Amorphous polycarbonate has been investigated from the point of view of free-volume microstructure in the temperature range 50-350 K by positron-annihilation-lifetime spectroscopy. Lifetime~3 and relative intensity I3 of 0-Ps show two regions of different behavior with the transition at T& =130 K. The temperature dependence of~3 has been analyzed using the model of a particle in a spherical potential well. The correlations between the dilatometric measurements and the~3{T) and I3{T) dependences have been interpreted in the framework of the free-volume model, which allowed us to estimate the fraction of free volume accessible to 0-Ps as well as the concentration of free-volume entities. We have determined that the polycarbonate is a relatively defect-full material. On the basis of a simple thermodynamical approach allowing for simultaneous change of the size and number of free-volume entities, an attempt has been made to specify the molecular mechanism responsible for the free-volume changes. The comparison of the results of such a thermodynamical model with the simulation of the structure of amorphous polycarbonate and the dynamics of the motion of phenyl groups suggests that partial flips of this group might be the potential generators of the increased free volume at T & Tb.

The annihilation characteristics of the orthopositronium (o-Ps) in the structurally simplest elastomer cis-1,4-poly(butadiene) has been measured in the temperature range from 15 to 313 K and interpreted in the framework of the free volume concept. The temperature dependence of the mean lifetime of the o-Ps, τ3, and its relative intensity, I 3, reflect a fine interplay between the free volume and microscopic chain dynamics. In addition to a pronounced break on the τ3−T plot at the glass transition temperature, T g, a further two bends exist. The first, in glassy state, is relatively slight. The other one, in an elastic state, can be correlated with the melting temperature T m of the crystalline phase. The order agreement between the temperature coefficients of free volume hole expansion αh and the mean square displacement of chain atoms α〈 u 2 〉 from a recent neutron scattering study indicates a microscopic cause for the hole size growth with temperature. The decrease of I 3 with temperature T above 120 K correlates with the onset temperature of the so-called fast motion from neutron scattering measurements as well as with the so-called Vogel temperature T o for the primary segmental dynamics. The N-like shape course above T g correlates with the cold crystallization from DSC measurements. In the melt region above 265 K, the slightly dependent τ3 and I 3 quantities correspond to a formation of the bubble states of the o-Ps in the soft matrix. Finally, the temperature dependence of free volume hole distributions exhibits the essential changes from relative narrow distributions in the glassy state to wide distributions above T g and ones that do not change much in the melt region of the polymer matrix.

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