Initiation of Polymerization - American Chemical Society

1 New Syntheses of Functional and Sequential Polymers by Exploiting Knowledge of the Mechanism of Initiation JOSEPH P. KENNEDY Downloaded by CORNELL UNIV on August 17, 2016 | http://pubs.acs.org Publication Date: April 19, 1983 | doi: 10.1021/bk-1983-0212.ch001

The University of Akron, Institute of Polymer Science, Akron,OH44325 The f i r s t part of t h i s presentation concerns a b r i e f overview of the mechanism of i n i t i a t i o n of carbocationic polymeri z a t i o n s ; in p a r t i c u l a r i t addresses head group control by protonation, cationation, and the controlled i n i t i a t i o n concept which led to a large new family of block, g r a f t , and bigraft copolymers. Subsequently the f i r s t carbocationic macromer synthesis y i e l d i n g polyisobutenylstyrene is described. The copolymerization of the l a t t e r macromer with acrylates gave r i s e to new graft copolymers. Then head group control with inorganic moieties, i.e., Cl-, NO - and Ø Si-, i s outlined. The first part concludes with a discussion of the s i m i l a r i t y between the mechanisms of i n i t i a t i o n and chain transfer, the appreciation of which led to the i n i f e r concept, which in turn yielded new t e l e c h e l i c s , networks, sequential copolymers, etc. The second part of t h i s presentation focuses on p r a c t i c a l consequences of understanding d e t a i l s of the mechanism of i n i t i a t i o n . The synthesis of a new family of t e l e c h e l i c l i n e a r and t r i - a r m star polyisobutylenes w i l l be described. Among the new prepolymers are t e l e c h e l i c o l e f i n s , epoxides, aldehydes, alcohols, and amines. The preparation of new ionomers and polyisobutylene-based polyurethanes w i l l be outlined and some fundamental properties of these new materials w i l l be discussed. 2

3

0097-6156/83/0212-0003$06.00/0 © 1983 American Chemical Society Bailey et al.; Initiation of Polymerization ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

4

INITIATION

OF

POLYMERIZATION

The s u r e s t way t o w a r d d e s i r a b l e new p o l y m e r s t r u c t u r e s i s by a s y s t e m a t i c e x p l o i t a t i o n o f t h e d e t a i l e d mechanistic understanding of p o l y m e r i z a t i o n processes. The a i m o f t h i s p r e s e n t a t i o n i s t o e x a m i n e i n some depth the mechanism of c a r b o c a t i o n i c p o l y m e r i z a t i o n s and s u b s e q u e n t l y to apply t h i s i n s i g h t toward the p r e p a r a t i o n o f new p o l y m e r i c m a t e r i a l s p o s s e s s i n g a d v a n tageous combinations of p r o c e s s i n g and/or p h y s i c a l mechanical c h a r a c t e r i s t i c s .

Downloaded by CORNELL UNIV on August 17, 2016 | http://pubs.acs.org Publication Date: April 19, 1983 | doi: 10.1021/bk-1983-0212.ch001

Initiation

i n Carbocationic

Polymerization

E a r l y Developments t i l l the D i s c o v e r y of C o n t r o l led I n i t i a t i o n . U n d e r s u i t a b l e c o n d i t i o n s any e l e c t r o philic s p e c i e s may i n d u c e c a t i o n i c p o l y m e r i z a t i o n s ( 1 ) . As a p r a c t i c a l m a t t e r , t h e m o s t c o n v e n i e n t cationogens are Bronsted a c i d s alone or i n c o n j u n c t i o n with Fried e l - C r a f t s acids ( 1 ) . Systematic r e s e a r c h on t h e i n i t i a t i o n o f c a r b o c a t i o n i c p o l y m e r i z a t i o n became p o s s i b l e by t h e d i s c o v e r y o f c o i n i t i a t i o n by B r i t i s h i n v e s t i g a t o r s (2-4). These workers found that the s t r o n g Lewis a c i d BF alone i s unable to i n i t i a t e isobutylene p o l y m e r i z a t i o n but i n the presence of s u i t a b l e c a t i o n ogens, i . e . , H2O, i m m e d i a t e and v i g o r o u s polymerization ensues. Their formalism: 3

BF e

H BF 0H 3

9

3

+ H 0

— ^

2

+ CH =C(CH ) -» 2

3

2

Η BF 3OH CH3-C(CH3)2BF30Η

Θ

p r o v i d e d v a l u a b l e g u i d a n c e f o r s u b s e q u e n t r e s e a r c h on the mechanism of p r o t i c i n i t i a t i o n and i n t h e c o n t e x t of t h i s p r e s e n t a t i o n i s r e g a r d e d as t h e f i r s t p r o p o s i t i o n of head group c o n t r o l , i . e . , t h e i n c o r p o r a t i o n of a p r o t o n as the "head group" of a m a c r o m o l e c u l e . Not much l a t e r P e p p e r ( 5 ) s u g g e s t e d t h a t c e r t a i n a l k y l h a l i d e s RX i n c o n j u n c t i o n w i t h F r i e d e l - C r a f t s a c i d s MX may a l s o a c t a s i n i t i a t o r s : n

RX + M X „ η

+ C=C

^ ^

9

R^MX n+1

> R-c-ce

A l t h o u g h t h e f o r m a l i s m o f c a t i o n a t i o n by a l k y l h a l i d e s was i n p r i n c i p l e c o r r e c t , t h e s i g n i f i c a n c e o f t h i s m e c h a n i s m f o r h e a d g r o u p c o n t r o l c o u l d n o t be e x p l o i t e d because the c o n v e n t i o n a l F r i e d e l - C r a f t s a c i d s ( B F , A I C I 3 , S n C l i f , ΤiC 1 0 u s e d by t h e e a r l y w o r k e r s w e r e 3

Bailey et al.; Initiation of Polymerization ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

1.

Syntheses of Functional and Sequential Polymers

KENNEDY

5

extremely moisture s e n s i t i v e ( i . e . , induced p o l y m e r i z a t i o n by protonation i n the presence of p u t a t i v e t r a c e s of moisture imp u r i t i e s ) and because l a r g e q u a n t i t i e s of C H 3 - head groups a l s o arose by unavoidable chain t r a n s f e r to monomer. In 1965 i t was discovered (6,7) that under conventional "open" l a b o r a t o r y c o n d i t i o n s ( i . e . , i n the presence of m o i s t u r e ) o l e f i n polymerizations can be r e a d i l y i n i t i a t e d by p r o t i c a c i d s or by " a c t i v e organic h a l i d e s (j^-butyl, b e n z y l , a l l y l ) i n conj u n c t i o n with c e r t a i n alkylaluminum compounds (MeaAl, E t 3 A l , E t A l C l , e t c . ) . Since these d i - and t r i a l k y l a l u m i n u m compounds are e f f e c t i v e moisture scavengers and t h e i r r e a c t i o n products with small amounts of H2O a r e p o l y m e r i z a t i o n i n a c t i v e , i n i t i a t i o n can occur only upon the purposeful a d d i t i o n of s u i t a b l e c a t i o n o gens. F o r reasons beyond the scope of t h i s présentation»polymeri z a t i o n s induced by RX/R2AIX combinations a r e chain t r a n s f e r l e s s ( t r a n s f e r l e s s polymerizations a r e discussed i n réf. 1) so that the head groups of polymers formed by these i n i t i a t i n g systems can be r e a d i l y c o n t r o l l e d . For example, (M = monomer): 11


2

CH

CP3

-Cl/Et AlCl + M CH

»

2

3

0 - ( Μ Λ Μ

Φ

Et AlCl 2

9 2

CH3

3

The head groups of polymers formed by such " c o n t r o l l e d i n i t i a t i o n " systems are determined by the nature of the i n i t i a t o r molecule. A l a r g e number of c o n t r o l l e d i n i t i a t i o n systems g i v i n g r i s e to polymers bearing d e s i r a b l e f u n c t i o n a l head groups e.g., a l l y l , b e n z y l , c y c l o p e n t a d i e n y l , s i l y l , have been d e s c r i b e d ( 1 ) . P o s s i b i l i t i e s o f f e r e d by c o n t r o l l e d i n i t i a t i o n have been ex p l o i t e d f o r the p r e p a r a t i o n of new s e q u e n t i a l copolymers and mac romers and a r e discussed below. Sequential (Block and G r a f t ) Copolymers by C o n t r o l l e d I n i t i a t i o n . C o n t r o l l e d i n i t i a t i o n by a c t i v e high molecular weight h a l i d e s ( i . e . , macromolecules c o n t a i n i n g t e r t i a r y alkyl or b e n z y l i c h a l i d e s ) i n conjunction with d i - and t r i a l k y l a l u m i n u m coi n i t i a t o r s l e d to the s y n t h e s i s of a l a r g e v a r i e t y of block, g r a f t and b i g r a f t copolymers. Schematically (X and Y = h a l i d e functions): AAAAAAAA-X

X-AAAAAAAA-X

—

+

n

B

>

>

AAAAAAAA-BBBBB diblocks BBBBB-AAAAAAAA-BBBBBB triblocks


6

INITIATION

AAAAAAAA

_±_Ξ5—±

I T X X

OF

POLYMERIZATION

AAAAAAAA

I Β

I Ç

? 5

? Β

grafts

Β AAAAAAAA

I

—

I

,

+

N

Η (

? '

, ?

>

:

selective i n i t i a t i o n

AAAAAAAA

r

|

r

Β

î


bigrafts

C

Β

A l a r g e number of s e q u e n t i a l copolymers comprising many combina t i o n s of glassy and elastomeric segments have been prepared (1). The block and g r a f t copolymers prepared by c o n t r o l l e d i n i t i a t i o n are remarkably w e l l defined and many are f r e e of homopolymers. Sequential copolymers obtained by c o n t r o l l e d c a t i o n i c i n i t i a t i o n have been r e c e n t l y comprehensively surveyed (1,8). Macromers by C o n t r o l l e d I n i t i a t i o n . New and unique g r a f t co polymers can be prepared by copolymerizing macromers (macromolecu l a r monomers) with conventional monomers. The synthesis of p o l y ( b u t y l acrylate-£-isobutylene), i . e . , the f i r s t g r a f t synthe s i s that i n v o l v e s c a r b o c a t i o n i c c o n t r o l l e d i n i t i a t i o n , has recent l y been accomplished by the f o l l o w i n g route (9):

CH =ÇH

CH =ÇH

2

2

Me Al/H (^ 3

+ jl-CifHs

2

>

CH -PIB 2

COOBu

R

>

P

o l

y(

b u t v l

acrylate-g-isobutylene

CH -PIB 2

The copolymerization of the p o l y i s o b u t e n y l s t y r e n e macromer with methyl methacrylate and styrene gave f u r t h e r i n t e r e s t i n g new mat e r i a l s (10,11). Inorganic Head Groups by C o n t r o l l e d I n i t i a t i o n . In a d d i t i o n to organic f u n c t i o n a l groups, i n o r g a n i c head groups, e.g., C l - , Br-, 0 N-, can a l s o be introduced i n t o polymers by c o n t r o l l e d i n itiation. For example, the i n c o r p o r a t i o n of CI- head group i n t o p o l y i s o b u t y l e n e has been accomplished by the C l / B C l 3 system (12) 2

2

Q i-C H BCliT + ~ > u

CI

2

+

BC1

3

cr

fy

ft

8

C1-CH -C(CH ) 2

3

2


Cl-PIB

1.


KENNEDY

7

S i m i l a r i t y between I n i t i a t i o n and Chain T r a n s f e r : 1. The I n i f e r Concept. A d e t a i l e d a n a l y s i s of the respec t i v e mechanisms of i n i t i a t i o n and v a r i o u s chain t r a n s f e r proces ses showed that the fundamentals of i n i t i a t i o n by a l k y l h a l i d e s and chain t r a n s f e r to a l k y l h a l i d e s a r e indeed very s i m i l a r . I t i s postulated that an a l k y l h a l i d e that i s able to i n i t i a t e c a r b o c a t i o n i c polymerizations, may a l s o be able to f u n c t i o n as a chain t r a n s f e r agent. Schematically (1): Initiation: 9

+


RX + MX R^MX ^ η ^r— n+1 Chain T r a n s f e r

C = C

>

R-C-C MX

9

n+1

9

9

{

C=C

^C-C^MX , + RX ~ * w \ £ - C X + R^MX " " > n+1 n+1 Λ

1

^C-CX +

9

R-C-Λχ Ί

n+1

A l k y l h a l i d e s that perform simultaneously as i n i t i a t o r s and chain t r a n s f e r agents a r e i n general termed i n i f e r s . Thus i n the ab sence of chain t r a n s f e r to monomer i . e . , when R ^ > R (rate of chain t r a n s f e r to i n i f e r i s l a r g e r than that £o\ionomer; , the t e r m i n i of polymers can be r e a d i l y c o n t r o l l e d by i n i f e r s . Monof u n c t i o n a l i n i f e r s termed m i n i f e r s can be used to c o n t r o l one terminus; b i f u n c t i o n a l i n i f e r s XRX, termed b i n i f e r s , are u s e f u l to c o n t r o l two t e r m i n i ; t r i f u n c t i o n a l i n i f e r s XRX, termed t r i n i f e r s , can c o n t r o l the three t e r m i n i of three-arm s t a r molecules, e t c . The f o l l o w i n g scheme helps to v i s u a l i z e the g i s t of the mechanism l e a d i n g to end group c o n t r o l i . e . , to t e l e c h e l i c p o l ymers, be these l i n e a r or star-shaped, by i n i f e r s (1): CI Cl-l-Cl

CI B C l 3

>

φ J

CI

Cl-R* B C L

Cl-twx*BCU

9

Inifer

e

CI C l - l w ^ C l + C l - R B C Vθ

1

e

2. New Products Prepared by the I n i f e r Technique. A new family of l i n e a r and three-arm s t a r polyisobutylenes have been prepared by the i n i f e r technique. The i n i f e r systems used were cumyl c h l o r i d e (minifer) p-dicumyl c h l o r i d e ( b i n i f e r ) and symt r i c u m y l c h l o r i d e ( t r i n i f e r ) always i n combination with BCI3 coi n i t i a t o r (1) : CH I

3

iCi+H8

-Cj-Cl

CH

3

>·

rp^

CH I

CH I

3

3

W

^^C'^PIB' H:H2-C-C]

CH

3

CH

3


8

INITIATION

CH

3

CH

3

CH

3

CH

3

CH

3

CH

3

CH

3

OF POLYMERIZATION

3

Cl-Ç-CH ^^PIBw^-(p-^Q^-^^PiBwbCH2-^-Cl 2

CH


CH

CH

3

CH

3

CH

3

3

CI

3

CH _/ 3

1 CH

\

Z™

3

BC1

3

3

Λ

CH

3

CH 3

CI

/w\,PIBw\,CH -C-Cl ÇH _^C I H3 CH,

ÇH

3

2

3

CI-^-CH2WVPIBWV(J;--^^ CH

3

CH

3

N

\

C

H

/P

A

H 3 P

C CH

3

__ CH

3

VAA,PIBW^CH -Ç-C1 2

CH

3

S i d e - r e a c t i o n s can be avoided without too much d i f f i c u l t y so that v i r t u a l l y t h e o r e t i c a l end group f u n c t i o n a l i t i e s can be obtained, i . e . , F = 1.0, 2.0 or 3.0. Molecular weight c o n t r o l can be r e a d i l y accomplished by a d j u s t i n g reagent concentrations and products ranging from l i q u i d s to rubbery s o l i d s can be prepared. The t e r t i a r y c h l o r i n e t e r m i n i are u s e f u l s t a r t i n g p o i n t s f o r a v a r i e t y of d e r i v a t i z a t i o n s , e.g., d i b l o c k , t r i b l o c k and t r i s t a r block syntheses with styrene, α-methylstyrene (by a l k y l a l uminum chemistry) and/or c y c l i c ethers (by s i l v e r s a l t chemis try) . For example, the s y n t h e s i s of the t r i b l o c k PaMeSt-b-PIBb-PaMeSt, a thermoplastic elastomer whose physical-mechanical p r o p e r t i e s a r e determined by the c e n t r a l saturated rubbery ΡΙΒ block sandwiched between two g l a s s y PaMeSt b l o c k s , i s o u t l i n e d by the f o l l o w i n g set of equations: n


1.


KENNEDY

CH

CH

3

3

CH

3

CH

3

CH

3

CH

3

9

Cl-(j:-CH2'w\,PIBw\£-C6^ CH

CH

3

I

3

E t A l C l ; aMeSt | C H C 1 , -50°C 2

2

CH

(pi

3

2

Initiation of Polymerization - American Chemical Society

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