Sulfonate group-containing polymer and method of producing the same

A sulfonate group-containing copolymer, comprising:

• a structural unit (a) derived from a sulfonate group-containing monomer (A);
• a structural unit (b) derived from a (poly)oxyalkylene monomer (B) represented by the following formula (1):
• wherein R1 represents a hydrogen atom or a methyl group;
• R2 represents a direct bond, CH2, or CH2CH2;
• and X0 represents a structural unit represented by the following formula (2):
• —Zn—OR0 (2)
• wherein Z may be the same or different and each represents a structural unit derived from a C2-C20 alkylene oxide;
• R0 represents hydrogen atom or a C1-C30 organic group;
• and n is an integer of from 1 to 200;
• and
• a structural unit (c) derived from a carboxyl group-containing monomer (C),
• wherein the sulfonate group-containing copolymer comprises from 20% to 90% by mass in an acid form equivalent of the structural unit (c) in 100% by mass of all the structural units constituting the sulfonate group-containing copolymer,
• wherein the product (P×Mw×n) of the ratio by mass P of the structural unit (b) to the structural unit (a) multiplied by the weight average molecular weight Mw of the sulfonate group-containing copolymer multiplied by the value n in the formula (2) is from 950,000 to 800,000,000.