The synthesis of amphiphilic macromolecules by amidation of hyperbranched polyethylenimine was studied. Amidation with palmitic acid or the methyl ester proceeds up to 84% degree of amidation (140 degrees C, vacuum). The primary amine end groups react preferentially. With carbonyldiimidazole (CDI)-activated acids nearly complete conversion of all primary amine end groups and secondary amine linear units can be achieved; with a corresponding limited amount of CDI the end groups can be amidated selectively. The products of these reactions are free of any unreacted carboxylic acid or other impurities (H-1 and C-13 NMR) and can be optionally purified by pressure ultrafiltration washing with a toluene/amine solution. Side-chain crystallization is observed (DSC), which can be supressed entirely employing branched alkyl moieties (2-hexyldecanoic acid as amidating agent). Solution structures were studied by SANS. In C6D6 radii of gyration of 2-5 nm (Guinier analysis) were observed for samples differing in PEI core molecular weight. These sizes and their observed independence of concentration in the range of 5-40 g L-1 indicate the presence of nonaggregated unimolecular inverted micelles.