Functional self-healable EVA elastomers based on reversible covalent networks: A potential new class of epoxy-based specialty adhesives

Multifunctional elastomers have gained tremendous attention in the material research community. In this study, an epoxy functionalized elastomer poly(ethylene-co-vinyl acetate-co-glycidyl methacrylate) (EVA-GMA) that is commercially available was modified with dynamic covalent chemistry to make it self-healable and recyclable, as well as to investigate its adhesive properties. EVA-GMA was modified to a furfuryl-appended diene elastomer (FA-EVA-GMA) and subsequently cross-linked with bifunctional 1,2,4-triazoline-3,5-dione (bis-TAD) and bismaleimide (BMI) derivatives via electrophilic substitution (ES) and Diels-Alder (DA) chemistry, respectively. The ES modification of the elastomer was ambiently completed using bis-TAD, whereas its maleimide modification required elevated conditions (65 °C) with a longer time of 24 h. The tensile study showed a remarkable improvement in the mechanical strength upon cross-linking the elastomers. The differential scanning calorimetry (DSC) analysis elucidated the thermoreversible characteristics of both the ES and DA-derived networks, showing the cleavage of ES and DA conjugates at 135 °C (retro-ES) and 140 °C (retro-DA), respectively. The cross-linked elastomers exhibited significant self-healing characteristics (with a healing efficiency of ≈ 88%) and monitored using an optical microscope and tensile analysis. Interestingly, the bis-TAD-derived and bismaleimide functionalized EVA-elastomer showed excellent adhesive properties toward the metal surfaces, as analyzed via lap shear test.