POLYSILACYCLOBUTASILAZANES - PRE-CERAMIC POLYMERS FOR THE PREPARATION OF SINTERED SILICON-CARBIDE MONOLITHS

A family of pre-ceramic polymers based upon silacyclobutasilazanes was prepared. Upon heating to 200-250-degrees-C the polymers crosslink to intractable resins through a ring-opening polymerization of the silacyclobutyl group. In an inert atmosphere the polymers convert to Si-C-N-O chars upon pyrolysis to 1200-degrees-C. At higher temperatures ( > 1400-degrees-C) the Si-C-N-O chars loose nitrogen and carbon monoxide to give stable chars containing only silicon carbide and carbon. The polymers were used as binders in press-and-sinter and transfer-moulding applications to give silicon carbide monoliths with sintered densities above 3.13 g cm-3 and four-point flexural strengths above 70 kpsi (483 MPa).