Anionic Polymerization - ACS Publications - American Chemical Society

15

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on May 14, 2016 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0166.ch015

Original Anionic Pathway to New PA(PO)2 Star-Shaped Block Polymers Based on Polyvinyl or Polydiene Hydrocarbons and Polyoxirane R.

JERÔME

and Ph. TEYSSIE

Laboratory of Macromolecular Chemistry and Organic Catalysis, University of Liege, Sart Tilman, 4000 Liege, Belgium G. HUYNH-BA Ε. I. du Pont de Nemours and Company, Inc., Polymer Products Department, Experimental Station, Wilmington, DE 19898

Naphthalene-terminated p o l y v i n y l aromatics and p o l y i s o p r e n e were obtained s u c c e s s f u l l y . These f u n c t i o n a l polymers were metalated by potassium in THF a t 25°C. The formation o f a s t a b l e di negative i o n is observed unless the naphthalene is directly attached t o the end o f the p o l y v i n y l aromatics, in which case a few isoprene u n i t s can be advantageously i n s e r t e d between t h e naphthalene end group and the p o l y v i n y l aromatics. The polymeric and s t a b l e d i n e g a t i v e i o n polymerizes oxirane by both a n i o n i c s i t e s and forms three -branched starshaped b l o c k copolymers. Thanks t o t h e i r m u l t i p h a s e c o n s t i t u t i o n , b l o c k copolymers have t h e o r i g i n a l i t y t o a d d a d v a n t a g e o u s l y t h e p r o p e r t i e s o f t h e i r c o n s t i t u t i v e sequences. These v e r y a t t r a c t i v e m a t e r i a l s c a n d i s p l a y n o v e l p r o p e r t i e s f o r new t e c h n o l o g i c a l a p p l i c a t i o n s . In t h i s r e s p e c t , t h e r m o p l a s t i c elastomers a r e demonstrated e x a m p l e s ( l , 2 , 3.) ; t h e y a r e c u r r e n t l y u s e d w i t h o u t a n y m o d i f i c a t i o n a s e l a s t i c b a n d s , s t a i r t r e a d s , s o l i n g s in t h e f o o t w e a r i n d u s t r y , impact r e s i s t a n c e o r f l e x i b i l i t y improvers f o r p o l y s t y r e n e , p o l y p r o p y l e n e and p o l y e t h y l e n e whereas s i g n i f i c a n t d e v e l o p m e n t s a s a d h e s i v e s a n d a d h e r e n d s a r e t o b e n o t e d (h 3). In s o l u t i o n , b l o c k copolymers d i s p l a y i n t e r e s t i n g c o l l o i d a l and i n t e r f a c i a l p r o p e r t i e s . They c a n b e u s e d a s e m u l s i f y i n g a g e n t s in w a t e r - o i l a n d o i l - o i l s y s t e m s (6). I n t h e l a t e r c a s e , the o i l phases a r e s o l i d and t h e y g i v e r i s e t o p o l y m e r i c a l l o y s (j) o r t h e y a r e l i q u i d a n d t h e y a l l o w t h e p r e p a r a t i o n o f l a t e x e s in o r g a n i c medium (0). H o w e v e r , t h e m o l e c u l a r s t r u c t u r e o f b l o c k copolymers based on p o l y b u t a d i e n e PB ( 7 0 $ ) and p o l y s t y r e n e PS b e h a v e a s t h e r m o p l a s t i c e l a s t o m e r s when engaged in m u l t i b l o c k ( P B - P S ) o r t r i b l o c k ( P S - P B - P S ) s t r u c t u r e s b u t n e v e r when i m p l i e d in i n v e r s e t r i b l o c k o r d i b l o c k a r r a n g e m e n t s . Similarly the 9

N

0097-6156/81/0166-0211$05.00/0 © 1981 American Chemical Society

McGrath; Anionic Polymerization ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


212

ANIONIC POLYMERIZATION

s u r f a c e a c t i v i t y o f b l o c k copolymers b a s e d on p o l y o x i r a n e (PO) and p o l y s t y r e n e seems t o d e p e n d on t h e i r m o l e c u l a r p a r a m e t e r s (8). The a c t u a l k n o w l e d g e o f t h e b a s i c m o l e c u l a r s t r u c t u r e p r o p e r t y r e l a t i o n s h i p s r e l i e s m a i n l y on t h e a v a i l a b i l i t y o f w e l l d e f i n e d l i n e a r a r c h i t e c t u r e s : t h e d i , t r i - and m u l t i b l o c k c o p o l y m e r s . New a n d w e l l c o n t r o l l e d m o l e c u l a r s t r u c t u r e s c o u l d u n d o u b t e d l y p r o v i d e a deep u n d e r s t a n d i n g o f t h e b e h a v i o r o f b l o c k c o p o l y m e r s a n d a more e f f i c i e n t m a s t e r i n g o f t h e i r a p p l i c a tions . The p u r p o s e o f t h i s c o n t r i b u t i o n is t o show how t h e d e s i g n o f a new d i a n i o n i c s p e c i e s c a n l e a d t o i n t e r e s t i n g a d v a n c e s in b l o c k c o p o l y m e r ! z a t i o n and e s p e c i a l l y t o o r i g i n a l P A ( P 0 ) stars h a p e d b l o c k c o p o l y m e r s . PA is a h y d r o p h o b i c b l o c k : polystyrene, p o l y t e r t i a r y b u t y l s t y r e n e (PTBS) o r p o l y i s o p r e n e ( P i ) . The s u r f a c e a c t i v i t y o f t h i s n o v e l and w e l l mastered m o l e c u l a r a r c h i t e c t u r e is c o n s i d e r e d a n d c o m p a r e d a s f a r as p o s s i b l e w i t h t h e b e h a v i o r o f t h e c o r r e s p o n d i n g ΡΑ-PO d i b l o c k c o p o l y m e r s . 2

M e t a l a t i o n o f N a p h t h a l e n e by P o t a s s i u m Room T e m p e r a t u r e

in

Tetrahydrofuran

at

A p o l y m e r PA t e r m i n a t e d w i t h a s t a b l e d i n e g a t i v e i o n a b l e t o p o l y m e r i z e o x i r a n e is a n i d e a l p a t h w a y t o w a r d s P A ( P 0 ) 2 s t a r shaped b l o c k copolymers. N a p h t h a l e n e is known t o f o r m a s t a b l e l i t h i u m d i a n i o n a t - 8 0 ° C in t e t r a h y d r o f u r a n (THF) a t c o n c e n t r a t i o n s l o w e r t h a n 0 . 5 mol.l""-*- ( 9 - 1 2 ) . U n f o r t u n a t e l y o r g a n o l i t h i u m compounds a r e u n able to polymerize oxirane (13). N a p h t h a l e n e c a n a l s o be m e t a l a t i o n b y s o d i u m a n d p o t a s s i u m in THF b u t no e x p e r i m e n t a l e v i d e n c e f o r a d i a n i o n o f n a p h t h a l e n e s o d i u m o r p o t a s s i u m is t o be f o u n d . A l t h o u g h n a p h t h a l e n e m e t a l a t i o n b y s o d i u m is t h o r o u g h l y d e s c r i b e d ( 9 . , l U , 1 5 . ) , v e r y few r e s u l t s a b o u t p o t a s s i u m a r e p u b l i s h e d (l6, 1777 As t h e r e d u c i n g p o w e r o f t h e a l k a l i m e t a l s decreases from l i t h i u m ( L i / L i = 3 . 0 2 v ) t o potassium (K/K = - 2 . 9 2 v ) a n d f i n a l l y t o s o d i u m ( N a / N a = 2.71v) ( l 8 ) , it is a t t r a c t i v e t o s t u d y in more d e t a i l t h e n a p h t h a l e n e m e t a l a t i o n b y Κ in t h e THF. +

+

+

T h e r e is a g r e a t s i m i l a r i t y in t h e c o u r s e o f t h e n a p h t h a l e n e m e t a l a t i o n b y L i a t - 8 0 ° C o n one h a n d a n d b y Κ a t RT o n t h e o t h e r h a n d . The t i t r a t i o n o f t h e c a r b a n i o n s f o r m e d (l£) p r o v e s t h e p r e s e n c e o f two a n i o n s p e r n a p h t h a l e n e o n l y a t n a p h t h a l e n e c o n c e n t r a t i o n s l o w e r t h a n 0 . 0 3 m o l . l " f o r Κ a t RT ( T a b l e I ) a n d 0 . 5 mol. 1-1 f o r L i at -80°C (9.). In both cases, the d i a n i o n i c 1


15.

JERÔME ET A L .

PA(PO)

2

Star-Shaped

Block

213

Polymers

s p e c i e s a r e a b l e t o t r a n s f e r one o f t h e i r e l e c t r o n s t o n e u t r a l naphthalene w i t h f o r m a t i o n o f the well-known naphthalene r a d i c a l a n i o n (NRA) ( 1 0 , 19). T h e n a p h t h a l e n e m e t a l a t i o n b y Κ a t RT p r o c e e d s in t w o s u c c e s s i v e s t e p s : i n i t i a l r e d u c t i o n t o t h e NRA ( F i g u r e 1A) and f i n a l f o r m a t i o n o f t h e d i a n i o n i c s p e c i e s a t n a p h t h a l e n e c o n c e n t r a t i o n l o w e r t h a n 0.03 m o l . l " ( F i g u r e I B ) . The assumed p o t a s s i u m d i a n i o n is s t i l l s t a b l e a t RT a f t e r 100 h r s ; h o w e v e r , in t h e p r e s e n c e o f a n e x c e s s o f n e u t r a l n a p h t h a l e n e , t h e a b s o r p t i o n o f t h e NRA is a g a i n o b s e r v e d ( F i g u r e 1 C ) . The h y d r o l y s i s p r o d u c t s o f t h e p o t a s s i u m n a p h t h a l e n e d i a n i o n h a v e b e e n a n a l y z e d b y p r o t o n NMR s p e c t r o s c o p y . As r e p o r t e d e l s e w h e r e (19.) » t h e y a g r e e w i t h e q [ l ] , w h e r e a s t h e r a t i o b e t w e e n t h e f o r m s I a n d I I is c l o s e t o 3.


1

[I]

[II]

On t h e b a s i s o f a l l t h e s e e x p e r i m e n t a l o b s e r v a t i o n s t h e f o l l o w i n g r e a c t i o n scheme c a n b e p r o p o s e d f o r t h e m e t a l a t i o n o f n a p h t h a l e n e b y Κ in THF a t RT ( e q [ 2 ] ) .

H

K

+

H

K

+

E q [3] t a k e s i n t o a c c o u n t t h e b e h a v i o r o f t h e p o t a s s i u m n a p h t h a l e n e d i a n i o n in t h e p r e s e n c e o f a n e x c e s s o f n a p h t h a l e n e .

H

K

+

H

K

+


214



M e t a l a t i o n o f g - E t h y l n a p h t h a l e n e b y P o t a s s i u m in THF a t Room Temperature Once f i x e d a t t h e e n d o f a p o l y m e r P A , t h e n a p h t h a l e n e is 3 s u b s t i t u t e d ; t o assess t h e i n f l u e n c e o f t h e s u b s t i t u t i o n on t h e m e t a l a t i o n o f n a p h t h a l e n e , β-ethylnaphthalene (EN) was s t u d i e d as a m o d e l compound. I n c o n t r a s t t o t h e p o t a s s i u m n a p h t h a l e n e d i a n i o n , EN g i v e s r i s e t o a d i a n i o n i c s p e c i e s a t c o n c e n t r a t i o n s h i g h e r t h a n 0.03 m o l . l " ( T a b l e I I ) . F u r t h e r m o r e t h e EN d i a n i o n is u n a b l e t o t r a n s f e r one e l e c t r o n t o a n o t h e r n a p h t h a l e n e m o l e c u l e . These sharp d i f f e r e n c e s a r e t o be a t t r i b u t e d t o t h e p a r t i c i p a t i o n o f t h e β-ethyl g r o u p in t h e m e t a l a t i o n p r o c e s s . The EN m e t a l a t i o n b y Κ in THF a t RT h a s b e e n a n a l y z e d b y UV s p e c t r o p h o t o m e t r y ( F i g u r e 2). ENRA ( F i g u r e 2A) a n d p o t a s s i u m EN d i a n i o n ( F i g u r e 2, Β t o b e compared t o F i g u r e I B ) a r e s u c c e s s i v e l y formed, b u t a d i a n i o n i c species c h a r a c t e r i z e d by spectrum C ( F i g u r e 2) is f i n a l l y f o r m e d w h i c h is s t a b l e in t h e p r e s e n c e o f p u r e n a p h t h a l e n e . The a b s o r p t i o n a t U35nm ( F i g u r e 2C) c o r r e s ponds t o t h e v a l u e r e p o r t e d f o r t h e d i h y d r o n a p h t h a l e n e m o n o a n i o n (DHNA) i+33-35nm (20). DHNA is e a s i l y h y d r o l y z e d i n t o d i h y d r o n a p h t h a l e n e (DHN) w h i c h c a n b e a g a i n m e t a l a t e d t o g i v e DHNA ( e q 1

h).

DHNA

DHN

DHNA

S i m i l a r l y t h e h y d r o l y s i s p r o d u c t o f t h e s t a b l e p o t a s s i u m EN d i a n i o n ( F i g u r e 2C) is m e t a l a t e d b y Κ in THF a t RT a n d t h e c h a r a c t e r i s t i c o f DHNA is a g a i n o b s e r v e d a t U35nm ( F i g u r e 2 D ) . However, t h e s p e c t r a a r e s l i g h t l y d i f f e r e n t . H e n c e , t h e EN d i a n i o n is a c c o r d i n g l y assumed t o b e c o n s t i t u t e d b y a DHNA a n i o n and a l s o b y a n e x t r a c y c l i c c a r b a n i o n r e s u l t i n g f r o m a n i n t r a m o l e c u l a r h y d r o g e n t r a n s f e r ( e q 5, 6). F o r c l a r i f i c a t i o n , t h e 1,2 d i h y d r o s t r u c t u r e is o m i t t e d .


JEROME E T A L .

PA(PO)

2

Star-Shaped

Block

Polymers

215

TABLE I Naphthalene M e t a l a t i o n by Potassium in THF a t Room Temperature


: Naphthalene

: Carbanions

: Concentration

te"]

(a) : Concentration

[N ] : [N]m.l

: [ C ] m.l 1

1

: U.5 10"

-

3

ί 0.9

ίο"

2

: 9.5 10"

3

: 1.9 i o -

: 2.0 10~

2

: h.O

: 3.0 10"

2

: 7.0 10"

2

: 1.1 ί ο -

: 1.1 10"

1

: 1.1 ί ο -

2

:

2.0

:

:

2.0

:

10 "

2

:

2.0

:

: 5.9 10 ~

2

:

1.97

:

1

:

1.57

:

1

:

1.00

:

(a) F i n a l constant values

TABLE I I M e t a l a t i o n o f β-ethylnaphthalene (EN) by Κ in THF a t Room Temperature : EN

:

Time o f

:

metalation

:

(hours)

:

(m.l" )

1

:

per EN

: 0.l60

:

120

:

0.32

:

2.0

: 0.125

:

96

:

0.2U

:

1.9

:

: 0.015

:

33

:

0.03

:

2.0

:

:

1

(m.l" )

: [Carbanions] : Nr o f carbanions :


:


216


Figure 1. Visible and UV spectra of (A ) naphthalene radical anion (NRA ) (THF, 25°C); (B) naphthalene dianion (OD values shifted upward by 0.2 unit); (C) naphthalene dianion after neutral naphthalene addition (OD values shifted upward by 1 unit; the NRA concentration is the same in A and B).

Figure 2. The β-ethylnaphthalene metalation by Κ in THF at RT. UV spectra after (A) 10 min, NRA spectrum; (B) 10 h, naphthalene dianion spectrum (OD shifted upward by 0.4 unit); (C) 50 h, isomerized β-substituted naphthalene dianion (OD shifted upward by 0.25 unit); (D) compound corresponding to Spec trum C, water deactivated, purified, and again metalated by Κ (OD shifted upward by 1 unit).


15.

JEROME E T A L .

PA(PO)

2

Star-Shaped

Block

217

Polymers

[6]


VII Forms I I I a n d I V must b e c o n s i d e r e d t o d e s c r i b e t h e n a p h t h a l e n e t y p e d i a n i o n w h i c h is f i r s t f o r m e d d u r i n g t h e EN m e t a l a t i o n ( F i g u r e 2, B ) . The p r o t o n NMR a n a l y s i s o f t h e h y d r o l y s i s p r o d u c t s (V a n d V I ) o f t h e i s o m e r i z e d EN d i a n i o n ( F i g u r e 2, C) a g r e e s w i t h t h e presence o f t h e e t h y l group on t h e dihydronaphthalene l»ing (19) a n d s u p p o r t s t h e e x i s t e n c e o f t h e f o r m s I V a n d V I I . A g a i n m e t a l a t e d b y K, t h e DHN e n t i t y ( V I ) g i v e s r i s e t o a DHNA ( V I I I ) ; ( e q 7) t h e UV a b s o r p t i o n o f w h i c h ( F i g u r e 2, D) is s l i g h t l y m o d i f i e d in t h e i s o m e r i z e d EN d i a n i o n ( V I I F i g u r e 2, C) b y t h e extra c y c l i c carbanion. C

V

C H

2lQ§)

- * - ,

CH -CH 3

VI

2

l

Qg

[ ] 7

)

VIII

From t h e e x p e r i m e n t a l r e s u l t s , t h e f o l l o w i n g mechanism is p r o p o s e d f o r EN m e t a l a t i o n ( e q 8 )

[8]

H transfer.

Synthesis o f Naphthalene Terminated Polymers The u s e o f l i t h i o n a p h t h a l e n e a n d l i t h i o β-methylnaphthalene as f u n c t i o n a l l y s u b s t i t u t e d a n i o n i c i n i t i a t o r s is v e r y d i s a p p o i n t i n g (21, 22). The d e a c t i v a t i o n o f l i v i n g p o l y a n i o n s o n t o α-bromonaphthalene o r b r o m o - 3 - m e t h y l n a p h t h a l e n e is a n o t h e r u n s a t i s f a c t o r y a p p r o a c h due t o m e t a l h a l o g e n i n t e r c o n v e r s i o n ( e q s 9 , 10) (23). H

*

PS"Li +fulf)l +

( 0 ) + P S - C H2- C - B r 0

Li IX + P S ~ L i

+

,

[9]

(IX)

L i B r + PS-PS


[10]

218


To l i m i t t h i s p r o c e s s , R i c h a r d s h a s p r o p o s e d t o t r a n s f o r m t h e l i v i n g p o l y a n i o n i n t o i t s G r i g n a r d a n a l o g u e w h i c h is much l e s s r e a c t i v e b u t s t i l l a b l e t o i n t e r a c t w i t h t h e u s u a l bromor e a g e n t s (2k). E q u a t i o n s 1 1 and 1 2 summarize t h e G r i g n a r d p o l y mer f o r m a t i o n a n d i t s r e a c t i o n w i t h 3-bromomethylnaphthalene


PS~Li

+

PS-MgBr

+

MgBr

+

,

2

PS-MgBr

Br-CH -f

,

2

+

LiBr

[ l l ]

PS-CH -rj 2

+ MgBr

2

[12]

By t h i s p a t h w a y t h e d e g r e e o f p o l y m e r c o u p l i n g is r e d u c e d t o about 5 t o 1 0 $ ( F i g u r e 3 ) and t h e t i t r a t i o n o f t h e n a p h t h a l e n e end g r o u p i n d i c a t e s a f u n c t i o n a l i t y h i g h e r t h a n 90% ( 2 1 , 2 2 , 25).

M e t a l a t i o n o f Naphthalene A t RT

E n d e d P o l y d i e n e b y P o t a s s i u m in t h e

The m e t a l a t i o n o f n a p h t h a l e n e 3 - s u b s t i t u t e d b y b o t h a n e t h y l g r o u p o r p o l y i s o p r e n e c h a i n ( P I P ) is c o m p l e t e l y s i m i l a r a s e s t a b l i s h e d b y t h e t i t r a t i o n o f t h e c a r b a n i o n s f o r m e d a n d t h e UV a n a l y s i s o f t h e r e a c t i o n medium ( 2 1 , 2 2 , 2 5 ) . A c c o r d i n g l y t h e naphthalene r a d i c a l a n i o n , naphthalene d i a n i o n and i t s f u r t h e r i s o m e r i z a t i o n by hydrogen t r a n s f e r a r e s u c c e s s i v e l y observed and t h e f i n a l s t a g e o f t h e m e t a l a t i o n c a n be r e p r e s e n t e d b y t h e following structure: PIP

CH-tf~ rl

M e t a l a t i o n o f Naphthalene P o t a s s i u m in THF A t RT

N

RESONANCE FORMS

Ended P o l y v i n y l A r o m a t i c Chains b y

When n a p h t h a l e n e is s u b s t i t u t e d b y a p o l y v i n y l a r o m a t i c c h a i n p o l y s t y r e n e P S , p o l y ( p - t e r t - b u t y l s t y r e n e ) PTBS o r poly(α-methylstyrene) PMS t h e c o u r s e o f t h e m e t a l a t i o n is d e e p l y modified ( 2 1 , 2 2 , 25.). Four c a r b o n i o n s can be formed p e r naphthalene end group ( F i g u r e h) w h e r e a s t h e n a p h t h a l e n e e n d g r o u p is c o m p l e t e l y r e l e a s e d a t t h e end o f t h e m e t a l a t i o n . T h i s phenomenon h a s b e e n t h o r o u g h l y s t u d i e d and w i l l be p u b l i s h e d elsewhere ( 2 2 ) . B r i e f l y when n a p h t h a l e n e is c o n j u g a t e d t o a n a r o m a t i c n u c l e u s t h e p o t a s s i u m d i a n i o n is u n s t a b l e a n d t h e n a p h t h a l e n e e n d g r o u p is r e l e a s e d w h e r e a s t h e p o l y v i n y l a n i o n is f r e e d a n d f i n a l l y i s o m e r i z e d ; eqs 1 3 t o I T summarize t h e s e o b s e r v a t i o n s .



15.

JERÔME ET A L . PA{PO)% Star-Shaped

Block

(XII)

R

219

Polymers

(XIII)

S i m i l a r i n s t a b i l i t y o f conjugated a n i o n i c systems has a l r e a d y been o b s e r v e d ; L a g e n d i j k and Szwarc have r e p o r t e d t h a t d i ( a n a p h t h y l ) e t h a n e d i a n i o n ( N N ~ ) in e t h e r s o l v e n t u n d e r g o e s s c i s s i o n o f t h e c e n t r a l C-C b o n d w i t h f o r m a t i o n o f t w o m o n o a n i o n (NN~ —, 2N~) (26). To s u p p r e s s t h e d e l e t e r i o u s e f f e c t o f c o n j u g a t i o n a n d t o o b t a i n a s t a b l e d i a n i o n t e r m i n a t e d PS o r PTBS, a t l e a s t o n e i s o p r e n e u n i t is t o b e i n s e r t e d b e t w e e n t h e p o l y v i n y l aromatic c h a i n and t h e naphthalene end group; t h i s o p p o r t u n i t y has been s u c c e s s f u l l y a p p l i e d . 2

2

Star-Shaped Block

Copolymerization

In the f i r s t step the oxirane polymerization i n i t i a t e d by t h e i s o m e r i z e d EN d i a n i o n h a s b e e n s t u d i e d . The r e s u l t s r e p o r t e d in T a b l e I I I a n d t h e l o w p o l y d i s p e r s i t y o b s e r v e d ( a b o u t 1 . 1 ; F i g u r e 5) a r e c o n c l u s i v e f o r a l i v i n g a n i o n i c system. Moreover t h e i n i t i a t i o n r a t e o f w h i c h is h i g h e r t h a n t h e p r o p a g a t i o n o n e .



Figure 3. G PC of a naphthalene-terminated polystyrene (M = 3400) obtained by reaction of polystyrylmagnesium bromide with β-bromomethylnaphthalene. n

TABLE I I I . O x i r a n e P o l y m e r i z a t i o n I n i t i a t e d

by t h e (a)

S t a b l e P o t a s s i u m β-ethylnaphthalene D i a n i o n

Sample

[initiator]

Conversion

1

(m.l )

(%)

Mn

Mn

t h e o r . (b)

exper.

PO 1

1 6 . 3 10"

100

2.6 χ 1 0

3

2,700

PO 2

8 . 2 10~

93

5.0 χ 1 0

3

5,200

PO 3

5.U 1 0

95

3 7.7 x 10°

k

-k

7,500

(a) [Oxirane] = 0 . 1 m . l , t i m e : 7 2 h r s , temperature: solvent: THF (Q0%) + Bz ( 2 0 $ ) . - 1

( b ) Mn c a l c u l a t e d o n t h e b a s i s o f t h e monomer o v e r molar r a t i o .

25°C

initiator


15.

JERÔME E T A L .

PA(PO)

2

Star-Shaped

Block

221

Polymers


C/N

0

20

40

60

80

100

120

UO ' 160 *

300 500 Time (hrs)

Figure 4. Kinetics of the metalation of naphthalene-terminated PTBS (M = 3400) by K (THF, 25°C, [naphthalene] = 3 X 10' mol/L); C/N = number of carbanions generated per naphthalene end group. n

2

PO 2

Figure 5.

GPC of polyoxirane using potassium β-ethylnaphthalene initiator.

dianion as



222

The o x i r a n e p o l y m e r i z a t i o n c a n b e d e s c r i b e d b y eqs 18 a n d 19: H

°3 :-CH

yH-CH -CH -0-

3

2

2

[

1

8

]


XIV

f4H-CH -CH -0-

X I V

2

2

a2 CH -CH -0" 2

[19]

2

f 3

0 3 " "H-CH -CH -0-CH -CH -0 2

2

2

2

From t h e k i n e t i c s o f t h e o x i r a n e p o l y m e r i z a t i o n i n i t i a t e d b y a l c o h o l a t e (l6) a n d b y f l u o r e n y l p o t a s s i u m (27) a n d a s f l u o r e n y l and d i h y d r o n a p h t h a l e n e mono a n i o n (28) h a v e a p p r o x i m a t e l y t h e same b a s i c i t y , t h e k 2 o v e r k p p r a t i o may b e e s t i m a t e d t o 20. T h e r e f o r e , t h e l e n g t h o f t h e t w o g r o w i n g p o l y e t h e r c h a i n s must be l a r g e l y i n d e p e n d e n t o n t h e n a t u r e o f t h e i n i t i a t i n g s i t e . I n t h e s e c o n d s t e p , o x i r a n e h a s b e e n a d d e d a t -30°C t o a n i s o m e r i z e d and s t a b l e naphthalene d i a n i o n f i x e d a t t h e end o f t h e PA c h a i n . O x i r a n e is c o m p l e t e l y p o l y m e r i z e d a t RT, a n d t h e c r u d e p r o d u c t o b t a i n e d is s e p a r a t e d i n t o b l o c k c o p o l y m e r , s t a r t i n g homopolymer PA a n d h o m o p o l y e t h e r . The s e p a r a t i o n scheme is d e s c r i b e d in T a b l e I V a n d t h e r e s u l t s o b t a i n e d f o r a g r e a t l o t o f PA ( P I P , P S , a n d PTBS) b a s e d c o p o l y m e r s a g r e e w i t h a r a t i o o f a b o u t 90$ b l o c k c o p o l y m e r , 10% homo PA a n d o n l y t r a c e s o f homopolyether. The c o m p o s i t i o n o f t h e s t a r - s h a p e d b l o c k c o p o l y m e r is e a s i l y d e t e r m i n e d b y p r o t o n NMR a n a l y s i s ; f r o m t h i s a n d t h e mean number a v e r a g e m o l e c u l a r w e i g h t (Mn) o f t h e s e q u e n c e P A , Mn o f t h e p o l y e t h e r component c a n b e c a l c u l a t e d . The l a t e r is v e r y s i m i l a r t o t h e v a l u e f r o m membrane o s o m e t r y . H y d r o x y l e n d g r o u p o f P A ( P 0 ) s t a r - s h a p e d b l o c k copolymers have been t i t r a t e d a n d t h e i r mean number p e r c o p o l y m e r (1.85) a g r e e s w i t h t h e p r e s e n c e o f t w o polyoxirane branches. On t h e a v e r a g e , t h e p o l y d i s p e r s i t y o f t h e s t a r - s h a p e d b l o c k c o p o l y m e r s v a r i e s b e t w e e n 1.2 a n d 1.3 ( F i g u r e a

r 0

2

6). The m o l e c u l a r p a r a m e t e r s o f a s e r i e s o f w e l l c h a r a c t e r i z e d P A ( P 0 ) b l o c k c o p o l y m e r s c a n b e f o u n d in T a b l e V. 2


15.

JEROME E T AL.

PA(PO)

Star-Shaped

2

Block

Polymers

223

TABLE I V S e p a r a t i o n o f PTBS ( P 0 )

2

Copolymers

f r o m C o r r e s p o n d i n g PTBS a n d PO Homopolymers (a) Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on May 14, 2016 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0166.ch015

H i g h l y powdery c r u d e p r o d u c t

Ψ

E x t r a c t i o n b y heptane under vigorous s t i r r i n g (b,c) Centrifugation

Soluble Part [S]

Insoluble Part [ i ]

drying

,(a) off

(a,

J-

v

drying o f f

i

E x t r a c t i o n by e i t h e r water o r e t h a n o l a t 30°c( »

Anionic Polymerization - ACS Publications - American Chemical Society

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