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

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 polyborosiloxa nes which underwent further condensation to give heterogeneous gels at room temperature and homogeneous gels with (TAS/BTB greater than or equal to 2) or without (TAS/BTB = 1) cracks at 60 degrees C. The addition of ethanol t o the reaction mixture formed homogeneous gels under milder conditions. In the presence of hydrochloric acid as a catalyst, transparent round gel plat es of B2O3 contents up to 34 mol % were obtained by the reaction in the mol ar ratios of TAS/BTB = 9/2-1/2. Polyborosiloxanes of molecular weight aroun d 1000 were found to be formed. It was found that the consisted of borosilo xanes incorporated with well cross-linked borosiloxane networks, which prov ided borosilicates containing B2O3 up to 30 mol % on heat treatment. (C) 19 99 Kluwer Academic Publishers.