The mechanism of copper adsorption by polyvinyl polyacrylate (PVPA) was examined using ESR and magnetic measurements. The copper adsorption by PVPA obeyed Langmuir adsorption isotherm with the maximum adsorption amounts of 4.17 mmol g(-1) adsorbent, being larger than those of uranium adsorption. Though copper in the solution was completely adsorbed by the resin above pH 4, the ESR intensity was remained low level and only increased above pH 8. The ESR spectrum of Cu(II) ion in PVPA are axial type with tetragonally distorted octahedral symmetry, having parameters of g(//) = 2.361, g(perpendicular to) = 2.057, vertical bar A(//)vertical bar = 14.0 m cm(-1) (pH 5), and g(//) = 2.329, g(perpendicular to) = 2.058, vertical bar A(//)vertical bar = 16.2 m cm(-1), vertical bar A(perpendicular to)vertical bar = 2.7 m cm(-1) (pH 9). The absorption peaks originated from Cu(II)-Cu(II) dimer was also observed (pH 5). The paramagnetic susceptibility of PVPA adsorbed Cu(II) ion at pH 5 explained by the dimer model with vertical bar J vertical bar = 220 K. These results suggested that most of copper was adsorbed and formed dimer in PVPA, being similar to that in Cu(II)-acetate monohydrate. (c) 2006 Wiley Periodicals, Inc.