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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 …