Self-healing materials are very promising due to their capacity to repair themselves. Among others, diphenyl disulfide-based compounds appear to be the best candidates to develop materials with optimum self-healing properties. However, few is known regarding both the reaction mechanism and the electronic structure that make possible such properties. In this work, we have carried out theoretical calculations on a wide set of different disulfide compounds, both aromatic and aliphatic, to elucidate the prevalent reaction mechanism and the electronic conditions needed for improved self-healing properties. Two competitve mechanisms were considered: the metathesis and the radical-mediated mechanism. According to our calculations, the latter is the responsible for this process. The formation of such radicals strongly depends on the S-S bond strength, which can be modulated chemically by the use of proper derivatives. At this point, amino derivatives appear to be the most promising ones. In addition to the S-S bond strength, hydrogen bonding between disulfide chains appear to be relevant to favour the contact among disulfide units. This is crucial for the reaction to take place. The calculated hydrogen bonding energies are of the same order of magnitude as the S-S bond energies. Finally, reaction barriers have been analyzed for some promising candidates. Two reaction mechanisms were compared, namely, the 2+2 metathesis and the 2+1 radical mediated mechanisms. No computational evidence was found for the former one, which indicates that the radical mediated mechanism is the one responsible in the self-healing process of these materials. The calculated reaction barriers are around 10 kcal/mol regardless the substituent employed. All these results suggest that the radical formation and the structural hydrogen bonding structures prevale over kinetics. Having this in mind, new compounds are proposed for the design of future improved self-healing materials.

Design of new disulfide-based compounds for the improvement of self-healing materials

251st National Meeting (2016)

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