h a t the r a t e o f i n i t i a t i o n i s c o n s i d e r a b l y lower than t h a t o f p r o p a g a t i o n and t h a t the p o l y m e r i ­ z a t i o n i s accompanied by some c h a i n b r e a k i n g r e a c t i o n s . The thermodynamic parameters o f the e q u i l i b r i u m p o l y ­ m e r i z a t i o n o f 111 (and some r e l a t e d c y c l i c f o r m a i s ) was s t u d i e d i n more d e t a i l by Yamashita e t a l . (22) and by B u s f i e l d and Lee ( 4 4 ) . Furthermore, i t was p o s t u l a t e d t h a t the monomer i n the p r e s e n c In our own work we were o c c u p i e d p r e d o m i n a n t l y w i t h the NMR-spectroscopic sequence a n a l y s i s , i n o r d e r t o see, whether the c o n c e p t f o r p r e p a r i n g sequenced copolymers, d e s c r i b e d a t the b e g i n n i n g , c o u l d be v a l i d a t e d (41). In the H-NMR-spectrum the monomer 11/ shows o n l y two sharp s i n g l e t s a t S = 3,8 ppm (E) and S = 4,9 ppm (M) w i t h a peak r a t i o o f 4 to 1 (see F i g . 5 ) . A d d i t i o n o f Eu (DPM)3 e f f e c t s a s h i f t t o lower f i e l d and a s t r o n g s p l i t t i n g o f the e t h y l e n e s i g n a l , as the p r o t o n s a t C4 and C8 are not e q u i v a l e n t to the p r o t o n s at C5 and C7. In the H-NMR-spectra o f the homo­ polymer a l s o o n l y two peaks o c c u r , h a v i n g the same peak r a t i o as i n the monomer (see F i g . 5 ) . From t h i s , i t can be c o n c l u d e d , t h a t not o n l y the o v e r a l l compo­ s i t i o n but a l s o the o r d e r o f M- and Ε-units i s the same i n polymer and i n monomer. Hence t h e r e i s o n l y one k i n d o f r i n g opening and rearrangements or e l i m i ­ n a t i o n s can be e x c l u d e d . That means, i n f a c t , t h a t a t the r i n g opening h o m o p o l y m e r i z a t i o n o f t r i o x o c a n e , a sequenced copolymer w i t h a r e g u l a r sequence o f (MEE)t r i a d s i s formed ( e q . v i i ) .

— CH 0 — CH CH 0 — CH CH 0 — M E Ε 2

2

2

2

2

(vii)

χ

T h i s f i n d i n g agrees w i t h the r e s u l t s o f W e i c h e r t (42) who a n a l y s e d the s t r u c t u r e o f p o l y t r i o x o c a n e by a c T 3 i c d e c o m p o s i t i o n . I n d i c a t i o n s o f endgroups have not been

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6.

SCHULZ ET AL.

Polymerization

of Macrocyclic

85

Acetàls

found, from which one s h o u l d not c o n c l u d e , t h a t macroc y c l i c polymers are i n hand. 1.3.6.9-tetraoxacycloundecane f o r m a l ) /3/

(triethylene

glycol

T h i s compound and i t s p o l y m e r i z a b i l i t y was f i r s t mentioned by C a r o t h e r s ( 4 5 ) . I t i s p r e p a r e d from t r i e t h y l e n e g l y c o l and p a r a f o r m a l d e h y d e ; by a d d i t i o n o f s t r o n g a c i d s a p r e p o l y m e r i s p r o d u c e d . From t h i s , the monomer /3/ i s s p l i t o f f i n a second s t e p by h e a t i n g i n vacuo. The monomer used by us has the f o l l o w i n g p r o p e r t i e s : m.p. 27°C; b.p. 56°C/0,4 T o r r ; ηβ° = 1,4541; NMR-signals o f /3/ were f i r s t r e p o r t e d by Burg ( 4 9 ) . NMR d a t T a b l e I I I and IV. /3/ i s p o l y m e r i z a b l e by s e v e r a l c a t i o n i c i n i t i a ­ t o r s i n s o l u t i o n and i n b u l k a t temperatures between -20°C and +150°C. The polymers are c o l o u r l e s s w a x l i k e s u b s t a n c e s ; they are r e a d i l y s o l u b l e i n water, THF, a r o m a t i c h y d r o c a r b o n s , a l c o h o l s and h a l o g e n a t e d hydro­ carbons . In the H-NMR spectrum o f the polymer o n l y 3 sharp peaks appear a t $ = 4,72; 3,67 and 3,65 ppm (see T a b l e I I I . T h e peak r a t i o o f M:E =1:6 agrees w i t h t h a t o f the monomer. The 13C-NMR-signals are at 5 =95,4; 70,4 and 66,8 ppm (see T a b l e IV) .There are no i n d i c a t i o n s o f an i r r e g u l a r s t r u c t u r e and we t h e r e f o r e c o n c l u d e , t h a t the polymer a t l e a s t c o n t a i n s v e r y l o n g b l o c k s o f (MEEE)-tetrads and c o n s e q u e n t l y can be d e s c r i b e d as a sequenced copolymer ( e q . v i i i ) .

— C H 0 — (CH CH 0) Μ Ε 2

2

2

3

(viii)

3

χ

A f t e r e s t a b l i s h i n g the s t r u c t u r e o f the polymer we s t u d i e d i n d e t a i l the way o f f o r m a t i o n . Hereto we c a r r i e d out s o l u t i o n - p o l y m e r i z a t i o n s i n methylene c h l o r i d e under argon-atmosphere ( 5 o ) . Monomer con­ c e n t r a t i o n s were between 0,15 and 2,5 Mol/1, tempe­ r a t u r e between -20°C and +20°C. T r i f l u o r o m e t h a n e s u l p h o n i c a c i d s e r v e s as c a t a l y s t . A f t e r d e f i n i t e t i m e s , p o l y m e r i z a t i o n was quenched by the a d d i t o n o f some b a s i c aluminium o x i d e o r t r i e t h y l a m i n e and the

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

Polymer

—

s

ο Figure 5. H-NMR spectra of tri­ oxocane /!/ and its polymer

5voV«u> 4 . ο " " 3

T a b l e I I I . H-NMR s i g n a l s o f t r i e t h y l e n e g l y c o l f o r m a l (M^), the polymer (P) and the oligomers o f the g e n e r a l formula/7/ -0-CH -02

-0-CH - CH -02

2

4.79

3.63

4.75

3.72

3.68

4.75

370

3.67

4.75

3.69

3.67

"δ

4.74

3.69

3.66

**6

4.74

3.69

3.66

M

4.75

3.69

3.66

"e

474

3fiB

3.67

Ρ

4.72

3.67

3.6S

7

3.69

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6.

SCHULZ ET AL.

Polymerization

of

Macrocyclic

Acetals

87

c o m p o s i t i o n o f the r e a c t i o n m i x t u r e was a n a l i z e d by h i g h p r e s s u r e g e l p e r m e a t i o n chromatography (HP-GPC) (Waters ALC/GPC 2ol w i t h Ri d e t e c t o r R 401; Stationary phase: S t y r a g e l ; 100 X + 500 X mobile phase: methylene c h l o r i d e ) . I t appears t h a t under the a p p l i e d r e a c t i o n con­ d i t i o n s not o n l y polymers (with m o l e c u l a r weights from 10,000 to 80,000) are formed, but a l s o n o t i c e a b l e amounts o f s e v e r a l o l i g o m e r s ( l a b e l l e d as M2 t o M± see F i g . 6 ) . I f the consumption o f monomer M, the f o r ­ mation o f o l i g o m e r M 2 , and the t o t a l o f a l l h i g h e r o l i g o m e r s and polymers are p l o t t e d as a f u n c t i o n o f t i m e , t i m e - c o n v e r s i o n c u r v e s r e s u l t as shown i n F i g . 7 . One can see, t h a t a f t e r about 3o minutes a f i n a l s t a t e i s r e a c h e d w i t h abou 9% M. I f pure polymer i s t r e a t e d w i t h trifluoromethane s u l p h o n i c a c i d under the same c o n d i t i o n s , e v e n t u a l l y e x a c t l y the same f i n a l s t a t e ( r e f e r r i n g t o type and amount o f monomer, o l i g o m e r and polymer) i s r e a c h e d (see F i g . 8 ) . Hence i t i s s u r e l y a m a t t e r o f a thermo­ dynamic e q u i l i b r i u m p o l y m e r i z a t i o n . W i t h i n a range o f i n i t i a l monomer c o n c e n t r a t i o n between 0,2 to 0,5 Mol/1 the e q u i l i b r i u m monomer c o n c e n t r a t i o n i s c o n s t a n t and amounts at 0°C t o (0,0146 ± 0,0016) Mol/1. The equili­ b r i u m c o n c e n t r a t i o n o f the dimer a t 0°C i s (0,0236 0,0013) Mol/1. The temperature dependence o f t h e s e c o n c e n t r a t i o n s was s t u d i e d f o r the p o l y m e r i z a t i o n i n methylene c h l o r i d e between -25°C and + 30°C w i t h t r i fluoromethane s u l p h o n i c a c i d as c a t a l y s t . A D a i n t o n p l o t o f the r e s u l t s i s shown i n F i g . 9 . We c a l c u l a t e d from the s l o p e and the i n t e r c e p t ^ H s s = (-1,9 * 0,2) k c a l / M o l = (-7,95 0,8)kJ/Mol and Δ S g = (+1,5 0,5) c a l / M o l * K = (+6,24 * 2,1) J/Mol*K. The s m a l l and p o s i t i v e entropy i s noticeable. 9

2

±

±

s

C y c l i c o l i g o m e r s o f the

t r i e t h y l e n e g l y c o l formal

From the above mentioned r e s u l t s , i t f o l l o w s t h a t the o b s e r v e d o l i g o m e r s are not b y - p r o d u c t s , but are a l l p r e s e n t i n a r e v e r s i b l e e q u i l i b r i u m w i t h the monomer and the polymer. T h e r e f o r e i t i s i m p o r t a n t to know t h e i r s t r u c t u r e and - i f p o s s i b l e - the way o f f o r m a t i o n . We succeeded i n i s o l a t i n g and i d e n t i f y i n g the f i r s t 8 members o f the homologous s e r i e s o f o l i g o m e r s by p r e p a r a t i v e GPC. R e c e n t l y a d e t a i l e d d e s c r i p t i o n has been p u b l i s h e d by us (51). The s u b s t a n c e c a l l e d M~

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

Table IV. C-NMR s i g n a l s o f t r i e t h y l e n e g l y c o l f o r m a l (M^), the polymer (P) and the oligomers o f the g e n e r a l formula / ? / -0-CI1 -CH -0-

-C-CH -0-

2

2

2

67.8

70A

96.2

70.6

M

95.1

70.8

70.6

C6A

"3

95.3

70A

702

C6.6

953

70/,

66.6

70A

66.7

2

%

95.

M

95,6 95.6

70.6

66#

"a

95.6

70.5

6Ô.9

P

95A

70A

66.8

6

S 10

1

15

19 mÎ

/M,/ « 0.5MotII; CH&i 0°C 0

Figure 6. HP-GPC curves of the reaction mixture during the polymerization of triethylene glycol formal /3/

[CF S0 H1 = 0.1 Mol-% 3

3

μ-εί/ΓΟ&δΟΟλ +100Ai 1.0 ml CH a lmin 2

2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

SCHULZ ET AL.

Polymerization

of Macrocyclic

Acetals

υ

20

min 10

Figure 7. Time-conversion curve for the consumption of monomer (M ), formation of polymer (P), and dimer (M ) during the polymerization of triethylene glycolformal /3/* (deter­ t

Γ

J

CF

3$0 H 3

t Ch^C^O^

2

0.5 Mol It ; 0,1Mol-%

startg. soin

•Ο

equilibrium

8 10 15 iSml tPlos [M^ 0.31Molll CH C^ o lCF S0 Hj=Q1Mol-% μ-Styragel 500A* 100 A Wm/CH q2/min s

3

:

2

3

;

2

:0

C

Figure 8. HP-GPC curves of the reaction mixture dur­ ing depolymerization of a polymer of triethylene gly­ colformal /3/

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

90

RING-OPENING POLYMERIZATION

i n HP-GPC t u r n e d out t o be the c y c l i c dimer o f compound /3/. The dimer i s p o l y m e r i z a b l e under the same c o n d i t i o n s as /3/ and a f t e r r e a c h i n g the e q u i l i b r i u m i t l e a d s t o the same o l i g o m e r d i s t r i b u t i o n as the monomer and the polymer (see F i g . l o ) . A l l o l i g o m e r s a r e c o l o u r l e s s c r y s t a l l i n e compounds.The m e l t i n g p o i n t s (see T a b l e V) o f the o l i g o mers w i t h even-numbered m u l t i p l e s o f t h e monomers a r e always h i g h e r than the odd-numbered ( 4 7 ) . The H-NMRs p e c t r a a r e n e a r l y i d e n t i c a l f o r a l l o l i g o m e r s and l e a d t o the c o n c l u s i o n , t h a t a l l have analogous s t r u c t u r e (compare T a b l e s I I I and I V ) . I n d i c a t i o n s o f endgroups a r e n o t a v a i l a b l e e i t h e r i n t h e NMR- o r i n the IR-spectra, v e r i f y i n g that i t i s a matter o f c y c l i c o l i g o m e r s . The mas t r i m e r ( M 3 ) gave th c h r o m a t o g r a p h i c e l u t i o n volumes f o r a l l o l i g o m e r s a r e on a common curve which i s , however, c l e a r l y d i f f e r e n t from the curve f o r open c h a i n e t h y l e n e g l y c o l o l i g o mers ( F i g . 1 1 ) . T h i s p r o v e s , t h a t the o l i g o m e r s occur i n g a t the p o l y m e r i z a t i o n o f /3/ ( c a t a l y z e d by t r i fluoromethane s u l p h o n i c a c i d ) have the f o l l o w i n g g e n e r a l s t r u c t u r e 111.

7

Whether a l s o the h i g h polymers have r i n g s t r u c t u r e , has h i t h e r t o n o t y e t been d e f i n i t e l y p r o v e d o r d i s proved. The f o r m a t i o n o f c y c l i c o l i g o m e r s can be exp l a i n e d by two d i f f e r e n t mechanisms: a) a s t e p w i s e r i n g e x t e n s i o n takes p l a c e by i n s e r t i o n a t the f o r m a l bond w i t h o u t f o r m a t i o n o f l i n e a r i n t e r m e d i a t e s ( 2 7 ) ; ( 5 2 ) ( s e e Scheme 1) b) the c h a i n growth proceeds by open c h a i n c a r b o x onium-ions ( p o s s i b l y i n e q u i l i b r i u m w i t h e s t e r g r o u p s ) ( 5 3 ) ; ( 5 4 ) and the c y c l i c o l i g o m e r s a r i s e by back-ïïTting (see Scheme 2 ) . From our r e s u l t s we cannot d e c i d e , which mechanism p r e v a i l s . F i n a l l y i t s h o u l d be mentioned t h a t d u r i n g s e v e r a l o t h e r p o l y c o n d e n s a t i o n s and i o n i c p o l y m e r i z a t i o n s , the

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6.

Polymerization

SCHULZ E T A L .

à H d S

of Macrocyclic

91

Acetals

- - 7,β5 ± 0,0 Κ J/Mol

s s

SS

a

*

6

i

2 4

± >* 7

J

/

K

M

o

1

•-25 C

4

M

- 1 0 ^

Figure 9. Monomer concentration at equilibrium in the polymerization of Methylene glycol formal /3/

5 70 2

19ml

/5

IM J

0.23 Mollh CH CI ; 0°C

Qs

2

2

[CF S0 H] = 0.18 Mol-% 3

3

μ-Styragel 500Â Wml Chimin :

Figure 10. HP-GPC curves of the reaction mixture during the polymerization of the aimer of Methylene glycol formal (M ) g

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

Table V.

Melting points of c y c l i c

oligomers o f the general

s t r u c t u r e /7/

Degree

number

melting

o f polym.

of ring

point

x

atoms

°C

Μ

χ

1

11

27

M

2

2

22

88

M

3

3

33

27

M

4

4

44

56

M

5

5

M

6

6

66

38

M

?

7

77

23

Μ

Λ

8

88

28

loçMW\MW 3.3 PEG1500l\

Ma

•1C00 RING •562

PEG60o\
-315

CHAIN

•173

«POC

TetraEG *\\,Λ/

;

TriEG * \ \ TOC -100

10

DiEG "\*yTOP

11

12

13

U

15

16

17

13 ml

Figure 11. HP-GPC elution curves for homotogous se­ ries of open chain ethylene glyols and cyclic formais (PEG, polyoxyethylene; EG, ethylene glycols; TOP, /!/; TOC, /!/; POC, / 4 / ; M / 3 / . M , M . . . cyclic oligo­ mers of the general structure / 7 / . u

g

3

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6.

Polymerization

SCHULZ E T A L .

of Macrocyclic

Scheme

Acetah

93

1

Scheme 2 CF^0 -0~CK ~0~(CK CM Q) H 2

\

I

Initiation

+K f-M 1

b

s

M 4-HA

i

s s S = s

^

2

3

J

:

9 4-Wxl-Mx

S

cyciitatlon

1

Β

J

enjn

3

Α + CH -O~(CH CH O) -CH,0-(C;: CH ,C;^

n S

a

R I N 9

2

\

M, ^K.O-(CH,CH O) L * â J ^ j 'a J °P

2

2

a. 1.2,3....

propa tion C8

Μ . + KA

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

94

RING-OPENING POLYMERIZATION

f o r m a t i o n o f c y c l i c o l i g o m e r s has been d e s c r i b e d , t o o . E.g. c y c l i c o l i g o m e r s o f formaldehyde w i t h 3 t o 15 u n i t s have been found when t r i o x a n e i s p o l y m e r i z e d ( 4 9 ) ; a l s o a t the p o l y m e r i z a t i o n o f e p i s u l p h i d e s o r d i o x o l a n e , c y c l i c o l i g o m e r s appear (55); f u r t h e r i n the c o u r s e o f the f o r m a t i o n o f p o l y e s t e r s and p o l y amides as w e l l as a t the m e t a t h e s i s r e a c t i o n o f c y c l o o l e f i n s ( 5 7 ) . I t i s t o be e x p e c t e d t h a t o l i g o m e r s c o u l d be shown t o be p r e s e n t i n o t h e r p o l y m e r i z a t i o n p r o c e s s e s by a p p l y i n g the GPC-technique. 1.3.6.9.12-pentaoxacyclotetradecane g l y c o l f o r m a l ) /4/

(tetraethylene

T h i s compound i s no mentioned i n a p a t e n i n an analogous way t o compound /3/ i n good y i e l d (46). A f t e r c a r e f u l p u r i f i c a t i o n , c o l o u r l e s s c r y s t a l s witlT" a m e l t i n g p o i n t o f 23,5°C are y i e l d e d (b.p. 51°C,lo-3 t o r r ; H-NMR ( C D C I 3 ) S - 4,70(s;2H); 3 , 7 3 (s;8H) 3,63 (s;8H). T h i s c y c l i c f o r m a l i s a l s o r e a d i l y p o l y m e r i z a b l e by s e v e r a l i n i t i a t o r s (as e.g. b o r o n t r i f l u o r i d e etherate, t i n t e t r a c h l o r i d e , t r i f l u o r o a c e t i c a c i d etc.) ( 5 9 ) . A t the s o l u t i o n p o l y m e r i z a t i o n i n methylene c K T o r i d e ( fMj = 2-3 Mole/1) a t 0°C w i t h t r i f l u o r o methane s u l p h o n i c a c i d (0,5 mole!) w a x l i k e polymers are o b t a i n e d ( m o l e c u l a r w e i g h t s 20,000 - 30,000), which are e a s i l y s o l u b l e i n water and i n o r g a n i c s o l v e n t s . In the H-NMR s p e c t r a o n l y two peaks appear: S = 4 , 7 3 ; 3,68 ppm. T h e r e f o r e here a l s o , the e x p e c t e d s t r u c t u r e w i t h a r e g u l a r sequence c o n s i s t i n g o f MEEEE-pentads, i s i n hand (see eq. I X ) .

A c c o r d i n g t o t h i s s t r u c t u r e the polymer i s v e r y s i m i l a r t o p o l y o x y e t h y l e n e i n some c h e m i c a l and p h y s i c a l p r o p e r t i e s . I t d i f f e r s , however, from t h i s p o l y mer w i t h r e s p e c t t o i t s v i s c o s i m e t r i c h e h a v i o u r i n water and i n o r g a n i c s o l u t i o n s . The polymer i s q u i c k l y decomposed by d i l u t e a c i d s o l u t i o n i n c o n t r a s t t h e

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6.

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95

Acetals

p o l y o x y e t h y l e n e (j>9). 1*3*6.9.12.15-hexaoxacycloheptadecane g l y c o l formal) /5/

(pentaethylene

P e n t a e t h y l e n e g l y c o l i s p r e p a r e d by c o n d e n s a t i o n o f 1 . 8 - d i c h l o r o - 3 . 6 - d i o x a o c t a n e w i t h 2 moles o f e t h y l e n e g l y c o l ( 6 0 ) . I n analogy t o the s y n t h e s i s d e s c r i b e d above, tïïê c y c l i c f o r m a l i s o b t a i n e d . The H-NMR ( i n CDCI3) shows t h e f o l l o w i n g peaks: 6 =4,73 ppm (2H); 3,76 (8H); 3,69 (12H). I n IR no OH-groups o r c a r b o n y l bands are d e t e c t a b l e but b r o a d a b s o r p t i o n i n e t h e r and a c e t a l r e g i o n i s o b s e r v e d ( 6 1 ) . 1.3-dioxacycloundecan C o r r e s p o n d i n g t o the c y c l i c a c e t a l s d e p i c t e d above, t h i s compound i s p r e p a r e d from 1 , 8 - o c t a n d i o l and p a r a formaldehyde (47). I t i s a c o l o u r l e s s l i q u i d (b.p. 5

196°C; n * = 1,4564;

dj

5

= o,985 g/ml; H-NMR (CDC1 ) 3

S = 4,66 ppm ( s ; 2H); 3,75 (m;4H); 1,56 (s;12H). P o l y m e r i z a t i o n i n b u l k o r i n s o l u t i o n between 0°C and 30°C w i t h t r i f l u o r o m e t h a n e s u l p h o n i c a c i d (0,2 mole %) l e a d s t o s o l i d c o l o u r l e s s polymers (H-NMR(CDCl3) £ = 4,71 ppm (s;2H); 3,57(m;4H); l,37(m;12H); o l i g o mers are a l s o formed, b u t under these c o n d i t i o n s no r e s i d u a l monomer c o u l d be d e t e c t e d . The polymers a r e s o l u b l e i n a r o m a t i c o r h a l o g e n a t e d hydrocarbons; they are i n s o l u b l e i n water, a l c o h o l and e t h e r ( 6 2 ) . Acknowle dgment We s h o u l d l i k e t o e x p r e s s our thanks t o "Deutsche Forschungsgemeinschaft f o r the f i n a n c i a l s u p p o r t w i t h i n the scheme o f S o n d e r f o r s c h u n g s b e r e i c h 41". C.Rentsch thanks the " S c h w e i z e r i s c h e r N a t i o n a l f o n d s " f o r g r a n t i n g him a s c h o l a r s h i p . We thank " H u t h i g and Wepf V e r l a g B a s e l " f o r the p e r m i s s i o n t o p u b l i s h some i f the f i g u r e s . 11

f,

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Literature Cited 1) Frisch, K . C . , Reegen, S.L., (Eds): "Ring-opening Polymerization", pp. 13, 111, 159; M. Dekker, New York, 1969. 2) H i l l , F.N., Bailey, F . E . , Fitzpatrick, J.T., Ind. Eng. Chem. (1958), 50, 5. 3) Sorenson, W.R., Campbell, T.W., "Preparative Meth­ ods in Polymer Chemistry",2nd ed., p. 367, Inter­ science Publ., New York, 1968. 4) Eastman, A.M., Advan. Polym. Sci. (1960), 2, 18. 5) Dreyfuss, P., Dreyfuss, M.P., Polym. J. (1976), 8, 81. 6) Kobayashi, S.,Danda, H.,Saegusa, Τ.,Macromolecules (1974), 7, 415. 7) Seitz, U . , Hoene Chem. (1975), 176, 8) Plesch, P.H., Westermann, P.H., J. Polym. Sci. C (1968), 16, 3837. 9) Donescu, D., Makromol. Chem. (1974), 175, 2355. 10) Busfield, W.K., Lee, R.M., Makromol. Chem. (1975), 176. 2017. 11) Chen, C.S., J. Polym. Sci.,Polym. Chem. Ed. (1975), 13, 1183. 12) Okada, M., Sumitomo, Η., Hibino, Y . , Polym. J. (1974), 6, 256. 13) Okada, Μ., Sumitomo, Η., Yamata, Υ . , Makromol. Chem. (1974), 175, 3023. 14) Hall, H.K., Steuck, M . J . , J. Polym. S c i . , Polym. Chem. Ed. (1973), 11, 1035. 15) Andruzzi, F . , Barnes, D.S., Plesch, P.H., Makromol. Chem. (1975), 176, 2053. 16) Bailey, W.J., J. Macromol. S c i . , Chem. (1975), A 9, 849. 17) Endo, T . , Katsuki, Η., Bailey, W.J., Makromol. Chem. (1976), 177, 3231. 18) Beaumont,R.H., Clegg,B., Gee,G., Herbert,J.B.M., Marks,D.J., Roberts,R.C., Sims,D., Polymer (1966), 7, 401. 19) Black, P . E . , Worsfold, D . J . , Can. J. Chem. (1976), 54, 3325. 20) Dreyfuss, M.P., J. Macromol. S c i . , Chem. (1975), A9,125, 729. 21) Plesch, P.H., Westermann, P.H., J. Polym. Sci. C (1968), 16, 3837. 22) Yamashita, Y . , Okada, M., Suyama, K . , Kasahara, H . , Makromol. Chem. (1968), 114, 146. 23) Kern,W., Jaacks,V., J. Polym. Sci. (1960), 48, 399. 24) Kern, W., Cherdron, H . , Jaacks, V . , Angew. Chem. (1961), 73, 177. In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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AL.

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25) Chen, C.S.H., J. Polym. S c i . , Polym. Chem. Ed. (1976), 14, 129, 143. 26) Enikolopyan, N.S., et al., Polym. Sci. USSR (1976) 17, 742, 759. 27) Plesch, P.H., "IUPAC International Symposium on Macromolecular Chemistry, Budapest, 1969, Plenary and Main Lectures", p. 213, Akadémiai Kiado, Budapest, 1971. 28) Enykolopyan, N.S., J. Macromol. S c i . , Chem. (1972), A 6, 1053. 29) Penczek, S., Makromol. Chem. (1974), 175, 1217. 30) Ledwith, Α . , Sherrington, D.C., Advan. Polym. Sci. (1975), 19, 1. 31) Weissermel,K., H.D., Kunststoff 32) Okada, M., Yamashita, Y . , Ischii, Y . , Makromol. Chem. (1964), 80, 196. 33) Miki, T . , Higashimura, T . , Okamura, S., J. Polym. Sci. Β (1967), 5, 583. 34) Boehlke, K . , Jaacks, V . , Makromol. Chem. (1971), 145. 219. 35) Mengoli,G., Furlanetto,F., Makromol. Chem. (1975), 176. 143. 36) Gresham , W.F., Bell, C D . , U.S. Pat. 2 475 610 (1949), Du Pont, C.A. (1950), 44, 175b. 37) Fleischer,D., Schulz.R.C., Makromol. Chem. (1975), Suppl. 1, 2355 (1976), 177, 3471 (Errata). 38) Duke, A.J., J. Chem. Soc. 1964. 1430. 39) Tran Thi, Q.V., unpublished results, Darmstadt, 1975. 40) Astle, M . J . , Zaslowsky, J.Α., Lafyatis, P.G., Ind. Eng. Chem. (1954), 46, 787. 41) Fleischer,D., Schulz,R.C., Makromol. Chem. (1972), 162. 103. 42) Weichert, D., J. Polym. S c i . , C (1967), 16, 2701. 43) Okada, M., Kozawa, S., Yamashita, Υ . , Makromol. Chem. (1969), 127, 66. 44) Busfield, W.K., Lee, R.M., Makromol. Chem. (1975), 176. 2017. 45) H i l l , J.W., Carothers, W.H., J. Amer. Chem. Soc. (1935), 57, 925. 46) Albrecht, Κ., unpublished results, Darmstadt, 1975. 47) Albrecht, Κ., Fleischer, D., Kane, Α . , Rentsch, C . , Tran Thi, Q.V., Yamaguchi, Η., Schulz, R.C., Makromol. Chem. (1977), 178. 881. 48) Albrecht, Κ., Fleischer, D., Rentsch, C.,Yamaguchi, Η., Schulz, R.C., Makromol. Chem., in press. 49) Burg, K.H., Hermann, H.D., Rehling, Η., Makromol. Chem. (1968), 111, 181.

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50) Rentsch, C . , Lectured at the Annual Assembly of Schweizerische Chemische Gesellschaft, Geneva, Oct. 1976. 51) Rentsch, C . , Schulz, R.C., Makromol. Chem., In press. 52) Cooper, J., Plesch, P.H., JCS., Chem. Commun. 1974. 1018. 53) Plesch, P.H.,Brit. Polym. J. (1973), 5, 1. 54) Matyjaszevski, K . . Penczek, S., J. Polym. S c i . , Polym. Chem. Ed. (1974), 12, 1905. 55) Semlyen, J.A., Advan. Polym. Sci. (1976), 21, 41. 56) Goethals, E.J., Advan. Polym. Sci. (1977), 23,103. 57) Höcker, H . , Reimann, W., Riebel, Κ., Szentivanyi, Z . , Makromol. Chem. (1976), 177. 1707. 58) U.S. Pat. 3 563 955; C.A (1967) 66 116143 r 59) Kane, Α . , unpublishe 60) Krespan, C.G., J. Org (1974), 39, 61) Albrecht, Κ., unpublished results, Mainz, 1977. 62) Tran Thi, Q.V., unpublished results, Mainz, 1977.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

7 Macrocyclic Formals YUYA YAMASHITA and YUHSUKE KAWAKAMI Department of Synthetic Chemistry, Faculty of Engineering, Nagoya University, Nagoya 464, Japan

Recent development of the chemistry of crown ethers pioneered by Pedersen (1) brought new interest to the old work of Carothers (2) on polymerization and ring formation. It is well recognized that cyclic oligomers are often formed during polymerization, and the development of high speed liquid chromatography made i t possible to obtain quantitative data on cyclic oligomers. Semlyen (3) studied on thermodynamic equilibrium of cyclic oligomers by using the Jacobson-Stockmayer theory (4). We noticed that considerable amounts of cyclic oligomers were often formed during ring-opening polymerization. This is essentially due to the fact that the elementary reaction in ringopening polymerization of cyclic compound containing heteroatom is nucleophilic substitution reaction and because the reactivity of the heteroatom in the polymer is not so different from the monomer, they compete with monomer for reaction with the propagating species causing backbiting reactions to form cyclic oligomers. We have been interested in the cationic polymerization of cyclic formals (5,6). We have synthesized macro-cyclic formals which have ether oxygen along with acetal oxygen, and found that the cationic polymerization of these monomers is accompanied with cyclic oligomers, which seems very interesting from kinetic and thermodynamic point of view. Besides, the chelating properties of these monomers and cyclic oligomers are also interesting. Results and Discussion Syntheses of Macrocyclic Formais. Quantitative yields of linear prepolymers having molecular weight of several thousands were obtained by refluxing poly99 In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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e t h y l e n e g l y c o l s w i t h p a r a f o r m a l d e h y d e i n benzene s o l u ­ t i o n by u s i n g p - t o l u e n e s u l f o n i c a c i d as c a t a l y s t and by c o n t i n u o u s removal o f water formed. A f t e r d i s t i l l ­ i n g o f f the s o l v e n t , thermal d e c o m p o s i t i o n o f the p r e polymers was c a r r i e d out by h e a t i n g w i t h o u t removing the c a t a l y s t on an o i l b a t h kept a t a p p r o p r i a t e tem­ perature. M a c r o c y c l i c f o r m a i s formed by d e p o l y m e r i z a t i o n were d i s t i l l e d under reduced p r e s s u r e . In case of t r i e t h y l e n e g l y c o l and t e t r a e t h y l e n e g l y c o l , y i e l d s o f more than 80% o f c y c l i c f o r m a i s are o b t a i n e d a t the b a t h temperature o f 2 5 0 ° C S m a l l amounts o f c y c l i c f o r m a i s c o n s i s t i n g o f s m a l l e r r i n g s are c o n t a m i n a t e d i n the d i s t i l l a t e . T h i s i s e x p r e s s e d i n the f o l l o w i n g scheme ( F i g u r e 1 ) . A l t h o u g h f a i r l y h i g h y i e l d o f c y c l i c formais i s obtained with p e n t a e t h y l e n e g l y c o l i t becomes d i f f i c u l from h e x a e t h y l e n e g l y c o o f l a r g e amounts o f c y c l i c f o r m a i s c o n s i s t i n g o f smaller rings. In the f o l l o w i n g , we use the abbre­ v i a t e d name such as l l - C F - 4 to express e l e v e n membered c y c l i c f o r m a l c o n t a i n i n g f o u r oxygen atoms. P r o p e r t i e s of M a c r o c y c l i c Formais. Macrocyclic f o r m a i s are h y g r o s c o p i c l i q u i d s and are s o l u b l e i n o r d i n a r y o r g a n i c s o l v e n t s and water. A l t h o u g h they are e a s i l y h y d r o l y z e d i n a c i d i c s o l u t i o n , they are f a i r l y s t a b l e i n b a s i c s o l u t i o n , and can be used as a c c e l e r a t i n g agents i n n u c l e o p h i l i c s y n t h e t i c r e a c ­ tions. We compared the r a t e o f an Sjyj2 r e a c t i o n between η-butyl bromide and a l k a l i m e t a l a c e t a t e a c c e l e r a t e d by a d d i t i o n o f equimolar amounts o f m a c r o c y c l i c f o r m a i s . nBuBr

+

CHjCOOM

> nBuOCOCH

3

+

MBr

T y p i c a l r e s u l t s are shown i n F i g u r e 2. It i s clear t h a t these c y c l i c f o r m a i s are l e s s e f f e c t i v e on the r a t e enhancement o f Sjsj2 r e a c t i o n compared w i t h crown ethers. I t was a l s o shown t h a t the e q u i l i b r i u m con­ s t a n t o f c h e l a t e f o r m a t i o n was s m a l l e r f o r these c y c l i c f o r m a i s than crown e t h e r s which have same number o f oxygen atoms. T h i s might be caused by the l e s s b a s i c a c e t a l oxygen atoms compared w i t h e t h e r oxygen atoms and by the n o n p l a n a r i t y o f the c h e l a t e complex o f c y c l i c f o r m a i s . C a t i o n i c Polymerization of l l - C F - 4 . Cationic p o l y m e r i z a t i o n o f l l - C F - 4 was c a r r i e d out w i t h boron t r i f l u o r i d e e t h e r complex i n d i c h l o r o m e t h a n e . The p r o g r e s s o f the r e a c t i o n was m o n i t o r e d by gas chromato­ graphy and l i q u i d chromatography by u s i n g n - t e t r a d e c a n e as an i n t e r n a l s t a n d a r d . In F i g u r e 3 i s shown the

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

7.

Y A M A S H I T A A N D KAWAKAMi

I

1 1

+ CH 0

> -O-C-0 -H 0 I

9

0

0-H

Macrocyclic

1

9

Formah

0

!

0

L

101

O-C--£-H

Jff

k

0

ο

> 7

ll-CF-4 Figure 1.

Synthesis of macrocyclic formah

18-CR-6(K)

20 time(hrs)

Figure 2. Rate enhancement by addition of macrocyclic formah. riBuBr, 0.01 mol; alkali metal acetate, 0.01 mol; benzene, 9 ml; toluene, 1 ml; chelating agent, 0.01 mol. Temperature, 90°C (reflux).

100r

50

100

200

Figure 3. Time-conversion curve in the polymerization of ll-CF-4. 0°C in dichioromethane; [ll-CF-4] = 3.25 X lO'M, [BF · EUO] = 1.38 X 10' M. 3

time(min)

2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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t i m e - c o n v e r s i o n r e l a t i o n s h i p determined by gas chromatography. I t i s s u g g e s t e d t h a t t h e r e are two s t a g e s i n monomer consumption. L i q u i d chromatograms are shown i n F i g u r e 4. I t i s c l e a r t h a t t h e r e are two s t a g e s i n the p o l y m e r i z a t i o n . The f i r s t stage i s a r e a c t i o n i n which o l i g o m e r s are formed and the second stage i s a one i n which polymers are formed. The m o l e c u l a r weight o f polymers formed i n the second stage i s about 20 χ 10* and does not change w i t h con­ version. Only the amount o f polymers i n c r e a s e w i t h r e a c t i o n time. The o l i g o m e r s formed i n the f i r s t stage were s e p a r a t e d ana i d e n t i f i e d as c y c l i c . The p o l y m e r i z a t i o n m i x t u r e was t e r m i n a t e d w i t h t r i e t h y l amine, and a f t e r e v a p o r a t i o n , the s t i c k y mass was e x t r a c t e d w i t h benzene-hexane mixed s o l v e n t . The e x t r a c t e d oligomer mixtur r e c r y s t a l l i z e d to y i e l i d e n t i f i e d as c y c l i c dimer o f l l - C F - 4 from mass, i r and nmr s p e c t r a . T h i s dimer c o r r e s p o n d s to peak A i n F i g u r e 4. The o l i g o m e r s B, C and D i n F i g u r e 4 were s e p a r a t e d by p r e p a r a t i v e l i q u i d chromatography and i d e n t i f i e d i n a s i m i l a r manner as c y c l i c t r i m e r , t e t r a m e r and pentamer o f l l - C F - 4 . The m e l t i n g p o i n t o f these c y c l i c compounds a l t e r n a t e r e g u l a r l y : 24°C f o r monomer, 85°C f o r dimer, l i q u i d f o r t r i m e r , 53°C f o r t e t r a m e r , l i q u i d f o r pentamer. There are some h i g h e r m o l e c u l a r weight o l i g o m e r s which can be sup­ posed t o be c y c l i c , were not i d e n t i f i e d . Because the polymers are h y g r o s c o p i c , i t i s d i f f i c u l t t o determine i f the polymers have t e r m i n a l , g r o u p o r n o t . The c o n c e n t r a t i o n o f each o l i g o m e r s seem t o r e a c h e q u i l i b r i u m s h o r t l y a f t e r the f i r s t stage and does not change d u r i n g the p o l y m e r i z a t i o n . The e q u i l i b r i u m c o n c e n t r a t i o n o f c y c l i c dimer i s 1.5 χ 10"2 mol/1 and the e q u i l i b r i u m c o n c e n t r a t i o n o f c y c l i c o l i g o m e r s h a v i n g h i g h e r membered r i n g s d e c r e a s e s w i t h the i n c r e a s e o f the number o f r i n g atoms. T h i s t r e n d i s c o n s i s t e n t w i t h the Jacobson-Stockmayer t h e o r y ( 4 ) , which t e l l s us t h a t the d e c r e a s e o f the e q u i l i b r i u m weight c o n c e n t r a t i o n o f c y c l i c o l i g o m e r s depends on the -1.5 power o f the degree o f o l i g o m e r i z a t i o n . The e q u i l i b r i u m monomer c o n c e n t r a t i o n o f l l - C F - 4 was determined as 1.33 χ 1 0 " mol/1 a t 0°C from p o l y m e r i z a ­ t i o n o f monomer and from d e p o l y m e r i z a t i o n o f polymer. By changing the p o l y m e r i z a t i o n temperature from -20°C to 30°C, thermodynamic parameters f o r the p o l y m e r i z a ­ t i o n o f l l - C F - 4 were determined by p l o t t i n g the l o g ­ a r i t h m s o f the e q u i l i b r i u m monomer c o n c e n t r a t i o n a g a i n s t r e c i p r o c a l temperature to f i t the D a i n t o n ' s equation ( 7 ) . ο ln[M] = — ^ ss RT R 2

a

H

a

S

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

7.

Y A M A S H I T A A N D KAWAKAMi

Macrocyclic

Formais

103

The o b t a i n e d v a l u e i s Δ Η „ = - 2 . 2 ± 0 . 3 k c a l / m o l , and S ° = 0 . 7 + 1 . 1 e.u. i n d i c h l o r o m e t h a n e . The heat o f p o l y m e r i z a t i o n o f c y c l i c f o r m a i s changes from 3.6 k c a l / mol f o r f i v e membered r i n g , 5.3 k c a l / m o l f o r e i g h t membered r i n g and here t o 2.2 k c a l / m o l f o r e l e v e n mem­ b e r e d r i n g , and seem t o become z e r o f o r l a r g e membered r i n g as e x p e c t e d . T h i s i s shown i n F i g u r e 5. The e n t r o p y o f p o l y m e r i z a t i o n o f c y c l i c f o r m a i s changes from -14 e.u. f o r f i v e membered r i n g , -9.3 e.u. f o r e i g h t membered r i n g and here t o +0.7 e.u. f o r e l e v e n membered r i n g . Although the i n c r e a s i n g trend i s s m a l l e r than e x p e c t e d , t h e d r i v i n g f o r c e f o r t h e p o l y ­ m e r i z a t i o n o f m a c r o c y c l i c f o r m a i s seems t o depend upon the d e c r e a s e d e n t r o p y o f l a r g e r i n g s f o r combining t h e f r e e c h a i n ends. The e f f e c t o f stage p o l y m e r i z a t i o e f f e c t o f changing s o l v e n t s on t i m e - c o n v e r s i o n c u r v e i n c a t i o n i c p o l y m e r i z a t i o n w i t h boron t r i f l u o r i d e e t h e r a t e i s shown i n F i g u r e 6. The r a t e o f monomer consumption was a f f e c t e d v e r y much by t h e n a t u r e o f solvents. The r e a c t i o n i n n i t r o m e t h a n e i s almost i n s t a n e o u s , and t h a t i n dioxane i s v e r y slow. However, the p r o d u c t d i s t r i b u t i o n i s more o r l e s s t h e same com­ p a r e d w i t h t h a t i n d i c h l o r o m e t h a n e and t h e p o l y m e r i z a ­ t i o n proceeds i n two s t a g e s , f o r m i n g c y c l i c o l i g o m e r s at t h e f i r s t s t a g e and polymers a t t h e second s t a g e . The e f f e c t s o f i n i t i a t o r s were a l s o s t u d i e d . The r a t e by t r i f l u o r o m e t h a n e s u l f o n i c a c i d i s v e r y f a s t compared w i t h t h e r a t e by boron t r i f l u o r i d e e t h e r a t e , s t a n n i c c h l o r i d e o r t u n g s t e n h e x a c h l o r i d e . A g a i n t h e two s t a g e n a t u r e i s s i m i l a r i n e v e r y i n i t i a t o r systems showing t h e same p r o d u c t d i s t r i b u t i o n i n l i q u i d c h r o matogram. Thus, i t c a n be c o n c l u d e d t h a t t h e two stage n a t u r e o f t h e p o l y m e r i z a t i o n o f l l - C F - 4 forming c y c l i c o l i g o m e r s a t t h e f i r s t stage and h i g h polymers at t h e second s t a g e seems t o be q u i t e g e n e r a l phe­ nomena.

A

S S

Mechanism o f C a t i o n i c P o l y m e r i z a t i o n o f l l - C F - 4 . S e v e r a l mechanisms a r e p r o p o s e d f o r t h e c a t i o n i c p o l y merization o f 1,3-dioxacycloacycloalkanes. 1) The growing s p e c i e s a r e t r i a l k y l o x o n i u m i o n and t h e c h a i n p r o p a g a t i o n proceeds through an S^2 mechanism. 2) The growing s p e c i e s a r e c a r b o c a t i o n and t h e c h a i n propaga­ t i o n proceeds by an S ^ l r e a c t i o n o f t h e i n t e r m e d i a t e oxonium i o n . 3) The growing s p e c i e s a r e m a c r o c y c l i c d i a l k y l o x o n i u m i o n and t h e p r o p a g a t i o n r e a c t i o n f o l ­ lows r i n g - e x p a n s i o n mechanism through f o u r c e n t e r reaction. 4) The growing s p e c i e s a r e l i n e a r t r i a l k y l ­ oxonium i o n formed by t h e r e a c t i o n o f t h e growing

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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I.S.

60min Figure 4. Liquid chromatogram of the polymerization mixture of 11-CF4. 0°C in dichhromethane; [U-CF4] = 3.25 X JO'M, [BF · Et 0] = 1.38χΐΟ- Μ. 3

200min. — 1 1

1

1

2

35

2

1 1

1

•• 30

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1

•t• •ιιιι • t 25 20 15

counts

•10

Figure 5. Heat of polymerization of cyclic ethers and formah as a function of ring number. (1) Oxirane, (2) oxetane, (3) tetrahydrofuran, (4) 1,3-dioxolane, (5) tetrahydrofuran, (6) 1,3-dioxepane, (7) 8-CF-3, (8) ll-CF-4.

-20

Figure 6. Time-conversion curve in the polymerization of ll-CF-4 in various sol­ vents 0°C. [ll-CF-4] = 3.25 X lO'M, [BF · Et 0] = 1.38 X 10 U. (a) Nitromethane, (b) acetonitrile, (c) dichloromethane (d) dimethoxy ethane, (e) dioxane. 3

2

9

2

6 ring

0

8 number

120

10

240

time(min)

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

7.

Y A M A S H I T A A N D KAWAKAMi

Macrocyclic

Formais

105

c h a i n end w i t h an oxygen atom o f a polymer c h a i n . Our o b s e r v a t i o n o f t h e f o r m a t i o n o f c y c l i c o l i g o m e r s might seem t o f a v o r t h e r i n g - e x p a n s i o n mechanism p r o p o s e d by P l e s c h ( 8 ) . However d i r e c t o b s e r v a t i o n o f t h e growing s p e c i e s F y nmr p r o v e d the e x i s t e n c e o f a c a r b o c a t i o n ( 9 ) , and e q u i l i b r i u m between oxonium i o n and c a r b o c a tTon was assumed t o e x p l a i n the p o l y m e r i z a t i o n behavi o r o f b i c y c l i c f o r m a l Ç10). A n o t h e r p o s s i b i l i t y i s t h a t t h e c y c l i c o l i g o m e r s are more r e a c t i v e than t h e monomer and might be t h e r e a c t i v e i n t e r m e d i a t e . This p o s t u l a t e i s d e n i e d by t h e f a c t t h a t t h e c y c l i c o l i g o m e r s are n o t so r e a c t i v e . To c l a r i f y the n a t u r e o f the p r o p a g a t i n g s p e c i e s d u r i n g t h e f i r s t and the second s t a g e , t h e f o l l o w i n g experiments were c a r r i e d out First c a t i o n i c copoly merization o f styren t r i f l u o r i d e etherat o f the p r o p a g a t i n g s p e c i e s . The change o f the concent r a t i o n o f each component was f o l l o w e d by gas chromatography and l i q u i d chromatography, and shown i n F i g u r e 7. S t y r e n e i s consumed o n l y a t t h e second s t a g e , where t h e c o n c e n t r a t i o n o f t h e o l i g o m e r s has r e a c h e d to e q u i l i b r i u m v a l u e , and i t i s i n c o r p o r a t e d as a r a n dom copolymer w i t h l l - C F - 4 , and i t i s n o t i n c o r p o r a t e d i n c y c l i c o l i g o m e r s formed a t t h e f i r s t s t a g e . The randomness o f the copolymer was p r o v e d by f r a c t i o n a l r e p r e c i p i t a t i o n from benzene i n t o methanol o r i n t o e t h e r and a n a l y z e d by l i q u i d chromatography and nmr. There were n o t any c o - o l i g o m e r s d e t e c t e d i n the f i r s t s t a g e , a l t h o u g h s m a l l amount o f s t y r e n e seems t o be i n c o r p o r a t e d i n o l i g o m e r s formed a t t h e second s t a g e . Thus t h e a c t i v e s p e c i e s i n the second stage seems t o be c a r b o c a t i o n i c i n n a t u r e and are r e s p o n s i b l e f o r t h e h i g h p o l y m e r i z a t i o n o f l l - C F - 4 and the c o p o l y m e r i z a t i o n with styrene. The mechanism o f t h e o l i g o m e r f o r m a t i o n was s t u d i e d by d i f f e r e n t e x p e r i m e n t s . The i s o l a t e d h i g h p o l y mers were d e p o l y m e r i z e d w i t h boron t r i f l u o r i d e etherate i n dichloromethane. From the chromatogram shown i n F i g u r e 8 , i t i s c l e a r t h a t t h e same d i s t r i b u t i o n o f c y c l i c o l i g o m e r s were found by d e p o l y m e r i z a t i o n and r e a c h e d t o t h e same e q u i l i b r i u m c o n c e n t r a t i o n . To e s t a b l i s h the mechanism o f t h e f o r m a t i o n o f c y c l i c o l i g o m e r s by b a c k b b i t i n g r e a c t i o n , p o l y m e r i z a t i o n o f c y c l i c dimer o f l l - C F - 4 i s o l a t e d from the p o l y m e r i z a t i o n m i x t u r e was s t u d i e d . The chromatogram i n F i g u r e 8 shows t h a t every c y c l i c o l i g o m e r s e x i s t e d i n t h e same d i s t r i b u t i o n as from the p o l y m e r i z a t i o n o f 11-CF4 and from the d e p o l y m e r i z a t i o n . This denies the f o r m a t i o n o f c y c l i c o l i g o m e r s by r i n g - e x p a n s i o n mechanism, because t h e f o r m a t i o n o f 33 and 55 membered r i n g s i s d i f f i c u l t t o e x p l a i n s t a r t i n g from 22 membered r i n g .

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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Thus the f o r m a t i o n o f c y c l i c o l i g o m e r s i s presumed to o c c u r through the b a c k - b i t i n g r e a c t i o n o f the oxonium i o n e x i s t e d d u r i n g the f i r s t s t a g e . The n a t u r e o f the a c t i v e s p e c i e s p r e s e n t a t the f i r s t stage i s d i f f e r e n t from c a r b o c a t i o n because c o p o l y m e r i z a t i o n o f s t y r e n e d i d not o c c u r r e d , and more s t a b l e s p e c i e s such as oxonium i o n b a c k - b i t e s e a s i e r than propagates to h i g h polymer. At p r e s e n t , we can o n l y s p e c u l a t e the n a t u r e o f the r e a c t i v e s p e c i e s . In the p o l y m e r i z a t i o n o f 11-CF4, oxonium i o n r e s p o n s i b l e f o r slow p r o p a g a t i o n and f a s t b a c k - b i t i n g r e a c t i o n i s formed a t the f i r s t s t a g e and o n l y c y c l i c o l i g o m e r s are formed. We n o t i c e d t h a t the i n d u c t i o n p e r i o d f o r h i g h polymer f o r m a t i o n i n the p o l y m e r i z a t i o n o f 1,3-dioxolane d e c r e a s e d by d e c r e a s i n g the c o n t e n t of p o l y m e r i z a t i o n of l l - C F - 4 the f i r s t stage was r e t a r d e d by a d d i t i o n o f water or methanol, and a l s o cause to d e l a y the i n i t i a t i o n o f the second s t a g e . However the r a t e o f the f o r m a t i o n o f h i g h polymers a t the second stage was not r e t a r d e d by a d d i t i o n o f methanol. The c a r b o c a t i o n seems to be more s t a b l e toward methanol. I t i s formed o n l y s l o w l y from the oxonium i o n and s t a r t s t o produce h i g h p o l y mers a t the second s t a g e . Two Stage P o l y m e r i z a t i o n o f 1 , 3 - p i o x a c y c l o a l k a n e s . In o r d e r t o e s t a b l i s h the two stage c h a r a c t e r o f the p o l y m e r i z a t i o n o f 1 , 3 - d i o x a c y c l o a l k a n e s , the p o l y m e r i z a t i o n o f v a r i o u s c y c l i c f o r m a i s were s t u d i e d u s i n g boron t r i f l u o r i d e e t h e r complex as an i n i t i a t o r a t 0°C i n dichloromethane. The p o l y m e r i z a t i o n were found to p r o c e e d i n two s t a g e s i n every c a s e . The s e l e c t e d monomers were 1 , 3 - d i o x o l a n e , 1,3-dioxacyclooctane, ( d i o x e p a n e ) , 1 , 3 , 6 - t r i o x a c y c l o o c t a n e ( t r i o x o c a n e ) , 8CF-3, 1 , 3 , 6 , 9 , 1 2 - p e n t a o x a - c y c l o t e t r a d e c a n e 14-CF-5, and 1,3,6,9,12,15-hexaoxa-eyeloheptadecane 17-CF-6 besides l l - C F - 4 . T i m e - c o n v e r s i o n c u r v e s are shown i n F i g u r e 9, showing the e x i s t e n c e o f two s t a g e s . The r a t e o f the f o r m a t i o n o f o l i g o m e r s a t the f i r s t s t a g e was a f f e c t e d v e r y much by the amount o f contaminated water i n the system. C o n t r a r y to t h i s , the r a t e o f f o r m a t i o n o f h i g h polymers were s c a r c e l y a f f e c t e d by the amount o f water. Thus the o r d e r o f the r e a c t i o n r a t e i n F i g u r e 9 may not be the t r u e o r d e r o f the r e a c t i o n r a t e because the amount o f contaminated water i n each monomer i s not n e c e s s a r i l y the same. The l i q u i d chromatogram o f the t y p i c a l r e a c t i o n system, the case o f 1 , 3 - d i o x a c y c l o o c t a n e , i s shown i n F i g u r e 10, where the f o r m a t i o n o f o l i g o m e r s a t the f i r s t s t a g e r e a c h i n g e q u i l i b r i u m and the c o n t i n u o u s format i o n o f h i g h polymers a t the second s t a g e w i t h o u t i n c r e a s i n g the m o l e c u l a r weight i s o b s e r v e d . Some o f

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

7.

Y A M A S H I T A A N D KAWAKAMi

Macrocyclic

Formah

107

ll-CF-4 polymer 5 1 1 units)

styrene

dimer 120

240 time (mm)

Figure 7. Time-conversion curve for the copolymerization of ll-CF-4 with 3.81 χ JO'M, /"SfJ = 3.70 X I0- M.

Figure 9. Time-conversion curve for the polymerization of 1,3-dioxacycloalkanes, 0°C in dichloromethane by BF · Et O. [BF · Et 0] = 1.20 X 10~ M. (a) [1,3-dioxolane] = 3.77M; (b) [1,3-dioxacyclooctane] = 5.0 X JO'M; (c) [8-CF-3] = 5.29 X 10->M; (d) [ll-CF-4] = 4.40 χ ΙΟ'Μ; (e) [14-CF-5] = 5.29 Χ ΙΟ'Μ; (f) [17CF-6] = 6.33 X 10-tM. S

t

S

2

2

120

240 time(min)

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

108

RING-OPENING

POLYMERIZATION

60min

120min

180min Figure 10. Liquid chromatogram the polymerization of 1,3-dioxacyclo­ octane. 0°C in dichloromethane; [BF . Et 0] = 1.20 X 10 M, [1,3-dioxa< cyclooctane] = 5.0 Χ ΙΟ M.

A _

o f

3

2

2

1

· 45

• 40

— 30

1

— 25

1

35

L

counts First

Stage R

/ Y. \ j°

BF--Et 0 5 1

n

C H

?

+

•

~0-R-OCH 0 < ?

2 [I]

[M] +

~0-R-OCH 0 <

»

2

+

-0-R-OCH 0-R-OCH 0-R-OCH 0 < 2

2

2

slow fast

+

-0-R-0CH 0 CH, Ο 7

Z

0 CH, Ο

I V R /

-0-R-OCH,0 <

+

z

0

0

CH,

CH,

Ο

Ο

Δ

Second Stage +

~0-R-0CH 0 < * 7

Π] Figure 11.

• -vO-R-OCH* -iL>~0-R-0CH 0-R-0CH* slow fast ^ 9

Δ

z

III] Mechanism of cationic polymerization of cyclic formals

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Δ

7.

Y A M A S H I T A A N D KAWAKAMi

Macrocyclic

Formais

the o l i g o m e r s were i s o l a t e d and i d e n t i f i e d t o be cyclic. The f o r m a t i o n o f c y c l i c o l i g o m e r s i n the c a t i o n i c p o l y m e r i z a t i o n o f c y c l i c f o r m a i s was r e p o r t e d by s e v e r a l a u t h o r s (11)(12)Ç13). The e x i s t e n c e o f these c y c l i c o l i g o m e r s i s oTifen c l a i m e d t o be e x p l a i n e d by r i n g - e x p a n s i o n mechanism ( 8 ) . However, o u r o b s e r v a t i o n t h a t c y c l i c o l i g o m e r s a r e formed a t d i f f e r e n t stage from n i g h polymer f o r m a t i o n suggests t h e e x i s t ence o f s e v e r a l s p e c i e s . T e n t a t i v e schemes a r e shown i n F i g u r e 11. Oxonium i o n [I] r e s p o n s i b l e f o r t h e c y c l i c o l i g o m e r f o r m a t i o n propagates s l o w l y and backb i t e s f a s t a t the f i r s t stage. Carbocation [II] s l o w l y formed a t t h e second stage propagates f a s t t o Experimental Monomers: M a c r o c y c l i c f o r m a i s was s y n t h e s i z e d from f r a c t i o n a l l y d i s t i l l e d p o l y e t h y l e n e g l y c o l and p a r a f o r m a l d e h y d e u s i n g p - t o l u e n e s u l f o n i c a c i d as c a t a l y s t by t h e s i m i l a r method i n the l i t e r a t u r e (14). They were p u r i f i e d and d r i e d by d i s t i l l a t i o n over l i t h i u m aluminum h y d r i d e f o r f o u r t i m e s . The p u r i t y was checked by gas chromatography. Rate measurement o f S^j2 r e a c t i o n : 0.01 Mol o f a l k a l i m e t a l a c e t a t e was mixed w i t h 0.01 mol o f nb u t y l bromide i n a m i x t u r e o f 9 ml o f benzene and 1 ml of toluene. 0.01 M o l o f c y c l i c f o r m a i s o r crown e t h e r s was added and s t i r r e d under r e f l u x a t 9 0 ° C The consumption o f η-butyl bromide and the f o r m a t i o n o f η-butyl a c e t a t e was f o l l o w e d by gas chromatography o f the p u l l e d out samples by u s i n g t o l u e n e as an i n t e r n a l standard. P o l y m e r i z a t i o n was c a r r i e d o u t under n i t r o g e n by u s i n g n - t e t r a d e c a n e as an i n t e r n a l s t a n d a r d f o r c h r o ­ matography. The r e a c t i o n was m o n i t o r e d by gas c h r o ­ matography and l i q u i d chromatography (Toyo Soda h i g h speed l i q u i d chromatograph model HLC 802 UR) on t h e p u l l e d out sample from the r e a c t i o n system w i t h s y r ­ inge a f t e r k i l l i n g w i t h t r i e t h y l a m i n e . The s e p a r a t i o n and i d e n t i f i c a t i o n o f o l i g o m e r s were c a r r i e d o u t as f o l l o w s . The p o l y m e r i z a t i o n mix­ t u r e was e v a p o r a t e d a f t e r k i l l i n g . The s t i c k y mass was e x t r a c t e d by benzene-hexane mixed s o l v e n t and t h e e x t r a c t was e v a p o r a t e d and r e c r y s t a l l i z e d t o g i v e nee­ dle c r y s t a l s . T h i s was i d e n t i f i e d by mass, i r and nmr spectra. P a r e n t peak i n mass s p e c t r a i s most impor­ t a n t f o r t h e i d e n t i f i c a t i o n t o g e t h e r w i t h nmr s p e c t r a showing c o r r e s p o n d i n g a c e t a l peak a r e a . The m e l t i n g p o i n t o f c y c l i c dimer o f 1 , 3 - d i o x o l a n e , 1,3,6-trioxocane and l l - C F - 4 was 67°C, 55°C and 85°C, r e s p e c t i v e l y .

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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RING-OPENING

POLYMERIZATION

Literature Cited ( 1) C. J. Pedersen, H. K. Frensdorff, Angew. Chem. Internat. Ed., (1972) 11, 16 ( 2) H. Mark, G. S. Whitby ed. "Collected Papers of W. H. Carothers on High Polymeric Substances", Wiley-Interscience, New York, (1940) ( 3) J. A. Semlyen, Advances in Polymer S c i . , (1976) 21, 41 ( 4) HT Jacobson, W. Stockmayer, J. Chem. Phys., (1950), 18, 1600 ( 5) Y. Yamashita, M. Okada, H. Kasahara, Makromol. Chem., (1968), 117, 242 ( 6) M. Okada, S. Kozawa, Y. Yamashita, Makromol. Chem., (1969), 127, 66 ( 7) Y. Yamashita, Makromol. Chem. ( 8) Y. Firat, F. R. Jones, Ρ. H. Plesch, P. H. Westerman, Makromol. Chem., (1975), S-1, 203 ( 9) Y. Yokoyama, M. Okada, H. Sumitomo, Makromol. Chem., (1975), 176, 795 ( 10) M. Okada, H. Sumitomo, Y. Hibino, Polymer J., (1974), 6, 256 ( 11) J. M. Andrews, J. A. Semlyen, Polymer, (1972) 13, 142 ( 12) P. E. Black, D. J. Worsfold, J. Macromol. Sci. Chem. (1975) A 9, 1523 13) J. W. Hill, W. H. Carothers, J. Am. Chem. Soc., (1935), 57, 925 ( 14) M. J. Astle, J. A. Zaslowsky, P. G. Lafyatis, Ind. Eng. Chem., (1954), 46, 787

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8 Stereoregularity as a Function of Side Chain Size in Perhaloacetaldehyde Polymerization D. W. LIPP and O. V O G L Polymer Science and Engineering, University of Massachusetts, Amherst, MA 01003 and C.N.R.S., Centre de Recherches sur les Macromolécules, Université Louis Pasteur, Strasbourg, France

Aldehyde polymerization publicized than olefi polymerization, provide very important contribution to almost a l l aspects of polymerization reactions. (1,2) It constitutes an alternative to the olefin polymerization, and because of the heteroatom in the main polymer chain, it also provides a link to ring opening polymerization and the preparation of polyesters and polyamides. Aldehyde polymers have also been important for the understanding of polymer stability, the recognition of the importance of end groups for polymer stability, reaction on polymers by end capping and the limitation of thermal and acidolytic stability of polyacetal chains. (3) Higher aliphatic aldehydes polymerize readily to isotactic polymers when proper attention is paid to the low ceiling temperature of these polymerizations. The formation of isotactic polymers is apparently favored as the side chain length of these aldehydes increases. A l l isotactic polyaldehydes, whose crystal structure has been determined, crystallize in a 4i helix, and when their melting behavior was studied, a dual melting point was observed. Isotactic polymers of higher aldehydes with aliphatic side chains of chain lengths between and Cjq have a melting point indicative for the melting of the paraffin side chain and at higher temperature the melting of the backbone may be observed. It is believed that these isotactic polymers of aldehydes with longer aliphatic side chains crystallize as microphase separated, polymer systems : The aliphatic side chains crystallize in the hexagonal paraffin structure and the more polar polyacetal main chains crystallize separately. At shorter side chains (up to C3), only the main chains and at longer side 111 In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

112

RING-OPENING

POLYMERIZATION

c h a i n s ( l o n g e r t h a n CJQ) o n l y the s i d e c h a i n s c o n t r i ­ b u t e to the c r y s t a l l i z a t i o n of the i s o t a c t i c p o l y aldehydes .(4-6). H a l o a l d e h y d e p o l y m e r i z a t i o n p r o v i d e s a new and q u i t e d i f f e r e n t a p p r o a c h f o r the study of the polyme­ r i z a t i o n b e h a v i o r o f a l d e h y d e s . The p r o p e r t i e s o f p e r haloaldehyde polymers are a l s o s u b s t a n t i a l l y d i f f e r e n t f r o m t h o s e of p o l y f o r m a l d e h y d e or of h i g h e r a l i p h a t i c p o l y a l d e h y d e s . We a r e d i s c u s s i n g h e r e t h e r e s u l t s o f o u r w o r k on t h e p r e p a r a t i o n and p o l y m e r i z a t i o n o f n i n e ( f l u o r o , c h l o r o , and b r o m o s u b s t i t u t e d ) perhaloacetald e h y d e s w i t h s p e c i a l e m p h a s i s on t h e s t e r e o r e g u l a r i t y o f t h e p o l m e r s o b t a i n e d . (JO I t has e a r l i e o n l y be p o l y m e r i z e d t i c p o l y m e r , no s o l u b l e f r a c t i o n , e v e n o f l o w m o l e c u l a r w e i g h t , has e v e r b e e n o b s e r v e d . (_8) F l u o r a l has b e e n known t o e x i s t a l s o i n a s o l u b l e f o r m . ( 9 ) I t h a s become v e r y d e s i r a b l e t o e s t a b l i s h c l e a r l y t h e s p a c e f i l l i n g s i z e of t r i h a l o m e t h y 1 s u s t i t u e n t of the p e r ­ h a l o a c e t a l d e h y d e ( w h i c h a f t e r p o l y m e r i z a t i o n becomes the s i d e group of the p o l y a c e t a l c h a i n ) t h a t i s n e c e s s a r y t o f o r m i s o t a c t i c p o l y m e r and isotactic polymer only. A l d e h y d e s , b o t h a l i p h a t i c and perhaloacetaldehy^ des p o l y m e r i z e by c a t i o n i c and a n i o n i c m e c h a n i s m s ( E q n . 1 ) , and a l l t h e v a r i o u s i n t i a t o r s w e r e i n v e s t i ­ g a t e d i n t h i s work. F l u o r a l has been r e p o r t e d t o have a l s o b e e n p o l y m e r i z e d by r a d i c a l i n i t i a t o r s ( 1 0 ) . S i n c e o u r p o l y m e r i z a t i o n s c o u l d be r e a d i l y a c c o m p l i s h e d w i t h w e l l e s t a b l i s h e d i n i t i a t o r s , i t was n o t f o u n d n e c e s ­ s a r y t o s t u d y o t h e r p o s s i b l e ways o f i n i t i a t i o n . Polymerization

ι

η C=0

Mechanism

of

Aldehydes

>

: Anionic Cationic

—(-C-0—)— I η

Eqn.1

Higher a l i p h a t i c aldehydes with e l e c t r o d o n a t i n g p a r a f f i n s i d e group are e x p e c t e d to have a r e l a t i v e

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8.

Lipp A N D V O G L

Perhaloacetaldehyde

Polymerization

113

h i g h e r e l e c t r o n d e n s i t y on t h e c a r b o n y l oxygen atom w i t h e a s i e r a l k y l a t i o n p o s s i b i l i t i e s and, consequently, e a s i e r i n i t i a t i o n and p o l y m e r i z a t i o n by e l e c t r o p h i l i c means. P e r h a l o a c e t a l d e h y d e s w i t h t h e s t r o n g l y e l e c t r o n w i t h d r a h i n g s i d e group a r e r e l a t i v e l y e l e c t r o n poor on the c a r b o n y l oxygen w i t h e a s i e r i n i t i a t i o n by n u c l e o p h i l e s and b e t t e r p r o p a g a t i o n by t h e a l k o x i d e a n i o n s . T h i s g e n e r a l c o n s i d e r a t i o n has a c t u a l l y been o b s e r v e d . Strong e l e c t r o p h i l e s are necessary f o r the polymeriza­ t i o n o f p e r h a l o a c e t a l d e h y d e s , b u t r e l a t i v e l y weak nucleophiles are s u f f i c i e n t f o r the anionic polymeria t i o n o f t h e s e a l d e h y d e s . The p o l a r i z a t i o n o f t h e car-^ b o n y l d o u b l e bond

w i t h t h e p a r t i a l p o s i t i v e charge on t h e carbon and t h e p a r t i a l n e g a t i v e c h a r g e on t h e o x y g e n atom i s w e l l e s t a b l i s h e d . As a consequence, a n i o n i c p o l y m e r i z a t i o n i s u s u a l l y the p r e f e r r e d p o l y m e r i z a t i o n f o r p e r h a l o a l d e h y d e s . ( 1 1 ) ( E q n . 2) CCI. , 3 + C=0

CCI. j 3. »R — C — 0

|ci *

3

çci

CCI. t + ηC—0 3

3

R4-C—0->—C—0~

Eqn. 2

A n i o n i c a l l y polymerized perhaloacetaldehyde polymers p r e c i p i t a t e g e n e r a l l y as a g e l , a r e prepared at h i g h p o l y m e r i z a t i o n r a t e s and g i v e polymers which c a n n o t be end capped and have a p p a r e n t l y o c c l u d e d end groups w i t h a l k o x i d e c h a r a c t e r . ( 1 2 )

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

114

RING-OPENING POLYMERIZATION

Perhaloacetaldehyde polymers are of d i f f e r e n t p h y s i c a l a p p e a r a n c e , p o w d e r y , h a v e o f t e n -OH end g r o u p s and a r e o b t a i n e d a t a v e r y s l o w p o l y m e r i z a t i o n r a t e . The s u g g e s t e d m e c h a n i s m i s i n d i c a t e d i n E q n . 3 ( 1 3 ) Cationic

Polymerization

CCI.

J R

+

ι

0=€

CCI.

+i

3

%

R

R—(—o-

i °

cc CCI,

3

i

— 0 - C

CCI.

of C h l o r a l

*"1

CCI.

ι

A l d e h y d e p o l y m e r i z a t i o n s a r e c h a r a c t e r i z e d by t h e i r l o w c e i l i n g t e m p e r a t u r e and by t h e i r l o w h e a t o f p o l y m e r i z a t i o n . As a c o n s e q u e n c e , a l m o s t a l l a l d e h y d e p o l y m e r i z a t i o n s a r e c a r r i e d o u t a t l o w t e m p e r a t u r e s and b e c a u s e o f t h e d e p e n d e n c e o f t h e c e i l i n g t e m p e r a t u r e on t h e monomer c o n c e n t r a t i o n , when t h e c e i l i n g t e m p e r a t u r e is very low, the polymerizations are c a r r i e d out at h i g h monomer c e n t r a t i o n s o r i n b u l k . I t h a d a l s o b e e n r e c o g n i z e d t h a t t h e c e i l i n g t e m p e r a t u r e c o u l d be u t i l i ­ zed f o r t h e p r e p a r a t i o n o f s o l i d p i e c e s o f p o l y m e r s as e x e m p l i f i e d by t h e c l o r a i p o l y m e r i z a t i o n by u s i n g t h e technique of c r y o t a c h e n s i c polymerization.(I4) The s t u d y o f t h e p e r h a l o a c e t a l d e h y d e polymeriza­ t i o n p r o v i d e s an i d e a l example f o r t h e i n v e s t i g a t i o n of t h e p o l y m e r i z a b i l i t y o f t h e a l d e h y d e s , t h e r e l a t i o n ­ s h i p o f t h e p o l y m e r s t e r e o r e g u l a r i t y as a f u n c t i o n o f s u b s t i t u e n t s i z e and s h a p e . No u n u s u a l i n i t i a t o r s , s u c h a s t r a n s i t i o n m e t a l complexes o r h e t e r o g e n e o u s c a t a l y s t s , a r e needed f o r perhaloacetaldehyde polymerizations, thep o l a r i z a t i o n o f t h e c a r b o n y l g r o u p o f t h e a l d e h y d e monomer i s w e l l d e f i n e d and does n o t c a u s e t h e f o r m a t i o n o f head t o h e a d l i n k a g e s i n t h e p o l y m e r . The s h o r t e r c a r b o n o x y ­ gen s i n g l e b o n d ( 1 . 4 3 Â) w h i c h i s f o r m e d b y r i n g o p e n i n g o f t h e c a r b o n y l d o u b l e b o n d ( l . 2 l Â) h a s a b e n e f i c i a l e f f e c t f o r the formation of a h e l i c a l s t r u c ­ t u r e f o r t h e i s o t a c t i c p o l y m e r and s h o u l d , c o n s e q u e n ­ t l y , favor the formation of i s o t a c t i c polymer. the

I t was e x p e c t e d t h a t t h e b u l k i n e s s a s w e l l a s p o l a r i z a b i l i t y o f t h e i n d i v i d u a l atoms and t h e

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8. L I P P A N D V O G L

Perhaloacetaldehyde

Polymerization

115

whole p e r h a l o m e t h y l group o f t h e p e r h a l o a c e t h a l d e h y d e would i n f l u e n c e t h e p o l y m e r i z a b i l i t y and t o which d e ­ gree of s t e r e o s p e c i f i c i t y t h e p o l y m e r i z a t i o n of t h e i n d i v i d u a l p e r h a l o a c e t a l d e h y d e c o u l d be c a r r i e d o u t . The t y p e a n d c o m b i n a t i o n o f t h e h a l o g e n a t o m s i n t h e t r i h a l o m e t h y 1 g r o u p w o u l d a l s o be a d e t e r m i n i n g f a c t o r for the rate of p o l y m e r i z a t i o n of theperhaloacetalde­ hyde and f o r t h e l o c a t i o n o f t h e c e i l i n g temperature of p o l y m e r i z a t i o n . The d i a m e t e r o f t h e t r i h a l o m e t h y 1 s i d e g r o u p c a n be c a l c u l a t e d , a n d i s f o r t h e CF g r o u p : 3.3 Â , f o r t h e C C l ^ g r o u p : 4.3 Â , a n d t h e c B r ^ g r o u p : 4.8 Â. T h e s e v a l u e s do n o t g i v e a n i n d i c a t i o n f o r t h e p o l a r i z a b i l i t y o f t h e i n d i v i d u a l h a l o g e n atoms b u t i t i s undoubtedly greate a t o m s i n c r e a s e s . Th 2.2 Â a n d t h e t e r t i a r y b u t y l g r o u p o f a b o u t 4.4 Â (without being p o l a r i z a b l e ) . C h l o r a l was known t o g i v e o n l y i n s o l u b l e , p r e s u ­ mably i s o t a c t i c p o l y m e r , f l u o r a l c o u l d be p o l y m e r i z e d to i n s o l u b l e and s o l u b l e presumable a t a c t i c polymer. The q u e s t i o n was now t o d e t e r m i n e t h e r e s u l t s o f t h e p o l y m e r i z a t i o n experiments w i t h perhaloacetaldehydes w i t h i n c r e a s i n g s u b s t i t u e n t s i z e a s shown i n E q n . 4. CX.

CCI,

Crystalline, i n ­ t r a c t a b l e polymer only

CF,

C r y s t a l l i n e and amorphous p o l y m e r

CC1 F: CC1F 2

Eqn. PREPARATION

2

:

4

OF MONOMERS AND POLYMERS

F l u o r a l was p r e p a r e d f r o m t h e c o m m e r c i a l l y a v a i ­ l a b l e f l u o r a l hydrate by d e h y d r a t i o n w i t h s u l f u r i c a c i d and u l t i m a t e l y w i t h Ρ °ς· polymerized with pyridine. I t : w

a

s

2

Fluorοchlorοacetaldehydes : D i f l u o r o c h l o r o a c e t a l ­ d e h y d e (DFCA) was p r e p a r e d b y d e h y d r a t i o n o f t h e m i x e d h e m i a c e t a l - h y d r a t e o f DFCA w i t h s u l f u r i c a c i d a n d a g a i n

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

116

RING-OPENING P

POLYMERIZATION

T l i e

w i t h 2°5* h y d r a t e was o b t a i n e d f r o m t h e r e v e r s e L i A l H , r e d u c t i o n o f C C 1 F C 0 0 C H . w h i c h was c o m m e r c i a l l y available.(16) 9

1

5

F l u o r o d i c h l o r o a c e t a l d e h y d e (FDCA) was a l s o p r e ­ p a r e d by L i A l H ^ r e d u c t i o n a t -78°C, b u t o f m e t h y l f l u o r o d i c h l o r o a c e t a t e , w h i c h i n t u r n was made f r o m m e t h y l t r i c h l o r o a c e t a t e and S b F ^ . ( E q n . 5 ) ( 1 7 ) The a l d e h y d e s w e r e p u r i f i e d by l o w t e m p e r a t u r e d i s t i l l a t i o n and f i n a l b u l b t o b u l b d i s t i l l a t i o n f r o m P^O^ and c o n t a i n e d i m p u r i t i e s o f n o t more t h a n 100 ppm as j u d g e d by g a s chromâtogrphy. P h y s i c a l c h a r a c t e r i s ­ t i c s o f t h e a l d e h y d e s a r e shown i n t h e T a b l e . Aldehyde CC1F -C00CH 2

Synthese y 3

L

i

A

1

Ji^CClFjCiUOH^

H

4

-78°Γ CCl F-C00CH — ^ y 2 3 rev.add. ' υ

o

o

^CC1F CH0 2

H

o 2

CCl FCH(0H) 2 o

< 5

S 0

/ >CCl FCH0 ' 2 4

o

2

Eqn.

5.

DFCA had b e e n p o l y m e r i z e d a t room t e m p e r a t u r e and a t -78°C and g a v e p o l y m e r i n a b o u t 50 % y i e l d . The p o l y m e r o b t a i n e d a t -78°C was c o m p l e t e l y s o l u b l e . H i g h y i e l d s o f p o l y m e r s w e r e a l s o o b t a i n e d w i t h A l E t ^ , LTB and SbCl,. as t h e i n i t i a t o r s . The p o l y m e r p r e p a r e d w i t h S b C l ^ as t h e i n i t i a t o r i s a l s o c o m p l e t e l y a c e t o n e s o l u ­ b l e . M o s t o t h e r DFCA p o l y m e r s o b t a i n e d w i t h v a r i o u s i n i t i a t o r s c o n t a i n e d s o l u b l e f r a c t i o n s of the polymer, e v e n t h e p o l y m e r f r o m DFCA and LTB h a d a 11 % s o l u b l e fraction. S o l u b l e p o l y - D F C A c a n be a c e t y l a t e d w i t h a c e t i c a n h y d r i d e and shows a b r o a d NMR p e a k b e t w e e n 5.5 and 6 ppm i n d i c a t i v e o f t h e a c e t a l p r o t o n w h i c h i s b o u n d t o a c a r b o n a t o m w h i c h h a s as t h e f o u r t h v a l e n c y a s t r o n g l y e l e c t r o n w i t h d r a w i n g group a t t a c h e d . The f i n e s t r u c t u r e o f t h e b a n d i s v e r y c o m p l i c a ­ t e d ; i t i s c l e a r l y i n f l u e n c e d by t h e s p l i t t i n g o f t h e a c e t a l p r o t o n by t h e 2 f l u o r i n e a t o m s o f t h e d i f l u o r o c h l o r o m e t h y l g r o u p . The p r o t o n r e s o n a n c e i s f u r t h e r b r o a d e n e d by t h e f a c t t h a t t h e p o l y m e r h a s an a t a c t i c s t r u c t u r e . L i n e b r o a d e n i n g because of the r i g i d i t y of the backbone c h a i n , w h i c h p r e v e n t s p r o p e r a v e r a g i n g of t h e p r o t o n s i g n a l may a l s o be o p e r a t i v e .

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8.

Lipp A N D V O G L

Perhaloacetaldehyde

117

Polymerization

FDCA was a l s o p o l y m e r i z e d w i t h a number o f i n i ­ t i a t o r s a t r o o m t e m p e r a t u r e a n d a t -78°C. T y p i c a l a n i o n i c i n i t i a t o r s , L T B a t 25°C o r Ph.P a t -5°C a n d SbCl a t -78°C g a v e h i g h y i e l d s o f p o l y m e r s o f FDCA. A l l FDCA p o l y m e r s w e r e i n s o l u b l e a l t h o u g h t h e y w e r e prepared under a v a r i e t y o f r e a c t i o n c o n d i t i o n s , and w i t h a n i o n i c and c a t i o n i c i n i t i a t o r s . (Table 1). Fluorobromoacetaldehydes : Difluorobromoacetald e h y d e (DFBA) and *f l u o r o d i b r o m o a c e t a l d e h y d e (FDBA) w e r e p r e p a r e d b y two d i f f e r e n t r o u t e s ( 1 8 ) . I n the f i r s t a p p r o a c h 1.1 - d i f l u o r o - 2 , 2 - d i b r o m o e t h y l e n e was o x i d i z e d w i t h o x y g e n a t 0°C a n d g a v e i n g o o d y i e l d a m i x t u r e o f d i f l u o r o b r o m o a c e t y l bromide and f l u o r o dibromoacety1 f l u o r i d e . This r e a c t i o n undoubtedly goes v i a the 1 , 1 - d i f l u o r o - 2 , 2 - d i b r o m o e t h y l e n c o u l d not be i s o l a t e d The m i x t u r e o f d i f l u o r o b r o m o a c e t y l b r o m i d e a n d f l u o r o d i b r o m o a c e t y 1 f l o r i d e was t r e a t e d w i t h m e t h a n o l to g i v e the m e t h y l e s t e r s . M e t h y l d i f l u o r o b r o m o a c e t a t e was r e a d i l y s e p a r a t e d f r o m m e t h y l fluorodibromoacetate by d i s t i l l a t i o n . ( E q n . 6) Sunthesis :F

Ο 9

o f CBr FCHO and CBrF CHO 2

Χ

^ 0°C

β

η

2

CBr — P F \ /

CBr FC0F Ζ o

9

n i I

L»n _ Un

CBrF COBr

CBr FCOF CBrF COBr

>

2

2

CBrFCOOCH. J CBrF COOCH

2

2

3

Eqn.

6.

The i n d i v i d u a l m e t h y l e s t e r s w e r e r e d u c e d w i t h L i A l H ^ a t 0°C a n d g a v e t h e c o r r e s p o n d i n g aldehyde h y d r a t e s , w h i c h w e r e d e h y d r a t e d i n t h e u s u a l way. This r o u t e i s the p r e f e r r e d method f o r the p r e p a r a t i o n o f FDBA. ( E q n . 7) CBr FC00CH o

2

3

o

LiAlH, -

o°c

CBr FCH(0H) 2

2

>CBr FCH(OH) 0

1

0

l

H SO = 2^CBr FCH0 2

An a l t e r n a t e b e t t e r r o u t e f o r t h e s y n t h e s i s o f DFBA s t a r t s f r o m t r i f l u o r o c h l o r o e t h y l e n e . B r o m i n a t i o n

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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POLYMERIZATION

Table 1 Bulk P o l y m e r i z a t i o n of Perhaloacetaldehydes. Aldehyde

CF CHO 3

CF C1CH0 2

Initiator Type tertiary amines, acids LTB Ph Ρ SbCl 5

Polymerization Bath Temp., Time, i n °C in hrs. several 1 1 1

Polyme Yield, in %

room temp. - 78 - 78 - 78

good b 91° 46° 56 c

CF BrCHO

LTB pyridine H S0

24 24

25 25

* t

CFC1 CH0

LTB Ph.P SbCl

2 48 1

25 - 5 - 78

85 70 80

2

2

2

4

5

CFBr CHO

LTB pyridine H S0

24 24 24

- 78 25 25

16 6 80

CC1 CH0

LTB pyridine SbCl

1 1 1

0 0 0

85 85 60

CCl BrCHO

LTB pyridine SbCl

3 3 70

- 30 - 30 - 10

80 72 58

CClBr CHO

pyridine SbCl

72 72

- 45 - 45

52 24

LTB pyridine

72 72

- 78 - 78

16 46

2

2

3

4

5

2

5

2

5

CBr CHO 3

a) I n i t i a t o r c o n c e n t r a t i o n

: 0.3 t o 2.0 mole %.

b) Contains acetone s o l u b l e polymer p o r t i o n . c) Completely acetone s o l u b l e . d) Some toluene used as d i l u e n t .

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8.

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Perhaloacetaldehyde

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119

a t 0°C i n F r e o n 113 g a v e i n 85 % y i e l d 1,1,2-trifluoro- 2 - c h l o r o - 1 , 2 - d i b r o m o e t h y l e n e w h i c h was t r e a t e d w i t h f u m i n g s u l f u r i c a c i d a n d HgO t o g i v e i n 75 % y i e l d d i f l u o r o b r o m o a c e t y l f l u o r i d e . Treatment w i t h methanol a t 0°C g a v e i n 75 % y i e l d m e t h y l d i f l u o r o b r o m o a c e t a t e w h i c h was r e d u c e d w i t h L i A l H , a t - 78°C. D e c o m p o s i t i o n of t h e r e a c t i o n p r o d u c t w i t h w a t e r and d e h y d r a t i o n o f t h e h y d r a t e w i t h s u l f u r i c a c i d g a v e i n 65 % y i e l d DFBA. (Eqn. 8) A l t e r n a t ive

Synthesis o f CBr CH0 2

0°C CF=-=CC1F

> CBrFr F r e o n 113

CBrF—CClFBr

+ fuming

H S0 2

4

CClFBr

+ HgO—^CBrF-COF LAH

C B r F ^ C O F + CH OH J

>CBrF-C00CH 0°C

1

5

> -78°C

> CBrF-CHO H S0 2

4

The monomers w e r e p u r i f i e d b y d i s t i l l a t i o n f r o m F 0,_ and p o l y m e r i z a t i o n g r a d e monomers w h i c h c o n t a i n e d l e s s t h a n 2 0 0 ppm o f i m p u r i t i e s w e r e o b t a i n e d . 2

P o l y m e r i z a t i o n s o f f l u o r o b r o m o a c e t a l d e h y d e s were c a r r i e d o u t f o r one day w i t h a n i n i t i a t o r c o n c e n t r a t i o n of one mole p e r c e n t . W i t h L i A l H , as t h e i n i t i a t o r , DFBA g a v e p o l y m e r i n up t o 5 0 % y i e l d a t -78°C a n d +25°C. The p o l y m e r p r e p a r e d a t room t e m p e r a t u r e h a d a 10 % s o l u b l e f r a c t i o n , b u t p o l y m e r p r e p a r e d w i t h Ph^P a t room t e m p e r a t u r e , a n d o b t a i n e d a t 25 % y i e l d , i s c o m p l e t e l y s o l u b l e . With p y r i d i n e , s u l f u r i c a c i d and S b C l ^ a s t h e i n i t i a t o r , DFBA p o l y m e r i z e d t o g i v e p o l y ­ m e r s , a l l o f w h i c h h a d v a r y i n g a m o u n t s of a n i n s o l u b l e fraction. FDBA d i d n o t p o l y m e r i z e r e a d i l y a t r o o m t e m p e r a ­ t u r e , o b v i o u s l y because o f the low c e i l i n g temperature of p o l y m e r i z a t i o n . S e v e r a l n u c l e o p h i l e s , w h i c h a r e n o r m a l l y good i n i t i a t o r s f o r p e r h a l o a c e t a l d e h y d e p o l y ­ m e r i z a t i o n g a v e l i t t l e o r no p o l y m e r . E v e n a t l o w t e m ­ p e r a t u r e s (-78°C). L T B g a v e p o l y m e r i n o n l y 16 % a n d p y r i d i n e i n 6 % y i e l d . C a t i o n i c i n i t i a t o r s , such as s u l f u r i c o r t r i f l i c a c i d were e f f e c t i v e i n i t i a t o r s even a t r o o m t e m p e r a t u r e a n d g a v e p o l y m e r s o f FDBA i n a s much a s 8 0 % y i e l d . dehyde

Chiorobromoacetaldehydes : Dichlorobromoacetal(DCBA) a n d c h l o r o d i b r o m o a c e t a l d e h y d e (CDBA)

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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RING-OPENING POLYMERIZATION

w e r e a l s o p r e p a r e d by two d i f f e r e n t s y n t h e t i c m e t h o d s . ( 1 9 , 2 0 ) . The r e a c t i o n p r o d u c t o f c h l o r a l and P h P , which i s d i c h l o r o v i n y l l o x y triphenylphosphonium c h l o r i ­ d e , was b r o m i n a t e d t o g i v e 1 , 1 - d i c h l o r o - 1 , 2 - d i b r o m o e t h o x y t r i p h e n y l p h o s p h o n i u m c h l o r i d e . T h i s compound i s v e r y s e n s i t i v e t o w a t e r and c a n be h y d r o l y z e d i n a q u e o u s d i o x a n e t o t h e h y d r a t e o f DCBA. T h i s m a t e r i a l was.now d e h y d r a t e d w i t h s u l f u r i c a c i d t o t h e f r e e a l d e h y d e . An a l t e r n a t e r o u t e f o r t h e p r e p a r a t i o n o f DCBA i s t h e b r o m i n a t i o n o f d i c h l o r o a c e t a l d e h y d e d i e t h y l a c e t a l f o l l o w e d by t h e r e a c t i o n o f t h e b r o m i n a ­ t i o n m i x t u r e w i t h s u l f u r i c a c i d t o DCBA'. A l t h o u g h t h i s r e a c t i o n a l s o g i v e s DCBA i n g o o d y i e l d , i m p u r i t i e s a r e r e t a i n e d i n t h i s p r e p a r a t i o n o f DCBA w h i c h c o u l d n o t be r e m o v e d and w h i c h i n t e r f e r e d w i t h t h p o l y m e r i z a t i o n 3

CDBA was p r e p a r e d e h y d e d i e t h y l a c e t a l . The d e c o m p o s i t i o n o f t h e b r o m i ­ n a t i o n p r o d u c t w i t h s u l f u r i c a c i d i s v e r y e a s y and no i m p u r i t i e s w h i c h were d e t r i m e n t a l t o the p o l y m e r i z a t i o n o f CDBA w e r e f o u n d . An a l t e r n a t e r o u t e f o r t h e p r e p a ­ r a t i o n o f CDBA was a l s o s t u d i e d w h i c h u s e d t h e r e a c t i o n p r o d u c t o f b r o m a l and Ph^P as t h e s t a r t i n g m a t e r i a l . C h l o r i n a t i o n of 1 , 1 - d i b r o m o v i n y l o x y t r i p h e n y 1 phosphonium bromide gave a c o m p l i c a t e d m i x t u r e , from w h i c h , a f t e r h y d r o l y s i s , no CDBA c o u l d be i s o l a t e d . DCBA was m o s t c o n v e n i e n t l y p o l y m e r i z e d a t -30°C. I n i t i a t o r and monomer w e r e m i x e d a t room t e m p e r a t u r e and t h e p o l y m e r i z a t i o n was c a r r i e d o u t f o r p e r i o d s o f 3 h o u r s t o 1 week. T h e s e t i m e s a r e n o t r e a l l y t h e t i m e s n e c e s s a r y to a c h i e v e the c o n v e r s i o n s i n d i c a t e d i n the T a b l e but t i m e s w h i c h were c o n v e n i e n t to t e r m i n a t e the r e a c t i o n . M o r e a c c u r a t e p o l y m e r i z a t i o n t i m e s c a n be e s t i m a t e d f r o m t h e c u r v e s o f t h e r a t e s t u d i e s o f some p o l y m e r i z a t i o n s w i t h t y p i c a l i n i t i a t o r s . With p y r i d i n e as t h e i n i t i a t o r a 72 % y i e l d was o b t a i n e d i n 3 h o u r s and w i t h LTB an 80 % y i e l d was r e l i z e d . S b C l gave a 58 % and t r i f l i c a c i d a 40 % y i e l d p o l y - D C B A . P o l y m e r i z a t i o n o f CDBA n e e d e d as l o w a t e m p e r a ­ t u r e as -45°C. W i t h p y r i d i n e as t h e i n i t i a t o r a 52 % y i e l d and w i t h SbCl,. a 24 % y i e l d o f p o l y - CDBA was o b t a i n e d , when t h e p o l y m e r i z a t i o n was s t o p p e d a f t e r 3 days. B r o m a l , w h i c h f o r a l o n g t i m e was c o n s i d e r e d i n c a p a b l e o f p o l y m e r i z a t i o n , was p u r i f i e d by h e a t i n g i t w i t h SbF. a t e l e v a t e d t e m p e r a t u r e s . T h i s t r e a t m e n t e l i m i n a t e d ζ i m p u r i t i e s which are the apparent i n h i ­ b i t o r s of the p o l y m e r i z a t i o n . Bromal p o l y m e r i z e d at -78°C w i t h p y r i d i n e o r LTB as t h e i n i t i a t o r s i n i s o l a -

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8.

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Polymerization

121

t e d y i e l d s o f up t o 46 %. B r o m a l a n d c h l o r o b r o m o a c e t a l d e h y d e s gave o n l y i n s o l u b l e p o l y m e r s . RATES OF PERHALOACETALDEHYDE POLYMERIZATION The r a t e o f p o l y m e r i z a t i o n o f some p e r h a l o a c e t a l ­ d e h y d e p o l y m e r i z a t i o n s was s t u d i e d b y o b s e r v i n g t h e d i s a p p e a r a n c e o f the aldehyde p r o t o n s i g n a l , and con­ s e q u e n t l y t h e d i s a p p e a r a n c e o f monomer. B e c a u s e o f c o n v e n i e n c e , t h e c h l o r o b r o m o a c e t a l d e h y d e s w e r e more e x t e n s i v e l y s t u d i e d . The r a t e o f p o l y m e r i z a t i o n o f DCBA, CDBA a n d b r o m a l a t _ 7 8 ° C . a t a n i n i t i a t o r c o n c e n ­ t r a t i o n o f 2 m o l e p e r c e n t p y r i d i n e i s shown i n F i g u r e 1. DCBA a n d CDBA ( c u r v e are polymerized i n a t 85 % monomer c o n v e r s i o n . B r o m a l p o l y m e r i z e s much s l o w e r ; o n l y a 50 % c o n v e r s i o n i s o b t a i n e d i n o n e hour and t h e u l t i m a t e c o n v e r s i o n . I n o r d e r t o compare t h e r a t e s o f p o l y m e r i z a t i o n of p e r h a l o a c e t a l d e h y d e polymerization with different i n i t i a t o r s , t h e p o l y m e r i z a t i o n o f DCBA was s t u d i e d a t -10°C. a n d a t i n i t i a t o r c o n c e n t r a t i o n s o f 2 m o l e p e r ­ c e n t . T h e r a t e o f p o l y m e r i z a t i o n o f DCBA w i t h p y r i d i n e i s v e r y f a s t . The r a t e o f DCBA p o l y m e r i z a t i o n w i t h s u l f u r i c a c i d i s much s l o w e r b u t i s f a s t e r t h a n t h a t o f c h l o r a l p o l y m e r i z a t i o n w h i c h i s shown i n c u r v e A. The s u l f u r i c a c i d i n i t i a t e d p o l y m e r i z a t i o n shows i n d u c ­ t i o n periods not normally encountered i n anionic poly­ merizations of perhaloacetaldehydes. The v a l u e s o f t h e s e r a t e s t u d i e s s h o u l d n o t b e taken as obsolute but as comprative values because the polymers p r e c i p i t a t e d u r i n g the p o l y m e r i z a t i o n , and h a v e a l l d i f f e r e n t m o r h p o l o g i e s , d e p e n d i n g u p o n t h e i n i t i a t o r u s e d . The n a t u r e o f t h e p r e c i p i t a t i n g polymer d e t e r m i n e s t h e r a t e o f p o l y m e r i z a t i o n and u l t i m a t e conversion of slow p o l y m e r i z a t i o n s . C 0 P 0 L Y M E R I Z A T I 0 N S OF PERHALOACETALDEHYDES Perhaloacetaldehydes copolymerize w i t h each o t h e r , most p r o m i n e n t l y w i t h c h l o r a l o r w i t h i s o c y a n a t e s . A t y p i c a l c o p o l y m e r i z a t i o n scheme w i t h DCBA i s g i v e n i n E q n . 9.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

122

Figure 1. Rate of perhaloacetaldehyde polymerization: NMR study. Initiator, pyri­ dine; initiator concentration, 2 mol %; polymerization bath temperature, — 78°C. B, DCBA; C, CDBA; D, bromal.

Figure 2. Rates of perhaloacetaldehyde polymerization: NMR study. Bulk polym­ erization; initiator concentration, 2 mol % ; polymerization bath temperature, — 1 0 ° C .

A

CCi CH0 (H S0 ) 3

2

B'

4

CCUBrCHO

Β

CCL BrCH0

C

CClBr CH0

D

CBrjCHO

2

2

Β CCl BrCH0 ( H S 0 ) 2

(pjritiif)

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2

4

8.

Lipp A N D V O G L

Perhaloacetaldehyde

Copolymerization

Polymerization

o f CCl BrCHO 2

CC1 CH0 3

CCl Br

CCl Br

CC1

2

1

/

2

123

3

"i

• ^ Τ - ° " ^ ϊ ~ ° " ' .

η c=o I

^

Ï6 5 C.H NCO» - f - ?A — 02- ) - C-NC 1

c

Â

, r

H

ΊΙ

Copolymerizatio taldehydes are s e n s i t i v t i o n temperature and i n i t i a t o r type. P e r h a l o a c e t a l d e hydes p o l y m e r i z e q u i t e r e a d i l y w i t h c h l o r a l ; f l u o r o s u b s i t i t u t e d p e r h a l o a c e t a l d e h y d e s a r e more p r e f e r e n ­ t i a l l y i n c o r p o r a t e d i n t o the copolymers. C h l o r o - and bromo- s u b s t i t u t e d p e r h a l o a c e t a l d e h y d e s were not v e r y r e a c t i v e i n the c o p o l y m e r i z a t i o n and c h l o r a l r i c h p o l y m e r s were o b t a i n e d . B r o m a l can be i n c o r p o r a t e d i n t o copolymers w i t h c h l o r a l o n l y w i t h g r e a t d i f f u c u l t y and f r o m a f e e d m i x t u r e c o n t a i n i n g 25 more % b r o m a l o n l y 1.5 m o l e % b r o m a l was i n c o r p o r a t e d i n t o t h e c o p o l y m e r , Copolymerizations o f aldehydes w i t h isocyanates a r e w e l l known a n d f o r p e r h a l o a c e t a l d e h y d e s , aromatic i s o c y a n a t e s a r e t h e b e s t c o m o n o m e r s . The p o l y m e r i z a ­ t i o n o f p h e n y l i s o c y n a t e s w i t h c h l o r a l has been most extensively studied. ( 2 1 , 2 2 ) . The c o p o l y m e r i z a t i o n o f BDCA i s d e s c r i b e d i n E q n . 9 a n d t h e r e s u l t s o f c o p o l y ­ merization of various perhaloacetaldehydes with phenyli s o c y a n a t e a r e shown i n T a b l e 2. The c o p o l y m e r s a r e g e n e r a l l y p r e p a r e d w i t h a n i o n i c i n i t i a t o r s , f o r exam­ p l e w i t h p y r i d i n e o r P h ^ P , b u t L T B was a l s o u s e d a s effective i n i t i a t o r , p a r t i c u l a r l y for chloral copolym e r i z a t i o n s . As i n h o m o p o l y m e r i z a t i o n s , low t e m p e r a ­ t u r e c o n d i t i o n s must be employed f o r an e f f e c t i v e c o p o l y m e r i z a t i o n a n d y i e l d s o f 30 % t o n e a r l y q u a n t i ­ t a t i v e y i e l d s have been o b t a i n e d . Most c o p o l y m e r s o f a p e r h a l o a c e t a l d e h y d e and p h e n y l i s o c y a n a t e are i n s o l u ­ b l e when t h e c o p o l y m e r c o n t a i n s o n l y s m a l l a m o u n t s o f p h e n y l i s o c y a n a t e , b u t p o l y m e r s w i t h more t h a n 20 m o l e % o f phenylisocyanate are normally s o l u b l e . A t r u l y a l t e r n a t i n g copolymer o f a p e r h a l o a c e t a l d e h y d e and p h e n y l i s o c y a n a t e has o n l y been p r e p a r e d w i t h b r o m a l as t h e monomer. Many a t t e m p t s t o p r e p a r e a n a l t e r n a t i n g c o p o l y m e r w i t h c h l o r a l f a i l e d . T h i s r e s u l t seems t o

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

124

RING-OPENING POLYMERIZATION

i n d i c a t e , t h a t t h e d e g r e e o f p o l a r i z a t i o n has an i n ­ f l u e n c e on t h e e a s e o f c o p o l y m e r i z a t i o n o f i s o c y a n a t e s with perhaloacetaldehydes.

C E I L I N G TEMPERATURE OF

PERHALOACETALDEHYDE POLYMERIZA­ TION

I n i t i a t i o n of p e r h a l o a c e t a l d e h y d e p o l y m e r i z a t i o n m u s t be done a b o v e t h e p o l y m e r i z a t i o n t h r e s h o l d t e m p e ­ r a t u r e ( a t one m o l a r monomer s o l u t i o n s , t h i s i s t h e c e i l i n g t e m p e r a t u r e of p o l y m e r i z a t i o n ) i n o r d e r t o p r o ­ v i d e c o m p l e t e m i x i n g o f i n i t i a t o r and monmer p r i o r t o p o l y m e r i z a t i o n . To f o r m a h o m o g e n e o u s m i x t u r e i s p a r ­ t i c u l a r l y important whe th initiatio equilibriu i s v e r y much on t h t i a t o r t o one m o l e (Effectiv initiation), because the polymer which forms r a p i d l y , p r e c i p i t a t e s and o c c l u d e s u n u s e d i n i t i a t o r . G r o w i n g p o l y m e r e n d s a r e a l s o o c c l u d e d and t h e p o l y m e r i z a t i o n comes t o a s t a n d s t i l l ; b o t h e f f e c t s c a u s e t h e p o l y m e r s t o be f o r ­ med i n l o w y i e l d a n d / o r l o w m o l e c u l a r w e i g h t . I n i t i a t i o n of p e r h a l o a c e t a l d e h y d e p o l y m e r i z a t i o n above the t h r e s h o l d t e m p e r a t u r e of p o l y m e r i z a t i o n a l l o w s c o m p l e t e i n i t i a t i o n , and maximum y i e l d s o f p o ­ l y m e r s may be o b t a i n e d , ( c r y o t a c h e n s i c p o l y m e r i z a t i o n ) . We h a v e b e e n a b l e t o d e t e r m i n e t h e c e i l i n g t e m ­ p e r a t u r e of p o l y m e r i z a t i o n of the p e r h a l o a c e t a l d e h y d e p o l y m e r i z a t i o n by d e t e r m i n i n g t h e t h r e s h o l d t e m p e r a t u ­ r e o f p o l y m e r i z a t i o n a t v a r i o u s monomer c o n c e n t r a t i o n s and e x t r a p o l a t i n g t h e A r r h e n i u s p l o t o f l n ( M ) v s 1/T t o one m o l a r c o n c e n t r a t i o n s o f monomers. The d e t e r m i ­ n a t i o n o f t h e t h r e s h o l d t e m p e r a t u r e was c a r r i e d o u t by an o p t i c a l m e t h o d , w h i c h d e t e r m i n e d t h e p o i n t o f r a p i d c h a n g e o f t h e o p a c i t y i n t h e p o l y m e r i z a t i o n medium and i s a v e r y a c c u r a t e method f o r the d e t e r m i n a t i o n of the onset of p o l y m e r i z a t i o n i n systems where the polymer even a t v e r y low m o l e c u l a r w e i g h t p r e c i p i t a t e s from the m i x t u r e . In T a b l e 3 the c e i l i n g t e m p e r a t u r e of p o l y m e r i ­ z a t i o n of a l l the p o l y a l d e h y d e s a r e l i s t e d t o g e t h e r w i t h s p e c t r a l c h a r a c t e r i s t i c s of the p e r h a l o a c e t a l d e ­ h y d e s . I t may be s e e n t h a t t h e Τ of f l u o r o s u b s t i t u t e d a c e t a l d e h y d e s a r e h i g h e r t h a t t h o s e o f c h l o r o - and b r o m o s u b s t i t u t e d p e r h a l o a c e t a l d e h y d e s . The " m i x e d " p e r h a l a l o a c e t a l d e h y d e s h a v e Τ s somewhere i n b e t w e e n those of the t h r e e h a l o - s u b s t i t u t e d p e r h a l o a c e t a l d e h y ­ des . f

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Lipp A N D V O G L

8.

Perhaloacetaldehyde

Polymerization

125

Table 2 Copolymerization of S e l e c t e d Perhaloacetaldehydes w i t h Phenyl­ isocyanate. PerhaloPhNCO, Initiator Polymerization Yield in % Temp, i n °C Time i n Type acetaldehyde i n Mole % 85

0.05

0

CC1 CH0

5 to 20

many

CCl BrCHO

5 to 50

pyridine

- 78

3

65 - 85

CClBr CHO

10 to 40

pyridine

- 78

3

50 - 90

5 to 50

pyridine

- 78

3

30 - 75

3

2

2

CBr CHO 3

CC1 FCH0

10

Ph P

- 5

2

50

CBrF CHO

30

Ph P

- 25

1

50

2

2

3

3

Table 3 P h y s i c a l C h a r a c t e r i z a t i o n of Perhaloacetaldehydes Infra-Red _ j PMR . . CMR R=CX \neat) C=0 Bands i n cm i n ppm i n ppm cx3 Hexane Gas C=0 Neat Sol. — CF 9.35 1785 1780 — 5.52 CF C1 9.25 1770 1775 9.15 CFC1 1770 0.32 1760 1772 8.95 CC1 1760 1777 1768 93.7 175.3 9.10 CF Br 8.53 1755 1770 1762 CFBr 8.85 1760 1755 1751 0.45 CCl Br 8.87 1754 79.4 176.7 1774 1763 CClBr 8.70 1750 63.5 176.3 1768 1758 CBr~ 1742 8.45 45.5 176.9 1765 1754 n

-

2

a

a

9

3

a

2

a

2

2

2

CX CH0. o

Dens. :i n g/ccm 1.47 1.45 1.43 1.45 1.80 2.25 1.87 2.27 2.73

19

CF C00H a) F NMR, e x t e r n a l standard Temperatures 3

CF C1 2

CFC1 CCI3

2

CF Br CFBr CCl Br CClBr CBr 2

2

2

2

3

C F

3

b.p. 18 56 98 43 116 127 148 174 - 18

C

63 41 11 48 - 7 -15 -40 -75 85

τ ,K 336 314 284 321 266 258 233 198 358

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

126

RING-OPENING

POLYMERIZATION

It appears that there i s a l i n e a r r e l a t i o n s h i p of the c o n t r i b u t i o n of t e m p e r a t u r e i n c r e m e n t of each o f t h e C-X b o n d s o f t h e t r i h a l o m e t h y 1 g r o u p s t o t h e v a l u e of the c e i l i n g temperature of p o l y m e r i z a t i o n f o r each of the p e r h a l o a c e t a l d e h y d e s . Some o f t h e m e a s u ­ r e m e n t s o f t h e t h r e s h o l d t e m p e r a t u r e s o f t h e more v o l a ­ t i l e p e r h a l o a c e t a l d e h y d e s are s t i l l i n the p r o c e s s of b e i n g r e f i n e d . Our c a l c u l a t i o n s and f i n a l v a l u e s w i l l be p r e s e n t e d a t a l a t e r t i m e . A n o t h e r a t t e m p t was made i n t h i s w o r k t o c o r r e l a ­ t e the s p e c t r a l c h a r a c t e r i s t i c s of the p e r h a l o t a l d e h y ­ des w i t h t h e i r p o l y m e r i z a b i 1 i t y as i t i s e x p r e s s e d i n t h e c e i l i n g t e m p e r a t u r e o f p o l y m e r i z a t i o n . As i n d i c a t e d e a r l i e r , t h e p o l y m e r i z a t i o n i s i n f l u e n c e d by t h e e l e c ­ tron d i s t r i b u t i o n o l a r i z a t i o n and t h e s p a c e f i l l i n t y o f t h e s i d e g r o u p . We h a v e t h e r e f o r e d e t e r m i n e d the PMR s p e c t r u m f o r t h e p o s i t i o n o f t h e p r o t o n s i g n a l , t h e CMR s p e c t r u m f o r t h e s i g n a l s o f t h e C-atoms o f t h e CX« g r o u p and t h e c a r b o n y l g r o u p ; t h e d a t a w e r e a c c u ­ mulated f o r the p e r h a l o a c e t a l d e h y d e s i n hexane s o l u t i o n , n e a t and i n t h e gas p h a s e . The d a t a w e r e t a k e n a t t h e same i n s t r u m e n t , as a c o n s e q u e n c e , an a c c u r a t e r e l a t i ­ ve r e l a t i o n s h i p o f t h e s e v a l u e s was o b t a i n e d . I n t r o d u c t i o n o f f l u o r i n e a t o m s i n t o t h e CX^ g r o u p c a u s e d a s i g n i f i c a n t down f i e l d s h i f t and i n t r o ­ d u c t i o n o f b r o m i d e atoms an u p f i e l d s h i f t o f t h e a l d e ­ h y d e p r o t o n s . The c a r b o n y l c a r b o n f r e q u e n c y i s r e l a t i ­ v e l y l i t t l e i n f l u e n c e d by t h e s u b s t i t u t i o n c h a n g e s , b u t , as e x p e c t e d t h e CX~ c a r b o n i s v e r y much e f f e c t e d . Even c h l o r o s u b s t i t u t i o n caused a d o w n f i e l d s h i f t to 93.7 ppm. b u t t h e c a r b o n atom o f t h e t r i b r o m o t h y l g r o u p h a s i t s r e s o n a n c e u p f i e l d 45.5 ppm. The i n f r a r e d s t r e t c h i n g f r e q u e n c y o f t h e c a r b o ­ n y l groups of the v a r i o u s p e r h a l o a c e t a l d e h y d e s r e f l e c t a l s o the d i f f e r e n t degrees of i n d u c t i v e e f f e c t s of the i n d i v i d u a l p e r h a l o m e t h y 1 g r o u p s . The d i f f e r e n c e b e t ­ ween t h e e x t r e m e s i s 25 wave n u m b e r s , d e p e n d i n g u p o n t h e t y p e o f m e a s u r e m e n t , and s t a t e o f t h e m a t e r i a l . The d i f f e r e n c e b e t w e e n t h e v a l u e s as gas o r i n b u l k r e f l e c t s t h e d e g r e e o f a s s o c i a t i o n and c a n be s e e n i n the p o s i t i o n of the c a r b o n y l a b s o r p t i o n . The t r i f l u o r o s u b s t i t u e n t c a u s e s t h e c a r b o n y l f r e ­ q u e n c y t o be s h i f t e d t o s h o r t e r wave n u m b e r s ; b r o m o s u b s t i t u t i o n g i v e s v a l u e s a t l o n g e r wave n u m b e r s , w h i c h i n d i c a t e d t h a t a g r e a t e r e l e c t r o n a v a i l a b i l i t y i n the d o u b l e b o n d and a l s o e x p l a i n s why b r o m a l p o l y m e r i z e d easier with cationic i n i t i a t o r s .

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8.

Lipp A N D V O G L

Perhaloacetaldehyde

Polymerization

127

The q u a l i t a t i v e c o n c l u s i o n o f o u r w o r k a t t h i s time i s t h a t a l l halogen s u b s t i t u t i o n causes t h e chan­ ge i n t h e s p e c t r a l b e h a v i o r a n d p o l a r i z a t i o n o f t h e a c e t a l d e h y d e w i t h f l u o r i n e s u b s t i t u t i o n . The a l d e h y d e proton i s s h i f t e d d o w n f i e l d , thecarbon resonance o f t h e CX^ g r o u p i s s h i f t e d d o w n f i e l d a n d t h e wave number of t h e s t r e t c h i n g f r e q u e n c y o f t h e c a r b o n y l d o u b l e bond i s s h i f t e d t o s h o r t e r wave n u m b e r s ; t h e s e c h a n g e s r e ­ s u l t e d i n an i n c r e a s e i n t h e c e i l i n g temperature o f p o l y m e r i z a t i o n . Bromine s u b s t i t u t i o n as p a r t i c u l a r l y e x e m p l i f i e d w i t h bromal, caused an u p f i e l d s h i f t o f t h e a l d e h y d e p r o t o n , a n u p f i e l d s h i f t o f t h e CX^ c a r b o n a n d a s h i f t of thecarbonyl stretching frequency to higher wave n u m b e r s w h i c h , t o g e t h e r w i t h t h e i n c r e a s e d s i z e of t h e s i d e group r e s u l t s i n t h e l o w e r i n g o f t h e c e i l i n g temperature o cetaldehydes .

ABSTRACTS Nine fluoro-, chloro-, or bromosubstituted perhaloacetaldehydes were synthesized and/or purified to polymerization grade monomers. They could be homopolymerized to substituted polyoxymethylenes which were crystalline and presumably isotactic. Similarly to polyfluoral, polydifluorochloroacetaldehyde and polydifluorobromoacetaldehyde exist also in the form of a soluble, presumably atactic polymer of reasonable molecular weight. The rate of polymerization of the perhaloacetaldehydes measured under comparable conditions depended on the type of substituent ; the polymerization was fastest for fluorine substitutions and lowest for bromine substituted perhaloacetaldehydes. In copolymerization with chloral, fluorosubstituted perhaloacetaldehydes are more readily incorporated into the copolymer than bromosubstituted aldehydes. The ceiling temperature for the perhaloacetaldehydes also reflected the case of polymerization and is highest for fluorosubstituted and slowest for bromosubstituted perhaloacetaldehyde polymerization. Attemps were made to correlate the ceiling temperature to the monomer structure with special emphasis to the key spectral properties of monomeric perhaloacetaldehydes Acknowledgements : This work was in part supported by the Materials Research Laboratory of the University of Massachusetts, and by the National Science Foundation. Some of the experimental work was done by R.W. Campbell and is published in detail elsewhere.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

128

RING-OPENING POLYMERIZATION

REFERENCES 1. J . Furukawa and T. Saegusa, Polymerization of Aldehydes and Oxides, Wiley-Interscience, New-York, 1963. 2. O. Vogl, Polyaldehydes, Marcel Dekker Inc., New-York 1967. 3. O. Vogl, Makromol. Chem., 175, 1281 (1974). 4. O. Vogl, J . Polymer S c i . , 46, 261 (1960). 5. I. Negulescu and O. Vogl, J . Polymer S c i . , Polymer Letters, B13, 17 (1975) 6. J . Wood, I. Negulescu and O. Vogl, J . Macromol. S c i . , Chem., in print. 7. D.W. Lipp, R.W. Campbell and O. Vogl, Preprints, ACS Division of Polymer Chemistry, 18(1), 40 (1977). 8. A. Novak and E Whalley Trans Farada Soc. 55 1490 (1959). 9. S. Temple and R.L. Thornton, J . Polyme S c i . , , 10, 7°9 (1972). 10. W.K. Busfield and I.J. McEwen, Europ. Polymer J . , 8 , 789 (1972). 11. O. Vogl, H.C. Miller and W.H. Sharkey, Macromolecules, 5, 658 (1972). 12. O. Vogl, J . Macromol. S c i . , Revs. Macromol. Chem., C12(1), 109 (1975).

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

9 Mechanism of the Cationic Polymerization of Lactams* M. ROTHE and G.

BERTALAN**

Lehrstuhl Organische Chemie II, University of Ulm, 7900 Ulm, Germany

Lactams a r e s t r o n g l showing low c a r b o n y t h e r m a l s t a b i l i t y . S m a l l amounts o f i n i t i a t o r s , however, are s u f f i c i e n t l y e f f e c t i v e to s t a r t ring-opening polym e r i z a t i o n s t h r o u g h t r a n s a c y l a t i o n r e a c t i o n s but t h e y are g e n e r a l l y a c t i v e only a t e l e v a t e d temperatures above 2oo°. In a l l r i n g - o p e n i n g p o l y m e r i z a t i o n s one l a c t a m mole c u l e a c t s as t h e a c y l a t i n g agent, i . e . as an e l e c t r o p h i l e , and t h e o t h e r one as t h e s u b s t r a t e which undergoes a c y l a t i o n , i . e . as a n u c l e o p h i l e . The i n i t i a t o r s s e r v e f o r a c t i v a t i o n o f t h e i n a c t i v e amide group which subsequently r e a c t s with f r e e lactam through successive transamidations l e a d i n g t o polyamides with d i f f e r e n t endgroups. T r a n s a m i d a t i o n s a r e w e l l known t o form p a r t o f c a r b o n y l r e a c t i o n s which a r e c a t a l y z e d by a c i d s and b a s e s . These a d d i t i o n a l e l e c t r o p h i l e s o r n u c l e o p h i l e s p r o v i d e e i t h e r an i n c r e a s e i n t h e e l e c t r o p h i l i c i t y o f the carbonyl carbon o f the a c y l a t i n g lactam molecule ( a c i d i c i n i t i a t i o n ) o r an i n c r e a s e i n t h e n u c l e o p h i l i c character of the lactam substrate (basic i n i t i a t i o n ) . T h e r e f o r e , a l l i n i t i a t o r s used f o r l a c t a m polymeri z a t i o n so f a r may be d i v i d e d i n t o two t y p e s : 1. s t r o n g bases which a r e c a p a b l e o f removing t h e amide p r o t o n t o form a l a c t a m a n i o n and t h u s can s t a r t an a n i o n i c p o l y m e r i z a t i o n (1_) , and 2. compounds w i t h a c t i v e hydrogen w h i c h can p r o t o n a t e t h e amide bond so t h a t c a t i o n i c p o l y m e r i z a t i o n s become p o s s i b l e ( 2 ) . An e x c e l l e n t * The C a t i o n i c Lactam P o l y m e r i z a t i o n , P a r t V I I I ; P a r t V I I : Rothe, M., B e r t a l a n , G., and Mazánek, J., C h i m i a (1974), 28, 527. ** A. v . Humboldt R e s e a r c h F e l l o w from t h e Department of Organic Chemical Technology, T e c h n i c a l U n i v e r s i t y o f Budapest, Hungary. 129

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

130

RING-OPENING POLYMERIZATION

r e v i e w o n t h e mechanism o f l a c t a m p o l y m e r i z a t i o n has been p u b l i s h e d by J . Sebenda (.3) · In t h e f o l l o w i n g a s u r v e y o f t h e p r e s e n t s t a t e o f c a t i o n i c lactam p o l y m e r i z a t i o n i s given. During t h e more r e c e n t y e a r s a d e t a i l e d i n s i g h t i n t o t h e c o m p l i ­ c a t e d r e a c t i o n mechanisms has been g a i n e d by means o f i n v e s t i g a t i o n s about t h e s t r u c t u r e o f t h e endgroups i n t h e o l i g o m e r and polymer range and by k i n e t i c measure­ ments. T h i s has l e d t o a c l e a r p i c t u r e o f t h e r e a c t i o n course o f the v a r i o u s types o f c a t i o n i c lactam p o l y ­ m e r i z a t i o n (4) . A c c o r d i n g t o a s u g g e s t i o n we made some time ago (2), t h i s term i s now b e i n g used f o r t h e r i n g - o p e n i n g p o l y m e r i z a t i o n s w i t h t h e f o l l o w i n g i n i t i a t o r s : 1.strong, anhydrous a c i d s H , p r i m a r y and secondar a c i d s (8, 9), and 5. even water as w e l l as amino a c i d s and s a l t s o f amines w i t h c a r b o x y l i c a c i d s s p l i t t i n g o f f water a t e l e v a t e d t e m p e r a t u r e s ( t o , V [ , 1_2) . The

Initiation

Reaction

These a c i d i c i n i t i a t o r s w i l l c o o r d i n a t e w i t h a lactam molecule i n a r a p i d p r e e q u i l i b r i u m t o g i v e a l a c t a m c a t i o n which i s t h e r e a c t i v e s p e c i e s i n t h e p o l y ­ m e r i z a t i o n . T h i s t y p e o f i n i t i a t i o n may a l s o t a k e p l a c e w i t h weakly a c i d i c compounds which cannot a c t u a l l y t r a n s f e r a p r o t o n t o t h e lactam, but which a r e a b l e t o form a hydrogen bond w i t h i t . I n a l l c a s e s i n i t i a t i o n and p r o p a g a t i o n a r e due to t h e high a c y l a t i n g p r o p e r t i e s o f the lactam c a t i o n formed which i n t u r n r e a c t s w i t h t h e s t r o n g e s t n u c l e o p h i l i c s p e c i e s p r e s e n t i n t h e p o l y m e r i z a t i o n medium. The h i g h r e a c t i v i t y o f t h e l a c t a m c a t i o n (or t h e Lewis a c i d a d d i t i o n p r o d u c t ) may be a t t r i b u t e d t o t h e de­ c r e a s e d e l e c t r o n d e n s i t y a t t h e c a r b o n y l c a r b o n atom t h u s making i t more a t t r a c t i v e t o n u c l e o p h i l i c a t t a c k by t h e l a c t a m amide bond. P r o t o n a t i o n o f amides i s known t o o c c u r on t h e oxygen (13) because o f t h e r e s o n a n c e s t a b i l i z a t i o n o f t h e c a t i o n formed, b u t t h e N - p r o t o n a t e d amidium form may be p r e s e n t i n v e r y low c o n c e n t r a t i o n i n a tautomeric equilibrium (2)(Equation 1).

H 0=C-NH —

ΗθΞ£ΞίΝΗ

® 0=C-NH

o

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

(1 )

9.

ROTHE A N D HERTALAN

Cationic

Polymerization

of

Lactams

131

A l t h o u g h no d i r e c t e v i d e n c e on t h e r e a c t i v e a c y l a t i n g species i s a v a i l a b l e the a c y l a t i o n r e a c t i o n s a r e p r e f e r a b l e d e s c r i b e d by means o f t h e N - c o n j u g a t e a c i d which s h o u l d be more r e a c t i v e due t o t h e l a c k o f resonance s t a b i l i z a t i o n . Furthermore, i t possesses a b e t t e r l e a v i n g group t h a n t h e O - p r o t o n a t e d form i n which t h e amino fragment i s e l i m i n a t e d as an a n i o n i c s p e c i e s . F i n a l l y , the equations using the N-protonated form f o r t h e i n i t i a t i o n and growth r e a c t i o n a r e more r e a d i l y comparable t o t h o s e o f t h e a n i o n i c p o l y m e r i z a ­ t i o n as we s h a l l see below. In each o f t h e i n i t i a t i o n s t e p s t h e l a c t a m c a t i o n r e a c t s w i t h t h e s t r o n g e s t n u c l e o p h i l e p r e s e n t , as men­ t i o n e d above. In t h e p o l y m e r i z a t i o n i n i t i a t e d by s t r o n g anhydrous B r ^ n s t e d a c i d th f r e lacta i acylated with the formation o salt i n i t i a t e d polymerizatio corresponding i s c o n v e r t e d t o t h e amino a c i d amide, and i n the h y d r o l y t i c p o l y m e r i z a t i o n t h e a c y l a t i o n of water (or 0H~) y i e l d s t h e u n s u b s t i t u t e d amino a c i d (2) ( E q u a t i o n 2 ) .

Η Ν CO-N-CO H,N-CO • Η,Ν-R _ ~ 2 2

H0 2

H$ CO-NH-R W\j

(2)

H (^OOH 3

• ®OCO-R Ξ = ± ^NGO-OCO-R A c c o r d i n g l y , w i t h weak c a r b o x y l i c a c i d s an a c y l a ­ t i o n o f t h e c a r b o x y l a t e a n i o n may be assumed l e a d i n g t o a mixed a n h y d r i d e o f t h e c a r b o x y l i c a c i d and t h e amino a c i d 0_4) . A t t h e same t i m e , an a c y l a t i o n o f t h e mono­ mer i s assumed t o t a k e p l a c e y i e l d i n g an ammonium group, as d e s c r i b e d above (J_5) . As i s w e l l known, N - a l k y l l a c t a m s can be polymer­ i z e d o n l y i n e x c e p t i o n a l c a s e s , and t h a t by a c a t i o n i c mechanism (1_6) . So f a r , o n l y t h e p o l y m e r i z a t i o n w i t h s t r o n g a c i d s has been s t u d i e d more t h o r o u g h l y . In t h i s c a s e t h e f r e e l a c t a m cannot be a c y l a t e d t o g i v e an a m i n o a c y l l a c t a m owing t o t h e N - s u b s t i t u e n t . I n s t e a d , t h e weakly n u c l e o p h i l i c a n i o n o f t h e i n i t i a t i n g a c i d , e.g. C l ~ , i s a c y l a t e d by t h e l a c t a m c a t i o n t o g i v e t h e

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

132

RING-OPENING POLYMERIZATION

amino acid c h l o r i d e (V7)(Equation R-NH-co

• α

θ

* —

3).

R-NHJ:OCI

(

3)

Accordingly, amino groups are formed i n a l l c a t i o n i c polymerizations during the i n i t i a t i o n step, the ammonium ion being the predominant form. The Structure of the Oligomers and Polymers The i n i t i a t i o n reactions mentioned above were stud­ ied i n great d e t a i l i n our group (2, 1J*, 1_9) and by others (2o) using chromatographical and spectroscopical techniques to elucidat formed i n the i n i t i a stage polymerizations Under s u i t a b l e conditions, e.g. short r e a c t i o n times, r e l a t i v e l y low temperatures and high i n i t i a t o r concentrations, mixtures of oligomers were obtained. These low molecular weight products s u f f i c i e n t l y d i f f e r from each other i n t h e i r p h y s i c a l properties and, thus, can be separated i n t o monodisperse homologues by chro­ matographical means. Their structure was determined un­ equivocally by IR spectroscopy and, i n p a r t i c u l a r , by i d e n t i f i c a t i o n of the f i r s t members of the homologous s e r i e s with authentic samples which had been prepared by a stepwise synthesis. The chain propagation was studied i n a s i m i l a r man­ ner. For t h i s purpose we examined the behavior of the oligomers under polymerization conditions. Pure mono­ disperse oligomers were heated to moderate temperatures either i n the presence of equivalent amounts of the monomer or without any a d d i t i o n a l compound. If t h i s r e a c t i o n i s interrupted a f t e r a short time, too, the polymerization i s r e s t r i c t e d to a few growth steps without producing side reactions to a considerable degree. Model reactions using monofunctional reactants with the same structure as the intermediates of the polymerization provide information about the course and the mechanism of each step of the r e a c t i o n . F i n a l l y , d e t a i l s about the change i n the concentration of the endgroups formed during the polymerization may be ob­ tained from potentiometric t i t r a t i o n s . In t h i s way the strongly a c i d i c as well as the weakly a c i d i c and the basic groups of the r e s u l t i n g oligomers and polymers can be detected (2Λ) . Some examples are given i n the following. Reactive endgroups are e a s i l y detected by IR-spectroscopy (17, 18, 19), e.g. N-acyllactam groups (ν^=ο = 1695/cm) or

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

9.

ROTHE A N D BERTALAN

Cationic

Polymerization

of

Lactams

133

a c i d c h l o r i d e groups ( v o = 18o6/cm). A n h y d r i d e groups, however, have n o t been found (15). T h e r e f o r e , an a l t e r ­ n a t i v e mechanism w i l l be d i s c u s s e d below. Chromatographic and e l e c t r o p h o r e t i c methods a l l o w the s e p a r a t i o n and i d e n t i f i c a t i o n o f complete s e r i e s o f o l i g o m e r s o f i d e n t i c a l s t r u c t u r e . T h i s was p r o v e d f o r the f i r s t 6 members o f the o l i g o - e - a m i n o c a p r o y l c a p r o l a c t a m s ( i n t h e p o l y m e r i z a t i o n i n i t i a t e d by s t r o n g a c i d s ) Π 8 , J_9) , t h e f i r s t 3 o l i g o - e - a m i n o c a p r o y l - b u t y l amides and b e n z y l a m i d e s ( u s i n g t h e amine h y d r o c h l o r i d e as i n i t i a t o r ) ( 2 o , 22), and t h e f i r s t 4 o l i g o - e - a m i n o c a p r o i c a c i d d e r i v a t i v e s w i t h s e m i c y c l i c a m i d i n e endgroups ( i n a l l c a t i o n i c p o l y m e r i z a t i o n s ) ( 2 o ) . F i n a l l y , t h e c o n c e n t r a t i o n o f a l l f u n c t i o n a l groups d u r i n g the p o l y m e r i z a t i o metric t i t r a t i o n s bot f i c a t i o n s o f t h e p o l y m e r s . The e q u i v a l e n c e p o i n t s were a s s i g n e d t o t h e endgroups w i t h t h e a i d o f monodisperse o l i g o m e r s and model compounds h a v i n g t h e c o r r e s p o n d i n g s t r u c t u r e s (4) ( F i g u r e 1 ) . Thus, s t r o n g l y a c i d i c g r o u p s (lactam s a l t s , a c i d c h l o r i d e s , a c y l a m i d i n e s a l t s ) and weakly a c i d i c g r o u p s (ammonium and c a r b o x y l groups) a r e d e t e r m i n e d c o n s e c u ­ t i v e l y by t i t r a t i o n w i t h tetraalkylammonium h y d r o x i d e . Amidines a r e s t r o n g b a s e s ; hence, t h e i r s a l t s a r e not i n c l u d e d . By t r e a t m e n t w i t h m e r c u r i c a c e t a t e , however, t h e y a r e t r a n s f o r m e d t o t h e f r e e bases w h i c h subsequent­ l y can be t i t r a t e d w i t h a c i d s {23, 24) · When t h e p o l y ­ mers a r e t r e a t e d w i t h an e x c e s s ôf a l k a l i new c a r b o x y l i c groups a r e formed by h y d r o l y s i s o f a c y l l a c t a m and a c y l a m i d i n e groups (25) . A m i n o l y s i s w i t h h y d r o x y l a m i n e r e s u l t s i n t h e f o r m a t i o n o f hydroxamic a c i d s w h i c h a r e d e t e r m i n e d a f t e r c o m p l e x a t i o n w i t h F e ( I I I ) s a l t s (19). u n f o r t u n a t e l y , t h e c u r v e s shown i n F i g u r e 1 which r e s u l t from t h e t i t r a t i o n o f model compounds cannot be o b t a i n e d w i t h t h e p o l y m e r s . O n l y t h e sum o f t h e s t r o n g a c i d s as w e l l as t h e sum o f t h e weak a c i d s can be t i t r a t e d . An e x c e s s o f amide groups has been found t o cause a l e v e l l i n g e f f e c t on t h e d e t e r m i n a t i o n o f t h e v a r i o u s s t r o n g l y a c i d i c groups ( F i g u r e 2 ) , which t h e r e f o r e cannot be d e t e r m i n e d s e p a r a t e l y so f a r . T h i s a l s o h o l d s f o r amine s a l t s and c a r b o x y l i c g r o u p s . c =

The

Propagation

Reaction

S i m i l a r l y , t h e p r o p a g a t i o n r e a c t i o n s were i n v e s t i g a t e d by d e t e r m i n a t i o n o f t h e endgroups (V5, 2±, 23, 24, 25) , by model r e a c t i o n s (1_9) and, i n p a r t i c u l a r , by e x t e n s i v e k i n e t i c s t u d i e s (2Ί, 26, 27, 28). From t h e s e r e s u l t s i t f o l l o w s t h a t t h e growth

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

134

RING-OPENING POLYMERIZATION

Figure 1. Potentiometric titration of cationic caprolactam polymers (initiator: CL · H Cl). 1 = Titration with base, 2 = back titration with acid, Ε = concentrations of acidic and basic groups, E = strong acids, E L · HCI = caprolactam · HCl, E + = acylamidinium groups, tjjfHs* ammonium groups, ECOOH = carboxylic groups, = carboxylic groups formed by hydrolysis of acyUactams. A

C

AA

=

6

4

2

=

0

4

2

1

0

4

2

2

3

0

4

5

6

4

7

2

8

0

Figure 2. Potentiometric titration of CL · HCl + acyhmidine · HCl in the presence ofCL

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

ml

9.

Cationic

ROTHE A N D BERTALAN

Polymerization

of

Lactams

135

r e a c t i o n s o c c u r by t r a n s a m i d a t i o n s between l a c t a m r i n g s and t h e ammonium groups formed i n t h e i n i t i a t i o n s t e p , b o t h f r e e l a c t a m and a c y l l a c t a m endgroups a r e i n v o l v e d . During t h e propagation r e a c t i o n a proton t r a n s f e r o c c u r s f i r s t l e a d i n g from t h e amine s a l t t o t h e l a c t a m (or a c y l l a c t a m ) t o g i v e l a c t a m (or a c y l l a c t a m ) c a t i o n s ( E q u a t i o n 4) w h i c h i n t u r n a c y l a t e t h e f r e e amine farmed w i t h t h e r e g e n e r a t i o n o f an ammonium (or amidium) group (Equation 5 ) .

_

(4a)

•

OC-NH

•

OCWCO-

-NH,

•

0(

C? 2 H

rNK,

•

(4b)

(5a)

-NH-qO^NH

-C0 •

OC-NH-GO-

NH -CO-.. 2

(5b)

0
-NH-CO- • OC-NH.

W 2 The r a t e o f t h e p r o p a g a t i o n r e a c t i o n f o l l o w i n g t h i s mechanism i s p a r t i c u l a r l y h i g h when t h e a m i n o l y s i s o c c u r s a t t h e c a r b o n y l group o f an a c t i v a t e d a c i d d e r i v a t i v e (such a s a c y l l a c t a m o r a c i d c h l o r i d e ) formed i n t h e i n i t i a t i o n s t e p ; i t i s slower when t h e amide group o f t h e monomer i s i n v o l v e d . The t y p e o f r e a c t i o n d e s c r i b e d i n E q u a t i o n 5b c o r r e s p o n d s t o a b i m o l e c u l a r c o n d e n s a t i o n o f two m o l e c u l e s o f a m i n o a c y l l a c t a m o r amino a c i d c h l o r i d e (2J[, 26) . The r e a c t i o n c o u r s e o f t h e p o l y m e r i z a t i o n i n i t i a t ed by c a r b o x y l i c a c i d s may be d i s c u s s e d i n a n a l o g o u s terms. Here, t h e a m i n o l y s i s o f t h e a n h y d r i d e formed i n t h e i n i t i a t i o n r e a c t i o n by another amino a c i d a n h y d r i d e molecule should r e s u l t i n chain propagation with t h e r e g e n e r a t i o n o f an a n h y d r i d e group a f t e r each s t e p . As a n h y d r i d e g r o u p s c o u l d n o t be d e t e c t e d d u r i n g t h e p o l y m e r i z a t i o n up t o now, an a l t e r n a t i v e mechanism may o p e r a t e . P o s s i b l y , t h e t e t r a h e d r a l i n t e r m e d i a t e formed from t h e O - p r o t o n a t e d l a c t a m c a t i o n and t h e c a r b o x y l a t e a n i o n decomposes d i r e c t l y v i a a f o u r - c e n t r e t r a n s i t i o n s t a t e t o g i v e t h e higher oligomer with a c a r b o x y l i c endgroup. The a c y l a t i o n s f o l l o w a n a d d i t i o n - e l i m i n a t i o n mechanism as a l l c a r b o n y l r e a c t i o n s do. A t f i r s t , a

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

136

t e t r a h e d r a l i n t e r m e d i a t e i s formed which l e a d s t o c h a i n propagation i n the f o l l o w i n g e l i m i n a t i o n step. At the same t i m e , water may be s p l i t o f f w i t h t h e f o r m a t i o n o f a m i d i n e s (2*4, 29) ( E q u a t i o n 6) . «.-NH

2

• OC-^lH

2

OH -NH-C-j?H

0 ...-NH-C^O^I NH

2

(6)

H0 2

-NH-C=NH <

. -NH=C-NH

S i m i l a r l y , a c y l a m i d i n i u m i o n s r e s u l t from dehy­ d r a t i o n o f t h e t e t r a h e d r a l i n t e r m e d i a t e s formed d u r i n g t h e r e a c t i o n o f a c y l l a c t a m s w i t h ammonium g r o u p s . Such groups a r i s e i n s i d e t h e p o l y m e r . m o l e c u l e s ; two s t r u c ­ t u r e s b e i n g p o s s i b l e , a s shown i n E q u a t i o n 7.

NH • OC-NH-CO 2

OH I Q -NH-C-NH-CO

X

OH Φ I OC-NH-C-NH-..

(7) -Hp

-NH=C-N-CO-

CO-N-C=NH-

The water r e l e a s e d i n t h e s e r e a c t i o n s s u b s e q u e n t l y h y d r o l y z e s a c y l l a c t a m s , a c y l a m i d i n e s a l t s and l a c t a m s a l t s t o y i e l d c a r b o x y l i c groups. The f o l l o w i n g scheme (Table I) shows t h e endgroups formed d u r i n g t h e c a t i o n i c l a c t a m p o l y m e r i z a t i o n . I n a l l t y p e s o f t h i s p o l y m e r i z a t i o n ammonium and amidinium groups form t h e N - t e r m i n a l c h a i n end whereas a c y l l a c t a m , c a r b o x y l i c and a l k y l a m i d e r e s i d u e s a r e p r e s e n t a t t h e C - t e r m i n a l end. S e m i c y c l i c a c y l a m i d i n e s a r e formed

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

9.

ROTHE AND BERTALAN

Cationic

Polymerization

Initiator

Hp

of Lactams

137

EDdgrouRS N-terminal

exterminai

Η,Ν-...

...-COOH

NH-C=5H-...

... - C O O ®

... - C O - N H R

R-NHj

NH-C=NH-...

• Η,Ν-... N^H-C=NH-..

...-COOH

...-CO-N-CO ...-C-N-CO ...-NH

Table

I . Endgroups forme izations.

polymer

i n s i d e t h e polymer m o l e c u l e s . The s t r u c t u r e w i t h a s i d e - c h a i n lactam r i n g represents a p o t e n t i a l C-termin a l group a s i t i s h y d r o l y z e d t o a s i d e - c h a i n c a r b o x y l ­ i c group. The r e a c t i v i t y o f a l l t h e endgroups formed d e c i s i v e l y determines the f u r t h e r course o f t h e p o l y ­ merization. The v a r i o u s t y p e s o f c a t i o n i c p o l y m e r i z a t i o n o f l a c t a m s a r e t h u s a t t r i b u t e d t o d i f f e r e n t endgroups which a r e formed i n t h e i n i t i a t i o n s t e p and t h e n may l e a d t o d i f f e r e n t c o n s e c u t i v e r e a c t i o n s owing t o t h e i r d i f f e r i n g r e a c t i v i t i e s . As a consequence, t h e mechanism o f t h e r e a c t i o n may be p r i n c i p a l l y changed. I n t h i s c o n n e c t i o n t h e f o r m a t i o n o f a m i d i n e s has t h e main i n ­ fluence (Figure 3 ) . T h e i r concentration increases ex­ t r a o r d i n a r i l y w i t h i n c r e a s i n g a c i d i t y and c o n c e n t r a t i o n o f t h e i n i t i a t o r and, p a r t i c u l a r l y , w i t h i n c r e a s i n g tem­ p e r a t u r e . I n t h e c o u r s e o f t h e a c i d and t h e amine s a l t i n i t i a t e d p o l y m e r i z a t i o n n e a r l y a l l amine s a l t g r o u p s a r e c o n v e r t e d t o amidine s a l t s s h o r t l y a f t e r i n i t i a t i o n (24). Amidines a r e a l s o o b s e r v e d d u r i n g t h e h y d r o l y t i c p o l y m e r i z a t i o n though t o a c o n s i d e r a b l y lower degree (3o). These s t r o n g l y b a s i c groups b i n d t h e i n i t i a t i n g a c i d v e r y f i r m l y . Amidinium s a l t s i n i t i a t e t h e polymer­ i z a t i o n o f l a c t a m s much l e s s e f f e c t i v e l y t h a n ammonium s a l t s . Therefore, t h e i r formation leads t o a high de­ c r e a s e o f t h e p o l y m e r i z a t i o n r a t e (2o, 23, 24, 25) which i s t y p i c a l f o r a l l c a t i o n i c l a c t a m p o l y m e r i z a ­ tions. The e f f e c t o f Lewis a c i d s may be i n t e r p r e t e d a n a l ­ o g o u s l y . Lactams r e a c t w i t h molar amounts o f P O C I 3 o r

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

138

RING-OPENING

POLYMERIZATION

P2O5 t o g i v e c y c l i c a c y l a m i d i n e s . I n t h i s way N - ( a z a c y c l o h e p t e n - (1 ) - y l - (2) ) - c a p r o l a c t a m a s w e l l as t h e c o r r e s p o n d i n g b u t y r o l a c t a m d e r i v a t i v e were o b t a i n e d i n 7o80% y i e l d on a p r e p a r a t i v e s c a l e (31). They a r e o b v i o u s l y formed by e l i m i n a t i o n o f water from t h e t e t r a h e d r a l i n t e r m e d i a t e which r e s u l t s from t h e r e a c t i o n o f t h e L e w i s a c i d adduct and f r e e l a c t a m d u r i n g t h e i n i t i a t i o n s t e p . I n t h e p r e s e n c e o f c o c a t a l y s t s , however, w h i c h a r e c a p a b l e o f t r a n s f o r m i n g t h e Lewis a c i d i n t o a proton a c i d , p o l y m e r i z a t i o n proceeds f o l l o w i n g the u s u a l mechanism, e.g. w i t h boron t r i f l u o r i d e and w a t e r . S i m u l t a n e o u s l y w i t h t h e f o r m a t i o n o f a m i d i n e s and from t h e v e r y b e g i n n i n g o f t h e p o l y m e r i z a t i o n i n i t i a t e d by s t r o n g a c i d s water i s e l i m i n a t e d i n amounts n e a r l y equivalent t o the i n i t i a t o used Subsequently b o x y l i c groups a r e hydrolysis of the a c t i v carboxyli mentioned above ( F i g u r e 4 ) . These g r o u p s c a n now a c t a s i n i t i a t o r s of the polymerization. Moreover, h y d r o l y t i c p o l y m e r i z a t i o n c a n o c c u r a s w e l l a f t e r l o n g r e a c t i o n t i m e s . T h i s f o l l o w s from t h e i n c r e a s e o f t h e N - t e r m i n a l groups beyond t h e i n i t i a l i n i t i a t o r c o n c e n t r a t i o n (broken l i n e i n F i g u r e 6 ) . T h i s can o n l y be e x p l a i n e d by t h e f o r m a t i o n o f an a d d i t i o n a l i n i t i a t o r , v i z . water. In t h a t way t h e c o m p l i c a t e d i n f l e c t i o n k i n e t i c s o f t h e c a t i o n i c p o l y m e r i z a t i o n (26) w i t h t h e d e c r e a s e and t h e r e i n c r e a s e o f t h e r e a c t i o n r a t e may be i n t e r p r e t e d . According t o the t i t r a t i o n studies of the strong a c i d - c a t a l y z e d p o l y m e r s , o n l y low amounts, i f any, o f a c y l a m i d i n i u m s a l t s c a n be p r e s e n t . As was shown by model compounds, t h e c o n c e n t r a t i o n o f t h e s e g r o u p s do n o t o n l y d e c r e a s e by h y d r o l y s i s , b u t a l s o by t h e r m a l d e c o m p o s i t i o n y i e l d i n g a m i d i n e s and a c i d c h l o r i d e s as w e l l a s amides and i m i d e c h l o r i d e s ( 3 2 ) ( T a b l e I I ) . -NH=Ç-N-Ç=0

JCHJ

>/

-NH=C-N^C=0

2

NH = C - N - C = 0

\

\ /

MH=C-N-C=0

(CH^

\/

(CHjJg

(c4 CjHj-NhUC-N-C^O

Table

I I . Acylamidine

s a l t s used a s model compounds.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Cationic

ROTHE AND BERTALAN

Polymerization

of

Lactams

0.3 τ

Ο N-terminal Groups • A midi ne HCl Groups Δ Amine HCl Groups — - Initial Initiator Concentration

ι 100

I 500

1000

ι 1500

2000 [min]

Figure 3. Concentration of N-terminal groups. Initiator, 3.54 · 10~ mol CL · HCl/mol CL; Τ = 216°C. 2

0.3-1-

• Carboxylic Groups Δ AmidineHCl Groups

cr φ ε

— Initial Initiator Concentration

100

500

1000

1500

2000

t [min]

Figure 4. Concentration of carboxylic and amidine · HCl groups. Initiator, 3.54 · 10 mol CL · HCl/mol CL; Τ — 216°C. 2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

140

RING-OPENING POLYMERIZATION

mequivyg polymer

03H

024 Initiator: ο CL- HCl (3I54-10' md/mol CL Î. T=216°C 2

• C^NH^HCI (4KT mol/mol CU.T=220°C 2

OH ι

Initial Initiator Concentration

-ι WO

1

1

1

200

300

400

ι 500

1

600

ι 700

ι 800

1

900

1

1 I '

1

r-

2100

2200

t [min]

Figure 5.

Concentration of amidine · HCl groups

Figure 6. Concentration of Ν-terminal groups. Initiator, 10 mol CL HCl/mol CL; Τ = 216°C. 2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

9. R O T H E A N D B E R T A L A N

Cationic

Polymerization

of Lactams

141

The h y d r o l y s i s o f t h e a c y l a m i d i n e groups r e p r e ­ s e n t s a second p o s s i b i l i t y o f f o r m a t i o n o f a m i d i n e s which o c c u r s v i a p o l y c o n d e n d a t i o n o f a m i n o a c y l l a c t a m s . T h i s r e a c t i o n , however, o n l y o c c u r s d u r i n g t h e polymer­ i z a t i o n u s i n g B r 0 n s t e d a c i d s b u t n o t d u r i n g t h e polymer­ i z a t i o n i n i t i a t e d by amine s a l t s because a c y l l a c t a m s a r e n o t formed a t a l l i n t h e l a t t e r c a s e (_4) . F i g u r e 5 shows t h e change i n t h e c o n c e n t r a t i o n o f t h e amidinium groups d u r i n g b o t h t h e s e c a t i o n i c t y p e s o f p o l y m e r i z a t i o n . The c o n s i d e r a b l y l a r g e r c o n t e n t o f a m i d i n e s i n t h e a c i d i n i t i a t e d p o l y m e r i z a t i o n c a n there­ f o r e o n l y be d e r i v e d from a c y l l a c t a m s . T h i s r e s u l t shows t h e h i g h e r r e a c t i o n r a t e o f t h e s e r e s i d u e s w i t h ammonium groups and a l a r g e r c o n t r i b u t i o n o f t h i s r e a c t i o n i n the propagation. The mechanism o r e f e r r e d t o a s p a r t i c u l a r l y c l e a r has t h u s t u r n e d o u t t o be v e r y c o m p l i c a t e d . However, from t h e r e c e n t i n v e s ­ t i g a t i o n s a s i m p l e scheme f o l l o w s c o n s i s t i n g o f o n l y two e q u a t i o n s . I n t h i s scheme a l l r e a c t i o n s a r e i n c l u d ­ ed which p r o c e e d d u r i n g i n i t i a t i o n , p r o p a g a t i o n , and exchange r e a c t i o n s a s w e l l a s d e p o l y m e r i z a t i o n and c y c l i z a t i o n t o higher r i n g oligomers (Equation 8 ) .

- C O - N - C O - • -IMH3 HO

- C O - N H - • - C O - N H - ZSZZ 2

I IΦ

-CO-N-C-NH 2

I

Φ

- C O - N - O N H - • H2O

-NH-COHO ...-NH3

•

-CO-NH-

• -NH3

Φ

-NH-C-NH2-

J

φ V

..-NH-C=NH-

• H0 2

F u r t h e r m o r e , a c l o s e a n a l o g y t o t h e mechanism o f t h e a n i o n i c p o l y m e r i z a t i o n r e s u l t s (Table I I I ) . I n b o t h cases t h e formation o f t h e i n i t i a t o r , t h e i n i t i a t i o n r e a c t i o n , t h e r a p i d proton-exchange, and t h e growth r e a c t i o n r u n p a r a l l e l , t h e lactam c a t i o n a c t i n g as t h e e l e c t r o p h i l i c , a c y l a t i n g s p e c i e s whereas t h e l a c t a m anion f u n c t i o n s as t h e n u c l e o p h i l i c s u b s t r a t e i n a l l s t e p s . Moreover, i n b o t h k i n d s o f t h e p o l y m e r i z a t i o n

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

142

RING-OPENING

POLYMERIZATION

the s t r u c t u r e ( i . e . endgroups) and some o f t h e s i d e r e a c t i o n s c o r r e s p o n d w i t h each o t h e r . Thus, a s a t i s ­ f a c t o r y p i c t u r e o f t h e c h e m i s t r y o f l a c t a m polymer­ i z a t i o n has now been d e v e l o p e d . Lactam anionic

HlCcO •

e

ΗΝΛΛΛΟΟ-Ν-CO

H N - C 0 * N H / w C O N - C O +± HJNA/WCO-N—CO

^ί—CO

cationic

B *=* T £ C O * B H

HN-C0 • N - C O

3=*

HN^CO *-CO-N- ^ ±

Polymerization

N-C0*H N'WC0-N-C0 2

H** H N ^ C O HjN-CO • H N - C O

5^ «dt

H^wvCO-N-Cf>HN-CO

H NAAAœ-N^^^-lCco I^Ca)*h^wCO-rQo 5 ^ 2

HJ£C0 H^WSCO-N-CO HjN^CO-N-CO^lÇl-CO Η Γ*ΛΛ0Ο&^00-{^

ΘΝ2(Χ)

T a b l e I I I . Comparison o f t h e mechanisms o f a n i o n i c and c a t i o n i c lactam polymerizations.

We g r a t e f u l l y acknowledge generous f i n a n c i a l s u p p o r t by t h e Deutsche F o r s c h u n g s g e m e i n s c h a f t , t h e Fonds d e r Chemischen I n d u s t r i e , and t h e BASF AG, Ludwigshafen, Germany. F i g u r e s 5 a n d 6 were t a k e n from C h i m i a (1974), 28, 527 by c o u r t e s y o f BAG Brunner V e r l a g AG, Z u r i c h .

Abstract The mechanism of the various types of cationic lactam polymerization i s discussed in detail. This term i s used for the ring-opening polymerization initiated by strong and weak Brønsted acids and salts of primary and secondary amines as well as for the hydrolytic polymerization. In all cases i n i t i a t i o n and propagation reactions are due to the high acylating properties of the lactam cation formed which reacts with the strongest nucleophilic compound present in the polymerization medium. In addition, large amounts of amidine (and acylamidine) groups are formed from the tetrahedral intermediates originated during the acylation reactions. These strongly basic groups bind the i n i t i a t i n g acid very firmly. Therefore, their formation leads to a high decrease of the polymerization rate.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

9. R O T H E A N D B E R T A L A N

Cationic

Polymerization

of

Lactams

143

Literature Cited. (1) Wichterle, O., Sebenda, J., and Králicek, J., Adv. High Polymers (1961), 2, 578. (2) Rothe, M . , Reinisch, G . , Jaeger, W., and Schopov,I. Makromol. Chem. (1962), 54, 183. (3) Sebenda, J., J. Macromol. Sci.-Chem. A (1972), 6, 1145. (4) Rothe, Μ., Bertalan, G . , and Mazánek, J., Chimia (1974), 28, 527 (5) Van der Want, G. Μ., and Kruissink, Ch. Α . , J. Polymer S c i . (1959), 35, 119. (6) Wiloth, F., Makromol. Chem. (1958), 27, 37. (7) Yumoto, Η., and Ogata, Ν . , Makromol. Chem. (1957), 25, 71. (8) Majury, T. G . (9) Puffr, R., and Sebenda, J., J. Polymer Sci. C (1973), 42, 21. (10) Hermans, P. Η., Heikens, D . , and van Velden, P. F., J. Polymer Sci. (1958), 30, 81. (11) Heikens, D . , Hermans, P. Η., and van der Want, G. M . , J. Polymer S c i . (1960), 44, 437. (12) Wiloth, F., Z. Phys. Chem. (1958), 11, 78. (13) Homer, R. Β . , and Johnson, C. D . , i n : Zabicky, J. (Edit.) "The Chemistry of Amides", 188, Wiley/ Interscience, New York 1970. (14) Wyness, K. G . , Makromol. Chem. (1960), 38, 189. (15) Lánská, Β . , and Sebenda, J., C o l l . Czech. Chem. Commun. (1975), 40, 1524. (16) Masar, Β . , and Sebenda, J., C o l l . Czech. Chem. Commun. (1974), 39, 110. (17) Masar, Β . , and Sebenda, J., C o l l . Czech. Chem. Commun. (1974), 39, 2581. (18) Rothe, Μ., Boenisch, Η., and Kern, W., Makromol. Chem. (1963), 67, 90. (19) Rothe, M . , Boenisch, Η., and Essig, D . , Makromol. Chem. (1966), 91, 24. (20) Csürös, Z . , Rusznák, I . , Bertalan, G . , T r é z l , L., and Körösi, J., Makromol. Chem. (1970), 137, 9. (21) Doubravszky, S., and Geleji, F., Makromol. Chem. (1967), 110, 246. (22) Rothe, Μ., Angew. Chem. (1968), 80, 245. (23) Csürös, Ζ . , Rusznák, I . , Bertalan, G . , Anna, P . , and Körösi, J., Makromol. Chem. (1972), 160, 27. (24) Bertalan, G . , and Rothe, Μ., Makromol. Chem. (1973), 172, 249. (25) Rothe, Μ., and Mazánek, J., Makromol. Chem. (1971), 145, 197. (26) Doubravszky, S., and Geleji, F., Makromol. Chem. (1967), 105, 261.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

144

RING-OPENING

POLYMERIZATION

(27) Doubravszky, S., and Geleji, F., Makromol. Chem. (1968), 113, 270. (28) Doubravszky, S., and Geleji, F., Makromol. Chem. (1971), 143, 259. (29) Schlack, P . , Pure Appl. Chem. (1967), 15, 507. (30) Csürös, Z . , Rusznák, I . , Bertalan, G . , and Körösi, J., Makromol. Chem. (1970), 137, 17. (31) Bredereck, Η., and Bredereck, Κ., Chem. Ber. (1961), 94, 2278. (32) Rothe, Μ., and Kerschbaumer, F., unpublished data.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

10 Ring-Opening Copolymerization of Some Cyclic Compounds Containing Oxygen and Nitrogen Atoms H. L. HSIEH Phillips Petroleum Co. Research and Development, Bartlesville, OK 74004

The copolymerization of cyclic polar monomers can be used for the preparation of various classes of linear, hetero-chain co­ polymers. Cyclic compounds of the same chemical type, differing from one another only in the number of units in the ring or the presence of various substituents, can be copolymerized to form products, some of which find a wide variety of application. The copolymerization of various oxides to form linear polyethers has been extensively studied.^ A number of investigations Jjjaye been made of the copolymerization of lactones- — and lactams™^ to form polyesters and polyamides respectively. Cyclic compounds of different chemical type can also be poly­ merized to produce copolymers with hetero-bonds in the macromolecular chain derived from both copolymerizing monomers. Lactones can polymerize with cyclic ethers such as epoxides, tetrahydrofuran, oxetans and trioxane as well as imines. The copolymerization of lactones with epoxides, for example, should lead to the formation of copolymers containing ether and ester links in the chain. 1

I t was a l s o reported t h a t l a c t o n e s undergo c o p o l y m e r i z a t i o n w i t h c y c l i c phosphites upon h e a t i n g o r i n the presence o f a b a s i c catalyst.

145

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

146

RING-OPENING

POLYMERIZATION

The a l t e r n a t i n g c o p o l y m e r i z a t i o n o f epoxides and d i b a s i c a c i d anhydride r i d e r e s u l t e d i n formation o f p o l y e s t e r s i ^ » 8,9,10) R ι

-CHC.H,C00CHRCH 06 4 2 o

A l t e r n a t i n g terpolymers o f epoxides, d i b a s i c a c i d anhydrides and t e t r a h y d r o f u r a n o r oxetane were s u c c e s s f u l l y prepared by u s i n g t r i a l k y l a l u m i n u m as c a t a l y s t : " * This unique f a m i l y o f polymers has r e p e a t i n g e t h e r - e s t e r - e s t e r l i n k a g e s along the c h a i n . CH -CH 2

CH -CH + \ / CH CH \ / 0

2

0

2

2

0

2

-co'

0

2

jx

Another i n t e r e s t i n g r e a c t i o n i s the c o p o l y m e r i z a t i o n o f a z i r i d i n e s w i t h c y c l i c imides, which leads t o the formation o f c r y s t a l l i n e polyamides5—' CH -CH 2

CH -C0 I 2 >NH-

2

0

\ v Ν Η Aziridine

v

COCH CH CONHCH CH NH 2

CH -C0

2

2

2

2

e

m.p. 300 C Succinimide

High molecular polyurethanes have been prepared by the ring-r opening c o p o l y m e r i z a t i o n o f a z i r i d i n e s w i t h c y c l i c carbonatesr *

CH

2

\

H

- CH / H

2

CH 0 >^ l / 2° 2

+

C

C H

no c a t . η y ^2 ^ > H+0Œ Œ 0C0NHŒ Œ 4-N Ι» ^0Η HO group a l k y l i m i n o group r

0

2

2

2

2

2

There are many other examples o f t h i s type o f copolymeri­ z a t i o n which i n v o l v e s the ring-opening o f two o r more h e t e r o c y c l i c monomers. For t h i s r e p o r t , I w i l l d i s c u s s the formation o f polyamidoesters by means o f t h i s k i n d o f r e a c t i o n . Experimental e p s i l o n - C a p r o l a c t o n e was d i s t i l l e d , and e p s i l o n - c a p r o l a c t a m was melted and purged w i t h n i t r o g e n , before use. P h t h a l i c

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

10. HSiEH

Copolymerization

of Cyclic

Compounds

147

anhydride and N - p h e n y l a z i r i d i n e were used as r e c e i v e d . The i n i t i a t o r , R ^ A l L i , was obtained from Foote M i n e r a l and i t s chemical formula f o r the R group i s not known although the molecular weight i s 253. I t i s s o l u b l e i n hydrocarbon s o l v e n t t o give a v i s c o u s s o l u t i o n . Toluene was d r i e d by countercurrent scrubbing w i t h n i t r o g e n . A l l p o l y m e r i z a t i o n s were done i n beverage b o t t l e s . Solid monomers were weighed i n t o the b o t t l e f i r s t and then the b o t t l e was f l u s h e d w i t h n i t r o g e n . Toluene was added and t h e b o t t l e was f l u s h e d w i t h n i t r o g e n again before capping. Caprolactone was then added by hypodermic s y r i n g e . I n i t i a t o r was g e n e r a l l y added a t room temperature. Polymers, i n most o f the runs, were i n s o l u b l e i n toluene and came out o f s o l u t i o n . They were s t i r r e d i n a c i d i ­ f i e d i s o p r o p y l a l c o h o l and d r i e d i n t h e vacuum oven. R e s u l t s and D i s c u s s i o n A. N-Substituted A z i r i d i n e and D i b a s i c A c i d Anhydride. J u s t as a l k y l e n e oxide under a p p r o p r i a t e c o n d i t i o n can a l t e r n a t i n g l y copolymerize w i t h a c i d anhydride t o y i e l d p o l y e s t e r , a z i r i d i n e compounds can a l s o copolymerize s i m i l a r l y w i t h a c i d anhydride t o form polyamidoester.

0

//

0

0

T r i i s o b u t y l a l u m i n u m , a very e f f e c t i v e i n i t i a t o r f o r a l k y l e n e o x i d e - d i b a s i c a c i d anhydride c o p o l y m e r i z a t i o n £L-? was used t o i n i t i a t e the c o p o l y m e r i z a t i o n o f N - p h e n y l a z i r i d i n e and p h t h a l i c anhydride (Table I ) . Both the conversion and the elementary a n a l y s i s i n d i c a t e d the two monomers a r e present i n equal mole r a t i o . Since p h t h a l i c anhydride cannot be h o m o p o l y m e r i z e d , — i t i s concluded t h a t t h e product i s an a l t e r n a t i n g copolymer. S u r p r i s i n g l y , when the same experiment was c a r r i e d out without i n i t i a t o r , the r e s u l t was the same. Obviously, these two monomers copolymerize r e a d i l y by simply h e a t i n g . The low s o f t i n g p o i n t o f t h i s polymer, however,

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

148

RING-OPENING

POLYMERIZATION

TABLE I N-PHENYLAZIRIDINE AND PHTHALIC ANHYDRIDE COPOLYMERIZATION N-Phenylaziridine P h t h a l i c anhydride Toluene Triisobutylaluminum

0.06 mole (7.1 g) 0.06 mole (9.0 g) 100 ml 4 mmole

Temperature, ° C Time, hours

70 16

Experimental Data Total Monomers Charged, G

Polymer Recovered, G

16.1

Soft Point, °C

16.5

60

% 0

% Ν 4.6

a

(5.2)

b

18.6

a

(18.0)

1

a - Found b - C a l c u l a t e d based on 1 t o 1 mole r a t i o l i m i t s i t s u s e f u l n e s s . Endic anhydride, c h l o r o e n d i c anhydride and s u c c i n i c anhydride a l s o copolymerize w i t h N - p h e n y l a z i r i d i n e t o form low-melting s o l i d s , but i n much lower y i e l d s . B. e p s i l o n - C a p r o l a c t o n e and epsilon-Caprolactam. Another i n t e r e s t i n g method f o r p r e p a r i n g polyamidoester i s the copolymeri­ z a t i o n o f a l a c t o n e such as c a p r o l a c t o n e w i t h a l a c t a m such as caprolactam.

c

I r° η (CH )c + 2

_o

ι — r ° η (CEL). |

1

D

NH

r ι > 4-0(CH )cC0NH(CH«),-Co4 9

L

Z

D

Δ

D

J

n

I n the f i r s t experiments, f i v e o r g a n o m e t a l l i c compounds were screened as i n i t i a t o r s . I t i s known t h a t c a p r o l a c t o n e polymerizes r e a d i l y i n the presence o f t r i i s o b u t y l a l u m i n u m , b u t y l l i t h i u m , potassium t e r t - a m y l o x i d e , and l i t h i u m t e t r a a l k y l a l u m i n a t e . However, the mixture o f caprolactone and caprolactam i n toluene formed polymer o n l y i n the presence o f the l a s t compound (Table ID. The f a c t t h a t polymer i n over 50% c o n v e r s i o n was formed i n ­ d i c a t e d both monomers p a r t i c i p a t e d i n t h e r e a c t i o n , and t h a t t h e product seemed homogeneous and i n s o l u b l e i n toluene ( c a p r o l a c t o n e homopolymer i s t o l u e n e - s o l u b l e ) prompted f u r t h e r experimentation w i t h R .4A l L i . The r e s u l t s a r e shown i n Table I I I .

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

10. HsiEH

Copolymerization

of Cyclic

Compounds

149

TABLE I I CAPROLACTONE AND CAPROLACTAM

COPOLYMERIZATION

WITH ORGANOMETALLIC COMPOUNDS Caprolactone Caprolactam Toluene Organometallic compound

10 g 10 g 200 ml 2 mmoles

Temperature, °C Time, hours

70 16

Experimenta Organometallic Compound

% Conversion

(i-BuKAl Et AlCI n-BuLi tert-AmylOK R,AlLi

0 trace 0 0 60

2

a

a - Polymer p r e c i p i t a t e d

TABLE I I I LITHIUM TETRAALKYLALUMINATE AS CATALYST FOR CAPROLACTONE AND CAPROLACTAM COPOLYMERIZATION Capro­ lactone, Grams

Capro­ lactam, Grams

100 70 50 30 0

0 30 50 70 100

Polymer, Grams 100° 72 80 0

d

%

a

Solubility i n Toluene

% Ν

b Caprolactam

0 3.7 6.7 9.9

0 30 54 79

Yes Yes No No

—

—

a - I n 1 l i t e r t o l u e n e w i t h 5.1 grams (20 mmoles) R . A l L i i n i t i a t o r . P o l y m e r i z a t i o n was c a r r i e d out a t 70°C f o r 16 hours. b - Based on % Ν i n polymer. c - Waxy s o l i d ; m e l t i n g p o i n t 60°C. d - M e l t i n g p o i n t 180 C. Nylon 6 melts a t 220°-230°C. e

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

150

RING-OPENING POLYMERIZATION

As was a n t i c i p a t e d , caprolactone was r e a d i l y polymerized by R ^ A l L i t o y i e l d homopolymer which i s low-melting and s o l u b l e i n t o l u e n e , t e t r a h y d r o f u r a n and chloroform. Caprolactam, on t h e o t h e r hand, d i d not homopolymerize. The composition o f t h e copolymers v a r i e d w i t h the charge r a t i o o f the monomers, i n d i ­ c a t i n g i t i s not an e x c l u s i v e l y a l t e r n a t i n g process. Polymers c o n t a i n i n g h i g h lactam content a r e h i g h - m e l t i n g and completely i n s o l u b l e i n the common s o l v e n t s . This leads t o the c o n c l u s i o n t h a t the products a r e not a mixture o f homopolymer s. To f u r t h e r e l u c i d a t e the s t r u c t u r e o f these copolymers, phase t r a n s i t i o n behavior of three copolymers o f caprolactone and capro­ lactam (see Table IV) were determined. Three methods were used t o determine the phase t r a n s i t i o n behavior o f these polymers. a. C a p i l l a r y d i l a t o m e t r y f l u i d , from -38°C t o +65 b. Dynamic measurements ( V i b r o n ) , a t 110 Hz, from -80°C t o the upper m e l t i n g p o i n t (120°-240°C). c. D i f f e r e n t i a l scanning c a l o r i m e t r y from 40°C t o 250°C. A l s o i n c l u d e d are r e s u l t s from a p h y s i c a l blend o f p o l y caprolactone and polycaprolactam made i n a Brabender P l a s t o g r a p h at 255°C. From the data on the p h y s i c a l blend i t appears t h a t the two homopolymers a r e i n c o m p a t i b l e i n both the amorphous and c r y s t a l l i n e s t a t e s . Only the expected t r a n s i t i o n s of the two homopolymers were observed. Apparently the three experimental polymers are random copolymers w i t h some homopolymer b l o c k on o r admixed. The polymer near 50/50 i n composition showed a very broad t r a n s i t i o n around 0 C i n both the d i l a t o m e t r i c experiment and i n the V i b r o n . The o n l y other t r a n s i t i o n was a m e l t i n g p o i n t (170°C ( V ) , 192 C [DSC]). The other two experimental polymers had s i m i l a r broad t r a n s i t i o n s near 0 C. I n a d d i t i o n , these polymers d i s p l a y e d d i s ­ p e r s i o n regions which appear t o be a s s o c i a t e d w i t h the t r a n s i t i o n s e

e

e

TABLE IV SUMMARY OF STUDIES OF PHASE TRANSITION BEHAVIOR OF COPOLYMERS Caprolactam, % 30 54 79

Copolymer 60 100 40-50

0

Composition, % Polycaprolactone

Polycaprolactam

40 0 0

0 0 50-60

a - Based on % Ν i n polymer. b - From the s o l u b i l i t y d a t a , i t seems most l i k e l y the homopolymers a r e present i n the form o f b l o c k , c - About 50-50 composition.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

10.

HSiEH

Copolymerization

of Cyclic

Compounds

151

o f the major components. The r e s u l t s would support t h e i d e n t i ­ f i c a t i o n o f t h e experimental polymers as copolymers o f ca. 50-50 composition p l u s excess homopolymer ( p o s s i b l y block)· I n c o n c l u s i o n , N - s u b s t i t u t e d polyamidoesters can be r e a d i l y formed by h e a t i n g N - s u b s t i t u t e d a z i r i d i n e s w i t h d i b a s i c a c i d anhydrides. The low s o f t i n g p o i n t o f these polymers l i m i t s t h e i r u s e f u l n e s s . Copolymerization o f caprolactam and caprolactone leads to very i n t e r e s t i n g products. They a r e g e n e r a l l y h i g h m e l t i n g and by a d j u s t i n g monomer charge r a t i o e i t h e r p o l y e s t e r o r polyamide b l o c k copolymer can be produced. ABSTRACT N - P h e n y l a z i r i d i n e and p h t h a l i anhydrid copolymeriz in a l t e r n a t i n g order t o g i v triisobutylaluminum or y heating softing p o i n polymer limits its u s e f u l n e s s . e p s i l o n - C a p r o l a c t o n e and epsilon-Caprolactam copolymerize in the presence o f R A1Li. The composition o f the copolymers v a r i e d w i t h the feed ratios o f the monomers. Polymers c o n t a i n i n g over 50 p e r cent lactam are h i g h - m e l t i n g and completely i n s o l u b l e in common s o l v e n t s . From t h e results o f s t u d y i n g the phase transi­ tion behavior o f these polymers it was concluded t h a t they a r e about o f 50/50 composition p l u s excess homopolymer p o s s i b l y in b l o c k form. 4

LITERATURE CITED Furukawa, J. and Saegusa, T. " P o l y m e r i z a t i o n o f Aldehydes and O x i d e s " , John W i l e y & Sons, New Y o r k , 1963. 2. Tada, K., Numata, Y., Saegusa, T., and Furukawa, J . , Makromol. Chem. 77, 220 (1964). 3. Y a m a s h i t a , Y., Tsuda, T., I s h i k a w a , J ., and H i m i d y , T., J . Chem. Soc. Japan, I n d . Chem. S e c t . , 66, 1493 (1963). 4. G l i c k m a n , S.M. and Miller, E. S., U.S. P a t e n t 3,016,367 (1962). 5. H e d r i c k , R. Μ., M o t t e r s , Ε. Η., and B u t l e r , Τ. Μ., U.S. P a t e n t 3,120,503 (1964). 6. McConnel, R.L. and Coover, H. W., U.S. P a t e n t 3,062,788 (1962). 7. F i s h , W., Hoffman, W., and K o s k i k a l l i o , J ., Chem. and I n d . , 756 (1956). 8. F i s h e r y R. F., J. Polymer Sci., 44, 155 (1960). 9. T s u r u t a , T., Matsumura, Κ., and I n o u e , S., Makromol. Chem. 75, 211 (1964). 10. H s i e h , H. L., J. Macromol. Sci-Chem., A7 ( 7 ) , 1525 (1973). 11. K a g i u a , T., N a r i s a w a , S., Manobe, Κ., and K o b a t a , M., J . Polymer Sci., A1, 2081 (1966). 12. D r e c k s e l , Ε. Κ., U.S. P a t e n t 2,824,857 (1958). 1.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

11 Ring-Opening Polymerizations: Mechanism of Polymerization of ε-Caprolactone R. H . YOUNG, M. MATZNER, and L. A. PILATO Union Carbide Corp., Bound Brook, NJ 08805

The first s y n t h e s i s o f Є-caprolactone was r e p o r t e d by C a r o t h e r s ( 1 ) . He a l s o i n v e s t i g a t e d its p o l y m e r i z a t i o n under t h e i n f l u e n c e o f h e a t and catalysts. S i n c e then t h e p o l y m e r i z a t i o n s o f this as w e l l as t h a t o f o t h e r l a c t o n e s were s t u d i e d by many r e s e a r c h e r s . Throughout t h e 1950's t o t h e 1970's t h e polymer f o r mation and its p r o p e r t i e s were t h e s u b j e c t o f s e v e r a l i n v e s t i g a t i o n s in o u r laboratories (2-5). Union Carbide is p r e s e n t l y t h e commercial p r o d u c e r o f t h e monomer and o f a s e r i e s o f polymers w h i c h range in m o l e c u l a r w e i g h t s from 500 t o 40,000. The starting Є-caprolactone is produced by t h e p e r a c e t i c a c i d o x i d a t i o n o f c y c l o h e x a n o n e as shown in E q u a t i o n (I).

In s p i t e o f t h e number o f investigations that were d e v o t e d t o t h e p o l y m e r i z a t i o n o f l a c t o n e 3, t h e e x a c t mechanism whereby t h e polymer is formed is still not entirely clear. I t is t h e purpose o f this paper t o present the various f a c t o r s that influence the r e a c t i o n and t o d e s c r i b e its c o m p l e x i t y when it is performed in the m e l t in t h e p r e s e n c e o f either a n i o n i c o r c o o r d i nation catalysts.

152

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

11.

YOUNG E T A L .

Polymerization

of

^-Caprolactone

153

Mechanisms ; In p r i n c i p l e , t h e p o l y m e r i z a t i o n o f a l a c t o n e s h o u l d f o l l o w mechanism(s) s i m i l a r t o t h e c a t a l y z e d r e a c t i o n s o f simple e s t e r s . The t r a n s f o r m a t i o n s that a r e o b s e r v e d a r e a f u n c t i o n o f t h e c a t a l y s t and c a n be s u b d i v i d e d i n t o (a) c a t i o n i c , (b) a n i o n i c , and (c) c o o r d i n a t i o n type. A s i m p l i f i e d d e s c r i p t i o n f o r the t h r e e mechanisms i s shown w i t h ^ - c a p r o l a c t o n e as an example· (a)

Cationic

I t was suggested (4,6,7) t h a t t h e c a t i o n i c c a t a lyzed polymerizatio Equation ( I I ) . F i r s species, w i t h t h e i n t e r m e d i a t e , Jô, i s e s t a b l i s h e d . T h i s i s f o l l o w e d by r i n g - o p e n i n g t o 7, which then p r o p a g a t e s u n t i l a h i g h polymer i s o b t a i n e d .

5

Ο II

Ο

3

6

7

(ID Monomer Polymer

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

154

RING-OPENING

(b)

POLYMERIZATION

Anionic

In t h i s c a s e , a t t a c k o f t h e base upon t h e c a r ­ b o n y l group o f t h e c y c l i c e s t e r i s t h e c h a r a c t e r i s t i c f e a t u r e i n t h e i n i t i a t i o n p r o c e s s (£) ( E q u a t i o n ( I I I ) ) ,

(III)

Monomer 1 ¥

Ο Polymer

M

o

n

o

m

\

R

Ο

R 2

κ

11 Once p r o d u c e d a n i o n i s then the p r o p a g a t i n g mediate u n t i l t h e f i n a l polymer i s formed. (c)

Coordination

inter­

Type

The c o o r d i n a t i o n c a t a l y z e d p o l y m e r i z a t i o n i s de­ f i n e d f o r t h e purpose o f t h i s paper as one w h i c h i n ­ volves a concerted i n s e r t i o n with concurrent cleavage o f a c o v a l e n t p o l y m e r - c a t a l y s t bond(£) . I t i s i l ­ l u s t r a t e d i n Equation (IV).

ÇJ Ο II

R-M 12

+

0'' \ R

II

V

"I Ο il R-C-(CH )

-0-M

9

5

Z

(IV)

13 Monomer

Ο Monomer M *t Polymer ^ R-C-(CH ) - 0 - C - ( C H ) -OM 5. 0

2

0

5

2

Note t h a t t h e c a t i o n i c and a n i o n i c mechanisms as d e p i c t e d above a r e " l i m i t i n g " c a s e s . Depending upon the r e a g e n t s and e x p e r i m e n t a l c o n d i t i o n s t he "whole spectrum" o f mechanisms i s o b s e r v e d ( F i g u r e 1 ) . As shown t h e c o o r d i n a t i o n mechanism i s b a s i c a l l y the " i n t e r m e d i a t e " c a s e between t h e two o t h e r modes o f reaction.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

11.

Polymerization

YOUNG ET A L .

of

^-Caprolactone

155

Both the p o l y m e r i z a b i l i t y and the mechanism o f p o l y m e r i z a t i o n a r e o b v i o u s l y dependent on the r i n g s i z e o f the l a c t o n e :

ό ô ô

α *

An i n t e r e s t i n g g e n e r a l i z a t i o n i n t h i s r e g a r d was made by H a l e (8). He f i n d s t h a t (1) i n t h e c a s e o f t h e f i v e - and six-membered r i n g - c o n t a i n i n g monomers t h e ease o f p o l y m e r i z a t i o which t h e monomers b e l o n a n h y d r i d e , l a c t a m , e t c . ) ; (2) monomers c o n t a i n i n g f o u r - , seven-, and eight-membered r i n g s appear t o p o l y m e r i z e i n a l l c a s e s ; and (3) a l k y l o r a r y l subs t i t u t i o n o f the r i n g has a d e l e t e r i o u s e f f e c t on the polymerization. Experimental

Approach

A c o r r e l a t i o n between t h e i n t r i n s i c v i s c o s i t y o f p o l y - £ - c a p r o l a c t o n e and i t s w e i g h t - a v e r a g e m o l e c u l a r w e i g h t has been r e p o r t e d p r e v i o u s l y ( 3 ) · A commonly known r e l a t i o n s h i p between the m e l t v i s c o s i t y a t e l e v a t e d t e m p e r a t u r e s and the w e i g h t - a v e r a g e m o l e c u l a r w e i g h t has been shown(SO t o a l s o h o l d f o r p o l y - £ c a p r o l a c t o n e (Equation V I ) . [n] = 9.9

χ 10"

5

μ=α M

Mw w

0

-

8

2

( i n benzene)

(V)

3.4

(VI)

Thus, an e x c e l l e n t m o n i t o r f o r f^cap^olactone p o l y m e r i z a t i o n s i s f o l l o w i n g the v i s c o s i t y as a f u n c t i o n of time. T h i s p r o c e d u r e was adapted and a t y p i c a l " r e a c t i o n p r o f i l e " ( a t 204°C, neat) i s shown i n F i g u r e 2. There a r e e s s e n t i a l l y t h r e e s t a g e s o f the reaction. F o r t h e time p e r i o d o f t to t ^ a r a p i d r i s e i n v i s ­ c o s i t y i s o b s e r v e d , d e s i g n a t e d as p o r t i o n a o f the curve. A t time t i t h e v i s c o s i t y r e a c h e s i t s maximum v a l u e , v i . F o l l o w i n g t h i s , a d e c r e a s e o f the v i s c o s i t y t a k e s p l a c e , a l t h o u g h the change i s n o t as r a p i d ( p o r t i o n b o f the c u r v e ) . A t time t 2 , the v i s c o s i t y l e v e l s o f f t o a p r a c t i c a l l y c o n s t a n t v a l u e , V2 (por­ t i o n c of the c u r v e ) . 0

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

156

RING-OPENING

POLYMERIZATION

The shape o f t h e c u r v e which r e f l e c t s changes r e l a t e d t o M^ i s s i g n i f i c a n t and has a d i r e c t b e a r i n g on t h e r e a c t i o n mechanism. I t i s d i f f e r e n t from t h e results reported f o r solution polymerizations carried o u t a t lower temperatures (10) . Kinetic

Considerations

The o v e r a l l mechanism o f an a n i o n i c - c o o r d i n a t i o n c a t a l y z e d p o l y m e r i z a t i o n o f £*-caprolactone i s depen­ dent upon a number o f f a c t o r s . The most i m p o r t a n t o f t h e s e a r e t h e type o f c a t a l y s t and whether a c o i n i t i a t o r i s u s e d . A v e r y l a r g e number o f b o t h have been r e p o r t e d (_2) . I f RjM r e p r e s e n t s t h e c a t a l y s t - i n i t i a t o r , R20H an a c t i v e hydroge the f-caprolacton t o be c o n s i d e r e d i n o r d e r t o a r r i v e a t a m e a n i n g f u l k i n e t i c expression: (a) P r e e q u i l i b r i u m : K

R -M + R OH 1

(b)

2

l ^

R -H + R -OM

(1)

Ο H R..-C-(CH ) -OM 5

(2)

^1

1

2

Initiation: 2 R,-M + CL — = - ^ » ^ΚΖΓ" "2 κ

1

0

1

2

Ο Κ. R -0M + CL ^ - ^ R -0-C-(CH ) -OM 2 ^κΖΓ 5 "3 Ο Κ 4 » R--OH + CL — ^ S. » R ) -OH τ» -0-C-(CH r\ r% o

o

o

(3)

o

o

(4)

2

1

2

^7-

2

2

5

We have shown t h a t r e a c t i o n (4) i s v e r y slow i n comparison t o r e a c t i o n s (2) and ( 3 ) . When ζ-capro­ l a c t o n e i s h e a t e d w i t h an a l c o h o l i n t h e absence o f any c a t a l y s t under o u r normal e x p e r i m e n t a l c o n d i t i o n s no v i s c o s i t y change was o b s e r v e d .

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Polymerization

11. Y O U N G E T A L .

of

^-Caprolactone

157

(c) P r o p a g a t i o n : 0

„

«

K

Rj-C-ÎCHp

-OM + CL 5

0

c

0

II

II

^ Rj-C-ÎCHp

"^5

-0-C-(CH >

O Il

K

o

-OM + C L

o

5

° κ

O

II

6

N

e t c . (5)

5

O

R 0C-(CH )

-OM ^r>

2

5

R 0-C-(CH ) o

o

5

-6

II

- 0 - C - ( C H ) -OM — > o

5

e t c . (6)

(d) T e r m i n a t i o n : R <0-C-(CH )

>

o

5

OM + R 0 R —

* R « 0 - C - ( C H ) > OH + R 0 M 5

o

o

η

o

(e) C h a i n T r a n s f e r : Il

M

R-(0-C-(CH ) > OM 5 η O 9

K

Q

+ R-(C-C-(CH ) )• OH 5 m K_ O

s

9

z

X

Q 8

R-fO-C(CH ) )· -OH + R-fO-C-(CH ) >· OM 5 η 5 m 2

2

(8)

(f) E s t e r I n t e r c h a n g e (both i n t r a - and i n t e r - m o l e c u l a r ) :

(9) The r e l a t i v e r a t e s o f t h e above p r o c e s s e s w i l l d e t e r m i n e t h e k i n e t i c s o f t h e p o l y m e r i z a t i o n and, c o n ­ s e q u e n t l y , t h e m o l e c u l a r weight o f t h e polymer and i t s m o l e c u l a r weight d i s t r i b u t i o n . Needless t o say, t h i s i s a complex r e a c t i o n and t h e d a t a t h a t f o l l o w s must be c o n s i d e r e d i n t h a t c o n t e x t .

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

158

RESULTS AND

DISCUSSION

Various authors (2^£, 11_) have suggested that the polymerization of ^-caprolactone proceeds v i a a " l i v i n g " mechanism. This should y i e l d polymers with very narrow molecular weight d i s t r i b u t i o n s r e f e r r e d to as a "Poisson d i s t r i b u t i o n " ( 3 , 1 2 ) . In t h i s case, the k i n e t i c s of the polymerization would be expected to be rather simple and s t r a i g h t forward. Figure 3 i l l u s t r a t e s three possible v i s c o s i t y p r o f i l e s f o r the polymerization of ξ-caprolactone at elevated temperatures. A Poisson molecular weight d i s t r i b u t i o n occurs only i f the following requirements are f u l f i l l e d : 1) the rate of i n i t i a t i o of polymerization; 2 of the monomer to the polymer chain end; and 3) there i s no termination, chain t r a n s f e r or any other secon­ dary r e a c t i o n . I f the polymerization of Ç-caprolactone were to proceed i n t h i s manner (M /M =l) i t would be followed by ester interchange reactions u n t i l the establishment of the most probable d i s t r i b u t i o n . This would r e s u l t i n a continuing increase i n M and hence of the melt v i s c o s i t y (Figure 3). The polymerization of £-caprolactone does i n f a c t f u l f i l l the second requirement above. However, f u l f i l l m e n t of conditions one and three are questionable making two a l t e r n a t i v e polymerization p r o f i l e s p o s s i b l e . In t h e _ f i r s t a l t e r n a t i v e the "normal" d i s t r i b u t i o n of M /M =2 i s established during the r e a c t i o n . In that case, no further change i n M i s expected i r r e g a r d l e s s of the f a c t that ester-interchange may continue to occur. As a r e s u l t the melt v i s c o s i t y of the polymer a f t e r having reached a plateau would r e main e s s e n t i a l l y constant. Another a l t e r n a t i v e c o n s i s t s i n the polymerization reaching a molecular weight d i s t r i b u t i o n of >2. The subsequent ester interchange reactions should then r e s u l t i n a decrease i n and melt v i s c o s i t y u n t i l the normal d i s t r i b u t i o n i s reached. A t y p i c a l p r o f i l e f o r melt v i s c o s i t y as a function of time f o r a polymerization r e a c t i o n was shown i n Figure 2. The shape of the curve r e f l e c t s the k i n e t i c processes which are occuring during the polymerization. A l l of the reactions were c a r r i e d out neat, at A-»200°C. The v i s c o s i t y / t i m e p r o f i l e s that were observed with both anionic and coordination type c a t a l y s t s were e s s e n t i a l l y the same. The data do not f i t a normal " l i v i n g " mechanism, with no side r e a c t i o n s . There i s w

n

w

w

n

w

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

11.

Polymerization

YOUNG E T AL.

όRÔ--M

ι R-C II ο

6+

R-0

<—

R-Ô—-M

M

ι

>

ι O-R

159

of ^-Caprolactone

;

—>

ι

<

, 1 R-C II ο

Cationic

I R-C II

O-R ο

Co-ordination

Figure 1.

O-R

Anionic

Mechanisms of initiation and polymerization

Figure 2. Melt viscosity vs. time for the polymerization of ^-caprolactone

19

MW/MN>2

/

\

/ / /

Φ

/

\ \

NORMAL MW/MN=2

\ V

POISSON MW/MN=1

2

Time Figure 3.

Suggested melt viscosity profiles for polymerization of ^-caprolactone

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

160

RING-OPENING POLYMERIZATION

no doubt that i n addition to the usual i n i t i a t i o n and propagation steps, several other processes are occurring. These include ester interchange reactions, side-reactions i n v o l v i n g the c o - i n i t i a t o r , chain t r a n s f e r phenomena, formation of c y c l i c s i n depolymerization reactions, etc. As stated above, the v i s c o s i t y p r o f i l e had the same general shape both i n the presence and absence of a c o - i n i t i a t o r (Figure 4) and c a t a l y s t (Figure 5). The concentration of the c a t a l y s t has a s i g n i f i c a n t e f f e c t on both the rate of polymerization and on the rate of subsequent reactions r e s u l t i n g i n the decrease i n melt v i s c o s i t y (Figure 5). In order to r a t i o n a l i z e these r e s u l t s , molecular weight d i s t r i b u t i o function of reactio i n Figure 6. The v a r i a t i o n i n molecular weight d i s t r i b u t i o n with time i n d i c a t e s that M i s i n i t i a l l y w

>2 and that M decreases with time. This i s consistent with the pattern predicted from v i s c o s i t y measurements (Figures 2, 4 and 5). In addition to ester interchange reactions, there i s a second post-polymerization equilibrium r e a c t i o n that occurs. I t was possible to show reformation of c y c l i c monomer as w e l l as the formation of other c y c l i c oligomers. Gas l i q u i d phase chromatography was c a r r i e d out during the course of the polymerization. I t was observed (Figure 7) that there i s a decrease i n monomer concentration to an equilibrium l e v e l (0.2%). Simultaneously the appearance of both c y c l i c dimer and c y c l i c trimer oligomers formed i n a depolymerization reaction was noted. w

0

0

It

0

»

II

^v^O-C-C-C-C-C-C-C-0-C-C-C-C-C-C-C-0-C-C-C-C-C-C-C-OH

Trimer

Dimer

Monomer

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

YOUNG E T AL.

Polymerization

of

^-Caprolactone

TIME

Figure 4. Viscosity-time caprolactone in the presence of an anionic catalyst with a hydroxyl containing co-initiator

' TIME

Figure 5. Polymerization t-caprolactone at constant co-initiator concentration (alcohol) at different levels of typical coordination catalysts

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING

POLYMERIZATION

3.0r-

1.0»

»

1

1

1

1

TIME

Figure 6. Change in molecular weight distribution for the polymerization of e-caprohctone

23

CYCLIC DIMER CYCLIC TRIMER CYCLIC MONOMER

TIME

Figure 7. Concentration of cyclic oligomers as a function of time for high-temperature polymerizations of ^-caprolactone

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

11.

YOUNG ET AL.

Polymerization of ^-Caprolactone

163

I t i s i n t e r e s t i n g t h a t these depolymerization p r o c e s s e s have v e r y s i m i l a r appearance p r o f i l e s t o t h o s e o f polymer v i s c o s i t y and . However, t h e y do n o t o c c u r a t s u f f i c i e n t l y h i g h l e v e l s t o a f f e c t either M o r t h e o v e r a l l m e l t v i s c o s i t y o f the r e a c t i o n mixture. In s t e p r e a c t i o n (condensation) p o l y m e r i z a t i o n s , the m o l e c u l a r w e i g h t d i s t r i b u t i o n i s r e l a t e d t o the number o f p r o p a g a t i n g p o l y m e r i c b r a n c h e s . The mole­ c u l a r w e i g h t d i s t r i b u t i o n becomes narrower w i t h i n ­ c r e a s i n g f u n c t i o n a l i t y , as shown i n the e q u a t i o n below: w

M

w/ w

+ 1±

where f i s t h e number o f p o l y m e r i c b r a n c h e s . The e f f e c t o f the number o f r e a c t i v e s i t e s o f t h e c o - i n i t i a t o r upon the m o l e c u l a r w e i g h t d i s t r i b u t i o n was e s t a b l i s h e d . T h i s was r e l a t i v e l y easy t o p e r f o r m by s i m p l y u s i n g mono- and d i h y d r o x y compounds as c o initiators. As p r e d i c t e d , a t the maximum M (νχ, F i g u r e 2) the v a l u e o f M ^-^ was h i g h e r when w

w

the monohydroxy i n i t i a t o r was used. I t i s c l e a r from o u r d a t a t h a t the h i g h tempera­ t u r e n e a t r e a c t i o n i s e x t r e m e l y complex. I t may be due i n p a r t t o the s e v e r e p o l y m e r i z a t i o n c o n d i t i o n s which were used. These r e s u l t s a r e n o t i n agreement w i t h t h o s e r e p o r t e d by T e y s s i e ( 1 0 ) . Under m i l d e r r e ­ a c t i o n c o n d i t i o n s he has o b s e r v e d t h e f o r m a t i o n o f a polymer w i t h a m o l e c u l a r w e i g h t d i s t r i b u t i o n c l o s e t o one. He d e s c r i b e s the p o l y m e r i z a t i o n as a " p e r f e c t l y ' l i v i n g ' process". The d i f f e r e n c e i n r e a c t i o n c o n ­ d i t i o n s c o u l d have caused t h e o b s e r v e d d i f f e r e n c e s . F u r t h e r work w i l l be r e q u i r e d t o make t h e s e d i s c r e ­ pancies f u l l y understood. CONCLUSIONS The r i n g o p e n i n g p o l y m e r i z a t i o n o f Ç-caprolactone a t h i g h temperatures f o l l o w s a p a t t e r n w h i c h i s r a d i c a l l y d i f f e r e n t from t h e one o b s e r v e d i n s o l u t i o n under m i l d low temperature c o n d i t i o n s . I t i s p o s t u l a t e d t h a t the phenomenon i s b e s t e x p l a i n e d by assuming t h a t s e v e r a l secondary p r o c e s s e s o c c u r s i m u l t a n e o u s l y w i t h the p r i m a r y i n i t i a t i o n and p o l y m e r i z a t i o n r e a c t i o n s .

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

164

RING-OPENING

POLYMERIZATION

Literature Cited (1) VanNatta, F. J., Hill, J. W. and Carothers, W. E., J. Amer. Chem. Soc. (1934), 56, 455 . (2) Lundberg, R. D. and Cox, E. F. "Ring-Opening Polymerization", Ed. Frisch, K. C. and Reagen, S. L.; Marcel Dekker, Ν. Y. (1969), pp. 247-302. (3) Lundberg, R. D., Koleske, J. V. Wischman, Κ. B., J. of Poly. Sci. (1969), 7, 2915 . (4) Brode, G. L. and Koleske, J. V., J. Macromol. Sci. (1972), A6(6), 1109 . (5) Cox, E. F. and Hostettler, F. (to Union Carbide Corp.) U.S. Patents 3,021,309 (1962). (6) Ludwig, Ε. B. and Bebenbaya, B. G., J. Macrmol. Sci. (1974) A8 (4), 819 . (7) Sekiguchi, H. and Clarisse, C., Die Makromol. Chem. (1976), 177, 591. (8) Hall, H. K. and Schneider, A. K., J. Amer. Chem. Soc. (1958), 80, 6409 . (9) Jones, T. R., Union Carbide, unpublished results. (10) Ouhadi, T., Stevens, C. and Teyssie, P., Die Makromol. Chem. Suppl. (1975), 1, 191 . (11) Teyssie, P., Provate Communication. (12) Billmeyer, F. W., Jr., "Textbook of Polymer Science", 2nd Ed., Wiley, Interscience, New York (1971).

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12

New

Prospects

in

Homogeneous

Ring-Opening

Polymerization of Heterocyclic Monomers

PH. TEYSSIÉ, J. P. BIOUL, A. HAMITOU, J. HEUSCHEN, L. HOCKS, R. JÉRÔME, and T. OUHADI Laboratory of Macromolecular Chemistry and Organic Catalysis, University of Liège, Sart-Tilman, 4000 Liège, Belgium The importance of ring-opening polymerization has been recognized from the very early days of the science of macramolecules (1,2), and this increasingly broad field has been illustrated by many interesting fundamental studies on various types of monomers (including lactones, lactams, oxiranes, oxetanes, tetrahydrofurans, dioxolanes, thiiranes, thietanes, aziridines, leuch's anhydrides, cyclosiloxanes and others). On the other hand, several of the products obtained exhibit remarkably useful properties, which have promoted extensive physical evaluation and industrial application, e.g. nylon 6, regular polyesters (polycapro- and -pivalolactones), and polyethers (elastomeric homo- and co-polymers of propylene oxide with f.i. epichlorohydrin). In most cases, these polymerizations have been achieved using different types of initiators, belonging respectively to acid-base, ionic and coordination catalysis. The highly active coordination type initiators have been extremely helpful in controlling the chain-growth processes and their stereospecif- icity : in particular, they are the only ones able to promote the ringopening polymerization of methyloxirane (propylene oxide, PO) to high molecular weight, eventually stereoregular, polyethers. However, most of these catalytic systems do not lend thenselves to a straightforward analysis of their structural and kinetic behaviour, owing to the often ill-defined composition and structure of the active site precursors; it is the purpose of this contribution to show how the design of a coordination ring-opening catalyst, having a well-defined composition which can be systematically modified, can lead to some interesting advances in the field. I . Bimetallic μ - o x o a l k o x i d e s : a new family of ring-opening coordination catalysts Both the incentives and the experimental bases of the pre­ sent work came frcm an analysis of the previously described 165

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

166

RING-OPENING POLYMERIZATION

catalytic systems. These were essentially obtained by controlled hydrolysis of f e r r i c organic salts (3,4,5), or of zinc (6,2)and aluminium (8,9) alkyIs. Other complex salts catalysts have been described, including the zinc xanthates and thiocarbamates stu­ died by L a i (10) and the hexacyanonetallate complexes investigated by Herold (11). From the indications obtained i n these studies, two impor­ tant requirements for the e f f i c i e n t production of high molecular weight, stereoregular PPO become apparent : (a) the method of preparation of the active catalysts generally imply that they include M.. .X.. .M μ-bridged groupings (mainly M.. .0.. .M ones formed by the hydrolysis reactions) ; (b) the p o s s i b i l i t y of obtaining stereoregular crystalline poly­ mers frcm monomers (like PO) which do not induce an important "chain end control" of wing "catalyst s i t e control Tsuruta (13) : /

v^w^O

\

... c — Ο Al Al

This type of control, as well as the linear 3-centers structure implied by the rear attack of the unsubstituted carbon, definite­ l y necessitate the presence of several metal atcms i n a polynuclear s i t e , as indicated experimentally by several studies (5,15, 16,17). On the basis of these conclusions, i t appeared wor1±while to synthesize purposely, i n a reproducible procedure, well-defined compounds containing several metal atcms linked together by μ-οχο bridges, and carrying an OR group which would foreshadow the growing polymer chain (like the M-R structure i n the Ziegler-tzype catalysts for olefins polymerization). A. Synthetic methods As already reported elsewhere (18,19} a réévaluation of pot e n t i a l direct methods yielding these -M-O-M-OR groupings led to the development (20) of a straightforward 2-steps condensation process between metal acetates and alkoxides, according to the following general scheme : 2 M (0R) + Y M (OCOCH ) A

z

n

m

3

z u u

2 C

u

» 10 18

( T O )

M

2n-2 2

M

(Y)

m°2

+

2 R O C O C H

3

H

The composition of these complexes has been confirmed by element a l and functional analysis, and an alternative synthetic route has been devised, involving the carefully controlled hydrolysis of a Meerwein's double alkoxide (21) and yielding products d i s playing similar

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12.

TEYSSIE E T A L .

Μ

(OR) ^ .Μ (OR) η Δ

1

Polymerization

0

„„ FDH

ί

»> , ·\ (exc.)

of Heterocyclic

(RO)

JVIIM 0 2η-ζ £

0

ο

Monomers

167

+ 4 ROH

2

cœnpositions and properties. This approach proved to be particularly general and versatil e , allowing the synthesis of a broad family of ccmpounds i n c l u ding most metals of the periodic table, and different types of OR groups introduced by quantitative displacement of the small O i . C ^ group by another alcohol). B. General properties Frcm the experimental kinetic and structural data gathered up to now (18,19), these μ-ρχο-alkoxides are believed to have the following structur determined by cryoscopic measurements, indicates the mean degree of association of the ccmpounds and ranks frcm 1 to 8 i n benzene or cyclohexane solutions. I t i s indeed obvious that these canpounds w i l l tend to f u l f i l their vacant coordination positions on metals M and M by using the electron pairs available on the OR groups of the same or other oxoalkoxide molecules, resulting i n a reversible coordinative association (characteristic of a l l metal alkoxides). This η value depends as expected on the nature of the solvent, of the metal atans, and strikingly of the R group. I t i s important to note that sane specific solvents or ligands l i k e alcohols lead to a complete dissociation of these aggregates. This aggregation might also explain the incredibly high s o l u b i l i ­ ty of the cranpounds i n saturated hydrocarbons (practical irasci­ b i l i t y ) , as being due to a compact oxide structure surrounded by a l i p o p h i l i c layer of alkoxide groups. I t also accounts for the electronic delocalization put i n evidence by spectroscopic and magnetic measurements. 1

C. Catalytic Properties In perfect agreement with the structural hypotheses discus­ sed above, these compounds rank among the best catalysts known for the ring-opening polymerization of several heterocyclic mono­ mers : a practical indication of their a c t i v i t y i s given i n Table I : Monomer :

Catalyst

i. (Zn) :M χ 10

J

ss (Moin) : Solvent :T°Cït]y2 : : : (min) : i M :

:Methyl; 1.0 [heptane] 30 ! 20 : oxirane ;Al Zn0 (On.Bu) J' 16.6 :Methyl;Al Zn0 (On.Bu) 1 6 6 : thiirane ! · !; î.o [heptane]30 :ε-capro;Al Zn0 (Oi.Pr) ; 6 ; î.o 'toluene] 0 : lactone ! 5-° ! Table I. A c t i v i t y of bimetallic oxoalkoxides 2

2

2

2

2

2

4

;

4

4

;

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

;

RING-OPENING

168

POLYMERIZATION

Although many oxoalkoxide derivatives are active, the aluminiumzinc ones are the most interesting, the more as they are less harmful (if l e f t i n the product) than those containing transition metals. They also promote theeqiilibrium polymerization of isocyanates to polyamides-1 of very high molecular weight (10 ). As expected, a l l these polymerizations have been shown (by structural analysis of o i l goner i c fractions) to proceed by an insert i o n process into the M^-HDR, and later M^—OP, bonds. Accordingly, these soluble compounds represent an interesting model inbetween homogeneous and heterogeneous catalysis; owing to their high a c t i v i t y , their well-defined composition, and the p o s s i b i l i t y to modify systematically their structure, they offer an attractive tool to study the ring-opening polymerization processes, i n particular the eventual topochemical influence of the aggregate on the activ generate new types of products r i z e our recent advances i n these prospects. I t might be also worthwhile to point out an additional point of interest of these derivatives, i . e . their capability to bind and activate molecular oxygen at roam temperature (22), when M2 i s a transition metal l i k e Fe(II), Cr(II) or Mo (II). 6

II. Qxiranes polymerization As already indicated above, these catalytic sytems rank among the most e f f i c i e n t ones for the conversion of typical oxiranes (like PO) into high molecular-weight, p a r t i a l l y stereoregular, polyethers : i n particular, they have been considered for an eventual production of PO rubbers (23). Kinetic and structural data point towards a coordinative-anîciiic mechanism, proceeding through ^-stereoselective opening and insertion into the Al-OR bond of the catalyst. Furthermore, the catalytic aggregate on which the reaction takes place i s apparently not dissociated, but may undergo a more or less thorough rearrangement depending on the nature of i t s R groups and of the monomer. The overall behaviour f i t s with a " f l i p - f l o p " mechanism between 2 (or more) metal atoms, i n agreement with the proposals of Vandenberg and Tsuruta. A rather extensive description of these reactions has been already published (18), and more detailed accounts are i n preparation; accordingly, t h i s chapter w i l l concentrate oiafew new trends which have emerged i n our exploratory research and seem to deserve further investigation. A. Specific controls of the catalytic béhaviour^in hgmopolymerization The kinetic and structural studies mentioned above (18) have put i n evidence the existence of 2 competing p a r a l l e l reactions, proceeding by the same insertion mechanism already mentioned, and both yielding (after the hydrolysis of the catalyst) linear

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12.

TEYSSié E T A L .

Polymerization

of Heterocyclic

Monomers

169

OH-terminated polyethers. However, the f i r s t one proceeds by a randcm ring-opening and produces atactic oligomers (DP : 2 to 40) having an intriguing non-monotonous molecular weight distribution, while the other one, which involves only a minor fraction of the active sites (less than 4 % ) , i s stereospecif i c and gives r i s e to p a r t i a l l y isotactic high molecular weight (10°) polyether. I t has been proposed (24) that these two types of propagation take place on active sites which have the same chemical structure, but very different steric environments. This view i s supported by several experimental results : the r e l a t i v e importance of these 2 processes may be modified up to the p r a t i c a l exclusion of one or the otter by changing the type of aggregate (in particular the value of n) ; the degree of stereospecificity depends also (frcm 5 to 75 %) on the~same parameter; and this control of the catalyt i c behaviour i s sensitiv the shape of the aggregat obtained with two closely related cattpounds having different coordination sphere geometries, e.g. the blue AI2C0O2 (On.Bu) and the red-violet AI2C0O2 (Oi.Pr)^) · In other words, i t might be suggested that these soluble systems exert seme degree of topochemical control on the kinetic and stereochemical course of the polymerization reactions. On the other hand, and maybe for similar reasons the stereos p e c i f i c i t y of the processes i s highly dependent on the structure of the monomer for a given catalyst, as i l l u s t r a t e d by the fact that Al2Zn02 (On.Bu) polymerizes, with rather similer rates, allylglycidylether to an essentially amorphous polymer and phenylglycidylether to a highly isotactic c r y s t a l l i n e material. The understanding of such a sensitive and subtle balance i n the catalytic behaviour, as related to the size and shape of the aggregates, i s certainly a provocative and worthwhile challenge. 4

4

11

B."0n purpose Modifications of the relative r e a c t i v i t y ratios i n copolymerizatlons As already reported i n ref. (18), the extent of incorporation of a given monomer i n a growing copolymer chain depends on other factors than i t s simple i n t r i n s i c reactivity versus a given bimet a l l i c oxoalkoxides catalyst. E.g., i t has been possible, by playing with the nature of the solvent, to favour the preferential insertion of either PO or of epichlorohydrin i n randan copolymerization experiments of these two monomers. In another similar approach, equimolar mixtures of PO and methylthiirane (PS) have yielded products containing essentially PO units or PS units, depending on the use of a Al2Fe0 (OR) or of a Al Zn0 (OR)4 catalyst. A tentative interpretation involves, i n sharp contrast with other types of catalyses, a powerful thermodynamic control of these apparent reactivity ratios, due to the corresponding r e l a t i v e formation constants of the different cattpeting complexes 2

4

2

2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

170

RING-OPENING POLYMERIZATION

formed between the catalyst and the monomers; obviously, the overa l l rate of the œpolymerization process should s t i l l be k i n e t i c a l l y determined by the relative i n t r i n s i c r e a c t i v i t i e s of these monomers as appearing i n the hcmopolymerization rates. Anyhow, we have a new and very powerful tool for studying mechanistic behaviours, and for controlling the composition of new products, i n particular azeotropic situations i n binary copolymerization reactions. III. Lactones polymerization A. HcTODpolym^ization reactions. For this type of monomer also, i n particular for ε-caprolac­ tone which i s an interestin oxoalkoxides are at leas already known (see table 1). The overall course of these reactions i s very similar to that one described for oxiranes; again, kinetic and structural data i n ­ dicate a typical anionic-coordinated mechanism (18, 25, 26). The molecular weight increases proportionaly to the conversion : the perfectly " l i v i n g " character of these polymerization reactions has been ascertained by the linear relationship between DP at 100% conversion and (M)/(C) ratios, as well as by the resumption of the polymerization on addition of fresh monomer to a polymerized reac­ tion mixture (with a proportional increase of DP). High molecular weights (up to 200.000) as well as narrow distributions (Ϊ^/^Ξ^ 1.05) can be controlled by avoiding side reactions. A structural analysis of the f i r s t products of the chain propagation indicates clearly that t h i s reaction proceeds through insertion of the lactone units i n the A1-0R bonds, with a specific cleasage of the acyloxygen bond, resulting i n the permanent binding of the growing chain to the catalyst through an alkoxide l i n k (rather than a carboxylate one) : ^A1-0R + η caprolactone

^ A l i Ο (CH ) C0f 0R 2

5

n

HfO(GH ) COf CR 2

5

n

An interesting and mechanistically important point i s that the number of active sites (potentially 4 per trinuclear catalytic molecule) depends i n fact on the type of aggregation of the oxoal­ koxides : i n other words, as indicated also by N.M.R. measurements (19), there are 2 different types of OR groups depending on their bridging i n the aggregates, and only one i s active i n the polyme­ r i z a t i o n process which results (before hydrolysis) i n a catalytic star-shaped entity. These views have been confirmed by the fact that dissociated catalysts (under the influence of the solvent or added alcohols) generate 4 growing chains per Α 1 Μ 0 (0^) 4 molecule. The reaction i t s e l f seems to proceed by the usual f l i p - f lop mecha­ nism, involving either one A l atom with a vacant cis-coordination position, or two more saturated atoms, again depending on the va­ lue of n. 2

2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12.

TEYSSIE ET AL.

Polymerization

of Heterocyclic

Monomers

171

B. Block œpolymerization The perfectly l i v i n g character of these lactone polymerizations was obviously a tempting tool to undertake the synthesis of block copolymers, and different successful approaches have been developed, which are summarized hereafter. Polylactone A -_PolYlactone_B_œpolymers have been studied f i r s t as models, to reach a good control of"these reactions. As expected, consecutive (and quantitative) polymerization of 2 different lactone monomers was easy to perform. However, high yields of block copolymers fe90%) are attained only under complete d i s s o c i ation of the aggregates, ensuring the use of a l l potentially a c t i ve OR groups which otherwise might start homopolymer chains (due to a rearrangement or a on addition of the secon As a typical example, different poly(caprolactone-b-propio lactone) samples have been prepared, which exhibit interesting mixed crystalline morphologies, depending on the thermal history of the samples (27). Polylactone - PolyH copolymers, where H i s any heterocyclic monomer susceptible to undergo ring-opening polymerization by oxoalkoxide catalysts, have also been easily obtained i n high yields under the same dissociative conditions. Typical examples include poly-(caprolactone-b-oxiranes), poly-(caprolactone-b-thiiranes), and poly- (caprolactone-b-isocyanates). Since these Α. Β chains are always OH-terminated (cfr polymerization mechanism), any e f f i ­ cient coupling technique may lead to the corresponding A-B-A structures (eventually thermoplastic elastomers). Polylactone - PolyX copolymers , where polyX i s any preformed polymer chain carrying a~suitable functionnal group able to react with the oxoalkoxide catalyst, are the most interesting products obtained. On the basis of the structural and kinetic behaviour of the oxoalkoxide entities (see above), a specific straightforward procedure has been developed (again under dissociative conditions) : i t involves the metathetic quantitative displacement of one OR group by the terminal hydroxy1 function of a preformed polymer, followed by caprolactone polymerization by the polymer-supported catalyst so obtained (29) : + KM

ΞΑΙ-OR + HO-JSLv -CA1-0

^A140-(CH )^C0i- OvJ^L 2

n

H +

»

Π

^

HO - PCL - PX

grafted, A-B diblocks, A-B-A and B-A-B triblocks may be synthesi­ zed by using these techniques. Since the OH-terminated preformed PX block i s often prepared by anionic polymerization with a good control of M and molecular weight distribution (as i t i s also the case for the polylactone

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

172

RING-OPENING

POLYMERIZATION

block), i t i s possible by this technique to t a i l o r a whole famil y of new materials with a broad range of carefully matched molecular characteristics; e.g. such copolymers where PX i s polystyrene, polybutadiene or polyether have been obtained i n 90% yields for individual block molecular weights ranging frcm 1.000 to 150.000. IV. Application properties for new materials obtained by ringopening polymerization. It has already been reminded that t h i s type of polymerization i s a f r u i t f u l source of interesting materials for practical a p p l i cations and i t seemed worthwhile, i n the frame of this contribution, to i l l u s t r a t e that point by seme examples generated from the study of the oxoalkoxid t i c u l a r l y significant copolymers of polystyrene and polycaprolactone (29) (prepared as described i n section III.B.), and the present section w i l l be devoted to a brief demonstration, on these materials, of some potentialities of this type of approach. A. Physical properties of poly- (caprolactone-b-styrene). As expected (at least for high M.W. blocks), these products exist under the form of heterophasic materials. Electron micrographs show that depending on the sample composition, one may have either a very fine dispersion of PCL domains (eventually amorphous) i n a r i g i d PSt matrix (PCL content lower than 3 5 % ) ; or of PSt domains i n a c r y s t a l l i n e PCL matrix (PCL content above 40 % ) . The size of these domains may be systematically modified frcm about 150 to 500 Â by controlling the molecular characterist i c s of the blocks. Obviously, the c r y s t a l l i s a t i o n behaviour (kinetics, morphology) i s also very sensitive to these composition and molecular size parameters. The mechanical consequences of t h i s heterophasic structure are well i l l u s t r a t e d by the torsion modulus curves of f i g . l (recorded with a Gehman's type apparatus). Not only the usual influence of the Tg and melting point of PCL blocks (around -65°C and + 50°C) and of the PSt blocks Tg (100°c) are clearly and i n dependently apparent, but they also suggest that the whole mater i a l has a viscoelastic behaviour up to ca. 140°C i n contrast with pure PCL. I f one considers the variation of the same modulus i n function of the PCL content of the copolymers, above the PCL c r y s t a l l i n e melting point e.g. a t 70°C, a definite transition i s apparent (fig.2) around the same composition where electron microscopy observations show a phase inversion : t h i s result suggests that indeed an heterophasic morphology (amorphous-amorphous) persists i n the product. Another i l l u s t r a t i v e behaviour may be found i n the stressstrain curves recorded on these materials (fig. 3). An important cold drawing i s observed, implying the formation of a well-

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12.

TEYSSIE ET AL. Log

Polymerization

of Heterocyclic

Monomers

173

[3«dyn,t/cm2j

Figure 1.

-80

-AO

0

«0

80

120

*C

Torsion modulus of poly-

of temperature (10 sec)

Figure 2. Torsion modulus of poly(CL-b-St) samples in function of the caprolactone content. (a)AtO°C,(b)at70°C.

0

100

^X>

300

400

Figure 3. Stress-strain curves for poly(CL-b-St) samples and pure PCL (molded films). Rate, 600% /min at 23°C.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

174

RING-OPENING POLYMERIZATION

organized f i b r i l l a r structure (evidenced by other techniques) ; i t i s followed by another zone of e l a s t i c behaviour ( s t i l l displaying a good modulus for the samples with a r e l a t i v e l y high PSt content). I t must be emphasized that the stretched material has a very high resistance to break even at very low temperatures, and peculiar fracture behaviour. In other words, t h i s type of material offers an attractive additive ccmbination of the properties of both components (high Young's modulus and tensile strenght, viscoelastic behaviour up to 140°C, good s t a b i l i t y ) , plus seme unexpected and valuable beneficial points (like the fracture behaviour at low temperature), Ii\ conclusion, these results represent a new confirmation of the power of the "properties additivity concept" i n block copolymers. B. Application o phology conteôls"în"pôîyme I t has already been known for seme time that a ΡΑ-PB block copolymer was able to bridge the canpatibility gap between two homopolymers PA and PB, and to help i n establishing a fine pha­ ses dispersion i n their mixtures. Thanks to the apparent compatibility of PCL with other PX poly­ mers, we have t r i e d to extend this concept to the dispersion of mixtures of PA and PX hcmopolymers with a PA-PCL block material. The v a l i d i t y of this concept i s demonstrated by the optical photomicrographs (fig. 4) of films casted frcm 80PVC/20PSt solu­ tion mixtures containing respectively Ο , 5 and 10 % of a 56/50 poly-(caprolactone-b-styrene) sample ( B 3 ) . The corresponding torsion modulus diagrams (Gehraan's curves, fig.5) show the existence of 3 phases i n the mixtures : a PSt phase (transition at 100°C) including both the homo-PSt and PSt blocks, a PVC phase (transition at 80°C) containing the pure PVC, and a third one consisting probably of PVC "plasticized" by PCL blocks (40-50°C). In other words, the block copolymer realizes an "anchorage" at the interface of the two homopolymers; increasing i t s concen­ tration promotes a development of the interface, i . e . a decrease i n the size of the domains, as confirmed by the microscopic ob­ servations. Another important consequence i s the increase of the mixtures modulus between 80 and 100°C when increasing the block copolymer content. As expected, the other physico-imechanical pro­ perties are also accordingly improved. Obviously, these concepts and techniques can be applied to a variety of block copolymers, using bimetallic oxoalkoxides or even other catalytic systems : another interesting example i s the synthesis of a nylon. 6-polybutadiene-nylon. 6 triblock copolymer using anionic techniques. The resulting material exhibits again a fine heterophasic gtructure where small PBD domains (mean diameter around 400 A) are homogeneously dispersed i n the c r y s t a l ­ l i n e nylon matrix (30).

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12.

TEYSSIE ET A L .

Polymerization

of Heterocyclic

Monomers

Figure 4. Optical photomicrographs (G = 180) of films obtained from solution mixtures of 80 PVC/ 20PSt, in the presence of 0 (al), 5 (a2), and 10% (a3) of 50/50 poly(CL-b-St)

Log [3G(dynes/cnn2)J

—

80/20

—

72 / 18 / 10 64 / 16 / 20

0

20

60

60

80

100

120

U0

160

*C

Figure 5. Torsion modulus in function of temperature for blends of PVC, PSt, and P(CL-b-St)

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

176

RING-OPENING POLYMERIZATION

Conclusions The good control and knowledge of new catalysts l i k e these bimetallic oxoalkoxides i s a powerful tool, leading to a better understanding and mastering of the key factors, sometimes unexpected, which govern the ring-opening polymerization processes. This approach also allows to f u l l y develop the very r i c h potentialities of this type of polymerization for the synthesis of new materials, mainly block copolymers, enjoying o r i g i n a l and useful sets of physical properties. Acknowledgments The authors want to recognize the pioneering work of M. Osgan (I.F.P.), and the contributions of N. Kohler, J.J. Louis, C. Stevens and P. Condé. They are also grateful to I.F.P. (France), Union and C.R.I.F. (Belgiun}

ο ο

ο

Literature Cited (1) Wurtz Α., Annalen (1859) 110; Ber. (1877) 10 (2) Staudinger H., Ann. Chem., (1933) 41, 505 Pruitt, Jackson and Bagguet, U.S. Pat. (1955), 2.706.181 (4) Colclough R.C. and Gee G., J. Polymer Sci., (1959) 34 171 (5) Osgan M., J. Polymer Sci. (1968), A1,6, 1249 (6) Furukawa J., Tsuruta T. and Saegusa T. Kogyo Kagaku Zasshi, (1959), 62, 1269 (7) Sakata R. and Tsuruta T., Makromol. Chem. (1960) 40, 64 (8) Vandenberg E.J., J. Polymer Sci. (1969), A1,7, 525 (9) Coclough R.C. and Wilkinson K.,J. Polymer Sci. (1964), 4, 311 (10) Lai J., Polymer Letters (1967), 5, 793 (11) Belner R.J., Herold R.J. and Milgrom J., U.S. Pat. (1969), 3.427.256 and 3.427.334.5 (12) Vandenberg E.J., J. Polymer Sci. (1960) 47, 489 (13) Tsuruta T., Int. Sci. Technol., (1967), 71, 66 (14) Hirano T., Kogyo Kagaku Zasshi (1963), 66, 1158 (15) Gurgiolo A.E., Rev. Macromol. Chem. (1966), 1, 39 (16) Gee G. and Higginson W., Polymer (1962), 3, 231 (17) Vandenberg E.J., J. Polymer Sci. (1969) A1,7, 525 (18) Teyssié Ph., Ouhadi T. and Bioul J.P., Int. Rev. of Sci., Phys. Chem. Ser. 2, 8, 192. Butterworths, London 1975 (19) Ouhadi T., Bioul J.P., Stevens C.,Warin R., Hocks L. and Teyssié Ph. Inorg. Chim. Acta (1976) 19, 203 (20) Osgan M. and Teyssié Ph., Polymer Letters (1967) B5, 789

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12. TEYSSIE E T A L .

Polymerization

of Heterocyclic

Monomers

(21) Osgan M., Pasero J.J. and Teyssié Ph., Polymer Letters (1970), B8, 319 (22) Teyssié PH. et al., in "Catalysis, heterogeneous and Homogeneous", Bd. B. Delmon and J. Jannes, p. 289, Elsevier, Amsterdam 1975. (23) Osgan,M., Teyssié Ph. and Wauquier J.P., A.C.S. Symp. 156 (1968) Div. Petr. Chem., Prepr. A, 89 (24) Bioul J.P., Ph. D. Thesis, University of Liège (1973) (25) Ouhadi T., Hamitou A., Jérône R. and Teyssié Ph., Macromolecules (1976) 9, 927 (26) Hamitou A., Ouhadi T., Jérôme R. and Teyssié Ph., J. Polymer Sci., (1977), A1, in press (27) Huynh Ba Gia, Licence Thesis, university of Liège (1975) (28) Heuschen J. , Jérôme R. and Teyssié Ph., Fr. Pat. (1977) dep. nr Β 7501 (29) Heuschen J., Ph. D. Thesis, University of (30) Petit D., Ph. D. Thesis, University of Liège (1975)

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

177

13 Optically Active Poly[oxy(l-alkyl)ethylene] TEIJI TSURUTA Department of Synthetic Chemistry, Faculty of Engineering, University of Tokyo, Bunkyo-ku, Tokyo, Japan 113

The optical rotation of poly(R-oxypropylene) has different signs at the sodium D line (589 nm) in different solvents. The specific rotation, [α] D , of poly(R-oxypropylene) is positive in cyclohexane and in chloroform, but negative in benzene and tri­ fluoroethanol. Since Price and Osgan (1) first reported this phenomenon, several attempts have been made to interprete this in terms of a collision complex formation (2) with the solvent or a change of conformation of polymer molecules in response to the nature of solvent. According to our knowledge, however, any decisive conclusion has not yet been drawn concerning the opti­ cally active behaviors of poly(R-oxypropylene). To solve this problem, a series of studies on optically active poly[oxy(l-alkyl) ethylene] has been carried out. It was found from these studies that the influence of solvent on the ORD spectra decreased with the increase in bulkiness of the alkyl substituent of the oxy­ ethylene unit (3),(4). The bulkiness of the alkyl substituent also exerts an enor­ mous i n f l u e n c e upon the nature o f s t e r e o s e l e c t i v e p o l y m e r i z a t i o n of alkyloxiranes. When the R , S - c o p o l y m e r i z a t i o n o f t - b u t y l ­ -oxirane was c a r r i e d out s t a r t i n g with a monomer mixture c o n s i s t i n g o f R/S=76/24 using t-BuOK as initiator, R-monomer was found to be incorporated i n t o polymer chain p r e f e r e n t i a l l y over S-monomer (5). T h i s i s explained i n terms o f the growing chain c o n t r o l mechanism, i n which the c h i r a l s t r u c t u r e o f the growing polymer chain i s r e s p o n s i b l e f o r the s t e r e o s e l e c t i o n . A unique and s i g n i f i c a n t e f f e c t o f the bulky s u b s t i t u e n t has r e c e n t l y been found a l s o i n a c a t i o n i c o l i g o m e r i z a t i o n o f (R)­ - t - b u t y l o x i r a n e with boron t r i f l u o r i d e etherate as i n i t i a t o r , where a c y c l i c tetramer was formed i n an e x c e l l e n t y i e l d ( 6 ) . In the present review a r t i c l e , the author intends to d i s c u s s on the e f f e c t o f the bulky s u b s t i t u e n t on the p h y s i c a l p r o p e r t i e s o f p o l y ( a l k y l o x i r a n e ) as well as the mechanism o f s e l e c t i v e p o l y ­ m e r i z a t i o n and o l i g o m e r i z a t i o n r e a c t i o n s .

178

1. Conformation and O p t i c a l Rotatory Behavior o f alkyl)ethylene]

Poly[0xy(l-

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

13. T S U R U T A

Optically

Active

Poly(oxy(l-alkyl)ethylene)

179

For the d i s c u s s i o n o f conformation o f poly(i?-oxypropylene) m o l e c u l e s , we have to c o n s i d e r stereochemistry with r e s p e c t to C-C and C-0 bonds along a polymer c h a i n , ( 0 - C H ( C H ) - C H ) n In order to get information on the r o t a t i o n a l isomers around the C-C bond, a deuterated poly(#-oxypropylene) was prepared s t a r t i n g from t r o n s - d e u t e r a t e d methyloxirane monomer ( 7 ) , ( 8 ) . The v i c i n a l c o u p l i n g c o n s t a n t s , |JAC|» between the methylene and the rnethine protons were found to be 5.3, 4.9 and 5.2 (Hz) i n cyclohexane, chloroform and benzene, r e s p e c t i v e l y . By assuming the standard values J = 2 . 6 (Hz) and 0 §=9.3 (Hz) reported i n a v a r i e t y o f 1 , 2 - d i o x y g e n - s u b s t i t u t e d propane d e r i v a t i v e s , i t was p o s s i b l e t o estimate the population o f the three r o t a t i o n a l isomers i n c y c l o ­ hexane, chloroform and benzene, r e s p e c t i v e l y . 3

3

e

6 0

3

2

ϊ8

From the r e s u l t s s t a t e d above, the d i s t r i b u t i o n s o f the three r o t a t i o n a l isomers wer i?-oxypropylene) i n the thre ences being not so l a r g e as to e x p l a i n the s i g n d i f f e r e n c e i n the [α]χ> o f the oxirane polymer. Studies on the d i p o l e moment o f an isotactic poly(oxypropylene) suggested the d i s t r i b u t i o n o f r o t a t i o n a l isomers around C-0 bonds to be s c a r c e l y changeable i n benzene and i n cyclohexane as shown i n Table I. We t h e r e f o r e c a r r i e d out a s e r i e s o f s t u d i e s on the c i r c u l a r dichroism spectrum o f poly(#-oxypropylene) i n a number o f s o l v e n t s i n the vacuum u l t r a v i o l e t region under the cooperation with W.C. Johnson, Oregon S t a t e U n i v e r s i t y . In the c i r c u l a r dichroism(CD) spectra o f poly(i?-oxypropylene), two CD bands were observed f o r cyclohexane, a c e t o n i t r i l e , and t r i f l u o r o e t h a n o l ( T F E ) s o l u t i o n s . The CD spectrum was extended to 140 nm and three bands were measured i n a 1,1,1,3,3,3-hexafluoro-2-propanol(HFIP) solution. A Kronig—Kramers transform o f the two CD bands observed i n cyclohexane accounts f o r the observed p o s i t i v e ORD spectrum. In contrast, a t h i r d large and negative ORD band centered a t 155.5 nm i s r e s p o n s i b l e f o r the negative ORD spectrum observed i n HFIP. In the l a t t e r s o l u t i o n as well as i n benzene, the ORD spectrum was found to f i t the Drude one term equation with λ = 1 5 0 nm. In the l i g h t o f the r e s u l t s o b t a i n e d , i t i s most probable to conclude t h a t the i n t e r a c t i o n between polymer main chain and s o l ­ vent molecules should be the major cause f o r the d i f f e r e n t s i g n o f ORD i n the two groups o f s o l v e n t i n the v i s i b l e r e g i o n . Since p o l y [ o x y ( l - a l k y l ) e t h y l e n e ] i s expected to possess lower degrees o f s o l v e n t i n t e r a c t i o n as the a l k y l - s u b s t i t u e n t becomes b u l k i e r , p o l y ( i ? - i s o p r o p y l o x i r a n e ) (3) and p o l y ( i ? - t - b u t y l o x i r a n e ) (4) were s y n t h e s i z e d and t h e i r o p t i c a l r o t a t o r y behaviors were examined i n a number o f s o l v e n t . As shown i n F i g . 1, the i n f l u e n c e o f s o l v e n t on the ORD s p e c t r a decreases with the i n c r e a s e i n b u l k i n e s s o f the a l k y l s u b s t i t u e n t o f the oxyethylene u n i t . The bulky t - b u t y l s u b s t i ­ tuent seems to make the main chain r e l a t i v e l y " r i g i d " and reduces the a c c e s s i b i l i t y o f the main c h a i n i n the p r e f e r r e d conformation (perhaps a l o c a l h e l i x ) to the s o l v e n t molecule. 0

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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RING-OPENING POLYMERIZATION

In order to get independent information concerning the degree of r i g i d i t y o f p o l y [ o x y ( l - a l k y l ) e t h y l e n e ] molecule, p a r t i a l l y relaxed FT C NMR spectra were examined. The C s p i n - l a t t i c e r e l a x a t i o n times f o r the three polyoxiranes are l i s t e d i n Table II, i n which η denotes the number of hydrogen atom bound to the r e l e v a n t carbon atom. The b u l k i e r the a l k y l s u b s t i t u e n t , the smaller nTi values were o b t a i n e d , which was regarded as a conse­ quence of slower segmental motion owing to the enhanced r i g i d i t y of the macromolecule possessing b u l k i e r s u b s t i t u e n t s . Under the extreme narrowing c o n d i t i o n s , the c o r r e l a t i o n time, τ # , f o r each carbon atom was c a l c u l a t e d . Results obtained are shown i n Table 1 3

1 3

β

It can be s a i d from the values f o r τ # / τ £ Λ t h a t the methylene-carbon undergoes more r a p i d movement than the methine-carbon i n poly(oxypropylene), wherea atoms synchronized i n th ene), suggesting more f l e x i b i l i t y i n the poly(oxypropylene) c h a i n . β

2. R e g i o s e l e c t i v i t y i n the Ring-Opening Polymerization of t-Butyloxirane It was p r e v i o u s l y reported (5) that the bulk polymerization o f t-butyloxirane i n i t i a t e d with potassium t - b u t o x i d e (t-BuOK) proceeded according to the l i v i n g mechanism with the i n i t i a t o r e f f i c i e n c y being 100%. In order to get information on the s i t e o f bond cleavage during the polymerization p r o c e s s , (i?)-t-butyloxirane was p o l y ­ merized i n bulk with the t-BuOK i n i t i a t o r . The C NMR spectrum o f p o l y [ ( i ? ) - t - b u t y l o x i r a n e ] i s given i n F i g . 2. Assignments o f the NMR s i g n a l s were made by the gated method. Each carbon s i g n a l i n F i g . 2 i s a sharp s i n g l e t and no e x t r a s i g n a l due to i r r e g u l a r s t r u c t u r e s can be observed, i n d i c a t i n g t h a t the sample of p o l y [ ( i ? ) - t - b u t y l o x i r a n e ] obtained i n 98% y i e l d from (i?)-t-butyloxirane by the bulk p o l y m e r i z a t i o n with t-BuOK i s c o n f i g u r a t i o n a l l y homogeneous ( i . e . , i s o t a c t i c ) , and t h a t the amounts o f head-to-head and t a i l - t o - t a i l sequences are too s m a l l , i f any, to be detected by C NMR. T h e r e f o r e , the bulk p o l y m e r i z a t i o n o f t - b u t y l o x i r a n e with t-BuOK was concluded to proceed to form h e a d - t o - t a i l sequences under the e x c l u s i v e c l e a v ­ age a t e i t h e r o f the 0-CH bond (α-opening) o r the 0-CH bond (β-opening). The C NMR studies c a r r i e d out on the l i v i n g p o l y m e r i z a t i o n system o f ( f l ) - t - b u t y l o x i r a n e l e d us to conclude the β-opening to be o p e r a t i v e i n the propagation process o f t - b u t y l o x i r a n e . This c o n c l u s i o n was drawn on the basis o f the f o l l o w i n g o b s e r v a t i o n s . In the C NMR spectrum o f the l i v i n g system i n i t i a t e d by l a r g e r amount o f t-BuOK, several new s i g n a l s were observable along w i t h . t h e s i g n a l s which,were assigned p r e v i o u s l y to - C H - (74.5 ppm ), - Ô H - (89 ppm) and - C - (35.1 ppm) o f the i n t e r n a l u n i t s of poly [ ( f l ) - t - b u t y l o x i r a n e ] . 'New s i g n a l s a t 64 ppm (-CH -) and 73 ppm (-0-) i n the l i v i n g system were assigned to s t r u c t u r e [ 1 ] , 1 3

1 3

2

1 3

1 3

2

2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

13.

TSURUTA

Optically

Table I

Dipole Moments of isotactic Solvent

Temp, i n °C

benzene

cyclohexane

Table II

Polymer

CH

in C D : 6

6

2.2 0.84 0.52

25 35 51 25 35 51

Poly(oxypropylene)

μ i n Debye 1.09 1.09 1.10 1.04 1.04 1.05

± ± ± ± ± ±

0.03 0.03 0.03 0.03 0.03 0.03

C S p i n - L a t t i c e Relaxation Times, nT

CH,

substituent C

Me isoPr t-Bu

181

Active Poly(oxy(l-alkyl)ethylene)

3.0 0.98 0.54 4.0

CH

CH

CH,

0.84 -

6.9 3.9 2.0

x

(sec)

substituent

CH,

CH 2.2 0.70 0.43

3.4 0.84 0.40

Cone.σα 10 \n/v%, a t 60°C i n C D g

1 2

0.70 3.4 -

CH, 6.9 3.9 2.2

: Cone.cal0 w/v%, a t 60°C

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

182

because these s i g n a l s were a l s o found i n the spectrum o f an oligomer which was obtained a f t e r the treatment o f the l i v i n g system with aqueous HCl s o l u t i o n . CH t 3 CH -C-0-CH -

Bu

0

Q

0-CH -CH-0K

9

2

! 3 73

! 64

81

ppm

ppm

ppm ppm

C H

[1]

83

[2]

The s i g n a l s at 81 ppm (-CH -) and 83 ppm (-CH-) observed i n the l i v i n g system were assigned to the s t r u c t u r e o f the growing chain end u n i t [ 2 ] l i v i n g system was t r e a t e with t h i s o b s e r v a t i o n , a s i g n a l a s s i g n a b l e to methine carbon o f s t r u c t u r e - C H ( £ - B u ) - 0 H was found a t 78 ppm i n the spectrum o f the oligomer. From these r e s u l t s , i t was unambiguously confirmed t h a t the bond cleavage o f t - b u t y l o x i r a n e takes place e x c l u s i v e l y at 0-CH bond during the p o l y m e r i z a t i o n process with t-BuOK as initiator. 2

2

3. E f f e c t of t - B u t y l S u b s t i t u e n t on the Polymerization o f t - B u t y l o x i r a n e

S e l e c t i v i t y i n the

It was p r e v i o u s l y reported (9) t h a t copolymerization study between i?- and S-monomer i s a useful tool f o r e l u c i d a t i o n o f the s t e r e o c o n t r o l mechanism. When the #,S-copolymerization of t - b u t y l oxirane was c a r r i e d out s t a r t i n g with a monomer mixture c o n s i s t i n g of i?/S=76/24 using t-BuOK as i n i t i a t o r , i?-monomer was incorporated i n t o polymer c h a i n p r e f e r e n t i a l l y over S-monomer (5). As the consequence, the o p t i c a l p u r i t y i n the recovered monomer became smaller than that o f the s t a r t i n g mixture i n the course of the i?,5-copolymerization ( F i g . 3 ) . This i s explained i n terms of the growing chain c o n t r o l mechanism, i n which the c h i r a l s t r u c t u r e of the growing polymer chain i s r e s p o n s i b l e f o r the s t e r e o s e l e c t i o n . (R)

-CH -CH{£-Bu)-0K

(S)

2

(i?)

^

„t-Bu

y

^ 7 ^ ^ - B u 0

(k

)

The curve f o r t - b u t y l o x i r a n e i n F i g . 3 was analyzed i n more d e t a i l by deviding the curve i n t o $ - s t a g e s . From experimental data a t every stage, i t was p o s s i b l e to c a l c u l a t e a parameter, α · , which i s d e f i n e d as f o l l o w s : 7

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

13. T S U R U T A Table III

Optically Active Poly(oxy(l-alkyl)ethylene) Ratio o f the C o r r e l a t i o n Times w / ^ " CH Carbons **

f o r CH, and

2

i

Substituent Me isoPr t-Bu

C0CI

3

Λ

90

Figure 2.

183

in C D 6

6

in CgD

0.76 0.87 0.97

f

2

12

0.67 0.83 1.1

ί

80

70

60

50

4-0

30

20

10

Tulsed FT C-NMR spectra (25.03 MHz) of P((R)-tert-butyloxirane) in the CDCl solution (10 w/v%) at 45°C 13

3

50

Conversion

100

(%)

Figure 3.

R-Content in unchanged mono­ mer vs. conversion

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

184

RING-OPENING POLYMERIZATION

[dR/dS^CR/S]^ The parameter oy i s regarded as a measure of the s t e r e o s e l e c t i v i t y which i s a s s o c i a t e d with a growing polymer chian a t j - s t a g e . The parameter, ou, was found to become g r e a t e r as the conversion i n c r e a s e s . S i n c e the polymerization o f t-butyl oxirane i n i t i a t e d by t-BuOK was proved p r e v i o u s l y to form a l i v i n g system ( 5 ) , the above r e s u l t s i n d i c a t e that longer chain o f growing polymer to possess the g r e a t e r s t e r e o s e l e c t i v i t y , sudden increase o f oy-value being observed when the degree o f polymerization o f growing chain a t t a i n s about 20. T h e r e f o r e , we can conclude t h a t not only the c h i r a l s t r u c t u r e o f growing chain end but a l s o the c h i r a l second­ ary s t r u c t u r e o f the polymer chains should be r e s p o n s i b l e f o r the s t e r e o s e l e c t i o n o f incoming monomers. Methyloxirane behave o x i r a n e , no change a t a l phase being observed i n the course o f i?,5-copolymerization under s i m i l a r r e a c t i o n c o n d i t i o n s ( F i g . 3). I t was a l s o confirmed t h a t the main chain o f poly(methyloxirane) formed possesses randomly d i s t r i b u t e d R- and s-monomeric u n i t s with the same R/S r a t i o as t h a t i n the monomer phase r e g a r d l e s s of the conversion o f p o l y ­ m e r i z a t i o n . These r e s u l t s i n d i c a t e t h a t no s t e r e o s e l e c t i o n takes place i n the i?,S-copolymerization o f methyloxirane with KOR i n i t i a t o r (9). C.C. P r i c e (10) reported the IsoSyn mechanism f o r the s t e r e o ­ chemistry o f p o l y m e r i z a t i o n o f #5-t-butyloxirane i n i t i a t e d with t-BuOK. For the formation o f IsoSyn p o l y ( t - b u t y l o x i r a n e ) , -RRSSRRSSRRSSRRSS-, the f o l l o w i n g c o n d i t i o n s should be e s t a b l i s h e d

P

SR/R

>

P

RR/R

P

RR/R

P

RR/S

P

i/s

P

SR/R

P

s/i

P

SR/S

P

s/s

P

i/i

Penultimate Effect

where Ρ means a c o n d i t i o n a l p r o b a b i l i t y . The r e a c t i v i t y o f the terminal u n i t R i s expected to be d e f i n i t e l y c o n t r o l l e d by the penultimate u n i t . In order t o e l u c i d a t e the nature o f the growing chain c o n t r o l mechanism, a s e r i e s o f NMR s t u d i e s was c a r r i e d out with p o l y ( t b u t y l o x i r a n e ) which was prepared by the polymerization o f racemic monomer i n i t i a t e d by t-BuOK (11). Pulsed FT C-NMR spectra of the polymer are shown i n F i g . 4. By comparison with NMR spectra o f p o l y [ ( i ? ) - t - b u t y l o x i r a n e ] shown i n F i g . 2, i t was p o s s i b l e to 13

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Optically

13. TsuRUTA

Active

Poly(oxy(l-alkyl)ethylene)

185

estimate t r i a d population i n the p o l y [ ( 2 ? S ) t - b u t y l o x i r a n e ] as follows: ii(SSS+RRR) 32%; is+si[(SSR+RRS)+(SRR+RSS)] 48%; ss(SRS+RSR) 20%. Assuming the F i r s t Order Markov Chain mechanism, the f o l l o w i n g values a r e c a l c u l a t e d f o r Ρί/s and P / £ : s

£/ ( "s+si)/[2(ii)+(is+si)]=0.43 P /|=(1s+si)/[2(ss)+(is+si)]=0.55 p

=

1

s

s

These r e s u l t s suggest the terminal u n i t r e a c t s with an incoming monomer without any s i g n i f i c a n t i n f l u e n c e from the penultimate u n i t , because P /i was found almost equal At the very i n i t i a l stage o f the i?,S-copolymerization (R/S: 76/24) o f t - b u t y l o x i r a n e , any ordered secondary s t r u c t u r e has not y e t been e s t a b l i s h e d i n the growing polymer c h a i n , so that i t i s reasonable to use the value k ^ / k ^ (or k £ £ / k £ g ) l . 3 [obtained from 0.55/0.43 (see above) est stage o f the i?,S-copolymerization =76/24, α - v a l u e can be c a l c u l a t e d as f o l l o w s : t

0

s

s

d£Rl

[R] j f e O T +

=

d[S]

kgOT

[S] ^ [ R * ] + k ^ [ S * ]

d£Ri

=

d[S]

[R]

(*RR/*SS)

[S]

where k

f f î

[R*3/(S*]

+ T

[ R * ] / [ S * ] + (K; tt ) S

=k^, k ^ k ^

^ α

SR

[

R

]

[S]

and [ R * ] / [ S * ] = [ R ] o / [ S ]

0

The v a l u e , 1.14, f o r the α^· a t the i n i t i a l stage f a l l s i n the range of value which i s a n t i c i p a t e d from the experimental curve. Since the copolymerization was s t a r t e d with a mixture o f i?-content being 76%, there i s an enhanced chance to form i s o t a c t i c enchain­ ment, which w i l l r e s u l t i n the formation o f a c h i r a l secondary s t r u c t u r e . T h e r e f o r e , the p r e f e r e n t i a l i n c o r p o r a t i o n of f?-monomer w i l l be much more a m p l i f i e d i n the l a t e r stage as observed i n the experiment. In order t o get c l e a r e r p i c t u r e as t o the c h i r a l secondary s t r u c t u r e o f the growing chain end, the l i v i n g polymerization system [3] was studied by p a r t i a l l y relaxed (PR) FT C NMR i n terms o f the s p i n - l a t t i c e r e l a x a t i o n behaviors. 1 3

(3)

(2)

O)

Me, Me, C C r ι Me C-0-CH -(-CH—0—CHg—)^CH—0—CH

(4)

2

3

J

2

73 (Ti) (sec)

64

89

74.5

(1.3)

(0.8)

(0.35) (0.3)

89.1

2

él

-CH—OK 83 ppm

(0.15)(0.25)

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

[3]

186

RING-OPENING POLYMERIZATION

The PRFT spectra o f the l i v i n g system [3] showed t h a t values o f the s p i n - l a t t i c e r e l a x a t i o n time ( T J f o r the carbon atoms l o c a t e d i n the growing end u n i t s , whose s i g n a l s appeared a t 83 ppm, 81 ppm and 89.1 ppm, were observed to be much s h o r t e r than T i values f o r other carbon atoms o f the l i v i n g system. T i values o f the methyl-carbons (1) and (2) were observed again to be s h o r t e r than those o f the methyl-carbons (3) and ( 4 ) . The observed T i values f o r the l i v i n g system make i t p o s s i b l e to c o n s i d e r that the segmental motion o f the u l t i m a t e and p e n u l t i ­ mate u n i t s o f the growing chain are r e s t r i c t e d to a s i g n i f i c a n t extent. We i n t e r p r e t the r e s t r i c t e d segmental motion i n terms o f the formation of a r a t h e r r i g i d s t r u c t u r e i n which ether-oxygen atoms o f the growing end u n i t s are bound together through c o o r d i n a t i o n bonds with potassium c a t i o n i n v o l v e d i n the growin isomerism, the growing end moiety w i l l e x h i b i t a s i g n i f i c a n t c h i r a l c h a r a c t e r around the counter c a t i o n K . We c o n s i d e r the nature o f the observed enhancement o f the s t e r e o s e l e c t i v i t y , oy, to be a s c r i b a b l e to the formation o f the c h i r a l secondary s t r u c ­ ture around the potassium c a t i o n . Under the r e a c t i o n c o n d i t i o n s f o r the a s y m m e t r i c - s e l e c t i v e i ^ s - p o l y m e r i z a t i o n stated above, p r o b a b i l i t i e s f o r formation o f such c h i r a l s t r u c t u r e w i l l be r a t h e r low before the degree o f polymerization o f the growing chain a t t a i n s about 20. +

4. S p e c i f i c Formation o f C y c l i c Tetramer by C a t i o n i c O l i g o m e r i z a t i o n o f (i?)-t-Butyloxirane A unique and s i g n i f i c a n t e f f e c t o f the bulky s u b s t i t u e n t has r e c e n t l y been found a l s o i n a c a t i o n i c o l i g o m e r i z a t i o n o f t - b u t y l o x i r a n e with B F - 0 E t as i n i t i a t o r ( 6 ) . When b u t y l o x i r a n e was t r e a t e d with 5 mol% o f B F 3 ^ 5 t t , a snow-white s o l i d was formed i n 89% y i e l d (by weight). After purification, the c r y s t a l l i n e product (melting p o i n t 168°C) was analyzed. Iff, no e x i s t e n c e o f OH group; Molecular Weight (by vapor pressure osmometry), 410; A n a l , C a l c d : as a c y c l i c tetramer, C 71.95, H 12.07; Found: C 71.91, H 12.45. [aU 50.8 (C 1.10, i n C H i ) ; 53.8 (C 1.28, i n C H ) . From these r e s u l t s , the c r y s t a l l i n e product was concluded to be a c y c l i c tetramer of ( f f ) - t - b u t y l o x i r a n e . *H NMR and C NMR show t h a t the tetramer c o n s i s t s o f f o u r i d e n t i c a l monomeric u n i t s . T h e r e f o r e , the oxirane r i n g o f ( # ) - £ - b u t y l o x i r a n e must have opened e x c l u s i v e l y a t e i t h e r o f the CH-0 bond ( α - o p e n i n g ) or the CH -0 bond ( β - o p e n i n g ) . In order to o b t a i n information on the s i t e o f r i n g - o p e n i n g , a model r e a c t i o n o f ( f ? ) - t - b u t y l o x i r a n e with B F - 0 E t was c a r r i e d out i n the presence of t - b u t y l a l c o h o l i n one to one mole r a t i o to the o x i r a n e . A f t e r the unchanged a l c o h o l was removed, the r e a c t i o n mixture was examined by C NMR. Three s i g n a l s were observed a t 78 ppm, 73 ppm and 64 ppm 3

2

2

5

6

6

6

1 3

2

3

2

Ï 3

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2

13. T S U R U T A

Optically

Active

Poly(oxy(l-alkyl)ethylene)

187

besides the s i g n a l s assigned to the i n t e r n a l o x y ( l - t - b u t y l ) ethylene u n i t s . The f i r s t s i g n a l (78 ppm) was assigned to methine carbon of -CH-OH, while the second and t h i r d s i g n a l s to the s t r u c t u r e [ 1 ] , When a s i m i l a r r e a c t i o n was conducted i n the presence of methanol, s i g n a l s assignable to - C H - 0 C H group, i n s t e a d o f [ 1 ] , were observed a t 75 ppm and 58 ppm. From these r e s u l t s o f the model r e a c t i a n , i t was concluded t h a t the c y c l i c t e t r a m e r i z a t i o n o f ( i ? ) - t - b u t y l o x i r a n e with B F - 0 E t c a t a l y s t proceeds under the cleavage o f the CH -0 bonds ( β - o p e n i n g ) , which r e s u l t e d i n the formation of (2#, 5i?, 8i?, l l i ? ) ( 2 , 5 , 8 , l l - t e t r a - t butyl-1,4,7,10-tetraoxacylododecane with the r e t e n t i o n o f the c o n f i g u r a t i o n a t the asymmetric carbons. The s p e c i f i c formation o f the tetramer o f ( i ? ) - t - b u t y l o x i r a n e forms a sharp c o n t r a s t with th r e s u l t obtained i th r e a c t i o of ( s ) - i s o p r o p y l o x i r a n e product was an o i l y compoun g majo compounds of low molecular weight. The bulky t - b u t y l s u b s t i t u e n t i s expected a l s o to cause more severe r e s t r i c t i o n i n the p o s s i b l e p r e f e r r e d conformation o f the c y c l i c tetramer i n comparison with the corresponding l i n e a r polymer, p o l y ( ( i ? ) - t - b u t y l o x i r a n e ) . The chemical s h i f t and c o u p l i n g constant values i n the *H NMR spectra o f the c y c l i c tetramer i n deuterated benzene and chloroform are l i s t e d i n Table IV. In Table IV, the s i g n a l s around δ 2.8 ppm were assigned to the methine proton He, those around δ 3.6 - 3.8 ppm and δ 3.8 4.0 ppm to Ηβ and H/\ methylene protons, r e s p e c t i v e l y . The Newman p r o j e c t i o n f o r the p o s s i b l e three conformers around the methylene-methine carbon bond i s shown i n F i g . 5. The assignment o f H/\ and Ηβ are made from J s and d e s h i e l d i n g e f f e c t of the ether oxygen atoms. On the b a s i s o f the Karplus-type dependency of J on d i h e d r a l angle (12), i t was concluded t h a t He should come approximately on the b i s e c t i o n plane of HA and Ηβ because both o f the observed J and J B were about 3 H (Table IV). T h e r e f o r e , the predominant conformation around the main c h a i n CH-CH bond should be G i n F i g . 5. The most p l a u s i b l e s p a t i a l s t r u c t u r e f o r the c y c l i c tetramer i s t h a t shown i n F i g . 6, where the main chain o f the tetramer predominantly takes a G+G+T conformation: 2

3

3

2

2

3

1

3

3

3

A

c

C

z

+

2

-0-CH(t-Bu)-CH 2

G G Τ According to t h i s s t r u c t u r e , H/\ should be more deshielded than Ηβ because two e t h e r oxygen atoms 0 ( i - 2 ) and 0(i+4) come c l o s e to Ηβ than Ηβ o f the methylene group ( £ ) , and so are assigned the H/\ and Ηβ protons to the observed two methylene s i g n a l s . The ORD spectra o f the c y c l i c tetramer i n benzene, i n cyclohexane and i n chloroform are shown i n F i g . 7. In c o n t r a s t to the corresponding l i n e a r p o l y ( a l k y l o x i r a n e ) s , the ORD curve o f the c y c l i c tetramer i n cyclohexane i s e x a c t l y the same as that i n benzene and very +

+

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

188

-CH

»

•

'

•

•

•

-200

I

0

I

200

I

I

400

1

» - — ι

600

800

1

«

1

'

1

3

—

1000 1200

Hz

Figure 4. FT C-NMR spectra (25.03 MHz) of ?((RS)-text-butyloxirane) initiated by t-BuOK in bulk. Solvent, CDCl (cone. 30 w/v%); Temp., 50°C. 13

s

Table IV

Solvent

Chemical S h i f t s and Coupling Constants f o r the C y c l i c Tetramer, (2i?,5i?,8i?,lli?)-2,5,8,11 - t e t r a - t e r t - b u t y l 1,4,7,1O-tetraoxacyclododecane, i n Deuterated Benzene and i n Deuterated Chloroform a t Various Temperatures Temp,°C

Chemical shift.appm Δ

C

6Ο 6Ο D

CDC1,

ό a

Α

Δ

Β

S

C

Coupling c o n s t a n t , Hz

I ABI I ACI I BCI 3J

3J

3J

30 50 75

3.70 3.76 3.81

3.64 3.68 3.71

2.66 2.71 2.75

11.7 11.8 11.7

2.6 2.7 2.6

3.0 3.3 3.3

30 50

3.90 3.90

3.78 3.79

2.83 2.83

12.0 11.9

3.0 2.9

3.2 3.3

Chemical s h i f t i s given i n ppm u n i t with plus value f o r downfield s h i f t (oscale) from the i n t e r n a l standard TMS.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Optically Active Poly(oxy(l-alkyl)ethylene)

13. T S U R U T A

'Bu

H

B

-t°-T-K H

3

H

c

A

a ' ά°' Hc

βίΓ Α

Η

Η

Βυ

H 'V^H B

0

**

H

H b 1J H

A

A

1

r

mp ( <

'

Figure 5. Tfcree possible rotational isomers around the main chain CHCH,

Bu^

168 °C 5 0

- (^-10,C H 8

6

1 2

Figure 6. A proposed spatial struc­ ture of the tetramer of (R)-tert-butyloxirane

)

53.8 (c 1-28, C H ) 6

200

300

400

6

500

Wavelength ( η m )

600

Figure 7. Optical rotatory dispersion (ORD) spectra of the cyclic tetramer of (R)-tert-butyloxirane at 25°C. ( ) In cyclohexane, (· · ·) in benzene, (- ' -)in chloroform.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

189

RING-OPENING POLYMERIZATION

190

s i m i l a r to that i n chloroform. The s i m i l a r i t y of the ORD spectra of the c y c l i c tetramer i n benzene and i n cyclohexane i n d i c a t e s the absence of an a p p r e c i a b l e i n t e r a c t i o n of s o l v e n t molecules with the main c h a i n , as was discussed i n Section 1. The proposed s t r u c t u r e o f the c y c l i c tetramer may e x p l a i n the s i m i l a r i t y of the ORD curves i n F i g . 7, because ether oxygen atoms are i n s u l a t e d from the s o l v e n t by the bulky hydrocarbon groups.

Literature C i t e d (1) Price,C.C., Osgan,M., J. Am. Chem. Soc. (1956) 78, 690; 4787. (2) Kumata,Y., Furukawa,J., Fueno,T., Bull. C h e m . Soc. Japan (1970) 43, 3663; 3920. (3) Tsuji,K., Hirano,T., Tsuruta,T., Suppl. 1, 55. (4) Sato,Α., Hirano,T., Tsuruta,T., Makromol. C h e m . (1976) 177, 3059. (5) Sato,Α., Hirano,T., Tsuruta,T., Makromol. C h e m . (1975) 176, 1187. (6) Sato,A., Hirano,T., Suga,M., Tsuruta,T., Polymer Journal, (1977) in press. (7) Pham,K.H., Hirano,T., Tsuruta,T., J. Macromol. Sci.-Chem. (1971) A5, 1287. (8) Hirano,T., Pham,K.H., Tsuruta,T., Makromol. Chem. (1972) 153, 331. (9) Tsuruta,T., J. Polymer Sci. (1972) D6, 179. (10) Price,C.C., Akkapedi,M.K., DeBona,B.T., Furie,B.C., J. Am. Chem. Soc. (1972) 94, 3964. (11) Sato,A., Hirano,T., Tsuruta,T., Makromol. Chem. (1977) 178, in press. (12) Karplus M., J. Chem. Phsy. (1959) 30, 11.

Acknowledgment: The author wishes to express his gratitude to Dr. T. Hirano and Dr. A. Sato for their cooperation with him to promote this study.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14 Stereoselective and Stereoelective Polymerization of Oxiranes and Thiiranes

NICOLAS SPASSKY Laboratoire de Chimie Macromoléculaire, Associé au CNRS, Universite Pierre et Marie Curie, 4, Place Jussieu, 75230 Paris Cedex 05, France

Ionic polymerizatio vided in three main type -"coordinated". While anionic and cationic polymerization produce random amorphous polymers, at least when starting from racemic monomers, stereospecific initiators may give isotactic crystalline polymers. Depending on the initial reagents and resulting products, several types of stereospecific processes could be considered : - stereoselective polymerization, - stereoelective also called asymmetric-selective polymerization, - asymmetric-polymer synthesis. The first two processes are dealing with monomers which are a mixture of stereoisomers, while the last one considers symmetric monomers having two asymmetric carbons of opposite configuration. Most of the work in the field of stereoselective and stereoelective polymerization of oxiranes and thiiranes was carried out on monosubstituted monomers and was reviewed in some publications (1-6). The stereochemical aspects of the polymerization of some di-substituted oxiranes and thiiranes were described in the work of Vandenberg (7,8). The aim of this paper is to give a review of the more recent results concerning such reactions, to include some new unpublished data and to make proposals for mechanisms. 1 - Stereoselective polymerization A "stereoselective" polymerization is a process in which macromolecules containing only one type of configurational unit are formed by incorporation of one stereoisomer from a mixture into a growing polymer chain. There are as many different types of macromolecules as different stereoisomers present in the initial monomer mixture. In the case of cyclic compounds with one chiral center such 191

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

192

RING-OPENING POLYMERIZATION

a p e r f e c t process produces a s t e r e o r e g u l a r polymer composed o f two d i s t i n c t i s o t a c t i c poly R and poly S chains. For example i n the case of propylene oxide one must have :

CH r

racemi c

\

stereoselective initiator*

., / h

,3 "

0

H

CH

>n

2

R

H

C — CH ^ 0 *

>

0

+

H

2

ι

( 0 - C - CH

2

)

n

poly S

CH Generally the process i s not as p e r f e c t and one obtains a strong predominance o f on chain. Since the f i r s t example described by P r u i t t & Baggett (9) i n 1955, many c a t a l y t i c systems have been used f o r s t e r e o s p e c i f i c po­ l y m e r i z a t i o n o f propylene oxide and others epoxides and some of them were r e c e n t l y reviewed (10,11). Most o f these c a t a l y t i c s y s ­ tems contain metal-oxygen bounïï.~limong metals i r o n , magnesium, z i n c , aluminium, a l c a l i n e - e a r t h and boron were the most used. The s t e r e o s e l e c t i v i t y , i . e . the % o f c r y s t a l l i n e f r a c t i o n , could be evaluated using the c r i t e r i o n o f i n s o l u b i l i t y o f the i s o t a c t i c polymer i n a s o l v e n t o r determined from DTA o r X-Rays measurements. Several c a t a l y t i c systems derived from the r e a c t i o n of d i e thyl z i n c with compounds containing an a c t i v e hydrogen were e x t e n s i v e l y s t u d i e d , among them Z n E t - r U ) and ZnEt -CrL0H systems, and the r e s u l t s discussed and l a r g e l y reported (±>3*±j It was found t h a t the best s t e r e o s p e c i f i c i t y Ts obtained f o r ZnEt -H20 system when the i n i t i a t o r i s prepared i n s i t u i n a nonp o l a r s o l v e n t using equimolar amounts o f reagents (10). The e f f i ciency can be increased by f r e e z e - d r y i n g the c a t a l y s t (12). For a given c a t a l y t i c system, the s t e r e o s e l e c t i v i t y i s depending on the enantiomeric composition and on the nature o f the monomer. For example, propylene oxide of d i f f e r e n t o p t i c a l p u r i t i e s , was polymerized using ZnEt2-HoO (1 : 0.7) system prepared i n s i tu (13). As shown i n table I the % o f c r y s t a l l i n e f r a c t i o n as well as the t a c t i c i t y are increased with an increase of the o p t i c a l purity. On the other hand, with the same i n i t i a t o r , the s t e r e o s e l e c t i v i t y i s very d i f f e r e n t depending on the nature o f the monomer. Almost purely i s o t a c t i c products are obtained with t - b u t y l - t h i i r a n e while l e s s than 30 % o f c r y s t a l l i n e f r a c t i o n i s i s o l a t e d i n the case of propylene oxide ( t a b l e I). A mechanism assuming the existence of two groups o f e n a n t i o morphic s i t e s having more or l e s s R and S c h a r a c t e r was p r o posed i n order to e x p l a i n the formation o f polymers of d i f f e r e n t 3

?

2

2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14. SPASSKY

Polymerization

stereoregularities

of Oxiranes and

Thiiranes

193

(1). Table

I

S t e r e o s e l e c t i v i t y of ZnEt -rU0 (1/1) i n i t i a t o r depending on the nature o f the monomer used and i t s enantiomeric composition. 2

Monomer

o. p. i n i t i a l crystallinity: tacticity: réf. (dyads) . monomer : i % . % %

Methyl

oxirane

0 47.5

t-butyl

oxirane

0

:

90

thiirane

: 0 : 50

: : :

Methyl t-butyl

t h i i r a n e . 0-90

61 72

27 38

:

(13)

:

• (14)

60-80 > 70

: 76 • > 80

.

(

100

: > 90

:

(15)

5

)

The dépendance on the nature of the monomer and i t s e n a n t i o meric composition seems to i n d i c a t e t h a t c h i r a l a c t i v e s i t e s are formed a f t e r the r e a c t i o n o f the monomer with the i n i t i a t o r . The mechanistic aspects r e l a t e d to the s t e r e o s e l e c t i v i t y o f these i n i t i a t o r s are d i f f i c u l t to study owing to t h e i r i n s o l u b i l i t y and o v e r a l l low e f f i c i e n c y . An i n t e r e s t i n g approach was t r i e d i n the case o f propylene s u l f i d e using cadmium and z i n c t h i o l a t e s which gave homogeneous s o l u t i o n s when f u l l y consumed by the monomer (16). The p o l y m e r i z a t i o n i s o f " l i v i n g - t y p e " process,the polymers having one l i v i n g end per metal atom. Depending on the temperature and the s o l v e n t used, c r y s t a l l i n e o r amorphous polymers are o b t a i ned ( t a b l e II). Z i n c t h i o l a t e s i n contrary to z i n c a l c o h o l a t e s were unable t o give c r y s t a l l i n e products. The increase i n s t e r e o r e g u l a r i t y with lowering o f the temperature and the negative e f f e c t of p o l a r solvents (HMPA) may be e x p l a i n e d by c o o r d i n a t i o n e q u i l i b r i u m of the monomer on the a c t i v e s i t e . Cadmium s a l t s are the best c a t a l y s t s f o r the p o l y m e r i z a t i o n o f t h i i r a n e s g i v i n g polymers o f the highest s t e r e o r e g u l a r i t y , w h i l e they are unable to polymerize o x i r a n e s . T h i s behaviour can be e x p l a i n e d by the h a r d - s o f t acid-base c l a s s i f i c a t i o n i n which s u l f u r and cadmium are c l o s e r i n t h e i r c h a r a c t e r than oxygen which belongs to "hard elements".

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

194

RING-OPENING POLYMERIZATION

Table

II

Influence of the temperature and of the solvents on the s t e r e o r e g u l a r i t y o f polymethyl t h i i r a n e s obtained by i n i t i a t i o n with z i n c and cadmium a l l y ! t h i o l a t e s .

T h i o l ate : initiator

solvent

temperature . c r y s t a l u n i t y : t a c t i c i t y i %(dyads) °C

;

:

: : Cd

Zn

benzene toiuene toluene : t o i uen :tetrahydroth :tetrahydrofuran : HMPA : :

20 20 10 0

:

: :

0 0

:

toiuene toiuene

: : : :

+ + + + +

-

20 0

. : : :

> 90 50 58 75

: :

76 50

: :

50 50

2 - S t e r e o e l e c t i v e polymerization A " s t e r e o e l e c t i v e " (17) o r " a s y m m e t r i c - s e l e c t i v e " (3) p o l y merization i s a process i n which a s i n g l e stereoisomer oT a mixture i s polymerized g i v i n g macromolecules containing one type o f c o n f i g u r â t ! o n a l base u n i t s . For example an o p t i c a l l y a c t i v e c a t a l y s t w i l l choose one enantiomer from a racemic mixture and form a macromolecule c o n t a i n i n g only one type o f enantiomeric u n i t s . Such an i d e a l r e a c t i o n should stop at 50 % y i e l d a f t e r consumpt i o n of the corresponding stereoisomer. optically racemic monomer (R=S)

active

initiator choosing

R

polymer *

p

o

l

y

R

unreacted monomer R/S

— *

0

In most o f the cases the choice i s not as p e r f e c t and one speaks of " s t e r e o e l e c t i v e " p r o c e s s when a p r e f e r e n t i a l p o l y m e r i z a t i o n of one of the enantiomers from a mixture i s observed. Thus, the enantiomorphic choice of the c a t a l y s t i s a predominant element i n t h i s process and should be defined by i t s e l e c t i v i t y and i t s s e l e c t i v i t y . The " s t e r e o e l e c t i v i t y " could be simply defined as the r e l a t i v e rate of consumption o f the enantiomers in the presence o f c h i r a l i n i t i a t o r . In the course of the r e a c t i o n the unreacted monomer i s continously enriched i n one enantiomer and t h e r e f o r e

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14.

SPASSKY

Polymerization of Oxiranes and Thiiranes

195

the " s t e r e o e l e c t i v i t y " could be simply determined from the o p t i c a l p u r i t y of unreacted monomer a t a given conversion. On the c o n t r a r y , i n s p i t e of the p r e f e r e n t i a l constant choice o f one enantiomer by the c a t a l y s t , the o p t i c a l a c t i v i t y of the polymer i s decreasing with conversion due to progressive enrichment i n t o the opposite antipode. The " s t e r e o s e l e c t i v i t y " concerns the p o s s i b i l i t y o f i n t r o d u c t i o n i n t o the polymer chain o f only one type o f enantiomer or both o f them and informations on s t e r e o s e l e c t i v i t y are obtained from s t u d i e s of the polymer s t r u c t u r e . We s h a l l d i s c u s s both of these aspects and compare r e s u l t s obtained with oxiranes and t h i i r a n e s on the b a s i s o f recent works reported i n the l i t t é r a t u r e and based on our own experimental data. The i n t e r a c t i o n between the monomer and the o p t i c a l l y a c t i v e i n i t i a t o r i s determinin one o f enantiomers. T h i the c o n f i g u r â t ! o n o f the e l e c t e d antipode and by the magnitude i . e . the o p t i c a l p u r i t y of the resolved monomer. These parameters are depending mainly on the c o n f i g u r a t i o n and the nature o f the c h i r a l l i g a n d o f the i n i t i a t o r and t h e r e f o r e we s h a l l examine f i r s t the i n f l u e n c e o f the nature of the c a t a l y s t on s t e r e o e l e c t i v e processes. Then we s h a l l demonstrate that f o r a given i n i t i a t o r , the n a t u r e of monomer and i t s enantiomeric composition can deeply i n fluence the s t e r e o e l e c t i v i t y . Other parameters l i k e temperature and s o l v e n t e f f e c t s w i l l be also discussed. 2-1) Influence of the nature o f the i n i t i a t o r Initiators res u l t i n g from the r e a c t i o n between an o r g a n o m e t a l l i c d e r i v a t i v e and a c h i r a l compound c o n t a i n i n g an a c i d i c hydrogen were the most u s u a l l y employed i n the s t e r e o e l e c t i v e p o l y m e r i z a t i o n o f oxiranes and thiiranes. The c h i r a l l i g a n d a s s o c i a t e d to the m e t a l l i c atom i s p l a y i n g an important r o l e i n the c o n f i g u r a t i o n and the magnitude o f the enantiomeric c h o i c e . 2-1-1) E f f e c t on the c o n f i g u r â t ! o n a l choice Several types o f c h i r a l compounds c o n t a i n i n g an a c i d i c hydrogen such as a l c o h o l s , d i o l s , aminoacids were used as coreagents with organometallic compounds ( Z n E t , CdEtp and CdMe are the most employed). C o n f i g u r a t i o n a l r e l a t i o n s could be e s t a b l i s h e d i n s e v e r a l c a ses. I f one considers the absolute c o n f i g u r a t i o n o f the c h i r a l l i gand and t h a t o f the c y c l i c monomer, the choice o f the i n i t i a t o r would correspond to an "homosteric" type process i f the chosen enantiomer has the same c o n f i g u r a t i o n as the c h i r a l l i g a n d used i n the i n i t i a t o r (18). Homosteric c o n f i g u r a t i o n a l r e l a t i o n s are i l l u s t r a t e d i n the next scheme. 2

2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

196

RING-OPENING

CH

V

POLYMERIZATION

2

/ CH

CH

<J\> R

R

]

3

monomer

Ligand

The f o l l o w i n g two relations = OH 1 = CH,0H (I) = alfcyl R,

(")

1

R« R,

X R

= =

—

NH, COoH I

=

alRyl, aryl

=

4=

X

=

0,S Me.Et.iPr.tBu

our group

0,S

R„ = Me

I t was a l s o p o s s i b l e t o e s t a b l i s h some c o r r e l a t i o n s with other s e r i e s of c h i r a l compounds e . g . a l c o h o l s , but one must be c a r e f u l i n the choice o f groups o f comparison f o r a given c o n f i g u r a t i o n . We t h i n k t h a t many r e s u l t s may be s a t i s f a c t o r y explained by these c o r r e l a t i o n s and some unknown c o n f i g u r a t i o n s p r e d i c t e d from s t e r e o e l e c t i v e experiments (21). The chemical composition o f the i n i t i a t o r could a l s o play a d e c i s i v e r o l e i n the enantiomeric c h o i c e . We were able to e s t a b l i s h i n the case o f m e t h y l t h i i r a n e t h a t when the i n i t i a t o r i s prepared i n such c o n d i t i o n s t h a t a l k y l a l c o hoiate species predominate over d i a l c o h o l a t e s p e c i e s , the i n i t i a t o r system e l e c t s the antipode the c o n f i g u r a t i o n o f which i s opp o s i t e t o that o f i t s c h i r a l l i g a n d . Such type o f e l e c t i o n was c a l led " a n t i s t e r i c " . The r e s u l t s were e s t a b l i s h e d i n the case o f 1,2 d i o l s o f s é r i e (I) and f o r several a l c o h o l s which were reacted with three d i f f e r e n t organometallic d e r i v a t i v e s (18). Thus the r a t i o I = R-M-0R*/R0-M-0R* had tcTEe considered (-0R* being the c h i r a l alcohol ate ligand) and the f o l l o w i n g r u l e was found: I, I_

s

<2

homosteric choice

. > 3

a n t i s t e r i c choice

For example, when Z n E t i s reacted at room temperature with K ^ - ; t B u - CHOH-CHpOH i n (1:17 amount t h i s system chooses p r e f e r e n t i a l l y the d e x t r o r o t a t o r y m e t h y l t h i i r a n e (homosteric choice ; 2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14. SPASSKY

Polymerization

of Oxiranes and

Thiiranes

197

I = 0.44).When the same reagents are reacted i n (1:0,5) amounts the choice i s opposite (I = 4; antisteric process). The chemical composition i s t h e r e f o r e depending on the r e a c t i v i t y o f reagents and c o n d i t i o n s of p r e p a r a t i o n . The r e a c t i v i t y o f organometallic compounds decrease i n the order Z n E t > CdEt > CdMe and as example CdMe gives with R(-) tBu-CH0H-CH 0H i n * ( 1 : 1 ; conditions an a n t i s t e r i c i n i t i a t o r (I > 3). We have r e c e n t l y v e r i f i e d these f i n d i n g s on the example o f two other t h i i r a n e s ( C H and CH 0CH s u b s t i t u t e d ) . 2

2

2

2

5

3

?

2

2

We were able to i s o l a t e species of both types i n the case o f d i e t h y l z i n c - ( + ) 3,3 dimethyl 2 butanol i n i t i a t o r system. The a n t i s t e r i c species has a composition close to E t Z n ( 0 R ) o r Z n ( 0 R ) . (EtZnOR) (-OR being the 3,3 dimethyl 2 butoxy group), while an homosteric i n i t i a t o r ha c i e s were s o l u b l e i n benzen was p o s s i b l e to transform one specie i n t o the other by a c t i n g Z n E t o r by drying o r heating ( l o s s o f Z n E t and d i s p r o p o r t i o n a fi

ft

?

6

2

2

te;.

Recently Ishimori and al (22)showed t h a t Zn(0Me) .(EtZnOMe) have a centrosymmetric s t r u c t u r e formed pf two enantiomorphic d i s turbed cubes. T h i s complex had n o * ' y a c t i v i t y at room temper a t u r e , but polymerized methyloxirane at 8 0 ° . A process of d i s s o c i a t i o n at 80° could e x p l a i n such a r e a c t i v i t y . We s h a l l now consider only homosteric type i n i t i a t o r s f o r simplicity. 2

c a

a

g

t l c

2-1-2) E f f e c t on s t e r e o e l e c t i v i t y I f one considers i n i t i a tors prepared i n homosteric c o n d i t i o n s (I < 1) i t i s p o s s i b l e to compare the e f f i c i e n c y o f r e s o l u t i o n depending on the c h i r a l hydroxy l i g a n d associated with the organometallic compound. The o p t i c a l p u r i t y of recovered monomer at h a l f r e a c t i o n could be used as c r i t e r i o n o f e f f i c i e n c y . Thus, when racemic m e t h y l t h i i r a n e i s polymerized using d i f f e rent i n i t i a t o r s derived from the r e a c t i o n o f d i e t h y l z i n c with c h i r a l a l c o h o l s and g l y c o l s one f i n d s the f o l l o w i n g o r d e r o f e f f i c i e n cy : ligand : tBu-CH0H-CH 0H > tBu-CHOH-OL > tBu-CH0H-CH 0CH (a/a )x/2 : 30 % 12 % 2.5 % 9

L

9

6

c

Q

6

0

It was confirmed on several examples that c h i r a l 1,2 d i o l s gave the best r e s o l u t i o n r e s u l t s . This can be due t o the p o s s i b l e formation o f r i g i d c y c l i c o r perhaps polymeric species (18). In an homologous s é r i e o f c h i r a l hydroxy compounds "ïiïe b u l k i ness of the s u b s t i t u e n t i s f a v o r i s i n g s t e r e o e l e c t i v i t y . For example i n the 1,2 d i o l s é r i e associated to d i e t h y l z i n c one f i n d s f o r m e t h y l t h i i r a n e f o l l o w i n g e f f i c i e n c i e s :

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

198

RING-OPENING POLYMERIZATION

1,2 d i o l substituent : (α/α )χ/2

tBu ~ i P r

:

0

30 %

>

Ph

28 %

>

Me

20 %

8 %

S i m i l a r r e s u l t s were obtained by Furukawa e t al (20) when using d i e t h y l z i n c - L - a m i n o a c i d systems i n polymerization o f methyl oxirane. Up to now we have found that the best s t e r e o e l e c t i v e i n i t i a ­ t o r system f o r polymerization of oxiranes and t h i i r a n e s r e s u l t e d from the r e a c t i o n o f d i e t h y l z i n c and (-)3,3 dimethyl 1,2 butane d i o l (DMBD) taken i n (1:1) p r o p o r t i o n . 2-2) Influence o f the nature of the monomer Oxiranes and t h i ­ iranes could be polymerized by the same type of i n i t i a t o r s which makes easy a way of compariso use our standard homosteri dy the i n f l u e n c e of the nature of the monomer on the s t e r e o s e l e c t i v i t y and the s t e r e o e l e c t i v i t y of the process. 2-2-1) E f f e c t on s t e r e o e l e c t i v i t y Let us consider o p t i c a l y i e l d s obtained at h a l f r e a c t i o n with several t h i i r a n e s and o x i ~ ranes. Substituent : tBu ^ i P r > Et ^ Me > CH-CH 0 Thiiranes (α/α )χ/2 : 46 % 30 % 16 % ά

0

Substituent Oxi ranes

:

CH-O-LO 6

(α/α ) χ/2

:

σ

>

ά

CH. 6

25 %

20 %

It appears t h a t in general the s t e r e o e l e c t i v i t y i s higher f o r t h i i r a n e s than f o r o x i r a n e s , but a l s o that i n the case of the f o r ­ mer the s t e r e o e l e c t i v i t y i s increased with the bulkiness o f the s u b s t i t u e n t . The o p t i c a l y i e l d at h a l f - r e a c t i o n allows a simple comparison between a l l types of monomers. However, t h i s value i s not r e f l e c t i n g the k i n e t i c scheme of r e s o l u t i o n and f o r t h i s p u r ­ pose a study of the o p t i c a l p u r i t y of recovered monomer during f u l l course of polymerization i . e . on a l l conversion scale i s necessa­ ry. The experimental data taken on the whole range of conversion i n d i c a t e that there are d i f f e r e n c e s i n k i n e t i c behaviour between monomers. Two c l a s s e s of monomers could be defined corresponding to two types of t h e o r e t i c a l k i n e t i c equations. F i r s t order consumption equation A f i r s t c l a s s of monomers obeys equation with f i r s t order i n enantiomer consumption. One can write f o r each enantiomer : - d |R|/dt

= K

R

|R|

- d

|S|/ dt = \

IS ι

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14. SPASSKY

Polymerization

dlRl

which give

K

=

d |S|

of Oxiranes and

R

| R |

Κ

=

| R |

r

|S|

Thiiranes

R R

— S

(1)

K and Κ are global rate constants r e l a t i v e to a c t i v e species afrd r tne s t e r e o e l e c t i v i t y r a t i o r e l a t i v e to R choice. r was found to be constant during the f u l l course o f polymerization and t h e r e f o r e equation (1) could be i n t e g r a t e d . I f one introduces experimental data which are α - o p t i c a l ac t i v i t y of recovered monomer, a - o p t i c a l a c t i v i t y of pure e n a n t i o ­ mer, χ - conversion, | R | and |S| i n i t i a l concentrations of enantiomers D

ς

D

g

0

c

R|

0

- |s|

+

|R|

|S|

α = α |R| One obtains

(l-x) "" 1

+ I

:

=

1

1 + (α/αο) — — Π " (a/a )|

2 " r

iRlo

r

0

which s i m p l i f i e s into :

|S| — ( mu + 1

r

— ι — Ν ο Γ

i f the i n i t i a l mixture i s racemic (|R|

0

, (i - χ )

Γ

=

1

-

( ) 2

1

=

1 + (a/oto) - r

I ι -

(a/a )|

|S| ) 0

(3) r

0

Experimental data found f o r racemic CH~(18) C HJ23),CH.CH 0 (24) t h i i r a n e s and CH (25),CH CH 0(24) o x i r a n e s , using our s t a n dard i n i t i a t o r were f i t t i n g with equation (3) with r e s p e c t i v e s t e r e o e l e c t i v i t y values (r) equal to 2.4, 2.4, 1.6, 1.8 and 2.0. In F i g . 1 are p l o t t e d experimental data f o r methyl t h i i r a n e . The r e s u l t s obtained with isopropyl and t - b u t y l t h i i r a n e were not f i t t i n g with equation (3)and t h e r e f o r e another k i n e t i c equat i o n o f second order was proposed (6,26). 9

?

?

é

3

3

2

Second order consumption equation The consumption i n enantiomer i s o f second order and the kinet i c equation becomes : d |R| d ιsι

|R|

2

|sr

K

which could be i n t e g r a t e d as p r e v i o u s l y a f t e r i n t r o d u c t i o n of and χ and gives f o r the racemic monomer : 1 (1-x)

(1 + ct/oo)

p

R

1

-

P

R

(1-χ)(1-α/α ) 0

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

(5)

α

RING-OPENING POLYMERIZATION

200 where It optical α

0

p

i s the s t e r e o e l e c t i v i t y constant of second order. appears t h a t f o r a complete conversion the l i m i t value f o r a c t i v i t y i s no more a as i n the case o f equation (3) but R

Q

. ρ ~ j-

and t h e r e f o r e o p t i c a l l y pure monomer could not be ob­

tained i n t h i s process. The experimental data found f o r t - b u t y l t h i i r a n e f i t t e d well with equation (5) as shown on F i g . 1 with p value equal to 8 at 20°C. Isopropyl t h i i r a n e gave almost the same value. P r e s e n t l y the d i s t i n c t i o n between both groups seems mainly based on the b u l k i ness on t h e i r s u b s t i t u e n t , the second order process being observed f o r the b u l k i e r compounds. Other examples are s t u d i e d f o r b e t t e r understanding. D

K

2-2-2) E f f e c t on s e l e c t i v i t y are obtained by studying the s t e r e o r e g u l a r i t y o f p o l y ­ mers. Generally they could be f r a c t i o n a t e d i n t o a c r y s t a l l i n e i s o ­ t a c t i c f r a c t i o n and i n t o an amorphous h e t e r o t a c t i c f r a c t i o n , both o f them o p t i c a l l y a c t i v e . With our standard i n i t i a t o r at room temperature the p e r c e n t a ­ ge of c r y s t a l l i n e i s o t a c t i c f r a c t i o n was 20 % f o r methyloxirane (25), (25), 35 % f o r methyl t h i i r a n e (2J[) and p r a c t i c a l l y 100 % f o r t butyl t h i i r a n e (27). The i s o t a c t i c f r a c t i o n comes from s i t e s o f almost pure R and S c h a r a c t e r and t h e r e f o r e the d i s t r i b u t i o n between d i f f e r e n t types of s i t e s f o r one t y p i c a l i n i t i a t o r i s again depending on the nature o f the monomer. It i s i n t e r e s t i n g to n o t i c e t h a t p o l y ( t - b u t y l t h i i r a n e ) ob­ t a i n e d i n s t e r e o e l e c t i v e experiments could be separated by s e l e c ­ t i v e s o l u b i l i t y i n two f r a n c t i o n s , one o f which was i d e n t i f i e d as pure poly R polymer m.p. 157°C |α|£5 = + 164 (CHC1-) and the o t h e r , as the racemate (poly R + poly S) fn.p. = 204° (27)7 These f r a c t i o n s were compared with authentic samples prepared p r e v i o u s l y from pure l e v o r o t a t o r y monomer and racemic monomer (15). The l a t t e r r e s u l t s show that the s t e r e o e l e c t i v e p o l y m e r i z a ­ t i o n i s a p o t e n t i a l method f o r obtention o f o p t i c a l l y pure p o l y ­ mers from racemic monomers. 2-3) Influence of the enantiomeric composition o f the mono­ mer. Super s t e r e o e l e c t i v e processes. The enantiomeric composition of the i n i t i a l monomer may have a strong e f f e c t on the s t e r e o e l e c ­ t i v i t y . It was shown on the example of methyl t h i i r a n e that the value of the s t e r e o e l e c t i v i t y r a t i o (r) could be r a i s e d up to 7 when using enriched monomers (28). The same phenomenon was r e c e n t ­ l y observed with e t h y l t h i i r a n e (23)and methoxymethyl t h i i r a n e (29). The s t e r e o e l e c t i v i t y i s d i r e c t l y depending on the i n i t i a l R/S composition and obeys the general f i r s t - o r d e r equation (2). P r a c t i c a l l y , i n order to obtain more and more enriched mono­ mers the f o l l o w i n g procedure was used. The recovered unreacted mo­ nomer from one polymerization was reused as i n i t i a l monomer f o r

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14.

SPASSKY

Polymerization

of Oxiranes

and

Thiiranes

201

the next step. As shown i n t a b l e III and F i g . 2 i t i s then p o s s i ­ b l e i n 3-4 steps to i s o l a t e monomers having o p t i c a l p u r i t i e s h i g ­ her than 95 %. Such a " s u p e r s t e r e o e l e c t i v e " process i s t h e r e f o r e i n t e r e s t i n g f o r the preparation o f small amounts o f almost o p t i c a l l y pure mo­ nomers from racemic mixtures. As an example methyl t h i i r a n e o.p. = 98 % was obtained i n three steps with an o v e r a l l y i e l d o f 11.5 % from the racemic compound ( t a b l e III). Table

III

E f f e c t o f the enantiomeric p u r i t y of the roonoroer on the s t e r e o e l e c t i v i t y ZnEt -(-)DMBD (1:1) 2

Monomer

was used as i n i t i a t o r

i n i t i a l : Conversion; Recovered : monomer : monomer · : % : (α/α ) . (α/α ) :

:

0 0.35 0.68

: ethyl thiirane . (b) :

0 0.33 0.44 0.54

80 20 13 61

methoxymethyl thiirane (c)

0 0.36

74 24

(a) (b) (c)

: :

r

:

0

0

methyl t h i i r a n e (a)

system

• ' .

59 39 50

: :

; :

:

0.35 0.68 0.98

; 2.2 4.4 : 6.8

0.33 0.44 0.54 0.95

1.5 3.2 : 4.5 : 6.0

0.36 0.55

: 1.6 . 4.2

l : : : :

:

: : :

p o l y m e r i z a t i o n c a r r i e d out at room temperature i n t o ­ luene s o l u t i o n . polym eri z a t i on c a r r i e d out at -30°C i n bulk. p o l y m e r i z a t i o n c a r r i e d out a t room temperature i n bulk.

A monomer o f the same o p t i c a l p u r i t y could be obtained i n a simple s t e r e o e l e c t i v e experiment only a t conversions higher than 98 % i . e . with l e s s than 2 % y i e l d . One must add that such s u p e r s t e r e o e l e c t i v e processes are a l s o i n t e r e s t i n g as a source of polymers of high o p t i c a l p u r i t y . Indeed, i f one uses mixtures e n r i c h e d i n the enantiomer chosen i n the p r o ­ c e s s , one can o b t a i n at low conversion (10 %) polymers o f high op­ t i c a l a c t i v i t y . For example, when using methyl t h i i r a n e or methyloxirane of 50 % o.p. ( i n R enantiomer) one gets polymers 90 % e n r i c h e d i n t h i s enantiomer (28). For monomers of the second group the s t e r e o e l e c t i v i t y was not a f f e c t e d by the i n i t i a l enantiomeric composition (26).

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

mon

Figure 1. Stereoelective polymerization of racemic thiiranes using ZnEt -(—)DMBD (1:1) initiator. ( ) first-order curve (·, exp. data for methylthiirane); ( ) second-order curve ( J , exp. data for tert hutylthiirane). g

mon

Figure 2. Superstereoelective procedure applied to the polymerization of methylthiirane using ZnEt (—)DMBD (1:1) initiator g

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14.

SPASSKY

Polymerization

of Oxiranes

and

Thiiranes

203

2-4) E f f e c t o f the temperature on s t e r e o e l e c t i v i t y Few r e ­ s u l t s only were reported on the e f f e c t of the temperature on s t e r e o e l e c t i o n . In the case of monomers o f f i r s t c l a s s the s t e r e o e l e c ­ t i v i t y was not modified by changing the temperature, while the s t e ­ r e o s e l e c t i v i t y o f the process increased by lowering the tempera­ ture o f p o l y m e r i z a t i o n as demonstrated i n the case of methyl o x i ­ rane (25). The temperature showed a strong e f f e c t i n the po lymeriz a tio n o f t - b u t y l t h i i r a n e (26) The s t e r e o e l e c t i v i t y p doubled i n v a ­ lue when temperature Towered from 20° to - 3 ° and on the c o n t r a r y P decreased with r a i s i n g of Τ and a t temperatures higher than 1T5° the choice o f the enantiomer was i n v e r t e d as shown i n t a b l e IV. The l i m i t value of the o p t i c a l p u r i t y of monomer was a l s o mo­ dified. A linear correlatio o v e r a l l d i f f e r e n c e i n energ e l e c t i v e process f o r both enantiomers could be c a l c u l a t e d (5 K c a l / mol). R

R

Table

IV

Influence o f the temperature on s t e r e o e l e c t i v i t y i n the p o l y m e r i z a t i o n of t - b u t y l t h i i r a n e with ZnEt -(-)DMBD (1:1) i n i t i a t o r system 2

(α/α ) recovered monomer: at χ % conversion : 0

: t°C

P

R .

: -3 : 20 : 63 :135 *)

: : :

14 8 2.5

χ = 50: l i m i t χ = 100 :

: :

58 48

;

!*>;

: :

87 78

: :

4 7*>

;

}

S enantiomer i s

4

preferentially elected

The d i f f e r e n c e i n temperature dépendance between both c l a s s o f monomers could be e x p l a i n e d i n terms o f mechanism o f p o l y m e r i z a t i o n as shown i n chapter 4. 2-5) E f f e c t o f solvents and a d d i t i v e s The r o l e o f s o l v e n t may be important i n such " a n i o n i c - c o o r d i n a t e d " p o l y m e r i z a t i o n s . It was shown f o r example i n the case o f methyl t h i i r a n e that a d d i t i o n of t e t r a h y d r o f u r a n decreased the s t e r e o e l e c t i v i t y , a competition o c c u r i n g between the monomer and the s o l v e n t f o r the c o o r d i n a t i o n on the m e t a l l i c atom (30). Very r e c e n t l y SepïïTchre (31) has shown the p o s s i b i l i t y to i n -

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

204

RING-OPENING POLYMERIZATION

crease s u b s t a n t i a l l y the s t e r e o e l e c t i v i t y by modifying the i n i t i a t o r with c h i r a l a g e n t s ( o p t i c a l l y a c t i v e t h i o e t h e r s , amines) o r by using c h i r a l s o l v e n t s (limonene). Such a way seems very promising and s t u d i e s are i n progress i n our l a b o r a t o r y . 3 - Asymmetric polymer

synthesis

In the previous chapter we have seen that an o p t i c a l l y a c t i v e c a t a l y s t was able to make a p r e f e r e n t i a l choice between two s t e r e i s o m e r i c molecules d i f f e r e n t i a t e d by the opposite c o n f i g u r a t i o n o f t h e i r asymmetric c e n t e r s . Now we wish to r e p o r t our i n v e s t i g a t i o n s on the behaviour o f the same i n i t i a t o r s i n the presence o f symmetric monomers having two asymmetric centers of opposite c o n f i g u r a t i o n i n neighbouring position. C i s - 2 , 3 dimethyl t h i i r a n were s t u d i e d f o r t h i s purpose. A few p r e l i m i n a r y r e s u l t s concerning t h e i r p o l y m e r i z a t i o n are given i n table V. O p t i c a l l y a c t i v e c r y s t a l l i n e polymers were obt a i n e d which could be separated by s e l e c t i v e s o l u b i l i t y i n f r a c t i o n s o f d i f f e r e n t o p t i c a l a c t i v i t y and c r y s t a l l i n i t y . Table Asymmetric polymer s y n t h e s i s

V

using ZnEto-(-)DMBD. (1:1)

initiator

C i s 2,3 dimethyl t h i i r a n e (DMT) and cyclohexene s u l f i d e were polymerized i n bulk at room temperature.

Polymer

(CS)

fractions

: S o l . toluene room temp. : S o l . CHClj room temp. : Conversion

:

%

;

%

•Ref:

tCXp)

: : (CHC1 ) : 3

30

:

29

:

+20

m.p. °C 60

:DMT:

les : (a)

:

: % : (CHC1 ) : 3

71 :

m. p. °C

+50

: 125

+66

126

32 : 100

33

'.

+24

45

35

; +

3.8< \

+ 20 i n t r i c h l o r o b e n z e n e

40/90 . 67 a

65

: i o : +8.4( >; b

80

: : 33 :

(b) + 39 i n trichlorobenzene..

The d i r e c t i o n of ring-opening i s o r i e n t e d by the c h i r a l choice o f the c a t a l y s t which attacks p r e f e r e n t i a l l y one o f the asymmetric carbons with i n v e r s i o n o f c o n f i g u r a t i o n of the l a t t e r . The r e s u l t i n g polymer i s o p t i c a l l y a c t i v e due to the prevalence o f one type o f c o n f i g u r a t i o n a l u n i t s |for example E(-RR-)> z ( - S S - ) | .

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14.

SPASSKY

Polymerization

of Oxiranes and

Thiiranes

205

According to Vandenberg ( 7 » 8 ) t h e ring-opening o f c i s compounds i n v o l v e s a process with i n v e r s i o n o f c o n f i g u r a t i o n o f the attacked carbon and depending on the type o f enchainment one can obtain d i i s o t a c t i c (I) o r d i s y n d i o t a c t i c ( I I ) s t r u c t u r e s . Structure C

C

\(R)

diisotactic

(I)

(S)/

c— c

/ \ HT

/ Χ

\ H

d i s y n d i o t a c t i c (II)

enchainment head-to-tail - RR - RR - SS - SS head-to-head - RR - SS -

X = 0,S According to such a be due to the prevalenc (I) typ chirality. It was not p o s s i b l e up to now to a s c e r t a i n the o p t i c a l p u r i t y o f prepared polymers. Using '3c NMR i t was found t h a t r e s u l t i n g po­ lymers presented d i f f e r e n t types of stereosequences. In poly c i s 2,3 dimethyl t h i i r a n e the peak l o c a t e d a t 45.8 ppm (CDCU s o l v e n t , reference to TMS) was c l e a r l y assigned to the methine chain carbon o f d i i s o t a c t i c s t r u c t u r e as i t was d i r e c t l y i n ­ c r e a s i n g with the o p t i c a l a c t i v i t y o f the polymer. Three other peaks corresponding to chain carbons were found, showing that other s t r u c t u r e s than the simple d i s y n d i o t a c t i c one (II) are a l s o p r e ­ sent. An i n t e r e s t i n g source of informations on the s t r u c t u r e o f such polymers may be obtained from t h e i r c a t i o n i c degradation as r e p o r ­ ted r e c e n t l y by Goethals (34). In the case o f c i s - d i m e t h y l t h i i r a ­ nes c y c l i c oligomers o f d i f f e r e n t s t r u c t u r e were i d e n t i f i e d , name­ l y t r i t h i e p a n e s and tetramers(35). The degradation o f o p t i c a l l y a c t i v e poly c i s DMT produced op­ t i c a l l y a c t i v e t r i t h i e p a n e s and tetramers of opposite s i g n . The magnitude o f t h e i r o p t i c a l a c t i v i t i e s i s d i r e c t l y depending on the o p t i c a l a c t i v i t y o f the polymer used and, t h u s , r e f l e c t s i t s s t r u c ­ t u r e . Further s t u d i e s are i n progress (36). The C NMR study of o p t i c a l l y a c t i v e poly(cyclohexene s u l f i d e ) showed a l s o a complicated s t r u c t u r e f o r the methine carbon o f the main chain with the presence o f f i v e or s i x peaks. S u r p r i s i n g l y , n e i t h e r c i s 2,3 dimethyl oxirane nor cyclohexene oxide have f u r n i s h e d products with s i g n i f i c a n t o p t i c a l a c t i v i t y when using the standard c h i r a l i n i t i a t o r . The reason o f t h i s be­ haviour i s not y e t known and s t r u c t u r e o f the polymers are under the study. One must mention that a poly c i s 2,3 dimethyl oxirane o f low o p t i c a l a c t i v i t y was obtained by Vandenberg (37) when using an aluminum i n i t i a t o r modified by 1-menthol. Thus, new types o f polymers could be obtained by means o f t h i s J

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

206

RING-OPENING POLYMERIZATION

asymmetric synthesis where a c h i r a l enantiomeric polymeric m a t e r i a l i s created from an a c h i r a l monomer. Such a process may be c a l l e d " a c h i r a l e n a n t i o g e n i c " as suggested by P r o f e s s o r J . P . G u e t t é . 4 - Mechanistic aspects o f the s t e r e o s p e c i f i c polymerization o f oxiranes and t h i i r a n e s From the above considerations some general mechanistic f e a t u res could be proposed f o r s t e r e o s e l e c t i v e and s t e r e o e l e c t i v e p o l y merization using modified organometallic c a t a l y s t s . In a f i r s t step the monomer reacts with the i n i t i a t o r t o form a f u l l spectrum o f s i t e s having d i f f e r e n t R and S c h a r a c t e r . Some of these formed species have a complete s e l e c t i v i t y and p r o duce c r y s t a l l i n e i s o t a c t i c polymers. The proportion of such s e l e c t i v e species f o r a give the monomer. We have see l i k e t - b u t y l t h i i r a n e almost a l l the s i t e s are purely s e l e c t i v e , while f o r other monomers l i k e methyl oxirane only 20 % o f the a c t i v e species are s e l e c t i v e . I f the i n i t i a t o r i s o p t i c a l l y a c t i v e there i s an unbalanced amount of R type and S type species and t h e r e f o r e s t e r e o e l e c t i o n w i l l occur when polymerizing a racemic monomer mixture. Other species have a much lower s e l e c t i v i t y and produce the amorphous p a r t o f the polymer. Again i f the i n i t i a t o r i s o p t i c a l l y a c t i v e , a predominance of one type o f species occurs and t h e r e f o r e an h e t e r o t a c t i c o p t i c a l l y a c t i v e polymer i s o b t a i n e d . In chapter 2 we have d i s t i n g u i s h e d two c l a s s e s of monomers a c cording t o t h e i r k i n e t i c behaviour i n s t e r e o e l e c t i o n . This d i f f e r e n c e i n behaviour can now be j u s t i f i e d by some mechanistic considerations. With monomers o f the f i r s t c l a s s , methyl oxirane f o r example, the a c t i v e s i t e s are formed i n an i r r e v e r s i b l e way a f t e r the r e a c t i o n (or very strong complexation) of the i n i t i a l monomer with the i n i t i a t o r . As a p r o o f , one f i n d s that the s t e r e o e l e c t i v i t y ( r ) , i . e . the enantiomorphic d i s t r i b u t i o n of s i t e s , i s not modified by a change of the temperature of p o l y m e r i z a t i o n , but (r) i s s t r o n g l y depending on the enantiomeric composition of the i n i t i a l monomer. On the c o n t r a r y , i n the case of monomers o f the second group ( t - b u t y l t h i i r a n e ) , the a c t i v e centers are formed a f t e r complexat i o n o f the monomer on the i n i t i a t o r s p e c i e s . Thus, the s t e r e o e l e c t i v i t y should depend on the temperature which i s indeed o b s e r ved i n a s i g n i f i c a n t way. The second order law could be explained by a two step process : the complexation - a r e v e r s i b l e s t e p , then the propagation step.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14.

SPASSKY

Polymerization

of Oxiranes and

Thiiranes

207

S i m p l i f i e d r e p r e s e n t a t i v e scheme o f both mechanisms i l l u s t r a t e d as f o l l o w s :

INITIATOR SITES highly \

n

could be

STEREOREGULARiT

selective C

Uc

R

s

I §

R

>

η Poly R > m poly S s

isotactic

First group tfNJow

selectivity C

+ R n|C.R|

η poly R

Second group

isotactic + S m|C.S|

-> m poly S

When C i s o p t i c a l l y a c t i v e η ^ m η ' Φ m'. There i s a mutual r e c o g n i t i o n between c h i r a l s i t e s and enan­ tiomers of s i m i l a r c o n f i g u r a t i o n . Moreover on the b a s i s o f asym­ m e t r i c s y n t h e s i s r e a c t i o n s i n v o l v i n g symmetric monomers, we may assume t h a t the c h i r a l i n i t i a t o r can d i s t i n g u i s h one p e c u l i a r asym­ m e t r i c carbon i n the molecule i n the course o f the ring-opening r e a c t i o n . T h i s ring-opening proceeds with i n v e r s i o n o f c o n f i g u r a t i o n at the carbon as p r e v i o u s l y e s t a b l i s h e d by Vandenberg (7). In the case o f monosubstituted monomers, the c a t a l y s t attacks the p r i m a ­ ry methylenic carbon and t h i s does not a f f e c t the c o n f i g u r a t i o n o f the asymmetric carbon. For symmetrically d i s u b s t i t u t e d monomers, however, when using c h i r a l i n i t i a t o r s , o p t i c a l l y i n a c t i v e polymers are obtained i f s t a r t i n g from trans compounds and o p t i c a l l y a c t i v e products may be prepared from c i s compounds. More i n v e s t i g a t i o n s are s t i l l necessary f o r complete under­ standing o f s t e r e o s p e c i f i c processes. 5 -

Conclusion

A great v a r i e t y o f products could be prepared using s t e r e o s p e ­ cific initiators. Three main d i r e c t i o n s seem promising : F i r s t , i s o t a c t i c o p t i c a l l y pure or h e t e r o t a c t i c products o f low o p t i c a l a c t i v i t y may be obtained s t a r t i n g from racemic mono-

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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mers. Second, monomers of high o p t i c a l p u r i t y could be i s o l a t e d i n l i m i t e d amounts s t a r t i n g from racemic mixtures. In such a case the s t e r e o e l e c t i v e p o l y m e r i z a t i o n can be considered as an o r i g i n a l r e ­ s o l u t i o n method o f s p e c i a l i n t e r e s t f o r monomers which are not e a ­ s i l y prepared by conventional s y n t h e t i c ways under t h e i r o p t i c a l l y a c t i v e form. Increase i n s t e r e o e l e c t i v i t y i s observed when using c h i r a l media, i . e . e n a n t i o m e r i c a l l y e n r i c h e d monomers or e x t e r n a l chiral additives. T h i r d , new o p t i c a l l y a c t i v e polymers are obtained by asymmetric transformation o f symmetric monomers. The author i s g r a t e f u l to Drs. Sepulchre, Dumas, MM. Coulon, D e f f i e u x , Khali 1, Momtaz, Pourdjavadi and Reix f o r t h e i r c o n t r i ­ bution to t h i s work and communication o f unpublished data. The a u ­ thor thanks P r o f e s s o r Sigwal nuscript and stimultating discussions. Literature Cited (1) Tsuruta T., Stereochemistry of Macromolecules, Ed. by Ketley A.D., Vol. 2, p. 177, M. Dekker, Inc., N.Y.,1967 (2) Sigwalt P., Int. J. Sulfur Chem. (1972) C7,83 (3) Tsuruta T., J. Polym. Sci. (1972) D, 179 (4) Tani H., Adv. Polym. Sci. (1973) 11, 57 (5) Spassky Ν., Dumas P., Sepulchre and Sigwalt P., J. Polym. Sci., Symposium n° 52 (1975) 327. (6) (7) (8) (9)

Sigwalt P., Pure and Applied Chemistry (197 ) (in press). Vandenberg E.J., J. Polym. Sci., (1969) A 1, 7, 529 Vandenberg E.J., J. Polym. Sci. (1972) A 1, 10, 329 Pruitt M.E. and Baggett I.M. (to Dow Chemical Co) U.S. Pat. 2, 706, 181 (1955) (10) Furukawa J. and Saegusa T., Polymerization of Aldehydes and Oxides, J. Wiley et Sons, N.Y. 1963 (11) Ishii Y. and Sakai S., Ring-Opening polymerization, Ed. by Frisch K.C. and Reegen S.L., Vol. 2, p. 13, M. Dekker, N.Y., 1969 (12) Oguni N., Watanabe S., Maki M. and Tani H., Macromolecules (1973) 6 (2), 195 (13) Inoue S. Tsukawa I., Kawaguchi M. and Tsuruta T., Makromol. Chem. (1967) 103, 151 (14) Price C.C., Akkapeddi M.K., Debona B.T. and Furie B.C. J. Amer. Chem. Soc. (1972) 94 (11), 3964 (15) Dumas P., Spassky N. and Sigwalt P., Makromol. Chem. (1972) 156, 55 (16) Guérin P., Boileau S. and Sigwalt P., European Pol. J. (1974) 10, 13 (17) Pino P., Adv. Polym. Sci. (1965) 4, 236 (18) Deffieux Α., Sépulchre Μ., Spassky N. and Sigwalt P., Makromol. Chem. (1974) 175/4, 339 (19) Furukawa J., Kawabata N. and Kato Α., J. Polym. Sci. (1967) B,5, 1073

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14.

SPASSKY

Polymerization

of Oxiranes

and

Thiiranes

(20) Furukawa J., Kumata Y., Yamada K. and Fueno T., J. Polym. Sci. (1968) C (23), 711 (21) Sépulchre M. and Spassky Ν., to be published (22) Ishimori M., Hagiwara T., Tsuruta T., Kai Y., Yasuako N. and Kasai Ν., Bull. Chem. Soc. Jap. (1976) 49 (4), 1165 (23) Khalil Α., Sepulchre M. and Spassky N., to be published (24) Spassky Ν., Pourdjavadi A. and Sigwalt P., European Polym. J. (1977) (in press). (25) Coulon C., Spassky N. and Sigwalt P., Polymer (1976) 17, 821 (26) Dumas P., Spassky N. and Sigwalt P., to be published. (27) Dumas P., Spassky N. and Sigwalt P., J. Polymer Sci., Polymer Chem. Ed. (1974) 12, 1001 (28) épulchre M., Coulon C., Spassky N. and Sigwalt P., 1-rst International Symposium on Ring-Opening Polymerization, Jablonna (1975), Preprints p. 80 (29) Reix Μ., Sepulchre M. and Spassky N., to be published (30) Spassky N. and Sigwalt P., European Polym. J. (1971) 7, 7 (31) épulchre Μ., Sigwalt and Spassky N., IUPAC International Symposium on Macromolecules, Dublin (1977), Preprint (32) Momtaz A. and Spassky Ν., unpublished results. (33) Reix M. and Spassky N., unpublished results. (34) Goethals E.J., Adv. Polymer Sci. (1977) 23, 103 (35) Van Crayenest W. and Goethals E.J., European Polymer J. (1976) 12, 859 (36) Tan Crayenest W., Goethals E.J., Momtaz A. and Spassky N. Unpublished results, in collaboration. (37) Vandenberg E.J., J. Polymer Sci. (1964) B, 2, 1085

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

209

15 Rate and Stereochemistry of the Anionic Polymerization of α,α-Disubstituted-β-propiolactones ROBERT W. LENZ, CHRISTIAN G. D'HONDT, and EBRAHIM BIGDELI Polymer Science and Engineering Program, Chemical Engineering Department, University of Massachusetts, Amherst, MA 01003

Previous investigations in this laboratory (1) and else­ where (2) have shown that polyesters prepared from chiral disubstituted-β-propiolactones by the following reactions:

are crystalline even when the two substituents, R1 and R2, are considerably different in size (e.g., R1 = CH3, R2 = C3H7). This observation is surprising because the anionic polymerization re­ action used is homogeneous in character, and no heterogeneous, stereoregular catalysts are required to achieve the polymer crys­ tallinity observed. Furthermore, crystalline structure deter­ minations by wide-angle x-ray diffraction analysis of poly-αmethyl-α-propyl-β-propiolactone showed that two crystalline forms were possible depending upon sample preparation and treatment. These two forms consisted of unit cells in which the polymer was present as either a 21 helix or as a fully-extended, planar zig­ zag conformation (1). One purpose of the present investigation was to obtain some additional information on structure-crystallinity relationships in this family of polymers by the preparation of stereoregular isotactic polyesters from a single asymmetric isomer of the chiral monomer; that is, from an o p t i c a l l y - a c t i v e α,α-disubstituted-βpropiolactone. Because the polymerization r e a c t i o n mechanism operates through s c i s s i o n of the alkyl-oxygen bond and does not i n v o l v e bond r e o r g a n i z a t i o n s a t the asymmetric c e n t e r , i t was f u l l y expected that polymerization of the o p t i c a l l y - a c t i v e monomer

210

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15. LENZ ET AL.

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of a,a-Disubstituted-fi-propiofoctones

211

would occur with complete r e t e n t i o n to y i e l d an i s o t a c t i c polymer i n which the m a j o r i t y o f the repeating u n i t s had the same abso­ l u t e c o n f i g u r a t i o n depending upon the o p t i c a l p u r i t y of the mono­ mer. A comparison o f the c r y s t a l l i n e p r o p e r t i e s o f that polymer with the one prepared from the racemic monomer should help to ex­ p l a i n the s t r u c t u r a l basis f o r the c r y s t a l l i n i t y observed f o r the latter (1). Another goal o f t h i s study was to determine the important parameters which determine the r a t e s o f polymerization of these c h i r a l 3-lactones. This study i s p r e s e n t l y d i r e c t e d a t i n v e s t i ­ gating the e f f e c t o f r e a c t i o n v a r i a b l e s (solvent and counterion) on polymerization r a t e , and i n the f u t u r e , attempts w i l l be made by r a t e s t u d i e s to a s c e r t a i n i f s t e r e o e l e c t i o n e x i s t s i n t h i s homogeneous, a n i o n i c polymerization r e a c t i o n . Polymerization o f O p t i c a l l y - A c t i v α - P h e n y l - α - e t h y l - 3 - p r o p i o l a c t o n e , PEL, was chosen as the monomer f o r i n v e s t i g a t i o n because the intermediate amino e s t e r had p r e v i o u s l y been resolved (3). Both the racemic and o p t i c a l l y - a c ­ t i v e monomers were converted i n t o t h e i r p o l y e s t e r s i n homogeneous systems using tetraethylammonium benzoate as the i n i t i a t o r i n tetrahydrofuran solvent a t room temperature. The p o l y m e r i z a t i o n of PEL was q u i t e slow under these c o n d i t i o n s and several days were r e q u i r e d to achieve high conversions o f the monomer. Because t h i s i s a " l i v i n g polymer" system, high r e a c t i o n conversions were r e ­ quired f o r the formation o f high molecular weight polymers. Polymers obtained from PEL monomers o f d i f f e r e n t o p t i c a l pu­ r i t y were c h a r a c t e r i z e d as f o l l o w s : (1) f o r c r y s t a l l i n e proper­ t i e s by d i f f e r e n t i a l scanning c a l o r i m e t r y (DSC) and wide-angle x ray d i f f r a c t i o n ; (2) f o r r e l a t i v e molecular weights by s o l u t i o n v i s c o s i t y ; (3) f o r s t r u c t u r e by IR and NMR spectroscopy; and (4) f o r c h i r o p t i c a l p r o p e r t i e s i n s o l u t i o n by o p t i c a l r o t a t o r y d i s p e r ­ s i o n (ORD) and c i r c u l a r dichroism (CD). Molecular weight and melting point data f o r both the racemic and o p t i c a l l y - a c t i v e PEL polymers are c o l l e c t e d i n Table I. Table I. P r o p e r t i e s o f Poly-a-Phenyla-Ethyl-3-Propiolactone Polymer P r o p e r t i e s M

n

T| ,°C tl

50

50

9500

110

27

73

7000

116

90

10

7700

260

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RING-OPENING POLYMERIZATION

The l a r g e d i f f e r e n c e between the melting points i n Table I o f the h i g h l y o p t i c a l l y pure, i s o t a c t i c PEL polymer, on the one hand, compared to those o f e i t h e r the racemic or p a r t i a l l y o p t i ­ c a l l y pure PEL polymer, on the o t h e r , must be a d i r e c t r e s u l t of the e f f e c t of d i f f e r e n c e s i n s t e r e o r e g u l a r i t i e s o f the two types o f polymers on c r y s t a l l i n e p r o p e r t i e s . Molecular weight was ap­ p a r e n t l y not an important f a c t o r f o r t h i s property because e q u i v ­ a l e n t values were obtained f o r a l l three polymers i n Table I. U n f o r t u n a t e l y , the t a c t i c i t y d i f f e r e n c e s expected f o r these p o l y ­ mers could not be determined q u a n t i t a t i v e l y by e i t h e r the IR spectra of polymer f i l m s or the NMR spectra a t 90 MHz of the p o l y ­ mers i n s o l u t i o n . However, wide-angle x - r a y d i f f r a c t i o n measure­ ments showed c o n s i d e r a b l y d i f f e r e n t c r y s t a l l i n e patterns and 2θ values f o r the o p t i c a l l y - a c t i v e PEL polymer o f high o p t i c a l p u r i t y on the one hand, as compared t e i t h e th racemi polyme that with low o p t i c a l p u r i t Table II, i n d i c a t i n g tha crystallin quite d i f f e r e n t . In the as-prepared form, a f t e r p r e c i p i t a t i o n from s o l u t i o n , both types o f polymers appeared to be h i g h l y c r y s t a l l i n e by t h i s method o f a n a l y s i s , and both were comparable i n t h i s property to p o l y p i v a l o l a c t o n e , which i s known to be a very h i g h l y c r y s t a l l i n e polyester. In a d d i t i o n , both the o p t i c a l l y - a c t i v e and racemic polymers had c o n s i d e r a b l y higher degrees o f c r y s t a l l i n i t y than those p r e v i o u s l y observed f o r racemic poly-a-methyl-α-propyl-3p r o p i o l a c t o n e Q). Also of importance, i n a d d i t i o n to the d i f ­ f e r e n t x - r a y d i f f r a c t i o n patterns of the racemic and o p t i c a l l y a c t i v e polymers, was that the racemic polymer d i d not r e a d i l y c r y s t a l l i z e from the melt i n the DSC c h a r a c t e r i z a t i o n while the o p t i c a l l y - a c t i v e polymer of high o p t i c a l p u r i t y d i d . Hence, the higher s t e r e o r e g u l a r i t y a l s o imparts a more f a v o r a b l e r a t e o f c r y s t a l l i z a t i o n to the polymer as would be expected. It seems l i k e l y that the observed d i f f e r e n c e s i n c r y s t a l l i n e p r o p e r t i e s between the o p t i c a l l y a c t i v e and racemic PEL polymers c l e a r l y i n d i c a t e s that the c r y s t a l l i n e regions i n the l a t t e r are not simply formed from p h y s i c a l l y - s e p a r a t e d blocks o f R u n i t s and S units. Nevertheless, such block arrangements of c h i r a l u n i t s could s t i l l be present i n the polymer and form a d i f f e r e n t type of c r y s t a l l a t t i c e than the separate R or S polymers as was found i n the c r y s t a l s t r u c t u r e determination of i s o t a c t i c , racemic p o l y ( t butylethylene o x i d e ) ( 4 ) . Another p o s s i b i l i t y to account f o r the d i f f e r e n t c r y s t a l l i n e p r o p e r t i e s o f the racemic polymer i s t h a t , because o f strong asym­ metric s e l e c t i v e e f f e c t s r e s u l t i n g from s t e r i c i n t e r a c t i o n s , the polymerization o f the racemic monomer favors the enchainment of a l t e r n a t i n g R and S u n i t s ; t h a t i s the formation o f a h i g h l y synd i o t a c t i c polymer. Both x - r a y d i f f r a c t i o n and k i n e t i c studies are i n progress to attempt to e l u c i d a t e t h i s q u e s t i o n , but the high degree o f c r y s t a l l i n i t y and ease o f r e c r y s t a l l i z a t i o n o f the 80% o p t i c a l l y - a c t i v e polymer does not support t h i s p o s s i b i l i t y be-

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

15. LENZ ET AL.

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of «,a-Disubstituted-fi-propiolactones

213

cause an a l t e r n a t i n g asymmetric s e l e c t i v i t y would reduce the s t e r e o r e g u l a r i t y o f that polymer. Indeeed, the s u p e r i o r c r y s t a l ­ l i n e p r o p e r t i e s o f the o p t i c a l l y - a c t i v e polymer are s u r p r i s i n g f o r a monomer o f t h i s o p t i c a l p u r i t y , even i f i t i s assumed that propagation i s n o n - s e l e c t i v e or B e r n o u l l i a n i n c h a r a c t e r . That i s , t h i s degree of monomer o p t i c a l p u r i t y should lead to a p o l y ­ mer o f only approximately 73% i s o t a c t i c t r i a d content (or 82% isotactic diads). Rate I n v e s t i g a t i o n s The r a t e o f polymerization o f racemic PEL was determined i n two d i f f e r e n t s o l v e n t s , tetrahydrofuran (THF) and dimethyl s u l ­ f o x i d e (DMSO), a t two d i f f e r e n t temperatures with tetraethylammo­ nium benzoate as i n i t i a t o r and the r e s u l t s are c o l l e c t e d i n Table III, The r e a c t i o n based upon the carbony group absorptio monomer and polymer, and the data was treated according to the f o l l o w i n g p s e u d o - f i r s t order r a t e equation: *n[M] = * n [ M ]

0

-

k t a

The absolute propagation r a t e constant, kp of Table III, was c a l ­ c u l a t e d from the apparent r a t e constant, ka, by d i v i d i n g by the i n i t i a t o r concentration. The k i n e t i c r e s u l t s f o r the racemic PEL monomer reveal that the value o f kp i s somewhat higher i n THF than i n DMSO a t 35°C. The average value f o r kp i n THF was 9.5 M-l min-1 compared to 8.3 M-l min-1 i n DMSO a t t h i s temperature, i n d i c a t i n g a s i g n i f i ­ c a n t l y lower a c t i v a t i o n energy f o r the former r e a c t i o n . Very s i m i l a r r e s u l t s were obtained p r e v i o u s l y in t h i s l a b o r a t o r y f o r the a n i o n i c polymerization of α-methyl-α-butyl-3-propiolactone (5), and the present authors have a l s o confirmed the e x i s t e n c e of t h i s solvent e f f e c t i n the e q u i v a l e n t polymerization r e a c t i o n s of the α-ethyl and α-propyl monomers of t h i s s e r i e s . The cause o f t h i s unexpected solvent e f f e c t i s not y e t known, but i t may be r e l a t e d to s p e c i f i c s o l v a t i o n c h a r a c t e r i s ­ t i c s o f the ion p a i r endgroups (5J. That i s , i t i s p o s s i b l e that the lower r a t e constant f o r the solvent o f higher p o l a r i t y , DMSO, may be an i n d i c a t i o n o f the formation of a s t r u c t u r e d ion p a i r between t h i s s o l v e n t , the c a r b o x y l a t e anion and the ammonium c o u n t e r i o n , as f o l l o w s :

V

CM, CH

3

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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MNG-OPENING POLYMERIZATION

Table II. Peak Angles and I n t e n s i t i e s o f X-ray D i f f r a c t i o n Spectra o f Poly-aPhenyl-o-Ethyl-e-Propiolactone Racemic Polymer Angle

O p t i c a l l y - A c t i v e Polymer

Intensity

7.8 9.2

m s

14.5° 15.0°

s m

Angle

16.0° 19.5° 21.3°

m w

Intensity

9.5° 14.5°

s m

17.5° 19.5° 21.4°

w m w

Table III. SOLVENT

THF II II DMSO II II THF II II DMSO II II

Rate Constants f o r the P o l y m e r i z a t i o n o f ot-Phenyl-o-Etnyl-B-Propiolactone [M] [Ι] k k T, C » u J -1 -l .-1 M M min M min 0

0

e

P

M

24 II II 24 II II 35 II II 35 II II

0.0123 0.1254 0.1147 0.1410 0.1320 0.1382 0.2076 0.2153 0.2412 0.2307 0.2152 0.2417

0.0057 0.0059 0.0068 0.0076 0.0098 0.0087 0.0056 0.0068 0.0056 0,00698 0.00696 0.0082

0.0243 0.0233 0.0279 0.0322 0.0379 0.0341 0.0551 0.0633 0.0533 0.0551 0.0614 0.068

4.3 4.0 4.1 4.2 3.9 3.9 9.8 9.3 9.5 7.9 8.8 8.3

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

15. LENZ ET AL.

Polymerization

of <*,a-Disubstituted~fi~propiohctones

215

T h i s ion p a i r c o u l d , c o n c e i v a b l y , be of lower r e a c t i v i t y than that present i n the s o l v e n t o f lower p o l a r i t y , THF, which might have greater f r e e ion c h a r a c t e r . These i n v e s t i g a t i o n s are c o n t i n u i n g to more f u l l y v e r i f y the s o l v e n t e f f e c t s observed, and i n a d d i t i o n , s i m i l a r s t u d i e s are i n progress on the e f f e c t o f s u b s t i t u e n t s i z e as well as r e a c t i o n s o l v e n t on the a n i o n i c polymerization o f a s e r i e s o f α-methyl-aa l k y l - 3 - p r o p i o l a c t o n e s . An e q u i v a l e n t s e r i e s of e-propiolactam monomers was r e c e n t l y i n v e s t i g a t e d i n t h i s l a b o r a t o r y with the s u r p r i s i n g r e s u l t that the r a t e s o f propagation w i t h i n t h i s s e r i e s increased with i n c r e a s i n g s i z e of the α - a l k y l s u b s t i t u e n t (6). This r e s u l t was a l s o r a t i o n a l i z e d on the basis o f changes i n ion p a i r s t r u c t u r e which, i n t h a t c a s e , were b e l i e v e d to be induced by s p e c i f i c s t e r i c i n t e r a c t i o n s . Acknow!edgement The authors are g r a t e f u l to the National Science Foundation, Grant No. GH-38848, f o r the support o f t h i s work. Use o f the f a ­ c i l i t i e s of the NSF-sponsored M a t e r i a l s Research Laboratory i s a l s o g r a t e f u l l y acknoledged. Literature Cited 1. Cornibert, J., Marchessault, R. H., Allegrezza, Jr., A. E., and Lenz, R. W., Macromolecules, (1973), 6, 676; Lenz, R. W., Bull. Soc. Chim. Beograd., (1974), 39, 395. 2. Thiebaut, R., Fischer, N., Etienne, Y., and Coste, J., Ind. Plast. Mod., (1962), 14, 1. 3. Fontanella, L. and Testa, E., Liebigs Ann. der Chemie,(1958), 616, 148. 4. Sakakihara, H., Takahaski, Y., Tadokoro, H., Oguni, N., and Tani, H., Macromolecules, (1973), 6, 205. 5. Eisenbach, C. D. and Lenz, R. W., Makromol. Chem., (1976), 177, 2539. 6. Eisenbach, C. D. and Lenz, R. W., Macromolecules, (1976), 9, 227.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

16 Specific Interactions of Lithium Chloride in the Anionic Polymerization of Lactams GIORGIO BONTÁ, ALBERTO CIFERRI, and SAVERIO RUSSO Centro Studi Chimico-Fisici di Macromolecole Sintetiche e Naturali C.N.R. and Istituto di Chimica Industriale, University of Genoa, 16132 Genoa, Italy

The ranking of simple anions and cations according to their ability to affect the properties of two-and three-component systems began to be reported in the earlier days of colloid chemistry (1). In binary salt-water mixtures, for instance, a well defined order of effectiveness of anions and cations in altering the entropy of dilution, or in shifting the maximum of infrared band to ward the position corresponding to the vapor phase was observed (2-4). In ternary systems such as salt, water,and a polar solute (e.g., an aminoacid), an order of ion effectiveness in altering the solubility of the polar solute was reported (5). Quite generally, the solubility was increased at low salt concentration (salting-in) and decreased at relatively high salt concentration (salting-out). With some ions however, notably SCN , Br , Li , the salting-in effect was always more pronounced, and occurring in a larger salt concentration range, than for the other ions, the so called salting-out agents such as F , S0 , Mg . Corresponding eff e c t s on the a c t i v i t y c o e f f i c i e n t o f poorly s o l u b l e s a l t s i n e l e c t r o l y t i c s o l u t i o n s were, of c o u r s e , observed i n e a r l i e r v e r i f i c a t i o n s o f the Debye-Hückel theory ( 6 , 7 ) . However, no t h e o r e t i c a l e l a b o r a t i o n based on purely e l e c t r o s t a t i c c o n s i d e r a t i o n s , nor a l t e r n a t i v e approaches based on such concepts as ion h y d r a t i o n , wat e r s t r u c t u r e , c o m p r e s s i b i l i t y of s o l u t i o n s or s a l t a c t i v i t y , were r e a l l y s u c c e s f u l i n o f f e r i n g a u n i f i e d d e s c r i p t i o n o f the various s a l t e f f e c t s described above ( 6 , 7 ) . -

-

2-

-

+

2+

4

When the r o l e of s a l t s on polymeric substances was c o n s i d e r e d , a s i m i l a r i t y with the e f f e c t s observed with simpler s o l u t e s was g e n e r a l l y f o u n d . For i n s t a n c e , the shrinkage temperature o f collagen tendons swollen i n aqueous s a l t s o l u t i o n i s depressed by i n c r e a s i n g the concentration o f s a l t s such as KSCN o r Li Br and increased by i n c r e a s i n g KF o r concentration (8-10).(Figure la). These e f f e c t s are obviously e q u i v a l e n t to an i n c r e a s e , and to a decrease, o f the s o l u b i l i t y of amorphous c o l l a g e n , r e s p e c t i vely ( 9 ) . Nagy and Jencks (11) i n v e s t i g a t e d the r o l e of s a l t s i n the polymerization o f G-actTTT i n aqueous s o l u t i o n and found that s a l t i n g - i n agents, such as L i B r , i n h i b i t the polymerization which, a g a i n , i s a manifestation o f a decrease o f the a c t i v i t y c o e f f i -

K0SQ4

216

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

16.

BONTA ET AL.. /

Anionic

c i e n t o f s o l u b l e G-actin

Polymerization

of

Lactams

217

due to the s a l t .

E a r l i e r i n v e s t i g a t o r s Q2) d e a l i n g with s a l t - p o l y m e r i n t e r a c t i o n s introduced an i n t e r p r e t a t i o n o f the observed e f f e c t s whicha p p a r e n t l y - was not considered by the i n v e s t i g a t o r s who dealt with the behavior o f simpler s o l u t e s . The i n t e r p r e t a t i o n i s the c l a s s i c a l one o f s o l u b i l i z a t i o n with binding o f a s o l v e n t component t o the s o l u t e s p e c i e s . It now appears t h a t t h i s i n t e r p r e t a t i o n may have general v a l i d i t y (13-16). However, the a l t e r n a t i v e i n t e r p r e t a t i o n o f an i n d i r e c t s a l t e f f e c t - mediated by the r o l e o f s a l t on the water s t r u c t u r e (2,3)- stimulated debates i n the e a r l y twenties ( V ) , and i t i s s t i l l not d e f i n i t i v e l y abandoned (17). It was i n order t o obtain a compelling evidence i n favor o f the b i n d i n g model, and against the water s t r u c t u r e r o l e , t h a t we decided to i n v e s t i g a t e complete absence o f wate t h a t water s t r u c t u r e - o r water i t s e l f - has no p r e v a l e n t r o l e i n s a l t - p o l y m e r i n t e r a c t i o n . In f a c t those s a l t s which are able to depress the melting temperature o f polymers i n the presence o f water are a l s o able t o cause a s i m i l a r e f f e c t i n the absence o f water. This i s i l l u s t r a t e d , f o r i n s t a n c e , i n Figure 1 by the comparison o f the r o l e o f s a l t s i n depressing the shrinkage temper a t u r e o f swollen c o l l a g e n tendons and i n depressing the melting temperature o f p o l y p y r r o l i d o n e (nylon 4).

(b>

Figure 1. (a) Effect of various salts on the melting temperature of collagen swollen in water; (b) Effect of Ltd on the melting and decomposition temperatures of polypyrrolidone

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

218

While a d i r e c t binding of s a l t i n g - i n agents to swollen c o l l a ­ gen could q u a n t i t a t i v e l y be determined (13), the f i n a l proof of the binding mechanism should be based oriThe corresponding demon­ s t r a t i o n o f s a l t - polymer adducts in the molten s t a t e , i n the absence o f water. The occurrence o f s p e c i f i c i n t e r a c t i o n s i n b i n a ­ ry system i s demonstrated i n the present i n v e s t i g a t i o n i n the c a ­ se of Li CI and lactams such as ε-caprolactam and p y r r o l i d o n e . The study o f binary p o l y m e r - s a l t systems - i n a d d i t i o n to i t s i n t e r e s t as a t o o l f o r e l u c i d a t i n g the p h y s i c a l chemistry o f the i n t e r a c t i o n - has i n d i c a t e d r e l e v a n t i m p l i c a t i o n s bearing on the processing o f s y n t h e t i c p o l a r polymers. The depression o f the melting temperature f o r polyamides o f the nylon s e r i e s (21) due t o O . O S L i C l mole f r a c t i o n i s e x h i b i t e d i n Figure 2. The i n c r e a -

0 2

4

6 N

CH

β 2

10 12

Figure 2. Difference between the melting temperature of pure polymer and that of LiCu-polymer mixtures containing 0.05 salt mole fraction as a function of the number of methylene groups per repeating unit

s i n g depression obtained with the more p o l a r members o f the s e ­ r i e s implies the p o s s i b i l i t y o f processing temperatures c o n s i d e ­ r a b l y below the conventional melting temperature of pure polymers. The b e n e f i c i a l e f f e c t o f s a l t s i s a l s o evidenced i n the a l t e r a t i o n o f other p r o p e r t i e s of the pure polymers - such as c r y s t a l l i z a ­ t i o n r a t e ^ 9 ) and melt v i s c o s i t y (20)-which c o n t r o l the proces­ s i n g behavior. In the p a r t i c u l a r case o f p o l y p y r r o l i d o n e , i t i s known that the proximity o f decomposition and melting temperature has posed formidable d i f f i c u l t i e s to the processing of the pure polymer. The a d d i t i o n o f small amounts o f L i C l does not a f f e c t the decomposition temperature and allows a large depression o f the melting temperature (^40°C at 5% w/w) (21), thus allowing p r o ­ cessing uncomplicated by thermal degradation. The presence of L i C l a l s o allows the obtainment o f nylon 6 f i b e r s with mechanical p r o p e r t i e s s u p e r i o r to those obtained i n the absence o f s a l t (22).

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

16.

ΒΟΝΤΑ' ET AL.

Anionic

Polymerization

of

Lactams

219

r\eces_

In s p i t e of the above des cri bed b e n e f i c i a l e f f e c t s , the sary step o f a c c u r a t e l y mixing polymer with s a l t adds some d i f f i ­ c u l t i e s , particularly i f a large-scale industrial application is c o n s i d e r e d . The p o s s i b i l i t y of polymerizing the monomer i n the pre sence of s a l t has been attempted i n order to avoid the mixing s t e p . Preliminary attempts to polymerize ε-caprolactam i n the presence of L i C l using the conventional h y d r o l i t i c p o l y m e r i z a t i o n f o r nylon 6 have g i v e n , however, discouraging r e s u l t s . The s a l t i n h i b i t s po­ l y m e r i z a t i o n and very low molecular weights(<5000) and poor y i e l d s were obtained. This r e s u l t i s not unexpected i n terms o f the effects c i t e d above, p e r t a i n i n g to the polymerization of G - a c t i n , and i s not i n c o n t r a s t with the binding hypothesis. We have nevertheless attempted the a n i o n i c polymerization o f the ε-caprolactam/LiCl s y ­ stem i n b u l k , under anhydrous c o n d i t i o n s t i n the hope that the a c t i v e s i t e of polymerizatio by binding o f L i C l as i In f a c t , i n t h i s case we have obtained high y i e l d s and high mole­ c u l a r weight polymers. The study of t h é l a t t e r polymerization i s described i n t h i s r e p o r t . It appears t h e r e f o r e t h a t a r a t h e r c l o s e relationship exists between binding o f L i C l to the carbonyl oxygen and the p o s s i b i l i t y of o b t a i n i n g high molecular weight p o l y c a prolactam by a n i o n i c bulk p o l y m e r i z a t i o n . Moreover, an i n t e r e s t i n g aspect o f the i n v e s t i g a t i o n i s that the approach used f o r ε-eaprolactam can be a p p l i e d to the polymerization o f other lactams, such as pyrrolidone*which polymerize only by a n i o n i c mechanism. This was a s c e r t a i n e d i n p r e l i m i n a r y r e s u l t s which w i l l be presented i n d e t a i l at a l a t e r time.. s

Interactions

Between Lithium C h l o r i d e and Lactams

The strong i n t e r a c t i o n s between l i t h i u m h a l i d e and polyamides which cause the r e l e v a n t melting p o i n t depression of the polymers (Figure 2 ) , can be b e t t e r understood i f we analyze the behavior of the model system l a c t a m - h a l i d e . In t h i s way, we can a l s o gain addi_ t i o n a l information m mechanisms and k i n e t i c s o f the a n i o n i c p o l y ­ merization. We have found that both the systems c a p r o l a c t a m - l i t h i u m c h l o r i ­ de and p y r r o l i d o n e - l i t h i u r n chloride,when d i s s o l v e d i n anhydrous methanol at room temperature,give by p r e c i p i t a t i o n with a large excess o f anhydrous d i e t h y l ether a c r y s t a l l i n e complex c o n t a i ­ ning f o u r molecules o f lactam and one molecule o f l i t h i u m c h l o ­ r i d e . The melting points of the complexes with caprolactam and p y r r o l i d o n e are 98.5°C and 101.7°C, r e s p e c t i v e l y . The presence o f complexed L i C l i n our polymerization c o n d i t i o n s has been f u r t h e r supported by a d e t a i l e d study o f the phase d i a ­ gram f o r the b i n a r y ε-caprolactam-LiCl system. Homogeneous s o l u ­ t i o n s (melts) of Li CI-caprolactam mixtures with d i f f e r e n t s a l t content were prepared at 120°C and cooled down. Heating and coo­ l i n g c y c l e s were followed by DSC. The r e s u l t i n g e q u i l i b r i u m d i a ­ gram i s shown i n Figure 3. An e u t e c t i c composition o f about 5 mole

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

220

RING-OPENING POLYMERIZATION

% o f L i C l has been found. The 1:4 complex behaves as a compound with congruent melting p o i n t . The s o l i d - l i q u i d e q u i l i b r i a , a t l e a s t i n the range o f 5-20 mole % L i C l , suggest complete comple­ xation o f L i C l by caprolactam. The formation o f c r y s t a l l i n e complexes between l i t h i u m s a l t s and lactams, such as N-methyl-Y-butirolactam,has a l s o been obser­ ved by o t h e r s . A c o o r d i n a t i o n number o f four i s commonly encoun­ t e r e d . In the c r y s t a l , t h e L i i o n i s coordinated t o the carbonyl oxygen o f each o f the f o u r lactam molecules,and the NH hydrogens are hydrogen bonded t o the anions (23-25). +

The r e s u l t s described above r e f e r to the formation o f a complex between L i C l and a lactam i n the c r y s t a l l i n e s t a t e . For the pur­ pose o f the present i n v e s t i g a t i o n i t i s , however, important t o e s t a b l i s h the occurrenc t i n g temperature o f th levant t o the melting point depression o f polymers takes place p r e v a l e n t l y i n the amorphous s t a t e (13,15). No evidence o f i n c l u ­ s i o n o f L i C l i n the c r y s t a l l i n e l a t t i c e o f nylon 6 was reported Q 8 ) . We have obtained a d i r e c t evidence o f such i n t e r a c t i o n s by a n a l y s i s o f the i n f r a r e d s p e c t r a a t high temperature f o r the s y ­ stem c a p r o l a c t a m - L i C l . The i n f r a r e d s p e c t r a a t 120° and 155°C i n the region o f the carbonyl s t r e t c h i n g bands have c l e a r l y shown the s h i f t o f the band from 1650 cm" (pure caprolactam) (26) to 1630 cm (1:4 complex). A l s o 10 mole % s o l u t i o n s o f L i C T i n caprolactam show s i m i l a r s h i f t s i n the d i r e c t i o n o f lower f r e quencies. The magnitude o f the red s h i f t i s even l a r g e r , i f comp-a red t o the vapor o r d i l u t e s o l u t i o n values,,where no s e l f - a s s o ­ c i a t i o n o f caprolactam i s present (1672 cm ). This i s i n d i c a t i v e o f bond weakening due to the e l e c t r o n withdrawal by the metal i o a T h e r e f o r e , the b i n d i n g s i t e which occurs i n the c r y s t a l i s main­ t a i n e d a l s o i n the melt. 1

Ring-Opening A n i o n i c P o l y m e r i z a t i o n : The Role o f Lithium C h l o r i d e The a n i o n i c p o l y m e r i z a t i o n o f lactams i s c a t a l y z e d by strong bases capable o f forming lactam anions. In the presence o f a s u i ­ t a b l e i n i t i a t o r such as an acyl lactam, a very f a s t r e a c t i o n o c ­ curs a t temperatures i n the range o f 100°C to 200°C. Without the i n i t i a t o r , polymerization temperatures appreciably above 200°C are necessary and a n o t i c e a b l e i n d u c t i o n p e r i o d i s p r e s e n t . Anhy­ drous conditions are an e s s e n t i a l p r e - r e q u i s i t e f o r good y i e l d s and rates and r e p r o d u c t i b l e r e s u l t s . The most r e l e v a n t r e a c t i o n s i n the a c t i v a t e d p o l y m e r i z a t i o n o f lactams are the f o l l o w i n g ones:

Initiation Θ RCO-N-ÇO + N-CO

Θ RCO-N CO-N-CO

initiator catalyst

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

(1)

16.

BONTA ET AL. /

RCO-N

Anionic

Polymerization

C0-N-Ç0 +NH-C0 ^

of

Lactams

RCO-NH C0-N-C0 + N-C0

221

(2)

The f i r s t r e a c t i o n i s a ring-opening transamidation and can be depicted as a n u c l e o p h i l i c attack o f the lactam anion on the carbonyl o f the imide group. Highly e l e c t r o n e g a t i v e s u b s t i t u e n t s (such as the acyl groups) at the imide nitrogen i n c r e a s e the rate of the r e a c t i o n . The second step i s a n e u t r a l i z a t i o n ^ proton exchange reaction,which i s much f a s t e r than r e a c t i o n 1 ) .

Propagation RCO-NH CO-N-CO +^00 =^RCO-NH C0-§ CQ-N-CO W W W W W W

(3)

RCO-NH CO-N CO-N-CO + NH-CO s=RC0-NH CO-NH C0-N-C0+N-C0 (4) w w w w W W ^ ^ Reaction (3) shows the prominent r o l e o f the imide linkage which i s the strongest e l e c t r o p h i l i c group i n the system and the actual propagation c e n t e r . The d e t a i l e d mechanism o f r i n g opening ( r e a c t i o n s (1) and (3) ) i s s t i l l open to c o n t r a s t i n g i n t e r p r e t a t i o n s (27-31). An e v a l u a t i o n o f t h e i r v a l i d i t y i s out o f the scope o f the present paper, even i f our r e s u l t s can throw some l i g h t on the dispute (32). A s i m p l i f i e d k i n e t i c scheme has been however proposed by Reimschuessel (33) and shows that the r a t e o f polymerization i s d i r e c t l y p r o p o r t i o n a l to the concentration o f imide groups ( g r o wth centers)times the concentration o f the lactam a n i o n s . The l a t t e r concentration depends among others on the d i s s o c i a b i l i t y of the lactam s a l t , which i n turn i s a f u n c t i o n o f the nature of the c a t i o n . Sebenda (34,35) claims that the i n i t i a t i o n and p r o pagation rates f o r the a n i o n i c p o l y m e r i z a t i o n of caprolactam depend on the c a t i o n , i n the f o l l o w i n g o r d e r : L i < Na < Κ < Cs i . e . t h e rates decrease by i n c r e a s i n g the e l e c t r o n e g a t i v i t y o f the c a t i o n . S i m i l a r r e s u l t s have been found by Sekiguchi (36),by com­ p a r i n g the a c t i v i t y of d i f f e r e n t c a t a l y s t s i n the polymerization of pyrrolidone.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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RING-OPENING POLYMERIZATION

The r e s u l t s o f our polymerization runs are c o l l e c t e d i n Table I. Table

I

Polymerization o f ε-caprolactam a t 154°C ( i n i t i a l polymerization temperature). I n i t i a t o r = N-acetyl caprolactam (1 mole % ) , C a t a ­ l y s t = a l k a l i metal caprolactamate (1 mole % ) .

Sample

a l k a l i metal component o f the c a t a l y s t

t 0.5' sec.

Τ 'm ·

140

63

222.3

165 198 235 270 235

117 90 108 132 135

222.5 214.7 215.6 195.5 190.4

b y hot p l a t e microscope (heating rate= 3°C/min , average

values).

15 G 16 G 27 G 26 G 18 G 20 G 21 G 19 G

a

LiCl

Polymerization time , sec. 3

weight % mole %

Li Na Li Na Li Na Na Li

0

0.35 0.78 1.29 3.50 3.86

1.00 2.06 3.37 8.83 9.68

b

l

c

op L

up to equilibrium conversion,

^ h a l f - c o n v e r s i o n time. c

^1 mole % o f sodium c h l o r i d e . The a l k a l i metal composing the c a t a l y s t (counterion t o ε-capro^ lactam ) and the excess added s a l t ( L i C l ) are i n d i c a t e d i n the second and t h i r d column, r e s p e c t i v e l y . Polymerization k i n e t i c s d a ­ t a are reported i n the f o r t h and f i f t h column,in terms o f reaction t i m e , while the l a s t column includes the melting temperatures o f the corresponding p o l y c a p r o l a c t a m - s a l t system. The l a t t e r data are a l s o i l l u s t r a t e d i n Figure 4. It appears that the polymerization c a t a l i z e d by L i ions (sample 15 6) i s f a s t e r than the one c a t a l i zed by Na ions (16 G) i n the absence o f added L i C l . This r e s u l t i s contrary t o the f i n d i n g s o f Sebenda (34,35). We a l s o note that added L i C l reduces the polymerization r a t e and decreases the m e l ­ t i n g temperature o f the pure polymer. However the depression o f T due t o L i C l appears to be an almost l i n e a r one only when the c a t a ­ l y s t i s the l i t h i u m s a l t o f caprolactam ( c f . , i n Figure 4, the d i f f e r e n c e between open and black c i r c l e s ) . e

+

m

In order t o c l a r i f y the r e l a t i v e r o l e o f N a and L i c o u n t e r ions and t o separate the e f f e c t o f L i counterion from that o f a d ­ ded L i C l , we observe t h a t i n our polymerization experiments one could expect* - c o n s i d e r i n g the high d i e l e c t r i c constant o f the reac t i o n medium - a s o l u b i l i t y o f both L i C l and NaCl. We have found, +

+

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

16.

ΒΟΝΤΑΈΤ AL.

Anionic

Polymerization

of

Lactams

223

100

5

10 15 LiCl,mole %

230h

220

210

200

190

ISO

I

ι 1

ι 2

ι 3

ι

1

4

UCI7.,w/w

Figure 4. Effect of the alkali metal counterion on the melting behavior of polycaprohctam as a func­ tion of LiCl content. (O) — Li*, (Φ) — Na*, (Q) = assuming full exchange between Li* and Na*.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

224

RING-OPENING POLYMERIZATION

however, t h a t NaCl i s completely i n s o l u b l e i n caprolactam at the polymerization temperature, whereas L i C l was found to be s o l u b l e at 120°C up to the c o n c e n t r a t i o n o f 16.6% by weight (34.7 mole %) Indeed, a f i r s t evidence of an exchange between Li and N a ions was derived by the observation that NaCl separated from the s y stem c a p r o l a c t a m - L i C l when m e t a l l i c sodium was d i s s o l v e d i n the l a t t e r . A f u r t h e r support to the exchange i s given by the melting behavior o f s a l t e d polycaprolactam (Figure 4 ) . Assuming a complete exchange between Li and Na" ", the amount of l i t h i u m c h l o r i d e i s reduced up to the f o l l o w i n g values : +

1

20 G 21 G 26 G

0.90% by weight 3.08% by weight 0 %

and 1 mole % sodium c h l o r i d our data as r e f e r r e d t gives the h a l f - f u l l c i r c l e values which f a l l very c l o s e to the s t r a i g h t l i n e . The melting temperature o f the sample 26 G i s c o h i n c i d e n t with the melting temperature o f pure polycaprolactam (samples 15 G and 16 G). This r e s u l t i s p o s s i b l e only assuming a complete exchange between Na and Li which are present i n e q u i molar amounts. The chemical nature o f the c a t i o n i n the c a t a l y s t has no det e c t a b l e i n f l u e n c e on the melting temperature of the pure polymer (samples 15 G and 16 G). Corresponding r e s u l t s have been obtained i n the a n i o n i c p o l y merization o f p y r r o l i d o n e i n bulk at 30°C.Higher i n i t i a l rates have been found when l i t h i u m p y r r o l i d o n a t e instead of sodium pyrroli^ donate was used as c a t a l y s t . Here a g a i n , the a d d i t i o n o f m e t a l l i c " sodium to the mixture o f p y r r o l i d o n e and l i t h i u m c h l o r i d e (1% by weiaht) causes the separation of sodium c h l o r i d e which gives a c h a r a c t e r i s t i c opalescence to the s o l u t i o n . It a p p e a r s , t h e r e f o r e , that i n order to study the " t r u e " r o l e o f l i t h i u m c h l o r i d e on the k i n e t i c s and mechanism o f the a n i o n i c polymerization o f lactams, i t i s a d v i s a b l e to u s e a s a c a t a l y s t o f the r e a c t i o n a metal lactamate which does not undergo chemical exchanges with Li ions. If we compare the p o l y m e r i z a t i o n times o f the samples 15 G, 18 G, and 19 G, we can see t h a t l i t h i u m c h l o r i d e acts as a r e t a r der of p o l y m e r i z a t i o n . The presence o f undissolved sodium c h l o r i de (samples 27 G, 20 G, and 21 G) provides an a d d i t i o n a l r e t a r d a t i o n , as evidenced by the data r e l a t e d to the p o l y m e r i z a t i o n o f the sample 27 G. The two r e t a r d a t i o n e f f e c t s are roughly a d d i t i ve. The r e t a r d a t i o n due to L i C l i s present from the beginning o f the polymerization r e a c t i o n , as evidenced by the tn data ( h a l f conversion t i m e ) . It i s n o t , t h e r e f o r e , caused by the m o d i f i c a t i o n s o f the k i n e t i c scheme due to the many s i d e r e a c t i o n s which occur at the l a t e r stages of the p o l y m e r i z a t i o n . 5

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

16. BONTA' ET AL.

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225

A d e t a i l e d study on the e f f e c t o f L i C l on the polymerization k i n e t i c s and mechanism i s i n progress and w i l l be published i n more d e t a i l elsewhere (32). Side Reactions

and I r r e g u l a r

Structures

It i s well known that the polyamides obtained by a n i o n i c po­ l y m e r i z a t i o n of lactams contain some i r r e g u l a r s t r u c t u r e s o r i g i n a ­ ted from a s e r i e s of s i d e r e a c t i o n s . The same high r e a c t i v i t y o f the a c t i v e species (growth centers and monomer a n i o n s ) , which i s r e s p o n s i b l e of the very f a s t polymerization k i n e t i c s , causes a corresponding increase i n the tendency toward s i d e r e a c t i o n s . The imide group, which c o n s t i t u t e s the strongest e l e c t r o p h i l i c group i n the system, undergoes a C l a i s e n - t y p e condensation i n the stron gly b a s i c medium provided that hydrogen on the α-carbon i s p r e ­ s e n t . The r e s u l t i n g product mides o f 3-keto a c i d s ) peratures and, through a sequence o f condensation and a c y l a t i o n r e a c t i o n s , are converted i n t o keto amides. Both keto imides and keto amides are comparatively strong a c i d s , and they c o n t r i b u t e to decrease the concentration o f lactam anions. T h e r e f o r e , the global e f f e c t i s not r e s t r i c t e d to the lowering o f the concentra­ t i o n o f the growth centers ( i m i d e s ) , but i t involves a l s o the de­ crease i n the b a s i c i t y of the medium (37). Further condensation reactions o f keto imides and keto ami­ des may y i e l d to many p o s s i b l e products: oxypyridone, i s o c i a n a t e , u r a c i l , malonamide, ketones, and so on. A scheme o f the most p r o ­ bable s i d e r e a c t i o n s i n the a n i o n i c polymerization o f lactams w i ­ th a methylene group next ID the carbonyl i s given i n Figure 5, t a ken from a comprehensive review of Sebenda (38). As already men­ t i o n e d , a complete and d e t a i l e d k i n e t i c scheme f o r the a n i o n i c polymerization o f lactams cannot d i s r e g a r d the complex r o l e o f si_ de r e a c t i o n s , which c o n t r i b u t e a l s o to the formation of a d d i t i o ­ nal growth c e n t e r s . For these reasons, only s i m p l i f i e d k i n e t i c equations with very l i m i t e d v a l i d i t y have been proposed so f a r (33). Some o f the above mentioned i r r e g u l a r s t r u c t u r e s show absor­ ption peaks i n the u l t r a v i o l e t region between 250-300 nm. As poir^ ted out by Sebenda Γ 3 7 ) , the absorption maxima at 277 nm ( s o l v e n t HoS0 50% w/w) are d i r e c t l y p r o p o r t i o n a l to the t o t a l amount of the products derived from the imide groups. In p a r t i c u l a r , by using model compounds he found that the degradation of keto ami­ de groups give r i s e to an absorption peak at 280 nm, thus sugge­ s t i n g that most of the i r r e g u l a r s t r u c t u r e s absorbing i n the uv a r i s e from the keto amide. 4

We have s t u d i e d i n d e t a i l nature and amount of the uv ab­ sorbing groups i n the polycaprolactam samples synthesized i n p r e ­ sence o f l i t h i u m c h l o r i d e . The solvent used f o r the spectrophoto­ m e t r y measurements was 99.5% formic a c i d , c o n t a i n i n g 4.5% (w/w)

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

226

l i t h i u m c h l o r i d e . A band maximum at 269 nm was found f o r a l l sam­ p l e s . Our p r e l i m i n a r y data are c o l l e c t e d i n Table II. Apart from the d i f f e r e n c e i n the concentrations of i n i t i a t o r and c a t a l y s t , the polymerization c o n d i t i o n s f o r the two sets o f data were s t r i c ­ t l y the same, and they have already been reported i n Table I. It i s e v i d e n t from the above data that the chemical nature o f the c a t a l y s t counterion ( L i or Na ) as well as i t s c o n c e n t r a ­ t i o n has no e f f e c t on the uv absorption i n t e n s i t y , whereas the presence of l i t h i u m c h l o r i d e i n the polymerization system s t r o n ­ g l y reduces the amount o f the i r r e g u l a r s t r u c t u r e s absorbing i n the uv r e g i o n . The e f f e c t seems to be l i n e a l l y dependent on the h a l i d e content. These s t r u c t u r e s are presumably formed through a sequence o f condensation r e a c t i o n s at the α-carbon atom of the Na c y l a t e d and N-carbamoylated amides. Lithium c h l o r i d e s h o u l d , t h e ­ r e f o r e , i n t e r f e r e very +

Table

II

O.D. values of 1% (w/w) polycaprolactam s o l u t i o n s i n HCOOH c o n t a ­ i n i n g 4.5% (w/w) o f L i C l . Band maximum at 269 nm.

Sample

LiCl weight % c

A l k a l i metal counter ion

cm

14 G

a

Na

0

0.44

28 G

a

Li

0

0.44

8 G

a

Na

2.43

0.37

10 G

a

Na

3.52

0.32

11 G

a

Na

5.19

0.26

13 G

a

Na

7.21

0.21

15 G

b

Li

0

0.43

27 G

b

Li

0

26 G

b

Na

0

0.41

20 G

b

Na

0.90

0.38

19 G

b

Li

3.86

0.35

0.45

d

i n i t i a t o r and c a t a l y s t c o n c e n t r a t i o n s : 0.5 mole%;

i n i t i a t o r and

c a t a l y s t c o n c e n t r a t i o n s : 1 mole %; c o r r e c t e d v a l u e s , on the b a ­ c

sis

of f u l l

exchange between L i

+

and N a ; +

c o n t a i n i n g 1 mole %

NaCl.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

16. BONTA' ET AL.

Anionic

Polymerization

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Lactams

227

t i o n i n a way which i s , a t p r e s e n t , under i n v e s t i g a t i o n (32). Evœ at t h i s p r e l i m i n a r y s t a g e , however, i t i s noteworthy to p o i n t out the r e l e v a n t r o l e of l i t h i u m c h l o r i d e toward the synthesis o f more r e g u l a r polymers o f caprolactam. We have a l s o c a r r i e d out molecular weight f r a c t i o n a t i o n s o f our polymer samples, i n order to study the e f f e c t o f l i t h i u m chlor i d e on the MWD. The data on MW and MWD w i l l be reported elsewhere (39), but we can mention here the r e s u l t s on the uv absorption o f tRë f r a c t i o n a t e d samples, i . e . the d i s t r i b u t i o n o f the uv abs o r b i n g groups as a f u n c t i o n o f polymer molecular weight. As an example, O.D. values f o r two u n f r a c t i o n a t e d (open c i r c l e s ) and f r a c t i o n a t e d ( f u l l c i r c l e s ) polymers are reported i n Figure 6. Curve a) r e f e r s to polycaprolactam synthesized i n the absence of L i C l (sample 14 6 ) , while curve b) gives the O.D values of the sample 11 G (5.19 % by the f r a c t i o n s i r r e s p e c t i v amount o f i r r e g u l a r s t r u c t u r e s . I d e n t i c a l behavior was found f o r the other samples. This r e l e v a n t r e s u l t i s not s u r p r i s i n g , being the s i d e r e a c t i o n s which cause the s t r u c t u r a l i r r e g u l a r i t i e s able i n part to generate new growth c e n t e r s , as evidenced i n F i g u r e 5. In f a c t , most o f the uv absorbing groups are o r i g i n a t e d from the imide end groups and are the l o c i f o r f u r t h e r growth. A f t e r our r e s u l t s , the s i d e r e a c t i o n s which do not c o n t r i b u t e to the formation o f new growth centers are not very probable i n our experimental conditions. Our data for the d i s t r i b u t i o n o f i r r e g u l a r s t r u c t u r e s as a f u n c t i o n o f MW do not support recent i n t e r p r e t a t i o n s (40) based on a c l o s e c o r r e l a t i o n between bimodal MWD and amoumTbf f a s t s i d e r e a c t i o n s . I f i r r e g u l a r i t i e s were p r e v a i l i n g i n the i n i t i a l stage o f p o l y m e r i z a t i o n , when higher molecular weights are pro duced, the amount o f uv absorbing species would be a f u n c t i o n o f the chain s i z e . A more d e t a i l e d i n t e r p r e t a t i o n o f the c o r r e l a t i o n s between MW, MWD and L i C l w i l l be presented a t a l a t e r time (39). It i s important, however, to emphasize here that l i t h i u m c h T ô r i d e causes only an unrelevant decrease o f the polymer molecular weight, which remains i n the range o f 15,000 to 25,000, i . e . w i t h i n the usual values o f a n i o n i c polycaprolactam Mini's. Some p r e l i m i n a r y data on p o l y p y r r o l i d o n e synthesized i n p r e sence o f l i t h i u m c h l o r i d e show absorption patterns s i m i l a r to those found f o r polycaprolactam, with the i n t e n s i t y o f the band maximum at 274 nm s t r o n g l y depressed by 1% by weight o f L i C l . This s i m i l a r i t y , which i s present d e s p i t e the f a c t t h a t the p o l y merization temperatures f o r the two monomers are very d i f f e r e n t (>120°C f o r caprolactam, and 30°C f o r p y r r o l i d o n e ) , i s i n s t r i k i n g c o n t r a s t with the i n t e r p r e t a t i o n s commonly encountered i n the l i t e r a t u r e that the s i d e r e a c t i o n s are determined by the simultaneo-

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION ANIONIC

POLYMERIZATION 0F NHC0CH > r

2

)

^

r

R-CO-N-CO

•

u

N-C0

s=

POLYMER

GROWTH CENTER ( IMIDE )

j KETONE + C 0

KETO IMIDE

•

OXYPYRIDONE +

(Wy

2

Cof

S T M I D Ï ! + KETO AMIDE

ι

K E T O N E + ISOCYANATE

S

r N

- -«GROWTH

CENTERI

X

MALONAMIDE

+

'JM'CEj

-COO®

\ DIALKYL

UREA

Figure 6. O.D. values vs. polymer concentration for sample 14 G (a) and 11 G (b) (path length = 1 cm)

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1

j

16. ΒΟΝΤΑ' ET AL.

Anionic

Polymerization

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Lactams

229

us effect o f high temperature and strong b a s i c i t y o f the medium (37,41,42). An attempt to c l a r i f y the true nature o f the e f f e c t whicn cause the s i d e r e a c t i o n s i s under way (32). It i s mainly b a ­ sed on the unique opportunity to use l i t h i u m " c R 1 o r i d e as an agent able to c o n t r o l and reduce the i r r e g u l a r s t r u c t u r e s . M e l t i n g Behavior o f Polycaproamide Synthesized from Caprolactam-

LiCl Mixtures.

—

E

The f u l l s e t o f data on the melting temperatures f o r t h e p o ­ lycaproamide samples as functions o f L i C l content i n the p o l y m e r i ­ z i n g mixture are p l o t t e d i n Figure 7 (curve a ) . The data r e f e r t o two d i f f e r e n t sets o f i n i t i a t o r and c a t a l y s t concentrations (0.5 and 1 mole %) and are already c o r r e c t e d and r e l a t e d to the " t r u e " concentration o f l i t h i u m c h l o r i d e . Our curve runs p a r a l l e l to the curve (b) based on som ving l i t h i u m c h l o r i d e i rence i s a t t r i b u t e d t o the d i f f e r e n t experimental techniques: our data are T™ v a l u e s , obtained by p o l a r i z i n g microscope equipped with hot s t a g e , whereas i n r e f * ( 1 9 ) the authors obtained T£ values using DSC a n a l y s i s and Hoffman p l o t s . In f a c t , T values o f some polycaproamide samples prepared as described i n r e f . ( 1 9 ) , were d e ­ termined f o l l o w i n g the present method and t h e i r melting values as functions o f L i C l content f a l l c l o s e to the curve ( a ) . We can t h e ­ r e f o r e conclude that i t i s p o s s i b l e to " d i r e c t l y " synthesize s a l ­ ted polycaproamide, c h a r a c t e r i z e d by the same melting behavior found with the other methods o f s a l t a d d i t i o n . This r e s u l t i s t e c h ­ n o l o g i c a l l y very r e l e v a n t and permits to by-pass a l l the p r a c t i c a l l i m i t a t i o n s o f the other mixing techniques as pointed out i n the i n t r o d u c t i o n s e c t i o n . Moreover, analogously to previous f i n d i n g s (18), the s a l t can be q u a n t i t a t i v e l y removed from the as-formed s a l t e d polyamide by washing with hot water ( ^ 9 0 ° C ) , a l l the p h y s i c a l p r o p e r t i e s o f polycaprolactam b e i n g e a s i l y r e s t o r e d . m

Conclusions Formation o f adducts between L i C l and ε-caprolactam o r p y r r o ­ l i d o n e having 1:4 composition was observed by s o l u b i l i t y and pha­ se diagram s t u d i e s . S p e c i f i c i n t e r a c t i o n s between L i C l and the lactams were a l s o evidenced i n the amorphous s t a t e , and i n the ab­ sence o f water, by i n f r a r e d spectroscopy. The a n i o n i c bulk p o l y m e r i z a t i o n o f caprclactam and p y r r o l i d Q ne i n the presence o f L i C l under anhydrous c o n d i t i o n s i s c h a r a c t e ­ r i z e d by good y i e l d s and f a s t r e a c t i o n s . The MW and MWD o f the p o l y ­ mers are comparable to those obtained by conventional h y d r o l i t i c p o l y m e r i z a t i o n . The extent o f s i d e r e a c t i o n s i s reduced during the a n i o n i c polymerization i n presence o f L i C l , thus l e a d i n g t o a mo­ re r e g u l a r polymer, a c t u a l l y s u p e r i o r to that obtained by the usual a n i o n i c technique. The melting temperature o f the r e s u l t i n g polymer-LiCl mixtures i s lower than t h a t o f the pure polymer, and

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

230

LiCl %, W/W Figure 7. Effect of LiCl on the melting temperature of polycaprolactam. (Ο, Φ) — Direct synthesis, (O) = 0.5 mol % initiator and catalyst, (Φ) = 1 mol % initiator and catalyst, (A) = salt added to melted polyamide.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

16.

BONTA ET AL.

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Polymerization

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Lactams

231

i s continuously depressed by i n c r e a s i n g L i C l content i n a way e n ­ t i r e l y s i m i l a r to that observed by mixing preformed polymer with LiCl. Binding of L i C l to the carbonyl oxygen o f the lactam i s po­ s t u l a t e d not to adversely i n t e r f e r e with the polymerization s i t e during the a n i o n i c p o l y m e r i z a t i o n . Binding of L i C l to the carbonyl oxygen o f the amide bond i s postulated to p e r s i s t i n the amorpho­ us s t a t e of the p o l y n s r , ' p o s s i b l y i n v o l v i n g m u l t i p l e i n t e r a c t i o n s l e a d i n g to l a b i l e c r o s s l i n k i n g e f f e c t s (20).

Acknowledg, mmtb The Autkosu aJid thankful to Ox.R.Biaggio, Μ-ό. E.Aglivtto, Wi.M.Nmcioni and Wi.E.Savà fan thûA keJLpiul coZJUboMution In tht (LxpoAJjnzvrtal pa/ut oh tht pKZAwvt mnk. Literature Cited 1) McBain J.W., Colloid Science, ed.D.C.Health, Boston,Mass, 1950. 2) Frank H.S., and Robinson A.L., J.Chem.Phys.,(1940), 8, 933. 3) Frank H.S., and Wen Yang Wen, Discuss.Faraday Soc., (1957), 24, 133. 4) Boswell A.M., Gore R.C., and Rodebush W.H., J.Phys.Chem., (1941) 45, 543. 5) Cohn E.J., and Edsall J.T., Proteins, Amino Acids, and Peptides, Reinhold Publishing Corp., New York, N.Y., 1943. 6) Long F.A., and McDevitt W.F., Chem.Rev., (1952), 51, 119. 7) Edsall J.T.,and Wyman J., Biophysical Chemistry, Academic Press, New YorK, 1958. 8) Gustavson K.H., The Chemistry and Reactivity of Collagen, Academic Press, New York, 1956 . 9) Ciferri Α., Rajagh L.V., and Puett D., Biopolymers, (1965), 3, 461. 10) Puett D., and Rajagh L.V., J.Macromol .Chem.,(1968), A2, 111. 11) Nagy B., and Jencks W.P., J.Am.Chem.Soc.,(1965), 87, 2480. 12) Katz J.R., and Weidinger Α., Biochem.Z., (1933),259, 385. 13) Ciferri Α., Garmon R., and Puett D., Biopolymers (T967),5,439. 14) Bianchi Ε., Conio G., Ciferri Α., Puett D., and Rajagh L.V., J.Biol.Chem.,(1967), 242, 1361. 15) Orofino T.A., Ciferri A., and Hermans J.J., Biopolymers,(1967), 5, 773. 16) Conio G., Patrone E., Rialdi G., and Ciferri Α., Macromolecu­ les, (1974), 7, 654. 17) Von Hippel P.H., and Wong K.Y., J.Biol.Chem.,(1965), 240,3909. 18) Valenti B., Bianchi E., Greppi G., Tealdi Α., and Ciferri Α., J.Phys.Chem., (1973), 77, 389. 19) Bianchi E., Ciferri Α., Tealdi Α., Torre R., and Valenti B., Macromolecules, (1974), 7, 495. 20) Acierno D., Bianchi E., Ciferri Α., De Cindio Β., Migliaresi C., and Nicolais L., J.Polym. Sci .C,(1976), 54, 259.

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RING-OPENING POLYMERIZATION

21) Valenti Β., Bianchi Ε., Tealdi Α., Russo S., and Ciferri Α., Macromolecules, (1976), 9, 117. 22) Acierno D., La Mantia F., Polizzotti G., Alfonso G.C., and Ciferri Α., J.Polym. Sci., Polym.Letters Ed., (1977), 23) Madan S.K., Inorg.Chem.(1967),6, 421. 24) Wuepper J.L., and Popov A.I., J.Amer.Chem.Soc.,(1969), 91,4352. 25) Balasubramanian D., and Shaikh R., Biopolymers, (1973), 12, 1639. 26) Millich F., and Seshadri K.V., in "Lactams", Ch.3 of "Cyclic Monomers", edr.Frisch, K.C., Wiley-Interscience, New York 1972. 27) Wichterle 0., Makromol.Chem., (1960), 35, 174. 28) Wichterle 0., Sebenda J., and Králíček J., Fortschr.Hochpolym. Forsch., (1961), 2, 578. 29) Champetier G., and Sekiguchi H., J.Polym.Sci., (1960), 48,309. 30) Sekiguchi H., J.Polym.Sci. A ,(1963), 1, 1627. 31) Sekiguchi H., and Coutin B., J.Polym.Sci.Polym.Chem.Ed.,(1973 ) 11, 1601. 32) Aglietto E., Bontà G., Ciferri Α., Nencioni M., and Russo S., to be published. 33) Reimschuessel H.K., in "Lactams", ch.7 of "Ring-Opening Poly­ merization", edrs.Frisch K.C., and Reegen S.L., M.Dekker, New York 1969. 34) Čefelín P., and Šebenda J., Coll.Czech.Chem.Comm., (1961),26, 3028. 35) ittler Ε., and Šebenda J., J.Polym.Sci. C ,(1967), 16, 67. 36) Sekiguchi H., Rapacoulia Tsourkas, P., and Coutin B., J.Polym.Sci. C, (1973), 42, 51. 37) ebenda J., Masar B., and Bukač Z., J.Polym. Sci. C (1967), 16, 339. 38) ebenda J., J.Macromol.Sci.-Chem. A , (1972), 6, 1145. 39) Ciferri Α., Russo S., and Savà E., to be published. 40) Roda J., Králíček J., and Sanda Κ., Eur.Polym.J.,(1976), 12, 729. 41) Bukač Ζ., and Sebenda J., Coll.Czech.Chem.Comm.,(1967), 32, 3537. 42) Bukač Ζ., Tomka J. and Šebenda J., Coll.Czech.Chem.Comm., (1968), 33, 3182.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

17 Isomerization Polymerization of Lactams H. K. REIMSCHUESSEL Chemical Research Center, Allied Chemical Corp., Morristown, NJ 07960

The isomerization polymerization of lactams is a rather recently discovered phenomenon. (1) It pertains to substituted lactams in which a particular substituent is or contains a car­ boxylic group capable of interacting with the amide function of the lactam. Whereas the ordinary ring opening polymerization of lactams yields polyamides, the isomerization polymerization results in the formation of polyimides. Either process is characterized by competition between an intramolecular reaction of cyclization and the intermolecular polymerization reaction. In the ordinary ring opening polymerization of lactams the former reaction is part of a polymer-monomer equilibrium, and the product of cyclization is the particular lactam itself. The chemical structure of the repeating unit of the corresponding polymer molecule is in this case identical to that of the opened lactam ring. This applies, of course, also to any cyclic oligomers formed during the polymerization process. A rather different situation, however, characterizes the isomerization polymerization for which no polymer-monomer equilibrium is indicated. The struc­ tures o f both the propagating species e n t a i l e d i n t h i s polymeriza­ t i o n r e a c t i o n and t h e p r o d u c t o f any c y c l i z a t i o n r e a c t i o n d i f f e r f r o m t h a t o f t h e p a r t i c u l a r l a c t a m . F u r t h e r m o r e , no s t r u c t u r a l i d e n t i t y e x i s t s i n t h i s case between t h e l a c t a m and t h e r e p e a t i n g u n i t o f t h e polymer molecule. Whether p o l y m e r i z a t i o n o r c y c l i z a t i o n i s t h e d o m i n a t i n g r e ­ a c t i o n depends f o r e i t h e r p r o c e s s o n t h e r m o d y n a m i c a n d k i n e t i c f a c t o r s , and on t h e t o t a l m o l e c u l a r s t r a i n energy o f t h e p a r t i c u ­ lar ring structure. I n case o f l a c t a m s , t h e six-membered 6 - v a l e r o l a c t a m , f o r i n s t a n c e , i s t h e most s t a b l e r i n g s t r u c t u r e and e x h i b i t s t h e l e a s t t e n d e n c y t o p o l y m e r i z e . R e g a r d l e s s o f t h e r i n g s i z e , introduction o f substituents g e n e r a l l y increases both the r a t e o f r i n g c l o s u r e and t h e s t a b i l i t y o f t h e r i n g , i t r e s u l t s consequently i n a decrease o f t h e p o l y m e r i z a b i l i t y o f t h e p a r ­ t i c u l a r lactam. This i s r e f l e c t e d i n a lower heat o f polymeriza­ t i o n a n d a h i g h e r monomer e q u i l i b r i u m c o n c e n t r a t i o n f o r l a c t a m s

233

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

234

RING-OPENING POLYMERIZATION

such a s methyl c a p r o l a c t a m and t h e r e s p e c t i v e e q u i l i b r i u m polymers.(2) Relative t o the unsubstituted lactam, r i n g closure o f t h e c o r r e s p o n d i n g s u b s t i t u t e d one i s c h a r a c t e r i z e d b y a l o w e r e n t h a l p y and h i g h e r entropy. Both e f f e c t s s h i f t t h e e q u i l i b r i u m t o w a r d t h e c y c l i c monomer a t t h e e x p e n s e o f t h e e x t e n t o f p o l y ­ m e r i z a t i o n . T h i s i s t r u e , however, o n l y f o r lactams c o n t a i n i n g substituents that are incapable o f reacting with other functions p r e s e n t i n t h e system. I f the p a r t i c u l a r s u b s t i t u e n t i s capable o f i n t e r - o r i n t r a m o l e c u l a r i n t e r a c t i o n w i t h t h e amide f u n c t i o n o f the lactam t o the extent t h a t e i t h e r a c y c l i c t r a n s i t i o n state o r a c y c l i c i n t e r m e d i a t e r e s u l t s , because t h e f o r m a t i o n o f such a p a r t i c u l a r c y c l i c structure i s h i g h l y favored both g e o m e t r i c a l l y and t h e r m o d y n a m i c a l l y , t h e n a d r a s t i c a l l y a l t e r e d r e a c t i v i t y o f t h e p a r e n t r i n g s y s t e m c o u l d b e t h e c o n s e q u e n c e . I t i s w e l l known t h a t c a r b o x y l groups a r T r a n s a m i d a t i o n and a c y l a t i o processes e n t a i l i n g t h i s i n t e r a c t i o n . Lactams c o n t a i n i n g c a r b o x y l g r o u p s a s s u b s t i t u e n t s o r a s p r i n c i p a l m o i e t y o f s u b s t i t u e n t s were t h e r e f o r e s y n t h e s i z e d and i n v e s t i g a t e d . S u b s t i t u t e d Lactams The l a c t a m s i n v e s t i g a t e d t h u s f a r may b e d i v i d e d i n t o t h r e e groups: 1) c a r b o x y m e t h y l l a c t a m s ; 2) c a r b o x y l a c t a m s ; 3) c a r b o x y lactams c o n t a i n i n g non-reactive s u b s t i t u e n t s . The f i r s t g r o u p c o n s i s t s o f α-carboxymethyl c a p r o l a c t a m , (OCM7), β-carboxymethyl c a p r o l a c t a m , (CM7), 4 - c a r b o x y m e t h y l - 2 - p i p e r i d o n e , (CM6), a n d 4c a r b o x y m e t h y l - 2 - p y r r o l i d o n e , (CM5). The s e c o n d g r o u p i s r e p r e ­ s e n t e d b y 4 - c a r b o x y - 2 - p i p e r i d o n e (C6) a n d 4 - c a r b o x y - 2 - p y r o l i d o n e , (C5), and t h e t h i r d group comprises 6,6-dimethyl-4-carboxy-2p i p e r i d o n e , (DMC6), 5 , 5 - d i m e t h y l - 4 - c a r b o x y l - 2 - p y r r o l i d o n e , (DMC5), 4 - c a r b o x y - 6 - m e t h y l - 2 - p i p e r i d o n e , (MC6), 4 - c a r b o x y - 6 - e t h y l - 2 p i p e r i d o n e , (ME6), 4 - c a r b o x y - 5 - m e t h y l - 2 - p y r r o l i d o n e , (MC5), a n d 4 - c a r b o x y - 5 - e t h y l - 2 - p y r r o l i d o n e , (EC5). The α-carboxymethyl c a p r o l a c t a m was o b t a i n e d f r o m a-bromoc a p r o l a c t a m v i a n u c l e o p h i l i c s u b s t i t u t i o n employing sodium d i e t h y l m a l o n a t e C3), w h e r e a s b o t h β-carboxymethyl c a p r o l a c t a m a n d 4c a r b o x y m e t h y l - 2 - p i p e r i d o n e were s y n t h e s i z e d v i a n u c l e o p h i l i c a d d i t i o n o f t h e m a l o n a t e a n i b n e t o t h e c o r r e s p o n d i n g α, β u n s a t u ­ r a t e d l a c t a m ( 4 , 5 ) . The 4 - c a r b o x y - m e t h y l - 2 - p y r r o l i d o n e was o b t a i n e d b y h y d r o l y s i s o f t h e c o r r e s p o n d i n g e t h y l e s t e r w h i c h was s y n t h e s i z e d a c c o r d i n g t o t h e p r o c e d u r e s g i v e n by Henecka e t a l . (6^5). The s y n t h e s i s o f 4 - c a r b o x y - 2 - p i p e r i d o n e e n t a i l e d a d d i t i o n o f hydrogen cyanide t o d i a l k y l i t a c o n a t e , and r e d u c t i v e c y c l i z a ­ t i o n o f t h e r e s u l t i n g d i a l k y l cyanomethyl s u c c i n a t e t o 4-alkoxyc a r b o n y 1 - 2 - p i p e r i d o n e f o l l o w e d b y s a p o n i f i c a t i o n (7) · * ^ her member o f t h i s g r o u p , 4 - c a r b o x y - 2 - p y r r o l i d o n e , was o b t a i n e d f r o m i t s m e t h y l e s t e r w h i c h was s y n t h e s i z e d v i a e s t e r i f i c a t i o n o f amino m e t h y l s u c c i n i c a c i d ( 8 ) . The 6,6 d i m e t h y l - 4 - c a r b o x y - 2 - p i p e r i d o n e was s y n t h e s i z e d b y r e d u c t i v e c y c l i z a t i o n o f m e t h y l 3-methoxys

ie

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

o t

17. REiMscHUEssEL

Isomerizotion

Polymerization

of

Lactams

235

carbonyl-5-methyl-5-nitrohexanoate, followed by s a p o n i f i c a t i o n o f t h e m e t h y l e s t e r g r o u p ( 8 ) . The 5 , 5 - d i m e t h y l - 4 - c a r b o x y - 2 p y r r o l i d o n e was p r e p a r e d b y t h e same s e q u e n c e o f r e a c t i o n s s t a r t ­ i n g f r o m e t h y l 3 - e t h o x y c a r b o n y l - 2 - p y r r o l i d o n e ( 8 ) . The s y n t h e s i s o f 4 - c a r b o x y - 6 - a l k y l (methyl and e t h y l ) - 2 - p i p e r i d o n e c o n s i s t e d o f n u c l e o p h i l i c a d d i t i o n o f n i t r o e t h a n e ( o r n i t r o propane) t o d i ­ m e t h y l i t a c o n a t e , r e d u c t i v e c y c l i z a t i o n o f t h e r e s u l t i n g a l k y l 3methoxycarbonyl-5-nitrohexanoate (or-heptanoate), and s a p o n i f i c a ­ t i o n o f t h e e s t e r g r o u p s ( 9 ) . The s y n t h e s i s o f 4 - c a r b o x y - 5 - a l k y l (methyl and e t h y l ) - 2 - p y r o l i d o n e e n t a i l e d M i c h a e l r e a c t i o n w i t h nitromethane (or 1-nitropropane) on e i t h e r d i e t h y l maleate o r fumarate, r e d u c t i v e c y c l i z a t i o n o f t h e e t h y l 3-ethoxycarbonyl-4nitropentanoate (orhexanoate), and s a p o n i f i c a t i o n o f t h e e s t e r f u n c t i o n ( 9 ) . The a d d i t i o n o f n i t r o a l k a n e s t o d i m e t h y l i t a c o n a t e and d i e t h y l m a l e a t e ( f u m a r a t e disastereoisomers. Thus i n g m i x t u r e s a f f o r d e d i n c a s e o f a l k y l 3-methoxy c a r b o n y l - 5 nitroalkanoate the formation o f both 4-methoxycarbonyl-6-alkyl-2p i p e r i d o n e and 3 - c a r b o x y m e t h y l - 5 - a l k y l - 2 - p y r r o l i d o n e , whereas t h e reduction o f a l k y l 3-ethoxycarbonyl-4-nitroalkanoate p r o d u c e d 4e t h o x y c a r b o n y l - 5 - a l k y l - 2 - p y r r o l i d o n e a n d a n a p p r e c i a b l e amount o f noncrystallizable material (9). G e n e r a l r e a c t i o n schemes f o r t h e s y n t h e s e s o f t h e p a r t i c u l a r s u b s t i t u t e d l a c t a m s have been summarized i n T a b l e I . P r i n c i p a l Reactions, S t r u c t u r e and P r o p e r t i e s o f Reaction Products Numerous r e a c t i o n s c a n b e e n v i s a g e d t h a t a r e p e c u l i a r t o t h e functions t h a t c h a r a c t e r i z e t h e considered lactams. For the p r e s e n t r e v i e w , however, o n l y those r e a c t i o n s a r e o f i n t e r e s t t h a t are thermally induced by heating t h e p a r t i c u l a r lactams i n an i n e r t atmosphere t o t e m p e r a t u r e s above t h e i r r e s p e c t i v e m e l t i n g p o i n t s . Under t h i s c o n d i t i o n e i t h e r o r b o t h p o l y m e r i z a t i o n and r e a r r a n g e m e n t may o c c u r . Whereas t h e l a t t e r may o r may n o t e n t a i l t h e f o r m a t i o n o f w a t e r t h e f o r m e r a l w a y s d o e s . The s t r u c t u r e s o f both t h e lactam d e r i v a t i v e s and t h e corresponding r e a c t i o n product ( p o l y m e r s o r / a n d r e a r r a n g e m e n t p r o d u c t s ) a r e shown i n T a b l e 2. The 4-carboxymethyl-2-pyrrolidone (CM5) was f o u n d t o b e t h e o n l y member o f t h e p r e s e n t s e r i e s o f l a c t a m s t h a t n e i t h e r p o l y m e r i z e d o r r e a r r a n g e d when h e a t e d a b o v e i t s m e l t i n g p o i n t . The t h r e e other carboxymethyl lactams polymerized. The p o l y m e r d e r i v e d f r o m α-carboxymethyl c a p r o l a c t a m (otCM7) was a c o l o r l e s s t r a n s p a r e n t m a t e r i a l t h a t d i d n o t m e l t o r decompose b e l o w 300°C ( 1 0 ) . I t was i n s o l u b l e i n a l l s o l v e n t s a n d d i d n o t c o n t a i n s o l u b l e compounds o r u n r e a c t e d monomer. T h i s p o l y m e r was o b v i o u s l y h i g h l y c r o s s l i n k e d . The p o l y m e r i z a t i o n o f b o t h 4 - c a r b o x y m e t h y l - 2 - p i p e r i d o n e (CM6) a n d ( ^ c a r b o x y m e t h y l c a p r o l a c t a m (CM7) r e s u l t e d i n h i g h m o l e c u l a r w e i g h t , l i n e a r , c r y s t a l l i z a b l e polymers t h a t were s o l u b l e i n s o l v e n t s such as formic a c i d , m-cresol, t r i f l u o r o e t h a n o l , and s u l f u r i c a c i d b u t i n s o l u b l e i n a l l common o r g a n i c s o l v e n t s . The p o l y m e r d e r i v e d f r o m CM6 d i d n o t m e l t b e l o w 400 °C b u t showed s i g n s

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

236

Table 1

G e n e r a l R e a c t i o n Schemes

+ CH (C00R), -

(CH,L- NH I I • CH-CH,-C = 0 I CH,-C00H

+ H,0. - CO,

(CH,) —NH

(CH, )„— NH I I CHBr — C = 0

CH,—C = 0

1) + No*

CH-(COOR),

2) + H , 0 , - C 0 , — -

{

C

j

H

N

I CH, — ,

•

β-CARBOXYMETHYL

(n = 4) (n = 3)

H

I C=0

B

CAPROLACTAM

/9-CARBOXYMETHYL - 2 - PIPERIDONE

o-CARBOXYMETHYL CAPROLACTAM

1) + CICH,C00R 2) - C O , ,-HOC T

3)

NC-CH,-C00C(CH,),

Η,/Νι,

1)

CH,-CN I CH-CH,-COOR

1) CH,OH(HCI) 2) KOH

CH, II C-CH,-COOR I COOR

4 - CARBOXYMETHYL - 2- PYRROLIDONE

t

C-CH, I COOR

CH-CH,-COOH

CH, NH I I CH-CH -C=0

T

H,0

HC-NO, = h

H,/Ni

2) Η,Ο

CH,-CH,-NH I I CH-CH,-C = 0 I COOH

CH, NH I I CH-CH,-C=0

CH, CH, CH,-C-NO, I

4 - CARBOXY - 2 - PYRROL IDONE

CH, CH,

CH,-CH,-COOR

.1

H,(Pd/C»

2)

Η,Ο

•

COOR

CH, I H,C-C-NO,

4-CARBOXY-2-PIPERIDONE

C

\

H

C

^

N

H

I I CH,-CH,-C»0 I COOH

6,6- DIMETHYL - 4 - CARBOXY - 2- PIPERIDONE

CH, H,C-C

CH-CH,-COOR

2)

H,0

CH-CH.-COOR I COOR

COOR

5.5- DIMETHYL - 4 - CARBOXY - 2- PYRROLIDONE

R

R

CH,-CH-NO, I ROOC-CH-CH,—COOR CH, II ROOC-CH,-COOR

R I Ο,Ν-CH-CH, ROOC

CH-CH,-COOR

I H,C-NO, I

ROOC-CH, H,C-COOR

•> ilW/C) H

2) Η,Ο

"

H

i

C W / c

2) Η,Ο

=

»

CH,—CH—NH I I • HOOC-CH-CH,-C=0

4 - CARBOXY - 6-ALKYL-2-PIPERIDONE

HN-CH-CH, I I 0 « CH CH - CH,- COOH R I H,C .

• HOOC-CH,

NH .

4 - CARBOXY- 5-ALKYL-2-PYRROLIDONE

H.C—C=0

0,N-CH, I ROOC-CH, H,C-COOR

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

17.

REIMSCHUESSEL

Isomerization

STRUCTURE

MONOMER

PRODUCTS

/<*

NO REACTION

CM 5

COOH

aCM7

0

Co v

COOH

••-c' ••

ο

0

0

V

COOH

0

0

-.-(C,,-H0----

p .

0

0 ••—ίο,-Λ

XX

ψ -

COOH

0

C5 COOH

U

0

CH, CH,

&

CH, CH,

DMC6 Λ Λ COOH

COOH

CH, CH,

DMC5

CH,

0

XNH

AA

0

COOH

R

MC6 EC6

Η

R

0

Η

f^NH COOH R · CH, , CjH,

COOH

0

CH, Η

MC5

237

o f decomposition a t temperatures s t a r t i n g f r o m 300°C. The c o n v e r s i o n o f monomer t o p o l y m e r was a b o u t 80 t o 8 5 % . The p o l y m e r ­ i z a t i o n o f CM7 r e s u l t e d i n e s s e n t i a l l y complete c o n v e r s i o n t o a polymer t h a t m e l t e d a t 281°C a n d h a d a g l a s s t r a n s i t i o n t e m p e r a t u r e o f a b o u t 90°C. B o t h 4 - c a r b o x y 2 - p i p e r i d o n e (C6) a n d 4 - c a r b o x y - 2 - p y r r o l i done (C5) p o l y m e r i z e d upon h e a t i n g t o t e m p e r a t u r e s i n t h e r a n g e o f 200°C t o f o r m l i n e a r amorphous p o l y m e r s (7,8) t h a t w e r e soluble i n formic acid, m-cresol, s u l f u r i c a c i d , and t r i f l u o r o e t h a n o l b u t i n s o l u b l e i n t h e common o r g a n i c s o l v e n t s . Essen­ tiall complet conversio f

ΛΛ COOH

gem dimethyl lactam derivatives d i dnot poly­ m e r i z e b u t r e a r r a n g e d . Upon h e a t i n g t o t e m p e r a t u r e s above t h e i r r e s p e c t i v e m e l t ­ i n g p o i n t ( 2 3 2 C , 206°C), 6 , 6 - d i m e t h y l - 4 c a r b o x y - 2 - p i p e r i d o n e (DMC6) i s o m e r i z e d q u a n t i t a t i v e l y t o 5,5-dimethyl-3-carboxym e t h y l - 2 - p y r r o l i d o n e whereas 5 , 5 - d i m e t h y l 4 - c a r b o x y - 2 - p y r r o l i d o n e (DMC5) r e a r r a n g e d w i t h e l i m i n a t i o n o f water t o i s o p r o p y l i d e n e s u c c i n i m i d e . The o c c u r r e n c e o f b o t h p o l y m e r i z a t i o n a n d i s o m e r i z a t i o n upon thermal treatment d i s t i n g u i s h e d the be­ havior o f the 4-carboxy-6-alkyl-2-piperidones. H e a t i n g e i t h e r t h e m e t h y l (MC6) o r t h e e t h y l (EC6) d e r i v a t i v e t o 230°C r e s u l t e d i n b o t h p o l y m e r i z a t i o n and t h e f o r m a t i o n o f t h e c o r r e s p o n d i n g 3-carboxym e t h y l - 5 - a l k y l - 2 - p y r r o l i d o n e . T h e r e was no i n d i c a t i o n o f p o l y m e r i z a t i o n when 4c a r b o x y - 5 - m e t h y l - 2 - p y r r o l i d o n e (MC5) was h e a t e d t o temperatures i n t h e range o f 200°C. The s o l e r e a c t i o n p r o d u c t was i n t h i s case e t h y l i d e n e s u c c i n i m i d e , which was f o r m e d w i t h e l i m i n a t i o n o f w a t e r . e

COOH

C6

of Lactams

NH

CM6

CM7

Polymerization

0

T a b l e 2. S t r u c t u r e o f Lactams a n d Reaction Products

The r e a c t i o n p r o d u c t s w e r e i d e n t i f i e d b y c o n v e n t i o n a l a n a l y s i s . The c h e m i c a l s t r u c t u r e o f t h e p o l y m e r s was d e d u c e d m a i n l y from t h e i n f o r m a t i o n o b t a i n e d from i n f r a r e d a n d NMR a n a l y s e s , a n d s o l u b i l i t y characteristics. The i n f r a r e d s p e c t r a o f a l l o f t h e p o l y m e r s showed s t r o n g a b s o r p ­ t i o n s r e l a t e d t o the imide moiety. Absorp­ t i o n s i n t h e 1675 t o 1705 c m " l a n d 1725 t o

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

238

RING-OPENING POLYMERIZATION

o H

Figure 1.

Conformations of PC M7

1790 cm r a n g e s were a t t r i b u t e d r e s p e c t i v e l y t o asymmetrical and symmetrical carbonyl v i b r a t i o n s , w h e r e a s C-N-C a n t i - s y m m e t r i c a l s t r e t c h i n g and imide group v i b r a ­

1150

ζρχ-^,ΟΚΤβΕΜ at c · f

Figure 2. X-ray pattern of oriented monofilament; configuration of polymer chains in the unit cell; schematic pro­ jection on the AB plane

cm~l ranges. A rather detailed structural a n a l y s i s was p e r f o r m e d o n t h e p o l y [(2,6-dioxo-l,4-piperidinediyl)tri­ me t h y l e n e ] w h i c h , a s h a s b e e n shown, i s t h e polymer obtained by thermal p o l y m e r i z a t i o n o f β-carboxymethyl c a p r o l a c t a m . ( 1 1 ) D e p e n d i n g upon the c o n d i t i o n s o f p o l y m e r i z a t i o n , t h i s polymer c o u l d be o b t a i n e d e i t h e r as a predominantly c r y s t a l ­ l i n e o r a n e s s e n t i a l l y amorphous material. Differences observed i n the i n f r a r e d s p e c t r a o f t h e c r y s t a l l i n e a n d amorphous p o l y m e r s have been c o n s i d e r e d i n d i c a t i v e o f the e x i s t e n c e o f d i f f e r e n t c o n f o r ­ mations o f the dioxopiperdine r i n g , w h i c h i n t u r n c a n g i v e r i s e t o two d i f f e r e n t chain conformations. As i n d i c a t e d i n F i g u r e 1, one i s c h a r a c t e r i z e d by an e q u a t o r i a l p o s i t i o n o f the trimethylene moiety with respect t o the plane o f the imide group, whereas t h e o t h e r p e r ­ t a i n s t o a s t r u c t u r a l u n i t i n which the t r i m e t h y l e n e group i s p o s i ­ tioned a x i a l l y t o the plane o f t h e ring.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

17.

REiMSCHUESSEL

Isomerization

Polymerization

of

239

Lactams

NMR a n a l y s i s i n d i c a t e d t h a t t h e l a t t e r c o n f o r m a t i o n i s t h e p r e d o m i n a n t s t r u c t u r e o f t h e p o l y m e r i n f o r m i c a c i d s o l u t i o n . The former has been a s c r i b e d t o t h e c r y s t a l l i n e m o d i f i c a t i o n . T h i s was s u p p o r t e d b y x - r a y a n a l y s i s w h i c h i n d i c a t e d a t r i c l i n i c u n i t c e l l c o n t a i n i n g e i g h t s t r u c t u r a l u n i t s a s shown i n F i g u r e 2. The u n i t c e l l h a d t h e f o l l o w i n g p a r a m e t e r s : a = 9 . 6 4 i , b=11.32A, c=15.80A, 0fc=98°, &=96°, >=114 . The p o l y m e r was f o u n d t o c r y s t a l ­ l i z e i n p o s i t i v e l y biréfringent s p h e r u l i t e s . I n T a b l e 3 a r e summarized t h e c h a r a c t e r i s t i c f r e q u e n c i e s o f t h e i n f r a r e d s p e c t r a of both the poly [(2,6-dioxo-l,4-piperidinediyl)trimethylene] (PCM7), a n d p o l y [ ( 2 , 5 - d i o x o - l , 3 - p y r r o l i d i n e d i y l ) d i m e t h y l e n e ] ( P C 6 ) , w h e r e a s T a b l e 4 l i s t s t h e nmr d a t a o b t a i n e d o n t h e s e two polymers. The r e s p o n s e o f t h e amorphous p o l y m e r d e r i v e d f r o m CM7 t o a n n e a l i n g was r a t h e r d i f f e r e n nylons and p o l y ( e t h y l e n when h e a t e d above t h e i r r e s p e c t i v e g l a s s t r a n s i t i o n t e m p e r a t u r e s . E v e n p r o l o n g e d a n n e a l i n g o f t h e u n o r i e n t e d amorphous p o l y i m i d e resulted i n only insignificant c r y s t a l l i z a t i o n . Annealing o f amorphous p o l y m e r w h i c h was o r i e n t e d b y c o l d d r a w i n g r e s u l t e d i n r a p i d and e x t e n s i v e c r y s t a l l i z a t i o n . However, no c r y s t a l l i z a t i o n was i n d u c e d d u r i n g t h e o r i e n t a t i o n p r o c e s s ; t h i s i s q u i t e d i f f e r e n t from t h e b e h a v i o r o f most l i n e a r p o l y m e r s such a s p o l y a m i d e s and polyesters. T h i s phenomenon c a n b e r a t i o n a l i z e d b y t h e a s s u m p t i o n t h a t t h e g l a s s y s t a t e o f t h i s polyimide i s c h a r a c t e r i z e d by the p r e s e n c e o f c h a i n segments o f e i t h e r o f t h e two c o n s i d e r e d conformations. C r y s t a l l i z a t i o n depends t h e r e f o r e n o t o n l y upon the m o b i l i t y o f t h e macromolecules b u t a l s o on r a t e and e x t e n t o f c o n f o r m a t i o n a l changes o f t h e d i o x o p i p e r i d i n e m o i e t y d u r i n g t h e o r i e n t a t i o n process. Except f o r the poly[2,6-dioxo-l,4-piperidinediyl)dimethylene] w h i c h was h i g h l y c r y s t a l l i n e , a l l o t h e r l i n e a r p o l y m e r s were amorphous. T h i s i s o f c o u r s e r e a d i l y e x p l a i n e d b y t h e p r e s e n c e o f an a s y m m e t r i c c e n t e r e n t a i l i n g t h e c a r b o n atom i n t h e 3 - p o s i t i o n i n the r i n g moiety o f the repeating u n i t . A d d i t i o n a l support f o r t h e c h e m i c a l s t r u c t u r e o f t h e p o l y m e r PCM7 was o b t a i n e d f r o m mass spectroscopical studies.(12) S u b j e c t i n g a polymer sample (Ά , = 2.7) t o 70 eV a t 270°C y i e l d e d a s a m a j o r f r e g m e n t [-CH -CH -CH -CH(CH CO) N-] H, m/e 3 0 7 , w h i c h c o r r e s p o n d s t o a p o l y m e r m o l e c u l e segment c o n t a i n i n g two r e p e a t i n g u n i t s . When t h e monomer was i n t r o d u c e d a t 270°C i n t o t h e p r e h e a t e d s o u r c e , s i g n a l s a p p e a r e d a t m/e 1 5 4 , 3 0 7 , 4 6 0 , Oy-H a n d 6 1 3 , a f t e r u n r e a c t e d monomer h a d // ( CH—CH — f l u s h e d o f f . These v a l u e s c o r r e s p o n d y t o fregments o f t h e g e n e r a l s t r u c t u r e N—CH [-CH -CH -CH -CH(CH CO) N-] H where η i s 1, 2, 3, a n d 4, r e s p e c t i v e l y . A p o s s i b l e mechanism f o r t h e f o r m a t i o n o f t h e s e f r e g m e n t s may e n t a i l t h e s i x center p y r r o l y s i s r e a c t i o n f o l l o w e d by 0

2

2

2

2

2

2

2

2

2

2

2

2

n

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1495

1445

1390

1150

1460

1437

1358

1139

2.32;2.58;2.74;2.85;3 .0

3.79 - 3.83 (t)

1.48 - 1.52 (m)

PCM7

o

f

1

^

^

PC6

2.49

3.26

(m)

(m)

r

a

., b

t

o

_ l

n

s

(11,12)

ring protons

ring protons

2

2

-N-OH -

-N-CH

2

-N-CH -CH

Assignment

2

(11,12)

t r i (di)methylene moiety

l

3

5

2

2

2

4

Measured Relative Number of Protons

anti-symmetrical stretching

imide group vibrations

-C-N-C

Θ

v

.

bending i n ring -CH^-

2

bending i n -CH ~

c a r b o n

symmetrical ) asymnetrical)

1.17-2.13 (m)

Proton Peak Position (ppm,TMS)

2

stretching vibrations o f -CH - i n the t r i (di) methylene moiety

Assignment

Table 4 NMR Data for PCM7 and PC6

1790 1705

1728 1677

PC6

2940

2930, 2867

PCM7

Frequency, cm"

1

Table 3 Characteristic Frequencies i n The Infrared Spectra o f PCM7 and PC6

17. REIMSCHUESSEL

Isomerization

Polymerization

of

241

Lactams

addition o f a proton. V i s c o s i t y - M o l e c u l a r Weight R e l a t i o n s . The r e l a t i o n s h i p b e t w e e n the v i s c o s i t i e s o f polymer s o l u t i o n s and polymer molecular weights was s t u d i e d i n some d e t a i l f o r b o t h t h e p o l y [ 2 , 6 - d i o x o - l , 4 p i p e r i d i n e d i y l ) t r i m e t h y l e n e ] ( P C M 7 ) and p o l y [ 2 , 5 - d i o x o - l , 3 pyrrolidinediyl)dimethylene](PC6). I n t r i n s i c v i s c o s i t i e s were determined on m-cresol s o l u t i o n s and evaluated by u s i n g t h e H u g g i n s e q u a t i o n s p / c = [η] + k ' t T f l C. The w e l l known Kuhn Mark - Houwink - S a k u r a d a - e q u a t i o n [η] = Κ . . M . . was employed f o r c o r r e l a t i n g t h e v i s c o s i t i e s w i t h t h e m o l e c u l a r weights. The l a t t e r w e r e o b t a i n e d e i t h e r f r o m l i g h t - s c a t t e r i n g (M^) o r o s m o t i c p r e s s u r e measurements (M ) . V a l u e s f o r t h e Huggins c o n s t a n t k and t h e i n t e r a c t i o n parameters Κ and a a r e l i s t e d i n T a b l e 5. 2

1

Table 5 :

V a l u e s f o r k' [η] + k' [ n ] 2

w(n) a n d [η] = Κ

c

1 Polymer PCM7

k

1

0.35

a 0.73

Κ w

^ .M* w(n) w(n) Κ n

4.5 χ 1 0 ~

4

7.5 χ 1 θ "

sp

4

4

PC6 0.41 0.65 4.3 χ 1 θ " A S c h u l z - F l o r y d i s t r i b u t i o n o f m o l e c u l a r w e i g h t s was i n d i c a t e d by a v a l u e o f 2 f o r t h e r a t i o M/M . The v i s c o s i t y - m o l e c u l a r w e i g h ? r e l a t i o n s f o r t h e c o n s i d e r e d two s y s t e m s w e r e d e r i v e d f r o m p o l y m e r s c h a r a c t e r i z e d b y w e i g h t number a v e r a g e m o l e c u l a r w e i g h t s u p t o 75000 (PCM7) a n d 150000 (PC6) r e s p e c t i v e l y . Considerably higher molecular weights a r e o b t a i n a b l e f o r t h e s e two systems. The p o l y m e r i z a t i o n o f t h e β-carboxy-methyl c a p r o l a c t a m f o r i n s t a n c e h a s r e s u l t e d i n p o l y m e r s o f m o l e c u l a r w e i g h t s i n e x c e s s o f 30000. Mechanical Properties. T e n s i l e p r o p e r t i e s were d e t e r m i n e d a c c o r d ­ i n g t o ASTM D1708 f o r PCM7 a n d PC6 o n f i l m s o b t a i n e d b y c o m p r e s ­ s i o n m o l d i n g , a n d f o r PCM7 o n m o n o f i l a m e n t s o b t a i n e d b y m e l t e x t r u s i o n and subsequent d r a w i n g , employing draw r a t i o s i n t h e r a n g e o f 4:1 t o 6:1. The v a l u e s o b t a i n e d d e p e n d e d u p o n t h e m o l e c u l a r w e i g h t s employed and t h e p a r t i c u l a r c o n d i t i o n s o f sample preparation. S i n c e t h u s f a r no a t t e m p t s w e r e made t o d e v e l o p optimum p r o c e s s i n g c o n d i t i o n s , t h e d a t a l i s t e d i n T a b l e 6 may n o t be r e p r e s e n t a t i v e o f u l t i m a t e l y a t t a i n a b l e v a l u e s . They show, however, t h a t m a t e r i a l s o f c o n s i d e r a b l e s t r e n g t h a r e r e a d i l y obtained. The c o r r e s p o n d i n g p o l y m e r s a m p l e s w e r e t e s t e d a t r e l a t i v e h u m i d i t i e s o f 0% a n d 50%. I t was f o u n d t h a t t h e m o i s t u r e c o n t e n t did not significantly affect the tensile properties. This i s explained by t h e r a t h e r low e q u i l i b r i u m moisture r e g a i n t h a t c h a r a c t e r i z e s these polymers. A t r e l a t i v e h u m i d i t i e s o f 50% and 100%, t h e m o i s t u r e c o n t e n t s o f PCM7 w e r e r e s p e c t i v e l y 0.56 a n d 1.40% w h e r e a s i n c a s e o f PC6 t h e y w e r e 3.6 a n d 1 1 . 3 % .

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

242

RING-OPENING

T a b l e 6:

POLYMERIZATION

Tensile Properties PCM7

Tensile strength p s i Elongation

12000 - 18000

%

450000 -580000

g/d

Elongation

6

%

T e n s i l e Modulus

3

10

320000 -520000

8.5

12 -

g/d

9000 - 16000

90

70

Modulus (2% secant) p s i Tensile strength

PC6

16

75 - 105

Thermal C h a r a c t e r i s t i c s . D i f f e r e n t i a l thermal a n a l y s i s , l o s s o f s t r e s s b i r e f r i n g e n c e , an the t r a n s i t i o n temperature corresponding v a l u e s a r e l i s t e d i n Table 7 t o g e t h e r w i t h t h e main decomposition temperatures as determined by both d i f f e r e n t i a l t h e r m a l a n a l y s i s a n d t h e r m o g r a v i m e t r i c a n a l y s i s a t a programmed h e a t i n g r a t e o f 10°C/min. T a b l e 7: Polymer

Thermal A n a l y s i s Data Melting Point C e

PCM6 PCM7 PC6 PC5

400 281

Glass e

Transition C

168 85 127 205

- 173 - 91 - 135 - 210

Main Decomposition °C 420 460 400 410

K i n e t i c s and Mechanisms o f R e a c t i o n I n f o r m a t i o n o n p o s s i b l e r e a c t i o n mechanisms w e r e o b t a i n e d from k i n e t i c s t u d i e s . The c o n v e r s i o n s o f β-carboxymethyl c a p r o ­ lactam t o t h e polyimide and o f 5,5-dimethyl-4-carboxy-2-pyrrolidone t o i s o p r o p y l i d e n e s u c c i n i m i d e h a v e b e e n c o n s i d e r e d r e p r e s e n ­ t a t i v e examples f o r r e s p e c t i v e l y t h e p o l y m e r i z a t i o n and rearrange­ ment r e a c t i o n s . The e v a l u a t i o n o f e x p e r i m e n t a l d a t a f o r t h e p o l y m e r i z a t i o n was b a s e d upon t h e c o n c e p t t h a t t h e e x t e n t o f r e a c t i o n i s r e p r e s e n t e d b y t h e momentary c o n c e n t r a t i o n o f i m i d e l i n k a g e s ( I ) which i s r e l a t e d t o t h e r e s p e c t i v e concentrations o f b o t h u n r e a c t e d monomer(M) a n d p o l y m e r m o l e c u l e s ( c ) b y t h e stoichiometric relation: (I)

I = M

- M - c = U c (1) ο Where M i s t h e i n i t i a l monomer c o n c e n t r a t i o n , a n d U t h e monomer c o n v e r s i o n , ( 1 4 ) . From e q u a t i o n 1 f o l l o w s : d l / d t = -dM/dt - d c / d t = d U / d t - d c / d t

(2)

E x p e r i m e n t a l d a t a w e r e u s e d t o c o n s t r u c t t h e p l o t shown i n F i g u r e s 3 a n d 4. T h e s e p l o t s show t h a t b o t h monomer c o n v e r s i o n

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

17. REiMSCHUEssEL

Isomerization

Polymerization

of

Lactams

243

and c h a i n g r o w t h a r e second o r d e r r e a c t i o n s . For t h e main phase o f t h e considered polymerization process, the rate o f poly­ m e r i z a t i o n was f o u n d t o b e adequately represented f o r the temperature range o f 210°C t o 290°C b y e q u a t i o n 3: 2

2

d l / d t = k ( M + 3 . 1 6 7 c ) (3) 7 where k = 74.9 χ 10 Ρ exp(-23800/RT) P

2IO C e

Figure 3.

Second-order rate plot of conversion data for CM7

Addition and Condensation Polymerization Process

Figure 4.

Second-order rate plot for chain growth (PCM7) (14)

dime t h y 1 - 4 - c a r b o x y - 2 pyrrolidone t o isopropylidene s u c c i n i m i d e was s t u d i e d a t t h e tempera­ t u r e s o f 225, 232, and 240°C ( 8 ) . A t t e m p t s t o determine t h e o v e r a l l order o f t h i s reaction showed t h a t a l s o i n t h i s case l i n e a r r e l a t i o n s h i p s were i n d i c a t e d o n l y i n second-order r a t e p l o t s as shown i n F i g u r e 5. The m o l e f r a c t i o n o f χ o f the pyrrolidone d e r i v a t i v e was c a l c u l a t e d according t o the r e l a t i o n χ = a /(a^awhere a and a ^ a r e t n e a r e a s o r t h e p e a k s a t 1.10, 1.35, and 1.78, 2.20 ( δ ) , respectively, i nthe cor­ r e s p o n d i n g nmr s p e c t r u m . The s l o p e s o f t h e s t r a i g h t lines i nFigure 5 repre­ sent values f o r the over­ a l l rate constant k f o r the p a r t i c u l a r tempera­ tures. The t e m p e r a t u r e d e p e n d e n c e o f k was found t o obey t S e Arrhenius equation, and the a c t i v a t i o n energy Ε and t h e p r e - e x p e r i m e n t a l

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f a c t o r A were e s t i m a t e d a c c o r d i n g t o the r e l a t i o n s h i p l o g k = l o g A-E/ (4.574T) t o b e A = 25.§5 χ k O a n d Ε = 34346 c a l / m o l e . Comparing the s t r u c t u r e s o f the lactams l i s t e d i n Table 2 w i t h those o f t h e i r corresponding reaction products i n d i c a t e s t h a t the conversion o f the former e n t a i l s i s o m e r i z a t i o n p r o c e s s e s . I n c a s e o f t h e β-carboxymethyl c a p r o ­ lactam, the i s o m e r i z a t i o n c o u l d be i 2

2

3 4 5 TIME (HOURS)

Figure 5. Second-order rate plot for the conversion of C5

e x p l a i n e d a c c o r d i n g t o a t y p e o f t h e commonly a c c e p t e d c a r b o n y l a d d i t i o n - e l i m i n a t i o n m e c h a n i s m , a n d f o r m u l a t e d a s f o l l o w s :(15)

Polymer f o r m u l a t i o n would then o f course be the r e s u l t o f polycondensation o f the i s o m e r i z a t i o n product v i a an intermolecul a r r e a c t i o n between the amino- and a n h y d r i d e f u n c t i o n s o f t h e 3 ( 3 - a m i n o p r o p y l ) g l u t a r i c a n h y d r i d e . Whereas s e c o n d o r d e r k i n e t i c s c a n b e r e a d i l y accommodated f o r t h i s p o l y c o n d e n s a t i o n which a f f e c t s the c o n c e n t r a t i o n o f the polymer molecules c , an i n ­ t r a m o l e c u l a r r e a c t i o n such a s the c o n s i d e r e d simple i s o m e r i z a t i o n a c c o r d i n g t o e q u a t i o n 4 s h o u l d o b e y f i r s t o r d e r k i n e t i c s . The second o r d e r k i n e t i c r e p r e s e n t a t i o n over r a t h e r extended ranges o f monomer c o n v e r s i o n s u g g e s t s t h e r e f o r e t h a t t h e i s o m e r i z a t i o n p r o c e s s may b e g o v e r n e d b y a more c o m p l e x mechanism. W i t h r e s p e c t t o c a r b o x y l i c a c i d s , lactams a r e n u c l e o p h i l e s o f moderate b a s i c power a n d a s s u c h c o n v e r t a c i d s i n t o t h e i r c o n j u g a t e b a s e s . I n case o f the c o n s i d e r e d carboxymethyl- and carboxy lactams, t h i s means t h a t b o t h , a n e l e c t r o p h i l i c g r o u p ( t h e l a c t a m c a r b o n y l f u n c t i o n ) , and a n u c l e o p h i l e (the c a r b o x y l a t e ion) are p r e s e n t i n t h e same m o l e c u l e . Thus, i f t h e c o n f i g u r a t i o n o f the p a r t i c u l a r lactam i s conducive t o r i n g formation,a b i c y c l i c intermediate o f t h e t y p e shown i n e q u a t i o n 4 w i l l f o r m . The c o m p e t i t i v e i n t e r m o l e c u l a r r e a c t i o n i s i n t h i s case thermodynamically l e s s f a v o r e d since the formation o f the corresponding intermediate n e c e s s i t a t e s two m o l e c u l e s c o m i n g t o g e t h e r t o f o r m o n e s p e c i e s . T h i s p r o c e s s w o u l d r e s u l t i n a l o s s o f t r a n s l a t i o n a l f r e e d o m and c o r r e s p o n d ­ i n g l y i n a l a r g e l o s s o f entropy. C y c l i z a t i o n , on the o t h e r hand, a f f e c t s o n l y i n t e r n a l , o r v i b r a t i o n a l , freedom which i s not v e r y l a r g e f o r t h e c o n s i d e r e d l a c t a m s i n a n y c a s e . The e n t r o p y l o s s

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f o r the formation o f the b i c y c l i c intermediate i s t h e r e f o r e much l e s s than f o r t h a t o f the i n t e r m o l e c u l a r analogue. I f i n a d d i t i o n the p a r t i c u l a r r i n g systems, such as most f i v e - , and six-membered r i n g s , are c h a r a c t e r i z e d by l i t t l e o r no molecular s t r a i n , then the considered i n t r a - and i n t e r m o l e c u l a r r e a c t i o n s w i l l not be d i s t i n g u i s h e d by l a r g e d i f f e r e n c e s i n the r e s p e c t i v e enthalpy changes. These changes w i l l i n t h i s i n s t a n c e t h e r e f o r e not o f f s e t the c y c l i z a t i o n f a v o r i n g entropy e f f e c t s and w i l l thus n o t c o n t r i b u t e s i g n i f i c a n t l y t o the f r e e energy change. I t i s t h e r e f o r e reasonable t o p o s t u l a t e t h a t the mechanisms o f the considered processes e n t a i l as the p r i n c i p a l i n i t i a l r e ­ a c t i o n the formation o f a b i c y c l i c i n t e r m e d i a t e . Once formed i t may undergo any o f three p o s s i b l e f a s t r e a c t i o n s : 1) e l i m i n a t i o n o f the i n t e r n a l n u c l e o p h i l e from the carbon atom o f the lactam carbonyl group; 2) e l i m i n a t i o amide f u n c t i o n ; 3) a d d i t i o be a r e v e r s a l o f the c y c l i z a t i o n and thus regenerate the o r i g i n a l lactam d e r i v a t i v e . The second r e a c t i o n i s the one d e p i c t e d i n equation 4 f o r the β-carboxymethyl caprolactam. I t i s however incompatible w i t h the second order k i n e t i c s t h a t was a c t u a l l y observed f o r the conversion o f t h i s lactam. Furthermore, t h i s r e a c t i o n c o u l d not be p a r t o f the rearrangement o f the 5,5dimethyl-4-carboxy-2-pyrolidone t o i s o p r o p y l i d e n e succinimide s i n c e no opening o f the lactam r i n g was i n d i c a t e d . The t h i r d r e a c t i o n , considered l e s s l i k e l y i n most o f the o r d i n a r y a d d i t i o n e l i m i n a t i o n r e a c t i o n s i n v o l v i n g c a r b o x y l i c a c i d d e r i v a t i v e s , en­ t a i l s the a d d i t i o n o f a proton t o the e l e c t r o n p a i r t h a t stems from the carbon-oxygen double band and has become l o c a l i z e d on the oxygen atom:

(5)

This a d d i t i o n , as i l l u s t r a t e d i n equation 5 f o r the β-carboxy­ methyl caprolactam, r e s u l t s i n a s t a b i l i z a t i o n o f the b i c y c l i c s t r u c t u r e and precludes the attainment t o c o p l a n a r i t y r e q u i r e d f o r the p - o r b i t a l o v e r l a p t h a t c h a r a c t e r i z e s the known e q u i l i b r i u m o f the amide moiety: -C(0)-N< -C(0) = S< For the considered lactam d e r i v a t i v e s the a d d i t i o n o f a proton seems t h e r e f o r e t o be the most l i k e l y r e a c t i o n , i t apparently r e s u l t s i n the formation o f s t a b l e b i c y c l i c s t r u c t u r e s t h a t have a f i n i t e e x i s t e n c e , and are presumed t o be the p r i n c i p a l r e a c t i o n i n t e r m e d i a t e s . The o v e r a l l k i n e t i c s o f the conversion o f the p a r t i c u l a r lactam d e r i v a t i v e s may thus be determined by r e a c t i o n s e n t a i l i n g these s p e c i e s . The second order k i n e t i c s observed f o r the conversion o f both the p o l y m e r i z i n g lactam d e r i v a t i v e s and those t h a t rearrange t o a d i f f e r e n t monomeric s t r u c t u r e may be

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e x p l a i n e d b y mechanisms t h a t i n v o l v e e i t h e r e l e c t r o p h i l i c c a t a l y ­ s i s o r i n t e r a c t i o n between two o f the c o n s i d e r e d p r o t o n a t e d species. C o n c e i v a b l e mechanisms e n t a i l i n g c a t a l y s i s b y i o n i z a b l e c a r b o x y g r o u p s a r e shown i n F i g u r e 6 f o r t h e c o n v e r s i o n o f 0-carb o x y m e t h y l c a p r o l a c t a m , t h e r e a r r a n g e m e n t o f 5,5-dimethy1-4carboxy-2-pyrrolidone, and the i s o m e r i z a t i o n o f 6,6-dimethyl-4carboxy-2-piperidone.

Figure 6.

Reaction mechanisms entailing electrophilic catalysis

Since each o f the lactam d e r i v a t i v e s c o n t a i n s a c a r b o x y l i c a c i d g r o u p , t h e r a t e o f c o n v e r s i o n may b e e x p r e s s e d b y e q u a t i o n 6 -dM/dt = k [COOH][M] = k [ M ] c c

2

(6)

A c c o r d i n g t o w h i c h t h e second o r d e r k i n e t i c r e p r e s e n t a t i o n c a n be readily rationalized. A l t e r n a t i v e mechanisms, c h a r a c t e r i z e d b y i n t e r a c t i o n s b e ­ tween i n t r a m o l e c u l a r l y p r o t o n a t e d s p e c i e s , a r e i l l u s t r a t e d i n F i g u r e 7 f o r t h e c o n v e r s i o n o f β-carboxymethyl c a p r o l a c t a m a n d the rearrangement o f 5,5-dimethyl-4-carboxy-2-pyrrolidone. Both i n v o l v e b i m o l e c u l a r r e a c t i o n s . Whereas t h e f o r m e r i s a n a s s o c i a ­ t i o n r e a c t i o n r e s u l t i n g i n the l i n e a r dimer o f the corresponding polymer, t h e f o r m u l a r i z a t i o n o f the l a t t e r corresponds t o t h a t o f an e x c h a n g e r e a c t i o n r e s u l t i n g i n t h e f o r m a t i o n o f t h e succinimide d e r i v a t i v e and the regeneration o f the o r i g i n a l p y r r o l i d o n e d e r i v a t i v e . Both are m u l t i - c e n t e r r e a c t i o n s e n t a i l i n g t h e

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Figure 7. Reaction mechanisms for himolecular reactions

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e l i m i n a t i o n o f w a t e r and r e a r r a n g e m e n t v i a a s i x - m e m b e r e d c y c l i c t r a n s i t i o n s t a t e . I n both cases the arrangement y i e l d s a cop l a n a r s p e c i e s t h a t h a s a l o w e r f r e e e n e r g y t h a n t h e s t r a i n e d and h i g h l y organized corresponding m u l t i - c y c l i c s t r u c t u r e . In case of the p y r r o l i d o n e d e r i v a t i v e the coplanar s t r u c t u r e i s the f i n a l product i n case o f the caprolactam d e r i v a t i v e the coplanar iminolactone rearranges v i a a f o u r center r e a c t i o n t o the e n e r g e t i c a l l y e v e n more f a v o r e d l i n e a r d i m e r . Whether i t i s e l e c t r o p h i l i c c a t a l y s i s o r a complex b i m o l e c u l a r r e a c t i o n t h a t c o n s t i t u t e s t h e p r i n c i p a l mechanism f o r t h e c o n v e r s i o n o f t h e p a r t i c u l a r l a c t a m d e r i v a t i v e s c a n n o t be deduced c o n c l u s i v e l y from p r e s e n t l y a v a i l a b l e i n f o r m a t i o n . How­ e v e r , mass s p e c t r o s c o p i c a l e x a m i n a t i o n (13) o f l o w m o l e c u l a r w e i g h t p o l y m e r w h i c h h a d b e e n o b t a i n e d b y p o l y m e r i z i n g β-carboxy­ methyl caprolactam a t temperature the presence o f a c y c l i h i g h m o l e c u l a r w e i g h t samples o b t a i n e d by p o l y m e r i z a t i o n a t t e m p e r a t u r e s a b o v e 280°C. I t c o u l d a l s o be shown t h a t t h i s c y c l i c s t r u c t u r e d i d not r e s u l t from p y r r o l y s i s r e a c t i o n s ; i t a c t u a l l y d i s a p p e a r e d upon p r o l o n g e d h e a t i n g a t t e m p e r a t u r e s i n t h e r a n g e o f 275°C t o 300°C w h i l e t h e p r e v i o u s l y m e n t i o n e d l i n e a r p y r r o l y s i s p r o d u c t s o f t h e f o r m u l a [-(CH ) C H ( C H C 0 ) N-]H s t a r t e d t o a p p e a r . This i s i n d i c a t i v e o f the c a p a b i l i t y o f tne c y c l i c dimer t o p o l y ­ m e r i z e by r i n g o p e n i n g . A p o s s i b l e mechanism f o r i t s f o r m a t i o n d u r i n g t h e i n i t i a l p o l y m e r i z a t i o n r e a c t i o n i s shown i n F i g u r e 8. 2

2

M o l e c u l a r m o d e l s show t h a t t h i s c y c l i c d i m e r i s c h a r a c t e r i z e d t h e a b s e n c e o f any m o l e c u l a r deformation. The p r e s e n c e o f t h e c y c l i c d i m e r i n t h e i n i t i a l r e a c t i o n p r o d u c t s l e n d s some s u p p o r t f o r t h e b i m o l e c u l a r r e a c t i o n m e c h a n i s m shown i n F i g u r e 7. The p o s t u l a t e d f o r m a t i o n o f a b i c y c l i c s t r u c ­ t u r e , i n v o l v i n g i n t r a m o l e c u l a r n u c l e o p h i l i c a d d i t i o n o f the c a r b o x y l a t e i o n t o t h e l a c t a m c a r b o n y l g r o u p and a d d i t i o n o f a p r o t o n , a p p e a r s t o be t h e i n i t i a l r e a c t i o n i n e i t h e r m e c h a n i s m . T h i s p o s t u l a t e i s s u p p o r t e d by t h e o b s e r v a t i o n t h a t n e i t h e r p o l y ­ m e r i z a t i o n n o r r e a r r a n g e m e n t o c c u r r e d when t h e c o r r e s p o n d i n g e s t e r l a c t a m s r a t h e r t h a n the carboxy l a c t a m s were employed. by

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F u r t h e r m o r e , w i t h r e s p e c t t o t h e r i n g s i z e , i t i s w e l l known t h a t among t h e l a c t a m s , t h e s i x - m e m b e r e d 2 - p i p e r i d o n e e x h i b i t s t h e l e a s t tendency toward r i n g - o p e n i n g p o l y m e r i z a t i o n , whereas t h e five-membered 2 - p y r r o l i d o n e p o l y m e r i z e s r a t h e r r e a d i l y . I f one w o u l d assume t h a t t h e phenomena r e l a t e d t o t h e c a r b o x y g r o u p c o n t a i n i n g l a c t a m s w e r e m e r e l y t h e r e s u l t o f some t y p e o f a c t i v a ­ t i o n o f t h e l a c t a m amide b o n d , t h e n t h e r e a c t i v i t i e s o f t h e p a r t i c u l a r d e r i v a t i v e s s h o u l d i n any i n s t a n c e p a r a l l e l those o f t h e c o r r e s p o n d i n g p a r e n t l a c t a m s . We h a v e s e e n t h a t t h i s i s n o t the case: t h e4-carboxymethyl-2-piperidone polymerized q u i t e e a s i l y upon h e a t i n g whereas t h e 4 - c a r b o x y m e t h y l - 2 - p y r r o l i d o n e , under c o r r e s p o n d i n g c o n d i t i o n s , d i d n o t r e a c t a t a l l . I t has t h e r e f o r e been concluded t h a t a b i c y c l i c i n t e r m e d i a t e o f the type shown i n F i g u r e 5 f o r t h e β-carboxymethyl c a p r o l a c t a m i s t h e r e ­ a c t i v e species i n both the a b i l i t y t o form suc the conversion o f the considered lactam d e r i v a t i v e s . The n o n r e a c t i v i t y o f the 4-carboxymethyl-2-pyrrolidone appears thus t o be a c o n s e q u e n c e o f t h i s compound's i n a b i l i t y t o f o r m a c o r r e s ­ ponding b i c y c l i c s t r u c t u r e a s i t c a n be r e a d i l y demonstrated w i t h m o l e c u l a r models. There appears t o be a r e c i p r o c a l r e l a t i o n between t h e e x t e n t o f r e a c t i o n and t h e e x t e n t o f bond a n g l e d i s t o r t i o n i n the c o r r e s ­ ponding b i c y c l i c i n t e r m e d i a t e . B i c y c l i c s t r u c t u r e s c h a r a c t e r i z e d by e s s e n t i a l absence o f bond a n g l e bending a c c o r d i n g t o m o l e c u l a r m o d e l s w e r e t h e β-carboxymethyl c a p r o l a c t a m a n d t h e 4 - c a r b o x y - 2 p i p e r i d o n e . F o r b o t h compounds t h e e x t e n t o f r e a c t i o n was p a r t i ­ c u l a r l y h i g h w i t h r e s p e c t t o b o t h t h e monomer c o n v e r s i o n a n d t h e degree o f p o l y m e r i z a t i o n . I n case o f the 6,6-dimethyl p i p e r i d o n e d e r i v a t i v e , i s o m e r i z a t i o n t o the 5,5-dimethyl-3-carboxymethyl-2p y r r o l i d o n e was e s s e n t i a l l y q u a n t i t a t i v e . On t h e o t h e r h a n d , b o t h c o n v e r s i o n i n rearrangement r e a c t i o n s , and m o l e c u l a r weights i n c a s e o f p o l y m e r i z a t i o n , w e r e l o w when t h e a t t a i n m e n t o f t h e p o s t u l a t e d b i c y c l i c i n t e r m e d i a t e was a c c o m p a n i e d b y a p p r e c i a b l e bond a n g l e d i s t o r t i o n , a s i n d i c a t e d f o r the p y r r o l i d o n e d e r i v a ­ t i v e s . Whereas t h e β-carboxymethyl c a p r o l a c t a m c a n f o r m t h e b i c y c l i c i n t e r m e d i a t e w i t h e s s e n t i a l l y no d i s t o r t i o n o f b o n d a n g l e s , s t e r e o models i n d i c a t e t h a t a c o r r e s p o n d i n g s t r u c t u r e d e r i v e d from ot-carboxymethyl c a p r o l a c t a m i s n o t f a v o r e d , though not i m p o s s i b l e , i t s formation r e s u l t s i n a c o n s i d e r a b l e molecular strain. I t i s conceivable t h a t t h i s c o n t r i b u t e s t o the observed i n t e r m o l e c u l a r c r o s s l i n k i n g o c c u r r i n g upon p o l y m e r i z a t i o n w h i c h should i n t h i s case r e s u l t i n a polymer s t r u c t u r e c h a r a c t e r i z e d by the presence o f s u c c i n i c imide u n i t s . Conclusion Isomerization p o l y m e r i z a t i o n i s f e a s i b l e w i t h lactams con­ t a i n i n g a c a r b o x y l i c group capable o f i n t e r a c t i n g w i t h the l a c t a m amide f u n c t i o n ; i t a f f o r d s m a c r o m o l e c u l e s whose r e p e a t i n g u n i t s d e r i v e f r o m i s o m e r s o f t h e o r i g i n a l monomers. T h u s , t h e p o l y m e r s obtained are polyimides rather than polyamides.

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Introduction o f additional but non-reactive substituents into the corresponding lactams r e s u l t s i n i s o m e r i z a t i o n t o other s t a b l e r i n g systems r a t h e r t h a n i n p o l y m e r i z a t i o n . Both p o l y m e r i z a t i o n and i s o m e r i z a t i o n presuppose t h e forma­ t i o n o f a b i c y c l i c i n t e r m e d i a t e w h i c h t h e n r e a c t s b y a mechanism entailing either electrophilic catalysis o r a bimolecular r e ­ action. LITERATURE CITED 1. R e i m s c h u e s s e l , H.K., J. P o l y m . Sci. P o l y m e r Letters (1966) 4, 953 2. Schaffler, Α., a n d W. Z i e g e n b e i n , Chem. Ber. (1955) 88, 1374, 1906 3. R e i m s c h u e s s e l , H.K., J. Heterocyclic Ch. (1964) 1, 193 4. R e i m s c h u e s s e l , H.K., J . P . Sibilia, a n d J . V . Pascale, J. O r g . Chem. (1969) 3 4 , 95 5. R e i m s c h u e s s e l , H.K. Sciences, S e r . II, (1971) 3 3 , 219 6. H e n e c k a , H., U. Horlein, a n d K.H. Risse, A n g . Chem. (1960) 7 2 , 960 7. R e i m s c h u e s s e l , H.K., K.P. Klein a n d G . J . Schmitt, M a c r o ­ m o l e c u l e s (1969) 2, 567 8. Klein, K.P., a n d H.K. R e i m s c h u e s s e l , J. P o l y m . Sci., A-1 (1971) 9, 2717 9. Klein, K.P., a n d H.K. R e i m s c h u e s s e l , J. P o l y m . Sci., A-1 (1972) 1 0 , 1987 1 0 . R e i m s c h u e s s e l , H.K., U.S.P. 3384625, Brit. P. 1042640 (Allied Chemical) 1 1 . R e i m s c h u e s s e l , H.K., L.G. R o l d a n , a n d J . P . Sibilia, J. Polym. Sci., A-2 (1968) 6, 559 12. R e i m s c h u e s s e l , H.K., K.P. Klein, J. P o l y m . Sci., A-1 (1971) 9, 3071 1 3 . M c C a r t h y , E.R., J . S . S m i t h a n d H.K. R e i m s c h u e s s e l u n p u b l i s h e d work. 14. R e i m s c h u e s s e l , H.K., A d v a n c e s in C h e m i s t r y Series (1969) 91, 717 15. B e n d e r , M.L., Chem. R e v . (1960) 60, 53

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

18 Copolymerization ofє-Caprolactamwith β-(3,4-Diaminophenyl) Propionic Acid S. W. SHALABY* and E. A. TURI Chemical Research Center, Allied Chemical Corp., Morristown, NJ 07960

P o l y m e r i c m a t e r i a l s h a v i n g w i d e r a n g e s o f m e c h a n i c a l and t h e r m a l p r o p e r t i e s h a v e b e e n made b y t h e c o p o l v m e r i z a t i o n o f ε - c a p r o l a c t a m w i t h s u i t a b l e a r o m a t i c monomers 1-3. C o p o l y a ­ m i d e s o f ε - c a p r o l a c t a m and m - x y l y l e n e d i a m m o n i u m i s o p h t h a l a t e o r β-(4-aminophenyl) p r o p i o n i c a c i d were s t u d i e d e a r l i e r i n t h i s l a b o r a t o r y 2 , 3 . While the l a t t e r group o f copolyamides, based on β - ( 4 - a m i n o p h e n y l ) p r o p i o n i c a c i d w e r e shown t o be c r y s t a l ­ l i n e o v e r a w i d e c o m p o s i t i o n r a n g e , m o s t members o f t h e f o r m e r g r o u p o f c o p o l y m e r s w e r e e s s e n t i a l l y amorphous. I t was a l s o shown t h a t t h e i n c o r p o r a t i o n o f a s m a l l f r a c t i o n o f t h e s e a r o m a t i c m o i e t i e s i n t o n y l o n 6 l e d t o some n o t i c e a b l e c h a n g e s i n i t s m e c h a n i c a l and t h e r m a l p r o p e r t i e s . C o p o l y m e r s b a s e d on 90/10 and 85/15 o f c a p r o l a c t a m and β - ( 4 - a m i n o p h e n y l ) p r o ­ p i o n i c a c i d w e r e shown t o be more r i g i d and somewhat more t h e r m a l l y s t a b l e a s compared t o n y l o n 6. T h i s was a t t r i b u t e d t o t h e r i g i d and i n t r i n s i c a l l y t h e r m o s t a b l e a r o m a t i c m o i e t i e s i n these copolyamides. On t h e o t h e r h a n d , t h e homolymer o f β - ( 4 - a m i n o p h e n y l ) p r o p i o n i c a c i d was l e s s t h e r m a l l y s t a b l e t h a n p o l y ( 2 , 5 - e t h y l e n e b e n z i m i d a z o l e ) ( P E B I ) , w h i c h was s t u d i e d e a r l i e r by t h e a u t h o r s ^ . T h i s , the well-documented h i g h t h e r m a l s t a b i l i t y and e x c e l l e n t t e n s i l e p r o p e r t i e s o f i m i d a z o l e - t y p e p o l y m e r s and o u r i n t e r e s t i n i m p r o v i n g t h e s e p r o p e r t i e s i n n y l o n 6, l e d t o t h e i n i t i a t i o n o f t h e p r e s e n t studies. I n t h i s communication, the p o s s i b l e f o r m a t i o n o f a c o p o l y m e r i c c h a i n o f ε - c a p r o a m i d e and e t h y l e n e b e n z i m i d a z o l e s e q u e n c e s and t h e p r o p e r t i e s o f t h e r e s u l t i n g c o p o l y m e r s a r e reported. S i n c e i t was shown e a r l i e r t h a t p o l y ( 2 , 5 - e t h y l e n e b e n z i m i d a z o l e ) c a n be f o r m e d e a s i l y b y h o m o p o l y m e r i z a t i o n o f β - ( 3 , 4 - d i a m i n o p h e n y l ) p r o p i o n i c a c i c T " (DPPA) o r i t s m e t h y l e s t e r (MDPP, t h e s e w e r e c h o s e n a s comonomers f o r t h e s y n t h e s i s o f the copolymers s u b j e c t o f the p r e s e n t s t u d i e s . The s t r u c t u r e o f n y l o n 6, P E B I and t h e c o p o l y m e r s o f c a p r o l a c t a m f

* Present address:

Ethicon,

Inc.,

Somerville,

N.J.

08876

251

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

252

RING-OPENING

POLYMERIZATION

and DPPA o r MDPP ( P - C L - c o - E B I ) c a n b e i l l u s t r a t e d a s f o l l o w s :

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EXPERIMENTAL

- a) A n a l y t i c a l M e t h o d s

R e d u c e d v i s c o s i t i e s (η ) were o b t a i n e d f o r polymer s o l u t i o n s i n s u l f u r i c a c i d Î6.5 g/100 m l ) . The i n f r a r e d s p e c t r a o f c o m p r e s s i o n - m o l d e d f i l m s (molded a t a b o u t 260°C) w e r e o b ­ t a i n e d o n a Beckman I R - 9 s p e c t r o p h o t o m e t e r . The d i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y (DSC) d a t a w e r e r e c o r d e d , i n most c a s e s , on a D u P o n t 990-DSC a p p a r a t u s i n n i t r o g e n a t a h e a t i n g r a t e o f 20 C/min. a n d u s i n g a b o u t 10 mg. s a m p l e . The p o l y m e r s u s e d i n t h e s e e x p e r i m e n t s w e r e a n n e a l e d a t 100 C i n v a c u o f o r 20 h r s . before o b t a i n i n g the i n i t i a l thermal a n a l y s i s heating data. A l t e r n a t i v e l y , i norder t o achieve s i m i l a r thermal h i s t o r y o f t h e e x a m i n e d c o p o l y m e r s , t h e s a m p l e s were h e a t e d t o a n d h e l d f o r a few m i n u t e s a t t e m p e r a t u r e s above t h e i r m e l t i n g tempera­ t u r e s , q u e n c h e d i n l i q u i d n i t r o g e n a n d t h e n r e h e a t e d a s shown i n T a b l e s V, V I , a n d V I I I . Two s a m p l e s ( T a b l e V I I I ) were a n a l y z e d o g a P e r k i n - E l m e r DSC-IB i n n i t r o g e n u s i n g a h e a t i n g r a t e o f 20 C/min. a n d a b o u t 10 mg. s a m p l e s . Most o f t h e t h e r m o g r a v i m e t r i c a n a l y s i s (TGA) d a t a w e r e o b t a i n e d o n a DuPont 9 5 1 T h e r m a l A n a l y z e r i n n i t r o g e n , u s i n g a h e a t i n g r a t e o f 10 C/min. a n d a b o u t 10 mg. s a m p l e s . The TGA d a t a o f t w o s a m p l e s ( T a b l e V I I I ) w e r e o b t a i n e d o n a Cahn RG E l e c t r o b a l a n c e

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

18. SHALABY AND TURi

Copolymerization

of

ε-Caprolactam

253

i n n i t r o g e n a n d a i r , u s i n g a h e a t i n g r a t e o f 10 C/min. a n d a b o u t 5 mg. s a m p l e s . A N o r e l c o d i f f r a c t o m e t e r w i t h c r y s t a l monoc h r o m a t i z e d c o p p e r x - r a d i a t i o n was u s e d t o o b t a i n t h e X - r a y powder d i f f r a c t i o n p a t t e r n s o f p o l y m e r g r a n u l e s w h i c h w e r e a n n e a l e d a t 100 C i n v a c u o f o r 20 h r s . The p e r c e n t c r y s t a l U n i t i e s ^ e r e d e t e r m i n e d b y t h e method o f Hermans a n d Weidinger""*. The t e n s i l e p r o p e r t i e s o f c e r t a i n c o p o l y m e r s w e r e measured on m i c r o t e n s i l e samples w h i c h were p r e p a r e d b y compression-molding. The d a t a w e r e o b t a i n e d a c c o r d i n g t o ASTM s p e c i f i c a t i o n s , u s i n g a n I n s t r o n h e a d s p e e d o f 0.5 i n . / m i n . b) G e n e r a l P o l y m e r i z a t i o n M e t h o d The r e q u i r e d amounts o f ε - c a p r o l a c t a m a n d DPPA o r MDPP w e r e p l a c e d i n a l a r g e p o l y m e r i z a t i o n t u b e ( a b o u t 20 t i m e s t h e volume o f t h e p o l y m e r i z a t i o s e v e r a l times w i t h argon one a t m o s p h e r e o f a r g o n f o r 5 h r s . a n d t h e t u b e was t h e n s e a l e d u n d e r r e d u c e d p r e s s u r e . The p o l y m e r i z a t i o n was t h e n c o n t i n u e d u n d e r d i f f e r e n c t c o n d i t i o n s a s shown i n T a b l e I . The r e s u l t i n g p o l y m e r was g r o u n d , e x t r a c t e d w i t h w a t e r i n a S o x h l e t e x t r a c t o r f o r 2 d a y s a n d d r i e d i n v a c u o a t 70 C t o a c o n s t a n t w e i g h t . A f t e r d e t e r m i n i n g t h e % e x t r a c t a b l e s (100-% c o n v e r s i o n ) , t h e p o l y m e r g r a n u l e s w e r e a n n e a l e d a t 100 C f o r 20 h r s . i n v a c u o . RESULTS & DISCUSSION S y n t h e s i s o f Polymers & Determination o f T h e i r Composition β-(3,4-Diaminophenyl) p r o p i o n i c a c i d (DPPA) a n d m e t h y l β - ( 3 , 4 - d i a m i n o p h e n y l ) p r o p i o n a t e (MDPP),.were p r e p a r e d a n d p u r i ­ f i e d as described i na previous report . ε - c a p r o l a c t a m was p u r i f i e d by d i s t i l l a t i o n i n vacuo b e f o r e use. Copolymers o f c a p r o l a c t a m a n d DPPA o r MDPP w e r e p r e p a r e d a c c o r d i n g t o t h e schemes o u t l i n e d i n T a b l e I . V i s c o s i t y d a t a o f a l l p o l y m e r s a r e a l s o summarized i n T a b l e I . A l l polymers r e v e a l e d r e a s o n a b l y h i g h reduced v i s c o s i t i e s . P o l y m e r s made a t m o d e r a t e t e m p e r a ­ t u r e s ( a maximum p o l y m e r i z a t i o n t e m p e r a t u r e o f 255 C) e x h i b i t e d higher s o l u t i o n v i s c o s i t i e s than those obtained u s i n g h i g h p o l y m e r i z a t i o n t e m p e r a t u r e s ( a maximum p o l y m e r i z a t i o n t e m p e r a ­ t u r e o f 270 C ) . C h a i n d e g r a d a t i o n a t t h e h i g h p o l y m e r i z a t i o n temperature c a n be r e s p o n s i b l e f o r t h e observed d e p r e c i a t i o n i n the reduced v i s c o s i t y o f t h e l a t t e r copolymers. F o r copolymers made u n d e r s i m i l a r r e a c t i o n c o n d i t i o n s (V t o V I I a n d V I I I t o X I ) t h e r e d u c e d v i s c o s i t y seems t o d e c r e a s e w i t h t h e i n c r e a s e o f t h e i r a r o m a t i c c o n t e n t . T h i s may b e a s s o c i a t e d w i t h t h e i n a ­ b i l i t y o f t h e more a r o m a t i c c o p o l y m e r s t o u n d e r g o a p p r e c i a b l e chain e x t e n s i o n a t r e a c t i o n temperatures which a r e s l i g h t l y o r moderately higher than t h e i r Τ . Three approaches f o r d e t e r m i n i n g t h e f i n a l c o m p o s i t i o n o f the copolymers were used i n t h e p r e s e n t s t u d i e s . The f i r s t

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

r e d

Using 90/1

Heated at

(a)

(b)

-

5 0.5 j 3 6.3 6.3

89.3 89.3 1.93 1.93

94.7 94.7 2.00 2.00

-

5 0.5 j 3 7.1 7.1

-

20

5 0.5 ;3 4.0 4.0

-

20

79.4 84.7 79.4 84.7 1.88 1.88 2.29 2.29

5 0.5 J 3 2.8 2.8

-

20

_

200*71

Atm.

0.5 3 * 4.6 4.6 0.5 3 « 5.0 5.0 0.5 3 s 6.2 6.2

84.3 89.5 89.5 84.3 1.18 1.75 1.18 1.75

-5

-20

-5 20

-5

20

20.0 49.4 94.7 64.5 64.5 20.0 94.7 2.04 1.28 1.28 1.43 2.94 2.04 2.94 1.43

0.4 0.4

3 s

3 s 2.2 2.2

3 s

2.0 2.0

-5 -0.5

-5 -0.5

5 -0.5

20 -

-5 0.5 3 * 9.8 9.8

20 -5 0.5 3 * 9.0 9.0

11.0 11.0

20

( t )

89.0 92.3 78.5 89.5 78.5 89.5 89.0 92.3 0.96 #0.82 0.87 1.17 Ό.82 0.96 1.17 0.87

8.8 8.8

3 ^

0.5

-5 20

(2)

4 4 4

4

4

4

4 20

4 20

4 20

4

20

„

4

4

_

4

10 5

-

-

7

-

-

-

-

-

-

-

-

-

-

-

93

90

95

20

XIV

XIII

XII

15

XI

10

X 80

90

Κ 85

5

20

15

10

5

65

80

80 95

VIII

50

VII

35

VI 20

V 50

IV

85

III

90

II

95

I

weight ratio of caprolactam and aminocaproic acid.

Caprolactam, mole % 3,4-diaminophenyl-£ propionic acid, mole $ Methyl 3,4-diaminophenylpropionate, mole # Reaction time, hr, i n the following order at 220°C/1 Atms. 240°C in sealed tube 255°C in sealed tube 270°C in sealed tube 240°C/l Atms 255°C/1 Atms 255°C/2 mm 230 C/2 mm Water extractables, $ Final caproamide content, mole * T J o f copolymer

Polymer Number

TABLE I COPOLYMERIZATIOM DATA

I

g

Ο

| 9 g |

m

18.

SHALABY AND Turn

Copolymerization

of

ε-Caprolactam

255

approach e n t a i l e d the use o f the p e r cent c o n v e r s i o n o b t a i n e d by e x t r a c t i o n and t h e assumption t h a t t h e e x t r a c t a b l e f r a c t i o n consists o f caprolactam or i t s water-soluble oligomers. In e s s e n c e , i t i s assumed t h a t t h e a r o m a t i c comonomers i n t h e i n i t i a l m i x t u r e were i n c o r p o r a t e d i n t h e copolymer c h a i n . T h i s a s s u m p t i o n c a n b e j u s t i f i e d i f one r e a l i z e s t h a t t h e p e r c e n t conversion increases w i t h the increase o f the aromatic content of t h e p o l y m e r i z a t i o n m i x t u r e and an a l m o s t q u a n t i t a t i v e con­ v e r s i o n c a n b e a c h i e v e d i n t h e f o r m a t i o n o f t h e a r o m a t i c homopolymer. Using the e x t r a c t i o n data i n Table I , the f i n a l c o m p o s i t i o n o f t h e c o p o l y m e r s w e r e c a l c u l a t e d a n d shown t o b e c o m p a r a b l e t o t h o s e o f t h e i n i t i a l comonomer m i x t u r e s ( T a b l e I ) . In a second attempt t o determine t h e c o m p o s i t i o n o f t h e c o p o l y m e r s , t y p i c a l samples were a n a l y z e d f o r t h e i r c a r b o n , hydrogen and n i t r o g e n elemental analysis dat c o p o l y m e r c o m p o s i t i o n s a r e c o m p a r a b l e t o t h e i n i t i a l compo s i t i o n s o f t h e comonomer m i x t u r e s . Due t o t h e m i n o r d i f f e r e n c e s i n t h e e l e m e n t a l c o n t e n t s o f t h e copolymers and t h e l e v e l o f e x p e r i m e n t a l e r r o r a s s o c i a t e d w i t h e l e m e n t a l a n a l y s i s , no a t t e m p t s w e r e made t o u s e t h e e l e m e n t a l a n a l y s i s d a t a , q u a n t i ­ t a t i v e l y , f o r determining the composition o f the copolymers. The i n f r a r e d s p e c t r a o f t h i n p o l y m e r f i l m s w e r e u s e d i n t h e t h i r d approach t o determine t h e composition o f t h e copolymers, as d i s c u s s e d i n t h e next paragraph. Three c h a r a c t e r i s t i c a b s o r p t i o n f r e q u e n c i e s were used i n the IR s t u d i e s . These a r e a s s o c i a t e d w i t h t h e a r o m a t i c o u t - o f - p l a n e C-H b e n d i n g (V ) , t h e a r o m a t i c i n - p l a n e C-H b e n d i n g (V ) and_£he ( C H ) s k e l g t | l v i b r a t i o n s ( V ) a t 8 1 0 , 1010 a n d 1170 cm , respectively ' . The r e l a t i v e a b s o r b a n c e s (A /A a n d / ) o f t h e a r o m a t i c a n d a l i p h a t i c m o i e t i e s w e r e c a l c u l a t e d a n d u s e d a s a measure o f t h e i r c o n c e n t r a t i o n a l o n g t h e c o p o l y m e r c h a i n a s shown i n T a b l e I I I . T h u s , t h e j / 3 d a t a were f i r s t p l o t t e d a g a i n s t t h e molar c o m p o s i t i o n o f t h e copolymers, as c a l c u l a t e d u s i n g the e x t r a c t i o n data, t o o b t a i n a s t r a i g h t l i n e r e l a t i o n s h i p a s shown i n F i g u r e 1. The s l o p e o f t h e s t r a i g h t l i n e was t h e n u s e d f o r d i v i d i n g t h e - j / 3 v a l u e s o f t h e i n d i v i d u a l c o p o l y m e r s t o o b t a i n a new m o l a r com­ p o s i t i o n , TCA (mole % o f t o t a l c h a i n a r o m a t i c s e q u e n c e s u s i n g A^/A^) B a s e d o n I R m e a s u r e m e n t s . The a g r e e m e n t b e t w e e n t h e I R a n d e x t r a c t i o n - b a s e d c o m p o s i t i o n s was f a i r f o r most c o ­ p o l y m e r s ; h i g h e r IR v a l u e s were r e c o r d e d f o r copolymers I , I I I a n d V I . Upon u s i n g t h e / 3 v a l u e s t o o b t a i n a n o t h e r s e t o f I R - b a s e d m o l a r c o m p o s i t i o n v a l u e s f o r t h e c o p o l y m e r s , TCA ( F i g u r e 2 a n d T a b l e I I I ) i t was f o u n d t h a t t h e a g r e e m e n t b e t w e e n e x t r a c t i o n a n d I R - b a s e d m o l a r c o m p o s i t i o n s was p o o r . Copolymer VII d i s p l a y e d a n o t i c e a b l e d e v i a t i o n from the s t r a i g h t l i n e r e l a t i o n s h i p shown i n F i g u r e 2. A l l I R - b a s e d m o l a r compo­ s i t i o n s w e r e much h i g h e r t h a n t h o s e b a s e d o n t h e e x t r a c t i o n data. 2

5

f i

3

1

A

A

2

3

A

A

A

A

A

A

2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

256

RING-OPENING POLYMERIZATION TABLE II ELEMENTAL ANALYSIS DATA OF COPOLYMERS

Initial mole # of Caprolactam

Polymer No. I II III IV V VI VII VIII

ft ft

95

90 85 80

9.56

65.23

9.33 8.81 8.74 7.85 7.46 6.44 9.43 9.29 8.76 8.73 9.53

69.70

20

ix

64.21 65.83 66.02 68.14

65 50

X XI XII XIII

Calculated (22...

- Found

72.22

95 90

64.17

85 80

66.09 65.87 64.30

65.30

95 90

12.52 12.98 13.84 13.76

15.03 16.09 17.64 12.65 13.09 13.84

13.65 12.58

ft 64.26 64.82 65.38 65.95 67.64 69.34 72.72 64.26 64.82 65.38 65.95 64.26

ft ft 9.59 9.38 9.17

8.33 7.70 6.43 9.59 9.38 9.17

12.73 13.09 13.44 13.79 14.85 15.91 18.02 12.73 13.09 13.**4

9.59

13.79 12.73

8.96

8.96

Based on i n i t i a l mole % of c a p r o a m i d e ( 0 Η Ν Ο , 1 1 3 . 2 ) and ethylene benzimidazole units ( C Q H ^ , 1 4 5 . 1 8 ) .

(a)

Α

0

1

ΗΙ

1

TABLE III INFRARED DATA AND POLYMER COMPOSITION

II

Initial Mole % of Aromatic Comonomers

10

III

15

IV

20

ν

VI

35

50

VII

100

80

a

IR Relative Absorbance Datai ^ 0.30 0.20 1.50

Clkl k lt? 2

12 Copolymer Composition •Mole $ of total chain aromatics using extraction data ( ) 5*3 •Mole % of total aromatics using Aj^.CrCA,) ,9.2 .Mole"> of total chain aromatics ' using A /A (TCA ) 14.6 •Relative concentration of un-/ ) cyclized chain aromatics(RUCA) using A /A 1.12 • (RUCA/TCAi) 100 = 12.2 c

2

3

2

0.38 0.24

1.58

0.71 0.33 2.15

0.69 0.36 1.92

1.14

0.5** 2.11

2.66 1.62

1.84

0.83 2.21

1.34

1.64

10.7

15.3

20.6

35.5

50.6

80.0

11.7

21.8

21.2

35.1

56.6

81.8

17.5

24.1

26.3

39.4

60.6

(ll8.2$

f)

-

e

x

(a)

2

1.18

10.1

1.60 7.3

1.43 6.7

1.57 4.5

1.64

2.9

1.22 1.5

(i.ooJ 1.0

e

A-j^ « Absorbance at 8 1 0 cm" due to CH in benzene ring. 1

A

2

= Absorbance at 1 0 1 0 cm~* due to CH in benzene ring. = Absorbance at 1170 cm"*" due to caproamide sequence.

(b)

See Reference # 4 , polymer no. C-l.

(c)

A slope of 0.0325 (from Fig. 1) was used for this calculation.

(d)

A slope of 0.0137 (from Fig. 2) was used for this calculation.

(e)

By dividing Ai/A of the copolymer by that of the homopolymer (C-l) in which a l l sequences were assumed to be benzimidazole.

(f)

Polymer displayed marked deviation in relative absorbance (Fig. 2).

2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

SHALABY AND TURi

Copolymerization

of

^-Caprolactam

3.0-1

0.21 Ο

1

1

10

20

30

40

50

60

70

80

90

Mole Per Cent of Aromatic Sequences in Copolymer (By Extraction)

Figure 1.

Effect of composition on absorbance at 810 (A ) and 1170 cm- (A ) t

1

Figure 2.

s

Effect of composition on absorbance at 1010 (A ) and 1170 cm (A ) 2

1

s

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

258

T h i s i n d i c a t e s t h a t t h e e f f e c t o f m o l a r c o m p o s i t i o n on t h e a b s o r b a n c e v a l u e s a s s o c i a t e d w i t h t h e o u t - o f - p l a n e (V ) a n d i n p l a n e d e f o r m a t i o n s (\>) i s n o t i d e n t i c a l f o r b o t h f r e q u e n c i e s . 2

TCA

X

=

(Α /Α )

TCA

2

=

(A /A )

λ

(1/0.0325)

3

2

(1/0.0137)

3

T h i s u n e x p e c t e d b e h a v i o r " " ^ " ^ r a n n o t be a s c r i b e d t o t h e c h a n g e i n the aromatic content o f the gross environment about the b e n z e n e r i n g i n t h e c h a i n . On t h e o t h e r h a n d , t h e u n p a r a l l e l e d dependence o f absorbance a t a n d \> may be a t t r i b u t e d t o s u b t l e d i f f e r e n c e s i n the micro-environment about the benzene ring w h i c h c a n be c a u s e d b y i n c o m p l e t e c y c l i z a t i o n o f a m i n o amide groups t o b e n z i m i d a z o l e s t r u c t u r e s A l t h o u g h one may expect t h a t the r e l a t i v r i n g i n the u n c y c l i z e b e n z i m i d a z o l e , i t i s p r o p o s e d t h a t t h e change i n t h e V ab­ s o r b a n c e , due t o t h e d i f f e r e n c e i n c h e m i c a l s t r u c t u r e , i s more than t h a t o f v^. Hence, one e x p e c t s t h a t t h e r e l a t i v e a b ­ sorbance o f and V w i l l v a r y w i t h c h a n g e s i n t h e c o n c e n ­ t r a t i o n o f u n c y c l i z e d amino-amide g r o u p s i n t h e a r o m a t i c f r a c t i o n i n c o p o l y m e r s h a v i n g t h e same t o t a l m o l a r c o m p o s i t i o n of a r o m a t i c sequences. T a k i n g t h i s i n t o c o n s i d e r a t i o n and u s i n g the r e l a t i v e absorbance ^ / a r o m a t i c homop o l y m e r , C - l ( i n w h i c h a l l a r o m a t i c s e q u e n c e s a r e assumed t o be made p r a c t i c a l l y o f b e n z i m i d a z o l e g r o u p s ) , t h e r e l a t i v e c o n c e n t r a t i o n o f t h e u n c y c l i z e d c h a i n a r o m a t i c (RUCA) was c a l c u l a t e d by d i v i d i n g the r e l a t i v e absorbance v a l u e s o f the copolymers by t h a t o f C - l (Table I I I ) . In o t h e r words, the d e v i a t i o n of the j / v a l u e s o f t h e c o p o l y m e r s f r o m t h e 1.34 v a l u e o f t h e homopolymer c a n be u s e d a s a measure o f t h e s t r u c t u r a l i m p e r f e c t i o n s i n t h e i r c h a i n s due t o t h e un­ c y c l i z e d amino-amide m o i e t i e s . Q u a l i t a t i v e l y , c o p o l y m e r s I a n d V I I r e f l e c t a minimum and maximum l e v e l o f c h a i n i m p e r ­ fections , respectively. 2

2

A

A

f o r

a n

2

A

A

2

RUCA =

( A / A ) c o p o l y m e r / (A /A^ 1

2

homopolymer

F o r q u a n t i t a t i v e o r s e m i - q u a n t i t a t i v e u s e o f t h e RUCA v a l u e s , t h e y were n o r m a l i z e d w i t h r e s p e c t t o t h e a r o m a t i c c o n t e n t o f t h e c o p o l y m e r s t h r o u g h d i v i d i n g them b y t h e c o r r e s p o n d i n g v a l u e s f o r t h e m o l e f r a c t i o n (mole % d i v i d e d b y 100) o f c h a i n a r o m a t i c s , TCA^. T h e s e (RUCA/TCA^)100 v a l u e s a r e u s e d l a t e r i n the Discussion f o r c o r r e l a t i n g the composition of the c o p o l y m e r s w i t h t h e i r t h e r m a l p r o p e r t i e s and w i l l be r e f e r r e d t o s i m p l y a s φ. C r y s t a l l i n i t y and T h e r m a l P r o p e r t i e s The e f f e c t o f c o m p o s i t i o n on t h e d e g r e e o f c r y s t a l ­ l i n i t y and t h e 2 Θ v a l u e s f o r t h e m a j o r r e f l e c t i o n s o f t h e

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

18. SHALABY AND TURi

Copolymerization

of

ε-Caprolactam

259

c o p o l y m e r s i s i l l u s t r a t e d b y t h e d a t a i n T a b l e I V . These d a t a i n d i c a t e t h a t (a) t h e p e r c e n t c r y s t a l l i n i t y d e c r e a s e s w i t h t h e i n c r e a s e i n t h e c o p o l y m e r a r o m a t i c c o n t e n t ; (b) l o w l e v e l s o f c r y s t a l l i n i t i e s , a b o u t 20%, w e r e r e c o r d e d f o r c o p o l y m e r s h a v i n g 15 a n d 20 m o l e % o f t h e a r o m a t i c s e q u e n c e s ; (c) c o p o l y m e r s w i t h £35% a r o m a t i c s w e r e amorphous t o X - r a y ; (d) w i t h t h e e x c e p t i o n o f c o p o l y m e r I I ( w h i c h d i s p l a y e d 30 a n d 6% c r y s t a l l i n i t y due t o t h e a - a n d γ-crystalline f o r m o f n y l o n 6, r e s p e c t i v e l y ) , a l l c r y s t a l l i n e c o p o l y m e r s r e v e a l e d t h e t w o c h a r a c t e r i s t i c α-form r e f l e c t i o n o f n y l o n 6; a n d , (e) t h e i n t e n s i t y o f t h e α-form r e f l e c t i o n a t 2 Θ o f a b o u t 23 d e ­ creased w i t h t h e increase i n t h e aromatic content o f t h e c o ­ polymer, w h i c h c a n be a s s o c i a t e d w i t h t h e e f f e c t o f t h e s t r u c t u r a l i m p e r f e c t i o n s on t h e normal l a t e r a l p a c k i n g o f t h e nylon 6 chains. The a b o v e X - r a y c r y s t a l l i n i t DSC d a t a i n T a b l e V, w h i c h i n d i c a t e t h a t c o p o l y m e r s h a v i n g £35% a r o m a t i c s i n t h e i r c h a i n s do n o t u n d e r g o a f i r s t o r d e r thermal t r a n s i t i o n . The DSC d a t a i n T a b l e V a l s o show t h a t (a) b o t h t h e i n i t i a l a n d r e h e a t i n g Τ i n c r e a s e w i t h t h e i n c r e a s e i n c o n c e n t r a t i o n o f t h e r i g i d a r o m a t i c moitiés i n t h e c h a i n s ; (b) b o t h t h e i n i t i a l a n d r e h e a t i n g Τ d e c r e a s e w i t h t h e i n ­ c r e a s e i n t h e aromatic c o n t e n t o f t h e copolymers; (c) t h e Τ i n c r e a s e s as t h e c o n c e n t r a t i o n o f aromatics i n t h e polymer c h a i n s i n c r e a s e s ; (d) c o p o l y m e r s w i t h 15 a n d 2 0 % a r o m a t i c s do n o t c r y s t a l l i z e r e a d i l y upon r e h e a t i n g t h e i r q u e n c h e d m e l t s ; a n d , (e) a n u n u s u a l d i f f e r e n c e i s p r e s e n t b e t w e e n t h e i n i t i a l and r e h e a t i n g Τ v a l u e s . I n o r d e r t o compare t h e i n i t i a l a n d r e h e a t i n g Τ anâ Τ v a l u e s o f t h e c o p o l y m e r s a n d t h e i r d e ­ p e n d e n c e o n ^ c o m p o s i t i o n , t h e g r a p h i c a l i l l u s t r a t i o n shown i n F i g u r e 3 was c o n s t r u c t e d . I t i s apparent from t h i s F i g u r e t h a t (a) b o t h t h e i n i t i a l (T ) a n d (T ) m e l t i n g t e m p e r a t u r e s d e c r e a s e l i n e a r l y w i t h t h e increase i n t h e aromatic content o f the co­ p o l y m e r s ; (b) t h e d e p e n d e n c e o f Τ o n c o m p o s i t i o n i s a l m o s t i d e n t i c a l t o t h a t o f Τ ; (c) b o t h t h e i n i t i a l (T ) a n d r e h e a t i n g g l a s s t r a n s i t i o n t e m p e r a t u r e s (T ) i n c r e a s e l i n e l r l y w i t h t h e i n c r e a s e i n t h e a r o m a t i c c o n t e n t o f t h e c o p o l y m e r s ; (d) t h e Τ and Τ o f t h e a r o m a t i c homopolymer ( C - l ) do n o t f a l l o n t h e ^ Τ - c o m p o s i t i o n s t r a i g h t l i n e o f t h e c o p o l y m e r s ; a n d , (e) t h e cflange i n Τ w i t h c o m p o s i t i o n i s more d r a m a t i c t h a n t h a t o f T ° . The u n u s u a l i n c r e a s e i n t h e Τ o f t h e c o p o l y m e r s a s a r e s u l t o f t h e t h e r m a l t r e a t m e n t s a s s o c i a t e d w i t h t h e r e h e a t i n g measure­ ments i s l i k e l y t o be r e l a t e d t o t h e f r a c t i o n o f u n c y c l i z e d a m i n o - a m i d e a r o m a t i c s e q u e n c e s . To e x a m i n e t h i s p o s s i b i l i t y , t h e i n c r e a s e i n g l a s s t r a n s i t i o n t e m p e r a t u r e (Τ -T ) was p l o t t e d a g a i n s t t h e p r e v i o u s l y c a l c u l a t e d composition f u n c t i o n φ (see Tables I I I and V ) , which i s proposed t o be an i n v e r s e c o n c e n t r a ­ t i o n f u n c t i o n o f t h e amino-amide m o i e t i e s a l o n g t h e copolymer backbone. T h i s i s achieved by c o n s t r u c t i n g p l o t C o f F i g u r e 4, w h i c h shows a g r a d u a l d e c r e a s e i n Τ -Τ w i t h t h e i n c r e a s e o f m

g

g

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

g

260

RING-OPENING POLYMERIZATION

TABLE IV X-RAY DATA*

Polymer Number

Mole $ of nuio 70 ox

/ %

Caprolactam**)

Reduced neuucea Viscosity

Major Reflections neixeciaons 20°(l/l ) o

ψ

XV

100

2.45

19.9

(92)

44

XVI

ÎÔ0

ÔT9Ï

23.6 2ÔTÔ

(100) (W

52Γ

23.6

(100) (93) -

I

"95

27Ô

XIV

93

_ ÔTB9

23.4 2θΤδ

eft)

Γ7^

90

θ 2

2Ô7Ô* T95Î 21.3 (100) 2 3 Λ (76) 19.9 (100)

— . XIII III _ _ _ _ _ XI

_ "râ * (a) (b) (c) (d)

2βΟ

(87) (100)

^ (dT 3δ" 35"

85

1788

20.0

g-

2729

23.4 (92) 19.8 (100)

80

ΟΤ9δ

23.4 ( 72) 19.8 (100)

21Γ

55

2795

23.5 (70) 20.0 (b)

fdF

19.6 (b)

(dT

19Λ (b)

{dT

3Ô ~~2Ô"

ÏT2§

/ »

Crystallinity* '

21 25

The powdered samples were annealed for 20 hrs. at 100°C before testing. Initial composition. Center of broad reflection. With the exception of sample II (which displayed 30 and 6% crystallinity due. to the el* and %~ crystalline form, respectively) a l l crystalline copolymers revealed the characteristic e<« form reflections of nylon 6. Essentially amorphous.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Copolymerization

SHALABY AND TUBI

18.

TABLE V DSC DATA**\

of

^-Caprolactam

261

EFFECT OF COMPOSITION ON THE

THERMAL TRANSITIONS OF COPOLYMERS Polymer Number (b) N-6 Composition Mole £ of CL< > 100 2.45

Initial heating, T* °C Initial heating,

90

95

d

*red.

Π

I

2.00

1.93 <*5

219

207

19^

40

56

67

69

100

220

210

III

IV

85

80

1.88

53


Reheating^) ι T .°C C

T

V J

, (

-

C )

°

-

•

-

190

-

22

12.2

89

85

(a)

DuPont 990-DSC, i n nitrogen, 20°C/rain. heating rate.

(b)

See Reference #3*

(e)

See reference #4, polymer C-l.

0.34

1.28

61

61

67

240

124

156

205

242

-

-

63

6.7

7.3

0

20

2.04

e )

27

31

10.1

2.94

C-l (c)

VII

50

65

2.29

5*

VI

V

-

2.9

*.5

-

2

138

95

1.0

1.5

(d)

Baaed on i n i t i a l composition of comonomers·

(e)

Minor endotherm.

(f)

Samples were heated to 260°C (except C-l, which was heated to 300°C), held for 2 min., then quenched i n liquid nitrogen. • Initial Melting Temp. ( T ° ) m

ο Reheating Melting Temp. (T ) m

• Initial Glass Transition Temp. (T °) g

• Reheating Glass Transition Temp. (Tg)

C-1~

220-

h220

Ε 180H

h210

Ε £ 140H ι i iooH

200

I I

Η

y* ν»

JS °

?

90 »-

180 60Ô 20

10

"2Ô"

30

—1— 40 40

—1— 50 50

—1— 60 60

170 70

80

100

90

Mole Per Cent of Total Chain Aromatic Sequences (By Extraction)

Figure 3.

Effect of composition on polymer initial and reheating Ί

0

and T

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

w

262

RING-OPENING POLYMERIZATION

0 Mole Pe Cen

20 40 60 80 100 f Total Chai Aromati Sequence (B Extraction)

1

Figure

3

5 7 9 11 Composition Function Φ

4. Effect of polymer composition on the change of Ί from thermal treatment ϋ

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

18. SHALABY AND TURi

Copolymerization

of

263

e-Caprohctam

the φ values. Before attempting t o e x p l a i n t h e a c t u a l source o f t h i s r e l a t i o n i n p l o t C, p l o t s A a n d Β o f F i g u r e 4 w i l l b e d i s ­ cussed. B o t h p l o t s A a n d Β i n d i c a t e t h a t t h e (Τ -T ) v a l u e s i n -

g

Q

crease w i t h t h e increase i n t h e aromatic content o f the copoly­ mers, whether t h e determined compositions a r e based on t h e e x t r a c t i o n ( p l o t A) o r I R d a t a ( p l o t B ) . The d a t a s c a t t e r i n g and t h e s l o p e o f t h e s t r a i g h t l i n e i n b o t h p l o t s s u g g e s t more d e p e n d e n c e a n d a b e t t e r c o r r e l a t i o n o f t h e (T -T ) d a t a w i t h I R d e t e r m i n e d c o m p o s i t i o n s , a s compared w i t h t h o l e S a s e d o n e x t r a c ­ t i o n data. The a b n o r m a l d e v i a t i o n o f t h e ( T -T ) v a l u e s o f t h e homopolymer ( C - l ) f r o m t h e s t r a i g h t l i n e reïatîonships o f p l o t s A and Β a n d t h e c u r v e o f p l o t C c a n be e a s i l y r e c o g n i z e d upon e x a m i n i n g F i g u r e 4. T h i s i s p r o p o s e d t o i n d i c a t e t h a t a m a j o r contribution t o thehig thermally-induced reaction w h i c h a r e p r e s e n t i n t h e c o p o l y m e r s a n d n o t t h e homopolymer. I f the aromatic m o i e t i e s a r e t h e o n l y p a r t i c i p a n t i n these r e ­ a c t i o n s , one w o u l d e x p e c t a n e s s e n t i a l l y l i n e a r dependence o f (Τ -T ) o n c o m p o s i t i o n f u n c t i o n <J>. S i n c e t h i s i s n o t t h e c a s e , as pl§t C i n d i c a t e s , i t i s s u g g e s t e d t h a t t h e caproamide s e ­ q u e n c e s do t a k e p a r t i n t h e s e r e a c t i o n s . R e - e x a m i n a t i o n o f p l o t C a n d t a k i n g i n t o a c c o u n t t h i s s u g g e s t i o n , a l l o w s one t o c o n c l u d e t h a t t h e e f f i c i e n c y o f t h e amino-amide m o i e t i e s i n i n c r e a s i n g t h e Τ upon r e h e a t i n g does d e c r e a s e w i t h t h e d e c r e a s e i n t h e c a p r o aâide c o n t e n t . I f o n e assumes t h a t t h e a m i n o - a m i d e m o i e t i e s undergo d e h y d r a t i o n i n t r a m o l e c u l a r l y and/or i n t e r m o l e c u l a r l y ( t h r o u g h r e a c t i o n w i t h c a r b o x y l i c e n d g r o u p s ) , f o r m a t i o n o f new ethylene-benzimidazole u n i t s and/or branching c a n occur d u r i n g t h e r m a l t r e a t m e n t s s i m i l a r t o t h o s e u s e d i n t h e DSC m e a s u r e m e n t s . The c y c l i z a t i o n a n d / o r b r a n c h i n g w o u l d a l s o b e e x p e c t e d t o i n ­ crease w i t h t h e decrease i n t h e r i g i d i t y o f t h e chains and/or t h e melt v i s c o s i t y o f t h e polymer m a t r i x . Both o f these p r o p e r t i e s depreciate gradually with the increase o f the a l i p h a t i c content o f t h e copolymer chains which, i n t u r n , i s t r a n s l a t e d t o a l o w e r i n g o f Τ . A c c o r d i n g l y , t h e (T -T°) v a l u e s w o u l d b e expected t o d i c r e a s e w i t h t h e decreale the efficiency o f the amino-amide group ( i . e . , t h e d e c r e a s e i n t h e c o m p o s i t i o n f u n c t i o n φ) i n i n d u c i n g b r a n c h i n g a n d / o r c y c l i z a t i o n . This i s indeed t h e c a s e a s shown i n p l o t C o f F i g u r e 4. I t a l s o i s i n t e r e s t i n g t o n o t e t h a t t h e ψ v a l u e s ( i n T a b l e s I I I a n d V) d e c r e a s e s t e a d i l y with increase i n the aromatic (or increase i n a l i p h a t i c ) content o f t h e copolymers, w h i c h does s u b s t a n t i a t e t h e above p h y s i c a l i n t e r p r e t a t i o n o f t h e r o l e o f ψ. The e f f e c t o f p o l y m e r i z a t i o n t e m p e r a t u r e a n d t y p e o f a r o m a t i c comonomer u s e d o n t h e d e g r e e o f p o l y m e r i z a t i o n , d e g r e e o f c r y s t a l l i n i t y a n d t h e r m a l p r o p e r t i e s o f t h e c o p o l y m e r was s t u d i e d and t h e d a t a a r e summarized i n Table V I . Comparison o f c o p o l y m e r s I I , I X , a n d X I I I w h i c h h a v e e s s e n t i a l l y t h e same a l i p h a t i c content, indicate that the solution v i s c o s i t y o f 9

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

264

RING-OPENING POLYMERIZATION

X I I I w h i c h was made f r o m a n a r o m a t i c d i a m i n o - e s t e r i s l o w e r than t h a t o f I I d e r i v e d from t h e corresponding a c i d . I n a d d i t i o n , t h e u s e o f a h i g h p o l y m e r i z a t i o n t e m p e r a t u r e (270 C) l e a d s t o (a) no s i g n i f i c a n t d i f f e r e n c e i n c r y s t a l l i n i t y ; (b) a d e c r e a s e i n Τ ; ( c ) a d e c r e a s e i n (Τ -T ) ; a n d , (d) a n i n c r e a s e i n thermal s t a b i l i t y . The change i n ( T - T ° ) a n d t h e r m a l s t a b i l i t y s u g g e s t s t h a t t h e p o l y m e r ( I X ? m l d e a t 270 C c o n t a i n s l e s s u n c y c l i z e d a r o m a t i c s , i n i t i a l l y , t h a n t h a t made a t 255 C (II). This i s l o g i c a l t o expect s i n c e c y c l i z a t i o n t o b e n z i m i d a z o l e i s expected t o be h i g h a t t h e h i g h temperature. A l s o , t h e e f f e c t o f t h e i n i t i a l c o n t e n t o f amino-amide g r o u p s on (Τ -T ) i s c o n s i s t e n t w i t h t h e d i s c u s s i o n i n t h e p r e v i o u s parag?ap8 r e g a r d i n g t h e r o l e o f φ. A s i m i l a r e f f e c t o f t h e p o l y m e r i z a t i o n temperature on t h e polymer p r o p e r t i e s c a n be r e c o r d e d a s one e x a m i n e Furthermore, t h e data s t a b i l i t y a n d (Τ -T ) copolymer due t o i t s h i g h e ? a r S m a t i c c o n t e n t . I t i s important t o note t h a t t h e thermal treatments o f V I I cause i n c r e a s e s i n i t s Τ b u t (T -T°) c h a n g e s p e r d e g r e e r i s e i n t h e maximum t e m p e r a t u r e o f t h e t h l r m a l t r e a t m e n t d e c r e a s e a b o v e 230°C. T h i s may s u g ­ g e s t t h a t t h e b r a n c h i n g a n d / o r c r o s s l i n k i n g due t o t h e a m i n o amide g r o u p s do n o t r e q u i r e e x c e s s i v e l y h i g h e r t e m p e r a t u r e s t h a n 200°C. The e f f e c t o f c o m p o s i t i o n ( i n t e r m s o f m o l e p e r c e n t caproamide) on t h e thermal s t a b i l i t y o f t h e copolymers i s i l l u s t r a t e d b y t h e TGA d a t a i n T a b l e V I I . T h e s e d a t a i n d i c a t e t h a t c o p o l y m e r s w i t h h i g h a r o m a t i c c o n t e n t s a r e g e n e r a l l y more s t a b l e , t h e r m a l l y , than those w i t h l e s s aromatics i n t h e i r c h a i n s . The e f f e c t o f c o m p o s i t i o n o n t h e t h e r m a l s t a b i l i t y i s most n o t i c e a b l e b e t w e e n 450 a n d 500°C. A t t h i s t e m p e r a t u r e r a n g e n y l o n 6 i s known t o u n d e r g o e x c e s s i v e d e g r a d a t i o n a n d , hence, i t i s l i k e l y t h a t t h e aromatic m o i e t i e s i n t e r f e r e w i t h t h e u n z i p p i n g mechanism b y w h i c h t h e p o l y c a p r o a m i d e d e p o l y merizes thermally. g

g

g

Thermal and T e n s i l e P r o p e r t i e s o f A T y p i c a l Copolymer and Nylon 6 The f a c t t h a t t h e c r y s t a l l i z a b i l i t y o f t h e p a r t i a l l y aromatic copolymers decreases d r a s t i c a l l y w i t h t h e i n c r e a s e o f t h e i r a r o m a t i c c o n t e n t makes t h e i r c o m p a r i s o n w i t h n y l o n 6# a s s e m i c r y s t a l l i n e m a t e r i a l s , a n u n e a s y t a s k . However, i t was f e l t i n s t r u c t i v e t o compare n y l o n 6 w i t h a h i g h l y c r y s t a l l i n e c o p o l y m e r h a v i n g a v e r y l o w a r o m a t i c c o n t e n t (7 m o l e %) s u c h a s c o p o l y m e r X I V . The t h e r m a l a n d t e n s i l e d a t a o f X I V a n d a n y l o n 6 s a m p l e (XVI) h a v i n g c o m p a r a b l e s o l u t i o n v i s c o s i t i e s a r e summarized i n T a b l e V I I I . T h e s e d a t a show t h a t (a) t h e a n n e a l e d s a m p l e o f X V I seems t o h a v e a h i g h e r d e g r e e o f c r y s t a l l i n i t y ( h i g h ΔΗ°) t h a n X I V , w h i c h i s a l s o a s s o c i a t e d w i t h 19°C d i f f e r e n c e i n T ° ; (b) a r e h e a t e d s a m p l e o f X V I i s

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

18.

SHALABY AND TURi

CopolymeHzation

of

265

e-Caprolactam

TABLE VI THERMAL ANALYSIS*** & X-RAY DATAi EFFECT OF POLYMERIZATION CONDITIONS Λ THERMAL TREATMENTS ON THE THERMAL BEHAVIOR & CRYSTALLINITY OF COPOLYMERS

Copolymer Composition, Mole $ of CL< ' Mole £ of DPPA Mole % of MDPP Maximum Polymerization Temp., C Red. Viscosity (in H S04) % Crystallinity of annealed (100°C/ 20 hr) Polymerι DSC Datât I n i t i a l heating T j °C I n i t i a l heating T j , °C Reheating data of samples quenche 260°C, b

(b)

XI

90

90

90

10

10

80 20

80 20

20 80

255

255

-

255

-

25

22

36

_

270 1.18 35

10 0.82

2.29

270 0.96

45 19

47 19

45 193

53 174

15* 190 22

190

17

194 14

36

-

27

.

_

cyclest from 150°C from 200 C from 230 C from 260 C

«.

10 29

64 86

_ _

10 35 57 90

12 33 73 94

ι.; 67

-

-

138

130

_

q

-

58 175

450°C 475°C 500°C

M

IV

1.93

(τ -τ·

g

XIII

255

T!.°C ).°C Τ ( ° C ) due t§ different heating l s t reheating after quenching 2nd reheating after quenching 3rd reheating after quenching 4th reheating after quenching TGA data, % Wt. loss at 425°C

IX

„

2

VII

II

180

-9 20 54 85

-9

208

18 41 83

8 12 34

203 7

DuPont 990. DSC and TGA, i n nitrogen, 20°C/raiii. and 10°C/min.heating rate, respectively, Based on i n i t i a l comonomer composition.

TABLE VII TGA DATA

(a)

EFFECT OF COMPOSITION ON

THERMAL STABILITY OF COPOLYMERS

Composition, Mole $ of CL "ired. (H2SO4) % Wt. loss i n nitrogen at 200 C 300°C 400°C 425°C 450°C 475°C 500°C 600°C 700°C 800°C 900°C 1000°C

(a)

I

II

95

90

2.00

1.93

1 2 4 9 24

1 2 4 10

65

64 86 90 93 98

95 97 _

29

-

Ill

IV

V

VI

85

80

65

50

1.88 1 1 3 8 20 45 86 88 91 95 99 100

2.29 2 3 5 9 20 54 85 88 89 93 97 100

2.94 2 2 4 6 13 31

70 81 82 85 90 96

DuPont-951 TGA, 10°C/min. heating rate.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2.04 3 3 5 7 12 33 65

74 76 80 86 93

VII 20 1.28 3 4 6 7 8 12 34 65 68 72 77 84

RING-OPENING POLYMERIZATION

266

TABLE VIII

COMPARISON OF THERMAL & TENSILE PROPERTIES OF NYLON 6 & A TYPICAL COPOLYMER Polymer Number

Molar Composition (CL/DPPA) Initial Final Reduced Viscosity DSC Data< 'i Initial heating, T j (°C), AHj (cal/g) Reheating Τ (°C), T - Δ Η . (cal/g? . T (OC), A H (cal/g TGA Data » # Wt. loss in nitrogen

XVI

XIV

100/0 100/0 0.91

93/7 92/8 0.89

b

(

m

24 6

225

16.2

204

f

vc;

& 200, 300, 350

400, 425 and 450°C

2, 20,

3.5.

44,

6.5

81

2,

1. 16,

37,

2, 21,

2.5, *·5 42, 74

77

# Wt. loss in a i r <§ 200 , 300 , 350 . 400, 425 and 450 C

3.

2, 31,

61,

6.5 86

40, 5^07

Tensile Propertiesi UE (#), UTS (psi) 182, WB (lb-in), SM (psi)

5268 0.11,

140802

3.71, 105682 8, 5^07

YE, YS 8, 4452

(a)

Samples were conditioned at 50#R.H. and 25°Cî UE = ultimate elongation, UTS = ultimate tensile strength, WB = work to break, SM = 2% secant modulus, YE « yield elongation, YS = yield strength.

(b) Perkin Elmer DSC-1B, in nitrogen, 20°C/min. heating rate. For reheating data, samples were heated up to 260°C, held for 2 min. then quenched in liquid nitrogen. (c)

Cahn RG electrobalance, 10°C/min. heating rate.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

18. shalaby AND TURi

Copolymerization of ^Caprolactam

267

more crystallizable (low Τ and high Δ H ) than XIV; (c) the reheated copolymer has a higher Τ and lower Τ than nylon 6 (this was associated with a difference of 13 and 15 C, re­ spectively) ; (d) the copolymer is more stable thermally than nylon 6; (e) nylon 6 is more pliable and tougher than XIV as indicated by its higher extensibility and work to break values as compared with the copolymer; and, (f) the copolymer has higher tensile strength and modulus than nylon 6. The notice­ ably higher modulus of XIV as compared with XVI is attributed to the high rigidity of the copolymer aromatic sequences. f

ACKNOWLEDGEMENT The authors wish to thank Dr. P.J. Harget, Mr. R.A. Kirk, Mrs. L.S. Komarowski, Mr. A.B. Szollosi and Mr. D.W. Richardson for their valuable contribution these studies. ABSTRACT Several copolymers of ε-caprolactam and ß - ( 3 , 4 - diaminophenyl) propionic acid were prepared using comonomer mixtures containing 95, 93, 90, 85, 80, 65, 50 and 20 mole per cent of caprolactam. In most cases, the composition of the resulting high molecular weight copolymers were comparable to the corresponding i n i t i a l comonomer compositions. Infrared spectroscopy and elemental analysis data of the copolymers suggest the presence of ethylene-benzimidazole moieties in their chains. Copolymers containing 35 mole per cent or more of the aromatic sequences were shown to be amorphous by differential scanning calorimetry and X-ray diffraction techniques. On the other hand, copolymers containing between 80 and 95 mole per cent of caprolactam moieties were semicrystalline and their degree of crystallinity ranged between about 20 and 40%. Similarly, the melting temperatures of these copolymers varied between 165 and 207°C. The glass transition temperature (T ) of both the amorphous and crystalline copolymers were shown to increase with the increase in their aromatic content. Upon subjecting the copolymers to certain thermal treatments, noticeable changes in Τ were recorded. This was ascribed to structural imperfections in the chain and the proposed thesis was sub­ stantiated by IR and addititional thermal analysis data. A comparison of the thermal and tensile properties of a typical semicrystalline copolymer and nylon 6 is also reported. g

g

LITERATURE CITED 1. 2. 3.

Ajrodli, G. Stea, G., Mattiussi, Α., & Fumagalli, Μ., J . Appl. Polym. Sci., (1973) 17, (3187). Shalaby, S.W., Turi, E.A. & Pearce, E.M., J. Appl. Polym. Sci., (1976) 20, (3185), and references therein. Shalaby, S.W., Turi, E.A. & Harget, P. J., J. Polym. Sci., Polym. Chem. Ed., (1976) 14, (2407), and references therein.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

268

RING-OPENING POLYMERIZATION

4. Shalaby, S.W., Lapinski, R.L. & Turi, E.A., J. Polym. Sci., Polym. Chem. Ed., (1974) 12 (2891). 5. Hermans, P.H. & Weidinger, Α., J. Appl. Phys., (1968) 19 (491) J. Polym. Sci., (1949) 4 (135), J. Polym. Sci., (1950). 5, (565). 6. Conley, R.T., "Infrared Spectroscopy", Chap. 5, Allyn & Bacon, Boston, Mass., 1966. 7. Eglinton, G. in "Physical Methods in Organic Chemistry", Chap. 3, Schwarz, J.C.P., Ed., Holden-Day, Inc. San Francisco, Calif., 1964. 8. Korshak, V.V., Teplyakov, M.M. & Fedorova, R.D., J. Polym. Sci., Part A-1, (1971), 9, (1027), and references therein. 9. Pearce, E.M., Shalaby, S.W., & Barker, R.H., in Flame Retardant Polymeric Materials", Chap. 6, Lewin, Μ., Atlas, S.M. & Pearce, E.M., Eds., Plenum Press, New York, N.Y., 1975.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

19 Anionic Polymerization of Fluorocarbon Epoxides JAMES T. HILL and JOHN P. ERDMAN Ε. I. du Pont de Nemours and Co., Inc., Elastomer Chemicals Department, Experimental Station, Wilmington, D E 19898

The o b j e c t i v e prepare p e r f l u o r i n a t e b o t h good low temperature flexibility and h i g h thermal stability. The r i n g opening p o l y m e r i z a t i o n s o f h e x a f l u o r o p r o p y l e n e epoxide (HFPO) and o c t a f l u o r o i s o b u t y l e n e epoxide (OFIBO) were examined as a potential r o u t e t o such m a t e r i a l s . 0 /\ CF CF-CF 5

0 /\ (CF^) C-CF x

2

2

HFPO

2

OFIBO

A number o f n u c l e o p h i l e s a r e c a p a b l e o f opening t h e epoxide r i n g s in t h e s e monomers (1,2,3). F l u o r i d e i o n opens t h e r i n g s r a p i d l y w h i l e p r e s e r v i n g the p e r f l u o r i n a t e d nature o f the products. Nucleo­ philic a t t a c k o c c u r s e x c l u s i v e l y a t the more sub­ stituted c a r b o n f o r m i n g isolable p e r f l u o r o a l k o x i d e s .

CF CF CF Cf M 5

2

+

(CF^) CFCF Cf

2

2

2

M

+

Under some c o n d i t i o n s t h e salts l o s e t h e elements o f MF and form t h e c o r r e s p o n d i n g acyl fluorides. The s o u r c e o f t h e fluoride i o n and n a t u r e o f its g e g e n i o n a r e i m p o r t a n t b o t h in t h e ring opening r e a c t i o n and to the stability of the alkoxide product. Of more +

-

269

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

270

RING-OPENING POLYMERIZATION

than 40 fluoride s a l t s i n v e s t i g a t e d cesium f l u o r i d e was f o u n d t o be most effective for initiating ring opening and f o r m i n g s t a b l e a l k o x i d e s . The a l k o x i d e s can r e a c t w i t h additional epoxide t o form s t r a i g h t c h a i n o l i g o m e r s ( 4 ) .

ο

^

CP

CP^CPCPg + Ρ

—

• CFy3F CF 0 2

2

HFPO

CP

I

I

-

t> C F C F C F 0 ( C F C F 0 ) C F C F 0 5

2

2

2

n

2

A medium i s r e q u i r e d f o r cesium f l u o r i d e t o r e a c t w i t h e i t h e r HFPO o r OFIBO a t room t e m p e r a t u r e . T e t r a g l y m e (TG) was f o u n d t o be t h e b e s t o f a number of p o l a r and n o n - p o l a r i n g opening by cesiu tetraglym d i f f i c u l t because o f t h e low s o l u b i l i t y o f t h e s a l t i n e i t h e r t h e s o l v e n t o r t h e l i q u i d monomers. Poly­ m e r i z a t i o n i s slow t o i n i t i a t e , d i f f i c u l t t o c o n t r o l and i s accompanied by a c h a i n t r a n s f e r r e a c t i o n w h i c h y i e l d s o n l y low m o l e c u l a r weight o l i g o m e r s . From t h e r e a c t i o n o f HFPO we were a b l e t o i s o l a t e and c h a r a c t e r i z e o l i g o m e r s up t o t h e t e t r a d e c a m e r . H i g h e r o l i g o m e r s were n o t d e t e c t e d . As shown below the c h a i n t r a n s f e r r e a c t i o n f o r m a l l y can be r e p r e ­ s e n t e d b y t h e e l i m i n a t i o n o f s o l v a t e d cesium f l u o r i d e from t h e growing a l k o x i d e f o l l o w e d by f l u o r i d e a t t a c k on epoxide t o g e n e r a t e new polymer c h a i n s . 0 - + R CF 0 Cs * R CF + 11

CsF

0 CsF|

+ C F ^ C F - C F ·> C F ^ C F ^ F ^ O Cs ·» new polymer 2

chains

To p r e p a r e h i g h m o l e c u l a r weight polymers r e q u i r e s t h e u s e o f s o l u b l e cesium p e r f l u o r o a l k o x i d e initiators. The p u r i f i e d a c y l f l u o r i d e o l i g o m e r s can be r e a c t e d w i t h cesium f l u o r i d e i n t e t r a g l y m e t o form w e l l d e f i n e d , s t a b l e , homogeneous i n i t i a t o r

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

19.

HILL AND ERDMAN

Polymerization

of Fluorocarbon

Epoxides

271

solutions. I n t h e c a s e o f HFPO t h e s e i n i t i a t o r s a r e more u s e f u l t h a n f l u o r i d e s a l t s s i n c e t h e y a r e more c o m p a t i b l e w i t h t h e monomer, smoothly i n i t i a t e t h e p o l y m e r i z a t i o n , p e r m i t good temperature c o n t r o l and a l l o w t h e s y n t h e s i s o f f l u i d polymers c o n t a i n i n g up t o 100 monomer u n i t s . We have been a b l e t o demon­ s t r a t e p o l y m e r i z a t i o n s from t h e m o n o f u n c t i o n a l and difunctional initiators shown below.

ο (CP ) CPCF 0Cs/TG + 0ΡΙΒ0 * (CP^ÎgCPCPgOfciCP^ÎgCPgO^CiCP^JgCP 5

2

2

η =<4

CP CP CP 0(CPCP 0) CPCP 0Cs/TG + HPPO * C ^ O C C F C F g O ^ C F C F 5

2

2

2

m

2

m * 0-12

η = < 100

CP , 3

OCF,

Λ

PCCPOCPgCFgOCPCF + CsF

•

TG/Cs0CP R CF 0Cs/tG 2

f

2

0CP_ CP, CF_ ι3 M » » Ρ FCCFiOCF-CF) 0 C F C F 0 ( C F C F 0 ) CFCF n

HPPO

3

^

3

3

o

o

1

o

m + η < 200

A wide v a r i e t y o f d i l u e n t s o l v e n t s , c o o r d i n a t i n g s o l v e n t s , c o u n t e r i o n s and p e r f l u o r i n a t e d a c y l f l u o r i d e s were examined i n an e f f o r t t o s u p p r e s s t h e c h a i n t r a n s f e r r e a c t i o n t h a t l i m i t s t h e degree o f p o l y m e r i z a t i o n (DP). Because o f t h i s l i m i t a t i o n t h e h i g h e s t number average m o l e c u l a r w e i g h t s ( M ) we have o b s e r v e d f o r p o l y HFPO a r e 1 5 , 5 0 0 from m o n o f u n c t i o n a l i n i t i a t o r s and ~ 2 5 , 0 0 0 from d i f u n c t i o n a l i n i t i a t o r s . I n c o n t r a s t , we have n o t been a b l e t o p o l y m e r i z e OFIBO beyond DP 4 . T h i s s u g g e s t s t h a t HFPO i s about 25 t i m e s as r e a c t i v e a s OFIBO w i t h r e g a r d t o r i n g opening p o l y m e r i z a t i o n i n i t i a t e d by s o l v a t e d perf l u o r o a l k o x i d e s a l t s (6). Since the attack i s a t the t e r t i a r y c a r b o n atom o f b o t h e p o x i d e r i n g s we n

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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272

c o n c l u d e t h a t s t e r i c h i n d r a n c e i n OFIBO i s m a i n l y r e s p o n s i b l e f o r i t s lower p r o p a g a t i o n r a t e , making t h e polymerization l e s s competitive with the chain transf e r r e a c t i o n . Increased i n d u c t i v e s t a b i l i z a t i o n of the n e g a t i v e l y c h a r g e d a l k o x i d e by t h e a d d i t i o n a l t r i f l u o r o m e t h y l group i n OFIBO may a l s o be a minor f a c t o r c o n t r i b u t i n g t o i t s lower r e a c t i v i t y . I f t h e homogeneous i n i t i a t o r s a r e h e a t e d t o g r e a t e r t h a n 100°C t h e a l k o x i d e s r e v e r t t o a c y l f l u o r i d e , cesium f l u o r i d e p r e c i p i t a t e s and t h e t e t r a glyme s e p a r a t e s from s o l u t i o n . On c o o l i n g and remixi n g t h e homogeneous i n i t i a t o r i s reformed q u a n t i t a tively. T h i s suggest

R CF OCs/TG f

2

II R C F + CsF/TG f

i s perhaps r e s p o n s i b l e f o r t h e c h a i n t r a n s f e r r e a c tion. Two o b s e r v a t i o n s d i s c o u n t t h i s h y p o t h e s i s . In F i g u r e 1 t h e F NMR s p e c t r a o f t h e d i f u n c t i o n a l a c y l f l u o r i d e and i t s c o r r e s p o n d i n g cesium a l k o x i d e i n i t i a t o r a r e compared. Resonances f o r t h e f l u o r i n e s on t h e end groups i n t h e two s p e c i e s a r e w e l l s e p a r a t e d and d i s t i n c t . I n temperature s t u d i e s o f t h e a l k o x i d e s o l u t i o n s o v e r t h e range -40 t o +80°C we observe n e i t h e r a c y l f l u o r i d e r e s o n a n c e s n o r changes i n chemic a l s h i f t s t h a t c o u l d be a s c r i b e d t o r a p i d l y e q u i l i b r a t i n g s p e c i e s . That t h e c h a i n t r a n s f e r r a t e i s v e r y s e n s i t i v e t o t h e p o l y m e r i z a t i o n temperature o v e r the range - 3 5 t o + 2 5 ° s u g g e s t s t h a t t h e e q u i l i b r i u m , i f i t p l a y s a s i g n i f i c a n t r o l e , s h o u l d be r e a d i l y observable. The second p o i n t i s t h a t i n t h e p r e s e n c e o f t h e a l k o x i d e i n i t i a t o r s a d d i t i o n a l u n r e a c t e d cesium f l u o r i d e does n o t i n c r e a s e t h e r a t e o f c h a i n t r a n s f e r d u r i n g HFPO p o l y m e r i z a t i o n s . As we know t h a t t h e metal s a l t i s by i t s e l f capable o f i n i t i a t i n g o l i g o m e r i z a t i o n when i t i s mixed w i t h t e t r a g l y m e , i t must have some f i n i t e s o l u b i l i t y i n t h e medium. We must conclude then t h a t f l u o r i d e i o n i n i t i a t i o n i s not 1 9

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

19. HILL AND ERDMAN

Polymerization

of Fluorocarbon

Epoxides

273

c o m p e t i t i v e w i t h a l k o x i d e i n i t i a t i o n and f u r t h e r t h a t the a l k o x i d e - a c y l f l u o r i d e e q u i l i b r i u m i s n o t important t o the chain t r a n s f e r r e a c t i o n . Our experiments show t h a t t h e s i z e o f t h e gegeni o n , t h e s o l v e n t ' s c o o r d i n a t i n g a b i l i t y , and t h e s o l u b l i t y o f t h e i n i t i a t o r system i n t h e r e a c t i o n medium a r e major v a r i a b l e s d e t e r m i n i n g t h e r a t e o f c h a i n transfer. With s m a l l c o u n t e r ! o n s , l i t h i u m , sodium, o r potassium, or with i n s o l u b l e i n i t i a t o r s a l t s high y i e l d s o f o n l y low m o l e c u l a r weight polymer a r e obtained. Cesium s a l t s r o u t i n e l y g i v e t h e l e a s t amount o f c h a i n t r a n s f e r S i m i l a r l y the t r a n s f e r rate d i m i n i s h e s as t h e a f f i n i t toward t h e l a r g e a l k a l i m e t a l i o n s i s i n c r e a s e d . These d a t a s u g g e s t t h a t t h e e q u i l i b r i u m between c o n t a c t , s o l v e n t s e p a r a t e d , and f r e e i o n p a i r s i s r e l a t e d t o t h e r a t e o f c h a i n t r a n s f e r . We b e l i e v e t h a t chain propagation occurs v i a r e a c t i o n o f the monomer e i t h e r d i r e c t l y w i t h f r e e i o n s o r by i n s e r t i o n o f t h e epoxide oxygen i n t o t h e c o o r d i n a t i o n sphere o f the m e t a l i o n f o l l o w e d by a l k o x i d e a t t a c k and r i n g o p e n i n g . The c h a i n t r a n s f e r p r o b a b l y a r i s e s from a b i m o l e c u l a r r e a c t i o n o f t h e monomer w i t h c o n t a c t i o n s v i a a six-membered c y c l i c p r o c e s s . Polymerization

Technique

F o r s u c c e s s f u l p o l y m e r i z a t i o n s s c r u p u l u s maintenance o f anhydrous m a t e r i a l s and c o n d i t i o n s a r e r e q u i r e d as even a few ppm o f water a r e d e l e t e r i o u s t o t h e degree o f p o l y m e r i z a t i o n . The f l u i d i n i t i a t o r i s p r e p a r e d i n a d r y box under n i t r o g e n by m i x i n g a c y l f l u o r i d e , cesium f l u o r i d e , and t e t r a g l y m e i n a p p r o x i m a t e l y 1:1:>2 molar r a t i o . A s l i g h t e x c e s s o f s a l t i n s u r e s comp l e t e conversion of the a c y l f l u o r i d e t o alkoxide. Cesium f l u o r i d e d i s s o l v e s r a p i d l y and when t h e e x c e s s i s removed b y c e n t r i f u g a t i o n t h e s i n g l e phase supern a t a n t i s c r y s t a l c l e a r and i s found t o c o n t a i n t h e t h e o r e t i c a l amount o f cesium. The i n i t i a t o r i s weighed i n t o t h e r e a c t i o n v e s s e l and i s c o o l e d t o -35° a t which p o i n t a s o l v e n t ®

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

274

f o r t h e polymer i s added. In most c a s e s t h i s i s l i q u i d h e x a f l u o r o p r o p y l e n e (HFP). We have f o u n d t h a t solvent i n a d d i t i o n t o tetraglyme i s necessary f o r successful polymerization. HFP i s a s o l v e n t f o r the p e r f l u o r i n a t e d ends o f the growing c h a i n s . We b e l i e v e t h a t i t s main f u n c t i o n s are t o keep the v i s c o s i t y o f the p o l y m e r i z i n g mass low and t o p r o v i d e f o r e f f i c i e n t t r a n s f e r o f the h e a t o f p o l y m e r i z a t i o n away from the growing polymer ends. There i s some e v i d e n c e t h a t HFP i s a t r a p f o r s t r a y f l u o r i d e i o n s which h e l p s t o s u p p r e s s c h a i n t r a n s f e r . However, a l t e r n a t e s o l v e n t s incapable of a c c e p t i n g f l u o r i d e i o n s have been use been shown t o have no measurable e f f e c t on the r a t e of chain t r a n s f e r . As soon as a l l the d i l u e n t i s added the m i x t u r e i s s t i r r e d r a p i d l y t o d i s p e r s e the s e m i s o l i d i n i t i a t o r as w e l l as p o s s i b l e ; i t i s n o t c o m p l e t e l y s o l u b l e at t h i s stage. HFPO i s t h e n added t h r o u g h c a l i b r a t e d meters a t a c o n s t a n t r a t e and condensed. Reaction t e m p e r a t u r e s a r e m a i n t a i n e d between -JO t o - 3 5 ° C Lower t e m p e r a t u r e s f r e e z e the i n i t i a t o r t o a comp l e t e l y i n a c t i v e s o l i d while h i g h e r temperatures r e s u l t i n the l o s s o f s o l v e n t and monomers and s h a r p l y i n c r e a s i n g c h a i n t r a n s f e r r a t e s . As the monomer i s consumed the i n i t i a t o r t h i n s out and becomes e v e n l y d i s p e r s e d t h r o u g h o u t the m i l k y mass. At ~ 5000-6000 M the r e a c t o r ' s c o n t e n t s s u d d e n l y becomes c l e a r . As a d d i t i o n a l monomer i s added the m i x t u r e a g a i n becomes c l o u d y as h i g h MW fluorocarbon polymer b e g i n s t o phase out o f s o l u t i o n . At the same time the s o l u t i o n v i s c o s i t y i n c r e a s e s markedly and the mass becomes d i f f i c u l t t o s t i r . n

When the d e s i r e d q u a n t i t y o f monomer has been added the r e a c t i o n i s s t i r r e d f o r a n o t h e r hour, a f t e r which no f u r t h e r i n c r e a s e s i n MW a r e o b s e r v e d . HFP i s removed under vacuum as the r e a c t o r i s warmed t o room t e m p e r a t u r e . M a t e r i a l b a l a n c e s a r e > 99$· No u n r e a c t e d monomer i s f o u n d i n the r e c o v e r e d s o l v e n t i n d i c a t i n g t h a t c o n v e r s i o n s of HFPO a r e c l o s e t o 100$. Though q u a n t i t a t i v e r e c o v e r y o f the a c y l f l u o r i d e

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

HILL AND ERDMAN

19.

Polymerization

of Fluorocarbon

Epoxides

275

t e r m i n a t e d polymer i s p o s s i b l e i n most c a s e s i t i s more c o n v e n i e n t t o q u a n t i t a t i v e l y c o n v e r t t h e end groups t o t h e e t h y l e s t e r by quenching w i t h a b s o l u t e e t h a n o l and s u b s e q u e n t l y removing t h e s a l t and t e t r a glyme which s e p a r a t e s from t h e polymer. Polymer

Characterization

Number average

molecular weights

(M ) f o r t h e s e n

polymers c a n be determined b y a v a r i e t y o f methods; v a p o r phase osmometry, IR, UV and s a p o n i f i c a t i o n w i t h a l c o h o l i c potassiu up t o t h e t e t r a d e c a m e e x t i n c t i o n c o e f f i c i e n t s f o r the a c i d f l u o r i d e (5.55 μπι) and t h e e t h y l e s t e r ( 5 . 6 μιη). Number average WW s up t o ~ 2 5 , 0 0 0 a r e a c c e s s i b l e w i t h t h e s e t e c h n i ­ ques; a l l gave e q u i v a l e n t r e s u l t s . F o r polymers i n i t i a t e d by d i f u n c t i o n a l c a t a l y s t s t h e IR method a f f o r d s e q u i v a l e n t weights which a r e c o r r e c t e d t o number average m o l e c u l a r weights w i t h an NMR measure­ ment o f t h e average f u n c t i o n a l i t y . When c h a i n t r a n s f e r o c c u r s d u r i n g a d i f u n c t i o n a l p o l y m e r i z a t i o n m o n o f u n c t i o n a l polymers r e s u l t w h i c h have a t one end a p e r f l u o r o p r o p y 1 e t h e r group. 1

ι 3J> CF CFgCFgO — ~ C F C O E t s, 133.33 ppm 0CF„ I 3 EtOCCF

monofunctional

polymer

t , 1 3 1 . 5 6 ppm

CF. 1 V> CFCOEt

d i f u n c t i o n a l polymer

The amount o f c h a i n NMR. The secondary ppm (CFCI3) and t h e f i n d that these w e l l

t r a n s f e r can be measured by F f l u o r i n e s ( s ) absorb a t 1 3 3 . 3 3 t e r t i a r y ( t ) a t 1 3 1 . 5 6 ppm. We d e f i n e d , s e p a r a t e d , and easy t o

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1 9

RING-OPENING POLYMERIZATION

276

i n t e g r a t e peaks o c c u r i n t h e r a t i o 2 : 1 f o r monof u n c t i o n a l polymer and t h a t no s" absorbances e x i s t f o r p u r e l y d i f u n c t i o n a l polymers. The r e l a t i v e q u a n t i t i e s i n a m i x t u r e o f mono- and d i f u n c t i o n a l m a t e r i a l s c a n be d e t e r m i n e d from t h e i n t e g r a l r a t i o , t / s , by a p p l y i n g t h e e q u a t i o n : 11

t/s-1/2 ^^ ·^/2

mole f r a c t i o n d i f u n c t i o n a l polymer, D = Examples (bottom) trated i the M i weight. n

3+

o f s p e c t r a f o r a 33$ d i f u n c t i o n a l polymer and a 95$ d i f u n c t i o n a l polymer a r e i l l u s ­ n F i g . 2. Fo s equal t o 1

Jv^, F u n c t i o n a l i t y , and Time One p o l y m e r i z a t i o n was conducted u s i n g a t e t r a ­ glyme s o l u t i o n o f HFPO t r i m e r a l k o x i d e f o r i n i t i a t i o n and HFP as t h e d i l u e n t ; monomer was added s l o w l y and c o n t i n u o u s l y o v e r 50 h r s . Samples were removed d u r i n g t h e p o l y m e r i z a t i o n t o f o l l o w t h e M as a n

f u n c t i o n o f time and t h e amount o f monomer added. F i g u r e 3 shows t h i s r e l a t i o n s h i p and i l l u s t r a t e s t h e s e v e r e l i m i t a t i o n on M by c h a i n t r a n s f e r . A t t h e end o f 50 h r s t h e Mn was o n l y 5000 compared t o 59*4-00 M e x p e c t e d i f no c h a i n t r a n s f e r had o c c u r r e d . A t 7 h r s i n t o t h i s r u n t h e c h a i n t r a n s f e r parameter, MW theory/Μη, was 8 . 0 , i n d i c a t i n g t h a t each m o l e c u l e o f i n i t i a t o r had undergone an average o f 7 t r a n s f e r reactions. T h i s parameter i n c r e a s e d t o o n l y 1 1 . 9 a t the end o f 50 h r s s u g g e s t i n g t h a t most o f t h e c h a i n t r a n s f e r takes p l a c e e a r l y i n the p o l y m e r i z a t i o n perhaps even a t t h e onset o f p o l y m e r i z a t i o n . We f i n d also that the rate of chain t r a n s f e r increases with i n c r e a s i n g monomer a d d i t i o n r a t e s . Under r e a c t i o n c o n d i t i o n s i d e n t i c a l t o t h o s e u s e d i n t h e above exper­ iment t r i p l i n g t h e monomer a d d i t i o n r a t e r e s u l t s i n a n

n

5- f o l d i n c r e a s e i n t h e c h a i n t r a n s f e r r a t e w h i l e a 6- f o l d monomer r a t e i n c r e a s e r e s u l t s i n a 1 6 - f o l d

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

19. HILL AND ERDMAN

Polymerization

of Fluorocarbon

Figure 1.

NMR

14

Epoxides

277

of the difunctional acyl

Figure 2. Partial expanded scale *'F NMR of 33% difunctional poly HFPO (bottom) and 95% difunctional poly HFPO (top)

1

10

j

1

1

20 30 40 TIME (hrs)

Γ

50

Figure 3. HFPO polymerization using cesium HFPO trimer alkoxide initiator

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

278

increase i n the t r a n s f e r rate. We o b t a i n e d more i n f o r m a t i o n from a s i m i l a r experiment u s i n g t h e d i f u n c t i o n a l i n i t i a t o r i n which b o t h f u n c t i o n a l i t y and Mn were f o l l o w e d as a f u n c t i o n of time. F i g u r e 4 shows t h e m o l e c u l a r weight response. I t i s o b v i o u s t h a t t h e r e i s an i n d u c t i o n p e r i o d f o r the polymerization. The M l a g s c o n s i d e r a b l y b e h i n d t h e t h e o r e t i c a l M up t o ~ 200 min and t h e n i t i n c r e a s e s , f o r a b r i e f p e r i o d f a s t e r than t h e r a t e o f monomer a d d i t i o n , i n d i c a t i n g t h a t t h e r e had been a l a r g e a c c u m u l a t i o n o f u n r e a c t e d monomer d u r i n g the i n d u c t i o n p e r i o d Thi slo initiatio i b a b l y caused by HFP mass o f v e r y v i s c o u s t e t r a g l y m e t o f i n d a l k o x i d e groups. Subsequent t h i n n i n g and d i s p e r s i o n o f t h e c a t a l y s t i n c r e a s e s t h e r a t e o f monomer r e a c t i o n . n

n

The o t h e r p o i n t t o observe i n t h i s f i g u r e i s t h e a p p a r e n t d i s c o n t i n u i t y a t 720 min. Here was one o f the p l a c e s t h a t t h e l i v i n g a n i o n i c n a t u r e o f t h e s e p o l y m e r i z a t i o n s was demonstrated. A f t e r 12 hours o f r e a c t i o n monomer a d d i t i o n was stopped and t h e p o l y m e r i z a t i o n m i x t u r e c o o l e d t o - 7 8 ° C and k e p t t h e r e f o r 8 h r . A f t e r rewarming t h e m i x t u r e t o -32°C, monomer a d d i t i o n was r e s t a r t e d and t h e p o l y m e r i z a t i o n continued. The d i s c o n t i n u i t y i s n o t u n u s u a l as a s l i g h t M i n c r e a s e was o b s e r v e d whenever a p o l y m e r i z a t i o n was shutdown and l a t e r r e s t a r t e d . The o b s e r v a t i o n s u g g e s t s t h a t r e l a t i v e t o t h e a l k o x i d e concent r a t i o n HFPO i s always p r e s e n t i n e x c e s s . Figure 5 i l l u s t r a t e s the d i f u n c t i o n a l i t y response f o r t h i s e x p e r i m e n t . The i n d u c t i o n p e r i o d and d i s c o n t i n u i t y a r e a l s o p r e s e n t . From t h e d i f u n c t i o n a l i t y measurements i t i s p o s s i b l e t o c a l c u l a t e a p s e u d o - f i r s t - o r d e r rate constant f o r chain t r a n s f e r , Kt. The average K t f o r t h i s r u n was 7 . 9 x 1 0 ~ s e c ~ . In t h e r a t e e x p r e s s i o n , t h e assumption t h a t t h e number o f a l k o x i d e ends i s c o n s t a n t a t a l l t i m e s l e a d s t o low v a l u e s f o r as c a l c u l a t e d from t h e f i r s t n

e

four points. T h i s might be e x p e c t e d f o r d u r i n g t h e i n d u c t i o n p e r i o d n o t a l l t h e a l k o x i d e ends a r e

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

l

19. HILL AND ERDMAN

Polymerization

of Fluorocarbon

Epoxides

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

280

a v a i l a b l e f o r propagation. L a t e r on as the i n i t i a t o r i s more e v e n l y d i s p e r s e d the assumption becomes v a l i d . C a l c u l a t i o n o f Kt from 20 o t h e r p o l y m e r i z a t i o n s r u n under s i m i l a r c o n d i t i o n s gave an average v a l u e o f 8.4 χ l O ^ s e c " . 1

Armed w i t h the c h a i n t r a n s f e r c o n s t a n t and t h e time dependence o f the m o l e c u l a r weight and d i f u n c t i o n a l i t y we d e v e l o p e d the a p p r o p r i a t e k i n e t i c expressions t o estimate the p s e u d o - f i r s t order r a t e c o n s t a n t f o r the r i n g opening p r o p a g a t i o n s t e p . We f i n d that a value o f 8 χ l O ^ s e c " g i v e s the best f i t t o a l l the d a t a the v a l u e s we o b t a i n e the maximum DP p o s s i b l e f o r a polymer i n i t i a t e d w i t h a m o n o f u n c t i o n a l a l k o x i d e i s about 100 (16,500 M ) . The d i f u n c t i o n a l m o l e c u l e s can be e x p e c t e d t o grow t o no more than DP 200 (33,000 M ) b u t t h i s m a t e r i a l would be contaminated w i t h a s u b s t a n t i a l f r a c t i o n o f lower DP m o n o f u n c t i o n a l polymer. U s i n g t h e k i n e t i c parameters d e r i v e d from our experiments we were a b l e to c a l c u l a t e r e a c t i o n t i m e s , monomer a d d i t i o n r a t e s and t h e c o r r e c t amount o f d i f u n c t i o n a l i n i t i a t o r t o use t o p r e p a r e moderate MW d i f u n c t i o n a l polymers c o n t a i n i n g no d e t e c t a b l e monof u n c t i o n a l contaminants. With c a r e f u l c o n t r o l we can r o u t i n e l y p r e p a r e 100$ d i f u n c t i o n a l polymers o f the s t r u c t u r e 1

n

n

0CP_

CF,

CF,

CF,

F C C F ( 0 C F C F ) -OCF^CF^O(CFCF^O) CFCF 2 m 2 2 2 n v

o

J

K

J

m + η a* 35 C h a i n Extended

Polymers

Because o f the c h a i n t r a n s f e r we were unable t o p r e p a r e e l a s t o m e r i c HFPO homopolymer. The h i g h e s t MW m a t e r i a l s p r e p a r e d were v e r y v i s c o u s l i q u i d s a t room temperature. The c h e m i c a l i n e r t n e s s o f t h e backbone and t h e h i g h r e a c t i v i t y o f t h e a c y l f l u o r i d e and e t h y l

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

19.

HILL AND ERDMAN

Polymerization

of Fluorocarbon

Epoxides

281

e s t e r end groups e n a b l e s t h e c h a i n e x t e n s i o n w i t h a wide v a r i e t y o f r e a g e n t s . A few examples a r e shown below.

R

(J ) F

diols

^

polyesters

diamines

^

polyamides

P o l y e s t e r s were p r e p a r e d by c o n d e n s a t i o n o f t h e d i a c i d f l u o r i d e s wit non-fluorinated d i o l s prepared by metal c a t a l y z e d e s t e r interchange u s i n g the p o l y HFPO d i e s t e r s . Polyamides can be p r e p a r e d e i t h e r by s o l u t i o n o r i n t e r f a c i a l t e c h n i q u e s . These m a t e r i a l s were d e f i c i e n t i n b o t h t h e r m a l and hydrolytic stability. A r o m a t i c c h a i n e x t e n s i o n l i n k s were p r e p a r e d i n an e f f o r t t o i n c r e a s e t h e h i g h temperature s t a b i l i t y o f t h e polymer. B e n z i m i d a z o l e s were s y n t h e s i z e d by condensing e i t h e r the a c i d f l u o r i d e s o r e s t e r s with d i a m i n o b e n z i d i n e and s u b s e q u e n t l y d e h y d r a t i n g w i t h heat. For l,3*^-oxadiazoles the precursor polyh y d r a z i d e s c o u l d n o t be p r e p a r e d by the d i r e c t r e a c t i o n o f t h e a c y l f l u o r i d e s w i t h h y d r a z i n e as i n t r a c t a b l e u n s t a b l e c o r s s l i n k e d m a t e r i a l s were formed. They were b e s t p r e p a r e d by c o n v e r t i n g t h e p r e p o l y m e r end groups t o p h e n y l e s t e r s and then r e a c t i n g w i t h h y d r a z i n e t o form t h e d i h y d r a z i d e s . Subsequent r e a c t i o n w i t h a v a r i e t y o f d i a c i d h a l i d e s afforded a t t r a c t i v e elastomers. Dehydration with phosphorous p e n t o x i d e gave t h e c o - p o l y o x a d i a z o l e s b u t t h e s e were no l o n g e r rubbery.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

282

Benzimidazole NH_ B (CF) . + N H f

2

2

- ^ ) - ^ - N H

— * · —R

2

f

- CNH - ^ g )

Η 1*3*4 O x a d i a z o l e s R(C0P)

n

0

.

1 + C H 0 K -*R (COC H )

N

+

2

6

5

f

6

5

2 4

2

ρο

•

R.C^ f

CCI

» R (CNHNH )

H

f

2

2

^ C -/OV

μ Ν N-

il N ^ / Ν

I

diamine

CCI

1*3*4 t r i a z o l e crosslink

We were u n a b l e t o c h a i n e x t e n d t h e d i f u n c t i o n a l HPPO beyond DP = 10 ( 6 0 , 0 0 0 VL^). As p r e d i c t e d t h e polymers e x h i b i t e d T g s c l o s e t o - 5 0 ° C . The a r o m a t i c l i n k s e x h i b i t e d o n l y f a i r s t a b i l i t y a t 350°C. Though t h e f l u o r i n a t e d c h a i n s i m p a r t some r e s i s t a n c e t o aqueous bases we f i n d t h e m a t e r i a l s c h a i n extended w i t h 5 membered h e t e r o c y c l e s do n o t s u r v i v e such exposure. The s t r o n g e l e c t r o n w i t h d r a w i n g e f f e c t o f f

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

19. HILL AND ERDMAN

Polymerization

of Fluorocarbon

Epoxides

283

the f l u o r i n a t e d s u b s t i t u e n t s r e n d e r t h e r i n g carbons very s u s c e p t i b l e to n u c l e o p h i l i c attack. I n aqueous base the polymers a r e degraded t o the o r i g i n a l molecular weights. The most i n t e r e s t i n g c h a i n extended polymers were t h e s - t r i a z i n e s . The d i e s t e r s can be c o n v e r t e d t o diamides w i t h ammonia and thence t o d i n i t r i l e s 0 •

0 ,

NH

R (C0Et) f

^

2

V

C

N

Ρ ο *

V 2

NH R

f

( c

S

N

)

2

— 3 +

R

f ( c

-NH ) 2

2

—

r •

4

3

AgO, Δ

R

j

f

C

(

f

s

N

)

2

f

Ν γ

γ * ^

N

R

N

f

X

w i t h phosphorous p e n t o x i d e . The n i t r i l e s can be c o n v e r t e d d i r e c t l y t o s - t r i a z i n e s a t h i g h tempera­ t u r e i n the presence o f s i l v e r oxide c a t a l y s t o r can be c o n v e r t e d t o b i s a m i d i n e s w i t h ammonia. When t h e s e f l u i d s a r e h e a t e d ammonia i s e v o l v e d and t h e t r i a z i n e networks form. L i k e t h e l i n e a r polymers these c r o s s l i n k e d m a t e r i a l s e x h i b i t g l a s s t r a n s i t i o n s i n t h e range - 5 0 t o - 6 0 ° C . They have good h y d r o l y t i c s t a b i l i t y and a r e v i r t u a l l y u n a f f e c t e d b y p r o l o n g e d h e a t i n g a t 350°C. The modulus, t e n s i l e s t r e n g t h , and e l o n g a t i o n a t b r e a k o f the b e s t t r i a z i n e polymers, however, a r e t o o low f o r g e n e r a l use i n molded goods. We b e l i e v e , however, t h a t t h e p o o r p h y s i c a l p r o p e r ­ t i e s a r e n o t due t o i n h e r e n t weaknesses o f t h e HFPO backbone o r the t r i a z i n e l i n k s b u t r a t h e r t o l o o s e c h a i n ends and s h o r t d i s t a n c e s between t h e t r i functional crosslinks.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

284

RING-OPENING POLYMERIZATION

Literature Cited 1 Hill, J. T., J. Macromol. Sci.-Chem., (1974), A8(3), 499. 2 Eleuterio, H. S., U. S. Patent 3,358,003 (1967). 3 Sianesi, D., Pasetti, A. and Tarli, F., J. Org. Chem. (1966), 31, 2312 4 Moore, E. P., U. S. Patent 3,322,826 (1967) 5 Fritz, C. G. and Moore, E. P., U. S. Patent 3,250,807 (1966) 6 J. T., Eighth Int. Symp. Fluor. Chem., Kyoto, Japan, Aug. 24, 1976.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

20 Ring-Opening Polymerization via C-C Bond Opening H. K. HALL, JR., H. TSUCHIYA, P. YKMAN, J. OTTON, S. C. SNIDER, and A. DEUTSCHMAN, JR. (1) Department of Chemistry, University of Arizona, Tucson, AZ 85721

Ring-opening polymerization usually involves compounds con­ taining strained C-O, C-N, or C-S single bonds. Polymerizations involving strained C-C single bonds are less familiar. Cyclo­ propane and cyclobutane do not give clean results, because reagents sufficiently vigorous to open the ring also attack the resulting chain. Two types of strained bicyclic compound undergo ring-opening polymerization via C-C bond opening. The first group consists of compounds with a strained polycyclic structure. Ex­ amples include a variety of bicyclobutanes 1, (2) bicyclopentane[2.1,0]carbonitrile 2 (3), benzocyclopropenecarDonitrile 3 (4), benzocyclobutene 4 (5,6), two tetracyclooctanes 5 and 6, (7,8), and 1,3-dehydroadamantane 7 (9,10).

285

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

SOO

RING-OPENING POLYMERIZATION

Two factors account for the ability of such polycyclic com­ pounds to polymerize. First, the strain energy is very high, and may be relieved on polymerization. Secondly, the compact cage molecule shows low steric hindrance to attack. Breaking a C-C single bond always encounters hindrance from substituents on the adjacent carbons, but this repulsion is minimized in compact ring structures. The second group o f monomers c o n t a i n s those i n which a double bond i s "conjugated" w i t h a s t r a i n e d s i n g l e bond. A number o f v i n y l c y c l o p r o p a n e s 8 (11,12) belong i n t h i s category, as do 1 - v i n y l b i c y c l o b u t a n e 9 (2) and [2,4]-spiroheptadiene 10 (13) . For these compounds, the double bond o f f e r s a p o i n t oi r e a c t i o n f o r the growing polymer c h a i n . Again, the p r o j e c t i n g 2 S P o f f e r s minimal s t e r i c hindrance. U n l i k e other ring-opening p o l y m e r i z a t i o n s , most C-C s i n g l e bond p o l y m e r i z a t i o n s hav i a t i o n , even though example a t i o n p o l y m e r i z a t i o n s have been presented. The b i c y c l o b u t a n e monomers, such as b i c y c l o b u t a n e - l - c a r b o n i t r i l e ( l a X = CN), are as r e a c t i v e i n f r e e r a d i c a l p o l y m e r i z a t i o n as v i n y l monomers ( 2 ) . A n i o n i c P o l y m e r i z a t i o n o f Bicyclobutane-1- a r b o n i t r i l e We i n q u i r e d whether a n i o n i c p o l y m e r i z a t i o n s o f ]La could a l s o be c a r r i e d out. The most s u c c e s s f u l a n i o n i c p o l y m e r i z a t i o n s o f m e t h a c r y l o n i t r i l e (the v i n y l analog o f l a ) , have been those o f Joh and h i s c o l l e a g u e s (14,15), who used dialkylmagnesium and magnes­ ium d i a l k y l a m i d e i n i t i a t o r s . Therefore we u t i l i z e d them w i t h bicyclobutane-l-carbonitrile. B i c y c l o b u t a n e - l - c a r b o n i t r i l e polymerized v e r y r e a d i l y w i t h these organomagnesium i n i t i a t o r s (Table I ) . The magnesium amides and " a t e " compounds gave h i g h e s t y i e l d s , w i t h the mercaptides c l o s e behind. Dialkylmagnesiums gave lower y i e l d s . Dioxane and toluene as s o l v e n t s gave the highest y i e l d s , and the polymer p r e c i p i t a t e d from these media. U n s t i r r e d , m a g n e t i c a l l y s t i r r e d , and m e c h a n i c a l l y s t i r r e d p o l y m e r i z a t i o n s gave comparable r e s u l t s . Homogeneous p o l y m e r i z a t i o n s were performed i n dimethylformamide, s u l f o l a n e and tetramethylene s u l f o x i d e s o l u t i o n . The y i e l d s under these c o n d i t i o n s were v e r y low or zero. P o l y b i c y c l o b u t a n e c a r b o n i t r i l e obtained i n t h i s way was a white powder, u n l i k e the f i b r o u s m a t e r i a l obtained by f r e e r a d i c a l i n i t i a t i o n . The inherent v i s c o s i t i e s i n dimethylforma­ mide were u s u a l l y about 0.1 d l . g . " and r a r e l y exceeded 0.5 d l . g." . The nmr s p e c t r a resembled those of the r a d i c a l - i n i t i a t e d polymer. When magnesium d i ( i s o p r o p y l m e r c a p t i d e ) was used as the i n i t i a t o r , isopropylmercapto end groups were v i s i b l e i n the nmr s p e c t r a . The i n f r a r e d s p e c t r a a l s o resembled those of the r a d i c a l - i n i t i a t e d polymer, and supported the 1-cyano-1,3-cyclob u t a n e d i y l s t r u c t u r e . One a b s o r p t i o n which d i d not conform t o t h i s s t r u c t u r e was v i s i b l e i n every i r spectrum. T h i s a b s o r p t i o n a t 1700 cm" i s a s c r i b e d to a ketone carbonyl group. T h i s a s s i g n ­ ment was confirmed by s t i r r i n g the polymer w i t h sodium borohydride overnight i n s u l f o l a n e - w a t e r (4:1), whereupon t h i s band d i s a p C H

=

r o u

1

1

1

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

20.

HALL ET AL.

Polymerization

via C-C

Bond

Opening

287

eared. The a b s o r p t i o n i n t e n s i t y o f t h i s carbonyl band c o r r e l a t e d i n v e r s e l y w i t h inherent v i s c o s i t y , i n d i c a t i n g t h a t i t was i n v o l v e d i n the termination reaction. We propose the f o l l o w i n g mechanism: I n i t i a t i o n - A d d i t i o n o f o r g a n o m e t a l l i c RM t o the s t r a i n e d 1,3 bond i s known t o occur even f o r t h e more s t e r i c a l l y crowded

3-methyl-1-bicyclobutanecarbonitril t e c t i o n o f the correspondin polymers i n i t i a t e d by magnesium d i ( i s o p r o p y l m e r c a p t i d e ) (and other i n i t i a t o r s ) . Propagation -

Termination -

We s t u d i e d a model system i n an e f f o r t t o determine whether or not a t t a c k o f a propagating a-cyanocylobutyl anion on n i t r i l e groups can take p l a c e q u i c k l y enough under our r e a c t i o n c o n d i t i o n s to represent a p l a u s i b l e t e r m i n a t i o n s t e p . Of a number o f strong bases s t u d i e d , o n l y triphenylmethylsodium c l e a n l y a b s t r a c t e d t h e a-H o f c y c l o b u t a n e c a r b o n i t r i l e t o g i v e the carbanion:

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

13 13

13 13

1.1.1

HgCn-C H ) (NC H ). MgCC^g)

9

7

5

10

5

5

10

13

0.2

2

Kg(s-i^: H )

7

7

3

7

Mg(S-i-C H )

3

3

2

13

0.2S

2

Mg(S-i-C H )

7

65

-

26

1.0

2

2

?

52

26

1.0

Mg(S-i-C » )

3

26

26

2

-

-

-

26

26

1.0

2

7

Hg(S-i-C H )

3

13

s

?

13

9

3

1.1.1

4

2

n-C H Li, Hg{C^i ) . i-C H SH

5

13

2

13

9

1.1.1

4

n-C H U. Mg(C H ) , i-C H SH

5

n - C ^ l i , MgCC^)^ HNC H

4

3

2

10

-

26

26

1.0

Mg(S-i-C H )(NC H )

9

2

-

13

26

2.0

Mg(S-i-C3H )(NC H )

4

5

l0

10

13

13

1.0

Mg(N-C H )

l0

7

-

13

26

2.0

2

5

Mg(NC H )

s

«WJAI

-

13

13

1.0

10

9

l0

Mg(NC H ) , HNC H

4

2

26

26

1.0

Mg(n-C H ) (NC H )

5

26

26

5

10

1.0

4

9

Mg(n-C H )(NC H )

26

26

1.0

10

Mg(C2H )(NC H )

5

-

13

13

1.0

MgCC^HNCjH^) (d)

5

Lewis Acid (a)

M/1

M moles Monomer, M

M noies Initiator, I

Initiator

64

0.23 0.18

28 23

0.15 Dioxane

20 Dioxane-DMF (2:5)

Toluene

58 Toluene

0.074

0.11 0.20

69 Dioxane-DMF (2:5) Dioxane

0.074

0.20 89 84

0.22 100

0.076

0.096

0.036

0.086

0.23

0.28 (e)

0.105

Dioxane

Dioxane

THF

36

90

Dioxane Dioxane-DMF (1:1)

47

Dioxane

51

88

Dioxane

75

Dioxane

44

0.21

73

(c

inh >

0.41

n

95

% Yield

Dioxane

Toluene

Dioxane

Oioxane

Solvent (b)

Table I. Selected Polymerizations of 1-Bicyclobutanecarbonitrile

Polymerization

HALL ET AL.

c

©

>o

r»»

*4

~4

©

-4

©

ΙΛ

l»»

Ο

Ο

Ο

Ο

Ο

Ο

CM

via C-C

Bond

Opening

ΙΑ

289

Ο

^

·Η

§i

e ο

ο

•H

Ή

ο

ο

ο

io

ο

, io

Ν

\0 Ν

Ν

~

'"iX

u

u

•Η

·Η

«Λ

V) ^

I I

I I

ΙΟ Η

Μ Η

Jg

ΙΟ

Κ)

Ν

Ν

•no

T-i

V

υ υ

I C/J

I Ή

Jft

W) ^

ν_/

Η

ΙΟ

^ «4

ΓΜ

·

β

ΙΛ !>.

ι

Ο (Μ

w

Γ Μ Μ

3» 2» > C?» 3> 3*

g * 2 g 2 g

<

'u»

Μ

Ν

'ΤΛ

<

Μ

Γ

>

'U»

4

Ν

Γ

4

Γ

4

0

>

(Μ Ο»

Ο· Ο»

"ν •> rv

2222222222

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Θ

V*© Θ

£ 2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

a. b.

Ι

4

1:1 Lewis acid: Monomer ratio. A l l runs S ni solvent.

9

Na®

^^C H

NLi

Γ©

S

1Q

13

13

13

2©

-

-

2

dinethylsulfoxide, TMS0 • tetramethylene sulfone.

c. Viscosities at 30*. 0.1%, DMF. d. NC H « DMF - Ν,Ν-dimethylformanide, DMSO -

I

0.5

23

91

e. Viscosity done in DMSO. f. 5 M noies Lewis acid.

THF

Dioxane

0.39 (e)

0.20

to

20.

HALL ET AL.

Polymerization

via C-C

Bond

Opening

291

This r e a c t i o n was confirmed by i s o t o p i c l a b e l l i n g . When c y c l o b u t a n e c a r b o n i t r i l e was i n excess, t h e product, even under m i l d c o n d i t i o n s , was d i c y c l o b u t y l ketone ( v = 1700 cm~l) formed by a r a p i d r e a c t i o n o f carbanion w i t h t h e CN group (Thorpe-Ziegler reaction). c

+

*

csN

o

C=N®


0


C=0

The a n i o n i c p o l y m e r i z a t i o n o f ^ i s t h e r e f o r e analogous t o the a n i o n i c p o l y m e r i z a t i o n o f m e t h a c r y l o n i t r i l e , whose termina­ t i o n a l s o i n v o l v e s Thorpe-Ziegler r e a c t i o n w i t h formation o f c a r bonyl groups (17,18). For m e t h a c r y l o n i t r i l e , t e r m i n a t i o n i n v o l ­ ves b a c k - b i t i n g o f t h e growing carbanion onto a cyano group i n the same polymer c h a i n , w i t h t h e formation o f a six-membered r i n g . For b i c y c l o b u t a n e - l - c a r b o n i t r i l e , six-membered r i n g formation i s s t e r i c a l l y i m p l a u s i b l e and the r e a c t i o n i s i n t e r m o l e c u l a r , as demonstrated i n t h e model r e a c t i o n . Lower y i e l d s o f polymer i n homogeneous s o l u t i o n (DMF, s u l f o l a n e ) , can be a t t r i b u t e d t o t h e higher c o n c e n t r a t i o n s o f a v a i l a b l e CN groups. A l s o , more f r e e i o n s , which a r e more r e a c t i v e and l e s s d i s c r i m i n a t i n g , a r e pre­ sent i n such s o l v e n t s . Synthesis o f a P o l y s u b s t i t u t e d Bicyclobutane - To broaden our c o l l e c t i o n o f bicyclobutane monomers, we have explored t h e u t i l i t y o f z w i t t e r i o n i c c y c l o a d d i t i o n reactions t o synthesize the r e q u i r e d cyclobutane p r e c u r s o r s . Such r e a c t i o n s o f e l e c t r o n r i c h o l e f i n s w i t h electron-poor o l e f i n s were s t u d i e d by Brannock and coworkers Ç19). To o b t a i n s u b s t i t u e n t s a t the proper l o c a ­ t i o n s on t h e cyclobutane r i n g , we used t r i s u b s t i t u t e d e l e c t r o p h i l i c o l e f i n s (20) i n t h e f o l l o w i n g r e a c t i o n sequence: Polysubstltutai

fcicyciobutjncs

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

292

RING-OPENING POLYMERIZATION

Trimethyl 4,4-dimethylbicyclobutane-l,2,2-tricarboxylate a white c r y s t a l l i n e s o l i d obtained by t h i s r o u t e , proved t o be u n r e a c t i v e i n e i t h e r homo- o r c o p o l y m e r i z a t i o n by r a d i c a l o r a n i o n i c r o u t e s . Therefore t o o many s u b s t i t u e n t s on t h e b i c y c l o ­ butane r i n g render the nucleus unpolymerizable, undoubtedly due to s t e r i c hindrance. We attempted t o l e s s e n t h e degree o f s t e r i c hindrance by c a r r y i n g out an analogous s e r i e s o f r e a c t i o n s beginning w i t h Ν,Ν-dimethylpropenylamine o r w i t h Ν,Ν-dimethylvinylamine. The former c o u l d be c a r r i e d through t o t r i m e t h y l - 4 - m e t h y l b i c y c l o b u t a n e - 1 , 2 , 2 - t r i c a r b o x y l a t e JLjl, but not i n the necessary p u r i t y . Ν,Ν-dimethylvinylamine, when allowed t o r e a c t w i t h t r i c a r b o m e t h oxyethylene, gave no cyclobutane (21). We conclude t h a t t h e r i n g methyl s u b s t i t u e n t s which f a v o r formation o f the r e q u i r e d cyclobutane intermediat ^ cyclobutan to h steri hindrance i n the f i n a l cyclobutane formation doe Bicyclo[2.1.0]pentane Monomers - E a r l i e r we showed t h a t b i c y c l o [ 2 . 1 . 0 ] p e n t a n e - l - c a r b o n i t r i l e 2 underwent a n i o n i c polymer­ i z a t i o n £3). Another monomer c o n t a i n i n g t h i s s t r a i n e d s t r u c t u r e has been synthesized r e c e n t l y from 4-chloro-1,2-butadiene and a c r y l o n i t r i l e (22).

We p r e f e r r e d t o f i n d another route which avoided t h e monovinylacetylene r e q u i r e d t o make 4-chloro-1,2-butadiene (23), and have devised a route based on 2 - b u t y n e - l , 4 - d i o l :

.CN

CH,C1

CH OSi(CH ) 2

CN

KOC(CH_) y 3

)

C H ^

IS

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

3

3

20.

HALL ET AL.

Polymerization

via C-C

Bond

Opening

293

4-Hydroxyl-l,2-butadiene (24,25) was converted t o ace­ t a t e 18 (26) and cycloadded t o a c r y l o n i t r i l e (27). H y d r o l y s i s of cycloadduct 19 gave a l c o h o l 20, which was best p u r i f i e d by conversion t o the t r i m e t h y l s i l y l d e r i v a t i v e 21, s p i n n i n g band d i s t i l l a t i o n , , and r e g e n e r a t i o n . I t was transformed by t h i o n y l c h l o r i d e t o c h l o r i d e ^5, which was converted t o monomer 1£ (22) Although l o n g e r , t h i s s y n t h e s i s can be r e a d i l y s c a l e d up and gave comparable y i e l d s . Monomer 16_ underwent f r e e r a d i c a l p o l y m e r i z a t i o n i n 59% y i e l d t o g i v e polymer w i t h t h e rearranged s t r u c t u r e 22.

The expected 1,5-polymerization t o g i v e s t r u c t u r e 24 was immediately excluded because t h e nmr and cmr s p e c t r a o f t h e polymer showed t h e presence o f methyl groups on a double bond but no v i n y l protons. The 1,3-polymerized s t r u c t u r e 25 was sim­ i l a r l y excluded. The C-H c o u p l i n g c o n s t a n t s , as determined by gated d e c o u p l i n g , favored s t r u c t u r e 22 over s t r u c t u r e 23. Car­ bons 4 and 5 o f 22 should have s i g n i f i c a n t l y d i f f e r e n t i a e - H c o u p l i n g c o n s t a n t s , as found, whereas carbons 9 and 12 o f 2^ would be expected t o show almost i d e n t i c a l c o u p l i n g constants (Table I I ) . 13

Table I I , Cmr Spectrum o f Poly-3-Methylenebicyclo[2.1.0]pentane1 - c a r b o n i t r i l e 22. Carbon Assignment 1 2 3 4 5 6 7

S h i f t (6) Number o f Hydrogens

J13

C-H(±1.5Hz)

40.6 142.3 139.5 41.9 34.3 10.7 122.0

142 129 127

Our preference f o r 22 i s a l s o supported by the c o u p l i n g constants found i n the followîftg model compounds.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

294

RING-OPENING POLYMERIZATION

G:

2 J13, C H = 140 Hz

CH,

-GHC1

CH-* 3

-€HC1

5

J13, C H - 127.3 5

(Ref. 28)

Hz

(Ref. 29)

The d i f f e r e n c e i n t h e chemical s h i f t s o f t h e methylene carbons 4 and 5 i n t h e cmr i s a l s o more s u p p o r t i v e o f s t r u c t u r e 22. Free r a d i c a l c o p o l y m e r i z a t i o n s o f monomer ^5 w i t h styrene gave t h e same isomerized s t r u c t u r e f o r t h e i n c o r p o r a t e d monomer u n i t s . The copolymer was composed o f 68% monomer 13 and 32% styrene. Both the homo- and copolymers were s o l u b l e i n DMSO, s u l f o lane and acetone and formed f i l m s r e a d i l y when c a s t from acetone. Both t h e homo and copolymers a u t o x i d i z e d a t room temperature and y e l l o w r a p i d l y when heated. The a u t o x i d a t i o n o f cyclobutenec o n t a i n i n g polymers has been shown t o be very f a c i l e (30). The mechanism o f p o l y m e r i z a t i o n i s b e l i e v e d t o be:

R- +

Δ

CN

CH„

CN

etc. H-ShTf R-CHI

[R-CH

2

26 The a d d i t i o n o f the growing r a d i c a l t o t h e double bond i s a n a l ­ ogous t o the f i r s t step o f 1-5 a d d i t i o n , but a p p a r e n t l y c o n f o r ­ mational r e s t r a i n t s caused by the cyclobutane r i n g prevents normal c y c l o p r o p y l r i n g opening. Instead a hydrogen s h i f t r e ­ s u l t i n g i n a r e s o n a n c e - s t a b i l i z e d r a d i c a l takes p l a c e . The p o s s i b i l i t y o f i n i t i a l thermal i s o m e r i z a t i o n f o l l o w e d by polymer­ i z a t i o n was excluded because monomer 13 when heated i n t h e presence o f DPPH d i d not i s o m e r i z e o r ^ o l y m e r i z e .

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

20.

HALL ET AL.

Polymerization via C-C Bond Opening

295

The a n i o n i c p o l y m e r i z a t i o n o f ^ was b r i e f l y examined. When 13 was t r e a t e d w i t h η-butyllithium, a low y i e l d o f oligomers was obtained which appeare m a t e r i a l was not isomerize presence o f f r e e r a d i c a l s , an a d d i t i o n a l b i t o f evidence d i s ­ f a v o r i n g s t r u c t u r e 18 f o r t h e f r e e r a d i c a l polymer o f Acknowledgement s Support o f t h i s r e s e a r c h by the A s a h i E l e c t r o c h e m i c a l Co., U. S. Army Research O f f i c e , Standard O i l Company o f Indiana, The Eastman Kodak Company and t h e Fulbright-Hayes Foundation i s g r a t e f u l l y acknowledged. We a l s o wish t o thank Dr. J . C. Kauer o f t h e duPont Co. f o r help w i t h t h e c y c l o a d d i t i o n r e a c t i o n o f 1acetoxy-2,3-butadiene and a c r y l o n i t r i l e , and Dr. R. B. Bates f o r helpful discussions. Experimental The i n f r a r e d s p e c t r a were obtained on a Perkin-Elmer 337 g r a t i n g i n f r a r e d spectrophotometer u s i n g KBr, f l u o r o l u b e , HCBD, or NaCl p l a t e s . Nmr s p e c t r a were obtained on a V a r i a n T60 spec­ trometer, cmr s p e c t r a were obtained on a Bruker WH-90 FT. Mass s p e c t r a data were measured on a H i t a c h i Perkin-Elmer RMU-6E double f o c u s i n g instrument. Gas chromatograms were obtained on a V a r i a n Aerograph 1700 instrument. Elemental a n a l y s i s was done by G a l b r a i t h L a b o r a t o r i e s , Inc., o r by Chemalytics, I n c . Reagents - B i c y c l o b u t a n e - l - c a r b o n i t r i l e ^ (31), t r i m e t h y l 3-trimethylammonio-4,4-dimethylcyclobutane-l,2,2-tricarboxylate t r i f l u o r o m e t h a n e s u l f o n a t e ^ and t r i m e t h y l 3-trimethylammonio-4methylcyclobutane-1,2,2-tricarboxylate trifluoromethanesulfonate were prepared by l i t e r a t u r e methods (18). Cyclobutanecarbonit r i l e , obtained from Ash-Stevens Company, was pure as r e c e i v e d . Anionic Polymerization - In a t y p i c a l anionic polymerization o f b i c y c l o b u t a n e - l - c a r b o n i t r i l e , a 100 ml t e s t tube was f i l l e d w i t h n i t r o g e n and 5 ml o f s o l v e n t . Dialkylmagnesium s o l u t i o n , and 1 ml o f c o - c a t a l y s t were added and allowed t o r e a c t a t 28° f o r 0.5 hr. B i c y c l o b u t a n e - l - c a r b o n i t r i l e , 1 ml (14 mmoles), was added t o t h i s c a t a l y s t s o l u t i o n . A f t e r a short w h i l e , a vigorous

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

296

RING-OPENING

POLYMERIZATION

r e a c t i o n took p l a c e and the polymer p r e c i p i t a t e d . The polymer­ i z a t i o n r e a c t i o n was stopped by a d d i t i o n o f methanol c o n t a i n i n g a small amount o f h y d r o c h l o r i c a c i d . The polymer thus obtained was washed w i t h methanol, f i l t e r e d , and d r i e d i n vacuo a t 28°. A white powder was always obtained; no f i b r o u s products were ob­ served. To o b t a i n i r s p e c t r a f r e e o f water, KBr p e l l e t s o f the polymers were made and the i r taken. The p e l l e t was then heated to 70°C under vacuum over P2O5 f o r 24-48 hrs and the i r again taken. This was repeated u n t i l there was no change i n the i r spectra. This procedure e l i m i n a t e d i r a b s o r p t i o n a t VL600 cm" . These p o l y m e r i z a t i o n c o n d i t i o n s were s u i t a b l e f o r the pre­ p a r a t i o n o f very h i g h molecular weight p o l y m e t h a c r y l o n i t r i l e . P o l y m e r i z a t i o n o f m e t h a c r y l o n i t r i l e (50 mmoles) w i t h 1 mmole o f magnesium d i ( i s o p r o p y l m e r c a p t i d e i dioxan 69 81 and 97% y i e l d s o f polyme magnesium gave 75% y i e l d and di-n-butymagnesium 63% y i e l d . I n herent v i s c o s i t i e s ranged between 2.0 and 3.0. Model Termination Reaction - T r i t y l s o d i u m was prepared as f o l l o w s : Under n i t r o g e n , a sodium d i s p e r s i o n (50% i n x y l e n e ) , 2 g, was washed w i t h n-hexane t w i c e , f i l t e r e d , and added w i t h s t i r r i n g to a s o l u t i o n o f 4.2 g (0.015 moles) o f t r i t y l c h l o r i d e i n 80 ml o f d r y ether. The mixture turned red a f t e r s e v e r a l hours and was s t i r r e d f o r 16 hours a t 28°. A f t e r f i l t r a t i o n under n i t r o g e n , the c o n c e n t r a t i o n s o f t r i t y l s o d i u m was determined by a c i d t i t r a t i o n to be 0.23 N. To an ether s o l u t i o n o f triphenylmethylsodium under n i t r o g e n and cooled t o 0°C was added the d e s i r e d amount o f cyclobutanec a r b o n i t r i l e . Reaction took p l a c e q u i c k l y and a p r e c i p i t a t e was formed. A f t e r 1 hour at 0°C, the r e a c t i o n product was f i l t e r e d under n i t r o g e n and washed w i t h 5 ml o f ether ( d i s t i l l e d over Na d i s p e r s i o n and d r i e d over molecular s i e v e s ) . This washing was repeated u n t i l the f i l t r a t e was no longer red ( u s u a l l y 5 t i m e s ) . a - S o d i o c y c l o b u t a n e c a r b o n i t r i l e (or i t s mixture w i t h the s o d i o d e r i v a t i v e o f d i c y c l o b u t y l k e t o n e or a - c y a n o d i c y c l o b u t y l ketone, i n those r e a c t i o n s i n which excess c y c l o b u t a n e c a r b o n i t r i l e was present) was obtained as a s l i g h t l y r e d - c o l o r e d , very a i r - s e n s i ­ t i v e powder. I t was r e d i s s o l v e d i n THF t o g i v e a deep red s o l u t i o n ( s t a b l e w i t h time) and decomposed w i t h 0.5 ml o f D2O. The products were e x t r a c t e d w i t h e t h e r , d r i e d and evaporated. Triphenylmethane was recovered by d r y i n g and evaporating the o r i g i n a l ether f i l t r a t e . 1 - D e u t e r o c y c l o b u t a n e c a r b o n i t r i l e and d i c y c l o b u t y l ketone were c o l l e c t e d by p r e p a r a t i v e gc, and the pure f r a c t i o n s were analyzed by i r , nmr, and mass spectrometry. The ketone was analyzed. 1

(From workup w i t h H 0) C a l c ' d . f o r C H 0 : C, 78.21; H, 10.21; N, 0. Found: C, 78.36; H, 10T3Ô; N, 0. 2

q

14

(From workup w i t h D 0) C a l c ' d . f o r CgH.-DO: C, 77.64; H(D), 10.86; N, 0. Found: C, 77.89; H(D), 10748; N, 0. 2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

HALL ET AL.

20.

Polymerization

via C-C

Bond

Opening

297

The mass spectrum showed the deuterated sample t o be a mixture o f monodeuterated (68%), d i d e u t e r a t e d (19%), and undeuterated (13%) m a t e r i a l . When the r a t i o o f t r i t y l s o d i u m t o cyclobutanecarboni t r i l e was changed from 1:1 t o 1:2 t h e r a t i o o f cyclobutanecarb o n i t r i l e t o d i c y c l o b u t y l ketone went from 20:1 t o 1:20. Several other bases were t r i e d . Trityllithium-TMEDA a t 60°C a l s o caused predominantly a-H a b s t r a c t i o n from cyclobutanecarboni t r i l e . Diethylmagnesium showed some a-H a b s t r a c t i o n but r e s u l t e d i n mostly a d d i t i o n t o the n i t r i l e . The f o l l o w i n g bases a l s o r e ­ s u l t e d i n a d d i t i o n products: n - C ^ g L i , n-C^gLi-TMEDA, t - C ^ g L i , a l l a t -78°C and ( 1 - C 3 H 7 ) N L i , ( C H N ) M g , a t 28°C. The l a s t two a l s o causing recovery o f unreacted c y c l o b u t a n e c a r b o n i t r i l e . The f o l l o w i n g bases showed no r e a c t i o n as determined by deuterium l a b e l l i n g experiments: ( C H ) C L i , ( C H ) C L i ( C H ) M g , a t 60°C, [CH ) S i ] N © Na © at -78°C 28°C Trimethyl 4,4-Dimethylbicyclobutane-l,2,2-tricarboxylat A 250 ml three-necked f l a s k f i t t e d w i t h a mechanical s t i r r e r , a n i t r o g e n i n l e t and a s i n t e r e d g l a s s i n l e t , was heated t o remove moisture and cooled under n i t r o g e n . A 57% d i s p e r s i o n o f sodium hydride i n mineral o i l (1.95 g, 0.0465 mole) was washed twice w i t h 25 ml o f low b o i l i n g petroleum e t h e r . The sodium hydride was covered w i t h 50 ml o f t e t r a h y d r o f u r a n d r i e d over molecular s i e v e s . Then 10.0 g (0.0215 mole) o f t r i m e t h y l 3-trimethylammonio-4,4-dimethyl-l,2,2-cyclobutanetricarboxylate trifluoromethane­ s u l f o n a t e (14) was added a t room temperature. The white s l u r r y was heated t o g e n t l e r e f l u x f o r 1 hour, causing e v o l u t i o n o f 0.935 1 o f gas ( c a l c ' d . 0.965 1 ) . The r e a c t i o n mixture was cooled and the supernatent l i q u i d was decanted. The remaining s a l t s and unreacted sodium h y d r i d e were washed w i t h a small q u a n t i t y o f t e t r a h y d r o f u r a n . To organic l a y e r s was added s o l i d carbon d i o x i d e . The décantation and the a d d i t i o n o f C 0 before t h e a d d i t i o n o f t h e s o l u t i o n o f sodium c h l o r i d e i n water were chosen t o minimize the r e a c t i o n o f water w i t h the excess o f sod­ ium h y d r i d e , because the base which i s formed may a t t a c k the b i ­ cyclobutane a l r e a d y prepared o r g i v e products i n which the c a r bomethoxy group has been r e p l a c e d by a methoxy group (compounds and 2£). The o r g a n i c l a y e r was then poured i n t o a mixture o f i c e , ether, and a saturated s o l u t i o n o f sodium s u l f a t e i n water and shaken. The ether l a y e r was separated, and the water l a y e r was e x t r a c t e d t w i c e w i t h 25 ml o f ether. The combined ether e x t r a c t s (200 ml) were back-washed w i t h a small amount o f water, d r i e d w i t h s t i r r i n g over magnesium s u l f a t e d u r i n g 10 minutes, f i l t e r e d and r o t a r y evaporated (bath temperature 30°C). Evapor­ a t i o n f o r 60 minutes a t 0.2 mm Hg gave a y e l l o w o i l , 2.63 g, (48%) which by gas chromatography was shown t o have t h r e e peaks. C r y s t a l l i z a t i o n from d i e t h y l ether a t -50° gave a 34% y i e l d o f t r i m e t h y l 4 , 4 - d i e m t h y l b i c y c l o b u t a n e - l , 2 , 2 - t r i c a r b o x y l a t e as white c r y s t a l s ; m e l t i n g p o i n t 45-46°C ( l i t . m.p. 44-46°C). A mixed m e l t i n g p o i n t w i t h an a u t h e n t i c sample was not depressed. 2

5

6

3

3

5

3

10

2

6

5

3

2

5

2

2

2

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

298

RING-OPENING POLYMERIZATION

A n a l . Calc'd f o r C H,.0.: C, 56.25; H, 6.29; 0, 37.46. Found: C, 56.16; H, 6731; 0, 37.61. Nmr ( C D C I 3 , TMS, τ) 6.30 ( s , 6H, COOMe) 6.35 ( s , 3H, COOMe) 6.75 ( s , 1H, bridgehead) 8.55 ( s , 3H, C H 3 ) 8.95 ( s , 3H, CH ) i r (KBr, cm" ) 1710 (COOMe). Mass spectrum: parent peak a t 256 ( c a l c . = 256). 19

A

3

1

The other two compounds i s o l a t e d by p r e p a r a t i v e gas chromato­ graphy, were: CH

/

3

CH3

\

^

C

0

Χ , Χ

0

C

H

C 0 0 C H

3

3

OCH3

A n a l . Calc'd f o r C H 0 : C, 57.38; H, 7.88; Found: C, 57.47; H, 7.70. Nmr spectrum ( C D C I 3 , TMS, τ) 6.25 ( s , 6 H , COOMe) 6.65 ( s , 3 H , 0 C H ) 8.65 ( s , 3 H , - Me) 6.156.85 (m, 3 H ) 9.00 ( s , 3 H , Me); i r ( l i q u i d , cm" ) 1710 (COOMe); mass spectrum: parent peak: 231 ( c a l c ' d f o r C l l H i s O s = 230). n

1

8

5

3

1

C 0 0 C H

C H

3

3

C00CH C H

° 3

3

28

A n a l . Calc'd f o r C H 0 : C, 54.16; H, Found: C, 54.52; H, 6;89; N t r a c e : nmr TMS, τ) 5.70 ( s , 1H) 6.30 ( t , 9H, COOMe) 8.80 ( s , 3H, Me) 6.55, 8.90 ( s , 3H, Me); (COOMe); mass spectrum: parent peak: 288 X

C

H

13 20°7 "

2 8 8

6.99; N, 0; spectrum, ( C D C I 3 , 5.74, 6.60 ( s , 3H) i r KBr, cm" ) 1710 (calc'd f o r r

>·

These products may r e s u l t from r e a c t i o n o f b i c y c l o b u t e n e ^ w i t h 0CH ~, perhaps formed by a r e a c t i o n o f H w i t h COOCH groups. S i m i l a r r e s u l t s were obtained u s i n g 1,2-dimethoxyethane as s o l v e n t . Using N-methylpyrrolidone caused h i g h e r y i e l d s o f com­ pounds 27 and 28. L i t h i u m hydride r e s u l t e d i n lower y i e l d s o f 15 i n both t e t r a h y d r o f u r a n and N-methylpyrrolidone. The use o f sodium methoxide gave o n l y compound 27 and no b i c y c l o b u t a n e . T r i m e t h y l - 4 - M e t h y l b i c y c l o b u t a n e - l , 2 , 2 - T r i c a r b o x y l a t e - In a 50 ml 3-necked f l a s k c o n t a i n i n g a s t i r r i n g bar and f i t t e d w i t h a r e f l u x condenser l e a d i n g t o a n i t r o g e n i n l e t were p l a c e d , a f t e r d r y i n g , 0.42g o f a 57% sodium hydride d i s p e r s i o n i n m i n e r a l o i l 6

3

3

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

20.

HALL ET AL.

Polymerization

via C-C

Bond

Opening

299

(10 mmol); t h e h y d r i d e was washed t w i c e w i t h 15 ml o f pentane. To t h e c l e a n h y d r i d e was added a s o l u t i o n o f t r i m e t h y l 3 - t r i methylammonio-4-methylcyclobutane-l,2,2-tricarboxylate t r i f l u o r o ­ methanesulfonate (2.26g, 5 mmol) i n N-methylpyrrolidone (10 ml) and t h e n i t r o g e n i n l e t was r e p l a c e d by a wet t e s t meter. A f t e r 25 minutes 59 ml (50% o f t h e o r e t i c a l ) o f gas had e v o l v e d , and t h e r e a c t i o n mixture was poured i n t o a mixture o f i c e water-ether. The e t h e r was washed t w i c e by 40 ml o f water, d r i e d w i t h s t i r r i n g f o r 5 minutes over magnesium s u l f a t e , f i l t e r e d and evaporated. The remaining o i l c o n s i s t e d mainly o f t h e d e s i r e d b i c y c l o b u t a n e . Nmr (CDC1 ) τ6.27, 6.30 and 6.32 (3s, 9, COOMe), 6.77 (d, J=1.5Hz, 1, bridgehead), 8.21 (d o f q, J = 1.5Hz and 5.5Hz, 1, r i n g proton) and 8.63 (d, J = 5.5Hz, 3, Me). From t h e c o u p l i n g constant between the methyl and t h e r i n g and t h e bridgehead protons t h e exo c o n f i g ­ u r a t i o n i s assigned t o t i o n by r e c r y s t a l l i z a t i o n matography d i d n o t succeed. 4-Chloro-2-butyne-l-ol - The procedure o f B a i l e y and F u j i wara (24) but r e p l a c i n g benzene w i t h dichloromethane, gave a 50% y i e l d , b.p. 70°C (20 mm Hg) from t e c h n i c a l grade 2 - b u t y n e - l , 4 - d i o l (Aldrich). 1,2-Butadien-4-o1 - The procedure o f B a i l e y and P f e i f e r (25) was used w i t h m o d i f i c a t i o n s . To 1800 ml o f anhydrous e t h y l e t h e r was added 42 gm o f l i t h i u m aluminum h y d r i d e (1.1 mole). The r e a c t i o n was c o o l e d i n an i c e bath w i t h s t i r r i n g and 155.24 gm o f 4-chloro-2-butyne-l-01 (1.48 mole) i n 300 ml o f anhydrous e t h y l e t h e r was added dropwise over a p e r i o d o f 3 h r s . The r e a c t i o n was then allowed t o warm t o room temperature and s t i r r e d f o r 18 h r s . The excess l i t h i u m aluminum h y d r i d e was destroyed by c a r e ­ f u l l y adding dropwise a s a t u r a t e d s o l u t i o n o f sodium s u l f a t e i n water u n t i l t h e lithium-aluminum s a l t s formed white p e l l e t s . The mixture was f i l t e r e d and t h e p e l l e t s washed w i t h e t h e r . The e t h e r was r o t a r y evaporated and t h e r e s i d u e d i s t i l l e d t o g i v e a 68% y i e l d o f l , 2 - b u t a d i e n - 4 - o l (79.8 gm). b.p. 69°C (45 mm Hg). 3

l-Acetoxy-2,3-butadiene - The procedure o f W. H. Carothers (26) was used t o convert t h e a l c o h o l t o the a c e t a t e . l - A c e t o x y - 2 , 3 - b u t a d i e n e / A c r y l o n i t r i l e C y c l o a d d i t i o n - The procedure o f H. K. H a l l , J r . , and R. E. Yancy (22) was used w i t h the convenient m o d i f i c a t i o n o f u s i n g l i q u i d n i t r o g e n i n s t e a d o f a Dry Ice-acetone bath i n t h e degassing procedure. F o r example, 9.39 gm o f a c r y l o n i t r i l e , 4.96 gm o f 1-acetoxy-2,3-butadiene, 8.40 gm o f benzene, and 0.50 gm o f 2,5-di-tert-butylhydroquinone were p l a c e d i n an a c i d washed Pyrex tube, the tube was degassed and heated t o 200°C a t the u n i v e r s i t y High Pressure Laboratory f o r 8 h r s . The r e a c t i o n was allowed t o c o o l , poured i n t o 100 ml o f e t h y l e t h e r and f i l t e r e d . The e t h e r was r o t a r y evaporated and t h e r e s i d u e d i s t i l l e d t o g i v e cycloadducts i d e n t i c a l t o those r e p o r t e d by C r i p p s (27). The 47.9% y i e l d i s l e s s than t h a t r e ­ p o r t e d by C r i p p s , prôFably because o f t h e g r e a t e r d i f f i c u l t y i n

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

300

RING-OPENING

POLYMERIZATION

m a i n t a i n i n g a uniform temperature and t h e use o f benzene as a d i ­ l u e n t , which i s necessary f o r reasons o f s a f e t y (32). The use o f the g l a s s tube does not seem t o have any advantage over an auto­ clave. ( 2 , 3 - B u t a d i e n y l o x y ) t r i m e t h y l s i l a n e - Hexamethyldisilazane 25g (0.15 mole), and 21g (0.30 mole) o f l,2-butadiene-4-ol were mixed f o r 1 h r , during which time the temperature rose t o 60°C. C h l o r o t r i m e t h y l s i l a n e , 0.5 m l , was added and the mixture s t i r r e d f o r 0.5 h r more. The mixture was then heated t o 120°C. (This was found h e l p f u l i n p r e v e n t i n g u n c o n t r o l l a b l e r e a c t i o n s i n the c y c l o a d d i t i o n s t e p ) . The compound was then f i l t e r e d and d i s t i l l ­ ed a t 60°C (60 mm Hg) t o o b t a i n 31.96g (96%) o f product. C y c l o a d d i t i o n s o f S u b s t i t u t e d Aliènes w i t h A c r y l o n i t r i l e With i s o c h l o r o p r e n e , the 3-methylene-2-chloromethylcyclobutanecarb o n i t r i l e 15 and l - c h l o r o - l - c y c l o h e x e n e - 4 - c a r b o n i t r i l was obtainea i n 21% y i e l d With l , 2 - b u t a d i e n e - 4 - o l , 3 - ( g - h y d r o x y e t h y l i d e n e ) - l - c y c l o b u t a n e c a r b o n i t r i l e , c i s and trans-3-methy1ene-2-hydroxymethy1-cyclobutanecarbonitrile were obtained i n 29.7% y i e l d a f t e r d i s t i l ­ l a t i o n on a s p i n n i n g band column at 60-70°C (0.01 mm Hg). The two compounds can be separated by p r e p a r a t i v e gc o r by s i l y l a t i o n , f o l l o w e d by c a r e f u l d i s t i l l a t i o n . A n a l . C a l c ' d f o r C H 0N: C, 68.27; H, 7.37; N, 11.37. Found: C, 67.97; H, 7.80; N, 11.58. 7

Q

In the case o f ( 2 , 3 - b u t a d i e n y l o x y ) t r i m e t h y l s i l a n e , the mater­ i a l was d i s t i l l e d on a s p i n n i n g band column twice t o y i e l d two main f r a c t i o n s i n an o v e r a l l y i e l d o f 47%. The f i r s t f r a c t i o n w was found t o be 21 by NMR, IR and mass s p e c t r a (43°C a t 0.01 mm Hg). A n a l . C a l c ' d f o r C H 0 N S i : C, 61.49; H, 8.77; N, 7.17. Found: C, 61.28: H, 8.81: N. 7.36. The second f r a c t i o n (60°C a t 0.01 mm Hg) was found t o be the s i l y l ether o f 3 - ( 3 - h y d r o x y e t h y l i d e n e - l - c y c l o b u t a n e c a r b o n i t r i l e by nmr, i r and mass s p e c t r a . A n a l . C a l c ' d f o r C 17 > 61.49; H, 8.77. Found: C, 61.48; H, 8.75. I n two out o f s i x t e e n runs d u r i n g t h i s c y c l o a d d i t i o n , u n c o n t r o l l a b l e exothermic r e a c t i o n s occurred. The method o f C r i p p s i s not usable w i t h i s o c h l o r o p r e n e due to the known m e t a l - c a t a l y z e d rearrangement o f the compound (23, 26). The presence o f a s t a i n l e s s s t e e l s u r f a c e a l s o r e s u l t e d i n no cycloadduct w i t h ( 2 , 3 - b u t a d i e n y l o x y ) t r i m e t h y l s i l a n e and i n lower y i e l d s w i t h 2 , 3 - b u t a d i e n - l - o l . S i l y l compounds have been r e p o r t e d to i n t e r a c t w i t h s t a i n l e s s s t e e l ( 3 3 ) . 3-Methylene-2-chloromethylcyclobutanecarbonitrile 15 - S i l y l compound 2^, 2g, was hydrolyzed i n 95% ethanol by the acfâition o f a t r a c e o f base. The r e s u l t i n g a l c o h o l 20 was i s o l a t e d and d r i e d over MgSO^ i n ether. The a l c o h o l was then converted t o the c h l o r i d e 15 by the dropwise a d d i t i o n o f p u r i f i e d t h i o n y l c h l o r i d e i n 80% y i e l d . T h i s was converted t o monomer 16 as be­ f o r e (22). ^ l ô

1 7

H

O N S i :

c

1 0

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

20.

HALL ET AL.

Polymerization

via

C-C

Bond Opening

301

Free R a d i c a l P o l y m e r i z a t i o n - 0.1483g o f 3-msthylene-[2.1.0]b i c y c l o p e n t a n e - l - c a r b o n i t r i l e ^6 and 0.5 ml o f s u l f o l a n e were p l a c e d i n a d r i e d f l a s k along w i t h a c r y s t a l o f AIBN o r benzoyl p e r o x i d e . The f l a s k was f i t t e d w i t h a rubber septum, f l u s h e d w i t h argon, and heated at 70°C f o r 15 h r s . The s o l u t i o n was then poured i n t o methanol, c o n t a i n i n g a t r a c e o f 2 , 5 - d i - t e r t - b u t y l hydroquinone, f i l t e r e d , d i s s o l v e d i n acetone, r e p r e c i p i t a t e d i n e t h y l e t h e r , f i l t e r e d , and d r i e d over P^Os under f u l l vacuum at room temperature, a f t e r f l u s h i n g w i t h n i t r o g e n . The r e s u l t i n g polymer was obtained i n 59% y i e l d , n = 0.95 at 30°C (0.396g/ lOOcc i n acetone). F l e x i b l e f i l m s were c a s t from acetone. i n h

A n a l . C a l c ' d f o r C7H7N: C, 79.98; H, 6.71; Found: C, 80.04; H, 6.79; N, 13.25.

N, 13.32.

The c o p o l y m e r i z a t i o [2.1.0]pentane-l-carbonitril 0.3160 gm o f 3 - m e t h y l e n e - b i c y c i O [ 2 . 1 . 0 ] p e n t a n e - l - c a r b o n i t r i l e (3.006 χ 10" moles), 0.3166 gm o f f r e s h l y d i s t i l l e d styrene (3.Ο4Ο χ ΙΟ" moles) i n 1.75 ml o f s u l f o l a n e w i t h AIBN a t 70°C f o r 23 h r s . A f t e r workup and d r y i n g , 0.3952 gm o f polymer was obtained which showed the presence o f both monomer u n i t s was confirmed by i r , nmr, and cmr. η. ^ = 0.34 at 30°C(0.445g/100cc). 3

3

Analysis:

C = 81.91; Η = 7.04;

Ν =

8.95.

The a n a l y s i s i s low due t o a u t o x i d a t i o n . A n a l y s i s when e x t r a ­ p o l a t e d t o 100% and nmr i n t e g r a t i o n i n d i c a t e s a r a t i o o f 2.2 t o 1 o f b i c y c l o monomer t o styrene monomer i n c o r p o r a t e d i n t o the polymer« Anionic Polymerization of 3-Methylene[2.1.0]Bicyclopentane1 - C a r F o n i t r i l e - The same procedure as used on [2.1.0]bicyclopent a n e c a r b o n i t r i l e 2 (3) was used t o give a 20% y i e l d o f y e l l o w o i l , which was analyzed by nmr t o g i v e the r e s u l t s mentioned i n the D i s c u s s i o n . When [ 2 . 1 . 0 ] b i c y c l o p e n t a n e c a r b o n i t r i l e was used, polymer was formed i n 81% y i e l d w i t h η . , 0.24 (DMF), as d e s c r i b ­ ed p r e v i o u s l y ( 3 ) . 1

Literature Cited 1. Professor of Nutrition and Food Sciences, University of Ariz. Tucson, Arizona 85721. 2. Hall, Jr., Η. K.; and Ykman, P.; J. Polym. Sci., Macro Re­ views (1976), 11, 1. 3. Hall, Jr., Η. K.; Macromol. (1971), 4, 139. 4. Closs, G. L.; Kaplan, L. R.; and Bendall, V. I.; J. Am. Chem. Soc. (1967), 89, 3376. 5. Koeberg-Telder, Α.; and Cerfonfain, H.; J.C.S., Perkin II, 1974, 1206. 6. Nametkin, N. S.; Finkelshtein, E. Sh.; Yatsenko, M. S.; Portnykh, Ε. B.; Vdovin, V. M.; Vysokomol. Soedin.; Ser. Β (1973), 15, 868. Chem. Abst., (1974), 81, 64012k.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

7. Wiberg, Κ. B.; Upton, Jr., E. C.; and Burgmaier, G. J.; J. Amer. Chem. Soc. (1969), 91, 3372. 8. Gassman, P. G.; Topp, Α.; Keller, J. W.; Tetrahedron Letters, 1969, 1093. 9. Scott, W. B.; Pincock, R. E.; J. Amer. Chem. Soc. (1973), 95, 2040. 10. Pincock, R. E.; Schmidt, J.; Scott, W. B.; Can. J. Chem. (1972), 50, 3958. 11. Takahashi, T.; J. Polym. Sci., A-1, (1968), 6, 403. 12. Lishanskii, I. S.; Linogradova, N. D.; Guliev, A. M.; Zak, A. C.; Zvyagina, A. B.; Kol'tav, A. I.; Fomina, 0. S.; Khachaturov, A. S.; Sin., Str. Svoistva, pulm., 1970, 35: Chem. Abst. (1972) 76, 113671g. 13. Ohara, 0.; Aso, C.; and Kunitake, T.; Nippon Kagakukuishi, 1973, 602. 14. Joh, Y.; Yoshihara, T.; Kotake, Y.; Imai, Y.; and Kurihara, S.; J. Polym. Sci., A-1, (1967), 5, 2503 15. Joh, Y.; Kurihara, S.; Sakurai, T.; Imai, Y.; Yoshihara, T.; J. Polym. Sci., A-1, (1970), 8, 377. Blanchard, Jr., E. P.; and Cairncross, Α.; J. Amer. Chem. Soc., (1966), 88, 487. 17. Joh, Y.; Hoshihara, T.; Kurihara, S.; Sakurai, T.; and Tom­ ita, T.; J. Polym. Sci., A-1, (1970), 8, 1901. 18. Tsvetanov, C.; and Panazotov, I.; European Polymer J. (1975), 11, 209. 19. Brannock, K. C.; Bell, Α.; Burpitt, R. D.; Kelly, C. Α.; J. Org. Chem. (1964), 29, 801. 20. Hall, Jr., H. K.; Ykman, P.; J. Amer. Chem. Soc. (1975), 97, 800. 21. Glogowski, M. E., unpublished results. 22. Hall, Jr., H. K.; and Yancy, R. E.; J. Org. Chem. (1974), 39, 3862. 23. Carothers, W. H.; Berchet, G. J.; Collins, A. M.; J. Amer. Chem. Soc. (1932), 54, 4066. 24. Bailey, W. J.; and Fujiwara, F.; J. Amer. Chem. Soc. (1955), 77, 165. 25. Bailey, W. J.; and Pfeifer, C. P.; J. Org. Chem. (1955), 20, 1337. 26. Carothers, W. H.; and Berchet, G. J.; J. Amer. Chem. Soc. (1933), 55, 2807. 27. Cripps, H. N.; Williams, J. K.; and Sharkey, W. H.; J. Amer. Chem. Soc. (1959), 81, 2723. 28. Hill, Ε. Α.; and Roberts, J. D.; J. Amer. Chem. Soc. (1967), 89, 2047. 29. Hüther, H.; and Brune, Η. Α., Org. Magn. Res. (1971), 3, 737. 30. Wu, C. C., and Lenz, R. W.; J. Polym. Sci: Polym. Chem. Ed. (1972), 10, 3555. 31. Hall, Jr., H. K.; Blanchard, Jr., E. P.; Cherkufsky, S. C.; Sieja, J. B.; and Sheppard. W. Α.; J. Amer. Chem. Soc. (1971), 93, 110. 32. Kauer, J. C., private communication. 33. "Handbook of Silylation", p. 7, Pierce Chemical Company, Rockford, I11., 1970. In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

21 New Polymers by Ring-Opening Polymerization of Norbornene Derivatives with Polar Substituents S. MATSUMOTO, K. KOMATSU, and K. IGARASHI Tokyo Research Laboratory, Japan Synthetic Rubber Co., Ltd., Kawasaki, Japan

The ring-opening polymerization of cyclic unsaturated hydrocarbons has been studied extensively(1-4), following the first report by Eleuterio(5) and subsequent discovery of homogeneous catalyst by Natta et al. (6). Typical catalyst is composed of a tungsten or a molybdenum compound and an organometallic compound. Now it is generally accepted that this polymerization involves the same type of intermediates as that of the olefin metathesis (olefin disproportionation) which was first reported by Banks et al.(7) and later extended to homogeneous system by Calderon et al.(8). The polymerization proceeds through ring-cleavage at the carbon-carbon double bond. Polymers of halogenated cyclic hydrocarbons have been prepared by this type of catalyst. Highly strained cyclic olefins like cyclobutene or norbornene have also been polymerized in alcoholic solvents or in aqueous emulsion by using, as catalyst, ruthenium, iridium or osmium salts, which are not active for the polymerization of less strained monomers like cyclopentene or cyclooctene(9). In addition, it has been shown t h a t t h e s e n o b l e metal c a t a l y s t s induce the r i n g - o p e n i n g p o l y m e r i z a t i o n o f norbornene d e r i v a t i v e s s u b s t i t u t e d by p o l a r groups(10-15). Monomers w i t h e s t e r , e t h e r , c a r b o x y l , h y d r o x y l , halogen and imide groups have been s u c c e s s f u l l y p o l y m e r i z e d . However, t h e s e c a t a l y s t s were r e p o r t e d t o be i n c a p a b l e o f p o l y m e r i z i n g the n i t r i l e - s u b s t i t u t e d d e r i v a t i v e ( 1 1 ) . In t h e c o u r s e o f the s t u d i e s on the b e h a v i o r o f u n s a t u r a t e d compounds c o n t a i n i n g p o l a r groups toward t h e m e t a t h e s i s c a t a l y s t ( 1 6 ) , we have found t h a t t h i s type o f c a t a l y s t can i n d u c e e f f i c i e n t l y the r i n g - o p e n i n g p o l y m e r i z a t i o n o f norbornene d e r i v a t i v e s w i t h v a r i o u s p o l a r s u b s t i t u e n t s , i n c l u d i n g n i t r i l e group. The p o l y m e r i z a t i o n of e s t e r , n i t r i l e , p y r i d y l and a c i d 303

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING

304

POLYMERIZATION

a n h y d r i d e d e r i v a t i v e s have been i n d e p e n d e n t l y d i s c l o s e d by Hepworth e t a l . ( 1 7 ) and by Ueshima et a l . ( 1 8 , 1 9 ) . The m e t a t h e s i s r e a c t i o n s of e s t e r g r o u p - c o n t a i n i n g o l e f i n s ( c y c l i c and a c y c l i c ) have a l s o been r e p o r t e d r e cently(20-23). The p r e s e n t paper r e p o r t s the r i n g - o p e n i n g p o l y m e r i z a t i o n o f norbornene d e r i v a t i v e s s u b s t i t u t e d by n i t r i l e , amide, imide, e s t e r , p y r i d y l and a c i d anhydr i d e groups by the above-mentioned c a t a l y s t s . The p o l y m e r i z a t i o n b e h a v i o r o f t h e s e monomers and the p h y s i c a l p r o p e r t i e s of the polymers o f n o r b o r n e n e n i t r i l e s w i l l be d e s c r i b e d . R e s u l t s and D i s c u s s i o n Polymerization The p o l y m e r i z a b i l i t y o f norbornene d e r i v a t i v e s s u b s t i t u t e d by n i t r i l e , amide, imide, e s t e r , p y r i d y l , a c i d a n h y d r i d e , ketone and aldehyde groups were, examined by u s i n g the t u n g s t e n - b a s e d b i n a r y and t e r n a r y c a t a l y s t systems. The r e s u l t s a r e summarized i n TABLE I . B e s i d e s the e s t e r and imide d e r i v a t i v e s t h a t are known t o be p o l y m e r i z e d by the n o b l e metal c a t a l y s t s , n i t r i l e , amide, p y r i d y l and a c i d a n h y d r i d e d e r i v a t i v e s were found t o undergo p o l y m e r i z a t i o n by t h e p r e s e n t c a t a l y s t systems. The e s t e r d e r i v a t i v e s were e a s i l y p o l y m e r i z e d by the b i n a r y c a t a l y s t t o a h i g h c o n v e r s i o n at the catalyst-to-monomer molar r a t i o as low as 10 "** . The n i t r i l e d e r i v a t i v e s were l e s s r e a c t i v e but c o u l d be p o l y m e r i z e d t o a h i g h c o n v e r s i o n by the t e r nary c a t a l y s t a c t i v a t e d by a t h i r d component. The o t h e r d e r i v a t i v e s were p o l y m e r i z e d much l e s s e f f i c i e n t l y even by the t e r n a r y c a t a l y s t . These d i f f e r e n c e s i n r e a c t i v i ty are presumed t o r e f l e c t the r e l a t i v e s t r e n g t h o f the i n t e r a c t i o n o f the a c t i v e c a t a l y s t s p e c i e s w i t h the norbornene double bond on one hand and w i t h the p o l a r s u b s t i t u e n t on the o t h e r . The ketone and aldehyde d e r i v a t i v e s , on the o t h e r hand, were not p o l y m e r i z e d by the c a t a l y s t systems examined. As w i l l be mentioned below, a l a r g e amount o f ketones and aldehydes c o m p l e t e l y i n a c t i v a t e s the c a t a lyst. A l l the polymers o b t a i n e d were a n a l y z e d t o be the p r o d u c t s through r i n g - o p e n i n g p o l y m e r i z a t i o n by means of i r and ^-nmr s p e c t r o s c o p y . F i g u r e 1 shows the Hnmr s p e c t r a o f t h r e e polymers. A l l o f them have an u n r e s o l v e d peak around 5.3 ppm(from t e t r a m e t h y l s i l a n e ) , which can be a s s i g n e d t o the p r o t o n s a t t a c h e d t o a c y c l i c C=C bond. The r e l a t i v e a r e a s o f the peaks i n the s p e c t r a were found t o be c o n s i s t e n t w i t h the s t r u c t u r e 1

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

21.

MATSUMOTO E T A L .

Polymerization

of Norbornene

TABLE I . P o l y m e r i z a t i o n o f V a r i o u s Derivatives. Catalyst system

Polymer yield %

^ WCle-paralde(1:1.5:3) hyde-Al(isoBu)

lOOD

Monomer

Or

CN

ΓΝ Q f C H

m

3

f^-COOMe

Or' 0

A

c

m

W C

3

l6-AlEt3(l:3)

WCl6-AlEt (l:3)

2

On£D

W(OPh) - A l E t a (1:2) 6

R 4 8

„v 0 . 5 4 " 165 3.16

8 )

62

0.65 >

5)

4

77

1

1

4

1

1

4

6 )

10

5 )

WCle-AlEta (1:2)

7

5 )

-

> 200

WCle-AlEta (1:2)

8

5 )

-

> 250

WCle-AlEts(1:2)

0

9)

CHO

3 )

;

140

25

WCle-AlEta(1:3)

WCle-MASC (1:3) (Q^Q^NPr"

(Π) Tg d l / g (DSC) Ç 7

85 >

3

jQj-C0NMe

Or Or

100

Norbornene

0.66 >

. 100^

305

Derivatives

x

WCle-AlEta (1:2)

U J

*) 0 7

1) P o l y m e r i z a t i o n a t 60°C f o r 4 h r . i n 1 , 2 - d i c h l o r o e t h ane; 1 mole% o f 1-hexene was added; t h e monomer-to-ca­ t a l y s t molar ratio(M/W) was 1000. 2) P o l y m e r i z a t i o n a t 70°C f o r 4 h r . w i t h 1.4 mole% o f 1-hexene. 3) Polymer­ i z a t i o n a t 30°C f o r 17 h r . i n c h l o r o b e n z e n e ; M/W,4000. 4) P o l y m e r i z a t i o n a t 25°C f o r 6 h r . i n c h l o r o b e n z e n e ; M/W, 1000; 5 mole% o f 1-heptene. 5) P o l y m e r i z a t i o n at 70°C f o r 17 h r . i n c h l o r o b e n z e n e ; M/W, 200. 6) P o l y ­ m e r i z a t i o n a t 70°C f o r 17 h r . i n e t h y l a c e t a t e ; M/W, 500. 7) Measured i n c h l o r o f o r m a t 30°C. 8) Measured i n t o l u e n e at 30°C. 9) MASC=AlMe C l . 1#5

l e 5

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

306

RING-OPENING POLYMERIZATION

( I ) formed

through

ring-opening polymerization.

Or? — (-A

i

CH=CH

n

(I)

The i r s p e c t r a o f t h e polymers from i m i d e , p y r i d y l and a c i d a n h y d r i d e d e r i v a t i v e s were s i m i l a r t o t h o s e o f the polymers from n i t r i l e and e s t e r d e r i v a t i v e s and had an a b s o r p t i o n at 970 c m c h a r a c t e r i s t i c o f C=C l i n k a g e , i n d i c a t i n g t h e s t r u c t u r e ( I ) . The polymers were r e s i n o u s and h a r d m a t e r i a l s . T h e i r g l a s s t r a n s i t i o n t e m p e r a t u r e s ( T g ) are g i v e n i n TABLE I. -1

Catalyst. Two p r e s e n t s t u d y . The on c a t a l y s t composed o f a t u n g s t e n , molybdenum o r rhenium compound (A component) and an o r g a n o m e t a l l i c compound (B component). The o t h e r t y p e o f c a t a l y s t i s composed of a c a r b o n y l - c a r b e n e complex o f t u n g s t e n and a Lewis acid(24). TABLE I I g i v e s the r e s u l t s o f the p o l y m e r i z a t i o n o f s e v e r a l monomers by v a r i o u s c a t a l y s t systems o f t h e f i r s t t y p e . As the A component, t u n g s t e n compounds a r e more e f f e c t i v e than molybdenum compounds. The a c t i v i t y o f the rhenium-based c a t a l y s t s was much lower than t h o s e o f the t u n g s t e n - o r molybdenum-based systems. B e s i d e s the compounds o f t h e elements shown i n TABLE II, o r g a n o m e t a l l i c compounds o f l i t h i u m , sodium, magnesium, z i n c , boron and germanium are e f f e c t i v e as t h e Β compo­ nent as shown i n TABLE I I I . Some metal h y d r i d e s a r e a l s o e f f e c t i v e . The n o n - o r g a n o m e t a l l i c system, H2WOi*-AlCl3 , which had c o n s i d e r a b l e a c t i v i t y f o r the m e t a t h e s i s r e a c t i o n ( p o l y m e r i z a t i o n ) o f c y c l i c and a c y c l i c u n s a t u r a t e d h y d r o c a r b o n s , has p r a c t i c a l l y no a c t i v i t y f o r the p r e s e n t p o l y m e r i z a t i o n . As i n t h e p o l y m e r i z a t i o n o f monomers w i t h o u t p o l a r s u b s t i t u e n t , t h e c a t a l y t i c a c t i v i t y was markedly enhan­ ced by t h e a d d i t i o n o f a t h i r d component (C component) such as a l c o h o l s , p e r o x i d e s , h y d r o p e r o x i d e s and epox­ i d e s . We have found t h a t k e t o n e s , aldehydes and polym­ e r i z a t i o n product of aldehydes are p a r t i c u l a r l y e f f e c ­ t i v e as the C component f o r t h i s t y p e o f c a t a l y s t . These compounds i n a c t i v a t e t h e c a t a l y s t i n l a r g e amounts as shown i n F i g u r e 2. C e r t a i n metal compounds such as Τΐ(ΟΙΙ)!» , FeCl3 , chromium a c e t y l a c e t o n a t e and A l ( O R ) 3 were a l s o e f f e c t i v e as t h e C component. TABLE IV summarizes the r e s u l t s o f t h e p o l y m e r i ­ z a t i o n by t h e second t y p e o f c a t a l y s t . The i o n i c ( I I ) and n o n - i o n i c ( I I I ) complexes o f t u n g s t e n were u s e d i n

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

21.

Polymerization

MATSUMOTO E T A L .

of Norbornene

Derivatives

307

TABLE I I P o l y m e r i z a t i o n o f Norbornene D e r i v a t i v e s by V a r i o u s C a t a l y s t Systems: polymer y i e l d (%). D

x=

X= Monomer

Π

J\

X=CN

CONMe

2

COOMe

X= 2-Pyridyl

W 29

WCl -AlEt (l:2) 6

3

WC16-AlEt3-acetone (1:3:6)

100

2 )

71

99

-

100

16 3 )

-

W(OPh) -AlEtaCI (1:2) 6

WCl6-Et SiH(l:4)

0.1

0.1

85

-

WCle-Ph Sb(1:10)

1

0

81

-

38

1

100

3

3

WCle -MenSn(l:1.3) H WOI>-A1C1 2

3

(1:3.2)

0

-

0

0

-

Mo MoCls-AlEtCla(1:4) Mo(OEt) Cl - A l E t (1:2) 2

3

3

Mo0 (acac)2-AlEtCl2 (1:4) 2

0.2

4

49

-

6

0.1

20

-

-

27

-

1

0.6

-

0.1

2

—

11

Re ReCls-AlEt (1:2) 3

ReCl -Mei»Sn(l:1.3) 5

—

1) P o l y m e r i z a t i o n s were c a r r i e d o u t i n c h l o r o ­ benzene a t 70°C f o r 17hr: t h e m o n o m e r - t o - c a t a l y s t molar r a t i o , 200. 2) P o l y m e r i z a t i o n i n 1,2d i c h l o r o e t h a n e a t 50°C f o r 4 h r : monomer-toc a t a l y s t molar r a t i o , 1000. 3) P o l y m e r i z a t i o n i n t o l u e n e at 30°C f o r 15 min: m o n o m e r - t o - c a t a l y s t molar r a t i o , 1000.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

308

RING-OPENING POLYMERIZATION

IT

NCH-s

-^S-CMsCH-

f

COM(CH ) 3

60MHz 2

ppm 6 Figure 1. Ή-NMR spectra of the polymers obtained from nitrile-, ester-, and amide-substituted norbornene derivatives: measured in CDCl at room temperature s

Figure 2. The effect of the addition of paraldehyde (PA), n-butyraldehyde (BA), and acetone (ACT) in the polymerization of 5-norbornene-2-nitrile by the WCle-Al(isoBu) system: polymerization in 1,2-dichloroethane at 25°C for 4 hr; the monomer-to-WCk molar ratio was 1000 s

RR'CO/W

(molar ratio)

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

21.

MATSUMOTO E T AL.

Polymerization

of Norbornene

Derivatives

309

TABLE I I I E f f e c t o f C o c a t a l y s t ( B component) i n t h e P o l y m e r i z a t i o n by B i n a r y Systems, WCle - C o c a t a l y s t . Polymer y i e l d (%).

Cocatalyst

B/WCle molar ratio

Monomer

jQ)CN

(QpCOOMe

n-BuLi

2

C H Na

2

-

CH MgBr

2

0.1

91

ZnEt

2

0.1

26

2

0

1

2

29

99

5

5

3

BEt

2

6

3

B(n-Bu) AlEt

3

3

Et SiH 3

Ge(CH ) 3

PEt

0.1

u

3

97

4

0.1

3

0

7

2

-

0

LiAlHif

ca.

20

0.1

29

NaBHi»

ca.

20

0

24

P o l y m e r i z a t i o n s were c a r r i e d out i n c h l o r o b e n z e n e at 70°C f o r 17 h r . The monomer-to-catalyst molar r a t i o was 200.

[(CH )i»N] [(CO)sWCOPh] 3

(II)

(CO) WC(OEt)Ph 5

(III)

the p r e s e n t s t u d y . As t h e Lewis a c i d component, o n l y t i t a n i u m t e t r a h a l i d e gave h i g h c a t a l y t i c a c t i v i t y . I t i s i n t e r e s t i n g t o note t h a t the r e l a t i v e e f f e c t i v e n e s s of the two complexes depends on t h e k i n d o f monomer t o be p o l y m e r i z e d . F o r t h e n i t r i l e d e r i v a t i v e , t h e complex ( I I ) i s more e f f e c t i v e than t h e complex ( I I I ) w h i l e the o r d e r i s r e v e r s e d f o r t h e e s t e r d e r i v a t i v e s . The reason f o r t h i s phenomenon i s not c l e a r at t h i s moment. The enhancement o f the c a t a l y t i c a c t i v i t y by t h e a d d i t i o n o f the t h i r d component was o b s e r v e d a l s o w i t h t h i s t y p e o f c a t a l y s t . E f f e c t i v e t h i r d components a r e t e r t i a r y p h o s p h i n e s , s u l f i d e s , s u l f o x i d e s , quinones and N - c h l o r o s u c c i n i m i d e . A l c o h o l s , k e t o n e s and a l d e h y d e s , on the o t h e r hand, d e a c t i v a t e d the c a t a l y s t even i n

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

310

RING-OPENING POLYMERIZATION

TABLE IV P o l y m e r i z a t i o n by t h e W Carbene ComplexBased C a t a l y s t s . 1 ) Polymer y i e l d ( % ) .

Cr

Monomer

Monomer/catalyst molar r a t i o

Qj-COOX

CN

1000

X=Me

X = @r

5000

B r

2000

3

2 )

[(CO) WCOPh] [Nile*] ( I I ) 5

(II)

- TiClu

(II)

- TiCL* - X X = PPh

12

89

3

3

50

-

MeSOMe

41

-

tBuSBut

36

-

48

-

70

-

0.2

-

5

-

3

-

PEt

Anthraquinone

Paraldehyde Benzoyl peroxide Benzophenone (CO) WC(OEt)Ph ( I I I ) 5

(III)

- TiCU

(III)

- TiCU

- PPh

[g:N-ci

3

3(100°C,6)

100

27

11

100

64

47

-

1) P o l y m e r i z a t i o n s were c a r r i e d out i n b u l k a t 70°C f o r 16 h r . The Ti/W r a t i o was 5 and t h e t h i r d component/W r a t i o was 1.5. 2) P o l y m e r i z a t i o n i n dichloroethane solution.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

21.

MATSUMOTO

ET AL.

Polymerization

of Norbornene

Derivatives

311

s m a l l amounts. Furthermore, the t h r e e components had t o be mixed i n the absence o f monomer and the o r d e r o f m i x i n g d i d not s i g n i f i c a n t l y a f f e c t the c a t a l y t i c ac­ t i v i t y . In c o n t r a s t , i n o r d e r t o a t t a i n a h i g h a c t i v ­ i t y w i t h t h e f i r s t t y p e o f c a t a l y s t , the A and the C components s h o u l d be r e a c t e d p r i o r t o m i x i n g w i t h mono­ mer o r the Β component, the former b e i n g added f i r s t . These o b s e r v a t i o n s suggest t h a t t h e mechanism o f the c a t a l y s t a c t i v a t i o n by t h e t h i r d component i n t h e f i r s t system i s d i f f e r e n t from t h a t i n the second system. I n f l u e n c e o f P o l a r F u n c t i o n a l Groups and A c y c l i c Double Bond on P o l y m e r i z a t i o n . The p o l y m e r i z a t i o n can be c a r r i e d out i n a p r o t i c p o l a r s o l v e n t s such as e t h e r , tetrahydrofuran, ethy methylformamide as w e l n a t e d h y d r o c a r b o n s . A l c o h o l s , ketones and s u l f o x i d e s s t r o n g l y i n h i b i t e d the r e a c t i o n . The m o l e c u l a r weight o f t h e polymer p r o d u c t i s reduced by the a d d i t i o n o f a c y c l i c u n s a t u r a t e d com­ pounds. O l e f i n s and n o n - c o n j u g a t e d d i o l e f i n s r e d u c e d the m o l e c u l a r weight w i t h o u t a p p r e c i a b l e e f f e c t on t h e r a t e o f p o l y m e r i z a t i o n , t e r m i n a l o l e f i n s b e i n g more e f f e c t i v e than i n t e r n a l o l e f i n s . A l l y l i c compounds w i t h p o l a r f u n c t i o n a l groups e x e r t e d a s i m i l a r e f f e c t . Con­ j u g a t e d d i o l e f i n s were l e s s e f f e c t i v e and caused r e d ­ u c t i o n of c a t a l y t i c a c t i v i t y i n l a r g e amounts. C y c l o p e n t a d i e n e , which r e t a r d s t h e p o l y m e r i z a t i o n o f c y c l o pentene even a t low c o n c e n t r a t i o n , d i d not e x e r t s i g n ­ i f i c a n t e f f e c t i n the present p o l y m e r i z a t i o n . Acet­ y l e n e s and aliènes caused r e d u c t i o n o f m o l e c u l a r weight at low c o n c e n t r a t i o n ( c a . 0.1 - 0.5 mole-% f o r monomer) and d e a c t i v a t e d the c a t a l y s t at h i g h e r c o n c e n t r a t i o n s . A c r y l i c e s t e r s , a c r y l o n i t r i l e and m a l e i c a c i d e s t e r s d e a c t i v a t e d the c a t a l y s t without s i g n i f i c a n t e f f e c t on the molecular weight. The p o l y m e r i z a t i o n and t h e r e a c t i o n w i t h a c y c l i c u n s a t u r a t e d compounds a r e c o n s i d e r e d t o t a k e p l a c e on the c o o r d i n a t i o n s i t e s o f the a c t i v e c a t a l y s t s p e c i e s . T h e r e f o r e , t h e e f f e c t o f v a r i o u s compounds d e s c r i b e d above r e f l e c t , at l e a s t i n p a r t , t h e i r r e l a t i v e a b i l i t y o f c o o r d i n a t i o n t o the a c t i v e s p e c i e s . The e f f e c t o f a c e t y l e n e s and aliènes as w e l l as t h a t o f a,$-uns a t u r a t e d e s t e r s and n i t r i l e s may r e a s o n a b l y be exp l a i n e d by t h e i r s t r o n g e r power o f c o o r d i n a t i o n i n com comparison w i t h t h a t o f the norbornene double bond. The l a t t e r i n t u r n c o o r d i n a t e s more s t r o n g l y than unc o n j u g a t e d p o l a r group as i n d i c a t e d i n t h e above results. I n a c t i v a t i o n o f t h e c a t a l y s t by ketone and a i d e -

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

312

RING-OPENING

POLYMERIZATION

hyde groups i s presumed t o be due t o a s p e c i f i c i n t e r a c t i o n o f t h e s e f u n c t i o n a l groups w i t h t h e a c t i v e spec i e s . Deoxygenation o f k e t o n e s and aldehydes by low v a l e n t t u n g s t e n s p e c i e s has been r e p o r t e d ( 2 5 ) . Copolymerization. Copolymers c o u l d be p r e p a r e d from t h e m i x t u r e s o f t h e norbornene d e r i v a t i v e s . They c o u l d a l s o be c o p o l y m e r i z e d w i t h c y c l o o l e f i n s without p o l a r group such as c y c l o p e n t e n e o r c y c l o o c t e n e . The f o r m a t i o n o f t h e copolymer was c o n f i r m e d by e l e m e n t a l a n a l y s i s , i r spectrum, t h i n l a y e r chromatography(TLC) and d i f f e r e n c i a l s c a n n i n g c a l o r i m e t r y ( D S C ) . Furthermore, t h e norbornene d e r i v a t i v e s c o u l d be p o l y m e r i z e d i n t h e p r e s e n c e o f u n s a t u r a t e d polymers l i k e polybutadiene o to give block o r g r a f the b l o c k ( g r a f t ) copolymer was s u b s t a n t i a t e d by t h e e l e c t r o n m i c r o s c o p y , which r e v e a l e d a two-phase s t r u c t u r e o f t h e p r o d u c t s i n t h e s o l i d s t a t e . The b l o c k c o p o l y m e r i z a t i o n w i t h a u n s a t u r a t e d rubbery polymer was s u c c e s s f u l l y u t i l i z e d t o improve t h e impact r e s i s t a n c e o f t h e homopolymers o f n o r b o r n e n e n i t r i l e s . Polymers o f N o r b o r n e n e n i t r i l e s . On t h e b a s i s o f p r e l i m i n a r y e v a l u a t i o n o f t h e p r o p e r t i e s çf v a r i o u s p o l y n o r b o r n e n e s , t h e monomer a v a i l a b i l i t y and t h e p o l y m e r i z a t i o n b e h a v i o r , t h e polymers o f t h e n i t r i l e d e r i v a t i v e s were c o n s i d e r e d most p r o m i s i n g as new m a t e r i a l s . The homopolymers o f 5 - n o r b o r n e n e - 2 - n i t r i l e and 2-methyl5 - n o r b o r n e n e - 2 - n i t r i l e and a b l o c k copolymer o f 5-norb o r n e n e - 2 - n i t r i l e w i t h SBR were p r e p a r e d and e v a l u a t e d w i t h r e s p e c t t o t h e i r p h y s i c a l p r o p e r t i e s . The t e r n a r y system, WC16-paraldehyde-Al(isoBu>3 was used as t h e c a t a l y s t , which e f f i c i e n t l y i n d u c e d t h e p o l y m e r i z a t i o n at a catalyst-to-monomer r a t i o as low as c a . 4 x 10"**. ^-nmr spectrum o f p o l y ( 5 - n o r b o r n e n e - 2 - n i t r i l e ) showed t h a t i t i s t h e p r o d u c t o f r i n g - o p e n i n g polymeri z a t i o n . Further d e t a i l e d i n v e s t i g a t i o n of the s t r u c t u r e was done by means o f C-nmr s p e c t r o s c o p y . In p r i n c i p l e , t h r e e k i n d s o f s t r u c t u r a l isomerism are p o s s i b l e , i . e . , c i s and t r a n s isomers o f t h e cyano group w i t h r e s p e c t t o t h e two 1,3-bonds o f t h e c y c l o pentane r i n g , c i s and t r a n s isomers about t h e C=C bond and t h e h e a d - t o - t a i l and head-to-head ( t a i l - t o - t a i l ) arrangements o f t h e c o n s e c u t i v e monomer u n i t s . 13

Head-to-tail

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

21.

MATSUMOTO ET A L .

Head-to-head

Polymerization

of Norbornene

Derivatives

313

Ctail-tp-ta.il)

CN

Of t h e s e , t h e f i r s t i s o m e r i s m i s ' d e t e r m i n e d by t h e monomer s t r u c t u r e , i . e . , t r a n s c o n f i g u r a t i o n from t h e exo monomer and c i s c o n f i g u r a t i o n from t h e endo monomer. The C-nmr spectrum o f p o l y ( 5 - n o r b o r n e n e - 2 - n i t r i l e ) had t h r e e s e t s o f peaks at 30 - 4 8 ppm, about 120 ppm and 128 - 135 ppm from t e t r a m e t h y l s i l a n e , which were a s s i g n e d t o t h e carbons o f t h e c y c l o p e n t a n e r i n g , t h e cyano group and t h e C=C bond, r e s p e c t i v e l y . The q u a n t i t a t i v e a n a l y s e s o f t h e s e peaks, u s i n g p o l y n o r b o r n e n e , poly(methyl 5-norbornene-2-carboxylate methyl 5 - n o r b o r n e n e - 2 , 3 - d i c a r b o x y l a t e gave t h e p r o p o r t i o n o f each isomer i n t h e t h r e e s t r u c t u r a l isomerism. The r e s u l t s a r e summarized i n TABLE V. The c i s / t r a n s r a t i o o f t h e cyano group about t h e c y c l o p e n t a n e r i n g i s i n good agreement w i t h t h e endo/ exo r a t i o o f t h e s t a r t i n g monomer d e t e r m i n e d by gas chromatography. The c o n t e n t o f t h e h e a d - t o - t a i l a r r a n gement o b t a i n e d shows t h a t a p p r o x i m a t e l y a h a l f o f t h e monomer u n i t s a r e i n t h e head-to-head and t a i l - t o - t a i l arrangements. The p r o p o r t i o n o f t h e c i s c o n f i g u r a t i o n about t h e C=C bond v a r i e s from 20 t o 80 % depending on t h e k i n d of t h e c a t a l y s t employed. The Tg o f t h e polymer was not changed much i n t h i s range o f t h e c i s c o n t e n t . 13

Physical Properties. The p h y s i c a l p r o p e r t i e s o f the polymers o f 5 - n o r b o r n e n e - 2 - n i t r i l e and 2-methyl-5n o r b o r n e n e - 2 - n i t r i l e and a b l o c k ( g r a f t ) copolymer o f 5 - n o r b o r n e n e - 2 - n i t r i l e w i t h SBR were e v a l u a t e d . Because the m o l e c u l a r weight a f f e c t e d t h e p r o c e s s a b i l i t y o f t h e polymers, polymers w i t h t h e i n t r i n s i c v i s c o s i t y v a l u e of 0.4 - 0.5 were p r e p a r e d . A l l t h e polymers were h a r d and t r a n s p a r e n t materi a l s which were amorphous as j u d g e d by DSC a n a l y s i s , which showed o n l y t h e secondary t r a n s i t i o n s a t 140° and 1 6 5 C f o r p o l y ( 5 - n o r b o r n e n e - 2 - n i t r i l e ) and t h e meth y l homologue, r e s p e c t i v e l y . TABLE VI summarizes t h e p h y s i c a l p r o p e r t i e s o f the polymers. The v a l u e s o f t h e a c r y l o n i t r i l e - b u t a d i e n e - s t y r e n e ( A B S ) r e s i n and o f p o l y c a r b o n a t e a r e i n c l u d ed f o r t h e sake o f comparison. The norbornene polymers have good t e n s i l e and f l e x u a l p r o p e r t i e s comparable t o t h o s e o f t h e ABS r e s i n . The heat d i s t o r t i o n temperature (HDT) o f p o l y ( 5 - n o r b o r n e n e - 2 - n i t r i l e ) i s r a i s e d by e

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

314

RING-OPENING POLYMERIZATION

TABLE V

S t r u c t u r a l A n a l y s i s o f Poly(5-norbornene2 - n i t r i l e ) by C-nmr. l5

Monomer

1

Catalyst ^ C=N ( r i n g ) t r a n s ?

0

exo 40 endo 60

exo

A

A

37

100

en do

Β

A 0

0

100

100

79

30

21

70

88

80

19

12

20

81

63

0

C=C C o n f i g u r a t i o n t o t a l polymer c i s %

53

—

trans%

47

-

cis7o

en do

Head-to-tail arrangement

Head-to-tail c i s % p

a

r

t

trans%

-

1) C a t a l y s t : A, W C l e - p a r a l d e h y d e - A l ( i s o B u ) 3 ; B, WCle-acetal-AlEtaCl. 2) The v a l u e showed c o n s i d ­ e r a b l e f l u c t u a t i o n because o f t h e c o m p l e x i t y o f the spectrum.

about 10°C i n t h e methyl d e r i v a t i v e and t h e s e v a l u e s l i e between t h e H D T s o f t h e ABS r e s i n and p o l y c a r b o n ­ ate. O u t s t a n d i n g p r o p e r t i e s o f t h e homopolymers a r e t r a n s p a r e n c y , h i g h c r e e p r e s i s t a n c e and h i g h a b r a s i o n r e s i s t a n c e t h a t a r e comparable t o t h o s e o f e n g i n e e r i n g plastics. The I z o d impact s t r e n g t h o f t h e homopolymer i s lower than t h o s e o f t h e ABS r e s i n and p o l y c a r b o n a t e , but t h i s can be g r e a t l y improved by b l o c k c o p o l y m e r i z a t i o n w i t h a s m a l l amount o f SBR as i s e v i d e n t from TABLE V I I . f

Experimental Section Materials. The monomers were p r e p a r e d by t h e D i e l s - A l d e r reaction of cyclopentadiene with the corres­ ponding v i n y l and m a l e i c compounds. The norbornene i m i des were p r e p a r e d by t h e r e a c t i o n o f norbornene d i c a r b o x y l i c a c i d a n h y d r i d e w i t h t h e c o r r e s p o n d i n g amines. L i q u i d monomers were p u r i f i e d by d i s t i l l a t i o n under r e ­ duced n i t r o g e n p r e s s u r e and f r e e d from r e s i d u a l w a t e r

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977. —

4

127

2

4

5

β

}

J

χ

2

1.9

0.8

-

1.3

15

52

123 122 109

120 17

15

broken

76

107

13

1) NN = 5 - N o r b o r n e n e - 2 - n i t r i l e . 2) MNN = 2 - M e t h y l - 5 - n o r b o r n e n e - 2 - n i t r i l e . ASTM D648, w i t h o u t a n n e a l i n g . 4) A t 25°C. 5) ASTM D790. 6) ASTM D256, n o t c h e d sample. 7) ASTM D1044. 8) 100 h r .

e

C r e e p ( % a t 7 5 C ; 1 0 0 kg/cm ) 8)

?

Taber a b r a s i o n r e s i s t a n c e x (mg a t 1 0 0 0 g ; 2 5 ° C )

Rockwell hardness(R s c a l e )

I z o d impact s t r e n g t h (kg-cm/cm; at 2 5 ° C )

F l e x u a l modulus(kg/cm ) ^ ' ^

2.8

2.5x10* 2.9x10* 2.1x10*

2.2x10*

2.1x10*

2

strength(kg/cm )

110

831 1170 790

820

898

Flexual

at y i e l d ^ at b r e a k '

3.2

10 50

14 250

-

(%) 4

145

Elongation

13 270

479 382

667 796

480 380

531 374

v '

2

T e n s i l e s t r e n g t h at y i e l d (kg/cm ) at break

87

111

1.08

139

-

1.22

-

P o l y c a r ­ • ABS Resin bonate

115

2 )

3)

-

1.07

1.03

0.54

(25 C)

e

0.5

0

MNN

Poly-

10

NN/SBR Block copolymer

0.37

1 )

(dl/g)

0

NN

Poly-

Properties of Polynorbornenenitriles.

HDT ( 2 4 6 p s i ; °C)

Density

[η]

SBR c o n t e n t ( w t - % )

P o l y m e r

TABLE VI

3)

RING-OPENING

316

POLYMERIZATION

by t r e a t i n g w i t h m o l e c u l a r s i e v e s 4A. S o l i d monomers were r e c r y s t a l l i z e d from a p p r o p r i a t e s o l v e n t s and d r i e d i n vacuo at room temperature. The W-carbene complexes were p r e p a r e d by t h e meth­ od r e p o r t e d by F i s c h e r e t a l . ( 2 6 ) . Other c a t a l y s t com­ ponents were commercial r e a g e n t s which were used w i t h ­ out f u r t h e r p u r i f i c a t i o n . S o l v e n t s were commercial r e a g e n t s o f a p p r o p r i a t e p u r i t y and p u r i f i e d by u s u a l methods. They were f r e e d from water by treatment w i t h m o l e c u l a r s i e v e s . O t h e r m a t e r i a l s were commercial r e a g e n t s and p u r i f i e d by usual techniques. Polymerization. P o l y m e r i c a t i o n runs were c a r r i e d out by u s u a l methods u s i n g s e a l e d g l a s s ampoules. The solvent-to-monomer weigh were r e c o v e r e d by p r e c i p i t a t i o case o f amide and p y r i d y l d e r i v a t i v e s , i n p e t r o l e u m e t h e r . F o r t h e e v a l u a t i o n o f p r o p e r t i e s , polymer sam­ p l e s were p r e p a r e d by u s i n g a 14 1 s t a i n l e s s - s t e e l auto­ c l a v e and r e c o v e r e d by steam d i s t i l l a t i o n o f t h e v o l a ­ t i l e m a t e r i a l s . The p r o d u c t s were f u r t h e r p u r i f i e d by r e p r e c i p i t a t i o n w i t h c h l o r o f o r m - m e t h a n o l when necessary. Measurements. The H-nmr and C-nmr s p e c t r a were r e c o r d e d on a Nihon Denshi MH 60 nmr s p e c t r o m e t e r and on a Nihon Denshi PS 100 nmr s p e c t r o m e t e r , r e s ­ p e c t i v e l y . I r s p e c t r a were taken on a Nihon Bunko I Μ ­ Ι g r a t i n g i n f r a r e d spectrophotometer. D i f f e r e n c i a l s c a n n i n g c a l o r i m e t r y was c a r r i e d out w i t h a Thermoflex 8001 d i f f e r e n c i a l s c a n n i n g c a l o r i m e t e r ( R i g a k u D e n k i ) . F o r t h e measurement o f t h e p h y s i c a l p r o p e r t i e s , polymers were i n j e c t i o n - m o l d e d t o p i e c e s o f s p e c i f i e d s i z e . Measurements were made by t h e s t a n d a r d p r o c e d u ­ r e s . P o l y c a r b o n a t e ( P a n l i t e 1225, T e i j i n Co.) and t h e ABS r e s i n (JSR ABS#55, Japan S y n t h e t i c Rubber Co.) were a l s o e v a l u a t e d as t h e r e f e r e n c e s . f

13

Acknowledgements. The a u t h o r s wish t o e x p r e s s t h e i r g r a t i t u d e t o Dr. F. Imaizumi f o r h i s a c t i v e c o l l a b o r a ­ t i o n s and h e l p f u l d i s c u s s i o n s . T h e i r g r a t e f u l thanks are a l s o due t o Mr. M. Ikeyama f o r nmr a n a l y s e s and t o Mr. M. Nagata f o r t h e e v a l u a t i o n o f t h e p h y s i c a l p r o p e r ­ t i e s . The a u t h o r s a r e much i n d e b t e d t o Japan S y n t h e t i c Rubber Co., L t d . f o r generous p e r m i s s i o n t o p u b l i s h t h i s work.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

21. M A T S U M O T O E T A L .

Polymerization

of Norbornene

Derivatives

Literature Cited (1) Calderon,N., J. Macromol. Sci., Revs. Macromol. Chem., (1972),C7, 105. (2) Günther,P., Haas,F., Marwede,G., Nützel,K., Ober­ kirch,W., Pampus,G., Shön,N., Witte,J., Angew. Makromol. Chem., (1971),16/17, 27. (3) Scott,K.W., Polymer Preprints, (1972),13(2), 874. (4) Calderon,N., Acc. Chem. Res., (1972),5, 127. (5) Eleuterio,H.C., US, 3,074,918(1963). Natta,G., Dall'Asta,G., Mazzanti,G., Angew.Chem. (1964), 76,765. (7) Banks,R.L., Bailey,G.C., Ind. Eng. Chem., Prod. Res. Develop., (1964),3, 170. (8) Calderon,N., Ofstead,E.A., Ward,J.P., Scott,K.W., J. Am. Chem. Soc., (1968), 90, 4133. (9) Natta,G., Dall'Asta,G., Mortani,G., Makromol. Chem., (1963), 69, 163. (10) Michelotti,F.W., Carter,J.H., Polymer Preprints, (1965),6,224. (11) Michelotti,F.W., Keaveney,W.P., J. Polym. Sci., Part A, (1965),3, 895. (12) Rinehart,R.E., Smith,H.P., J. Polym. Sci., Part B, (1965),3, 1049. (13) Charbonnage de France, Fr, 1,594,943(1970). (14) Charbonnage de France, Fr, 1,543,497(1968). (15) Porri,L., Rossi,R., Diversi,P., Lucherini,A., Polymer Preprints, (1972),13(2), 897. (16) Nakamura,R., Matsumoto,S., Echigoya,E., Chem. Lett., (1976), 1019. (17) Hepworth,P.(to ICI), Ger. Offen., 2,231,995(1973). (18) Ueshima,T., Kobayashi,S., Matsuoka,M.(Showa Denko), Ger. Offen., 2,316,087(1973). (19) Ueshima,T., Kobayashi,S., Japan Plastics, (1974), 11. (20) Van Dam,P.B., Mittelmeijer,M.C., Boelhouwer,C., Chem. Commun., (1972), 1221. (21) Van Dam,P.B., Mittelmeijer,M.C., Boelhouwer,C., Fette. Seifen Anstrichm, (1974),76, 264. (22) Ast,W., Rheinwald,G., Kerber,R., Makromol. Chem., (1976), 177, 1341. (23) Ast,W., Rheinwald, G., Kerber,R., Makromol. Chem., (1976), 177, 1349. (24) Kroll,W.R., Doyle,G., Chem. Commun., (1971), 839. (25) Sharpless,K.B., Umbreit,Μ.A., Nieh,M.T., Flood, T.C., J. Am. Chem. Soc., (1972), 94, 6538. (26) Fischer,Ε.Ο., Maasbol,A., Chem. Ber., (1967), 100, 2445.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

317

22 Polymerization of Aryl Cyclic Sulfonium Zwitterions D. L. SCHMIDT The Dow Chemical Co., Midland, MI 48640

Trialkyl sulfonium salts react with nucleophiles by dis­ placement at a carbon atom adjacent to the trivalent sulfur (1). Dialkyl sulfide is eliminated and the nucleophile becomes alkylated [eq. (1)]. Nue" + R S+ --> R-Nuc + R S (1) 3

2

Since sulfonium groups are hydrophilic, water soluble polymers may be prepared by incorporating enough of this functionality onto the polymer chains. Subsequent removal of the water and thermal curing destroys the sulfonium groups and yields water­ -insensitive polymers (2)(3)(4). Benzylmethylsulfonium salts are much more labile than simple trialkyl sulfoniums, and they react with almost exclu­ sive cleavage of the benzyl to sulfur bond (5). Because of this reactivity, polymers may be prepared at moderate temperatures by reacting [arylenebis(methylene)]bis(dimethylsulfonium) salts wit difunctional nucleophiles such as dicarboxylates or diphenolates (6)(7). Hatch (8) utilized the unique chemistry of sulfoniums by designing a zwitterionic structure that has a cyclic sulfonium attached through the sulfur to a phenolic, aromatic ring. Upon heating, these "monomers" polymerize by a mechanism involving n u c l e o p h i l i c a t t a c k by the phenolic anion upon the r i n g carbon a to the sulfonium s u l f u r [eq. (2)1.

P o l y m e r i z a t i o n proceeds by ring-opening and l o s s of charge to y i e l d a n o n i o n i c polymer (9). There are no s u l f i d e by-products from t h i s r e a c t i o n s i n c e no s u l f u r - p h e n y l bond cleavage occurs.

318

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22.

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Sulfonium

Zwitterions

319

P r e p a r a t i o n o f Monomers Five-membered c y c l i c sulfonium z w i t t e r i o n s may be prepared by three d i f f e r e n t methods. The f i r s t method (1) i n v o l v e s the r e a c t i o n of a p h e n o l i c compound w i t h tetrahydrothiopene 1-oxide and hydrogen c h l o r i d e (10). A s i m i l a r method r e q u i r e s t h e use of tetrahydrothiophene and c h l o r i n e o r s u l f u r y l c h l o r i d e w i t h a p h e n o l i c (method 2) (11)(12).

(Method 2) In both methods 1 and 2, the h y d r o c h l o r i d e s a l t s a r e converted to the z w i t t e r i o n w i t h anion exchange r e s i n (OH form). The tetrahydrothiophene s u b s t i t u t i o n goes e s s e n t i a l l y a l l para t o the p h e n o l i c hydroxy. I f the para p o s i t i o n i s blocked, the tetrahydrothiophene s u b s t i t u t e s i n the ortho p o s i t i o n ; no meta s u b s t i t u t i o n has been observed. P h e n o l i c compounds t h a t have electron-withdrawing groups (such as CI) w i l l not r e a c t under c o n d i t i o n s o f e i t h e r method 1 o r 2. C h l o r i n e - c o n t a i n i n g d e r i v a ­ t i v e s may be prepared by c h l o r i n a t i o n of the a p p r o p r i a t e z w i t t e r i o n h y d r o c h l o r i d e ( 9 ) . S i x membered c y c l i c sulfonium z w i t t e r i o n s can be prepared i n o n l y very low y i e l d s by methods 1 and 2. These compounds may be obtained by t h e r e a c t i o n o f 1,5-dibromopentanes w i t h 4-(methylthio)phenol i n r e f l u x i n g chlorobenzene t o y i e l d t h e sulfonium s a l t and methyl bromide (method 3 ) ( 9 ) . Method 3 i s a l s o a p p l i c a b l e t o the p r e p a r a t i o n of meta s u b s t i t u t e d d e r i v a t i v e s (13).

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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Br{CH > Br + CH -S 2

(Method 3)

3

OH

\ OH + CH Br 3

P r o p e r t i e s of Monomers S u l f u r to phenyl bond cleavage has not been observed w i t h a r y l c y c l i c sulfonium compounds Presumably t h i s i s because the sulfonium s u l f u r to pheny to a l k y l bond (14). Cleavag a l k y l a r y l sulfonium z w i t t e r i o n s i s much more d i f f i c u l t than w i t h five-membered c y c l i c sulfonium z w i t t e r i o n s . This i s probably due to the s t r a i n i n the five-membered r i n g . The c y c l i c sulfonium r i n g probably gains c o n s i d e r a b l e s t a b i l i t y due to the c o n t r i b u ­ t i o n of the q u i n o i d form of the resonance h y b r i d [eq. ( 3 ) ] . The r e s u l t i n g system would be d e l o c a l i z e d and thus the phenolate i o n would have decreased n u c l e o p h i l i c i t y and the c y c l i c sulfonium would have decreased p o s i t i v e charge d e n s i t y and increased s t a b i l i t y toward n u c l e o p h i l e s . T h i s i s c o n s i s t e n t w i t h the

(3)

observed l a r g e d i f f e r e n c e i n s t a b i l i t y between z w i t t e r i o n mono­ mers w i t h the sulfonium group ortho or para and those meta to the p h e n o l i c oxygen. Doorakian et a l . (13) demonstrated t h a t the meta isomers w i l l polymerize much f a s t e r and at lower temperatures (10 min. a t 40°C) than the ortho and para isomers. A l s o c o n s i s ­ t e n t w i t h resonance s t a b i l i z a t i o n of the z w i t t e r i o n i s the obser­ v a t i o n t h a t m e t h y l a t i o n of the p h e n o l i c oxygen g r e a t l y i n c r e a s e s the r e a c t i v i t y of the r e s u l t i n g c y c l i c sulfonium (15). Z w i t t e r i o n monomers t h a t are not s u b s t i t u t e d w i t h an electron-withdrawing group, such as c h l o r i n e , may be i s o l a t e d only as c r y s t a l l i n e hydrates. Attempts t o remove the water of h y d r a t i o n i n a l l cases causes p o l y m e r i z a t i o n of the monomer. S t a b i l i t y of the c r y s t a l l i n e , hydrated z w i t t e r i o n s i s probably due to t h e i r high energies of i n t e r a c t i o n w i t h the p o l a r water mole­ c u l e s i n the c r y s t a l l a t t i c e . I n t r o d u c i n g enough energy t o r e ­ move the water of h y d r a t i o n from the c r y s t a l l i n e s o l i d i s s u f f i ­ c i e n t to cause p o l y m e r i z a t i o n . In s o l u t i o n , the s t a b i l i t y of the monomers i n c r e a s e s w i t h i n c r e a s i n g p o l a r i t y of the s o l v e n t . For example, the r a t e s of p o l y m e r i z a t i o n of v a r i o u s z w i t t e r i o n s i n

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

22.

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Sulfonium

Zwitterions

321

methanol a r e between 3 and 46 times f a s t e r than the r a t e s measured i n water. Z w i t t e r i o n monomers t h a t a r e s u b s t i t u t e d w i t h c h l o r i n e have markedly d i f f e r e n t p r o p e r t i e s than the u n s u b s t i t u t e d monomers. Monomers I and I I a r e examples o f these two c l a s s e s of monomer and t h e i r p h y s i c a l p r o p e r t i e s , and p o l y m e r i z a t i o n s have been s t u d i e d i n some d e t a i l . The thermal s t a b i l i t y o f l-(4-hydroxy-3-methylphenyl)tetrahydrothiophenium hydroxide inner s a l t ( d i h y d r a t e ) , monomer I i s much lower than l - ( 3 , 5 - d i c h l o r o - 4 - h y d r o x y p h e n y l ) t e t r a h y d r o t h i o phenium hydroxide inner s a l t , monomer I I . D i f f e r e n t i a l thermal a n a l y s i s of I i n d i c a t e s p o l y m e r i z a t i o n begins a t 75°C,but monomer I I does not begin p o l y m e r i z a t i o n u n t i l 150°C (9). CI

Monomer I

Monomer I I

The s t a b i l i t y o f I I can be r a t i o n a l i z e d by two arguments: f i r s t , the n u c l e o p h i l i c i t y o f the phenoxide group i s g r e a t l y de­ creased due t o the ortho electron-withdrawing c h l o r i n e atoms; second, monomer I I does not c o n t a i n water o f h y d r a t i o n and i s a s t a b l e , c r y s t a l l i n e m a t e r i a l . Z w i t t e r i o n molecules should g a i n s t a b i l i t y by arrangement i n a c r y s t a l l a t t i c e . Monomer I prob­ a b l y gains l e s s s t a b i l i t y from c r y s t a l energy than I I because of the ease w i t h which water may be removed. Monomer I kept i n a sealed c o n t a i n e r a t room temperature polymerizes o n l y about 0.7% per year but w i l l polymerize s i g n i f i c a n t l y under vacuum i n 24 hours. Polymerization The mechanism o f p o l y m e r i z a t i o n of a r y l c y c l i c sulfonium z w i t t e r i o n s i n v o l v e s i n i t i a t i o n by displacement o f the sulfonium moiety o f one monomer by the phenolate i o n of another. The r e ­ s u l t i n g a c t i v a t e d , l i n e a r dimer has both a more r e a c t i v e c y c l i c sulfonium and a more n u c l e o p h i l i c phenolate i o n than the i n i t i a l monomer. The sulfonium moiety has increased r e a c t i v i t y because of the disappearance o f negative charge attached t o the aromatic r i n g and the l o s s o f t h e s t a b i l i z a t i o n c o n t r i b u t i o n o f the q u i n oid resonance h y b r i d . The phenolate anion o f the l i n e a r dimer has both increased n u c l e o p h i l i c i t y and b a s i c i t y due t o the l o s s of the electron-withdrawing sulfonium on the aromatic r i n g [eq. ( 4 ) ] . Thus, a f t e r i n i t i a t i o n , a z w i t t e r i o n i c , b i f u n c t i o n a l propagating species i s produced which can grow by r e a c t i o n w i t h monomer o r l i n e a r dimer from e i t h e r or both ends. I n theory, t e r m i n a t i o n o f only one end o f t h e growing polymer c h a i n should

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

322

•0 (4)

0

)

GO

A c t i v a t e d , L i n e a r Dimer

Initiation r e t a r d but not stop p o l y m e r i z a t i o n . A monofunctional c h a i n can r e a c t w i t h monomers, dimers or b i f u n c t i o n a l c h a i n s , but the monof u n c t i o n a l u n i t s cannot r e a c t w i t h each other. I f i n i t i a t i o n i s slow, chains c o u l d gro of growing, d i m e r - i n i t i a t e p l e t i o n of monomer, p o l y m e r i z a t i o n should proceed by combination of dimers and growing chains. I f i n i t i a t i o n i s f a s t , then chains would reach moderate molecular weight o n l y by the combination of s h o r t , growing chains. Because both ends are r e a c t i v e , the l i n e a r dimer or subse­ quent s h o r t , growing chains can r e a c t i n t r a m o l e c u l a r l y to form c y c l i c s . Because of the a t t r a c t i o n of the opposite charged ends of these molecules, c y c l i z a t i o n of z w i t t e r i o n i c species should be much e a s i e r than other n o n i o n i c b i f u n c t i o n a l systems. C y c l i ­ z a t i o n can proceed u n t i l the growing chains become long enough t h a t the p r o b a b i l i t y of the ends coming i n contact i s s m a l l or u n t i l t e r m i n a t i o n of e i t h e r or both ends occurs. P o l y m e r i z a t i o n s t u d i e s of c r y s t a l l i n e monomers I and I I have been reported e a r l i e r ( 9 ) . In the c r y s t a l l i n e forms, z w i t t e r i o n i c monomers should arrange themselves, due to e l e c t r o s t a t i c i n t e r ­ a c t i o n , w i t h a l t e r n a t e p o s i t i v e and negative s i t e s i n c h a i n pat­ t e r n s s i m i l a r to the arrangement of the atoms i n the polymer. T h i s o r i e n t a t i o n should f a v o r r a p i d p o l y m e r i z a t i o n and i s probably one reason f o r the f a s t p o l y m e r i z a t i o n (1-2 min.) of c r y s t a l l i n e z w i t t e r i o n s a t e l e v a t e d temperatures. Monomer I e a s i l y polymerizes merely by removal of the water of h y d r a t i o n to g i v e polymer A, p o l y [oxytetramethylenethio(3methyl-l,4-phenylene)]. A g e l permeation chromatograph (GPC) of polymer A, prepared by h e a t i n g (105°C f o r 35 min.) r e c r y s t a l l i z e d I , i s shown i n F i g u r e 1. This a n a l y s i s i n d i c a t e s t h a t be­ s i d e s polymer, c y c l i c dimer and t r i m e r are present. Mass s p e c t r o m e t r i c a n a l y s i s of the l a t t e r m a t e r i a l gave m/e peaks at 388 (dimer) and 5 8 2 ( t r i m e r ) . The dimer may be i s o l a t e d by s u b l i m a t i o n upon heating polymer A under vacuum. There was l i t t l e change i n the chromatographs of samples polymerized under vacuum or over a wide range of temperatures and times. R e c r y s t a l l i z e d samples of monomer I were mixed w i t h v a r i o u s n u c l e o p h i l e s by d i s s o l v i n g them i n methanol c o n t a i n i n g the a d d i ­ t i v e f o l l o w e d by vacuum removal of the s o l v e n t . Amines, sodium

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

22.

SCHMIDT

Polymerization

of Aryl Cyclic

Sulfonium

Zwitterions

323

i o d i d e and sodium methoxide were among the n u c l e o p h i l e s added. Changing the n u c l e o p h i l e (sodium methoxide) t o monomer I mole r a t i o between 1/500 and 1/1000 had l i t t l e e f f e c t on the g e l permeation chromatographs of polymer A samples. When the a d d i ­ t i v e t o monomer r a t i o was increased t o 1/100, the c y c l i c s t o p o l y ­ mer r a t i o was decreased and the molecular weight was lowered (Figure 1 ) . P o l y m e r i z a t i o n of c r y s t a l l i n e monomer I I , t o o b t a i n polymer B, r e q u i r e s a c o n s i d e r a b l y higher optimum p o l y m e r i z a t i o n tempera­ t u r e (170°C) than monomer I . Polymer B, polyfoxytetramethylenet h i o ( 3 , 5 - d i c h l o r o - l , 4 - p h e n y l e n e ) ] , g e n e r a l l y has a higher number average molecular weight (M^) than polymer A. U n l i k e monomer I , the p o l y m e r i z a t i o n o f I I i s very dependent upon p u r i t y . A s e r i e s of n u c l e o p h i l e s were i n c o r p o r a t e d i n t o samples of r e c r y s t a l l i z e d monomer I I and then polymerize the e f f e c t of a d d i t i v e chlorobenzene of the r e s u l t i n g polymers. I t i s evident t h a t most Table I EFFECT OF ADDITIVES ON POLYMERIZATION OF MONOMER I I ( I n i t i a l nsp = 0.22)

Additive NaCl NaBr Nal + N(CH )AOH

Additive in I I , mole-% 0.10-0.50 0.10-0.50 0.10-0.50

ηβρ A f t e r Polymerization 0.25-0.27 0.31-0.35 0.34-0.38

0.10-0.50

0.34-0.37

0.10-0.50

0.40-0.43

0.10-1.00 0.10-2.00 0.10-3.00

0.30-0.38 0.39.0.51 0.22-0.23

3

Ν,Ν,Ν,'Ν,'-Tetramethylethylenediamine N,N -Dimethyl-1,6-hexanediamine NaOCH Monomer I f

3

n u c l e o p h i l e s introduced a t an a d d i t i v e t o monomer r a t i o between 1/500 and 1/1000 increased the nsp. T y p i c a l g e l permeation chro­ matographs of polymer Β prepared from both pure monomer I I and I I w i t h added n u c l e o p h i l e a r e shown i n F i g u r e 2 (16). Although p a r t of the high molecular weight p o r t i o n o f the polymer samples i s in­ s o l u b l e i n the t e t r a h y d r o f u r a n s o l v e n t , these GPC s t u d i e s c l e a r l y i n d i c a t e t h a t l e s s c y c l i c m a t e r i a l i s formed when a n u c l e o p h i l e i s present d u r i n g p o l y m e r i z a t i o n . Solvent e x t r a c t i o n o f polymer Β samples, prepared w i t h and without added n u c l e o p h i l e , a l s o shows t h a t these a d d i t i v e s s i g n i f i c a n t l y lower the amount of c y ­ c l i c s . Most of the c y c l i c s may be removed by d i s s o l v i n g polymer Β i n hot chlorobenzene and then c o o l i n g and c o l l e c t i n g the

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

324

RING-OPENING POLYMERIZATION

(—) Polymer A from pure crystalline Monomer I (

) Polymer A from N a O C H / Monomer I = l/100 3

HEIGHT

34

32

RETENTION

30

28

26

VOLUME IN

COUNTS

Figure 1. Gel permeation ckromatographs of polymer A with and without NaOCH present during solid state polymerization (high M column H) s

n

POLYMER Β FROM R E C R Y S T A L L I Z E D II POLYMER Β FROM H WITH A D D E D ( NUCLEOPHILE.

)

HEIGHT

DIMER

Figure 2. Gel permeation chromatographs of polymer Β with and without nucleopnile present during soUd state polymerization (high M column D) n

34

32 30 28 26 24 22 RETENTION VOLUME IN COUNTS

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

SCHMIDT

22.

Polymerization

of Aryl Cyclic

Sulfonium

Zwitterions

325

p r e c i p i t a t e d polymer. These p u r i f i e d polymers have increased nsp values but the samples obtained by p o l y m e r i z i n g I I w i t h t r a c e s o f n u c l e o p h i l e s s t i l l have c o n s i d e r a b l y higher ηβρ v a l u e s than p o l y ­ mers from pure I I . Thus, the a d d i t i o n of s m a l l amounts o f n u c l e o ­ p h i l e s t o I I not o n l y g i v e s l e s s c y c l i c m a t e r i a l but a l s o y i e l d s polymers w i t h higher molecular weights. A sample o f polymer Β prepared by u s i n g sodium methoxide as an a d d i t i v e had a nsp o f 0.5 and a o f 46,000 ( 9 ) . The g l a s s t r a n s i t i o n temperature was between 4 and 10°C and the c r y s t a l l i n e m e l t i n g p o i n t was between 140 and 160°C. The s p e c i f i c g r a v i t i e s of monomer I I and polymer Β a r e r e s p e c t i v e l y 1.528 and 1.483; t h i s would i n d i c a t e an expansion upon p o l y m e r i z a t i o n . The mechanical p r o p e r t i e s o f t h i s sample o f polymer Β a r e shown i n Table I I (16).

MECHANICAL PROPERTIES OF POLYMER Β

Mechanical

Test

Ultimate t e n s i l e , p s i (ASTM D638-68) T e n s i l e modulus X 1 0 , p s i (ASTM D638-68) Elongation, % (ASTM D638-68) Heat d i s t o r t i o n , °C (ASTM D648-61) Impact s t r e n g t h , f t - l b / i n . o f notch (ASTM D256-61) s

a

Unannealed Polymer

Annealed Polymer

2960

4100

0.91

1.28

>260

>260

34

79

16+

1.84

3

Annealed 48 hr a t 110°C, then 7 days a t 70°C.

Obtaining a s o l v e n t a p p l i c a b l e f o r studying the p o l y m e r i z a ­ t i o n o f z w i t t e r i o n monomers i s d i f f i c u l t because o f the l a r g e d i f f e r e n c e i n s o l u b i l i t y between the i o n i c monomer and the noni o n i c polymers. Monomers I and I I and t h e i r subsequent polymers may be kept i n s o l u t i o n by u s i n g a s p e c i a l s o l v e n t c o n s i s t i n g of 2% d i p r o p y l e n e g l y c o l , 13% d i e t h y l e n e g l y c o l and 85% chlorobenzene. Studies o f both monomer systems were c a r r i e d out i n s e a l e d tubes a t 1% (weight s o l i d s ) s o l u t i o n . The s o l u t i o n s were heated at 65°C f o r f i v e days and the r e s u l t i n g polymers i s o l a t e d and analyzed by GPC. Monomer I was polymerized i n s o l u t i o n both as a p u r i f i e d monomer and w i t h a sodium methoxide t o monomer mole r a t i o of 1/100. The g e l permeation chromatographs of the r e s u l t i n g p o l y ­ mer A samples are shown i n F i g u r e 3. I t i s evident t h a t the nuc l e o p h i l e decreases the c y c l i c dimer t o polymer r a t i o but the r e l a t i v e amount o f dimer i s s t i l l h i g h . There i s no apparent

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

326

RING-OPENING POLYMERIZATION

change i n molecular weight w i t h t h e a d d i t i o n of n u c l e o p h i l e . The molecular weight of t h i s polymer i s much lower than those obtained by s o l i d s t a t e p o l y m e r i z a t i o n . Monomer I I was polymerized i n the s o l v e n t system w i t h v a r y ­ ing amounts o f sodium methoxide. The chromatographs of the p o l y ­ mer Β samples, obtained by u s i n g n u c l e o p h i l e t o monomer r a t i o s of 1/50 and 1/300, a r e shown i n F i g u r e 4. I t i s evident t h a t t h e a d d i t i o n of n u c l e o p h i l e decreases the c y c l i c t o polymer r a t i o but does not a f f e c t the polymer molecular weight. The of polymer B, from s o l v e n t p o l y m e r i z a t i o n of I I , i s much lower than t h a t ob­ t a i n e d by s o l i d s t a t e p o l y m e r i z a t i o n , but i t i s higher than the M of polymer A obtained from s o l v e n t p o l y m e r i z a t i o n of I . The p o l y d i s p e r s i t i e s (Μ^/Μ ) o f polymer Β samples, prepared i n s o l u ­ t i o n , have r e a l a t i v e l y low values of about 1.2. A f t e r polymer Β was i s o l a t e d from the 1/5 was allowed t o r e a c t w i t z a t i o n c o n d i t i o n s . The r e s u l t i n g polymer had a higher molecular weight and could not be completely analyzed by GPC s i n c e i t was p a r t i a l l y i n s o l u b l e _ i n the GPC s o l v e n t . The low molecular weight f r a c t i o n gave a M /M of 1.5. From t h e l i m i t e d data a v a i l a b l e , one can o n l y speculate on the d i f f e r e n c e s i n the p o l y m e r i z a t i o n mechanisms of monomers I and I I . One p o s s i b l e theory r e q u i r e s three assumptions: first, the monomers a r e more s t a b l e to p o l y m e r i z a t i o n than l i n e a r dimers and z w i t t e r i o n chains and t h i s d i f f e r e n c e i n s t a b i l i t y i s g r e a t ­ est w i t h the monomer I I system; second, z w i t t e r i o n dimers and chains can terminate by β-elimination t o give a t e r m i n a l double bond, -S-iCH2^2CH=CH ; t h i r d , z w i t t e r i o n monomers are more s t a b l e towards β-elimination than the corresponding sulfonium end groups of t h e l i n e a r z w i t t e r i o n dimers and chains. The monomers have both lowered p o s i t i v e charge on the s u l f u r s and l e s s b a s i c phen­ o l i c oxygens than the l i n e a r dimers. Both of these e f f e c t s should s t a b i l i z e the monomer c y c l i c sulfonium m o i e t i e s toward e l i m i n a ­ t i o n ( 1 ) . The s t a b i l i t y of I and I I i s born out by the observa­ t i o n t h a t r e a c t i o n of the monomers w i t h excess sodium methoxide y i e l d s mostly methoxy d e r i v a t i v e s r a t h e r than β-elimination. I n the case of z w i t t e r i o n dimers and c h a i n s , the higher p o s i t i v e charge d e n s i t y and the presence of a more b a s i c phenolate anion should promote e l i m i n a t i o n [eq. ( 5 ) ] . n

η

w

n

2

(5)

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

22.

SCHMIDT

Polymerization of Aryl

Cyclic

Sulfonium

Zwitterions

Polymer A from / » pure Monomer 1 ' Po lo ymO er m-N CHAJ__fro( Monomer I 100 1

3 =

HEIGHT

Figure 3. Gel permeation chromatographs of polymer A with and with­ out NaOCH present during solu­ tion polymerization (high M» col­ umn H) 3

36 34 RETENTION

28 32 30 VOLUME IN COUNTS

Polymer Β from ( ) JJ JJ N Oo C _0 Mo on mH erU J_ 5 J ι Polymer Β from ( ) J ι NoOCH j__ j ι Monomer IE 300 3

s

3 s

HEIGHT

J

36 34 RETENTION

32 30 28 VOLUME IN COUNTS

I 26

Figure 4. Gel permeation chromatographs of polymer Β with and without NaOCH present during the solution polymerization (high M „ column Η) s

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

328

S o l i d monomer I undergoes f a s t i n i t i a t i o n . The monomer q u i c k l y disappears and p o l y m e r i z a t i o n proceeds by combination o f dimers and s m a l l chains [eq. ( 6 ) ] . Termination can occur by c y c l i z a t i o n and β-elimination a t the s u l f o n i u m - c o n t a i n i n g end groups of the growing chains. Without t e r m i n a t i o n , these chains would continue t o grow by combination t o a t t a i n much higher than has been observed f o r polymer A. A sample of polymer A e x h i b i t e d a

I + I Î â â % L i n e a r dimer

Combination » of Small chains

/ Cyclization

> Polymer

(6)

\ β-elimination

weak i n f r a r e d band a t 91 ging v i b r a t i o n of a t e r m i n a w i t h the proposed t e r m i n a t i o n by β-elimination. Small amounts of n u c l e o p h i l e have l i t t l e e f f e c t on the p o l y ­ m e r i z a t i o n o f I . I n i t i a t i o n by a n u c l e o p h i l e i s probably not much f a s t e r than monomer t o monomer i n i t i a t i o n . Larger amounts of n u c l e o p h i l e ( F i g u r e 1) show an e f f e c t by d e s t r o y i n g more sulfonium end groups, thus preventing c y c l i z a t i o n , and a l s o by t e r m i n a t i n g the end o f growing chains. T h i s decreases the amount of c y c l i c m a t e r i a l and a l s o lowers the molecular weight o f polymer A. In s o l u t i o n , p o l y m e r i z a t i o n o f I y i e l d s h i g h amounts o f c y c l i c s and low polymer A. The low p o l a r i t y s o l v e n t system speeds i n i t i a t i o n and g r e a t l y promotes c y c l i z a t i o n due t o the i n ­ a b i l i t y of the charged species t o extend themselves and o b t a i n the charge s e p a r a t i o n needed f o r p o l y m e r i z a t i o n . The s m a l l amount of polymer probably r e s u l t s both from chains t h a t a t t a i n a nonc y c l i z a b l e s i z e and from sulfonium end group t e r m i n a t i o n . The chains then grow t o l i m i t e d s i z e by r e a c t i o n w i t h what l i t t l e monomer i s l e f t . A d d i t i o n of n u c l e o p h i l e g i v e s an e q u i v a l e n t amount of low molecular weight polymer by preventing c y c l i z a t i o n . I f monomer I I i s c o n s i d e r a b l y more s t a b l e than i t s dimer, then slow i n i t i a t i o n w i l l be f o l l o w e d by a f a s t r e a c t i o n of i n i ­ t i a t e d species w i t h monomers t o form growing chains. This mech­ anism [eq. (7)] w i l l l e a d t o h i g h molecular weight and should not be very s e n s i t i v e t o t e r m i n a t i o n by β-elimination. The concenII + 1 1 - ^ ^

ι

Dimer + I I ^ I L » Polymer Β

(7)

C y c l i c dimer t r a t i o n o f low molecular weight chains capable o f t e r m i n a t i o n would remain low. When monomer becomes depleted, then growth by combination of chains would predominate. Because o f the decreased b a s i c i t y o f t h e c h l o r i n e - f l a n k e d phenolate anion o f I I ,

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

22.

SCHMIDT

Polymerization

of Aryl Cyclic

Sulfonium

Zwitterions

329

t e r m i n a t i o n by β-elimination should be l e s s l i k e l y d u r i n g the p o l y m e r i z a t i o n o f monomer I I than I . Added n u c l e o p h i l e can r e a c t w i t h I I a t temperatures w e l l below the p o l y m e r i z a t i o n o f pure I I (9). N u c l e o p h i l e would pro­ duce an end-capped, i n i t i a t e d species and propagation would pro­ ceed c h i e f l y by r e a c t i o n o f monomer w i t h growing chains [eq. ( 8 ) ] . This would r e s u l t i n both an i n c r e a s e i n molecular weight and l e s s cyclic material. Nuc"

fast

+ II

(8)

•Polymer Β

>Nuc{CH >4S 2

CI

Cyclization

In s o l u t i o n , as i n t h e case o f monomer I , c y c l i z a t i o n should predominate. The polyme from those chains t h a t end-capped. The polymer Β produced has a l a r g e r M than polymer A obtained under the same r e a c t i o n c o n d i t i o n . Presumably, t h i s i s because the higher c o n c e n t r a t i o n o f t h e more s t a b l e I I a l l o w s longer chains t o form. I n s o l u t i o n , the a d d i t i o n of n u c l e o p h i l e a l s o prevents c y c l i z a t i o n and thus i n c r e a s e s the amount o f p o l y ­ mer B. The r e l a t i v e l y low M^/Mn o f 1.2 would be c o n s i s t e n t w i t h most o f the i n i t i a t i o n o c c u r r i n g a t the beginning o f t h e r e a c t i o n f o l l o w e d by r e a c t i o n o f monomer w i t h growing chains. A d d i t i o n o f I I t o p r e v i o u s l y prepared polymer Β g i v e s higher molecular weight golvmer by growth o f p r e v i o u s l y formed polymer w i t h monomer. The i n c r e a s e s i n t h i s case because, besides growth due t o p r e ­ v i o u s l y formed c h a i n s , new i n i t i a t i o n o c c u r r s t o g i v e a lower molecular weight polymer f r a c t i o n . n

Utility L i n e a r polymers from monomers s i m i l a r t o I and I I do n o t appear t o have very much commercial p o t e n t i a l because of t h e i r h i g h p r o d u c t i o n c o s t s and poor p r o p e r t i e s . By i n c o r p o r a t i n g two or more z w i t t e r i o n s i n the same molecule, monomers a r e obtained that y i e l d h i g h l y c r o s s l i n k e d polymers (17) [eq. (9)] . These

h e a t

- δ

O Î - 0 - -

ο

> Crosslinked polymer

X = b r i d g i n g group

(-CH -, L K C H > 0 » 2

2

2

or - C ( C H ) -

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

3

2

(9)

RING-OPENING POLYMERIZATION

330

monomers appear promising i n water-based c o a t i n g a p p l i c a t i o n s . The p o l y f u n c t i o n a l monomers g i v e h i g h - s o l i d s , l o w - v i s c o s i t y , aqueous s o l u t i o n s which cure a t low temperatures t o y i e l d h i g h l y crosslinked coatings. P o l y f u n c t i o n a l monomers may a l s o be used as an e f f i c i e n t method of c r o s s l i n k i n g w a t e r - s o l u b l e or waterd i s p e r s i b l e carboxy-containing polymers (18). The carboxy groups r e a d i l y open sulfonium r i n g s to y i e l d e s t e r s . The adhesion of c a r b o x y - c o n t a i n i n g , l a t e x based f i l m s i s g r e a t l y increased by the a d d i t i o n o f as l i t t l e as 1 t o 5 weight % of p o l y f u n c t i o n a l monomers (19)(20). Acknowledgment I am indebted t o J . R. Runyon and J . E. Jones f o r the g e l permeation chromatograp i n t e r p r e t a t i o n of i n f r a r e mental work c a r r i e d out by D. U r c h i c k and f o r v a l u a b l e d i s c u s s i o n s w i t h T. A l f r e y , G. D. Jones, T. C. K l i n g l e r , W. C. Meyer R. A. Wessling, J . W. Rakshys and R. A. K i r c h h o f f . Literature Cited 1. Ingold, C. Κ., "Structure and Mechanism in Organic Chemistry" 2nd ed., Cornell Univ. Press, Ithaca, N.Y., 1969, Chapter VII and IX. 2. Hatch, M. J. and McMaster, E. L., U.S. Patent 3,078,259 (1963); Chem. Abstr. 58, 10327a (1963). 3. Wessling, R. A. and Zimmerman, R. G., U.S.Patent 3,401,152 (1968); Chem. Abstr. 69, 87735 (1968). Fang, J. C., U.S. Patent 3,310,540 (1967); Chem. Abstr. 66, 106007 (1967). 5. Swain, C. G. Burrows, W. D. and Schowen, B. J., J. Org. Chem. 33, 2534 (1968). Hatch, M. J., U.S. Patent 3,502,710 (1970); Chem. Abstr. 72, 121180 (1970). 7. Alfrey, T., paper presented in part at the Biannual Polymer Symposium, Ann Arbor, Michigan, June 13, 1972. 8. Hatch, M. J., Yoshimine, Μ., Schmidt, D. L. and Smith, Η. Β., J. Amer. Chem. Soc., 93, 4617 (1971). 9. Schmidt, D. L., Smith, Η. Β., Yoshimine, M. and Hatch, M. J., J. Polym. Sci., A-1,10, 2951 (1972). 10. Goethals, E. and deRadzitsky, P., Bull. Soc. Chem. Belg., 73, 546 (1964). 11. Cisney, M. E. and Camas, Μ., U.S. Patent 3,259,660 (1966). 12. Klingler, T. C., Schmidt, D. L., Jensen, W. J. and Urchick, D., U.S. Patent applied for. 13. Doorakian, G. A. and Schmidt, D. L., U.S. Patent applied for. 14. Price, C.C. and Oae, S., "Sulfur Bonding", Ronald Press, New York, N.Y., 1962, pp. 151-158.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

22.

SCHMIDT

Polymerization

of Aryl Cyclic

Sulfonium

Zwitterions

15. Schmidt, D. L., Smith, Η. Β., Hatch, M. J. and Broxterman, W. Ε., U.S. Patent 3,898,247 (1975); Chem. Abstr., 84, 5824 (1976). 16. Used by permission of John Wiley and Sons, Inc., Publishers, 605 Third Ave., New York, N.Y. see Reference 9. 17. Schmidt, D. L., Smith, H. B. and Broxterman, W. E., J. Paint Technol. 46, 41 (1974). 18. Julier, R. Μ., The Dow Chemical Company, personal communi­ cation, 1976. 19. Plueddemann, E. P., paper presented at Symposium on Polyelec­ trolytes and Their Applications, California Institute of Technology, May 23-25, (1973). 20. Bergman, R. W. and Schmidt, D. L., The Dow Chemical Company, private communication, 1977.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

331

23 Spontaneous Alternating Copolymerization of Cyclic Phosphorus Compounds via Phosphonium Zwitterion Intermediates ΤΑΚΕΟ SAEGUSA, SHIRO KOBAYASHI, YOSHIHARU KIMURA, and TSUNENORI ΥΟΚΟΥΑΜΑ Department of Synthetic Chemistry, Faculty of Engineering, Kyoto University, Kyoto 606, Japan

Induction of polymerization reaction usually requires initiator (or catalyst) or radiation. Recently we have explored a new type of copolymerization which takes place spontaneously without any added catalyst (1). In this copolymerization, the reactivity characters of two monomers are very important, i.e., one is of nucleophilic reactivity (MN) and the other is of electrophilic reactivity (ME). Reaction occurs between two monomers to produce a zwitterion 1 (Eq 1), which is responsible for initiation as well as for propagation.

The two moles of the "genetic zwitterion" 1 react with each other to produce its dimer 2 which is the smallest species of propaga­ tion (Eq 2). Then, the propagation species grows by its reaction with 1 (Eq 3). Zwitterions 2 and 3 (n ≥ 21) are called "macro zwitterion", which are differenciated from genetic zwitterion 1. The intermolecular reaction between two moles of macrozwitterion and the intramolecular cyclization of macro zwitterion are also possible, although the contribution of each process depends upon the natures o f monomers, r e a c t i o n c o n d i t i o n s and the extent of monomers conversion. In a d d i t i o n , f r e e monomers sometimes take p a r t i n propagation, i . e . , Mfl and may r e a c t r e s p e c t i v e l y w i t h t h e c a t i o n i c and a n i o n i c s i t e s of z w i t t e r i o n (genetic o r macro)(Eqs 4 and 5 ) . 1

332

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Phosphonium Zwitterion Intermediates

SAEGUSA ET AL.

23.

^ +

M -eM M ^-M N

E

N

+

333

M M -f M M ^ - M N

N

E

N

(4)

E

E

(5) (nil)

When the processes o f Eqs 1-3 occur e x c l u s i v e l y throughout the course o f p o l y m e r i z a t i o n , a l t e r n a t i n g copolymer -(· MJJM is produced. I n many combinations o f MJJ and Mg, the s o - c a l l e d spontaneous a l t e r n a t i n g copolymerizatiens have been r e a l i z e d . I n some cases, however, one o f homo-propagations o f Eqs 4 and 5 takes p l a c e t o r e s u l t i n copolymer e

I l l u s t r a t i v e Example of Spontaneous Alternating Copolynerization A l t e r n a t i n g c o p o l y m e r i z a t i o n between 2-oxazoline and ft p r o p i o l a c t i o n e 5 (BPL) occurs t room temperature through t h e g e n e t i c z w i t t e r i o n 6, where 4 a c t s as and 5 behaves as ( 2 , 3). a

-f-CH CH N 9

9

HC=0

CH CH C0 ±r 9

9

0

The i n t e r a c t i o n between two z w i t t e r i o n s ( g e n e t i c z w i t t e r i o n o r macro z w i t t e r i o n ) occurs v i a the opening o f the o x a z o l i n i u m r i n g of the c a t i o n i c s i t e (Eq 6 ) . Ν Ν

CO"

C O ' ^ ^ 5 II

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

(6)

RING-OPENING POLYMERIZATION

334 Scope o f Spontaneous C o p o l y m e r i z a t i o n

On the b a s i s of the above-mentioned p r i n c i p l e , many c o p o l y m e r i z a t i o n s have been explored by the combinations o f s e v e r a l M ^ and monomers. Table I shows the s t r u c t u r e s of s i x monomers and seven ME monomers as w e l l as the c a t i o n i c and a n i o n i c s p e c i e s which are d e r i v e d r e s p e c t i v e l y from these two groups of monomers. Among 42 p o s s i b l e combinations of copolymeri­ z a t i o n , 2 4 e s s e n t i a l ones have been examined, which are shown by the r e s p e c t i v e r e f e r e n c e s . A l t e r n a t i n g C o p o l y m e r i z a t i o n s o f C y c l i c Phosphorus Compounds The main t o p i c of the present paper i s the c o p o l y m e r i z a t i o n of c y c l i c phosphorus compounds and 2-phenoxy-l,3,2-dioxaphospholan

Copolymerizations o f 2-Phenyl-l,3,2-dioxaphospholane 11 Without any added c a t a l y s t , 11 has s u c c e s s f u l l y been copolymerized w i t h s e v e r a l ME monomers such as /3 - p r o p i o l a c t o n e 13 ( 1 3 ) , 3-hydroxypropanesulfonic a c i d l a c t o n e (propanesultone) 15 ( 1 4 ) , a c r y l i c a c i d 16 ( 1 3 ) , acrylamide 17 ( 1 3 ) , ethylenesulfonamide 19 ( 1 4 ) , a c r y l i c e s t e r ( 1 6 ) , v i n y l ketone ( 1 6 ) and o( -keto a c i d (17). I n every case, c o p o l y m e r i z a t i o n occurs at temperatures above 100°C to produce a l t e r n a t i n g copolymer. The two copolymers o f the combinations of 11-BPL and 11-acryl i c a c i d have the i d e n t i c a l s t r u c t u r e of 23 which i s d e r i v e d from the common z w i t t e r i o n 22. I n the case w i t h a c r y l i c a c i d , an unstable carbanion i n t e r m e d i a t e i s f i r s t formed, which i s then transformed i n t o 22 by hydrogen t r a n s f e r .

η

—fr\

+/Ph

a c r y l i c acid

CH CHCO HJ 2

2

21

11 I —

BPL

c

Ph 1

-f-CH CH 0-P-CH CH CO-^ 2

(/ CH,CH,C0 '

2

2

N

22

£

1

ά

23

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2

Phosphonium

23. SAEGUSA E T A L .

Zwitterion

Intermediates

335

Table I N u c l e o p h i l i c and E l e c t r o p h i l i c Monomers and Ionic Groups Derived from Them

M

I

N

+

- M

—

E

-

Ν -CH CH C0 " 2

^ O ^ R

7

Ox

(Z» 8.12)

8

Ç^NR

0 ' + 'Ν I

(U)

9

> / \ - M e Me

-

« 0

14

°

2

2

2

(1. ] 5 )

N^so 15

R

2

0 10-13 \ 15 /

13

(2-9)

2

-(CH ) S0 " 2

3

3

2

(5, 14)

M

\y 10

11

x

C0 H

Me

2

2

2

16 (6,10-1_3,J15)

s* NH C0NH

17

(13, 14)

(15)

-CH CH C0 "

2

Ph

Ph-CH=N-Ph

12

\y

(12)

L /0

Me

Ph-CHTT^=N+ I

-CH2 CH2 C ν ™ 0

2

(7, 13)

^COCH.CH, II 21 2 0

Ph

18

0

OH

-CHgCHgCO^

CCH2CH2 " 0

(8)

=\

0

S0 NH 2

19

^o

-CH,CH,S,— 0 2

( 9 , 14)

2

"s.-

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

336

RING-OPENING POLYMERIZATION

The r e a c t i o n mode o f the opening o f the phosphonium r i n g o f 22 i s understood on the b a s i s o f the scheme o f the Arbuzov r e a c t i o n . Here i t i s t o be noted t h a t the t r i v a l e n t phosphorus i n 11 i s o x i d i z e d t o pentavalent s t a t e d u r i n g c o p o l y m e r i z a t i o n . In the c o p o l y m e r i z a t i o n s o f 11 w i t h acrylamide 17 and ethylenesulfonamide 19, hydrogen t r a n s f e r occurs s i m i l a r l y i n t h e f i r s t - f o r m e d carbanion z w i t t e r i o n s 24 and 26, r e s p e c t i v e l y .

η

o +/ N

17

1

h

O^CHgCHCONHgJ

-c

0 +/Ph N

Λ Ο'

CH,CH,,CNH

24 11

t

19

2

( 0

2

8

25 /

x

CH CHS0 NH . 2

2

(/

2

26

N

CH CH S0 NH 2

2

2

27

The r e a c t i o n s i t e s o f the a n i o n i c p a r t o f ambident nature i n 25 and 27 are d i f f e r e n t from each o t h e r , i . e . , the r e a c t i o n occurs at n i t r o g e n atom i n 25 and oxygen atom i n 27. The s t r u c t u r e s o f the two a l t e r n a t i n g copolymers are expressed by 28 and 29, r e s p e c t i v e l y . The r e g i o s p e c i f i c i t y o f the ambident anions was q u i t e h i g h . The understanding o f the d i f f e r e n c e o f the s i t e o f n u c l e o p h i l i c r e a c t i o n between the two ambident anions r e q u i r e s further studies. Ph 25

27

- f CH CH OP-CH CH CONH - f c Z c (ι Ζ I 'p 0 28 Ph 0 I H CH CH OP-CH CH S-0 - h 2 2 H 2 2 p 0 NH 29 0

_ ·=^--,

9

9

9

9

9

9

9

7

M

In the r e a c t i o n s o f 11 w i t h 16 (or 13) and w i t h 17 a t lower temperatures (e.g., room t e m p e r a t u r e — 5 0 ° C ) , pentacovalent phosphorus compounds o f s p i r o r i n g system, 30 and 31 were produced i n h i g h y i e l d s , which were i s o l a t e d i n c r y s t a l l i n e form ( 1 8 ) . The two compounds o f 30 and 31 are a new c l a s s o f pentacovalent organophosphorus compounds, which are d e r i v e d by the i n t r a m o l e ­ c u l a r r i n g c l o s u r e s i n the z w i t t e r i o n s 22 and 25. On h e a t i n g at temperatures above 1 2 0 ° C , each o f 30 and 31 was polymerized to produce 23 and 28, r e s p e c t i v e l y . At h i g h temperatures, P - 0

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

23.

Phosphonium Zwitterion Intermediates

SAEGUSA E T A L .

11

+

337

16 (or 13)

30 (mp,80°C)

11

17

bond o f 30 and P-N bond o f 31 are broken i n a h e t e r o l y t i c way t o generate z w i t t e r i o n s 22 and 25, and the p o l y m e r i z a t i o n s proceed v i a these z w i t t e r i o n s . Thus, the homopolymerizations o f 30 and 31 c o n s t i t u t e a n o v e l p a t t e r n o f the " t h e r m a l l y induced r i n g - o p e n i n g polymerization v i a zwitterion." A l t e r n a t i n g c o p o l y m e r i z a t i o n s o f 11 w i t h a c r y l a t e (32a) and w i t h v i n y l ketones (32b and 32c) o c c u r r e d a t 130°C t o g i v e lower molecular weight polymers (mol. wt. 700-1600) (Eq 7) (16).

11

+

CH =CHCZ 2 n 0

32a b c

Z=0Me Z=Me Z=Ph

f

0-P

yo ζ

Ph ι CH CH 0P-CH,ÇH 2, CZ 2

2

II

0

33 (7)

At lower temperatures (room temperature t o 50°C), pentacovalent phosphorus compounds o f a s p i r o s t r u c t u r e , 35a and 35b were obtained i n f a i r l y good y i e l d s . They were formed by the combi­ n a t i o n o f c a t i o n i c s i t e (phosphorus atom) and a n i o n i c s i t e (oxygen o f e n o l a t e ) .

C

0-P

i^Ph I 0.

35a Z=0Me (bp, 107-nO°C/0.04 mmHg) b Z=Me

(mp,131°C)

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

338

Heating o f i s o l a t e d samples o f 35a and 35b i n b u l k a t 200°C gave polymers 34a and 34b, r e s p e c t i v e l y . E x t e n s i o n o f the c o p o l y m e r i z a t i o n o f Eq 7 has brought about a very i n t e r e s t i n g f i n d i n g o f the 1:1:1 a l t e r n a t i n g t e r p o l y m e r i z a t i o n o f 11, 32a and C 0 (Eq 8) ( 1 6 ) . 2

0 11

+

32a

+

C0 2

—

9

- f CH CH OP-CH CH 2 2 ι 21 9

9

Ph Thus, was i n t r o d u c e d a t atmospheric mixture o f 11 and 32a a the key i n t e r m e d i a t e whic the carbanion o f e n o l a t e anion o f 37. ?. Π+

Ph

co,

32a—- 0-P*^ CH„CH I C0 Me 37 %

1

( N

- C 0 4rκ 'ρ

9

C0 Me

0

2

36 (8) pressure t o an equimolar

? 0 - P

Ph +

—

/

36

CH„CH-C0, " 2| 2 C0 Me 38

9

9

ά

ά

In the above t e r p o l y m e r i z a t i o n , 32a can be r e p l a c e d by a c r y l o n i t r i l e , i . e . , a 1:1:1 a l t e r n a t i n g terpolymer o f 39 was success­ f u l l y prepared under atmospheric pressure o f CO^ (Eq 9 ) . 0 + CH =CHCN +

11

9

C0

9

— —

-tCH CH 0P-CH CH-C0^9

9

(9)

9

Ph

CN 0

39 Copolymerization o f 11 w i t h 3-hydroxypropanesulfonic a c i d s u l t o n e 15 proceeds a t 140°Cin b e n z o n i t r i l e t o produce the a l t e r n a t i n g copolymer o f 41 (14). The f o l l o w i n g scheme may w e l l be assumed.

11 + < f \ , N

—

15

°\

cn

—

0-P^

P h

\ ^

o UJn

\ ^ \

2

= = - - e C H , C H , 0 P - ( C H , ) , S 0 1_ I 3||η ρ nu 2

^ en

^\^S0~

ΜΛ

2

2

Ph 4

0

1

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Phosphotiium

23. SAEGUSA E T A L .

Zwitterion

Intermediates

339

Another i n t e r e s t i n g c o p o l y m e r i z a t i o n o f 11 was discovered w i t h 4-carboxybenzaldehyde 42 . At 130-140t, a l t e r n a t i n g copolymer 43 was produced (20).

0 11

+

- f CH CH 0P-0CH -^J^-C0 -^

0HC-£j^-C0 H

2

2

2

2

2

Ph

42

43

A z w i t t e r i o n 44 i s assumed t o be the key i n t e r m e d i a t e .

Cl

c

11 + 42

0-P OCH-@-CO HJ 2

0 C H

44

2Vl/ 45

C 0

2"

These copolymerizations a r e c l o s e l y r e l a t e d t o the a l t e r n a t i n g c o p o l y m e r i z a t i o n o f c y c l i c phosphite 20 w i t h o(-keto a c i d which i s discussed i n the f o l l o w i n g s e c t i o n . Copolymerization of 2-Phenoxy-l,3,2-dioxaphospholane 20 The second c y c l i c phosphorus compound which was s u c c e s s f u l l y adopted as Mfl i s 2-phenoxy-l,3,2-dioxaphospholane 20, a c y c l i c phosphite. The c o p o l y m e r i z a t i o n o f 20 w i t h ^C-keto a c i d 46 i s of b i g i n t e r e s t (19).

0 20

+

RCOLH

0 46a b

—

il

- f CHΖ CH20P-0CHC0 r ι ι 2- h'p o

O

O

OPhR R=Me R=Ph

47a b

The above a l t e r n a t i n g c o p o l y m e r i z a t i o n occured a t 120°C. At 0°C, an equimolar mixture o f 20 and 46 i n ether produces a c y l pentaoxyphosphorane d e r i v a t i v e s 48 (21). This f i n d i n g has opened a new s y n t h e t i c method of pentaoxyphosphorane.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

340

RING-OPENING POLYMERIZATION

0 48a b

R=Me (mp,87°C) R=Ph (mp 60-62°C) ;

Heating o f 48a i n b u l k a t 120°Cproduced i t s polymer 47a. The f o l l o w i n g scheme o f r e a c t i o n s e x p l a i n s the a l t e r n a t i n g c o p o l y m e r i z a t i o n as w e l oxyphosphorane. A z w i t t e r i o hydrogen t r a n s f e r i n a t r a n s i e n t z w i t t e r i o n 49, acts as a key i n t e r m e d i a t e i n these two i n t e r e s t i n g r e a c t i o n s .

20+46

Two s i g n i f i c a n t p o i n t s a r e t o be p o i n t e d out from the view­ p o i n t o f p o l y m e r i z a t i o n chemistry. Thus, o< -keto a c i d has been copolymerized f o r the f i r s t time. I n the c o p o l y m e r i z a t i o n , one monomer i s o x i d i z e d and the other i s reduced. I t may be w e l l c a l l e d "Redox C o p o l y m e r i z a t i o n " , which i s e n t i r e l y d i f f e r e n t from the s o - c a l l e d " R e d o x — i n i t i a t e d P o l y m e r i z a t i o n " where a f r e e r a d i c a l i s produced by the redox r e a c t i o n between an o x i d i z i n g and a reducing components. From organic s y n t h e s i s , the above f i n d i n g s a r e a l s o s i g n i f i c a n t , i . e . , aC-hydroxy a c i d i s r e a d i l y obtained by the h y d r o l y s i s o f 48. I n p r a c t i c a l s y n t h e s i s , t h e i s o l a t i o n o f 48 i s not necessary. Reduction o f oC-keto a c i d t o oL -hydroxy a c i d i s r e a d i l y performed i n a s i n g l e batch process at room temperature, i . e . , admixing o f 20 w i t h 46 followed by the h y d r o l y s i s o f the r e a c t i o n mixture (22). Copolymerization o f a six-membered c y c l i c phosphite 51 w i t h 46 a l s o occurred without added c a t a l y s t (23). However, t h e product copolymer d i d not possess the 1:1 a l t e r n a t i n g s t r u c t u r e as expressed by 52 (Eq 1 1 ) .

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Phosphonïum

23. SAEGUSA E T A L .

C o'

>

Zwitterion

Intermediates

341

+ 46

51

R

0

CHCO-)i n 0

-f(CH ) 0P0 2

3

OPh 52

^-0

OPh

(H)

(n-1.5-3.0)

P r o d u c t i o n o f excess amoun i s due t o the n u c l e o p h i l i growing s p e c i e s onto the oC-carbon atom o f c a r b o x y l a t e o r c a r b o x y l i c group i n a z w i t t e r i o n 53. 0

path 1

OPh

path 1 2 path 2

-C0-(CH )~P-0CHC0 9

0

0 CHCO"

ι

R

*

p

a

t

h

I

9

OPhR

r \ /°

'

-C0-CHC0 ~ + ( 9

Ph

χ

53

I n t h e case o f five-membered r i n g , t h e r i n g - o p e n i n g path occurred e x c l u s i v e l y t o produce the a l t e r n a t i n g copolymer. The d i f f e r e n c e may be a t t r i b u t e d t o t h e d i f f e r e n c e o f the r i n g - o p e n i n g r e a c t i v i t y between f i v e - and six-membered c y c l i c phosphonium r i n g s . Furthermore, t h e r e l a t i v e c o n t r i b u t i o n o f each path i n 53 i s dependent upon the nature o f R and t h e r e a c t i o n c o n d i t i o n s such as temperature and s o l v e n t . try Spontaneous a l t e r n a t i n g c o p o l y m e r i z a t i o n s o f two c y c l i c phosphorus compounds, 2-phenyl-l,3,2-dioxaphospholane 11 and 2phenoxy-l,3,2-dioxaphospholane 20, w i t h s e v e r a l e l e c t r o p h i l i c monomers were d i s c u s s e d . As the e l e c t r o p h i l i c monomers, fip r o p i o l a c t o n e 13, 3-hydroxypropanesulfonic a c i d l a c t o n e (propanes u l t o n e ) 15, a c r y l i c a c i d 16, acrylamide 17, a e r y l a t e were s u c e s s f u l l y copolymerized w i t h 11. At temperatures lower than those of c o p o l y m e r i z a t i o n , the combinations o f 1 1 — 1 3 , 11—16, 11 — 17 and 1 1 — a e r y l a t e produced trioxyphosphorane d e r i v a t i v e s having s p i r o - r i n g s t r u c t u r e s , which were s i g n i f i c a n t i n two

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

RING-OPENING POLYMERIZATION

342

r e s p e c t s , i . e . , a s t r o n g support to the p o l y m e r i z a t i o n mechanism as w e l l as a new f a m i l y of organophosphorus compounds. These s p i r o - r i n g P compounds were polymerized on h e a t i n g . These p o l y m e r i z a t i o n s c o n s t i t u t e a new type of ring-opening polymeriza­ t i o n , which i s induced t h e r m a l l y and proceed through z w i t t e r i o n i n t e r m e d i a t e . Another c y c l i c phosphite of 20 was s u c c e s s f u l l y copolymerized w i t h oC-keto a c i d s such as p y r u v i c a c i d 46a and p h e n y l g l y o x i l i c a c i d 46b without any added c a t a l y s t . This c o p o l y m e r i z a t i o n may w e l l be c a l l e d "Redox Copolymerization" i n which 20 was o x i d i z e d and o(-keto a c i d was reduced. v

"Literature Cited" 1. Review articles on "Spontaneous Alternating Copolymerization via Zwitterion Intermediate". a) Saegusa, T., Chem. Tech. (Amer. Chem. Soc), (1975) b) Saegusa, T., Kobayashi, S., Kimura, Y. and Ikeda, Η., J. Macromol. Sci. Chem., (1975) A-9, 641; c) Saegusa, T., Kobayashi, S. and Kimura, Y., Pure and Appl. Chem., in press. Saegusa, T., Angew. Chem., in press. Saegusa, T., Ikeda, H. and Fujii, Η.,Macromolecules, (1972) 354. Saegusa, T., Kobayashi, S. and Kimura, Y., Macromolecules, (1974) 7, 1. 4. Saegusa, T., Kimura Y. and Kobayashi, S.,Presented at 28th Annual Meeting of Soc. Polymer Sci., Japan, April, 1973. 5. Saegusa, T., Ikeda, H., Hirayanagi, S. and Kobayashi, S., Macromolecules, (1975) 8, 259. 6. Saegusa, T., Kobayashi, S. and Kimura Y., Macromolecules, (1974) 7, 139. Saegusa, T., Kobayashi, S. and Kimura, Y., Macromolecules, (1975) 8, 374. 8. Saegusa, T., Kimura Y. and Kobayashi, S., Macromolecuels, (1977) 10, in press. 9. Saegusa, T., Kobayashi, S. and Furukawa, J., Macromolecules, (1976) 9, 728. Saegusa, T., Kimura, Y. and Kobayashi, S., Macromolecuels, (1977) 10, in press. 11. Saegusa, T., Kimura, Y. and Sawada, S. and Kobayashi, S., Macromolecules (1974) 7, 956. 12. Saegusa, T., Kimura, Y., Sawada, S. and Kobayashi, S., Macromolecules (1974) 7, 956. 13. Saegusa, T., Kimura, Y., Ishikawa, N. and Kobayashi, S., Macromolecules (1976) 9, 724. 14. Saegusa, Τ. , Kobayashi, S. and Furukawa, J., Macromolecules, (1977) 10, in press. 15. Saegusa, T., Kobayashi, S. and Furukawa, J., Macromolecules, (1975) 8, 703.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

23. SAEGUSA E T A L .

Phosphonium Zwitterion Intermediates

16. Saegusa, T., Kobayashi, S. and Kimura, Y., Macromolecules, (1977) 10, in press. 17. Saegusa, T., Yokoyama, T. and Kobayashi, S., to be published. 18. Saegusa, T., Kobayashi, S. and Kimura, Y., J. Chem. Soc., Chem. Commun., 1976, 443. 19. Saegusa, T., Yokoyama, T., Kimura, Y. and Kobayashi, S., to be published. 20. Saegusa, T., Yokoyama, T., Kimura, Y. and Kobayashi, S., Presented at 26th Annual Meeting of Soc. Polymer Sci., Japan, May 1976; Submitted to Macromolecules. 21. Saegusa, T., Kobayashi, S., Kimura, Y. and Yokoyama, T., J. Amer. Chem. Soc., (1976) 98, 7843. 22. Saegusa, T., Kobayashi, S., Kimura, Y. and Yokoyama, T., Submitted to J. Org. Chem. 23. Saegusa, T., Yokoyama, T. and Kobayashi, S., Unpublished results.

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

343

INDEX

Absorbance, effect of composition on 257 Acetals 60,65,77 Acetone 308 l-Acetoxy-2,3-butadiene 299 Achiral enantiogenic process 206 Acid anhydride, dibasic 146,147 Acrylamide 334,336 Acrylic acid 33 Acrylic ester 33 Acrylonitrile 300 cycloaddition, 1-acetoxy2,3-butadiene/ 299 Acylamidine salts used as model compounds 138 Acylamidinium ions 136 Acyl fluoride, difunctional 277 Additives on polymerization, effect of 203,323 AgX precipitation 30 Aldehyde syntheses 116 Aldehydes, polymerization of 112 Alkali metal counterfoil 223 Alkoxide initiator, trimer 277 Alkylimino group 146 Aliènes, cycloadaitions of substituted 300 Allyl chloride 26 Allyl halide 27,32 Amides, protonation of 130 Amidine HC1 groups 139 Amines, cyclic 1 jS-(4-Aminophenyl) propionic acid ... 251 Anion, α-cyanobutyl 287 Anionic polymerization (see Polymerization, anionic) Antisteric choice 196 Antisteric process 196 Asymmetric polymer synthesis 204 N- ( Azacyclohepten- ( 1 ) -yl- ( 2 ) ) caprolactam 138 Azetidines 9 Aziridine, N-substituted 147

Β Benzimidazole Benzocyclobutene Benzocyclopropenecarbonitrile Benzonate end-groups 1-Benzyl aziridine (BA)

282 285 285 68 6,9

l-Benzyl-2,2-dimethyl aziridine (BDMA) 9 l-Benzyl-2-methyl aziridine (BMA) .. 9 BenzylmethylsuEonium salts 318 Bicyclobutane-l-carbonitrile 286 Bicyclobutanes 285,291 Bicyclopentane-[1.1.0]carbonitrile .... 285 Bicyclo[2.1.0]pentane monomers 292 Bimolecular reactions 247 Bisoxonium salt, monomer bisester and trimer 21 Bisphenol-A diglycidyl ether 51 Block copolymerization 5,171 Bond acyclic double 311 angle distortion 249 carbonyl double 113 Bromal 120 Bulk polymerization of perhaloacetaldehydes 118 Bulky substituent 178 l,2-Butadien-4-ol 299 (2,3-Butadienyloxy)trimethylsilane .. 300 l-ter£-Butylaziridine 5,6 (R)-teri-Butyloxirane 180,182,186,189 P((RS)-ieri-Butyloxirane) 188 Butyl rubbers, halogenated 33,34 terf-Butylthiirane 203 n-Butyraldehyde (BA) 308

C - C bond opening, ring-opening polymerization via 285 ll-CF-4, polymerization of 100,107 CM7, conversion data for 243 Cadmium allyl thiolates 194 Cadmium salt catalysts 193 Caprolactam copolymeriaztion with organometallic compounds 149 epsilon ( c-caprolactams) 63,148 with £-(3,4-diaminophenyl) propionic acid, copolymeri­ zation of 251 - L i C l , phase diagram of 223 polymerization of 222

345

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

346

RING-OPENING

Caprolactam ( Continued ) - L i C l mixtures, polycaproamide synthesized from 229 polymers, cationic 134 Caprolactone copolymerization with organometallic compounds 149 Carprolactone, epsilon ( c-caprolactone ) 148,152 polymerization of 152 Carbene complex-based catalysts, W 310 Carbocation 109 Carbonyl double bond, polarization of the 113 4-Carboxy-6-alkyl-2-piperidone 236 4-Carboxy-5-alkyl-2-pyrrolidone 236 4-Carboxy-6-ethyl-2-piperidone 234 4-Carboxy-5-ethyl-2-pyrrolidone 234 Carboxylic groups, concentration of .. 139 α-Carboxymethyl caprolactam 234,23 β-Carboxymethyl caprolactam 234,236 Carboxymethyl lactams 234 4-Carboxymethyl-2-piperidone 234 4-Carboxy-6-methyl-2-piperidone 234 /3-Carboxymethyl-2-piperidone 236 4-Carboxymethyl-2-pyrrolidone 234,236 4-Carboxy-5-methyl-2-pyrrolidone .... 234 4-Carboxy-2-piperidone 234,236 4-Carboxy-2-pyrrolidone 234,236 Catalysis, electrophilic 246 Catalyst(s) cadmium salt 193 coordination 161,165 lithium tetraalkylaluminate 149 metathesis 303 ring-opening coordination 165 site control 166 W carbene complex-based 310 Ziegler type 306 Catalytic activity, enhancement of the 309 behavior in homopolymerization ... 168 properties 167 Cationic oligomerization of (R)-terf-butyloxirane 186 Cationic polymerization (see Polymerization, cationic) Ceiling temperature of perhaloacetaldehyde polymerization 124 1- ( 2-Ceproethyl ) aziridine 6 Cesium fluoride 270 Chain(s) aromatic, uncyclized 258 configuration of polymer 238 end control 166 ethylene glycols and cyclic formais, open 92 extended polymers 280,283 growth 243

POLYMERIZATION

Chain(s) (Continued) propagation 132 transfer 157 Chiral ^-lactones 211 Chiral sites 207 Chloral 112,114 Chlorobromoacetaldehydes 119 Chlorobutyl rubber in isooctane 35 4-Chloro-2-butyne-l-ol 299 Chlorodibromoacetaldehyde ( CDBA ) 119 Claisen-type condensation 225 Co-initiator, hydroxyl containing 161 Collagen, melting temperature of 217 Composition on absorbance, effect of 257 Condensation, Claisen-type 225 Condensation process 166 Configurational choice 195 Consumption equation, second order 199 Conversion data for CM7 243 Coordination catalysts, ring-opening .. 165 Coordination type 154 Copolymers(s) block5 nylon.6-polybutadiene-nylon.6 triblock 174 phase transition behavior 150 sequenced 78 Copolymerization(s) 312 block 171 of ll-CF-4 with styrene 107 of c-caprolactam with β-(3,4diaminophenyl) propionic acid 251 caprolactone and caprolactam 149 of cyclic compounds containing Ο and Ν atoms 145 of cyclic phosphorus compounds 322,334 by oxonium ion, graft 24 of perhaloacetaldehydes 121,125 N-phenylaziridine and phthalic anhydride 148 of 2-phenoxy-l,3,2-dioxaphospholane 334,339 R,S178 relative reactivity ratios in 169 Correlation time 180 Counterion, alkali metal 223 Counterion, reaction with 27 Crystalline fraction 192 Crystalline properties of the racemic polymer 212 Crystallinity properties 258 Crystallinity relationships, structure- 210 a-Cyanocyclobutyl anion 287 1, ( 2-Cyanoethyl ) -2-methyl aziridine (CEMA) 8

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

347

INDEX

Cyclic compounds containing Ο and Η atoms, copolymerization of .... 145 Cyclization 233,328,329 Cycloaddition, l-acetoxy-2,3butadiene/acrylonitrile 299 Cycloadditions of substituted aliènes with acrylonitrile 300 Cyclohexane rings 42 Cyclohexanone 152 Cyclohexene sulfide (CS) 204 D Daintons equation 102 Decomposition temperatures on polypyrrolidone 217 1.3- Dehydroadamantane 285 Depolymerization of the polyme Diamines 28 /?-(3,4-Diaminophenyl) propionic acid, copolymerization of e-caprolactam with 251 Dichlorobromoacetaldehyde ( DCBA ) 119 1- ( 3,5-Dichloro-4-hydroxyphenyl ) tetrahydrothiophenium hydroxide inner salt 321 l,l-Dichloro-2-vinylcyclopropane 49 Diethylzinc-(-f) 3,3 dimethyl 2 butanol initiator system 197 Difluorobromoacetaldehyde ( DFBA ) 117 Difluorochloroacetaldehyde ( DFCA ) 115 l,l-Difluoro-2,2-dibromoethylene 117 Diisotactic structures 205 Dimer, cyclic 107,248 ( - )3,3 Dimethyl 1,2 butane diol (DMBD) 198 6,6-Dimethyl-4-carboxy-2piperidone 234,236 5,5-Dimethyl-4-carboxy-2-pyrrolidone 236 5,5-Dimethyl-4-carboxyl-2-pyrrolidone 234 Dimethyl cyclobutene-1,2dicarboxylate 58 4.4- Dimethyl-Diox 63 cis-4,5-Dimethyl-Diox 63 irans-4,5-Dimethyl-Diox 63 Dimethyl sulfoxide (DMSO) 213 cis-2,3 Dimethyl thiirane (DMT) 204 3,9-Dimethylene-l,5,7,ll-tetraoxaspiro[5.5]undecane 49 Diols 281 1,3-Dioxacycloacycloalkanes .103,106,107 1,3-Dioxacyclooctane 108 1,3-Dioxacycloundecane ( octanediol formal) 95 1,3-Dioxlan (Diox) 60,64 Dioxolan formation 82 Dioxolans, polymerizability of 62 a,a-Disubstituted-£-propiolactones .... 210

Disyndiotactic structures Di-feri-butyl peroxide

205 50

£ Electrophilic monomers 335 ^-Elimination 326,328 Enantiomer consumption 198 Enantiomeric composition of the monomer 200 Enantiomeric purity of the monomer 201 End-groups benzonoate 68 formed in cationic lactam polymerizations 137 in polyacetals 67 Epoxides 146 Ester interchange 157 Ethylene glycols, open chain 92 Ethylenesulfonamide 334,336 Ethylenimines, N-substituted 3 Expansion during polymerization 47 Expansion in volume, ring-opening polymerization with 38

F F NMR 14 Flip-flop mechanism 168 Flory parameter 61 Fluoral 112,115 Fluorobromoacetaldehydes 117 Fluorocarbon epoxides 269 Fluorochloroacetaldehydes 115,116 Formais, macrocyclic 99 Formais, polymerization of cyclic .104,108 Free radical polymerization 301 Functional groups, influence of polar 311 19

G Gauche interactions Global rate constants Glycols, open chain ethylene GPC Graft copolymerization by oxonium ion mechanism Grafting from halogenated butyl rubbers

64 199 92 16 24 34

H Halide, allyl Halide precipitated from halogenated butyl rubbers Halogenated polymers Hexafluoropropylene (HPF)

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

32 33 31 274

RING-OPENING POLYMERIZATION

348 Hexafluoropropylene epoxide (HFPO) 269 HO group 146 1.3.6.9.12.15-Hexaoxacycloheptadecane (pentaethylene glycol formal) 95 Homopolymerization 168,170 Homosteric correlations 196 HX from allyl halide, elimination of .. 27 Hydrogen abstraction from 2-methyltetrahydrofuran 27 Hydroxy1 containing co-initiator 161 4-Hydroxyl-l,2-butadiene 293 1- ( 4-Hydroxy-3-methylphenyl ) tetrahydrothiophenium hydroxide inner salt 321 3-Hydroxypropanesulfonic acid lactone (propanesultone) I Imide linkage Imides, cyclic Initiation

221,242 146 13,27,156,130 220,287,322 25 159 13

efficiency of mechanisms of triflic anhydride Initiator(s) diethylzinc-(-f) 3,3 dimethyl 2 butanol 197 difunctional 279 influence of the nature of the 195 monofunctional and difunctional .. 271 pyridine 122 triethyloxonium tetrafluoroborate .. 2,6 trimer alkoxide 277 on the two-stage polymerization, effect of 103 Isolation of silver halide 29,31 ïsomerization polymerization of lactams 233 Isomers, rotational 189 Isooctane, chlorobutyl rubber 35 IsoSyn mechanism 184

J Jacobson-Stockmayer theory

102

Κ fcp/fct, determination of

Killing agent Kinetic considerations Kinetics

2

72 156 242

L Lactam(s) carboxymethyl 234 isomerization polymerization of 233 -lithium chloride interactions .216,219 polymerizations, anionic 142,216,228 polymerizations, cationic 129,137,142 substituted 234 Lactone 145 polymerization 170,211 ^-Lactones, chiral 211 Ligand 196 Lithium chloride (LiCl) in the anionic polymerization of lactams 216 -lactam interactions 219 on the melting and decomposition thesized from caprolactam- .... phase diagram of c-caprolactam- .. Lithium tetraalkylaluminate Living macromolecules mechanism tetrahydrofuran polymers

229 223 149 70 158 13

M Macrocyclic formais, addition of 101 Macroester and macroion, equilibra­ tion between 13 Macroion/macroester ratio 15 Macromolecules, living 70 Markov chain mechanism, first order 185 Mechanical properties 241 Melt viscosity for polymerization of c-caprolactone 159 Melting behavior of polycaprolactam 223,229 point depression of the polymers .... 219 temperature of collagen 217 temperatures of polypyrrolidone .... 217 Metathesis catalyst 303 1- Methylazetidine 10 a-Methyl-a-butyl-/3-propiolactone 213 Methyl β- ( 3,4-diaminophenyl ) propionate 253 3-Methy lene [ 2.1.0] bicy clopentane1-carbonitrile, anionic polymeri­ zation of 301 2- Methylene-1,5,7,11-tetraoxaspiro[5.5]undecane 51 Methylene groups 218 2-Methyl-5-norbornene-2-nitrile 312 Methyloxirane 184 2-Methyltetrahydrofuran 26,27,32 Methylthiirane 197,202

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

349

INDEX

Model compounds, acylamidine salts used as 138 Model studies, isolation of silver halide from 29 Molecular weight distributions 162,275 Molecular weight-viscosity relations 241 Monofilament, oriented 238 Monomer 196 bisester salt, mechanisms of formation of 21 -to-catalyst molar ratio 309 enantiomeric composition of the ... 200 enantiomeric purity of the 201 influence of the nature of the 198 nucleophilic and electrophilic 335 preparation of 115,319 properties of 320 R-content in unchanged 183 ring-opening polymerization heterocyclic 165 structure 2 Morphology controls in polymer blends 174

Organometallic compounds, caprolactone and caprolactam copolymerization with 149 1,3,4 Oxadiazoles 282 2-Oxazoline 333 Oxiranes 198 polymerization 168,191,206 /a-Oxo-alkoxides 165,167 Oxonium ion 109 mechanism, graft copolymerization by 24 Oxygen atoms, ring-opening copolymerization of cyclic compounds containing 145 Oxymethylene and oxyethylene units 78

Ρ

Paraldehyde (PA) 308 PC6 240 PCM7 238,240 Pentaethylene glycol formal ( 1.3.6.8.12.15-hexaoxacycloheptadecane) 95 Ν 1.3.6.9.12-Pentaoxacyclotetradecane N-substituted (tetraethylene glycol formal) ... 94 aziridine 147 Penultimate effect 184 ethylenimines 3 Perhaloacetaldehyde propylenimines 7 polymerization 111, 118,121,122,125 N-terminal groups 138,139 Perhaloaldehyde polymerization 113 Nitrogen atoms, copolymerization of Phase diagram of c-caprolactamcyclic compounds containing 145 LiCl 223 NMR data for PCM7 and PC6 240 Phase transition behavior of NMR studies 26 copolymers 150 Norbornene derivatives 303,305 2-Phenoxy-l,3,2-dioxaphospholane 334,339 5-Norbornene-2-nitrile 308,312 N-Phenylaziridine and phthalic Norbornenenitriles 312 anhydride copolymerization 148 Nucleophilic monomers 335 Phenyl ether-terminated products 17 Nylon.6-polybutadiene-nylon.6 1- ( 2-Phenylethyl ) aziridine 6 triblock copolymer 174 1- ( 2-Phenylethyl ) -2-methyl aziridine (ΡΕΜΑ) 8 a-Phenyl-a-ethyl-/?-propiolactone 214 Ο Phenylisocyanate, copolymerization Octafluoroisobutylene epoxide of perhaloacetaldehydes with 125 (OFIBO) 269 Phosphonium zwitterion Octanediol formal, intermediates 332 (1.3-dioxacycloundecane) 95 Phosphorus compounds, cyclic 332,334 1,4,6,10,12,15,16,19-Octaoxatrispiro Phthalic anhydride copolymerization, [4.2.2.4.2.2] nonadecane 55 N-phenylaziridine and 148 Oligomerization of (R)-tertPoisson molecular weight butyloxirane 186 distribution 158 Oligomers, cyclic 87,102,162 Polar substituents, polymerization Oligomers, structure of 132 of norbornene derivatives with .. 303 Optical purity 197 Polarization of the carbonyl double Optical rotatory dispersion spectra bond 113 of poly ( alkyloxirane) 181 Polyacetals, end-groups in 67

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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RING-OPENING POLYMERIZATION

Poly(alkyloxirane) 178,181 Polyamides 281 Poly ( R-terf-butyloxirane ) 179 Poly(teri-butyl thiirane) 200 Polycaproamide, melting behavior of 229 Polycaprolactam, melting behavior of 223 Poly ( caprolactone-b-isocyanates ) ... 171 Poly(caprolactone-fc-oxiranes) 171 Poly ( caprolactone-fc-styrene ) ... 172-174 Poly(caprolactone-b-thiiranes) 171 Poly(cyclohexene sulfide) 205 Poly-Diox 70 Poly-l,3-dioxolan 67 Polyesters 281 Poly(2,5-ethylene benzimidazole) .... 251 Polyethyleneglycol 100 Poly(R-isopropyloxirane) 179 Polymer(s) blends, morphology controls in 174 chain extended 283 chains, configuration of 238 characterization 275 crosslinked 329 crystalline properties of the racemic 212 depolymerization of the 107 difunctional 275 halogenated 31 living tetrahydrofuran 13 melting point depression of the 219 mole fraction difunctional 276 monofunctional 275 of norbornenenitriles 312 preparation of 115 -salt interactions 216 structure of 132 synthesis, asymmetric 204 Polymerization of acetals 60,65,77 addition 39 of aldehydes 112 anionic 295 of bicyclobutane-l-carbonitrile.. 286 coordinated 203 of a,a-disubstituted-£propiolactones 210 offluorocarbonepoxides 269 lactam 142,216,228 of 3-methylene [2.1.0] bicyclopentane-l-carbonitrile 301 ring-opening 220 of aryl cyclic sulfonium zwitterions 318 by binary systems 309 bulk 118 ofteri-butyloxirane,selectivity in the 182

Polymerization (Continued) ofteri-butylthiirane,stereoelectivity in the 203 of c-caprolactam 152, 222 of €-caprolactone 159 cationic of ll-CF-4 100 of chloral 114 of cyclic amines 1 of cyclic formais 108 of lactams 129,137 of cyclic acetals 60,65,67,77 amines 1 dimer 107 ethers 104 formais 108 of 1,3-dioxacyclooctane 108 effect of additives on 323 effect of initiators and solvents on the two-stage 103 expansion during 47 influence of polar functional groups and acyclic double bond on .... 311 isomerization of lactams 233 of lactams, anionic 216,228 of lactams, isomerization 233 lactones 170 mechanisms 159 of 3-methylene[2.1.0]bicyclopentane-l-carbonitrile 301 of norbornene derivatives 303,305 oxiranes 168,191,206 perhaloacetaldehyde 111, 118,121,124 for perhaloaldehydes 113 of a-phenyl-a-ethyl-/3-propiolactone 214 rate of 2,31,121 ring opening anionic 220 of ferf-butyloxirane 180 via C - C bond opening 285 with expansion in volume 38 of heterocyclic monomers 165 of macrycyclic acetals 77 of norbornene derivatives 303 shrinkages for 40 solid state 324 solution 237 stereoelective 191,194 stereoselective 191 tetrahydrofuran 31 thermodynamics of 61 of thiiranes 191,206 by the W carbene complex-based catalysts 309

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

351

INDEX

Ring (Continued) Poly-3-methylenebicyclo[2.1.0]opening pentane-l-carbonitrile 293 coordination catalysts 165 Poly-a-methyl-«-propyl-0copolymerization of cyclic compropiolactone 210 pounds containing Ο and Polymeâiyl thiiranes 194 Ν atoms 145 Poly ( 5-norbornene-2-nitrile ) 314 polymerization (see Polymeriza­ Polynorbomenenitriles 314 tion, ring-opening) Poly[oxy(l-alkyl)ethylene] 178 189 Polyoxycarbonate 48, 52 Rotational isomers 35 Poly(R-oxypropylene) 178,179 Rubber in isooctane, chlorobutyl Rubbers, halogenated butyl 33,34 Poly-a-phenyl-a-ethyl-0propiolactone 211 Polypivalolactone 212 S Polypyrrolidone 217 Poly(styrene-b-aziridine) 5 Salt(s) benzylmethylsulfonium 318 Polytetrahydrofuran (PTHF) 25,35 on the melting temperature of Poly(THF-fc-aziridine) 5 collagen, effect of 217 Poly-l,3,5-trioxan 6 Preequilibrium 15 trialkyl sulfonium 318 Product distribution 18 Selectivity in the polymerization of Propagation 13,157,221,287 ferf-butyloxirane 182 kinetics of 74 Shrinkages for addition reaction 1,133 polymerization 39 Propanesultone ( 3-hydroxypropaneShrinkages for ring-opening sulfonic acid lactone) 334 polymerization 40 0-Propiolactone 333,334 Side chain size in perhaloPropylene oxide 192 acetaldehyde polymerization Ill Propylenimines, N-substituted 7 Side reactions and irregular Protonation of amides 130 structures 225 Pyridine initiator 122 Silver halide, isolation of 29,31,32 hexafluorophosphate 26 triflate 25 Solid state polymerization 324 Solution polymerization 327 Racemic polymer, crystalline 103,203 properties of the 212 Solvents, effect of Spin-lattice relaxation time 186 Rate [2,4]-Spiroheptadine 286 constants for the polymerization of Spiro ortho carbonate 48,52 a-phenyl-a-ethyl-^-propioSpiro-o-xylylene 49 lactone 214 Spontaneous alternating copolymeri­ enhancement by addition of zation of cyclic phosphorus macrocyclic formais 101 compounds 332 investigations 213 Stereoelective polymerization 191,194 polymerization 2,31,121 Stereoelectivity, effect of 197,198,203 R-content in unchanged monomer .... 183 Stereoelectivity ratio 200 Reactivity, electrophilic and Stereoregularity in perhaloacetaldenucleophilic 332 hyde polymerization Ill Reactivity ratios in copolymerizaStereoregularity of polymethyl tions, relative 169 thiiranes 194 Regioselectivity in the ring-opening Stereoselective polymerization of polymerization 180 oxiranes and thiiranes 191 184,200 Relaxation time, spin-lattice 186 Stereoselectivity Stereospecific polymerization of Ring oxiranes and thiiranes 206 expansion assumption 74 Stress-strain curves for number, heat of polymerization as poly(CL-b-St) 173 a function of 104

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

352

RING-OPENING POLYMERIZATION

Structure-crystallinity relationships .. Structures, side reactions and irregular Styrene, copolymerization of ll-CF-4 with Succinimide Sulfonium zwitterions, polymerization of aryl cyclic Synthetic methods

210 225 107 146 318 166

Τ Temperature of perhaloacetaldehyde polymerization, ceiling 124 Tensile properties 242,264 Termination reaction 1,157,287,296 Tetracyclooctanes 285 Tetraethylene glycol formal ( 1.3.6.9.12-pentaoxacyclotetra decane) 9 Tetraglyme 270 Tetrahydrofuran (THF) 213 Tetrahydrofuran polymerizations 13,31 Tetrahydropyran 32 Tetramer of (R)-terf-butyloxirane 186,189 1.3.6.9-Tetraoxacycloundecane ( triethylene glycol formal ) 85 Thermal properties 242,258,264 Thermodynamics of polymerization .. 61 Thiiranes, stereoselecitve and stereoelective polymerization of 191,198,206 Thorpe-Ziegler reaction 291 Titration of cationic caprolactam polymers, potentiometric 134 Torsion modulus of poly(caprolactone-b-styrene) 173 Trialkyl sulfonium salts 318 s-Triazines 283 1,3,4 Triazole crosslink 282 Triethylene glycol formal, ( 1.3.6.9tetraoxacycloundecane ) 85,87 Triethyloxoniumhexafluorophosphate 67 Triethyloxonium tetrafluoroborate initiator 2,6 Triflic anhydride initiation 13

Trifluoromethane sulfonic anhydride initiator 13 Triisobutylaluminum 147 Trimer alkoxide initiator 277 Trimer bisoxonium salt 21 1,3,3-Trimethylazetidine 9 Trimethyl 4,4-dimethylbicyclobutane-l,2,2-tricarboxylate 292,297 Trimethyl-4-methylbicyclobutane1,2,2-tricarboxylate 292,298 2,6,7-Trioxabicyclo[2.2.2]octanes 45 1.3.5-Trioxacycloheptane ( trioxepane) 79 1.3.6- Trioxacyclooctane (trioxocane) 83 l,4,6-Trioxaspiro[4,4]nonane 40 Trioxepane, polymer of 81 Triphenylmethylsodium 87

δ-Valerolactam 233 van der Waals' distance 39 1-Vinylbicyclobutane 286 Vinylcyclopropanes 49,286 2- Vinyl-l,3-dioxane 65 2-Vinyl-l,3-dioxolan 65 Vinyl ketone 334 Viscosity-molecular weight relations 241 W

Water structure role

217

m-Xylylenediammonium isophthalate

251

Ζ Ziegler type catalyst Zinc allyl thiolates Zwitterion aryl cyclic sulfonium genetic intermediates, phosphonium macro

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

306 194 318 332 332 332