GB823039A - Improvements in or relating to organosiloxane resins - Google Patents

Abstract

A composition comprises (1) from 5 to 95% (by weight) of a copolymer composed of 4.5 to 17 mol. per cent of diphenylsiloxane, 22 to 55 mol. per cent of monophenylsiloxane, 40 to 65 mol. per cent of monomethylsiloxane and up to 38 mol. per cent of phenylmethylsiloxane, and (2) from 95 to 5% of a polysiloxane having a viscosity of at least 500 cs. at 25 DEG C. and an average of at least 1.5 hydrocarbon radicals which are phenyl and vinyl and optionally methyl radicals, per Si atom, the siloxane having a phenyl to Si ratio of at least 0.7:1 and a vinyl to Si ratio of from 0.3:1 to 1:1. The compositions may be cured by incorporating two types of curing catalyst, (1) an organosilanol condensation catalyst, e.g. lead octoate, zinc hexoate, cobalt-naphthenate, indium octoate, triethanolamine, trimethylammonium-butoxide, benzyltrimethyl ammonium 2-ethylhexoate, b -hydroxyethyltrimethylammoniumbutoxide and phenyltrimethylammonium acetate, and (2) an organic peroxide, e.g. dicumyl and di-tertiary butyl peroxides and tertiary butyl perbenzoate, type (1) catalyst being used, e.g., in amount of 0.05 to 10% by weight of siloxane (1) and type (2) in amount of 0.25 to 10% by weight of siloxane (2). Copolymerization is believed to occur by interaction of the vinyl radicals in (2) with the methyl radicals in (1). If desired the compositions may be diluted with up to 50% by weight of a low molecular weight vinyl-containing silicon compound compatible with siloxanes (1) and (2) and having a viscosity of less than 500 cs. at 25 DEG C., the compound having at least 2 Si-bonded vinyl radicals per molecule and the remaining valencies of the Si atom being satisfied with oxygen atoms, and phenyl, methyl, phenylene and methylene radicals, e.g. divinyldiphenyldimethyldisiloxane, tetraphenyldivinyldisiloxane, tetraphenyltetravinylcyclotetrasiloxane, <FORM:0823039/IV (a)/1> and <FORM:0823039/IV (a)/2> where Me, Ph and Vi represent methyl, phenyl and vinyl respectively. The compositions with or without fillers, e.g. glass or asbestos fibres, clay, glass flakes, diatomaceous earth, sand, ferric oxide, titania, zinc oxide and alumina, pigments and oxidation inhibitors, may be moulded and cured. In a typical example, (1), a laminating resin consisted of a mixture of 60% (by wt.) of a copolymer of 10 mol. per cent of diphenylsiloxane, 35 mol. per cent of monophenylsiloxane and 55 mol. per cent of monomethylsiloxane and 40% a phenylvinyl- and phenylmethyl-siloxane copolymer having a viscosity of 1800 cs. at 25 DEG C., to which had been added 0.8% of dicumylperoxide and 0.12% of b -hydroxyethyl trimethyl ammonium 2-ethyl-hexoate, and the resulting mixture was dissolved in toluene. Uses.-For impregnating electrical equipment, forming cast articles, forming structural laminates and for forming hot air conduits. Specifications 755,198, 762,978, 797,979 and 823,040 are referred to.