Potentiometric study of Cu(II) and Ni(II) complexation with two high molecular weight poly(acrylic acids).

The copper (II) or nickel (II) complex formation with two poly(acrylic acids) of high molecular weight (Mw=2.5x10(5) and 3x10(6)) was investigated in aqueous dilute solution (NaNO(3) 0.1 mol l(-1); 25 degrees C). Potentiometric titrations were carried out, first to precise the acid-base properties of the two polymers, and secondly to determine the stability constants of the MA and MA(2) complex species formed. The Bjerrum's method, modified by Gregor et al. (J. Phys. Chem., 59 (1955) 34-39), for the study of polymeric acids was used. The results obtained showed that both polymers present very similar properties. As expected, copper(II) is more readily bound to poly(acrylic acids). CuA(2) was the predominant observed species; the global stability constant logbeta(102) was found to be close to 6.6. With nickel(II), none of the complex species MA or MA(2) becomes predominant (logbeta(102)=5.5). Finally, the PAA complexes present a greater stability compared with that of monomeric analogs.