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ABSTRACT: We synthesized and characterized polystyrene brushes on a silicon wafer using surface-initiated atom transfer radical polymerization. The thickness of the polymer brush was controlled by adjusting the reaction time. We investigated monomer conversion as well as the molecular weight and density of the polymer brushes. When the monomer conversion reached 100%, the number-average molecular weight and film thickness reached 135,000 and 113 nm, respectively. The estimated densities of the synthesized polystyrene brushes were in the range 0.34-0.54 chains/nm2, high enough to be categorized in the "concentrated brush" regime. The synthesized polymer brush was used as an insulating layer in an organic thin-film transistor. Organic thin-film transistors were fabricated using pentacene as an active p-type organic semiconductor and a polystyrene brush on a SiO2 layer as a gate dielectric. The pentacene based organic thin-film transistor with the polystyrene brush exhibited a field-effect mobility microFET of 0.099 cm2/(V x s).
Journal of Nanoscience and Nanotechnology 05/2012; 12(5):4137-41. · 1.56 Impact Factor
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ABSTRACT: The physiological properties of polymer brush-afforded silica particles prepared by surface-initiated living radical polymerization were investigated in terms of the circulation lifetime in the blood and distribution in tissues. Hydrophilic polymers consisting mainly of poly(poly(ethylene glycol) methyl ether methacrylate) were grafted onto silica particles by surface-initiated atom transfer radical polymerization that was mediated by a copper complex to produce hairy hybrid particles. A series of hybrid particles was synthesized by varying the diameter of the silica core and the chain length of the polymer brush to examine the relationship between their physicochemical and physiological properties. The hybrid particles were injected intravenously into mice to investigate systematically their blood clearance and body distribution. It was revealed that the structural features of the hybrid particles significantly affected their in vivo pharmacokinetics. Some hybrid particles exhibited an excellently prolonged circulation lifetime in the blood with a half life of ∼20 h. When such hybrid particles were injected intravenously into a tumor-bearing mouse, they preferentially accumulated in tumor tissue. The tumor-targeted delivery was optically visualized using hybrid particles grafted with fluorescence-labeled polymer brushes.
Biomacromolecules 02/2012; 13(3):927-36. · 5.48 Impact Factor
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Advanced Materials 09/2011; 23(42):4868-72. · 13.88 Impact Factor
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09/2011: pages 1137 - 1178; , ISBN: 9783527631421
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ABSTRACT: The lubrication mechanism of concentrated polymer brushes (CPBs) exhibiting ultralow frictional property was investigated. The frictional force and hence the frictional coefficient μ between CPBs of polystyrene (PS) were measured as a function of shear velocity υ and degree of swelling. The degree of swelling was precisely controlled by varying the composition of solvent , which consisted of a mixture of toluene (good solvent for PS) and 2-propanol (nonsolvent for PS), from the brush highly stretched state (toluene rich) to glassy state (2-propanol rich). The μ data of the mixtures revealed two lubrication mechanisms, i.e., boundary and hydrodynamic lubrication. Boundary lubrication with μ values less dependent on shear velocity was observed both in ultralow (μ on the order of 10–4) and high frictional (μ on the order of 0.1) regimes. On the other hand, hydrodynamic lubrication was well described by the relation μ = β·υα with α having an almost constant value of ca. 0.7. It was found that parameter β depended on the solvent composition and was scaled by the degree of swelling. It should be noted that the confronted polymer brushes interacted with each other even in this regime. Thus, CPBs in solvents may be employed as an efficient lubricating layer due to their unique features.
05/2011;
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ABSTRACT: Main mesomorphic properties of cellulose and cello- and chito-oligosaccharide derivatives are overviewed, and their structuring principles are briefly discussed with some new analyses incorporated.
Macromolecular Symposia 03/2011; 99(1):257 - 267.
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Shinpei Yamamoto,
Gallage Ruwan,
Yoshinori Tamada,
Kaori Kohara,
Yoshihiro Kusano,
Tatsuya Sasano,
Kohji Ohno, Yoshinobu Tsujii,
Hiroshi Kageyama,
Teruo Ono,
Mikio Takano
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ABSTRACT: Nanoparticles of α-Fe, an excellent soft magnet, have been successfully made corrosion-resistant and dispersible in polar and nonpolar solvents by coating these with inner and outer layers of amorphous silica and organics like poly(ethylene glycol), respectively. The double coating was facilitated by using stable and easy-to-handle oxide particles as the core to be subsequently metallized at temperatures low enough to keep the organic layer intact. Use of CaH2 as a reductant lowered the working temperature down to 200−300 °C, where thermal particle adhesion did not take place, formation of impurities like iron silicates was suppressed, and the overall morphological features of the starting particles were preserved. The feasibility of organo-functionalization of the surface will open a way for this nanomagnet toward bioscientific and medical applications.Keywords: α-Fe nanoparticle; CaH2; low-temperature reduction
02/2011;
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ABSTRACT: Surface-initiated atom transfer radical polymerizations (ATRP) from narrowly size-distributed silica nanoparticles (SiNPs) of diameters less than 100 nm were investigated. Two methods were used for the preparation of the SiNP cores: one was the reverse-micelle technique, which gave monodisperse SiNPs of average diameter 55 nm, and the other was the lysine-addition technique, which gave nearly monodisperse SiNPs of average diameter 15 nm. These nanoparticles were surface-modified with a triethoxysilane derivative containing an ATRP-initiating group. The surface-initiated ATRP of methyl methacrylate (MMA) mediated by a copper complex was carried out with the initiator-fixed SiNPs in the presence of a “sacrificial” free initiator. Well-defined poly(methyl methacrylate) (PMMA) brushes of a target molecular weight were successfully grafted with a surface density as high as 0.4−0.8 chains/nm2. These core−shell hybrid particles were highly dispersible, without any aggregation, in various solvents for PMMA. Because of the exceptionally high uniformity and perfect dispersibility, these hybrid particles formed two- and three-dimensional ordered arrays at the air−water interface and in suspension, respectively.
10/2010;
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ABSTRACT: Simple phenols and hydrocarbons were used as novel and efficient organic catalysts for reversible chain transfer catalyzed living radical polymerization (RTCP). This is the first use of oxygen- and carbon-centered compounds as catalysts of living radical polymerization. The catalysts include such common compounds as phenol itself, phenol-based antioxidants for foods and resins (e.g., 3,5-di-tert-butyl-4-hydroxytoluene (BHT)), phenol-based natural antioxidants (e.g., vitamin E), and dienes (e.g., 1,4-cyclohexadiene). Their cheapness, excellent environmental safety, and ease of handing may be quite attractive in practice. The catalysts were highly active and tolerant to functional groups. The required amounts of the catalysts were typically as small as 100−500 ppm, yielding low-polydispersity polymers (Mw/Mn 1.1−1.4) at moderate temperatures (40−100 °C), where Mw and Mn are weight- and number-average molecular weights, respectively. A wide variety of functional monomers with alkyl, aryl, hydroxyl, poly(ethylene glycol), alkylamino, amino, and carboxylic acid groups were adopted to the homo- and copolymerizations. Kinetic studies supported that, mechanistically, the polymerization is based on reversible chain transfer (RT) for these catalysts.
08/2010;
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ABSTRACT: A facile yet robust approach to chemically fix an initiating group for atom transfer radical polymerization (ATRP) on various polymeric substrates is described. Conventional free radical copolymerization was conducted with methyl methacrylate (MMA), 2-(2-bromoisobutyryloxy)ethyl methacrylate (an ATRP initiator-carrying monomer, BIEM), and 2-((4-azidobenzoyl)oxy)ethyl methacrylate (a photoreactive phenylazide-carrying monomer, ABEM) in N,N-dimethylformamide at 75 °C, giving a random (statistical) copolymer. Thin films of the obtained copolymer were fabricated on poly(ethylene terephthalate) (PET) film surface by spin-casting a toluene solution of the terpolymer and were immobilized on the PET substrate via UV-irradiation using the photoreactivity of the phenylazido units. The surface-initiated ATRP (SI-ATRP) of poly(ethylene glycol) methacrylate (PEGMA) mediated by a copper complex was carried out in water at 30 °C in the presence of a sacrificial (free) initiator and the initiator-immobilized PET film as the solid substrate. The polymerization proceeded in a living fashion. The molecular weight of free polymer increased with polymerization time while retaining low-polydispersity index, and more importantly, the thickness of the poly(PEGMA) graft layer increased as a function of polymerization time with a reduced graft density (surface occupancy) as high as 0.5 in all examined time. This initiator immobilization technique was applied to various polymeric substrates including polystyrene, polypropylene, polyethylene, and polylactide. The fabrication of micropatterned polymer-brush surfaces was also demonstrated by photopatterning the initiator layer followed by SI-ATRP.
06/2010;
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Macromolecular Reaction Engineering 01/2010; 4(3‐4):272 - 277. · 1.85 Impact Factor
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ABSTRACT: A novel class of living radical polymerizations with germanium, tin, and phosphorus catalysts were developed. The polymerizations are based on a new reversible activation mechanism, Reversible chain Transfer (RT) catalysis. Low-polydispersity (M(w)/M(n) approximately 1.1-1.3) polystyrene, poly(methyl methacrylate), poly(glycidyl methacrylate), and poly(2-hydroxyethyl methacrylate) with predicted molecular weight were obtained with fairly high conversion in a fairly short time. The pseudo-first-order activation rate constant kact for the styrene/GeI4 (catalyst) system was large enough, even with a small amount of GeI4, explaining why the system provides low-polydispersity polymers from an early stage of polymerization. The retardation in the polymerization rate observed for the styrene/GeI4 system was kinetically proven to be mainly due to the cross-termination between the propagating radical with GeI3*. Attractive features of the germanium, tin, and phosphorus catalysts include their high reactivity hence small amounts (1-10 mM) being required under relatively mild conditions (at 60-100 degrees C), high solubility in organic media without ligands, insensitivity to air hence sample preparation being allowed in the air, and minor color and smell. The germanium and phosphorus catalysts may also be attractive for their low toxicity. The phosphorus catalysts may also be attractive for their low cost.
Journal of the American Chemical Society 11/2007; 129(43):13347-54. · 9.91 Impact Factor
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Journal of Polymer Science Part A Polymer Chemistry 09/2007; 45(21):4795 - 4803. · 3.92 Impact Factor
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ABSTRACT: A novel cellulose derivative, 6-O-dihydrophytylcellulose (DHPC), was first synthesized via a ring-opening polymerization and allowed to self-assemble onto an air-water interface. Langmuir-Blodgett (LB) films were characterized with atomic force microscope (AFM), UV-vis spectroscopy, and Fourier transform infrared spectroscopy. The surface pressure-area (pi-A) isotherms for DHPC and beta-carotene (betaC) mixture indicated strong interaction between these compounds to pack well. Thus, DHPC has the ability to anchor betaC in the monolayer. It was proved that a betaC-DHPC monolayer was transferred successfully onto a substrate, yielding Y-type LB films by UV spectroscopic analysis. The transmission and reflection-absorption IR spectra (RAS) indicated that the dihydrophytyl chains had almost trans-zigzag conformation and were oriented nearly perpendicular to the substrate. AFM section analysis revealed the thickness per layer to be 2.32 nm. Consequently, DHPC was found to be an appropriate matrix to fabricate the mixed LB films containing betaC.
Biomacromolecules 07/2006; 7(6):1960-7. · 5.48 Impact Factor
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ABSTRACT: Atomic force microscopy was used to characterize an anatase TiO2 surface, prepared by the helical vapor preparation method. The forces between two bare TiO2 surfaces were measured in the presence of water at various pH values. This TiO2 isoelectric point (iep) was characterized by the presence of only a van der Waals attraction and was measured at pH 5.8; this value is similar to that for a rutile TiO2 surface. The adsorption mechanism of a nonionic surfactant molecule to this anatase TiO2 surface was investigated by measuring the forces between two such TiO2 surfaces at their iep pH in the presence of linear dodecanol tetraethoxylate (C12E4), a poly(ethoxylene oxide) n-alkyl ether. C12E4 was seen by the presence of steric forces to adsorb to the uncharged TiO2 surface. For low surfactant concentrations, C12E4 adsorbed with its hydrophobic tail facing the TiO2 substrate, to reduce its entropically unfavorable contacts with water. Additional surfactant adsorption occurred at higher surfactant concentrations by the hydrophobic and hydrophilic interactions between the surfactant tails and heads, respectively, and gave sub-bilayers. A two-step adsorption isotherm was subsequently proposed with four regions: (1) submonolayer, (2) complete monolayer, (3) sub-bilayer, and (4) bilayer. The absence of a long-range repulsive force between the two TiO2 surfaces in the presence of the C12E4 surface aggregates indicated that a C12E4 nonionic surfactant aggregate did not possess charge.
Langmuir 12/2005; 21(24):11283-8. · 4.19 Impact Factor
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ABSTRACT: Multilayer films of 2,3-di-O-acetyl-6-O-(4-stearyloxytrityl)cellulose (ASTC) were prepared and investigated. The fairly high surface pressure (π)–area (A) isotherms (36– 47mN/m) suggest that the balky and hydrophobic trityl group contribute to form a condensed monolayer. The
cellulose derivative formed a homogeneous monolayer at 10mN/m. The monolayer on the water surface was transferred successfully
at 10mN/m onto various substrates by modifying the preparation methods, to form Z-type multilayer films. The ultraviolet–visible
(UV–Vis) absorbance was independent of the number of layers, indicating that each layer is made of definite number of anhydroglucose
unit (AGU). The monolayer thickness determined from atomic force microscope (AFM) and ellipsometry was calculated to be about
1.9nm, suggesting that the long alkyl chain in the film has a so-called hairy-rod type structure. This is the first paper
about the Z-type LB film prepared from cellulose derivatives having long mono-alkyl chain only at 6-O-position.
Cellulose 07/2005; 12(4):361-369. · 3.60 Impact Factor
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06/2005: pages 273 - 286; , ISBN: 9783527603824
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Kyoungmoo Koh,
Satoshi Sugiyama,
Takashi Morinaga,
Kohji Ohno, Yoshinobu Tsujii,
Takeshi Fukuda,
Mikio Yamahiro,
Takashi Iijima,
Hisao Oikawa,
Kenichi Watanabe,
Tokuji Miyashita
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ABSTRACT: Incompletely condensed, fluorinated polyhedral oligomeric silsesquioxane with the highly reactive group of trisodium silanolate was used for the synthesis of an initiator for atom transfer radical polymerization. The initiator was applied to solution polymerization of methyl methacrylate (MMA) in the presence of a copper complex. The polymerization proceeded in a living fashion, providing tadpole-shaped polymers with an “inorganic head” of polyhedral oligomeric silsesquioxane (POSS) and an “organic tail” of well-defined PMMA. A blend film composed of the tadpole-shaped polymer and a matrix PMMA was annealed at 180 °C for 5 days and then analyzed by neutron reflectometry, X-ray photoelectron spectroscopy, and contact angle measurement. These analyses revealed that the tadpole-shaped polymer was preferentially populated at the air/polymer interface, and the outermost layer of the film was almost completely covered by the POSS heads. This was mainly due to the low surface free energy of the fluorinated POSS moiety. Owing to this unique structure, the blend film showed strong resistance against Ar+ ion etching, despite the overall POSS content was only 2 wt %.
01/2005;
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Angewandte Chemie International Edition 10/2003; 42(35):4194-7. · 13.45 Impact Factor
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Angewandte Chemie International Edition 07/2003; 42(24):2751-4. · 13.45 Impact Factor
