Alkali-Metal Monophenolates with a Sandwich-Type Catalytic Center as Catalysts for Highly Isoselective Polymerization of <i>rac</i>-Lactide

Highly isoselective ring-opening polymerization (ROP) of <i>rac</i>-lactide is a challenge for sodium and potassium complexes under mild conditions. In this work, three sodium and potassium complexes with a sandwich-type catalytic center are highly active catalysts for the polymerization of <i>rac</i>-lactide and show high isoselectivities with <i>P</i>_<i>m</i> values of 0.72–0.82. The best isoselectivity of <i>P</i>_<i>m</i> = 0.82 is the highest value for alkali-metal complexes under mild conditions. The molecular weights of the obtained PLA are close to the theoretical values, and the molecular weight distributions are narrow

Iso-Selective Ring-Opening Polymerization of <i>rac</i>-Lactide Catalyzed by Crown Ether Complexes of Sodium and Potassium Naphthalenolates

Two crown ether complexes of sodium and potassium naphthalenolates were synthesized and entirely characterized. The two complexes can iso-selectively catalyze the ring-opening polymerization (ROP) of <i>rac</i>-lactide at room temperature and afford polylactides with desired molecular weights and narrow PDIs; the best isotacticity (<i>P</i>_m) achieved was 0.73

Stereoselective Alkali-Metal Catalysts for Highly Isotactic Poly(<i>rac</i>-lactide) Synthesis

A high degree of chain end control in the isoselective ring-opening polymerization (ROP) of <i>rac-</i>lactide is a challenging research goal. In this work, eight highly active sodium and potassium phenolates as highly isoselective catalysts for the ROP of <i>rac-</i>lactide are reported. The best isoselectivity value of <i>P</i>_m = 0.94 is achieved. The isoselective mechanism is chain-end control through the analysis of the stereoerrors in the microstructure of a final polymer; thus, isotactic multiblock structure polymers are obtained, and the highest melt point can reach 192.5 °C. The donating group in phenolate can clearly accelerate the ROP reaction, potassium complexes are more active than the analogous sodium complexes, and the big spacial hindrance of the ligand can decrease the activity. The high isoselectivities of these complexes mostly result from their sandwich structure constructed by the plane of the crown and the plane of the anthryl group

Trinuclear and Tetranuclear Magnesium Alkoxide Clusters as Highly Active Initiators for Ring-Opening Polymerization of l‑Lactide

Trinuclear and tetranuclear magnesium alkoxide clusters supported by bulky phenolates with triangular or rhombic structures were readily synthesized in acceptable yields via the reaction of 2-<i>N</i>,<i>N</i>-dimethylaminoethanol/methoxyethanol, different phenols, and dibutylmagnesium. These complexes have been characterized using ¹H and ¹³C NMR, elemental analyses, and X-ray crystallography. The experimental results indicate that these clusters are efficient and excellent initiators for the ring-opening polymerizations (ROPs) of l-lactide (LA) and afford polylactides with desired molecular weights and narrow polydispersity indexes (PDIs). Complex <b>2</b> can even catalyze the ROP of 4000 equiv of l-lactide in 1 min in a controlled model. Kinetic studies indicate that the polymerization is first-order for both the trinuclear magnesium complex <b>3</b> and LA. However, for the tetranuclear magnesium complex <b>5</b>, the polymerization rate is first order for <b>5</b> and second order for LA