GB635994A - Improvements in the manufacture of siloxane resins - Google Patents

Abstract

A siloxane resin, essentially all the siloxane units of which have the structure CH3SiO1,5, C6H5SiO1,5, and (CH3)3SiO0,5, of which between 1 and 25 mol. per cent are trimethyl siloxane units and the monomethyl and monophenyl siloxane units are present to the extent of at least 2 mol. per cent, is prepared by hydrolysing a mixture of a mono-methyl silane, a monophenyl silane and a trimethyl silane in which the remaining valencies of the silanes are satisfied by readily hydrolysable atoms or radicals (e.g. halogen atoms or alkoxy, aroxy, or alkaroxy radicals) and co-condensing the hydrolysed silanes. Gel formation is prevented when hydrolysing mixtures containing monomethyl silicon trichloride by adding alcohol to the hydrolysis mixture and in all cases a catalyst such as hydrochloric or oxalic acid is preferably used. Examples describe: (1) the hydrolysis of a mixture of ethoxy trimethyl silane, and phenyl- and methyl-silicon tri-chlorides by adding it to a mixture of water, toluene, and isopropyl alcohol. The product, with triethanolamine as curing catalyst is used in forming laminated glass fibre or asbestos boards, and in solution in carbon tetrachloride for waterproofing asbestos; (2) the hydrolysis of mixtures of methyl-, dimethyl, and phenyl-, ethoxy silicones in five different proportions, by addition to a mixture of aqueous oxalic acid, and denatured alcohol, at 30 DEG C., followed by heating at 60 DEG C. and then the addition of toluene; (3) a process as in (2), using three other ratios of reactants, and with the addition of HC1 during the heating at 60 DEG C. The products of examples 2 and 3 are mixed with asbestos and calcium stearate and moulded under heat and pressure followed by heat curing. If an ethanolamine catalyst is used, the mix may be moulded at room temperature, followed by curing in an oven.