is an alkylene having 1 to 8 carbon atoms, B is a hydroxy or an alkoxy having 1 to 8 carbon atoms and n is an integer of 1, 2, or 3 with the proviso that if n is 1 or 2, each B need not be identical; and (II) a disylyl crosslinking agent having the structure ##STR14## wherein R1, R2, R3, R4, R5 and R6 independently of the other is an alkyl with 1 to 8 carbon atoms and where R denotes an alkylene