Moderate route for the utilization of CO2-microwave induced copolymerization with cyclohexene oxide using highly efficient double metal cyanide complex catalysts based on Zn3[Co(CN)6]

Abstract

Zn₃[Co(CN)₆] based double metal cyanide complexes are currently used as catalysts for both the ring-opening polymerization of epoxides and the copolymerization of epoxides and CO₂. This paper reports an environmentally friendly route for the copolymerization of cyclohexene oxide (CHO) with CO₂ using microwave irradiation. The reaction occurred over a faster reaction time (2–30 min) and a much lower pressure (9.7 bar) than conventional methodologies giving a high molecular weight (19.3 kg mol⁻¹) polycarbonate with a higher level of CO₂ incorporation (f_CO2 = 75%). The catalysts were prepared from an aqueous solution of ZnX₂ and K₃[Co(CN)₆] using tert-butanol and polyethers as complexing agents. All the catalysts were characterized by elemental analysis, ICP-OES, XRD, XPS and IR spectroscopy. The catalysts were found to be highly selective for the copolymer with a high TOF (TOF = 25 177 h⁻¹) values. Unlike conventional synthesis, there was no induction period noticed for the catalyst to initiate copolymerization. The high reactivity and excellent properties of the copolymer might be due to the higher activation of CHO by microwaves due to its high polarizability and higher dielectric constant.