Quantitative comparison of selectivities in the polymerization of cyclic esters

Chain transfer processes (k(tr)) laking place in the polymerization (anionic and pseudoanionic) of cyclic esters (lactones) are reviewed. These reactions are mostly responsible for the departure of these systems from the fully controlled (living) polymerizations. The ratios of k(p)/k(tr) have been determined for a number of initiating systems and the structures of the growing species are related to their selectivity, expressed by k(p)/k(tr). It has been shown that the less reactive and more sterically crowded active species polymerize more selectively.