PURPOSE: To obtain an unsaturated polyurethane useful as a reactive emulsifier for the production of a dispersion of a hydrophobic synthetic resin which can be cured by means of free radicals and/or oxidation.

CONSTITUTION: There is provided an unsaturated polyurethane which contains 20-80 wt.% polyethylene glycol units and can be prepared by reacting a) at least one organic polyisocyanate, b) an unsaturated fatty alcohol, a polyalkylene glycol ether thereof or an unsaturated acid ester containing one hydroxyl group, c) one or more diols which additionally contain at least one further hydroxyl group or carboxyl group, and d) a polyethylene glycol having a molecular weight in the region of 750 to 10,000, with maintenance of an NCO/OH equivalent ratio, based on all the starting components a) to d), of 0.7:1 to 1.2:1.