Journal of Membrane zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Science, 50 (1990) 285-297 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands 285 zyxwvut ISOMERIC POLYIMIDES BASED ON FLUORINATED DIANHYDRIDES AND DIAMINES FOR GAS SEPARATION APPLICATIONS M.R. COLEMAN and W.J. KOROS* Department of Chemical Engineering, University of Texas at zyxwvutsrqponmlkjihgfedcbaZYXWV Austin, Austin, TX 78712- 1062 (U.S.A.) (Received September 18,1989; accepted in revised form January 3,199O) zyxwvutsrqponmlkjihgf Summary The gas sorption and transport properties of two isomeric polyimides with hexafluoroisopro- pylidene moieties in the diamine and dianhydride monomers were characterized for a variety of gases at 35°C at pressures up to 60 atm. These materials have structural properties which inhibit intrasegmental rotational mobility and intersegmental chain packing. The effect of isomerism on the physical and gas separation properties of these rigid materials was investigated. The effect of isomerism on the hindrance to packing is reflected in the wide angle X-ray diffraction (WAXD) measurements of the average spacing between adjacent polymer chains. The para connected po- lyimide showed significant increases in permeability relative to a series of polyimides studied earlier with less packing-disruptive substituents on the polymer backbone. The permeability of the higher flux material was 64 barrers for CO, and 16 barrers for 0,. The meta connected polyi- mide showed large decreases in permeability with corresponding increases in permselectivity when compared to its para counterpart. For example, the permselectivity of the meta material for 0, relative to Nz is 6.9 which is 50% greater than that of thepara connected material. The differences in permeability and permselectivity are due to both penetrant solubility and diffusivity effects. Introduction Recent studies of a series of polyimides have shown that systematic varia- tions of intrasegmental mobility and intersegmental chain packing can be used to achieve increases in permeability without the decreases in permselectivity which are typically seen for most polymers [l-4]. Similar results have also been achieved for novel polycarbonates and polysulfones [ 5,6]. The present work extends the study of novel polyimides by determining the *To whom correspondence should be directed. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPO 0376-7388/90/$03.50 0 1990 Elsevier Science Publishers B.V.