Synthesis of Homo- and Copolyesters Using an AB-Type Aromatic Monomer Based on Homovanillic Acid

There is currently intensive research ongoing with the aim to utilize various lignin-derived molecules to produce aromatic monomers and polymers. In the present work, homovanillic acid (HVA), derived from lignin, was used to prepare sustainable polyesters for the first time. An AB-type monomer with an alcohol group and a carboxylate ester group was conveniently synthesized by using HVA and ethylene carbonate. The monomer was employed in bulk polycondensation to yield the corresponding homopolyester. The polymerization temperature, catalyst, and time were optimized, and it was found that the addition of a small quantity of a dicarboxylate monomer facilitated a stoichiometric balance throughout the homopolycondensation of the AB-type monomer, and thus significantly enhanced the molecular weight of the polyester (M_n = 36 kg mol^–1, [η] ∼ 1.1 dL g^–1). Copolymerization of the HVA-based monomer with another lignin-based AB monomer, methyl 4-(2-hydroxyethoxy) benzoate, produced a series of copolyesters with high yields and moderate molecular weights (M_n = 9.5–11 kg mol^–1, [η] ∼ 0.5 dL g^–1). The resulting copolyesters showed a reasonably high thermal stability (T_d,5% > 318 °C) and tunable thermal properties, e.g., T_g = 44–72 °C and T_m = 154–200 °C, depending on the monomeric composition. Consequently, the findings of this work demonstrated the great potential of HVA in the development of new biobased aromatic (co)polyesters with modulated crystallinity.