Pulling makes a covalent bond last longer: ADF reveals a design principle for adaptive polymers

Some molecular bonds fail faster when pulled. Catch bonds do the opposite: their lifetime increases under mechanical load. This unusual behavior is well known in biology, where it helps molecular assemblies respond to stress, but translating it into compact synthetic covalent chemistry remains challenging.

In this combined experimental and theoretical study, the authors show how hydroxyethyl phosphate triesters can act as covalent catch bonds inside polymer systems. The concept relies on neighbouring group participation, a common intramolecular mechanism that can accelerate bond dissociation. Under tensile force, however, the geometry needed for this intramolecular assistance becomes harder to reach. Instead of helping the bond break, the molecular structure is forced into a less favorable pathway.

ADF calculations in AMS were central to uncovering this mechanism. By modeling the force-dependent phosphate transesterification reaction, the simulations showed that pulling on the molecular motif raises the barrier for the neighbouring-group-assisted dissociation pathway. In other words, force can slow down the very reaction that would normally break the linkage.

Single-molecule force spectroscopy then provided experimental support: the HEP triester bond lifetime increased by more than threefold between 200 and 400 pN. Together, the ADF modeling and single-molecule experiments connect a counterintuitive mechanical response to a clear molecular picture.

The work points toward new strategies for force-adaptive polymer materials, where molecular bonds do not simply weaken under stress, but can be designed to persist longer when load is applied.