Synthesis and characterization of PNIPAM‐b‐(PEA‐g‐PDEA) double hydrophilic graft copolymer

Abstract

A series of well-defined double hydrophilic graft copolymers, consisting of poly(N-isopropylacrylamide)-b-poly(ethyl acrylate) (PNIPAM-b-PEA) backbone and poly(2-(diethylamino)ethyl methacrylate) (PDEA) side chains, were synthesized by successive atom transfer radical polymerization (ATRP). The backbone was firstly prepared by sequential ATRP of N-isopropylacrylamide and 2-hydroxyethyl acrylate at 25 °C using CuCl/tris(2-(dimethylamino)ethyl)amine as catalytic system. The obtained diblock copolymer was transformed into macroinitiator by reacting with 2-chloropropionyl chloride. Next, grafting-from strategy was employed for the synthesis of poly(N-isopropylacrylamide )-b-[poly(ethyl acrylate)-g-poly(2-(diethylamino)ethyl methacrylate)] (PNIPAM-b-(PEA-g-PDEA)) double hydrophilic graft copolymer. ATRP of 2-(diethylamino)ethyl methacrylate was initiated by the macroinitiator at 40 °C using CuCl/hexamethyldiethylenetriamine as catalytic system. The molecular weight distributions of double hydrophilic graft copolymers kept narrow. Thermo- and pH-responsive micellization behaviors were investigated by fluorescence spectroscopy, 1 H NMR, dynamic light scattering, and transmission electron microscopy. Unimolecular micelles with PNIPAM-core formed in acidic environment (pH = 2) with elevated temperature (≥32 °C); whereas, the aggregates turned into vesicles in basic surroundings (pH >7.2) at room temperature.