Radical polymerization of alkyl crotonates as 1,2-disubstituted ethylenes leading to thermally stable substituted polymethylene

Radical polymerization of several alkyl crotonates (RCr) was carried out in bulk or in benzene in the presence of radical initiators. Homopolymerization of RCr bearing bulky ester alkyl groups, e.g. tert-butyl (tBCr), 1-adamantyl (AdCr), and 3,5-dimethyl-1-adamantyl crotonate (DMAdCr) proceeded to give a polymer with molecular weight of several thousands despite of the steric hindrance and chain transfer by the presence of the β-methyl group, while the methyl and ethyl esters gave no polymer. The kinetics of the polymerization was examined in detail and absolute rate constants were evaluated by means of electron spin resonance spectroscopy. The propagation rate constants of RCr were 0.41–1.0 L/mol s, being much smaller than those of the corresponding methacrylates (530–570 L/mol s). The termination rate constants were also determined from the analyses of steady state and non-steady state polymerizations. Radical copolymerizations of AdCr (M₂) with several vinyl monomers (M₁) were carried out in bulk at 60°C and the rate constants for cross propagations were calculated to examine reactivities of the monomer and its polymer radical. The structure and thermal properties of the resulting poly (AdCr) were also investigated. Onset temperature of decomposition and glass transition temperature of poly(AdCr) were revealed to be much high as 302 and 234°C, respectively. © 1994 John Wiley & Sons, Inc.     

A 128 × 128 Pixel Complementary Metal Oxide Semiconductor Image Sensor with an Improved Pixel Architecture for Detecting Modulated Light Signals

A complementary metal oxide semiconductor (CMOS) image sensor for the detection of modulated light under background illumination has been developed. When an object is illuminated by a modulated light source under background illumination the sensor enables the object alone to be captured. This paper describes improvements in pixel architecture for reducing fixed pattern noise (FPN) and improving the sensitivity of the image sensor. The improved 128 × 128 pixel CMOS image sensor with a column parallel analog-to-digital converter (ADC) circuit was fabricated using 0.35-mm CMOS technology. The resulting captured images are shown and the properties of improved pixel architecture are described. The image sensor has FPN of 1/28 that of the previous image sensor and an improved pixel architecture comprising a common in-pixel amp and a correlated double sampling (CDS) circuit. The use of a split photogate increases the sensitivity of the image sensor to 1.3 times that of the previous image sensor.     

Application of an atmospheric pressure helium microwave-induced plasma as an element-selective detector for gas chromatography

An atmospheric pressure helium microwave-induced plasma (MIP) was combined with a gas chromatograph (GC). and used as an element-selective detector for GC. The detection limits, dynamic ranges and selectivities were obtained for H, C, F, Cl, Br, I and S. Such data for nitrogen and oxygen could not be obtained because of the interference from air which was entrained into the system through the leakages of the tubing and the valve system. The detection limits and dynamic ranges for all the elements investigated were in a range between 1.8 and 39pgs^?1 and between 1.6 × 10³ and 1.1 × 10⁵, respectively. Furthermore, the relative sensitivities of C, H, Cl and Br for various compounds were examined. In the cases of carbon and hydrogen, the relative sensitivities were not the same for different compounds containing oxygen and nitrogen. This result may be explained by the incomplete decomposition of such compounds due to the low microwave power (75 W) applied in the present system.     

Dynamical properties of nucleus boundaries in photoinduced structural change

Dynamics of the boundaries of photoinduced nuclei in electron–phonon systems is theoretically studied. By regarding the spatial distribution of the excited electronic state population as a geometric pattern, we applied the multifractal analysis to it and calculated the temporal behavior of the fractal dimension f(α)$f(\alpha )$ as a function of the Lipschitz–Hölder exponent α, which is an appropriate method for understanding the cooperative relaxation process of photoexcited states. We found that the incubation period observed in various types of photoinduced cooperative phenomena corresponds to the formation of embryonic nuclei which is driven by nonadiabatic/adiabatic transition between electronic states during the relaxation of the Franck–Condon state.     

A novel stereocontrolled approach to steroid side chain construction: asymmetric synthesis of potential synthon of the vitamin D series

Stereocontrolled synthesis of (?)-de-AB-8-oxa-cholest-14-en-9-one (2) as an optically active form was achieved starting from the methylene ketone (7). This work constitutes a formal synthesis of de-AB-cholestan (1).     

Synthetic approach to grayanotoxins and asebotoxins: a new construction of the a-homograyanotoxane ring system

The tetracyclic compounds ～3 and ～4 corresponding to A-homograyanotoxane system were synthesised by a thermolysis of the benzocyclobutene ～8, followed by a Wagner-Meerwein rearrangement of the kaurane type of compounds ～15 and ～16.     

Determination of isoniazid in tablets by second-derivative ultraviolet spectrophotometry of scraped-spot solutions from thin-layer chromatography

Isoniazid in solutions of tablets was separated by thin-layer chromatography (TLC). The portion of the precoated plate carrying the isoniazid spot was cut out and the coating was scraped off into water. The isoniazid was quantified in the solution, without separation of suspended adsorbent, by second-derivative spectrophotometry, which eliminated the background in the zero-order spectra. Relative standard deviations (n = 5) were <1%. Results obtained for commercial tablets were in good agreement with those given by a liquid-chromatographic method.