Recently there has been a growth of interest in the use of diaryliodonium salts (Ar2I+X-), triarylsulfonium salts (Ar3S+X-) and triarylselenonium salts (Ar3Se+X-) as photochemical initiator for cationic polymerizations. It is suggested by Ledwith that electron transfer to these cations results in fragmentation with the formation ofaryl radicals and if the reducing species is a suitable free radical, a chain reaction for formation of cation will occur. We carried out radiation-induced polymerization of a-methyl-styrene in dichloromethane and bulk cyclohexene oxide in the presence of triphenyliodonium salt (C6H5)2 I ' P F -)
. Polymerization of these monomers was observed in the presence of these salts (G(-M)C1300), while no polymer was obtained in the absence of salts. merization was negligibly small. to be initiated by the reaction of free radicals produced by radiation with cation salts and to proceed by cationic mechanism, since a-methylstyrene polymerized by ionic mechanism but hardly polymerizes by radical mechanism and this polymerization was sup- pressed in the presence of a small amount of water. The initiation mechanism of this polymerization was investigated by the use of pulse radiolysis technique.