Storage-stable polyurethane one-pack systems are usually cured either by moisture from the environment or by splitting off a blocking agent. The curing characteristics of moisture-curing isocyanate-prepolymers are strongly dependent on humidity and temperature whilst in the case of blocked isocyanate systems special care has to be taken to avoid air pollution. New heterogeneous systems on the basis of usual isocyanate-reactive compounds and solid polyisocyanate particles, which are surrounded by a diffusion-barrier-layer, are highly storage-stable und cure even in thick layers without the need of humidity and without formation of volatile blocking agents or by-products. After curing the systems, preferably by heating, polyurethanes with very good overall mechanical properties are obtained, which feature high temperature stability und high dimensional stability under heat. The new systems with practically unlimited pot-life offer new applications so far unaccessible for polyurethane chemistry.Vortrag anlanlich der Tagung der Fachgruppe "Makromolekulare Chemie" der Gesellsckaft Deutscher Chemiker uber "Fortschritte in der Polymersynthese" in Bad Nauheim, 21. -22. Marz 1994 0 1994 Huthig 8t Wepf Verlag, Zug CCC 0003-3146/95/$07.00