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To fulfill the current circular economy concept, the academic and industrial communities are devoting significant efforts to plastic materials' end-of-life. Unlike thermoplastics, which are easy to recover and re-valorize, recycling thermosets is still difficult and challenging. Conversely, because of their network structure, thermosetting polymer systems exhibit peculiar features that make these materials preferable for several applications where high mechanical properties, chemical inertness, and thermal stability, among others, are demanded. In this view, vitrimers have quite recently attracted the attention of the scientific community, as they can form dynamic covalent adaptive networks that provide the properties typical of thermosets while keeping the possibility of being processed (and, therefore, mechanically recycled) beyond a certain temperature. This review aims to provide an overview of vitrimers, elucidating their most recent advances and applications and posing some perspectives for the forthcoming years. [ABSTRACT FROM AUTHOR]

Copolymerization allows tuning polymer's properties and a synergetic effect may be achieved for the resulting hybrid, i.e., outperforming the properties of its parents as often observed in natural materials. This synergetic concept is herein applied to enhance both dynamicity and properties of vitrimeric materials using poorly dynamic hydroxyurethane and non‐dynamic epoxy thermosets. The latter generates activated hydroxyl, promoting exchange reactions 15 times faster than pure polyhydroxyurethanes. This strategy allows obtaining catalyst‐free high‐performance vitrimers from conventional epoxy‐amine formulations and an easily scalable (bio‐)CO2‐based yet poorly efficient dynamic network. The resulting hybrid network exhibits modulus retention superior to 95% with fast relaxation (<10 min). The hydroxyurethane moieties actively participate in the network to enhance the properties of the hybrid. The material can be manufactured as any conventional epoxy formulation. This new strategy to design dynamic networks opens the door to large‐scale circular high‐performance structural carbon fiber composites (CFRP). The CFRP can be easily reshaped and welded from flat plates to complex geometries. The network is degradable under mild conditions, facilitating the recovery and re‐use of high‐added‐value fibers. This accessible and cost‐effective approach provides a versatile range of tunable dynamic epoxides, applicable across various industries with minimal adjustments to existing marketed products. [ABSTRACT FROM AUTHOR]

Covalent adaptive networks (CANs) are capable of undergoing segment rearrangement after being heated, which endows the materials with excellent self-healing and reprocessing performance, providing an efficient solution to the environment pollution caused by the plastic wastes. The main challenge remains in developing CANs with both excellent reprocessing performance and creep-resistance property. In this study, a series of CANs containing dynamic covalent benzopyrazole-urea bonds were developed based on the addition reaction between benzopyrazole and isocyanate groups. DFT calculation confirmed that relatively low dissociation energy is obtained through undergoing a five-member ring transition state, confirming excellent dynamic property of the benzopyrazole-urea bonds. As verified by the FTIR results, this nice dynamic property can be well maintained after incorporating the benzopyrazole-urea bonds into polymer networks. Excellent self-healing and reprocessing performance is observed by the 3-ABP/PDMS elastomers owing to the dynamic benzopyrazole-urea bonds. Phase separation induced by the aggregation of the hard segments locked the benzopyrazole-urea bonds, which also makes the elastomers display excellent creep-resistance performance. This hard phase locking strategy provides an efficient approach to design CANs materials with both excellent reprocessing and creep-resistance performance. [ABSTRACT FROM AUTHOR]

Herein, a non-conventional fluorescent polymer (NCFP) was established by coupling in-situ Schiff base reaction with epoxy ring-open polymerization, which were constructed by hyperbranched polyamidoamine (HPAMAM) and bio-based vanillin epoxy monomer with an aldehyde group (MB). The resulting hybrid covalent adaptive networks (HP/MB) could emit strong intrinsic fluorescence due to the non-conjugated fluorescence derived from HPAMAM, and the fluorescence intensity shows a good linear correlation with the crosslink density. Meanwhile, owing to the epoxy-Schiff base hybrid covalent adaptive network, HP/MB exhibit excellent mechanical properties and self-healing that can be monitored in real time by fluorescence imaging. As a representative, HP/MB-3 exhibited a tensile strength up to 76.4 MPa, and achieved 100% repair of the crack within 4 min at 140 °C under 1.5 MPa pressure. Especially, HP/MB-3 also showed strong fluorescence quenching by Fe3+ ion. Based on the above unique properties, the application potential of HP/MB in responsive metal coating were further explored, and the coated sample could exhibit different degree of fluorescence quenching effect at different corrosion stages. Therefore, the NCFP-based HP/MB possesses great application potential in the areas of fluorescent sensors, anti-counterfeiting labels, self-detecting anticorrosive coatings and engineering damage assessment.

Covalent adaptable networks (CANs) offer innovative solutions for the reprocessing and recycling of thermoset polymers. However, achieving a balance between easy reprocessing and creep resistance remains a challenge. This study focuses on designing and synthesizing polyurethane (PU) materials with tailored properties by manipulating the stereochemistry of diamine chain extenders. By employing cis- and trans-configurations of diamine extenders, we developed a series of PU materials with varying mechanical properties and creep resistance. The trans-configured materials (R,R-DAC-PU or S,S-DAC-PU) exhibited superior creep resistance and mechanical strength due to dense hydrogen bonding networks. The cis-configured materials (Cis-DAC-PU) exhibited enhanced processability and elasticity. Under 0.1 MPa stress, R,R-DAC-PU showed a mere 3.5 % strain change at 170 °C over 60 minutes, highlighting its superior creep resistance. Both configurations can be recycled via urea bond exchange reactions using hot pressing or solvothermal methods. Density Functional Theory (DFT) calculations indicate that both the (R,R-DCA-UB-U) 2 and (S,S-DCA-UB-U) 2 segments form six hydrogen bonds with shorter bond lengths, leading to stronger hydrogen-bonding interactions. Conversely, the (Cis-DCA-UB-U) 2 segment forms four hydrogen bonds with longer bond lengths, resulting in weaker interactions. This work highlights the critical role of stereochemistry in designing high-performance, recyclable polymer materials with tailored properties., (© 2025 Wiley-VCH GmbH.)

Covalent adaptive networks (CANs) have numbers of versatile abilities derived from topological reshuffling with interesting potentials. Here, self‐healable solid‐state polymer electrolytes were developed by integrating epoxy‐resin‐based CANs enabled by disulfide bond with a solid lithium salt (LiTFSI). The disulfide bond was introduced by using a disulfide‐containing aliphatic polyamine as the epoxy‐curing agent. To determine the cure cycle of this epoxy‐resin system, the curing kinetics in the presence of LiTFSI was studied by nonisothermal differential scanning calorimetry. The prepared ion‐conducting (IC) CANs with different LiTFSI content were optically transparent and self‐healable at temperatures above glass transition temperature (Tg). The effect of LiTFSI content on the thermal stability and tensile properties was investigated. The electrical properties of the IC CANs were studied by impedance spectroscopy at various temperatures. Their ionic conductivity was analyzed by the Vogel–Tamman–Fulcher model and equivalent‐circuit fitting. Due to the high mobility of charge carriers, the IC CAN sample (containing15 wt% LiTFSI) exhibited the best ionic conductivity, which reached a value of 3.35 × 10−6 S cm−1 at 80 °C and 8.31 × 10−6 S cm−1 at 100 °C, presenting great attraction for self‐healing iontronics. [ABSTRACT FROM AUTHOR]

Polyurethane (PU) has not only been widely used in the daily lives, but also extensively explored as an important class of the essential polymers for various applications. In recent years, significant efforts have been made on the development of self‐healable PU materials that possess high performance, extended lifetime, great reliability, and recyclability. A promising approach is the incorporation of covalent dynamic bonds into the design of PU covalently crosslinked polymers and thermoplastic elastomers that can dissociate and reform indefinitely in response to external stimuli or autonomously. This review summarizes various strategies to synthesize self‐healable, reprocessable, and recyclable PU materials integrated with dynamic (reversible) Diels–Alder cycloadduct, disulfide, diselenide, imine, boronic ester, and hindered urea bond. Furthermore, various approaches utilizing the combination of dynamic covalent chemistries with nanofiller surface chemistries are described for the fabrication of dynamic heterogeneous PU composites. [ABSTRACT FROM AUTHOR]

Conventional polyurethanes from non-renewable resources have been widely used for their excellent mechanical properties and thermal stability, which are difficult to be reprocessed and recycled due to the permanent crosslinked networks. In this study, dynamic acetal bonds were synthesized using bio-based vanillin and then embedded in polymer with castor oil to construct bio-based recyclable polyurethane. The ratio of castor oil to bio-spiroacetal diols was varied to control the thermodynamics and mechanical performance of bio-based polyurethanes. Experimental results of dynamic mechanical analysis, differential scanning calorimetry, tensile test and stress relaxation test suggested that a decrease in the content of acetal diols as a hard segment, led to a decrease in the glass transition temperature and tensile strength. Additionally, the activation energy initially increased and then decreased. The reversibility of the acetal structure endowed green polyurethane materials with the ability of reprocessing, self-repairing and closed-loop recycling. [Display omitted] • The bio-based spiro acetal (VP) was successfully synthesized using vanillin with pentaerythritol. • The mechanical properties of bio-based polyurethane networks could be adjusted by the ratio of VP and castor oil. • The vanillin and castor oil significantly reduced the consumption of non-renewable resources. • The acetal structure endowed the materials with closed-loop recyclability, self-repairing, and reprocessability. [ABSTRACT FROM AUTHOR]

Given the substantial environmental challenge posed by global plastic waste, recycling technology for thermosetting polymers has become a huge research topic in the polymer industry. Covalent adaptive networks (CANs), which can reversibly dissociate and reconstruct their network structure, represent a key technology for the self-healing, reprocessing, and recycling of thermosetting polymers. In the present study, we introduce a new series of polyurethane CANs whose network structure can dissociate via the self-catalyzed formation of dithiolane from the CANs' polydisulfide linkages when the CANs are treated in N , N -dimethylformamide (DMF) or dimethyl sulfoxide at 60 °C for 1 h. More interestingly, we found that this network dissociation even occurs in tetrahydrofuran-DMF solvent mixtures with low DMF concentrations. This feature enables a reduction in the use of high-boiling, toxic polar aprotic solvents. The dissociated network structure of the CANs was reconstructed under UV light at 365 nm with a high yield via ring-opening polydisulfide linkage formation from dithiolane pendant groups. These CAN films, which were prepared by a sequential organic synthesis and polymerization process, exhibited high thermal stability and good mechanical properties, recyclability, and self-healing performance. When lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt was added to the CAN films, the films exhibited a maximum ion conductivity of 7.48 × 10 -4 S cm -1 because of the contribution of the high concentration of the pendant ethylene carbonate group in the CANs. The ion-conducting CAN films also showed excellent recyclability and a self-healing performance.

[Display omitted] • A catalyst-free CFRC is constructed showing good reprocessable performance. • The matrix has the similar mechanical and thermal properties as traditional resins. • The matrix can be quickly reprocessed, repaired, and recycled. • The CFRC possesses strong mechanical and unique welding abilities. • Carbon fibers are recycled efficiently without damage. Carbon fiber-reinforced composites (CFRCs) have been extensively applied in high-tech industry due to their superior mechanical properties. However, the permanent crosslinked networks of thermosetting matrices cause them difficult to reshape, repair and recycle. In this work, we devise a series catalyst-free covalent adaptable networks (CANs) by curing diglycidyl 4,5-epoxycyclohexane-1,2-dicarboxylate (DGEDC) with phthalic anhydride (PA) and glycerol. Benefiting from the rigidity of PA, the resulting DGEDC/PA/Glycerol (DPG) networks possess high mechanical and thermal properties, with glass transition temperature (T g) of 140–165 °C, thermal degradation temperature (T d5%) of 289–322 °C, fracture strength of 65–78 MPa, and Young's modulus of 3.2–3.9 GPa. More importantly, the multiple hydroxyl sites endow DPG networks with rapid transesterification reactions (the shortest relaxation time is only 205 s at 180 °C), which allows for material reprocessing, repairing, and degradation. In addition, taking DPG networks as matrix and carbon fibers (CFs) as reinforcement, the obtained DPG/CFs composite exhibits strong mechanical properties (tensile strength and modulus of 559 MPa and 8.5 GPa, bend strength and modulus of 420 MPa and 6.2 GPa) and good welding ability (shear strength of 19 MPa). Furthermore, the composite can be completely degraded in ethylene glycol at 190 °C, achieving efficient and non-destructive recycling of CFs. This research presents an alternative approach for the fabrication of reprocessable and recyclable high-performance CFRCs, which might have broad practical applications in aeronautic engineering and automobile equipment. [ABSTRACT FROM AUTHOR]

Shear-thickening materials have been widely applied in fields related to smart impact protection due to their ability to absorb large amounts of energy during sudden shock. Shear-thickening materials with multifunctional properties are expanding their applications in wearable electronics, where tactile sensors require interconnected networks. However, current bifunctional shear-thickening cross-linked polymer materials depend on supramolecular networks or slightly dynamic covalently cross-linked networks, which usually exhibit lower energy-absorption density than the highly dynamic covalently cross-linked networks. Herein, we employed boric ester-based covalent adaptive networks (CANs) to elucidate the shear-thickening property and the mechanism of energy dissipation during sudden shock. Guided by the enhanced energy-absorption capability of double networks and the requirements of the conductive networks for the wearable tactile sensors, tungsten powders (W) were incorporated into the boric ester polymer matrix to form a second network. The W networks make the materials stiffer, with a 13-fold increase in Young's modulus. Additionally, the energy-absorption capacity increased nearly 7 times. Finally, we applied these excellent energy-absorbing and conductive materials to bifunctional shock-protective and strain rate-dependent tactile sensors. Considering the self-healable and recyclable properties, we believe that these anti-impact and tactile sensing materials will be of great interest in wearable devices, smart impact-protective systems, post-tunable materials, etc.

Vitrimers are a class of covalent adaptive networks which, unlike other covalent networks, can be thermally reprocessed, recycled, and are self‐healing. In this research, a polyurethane vitrimer network is prepared using 1,4‐phenylene diisocyanate and excess amount of polycaprolactone polyol. The dynamic nature of this network is provided by a dual effect of dynamic transesterification reactions as well as dynamic transcarbamoylation reactions. This vitrimer can be reshaped, be recycled, and heal potential defects at high enough temperatures. A fast healing strategy is developed by the addition of small amounts (0.05 wt%) of carbon nanotubes (CNTs) which enables the use of microwave radiation for an efficient fast healing process. Using this strategy the healing time decreases more than 30 times compared to using a conventional oven. CNTs also enhance the vitrimer mechanical properties and compensate for the mechanical property loss of the dynamic PU network in comparison to the permanent PU network. Carbon nanotubes absorb microwaves and provide the required heat for acceleration of the dynamic exchange reactions. This enables the PU cross‐linked network to be reshaped, recycled, and self‐healed. Due to good dispersion of CNTs and their superb microwave absorption capacity, the self‐healing is ultrafast and happens in less than a minute. [ABSTRACT FROM AUTHOR]