Polymeric membrane for gas separation

Claim 1

A polymeric membrane having improved selectivity for use in separating a feed gas mixture containing at least two gaseous components, said membrane comprising a polymer having the general structural formula: ##STR7## wherein R 1 is a linear or branched C 1 -C 4 alkyl group; R 2 and R 3 are independently linear or branched C 1 -C 4 alkyl groups; R 4 is a linear or branched C 1 -C 12 alkyl group or aryl group; X is a C 1 -C 3 alkyl group or phenyl; m is at least 100 and n is 0 or 1, to which has been added between about 5 and 50 wt. % of an additive which is miscible with said polymer, has a boiling point>300° C. at atmospheric pressure, is soluble in a common solvent for the polymer, and increases the selectivity ratio for O 2 /N 2 by at least 15% over the polymer without said additive, and wherein said additive is selected from the group consisting of: silicon oils, non-ionic surfactants, hydrocarbon oils, flame retardant additives, epoxides, natural oils, liquid poly(vinyl chloride) stabilizers, aromatic compounds containing nitrogen groups, aromatic compounds containing sulfur groups, and mixtures thereof.