Molecular separation, such as gas separation, is central to many technological innovations and advancements in clean energy (e.g., H2 purification) and environmental remediation (e.g., carbon capture). Membrane technology, which takes advantage of material’s selectivity rather than energy to perform separations, represents a simple but powerful separation technology. Particularly, polymers with finely tailored microporosity are highly desirable for gas separation membranes considering the very small size differences between gas molecules—several tenths of an Ångstrom difference. Here we report a new family of molecularly porous polymers with super rigid backbone and facilely-tunable microporosity for gas separation membranes. These new ladder-like polymers exploit the molecular configurations of shape-persistent pentiptycene-based building blocks to construct non-collapsible free-volume-based microporous structure to provide diffusing molecules with a low-resistance transport avenue. The framework profiles defined by the shape of pentiptycene (i.e., S-shaped or C-shaped in Figure 1) provide a convenient way to tune the tortuosity of the ladder backbone and consequent free volume architecture that effectively regulates molecular transport in these membranes for various separation needs. Moreover, varying the content of pentiptycene units provides further tunability in selectivity by introducing internal free volume of iptycene moieties for size sieving. Thin films of these ladder polymers show superb separation performance. For example, a thin film containing only 17 mol% C-shaped pentiptycene units outperformed the 2008 upper bounds for all common gas pairs including CO2/CH4, O2/N2, CO2/N2, H2/N2, and H2/CH4. In this talk, synthesis and characterization of these new ladder polymers will be presented. Discussions will focus on elucidating the fundamental correlations between microscopic structure and gas transport properties for these innovative polymers.

Engineering microporosity in polymeric membranes for fast and selective gas transport

2019 Spring National Meeting

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