(659d) Investigating Facilitated Transport Membranes for CO2 Separations Using Tunable Polymer Films

Polymer membranes represent a promising avenue for energy-efficient CO₂ separations due to their compact size, cost-effectiveness, and intrinsic energy efficiency. However, traditional polymer membranes exhibit a fundamental trade-off between CO₂ permeability and selectivity as outlined by the Robeson upper bound. Facilitated transport membranes (FTMs) offer a potential solution. These membranes leverage specific functional groups, typically amines, integrated into a polymer matrix to enhance CO₂ diffusion relative to other gases. However, limitations with conventional synthetic methods hinder development of systematic structure-property relationships for crucial parameters like amine grafting density, amine basicity, and crosslinking density.

This study aims to unravel the molecular mechanisms governing facilitated transport by harnessing precise synthetic control over polymer structure. Leveraging polymer post-functionalization strategies employing active ester "click" chemistry provides avenues to fabricate well controlled, molecularly-tunable polymer membranes. These networks serve as scaffolds for subsequent functionalization with various types of CO₂-philic Lewis base ligands while maintaining constant crosslinking and amine density. We have systematically examined the gas permeation, sorption, and diffusion properties of a diverse array of co-polymer networks containing both poly(ethylene glycol) and Lewis base functional groups. We have observed a decrease in CO₂ and N₂ diffusivity with an increase in ligand density due to a decrease in chain mobility. We also observed that a decrease in Lewis basicity results in an increase in CO₂ diffusivity relative to that of N₂. Membranes functionalized with pyridine groups surpass the 2008 Robeson upper bound for CO₂/N₂ separation. Moving forward, this versatile synthetic platform will continue to enable us to develop fundamental structure-property design principles for FTMs capable of efficiently separating CO₂ mixtures.