Salen-Manganese Complexes and their Application in the Ring-Opening Polymerization of Lactide and ε-Caprolactone

Efficiency and sustainability are of vital concern to the polymer industry. Ring-opening polymerizations (ROP) of lactide (LA) and epsilon-caprolactone (E-CL) producing biodegradable polymers polylactide (PLA) and polycaprolactone (PCL) were widely researched. Owing to their abundance and non-toxicity, manganese catalysts are a very good choice. A group of salen manganese (III) complexes were synthesized. Their catalytic activity in the ROP of LA and epsilon-CL in propylene oxide (PO) was. Under activation of PO, manganese complexes could efficiently mediate the ROP of LA and epsilon-CL. The molecular weight distributions could be controlled well. The influence of the bridging part and substitutions were fully discussed. Surprisingly, chlorine substituents showed a negative effect on catalytic activity. The analog computation results indicated that the metal center of 7 a did not become more electron-deficient. By switching the ligand backbone and substituents, the configuration of polylactide (PLA) turned from slight isotactic to slight heterotactic.