Initiation of Polymerization - American Chemical Society

24 Catalytic Control of Architecture and Properties of Butadiene Block Copolymers

Downloaded by MONASH UNIV on November 27, 2015 | http://pubs.acs.org Publication Date: April 19, 1983 | doi: 10.1021/bk-1983-0212.ch024

PH. TEYSSIE, G. BROZE, R. FAYT, J. HEUSCHEN, R. JEROME, and D. PETIT University of Liège, Laboratory of Macromolecular Chemistry and Organic Catalysis, Sart-Tilman, 4000 Liège, Belgium It i s shown how a precise c o n t r o l of the initiation and s e l e c t i v i t y of butadiene block polymerization reactions allows the molecular engineering of a v a r i e t y of new heterophase materials. The t y p i c a l examples presented illustrate 3 main p o t e n t i a l i t i e s of these copolymers. First, the stable e m u l s i f i c a t i o n of blends of 2 immiscible homopolymers (PE/PS; PVC/PBD) by the corresponding diblock copolymer. Second, the p o s s i b i l i t y to obtain high performance thermoplastic elastomers from t r i b l o c k copolymers containing endblocks of high cohesive energy density ( i . e . nylon-6, p o l y p i v a l o l a c t o n e ) . T h i r d , the opportunity to t a i l o r "multiblock" systems i n which the "hard" segment i s an i o n i c group (halatotelechelic polymers), imparting to these systems i n t e r e s t i n g r h e o l o g i c a l properties. C a t a l y t i c polymerizations of 1,3-butadiene i n t o e s s e n t i a l l y 1,4 elastomeric polymers are by now pretty well-mastered processes. It i s the purpose of t h i s paper to demonstrate the s t i l l very v i v i d interest i n that time-honored backbone, within the frame of a much broader trend developing now i n the f i e l d of polymeric materials. It i s obvious indeed that industry i s not w i l l i n g anymore to produce many of these necessary materials from new monomers; the key approach here i s thus d i v e r s i f i c a t i o n , but s t a r t i n g from basic feedstocks and materials already available at low prices i n large amounts. On the 0097-6156/83/0212-0323$06.00/0 © 1983 American Chemical Society In Initiation of Polymerization; Bailey, F., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.


324

INITIATION OF

POLYMERIZATION

o t h e r hand, i n a time of e x p l o s i v e development o f "genet i c e n g i n e e r i n g " t e c h n i q u e s i n b i o l o g y , i t i s o n l y too f a i r t o acknowledge a s i m i l a r type o f achievement i n p o l y m e r i c m a t e r i a l s s c i e n c e , i . e . the " m o l e c u l a r e n g i n e e r i n g o f t h e i r b u l k p r o p e r t i e s " . That r e c e n t c a p a b i l i t y t o a c h i e v e , through p r e c i s e ( a l t h o u g h sometimes small) m o d i f i c a t i o n s of molecular s t r u c t u r e s , a " f i n e t u n i n g " o f the f i n a l b u l k p r o p e r t i e s and macroscopic b e h a v i o u r o f these p o l y m e r i c m a t e r i a l s , has a r i s e n from our r a p i d l y i n c r e a s i n g knowledge and m a s t e r i n g of i n i t i a t i o n and p r o p a g a t i o n mechanisms, p a r t i c u l a r l y i n terms o f s e l e c t i v i t y . T h a t a l l o w s us i n t u r n t o c o n t r o l a c c u r a t e l y the m o l e c u l a r a r c h i t e c t u r e of the polymers used, t h a t means a l s o the morphology and f u r t h e r the p h y s i c o - c h e m i c a l as w e l l as p h y s i c o - m e c h a n i c a l b e h a v i o u r of the c o r r e s p o n d i n g f i n a l m a t e r i a l s . A l l o f the examples p r e s e n t e d h e r e , l e a d i n g t o d i f f e r e n t types o f p r o p e r t i e s and a p p l i c a t i o n s , are based on copolymers o f v a r y i n g a r c h i t e c t u r e , but a l l i n v o l v i n g e s s e n t i a l l y 1,4 p o l y b u t a d i e n e b l o c k s . C l e a r l y , t h e i r p r o p e r t i e s w i l l thus r e f l e c t t h r e e i m p o r t a n t pot e n t i a l i t i e s o f heterophase b l o c k copolymer-based mater i a l s : 1) t h e i r " o r g a n i z a t i o n " i n t o mesomorphic phases (1), g i v i n g r i s e t o o r i g i n a l , o f t e n a n i s o t r o p i c , p r o p e r t i e s ; 2) t h e i r a b i l i t y t o s t a b i l i z e l i q u i d emulsions (2,) and more i m p o r t a n t l y f i n e d i s p e r s i o n s o f c o r r e s p o n d i n g homopolymers ( 3 ) , so b r i d g i n g t h e i r " c o m p a t i b i l i t y gap" and a l l o w i n g trie development o f a new " p l a s t u r g y " ; 3) t h e i r use as high-performance e n g i n e e r i n g p r o d u c t s , and p a r t i c u l a r l y as m a t e r i a l s s i m i l a r t o K r a t o n thermoplastic elastomers (4). Experimental A l l of the i m p o r t a n t e x p e r i m e n t a l d e t a i l s , as w e l l as the g e n e r a l p r o c e d u r e s taken from l i t e r a t u r e , were r e p o r t e d i n the r e f e r e n c e s c i t e d i n each s e c t i o n . As a g e n e r a l r u l e , most o f the r e a g e n t s were p u r i f i e d c a r e f u l l y ( p a r t i c u l a r l y f o r m o i s t u r e ) , and a l l o f the r e a c t i o n s c a r r i e d o u t e i t h e r u s i n g vacuum t e c h n i q u e s o r under pure argon atmosphere. Polymer p r o p e r t i e s were i n v e s t i g a t e d by s t a n d a r d methods, u n l e s s o t h e r w i s e ment i o n e d . Polymer b l e n d i n g was u s u a l l y performed f o r 5 minutes a t 190°C on a C.A.M.I.L. t w o - r o l l l a b o r a t o r y mill. Results è-EïËiiîîiDËiY-.EiQ^iëîi}- The u n s a t u r a t e d s t r u c t u r e of the 1,4 p o l y b u t a d i e n e (PBD) backbone i s u n f o r t u n a t e l y

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


24.

TEYSSIE ET AL.

Butadiene

Block

Copolymers

325

r a t h e r s e n s i t i v e t o a number o f e a s i l y o c c u r r i n g secondar y r e a c t i o n s , and p a r t i c u l a r l y t o d i f f e r e n t t y p e s o f c r o s s - l i n k i n g and o x i d a t i o n p r o c e s s e s ( t h e r m a l , p h o t o c h e m i c a l , and c a t a l y t i c ) . T h i s drawback has been e l e g a n t l y c i r c u m v e n t e d by a f a c i l e c a t a l y t i c hydrogénation o f t h e c h a i n s , u s i n g e f f i c i e n t s o l u b l e Z i e g l e r - t y p e complexes ( 5 ) p r e p a r e d f r o m c o b a l t ( o r n i c k e l ) s a l t s and mixed aluminum a l k y l s i n d i f f e r e n t r a t i o s . T h i s p r o c e s s has a t w o f o l d advantage : 1) i t i s possible t o control i t s s e l e c t i v i t y (varying the r e a c t i o n c o n d i t i o n s and t h e a l u m i n u m - t r a n s i t i o n m e t a l m o l a r r a t i o ) , so t h a t p o l y b u t a d i e n e o n l y c a n be hydrogenated i n the presence of other unsaturated chains l i k e p o l y i s o p r e n e o r p o l y s t y r e n e , w h i c h i n t u r n c a n be h y d r o g e n a t e d l a t e r , i f n e c e s s a r y by c h a n g i n g t h e s e r e a c t i o n parameters; 2 ) t h e hydrogénation i s p r a c t i c a l l y q u a n t i t a t i v e and y i e l d s a product n o t very d i f f e r e n t from t h e correspond i n g p o l y e t h y l e n e s . F o r i n s t a n c e , s t a r t i n g from an a n i o n i c a l l y i n i t i a t e d p o l y b u t a d i e n e ( i n a p o l a r medium) c o n t a i n i n g a c c o r d i n g l y c a . 1 0 - 1 5 % 1 2 u n i t s , one o b t a i n s a p r o d u c t r a t h e r s i m i l a r t o low d e n s i t y l i n e a r p o l y e t h y l e n e LLDPE ( i n f a c t a copolymer o f e t h y l e n e and 1-butène) , d i s p l a y i n g a moderate s e m i - c r y s t a l l i n i t y and a m e l t i n g p o i n t c a 9 0 t o 1 0 0 ° C . On t h e o t h e r hand, t h e u s e o f a l i n e a r pure 1 , 4 PBD ( 9 9 %) o b t a i n e d by Z i e g l e r t y p e c a t a l y s i s ( n i c k e l o r c o b a l t complexes) y i e l d s a high-density p o l y e t h y l e n e - l i k e product, with a higher degree o f c r y s t a l l i n i t y and a m e l t i n g - p o i n t c l o s e t o 130°C.

O b v i o u s l y , t h e r e s i s t a n c e o f t h e s e p r o d u c t s towards l i g h t , oxygen and o t h e r c h e m i c a l s w i l l be much b e t t e r , and c l o s e t o t h a t o f t h e c o r r e s p o n d i n g p o l y o l e f i n s . Moreover, t h e hydrogénation can be stopped a t d i f f e r e n t c o n v e r s i o n s o p e n i n g a much b r o a d e r range o f a p p l i c a t i o n s c o n d i t i o n s . I n d u s t r i a l developments a l r e a d y i n c l u d e s u c c e s s f u l m a t e r i a l s l i k e Kraton G thermoplastic elastomers. sifiers__(PS-b-PBDh)_. Combination o f d i f f e r e n t polymers i n t o h e t e r o p h a s e systems r e p r e s e n t s a v e r y a t t r a c t i v e r o u t e towards new and t a i l o r - m a d e m a t e r i a l s ( 3 J d i s p l a y i n g most o f t h e p r o p e r t i e s o f t h e s t a r t i n g p r o d u c t s . The i n c o m p a t i b i l i t y between p a r t n e r s (a r a t h e r g e n e r a l r u l e ) i s however r e s p o n s i b l e f o r t h e poor p r o p e r t i e s o f many blends, w h i c h d i s p l a y l a r g e domain s i z e w i t h poor i n t e r f a c i a l a d h e s i o n . A c c o r d i n g l y , d i b l o c k copolymers (6) c o n t a i n i n g sequences m i s c i b l e w i t h t h e homopolymers t o be b l e n d e d , have been used t o a l l e v i a t e t h a t s i t u a t i o n as a


326

INITIATION OF

POLYMERIZATION

r e s u l t of t h e i r i n t e r f a c i a l a c t i v i t y ; i n that respect, t h e y have p r o v e n t o be s u p e r i o r (7) t o c o r r e s p o n d i n g t r i b l o c k and g r a f t copolymers r e s p e c t i v e l y ( u n l e s s t h e t r i b l o c k c a n undergo a t r i d i m e n s i o n a l domain o r g a n i z a t i o n p r o v i d i n g an a d d i t i o n a l b o n u s ) . Two d i f f e r e n t t y p e s o f (PS-b-PBDh) d i b l o c k c a n be p r e s e n t l y s y n t h e s i z e d . The f i r s t one by c l a s s i c a l a n i o n i c i n i t i a t i o n ( s - b u t y l - l i t h i u m ) and " l i v i n g " p r o p a g a t i o n o f t h e (PS-b-PBD) copolymer (8) , f o l l o w e d by t h e h y d r o génation p r o c e d u r e d e s c r i b e d "here; as d i s c u s s e d above, t h e r e s u l t i n g p r o d u c t w i l l be c l o s e t o a (PS-bLLDPE) copolymer. The second one came from t h e d i s c o v e r y (9) o f a " l i v i n g " p o l y m e r i z a t i o n o f b u t a d i e n e i n t o a pure (99 %) 1,4 polymer by a b i s η -allylnickel-trif l u o r o a c e t a t e ) c o o r d i n a t i o n c a t a l y s t , f o l l o w e d by s t y rène 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 , t h e l e n g t h o f t h e p o l y s t y r e n e b l o c k i s l i m i t e d ( t o a M.W. o f c a . 20,000) by t r a n s f e r r e a c t i o n s . I n a g e n e r a l s t u d y o f t h e u s e f u l n e s s o f t h e f i r s t type c o p o l y m e r s , we have developed ways t o d r a s t i c a l l y improve w i t h them t h e p r o p e r t i e s o f b o t h l o w (LD) and h i g h (HD) d e n s i t y p o l y e t h y l e n e (PE)/PS b l e n d s (2,10). The a d d i t i o n (by h o t - m i l l i n g ) o f moderate amounts o f the s u i t a b l e PS-b-PDBh copolymer g r e a t l y r e d u c e s t h e d i s p e r s e d p a r t i c l e s s i z e a t e v e r y c o m p o s i t i o n ( c a . 2to 5,000 A ) ; moreover, i t s t a b i l i z e s e f f i c i e n t l y t h a t s i t u a t i o n , i . e . even t h r o u g h o u t s t a n d a r d p r o c e s s i n g . A s i g n i f i c a n t enhancement o f b o t h t h e s t r e s s a t b r e a k σβ and t h e e l o n g a t i o n a t break εβ, r e s u l t i n g i n a s t r i k i n g i n c r e a s e o f t h e t o t a l energy a t break (Εβ v a l u e s ) , i s noted ( F i g . 1 ) . The l e v e l o f performance o b t a i n e d depends a s y m p t o t i c a l l y on t h e amount o f copolymer added and, w h i l e a s i g n i f i c a n t improvement i s a l r e a d y noted f o r 0.5 % by w e i g h t o f t h e a d d i t i v e , most o f t h e p e r f o r m a n c e s i n c r e a s e i s r e a c h e d w i t h i n 2-3 %. As e x p e c t e d , t h e l e n g t h o f t h e two b l o c k s has a l s o a g r e a t i n f l u e n c e on t h e f i n a l p r o p e r t i e s : a l t h o u g h s m a l l e r ones a l r e a d y have a g r e a t i m p a c t on t h e i n t e r f a c i a l s i t u a t i o n ( s m a l l e r domains, h i g h e r σ β ) , t h e use o f h i g h e r M.W. d i b l o c k s ( i . e . i n w h i c h each b l o c k i s s i m i l a r i n s i z e t o t h e c o r r e s p o n d i n g homopolymers t o be blended) y i e l d s P S - r i c h b l e n d s d i s p l a y i n g t h e m e c h a n i c a l c h a r a c t e r i s t i c s o f an e x c e l l e n t toughened p l a s t i c , w i t h a h i g h εβ v a l u e (up t o 40 %) a t y p i c a l l y d u c t i l e b e h a v i o u r , and a s t r i k i n g r e s i s t a n c e towards c r y o f r a c t u r e . These f e a t u r e s a r e probably c h a r a c t e r i s t i c o f the importance o f entangle ments between c h a i n s o f homo- and copolymer near t h e interface. I n t e r e s t i n g and s i g n i f i c a n t d i f f e r e n c e s a r e a l s o promo-


3

0



24.

TEYSSIE ET AL.

Butadiene

Block

327

Copolymers

Figure 1. Ultimate tensile strength (σ ) and elongation at break (e ) of LDPE (M = 40,000)/PS (M = 10 ) blends. Key: ·, without copolymer; Δ , with 9% of a poly(styrene-b-hydrogenated butadiene), M total = 58,000; O , with 9% of a poly(styrene-b-hydrogenated butadiene), M„ total = 155,000. (Reproduced with permission from Ref. 7. Copyright 1981, John Wiley & Sons, Inc.) Β

B

5

n

n

n


328

INITIATION OF POLYMERIZATION


ted by r a t h e r s u b t l e m o d i f i c a t i o n s i n t h e d i b l o c k s t r u c t u r e . Compared t o "pure" d i b l o c k s p r e p a r e d by c o n s e c u t i ve a n i o n i c p o l y m e r i z a t i o n , " t a p e r e d " b l o c k s o b t a i n e d by a n i o n i c p o l y m e r i z a t i o n o f t h e comonomers m i x t u r e ( 1 1 ) are s t i l l more e f f i c i e n t e m u l s i f i e r s f o r PS/LDPE b l e n d s ; owing t o t h e i r l o w e r m e l t v i s c o s i t y and p a r t i c u l a r i r a s c i b i l i t y c h a r a c t e r i s t i c s , t h e y n o t o n l y a c t as s o l u b i l i z i n g agents o f t h e homopolymers b u t p r o v i d e a t t h e i n t e r f a c e a "graded" modulus r e s p o n s i b l e f o r an improved mechanical response o f the o v e r a l l m a t e r i a l ( 1 2 ) . In o r d e r t o o b t a i n t h i s new t y p e o f macromoïecule, an OH-terminated homopolymer, i . e . PBD o r PS o b t a i n e d by a n i o n i c i n i t i a t i o n combined w i t h o x i r a n e - w a t e r t e r m i n a t i o n , was end-capped (an a l c o h o l d i s p l a c e m e n t r e a c t i o n ) w i t h an a l k o x i d e c a t a l y s t a b l e t o f u r t h e r ensure a p e r f e c t l y " l i v i n g " p o l y m e r i z a t i o n o f CL, t h e r e b y y i e l d i n g the d e s i r e d b l o c k copolymers ( 1 3 ) . I n t h i s case however the PBD hydrogénation ( i f needed) can be conducted p r i o r t o b l o c k c o p o l y m e r i z a t i o n t o a v o i d any i n t e r f e r e n c e from, o r secondary r e a c t i o n w i t h , t h e p o l y e s t e r b l o c k . The f i n a l p r o d u c t s d i s p l a y a number o f a t t r a c t i v e f e a t u r e s (14): t h e y undergo l a m e l l a r mesomorphic o r g a n i z a t i o n ( p e r i o d i c i t y c a . 8 0 Â ) even under t h e form o f h e x a g o n a l s i n g l e c r y s t a l s ( P S - c o p o l y m e r s ) , and e x h i b i t a d u c t i l e b e h a v i o u r as w e l l as a h i g h r e s i s tance t o c r y o f r a c t u r e . Moreover, they are m a c r o s c o p i c a l l y b i o d e g r a d a b l e , a t l e a s t when PCL r e p r e s e n t s t h e c o n t i n o u s phase. The b l e n d i n g approach d e s c r i b e d above has been extended t o t h e s e p r o d u c t s , t a k i n q advantage o f t h e r e m a r k a b l e m i s c i b i l i t y o f PCL w i t h o t h e r p o l y m e r s , i . e . PVC, SAN, p o l y c a r b o n a t e In particular,excellent b l e n d s o f r i g i d PVC w i t h PS and PBD have been p r e p a r e d through h o t - m i l l i n g . A g a i n , they d i s p l a y a very f i n e morphology (domain s i z e c a 5 , 0 0 0 Â ) which i s remarkab l y s t a b l e i n t i m e , and some improved p h y s i c o m e c h a n i c a l p r o p e r t i e s as l o n g as t h e c o r r e s p o n d i n g m o l e c u l a r p a r a meters have been p r o p e r l y o p t i m i z e d ( 1 5 , 1 6 ) . I t s h o u l d be s t r e s s e d here t h a t t h e need f o r s u c E " a n o p t i m i z a t i o n p r o c e s s cannot be o v e r - e s t i m a t e d as r a t h e r minute modif i c a t i o n s c a n l e a d t o improvements o f one o r d e r o f magnitude. Other i n t e r e s t i n g i n d i c a t i o n s have been o b t a i n e d on t h e s e PVC b l e n d s : i n t h e p r e s e n c e o f an e x c e s s rubber y phase, t h e p r e s e n c e o f t h e copolymer ( i . e . PCL-bPBD) promotes i n d e e d good impact r e s i s t a n c e , i n d i c a t i n g a s t r o n g anchorage o f t h a t r u b b e r y phase i n t h e r e s i n matrix.


24.

TEYSSIE ET AL.

Butadiene

Block

Copolymers

329

I n o t h e r words, t h i s example emphasizes c l e a r l y the v e r y b r o a d a p p l i c a b i l i t y o f the " e m u l s i f i e r s " c o n c e p t d e p i c t e d above, t o p r a c t i c a l problems i n v o l v i n g l a r g e s c a l e polymers.


§1§§ΐ:22!§£§_ίΐΙΙΣ_ΐΐΝ^ The i n t e r e s t of TPË has been l a r g e l y d e m o n s t r a t e d by the numerous and a c t i v e i n v e s t i g a t i o n s l e d i n the f i e l d , and by the c o m m e r c i a l s u c c e s s o f the K r a t o n - t y p e p r o d u c t s , p o l y ( s t y r e n e - c o - d i e n e - c o - s y t r e n e ) . I t i s however a well-known problem t h a t these m a t e r i a l s are u s u a l l y c o n f i n e d t o a p p l i c a t i o n s under r a t h e r m i l d c o n d i t i o n s , due t o the r e l a t i v e l y low Tg of the g l a s s y phase and/or the mediocre t h e r m a l s t a b i l i t y o f the r u b b e r y phase. I n p r i n c i p l e a t l e a s t , answers t o t h a t c h a l l e n g e can be o f f e r e d by the same t y p e o f s y n t h e s i s s t r a t e g y . As d e s c r i b e d p r e v i o u s l y (17), an α,ω-dihydroxyîpolybutadiene can be end-capped w i t h i s o c y a n a t e f u n c t i o n s (through r e a c t i o n w i t h an e x c e s s d i i socyanate), which are f u r t h e r converted i n t o N - a c y l l a c tam g r o u p i n g s (by r e a c t i o n w i t h c a p r o l a c t a m CLM) a c t i v e f o r the p o l y m e r i z a t i o n o f t h a t CLM monomer i n t o N y l o n - 6 b l o c k s a t b o t h ends of the p o l y b u t a d i e n e . Under c l o s e c o n t r o l of the r e a c t i o n c o n d i t i o n s , n e i t h e r the u r e t h a n e nor the u r e a l i n k a g e s formed are b r o k e n d u r i n g the subsequent b l o c k c o p o l y m e r i z a t i o n , and a h i g h y i e l d i n b l o c k copolymer i s o b t a i n e d . That t r i b l o c k copolymer d i s p l a y s i n d e e d a s e t of h i g h p e r f o r m a n c e p r o p e r t i e s : even a t 30 % o f PBD p h a s e , the m a t e r i a l has a n y l o n - 6 c o n t i n u o u s phase, w i t h a c r y s t a l l i n e m e l t i n g p o i n t c a . 225°C and a h i g h t e n s i l e s t r e n g t h ( q u i t e comparable t o t h a t o f p u r e n y l o n - 6 ) . On the o t h e r hand, the r u b b e r y phase i s f i n e l y d i s p e r s e d i n v e r y s m a l l domains ( c a . 250 Â) a l l o v e r the h i g h l y c r y s t a l l i n e n y l o n phase,impart i n g to the m a t e r i a l h i g h e r f l e x i b i l i t y and h y d r o p h o b i c i t y . A l t h o u g h the above p r o d u c t i s not a TPΕ i n the s t r i c t sense o f the t e r m (see ASTM D 1 5 6 6 ) , i t can be p r e p a r e d w i t h a h i g h e r r u b b e r c o n t e n t t o meet t h a t t y p e of b e h a v i o u r . I t has t o be s t r e s s e d however t h a t b l o c k s o f so d i f f e r e n t s o l u b i l i t y p a r a m e t e r s impose a h e t e r o p h a s e s i t u a t i o n w i t h s t r o n g i n t e r m o l e c u l a r i n t e r a c t i o n s (on the p o l a r s i d e ) , even i n the m o l t e n s t a t e w e l l above the c r y s t a l l i n e melting p o i n t : corresponding stained micro graphs are v e r y i n f o r m a t i v e i n t h a t r e s p e c t (see r e f . (17), f i g . 4 d ) . Such a s i t u a t i o n r a i s e s o b v i o u s l y s e v e r e r h e o l o g i c a l p r o c e s s i n g p r o b l e m s , w h i c h might be d i f f i c u l t t o s o l v e . Anyhow, i t i m p l i e s a l s o t o work a t a t e m p e r a t u r e w h i c h i s e x c e e d i n g l y d e t r i m e n t a l f o r the


330

INITIATION OF

POLYMERIZATION

unsaturated 1,4-polybutadiene b l o c k ; again, p r e l i m i n a r y q u a n t i t a t i v e hydrogénation o f t h e s t a r t i n g p o l y b u t a d i e ne i s t h e answer t o t h a t p r o b l e m , even though t h e d i f u n c t i o n a l m a c r o m o l e c u l e s form a h i g h l y s w o l l e n g e l i n the p r e s e n c e o f an e x c e s s c a t a l y s t .


e

^it^_§«lY2§2ii2_îPyiii^Ï22lS-§£Elî2£]iE2 h e general i n t e r e s t o f muïtiblock copolymers i s by now w e l l documented p a r t i c u l a r l y i n t h e f i e l d o f TPE. Based on t h e e f f i c i e n t c r o s s - l i n k i n g a c t i o n o f the harder b l o c k s , i n t e r e s t i n g developments have t a k e n p l a c e , l e a d i n g t o some s u c c e s s f u l i n d u s t r i a l m a t e r i a l s such as HYTREL p o l y e t h e r e s t e r t h e r m o p l a s t i c e l a s t o m e r s . The v e r y r a p i d d e v e l o p ments o f i n c r e a s i n g l y s o p h i s t i c a t e d c a t a l y s t s has a l s o promoted new u n e x p e c t e d achievements; a t y p i c a l examp l e (18) i s t h e " c o d i n g " 1,4 p o l y m e r i z a t i o n o f b u t a d i ene by " t a i l o r e d " c a t a l y s t s , namely b i s (η -allylnickel -X) complexes. Under p r e c i s e l y c o n t r o l l e d k i n e t i c c o n d i t i o n s , a m u l t i s t e r e o b l o c k ( p o l y . c i s 1,4-b-poly.trans 1 , 4 ) - b u t a d i e n e c a n be o b t a i n e d , t h a t r e p r e s e n t s t h e f i r s t example o f a t h e r m o p l a s t i c e l a s t o m e r ( s e m i c r y s t a l l i n e m e l t i n g p o i n t c a . 135°C) o b t a i n e d i n one s t e p from one s i n g l e monomer. A c o m p l e t e l y d i f f e r e n t a p p r o a c h has been r e c e n t l y d e v e l o p e d i n t h a t p r o s p e c t , based on t h e assumption t h a t " p r o p e r t i e s s i m i l a r t o those o f m u l t i b l o c k c o p o l y mers c o u l d be r e a c h e d , i n a more v e r s a t i l e manner, by r e p l a c i n g t h e i r h a r d segments by s i n g l e g r o u p i n g s , p r o v i d e d the molecular c h a r a c t e r i s t i c s o f these groupings promote v e r y s t r o n g m u t u a l i n t e r a c t i o n s , a t l e a s t i n the media e n v i s o n e d f o r t h e i r a p p l i c a t i o n s " . That c o n c e p t had l e d t o t h e s y n t h e s i s o f s o - c a l l e d " h a l a t o - t e l e c h e l i c p o l y m e r s " (which means a " s a l t " o r " n e u t r a l i z e d " t e l e c h e l i c polymer, a c i d i c o r b a s i c ) . Although t h a t i s a very g e n e r a l denomination c o v e r i n g a l l t h e c h a i n s formed by any t y p e o f i o n - p a i r c o u p l i n g i n any way, a p a r t i c u l a r l y handy and r e p r e s e n t a t i v e c l a s s o f such s t r u c t u r e s c a n be o b t a i n e d from t h e com plete n e u t r a l i z a t i o n of α,ω-dicarboxylato-polymers (PX), by a d i ( o r m u l t i - ) v a l e n t m e t a l d e r i v a t i v e , (19) , according t o the general equation : T

3

n

n

H00C-PX-C00H + — ΜΑ ώ f00C-PX-C00-M l - + 2n HA ν ν ~ I* 2J n ν o

Such a r e a c t i o n has been p e r f o r m e d s u c c e s s f u l l y , s t a r t i n g from a n i o n i c a l l y p r e p a r e d t e l e c h e l i c p o l y m e r s PX, and n e u t r a l i z i n g them q u a n t i t a t i v e l y w i t h v e r y r e a c t i v e



24.

TEYSSIE ET AL.

Butadiene Block

331

Copolymers

m e t a l d e r i v a t i v e s such as m e t a l a l k y I s o r a l k o x i d e s (20); the l a t t e r t e c h n i q u e p r o v e d t o be t h e most v e r s a t i l e one, p r o v i d e d a complete e l i m i n a t i o n o f t h e a l c o h o l evolved i n order t o d i s p l a c e the r e a c t i o n but a l s o t o a v o i d s o l v a t i o n by t h a t a l c o h o l : t h a t meets t h e e s s e n t i a l r e q u i r e m e n t o f any s t e p w i s e p o l y m e r i z a t i o n , i . e . the n e c e s s i t y t o e n s u r e a v e r y h i g h (99 %+) c o n v e r s i o n t o r e a c h t h e h i g h degree o f p o l y m e r i z a t i o n n e c e s s a r y f o r t h e p r o m o t i o n o f t h e most i n t e r e s t i n g p h y s i c a l p r o p e r t i e s , t h a t i n t u r n would be overshadowed i f i o n s o l v a t i o n by t h e a l c o h o l t a k e s p l a c e (see b e l o w ) . I n t h a t way, a b r o a d f a m i l y o f HTP has been s y n t h e s i z e d , wherei n t h e n a t u r e and s i z e o f b o t h t h e polymer and t h e i o n i n v o l v e d c a n be s y s t e m a t i c a l l y m o d i f i e d , as w e l l as t h a t o f t h e s o l v e n t and l i g a n d s . They r e p r e s e n t a c c o r d i n g l y a v e r s a t i l e c l a s s o f m a t e r i a l s w i t h a b r o a d pot e n t i a l range o f " m o l e c u l a r l y e n g i n e e r e d " c h a r a c t e r i s t i c s . The m o s t _ t Y p i c a l _ p r o p e r t Y o f _ h y d r o c a r b o n - s o l u b l e HTP ( i . e . , w h e r e PX i s a polydienê " o r PS, o r p o l y i s o b u tene) w i t h a h i g h enough MW (> 1,000) t o a v o i d e x c e s s i ve charge d e n s i t y ) , i s t h e s t r o n g dependence o f i t s d i l u t e - s o l u t i o n v i s c o s i t y upon c o n c e n t r a t i o n ( 2 0 ) . A l t h o u g h v e r y s i m i l a r t o t h a t o f PX a t v e r y low concent r a t i o n s , i t i n c r e a s e s a b r u p t l y and a s y m p t o t i c a l l y between c a . 1 and 2 %, r e s u l t i n g i n a g e l a t i o n _ p h e n o m e non. T h i s g e l a t i o n c a n u s u a l l y be reduce3 by i n c r e a s i n g the t e m p e r a t u r e , o r upon a d d i t i o n o f s t r o n g l i g a n d s ( F i g . 2 ) . The c r i t i c a l g e l c o n c e n t r a t i o n , C , d e p e n d s e s s e n t i a l l y on t h e n a t u r e o f PX, i t s end-groups, the s o l v e n t , t h e c a t i o n s i z e , and on P X _ m o l e c u l a r w e i g h t f o l l o w i n g t h e r e l a t i o n s h i p Cg = k.M^ (where k " / i s d i r e c t l y p r o p o r t i o n a l to^(r2j|^» , i . e . , depends g

5

1

3

5

on t h e mean end-to-end d i s t a n c e o f t h e f r e e c h a i n ) (21). These a r e o f c o u r s e c l e a r - c u t m a n i f e s t a t i o n s o f t h e e l e c t r o s t a t i c i n t e r a c t i o n s between i o n - p a i r s i n a n o n - p o l a r s o l v e n t , l e a d i n g t o a g g r e g a t e s o f v a r i a b l e s i z e s depend i n g on t h e c o n d i t i o n s ; f o r t h e same r e a s o n s , t h e same type o f i n t e r m o l e c u l a r a s s o c i a t i o n w i l l o b v i o u s l y occur i n t h e n e a t m a t e r i a l . I t i s a l s o n o t e w o r t h y t h a t such a "multiblock" s t r u c t u r e i s a dynamic one, i . e c a r b o x y l i c l i g a n d s e x c h a n g i n g around t h e m e t a l i o n r e s u l t i n g i n a c o n s t a n t s c r a m b l i n g n o t o n l y o f t h e i o n i c aggregat e s b u t a l s o o f t h e c h a i n b l o c k s t h e m s e l v e s . That s i t u a t i o n i s i n f a c t r e s p o n s i b l e f o r t h e dynamic m e c h a n i c a l p r o p e r t i e s of these m a t e r i a l s . W i t h _ c o n c e n t r a t e d s o l u t i o n s {over 50_%)_ a t _ e g u i l i b r i u m as w e l l as w i t h t h e n e a t p r o d u c t s , i t i s p o s s i b l e t o o b s e r v e t y p i c a l SAXS p a t t e r n s , o f t e n e x h i b i t i n g two d i f f r a c t i o n o r d e r s w i t h B r a g g s s p a c i n g i n 1:2 r a t i o s u g 1


332

POLYMERIZATION


INITIATION OF

Figure 2. Relative viscosity-concentration plots in toluene. Key: A , nonneutralized α,ω-dicarboxylic PBD (M = 4,600); ·, Mg salt of α,ω-dicarboxylic PBD, 25 °C; M, Mg salt of α,ω-dicarboxylic PBD, 80 °C. n


24.

TEYSSIE ET AL.

Butadiene

Block

333

Copolymers

g e s t i n g the presence of a l a m e l l a r o r g a n i z a t i o n (22). The c a l c u l a t e d l a m e l l a r t h i c k n e s s seems independent o f t h e n a t u r e o f t h e i o n as w e l l as o f temperature (below a c r i t i c a l d i s s o c i a t i o n v a l u e ) , but again s t r o n g l y r e f l e c t s the mean d i m e n s i o n s o f t h e f r e e c h a i n s . The r h e o l o g i c a l b e h a v i o u r of t h e s e p r o d u c t s has a l s o been i n v e s t i g a t e d "(23) . The s t e a d y - f l o w v i s c o s i t y depends markedly on the s h e a r - r a t e , and f o r v a l u e s h i g h e r t h a n c a . 10 s e c " a s i g n i f i c a n t d i l a t a n t e f f e c t i s obs e r v e d , s i n c e preformed i o n i c c r o s s - l i n k s p r e v e n t t h e c h a i n s t o r e l a x as the d e f o r m a t i o n t i m e - s c a l e d e c r e a s e s . I n _ t e r m s _ o f dynamic m e c h a n i c a l _ b e h a v i o u r , s t o r a g e (G ) and l o s s (G"T m o d u l i have been~dëtërmined (23) o v e r a range of f r e q u e n c i e s f o r d i f f e r e n t p o l y m e r s . A t h i g h e r f r e q u e n c y (>0.5 s e c . " ) , G i s h i g h e r t h a n G", w h i c h i n t u r n p r e s e n t s a maximum c h a r a c t e r i s t i c o f the i o n i c component r e l a x a t i o n mechanism. These e l a s t i c g e l s have r e l a x a t i o n s p e c t r a w h i c h i n d i c a t e a g a i n the i o n s a g g r e g a t i o n : a broad d i s t r i b u t i o n o f r e l a x a t i o n t i m e s app e a r s , the maximum o f w h i c h depends on t h e s t a b i l i t y of the i o n i c network. S i n c e t h e s e m a t e r i a l s d i s p l a y a n i c e t h e r m o r h e o l o g i c a l s i m p l i c i t y ( a t l e a s t when P has a M lower t h a n 20,000, i . e . , n o entanglements i n t e r f e r e n c e ) , master c u r v e s have been e s t a b l i s h e d . The c o r r e s p o n d i n g s h i f t f a c t o r s c o r r e l a t e n i c e l y i n an A r r h e n i u s - t y p e r e l a t i o n s h i p , a l l o w i n g the d e t e r m i n a t i o n o f the a c t i v a t i o n energy o f the secondary r e l a x a t i o n mechanism. F o r d i f f e r e n t i o n s , t h e s e e n e r g i e s a r e d i r e c t l y dependent on t h e i o n e l e c t r o s t a t i c f i e l d . I n _ o t h e r _ w o r d s , t h e s e p r o p e r t i e s can be i n t e r p r e ted i n terms o f a system i n w h i c h the d e f o r m a t i o n p r o c e s s e s are governed by i o n i c m u l t i p l e t s t h e r m a l d i s s o c i a t i o n ; however, w h i l e e l e c t r o s t a t i c a t t r a c t i v e f o r c e s a r e d e t e r m i n a n t i n the a g g r e g a t i o n p r o c e s s , the f r e e c o n f o r m a t i o n o f the macromolecule w i l l c o n t r o l t h e o v e r a l l morphology o f t h e g e l s as w e l l as the mean number of i o n s i n the m u l t i p l e t s . S e v e r a l i n t e r e s t i n g a p p l i c a t i o n s can be e n v i s i o n e d on the b a s i s o f t h a t b e h a v i o u r , b u t a g a i n s a t u r a t e d elastomers w i l l be more s u i t a b l e f o r most o f them, i n terms o f a g e i n g . Here a g a i n , h y d r o g e n a t e d t e l e c h e l i c p o l y b u t a d i e n e i s a p o s s i b l e answer t o t h a t problem, a l t h o u g h t e l e c h e l i c p o l y i s o b u t e n e might a l t e r n a t i v e l y be used i n some c a s e s . 1


1

1

f

x

n

1

General_Conclusion. At t h i s p o i n t , i t i s probably u s e f u l and c e r t a i n l y e n c o u r a g i n g t o s t r e s s a g a i n t h a t a l l o f t h e s e examples c o n f i r m t h e v e r s a t i l i t y o f t h e molecular engineering techniques p r e s e n t l y a v a i l a b l e , as w e l l as t h e i r p o t e n t i a l i t i e s i n b r o a d e n i n g and d i v e r -


334

INITIATION OF POLYMERIZATION

s i f y i n g the applications of such a time-honored commod i t y polymer as polybutadiene. That is c e r t a i n l y a worthwhile goal i n today's technology and economy. L i t e r a t u r e Cited 1.

2.


3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

19.

Sadron, C.; G a l l o t , B. Makromol. Chem. 1973, 164, 301; G a l l o t , B. " L i q u i d C r y s t a l l i n e Order i n Polymers," Blumstein, A, E d . ; Academic: New York, 1978; 191. M a r t i , S.; Nervo, J.; Riess, G. Progr. C o l l o i d . Polym. S c i . 1975 , 58, 114. Paul, D.R. "Polymer Blends," Paul,D.R. and Newman, S.; E d s . ; Academic: New York, 1978; 168. Holden, G.; Bishop, E.T.; Legge, N.R. J . Polymer S c i . 1969, C36, 37. Falk, J.C. J . Polym. S c i . 1971, A - 1 , 9 , 2617; Gillies, G.A. (to Shell O i l Co.), U.S. Patent 3,792,127 (1974). Fayt, R.; J é r ô m e , R. A c t u a l i t e Chimique 1980, 21. Fayt, R.; J é r ô m e , R.; Teyssié, Ph. J. Polym. S c i . Polym. Lett. Ed. 1981, 19, 79. Szwarc, M. "Carbanions, L i v i n g Polymers and E l e c t r on-Transfer Processes," and references t h e r e i n , Wiley-Interscience : New York, 1968. Hadjiandreau, P. P h . D . , Thesis, University of Liege, Liege, 1980. Fayt, R.; J é r ô m e , R.; Teyssié, Ph. J. Polym. S c i . Polym. Phys. Ed. 1981, 19, 1269. Kuntz, I. J. Polym. S c i . 1961, 54, 569. Fayt, R.; J é r ô m e , R.; Teyssié, Ph. J . Polym. S c i . Polym. Phys. Ed. (in p r e s s ) . Heuschen, J.; Jerome, R.; Teyssie, Ph. Macromolecules 1981, 14, 242. Herman, J . J . Ph.D., Thesis, University of Liege, Liege, 1978. Teyssié, Ph.; B i o u l , J.P.; Hamitou, A.; Heuschen,J.; Hocks, L.; Jérôme, R.; Ouhadi, T. ACS Symposium Series No.59, T. Saegusa and E. Goethals Eds., 1977. Heuschen, J.; J é r ô m e , R.; Teyssié, Ph. French Patent 2,383,208 (1977); U.S.Patent 4,281,087(1981). P e t i t . D . ; J é r ô m e , R.; Teyssié, Ph. J . Polym. S c i . Polym. Chem. Ed. 1979, 17, 2903. Teyssié, P h . ; Devaux, A.; Hadjiandreou, Ρ.; J u l é m o n t , M . ; Thomassin, J.M.; Walckiers, E.; Ouhadi, T. "Preparation and Properties of Stereoregular Polymers," Lenz, R.W. and Ciardelli, F.; Eds.; M. R e i d e l : Hingham, Mass., 1980; 144. Moudden, A.; Levelut, A.M.; P i n e r i , M. J . Polym. S c i . Polym. L e t t . Ed. 1977, 15, 1707.


24.

TEYSSIÉ ET AL.

Butadiene Block Copolymers

335

20. Broze, G . ; J é r ô m e , R.; T e y s s i é , Ph. Macromolecules ( i n press) and references t h e r e i n . 21. Broze, G . ; J é r ô m e , R.; T e y s s i é , Ph. Macromolecules ( i n p r e s s ) . 22. G a l l o t , B.; Broze, G . ; J é r ô m e , R. ; Teyssié, Ph. J . Polym. S c i . Polym. L e t t . Ed. 1981, 19, 415. 23. Broze, G . ; J é r ô m e , R.; Teyssié, Ph. Polym. B u l l . 1981, 4, 241; Part V I I , J. Polym. S c i . Polym. Phys. Ed. (to be published).


RECEIVED December 23, 1982


Initiation of Polymerization - American Chemical Society

Recommend Documents