Spectroscopic and Equilibrium Dialysis Studies of the Poly(acrylic acid)–Cu(II) Complex in the pH Range 3.5–7

The complex formation between poly(acrylic acid), poly(Acr), and Cu2+ ion was studied in 150 mM NaCl solutions at 25 °C and at the mixing ratios of Acr residues-to-Cu2+, R, of 32, 16 and 8, in the pH range of 3.5–7 by the spectroscopic and equilibrium dialysis methods. The dialysis results showed that more than 90% of the Cu2+ ions remain bound to the polymer at pH’s higher than 4.5, but the bound Cu(II) begins to dissociate at lower pH values. The data also revealed that the true absorption spectra of poly (Acr)–Cu(II) complexes varied with pH and R in a complicated manner. The analysis of the bound Cu(II) spectra disclosed the presence of three different kinds of Cu(II)–Acr complexes over the entire pH range. It is the relative amounts of these three complexes that vary with pH and R. With a newly devised plot of the dialysis data, the stability constant for each Cu(II)–Acr complex was determined. In the poly(Acr)–Cu(II) macrocomplex, each Cu(II) was estimated to bind to two or four carboxylato ligands.