During the last decade enormous efforts have been made to develop new catalysts for the controlled polymerization of lactide and other cyclic esters. There were some very important review. Many studies have focused on the use inorganic complexes in the polymerization of esters of cyclic ring opening. These systems typically operate using so-called mechanism of coordination, administration, in which the catalyst activates monomer for the aggressive influence of alkoxide ligands within the same complex. That is why the community uses the terms "catalyst" and "initiator" interchangeably.
Attempts have been made in detail to understand this mechanism, there have been several reports of highly active catalysts. For example, the complex metal alkoxide diketiminat (M = Mg, Zn and Ca), zinc ethoxide phenoxy diamine and gomolepticheskie phenates Yttrium can perform the polymerization of lactide at very high speed addition to the high rate of polymerization is also possible to regulate stereobalansa in the polymerization of racemic mixtures of S, S-and R, R-lactide or R, S-lactide, which allows PLA with controlled symmetrical molecular structure. Since the symmetry of the molecular structure influences, such as its order, the temperature melting and degradation rate of these systems proved to be quite useful for monitoring the properties of PLA. For example, chiral complexes of Al (salen) (Fig. 2) showed a remarkable selectivity for the polymerization of racemic lactide, and the rate constant for the addition of R, R enantiomer is 20 times greater than that of S, S enantiomer. As a result of these initiators to create a "Stereoblock-PLA from racemic lactide.