The invention relates to polymer comprising structural units according to formula (I), R1—X—(C═O)—NH—R2—NH—(C═O)—O—POA-R3—(O—POA-R4)n wherein R1 represents an organic group terminated by a hydrocarbyl group having 6 to 50 carbon atoms, X represents O or N—R5, wherein R5 represents a hydrogen atom or a hydrocarbyl group having 1 to 30 carbon atoms, R2 represents an aliphatic hydrocarbyl group having 4 to 40 carbon atoms, POA represents a polyoxyalkylene group, R3 represents an organic group having 2 to 40 carbon atoms, n is an integer from 1 to 6, R4 is independently selected from —(C═O)—NH—R2—NH—(C═O)—X—R1, —(C═O)—NH—R1, —R6, wherein R6 represents a hydrogen atom or an aliphatic or aromatic group having 1 to 24 carbon atoms, and wherein the polymer has an average of at least 1.8 end groups R1 per molecule, a number average molecular weight in the range of 2000 to 100000 Daltons, a polydispersity in the range of 1.0 to 5.0, wherein the quotient of the polydispersity divided by (n+1) is less than 1.0, with the proviso that the polymer is not the reaction product of a) the mono-adduct of isophorone diisocyanate with 1-dodecanol and b) a polyether based on glycerol and a mixture of ethylene oxide and propylene oxide with an OH number of 18 mg KOH/g.