in which R1 is a halogen atom, a hydroxyl group, a C1 - to C18 -alkoxy group, a C1 - to C18 -alkyl group or a cholesteryl radical, R5 is a phenylene or biphenylene radical which may be linked to a phenylene radical via the --OOC-- group or a phenylene radical linked the --OOC-- group, y is an integer of from 3 to 12, R2 is selected from the group consisting of a radical of the formula