Dissociation of weak polymeric acids and bases

The electrolytic dissociation of several polymeric acids and bases in aqueous solutions has been investigated. The potentiometric behavior is well described by the following equations, For polyacids: and for polybases: pK₀ is the intrinsic dissociation constant of the monomeric unit, α and β are the degrees of ionization of the polyacid and the polybase respectively, ψ₀ is the electrostatic surface potential of the polyion. It is shown that ψ₀ is equal to (1/ϵ) (δF_e/δv) for polyacids and (1/ϵ) (δF_e/δζ) for polybases where F_e is the electrostatic energy of the polyion and v or ζ the number of negative or positive ionized groups respectively. Equations for the calcualtion of ψ₀ in the cases of randamly kinked and stretched polyelectrolytes are given and discussed. As the potential ψ₀ can be obtained independently from electrophoretic measurements, the above equations correlate potentiometry and electrophoresis. The potentials of polymethacrylate ions were calculated from theory and obtained from electrophoretic and potentiometric measurements. The potentials obtained by the three methods agree within 3% thus justifying the use of the combined potentiometric and electrophoretic measurements for the evaluation of pK₀. Application of this method to the potentiometric analysis of pectic acids gave good agreement with experiment and lead to pK₀ = 3.40. Combined potentiometric‐electrophoretic analysis for polyaspartic acid gave pK₀ = 3.53 and for polylsine pK₀ = 10.44.