Poly(methylphenylsilane) (PhMeSi)(n) was used in combination with the addition-fragmentation agents (AFA), namely 2-ethoxycarbonyl-2-propenylpyridinium hexafluoroantimonate (EPP+), ethyl-alpha-tetrahydrothiophenium methyl acrylate hexafluoroantimonate (ETM+) and 2-ethoxycarbonyl-propenyl triphenyl phosphonium hexafluroantimonate (ethoxy carbonly allyl phosphonium salt) (ECAP(+)) to photoinitiate the cationic polymerization of cyclic ethers such as cyclohexane oxide (CHO), alkyl ethers Like n-buthyl vinyl ether (BVE) and vinyl monomers such as methoxy styrene (MOS). By using poly(methyl phenyl silane), the spectral response was extended to 330 nm at which the allyl onium salts are transparent. The feasible mechanism involves radical addition to the allylic bond and subsequent fragmentation to yield reactive species capable of initiating cationic polymerization of related monomers. An alternative mechanism which involves the oxidation of electron donor radicals is also discussed. The initiation efficiency of the salts was studied by determination of the conversion of CHO and BVE. (C)2000 Elsevier Science S.A. All rights reserved.