A synthetic rubber composition of improved flexibility at low temperatures is obtained by incorporating in the rubber an organic silicate containing an aliphatic radical having more than five carbon atoms, preferably comprising 6 to 14 carbon atoms. Specified rubbers are polychloroprene, butyl rubbers and copolymers of butadiene with styrene or acrylonitrile. The silicate may be an orthosilicate containing one or more aliphatic radicals having more than five carbon atoms, e.g. tetraoctyl orthosilicate, dioctyl diphenyl orthosilicate, and dinonyl phenyl cresyl orthosilicate. Specification 694,313, [Group IV (b)], is referred to.ALSO:A natural or synthetic rubber composition of improved flexibility at low temperatures is obtained by incorporating in the rubber an organic silicate containing an aliphatic radical having more than five carbon atoms, preferably comprising 6 to 14 carbon atoms. The silicate may be an orthosilicate containing one or more aliphatic radical or radicals having more than five carbon p atoms. Several such silicates are referred to, including tetraoctyl orthosilicate, dioctyl diphenyl orthosilicate, and dinonyl phenyl cresyl orthosilicate. In one example is described the preparation and vulcanization of a stock comprising (in parts by weight) pale crepe rubber 100, zinc oxide 5, sulphur 2,5, stearic acid 2, dibenzythiazyl disulphide 1, and tetra-octyl orthosilicate 20. The tetra octyl orthosilicate is derived from a commercial "octyl" alcohol comprising a mixture of heptanols, octanols and nonanols in the ratio 45 : 43 : 12 by weight, together with a small quantity of saturated cyclic alcohols. Three other examples are described in which vulcanizable compositions are preferred using (a) butadiene-styrene copolymer and tetraoctyl orthosilicate, (b) tetradodecyl orthosilicate and natural rubber, and (c) dinonyl diphenyl orthosilicate and natural rubber respectively. Specification 694,313, [Group IV(b)], is referred to.
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