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

Variations in free volume V-f and free-volume size distribution in polymers were analyzed by positron annihilation lifetime spectroscopy. The PATFIT a nd CONTIN programs were used to treat the corresponding positron annihilati on lifetime spectra. The positron annihilation lifetime measurements were c arried out for glassy PMMA plasticized with a thermodynamically incompatibl e diethylsiloxane oligomer, for a random copolymer of methyl methacrylate w ith octyl methacrylate, and for glassy PC (undeformed samples and samples a fter their uniaxial compression and annealing at T < T-g). For the first ti me, transitions between the structures of polymer glasses with unimodal and bimodal positronium lifetime distributions (the size distribution of free- volume elements) were identified. Under uniaxial compression of PC, variati ons in V-f are likely to be controlled only by an anelastic strain componen t, whereas the conformational component is virtually not associated, with t he above changes.