Complexes of poly(acrylic acid) with some divalent, trivalent and tetravalent metal ions

The formation of metal complexes between poly(acrylic acid) and divalent, trivalent and tetravalent metal ions was studied. For divalent and pseudodivalent metal ions, the stability constants determined according to the method of Gregor et al. [J. Phy. Chem. 59 (1954) 34] are in the order Cu2+>VO2+>Co2+>Ni2+, Zn2+. The values were nearly insensitive to the ligand to metal concentration ratio in the range R=1–10. Trivalent and tetravalent ions also induced a strong decrease of the pH but stability constants could not be determined from the formation curves. The metal ions were divided in four groups depending on the shape of the curve ΔpH vs α. These groups differ from one another by (i) the speed of water exchange or (ii) by the speed of ligand exchange in the coordination sphere of the metal in the case of lanthanideʹs.