UNDERSTANDING THE BEHAVIOUR OF SULPHUR-CENTRED RADICALS DURING POLYMER SELF-HEALING

Abstract

High-level ab initio molecular orbital theory calculations have been used to study self-healing mechanism of materials based on thiuram disulfides and their derivatives (S=C(Z)S–SC(Z)=S, for Z = CH3, NEt2, N(Et)CH2CH2OH, Ph, Bz), and the effects of these Z-substituents on their efficacy. The relative contributions of cross-over and reversible addition fragmentation chain transfer reactions were ascertained, and the likelihood of chain-breaking side reactions was assessed. To rationalize the results, the various stabilization energies of the radicals and closed-shell species were also evaluated. The study revealed that the self-healing mechanism of thiuram disulfides follows predominantly the cross-over reaction because of the high energies of intermediate radicals in the chain transfer mechanism. Based on the study, the most effective self-healing materials are predicted to contain amines as Z-groups, while those containing benzyl and its derivatives are most likely to undergo side reactions.