Phase-Transfer Catalysis - ACS Publications - American Chemical

Chapter 9

New Developments in Polymer Synthesis by Phase-Transfer Catalysis Virgil Percec

Downloaded by UNIV OF PITTSBURGH on May 3, 2015 | http://pubs.acs.org Publication Date: December 19, 1987 | doi: 10.1021/bk-1987-0326.ch009

Department of Macromolecular Science, Case Western Reserve University, Cleveland, OH 44106

Some particularities of the extraction of ions from an aqueous organic phase, and of the phase catalyzed polyetherification will be summarized. These will represent the fundamentals of our work on the synthesis of some novel classes of functional polymers and sequential copolymers. Examples will be provided for the synthesis of: functional polymers containing only cyclic imino ethers or both cyclic imino ethers as well as their own cationic initiator attached to the same polymer backbone; ABA triblock copolymers and (AB)n alternating block copolymers; and a novel class of main chain thermotropic liquid crystalline polymers containing functional chain ends, i.e., polyethers. Phase transfer catalysis, a term which has been coined by Starks in 1 9 7 1 ( 1 ) , became, w i t h i n o n l y a s h o r t p e r i o d o f t i m e , an a c t i v e s u b j e c t o f r e s e a r c h w i t h deep i m p l i c a t i o n s e s p e c i a l l y i n p r e p a r a t i v e organic, organometallic and polymer c h e m i s t r y ( 2 - 7 ) . T r a d i t i o n a l f i e l d s o f polymer c h e m i s t r y l i k e r a d i c a l , a n i o n i c and c o n d e n s a t i o n p o l y m e r i z a t i o n s , as w e l l as c h e m i c a l m o d i f i c a t i o n o f p o l y m e r s , have s u b s t a n t i a l l y b e n e f i t e d from t h e use o f phase t r a n s f e r c a t a l y s i s . Some o f t h e most s i g n i f i c a n t p r o g r e s s made i n t h i s f i e l d by e x p l o i t i n g the phase t r a n s f e r c a t a l y s i s c o n c e p t has been the s u b j e c t o f a p r e v i o u s ACS meeting, and i t ' s p r o c e e d i n g s were p u b l i s h e d i n a r e c e n t b o o k ( 7 ) . Our r e s e a r c h group h a s become a c t i v e i n t h i s f i e l d o n l y r e c e n t l y , and i t i s t h e a i m o f t h i s paper t o s h o r t l y r e v i e w some o f the work a c c o m p l i s h e d , o r i n p r o g r e s s w i t h i n our l a b o r a t o r y . E x t r a c t i o n o f Ions from an Aqueous S o l u t i o n . I t s I m p l i c a t i o n s on the Mechanism o f Phase T r a n s f e r C a t a l y z e d P o l y e t h e r i f i c a t i o n s For a two phase system (water and a w a t e r n o n m i s c i b l e o r g a n i c s o l vent) containing a hydrophobic salt QX d i s s o l v e d i n water (Qk + X w ^ ^ Q X s ) » c o n d i t i o n a l e x t r a c t i o n c o n s t a n t e* i s d e f i n e d QXs Q X t Q ] w [X"]w> where C Q X i s the t o t a l c o n c e n t r a t i o n o f Q (quat) and X~ ( c o r r e s p o n d i n g a n i o n ) p r e s e n t i n the o r g a n i c phase i n the m o l a r r a t i o 1 t o 1; and [ Q ] and [ X " ] respective t

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0097-6156/87/0326-0096$06.00/0 © 1987 American Chemical Society

In Phase-Transfer Catalysis; Starks, C.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

9. PERCEC

Polymer Synthesis by Phase-Transfer Catalysis

c o n c e n t r a t i o n s i n t h e water phase. S i n c e t h e Q p a r t o f t h e QX s a l t i s always h y d r o p h o b i c , i t i s t h e e n t r o p i e f a c t o r w h i c h w i l l t e n d t o d r i v e t h e QX compound o u t o f t h e aqueous l a y e r . T h e r e f o r e , t h e e x t r a c t i o n c o n s t a n t s a r e s t r o n g l y dependent on t h e s t r u c t u r e o f b o t h the a n i o n (X") and c a t i o n ( Q ) ( o r i n o t h e r words on t h e i r hydrop h o b i c i t y ) and on the s o l v e n t n a t u r e , b u t due t o t h e dominant i n f l u e n c e o f e n t r o p y f a c t o r , i t i s n o t v e r y dependent on t h e temperature. F o r a s p e c i f i c Q , t h e v a l u e o f t h e e* w i l l be c o n t r o l l e d by t h e h y d r o p h o b i c i t y o f t h e X", and t h e r e a r e q u a n t i t a t i v e examples i n t h e l i t e r a t u r e d e m o n s t r a t i n g t h i s ( 3 . ) . I t i s known f o r example t h a t t h e e x t r a c t i o n c o n s t a n t o f a s a l t h a v i n g PhO" as a n i o n i s h i g h e r by a f a c t o r o f about 10^ t h a n t h e e x t r a c t i o n c o n s t a n t o f a s a l t h a v i n g OH" as a n i o n . T h e r e f o r e , i t c a n be c e r t a i n l y assumed t h a t when t h e PhO" a n i o n becomes a polymer c h a i n end, t h e e x t r a c t i o n c o n s t a n t o f i t s s a l t w i t h Q s h o u l d be m o l e c u l a r w e i g h t dependent based on t h e f a c t t h a t t h e h y d r o p h o b i c i t y o f t h e phenoxy a n i o n i n c r e a s e s w i t h t h e i n c r e a s e o f t h e polymers m o l e c u l a r w e i g h t , i . e . , e*phO-(PhO)n-PhO"Q+ » *PhO"Q+c o n c l u s i o n has some i m p o r t a n t implications f o r t h e two-phase phase transfer c a t a l y z e d r e a c t i o n s e s p e c i a l l y when t h e t r a n s f e r o f t h e i o n - p a i r i n t o t h e o r g a n i c phase i s t h e r a t e d e t e r m i n i n g s t e p . Under these c o n d i t i o n s we c a n s p e c u l a t e t h a t t h e n u c l e o p h i l i c i t y o f a p h e n o l a t t a c h e d t o a polymer c h a i n end i s m o l e c u l a r w e i g h t dependent and i n c r e a s e s w i t h t h e i n c r e a s e o f t h e polymer m o l e c u l a r w e i g h t . T h i s b e h a v i o r c a n be c o n s i d e r e d as a unique s i t u a t i o n i n which t h e r e a c t i v i t y o f a f u n c t i o n a l group a t t a c h e d t o a polymer c h a i n end i n c r e a s e s w i t h t h e i n c r e a s e o f t h e polymer m o l e c u l a r w e i g h t . T h i s p a r t i c u l a r i t y , p e r m i t s us t o t a i l o r q u a n t i t a t i v e r e a c t i o n s o f ω-phenol o l i g o m e r s and a, ω-bisphenol o l i g o m e r s w i t h b o t h e l e c t r o p h i l i c low m o l e c u l a r w e i g h t compounds and w i t h α ,ω-di(electrophilic) o l i g o m e r s ( 8 - 1 4 ) . An i m p o r t a n t s i d e r e a c t i o n which has t o be a v o i d e d i n b o t h cases i s t h e d i s p l a c e m e n t o f t h e e l e c t r o p h i l e p r e s e n t i n t h e o r g a n i c phase w i t h t h e OH" t r a n s f e r r e d from t h e water phase i n t o t h e o r g a n i c phase. When w o r k i n g w i t h α ,ω - b i s p h e n o l o l i g o m e r s , t h i s s i d e r e a c t i o n c a n be a v o i d e d by u s i n g s o l v e n t s which w i l l u s u a l l y p r o v i d e a low e x t r a c t i o n c o n s t a n t f o r t h e t r a n s f e r o f t h e a n i o n s from water to o r g a n i c phase. S i n c e p o l y m e r i c onium p h e n o l a t e s have v e r y l a r g e e x t r a c t i o n c o n s t a n t s , t h e use o f a r o m a t i c s o l v e n t s w i l l depress t h e i r e x t r a c t i o n i n t o t h e o r g a n i c phase t o t h e l e v e l o f a low m o l e c u l a r w e i g h t p h e n o l , b u t a t t h e same time t h e t r a n s f e r o f t h e OH" i n t o o r g a n i c phase w i l l be d e c r e a s e d below t h e l e v e l i t c a n compete w i t h t h e o t h e r n u c l e o p h i l e . We have demonstrated t h a t t h i s s i t u a t i o n c a n be e a s i l y a c c o m p l i s h e d ( 1 5 ) . A s h o r t comparative d i s c u s s i o n o f c o n v e n t i o n a l and phase t r a n s f e r c a t a l y z e d s t e p p o l y m e r i z a t i o n s would l e t us p o i n t o u t some b a s i c d i f f e r e n c e s between these two r e a c t i o n s . C o n v e n t i o n a l s t e p p o l y m e r i z a t i o n i s a s t a t i s t i c a l r e a c t i o n whose k i n e t i c t r e a t m e n t i s b a s e d on the e q u a l r e a c t i v i t y o f f u n c t i o n a l groups p a r t i c i p a t i n g i n p o l y m e r i z a t i o n , i n d i f f e r e n t o f t h e m o l e c u l a r w e i g h t o f t h e polymer a t which c h a i n ends a r e a t t a c h e d . F o r an e q u i m o l a r r a t i o o f t h e two monomers, the p o l y m e r i z a t i o n degree c a n be c a l c u l a t e d from t h e " e x t e n t o f r e a c t i o n " p, i . e . , DP » l / ( l - p ) . Only a t v e r y h i g h c o n v e r s i o n s ( h i g h e r than 99.5%) and o n l y when s t o i c h i o m e t r i c monomer r a t i o s a r e u s e d ( i . e . , 1:1) c a n h i g h degrees o f p o l y m e r i z a t i o n be o b t a i n e d . F o r a 100 p e r c e n t c o n v e r s i o n , t h e t h e o r e t i c a l p o l y d i s p e r s i t y o f t h e +

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o b t a i n e d polymer i s e q u a l 2, i . e . , Mw/Mn - 2.0. When t h e r e a c t i o n i s p e r f o r m e d w i t h a 1:1 mole r a t i o o f t h e two monomers, a t any time i n c l u d i n g a t 100 p e r c e n t c o n v e r s i o n t h e polymer c h a i n ends w i l l have a s t a t i s t i c a l d i s t r i b u t i o n o f t h e f u n c t i o n a l groups a t t a c h e d t o them. S e v e r a l p a r t i c u l a r i t i e s o f phase t r a n s f e r c a t a l y z e d p o l y e t h e r i f i c a t i o n a r e as f o l l o w s . S t o i c h i o m e t r i c phase t r a n s f e r c a t a l y z e d p o l y m e r i z a t i o n s do n o t t a k e p l a c e between s t o i c h i o m e t r i c r a t i o o f monomers, s i n c e t h e n u c l e o p h i l i c monomer i s always t r a n s f e r r e d i n a s m a l l amount i n t o t h e o r g a n i c phase. C o n s e q u e n t l y , because t h e i r r e a c t i o n i s a n o n - s t o i c h i o m e t r i c one t h e r e i s no need f o r an e q u i m o l a r r a t i o between t h e two monomers t o g e t polymers w i t h h i g h molecular weights. High molecular w e i g h t polymers a r e u s u a l l y obtained a l s o a t low c o n v e r s i o n s . I n s e v e r a l cases, even a t 100 p e r c e n t c o n v e r s i o n t h e p o l y d i s p e r s i t y o f t h e o b t a i n e d polymers i s l o w , i . e . , E w / H h < L l . 3 . A t any c o n v e r s i o n , t h e o r g a n i c phase c o n t a i n s o n l y polymers w i t h e l e c t r o p h i l i c c h a i n ends, even when t h e n u c l e o p h i l i c monomer was used i n e x c e s s . A t t h i s t i m e , o n l y some o f these p a r t i c u l a r i t i e s c a n r e c e i v e an e x p l a n a t i o n . Onium b i s p h e n o l a t e s are nonsolvated ion-pairs with r e d u c e d c a t i o n - a n i o n i n t e r a c t i o n energy, and c o n s e q u e n t l y a r e v e r y r e a c t i v e . T h e i r low c o n c e n t r a t i o n i n t h e o r g a n i c phase e a s i l y e x p l a i n s t h e e l e c t r o p h i l i c n a t u r e o f t h e c h a i n ends, a t l e a s t when the r a t e d e t e r m i n i n g s t e p i s t h e i r t r a n s f e r from t h e w a t e r i n t o t h e o r g a n i c phase: E-E + "N-N" + E-E-

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E-E-N-N-E-E Ε-Ε-Ν-Ν-Ε-Ε-Ν-Ν-Ε-Ε etc.

The s i d e r e a c t i o n p r e v i o u s l y d i s c u s s e d , i . e . , t h e d i s p l a c e m e n t o f the e l e c t r o p h i l i c c h a i n ends by OH", c a n g i v e r i s e t o a new n u c l e o p h i l e w i t h a d i f f e r e n t r e a c t i v i t y . T h i s r e a c t i o n c a n be a v o i d e d , b u t i t s p r e s e n c e o r absence a p p a r e n t l y c a n n o t e x p l a i n any o f t h e above p a r t i c u l a r i t i e s . A major p o i n t o f c o n c e r n r e f e r s t o t h e r e a c t i v i t y o f n u c l e o p h i l i c and e l e c t r o p h i l i c groups p r e s e n t i n t h e r e a c t i o n m i x t u r e a t d i f f e r e n t s t a g e s o f t h e p o l y m e r i z a t i o n . An o b v i o u s q u e s t i o n would be: i s t h e r e a c t i v i t y o f t h e n u c l e o p h i l i c and e l e c t r o p h i l i c polymeric c h a i n ends t h e same w i t h t h a t o f t h e monomeric ones? A p p a r e n t l y , as a r e s u l t o f t h e p r e v i o u s d i s c u s s i o n , the n u c l e o p h i l i c i t y depends upon and i n c r e a s e s w i t h t h e m o l e c u l a r w e i g h t . A t t h i s time we cannot say much about t h e r e a c t i v i t y o f t h e e l e c t r o p h i l i c groups, a l t h o u g h i n s e v e r a l cases we have s p e c u l a t e d a p o s s i b l e enhanced e l e c t r o p h i l i c i t y b a s e d on a n c h i m e r i c assis tance (16^17 ) . A f i n a l comment concerns t h e o v e r a l l p o l y m e r i z a t i o n behavior a t d i f f e r e n t stages o f the r e a c t i o n . U s u a l l y , the i n i t i a l c o n c e n t r a t i o n o f t h e phase t r a n s f e r c a t a l y s t , r e p r e s e n t s 5-10 mole % from t h e n u c l e o p h i l i c monomer, and, t h e r e f o r e , t h e r e a c t i o n proceeds under two phase c o n d i t i o n s . A t h i g h c o n v e r s i o n , t h e c o n c e n t r a t i o n o f the n u c l e o p h i l e d e c r e a s e s and t h e amount o f phase t r a n s f e r c a t a l y s t r e a c h e s and even exceeds 100 mole % from t h e c o n c e n t r a t i o n o f t h e n u c l e o p h i l e . Consequently, a t t h i s stage o f the r e a c t i o n the e n t i r e amount o f n u c l e o p h i l e w i l l be p r e s e n t i n s o l u t i o n , and t h e p o l y m e r i z a t i o n c a n be c o n s i d e r e d as e m p l o y i n g t h e o r g a n i c phase o n l y . I n o t h e r words, even i f we have a two-phase system, t h e w a t e r phase no


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l o n g e r p l a y s t h e same r o l e as b e f o r e and t h e r e a c t i o n c a n be con s i d e r e d as b e i n g a one-phase r e a c t i o n . A l l these p a r t i c u l a r i t i e s o f phase t r a n s f e r c a t a l y z e d p o l y e t h e r i f i c a t i o n were s t a y i n g b e h i n d o u r approach t o t h e d e s i g n o f new macromolecules. Three major t o p i c s o f r e s e a r c h w h i c h a r e b a s e d on phase t r a n s f e r c a t a l y z e d r e a c t i o n s w i l l be p r e s e n t e d w i t h examples. These r e f e r t o t h e s y n t h e s i s o f f u n c t i o n a l polymers c o n t a i n i n g f u n c t i o n a l groups ( i . e . , c y c l i c imino e t h e r s ) s e n s i t i v e b o t h t o e l e c t r o p h i l i c and n u c l e o p h i l i c r e a g e n t s ; a n o v e l method f o r t h e p r e p a r a t i o n o f r e g u l a r , segmented, ABA t r i b l o c k and (A-B)n a l t e r n a t i n g b l o c k copolymers, and t h e development o f a n o v e l c l a s s o f main c h a i n t h e r m o t r o p i c l i q u i d - c r y s t a l l i n e polymers, i . e . , p o l y e t h e r s . F u n c t i o n a l Polymers C o n t a i n i n g C y c l i c Imino E t h e r s Scheme 1 p r e s e n t s b o t h t h e s y n t h e s i s and t h e r i n g opening r e a c t i o n s of 2-(p-hydroxyphenyl)-2-oxazoline (HPO). HPO r e a c t s w i t h NaOH on h e a t i n g t o p r o v i d e N-(2-hydroxyethyl)-p-hydroxybenzamide, and w i t h weak e l e c t r o p h i l i c compounds l i k e b e n z y l bromide o r a l l y l c h l o r i d e t o p r o v i d e p o l y [N-(p-hydroxybenzoyl) e t h y l e n i m i n e ] . Consequently, the e t h e r i f i c a t i o n r e a c t i o n o f an α,ω-di(electrophilic) oligomer w i t h t h e sodium s a l t o f 2 - ( p - h y d r o x y p h e n y l ) - 2 - o x a z o l i n e i n an a p r o t i c d i p o l a r s o l v e n t l i k e DMSO o r DMF would be accompanied by these two s i d e r e a c t i o n s , even i f t h e n u c l e o p h i l i c i t y o f t h e phenol a t e i s h i g h e r than t h a t o f the o x a z o l i n e r i n g . A p h a s e - t r a n s f e r catalyzed Williamson etherification o f an α ,ω - d i ( e l e c t r o p h i l i c ) o l i g o m e r p e r f o r m e d i n chlorobenzene-aqueous NaOH and s t o i c h i o m e t r i c amount o f phase t r a n s f e r c a t a l y s t as d e t a i l e d elsewhere(18.20) g i v e s rise to perfectly b i f u n c t i o n a l α,ω-di[2-(p-phenoxy)-2-oxazoline] o l i g o m e r s . The same b i f u n c t i o n a l o l i g o m e r s c a n be p r e p a r e d through a c h a i n e x t e n s i o n o f an α, ω,-di(phenol) o l i g o m e r o r b i s p h e n o l monomer w i t h methylene c h l o r i d e as o u t l i n e d i n Scheme 2. The m e c h a n i s t i c reasons f o r t h i s l a s t s u c c e s s f u l r e a c t i o n a r e o u t l i n e d i n Scheme 3, w h i l e Scheme 4 p r e s e n t s t h e s y n t h e t i c r o u t e s f o r t h e p r e p a r a t i o n o f α , a > - d i ( e l e c t r o p h i l i c ) a r o m a t i c p o l y e t h e r s u l f o n e s . The d e t a i l e d s y n t h e s i s o f these l a s t o l i g o m e r s has been a l r e a d y d i s c u s s e d e l s e where ( 1 5 ) . F i g u r e 1 g i v e s an example o f 200 MHz ^H-NMR s p e c t r a o f the s t a r t i n g a, u > - d i ( e l e c t r o p h i l i c ) o l i g o m e r and the obtained α ,u)-di[2-(p-phenoxy)-2-oxazoline] oligomer to demonstrate the q u a n t i t a t i v e n a t u r e o f t h i s r e a c t i o n . A d d i t i o n a l examples c a n be obtained from other previous publications from our laboratory(18^_20) . The second case r e f e r s t o t h e s y n t h e s i s o f t h e f i r s t example o f a b i f u n c t i o n a l polymer c o n t a i n i n g n o t o n l y c a t i o n i c a l l y p o l y m e r i z a b l e h e t e r o c y c l e s , b u t a l s o t h e i r own c a t i o n i c i n i t i a t o r as pendant g r o u p s ( 1 9 ) . Scheme 5 p r e s e n t s t h e s y n t h e s i s o f a p o l y ( 2 , 6 - d i m e t h y l 1,4-phenylene o x i d e ) c o n t a i n i n g b o t h 2 - ( p - p h e n o x y ) - 2 - o x a z o l i n e and bromobenzylic pendant groups. Incomplete etherification of a poly(2,6-dimethyl-1,4-phenylene o x i d e ) c o n t a i n i n g 0.14 -CH2Br groups per s t r u c t u r a l u n i t w i t h HPO l e a d s t o a polymer c o n t a i n i n g 0.106 2 - ( p - p h e n o x y ) - 2 - o x a z o l i n e groups and 0.033 -CH2Br groups p e r s t r u c t u r a l u n i t , c o r r e s p o n d i n g t o a 3.21/1 mole r a t i o between t h e h e t e r o c y c l i c monomer and i t s i n i t i a t o r . A 200 MHz ^H-NMR spectrum o f t h i s polymer i s p r e s e n t e d i n F i g u r e 2. T h i s polymer i s s t a b l e a t



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+

"OPhOxz

2

2

2

Scheme 3·

-PhOCH Cl

9

LJ •

-PhO" *-

+

CH 0 2

-Ph0CH 0Ph2

».

-Ph0CH 0Ph0xz 2

Reactions occurring during the preparation of α ω-ά±[2(£-phenoxy)-2-oxazoline] o l i g o m e r s a c c o r d i n g t o t h e second and t h i r d s y n t h e t i c r o u t e s i n Scheme 2.


9

PERCEC



9.


103



104

Figure l a .

200MHz

H-NMR

spectrum

(CDC1

3>

TMS)

of

«^-di(bromobenzyl )

aromatic polyether sulfone (PSU) from Scheme 4.



9.

PERCEC

Polymer Synthesis by Phase- Transfer Catalysis

Figure l b . 200 MHz

H-NMR

spectrum

α,ω-di[2-(p-phenoxy)-2-oxazoli ne] obtained from e,«-di(bromobenzyl)

(CDC1 aromati c

105

TMS)

3>

polyether

PSU.


of su!fone



106

Scheme 5.

Synthetic routes used for the preparation of functional polymers containing pendant 2-oxazoline and bromobenzyl groups.


9.

PERCEC


107

room t e m p e r a t u r e , b u t upon h e a t i n g above i t s g l a s s transition t e m p e r a t u r e , t h e -CH2Br groups i n i t i a t e t h e c a t i o n i c r i n g opening p o l y m e r i z a t i o n o f t h e c y c l i c imino e t h e r g i v i n g r i s e t o a polymer network and a s u b s t a n t i a l i n c r e a s e i n t h e g l a s s t r a n s i t i o n tempera t u r e . T h i s i s i l l u s t r a t e d b y t h e F i g u r e 3. Phase T r a n s f e r C a t a l y z e d P o l y e t h e r i f i c a t i o n o f C h a i n Ended F u n c t i o n a l Polymers, a New Method f o r t h e S y n t h e s i s o f S e q u e n t i a l Copolymers We have r e c e n t l y demonstrated t h a t t h e phase t r a n s f e r c a t a l y z e d polyetherification o f an ,ω-di(electrophilic) o r α,ω-di(nucleo philic) oligomer with a bisphenol o r an a,ω-di(electrophilic) oligomer represents a new and v e r y e f f i c i e n t method f o r t h e s y n t h e s i s o f r e g u l a r c o p o l y m e r s ( 8 . 2 1 ) . The c h a i n e x t e n s i o n o f two d i f f e r e n t a,ω-di(phenol) o l i g o m e r s w i t h a d i e l e c t r o p h i l i c monomer a g a i n t h r o u g h a phase t r a n s f e r c a t a l y z e d e t h e r i f i c a t i o n g i v e s r i s e t o segmented copolymers(22.) . Under c a r e f u l l y s e l e c t e d r e a c t i o n c o n d i t i o n s , t h e p o l y e t h e r i f i c a t i o n o f an ω-phenol o l i g o m e r w i t h an α,ω-di(electrophilic) o l i g o mer produces u n e x p e c t e d l y pure ABA t r i b l o c k copolymers(11)» w h i l e the p o l y e t h e r i f i c a t i o n o f an a, a > - d i ( e l e c t r o p h i l i c ) o l i g o m e r w i t h an α,ω-di(nucleophilic) o l i g o m e r represents a new method f o r t h e s y n t h e s i s o f p e r f e c t l y a l t e r n a t i n g ( A B ) b l o c k copolymers(9-12.22). An example f o r t h e s y n t h e s i s o f p o l y ( 2 , 6 - d i m e t h y l - 1 , 4 - p h e n y l e n e oxide) - aromatic p o l y ( e t h e r - s u l f o n e ) - poly(2,6-dimethyl-1,4-pheny l e n e o x i d e ) ABA t r i b l o c k copolymer i s p r e s e n t e d i n Scheme 6. Q u a n t i t a t i v e e t h e r i f i c a t i o n o f t h e two polymer c h a i n ends has been accom p l i s h e d under m i l d r e a c t i o n c o n d i t i o n s d e t a i l e d elsewhere(11). F i g u r e 4 p r e s e n t s t h e 200 MHz T-H-NMR s p e c t r a o f t h e - ( 2 , 6 - d i m e t h y l phenol) poly(2,6-dimethyl-1,4-phenylene oxide), of the a, u ) - d i ( c h l o r o a l l y ) a r o m a t i c p o l y e t h e r s u l f o n e and o f t h e o b t a i n e d ABA t r i b l o c k copolymers as c o n v i n c i n g e v i d e n c e f o r t h e q u a n t i t a t i v e r e a c t i o n o f t h e p a r e n t polymers c h a i n ends. A d d i t i o n a l e v i d e n c e f o r the v e r y c l e a n s y n t h e t i c p r o c e d u r e comes from t h e g e l p e r m e a t i o n chromatograms o f t h e two s t a r t i n g o l i g o m e r s and o f t h e o b t a i n e d ABA t r i b l o c k copolymer p r e s e n t e d i n F i g u r e 5.


α

n

ω

Thermotropic Polyethers A New C l a s s o f M a i n C h a i n L i q u i d C r y s t a l l i n e Polymers R e c e n t l y we have d e v e l o p e d a new c l a s s o f t h e r m o t r o p i c liquid c r y s t a l l i n e (LC) m a i n - c h a i n p o l y m e r s , i . e . , p o l y e t h e r s o f mesogenic bis-phenols(16-17.23-26). Since the obtained polymers a r e n o t s o l u b l e i n d i p o l a r a p r o t i c s o l v e n t s , the only a v a i l a b l e s y n t h e t i c avenue f o r t h e i r p r e p a r a t i o n c o n s i s t s i n t h e phase t r a n s f e r catalyzed polyetherification. There a r e s e v e r a l v e r y i m p o r t a n t advantages we o b t a i n from t h i s n o v e l c l a s s o f LC p o l y m e r s . They c a n be p r e p a r e d w i t h w e l l d e f i n e d c h a i n ends and narrow m o l e c u l a r w e i g h t d i s t r i b u t i o n . T h e r e f o r e , we could provide important i n f o r m a t i o n concerning the i n f l u e n c e o f the nature of t h e polymer chain ends on their mesomorphic behavior(16.23-24). They a r e s o l u b l e i n c o n v e n t i o n a l s o l v e n t s , have lower m e l t i n g and i s o t r o p i z a t i o n t e m p e r a t u r e s and s t i l l b r o a d e r t h e r m a l s t a b i l i t y o f t h e mesophase t h a n t h e c o r r e s p o n d i n g poly-



108


τ 8

1

1 6

1 6,Ρ

Figure 2.

200 MHz

1 4

1

1 2

1

Γ 0

Ρ Μ

*H-NMR

spectrum

poly(2,6-dimethyl-l,4-phenylene

(CDC1 ) 3

oxide)

containing

of

the 2-oxazo

l i n e and bromobenzyl pendant groups.

MO

180

220

260

300

340

T/°C

Figure 3.

DSC

heating scans

(20°C/min) of the

poly(2,6-dimethyl-2,4-pheny-

lene oxide) containing 2-oxazoline and bromobenzyl pendant groups. A) second heating scan ( f i r s t heating scan up to 200°C); B) t h i r d heating

scan; C) fourth heating scan (after annealing 30 min. at

270°C). In Phase-Transfer Catalysis; Starks, C.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.


Scheme 6.

Synthesis of poly(2,6-dimethyl-l,4-phenylene oxide)aromatic polyether sulfone-poly(2,6-dimethyl-l,4-phenylene oxide) (PPO-PSU-PPO) t r i b l o c k copolymer.


•Ό

ο ν©

m n m π


110


8

Figure 4a.

200 MHz H-NMR

1

6

spectrum

2

0 δ in p p m

of ω-(2,6-dimethylphenol)

poly(2,6-di

methyl-1,4-phenylene oxide) (PPO) (M « 2,235. CC1 , TMS). p

τ

1

8

Figure 4b.

200 MHz

1

6

1

1

4

1

1

4

1

Γ

2 0 δ in p p m

H-NMR spectrum of a,ci>-di(chloro a l l y l ) aromatic poly

ether sulfone (PSU) from Scheme 4 (M * 1,930, CDC1 , TMS). R

3


PERCEC


111


9.

22 26 30 34 Elution volume in ml

Figure 5.

GPC

curves of:

Α) ω-(2,6-dimethylphenol ) PPO,

ο,ω-dKchloroallyl) PSU (M

n

(M

p

« 1.930); B)

« 3.900); and C) PP0-PSU-PP0 triblock

copolymer.




112

e s t e r s ( 2 5 ) . The s y n t h e s i s o f LC c o p o l y e t h e r s a l l o w s us t o t a i l o r t h e i r t h e r m a l t r a n s i t i o n s over a v e r y b r o a d range o f tempera t u r e s (23_i25). A t t h e same time, they l e t us o b t a i n i n f o r m a t i o n concerning t h e i n f l u e n c e o f sequence distribution on t h e i r mesomorphic p r o p e r t i e s ( 2 6 ) . L a s t b u t n o t l e a s t , b y v a r y i n g t h e p r e v i o u s l y d i s c u s s e d methods f o r t h e s y n t h e s i s o f s e q u e n t i a l copolymers we c o u l d develop t h e f i r s t c l a s s e s o f b o t h segmented copolymers and a l t e r n a t i n g b l o c k copolymers c o n t a i n i n g t h e r m o t r o p i c LC segments i n one b l o c k and e i t h e r e l a s t o m e r i c o r t h e r m o p l a s t i c segments as t h e second block(27.). Scheme 7 o u t l i n e s an example f o r the s y n t h e s i s o f t h e t h e r m o t r o p i c p o l y e t h e r s and c o p o l y e t h e r s based on 4,4* - d i h y d r o x v b i p h e n y 1 (25). A c o m p a r i s o n between t h e t h e r m a l t r a n s i t i o n s o f a s e t o f p o l y e t h e r s and t h e c o r r e s p o n d i n g p o l y e s t e r s i s presented i n F i g u r e 6. F i g u r e 7 demonstrates t h e a b i l i t y t o tailor the thermal stability range o f t h e mesophase through copolyetherification. There a r e s e v e r a l o t h e r a c t i v e t o p i c s under e x a m i n a t i o n i n o u r l a b o r a t o r y , f o r example, s u r f a c e m o d i f i c a t i o n o f polymers under phase t r a n s f e r c a t a l y z e d r e a c t i o n s and s i n g l e e l e c t r o n t r a n s f e r phase transfer catalyzed polymerizations. The l i m i t e d space, however, p r e c l u d e s d i s c u s s i o n here. What w i l l phase t r a n s f e r c a t a l y s i s p r o v i d e polymer c h e m i s t r y w i t h i n the near future? I t i s apparently s t i l l t o e a r l y t o p r e d i c t t h i s . We a r e n o t y e t i n t h e p o s s e s s i o n o f many e l e m e n t a l m e c h a n i s t i c and k i n e t i c u n d e r s t a n d i n g s i n o r d e r t o answer q u e s t i o n s l i k e , f o r example, why n o t " l i v i n g p o l y e t h e r i f i c a t i o n ? " Br-(CH )-Br 2

+

Η0-^5^-^Ο^-0Η

TBAH Aqueous NaOH Nitrobenzene

Where: η « 5, 7, 9 o r 11

TBAH Aqueous NaOH Nitrobenzene

BHCH * [0-^o)--@ 2

7

Where: x/y = 0.1 - 9.0

Scheme 7.

mole/mole

S y n t h e t i c avenues used f o r t h e s y n t h e s i s o f A j A ' - d i h y d r o x y b i p h e n y l p o l y e t h e r s and c o p o l y e t h e r s .


9.

113


PERCEC

260 240 220 200 ο

g' 130


I

160 140 120

5

Figure

6.

Thermal versus

transition n,

the

(A)

T

m

number

,

9

temperatures of

(Δ)

for:

T.

(data

1)

11

(T^ = m e l t i n g ,

methylene

4,4'-dihydroxybiphenyl esters

7

units

in

polyethers

from

T.

the (t)

reference

=

isotropization)

polymers Τ

,

(ο)

T.;

containing 2)

poly

the

mole

% of

the

homo-

25).

230 210 190

°I-

£ 170 150 130 0

10

20

30

40

50

60

70

80

90

MOLE X

r

igure

7.

Thermal

transition

1,7-dibromoheptane copolymers and

based

temperatures in on

the

(Τ

reaction

,

T. )

100

-(CH ) 2

7

versus

mixture,

4,4'-dihydroxybiphenyl,

for

and

1,7-dibromoheptane,

1,4-dibromononane.



114 Acknowledgments

Most o f t h i s work has been s u p p o r t e d by t h e Polymers Program o f the N a t i o n a l S c i e n c e F o u n d a t i o n under G r a n t N o . DMR 82-13895. I am d e e p l y g r a t e f u l t o my d e d i c a t e d coworkers l i s t e d as c o a u t h o r s i n the referenced papers.


References 1. C. M. Starks, J . Amer. Chem. Soc., 93, 195 (1971). 2. A. Brandstrom, "Preparative Ion Pair Extraction," an Introduction to Theory and Practice, Apotekarsocieteten, Hassle Lakemedel, First Ed., 1974; Second Ed., 1976. 3. A. Brandstrom, "Principles of Phase Transfer Catalysis by Quaternary Ammonium Salts," in "Advances in Physical Organic Chemistry," Vol. 15, V. Gold, Ed., Academic Press, London and New York, 1977, p. 267. 4. W. P. Weber and G. W. Gokel, "Phase Transfer Catalysis in Organic Synthesis," in Reactivity and Structure, Vol. 4, K. Hafner et a l . , Eds., Springer-Verlag, Berlin - Heidelberg, 1977. 5. C. M. Starks and C. Liotta, "Phase Transfer Catalysis. Principles and Techniques," Academic Press, London and New York, 1978. 6. Ε. V. Dehmlov and S. S. Dehmlov, "Phase Transfer Catalysis." First Ed., 1980; Second Revised Ed., Verlag Chemie, Weinheim, 1983. 7. L. J . Mathias and C. E. Carralier J r . , Eds., "Crown Ethers and Phase Transfer Catalysis in Polymer Science," Plenum Press, New York 1984. 8. V. Percec and B. C. Auman, Makromol. Chem., 185, 617 (1984). 9. V. Percec and B. C. Auman, Makromol. Chem., 185, 1867 (1984). 10. V. Percec, B. C. Auman and P. L. Rinaldi, Polym. Bull., 10, 391 (1983). 11. V. Percec and H. Nava, Makromol. Chem., Rapid Commun., 5, 319 (1984). 12. V. Percec, H. Nava and B. C. Auman, Polym. J., 16, 681 (1984). 13. V. Percec, P. L. Rinaldi and B. C. Auman, Polym. Bull., 10, 215 (1983). 14. V. Percec, P. L. Rinaldi and B. C. Auman, Polym. Bull., 10, 397 (1983). 15. V. Percec and B. C. Auman, Polym. Bull., 12, 253 (1984). 16. Percec, T. D. Shaffer and H. Nava, J . Polym. Sci., Polym. Let. Ed., 22, 637 (1984). 17. T. D. Shaffer and V. Percec, J . Polym Sci., Polym. Chem. Ed., 24, 451 (1986). 18. V. Percec, H. Nava and J . M. Rodriquez-Parada, J . Polym. Sci., Polym. Lett. Ed., 22, 523 (1984). 19. V. Percec, H. Nava and J . M. Rodriquez-Parada, Polym. Bull., 12, 261 (1984). 20. V. Percec, H. Nava and J . M. Rodriguez-Parada, in "Advances in Polymer Synthesis," J . E. McGrath and Β. M. Culbertson, Eds., Plenum Press, New York, 1985, p. 235. 21. V. Percec and B. C. Auman, Polym. Bull., 10, 385 (1983).


9. PERCEC 22. 23. 24. 25. 26.


27.


115

V. Percec, i n "Cationic Polymerization and Related Processes." E. J . Goethals, Ed., Academic Press, London and New York, 1984, p. 347. V. Percec and T. D. Shaffer, i n "Advances in Polymer Synthesis," J . E. McGrath and Β. M. Culbertson, Eds., Plenum Press, New York, 1985, p. 133. T. D. Shaffer and V. Percec, Makromol. Chem. Rapid Commun., 6, 97 (1985). T. D. Shaffer and V. Percec, J . Polym. Sci., Polym. Lett. Ed., 23, 185 (1985). T. D. Shaffer, M. Jamaludin and V. Percec, J . Polym. Sci., Polym. Chem. Ed., 24, 15 (1986). T. D. Shaffer and V. Percec, J . Polym. Sci., Polym. Lett. Ed., 24, 185 (1985).

RECEIVED August 20, 1986


Phase-Transfer Catalysis - ACS Publications - American Chemical

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