Physical Aging of Polycarbonate Investigated by Dynamic Viscoelasticity

摘要

The physical aging of polycarbonate was investigated with dynamic vis- coelastic measurements. Physical aging was observed for samples aged at 110 °C (QA) and room temperature (QP) after being quenched from the molten state. The shapes of the temperature dispersion curves of the dynamic viscoelastic functions (E' , E", and tan <5) of the QA and QP samples changed with aging time in a temperature range below the glass-transition temperature (T_ g). However, at temperatures close to but below T_g' the curves for the aged samples merged into the curve of the quenched sample at a temperature denoted T_H. T_H increased with aging time. The experimental results suggest that the aged sample has a memory of having been quenched and that as the sample approaches the equilibrium state, this memory is lost. Differential scanning calorimetry thermograms showed an endotherInic peak below T_p for the QA samples. The peak temperature (T p) also increased with aging time. T_H and T_p of the QA samples were approximately the same. The increase ofboth T_H and T_p with aging time indicates that the structure of the polymeric chain in the glassy state relaxes over larger segment scale lengths because the scale of the movable segments is related to temperature.