We carried out the free-radical copolymerization of N-phenylmaleimide with acrylic acid and acrylamide with an equimolar feed monomer ratio. We carried out the synthesis of the copolymers in dioxane at 70 degrees C with benzoyl peroxide as the initiator and a total monomer concentration of 25M. The copolymer compositions were obtained by elemental analysis and H-1-NMR spectroscopy. The hydrophilic polymers were characterized by elemental analysis, Fourier transform infrared spectroscopy, H-1-NMR spectroscopy, and thermal analysis. Additionally, viscosimetric measurements of the copolymers were performed. Hydrophilic poly(N-phenylmaleimide-co-acrylic acid) and poly(N-phenylmaleimide-co-acrylamide) were used for the separation of a series of metal ions in the aqueous phase with the liquid-phase polymer-based retention method in the heterogeneous phase. The method is based on the retention of inorganic ions by the polymer in conjunction with membrane filtration and subsequent separation of low-molecular-mass species from the formed polymer/metal-ion complex. The polymer could bind several metal ions, such as Cr(III), Co (II), Zn(II), Ni(II), Cu(II), Cd(II), and Fe(III) inorganic ions, in aqueous solution at pH values of 3, 5, and 7. The interaction of the inorganic ions with the hydrophilic polymer was determined as a function of pH and a filtration factor. Hydrophilic polymeric reagents with strong metal-complexing properties were synthesized and used to separate those complexed from noncomplexed ions in the heterogeneous phase. The polymers exhibited a high retention capability at pH values of 5 and 7. (c) 2005 Wiley Periodicals, Tnc. J Appl Polym Sci 99: 2359-2366, 2006