Crystallinity determination by x-ray

The value for the heat of fusion of PPS, extrapolated to a hypothetical 100% crystalline state, is not agreed upon in the literature. Reported values range from approximately 80 J/g (19 cal/g) (36,96,101) to 146 J/g (35 cal/g) (102), with one intermediate value of 105 J/g (25 cal/g) (20). The lower value, 80 J/g, was originally measured by thermal analysis and then correlated with a measure of crystallinity determined by x-ray diffraction (36). The value of 146 J/g was determined independently on uniaxially oriented PPS film samples by thermal analysis, density measurement via density-gradient column, and the use of a calculated density for 100% crystalline PPS to arrive at a heat of fusion for 100% crystalline PPS (102). The value of 105 J/g was obtained by measuring the heats of fusion of well-characterized linear oligomers of PPS and extrapolation to infinite molecular weight. 

CA resonance line vs. degree of crystallinity determined by x-ray analysis. native cellulose, o regenerated cellulose,... 

It is important to note that the conductivity values reported here are measured on films and layers, which have been spin-coated or deposited from dispersion. These samples have not been stretched. The conductivity is isotropic. The crystallinity, determined by x-ray, does not seem to be increased. 

Fig. 16. Integrated fraction of the downfield component of the C4 resonance line versus degree of crystallinity, /, determined by X-ray analysis., Native cellulose O, regenerated cellulose , mercerized cotton and ramie. (The data for regenerated cellulose samples, except for cupra rayon fibres, were reproduced from ref. 45).

The equimolar copolymer of ethylene and tetrafluoroethylene is isomeric with poly(vinyhdene fluoride) but has a higher melting point (16,17) and a lower dielectric loss (18,19) (see Fluorine compounds, organic-poly(VINYLIDENE fluoride)). A copolymer with the degree of alternation of about 0.88 was used to study the stmcture (20). Its unit cell was determined by x-ray diffraction. Despite irregularities in the chain stmcture and low crystallinity, a unit cell and stmcture was derived that gave a calculated crystalline density of 1.9 g/cm. The unit cell is befleved to be orthorhombic or monoclinic (a = 0.96 nm, b = 0.925 nm, c = 0.50 nm 7 = 96%. 

Crystallinity of polypropylene is usually determined by x-ray diffraction (21). Isotactic polymer consists of heHcal molecules, with three monomer units pet chain unit, resulting in a spacing between units of identical conformation of 0.65 nm (Fig. 2a). These molecules interact with others, or different... 

Chemical conversion of compounds to intermediates of known absolute configuration is a method routinely used to determine absolute configuration (86). This is necessary because x-ray analysis is not always possible suitable crystals are required and deterrnination of the absolute configuration of many crystalline molecules caimot be done because of poor resolution. Such poor resolution is usually a function of either molecular instability or the complex nature of the molecule. For example, the relative configuration of the macroHde immunosuppressant FK-506 (105) (Fig. 8), which contains 14 stereocenters, was determined by x-ray crystallographic studies. However, the absolute configuration could only be elucidated by chemical degradation and isolation of L-pipecoUc acid (110) (80). 

The molecular structure of yellow crystalline Xe(OTep5)4 has been determined by X-ray analysis (see Pig. 18.3b) / the Xe atom is surrounded by a square-planar array of four O atoms, with the adjacent TeFj groups pointing, curiously, pair-wise up and down from this plane (Xe-O 203.9(5) and 202.6(5) pm, Te-O 188.5 pm). 

Polyester fibers contain crystalline as well as noncrystalline regions. The degree of crystallinity and molecular orientation are important in determining the tensile strength of the fiber (between 18-22 denier) and its shrinkage. The degree of crystallinity and molecular orientation can be determined by X-ray diffraction techniques. ... 

Peptoids based on a-chiral aliphatic side chains can form stable helices as well [43]. A crystal of a pentameric peptoid homooligomer composed of homochiral N-(1-cyclohexylethyl)glycine residues was grown by slow evaporation from methanol solution, and its structure determined by X-ray crystallographic methods. In the crystalline state, this pentamer adopts a helical conformation with repeating cis-... 

It was not until 1981 that the first brevetoxin structure was determined (13), PbTX-2, the most plentiful of the brevetoxins, was purified to crystallinity and the structure determined by x-ray crystallography. This important first step was the result of a three-group collatoration among Clardy, Lin, and Nakanishi. The yields of the major components from 50 L of culture (ca. 5 x 10 cells) were 0.8 mg of PbTX-1, 5.0 mg of PbTX-2, and 0.4 mg of PbTX-8. The structure of PbTX-2,... 

There are no known examples of supported clusters dispersed in crystallo-graphically equivalent positions on a crystalline support. Thus, no structures have been determined by X-ray diffraction crystallography, and the best available methods for structure determination are various spectroscopies (with interpretations based on comparisons with spectra of known compoimds) and microscopy. The more nearly uniform the clusters and their bonding to a support, the more nearly definitive are the spectroscopic methods however, the uniformities of these samples are not easy to assess, and the best microscopic methods are limited by the smallness of the clusters and their tendency to be affected by the electron beam in a transmission electron microscope furthermore, most supported metal clusters are highly reactive and... 

The crystallinity of zeolites was determined by X-ray powder diffraction with a Broker D8 Advance X-ray powder diffractometer. Diffractograms of both zeolites exhibited good crystallinity and characteristic diffraction lines with no additional crystalline phases. This was further supported by SEM images. 

The crystalline compound (109) exists in a bicyclic form, as determined by X-ray analysis. In benzene solution absorption of an hydroxyl group appears. At the same time all three methine protons in the H NMR spectra are equivalent and in the 31P NMR spectrum there is only one signal. 

The thermal decomposition of 91a gave rise to a 2 1 mixture of 92a and 93 in a total yield of 33%. 91b afforded diazoalkane 94 in 76% yield, which was a crystalline compound, whose structure could be determined by X-ray analysis. Besides 94, 92b was produced in trace quantities. However, when the pyrolysis reaction of 91b was carried out at 9 torr, 92b was isolated in 48% yield. Decomposition of 91c resulted also in a 1.4 1 mixture of 92c and 95 in 34% yield, whereas 92d was the sole product (37% yield) of 91d.27... 

Research into these compounds has followed the usual pattern for the study of very reactive compounds.584 585 First, the compounds are obtained only as transient intermediates that are characterized by their reactions, then longer-lived compounds are obtained that can be studied in solution at low temperature finally, compounds are designed, usually by building in steric protection, that can be obtained as crystalline solids, the structures of which can be determined by X-ray crystallography. These advances have been made alongside related studies of the chalcogenides of the other group 14 metals.584,585... 

A variety of techniques have been used to determine the extent of crystallinity in a polymer, including X-ray diffraction, density, IR, NMR, and heat of fusion [Sperling, 2001 Wunderlich, 1973], X-ray diffraction is the most direct method but requires the somewhat difficult separation of the crystalline and amorphous scattering envelops. The other methods are indirect methods but are easier to use since one need not be an expert in the field as with X-ray diffraction. Heat of fusion is probably the most often used method since reliable thermal analysis instruments are commercially available and easy to use [Bershtein and Egorov, 1994 Wendlandt, 1986], The difficulty in using thermal analysis (differential scanning calorimetry and differential thermal analysis) or any of the indirect methods is the uncertainty in the values of the quantity measured (e.g., the heat of fusion per gram of sample or density) for 0 and 100% crystalline samples since such samples seldom exist. The best technique is to calibrate the method with samples whose crystallinites have been determined by X-ray diffraction. 

Elemental composition Co 38.03%, 8 20.68%, O 41.29%. 8ohd cobalt(Il) suhate is brought to aqueous phase by acid digestion, appropriately diluted, and analyzed for cobalt by flame or furnace AA or ICP. It also may be determined in the solid crystalline form by x-ray methods. The suhate anion may be measured by dissolving an accurately measured small amount of salt in measured quantities of water and analyzing the solution by ion chromatography. 

FIGURE 2. Stmctural data of the crystalline dimesityldioxirane as determined by X-ray analysis. (Courtesy of Prof. Dr. Wolfram Sander, Reference 16b)... 

Apart from nitrile-hydrolyzing enzymes, some esterases and cutinases have been used for surface hydrolysis of PAN [74], These enzyme were shown to specifically hydrolyse vinyl acetate moieties present as co-monomer in many commercial PAN materials, with no changes in crystallinity as determined by X-ray diffraction [74],... 

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