INTERACTION BETWEEN CALCIUM, A MODEL DIVALENT-CATION, AND A RANGE OF POLY(ACRYLIC ACID) RESINS AS A FUNCTION OF SOLUTION PH

The interaction between calcium, a small divalent cation, and selected polyacrylic acid polymers has been studied. The addition of calcium chloride to dispersions of the polymer reduced the maximal viscosity through an interaction which was not dependent upon physical entrapment of the cation by the viscous medium. The binding interaction between the cation and the polymer was pH dependent and apparently related to an ionic interaction with the ionized carboxylate groups in the polymer. The pH dependency of the calcium binding was more closely related to the intrinsic pKa (4.3) of the acrylic acid residues in the polymer rather than the apparent pKa (6.8) of the polymeric species.