Monte Carlo Simulation of Long Chain Polymer Melts: Crossover from Rouse   to Reptation Dynamics
  We present data of Monte Carlo simulations for monodisperse linear polymer chains in dense melts with degrees of polymerization between N=16 and N=512. The aim of this study is to investigate the crossover from Rouse-like dynamics for short chains to reptation-like dynamics for long chains. To address this problem we calculate a variety of different quantities: standard mean-square displacements of inner monomers and of the chain's center of mass, the recently proposed cubic invariant, persistence of bond-vector orientation with time, and the auto-correlation functions of the bond vector, the end-to-end vector and the Rouse modes. This analysis reveals that the crossover from non- to entangled dynamics is very protracted. Only the largest chain length N=512, which is about 13 times larger than the entanglement length, shows evidence for reptation. 
T. Kreer, J. Baschnagel, M. Mueller, K. Binder