Synthesis and Properties of a Shape Memory–Assisted Self-Healing Supramolecular Polyurethane Coating Based on Quadrupole Hydrogen Bonding

In this research, the synthesis and characterization of a shape memory–assisted self-healing polyurethane (SHSMPU) coating based on strong quadrupole hydrogen bonding interaction have been investigated. The coating was fabricated with an acrylic polyol, an isocyanate functionalized ureidopyrimidinone (UPy-NCO) as a hydrogen bonding provider, and methylene diphenyl diisocyanate (MDI) as chain extender. Fourier-transform infrared spectroscopy (FT-IR) confirmed that by incorporating the UPy-NCO dimer in the polyurethane (PU) structure, strong hydrogen bonding appears, which can provide the healing function of the polymer. In addition, differential scanning calorimetry (DSC) showed that by increasing the UPy-NCO amount, the overall Tg decreased and the material becomes more flexible. A rheometric investigation revealed that a sample containing 45% of UPy-NCO as total diisocyanate shows good shape recovery and an healing efficiency of macroscale cracks of around 94.2%, which is much higher than the corresponding sample without UPy-NCO (50.4%). Even better performances were obtained with microcracks, where tested samples were significantly healed at around 80°C in 10 min. Furthermore, the introduction of polyethylene glycol 400 (PEG400) into the polymer's backbone led to a reduced Tg and thus higher flexibility at room temperature. The combination of the observed properties makes these materials promising for application as durable and flexible polyurethane coatings.