An Efficient Process of Cross-Linking Poly(methylsilane) for SiC Ceramics

Abstract

Reflux-treated poly(methylsilane) (PMS) at 420−570 K improves its ceramic yield dramatically. This efficient process was investigated by TG, GC, 29Si, 13C, and 1H NMR, and FT-IR methods. The structural transformation process of the PMS polymer consists of three stages. In the first stage below 500 K, PMS forms Si−Si3 cross-link units predominantly by evolving MeSiH3. This process may proceed mainly via silylene formation. The Si−Si cross-link structure leads to a high ceramic yield up to 89%. In the second stage around 625 K, thermal rearrangement of the Si−Si3 units to Si−CH2−Si units (Kumada rearrangement) begins to convert the polymers into polycarbosilanes. The third stage occurs above 673 K where almost all polymer units are converted into SiC4 units. Evolution of H2 and CH4 begins in the second stage and becomes the dominant process in the third stage.