Radiation crosslinking studies on branched polyvinyl acetate

Abstract

Crosslinking and chain scission caused by gamma radiation in branched polyvinyl acetate have been studied. Gel fraction was measured as a function of radiation dose in five well-characterized samples, ranging in structure from almost linear to approximately 1.7 branch points per molecule. Apparent Gvalues (events per 100 eV of energy absorbed) from random scission and cross-linking, G(S) and G(X) respectively, were obtained from the solubility behaviour at high doses, and G(X) was separately evaluated at low doses from gel point measurements. For each sample the values of G(X) were similar at high and low doses, but they decreased from sample to sample as the branching density increased. All observations were consistent with the supposition that approximately 15 per cent of the branch points are sensitive to radiation and break preferentially prior to the gel point. Several types of branches are known to exist in polyvinyl acetate, which may account for the apparent differences in radiation sensitivity among branches.