It is challenging to develop hydrogels with a combination of excellent mechanical properties, versatile functions, and good processability. Here we report a physical hydrogel of poly­(acrylamide-co-acrylic acid) (P­(AAm-co-AAc)) cross-linked by carboxyl–Fe3+ coordination complexes that possesses high stiffness and toughness, fatigue resistance, and stimulation-triggered healing along with shape memory and processing abilities. The copolymers have randomly dispersed AAm and AAc repeat units, making the physical cross-links with different strength. The strong coordination bonds and their associations serve as permanent cross-links, imparting the elasticity, whereas the weak ones reversibly rupture and re-form, dissipating the energy. Furthermore, a stick–slip instability is observed during the tearing test, which should be associated with the specific nature of metal-coordination bonds that are strong yet fragile. Because of the dynamic nature of coordination bonds, both tensile and tearing mechanical properties are rate dependent. By tuning the bond strength via pH, the gels show distinct mechanical properties, shape memory ability, and even reversible sol–gel transition. The system also shows good processability; the copolymer solutions can be processed into tough gels with different structures by three-dimensional printing technology. These versatile, tough, yet processable hydrogels should be a promising material as structural elements in various applications.

Non-isocyanate polyurethane (NIPU) is a novel kind of polyurethane prepared by reaction of cyclo-carbonates and amines without use of toxic isocyanates. NIPU has attracted increasing attention because of its improvements in porosity, water absorption, and thermal and chemical resistance over conventional polyurethanes. Their potential technological applications include chemical-resistant coating, sealants, foam, etc. In this paper, on the basis of a comprehensive survey of the currently available literature on NIPU, we summarize recent progress in NIPU, and mainly discuss the syntheses of cyclo-carbonates oligomers, the reaction mechanism, and the preparation and application of different kinds of NIPU.

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