Described is a method for the production of a moisture curable composition whereby the reactive end groups of a reactive polymer are reacted with a cross-linking agent for forming a prepolymer, whereby the method is operated in batch mode and the production of the prepolymer occurs in a mixing vessel, characterized in that the reactive polymer and the cross-linking agent, as well as the additional ingredients necessary for the production step in the mixing vessel, are introduced into the closed mixing vessel and react without opening the mixing vessel, and the mixing takes place without opening the mixing vessel, and the product is removed from the mixing vessel without opening the mixing vessel.