Curable organosiloxane composition

Claim 1

In an improved curable organopolysiloxane composition comprising (i) an organopolysiloxane containing at least two lower alkenyl radicals per molecule and having the average unit formula R.sup.1.sub.a SiO.sub.(4-a)/2 where R 1 represents a monovalent hydrocarbon or halogenated hydrocarbon radical and the average value of a is from 0.8 to 2.2, inclusive; (ii) an organohydrogenpolysiloxane containing at least 2 silicon-bonded hydrogen atoms in each molecule and no alkenyl radicals, where the molar ratio of the total number of silicon-bonded hydrogen atoms in this component to the total number of all alkenyl groups in components (i) and (iv) is from 0.5 to 3.0, inclusive; (iii) a platinum-containing catalyst in an amount equivalent to from 0.1 to 100 parts by weight of platinum metal for each one million parts of combined weight of components (i), (ii) and (iv); and (iv) from 0.5 to 20 parts by weight per 100 weight parts of component (i), of an adhesion promoter, the improvement wherein ingredient (iv) is the hydrolysis reaction product of (a) 1 part by weight of a tetraalkoxysilane of the general formula Si(OR 2 ) 4 , where R 2 represents an alkyl radical, (b) from 0.1 to 100 parts by weight of an organopolysiloxane containing at least 1 lower alkenyl radical or silicon-bonded hydrogen atom in each molecule and having the unit formula R 3 2 SiO, where each R 3 individually represents a hydrogen atom, a monovalent hydrocarbon radical or a monovalent halogenated hydrocarbon radical, and (c) from 0 to 10 parts by weight of an alkoxysilane of the general formula ##STR3## where R 4 represents a hydrogen atom or an alkyl radical, R 5 represents an alkylene radical, R 6 is selected from the same group as R 1 , R 7 is selected from the same group as R 2 , the value of x is 0 or 1, and said hydrolysis reaction product is prepared in the presence of water and an acid catalyst.