Ring-Opening Polymerization

6 Ring-Opening Polymerization of Macrocyclic Acetals ROLF C. SCHULZ, K. ALBRECHT, C. RENTSCH, and Q. V. TRAN THI

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 10, 2015 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0059.ch006

Institute of Organic Chemistry, University of Mainz, D-65 Mainz, West Germany

Numerous oxacyclic compounds are well known to form polymers in the presence of cationic initiators. In this way polyethers and polyacetals are obtained (1)(11). Besides the parent compounds, listed in Table 1 many substituted oxacycles, furthermore bicyclic (12)-

Table I. Some polymerizable oxacyclic compounds

77

In Ring-Opening Polymerization; Saegusa, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.


78

RING-OPENING

POLYMERIZATION

(15) as w e l l as spirocyclic oxygen c o n t a i n i n g compounds (16);(17) a r e p o l y m e r i z a b l e . The p o l y m e r i z a t i o n mechanism does n o t o n l y depend on the monomer, b u t a l s o on the initiator and the e x p e r i m e n t a l c o n d i t i o n s . In particular the p o l y m e r i z a t i o n o f 1.2.- and 1.3-epoxides ( 1 ) - ( 5 ) ; ( 1 8 ) ; ( 1 9 ) ; t e t r a h y d r o f u r a n e ( 1 ) ( 4 ) ; ( 6 ) ; ( 2 0 ) ; d i o x o l a n e (21);(22) and t r i o x a n e ( 1 1 ) ; (23)-(26) was t h o r o u g h l y i n v e s t i g a t e d . F o r reviews see ( 4 ) ; ( 8 ) ; ( 2 7 ) ; ( 2 8 ) ; ( 3 0 ) . I t s h o u l d be emphasized, t h a t different o x a c y c l i c monomers c a n a l s o be c o p o l y m e r i zed by cationic catalysts. Of g r e a t practical importance is e.g. the c o p o l y m e r i z a t i o n o f t r i o x a n e w i t h e t h y l e n e o x i d e o r d i o x o l a n e ( 3 1 ) . Macromolecules w i t h a statistic distribution o f oxymethylene- and oxye t h y l e n e - u n i t s a r e formed i n t h i s way. On the o t h e r hand, however, t h e h o m o p o l y m e r i z a t i o n o f d i o x o l a n e y i e l d s a polymer c o n s i s t i n g o f s t r i c t l y a l t e r n a t i n g oxymethylene- and o x y e t h y l e n e u n i t s ( 2 1 ) ; ( 3 2 ) ; t h e r e f o r e i t can f o r m a l l y be c o n s i d e r e d as an a l t e r n a t i n g copolymer ( e q . i ) .

- C H O - •CH CH 0M E a

2

2

(i)

I t i s not formed by a normal c o p o l y m e r i z a t i o n s t a r t i n g from 2 d i f f e r e n t monomers, b u t s i n c e t h e monomer i t s e l f a l r e a d y c o n t a i n s both u n i t s i n the r a t i o o f 1 t o 1. We wanted t o i n v e s t i g a t e , whether i t would be poss i b l e t o p r e p a r e copolymers w i t h o t h e r sequences from analogous monomers by h o m o p o l y m e r i z a t i o n . F o r t h i s purpose one needs c y c l i c a c e t a l s , which c o n t a i n the oxymethylene- and o x y e t h y l e n e - u n i t s i n the d e s i r e d molar r a t i o . Of course d u r i n g t h e p o l y m e r i z a t i o n o f these monomers no e l i m i n a t i o n o f formaldehyde o r r e arrangement may o c c u r , s i n c e o t h e r w i s e the r e g u l a r sequence i n t h e polymer i s d i s t u r b e d . Monomers, which s h o u l d be a b l e t o form sequenced copolymers a c c o r d i n g t o t h e d e s c r i b e d p r i n c i p l e , a r e the compounds /1/-/6/. In t h e f o l l o w i n g , p r e p a r a t i o n and p r o p e r t i e s o f these monomers and the c o r r e s p o n d i n g polymers w i l l be described.



6.

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79

1.3.5-trioxacycloheptane *(trioxepane)/!/ T r i o x e p a n e / l / i s formed as a b y - p r o d u c t d u r i n g t h e copolymerization o f trioxane or tetroxane with e t h y l e n e oxide o r d i o x o l a n e ( 3 3 ) - ( 3 5 ) . F o r i t s p r e p a r a t i o n a mixture o f d i o x o l a n e , paraformaldehyde and s u l p h u r i c a c i d as c a t a l y s t i s h e a t e d up t o 100°C f o r 5 h. A f t e r w a r d s one d i s t i l s a t 12 t o r r and 50°C ( 3 6 ) . A f t e r r e p e a t e d f r a c t i o n a t i o n a l d i s t i l l a t i o n s from lithium-aluminium hydride a gaschromatographically pure monomer i s o b t a i n e d (b.p. 1 3 0 ° C ) . I n t h e H-NMR spectrum o n l y two sharp s i n g l e t s appear (see F i g . l ) . The s i g n a l a t B = 4.92 ppm i s a s s i g n e d t o the methyl e n e p r o t o n s (M) and the s i g n a l a t S = 3.8 2 ppm t o the e t h y l e n e p r o t o n s ( E ) . The peak r a t i o i s e x a c t l y 1 t o 1. An a d d i t i o n o f s h i f t r e a g e n t s (Eu(F0D)3) l e a d s to a s h i f t w i t h o u t s p l i t t i n g o f t h e s i g n a l s ( 3 7 ) . The monomer i s e a s i l y p o l y m e r i z a b l e by c a t i o n i c c a t a l y s t s i n s o l u t i o n and i n b u l k . C o l o u r l e s s , w a x l i k e polymers a r e o b t a i n e d . At the p o l y m e r i z a t i o n o f / l / , e i t h e r the bond between 01 and C2 o r the bond between C2 and 03 can be c l e a v e d . In b o t h cases polymers w i t h the same t r i a d - s e q u e n c e c o n s i s t i n g o f 2 oxymethylene and 1 o x y e t h y l e n e - u n i t s (MME) would o c c u r .


RING-OPENING POLYMERIZATION


80

A change o f the r i n g opening mechanism o r a t r a n s a c e t a l i z a t i o n would o f c o u r s e l e a d to o t h e r sequences. Whereas Gresham and B a l l (36) assume, t h a t the polymers o f t r i o x e p a n e have a r e g u l a r s t r u c t u r e w i t h a r a t i o o f 2 M to I E , Duke (38) c o n c l u d e d from IRand NMR-measurements, t h a t l o n g e r M-sequences must e x i s t . In our own NMR-spectroscopic i n v e s t i g a t i o n s we a l s o found, t h a t i n the homopolymers o f t r i o x e p a n e also MMM-triads ( S = 4,89 ppm) and E M E - t r i a d s ( 6 = 4,77 ppm) o c c u r b e s i d e the e x p e c t e d MME-triads (see F i g . l ) . Furthermore from the 13C-NMR-spectra we were a b l e t o determine pentad-sequences (see F i g . 2 ) and a f t e r a d d i t i o n o f Eu(F0D)3 even heptad-sequences (37). B e s i d e t h i s we c o n f i r m e d , t h a t i n the polymer the mole f r a c t i o n o f the M-units i s e v i d e n t l y l a r g e r than the c a l c u l a t e d v a l u e o f 0,666. T h e r e f o r e the polymer made from / l / has n e i t h e r the r i g h t o v e r a l l c o m p o s i t i o n nor the e x p e c t e d r e g u l a r s t r u c t u r e . In o r d e r t o c l e a r up t h e s e anomalies the p r o g r e s s o f the p o l y m e r i z a t i o n i n d i c h l o r o e t h a n e w i t h boront r i f l u o r i d e a t d i f f e r e n t temperatures was i n v e s t i g a t e d . H e r e t o the d e c r e a s e o f the monomer has been d e t e r m i n e d by gas chromatography ( 3 9 ) . An example o f a t i m e - c o n v e r s i o n curve i s shown i n F i g . 3 . The p o l y m e r i z a t i o n proceeds r a t h e r q u i c k l y ; the monomer con c e n t r a t i o n reaches a f i n a l s t a t e , which does not change o v e r s e v e r a l h o u r s . T h i s c o n c e n t r a t i o n i n c r e a s e s w i t h i n c r e a s i n g p o l y m e r i z a t i o n temperature (see T a b l e 2 ) . These f a c t s l e a d us to c o n c l u d e t h a t i t i s an e q u i l i b r i u m p o l y m e r i z a t i o n . The p l o t o f In (M) a g a i n s t 1/T f o r temperatures between 0° and 60°C i s shown i n F i g . 4 . We c a l c u l a t e d Δ S • -18,9 J/Mol*K and H = -6,6 k J / M o l . By e x t r a p o l a t i o n t o a monomer c o n c e n t r a t i o n o f (M) = 1 Mol/1 i n e q u i l i b r i u m , a f o r m a l c e i l i n g temperature o f 80°C r e s u l t s . In f a c t a t 80°C and w i t h a monomer concen t r a t i o n o f 1 Mol/1 no p o l y m e r i z a t i o n t a k e s p l a c e . But as we found, i n the gas chromatogramm o f the r e a c t i o n m i x t u r e , d i o x o l a n e too i s formed d u r i n g p o l y m e r i z a t i o n (see F i g . 3 ) . T h i s f a c t e x p l a i n s the NMRs p e c t r o s c o p i c s t a t e m e n t , t h a t the polymer does not have the same c o m p o s i t i o n as the monomer, but c o n t a i n s an excess o f M - u n i t s . The c o n c e n t r a t i o n o f d i o x o l a n e a l s o reaches a f i n a l v a l u e , which i n c r e a s e s w i t h r i s i n g p o l y m e r i z a t i o n temperature (see T a b l e 2 ) . But t h i s means, t h a t the c o m p o s i t i o n o f polymer depends on temperature and approaches the t h e o r e t i c a l v a l u e o n l y at low p o l y m e r i z a t i o n t e m p e r a t u r e . The d e s c r i b e d r e s u l t s show, t h a t i n the p o l y m e r i z a t i o n o f t r i o x e p a n e s s

A

S

S


Polymerization

SCHULZ ET AL.


6.

of Macrocyclic

Acetals

Figure 1. H-NMR spectra of trioxepane / l / and the polymer

ι

2

Figure 2. C-NMR spectrum of a polymer of trioxepane (CDCU; 25, 2 MHz). (1) MEMEM; (2) MMMEM; (3) EMMEM; (4) MMMMM; (5) EMMMM; (6) EMMME; (7) MMEMM; (8) ΎΜΕΜΕ, EMEMM. 13

Γ92.35 89.06!88,27 67.41 66.79 95,45 91.99 88.68

6 in ppm


81

82

RING-OPENING POLYMERIZATION Polymerization of trioxepane at 20°C with BF .Et 0 in CH-pCHfl


3

2

Figure 3. Time-conversion curve for the consumption of monomer (χ) and forma tion of dioxolane (O) during the polymeri zation of trioxepane /!/

*

*

11-

rit-

Table II· E q u i l i b r i u m c o n c e n t r a t i o n o f Dioxolane £DOlJ d u r i n g p o l y m e r i z a t i o n o f t r i o x e p a n e / l / w i t h BF^-etherate i n dichloroethane e

[m£ (Mol/1)

temp.(°C)

JDOLj

Q

5,55

0

5,72

20

0,50

5,82

30

0,60

5,50

45

1,01

5,71

60

1,36

(Mol/1)

0,23

Polymerization of

0

in Cf^CICH a 2

-0J

mth BF .Et 0 3

2

-0.3

-05 -Q6 Ό.7 -0.6 Figure 4. Monomer concentration at equilibrium in the polymerization of trioxepane /!/

3.5 eo

30

0

I VTtK .1(P] 4

X


2Ch

6.

SCHULZ ET AL.

Polymerization

of Macrocyclic

Acetals

83

s e v e r a l r e a c t i o n s o c c u r s i m u l t a n e o u s l y and d i f f e r e n t polymers and monomers are formed s i d e by s i d e . The f o l l o w i n g scheme comprises the o b s e r v a t i o n s .


stst. copolymer

(iii)

J polymer +X

3o) i n d i c a t i n g t h a t the r a t e o f i n i t i a t i o n i s c o n s i d e r a b l y lower than t h a t o f p r o p a g a t i o n and t h a t the p o l y m e r i z a t i o n i s accompanied by some c h a i n b r e a k i n g r e a c t i o n s . The thermodynamic parameters o f the e q u i l i b r i u m p o l y m e r i z a t i o n o f 111 (and some r e l a t e d c y c l i c f o r m a i s ) was s t u d i e d i n more d e t a i l by Yamashita e t a l . (22) and by B u s f i e l d and Lee ( 4 4 ) . Furthermore, i t was p o s t u l a t e d t h a t the polymer degraded e x c l u s i v e l y to monomer i n the p r e s e n c e o f boron t r i f l u o r i d e . In our own work we were o c c u p i e d p r e d o m i n a n t l y w i t h the NMR-spectroscopic sequence a n a l y s i s , i n o r d e r t o see, whether the c o n c e p t f o r p r e p a r i n g sequenced copolymers, d e s c r i b e d a t the b e g i n n i n g , c o u l d be v a l i d a t e d (41). In the H-NMR-spectrum the monomer 11/ shows o n l y two sharp s i n g l e t s a t S = 3,8 ppm (E) and S = 4,9 ppm (M) w i t h a peak r a t i o o f 4 to 1 (see F i g . 5 ) . A d d i t i o n o f Eu (DPM)3 e f f e c t s a s h i f t t o lower f i e l d and a s t r o n g s p l i t t i n g o f the e t h y l e n e s i g n a l , as the p r o t o n s a t C4 and C8 are not e q u i v a l e n t to the p r o t o n s at C5 and C7. In the H-NMR-spectra o f the homo polymer a l s o o n l y two peaks o c c u r , h a v i n g the same peak r a t i o as i n the monomer (see F i g . 5 ) . From t h i s , i t can be c o n c l u d e d , t h a t not o n l y the o v e r a l l compo s i t i o n but a l s o the o r d e r o f M- and Ε-units i s the same i n polymer and i n monomer. Hence t h e r e i s o n l y one k i n d o f r i n g opening and rearrangements or e l i m i n a t i o n s can be e x c l u d e d . That means, i n f a c t , t h a t a t the r i n g opening h o m o p o l y m e r i z a t i o n o f t r i o x o c a n e , a sequenced copolymer w i t h a r e g u l a r sequence o f (MEE)t r i a d s i s formed ( e q . v i i ) .

— CH 0 — CH CH 0 — CH CH 0 — M E Ε 2

2

2

2

2

(vii)

χ

T h i s f i n d i n g agrees w i t h the r e s u l t s o f W e i c h e r t (42) who a n a l y s e d the s t r u c t u r e o f p o l y t r i o x o c a n e by a c T 3 i c d e c o m p o s i t i o n . I n d i c a t i o n s o f endgroups have not been


6.

SCHULZ ET AL.

Polymerization

of Macrocyclic

85

Acetàls

found, from which one s h o u l d not c o n c l u d e , t h a t macroc y c l i c polymers are i n hand.


1.3.6.9-tetraoxacycloundecane f o r m a l ) /3/

(triethylene

glycol

T h i s compound and i t s p o l y m e r i z a b i l i t y was f i r s t mentioned by C a r o t h e r s ( 4 5 ) . I t i s p r e p a r e d from t r i e t h y l e n e g l y c o l and p a r a f o r m a l d e h y d e ; by a d d i t i o n o f s t r o n g a c i d s a p r e p o l y m e r i s p r o d u c e d . From t h i s , the monomer /3/ i s s p l i t o f f i n a second s t e p by h e a t i n g i n vacuo. The monomer used by us has the f o l l o w i n g p r o p e r t i e s : m.p. 27°C; b.p. 56°C/0,4 T o r r ; ηβ° = 1,4541; NMR-signals o f /3/ were f i r s t r e p o r t e d by Burg ( 4 9 ) . NMR d a t a o b t a i n e d by us are summarized i n T a b l e I I I and IV. /3/ i s p o l y m e r i z a b l e by s e v e r a l c a t i o n i c i n i t i a t o r s i n s o l u t i o n and i n b u l k a t temperatures between -20°C and +150°C. The polymers are c o l o u r l e s s w a x l i k e s u b s t a n c e s ; they are r e a d i l y s o l u b l e i n water, THF, a r o m a t i c h y d r o c a r b o n s , a l c o h o l s and h a l o g e n a t e d hydro carbons . In the H-NMR spectrum o f the polymer o n l y 3 sharp peaks appear a t $ = 4,72; 3,67 and 3,65 ppm (see T a b l e I I I . T h e peak r a t i o o f M:E =1:6 agrees w i t h t h a t o f the monomer. The 13C-NMR-signals are at 5 =95,4; 70,4 and 66,8 ppm (see T a b l e IV) .There are no i n d i c a t i o n s o f an i r r e g u l a r s t r u c t u r e and we t h e r e f o r e c o n c l u d e , t h a t the polymer a t l e a s t c o n t a i n s v e r y l o n g b l o c k s o f (MEEE)-tetrads and c o n s e q u e n t l y can be d e s c r i b e d as a sequenced copolymer ( e q . v i i i ) .

— C H 0 — (CH CH 0) Μ Ε 2

2

2

3

(viii)

3

χ

A f t e r e s t a b l i s h i n g the s t r u c t u r e o f the polymer we s t u d i e d i n d e t a i l the way o f f o r m a t i o n . Hereto we c a r r i e d out s o l u t i o n - p o l y m e r i z a t i o n s i n methylene c h l o r i d e under argon-atmosphere ( 5 o ) . Monomer con c e n t r a t i o n s were between 0,15 and 2,5 Mol/1, tempe r a t u r e between -20°C and +20°C. T r i f l u o r o m e t h a n e s u l p h o n i c a c i d s e r v e s as c a t a l y s t . A f t e r d e f i n i t e t i m e s , p o l y m e r i z a t i o n was quenched by the a d d i t o n o f some b a s i c aluminium o x i d e o r t r i e t h y l a m i n e and the




Polymer

—

s

ο Figure 5. H-NMR spectra of tri oxocane /!/ and its polymer

5voV«u> 4 . ο " " 3

T a b l e I I I . H-NMR s i g n a l s o f t r i e t h y l e n e g l y c o l f o r m a l (M^), the polymer (P) and the oligomers o f the g e n e r a l formula/7/ -0-CH -02

-0-CH - CH -02

2

4.79

3.63

4.75

3.72

3.68

4.75

370

3.67

4.75

3.69

3.67

"δ

4.74

3.69

3.66

**6

4.74

3.69

3.66

M

4.75

3.69

3.66

"e

474

3fiB

3.67

Ρ

4.72

3.67

3.6S

7

3.69


6.

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87

c o m p o s i t i o n o f the r e a c t i o n m i x t u r e was a n a l i z e d by h i g h p r e s s u r e g e l p e r m e a t i o n chromatography (HP-GPC) (Waters ALC/GPC 2ol w i t h Ri d e t e c t o r R 401; Stationary phase: S t y r a g e l ; 100 X + 500 X mobile phase: methylene c h l o r i d e ) . I t appears t h a t under the a p p l i e d r e a c t i o n con d i t i o n s not o n l y polymers (with m o l e c u l a r weights from 10,000 to 80,000) are formed, but a l s o n o t i c e a b l e amounts o f s e v e r a l o l i g o m e r s ( l a b e l l e d as M2 t o M± see F i g . 6 ) . I f the consumption o f monomer M, the f o r mation o f o l i g o m e r M 2 , and the t o t a l o f a l l h i g h e r o l i g o m e r s and polymers are p l o t t e d as a f u n c t i o n o f t i m e , t i m e - c o n v e r s i o n c u r v e s r e s u l t as shown i n F i g . 7 . One can see, t h a t a f t e r about 3o minutes a f i n a l s t a t e i s r e a c h e d w i t h about 3,51 r e s i d u a l monomer and about 9% M. I f pure polymer i s t r e a t e d w i t h trifluoromethane s u l p h o n i c a c i d under the same c o n d i t i o n s , e v e n t u a l l y e x a c t l y the same f i n a l s t a t e ( r e f e r r i n g t o type and amount o f monomer, o l i g o m e r and polymer) i s r e a c h e d (see F i g . 8 ) . Hence i t i s s u r e l y a m a t t e r o f a thermo dynamic e q u i l i b r i u m p o l y m e r i z a t i o n . W i t h i n a range o f i n i t i a l monomer c o n c e n t r a t i o n between 0,2 to 0,5 Mol/1 the 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 i s c o n s t a n t and amounts at 0°C t o (0,0146 ± 0,0016) Mol/1. The equili b r i u m c o n c e n t r a t i o n o f the dimer a t 0°C i s (0,0236 0,0013) Mol/1. The temperature dependence o f t h e s e c o n c e n t r a t i o n s was s t u d i e d f o r the p o l y m e r i z a t i o n i n methylene c h l o r i d e between -25°C and + 30°C w i t h t r i fluoromethane s u l p h o n i c a c i d as c a t a l y s t . A D a i n t o n p l o t o f the r e s u l t s i s shown i n F i g . 9 . We c a l c u l a t e d from the s l o p e and the i n t e r c e p t ^ H s s = (-1,9 * 0,2) k c a l / M o l = (-7,95 0,8)kJ/Mol and Δ S g = (+1,5 0,5) c a l / M o l * K = (+6,24 * 2,1) J/Mol*K. The s m a l l and p o s i t i v e entropy i s noticeable.


9

2

±

±

s

C y c l i c o l i g o m e r s o f the

t r i e t h y l e n e g l y c o l formal

From the above mentioned r e s u l t s , i t f o l l o w s t h a t the o b s e r v e d o l i g o m e r s are not b y - p r o d u c t s , but are a l l p r e s e n t i n a r e v e r s i b l e e q u i l i b r i u m w i t h the monomer and the polymer. T h e r e f o r e i t i s i m p o r t a n t to know t h e i r s t r u c t u r e and - i f p o s s i b l e - the way o f f o r m a t i o n . We succeeded i n i s o l a t i n g and i d e n t i f y i n g the f i r s t 8 members o f the homologous s e r i e s o f o l i g o m e r s by p r e p a r a t i v e GPC. R e c e n t l y a d e t a i l e d d e s c r i p t i o n has been p u b l i s h e d by us (51). The s u b s t a n c e c a l l e d M~



Table IV. C-NMR s i g n a l s o f t r i e t h y l e n e g l y c o l f o r m a l (M^), the polymer (P) and the oligomers o f the g e n e r a l formula / ? / -0-CI1 -CH -0-

-C-CH -0-

2


2

2

67.8

70A

96.2

70.6

M

95.1

70.8

70.6

C6A

"3

95.3

70A

702

C6.6

953

70/,

66.6

%

95.4

70A

66.7

M

95,6

70.5

66J9

95.6

70.6

66#

"a

95.6

70.5

6Ô.9

P

95A

70A

66.8

2

6

S 10

1

15

19 mÎ

/M,/ « 0.5MotII; CH&i 0°C 0

Figure 6. HP-GPC curves of the reaction mixture during the polymerization of triethylene glycol formal /3/

[CF S0 H1 = 0.1 Mol-% 3

3

μ-εί/ΓΟ&δΟΟλ +100Ai 1.0 ml CH a lmin 2

2


SCHULZ ET AL.

Polymerization

of Macrocyclic

Acetals


υ

20

min 10

Figure 7. Time-conversion curve for the consumption of monomer (M ), formation of polymer (P), and dimer (M ) during the polymerization of triethylene glycolformal /3/* (deter mined by HP-GPC) t

Γ

3$0 H

J

CF

3

t Ch^C^O^

2

0.5 Mol It ; 0,1Mol-%

startg. soin

•Ο

equilibrium

8 10 15 iSml tPlos [M^ 0.31Molll CH C^ o lCF S0 Hj=Q1Mol-% μ-Styragel 500A* 100 A Wm/CH q2/min s

3

:

2

3

;

2

:0

C

Figure 8. HP-GPC curves of the reaction mixture dur ing depolymerization of a polymer of triethylene gly colformal /3/



90


i n HP-GPC t u r n e d out t o be the c y c l i c dimer o f compound /3/. The dimer i s p o l y m e r i z a b l e under the same c o n d i t i o n s as /3/ and a f t e r r e a c h i n g the e q u i l i b r i u m i t l e a d s t o the same o l i g o m e r d i s t r i b u t i o n as the monomer and the polymer (see F i g . l o ) . A l l o l i g o m e r s a r e c o l o u r l e s s c r y s t a l l i n e compounds.The m e l t i n g p o i n t s (see T a b l e V) o f the o l i g o mers w i t h even-numbered m u l t i p l e s o f t h e monomers a r e always h i g h e r than the odd-numbered ( 4 7 ) . The H-NMRs p e c t r a a r e n e a r l y i d e n t i c a l f o r a l l o l i g o m e r s and l e a d t o the c o n c l u s i o n , t h a t a l l have analogous s t r u c t u r e (compare T a b l e s I I I and I V ) . I n d i c a t i o n s o f endgroups a r e n o t a v a i l a b l e e i t h e r i n t h e NMR- o r i n the IR-spectra, v e r i f y i n g that i t i s a matter o f c y c l i c o l i g o m e r s . The mass s p e c t r a o f the dimer ( M 2 ) and the t r i m e r ( M 3 ) gave the e x p e c t e d m o l e c u l a r i o n s . The g e l c h r o m a t o g r a p h i c e l u t i o n volumes f o r a l l o l i g o m e r s a r e on a common curve which i s , however, c l e a r l y d i f f e r e n t from the curve f o r open c h a i n e t h y l e n e g l y c o l o l i g o mers ( F i g . 1 1 ) . T h i s p r o v e s , t h a t the o l i g o m e r s occur i n g a t the p o l y m e r i z a t i o n o f /3/ ( c a t a l y z e d by t r i fluoromethane s u l p h o n i c a c i d ) have the f o l l o w i n g g e n e r a l s t r u c t u r e 111.

7

Whether a l s o the h i g h polymers have r i n g s t r u c t u r e , has h i t h e r t o n o t y e t been d e f i n i t e l y p r o v e d o r d i s proved. The f o r m a t i o n o f c y c l i c o l i g o m e r s can be exp l a i n e d by two d i f f e r e n t mechanisms: a) a s t e p w i s e r i n g e x t e n s i o n takes p l a c e by i n s e r t i o n a t the f o r m a l bond w i t h o u t f o r m a t i o n o f l i n e a r i n t e r m e d i a t e s ( 2 7 ) ; ( 5 2 ) ( s e e Scheme 1) b) the c h a i n growth proceeds by open c h a i n c a r b o x onium-ions ( p o s s i b l y i n e q u i l i b r i u m w i t h e s t e r g r o u p s ) ( 5 3 ) ; ( 5 4 ) and the c y c l i c o l i g o m e r s a r i s e by back-ïïTting (see Scheme 2 ) . From our r e s u l t s we cannot d e c i d e , which mechanism p r e v a i l s . F i n a l l y i t s h o u l d be mentioned t h a t d u r i n g s e v e r a l o t h e r p o l y c o n d e n s a t i o n s and i o n i c p o l y m e r i z a t i o n s , the


6.

Polymerization

SCHULZ E T A L .

à H


d S

of Macrocyclic

91

Acetals

- - 7,β5 ± 0,0 Κ J/Mol

s s

SS

a

*

6

i

2 4

± >* 7

J

/

K

M

o

1

e

•-25 C

4

M

- 1 0 ^

Figure 9. Monomer concentration at equilibrium in the polymerization of Methylene glycol formal /3/

5 70 2

19ml

/5

IM J

0.23 Mollh CH CI ; 0°C

Qs

2

2

[CF S0 H] = 0.18 Mol-% 3

3

μ-Styragel 500Â Wml Chimin :

Figure 10. HP-GPC curves of the reaction mixture during the polymerization of the aimer of Methylene glycol formal (M ) g



Table V.

Melting points of c y c l i c


oligomers o f the general

s t r u c t u r e /7/

Degree

number

melting

o f polym.

of ring

point

x

atoms

°C

Μ

χ

1

11

27

M

2

2

22

88

M

3

3

33

27

M

4

4

44

56

M

5

5

55

19

M

6

6

66

38

M

?

7

77

23

Μ

Λ

8

88

28

loçMW\MW 3.3 PEG1500l\

Ma

•1C00 RING •562

PEG60o\

Ring-Opening Polymerization

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