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


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Abstract

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 °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 B2O3 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 around 1000 were found to be formed. It was found that the consisted of borosiloxanes incorporated with well cross-linked borosiloxane networks, which provided borosilicates containing B2O3 up to 30 mol % on heat treatment.

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