Copolymer, aqueous ink, and ink cartridge

摘要

A copolymer contains repeating units represented by the following chemical formulae 1 and 2: In the chemical formulae I and 2, R represents a hydrogen atom or a cation; X represents an alkylene group having 2 to 18 carbon atoms; Y represents a single bond, an oxycarbonyl group [(X)-O-CO-(Z)], a carbonyloxy group [(X)-CO-O-(Z)], an ether group (-O-), or an imido group [(X)-N-CO-(-CO-)(Z)]; and Z represents a biphenyl group or a naphthyl group).