Bottlebrush Polymers of Poly(1,3-dioxolane) Acetate for Membrane CO₂/N₂ Separation

Cross-linked bottlebrush polymers based on poly(1,3-dioxolane) have emerged as an attractive platform for designing ether-oxygen-rich yet amorphous CO₂-philic polymers for membrane CO₂/N₂ separation. However, the brushes often have -OH end groups that reduce gas permeability, and their cross-linked nature prevents them from being fabricated into industrial thin-film composite (TFC) membranes. Herein, we design and synthesize high-molecular-weight and soluble bottlebrush polymers from poly(1,3-dioxolane) acrylate with an acetate brush end group (DXLAc) using reversible addition-fragmentation chain transfer polymerization and successfully fabricate them into TFC membranes for CO₂/N₂ separation. The effects of the brush length and end groups on polymers’ physical and gas transport properties are investigated. Furthermore, the bottlebrush polymers were fabricated into membranes with defect-free selective layers as thin as 55 nm. The membranes exhibit CO₂ permeance of 1250-2150 GPU and CO₂/N₂ selectivity of 71-34, surpassing Robeson’s upper bound, and show good stability when challenged with simulated flue gas. This work highlights that bottlebrush polymers with suitable brush lengths and end groups can incorporate high contents of polar groups and can be useful for developing scalable, high-performance membranes for various separations.