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

A systematic coarse-grained (CG) model, as a promising and helpful tool to access the accurate knowledge of the local and global polymer dynamics of real polymers, is required to preserve structural, thermodynamic, and dynamic properties of the underlying atomistic model over a wide temperature range. In the present work, to explore the temperature-dependent local and global dynamic properties of atactic polystyrene (PS) as well as the dynamic consistency of a PS CG model constructed via a structure- and thermodynamics-based CG approach with the united-atom (UA) counterpart, we have investigated and compared the translational and rotational dynamics of the two models in the scale from a single monomer to a global chain in a broad temperature range. The CG model accurately reproduces the time-dependent translational diffusion scaling and the shift from a multistep relaxation to a single-step long-time decay process with increasing span of bond vectors as the UA model. There exists the coupling of the conformational relaxation and diffusion of the PS chains to the local structural α-relaxation. Both diffusion coefficients and relaxation times of the UA and CG models show the same temperature dependence and follow a power-law relationship of mode-coupling theory. These findings advance our understanding of the complex dynamics of atactic PS and give a sounder basis for the further development of CG PS models with the (time-dependent) frictional correction to perform a quantitative study of structural relaxation and dynamical heterogeneity near glass transition temperature.