Investigation of transitions and relaxation processes in polystyrene by using positron annihilation

The glass transition and relaxation processes in polystyrene resins with the number average molecular weight ranging from 7.0·10² to 9.8·10⁴ were studied with the positron annihilation technique. The pick-off annihilation lifetime of ortho-positronium (₃) and its intensity (I₃) were measured in the temperature range from 20 to 430 K. The glass transition temperature (T_g) was determined as an onset temperature coefficient of ₃.T_g shows the molecular weight dependence in these samples. BelowT_g, local motions were detected by measurements ofI₃. The local motions could be observed above 100 K in this experiment.I₃ show the minimum at around 250 K and it does not show molecular weight dependence.