The detailed synthesis of polyglycerol (PG) as well as its functionalization have been described previously (SI Figure ). Sulfation of dendritic and linear precursor molecules (dPG and lPG) was achieved with sulfamic acid and gave the corresponding polysulfates dPGS and lPGS. For carboxylation, succinic anhydride was added to linear or dendritic PG. All products were purified by dialysis. The degree of sulfation was determined via elemental analysis and the degree of carboxylation by NMR spectroscopy (SI Figure ). Compounds dPGS50 and dPGS100 were prepared as published previously and contained 3.3 % caprolactone units in the polymer backbone.