Sub-Tg relaxation in cold-drawn polymers: thermally-stimulated-current methods

Thermally stimulated depolarization current (TSDC), thermally stimulated polarization current (TSPC), and differential scanning calorimetry (DSC) methods have been used to study the intermediate relaxation induced in glassy polycarbonate (PC) by uniaxial cold-drawing at various drawing ratios, rates, and temperatures (below the glass transition temperature T_g). A well-defined α´ peak has been observed in the intermediate temperature range located between the local mode β transition and the α glass transition domains. The corresponding relaxation is very sensitive to physical aging effects, its characteristics differ markedly in TSPC and TSDC experiments, and they are also very different from those observed in PC subjected to other types of mechanical deformations such as cold rolling. It is a nonequilibrium relaxation, presumably resulting from local orientation (TSPC) or disorientation (TSDC) of chain segments made possible by the increase in free volume and molecular mobility subsequent to the drawing process and, as such, could be considered as a proximate precursor of the glass transition