High-Performance Poly(imide-co-benzoxazole) Gas Separation Membranes Based on Synergy Effect of Hydrogen-bonding Interaction, Thermo-Oxidative Crosslinking and Thermal Rearrangement Reaction

Breaking the trade-off effect between permeability and selectivity and preparing membranes with an excellent comprehensive separation performance is a relentless pursuit in the field of membrane separation technology. Herein, a new series of crosslinked thermally rearranged poly(imide- co -benzoxazole) membranes were successfully synthesized with greatly improved comprehensive gas separation performance. The o rtho -hydroxycopolyimide precursor was synthesized by reacting the newly designed dianhydride bearing the amide structure and thermally crosslinkable benzyl groups, N, N'-(2,4,6-trimethyl-1,3-phenylene)bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxamide) (MPADA), with hexaffuoroisopropylidene diphthalic anhydride (6FDA) and thermally rearrangeable diamine, 2,2-bis(3-amino-4-hydroxyphenyl)- hexafluoropropane (6FAP). Sequential thermal treatment at 375-450 °C under air and at 450-465°C under N 2 resulted in the benzyl-induced crosslinking reaction and thermal rearrangement (TR) reaction of ortho -hydroxyimide, respectively, within the precursor membrane. It demonstrates that the above reactions combined with the inherently existing interchain hydrogen bonding not only effectively expand the chain packing enabling microporous structure for gas transport but also introduce multi-scale microporosity via the unique dual crosslinked network that allows for molecular sieving capability in the resulting membrane. The resulting membranes exhibited a remarkable CO 2 permeability (341.2 Barrer) and ideal CO 2 /CH 4 selectivity (53), which outperformed some typical thermally rearranged polymer membranes and the state-of-the-art 2008 upper bound for CO 2 /CH 4 separation. More importantly, the resulting membranes demonstrated a superior anti-aging and high anti-plasticization property attributed to their highly stable molecular skeleton structure. This work provides a reliable route for constructing polymeric membranes with highly improved gas separation performance and stability.