Microwave processing, thermoplastic modification with reactive poly(arylene ether sulfone)s and improved flame retardance of di- and higher functionality epoxy resins were investigated. The influence of curing temperature and time on morphological development and fracture behavior was also studied. Arylamine functionalized poly(arylene ether sulfone)s of controlled molecular weight were synthesized as soluble, but reactive thermoplastic modifiers for aromatic amine cured epoxy resins. These materials were characterized via spectroscopy, thermogravimetric analysis, differential scanning calorimetry (DSC), dilute solution viscosity, potentiometric titration of their end groups and model chain extension reactions. Thermoplastic modification of the epoxy networks was demonstrated to afford materials with improved fracture resistance. Two glass transition temperatures were detected in the modified network systems via DSC. Scanning electron microscopy further confirmed the development of a two phase morphology in modified systems and that it could be controlled from a dispersed thermoplastic in a continuous epoxy phase, to a phase inverted morphology as the modifier increased from approximately 15 to 30 weight percent. Improvements in adhesive strength to titanium and fracture toughness were also attributed to the utilization of reactively endcapped polysulfone modifiers and the highest values were obtained with the phase inverted morphology. / Ph. D.