POLYETHERIMIDE-MODIFIED EPOXY NETWORKS - INFLUENCE OF CURE CONDITIONSON MORPHOLOGY AND MECHANICAL-PROPERTIES

The morphologies and mechanical properties of thermoplastic-modified e poxy networks generated through the reaction-induced phase separation procedure were studied as a function of isothermal cure conditions. Th e selected model system was diglycidyl ether of bisphenol A cured with 4,4'-methylenebis [3-chloro,2,6-diethylaniline] in the presence of a nonfunctionalized polyetherimide. Appropriate precuring and postcuring schedules were selected. The precure temperature had a strong effect on final morphologies because it affected the viscosity of the system at the cloud point and the extent of the separation process. The morph ologies generated are discussed in connection with phase separation me chanisms. The ratio of the height of the loss peaks corresponding to e ach phase was an appropriate parameter to qualitatively predict the sh ape of morphology and to determine if the system was phase-inverted or not. The fracture toughness, K-Ic was significantly improved only whe n bicontinuous or inverted structures were generated, resulting from t he plastic drawing of the thermoplastic-rich phase. Before phase inver sion, K-Ic was hardly higher than that of the neat matrix due to poor interfacial adhesion. Nevertheless, the thermoplastic-rich particles c onstitute obstacles to the propagation of the crack and contribute to the toughening of the material, measured through impact resistance mea surements. The observation of fracture surfaces revealed the occurrenc e of microcracking and crack-pinning. Strain recovery experiments show ed that particle-induced shear yielding of the matrix was present as w ell. (C) 1997 John Wiley & Sons, Inc.