Carveol-Derived Cycloaliphatic Epoxy for Bio-Based High-Performance Thermosets

Carveol, a terpenoid alcohol, was selected as a platform molecule for the development of high-performance bio-based epoxy thermosets. A cycloaliphatic diepoxy monomer, carveol dioxide (CDO), was synthesized and subsequently cured with branched polyethyleneimine (BPEI) to afford epoxy thermosets exhibiting outstanding thermomechanical properties, including a storage modulus of 2.5 GPa at 30 °C and a glass transition temperature (Tg) of 97 °C. The resulting thermoset also exhibited strong adhesion to stainless steel, reaching a lap-shear strength of 10.1 MPa, which compares favorably with previously reported bio-based epoxy adhesives. To further enhance network performance, the pendant secondary hydroxyl group of CDO was exploited to introduce urethane crosslinks prior to epoxy curing. Urethane incorporation markedly increased the crosslink density and raised Tg to 137 °C, which, to the best of our knowledge, is the highest value reported for terpene-based epoxy thermosets. These results highlight carveol as a promising renewable platform for high-performance epoxy thermosets and adhesives because its unique combination of C=C bonds and a secondary hydroxyl group enables both epoxide formation and subsequent network modification.