One-Component Intrinsic Self-Healing Coatings Based on Reversible Crosslinking by Diels-Alder Cycloadditions

Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bonds

Four amino acid-bearing acrylamides, N-acryloyl-l-threonine (AThrOH), N-acryloyl-l-glutamic acid (AGluOH), N-acryloyl-l-phenylalanine (APheOH), and N-acryloyl-l, l-diphenylalanine (APhePheOH), were selected for copolymerization with n-butyl acrylate (nBA) to develop amino acid-based self-healable copolymers. A series of copolymers comprising amino acid-bearing acrylamides and nBA with tunable comonomer compositions and molecular weights were synthesized by free radical and reversible addition-fragmentation chain-transfer copolymerization. Self-healing and mechanical properties originated from the noncovalent bonds between the carboxyl, hydroxyl, and amide groups, and π-π stacking interactions among the amino acid residues in the side chains were evaluated. Among these copolymers, P(nBA-co-AGluOH) with suitable comonomer compositions and molecular weights (nBA : AGluOH = 82 : 18, Mn = 18 300, Mw/Mn = 2.58) exhibited good mechanical properties (modulus of toughness = 17.3 MJ m-3) and self-healing under ambient conditions. The multiple noncovalent bonds of P(nBA-co-AGluOH)s were also efficient in improving the optical properties with an enhanced refractive index and good transparency.

Self-Healing Polymeric Soft Actuators

Natural evolution has provided multicellular organisms with sophisticated functionalities and repair mechanisms for surviving and preserve their functions after an injury and/or infection. In this context, biological systems have inspired material scientists over decades to design and fabricate both self-healing polymeric materials and soft actuators with remarkable performance. The latter are capable of modifying their shape in response to environmental changes, such as temperature, pH, light, electrical/magnetic field, chemical additives, etc. In this review, we focus on the fusion of both types of materials, affording new systems with the potential to revolutionize almost every aspect of our modern life, from healthcare to environmental remediation and energy. The integration of stimuli-triggered self-healing properties into polymeric soft actuators endow environmental friendliness, cost-saving, enhanced safety, and lifespan of functional materials. We discuss the details of the most remarkable examples of self-healing soft actuators that display a macroscopic movement under specific stimuli. The discussion includes key experimental data, potential limitations, and mechanistic insights. Finally, we include a general table providing at first glance information about the nature of the external stimuli, conditions for self-healing and actuation, key information about the driving forces behind both phenomena, and the most important features of the achieved movement.

Synthesis, characterization and post-modification of aromatic (Co)polyesters possessing pendant maleimide groups

A new series of (co)polyesters possessing pendent maleimide groups was synthesized by low temperature solution polycondensation of 4, 4’-(5-maleimidopentane-2, 2-diyl) diphenol (BPA-MA) with isophthalic acid chloride (IPC), terephthalic acid chloride (TPC) and a mixture of TPC and IPC (50:50 mol %). Copolyesters were also synthesized by polycondensation of varying compositions of BPA-MA and bisphenol-A (BPA) with IPC. The chemical structures and compositions of (co)polyesters were confirmed by NMR spectroscopy. Inherent viscosity values and number-average molecular weights of (co)polyesters were in the range 0.50–0.76 dL/g and 17,700-32,100 g/mol, respectively, indicating the formation of reasonably high molecular weight polymers. (Co)polyesters were readily soluble in common organic solvents and could be cast into tough, transparent and flexible films from chloroform solutions. (Co)polyesters exhibited 10% weight loss and glass transition temperatures in the range 464–468 and 142–178°C, respectively. A representative copolyester possessing pendant maleimide groups was chemically modified via metal-free azide-maleimide 1,3-dipolar cycloaddition click reaction with two azido compounds, namely, (azidomethyl)benzene (Bz-N3) and 1-(azidomethyl)-pyrene (Py-N3) to yield corresponding modified copolyesters in a quantitative manner.

An Overview of Self-Healable Polymers and Recent Advances in the Field

The search for materials with better performance, longer service life, lower environmental impact, and lower overall cost is at the forefront of polymer science and material engineering. This has led to the development of self-healing polymers with a range of healing mechanisms including capsular-based, vascular, and intrinsic self-healing polymers. The development of self-healable systems has been inspired by the healing of biological systems such as skin wound healing and broken bone reconstruction. The goal of using self-healing polymers in various applications is to extend the service life of polymers without the need for replacement or human intervention especially in restricted access areas such as underwater/underground piping where inspection, intervention, and maintenance are very difficult. Through an industrial and scholarly lens, this paper provides (a) an overview of self-healing polymers, (b) classification of different self-healing polymers and polymer-based composites, (c) mechanical, thermal, and electrical analysis characterization, (d) applications in coating, composites, and electronics, (e) modeling and simulation, and (f) recent development in the past 20 years . This review highlights the importance of healable polymers for an economically and environmentally sustainable future, the most recent advances in the field, and current limitations in fabrication, manufacturing, and performance. This article is protected by copyright. All rights reserved.

Effect of Radical Copolymerization of the (Oxa)norbornene End-group of RAFT-prepared Macromonomers on Bottlebrush Copolymer Synthesis via ROMP

Bottlebrush polymers are attractive for use in a variety of different applications. Here we report synthesis of two novel trithiocarbonate RAFT agents bearing either a oxanorbornyl or norbornenyl moiety for...

The Versatility of Polymeric Materials as Self-Healing Agents for Various Types of Applications: A Review

The versatility of polymeric materials as healing agents to prevent any structure failure and their ability to restore their initial mechanical properties has attracted interest from many researchers. Various applications of the self-healing polymeric materials are explored in this paper. The mechanism of self-healing, which includes the extrinsic and intrinsic approaches for each of the applications, is examined. The extrinsic mechanism involves the introduction of external healing agents such as microcapsules and vascular networks into the system. Meanwhile, the intrinsic mechanism refers to the inherent reversibility of the molecular interaction of the polymer matrix, which is triggered by the external stimuli. Both self-healing mechanisms have shown a significant impact on the cracked properties of the damaged sites. This paper also presents the different types of self-healing polymeric materials applied in various applications, which include electronics, coating, aerospace, medicals, and construction fields. It is expected that this review gives a significantly broader idea of self-healing polymeric materials and their healing mechanisms in various types of applications.

Emissive semi-interpenetrating polymer networks for ink-jet printed multilayer OLEDs

Solution-processing of multi-layered Organic Light Emitting Diodes (OLEDs) remains challenging. Herein, we introduce a facile blending process of emitting polymers with photoreactive polymer strands, allowing for the generation of solvent resistant emissive layers.

Self-Healing in Mobility-Restricted Conditions Maintaining Mechanical Robustness: Furan-Maleimide Diels-Alder Cycloadditions in Polymer Networks for Ambient Applications

Two reversible polymer networks, based on Diels–Alder cycloadditions, are selected to discuss the opportunities of mobility-controlled self-healing in ambient conditions for which information is lacking in literature. The main methods for this study are (modulated temperature) differential scanning calorimetry, microcalorimetry, dynamic rheometry, dynamic mechanical analysis, and kinetic simulations. The reversible network 3M-3F630 is chosen to study the conceptual aspects of diffusion-controlled Diels–Alder reactions from 20 to 65 °C. Network formation by gelation is proven and above 30 °C gelled glasses are formed, while cure below 30 °C gives ungelled glasses. The slow progress of Diels–Alder reactions in mobility-restricted conditions is proven by the further increase of the system’s glass transition temperature by 24 °C beyond the cure temperature of 20 °C. These findings are employed in the reversible network 3M-F375PMA, which is UV-polymerized, starting from a Diels–Alder methacrylate pre-polymer. Self-healing of microcracks in diffusion-controlled conditions is demonstrated at 20 °C. De-gelation measurements show the structural integrity of both networks up to at least 150 °C. Moreover, mechanical robustness in 3M-F375PMA is maintained by the poly(methacrylate) chains to at least 120 °C. The self-healing capacity is simulated in an ambient temperature window between −40 and 85 °C, supporting its applicability as self-healing encapsulant in photovoltaics.

Biomimetic Self-Healing Cementitious Construction Materials for Smart Buildings

Climate change is anticipated to have a major impact on concrete structures through increasing rates of deterioration as well the impacts of extreme weather events. The deterioration can affect directly or indirectly climate change in addition to the variation in the carbon dioxide concentration, temperature and relative humidity. The deterioration that occurs from the very beginning of the service not only reduces the lifespan of the concretes but also demands more cement to maintain the durability. Meanwhile, the repair process of damaged parts is highly labor intensive and expensive. Thus, the self-healing of such damages is essential for the environmental safety and energy cost saving. The design and production of the self-healing as well as sustainable concretes are intensely researched within the construction industries. Based on these factors, this article provides the materials and methods required for a comprehensive assessment of self-healing concretes. Past developments, recent trends, environmental impacts, sustainability, merits and demerits of several methods for the production of self-healing concrete are discussed and analyzed.

Tuning the thermoreversible temperature domain of PTMC-based networks with thermosensitive links concentration

In this work, thermoreversible poly(trimethylene carbonate) (PTMC) based networks with different crosslinking densities were obtained by Diels-Alder (DA) reaction between furan-functionalized PTMC precursors and a bismaleimide. Furan-grafted PTMC with various functionalities determined by ¹H-NMR analyses were prepared from telechelic PTMC oligomer, glycerol, 4,4'-methylenebis(cyclohexyl isocyanate) (H₁₂MDI) and furfuryl alcohol. The formation of network structures by DA reaction between furan and maleimide groups were proved by Fourier-transform infrared spectroscopy (FT-IR). Although both exo and endo DA adduct forms exist, the thermally more stable exo form dominates. The thermoreversibility of networks was evidenced by FT-IR, solubility, differential scanning calorimetry (DSC) and rheology experiments at different temperatures. By increasing furan functionality or node concentration, denser and stiffer networks could be formed with higher Young's modulus and true stress at break in tensile tests, as well as higher crossover temperature, which indicates a nominal transition from elastic behavior to viscous state. The disruption of networks was found to occur in high temperature ranges from 130 to 160 °C, depending on their crosslinking density.

Remarkable Reactivity of Boron-Substituted Furans in the Diels-Alder Reactions with Maleic Anhydride

The reactivity of boron-substituted furans as dienes in the Diels-Alder reaction with maleic anhydride has been investigated. Gratifyingly, the furans with boryl substituents at C-3 gave the exo cycloadduct exclusively with excellent yields. In particular, the potassium trifluoroborate exhibited outstanding reactivity at room temperature. Theoretical calculations suggested that the trifluoroborate group is highly activating and also that the thermodynamics is the main factor that determines whether the products can be obtained efficiently or not.

Reprocessable and recyclable styrene-based resins with low dielectric and good mechanical properties

Current low dielectric materials can't be recycled, causing significant serious environmental pollution. In this work, to create a type of recyclable and reprocessable low dielectric materials, pyridine was incorporated into styrene-based polymers by copolymerization. Subsequently, this copolymer was cross-linked by incorporating zinc ions and forming coordination bonds. These resins exhibited low dielectric constant (ε = ∼3) and good tensile strength (∼40 MPa) and modules (∼700 MPa). Meanwhile, these resins can be decrosslinked and dissolved in tetrahydrofuran and be reprocessed at above 200 °C. After 3 cycles of reprocessing, the low ε and mechanical properties of the styrene resins can still be preserved, indicating a good recyclability of these new styrene-based resins.

In this work, we create a new recyclable and reprocessable low-dielectric materials by introducing coordination bonds in styrene resins.

A comprehensive review on self-healing of asphalt materials: Mechanism, model, characterization and enhancement

Self-healing has great potential to extend the service life of asphalt pavement, and this capability has been regarded as an important strategy when designing a sustainable infrastructure. This review presents a comprehensive summary of the state-of-the-art investigations concerning the self-healing mechanism, model, characterization and enhancement, ranging from asphalt to asphalt pavement. Firstly, the self-healing phenomenon as a general concept in asphalt materials is analyzed including its definition and the differences among self-healing and some viscoelastic responses. Additionally, the development of self-healing in asphalt pavement design is introduced. Next, four kinds of possible self-healing mechanism and corresponding models are presented. It is pointed out that the continuum thermodynamic model, considering the whole process from damage initiation to healing recovery, can be a promising study field. Further, a set of self-healing multiscale characterization methods from microscale to macroscale as well as computational simulation scale, are summed up. Thereinto, the computational simulation shows great potential in simulating the self-healing behavior of asphalt materials from mechanical and molecular level. Moreover, the factors influencing self-healing capability are discussed, but the action mechanisms of some factors remain unclear and need to be investigated. Finally, two extrinsic self-healing technologies, induction heating and capsule healing, are recommended as preventive maintenance applications in asphalt pavement. In future, more effective energy-based healing systems or novel material-based healing systems are expected to be developed towards designing sustainable long-life asphalt pavement.

Probing the in-air growth of large area of 3D functional structures into a 2D supramolecular nanoporous network

2D host–guest chemistry combined with drop-casting allows to trap functionalized 3D Zn–phthalocyanine complex into a large 2D porous supramolecular template.

Thermally-Induced Self-Healing Behaviors and Properties of Four Epoxy Coatings with Different Network Architectures

The thermally-induced self-healing behavior of polymer coatings consists of two steps, i.e., gap closure and crack repair. In addition, the polymer coatings with thermally-induced self-healing capability are expected to show satisfied properties to ensure the application. Here, four epoxy coatings with dense irreversible Network I, dense reversible Network II based on a Diels⁻Alder (DA) reaction, loose irreversible Network III, as well as partially irreversible and partially reversible Network IV were prepared, respectively. The dense irreversible Network I showed an evident gap closure upon heating, while the crack still existed at the high temperature. The dense reversible Network II presented good self-healing upon direct heating at a high temperature of 150 °C, leading to the quick gap closure in 40 s and subsequent crack disappearance in 80 s. The loose irreversible Network III showed negligible crack variations upon heating, while the partially reversible and partially irreversible Network IV showed quick gap closure as well but only partial crack disappearance. Besides, the coating with the reversible Network II based on the DA reaction not only presented good self-healing capability but also possessed the satisfied mechanical properties and the best electrochemical corrosion property, ensuring its further exploitation and potential practical applications.

A novel self-healing electrochromic film based on a triphenylamine cross-linked polymer

A novel electrochromic material with self-healing properties, which may hold great potential to overcome the scar generation in ECDs, has been synthesized and studied.

One-component Diels–Alder based polyurethanes: a unique way to self-heal

In the present work, we synthesized one-component self-healing polyurethanes based on thermo-reversible furan/maleimide Diels–Alder reactions.

Ambient temperature induced Diels–Alder crosslinked networks based on controlled methacrylate copolymers for enhanced thermoreversibility and self-healability

An effective thermoreversible crosslinked network fabricated at ambient temperature from a new, controlled methacrylate copolymer having reactive maleimide pendants and a trifunctional furan (TFu) exhibiting effective self-healability.