Association Equilibria Theory for Polymers in Mixed Solvents with Specific Interactions

Hydrogen bonding plays an important role in determining the physical and thermodynamic properties of polar fluids. Theoretical and experimental aspects of polymers, in mixed solvents with hydrogen‐bonding‐specific interactions, are investigated using a simple association model based on the theory of association equilibria developed by Pouchlý et al. The thermodynamic non‐idealities are accounted for using a modified Flory‐Huggins theory with effective gij parameters. The entropic term of the above formalism has been formulated taking into account the polymer segment‐solvent as well as the solvent‐solvent hydrogen‐bond formation. Four equilibrium constants are introduced to make a realistic picture between the associated and non‐associated species. By application of “multiple association equilibria theory”, sorption coefficients λ and Y have been deduced for the ternary systems with specific interactions i.e., alcohol(C1–C3)/heptan‐3‐one/poly(N‐vinyl pyrrolidone). Numerical values for the self‐association constants of the alcohols, association constants for the alcohols and ketone and for the alcohols and polymer, have been evaluated. These were determined as parameters adjusting best the predicted values of both preferential solvation, λ, and the second virial coefficient, A2, to experimental ones. Comparison of the theoretical (lines) and experimental (points) λ values as a function of propanol/heptan‐3‐one mixture composition for diverse poly(N‐vinyl pyrrolidone) samples. PVP‐K90 (, ×); PVP‐700K (, ⋄); PVP‐K40 (, ♦); PVP‐K24 (, ▴); and PVP‐K15 (, ▪).