Polyesters derived from bio-based eugenol and 10-undecenoic acid: synthesis, characterization, and structure–property relationships

Abstract

Renewable monomers derived from eugenol and 10-undecenoic acid were synthesized via thiol-ene click and nucleophilic substitution reactions. With these monomers in hand, a series of thermoplastic polyesters with tunable thermo-mechanical properties were prepared via two-step melt polycondensation. The prepared polyesters exhibit weight-average molecular weights in the range of 21 000–48 000 g mol⁻¹, together with polydispersity values between 1.8 and 2.1. Experiments involving thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were carried out in order to study the thermal and mechanical properties of the polymers. All prepared polyester species prove to be thermally stable at temperatures up to 300 °C. Furthermore, the aromatic and semi-aromatic polyesters exhibit fully amorphous behaviours with glass transition temperatures (T_gs) ranging between −34.13 and 6.97 °C. Herein, the density of the rigid aromatic rings along the main chains of the polyester has a distinct influence on the T_g values. Furthermore, the fully aliphatic polyesters prove to be semi-crystalline with inconspicuous T_g. The incorporation of aromatic eugenol into the polyester chains and the density of the benzene rings were also found to result in a significant improvement in the mechanical properties, including Young's modulus and elongation at break in the range of 11.6 to 44.2 MPa and 33.6–106.7%, respectively. The relatively high tan δ and the low storage modulus indicate that eugenol-based polyesters feature superior viscosity properties and may therefore find future applicability in a variety of high-tech materials.