Effect of photodegradation on the beta-relaxation in poly(methylmethacrylate)

The effect of photodegradation using UV radiation on the beta-relaxation in poly(methylmethacrylate), PMMA, was investigated dielectrically within the temperature range 60-90 degrees C and a 20-10(5) Hz frequency band. It is shown that the irradiated samples exhibit a beta-relaxation process similar to that of unirradiated PMMA but with broader distribution of the relaxation times. Increasing the time of UV exposure increases the magnitude of the relaxation and displaces the peak toward lower temperature. The apparent activation energy decreases with irradiation. It is suggested that these observations can be interpreted in terms of the chain scissioning of the polymer chains without extensive depolymerization. (C) 1996 Elsevier Science Limited