Successful reaction coupling was confirmed by FT-IR spectroscopy (Figure ) and final modified PEI products were characterized by 1D-NMR ( 1 H) and 2D-NMR (HSQC, HMBC). For NMR analysis, 6.5 mg of the lyophilized polymer was dissolved in 0.65 mL D2O, and NMR spectra were recorded using a 400 MHz Bruker Avance NEO spectrometer equipped with a smart probe.