RELATIONSHIP BETWEEN GAS SEPARATION PROPERTIES AND CHEMICAL STRUCTURES IN A SERIES OF AROMATIC POLYIMIDES.

Gas permeabilities and permselectivities for various gas pairs are reported for a series of aromatic polyimides. Gas solubility and diffusivity data are also reported for some of the polyimides. Systematic variations in chemical structure were found to lead to significant changes in permeabilities and selectivities. Further analysis shows that the permeability and selectivity changes in these cases are primarily due to the alteration of diffusivity factors. Generally, increases in permeability are attended by losses in permselectivity, however some of the polyimides in the series were found to deviate very favorably from this typical behavior. Specifically, materials were discovered having simultaneously higher permeabilities and permselectivities than commercial polymers currently being used as membrane materials. The relationship between gas separation properties and chemical structures is discussed in terms of intrasegmental mobility and intersegmental packing of the constituent polymers. The experimental data and their physical implications suggest the possibility that many new polymers having both high permeability and selectivity can be designed by tailoring the intrasegmental mobility and intersegmental packing of membrane polymers.