Poly(ethylene glycol)-b-poly(2-(diethylamino)ethyl methacrylate-co-2-cinnamoyloxyethyl acrylate) (PEG-b-P(DEAEMA/CEA)) was prepared by reversible addition-fragmentation chain transfer (RAFT)-controlled radical polymerization. As solution pH is increased from an acidic pH, the hydrodynamic radius (R(h)) increases abruptly near pH 7, indicative of the micelle formation at pH > 7. The micelle formation at pH > 7 was supported by (1)H NMR and light scattering data. Upon irradiation of light, polymer chains in the core of the polymer micelle are cross-linked as a result of the photodimerization of the cinnamoyl groups, yielding a nanogel. The nanogel was characterized by gel-permeation chromatography (GPC), light scattering, small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and fluorescence techniques. The nanogel displayed an ability to solubilize N-phenyl-1-naphthylamine (PNA) and 1-pyrenemethanol (hydrophobic guest molecules) into the hydrophobic core at pH > 7. It was confirmed with PNA that the solubilization of a guest molecule occurred at polymer concentrations (C(p)) lower than the critical micelle concentration (cmc) for PEG-b-P(DEAEMA/CEA) because the nanogel retains its micellar structure at C(p) < cmc. 1-Pyrenemethanol is strongly captured by the nanogel at pH 10, whereas it is easily released from the nanogel when pH is reduced to 3. This indicates that the hydrophobicity of the core of the nanogel can be modulated by a change in the degree of protonation of the DEAEMA units in the core, and thus the capture of a guest molecule and its release can be controlled by a change in solution pH.

Poly(sodium styrenesulfonate)-block-poly(acrylic acid) (PNaSS-b-PAA) and poly(sodium styrenesulfonate)-block-poly(N-isopropylacrylamide) (PNaSS-b-PNIPAM) were prepared via reversible addition-fragmentation chain transfer (RAFT) radical polymerization using a PNaSS-based macro-chain transfer agent. The molecular weight distributions (M w /M n ) of PNaSS-b-PAA and PNaSS-b-PNIPAM were 1.18 and 1.39, respectively, suggesting that these polymers have controlled structures. When aqueous solutions of PNaSS-b-PAA and PNaSS-b-PNIPAM were mixed under acidic conditions, water-soluble PNaSS-b-PAA/PNaSS-b-PNIPAM complexes were formed as a result of hydrogen bonding interactions between the pendant carboxylic acids in the PAA block and the pendant amide groups in the PNIPAM block. The complex was characterized by 1 H NMR, dynamic light scattering, static light scattering, and transmission electron microscope measurements. The light scattering intensity of the complex depended on the mixing ratio of PNaSS-b-PAA and PNaSS-b-PNIPAM. When the molar ratio of the N-isopropylacrylamide (NIPAM) and acrylic acid (AA) units was near unity, the light scattering intensity reached a maximum, indicating stoichiometric complex formation. The complex dissociated at a pH higher than 4.0 because the hydrogen bonding interactions disappeared due to deprotonation of the pendant carboxylic acids in the PAA block.

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