Low molar mass poly (phenylene ether) (LMW-PPE) with phenol-reactive chain ends was used as modifier of epoxy thermoset. The epoxy monomer was diglycidylether of bisphenol A (DGEBA), and several imidazoles were used as initiators of anionic polymerization. The curing and phase separation processes were investigated by different techniques: Differential Scanning Calorimetry, Size Exclusion Chromatography, and Light Transmission measurements. The final morphology of blends was observed by Environmental Scanning Electron Microscopy and Transmission Electron Microscopy. The epoxy network is obtained by imidazole initiated DGEBA homopolymerization. Initial LMW-PPE/DGEBA mixtures show an UCST behavior with cloud. point temperatures between 40 and 90degreesC. PPE phenol end-groups can react with epoxy, leading to a better interaction between phases. The curing mechanism and phase separation process are not influenced by the chemical structure of initiators, except when reactive amine groups are present. The phase inversion is observed at 30 wt % of PPE. The mixtures with amine-substituted imidazole present important differences in the initial miscibility and curing process interpreted in terms of fast room temperature amine-epoxy reaction during blending. Final domain size is affected by this prereaction. (C) 2004 Wiley Periodicals, Inc.