Reactive thermoplastics are increasingly used as toughening modifiers for epoxy resins. A way to understand the influence of the reactive end-groups on the toughening and curing mechanisms is to observe in situ the reaction between the thermoplastic and the growing epoxy network. For this purpose, Raman spectroscopy has been used to follow the reaction of aromatic amines with epoxide monomers through the evolution of an amine-substituted aromatic vibration. A double shift of this peak was correlated with the formation of secondary and tertiary amines. Band assignment was confirmed by the study of model compounds. Through this method, qualitative observation of the reaction between an amine-ended copolyethersulphone thermoplastic and epoxide was performed. Unfortunately, in the studied blend containing the curing agent, a band appearing upon curing overlapped with the band characterising the end-group reaction. (C) 2000 Elsevier Science Ltd. All rights reserved.