Excited states of ketones as electron donors-ketone-iodonium salt systems as photoinitiators for radical polymerization

Abstract

The excited states of the aromatic ketones benzophenone, 4,4′-bis(dimethylamino)benzophenone (Michler's ketone), xanthone, thioxanthone, acridone and 10-methylacridone sensitize the decomposition of diphenyl-iodonium salts via electron transfer processes. Owing to the long lifetime of the excited singlet state, at high concentrations of iodonium salts both the singlet and triplet states can function as electron donors. In the presence of methylmethacrylate an additional quenching takes place. Determination of the processes which occur in the excited states allows the photoinitiation step of the reaction to be discussed. The quantum yields of the sensitized photolysis of diphenyliodonium salts and of the polymerizations initiated by the ketone-iodonium salts systems have been determined. Some of these systems are effective photoinitiators for radical polymerization. © 1990.