GLASS-TRANSITION TEMPERATURES OF POLYMERS FROM MOLECULAR-DYNAMICS SIMULATIONS

Progress has been made recently in using molecular dynamics (MD) simul ations to generate PVT properties of amorphous polymers. In the presen t work previous MD simulations of V-T curves for several polymers are extended to lower temperatures, including through the glass transition . It is demonstrated that these V-T curves can be used to locate volum etric glass transition temperatures (T-g) reliably. Four polymers, nam ely, cis-poly(1,3-butadiene), polyisobutylene, atactic polypropylene, and polystyrene were studied, and previously determined MD data for po lyethylene (PE) are available. The T-g values span a range of 200 K, f rom 170 to 370 K. The values from the MD V-T curves tend to be displac ed, as expected, to somewhat higher temperature than the longer time e xperimental values. However, the displacements are minor compared to t he range of T-g values considered. Determination of T-g from MD simula tions appears to be a practical procedure. The relation of the MD-dete rmined T-g of wholly amorphous PE to experimental values in the semicr ystalline environment is discussed.