A “transient-comonomer” strategy for polycondensation of lignin-derived AB-type aromatic polyesters to high molecular weight

In the active exploration of novel biobased semicrystalline polyesters to replace petrochemical plastics, AB-type aromatic condensation polymerization is relatively rarely investigated but gains growing attention due to the straightforward synthesis of AB-type monomers from diverse asymmetric biobased feedstocks. However, achieving high molecular weights through AB-type melt polycondensations is often challenging due to premature crystallization and limited thermal stability of the bio-based monomers. Herein, we investigate the polycondensation of methyl 4-(2-hydroxyethoxy)benzoate (MEB), a biobased aromatic hydroxy-ester monomer (AB-type), via the classical two-stage melt transesterification polycondensation process. We demonstrate an efficient “transient-comonomers” strategy to enhance the molecular weight of PEB up to 1.15 dL g −1 by adding a small amount of aliphatic AA/BB-type comonomer pair at the beginning of polymerization. These comonomers suppress premature solidification during the initial stages of melt polycondensation and are partially depleted during the later stages of the reaction. In addition, we also investigated the effects of various metal-based catalysts, including a kinetic analysis of the transesterification steps, which revealed that titanium-based catalysts exhibited a faster reaction rate compared to other catalysts based on antimony, tin, manganese, and zinc. Furthermore, the catalyst also influenced the thermal properties of the resulting polyester, particularly the crystallinity and crystallization kinetics. Overall, this study provides new insights into achieving high-molecular-weight biobased aromatic polyesters via AB-type polycondensation and offers a promising approach for broadening the synthesis approaches for sustainable condensation polymers.