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Gas permselectivity properties of high free volume polymers modified by a low molecular weight additive

The permselectivity properties of mixtures of the highly substituted polymers tetramethylhexafluoro polysulfone (TMHFPSF) and tetramethylhexafluoro bisphenol A t-butyl isophthalate (TMHFBPA-tBIA) with a low molecular weight glassy additive Kenflex A (denoted here as KXA) were measured for different gases and compared with the permselectivity properties shown by the base, unsubstituted polymers polysulfone (PSF) and bisphenol A t-butyl isophthalate (BPA-tBIA). The results show that the selectivity-permeability balance of polymer membranes may be appropriately tailored by a combination of chemical and physical alterations of the base polymer. The addition of modest amounts of KXA (ca. 20 wt %) into TMHFPSF or TMHFBPA-tBIA leads to materials whose permeability/selectivity combination is better than that of the unsubstituted materials, PSF or BPA-tBIA. The polymer TMHFPSF responds more beneficially to the incorporation of KXA than TMHFBPA-tBIA. At the same level of permeability, mixtures based on TMHFPSF have higher selectivity factors for H2/CH4 and CO2/CH4 than those based on TMHFBPA-tBIA. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 403–415, 1998