TECHNOLOGY FOCUS - POLYMERS - Preferred Process: The process may further comprises desolvating the membranes in the coagulation medium; optionally, treating the membranes with an organic non-solvent; drying the membranes; and coating the dried membranes with a coating solution.The hollow fiber is formed using a tube-in-orifice spinneret, and water is introduced into the nascent hollow fiber as it is extruded from the spinneret.Preferred Components: The non-solvent additive is a polar compound which is liquid at room temperature, e.g. a 1-4C alcohol (preferably ethanol), water or a mixture.The polymer dope comprises a polyether sulfone.The solvent may be N-methyl-2-pyrrolidone or N,N-dimethylacetamide.The dope has a coagulation of 1-3 g for water by the addition of the non-solvent additive.The coagulation medium is water.The coating solution comprises polydimethylsiloxane and n-pentane. EXAMPLE - A polymer dope comprising Vitex 4800P(TM) (polyether sulfone) (29.4 wt.%) in N-methyl-2-pyrrolidone and water (non-solvent) in a weight ratio of 8.38:1 and having a coagulation value of 3 g and a viscosity at 25 degreesC of 46,786 cPs was formed into hollow fibers using a spinneret with an orifice diameter/inner diameter of 2.0/0.8 mm at an air gap length of 10 or 22 cm. All components of the dope were vacuum degassed, the dope was stored for 48 hours before use and coagulation was performed in tap water at room temperature. The hollow fibers were washed with water for up to 3 days and dried at room temperature. The test cells comprising 6-20 fibers of length 15-20 cm. The hollow fibers formed had an outer diameter of 1,800 mum and an inner diameter of 1,200 mum. They were coated with solution of Sylgard-184(TM) (3 wt.%) in n-pentane.    Permeabilities (in GPU, 1 GPU = 1 x 10-6 cm3 (STP)/cm2.cm Hg.second) and ideal separation factors were measured at 50 degreesC and a pressure difference of 5 bar. The permeability values for fibers prepared using the different air gap lengths were 180.8 and 200.7 respectively for helium; 78.3 and 85.5 respectively for carbon dioxide; 17.1 and 18.9 respectively for oxygen and 3.15 and 3.24 respectively for nitrogen. The ideal separation factors were 57 and 63 respectively for He/N2; 25 and 26 respectively for CO2/N2 and 5.4 and 5.8 respectively for O2/N2.    A membrane prepared using the solvent system containing propionic acid and N-methyl-2-pyrrolidone described in U.S. Pat. No. 4,871,494 had a nitrogen permeability of 13.1 and an O2/N2 ideal separation factor of 5.1.