One-component Diels–Alder based polyurethanes: a unique way to self-heal
In this work, we introduce single-component self-healing polyurethanes based on reversible maleimide/furan Diels–Alder reactions with good physical integrity on healing. Diols bearing thermo-reversible furfuryl and maleimide moieties were synthesized by a four-step coupling strategy starting from commercially available 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) and thermo-responsive mono-alcohol (with furfuryl or maleimide functions). These diols were reacted in presence of 1,6-hexamethylene diisocyanate and polypropylene glycol (PPG), in order to obtain amorphous polyurethanes with good chain mobility for the self-healing processes (Tg < RT). The cross-linking density, related to the healing process, could be readily tuned with the amount of thermo-responsive moieties as well as the PPG chain length. Swelling test and FTIR spectroscopy confirmed the formation of reversible networks. Qualitative micro-scratch test on thin films indicated tunable healing efficiencies based on the polyurethane composition as a function of the content, the chemical nature of the thermo-responsive moieties (reversible vs. irreversible), the PPG nature (hydroxyl or amino terminated) and chain length. This new structural concept is of great interest for thermally mendable, self-healing and adhesive polyurethanes.