Cooperative Binding of Nonionic Surfactant to Hydrophobically Modified Polyanions as Studied by Frontal Analysis Continuous Capillary Electrophoresis

The binding of a nonionic surfactant, Triton X-100 (TX), to amphiphilic copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate and N-dodecylmethacrylamide (C12) (p(A/C12(x)), where x denotes the mol % content of C12) was investigated by frontal analysis continuous capillary electrophoresis (FACCE) combined with dynamic light scattering focusing on the effect of the hydrophobe content on the binding in a wide range of x (5−60 mol %). From binding isotherms obtained from FACCE data, the binding was found to be cooperative in the whole range of x. Furthermore, a significant change in the binding behavior, i.e., cooperativity, was found to occur in a relatively narrow range of x (38−50 mol %), which is attributable to a change in the self-association behavior of p(A/C12(x)) in this x range

Synthesis of Oppositely Charged Block Copolymers of Poly(ethylene glycol) via Reversible Addition−Fragmentation Chain Transfer Radical Polymerization and Characterization of Their Polyion Complex Micelles in Water

Diblock copolymers consisting of a water-soluble nonionic block and either an anionic or cationic block were prepared from sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) or (3-(methacryloylamino)propyl)trimethylammonium chloride (MAPTAC) via reversible addition−fragmentation chain transfer (RAFT)-controlled radical polymerization using poly(ethylene glycol) (PEG)-based chain transfer agent (PEG-CTA) in water. The RAFT polymerization proceeded in a living fashion, as suggested by the observation that the number-average molecular weight (Mn) increased linearly with the monomer conversion (up to conversions of 30% for MAPTAC and 50% for AMPS), whereas the polydispersity (Mw/Mn) remained nearly constant (Mw/Mn b-PAMPS and PEG-b-PMAPTAC, led to the spontaneous formation of polyion complex (PIC) micelles. The PIC micelles were characterized by 1H NMR spin−spin relaxation time, static light scattering (SLS), dynamic light scattering (DLS), and scanning electron microscopy (SEM) techniques. The hydrodynamic size of the micelle depended on the mixing ratio of PEG-b-PAMPS and PEG-b-PMAPTAC with the size maximizing at the mixing ratio of stoichiometric charge neutralization. The mixing of the oppositely charged diblock copolymers with shorter charged blocks formed a core−shell PIC micelle. In contrast, a complicated aggregate was formed from a pair of longer blocks. The exact structure of the aggregate is still an open question, but it is speculated to be a multicore intermicellar aggregate on the basis of various characterization data

Synthesis of Amphiphilic Block Copolymers of 4-Substituted Styrene and Cyclohexene Oxide Utilizing Radical/Cation Transformation Polymerization

Synthesis of Amphiphilic Block Copolymers of 4-Substituted Styrene and Cyclohexene Oxide Utilizing Radical/Cation Transformation Polymerizatio

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

Flower Micelle of Amphiphilic Random Copolymers in Aqueous Media

The structure of the flower micelle formed by an amphiphilic random copolymer, sodium (2-acrylamido)-2-methylpropanesulfonate and N-dodecylmethacrylamide p(AMPS/C12), in 0.05 M aqueous NaCl was investigated by fully atomistic molecular dynamics simulation as well as by light scattering, and the results were compared with the flower micelle model of the minimum loop size, recently proposed by Kawata et al. [Macromolecules 2007, 40, 1174−1180]. After a sufficiently long simulation time, simulated p(AMPS/C12) chain with the degree of polymerization of 200 and C12 content of 50 mol % formed a unicore micelle, of which radius of gyration was much smaller than the AMPS homopolymer with the same degree of polymerization. The simulated micellar structure was analyzed in terms of density distribution functions for dodecyl groups, the main chain, and sulfonate groups as functions of the radial distance r from the center of mass of dodecyl groups. Only dodecyl groups exist at r ≲ 1.5 nm, and the main chain and sulfonate groups distribute in the range of r between 1.5 and 3.5 nm, but there were dodecyl groups coexisting with the main chain and sulfonate groups beyond r = 1.5 nm. All these structural features, as well as hydrodynamic radius data for p(AMPS/C12) with C12 contents higher than ca. 20 mol % obtained by light scattering, agreed with the predictions of the flower micelle model of the minimum loop size

Adenine Molecularly Imprinted Polymer-Coated Submicrometer Silica Gel Particles

Adenine molecularly imprinted material was obtained. Well-defined silica gel particles of submicrometer size were coated with ultrathin polymeric layers, first with a polycationic poly(allylamine hydrochloride) layer that acted as a binder for the second outer layer of a photo-cross-linkable thymine-containing polyanion. Adenine template was adsorbed by the complementary thymine chromophores attached to the polymer and its imprints were created by photo-cross-linking of the outer polymer layer. The imprinted particles have shown the ability to recognize adenine and adenosine, an adenine-based nucleoside, whereas no imprinting effect was observed for purine

Molecularly Imprinted Hybrid Adsorbents for Adenine and Adenosine-5′-triphosphate

Submicrometer-sized silica gel particles were coated with a polyanion and a polycation bearing thymine chromophores. The polymer-coated particles were found to selectively adsorb adenine and adenosine-5′-triphosphate (ATP), as compared to other nucleobases and nucleotides, respectively. The adsorption was enhanced by the irradiation of the particles in the presence of adenine which resulted in the molecular imprinting of adenine. ATP adsorption was strongly pH-dependent

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

Salt Effect on the Heat-Induced Association Behavior of Gold Nanoparticles Coated with Poly(<i>N</i>-isopropylacrylamide) Prepared via Reversible Addition−Fragmentation Chain Transfer (RAFT) Radical Polymerization

Poly(N-isopropylacrylamide) (PNIPAM) with a narrow molecular weight distribution was prepared by reversible addition−fragmentation chain transfer (RAFT) radical polymerization. A dithioester group at the chain end of PNIPAM thus prepared was cleaved by treating with 2-ethanolamine to provide thiol-terminated PNIPAM with which gold nanoparticles were coated via reactions of the terminal thiol with gold. The thermoresponsive nature of the maximum wavelength of the surface plasmon band and hydrodynamic radius (Rh) for the PNIPAM-coated gold nanoparticles were found to be sensitively affected by added salt. In pure water, Rh for the PNIPAM-coated gold nanoparticles at 40 °C (>lower critical solution temperature (LCST)) was smaller than that at 25 °C (Rh for the PNIPAM-coated gold nanoparticles at 40 °C was significantly larger than that at 25 °C. Heat-induced association and dissociation for the PNIPAM-coated gold nanoparticles were completely reversible in 50 mM NaCl aqueous solutions, which is responsible for the reversible thermoresponsive color change