The amount of adduct in the amine solution can be used to control the extent of functionalization and final properties of the sample, illustrated in Fig. . The CO2 uptakes were measured gravimetrically using a temperature swing adsorption process (adsorption: 30°C, 400 ppm CO2 in He; regeneration: 110°C, He), and the CO2 heats of adsorption were measured in a thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) system under 400 ppm. As expected, unmodified PEI/SBA-15 exhibited the highest CO2 uptake (1.2 mmol/g) and heat of sorption (-80 kJ/mol); these measurements are consistent with previous literature. Quantitative liquid-phase C NMR (Fig. ) was used to characterize the amine state distributions in the unmodified and modified PEIs. As the amount of adduct in solution and subsequent functionalization increases, the proportion of primary amines in the sample decreases, while secondary and tertiary amines increase. According to the quantitative analysis, the unmodified PEI possesses a primary: secondary: tertiary amine ratio of 36:38:26, respectively. After the functionalization with methyl, propyl, and 2-hydroxypropyl groups, the proportion of primary amines gradually decreased, while the proportions of secondary and tertiary amines increased.