In order to modify the toughness of epoxy resin, the blending method of multi polymer components was investigated. An epoxy resin based on diglycidyl ether of bisphenol A was modified with poly(ether sulfone)(PES) and poly (acrylonitrile-co-butadiene) rubber (NBR) and then cured with 4,4’-diaminodipheylsulfone. Morphology, dynamic mechanical properties, bending properties and fracture toughness of this ternary blend of were evaluated. Depending on the composition of PES and NBR, two distinct morphological states were observed, and the fracture behaviour varied from brittle to ductile with the change of morphology. From the morphology observation by various microscopes, the ternary blends that showed ductile behaviour have phase-inverted morphology in which the NBR-rich phase forms a continuous matrix, the epoxy-rich phase forms particles and the PES-rich phase also forms particles around the epoxy particles. Even at low loading level of PES and NBR which shows phase inversion, the storage modulus and Tg by dynamic mechanical analysis were as high as unmodified epoxy resin. And the bending properties were controlled by the loading level of PES and NBR, the kind of terminal functional groups and curing temperature.
