Synergistic Dual Dynamic Bonds in Covalent Adaptable Networks

Covalent adaptable networks(CANs),comprising polymer networks crosslinked by dynamic covalent bonds(DCBs),have garnered considerable attention as sustainable materials.Mastering the stress relaxation of CANs is essential for controlling their viscoelastic properties.An unexpected acceleration of stress relaxation has been observed in CANs containing dual dynamic bonds.The dynamic behavior of the second dynamic bonds can accelerate stress relaxation and lower the relaxation activation energy of dual dynamic CANs compared to analogous CANs that rely on only one type of DCB.These findings complement current approaches that utilize catalysts or adjust network parameters.In this minireview,we summarize the synergistic acceleration effects in various CANs containing dual dynamic bonds.We classify these effects based on the second dynamic bonds,including noncovalent bonds,mechanical bonds,and the second DCBs.We also discuss the mechanisms behind this synergy.Finally,we highlight the challenges and offer perspectives on harnessing the synergistic effects of these dual dynamic systems to expand the chemistry and applications of CANs.

Construction of interfacial dynamic bonds for high performance lignin/polymer biocomposites

Lignin is the largest natural aromatic biopolymer,but usually treated as industrial biomass waste.The development of lignin/polymer biocomposites can promote the high value utilization of lignin and the greening of polymers.However,the weak interfacial interaction between industrial lignin and polymer induces poor compatibility and serious agglomeration in polymer owing to the strong intermolecular force of lignin.As such,it is extremely difficult to prepare high performance lignin/polymer biocomposites.Recently,we proposed the strategy of in situ construction of interfacial dynamic bonds in lignin/polymer composites.By taking advantage of the abundant oxygen-containing polar groups of lignin,we inserted dynamic bonding connection such as hydrogen bonds and coordination bonds into the interphase between lignin and the polymer matrix to improve the interfacial interactions.Meanwhile,the natural amphiphilic structure characteristics of lignin were utilized to construct the hierarchical nanophase separation structure in lignin/polymer composites.The persistent problems of poor dispersity and interfacial compatibility of lignin in the polymer matrix were effectively solved.The lignin-modified polymer composites achieved simultaneously enhanced strength and toughness.This concise review systematically summarized the recent research progress of our group toward building high-performance lignin/polymer biocomposites through the design of interfacial dynamic bonds(hydrogen bonds,coordination bonds,and dynamic covalent bonds)between lignin and different polymer systems(polar plastics,rubber,polyurethane,hydrogels,and other polymers).Finally,the future development direction,main challenges,and potential solutions of lignin application in polymers were presented.

A Self-Healing and Nonflammable Cross-Linked Network Polymer Electrolyte with the Combination of Hydrogen Bonds and Dynamic Disulfide Bonds for Lithium Metal Batteries

The self-healing solid polymer electrolytes(SHSPEs)can spontaneously eliminate mechanical damages or micro-cracks generated during the assembly or operation of lithium-ion batteries(LIBs),significantly improving cycling performance and extending service life of LIBs.Here,we report a novel cross-linked network SHSPE(PDDP)containing hydrogen bonds and dynamic disulfide bonds with excellent self-healing properties and nonflammability.The combination of hydrogen bonding between urea groups and the metathesis reaction of dynamic disulfide bonds endows PDDP with rapid self-healing capacity at 28°C without external stimulation.Furthermore,the addition of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide(EMIMTFSI)improves the ionic conductivity(1.13×10^(−4)S cm^(−1)at 28°C)and non-flammability of PDDP.The assembled Li/PDDP/LiFePO_(4)cell exhibits excellent cycling performance with a discharge capacity of 137 mA h g^(−1)after 300 cycles at 0.2 C.More importantly,the self-healed PDDP can recover almost the same ionic conductivity and cycling performance as the original PDDP.

Aggregates of fluorescent gels assembled by interfacial dynamic bonds

Life,defined as the specific form of substance,is an integration of aggregates at various scales,ranging from single molecules to tissues.However,these building blocks of common aggregates are usually recognized as confining at the microscopic level,while there are few studies focusing on macroscopic building blocks for aggregates.Fluorescent gels,as the important macroscopic building blocks,are drawing researchers’attention on account of their extraordinary fluorescence as well as soft material properties.Inspired by nature,fluorescent gels can be aggregated through interfacial adhesion.According to the driving forces for interfacial adhesion,a series of aggregates of fluorescent gels(AFGs)was summarized,including H-bond,metal coordinations,host-guest interactions,hydrophobic interactions,electrostatic interactions,dynamic covalent bonds as well as multiple driving forces.These AFGs own dynamic assembled behaviors and rich stimuli responsiveness,which could be applied to information storage,sensing,biomedical systems,and so on.The authors anticipate this review can accelerate the development of aggregate science,especially based on macroscopic building blocks.

Ab Initio Study of the Dynamical Si-O Bond Breaking Event in α-Quartz

The Si-O bond breaking event in the a-quartz at the first triplet （T1） excitation state is studied by using ab initio molecular dynamics （AIMD） and nudged elastic band calculations. A meta-stable non-bridging oxygen hole center and E1 center （NBOHC-E） is observed in the AIMD which consists of a broken Si-O bond with a Si-O distance of 2.54A. By disallowing the re-bonding of the Si and 0 atoms, another defect configuration （lll- Si/V-Si） is obtained and validated to be stable at both ground and excitation states. The NBOHC-E is found to present on the minimal energy pathway of the initial to IlI-Si/V-Si transition, showing that the generating of the NBOHC-E is an important step of the excitation induced structure defect. The energy barriers to produce the NBQHC-E＇ and Ⅲ-Si/V-Si defects are calculated to be 1.19 and 1.28eV, respectively. The electronic structures of the two defects are calculated by the self-consistent GW calculations and the results show a clear electron transition from the bonding orbital to the non-bonding orbital.

MOLECULAR DYNAMICS SIMULATION ON VIERATIONAL SPECTROSCOPIC FEATURES OF HYDROGEN BONDS IN CRYSTALLINE POLYMERS

Introduction The molecular dynamics simulation technique has recently proved to be a suitable alternative approachfor simulation of vibrational spectroscopy. In this study, molecular dynamics was utilized to understandlow frequency vibrations in highly ordered poly(ρ-phenylene terephthalmide) (PPTA). A key structuralfeature of this polymer is the presence of hydrogen bonds. There is little question that this strong localized

Regulating Actuations and Shapes of Liquid Crystal Elastomers through Combining Dynamic Covalent Bonds with Cooling-Rate-Mediated Control

Realizing multiple locked shapes in pre-oriented liquid crystal elastomers(LCEs)is highly desired for diversifying deformations and enhancing multi-functionality.However,conventional LCEs only deform between two shapes for each actuation cycle upon liquid crystal-isotropic phase transitions induced by external stimuli.Here,we propose to regulate the actuation modes and the locked shapes of a pre-orientated epoxy LCE by combining dynamic covalent bonds with cooling-rate-mediated control.The actuation modes can be adjusted on demand by exchange reactions of dynamic covalent bonds.Derived from the established actuation modes,such as elongation,bending,and spiraling,the epoxy LCE displays varied locked shapes at room temperature under different cooling rates.Various mediums are utilized to control the cooling rate,including water,silicone oil,and copper plates.This approach provides a novel way for regulating the actuation modes and locked shapes of cuttingedge intelligent devices.

Carbon dots-enhanced pH-responsive lubricating hydrogel based on reversible dynamic covalent bondings

Due to the various pH liquid environment in nature,the pH-responsive lubricating hydrogel is widely investigated and developed for tissue interface substitute.However,the applied liquid environment will lead to poor mechanical property and weaken the pH-responsive capability.In this work,a carbon dotsenhanced pH-responsive lubricating hydrogel is developed by combining a pH-responsive section of dynamic PVA-borax network into a PAAm covalent polymer network.The formed hydrogel presents a partial gel-sol transition under controlled pH environments.At low pH environments(<6.0),the formed lubricating layer originated from dynamic disassembly of PVA-borax hydrogel,and brings the lubricating properties on the hydrogel surface.Moreover,the mechanical strength and lubrication properties are well promoted by introducing the carbon dots into the hydrogel,the blue sol layer can be observed more visually under the fluorescence microscope.The pH-response also exhibits well reversibility.The prepared hydrogel broadens the idea for designing pH-responsive soft materials for soft lubricating actuator or robot.

A Dynamic Covalent Bonding-based Nanoplatform for Intracellular Co-Delivery of Protein Drugs and Chemotherapeutics with Enhanced Anti-Cancer Effect

Efficient intracellular delivery of protein drugs is critical for protein therapy.The combination of protein drugs with chemotherapeutics represents a promising strategy in enhancing anti-cancer effect.However,co-delivery systems for efficient delivery of these two kinds of drugs are still lacking because of their different properties.Herein,we show a well-designed delivery system based on dynamic covalent bond for efficient intracellular co-delivery of ribonuclease A(RNase A)and doxorubicin(DOX).Two polymers,PEG-b-P(Asp-co-AspDA)and PAE-b-P(Asp-co-AspPBA),and two 2-acetylphenylboronic acid(2-APBA)-functionalized drugs,2-APBA-RNase A and 2-APBA-DOX,self-assemble into mixed-shell nanoparticles(RNase A/DOX@MNPs)via dynamic phenylboronic acid(PBA)-catechol bond between PBA and dopamine(DA)moieties.The PBA-catechol bond endows the nanoparticles with high stability and excellent stimulus-responsive drug release behavior.Under the slight acidic environment at tumor tissue,RNase A/DOX@MNPs are positively charged,promoting their endocytosis.Upon cellular uptake into endosome,further protonation of PAE chains leads to the rupture of endosomes because of the proton sponge effect and the cleavage of PBA-catechol bond promotes the release of two drugs.In cytoplasm,the high level of GSH removed the modification of 2-APBA on drugs.The restored RNase A and DOX show a synergistic and enhanced antic-cancer effect.This system may be a promising platform for intracellular co-delivery of protein drugs and chemotherapeutics.

Creep-Resistant Covalent Adaptable Networks with Excellent SelfHealing and Reprocessing Performance via Phase-Locked Dynamic Covalent Benzopyrazole-Urea Bonds

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.

Dynamic Crosslinked Phosphorescent Poly(vinyl alcohol)-Terpyridine Films with Enhanced Mechanical Properties and Tunable Shape Memory

Achieving versatile room temperature phosphorescence(RTP)materials,especially with tunable mechanical properties and shape memory is attractive and essential but rarely reported.Here,a strategy was reported to realize multi-functional RTP films with multicolor fluorescence,ultralong afterglow,adjustable mechanical properties,and shape memory through the synergistic dynamic interaction of lanthanide(Ln~Ⅲ)-terpyridine coordination,borate ester bonds,and hydrogen bondings in a poly(vinyl alcohol)(PVA)matrix.By varying the amount of borax,the mechanical properties of the films could be finely controlled due to the change of crosslinking degree of dynamic borate ester bonds in PVA.The assembly and disassembly of borate ester bonds upon the trigger of borax and acid were applied as reversible linkage to achieve programmable shape memory behavior.In addition,the films displayed both fascinating multicolor fluorescence and ultralong afterglow characteristics due to the presence of Ln III doping and confinement of terpyridine in PVA.This study provides a new avenue to impart modulable mechanical strength and shape memory to RTP materials.

Solvent-Free Synthesis of Self-Healable and Recyclable Crosslinked Polyurethane Based on Dynamic Oxime-Urethane Bonds

Polyurethane is widely used for its versatility in design and range of performance.Self-healing and recyclable dynamic polyurethane networks have attracted extensive attention due to their potential to extend service life and ensure safety in use,as well as to promote sustainable use of resources.Developing green and environment-friendly methods to obtain this material is an interesting and challenging task,as the majority of current dynamic polyurethane networks utilize the solution polymerization method.The use of solvents makes the processes complicated,harmful to environment,and increase the cost.Poly(oxime-urethanes)(POUs)are emerging dynamic polyurethanes and show great potential in diverse fields,such as biomaterials,hot melt adhesives,and flexible electronics.In this study,we utilized the solubility properties of dimethylglyoxime in raw material poly(ethylene glycol)to prepare POUs through bulk polymerization for the first time.This method is simple,convenient and cost-efficient.Simultaneously,copper ion coordination improves POUs strength and dynamic properties,with mechanical strength up from 0.54 MPa to 1.03 MPa and self-healing recovery rate up from 85.5%to 91.8%,and activation energy down from 119.6 k J/mol to 95.4 k J/mol.To demonstrate the application of this technology,self-healing and stretchable circuits are constructed from this dynamic polyurethane network.

Visible light responsive spiropyran derivatives based on dynamic coordination bonds

Spiropyrans(SPs) are a well-known class of photochromic compounds and have found widespread application due to their unique properties. However, for many conventional SPs, high energy ultraviolet(UV)light is commonly essential to drive photoisomerization, leading to poor fatigue resistance. Moreover, the practical application of spiropyrans is hindered by their fast fading speed due to the instability of closed forms(SP) or open forms(MC). Herein, we disclose a novel strategy to address these challenges through introducing both electron-donating substituents to stabilize the SP and dynamic coordination bonds to stabilize the MC. The resulting new spiropyrans complexes exhibit negative photochromic properties, with fast visible light response, good stability of both SP and MC, and significantly improved fatigue resistance.

Dynamic Sulfur-Rich Polymers from Elemental Sulfur and Epoxides

Sulfur-containing dynamic polymers had attracted significant attention due to their unique chemical structures with high reversibility.Utilizating sulfur, an inexpensive industrial waste product, to synthesize dynamic polysulfide polymers through reverse vulcanization has been a notable approach. However, this method required high temperatures and resulted in the release of unpleasant oders. In this study, we presented a robust method for the preparation of sulfur-rich polymers with dynamic polysulfide bonds from elemental sulfur and inexpensive epoxide monomers via a one-pot strategy at the mild room temperature. Different types of polysulfide molecules and polymers were synthesized by reacting various epoxide compounds with sulfur, along with the investigation of their structures and dynamic behaviors. It was noteworthy that the obatined polymers prepared from m-(2,3-epoxypropoxy)-N,N-bis(2,3-epoxypropyl)aniline and elemental sulfur exhibit multiple dynamic behaviors, including polysulfide metathesis and polysulfide-thiol exchange, enabling their rapid stress relaxation, self-healing, reprocessing and degradable properties of the cross-linked polymer. More importantly, the hydroxyl groups at the side chains from epoxide ring opening exhibited potential transesterification. This work provided a facile strategy for designing dynamic sulfur-rich polymers via a mild synthesis route.

Engineering the viscoelasticity of gelatin methacryloyl(GelMA)hydrogels via small“dynamic bridges”to regulate BMSC behaviors for osteochondral regeneration

The dynamic extracellular matrix(ECM)constantly affects the behaviors of cells.To mimic the dynamics of ECM with controllable stiffness and energy dissipation,this study proposes a strategy in which a small molecule,3,4-dihydroxybenzaldehyde(DB),was used as fast"dynamic bridges"to construct viscoelastic gelatin methacryloyl(GelMA)-based hydrogels.The storage modulus and loss modulus of hydrogels were independently adjusted by the covalent crosslinking density and by the number of dynamic bonds.The hydrogels exhibited self-healing property,injectability,excellent adhesion and mechanical properties.Moreover,the in vitro results revealed that the viscous dissipation of hydrogels favored the spreading,proliferation,osteogenesis and chondrogenesis of bone marrow mesenchymal stem cells(BMSCs),but suppressed their adipogenesis.RNA-sequencing and immunofluorescence suggested that the viscous dissipation of hydrogels activated Yes-associated protein(YAP)by stabilizing integrinβ1,and further promoted nuclear translocation of smad2/3 andβ-catenin to enhance chondrogenesis and osteogenesis.As a result,the viscoelastic GelMA hydrogels with highest loss modulus showed best effect in cartilage and subchondral bone repair.Taken together,findings from this study reveal an effective strategy to fabricate viscoelastic hydrogels for modulating the interactions between cells and dynamic ECM to promote tissue regeneration.

THE CORRELATION EFFECT ON THE CHAIN MOTION CONTRIBUTION TO IONIC TRANSPORT IN POLYMER ELECTROLYTES

The ionic transport process in polymer electrolytes (such as polyethylene oxide) wassimulated numerically on a two dimensional square lattice where charge carriers areaccommodated by the lattice sites connected randomly with available bonds to represent theamorphous chain configuration. Following the dynamic bond percolation theory(DBPT),the chainmotion contribution to the ionic conduction was incorporated via periodical renewal of the randombond configuration. To check and extend the prediction made by DBPT employing global abruptbond renewal,spatial correlation of the bond reassignment was introduced to the system by: 1)regional bond renewal and 2) organized bond motion. It is found that the difference between thediffusivities simulated involving regional bond renewal and those of DBPT becomes negligiblewhen the bond renewal rate approaches the carrier hopping rate.

Dynamic Oxime-Urethane Bonds, a Versatile Unit of High Performance Self-healing Polymers for Diverse Applications

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.

Cancer Therapy by Targeting Thioredoxin Reductase Based on Selenium-Containing Dynamic Covalent Bond

Thioredoxin Reductase(TrxR)plays a pivotal role in defending cells against reactive oxygen species(ROS)and maintaining a reduced intracellular environment.It has been discovered that TrxR is elevated significantly in human cancer,evidenced by its association with the promotion of tumor cell proliferation,inhibiting tumor cell apoptosis,as well as enhancing tumor drug resistance.Hence,finding highly selective inhibitors of TrxR is urgently needed.Herein,we developed a selenium-containing small molecule(EbD),which had two Se–N bonds.Under reduction conditions,the two Se–N bonds reacted with Se–H bond and S–H bond in TrxR to form new Se–Se bond and Se–S bonds,respectively.Subsequently,the newly formed bonds were able to disrupt the thioredoxin(Trx)reduction catalytic cycle,and thus,inhibited the TrxR activity irreversibly,which resulted in the collapse of the antioxidant system.As a consequence,ROS levels elevated that triggered cancer cell apoptosis.This strategy,based on selenium-containing dynamic covalent bonds,provides a new avenue for cancer therapy via targeting TrxR.

Dynamic covalent nano-networks comprising antibiotics and polyphenols orchestrate bacterial drug resistance reversal and inflammation alleviation

New antimicrobial strategies are urgently needed to meet the challenges posed by the emergence of drug-resistant bacteria and bacterial biofilms.This work reports the facile synthesis of antimicrobial dynamic covalent nano-networks(aDCNs)composing antibiotics bearing multiple primary amines,polyphenols,and a cross-linker acylphenylboronic acid.Mechanistically,the iminoboronate bond drives the formation of aDCNs,facilitates their stability,and renders them highly responsive to stimuli,such as low pH and high H2O2 levels.Besides,the representative A1B1C1 networks,composed of polymyxin B1(A1),2-formylphenylboronic acid(B1),and quercetin(C1),inhibit biofilm formation of drug-resistant Escherichia coli,eliminate the mature biofilms,alleviate macrophage inflammation,and minimize the side effects of free polymyxins.Excellent bacterial eradication and inflammation amelioration efficiency of A1B1C1 networks are also observed in a peritoneal infection model.The facile synthesis,excellent antimicrobial performance,and biocompatibility of these aDCNs potentiate them as a much-needed alternative in current antimicrobial pipelines.