α-Bromoisobutyryl bromide (1.28 mL, 11. 85 mmol) was added dropwise to a solution of [PEO55-NH2]4 (3 g, 3 mmol) and trimethylamine (TEA, 1.68 mL, 2.5 mmol) in DCM (120 mL) at 0 °C. Afterwards, the solution was stirred for 72 h at room temperature. The resulting solvent mixture was extracted once each with saturated sodium bicarbonate, deionized water, saturated saline solution. The organic phase dried over MgSO4. After evaporation of the DCM, the concentrated solution was precipitated twice into cold diethyl ether. The white precipitate was dried under vacuum (2 g, 1.9 mmol, 62 % yield).