Different thermodynamics in phenolic blends with different polymeric modifiers, i.e., phenoxy, poly(decamethylene adipate), poly(ethylene oxide), and poly(vinyl alcohol), calculated by the Painter and Coleman association model (PCAM) are examined. The thermodynamics is calculated based upon the equilibrium constants derived experimentally from infrared spectroscopies of low molecular weight analogues with similar hydrogen-bonding formation. The discrepancies between the PCAM predictions and the experimentally observed T g and free volume variation with blending composition are attributed to the additional entropic effects introduced by the long repeated units of modifiers. The structural characteristics and hydrogen-bonding heterogeneity as derived from solid-state NMR and IR spectra support the notion that the length and size of the modifier repeated unit are responsible for such discrepancies. These observed nonidealities can be interpreted as competition between inter- and intraassociations (ΔH m favored), which depend on the entropy rise associated with the amount of increase of the breaking off of the self-association in phenolic and modifiers within blends. While PCAM is based on “true” miscibility, however, minor modification is required to better describe the thermodynamics for “real” blends where microdomain heterogeneity with size greater than that defined by thermodynamic criteria may be present.

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The interassociation constants of Painter−Coleman association model, obtained from the results of Fourier transform infrared spectroscopy of low molecular weight analogues in dilute solution, were used to predict the thermodynamic properties of phenolic and polyester polymer blends. The miscibility window, phase diagram, and degree of hydrogen bonding were discussed with the transferability of the association constant between the model compound and the polymer blends. All the predicted results coincided with the actual hydrogen bonding, regular photograph, and proton spin−lattice relaxation in the rotating flame (T 1 ρ H). This model provides a reasonable explanation of analogues of phenolic resin blends. The predicted thermodynamic properties are in harmony with the experimental results due to the high hydroxyl group density and low molecular weight of the phenolic resin which improves the compositional homogeneity of the phenolic/polyester blend.