NMR-Untersuchung von Polyoxymethylen

Ohne Zusammenfassung     

Vacuum arc investigation of dual-part cathode electrodes

The basic characteristics of a vacuum arc are investigated with a special electrode whose cathode consists of two half-disks. Pure copper is used for one part of the cathode, while copper, chromium, silver, and titanium are used for the other part. The tested arc current value is less than 4000 A, and the flux density of the axial magnetic field applied to a vacuum arc is less than 0.015 T. Experimental results show that the arc voltages of dual-part cathode electrodes are much lower than those of the individual pure metals, and that current sharing between the two parts is roughly determined by the arc current-voltage characteristics of the metals. The arc voltage of the dual-part cathode electrode is extremely low when the current is less than 1000 A     

Photosensitivity of polyvinylesters of substituted cinnamylideneacetic acids

Several polyvinylesters of substituted cinnamylideneacetic acids were synthesized and their photosensitivities were investigated. It was found that polyvinylesters of planar acids reacted photochemically effectively and were spectrally sensitized by usual triplet sensitizer. On the other hand, polyvinylesters of twisted acids exhibited poor photosensitive properties. Poly(vinyl α-cyanocinnamylideneacetate) (PV-V) was found to be an excellent photosensitive polymer with respect to both photosensitivity and thermal stability (or storage stability).     

Efficient synthesis of 2-oxazolidinones and quinazoline-2,4(1H,3H)-diones from CO2 catalyzed by tetrabutylammonium fluoride

By employing tetrabutylammonium fluoride (TBAF) as a catalyst, the various carboxylative cyclizations of the propargylic amines having internal alkynes with CO₂ proceeded to afford the corresponding 2-oxazolidinones. In this case, it was also found that the generated 2-oxazolidinones were tautomerized into the corresponding 2-oxazolones due to the basicity of TBAF. In addition, we performed the synthesis of quinazoline-2,4(1H,3H)-dione from 2-aminobenzonitrile and CO₂ by using TBAF as a catalyst.     

Microampere laser threshold at 80°C with InGaAs/GaAs/InGaP buried heterostructre strained quantum well lasers

An extremely low CW threshold current of 670 μA and a high slope efficiency of 0.14 W/A at a high junction temperature of 80°C were obtained with a 200 μm long Al-free InGaAs/GaAs/InGaP buried heterostructure (BH) quantum well laser grown by three-step metal organic vapor phase epitaxy (MOVPE). The maximum energy conversion efficiency of a 500 μm long laser was as high as 50% at a output power level of 1 mW. Regrowth conditions of InGaP layers were found to be crucial for planarizing the grown surface to realize the high performances.     

HRTEM and ELNES analysis of polycarbosilane-derived Si–C–O bulk ceramics

A series of analyses by high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS) has been carried out to investigate the nanostructure and the chemical bonding of Si–C–O bulk ceramics prepared by pyrolysis of oxygen-controlled polycarbosilane (PCS). HRTEM revealed that the Si–C–O ceramics with higher oxygen content tended to keep an amorphous microstructure. EELS allowed the examination of energy-loss, near-edge-structures (ELNES) that detected clear transition signals of the chemical bonding around Si atoms from Si–C bonding to Si–O bonding with an increase of oxygen content. The microstructure of the PCS-derived Si–C–O bulk ceramics is characterized as a function of oxygen content.