Radiation effects on trisiloxanes

Irradiations of three kinds of methyl-phenyltrisiloxanes, 1,2,2,3-tetramethyl, 1,1,3,3-tetraphenyltrisiloxane (F-4), 1,2,3-trimethyl, 1,1,2,3,3-pentaphenyltrisiloxane (F-5), 1,3-dimethyl, 1,1,2,2,3,3-hexaphenyltrisiloxane (F-6), were carried out. Yields of gaseous products, changes of molecular weights of the trisiloxanes, effect of oxygen on the changes of molecular weights and liquid chromatograms of the trisiloxanes were measured. Gaseous products were mainly hydrogen, methane and benzene. The yields of hydrogen and methane decreased with the increasing content of phenyl groups in trisiloxane. The yield of benzene, on the other hand, increased with the increasing content of phenyl groups in trisiloxane. G(benzene) of F-6 was considerably high, i.e., 0.22, while G(benzene) of F-4 and F-5 were 0.03 and 0.05, respectively. G(polymerization) of F-4, F-5 and F-6 were shown to be 0.41, 0.28 and 0.36, respectively. These results were considered to be due to an ease of scission of the bonds between phenyl groups and trisiloxane groups by steric hindrance in the case of the F-6, in which two large phenyl groups were bonded to the central silicon atom. Molecular weights of trisiloxanes increased by the irradiation and the increments were depressed in the presence of oxygen. It was concluded that radical processes participated in the polymerization of the trisiloxanes. (author)