Synthesis of Zn–Fe double metal cyanide complexes with imidazolium-based ionic liquid cocatalysts <i>via</i> ball milling for copolymerization of CO₂ and propylene oxide

Abstract

In this work, Zn-Fe double metal cyanide (DMC) catalysts were successfully synthesized <i>via</i> clean and efficient ball milling. Imidazolium-based ionic liquids as cocatalysts were incorporated into the structure of the DMC catalysts during the grinding process. The modified Zn-Fe DMC catalysts were effective for the alternating copolymerization of carbon dioxide and propylene oxide under controlled reaction conditions. The properties and structures of the Zn-Fe DMC catalysts and the resulting polymers were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, elemental analysis, ¹H and ¹³C NMR spectroscopy, gel permeation chromatography, and thermogravimetric analysis. The results indicate that the Zn-Fe DMC catalysts exhibit higher thermal stability compared to the DMC catalysts without imidazolium-based ionic liquids (DMC-Blank). We determined that the introduction of a small amount of imidazolium-based ionic liquids can increase the carbonate content of the poly(propylene carbonate) (PPC) copolymer in the range of 18.48-29.00%. The turnover numbers of PPC were ∼4.40. In addition, the measured number-average relative molecular mass was in the range of 2.96 × 10³-4.98 × 10³ with a narrow polydispersity index of 1.00-1.08.