Polyesters of 2-Pyrone-4,6-Dicarboxylic Acid (PDC) Obtained from a Metabolic Intermediate of Lignin

2-Pyrone-4,6-dicarboxylic acid (PDC), a chemically stable metabolic intermediate of lignin, was for the first time utilized to prepare polyesters. Condensation polymerization at about 200 °C with 1,2-ethanediol, 1,3-propanediol or bis(2-hydroxyethyl) terephthalate was effectively promoted by the catalytic amount of Sb2O3. The corresponding polyesters, P(PDC2), P(PDC3) or P(PDCB)x (x: PDC unit content, and x≤0.5), became insoluble when the number-average molecular weight exceeded about 4×103. Due to the pseudo-aromatic nature of PDC ring, these polyesters were thermally stable up to 210 °C. From the measurements of strain-stress characteristics, Yong’s modulus of P(PDC2) or P(PDC3) was as high as 250 MPa and 2 times larger than that of amorphous PET. The accelerated hydrolysis of P(PDC2) or P(PDC3) in basic, acidic, and pure water at 60 °C gave 60–100% degradation in 1.5–3 weeks. The degradability could be controlled by changing the PDC content “x” in the case of P(PDCB)x, because the lactone ring cleavage as well as ester hydrolysis were considered to be the major events in the main-chain scission.