Object of the invention are new diisatoic acid and triisatoic acid derivatives of the general formula I ##STR1## wherein n represents 2 or 3, X stands for oxygen or sulfur and R for a group of the general formula II in which m stands for 1 or 2, Y for B when m is 1 and Y further represents a di- or trivalent alkyl group with 1 to 5 carbon atoms when m is 2, B represents alkylene with 1 to 4 carbon atoms and Z stands for phenylene-1,4-dioxy or diphenylene-4,4'-dioxy optionally singly or multiply ...