Tacticity Effects on Polymer Glass Transition Revisited by Coarse-Grained Simulations

Molecular dynamics simulations have been extensively carried out to study glass transition of polymers for over 20 years, in which a central but still open question is how to quickly and reliably determine the glass transition temperature (T-g). To address this issue, the two moderate big bulk model systems comprised of the mono-disperse isotactic or syndiotactic poly(methyl methacrylate) (iPMMA, sPMMA) chains have been separately simulated with the chemically specific coarse-grained potentials. The model systems are first equilibrated at an enough high temperature and then cooled to an enough low temperature with three different rates. It is demonstrated that the densities and non-bonded interaction energies qualitatively reveal glass transition whereas the reorientation functions of bond vectors quantitatively locate the T-g. Despite all, consistent result is yielded that sPMMA exhibits a higher T-g than iPMMA, which is in good agreement with the experimental observation. More importantly, the tacticity effects can be well dictated by the activation energy for the fast relaxation mode identified in the rubbery domain, which paves the way for quick assessment of polymer T-g.