Studies on the synthesis of silicon-substituted polyaromatic mesophase from a coal tar hard pitch and phenylsilanes

Formation of a silicon-substituted polyaromatic mesophase was investigated by co-pyrolysis of mixtures of a soft and a hard pitch with mono-, di- and tetraphenylsilane. The studies were performed in autoclaves at a constant argon pressure of 1 MPa and a temperature of 440degreesC using pyrolysis times of 5 and 10h. With 2 % silicon in the starting mixtures a silicon substituted mesophase is not formed. Studies with the hard pitch and lower silicon additions of 1.0 and 0.5 % clearly show formation of a silicon-substituted mesophase, but not as a single phase. The pyrolysis residues are composed of a silicon-substituted bulk mesophase in which mesophase spherolites without silicon are homogeneously dispersed.