In a preferred embodiment, a cycloaliphatic radical R or R' is one of the formula ##STR8## in which q is 0 or 1, the radicals R4 independently one another are hydrogen or alkyl with 1 to 6 C atoms and X is a direct bond, O, S, SO2, alkylene with 1 to 3 C atoms or alkylidene with 2 to 6 C atoms.