Conditions of preparation

Although PS is normally considered a rather brittle material, biaxial orientation imparts some extremely desirable properties, particularly in regard to an increase in elongation. Thus, the 1.5—2% of elongation normally associated with unoriented PS can become as high as 10%, depending on the exact conditions of preparation (267,268). [Pg.528]

With aldehydes some diaziridines condense under the conditions of preparation. The formation of a fused triazolidine ring occurs regularly if aldehydes are treated with ammonia and chloramine to give diaziri-dines [Eq. (39)]. If, however, chloral is added previously to the reaction mixture, the 3-aIkyl-diaziridines (45) arc caught as their chloral adducts. By the alkali fission of these chloral adducts, 3-alkyl-diaziridines, e.g. (45), can be prepared. [Pg.112]

A polymer is a complex mixture of molecules that is difficult to define and reproduce. The quality of the polymer is markedly affected by the conditions of preparation. Different degrees and types of branching, differences in the number and distribution of various irregular structures, along with the degree of purity of the finished product and conditions of further treatment all influence the thermal stability of the polymer and the course of its thermal degradation. This further complicates the study of this polymer and explains the differences be-... [Pg.319]

Most of the studies have involved the alloying of a second metal to platinum. The second metal was generally chosen because of its ability to increase the concentration of oxygenated species on the electrode surface, but also for its corrosion resistance. Even if some discrepancies exist in the literature, R-Ru is now widely accepted as the most interesting one, and hence our analysis will focus on this alloy in the next subsection. Other alloys such as R-lr, R-Os, or R-Re have also been reported to be good candidates, and R-Mo under specific conditions of preparation was claimed to have the desired properties. The Pt-Sn alloy is still a subject... [Pg.88]

CdjPj and CdjAs are low band gap semiconductors (0.5 and 0.1 eV, respectively). The bulk materials are black and start to absorb in the infrared. These materials have been prepared as colloids in alkaline solution by precipitation of Cd with phosphine and arsine Depending on the conditions of preparation, particles of different sizes (between about 2 and 10 nm) were obtained, which could also be recovered in the solid state after evaporation of the solvent. The color of these materials ranged from black to colorless with decreasing particle size, with all kinds of intermediate colors in the visible. [Pg.168]

Increased coefficients relating to the conditions of preparation and the handling procedure are then applied. The aim is to quantify the risk in industrial plants. This might be where this approach may appear to be too specialised to be of use in small scale reactions. The table below gives these coefficients. ... [Pg.155]

The stereochemistry of the silyl ketene acetal can be controlled by the conditions of preparation. The base that is usually used for enolate formation is lithium diisopropyl-amide (LDA). If the enolate is prepared in pure THF, the F-enolate is generated and this stereochemistry is maintained in the silyl derivative. The preferential formation of the F-enolate can be explained in terms of a cyclic TS in which the proton is abstracted from the stereoelectronically preferred orientation perpendicular to the carbonyl plane. The carboxy substituent is oriented away from the alkyl groups on the amide base. [Pg.568]

Golshan-Shirazi, S. and Guiochon, G., Theory of optimization of the experimental conditions of preparative liquid chromatography optimization of column efficiency, Anal. Chem., 61, 1368, 1989. [Pg.126]

By irradiation with light or by heating it to temperatures above 180 °C, white phosphorus is transformed to red phosphorus. Its tint, melting point, vapor pressure and especially its density depend on the conditions of preparation. Usually, it is amorphous or microcrystalline, and it is rather laborious to grow crystals. [Pg.108]

They were easily separated by standard chromatography [32] or HPLC [37] over silica. The yields of the isolated products (107a and b) were low because some decomposition occurred during chromatography over silica [32], No details have been reported regarding the optimization of the yields or determining whether ratios of isomers are constant or vary with time or with the conditions of preparation. [Pg.120]

There are numerous ways in which a metal atom can be incorporated into a dye molecule to form a metal complex. Most attention has been given to complexes of chromium, cobalt and copper. There are essential differences in the conditions of preparation of these compounds. [Pg.248]

The effect of the components and conditions of preparation on the properties of a 70/30 LDPE/clay composite is shown in Table I. The 10/90 mixture of LDEE Bakelite Polyethylene Resin DYNH-1 (Union Carbide Corp.) and Hydrite 10 clay (Georgia Kaolin Co.) was compounded at 150 C in the Brabender Plasticorder in the presence of MAH and/or t-butyl perbenzoate (tBPB). The EE-coated clay was then mixed with additional DYNH-1 LDPE at 130°C to yield a 70/30 PE/clay composite. A 30 70 PE/clay concentrate was prepared in a similar manner at 150 C and converted to a 70/30 EE/ clay composite at 130 C. The 10/90 PE/clay concentrate is an easily handled, clay-like product while the 30/70 concentrate is... [Pg.472]

The method of preparation of the proteins is of great importance. Not only does it affect the amount of polydispersity, but the conformation of the proteins themselves varies depending upon the conditions of preparation. Urea-treated proteins can be renatured if sufficient care is taken to prevent precipitous changes in ionic conditions. Proteins have also been prepared using LiCl which avoids the harsh effects of urea. [Pg.18]

In some cases crystalline polymers show additional absorption bands in the infrared spectrum, as in polyethylene ( crystalline band at 730 cm amorphous band at 1300 cm" ) and polystyrene (bands at 982,1318, and 1368 cm" ). By determining the intensity of these bands it is possible to follow in a simple way the changes of degree of crystallinity caused, for example, by heating or by changes in the conditions of preparation. [Pg.119]

Of RuFa and IrFa small variations of the cell dimensions were reported, depending on the conditions of preparation (139). Probably cations of higher valency were still present by incomplete reaction in reducing the higher fluoride starting material. [Pg.40]

In this communication, we compare VPO catalysts which differ by their conditions of preparation, considering both their LRS spectra registered under reaction conditions and the corresponding catalytic results. LRS data are discussed in relation with results for n-butane oxidation to maleic anhydride. [Pg.218]

Thioamide enolates are also interesting substrates for the stereoselective aldol-type reactions. The aldol stereochemistry is very sensitive to the conditions of preparation of magnesium thioamide enolates and it generally gives different results depending on the procedure used. Illustrations of some aspects of the reactivity are provided in the examples presented below. [Pg.500]

The conditions of preparation and activation of the MgOare very different between the work of Tench et al. (333, 338) and Lunsford et al. (334, 339). Although the resolution is higher in the case of Tench et al. (333, 338), it is difficult to see specific reasons for the difference observed in the 03 spectra and more work is required to resolve this question. [Pg.86]

Anhydrous silver-olefin complexes are readily dissociable, low-melting, and variable in composition 92a, 176, 183). Cyclic olefins and polyolefins form stable complexes with silver nitrate or perchlorate, but again the Stoichiometry of the complexes varies considerably, sometimes depending on the conditions of preparation. The following types have been isolated [Ag(un)2]X (un = e.g., cyclohexene, a- and /3-pinene) ISO), [Ag(diene)]X diene = e.g., dicyclopentadiene 220), cyclo-octa-1,5-diene 50, 130), bi-cyclop, 2,1 ]hepta-2,5-diene 207), and cyclo-octa-1,3,5-triene 52), and [Ag2(diene)]X2 (diene = e.g., cyclo-octa-1,3- and -1,4-diene 180), bi-cyclo[2,2,l]hepta-2,5-diene 1) and tricyclo[4,2,2,0]-decatriene 10)). Cyclo-octatetraene (cot) forms three adducts with silver nitrate 52), viz., [Ag(cot)]NOs, [Ag(cot)2]N03, and [Ag3(cot)2](N03)3. On heating, the first two lose cyclo-octatetraene and all three decompose at the same temperature. From the stoichiometry of the above complexes it appears that the... [Pg.102]

In a more recent publication 43> Savy and co-workers have studied the influence on oxygen activity of the conditions of preparation of iron phthalocyanine in the presence of carbon. They have also discussed a possible mechanism of reaction. [Pg.149]

As noted earlier, gelatin can be converted to macro- or microparticulate systems, depending on the conditions of preparation. [Pg.220]

Many methods have been used to produce and characterize protein foams. The foaming characteristics of proteins are markedly influenced by conditions of preparation, measurement, and so forth (13-18). Because of the variety of methods employed, it is difficult to compare data from different sources. [Pg.154]

The final surfactant structures we consider as models for biological membranes are vesicles. These are spherical or ellipsoidal particles formed by enclosing a volume of aqueous solution in a surfactant bilayer. When phospholipids are the surfactant, these are also known as liposomes, as we have already seen in Vignette 1.3 in Chapter 1. Vesicles may be formed from synthetic surfactants as well. Depending on the conditions of preparation, vesicle diameters may range from 20 nm to 10 pirn, and they may contain one or more enclosed compartments. A multicompartment vesicle has an onionlike structure with concentric bilayer surfaces enclosing smaller vesicles in larger aqueous compartments. [Pg.398]

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