Exploring thiol–ene and thiol–methacrylate reactions in the production of renewable materials from methacrylated eugenol

Abstract

Methacrylated eugenol (ME) is a promising biobased monomer for sustainable polymer networks due to its reactive carbon–carbon double bond and aromatic structure, which can enhance stiffness and thermal stability. Despite increasing interest in eugenol-derived polymers, systematic studies evaluating the relative contributions of thiol–ene and thiol–methacrylate reactions in ME-based systems, as well as their impact on material properties, remain scarce. In this work, eugenol was successfully methacrylated to obtain a versatile monomer containing two reactive sites, enabling polymerization via free-radical homopolymerization and thiol–ene/thiol–methacrylate pathways. Photocurable resins were formulated using ME, a type I photoinitiator, and pentaerythritol tetrakis(3-mercaptopropionate), with varying –CC/–SH molar ratios, to elucidate the theoretical extent of each polymerization mechanism. The resins exhibited high reactivity under UV irradiation, allowing the formation of renewable thermosets within seconds. Increasing the thiol content significantly promoted an increase in thiol–ene and thiol–methacrylate reactions, resulting in higher double-bond conversion, whereas lower thiol concentrations favoured homopolymerization and reduced overall conversion. These differences in reaction pathways strongly influenced the physicochemical properties of the resulting materials, yielding thermosets with tunable thermal stability, mechanical properties, and degradation profiles. Furthermore, the optimized formulation demonstrated suitable reactivity characteristics for vat photopolymerization 3D printing. Three-dimensional objects were successfully fabricated, exhibiting shape-memory behaviour and confirming the applicability of ME-based resins in additive manufacturing. Overall, this study establishes methacrylated eugenol as an active functional monomer rather than a simple reactive diluent, highlighting its potential for the development of sustainable, high-performance, and smart polymeric materials.