Investigation of the Pyrolytic Conversion of Poly(silylenemethylene) to Silicon Carbide

Abstract

The pyrolysis of poly(silylenemethylene) (PSE), [SiH2CH2]n, a linear polycarbosilane with a regularly alternating Si−C backbone structure and a high-yield precursor to stoichiometric SiC, was investigated by using a combination of thermogravimetric analysis, evolved gas analysis, and solid-state NMR and IR spectroscopies. The observed evolution of D2 from the deuterio-derivative of PSE, [SiD2CH2]n, as the primary gaseous product in the range of ca. 250−400 °C, where cross-linking of the polymer occurs, suggests that loss of H2 from the Si is a key step in the cross-linking process. A reaction pathway is postulated for the cross-linking and pyrolysis of PSE in which both 1,1-H2 elimination and intramolecular H-transfer reactions lead to highly reactive silylene intermediates; these insert into Si−H bonds of neighboring polymer chains forming Si−Si bonds which rapidly rearrange to Si−C bonds at these temperatures to form Si−C interchain cross-links. The cross-links prevent extensive fragmentation of the pol...