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A facile method was found to incorporate a mussel-inspired adhesive moiety into synthetic polymers, and mussel mimetic polyurethanes were developed as adhesive hydrogels. In these polymers, a urethane backbone was substituted for the polyamide chain of mussel adhesive proteins, and dopamine was appended to mimic the adhesive moiety of adhesive proteins. A series of mussel mimetic polyurethanes were created through a step-growth polymerization based on hexamethylene diisocyanate as a hard segment, PEG having different molecular weights as a soft segment, and lysine-dopamine as a chain extender. Upon a treatment with Fe(3+), the aqueous mussel mimetic polyurethane solutions can be triggered by pH adjustment to form adhesive hydrogels instantaneously; these materials can be used as injectable adhesive hydrogels. Upon a treatment with NaIO4, the mussel mimetic polyurethane solutions can be cured in a controllable period of time. The successful combination of the unique mussel-inspired adhesive moiety with a tunable polyurethane structure can result in a new kind of mussel-inspired adhesive polymers.

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Crosslinked self-healing polyurethane/urea based on a Diels-Alder reaction (C-PMPU-DA) was synthesized from a multiple-furan monomer and a commercial bismaleimide. The multiple-furan monomer (PMPU-furan) was obtained from a functionalized prepolymer (polymeric MDI: PBA-2000 5 2:1) by furfuryl amine. The structures of both the PMPU-furan and C-PMPU-DA were characterized by attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and 1 H-NMR. The Diels-Alder bonds enabled C-PMPU-DA thermal reversibility, which was investigated by ATR-FTIR spectroscopy, 1 H-NMR, gel-solution-gel experiments, and viscosity tests. Meanwhile, the self-healing properties of C-PMPU-DA were also investigated by the recovery of the mechanical properties. The results showed that C-PMPU-DA exhibited good thermal reversibility and self-healing properties. C-PMPU-DA exhibited thermosetting properties at room temperature, although it exhibited thermoplastic properties at higher temperatures and may find applications in self-healing materials, recyclable materials, or removable materials.

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