Using chromatographic analysis and viscometric investigations of polyamic acids, it has been shown that the linear relationship of the logarithm of intrinsic viscosity and the logarithm of molecular weight of flexible-chain macromolecules exhibits a break on passing from the oligomeric to the polymeric range. Simultaneously, the Huggins constant also changes. These changes result from a decrease in the draining of macromolecules with increasing number of statistical segments. In particular, draining affects the hydrodynamic dimensions determining the SEC-behavior of macromolecules. Semi-empirical expressions have been obtained for the Flory constant Φ and the constants in the Mark-Kuhn-Houwink equation as functions of the draining of macromolecules, the number of their statistical segments and the parameter of volume interaction characterizing the thermodynamic strength of solvent. For this purpose the solution of an integral equation for eigen-functions in the Zimm theory found by Tschoegl was applied.