Use of Bis(2,2,6,6-tetramethylpiperidin-1-yl)trisulfide as a Dynamic Covalent Bond for Thermally Healable Cross-Linked Polymer Networks

Dynamic covalent bonds (DCBs), which can undergo reversible cleavage and reformation upon exposure to readily useable stimuli, have attracted dramatic attention, but the library of such bonds still remains to be developed. Herein, we report molecular structures, dynamic behaviors, and healability of bis(2,2,6,6-tetramethylpiperidin-1-yl)trisulfide (BITEMPS-S3) to compare with its disulfide analogue (BITEMPS-S2) exchanged at moderate temperature. Unsymmetrical cleavage of trisulfide linkage induced relatively rapid disproportionation to di- and tetrasulfide derivatives. In the bulk, poly(hexyl methacrylate) networks partially containing the BITEMPS-S3 moiety as a cross-linking point afforded nearly quantitative damage healability only by simple hot pressing at 110 °C under mild pressure. A slightly higher healability of BITEMPS-S2 compared to that of BITEMPS-S3 would be due to the differences in the chain-transfer reaction for the trisulfide linkage during free-radical polymerization rather than thermal exchangeability of the BITEMPS-S3 moiety. Therefore, not only BITEMPS-S2 but also BITEMPS-S3 should be regarded as one of DCBs triggered upon exposure to mild external stimuli.