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SYNTHESIS OF GRAFT AND BLOCK
COPOLYMERS CONTAINING (CH)x SEGMENTS
G. Dandreaux, M. Galvin, G. Wnek
To cite this version:
G. Dandreaux, M. Galvin, G. Wnek. SYNTHESIS OF GRAFT AND BLOCK COPOLYMERS CON- TAINING (CH)x SEGMENTS. Journal de Physique Colloques, 1983, 44 (C3), pp.C3-135-C3-138.
�10.1051/jphyscol:1983325�. �jpa-00222676�
JOURNAL DE PHYSIQUE
Colloque C3, supplément au na6, Tome 44, juin 1983 page C3-135
SYNTHESIS OF GRAFT AND BLOCK COPOLYMERS CONTAINING ( C H )
XSEGMENTS
G.F. Dandreaux, M.E. Galvin and G.E. Wnek
Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, U.S.A.
Résumé - Deux approches ont été étudiées pour étendre l ' i n t é r ê t des dérivés polyacétylëniques, respectivement (1) 1'usage du polyacétylène dopé comme i n i t i a t e u r macromolëculaire pour la synthèse de copolymères greffés, et (2) les réactions de transformation comme moyen de synthèse de copolymères en bloc.
Abstract - Two approaches have been investigated to expand the scope of poly- acetylene derivatives, namely (1) the use of doped (CH)X as a macromolecular initiator for the synthesis of graft copolymers, and (2) transformation reac- tions as a route to block copolymer syntheses.
I - INTRODUCTION
Copolymerization has traditionally been a fruitful approach for the construction of organic materials possessing specific chemical, physical and mechanical properties.
Copolymers are classified as random, alternating, graft or block depending upon the structural arrangement of the comonomer units. Random (or nearly so) copolymers of acetylene and methyl acetylene have been prepared /l/ which exhibit, as expected, electrical conductivities upon doping which are highly dependent upon comonomer con- centration. The decrease in conductivity with increasing methyl acetylene concentra- tion has been rationalized /l ,2/ as being due to disruption of planarity of the back- bone. A similar argument apparently applies to the acetylene/phenylacetylene system, /3/. Interest has developed in this laboratory concerning the possibility of
attaching a wide variety of polymer chains to the (CH)X backbone (i.e., grafting). A motivation for such work is the possibility of tailoring the surface properties of
(CH)x for electrode applications. The ability of alkali metal graphitides / 4 / to initiate polymerization of several monomers suggested the use of doped (CH)X in this capacity with the prospect of covalently binding polymer chains to (CH)X backbones.
Block copolymers are also of interest because the planarity of the (CH)X block is expected to remain essentially intact, allowing the electrical properties to be pri- marily determined by percolation of (CH)X domains. Furthermore, soluble and tracta- ble derivatives could be envisioned by judicious choice of the remaining block(s).
Acetylene polymerization will necessarily be initiated by coordination catalysts.
We have considered the possibility of using the "alternate feed" method to produce, for example, ethylene-acetylene block copolymers from appropriate transition metal catalysts. However, such catalytic systems are typically not suitable for the syn- thesis of well-defined blocks / 5 / due to variable initiation rates of the catalytic centers and undesirable termination reactions. The exploitation of active polymer - transition metal bonds for the synthesis of block copolymers /6,7/ suggested a poten- tially viable approach. Specifically, we have attempted to use "living" polystyrene to alkylate T U 0 B u ) 4 followed by acetylene polymerization, viz
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983325
JOURNAL DE PHYSIQUE
1
*
R -
Ti-)
A p o t e n t i a l advantage o f such a t r a n s f o r m a t i o n r e a c t i o n / 7 / i s t h a t a t l e a s t t h e f i r s t b l o c k ( p o l y s t y r e n e ) can be s y n t h e s i z e d w i t h a w e l l - d e f i n e d c h a i n l e n g t h . Pre- l i m i n a r y experiments and o b s e r v a t i o n s a r e p r e s e n t e d i n t h i s a r t i c l e .
P o l y a c e t y l e n e f i l m s were s y n t h e s i z e d a t -78°C u s i n g t e c h n i q u e s s i m i l a r t o t h o s e developed by Shirakawa and coworkers /8/. R e d u c t i v e d o p i n g was c a r r i e d o u t i n a d r y box by immersion o f (CH), f i l m s i n 1 I1 sodium n a p h t h a l i d e / T l ; F s o l u t i o n s f o r 2 min.
The f i l m s were t h e n washed s e v e r a l t i m e s w i t h d r y , 0 2 - f r e e 'iiiF and a l l o w e d t o s t a n d i n f r e s h THF f o r a p p r o x i m a t e l y 1 hour. The c o n d u c t i v i t i e s and c o m p o s i t i o n s o f t h e f i l m s were i n t h e range 5-50 S/cm and iCHNa0.20-0. 25Ix, r e s p e c t i v e l y .
Exposure o f t h e n - t y p e f i l m s t o e i t h e r l i q u i d ( s t y r e n e , methyl m e t h a c r y l a t e ) o r gaseous ( e t h y l e n e o x i d e , i s o p r e n e ) monomers r e s u l t e d i n p o l y m e r i z a t i o n . Much o f o u r i n i t i a l work has focused on g r a f t i n g o f p o l y ( e t h y 1 e n e o x i d e ) (PEO) t o (CH), i n an e f f o r t t o r e n d e r t h e (CH)x s u r f a c e more h y d r o p h i l i c and t o p r o v i d e c o v a l e n t a t t a c h - ment o f a m a t e r i a l c a p a b l e o f f u n c t i o n i n g as a s o l i d e l e c t r o l y t e /9/. F i l m s o f n - t y p e (CH)x were exposed t o d r y (CaH2-treated), gaseous e t h y l e n e o x i d e i n t h e r a n g e 55-75OC w i t h i n i t i a l p r e s s u r e s b e i n g
ca,
500 t o r r . R e a c t i o n t i m e s were t y p i c a l l y 5 hours. The f i l m s were washed w i t h d r y , 0 2 - f r e e methylene c h l o r i d e t o remove non- c o v a l e n t l y bound PEO and t h e n w i t h d e a e r a t e d Hz0 t o p r o t o n a t e oxyanions and remove t h e NaOH b y p r o d u c t . The presence o f bound PEO a f t e r e x t r a c t i o n was c o n f i r m e d by I R spectroscopy.The s y n t h e s i s o f b l o c k copolymers were a t t e m p t e d i n t h e f o l l o w i n g manner. " L i v i n g "
p o l y s t y r e n e was f i r s t p r e p a r e d by c o n v e n t i o n a l a n i o n i c t e c h n i q u e s u s i n g n-BuLi as t h e i n i t i a t o r i n THF a t -78°C. (The a p p r o p r i a t e s t y r e n e / n - B u L i r a t i o n was employed t o a f f o r d an
fin
of a p p r o x i m a t e l y 10,000 f o r t h e p o l y s t y r e n e b l o c k ) . I n i n i t i a l e x p e r i - ments, t h i s p o l y s t y r y l l i t h i u m p r o d u c t was t r e a t e d w i t h A l C l 3 t o a f f o r d a p o l y s t y r y l A1 s p e c i e s which c o u l d be capable o f a l k y l a t i n g T i (OBu)4. However, we f i n d i t t o be more u s e f u l t o d i r e c t l y a l k y l a t e Ti(OBu)4 w i t h t n e p o l y s t y r y l t i . The orange-red p o l y s t y r y l L i s o l u t i o n became deep r e d upon t r e a t m e n t w i t h Ti(OBu)4 a t -78OC ( L i / T i = 2 : l ) . The s o l u t i o n was warmed t o room t e m p e r a t u r e and d r y , 0 2 - f r e e a c e t y - l e n e ( i n i t i a l p r e s s u r e sc.
790 t o r r ) was i n t r o d u c e d on a vaccum l i n e . The s o l u t i o n became deep b l u e i n c o l o r and a f t e r a p p r o x i m a t e l y 30 min. f i n e b l u e - b l a c k p a r t i c u - l a t e s were observed. The p o l y m e r i z a t i o n s were t e r m i n a t e d b y a d d i t i o n o f MeOH. The p r e c i p i t a t e d polymers were e x t r a c t e d w i t h TtIF f o r 6 hours.I 1 1
-
RESULTS Ai4D 3ISCUSSIONThe p r i m a r y r e a c t i o n o f n - t y p e (CH), and e t h y l e n e o x i d e i s presumably a t t a c k o f a c a r b a n i o n on a methylene carbon r e s u l t i n g i n r i n g opening and oxyanion f o r m a t i o n , f o l l o w e d by s u c c e s s i v e monomer a d d i t i o n s :
The f a c t t h a t approximately h a l f o f t h e product can be removed by CH2C12 e x t r a c t i o n may suggest t h a t e l e c t r o n t r a n s f e r from a (CH)x r a d i c a l anion t o ethylene oxide occurs l e a d i n g t o p o l y m e r i z a t i o n w i t h o u t attachment t o t h e (CHjx o r t h a t some attached PEO s u f f e r e d m e c h a n i c a l l y i n d u c e d s c i s s i o n . The o i l y c h a r a c t e r o f t h e ex- t r a c t e d PEO suggests a low molecular weight. We have no i n f o r m a t i o n r e g a r d i n g t h e molecular weight o f t h e c o v a l e n t l y bound PEO o r the number o f PEO branches. The
(CH)x/PEO m a t e r i a l s can be doped w i t h I 2 t o a f f o r d c o n d u c t i v i t i e s o f approximately 1~-'cm-'. Problems w i t h e l e c t r i c a l c o n t a c t s due t o an i n s u l a t i n g PEO l a y e r may be a f a c t o r i n t h i s lower c o n d u c t i v i t y compared w i t h 12-doped (CH), b u t i t should be noted t h a t t h e (CH), c o n j u g a t i o n i s broken a t t h e g r a f t p o i n t s and t h i s i s expected t o r e - duce the i n t r a c h a i n h o l e m o b i l i t y . More d e t a i l e d c h a r a c t e r i z a t i o n o f these mate- r i a l s i s i n progress.
The work on block copolymers i s very r e c e n t and t h e r e f o r e l i t t l e d e f i n i t i v e informa- t i o n i s a v a i l a b l e . A c r u c i a l p o i n t i s o f course a formal p r o o f o f block copolymer formation and a t t h i s t i m e we have no c o n c l u s i v e evidence. However, t h e transforma- t i o n approach has been demonstrated t o be e f f e c t i v e i n t h e synthesis o f block co- polymers /7/ and t h e r e i s no reason why a p r i o r i t h e chemistry described i n t h e ex- perimental s e c t i o n i s n o t f e a s i b l e . I t i s worth n o t i n g t h a t e x t r a c t i o n o f a p r e - sumed block copolymer having a p ~ l y s t y r e n e / ( C t l ) ~ r a t i o o f
s.
1 0 : l (based on t h e amount o f p o l y s t y r e n e i n t h e r e a c t i o n vessel and molar uptake o f acetylene d u r i n g subsequent p o l y m e r i z a t i o n ) removes approximate1 y 40 wt.% o f m a t e r i a l which i s homo- polystyrene. The remainder may be p o l y s t y r e n e attached t o (CH)x blocks, t h e l a t t e r being aggregated i n t o c r y s t a l l i n e domains which are i n s o l u b l e . Doping o f t h e mate- r i a l w i t h I 2 a f f o r d s a c o n d u c t i v i t y o f S/cm and our f e e l i n g i s t h a t probably an i n s u l a t i n g p o l y s t y r e n e l a y e r prevented the formation o f good e l e c t r i c a l contacts.The e f f i c i e n c y o f t h e b l o c k copolymerization chemistry, p r o o f o f block f o r m a t i o n and, u l t i m a t e l y , the i n f l u e n c e o f microphase separation on e l e c t r i c a l p r o p e r t i e s are t h e s u b j e c t s o f f u t u r e study. The observation o f t r a n s p a r e n t b l u e s o l u t i o n s i n the e a r l y stages o f t h e acetylene polymerizations i s p a r t i c u l a r l y i n t e r e s t i n g .
T h i s work was supported i n p a r t by P o l a r o i d Corporation ( f e l l o w s h i p t o T4.E. Galvin) and a DuPont Young F a c u l t y Award ( t o G.E. klnek).
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