Viscosity of Polymer Solutions and Molecular Weight Characterization

Since the pioneering research by Staudinger on dilute solution viscosity and its relation to the polymer molecular weight, viscosity analysis has become a valuable technique for polymer characterization. The conventional approach is based on the Huggins approximation of the solution-specific viscosity by a quadratic function of concentration, c. We show how to reformulate this approach in a universal form by representing a solution-specific viscosity, η_sp, as a generalized universal function η_sp(c) = α(c/c*) + (1 - α)(c/c*)² of chain overlap concentration, c*, determined at η_sp = 1, with numerical coefficients α = 0.745 ± 0.005 for good and 0.625 ± 0.008 for a θ solvent. This viscosity representation can be viewed as a calibration curve for molecular weight determination from a measurement of the solution viscosity at a given solution concentration. Furthermore, the molecular weight dependence of the overlap concentration provides a means for quantifying the polymer/solvent affinity and the solvent effect on chain flexibility. The extension of the approach to semidilute solutions opens a path for obtaining molecular weight in a broad concentration range without requiring a dilution and monitoring its change during the polymerization reaction from solution viscosity.