A special model system based on trimethylene glycol di(p-aminobenzoate) and its glycidyl derivative was evaluated to study the extent of cyclization in glycidylamine epoxies. The cured resins were degraded by alkaline hydrolysis, which left the cycles unaffected. The cycle concentration obtained by high-performance liquid chromatography was 15%. The oligomer distribution of the degradation products strongly indicated that up to 40% of the epoxy groups were lost to side reactions, and this resulted in a large number of structural defects in the network. (C) 2003 Wiley Periodicals, Inc.