Synthesis and characterization of bis(phenyl)fluorene-based cardo polyimide membranes for H2/CH4 separation
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Three bis(phenyl)fluorene-based cardo diamine monomers with different side groups (–CF3, –H, and –CH3) were synthesized and used to synthesize three 6FDA-based polyimides (6FDA-FBPF, 6FDA-BPF, and 6FDA-MBPF). The influence of bis(phenyl)fluorene cardo moiety and different side groups on the glass transition temperature (Tg), thermal stabilities, and chain packing of the synthesized polyimides were systematically studied. The gas permeabilities and selectivities of three bis(phenyl)fluorene-based polyimide membranes were studied and correlated with their fractional free volumes and chain packing conditions. As a result, the obtained polyimides showed promising performance for hydrogen separation. Among the three polyimides, 6FDA-FBPF had the highest gas permeabilities which exhibited H2 permeability of 151.12 Barrer and H2/CH4 selectivity of 62.19. The high gas separation performance of 6FDA-FBPF mainly attributed to the ineffective chain packing via the incorporation of bi(phenyl)fluorene cardo moiety and introduction of bulky CF3 side groups into the polyimide backbones that is favorable to formation hourglass-shaped pores.
The author acknowledges the financial support of this work by the Natural Science Foundation of Beijing Municipality (2194071).
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Conflict of interest
The author declares no competing financial interest.
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