Kinetics of D,L-Lactide Polymerization Initiated with Zirconium Acetylacetonate

Living ring-opening polymerization of β-butyrolactone initiated by mononuclear zirconium compounds containing sterically hindered N,O-chelate and anionic dimethylamide ligands†

The ring-opening polymerization of β-lactones into polyhydroxyalkanoates (PHA), biodegradable polymers with high molecular weight and narrow polydispersity, is of significant interest. The mononuclear zirconium compound containing sterically hindered N,O-chelate and anionic dimethylamide ligands was used as an initiator for the polymerization of β-butyrolactone (BBL), resulting in polyhydroxylbutyrate (PHB) with a number-average molecular weight of 12 000 g mol⁻¹. Kinetic studies demonstrate a first-order dependence on β-butyrolactone (BBL) concentration at room temperature, accompanied by narrow molecular weight distributions (ca. 1.03–1.07), indicating a well-controlled living polymerization.

The ring-opening polymerization of β-lactones into polyhydroxyalkanoates (PHA), biodegradable polymers with high molecular weight and narrow polydispersity, is of significant interest.

Synthesis of Polyacids by Copolymerization of l-Lactide with MTC-COOH Using Zn[(acac)(L)H2O] Complex as an Initiator

This work presents the results of research on the preparation of bioresorbable functional polyestercarbonates containing side carboxyl groups. These copolymers were synthesized in two ways: the classic two-step process involving the copolymerization of L-lactide and a cyclic carbonate containing a blocked side carboxylate group in the form of a benzyl ester (MTC-Bz) and its subsequent deprotection, and a new way involving the one-step copolymerization of L-lactide with this same carbonate, but containing an unprotected carboxyl group (MTC-COOH). Both reactions were carried out under identical conditions in the melt, using a specially selected zinc chelate complex, with Zn [(acac)(L)H₂O] (where: L-N-(pyridin-4-ylmethylene) phenylalaninate ligand) as an initiator. The differences in the kinetics of both reactions and their courses were pictured. The reactivity of the MTC-COOH monomer without a blocking group in the studied co-polymerization was much higher, even slightly higher than L-lactide, which allowed the practically complete conversion of the comonomers in a much shorter time. The basic final properties of the obtained copolymers and the microstructures of their chains were determined. The single-step synthesis of biodegradable polyacids was much simpler. Contrary to the conventional method, this made it possible to obtain copolymers containing all carbonate units with carboxyl groups, without even traces of the heavy metals used in the deprotection of the carboxyl groups, the presence of which is known to be very difficult to completely remove from the copolymers obtained in the two-step process.