Photo- and radiation-induced degradation of poly(styrene-co-methyl methacrylate)

Abstract

The photo- and radiation-induced degradation of poly(styrene-co-methyl methacrylate) (poly(St-co-MMA)) has been investigated by both electron spin resonance (ESR) and viscosity measurements. On ultraviolet irradiation of poly(St-co-MMA) film at 30°C in vacuum, the scission type radical from poly(methyl methacrylate) is produced in the initial stages of the photo-irradiation. The polystyryl radical from polystyrene gradually increases with irradiation time. The resulting ESR spectrum is composed of those of both radicals. The ratio of the radicals produced in poly(St-co-MMA) by photo-irradiation was estimated by comparison with simulated ESR spectra. The viscosity average molecular weight, Mv of photo-irradiated poly(St-co-MMA) decreases at short irradiation times and gradually increases at longer irradiation times. This phenomenon reflects the fact that the photo-degradation of the copolymer begins from the MMA component in poly(St-co-MMA). The γ-ray-induced degradation of poly(St-co-MMA) has also been examined by the same methods as those used in the photo-degradation and confirms that the degradation begins from the MMA component in the copolymer. The protective effect of polystyrene was also found for the radiation-induced degradation of the polymethyl methacrylate units in poly(St-co-MMA).