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 for thermal decomposition of BPMA and BPAc in PS are equal to and are larger than in the BPMA/S copolymer. The lower rate constant of BPMA/S, as well as the worse fit of the rate data from BPMA and BPAc in PS to a unimolecular decomposition model, is ascribed to some bimolecular decomposition, probably from aggregated peroxides. There is no indication of a bimolecular decomposition component in the copolymer. A very large portion (91 wt %) of BPMA/S, from irradiation of BZMA/S, is THF insoluble (i.e., cross-linked). The insoluble part increases to about 99 wt % after the BPMA/S film is treated at 91 °C for 6 h. Both of the corresponding doped polymers remain completely soluble in THF after irradiation and thermolysis. Cross-linking during the irradiation and heating is ascribed to formation of ester linkages (through abstraction of H atoms from -O-CH 2-CH2-O-groups by acyloxy radicals) and combination of pendant acyloxy radicals with radical sites on neighboring chains; abstraction from benzylic carbon atoms along PS chains leads to scission. By contrast, irradiation and subsequent heating of BZMA-PS or BZAc-PS films results in more chain scissions than cross-linking since the average molecular weights are decreased.

No abstract

No abstract