Highly Polar but Amorphous Polymers with Robust Membrane CO2/N2 Separation Performance

Highly polar polymers with an affinity toward CO2 are desired to achieve superior CO2/N-2 separation properties for post-combustion CO2 capture from fossil fuel-fired power plants. However, polar groups improve chain packing efficiency and induce polymer crystallization, both decreasing gas permeability. Herein, we report a series of highly branched amorphous polymers containing poly(1,3-dioxolane) (PDXL) in the branches, which interacts favorably with CO2 but not N-2. The length of the branches is tuned to yield amorphous nature, and mobile ethoxy chain end groups are introduced to provide high free volume and thus high gas diffusivity. These ether oxygen-rich polymers exhibit unprecedented CO2/N-2 separation properties at practical conditions for CO2 capture, and above the separation performance limit of the state-of-the-art non-facilitated transport polymers. This work demonstrates that incorporating polar groups in short branches with flexible chain ends is an effective strategy in designing solubility-selective membrane materials with superior performance for gas separations.