New publication in ChemSusChem about lactide polymerisation online


The development of novel and sustainable catalysts for the ring-opening polymerization of lactide is one of the research fields of the Herres-Pawlis group. In order to obtain an alternative to the currently applied tin(II)octanoate, the applicability of the developed catalysts in industrial conditions is of special interest.

In contrast to the so far mainly investigated zinc(II)-complexes, this publication deals with iron(II)-complexes. Three novel and promising iron(II)-complexes where synthesized from iron(II)chloride and a N,N-donor-hybrid guanidine and two N,O-donor-hybrid guanidine ligands, respectively. The X-ray structures of these complexes were determined. Moreover, the complexes where applied in the bulk polymerization of technical-grade rac-lactide. The polymerizations were monitored with in-situ Raman spectroscopy.

The observed activity of the three complexes proved that the catalysts are robust and tolerate the impurities present in technical-grade lactide. However, the two investigated iron(II)-N,O-donor complexes showed a significantly higher activity than the iron(II)-N,N-complex. The two complexes exhibit an even higher activity than the fastest known robust zinc(II)-catalysts.

In addition, the rate constant of propagation k p was determined for the two N,O-donor complexes: One of the complexes shows an activity similar to tin(II)-octanoate, the other complex surpasses the activity of the tin catalyst by one order of magnitude. With molar masses above 90.000 g mol-1, the produced polymers are suited for industrial processing.

In conclusion, the presented novel iron(II)-hybrid guanidine catalysts provide promising results and represent a decisive advance towards the tin-free lactide polymerization.

The article New kids in lactide polymerization: highly active and robust iron guanidine complexes as superior catalysts is available on the webpage of the publisher.