The role of internal rotational barriers in polymer melt chain dynamics

We present molecular dynamics simulations on 1,4-polybutadiene comparing the dynamics of melt chains between chemically realistic models and a freely rotating chain version of one of the models. These models exhibit the same liquid structure, as measured by the structure factor, and meso- to large- scale chain structure, as measured by the Rouse-mode amplitudes. We show that in this case the Rouse- like chain dynamics as observable in the momentum transfer range of neutron spin-echo experiments is the same for the chains with and without torsion barriers. Our results bear on a recent comparative neutron spin-echo study of the chain dynamics of two polymers with similar chain structure which revealed a strong difference of the dynamics as quantified by the level of agreement of the scattering data with the Rouse model predictions.