  We use molecular dynamics simulations to investigate the microscopic and
macroscopic response of model polymer networks to uniaxial elongations. By
studying networks with strands lengths ranging from $N_s=20$ to 200 we cover
the full crossover from cross-link to entanglement dominated behavior. Our
results support a recent version of the tube model which accounts for the
different strain dependence of chain localization due to chemical cross-links
and entanglements.
