  We analyze, through molecular dynamics simulations, the temperature
dependence of the thermal conductivity (k) of chain-oriented amorphous
polyethylene (PE). We find that at increasing levels of orientation, the
temperature corresponding to a peak k progressively decreases. Un-oriented PE
exhibits the peak k at 350 K, while aligned PE under an applied strain of 400%
shows a maximum at 100 K. This transition of peak k to lower temperatures with
increasing alignment is explained in terms of a crossover from disorder to
anharmonicity dominated phonon transport in aligned polymers. Evidence for this
crossover is achieved by manipulating the disorder in the polymer structure and
studying the resulting change in temperature corresponding to peak k. Disorder
is modified through a change in the dihedral parameters of the potential
function, allowing a change in the relative fraction of trans and gauche
transformations. The results shed light on the underlying thermal transport
processes in aligned polymers and hold importance for low temperature
applications of polymer materials in thermal management technologies.
