Dissociation of poly(allylammonium) cations in salt solutions

Potentiometric titration in various 1‐1 salt solutions was carried out to study the dissociation behavior of the poly(allylammonium) cation (PAAH⁺). The titration curves show that proton release from cationic PAAH⁺ is markedly suppressed by addition of simple salt and depends on the counterion species. From an analysis of the titration curves it is found that the electrostatic free energy change ΔG_el upon the proton release is negative in all systems examined, and its absolute value decreases with increasing ionic strength of the medium. Also, at a constant added salt concentration (0.1 mol L⁻¹) ΔG_el depends significantly on the counterion species added and increases in the order $\[ {\rm ClO}_{\rm 4}^ - > {\rm NO}_3^ - > {\rm Cl}^ - > {\rm Br}^ - > {\rm SCN}^ - > {\rm I}^ - . \]$ The value of ΔG_el correlates well with the electron donor constant En of the counterions. The dissociation behavior of PAAH⁺ is discussed in terms of electrostatic interaction among the ionized groups on the chain, the charge shielding effect, and the ion‐solvent interaction of the added counterions.