Poly(ethylene oxide) (PEO) based polymers are leading membrane materials for post-combustion carbon capture (i.e., CO2/N2 separation) with high CO2 permeability and CO2/N2 selectivity because the ether oxygen groups show affinity towards CO2. Herein we prepare a series of highly branched amorphous polymers containing poly(1,3-dioxolane) (PDXL), which has an O:C ratio of 0.67, higher than 0.5 in PEO. The chemical structure of the macromonomers was confirmed using NMR and MS, and the amorphous nature of the polymers was validated using DSC and WAXD. The length of the poly(1,3-dioxolane)-based branches are tuned to yield amorphous nature, and mobile ethoxy chain end groups are introduced to provide high free volume and gas diffusivity. These ether oxygen-rich polymers exhibit CO2/N2 separation properties superior to the PEO-based materials at practical conditions for flue gas processing and above Robeson’s upper bound for the state-of-the-art non-facilitated transport polymers. For example, a PDXL-containing polymer exhibits a mixed-gas CO2 permeability of 1500 Barrer and CO2/N2 selectivity of 70 at 70 oC when tested with a gas mixture containing 20% CO2 and 80% N2. The mixed-gas separation performance is stable in the presence of water vapor for more than 88 h at 70 oC. The polymers can be plasticized with liquid additives, such as poly(ethylene glycol) dimethyl ether (PEGDME, average Mn ~240), to further increase gas permeability while retaining the selectivity. The structure/property relationship in these new amorphous polyethers with exciting separation performance can be elucidated using a Tg-augmented free volume model.

Polyethers beyond poly(ethylene oxide) with superior CO2/N2 separation properties

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