| Polyurethane has excellent chemical resistance,mechanical/physical durability,heat resistance,and p H stability,so it is widely used in state-of-the-art technology fields such as aerospace and biomedicine.According to the requirements of sustainable development,next-generation polyurethane elastomers are expected to have recycling,damage resistance,high strength,high elasticity,and self-healing properties.However,self-healing polymers are usually highly viscoelastic and have weak mechanical properties.The characteristics made the preparation of self-healing materials with strong mechanical properties a challenging work.At present,the study of intrinsic self-healing mechanism is mainly through non-covalent bond interaction and reversible covalent bond.The main content of this paper is divided into the following two parts:(1)High strength polyurethane(PU)elastomers with excellent self-healing and recyclable properties based on hierarchical hydrogen bonds(urethane,urea,2-ureido-4[1H]-pyrimidinone groups)and dynamic covalent bonds(Diels-Alder reaction)were designed and synthesized.The original PU elastomer has excellent self-healing performance at room temperature.The mechanical properties and healing efficiency can be greatly improved by heating.The reinforced PU elastomer(P3)has high tensile strength(50.8 MPa),excellent elasticity and super toughness(452 MJ/m~3),which is one of the highest record of self-healing elastomer.High strength P3 elastomer still has self-healing performance at room temperature,and the self-healing efficiency can reach 95%after heating at 120-80°C.Based on hierarchical hydrogen bonds and reversible covalent bonds,the dynamic physical and chemical crosslinking networks formed in PU can improve the mechanical strength and healing properties.After heating treatment,the hydrogen bond interaction and microphase separation are further enhanced,which leads to excellent mechanical strength.The fracture and recombination of hierarchical hydrogen bonds can dissipate a lot of energy and give the elastomer robust toughness.The reversible physical and chemical crosslinking structure gives PU elastomer good repairable and recyclable properties.(2)A series of high-strength,super-tough,highly transparent,repairable and recyclable polyurethane elastomers based on hierarchical hydrogen bonding were designed and synthesized.P4 elastomer shows amazing tensile strength(?86.15 MPa),which is the highest record of self-healing elastomer,and has large elongation at break(?1690%).P3 elastomer also has excellent self-healing performance at room temperature.After heating at 80°C for 2 h,P1-P4 elastomers show excellent self-healing efficiency(close to 100%).At the same time,we found that the mechanical properties of the initial P3 elastomer were further improved after heating treatment at80°C.The reinforced P3 elastomer showed record high tensile strength(?93.5 MPa),large elongation at break(?1120%)and excellent elasticity and high toughness(386 MJ/m~3).The ultra-high tensile strength is mainly attributed to the enhancement of hydrogen bond interaction,the improvement of crystallinity and the increase of microphase separation.The hydrogen bonds array of acyl semicarbazide on the polyurethane main chain,and the hierarchical hydrogen bonds of urea group and UPy dimer on the side chain,resulting in the formation of crystalline small-size hard domains containing dense hydrogen bonds.This gives the elastomer high toughness.The excellent room temperature self-healing performance is attributed to the high-density weak hydrogen bonds in polyurethane elastomer.Due to the large steric hindrance of IPDI,the hydrogen bond formed between ureathane have very low activation energy,and can also be dynamically broken and recombined at room temperature.All PU elastomers have high transmittance(>95%)in the visible light band and high transparency(>90%)even after aging.These synthetic PU elastomers have excellent mechanical properties and self-healing properties. |
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