Structure change of atactic polystyrene upon aging

Abstract

We report the changes of atactic polystyrene (a-PS) upon annealing below the glass transition based on X-ray scattering, volume, and differential scanning calorimetry measurements of samples in the quenched and annealed states. Upon relaxation, an increase of the main diffuse diffraction peak and a decrease of the polymerization peak, typical for a-PS, are proportional to the enthalpy changes.The relaxation of enthalpy corresponds to a change of the fictive temperature by 6.1 K for annealing at 80 C for 24 h. The changes of the fictive temperature derived from the X-ray structure factor are between 5.4 and 6.8 K, depending on the range of scattering vector. The relaxation signal has a zero crossing at low scattering angles. The volume of the samples, measured at ambient conditions, did not change upon relaxation. We attribute these observations to localized relaxation processes that involve a small number of phenyl groups.