Physical aging kinetics of syndiotactic polystyrene as determined from creep behavior

Creep experiments in uniaxial extension have been performed to explore the kinetics of the physical aging process in semicrystalline syndiotactic polystyrene (sPS) having two processing histories. Classical time-aging time superposition behavior was found for both materials at temperatures from 70 to 95°C, with the shift rate μ decreasing as temperature was increased. Virtually no aging was seen at 95°C, the DSC determined glass transition, T_g. This behavior was atypical for a semicrystalline polymer and reminiscent of the behavior of glassy amorphous thermoplastics. Some evidence for a separate crystalline aging mechanism > T_g, which manifests itself as only vertical shifts without timescale shifts, is seen in experiments at T > 100°C. Finally, the two different materials age differently, suggesting that some control of aging can be obtained by altering processing conditions or morphology.