Comment on the dynamic bead size and Kuhn segment length in polymers: Example of polystyrene

Discrepancies between the length of a traditionally defined Kuhn segment length (l _k) and a bead size estimated from experimental data have been reported in a number of articles. In this work we emphasize that the traditional definition of the Kuhn segment is an oversimplification and the characteristic ratio, C _∞, is not the only parameter that defines a bead size. We show that the dynamic bead size in polystyrene (PS) might be as large as ∼50 monomers, whereas the traditionally defined Kuhn segment is ∼8-10 monomers. It is shown that with 50 monomers (M ∼ 5000) as a size of the dynamic bead, one can explain many inconsistencies in the interpretation of compliance and mechanical relaxation data known for low-molecular weight PS.