SBA-15 was impregnated with modified PEIs by wet impregnation. First, SBA-15 was dried overnight under vacuum (<20 mTorr) at 110 °C. The desired amount of PEI was dissolved in 15 mL methanol and added to the desired amount of SBA-15. The mixture was allowed to stir at room temperature for at least 6 h. Methanol was removed by rotary evaporation at room temperature. The resulting powder was dried overnight under vacuum (<20 mTorr) at room temperature. The resulting dried powder composites were stored in ambient lab conditions. The composites were characterized using quantitative C NMR spectroscopy, N2 physisorption, gravimetric CO2 adsorption, and differential scanning calorimetry. More details on the synthesis procedures and characterization procedures are provided in section S6 in the SI.