Figure 3 Self-Healing of Film Show full caption (A–C) Optical microscope images of a damaged PRx-PB (8) film (A), Pul-PB (8) film (B), and PRx-CC (8) film (C) measured with a laser microscope before and after heating at 60°C under humid conditions for 30 min. Scale bars, 100 μm. (D) Recovery ratio of the cross-sectional area of the scar plotted as a function of the healing time for the PRx-PB (8) film, Pul-PB (8) film, PRx-CC (8) film, and PRx-pAAm (1) film. Error bars represent the SD based on three independent experiments.

We used photopolymerization to investigate the suitability of PRx-PB gels as scratch-resistant, healable top coatings for hard materials. Scheme S10 shows the procedure used for coating glass substrates. A 1 mL solution containing HPPRx, Vi-PB, AAm, and a photoinitiator (Irgacure 2959) was cast onto a glass substrate, followed by irradiation with UV light (λ = 365 nm) for 1 hr to form a thin gel on the substrate; the gel was subsequently dried in vacuo to form a film: PRx-PB (x) film. Figures S19–S23 show the thermal properties of the bulk films. Figure S9 shows scratch tests for PRx-PB (8) film and Pul-PB (8) film. Both samples have almost the same value of stiffness. The film was scratched with a razor to create a scar and then incubated in an oven (60°C) containing water vapor ( Figures S10 and S24 ). Figures S15–S18 show 3D laser micrographs of the films. Figure 3 A shows 2D micrographs of the PRx-PB (8) film immediately after scratching and after incubation. The scar healed sufficiently, recovering the original coating. Cross-sectional height profiles ( Figure S11 ) measured with a laser microscope show that the cross-sectional area (see also Scheme S11 ) of the scar decreased from 16 to ∼0 μm Figures 3 B and S12 show the results of self-healing experiments on the Pul-PB (8) film. The Pul-PB (8) film did not heal efficiently, even after incubation under humid conditions. Figures 3 C and S13 show the results on the PRx-CC (8) film. The PRx-CC (8) film did not heal. The cross-sectional areas of the scars on the PRx-PB (8) film, the Pul-PB (8) film, the PRx-CC (8) film, and the PRx-pAAm film (see also Table S1 and Figure S14 ) as estimated by the height profiles are plotted as functions of the incubation time in Figure 3 D. Figure 3 D indicates that the PRx-PB film self-healed most efficiently among all samples, given that it reached approximately 100% recovery within 30 min. PRx-PB films showed efficient self-healing in the semi-dry state, whereas Pul-PB films and PRx-CC films showed insufficient self-healing. Therefore, the combination of the physical self-healing mechanism based on the PRx structure and the chemical self-healing mechanism based on reversible bonds is necessary for achieving 100% self-healing.