Flexible Self-healing Cross-linked Polyamides Synthesized Through Bulk Michael Addition, Polycondensation, and Diels-Alder Reaction

Three new thermally responsive self-healing cross-linked polyamides(cPA-FU-DAs) with good tensile strength and toughness were synthesized through bulk Michael addition, polycondensation, and Diels-Alder reaction. Unlike common stable polymers, cPA-FU-DAs can seal cracks by mere heating. First, the Michael addition of methyl acrylate and furfurylamine was conducted, and a furfurylamine-diester(FU-DE) was prepared. FU-DE was transformed into polyamide prepolymers that contained furfuryl pendant groups(PA-FUs) through bulk polycondensation with a poly(propylene glycol)(PPG) diamine and a PPG triamine. PA-FUs were crosslinked by bismaleimide, and cPA-FU-DAs were prepared. The Michael addition was monitored by Fourier transform infrared spectroscopy and electrospray ionization mass spectroscopy. The reverse DA reaction of the cPA-FU-DAs was demonstrated by differential scanning calorimetry and dissolution property. Their thermally self-healing properties were verified by polarizing optical microscopy and tensile test. The cPA-FU-DAs exhibited good mechanical properties and high self-healing efficiency. They self-healed at 130 °C. The tensile strength after repairing was up to 19 MPa with self-healing efficiency reaching 92%.