Reaction mechanisms, microstructure, and fracture properties of thermoplastic polysulfone‐modified epoxy resin

摘要

AbstractThe microstructure and fracture properties of diglycidyl ether of bisphenol A (DGEBA) epoxy resins modified with phenolic hydroxyl‐terminated polysulfone (PSF) and cured with diaminodiphenyl sulfone (DDS) hardener have been investigated as a function of the molecular weight and concentration of PSF. The microstructure changed from a typical particulate structure to a phase‐inverted structure as the molecular weight and/or the concentration of the modifier increased. The fracture toughness, measured by compact tension tests, increased with the microstructural changes toward the phase‐inverted structure. The microstructural changes observed have been interpreted in terms of variation in the reaction mechanisms as determined by near‐infrared spectroscopy. The level of minor reactions such as etherification and homopolymerization reactions increased with increasing molecular weight and/or concentration of the modifier, in line with the tendencies observed in microstructure and fracture toughness. In the system containing 20 wt ofMn10,000 PSF, about 30 of the epoxy groups were consumed by etherification and homopolymerization reactions, whereas none of these reactions occurred in the unmodified system. The increase in minor reactions in the modified systems may be to be due to the restricted molecular mobility, resulting from the increase of system viscosity caused by the modification. This increase in viscosity also reduced the rate of phase separation. The degree of heterogeneity in the epoxy network must increase with the increasing side reactions. The formation of the heterogeneous epoxy network and the slowdown of phase separation will prevent a uniform precipitation of the modifier and finally result in a heterogeneous partially phase‐inverted structure or the completely phase‐inverted structure, depending on the amount of modifier incorporated over the critical concentration. © 1993 John Wil