Thermodynamic Properties of Aqueous Solutions of Polyelectrolyte Containing Carboxyl Groups

Abstract

Thermodynamic properties of salt-free aqueous solutions consisting of a polyelectrolyte [poly(acrylamide) containing carboxyl groups (PAAm-A) and poly(acrylic acid) partially neutralized by NaOH] and a nonelectrolytic polymer [poly(vinyl alcohol)] were investigated by pH, light scattering and isopiestic pressure measurements in regard to the influence of polymer concentration, COOH content ρ, and molecular weight P. Regardless of whether the polyelectrolyte was weakly or strongly charged, the degree of dissociation of COOH groups increased with increasing P or ρ, i.e., with an increase in the number of COOH groups in the polyelectrolyte chain. It was also found that the chemical potential of water in aqueous solutions of PAAm-A was lower for higher molecular weight even at relatively high polymer concentrations. The thermodynamic properties and phase behavior were compared using a semi-empirical equation established on the basis of the present thermodynamic data. This equation predicted the anomalous molecular weight dependence of phase diagrams. It is suggested that the greater ease of dissociation of COOH groups at larger P is closely related to the anomalous molecular weight dependence of phase behavior observed previously.