A bicyclic conjugated diene monomer,tetrahydroindene, for cationic polymerization and a novel alicyclic hydrocarbon polymer with heat resistance

This study was directed toward the cationic polymerization of tetrahydroindene (i.e., bicyclo[4.3.0]‐2,9‐nonadiene), a bicyclic conjugated diene monomer, with a series of Lewis acids, especially focusing on the synthesis of high‐molecular‐weight polymers and subsequent hydrogenation for novel cycloolefin polymers with high service temperatures. EtAlCl₂ or SnCl₄ induced an efficient and quantitative cationic polymerization of tetrahydroindene to afford polymers with relatively high molecular weights (number‐average molecular weight > 20,000) and 1,4‐enchainment bicyclic main‐chain structures. The subsequent hydrogenation of the obtained poly(tetrahydroindene) with p‐toluenesulfonyl hydrazide resulted in a saturated alicyclic hydrocarbon polymer with a relatively high glass transition (glass‐transition temperature = 220 °C) and improved pyrolysis temperature (10% weight loss at 480 °C). The new diene monomer was randomly copolymerized with cyclopentadiene at various feed ratios in the presence of EtAlCl₂ to give novel cycloolefin copolymers, which were subsequently hydrogenated into alicyclic copolymers with variable glass‐transition temperatures (70–220 °C). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6214–6225, 2006     

Singularities of maximal surfaces

We show that the singularities of spacelike maximal surfaces in Lorentz–Minkowski 3-space generically consist of cuspidal edges, swallowtails and cuspidal cross caps. The same result holds for spacelike mean curvature one surfaces in de Sitter 3-space. To prove these, we shall give a simple criterion for a given singular point on a surface to be a cuspidal cross cap. Dedicated to Yusuke Sakane on the occasion of his 60th birthday.     

Pyrolysis and mass spectra of trimethylsilyl derivatives of monosaccharides

The pyrolysis of trimethylsilyl derivatives of saccharides (1) was investigated by DTA-TG, MS, GC/MS and TG-GC/MS. The DTA-TG/DTG curves showed that the pyrolysis of 1 occurred in one stage. The exothermic peaks were due to sublimation or thermal decomposition by vaporization. The cleavage mechanism by electron impact of 1 was classified into four categories: 1) stepwise elimination of the side-chain, 2) cleavage of the side-chain, 3) cleavage of the pyranose ring, and 4) cleavage of the pyranose ring and side-chain at the same time. The mass-spectrum for 1 revealed the main common four fragment ions, such asm/z 73, 191, 204 and 217, with cleavage of the pyranose ring. These fragment ions were detected with a similar retention time in the gas cromatogram by GC/MS or TG-GC/MS. The retention time for 1 increased in the sequence aldopentose相似文献   

Formation of uniformly sized metal droplets from a capillary jet by electromagnetic force

A new method for producing uniformly sized metal droplets is proposed. In this method, an intermittent electromagnetic pinch force is applied to a capillary jet of liquid metal to generate fluctuations of equal interval on the surface of the jet. As the fluctuations grow, the liquid metal jet breaks into small droplets whose size depends on the frequency of the intermittent electromagnetic pinch force. The breakup of the capillary jet is numerically simulated by performing multiphase fluid flow analysis with surface tracking (volume of fluid method) and electromagnetic force analysis. The simulation results agree well with the results of model experiments. The jet breaks up into uniformly sized droplets when the frequency of the intermittent force equals the frequency that corresponds to the natural disturbance wavelength of the capillary jet.     

Nickel-catalyzed Suzuki-Miyaura reaction of aryl fluorides

Two protocols for the nickel-catalyzed cross-coupling of aryl fluorides with aryl boronic esters have been developed. The first employs metal fluoride cocatalysts, such as ZrF(4) and TiF(4), which enable Suzuki-Miyaura reactions of aryl fluorides bearing electron-withdrawing (ketones, esters, and CF(3)), aryl and alkenyl groups as well as those comprising fused aromatic rings, such as fluoronaphthalenes and fluoroquinolines. The second protocol employs aryl fluorides bearing ortho-directing groups, which facilitate the difficult C-F bond activation process via cyclometalation. N-heterocycles, such as pyridines, quinolines, pyrazoles, and oxazolines, can successfully promote cross-coupling with an array of organoboronic esters. A study into the substituent effects with respect to both coupling components has provided fundamental insights into the mechanism of the nickel-catalyzed cross-coupling of aryl fluorides.     

Simple cubic self-assembly of PbS quantum dots by finely controlled ligand removal through gel permeation chromatography

The geometry in self-assembled superlattices of colloidal quantum dots (QDs) strongly affects their optoelectronic properties and is thus of critical importance for applications in optoelectronic devices. Here, we achieve the selective control of the geometry of colloidal quasi-spherical PbS QDs in highly-ordered two and three dimensional superlattices: Disordered, simple cubic (sc), and face-centered cubic (fcc). Gel permeation chromatography (GPC), not based on size-exclusion effects, is developed to quantitatively and continuously control the ligand coverage of PbS QDs. The obtained QDs can retain their high stability and photoluminescence on account of the chemically soft removal of the ligands by GPC. With increasing ligand coverage, the geometry of the self-assembled superlattices by solution-casting of the GPC-processed PbS QDs changed from disordered, sc to fcc because of the finely controlled ligand coverage and anisotropy on QD surfaces. Importantly, the highly-ordered sc supercrystal usually displays unique superfluorescence and is expected to show high charge transporting properties, but it has not yet been achieved for colloidal quasi-spherical QDs. It is firstly accessible by fine-tuning the QD ligand density using the GPC method here. This selective formation of different geometric superlattices based on GPC promises applications of such colloidal quasi-spherical QDs in high-performance optoelectronic devices.

Gel permeation chromatography can finely control ligand coverage of PbS quantum dots. Self-assembly of these QDs with different ligand density leads to the formation of 2D square, hexagonal and 3D simple cubic and face-centered cubic superlattices.     

Walking nanothermometers: spatiotemporal temperature measurement of transported acidic organelles in single living cells

We fabricated fluorescent nanoparticles which monitor temperature changes without sensitivity to pH (4-10) and ionic strength (0-500 mM). The nanothermometers spontaneously enter living HeLa cells via endocytosis, enclosed in acidic organelles, i.e., endosome/lysosome, and then transported along microtubules in a temperature-dependent manner, working as "walking nanothermometers".     

Development of UV-Excitable Red and Near-Infrared Fluorescent Labels and Their Application for Simultaneous Multicolor Bioimaging by Single-Wavelength Excitation

We report a new type of UV-excitable red/NIR-emissive fluorescent dyads (PKF series). Conjugation of a pyrene and a novel bright red/near-infrared (NIR) fluorophore resulted in large quasi-Stokes shift while retaining intense fluorescence emission and sharp spectral bands. Labeling of PKF dyads to biomolecules was performed by means of introduction of a succinimidyl ester. Simultaneous Ca²⁺/albumin dual-color intracellular imaging by PKF in combination with fura-2 (UV-excitable/VIS-emissive Ca²⁺ indicator) reveals its usefulness as a new bioimaging tool.     

In Situ Direct Mechanistic Transformation from FeCl3-Catalyzed Living Cationic to Radical Polymerizations

A trivalent iron chloride (FeCl₃) catalyst induced both living cationic and radical polymerizations of various monomers in the presence of an appropriate additive or ligand to yield polymers with controlled molecular weights and narrow molecular-weight distributions. The in-situ mechanistic transformation from a living cationic to a radical growing species during the styrene polymerization was achieved in a FeCl₃-based system with the simple addition of phosphine followed by an elevation of the reaction temperature. The growing cationic species was effectively converted into the radical species to produce a series of block copolymers that consist of styrene and various acrylic monomers.