The problem of finding conditions of the loss of thermodynamic stability by the reaction system was solved on the basis of the developed theory of living free-radical copolymerization. The spinodal's calculations were carried out for a significant number of systems differing in the values of kinetic, stoichiometric, and thermodynamic parameters. Analysis of the results of such calculations revealed some regularities in the spinodal curves' behavior and permitted us to classify their possible topological types. (C) 2003 Wiley Periodicals, Inc.