GB786434A - Improvements in or relating to organosilicon polymers and compositions containing the same - Google Patents

Abstract

An elastomer-forming copolymer of one or more di-organosiloxanes and one or more tri-organosilyl end-blocked di-organosiloxanes, wherein the ratio of silicon atoms (in the copolymer) per tri-organosilyl unit is between 1000 and 6000 whereby the end-blocking unit is present in amount sufficient to prevent crepeageing of the copolymer when mixed with a reinforcing silica filler, but insufficient to affect deleteriously the physical properties of the vulcanized elastomer, the organic radicals being aliphatic hydrocarbon radicals containing less than 7 carbon atoms with or without aryl hydrocarbon radicals, may be made by polymerizing the respective siloxanes by reaction with an alkali metal hydroxide or an alkali metal salt of a triorganosilanol. The end-blocked siloxane starting material preferably has a viscosity between 1 and 30 cs. at 25 DEG C. and the reaction is effected, e.g. at 80 DEG to 200 DEG C. Siloxane hydrocarbon radicals specified are methyl, ethyl, butyl, vinyl, allyl, hexenyl, phenyl and tolyl. The silica filler is used in amount, e.g. of 10 to 80 parts per 100 parts of copolymer. In examples, a liquid trimethylsilyl end-blocked dimethyl-siloxane was copolymerized with (1) a mixture of cyclic vinylmethyl- and dimethyl-siloxanes, (2) a mixture of cyclic dimethyl- and phenylmethyl-siloxanes, and (3) a mixture of cyclic dimethyl siloxanes. The products were then milled with silica aerogel and benzoyl peroxide and vulcanized.