NSSN-Type Group 4 Metal Complexes in the Ring-Opening Polymerization of l-Lactide

Ring-Opening Polymerization of rac-β-Butyrolactone Promoted by New Tetradentate Thioether-Amide Ligand-Type Zinc Complexes

In this work, thioether-amide ligands featuring a combination of hard amide groups with soft donor groups have been employed to develop new zinc catalysts for the ring-opening polymerization of cyclic esters. All complexes were prepared in high yields through alkane elimination reactions with diethyl zinc and characterized using nuclear magnetic resonance (NMR) spectroscopy. Density functional theory (DFT) characterization provided insight into the parameters that influence catalytic activity, such as steric hindrance at the metal center, Lewis acidity and electronic density of thioether-amide ligands. In the presence of one equivalent of isopropanol, all complexes were active in the ring-opening polymerization of rac-β-butyrolactone. Quantitative conversion of 100 monomer equivalents was achieved within 1 h at 80 °C in a toluene solution. Number-average molecular weights increased linearly with monomer conversion; the values were in optimal agreement with those expected, and polydispersity index values were narrow and relatively constant throughout the course of polymerization. The most active complex was also effective in the ring-opening polymerization of ε-caprolactone and L-lactide. To propose a reliable reaction path, DFT calculations were undertaken. In the first step of the reaction, the acidic proton of the alcohol is transferred to the basic nitrogen atom of the amide ligand coordinated to the zinc ion. This leads to the alcoholysis of the Zn-N bond and the formation of an alcoholate derivative that starts the polymerization. In subsequent steps, the reaction follows the classical coordination-insertion mechanism.

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.

Metallocene catalysts for the ring-opening co-polymerisation of epoxides and cyclic anhydrides

The ring-opening co-polymerization (ROCOP) of epoxides and cyclic anhydrides is a versatile route to new polyesters. The vast number of monomers that are readily available means that an effectively limitless...