Climate change has attracted immense quantitative attention in 2016, marking an unprecedented high of 403.3 ppm in CO₂ levels, continuing to grow to 414.72 ppm despite the economic slump caused due to the Covid pandemic. These findings have placed academic, industrial, federal, and community focus on designing Direct Air Capture (DAC) carbon-negative processes. Polysulfones are a class of rigid glassy polymers that proffer the desirable structural integrity required for membrane-based gas separations. Further, intrinsically, the sulfonyl groups form Lewis acid/base pairs, while the aromatic content interacts strongly with carbon dioxide through pi-pi interactions. This study envisions making a new mark in sustainability by designing novel polysulfones doped with imine linkages that are not only capable of reversible direct air capture but can be chemically depolymerized upon exposure to specific reaction triggers. To enable a recyclable design, the polymer chain is seeded with reactive moieties (imine linkages) nicknamed Trojan Horse Units (THUs) that serve as a toggle for switching between CO₂ sequestration while in its functional life and initiating depolymerization nearing the end of life. A series of telechelic polysulfone oligomers end-capped with bioderived aldehydes are coupled by leveraging Schiff base chemistry for achieving high molecular weight, thus enabling processability and tunability of performance characteristics. The chemical modification of the conventional polysulfone backbone with imine linkages instills a reversible CO₂ sorption modality to promote DAC of CO₂ from atmospheric air in dry conditions that can later be released by exposure to temperature and moisture swings. These imines also can be reversibly hydrolyzed under mildly acidic conditions, thus ensuring recyclability in design.

Lisa Stanley

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