Bio-based tetrafunctional thiol EUGSFH: Eco-friendly design and versatile features from eugenol to superior epoxy curing agent

The biobased eugenol is mainly utilized as a source for epoxy monomers, but it is not readily available for hardeners. As to the related biobased epoxy resins, the multifunctional outlines are still largely undocumented. Herein, a novel bio-based tetrafunctional thiol curing agent, 3,3′-(6,6′-bis(3-mercaptopropoxy)-5,5′-dimethoxy-[1,1′-biphenyl] -3,3′-diyl)bis(propane-1-thiol)) (EUGSFH) was fabricated via oxidation coupling/allylation/thiol-ene click chemistry/hydrolysis. Moreover, oil-based 2,2-bis(((3-mercaptopropanoyl)oxy)methyl)propane-1,3-diyl bis(3-mercaptopropan-tate) (PETMP) was employed for comparison. It was disclosed that EUGSFH-cured networks had an activation energy as low as 64 kJ mol −1 , which was about 9 kJ mol −1 lower than that of PETMP. Among them, the biobased (E)-2,2′-(((5-(4-(oxiran-2-ylmethoxy)styryl)-1,3-phenylene)bis(oxy))bis(methylene))bis(oxirane) (OSPBBB) /EUGSFH allowed the networks with T g as high as 115 °C due to its high crosslinking density (~5.24 mol dm −3 ). Meanwhile, its initial decomposition temperature reached 352.8 °C, exceeding the PETMP counterpart as well. Except for the outstanding mechanical properties, the EUGSFH showed an excellent UV/blue light shielding feature in the 200–500 nm range. The relatively low dielectric loss ε”  < 0.04 indicated its suitability for high-frequency electronic packaging. Moreover, the ready alkaline hydrolysis of PETMP-cured matrices achieved 100% degradation via 1) (CO)-O cleavage of ester bonds via hydrolysis, 2) C S breakdown via Retro-Michael reaction, and 3) C O cleavage of the ether bonds, making the sustainable recycling of reinforcing materials. On the contrary, the EUGSFH-fabricated networks are chemically stable for long-life, durable applications. In light of green high-end function, EUGSFH may therefore significantly provide an upgrading avenue, especially for their sustainable applications in weather-resistant, optical, dielectric, and high-temperature scenarios.