Synthesis and Aggregation Behaviors of Nonlinear Multiresponsive, Multihydrophilic Block Copolymers

The well-defined nonlinear multiresponsive, multihydrophilic block copolymers (MHBCs), poly(N-isopropylacrylamide)2−[poly(N-vinylpyrrolidone)-b-poly(acrylic acid)]2 ((PNIPAAM)2(PNVP-b-PAA)2) and poly[N-isopropylacrylamide-b-(acrylic acid)]2−poly(N-vinylpyrrolidone)2 ((PNIPAAM-b-PAA)2(PNVP)2), 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 1H 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.