Polymer filtration (PF) uses a size-exclusion ultrafiltration membrane to retain higher molecular weight species while allowing the passage of smaller species through the membrane. Metal-ion separations from aqueous streams are accomplished with PF by using water-soluble chelating-polymers (WSCP), which are appropriately sized polymers that have covalently attached metal-binding ligands. In this study, a new WSCP was prepared by modifying polyethylenimine (PEI) through an amide linkage to attach 2,3-dihydroxyterephthalamide (TAM) groups that have high binding constants for high valent metal cations. The TAM ligand contains a dimethylethylenediamine side chain that was found to maintain polymer solubility throughout the working pH and ionic strength ranges studied. The new WSCP (designated PDT) showed selectivity for Pu(IV) over Am(III). For example, at pH 4.5, the distribution coefficient (D) was 1.6 x 10(3) for Am(III) (14% bound) and 1.3 x 10(6) for Pu(IV) (99.3% bound). The Pu(IV) D increased as a function of pH, and the highest D was 4.8 x 10(6) at pH 11.4, corresponding to 99.8% bound. Varying the PDT concentration from 0.1% to 0.001% had little effect on Pu(IV) D values. The high formation constant of the Pu(IV)-PDT complex appears to promote the oxidation of Pu(Ill) to Pu(IV), even in the presence of a high concentration of reductant, 0.25-M hydroxylamine nitrate (HAN). The same high formation constant allows the TAM-containing polymer to compete with plutonium polymer formation, as plutonium absorbed on the walls of a glass vessel dissolved after contacting it with PDT for 2 days.