NOVOLAC EPOXY-RESINS AND POSITRON-ANNIHILATION

Four kinds of epoxy resins: cresol novolac, tris-hydroxyphenylmethane, tetramethylbiphenol, and bisphenol A, were cured with phenol novolac epoxy resins. Characteristics of these epoxy compounds were studied by the positron annihilation lifetime (PAL) technique. Glass transition temperatures, thermal expansion coefficients, and volume of intermolec ular-space holes among polymer chains were obtained from the lifetime, tau3, of the long-lived component of ortho-positronium. It was reveal ed that, at the glass transition temperature, T(g), the volume of the hole created among polymer chains expanded 1.4 times the volume at roo m temperature. The smaller flexural modulus of tris-hydroxyphenylmetha ne than that of the other samples was explained by the volume of inter molecular-space holes obtained from tau3. Aging effects were seen in t he data of the intensities, I3, of ortho-positronium, which became sma ller after heating the samples above T(g). I3 and tau3 were strongly a ffected by the density of cross-linkings and their chemical structures . The larger the density of cross-linkings, the smaller I3 and higher T(g) were obtained. Epoxy compounds with the higher water-absorption r ates had larger intermolecular-space holes. (C) 1993 John Wiley & Sons , Inc.