To realize a robust, transparent, and easily processable polymer that is intrinsically selfhealable at room temperature, the following three material design criteria were established: (1) a readily processable and physically tunable base material, (2) a dynamic covalent bond that is operable at room temperature, and (3) optimal self-healing efficiency and mechanical properties.Thermoplastic polyurethane (TPU) is a thermoprocessable elastomer that is widely used as a protective film in the automotive and electronic industries. TPU was selected as the base material to satisfy the first criterion because its chemical structure can be fine-tuned to generate the desired transparency and mechanical properties. [4] Urethane structures containing polytetramethylene ether glycol (PTMEG) have been utilized to prepare shape memory effectassisted self-healing materials. [5] To satisfy the second criterion, an aromatic disulfide bond was selected as the chemical operator. [6] Intrinsic self-healing is chemically driven by noncovalent bonds such as hydrogen bonds, [3c-e,5c,7] metal-ligand, [8] host-guest interactions, [2e,9] or reversible (dynamic) covalent bonds [10] such as Diels-Alder, [11] radical recombination, [12] urea chemistry, [13] olefin metathesis, [14] polysiloxanes, [15] boronic esters, [16] acylhydrazones, [17] and other reactions. [18] Among these, disulfide metathesis has attracted significant attention since it can be activated at moderate temperatures (60-90 °C) and without external stimuli. [5d,19] In particular, an aromatic disulfide-based poly(urea-urethane) shows efficient room-temperature self-healing because aromatic disulfides undergo more efficient metathesis than aliphatic disulfides. [6e,f,20] The third criterion was addressed by optimizing the mechanical properties and self-healing efficiency of TPU through the design of a hard segment of the polymer containing the chemical operator, i.e., an aromatic disulfide moiety. Generally, TPUs with tightly packed hard segments have better mechanical properties but lower self-healing efficiency because the restricted chain mobility hinders disulfide metathesis. [5d,21] Loosely packed hard segments produce the opposite effect. Room-temperature self-healable cross-linked poly(urea-urethane) has an undesirable ultimate tensile strength (UTS) of ≈0.8 MPa with a toughness of ≈13 MJ m −3 . [6e] Other disulfide-containing TPUs have UTS values greater than 10 MPa, but they must be heated above 80 °C to initiate self-healing. [5d] The most important properties of self-healing polymers are efficient recovery at room temperature and prolonged durability. However, these two characteristics are contradictory, making it difficult to optimize them simultaneously. Herein, a transparent and easily processable thermoplastic polyurethane (TPU) with the highest reported tensile strength and toughness (6.8 MPa and 26.9 MJ m −3 , respectively) is prepared. This TPU is superior to reported contemporary roomtemperature self-healable materials and conveniently heals w...

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Perishable foods at undesired temperatures can generate foodborne illnesses that present significant societal costs. To certify refrigeration succession in a food‐supply chain, a flexible, easy‐to‐interpret, damage‐tolerant, and sensitive time‐temperature indicator (TTI) that uses a self‐healing nanofiber mat is devised. This mat is opaque when refrigerated due to nanofiber‐induced light scattering, but becomes irreversibly transparent at room temperature through self‐healing‐induced interfibrillar fusion leading to the appearance of a warning sign. The mat monitors both freezer (−20 °C) and chiller (2 °C) successions and its timer is tunable over the 0.5–22.5 h range through control of the polymer composition and film thickness. The thin mat itself serves as both a temperature sensor and display; it does not require modularization, accurately measures localized or gradient heat, and functions even after crushing, cutting, and when weight‐loaded in a manner that existing TTIs cannot. It also contains no drainable chemicals and is attachable to various shapes because it operates through an intrinsic physical response.