the present invention relates to polymer compositions comprising a polymer comprising an arylene oxide moiety and a dendritic polymer , a hyperbranched polymer or a mixture thereof , and the use of these polymer compositions as membrane materials for the separation of gases . the present invention further relates to the use of a dendritic polymer , a hyperbranched polymer or a mixture thereof as permeability and / or selectivity enhancing additives in gas separation membranes . the dendritic polymer is preferably a boltorn polymer .