Cationic Photoinitiation Efficiency

Abstract

The results of these photochemical studies form guidelines for the choice of sensitizers, onium salts and other additives potentially useful in the cationic curing of coatings. The sensitized photochemistry of diphenyliodonium hexafluoroarsenate and triphenylsulfonium hexaflurorarsenate was investigated at 366 nm. Product quantum yields are compared to relative rates of photoinitiated cationic polymerization of an epoxy resin. Sensitized photolysis of both salts resulted in the formation of the same major products as was observed in direct irradiation, iodobenzene, or phenylsulfide and acid. Quantum yields of organic and acidic products were measured using nine sensitizers. Product quantum yields were relatively high (< 1) under conditions where electron transfer sensitization was expected to occur. Quantum yields > 2 were obtained in solvents likely to be substrates for hydrogen abstraction, indicating that a chain reaction was involved. Triplet energy sensitization resulted in low product quantum yields.