Composition analysis of an ethylene–propylene block copolymer by fractionation and turbidity measurements at the lower critical solubility gap

The composition of an ethylene-propylene block copolymer with a nominal 15% content of ethylene by weight (EP?B15%) has been investigated through fractionation near the lower critical solution temperature (LCST). Observation of the solution heated above the boiling point of the solvent indicated that some polymer was phase separating, apparently continuously, between the LCSTs of polyethylene (PE) an polypropylene (PP) of similar molecular weight. IR and DSC analysis of three fractions obtained by twice separating the concentrated phase from the dilute phase gave the following result: EP?B15% consists of an ethylene-rich block copolymer (93% E), an EP copolymer of intermediate composition, and a propylene-rich copolymer (94% P). The three fractions constitute respectively 12%, 12%, and 76% of the total weights. In order to choose a suitable temperature for fractionation, a turbidity analysis of the solution of the initial polymer is made continuously during phase separation. The trace of turbidity against temperature shows three peaks of turbidity at temperatures T₀, T₁ and T₂, which can be associated with the above fractions. A mixture of PE, PP, and a 33% E random copolymer gives a turbidity trace with characteristic temperatures very similar to that of EP-B15% in the same solvent. Fractionation from several solvents or mixtures of solvents indicated that the composition of the fractions did not depend significantly on the nature of the solvent. Conditions for obtaining a quantitative analysis of a mixture from a thermogram are discussed. Turbidity analysis during phase separation and fractionation at the LCST can be a useful tool in analyzing and separating complex mixtures before use of powerful analytical techniques such as NMR or IR spectroscopy.     

Rhodium(I) catalyzed carbonylation reactions of halides and ethers

Benzylic bromides and methyl iodide react with ethers, carbon monoxide, potassium iodide, and the dimer of chloro(1,5-hexadiene)rhodium($\text{I}$) to give esters in good yields.     

High density amorphous ices: disordered water towards close packing

The structure of amorphous ice under pressure has been studied by molecular dynamics at 160 K. The starting low-density phase undergoes significant changes as the density increases, and at rho=1.51 g/cm(3) our calculated g(OO)(r) is in excellent agreement with in situ neutron diffraction data obtained at 1.8 GPa and 100 K on very high density amorphous ice made at 150 K. As the system is further compressed, in the theoretical simulations, up to rho=1.90 g/cm(3), the structural modifications are continuous up to the highest density. The analysis of orientational distributions reveals that dense amorphous ice is characterized by major distortions of the tetrahedral geometry, and that the pressure structural changes, already observed experimentally at lower densities, can be interpreted as a trend towards a disordered closed-packed structure.     

Cyclization of 2- and 3-indolylthiobenzoic,phenylacetic and nicotinic acids and esters to novel indole-containing tetracyclic ring systems

A series of 2- and 3-indolylthio benzoic, phenylacetic and nicotinic acids or esters were cyclized under dehydrative conditions affording several tetracyclic indole-containing ketones, several of which constitute the first reported examples of novel ring systems, such as the [1]benzothiepino[2,3-b] and [3,2-b]indole and the pyrido[3′2′:5,6] and [3′4′:5,6]thiopyrano[2,3-b] and [3,2-b]indole as well as the [3′2′:5,6] and [3′4′:5,6][1,3]thiazino[3,2-a]indole ring systems.     

UV and IR absorption cross-sections of HCHO, HCDO, and DCDO

UV (240-370 nm) and IR (3200-1500 cm(-1)) absorption cross-sections of HCHO, HCDO, and DCDO in a bath gas of N(2) at atmospheric pressure and 296 K are reported from simultaneous measurements in the two spectral regions. Cross-sections were placed on an absolute scale through quantitative conversion of formaldehyde to CO and HCOOH by titration with Br atoms, also monitored by FTIR. The integrated UV absorption cross-sections of HCHO, HCDO, and DCDO are equal to within the experimental uncertainty.     

Dérives de l'imidazo[2,1-b]thiazole. V. Transposition allylique observée au cours de la synthése d'(imino-2 alkyl-3 thiazolinyl-4) acetates d'ethyle et de (dihydro-5,6 imidazo[2,1-b]thiazolyl-3) acetates d'éthyle

Ethyl (6-phenyl-5,6-dihydroimidazo[2,1-b]thiazol-3-yl) acetate hydrobromide shows an allylic transposition in alkaline medium and gives ethyl (6-phenyl-2,3,5,6-tetrahydroimidazo[2,1-b]thiazol-3-ylidene)acetate. This compound possesses an exocyclic double bond which is stable upon acidification. The intermediate ethyl (2-imino-3-alkylthiazolin-4-yl)-acetates undergo an analogous transposition upon treatment with base, which is reversible upon acidification. These transpositions were observed in the pmr data. The steric constraint and π p π conjugation are discussed in this work.     

Determination of vanadium in biological tissue by anion exchange chromatography and neutron activation analysis

A method is described for determination of vanadium in biological tissues. This method consists of a wet digestion of the tissue with nitric acid followed by anion exchange chromatography, neutron irradiation, and radioassay. The chromatographic separation will allow the decontamination of vanadium from radioactivatable sodium and chlorine which are present in large quantities in biological tissues. The validity of the method is evaluated by employing NBS-SRM 157 and 157a Bovine Liver employing the method of standard additions. The method is successfully applied to human, cow and rat liver specimens. The detection limit of the method is one ppb.     

Improvement of quantum efficiency using surface texture of solar cell in the form of pyramid

The work presented in this paper is concerned a detailed study about the light transmission through textured surfaces in a surface made up of pyramids [1, 2]. We investigate to what extent and under what conditions we want to take advantage of ray incidence five times and more [3, 4]. It is found that these analyses can be used to determine the optimal surface texture which provides the best light trapping for solar cells in terms of the total internal reflection occurring in the high-index medium at incidence angles larger than the nominal critical angle [5–11]. One of the main contributions of this paper is the analysis and quantification of the influence of the opening between the heads of the two closest pyramids in textured surface for solar cells and its application on the photovoltaic parameters such as the quantum efficiency. In this model we show that the material can have five and more successive incident ray absorptions instead of three currently, where we changed the direction of the reflected ray, by varying the angle between the two neighbouring pyramids, the incidence angle, the opening between the heads of the two closest pyramids and their height. Thus, with an angle between the two neighbouring pyramid varying between 20° and 12° and for angle of incidence varying between 80° and 84°. For these values of the angle between the two neighbouring pyramids and incidence angle, the opening between the heads of the two closest pyramids varied respectively from 3.53 to 2.10 µm for a pyramid height of 10 µm. This lead to a substantial increase of the quantum efficiency thus the photovoltaic efficiency.