We describe here a novel approach to photoinitiate free radical and cationic polymerizations concurrently, involving the use of benzoin in conjunction with an onium salt such as diphenyl iodonium or N-alkoxy pyridinium salt. On photolysis, benzoyl radicals formed from the decomposition of benzoin initiate free radical polymerization of methyl methacrylate. The hydroxy benzyl radicals formed concomitantly are readily oxidized to the corresponding cation by the onium salt to initiate cationic polymerization of cyclohexene oxide in the same system. Evidence for two independent polymerizations was obtained from studies involving gel permeation chromatography, extractions, and infrared and proton nuclear magnetic resonance analysis of the polymers. The effect of the type of the onium salt on each polymerization was also investigated. (C) 2002 Wiley Periodicals, Inc.