Positron annihilation studies of the effect of composition and external actions on free volume of glassy polymers

Variations in free volume V f and size distribution of sites bearing free volume in polymers were analyzed by positron annihilation lifetime spectroscopy. The PATFIT and CONTIN programs were used to treat the corresponding positron annihilation lifetime spectra. The positron annihilation lifetime measurements were carried out for glassy PMMA plasticized with a thermodynamically PMMA-incompatible diethylsiloxane oligomer, for a random copolymer of methyl methacrylate with octyl methacrylate, and for glassy PC (undeformed samples and samples after uniaxial compression and annealing at T< T g ). For the first time, transitions between the structures of polymer glasses with unimodal and bimodal positronium lifetime distributions (the size distribution of structural elements bearing free-volume) were identified. Under uniaxial compression of PC, variations in V f are likely to be controlled only by an anelastic strain component, whereas the conformational strain component is virtually not associated with the above changes.