Aromatic polyimide and crosslinked thermally rearranged poly(benzoxazole-co-imide) membranes for isopropanol dehydration via pervaporation

• Novel 6FDA–HAB/DABA polyimide and C-TR-PBO have been successfully synthesized.
• C-TR-PBO membranes exhibit impressive results for isopropanol dehydration.
• C-TR-PBO membranes show synergistic effect of high permeability and selectivity.
• C-TR-PBO membranes display a stable isopropanol dehydration performance.

Novel crosslinked thermally rearranged polybenzoxazole (C-TR-PBO) membranes, which show impressive results for isopropanol dehydration, have been obtained via in-situ thermal conversion of hydroxyl-containing polyimide precursors. The polyimide precursors are synthesized by the polycondensation of three monomers; namely, 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 3,3′-dihydroxybenzidine diamine (HAB) and 3,5-diaminobenzoic acid (DABA). Due to the incorporation of the carboxylic-group containing diamine DABA into an ortho-hydroxypolyimide precursor, the thermally induced crosslinking reaction can be achieved together with the thermal rearrangement process. Consequently, a synergistic effect of high permeability and high selectivity can be realized in one step. The resultant C-TR-PBO membrane exhibits an unambiguous enhancement in permeation flux compared to its polyimide precursor. Moreover, the newly developed C-TR-PBO membrane displays stable isopropanol dehydration performance at 60 °C throughout the continuous 200 h. The promising preliminary results achieved in this study may offer useful insights for the selection of membrane materials for pervaporation and new methods to molecularly design next-generation pervaporation membranes.

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