Molecular Weight size average

In the bad batch all of the molecular chains are 4 in. long and all weigh the same (Fig. 2-16a). This is the molecular size and molecular weight. The average molecular size can be determined statistically 4 in. + 4 in. + 4 in. = 12 in. divided by 3 molecules = 4 in. which is the average molecular size of the polymer chains. 

What does exist, however, is GPC, which separates the molecules in a polymer on the basis of molecular size (weight). The large molecules elute from the column earlier than small molecules and from this elution profile both the weight-average molecular weight (size) and the molecular weight (size) distribution can be calculated. 

One way to specify molecular size is by the length of the end-to-end vector r (Fig. 3.6) that runs from the start to the end of an isolated chain, or between the crosslinks at the end of a network chain. The molecule is assumed to be unstressed, so its equilibrium shape has end-to-end vector tq. The average length of to will be calculated for a polymer with a C—C single bond backbone of a particular molecular weight. The average is over a large number of similar chains, and over a period of time. 

Fig. 26. Top bivariate distribution of chain sizes and compositions for poly(MMA-co-BA) obtained at high conversions. Bottom corresponding contour map. The random copolymer was fractionated by SEC and the average molecular weight and average composition of each fractions were determined by MALDI-TOF MS and NMR, respectively. The mol fraction of MMA was calculated according to the Stockmayer s theoretical prediction. Reproduced from [142] with permission...

I do, however, consider it sensible to introduce the word primary valence chain , because it refers to structures that are not completely identical to what has been called a molecule up to now. 1 always associate the word molecule with the concept of a large number of completely identical structures, whereas the term primary valence chain is specifically supposed to include the fact that the same substance contains structures that are very similar to each other, cannot be separated from each other by chemical methods but differ from one another a little in their size, so that while it is not possible to indicate a precise molecular weight, an average primary valence chain length can be quoted. If this fact is specifically added to your macromolecule, then the two terms are, as far as I can see, identical and it is a question of convenience whether one says primary valence chains or macromolecules of fluctuating size . 

In addition to the amino acid sequence, the identity of a protein can be distinguished by certain physical parameters such as molecular weight, size, and shape. The average density of a soluble protein is 1.33 g/cm. ... 

The various expressions we have developed in this section relating p to the size of the polymer are all based on h. Accordingly, we note that the average reactant molecule in this mixture has a molecular weight of 100 as calculated above. Therefore the desired polymer has a value of = 50 based on this concept. 

Three polystyrene samples of narrow molecular weight distribution were investigatedf for their retention in GPC columns in which the average particle size of the packing was varied. In all instances the peaks were well resolved. The following results were obtained ... 

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