Abstract: The invention relates to a process for preparing a polyurethane prepolymer having terminal isocyanate groups by reacting polyisocyanates with polyols. The process includes a first synthesis stage and a second synthesis stage. A component (A) is prepared in the first synthesis stage using as polyisocyanate (X) at least one asymmetric polyisocyanate and using as polyol at least one polyol having an average molecular weight (Mn) of 60 to 3000 g/mol, with the ratio of hydroxyl groups to isocyanate groups being less than 1. In the second synthesis stage, a further polyol is added to component (A), the reaction ratio of the hydroxyl groups of the further polyol to isocyanate groups of component A being set in the range from 1.1:1 to 2.0:1.