Breaking bonds by mechanical stress: when do electrons decide for the other side?

Area of Science:

• Polymer chemistry
• Computational materials science
• Quantum mechanics

Background:

• Mechanical stress can induce chemical reactions in polymers.
• Understanding bond cleavage mechanisms under external forces is crucial for materials design.
• First-principles simulations offer insights into reactive processes at the molecular level.

Purpose of the Study:

• To simulate and investigate stress-induced reactions in poly(ethylene glycol) (PEG) at a quantum mechanical level.
• To observe and analyze the dynamics of electron motion and bond breaking during mechanical stretching.
• To elucidate the role of solvent molecules in initiating polymer degradation under stress.

Main Methods:

• First-principles molecular dynamics simulations were employed.
• Poly(ethylene glycol) (PEG) in water was subjected to mechanical stretching at finite temperature.
• Both the polymer molecule and the surrounding water solvent were treated quantum mechanically with equal rigor.

Main Results:

• Simulations revealed the formation of ions, indicating heterolytic bond cleavage within the PEG molecule.
• The motion of electrons during the reaction process was successfully monitored.
• Electron transfer and bond breaking were observed to occur nearly simultaneously.
• The initiation of these processes was linked to the approach of a solvent molecule towards the destabilized polymer bond.

Conclusions:

• Mechanical stress can lead to ion formation and bond cleavage in PEG via a quantum mechanical pathway.
• Solvent-induced destabilization plays a critical role in initiating stress-driven polymer reactions.
• Simultaneous electron transfer and bond breaking are key features of this mechanically induced degradation process.