Fabrication of ether-oxygen-functionalized flexible thermally rearranged (TR) membranes with enhanced hydrogen separation

Ether-oxygen-functionalized hydroxy polyimide precursors were thermally converted into flexible TR membranes with enhanced gas transport, as confirmed by molecular dynamics simulations showing increased free volume. • Introducing ether-oxygen groups improved polymer’s flexibility. • The performance of functionalized TR membranes exceeded Robeson’s 2008 limit. • Molecular dynamics revealed relationship between free volume and gas permeability. An ideal gas separation membrane requires high permeability, selectivity, and mechanical flexibility. In this study, we developed functionalized polyimide precursors (coPI) by copolymerizing hydroxy-diamine, flexible diamine, and dianhydride, and then calcined to prepare the thermal rearranged (coTR) membranes. 1 H NMR and FTIR confirmed coPI synthesis, while tensile tests and DSC showed improved mechanical strength (51.84–72.74 N) and moderate glass transition temperatures (144–176 ℃) due to ether-oxygen segments and imide groups. SEM and SAXS revealed morphological changes in thermally rearranged (coTR) membranes. Gas permeation tests demonstrated that coTR-5, treated at 450 ℃, achieved an 18-fold increase in H 2 permeability (578.66 Barrer) with high H 2 /CH 4 selectivity (46.15), surpassing the 2008 Robeson limit. The membrane also exhibited flexibility, pressure tolerance, and long-term stability. Molecular dynamics simulations indicated a high free volume (18.75 %), highlighting ether-oxygen diamine copolymerization as an effective strategy for designing advanced TR membranes.