A composition according to claim 6 wherein R1 contains from 2 to 20 carbon atoms, R2 is an alkyl radical containing said organofunctional substituent, R3 is selected from the group consisting of alkyl, alkenyl, epoxyalkyl and methacryloxyalkyl, and X represents an alkoxy group containing from 1 to 4 carbon atoms, m is 2 or 3 and n is 1, 2 or 3.