Preparation and properties of flower-like polyimide/polyimide and thermally rearranged mixed matrix membranes

Mixed matrix membranes (MMMs) show strong competitiveness in the field of gas separation due to their simple preparation method and excellent comprehensive performance. In order to improve the compatibility between fillers and polymer matrix, a series of flower-like polyimide(PI)/polyimide and their thermally rearranged (TR) mixed matrix membranes were prepared by in situ polymerization method, using the flower-like polyimide synthesized from solvothermal method as fillers and the hydroxyl-containing polyimide as matrix, followed by thermal imidization and thermal rearrangement treatment. Because the polyimide filler and matrix can form better compatibility because of their similar chemical structures, the mixed matrix membranes showed superior gas separation performance. When the doping content of the flower-like PI particles was 3wt%, the mixed matrix membrane TR-3wt% exhibited a d-spacing value of 0.64 nm, and the gas permeabilities of H₂, CO₂, O₂, CH₄ and N₂ were respectively increased by 61.36%, 67.90%, 81.58%, 37.88%, and 51.72% compared to the TR membrane. Moreover, the ideal selectivity of O₂/N₂ was 5.49, close to the 2015 Upper Limit. The selectivity of CO₂/CH₄ reached 22.36, exceeding the 2008 Robeson Upper Limit. Therefore, this design strategy will provide a certain reference for the interface design of MMMs.