1.5c.3c Viscosity-Average Molecular Weight. The viscosity average molecular weight is written as
The logic of this definition follows the logic used in defining average diameters based on surface area or volume discussed above and, as its name implies, is a molecular weight average determined from viscosity measurements on polydisperse polymer samples. The exponent a in this definition is called the Mark-Houwink coefficient, generally 0.5 < a < 1.0. The exponent is characteristic of the polymer-solvent-temperature conditions of the experiment. We see how these experiments are conducted and the significance of the Mark-Houwink coefficient in Chapter 4. For now, we may take Equation (20) as merely ...