Analysis of Chain Scission in Polymers Using Reactive Molecular Dynamics

Understanding microscopic-level information is key to understanding the underlying physics of condensed-phase pyrolysis. However, current experimental techniques can only evaluate macroscopic properties. The insight gained from microscopic rates constants including the effects of degree of polymerization is important for use in population balance and kinetic models that extend the predictions to full-scale product distributions. Reactive Molecular Dynamics (RMD) is a tool that probes individual kinetic events through the natural evolution of temporal dynamics. The simulations were conducted using our new RMD code named RxnMD. The reactions are represented using RMDff, which is a valence-bond description which uses switching functions to smoothly represent the atomistic changes that occur during a chemical reaction. Simulations were conducted using linear polyethylene in order to ascertain the effects of polymer size and conformation on decomposition kinetics. The calculations reveal that the rate of backbone scission is dependent on the polymer size, which saturates as the polymers become sufficiently long.