Membranes based on modified polyimides for gas and organic vapour separations

The non-porous, flat membranes were prepared from soluble polyimides based on 4,40-oxydi(phthalic anhydride) or 4,40-(hexafluoroisopropylidene)diphthalic anhydride and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane. Poly(ethylene adipate) terminated with 4-methyl-1,3-phenylene diisocyanate with a controlled number average molecular weight 1300 or 2700 g mol−1 was used as a crosslinking agent (0-80 wt.%). The morphology of these materials was monitored by using dynamic mechanical analysis and scanning electron microscopy. All the materials were insoluble and showed no weight losses up to 240C. The permeability coefficient of methanol in the membranes with more than 50 wt.% of non-polyimides was 2-3 orders of magnitude higher than that of carbon dioxide. The different transport properties of pure hexane and cyclohexane from those of a hexane-cyclohexane mixture were found.