关键词: 聚氨酯, 自修复, 无溶剂, R值, 二硒键

Abstract: The polyurethane (PU) resin, synthesized from isocyanate, polyol and small molecule chain extender, is a kind of polymer compound with carbamate groups on the main chain. It can be made into plastics, fibers, elastomers and adhesives, etc., and has a wide application prospect in intelligent textiles, high-end leather and flexible electronics. However, the PU resin is prone to damage during use, which affects the service life of the material. Therefore, the development of self-healing PU will have broad application prospects. A large number of toxic and harmful solvents are used in the conventional PU preparation methods. The evaporation of solvents during the preparation process causes environmental pollution, or the residual organic solvents in the final products affect the use safety of consumers. In this scheme, a new type of PU material with self-healing function was prepared by an innovative green and environment-friendly solvent-free method. To achieve its self-healing performance, the diselenide bond was introduced into the soft segment structure of the macromolecule. Since the diselenide bond is a dynamic covalent bond, it is characterized by the reversible reaction that can be triggered under the visible light irradiation condition for exchange recombination, so that the material has self-healing ability. In this paper, the influence of the R value on the self-healing and mechanical properties of PU was explored by adjusting the value of R under the condition that the content of the diselenide bond in the material was unchanged.
The results show that as the R value increases from 0.90 to 1.10, the tensile fracture strength increases, while the elongation at break decreases. When R value is less than 1.00, the molecular structure of PU presents linear macromolecules, and the molecular chains of PU are easy to slip during tensile process. The mechanical strength of PU is low, and the elongation at break is large. When the R value is equal to 1.00, the molecular weight of PU is larger, the molecular structure of the synthesized PU is more complete, and the mechanical properties are greatly improved. When the R value is greater than 1.00, the reaction forms a cross-link, and the cross-linked body structure is formed between the PU molecules, which greatly improves the tensile strength of PU. The cross-link also hinders the slip of the molecular chain, so the elongation at break of PU decreases obviously.
After 12 hours of repair at room temperature and light condition, with the increase of the R value, the repair strength of PU first increases to 2.13 MPa, and then gradually decreases, and the repair efficiency of elongation gradually decreases to 24%. When the R value is less than 1.0, the strength repair efficiency remains almost 100%; when the R value is greater than 1.0, the strength repair efficiency decreases to 83% with the increase of the R value, which is mainly due to the influence of cross-linking on the movement of molecular chains and the limitation of the exchange and recombination of diselenide bonds. The movement, exchange and rearrangement of the diselenide bond in the soft segment of PU molecule are the direct causes that affect the self-healing ability of the material. The degree of intermolecular crosslinking and hydrogen bonding is the internal reason for the R value affecting the self-healing property, physical and mechanical properties, thermal stability and crystallization properties of PU. The above results will provide useful reference for the preparation and application of self-healing PU materials.

Key words: polyurethane, self-healing, solvent-free, R value, diselenide bond