  We consider equilibrium relaxation properties of the end-to-end distance and
of principal components in a one-dimensional polymer chain model with nonlinear
interaction between the beads. While for the single-well potentials these
properties are similar to the ones of a Rouse chain, for the double-well
interaction potentials, modeling internal friction, they differ vastly from the
ones of the harmonic chain at intermediate times and intermediate temperatures.
This minimal description within a one-dimensional model mimics the relaxation
properties found in much more complex polymer systems. Thus, the relaxation
time of the end-to-end distance may grow by orders of magnitude at intermediate
temperatures. The principal components (whose directions are shown to coincide
with the normal modes of the harmonic chain, whatever interaction potential is
assumed) not only display larger relaxation times but also subdiffusive
scaling.
