Viscosity averaged molecular weight

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. 

A slightly different but useful way of defining the viscosity average molecular weight is the following ... 

MWR = is used, where Af is a melt-viscosity-average molecular weight defined by the equation Af = antilog, (0.493 log Tf + 3.5576, where Tj is... 

Table 3. Intrinsic Viscosity—Viscosity Average Molecular Weight Relationships as a Function of Hydrolysis...

For commercial purposes the molecular weight is usually characterised from measurements of the viscosity of dilute solutions. It has been shown that, for dilute solutions, the relation between the viscosity and the molecular weight (in this case the viscosity average molecular weight) may be given by the relationship... 

Viscosity average molecular weights Mv were determined using a Ubbelohde viscometer and diisobutylene solutions at 20 °C with at least three dilutions for every solution. The Mv was calculated from intrinsic viscosity28. Averages of two determinations are reported. Reproducibility was 10%. 

IV. Viscosity Average Molecular Weights of Polyisobutylenes 1. Introduction... 

The viscosity average molecular weight of PGA was determined using the Mark-Hownik-Sakurade equation with the necessary constants from ref. [8]... 

The viscosity average molecular weight depends on the nature of the intrinsic viscosity-molecular weight relationship in each particular case, as represented by the exponent a of the empirical relationship (52), or (55). However, it is not very sensitive to the value of a over the range of concern. For polymers having the most probable distribution to be discussed in the next chapter, it may be shown, for example, that... 

My Number, weight, and viscosity average molecular weights, respectively. 

To perform this analysis, we first prepare a dilute solution of polymer with an accurately known concentration. We then inject an aliquot of this solution into a viscometer that is maintained at a precisely controlled temperature, typically well above room temperature. We calculate the solution s viscosity from the time that it takes a given volume of the solution to flow through a capillary. Replicate measurements are made for several different concentrations, from which the viscosity at infinite dilution is obtained by extrapolation. We calculate the viscosity average molecular weight from the Mark-Houwink-Sakurada equation (Eq. 5.5). 

The viscosity average molecular weight typically falls somewhere between Mn and 5.2.3.3 Melt Flow Rate... 

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