Effect of low-temperature physical aging on the dynamic transitions of atactic polystyrene in the glassy state

The local and cooperative dynamics of atactic PS (a-PS) were studied by broadband dielectric relaxation spectroscopy (BDRS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The a-PS has been subjected to thermal rejuvenation and subsequent quenching, short-term aging (6 weeks), and long-term aging (1 year) at ambient conditions. Where for the rejuvenated sample only an α- and a γ-relaxation is observed, short-term aging results in an additional β*-relaxation that merges with the α-relaxation at longer aging times. The γ-relaxation is increasing in intensity and activation energy during aging. The α-process shows no spectral changes and shift in the relaxation time upon aging. This may be attributed to a possible erasure of history of the material during the temperature-sweep mode measurement. Fourier transform infrared spectroscopy (FTIR) results suggest that the energetically favorable trans-trans (tt) conformers are increased in population with aging.