Gas permeability of fluorinated hyperbranched polyimide

The gas permeability of carbon dioxide, oxygen and nitrogen for hyperbranched polyimide (HBPI) containing trifluoromethyl groups were investigated. The HBPIs were prepared by condensation polymerization of a triamine monomer, 1,3,5‐tris(2‐trifluoromethyl‐4‐aminophenoxy) benzene (TFAPOB) and a commercially available dianhydride monomer 1,4‐bis(3,4‐dicarboxyphenoxy) benzene dianhydride (HQDPA). With different monomer addition methods and different monomer molar ratios, amine terminated HBPI (AM‐HQDPA) and anhydride terminated HBPI (AD‐HQDPA) were obtained, subsequently, the trifluoromethylphenyl amine terminated HBPI (CF 3 ‐HQDPA) was achieved by modifying the end groups of AD‐HQDPA with (3,5‐ditrifluoromethyl)aniline. The CF 3 ‐HQDPA exhibited a good mechanical and thermal stability as well as AM‐HQDPA, and showed better gas permeabilities than that of AM‐HQDPA because of increase of free volume contributed by the bulky trifluoromethyl group introduced, but, the selectivity ofCF 3 ‐HQDPA was lower than that of AM‐HQDPA. This result was consistent with the trade‐off relationship.