1491365 Organopolysiloxane compositions WACKER-CHEMIE GmbH 3 Oct 1975 [3 Oct 1974] 40567/75 Heading C3T A heat-curable organopolysiloxane composition comprises (i) an organopolysiloxane containing at least 40 mole per cent of monoorganosiloxane units and at least 0À1% by weight of condensable groups, (ii) a filler, (iii) from 15-30% wt., relative to the weight of organopolysiloxane (1), of a diorganopolysiloxane having a viscosity of at least 30 cst. at 25‹ C. and that at room temperature is no more than partially miscible with organopolysiloxane (i), and optionally (iv) a condensation catalyst. Organopolysiloxane (i) preferably comprises at least 40% of RSiO 3/2 units and optionally units selected from R 2 SiO, R 3 SiO 1/2 and SiO 4/2 wherein R is a monovalent optionally substituted hydrocarbon radical having up to 12 carbon atoms, and up to 5% by number of the R radicals may be hydrogen, provided that there are at least 40 mole per cent of RSiO 3/2 in which R is a hydrocarbon radical as defined above. Preferably at least 85% by number of the R radicals are CH 3 and/or phenyl and at least 50% are CH 3 radicals. Preferably organopolysiloxane (i) has an average of 0À3 to 1À2 phenyl radicals per Si atom, an average of 0À9 to 1À7 Si-C bonded organic radicals per Si atom, at least 0À1% wt. of Si-OH groups, and optionally up to 3% wt. Si-bonded alkoxy groups. Organopolysiloxane (i) may be solid at room temperature and pulverulent prior to being mixed with diorganopolysiloxane (iii). Alternatively organopolysiloxane (i) may have been prepared by hydrolysing a hydrolysable mono-organosilane or a mixture of hydrolysable silanes containing at least 40 mole per cent of monoorganosilane in the presence of a diorganopolysiloxane (iii) having a viscosity of at least 200 cSt. at 25‹ C. Diorganopolysiloxane (iii) preferably has the formula where R is as defined above, a is 0 or 1 and preferably has a viscosity not exceeding 10SP5/SP cSt. at 25‹ C. The filler is preferably fibrous, e.g. glass fibres, asbestos fibres and naturally occurring fibrous magnesium silicate. The filler may be a reinforcing filler e.g. yarns, rovings, woven materials and fleeces of glass or asbsestos fibres. Other fillers include pyrogenic silica, silica xerogels, diatomaceous earths, quartz powder, ground quartz glass, mica powder, ground porcelein, calcium or Zirconium silicate, TiO 2 and aluminium oxide. The filler may be used in an amount of 30-500% wt. relative to the weight or organopolysiloxane (i). The condensation catalyst may be a lead compound, a carboxylic acid salt of Ca, Al, Fe, Zn, Sn, Co or Ce, a quaternary ammonium compound or a metal alcoholate. Optional additives include pigments, stabilizers, e.g. resorcin, release agents and lubricants, e.g. calcium or aluminium stearate; flow-control agents, e.g. carboxylic acids, their ammonium salts, ketones and metal enolates of ketones. In Examples 1 and 3 compositions are prepared from an organopolysiloxane (i) that has been prepared by hydrolysing a mixture of phenyltrichlorosilane, methyltrichlosilane, diphenyldichlorosilane and dimethyldichlorosilane in a molar ratio of 3 : 3 : 1 : 1, and either (A) a trimethylsiloxy-terminated dimethylpolysiloxane (200 cSt.), glass fibres, quartz powder, calcium stearate, lead carbonate and ammonium stearate, or (B) an OH terminated diorganopolysiloxane (80,000 cSt.) comprising (CH 3 ) 2 SiO and (C 6 H 5 ) 2 SiO units, ground quartz glass, lead carbonate and ammonium stearate, and are moulded into test rods and cured by heating under pressure. Example 2 is similar to Example 1 except that organopolysiloxane (i) is first prepared in the presence of an OH- terminated dimethylpolysiloxane (200 cSt.). Uses.-Mouldings; coatings.
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