Theory-driven Discovery of Thermally Stable Mechanophore for Self-strengthening Materials

Mechanophores that readily undergo bond cleavage upon mechanical stimuli normally contain a highly strained ring or reactive unit with weak bonds, which are usually thermally unstable. Here, we propose a general theory-driven procedure for selecting thermally stable radical-type mechanophore which can be used in self-strengthening materials. First, following our previous work, it is confirmed that a conformational motif called “node” along the force transduction direction enhances the force effect by generating a severe distortion on the breaking covalent bond. Molecules possessing bridged rings are ideal candidates to have a “node”, as the bridged structure helps to fix the key dihedral angle. Our computational exploration then focused on camphanediol and pinanediol, which do not have highly strained ring or intrinsically weak covalent bond, but a node ensured by a small dihedral angle. Our simulations predicted that polymer chains including these molecular skeletons easily undergo a C−C bond homolysis under relatively low tensile force and efficiently generate mechanoradicals. Subsequently, our automated reaction path exploration calculations unveiled the fate of the mechanoradicals by enumerating their possible reaction channels, and suggested that camphanediol can generate long-lived radicals, which can be utilized to develop self-strengthening materials. Therefore, we prepared double-network (DN) hydrogels containing camphanediol moiety and found that these novel DN hydrogels do have a good self-strengthening performance. Moreover, thanks to the present design guideline not assuming strained rings or weak bonds, such a camphanediol-containing DN hydrogel showed a good thermal and UV stability.