Thermodynamic Parameters for the Protonation of Poly(allylamine) in concentrated LiCl(aq) and NaCl(aq)

The acid-base properties of poly(allylamine) (MW ) 15 kDa) were determined by potentiometry andcalorimetry in aqueous solutions at t ) 25 °C. Potentiometric measurements were carried out in a widerange of ionic strengths (0.1 e I/molâL-1 e 5.0) in NaCl(aq) and LiCl(aq), while enthalpy changes for theprotonation of poly(allylamine) were determined by calorimetry in the same ionic strength range butonly in NaCl(aq). Analysis of the experimental data was carried out using two different models: the firstbased on a modified Henderson-Hasselbalch two parameter equation and the second on the threeparameter equation proposed by Ho¨gfeldt. Protonation constants are given for both models and ionicmedia at t ) 25 °C, while ¢G, ¢H, and T¢S values were determined using the three parameter modelalone. The dependence on ionic strength of protonation constants was determined by the SIT model(Specific ion Interaction Theory), while the parameters for the dependence on ionic strength of ¢H andT¢S were determined by a simple empirical equation. Comparison is also made of the protonationconstants of poly(allylamine) and some low molecular weight polyamines. Thermodynamic parametersfor the protonation of poly(allylamine) are very close to those of low molecular weight polyamines, whichare included for purposes of comparison.