High yield polycarbosilane precursors to stoichiometric SiC. Synthesis, pyrolysis and application
- Rensselaer Polytechnic Inst., Troy, NY (United States). Dept. of Chemistry
- Starfire Systems, Inc., Glenville, NY (United States)
- Colorado State Univ., Fort Collins, CO (United States). Dept. of Chemistry
The synthesis and properties of two polycarbosilanes that have essentially a ``SiH{sub 2}CH{sub 2}`` composition is described. One of these polymers is a highly branched hydridopolycarbosilane (HPCS) derived from Grignard coupling of Cl{sub 3}SiCH{sub 2}Cl followed by LiAlH{sub 4} reduction. This synthesis is amenable to large scale production and the authors are exploring applications of HPCS as a source of SiC coatings and its allyl-derivative, AHPCS, as a matrix source for SiC and C-fiber reinforced composites. These polymers thermoset on heating at 200--400 C (or at 100 C with a catalyst) and give near stoichiometric SiC with low O content in ca. 80% yield on pyrolysis to 1,000 C. The second method involves ring-opening polymerization of 1,1,3,3-tetrachlorodisilacyclobutane and yields a high molecular weight, linear polymer that can be reduced to [SiH{sub 2}CH{sub 2}]{sub n} (PSE), the monosilicon analog of polyethylene. In contrast to high density polyethylene which melts at 135 C, PSE is a liquid at room temperature which crystallizes at ca. 5 C. On pyrolysis to 1,000 C, PSE gives stoichiometric, nanocrystalline, SiC in virtually quantitative yield. The polymer-to-ceramic conversion was examined for PSE by using TGA, mass spec., solid state NMR, and IR methods yielding information regarding the cross-linking and structural evolution processes. The results of these studies of the polymer-to-ceramic conversion process and their efforts to employ the AHPCS polymer as a source of SiC matrices are described.
- OSTI ID:
- 51618
- Report Number(s):
- CONF-940411--; ISBN 1-55899-246-4
- Country of Publication:
- United States
- Language:
- English
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