Large-scale computer simulation of local segmental dynamics in amorphous atactic polystyrene

Molecular dynamics computer simulations of amorphous atactic polystyrene have been performed for chains of up to 320 monomer units in a temperature range from 100 to 600 K and in a pressure range from 0.1 to 1000 MPa. The MD-determined values of the glass transition temperature T-g are in a good agreement with experimental PVT data at different values of applied pressure. Local translational mobility has been investigated by measuring the mean square translational displacements of monomers as a function of time. The long-time asymptotic slope of these dependencies is close to 0.6 at T > T-g, showing diffusive behaviour. The cage effect when local translational motions are essentially frozen in the glassy state has been studied. Local orientational mobility is studied with the help of Legendre polynomials of the first, P-1 (t), and second, F-2 (t), order for the bonds in the main chain and along the phenyl side groups. Temperature dependencies of the orientational relaxation times at different values of pressure are well described by the Vogel-Fulcher law. (C) 2002 Elsevier Science B.V. All rights reserved.