Molecular weight dependence in a relaxation phenomenon at glassy state: Physical aging of polycarbonate

At the glassy state of polymers, the reptation-type molecular motion should be frozen-in and the relaxation should be only by local motions, such as rotation, vibration, and torsion. Such local motions would not depend on molecular weight. This may be current understanding of the polymer glass. By contrast, we found that the rate of enthalpy relaxation in polycarbonate at 100 °C (50 °C below Tg) clearly depends on molecular weight. Deterioration of impact strength was also found to depend on molecular weight. The surprising results are presented in this letter.