Bio-based epoxy thermosets from 2,5-furan dicarboxylic acid derivates with tunable chain length

Due to safety concerns over bisphenol-A-based epoxy thermosets, many European countries have implemented stricter regulations, increasing the demand for bio-based alternatives. In this view, furan-based monomers, such as 2,5-furandicarboxylic acid (FDCA) derived from carbohydrates, have been widely explored as sustainable building blocks for high-performance epoxy resins. However, most studies focused on short-chain FDCA-derived epoxides, like C3-based glycidyl ester derivatives, with little research on FDCA-derived epoxides of varying chain lengths. Building on these premises, this work focuses on synthesizing a new family of bisepoxide FDCA monomers with chain lengths of four, six, and ten carbons. These bio-based monomers were synthesized via oxidation of α,ω-diene ester furan monomers and thus thermally cured using two bisamine hardeners, namely 4,4′-methylenebis(cyclohexan-1-amine) and 4,4′-methylenedianiline leading to FDCA-based epoxy thermosets. Structural analysis confirmed the successful curing and crosslinking of these monomers. Data collected highlighted the influence of the monomer length on the properties of the thermoset materials, with longer bisepoxide monomers exhibiting enhanced thermal stability and flexibility. Furthermore, it was found that the length of the bisepoxide monomer also affected the crosslinking density of the final materials. Interestingly, the bisepoxide FDCA monomer with six-carbons chain cured with 4,4′-methylenedianiline showed the highest crosslinking density, comparable to conventional DGEBA-based thermosets. Finally, a simple methanolysis can efficiently depolymerize the thermoset into its starting monomer, FDCA dimethyl ester, and a polyol offering potential for recycling or the development of new polymers.