Abstract
Positron lifetime spectra in polycarbonate were measured as a function of temperature and time. Ortho positronium (o-Ps) lifetime remained constant with prolonged measuring time, but its intensity decreased and increased with time at room temperature and low temperatures, respectively. The temperature dependence was measured from 30 to 375 K for two samples: one was pre-irradiated by positrons at 30 K for 166 h, the other was a fresh sample. The variation of o-Ps intensity differed greatly between the two samples. We explained these results in terms of free radicals and trapped electrons. We observed a large decrease of I3 at 100–130K and a change in the slope of τ3 at 230 K. The observations are considered to be related to the movement of the methyl group and the brittle-ductile transition, respectively, which were measured by other methods. By measuring the positron lifetime spectra between 293–493 K, the glass transition temperature was determined to be approximately 413 K.
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