| Self-healing materials can not only effectively extend the service life and thus reduce material costs,but also provide a very effective solution path in terms of sustainability,energy saving and environmental protection,thereby promoting their rapid development in the application in smart protective coatings,healthcare materials,3D printing,and wearable electronics.However,the production of self-healing elastomers with superior physical properties is formidable challenging.Based on the principle of molecular design,novel self-healing cross-linked polymers with multiple functions were developed by introducing dynamic covalent urea bond and rational optimization of the soft and hard segments into the polymer chain via a facile synthesis method.In addition,the micro-molecular structure,physical properties,dynamic reversibility,and self-healing mechanism of cross-linked polymers were investigated.Self-healing conductive materials were fabricated by a simple self-assembly method,and their applications in smart protective coatings and flexible wearable electronic devices were studied.The main research contents and conclusions are as follows:（1）Robust,intrinsically self-healing,crosslinked polyureas were prepared via a facile one-pot photo-induced copolymerization to address the aforementioned limitation.The key strategy involves the introduction of a novel functional monomer with reversible urea bonds into the polymer network as a versatile dynamic crosslinker.The resultant crosslinked polyureas are a class of resource-saving materials with a combination of excellent intrinsic self-healing capability（self-healing efficiency up to99%）with outstanding mechanical robustness（storage modulus up to 1.21 GPa）.Notably,the properties of the materials can be easily tuned by simply adjusting the dynamic crosslinker content.In addition,an environmentally friendly crosslinked polymer reprocessing was achieved and the potential of the materials in the smart anticorrosion application was investigated.These desirable properties are attributed to the underlying topological network rearrangement enabled by the dynamic urea bond exchange reaction,which was confirmed by stress relaxation tests.（2）Self-healing,highly stretchable,and robust poly（urethane–urea）elastomers were prepared via a thiol-ene click reaction by in situ photopolymerization method.The objective of the utilized approach is to incorporate weak noncovalent H-bonds,dynamic covalent urea bonds,and products of a thiol-ene click reaction into a polymeric backbone.This study also applies polytetramethylene ether glycol domains as soft segments to facilitate the polymeric chain diffusion and dynamic exchange reaction.Owing to these unique molecular characteristics,the resultant elastomer possessed a uniform structure and versatile properties,such as high stretchability up to 464%,ultimate tensile strength of 10.9 MPa,self-recoverability,high self-healing efficiency of 99%,high recyclability,and good weldability.Upon rupture,the elastomer completely restored its original mechanical properties after heating to 80°C for 5 h.The dynamic reversibility of the elastomer was evidenced by stress relaxation analysis and rheological testing.（3）A crosslinked polymer blend that is based on a urethane–arcylate system with a combination of reversibly noncovalent intrachain and interchain hydrogen bonds and dynamically covalent urea bonds was developed through facile in situ photo-induced copolymerization.An essential step is the introduction of a flexibly dynamic crosslinker bearing robustly hindered urea bonds and urethane–urea structures into the network,which endows the dynamic network with a synergy of mechanical robustness and desirable self-healing ability.The dynamic networks exhibited rapid self-healing at mild condition（70°C,30 min）,extreme toughness(～34.76 MJ m–3),high tensile strength（～7.78 MPa）,superior stretchability（～932%）,long-term stability,recyclability,and weldability.The mechanical and self-healing properties of the resultant materials can be fine-tuned by adjusting the dynamic crosslinker content.These superior properties are attributed to the dynamic reversibility of hydrogen bonds and urea bonds as monitored by rheological tests.The facile fabrication approach and superior properties of the resulting self-healing polymers can find applications in sustainable smart materials and conductive sensors.（4）A flexible strategy is described to develop intrinsically dynamic crosslinked elastomers with RT self-healing via a photo-initiated copolymerization.The key is to incorporate a urea–urethane structure with dynamic urea bond into the polymer network as a flexible crosslinking unit.This strategy endows the crosslinked elastomer with superior properties,including autonomously rapid self-healing at RT,extreme stretchability of up to 1726%,high toughness(～24.45 MJ m–3),extended stability,and recyclability.Upon damaged,the resultant elastomers instantly self-healed at RT and completely self-healed within 10 min without the assistance of external triggers.These amazing properties of the dynamic elastomer are attributed to the synergistic effect of the robustly dynamic urea bonds and inter-and intrachain hydrogen bond interactions.Notably,the self-healing and mechanical properties of the network can be optimized by tuning the dynamic crosslinker content.Dynamic reversibility occurred at RT evidenced by rheological tests.The self-healable and stretchable crosslinked elastomer shows great potential in smart protective coating and wearable electronics industry.（5）Dynamic nanocomposites based on carboxyl-functionalized multiwalled carbon nanotube(CNT-COOH)fillers and a crosslinked polyurea（CPU）matrix were prepared through a novel and facile two-step method involving in situ photo-induced polymerization and hot compression.This strategy strongly enhances the interfacial bonding interaction between CNT-COOH and CPU matrix.The resulting nanocomposites exhibited excellent and rapid photo-induced self-healing abilities and regained their mechanical properties after damage.The exceptional self-healability is attributed to the synergy of hindered urea bond-based dynamic CPU and rapidly efficient photo-thermal effect of CNT-COOH.The nanocomposite prepared using 1%CNT-COOH exhibited excellent toughness(up to 36.57±1.28 MJ m-3),high stretchability（ca.607±50%）,high tensile strength（7.36±0.51 MPa）,efficient photo-thermal shape memory effect,and good recyclability.（6）Using polydopamine（PDA）particles as functional nanofillers and hindered urea bonds as dynamic motifs,a unique concept is demonstrated to design and produce dynamic crosslinked copolymer/PDA（DCPU/PDA）nanocomposites through a facile in situ photo-initiated copolymerization.The PDA particles have good interfacial bonding with the DCPU matrix,which endow the resulting DCPU/PDA with enhanced thermomechanical and remotely photo-responsive self-healing properties as well as excellent photo-thermal effect.The as-prepared DCPU/PDA possesses higher toughness(～14.96 MJ m-3)and stretchability（up to 334±20%）than those of pure DCPU.Upon damage,the resulting DCPU/PDA self-healed rapidly and effectively through near-infrared light irradiation.The fast responsive self-healability is enabled by the excellent photo-thermal effect of PDA and the dynamic exchange reaction of the hindered urea bonds.The outstanding photoactuation based on the resulting DCPU/PDA can find application potential in soft actuators and robots. |
PDF Full Text Request