Preparation and properties of borosilicate gels by the reaction of tetraacetoxysilane with boron tri-n-butoxide

摘要

The preparation and properties of gels via borosiloxane polymers formed by the reaction of tetraacetoxysilane (TAS) with boron tri-n-butoxide (BTB) in tetrahydrofuran (THF) was investigated. The reaction formed polyborosiloxanes which underwent further condensation to give heterogeneous gels at room temperature and homogeneous gels with (TAS/BTB>=2) or without (TAS/BTB=1) cracks at 60 deg C. The addition of ethanol to the reaction mixture formed homogeneous gels under milder conditions. In the presence of hydrochloric acid as a catalyst, transparent round gel plates of B sub 2 O sub 3 contents up to 34 mol.% were obtained by the reaction in the molar ratios of TAS/BTB=9/2-1/2. Polyborosiloxanes of molecular weight approx1000 were found to be formed. It was found that the gels consisted of borosiloxanes incorporated with well cross-linked boroisoxane networks, which provided borosilicates containing B sub 2 O sub 3 up to 30 mol.% on heat treatment.