Evaluation of potentiometric data of weak polyelectrolytes taking account of nearest‐neighbour interaction

For a number of weak polyelectrolytes potentiometric titration data are interpreted on the basis of the dependence of the p K on the degree of ionization σ by considering the separate contributions for a) the mean electrostatic potential field, b) interactions between neighbouring functional groups, c) the distribution of the functional groups over the macromolecule, d) specific conformational aspects and branching. For the various polyelectrolytes this procedure leads at low ionic strength to a satisfactory picture of the charging process. However, on increasing the ionic strength definite discrepancies between the two weak polybases with strong neighbour interactions, poly(ethylene‐imine) and poly(vinylamine), and the other polyelectrolytes are found. The very strong dependence of p K on σ in these two cases even at high ionic strength can only be explained by concluding that the electrostatic potential at the site of reaction in these molecules is much higher than expected on the basis of additivity of the various specific effects.