Aromatic poly(ether ester)s derived from a naturally occurring building block nipagin and linear aliphatic α,ω-diols

Abstract

Nipagin, the methyl ester of p-hydroxybenzoic acid, which is present naturally in campanulaceae and ericaceous plants, was used to prepare poly(ether ester)s. In this study, two nipagin-based aromatic dimethyl esters were synthesized via one-step simple nucleophilic substitutions with methyl chloroacetate and 1,4-dibromobutane, respectively. Subsequently, two series of poly(ether ester)s, PN1-ωs and PN2-ωs, were synthesized using linear aliphatic α,ω-diols (n = 2, 3, 4, 6, 10, 12) after optimizing the reaction conditions, like feed ratio, reaction catalyst, time and temperature. The synthesized poly(ether ester)s exhibit weight-average molecular weights (M_ws) in the range of 9300–32 100 g mol⁻¹, together with dispersity (D) values between 1.5 and 1.8. ¹H NMR, ¹³C NMR and FTIR spectroscopy were used to characterize their chemical structures. The thermal properties were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results show that the nipagin-based poly(ether ester)s exhibit excellent thermal stability with the initial decomposition temperature above 350 °C and a two-step degradation mechanism. Glass transition (T_g), melting and crystallization temperatures (T_m, T_c), and the corresponding melting and crystallization enthalpies (ΔH_m, ΔH_c) are closely related to the lengths of the α,ω-diols. The T_g values show a decreasing trend with a gradual increase in α,ω-diol length in both PN1-ωs and PN2-ωs. The crystallization behaviors were also studied by isothermal crystallization and wide-angle X-ray diffraction (WAXD). The crystallizability proves to be enhanced with a gradual increase in α,ω-diol length in each series. The mechanical properties were studied using tensile assays and dynamic mechanical analysis (DMA), which show that the nipagin-based poly(ether ester)s feature excellent mechanical properties with elastic modulus and tensile strength values reaching 600–800 MPa and 10–35 MPa, respectively. Finally, the nipagin-based poly(ether ester)s feature excellent comprehensive performance and the renewable nipagin will broaden the thermoplastic spectrum and have practical applications in the field of polymeric materials.