Experimental and simulation study of single-matrix, all-polymeric thin-film composite membranes for CO2 capture: Block vs random copolymers

Abstract

High-performance, additive-free, all-polymeric thin-film composite (TFC) membranes were developed for CO₂ capture, focusing on a comparison between block and random copolymers (referred to as PTF) composed of hydrophobic poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) and CO₂-philic polar poly(oxyethylene methacrylate) (POEM) chains. The PTF random copolymer, synthesized via free-radical polymerization (FRP), exhibited a disordered morphology. In contrast, the PTF block copolymer, synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization, formed a well-ordered hexagonally packed cylindrical structure, creating an amphiphilic, microphase-separated nanostructure. Molecular dynamics (MD) simulations revealed that in both copolymers, there was minimal interaction between the gases (CO₂ and N₂) and the hydrophobic PTFEMA segments, while CO₂ showed strong affinity for the hydrophilic POEM segments. The block and random copolymers demonstrated similar CO₂ permeance, which can be attributed to their comparable CO₂ diffusivity and solubility. However, the block copolymer exhibited significantly lower N₂ permeance than the random copolymer, resulting in nearly quadruple the CO₂/N₂ selectivity. This increase in selectivity was supported by the lower N₂ mean squared displacement (indicating reduced diffusivity) observed in the block copolymer. The PTF block copolymer outperformed the commercial Pebax block copolymer, achieving CO₂ capture efficiencies that surpass industrial standards for CO₂ separation and capture. This positions the single-matrix PTF block copolymer as a promising alternative to mixed-matrix membranes for practical applications in gas separation technologies.