Nanofilm Composite Membranes of Bottlebrush Poly(1,3-Dioxolane) Plasticized by Poly(Ethylene Glycol) for CO₂/N₂ Separation

Poly(1,3-dioxolane) has emerged as a leading membrane material for post-combustion CO₂ capture due to its high ether oxygen content and strong affinity toward CO₂. However, they are often cross-linked to inhibit crystallization, which makes them impossible to fabricate into industrial thin-film composite membranes. Herein, soluble and high molecular weight bottlebrush polymers (bPDXLA) are synthesized using reversible addition-fragmentation chain transfer polymerization and demonstrate the feasibility of fabricating nanofilm (≈100 nm) composite membranes (NCMs). Furthermore, bPDXLA can be plasticized using a miscible additive of poly(ethylene glycol) dimethyl ether (PEGDME) to improve CO₂ permeability while retaining good CO₂/N₂ selectivity. For example, adding 20 mass% PEGDME improves CO₂ permeance from 930 to 1300 GPU and decreases CO₂/N₂ selectivity from 74 to 53 at 25 °C; the membrane exhibits stable separation performance competitive with state-of-the-art commercial membranes. This work unveils a practical approach to designing uncross-linked, highly polar polymers for practical membrane gas separation and highlights a facile way to enhance performance by incorporating miscible plasticizers using industrial manufacturing processes.