The interactions of poly(methacrylic acid) (PMA), poly(acrylic acid) (PAA) and a copolymer of acrylamide and acrylic acid (CAMAA) with copper (II) ions in aqueous solutions were studied by electron paramagnetic resonance (e.p.r.) spectroscopy as a function of the degree of neutralization cr. A procedure for decomposition of the e.p.r. spectra was developed in order to evaluate the fraction of free copper and bound copper ions. When a loss of the e.p.r. signal intensity is observed in the solutions containing polymer with respect to the one of the reference copper salt solutions without polymer, this effect is attributed to the formation of a binuclear polymer/copper complex (copper : carboxylates, 2/4), inactive in e.p.r. The complex visible in e.p.r, is assumed to be mononuclear (copper : carboxylates, 1/2). This indicates that the main PMA/copper complex is binuclear. PAA and copper interactions lead to both bi-and mono-nuclear complexes, but this last species is preponderant at the higher ct values. In the case of CAMAA of lower charge density and where the charges are quenched, only a mononuclear complex was found. The constants of formation of the mono-and bi-nuclear complexes were evaluated by assuming that the system was ruled by a series of equilibrium laws : copper hydrolysis, polymer ionization and polymer/copper complexation. The peculiar behaviour for PAA may be explained by considering that the constant of formation for the binuclear complex decreases when the intramolecular monomer concentration is lowered by the chain expansion.