Mechanically Robust Self-Healing Polymeric Materials:Fabrication And Functions

Self-healing polymeric materials are capable of healing their mechanical damages either autonomously or under the assistance of a stimulus.Because of their enhanced reliability and longevity,the materials have received particularly concerns as the next generation materials for the construction of “resource-conserving society” and “sustainable development of human society”.To promote the application of self-healing materials,lots of functional polymeric materials have attempted to be endowed with self-healing capacity.The healing capacity of polymeric materials are accomplished through two key steps: i)the diffusion of polymer chains between the damaged interfaces,and ii)the rebuilding of dynamic interactions among the polymer chains.Based on this working principle,the self-healing polymeric materials are usually constructed by a method that using the dynamic interactions,including physical interactions and dynamic covalent bonds,as crosslinks to fabricate the dynamic but weak networks.However,for applications as load bearing materials,there is a need for self-healing polymers that it should be mechanically robust to withstand the loading force.Herein,it is challenging that fabricating the mechanically robust polymeric materials capable of healing mechanical damages,because of the mutually exclusive molecular mechanism they required.In this thesis,we focus on circumventing the trade-off relationship between mechanical strength and self-healing efficiency to fabricate the mechanically robust polymeric materials with self-healing ability.The classifications of the high performance polymeric materials we fabricated in this thesis include supramolecular polymer,polymeric nanocomposites,and elastomer.These fabricated highperformance polymeric materials are capable of atomic oxygen?AO?resistance,shape memory,and recyclablity that are presented.1.We present the fabrication of durable AO resistant coatings that are capable of autonomously healing mechanical damage under Low Earth orbit?LEO?environment.The self-healing AO resistant coatings are comprised of 2-ureido-4[1H]-pyrimidinone?UPy?-functionalized polyhedral oligomeric silsesquioxane?POSS??denoted as UPyPOSS?that forms hydrogen-bonded three-dimensional supramolecular polymers.The UPy-POSS supramolecular polymers can be conveniently deposited on polyimides by a hot pressing process.The UPy-POSS polymeric coatings are mechanically robust,thermally stable,and transparent and have a strong adhesion toward polyimides to endure repeated bending/unbending treatments and thermal cycling.The UPy-POSS polymeric coatings exhibit excellent AO attack resistance because of the formation of epidermal SiO₂ layer after AO exposure.Due to the reversibility of the quadruple hydrogen bonds between UPy motifs,the UPy-POSS polymeric coatings can rapidly heal mechanical damage such as cracks at 80 ? or under LEO environment to restore their original AO resistant function.2.We present the fabrication of high performance shape memory nanocomposites that are capable of healing mechanical damage and fatigued shape memory effect?SME?under the assistance of water.The nanocomposites were fabricated by blending 2.7 wt% pyridine?py?-functionalized polyhedral POSS nanoparticles?denoted as py-POSS NPs?into polyvinyl alcohol?PVA?matrix.Based on the hydrogen bonds between py-POSS NPs and PVA,the mechanically robust nanocomposites with a tensile strength of 83.8 MPa and modulus of 6.5 GPa can achieve the better SME with shape recovery ratio?Rr?around 99% and shape fixing ratio?Rf?around 99%.The fatigue of SME origins from the changed molecular conformation caused unrecoverable deformation.Due to the reversibility of the hydrogen bonds and semi-crystalline of PVA,the nanocomposites can rapidly heal mechanical damage and fatigue under the assistance of water.3.We present the fabrication of the healable and recyclable mechanically robust polyurethane elastomer with excellent damage-torlarant ability.The elastomer with hard-soft multiphase was fabricated using a newly designed multiblock poly?polydimethylsiloxane/polycaprolactone?urethanes.Zinc-to-bipyridine coordination bonds,hydrogen bonds and crystalline polycaprolactone?PCL?segments co-assemble to form the hybrid hard phases,which crosslink the flexible polydimethylsiloxane?PDMS?segments to ensure the excellent rubber elasticity of materials.When the elastomer was stretched to the strain above 4 mm mm-1,PCL segments would slip along the stretching direction,resulting in the strain-induced crystalline?SIE?of polymer chains.Meanwhile,the dynamic interactions as sacrificial bonds rupture to dissipate the applied energy and release the hidden length.The synergy between sacrificial bonds and SIE behavior endows the elastomer with a tensile strength of 43.8 MPa,strain at break of 18.1 mm mm-1 and ultrahigh fracture energy of 129.3 k J m-2.Moreover,the obtained elastomer is similar to biological tissue,which exhibits the strain-adaptive stiffening behavior.The reversibility of dynamic interactions among the polymer chains enable healability and recyclability of materials.