A hydroxyl-functionalized polybutadiene polyurethane hotmelt prepolymer that comprises the chemical reaction product of at least one polybutadiene diol, at least one chain extender having a hydroxyl functionality of two and a molecular weight of less than or equal to 300 g/mol and optionally at least one polybutadiene polyol that has a number-average mean functionality between greater than 2.0 and less than or equal to 3.0 with at least one aliphatic or alicyclic diisocyanate, is thermally vulcanizable, and at room temperature is sufficiently solid or high-viscosity that it can be rolled into a roll as a film applied to a carrier without flowing out or being squeezed out on the side.