POSITRON LIFETIME DISTRIBUTIONS AND FREE-VOLUME PARAMETERS OF PEO PMMA BLENDS DETERMINED WITH THE MAXIMUM-ENTROPY METHOD/

The temperature dependence of the average free volume hole size and it s distribution in blends of poly(methyl methacrylate) and poly(ethylen e oxide) were studied by positron annihilation lifetime spectroscopy. Measurements at room temperature, 70 degrees C, and 110 degrees C all indicate that the average ortho-positronium lifetime (tau(3)), and thu s the free volume hole size of the blends, shows a positive deviation from additivity of the values of the pure components. Mean ortho-posit ronium (o-Ps) lifetimes and intensities were calculated with the POSIT RONFIT program, while o-Ps lifetime distributions were obtained from e valuations made with a recently introduced program based on Bayes' the orem and the maximum entropy principle. o-Ps lifetime distributions we re successfully calculated for all measured spectra and offer valuable additional information about the structure of the studied blends. At 70 degrees C, the distributions seem to reflect the lifetimes in a ble nd of binodal composition. Large differences in width of the o-Ps life time distributions as a function of blend composition and temperature are observed.