Mechanochemical Triggers for Self -Healing Polymers

Abstract

Mechanochemical triggers based on the electrocyclic ring opening of both trans and cis substituted benzocyclobutenes was studied. The products of mechanically-accelerated ring opening were studied by trapping experiments. Ultrasound induces ring opening at 10°C, whereas thermal activation only took place at temperatures over 105°C. It was found that the substitution pattern around the four-membered ring influenced the rotational preference for ring opening. 13C labeling studies indicate that while the trans isomer prefers to open in a conrotatory manner, the cis isomer prefers to open in a disrotatory manner. It is proposed that these rotational preferences are a result of the efficiency of stress release; mechanical activation is greatest for those pathways which most efficiently relieve the applied force upon transformation from substrate to products.