A compound that forms reactive species which will initiate chain reaction to cause polymer formation when exposed to specific wavelengths of energy.

Agent which when exposed to a specific wavelength of energy forms a reactive element which starts the chain reaction to cause polymer formation. Most commercial photo-iniators for radical curing reactions contain benzoil groups, which are mainly responsible for the absorption of energy from light. Aryl sulfonium salts can generate both radical type and cationic active centers. Syn. Photo-curing material