Progress in Polymerization of Cyclic Acetals - ACS Publications

the structure of the end-groups in poly-Diox is descri- bed, and the mechanistic consequences of the alleged macrocyclic or linear structures of the i...
0 downloads 0 Views 2MB Size
5 Progress i n Polymerization of C y c l i c Acetals

STANISŁAW PENCZEK and PRZEMYSŁAW KUBISA Polish Academy of Science, 90-362-Łodz, Poland

In our previous review paper, presented at the Rouen Symposium on Cationic Polymerization, we stressed some of the major differences between the c a t i o n i c po­ lymerization of c y c l i c ethers and c y c l i c acetals |1|. These differences are mainly caused by the much larger b a s i c i t y ( n u c l e o p h i l i c i t y ) of c y c l i c ethers, than that of c y c l i c a c e t a l s ; moreover, c y c l i c ethers are more basic (nucleophilic) than t h e i r polymers, whilst poly­ acetals seem to be more basic than t h e i r corresponding monomers. Thus, i n polymerization of c y c l i c ethers (or,at least i n polymerization of T H F ) , t e r t i a r y oxonium ions 1. are the only growing species |2| | 3 | |4|:

whereas i n the polymerization of c y c l i c a c e t a l s , i n c l u ­ ding 1,3-dioxolan (Diox), the equilibrium between the macroalkoxycarbenium ions 2 with t h e i r t e r t i a r y oxo ­ nium 2 counterparts i s i n our opinion the best represen­ of the active snecies : t a t i o n

Unfortunately, our knowledge of the carbenium-oxo­ nium ion e q u i l i b r i a i s very l i m i t e d ; some f i r s t 60

5.

PENCZEK AND KUBisA

Polymerization

of

Cyclic

Acetals

61

q u a n t i t a t i v e d a t a from our l a b o r a t o r y |5j were d i s c u s s e d i n the Rouen paper |1|, P r o p e r t i e s o f 2""and 3^ ^ e q u i l i b r i u m (1) may depend v e r y much on tïïe p o l y m e r i z a t i o n c o n d i t i o n s and s t r u c t u r e o f the c y c l i c a c e t a l . At the s u f f i c i e n t l y l a r ge excess o f a p o l y a c e t a l , £ can become the predominant structure. The o t h e r t o p i c , which w i l l be c o v e r e d i n t h i s pap e r , was p r e v i o u s l y r e v i e w e d by P l e s c h a t the IUPAC Symposium i n Budapest |6|, and more r e c e n t l y a t the I - s t IUPAC Symposium on"~Ring-Opening P o l y m e r i z a t i o n h e l d i n J a b l o n n a (1975) | 7 j . In t h i s p a r t o f our paper the s t r u c t u r e o f the end-groups i n p o l y - D i o x i s d e s c r i bed, and the m e c h a n i s t i c consequences o f the a l l e g e d m a c r o c y c l i c or l i n e a r s t r u c t u r e s o f the i s o l a t e d dead macromolecules i s d i s c u s s e d . In 1975 Rosenberg, Irzhakh and E n i k o l o p i a n p u b l i s hed a book e n t i t l e d " I n t e r c h a i n exchange i n p o l y m e r s " I 8 j , summarizing r e s u l t s o f the Moscow group on the p o l y m e r i z a t i o n o f c y c l i c a c e t a l s . A l t h o u g h some o f the conc l u s i o n s o f t h i s book would c e r t a i n l y be p r e s e n t e d today d i f f e r e n t l y i n l i g h t of the new e x p e r i m e n t a l data, the r e a d e r may f i n d t h e r e an unorthodox s o l u t i o n o f the m a j o r i t y o f k i n e t i c problems p e r t i n e n t to the n o n s t a t i o n a r y polymerizations, i n c l u d i n g polymerization of cyclic acetals. We s h a l l s t a r t , however, t h i s r e v i e w o f the p r o g r e s s i n the p o l y m e r i z a t i o n o f c y c l i c a c e t a l s from a b r i e f d e s c r i p t i o n o f the new p o l y a c e t a l s p r e p a r e d , and from summarizing o f the new d a t a on the thermodynamics o f polymerization of substituted 1,3-dioxolans. n

Thermodynamics o f P o l y m e r i z a t i o n .

New

Polyacetals.

I v i n and Leonard |9| extended the thermodynamic t r e a t m e n t o f the polymer-monomer e q u i l i b r i u m to the non i d e a l systems, a c c o u n t i n g f o r the polymer-monomer i n t e r a c t i o n d e s c r i b e d by the F l o r y parameter x p « b u l k p r o c e s s , the f o l l o w i n g e x p r e s s i o n was o b t a i n e d f o r the f r e e energy change upon the c o n v e r s i o n o f one mole o f pure monomer i n t o one base-mole o f amorphous polymer ( A G ) : F

o

r

a

m

l c

A

G

il ^c = RT [ i n mΦ • lm+pX ^pU -Φ™)] (2) m/ where φ ( = 1 - Φ ) i s the e q u i l i b r i u m monomer volume f r a c ­ tion, ^computed from the e x p e r i m e n t a l l y d e t e r m i ­ ned e q u i l i b r i u m monomer c o n c e n t r a t i o n a t the g i v e n tem­ p e r a t u r e T. In t h i s method the F l o r y parameter χ is a r b i t r a r l y chosen (e.g. 0.4 f o r D i o x - p o l y - D i o x i n t e r a c t i o n ) and assumed to be independent on temperatu­ r e . L i n e a r i t y o f the p l o t o f AG /RT as a f u n c t i o n o f 1

T

A

V Y

Y

J

Ό

p

1

62

RING-OPENING POLYMERIZATION

1/T i n d i c a t e s t h e r e l i a b i l i t y o f these s i m p l i f i c a t i o n s . More r e c e n t l y i t has been o b s e r v e d | K)|, t h a t i n t r o d u c ­ t i o n o f a term i n c l u d i n g t h e monomer-solvent and p o l y ­ m e r - s o l v e n t i n t e r a c t i o n s a l l o w s t h e polymer-monomer e q u i l i b r i a i n s o l u t i o n t o be u n i f o r m l y t r e a t e d . T h i s term i s r e l a t e d t o t h e heat o f m i x i n g o f t h e s o l v e n t used w i t h monomer and polymer. I t does not depend, however, v e r y much on t h e s o l v e n t s t r u c t u r e f o r Diox, and. t h e r e f o r e , I D i o x I i s almost s o l v e n t independent \l±\ (although, only C H C 1 , C H r C l and C,H, were s t u d i e d ) . I t i s worth * noting, t h a t i n c o n t r a s t t o Diox, d i f f e r e n c e s between t h e e q u i ­ l i b r i u m monomer c o n c e n t r a t i o n s a r e much more pronounced i n the p o l y m e r i z a t i o n o f THF |1j2J . Indeed, |THFl =5.5 mole»l"' i n CH-,N0 s o l v e n t and o n l y 3.5 mole»l-1 i n CC1 s o l v e n t (fTHF| =7.0 m o l e - l " , 2 5 ° ) . These l a r g e d i f f e r e n c e s r e f l e c t t h e h i g h e r b a s i c i ­ t y o f THF and much s t r o n g e r a c i d - b a s e i n t e r a c t i o n s between s o l v e n t s and THF, than s o l v e n t s and D i o x . The thermodynamic n o n - i d e a l i t y o f these systems are s t r e s s e d , because some a u t h o r s a r e s t i l l t e n d i n g to determine what they a r e c a l l i n g t h e thermodynamic q u a n t i t i e s ( l i k e ΔΗ° and AS*?) on t h e b a s i s o f s i m p l e r r e l a t i o n s h i p s , h o l d i n g o n l y * r o r t h e i d e a l systems. On t h e o t h e r hand, i t has t o be remembered, t h a t i n the p o l y m e r i z a t i o n k i n e t i c s , the proper value o f |monomerl has t o be used, and t h a t i t changes w i t h b o t h jmonomer I and s o l v e n t s t r u c t u r e . The combined r e s u l t s of bulk |l_3| and s o l u t i o n p o l y m e r i z a t i o n o f Diox (taken l a r g e l y from R e f e r e n c e |1J_|) a l l o w e d Leonard t o c a l c u l a t e ΔΗ, = -4.0±0.1 k c a l - m o l e " and A S =-11 ,0±0.3 cal*mole"1·deg~1, These r e s u l t s agree w e l l with v a l u e s o b t a i n e d from an e q u i l i b r i u m between gaseous monomer and amorphous polymer |14|. F o l l o w i n g t h e Ivin-Leonara "? method, Okada d e t e r m i ­ ned r e c e n t l y the thermodynamic f u n c t i o n s f o r the p o l y ­ m e r i z a t i o n o f 4-methyl-Diox |15| and, (assuming X . 0.3) found ΔΗ, =-3.2±0,2 k c a l / m o l e and AS° = - 1 2 . 7 ± 0 . 8 cal*mole~'»deg-1 , Another work, performed i n C H C l 2 s o l v e n t f o r t h e some monomer, and not a c c o u n ­ ting f o r t h e d i s c u s s e d above i n t e r a c t i o n s , g a v e t h e apparent v a l u e s ( ΔΗ P P and AS P P ) d e p e n d i n g , as i t c o u l d be e x p e c t e d , on the s t a r t i n g monomer c o n c e n t r a ­ t i o n 116 I , 9

z

9

z

9

z

0

0

9

1

4

e

o

1

X

1

mr

=

m p

9

a

of

Theoretical Dioxolans.

a

I n t e r p r e t a t i o n o f the P o l y m e r i z a b i l i t y

T h e o r e t i c a l i n t e r p r e t a t i o n o f the r i n g - c h a i n e q u i ­ l i b r i a , p u b l i s h e d by Jacobson and Stockmayer i n 1950 117 I c a n o n l y be a p p l i e d t o t h e case when c h a i n s o r

9

5.

PENCZEK AND KUBisA

Polymerization

of Cyclic

Acetals

63

r i n g s a r e so l a r g e t h a t the c o n f i g u r a t i o n a l e n t r o p y i s governed by the G a u s s i a n f u n c t i o n and the energy d i f f e ­ rence between the c h a i n and r i n g forms i s n e g l i g i b l e . F o r a s m a l l r i n g , such as the five-membered r i n g o f Diox, Jacobson-Stockmayer e q u a t i o n cannot be a p p l i e d . In such c a s e , as shown i n many works, summarized r e c e n ­ t l y by H a l l f o r v a r i o u s c y c l i c monomers I l 8 j l l ? . | > s t a b i l i t y o f the r i n g i s c o n n e c t e d o n l y w i t h the s t r a i n i n the r i n g , caused m o s t l y by the d e v i a t i o n i n v a l e n c y a n g l e s . H a l l e x p l i c i t l y showed t h a t the d i f f e r e n c e i n s t r a i n energy between monomer and polymer e q u a l s the e n t h a l p y o f p o l y m e r i z a t i o n , p r o v i d e d t h a t no s u b s t i tuents are p r e s e n t , or e l s e c o n f o r m a t i o n a l s t r a i n s i n the polymer may outweigh the s t r a i n i n the r i n g . I t has a l r e a d y been o b s e r v e d i n the p o l y m e r i z a t i o n o f s u b s t i t u t e d ε-caprolactams\20||2jJ , t h a t the s u b s t i ­ t u t i o n o f hydrogen atoms d e c r e a s e s the p o l y m e r i z a b i l i t y o f monomers. The same phenomena were o b s e r v e d i n the p o l y m e r i z a t i o n o f 4 , 4 - d i m e t h y l - , c i s - 4 , 5 - d i m e t h y l and t r a n s - 4 ,5-dimethyl-Diox |lj>| . These d i f f e r e n c e s were i n t e r p r e t e d i n the p o l y m e r i ­ z a t i o n o f ε-caprolactams |20| from the change o f thermodynamical p r o p e r t i e s caused by the e x i s t e n c e o f r o t a t i o n a l isomers. In a n a l y s i n g p o l y m e r i z a t i o n o f s u b s t i t u t e d d i o x o l a n s Okada took a s l i g h t l y m o d i f i e d approach, comparing e n e r g e t i c a l d i f f e r e n c e s between d i o x o l a n s and t h e i r p o l y m e r s . Low - m o l e c u l a r weight a c e t a l s , e.g. dimethoxymethane and i t s homologues exist p r e d o m i n a n t l y i n the gauche form to a v o i d the r a b b i t -ear e f f e c t s i n the a n t i - f o r m 122|:

gauche

anti

P o l y d i o x o l a n s a r e a l s o assumed to e x i s t i n the gauche form, because the r a b b i t - e a r e f f e c t i n the a n t i form i s l a r g e r (1 k c a l m o l e ~ 1 ) t h a n the gauche i n t e r a c ­ t i o n o f the methyl groups { u s u a l l y c o n s i d e r e d to be from 0.6 to 0.9 k c a l * m o l e " ' ) . S u b s t i t u t i o n o f the H atoms by CH., groups d e s t a b i ­ l i z e s monomers by r e p l a c i n g the c i s - geminal C^-H and C -H bonds o p p o s i t i o n w i t h a g r e a t e r C^-H and C - C H opposition. e

5

5

3

64

RING-OPENING POLYMERIZATION

A l l o f the Okada's c a l c u l a t i o n s were based on the assumption, t h a t the s t a b l e c o n f o r m a t i o n o f Diox i s the " e n v e l o p e " form, i n which one o f the c a r b o n atoms o f the e t h y l e n e group i s l o c a t e d a t the t i p o f the f l a p , g i v i n g the d i h e d r a l angle o f the c i s - n e i g h b o r i n g hy­ drogens o f the e t h y l e n e group e q u a l to 35 degree. S u b s t i t u t i o n i n a polymer c h a i n l e a d s to the i n c r e a s e d energy o f the g a u c h e - i n t e r a c t i o n s and the d i f ­ f e r e n c e between these two e f f e c t s g i v e s e v e n t u a l l y a d e v i a t i o n i n ΔΗ, (ΔΔΗ, ) f o r a s u b s t i t u t e d Diox from unsubstituted monomer. These c a l c u l a t i o n s l e d Okada to the f o l l o w i n g e s t i m a t e d v a l u e s o f - ΔΗ- ( g i ­ ven below i n kcal»mole~1) f o r v a r i o u s methyl s u o S t i t u t e d Diox :

For 4-methyl-Diox t h e r e i s a good agreement w i t h the v a l u e determined e x p e r i m e n t a l l y (3.2 k c a l - m o l e " ) . Thus, these f i n d i n g a r e i n accordance w i t h a gene­ r a l o b s e r v a t i o n t h a t i n the p o l y m e r i z a t i o n o f h e t e r o c y c l i c monomers s u b s t i t u t i o n l e a d s to d e c r e a s e d probabi­ l i t y o f c h a i n f o r m a t i o n . The e x t e n t o f s e n s i t i v i t y o f a g i v e n c l a s s o f monomers t o s u b s t i t u t i o n i s g i v e n by the r i n g s t r a i n o f the p a r e n t , u n s u b s t i t u t e d monomer. Thus, even f o r h i g h l y s u b s t i t u t e d o x i r a n e s ( e . g . t e t r a ­ me t h y l o x i r a n e ) complete p o l y m e r i z a t i o n c a n be a c h i e ved, because the r i n g s t r a i n overshadows any o t h e r effect. J e d l i n s k i a n a l y s e d i n a s e r i e s o f papers the H-NMR s p e c t r a o f v a r i o u s s u b s t i t u t e d 1,3-dioxolans i n o r d e r to u n d e r s t a n d the s t e r e o c h e m i s t r y o f these monomers. Then, f o l l o w i n g e a r l i e r work, d e s c r i b e d p r e v i o u s l y f o r the u n s u b s t i t u t e d d i o x o l e n i u m s a l t s , s t u d i e d the k i n e ­ t i c s o f H" t r a n s f e r from these monomers t o the t r i p h e n y l m e t h y l i u m c a t i o n |23|, as the f i r s t r e a c t i o n , p r e c e ­ d i n g the t r u e i n i t i a t i o n . T h i s approach, i s complemen­ t a r y t o t h a t o f Okada,which g i v e s a thermodynamic i n f o r m a t i o n about the p o l y m e r i z a b i l i t y , w h i l e J e d l i n s k i tends t o c h a r a c t e r i z e the i n f l u e n c e o f s t r u c t u r e ( s t e ­ r e o c h e m i s t r y ) on the r a t e o f reactions pertinent to elementary r e a c t i o n s . There a r e t i l l now, however,no 1

5. PENCZEK AND KUBisA

Polymerization

of Cyclic

Acetals

65

q u a n t i t a t i v e i n f o r m a t i o n s a v a i l a b l e about t h e r e a c t i o n s related to the a c t u a l polymerization process (initiat i o n , c h a i n g r o w t h ) . Recently,Kops r e p o r t e d on t h e pol y m e r i z a t i o n o f b i c y c l i c d i o x o l a n s , c y c l i c formais o f t r a n s - and c i s - c y c l o h e x a n e d i o l s :

cis-

Only the t r a n s - monomer p o l y m e r i z e d , g i v i n g h i g h molec u l a r weight, s o l i d polymer |24j . T h i s r e s u l t i s i n accordance w i t h a more g e n e r a l phenomenon o f t h e i n c r e a s e d s t r a i n i n t h e t r a n s - j o i n e d r i n g s , due t o t h e enhanced a n g u l a r s t r a i n . In t h e p r e v i o u s p a r a g r a p h we d i s c u s s e d p o l y m e r i z a t i o n o f 1,3-dioxolans s u b s t i t u t e d a t C and C . I n f o r m a t i o n on t h e p o l y m e r i z a t i o n o f d i o x o l a n s s u b s t i t u t e d at C i s v e r y l i m i t e d ; we s h a l l c o n f i n e o u r s e l v e s t o the p o l y m e r i z a t i o n o f 2 - v i n y l - d i o x o l a n s and 2 - v i n y l -dioxans. 4

5

2

Polymerization

o f the Unsaturated

Cyclic Acetals.

Polymerization o f 2-vinyl-1 ,3-dioxolan (4) I 25| |26| 2-vinyl-1,3-dioxane (5) |27j |2J31 |29j and relatecT mono mers, s u b s t i t u t e d a t C : 2

/CH

I

2

J

, 2

9

2

CH

XH

CH -CH 4

CH -CH 5

2

I

2

2

have been i n v e s t i g a t e d d u r i n g t h e l a s t f i f t e e n y e a r s i n a t l e a s t f i v e l a b o r a t o r i e s , A f t e r the o r i g i n a l d i s c o v e r y o f Mukaiyama 125j|, who found t h a t 4 p o l y m e r i z e s , at l e a s t p a r t i a l l y , t o the l i n e a r p o l y e s t e r : {CH CH CH COCH > 2

2

2

2

Tada, Saegusa, and Furukawa |26| i n t e r p r e t e d t h i s result as a consequence o f t h e hydri3ê-shift p o l y m e r i z a t i o n , s i m i l a r t o t h a t e l a b o r a t e d e x t e n s i v e l y by Kennedy |30| f o r branched α-olefins :

66

RING-OPENING POLYMERIZATION

CH =CH-CHC' 7

0-CH I 0-CH

ù

^ (RCH CH-C-H

9

R

-

L

9

^ 0 - C H

L 2

o~ çU^r*

O-QL |

+

+

)

S

"

N

I

I

X

~

2

(3) + .0-CH, •RCH-CH-C 2

2

I

Z

^ - O - C H , +

CH-=CH-CH 2

^ O - C H ,

I

\ 0 - C H

Z

+

L



RΠCH C-0-ΠCH,CH 0

2 7

9

9

2

II

1

2

2

9

2

-CH j

0

.CH

0

0 1

I

CH CH 2

2

A l t h o u g h the most n u c l e o p h i l i c s i t e o f a t t a c k i n 4 are r a t h e r the oxygen atoms, but, a p p a r e n t l y the c a t i o n a t e d 4, e.g.: CH.

R - C H

2

C H

2

C O C H

2

C H ^ — 0

C H

2

J

I ,0

χ

CH =CH' 2

9

2

N

H

or i t s o p e n - c h a i n isomer, s t a b i l i z e d by the f o r m a t i o n o f the a l l y l i c - type carbenium i o n , are not s u f f i c i e n ­ t l y r e a c t i v e i n the c h a i n growth to compete w i t h the H " ion t r a n s f e r processes. More d e t a i l e d a n a l y s i s o f p o l y m e r i z a t i o n o f £, and p a r t i c u l a r l y an a n a l y s i s o f the ^H-NMR s p e c t r a o f p o l y -5 r e v e a l e d |j27| , t h a t the complete s t r u c t u r e o f p o l y ­ mers i s much more complex. Almost a l l o f the r e p e a t i n g u n i t s t h a t one c o u l d imagine were found, the most im­ p o r t a n t ones b e i n g ( f o r p o l y - 5 ) as shown below:

• · · —CH ~CH—.. · , 2

. . . —OCH CH CH OCH— · · · , 2

2

2

CH

q

ρ

%· · —CH CH COCH CH CH — · . 2

2

2

2

2

·,

0

il C H 2

The two f i r s t s t r u c t u r e s c o n t a i n groups s t i l l r e a c ­ t i v e i n the c h a i n , and t h i s i s why these polymers are o f i n t e r e s t f o r polymer chemists working i n the polymer s y n t h e s e s , The two-stage p o l y m e r i z a t i o n o f these e a s i l y a v a i l a b l e monomers has been expected to p r o v i d e a new group o f r e a c t i v e p o l y m e r s . F r e e - r a d i c a l p o l y m e r i z a t i o n , f o l l o w e d by the c a t i o n i c f o r m a t i o n o f the network (and,

5.

PENCZEK AND KUBisA

Polymerization

of Cyclic

Acetals

67

i n p r i n c i p l e , v i c e v e r s a ) was a l s o s u c c e s s f u l l y a p p l i e d by Minato t o ( 1 , 3 - d i o x o l a n - 4 - y l ) methyl a c r y l a t e |31 I. End-Groups i n P o l y a c e t a l s . P o l y - 1 , 3 , 5 - t r i o x a n i s known t o c o n t a i n h e m i a c e t a l -OH groups; some o f t h e s e are formed because o f the c h a i n t r a n s f e r t o water |32|, A c e t y l a t i o n o f the -OH groups g r e a t l y enhances tEermal s t a b i l i t y o f the p o l y oxymethylene polymers,and i s a t the base o f the com m e r c i a l i z a t i o n o f the f i r s t p o l y a c e t a l (a homopolymer o f CH 0) 132a| known, i n fact»many y e a r s ago from the c l a s s i c a l works o f S t a u d i n g e r and Kern. Jaacks a.o. d i s c o v e r e d |32| f o r m a t i o n o f the meth o x y l end groups i n p o l y - 1 , 3 , ! T t r i o x a n , determined by the Z e i s e l method, and assumed, t h a t t h e s e groups result from the H" i o n s h i f t ( i n t r a m o l e c u l a r l y ) o r t r a n s f e r (intermolecularly). S i m i l a r r e a c t i o n was proposed by us more r e c e n t l y i n the p o l y m e r i z a t i o n o f Diox, conducted above 0 ° , t o account f o r the methoxyl end-groups o b s e r v e d i n the 'H-NMR s p e c t r a |33|. 2

::

End-Groups i n P o l y - 1 , 3 - d i o x o l a n . Gresham p o l y m e r i z e d Diox w i t h m i n e r a l and Lewis a c i d s and was unable t o d e t e c t any end-groups |34j . P l e s c h c o n f i r m e d Gresham s o b s e r v a t i o n |35|, assumed t h a t p o l y - D i o x are m o s t l y c y c l i c and on tïïis b a s i s proposed a mechanism o f p r o p a g a t i o n w i t h p r o t o n i c a c i d s ( r i n g - e x p a n s i o n ) . J a a c k s , i n a p p a r e n t l y s i m i l a r cond i t i o n s (HC10 , C H C 1 s o l v e n t ) found e a r l i e r , t h a t polymers are r a t h e r l i n e a r , and q u a n t i t a t i v e l y d e t e r m i ned e t h y l a l c o h o l from the h y d r o l y z e d end-groups, formed when a l i v i n g - l i n e a r (on h i s o p i n i o n ) p o l y c a t i o n was k i l l e d w i t h sodium e t h y l a t e |36|. These r e s u l t s were r e c e n t l y c h a l l e n g e d by P l e s c h T ^ I · In the p o l y m e r i z a t i o n o f Diox i n i t i a t e d w i t h triethyloxoniumhexafluorophosphate ((C H )^0 PF7) W o r s f o l d |38| c l a i m e d t h a t he c o u l d not f i n e any end-groups i n p o l y - D i o x formed, a l t h o u g h a t r i p l e t from a CH^CH 0 group i s seen i n the 'H-NMR spectrum g i v e n i n n i s paper. Ponomarenko a.o. |39|, by u s i n g ( C H ) - 0 S b C l , l a b e l l e d w i t h 14c i n tïïe e t h y l group, c o n c l u d e d , t h a t the number o f moles o f Co^S groups, i n c o r p o r a t e d i n t o the macromolecules, i s c l o s e t o t h e number o f moles o f the used i n i t i a t o r , Okada |40| i n h i s study o f oligomers i s o l a t e d a t low c o n v e r s i o n ( p o l y m e r i z a t i o n o f Diox i n i t i a t e d w i t h w i t h ( C H ) 0 + BF" and k i l l e d w i t h CH^ONa) o b s e r v e d l i n e a r o l i g o m e r s w i t h e t h y l a t e and m e t h y l a t e end-groups, 1

ff

n

4

2

2

7

+

2

q

2

+

2

5

6

2

5

3

68

RING-OPENING

POLYMERIZATION

Semlyen |4jJ i n a r e p o r t d e s c r i b i n g p o l y m e r i z a t i o n i n i t i a t e d w i t h BF^ ° ( 2 5 ) ? t h a t gc-ms method ga­ ve e v i d e n c e f o r tile e x i s t a n c e o f c y c l i c o l i g o m e r s formed i n the p r o c e s s , which l e d to the m i x t u r e o f l i n e a r and c y c l i c p r o d u c t s w i t h a d i s t r i b u t i o n governed f o r l a r g e r m a c r o c y c l i c s by the Jacobson-Stockmayer theory. T h i s i s an i m p o r t a n t r e s u l t , because an agreement between the o b s e r v e d d i s t r i b u t i o n o f the c y c l i c oligomers w i t h a d i s t r i b u t i o n p r e d i c t e d by the Jacobson-Stockmayer t h e o r y (a s l o p e e q u a l to 2.5 f o r the p l o t o f l o g Κ on l o g x, where Κ i s the molar c y c l i z a t i o n - e q u i l i b r i u m c o n s t a n t f o r m a c r o c y c l e s w i t h a p o l y m e r i z a t i o n degree e q u a l to x) s t r o n g l y i n d i c a t e s t h a t p o l y m e r i z a t i o n p r o ­ ceeds w i t h a l i n e a r a c t i v e s p e c i e s , f o r m i n g m a c r o c y c l e s by b a c k - b i t i n g and end-to-end c l o s u r e . Thus, because o f the e x i s t i n g c o n t r o v e r s y , whether and when p o l y - D i o x c o n t a i n the end-groups, and because of the f a r r e a c h i n g c o n c l u s i o n s based on e i t h e r macroc y c l i c o r l i n e a r s t r u c t u r e s o f the i s o l a t e d p o l y - D i o x , we r e i n v e s t i g a t e d r e c e n t l y t h i s problem. F i r s t o f a l l we d e c i d e d to use methods which would not i n v o l v e d e s t r u c t i o n o f the end-groups ( l i k e hydro­ l y s i s used by J a a c k s |36| and then by P l e s c h |37j as a p o s s i b l e s o u r c e o f a m i F T g u i t y . S e c o n d l y , we assumed, t h a t b o t h end-groups s h o u l d be o b s e r v e d ; the i n i t i a l one, formed from an i n i t i a t o r , and the t e r m i n a l one, coming from the k i l l i n g agent. Thus, we i n i t i a t e d p o l y ­ m e r i z a t i o n e i t h e r by b e n z o i l i u m h e x a f l u o r o a n t i m o n a t e ( C ^ H r C 0 S b F 7 ) , assuming t h a t the benzoate end-groups s h o u l d be o D s e r v a b l e i n UV, o r w i t h ( C H c ) ^ 0 S b F 7 , a s ­ suming, t h a t i n the FPT-^H-NMR s p e c t r a ; CH^C^O t r i p l e t from the end-group s h o u l d be seen. C H ONa, N(CH-)- and P ( C , H r ) - k i l l i n g agents were used a f t d ^ s t u d i e d i l l * * F P T - 1 H - N M R . The benzonoate end-groups absorb a t * 0 ( l i k e the low m o l e c u l a r - w e i g h t b e n z o a t e s ) ; thus as suming t h a t ε f o r e t h y l benzoate i s e q u a l to ε of the benzoate end-groups the DP of poly-Diox were c a l c u l a t e d . T a b l e 1 summarizes some o f these results where DP ( c a l c d . ) are compared w i t h DP (UV) and DP (osm.). The former v a l u e s were c a l c u l a t e d assuming, t h a t tne p o l y m e r i z a t i o n i s a l i v i n g one, i . e . t h a t e v e r y molecul e o f i n i t i a t o r g i v e s one macromolecule w i t h no t r a n s f e r , DP (UV) was c a l c u l a t e d as d e s c r i b e d above, and DP (osm.) was measured by h i g h - s p e e d osmometry. S i n c e polymers taken f o r measurements were i s o l a t e d and p u r i f i e d by s e v e r a l d i s s o l u t i o n / p r e c i p i t a t i o n c y c l e s , some amount of the lower m o l e c u l a r - w e i g h t m a t e r i a l c o u l d be l o s t . P o l y m e r i z a t i o n was conducted i n CH-NO- o r i n Cï^Cl? solvents at -15 i n o r d e r to minimize the H" i o n t r a n s f e r ( i t has been shown i n our l a b o r a t o r y t h a t below -20° C

H

s

h

o

w

e

d

+

+

7

9

q

0

= 2 3

n

m a x

m

a

x

m

n

n

a

m

5.

PENCZEK AND KUBisA

Polymerization

of Cyclic

Acetals

69

the H~ion t r a n s f e r f r o c e.g^ dimethoxymethane to methoxycarbenium i o n -CH^OCH^bF^- becomes immeasurably slow) T a b l e 1 |42| _ Comparison o f DP ( c a l c d . ) DP (UV) and DP (osm-l o f p o l y - 1 , 3 - d i o x o l a n s p r e p a r e d w i t h C H -UO SbF i n CH-N0 o r C H C 1 s o l v e n t s a t - 1 5 ° , and « t e r m i n a t e d w i t h C H ONa. | D i o x | =5.4 m o l e - l +

6

2

2

+

6

χ 10,πκ>1β·Γ

5

n

lF (calcd.)

5

n

Ί

6

2

2

|C H CO SbF-|

t

DP (UV)

lF (osm.)

10-3

10-3

n

|Diox| -|Diox| 0

e

i o

_

3

n

+

|C H CO SbF-| 6

5

o

4.05

I

1.15

1.30

1.39

2.75

i

1.69

1 .73

1 .77

2.70

1.72



2.07

1 .88

2.65

1.41

I

1.23

1 .33

1.10

4.19

5.24

4.35

0.95

4.81

3.69

4.00

The second end-group, i n t r o d u c e d upon a t e r m i n a t i o n r e ­ a c t i o n , was o b s e r v e d by FPT-1H-NMR f o r samples o f p o l y -Diox, p r e p a r e d from a p e r d e u t e r a t e d Diox(Diox-dg).This approach d e c r e s a s e s an o v e r - a l l number o f p r o t o n s i n the sample and i n c r e a s e s p r o p o r t i o n o f p r o t o n s i n the end-groups. A p p l i c a t i o n o f the F o u r i e r - P u l s e - T r a n s f o r m method f o r a c c u m u l a t i o n o f the s p e c t r a enhanced the s i g n a l to n o i s e r a t i o s u f f i c i e n t l y to observe s t r u c t u r e and c o n c e n t r a t i o n o f the end-groups by FPT-'H-NMR. Some o f the p e r t i n e n t r e s u l t s are shown i n T a b l e 2. An agreement ( w i t h i n 20-251) between DP c a l c u l a t e d and measured by UV and/or ^H-NMR methods i n d i c a t e s t h a t p r a c t i c a l l y a l l o f the i n i t i a t o r used i s p r e s e n t i n the macromolecules. An agreement between DP found from the end-groups and DP measured o s m o m e t r i c a l l y means, t h a t the p r o p o r t i o n o f c y c l i c macromolecules i s low, as i t c o u l d be p r e d i c t e d , f o r i n s t a n c e , from the Jacobson-Stockmayer t h e o r y . T h i s p r o p o r t i o n , i n p r i n c i ­ p l e , _ c o u l d be d e t e c t e d by comparing DP (end groups) and DP '(osmometry) but our a c c u r a c y o f measurements i s ,

70

RING-OPENING POLYMERIZATION

at l e a s t a t p r e s e n t , comparisons.

not s u f f i c i e n t l y

high

f o r these

Table 2 Comparison o f DP ( c a l c d . ) and DP (NMR) o f p o l y -1,3-Diox, p r e p a r e d from p e r d e u t e r a t e d Diox(-d^). P o l y m e r i z a t i o n c o n d i t i o n s : C H N 0 s o l v e n t , -15®, 12 h r s . 7

9

6

Starting concn. of i n i t i a t o r 103 mole*1 1

|Diox-d | 6

n

IDioxI -IDioxI

mole*l ^

0

n



I initiator|

+

|C H CO SbF-| 6

5

4.05

o

Initiator

6

5

2

4.75

+

0

750

C

H

2 5°1000

5.2

5

575

650

; Kc^jP3p aF-|

Terminating agent

C H C(0)0 -OC H

700

4.7

I

DP„ found 1 from H-NMR

T3F (calcd.)

Q

-

-

L

-P(C H )5 6

5

920

Thus, we c a n c o n c l u d e , t h a t p o l y - D i o x , prepared with C HrCO SbF7 or ( C ^ H r ) 3 6 are m o s t l y l i n e a r , and macromoleculës c o n t a i n an i n i t i a l end-group coming from an i n i t i a t o r and the t e r m i n a l end-group coming from the t e r m i n a t i n g agent, e.g.: +

0 + s b F

i

n

i

t

i

a

t

o

r

s

6

C H CfOCH CH OCH > OCH CH 6

5

2

2

2

n

2

3

(4) CH CH iOCH CH OCH > P(C H ) 3

2

2

2

2

n

6

5

3

P o l y m e r i z a t i o n degrees measured i n d i c a t e a l s o , t h a t p o l y m e r i z a t i o n ( a t l e a s t i n c o n d i t i o n s g i v e n i n Table 1 and 2) p r o c e e d s w i t h o u t an a p p r e c i a b l e t r a n s f e r a f f e c t i n g the p o l y m e r i z a t i o n degree. S t r u c t u r e o f P o l y - D i o x ( c y c l i c vs l i n e a r ) and Mechanism o f P o l y m e r i z a t i o n |43|. As i t w i l l be shown i n t h i s p a r a g r a p h , n e i t h e r predominantly l i n e a r nor predominantly c y c l i c s t r u c t u r e s o f the i s o l a t e d , k i l l e d macromoleculës a r e the s t r a i g h t f o r w a r d arguments by themselves f o r the l i n e a r or c y c l i c growth o f the l i v i n g macromoleculës. Indeed, l e t us c o n s i d e r an assumed e q u i l i b r i u m between l i v i n g

5.

PENCZEK AND KUBISA

cyclic

Polymerization

and l i v i n g

linear

of Cyclic

71

Acetals

poly-Diox: (5)

X

^linear living "^macromolecule

—• 0 0 ( bl ^ CH —Oww 2

7A 7C E q u i l i b r i u m (5) , d e s c r i b i n g the instantaneous state,should a l s o be supplemented w i t h the t e m p o r a r i l y dead c y c l i c and l i n e a r ( h o l d i n g two ends coming from an i n i t i a t o r X) macromolecules. C y c l i c l i v i n g macromolecules 7A and 7B a r e r e s u l t s o f the b a c k - b i t i n g l e a d i n g to the end-to-end c l o s u r e (7A) o r a b a c k - b i t i n g to any o f the oxygen atoms i n tïïê c h a i n . The p r o b a b i l i t y o f the f o r mer p r o c e s s i s enhanced v e r y much, p a r t i c u l a r l y a t the e a r l y s t a g e s o f p o l y m e r i z a t i o n , when the oxygen atom i n the i n i t i a l end-group ( e . g . oxygen atom i n the ether end-group) i s much more n u c l e o p h i l i c than the oxygen atoms i n the a c e t a l bonds a l o n g the c h a i n . L e t us now examine r e a c t i o n o f a k i l l i n g agent with these l i v i n g macromolecules. The l i n e a r l i v i n g macro m o l e c u l e s w i l l g i v e t h e i r l i n e a r dead r e p l i c a / b u t the c y c l i c - l i v i n g ones may g i v e e i t h e r c y c l i c - d e a d o r l i n e a r - d e a d macromolecules, depending on the i n i t i a t o r used, and t h e r e f o r e on a s t r u c t u r e o f Χ i n 7A. In t h i s s t r u c t u r e t h e r e a r e t h r e e n o n e q u i v a l e n t boncTs: a, b, and c, t h a t can be b r o k e n upon an a t t a c k o f the k i l l i n g agent. I f X=e.g. CH- o r C H r , ^ th i IA r a t h e r s t a b l e bonds a and c, and one much l e s s s t a b l e a c e t a l bond b. Thus, even i f c y c l i c 7A were a predomi­ nant s t r u c t u r e a t some s t a g e o f p o l y m e r i z a t i o n , then t h e i r r e a c t i o n w i t h k i l l i n g agent would g i v e m o s t l y l i n e a r dead macromolecules. Thus, a l t h o u g h i t has been shown i n the p r e v i o u s p a r a g r a p h , t h a t p o l y - D i o x p r e p a r e d w i t h C.HrC0 SbF7 and ( C H ) ~0 SbF""are l i n e a r , t h i s i s not s u f f i c i e n t to argue t h a t - t h e c h a i n growth proceeds w i t h a l i n e a r m a c r o c a t i o n 7C. In o r d e r to d i s t i n g u i s h between the extreme s t r u c 7Λ ^ predominant d u r i n g the c h a i n growth, i t i s , t h e r e f o r e , n e c e s s a r y to o b s e r v e d i r e c t l y the p o s i t i o n o f X; i n 7A i t i s a d j a c e n t to the p o s i t i v e l y c h a r g e d oxygen atom, i n 7_C i t i s a p a r t o f the e t h e r c h a i n end. I f X=C Hr, t h e n the d i f f e r e n c e s between the chemical s h i f t s i n ^H-NMR are as f o l l o w s : Θ

η

e r e

a

r

e

2

+

+

2

t

u

r

e

s

a n

a

5

s

2

+

6 1.75(t)

δ 1 .15(t)

R

t

w

o

72

RING-OPENING POLYMERIZATION

t h u s , the difference between c h e m i c a l s h i f t s i s s u f f i ­ c i e n t l y l a r g e and both s t r u c t u r e s can be i n d e p e n d e n t l y observed by ^H-NMR. T h i s i s shown i n F i g u r e 1, t a k e n from R e f e r e n c e |43|, and i l l u s t r a t i n g the change o f the p o s i t i o n o f a t r i p l e t o f the CH^CH^-protons d i r e c t l y i n the l i v i n g p o l y m e r i z a t i o n system, c o n s i s t i n g o f a d e u t e r a t e d D i o x ( - d ) and ( C H ) - 0 S b F " i n i t i a t o r i n CD^CK s o l v e n t . At the b e g i n n i n g o f p o l y m e r i z a t i o n o n l y tne 61.75 t r i p l e t i s seen, w h i l e a t e q u i l i b r i u m o n l y the 61.15 t r i p l e t ; i n the i n t e r m e d i a t e s t a g e s b o t h t r i p l e t s are o b s e r v e d . A d d i t i o n a l s p l i t t i n g o f the 61.15 t r i p l e t i n ­ to two t r i p l e t s w i t h a d i f f e r e n c e i n c h e m i c a l s h i f t s e q u a l l i n g o n l y 13 Hz (300 MHz spectrum) and the r a t i o o f i n t e g r a t i o n s 1:2, appears as a r e s u l t o f the s i m u l ­ taneous p r e s e n c e o f two k i n d s o f ethoxy groups, namely one from the polymer end-group, and the second one from e t h y l e t h e r , l i b e r a t e d from the i n i t i a t i n g t e r t i a r y oxonium s a l t . E v a c u a t i o n o f the sample i n high-vacuum removes c o m p l e t e l y e t h y l e t h e r , as i t can be judged from the d i s a p p e a r a n c e o f i t s t r i p l e t from the spectrum. A d d i t i o n o f the N ( C H ) k i l l i n g agent to the l i v i n g system does not change the p o s i t i o n o f the 61.15 t r i p l e t . The f i n a l spectrum o f the k i l l e d system i s shown i n F i g u r e 2 ( a l s o t a k e n from R e f e r e n c e 143j . In t h i s spectrum two s i n g l e t s due to the (CH-r) N and (CH-)-N p r o t o n s are o b s e r v e d , the r a t i o |CH CH 0-|/|-N (CH )-| (from the c o r r e s p o n d i n g i n t e g r a ­ t i o n s ) i s e q u a l to 1:1.1. R e s u l t s r e p o r t e d i n t h i s pa­ r a g r a p h , and based on the r e c e n t work from our l a b o r a ­ t o r y , s t r o n g l y i n d i c a t e t h a t p o l y m e r i z a t i o n o f Diox, i n i t i a t e d by ( C H r ) 0 S b F 7 p r o c e e d s , a t l e a s t i n C H N 0 s o l v e n t , on the l i n e a r a c t i v e s p e c i e s . Systems w i t h p r o t o n i c a c i d s i n i t i a t o r s may behave d i f f e r e n t l y , because i f X=H i n 7A, then the bond a (Η-δ | . Perhaps, i n the p o l y m e r i z a t i o n o f c y c l i c a c e t a l s the m a c r o e s t e r - m a c r o i o n - p a i r e q u i l i b r i u m , d e s c r i b e d f o r the p o l y m e r i z a t i o n o f THF, a l s o takes p l a c e , as p r o p o s e d r e c e n t l y f o r the C I O 4 a n i o n |46 |. +

6

e

P

2

2

p

REFERENCES : 1. S.Penczek, Makromol.Chem. 175, 1217 (1974) 2. B.A.Rosenberg, E.B.Ludvig, A.R.Gantmacher and S.S. Miedwiediew, Vysokomol. Soed. 6, 2035 (1964) 3. K.Matyjaszewski, P.Kubisa and S.Penczek, J.Polymer Sci. A12, 1333 (1974) 4. T.K.Wu and G.Prukmayr , Macromolecules 7, 136 (1974) 5. S.Slomkowski and S.Penczek, J.Chem.Soc.Perkin II (1974), 1718 6. P.H.Plesch IUPAC International Symposium on Macromolecules Budapest 1969, Plenary Lecture, p.213 7. P.H.Plesch, I-st IUPAC International Symposium on Rings-Opening Polymerization, Jablonna (Poland), 1975, Plenary Lecture, Pure & Appl.Chem., in press 8. B.A.Rosenberg, W.I.Irzak and W.S.Enikolopian "Interchain exchange in polymers" Chimia, Moscow, 1975 (in Russian) 9. K.Ivin and J.Leonard, European Pol.J. 6, 331 (1970) 10. J.Leonard, Macromolecules 2, 661 (1969) 11. L.I.Kozub, M.A.Markevich, A.A.Berlin and N.S. Enikolopian Vysokomol.Soed. 10, 2007 (1968) 12. S.Penczek and K.Matyjaszewski, submitted for publication 13. R.Binet and J.Leonard, Polymer 14, 355 (1973) 14. W.K.Busfield, R.M.Lee and D.Merigold, Makromol.Chem. 156, 183 (1972) 15. M.Okada, K.Mita and H.Sumimoto, Makromol.Chem. 176, 859 (1975) 16. Y.Firat and P.H.Plesch, Makromol.Chem. 176, 1179 (1975) 17. H.Jacobson and W.H.Stockmayer, J.Chem.Phys. 18, 1600 (1950) 18. H.K.Hall J r . , M.K.Brandt and R.M.Mason, J.Amer.Chem. Soc. 80, 6420 (1958) 19. H.K.Hall Jr. and J.H.Baldt, J.Amer.Chem.Soc. 93, 140 (1971)

76

RING-OPENING POLYMERIZATION

20. Y.Yumoto, J.Chem.Phys. 29, 1234 (1958) 21. J.Sebenda, I-st IUPAC International Symposium on Ring-Opening Polymerization, Jablonna (Poland), 1975, Plenary Lecture, Pure & Appl.Chem., in press 22. K.Pihlaja, Acta Chem.Scand. 25, 451 (1971) 23. Z.Jedlinski, J.Lukaszczyk, J.Dudek, and M.Gibas, Macromolecules 9, 622 (1976) and references cited thereof 24. J.Kops and Spanggaard, Makromol.Chem. 175, 3077 (1974) 25. T.Mukaiyama, T.Fujisawa, H.Nohira,and T.Hyngaji, J.Org.Chem. 27, 3337 )1962) 26. K.Tada, T.Saegusa.and J.Furukawa, Makromol.Chem. 95, 168 (1966) 27. M.Sumitomo, M.Okada,and H.Ito, J.Polymer Sci. A1, 6, 3182 (1968) 28. J.Martinez-Madrid and J.L.Mateo, Makromol.Chem. 136, 113 (1970) 29. Z.Jedlinski, J.Maslinska-Solich, J.Polymer Sci.A1, 6, 3182 (1968) 30. J.P.Kennedy and A.L.Langer, Fortschr, Hochpolym. Forsch. 3, 508 (1964) 31. H.Minato and N.Muramatsu, Bull.Chem.Soc.Japan 42, 1146 (1969) 32. W.Kern, H.Deibing, A.Giefer, and V.Jaacks, Pure & Appl.Chem.12, 37 (1966) 32a.C.E.Schweitzer, R.N.Mc Donald, and J.O.Punderson, J.Appl.Polymer Sci. 1, 185 (1959) 33. A.Stolarczyk, P.Kubisa and S.Penczek, submitted for publication 34. W.S.Gresham, U.S.P. 2394910 (1946) 35. P.H.Plesch and P.H.Westermann, J.Polymer Sci C16 , 3837 (1968) 36. V.Jaacks, K.Boehlke, and E.Eberius, Makromol.Chem. 118, 354 (1968) 37. Y.Firat, F.R.Jones, P.H.Plesch, and P.H.Westermann, Makromol.Chem.Suppl. 1, 203 (1975) 38. E.J.Black and D.J.Worsfold, J.Macromol.Sci. A9, 1523 (1975) 39. Z.N.Nysenko, E.L.Berman, E.B.Ludvig, A.P.Klimow, W.A.Ponomarenko, and G.W.Isagulanz, Vysokomol. Soed. 18, 1696 (1976) 40. Y.Yamashita, M.Okada,and H.Kasahara, Makromol.Chem. 117, 256 (1968) 41. J.M.Andrews and J.A.Semlyen, Polymer 13, 142 (1972) 42. P.Kubisa and S.Penczek, submitted for publication 43. R.Szymanski in preparation 44. P.Kubisa, Bull.Acad.Pol.Sci.,in press