Radiation effects of polycarbosilane as precursor of ceramic fibers

The radiation effects on polycarbosilane were investigated by ESR and gas chromatography measurements, in order to clarify the radiation curing mechanisum of polycarbosilane fiber as a precuser of ceramic fibers. The radio-chemical yields (G-value) of polycarbosilane were 2.5±0.5 for radical formation at 77 K and 1.4±0.1 for hydrogen evolution at room temperature, respectively. Most of the radicals reacted with each other, and polycarbosilane molecules were crosslinked under vacuum. At room temperature some of the radicals, which didn't contribute to the crosslinking, were trapped and were fairly stable under vacuum, but were well oxidized by the exposure in air. In the presence of oxygen, the radicals reacted rapidly with oxygen to convert to oxidation products, and the G-values were much more than the radical's one. The oxidation of trapped radicals in polycarbosilane must be decreased in the radiation curing process, in order to exclude oxygen in silicon carbide fiber. (author)