Rather, these radicals may be chosen freely in each of the a fragments The radicals A?????? and A?????? may be identical or different and are preferably chosen from the group where R8 and R9 may be identical or different and are chosen from the group of saturated and unsaturated alkyl and acyl radicals having 1-30 carbon atoms, p is a number from 1-20 and Y is a single bond or the group where R3 i