Abstract
Polystyrene specimens with different molecular weights were characterized by the positron annihilation technique. Lifetime spectra of positrons were measured in the temperature range between room temperature and ∼ 150 °C. The observed lifetime spectra were resolved into three components, where the longest lifetime, τ3, was associated with pick-off annihilation of orthopositronium (o-Ps) trapped by free-volumes. Above the glass transition temperature (T g ), the temperature coefficient of τ3 was found to be about 4 times larger than that below T g , while no drastic change in the intensity corresponding to the annihilation of o-Ps was observed at T g . These facts suggest that the glass transition mainly affects the expansion rate of the free volumes in polystyrene specimens
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