Synthesis and development of novel cyclobutane mechanophores

Mechanical damage of polymers is often a destructive and irreversible process. However, desirable effects may be achieved by controlling the location of chain cleavage events through careful design and incorporation of mechanically active chemical moieties known as mechanophores. These mechanophores could then be utilized for localized self-healing or self-repair of polymer composites. To date there have been few attempts at systematically investigating the effects of mechanophore structure upon rates of activation. Through the synthesis and study of a systematic series of cyclobutane mechanophores, methodology was developed for measuring relative mechanophore reactivity rates and results from these studies were compared to experimentally determined reactivity rates. The straightforward calculations and experimental methods developed herein are useful in guiding the future design and development of new mechanophores for targeted applications including self-repair or damage sensing in polymer composites. In addition to a systematic study of cyclobutane reactivity, the dicyano-substituted cyclobutane mechanophore was shown to form reactive cyanoacrylate-terminated polymers due to mechanically induced retro [2+2] cyclization of the cyclobutane when exposed to external stress. These reactively-terminated polymers have potential applications in self-healing.