Efficient, Room-Temperature Self-Healing Polyurethane Elastomers with Superior Tensile Properties and Solvatochromic Capacities

Designing a polymeric elastomer that exhibits superior tensile properties, as well as efficient self-healing ability at mild temperatures, remains challenging. This study reports a polyurethane elastomer that contains imine and metal coordination bonds, by a facile method. The linear polyurethane (HPPU), bearing pendant ligands of phenolic oxygen and imine groups, originates via two-step polycondensation of hexamethylene diisocyanate, polytetrahedrofuran, and 2-{[(2-hydroxyphenyl) methylene]amino}-1,3-propanediol. Upon incorporation of Co(II) into the polymeric matrix, HPPU becomes an elastomer (HPPU-Co) with a physical crosslinked structure by the formation of metal coordination bonds. The dynamic reversible Co(II)–ligand coordination bonds in the structure impart the HPPU-Co elastomers with autonomous self-healing capacity at mild temperatures, and the tensile properties are adjustable by controlling the Co(II)/ligand ratio. When the mole ratio of Co(II)/ligand is 1:2, the as-prepared elastomer (HPPU-Co-1/2) exhibits superior tensile properties (ultimate tensile strength: 48.7 MPa; elongation at break: 1678%; fracture toughness: 287.7 MJ m^–3) as well as self-healing abilities and repeated healing at room temperature [healing efficiency: 99.7% for the first healing and 81.2% for the sixth healing (24 h)]. Furthermore, the HPPU-Co elastomers exhibit reversible solvatochromic behaviors: the film color changes from blackish-green to red-brown upon dipping into water. The design concept in this work is an approach to preparing multifunctional polyurethane materials. The resultant polyurethane elastomers have multiple useful features and show promise for many fields that require long functional lifetimes.