Study on the coupling reaction of mixed dibasic acid dimethyl esters with propylene carbonate catalyzed by diacidic ionic liquids.

Three sulfonic acid-functionalized imidazolium-based diacidic ionic liquid catalysts, [HO3S-(CH2)3-mim]Cl-SnCl4, [HO3S-(CH2)3-mim]Cl-FeCl2, and [HO3S-(CH2)3-mim]Cl-TiCl4, were designed to promote the coupling reaction of mixed dibasic acid dimethyl esters (DBE) with propylene carbonate (PC), yielding poly(propylene mixed dibasic acid ester) (PDBE) and dimethyl carbonate (DMC). Catalyst structures and thermal properties were confirmed by FT-IR, 1H NMR, XRD, acetonitrile/pyridine probe FT-IR, and TGA. Orthogonal and single-factor experiments optimized transesterification and polycondensation conditions. [HO3S-(CH2)3-mim]Cl-FeCl2 exhibited the best performance. Optimal transesterification conditions (205 °C, 12 h, 1.0 wt% catalyst, PC/DBE molar ratio 2.8) gave a prepolymer yield of 46% and conversion of 50%. Optimal polycondensation (235 °C, 15 h) produced PDBE with an intrinsic viscosity of 0.472 dL g-1. The resulting PDBE exhibited a weight-average molecular weight of 15 263, a glass transition temperature of -28 °C, and thermal decomposition above 300 °C. After 31 days of enzymatic degradation, the mass retention was 24%. This work offers a new route for high-value utilization of industrial by-product nylon mixed dibasic acid and the development of green, biodegradable polyester materials.