Self-healing UV-curable polymer network with reversible Diels-Alder bonds for applications in ambient conditions

The ambient-temperature self-healing potential of a poly(methacrylate) network, containing reversible furan-maleimide Diels-Alder crosslinks, is studied. A reversible bis(methacrylate) monomer, containing Diels-Alder bonds, is synthesized and characterized by means of H-1 NMR spectroscopy. Subsequent polymerization via UV-cure yields a reversible polymer network, consisting of thermoplastic poly(methacrylate), crosslinked by Diels-Alder bonds. Characterization of the polymer network via high-resolution solid-state C-13 NMR indicates that undesirable side reactions, such as the formation of irreversible maleimide homo- and copolymers, are prevented by protecting the maleimide functionality in the Diels-Alder adduct. The thermal reversibility of the polymer network is studied by means of Fourier transform infrared spectroscopy and differential scanning calorimetry, and it is confirmed that the reversibility of the Diels-Alder reaction remains during several thermal cycles between -40 degrees C and 85 degrees C. Dynamic mechanical analysis confirms that the reversible polymer network maintains sufficient mechanical properties even at elevated temperatures up to 110 degrees C, at which retro Diels-Alder reaction is favored. Self-healing of the polymer network at ambient temperature, even in the fully vitrified state at 20 degrees C, is demonstrated by grinding the polymer material into a powder and then healing the powder (after compression) to form a rectangular bar with recovered mechanical properties. Ambient temperature healing without human intervention is therefore feasible, making this material suitable as e.g. encapsulant in photovoltaic modules for outside applications.