Some of the best performing polymers for membrane-based gas separations are formed from linear polymers with contorted and rigid backbone structures. Such characteristics enable solution casting to form films, and their extreme contortions and rigidity allow polymeric structures to pack inefficiently, thereby creating ultramicroporosity that can enable ultrahigh permeabilities and good selectivities relative to the polymer upper bound. However, these traditional polymers of intrinsic microporosity (PIMs) have several key limitations, including limited opportunities for structural design, pronounced physical aging, and plasticization effects. Herein, we present an alternative strategy for forming ultramicroporous polymers by using a flexible ring-opening metathesis polymerization (ROMP) backbone with porous side chains attached. This approach enables the design of membrane property sets based on side chain chemistries instead of more difficult-to-control backbone packing structures. Transport properties for two side-chain variants are presented, including a polymer that is the second most permeable linear ultramicroporous polymer to date. This polymer exceeds the H2/CH4 upper bound and has separation performance near the upper bound for H2/N2 and CO2/CH4 separations. Plasticization and physical aging data are presented relative to the state-of-the-art PIM, PIM-1. By incorporating ultramicroporosity via side chain units instead of the main chain, it is possible to reduce plasticization and physical aging effects.

Membrane-based gas separations with a new class of ultrapermeable porous polymers

2019 Spring National Meeting

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