GB891199A - Improvements in or relating to vulcanisable organopolysiloxane compositions - Google Patents

Abstract

Vulcanizable compositions consist essentially of (by wt.) (1) 100 pts. of a polysiloxane having a viscosity at 25 DEG C. of at least 100,000 cs. and consisting of at least 90 mol. per cent units of the formula RCH2CH2Si(R1)O, in which R is a perfluoroalkyl radical of 1 to 3 C atoms and R1 is a lower alkyl or alkenyl radical or an aryl radical, any remaining siloxane units having the formula <FORM:0891199/IV (a)/1> , in which each Z is an aliphatic hydrocarbon radical of 1 or 2 C atoms or a phenyl radical and m is 1, 2 or 3, (2) from 1 to 30 pts. of a liquid hydroxylated organosilicon compound containing not more than 110 Si atoms, having attached to at least 50% of the Si atoms by a C-Si bond at least one radical of the formula RCH2.CH2-, any other organic radicals attached to Si being monovalent hydrocarbon radicals containing less than 7 C atoms, the compound (2) containing per molecule at least 0,25% by weight of Si-bonded OH groups, essentially all the remaining Si valencies being satisfied by oxygen atoms attached to other Si atoms, (3) from 0,25 to 10 pts. of a material having a boiling point above 100 DEG C. at atmospheric pressure and which is an organic compound which is inert to siloxane (1) or a benzene-soluble organosilicon compound containing the group R11nSi, wherein R11 is a hydrocarbon, hydrocarbonoxy, halohydrocarbonoxy or halohydrocarbon radical containing less than 3 fluorine atoms, n is an integer from 1 to 4 inclusive, and the remaining Si valencies are satisfied by H atoms, O atoms, OH groups or other Si atoms, (4) optionally a vulcanizing agent and (5) a reinforcing silica filler. Preferably R1 is methyl, R is perfluoromethyl and every Z is methyl, and the silica filler is present in amount of from 15 to 100 pts. (by wt.) per 100 pts. of siloxane (1). Siloxanes (1) may be made by the process of Specification 832,489. Constituent (2) is a silanol and/or siloxanol. Constituent (3) may be a silane and/or siloxane or any of the organic and organometallic compounds set forth in Example (6). Other fillers, e.g. TiO2, ZnO, Fe2O3, clays, diatomaceous earth and crushed quartz, compression set additives, pigments and oxidation inhibitors may also be added. If desired, the fillers may be surface modified with various organosilyl groups by the process shown in Specification 699,759. The compositions are vulcanized either by heating with an organic peroxide or at room temperature by radiation or by adding a carboxylate, e.g. Pb 2-ethylhexoate, together with a siloxane containing Si-H. In a typical Example (1) a 3,3,3-trifluoropropylmethylsiloxane gum was milled with fume silica and silica aerogel. A liquid 3,3,3-trifluoropropylmethylsiloxane containing terminal Si-OH groups and containing an average of 14,4 Si atoms per molecule, was added thereto and the resulting mixture was heated for 3 hours at 170 DEG C. ZnO, a siloxane gum composed of dimethyl- and methylvinylsiloxane units and 2,4-dichlorobenzoyl peroxide (dispersed in a liquid dimethylsiloxane) were added and the whole mixture was milled. Uses: For the preparation of hoses, seals and linings for fuel tanks; for coating electrical insulation. Specifications 832,487 and 832,488 also are referred to.