Dual-phase all-polymeric membranes with graft copolymer filler for CO₂ capture

We describe high-performance, dual-phase, all-polymeric membranes that simultaneously exhibit improved CO₂ permeability and CO₂/N₂ selectivity. The membranes are fabricated by incorporating the graft copolymer poly(2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]ethyl methacrylate)-graft-poly(oxyethylene methacrylate) (PBE) in a poly(amide-b-ether) block copolymer (Pebax) matrix. The amphiphilic PBE filler selectively interacts with Pebax, resulting in the formation of interconnected CO₂-philic network channels within the matrix. The membranes exhibit a dual-phase, microphase-separated morphology, and good thermal/mechanical properties, as confirmed using transmission electron microscopy, differential scanning calorimetry, X-ray diffraction analysis, thermogravimetry analysis, and measurements performed on a universal testing machine. The CO₂ and N₂ permeabilities increase with the PBE content, with the maximum selectivity being observed at a PBE content of 5 wt%. The improved performance is attributable to the increased CO₂ solubility owing to the efficient clustering of CO₂-philic groups such as ether oxygens and triazole groups resulting from the dual-phase, interconnected morphology. The best performance corresponded to a CO₂ permeability of 175.3 Barrer and a CO₂/N₂ selectivity of 48.2, which are much higher than those of neat Pebax (CO₂ permeability of 103.3 Barrer and selectivity of 31.2) and approach the 2008 Robeson upper limit. Thus, these all-polymeric membranes are suitable for the commercialization of gas separation owing to their simple fabrication method and low cost.