Cationic ring-opening polymerization behavior of 2-ethenyl-4-methylene-1,3-dioxolane

The cationic ring-opening polymerization of 2-ethenyl-4-methylene-1,3-dioxolane (3) was carried out. The unsaturated cyclic acetal 3 was prepared by dehydrochlorination of 4-chloromethyl-2-ethenyl-1,3-dioxolane, which was readily obtained from acrolein and epichlorohydrin, with sodium methoxide at ambient temperature. The cationic polymerization of 3 with BF3OEt2 or CF3SO3H at −78°C afforded cross-linked polymers, whereas the polymerization by CH3SO3H gave a soluble poly(keto-ether) which consisted of a unit containing a carbon-carbon double bond in the side chain (unit 4) and a unit containing a vinyl ether group in the main chain (unit 5). The reaction of 3 with ethanethiol in the presence of a protic acid was also carried out as a model reaction of the polymerization. The reaction was initiated by addition of a proton to the 4-methylene group of 3, followed by quantitative ring-opening isomerization to afford acyclic ketones containing the ethylthio group. On the basis of the model reaction, some speculation on the polymerization mechanism is disclosed.