or Nucleophile in

3

Initiation Reactions with and/or

Nucleophile

Activated

Monomer

in Ionic Polymerizations

Downloaded by NANYANG TECHNOLOGICAL UNIV on June 8, 2016 | http://pubs.acs.org Publication Date: April 19, 1983 | doi: 10.1021/bk-1983-0212.ch003

TEIJI TSURUTA Science University of Tokyo, Faculty of Engineering, Department of Engineering, Kagurazaka, Shinjuku-ku, Tokyo 162, Japan This review article is concerned with chemical behavior of organo-lithium, -aluminum and -zinc compounds in initiation reactions of diolefins, polar vinyls and oxirane compounds. Discussions are given with respect to the following five topics: 1) lithium alkylamide as initiator for polymeriza tions of isoprene and 1,4-divinylbenzene; 2) initiation of N-carboxy-α-aminoacid anhydride(NCA) by a primary amino group; 3) activated aluminum alkyl and zinc alkyl; 4) initiation of stereospecific polymerization of methyloxirane; and 5) comparison of stereospecific polymerization of methyloxirane with Ziegler-Natta polymerization. A comprehensive interpretation is proposed for chemistry of reactivity and/or stereospecificity of organometallic compounds in ionic polymerizations. This review article is concerned with chemical behavior of organo-lithium, -aluminum and -zinc compounds in initiation reactions of diolefins, polar vinyls and oxirane compounds. A comprehensive interpretation is proposed for metallic compounds in ionic polymerizations. Lithium Alkyl Amide as Initiator for Polymerizations of Isoprene and 1,4-Divinylbenzene Lithium dialkylamide having bulky alkyl groups, such as isopropyl groups, exhibits unique behavior in polymerization reactions of isoprene and divinylbenzene. It was previously reported by us that lithium dialkylamide underwent a stereospecific addition reaction with butadiene in the presence of an appropriate amount of dialkylamine in cyclohexane as solvent (1_, 2). For instance, on reacting with butadiene, lithium diethyl amide gave the sole adduct, 1-diethylamino-cis-butene-2, in a 98-99% purity. In the absence of free amine, on the other hand, no reaction took place under the same experimental conditions ( 50° C 0097-615 6/ 83/0212-0023$06.00/0 © 1983 American Chemical Society Bailey et al.; Initiation of Polymerization ACS Symposium Series; American Chemical Society: Washington, DC, 1983.


24

INITIATION

OF

POLYMERIZATION

in cyclohexane for 60 min.). By kinetic and spectroscopic studies, i t was concluded that the r e a c t i v e species in this addition reaction is the one to two complex of lithium d i l k y l a m i d e and d i a l k y l a m i n e . I n t h e one t o two complex, l i t h i u m d i a l k y l a m i d e i s a c t i v a t e d enough t o u n d e r g o t h e a d d i t i o n r e a c t i o n with butadiene. A regioselective product, l-diethylamino-3m e t h y l b u t e n e - 2 , was formed w i t h i s o p r e n e as the d i e n e r e a c t a n t u n d e r r e a c t i o n s c o n d i t i o n s s i m i l a r t o t h o s e f o r b u t a d i e n e ( 3 ) . In contrast, sodium alkylamide showed a lower degree of regios e l e c t i v i t y ( 4 ) . As r e p o r t e d p r e v i o u s l y (2,), l i t h i u m d i i s o p r o p y l amide e x h i b i t e d only a s l i g h t r e a c t i v i t y i n t h i s addition r e a c t i o n . A c t u a l l y , none o f a d d i t i o n p r o d u c t s was o b s e r v e d t o be formed i n a 6 0 - m i n u t e r e a c t i o n w h i c h was c a r r i e d out i n c y c l o hexane a t 50°C. I t has been f o u n d r e c e n t l y t h a t l i t h i u m d i i s o p r o p y l a m i d e i s a b l e t o i n i t i a t e i s o p r e n e p o l y m e r i z a t i o n a t 80° C t o an o l i g o m e r h a v i n g t h e a l k y l a m i n o g r o u p a t the end o f t h e p o l y m e r c h a i n . The r e a c t i o n c o n d i t i o n s a r e more s e v e r e t h a n t h o s e i n p r e v i o u s s t u d y . The degree of p o l y m e r i z a t i o n of the isoprene oligomers v a r i e d a c c o r d i n g t o the r a t i o o f amine t o amide. T h i s i s u n d e r standable i n terms o f a t r a n s f e r r e a c t i o n w h i c h i n v o l v e s f r e e amine. The w r i t e r and h i s coworkers focused t h e i r e f f o r t s on f i n d i n g the b e s t c o n d i t i o n s f o r g e t t i n g a m i n o - c o n t a i n i n g i s o p r e n e o l i g o m e r h a v i n g m o l e c u l a r w e i g h t o f 1000 t o 2000. In the c o u r s e of s t u d y , i t was n o t i c e d that "preformed o l i g o m e r " i n the r e a c t i o n s y s t e m was one o f the most s u i t a b l e t r a n s f e r r e a g e n t s f o r molecular design of the amino-containing oligomers having a m o l e c u l a r weight o f 1000. The r e a c t i o n s were c a r r i e d out w i t h lithium d i i s o p r o p y l a m i d e as initiator i n the absence of free amine b e c a u s e much lower m o l e c u l a r w e i g h t oligomers including members o f the t e r p e n o i d f a m i l y were f o r m e d i n the p r e s e n c e o f f r e e amine. The " p r e f o r m e d o l i g o m e r " has an a l l y l a m i n e s t r u c t u r e a t t h e chain-end. Examinations o f c h e m i c a l b e h a v i o r were a l s o carried out w i t h low m o l e c u l a r w e i g h t t e r t i a r y amines h a v i n g a l l y l a m i n e structure such as (i-Pr) N-CH -CH=C(CH ) Et N-CH -CH=CH and others. ' 2

2

3

2

2

2

R e s u l t s o f e x a m i n a t i o n o f GPC p a t t e r n s o f o l i g o m e r s p r e p a r e d i n t h e p r e s e n c e o f t h e s e t e r t i a r y amines d e m o n s t r a t e d that "the preformed o l i g o m e r " shows a u n i q u e b e h a v i o r as c h a i n t r a n s f e r r e a g e n t ; e s s e n t i a l l y no f o r m a t i o n o f t h e lower m o l e c u l a r w e i g h t o l i g o m e r s i s o b s e r v e d . Other a l l y l a m i n e homologues, i n c o n t r a s t , f a i l e d t o s u p p r e s s t h e f o r m a t i o n o f t h e lower m o l e c u l a r w e i g h t o l i g o m e r s . S t u d i e s t o e l u c i d a t e mechanism f o r the u n i q u e b e h a v i o r o f " t h e p r e f o r m e d o l i g o m e r " a r e now i n p r o g r e s s . As the w r i t e r r e p o r t e d p r e v i o u s l y , l i t h i u m the p r e s e n c e o f d i e t h y l a m i n e , underwent t h e one reaction with styrene (5) or divinylbenzene reaction, however, t o o k p l a c e between l i t h i u m and s t y r e n e . A s u r p r i s i n g r e s u l t , i n c o n t r a s t ,

diethylamide, i n t o one a d d i t i o n (DVB) (6). No diisopropylamide was o b t a i n e d i n

Bailey et al.; Initiation of Polymerization ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

3.

TSURUTA

25

Initiation Reactions in Ionic Polymerizations

the r e a c t i o n o f 1,4-DVB w i t h lithium diisopropylamide, which i n i t i a t e d a prompt p o l y m e r i z a t i o n o f 1,4-DVB a t 20°C i n t e t r a h y d r o f u r a n t o form a s o l u b l e p o l y m e r (7^)· R e m a r k a b l y enough, t h e propagation r e a c t i o n proceeded to g i v e a r e l a t i v e l y h i g h molec u l a r w e i g h t ( e . g . 100,000) p o l y m e r , e v e n i n t h e p r e s e n c e o f a large excess of diisopropylamine (e.g. i-Pr NH/i-Pr NLi molar r a t i o = 11/1).


9

The much g r e a t e r r e a c t i v i t y o f 1,4-DVB i n t h e p r o p a g a t i o n s t e p i s i n c o n t r a s t t o the lower r e a c t i v i t y o f i s o p r e n e . Poly (1,4-DVB) o b t a i n e d was s o l u b l e i n THF, b e n z e n e and chloroform., and gave t y p i c a l g e l p e r m e a t i o n c h r o m a t o g r a m s . When t h e p o l y m e r i z a t i o n was c a r r i e d o u t w i t h o n l y a s m a l l e x c e s s o f d i i s o p r o p y l amine, an i n s o l u b l e c r o s s l i n k e d p o l y m e r was f o r m e d i n a s i m i l a r way t o t h e r e a c t i o n i n t i t i a t e d w i t h b u t y l l i t h i u m . I n a n o n p o l a r solvent such as b e n z e n e , lithium diisopropylamide exhibited l i t t l e a b i l i t y t o add t o 1,4-DVB e v e n i n t h e p r e s e n c e o f e x c e s s amine. The n u c l e o p h i l i c i t y o f t h e p r o p a g a t i n g c a r b a n i o n s h o u l d be an i m p o r t a n t f a c t o r d e t e r m i n i n g t h e n a t u r e o f t h e p o l y m e r i z a t i o n . The c a r b a n i o n a t t h e g r o w i n g c h a i n end o f p o l y ( 1,4-DVB) i s so s t a b i l i z e d owing t o t h e e x t e n d e d c o n j u g a t i o n w i t h t h e p a r a - v i n y l group that the c a r b a n i o n a t t a c k s p r e d o m i n a n t l y t h e more r e a c t i v e double bond o f t h e DVB monomer. The p e n d a n t v i n y l group of poly(DVB) was found t o have a diminished reactivity toward nucleophilic reagents. This should be a n o t h e r reason f o r the a b s e n c e o f t h e c r o s s - l i n k i n g r e a c t i o n . Under t h e same c o n d i t i o n s , lithium isopropylamide, instead of lithium diisopropylamide, underwent t h e one t o one a d d i t i o n r e a c t i o n w i t h 1,4-DVB t o form 4-isopropylaminoethylstyrene. The s o l u b l e p o l y ( D V B ) r e a c t s w i t h various types o f amine, so t h a t i t i s p o s s i b l e to prepare a v a r i e t y of amino-containing polymer. I n i t i a t i o n o f N - C a r b o x y - q - A m i n o a c i d A n h y d r i d e ( N C A ) by a Amino Group

Primary

Starting f r o m a monomer o r p o l y m e r h a v i n g primary amino g r o u p s , Inoue and h i s c o w o r k e r s have r e c e n t l y p r e p a r e d a macromer (8) o r g r a f t c o p o l y m e r ( 9 ) h a v i n g p o l y p e p t i d e s i d e c h a i n s . They found t h a t the p o l y m e r i z a t i o n o f N-carboxy-CV-amino a c i d anhydride (NCA) was i n i t i a t e d by t h e p r i m a r y amino g r o u p s o f t h e o r i g i n a l monomer o r p o l y m e r t o f o r m t h e p o l y p e p t i d e s i d e c h a i n . T e r t i a r y amino g r o u p s d i d n o t i n i t i a t e t h e NCA p o l y m e r i z a t i o n . The mechanism o f NCA p o l y m e r i z a t i o n w i t h amine as i n i t i a t o r has a l s o been d i s c u s s e d e a r l i e r by many r e s e a r c h e r s ( 1 0 ) . "The a c t i v a t e d monomer mechanism" p r o p o s e d by B a m f o r d and Szwarc is one of the most widely accepted mechanisms. Proton a b s t r a c t i o n r e a c t i o n f r o m -NH- g r o u p o f NCA by t e r t i a r y amine i s t h e e s s e n t i a l s t e p f o r t h e f o r m a t i o n o f a c t i v a t e d monomer, w h i c h undergoes a nucleophilic attack at carbonyl carbon at 5th p o s i t i o n o f NCA t o c l e a v e t h e N C A - r i n g .


26

INITIATION

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POLYMERIZATION

The a c t i v a t e d monomer mechanism was b a s e d on t h e a s s u m p t i o n t h a t t h e m a j o r p a r t o f p r o p a g a t i o n r e a c t i o n was c a r r i e d o u t by NCA s p e c i e s r a t h e r t h a n NHCOOH o r - N H ( w i t h C 0 e l i m i n a t i o n ) 2

group a t the growing

2

c h a i n end.

HNR

3


HN-

NH—Ο

>

-j CO^ (-)N—CO^

NCA - j CO -| CCk. * HNCOOH^^N—CO-^

(

;

- NCA

More d e t a i l s o f t h e Inoue e x p e r i m e n t s a r e a s f o l l o w s : t h e poly (amino a c i d ) macromer was s y n t h e s i z e d i n THF by r e a c t i n g OL - b e n z y l - L - g l u t a m a t e (BLG) — NCA with N-methyl-N-(4-vinylphenethyl)-ethylenediamine. In their experiments, t h e NCA polymerization must be i n i t i a t e d by t h e p r i m a r y amino g r o u p i n ( I ) , b e c a u s e DP (number a v e r a g e ) o f t h e macromer ( I I ) was a l m o s t e q u a l t o t h e mole r a t i o of t h e NCA t o ( I ) , a n d t h e g e l p e r m e a t i o n chromatogram showed a u n i m o d a l peak f o r ( I I ) .

CH =CH-(

VCH CH N(CH )CH CH NH

2

2

2

3

2

2

+

2

η

|

J>

(1)

CH =CH-

-CH CH(Me )0 2

OCH CH (Me) 0 —} 2

of S t e r e o s p e c i f i c

2

blocked

prepolymer Initiation

( C H CH (Me) 0 —>-

P o l y m e r i z a t i o n of

chain

Methyloxirane

I t i s w i d e l y r e c o g n i z e d t h a t E ^ Z n - H ^ O s y s t e m i s one o f t h e most a c t i v e c a t a l y s t s f o r t h e s t e r e o s p e c i f i c p o l y m e r i z a t i o n of oxiranes. A variety of chemical s p e c i e s are formed i n the f o l l o w i n g way: r a p i d f o r m a t i o n o f e t h y l z i n c h y d r o x i d e , i t s a g g r e g a t i o n , and e l i m i n a t i o n o f e t h a n e t o f o r m z i n c o x i d e s t r u c t u r e . The maximum c a t a l y s t a c t i v i t y was a c h i e v e d when the mole r a t i o o f z i n c t o w a t e r was one t o one, where the p r e d o m i n a n t f o r m a t i o n of a s p e c i e s , E t ( Z n O ) H, ( I I I ) , was o b s e r v e d . I f we use less amount o f w a t e r , a n o t h e r s p e c i e s , E t ( Z n O ) Z n E t , ( I V ) , was also produced c o n c u r r e n t l y . C o n t r a r y t o the a n i o n i c n a t u r e o f the former species (III), the latter species (IV) exhibited a c a t i o n i c n a t u r e . F o r i n s t a n c e , more t h a n 95% o f r i n g c l e a v a g e o f m e t h y l o x i r a n e t a k e s p l a c e a t 0-CH bond w i t h s p e c i e s ( I I I ) , w h i l e the c l e a v a g e a t O-CH bond a l s o takes p l a c e c o n c u r r e n t l y w i t h species (IV). 2

a

A r e c e n t GPC study (Γ7) °f poly(methyloxirane) sample p r e p a r e d by E ^ Z n - H ^ O (one t o 0.1 s y s t e m ) c l e a r l y showed the c a t i o n i c n a t u r e o f t h i s c a t a l y s t s y s t e m . More t h a n 50 w e i g h t % o f the p o l y m e r o b t a i n e d was f o u n d t o be o l i g o m e r s i n c l u d i n g pentamer and lower m o l e c u l a r w i g h t compounds i n c o n t r a s t w i t h the h i g h m o l e c u l a r weight p o l y m e r o b t a i n e d w i t h E t Z n - H 0 , one t o one, system. 2

2


30

INITIATION

OF

POLYMERIZATION


C-NMR s t u d i e s o f t h e s e p o l y m e r s showed t h a t t h e s p e c t r u m o f t h e o l i g o m e r f r a c t i o n h a d v e r y c o m p l i c a t e d f e a t u r e s owing t o the i r r e g u l a r s t r u c t u r e admixed w i t h h e a d - t o - h e a d a n d t a i l - t o t a i l e n c h a i n m e n t s o f t h e monomeric u n i t , w h i c h a g a i n i s i n s h a r p contrast with the c l e a r - c u t NMR patterns f o r the polymers p r e p a r e d w i t h t h e one t o one c a t a l y s t s y s t e m . The a c t i v e s p e c i e s o f t h e d i e t h y l z i n c - m e t h a n o l s y s t e m was p r e v i o u s l y proven t o be z i n c d i m e t h o x i d e (18). C o n t r a r y t o t h e z i n c - w a t e r s y s t e m , no t r a c e o f c a t i o n i c n a t u r e was o b s e r v e d i n t h e z i n c - m e t h a n o l s y s t e m a t any r a t i o o f t h e two components. When r a c e m i c m e t h y l o x i r a n e i s p o l y m e r i z e d w i t h z i n c d i m e t h o x i d e , D-and L-monomers a r e s e p a r a t e l y i n c o r p o r a t e d i n t o g r o w i n g c h a i n s t o form a n i s o t a c t i c p o l y m e r c o n s i s t i n g o f p o l y ( D - m e t h y l o x i r a n e ) and p o l y ( L - m e t h y l o x i r a n e ) . T h i s s t e r e o s e l e c t i v e polymer i z a t i o n c a n be s a t i s f a c t o r i l y e x p l a i n e d i n terms o f t h e e n a n t i o m o r p h i c c a t a l y s t s i t e s model (18). The d * - s i t e s a c c e p t D - m e t h y l oxirane i n preference t o t h e L-monomer, resulting i n the f o r m a t i o n o f -DDDD- i s o t a c t i c s e q u e n c e s . The same s i t u a t i o n i s v a l i d f o r the l * - c a t a l y s t s i t e s . I t was most d e s i r a b l e f o r us t o e l u c i d a t e t h e s t e r e o c o n t r o l mechanism i n terms o f m o l e c u l a r l e v e l c o n s i d e r a t i o n s r a t h e r t h a n a phenomenological a p p r o a c h . No i n f o r m a t i o n , however, was a v a i l able concerning the c h i r a l s t r u c t u r e o f d*- and l * - c a t a l y s t s i t e s , b e c a u s e none o f t h e a c t i v e c a t a l y s t s p o s s e s s e s a w e l l - d e f i n e d s t r u c t u r e . The a c t i v e z i n c m e t h o x i d e , f o r i n s t a n c e , was a disordered powdery substance and i t s c a t a l y s t e f f i c i e n c y was e x t r e m e l y low. S e v e n t e e n y e a r s ago, we i s o l a t e d (1^9) an o r g a n o z i n c complex i n t h e form o f s i n g l e c r y s t a l , w h i c h h a d t h e c o m p o s i t i o n : [ΕtZnOCH ] 3

[Zn(0CH ) ] 3

2

I t was s o l u b l e i n b e n z e n e , a n d t h e b e n z e n e s o l u t i o n e x h i b i t e d a c a t a l y t i c a c t i v i t y f o r t h e o x i r a n e p o l y m e r i z a t i o n a t 80 C, b u t no a c t i v i t y a t room t e m p e r a t u r e . According t o the X-ray a n a l y s i s by K a s a i , t h e o r g a n o z i n c complex c o n s i s t e d o f t w o ^ n a n t i o m o r p h i c d i s t o r t e d c u b e s , d-cube and 1-cube ( 2 0 ) . I n t h e C-NMR s p e c t r u m o f t h e o r g a n o z i n c com p l e x , f o u r s i n g l e t s were o b s e r v e d . Two o f them were a s s i g n e d t o t h e i n n e r a n d o u t e r m e t h o x y - c a r b o n s , r e s p e c t i v e l y . We c a r r i e d o u t NMR a n a l y s i s o f a r e a c t i o n s y s t e m i n w h i c h t h e o r g a n o z i n c complex and r a c e m i c m e t h y l o x i r a n e were a l l o w e d t o r e a c t i n b e n z e n e ( 2 1 , 22, 2 3 ) . A s p e c t r u m o f t h e r e a c t i o n s y s t e m a t 30° C was p r o v e n t o be the simple overlapping of the i n d i v i d u a l spectrum of m e t h y l o x i r a n e and t h e z i n c c o m p l e x . No r e a c t i o n t o o k p l a c e a t 3 0 C. I n a s p e c t r u m a t 8 0 C, a number o f new s i g n a l s and shape c h a n g e s i n t h e o r i g i n a l s i g n a l s were o b s e r v e d owing t o t h e o c c u r rence o f the p o l y m e r i z a t i o n r e a c t i o n a t 80°C. A l l o f the observed s i g n a l s i n t h e r e a c t i o n s y s t e m c o u l d be e x p l a i n e d r e a s o n a b l y by e

e


3.

TSURUTA

31


t h e i n i t i a t i o n mechanism by one o f t h e i n n e r methoxy g r o u p s . T a c t i c i t y d a t a o f p o l y ( m e t h y l o x i r a n e ) p r e p a r e d by the o r g a n o z i n c complex was f o u n d t o a g r e e w e l l w i t h t h e p r e d i c t e d v a l u e s from t h e e n a n t i o m o r p h i c m o d e l . A p o s s i b l e mechanism i s as f o l l o w s : a t 8 0 C, two of the l o n g e s t bonds a r e l o o s e n e d . I f t h e bondl o o s e n i n g t a k e s p l a c e a t d-cube, t h e s t e r i c c o u r s e o f an e n t e r i n g monomer w i l l be i n f l u e n c e d by the c h i r a l s t r u c t u r e a r o u n d the central zinc atom. A molecular model study suggested that L-monomer w i l l be preferentially accepted in this particular example. The i n i t i a t i o n r e a c t i o n t a k e s p l a c e t h r o u g h the n u c l e o p h i l i c a t t a c k by the i n n e r methoxy g r o u p . T h i s may be t h e o r i g i n o f t h e l * - c a t a l y s t s i t e . The p r o b a b i l i t y o f t h e bond l o o s e n i n g i n 1-cube i s e x a c t l y the same as t h a t i n d-cube, so t h a t an e q u a l number of d * - s i t e s and l*-sites will be established i n the reaction system. T h i s e x p l a i n s the e x p e r i m e n t a l r e s u l t s that poly(D-methyloxirane) and p o l y ( L - m e t h y l o x i r a n e ) are formed in e q u i m o l a r amounts i n the r e a c t i o n s y s t e m .


e

Comparison of S t e r e o s p e c i f i c P o l y m e r i z a t i o n of M e t h y l o x i r a n e Ziegler-Natta Polymerization

with

The l a s t t o p i c t h a t i s t o be d i s c u s s e d i s t h e c o m p a r i s o n o f o r g a n o z i n c complex w i t h Z i e g l e r - N a t t a c a t a l y s t s . It i s w i d e l y a c c e p t e d t h a t the f o r m a t i o n of i s o t a c t i c p o l y p r o p y l e n e i s b r o u g h t about by t h e c h i r a l s t r u c t u r e , d* o r 1*, o f t h e t i t a n i u m s p e c i e s i n the c a t a l y s t s y s t e m . The c o n c e p t o f the s t e r i c c o n t r o l i n p r o p y l e n e p o l y m e r i z a t i o n i s t h e same as t h a t i n t h e m e t h y l o x i r a n e p o l y m e r i z a t i o n s w h i c h have been d i s c u s s e d i n the foregoing sections. An active center having d*or 1*c h i r a l i t y i s formed a l o n g t h e c r y s t a l s u r f a c e o f ô' -titanium trichloride. our

v

One of t h e most i m p o r t a n t p o i n t s o f argument about the n a t u r e o f t h e " s u p e r a c t i v e Z i e g l e r c a t a l y s t " i s the r o l e o f e t h y l b e n z o a t e . The w r i t e r w i l l d i s c u s s t h i s i n r e f e r e n c e t o a c a t a l y s t s y s t e m w h i c h was r e p o r t e d (24) r e c e n t l y by K a s h i w a o f M i t s u i P e t r o c h e m i c a l Co. As the f i r s t step f o r the c a t a l y s t p r e p a r a t i o n , the b a l l milled magnesium c h l o r i d e was allowed to stand w i t h t i t a n i u m t e t r a c h l o r i d e a t 80° C f o r two h o u r s . The M g C l ^ T i C l ^ , i . e . , T i C l ^ a d s o r b e d on M g C l ^ was t h e n t r e a t e d w i t h A l E t ^ and ethyl b e n z o a t e (EB) a t 6 0 ° C . The c a t a l y s t ( 2 4 ) ) t h u s o b t a i n e d gave t h e following analytical results:

Ti

CI

Mg

Al

EB

weight percent

0.6

71.0

28.0

0.3

1.2

mole ratio

1.2

1.1

0.8

200

115


32

INITIATION

OF

POLYMERIZATION

I t i s t o be n o t e d t h a t T i , A l and e t h y l b e n z o a t e a r e p r e s e n t i n n e a r l y equal molar r a t i o . R e s u l t s of propylene p o l y m e r i z a t i o n w i t h t h i s type o f c a t a l y s t showed t h a t e t h y l b e n z o a t e e n h a n c e d the r a t e o f f o r m a t i o n o f i s o t a c t i c p o l y p r o p y l e n e , w h i l e i t d e c r e a s e d t h e r a t e f o r a t a c t i c p o l y p r o p y l e n e . E t h y l b e n z o a t e seems t o make t h e c a t a l y t i c s i t e s s t e r i c a l l y more s p e c i f i c .


A c c o r d i n g t o Kashiwa, T i C l , chemisorbs l o o s e l y a t the nons p e c i f i c s i t e so t h a t some o f T i C l ^ m o l e c u l e s may be e x t r a c t e d by ethyl benzoate, which causes the d e a c t i v a t i o n o f the nonspecific site. Furthermore, non-specific sites having the s t r o n g e r a c i d i t y w i l l be p o i s o n e d more e a s i l y by e t h y l b e n z o a t e . R e s u l t s o f s t u d y on t h e m o l e c u l a r w i g h t d i s t r i b u t i o n o f t h e "isotactic fraction" of polypropylene showed that isotactic polymer having higher molecular weight was produced i n the p r e s e n c e o f e t h y l b e n z o a t e . T e r m i n a t i o n r e a c t i o n i s b e l i e v e d t o be a t r a n s f e r o f g r o w i n g c h a i n " from T i - c e n t e r t o A l - c e n t e r and t h e c o o r d i n a t i o n o f e t h y l b e n z o a t e o n t o aluminum s h o u l d be o p p o s i t e to t h e d i r e c t i o n o f e l e c t r o n flow f o r the t r a n s f e r reaction, w h i c h makes t h e t r a n s f e r r e a c t i o n more d i f f i c u l t t o t a k e p l a c e . ?î

S y n d i o t a c t i c propagation of propylene i s know t o be c a t a l y z e d by homogeneous v a n a d i u m c a t a l y s t (1_8). I n t h e p o l y p r o p y l e n e samples p r e p a r e d w i t h t h e homogeneous c a t a l y s t s , the r e l a t i v e p o p u l a t i o n o f i s o - , h e t e r o - and s y n d i o t a c t i c t r i a d s i s i n a c c o r d ance w i t h t h a t p r e d i c t e d from t h e f i r s t o r d e r Markov model ( 2 5 , 2 6 ) . T h e r e i s no c h i r a l s t r u c t u r e a r o u n d t h e homogeneous v a n a d i u m species. The s t e r e o c h e m i s t r y o f t h e e n t e r i n g monomer i s cont r o l l e d by t h e c h i r a l i t y o f t h e g r o w i n g c h a i n end, i n c o n t r a s t w i t h the i s o t a c t i c p r o p a g a t i o n . Inoue e t a l . (21) f o u n d t h a t a p o r p h y r i n - Z n a l k y l c a t a l y s t polymerized methyloxirane t o form a p o l y m e r h a v i n g s y n d i o - r i c h tacticity. The relative p o p u l a t i o n of the t r i a d tacticities suggests that the s t e r e o c h e m i s t r y of the placement of incoming monomer i s c o n t r o l l e d by t h e c h i r a l i t y o f t h e t e r m i n a l and p e n u l t i m a t e u n i t s i n t h e g r o w i n g c h a i n . T h e r e i s no c h i r a l i t y a r o u n d t h e Z n - p o r p h y r i n c o m p l e x . A c h i r a l z i n c complex forms s y n d i o - r i c h p o l y ( m e t h y l o x i r a n e ) , w h i l e c h i r a l z i n c complex, as s t a t e d above, forms i s o t a c t i c - r i c h p o l y ( m e t h y l o x i r a n e ) . The s i t u a t i o n i s j u s t t h e same as t h a t f o r p r o p y l e n e p o l y m e r i z a t i o n s . A c h i r a l v a n a d i u m catalyst produces syndiotactic polypropylene, while chiral t i t a n i u m c a t a l y s t produces i s o t a c t i c polypropylene.

Literature Cited 1. 2. 3.

Imai, N.; Narita, T.; Tsuruta, T. Tetrahedron Lett. 1971, 38, 3517. Narita, T.; Imai, N.; Tsuruta, T. Bull. Chem. Soc. Japan 1973, 46, 1242. Narita, T., Nitadori, Y.; Tsuruta, T. Polymer J . 1977, 9, 191.


3. 4. 5. 6. 7. 8.


9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27.

TSURUTA


33

Noren, G. K. J. Org. Chem. 1975, 40, 967. Narita, T.; Yamaguchi, T; Tsuruta, T. Bull. Chem. Soc. Japan 1973, 46, 3825. Tsuruta, T.; Narita, T.; Nitadori, Y.; Irie, T, Makromol. Chem. 1976, 177, 3255. Nitadori, Y.; Tsuruta, T. Makromol. Chem. 1978, 179, 2069. Maeda, M.; Inoue, S. Makromol. Chem., Rapid Commun. 1981, 2, 537. Kimura, M.; Egashira, T.; Nishimura, T.; Maeda, M.; Inoue, S. Makromol. Chem. 1982, 183, in press. Sekiguchi, H. Pure & Appl. Chem. 1981, 53, 1689. Ikeda, M.; Hirano, T.; Nakayama, S.; Tsuruta, T. Makromol. Chem. 1974, 175, 2775. Tsuruta, T.; Tsushima, R. Makromol. Chem. 1976, 177, 337. Aoi, H.; Ishimori, M.; Yoshikawa, S.; Tsuruta, T. J. Organometal. Chem. 1975, 85, 241. Takeichi, T.; Arihara, M.; Ishimori, M.; Tsuruta, T. Tetrahedron 1980, 36, 3391. Aida, T.; Inoue, S. Macromolecules 1981, 14, 1162. Aida, T.; Inoue, S. Macromolecules 1981, 14, 1166. Tsuruta, T. Pure & Appl. Chem. 1981, 53, 1745. Tsuruta, T. J. Polymer Sci. 1972, D6, 179. Ishimori, M.; Tomoshige, T.; Tsuruta, T. Makromol. Chem. 1968, 120, 161. Ishimori, M.; Hagiwara, T.; Tsuruta, T.; Kai, Y., Yasuoka, N.; Kasai, N. Bull. Chem. Soc. Japan 1976, 49, 1165. Tsuruta, T. J. Polymer Sci. Polymer Symposium 1980, 67, 73. Hagiwara, T.; Ishimori, M.; Tsuruta, T. Makromol. Chem. 1981, 182, 501. Tsuruta, T. Makromol. Chem. Suppl. 1981, 5, 230. Kashiwa, N. Paper presented at "International Symposium on Transition Metal Catalyzed Polymerizations: Unsolved Problems" (August, 1981, Michigan Molecular Institute). Doi, Y. Macromolecules 1979, 12, 249; 1012. Doi, Y.; Ueki, S.; Keii, T. Macromolecules 1979, 12, 814. Takeda, N.; Inoue, S. Makromol. Chem. 1978, 179, 1377.

RECEIVED September 10, 1982


or Nucleophile in

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