Temperature and time dependence of free volume in bisphenol A polycarbonate studied by positron lifetime spectroscopy

New positron lifetime expts. were carried out for Bisphenol-A polycarbonate. The influence of unavoidable pos. charged positron irradn. on the lifetime and intensity of o-positronium (o-Ps) annihilation was studied. Results obtained using a state-of-the-art lifetime spectrometer (count rate 670 cps with a 30-mCi 22Na source, time resoln. 260 ps for 22Na) were free from potential artifacts due to irradn. damage. Three lifetime components were computed from each spectrum. The temp. dependence of the o-Ps lifetime (t3) and intensity (I3) were measured at 20-150 Deg for the as-received material and between -30 and +180 Deg after annealing above the glass transition temp. (Tg). The value of t3 was unaffected by annealing but I3 was significantly larger for the annealed samples. In addn., the time dependence of t3 and I3 due to phys. aging in the glassy state was investigated at 30 and 90 Deg, resp. While t3 appeared const. for both temps., I3 decreased significantly with aging time. Anomalies in the abs. t and I values derived from such fits and the temp. dependence of these values indicated that a distribution of t3 lifetimes must be present in the o-Ps decay. This was consistent with the presence of a distribution of hole sizes which would be expected from current models of free vol. in amorphous polymers. Variations in the distribution, e.g. conversion of larger into smaller holes, may result in changes of the apparent I3. Adopting a simple free vol. definition, a comparison of the thermal expansivity of the vacancy fraction and of the macroscopic value yields a free vol. fraction f of 8% at Tg = 150 Deg. [on SciFinder (R)]