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

• Bottlebrush polymers with PEG and PDMS side chains were optimized for CO 2 /N 2 separation. • An optimized polymer exhibits CO 2 permeability of 1300 Barrer and CO 2 /N 2 selectivity of 31. • A membrane shows excellent CO 2 permeance of 2600 GPU and sufficient CO 2 /N 2 selectivity of 25. • Membranes demonstrate superior and stable carbon capture performance. Poly(ethylene glycol) (PEG)-based polymers have emerged as leading membrane materials for CO 2 /N 2 separation, and higher CO 2 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 CO 2 /N 2 separation properties. The PDMS forms a separate phase and is partially miscible in the PEG phase, increasing CO 2 permeability. The flexible brush end groups can also increase gas permeability. One of the copolymers having the best combination of CO 2 permeability of 1300 Barrer and CO 2 /N 2 selectivity of 31 was fabricated into thin-film composite membranes with the selective layer of 110 nm, which exhibits stable CO 2 permeance of 2600 GPU and CO 2 /N 2 selectivity of 25, meeting the performance target and comparable with state-of-the-art membranes for CO 2 /N 2 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.