A novel addition-fragmentation agent (AFA), 4,4/-bis(N,N,dimethyl, N (2-ethoxy carbonyl-1-propenyl) ammonium hexafluoro antimonate)benzophenone (MKEA) as a photo-initiator for cationic polymerization was synthesized from the precursor Michler's ketone (MK) and characterized. MKEA initiates cationic photo-polymerization of cyclic ethers like cyclohexene oxide (CHO) via conventional addition fragmentation mechanism. Unlike the previously reported AFAs, this initiator does not require supplementary free radical sources. Poly merizations and spectroscopic investigations were performed to help understand the mechanism, with results suggesting that radicals steming from the photo-induced hydrogen abstraction participate addition fragmentation reactions to yield reactive species capable of initiating cationic polymerization. Photo-induced polymerizations of vinyl monomers such as butyl vinylether, isobutyl vinylether and N-vinylcarbazole and a bisepoxide such as 3',4'-epoxycyclohexyl-3',4'-epoxycyclohexene carboxylate by using MKEA were also achieved. (C) 2001 Elsevier Science Ltd. All rights reserved.