Functionalization of PEI with hydrophobic groups (such as methyl, propyl) was carried out by a simple single-step addition reaction with alkyl halides under refluxing conditions (Schemes S1-S2). In comparison, the functionalization of PEI with 1,2 epoxypropane was carried out in ambient conditions (Scheme S3). This ambient temperature is attributed to the high reactivity of epoxides with nucleophilic amines. Controlled amounts of adducts were added dropwise to methanolic solutions of PEI (MW 800, nitrogen content: 18 mmol g-1) under stirring. The modified PEI sorbents are denoted as n-x-PEI, where "x" denotes the functional group such as methyl (M), propyl (P) and 2-hydroxypropyl (HP) and "n" denotes the molar ratio of the functional reagent (e.g., 1,2-epoxypropane) to total moles of nitrogen in PEI. Total moles of nitrogen includes the nitrogen in primary, secondary, and tertiary amines.