Probe rotation near and below the glass transition temperature: Relationship to viscoelasticity and physical aging

Reorientation times tau(c) for two probes in several amorphous polymers near the glass transition temperature T-g are reported. T-g for these polymers ranges from 205 to 459 K. Probe reorientation was measured in the time window from 10(-2) to 10(4) s with a recently developed photobleaching method. tau(c) for a given probe at the T(g)s of the different polymers varies more than three decades. Viscoelastic relaxation times characteristic of the Rouse modes of the matrix polymers are closely related to probe rotation times and thus also not constant at T-g. The characteristic length scale of motions responsible for the glass transition varies significantly for the three polymers studied. Preliminary physical aging results indicate that probe reorientation in polystyrene ages slighly faster than the volume.