Controlled polymerization of cyclic esters. structure of initiators and of active species related to the selectivity of initiation and propagation

This paper reviews mostly the already published work of our own, complemented with some new data and related to the control (i.e. selectivity) in the anionic and covalent (pseudoanionic) polymerization of cyclic esters. Ionic and covalent growing species are briefly compared in terms of their susceptibility to undergo side reactions. Then, structures of covalent initiators (mostly multivalent metal alkoxides) are discussed from the view point of their behavior in initiation and formation of active species. R₂AlOR', (RO)₃Al, and other metal alkoxides are discussed.