The invention is a process for the preparation of a POWADIR membrane comprising bisphenol-based polycarbonates wherein at least 25 percent by weight of the bisphenol moieties are tetrahalogenated wherein the halogen is Cl or Br, and the membrane prepared by such process. The process generally comprises: forming a mixture comprising (i) a bisphenol-based polycarbonate wherein at least 25 percent by weight of the bisphenol moieties are tetrahalogenated, wherein the halogen is Cl or Br, (ii) a solvent for such polycarbonate, and (iii) a non-solvent for such polycarbonate, wherein the mixture has a sufficient viscosity to allow extrusion at temperatures at which the mixture is homogeneous; heating the mixture to a temperature at which the mixture is a homogeneous fluid and extrudable; extruding the heated mixture into a shape suitable for membrane use; passing the formed membrane through a quench zone wherein the mixture undergoes phase separation, and the major portion of the solvent and non-solvent are removed from the formed membrane; wherein the membrane formed is a POWADIR membrane with a discriminating region capable of separating oxygen from nitrogen.