Polymerization of (p‐vinylphenyl)hydrogalvinoxyl and formation of a stable polyradical derivative

4‐[(3,5‐Di‐tert‐butyl‐4‐hydroxyphenyl)(3,5‐di‐tert‐butyl‐4‐oxo‐cyclohexa‐ 2,5‐dienylidene)methyl]styrene (abbreviated as (p‐vinylphenyl)hydrogalvinoxyl) was polymerized using AIBN as an initiator to give a bright yellow polymer with M w = 3.2 × 10⁴. The polymer was oxidized to give the corresponding polyradical derivative, whose spin concentration could be increased up to about 70 mol % depending on oxidative conditions. ESR signal line‐width in the solid state was greatly increased below 200 K for the polyradical with a high spin concentration (> 50 mol %). The magnetization and magnetic susceptibility indicated weak antiferromagnetic interaction among the radical sites. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 189–198, 1999     

Oxygen permeability of biodegradable copolycaprolactones

Polycaprolactone is one of the biodegradable polymers with good drug permeability. In the present paper, polycaprolactone and three kinds of copolycaprolactone–polycaprolactone–poly(ethylene oxide)– polycaprolactone triblock copolymer (PCE), polycaprolactone/polycaprolactone‐poly(ethylene oxide)/polylactide tricomponents random block copolymer (PCEL) and polycaprolactone/poly(ethylene terephthalate) random block copolymer (PETCL)– were synthesized. The biodegradation behavior of these polymers were shown by degradation tests in vitro, ex vivo and in vivo. The oxygen permeabilities of these polymers were in the range of 10⁻¹⁰ ∼ 10⁻⁹ cm³ (STP) cm/cm² sec cm Hg. Copolymers PCE and PCEL displayed O₂ and N₂ permeability coefficients (PO₂/PN₂) ratios of about 9. The effects of composition and crystallinity of the copolymers on biodegradability and the oxygen permeability of the polymer were discussed. Copyright © 1999 John Wiley & Sons, Ltd.     

Near-Field Optical Microscope with Tapping Illumination and Synchronous Detection

We use the tapping illumination and synchronous detection in a scanning near-field optical microscopy to obtain a near-field optical signal that is separated from the far-field signal. The illumination light was irradiated from the bent fiber tip vibrating normal to the sample surface. The transmitted light synchronized with the tapping vibration was observed. The obtained image of an organic film shows that this technique is effective for the weak contrast samples.This paper was originally presented at the 5th International Conference on NEAR FIELD OPTICS and RELATED TECHNOLOGIES (NFO-5), which was held on December 6–10, 1998 at Coganoi Bay Hotel, Shirahama, Japan, in cooperation with the Japan Society of Applied Physics and Mombusho Grant-in Aid for Scientific Research on Priority Areas “Near-field Nano-optics” Project, sponsored by Japan Society for the Promotion of Science.     

Mössbauer study of Lu2Fe3O7: A two-dimensional antiferromagnet on a triangular lattice

Mössbauer studies reveal that there are two kinds of Fe³⁺ spins with completely different characteristics in Lu₂Fe₃O₇: one is an Ising-like property and the other is a Heisenberg-like property in a two-dimensional antiferromagnet on a triangular lattice. The former spin orders ferrimagnetically along thec-axis at around 220 K. The latter spin is lying in thec-plane and a corresponding hyperfine magnetic field is observed at temperatures below 50 K. At very low temperatures, however, the latter spin has a component parallel to thec-axis and couples with the former spin. This finding is consistent with the modulated profile of the magnetic scattering in neutron diffraction and the result of a magnetization measurement.     

Two‐dimensionally extended aromatic polyamines for optimization of charge‐transporting properties by partial oxidation

This article describes the synthesis of the two‐dimensionally extended aromatic polyamines by polycondensation between the tri‐sec‐amine monomer and p‐phenylenediamine‐based dibromide, the polyradical generation by chemical and electrochemical oxidations, and the hole‐transporting properties. The molecular weights (M_n) of the polyamines, 3a and 3b , were 7700 and 5000, respectively, and both polymers were very soluble in the typical organic solvents, ensuring a good film formation capability by a spin‐coating technique. The thermal stability of the aromatic polyamines, elucidated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), was quite high. More important, the cross‐conjugated structure is essential for the controlled radical generation and the maintenance of the radical stability. Cyclic voltammograms of the neutral polyamines in the presence of 1 vol % of trifluoroacetic acid and the intervalence bands of the partially oxidized polyamines with NOPF₆ revealed that the generated radicals delocalize over the p‐phenylenediamine moieties. The half‐life of the polyradicals was about 12 h even under ambient conditions, which allowed us to fabricate and measure the hole‐only devices. The charge‐transporting properties of the polyamines were dramatically changed by the partial oxidation (20 mol %/aminium unit) with NOPF₆. The neutral polyamines showed the conventional injection‐limit behaviors, whereas the hole‐transporting behaviors of the polyradicals are bulk‐limit and highly dependent on the chemical structure. The efficient hole‐transport of the all‐conjugated poly(aminium cationic radical)s was for the first time realized for the polyradical of 3b . © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4577–4586, 2009     

Oxygen-binding property of hemoglobin films

Oxygenated and deoxygenated hemoglobin films were obtained by drying corresponding hemoglobin solutions with maltose (≧0.3 M). The resulting hemoglobin films were homogeneous and smooth, and the methemoglobin formation in the oxyhemoglobin film was well suppressed. The dry, rigid networks of maltose molecules work to preserve the conformation of hemoglobin against the removal of water. The coordination of oxygen to the deoxygenated hemoglobin film was slow and saturated up to 50%, while nearly 100% saturation was achieved if the film contained a residual moisture of 8.7%.     

Oxygen dissolution and transport in cobaltporphyrin-bound organophosphazene membranes

Rubbery poly(organophosphazene)s were synthesized, and were combined with cobaltporphyrin (CoP) which binds molecular oxygen rapidly and reversibly. The apparent oxygen-binding equilibrium constant (K_app) is in proportion to the physical solubility coefficient of oxygen in the polymer, although the reduced equilibrium and thermodynamic parameters are not dependent on the polymer matrix species. Diffusivity of oxygen via the fixed CoP(D_C) is enhanced for poly(organophosphazene) membranes with a larger oxygen diffusion constant. Poly(organophosphazene) membranes with both a large K_app and D_C yield high oxygen permeability.     

Mobile customer model with retrials

A cellular system consisting of small zones is studied. Since their zones are small, the change of the number of mobile customers in a cell influences the performance. The hand-off failure probability and blocking probability may be important as the performance measures. In this paper, we consider the retrial behavior of customers who meet the hand-off failure and blocking. We classify customers into three types: the retrial resignation type, the ordinary retrial type and the persistent retrial type. We evaluate the effect of the existence of mobile customers with retrials.