**4. Conclusions**

In this paper, based on the principle of introducing reversible covalent bond containing SS into polymer, functional self-healing waterborne polyurethane was synthesized with PTMG as soft segment, IPDI as hard segment and DMPA containing hydrophilic group as auxiliary. The zeta potential revealed that all the synthesized WPU emulsions displayed excellent stability, and the particle sizes of WPU1 and WPU2 emulsions were relatively small. The characteristic peaks of N-H and S-S in urethane were verified by FTIR. Furthermore, the tensile strength, self-healing process and repair effect of WPU-SS film

were quantitatively evaluated by tensile measurement. After the cut spline WPU2 sample was heat treated at 70 ◦C for 4 h, it could maintain the tensile strength and the self-healing efficiency could reach 96.14%, whilst the repair efficiency of the sample was 84.21% after 24-h self-repair at 25 ◦C. In addition, to realize the reprocessing of the self-healing film, the cut WPU2 film fragments were hot pressed at 130 ◦C for 20 min to reshape into a square film by a flat vulcanizing machine. The results indicated that the tensile strength of the reprocessed WPU2 film was 3.39 MPa, and it possessed good reprocessing performance.

**Author Contributions:** G.Y. conceived the project and wrote the paper; T.J. was in charge of all the experiments, all the authors contributed to the scientific discussion. Both authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors also would like to thank Yunyun Zou from the Shiyanjia lab for the XPS analysis (www.Shiyanjia.com, accessed on 19 August 2021).

**Conflicts of Interest:** The authors declare no conflict of interest.
