(592c) Quaternary Ammonium Functionalized Poly(arylene ether sulfone) Copolymers for Direct Air Capture

Unprecedented rise in atmospheric CO₂ levels has amplified Earth’s greenhouse gas effects and significantly contributed to global warming. Direct air capture (DAC) has the potential to develop into an important tool to keep below the critical temperature rise threshold of 1.5 °C reported in the latest Intergovernmental Panel on Climate Change (IPCC). The moisture swing process is advantageous for DAC because it has low energy requirements. In this study, novel quaternary ammonium functionalized poly(arylene ether sulfone) polymers with bicarbonate (HCO₃^-) counterions with various ion exchange capacities (IEC) are synthesized for direct air capture by the moisture swing process. The backbone of the polymer is allyl modified poly(arylene ether sulfone) copolymer (PAES-co-APAES) synthesized by step growth polymerization, and quaternary ammonium group is added to the backbone through post-polymerization functionalization to make PAES-co-QAPAES[HCO₃^-] random copolymers. Size exclusion chromatography (SEC) is utilized to measure the molecular weight of the novel polymers and the chemical structure and IEC is analyzed through nuclear magnetic resonance (¹H NMR) spectroscopy. Thermogravimetric analysis (TGA) showed good thermal stability with 5% degradation temperature (T_d5%) above 240 °C. Experimental data show stable atmospheric CO₂ capture and release response with changes in humidity from 8 (30% RH) to 25 ppt (95% RH) at 22 °C for six consecutive cycles.