CO2 Copolymerization Catalyzed by the Double Metal Cyanide Catalysts Zn-Fe(III)/Zn-Co( III) with Nanometer-Sized γ-Al2O3 as Co-Catalyst

In this work, Zn-Fe(III) and Zn-Co(III) double metal cyanide (DMC) catalysts were successfully synthesized via clean and efficient ball milling and characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD). Different proportions of gamma-Al2O3 as co-catalyst were added in the CO2/PO copolymerization catalyzed by Zn-Fe(III) DMC/Zn-Co(III) DMC. The structure and thermal stability of the polymer product polypropylene carbonate (PPC) were analyzed and characterized by FTIR, H-1 and C-13 nuclear magnetic resonance (H-1-NMR, C-13-NMR), gel permeation chromatography (GPC), and thermogravimetric analysis (TGA). The results show that gamma-Al2O3 as co-catalyst successfully aids DMC in the synthesis of copolymers, and effectively enhances the catalytic performance of the catalysts. The amount of co-catalyst has a great influence on the catalytic activity. The number-average molecular weight of the polymers is 1.8-8.9 K, with a polydispersity index (PDI) of 1.04-2.06 and turnover number (TON) of 69.21-392.12. The thermal stability of the polymer products is greatly improved in comparison with those without the co-catalyst. The highest decomposition temperature of PPC catalyzed by Zn-Co(III) DMC with 3 wt.% gamma-Al2O3 is 378.8 degrees C.