Block Copolymers: Maturation of an Old Concept into a Versatile

20 Block Copolymers: Maturation of an Old Concept into a Versatile Modern Tool P. TEYSSIE

Downloaded by UNIV OF PITTSBURGH on May 12, 2016 | http://pubs.acs.org Publication Date: December 10, 1981 | doi: 10.1021/bk-1981-0175.ch020

University of Liege, Laboratory of Macromolecular Chemistry and Organic Catalysis, Sart Tilman, 4000 Liege, Belgium

rials

As one t r i e s to write down an analysis of the developments in the block polymers area, one r e a l i z e s very soon that i t is going to consist of a series of variations on a theme : a theme which is the increasingly stronger r e a l i t y , in our everyday s c i e n t i f i c l i f e , of what can be now r e a l l y called "the molecular engineering of polymers properties", i . e . the p o s s i b i l i t y to c o n t r o l , through precise (although sometimes small) modifications of molecular structures, the f i n a l bulk properties and macroscopic behaviour of polymeric materials. In other words, one deals there with a very a c t i ve version of the studies on structure-properties interr e l a t i o n s h i p s , a question which by the way has always been a focal point among the many d i v e r s i f i e d interests of Professor Mark. More s p e c i f i c a l l y , the use of well-designed block copolymers can lead to a fine-tuning of polymeric matemorphology, obviously a key-point in devising their f i n a l (bulk) physical properties. Among the spectacular consequences of such a c a p a b i l i t y , suffice i t to r e c a l l : - the use o f these b l o c k copolymers as h i g h - p e r f o r m a n c e engineering products, p a r t i c u l a r l y i n the f i e l d of thermoplastic e l a s t o m e r s (1) ( K r a t o n - t y p e ) ; - t h e i r a b i l i t y to s t a b i l i z e e m u l s i o n s , and i n a v e r y important e x t e n s i o n of that concept, to s t a b i l i z e f i n e d i s p e r s i o n s o f t h e c o r r e s p o n d i n g homopo1ymers, b r i d g i n g the " c o m p a t i b i l i t y gap" e x i s t i n g between t h e s e i n d i v i d u a l i s t i c m o l e c u l e s ( 2 ) , and p r o m o t i n g t h e d e v e l o p m e n t o f a new " P l a s t u r g y " ; - t h e i r " o r g a n i z a t i o n " i n t o mesomorphic phases ( 3 ) , g i v i n g r i s e to h i g h l y o r i g i n a l , o f t e n a n i s o t r o p i c , properties.

0097-6156/81/0175-0307$5.00/0 © 1981 American Chemical Society

Stahl; Polymer Science Overview ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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Of c o u r s e , a l l t h e s e a c h i e v e m e n t s i m p l y t o meet a s t r i c t and d i f f i c u l t r e q u i r e m e n t , i . e . t o be a b l e t o c o n t r o l p r e c i s e l y and s i m u l t a n e o u s l y , b o t h t h e s t r u c t u r a l and 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 b l o c k polymers i n v o l v e d : i t i s t h e r o l e (maybe too o f t e n underestimated) o f s y n t h e t i c p o l y m e r c h e m i s t r y , t o meet t h e s e c h a l l e n ges . The a p p r o a c h e s a n a l y z e d h e r e a f t e r a r e meant t o i l l u s t r a t e t h e s e v i e w s , m a i n l y on t h e b a s i s o f c u r r e n t work p e r f o r m e d i n o u r l a b o r a t o r y , and so t o show t h e d i r e c t and p o w e r f u l c o n n e c t i o n b e t w e e n t h e s y n t h e t i c performances, t h e r e s u l t i n g p h y s i c a l p r o p e r t i e s , and t h e p o t e n t i a l a p p l i c a t i o n s b a s e d u p o n them. I . The

older

route

U n t i l q u i t e r e c e n t l y , t h e b e s t known a n s w e r t o t h e c h a l l e n g e o f c o m b i n i n g d i f f e r e n t p r o p e r t i e s i n an a d d i t i v e manner i n a s i n g l e p o l y m e r i c p r o d u c t , h a s b e e n t h e use of s o - c a l l e d " l i v i n g " i n i t i a t o r s to produce b l o c k copolymers, i n a 2- o r 3 - s t e p s p r o c e s s d e p e n d i n g wether a d i - o r a t r i - b l o c k w a s n e e d e d , ( s e e scheme I ) . T h i s very e f f i c i e n t , time-honoured pathway s u f f e r s however a v e r y s e v e r e l i m i t a t i o n , i . e . the r e l a t i v e r e a c t i v i t y o f t h e l i v i n g c e n t r e C* must be a d a p t e d t o t h e s t r u c t u r e and r e a c t i v i t y o f monomer M2, a r e q u i r e m e n t w h i c h i s n o t v e r y o f t e n met. F o r t u n a t e l y t h i s approach, i l l u s t r a t e d mainly i n a n i o n i c c o p o l y m e r i z a t i o n , has b e e n e x t e n d e d s i g n i f i c a n t l y a l o n g two d i f f e r e n t l i n e s o f a c h i e v e m e n t s . (4) F i r s t , new " l i v i n g " i n i t i a t o r s h a v e b e e n d i s c o v e r e d ( a l t h o u g h n o t a l w a y s as e f f i c i e n t ) , w h i c h r e s p o n d t o o t h e r m e c h a n i s m s , i . e . c a t i o n i c (5) o r e v e n r a d i c a l o n e s ( 6 ) , and c a n a c c o r d i n g l y a c c o m o d a t e o t h e r t y p e s o f monomers. A r e c e n t t y p i c a l example i s the c o o r d i n a t i o n 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 by b i s ( η - a l l y l - t r i f l u o r o a c e t a t o - n i c k e l ) t o y i e l d a " l i v i n g " p u r e 1.4 cis-polyb u t a d i e n y l - n i c k e l , a b l e to i n i t i a t e i n t u r n the polyme r i z a t i o n o f monomers l i k e i s o p r e n e o r s t y r e n e ( 7 ) . 3

S e c o n d , t h e c o n v e r s i o n o f one o f t h e b l o c k s i n t o a n o t h e r t y p e o f s t r u c t u r e by a s u i t a b l e q u a n t i t a t i v e c h e m i c a l r e a c t i o n , a l l o w s a broad d i v e r s i f i c a t i o n of the p r o p e r t i e s o f t h e a v a i l a b l e b l o c k c o p o l y m e r s . The b e s t e x a m p l e o f s u c h an o p p o r t u n i t y i s p r o b a b l y t h e h y d r o g é n a t i o n of p o l y ( b u t a d i e n e - b - s t y r e n e ) copolymers, which y i e l d s a p r o d u c t c l o s e t o a low d e n s i t y p o l y ( e t h y 1 e n e b - s t y r e n e ) when s t a r t i n g f r o m an a n i o n i c a l l y p r e p a r e d d i b l o c k ( i n c l u d i n g a c e r t a i n amount, c a . 10 %, o f 1.2 u n i t s ) , while a high density poly(ethy1ene-b-styrene)


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309

i s o b t a i n e d ( c r y s t a l l i n e m . ρ . c a . 1 2 5 ° C ) when h y d r o g e n a t i n g the polymer o b t a i n e d from the η - a l l y l - n i c k e l s y s tem m e n t i o n e d above ( 7 ) .


3

A n _ a t t r a c t i v e _ a g 2 l i £ § £ i 2 D o f f e r e d by t h e s e l a s t d i b l o c k copolymers i s t h e i r u s e as b l e n d i n g a i d s ( o r "emulgators") f o r mixtures of homopolystyrene (PS) and p o l y e t h y l e n e (ΡΕ, b o t h low and h i g h d e n s i t y ) . I n t h a t c a p a c i t y t h e y p e r f o r m i n d e e d two i m p o r t a n t f u n c t i o n s (8) : - f i r s t , they c o n t r o l the o v e r a l l morphology of the b l e n d by r e d u c i n g , thanks t o t h e i r i n t e r f a c i a l p r o p e r t i e s , the s i z e of the domains w e l l underlym, e n s u r i n g a c c o r d i n g l y homogeneous p h y s i c o - m e c h a n i c a l properties. O f c o u r s e , t h e k e e p i n g o f t h e s e domains i s a must, s i n c e o n l y an h e t e r o p h a s i c s i t u a t i o n w i l l a l l o w a c u m u l a t i v e a d d i t i o n of p r o p e r t i e s i n the f i n a l blended m a t e r i a l ; - on t h e o t h e r hand, i f t h e m o l e c u l a r w e i g h t s o f t h e two b l o c k s a r e a t l e a s t c l o s e t o t h o s e o f t h e h o m o p o l y mers t o b e b l e n d e d , i n t e r a c t i o n s t a k e p l a c e ( f . i . t h r o u g h entanglements and Van d e r Waals type f o r c e s ) w h i c h anchor the phases i n t o each o t h e r ( s t r o n g e r types of i n t e r a c t i o n s m i g h t f u r t h e r m o r e o v e r s h a d o w t h a t M.W. requirement). As a r e s u l t , g o o 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 r e o b t a i n e d over the whole range of b l e n d i n g c o m p o s i t i o n s , i n s t e a d o f h a v i n g a monotonous v a r i a t i o n , o r worse (as o f t e n observed) a depressed s i t u a t i o n (fig.l). S t i l l more i n t e r e s t i n g l y . " s y n e r g i s t i c " b e h a v i o u r s a p p e a r i n some c a s e s , w h e r e t h e l e v e l o f c e r t a i n p r o p e r t i e s c a n b e h i g h e r t h a n t h e one o f t h e b e s t p e r f o r m i n g compo nent, b u t a l s o where r a t h e r a n t a g o n i s t i c p r o p e r t i e s l i k e s t r a i n and t e n s i l e s t r e n g t h c a n be improved simul taneous l y. II.

A newer

scheme

D e s p i t e s a l l of i t s v i r t u e s , the c l a s s i c a l approach d e s c r i b e d h e r e a b o v e s u f f e r s t o o many c o n s t r a i n t s t o b e f u l l y s a t i s f a c t o r y , and a c t i v e e f f o r t s have been d e v o t e d to t h e s u c c e s s f u l l d e s i g n i n g o f a more g e n e r a l a n d v e r s a t i l e r o u t e to these d e s i r a b l e b l o c k s t r u c t u r e s . S i n c e q u i t e a few y e a r s now, t h e p a t h w a y d e s c r i b e d i n scheme 2 h a s b e e n i l l u s t r a t e d b y a n i n c r e a s i n g number o f v e r y i n t e r e s t i n g achievements. (9). I t implies again the f o r mation of a " l i v i n g " polymer c h a i n Ρ , the a c t i v e endgroup of which (C* ) i s then c o n v e r t e d i n t o a f u n c t i o nal g r o u p a b l e t o p r o m o t e t h e f o r m a t i o n o f a new " l i v i n g " i n i t i a t o r , which w i l l then ensure the p o l y m e r i z a t i o n of t h e s e c o n d monomer. T r i b l o c k s c a n b e o b t a i n e d b y u s i n g d i f u n c t i o n a l s t a r t i n g p o l y m e r s , o r by f u r t h e r c o u p l i n g of t h e f i n a l p r o d u c t s .


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Scheme 1. Pi

P

2


XY

Reaction (specific)

(Tg ( k g / m m 1 )

g

t 20

ι 40

ι 60

7.PE L

80

100

Figure 1. Ultimate tensile strength (σ ) and elongation at break (e ) of l.d. PE (Mn = 40,000)/PS)Mn — 10 ) blends. Key: O, without copolymer; Δ, with 9% of a polystyrene-b-hydrogenated butadiene), Μ η total = 58,000; Ο, with 9% of a polystyrene-b-hydrogenated butadiene, Mn total = 155,000. Β

B

5


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Block

311

Copolymers

A l t h o u g h the b a s i c p r i n c i p l e s u n d e r l y i n g t h i s second method a r e not t h a t d i f f e r e n t from the f i r s t one, i t e n j o y s o b v i o u s l y a much b r o a d e r e f f i c i e n c y and v e r s a t i l i t y , i f one i s a b l e t o d e s i g n p r o p e r l y C* to f i t t h e s t r u c t u r a l and k i n e t i c r e q u i r e m e n t s o f monomer M 2 · Two v e r y d i f f e r e n t i l l u s t r a t i o n s o f t h i s c o n c e p t w i l l be p r e s e n t e d h e r e a f t e r , somewhat s h o w i n g t h e d i v e r s i t y o f consequences i m p l i c i t i n t h a t k i n d of approach.


A.

The_amazing_blοck_co£olymers_of_ε-caprο l a c t o n e _ ( C L )

I t has b e e n shown r e c e n t l y (10) t h a t s u c h b l o c k s t r u c t u r e s c o u l d be t a i l o r e d p r e c i s e l y by t h e g e n e r a l method summarized h e r e a b o v e . I t i s i n d e e d p o s s i b l e to c o n v e r t t h e h y d r o x y l e n d - g r o u p o f a v i n y l p o l y m e r PA ( f . i . p o l y s t y r e n e , o r p o l y b u t a d i e n e 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 t e r m i n a t e d w i t h e t h y l e n e o x i d e ) , i n t o an a l u m i n u m a l c o h o l a t e s t r u c t u r e ; s i n c e i t i s w e l l known t h a t CL p o l y m e r i z e s i n a p e r f e c t l y " l i v i n g " manner by r i n g - o p e n i n g i n s e r t i o n i n t o t h e A l - 0 bond ( 1 1 ) , t h e f o l l o w i n g r e a c t i o n sequence p r o v i d e s a d i r e c t a c c e s s to the d e s i r e d copolymers, w i t h an a c c u r a t e c o n t r o l o f t h e m o l e c u l a r p a r a m e t e r s o f t h e two b l o c k s :

PA

R0-Al( (-R0H)

PA

CL N

(+

PA

PCL

HX)

T h a n k s t o t h e a m a z i n g p r o p e r t i e s o f PCL i t s e l f , these block copolymers enjoy s e v e r a l i n t e r e s t i n g c h a r a c t e r i s t i c s , l e a d i n g t o new t y p e s o f a p p l i c a t i o n s . F i r s t of a l l , t h e s e m a t e r i a l s a r e § t t r a c t i v e _ " p e r se". In p a r t i c u l a r , poly(styrene-b-caprο l a c tone) i s a s e m i - c r y s t a l l i n e p r o d u c t d i s p l a y i n g an a m a z i n g r e s i s t a n c e to c o l d - f r a c t u r e , and a l s o m a c r o s c o p i c a 1 1 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 u o u s p h a s e . I t c a n be " o r g a n i z e d " i n t o s i n g l e c r y s t a l s , wherein l a m e l l a e o f P S t and PCL a l t e r n a t e w i t h a p e r i o d i c i t y o f a b o u t 80 A. But t h e y a r e a l s o v e r y h e l u f u l _ a s _ b 1 e n d i n g _ a i d s a g a i n , thanks to the m i s c i b i l i t y ( i f not t r u e c o m p a t i b i l i t y ) o f PCL w i t h s e v e r a l o t h e r i m p o r t a n t p o l y m e r s , i n c l u d i n g PVC and a c r y l o n i t r i l e c o p o l y m e r s ( i . e . SAN). I n d e e d , t h e u s e o f a PA-PCL d i b l o c k w i l l now a l l o w t o s t a b i l i z e f i n e d i s p e r s i o n s o f h o m o - Ρ Α and any PB m i s c i b l e w i t h PCL. A l o n g t h e s e l i n e s , good b l e n d s o f PVC with PS o r e v e n w i t h PE h a v e b e e n o b t a i n e d ( i . e . t h r o u g h h o t m i l l i n g ) , w h i c h d i s p l a y a f i n e m o r p h o l o g y (< 1 ym) and


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good m e c h a n i c a l p r o p e r t i e s , a g a i n as l o n g 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 timized (12).

SCIENCE

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as t h e c o r p r o p e r l y op

In o t h e r words, t h i s example s t r e s s e s c l e a r l y t h e very broad a p p l i c a b i l i t y of the "emulgator concept reminded above, to p r a c t i c a l problems i n v o l v i n g l a r g e scale polymers. 1 1


Β.

The_chal1enge_of_synthesizing_high-2erformance_ther-

I t i s another well-known problem that c l a s s i c a l t r i b l o c k T E P s, i . e . t h o s e o f t h e K r a t o n - t y p e , a r e o f t e n c o n f i n e d to 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 t h e r e l a t i v e l y low Tg o f t h e g l a s s y p h a s e , a n d / o r t h e medium 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 phase. I n p r i n c i p l e a t l e a s t , good a n s w e r s 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 t h e type o f s y n t h e s i s d i s c u s s e d i n this section. 1

S u c h a n e x a m p l e h a s b e e n r e c e n t l y w o r k e d o u t , com b i n i n g a very hard b l o c k i . e . p o l y p i v a l o l a c t o n e (PPVL), w i t h a t h e r m o s t a b l e e l a s t o m e r segment i . e . p o l y d i m e t h y 1 s i l o x a n e (PDMS), u s i n g t h e r e a c t i o n s s e q u e n c e d e s c r i b e d i n scheme 3. (One s h o u l d n o t e t h a t t h e s t a r t i n g PDMS has b e e n o b t a i n e d t h r o u g h a p r e v i o u s l y d e s c r i b e d p r o c e dure ( 1 4 ) , a v o i d i n g any u n s t a b l e Si-O-C bond i n t h e f i nal product). As e x p e c t e d , the r e s u l t i n g polymers a r e indeed heter o p h a s i c m a t e r i a l s , e x h i b i t i n g ( b e s i d e s t h a t one o f PDMS b l o c k s a t -42°C)acrystal1ine m e l t i n g p o i n t a t 225°C, v e r y c l o s e t o t h e one o f p u r e PPVL. O p t i c a l m i c r o g r a p h s under p o l a r i z e d l i g h t d e m o n s t r a t e an o v e r a l l formation of v e r y l a r g e s p h e r u l i t e s , w h i l e t r a n s m i s s i o n e l e c t r o n m i c r o g r a p h s show y e r y s m a l l , r a n d o m l y d i s t r i b u t e d PDMS d o m a i n s ( c a . 200 A ) , a n i d e a l s i t u a t i o n f o r i n t e r e s t i n g macroscopic physico-mechanical properties.

Ill.

The l a s t

general

answer

Thanks t o i t s v e r s a t i l i t y , t h e g e n e r a l approach d e s c r i b e d h e r e a b o v e g i v e s a good g r i p o f t h e s y n t h e s i s o f many d i f f e r e n t f a m i l i e s o f b l o c k p o l y m e r s . H o w e v e r , i n s e v e r a l c a s e s where t h e f o r m a t i o n mechanisms o f t h e two t y p e s o f c h a i n s a r e n o t a m e n a b l e t o t h i s q u a n t i t a t i v e a c t i v e end-group c o n v e r s i o n t e c h n i q u e , a s t i l l more g e n e r a l a n s w e r i s n e e d e d . I n p r i n c i p l e , i t s h o u l d be f o u n d i n t h e c o u p l i n g o f 2 d i f f e r e n t p o l y m e r s , PA-x a n d P B - y , t h r o u g h interaction of t h e i r r e a c t i v e e n d - g r o u p s χ and y, t o y i e l d a c o p o -


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Copolymers

Scheme 2.


XY

P.

P

2

,

X'Y'

Scheme 3.

PDMS CH rgOH 2

0 M

\

0

II

0

PDMS

0

II

.CH rfcO-Ci-CH2l2COO 2

r—0

CH,

PDMS

(PVL

I

R^-N OH

ϋ

PPVL

0

:H2*-6o-c>cH t2 2

coo^mmmmiiwu

( mp. - 220*C)


P O L Y M E R

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SCIENCE

O V E R V I E W


l y m e r P A - z - P B . I t i s known however, t h a t t h i s s i m p l e i d e a i s u s u a l l y w i s h f u l - t h i n k i n g when i t comes t o c o m b i n e two d i f f e r e n t p o l y m e r s o f h i g h m o l e c u l a r w e i g h t , and so f o r two o b v i o u s r e a s o n s . A k i n e t i c one, w h i c h i s the v e r y low c o n c e n t r a t i o n o f r e a c t i v e e n d - g r o u p s ; b u t a l s o a t h e r m o d y n a m i c one : i . e . t h e r e p u l s i o n o f t h e two uncomp a t i b l e p o l y m e r i c c o i l s o f d i f f e r e n t n a t u r e , as s o o n as t h e i r i n t e r a c t i o n p a r a m e t e r s d i f f e r e v e n by a s m a l l v a l u e , what i s u s u a l l y t h e c a s e f o r t h e d e s i r a b l e p a i r s . An a n s w e r t o t h a t i m p o r t a n t c h a l l e n g e c a n now be provided, t h a n k s to the use of a two-phases l i q u i d sys tem. I n t h a t s y s t e m , t h e two d i f f e r e n t p o l y m e r s a r e d i s s o l v e d e a c h i n a good s o l v e n t o f t h e i r s , t h e two solvents u s e d b e i n g i m m i s c i b l e . The c r i t i c a l p o i n t i s t o provide one o f t h e two p a r t n e r s w i t h a r e a c t i v e e n d - g r o u p ( i . e . χ on PA i n s o l v e n t A ) having a p r e f e r e n t i a l c o m p a t i b i l i ty w i t h the s o l v e n t ( i . e . B ) of the o t h e r p a r t n e r ( i . e . P B - y ) , and vice-versa. I n t h i s m a n n e r , i t b e c o m e s p o s s i b l e to b y p a s s b o t h t h e k i n e t i c l i m i t a t i o n ( s i n c e t h e r e i s an i n c r e a s e d concen t r a t i o n o f a c t i v e g r o u p s a t t h e i n t e r f a c e ) , and t h e t h e r m o d y n a m i c one (each p o l y m e r b e i n g i n a f a v o r a b l e s o l v e n t ) . 1

f

The e f f i c i e n c y o f t h i s new c o n c e p t has b e e n demons t r a t e d (15) by t h e f a c i l e s y n t h e s i s , i n 90 % y i e l d i n 2 h o u r s a t 5 0 ° C , o f _the m u l t i b l o c k p o l y f a me t h y 1 s t y r e n e b - e t h y l e n e o x i d e } - (Mn c a . 7 0 . 0 0 0 ) , s t a r t i n g f r o m B r { C H ^ o f c H - C H - 0 + - (CH ) - B r i n w a t e r and 0

0

0

0

+

[(CH ) N-(CH >- N (Br")^CH 3-^C(CH ) ( C ^ - C I ^ * ^ 3

2

2

6

2

3

in

toluene (M c a . 10.000 e a c h ) . I f one i s a b l e t o c o n t r o l p r e c i s e l y t h e f o r m a t i o n o f endf u n c t i o n a l i zed p o l y m e r s c a r r y i n g g r o u p s o f t h e p r o p e r r e a c t i v i t y and p h i l i c i t y , t h i s scheme s h o u l d o p e n e f f i c i e n t and d i v e r s i f i e d new ways o f a c c e s s t o i n t e r e s t i n g b l o c k c o p o l y m e r s . The b a s i c p r o b l e m r e m a i n s a c c o r d i n g l y a c a t a l y t i c one, i . e . the q u a n t i t a t i v e e n d - f u n e t i o n a l i z a t i o n o f g r o w i n g h o m o p o l y m e r c h a i n s by e f f i c i e n t termi n a t i o n or t r a n s f e r r e a c t i o n s : t h a t i s f o r t u n a t e l y a r a p i d l y improving field. IV.

The

multiblock

structures

The i n t e r e s t o f t h a t t y p e o f m a t e r i a l has b e e n l a r g e l y d e m o n s t r a t e d , f . i . by t h e H y t r e l - t y p e o f p r o d u c t s ( i . e . p o l y e t h e r - e s t e r m u l t i b l o c k s ) , p a r t i c u l a r l y i n the f i e l d of t h e r m o p l a s t i c e l a s t o m e r s thanks to the 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 of t h e h a r d e r b l o c k s . Due a g a i n t o the s w i f t development of 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 t i c techniques, more and more o r i g i n a l a c h i e v e m e n t s


20.

TEYSSIE

Block

315

Copolymers

are r e g u l a r l y r e p o r t e d . S u f f i c e i t to c i t e (16) the " 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 e n e b y " t a i l o r e d " c o o r d i n a t i o n c a t a l y s t s ( n a m e l y η - a l l y 1 - n i c k e l - X com p l e x e s ) , y i e l d i n g a m u l t i s t e r e o b l o c k polymer, poly ( c i s 1 . 4 - b - t r a n s 1 . 4)--butad i e n e , t h e f i r s t e x a m p l e o f a t h e r moplastic elastomer ( s e m i - c r y s t a l l i n e m.p. c a . 1 3 5 ° 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.


3

A n o t h e r r e s e a r c h avenue has been r e c e n t l y opened i n t h a t p r o s p e c t , b a s e d on t h e i d e a t h a t i t s h o u l d b e p o s s i ble to r e p l a c e t h e h a r d e r b l o c k s 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 i r s t r u c t u r e promote v e r y s t r o n g mutual i n t e r a c t i o n s i n t h e medium w h e r e i n t h e y a r e u s e d . A t y p i c a l example a l o n g t h e s e l i n e s i s 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 - (or s a l t - ) t e l e c h e l i c polymers", d i s p l a y i n g the g e n e r a l and o b t a i n e d f r o m t h e c o m p l e t e n e u t r a l i z a t i o n o f any α , ω - d i c a r b o x y 1 a t o - p o l y m e r (PA) b y a d i v a l e n t m e t a l deri v a t i v e ( 1 7 ) . When PA i s a l i p o p h i l i c c h a i n , t h e c o r r e s p o n d i n g p r o d u c t s w i l l s t i l l be s o l u b l e i n h y d r o c a r b o n s (at l e a s t i f the charge d e n s i t y i s not too h i g h , i . e . i f PA m o l e c u l a r w e i g h t i s l a r g e e n o u g h ) , a k i n d o f me dium w h e r e i n the i o n - p a i r s a s s o c i a t e i n c l u s t e r s of v a r i a b l e s i z e s ( d e p e n d i n g on t h e c o n d i t i o n s ) . T h e same t y p e of 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 product for t h e same r e a s o n s . These a s s o c i a t i o n s generate a whole s e t of i n t e r e s t i n g properties, i.e. : - the f o r m a t i o n of strong e l a s t i c g e l s , e x h i b i t i n g r e s o n a n c e phenomena, a t v e r y low c r i t i c a l c o n c e n t r a t i o n s (ca. l-2g/dl). This g e l i f i c a t i o n i s t o t a l l y r e v e r s i b l e b o t h upon d i l u t i o n o r i n c r e a s e o f temperature; - the f o r m a t i o n of p e r i o d i c a l s t r u c t u r e s i n c o n c e n t r a t e d s o l u t i o n s or i n the neat s t a t e , s t r u c t u r e s which a r e probably b u i l t - u p of e q u i d i s t a n t small " p l a t e s " , the p e r i o d i c i t y b e i n g c a . 7 0 A f o r a n 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 , q u i t e i r r e s p e c t i v e o f i o n n a t u r e and p r e s e n c e of s o l v e n t . I n f a c t , t h a t p e r i o d i c i t y seems t o b e l a r g e l y c o n t r o l l e d b y t h e mean p o l y m e r c h a i n l e n g h t , and t h e u s e o f a v i n y l - t y p e p o l y i s o p r e n e r e d u c e s i t to 55 A; - unexpected r h e o l o g i c a l responses, i n c l u d i n g anti-thix o t r o p i c and " b o u n c i n g - s o l u t i o n s " b e h a v i o u r s . O b v i o u s l y enough, t h a t k i n d o f a p p r o a c h r e p r e s e n t s a v e r y f l e x i b l e method f o r t h e m o l e c u l a r t a i l o r i n g o f b r o a d l y d i v e r s i f i e d m a t e r i a l s , by c h a n g i n g the nature (and d i m e n s i o n s ) o f t h e p o l y m e r and t h e i o n s i n v o l v e d , as w e l l as t h a t o f t h e medium. T h e m a i n p r o b l e m t o b e met h e r e i s t h e n e c e s s i t y , l i k e i n any s t e p - w i s e type of p o l y m e r i z a t i o n , t o e n s u r e a v e r y h i g h c o n v e r s i o n (ca. 99 %) t o r e a c h a 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 , a key to t h e g e n e r a t i o n o f t h e most i n t e r e s t i n g proper-


316

P O L Y M E R

SCIENCE


t i e s ; t h a t g o a l has been s u c c e s s f u l l y a c h i e v e d use of v e r y r e a c t i v e m e t a l intermediates.

O V E R V I E W

by

the

In c o n c l u s i o n , the examples which i l l u s t r a t e the a n a l y s i s p r e s e n t e d h e r e a b o v e , c e r t a i n l y s u p p o r t an o p t i m i s t i c v i e w of the f u t u r e of b l o c k p o l y m e r s , p a r t i c u l a r l y a l o n g the t h r e e main l i n e s of a p p l i c a t i o n reminded i n the i n t r o d u c t i o n . A f t e r a sometimes d i s c o u r a g i n g maturat i o n p e r i o d ( c o n s i d e r i n g the huge r e s e a r c h e f f o r t involv e d i n t h e i r d e v e l o p m e n t ) , t h e i r come o f age h a s b e e n w i t n e s s e d by s e v e r a l b r i l l i a n t achievements,including v e r y s u c c e s s f u l i n d u s t r i a l d e v e l o p m e n t s.and w i l l undoubt e d l y l e a d t o f u r t h e r , and h o p e f u l l y u n e x p e c t e d , r e a l i zations . I n p a r t i c u l a r , t h e y h a v e c o n t r i b u t e d , more t h a n any o t h e r t y p e of p r o d u c t , to t r a n s l a t e t h a t g e n e r a l c o n c e p t of m o l e c u l a r e n g i n e e r i n g of b u l k m a t e r i a l s p h y s i c a l p r o p e r t i e s i n t o a v e r y a c t u a l and v i v i d reality. S t i l more i m p o r t a n t , now t h a t we m a s t e r t h e i r synt h e s i s q u i t e s a t i s f a c t o r i l y , they g i v e us new k e y s t o i m p r o v e and t o d i v e r s i f y b r o a d l y ( e v e n u s e d i n s m a l l amounts) c l a s s i c a l p o l y m e r i c m a t e r i a l s of l a r g e d i f f u s i o n : t h a t i s c e r t a i n l y a v e r y w o r t h w h i l e g o a l i n our t o d a y s t e c h n o l o g y and economy. 1

A c k n o w l e d g e m e n t s : the a u t h o r i s d e e p l y i n d e b t e d to h i s coworkers f o r t h e i r devoted and e n t h u s i a s t i c c o l l a b o r a t i o n ( p a r t i c u l a r l y to Dr R. J e r o m e , and a l s o t o D r s G. B r o z e , R. F a y t , P. H a d j i a n d r e o u , J . H e u s c h e n and P. L e f e b v r e ) , as w e l l as t o t h e S e r v i c e s de l a P r o g r a m m a t i o n de l a P o l i t i q u e S c i e n t i f i q u e ( B r u s s e l s ) f o r t h e i r very e f f i c i e n t support.


20.

TEYSSIE

Block

Copolymers

317


References

1. G. Holden, E.T. Bischop and N.R. Legge, J . Polym. Sci. Part C (1969), 36, 37. 2. S. Marti, J. Nervo and G. Riess, Progr. Colloid. Polymer Sci., 58, 114 (1975); D.R. Paul, "Polymer Blends", Vol.2, D.R. Paul and S. Newman Edit., Academic Press, (1978), p.168. 3. C. Sadron and B. Gallot, Makromol. Chem., 164, (1973) 301; B. Gallot, "Liquid crystalline order in polymers", A. Blumstein Edit., Academic Press, (1978), p.191. 4. M. Szwarc, "Carbanions, living polymers and electrontransfer processes", Wiley-Interscience, 1968. 5. G. Berger, M. Levy and D. Vofsi, J. Polym. Sci., B4, 183 (1966); Y. Yamashita and K. Chiba, Polymer J, 4 (1 973), 200. 6. R.B. Seymour, G.A. Stahl, D.R. Owen, and H. Wood, "Copolymers, Polyblends and Composites", N.A. Platzer Edit., Advances in Chemistry Series 142, (1975) p.309. 7. P. Hadjiandreou, Ph. D. Thesis, University of Liège, 1980; Ph. Teyssié et al., Symposium on Coordination Polymerization, A.C.S., 181th Meeting, Atlanta, 1981. 8. R. Fayt, R. Jérôme and Ph. Teyssié, I, Polymer Letters accepted for publication; II, J. Polym. Sci., part B, in press. 9. D.H. Richards, Symposium on Anionic Polymerization, J. McGrath Edit., A.C.S. 179th Meeting, Houston, 1980. 10. J. Heuschen, Ph.D. Thesis, University of Liège, 1977; J. Heuschen, R. Jerome and Ph. Teyssié, Macromolecules, in press. 11. T. Ouhadi, A. Hamitou, R. Jérôme and Ph. Teyssié, Macromolecules, 9, 927 (1976); J. Polym. Sci., A l 5 , 865 (1977). 12. J. Heuschen, R. Jérôme and Ph. Teyssié, French Patent 2.383.208. 13. P. Lefebvre, Ph. D. Thesis, University of Liège, 1978; R. Jèrôme, P. Lefebvre and Ph. Teyssié, J . Polym. Sci., in preparation. 14. P. Lefebvre, R. Jèrôme and Ph. Teyssié, Macromolecules, 10), 871 (1977). 15. G. Broze, R. Jèrôme and Ph. Teyssié, U.S. Pat. application pending; submitted for publication in Macromolecules. 16. Ph. Teyssié et a l . , in "Preparation and Properties of Stereoregular Polymers", p.144, R.W. Lenz and F. Ciardelli Edit., D. Reidel Publ.C°, 1980. 17. A. Moudden, A. M. Levelut and M. Pineri, J. Polym.Sci. Β1 5, 1707 (1977); G. Broze, R. Jèrôme and Ph. Teyssié, Macromolecules,in press; J . Polymer S c i . , Part A, in press; J. Macromol. Sci., in press. RECEIVED

May

19,

1981.


Block Copolymers: Maturation of an Old Concept into a Versatile

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