A Highly Self-Healable Elastomer Based on Urea Oligomeric Blocks for the Enhanced Mechanical Properties and Long-Term Storage Stability

Flexible electronics are enjoying a renaissance with the 4^th industrial revolution. However, the change of form factor toward flexibility requires replacing the hard glass with the flexible elastomer as a protective coating layer. The softened surface suffers from repeated cracks and scratches. To address these issues, two kinds of elastomers are developed to strengthen surface hardness and to give self-healing properties. Herein, a highly self-healable elastomer with superior optical and mechanical properties is synthesized based on the urea oligomer in this study. Acrylate-based polyol, linear urea oligomer with isocyanate group at both ends, and cross-linker containing multiple isocyanate groups are blended and the resulting blended precursor is reacted to generate the self-healable elastomer (EUo). The process of oligomer synthesis of urea can successfully ensure processability, thus avoiding potential reactor fouling during commercialization. EUo exhibits a high transmittance (~92%) and low yellow index (~1.5), which makes it applicable to optical-electronic devices as a protective film. The elastomer based on urea oligomer shows remarkable self-healing efficiency (94%), which is extremely enhanced compared to conventional elastomer without urea oligomer (47%) and the elastomer based on urea diol (62%). This result is due to the strong hydrogen bonding interaction between urethane and urea groups, and we thoroughly analyze this result through a modeling system of FT-IR spectroscopy. Moreover, the strong hydrogen bonding produces a secondary cross-linking network, resulting in enhanced tensile strength (43 MPa) and surface hardness (0.177 GPa). This study suggests a facile strategy that can overcome the conventional trade-off between self-healing property and mechanical robustness that limit the application of self-healing polymers.