A thermodynamic approach to study hydrogen-bonding interactions in solvent/solvent/polymer ternary systems

A thermodynamic approach based on both the classical Flory–Huggins (FH) formalism and the association equilibria (AE) theory has been developed to study the solubility properties of a system formed by a proton-donor solvent (A), a proton-acceptor solvent (B) and a proton-acceptor polymer (C). The miscibility of this ternary system is attained by competitive specific interactions via hydrogen-bonding established between the hydroxyl and carbonyl interacting groups of either solvent–solvent (AB) or solvent–polymer (AC) system components. The binary AB and AC specific interactions and their dependence with the system composition as well as with the extent of the association equilibrium have been quantified by means of two new parameters, ΔgAB and ΔgAC. These excess functions have appeared to be equivalent to the combinatorial or entropic term of the Gibbs free energy of the complex formation process, which accounts for the entropy of mixing plus the intermolecular specific interactions. The theoretical predictions have reasonablely agreed with experimental data on preferential solvation of two systems taken from literature: methanol(A)/1,4-dioxane(B)/poly(alkyl methacrylate)(C) and n-alcohol(A)/heptan-3-one(B)/poly(vinyl pyrrolidone)(C).