A new variety of heterocyclic polyamide membrane material has been studied for the micro-void size and its dominant associative features through positronium annihilation method, concomitantly its molecular characterization was confirmed through FTIR spectroscopy. A nonmonotonous temperature dependence of annihilation rate constant related to configurational energy changes have been discussed through the paradigm of activated process for positronium-molecular interaction, and a plausible explanation for the corresponding inhibition of positronium formation at the low temperature has been presented. (C) 2003 Published by Elsevier B.V.