Size-exclusion chromatography weight average

Size-exclusion chromatography (sec) easily and rapidly gives the complete molecular weight distribution and any desired average (6). Thus, it has become the technique of choice for determining molecular weights despite its relatively high initial cost. 

ASTM D 5296 - 92 (1994). Standard Test Method for Molecular Weight Averages and Moleeular Weight Distribution of Polystyrene by High Performance Size-Exclusion Chromatography. Annual Book of ASTM Standards, Vol.08.03, pp. 419-431. 

In 1971, Hiatt et al. found that polyethylene oxide (PEO) of molecular weight about 100000 prevented the adsorption of rabies virus to porous glass with an average pore diameter of 1250 A. The support was modified by passage of one void volume of 0.4% solution of the polymer in water, followed by 5 or more volumes of distilled water or buffered salt solution. The virus was effectively purified from the admixtures of brain tissue fluid by means of size-exclusion chromatography on the modified glass column [28]. 

When the full distribution is needed, it is measured by size-exclusion chromatography (also called gel permeation chromatography). This is a solution technique that requires dissolution of the polymer in a reasonable solvent such as tetrahydrofuran or tetrachlorlobenzene. For polymers that require exotic solvents or solution temperatures above about 150°C, a simple measurement of solution viscosity can be a useful surrogate for the actual molecular weight. The viscosity of the pure polymer (i.e., a polymer melt viscosity) can also be used. Such simplified techniques are often satisfactory for routine quality control, particularly for condensation polymers such as PET that vary in average molecular weight but usually have a polydispersity of 2. 

Ordinate values of the molecular weight distribution rather than molecular weight averages obtained from size exclusion chromatography were used in the modelling (3.9). [Pn] in Equation (1) can be transformed into (log M), the ordinate of the molecular weight distribution using (2) ... 

Determination of the average molecular weight and its distribution can be assessed by gel permeation or size-exclusion chromatography on solution polymers. The crystallinity of a polymer can be measured by DSC, density or X-ray diffraction. 

A reliable procedure for determination of molecular parameters number, weight and z-averages of the molecular weight (Mj, i = n, w and z respectively) for polyethylenes, PE, by means of Size Exclusion Chromatography, SEC, has been developed. The Waters Sci. Ltd. GPC/LC Model 150C was used at 135 C with trichlorobenzene, TCB, as a solvent. The standard samples as well as commercial stabilized and not stabilized PE-resins were evaluated. The effects of sampling, method of solution preparation, addition of antioxidant(s), thermal and shear degradation were studied. The adopted procedure allows reproducible determination of and M , with a random error of 4% and M2, with 9%, within 2 to 72 hrs from the initial moment of preparation of solutions. 

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