Abstract
Photoinitiator systems for the polymerization of methyl methacrylate (MMA), based on combinations of benzophenone (Ph 2CO, light absorbing species), p-chlorobenzenediazonium tetrafluoroborate (ArN 2 +) and tetrahydrofuran (THF), have been investigated by means of quantum yield measurements of ArN 2 +-decomposition ( Φ N2) and MMA-consumption ( Φ p). In the presence of THF, the main reaction of ArN 2 +-decomposition consists of an electron-transfer reaction from Ph 2CO triplet state forming aryl radicals. MMA quenches the T 1 of Ph 2CO, which decreases the Φ N2-values in the presence of monomer. The Ph 2CO or the Ph 2CO/THF initiated MMA polymerizations possess low Φ p, caused by triplet quenching and termination by diphenyl ketyl radicals. In ArN 2 + containing systems, Φ p are much higher. This behaviour can be interpreted at low ArN 2 + concentrations (< 10 −2 M) by means of electron-transfer from nucleophilic ketyl radicals. At higher concentrations, the efficiency is increased because the electron transfer from Ph 2CO triplet state to ArN 2 + competes with the monomer quenching.
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