This paper examines the effect of the addition of PSF upon the final properties and network structure of the TGAP/DDS system after cure and post-cure. It also compares the differences in the network structure and properties of the modified system between samples in which the epoxy resin and thermoplastic had been prereacted and those which had been simply mixed together. The thermal properties of the network structure were investigated using dynamic mechanical thermal analysis while the chemical structures were characterised using near infra-red spectroscopy. Physical properties such as water uptake, density and mechanical properties such as toughness, modulus, compressive strength and yield stress were measured. (C) 2001 Elsevier Science Ltd. All rights reserved.