Silicon-modified bis-phthalic acid derivatives

A compound of the formula I ##STR18## and the corresponding cyclised imide derivatives, in which X.sub.1 and X.sub.2 independently of one another are a group ##STR19## the two R independently of one another are --OH, alkoxy with 1-12 C atoms or phenoxy, R.sub.1 is alkyl with 2-7 C atoms, cycloalkyl with 5-7 C atoms, benzyl or ##STR20## Q is methyl, phenyl or --OQ.sub.3, Q.sub.1 Q.sub.2 and Q.sub.3 independently of one another are alkyl with 1-6 C atoms or phenyl and Y is a structural element of the formula II ##STR21## in which a is an integer from 1 to 15, the individual indices m and n independently of one another are 1 to 2, the individual radicals Z.sub.1 independently of one another are an aliphatic radical with at least 2 C atoms, or a cycloaliphatic, araliphatic, carbocyclic-aromatic or heterocyclic-aromatic radical and the individual radicals Z.sub.2 independently of one another are an aliphatic radical with at least 2 C atoms, or a cycloaliphatic, carbocyclic-aromatic or heterocyclic-aromatic radical, in which the carboxamide and carboxyl groups are bonded to different C atoms, and carboxyl groups bonded to cyclic radicals Z.sub.2 are each in the ortho-position to a carboxamide group.