Systematic Study of Thermal and (Bio)Degradable Properties of Semiaromatic Copolyesters Based on Naturally Occurring Isosorbide

Here we present a series of copolyesters of poly­(butylene terephthalate) (PBT) with the renewable building block isosorbide (1,4:3,6-dianhydro-d-glucitol, IS), designated PBIT. The aim of this work is to systematically elucidate how the inherent properties (reactivity, structural asymmetry, structural rigidity, and hydrophilicity) of IS would affect the synthesis and thermal/(bio)­degradable performance of PBIT copolyesters. The target copolyesters containing 0–50 mol % IS units were successfully synthesized by melt polycondensation and were afforded in fully random microsequential structures. Their number-average molecular weights and intrinsic viscosities are in the ranges of 22 400–31 000 g/mol and 0.5–0.65 dL/g, respectively. The thermal properties determined by differential scanning calorimetric analysis firmly confirmed the remarkable T_g-enhancing effect of IS. Comprehensive degradation study further revealed that IS incorporation promotes remarkable hydrolytic degradation in a relatively harsh acidic environment at high temperature (80 °C), but maintains excellent stability in a neutral hydrolytic and enzymatic environment (with porcine pancreatic lipase) at low temperature (37 °C). The synergistic effects of IS incorporation on thermal properties and degradability are dependent on degrading conditions. The results shown in this work are expected to give some insights regarding property improvement of the existing semiaromatic polyesters via copolymerization, as well as consideration of suitable working conditions for these polymers.