Thomas Wideman

Second‐generation polymeric precursors for BN and SiNCB ceramic materials

Our recent work directed at the design, synthesis, characterization and applications of new types of polyborazylene and polyborosilazane polymers is reviewed with a focus on the use of these polymers as processable precursors to BN and SiNCB composites. A design strategy based on the controlled functionalization of preformed polymers with pendant groups of suitable compositions and crosslinking properties has been employed to yield second-generation dipentylamine‐polyborazylene (DPA) and pinacolborane‐hydridopolysilazane (PIN‐HPZ) polymers, which, unlike the parent polyborazylene (PB) and the borazine‐hydridopolysilazane (B‐HPZ) polymers, are stable as melts and can be easily melt-spun into polymer fibers. Subsequent pyrolyses of these polymer fibers then provide excellent routes to BN and SiNCB ceramic fibers.# 1998 John Wiley & Sons, Ltd.

New Polymer Precursors To SiNCB Materials

The first borazine/silazane backbone copolymers derived from the parent borazine, B{sub 3}N{sub 3}H{sub 6}, have been obtained by the thermal condensation of borazine with either of two silazanes, tris(trimethylsilylamino)silane (TTS) or 1,1,3,3,5,5-hexamethylcyclotrisilazane (HCT), to yield copolymers of typical composition (B{sub 3}N{sub 3}H{sub 4}){sub 1.00}(N){sub 1.17}(SiMe{sub 3}){sub 1.16}(SiH){sub 0.34} and (B{sub 3}N{sub 3}H{sub 4}){sub 1.00}(N){sub 1.67}(SiMe{sub 2}){sub 1.49}(H){sub 1.5}, respectively. Despite their similar compositions, upon pyrolysis the TTS copolymers yield B{sub 1.0}N{sub 1.0}Si{sub <0.2} ceramics, while the ceramics derived from the HCT copolymers showed greater retention of silicon and carbon with typical compositions of B{sub 1.0}N{sub 1.5}Si{sub 0.4}C{sub 0.2}. The XRD spectra show the materials are amorphous to 1,400 C, but show crystalline phases of {beta}-Si{sub 3}N{sub 4}, {beta}-SiC and Si at 1,800 C, with no diffraction from any boron-containing species. The DRIFT spectra of the ceramics, however, indicate the presence of boron nitride.

Solution properties and spectroscopic characterization of polymeric precursors to SiNCB and BN ceramic materials

Boron Nitride, BN, and composite SiNCB ceramic fibers are important structural materials because of their excellent thermal and oxidative stabilities. Consequently, polymeric materials as precursors to ceramic composites are receiving increasing attention. Characterization of these materials requires the ability to evaluate simultaneous molecular weight and compositional heterogeneity within the polymer. Size exclusion chromatography equipped with viscometric and refractive index detection as well as coupled to a LC-transform device for infrared absorption analysis has been employed to examine these heterogeneities. Using these combined approaches, the solution properties and the relative amounts of individual functional groups distributed through the molecular weight distribution of SiNCB and BN polymeric precursors were characterized.