A polymer of intrinsic microporosity, 1, has been incorporated into a series of polyelectrolyte multilayers via the layer-by-layer deposition method. One of these assemblies [a 6 nm multilayer derived from 1 plus poly(diallyldimethylammonium chloride)] showed exceptional permeation properties with respect to CO₂ and N₂. Specifically, this film exhibited a CO₂ permeance of 130 GPU and a CO₂/N₂ selectivity of 33.