Radiation Effects on Dimethyl-diphenyl Siloxane Copolymer. I. Protective Effect of Phenyl Radical on the Cross-linking.

The radiation effects both of polydimethyl siloxane and dimetyl-diphenyl siloxane copolymers were studied by the use of gamma rays of cobalt-60 in order to estimate the protective effect due to phenyl radical against the radiation-induced cross-linking. The viscosity of irradiated sample increased with the absorbed dose and finally the sample became gel. The efficiency of cross-linking of copolymers is remarkably reduced with increasing concentration of diphenyl siloxane. The minimum absorbed dose for gel formation, the efficiencies of cross-linking per monomer unit were obtained as a function of the concentration of phenyl radical. It is estimated that the protective effect of diphenyl siloxane may extend over five or six neighbouring monomers of dimethyl siloxane.