  Nonequilibrium molecular dynamics simulations are used to study the shear
thinning behavior of immiscible symmetric polymer blends. The phase separated
polymers are subjected to a simple shear flow imposed by moving a wall parallel
to the fluid-fluid interface. The viscosity begins to shear thin at much lower
rates in the bulk than at the interface. The entire shear rate dependence of
the interfacial viscosity is consistent with a shorter effective chain length
$s^*$ that also describes the width of the interface. This $s^*$ is independent
of chain length $N$ and is a function only of the degree of immiscibility of
the two polymers. Changes in polymer conformation are studied as a function of
position and shear rate.Shear thinning correlates more closely with a decrease
in the component of the radius of gyration along the velocity gradient than
with elongation along the flow. At the interface, this contraction of chains is
independent of $N$ and consistent with the bulk behavior for chains of length
$s^*$. The distribution of conformational changes along chains is also studied.
Central regions begin to stretch at a shear rate that decreases with increasing
$N$, while shear induced changes at the ends of chains are independent of $N$.
