Isocyanate prepolymer with differently reactive NCO groups

There is described a method in which a polyol having 2 to 10 OH groups is reacted with a diisocyanate having differently reactive NCO groups, wherein the ratio val OH: mol diisocyanate is an integer and less than 1, an intermediate product with NCO and OH groups is obtained, this with an excess of an isocyanate with higher reactive groups in an amount of at least 4: 1 is reacted, and distilling off the monomeric, unreacted isocyanates. Furthermore, a prepolymer is described which has a predominantly ideal structure and having at least two NCO groups of different reactivity.