POLYMERIZATION PHOTOINITIATED BY CARBONYL-COMPOUNDS .10. METHYL-METHACRYLATE POLYMERIZATION PHOTOINITIATED BY FLUORENONE IN THE PRESENCE OFTRIETHYLAMINE

The photoinitiation efficiency of the fluorenone/triethylamine (TEA) s ystem in the polymerization of methylmethacrylate (MMA) has been evalu ated as a function of the monomer concentration, the amine concentrati on, and the polarity of the reaction medium. The polymerization procee ds readily in low polarity media (benzene/monomer), but it is negligib le in more polar solvents (acetonitrile/monomer). The polymerization r ate increases with the amine concentration up to 0.01 M TEA. Further i ncrease in amine concentration produces a decrease in the polymerizati on rate. A similar behavior was observed for the fluorenone photoreduc tion yield and the yield of fluorenone derived radicals. All these pro cesses are considered to involve the excited triplet, while quenching of the excited singlet by the amine decreases the rate of these proces ses. However, the decrease in photoinitiation efficiency observed at h igh amine concentration is larger than that expected from the singlet quenching extent, as estimated from the effect of the amine on the flu orescence yield under the same experimental conditions. This discrepan cy indicates that other process(es) must contribute to the protection afforded by high amine concentrations. Quenching of the charge transfe r intermediate by the amine is postulated as a competitive process tha t could explain the above mentioned effects. (C) 1994 John Wiley & Son s, Inc.