Solvent independent parameters in the viscometry of polymer solutions

Evidence is discussed for and against the existence of a common meeting point when linear plots of ηsp/C against C for polystyrene in a number of solvents are extrapolated to negative concentrations. There is rather more evidence in favor than against, and most of the contrary evidence falls into a category for which exceptional behavior might be anticipated. The ordinate of the common meeting point, unlike the limiting viscosity number, is independent of solvent and is conveniently called the true limiting viscosity number [η]T. [η]T has been identified with the intrinsic configurational character of a polymer chain. The common point of intersection has the coordinates [η]T and C2, where Cx is a negative concentration. The product of [η]T and Cx has been found to be constant over a considerable molecular weight range. This leads to an expression for [η]/[η]T in terms of Huggins' k′. [η]/[η]T represents the ratio of the hydrodynamically equivalent volume of a polymer in an actual solvent to the equivalent volume of the chain in its natural state of extension. [η]T is considered in relation to [η]θ (Flory‐Fox) and [η]P (Bawan). The effect of polymer heterogeneity is discussed.