DIELECTRIC, MECHANICAL AND STRUCTURAL, AND WATER-ABSORPTION PROPERTIES OF A THERMOPLASTIC-MODIFIED EPOXY-RESIN - POLY(ETHER SULFONE)-AMINE CURED EPOXY-RESIN

Dynamic mechanical thermal analysis (DMTA) on a series of poly(ethersu lfone)-amine-cured epoxy resin systems indicates phase separation is o ccurring, in agreement with previous electron microscopic and dielectr ic observations. Atomic force microscopy (AFM) measurements reveal tha t the surface roughness changes with composition and is greatest for t he cocontinuous phase structure. Dielectric and gravimetric studies ar e reported on the absorption of water by these resin systems. Gravimet ric measurements yield diffusion coefficients, obtained from the initi al slopes, which vary slightly with thermoplastic composition. The equ ilibrium water uptake decreases with increasing thermoplastic content and when normalized by the volume fraction of epoxy resin exhibits a f airly constant value which infers that the majority of the water is di spersed in the epoxy phase. Analysis of the dielectric data at 10 Hz i ndicates that behavior similar to that obtained from gravimetric analy sis is observed outside the cocontinuous phase region. At the cocontin uous composition, anomalous behavior was observed and is attributed to polarization phenomena associated with the microporous structure of t he surface of these polymers. Dielectric analysis indicates that the r elative rates of absorption depend on the frequency of observation and that there are two extreme types of environment present in these syst ems. Some of the water molecules are ''bound'' to hydroxyl groups gene rated in the cure process and others exist as ''free'' molecules in mi crocavities.