Acid-base and chelating properties of Gantrez copolymers

The Gantrez (GTZ) copolymers (GTZ AN169, GTZ S97 and GTZS95) are poly(methyl vinyl ether co-maleic acid) at high molecular weight (2000, 1200 and 220 kDa), in anhydride (AN) and acid (S) form, with important characteristics (high chelating power, excellent dispersion and antisoil redeposition properties) that allow to employ them in several applications: in cosmetic, medical and industrial products. The GTZs can be considered to be a good model molecule for the study of more complex natural macromolecules, such as natural organic matter, owing to rich in carboxylic groups, which acts as a binding site for organic and inorganic cations over a wide pH range. The GTZs, when dissolved in water, form sticky and jelly solutions due to the formation of micelles in solution. The determination of the critical micelle concentration (CMC) was determined by different techniques: light scattering, conductivity, surface tension and DOSY NMR [1]. The acid-base behavior of the GTZs were studied take into account the CMC, in widely range of temperature, ionic strength and different ionic media. In the calculation of the protonation constants, a simplified approach, the diprotic-like model, was used; the model allows to treat, from acid−base and complexing points of view, a polyelectrolyte like a simple low molecular weight ligand, considering a minimum number of protonation sites necessary to extensively depict the system and in the case of the GTZs, two methyl vinyl ether co-maleic units were considered. From the analysis of the experimental data of GTZ AN169, S97 and S95, in the same experimental conditions of temperature, ionic strength and ionic medium, it was possible to observe a trend in the protonation constants, namely an increase of the basicity of the ligands, increasing the molecular weight. The binding ability of the three copolymers was studied towards two different metal cations, Zn2+ and Sn2+ in NaCl aqueous solutions at I = 0.15 mol dm-3 and T = 298.15 K. The speciation model of the GTZs were compared from them and sequestering ability of these polyelectrolytes was evaluated by means the empirical parameter pL50.