CHARACTERIZATION OF MOLECULAR-ORIENTATION BY DIFFERENTIAL SCANNING CALORIMETRY .2. INJECTION-MOLDED AND BIAXIALLY ORIENTED POLYSTYRENE

Differential scanning calorimetry was used to study the injection moulding and biaxial orientation of polystyrene. Single exothermic peaks were observed for uniaxial orientation, whereas multiple relaxations were observed for biaxial orientation. The temperatures of the relaxations followed the general relationship T(j) = 1.02 T(i)(K) where T(j) > T(i) greater-than-or-equal-to T(g) and (j-i) = 1. In the case of injection-moulded samples, the overall dimensional shrinkage did not correlate with the enthalpy determined by differential scanning calorimetry, indicating nonaffine behaviour between dimensional and molecular orientation.