A bio-based epoxy resin derived from p-hydroxycinnamic acid with high mechanical properties and flame retardancy

Recent advances in epoxy resins have been forward to achieving high mechanical performance, thermal stability, and flame retardancy. However, seeking sustainable bio-based epoxy precursors and avoiding introduction of additional flame-retardant agents are still of increasing demand. Here we report the synthesis of p-hydroxycinnamic acid-derived epoxy monomer (HCA-EP) via a simple one-step reaction, and the HCA-EP can be cured with 4,4′-diaminodiphenylmethane (DDM) to prepare epoxy resins. Compared with the typical petroleum-based epoxy resin, bisphenol A epoxy resin, the HCA-EP-DDM shows a relatively high glass transition temperature (192.9 °C) and impressive mechanical properties (tensile strength of 98.3 MPa and flexural strength of 158.9 MPa). Furthermore, the HCA-EP-DDM passes the V-1 flammability rating in UL-94 test and presents the limiting oxygen index of 32.6%. Notably, its char yield is as high as 31.6% under N₂, and the peak heat rate release is 60% lower than that of bisphenol A epoxy resin. Such findings provide a simple way of using p-hydroxycinnamic acid instead of bisphenol A to construct high-performance bio-based thermosets.