Sorption-Enhanced Mixed-Gas Transport in Amine Functionalized Polymers of Intrinsic Microporosity (PIMs)

Polymers of intrinsic microporosity (PIMs) have shown excellent pure-gas separation performance due to their rigid backbones, inefficient packing, and high free volume. Their out-of-equilibrium packing structures, however, make PIMs susceptible to physical aging and their intrachain rigidity alone has proven insufficient to mitigate plasticization. Moreover, pure-gas transport performance for PIMs rarely matches mixed-gas performance for industrially relevant conditions. For instance, several studies on the mixed-gas transport in PIMs have demonstrated the beneficial effects of competitive sorption on separation performance, where gases with high polymer affinity (e.g., CO₂) can reduce the sorption of co-penetrants in a mixture (e.g., CH₄ and N₂) and increase selectivity. However, due to CO₂-induced plasticization at high pressures, decreases in diffusion selectivity can outweigh beneficial competition effects. This trade-off in performance is especially detrimental for PIMs with little CO₂ affinity and poor plasticization resistance, as they rely primarily on diffusion-selective transport that may be significantly reduced at high pressure.

Here, we report on mixed-gas transport properties of polymers of intrinsic microporosity (PIMs) with identical benzodioxane backbones, but a diverse set of backbone functionalities. Low-pressure mixed-gas tests indicate a relationship between CO₂ sorption affinity and enhancements in CO₂/CH₄ and CO₂/N₂ mixed-gas selectivity compared to pure-gas scenarios. The amine-functionalized PIM-1 (PIM-NH₂), showed an unprecedented 140% and 250% increase in mixed-gas CO₂/CH₄ and CO₂/N₂ mixed-gas selectivity, respectively, compared to pure-gas. Moreover, PIM-NH₂ films retained a CO₂/CH₄ mixed-gas selectivity over 20 up to a total mixed-gas pressure of 26 bar, demonstrating strong plasticization resistance compared to pristine PIM-1. Pure-gas sorption and mixed-gas permeation performance for six PIMs were­ compared across a range of reported microporous polymers, elucidating structure/property relationships that can enable rational design of high-performance chemistries for industrially relevant scenarios. Results demonstrate the promise of primary amine functionalization for developing highly sorption-selective and plasticization-resistant membranes for gas separations.