A paradigm for the efficient synthesis of bio-based polycarbonate with deep eutectic solvents as catalysts by inhibiting the degradation of molecular chains

Abstract

In this study, an efficient catalytic system composed of deep eutectic solvents (DESs) was developed by adjusting the basicity of hydrogen bond donors (HBDs) to synthesize poly(isosorbide) carbonate (PIC) with high weight average molecular weight (M_w). It was demonstrated that the M_w of PIC prepared by using nearly neutral [EminOH]Cl–2EG was the highest. The results of the transesterification kinetics with different catalysts supported that the transesterification rate was significantly promoted as the basicity of DESs increased but their strong alkalinity inhibited the M_w of PIC. Therefore, the degradation of PIC was investigated to reveal the mechanism of the influence of basicity on the molecular weight of PIC. The strong alkalinity of DESs would cause the depolymerization of the macromolecular chains and ultimately limit the molecular weight of the product, proving the experimental fact that a near-neutral catalyst was more conducive to the M_w of PIC. Finally, a reasonable mechanism of synergistic catalysis was proposed based on ¹H NMR spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and experimental results. The metal-free, low-cost, high catalytic activity DES catalyst involved here is a practical candidate for advanced bio-based polycarbonate.