Abstract
A series of new semifluorinated sulfonated polyimide copolymers (DHNHXX) were prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), 4,4′-diaminostilbene-2,2′-disulfonic acid (DSDSA) and 1,4-bis-[{2′-trifluoromethyl-4′-(4′′-aminophenyl)phenoxy}] benzene (HQA). The degree of sulfonation of DHNHXX was varied by changing the molar ratio of the sulfonated diamine, DSDSA to the non-sulfonated diamine, HQA. The flexible DHNHXX membranes showed high thermal stability (desulfonation temperature above 270 °C) and good mechanical properties. The oxidative stability of DHNHXX improved with increasing the fluorine content. DHNHXX showed anisotropic dimensional changes, and good water stability (did not dissolve for up to 415 h), higher than many other sulfonated polyimides. Transmission electron microscopy (TEM) analysis revealed cluster-like microstructures for the DHNHXX membranes, suggesting good phase-separated morphology. DHNH70 with IEC = 2.10 meq. g−1 exhibited high proton conductivity, with a maximum up to 129 mS cm−1 at 90 °C in water.
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