Preparation of biacidic tin-based ionic liquid catalysts and their application in catalyzing coupling reaction between ethylene carbonate and dimethyl succinate to synthesize poly(ethylene succinate)

Abstract

Three biacidic tin-based functional ionic liquid catalysts were prepared, including [HO₃S-(CH₂)₃-mim]Cl-SnCl₄, [HOOC-(CH₂)₂-mim]Cl-SnCl₄, and [HO-(CH₂)₂-mim]Cl-SnCl₄. A Fourier transform infrared (FT-IR) spectrometer, a nuclear magnetic resonance instrument (¹H NMR), an X-ray diffractometer (XRD), and a thermal gravimetric analyzer (TGA) were used to test and analyze the structures, molecular structure, crystal structures, and thermal performance of the three catalysts. And investigate their performance in catalyzing the coupling reaction between ethylene carbonate (EC) and dimethyl succinate (DMSu) to synthesize poly(ethylene succinate) (PES). Orthogonal tests were performed to optimize process parameters, explore the effect of polycondensation temperature on the intrinsic viscosity number ([η]) of PES, and discuss the effect of acidic groups on catalytic performance and the mechanism of the catalytic action. An FT-IR spectrometer and a TGA were used for structural characterization and thermal performance tests on polymer PES, and biodegradability tests (enzymolysis tests) on PES. The results showed that the three biacidic tin-based functional ionic liquid catalysts prepared in this study had a satisfactory catalytic effect. Among them, the sulfonic acid imidazole tin-based ionic liquid catalyst ([HO₃S-(CH₂)₃-mim]Cl-SnCl₄) manifested the best catalytic performance. The catalytic mechanism of the biacidic tin-based ionic liquid catalysts was further explained and discussed. Under the optimal process conditions for the transesterification reaction (temperature: 227 °C; material ratio: EC : DMSu = 1; catalyst consumption: 1.0 wt%; time: 5.5 h), PES had a yield of 67.12%, a selectivity of 82.47%, and an intrinsic viscosity number of [η] = 1.052 dL g⁻¹, and had good thermal stability and biodegradability.