FIGURE 1.

Schematic drawing of the basic principle of the sacrificial bond-hidden length mechanism. Before a sacrificial bond is broken, only the black length of the molecule contributes to entropic spring and therefore to the force with which the molecule resists the stretching. The red length of the molecule is hidden from the applied force by the sacrificial bond. When the bond breaking force is reached, only a small amount of energy is needed to break the sacrificial bond. After that, the whole length (black plus red) contributes to the entropy of the molecule. In total, the energy that has to be put in to break the molecule is increased by the shaded area under the first peak. Additionally, the initial slope of the force curve is steeper, which indicates that the molecule is initially stiffer.