Bisphenol-A based poly(arylene ether)ketones (PAEKs) are tough, amorphous processable thermoplastics possessing a glass transition temperature of approximately 160°C. In the form of a thermoset, these polymers have potential usages as structural engineering matrix resins or adhesives, as well as modifiers for existing engineering polymers. Thermosets of PAEKs can be prepared through the incorporation of amine, maleimide, or nadimide groups onto the ends of the polymer chains followed by the curing of the materials at elavated temperatures. Plates for mechanical testing, 1/8 inch in thickness or greater, were prepared by first degassing the polymeric powder under vacuum at temperatures 10-50°C above the Tg of the respective oligomer for short periods of time, followed by compression molding of the resulting material. The networks exhibited high fracture toughness values, as determined by 3 point bend measurements, Tg’s around 160 °C as well as a stable rubbery modulus to above 350°C, as determined by dynamic mechanical measurements. Toughness of these networks increased dramaticly with increasing Mc up to the chain entanglement molecular weight. Tg and rubbery modulus were only slightly altered by Mc. The swelling of these networks in chloroform reveals a two stage increase in solvent absorption. The two stages are believed to be related to the viscoelastic extension of the chains followed by subsequent disentanglement of dangling ends allowing further extension. The toughness behavior of thermoplastic PAEK oligomers versus molecular weight was found to parallel the oligomer’s melt viscosity behavior. As a modifier, PAEK cocured with bismaleimide produces network substantially tougher than the unmodified bismaleimide network. Control experiments with non-reactive PAEK oligomers demonstrated the necessity to functionalize the oligomers to produce the toughening effect. Cocured systems were found to possess a homogeneous morphology while physically blended systems phase separated. Swelling occurred in a single stage, possibly due to the high concentration of functional groups which eliminated dangling ends from the network. These networks possess a Tg at 160°C, associated with the relaxation of PAEK, and stable rubber modulus of above 350°C whose absolute value was a function of the BMI/PAEK ratio. / Ph. D.