Solvent effects on phase behavior with false UCST in blends of PVPh with aliphatic polyesters

Solvent effects on phase behavior in blends were examined. Misinterpretation might be resulted if effects of solvent were not properly evaluated and avoided. Solvent effects were found to influence to widely different levels on blend systems comprised of poly(4-vinyl phenol) (PVPh) and a homologous series of polyesters of different CH2/CO ratios. Confusion and misinterpretation in phase behavior between miscibility and immiscibility with upper-critical-solution-temperature (UCST) could be resulted if solvent effects were not fully excluded from true thermodynamic phase behavior in the blends. However, apparent solvent effects on interfering true phase behavior were found in the blends of PVPh with several polyesters whose structures led to borderline miscibility. Superficially, the blends prepared by solvent casting behaved similarly to phase-separated blends with UCST. By comparison, regardless of methods of blend preparation, the miscibility was straightforwardly proven for the blends of PVPh with poly(hexamethylene adipate) (PHA) that possesses an average CH2/CO ratio = 5.0 located on the center of window, and the phase behavior of PVPh/PHA blends is largely free of solvent interference. Care must be exercised in interpretation of phase behavior by excluding the solvent effects, especially for those blends with borderline miscibility with weak interactions.