GB844128A - Siloxane elastomers - Google Patents

Abstract

A composition curable at room temperature to an elastomer comprises by weight (1) 100 parts of a siloxane of at least 100cs. viscosity at 25 DEG C., containing Si-bonded OH groups and being composed of units of the formula <FORM:0844128/IV(a)/1> , wherein each R is a monovalent hydrocarbon or halogenated hydrocarbon radical and in which the average value of n in the polymer is from 1,99 to 2,0 inclusive, (2) from 0,2 to 10 parts of a silicate of the formula R14-mSi(OCH2CH2OR11)m, in which each R1 is a monovalent hydrocarbon or halogenated hydrocarbon radical containing less than 7 C atoms, each R11 is a monovalent aliphatic hydrocarbon radical containing less than 6 C atoms and m is 3 or 4, or a partial hydrolysate thereof, and (3) from 0,01 to 10 parts of a catalyst which is a carboxylate of a metal ranging above H in the electromotive series of metals, and in which the acid radical contains less than 16 C atoms. The radicals in siloxane (1) may be alkyl, alkenyl, cycloaliphatic, aryl, aralkyl or alkaryl, and may be halogenated. The silicate (2) may be diluted with conventional orthosilicates or polysilicates in amounts up to 50% by weight based on siloxane (1). The catalysts, many examples of which are given, can be dispersed in the compositions by means of mutual solvents with siloxane or by dispersion on fillers and thereafter milled into the siloxane. Fillers, e.g. cork, wood, flour, cotton linters, CaCO3, TiO2, C black and SiO2 powders, oxidation inhibitors, compression set additives and pigments, may also be added. If the compositions are to be stored prior to use, the carboxylate or the silicate must be stored separately. The compositions cure at room temperature, though, if desired, they may be press-cured at 150 DEG to 250 DEG C. In a typical Example (1) 100 pts. (by weight) of a liquid end-blocked dimethylpolysiloxane containing Si-OH groups was mixed with 30 parts of diatomaceous earth, 0,5 pt. of lead octoate and varying amounts of different silicates, the lead octoate being added as a mixture of 100 parts of a liquid hydroxyl-free dimethylpolysiloxane, 30 parts of diatomaceous earth, 2 parts of ferrous oxide and 31 parts of lead octoate. The silicate (2), in which R1 can be methyl, ethyl, isohexyl, phenyl, vinyl, allyl, butadienyl, cyclopentenyl, cyclohexyl, chloromethyl, 2-bromo 4-, 6-diiodophenyl, 1, 2-difluorovinyl, 3, 4-dichlorocyclopentyl, 2-bromocyclopentene-2, 3-yl or 6-chlorohexyl, and R11 can be methyl, isopropyl, t-butyl, pentyl, vinyl, allyl, methallyl or butadienyl, can be made by reacting a chlorosilane with the corresponding monoethers of ethylene glycol or a mixture thereof to produce HCl and the required silicate. Uses: for electrical insulation, sealing voids and for taking dental impressions. Specifications 687,759, 746,246 and 804,199 are referred to.