gas separation membranes formed from polyether - urethane or polyether - urea block copolymers are useful for separating gases from gas mixtures . the membranes and processes are especially suited for separating polar gases from mixtures that contain polar and non - polar species . the novel membranes exhibit good permeability and permselectivity , as well as durability , making them well suited for industrial applications such as removal of acid gases from natural gas and removal of carbon dioxide from synthesis gas .