Radical copolymerizations of 1-vinyl-2-pyrrolidone with acrylamide and N,N'-dimethylacrylamide at different feed ratios were investigated. The copolymers were characterized by Fourier transform infrared spectroscopy, H-1 NMR, and C-13 NMR spectroscopy. The copolymer composition was determined from the H-1 NMR spectra and found to be statistical. The metal complexation of poly(acrylamide-co-1-vinyl-2-pyrrolidone) and poly(N,N'-dimethylacrylamide-co-1-vinyl-2-pyrrolidone) for the metal ions Cu(II), Co(II), Ni(II), Cd(II), Zn(II), Pb(II), Fe(III), and Cr(III) were investigated in an aqueous phase. The liquid-phase polymer-based retention method is based on the retention of inorganic ions by soluble polymers in a membrane filtration cell and subsequent separation of low-molecular compounds from the polymer complex formed. The metal ion interaction with the hydrophilic polymers was determined as a function of the pH and the filtration factor. Poly(N,N-dimethylacrylamide-co-2-vinyl-2-pyrrolidone) showed a higher affinity for the metal ions than poly(acrylamide-co-1-vinyl-2-pyrrolidone). According to the interaction pattern obtained, Cr(III) and Cu(II) formed the most stable complexes at pH 7. Pb(II) and Zn(II) were not retained.