Membrane with immobilized anticoagulant and process for producing same

A process for preparing a porous hollow fiber membrane having an anticoagulant immobilized thereon, said process comprising the steps of

• a) dissolving i) at least one polyethersulfone, ii) at least one polyvinylpyrrolidone, and iii) at least one polymer bearing ammonium groups in N-methyl-2-pyrrolidone to form a polymer solution;
• b) extruding the polymer solution through an outer ring slit of a nozzle with two concentric openings into a precipitation bath;
• simultaneously
• c) extruding a center fluid through the inner opening of the nozzle;
• d) washing the membrane obtained;
• and subsequently
• e) grafting an anticoagulant onto at least one surface of the membrane;
• wherein the polymer solution comprises from 10 to 15 wt %, relative to the total weight of the polymer solution, of polyethersulfone, and from 5 to 10 wt %, relative to the total weight of the polymer solution, of polyvinylpyrrolidone, and from 0.03 to 2 wt %, relative to the total weight of the solution, of at least one polymer bearing ammonium groups, the polymer bearing ammonium groups being selected from polyvinylpyridines bearing ammonium groups and copolymers of vinylpyridine and styrene bearing ammonium groups.