Preceramic polymers offer exceptional potential for low-temperature processing of both oxide and non-oxide ceramics. In addition, shapes such as fibers, films, and membranes that are not commonly available using standard processing techniques are readily available using preceramic polymers. In non-oxide ceramics, the ceramic products generally available from preceramics do not exhibit all of the typical properties associated with the same materials produced by standard, high-temperature processing approaches. In part, this appears to be because there are very few preceramic polymers that lead to high-purity, singlephase materials. Poly(methylsilane), (-[MeHSi],-), produced from MeSiH3, can be used to produce relatively pure, bulk Sic at temperatures below 1000°C. The transformation process from polymer to ceramic is followed by 29Si NMR and diffuse reflectance IR. The polymer first undergoes a major rearrangement from poly(si1ane) to poly(carbosi1ane) at 400°C. Above 400"C, the resulting poly(carbosi1ane) decomposes to a hydrogenated form of Sic as shown by spectroscopic analysis of the 600°C material. Further heating, to 1000°C for 1 h, provides very narrow 29Si peaks indicative of B-Sic mixed with small amounts of a-Sic polytypes. Chemical analysis, when coupled with the 29Si and XRD results, suggests that poly(methylsi1ane) produces resonably pure, nanocrystalline Sic at temperatures much lower than previously observed for other Sic preceramic polymers. [

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The pyrolytic evolution of poly(N‐methylsilazane), –[H2SiN‐Me]x–, from preceramic polymer to ceramic product is followed by heating samples of the partially cross‐linked polymer, in 200°C increments, from ambient temperature to 1400°C. The intermediate products are characterized by chemical analysis, diffuse reflectance Fourier transform IR spectroscopy (DRIFTS), Raman spectroscopy, and 29Si and 13C magic‐angle spinning (MAS) solid‐state NMR. Spectro‐scopic characterization indicates that the 1400°C pyrolysis products are amorphous silicon nitride mixed with amorphous and graphitic carbon (as determined by Raman spectroscopy), rather than silicon carbide nitride, as expected based on the presence of up to 20 mol% retained carbon. Efforts to crystallize the silicon nitride through heat treatments up to 1400°C do not lead to any crystalline phases, as established by transmission electron microscopy (TEM) and small‐area electron diffraction (SAD). It appears that the presence of free carbon, along with the absence of oxygen, strongly inhibits crystallization of amorphous silicon nitride. These results contrast with the isostructural poly‐(Si‐methylsilazane), –[MeHSiNH]x–, which is reported to form silicon carbide nitride on pyrolysis.