Polymeric dispersant and production method therefor, aqueous pigment dispersion, and water-based ink-jet ink

A polymeric dispersant for dispersing a pigment and is configured to be blended in an aqueous pigment dispersion for an aqueous inkjet ink and to be printed on a plastic media or a textile, the polymeric dispersant comprising a polymer, wherein

• (1) the polymer comprises:
• (i) a styrene-based constituent unit formed from a styrene monomer in an amount from 10 to 30% by mass,
• (ii) a first methacrylate-based constituent unit in an amount from 10 to 30% by mass, wherein a first methacrylate monomer forming the first methacrylate-based constituent unit is at least one material selected from the group consisting of methyl methacrylate and ethyl methacrylate,
• (iii) a second methacrylate-based constituent unit in an amount from 10 to 30% by mass, wherein a second methacrylate monomer forming the second methacrylate-based constituent unit is at least one material selected from the group consisting of 2-ethylhexyl methacrylate and dodecyl methacrylate,
• (iv) a third methacrylate-based constituent unit in an amount from 10 to 20% by mass, wherein a third methacrylate monomer forming the third methacrylate-based constituent unit is at least one material selected from the group consisting of 2-hydroxyethyl methacrylate and 2-hydroxypropyl methacrylate, and
• (v) a methacrylic acid-based constituent unit formed from a methacrylic acid monomer in an amount of 10 to 20% by mass, wherein the methacrylic acid-based constituent unit has a carboxylic acid group of the methacrylic acid monomer therein, and at least part of the carboxylic acid group is neutralized with at least one alkali selected from the group consisting of ammonia and dimethylaminoethanol,
• a total content of the constituent units (i) to (v) is 90% by mass or more, and
• the polymer comprises the constituent units (i) to (v) formed from 6 or more different monomers, and
• (2) the polymer has:
• a number average molecular weight in a range from 15,000 to 25,000,
• a peak top molecular weight in a range from 25,000 to 50,000,
• a polydispersity index, which is a ratio of weight average molecular weight/number average molecular weight, being in a range from 1.7 to 2.4, and
• an area ratio (H/T) is in a range from 15 to 30%, where an area H is a peak of a molecular weight of 50,000 or higher, and an area T is a total area of a molecular weight peak, in a gel permeation chromatograph.