Molecular weight different averages

FIGURE 3.31 Experimental slurry viscosity with surfactants of different molecular weights (a) average slurry viscosity as a function of the surfactant concentration and molecular weight, and (b) intrinsic viscosity calculated from eqs. 1 and 2. 

Due to the high molecular weights of the asphaltene particles, these species were absent in all temperature cuts with the exception of the high boiling residue. The difference in the dynamic interfacial tensions of cut 2 and 3 can be explained by the corresponding average molecular weights differences for these two cuts. 

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 . 

An alternative approach is to produce self-crimped fibers by using the bicomponent fiber structures discussed in section 3.5.1. The two components in the fibers can be different polymers or the same polymer but with different average molecular weights, different molecular weight distributions, different additives, or other structural differences. The key to introduce self-crimp is to design stmc-tural asymmetry across the fiber cross-section. 

In this chapter, different mechanisms of chain-reaction polymerization have been discussed in detail. Based on the mechanism involved, expressions for the rate of polymerization, molecular-weight disiributiorr, average chain lengths, and the polydispersity index can be derived. 

The terminal groups of a polymer chain are different in some way from the repeat units that characterize the rest of the molecule. If some technique of analytical chemistry can be applied to determine the number of these end groups in a polymer sample, then the average molecular weight of the polymer is readily evaluated. In essence, the concept is no different than the equivalent procedure applied to low molecular weight compounds. The latter is often included as an experiment in general chemistry laboratory classes. The following steps outline the experimental and computational essence of this procedure ... 

The molecular weights obtained by this method are averages. This is particularly evident from the situations where additives are present. In these cases, two different kinds of chains result, with those terminated by the same end group being stunted in growth compared to the normal polycaprolactam. Yet it is the total weight of polymer and the total number of ends that are... 

The viscosity average molecular weight is not an absolute value, but a relative molecular weight based on prior calibration with known molecular weights for the same polymer-solvent-temperature conditions. The parameter a depends on all three of these it is called the Mark-Houwink exponent, and tables of experimental values are available for different systems. 

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