Synthesis of tetramethyl-p-silphenylenesiloxanedimethylsiloxane triblock copolymer by employing living anionic polymerization

Dimethylsiloxane-tetramethyl-p-silphenylenesiloxane-dimethylsiloxane (DMS-TMPS-DMS) triblock copolymer was synthesized by employing living anionic polymerization of hexamethylcyclotrisiloxane (D₃). Two synthetic methods were carried out for the polymerization. One of those methods was the anionic polymerization of D₃ initiated at the silanolate anion which was prepared from the terminal hydroxyl group of silanol-terminated TMPS prepolymer by reaction with n-butyllithium (method 1). The other was the coupling reaction of vinyl-terminated TMPS prepolymer with hydrosilyl-terminated DMS prepolymer obtained from the anionic polymerization of D₃ by using diphenylmethylsilanolate anion as initiator (method 2). In method 1, DMS contents of the copolymers ranged from 25.8 to 72.5 wt% and the values agreed with the ratio of D₃ to TMPS prepolymer. The weight-average molecular weights ranged from 1.36×10⁴ to 19.4×10⁴ and were close to the predicted values calculated from the $\text{M}\text{?}{}_{\mathrm{v}}$ of the TMPS prepolymer and the amount of D₃ added. In the case of method 2, weight-average molecular weights ranged from 19.5×10⁴ to 24.2×10⁴. The high molecular weight copolymer could thus be obtained by method 2. Intrinsic viscosity values of the triblock copolymers agreed with calculated values obtained by considering the copolymer as a binary mixture of these homopolymers. Differential scanning calorimetry and thermogravimetry were carried out on the triblock copolymers. The equilibrium melting temperatures of each of the copolymers were very close to that of poly-TMPS (160°C). The glass transition temperature and heat of fusion were decreased as the DMS content was increased. The thermogravimetric curves for the copolymers indicated that the thermal stability of the triblock copolymer was intermediate between the DMS and TMPS homopolymers.     

Status report of the JAERI on-line isotope separator

A mass separator has been connected on line to the 20 MV tandem accelerator at JAERI/Tokai. Using a thermal ion source, decay spectroscopic studies have been carried out for neutron-deficient isotopes in the mass 120–130 region. A study with collinear laser spectroscopy has begun recently. The present paper describes the status of the mass separator facility together with some experimental results.     

Recent Advances in New Hard High‐Pressure Nitrides

Since the discovery of spinel nitrides in 1999, there has been a lot of effort in basic science to further develop advanced nitrides and electronic nitrides. The aim and scope of the research in this field is to synthesize novel nitrides for structural and functional applications. Silicon‐based spinel nitrides combine ultrahigh hardness with high thermal stability against decomposition in different environments, suggesting potential applications as cutting tools. These materials are also expected to show interesting optoelectronic properties, which may lead to applications in light‐emitting diodes. The synthesis of spinel silicon and germanium nitrides at ultrahigh pressures and temperatures, as well as the successful synthesis of tin nitride at ambient pressure, has created an enormous impact on both the basic science and technological development of advanced nitrides. Moreover, the discovery of novel phases of transition metal nitrides, such as Zr₃N₄ and Hf₃N₄ with a Th₃P₄ structure, as well as the recently reported nitrides of Pt and Mo, demonstrates the scientific potential of high‐pressure synthesis techniques in the field of materials science. Here, the state of the art in the field of novel hard materials based on nitrides synthesized reproducibly under high pressure is reviewed.     

Selection of the best siting of static var compensators for effective damping

A static Var compensator (SVC) can improve the steady-state stability (or the small signal stability), if it is located appropriately. The present paper proposes a method for selecting the best siting of SVC in large-scale power systems for damping effectively. Conventionally, it is thought that SVC improves steady-state stability by its voltage regulating ability. From this point of view, the stability can be improved significantly if SVC is located at the bus which has a large voltage fluctuation due to the lightly damped power swing mode. In contrast to the conventional viewpoint, the present paper makes it clear that the steady-state stability deteriorates by the conventional voltage regulating control of SVC in some cases. Therefore, the voltage fluctuation is not an appropriate index for effective damping. This paper explains the mechanism of improvement of steady-state stability by SVC in terms of modal analysis. On the basis of modal analysis, an index for determining the location of SVC is derived. The index is called LIED (Location Index for Effective Damping) by the authors. Digital simulations are conducted for an 8-machine longitudinal system and a 29-machine looped system to demonstrate the validity of the proposed index.     

Electrical properties of polyimide Langmuir-Blodgett films sandwiched between superconducting electrodes: detection of microwaves

We have examined the electrical properties of ultrathin insulating layers of cadmium arachidate (C₂₀), polyamic acid long alkyl amine salts (PAA) and polyimide (PI) by using tunnel junctions with structures of (Pb-Bi)/PAA (or C₂₀)/(Pb-Bi), Au/PI/(Pb-Bi) and Au/PI/Au. Typical current-voltage (I-V) characteristics of weakly coupled superconductors were obtained for (Pb-Bi)/PAA (or C₂₀)/(Pb-Bi) junctions with one, two or three deposited layers at a temperature below the critical temperature of a Pb-Bi alloy. On the contrary, typical I-V characteristics of tunnel junctions were obtained for Au/PI/(Pb-Bi) and Au/PI/Au junctions, when the number of deposited layers is greater than about 30. Finally, we concluded that the efficiency of detecting microwaves is excellent in (Pb-Bi)/PAA (or C₂₀)/(Pb-Bi) junctions, although bridging filaments exist in the PAA (or C₂₀) Langmuir-Blodgett (LB) layers, and that the PI LB layers become good electrical insulating spacers when the thickness of deposited layers is more than about 11 nm.     

Electronic structures of polyacenacene and polyphenanthrophen anthrene. Design of one-dimensional graphite

The electronic structures of polyacenacene (PAA) and its geometrical isomer, polyphenanthrophenanthrene (PPhP) have been studied using the tight-binding SCF-CO (self consistent field-crystal orbital) method with respect to a design of one-dimensional (1D) graphite. The geometry of each polymer is optimized from the energetic point of view. It has been found that from the analysis of the electronic structure of its optimized geometry, PAA favours the structure without the carbon-carbon bond alternations, yielding no band gap. In this sense, PAA is a typical 1D-graphite. On the other hand, it is predicted that the magnitude of the band gap of PPhP in its optimized geometry is almost equal to that of trans-polyacetylene.     

Thermal-stress intensity factors for an insulated crack in a semi-infinite medium with a thin conductive stiffener

In the present paper is analyzed the thermal stress problem of the interaction between an insulated crack and a thin conductive elastic stiffener of finite length bonded to the surface of a semi-infinite medium under uniform heat flow on the basis of the two-dimensional theory of thermoelasticity. The singular point method is adopted to solve the problem and a system of singular integral equations is derived. Numerical results for the thermal-stress intensity factors are presented in terms of normalized parameters which consist of the dimensions and the geometrical arrangement of the crack and the stiffener, and the physical properties of the stiffener and the semi-infinite medium.