To provide a hydrophilic graft polymer having high grafting ratio of monoethylenic unsaturated monomer, low content of unreacted polyether compound and high purity, a method for producing the polymer and the use of the polymer.

The hydrophilic graft polymer is produced by the graft polymerization of a monoethylenic unsaturated monomer containing an unsaturated carboxylic acid monomer as an essential component to a polyether compound having a number-average molecular weight of ≥200 and containing a repeating unit expressed by general formula: -RCH-CH2-O- (R is at least one kind of hydrogen atom or methyl group and different groups may be present in the same molecule) in an amount of ≥30 mol% based on the total polyether compound, and the polymer has a purity of ≥75%. The method for the production of the hydrophilic graft polymer comprises the graft polymerization of the monoethylenic unsaturated monomer to the polyether compound in the presence of an organic peroxide of at least one kind of acidic substance selected from organic sulfonic acid compound, phosphoric acid compound and inorganic acid.

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