SynopsisThe intrinsic viscosity [q] and the translational friction coefficientf of polymer molecules in solution are calculated on the basis of the porous sphere model. The only information needed to predict [q] and f is the polymer molecular weight, the radius of gyration in the solvent, and the permeability as a function of position in the "porous sphere." For systems for which this information is available there is satisfactory agreement between predicted and directly measured values of
INTRODUCTIONWell known quantities, used to characterize polymer molecules in solution are [q], the intrinsic viscosity, and f, the translational friction coefficient of the polymer molecules at infinite dilution. The determination of [q] and f from viscosity and sedimentation measurements, respectively, is relatively simple. However, in the interpretation of the measured values in terms of polymer molecular weight, radius of gyration, and, in particular, solvent flow through and around the polymer coils, some questions have remained unanswered.Almost invariably the molecular theory of Kirkwood and Riseman1,2a is taken as a starting point in this interpretation. In the Kirkwood-Riseman theory the degree of hydrodynamic interaction (influence of nearby as well as more remote parts of the polymer chain on the solvent flow at a certain point) is expressed by the value of the so-called draining parameter h, which may run from zero (no hydrodynamic interaction) to infinity (dominant hydrodynamic interaction). The parameter h is* a combination of quantities that occur in the molecular model. It is almost impossible to derive their value, and therefore that of h, from the chemical structure of the particular polymer and solvent considered.For this reason h is often treated as an adjustable parameter and the value assigned to it is the one that makes theoretical and experimental values of [q] and f agree.It then appears that all flexible polymers, whatever the quality of the solvent, show a behavior that corresponds to "dominant hydrodynamic interaction" ( h