The present invention relates to a method for producing a
phosphoric acid ester-based
polymer, including copolymerizing a
monomer 1 represented by the following formula (1), a
monomer 2 represented by the following formula (2), and a
monomer 3 represented by the following formula (3), at pH 7 or lower, in the present of a
polymerization solvent having a dissolved
oxygen concentration at 25° C. of 0.01 to 4.0 mg / kg. The invention also relates to a method for producing a
phosphoric acid ester-based
polymer, including copolymerizing the monomers 1, 2 and 3 at pH 7 or lower, in the presence of a phosphonic acid-based chelating agent. The invention also relates to a method for producing a
phosphoric acid ester-based
polymer from a
mixed solution containing the monomer 1, 2 and 3, including obtaining a
mixed solution by mixing the monomers 1 to 3 at a temperature of 10 to 50° C., initiating a
polymerization within 72 hours after the mixing of the monomers 1 to 3, and maintaining the temperature of the
mixed solution in the range of 10 to 50° C. until the
polymerization is initiated:wherein R1 and R2 each represent a
hydrogen atom or a
methyl group; and R3 represents a
hydrogen atom or —COO(AO)nX [wherein AO represents an oxyalkylene group or oxystyrene group having 2 to 4 carbon atoms; n represents an average number of added moles of AO, and is a number from 3 to 200; and X represents a
hydrogen atom or an
alkyl group having 1 to 18 carbon atoms],wherein R4 represents a
hydrogen atom or a
methyl group; R5 represents an alkylene group having 2 to 12 carbon atoms; m1 represents a number from 1 to 30; and M represents a
hydrogen atom, an
alkali metal or an
alkaline earth metal, andwherein R6 and R8 each represent a
hydrogen atom or a
methyl group; R7 and R9 each represent an alkylene group having 2 to 12 carbon atoms; m2 and m3 each represent a number from 1 to 30; and M represents a hydrogen atom, an
alkali metal or an
alkaline earth metal.