A polyurethane polymer comprising from 35% to 90% (w/w) of a poly (C2-4-alkylene oxide) based on the total weight of the polymer wherein not less than 60% by weight of the poly (C2-4-alkylene oxide) is polyethylene oxide and wherein at least 5% of the poly (C2-4-alkylene oxide) based on the total weight of the polymer is incorporated in lateral chains and which contains 10 to 180 milliequivalents of add groups for each 100 gm polymer when the polyurethane contains from 35 to 45% by weight poly (C2-4-alkylene oxide), e.g. a polymer made by reacting dimethylolpropionic acid, cyclohexane dimethanol, polypropylene glycol (1000), N-methyl pyrrolidone and an α,α-diydroxy polyethylene glycol obtainable from 2,4-toluene diisocyanate, methoxy polyethylene glycol (750) and diethanolamine.