| Self-healing materials can independently repair internal or surface damages of materials to extend the service life span,so they have great application potential in many fields.However,the dependence of mechanical strength and toughness on the chain mobility is incompatible with the self-healing properties.Therefore,it remains a great challenge to develop polymeric materials with high strength and toughness and room-temperature self-healing at the same time.Researchers have made a lot of efforts to find that hydrogen bonds are candidates that can solve this problem,although the bonding energy is much lower than that of covalent bonds.When the number of hydrogen bonds is large enough,the material shows improved toughness,and the reversibility of hydrogen bonds can bestow the material self-healing properties.Therefore,polymers based on hydrogen bonding self-assembly are expected to achieve both self-healing and excellent mechanical properties.Based on the above view,we explored a new strategy of "mechano-responsive self-reinforcement".Basically,the strain-induced crystallization(SIC)of soft-segment initiated by external stress to implement self-reinforcement,and the loosely-stacked hierarchical hydrogen bonds gives rise to self-healing ability to achieve room temperature self-healing elastomer while synchronously maintaining high strength and tougheness,as a result,it successfully circumvents the abovementioned chain segment motion dependent dilemma.Three types of self-healing polymer materials were developed by changing the type of chain extenders and conducting reasonable molecular design and regulation of hard phase,and also bestowing additional functions such as rapid recovery,adhesion and anti-aging properties.The specific work contents are as follows:(1)In order to solve the contradiction between mechanical properties and roomtemperature self-healing efficiency,we adopt polytetramethylene ether glycol(PTMEG)and isophorone diisocyanate(IPDI)as starting materials,and mXylylenediamine(MXDA)as chain extender to synthesize polyurethane urea elastomer.It contains a large number of doublet hydrogen bonds through carbamate and urea group,endowing the material with self-repairing performance and toughness.The tensile strength of MXDA-1.7 elastomer can reach 13.36 MPa after repairing at room temperature for 24 hours,and the self-healing efficiency of its elongation at break is 90%.According to the results of the mechanical performance test,we found that SIC plays a key role in the enhancement and toughness of the elastomer and the material has a rapid recovery after large deformation.(2)In order to improve the self-healing efficiency at room temperature,we changed the chain extender to 2,6-pyridinedimethanol(PDM).By reasonably optimizing the effective soft chain length,a hysteresis and reversible SIC phenomenon is produced,which can improve the mechanical strength of the material after large deformation.Utilizing the strong hydrogen bonding between pyridine-carbamate and the weak hydrogen bonding between carbamate-carbamate,the tensile strength of PDM-2.5 elastomer can reach 25.8 MPa after being repaired at room temperature for 24 hours,and the repair efficiency of elongation at break can be increased to 98%.In addition,the lap-shear tensile strength of PDM-2.5 elastomer on the aluminum substrate is 7.33 MPa,and its excellent adhesion performance expands the application field of self-healing elastomers.(3)It has self-repairing function at room temperature while giving the material anti-aging performance.We changed the chain extender to piperazine(PPA),and after the amidation reaction of PPA and isocyanate group,it has similar structure of the hindered amine light stabilizer.Through tactful molecular design,both IPDI and PPA participate in chain extension to form a unique hard segment phase containing short hard segments and long hard segments,and adjusting their relative content leads to the occurrence of SIC phenomenon.The self-healing efficiency of maintaining the elongation at break at room temperature reaches 97%while giving the material antiaging performance,so that the material can be applied to the protective layer of automobile topcoat and anti-perforation tire sealant. |
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