Molecular weight measuring

The solubility parameter of poly(ethylene terephthalate) is about 21.8 MPa but because it is a highly crystalline material only proton donors that are capable of interaction with the ester groups are effective. A mixture of phenol and tetrachloroethane is often used when measuring molecular weights, which are about 20 000 in the case of commercial polymers. 

Column dispersity (band spreading) causes the measured molecular weight distribution to be broader than the true molecular weight distribution (Fig. 3.5). Because Zorbax PSM columns exhibit very low band-spreading characteristics, these columns have historically provided better molecular weight distribution accuracy than many gel-type columns. 

FIGURE 3.5 Measured molecular weight distribution (by HPSEC) is broader chan the true molecular weight distribution. 

We have already seen that the behavior of gases is important to a chemist. The pressure-volume behavior leads to the particle model of a gas. Differences among gases (in properties such as color, odor, and solubility) show that the particles of one gas differ from the particles of another gas. In chemical reactions, the simple combining volume relationships support Avo-gadro s Hypothesis and, hence, give us a way to measure molecular weights. 

This returns us to the problem of the determination of molecular weight. Avogadro s Hypothesis provides one of the convenient ways of measuring molecular weight if the substance can be vaporized. 

The viscosity of a dilute solution of polymer depends on the molecular weight of the polymer. This gives us a simple method for measuring molecular weight based on viscosity, which is readily measured. 

To measure Molecular weight prepare a solution of polystyrene log/litre and from this solution, 10 ml of solutions having concentrations 8, 6, 4, 2 g/litre respectively were prepared by diluting with toluene. The Osmotic pressure of various solutions were measured. 

Light scattering from solutions can be used to measure Molecular weights as low as that of sucrose and as high as those of proteins. In actual practice, polymer Molecular weights are of the order of 10,000-10,000,000 and can readily be measured. The method has been used for determination of absolute values... 

Mark returned to research after the modernization program was organized and operating smoothly. Limited to cellulose chemistry by the necessity of commercial feasibility, he studied cellulose acetate and the effect of the degree of acetylation on product solubility. At the same time he worked closely on the development of suitable analytical methods to measure molecular weight distribution and the degree of functionality. 

Gel electrophoresis, a common analytical method in biological and medical research, can be conveniently applied in the analysis of dendritic polymers, owing primarily to the unique structure of the dendrimer analytes. It has currently been used to assess purity, measure molecular weight of dendrimers,... 

Table 17. Comparison of different techniques for measuring molecular weight...

What are colligative methods for measuring molecular weight and what kind of molecular weight do... 

What is the advantage of using viscometry to measure molecular weight ... 

Polyvinyl Chloride. The results obtained for a polyvinyl chloride sample are listed in Table 5. It is seen that the measured molecular weight statistics are in reasonable agreement with the nominal values. The Mark-Houwink parameters K and a obtained from the linear plot of log [nl vs. log M are in good agreement with one group of literature values (41-43) while the a value is lower than that of another group. (3,44-46)... 

The radiation G values, G(s) and G(x), of a polymer can be determined by measuring molecular weight changes which occur during irradiation and applying equations 1 and 2 (5.61. 

Why are isotonic drinks useful Osmotic pressure in living systems is incredibly important yet how often is the topic dismissed or merely discussed as a means to measure molecular weight of polymers Why not consider polymers as biological macromolecules and add to the discussion that a balance of osmotic pressure keeps our cells from bursting - which goes back to why the isotonic sport drinks are useful Relevance in the examples used in our courses is possible. 

Like the vinyl ethers, isopropenyl acetate does not readily form homopolymers by free radical initiation. It does participate in the donor-acceptor mode of polymerization with maleic anhydride and the copolymer was made by free radical polymerization (see Table III). When attempts were made to measure molecular weight by GPC using THF as a solvent on STYRAGEL columns, the polymer did not elute. Therefore, viscosity in acetone at 30"C was used as a measure of molecular size changes on irradiation. The changes on exposure... 

Another recent trend in molecular weight work that was discussed at the ACS Symposium but is not covered formally in the book is the work of the American Society for Testing and Materials ASTM is in the process of preparing and testing standard methods of measuring molecular weight. Those who are interested or have suggestions to make may write to ASTM, 1916 Race Street, Philadelphia, Pa. 19103. The committee numbers are D20.70.04 and. 05. 

The Use of Mass Chromatography to Measure Molecular Weights and to Identify Compounds Related to the Polymer Field... 

Bisphenol-A oligomers can be characterized by end-group analysis and by other conventional methods for measuring molecular weight, but... 

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