4 azidoaniline hydrochloride

Branched PEI (M_w 25 000), PAA (35 wt%, M_w 100 000), and 4‐azidoaniline hydrochloride were purchased from Sigma‐Aldrich (Shanghai, China). 1‐Ethyl‐3‐(3‐(dimethylamino)propyl)‐carbodiimide hydrochloride (EDC), N‐hydroxysulfosuccinimide sodium salt (NHSS) were from Aladdin (Shanghai, China). Deionized water used in all experiments was obtained through a Milli‐Q water purification system (Millipore, Billerica, America). The pH of various aqueous solutions was adjusted by 1.0 m HCl or 1.0 m NaOH as needed.

The synthetic scheme of N-(4-azidophenyl)methacrylamide is illustrated in Scheme 1, according to a previous procedure [27 (link)]. Briefly, 153.2 mg (0.9 mmol) 4-azidoaniline hydrochloride (Cat. No. 359556, Sigma-Aldrich, St. Louis, MO, USA) and 159 mg (1.5 mmol) sodium carbonate were dissolved in 35 mL of deionized water in the dark. 274.14 mg (1.5 mmol) N-succinimidyl methacrylate (Cat. No. 38862-25-8, Tokyo Chemical Industry, Japan) was dissolved in 3 mL of dioxane and then added to the 4-azidoaniline hydrochloride solution. The mixture was allowed to react at room temperature for 6 h in the dark under constant stirring. The product, N-(4-azidophenyl)methacrylamide (AzMA), was precipitated, filtrated, washed with deionized water, and then dried. The product was identified by ¹H NMR (D-methanol, 500 MHz). The characteristic peaks of the hydrogen in the aromatic ring appear at 7.0 and 7.6 ppm (Supplementary Figure S1).