Glass Transition Temperatures of Polymers from Molecular Dynamics Simulations

Progress has been made recently in using molecular dynamics (MD) simulations to generate PVT properties of amorphous polymers. In the present 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 volumetric glass transition temperatures (T sub g ) reliably. Four polymers, namely, cis-poly(1,3-butadiene), polyisobutylene, atactic polypropylene, and polystyrene were studied, and previously determined MD data for polyethylene (PE) are available. The T sub g values span a range of 200K, from 170-370K. The values from the MD V-T curves tend to be displaced, as expected, to somewhat higher temperature than the longer time experimental values. However, the displacements are minor compared to the range of T sub g values considered. Determination of T sub g from MD simulations appears to be a practical procedure. The relation of the MD-determined T sub g of wholly amorphous PE to experimental values in the semicrystalline environment is discussed.