Thermo- and pH-Responsive Nanogel Particles Bearing Secondary Amine Functionalities for Reversible Carbon Dioxide Capture and Release

We report the synthesis of temperature- and pH-responsive nanogel particles (NPs) consisting of N-isopropylacrylamide (NIPAM) and N-(2,2,6,6-tetramethylpiperidin-4-yl)methacrylamide (TMPMA). NPs can reversibly capture and release carbon dioxide via temperature-induced volume phase transition and changes in pH. These stimuli-responsive particles contain sterically hindered secondary amine functionalities and exhibit a volume phase transition temperature (VPTT) in aqueous solution. The fully reversible VPTT behavior involves a precise shrinkage to 40% of the initial particle size along with a large change in pH from 10.25 to 7.65 upon increasing temperature. We could reversibly release 35 mL (1.4 mmol) of CO2 per gram of polymer in very short heating times, thereby significantly increasing the amount of CO2 with respect to the regeneration time. This behavior could be repeated for various cycles at moderate temperatures (85 °C).