**1. Introduction**

To date, polymer materials have been widely used in various fields because of their excellent corrosion resistance and mechanical and barrier properties. However, it is accessible to produce micro-slaps on the surface and inside of the traditional polymer materials due to the influence of mechanical, light and chemical substances in the manufactural processing and practical applications. These cracks are difficult to detect with the naked eye and may cause further damage to the materials, thus reducing the mechanical properties and safety of the materials and shortening their service time. Therefore, some researchers introduced the biological self-healing characteristics and mechanisms into polymer materials and formed functional self-healing materials through bionic design. These materials can recover their original properties spontaneously after damage or under external stimulation, resulting in new intelligent/smart materials with longer lives and more reliable performances, such as shaped memory polymer [1–3] and self-healing polymer [4,5] intelligent polymer materials.

From the perspective of bionics, self-healing materials can be divided into extrinsic and intrinsic types according to whether they contain additional repair reagents or not. Extrinsic self-healing can preinstall some special structural components (such as microcapsules or micro-vessels) in the polymer composites by implantation technology. When the material is damaged, the repair reagent at the damaged part is released rapidly, which promotes the polymerization reaction and repairs the material structure in time [6], whereas intrinsic self-healing materials can achieve multiple internal repairs through the breaking and recombination of reversible chemical bonds within or between molecules. Therefore, it is not necessary to add additional repair reagents in advance [7,8].

As the earliest discovered dynamic polymerization reaction, disulfide exchange reaction can be carried out at a low temperature and has great advantages in preparing dynamic polymers [9,10] For instance, aromatic disulfide compounds can form a rapid self-healing system [11]. In 2007, Nitschke et al. found that disulfide bonds in aromatic

disulfides were easier to reach the translocation exchange equilibrium than that in aliphatic disulfides [12]. Ibon Odriozola et al. successfully prepared a catalyst-free disulfide bond polymer elastomer that can be repaired at room temperature by the condensation reaction of 4, 4 -dithiodianiline with isocyanate [13]. Kim et al. developed a transparent and easy-to-process polyurethane elastomer (IP-SS), which can be rapidly self-healed at room temperature and possess a maximum tensile strength of 6.8 MPa [14]. Zhang et al. prepared a self-healing polyurethane material based on solar light-induced disulfide bond metathesis reaction [15]. In addition to the electron-donating groups connected with disulfide bonds, it helps to reduce their bond energy and form hydrogen bonds between macromolecular chains, the amorphous structures of aliphatic monomers and soft and hard segments also play a key role in the self-healing of hydrogen sulfide. However, there are still some problems in the development of the disulfide exchange reaction. Aromatic disulfide monomers are usually expensive and not conducive to large-scale industrial production. At the same time, the molecular design usually leads to the yellowish appearance and low transparency of self-healing materials.

Herein, the low-cost aliphatic bis (2-alkylethyl) disulfide (HEDS) with flexible segments was used to prepare the self-healing waterborne polyurethane materials, which was synthesized by introducing HEDS-containing −OH groups into the WPU and reacted with −NCO groups. The successful introduction of SS bond in the polymer chain was verified by FTIR. Then, the influence of SS bond content on the self-healing efficiency of WPU film was studied by the tensile test, the dispersion and stability of WPU were assessed by the particle size and zeta potential analysis and the thermal properties of the polymer were tested by DMA and TGA. In addition, the reprocessing performance of the film was investigated by a plate vulcanizing machine.
