Cationic ring‐opening polymerization of 2‐isopropenyl‐4‐methylene‐1,3‐dioxolane

Abstract

Abstract Preparation and cationic ring‐opening polymerization of 2‐isopropenyl‐4‐methylene‐1,3‐dioxolane ( VI ) was performed. Unsaturated cyclic acetal VI was prepared by dehydrochlorination of 2‐isopropenyl‐4‐chloromethyl‐1,3‐dioxolane, which was easily obtained from methacrolein and epichlorohydrin, with sodium methoxide at ambient temperature. The cationic polymerization of VI with BF 3 OEt 2 or CF 3 SO 3 H at −78°C afforded only crosslinked polymers, whereas the polymerization by CH 3 SO 3 H gave soluble poly(keto‐ether) which consisted of units VII containing an isopropenyl group in the side chain and units VIII containing a carbon‐carbon double bond in the main chain. The reaction of VI with ethanethiol in the presence of protic acid was also carried out as a model reaction of the polymerization. The reaction initiated by the addition of proton to the 4‐methylene group of VI , and quantitative ring‐opening isomerization followed by the addition of ethanethiol afforded acyclic ketone IX and X . On the basis of the model reaction, the polymerization mechanism is also discussed. © 1993 John Wiley & Sons, Inc.