Vinyl-functionalized poly(borosiloxane) as precursor for SiC/SiBOC nanocomposite

Vinyl-functionalized borosiloxane oligomers were synthesized by reacting boric acid and vinyltris(2-methoxyethoxy)silane (VTMEOS) in the mole ratio 1:2, 1:1.5 and 1:1 under non-aqueous conditions using diglyme as solvent. Use of vinyltris(2-methoxyethoxy)silane instead of vinyltriethoxysilane overcomes the premature gelation of borosiloxane oligomer. The effect of monomer feed ratio on the molecular weight, microstructure, thermal stability and ceramic residue of the oligomers was studied. The oligomers were characterized by FT-IR and NMR spectroscopy, GPC and TGA. The oligomers on heat treatment at 900 °C in inert atmosphere give amorphous SiBOC ceramic which on further heating at 1500 °C forms SiC/SiBOC nanocomposite. The extent of conversion of SiBOC to SiC is influenced by both carbon and boron content of SiBOC which in turn is controlled by the monomer feed ratio. This is evident from the observation that the extent of formation of β-SiC nano crystals follow the trend BSiVME-2>BSiVME-1>BSiVME-3.