SUSTAINABLE ALIPHATIC POLYESTERS AND POLYCARBONATES BY NHC-BASED ZINC AND MAGNESIUM COMPLEXES

Aliphatic polyesters and aliphatic polycarbonates respond excellently to the urgency of a transition from fossil-based polymers to more environmentally sustainable alternatives. In fact, most of them are derived from renewable resources and boast biodegradability. In recent years, aliphatic polyesters and aliphatic polycarbonates with controlled architectures have garnered significant attention for both biomedical applications and packaging. The optimal strategy for obtaining these polymers in a controlled manner is the ring-opening polymerization (ROP) of their corresponding cyclic monomers. In this context, metal complexes based on non-toxic and readily available metals have emerged as the catalysts of choice, promoting sustainable and efficient ROP processes. In this contribute, we report N-Heterocyclic Carbene (NHC) ligands used as coordinative environments for zinc and magnesium centres. The synthesized complexes are active as catalysts in the ROP of different cyclic monomers: both lactones, as lactide and -caprolactone, and cyclic carbonates such as trimethylene carbonate and its alkyl-substituted congeners, purposely obtained from renewable substrates, such as CO2 and 1,3-diols. Various characterization techniques, such as NMR, MALDI-ToF, and SEC analyses, confirmed that the obtained polymers have the desired structures and molecular weights. In-depth studies of the polymerization reactions were conducted through kinetic studies and NMR-scale reactions to understand the nature of the species involved in the catalytic cycle. Finally, we highlighted the versatility of the catalytic species by demonstrating their ability to close the life-cycle of the polylactide by promoting its chemical recycling.