Open- and Closed-Loop Recycling: Highly Active Zinc Bisguanidine Polymerization Catalyst for the Depolymerization of Polyesters.

In this study, the aliphatic N,N-bisguanidine zinc complex [Zn(DMEG2ch)2](OTf)2·THF is introduced as a promising candidate for the chemical recycling of (bio)polyesters. This catalyst is highly active in the ring-opening polymerization (ROP) of lactide (LA) and ε­caprolactone (CL). The combination of polymerization and depolymerization activity creates new pathways towards a sustainable circular economy. The catalytic activity of [Zn(DMEG2ch)2](OTf)2·THF for the chemical recycling of polylactide (PLA) via alcoholysis was investigated by detailed kinetic and thermodynamic studies. It is shown that various high value-added alkyl lactates can be obtained efficiently under mild reaction conditions. Catalyst recycling was successfully tested using ethanol for the degradation of PLA. In addition, LA can be recovered directly from PLA, enabling either open- or closed-loop recycling. Selective PLA degradation from mixtures with polyethylene terephthalate (PET) and polymer blends are presented. For the first time, a cascade recycling reaction of a PLA/polycaprolactone (PCL) blend is tested with a zinc-based bisguanidine catalyst, whereby PLA is degraded selectively at first and subsequent modification of the reaction conditions leads to efficient degradation of the remaining PCL. The highly active, universally applicable benign zinc catalyst allows the implementation of a circular plastics economy and thus the reduction of plastic pollution in the environment.

Effective Ligand Design: Zinc Complexes with Guanidine Hydroquinoline Ligands for Fast Lactide Polymerization and Chemical Recycling.

In this study, the synthesis of two new guanidine hydroquinoline ligands served as basis for six new zinc guanidine complexes. Two of these complexes showed very high activity in the lactide polymerization under industrial conditions. The lactide polymerization was demonstrated in solution and melt conditions observing high activity and molar masses up to 90 000 g mol-1 . Density functional theory studies elucidated the high activity of the complexes associated with the influence of the ligand backbone and the use of triflate counterions. On the way towards a circular economy, polymerization and depolymerization go hand in hand. So far, guanidine complexes have only shown their good activity in the ring opening polymerization of esters, and guanidine complexes with pure N donors have not been tested in recycling processes. Herein, the excellent ability of zinc guanidine complexes to catalyze both polymerization and depolymerization was demonstrated. The two most promising zinc complexes efficiently mediated the methanolysis of polylactide into methyl lactate under mild reaction conditions.

Effective Ligand Design: Zinc Complexes with Guanidine Hydroquinoline Ligands for Fast Lactide Polymerization and Chemical Recycling.

Invited for this month's cover is the group of Sonja Herres-Pawlis at RWTH Aachen University. The image shows how the zinc guanidine complexes help a circular economy of bioplastics by mediating the ring-opening polymerization of lactide and the depolymerization of polylactide (PLA). The Research Article itself is available at 10.1002/cssc.202201075.