THERMODYNAMICS OF HYDROGEN-BONDING IN SOLUTIONS OF POLY(VINYLPYRROLIDONE) IN ETHANOL CCL4 MIXTURES/

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.