Graft copolymers having hydrophobic backbone and hydrophilic branches. XXX. Preparation of polystyrene‐core nanospheres having a poly(2‐methacryloyloxyethyl phosphorylcholine) corona

Polystyrene core nanosphere particles possessing 2‐methacryloyloxyethyl phosphorylcholine (MPC) polymers on the corona were prepared by the free radical polymerization of hydrophilic polyMPC macromonomer and hydrophobic styrene with AIBN as a radical initiator in ethanol as a polar solvent. The morphology of the nanospheres was observed by transmission electron micrograph (TEM). The nanospheres were spherical in form and have a narrow size distribution. Their sizes could be controlled by varying the molecular weight of the macromonomer and the amount of it in feed. Electron spectroscopy for chemical analysis (ESCA) of the nanosphere surfaces suggested that polyMPC chains were located favorably on the surface of the nanosphere. The nanospheres having the polyMPC chains on their surfaces can be significant and useful materials in technological and medical fields. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3052–3058, 2000     

Graft copolymers having hydrophobic backbone and hydrophilic branches. XVIII. Poly(styrene) nanospheres with novel thermosensitive poly(N-vinylisobutyramide)s on their surfaces

Poly(styrene) nanospheres having poly(N-vinylisobutyramide)s (PNVIBA)s, which are structurally the same composition as well-known thermosensitive poly(N-isopropylacrylamide)s (PNIPAAm)s and show the thermosensitive property as well, on their surfaces were synthesized by the free radical polymerization of hydrophilic PNVIBA macromonomers and hydrophobic styrene with AIBN as a radical initiator in ethanol as a polar solvent and were characterized in regard to their thermosensitive properties. Both the NVIBA oligomers and PNVIBA macromonomers that we synthesized showed a lower critical solution temperature (LCST) at around 40°C, as was predicted by our previous research. The nanospheres were spherical in form and have a narrow size distribution. Their sizes could be controlled by varying the molecular weight of the macromonomers and the amount of it in feed. The size in the nanosphere became small above the LCST of the corresponding macromonomer, possibly due to thermosensitive shrinking of the PNVIBA on the nanosphere surface, while transmittance of its dispersion did not change at all at studied temperature range. The nanospheres having the PNVIBA on their surfaces, which response sharply to atmospheres such as dispersion temperature, can be significant and useful materials in technological and medical fields. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2581–2587, 1998     

A ferroelectric barium titanate,BaTi2O5

The crystal structure of monobarium dititanium pentaoxide, BaTi₂O₅, synthesized by a floating‐zone method, was studied by X‐ray diffraction. Previous reports describe the structure as being in the monoclinic centrosymmetric space group C2/m. We have recently found that this material exhibits ferroelectricity, and therefore BaTi₂O₅ should have lower symmetry. The crystal structure of BaTi₂O₅ was refined in space group C2, revealing a displacement of the Ti atoms along the b axis. This result is consistent with the fact that the ferroelectricity of BaTi₂O₅ was only observed along the b axis.     

Synthesis of polystyenes with different stereoregularities by anionic polymerization

The stereoregularity of polystyrene prepared by anionic polymerization was determined by means of ¹³C-NMR spectroscopy. The stereoregularity changed with such polymerization conditions as catalyst, solvent, and temperature. Sodium naphthalene as catalyst gave a syndiotactic-rich polystyrene of 66–68% syndiotactic dyads independently of solvent and temperature, while potassium and cesium naphthalenes as catalyst produced polystyrenes with different stereoregularities ranging from syndiotactic-rich to isotactic-rich configurations, depending on solvent and temperature. The mechanism of anionic polymerization which caused the difference in stereoregularity was discussed from the viewpoint of growing ionic species.     

Aerosol generation and measurement of multi-wall carbon nanotubes

Mass production of some kinds of carbon nanotubes (CNT) is now imminent, but little is known about the risk associated with their exposure. It is important to assess the propensity of the CNT to release particles into air for its risk assessment. In this study, we conducted aerosolization of a multi-walled CNT (MWCNT) to assess several aerosol measuring instruments. A Palas RBG-1000 aerosol generator applied mechanical stress to the MWCNT by a rotating brush at feed rates ranging from 2 to 20 mm/h, which the MWCNT was fed to a two-component fluidized bed. The fluidized bed aerosol generator was used to disperse the MWCNT aerosol once more. We monitored the generated MWCNT aerosol concentrations based on number, area, and mass using a condensation particle counter and nanoparticle surface area monitor. Also we quantified carbon mass in MWCNT aerosol samples by a carbon monitor. The shape of aerosolized MWCNT fibers was observed by a scanning electron microscope (SEM). The MWCNT was well dispersed by our system. We found isolated MWCNT fibers in the aerosols by SEM and the count median lengths of MWCNT fibers were 4–6 μm. The MWCNT was quantified by the carbon monitor with a modified condition based on the NIOSH analytical manual. The MWCNT aerosol concentration (EC mass base) was 4 mg/m³ at 2 mm/h in this study.     

Preparation of Size Tunable Amphiphilic Poly(amino acid) Nanoparticles

Size tunable amphiphilic NPs composed of poly(γ‐PGA) and hydrophobic amino acids, such as Phe or Trp, were prepared. To prepare these size‐regulated NPs, γ‐PGA‐g‐Phe or γ‐PGA‐g‐Trp dissolved in DMSO was added to various concentrations of NaCl solution. The γ‐PGA‐Phe and γ‐PGA‐Trp formed monodispersed NPs, and the size of NPs can be easily controlled by NaCl concentration. The different‐sized NPs showed the same structure. The encapsulation of protein into the different‐sized NPs was successfully achieved and the size of protein‐encapsulated γ‐PGA‐Phe NPs was increased when protein was encapsulated.

     

Syntheses and characterization of oxygen/sulfur-bridged incomplete cubane-type clusters, [Mo3S4Tp3]+ and [Mo3OS3Tp3]+, and a mixed-metal cubane-type cluster, [Mo3FeS4ClTp3]. X-ray structures of [Mo3S4Tp3]Cl, [Mo3OS3Tp3]PF6, and [Mo3FeS4ClTp3

The reaction of [Mo3S4(H2O)9]4+ (1) with hydrotris(pyrazolyl)borate (Tp) ligands produced [Mo3S4Tp3]Cl x 4 H2O ([3]Cl x 4 H2O) in an excellent yield. An X-ray structure analysis of [3]Cl x 4 H2O revealed that each molybdenum atom bonded to the Tp ligand. We report four salts of 3, [3]Cl x 4 H2O, [3]tof x 2 H2O, [3]PF6 x H2O, and [3]BF4 x 2 H2O in this paper. The solubility and stability of the chloride salt in organic solvents differ completely from those of the other salts. We have also prepared a new compound, [Mo3OS3Tp3]PF6 x H2O ([4]PF6 x H2O), via the reaction of [Mo3OS3(H2O)9]4+ (2) with KTp in the presence of NH4PF6. All the molybdenum atoms bonded to Tp ligand. 1H NMR signals corresponding to nine protons bonded to three pyrazole rings in one Tp were observed in a spectrum (at 253 K) of [3]BF4 x 2 H2O. It shows that cluster 3 has a 3-fold rotation axis in CD2Cl2 solution. Twenty-one 1H NMR signals corresponding to twenty-seven protons bonded to nine pyrazole rings in three Tp ligands were observed in a spectrum (at 233 K) of [4]PF6 x H2O; obviously, 4 has no 3-fold rotation axis, in contrast to 3. The short CH...mu3S distance caused large upfield chemical shifts in the 1H NMR spectra of 3 and 4. The reaction of 3 with metallic iron in CH2Cl2 produced [Mo3FeS4XTp3] (X = Cl (5), Br (6)). X-ray structure analysis of 5 has revealed the existence of a cubane-type core Mo3FeS4. Complex 3 functions as a metal-complex ligand for preparing a novel mixed-metal complex even in nonaqueous solvents. The cyclic voltammogram of 5 shows two reversible one-electron couples (E(1/2) = -1.40 and 0.52 V vs SCE) and two irreversible one-electron oxidation processes (E(pc) = 1.54 and 1.66 V vs SCE).