Separation*

Membrane technology has emerged as a potentially economically viable alternative for CO₂ captures from fossil fuel-fired powers, enabled by advanced membrane materials with high CO₂ permeability and high CO₂/N₂ selectivity. Current leading membrane materials usually contain poly(ethylene oxide) (PEO) because the ether oxygen in PEO interacts favorably with CO₂, resulting in high CO₂/N₂ selectivity. Herein we prepare a series of highly branched amorphous polymers containing poly(1,3-dioxolane), which has an O:C ratio of 0.67, higher than 0.5 in PEO. The length of the poly(1,3-dioxolane)-based branches are tuned to yield amorphous nature, and mobile ethoxyl chain end groups are introduced to provide high free volume and gas diffusivity. These ether oxygen-rich polymers exhibit more superior CO₂/N₂ separation properties than the PEO-based materials at practical conditions for flue gas processing, and above the Robeson’s upper bound. This work demonstrates that harnessing the interactions between polymers and CO₂ may provide unprecedented opportunities in designing gas separation membranes with robust performance under practical conditions.