Unimolecular Micelle Derived from Hyperbranched Polyethylenimine with Well-Defined Hybrid Shell of Poly(ethylene oxide) and Polystyrene: A Versatile Nanocapsule

The synthesis and properties of a macromolecular nanocapsule derived from hyperbranched polyethylenimine (HPEI) with well-defined hybrid shell of poly(ethylene oxide) monomethyl ether (mPEO) and polystyrene (PS) are described. HPEI is treated in sequence with 4-glycidol-2,2,6,6-tetrametyl-piperidin-1-oxyl, succinic anhydride, mPEO, leading to a HPEI derivative compatible with nitroxide-mediated living radical polymerization of styrene, thus a macromolecular nanocapsule, HPEI@PEO/PS, is available with a well-defined and tunable hybrid shell of PEO and PS. Within certain PEO/PS ratio, the nanocapsule is soluble in a number of organic solvents as well as in water. The nanocapsule exists as three layer onion-like particle (HPEI@PS@PEO) in water, whereas in chloroform it exists as a hybrid shell particle (HPEI@PEO/PS), and the particles generally exist in the form of unimolecular micelle. In a biphasic water/chloroform mixture, the nanocapsule can transfer anionic, water-soluble guest from an aqueous phase to the chloroform phase; while when dissolved in water, the nanocapsule can efficiently capture both ionic and apolar solutes. Release of the guest can occur under the stimulus of pH or the switch of medium. This is the first example of a unimolecular micelle that can simultaneously deliver both polar and apolar guests. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 681-691, 2010