NMR experiments and molecular dynamics simulations of the segmental dynamics of polystyrene

We have performed NMR spin?lattice relaxation experiments and molecular dynamics (MD) computer simulations on atactic polystyrene (a-PS). The segmental correlation times of three different molecular weight a-PS (Mn = 1600, 2100, 10 900 g/mol) were extracted from NMR by measuring the 2H spin?lattice relaxation times (T1) over a broad temperature range (390?510 K). MD simulations of an a-PS melt of molecular weight 2200 g/mol were carried out at 475, 500, and 535 K. Comparisons between experiments and simulations show that the MD simulations reproduce both the shape of the P2(t) orientation autocorrelation function and its temperature dependence, while the simulated segmental correlation times are slower than experimental results by a factor of 1.8. If the simulations are rescaled by this factor, they reproduce both the experimental T1 values and the slight difference in dynamics between the backbone and side group of PS.