ZnO/SiO2-modified rare-earth-metal ternary catalyst bearing quaternary ammonium salts for synthesis of high molecular weight poly(propylene carbonate)

Abstract

A modified rare-earth-metal catalyst system combined with quaternary ammonium salts (QASs) as cocatalysts was investigated in the alternating copolymerization of CO2/propylene oxide (PO) to produce poly(propylene carbonate) (PPC). In the presence of ZnO/SiO2, the ZnEt2-glycerine- Y(CCl3OO)3 catalyst presented higher activity for CO2/PO copolymerization, as well as a higher molecular weight of polycarbonate, while maintaining the high carbonate content originating from the neat ZnEt2-glycerine-Y(CCl3OO)3 catalyst. In the presence of QASs bearing different halide anions (F−, Cl−, and Br−), the type of the halide anion had a strong influence on the activity of the catalyst for CO2/PO alternating copolymerization. Only tetramethylammonium fluoride (TMAF) could promote the alternating copolymerization without increasing the by-product. Combined the ZnO/SiO2 catalyst and TMAF, the catalytic activity for CO2/PO polymerization increased dramatically compared to the basic ternary catalyst system. The improved catalyst system produced a polymer with a high carbonate unit level equivalent to that of the polycarbonate produced by the basic ZnEt2-glycerine- Y(CCl3OO)3 catalyst system.