Determination of weight-average molecular weights

Determination of Weight Average Molecular weight by Light Scattering... 

ASTM D 4001-93, Test Method for Determination of Weight-Average Molecular Weight of Polymers by Light Scattering, ASTM, West Conshohocken, Pennsylvania, 1997. 

Table 4.2. Determination of weight average molecular weight and particle scattering factor by light scattering for connective tissue macromolecules reproduced...

The presence of two hydroxyl groups per molecule in poly-(methyl methacrylate) and in polystyrene, each polymerized in aqueous media using the hydrogen peroxide-ferrous ion initiation system, has been established " by chemical analysis and determination of the average molecular weight. Poly-(methyl methacrylate) polymerized by azo-bis-isobutyronitrile labeled with radioactive has been shown to... 

The determination of the molecular weight of nanoparticles is performed by gel permeation chromatography (GPC). The experimental setup consists of a high performance liquid chromatography system with a size exclusion column and a refractive index detector. The nanoparticles are usually freeze-dried and dissolved in tetrahydrofuran for analysis on the system. Poly(styrene) or poly(methylmethacrylate) standards are used to calibrate the column, to enable the determination of number average molecular weight (Mn), as in... 

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. 

Determination of Number-Average Molecular Weights by Ebulliometry... 

The introduction of the kinematic viscosity has been proved to be of high value for the investigation and characterization of mineral oils it can replace in many cases the determination of the average molecular weight which now can be predicted. 

FIGURE 7.8 Determination of number average molecular weight by osmometry. [Graph reconstructed from data by Roughton and Kendrew, Haemoglobin, Butterworth, London, 1949, p. 197.]... 

Example Determination of the average molecular weight of a mixture ... 

Molecular weight and fractionation data have to be consulted in order to decide for set a or set b. The exact determination of the average molecular weight of an oligomer is always complicated by the possible loss of volatile parts. Whereas, with some care, hexene and octane may be recovered more or less quantitatively, some loss of butene appears inevitable. By applying Eq. (12) one can correct for this loss. From this equation it follows that a may be determined from the weight fractions of two successive degrees of polymerization as... 

Bradley, and A. B. Holmes, Determination of the average molecular weight of poly(p-phenylene vinylene), Synth. Met. 55-57 902 (1993). 

Determination of the average molecular weight by all the above-mentioned methods (except the end-group analysis method, which is applicable only in a few cases) is the job of specialists, and expensive equipment is required. But tlie advantage is that the determination is not dependent on any previous measurement. These methods are thus absolute and. serve as the ultimat asis for a third type of average termed as Viscosity-Average Molecular Weight, M . 

In the next section we shall describe the use of Eq. (8.83) to determine the number average molecular weight of a polymer, and in subsequent sections we shall examine models which offer interpretations of the second virial coefficient. 

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