FIELD: selective separation of materials. SUBSTANCE: gas mixture including oxygen, carbon dioxide and helium is concentrated from one side of gas permeable membrane and component penetrating the membrane due to pressure differential is removed to the other side of membrane. Membrane is made in form of film of polyester produced by reaction of 2,2,2′-bis(3,5-dibrom-4-hydroxyphenyl)propane or its mixture with 4, 4,4′-(2,2,2-trifluoro-1-(trifluoromethyl)ethylene(bis)2,6-dibromophenol in mole ratio of 50:50 with mixture of isophthaloyl chloride with terephthaloyl chloride in mole ratio of 25-80:20-75, respectively. EFFECT: higher efficiency. 2 cl, 3 tbl
