Synthesis and Aggregation Behaviors of Nonlinear Multiresponsive, Multihydrophilic Block Copolymers

The well-defined nonlinear multiresponsive, multihydrophilic block copolymers (MHBCs), poly(<i>N</i>-isopropylacrylamide)<sub>2</sub>−[poly(<i>N</i>-vinylpyrrolidone)-<i>b</i>-poly(acrylic acid)]<sub>2</sub> ((PNIPAAM)<sub>2</sub>(PNVP-<i>b</i>-PAA)<sub>2</sub>) and poly[<i>N</i>-isopropylacrylamide-<i>b</i>-(acrylic acid)]<sub>2</sub>−poly(<i>N</i>-vinylpyrrolidone)<sub>2</sub> ((PNIPAAM-<i>b</i>-PAA)<sub>2</sub>(PNVP)<sub>2</sub>), were successfully synthesized via a combination of single-electron transfer living radical polymerization (SET-LRP) and reversible addition−fragmentation chain transfer (RAFT) polymerization techniques. All the final miktoarm star block copolymers were characterized by GPC and <sup>1</sup>H NMR spectra. Interestingly, the hydrogen bonding interactions have a great effect on the water solubility of PAA chains, and the nonlinear MHBCs solutions showed sharp phase separation at pH = 7.0. The novel water-soluble nonlinear MHBCs consisting of pH-responsive PAA segments, thermoresponsive PNIPAAM segments, and hydrophilic, noncharged and biocompatible PNVP segments tend to self-assemble into three different types of micellar aggregates and umimers, which can be reversibly controlled by pH value and temperature of aqueous solution of these copolymers.