POLYMERIZATION PHOTOINITIATED BY CARBONYL-COMPOUNDS .8. SOLVENT AND PHOTOINITIATOR CONCENTRATION EFFECTS

The interaction of benzil and thioxanthone triplets with triethylamine leads to the production of free radicals that are able to initiate the polymerization of methylmethacrylate and vinyl acetate. The process is mediated by a charge-transfer complex. The initiation efficiency is higher in benzene than in acetonitrile, a result explained in terms of competition between back electron transfer, production of free ions and ketyl radical formation. The initiation efficiency decreases when the carbonyl concentration increases, because of the occurrence of a radical molecule reaction leading to the production of α-hydroxyl radicals which are unable to initiate the polymerization chain.