ORGANOSILICON POLYMERS - PYROLYSIS CHEMISTRY OF POLY[(DIMETHYLSILYLENE)DIACETYLENE]

The pyrolysis of [-Si(CH3)2C=CC=C-]n under a stream of argon to 1400-degrees-C gives a beta-SiC-containing ceramic in high yield (84%). The polymer-to-ceramic conversion chemistry was studied by means of thermal analysis, infrared spectroscopy, solid-state C-13 NMR spectroscopy, and X-ray powder diffraction. Gaseous products were analyzed by mass spectrometry. The polymer primarily undergoes low-temperature cross-linking through the diacetylene groups at about 200-degrees-C, i.e., 300-degrees-C below the mineralization stage. Decomposition reactions occur between 450 and 800-degrees-C inside a highly cross-linked carbon network. The weight decrease arises only from loss of CH4 and H-2. The total amount of silicon remains in the final residue. From a mechanistic point of view, [-Si(CH3)2C=CC=C-], is of interest as a suitable model to explore the mechanism of the thermal conversion of silicon-containing polymers into silicon carbide. The formation of SiC takes place inside an amorphous carbon matrix and only involves silyl units that contain no Si-H or functional groups and that are separated from one another. Some implications are discussed. Pyrolysis under ammonia leads to Si3N4 with loss of carbon and evolution of HCN.