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Effects of Chain Length on the Rates of C-C Bond Dissociation in Linear Alkanes and Polyethylene



Vadim D. Knyazev


Molecular dynamics modeling of C-C bond dissociation is performed for a series of linear alkanes and polyethylene macromolecules with the chain lengths ranging from one to a thousand of constituent ethylene monomers (PE-1 - PE-1000). The rate constants obtained in molecular dynamics calculations are compared with those determined using variational transition state theory using the same potential energy surface and classical (non-quantum) partition functions. The results of simulations demonstrate significant accelerating effect of chain length on the rates of C-C bond scission. Per-bond rate constant values increase with the increasing chain length, up to an order of magnitude, in the sequence of linear alkanes from PE-1 (ethane) to PE-5 (decane); this dependence becomes saturated for longer chain lengths. Stiffening the potentials of bending and especially torsional degrees of freedom diminishes the accelerating effect of chain length, while constraining the bond distances for all C?C bonds except the one undergoing dissociation has no effect. An explanation of the observed effects based on reduction of the effective reaction barrier by the action of centrifugal forces induced by bending and torsional motions is presented.
Journal of Physical Chemistry A


chemical kinetics, molecular dynamics, polyethylene, reaction rates


Knyazev, V. (2008), Effects of Chain Length on the Rates of C-C Bond Dissociation in Linear Alkanes and Polyethylene, Journal of Physical Chemistry A (Accessed April 15, 2024)
Created October 16, 2008