  Reptation theory has been highly successful in explaining the unusual
material properties of entangled polymer solutions. It reduces the complex
many-body dynamics to a single-polymer description where each polymer is
envisaged to be confined to a tube through which it moves in a snake-like
fashion. For flexible polymers, reptation theory has been amply confirmed by
both experiments and simulations. In contrast, for semiflexible polymers
experimental and numerical tests are either limited to the onset of reptation,
or were performed for tracer polymers in a fixed, static matrix. Here we report
Brownian dynamics simulations of entangled solutions of semiflexible polymers,
which show that curvilinear motion along a tube (reptation) is no longer the
dominant mode of dynamics. Instead, we find that polymers disentangle due to
correlated constraint release which leads to equilibration of internal bending
modes before polymers diffuse the full tube length. The physical mechanism
underlying terminal stress relaxation is rotational diffusion mediated by
disentanglement rather than curvilinear motion along a tube.
