Solvent-free mechanochemical synthesis of zinc glutarate for the heterogeneous catalysis of propylene oxide and CO2 copolymerization

Zinc glutarate (ZnGA) is used as a solid-state heterogeneous catalyst for the synthesis of aliphatic polycarbonate from the alternating copolymerization of CO2 and epoxide. However, the conventional synthesis of ZnGA involves the use of a large amount of toluene, which is a toxic substance. In the present study, we developed a solvent-free, environmentally friendly synthesis for ZnGA using a mechanochemical process. This accelerated the formation of flake-like ZnGA microcrystals in a shorter reaction time than that of the conventional method. X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption fine structure analyses, and Fourier-transform infrared spectroscopy revealed that ZnO is the most effective source of Zn. This catalyst selectively produced poly(propylene carbonate) from CO2 and propylene oxide, with a molecular weight (Mn) of 25,000 and a molecular weight distribution (Mw/Mn) of 5.27. We believe that this mechanochemical synthesis is a sustainable alternative to conventional approaches.