Methods of measuring molecular weights

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. 

TABLE 12-1 Major Methods of Measuring Molecular Weight... 

Ebulliometry n. Method of measuring molecular weight of polymers under 20,000 based on vapor pressure lowering and boding point elevation. Pethrick RA, Dawkins JW (eds) (1999) Modern techniques for polymer characterization. John Wiley and Sons, New York. 

Different methods of measuring molecular weights and subsequently relating them to dilute solution viscosities [4-10]. 

Method G refers to the method of measuring molecular weight (MW) and molecular weight distribution (MWD) by... 

ASTM D-2502 is one of the most accurate methods of determining molecular weight. The method uses viscosity measurements in the absence of viscosity data, molecular weight can be estimated using the TOTAL correlation. 

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. 

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. 

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

Traditional methods for measuring molecular weight date from the dawn of modem physical chemistry in the 19th century. These relied on so-called colligative property measurements (see box opposite), such as boiling point elevation and freezing... 

Figure 1.6 Gel permeation chromatography (GPC) method to measure molecular weight and its distribution of a polymer.

One approach is the SEC fractionation under the assumption that SEC separates random copolymers in terms of molecular weight and the analysis of the fractions using multiple detection methods to measure molecular weight as well as composition. For example, Montaudo and Montaudo fractionated two copolymers, poly(MMA-co-BA) obtained at high and low conversions by SEC and measured the molecular weight and composition of the fractions by MALDI-TOF MS... 

Nowadays the most common technique for determining the molecular weight distribution of polymers is size-exclusion chromatography (SEC), also known as gel-permeation chromatography (GPC). Other methods for measuring molecular weight distributions exist, but the ease of use and imiversality of SEC makes it the technique of choice for this type of fractionation. 

The relation between density and molecnlar weight of a gas suggests that you could use a measurement of gas density to determine its molecular weight. In fact, gas-density (vapor-density) measurements provided one of the first methods of determining molecular weight. The method was worked out by the French chemist Jean-Baptiste Andre Dumas in 1826. It can be applied to any substance that can be vaporized without decomposing. 

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