Abstract: A hardening agent for epoxy compounds prepared by reacting A) at least one member of the group consisting of polyalkyleneetherdiols and polyalkyleneetherpolyols with B) at least one polyisocyanate with a molar ratio of hydroxy groups to isocyanate group of 1:1.8 to 3, reacting the resulting product with C) an amine having at least one free primary or secondary amino group and at least one protected primary amino group with a molar ratio of isocyanate to amino groups of 1:1 to 2 and subjecting the latter product to hydrolysis useful for preparation of flexible hardened products with excellent mechanical properties.