Magnesium bromide (MgBr2) as a catalyst for living cationic polymerization and ring-expansion cationic polymerization

Abstract

Magnesium bromide (MgBr₂) was found to be an effective catalyst for the ring-expansion cationic polymerizations of isobutyl vinyl ether (IBVE) initiated by a “cyclic” hemiacetal ester (HAE) bond-based initiator leading to the syntheses of cyclic poly(IBVE)s. Crucial to the achievement is the choice of the quencher (e.g., DMF or DMSO) instead of methanol as well as the realization of living cationic polymerization with an “acyclic” HAE-based initiator under magnesium catalysis. The advantage of MgBr₂ over a conventional catalyst (i.e., SnBr₄) is that several types of cyclic molecules are available as initiators, including a methacrylate type vinylidene group-embedded cyclic compound. The reactive group-carrying initiator allowed the pin-point incorporation of a polar group (e.g., glycerol) into the resultant cyclic polymer via a thiol-Michael addition reaction while retaining the cyclic topology.