| abstract |
The present invention provides a polymer having sufficient gel resistance as compared with conventional polymers. A structural unit (a), 78 derived from a monomer represented by the following general formula (1) of 5 mol% or more and 22 mol% or less with respect to 100 mol% of a structure derived from all monomers. A copolymer having, as an essential structural unit, a structural unit (b) derived from (meth) acrylic acid (salt) in an amount of from mol% to 95 mol%, and having at least one main chain terminal at a sulfonic acid (salt) group The (meth) acrylic acid copolymer is characterized by having a weight average molecular weight of 13,000 to 50,000. In general formula (1), R 2 represents a hydrogen atom or a methyl group, and X and Y each independently represent a hydroxyl group or a sulfonic acid (salt) group (provided that at least one of X and Y is sulfonic acid) (Salt) group). [Selection figure] None |