INTERPLAY BETWEEN ELECTRON-AFFINITY AND FREE-VOLUME ON POSITRONIUM FORMATION IN POLYIMIDES

Our recent PAL results on a series of polyimides (PI) are summarized. It is shown that PIs are properly grouped according Lo whether there is long-lived o-Ps or not, and that those that do not produce o-Ps have strong electron affinities. Secondly the pore size was changed by exposing PIs to 50 atm CO2 gas. I3 was increased substantially for the PIs that have moderate 13 values. For the PIs that have large o-Ps yield the increase in I3 was small, and for those having no o-Ps the o-Ps component did not appear. In a third experiment where the pore structure was changed by introducing vapor molecules, both tau3 and I3 were reduced. This contrasts to low density polyethylene for which tau3 and I3 were increased. These results are viewed as an aspect of the spur model in which both electron affinity and pore size are affecting Ps formation.