roup consisting of methyl, vinyl and phenyl and R is an organic radical selected from the group consisting of methyl, ethyl and phenyl, (D) 0.25 to 7 parts by weight of an aminoxysilicon compound having from 1 to silicon atoms per molecule and from 3 to 10 aminoxy groups per molecule, said aminoxy group having a general formula OX in which X is a monovalent amine radical selected from the group co