Effect of Methyl Ester End Group Concentration on Solid-State Polycondensation of Poly(ethylene furandicarboxylate)

Poly(ethylene furandicarboxylate) (PEF) is an emerging biobased polyester with high performance and excellent sustainability. However, synthesizing high-molecular-weight PEF via solid-state polycondensation (SSP) in a sufficiently short time is still a great challenge, and the effect of end groups on the SSP rate of PEF needs to be elucidated. In this study, PEF prepolymers with a wide range of methyl ester end group (MEG) concentrations (Cm) were synthesized from dimethyl furandicarboxylate and ethylene glycol via transesterification followed by melt polycondensation at varying diol/diester molar ratios, and the effect of Cm on the SSP rate of PEF was investigated. With decreasing Cm, the SSP sped up clearly, and the intrinsic viscosity ([η]) after SSP for 10 h increased significantly. It reached 1.66 dL/g at a Cm lower than 1.0 mmol/kg and then leveled off. To ensure a rapid enough SSP rate of PEF, the Cm value of PEF prepolymer is recommended not to exceed 4 mmol/g. In comparison with hydroxyethyl ester end group (HEG) and carboxyl end group (CEG), MEG displayed learly lower reaction degree during SSP. The unreacted MEGs acted like inactive end groups (IEGs). This is supported by the Cm dependence of the IEG concentration calculated from Duh’s empirical model.