Photodegradation of 1-naphthyl methacrylate-butyl methacrylate copolymers in benzene solution. III. Comparison with the thermal and radiation-induced degradations

Abstract

Photodegradation characteristics of 1-naphthyl methacrylate (1NMA) homopolymer and 17·1 mol% 1NMA-containing copolymer with butyl methacrylate (BMA) were compared with their thermal and γ-ray-induced degradation behaviour. The TG-DSC analyses under N₂ showed that both the poly(1NMA) and poly(1NMA-co-BMA) powders degrade at 300–400°C. Heating of the copolymer up to 380°C under deaerated conditions produced 1NMA and BMA monomers. These polymers underwent main-chain scission simultaneously with a Fries rearrangement of the pendant 1-naphthyl ether groups by γ-radiolysis of the deaerated benzene solutions. The G-value of the main-chain scission was evaluated as 0·14 independent of the 1NMA content. The $\text{M}{}_{\mathrm{w}}\text{M}{}_{\mathrm{n}}$ ratio decreased and approached 2·0 asymptotically upon increasing the irradiation dose. On photoirradiation (>286 nm) of the deaerated benzene solution, the apparent rate constant for the main-chain scission of poly(1NMA-co-BMA) was larger by 1·4 times than that of poly(1NMA). Although the $\text{M}{}_{\mathrm{w}}\text{M}{}_{\mathrm{n}}$ ratio of the copolymer decreased monotonously to 2·0, that of the homopolymer increased initially and then decreased with photoirradiation time. The characteristic change in the intensity of excimer emission relative to monomer emission with photoirradiation time was also observed for the homopolymer system.