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Both shape memory and self-healing polymers have received significant attention from the materials science community. The former, for their application as actuators, self-deployable structures, and medical devices; and the latter, for extending the lifetime of polymeric products. Both effects can be stimulated by heat, which makes resistive heating a practical approach to trigger these effects. Here we show a conductive polyketone polymer and carbon nanotube composite with cross-links based on the thermo-reversible furan/maleimide Diels–Alder chemistry. This approach resulted in products with efficient electroactive shape memory effect, shape reprogrammability, and self-healing. They exhibit electroactive shape memory behavior with recovery ratios of about 0.9; requiring less than a minute for shape recovery; electroactive self-healing behavior able to repair microcracks and almost fully recover their mechanical properties; requiring a voltage in the order of tens of volts for both shape memory and self-healing effects. To the best of our knowledge, this is the first report of electroactive self-healing shape memory polymer composites that use covalent reversible Diels–Alder linkages, which yield robust solvent-resistant polymer networks without jeopardizing their reprocessability. These responsive polymers may be ideal for soft robotics and actuators. They are also a step toward sustainable materials by allowing an increased lifetime of use and reprocessability.

A novel but simple design is presented of a multi-ion network with polyamic acid that combines high extensibility and toughness with spontaneous healing ability. Taking advantage of the carboxylate structure of polyamic acid, the introduction of a sufficient number of metal ions to neutralize the carboxylated groups can form reversible ionic bonds within the polymeric network. Dry-solid zinc(II)-poly(amic acid-PDMS) is transparent and exhibits good mechanical properties, including good ultimate strength (~0.267 MPa) and high stretchability (~360%). In addition, this dynamic network can self-heal at ambient temperature without requiring stimulation from heat, a plasticizer, or a solvent. The very simple method of our proposed polyamic acid polymers opens up the possibility of increasingly utilizing high-performance, low-cost, and environmentally friendly polyamic acids instead of polyimides. A simplified multi-ion network is presented, which can toughen and modulate the spontaneous self-healing capability of dry-solid Zn(II)-carboxylate polyamic acid under ambient conditions.

Polymer materials are vulnerable to damages, failures, and degradations, making them economically unreliable. Self-healing polymers, on the other hand, are multifunctional materials with superior properties of autonomic recovery from physical damages. These materials are suitable for biomedical and tissue engineering in terms of cost and durability. Schiff base linkages-based polymer materials are one of the robust techniques owing to their simple self-healing mechanism. These are dynamic reversible covalent bonds, easy to fabricate at mild conditions, and can self-reintegrate after network disruption at physiological conditions making them distinguished. Here we review self-healing polymer materials based on Schiff base bonds. We discuss the Schiff base bond formation between polymeric networks, which explains the self-healing phenomenon. These bonds have induced 100% recovery in optimal cases.

We present here a small series of compounds designed to modify the polymer chain of various polyurethanes in order to introduce a structural fragment with the ability of thermally-triggered reversible covalent interactions. Bismaleimides (2a-2e) were synthesized from commercially available aromatic and aliphatic symmetric diamines (1a-1e) and were further introduced into the Diels-Alder reaction with furfuryl alcohol as dienophiles. The Diels-Alder adducts (3a-3e) were obtained as a mixture of endo- and exo-isomer. The presence of symmetrical hydroxyl groups in the structure of the obtained compounds makes them suitable as chain extenders of low molecular weight diisocyanate prepolymers. The presence of a thermally reversible Diels-Alder reaction adduct in the structure of potential chain-extenders opens a possibility to create unique materials with self-healing properties. All compounds obtained were characterized by 1H, 13C NMR, ESI-HRMS, and IR spectroscopy. The thermochemical parameters of the reverse Diels-Alder reaction were established using DSC analysis.

Oxime-urethane bond featuring with high reversibility even at room temperature and multiple reactivity is an emerging dynamic covalent bond, and has shown great potential for self-healing polymers, which are one of the most attractive development directions for next generation of polymeric materials. In this review, recent progresses on the oxime-urethane-based self-healing polymers, including their designs and applications in diverse fields such as biomedicine, flexible electronics, soft robots, 3D printing, protective materials, and adhesives, are summarized, and outlooks on the future development of this field are discussed.

The research of self-healable polymers intended for medical use has increased in the last 20 years. These materials can self-repair and recover their functionality after damage; thus, they are of significant interest in diverse academic areas, including the biomedical field. In this regard, numerous synthetic and natural polymers are being used to develop self-healing hydrogels for tissue engineering applications, particularly for the restoration of bones, cartilage, skin, and even the central nervous system. These materials possess distinct advantages; for example, natural polymers are usually biocompatible and biodegradable, whereas synthetic polymers could be more suitable when rigid hydrogels with fast kinetics are required. Moreover, the intrinsic reticular matrix of these self-healing systems allows the load of diverse drugs and their controlled release. Remarkably, polymers may be mixed to obtain hydrogels with enhanced mechanical and biological properties. The elaboration of self-healable hydrogels is carried out through either covalent crosslinking or non-covalent crosslinking; the selection of the method depends on many factors, including the required mechanical properties and desired use. Although some articles have reviewed self-healing hydrogels, papers focused on utilizing these systems in tissue engineering are scarce. In this article, we perform a concise description of fabrication methods of self-healing hydrogels and the employed polymers. Furthermore, we provide numerous examples of hydrogels intended for biomedical purposes and discuss their key functional properties. Our main objective was to point out the most recent progress in utilizing self-healing polymers in tissue engineering.

Triboelectric nanogenerators (TENGs) are an advanced mechanical energy harvesting system that has a wide range of advantages and has great prospects for use in various fields of science and technology. Among the factors that have a significant impact on the performance of TENGs, a special role belongs to the nature of triboelectric polymer materials. Over the past few years, there has been an exponential growth in research on polymers with shape memory assisted self-healing (SMASH) properties for TENGs. This mini review presents the state of the art in SMASH polymers for TENGs and attempts to assess the impact of modern polymer chemistry on the development of advanced materials for TENGs. Particular attention is paid to the relationship between these polymeric materials and the performance of TENGs. Finally, the problems and promising research directions for polymers with SMASH properties for TENGs are outlined.

Novel bio-derivable tricyclic oxanorbornene polymers, based upon secondary furfurylamine and maleic anhydride derived monomers, prepared via ring opening metathesis polymerization (ROMP) are reported. The tricyclic oxanorbornenes with fused lactam ring are exo Diels–Alder adducts. DFT calculations support the cycloaddition is the first step, followed by lactamization. The polymerizations are rapid and deliver polymers with targeted molar mass and low dispersity (Đ). The prepared polymers with furanyl pendant groups have reactivity towards maleimide-bearing compounds to form thermally induced crosslinked networks through thermoreversible Diels–Alder reactions. The thermoreversible (self-healing) behavior is confirmed by sol gel transition. This new class of bio-derived polymer could be further modified with different active moieties as pendant groups and hence be tailored for more applications in the future.

Water-induced self-healing materials were prepared by the hybridization of a water-soluble polymer, poly(vinyl alcohol), with a smectite clay via mixing in an aqueous medium and subsequent casting. Without using chemical crosslinking agents or heat treatment, the poly(vinyl alcohol)–clay hybrid adhered strongly to substrates, showing self-healing when immersed in water (25 °C). The healing was completed within 1 min by soaking a damaged poly(vinyl alcohol)–clay film under such conditions as in cold water (2 °C), simulated seawater, steam, HCl solutions (pH = 1) and NaOH solutions (pH = 14). The healing was seen repeatedly 10 times.

Intrinsic self-healing polymeric materials are substances that relieve external stress and restore their original mechanical properties after extreme damage via dynamic covalent bonding in the polymeric structure or the reversible association of supramolecular motifs. Boronic ester-based dynamic covalent bonds formed between boronic acids and diols impart excellent self-healing properties to the hydrogels, organic gels, elastomers, and plastics depending on the characteristics of the corresponding polymer. In addition, these bonds induce internal reorganization in the chemical/physical structure in response to changes in the biological signals and biomaterials, such as hydrophilicity, pH, and the presence of glucose. This multi-responsiveness to stimuli as well as the self-healing, injectability, and biocompatibility of boronic ester-based polymers have led to several technological achievements with applicability in biomedical fields, including drug delivery, medical adhesion, bioimplants, and healthcare monitoring. This review provides an overview of various self-healing polymeric materials based on reversible B–O bonds, with a focus on boronic/boronate esters, borax, and benzoxaborole and their properties, responses to external stimuli, and applications.

International audience; Lignocellulose-derived p-hydroxycinnamic acids possess the photo-responsive reversible α,β-unsaturated ester moiety, a reactive structural feature that functions as the basis of the photo-reversible [2 + 2] cycloaddition reaction. To explore the potential of these naturally occurring compounds in the field of self-healing materials, novel bio-based photo-crosslinkable lignin- and glycerol-derived polyfunctional monomers having cinnamate groups were produced using a sustainable process from vanillin and syringaldehyde, two compounds readily obtained from the oxidation of lignin. Through a Structure–Activity Relationship (SAR) study, the structural design of these bio-based monomers was optimized with regards to the crosslinking/decrosslinking extent and the self-healing capacity of the corresponding polymer material. The lignin- and glycerol-derived tri-functional monomer with 4-O-propyl-ferulate moieties has facilitated the design of a new family of bio-based, environment-friendly and reversible self-healing materials for widespread applications. Computational density-functional theory (DFT) and time-dependent DFT calculations were further used for the verification of the SAR study in terms of dimerization energy of the synthesized monomers.

Self-healing coatings or materials have received significant importance in paint, coating, and other industries, as well as in academia, because of their capability to extend materials service life, improving protection, and ensuring sustainability. This review article emphasizes significant advances accomplished in the preparation and properties of intrinsic self-healing materials exclusively based on hydrogen bonding interactions, with possible applications in coatings and adhesives. The main topic of discussion in this review article is the preparation, healing conditions, healing efficiency, and mechanical property recovery after healing. The last part of the review discusses the conclusions and outlook of self-healing materials.

Self-healing polymers have the capability to autonomically heal themselves. Recent breakthroughs in self-healing systems rely on integrating nanoparticles into relevant polymers. This article overviews the self-healing performance of polymer/carbon nanotube nanocomposite. Self-healing carbon nanotube nanocomposites have been designed using epoxy, polyurethane, poly(methyl methacrylate), and rubbers. Great versatility of self-healed polymer/carbon nanotube depends on matrix modification, nanotube functionality, processing strategies, and matrix-nanofiller interaction/compatibility. Special consideration is given to self-healing efficiency of nanocomposites in technical fields, such as coatings, sensors, electronics, radiation shielding, drug delivery, and tissue engineering. Moreover, critical issues and challenges associated with self-healing nanocomposites are considered.

It is a formidable challenge to fabricate healable polymeric materials with high mechanical strength and stiffness due to the highly suppressed diffusion of their polymer chains. Herein, a high-strength, highly stiff, and repairable/healable supramolecular polymer composite was fabricated by complexing poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) in aqueous solutions, followed by molding into desired shapes. Exquisitely tuning the electrostatic and H-bonding interactions between PAA and PAH led to associative phase-separation and in situ formation of nanostructures in the resultant PAA–PAH composites. The H-bonded assembly of PAA–PAH complexes existed as nanospheres were dispersed homogeneously in the continuous phase as an electrostatic assembly of PAA–PAH complexes. Such a structural feature endowed the PAA–PAH copolymer with a double-cross-linked structure, enabling significant reinforcement of the material. The PAA–PAH composites exhibited a tensile strength and an elastic modulus as high as ∼ 67 MPa and ∼ 2.0 GPa, respectively. Due to the benefits from the reconstruction of the complexes, such as reversible electrostatic interactions and H-bonds between PAA and PAH, the PAA–PAH composite could be repaired/healed readily under ambient conditions (25 °C, 40% humidity) by using the liquid-like form of the PAA–PAH complexes (i.e., coacervate). The healing strategy reported here provides a supplementary method for easy repair or healing of high-strength and stiff supramolecular polymer materials.

Recent advances in the synthesis of block copolymers have enabled the creation of smart and functional designer polymers possessing specific intermolecular interactions. The long-range nature of these interactions strongly affects the molecular packings and microstructures of such polymers, which are intimately related to their properties. In addition to various applications, their unique physicochemical properties, distinguished from conventional block copolymers, are attracting significant attention from polymer and materials scientists. In this review, we describe the current understanding of the structure-property relationship of block copolymers having long-range interactions and suggest possible directions of technological development. We particularly focus on how specific interactions, such as Coulombic, π-π stacking, hydrogen-bonding, and metal/ion-dipole interactions, affect the molecular arrangements of block copolymers on the nanometer and molecular scales. Such information could lead to block copolymers with more advanced functions for future nanotechnologies.

There is a growing demand for antibacterial materials around the world in recent years because they can be used for preventing pathogen infection, which is one of the major threats to human health. However, the mechanical damage of the antibacterial materials may weaken their protective effect since bacteria can invade through the cracks of the material. Therefore, antibacterial materials with self-healing ability, in which the mechanical damage can be spontaneously healed, exhibit better reliability and a longer lifespan. In this article, we prepared a series of low-cost antibacterial polymer blends and polymer/small molecule blend materials with excellent self-healing ability and high mechanical strength by a one-pot reaction under mild conditions. These materials were facilely obtained by blending a tiny amount of commercialized cationic antibacterial chemicals, poly(ethylene imine) (PEI) or cetyltrimethylammonium bromide (CTAB), into a self-healing, mechanically robust polymer, poly(ether-thioureas) (PETU). It can be found that they can effectively kill

Supramolecular polymers that can heal themselves automatically usually exhibit weakness in mechanical toughness and stretchability. Here we exploit a toughening strategy for a dynamic dry supramolecular network by introducing ionic cluster-enhanced iron-carboxylate complexes. The resulting dry supramolecular network simultaneous exhibits tough mechanical strength, high stretchability, self-healing ability, and processability at room temperature. The excellent performance of these distinct supramolecular polymers is attributed to the hierarchical existence of four types of dynamic combinations in the high-density dry network, including dynamic covalent disulfide bonds, noncovalent H-bonds, iron-carboxylate complexes and ionic clustering interactions. The extremely facile preparation method of this self-healing polymer offers prospects for high-performance low-cost material among others for coatings and wearable devices.

Mechanically tough polymers with excellent room temperature self-healing capacity have aroused strong interest in soft electronics, electronic skins and flexible energy storage devices. However, achieving such polymers remains a challenge due to tardy diffusion dynamics. Herein, a robust and readily self-healing polymer, which is synthesized by one-pot polymerization among 2,4′-tolylene diisocyanate, isophorone diisocyanate, and poly(oxy-1,4-butanediyl), is achieved through reasonably tuning the hardness of the molecular segment and the strength of the dynamic crosslinking bond. The poly(oxy-1,4-butanediyl) that act as a soft segment can effectively avoid the microphase separation, enabling rapid chain mobility of the polymer at the room temperature. Furthermore, the dual H-bonding from 2,4′-tolylene diisocyanate segment acting as a relatively strong crosslinking bond contributes to high mechanical strength, while the weaker single H-bonding from isophorone diisocyanate segment can efficiently dissipate strain energy by bond rupture, endowing the polymer with rapid room temperature self-healing ability. Featuring state-of-the-art of robust stress strength (≈1.3 MPa), high self-healing efficiency (97% within 6 h), and large tensile strain (≈2100%), the resulting polymers are used for the fabrication of stretchable and self-healable electrical sensor, which can be employed to monitor a variety of physiological activities in real time. The described strategy is promising and universal for healable materials, displaying great potential for developing soft electronics.

Polymer materials containing dynamic bonds have many potential applications including adhesives, elastomers, and coatings with long lifetimes. Interpenetrated networks (IPNs) were studied, where on...

The need to minimize the amount of polymeric waste entering landfills and oceans has led to several research avenues in the field of polymer science. Particularly, the development of intrinsically self-healing and reprocessable thermoset polymers containing dynamic crosslinks has garnered significant interest in the recent years. Reversible B–O bonds in certain orgonoboron compounds have shown great versatility and promise as dynamic crosslinks for the design of self-healing and reprocessable bulk polymer networks. This review provides an overview of the chemistry of organoboron species with dynamic B–O bonds amenable to the design of healable/reprocessable thermosets. Recent developments in this fairly young and interesting research topic are highlighted, along with a critical commentary on the scope and future challenges in designing robust dynamic materials with reversible B–O bonds.

The introduction of non-covalent bonds is effective for achieving self-healing properties because they can be controlled reversibly. One approach to introduce these bonds into supramolecular materials is use of host-guest interactions. This feature article summarizes the development of supramolecular materials constructed by non-covalent cross-linking through several approaches, such as host-guest interactions between host polymers and guest polymers, 1 : 2-type host-guest interactions, and host-guest interactions from the polymerization of host-guest inclusion complexes. Host-guest interactions show self-healing functions while also enabling stimuli-responsiveness (redox, pH, and temperature). The self-healing function of supramolecular materials is achieved by stress dispersion arising from host-guest interactions when stress is applied. Reversible bonds based on host-guest interactions have tremendous potential to expand the variety of functional materials.

Mechanical performances are among the most fundamental properties that dictate the applicability and durability of polymeric materials. Reinforcement of polymeric materials is eternally pursued to broaden the applications of polymers with light‐weight, low‐cost and easy‐processing advantages. Noncovalent aggregates of biomacromolecules have been found to play a significant role in the mechanical properties of many natural materials, such as the spider silk. Increasing numbers of reports have demonstrated that the in situ formed noncovalent aggregates of polymer chains in polymeric systems are highly effective for enhancing the mechanical properties of artificial polymeric materials, in terms of strength, stiffness, toughness, and/or elasticity. The in situ formed noncovalent aggregates act as additional crosslinking domains and well‐dispersed “hard” nanofillers in the polymer networks, significantly strengthening, stiffening and/or toughening the polymeric materials. Moreover, the noncovalent crosslinking of polymer chains favors the development of healable and recyclable polymeric materials, thanks to the reversible and dynamic properties of noncovalent bonds. This review provides an overview of the recent advances on the enhancement of the mechanical properties of different polymeric materials by the in situ formed noncovalent aggregates of polymer chains. It is expected to arouse inspirations for the development of novel polymeric materials with extraordinary mechanical performances and functionalities.

The self-healing behavior of two supramolecular polymers based on π–π-interactions featuring different polymer backbones is presented. For this purpose, these polymers were synthesized utilizing a polycondensation of a perylene tetracarboxylic dianhydride with polyether-based diamines and the resulting materials were investigated using various analytical techniques. Thus, the molecular structure of the polymers could be correlated with the ability for self-healing. Moreover, the mechanical behavior was studied using rheology. The activation of the supramolecular interactions results in a breaking of these noncovalent bonds, which was investigated using IR spectroscopy, leading to a sufficient increase in mobility and, finally, a healing of the mechanical damage. This scratch-healing behavior was also quantified in detail using an indenter.

Most natural biomaterials have an intrinsic ability to self-heal upon encountering damages. Therefore, living beings can recover when wounded. To mimic the self-healing properties of natural biomaterials and prolong the lifetime of the material in various applications, many synthetic self-healing polymers which can repair the internal or external damages have been developed. So far, a lot of synthetic polymers have been designed to self-heal by encapsulating healing agents (in microcapsules or microvascular networks, classified as extrinsic self-healing) or incorporating dynamic chemical bonds (including reversible covalent bonds such as alkoxyamine, disulfide, boronic ester and boroxine bonds or bonds formed by Diels-Alder reaction, or non-covalent interactions such as hydrogen bonds, π-π stacking interactions, host-guest interactions, ionic interactions and metal-ligand interactions, classified as intrinsic self-healing) into the polymer matrix. Due to the consumption of the encapsulated agents, the repair in extrinsic self-healing system is generally not repeatable. Therefore, intrinsic self-healing systems based on reversible covalent bonds or noncovalent interactions are preferred. Highly stretchable self-healing polymers are desirable due to their widespread application in flexible and stretchable electronic devices, including transistors, sensors, energy-storage devices, and light-emitting diodes (LEDs). However, the design of such materials is a nontrivial task. Elastomers are typically made up of cross-linked networks of long chains of polymers. The elasticity arises from the ability of the chains to reconfigure under an applied tension. The crosslinking sites between the long polymer chains ensure that the network returns to its original configuration when the tension is removed. Therefore, the cross-linking bonds should be as strong as possible, otherwise they will be disassociated upon tension and a permanent deformation will be resulted. However, for an autonomous self-healing material, weak dynamic bonds should present as crosslinking sites so that they will break first upon damaging and reform to heal. Polymers crosslinked by weak dynamic bonds tend to be soft and viscoelastic. Therefore, it is highly challenging to design materials that simultaneously exhibit good elasticity and autonomous self-healing properties. In this review, we highlighted the recent advances in design and synthesis of highly stretchable self-healing materials. The main strategy for designing self-healing materials, including (1) double network; (2) incorporating nano-fillers; (3) inducing multi-phase separation; (4) introducing sacrificial bonds; (5) increasing the energy of dynamic bonds, have been described. From this review, one could witness that the combination of high stretchability and self-healing can be realized by various strategies. However, it should be noted that most of the reported highly stretchable self-healing polymers exhibit slow elastic recovery behavior, i.e., they can only recover to their original length after relaxation for a long time after stretching. This is reasonable, because the weak and dynamic dynamic bonds between polymer chains break more readily upon stretching but it takes some time for them to reform, which invariably leads to poor recovery behavior. Therefore, it is still challenging to create materials that have both good elastic performance and autonomous healing capability. If self-healing polymer with fast elastic recovery upon stretching can be developed through continuing efforts of scientists, more widespread applications of self-healing materials can be expected.

Ultraviolet (UV), light-activated, self-healing polymers are an emerging technology that was proposed to enhance the elastic behavior of asphalt binder, while improving its self-healing properties. The objective of this study was to evaluate the effects of self-healing polymer on the rheological properties of binder blends prepared with or without recycled asphalt materials. Binder blends were prepared with two different binders (PG 67-22 and PG 70-22M), with or without recycled asphalt materials, and 5% self-healing polymer (Oxetane-substituted Chitosan-Polyurethane). High-Pressure Gel Permeation Chromatography (HP-GPC) results showed an increase in High Molecular Weight (HMW) components in the binder with an increase in stiffness through the addition of recycled materials. A further increase was observed with the addition of self-healing polymer. Fourier Transform Infrared Spectroscopy (FTIR) confirmed High-Pressure Gel Permeation Chromatography (HP-GPC) results with an increase in the carbonyl index. Furthermore, the addition of recycled materials led to an increase in the high-temperature grade and the low-temperature grade of the binder blends, while the self-healing polymer did not have a significant effect on the PG-grade. Overall, the addition of self-healing polymer led to an increase in stiffness and an improvement in the rutting performance, while it did not have a positive effect on low-temperature cracking performance. For unmodified binder (PG 67-22), self-healing polymer incorporation improved the elastic and fatigue cracking properties of the binder. However, when it was added to a polymer-modified binder (PG 70-22M) and/or binder blends containing recycled asphalt materials, the potential of this material was low to negative on the low temperature and fatigue cracking performances.

The development of polymeric materials with a combination of excellent mechanical performance and room-temperature self-healing property is still a huge challenge. Here, we report a facile method for the fabrication of dual dynamic cross-linked polymer complexes that simultaneously possess multiple remarkable mechanical properties and room-temperature self-healability by simply mixing polymers that have complementary interactions in solutions. Thanks to the synergistic effects of electrostatic and hydrogen-bonding interactions within their networks, the complexes obtained a superhigh tensile strength of 27.4 MPa and toughness of 110.0 MJ/m3 when compared with other polymers that can self-heal at room temperature. More importantly, the complexes can repair a physical cut in an ∼90% relative humid environment at room temperature with a high healing efficiency of ∼96% because of the dynamic nature of the noncovalent interactions. This method is a simple, low-cost, and widely applicable strategy for the large-scale fabrication of room-temperature self-healing materials that possess superior and controllable mechanical performances.

The development of self-healing polymers with tunable mechanical performances is an enormous challenge. Herein, self-healing polymers with tunable mechanical strengths via combined hydrogen bonding and Zn(II)-imidazole interactions were successfully synthesized. This synthesis was accomplished by introducing urea hydrogen bonding and Zn(II)-imidazole interactions into self-healing polymers polymerized from a new bifunctional monomer of 2-(3-(3-imidazolylpropyl)ureido)ethyl acrylate (IUA). The dual dynamic effects of urea hydrogen bonding and Zn(II)-imidazole interactions can simultaneously endow polymers with better self-healing capacities and mechanical properties. The synthesized polymers with urea hydrogen bonding and Zn(II)-imidazole interactions motifs exhibited over 90% self-healing efficiency under mild conditions. The mechanical strengths of the polymers can be flexibly tuned from 35.0 kPa to 4.41 MPa by varying the molar ratio of imidazole/Zn(II). When the polymers are damaged, the urea hydrogen bonds and Zn(II)-imidazole coordination can contribute to the reconstruction of the broken polymer networks and thus provide self-healing abilities. The interactions of hydrogen bonding and Zn(II)-imidazole coordination were confirmed by in-situ FT-IR spectra of the self-healing polymers at different temperatures.

It is a challenge to manufacture self-healing material that possesses rapid, efficient and multichannel self-healing capability. Herein, we design and synthesize a polymer/graphene based self-healing material with a cross-linking network structure via Diels-Alder (D-A) reaction. The as-prepared material can be healed after damage under the stimuli of heat, infrared light, and microwave with controlling the formation and cleavage of D-A bonds. And it exhibits rapid (IR light-5 s, Heat/Microwave-60 s), efficient (efficiencies are 90% after heat-healed, 106% after IR-healed, and 133% after microwave-healed, respectively), and multichannel self-healing ability (i.e. can be self-healed in multiple ways). Furthermore, functionalized graphene oxide (FGO) has high grafting rate of 47.5% for GO-FA (graphene oxide (GO) was functionalized by Furfurylamine, FA), and 85.3% for GO-MDA (GO was functionalized by 6-Maleimidocaproic acid, MDA). In addition, photo-thermal conversion efficiency of the self-healing material was calculated with the average value reached up to 59.8%. The outstanding self-healing performances suggest that this self-healing material has huge promising potential applications in military equipment, protective coating and building materials, etc.

The development of multifunctional nanocontainers for self-healing coatings is of great interest for environmental and healthcare applications. In this study, we developed a synthetic strategy for a hydrophobic and self-healing anticorrosion coating from carboxylic acid- and fluorine-containing nanocontainers. Initially, well-defined poly (acrylic acid-co-trifluoroethyl methacrylate) microspheres were synthesized with different crosslinking agents by precipitation polymerization. The carboxylic acid groups allow for pH-responsive function to control the release of the encapsulated healing inhibitor to the cracks of polymer coatings on metal surfaces. The fluorinated groups of the polymer nanocontainers can endow the coatings with hydrophobicity. The as-synthesized multifunctional nanocontainers were further doped into the polymer coatings to generate self-healing coatings. The self-healing polymer coatings exhibited good crack inhibition since the inhibitor benzotriazole in pH-responsive nanocontainers can autonomously form new nanobarriers on metal surfaces around cracks after corrosion occurs. Furthermore, due to the micro/nanostructures of hydrophobic microspheres in the polymer coatings, the self-healing coating also exhibited good water resistance. The hydrophobic self-healing polymer coatings from the as-synthesized carboxylic acid- and fluorine-containing nanocontainers for anticorrosion were analyzed by electrochemical impedance spectroscopy (EIS).

A simple nanostructured, photoresponsive film made from a coumarin-modified tetrafunctional monomer, which is both photodegradable and photoreproducible, was prepared using a simple spin-coating pr...

Optically healable polymers represent an interesting stimuli-responsive self-healing material as the healing process can be controlled on-demand and remotely. The fundamental mechanism of the light-activated interfacial self-healing process has not been theoretically understood. Here, we present a theoretical framework to understand the light-activated interfacial self-healing of soft polymers with light-responsive photophores. We consider that the light propagation through the material matrix triggers the production of free radicals that facilitate the interfacial self-healing process. The self-healing process is considered as a coupled behavior that polymer chains diffuse across the interface and re-form the dynamic bonds assisted by the free radicals. We theoretically relate the light property to the interfacial self-healing strength of the polymers. We predict that the interfacial self-healing strength of the polymer increases with the light illumination time until reaching a plateau. We theoretically explain the effects of the light intensity, light wavelength, and photoinitiator concentration on the self-healing performance. We then apply the theory to two types of soft polymers with inorganic and organic photophores, respectively. The experimentally measured stress–strain behaviors of the original and self-healed samples can be consistently explained by the theory. The experimentally measured relationships between the healing strength and the healing time also agree well with the theoretical results.

The aliphatic polycarbonate based polyurethanes (PU) from poly(hexamethylene) carbonate diol (PC), hexamethylenediisocyanate and hexanediol were synthesized, characterized and designed as promising self healing polymers. The symmetrical linear PU structure containing the hexamethylene sequences results in a high degree of ordering and strong superstructures, manifested by a high crystallinity of the PC soft phase and a strong self-assembly of linear hard segments (HS). At the optimum composition, both supramolecular structures percolate resulting thus in the singnificant reinforcement. The PU, undergoing order–disorder transitions, involves three types of physical crosslinks with different thermal stability; PC crystalline phase, HS domains and in addition the entanglements. The structure evolution and reversible sol–gel transition during formation/breaking of the corresponding physical networks was followed by rheology, DSC and FTIR. The kinetics of build-up and stability of physical networks is governed by the content of HSs. The investigation contributed to the understanding and control of the thermal phase transitions of supramolecular structures in aliphatic PCPUs. The strong supramolecular structure undergoing order–disorder transitions, presence of thermally stable entanglement network and excellent mechanical properties make the PCPU suitable as a strong self-healing polymer. Two structural motifs are present: the thermally sensitive structure generating self-healing properties and the shape persistent entanglement network structure preventing the irreversible deformation. The efficient healing and restoration of the original structure and mechanical properties after damage of the polymer were checked by microscopy and tensile testing.

Self-healing polymer materials have drawn rapidly increasing interest over the last decade, and have been studied and used in an ever-increasing range of applications. Herein, we successfully make the covalent urea bond – a pinnacle of stability due to strong resonance effects – dynamic in nature through mediation of zinc salts. The dynamic covalent character of urea in the presence of zinc ions is confirmed through dissociation reaction experiments and quantum chemical calculations of small-molecule model urea compounds. In line with our experiments, the modelling results suggest that the presence of zinc ions speeds up the reaction of urea dissociation by two orders of magnitude via the formation of O-bound Zn complexes. Based on such dynamic covalent urea bonds, we then develop a novel class of self-healing polymer materials with excellent healing efficiencies. Different kinds of self-healing and reprocessable polyurea materials were prepared, with polymer properties that can be easily tuned by varying the degree of crosslinking and the molecular weight of the siloxane precursor. Since different kinds of self-healing polyurea materials could easily be prepared due to the commercial availability of a very wide range of amine and isocyanate monomers, this introduction of self-healing properties is expected to have significant potential in a range of applications, such as coatings, paints, and 3D printing. In addition, this introduces polyureas and other urea-containing polymers as a class of highly stable, yet easily reprocessable plastics, which is highly relevant given the globally desired more sustainable use of plastics.

Microencapsulation of curing agents is a major strategy for the development of self-healing polymers. Isocyanates are among the most promising compounds for the development of one-part, catalyst free, self-healing materials, but their microencapsulation is challenging due to their high reactivity. To keep the healing agent intact in the liquid state and containing free-NCO groups, the monitoring of several synthesis parameters is essential. This review aims to summarise the outcomes in the microencapsulation of isocyanates, emphasising the efforts reported in the literature to modulate the microcapsule properties. In this regard, the main synthesis procedures are presented, followed by the most relevant characterisation methods used to assess microcapsule properties. The correlation between these properties and synthesis parameters is also discussed, and finally the main potential and challenges for industrial applications are highlighted.

Polymers crosslinked via furan/maleimide thermo-reversible chemistry have been extensively explored as reprocessable and self-healing thermosets and elastomers. For such applications, it is important that the thermo-reversible features are reproducible after many reprocessing and healing cycles. Therefore, side reactions are undesirable. However, we have noticed irreversible changes in the mechanical properties of such materials when exposing them to temperatures around 150 °C. In this work, we study whether these changes are due to the self-reaction of maleimide moieties that may take place at this rather low temperature. In order to do so, we prepared a furan-grafted polyketone crosslinked with the commonly used aromatic bismaleimide (1,1′-(methylenedi-4,1-phenylene)bismaleimide), and exposed it to isothermal treatments at 150 °C. The changes in the chemistry and thermo-mechanical properties were mainly studied by infrared spectroscopy, 1H-NMR, and rheology. Our results indicate that maleimide self-reaction does take place in the studied polymer system. This finding comes along with limitations over the reprocessing and self-healing procedures for furan/maleimide-based reversibly crosslinked polymers that present their softening (decrosslinking) point at relatively high temperatures. On the other hand, the side reaction can also be used to tune the properties of such polymer products via in situ thermal treatments.

Nowadays, the self-healing approach in materials science mainly relies on functionalized polymers used as matrices in nanocomposites. Through different physicochemical pathways and stimuli, these materials can undergo self-repairing mechanisms that represent a great advantage to prolonging materials service-life, thus avoiding early disposal. Particularly, the use of the Joule effect as an external stimulus for self-healing in conductive nanocomposites is under-reported in the literature. However, it is of particular importance because it incorporates nanofillers with tunable features thus producing multifunctional materials. The aim of this review is the comprehensive analysis of conductive polymer nanocomposites presenting reversible dynamic bonds and their energetical activation to perform self-healing through the Joule effect.

Metal-coordinated hydrogels are physical hydrogels entirely crosslinked by complexes between ligand decorated polymers and metal ions. The mechanical properties of these hydrogels strongly depend on the density and dynamics of metal-coordinated interactions. Most commonly, telechelic metal-coordinated hydrogels contain catechol or histidine ligands, although hydrogels containing a stronger complexation agent, nitrocatechol, have been reported. Here, we introduce a pyrogallol end-functionalized polymer that can be crosslinked with di-and trivalent ions, in contrast to previously reported metal-coordinated hydrogels. We can tune the mechanical properties of the hydrogels with the types of ions used and the density of crosslinking sites. Ions form nm-sized precipitates that bind to pyrogallols and impart distinct properties to the hydrogels: strong ion-pyrogallol interactions that form in the presence of Al3+, V3+, Mn2+, Fe3+, Co2+, Ni2+ and Cu2+ result in long relaxation times. The resulting hydrogels display solid-like yet reversible mechanical properties, such that they can be processed into macroscopic 3D structures that retain their shapes. Weak ion-pyrogallol interactions that form in the presence of Ca2+ or Zn2+ result in short relaxation times. The resulting hydrogels display a fast self-healing behavior, suited for underwater glues, for example. The flexibility of tuning the mechanical properties of hydrogels simply by selecting the adequate ion-pyrogallol pair broadens the mechanical properties of metal-coordinated hydrogels to suit a wide range of applications that require them to retain their shape for a given time to act as dampers. This journal is. © The Royal Society of Chemistry., Nanoscale, 13 (7), ISSN:2040-3364, ISSN:2040-3372

Self-healing property is now being pursued worldwide with avid interest as an alternative process in checking damages in materials. Incorporating self-repair elements inside hollow fibers is one such approach which is considered here along with study of damage occurrence and restoration of mechanical strength. In present work, hollow glass fiber reinforced self-healing polymer is fabricated, and mechanical response to tensile loading is studied. In our approach, hollow glass fibers of 200–300 micron inner diameter are fabricated and further utilized as fiber reinforcement for self-healing polymer composite. During curing process, initial setup consists of Bisphenol-A-based resin as material for matrix. Hollow glass fiber, which is filled with self-healing agents, is embedded uniformly within the matrix. Further, the material is tested for its tensile strength in the presence of healing agent. The result demonstrates weak fracture toughness of hollow glass fiber with regards to Bisphenol-A epoxy resin. This may be attributed to higher hollowness percentage of glass fiber.

Polymers and polymer nanocomposites (PNCs) are extensively used in daily life. However, the growing requirement of advanced PNCs laid persistent environmental issues due to deformation-induced damage that once formed, does not vanish at future stages. Therefore, self-healing materials with significantly enhanced long life and safety have been designed to epitomize the forefront of recent advances in materials chemistry and engineering. Self-healing PNC (SH-PNCs) materials are a class of smart composites in which nanoparticles induce interfacial reconstruction via multiple covalent and non-covalent interactions culminating in improved mechanical strength and self-healing capability. However, since the filler nanoparticles are independent of the reversible supramolecular network, the filler incorporation destroys the self-healing ability but could enhance the mechanical strength. Hence, the molecular parameters controlling the alliance of robust mechanical strength with virtuous self-healing ability is a crucial challenge. Herein, we review the latest developments that have been made in self-healing materials and puts advancing insights into the fabrication of SH-PNCs in which the combination of covalent bonds and non-covalent interactions provides an optimal balance between their mechanical performance and self-healing capability. We highlight the importance of specific entropic, enthalpic changes, polymer chain conformations and flexibility that enable the reconstruction of damaged surface and physical reshuffling of dynamic bonds at the interface of cut surfaces.

Dynamic covalent chemistry applied to polymers has attracted significant attention over the past decade. Within this area, this review highlights the recent research on polysaccharide-based hydrogels cross-linked by boronic acid moieties, illustrating its versatility and relevance in biomaterials science to design selfhealing, multiple stimuli-responsive, and adaptive biointerfaces and advanced functional devices. Ministerio de Ciencia, Innovación y Universidades MINECO-FEDER Agència de Gestió d’Ajuts Universitaris i de Recerca

The synthesis of polymeric materials that simultaneously possess multiple excellent mechanical properties and high-efficient self-healability at room temperature is always a huge challenge. Here, we report the synthesis of a transparent polyurea material that can self-heal at room temperature with the aid of water and, meanwhile, has multiple remarkable mechanical performances, including super-high strength, excellent toughness, and large stretchability. Thanks to the synergistic enhancement of both dynamic imine bonds and hierarchical hydrogen bonds within the networks, the resulting polyureas have a world-record tensile strength of 41.2 MPa when compared with other polyurethanes that can self-heal at room temperature and, at the same time, a large breaking strain of 823.0% and a superior toughness of 127.2 MJ/m3. Besides the influence of imine bonds, the mechanical properties of the polyureas are also strongly related to the density and strength of the hierarchical hydrogen bonds within the polyurea networks, and these two factors could be finely controlled by adjusting the mass ratio of the soft segments with different chain lengths and the types of diisocyanates used for polyurea synthesis, respectively. More importantly, the highly dynamic characteristic of both imine bonds and hierarchical hydrogen bonds within the polyureas endows the materials with repeated water-enabled room-temperature self-healing capacity with a high healing efficiency of 92.2%. Moreover, the polyureas can also be recycled or remolded under mild conditions by the hot-pressing or dissolution/casting process. The synthesized polyureas also show great potential in damping applications with a loss factor larger than 0.3 over the temperature range from 12 to 75 °C. It is believed that polyureas with super-high and well-tunable mechanical properties and high-efficient room-temperature self-healing ability have great potential to substitute traditional irreparable polymers in diverse practical applications.

© 2019 American Chemical Society. Luminescent solar concentrators (LSCs) are a promising solar energy technology for reducing architectural barriers to the integration of photovoltaic systems into the built environment. In this work, the first demonstration of thin-film LSCs based on a thermally reversible cross-linked host polymer is presented. This smart material is obtained via a dynamic-chemistry approach based on the Diels-Alder (DA) reaction between a furan-functionalized acrylic copolymer and an aliphatic bismaleimide to obtain optically clear, cross-linked systems capable of healing mechanical damage upon heat treatment. By carefully tuning the concentration of a perylene-based luminophore dopant, an optical efficiency as high as 4.9% can be achieved with this DA-based LSC. In addition, full recovery of device efficiency is demonstrated after complete thermal healing of mechanically induced surface damages as a result of the embedded DA functionality. The approach presented here paves the way to the development of highly efficient multifunctional thermoresponsive smart LSC systems.

Damage occurrence is an inevitable truth in natural or artificial materials. A variety of materials and methods have been introduced to deal with this concern, which self-healing phenomenon has been revealed to be one of the most promising and cost-effective methods. Self-healing property is a smart aptitude of materials to the autonomous or induced repair of damages. Self-healing property is typically accomplished through intrinsic or extrinsic mechanisms when the polymer matrix is comprised of a latent functionality that actuates repairing wounds by hydrogen bonding, thermally reversible reactions, ionomeric materials, or molecular diffusion and entanglement, it is called intrinsic self-healing. In the extrinsic mechanism, healing operant materials are added or implanted into the polymeric matrix, through different approaches such as fibers, capillaries or microcapsules. The mission of self-healing materials is to extend the efficient service life of the materials, by implementing the concept of spontaneous repair instead of increasing their initial performance. Ionomers are polymers with repeating units of ionic groups and their counterions. Ionomers are a type of polymers consisting of up to 20 mol.% ionic groups and their counterions which various new ionomers with different monomers and countercations. Discussion on the self-repairing property revealed by ionomers arising from their chemical arrangement is the subject of this chapter.

Self-healing polymers look back on almost 40 years of history. Beginning in the early 1980s, many different examples were studied—for instance, the self-healing polymers based on microcapsules in 2001. These materials were able to close cracks, to heal damage, and to restore their (mechanical) properties almost like the big role model: nature. The chapter will provide a general discussion of the basic principles of self-healing polymers and will elucidate the underlying healing mechanisms. Thus it will go beyond a pure description of several aspects of self-healing polymers, and it will contain information on how a polymer must be designed to show self-healing. Within this context, a view on the mechanism of extrinsic and intrinsic self-healing polymers will be presented.

Self-healing polymeric materials are at the state-of-art of advanced materials for the last three decades. Among the three self-healing approaches, intrinsic, vascular, and capsule-based, the most easily applicable method is that of the encapsulation of the healing agent into distinct capsules and the subsequent incorporation of these capsules inside the matrix material. Capsule-based self-healing systems have already been studied for a variety of applications in polymers and composites. In this chapter, a detailed review of the research on capsule-based self-healing systems is presented. Beginning with the design of such systems, and ranging from the synthesis and characterization to the application of these advanced materials in polymer matrices, coatings, and composites. The chapter aims to give an overview of the state-of-art as well as to identify the possible gaps and provide suggestions for further research.

One of the vital properties of the human biological organs is repairing injured tissues without any external stimuli. Inspired from the natural systems, scientists have been trying to fabricate man-made materials, having self-healing properties. Self-healing is described as the ability of materials to recover or repair mechanical damages. Self-healing materials are a group of smart man-made materials that can possibly heal different kinds of damages such as fracture toughness, tensile strength, and surface smoothness with or without external stimulus. This chapter covers the design and generic principles of self-healing polymers with different approaches. In addition, recent research about self-healing materials in different applications such as coating, aerospace, conductive device, and biological and pharmaceutical applications is discussed and evaluated.

Coordination bonds are most often reversible. Using them to crosslink polymers into for example hydrogels can therefore be expected to result in reversible crosslinks, which in turn provides self-healing properties. Polyphenols such as the catechol group of the special amino acid DOPA ( l -3,4-dihydroxyphenylalanine), which is used in mussel byssal threads to form a self-healing coating and for adhesion, are excellent coordinators of hard metal ions like iron(III). We will discuss the use of polyphenols and metal crosslinking to form self-healing hydrogels. We also treat less specific effects of metal ions on hydrogel gel mechanical properties by describing Hofmeister effects of cations on hydrogel rheological properties.

Self-healing is most advantageous as it can prolong the service life of a material, which is considered to be the vital aspect in designing the structures. The phenomenon of revamping the damaged structures without any external aid is called self-healing. During the past decade, various self-healing polymers were manufactured using various techniques for a wide range of applications. Autonomic healing is the sole objective of repairing the composites. In fiber-reinforced polymers, damage is initiated at the fiber–matrix interface where initiation and propagation of microcracks is the most common occurrence. This reduces the properties and strength of the structures. In general, conventional method of repairing is carried out by bolting or binding the layers which follows steps such as disassembling the structure, repairing material collection, and restoring them. This chapter deals with the techniques of self-healing and repair of polymers with special attention toward structural materials. This survey describes the mechanism and chemistry that inducted self-healing, beginning from the inherent healing polymers to self-healing-enabled polymers that contain dispersed networks or vascular agents.

The development of dynamic plastics that can self-repair materials properties on demand will provide tremendous leaps forward in the ability to reprocess commodity plastics on a global scale. To this end, the utilization of dynamic, supramolecular bonds as reversible cross-links has the potential for great impact. These supramolecular bonds have been implemented for a vast range of polymers and materials with differing levels of dynamicity depending on the interaction. Supramolecular interactions utilized in self-healing materials are described herein and include such dynamic bonds as host–guest complexes, ligand–metal coordination, hydrogen bonding, dynamic covalent bonds, and electrostatic interactions.