New Kids in Lactide Polymerization: Highly Active and Robust Iron Guanidine Complexes as Superior Catalysts.

Polylactide is a biodegradable versatile material based on annually renewable resources and thus CO -neutral in its lifecycle. Until now, tin(II)octanoate [Sn(Oct )] was used as catalyst for the industrial ring-opening polymerization of lactide in spite of its cytotoxicity. On the way towards a sustainable catalyst, three iron(II) hybrid guanidine complexes were investigated concerning their molecular structure and applied to the ring-opening polymerization of lactide. The complexes could polymerize unpurified technical-grade rac-lactide as well as recrystallized l-lactide to long-chain polylactide in bulk with monomer/initiator ratios of more than 5000:1 in a controlled manner following the coordination-insertion mechanism. For the first time, a biocompatible complex has surpassed Sn(Oct) in its polymerization activity under industrially relevant conditions.