A colorless, transparent and self-healing polyurethane elastomer modulated by dynamic disulfide and hydrogen bonds†
Self-healing polyurethanes (PUs) represent a new type of functional material which are highly desirable for applications such as surface protection coatings and transparent films. However, it is still challenging to obtain self-repairable PUs with good mechanical properties and excellent optical properties. Herein, in view of molecular design, a self-healing thermoplastic polyurethane (TPU) was designed with polytetramethylene ether glycol (PTMEG) as the soft segment and aliphatic isocyanate (m-xylylene diisocyanate, XDI) and aliphatic disulfide (bis(2-hydroxyethyl)disulfide, HEDS) as the hard segment. The TPU exhibited widely tunable mechanical properties, i.e., tensile stress values of 3.51–8.12 MPa with elongation at break values of 825–1320%. The cooperation of dynamic disulfide bonds and hydrogen bonding endowed the TPU elastomer with self-healing capacity and a self-healing efficiency of about 39% at a moderate temperature. Both the amorphous phase structure and XDI chemical structure contributed to a colorless, transparent and anti-yellowing TPU film with nearly 97% transparency and long-term optical stability. The tough, colorless and transparent self-healable elastomers have wide applications in optical and protective fields, including in automotive laminated glass, flexible displays, printers, and photographic equipment cleaning scrapers.