Macromol. Rapid Commun. 15,579-585 (1994) 579

Regioselective polymerization of vinyl ketene cyclic acetal by means of cationic initiators

Hiroyuki Fukuda*, Mitsuo Oda

Nagoya Municipal Industrial Research Institute Rokuban, Atsuta-ku, Nagoya 456, Japan

Takeshi Endo

Research Laboratory of Resources Utilization, Tokyo Insitute of Technology, Nagatsuta, Midori-ku, Yokohama 227, Japan

(Received: March 16, 1994)

Introduction

It is known that the /%carbon atom of the carbon-carbon double bond of ketene acetals is highly polarized and has a strong anionoid character which arises from the electron-donating property of the conjugated two oxygen atoms. Therefore, most of the ketene acetals are prone to react with protic substrates and easily undergo cationic polymerization. It can be expected that this unique character of the /3-carbon atom is applicable to develop new reaction processes. We have reported cationic polymerization of cyclic ketene acetals I) , reaction of cyclic ketene acetals with methanol2), isocya- nate 3, and i~othiocyanate~), and copolymerization of cyclic ketene acetals with carbon disulfide '). From a different viewpoint, radical polymerization of cyclic ketene acetals has been reported6-').

In the course of our study of ketene acetal chemistry, we have designed vinyl ketene cyclic acetals, which are new 1,3-diene monomers having one more conjugated carbon- carbon double bond at thep-carbon atom of the unsaturated double bond of the ketone acetal. We have great interest in their cationic polymerizability, and there are few papers on cationic polymerization of 1,3-diene monomers to our knowledge. Further, several polymerization modes can be anticipated, as shown in Scheme 1. Recently, Cho and Kim have reported radical polymerization of a vinyl ketene cyclic acetal lo).

In this article, we describe the regioselective polymerization of 4-phenyl-2-propenyl- idene-I ,3-dioxolane by means of cationic initiators.

Experimental part

4-Phenyl-2-propenylidene-I,3-dioxolane (1)

To a solution of 5.05 g (45 mmol) of potassium tert-butoxide in 25 mL of DMF was added a solution of 8,07 g (30 mmol) of 2-bromo-2-phenylethyl 3-butenate, which was prepared from vinylacetic acid and 2-bromo-2-phenylethano1, in 25 mL of DMF dropwise with stirring at - 15 "C for 1 h. After the reaction mixture had been stirred at the same temperature overnight, DMF was removed under reduced pressure. The residue was dissolved into 50 mL of ether, the precipitated solid was filtered off. After the evaporation of the ether, the residue was fractionally distilled over metallic sodium in vacuo. The purification of the product was carried out by further

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580

Scheme I:

H. Fukuda, M. Oda, T. Endo

1,4-Polymerization

+[ 'k0J ] -+ +CHzCH=CHCOCHzCHz+j II

0 1,7-PoIymerization

I X; Initiator

CH,= FH

3,4-Polymerization

-(- CH - COCH,CH,--fT; II 0

3,7-Polymerization

- CH2=Y

distillation over metallic sodium to give 2,64 g (50%) of 1; b.p. 95-96"C/0,12 Torr [lit"): 96"C/0,05 Torr].

IR (neat): 1 680, 1040 cm-'. IH NMR (CDCI,): 6 = 3,94-4,16 (dt, J = 8,2 Hz, 1 H), 4,42-4,96 (m, 3H), 5,27-5,50 (dt,

J = 8,2 Hz, lH), 6,51 (ddd, 10,7, 10,7, 17,6 Hz). "C NMR (CDCI,): 6 = 69,6, 70,1, 73,4, 76,0, 764, 104,8, 104,9, 1235, 125,7, 126,0, 126,3,

128,4, 128.5, 158,l.

Model compound 2

To a solution of 1,5 g (8,5 mmol) of 1 in 4 mL of chloroform was added 4 mL of methanol at 0 "C. The reaction mixture was allowed to stand at room temperature overnight. After the solvent and excess methanol had been removed under reduced pressure, the residue was fractionally distilled in vacuo to give 1,78 g (95%) of 2-allyl-2-methoxy-4-phenyl-1,3-dioxolane (2); b. p. 105 - 106 "C/0,2 Torr.

IR (neat): 1 640, 1 070 cm - I . 'H NMR (CDC13): 6 = 2,50-2,83 (m, 2H), 3,39 (s, 3H), 3,52-3,96 (m, 1 H), 4,14-4.56 (m,

1 H), 4,90-5,38 (m, 3H), 5,65-6,21 (m, 1 H), 7.34 (s, 5H).

128,1, 128,4, 131.9, 138,4. 13C NMR (CDCI,): 6 = 40,2, 40,6, 49,5, 71,7, 72,3, 78,1, 78,4, 118,l. 122,3, 125,9, 126,0,

Regioselective polymerization of vinyl ketene cyclic acetal . . . 581

Cationic polymerization

Cationic polymerization was performed under argon atmosphere. Typically (Tab. 1, entry No. 1), a solution of 0,s g (2,7 mmol) of 1 in 4 mL of dichloromethane was placed in a polymerization tube equipped with a No-Air stopper. After the solution had been purged with a stream of argon at -30°C for 30 min, 1 mL of dichloromethane solution containing 5,75 mg (1,5 mol-%) of boron trifluoride etherate was added by a syringe. The reaction mixture was maintained at the same temperature for 10 min and then allowed to stand at room temperature for 72 h. The reaction mixture was poured into hexane to precipitate a white solid. The precipitated polymer was collected, and then the isolated polymer was purified by reprecipitation from chloro- form solution into hexane to afford 0,48 g (96% of Poly-1.

IR (film) 1745, 1 510, 1460, 1 165, 1035 cm-'. 'H NMR (CDCI,): 6 = 1,07-3,10 (br m, 1 H), 3,20-3,85 (br m, 1 H), 3,92-4,47 (br m, 1 H),

I3C NMR (CDCI,): 6 = 35,3, 43,0, 53,8, 65,5, 67,8, 71,3, 78,8, 112,5, 120,0, 126,0, 128,0, 4,60-5,40 (br m, 2H), 5,57-6,15 (br m, 1 H), 6,42-7,68 (br s, 5H).

136,5, 138,0, 171,3.

Results and discussion

4-Phenyl-2-propenylidene-1,3-dioxolane (1) was synthesized in fairly good yield by the reaction of 2-bromo-2-phenylethyl 3-butenate and potassium tert-butoxide in N,N-dimethylformamide at - 15 "C.

r

Tab. 1. Results of cationic polymerization of vinyl ketene cyclic acetal 1 a)

No. Reaction conditions Polymer

initiator (mol-%) solvent yield in 070 b, a,,') Mw/Mnc)

1 BF, . OEt, (1.5) CH2CI2 96 6 800 3,1 2 SnCl, (45) CHCI, 28 d, 4 200 290 3 CF3S03H (2.0) CH2C12 91 2 800 2 2 4 I2 ( 2 3 CCl, 55 2 300 2,s 5 AICI, (43) CHCl, 64 19OOo 1 3

a) Cationic polymerization of 1 was carried out at 25 "C for 72 h. b, Insoluble in hexane. ') Estimated by GPC calibrated with polystyrene standards. dl Insoluble in diethyl ether.

582 H. Fukuda, M. Oda, T. Endo

Cationic polymerization of 1 was carried out by using iodine, trifluoromethanesul- fonic acid and Lewis acids such as boron trifluoride, tin(1V) chloride, and aluminium chloride. The polymers were isolated by pouring the reaction mixture into hexane. The results are summarized in Tab. 1. The obtained polymers were stable and soluble in chloroform, THF, acetone, and so on. The structure of the polymers was confirmed by IR, 'H and I3C NMR spectra.

IR spectra of Poly-1 (entry No. 1 - 5 ) are shown in Fig. 1. IR spectra of the polymers obtained from boron trifluoride, trifluoromethanesulfonic acid, and tin(1V) chloride showed the strong broad absorption band ascribed to ketal linkage at about 1035 cm-' together with the ester band at 1745 cm-I. 'H NMR spectrum of Poly-1

4000 3000 2000 1700 1000 500 Wavenumber in cm-'

Fig. 1. IR spectra of Poly-1 obtained by various initiators: (A) BF, . OEt,; (B) SnCI,; (C) CF3SO3H; (D) 1,; (E) AICI3

Regioselective polymerization of vinyl ketene cyclic acetal . . . 583

obtained from boron trifluoride (entry No. 1) is depicted in Fig. 2. Five broad signals centered at 5,7 ppm (CH,=CI-J-), 5,O ppm (C&=CH- and -CHPh-), 4,2 ppm and 3,6 ppm (-OCbCHPh-), and 2,4 ppm (-CI-J- of polymer backbone) were observed in 'H NMR spectrum, and the intensity ratio of these signals was 1 : 3 : 1 : 1 : 1. In order to confirm whether these assignments were reasonable or not, the model compound 2-allyl-2-methoxy-4-phenyl- 1,3-dioxolane (2) was prepared by the reaction of 1 with methanol. It is obvious that the 'H NMR spectrum of Poly-1 is in good agreement with that of the model compound 2. These results may suggest that the obtained polymer is composed of the 3,4-polymerization structure. However, the IR spectrum (Fig. 1 (A)) clearly showed the presence of the ester structure coming from the ring-opening of the 1,3-dioxolane ring. Therefore, it can be assumed that polymeri- zation of 1 by using boron trifluoride, trifluoromethanesulfonic acid, or tin(1V) chloride as an initiator gives a polymer with almost complete 3,4-polymerization structure containing the 3,7-polymerization structure as an irregular structure.

a h

a e d 2 2 i A, ,O~H~

10 9 8 7 6 5 L 3 2 1 0 6 in pprn

Fig. 2. with BF, . OEt,; (B) 2-allyl-2-methoxy-4-phenyl-1,3-dioxolane (2)

'H NMR spectra of Poly-1 and the model compound in CDCl,: (A) Poly-1 obtained

5 84

(A1

H. Fukuda, M. Oda, T. Endo

1 0

a b c \ I d e

d Y

CHz=r - Y&p- +CHo-C,%

1 \ 52 cat. BF, * OEtz ,CF,SO,H , SnCI,

[Ed

b d

On the contrary, it was found that IR spectra of Poly-1 initiated by iodine and aluminium chloride (Fig. 1 (D) and (E)) showed characteristic strong absorption bands at 1715 cm and 1645 cm-' which were assignable to the conjugated ester carbonyl and carbon-carbon double bonds. As depicted in Fig. 3 (A), 'H NMR spectrum of Poly-1 showed the olefinic a-methine and P-methine protons adjacent to carbonyl group at 5,s-5,9 ppm (-CH=CE-CO--, br d, J = 15,2 Hz) and 6,4-6,9 ppm

0 a f i c t l e f + CH2CH=CHCOCHlCH-t;;

Q g

C

Fig. 3. (A) 'H and (B) l3C NMR spectra of

I I I I I I I I I I

1 0 9 8 7 6 5 L 3 2 1 0 6 in ppm

Regioselective polymerization of vinyl ketene cyclic acetal . . . 585

(-CH=CH-CO-, br m), respectively. The I3C NMR spectrum (Fig. 3 (B)) showed six signals (except for absorptions due to aromatic carbons) at 165,6 ppm (--_COO-), 146,2 ppm (--_CH=CH-CO-), 122,7 ppm (-CH=cH-CO-), 67,2 ppm (-OCH,CHPh-), 44,l ppm (-OCHSHPh-), 35,l ppm (-CHPh-_CH,CH=). It is noteworthy that any signals based on the remaining ketal ring structure can not be detected in both 'H and 13C NMR spectra. Therefore, it may be suggested that cationic polymerization of 1 with iodine or aluminium chloride completely proceeds through the 1,7-polymerization process and that the resulting polymer only consists of the trans structure judging from the coupling constant.

Further studies on regioselective polymerizations such as 1,2-, 1,4- and 3,7-polymeri- zations are now in progress.

') H. Fukuda, M. Hirota, Y. Nakashima, J. Polym. Sci., Polym. Lett. Ed. 21, 171 (1983) 2, H. Fukuda, M. Hirota, T. Endo, Tetrahedron Lett. 27, 1587 (1986) 3, H. Fukuda, M. Hirota, T. Endo, Tetrahedron Lett. 29, 1587 (1988) 4, M. Hirota, H. Fukuda, T. Endo, Polym. Prepr. Jpn. 34, 2327 (1985) 5, T. Endo, H. Fukuda, M. Hirota, J. Am. Chem. SOC. 106, 3035 (1984) 6, W. J. Bailey, Z . Ni, S. R. Wu, Macromolecules 15, 711 (1982) ') W. J. Bailey, S. R. Wu, Z. Ni, MakromoE. Chem. 183, 1913 (1982) *) I. Cho, M. S . Gong, J. Polym. Sci., Polym. Lett. Ed. 20, 361 (1982) ') W. J. Bailey, Z . Ni, S. R. Wu, J. Polym. Sci., Polym. Chem. Ed. 20, 3021 (1982)

lo) I. Cho, S. K. Kim, 1 Polym. Sci., Part C: Polym. Lett. 28, 417 (1990)