The present invention provides a copolymer or the like obtained by polymerizing a monomer mixture including at least compounds represented by formulas (A), (B), and (C) (in the formulas, T a , T b , T c , U a1 , U a2 , U b1 , U b2 , U b3 , Q a , Q b , Q c , R a , R b , R c , An - , and m are as defined in the description and claims). The copolymer of the present invention can be utilized as an ion complex material having an exceptional ability to inhibit adhesion of biological materials.
