Miscibility and Phase Separation in Poly(methyl methacrylate)/Poly(vinyl chloride) Blends: Study of Thermodynamics by Thermal Analysis

Amorphous blends of poly(methyl methacrylate) (PMMA) and poly(vinyl chloride) (PVC) were prepared via solution precipitation. From the study of T_g composition behavior, the blends were found to show large positive deviations from volume additivity and to be miscible over the entire composition range at temperatures below 180 °C. An endothermic heat of dexising and its concentration and temperature dependences have been measured by DSC. Spinodal and “cloud point” curves were extrapolated from these measurements. The results have been interpreted in terms of the modified Flory's equation-of-state theory by Hamada et al.¹ and compared with predictions of the directional specific interaction model proposed by ten Brinke and Karasz.² The modified equation-of-state theory can almost quantitatively reproduce the concentration dependence of the heat of mixing but failed to predict the positive excess heat capacity for this blend system, whereas the ten Brinke‒Karasz model can describe qualitatively both the concentration and temperature dependence of the heat of mixing of homopolymer blends.