MICROSTRUCTURAL CHARACTERIZATION OF SEMIINTERPENETRATING POLYMER NETWORKS BY POSITRON LIFETIME SPECTROSCOPY

Thermoset and thermoplastic polyimides have complementary physical/mec hanical properties. Whereas thermoset polyimides are brittle and gener ally easier to process, thermoplastic polyimides are tough but harder to process. II is expected that a combination of these two types of po lyimides may help produce polymers more suitable for aerospace applica tions. Semi-Interpenetrating Polymer Networks (S-IPNs) of thermoset La RC(TM)-RP46 and thermoplastic LaRC(TM)-IA polyimides were prepared in weight percent ratios ranging from 100:0 to 0:100. Positron lifetime m easurements were made in these samples to correlate their free volume features with physical/mechanical properties. As expected, positronium atoms are not formed in these samples. The second life time component has been used to infer the positron trap dimensions. The ''free volum e'' goes through a minimum at about 50:50 ratio, suggesting that S-IPN samples are not merely solid solutions of the two polymers. These dat a and related structural properties of the S-IPN samples have been dis cussed in this paper. Published by Elsevier Science B.V.