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 i s 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 exp osing PIs to 50 atm CO2 gas. I3 was increased substantially for the PI s 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 c omponent did not appear. In a third experiment where the pore structur e was changed by introducing vapor molecules, both tau3 and I3 were re duced. This contrasts to low density polyethylene for which tau3 and I 3 were increased. These results are viewed as an aspect of the spur mo del in which both electron affinity and pore size are affecting Ps for mation.