Design,Synthesis And Properties Of Self-Healing Materials Based On Ionic Interaction

The intrinsic self-healing materials can heal the mechanical damage and cracks via the segment movement and reconstruction of dynamic interactions.The unique self-healing behavior largely enhances the lifetime and reliability of the materials which has attracted extensive attention and been widely studied.However,there is a trade-off between mechanical strength and self-healing performance of self-healing polymer materials.Therefore,integrating diverse merits into a single entity is highly desirable,but remains a great challenge.Ionic interactions are promising means to construct high-performance self-healing materials attributing to their tunable bond energy,spontaneous aggregation,and kinetic lability.As a new type of polyelectrolyte,polymerized ionic liquids（PILs）carry ionic groups in each repeating unit,which have been widely used in energy harvesting/generation,sensing and biological fields.Hence,it is of great academic significance and application value to study healable PILs.In this doctoral dissertation,several novel self-healing cycloolefin ionic polymers were prepared via ring-opening metathesis polymerization（ROMP）by utilizing Grubbs 3rd catalysts.The influence of molecular structure on ionic aggregation dynamics and macroscopic properties was thoroughly studied.Furthermore,multiple reversible interactions were introduced into PILs and their synergistic mechanisms were unraveled,thereby achieving a win-win situation of both self-healing efficiency and mechanical strength.The specific research contents and achievements of this paper are as follows:（1）The self-healing properties of PILs were optimized by utilizing the ionic groups and designing the structure of side chains of PILs.A series of novel imidazolium-based norbornene PILs with fine-tuned side-chain microstructures were synthesized in the present work.Thereinto,the inserted imidazolium groups divide side chains into two parts:spacer and tail.By tuning the length of these two parts independently,the influence of molecular structure on ionic aggregation dynamics,segment mobility and macroscopic properties was proposed.More importantly,our results revealed that long tail segments formed an additional tail region between ionic aggregations,which remarkably reduced the average aggregation distance and consequently accelerated healing kinetics.The outcome of this work further illustrated the self-healing mechanisms of ionic materials and provided a guidance for regulating dynamics of ionic aggregations,thereby enabling the effective regulation and optimization of mechanical strength and healing efficiency of PILs via monomer molecular design.（2）A series of novel multiple dynamic cross-linked networks were prepared by introducing reversible covalent boronic ester and boron-nitrogen（B-N）coordination into hard-soft diblock ionic copolymers.Thereinto,the high sterically hindered monomer was the hard segment and the copolymers of the ionic and functional monomers were the soft segments.The introduction of dynamic ionic interaction and boronic ester cross-linking into the soft segment enhanced the interchain interactions,and thus improved the mechanical properties of the diblock copolymer.However,the covalent boronic esters cross-links reduced the network dynamics,resulting in poor healing efficiency.To resolve this dilemma,the synthetic tertiary amine-bearing norbornene was used as the bulky monomer to incorporate the nitrogen donors into the hard segment.It revealed that the B-N coordination not only accelerated the transesterification of boronic esters but also dramatically improved the mechanical properties by the intermolecular coordinated chain crosslinking and intramolecular coordinated chain folding.The synergy effect between the dynamic covalent boronic ester and boron-nitrogen coordination provided a guidance for the design and construction of high-performance self-healing materials.（3）Herein,a dynamic dual-cross-linked networks strategy was employed to develop the PIL elastomers via introducing ureido-pyrimidinone（UPy）groups into functional PILs.Specifically,UPy exhibited a unique gradient distribution on ionic polymer chains.Large UPy clusters formed in the dense UPy region with robust cross-links that could stabilize the system,while UPy dimers in sparse regions with weak ionic interactions could act as sacrificial bonds for energy dissipation.Therefore,the obtained elastomers exhibited superb mechanical properties with high stretchability（1900%）,high toughness(33.8 MJ m^-3),and excellent elasticity（>85%）.Importantly,deactivated[Ru]=CHOEt complex（G3 derivative）was proved to have an inherently outstanding photothermal effect under near-infrared（NIR）irradiation.Benefiting from this feature,the elastomers achieved nearly complete self-healing within 4.5 min under NIR.Furthermore,the elastomers served as an intrinsically self-healing wearable sensor could accurately monitor human movements.In addition,the elastomers were employed as ideal base materials to construct flexible self-healing conductors by encapsulating conductive liquid metal.This work opened up a new design principle of highly efficient and multifunctional self-healable materials.