GB821395A - Improvements in alkyl aryl vinyl silicone elastomers - Google Patents

Abstract

The physical properties of a cured silica-filled alkyl aryl vinyl siloxane elastomer are improved by subjecting the uncured siloxane to a smearing or wiping and shearing mixing operation at a temperature above 25 DEG C. The operation may be effected in a dough-mixer or Banbury mixer and during the addition of the filler to the siloxane; alternatively the filler may first be compounded with the siloxane and the mixture then treated as above. Generally, the aryl radicals, e.g. phenyl, xylyl, benzyl, tolyl and chlorophenyl, comprise 2 to 20%, the vinyl radicals 0.05 to 2%, and the alkyl radicals, e.g. methyl, ethyl and propyl, 78 to about 98% by weight of the total Si-bonded organic radicals. In the examples, comparative physical properties are given of a methylphenylvinyl siloxane gum (a) doughmixed at 150 DEG C., (b) compounded on a rubber mill, with finely-divided silica and diphenylsilane diol, and when cool mixed with bis-(2 : 4-dichlorobenzoyl)-peroxide and cured. The physical properties are further improved by using dimethylcyclopinacoxysilane <FORM:0821395/IV (a)/1> together with the diphenylsilane diol. Other curing catalysts specified are benzoyl peroxide and t-butyl perbenzoate. Uses.-For making gaskets, tubing, insulation and shock-absorbers.