Micelles Possessing Mixed Cores and Thermoresponsive Shells Fabricated from Well-Defined Amphiphilic ABC Miktoarm Star Terpolymers

Amphiphilic ABC miktoarm star terpolymers consisting of polystyrene, poly(epsilon-caprolactone), and poly(N-isopropylacrylamide) arms, PS(-b-PNIPAM)-b-PCL, were synthesized via a combination of atom transfer radical polymerization, ring-opening polymerization (ROP), and click chemistry. Difunctional PS bearing an alkynyl and a primary hydroxyl moiety at the chain end, PS-alknyl-OH, was prepared by reacting azido-terminated PS with an excess of 3,5-bis(propargyloxy)benzyl alcohol (BPBA) under click conditions. The subsequent ROP of epsilon-caprolactone using PS-alknyl-OH macroinitiator afforded PS(-alkynyl)-b-PCL copolymer bearing an alkynyl moiety at the diblock junction point. Target PS(-b-PNIPAM)-b-PCL amphiphilic ABC miktoarm star terpolymers were then prepared via click reaction between PS(-alkynyl)-b-PCL and an excess of azido-terminated PNIPAM (PNIPAM-N-3). The removal of excess PNIPAM-N-3 was accomplished by clicking onto alkynyl-functionalized Wang resin. All the intermediate and final products were characterized by gel permeation chromatography, H-1 NMR, and FTIR. In aqueous solution, the obtained amphiphilic ABC miktoarm star terpolymer self-assembles into micelles possessing mixed PS/PCL cores and thermoresponsive shells, which were further characterized by dynamic laser light scattering and transmission electron microscopy. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1636-1650, 2009