GB618453A - Improvements in and relating to methyl silicone gums and elastomers - Google Patents

Abstract

A methyl silicone gum is prepared by hydrolyzing a mixture of mono-, di- and trimethyl silanes and treating the oily product with a polymerization catalyst which is (a) ferric chloride, or (b) ferric oxide and aluminium chloride, or (c) sulphuric acid. Preferably the average methyl to silicon ratio of the hydrolysis mixture is 1.98 to 2.0. The mixture should contain less than 5 mol. per cent of monomethyl silane and 0.4-0.95 mols. of trimethyl silane per mol. of monomethyl silane. Elastomers may be prepared by compounding the gums with catalysts and fillers as in Specification 594,481. The products are soft, with low permanent set at high temperatures, and are particularly useful for gaskets. In the examples, (1) a mixture of 98.081 mol. per cent dimethyldichlorosilane, 0.984 per cent methyl trichlorosilane, and 0.934 per cent trimethylchlorosilane was hydrolysed and the oil polymerized to a soft elastic gum by heating with ferric chloride hexahydrate. The gum was compounded with lead oxide, titanium dioxide and benzoyl peroxide, and the product moulded and cured. Examples (2) and (3) use different proportions of the various methyl silanes; example (4) employs more ferric chloride hexahydrate. Example (5) employs an oil prepared by blending the products of hydrolysis of methyltrichlorosilane and dimethyldichlorosilane, with the product of hydrolysis of dimethyldichloroand trimethylchlorosilane. Curing may be performed in two stages, with a second addition of benzoyl peroxide. Specification 618,452 also is referred to.