Cationic Polymerization of Pendant-Reactive Styrene Derivatives Using Diaryliodonium Salts as Both a Lewis Acid Catalyst and a Photoreactive Reagent

Polymerization of vinyl monomers bearing reactive side chains selectively proceeds via the vinyl addition reactions while keeping the side chains intact by suitably designing reaction conditions. In this study, cationic polymerization of p-chloromethylstyrene, which has a reactive chloromethyl group, was conducted using a diaryliodonium (DAI) salt as both an organic Lewis acid catalyst and a photoreactive reagent. Polymerization proceeded very slowly in the absence of UV irradiation, while the polymerization was accelerated when UV light was irradiated during polymerization. The acceleration likely occurred via the change of the dominant mechanism from atom transfer type into degenerative chain-transfer type as a result of partial consumption of halide anions derived from the carbon–halogen bonds at the propagating ends. Indeed, acceleration occurred when a silver salt was used for halide anion consumption instead of DAI salts. In addition, side reactions at the pendant chloromethyl groups were suppressed during the cationic polymerization with a DAI salt. We also conducted cationic polymerization of p-iodomethylstyrene and p-(1-ethoxyethoxy)styrene as other pendant-reactive styrene derivatives. Side reactions at pendant reactive groups of these monomers were also suppressed in the cationic polymerization with DAI salts.