Advanced Gas Separation Membrane Materials: Rigid Aromatic Polyimides

Permeabilities, solubilities, diffusivities, and selectivities for He/CH4 and CO2/CH4 gas pairs are reported for four aromatic polyimides having systematic variations in intersegrnental packing and intrasegmental mobility. As intersegmental packing is disrupted by bulky substituents, gas diffusivities are generally increased, but diffusivity selectivities of He/CH4 and CO2/CH4 are correspondingly decreased. Simultaneous suppression of intrasegmental mobility and intersegmental packing, however, yields significant increases in both diffusivity and diffusivity selectivity, and consequently in permeability and permselectivity. For example, packing-disrupted and mobility-restricted 6FDA-DAF polyimide provides significantly higher permeabilities and permselectivities than commercially available polymers currently being used as membrane materials.