Physical aging and molecular dynamics in poly(4-alkylstyrene)

To elucidate the relationship between physical aging and molecular dynamics in poly(4-alkylstyrene), three types of measurements were performed: capacitive dilatometry (CD), differential scanning calorimetry (DSC), and dielectric relaxation spectroscopy (DRS). Using CD and DSC, we successfully observed volume and enthalpy relaxation processes during isothermal aging in the glassy state. DRS measurements revealed four dynamical processes: the α-process, β-process, γ-process, and a slower process, in addition to the contribution from DC conductivity. The relaxation times of volume and enthalpy relaxation processes below the glass transition temperature, Tg, were well described by the Arrhenius law, and their activation energies were nearly identical to that of the slower process. This suggests that the microscopic origin of the kinetics of the volume and enthalpy relaxation processes below Tg may be the same as that of the slower process observed above Tg. Near Tg, the relaxation times for volume and enthalpy relaxations deviate from the Arrhenius law and follow the Vogel-Fulcher-Tammann law for the α-process. The α-process appears to govern physical aging near Tg.