Preparation and properties of ferrocene/rearrangeable polyimide composite membranes

In this paper, the 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP) were used as monomers, ferrocene (Fc) was introduced by in-situ polymerization method to prepare a series of Fc/polyimide (PI) composite membranes through thermal imidization. Then, these membranes were thermally treated to obtain the corresponding Fc/thermally rearranged (TR) composite membranes. The test results show that during the thermal treatment process, part of Fe²⁺ in ferrocene is transformed into Fe³⁺. When the Fc content increases from 0 to 5wt%, the glass transition temperatures of these Fc/PI composite membranes increase from 314℃ to 347℃, but the tensile strength values decrease from 112.68 MPa to 44.36 MPa. Owing to the TR reaction, the gas permeability of the membranes is significantly improved. When the Fc concentration is 1wt%, the ideal selectivities of the membranes reach optimal values. Specifically, the CO₂/N₂, O₂/N₂, and CO₂/CH₄ are 26.91, 6.13, and 27.60, respectively. The gas permeabilities of the membranes reach a maximum at an Fc content of 3wt%, with the permeabilities of CO₂, H₂, O₂, N₂, and CH₄ reaching 5870, 5265, 1059, 338, and 244 Barrer, respectively. Therefore, this composite strategy provides certain reference for the preparation of high-performance gas separation membrane materials.