THERMAL-DEGRADATION OF GAMMA-IRRADIATED POLYMERS .1. POLY(METHYL METHACRYLATE)

The effect of gamma-irradiation on the thermal stability of poly(methyl methacrylate) has been examined for doses from 10 to 300 kGy. It has been found that irradiation causes some side-group scission: the irradiated polymer retains amounts of methyl formate until it reaches softening point. The thermal degradation behaviour, studied by thermal volatisation analysis (TVA) and subambient TVA separation of condensable volatile degradation products, shows that in the irradiated samples, small amounts of products other than monomer are formed, including traces of benzene: the formation of the latter is explained by the decomposition of conjugated double bonds produced in the polymer during irradiation as a result of scissions. of adjacent side-groups. The initial degradation stage in the polymer, associated with unzipping from unsaturated chain ends, is progressively reduced with increasing dose: this is attributed to the effect of abnormal chain structures resulting from side-group... elimination.