Flash photolysis investigation on primary processes of the sensitized polymerization of vinylmonomers. III. Photoreactions of benzoin compounds and stationary polymerization experiments

Benzoin (B), benzoinacetate (BA), benzoinmethylether (BME) and benzoinisopropylether (BIPE) were irradiated at room temperature in benzene solution in the presence of styrene (St), methyl methacrylate (MMA), vinylacetate (VAc) or acrylonitrile (AN). Flash photolysis experiments at λ=347 nm yielded (a) rate constants kq (in 1 mol‐1s‐1) of the reaction between excited sensitizers and monomers: 8·109 (B/St), 5·108 (B/MMA), 5·109 (BA/St), 8·108 (BA/MMA); (b) rate constants KR.+M (in 1mol‐1 s‐1) of the reaction between sensitizer radicals and monomers: about 1.5·105 (BME/St, BME/VAc, BA/VAc, B/VAc), 9· 104 (BME/MMA), 2·104 (BME/AN). The reaction R·+M caused in certain cases (B/St, B/VAc, BME/St) the formation of an additional optical absorption after the flash. Stationary irradiations at λ>320 nm of monomer solutions (5mol/1) showed that BA is least effective. Rates of polymerization increased in the series BAi=i+0.6αR (ϕi=quantum yield for the initiation of kinetic chains, αR =fraction of triplets converted to radicals). The fraction of radicals starting kinetic chains is ca. 0.3 in these cases.