Influence of polyol impurities on the transesterification kinetics, molecular structures and properties of isosorbide polycarbonate†

Abstract

Isosorbide polycarbonate (PIC) is a promising bio-based and ecofriendly alternative of the conventional bisphenol-A polycarbonate. Trace organic impurities existing in the isosorbide raw material is a significant factor impeding the high-quality (high molecular weight, good color and narrow polydispersity) production of PIC. In this work, a set of multifunctional polyol impurities were recognized as the major impurities, and then a so-called “reverse-addition” model protocol based on two kinds of polyols (glycerol and 2-deoxy-d-ribose) was established to systematically demonstrate their influences on the polymerization and properties of PIC. The presence of glycerol impurity significantly increases the transesterification rate and transesterification equilibrium time between isosorbide and diphenyl carbonate. Additionally, the hydroxyl end-groups of the isosorbide unit on PICs increased significantly due to the addition of glycerol which hindered the polymerization, resulting in a decrease in the viscosity-average molecular weight (M_η) of PIC by 30 754 g mol⁻¹. In comparison, 2-deoxy-d-ribose impurity decreased the transesterification rate and prolonged the transesterification equilibrium time, inducing a ring-opening side reaction of isosorbide and eventually leading to the cross-linking of PIC, thus increasing the M_η of the polymer by 18 655 g mol⁻¹. Moreover, both impurities can cause yellowing of PIC and 2-deoxy-d-ribose impurity has an even stronger effect than glycerol. This protocol holds great significance in advancing the quality control and industrial scale-up of isosorbide polycarbonate polymers and can also be an effective methodology for other polymer systems.