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

Highly Iso-Selective and Active Catalysts of Sodium and Potassium Monophenoxides Capped by a Crown Ether for the Ring-Opening Polymerization of <i>rac</i>-Lactide

Sodium and potassium complexes supported by a bulky monophenoxy with one xanthenyl group at the ortho-position and 18-crown-6 or 15-crown-5 as an auxiliary ligand were synthesized and characterized. These complexes are highly iso-selective and active catalysts for the controlled ring-opening polymerization of <i>rac</i>-lactide. The best isotacticity (<i>P</i>_m) achieved was 0.86, which is the highest iso-selectivity reported to date for an alkali-metal complex. In addition, the corresponding polymer exhibited a high <i>T</i>_m of 182 °C. Furthermore, the polymerization looks like an anti-Arrhenius reaction, which is slower at high temperatures than at low temperatures

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

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