A low-molar-mass, hydroxyl-terminated polyether [polypropylene glycol/poly(ethylene glycol) copolymer (POPE)] was functionalized with isocyanate groups and used to improve the impact resistance of a diglycidyl ether of bisphenol A based epoxy resin cured with triethylene tetramine (TETA). The effect of polyether-based modifiers (with and without NCO groups) on the curing rate of the epoxy/TETA system was investigated with rheological techniques. The NCO-functionalized polyether reduced the gel time, and this indicated an accelerating effect of the curing process. In addition, a significant improvement in the impact resistance was observed with only a slightly detrimental effect on the stiffness and mechanical strength. Scanning electron microscopy of the corresponding epoxy network revealed a homogeneous morphology with no phase separation. The miscibility of NCO-modified POPE and the epoxy resin was also confirmed with atomic force microscopy. The glass-transition temperature of the epoxy networks was also investigated with dynamic mechanical techniques. (C) 2007 Wiley Periodicals, Inc.