PYROLYSIS CHEMISTRY OF AN ORGANOMETALLIC PRECURSOR TO SILICON-CARBIDE

The cross-linking reactions and decomposition of a vinylic polysilane precursor to silicon carbide were systematically investigated in the course of thermolysis to 1000-degrees-C in N2. The polymer-to-ceramic conversion chemistry was studied by means of thermogravimetry, infrared spectroscopy, solid-state NMR spectroscopy (H-1 CRAMPS; C-13 and Si-29 magic-angle spinning), X-ray powder diffraction, and elemental analysis of isolated solid intermediates. Gaseous byproducts were analyzed by gas chromatography, mass spectrometry, and infrared spectroscopy. The polymer primarily undergoes cross-linking through the vinyl groups below 300-degrees-C, although there is evidence for some hydrosilylation. Decomposition reactions consist of chain scission, with production of radical species, and methylene insertion, which converts the polysilane backbone to polycarbosilane. Crystallization to carbon-rich beta-SiC ceramic occurs above 750-degrees-C.