The hydrophilic tetra-PEG-based 5 was synthesized using commercially available monodisperse tetra-PEG-OH with a molar mass of 10 kg mol -1 . After removal of low molecular weight fractions, the terminal hydroxy groups of tetra-PEG-OH were reacted first with mesyl chloride to give 4 and then with ammonia to yield amino-terminated tetra-PEG 5 (see Scheme 2b). Comparison of the 1 H NMR spectra of 1 and 3 as well as tetra-PEG-OH, 4 and 5 showed that the respective end group modification occurred quantitatively. The molar masses of 3 and 5 (see Table ) were determined by H NMR end group analysis (see SI Figure and S2) and SEC. There is a very good correlation between the number-average molar masses determined by NMR spectroscopy and SEC.