Bimetallic Manganese Catalysts: A Route to Controlled and Switchable Polymerization of Lactones

The sustainable solution to the environmental problem of polymeric materials calls for efficient and well-controlled ring-opening polymerization catalytic systems. Inspired by the highly reactive and stereospecific bimetallic catalysts, three kinds of bimetallic Salen-Mn catalysts supported by biaryl linking moieties are synthesized and applied to polymerization catalysis of lactide (LA) and epsilon-caprolactone (epsilon-CL) in this work. The polymerization is initiated in situ by the ring-opening of epoxide compounds, in which the ionic cocatalyst could accelerate the reaction process. The Mn-Mn coordination effect contributes to the higher activity and iso-selectivity towards LA compared to the mononuclear Salen-Mn catalyst. The reactivity and stereoselectivity are determined by the conformation of catalysts, specifically the Mn-Mn separation and dihedral angle. Finally, the CO2-controlled switchable polymerizations are carried out with LA and epsilon-CL. The reversibility of the on-off switching operation is influenced by the combination between CO2 molecules and active species. The success in binuclear Salen-Mn catalysts not only expands the range of bimetallic catalyst analogues but also claims the promising potential of Mn-based catalysts in practical and theoretical research. Bimetallic Salen-Mn catalysts with biaryl-linkers were developed for ring-opening polymerization of lactide and epsilon-caprolactone. Advanced activity and the iso-selective tendency towards lactide are determined by catalyst conformation and Mn-Mn separation. Finally, the CO2-controlled switchable polymerization succeeded in this catalytic system, in which the on-off reversibility is related to the combination between active species and CO2 molecules.image

Automated summary

This study successfully developed biaryl-linked bimetallic Salen-Mn catalysts for the ring-opening polymerization of lactide and epsilon-caprolactone. The activity and iso-selective tendency towards lactide are determined by the conformation and Mn-Mn separation of the catalysts. Finally, the CO2-controlled switchable polymerization succeeded in this catalytic system, and the reversibility of the on-off switch is related to the combination between active species and CO2 molecules.