Source:The Journal of Chemical Physics, 86:7164–7174, 1987
Dynamic Monte Carlo simulations of long chains confined to a cubic lattice system at a polymer volume fraction of ϕ=0.5 were employed to investigate the dynamics of polymer melts. It is shown that in the range of chain lengths n, from n=64 to n=800 there is a crossover from a weaker dependence of the diffusion coefficient on chain length to a much stronger one, consistent with D∼n−2. Since the n−2 scaling relation signals the onset of highly constrained dynamics, an analysis of the character of the chain contour motion was performed. We found no evidence for the well‐defined tube required by the reptation model of polymer melt dynamics. The lateral motions of the chain contour are still large even in the case when n=800, and the motion of the chain is essentially isotropic in the local coordinates. Hence, the crossover to the D∼n−2 regime with increasing chain length of this monodisperse model melt is not accompanied by the onset of reptation dynamics.