C3 Cyclopolymerization - American Chemical Society

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C3 Cyclopolymerization: Cationic Cyclopolymerization of 1,3-Bis(p-vinylphenyl)propane and Its Derivatives JUN NISHIMURA and SHINZO YAMASHITA Kyoto Institute of Technology, Department of Chemistry, Faculty of Polytechnic Science, Sakyoku, Kyoto 606, Japan The cyclopolymerization of the title compound (St-C -St), C3 cyclopolymerization, is reviewed. The polymerization has the similar behavior to the fluores cence emission of 1,3-diphenylpropane and its deriva tives (n=3 rule or C3 rule). The monomer and its derivatives were prepared by the convenient method from the corresponding α-phenethylalcohol derivatives, using dimethyl sulfoxide-ZnCl -CCl COOH system. St-C -St gave a cyclopolymer only by cationic initiators, and the presence of cyclized units in the main chain was elucidated by several spectroscopic analyses and also by the isolation of cyclocodimers obtained from the reaction of the monomer with styrene in the presence of the catalytic amount of CF SO H. The cyclopolymerization is revealed to be extreme ly sensitive to the structure of the monomer. Among the monomers investigated, St-C -St, 1,4-bis(p-vinylphenyl)butane (St-C -St), 1,3-bis(p-vinylphenyl)butane, 1,3-bis(p-vinylphenyl)-2-methylpropane, and 1,3-bis(4-vinylnaphthyl)propane (VN-C -VN) were cyclopolymerized. 3

2

3

3

3

3

3

4

3

The i n t r a - and i n t e r m o l e c u l a r i n t e r a c t i o n between c a t i o n i c center and π-electron system have a t t r a c t e d many chemists and much knowledge on the i n t e r a c t i o n has been accumulated (1 ) . In 1975, we intended t o apply such a kind o f i n t e r a c t i o n to c y c l o p o l y m e r i z a t i o n . Thus, i t i s expected that the t r a n s i t i o n s t a t e l e a d i n g to a s t r a i n e d c y c l i c u n i t i n the p o l y m e r i z a t i o n could be s t a b i l i z e d by the i n t r a m o l e c u l a r a t t r a c t i v e i n t e r a c t i o n between c a t i o n i c growing-end and π-system: There had been few examples o f c y c l o polymerizations g i v i n g s t r a i n e d u n i t s . A paracyclophane u n i t was employed as a s t r a i n e d c y c l i c u n i t i n the polymer main c h a i n . In Table I are summarized some cyclophanes with t h e i r s t r a i n energies. According t o the c a l c u l a t i o n reported by Boyd ( 4 ) , most of the s t r a i n of [3.3]paracyclophane (I) i s due to the r e p u l s i o n o f 0097-6156/82/0195-0177$06.00/0 © 1982 American Chemical Society

Butler and Kresta; Cyclopolymerization and Polymers with Chain-Ring Structures ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

178

POLYMERS WITH CHAIN-RING STRUCTURES

Table I Cyclophane

S t r a i n Energies of Some Cyclophanes

S t r a i n Energy kcal/mol(kJ/mol)

Cyclophane

S t r a i n Energy kcal/mol(kJ/mol)

12 (50)

2 (8)

a

See references 2, 3 and 4. given by the present authors.

The values i n parentheses were

the f a c e - t o - f a c e o r i e n t e d π-clouds of benzene r i n g s . When the s t r a i n energy could be reduced o r compensated by the donor-accept or i n t e r a c t i o n between two benzene r i n g s , the s t r a i n e d p a r a c y c l o phane u n i t would be r e a d i l y introduced i n the main chain by a polymerization. In f a c t , the t i t l e compound, l,3-bis(£-vinylphenyl)propane (St-C3-St), was polymerized by some c a t i o n i c i n i t i ators t o a f f o r d the polymer c o n t a i n i n g [3.3]paracyclophane u n i t i n the main chain ( 5 ) .

In t h i s paper, we would l i k e to present the r e s u l t s on the c y c l o p o l y m e r i z a t i o n as a review f o c u s i n g on the s t r u c t u r e o f the monomers and t h e i r c y c l o p o l y m e r i z a b i l i t i e s . P r e p a r a t i o n of S t - C - S t 3

and i t s D e r i v a t i v e s

Since monomers used f o r the c y c l o p o l y m e r i z a t i o n are r a t h e r unusual, but a r e considered to have the usage as c r o s s l i n k i n g agents, a b r i e f d i s c u s s i o n o f t h e i r p r e p a r a t i o n seems to be beneficial. In 1963, S t - C - S t and i t s d e r i v a t i v e s were prepared f o r the 3


14.

NISHIMURA AND

C3 Cyclopolymerization

YAMASHITA

179

f i r s t time by Wiley and Mayberry (6) f o r the study o f t h e i r copolymerizations with s t y r e n e . They used the p y r o l y s i s of a-phenethyla l c o h o l d e r i v a t i v e s over A I 2 O 3 . Recently, Schwachula and Lukas (7) modified the dehydration of α-phenethy1alcohol i n dimethyl s u l f o x i d e (DMSO), which was o r i g i n a l l y discovered by T r a y n e l i s e t a l . (8), and c a r r i e d out the p r e p a r a t i o n of S t - C i - S t i n DMSO i n the presence of a c a t a l y t i c amount of H S0i*. We a l s o independently modified the dehydration i n DMSO with ZnCl -CCl C00H ( 9 ) . 2

2

CH

3

3

CHOH ZnCl 'CCl3COOH

(2)

2

DMSO Our method i s e f f i c i e n t and gives s e v e r a l d i s t y r y l compounds r e l a t e d to St-C3~St i n reasonable y i e l d s . R e s u l t s of the prepara t i o n are l i s t e d i n Table I I . These monomers now can be e a s i l y prepared. Table I I P r e p a r a t i o n of Monomers Monomer

Yield

St-Cx-St St-C -St St-C -St St-C^-St St-C -St VN-C3-VN

(%) 52 68 87 88 73 54

2

3

5

Monomer

Yield

43

u

55^ 59

a

Reference 9.

b

L

Unpublished

S t r u c t u r e o f Cyclopolymer

data.

from S t - C - S t or VN-C3-VN 3

I t i s g e n e r a l l y d i f f i c u l t to confirm the presence of c y c l i z e d u n i t i n a polymer. We can see one of the complete, b e a u t i f u l s t r u c t u r a l proofs i n the s t u d i e s of B u t l e r and h i s a s s o c i a t e s (10, 11). Such a k i n d of proof, however, i s not done u s u a l l y . The polymers, which are made of d i v i n y l monomers and s o l u b l e d e s p i t e of low r e s i d u a l u n s a t u r a t i o n , are apt t o be regarded as c y c l o p o l y -


POLYMERS WITH CHAIN-RING STRUCTURES

180

mers. The c r i t e r i o n i s considered to be v a l i d i f the c y c l i c u n i t i s f i v e - or six-membered, and the degree of p o l y m e r i z a t i o n i s high enough. But more evidences other than the s o l u b i l i t y should be necessary when the c y c l i c u n i t has a p e c u l i a r s t r u c t u r e l i k e a cyclophane. The chemistry of cyclophanes has been s t u d i e d e x t e n s i v e l y by Cram and others (12) , and t h e i r f o l l o w i n g s p e c t r o s c o p i c p r o p e r t i e s are r e v e a l e d : C h a r a c t e r i s t i c absorption around 11 μ i n IR s p e c t r o scopy (13), high f i e l d s h i f t of aromatic protons i n *NMR s p e c t r o scopy due t o the s h i e l d i n g e f f e c t of the opposite aromatic nucleus (14), abnormal absorption at c a . 240 nm and r e d - s h i f t e d , broad Bband i n UV spectroscopy (15), r e d - s h i f t e d CT-band with TCNE i n v i s i b l e spectroscopy (VS) (14, 16), and c h a r a c t e r i s t i c p r o p e r t i e s i n f l u o r e s c e n c e spectroscopy (FS) (17, 18) and CNMR spectroscopy (19), which are d i s c u s s e d below. 13

Table I I I S p e c t r a l Data

1

IR (cm" )

919

UV

Absorption a t ca. 240 nm. Characteristic Β-band.

VS (CT-complex with TCNE, nm) 1

NMR (Aromatic protons, 6)

928 Absorption at ca. 240 nm. Characteristic B-band.

904, 988 Minimum a t ca. 240 nm.

599

608

520

6.4

6.5

7.1

P o l y ( S t - C - S t ) obtained by c a t i o n i c i n i t i a t o r s has the same c h a r a c t e r i s t i c s p e c t r o s c o p i c p r o p e r t i e s as [3.3]paracyclophane. The s p e c t r a l data o f the cyclopolymer and the l i n e a r polymer are shown i n Table I I I , F i g u r e s 1 and 2, together with the cyclophane. I t i s known that [3.3]paracyclophane, which has the almost highest transannular i n t e r a c t i o n of the l e s s d i s t o r t e d benzenes (12), has the f l u o r e s c e n c e emission a t longer wavelength (356 nm) (18) than the excimer of 1,3-diphenylpropane (332 nm). The f l u o r e s c e n c e spectrum of the cyclopolymer, p o l y ( S t - C 3 - S t ) , r e c o r d ed under the same c o n d i t i o n s as f o r [3.3]paracyclophane i s i l l u s t r a t e d i n F i g u r e 1 (20). Both have the f l u o r e s c e n c e a t the same wavelength, and t h e r e f o r e the polymer i s supported to c o n t a i n [3.3]paracyclophane u n i t s as sequence u n i t s . The f l u o r e s c e n c e emission a t 312 nm i s a s c r i b e d t o the r e s i d u a l s t y r y l groups. 3


14.

NiSHiMURA A N D YAMASHiTA


181 1 3

The s t r u c t u r e of poly(St-C3~St) can be a l s o c l a r i f i e d by C NMR spectroscopy. Although the polymer gave a r a t h e r complicated spectrum, carbons i n the l i n k a g e and a p a r t of aromatic carbons, numbered from 1 to 4 i n the s t r u c t u r e i l l u s t r a t e d i n equation (1), were able to be assigned e a s i l y . The chemical s h i f t s o f these carbons are almost the same as those of [3,3]paracyclophane.

(I) The comparison of the chemical s h i f t s with those of the model compounds i s shown i n F i g u r e 2 (20). The carbons at p o s i t i o n 1 and 3 are a f f e c t e d s i g n i f i c a n t l y by the s t r a i n . Recently we i s o l a t e d the cyclodimers shown i n equation (3) , under a c a t i o n i c c o n d i t i o n (21) , so that the s t r u c t u r e of the cyclopolymer, o r the cyclophane-containing polymer i s now f i r m l y established.

Φ

The next i n t e r e s t i n g subject on the s t r u c t u r e would be the e l u c i d a t i o n of the m i c r o s t r u c t u r e of the polymer, u s i n g the s p e c t r o s c o p i c data of model compounds, cyclocodimers and t h e i r derivatives. The s t r u c t u r e of the naphthalenophane-containing cyclopolymer was a l s o c l a r i f i e d i n the same manner as f o r poly(St-C3~St) (22). A l l s p e c t r o s c o p i c r e s u l t s shown i n Table IV are c o n s i s t e n t with the proposed s t r u c t u r e f o r the polymer. Again the recent c y c l o c o d i m e r i z a t i o n f i n a l l y concluded the presence of naphthalenophane u n i t s i n the polymer c l e a r l y (21).

(4)

VN-C3-VN

syn unit

antiunit


182

POLYMERS WITH CHAIN-RING

STRUCTURES

CO s eu

>

u

CO

Wavelength, Figure 1.

400

360

320

nm

Fluorescence spectra of the cyclopolymer and linear polymer of bis(pvinylphenyl)propane.

• P(St-C -St) 3

0 (I)

Β Ο*

< -2

-4

Figure 2. Chemical shift differences in the cyclopolymer and linear polymer of bis(p-vinylphenyl)propane. The standard was 1 3-bis(p-isopropylphenyl)propane. t


14.

NISHIMURA AND

183


YAMASHITA

As shown i n Figure 3, poly(VN-C -VN) have a maximum f l u o r e s cence emission at 356 nm due to r e s i d u a l v i n y l n a p h t h y l groups, 3

Table IV

VS FS

(with TCNE, (nm)

nm)

X

HNMR (aromatic protons, δ)

Spectroscopic Data of Poly(VN-C -VN) and Related Compounds 3

802 356 465 8.0 (br 7.3 (br 6.8 (br

760

m) m)

745 complex

640 358

465 7.27 , 7.77 , (m,8H)° (m,8H) 6.90 , 5.98 . (s,4H) (s,4H)° D

b

7.95 (m,4H) 7.30 (m,10H)

m)

a See Figure 3. b Reference 23. c I n c l u d i n g v i n y l protons, and another at 465 nm due to syn-[3.3](l,4)naphthalenophane u n i t , but e x h i b i t e d l i t t l e emissions from the excimer of open-chain d i naphthylpropane u n i t s and anti-[3.3](l,4)naphthalenophane units. T h i s evidence and that from NMR spectroscopy, which showed almost no resonance at 67.77 f o r a n t i u n i t s , c l e a r l y l e d the c o n c l u s i o n that poly(VN-C -VN) contained syn u n i t s predominantly among two p o s s i b l e isomeric c y c l i z e d u n i t s . In c o n c l u s i o n , d i f f e r i n g from polymers having ordinary c y c l i c u n i t s , the s t r u c t u r e of these cyclophane-containing polymers can be e l u c i d a t e d r e a d i l y and f i r m l y by s e v e r a l s p e c t r o s c o p i c methods. 3

S e v e r a l E f f e c t s on the

Cyclopolymerization

Can any k i n d of i n i t i a t o r produce the cyclopolymer from S t - C St? Since the monomer i s a k i n d of styrene d e r i v a t i v e , so i t could be polymerized by a v a r i e t y of i n i t i a t o r s ; c a t i o n i c , r a d i c a l , a n i o n i c , and c o o r d i n a t i o n c a t a l y s t s , and the question could be answered by the r e s u l t s of the p o l y m e r i z a t i o n . When common r i n g s are incorporated i n cyclopolymers as sequence u n i t s , r a d i c a l and c a t i o n i c i n i t i a t o r s are known g e n e r a l l y to give h i g h l y c y c l i z e d polymers (24). However, a n i o n i c i n i t i a t o r s give a l i t t l e or almost no c y c l i z e d u n i t s i n the main 3


ce

W

Η

§

G η

Figure 3. Fluorescence spectra. (Reproduced, with permission, jrom Ref. 22.)

ο

5

1

ï

S

Ο

H

Jg

m

ce

00

Ο r


14.

185


NISHIMURA AND YAMASHITA

chain. McCormick and B u t l e r suggested that a n i o n i c species must form the unstable 4n7T-system with a double bond i n t r a m o l e c u l a r l y to introduce c y c l i z e d u n i t s i n the main c h a i n , so that the c y c l i z a t i o n does not take p l a c e smoothly (25). We found that r a d i c a l , a n i o n i c , and c o o r d i n a t i o n polymerizat i o n gave benzene-insoluble polymer or s o l u b l e polymer as shown i n Table V (26). These polymers, however, d i d not e x h i b i t the c h a r a c t e r i s t i c s p e c t r a f o r [3.3]paracyclophane u n i t s above mentioned. Therefore they were concluded not to be cyclopolymer. Only c a t i o n i c i n i t i a t o r s could induce c y c l o p o l y m e r i z a t i o n of St-C3~St (27, 28). Before the d i s c u s s i o n on the f a c t that the r a d i c a l i n i t i a t o r s f a i l e d to cyclopolymerize St-C3~St, we need the c l o s e examination of examples f o r the s y n t h e s i s of the [3.3]paracyclophane s k e l e t o n . Because, f o r the syntheses of s t r a i n e d c y c l i c compounds l i k e [3.3]paracyclophane, the p r o p e r t i e s of intermediates formed during r e a c t i o n s seem to a f f e c t the c y c l i z a t i o n of open-chain s t a r t i n g materials. Cram and h i s a s s o c i a t e s (15) used the f o l l o w i n g a c y l o i n r e a c t i o n f o r the c y c l i z a t i o n of the s t a r t i n g m a t e r i a l to [3.3]paracyclophane s k e l e t o n , because the r e a c t i o n of the diphenylpropane d e r i v a t i v e (II) gave very l i t t l e amount of the d e s i r e d c y c l i z e d product, even i f the high d i l u t i o n technique was employed.

/-

C3 Cyclopolymerization - American Chemical Society

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