Fluorine-containing urethanes represented by the general formula: [Rf-A1-Z—X1—OC(═O)NH—]mI[—NHC(═O)O—Y1]n[—NHC(═O)O—(ClCH2—)X2O)a—R1]k   (1) wherein I is a group derived from a polyisocyanate by removal of the isocyanato groups; Rf is perfluoroalkyl of 1 to 21 carbon atoms; A1 is a direct bond or an organic group of 1 to 21 carbon atoms; Z —SO2—; X1 is a divalent, straight-chain or branched, C1-5 aliphatic group which may have at least one hydroxyl group; X2 is a trivalent, straight-chain or branched, C2-5 aliphatic group; Y1 is a monovalent organic group which is optionally hydroxylated; and R1 is hydrogen or alkyl of 1 to 10 carbon atoms.