ups being phenyl or 3,3,3-trifluoropropyl radicals and no more than 10 percent of the organic groups being vinyl radicals, (B) 0 to parts by weight of a non-acidic, nonreinforcing filler, (C) 2 to 20 parts by weight of a silane of the general formula in which R is an organic radical selected from the group consisting of methyl, vinyl and phenyl and R is an organic radical selected from the group c