Correlation between Positron Annihilation and Gas Diffusion Properties of a Series of Polyimides

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Abstract
The lifetime and the intensity of ortho-positronium (o-Ps), τ3 and I3, respectively, were measured for a series of polyimides prepared from 4,4′-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]diphthalic dianhydride. Average size of free space holes probed by o-Ps, υh,Ps, was evaluated from τ3 using an empirical equation. There was a clear correlation between logarithm of diffusion coefficients, , of CO2 and CH4 and υh,Ps for the polyimides. Large differences in among the polyimides having the same fractional free space, VF, were attributed to differences in υh,Ps. There was a fairly good correlation between log and (υh,PsI3)−1, suggesting that I3 is a measure of the concentration of free space holes which can accommodate o-Ps, at least for the polyimides with the similar chemical structure. Correlation between VF and υh,PsI3 was rather poor.