GB832966A - Improvements in or relating to liquid polysiloxanes - Google Patents

Abstract

A reactive liquid siloxane, having a viscosity not in excess of 1 poise at 25 DEG C. and a vapour pressure of less than 0.1 mm. Hg at 100 DEG C., is made by mixing (a) two mols. of a silane of the formula <FORM:0832966/IV (a)/1> or 1 mol. of a disiloxane capable of producing two mols. of the monovalent silyl radical <FORM:0832966/IV (a)/2> and (b) from 2 to 10 mols. of a silane having the formula <FORM:0832966/IV (a)/3> wherein R is an alkyl having from 1 to 4 C atoms, or a phenyl, tolyl or xylyl radical, R1 is a vinyl or methyl radical, and Y is a hydrolysable radical, there being an average of at least 2 vinyl radicals per siloxane molecule, hydrolysing and condensing the mixture, separating the resulting siloxane, and fractionating the product to remove di- and tri-siloxanes therefrom. The hydrolysis and condensation may be effected in the presence of organic or mineral acids, NaOH, KOH or trimethylbenzyl-ammonium hydroxide. The liquid polymers may be polymerized with or without the addition of fillers, e.g. silica, either by irradiation or by heating with catalysts, e.g. benzoyl-, lauroyl-, methylethylketone- or tertiary-butylhydro-peroxide, ascaridole, t-butyl perbenzoate, di-t-butyl diperphthalate or ozonides. The liquids may also be mixed and subsequently copolymerized with other siloxanes containing ethylenic unsaturation and having higher viscosities, such as the allyl and methallyl siloxanes disclosed in Specifications 624,361 to 624,364. A non-olefinic siloxane or hydrogenated terphenyl, as disclosed in Specification 633,973, may also be added as a plasticizer. In examples: (1) a benzene solution of phenylvinyldiethoxysilane and hexamethyldisiloxane was stirred with 80% H2SO4 in an ice bath and ice was subsequently added thereto; after separation into 2 layers, the benzene layer was decanted, washed and freed of acid, dried and fractionated to yield a trimethylsilyl end-blocked phenylvinylsiloxane trimer, which on heating with t-butylperbenzoate or reaction with methyl-methacrylate or triallyl cyanurate yielded solid products; similarly (2) phenylvinyldichloro- and trimethylchloro- or ethyldimethylchloro-silanes, (3, 5) phenylvinyldiethoxy silane and 1,3-dimethyl-1,3-divinyl-1,3-diphenyl disiloxane, and (4) phenylvinyldiethoxysilane and hexamethyldisiloxane were hydrolysed and condensed; (6) a viscous vinyl-containing siloxane was prepared and copolymerized with the polymer of (1); (7) diethoxy diphenyldivinyldisiloxane was prepared and copolymerized with the polymer of (1). Uses.-As potting compounds for electrical transformers, coils and resistors and for impregnating porous metal castings. 1,3 - Dimethyl - 1,3 - diphenyl - 1,3 - divinyldisiloxane was made by hydrolysing with H2SO4, according to Example I, methylphenylvinylethoxysilane obtained by passing methylbromide gas into dry ether containing phenylvinyldiethoxysilane and Mg, and refluxing the mixture with subsequent filtration of the salts formed and distillation of the filtrate. 1,3 - Diethoxy - 1,3 - diphenyl - 1,3 - divinyldisiloxane (Example VII) was made by hydrolysing phenylvinyldiethoxysilane with aqueous H2SO4 in amount insufficient to hydrolyse completely the ethoxy groups. Specification 832,965 also is referred to.