查看更多>>摘要：Crystal polymers or liquid crystal elastomers undergo a phase transition that results in a change in the corresponding optical proper-ties,which has the potential to be applied in areas such as information encryption and anti-counterfeiting.The utilization of these materials for patterning purposes requires different phase transition temperatures.However,once prepared,altering the phase transition temperature of them presents significant challenges.Herein,a poly(oxime-ester)(POE)network is developed to achieve high-resolution and multilevel pattern-ing by photo-induced isomerization.The as-prepared POE exhibits the ability to transition from an opaque state to a transparent state under tem-perature stimuli,with the transition temperature and kinetics dependent on UV light exposure time.Thus,complex patterns and information can be encrypted through different selective regional exposure time and decrypted under specific temperature or cooling time.Furthermore,we il-lustrate an example of temporal communication,where cooling time or temperature serves as the encoded information.This research expands the application scope of advanced encryption materials,showcasing the potential of POE in dynamic information encryption and decryption pro-cesses.
查看更多>>摘要：In this study,we synthesized a series of ABA-type vitrimers by crosslinking the short A moieties of precursors with a bifunctional crosslinker and evaporating the small molecular byproduct.The vitrimer samples thus prepared exhibit linear viscoelasticity dependent on the length of A moiety as well as the content of the crosslinks.When the average number of A monomers per end moiety m=1.1,the crosslinker can only extend the chain but not crosslink the chain.When m becomes 2.8 or higher,introducing a crosslinker first leads to the gelation,whereas ex-cess in crosslinker molecules leads opening of the crosslinking sites and accordingly reentry into the sol regime.Surprisingly,a further increase in the length of the A moieties increases the relaxation time much weaker than the exponential increase seen for the physically crosslinked ABA-type ionomers.We attribute this difference to the distinct relaxation mechanisms:the relaxation of the vitrimer samples is based on relatively in-dependent exchange reactions,which contrasts with the ABA-type ionomers that relax through the collective hopping of connected ionic groups from one ion aggregate to another.
查看更多>>摘要：Poly(butylene adipate-co-terephthalate)(PBAT),a widely studied biodegradable material,has not effectively addressed the problem of plastic waste.Taking into consideration the cost-effectiveness,upcycling PBAT should take precedence over direct composting degradation.The present work adopts a chain breaking-crosslinking strategy,upcycling PBAT into dual covalent adaptable networks(CANs).During the chain-breaking stage,the ammonolysis between PBAT and polyethyleneimine(PEI)established the primary crosslinked network.Subsequently,styrene maleic anhydride copolymer(SMA)reacted with the hydroxyl group,culminating in the formation of dual covalent adaptable networks.In con-trast to PBAT,the PBAT-dual-CANs exhibited a notable Young's modulus of 239 MPa,alongside an inherent resistance to creep and solvents.Ow-ing to catalysis from neighboring carboxyl group and excess hydroxyl groups,the PBAT-dual-CANs exhibited fast stress relaxation.Additionally,they could be recycled through extrusion and hot-press reprocessing,while retaining their biodegradability.This straightforward strategy offers a solution for dealing with plastic waste.
查看更多>>摘要：Recycling of carbon fiber reinforced composites is important for sustainable development and the circular economy.Despite the use of dynamic chemistry,developing high-strength recyclable CFRPs remains a major challenge due to the mutual exclusivity between the dynamic and mechanical properties of materials.Here,we developed a high-strength recyclable epoxy resin(HREP)based on dynamic dithioacetal cova-lent adaptive network using diglycidyl ether bisphenol A(DGEBA),pentaerythritol tetra(3-mercapto-propionate)(PETMP),and vanillin epoxy resin(VEPR).At high temperatures,the exchange reaction of thermally activated dithioacetals accelerated the rearrangement of the network,giv-ing it significant reprocessing ability.Moreover,HREP exhibited excellent solvent resistance due to the increased cross-linking density.Using this high-strength recyclable epoxy resin as the matrix and carbon fiber modified with hyperbranched ionic liquids(HBP-AMIM+PF6-)as the reinforc-ing agent,high performance CFRPs were successfully prepared.The tensile strength,interfacial shear strength(IFSS)and interlaminar shear strength(ILSS)of the optimized formulation(HREP20/CF-HBPPF6)were 1016.1,70.8 and 76.0 MPa,respectively.In addition,the CFRPs demon-strated excellent solvent and acid/alkali-resistance.The CFRPs could completely degrade within 24 h in DMSO at 140 ℃,and the recycled CF still maintained the same tensile strength and ILSS as the original after multiple degradation cycles.
查看更多>>摘要：Polyimides are a family of high-tech plastics that have irreplaceable applications in the fields of aerospace,defense,and opto-electron-ics,but polyimides are difficult to be reprocessed and recycled at the end of their service life,resulting in a significant waste of resources.Hence,it is of great significance to develop recyclable polyimides with comparable properties to the commercial products.Herein,we report a novel poly-mer-to-monomers chemically recyclable poly(imide-imine)(PtM-CR-PⅡ)plastic,synthesized by cross-linking the amine-terminated aromatic bisimide monomer and the hexa-vanillin terminated cyclophosphazene monomer via dynamic imine bonds.The PtM-CR-PⅡ plastic exhibits com-parable mechanical and thermal properties as well as chemical stability to the commercial polyimides.The PtM-CR-PⅡ plastic possesses a high Young's modulus of ≈3.2 GPa and a tensile strength as high as ≈108 MPa,which also exhibits high thermal stability with a glass transition temper-ature of ≈220 ℃.Moreover,the PtM-CR-PⅡ plastic exhibits outstanding waterproofness,acid/alkali-resistance,and solvent-resistance,its appear-ance and mechanical properties can be well maintained after long-term soaking in water,highly concentrated acid and base,and various organic solvents.Furthermore,the cyclophosphazene moieties endow the PtM-CR-PⅡ plastic with excellent flame retardancy.The PtM-CR-PⅡ plastic ex-hibits the highest UL-94 flame-retarding rating of V-0 and a limiting oxygen index(LOI)value of 45.5％.Importantly,the PtM-CR-PⅡ plastic can be depolymerized in an organic solvents-acid mixture medium at room temperature,allowing easy separation and recovery of both monomers in high purity.The recovered pure monomers can be used to regenerate new PtM-CR-PⅡ plastics,enabling sustainable polymer-monomers-poly-mer circulation.
查看更多>>摘要：Supramolecular polymer networks(SPNs)are celebrated for their dynamic nature,yet they often exhibit inadequate mechanical pro-perties.Thus far,the quest to bolster the mechanical resilience of SPNs while preserving their dynamic character presents a formidable challenge.Herein,we introduce[2]rotaxane into SPN to serve as another cross-link,which could effectively enhance the mechanical robustness of the poly-mer network without losing the dynamic properties.Compared with SPN,the dually cross-linked network(DPN)demonstrates superior breaking strength,Young's modulus,puncture force and toughness,underscoring its superior robustness.Furthermore,the cyclic tensile tests reveal that the energy dissipation capacity of DPN rivals,and in some cases surpasses,that of SPN,owing to the efficient energy dissipation pathway facilitat-ed by[2]rotaxane.In addition,benefiting from stable topological structure of[2]rotaxane,DPN exhibits accelerated recovery from deformation,indicating superior elasticity compared to SPN.This strategy elevates the performance of SPNs across multiple metrics,presenting a promising avenue for the development of high-performance dynamic materials.
查看更多>>摘要：Covalent adaptive networks(CANs)are capable of undergoing segment rearrangement after being heated,which endows the materi-als 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 ben-zopyrazole and isocyanate groups.DFT calculation confirmed that relatively low dissociation energy is obtained through undergoing a five-mem-ber ring transition state,confirming excellent dynamic property of the benzopyrazole-urea bonds.As verified by the FTIR results,this nice dynam-ic property can be well maintained after incorporating the benzopyrazole-urea bonds into polymer networks.Excellent self-healing and repro-cessing 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.
查看更多>>摘要：Vitrimers have emerged as a prominent research area in the field of polymer materials.Most of the studies have focused on synthesiz-ing polymers with versatile dynamic crosslinking structures,while the impact of chemical structure on aggregate structure of vitrimers,particular-ly during polymer processing,remains insufficiently investigated.The present study employed commercial maleic anhydride-grafted-high densi-ty polyethylene(M-g-HDPE)as the matrix and hexanediol as the crosslinker to facilely obtain fiber-shaped HDPE vitrimers through a reaction ex-trusion and post-drawing process.Through chemical structure characterization,morphology observation,thermal and mechanical properties in-vestigation,as well as aggregate structure analysis,this work revealed the influence of dynamic bonds on the formation of aggregate structures during fiber-shaped vitrimers processing.A small amount of dynamic bonds in HDPE restricts the motion of PE chain during melt-extruding and post-drawing,resulting in a lower orientation of the PE chains.However,lamellar growth and fibril formation during post-drawing at high tem-perature are enhanced to some extent due to the competition between dynamic bond and chain relaxation.The uneven morphology of fiber-shaped HDPE vitrimers can be attributed to the stronger elastic effect brought by dynamic bonding,which plays a more dominant role in deter-mining the mechanical properties of fiber-shaped vitrimers compared to aggregate structure.
查看更多>>摘要：Polydimethylsiloxane(PDMS)is an electron-withdrawing material that is widely used in triboelectric nanogenerators(TENGs).Howev-er,PDMS has poor mechanical properties after curing and is easily damaged when subjected to long-term workloads.Thus,the long-term stable operation of TENGs under mechanical deformation cannot be guaranteed.In this work,multiple hydrogen bonds and aromatic disulfide bonds were introduced into PDMS elastomers.These elastomers exhibited high toughness(a tensile strength of 1.91 MPa and an elongation at break of 340％),good recyclability,and room-temperature self-healing properties(healing efficiency of 96.4％in 24 h).Recyclable sandwich-like triboelec-tric nanogenerators with excellent electrical output performance(13.5 V)and room-temperature self-healing performance(24 h,98％recovery of self-generating performance)were prepared by utilizing the hydrogen bonding between the PDMS elastomer and MXene.The work reported herein offers theoretical guidance and a compelling strategy for developing high-performance TENG negative friction layers.
查看更多>>摘要：The development of physically crosslinked hydrogels with excellent mechanical and sensing properties is of importance for expand-ing the practical applications of intelligent soft hydrogel materials.Herein,after copolymerization of hydroxyl-containing amino acid derivative N-acryloyl serine(ASer)with acrylamide(AM),we introduce Zr4+through an immersion strategy to construct metal ion-toughened non-covalent crosslinked hydrogels(with tensile strength of up to 5.73 MPa).It is found that the synergistic coordination of hydroxyl and carboxyl groups with Zr4+substantially increases the crosslinking density of the hydrogels,thereby imparting markedly superior mechanical properties compared to hydroxyl-free Zr4+-crosslinked hydrogels,such as N-acryloyl alanine(AAla)copolymerized with AM hydrogels(with tensile strength of 2.98 MPa).Through the adjustment of the composition of the copolymer and the density of coordination bonds,the mechanical properties of the hydrogels can be modulated over a wide range.Additionally,due to the introduction of metal ions and the dynamic nature of coordination bonds,the hy-drogels also exhibit excellent sensing performance and good self-recovery properties,paving the way for the development of flexible electronic substrates with outstanding comprehensive performances.
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