  Based on a modified expression of the rate of the convective constraint
release, we present a new contour-variable model of constitutive equations in
which the non-uniform segmental stretch and the non-Gaussian chain statistical
treatment of the single chain are considered to describe the polymer chain
dynamics and the rheological behavior of an entangled system composed of linear
polymer chains. The constitutive equations are solved numerically in the cases
of steady shear and transient start-up of steady shear. The results indicate
that the orientation and stretch, as well as the tube survival probability,
have strong dependence on the chain contour variable, especially in the
high-shear-rate region. However, the inclusion of the non-uniform features in
the constitutive models has little modification comparing with the uniform
models in determining the rheological properties both qualitatively and
quantitatively.
