Graft copolymers containing sulfonate and phosphonate groups having particular utility as pigmented ink dispersants

A dispersion comprising an aqueous carrier medium, a particulate solid, and a graft copolymer dispersant consisting essentially of:

• (a) a hydrophilic backbone wherein 2 to 100% of the backbone is prepared from monomers containing an acid which, in unneutralized form, has a pKa up to or equal to 3, and wherein the backbone is soluble in water and insoluble in non-polar organic solvents;
• and
• (b) at least one discrete hydrophobic side chain, wherein 20 to 100% of the side chain(s) are prepared from non-polar aromatic monomers or aliphatic monomers having a chain length of at least 4 carbon atoms;
• wherein (i) at least one side chain has a weight average molecular weight in the range of 1,000 to 30,000 and (ii) the weight ratio of hydrophobic side chain(s) to hydrophilic backbone is in the range of 90:10 to 10:90.