ESTIMATION OF FREE VOLUMES OF IONOMERS BY POSITRON-ANNIHILATION TECHNIQUE

Positron annihilation lifetime measurement was performed from room temperature to melting temperature for ethylene-methacrylic acid (EMAA) and the ionomers, whose 60% of acid groups were neutralized with metallic cations such as Zn2+, Na+, and Mg2+, using melt reaction. The lifetime spectra were analyzed by the methods of non-linear least squares and inverse Laplace transformation. The free volume radii of EMAA and the ionomers expanded with temperature from about 0.34nm (24 degrees C) to 0.37 nn (110 degrees C). The expansion of EMAA and the ionomers was close to that of polyethylene, but smaller than that of polypropylene, whose free volume radius expanded from about 0.34 nm (24 degrees C) to 0.38 nm (60 degrees C) and 0.40 nm (100 degrees C). Bridging structure of the ionomers prevented thermal hysterisis recognized in the relative intensity of free volume. Differences in the relative intensity of free volume were the smallest for ionomers neutralized with Zn2+, This proves that bridging structures of EMAA-0.6Na and EMAA-0.6Mg are more stiff than that of EMAA-0.6Zn and that the variation of free volume concentration become greater upon the elevation of temperature.