Effect of oligomers extraction in polycondensation reactions on number and weight average degree of polymerization

In many polycondensation reactions, the isolated polymer does not contain molecules with low degrees of polymerization. The absence of oligomers affects significantly the average degrees of polymerization, the number-average value, Xn, in particular. Using the Flory theory of linear polycondensation, formulas have been derived for the calculation of the number-average and weight-average degree of polymerization, Xn and Xw, respectively, as a function of the extent of reaction, p, and the minimum degree of polymerization of molecules present in the polymer.