Potentiometric titrations of polymethacrylic acid were performed at different concentrations, different molecular weights, and in the presence of neutral salts, as well as in dioxane‐water mixtures. It was shown that the pH of the solutions fulfills the relation, pH = pK — n log [(1 — α)/α]. pK and n are independent of the molecular weight and concentration if a suitable activity factor is introduced. The equation is applicable to free acid solutions as well as acid mixtures. Copolymers of the type, polyallyl acetate‐maleic acid, show a more complicated curve. The curve is of the “polydibasic” type. Each branch of it fits equation (2) well. The formula is analyzed and is proposed to be the result of the action of the Maxwell‐Partington statistical factor, as well as of the decrease in entropy accompanying the stretch of the randomly kinked molecule. This stretch is caused by the repulsive forces between the ionized carboxyl groups. The distribution curves of the various degrees of ionization present, for any pH, are given. The activity correction implies small units of the size of one or two carboxyl groups. The behavior in salt solutions is dependent not only on the activity correction, but also on the salting‐out factor. This factor is high in polyvalent salts. The titration curves in dioxane‐water mixtures are satisfactorily accounted for by the change in the activity factor with the dielectric constant.

The polybase properties of polyvinylamine hydrobromide were studied by pH‐metric titration at concentrations ranging from 10−4 to 10−1 M, in the presence, as well as in the absence, of neutral monomonovalent salt at high concentrations. The dependence of pH on degree of ionization, in all the range of concentrations studied, diverges from the known behavior of polyacids and polybases. The titration curve could not be characterized by a single dissociation constant, even when the electrostatic potential, determined electrophoretically, was taken into account, or when this potential was suppressed by high concentrations of neutral salt. An attempt is made to explain the unusual behavior of polyvinylamine by taking into account the nearest neighbor interaction. A statistical treatment, based on the unidimensional Ising model, leads to potentiometric equations involving two constants‐the intrinsic dissociation constant pK, and a nearest neighbor interaction constant ΔpK. The experimental titration curve could be satisfactorily described by these theoretical potentiometric equations. The titration constants for polyvinylamine derived by this procedure are pK = 9.4 and ΔpK = 1.20. These values compare favorably with the constants obtained from the microscopic dissociation constants of diethylenetriamine and of triethylenetetramine.

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