Study of Metal–Polycarboxylate Complexes Employing Ion-selective Electrodes. III. Complex Formation between Maleic Acid Copolymers and Bivalent Transition Metal Ions

Abstract

Abstract The complex formation of bivalent transition metal ions, Mn(II), Co(II), Ni(II), Cu(II), and Zn(II), with copoly(maleic acid–ethylene) and copoly (maleic acid-styrene) in aqueous solution was studied by potentiometric titration at 25 °C and the ionic strength of 0.1. The systems containing copper(II) ions were investigated by potentiometry employing the copper(II) ion-selective electrode. The titration curves of the bivalent metal–copoly(maleic acid–ethylene) systems were situated in a lower pH region than in the absence of the metal ions. The complex formed involves two carboxylate groups: primary and secondary. The equilibrium constant of the copper(II) complex was estimated to be 10−2.6. In copoly (maleic acid–styrene) systems, however, the titration curves in the absence and presence of bivalent metal ions overlapped partly in the first neutralization step. From the potentiometric results employing the ion-selective electrode, it was observed that the concentrations of copper(II) ions decrease slightly in the region of overlap. This anomalous behavior is due to the acid dissociation influenced by the conformational transition, including the effect of the side groups of the polymers.