Polymers for inkjet ink compositions

A composition, e.g. an inkjet ink, comprises a liquid vehicle and a pigment encapsulated by a copolymer having first and second monomeric units, the copolymer being crosslinked via the second units. The first unit is derived from an ethylenically unsaturated hydrophobic monomer of formula CH2=CR1R2 in which R1 and R2 are independently H, C1-12 alkyl, C5-20 aryl, or C6-20 alkaryl, one or more carbon atoms being optionally substituted with oxygen, nitrogen, or sulphur. The second unit is derived from maleic anhydride, maleic acid, or salts, esters, imides, or amides thereof. Typically, the first unit is styrene, α-methylstyrene, ethylene, propylene, 1-butylene, isobutylene, butadiene, or methyl vinyl ether. The copolymer is usually crosslinked by ester linkages formed between carboxylate-containing groups of the second unit and an epoxy-containing compound like trimethylolpropane triglycidyl ether. A method of making a polymer is also disclosed, which comprises combining a copolymer containing the first and second monomeric units with an epoxy-containing crosslinker.