Designing microphase-separated bottlebrush copolymers of polydimethylsiloxane and poly(ethylene glycol) for carbon capture

Poly(ethylene glycol) (PEG)-based polymers have emerged as leading membrane materials for CO₂/N₂ separation, and higher CO₂ permeability is desirable to reduce carbon capture costs. Herein, we design two series of microphase-separated bottlebrush copolymers containing PEG and highly permeable polydimethylsiloxane (PDMS) and systematically optimize the PDMS content to enhance CO₂/N₂ separation properties. The PDMS forms a separate phase and is partially miscible in the PEG phase, increasing CO₂ permeability. The flexible brush end groups can also increase gas permeability. One of the copolymers having the best combination of CO₂ permeability of 1300 Barrer and CO₂/N₂ selectivity of 31 was fabricated into thin-film composite membranes with the selective layer of 110 nm, which exhibits stable CO₂ permeance of 2600 GPU and CO₂/N₂ selectivity of 25, meeting the performance target and comparable with state-of-the-art membranes for CO₂/N₂ separation. This study demonstrates that incorporating a highly permeable phase in a highly selective phase can maximize both permeability and selectivity for various molecular separations while retaining the large-scale manufacturability of the membranes.