Synthesis of Well-Defined PNIPAM-b-(PEA-g-P2VP) Double Hydrophilic Graft Copolymer via Sequential SET-LRP and ATRP and Its 'Schizophrenic' Micellization Behavior in Aqueous Media

摘要

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 degrees 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 degrees 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 H-1 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 degrees 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.