How is the z‐Average Molar Mass Related to the Sedimentation Data?

Abstract Nowadays, students, professors, and researchers in the field of polymer education and research know how different average molar masses of polymer chains are defined in textbooks, but not everyone knows that these different averages actually come from different experimental methods, not purely from different mathematical definitions and calculations. Some of the detailed knowledge have been lost in literature and even textbooks during the polymer development process. The z‐ average molar mass ( M z ) is one of the typical examples; namely, why it is called the z‐ average and how it is related to the concentration profile inside an ultracentrifuge cell. Currently, it is rather difficult, if not impossible, to find how to derive the final equation used in the calculation of M z . It is the purpose of this paper to show a simple and nontedious derivation of how to obtain M z from a sedimentation experiment, very different from the original old paper published by Lansing and Kraemer in 1935. It is also experimentally shown how to calculate M z by using the ultracentrifuge data from a mixture of three polystyrene standards.