F. Schwager et al., THERMODYNAMICS OF HYDROGEN-BONDING IN SOLUTIONS OF POLY(VINYLPYRROLIDONE) IN ETHANOL CCL4 MIXTURES/, Macromolecules, 30(5), 1997, pp. 1449-1456
The Gibbs free energy, the enthalpy, and the entropy of mixing of etha
nol with the polymer poly(vinylpyrrolidone) (PVP) and with its low mol
ecular weight analog, N-ethylpyrrolidone (NEP) were calculated. The ca
lculation of the free energy of mixing was achieved with the thermodyn
amic model for hydrogen-bonded polymer systems developed by Painter, C
oleman, and Graf. This model, based on the use of an association model
, gives the free energy of mixing as a function of the Flory-Huggins i
nteraction parameter, the composition of the mixture, and the associat
ion equilibrium constants. The self-association of the ethanol molecul
es was described by two equilibrium constants, one for the formation o
f dimers and one for the formation of multimers. The equilibrium const
ants of interassociation of PVP or NEP with ethanol were determined fr
om the quantitative analysis of NEP/ethanol and PVP/ethanol FTIR spect
ra at various temperatures and compositions. The values of the equilib
rium constants were then used to calculate the theoretical Gibbs free
energy of mixing as a function of the composition. The enthalpic and e
ntropic contributions to mixing were compared for the NEP/ethanal and
PVP/ethanol mixtures.