Dendritic polyamine architectures with lipophilic shells as nanocompartments for polar guest molecules:: A comparative study of their transport behavior

Dendritic core-shell architectures were synthesized by simple melt reactions of polyethylenimine (PEI) with different fatty acids. These systems were investigated towards their ability to encapsulate various guest molecules. Parameters, such as the length of the attached alkyl chain, size of the polymer core, concentration of the core-shell architecture in solution, pH, and nature of the guest molecule were investigated and compared. Guest molecules that bear anionic groups, such as carboxylate, phosphate, sulfonate, or acidic OH groups, as present in phenol units, are readily encapsulated and transferred from the aqueous phase to the organic phase because of multiple anionic-cationic interactions. Hyperbranched polymer architectures exhibit enhanced encapsulation properties when compared with their linear counterparts. In case of the hyperbranched system PEI(25)C16 amide higher transport capacities were observed at lower concentrations of the polymer, for example, 26 guest molecules at 10(-5) mol L-1 versus 143 at 10(-6) mol L-1, Suggesting formation of larger aggregates. The aggregation behavior of these polar nanocompartments were investigated at different concentrations by AFM showing particle aggregates of typically 250 nm at a concentration of 10(-5) M. The individual particle sizes in these aggregates are similar to the particle size at 10(-6) M concentration, typically 4.0-5.5 nm (AFM height). This indicates that aggregate formation takes place at concentrations higher than 10(-8) M and transport might be mediated by small aggregates rather than unimolecular particles. (C) 2007 Wiley Periodicals, Inc.