Catalytic Control of Architecture and Properties of Butadiene Block Copolymers

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Catalytic Control of Architecture and Properties

of Butadiene Block Copolymers

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 is shown how a precise control of the initiation and s e l e c t i v i t y

of butadiene block polymerization reac-tions allows the molecular engineering of a variety of new heterophase materials. The typical examples presented illustra-te 3 main poillustra-tentialities of these copoly-mers. First, the stable emulsification of blends of 2 immiscible homopolymers (PE/PS; PVC/PBD) by the corresponding diblock co-polymer. Second, the p o s s i b i l i t y to obtain high performance thermoplastic elastomers from triblock copolymers containing end-blocks of high cohesive energy density

(i.e. nylon-6, polypivalolactone). Third, the opportunity to t a i l o r "multiblock" systems i n which the "hard" segment is an ionic group (halatotelechelic poly-mers), imparting to these systems inte-resting rheological properties.

Catalytic polymerizations of 1,3-butadiene into essentially 1,4 elastomeric polymers are by now pretty well-mastered processes. It i s the purpose of this 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 is not w i l l i n g any-more to produce many of these necessary materials from new monomers; the key approach here is thus d i v e r s i f i -cation, but starting from basic feedstocks and materials already available at low prices in large amounts. On the

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o t h e r hand, i n a time o f e x p l o s i v e d e v e l o p m e n t o f "gene-t i c e n g i n e e r i n g " "gene-t e c h n i q u e s i n b i o l o g y , i "gene-t i s o n l y "gene-t o o f a i r t o acknowledge a s i m i l a r t y p e o f a c h i e v e m e n t 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 . t h e " 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 " . T h a t 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 , -t h r o u g h p r e c i s e ( a l -t h o u g h some-times s m a l l ) m o d i f i c a t i o n s o f m o l e c u l a r s t r u c t u r e s , a " f i n e -t u n i n g " o f -t h e f i n a l b u l k p r o p e r -t i e s and m a c r o s c o p i c b e h a v i o u r o f t h e s e 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 f r o m o u r 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 o f 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 t h e m o l e c u l a r a r c h i t e c t u r e o f t h e p o l y m e r s u s e d , t h a t means a l s o t h e morphology and f u r t h e r t h e 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 o f 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 t h e 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 t y p e s 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 , a r e based on c o p o l y m e r s o f v a r y i n g a r c h i t e c t u r e , b u t 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 t h u s r e f l e c t t h r e e i m p o r t a n t po-t e n po-t i a l i po-t i e s o f h e po-t e r o p h a s e b l o c k c o p o l y m e r - b a s e d mapo-te- mate-r i a l s : 1) t h e i mate-r " o mate-r g a n i z a t i o n " i n t o mesomomate-rphic p h a s e s (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 e m u l s i o n s (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 d e v e l o p m e n t o f a new " p l a s t u r g y " ; 3) t h e i r use as h i g h - p e r f o r m a n c e 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 t h e r m o p l a s t i c e l a s t o m e r s ( 4 ) . E x p e r i m e n t a l A l l o f t h e 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 t h e g e n e r a l p r o c e d u r e s t a k e n f r o m l i t e r a t u r e , were r e p o r t e d i n t h e 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 t h e 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 t h e 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 p u r e a r g o n 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 men-t i o n e d . Polymer b l e n d i n g was u s u a l l y p e r f o r m e d f o r 5 m i n u t e s 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 m i l l . R e s u l t s 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 o f t h e 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

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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 s e c o n d a -r 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 h a s been e l e g a n t -l y c i r c u m v e n t e d b y 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 c o m p l e -xes ( 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 h a s a t w o f o l d a d v a n t a g e : 1 ) i t i s p o s s i b l e t o c o n t r o l i t s s e l e c t i v i t y ( v a r y i n g t h e 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 ) , s o 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 h y d r o g e n a t e d i n t h e p r e s e n c e o f o t h e r u n s a t u r a t e d c h a i n s 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 b y c h a n g i n g t h e s e r e a c -t i o n p a r a m e -t e r s ; 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 p r o d u c t n o t v e r y d i f f e r e n t f r o m t h e c o r r e s p o n d 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 f r o m 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 l o w 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 c o p o -l y m e r o f e t h y -l e n e and

1butène) , d i s p l a y i n g a m o d e r a t e 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 h a n d , t h e u s e o f a l i n e a r p u r e 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 c o m p l e x e s ) y i e l d s a h i g h - d e n s i t y p o l y e t h y l e n e - l i k e p r o d u c t , w i t h 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 and a m e l t i n g - p o i n t c l o s e t o 1 3 0 ° 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 t o w a r d s l i g h t , o x y g e n 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 . M o r e o v e r , t h e hydrogénation c a n be s t o p p e d 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 r a n g e 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 d e v e l o p m e n t s 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 K r a t o n G t h e r m o p l a s t i c e l a s t o m e r s . s i f i e r s _ _ ( P S - b - P B D h ) _ . C o m b i n a t i o n o f d i f f e r e n t p o l y m e r s i n t o h e t e r o p h a s e s y s t e m s 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 t o w a r d s 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 p o o r p r o p e r t i e s o f many b l e n d s , 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 p o o r 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 c o p o l y m e r s (6) c o n -t a i n i n g s e q u e n c e s 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 u s e d 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

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r e s u l t o f 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 t h a t r e s p e c t , 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 c o p o l y m e r s 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 u n d e r g o 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 (PSbPBDh) 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 (PSbPBD) c o p o l y m e r (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; a s d i s c u s s e d a b o v e , 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 (PSbLLDPE) c o p o l y m e r . The s e c o n d one came f r o m 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 p u r e (99 %) 1,4 p o l y m e r by a b i s η3 -allylnickel-tri-f 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 , -allylnickel-tri-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 t y p e c o p o l y m e r s , we have d e v e l o p e d ways t o d r a s t i c a l l y i m p r o v e 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 t h e s u i t a b l e PS-b-PDBh c o p o l y m e r 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 d0p 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 . 2-t o 5,000 A ) ; m o r e o v e r , i 2-t s 2-t a b i l i z e s e f f i c i e n 2-t l y 2-t h a 2-t s i t u a t i o n , i . e . e v e n 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 b r e a k 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 e n e r g y a t b r e a k (Εβ v a l u e s ) , i s n o t e d ( F i g . 1 ) . The l e v e l o f p e r f o r m a n c e 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 c o p o l y m e r added a n d , 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 n o t e d 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 h a s 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 d o m a i n s , h i g h e r σ β ) , t h e u s e 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 e a c h 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 b l e n d e d ) 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 t o u g h e n e d 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 t o w a r d s c r y o f r a c t u r e . These f e a t u r e s a r e p r o b a b l y c h a r a c t e r i s t i c o f t h e i m p o r t a n c e o f e n t a n g l e ments between c h a i n s o f homo- and c o p o l y m e r n e a r t h e i n t e r f a c e .

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

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Figure 1. Ultimate tensile strength (σΒ) and elongation at break (eB) of LDPE

(Mn = 40,000)/PS (Mn = 105) blends. Key: ·, without copolymer; Δ , with 9%

of a poly(styrene-b-hydrogenated butadiene), Mn total = 58,000; O , with 9% of

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t e d 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 " p u r e " 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 ) a r e 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 ; o w i n g 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 a g e n t s 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 " g r a d e d " modulus r e s p o n s i b l e f o r an i m p r o v e d m e c h a n i c a l r e s p o n s e o f t h e o v e r a l l m a t e r i a l ( 1 2 ) . I n 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 O H - t e r m i n a t e d 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 e n s u r e 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 t h e d e s i r e d b l o c k c o p o l y m e r s ( 1 3 ) . I n t h i s case however t h e PBD hydrogénation ( i f needed) c a n be c o n d u c t e d 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 f -r o m , o -r s e c o n d a -r y -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 u n d e r g o 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 f o r m 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 t a n c e t o c r y o f r a c t u r e . M o r e o v e r , t h e y a r e 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 p h a s e .

The b l e n d i n g a p p r o a c h d e s c r i b e d above h a s been e x t e n d e d t o t h e s e p r o d u c t s , t a k i n q a d v a n t a g e 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 I n p a r t i c u l a r , e x c e l l e n t 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 t h r o u g h h o t - m i l l i n g . A g a i n , t h e y d i s p l a y a v e r y f i n e m o r p h o l o g y (domain s i z e c a 5 , 0 0 0 Â ) w h i c h i s r e m a r k a -b l y s t a -b l e i n t i m e , and some i m p r o v e d 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 a s l o n g a s 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 -m e t e r s 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 h e r e 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 c a n n o t be o v e r e s t i m a t e d a s r a t h e r m i n u t e m o d i -f i c a t i o n s c a n l e a d t o i m p r o v e m e n t s o -f one o r d e r o -f ma-g n i t u d e . O t h e r 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 r u b b e -r y p h a s e , t h e p -r e s e n c e o f t h e c o p o l y m e -r ( i . e . PCL-b-PBD) p r o m o t e s i n d e e d good i m p a c t 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 a n c h o r a g e o f t h a t r u b b e r y phase i n t h e r e s i n m a t r i x .

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I n o t h e r w o r d s , t h i s example emphasizes c l e a r l y t h e v e r y b r o a d a p p l i c a b i l i t y o f t h e " 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 a b o v e , t o p r a c t i c a l p r o b l e m s i n v o l v i n g l a r g e

-s c a l e p o l y m e r -s .

§1 §§ΐ:22!§£§_ίΐΙΙΣ_ΐΐΝ^

The i n t e r e s t o f TPË has been l a r g e l y d e m o n s t r a t e d by t h e 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 t h e f i e l d , and by t h e c o m m e r c i a l s u c c e s s o f t h e 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 w e l l - k n o w n p r o b l e m t h a t t h e s e m a t e r i a l s a r e 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 u n d e r r a t h e r m i l d c o n d i t i o n s , due t o t h e r e l a t i v e l y l o w Tg o f t h e g l a s s y phase a n d / o r t h e m e d i o c r e t h e r m a l s t a b i l i t y o f t h e r u b b e r y p h a s e . 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 c a n be o f f e r e d by t h e 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,ωdihydroxyîpolybutadiene c a n be endcapped 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 s o c y a n a t e ) , w h i c h a r e f u r t h e r c o n v e r t e d 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 t h e 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 o f t h e 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 o f t h e 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 t h e u r e t h a n e n o r t h e u r e a l i n k a g e s f o r m e d a r e b r o k e n d u r i n g t h e s u b s e q u e n t 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 c o p o l y m e r i s o b t a i n e d . T h a t t r i b l o c k c o p o l y m e r d i s p l a y s i n d e e d a s e t o f 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 : e v e n a t 30 % o f PBD p h a s e , t h e 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 p h a s e , 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 t h e 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 p h a s e , i m p a r t i n g t o 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 -t h e above p r o d u c -t i s n o -t a TPΕ i n -t h e s t r i c t s e n s e o f t h e 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 o f 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 t h e p o l a r s i d e ) , e v e n i n t h e m o l t e n s t a t e w e l l above t h e c r y s t a l l i n e m e l t i n g p o i n t : c o r r e s p o n d i n g s t a i n e d m i c r o g r a p h s a r e 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 . ( 1 7 ) , 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 m i g h t 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 t h e

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u n s a t u r a t e d 1 , 4 - p o l y b u t a d i e n e b l o c k ; a g a i n , 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 , e v e n t h o u g h 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 -f o r m a h i g h l y s w o l l e n g e l i n t h e 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 . ^ i t ^ _ § « l Y 2 § 2 i i 2 _ î P y i i i ^ Ï 2 2 l S - § £ E l î 2 £ ] i E 2e Th e g e n e r a l i n t e

-r e s t o f muïtiblock c o p o l y m e -r s 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. B a s e d 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 t h e h a r d e r 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 s u c h a s 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 h a s a l s o p r o m o t e d new u n e x p e c t e d a c h i e v e m e n t s ; 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 examp 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 (η3-allylnickel

-X) c o m p l e x e s . 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 - p o l y . t r a n s 1 , 4 )n- 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 f r o m 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 h a s 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 , b a s e d o n t h e a s s u m p t i o n t h a t " p r o p e r t i e s s i m i l a r t o t h o s e 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, b y 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 t h e m o l e c u l a r c h a r a c t e r i s t i c s o f t h e s e g r o u p i n g s 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 t h e 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 " . T h a t c o n c e p t h a d 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 " ( w h i c h 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 p o l y m e r , a c i d i c o r b a s i c ) . A l t h o u g h t h a t i s a v e r y g e n e r a l d e n o m i n a t i o n 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 s u c h s t r u c t u r e s c a n be o b t a i n e d f r o m t h e com p l e t e n e u t r a l i z a t i o n o f α , ω - d i c a r b o x y l a t o - p o l y m e r s ( P X ) , 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) , a c c o r d i n g t o t h e g e n e r a l e q u a t i o n : n H00C-PX-C00H + — ΜΑ ώ f 0 0 C - P X - C 0 0 - Mol - + 2n HA ν ν ~ I* 2 J n ν Such a r e a c t i o n h a s 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 f r o m 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

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m e t a l d e r i v a t i v e s s u c h as m e t a l a l k y I s o r a l k o x i d e s ( 2 0 ) ; t h e 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 c o m p l e t e e l i m i n a t i o n o f t h e a l c o h o l e v o l v e d i n o r d e r t o d i s p l a c e t h e r e a c t i o n b u t 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 . t h e 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 d e g r e e 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 w o u l d 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 ( s e e 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 h a s been s y n t h e s i z e d , where-i n t h e n a t u r e and s where-i z e o f b o t h t h e p o l y m e r and t h e where-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 p o t e n t i a l r a n g e 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 P S , o r p o l y i s o b u t e n e ) 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 c h a r g e 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 l o w c o n c e n -t 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 r e d u c e 3 by i n c r e a s i n g t h e 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 , Cg, 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 e n d - g r o u p -s , t h e 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^ 5 (where k "1/3 i s d i r e c t l y p r o p o r t i o n a l t o ^ ( r 2 j | ^ »5, i . e . , depends on t h e mean e n d - t o - e n d d i s t a n c e o f t h e f r e e c h a i n ) ( 2 1 ) . 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 be-tween 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 depen-d i n g on t h e c o n depen-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 t y p e 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 o c c u r 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 s u c h a " m u l t i b l o c k " s t r u c t u r e i s a dynamic o n e , 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 a r o u n d 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 a g g r e g a t 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 . T h a t 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 d y n -a m i c m e c h -a n i c -a l p r o p e r t i e s o f t h e s e 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 g1s s p a c i n g i n 1:2 r a t i o s u g

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Figure 2. Relative viscosity-concentration plots in toluene. Key: A , nonneutralized

α,ω-dicarboxylic PBD (Mn = 4,600); ·, Mg salt of α,ω-dicarboxylic PBD, 25 °C;

M, Mg salt of α,ω-dicarboxylic PBD, 80 °C.

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g e s t i n g t h e p r e s e n c e o f a l a m e l l a r o r g a n i z a t i o n ( 2 2 ) . 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 i n d e p e n d e n t 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 t e m p e r a t u r e (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 ) , b u t a g a i n s t r o n g l y r e -f l e c t s t h e 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 o f 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 d e -pends m a r k e d l y on t h e 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 "1 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 ob-s e r v e d , ob-s i n c e p r e f o r m e d i o n i c c r o ob-s ob-s - l i n k ob-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 t h e 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 (G1)

and l o s s (G"T moduli have been~dëtërmined (23) over a r a n g e o f 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 . "1) , Gf 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 t h e 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 t h e i o n s a g g r e -g a t i o n : a b r o a d 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 ap-p e a r s , t h e maximum o f w h i c h deap-pends on t h e s t a b i l i t y o f t h e i o n i c n e t w o r k . 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 Px has a Mn l o w e r t h a n 20,000, i . e . , n o e n t a n g l e m e n t s i n t e r f e r e n c e ) , m a s t e r 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 t h e d e t e r m i n a t i o n o f t h e a c t i v a -t i o n e n e r g y o f -t h e s e c o n d a r y 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 d e p e n d e n t 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 c a n be i n t e r p r e t e d i n t e r m s o f a s y s t e m i n w h i c h t h e d e f o r m a t i o n p r o -c e s s e s a r e g o v e r n e d by i o n i -c m u l t i p l e t s1 t h e r m a l d i s s o -c i a t i o n ; h o w e v e r , 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 t h e a g g r e g a t i o n p r o c e s s , t h e f r e e c o n f o r m a t i o n o f t h e m a c r o m o l e c u l e w i l l c o n t r o l t h e o v e r -a l l m o r p h o l o g y o f t h e g e l s -as w e l l -as t h e me-an number o f i o n s i n t h e 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 c a n be e n v i s i o n e d on t h e 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 -e l a s t o m -e r s w i l l b-e mor-e s u i t a b l -e f o r most o f th-em, i n t e r m s o f a g e i n g . H e r e 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 p r o b l e m , 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 m i g h t a l t e r n a t i v e l y be u s e d i n some c a s e s . G e n e r a l _ C o n c l u s i o n . A t t h i s p o i n t , i t i s p r o b a b l y 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 e x a m p l e s 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 m o l e c u l a r e n g i n e e r i n g t e c h n i q u e s 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

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sifying the applications of such a time-honored commo-dity polymer as polybutadiene. That is certainly a worthwhile goal i n today's technology and economy. Literature Cited

1. Sadron, C.; Gallot, B. Makromol. Chem. 1973, 164, 301; Gallot, B. "Liquid Crystalline Order i n Poly-mers," Blumstein, A, E d . ; Academic: New York,

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3. Paul, D.R. "Polymer Blends," Paul,D.R. and Newman, S.; Eds.; Academic: New York, 1978; 168.

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Polym. Lett. Ed. 1981, 19, 79.

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11. Kuntz, I. J. Polym. S c i . 1961, 54, 569.

12. Fayt, R.; Jérôme, R.; Teyssié, Ph. J. Polym. S c i . Polym. Phys. Ed. (in press).

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15. Teyssié, Ph.; Bioul, J.P.; Hamitou, A.; Heuschen,J.; Hocks, L.; Jérôme, R.; Ouhadi, T. ACS Symposium

Series No.59, T. Saegusa and E. Goethals Eds., 1977. 16. Heuschen, J.; J é r ô m e , R.; Teyssié, Ph. French

Patent 2,383,208 (1977); U.S.Patent 4,281,087(1981). 17. Petit. D.; Jérôme, R.; Teyssié, Ph. J. Polym. S c i .

Polym. Chem. Ed. 1979, 17, 2903.

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"Preparation and Properties of Stereoregular Polymers," Lenz, R.W. and Ciardelli, F.; Eds.; M. Reidel: Hingham, Mass., 1980; 144.

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20. Broze, G . ; Jérôme, R.; T e y s s i é , Ph. Macromole-cules (in press) and references therein.

21. Broze, G . ; Jérôme, R.; T e y s s i é , Ph. Macromole-cules (in press).

22. Gallot, B.; Broze, G . ; Jérôme, R. ; Teyssié, Ph. J. Polym. Sci. Polym. Lett. Ed. 1981, 19, 415. 23. Broze, G . ; Jérôme, R.; Teyssié, Ph. Polym. B u l l .

1981, 4, 241; Part VII, J. Polym. S c i . Polym. Phys. Ed. (to be published).

RECEIVED December 23, 1982