Hyperbranched polyethylenimines as versatile precursors for the preparation of different type of unimolecular micelles

Hyperbranched polyethylenimine (HPEI) was successfully employed as precursor for the preparation of unimolecular inverted and aqueous micelles. The unimolecular inverted micelles (UlMs) obtained by the amidation of HPEI with 1,1'carbonyidiimidazole (CDI) activated palmitic acid exhibited high encapsulation efficiency for hydrophilic anionic dyes and the efficiency could be enhanced significantly by decreasing the degree of amidation or quaternizing the residual amines. The weight ratio of loaded guests to the amidated HPEls was not dependent on the molecular weight of HPE1 core when the degree of amidation was kept constant. Decreasing the length of the aliphatic chain from 16 to 12 carbons led the hydrophilic anionic dye encapsulation of the resultant UlMs to be less efficient. The amidated linear polyethylenimine (LPEI) analogue had also been prepared for structural comparison. Amidated LPEi could also encapsulate hydrophilic anionic guest molecules, but much inefficiently compared with its hyperbranched analogues. All the UlMs could also encapsulate hydrophilic cationic dye, but those with cationic interior were much more efficient than the others. Unimolecular aqueous micelle was synthesized by the Michael-addition reaction of HPEI with poly(ethylene glycol) methyl ether acrylate. Pyrene was used as the hydrophobic probe for testing its encapsulation behavior and it was found that the encapsulated pyrene molecules not only spread in the HPEI core, but also in the poly(ethylene glycol) shell. The pyrene molecules in the poly(ethylene glycol) shell could be released by the addition of NaCl. (c) 2007 Elsevier Ltd. All rights reserved.