Light-induced polymer and polymerization reactions—42. A kinetic study of cationic photopolymerization with (benzoin derivative)/(onium salt) systems

Abstract

Epoxides can be polymerized by cations produced by electron-transfer from photochemically generated nucleophilic radicals to onium salts. Effects of various parameters such as absorbed light intensity ( I abs), onium salt concentration ([On +]), and type of radical source on the rate of polymerization have been measured and appropriate kinetic expressions explaining these dependencies have been derived. For these studies 2,3-epoxypropyl phenyl ether (phenyl glycidyl ether) was used as monofunctional epoxide. The radical sources were 2,3-dimethoxy 2-phenyl acetophenone (benzil dimethyl ketal) (BDMK), benzoin isopropyl ether (BIPE) and α-phenyl benzoin (α-PhB). Diphenyliodonium hexafluorophosphate was the electron acceptor. The quantum yields ( φ P ) of the polymerization, calculated from the polymerization rate R p, follow the order BDMK ⪢ BIPE > α-PhB. Both iodonium salt concentration and light intensity are related reciprocally to monomer conversion. The k p/ k t values calculated from the kinetic expressions lie in the range 22–54 l mol −1.