Abstract: The invention pertains to polymeric polydentate complexons (i.e. chelating agents) of general formulae I and II ##STR1## where P is a linear or three-dimensional polymeric skeleton and X is --0-- or ##STR2## while R is H, C.sub.1 -C.sub.6 alkyl, or phenyl or phenyl substituted with 1-2 C.sub.1 -C.sub.6 alkyl or alkoxy groups. Another objective of the invention is a method for producing the polymeric polydentate complexons described above, wherein a compound P -XH, where P and X have the above given meaning, reacts with 4,4'-ethylenebis(2,6-morpholinedione) the presence of an inert solvent and, if it is desired, also in the presence of acidic or basic catalysts, e.g. protic acids, Lewis acids, tertiary amines, and alkaline or alkaline earth salts of carboxylic acids.