Ap. Safronov et al., THERMODYNAMICS OF THE INTERACTION OF POLY ACRYLIC-ACID WITH WATER, Vysokomolekularnye soedinenia. Seria A, 35(6), 1993, pp. 10000700-10000704
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.