Fully Biobased Epoxy–Imine Monomer: Synthesis and Curing with Amines Toward Vitrimeric Materials

This study presents the synthesis of a new biobased epoxy monomer derived exclusively from biobased vanillin and epichlorohydrin. Using only sustainable processes, vanillin is first converted to vanillin amine hydrochloride, which is then condensed with vanillin to obtain a diphenol containing an imine moiety. This diphenol subsequently reacts with epichlorohydrin to produce the epoxy monomer. Unlike thermosetting networks in which the imine is formed during the curing reaction, this epoxy monomer incorporates the imine moiety, and no further processing is needed after network formation due to water release. It presents a low molecular weight (399.44 g/mol), enabling the formation of a wide range of highly cross-linked materials. The epoxy monomer can be melted at 100 °C, which facilitates its formulation with the curing agents without the need for solvents. The monomer was cured in this work with two diamines, isophorone diamine (IPDA), a commonly used curing agent, and cystamine (Cyst) as a biobased amine that contains a dynamic disulfide group, to obtain a 100% biobased material. The resulting materials were compared with DGEBA/IPDA and DGEBA/Cyst formulations in terms of thermomechanical properties to evaluate whether the new monomer could be a promising alternative to DGEBA. No less important is the fact that the presence of the imine moiety in the monomer gives vitrimeric behavior to the material. This feature enables reprocessing of the material and allows for both chemical and mechanical recycling. Such properties are particularly promising for applications such as reversible adhesives or degradable matrices in composite materials.