Thermo-Optical Analysis of Poly(2,6-disubstituted-1,4-phenylene Oxide) Blends

Mobility transitions closely related to the glass transitions of three binary polymer-polymer blend systems have been determined by thermo-optical analysis (TOA). TOA in this instance consists of the automated observation of birefringence relaxation in scratched transparent polymer and polymer blend films during their programmed heating. The blend systems studied were: I. polystyrene (PS) + poly (2,6-dimethyl-1,4-phenylene oxide) (PMMPO); II. poly (2-methyl-6-phenyl-1,4-phenylene oxide) (PMPPO) + PMMPO; and III. PS + PMPPO. Blend Systems I and II display a single TOA transition temperature at each blend composition indicating homogeneity and true thermodynamic compatibility of the polymer pairs. Blend System III displays two TOA transition temperatures at each blend composition indicating incompatibility and resultant liquid-liquid phase equilibration in molten mixtures of PS and PMPPO. The shapes of the transmitted light intensity vs temperature curves for scratched PS + PMMPO films between 90° crossed plane polarizer and analyzer are examined at three heating rates of the microscope hot stage. The use of green light rather than white light in the analysis was examined briefly in System II blends. Glass transitions T g (DSC) obtained by differential scanning calorimetry are also reported.