Solution-processable polymer-based membranes have attracted great attention in some important gas separations areas, including hydrogen recovery from ammonia purge gas streams (H2/N2), onsite nitrogen enrichment (O2/N2) as well as rapidly emerging applications such as natural gas sweetening (CO2, H2S) and flue gas (CO2) treatment. Ideal membranes should possess both high permeability and selectivity, but these parameters are limited by a trade-off known as Robeson “upper bound”. One promising strategy is the rational design of polymers of intrinsic microporosity (PIMs), which are composed of an extremely rigid structure connected by contortion sites that increase their free volume. Such polymers can have BET surface areas exceeding 800 m2/g and exhibit permeabilities and selectivities surpassing 2008 Robeson’s upper bounds. This design principle has been extended to polyimides of intrinsic microporosity (PIM-PIs), which often employ a spirobisindane moiety as a site of contortion. However, the spirobisindane center is relatively flexible and improvements can be made to further enhance backbone rigidity. One example, a spirobifluorene-based ladder-type PIM (SBF-PIM), has recently been reported with improved separation performance for O2/N2 and CO2/N2 over its spirobisindane-based analog, PIM-1. Here, we report a novel route for synthesis of PIM-PIs using spirobifluorene-based non-extended dianhydrides. The resulting polyimides demonstrate good solubility, excellent thermal stability and significant microporosity with BET surface areas in the range of 600 to 750 m2/g. Compared to previous spirobisindane-based PIM-PIs analogs, the spirobifluorene-based PIM-PIs exhibit higher permeabilities while maintaining good selectivities, which can be attributed to the enhanced rigidity of the spirobifluorene center.

Design, synthesis, and gas transport properties of spirobifluorene-based intrinsically microporous polyimides (SPIM-PI)

249th National Meeting (2015)

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