Understanding the Behaviour of Sulphur-Centred Radicals During Polymer Self-Healing

The high-level composite ab initio G3(MP2)-RAD method has been used to study the self-healing mechanism of materials based on thiuram disulfides and their derivatives (S=C(Z)S–SC(Z)=S, for Z = CH 3 , NEt 2 , N(Et)CH 2 CH 2 OH, Ph, B z ), 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 stabilisation 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.I.D. gratefully acknowledges the Scientific and Technological Research Council of Turkey (TUBITAK) under 2219 grant. M.L.C gratefully acknowledges generous allocations of supercomputing time on the National Facility of the Australian National Computational Infrastructure and financial support from the Australian Research Council Centre of Excellence for Electromaterials Science. Many useful discussions with Professor Krzysztof Matyjaszewski are also gratefully acknowledged