Water-soluble polyurethane having comb-shaped hydrophobic group and application thereof

Water-soluble polyurethane comprising a repeating unit (U-1) represented by the following general formula (1):

• and a repeating unit (U-2) represented by the following general formula (2)
• wherein the molar ratio of (U-1) to (U-2) is 0.5-0.999 to 0.001-0.5, wherein the sum of the respective values of (U-1) and (U-2) is one, and the weight average molecular weight, as determined by GPC, is in the range of 10,000 to 10,000,000,
• wherein A is a bivalent group such that HO-A-OH is a water-soluble polyoxyalkylene polyol having hydroxyl groups on both ends and having a number average molecular weight of 400 to 100,000 (compound A), and said bivalent group A is optionally further substituted with at least one hydroxyl group,
• B is a bivalent group such that OCN-B-NCO is a polyisocyanate compound selected from the group consisting of polyisocyanates whose total number of carbon atoms is 3 to 18 (compound B), and
• D is a bivalent group such that HO-D-OH is comb-shaped hydrophobic diol having the following general formula (3) (compound D):
• wherein R1 is a hydrocarbon group or a nitrogen-containing hydrocarbon group of 1 to 20 carbon atoms;
• each of R2 and R3 is a hydrocarbon group of 4 to 21 carbon atoms;
• part of or all of the hydrogen atoms of the hydrocarbon groups R1, R2 and R3 are optionally substituted by fluorine, chlorine, bromine, or iodine;
• R2 and R3 are the same or different from each other;
• each of Y and Y′ is hydrogen, a methyl group or a CH2Cl group;
• Y and Y′ are the same or different from each other;
• each of Z and Z′ is oxygen, sulfur or a CH2 group;
• Z and Z′ are the same or different from each other;
• n is an integer of 0 to 15 when Z is oxygen and is 0 when Z is sulfur or a CH2 group;
• n′ is an integer of 0 to 15 when Z′ is oxygen and is 0 when Z′ is sulfur or a CH2 group;
• and n and n′ are the same or different from each other.