Curable organosiloxane compositions

Claim 1

A curable organosiloxane composition comprising (a) a polyorganosiloxane having an average unit formula R a SiO.sub.(4-a)/2, where R represents a monovalent hydrocarbon radical, with the proviso that at least two of the R radicals in each molecule are lower alkenyl, and the value of a is from 0.8 to 2.2, inclusive; (b) a polyorganohydrogensiloxane containing at least 2 silicon-bonded hydrogen atoms per molecule and which is substantially free of silicon-bonded alkoxy groups and alkenyl radicals, the quantity of polyorganohydrogensiloxane being sufficient to provide a molar ratio of silicon-bonded hydrogen atoms in ingredients (b) and (d) to the moles of alkenyl radicals in ingredient (a) of from 0.5:1 to 3.0:1, respectively; (c) a platinum-containing hydrosilation catalyst in an amount equivalent to from 0.1 to 100 ppm by weight of platinum, based on the combined weight of ingredients (a), (b) and (c); (d) from about 1 to 20%, based on the weight of ingredient (a), of a polysiloxane represented by the general formula (HR' 2 SiO 1/2 ) b (R"O 1/2 ) c (SiO 4/2 ) d where R' and R" represent monovalent hydrocarbon radicals containing from 1 to 3 carbon atoms, the value of b/c in said general formula is from 0.2 to 2, inclusive, the value of b+c)d in said general formula is from 0.4 to 4, inclusive, and d represents a number greater than 0 and less than 30.