Photoreduction of benzophenone by trithianes as the initiation step in radical polymerization

This work was presented at the Workshop on Reactive Intermediates in Sulfur Chemistry (Poznan, 1998). It is a summary of earlier investigations on the role of cyclic sulfides (1,3,5-trithiane derivatives) in accelerating the initiation of polymerization induced by benzophenone (BP). The primary phot ochemical reactions between BP and trithianes were followed by nanosecond l aser flash photolysis. Triplet-quenching rate constants and quantum yields for electron-transfer products and ketyl-radical formation were measured. P hotoinduced polymerizations with model monomers initiated by BP/trithiane c ouples were followed by isothermal differential scanning calorimetry (DSC). The kinetics of these polymerizations were compared with the photochemical information on the quenching of excited BP by the trithianes. The polymeri zation efficiency using the various coinitiators did not follow the efficie ncy of photo-induced formation of the initiating radicals. The reasons for this lack of correlation were discussed in terms of the various factors tha t influence the polymerization aside from the efficiency of radical formati on.