How Pigment Influences Self-Healing in Coatings based on Vinylogous Urethanes

Polymer coatings represent a nearly $9 billion market that provides protection and appearance to a wide range of products. Inclusion of self‐healing properties to repair minor damage could revolutionize the coating industry by increasing service life, sustainability, and long term optical appearance. Covalent adaptable networks (CANs) provide a platform that is appliable to chemistries of interest, but healing tends to lead to scars that detract from the desired appearance. We have demonstrated scar-free healing of scratches of vinylogous urethane-based CANs through covalent surface tethering. However, most industrially relevant coatings are highly engineered with fillers and additives to provide desired characteristics. Here, we describe how the addition of pigments influence the extent and kinetics of self-healing of scratches. The addition of pigment reduces the self-healing kinetics, but this is dependent on the pigment. Molecular organic pigment leads to minimal change in the self-healing rate relative to the CAN coating alone, while inorganic pigments more severely slow the healing process. During healing, the crack zips in reverse from the direction of the scratch. Although differences in rate, there is no visible scar after self-healing - indicating that the pigments are moving with the CAN into the crack to maintain the color.