Membranes based on modified polyimides for gas and organic vapour separations

摘要

The non-porous, flat membranes were prepared from soluble polyimides based on 4,4'-oxydi(phthalic anhydride) or 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoro-propane. 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 240°C. 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.