Zinc-complexes for the synthesis and chemical degradation of polyesters

Aliphatic polyesters represent very promising alternatives to traditional plastics due to their general biocompatibility, agile hydrolytic degradation, and good physical properties. Moreover, these characteristics can be modulated by varying the microstructure, composition, and architecture of the polymer chain. In this class of polymers, polylactide (PLA) plays a leading role as it is obtained from annually renewable sources and it is already currently used for several applications (packaging, medical and agriculture fields). Also noteworthy are linear aliphatic polyesters (such as, polycaprolactone PCL, polypentadecalactone PPDL), for which increasing the number of methylene units between the ester groups along the polymer chain improves mechanical properties, such as ductility and strength, at the expense of biodegradability. However, the renewability of the starting monomers and the intrinsic biodegradability of the polymer do not indicate sustainability in themself. Thus, to build a circular economy of the plastic, efficient strategies of chemical degradation into monomers and/or production of value-added material with a relative high market value, must be implemented (Figure 1).1 Figure 1: Possible circular economy for polylactide (PLLA), polycaprolactone (PCL) and polypentadecalactone (PPDL). In this contribution, we introduce new zinc complexes supported by tridentate imino-phenolate ligands with different substituents. They have demonstrated high efficiency and control for synthesis and chemical degradation of different polyesters. While the PLA chemical degradation has already been reported with other catalytic systems in the literature, here we report the first example of PPDL degradation under solvent-free condition and at room temperature.2