Toughening of epoxy resins with thermoplastics. Ii. Tetrafunctional epoxy resin‐polyetherimide blends

A series of blends has been prepared by adding a polyetherimide (PEI), in varying proportions, to a tetrafunctional epoxy resin, tetraglycidyl‐diaminodiphenylmethane (TGDDM), cured with 4,4′‐diaminodiphenylsulphone (DDS). All the materials exhibited two‐phase morphologies which were characterised by dynamic mechanical thermal analysis and scanning electron microscopy. Addition of the thermoplastic gave a modest improvement in fracture properties ( K 1c and G 1c ), as determined by three‐point bending experiments, although no obvious correlation with the marked morphological changes was observed.