The influence of internal rotational barriers and temperature on static and dynamic properties of bulk atactic polystyrene

Abstract

We present molecular dynamics simulations of a chemically realistic model as well as a quasi-freely rotating chain model for bulk atactic polystyrene in a temperature range from 240 to 500 K to characterize the role of temperature and internal rotational barriers on static and dynamics properties of bulk polystyrene. We demonstrate that on different length scales, the change of structure shows different behavior upon cooling, and the internal rotational barriers play a similar role as temperature in this respect. We also show that larger plateau value of particle mean-squared displacement does not comply with the cage size predicted by the mode-coupling theory. It can be attributed to large steric hindrance between styrene units in the system. When the temperature is decreased, dynamic heterogeneity of conformational transition is found to become increasingly important for the conformational relaxation. Moreover, we have established a relation among the cage effect, the dynamic heterogeneity, and the conformational relaxation on the time scale of α- and β-relaxations.