Photoreaction Mechanism of Benzilmonooxime Methacrylate Polymer and its Model Compounds.

Abstract

We studied the mechanism of the photoreaction of benzilmonooxime methacrylate (BIMA) polymers, which are highly photosensitive materials, using stationary photoirradiation and laser flash photolysis (LFP) of the copolymer of methyl methacrylate with BIMA (3.6mol%). Since the Stern-Volmer relationship for the quenching of the main chain degradation was curved, the reaction proceeded through both excited singlet and triplet states. When the singlet contribution was assumed to be ca. 30% of the whole reaction, a linear relationship was obtained. In 266, 308 and 355nm LFP of the BIMA polymer, we could not detect any transient absorption bands. The triplet energy level of the polymer was estimated to be between 274 and 289kJ mol-1 by means of sensitized reactions. To clarify the reaction mechanism, we carried out 266nm LFP of model compounds: benzilmonooxime phenylacetate (BIPA) and benzilmonooxime diphenylacetate (BIDA). In LFP of BIPA, a transient absorption band was measured at 310nm immediately afte r the flash. At 4μs after the flash, another new band was detected at 460nm. These bands were assigned to benzyl and benzoyl radicals, respectively. In LFP of BIDA, we measured new transient absorption at 340nm, which was assigned to diphenylmethyl radical.