Gas-transport properties of indan-containing polyimides

A series of Indian-containing polyimides were synthesized, and their gaspermeation behavior was characterized. The four polyimides used in this study were synthesized from an indan-containing diamine [5,7-diamino-1,1,4,6- tetramethylindan (DAI)] with four dianhydrides [3,3′4,4′- benzophenone tetracarboxylic dianhydride (BTDA), 3,3′4,4′- oxydiphthalic dianhydride (ODPA), (3,3′4,4′-biphenyl tetracarboxylic dianhydride (BPDA), and 2,27prime;-bis(3,4′-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA)]. The gas-permeability coefficients of these four polyimides changed in the following order: DAI-BTDA < DAI-ODPA < DAI-BPDA < DAI-6FDA. This was consistent with the increasing order of the fraction of free volume (FFV). Moreover, the gas-permeability coefficients were almost doubled from DAI-ODPA to DAI-BPDA and from DAI-BPDA to DAI-6FDA, although the FFV differences between the two polyimides were very small. The gas permeability and diffusivity of these indan-containing polyimides increased with temperature, whereas the permselectivity and diffusion selectivity decreased. The activation energies for the permeation and diffusion of O ₂, N ₂, CH ₄, and CO ₂ were estimated. In comparison with the gas-permeation behavior of other indan-containing polymers, for these polyimides, very good gas-Permeation performance was found, that is, high gas-permeability coefficients and reasonably high permselectivity.