The free-radical copolymerization of water-soluble poly(1-vinyl-2-pyrrolidone-co-hydroxyethylmethacrylate) was carried out with a feed monomer ratio of 75:25 mol %, and the total monomer concentration was 2.67M. The synthesis of the copolymer was carried out in dioxane at 70 degrees C with benzoyl peroxide as the initiator. The copolymer composition was obtained with elemental analysis and H-1-NMR spectroscopy. The water-soluble polymer was characterized with elemental analysis, Fourier transform infrared, H-1- and C-13-NMR spectroscopy, and thermal analysis. Additionally, viscosimetric measurements of the copolymer were performed. The thermal behavior of the copolymer and its complexes were investigated with differential scanning calorimetry (DSC) and thermogravimetry techniques under a nitrogen atmosphere. The copolymer showed high thermal stability and a glass transition in the DSC curves. The separation of various metal ions by the water-soluble poly(1vinyl-2-pyrrolidone-co-hydroxyethylmethacrylate) reagent in the aqueous phase with liquid-phase polymer-based retention was investigated. The method was based on the retention of inorganic ions by this polymer in a membrane filtration cell and subsequent separation of low-molar-mass species from the polymer/metal-ion complex formed. Poly(1-vinyl-2-pyrrolidone-co-hydroxyethylmethacrylate) could bind metal ions such as Cr(III), Co(II), Zn(II), Ni(II), Cu(II), Cd(II), and Fe(III) in aqueous solutions at pHs 3, 5, and 7. The retention percentage for all the metal ions in the polymer was increased at pH 7, at which the maximum retention capacity could be observed. The interaction of inorganic ions with the hydrophilic polymer was determined as, a function of the pH and filtration factor. (c) 2006 Wiley Periodicals, Inc.