Preparation and Characterization of a pH-Responsive Nanogel Based on a Photo-Cross-Linked Micelle Formed From Block Copolymers with Controlled Structure

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 (Rh) increases abruptly near pH 7, indicative of the micelle formation at pH > 7. The micelle formation at pH > 7 was supported by 1H 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 (Cp) lower than the critical micelle concentration (cmc) for PEG-b-P(DEAEMA/CEA) because the nanogel retains its micellar structure at Cp < 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

Thermo-Responsive Diblock Copolymers of Poly(<i>N</i>-isopropylacrylamide) and Poly(<i>N</i>-vinyl-2-pyrroridone) Synthesized via Organotellurium-Mediated Controlled Radical Polymerization (TERP)

Diblock copolymers of poly(N-isopropylacrylamide) (PNIPAM) and poly(N-vinyl-2-pyrrolidone) (PNVP) (PNIPAMm-b-PNVPn) with well-defined block lengths were successfully synthesized by organotellurium-mediated controlled radical polymerization (TERP) based on the finding that the homopolymerization of N-vinyl-2-pyrrolidone was better-controlled by TERP than by macromolecular architecture designed by interchange of xanthates (MADIX), TERP resulting in a narrower molecular weight distribution of PNVP. Heat-induced association properties in water of three block copolymers with different block lengths, PNIPAM110-b-PNVP53, PNIPAM110-b-PNVP234, and PNIPAM76-b-PNVP219, were characterized by 1H NMR, turbidity, quasi-elastic light scattering (QELS), and static light scattering (SLS) techniques. All three block copolymers dissolve in water molecularly (as a unimer state) when the solution temperature is below an aggregation temperature (Ta) that is near a lower critical solution temperature (LCST) for the PNIPAM block. Comparing Ta between the two block copolymers of the same the PNIPAM block lengths (DPn = 110), the diblock copolymer with a shorter PNVP block length tend to associate at a lower temperature. On the other hand, the association occurred at a higher temperature for the diblock copolymers with shorter PNIPAM block lengths. When the temperature was raised above Ta, PNIPAM110-b-PNVP234 and PNIPAM76-b-PNVP219 formed apparently spherical core−corona micelles with aggregation numbers (Nagg) of 808 and 298, respectively at 60 °C. In contrast, PNIPAM110-b-PNVP53 formed a much larger aggregate with Nagg = 27 000. This aggregate was speculated to be a multi core aggregate formed by the association of individual core−corona micelles. The copolymers were found to be bound to gold nanoparticles in water through coordination interaction of the PNVP block with Au. The polymer coated gold nanoparticles indicated a temperature-dependent color change arising from a shift of the maximum wavelength of the plasomon band