Temperature-dependent local and global dynamics of atactic polystyrene: A coarse-grained molecular dynamics simulation study.

This article focuses on the temperature-dependent local and global dynamic properties of atactic polystyrene (PS) and evaluates the dynamic consistency of a coarse-grained (CG) PS model—constructed via a structure- and thermodynamics-based coarse-graining approach—with its united-atom (UA) counterpart. Through molecular dynamics simulations, the study compares translational and orientational dynamics from the monomer scale to the entire polymer chain across a broad temperature range, including near the glass transition temperature (Tg). Results show that the CG model reproduces key dynamic features of the UA model, such as time-dependent translational diffusion scaling and the transition from multistep to single-step relaxation with increasing bond vector span, although the CG model exhibits accelerated dynamics due to reduced friction and smoother potentials. Both models' diffusion coefficients and relaxation times follow a power-law temperature dependence consistent with mode-coupling theory (MCT), with nearly identical exponents but differing critical temperatures, indicating that the CG model captures the essential structural relaxation processes of atactic PS while highlighting areas for further refinement through frictional corrections to improve quantitative accuracy near Tg.