Living polymerization with reversible chain transfer and reversible deactivation: The case of cyclic esters

Polymerization of cyclic esters at the properly chosen conditions can be tr eated as living polymerization, in agreement with the tentative definition of the Nomenclature Commission of IUPAC (Macromolecular Division) requiring that no irreversible transfer or irreversible termination take place. For these processes the most kinetic or structural (end group) studies do not r eveal any deviation. However, since in these polymerizations reversible tra nsfer to backbones of macromolecules and/or reversible deactivation take pl ace, the molar mass distribution can be Poissonian only at certain conditio ns. These processes have been studied quantitatively and the corresponding rate constants were determined. Thus, the importance of these processes cou ld be established by comparing the rate constants of propagation. In this w ay, polymerizations of cyclic esters were used to illustrate the meaning an d scope of the definition of "living polymerization", a process from which irreversible transfer and deactivation are absent and in which living polym ers are formed, i.e. composed of macromolecules that do not irreversibly lo ose their ability to grow.