Enhancement of CO₂ Affinity in a Polymer of Intrinsic Microporosity by Amine Modification

Abstract

Nitrile groups in the polymer of intrinsic microporosity PIM-1 were reduced to primary amines using borane complexes. In adsorption experiments, the novel amine-PIM-1 showed higher CO₂ uptake and higher CO₂/N₂ sorption selectivity than the parent polymer, with very evident dual-mode sorption behavior. In gas permeation with six light gases, the individual contributions of solubility and diffusion to the overall permeability was determined via time-lag analysis. The high CO₂ affinity drastically restricts diffusion at low pressures and lowers CO₂ permeability compared to the parent PIM-1. Furthermore, the size-sieving properties of the polymer are increased, which can be attributed to a higher stiffness of the system arising from hydrogen bonding of the amine groups. Thus, for the H₂/CO₂ gas pair, whereas PIM-1 favors CO₂, amine-PIM-1 shows permselectivity toward H₂, breaking the Robeson 2008 upper bound.