AbstractRelations between molar massMand molar mass dependent propertiesEof polymers are mostly strictly valid only for monomolecular samples i:\documentclass{article}\pagestyle{empty}\begin{document}$ M_i = {\rm f (}E_i )\quad \quad \quad \quad \quad \quad (1{\rm a}) $\end{document}For polymolecular polymer samples thecorresponding averagesMavandEavmust be applied:\documentclass{article}\pagestyle{empty}\begin{document}$ M_{{\rm av}} = {\rm f (}E_{{\rm av}} )\quad \quad \quad \quad \quad \quad (1{\rm b}) $\end{document}Provided the kind of average (number‐, weight‐ or any general average) of e.g.Mavis known, the corresponding averageEavis given by. Eqs. (1a, b). This is demonstrated for the relationships of van't Hoff and Mark‐Houwink, frequently used for the determination of molar masses of polymers. It is also shown that the four different relations for the expansion factor α by Flory‐Stockmayer, Fixman, Ptitsyn, and by Yamakawa‐Tanaka can be applied topolymolecularpolymer samples (i.e. without fractionation), provided the corresponding averages[η]avandMavfrom the Mark‐Houwink relationship are taken for the evaluation of the para