Aqueous graft copolymer pigment dispersants

A process for forming a pigment dispersion of comprising pigment, an aqueous carrier and a polymeric dispersant which consists essentially of a graft copolymer having a weight average molecular weight of about 5,000-100,000 and comprises about 90-50% by weight, of a polymeric backbone having about 10-50% by weight, of macromonomer side chains attached thereto, where the backbone is hydrophobic relative to the hydrophilic side chains;

• the process comprising
• (a) preparing macromonomer, in an organic solvent, by polymerizing, using a catalytic chain transfer agent containing Co.sup.+2, ethylenically unsaturated monomers and 20-50% by weight, based on weight of the resulting macromonomer, of ethylenically unsaturated acid monomers to form a macromonomer containing acid groups and a terminal ethylenically unsaturated group,
• (b) forming, in an organic solvent, the graft copolymer by polymerizing, in the presence of said macromonomers prepared in step (a) ethylenically unsaturated hydrophobic monomers and up to 20% by weight, based on the weight of the graft copolymer, of ethylenically unsaturated acid monomers whereby said terminal group of the macromonomer is polymerized into the backbone to form the graft copolymer and neutralizing the acid groups of the copolymer with an inorganic base or an amine,
• (c) mixing the graft copolymer solution prepared in step (b) with an aqueous medium and pigment and dispersing the pigment therein to form a pigment dispersion.