In situ azetidine polymerization elevates the performance of commercial polymer resin sorbents in carbon dioxide capture.

Commercial, amine-containing porous polymer resins are popular sorbents for CO2 removal from air, otherwise known as direct air capture (DAC). However, their limited amine density and poor oxidative stability constrain performance. Herein, we introduce a simple one-step method to add additional amine groups onto a commercial resin, such as Lewatit VP OC 1065, by grafting branched poly(propyleneimine) oligomers via in situ acid-catalyzed ring-opening polymerization of azetidine. This "grafting-from" modification strategy enhances the CO2 capacity by >1.4-fold compared to pristine resin, reaching 1.54 and 3.34 mmol⋅g-1 under dry DAC (400 ppm CO2, 30°C) and flue-gas (15% CO2, 40°C) conditions, respectively. Under humid DAC conditions, the capacity reaches ∼2.5 mmol⋅g-1 at 25°C and further increases to ∼3.0 mmol⋅g-1 at -5°C. The optimal sample shows enhanced oxidation resistance under air and maintains improved cycling stability over 150 adsorption-desorption cycles under simulated flue-gas conditions. Overall, this work demonstrates a scalable, versatile strategy to upgrade commercial materials into more efficient and durable sorbents for carbon capture.