Polymer Blends Containing Isotactic Polystyrene: Thermal Behavior of Model Systems

Model blends containing isotactic polystyrene were prepared by embedding i-PS single crystals in both compatible and incompatible polymer matrices. The melting point of the i-PS crystals was monitored for each blend system. Blends prepared with incompatible matrix polymers exhibited melting behavior significantly different from that of the pure i-PS crystals. This is interpreted in terms of the physical constants of the matrix polymers. Significant changes in T_m were found to occur in the incompatible blends only when the matrix was glassy. Blends consisting of i-PS crystals with compatible polymer matrices exhibited, in general, somewhat larger Tm depressions. Analysis of the depression of the T_m via the Flory-Huggins treatment yielded values for the polymer-polymer interaction parameter. Considering both the physical nature of the matrix and finite molecular weight effects, it is concluded that the interaction parameter for the compatible systems studied is virtually zero.