  Drawing an analogy to the paradigm of quasi-elastic neutron scattering, we
present a general approach for quantitatively investigating the spatiotemporal
dependence of structural anisotropy relaxation in deformed polymers by using
small-angle neutron scattering. Experiments and non-equilibrium molecular
dynamics simulations on polymer melts over a wide range of molecular weights
reveal that their conformational relaxation at relatively high momentum
transfer $Q$ and short time can be described by a simple scaling law, with the
relaxation rate proportional to $Q$. This peculiar scaling behavior, which
cannot be derived from the classical Rouse and tube models, is indicative of a
surprisingly weak direct influence of entanglement on the microscopic mechanism
of single-chain anisotropy relaxation.
