A seawater‐assisted self‐healing metal–catechol polyurethane with tunable mechanical properties

Recently, self‐healing polymers have been one of the most intriguing academic fields due to the fact that they can increase their service lives and reduce the amount of waste. Here we designed and synthesized a novel telechelic polyurethane with dopamine (DA) end groups that are coordinated with Ca²⁺ to form dynamic non‐covalent bonds. The tensile stress of the designed polyurethanes increases with increase in the amount of metal cation added, while the strain at break slightly decreases. Rheological tests show that the ionic coordination between Ca²⁺ and catechol can dynamically break and recombine under the stimulation of seawater, endowing the polymer with superior self‐healing properties (up to 84% based on toughness). Therefore, the seawater‐triggered self‐healable, super tough polyurethane presented here is very intriguing as it has many potential applications especially in the marine environment. © 2019 Society of Chemical Industry     

Perspectives on main‐chain hydrogen bonded supramolecular polymers

Supramolecular polymers are assembled from monomeric units held together by reversible non‐covalent interactions. These supramolecular materials display polymeric properties and may soon have important industrial applications. This mini review focuses on the advances in main‐chain supramolecular polymers whose assembly is guided primarily by hydrogen bonding interactions. The design constraints of these new systems discussed include assembly motifs, the strength and directionality of the non‐covalent interactions, association versus reversibility, and environmental effects on the degree of polymerization. Selected literature examples including Meijer's ureidopyrimidinone system are used to highlight the challenges and potential of these supramolecular polymeric materials. Copyright © 2007 Society of Chemical Industry     

Self‐healing properties of layer‐by‐layer assembled multilayers

The review is focused on the formation and the self‐healing properties of polymer and hybrid multilayers formed via the layer‐by‐layer approach. In the first part of the review the recent developments in the construction of polymer multilayers are highlighted. In the second part the design and the self‐healing properties of inorganic ? polymer hybrid multilayers are described. It is shown that self‐healing multilayers have a broad spectrum of applications including corrosion protection, as elements of antifouling and antimicrobial coatings and bio‐inspired superhydrophobic interfaces. It is demonstrated that dynamic functional interfaces have a complex hierarchical organization of non‐covalently bonded polymers and colloidal particles. Mechanisms of self‐healing behavior of the multilayers and the role of water and external stimuli (pH, ionic strength and temperature, light) in swelling of multilayers and rearrangement of polymer segments are discussed. Future trends, perspectives and research strategies for the design of ‘smart’ self‐assemblies with self‐healing properties are proposed. © 2015 Society of Chemical Industry     

Heat‐triggered poly(siloxane‐urethane)s based on disulfide bonds for self‐healing application

Polydimethylsiloxane (PDMS) is one of the most widely employed silicon‐based polymers for its high flexibility, low usage temperature, excellent water resistance, outstanding electrical insulting property, and physiological inert, etc. However, the covalent‐bonded Si? O bonds are unable to heal automatically when damaged, which would result in the failure of the materials and devices. Disulfide bond based polymers show high healing efficiency at moderate temperature and have been investigated intensively. Herein, we report a PDMS‐based polyurethane self‐healing polymer (PDMS‐PU) modified with disulfide bonds, which exhibited a reinforced thermal stability, excellent stretchability, and satisfactory self‐healing ability. The effect of different ratio of PDMS and disulfide bond contents on the elastomer properties was investigated. With the increase of PDMS content, the decomposition temperature of the PDMS‐PU‐3 (332 °C) elastomer with highest content of PDMS was increased by 34 °C compared to PDMS‐PU‐1 (298 °C) with lowest content of PDMS and exhibited a largest elongation at break of 1204%. PDMS‐PU‐1 with highest content of disulfide bond possessed a highest healing efficiency of 97%. The results indicated the PDMS‐PU elastomers can be used as self‐healing flexible substrate for flexible electronics. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46532.     

Thermally assisted self‐healing polyurethane containing carboxyl groups

Self‐healing polymer is a kind of intelligent material with the capability to repair damage automatically. In this paper, a type of polyurethane containing carboxyl groups is reported that demonstrates thermally assisted healing effects. This polymer can be healed even 72 h after cutting and also has a repeatable healing property. The self‐healing efficiency can reach 90% when comparing the tensile strength of the healed sample to the original sample. Carboxyl content plays an important role in the self‐healing property; polyurethane with no carboxyl groups cannot be healed. The mechanism of self‐healing showed that hydrogen bonding interactions between carboxyl groups and diffusion of poly(ethylene glycol) chains contribute to the self‐healing behavior. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45929.     

Novel collagen‐based hydrogels with injectable,self‐healing,wound‐healing properties via a dynamic crosslinking interaction

Collagen‐based hydrogels have gained significant popularity in biomedical applications; however, traditional collagen hydrogels are easily disabled for lack of self‐healing properties due to their non‐reversible bonds. Here, a self‐healing collagen‐based hydrogel has been developed based on dynamic network chemistry, consisting of dynamic imine linkages between collagen and dialdehyde guar gum, as well as diol‐borate ester bonds between guar gum and borax. In addition, macromolecular interactions amongst macromolecules are involved. The above‐mentioned interactions were validated by Fourier transform infrared spectroscopy, sodium dodecyl sulfate polyacrylamide gel electrophoresis and DSC. The as‐prepared collagen‐based hydrogels showed good injectability and rapid self‐healing capacity (within 3 min) as reflected from injection tests, optical microscope observations, rheological measurements, as well as self‐healing studies. In addition, the collagen‐based hydrogels showed accelerated wound‐healing properties. This study offers a facile strategy to endow self‐healing ability on collagen‐based hydrogels without any external stimulus, which show great application potential as wound dressings. © 2020 Society of Chemical Industry     

RAFT (Reversible addition–fragmentation chain transfer) crosslinking (co)polymerization of multi‐olefinic monomers to form polymer networks

The use of reversible addition–fragmentation chain transfer (RAFT) crosslinking (co)polymerization of multi‐olefinic monomers to produce three‐dimensional polymer networks is reviewed. We give specific attention to differences between RAFT and conventional processes, differences between RAFT and other forms of reversible deactivation radical polymerization (such as atom transfer radical and nitroxide‐mediated polymerizations) and the dependence of the polymerization process and network properties on RAFT agent structure. This knowledge is important in network optimization for applications as dynamic covalent polymers (in self‐healing polymers), as porous polymer monoliths or gels (used as chromatographic media, flow reactors, controlled release media, drug delivery vehicles and in molecular imprinting) and as coatings. © 2014 Society of Chemical Industry     

Tung oil‐based thermosetting polymers for self‐healing applications

Several bio‐renewable thermosetting polymers were successfully prepared from tung oil through cationic polymerization for the use as the healing agent in self‐healing microencapsulated applications. The tung oil triglyceride was blended with its methyl ester, which was produced by saponification followed by esterification. The changes in storage modulus, loss modulus, and glass transition temperature as functions of the methyl ester content were measured using dynamic mechanical analysis. In addition, the fraction of cross‐linked material in the polymer was calculated by Soxhlet extraction, while proton nuclear magnetic resonance, Fourier transform infrared spectroscopy and TEM were used to investigate the structure of the copolymer networks. The thermal stability of the thermosets as a function of their methyl ester blend contents was determined by thermogravimetric analysis. Finally, the adhesive properties of the thermosets were studied using compressive lap shear and the fracture surfaces were analyzed using SEM. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40406.     

A Bio‐Inspired and Biomass‐Derived Healable Photochromic Material Induced by Hierarchical Structural Design

Utilization of bionics to develop stimuli responsive polymers that can heal damage with excellent restorability is particularly attractive for a sustainable society. Herein, inspired by chameleons, a hierarchical structural design strategy is proposed and illustrated to fabricate a healable photochromic material based on a self‐healable polymeric matrix and a finely dispersed photochromic spirooxazine. The self‐healable polymeric matrix is fabricated via the integration of multiple hydrogen bonds (H bonds) and covalent cross‐links into a biomass‐derived elastomer. The dynamic nature and soft characteristics enable the as‐prepared elastomer superior extensibility as well as self‐healing ability, while the covalent cross‐links can assist the reassociation of ruptured H bonds. The representative elastomer exhibits an extensibility of 2600% and toughness of 42.76 MJ m^?3. Furthermore, it shows good self‐healing ability with complete recovery of scratch as well as restoration against 1900% of elongation and 24.1 MJ m^?3 of toughness after healing at 60 °C for 24 h. This combination of moderate toughness, good self‐healing ability, and smart photochromic property in biomass‐derived materials should largely improve their applicability, reliability, and sustainability in various materials and devices.     

Hydrogen‐bonded supramolecular polyurethanes

As a class of materials, supramolecular polymers represent an exciting area of advanced materials research. The combination of unique properties, easy synthesis and response to the environment or external and temporal stimuli makes them important as a focus for the next generation of materials. Understanding and manipulating the non‐covalent interactions leading to polymer assembly allows control over properties by selecting specific building blocks with well‐understood non‐covalent chemistry from an established toolkit. This allows assembly of defined and easily manipulated architectures, where physical characteristics similar to conventional high‐molecular‐weight polymers can be realized. Herein, we describe recent studies of the self‐assembly of polyurethane‐based supramolecular materials. © 2014 Society of Chemical Industry     

Side‐chain functionalized supramolecular polymers

Over the past two decades, the field of supramolecular polymer chemistry has developed from a curiosity to a mature area of polymer science. Among the most promising subjects in this large field are noncovalently functionalized side‐chain polymers that have been investigated extensively as a result of their modular character and ease of synthesis. Side‐chain functionalized polymers have the potential for a profound impact on complex materials. For example, for side‐chain functionalized polymers based on a single noncovalent interaction, materials for a variety of applications ranging from liquid crystalline and electro‐optical materials to drug delivery systems have been reported. Furthermore, materials based on this novel methodology may overcome several shortcomings of current covalent multifunctionalization strategies such as highly complex materials that are extremely difficult or impossible to fabricate with current methods. In this review, basic design requirements, advantages and potential applications are presented. Copyright © 2006 Society of Chemical Industry     

Multi‐stimuli responsive shape memory polymers synthesized by using reaction‐induced phase separation

Thermo‐induced multishape memory polymers are a growing focus of smart materials because of its promising applications. Multishape memory effect is generally attained by using polymers with broad phase transition and multiphase polymers. The latter is of particular interest for copolymerization and polymer compositing. One requirement has to be fulfilled to achieve multishape memory effect, which is to have two reversible phase transitions. In this study, we report synthesis of polymer composite composed of strong segregated polymers by using reaction‐induced phase separation. We demonstrate the method by using polyurethane (PU) and poly(methacrylic acid) (PMAA). With adjusting the weight ratio, the polymer composites exhibit a phase spectrum from phase separation to miscible composite. The composite with PU/PMAA =3:1 demonstrated triple‐shape memory effect. Based on the results, we argued the effect of segregation on the shape memory effect for polymer composites. With the addition of PMAA, the polymer composite also exhibits pH/water‐induced shape memory effect. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43534.     

Super‐Tough,Self‐Healing Polyurethane Based on Diels‐Alder Bonds and Dynamic Zinc–Ligand Interactions

Self‐healing polymer materials have attracted extensive attention and have been explored due to their ability of crack repairing in materials. This paper aims to develop a novel polyurethane‐based material with high self‐healing efficiency and excellent mechanical properties under 80 °C on the basis of reversible Diels–Alder bonds as well as zinc–ligand structure (DA‐ZN‐PU). By integrating DA bonds and zinc–ligand structure, as‐prepared DA‐ZN‐PU samples reach the maximum tensile strength as much as 28.45 MPa. After self‐healing, the tensile strength is 25.85 MPa, leading to the high self‐healing efficiency of 90.8%. In addition, by introducing carbonyl iron powder (CIP), a new polyurethane containing carbonyl iron powder (DA‐ZN‐CIP‐PU) can be achieved, exhibiting microwave‐assisted self‐healing property. And the self‐healing efficiency can be reached to 92.6% in 3 min. Due to high self‐healing efficiency and excellent mechanical properties of the prepared novel polyurethane, it has application attributes in crack repair of functional composite materials.     

A Thermo‐ and Moisture‐Responsive Zwitterionic Shape Memory Polymer for Novel Self‐Healable Wound Dressing Applications

Developing wound dressings that have strong adhesion strength without causing any conglutination to the wound site is still challenging. Herein, is proposed that zwitterionic shape memory polymers can be applied as promising candidates for wound dressing. Sulfobetaine methacrylate (SBMA) is copolymerized with 2,3‐dihydroxypropyl methacrylate (DHMA) in the presence of boric acid as a cross‐linking agent. The prepared material exhibits multi‐stimuli responsive shape memory behaviors: it can rapidly return to its initial shape upon heating to 90 °C, and a gradual recovery is also observed by absorbing moisture in humid environments. The shape memory effect can be well adjusted via incorporation of sodium chloride to induce the dissociation of electrostatic interactions between PSBMA chains, leading to reduced transition temperature and faster shape recovery rate. Moreover, the dynamic nature of boron ester bonds and electrostatic interaction endows the material with effective and rapid self‐healing ability. It is also demonstrated that the deployment process of the dressing that a sample with an initially circular shape can perfectly fit and tightly bind to the wound site after moisture‐induced shape recovery. The proposed zwitterionic polymer can possibly extend the application scope of shape memory polymers and pave a new way for the design of wound dressings.     

Thermo‐reversible healing in a crosslinked polymer network containing covalent and thermo‐reversible bonds

The self‐healing behavior of a modified ureido‐amide based thermoplastic hybrid elastomer was investigated by increasing the concentration of non‐reversible (covalent) bonds compared to reversible (hydrogen) bonds. A crosslinked polymer network was synthesized using varying amounts of diglycidylether of bisphenol A and reacting with the ureido‐amide thermoplastic. Increasing epoxy content produced a more rigid and thermally stable hybrid network, which in turn decreased overall thermo‐reversible or healing behavior. Fracture toughness recoveries varied from 25% for the system containing the greatest number of covalent bonds to well over 200% for systems containing higher thermoplastic content. Substantial levels of healing, about 62% recovery, were still achieved despite the crosslinked network having a T_g above room temperature, 31°C as measured by differential scanning calorimetry (DSC). Dynamic mechanical thermal analysis was used to monitor thermo‐reversible behavior of the elastic moduli and thus probe molecular mobility within the glassy state. The extent and rate of recovery of the elastic modulus was dominated by the extent of thermal activation above the glass transition temperature. Fourier transform infrared spectroscopic and DSC studies confirmed that reacting the thermoplastic with an epoxy resin produced a covalently bonded crosslinked network and the epoxide groups were completely consumed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Self‐Detecting and Self‐Healing Reinforce Elastomer Doped with Aggregation‐Induced Emission Molecules

Most of elastomers for fabrication of comfortable epidermal devices and smart actuators produce responsive signals by the stimuli‐induced deformation. Herein, a dynamic visualization of external stimuli rather than the deformation through synthesis of a self‐healing poly(dimethylsiloxane) (PDMS)‐based elastomer doped with aggregation‐induced emission (AIE) molecules is reported. The self‐healing PDMS‐based elastomer is designed and synthesized through molecule integration of reversible multi‐strength H‐bonds and permanent covalent crosslink sites. The adjustment of the weight ratio of elastic cross‐linker offers tunable mechanical properties of the resultant elastomer. After doping such an elastomer with AIE molecules of 1,1,2,2‐tetrakis(4‐nitrophenyl)ethane, the elastomer composite displays strong on–off fluorescence depending upon mechanical damage and temperatures, which can be used to detect the breaking and self‐healing performances, as well as the temperature change. The strategy described here provides another way to develop smart polymeric elastomers for practical applications.     

Recyclable bio‐based crosslinked polyurethanes with self‐healing ability

We report the synthesis of a linear bio‐based polyurethane (bio‐PU) containing furan ring by using renewable polylactide copolymer diol and 2,5‐furandimethanol as a soft segment and chain extender, respectively, in which the reversible crosslinked covalent bonds between hard segments were incorporated via Diels–Alder (D‐A) reaction between the furan ring of the chain extender and bismaleimide (BM) crosslinker. By simply controlling the amount of BM, mechanical properties of the obtained crosslinked bio‐PUs (CBPUs) were varied widely. In particular, the CBPU100 sample shows the highest tensile strength of 10.8 MPa, Young's modulus of 193 MPa, and an elongation of 155%. The differential scanning calorimetry experiments verify the recycle property of the CBPUs by the D‐A/retro‐D‐A reaction at the proper temperature. The thermal recyclability and remolding ability of these materials are demonstrated by two kinds of polymer processing methods, i.e., solution casting and hot‐compression molding. The recycled CBPUs display almost identical elongation and slightly decreased tensile strength compared to the as‐synthesized samples. Furthermore, the CBPUs also exhibit excellent self‐healing ability. Therefore, the resulting CBPUs possess tunable mechanical properties, good thermal recyclability, re‐mending, and self‐healing ability, which makes the bio‐based materials more eco‐friendly. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46272.     

Increased stability in self‐healing polymer networks based on reversible Michael addition reactions

A reversible thiol‐ene click reaction is utilized to design novel self‐healing polymers. These materials are based on a new methacrylate monomer featuring a benzylcyanoacetamide derivative, which is copolymerized with butyl methacrylate. Afterwards, the crosslinking is performed by the addition of a dithiol and a tetrathiol, respectively. Self‐healing behavior is obtained by heating the crosslinked polymers to 100 °C (150 °C) for several hours and is monitored by scratch healing experiments utilizing an optical microscope. The thermal properties are studied in detail by differential scanning calorimetry as well as thermogravimetric analysis. Moreover, depth‐sensing indentation measurements are performed to determine the mechanical properties. The healing process is based on the reversible cleavage/closing of the bonds (i.e., thiol‐ene reaction), which could be demonstrated by Raman spectroscopy. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44805.     

Oxime crosslinked polymer networks: Is every reversible covalent bond suitable to create self‐healing polymers?

The incorporation of reversible covalent bonds into polymeric materials offers the possibility to generate polymers with self‐healing ability. For this purpose, three new oxime crosslinkers are synthesized and crosslinked by the copolymerization with different commercially available methacrylates via a photo‐polymerization process. These crosslinked materials are investigated regarding a potential self‐healing behavior. Moreover, the influence of different additives (polymerizable acids, photo acids, and acid developers) to enable self‐healing is studied in detail. Thereby, the limit of self‐healing based on reversible covalent bonds is reached in these materials. Due to the high stability of the oxime bonds in bulk materials no exchange reactions as well as no self‐healing behavior could be observed. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44168.     

Post‐polymerization modification of bio‐based polymers: maximizing the high functionality of polymers derived from biomass

The renaissance of the bio‐based chemical industry over the last 20 years has seen an ever growing interest in the synthesis of new bio‐based polymers. The building blocks of these new polymers, so called platform molecules, contain significantly more chemical functionality than their petrochemical counterparts (such as ethene, propene and para‐xylene). As a result bio‐based polymers often contain greater residual chemical functionality in their chains, with groups such as alkenes and hydroxyls commonly observed. These functional groups can act as sites for post‐polymerization modification (PPM), thus further extending the range of applications for bio‐based polymers by tailoring the polymers' final properties. This mini‐review highlights some of the most recent and compelling examples of how to make use of bio‐based polymers with residual functional groups for PPM. It also looks at how the emerging interdisciplinary field of enzymatic polymer synthesis allows for increased functionality in polymers by avoiding side‐reactions as a result of milder reaction conditions, and additionally offers an alternative means of polymer surface modification. © 2018 Society of Chemical Industry