Synthesis of functional polymers bearing cyclic carbonate groups from (2-oxo-1,3-dioxolan-4-yl) methyl vinyl ether

(2-Oxo-1,3-dioxolan-4-yl) methyl vinyl ether (OVE) was synthesized with high yield by addition reaction of glycidyl vinyl ether with carbon dioxide using tetrabutylammonium bromide (TBAB) as a catalyst. OVE was also prepared by reaction with β-butyrolactone or sodium hydrogencarbonate in the presence of TBAB as the catalyst. Poly [(2-oxo-1,3-dioxolan-4-yl) methyl vinyl ether] [P(OVE)] was obtained with high yield by cationic polymerization of OVE catalyzed using boron trifluoride diethyl ether complex in dichloromethane. Polymers bearing pendant 5-membered cyclic carbonate groups were also prepared by radical copolymerization of OVE with some electron-accepting monomers. Furthermore, addition reaction of P(OVE) with alkyl amines yielded the corresponding polymer having pendant 2-hydroxyethyl carbamate residue with high conversions. © 1994 John Wiley & Sons, Inc.     

Laser-induced trench etching of GaAs in aqueous KOH solution

Maskless etching of n-type GaAs in a KOH aqueous solution by irradiation of an argonion laser has been investigated to obtain high etching rates and aspect-ratios of etched grooves. High etching rates of up to 805 m/s and an aspect ratio of 8 have been achieved by a single scan of a laser beam. Microprobe photoluminescence (PL), Raman scattering, and Auger electron spectroscopy (AES) measurements were carried out on the trench surface to characterize damage induced by laser wet etching.     

Formation of microcrystalline structure in a-Si:H films prepared by RF sputtering

Formation of microcrystalline structure in a-Si:H films prepared by RF sputtering has been investigated by TEM and FT-IR. The Films deposited in pure H₂ have grain-like structure and tend to crystallize with increasing the gas pressure, while the films deposited in Ar containing 10 % H₂ usually become amorphous. With increasing input power and the gas pressure, however, the latter films tend to have amorphous-microcrystalline mixed structure, and corresponding to this structural change, shift of optical absorption edge to lower energy and decreases of resistivity and activation energy of its temperature dependence are observed.     

Pulsed laser-induced oxygen deficiency at TiO2 surface: Anomalous structure and electrical transport properties

We have studied pulsed laser-induced oxygen deficiencies at rutile TiO₂ surfaces. The crystal surface was successfully reduced by excimer laser irradiation, and an oxygen-deficient TiO_2−δ layer with 160 nm thickness was formed by means of ArF laser irradiation at 140 mJ/cm² for 2000 pulses. The TiO_2−δ layer fundamentally maintained a rutile structure, though this structure was distorted by many stacking faults caused by the large oxygen deficiency. The electrical resistivity of the obtained TiO_2−δ layer exhibited unconventional metallic behavior with hysteresis. A metal–insulator transition occurred at 42 K, and the electrical resistivity exceeded 10⁴ Ω cm below 42 K. This metal–insulator transition could be caused by bipolaronic ordering derived from Ti–Ti pairings that formed along the stacking faults. The constant magnetization behavior observed below 42 K is consistent with the bipolaronic scenario that has been observed previously for Ti₄O₇. These peculiar electrical properties are strongly linked to the oxygen-deficient crystal structure, which contains many stacking faults formed by instantaneous heating during excimer laser irradiation.     

Facile preparation of methyl 5-aryl-4-hydroxyhex-2(E)-enoate,chiral synthon of bisabolane-type sesquiterpenes,based on lipase-catalyzed kinetic resolution and rearrangement of an aryl group

The lipase-catalyzed enantioselective acetylation of racemic methyl (4S¹,5S¹)-4-aryl-5-hydroxyhex-2(E)-enoates 1a–h was performed and efficient resolutions were achieved (E >400) by using CAL-B. After brosylation of the obtained optically active 1a–h, solvolysis of brosylates 13a–h afforded the corresponding methyl (4S¹,5S¹)-5-aryl-4-hydroxyhex-2(E)-enoates 3a–h (26–94% yield). The yields of 3a and 3c on the solvolysis of the corresponding 13 were 92% and 40%, respectively, while solvolysis of the corresponding tosylate was reported at 70% and 17%, respectively. This procedure is a facile and practical route to the synthesis of bioactive and optically active bisabolane-type sesquiterpenes.     

Bis(tetrahydrofuran-κO)(meso-5,10,15,20-tetraisopropylporphy­rinato-κ4N)iron(III) perchlorate

The title complex, [Fe(C₃₂H₃₆N₄)(C₄H₈O)₂]ClO₄, shows an S₄-ruffled porphyrin ring, where the maximum deviation of the meso-carbon from the least-squares plane of the [Fe(C₂₀N₄)] core is as high as 0.675 (9) Å. This is the highest class of deviation among S₄-ruffled iron(III) porphyrin complexes. The average Fe—N_p bond distance is 1.967 (12) Å (N_p denotes an N atom of the equatorial ligand).     

Float zone growth of Dy:GdVO4 single crystals for potential use in solid-state yellow lasers

Single crystals of dysprosium-doped gadolinium orthovanadate (Dy:GdVO₄) were successfully grown by the floating zone method and their fluorescence properties were investigated. The as-grown crystals did not contain any macroscopic defects such as cracks and inclusions for any Dy-concentration of up to 4 at%. Every crystal showed optical homogeneity under observation with a polarizing microscope; that is, no low-angle grain boundaries and growth striations were detected. In the visible region, two distinct fluorescence bands were observed around 480 and 575 nm, corresponding to ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions, respectively. The excitation spectrum for the emission of 573 nm indicates the possibility to use a commercially available laser diode of 450 nm as a pumping source for solid-state yellow laser.     

Extraction of uranium from simulated ore by the supercritical carbon dioxide fluid extraction method with nitric acid-TBP complex.

The supercritical fluid extraction (SFE) method using CO(2) as a medium with an extractant of HNO(3)-tri-n-butyl phosphate (TBP) complex was applied to extract uranium from several uranyl phosphate compounds and simulated uranium ores. An extraction method consisting of a static extraction process and a dynamic one was established, and the effects of the experimental conditions, such as pressure, temperature, and extraction time, on the extraction of uranium were ascertained. It was found that uranium could be efficiently extracted from both the uranyl phosphates and simulated ores by the SFE method using CO(2). It was thus demonstrated that the SFE method using CO(2) is useful as a pretreatment method for the analysis of uranium in ores.