FREE-VOLUME DISTRIBUTION OF HIGH PERMEABILITY MEMBRANE MATERIALS PROBED BY POSITRON-ANNIHILATION

Positron annihilation lifetime (PAL) spectroscopy was applied to measu re free-volume size distribution in polymer samples with unusually lon g lifetimes: in dense films of poly(trimethylsilylpropyne) (PTMSP) and in porous membranes prepared from poly(phenylene oxide) (PPO). PAL da ta were treated by finite-term lifetime analysis (PATFIT program) and continuous lifetime analysis (CONTIN program). Lifetime distributions of positron annihilation in these samples consist of two positronium c omponents: in the range 1-2 and 4-8 ns (PTMSP) and in the range 20-70 ns (porous PPO). In the case of PTMSP the longer lifetimes correspond to continuous free-volume size distribution in the range R = 4.5-5.5 A ngstrom. These radii are much larger than those characteristic for ''n ormal'' glassy polymers. A good agreement was obtained between the par ameters of PAL distributions obtained by means of PATFIT and CONTIN pr ograms in PTMSP and PPO dense films. An analysis of the CONTIN peak wi dths of free-volume size distribution in different polymers both studi ed in this work and reported in the literature indicated that the rati o of peak width and average radius R-av levels off at larger sizes of free volume. An estimate of the diffusion coefficient of positronium w as made for PPO samples with different surface area.