(DE3781449-G)      A gas sepn. membrane comprises a thin discriminating layer of a polycarbonate formed from a bisphenol R = H, Cl, Br, 1 - 4C alkyl; R1 = -CO-, -S-, -SO2-, -O-, or 1-6C divalent hydrocarbon, 1 - 6C divalent fluorocarbon or inertly substd. 1-6C divalent hydrocaron with the proviso that at least 25 wt.% of the R gps. are exclusively Br, Cl or mixts. of these. The membrane has a sepn. factor for O2 and N2 of at least 6 : 1 at ambient temps. The membrane is pref. annealed by heating to above the beta transition temp. and below the Tg to partly densify the polymer.    (I) is tetrabromobisphenol A and the gas sepn. factor is at least 7.0.    Gases are sepd. by (i) contacting the gas mixt. with one side of the membrane while maintaining a pressure difference across the membrane with the lower pressure on the other side of the membrane. (ii) removing the permeated gas.    The gas mixt. may contain N2 and O2, and the permeated gas is O2, or CO2 and CH4 and the permeated gas is CO2. The gas mixt. may be contacted with the membrane at 0 - 80, esp. 5 - 45 deg.C and a pressure difference of 275-1375, esp. 650 - 825 kPa, (40 - 200, 95 - 120 psia).    USE/ADVANTAGE -   Semi-permeable membranes are highly selective under high pressures and temps.    (JP2699168-B2)      A gas sepn. membrane comprises a thin discriminating layer of a polycarbonate formed from a bisphenol R = H, Cl, Br, 1 - 4C alkyl; R1 = -CO-, -S-, -SO2-, -O-, or 1-6C divalent hydrocarbon, 1 - 6C divalent fluorocarbon or inertly substd. 1-6C divalent hydrocaron with the proviso that at least 25 wt.% of the R gps. are exclusively Br, Cl or mixts. of these. The membrane has a sepn. factor for O2 and N2 of at least 6 : 1 at ambient temps. The membrane is pref. annealed by heating to above the beta transition temp. and below the Tg to partly densify the polymer.    (I) is tetrabromobisphenol A and the gas sepn. factor is at least 7.0.    Gases are sepd. by (i) contacting the gas mixt. with one side of the membrane while maintaining a pressure difference across the membrane with the lower pressure on the other side of the membrane. (ii) removing the permeated gas.    The gas mixt. may contain N2 and O2, and the permeated gas is O2, or CO2 and CH4 and the permeated gas is CO2. The gas mixt. may be contacted with the membrane at 0 - 80, esp. 5 - 45 deg.C and a pressure difference of 275-1375, esp. 650 - 825 kPa, (40 - 200, 95 - 120 psia).    USE/ADVANTAGE -   Semi-permeable membranes are highly selective under high pressures and temps.