Kinetics and Mechanism of Anionic Polymerization of Lactones

18

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on September 7, 2015 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0166.ch018

Kinetics and Mechanism of Anionic Polymerization of Lactones STANISLAW

SŁOMKOWSKI

and S T A N I S L A W

PENCZEK

Polish Academy of Sciences, Center of Molecular and Macromolecular Studies, 90-362Łodz, Poland

In s p i t e o f hundreds o f papers and p a t e n t s devoted to the p o l y m e r i z a t i o n o f l a c t o n e s o n l y r e c e n t l y t h e first d a t a on the r a t e s o f elementary r e a c t i o n s became a v a i l a b l e [1,2]. The earlier and comprehensive kinetic study by Hall [3] gave the r a t e coefficients f o r a number o f l a c t o n e s , w i t h o u t however d e t e r m i n i n g t h e i n v o l v e d r a t e components, i.e. r a t e c o n s t a n t s f o r v a r i o u s i o n i c s p e c i e s s i m u l t a n e o u s l y p r e s e n t , in t h e s t u d i e d solutions. More r e c e n t l y T e y s s i e ' determined t h e r a t e constants in the p o l y m e r i z a t i o n o f ε-caprolactone (εCL) initiated w i t h aluminium a l k o x i d e s , b e l i e v i n g t h a t t h e c o v a l e n t s p e c i e s a r e t h e o n l y ones r e s p o n s i b l e f o r propagation [4]. For t h e same monomer Yamashita e s t i m a t e d t e n t a t i v e l y rate coefficients o f p r o p a g a t i o n u s i n g an a n i o n i c initiator [5]. Lenz in h i s s t u d i e s o f s u b s t i t u t e d β-propiolactones (βPL) o b s e r v e d p e c u l i a r i n f l u e n c e o f s t r u c t u r e on reactivity t h a t can have its origin in the multiplicity o f ionic s t r u c t u r e s i n v o l v e d [ 6 ] . Thus, in t h e p r e s e n t paper we r e v i e w the a v a i l a b l e d a t a , p e r t i n e n t t o t h e kinetics and mechanism o f anionic p o l y m e r i z a t i o n o f l a c t o n e s and d i s c u s s t h e r e c e n t d a t a o f our own, g i v i n g e v e n t u a l l y an a c c e s s t o the r a t e c o n s t a n t s o f p r o p a g a t i o n on macroions and macroion-pairs. Some u n u s u a l monomer p r o p e r t i e s and major c h a r a c t e r i s t i c s o f p o l y m e r i z i n g systems i n v o l v i n g lactone's? There a r e a t l e a s t two f e a t u r e s o f monomeric l a c t o n e s t h a t make them p a r t i c u l a r l y attractive f o r m e c h a n i s t i c s t u d i e s . Lactones a r e h i g h l y p o l a r compounds (e.g. &PL: D = 46, eCL: D = 40, b o t h a t 25°) and c a n r e a c t ambidently, namely by 0 - a l k y l o r 0 - a c y l 0097-6156/81/0166-0271$05.00/0 © 1981 American Chemical Society

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


272

ANIONIC POLYMERIZATION

r i n g o p e n i n g . The l a t t e r a b i l i t y opens an i m p o r t a n t new d i r e c t i o n f o r s t u d i e s o f c o p o l y m e r i z a t i o n . Since both 3PL and eCL have been shown t o g i v e l i v i n g systems in a n i o n i c p o l y m e r i z a t i o n [1,4] one c a n e x p e c t t h a t t h e q u a n t i t a t i v e understanding o f the a n i o n i c polymerization o f l a c t o n e s w i l l a l l o w t o answer some q u e s t i o n s open by s t u d i e s o f t h e l e s s p o l a r monomers and, t h u s , l e s s a c c e n t u a t i n g the n o v e l t y o f these systems in comparison w i t h h y d r o c a r b o n s , namely e t h y l e n e o x i d e and p r o p y l e n e sulphide [7,8]. Initiation

and S t r u c t u r e o f Growing S p e c i e s

The e a r l i e r d a t a on i n i t i a t o r s used, and on t h e mechanism o f i n i t i a t i o n a r e c o m p r e h e n s i v e l y collected in the Lundberg's r e v i e w [j9] . U n f o r t u n a t e l y , t h e e v i d e n c e p r e s e n t e d t i l l now on t h e mode o f i n i t i a t i o n and bond c l e a v a g e ( O - a l k y l o r O - a c y l ) as a f u n c t i o n o f i n i t i a t o r and monomer s t r u c t u r e s :

is n o t , a t l e a s t in our judgment, s u f f i c i e n t l y convincing and t h i s a r e a w i l l have t o be r e i n v e s t i g a t e d by u s i n g the modern i n s t r u m e n t a l methods. N e v e r t h e l e s s , t h e s u g g e s t i o n o f Cherdron [1Q], t h a t t h e growing s p e c i e s for polymerization of unsubstituted lactones are a l c o h o l a t e a n i o n s has been w i d e l y a c c e p t e d , $ - p r o p i o l a c t o n e s , however, b e i n g a p p a r e n t l y an e x c e p t i o n and propagate w i t h c a r b o x y l a t e anions [ l l ] . T h i s p a r t i c u l a r b e h a v i o u r o f 3PL is p r o b a b l y due to its lower b a s i c i t y and h i g h e r e l e c t r o p h i l i c i t y in c o m p a r i s o n w i t h eCL (pK = 10.06 f o r 3PL and 5.31 f o r eCL r e s p e c t i v e l y [ 1 1 ] ) . Thus, even a weaker n u c l e o p h i l e , l i k e c a r b o x y l a t e a n i o n c a n a c c o m p l i s h i n i t i a t i o n o f 3PL. T e r t i a r y amines i n i t i a t e p o l y m e r i z a t i o n by zwitteri o n f o r m a t i o n [13.14]. R e c e n t l y we s t u d i e d i n i t i a t i o n o f 3PL p o l y m e r i z a t i o n w i t h phosphines, i n c l u d i n g the o p t i c a l l y a c t i v e methyl,η-propyl,phenylphosphine, and e s t a b l i s h e d t h e structure o f the betaine-type species directly by P-NMR ( 6 P = 28.2 ppm) [15,16]. 31

3 1


18.

SLOMKOWSKi AND PENCZEK

R-P

Lactones

273

(1)

+

ο

ι Ζ

ι

Ζ

0—c


0 Z w i t t e r i o n s a r e s t a b l e and c a n p r o v i d e a l i v i n g p o l y m e r i z a t i o n , however, a t t h e s m a l l e r c h a i n l e n g h t ( s m a l l e r d i s t a n c e between i o n s ) f o r m a t i o n o f y l i d s was noted : ~

R P=CH-CH C-OfCH CH ) CH CH COOH 3

2

2

2

n1

2

2

S i m i l a r p r o c e s s o f d e c o m p o s i t i o n o f b e t a i n e s has been known in case o f a r o m a t i c amines, b u t p r o c e e d i n g w i t h e l i m i n a t i o n o f p r o t o n a t e d amine [ 1 7 ] . Data on k i n e t i c s o f i n i t i a t i o n a r e a v a i l a b l e o n l y f o r i n i t i a t i o n o f $PL p o l y m e r i z a t i o n w i t h t r i p h e n y l p h o s p h i n e and methyl,η-propyl,phenylphosphine [ 1 6 ] . The r a t e c o n s t a n t s k i ( c f . eqn ( 1 ) ) were found a t 25° to be e q u a l t o 2.3-10" mole" . 1 .s"* and 5.2.10~ m o l e " .1»s~ r e s p e c t i v e l y . 5

1

1

1

4

1

Mechanism and K i n e t i c s o f P r o p a g a t i o n K i n e t i c s o f anionic ring-opening polymerization has h i t h e r t o been q u a n t i t a t i v e l y s t u d i e d and gave f o r two monomers, namely e t h y l e n e o x i d e [18,19] and p r o p y l e n e s u l f i d e [8,20] . S t u d i e s on t h e s e systems r e v e a l e d t h a t t h e l i v i n g c o n d i t i o n s c a n be a c h i e v e d , f a c i l i t a t i n g q u a n t i t a t i v e d e t e r m i n a t i o n o f rateconstants o f p r o p a g a t i o n on v a r i o u s k i n d s o f i o n i c growing species. These and r e l a t e d h e t e r o c y c l i c monomers a r e u s u a l l y h i g h l y p o l a r and s t r o n g l y n u c l e o p h i l i c compounds. D u r i n g p o l y m e r i z a t i o n c h a i n s c o n t a i n i n g heteroatoms are formed and t h e y c a n , as w e l l as monomers themselves, i n t e r a c t w i t h components o f i o n i c growing s p e c i e s . The i n t e r a c t i o n o f the m a c r o i o n - p a i r s w i t h t h e elements o f the c h a i n s has w e l l been documented f o r t h e p o l y m e r i z a t i o n o f e t h y l e n e o x i d e [2]. L a c t o n e s b e l o n g t o t h e most p o l a r compounds and c o n s t i t u t e a group o f monomers o f h i g h e s t d i e l e c t r i c c o n s t a n t s ( c f . p r e c e d i n g s e c t i o n ) . Thus, one c o u l d e x p e c t even more pronounced e f f e c t s in t h e polymerization


ANIONIC


274

POLYMERIZATION

o f t h i s c l a s s o f monomers and due t o i n t e r a c t i o n s o f monomers t h e m s e l v e s w i t h d i f f e r e n t i o n i c g r o w i n g species. We have r e c e n t l y shown, t h a t the l i v i n g c o n d i t i o n s can be a c h i e v e d in the p o l y m e r i z a t i o n o f 3PL by u s i n g as i n i t i a t o r s compounds p r o v i d i n g h i g h e r p r o p o r t i o n o f m a c r o i o n s . T h i s f a v o u r a b l y d e c r e a s e s the i m p o r t a n c e o f the p a r a s i t i c s i d e r e a c t i o n s by r e l a t i v e l y i n c r e a s i n g the o v e r a l l r a t e o f p r o p a g a t i o n p r o c e s s e s [2]. The f o l l o w i n g i n i t i a t o r s were used:

2

1

(where in jL the crown e t h e r is dibenzo-18-crown-6 e t h e r (DBC) and Φ in 2 d e n o t e s C Ô H ) . A p p a r e n t l y s i m i l a r enhancement o f the p r o p a g a t i o n p r o c e s s e s was a c h i e v e d w i t h c r y p t a t e d c a t i o n s a l t h o u g h in t h i s c a s e a s p e c i a l c a r e has t o be t a k e n not t o i n t r o d u c e the z w i t t e r i o n i c i n i t i a t i o n . Data on k i n e t i c s o f p r o p a g a t i o n , as it has a l r e a d y been m e n t i o n e d , are a v a i l a b l e a t p r e s e n t o n l y f o r p o l y m e r i z a t i o n o f u n s u b s t i t u t e d and s u b s t i t u t e d $PL [1-3.6]. i n i t i a t e d w i t h c a r b o x y l a t e s , and f o r 3PL and eCL, i n i t i a t e d with b i m e t a l l i c oxoalkoxides [4,23]. In a l l but one o f t h e s e s t u d i e s the a p p a r e n t r a t e c o n s t a n t s o f p r o p a g a t i o n were d e t e r m i n e d . The o b s e r v e d a p p a r e n t p r o p a g a t i o n r a t e c o n s t a n t (kâP) is a summ o f p r o d u c t s o f r a t e c o n s t a n t s on v a r i o u s forms o f a c t i v e c e n t e r s ( e . g . f r e e i o n s , i o n - p a i r s , a g g r e g a t e s ) and t h e i r f r a c t i o n s in the p o l y m e r i z i n g m i x t u r e 5

L2JL],

k

o

P P

=

a

k

' D

+

k

&- n

* .'.

( 3 )

where a and 3 a r e f r a c t i o n s o f f r e e i o n s and i o n - p a i r s . Any change o f l a c t o n e s t r u c t u r e , o f n a t u r e o f s o l v e n t or t e m p e r a t u r e w i l l i n f l u e n c e the r a t e c o n s t a n t s o f e l e m e n t a r y p r o p a g a t i o n r e a c t i o n s and p o s i t i o n o f e q u i l i b r i a between d i f f e r e n t k i n d s o f a c t i v e c e n t e r s . In our r e c e n t l y p u b l i s h e d p a p e r on k i n e t i c s o f e l e m e n t a r y r e a c t i o n s in p o l y m e r i z a t i o n o f 3PL, i n i t i a t e d w i t h a c e t a t e a n i o n w i t h p o t a s s i u m crowned w i t h d i b e n z o -18-crown-6 e t h e r (DBCK ) c o u n t e r i o n in methylene +


18.


Lactones

275

d i c h l o r i d e , we d e t e r m i n e d kp and kp (where kp denotes r a t e c o n s t a n t o f p r o p a g a t i o n on crowned m a c r o i o n - p a i r s ) [i] . I n t h e t e m p e r a t u r e r a n g i n g from -20 t o +35°C... and f o r s t a r t i n g monomer c o n c e n t r a t i o n s 1.0 and 3.0 m o l e - l " p o l y m e r i z a t i o n was found t o be t h e l i v i n g p r o c e s s w i t h m o l e c u l a r w e i g h t o f polymer i n c r e a s i n g l i n e a r l y w i t h monomer c o n v e r s i o n . C o n d u c t i v i t y measurements f o r s o l u t i o n s o f l i v i n g p o l y - 3 P L w i t h DBCK c o u n t e r i o n in C H 2 C I 2 / 3 P L m i x t u r e i n d i c a t e d t h a t macroions and m a c r o i o n - p a i r s a r e p r e s e n t in the system. I n F i g . l , t a k e n from Ref. 2 t h e V a n t , Hoff,s p l o t s are given f o r d i s s o c i a t i o n constants o f p o l y - 3 P L m a c r o i o n - p a i r s w i t h DBCK c o u n t e r i o n (Κβ) and s i m i l a r p l o t f o r d i s s o c i a t i o n constants o f Ph4B"DBCK (KDI). D i s s o c i a t i o n o f P h 4 B ~ D B C K was i n v e s t i g a t e d because t h i s s a l t was f u r t h e r used in t h e k i n e t i c measurements t o s h i f t t h e e q u i l i b r i u m between macroi o n s and m a c r o i o n - p a i r s towards t h e l a t t e r ones. In T a b l e 1 v a l u e s o f thermodynamic e q u i l i b r i u m parameters and v a l u e s o f Kj) and Kp a t 25° a r e g i v e n .


1

+

+

+

+

T a b l e

1

D i s s o c i a t i o n c o n s t a n t s and p e r t i n e n t a c t i v a t i o n parameters Solvent

p o l y - 3PL,

DBCK

+

(C H ) B",DBCK 6

AH

4

AS

D1

+

4

D1

K

D1°

CH Cl2/3PL 2

[3PL] = 3.0 0

mole-l"

0.5±2

5

-18±3 5-10"

3

0.6±0.5

-10±2 2.3.10"

1

CH2C1 /3PL 2

[3PL] = 1.0 0

mole-l"

0.6±0.2 -22±2 5.6.10"-6

1

Δ Η and ΛΗβΐ in k c a l - m o l e " ; ASD deg ; and in mole«l" . 1

β

and AS

D1

in

1

cal-mole" *

1

By u s s i n g t h e Fuoss» e q u a t i o n d i s t a n c e (a) between i o n s c o n s t i t u t i n g t h e i o n - p a i r was c a l c u l a t e d . For [3PL]o = 1.0 m o l e - l - a=3.3 A° and f o r [ B P L ] = 3.0 a=2.6 A , b o t h b e i n g independent on t e m p e r a t u r e . 1

0

0



276 ANIONIC POLYMERIZATION


18.


to

Lactones

Ο

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Γ>-

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CM

m Τ -

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278

Propagation rateconstants on macroions (kp) and on m a c r o i o n - p a i r s (k?) were determined from t h e dependence o f kâPP o n t h e f r a c t i o n o f m a c r o i o n s (degree of d i s s o c i a t i o n a ) . For systems w i t h only macroions and m a c r o i o n - p a i r s p a r t i c i p a t i n g in e q u i l i b r i u m e q n (3) simplifies to:


k P

=

k©

•

«(ΐς -

(4)

k© )

Degree o f d i s s o c i a t i o n (a) was c a l c u l a t e d b y u s i n g v a l u e s o f Kj) a n d a s s u m i n g t h e q u a n t i t a t i v e initiation. I n some e x p e r i m e n t s Ph4B"DBCK w a s a d d e d w i t h p u r p o s e to increase f r a c t i o n ofmacroion-pairs. V a l u e s o f k ~ a n d k § f o r ePL p o l y m e r i z a t i o n w i t h s t a r t i n g m o n o m e r c o n c e n t r a t i o n s 1.0 a n d 3 . 0 m o l e « Ι * " c a r r i e d o u t in t e m p e r a t u r e r e g i o n f r o m - 2 0 t o 35°C... a r e g i v e n in T a b l e 2 ( P v e f . 2). From t h e A r r h e n i u s p l o t s ( F i g . 2 ) t h e a c t i v a t i o n parameters f o r propagation on macroions and on macro i o n - p a i r s w e r e e v a l u a t e d . T h e y a r e g i v e n in T a b l e 3 . +

1

T a b l e

3

A c t i v a t i o n parameters f o r propagation on macroions and o n m a c r o i o n - p a i r s in p o l y m e r i z a t i o n o f $ P L w i t h D B C K counterion. +

Solvent

ASJ(-)

AHjJ(-) kcal-mole"

1

e.u.

ΔΗ*(φ) kcal-mole"

AS*(©) 1

e.u.

CH 2/ePL 2

cl

' [BPLJ = 3.0 0

mole-l"

16±1

-10±4

1

CH C1 /3PL 2

6

2

[3PL] = 1.0 0

mole-1"

6±1

±

1

"

5

2

±

4

-40±5

1

Before discussing r e a c t i v i t i e s of both kinds o f a c t i v e c e n t e r s it is n e c e s s a r y t o e s t a b l i s h t h e s t r u c t u r e o f i o n - p a i r s i n v o l v e d in p r o p a g a t i o n . Independence o f Δ Η * ( φ ) a n d ASp(è) o n t h e s t a r t i n g c o n c e n t r a t i o n o f monomer, b e i n g t h e most p o l a r component o f t h e s y s t e m , ( T a b l e 3) a n d l i n e a r i t y o f A r r h e n i u s p l o t s f o r k©


18.


Lactones

279

ο

·


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à"

tri "δ H "S

gOII • * * ·

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£ε



280


( F i g . 2 ) suggest t h a t o n l y one t y p e o f i o n - p a i r s is p r e sent in t h e system. E n t h a l p y o f d i s s o c i a t i o n c l o s e t o z e r o and e n t r o p y o f d i s s o c i a t i o n h i g h e r than -25 e.u. i n d i c a t e t h a t a d d i t i o n a l s o l v a t i o n o f i o n s upon d i s s o c i a t i o n is low and e n t h a l p y o f t h i s s o l v a t i o n m e r e l y b a l a n c e s t h e e l e c t r o s t a t i c energy n e c e s s a r y t o s e p a r a t e t h e i o n s . A p p a r e n t l y , t h e o n l y moderate i n c r e a s e o f s o l v a t i o n o f i o n s accompanying t h e d i s s o c i a t i o n is observed because the charges a r e d i f f u s e d in b o t h c a r b o x y l a t e a n i o n and DBCK c a t i o n . D i f f u s i o n o f charge in DBCK c a t i o n means t h a t due t o p o l a r i z a t i o n some p o s i t i v e charge is i n d u ced in t h e e x t e r i o r p a r t o f crown e t h e r m o l e c u l e . Low v a l u e o f t h e i n t e r i o n i c d i s t a n c e ( a 3 A°) i n d i c a t e s t h a t t h e i o n - p a i r s a r e t h e c o n t a c t ones. T h e r e f o r e , we p o s t u l a t e f o r the s t r u c t u r e o f i o n - p a i r s the d i s k - l i k e shape o f crowned c a t i o n w i t h a n i o n a p p r o a c h i n g t h e c a t i o n p e r p e n d i c u l a r l y t o t h e p l a n e o f t h e d i s k , and assume t h a t t h i s is t h e o n l y k i n d o f i o n - p a i r s p a r t i c i p a t i n g in p o l y m e r i z a t i o n . Thus, t h e o t h e r isomer p o s t u l a t e d by Hogen Esch and Smid in t h e p o l y m e r i z a t i o n w i t h c a r b a n i o n s [24,2Ji], where K c a t i o n is w i t h d r a w n from the immediate p r o x i m i t y o f a n i o n , and p h y s i c a l l y sepa r a t e d from it by elements o f t h e crown e t h e r does n o t have t o be i n v o l v e d in t h e p o l y m e r i z a t i o n o f $PL. A c t i v a t i o n p a r a m e t e r s f o r p r o p a g a t i o n on macroions were found t o depend s i g n i f i c a n t l y on t h e s t a r t i n g c o n c e n t r a t i o n o f &PL, whereas t h e c o r r e s p o n d i n g a c t i v a t i o n p a r a m e t e r s f o r p r o p a g a t i o n on m a c r o i o n - p a i r s were found t o be v i r t u a l l y independent on t h e composi t i o n o f t h e medium. A p p a r e n t l y , s o l v a t i o n o f i o n - p a i r s is n o t v e r y much d i f f e r e n t from s o l v a t i o n o f a c t i v a t e d complex. Dependence o f ΔΗί(-) and AS*(-) on t h e s t a r t i n g c o n c e n t r a t i o n o f 3PL, showing a t y p i c a l compensation phenomenon ( T a b l e 3) c a n o n l y have its o r i g i n in t h e s p e c i f i c s o l v a t i o n o f t h e growing s p e c i e s by m o l e c u l e s o f monomer i t s e l f . I t does n o t mean, however, t h a t m o l e c u l e s o f monomer engaged in t h e s o l v a t i o n s h e l l are p r o p e r l y o r i e n t e d f o r t h e c h e m i c a l change. B e i n g p r o p e r l y o r i e n t e d from t h e s o l v a t i o n view p o i n t t h e s e m o l e c u l e s e n e r g e t i c a l l y d i f f e r from an average m o l e c u l e in b u l k s o l u t i o n and it may be n e c e s s a r y t o remove, r e o r i e n t and/or p r o v i d e a d d i t i o n a l energy t o t h e s e p a r t i c u l a r m o l e c u l e s t o f o r c e them t o p a r t i c i p a t e in the c h e m i c a l change ( p r o p a g a t i o n s t e p ) . At h i g h e r s t a r t i n g c o n c e n t r a t i o n o f 3PL i n c r e a s e s the energy needed t o d e s o l v a t e t h e ground s t a t e in o r d e r t o p e r m i t t h e c h e m i c a l r e a c t i o n t o p r o c e e d . Thus, w i t h i n c r e a s i n g t h e s t a r t i n g c o n c e n t r a t i o n o f monomer: +

+

+

p


18.

SLOMKOWSKI

AND PENCZEK

281

Lactones 1

1

[&PL]o from 1.0 m o l e - l - t o 3.0 m o l e ' l ' the e n t h a l p y o f a c t i v a t i o n i n c r e a s e s as much as by 10.0 k c a l - m o l e " . Schematic r e p r e s e n t a t i o n o f two modes o f s o l v a t i o n : namely n o n s p e c i f i c f o r the m a c r o i o n - p a i r s and s p e c i f i c f o r m a c r o i o n s is g i v e n below :


1

(where S and M denote s o l v e n t and monomer m o l e c u l e s respectively). Thus, we assume, t h a t in case o f the m a c r o i o n - p a i r s o l v e n t and monomer m o l e c u l e s a r e n o t o r i e n t e d in any s p e c i f i c way and d i s o r d e r l y pack the a v a i l a b l e space around the m a c r o i o n - p a i r . On the c o n t r a r y , m a c r o a n i o n is s p e c i f i c a l l y s o l v a t e d a t l e a s t by monomer m o l e c u l e s , due t o the s t r o n g i n t e r a c t i o n between a n e g a t i v e charge and h i g h l y p o l a r monomer and the f u r t h e r passage t o the t r a n s i t i o n s t a t e , b e i n g much l e s s p o l a r t h a n the ground s t a t e o f m a c r o a n i o n , r e q u i r e s h i g h e r energy. T h i s is much more apparent a t h i g h e r monomer c o n c e n t r a t i o n . Comparison o f e n t r o p i e s o f a c t i v a t i o n f o r propaga tionβon m a c r o i o n s and on m a c r o i o n - p a i r s l e a d s t o con c l u s i o n s b e i n g hand in hand w i t h the a n a l y s i s o f e n t h a l p i e s . The l a r g e n e g a t i v e e n t r o p y o b s e r v e d f o r m a c r o i o n - p a i r s (-52.0 c a l - m o l e " *deg"" ) may r e f l e c t f o r m a t i o n o f t r a n s i t i o n s t a t e w i t h more i o n i c character. Thus, some o f the s o l v e n t and monomer m o l e c u l e s may even become more f i r m l y o r i e n t e d t h a n in the corresponding ground s t a t e . 1

x

Abstract The q u a n t i t a t i v e a s p e c t s o f the elementary re actions i n v o l v e d in the p o l y m e r i z a t i o n o f l a c t o n e s a r e d i s c u s s e d . Some earlier papers a r e reviewed and ana l y s e d t o g e t h e r w i t h the r e c e n t d a t a o f the p r e s e n t a u t h o r s . I t has been shown, t h a t in the p o l y m e r i z a t i o n o f βPL rate c o n s t a n t o f p r o p a g a t i o n on macroanions (k-p) d e c r e a s e s w i t h i n c r e a s i n g the starting c o n c e n t r a t i o n o f monomer ([βPL] ), whereas the rate c o n s t a n t s o f p r o p a g a t i o n on m a c r o i o n - p a i r s (kΘp) do n o t depend on [βPL] . Thus, the ratio k-p/kΘp does depend on [βPL] . These o b s e r v a t i o n s stem from the h i g h dielectric c o n s t a n t o f βPL and its h i g h s o l v a t i o n ability, a p p a r e n t l y s t r o n g e r f o r i o n s than f o r the i o n - p a i r s . 0

0

0


282

ANIONIC


Literature

POLYMERIZATION

Cited

1. St.Slomkowski and St.Penczek, Macromolecules, 9, 367 (1976). 2. St.Slomkowski and St.Penczek, M a c r o m o l e c u l e s , i n press. 3. H . K . H a l l , Jr., Macromolecules, 2, 488 (1969). 4. A.Hamitou, T.Ouhadi, R.Jerome, and P . T e y s s i e , J.Polym.Sci.,Polym.Chem.Ed., 15 865 (1977). 5. K . I t o , Y.Hashizuka, and Y.Yamashita, Macromolecules 10, 821 (1977). 6. E . B i g d e l i and R.W.Lenz, Macromolecules, 11, 493 (1978). 7. K . S . K a z a n s k i i , Chimia i T e c h n o l o g i a Vysokomol. S o e d i n . , Ed. N.S.Enikolopov, VINTI, Moscow, 9, 5 (1977). 8. P . S i g w a l t and S . B o i l e a u , J.Polym.Sci.: Polymer Symp., 62, 51 (1978). 9. R.D.Lundberg and E.F.Cox in "Ring-Opening Polymerization", Ed. K.C. Frisch and S.L.Reegen, M a r c e l Dekker, New York and London, 1969, p.266. 10. H.Cherdron, H.Ohse, and F . K o r t e , Makromol.Chem., 56, 187 (1962). 11. T . S h i o t a , Y.Goto, and K.Hayashi, J.Appl.Polym.Sci., 11, 753 (1967). 12. T.Tsuda, T . S h i m i z u , and Y.Yamashita, Kogyo Kagaku Z a s s h i , 68, 2473 (1965). 13. Y. E t i e n n e and R.Soulas, J.Polym.Sci., C4, 1061 (1963). 14. V.Jaacks and N.Mathes, Makromol.Chem., 131, 295 (1970). 15. T . B i e l a , L.S.Corley, J.Michalski, St.Slomkowski, St.Penczek, and O.Vogl, Makromol.Chem., in p r e s s . 16. L.S.Corley, St.Slomkowski, St.Penczek, T . B i e l a , nad O.Vogl, Makromol.Chem., in p r e s s . 17. Y.Yamashita, K . I t o , and F . N a k a k i t a , Makromol.Chem., 127, 292 (1969). 18. A.A.Solov'yanov and K . S . K a z a n s k i i , Vysokomol. S o e d i n . , A12, 2114 (1970), ibid A14, 1063 (1972). 19. A . D e f f i e u x and S . B o i l e a u , Polymer,18 1047 (1977). 20. P.Hemery, S . B o i l e a u , and P . S i g w a l t , Europ.Polym.J., 7, 1581 (1971). 21. D.Kotynska, St.Slomkowski, and St.Penczek, in p r e paration. 22. A . D e f f i e u x and S . B o i l e a u , Macromolecules, 9, 369 (1976). 23. T.Ouhadi and J.M.Heuschen, J.Macromol.Sci.,-Chem., A9, 1183 (1975). 24. T.E.Hogen E s c h and J.Smid, J.Phys.Chem., 79, 233, (1975). 25. U.Takaki, T.E.Hogen E s c h , and J.Smid, J.Am.Chem. Soc., 93, 6760 (1971). RECEIVED March 5, 1981. In Anionic Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

Kinetics and Mechanism of Anionic Polymerization of Lactones

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