Dilute solution method

For gel-containing rubbers the dilute solution properties of the soluble fraction obviously do not represent the gum rubber. 

Because determination of osmotic pressure and light scattering requires special instrumentation and skill to operate, they are usually used for fundamental research only. Because of the convenience, DSV and GPC are more frequently nsed. GPC provides a fractionation curve, not just mass-average and number-average. DSV is usually just used to obtain a bench-mark of MW, without questioning a presence or absence of branching. The following discnssion covers the reliability of information obtainable from GPC with processability in mind. 

GPC is often described as a method for determining MW and its distribntion. This is not true - it is a method for fractionation according to the hydrodynamic size of the swollen polymer coil. The fractionation uses columns packed with porous material usually it is 

When the branch pattern of a sample in question is not known, there is no way to calibrate. The question of calibration is often ignored. The data of MW and MW distribution reported in the literature are often only relative values, based on the linear polystyrene standards. This may still be useful if a sample in question is unbranched. For branched polymers, such data does not have a precise meaning. 

Some elaborate methods have been developed for obtaining information about the degree of branching from GPC data. It requires a rather tedious procedure. Moreover, degree of branching ignores the difference of branch patterns. Therefore, it has only a very limited use. 

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Powling, J., and H. J. Bernstein A dilute solution method for the spectroscopic determination of the energy difference between rotational isomers. J. Amer. chem. Soc. 73, 1815 (1951). 

The diffusion coefficient of the solvent can be determined from the tracer coefficient Df by the use of the correlation factor / and the relationship D f—Df as in the case of the pure substance. However, is not required in the description of the chemical reaction (i.e. in Pick s equations) for this case of dilute solutions. Methods exist whereby the changes in the values of and Z>2 on going from dilute to no longer dilute metallic solutions with the addition of solute 2 can be estimated. These approximations are based upon detailed atomic models of the same sort as are used to calculate jump frequencies of individual atoms or defects from measured tracer diffusion coefficients. In the first approximation, the diffusion coefficients are given by expressions of the form D cs jD° (1 + otiNa) [15, 16], where a is a factor of proportionality. This type of expression has already been discussed. 

Rheological properties are far more sensitive to the molecular weight distribution, and particularly to the high molecular weight tail, than are properties measured by dilute-solution methods such as SEC. It is not unusual to find, for example. 

Characterisation of Gum Rubber Using Dilute Solution Methods... 

The dilute solution methods have been used for characterising polymers since day one of polymer science. Measurements of dilute solution viscosity, osmotic pressure and light scattering have been well-established in theory as well as in practice. They are described practically in every textbook and in many review articles. More than 30 years have passed since the introduction of size exclusion chromatography (or gel permeation chromatography CPC), which provides fractionation data very conveniently. This chapter is not intended to be a review of these methods. It is directed to examining how useful these methods are with respect to sensitivity, reproducibility, and reliability. Stated differently, the question is whether or not differences in processability can be explained on the basis of information available from the dilute solution methods. 

As described in Chapters 1, 2 and 4, gels are present in many gum rubbers, exerting a critical influence on their processability. For gel-containing rubbers, the dilute solution methods are not applicable, because gels are removed by filtration. Therefore, the determination of gel content is the first order of the business in the characterisation of gum rubbers. 

The Mooney index is often called Mooney viscosity hut there is no rationale that the index represents viscosity. It is an expression of some aspect of viscoelasticity in that there may be some relationship to the processability. The method uses an instrument with a particular design, which provides a simple operation and a quick result. Compared to the dilute solution method, the sample size required is much larger so that it is more representative of the commercial lot. The Mooney index has been used worldwide as a specification for gum rubbers. 

The long relaxation times introduced by the long branches of commercial gum rubbers have significant influence, even though the amount of the branched fraction may be very small. In the characterisation using dilute solution methods sometimes the branched fraction is filtered off. Then, the interpretation of the processability becomes very difficult. 

It seems appropriate to assume the applicability of equation (A2.1.63) to sufficiently dilute solutions of nonvolatile solutes and, indeed, to electrolyte species. This assumption can be validated by other experimental methods (e.g. by electrochemical measurements) and by statistical mechanical theory. 

Describe one laboratory method for the preparation of a dilute solution of hydrogen peroxide. 

When the ascending solvent-front has reached a convenient height, the strip is removed, the position of the solvent-front marked, and the paper strip dried. The positions of the various solutes, if they are coloured compounds, now appear as clear separate spots. Frequently however, the solutes are colourless, and the position of their spots must be determined by indirect methods, such as their fluorescence in ultraviolet light, or their absorption in such light (when the spots appear almost black), or by spraying the paper with a dilute solution of a reagent which will give a coloured insoluble derivative with the solutes. 

Noth. The above method can be successfully applied only to dilute solutions of formaldehyde which are free in particular from other alfphatic aldehydes, since the latter, if present, would undergo a similar oxidation. Formaldehyde, if mixed with other aldehydes, should be estimated by quantitative addition of potassium cyanide for details, see advanced text-books of quantitative organic analysis. 

Description of Method. Quinine is an alkaloid used in treating malaria (it also is found in tonic water). It is a strongly fluorescent compound in dilute solutions of H2SO4 (f = 0.55). The excitation spectrum of quinine shows two absorption bands at 250 nm and 350 nm, and the emission spectrum shows a single emission band at 450 nm. Quinine is rapidly excreted from the body in urine and is easily determined by fluorescence following its extraction from the urine sample. 

The ratio of reactants had to be controlled very closely to suppress these impurities. Recovery of the acrylamide product from the acid process was the most expensive and difficult part of the process. Large scale production depended on two different methods. If soHd crystalline monomer was desired, the acrylamide sulfate was neutralized with ammonia to yield ammonium sulfate. The acrylamide crystallized on cooling, leaving ammonium sulfate, which had to be disposed of in some way. The second method of purification involved ion exclusion (68), which utilized a sulfonic acid ion-exchange resin and produced a dilute solution of acrylamide in water. A dilute sulfuric acid waste stream was again produced, and, in either case, the waste stream represented a... 

The most popular device for fluoride analysis is the ion-selective electrode (see Electro analytical techniques). Analysis usiag the electrode is rapid and this is especially useful for dilute solutions and water analysis. Because the electrode responds only to free fluoride ion, care must be taken to convert complexed fluoride ions to free fluoride to obtain the total fluoride value (8). The fluoride electrode also can be used as an end poiat detector ia titration of fluoride usiag lanthanum nitrate [10099-59-9]. Often volumetric analysis by titration with thorium nitrate [13823-29-5] or lanthanum nitrate is the method of choice. The fluoride is preferably steam distilled from perchloric or sulfuric acid to prevent iaterference (9,10). Fusion with a sodium carbonate—sodium hydroxide mixture or sodium maybe required if the samples are covalent or iasoluble. 

For many years fluorine has been deterrnined by the Willard-Winters method in which finely ground ore, after removal of organic matter, is distilled with 72% perchloric acid in glass apparatus. The distillate, a dilute solution of fluorosiUcic acid, is made alkaline to release fluoride ion, adjusted with monochloroacetic acid at pH 3.4, and titrated with thorium nitrate, using sodium a1i2arine sulfonate as indicator. 

Analytical and test methods for the characterization of polyethylene and PP are also used for PB, PMP, and polymers of other higher a-olefins. The C-nmr method as well as k and Raman spectroscopic methods are all used to study the chemical stmcture and stereoregularity of polyolefin resins. In industry, polyolefin stereoregularity is usually estimated by the solvent—extraction method similar to that used for isotactic PP. Intrinsic viscosity measurements of dilute solutions in decahn and tetraHn at elevated temperatures can provide the basis for the molecular weight estimation of PB and PMP with the Mark-Houwiok equation, [rj] = KM. The constants K and d for several polyolefins are given in Table 8. 

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