Sulfenamides as Building Blocks for Efficient Disulfide-Based Self-Healing Materials. A Quantum Chemical Study

The theoretical self-healing capacity of new sulfenamide-based disulfides is estimated by using theoretical methods of quantum chemistry. Starting from previously studied aromatic disulfides, the influence of inserting a NH group between the disulfide and the phenyl ring (forming the sulfenamide), as well as the role of the phenyl ring in the self-healing process is analyzed. Three parameters are used in the evaluation of the self-healing capacity: i) the probability to generate sulfenyl radicals, which is the first step of the process; ii) the effect of the hydrogen bonding, which affects the mobility of the chains; and iii) the height of the exchange reaction barrier. The insertion of the NH group notably decreases the bond dissociation energy and, therefore, increases the probability to produce sulfenyl radicals and helps the approach of these radicals to neighboring disulfides, favoring the self-healing process. The role of the phenyl rings is clearly observed in the reaction barriers, where the π-π stacking interactions notably stabilize the transition states, resulting in larger rate constants. Nevertheless, this stabilization is somewhat reduced in the aromatic sulfenamides, owing to a less effective π-π interaction. Therefore, the sulfenamide-based aromatic disulfides may be considered as promising candidates for the design of efficient self-healing materials.