Superior Toughness and Fast Self‐Healing at Room Temperature Engineered by Transparent Elastomers

Abstract

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...

Colorless, Transparent, Robust, and Fast Scratch‐Self‐Healing Elastomers via a Phase‐Locked Dynamic Bonds Design

“…[4d,9a,b,10] The utilization of the aromatic disulfide compounds can yield rapid self‐healing systems; however, this molecular design usually results in yellowish appearance as well as less transparency of the self‐healing materials. [7b,f,11,12] In fact, the integration of excellent optical properties and mechanical properties for robust self‐healing materials is a challenging task, which attracts great interest in both academia and industry.…”

“…In particular, PUDS‐8 has the highest maximum tensile stress of 25.0 MPa, which is very impressive among the reported self‐healing materials. [5b‐f,6c,d,7b,f,8a‐c,9a,12,15‐18] The increase of the disulfide content was accompanied by an increasing amount of hard segments, which act as physical crosslinks and a reinforcing element. As a result, the modulus and stiffness increase with the disulfide content.…”

Polar‐Functionalized, Crosslinkable, Self‐Healing, and Photoresponsive Polyolefins

“…Thea ddition of citric acid can modulate crosslinking density and aid in the healing process.Notably,the repaired samples for both cases exhibited at ensile strength and toughness of more than 20 MPa and 6560 MJ m À3 ,r espectively.T hese values are among the highest for previously reported selfhealing polymeric materials. [51][52][53][54] Ethylene/ENB copolymer (sample 1)c annot be healed at all after 24 ha t8 08 8C. Under the same conditions,s ample 11 healed much slower than its hydrolyzed counterpart (Supporting Information, Figure S6).…”

53‐2: Highly Self‐healable Coating Materials with Improved Mechanical Surface Properties for Flexible Electronic Displays

“…Although the extrinsic self-healing polymer has an advantage in healing large damaged areas, they can be healed only once at the same damaged location because the healing agents are exhausted after the healing process. On the other hand, intrinsic self-healing polymers based on specific reversible bonding forces can recover repeatedly their original shapes and properties at the same damaged location [9][10][11][12][13][14][15][16][17][18][19][20]. Intrinsic self-healing system can be divided into chemical bond systems (Diels-Alder reaction, radical reaction, and disulfide reaction, etc.)…”