Abstract: The invention relates to a poly(aryl ether sulfone) (PAES) copolymer (P2) with ionically and/or covalently attached bioactive compound(s), articles comprising (P2), methods of making (P2), and methods for making articles such as membranes comprising (P2). Functionalized side-chain PAES copolymers (P1) permit the immobilization of a bioactive compound on copolymer's functionalized side chains for preparing bioactive articles. In particular, an antithrombotic agent such as heparin may be immobilized to form a bioactive membrane structure suitable for hemodialysis to avoid or eliminate the injection of such antithrombotic agent to a patient undergoing hemodialysis. Preferred embodiments include heparinized PAES copolymers and membranes comprising them.