Polyurethane prepolymer and aqueous polyurethane dispersion

The invention relates to a polyurethane prepolymer prepared by reacting a mixture comprising a short-chain renew­ able diisocyanate and a long-chain renewable diisocyanate and one or more dials. The short-chain renewable diisocyanate has at most IO atoms and at most two ether group between the two isocyanate groups, and has at most 16 carbon atoms in the molecule. The long-chain renewable diisocyanate has either more than 12 atoms or more than ether group between the two isocyanate groups, or has more than 20 carbon atoms in the molecule. The invention also relates to an aqueous dispersion comprising the polyurethane prepolymer and a coating obtainable from the prepolymer.