Thermal expansion and glass transition of polymethylmethacrylate after exposure to Co-60 gamma irradiation

A study is made of the thermal expansion coefficient and the glass transition temperature in atactic polymethylmethacrylate (PMMA) irradiated first with gamma-ray doses between 50 and 200 kGy, The change of the molecular weight due to the damage of the polymer chain produced by the gamma-irradiation was also measured. Besides the glass transition temperature, the alpha' transition is observed in our dilatometric tests and this transition shifts to lower values of temperatures at higher doses and virtually disappears at 200 kGy. This result suggests that the irradiation changes the degree of atacticity of the polymer.