Mechanisms and relative efficiencies in radical polymerization photoinitiated by benzoin, benzoin methyl ether and benzil

Contrary to widely held views, detailed studies of light absorption characteristics, reaction rates, and molecular weights in radical polymerization of methyl methacrylate photoinitiated by benzoin and benzoin methyl ether indicate that the two photoinitiators have comparable efficiencies; benzil is much less efficient. Mechanisms for initiation, and possible termination processes, for systems involving all three photoinitiators are discussed in the light of results from studies of radical characterization by the spin trapping technique.