A calorimetric study of the acid dissociation of the conjugate acids of poly(N-vinylimidazole) and polyallylamine

Thermodynamic parameters for acid dissociation of the conjugate acids of po ly(N-vinylimidazole) and polyallylamine have been determined in the presenc e of sodium chloride and sodium nitrate. Even though the plots of Delta G(0 ) against the degree of dissociation, alpha, are highly dependent on the ad ded salt concentration levels, the concentration effect has never been obse rved for the corresponding Delta H-0 versus alpha plots. The effect on the Delta G(0) versus alpha plots has been attributed to the entropy change of the counterions between a polyelectrolyte phase and a bulk solution phase. The alpha dependency of Delta H-0 is affected remarkably by the kinds of ca tionic polymers and counter-anions. Each Delta H-0 value at completely neut ralized conditions is quite close to the corresponding Delta H-0 value of t he monomer analog. The difference in the Delta H-0 values at fully charged conditions has been explained by the heats due to 1.Contact ion-pair formation of counter-anions to singly charged sites of t he polymer. 2. Hydration of counter-anion and polymer charged sites. The ion-pair formation of chloride anion to the conjugate acids of poly(N-v inylimidazole) and polyallylamine has been supported by Cl-35 NMR measureme nt. It has also been suggested that chloride anions bind the basic polymer molecules even at fully neutralized conditions.