Thymol-Derived Trifunctional Epoxy Novolac from Controllable Synthesis to Performance-Advantaged Thermosets

In order to develop biobased epoxy resins with superior performance, this study highlights the synthesis, characterization, and properties of a biobased thymol-derived epoxy novolac and related thermosets. Thymol is cocondensated with 2,6-bis(hydroxymethyl)-p-cresol under catalysis of an acidic ion-exchange resin to yield a novolac (TPF) in an easy and controllable way. TPF is found to mainly consist of condensation products with three phenolic nuclei including two from thymol and one from 2,6-bis(hydroxymethyl)-p-cresol connected to two methylene bridges. Then, TPF is efficiently converted into a titled epoxy novolac (TEP) through O-glycidation. TEP and a curative (4,4′-diaminodiphenyl sulfone (44DDS) or methyl nadic anhydride (MNA)) are formed together to afford thermosets expressing highly desirable properties such as high Tg and low water absorption. A correlation is established between thermosetting network structures and their exhibited Tg, thermal stability, dynamic thermomechanical, dielectric and adhesion properties, solvent resistance, thermal diffusivity, and water absorption. Furthermore, TPF is used as a curative for TEP, to result in a TEP/TPF thermoset with significantly increased content of thymol blocks. This thermoset exhibits even superior properties, such as very low water uptake (<1%), decreased density, and good adhesion (>10 MPa), as well as moderate heat resistance (Tg = 136 °C). To conclude, TPF and TEP could be readily prepared in a more controlled manner, and their based epoxy thermosets exhibit multiple properties of interest with more tunability in network structures and ultimate performance, providing a robust candidate for performance-advantaged, value-added applications to advance sustainable epoxy chemistry and technology.