Effect of α-, β-, γ-, and δ-dicarbonyl complexing agents on the double metal cyanide-catalyzed ring-opening polymerization of propylene oxide

Organic complexing agent (CA) plays a crucial role in generating active sites of double metal cyanide (DMC) catalyst in the ring-opening polymerization (ROP) of epoxides. Considering dicarbonyl compounds are versatile and present a great variety of coordination modes besides the usual bidentate behavior of monoanions, the usefulness of the dicarbonyl compounds as CAs for Zn(II)-Co(III) DMC catalysts is investigated. The structural properties of the catalysts were defined by X-ray powder diffraction patterns, elemental analysis, and thermogravimetric analysis. The interaction of the dicarbonyl ligand on the catalyst surface is evaluated by integrating infrared, UV–vis absorption and X-ray photoelectron spectroscopies. The turnover frequencies (calculated by mol-PO per mol-Zn per minute) of the DMC catalysts bearing β-, γ-, and δ-diesters are significantly higher than those of conventional catalysts specifically bearing tert-butyl alcohol as a CA. The resultant polyols exhibit very low levels of unsaturation and narrow polydispersity indexes. The molecular weight and functionality of the resultant polyols can be tuned by modifying the polymerization parameters. Systematic studies on the effect of the new CAs on the catalytic behavior offer great potential for the synthesis of high quality polyols.