Photochemically and thermally induced radical promoted cationic polymerization using an allylic sulfonium salt

Abstract

The photochemically and thermally generated radical promoted cationic polymerization of epoxides such as cyclohexene oxide (CHO) and vinyl monomers such as n-butyl vinyl ether (BVE) and N-vinyl carbazole (NVC) is reported. This system consists of an allylic sulfonium salt, and photochemical and thermal radical initiators. Photoinduced radical generation was achieved with benzoin (B) and 2,4,6-trimethylbenzoyl diphenylacylphosphine oxide (TMDPO) which absorb light at wavelengths where the sulfonium salt is transparent. A feasible mechanism involves radical addition to the allylic double bond and subsequent fragmentation to yield reactive species capable of initiating cationic polymerization. An alternative mechanism which involves the oxidation of electron donor radicals is also discussed. The enhanced activity of the thermal initiators, 2,2′-azobisisobutyronitrile (AIBN), benzoyl peroxide (BP) and phenylazotri phenylmethane (PAT) was confirmed in the polymerization of CHO initiated by the sulfonium salt at 60°C.