Unimolecular micelles and globular amphiphiles: dendritic macromolecules as novel recyclable solubilization agents

Abstract

The synthesis of dendritic polyether macromolecules based on a 3, 5-dihydroxybenzyl alcohol building block and having carboxylate groups as chain-ends is described. These novel macromolecules behave as unimolecular micelles and their ability to solvate hydrophobic molecules has been investigated by UV–VIS spectroscopy. A dramatic increase in the saturation concentration of various polycyclic aromatic compounds in water was observed which was of a magnitude similar to that observed for micelles derived from sodium dodecyl sulfate. A relationship between the solubilizing power of the dendrimer and the electron density of the polycyclic aromatic was found. A linear relationship between the solubilizing ability and the concentration of the dendrimer, even at concentrations as low as 5 × 10^–7 mol dm^–3, indicates that these materials do not have a critical micelle concentration. Increases in the ionic strength of an aqueous solution of the dendrimer caused an increase in the saturation concentration of the hydrophobic molecules. A recyclable solubilization and extraction system is discussed. The synthesis of a globular dendritic macromolecular amphiphile designed to reside at the interface of an organic solvent and water is also described. This ‘hybrid’ dendritic amphiphile consisting of two distinct sectors, one hydrophilic and the other hydrophobic is prepared by stepwise alkylation of a core molecule, 4,4′-dihydroxybiphenyl with the two dissimilar dendritic fragments.