Photopolymerizable organopolysiloxane/silane compositions

A liquid, storage stable organopolysiloxane having a viscosity of from 60 mPa.s to 20,000 mPa.s at 25.degree. C., comprising the reaction product of (i) an .alpha.,.omega.-dihydroxydiorganopolysiloxane oil, the organo functions being selected from the group consisting of methyl, ethyl, n-propyl, vinyl, phenyl and trifluoropropyl, with at least 70% of such functions being methyl and no greater than 3% being vinyl, and said oil having a viscosity ranging from about 70 to 500 mPa.s at 25.degree. C., (ii) a silane having the formula Z(G)SiR.sub.a (Q).sub.3-a wherein Z is CH.sub.2 .dbd.C(R')--COO-- or HS--, and further wherein the symbols R, which may be the same or different, are methyl, ethyl, n-propyl, vinyl or phenyl, R' is hydrogen or methyl, the symbols Q, which may be the same or different, are methoxy, ethoxy, n-propoxy, .beta.-methoxyethoxy or, when any two are taken together, the divalent radical --O--C(CH.sub.3).sub.2 --C(CH.sub.3).sub.2 --O--, G is a linear or branched chain alkylene radical having from 1 to 8 carbons, a is a number ranging from 0 to 2;

• and (iii) a catalyst selected from the group consisting of alkyl titanates and polytitanates and diorganotin salts of aliphatic carboxylic acids, said organopolysiloxane being prepared by reacting an intimate admixture of the .alpha.,.omega.-dihydroxydiorganopolysiloxane (i), the silane (ii) and the catalyst (iii) wherein the ratio of the hydroxyl functions of the oil (i) to the Q radicals of the silane (ii) comprises from about 0.1 to about 0.95 at a temperature of from about 5.degree. to 180.degree. C. for a contact time such that no greater than 45% by weight of the theoretical amount of byproduct alcohol, QH, is evolved during the reaction.