The efficiency of aryl ketone and thioxanthone derivative catalysts for photopolymn. of n-Bu methacrylate was studied. For thioxanthone derivatives a correlation existed between their electron-accepting ability with a tertiary amine and their photopolymn. efficiency. Evidence from flash photolysis indicated the presence of the radical anion in this case but not with benzophenone or Ph ketone catalysts. In the latter cases, direct H atom abstraction from the amine was predicted to occur by either the triplet carbonyl or catalyst free radicals. Benzil was activated primarily by photochem. fragmentation. Water-sol. thioxanthone catalysts operated primarily via the singlet state involving an initial step of H atom abstraction and the free radical formation was unaffected by the presence of O.

Key words: PROPENOIC ACID ESTER P, PHOTO POLYMERIZATION, INITIATOR, PHOTOCHEMISTRY, PYROLYSIS, SPECTROGRAPHIC ANALYSIS, CARBONYL COMPOUNDS, BUTANOL P, LASER, FLASH PHOTOLYSIS, THIOXANTHENE P