Polyacrylate protonation in various aqueous ionic media at different temperatures and ionic strengths

The protonation constants of the polyacrylate anion (molecular mass 2000 Da ) in Et4NI, Me4NCl, LiCl, LiNO3, NaCl, NaNO3, and KCl aqueous solution, wer e determined in a wide range of ionic strengths. A three-parameter approxim ation was used to express protonation constants as a function of the dissoc iation degree alpha, and their dependence on ionic strength was considered using a simple polynomial expansion. Differences in log K-H between differe nt data in different media were interpreted in terms of weak complex format ion between polyacrylate and alkali metal cations. Measurements were also p erformed at different; temperatures (15 less than or equal to T/degrees C l ess than or equal to 55) in order to calculate enthalpy and entropy changes for the protonation of the polyacrylate. Thermodynamic parameters for the protonation of monomer, acrylic acid, were studied potentiometrically at di fferent temperatures and ionic strengths for purposes of comparison.