Thermally Adjustable Dynamic Disulfide Linkages Mediated by Highly Air‐Stable 2,2,6,6‐Tetramethylpiperidine‐1‐sulfanyl (TEMPS) Radicals

Abstract

Intrinsically exchangeable dynamic covalent bonds that can be triggered by readily usable stimuli offer easy incorporation of their dynamic properties in various molecular systems, but the library of such bonds is still being developed. Herein, we report the dynamic covalent chemistry of 2,2,6,6-tetramethylpiperidine-1-sulfanyl (TEMPS) dimers derived from thermally reversible homolytic dissociation of disulfide linkages. High air stability of TEMPS was observed even at 100 °C, affording facile employment of thermal dissociation-association equilibria and adjustable bond exchange properties under atmospheric conditions. We also established an efficient synthetic route for a modifiable derivative of the dimer that enabled incorporation of dynamic properties into linear and network polymer structures. The obtained polymers showed controllable molecular weights, temperature-dependent swelling properties, healing ability, and recyclability, reflecting the thermally tunable dynamics of the dimer.

A Strategy toward Cyclic Topologies Based on the Dynamic Behavior of a Bis(hindered amino)disulfide Linker

“…We have previously reported that the BiTEMPS unit behaves as a stable covalently bound structure at room temperature, while it exchanges disulfide bonds above 80 8C. [37] We have also demonstrated that a solution of polyurethanes containing BiTEMPS units in the polymer repeating units undergo an entropy-driven transformation from linear polymers to oligomers under high dilution conditions, which can be reversed under concentrated conditions upon heating. This finding inspired us to develop a strategy toward compounds with a cyclic topology since the main oligomer structures obtained by entropy-driven transformations (mainly translational entropy of cyclic oligomers and polymer are both greatest at high dilution, while both decrease as the concentration increase) should be cyclic given the recombination of dynamic covalent bonds and the small number of terminal structures on the polymer chain.…”

“…Considering that a cyclization process is inevitable at some point during the synthesis of compounds with a cyclic topology and that this step is presumably the most difficult, we thought that using a spontaneous and selective cyclization would be ideal. In this work, we focus on the dynamic covalent chemistry [34][35][36] of bis(2,2,6,6-tetramethylpiperidin-1yl)disulfide (BiTEMPS) [37] and use it as the driving force to induce an ideal cyclization. We have previously reported that the BiTEMPS unit behaves as a stable covalently bound structure at room temperature, while it exchanges disulfide bonds above 80 8C.…”

“…The target for a compound with a cyclic topology reacts with a BiTEMPS derivative to afford the corresponding linear polymer, which is subsequently converted into a cycle via an entropy-driven transformation. The key points of the present method based on the dynamic nature of BiTEMPS are: 1) any structure can be cyclized if it can react with BiTEMPS derivatives, that is, by covalently connecting BiTEMPS units and the target molecule; 2) the radical generated upon heating exhibits high tolerance toward functional groups due to its poor reactivity with a variety of chemical species, including oxygen-based moieties and olefins, [37] while it exhibits high reactivity in exchange reactions, which renders it applicable to variety of skeletons; and 3) simple heating can induce the cyclization, that is, catalysts and/or additives are not required.…”

A Strategy toward Cyclic Topologies Based on the Dynamic Behavior of a Bis(hindered amino)disulfide Linker

“…Considering that a cyclization process is inevitable at some point during the synthesis of compounds with a cyclic topology and that this step is presumably the most difficult, we thought that using a spontaneous and selective cyclization would be ideal. In this work, we focus on the dynamic covalent chemistry of bis(2,2,6,6‐tetramethylpiperidin‐1‐yl)disulfide (BiTEMPS) and use it as the driving force to induce an ideal cyclization. We have previously reported that the BiTEMPS unit behaves as a stable covalently bound structure at room temperature, while it exchanges disulfide bonds above 80 °C .…”

“…In this work, we focus on the dynamic covalent chemistry of bis(2,2,6,6‐tetramethylpiperidin‐1‐yl)disulfide (BiTEMPS) and use it as the driving force to induce an ideal cyclization. We have previously reported that the BiTEMPS unit behaves as a stable covalently bound structure at room temperature, while it exchanges disulfide bonds above 80 °C . We have also demonstrated that a solution of polyurethanes containing BiTEMPS units in the polymer repeating units undergo an entropy‐driven transformation from linear polymers to oligomers under high dilution conditions, which can be reversed under concentrated conditions upon heating.…”