Water-Driven Malleable,Weldable and Eco-Friendly Recyclable Carbon Fiber Reinforced Dynamic Composites

Traditional carbon fiber-reinforced polymers based on thermoset matrix have been extensively used in the fields of wind turbine blades,automotive sector,and aerospace,among many others.However,there is still a major challenge of recycling those polymers due to the high cost and adverse impacts on the environment.In this work,we apply a polyimine network as matrix,which possess considerable tensile and thermal properties,to prepare the carbon fiber reinforced polyimine materials with trifluoromethyl diphenoxybenzene units(CFRFP)using a prepreg-based compression molding method.The CFRFP can be reshaped or reprocessed by heat or with water rapidly,and exhibited multifunction,including welding,chemical recycling,etc.These unique findings gained from our study will facilitate the manufacturing capability and enrich the types of fiber-reinforced composites.

Recent Progress in Constructing Structurally Ordered Polymeric Architectures via Dynamic Covalent Chemistry

Although dynamic covalent chemistry(DCvC)has been widely utilized to synthesize small molecules and polymers,it remains challenging to construct highly ordered polymeric architectures via DCvC.Further exploration of novel dynamic linkages(in addition to commonly used imine and boronate ester)will expand the library of readily accessible dynamic linkages,diversify the polymeric structures,and unlock new functionality.In this mini-review,the DCvC-based synthetic strategies for enhancing the structural orders of polymeric architectures will be discussed from both thermodynamic control and kinetic control aspects.The relationship between the structure,stability,and dynamic behavior of a DCvC bond will be presented.Then recent examples of constructing polymers with DCvC and supramolecular bonding interactions,such as metal-ligand coordination,host-guest binding,and hydrogen bonding,will be reviewed to demonstrate their synergistic relationship.Furthermore,polymers featuring relatively unexplored DCvC will be highlighted to underscore how developing novel dynamic linkages and fundamental DCvC studies can broaden the scope of functional polymeric architectures.In the end,the challenges in the current field and possible future directions will also be discussed.Advancements in using these design principles will undoubtedly lead to the development of intriguing chemistries,polymeric architectures,and functionality.

Enhancing hydrolytic stability of dynamic imine bonds and polymers in acidic media with internal protecting groups

Imine bonds are among the most explored building motifs in dynamic chemistry,polymers,and materials,and yet,their acid-resistance remains a longstanding issue.Herein we demonstrate a concept of internal protecting groups for improving the kinetic stability of dynamic imine bonds and polymers.Systematic examination of structure-reactivity relationship of a series of aldehydes/imines bearing a neighboring carboxyl allowed uncovering of required structural features for dynamically masking imine bonds with cyclic structures.Mechanistic studies indicated that noncovalent interactions along with sterics control the ringchain equilibrium and the stability of imine bonds.The incorporation of internal protecting groups into imine polymers further enabled their controlled stability in acidic media.Moreover,a combination of dynamic covalent network and coordination supramolecular network provided a facile means for the modulation of luminescent and mechanical properties of polymers.The strategies and results reported should be beneficial to molecular assemblies,dynamic polymers,biological delivery,and intelligent materials.

Photoswitchable Molecular Recognition Enabled by Dithienylethene-Mediated Structural Changes of Dynamic Covalent Hydrazone Bonds

Light-induced recognition,assemblies,and materials are intensive areas of research due to their high spatiotemporal resolution.Herein,we demonstrated photoswitchable molecular recognition via dithienylethene-triggeredreversible structural regulation of dynamic covalent hydrazone bonds.By combining dithienylethenes and cyclic hemiacetals,the photochemical open-ring and closed-ring forms enabled turningoff and on the creation of awide range of hydrazones when desired.Light-induced bidirectional switching between hydrazones and their cyclization structures promoted by a neighboring carboxyl group was further achieved.By taking advantage of reversible structural changes totoggleon andoff the binding pocket,photoswitchable recognitionofmetal ionswas realized.Finally,the construction of an acylhydrazone polymer offered a facile way for light-mediated selective extraction/release.The strategies and results reported here should find applications in many contexts,such asdynamicassemblies,molecular switches,and smart materials.

Dynamic covalent chemistry-regulated stimuli-activatable drug delivery systems for improved cancer therapy

Drug delivery systems(DDSs)are of paramount importance to deliver drugs at the intended targets,e.g.,tumor cells or tissue by prolonging blood circulation and optimizing the pharmaceutical profiles.However,the therapeutic efficacy of DDSs is severely impaired by insufficient or non-specific drug release.Dynamic chemical bonds having stimuli-liable prope rties are the refore introduced into DDSs for regulating the drug release kinetics.This review summarizes the recent advances of dynamic covalent chemistry in the DDSs for improving cancer therapy.The review discusses the constitutions of the major classes of dynamic covalent bonds,and the respective applications in the tumor-targe ted DDSs which are based on the different responsive mechanisms,including acid-activatable and reduction-activatable.Furthermore,the review also discusses combination strategies of dual dynamic covale nt bonds which can response to the complex tumor microenvironment much more accurately,and then summarizes and analyzes the prospects for the application of dynamic covalent chemistry in DDSs.

Change in Continuous Detonation Wave Propagation Mode from Rotating Detonation to Standing Detonation

We perform a three-dimensional numerical simulation based on a one-step chemical reaction model to investigate changes in the mode of H2-Air detonation wave propagation from rotating detonation wave （RDW） mode to standing detonation wave mode. The physical characteristics of an RDW with injection velocity of 500 m/s are analyzed to investigate the physical mechanisms involved. We find that with increasing injection velocity, the detonation wave gradually changes from perpendicular to the head wall to parallel to the head wall. When the injection velocity exceeds the Chapman-Jouguet velocity VCJ （about 1984 m/s）, the detonation wave changes orientation to become perpendicular to the fuel injection direction, and the rotating mode changes accordingly to a standing mode. Finally, the plane detonation characteristic triple-wave structures can be found from the standing mode.

Cucurbit[7]uril-threaded flexible organic frameworks: Quantitative polycatenation through dynamic covalent chemistry

A three-dimensional flexible organic framework FOF-1 has been synthesized from the condensation of a tetratopic acylhydrazine and a rigid 4,4-diphenyl-4,4-bipyridinium dialdehyde in water through the quantitative formation of hydrazone bond. FOF-1 is further applied to construct a polycatenane framework FOF-pc-1 through the quantitative cucurbit[7]uril encapsulation for the diphenylbipyridinium subunits of the framework by making use of the dynamic nature of the hydrazone bond in water. The bipyridinium subunits in both frameworks can be reduced their radical cation counterparts to produce conjugated radical cation-linked dynamic organic frameworks rc-FOF-1 or rc-FOF-pc-1. Polycatenation is revealed to enhance the stability of the dynamic frameworks in water, whereas depolycatenation can be reached for both FOF-pc-1 and rc-FOF-pc-1 by using a ferrocene guest to form a more stable complex with CB[7].

Aggregation-induced emission luminogens and tunable multicolor polymer networks modulated by dynamic covalent chemistry

Aggregation-induced emission(AIE) based luminescent materials are generating intensive interest due to their unique fluorescence in the aggregation state. Herein we report a strategy of dynamic covalent chemistry(DCC) controlled AIE luminogens for the regulation of multicolor emission in reversible covalent polymer networks. Tetraphenylethene derived ring-chain tautomers were prepared, and the emission was readily controlled through multimode, such as changing the solvent, adding the base, and dynamic covalent reactions with amines. Moreover, the construction of dynamic covalent cross-linked luminescent hydrogels with tunable fluorescent, self-healing, and mechanical properties, was realized. The combination of AIE and aggregation-caused quenching(ACQ) fluorophores in the polymer network further enabled the realization of a multicolor modulator, including white emission, in both solution and gel states. The strategies and results presented should find utility in dynamic assemblies, polymer networks, chemical sensing, and responsive materials.

Injection molding of highly filled microcrystalline cellulose/polycaprolactone composites with the aid of reversible Diels-Alder reaction

To tackle the challenge of producing highly filled polymer composites using the traditional injection molding technique,which is characterized by the fairly high melt viscosity that makes mold filling difficult,the authors propose a solution based on dynamic covalent chemistry.As demonstrated by the proof-of-concept experiments,the 4-arm starshaped polycaprolactone(PCL)oligomers and microcrystalline cel-lulose(MCC)are crosslinked by the reversible Diels-Alder(DA)bonds.The flowability of the compounds greatly decreases due to the dissociation of the intercomponent DA bonds at the retro-reaction tempera-ture,and the networked architecture is reconstructed during cooling as a result of the forward DA reaction.Consequently,the high-loading MCC fillers are well distributed in the matrix and covalently bonded to the nearby PCL,forming a striking contrast to the control in which linear PCL acts as the matrix.The DA bonds crosslinked biodegradable PCL composites exhibit decent mechanical strength(20.7 MPa)even at the MCC fraction of 65 wt%,which is superior to those(5-12.2 MPa)of the highly filled PCL composites(with filler contents of 50-63.8 wt%)reported so far.The proposed approach has sufficient expansibility for the fabrication of the highly filled polymer composites constructed by other types of matrix and fillers.

On Depolymerization

Polymers have become an essential part of modern life and the global economy on account of their costeffectiveness and versatile properties.However,most postconsumer polymer wastes are unrecycled,leading to environmental pollution and resource wastage.Depolymerization,as an efficient chemical recycling approach,holds great promise in establishing a circular polymer economy.In this review,we attempt to highlight recent and significant advancements in depolymerization methodologies.Two key research topics are discussed:(1)depolymerization of commodity polymers to produce reusable monomers and high-value chemicals;(2)depolymerization of intrinsically depolymerizable polymers.It is anticipated that this review will reflect the present status and future trends of this rapidly evolving realm of depolymerization.

Adaptable hydrogel with reversible linkages for regenerative medicine:Dynamic mechanical microenvironment for cells

Hydrogels are three-dimensional platforms that serve as substitutes for native extracellular matrix.These materials are starting to play important roles in regenerative medicine because of their similarities to native matrix in water content and flexibility.It would be very advantagoues for researchers to be able to regulate cell behavior and fate with specific hydrogels that have tunable mechanical properties as biophysical cues.Recent developments in dynamic chemistry have yielded designs of adaptable hydrogels that mimic dynamic nature of extracellular matrix.The current review provides a comprehensive overview for adaptable hydrogel in regenerative medicine as follows.First,we outline strategies to design adaptable hydrogel network with reversible linkages according to previous findings in supramolecular chemistry and dynamic covalent chemistry.Next,we describe the mechanism of dynamic mechanical microenvironment influence cell behaviors and fate,including how stress relaxation influences on cell behavior and how mechanosignals regulate matrix remodeling.Finally,we highlight techniques such as bioprinting which utilize adaptable hydrogel in regenerative medicine.We conclude by discussing the limitations and challenges for adaptable hydrogel,and we present perspectives for future studies.

Polymeric partners breathe together: using gas to direct polymer self-assembly via gas-bridging chemistry

The quest for a general and facile way to regulate polymer self-assembled nanostructures with low-to high-order ergodicity is an eternal theme in soft nanoparticle fabrication. Here we present an unprecedented gas-bridging strategy that allows to use gas to direct polymer self-assembly in continuous and tunable manners. Such system comprises a partner of frustrated Lewis polymers with bulky Lewis acid and base groups. They can together “breathe in” external gases to form gas-bridged structures between the two complementary moieties, which drive their mutual complexation and assemble into polymer nanoparticles of diverse geometries and dimensionalities. This strategy is applicable to a broad family of gas substances including but not limited to carbon oxides, nitrogen oxides, sulfur oxides, and even olefins;moreover, tailoring gas types and levels can dictate distinct assembling evolutionary pathways and deformable behaviors among spherical, fibrous, polymersomal, tubesomal and cubosomal morphologies. We also discover that the gas-based bonding chemistry is the mechanistic basis underlying the phase transitional control and phase window regulation. This will open a new direction of making bespoke polymer nanostructures with gas.

“Living”fluorophores:thermo-driven reversible ACQ-AIE transformation and ultra-sensitive in-situ monitor for dynamic Diels-Alder reactions

Organic fluorophores play essential roles in both academic and applied fields.Most of the fluorescent molecules can be divided into aggregation-caused quenching(ACQ)and aggregation-induced emission(AIE)types based on the diverse emission properties in solution and aggregated states.Currently,a large part of studies focuses on the ACQ-to-AIE one-way transformation and the complex synthesis of chemical bonds is inevitable in all existing methods.To maximize the advantages of ACQ and AIE types fluorophores and avoid complex chemosynthesis,we propose a facile strategy first realizing the reversible ACQAIE transformation with the dynamic Diels-Alder(DA)reactions.Besides,the fluorescent platform can monitor DA reactions in microscale ultra-sensitively and quantitively.The dynamic covalent bonds can help to develop novel fluorophores creatively,and the reversible ACQ-AIE platform is expected to offer fresh insights into the dynamic covalent chemistry.

Dynamic covalent gels assembled from small molecules：from discrete gelators to dynamic covalent polymers

Dynamic covalent chemistry has emerged recently to be a powerful tool to construct functional materials.This article reviews the progress in the research and development of dynamic covalent chemistry in gels assembled from small molecules.First dynamic covalent reactions used in gels are reviewed to understand the dynamic covalent bonding.Afterwards the catalogues of dynamic covalent gels are reviewed according to the nature of gelators and the interactions between gelators.Dynamic covalent bonding can be involved to form low molecular weight gelators.Low molecular weight molecules with multiple functional groups react to form dynamic covalent cross-linked polymers and act as gelators.Two catalogues of gels show different properties arising from their different structures.This review aims to illustrate the structure-property relationships of these dynamic covalent gels.

Highly Ordered Supramolecular Assembled Networks Tailored by Bioinspired H-Bonding Confinement for Recyclable Ion-Transport Materials

Controlling dynamic molecular self-assembly to finely tune macroscopic properties offers chemical solutions to rational material design.Here we report that combining disulfide-mediated ring-opening polymerization withβ-sheet-like H-bonding self-assembly can drive a direct small-molecular assembly into a layered ionic network with precise architectural tunability and controllable functions as ion-transport membranes.This strategy enables a one-step evaporationinduced self-assembly from discrete small molecules to layered ionic networks with high crystallinity.The interlayer distances can be readily engineered with nanometer accuracy by varying the length of the oligopeptide side chain.The synergy of the layered structure and hydrophilic terminal groups facilitates the formation and ordering of interlayer water channels,endowing the resulting membranes with high efficiency in transporting ions.Moreover,the inherent dynamic nature of poly(disulfide)s allows chemical recycling to monomers under mild conditions.We foresee that the robust strategy of combining dynamic disulfide chemistry and noncovalent assembly can afford many opportunities in designing smart materials with unique functions and applications.

Pseudorotaxane Ligand-Induced Formation of Copper(I)lodide Cluster Based Assembly Materials:From Zero to Three Dimensional

Comprehensive Summary In this work,we have successfully obtained a series of novel copper(I)–iodide clusters(CuI NCs)based assembly materials by combining supramolecular pseudorotaxane ligands{[Mebpe^(+)]PF_(6)^(–)@CB[6](CB[6]=cucurbit[6]uril),L’·PF_(6)}and linkers{BPHF@CB[6],[BPHF=C_(14)H_(20)N_(4)(PF_(6))_(2)],L·PF_(6)},including discrete cluster CuI 1 and extended cluster organic frameworks MORF 1 and MORF 2.CuI 1 can be described as a dumbbell-shaped molecule with its body-centered site and two vertexes respectively occupied by one[Cu_(5)I_(6)]^(–)cluster and two CB[6]held together by two L’·PF_(6) ligands.The crystal structures of MORF 1 and MORF 2 are 1D anionic chain and four-fold interpenetrated 3D cationic diamondoid structure,respectively,which all featured intriguing alternating CB[6]and CuI NCs.

Progress in synthesis of highly crystalline covalent organic frameworks and their crystallinity enhancement strategies

Covalent organic frameworks(COFs) have been attracting growing concerns since the first report in2005. With the well-defined and ordered structures, COFs express big potential in mass transport, storage/separation and energy conversion applications. From the perspective of both theory and application,the construction of crystalline COFs with high quality and variety is highly worth to be devoted to. To give insight into the crystalline process of COFs and deeply understand the factors of COFs crystallization,this review was concentrated on the recent progress in construction of crystalline COFs. Accordingly, the types and crystallization process of COFs were summarized firstly. And then the factors on crystallinity and the measures for improving the crystallinity of COFs were classified and discussed in detail. Finally,the perspectives for the development of COFs in further was given at the end of this review.

Selenium-Sulfur-Doped Carbon Dots with Thioredoxin Reductase Activity

Thioredoxin reductase(TrxR)is an essential enzyme for regulating the redox balance in cells,promoting cell proliferation,and inhibiting cellular apoptosis.The biochemical pathway of TrxR metabolism involves a series of selenium-sulfur(Se-S)dynamic chemistry.Theoretically,nanomaterials with Se-S dynamic bonds could exhibit TrxRmimetic activities to tune TrxR activity,affecting cellular activities.Herein,we report the fabrication of Se-S-doped carbon dots(Se-S-CDs),synthesized by a facile hydrothermal method.The Se-S-CDs exhibited good stability and solubility in an aqueous solution,with a quantum yield of 13.27%.The doping of Se-S bonds endowed the Se-S-CDs with great capability of enhancing the TrxR activity,and consequently,a remarkable promotion of cell viability.The significance of Se-S bonds,as well as CDs’role as matrices,are discussed.Moreover,the Se-S-CDs could also revive the cells from the damage induced by oxidative stress.The abovementioned properties demonstrated the potential of the Se-S-CDs for cells and tissues culturing,solving the poor cell viability issue,which is desperately needed for organ transplantation and revitalization of prematurely aging cells,especially those exposed to oxidative stress.

Crystallinity and stability of covalent organic frameworks

Covalent organic frameworks(COFs)are a class of organic porous polymers with high crystallinity,and their structures can be precisely tailored via topology design.Owing to the characteristics of permanent pores,periodic structures and rich building blocks,COFs have triggered tremendous attention in the past fifteen years and are extensively investigated in various fields.Crystallinity and stability are two crucial features for practical applications.In general,these two features are contradictory for COFs formed via dynamic covalent chemistry(DCC).High thermodynamic reversibility is usually required to attain exceptional crystallinity of COFs,often resulting in limited stability.The first two reported COFs are based on the boroxine and boronate ester linkages,which are unstable in water and even in humid conditions.Therefore,many researchers doubt the stability of COFs for real applications.Actually,in these years,various novel linkages have been developed for the construction of COFs,and numerous newly synthesized COFs are robust towards strong acid/base and even some of them can resist the attack of strong oxidizing and reducing agents.In this review,we focus on the linkage chemistry of the COFs in terms of crystallinity and stability,further extending it to the investigation in the mechanisms of the crystal growth and the overall regulation of the contradiction between stability and crystallinity.The strategies for improving the crystallinity,including selecting building units,introducing non-covalent interactions and slowing nucleation and growth rate,are described in the third section,while the methodologies for increasing the stability from the viewpoints of chemical modification and non-covalent interactions are summarized in the fourth section.Finally,the challenges and perspectives are presented.

Two-dimensional porphyrin- and phthalocyanine-based covalent organic frameworks

Covalent organic frameworks（COFs） represent an emerging class of porous crystalline materials and have recently shown interesting applications from catalysis to optoelectronic devices.In this review,by covering most of the reported work,we summarized the research progress of two-dimensional（2D）porphyrin- and phthalocyanine-based COFs,with highlighting the synthesis of these 2D COFs via various dynamic covalent reactions and emphasizing their potential applications in different areas.