Photochemical Transformation of Benzil Pendant Groups of Polystyrene Copolymers into Benzoyl Peroxide Moieties and Their Subsequent Thermal Decomposition. Cross-Linking or Chain Scission?

Abstract

Films of the copolymer, 11 wt % 1-{4-(2-methacroyloxyethoxyphenyl}-2-phenyl-1,2-ethanedione (BZMA) and styrene (S) (BZMA/S), as well as polystyrene (PS) doped with either the BZMA monomer (BZMA-PS) or 1-{4-(2-acetyloxyethoxy-phenyl}-2-phenyl-1,2-ethanedione (BZAc-PS) in concentrations that match the composition of the copolymer, have been irradiated (λ > 400 nm) in the presence of molecular oxygen at ambient temperatures. The rates of consumption of BZMA and BZAc and the concurrent formation of the corresponding benzoyl peroxide-containing units (BPMA and BPAc) were followed by infrared spectroscopy. The rates of benzil-group consumption and peroxide formation matched each other and were virtually the same in the three film types. Larger concentrations of oxygen increased the rate of consumption of BZMA. From a kinetic treatment of data at two concentrations of oxygen in PS, it is concluded that BZMA photooxidation is more than 10 times faster than that of benzil. At 91 °C, the first-order rate constants ...