Synthesis and Influence Factors of Cyano-polycarbosilane
Polycarbosilane(PCS)is an important precursor of silicon carbide(SiC)fibers and ceramics.As a precursor for preparing SiC fibers and ceramics,it has several deficiencies,such as low ceramic yield,which affect the properties of final products.Cyano-polycarbosilane,a new SiC precursor,was synthesized by using hydrosilylation addition reaction of PCS and acrylonitrile,which is not easy for hydrosilylation generally.During the synthetic process,rhodium-containing catalyst and 2-methylpropionitrile were used.The ceramic yield of PCSCN would be significantly increased to over 80％,as compared with that of PCS,especially as the rhodium-containing catalyst was used.The molecular structure of PCSCN was analyzed by using IR and NMR,showing that the hydrosilylation reaction was mainly α-addition.In addition,the degree of hydrosilylation increased with increasing reaction time and reaction temperature at the initial stage,but remained almost unchanged when the time was longer than 5 h or the temperature was higher than 60 ℃.Increasing the content of acrylonitrile would lead to increase in the degree of reaction and thus more cyano groups were introduced in PCSCN,but the magnitude was low.
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