To improve the isocyanate stability of dimorpholinodiethyl ether to prepare a composition useful for a high-speed curing agent for sealing, by treating dimorpholinodiethyl ether with hydrogen over a reducing catalyst under a reducing condition.

The purpose of this invention is achieved by treating dimorpholinodiethyl ether with hydrogen over a reducing catalyst [e.g. a nickel- based catalyst comprising about 70-80 mol.% of nickel, about 20-25 mol.% of copper and about 1-5 mol.% of chromium, or a cobalt-based catalyst] under a reducing condition (e.g. at the temperature of about 120-250°C and the pressure of about 50-5,000 psig). This composition preferably contains a polyurethane prepolymer having isocyanate end group(s).