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 Et(4)NI, Me(4)NCl, LiCl, LiNO(3), NaCl, NaNO(3), and KCl aqueous solution, were determined in a wide range of ionic strengths. A three-parameter approximation was used to express protonation constants as a function of the dissociation degree alpha, and their dependence on ionic strength was considered using a simple polynomial expansion. Differences in log K(H) between different data in different media were interpreted in terms of weak complex formation between polyacrylate and alkali metal cations. Measurements were also performed at different; temperatures (15 less than or equal to T/degrees C less 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 different temperatures and ionic strengths for purposes of comparison.