Preparation of Keggin-type monosubstituted polyoxometalate ionic liquid catalysts and their application in catalyzing the coupling reaction of ethylene carbonate and dimethyl succinate to synthesize poly(ethylene succinate)

Abstract

A series of Keggin-type monosubstituted polyoxometalate-ionic liquids catalysts (POM-ILs) were synthesized. The chemical structure, crystal structure, catalyst morphology, elemental and thermal stability properties of POM-ILs were characterized and analyzed. And the performance of catalyzing the coupling reaction of ethylene carbonate (EC) and dimethyl succinate (DMSu) to synthesize poly(ethylene succinate) (PES) was studied, and the effects of different metals on the catalytic performance and catalytic mechanism were discussed. An orthogonal experimental design was carried out to explore the optimal process parameters for the coupling reaction. Then, the effect of different polycondensation temperatures on the intrinsic viscosity ([η]) of poly(ethylene succinate) was investigated to determine the optimal polycondensation reaction temperature. The structure and thermal stability of PES were investigated by FT-IR spectroscopy and TGA. The results show that the catalytic performance of the tin monosubstituted zinc-tungstate ionic liquid catalyst (d-[Bmim]₆Zn^IIW₁₁Sn^IVO₃₉(H₂O)) is optimal under the same process parameters. Under the optimal process parameters, the selectivity of d-[Bmim]₆Zn^IIW₁₁Sn^IVO₃₉(H₂O) is 85.66% and has an obvious inhibitory effect on the side reaction, and the yield and intrinsic viscosity of the PES prepolymer are 76.27% and 0.829 dL g⁻¹, respectively, exhibiting high thermal stability and excellent thermal performance.