1. For polydisperse commercial polymers synthesized in different reactors, there is no single relationship between the basic indices of molecular structure and the rheological characteristics of the polymer. Such a relationship, independent of the manufacturing technology, exists only for linear polymers with narrow MWD. 2. The molecular structure of polydisperse polymers synthesized in different units has certain specific features that are not taken into account by the weight-average molecular weight, the polydispersity index, or the degree of molecular branching. These specific features of polymers can be taken into account by the use of coefficients that are constants for each synthesis unit, applying these coefficients in equations relating these indices to the rheological characteristics of the polymer. 3. Since polymers synthesized in a given unit are monotypical in MWD, their properties can be described by using a very few indices of molecular structure.