Preparation and gas transport properties of thermally induced rigid membranes of copolyimide containing cardo moieties

The diamine monomer with ortho-hydroxyl groups and fluorene moiety, 9,9-bis (3-amino-4-hydroxyphenyl)fluorene (BisAHPF), was prepared. The 6FDA-FDA-BisAHPF copoly(amic acid) (PAA) solution was synthesized from the diamines 9,9-bis(4-aminophenyl)fluorene (FDA), BisAHPF and aromatic dianhydride 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) by a low-temperature solution polymerization. The thernally treated PAA films were used as precursor to prepare thermally induced rigid membranes in N2 and air atmosphere at the temperature range of 300-480 °C, respectively. The thermally induced rigid membranes included thermal oxidative membranes and thermally rearrangement (TR) membranes. Their physical and chemical properties were characterized by FTIR, XPS, XRD, DSC and TGA. Single gas permeation performances of thermally induced rigid membranes were studied for five representative gases of interest including H2, O2, N2, CO2, and CH4. Highly gas permeability were obtained after the thermal treatment. Therefore, the introduction of “cardo” moieties helped to improve the gas permeability. In addition, a proper thermal treatment could tune to the gas separation performance of the thermally induced rigid membrane materials