TEMPERATURE-DEPENDENCE OF MOLECULAR MOTIONS IN BULK POLYSTYRENE

Time-resolved optical spectroscopy is used to investigate the reorient ation of three rigid probes and one labeled chain in bulk polystyrene. Orientational correlation times for these probes and labels are found to be in the range of 10(-8)-10(-10) s at temperatures of 180-300 deg rees C. Consistent with previous studies, the attachment of a chromoph ore into the chain backbone slows its dynamics by about an order of ma gnitude. The temperature dependences of the correlation times are simi lar to the temperature dependence of the viscosity. When combined with probe reorientation times near and below T-g, these results indicate that probe reorientation tracks the temperature dependence of the visc osity quite well over twelve decades in time. In contrast, literature results for the translational diffusion of similarly sized probes indi cates a substantially weaker temperature dependence near T-g. Thus it appears that a fundamental change in the mechanism of probe motion occ urs near T-g. (C) 1994 John Wiley and Sons, Inc.