On the propagation reactions in the cationic copolymerization of β-propiolactone and styrenes

Die Makromolekulare Chernie 117 (1968) 279-282 (Nr . 2836)

From the Department of Synthetic Chemistry, Faculty of Engineering, Nagoya University ; Furo-cho, Chikusa-ku, Nagoya, Japan

Kurzmitteilung

On the Propagation Reactions in the Cationic Copolymerization of P-Propiolactone and Styrenes

By KOICHI ITO, TOSHIHIDE INOUE, and YUYA YAMASAITA

(Eingegangen am 21. Juni 1968)

We have shown in the previous papers1-3) that the supposed cross- propagation reactions, (1) and (2), proceed very difficultly in the attempt- ed copolymerization of P-propiolactone and styrene (R = H) by SnC14, resulting almost exclusively in the formation of homopolymer mixtures.

CH2 R R @/ \ I I

\ / 1 II I . . .-0 CH2 + CH2=C j . . .-OCH~CH~CCHZC@ (1)

C CsH5 0 C6H5 I1 0

R CH2 R CH2 I / \ I e / \

..-CH2C@ + 0 CH2 + ...- CH2C-0 CH2 (2 ) I \ / I \ /

C6H5 / I / I

0 0 C6H5

The determination of the ketone group contents of the products have proved very little occurrence of the reaction (1). Moreover, such reactions, if any, appear to occur only in the initiation steps because the molecular weights of the products do not change after the hydrolyses of the ester linkages of the P-propiolactone sequences 3). Indeed, no cross-propagation was observed in the a-methylstyrene/p-propiolactone system (R = CH3) using various catalysts such as SnC14, BF30Et2 (boron fluoride etherate), EtsOeBFf (triethyloxonium tetrafluoroborate), Ph&@SbClz (triphenylmethyl hexachloroantimonate), and PhNzPFz (benzenediazonium hexa- fluorophosphinate) 4).

The present communication is intended to prove the absence of the cross-propagation reactions, (1) and (2), by checking the mole-mole reactions using Et30QBFz and Ph3C@SbCl: as the model compounds of

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K. ITO, T. INOUE, and Y. YAMASHITA

oxonium and carbonium ions, respectively, and to examine the reaction mechanism.

All reactions were carried out a t room temperature under nitrogen atmosphere in a dry box. Monomer solution in a dropping funnel was slowly added into the catalyst solution in methylene chloride with mag- netic stirring. The isolated products were analysed by I R and NMR meas- urements and identified by refering to the authentic compounds which had separately been prepared.

1. Reaction of Et30eBFF and 1.1 -DiphenyEethylene

7.4 g (39 m o l e s ) of EtsOeBFs and 7.0 g (39 m o l e s ) of 1.1-diphenylethylene were reacted in 40 ml CHzCl2 for 20 hrs to give a greenish brown solution. After termination by sodium in methanol, the organic products were extracted by ether and the solvent was evaporated. The mixtures were then separated by repeated fractional recrystallizations from methanol into the linear dimer (I) (0.8 g, 11 yo yield) and the cyclic dimer (11) (0.5 g, 7.2 yo yield). The residual oil (5.7 g) consists mostly of unreacted 1.1-diphenylethylene.

C6H5 C6H5 I I mp 114-116°C (lit.5) 113°C)

I I mo1.-wt. 362 (calcd. 360.5) CH3-C-CH=C

NMR: CH3 9.1 7 , =CH 3.3 T, CsH5 2.9 7

C6H5 mp 145-147°C (lit.5) 143OC) I

CHs-C----CHg mo1.-wt. 365 (calcd. 360.5)

NMR: CH3 9.1 T, CH2 6.9 T (AB quartet) I

b y 7 5 C6H5, C6H4 3.0-3.2 T

(11)

NO compound including an ethyl group from EtsOeBFf was detected, indicating that a nucleophilic attack of a x-bond in a vinyl monomer toward an oxonium ion to give a carbonium ion, Eq. (1) or (3), is very difficult.

Et C6H5 C6H5 @/ I I

Et-o B F F + CH,==C + EtCH2C@ B F F + Et,O (3) I I \

C6H5 C6H5 Et

Instead, the formation of the dimeric compounds (I) and (11) may be explained by the presence of traces of water in the reaction system, because water may react with EtsO@BF? to generate a proton which can readily initiate the dimerization of 1.1-diphenylethylene in the same man- ners as found by EVANS et al. using CC13COOH, SnC14/H20, etc.5).

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Cationic Copolymerization of P-Propiolactone and Styrenes

2. Reaction of Ph3C’SbClg and p- Propiolactone

3.6 g (50 mmoles) P-propiolactone and 29 g (50mmoles) Ph,C%bCIF were reacted in 400 ml CHzClz for 28.5 hrs to a dark red solution and terminated by adding isopropyl alco- hol. After evaporation of the solvent, the products were extracted by petroleum ether. Tri- phenylmethane (111) (4 g, 33% yield) was isolated from the soluble fraction in petroleum ether. The insoluble fraction which mostly contains catalyst fragments was not examined further.

(CsH&CH mp 93-94’C (lit.6) 92OC)

(111) NMR: CeH5 3.1 7, CH 4.7 T

No phenyl group was found by I R in the poly-p-propiolactone obtained by Ph3C 8SbCl:. Therefore, a triphenylmethyl carbonium ion appears more readily to abstract a hydrogen from a lactone ring, Eq. (4), rather than to attack on a basic oxygen of a lactone, Eq. (2).

R R ca I H2C-0 I HzC-0

I HzC-GO R R 8

Hydride ion abstraction from a cyclic compound was also reported in the polymerizations of tetrahydrofuran7) and styrene oxides) by Ph3C @SbClz.

3. Reaction of Et30aBFF and p- Propiolactone

This reaction was performed to check the homopropagation step of p-propiolactone, Eq. (5 ) ,

CHz CHz CHz @/ \ / \ @/ \

\ / \ / Ii \ / C C o c ...- 0 CH2 + 0 CH2 + ...- OCHzCH2C-0 CHZ (5)

II II I! 0 0 0

which is supposed to occur by a nucleophilic attack of a basic ether oxygen of p-lactone toward a carbonyl group of an oxonium ion.

10.0 g (137 mmoles) of P-propiolactone and 27.8 g (146 mmoles) of Et,O@BFF were reacted in 65 ml CHZC12 for 28 hrs and terminated by adding methanol. After being”extracted with ether, the products were analysed and separated by gaschromatography. The products isolated were mainly methyl P-ethoxypropionate (IV), accompanied with small amounts of methyl acrylate and methyl P-methoxypropionate. Unreacted P-propiolactone was not detected.

CH3CH20CH2CH2COCH3 NMR : CH3 (a) 8.9 T (triplet), (b) 6.4 T (singlet) I / CH2 (c) 7.5 T (triplet), (d) -6.5 7 (multiplet)

( 4 (d) ( 4 ( 4 0 (b) (IV)

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K. ITO, T. INOUE, and Y. YAMASHITA

Therefore, the reaction (6), as a model reaction of Eq. ( S ) , was proved to occur as expected.

I 1 I ' 0 eBF4 0

MeOH -> EtOCHzCHzCOOMe (IV)

In summary of the above model reactions, we suggest that the cross- propagation reactions, (1) and (2), are difficult to occur because the oxonium ion is not so reactive to attack a x-bond of styrene and because a carbonium ion more readily abstracts a hydride than adds to an ether oxygen of p-lactone. By the same reasons it may be reasonable to say generally that a cationic copolymerization between a vinyl monomer and a cyclic oxygen compound is difficult to produce a random copolymer so long as they propagate through carbonium and oxonium ions, respectively. On the other hand, the success of random copolymerization between styrene and 1.3-dioxolane or benzaldehyde or epoxide suggests a similarity of the propagating speciesg).

1) T. TSUDA and Y. YAMASHITA, Makromolekulare Chem. 86 (1965) 304. 2 ) T. TSUDA, T. SECIMIZU, and Y. Y A M A S ~ A , J. chem. SOC. Japan, ind. Chem. Sect.

3) Y. YAMASHITA, K. UMEHARA, K. ITO, and T. TSUDA, J. Polymer Sci. B 4 (1966) 241. 4) K. ITO, K. UMEHARA, and Y. YAMASHITA, J. chem. SOC. Japan, ind. Chem. Sect. [Kijgya

5 ) A. G. EVANS and D. PRICE, J. chem. SOC. [London] 1959, 2982. 6 ) J. P. NORRIS, in H. GILMAN, Ed., Organic Syntheses, Coll. Vol. 1, 1956, John Wiley

7) I. KUNTZ, J. Polymer Sci. B 4 (1966) 427; J. Polymer Sci. 5, Part A-1 (1967) 193. 8 ) W. M. PASIKA, J. Polymer Sci. A 3 (1965) 4287. 9 ) Y. YAMASHITA, T. TSUDA, M. OKADA, and S. IWATSUKI, J. Polymer Sci. 4, Part A-1

[Kijgya Kagaku Zasshi] 67 (1964) 2145.

Kagaku Zasshi] 70 (1967) 2040.

& Sons, p. 548.

(1966) 2121.

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On the propagation reactions in the cationic copolymerization of β-propiolactone and styrenes

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