Toughening of an epoxy resin with an isocyanate‐terminated polyether

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.