Among the dynamic covalent bonds, imine bonds are a promising option due to their reversibility, which allows for damage response while maintaining mechanical stability at ambient conditions. Traditional polymer networks are typically formed using crosslinking agents, which, while effective, can present challenges. Residual crosslinkers left after polymerization may affect material properties or leach out, potentially leading to environmental concerns. Additionally, ensuring a uniform network structure can be difficult due to variations in local concentrations, reactivity, and diffusion of crosslinkers.
In this study, we consider an approach for making imine-based self-healing polydimethylsiloxane coatings without the need for an additional crosslinking agent. Instead, amine-functionalized PDMS is employed to form imine bonds through catalytic oxidation facilitated by the metal substrate. This allows the polymer to gel while in contact with the metal substrate; the gelled polymer systems can exhibit self-healing properties, regulated by humidity. The solidification time and mechanical properties can be controlled by adjusting factors such as curing time, amine concentration, temperature, and the type of metal substrate. The key advantage of this approach lies in its ability to crosslink without the need for additional chemical crosslinking molecules. This likely improves uniformity of the material and also minimizes environmental impact, making it a more sustainable option. Moreover, the dynamic imine bonds enhance the durability of the coating, allowing it to recover from damage over its lifespan.