Determination of number-average molecular weights

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 Number-Average Molecular Weights by Ebulliometry... 

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.]... 

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. 

In addition to its major use in determining the number-average molecular weight (Ma) of polymers, osmometry has also been used to determine M of block copolymer micelles. The method involves determining the osmotic pressure (77) across a membrane that is permeable to solvent only. Because osmotic pressure is a colligative property, it depends on the number of particles, and hence yields Ma. It also depends on the interactions between particles, and thus... 

Evaluation of the various kinetic parameters using Eq. (9.39) requires a determination of the concentration of polymerization centers [C j. This quantity is usually determined from experiments in which the C sites are quenched (made inactive) with CHsO H, CO, or C02 [7,25]. Other methods include the use of number-average molecular weight (combined with polymer yield) and C-labeled Group I-III-metal alkyl component. Each of the techniques has limitations that require careful consideration if reliable results are to be obtained. 

Membrane osmometry was measured on a few samples to determine the number average molecular weight (Mn). Regenerated cellulose membranes were used, and were found to be highly swollen in NMP, leading to both very long equilibration times and excellent retention of low molecular weights. Table I below shows the results of these and the above measurements for the samples reported here. 

From these equations one may determine, in particular, Gf from the data of number-average molecular weight and Gp at a given type of termination. 

Perdue et al. (1976) observed an excellent linear correlation between the combined concentrations of Fe and Al and DOM in the Satilla River system (southeast U.S.A.). Such a correlation is likely to result from the formation of dissolved organic complexes rather than the adsorption of DOM onto colloidal iron hydroxide particles. Furthermore, using vapour pressure osmometry, Perdue et al. (1976) determined the number-average molecular weight of the DOM to be 1296, thus enabling them to derive an (Fe + Al) DOM stoichiometric binding ratio of 0.8—1.1, in agreement with the values for soil... 

Determined by a measure of elastic deformation plotted as a function of number average molecular weight... 

The phenolic end groups of the polysulfone oligomers were titrated potentiometrically with tetramethylammonium hydroxide in N,N Dimethylformamide to determine the number average molecular weight (Mn) by a method developed in our laboratory (10). 

The chain-transfer rate constants, ktr, are determined from the average molecular weight in a polymerizing system. The intercept of a Mayo plot of number-average molecular weight against [I]/Rp where [I] is the initiator concentration and i p is the polymerization rate (20). Extensive compilations of tr values are found in the open literature (21). Dodecyl mercaptan is used in the manufacture of commercial Neoprene W. The chain-transfer rate constant for dodecyl mercaptan with chloroprene was determined using the Mayo plot technique (22) as follows ... 

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