This work describes the synthesis and characterization of polyamides, copolyamides, and polyamide blends containing cation- and anion-selective host units in the pendant structure and their application to the extraction of environmentally polluting cations from aqueous media. The cation host unit consists of a crown ether subunit and the anion receptor is a urea group. The preparation of the copolymers involves the copolymerization of two isophthalic acid derivatives-one containing a lateral urea group and the other a crown ether moiety-with m-phenylenediamine. The molar ratio of crown ether to urea subunits is varied from 1/1 to 1/2 and 1/3 to fit the ion and counterion ratio of metals with valences I, II, and III. The extraction effectiveness and selectivity is related to the composition of the copolymer or the polymer blend, and thus formally to the cation to anion host units ratio, which therefore permits the a la carte design of materials to be used in the decontamination and elimination of polluting cations. With regard to the cation extraction from aqueous media with polyamide solid phases, the polymer structure design leads to the extraction of high percentages of Hg-II (almost 100%) and moderate extraction of Pb-II, and Cr-III. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 670-681, 2009