Wide molecular weight

Concretes and absolutes, both obtained by total extraction of the plant material and not subject to any form of distillation other than solvent removal, are complex mixtures containing many chemical types over wide molecular weight ranges. In some cases, gas chromatographic analysis shows httle volatile material. Yet these products have powerful odors and contribute in important ways to the perfumes in which they are used. 

The primary polymerization product ia these processes has a relatively wide molecular weight distribution, and a separate step is often used to narrow the polydispersity. Such a narrowkig step may consist of high vacuum stripping to remove volatile polymer chains, often followed by a solvent fractionation step (35,36), sometimes a solvent fractionation step alone (37,38), or a fractional precipitation from organic solvent (32). The molecular weight distribution can also be narrowed by depolymerization at elevated temperatures ia the presence of a depolymerization catalyst (217—220). 

Wax usually refers to a substance that is a plastic solid at ambient temperature and that, on being subjected to moderately elevated temperatures, becomes a low viscosity hquid. Because it is plastic, wax usually deforms under pressure without the appHcation of heat. The chemical composition of waxes is complex all of the products have relatively wide molecular weight profiles, with the functionaUty ranging from products that contain mainly normal alkanes to those that are mixtures of hydrocarbons and reactive functional species. 

In addition, subsequent chain transfer reactions may occur on side chains and the larger the resulting polymer, the more likely will it be to be attacked. These features tend to cause a wide molecular weight distribution for these materials and it is sometimes difficult to check whether an effect is due inherently to a wide molecular weight distribution or simply due to long chain branching. 

Addition of low molecular weight resins with narrow molecular weight distribution produces compatible resin-elastomer blends, while incompatible blends are obtained with resins having a wide molecular weight distribution. In a recent study... 

Nonionic polysaccharides are one of the most simple substances to analyze by size exclusion chromatography because they seldom exhibit nonsize exclusion effects. Due to their wide molecular weight distribution, TSK-GEL PW columns are recommended for their analysis. 

This paper reviews the experiences of the oil industry in regard to asphaltene flocculation and presents justifications and a descriptive account for the development of two different models for this phenomenon. In one of the models we consider the asphaltenes to be dissolved in the oil in a true liquid state and dwell upon statistical thermodynamic techniques of multicomponent mixtures to predict their phase behavior. In the other model we consider asphaltenes to exist in oil in a colloidal state, as minute suspended particles, and utilize colloidal science techniques to predict their phase behavior. Experimental work over the last 40 years suggests that asphaltenes possess a wide molecular weight distribution and they may exist in both colloidal and dissolved states in the crude oil. 

The polymers of 1,4-hexadienes have unusually wide molecular weight distributions. This is illustrated by the gel permeation chromatogram of the methanol-insoluble fraction of poly(5-methyl-1,4-hexadiene) in tetrahydrofuran (Figure 9). The polymer was obtained in 82% conversion and had an inherent viscosity of 2.1 dl./g. in toluene at 25°C. 

PAMAM dendrimers provide a series of nearly precise macromolecules with almost equivalent charge density, yet a wide molecular weight range (a few hundred to almost a million), of which gel electrophoretic analysis can be carried out under native conditions [21],... 

SEC calibration methods which employ a series of narrow MWD standards are based upon a peak position method and traditionally have been the most widely practiced calibration procedures. The peak position method simply correlates the peak elution volume of each standard to its nominal molecular weight or size value. A curve fitting procedure (usually a least squares regression) is used to obtain a working calibration curve. The serious limitation of polymer chemical types for which a series of narrow MWD standards covering a wide molecular weight range can be obtained led to the development of experimental approaches which could be applied to polymer chemical types other than that of the narrow MWD standards employed in calibration. 

These results are reminiscent of and very similar to those reported here for the relaixation parameters of polyethylene oxide as illustrated in Figs. 5 and 7. We have found that the s are continuous with teit5>erature over a very wide molecular weight range. However, as is shown in Fig. 5, there are discontinuities in linewidths at the melting temperatures for the low molecular weight samples, but the linewidths are continuous... 

Without doubt, electrospray is the method of choice in the case of CE/ MS hyphenation. The domain of ESI is polar compounds of a wide molecular-weight range, such as the typical CE analytes. Molecules can be transferred directly from the separation capillary to the mass spectrometer via an interface. This allows the detection of multiply chargeable species of high molecular mass. 

Field ionization mass spectrometry (FIMS) was applied to the different compound classes by Boduszynski et al. (1980). The FIMS molecular weight envelopes shown in Fig. 8 illustrate the similar but wide molecular weight distribution for each compound class. Furthermore, the FIMS molecular weight of about 1000 are considerably lower than those obtained by other methods in which intermolecular association may influence measured values. This is evident in Table IX by the comparison of VPO... 

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