THERMODYNAMICS OF THE INTERACTION OF POLY ACRYLIC-ACID WITH WATER

The Gibbs energies, enthalpies, and entropies of mixing water with pol yacrylic acid (PAA) having a molecular mass (MM) in the range from 4 x 10(3) to 2 x 10(6) were determined over the entire range of compositi ons. The plots of the enthalpy and entropy of mixing versus the soluti on composition have shapes that have not been reported earlier for pol ymer solutions: the curves for all MMs exhibit additional minima and m axima at a PAA content of 65 - 75% in the solution. The results were a nalyzed taking into account the glassy state of PAA, interactions betw een AA units and water molecules, UCST and LCST criteria, and conforma tional changes in PAA. It is suggested that the observed additional ex trema in the concentration dependence of enthalpy and entropy of mixin g are due to the conformational transitions in PAA macromolecules.