No 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 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.

When irradiated at >400 nm in air, pendant benzil groups of 1-phenyl-2-(4-vinylphenyl)-1,2-ethanedione/styrene (VBz/S) copolymer films are transformed almost quantitatively into benzoyl peroxide (BP) groups. Subsequent heating at 91 °C converts the pendant benzoyl peroxide groups to esters and benzoic acid moieties, and there is significantly more cross-linking than main-chain cleavage. Irradiation of the VBz/S copolymer films at 366, 313, and 254 nm also results in formation of BP groups, but they are transformed in situ upon absorption of a second photon by the matrix. The ratios of the relative rate constants for BP formation and subsequent transformation upon absorption by a second photon decrease with decreasing wavelengths of radiation. Irradiation of a film composed of a nonmiscible intimate mixture of poly(1-phenyl-2-(4-vinylphenyl)-1,2-ethanedione) (PVBz) and polystyrene (PS) at >400 nm in air does not lead to discernible BP concentrations as well. Instead, the unreacted pendant benzil groups act as photosensitizers to transform the peroxy moieties almost immediately. In addition, we demonstrate that cross-linking of the VBz/S copolymer film, induced by 254 nm radiation, can be utilized to record a negative image.

No abstract

When irradiated at >400 nm in air, the benzil carbonyl groups (BZG) of 1-phenyl-2-(4propenoylphenyl)-1,2-ethanedione/styrene (PCOCO/S) copolymer films are transformed almost quantitatively to benzoyl peroxide carbonyl groups (BPG). Subsequent additional irradiation (at 366 nm) or heating (at 91 °C) of the BPG-containing copolymer films generates ester moieties, and significantly more cross-linking than main-chain cleavage is manifested in the copolymer. At 91 °C, the rate of the thermal decomposition of the pendant BPG is 3 times slower than that of noncovalently attached benzoyl peroxide molecules in polystyrene films.