WATER-ABSORPTION IN NOVOLAC EPOXY-RESINS STUDIED BY POSITRON-ANNIHILATION

Water absorption rates of four kinds of epoxy resins cured with phenol novolac (PH) were compared with the results of positron annihilation lifetime measurements (PAL). Three samples: cresol novolac (CR), tetra -methyl-biphenol (TMB) and bis-phenol A (BA), showed almost similar ab sorption rates, while tris-hydroxy-phenyl-methane (THPM) absorbed wate r twice as fast as others. Since THPM has a larger tau3 value (hence l arger intermolecular-space holes) than the other samples, the correlat ion between tau3 and the absorption rate seems evident. For THPM, the lifetime distribution was shifted toward a shorter lifetime after abso rbing water, which is interpreted in terms of the particular structure of three-dimensional holes.