Efficient, Room-Temperature\nSelf-Healing Polyurethane\nElastomers with Superior Tensile Properties and Solvatochromic Capacities

Abstract

Designing\na polymeric elastomer that exhibits superior tensile\nproperties, as well as efficient self-healing ability at mild temperatures,\nremains challenging. This study reports a polyurethane elastomer that\ncontains imine and metal coordination bonds, by a facile method. The\nlinear polyurethane (HPPU), bearing pendant ligands of phenolic oxygen\nand imine groups, originates via two-step polycondensation of hexamethylene\ndiisocyanate, polytetrahedrofuran, and 2-{[(2-hydroxyphenyl) methylene]amino}-1,3-propanediol.\nUpon incorporation of Co(II) into the polymeric matrix, HPPU becomes\nan elastomer (HPPU-Co) with a physical crosslinked structure by the\nformation of metal coordination bonds. The dynamic reversible Co(II)–ligand\ncoordination bonds in the structure impart the HPPU-Co elastomers\nwith autonomous self-healing capacity at mild temperatures, and the\ntensile properties are adjustable by controlling the Co(II)/ligand\nratio. When the mole ratio of Co(II)/ligand is 1:2, the as-prepared\nelastomer (HPPU-Co-1/2) exhibits superior tensile properties (ultimate\ntensile strength: 48.7 MPa; elongation at break: 1678%; fracture toughness:\n287.7 MJ m^–3) as well as self-healing abilities\nand repeated healing at room temperature [healing efficiency: 99.7%\nfor the first healing and 81.2% for the sixth healing (24 h)]. Furthermore,\nthe HPPU-Co elastomers exhibit reversible solvatochromic behaviors:\nthe film color changes from blackish-green to red-brown upon dipping\ninto water. The design concept in this work is an approach to preparing\nmultifunctional polyurethane materials. The resultant polyurethane\nelastomers have multiple useful features and show promise for many\nfields that require long functional lifetimes.