Permeation modified asymmetric gas separation membranes having graded density skins

摘要

Asymmetric gas separation membranes having graded density skins and macrovoid-free morphology comprised of glassy, hydrophobic polymers which when contacted on the graded density skin surface with an effective amount of permeation modifier and a coating in occluding contact, exhibit permeation selectivities greater than the intrinsic permeation selectivities for at least one gas of a gaseous mixture than a bulk sample of the polymers. The permeation modified membranes have increased free volume as evidenced by the membrane first heat T_g which is greater than the T_g of the bulk sample of the glassy, hydrophobic polymers; however the permeation modified membranes having an effective amount of permeation modifier added in non-uniform mode are achieved without signif­icant loss in the physical properties of the membrane, including T_g.