Synthesis of well‐defined PNIPAM‐<i>b</i>‐(PEA‐<i>g</i>‐P2VP) double hydrophilic graft copolymer via sequential SET‐LRP and ATRP and its “schizophrenic” Micellization behavior in aqueous media

Abstract

Abstract A series of well‐defined double hydrophilic graft copolymers, consisting of poly( N ‐isopropylacrylamide)‐ b ‐poly(ethyl acrylate) backbone and poly(2‐vinylpyridine) side chains, were synthesized by successive single‐electron‐transfer living radical polymerization (SET‐LRP) and atom transfer radical polymerization (ATRP). The backbone was prepared by sequential SET‐LRP of N ‐isopropylacrylamide and 2‐hydroxyethyl acrylate at 25 °C using CuCl/tris(2‐(dimethylamino)ethyl)amine as the catalytic system. The obtained diblock copolymer was transformed into the macroinitiator by reacting with 2‐chloropropionyl chloride. Next, grafting‐from strategy was used for the synthesis of poly( N ‐isopropylacrylamide)‐ b ‐[poly(ethyl acrylate)‐ g ‐poly(2‐vinylpyridine)] double hydrophilic graft copolymer. ATRP of 2‐vinylpyridine was initiated by the macroinitiator at 25 °C using CuCl/hexamethyldiethylenetriamine as the catalytic system. The synthesis of both the backbone and the side chains are controllable. Thermo‐ and pH‐responsive schizophrenic micellization behaviors were investigated by 1 H NMR, fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. Unimolecular micelles with PNIPAM‐core formed in acidic environment (pH = 2) with elevated temperature ( T ≥ 32 °C), whereas the aggregates turned into spheres with PEA‐ g ‐P2VP‐core accompanied with the lifting of pH values (pH ≥ 5.3) at room temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 15–23, 2010