Study On The Preparation Of Self-healing Polyurethane And Its Interface Healing Mechanism

Self-healing polymer materials are the forefront of material science research and have important research significance for improving the intelligence and prolong the lifetime of materials.They have broad application prospects in flexible electronics,wearable devices,biomedicine,etc.By introducing supramolecular systems into traditional polymer materials,using the dynamic and reversible characteristics of intermolecular interactions to achieve the structural reconstruction and property repair of polymer systems after damage has become a crucial method to design the self-healing polymer.However,the bond energy of supramolecular interaction is weak,which leads to the decrease of the mechanical properties of the supramolecular polymer system.At the same time,the mechanism of supramolecular interaction in the self-healing system is also to be clarified.Therefore,how to deeply understand the healing mechanism of supramolecular system theoretically and develop self-healing polymer materials with outstanding mechanical properties is a long-term challenge in this research field.Based on this,in this paper,polyurethane material is used as a research model,dual cross-linked self-healing polyurethanes were prepared by introducing hierarchical hydrogen bonds and covalent crosslink,and their self-healing and mechanical properties were characterized.Furthermore,the research platform of macroscopic supramolecular assembly is used to explain the interface healing mechanism of self-healing polyurethane,which provides guidance for the design and optimization of self-healing supramolecular polymer materials.The main research contents are as follows:First of all,a diol chain extender(U2-diol)containing 2-ureido-4[1H]-pyrimidone(UPy)and urea two segments was designed and synthesized.Then,we introduced U2-diol into the polyurethane system.The polyurethane material with self-healing property were prepared through the introduction of hierarchical hydrogen bond interactions formed by UPy moiety,urea group and urethane group(quadruple,double and single hydrogen bonds).Secondly,the mechanical and self-healing properties of the synthesized dual cross-linked self-healing polyurethanes were systematically studied.Since the covalent crosslink network formed by trimethylpropane and supramolecular crosslink network formed by hierarchical hydrogen bonds in the structure can provide the strength and toughness of the material,respectively,the tensile strength and fracture toughness of the polyurethane can reach 44 MPa and 328 MJ/m3,respectively.In the meantime,supramolecular crosslink can promote the self-healing of materials,so the synthesized polyurethanes have both high mechanical property and self-healing property.Thirdly,the research method of macroscopic supramolecular assembly was used to elucidate the mechanism of supramolecular system at the initial stage of healing process,namely,through multivalent interactions to promote interface contact closely and the diffusion and entanglement of polymer chains to achieve self-healing.Combined with in-situ measurement of interfacial forces and by comparing the self-healing efficiency of polyurethane with and without supramolecular system,we find that the supramolecular interactions at the early stage of healing process is mainly to draw the cracked surface reach the force range of intermolecular forces,which is equivalent to the effect of forcing the interface contact closely with external mechanical forces.