Solution Properties of Three Polyzwitterions Basedon Poly(N-vinylimidazole)

The solution properties of the poly(carboxybetaine)s possessing structural units of[1-vinyl-3-(1-carboxymethyl) imidazolium betaine] (PNVIB-1); [1-vinyl-3-(2-carboxyethyl) imidazolium betaine] (PNVIB-2) and [1-vinyl-3-(2-carboxyisopropyl)imidazolium betaine] (PNVIB-3) were investigated by viscometric measurementsand potentiometric titration. Deionized water as well as CaCl2 and NaClaqueous solutions with different concentrations and two alcohols, i.e., methanol andethanol were used as solvents. The solubility and viscometric behaviours of threepoly(carboxybetaine)s were strongly dependent on the chemical nature of the spacerbetween N+ and COO- groups and the nature of the solvent. From the studies achievedthe polyelectrolyte behaviour of PNVIB-2 in methanol and PNVIB-3 in all the solventsas well as an anti-polyelectrolyte behaviour of PNVIB-2 in water were all observed.Fuoss and Rao equations were used to assess intrinsic viscosity, [ç], values in the caseof polymers with polyelectrolyte behaviours as well as Einstein-Simha and Raoequations in the case of the polymer with anti-polyelectrolyte behaviour. UsingHenderson-Hasselbach equation and potentiometric titrations of aqueous solutions ofpoly(carboxybetaine)s with 0.5 M HCl the apparent pKa values were determined. Thesevalues are strongly dependent on the solvent nature. Also, when the water is used assolvent for polymers, it is observed that the PNVIB-2 and PNVIB-3 present the lowestpKa values, because of the lowest binding ability of the H+ by COO- groups.