Atomistic investigation of segmental mobility in atactic poly(propylene)

An atomistic model previously developed for atactic poly(propylene) has bee n analyzed through molecular dynamics simulation to study the variation of static and dynamical properties across a temperature range centered around the experimental glass transition temperature. Although few effects are see n in structural measures such as chain conformation, shape, and packing, ch aracteristic features associated with the onset of segmental motions are re vealed in the simulation results on local dynamics. The mechanism by which the vinyl polymer chain undergoes thermally activated motion is found to in volve a series of spatial displacement events (SDE) occurring topologically , spatially, and temporally in a discrete fashion. An attempt was made to c orrelate the motions of the active chain segments with structural and mecha nical properties such as local volume and rotational stiffness. The results indicate that the ability of the segmental mobility to diffuse in space an d time, in a dynamically percolative manner, is a significant feature of at omic motions in glassy polymers. (C) 2000 Elsevier Science Ltd. All rights reserved.