Synthesis of a Recyclable Epoxy and its Thermomechanical Behavior During Depolymerization

Conventional epoxies are typically used for long term applications as they are incredibly versatile. However, they are considered non-recyclable and nearly impossible to remove at the end of their lives. To address these limitations, recyclable epoxies were synthesized by introducing the Diels–Alder reaction using maleimide and furan functional groups. The retro-Diels–Alder (rDA) reaction at elevated temperature can serve as a recycling process through depolymerization of the epoxy network. Various precursors were synthesized by manipulating molecular weights, architecture (e.g., 4-arm or 6-arm), and spacers between functional groups. Different stoichiometric ratios between furan and maleimide precursors were examined to control crosslinking density of the recyclable epoxy. Thermomechanical behavior of these recyclable epoxies was characterized by calorimetry and rheometry. The epoxies demonstrated a high-temperature (~120°C) endotherm corresponding to the rDA reaction. Moduli dropped at high temperature which indicates depolymerization of the epoxy network through the rDA reaction. The reaction was further confirmed by observing changes in FTIR data consistent with the rDA reaction. Removal and recycling processes were examined by multiple cycles of adhesive tests.