Synthesis And Application Of Polyurethanes Containing Multiple Self-healing Systems

As we all know,polyurethane(PU)elastomeric material,which is known for its excellent properties,has outstanding properties and indispensable applications in many fields such as electronics,medicine and engineering.However,in the practical application of polyurethane materials,tiny cracks are generated inside or outside the material due to suffering from the extrusion bending on the outside versus scratching wear,and the creation of microfractures tends to cause the failure of polyurethane materials.Therefore,to conserve the limited resources and realize the maximum utilization of resources,it is of great significance to study self-healing polyurethanes.Self-healing technology is a skin inspired technology that,by mimicking a biological system,enables active repair of wounds in response to a complex external environment,resulting in a higher life span for survival.Based on the current research status of a single healing system in existing self-healing polymer materials,in order to better coordinate the contradictory relationship between the healing properties and mechanical properties of materials,and improve the application of self-healing materials in practical settings.In this paper,two types of self-healing polyurethanes with multiple healing systems were designed and applied in flexible sensors.The main work of this thesis is as follows:1.Preparation and properties of self-healing polyurethane based on disulfide bond and hydrogen bondFirstly,the cross-linked polyurethane prepolymer was synthesized by the reaction of trifunctional polyether polyol and isophorone diisocyanate.Then,1,4-butanediol was added to the prepolymer to participate in the chain extension of the prepolymer.At the same time,it reacted with excessive unreacted isocyanate monomer to form low molecular weight linear polyurethane.Finally,carboxyl disulfide was added to participate in the chain extension reaction of the cross-linked polyurethane and linear polyurethane,The self-healing polyurethane elastomer based on dynamic disulfide bond and high density hydrogen bond was prepared.Variable temperature infrared spectroscopy analysis proved the hydrogen bond repair of the polyurethane segments(the breakage and recombination of hydrogen bonds).Gel permeation chromatography analysis proved that the elastomeric crosslinked linear interpenetrating network structure.The effects of the ratio of hard and soft segments and the structure of molecular segments on the mechanical properties and self-healing properties of polyurethane were also investigated.The results show that the maximum tensile strength of the self-healing polyurethane is 4.14 MPa,the maximum tensile rate is 551.7%,and the repair rate is 87.1%after heating at 70 ^oC for 12 h.Compared with single linear structural polyurethane with single hydrogen bond healing system,polyurethane with crosslinked linear interpenetrating structure network based on hydrogen bond and disulfide bond healing system has better healing properties and mechanical properties.2.Preparation and properties of self-healing polyurethane based on disulfide bond and metal coordination bondSince the polyurethane elastomers of hydrogen bond and disulfide bond healing system also have a large lifting space in the healing properties and mechanical properties,so to further improve the healing properties and mechanical properties of polyurethane materials,metal coordination bonds were introduced.Firstly,polytetramethylene ether glycol and isophorone diisocyanate were used to synthesize polyurethane prepolymers,then carboxyl disulfide was added to participate in the chain extension reaction of the prepolymer.Finally,aminopyridine ligands were introduced in the polyurethane segments to prepare a cross-linked structural self-healing polyurethane elastomer based on the dynamic disulfide bond and reversible metal coordination bond by forming coordination bond with Fe³⁺.The migration of the characteristic peaks in the IR spectra proved the formation of coordination bonds between aminopyridine ligands and Fe³⁺.The effects of the proportion of soft and hard segments and the proportion of components of polyurethane on the mechanical properties,self-healing properties were investigated.The results showed that the maximum tensile strength of the prepared self-healing polyurethane was 5.21 MPa,and the maximum tensile rate reached 475%,and the healing rate reached 93.5%after heating at 70 ^oC for 12h.It was found experimentally that the repair properties and mechanical properties of polyurethane elastomers can be effectively adjusted by adjusting the contents of metal coordination bonds and disulfide bond.3.Fabrication and performance of flexible sensors based on two multiplex self-healing systems of polyurethaneTo realize the large-area preparation of wearable flexible sensors,two most prevalent and easy methods to prepare flexible sensors were chosen:(1)coating conductive particles on the surface of elastomer film to make flexible sensors with“Sandwich”structure;(2)Co-doping conductive particles in elastomers to create a flexible sensor with a single layer film structure.The two self-healing polyurethanes were taken as flexible matrices,and the two sensing preparation methods were used to fabricate the corresponding flexible sensors,respectively.Finally,the fabricated sensors were attached to the human limb joints to get the peak plots of time relative resistance changes.The effects of different sensing preparation methods of the same flexible matrix material and different flexible matrix materials of the same sensing preparation method on the sensing sensitivity were investigated,respectively.The sensing performance of the flexible sensor with cut-off after healing was also investigated.Studies have shown that flexible sensors prepared by coating method have better sensitivity than those prepared by doping method because of excellent electrical conductivity;Self-healing polyurethane with cross-linked linear interpenetrating structure has better sensitivity than those prepared by cross-linked self-healing polyurethane due to their excellent resilience;Flexible sensors that undergo healing after severing have reduced sensitivity,but nonetheless retain high sensitivity for detecting human limb joint motion.