Dynamics of a supercooled polymer melt above the mode-coupling critical temperature: cage versus polymer-specific effects

This paper reports results of molecular dynamics simulations fora glassy po lymer melt consisting of shea, non-entangled chains. The temperature region studied covers the supercooled state of the melt above the mode-coupling c ritical temperature. The analysis focuses on the interplay of simple-liquid and polymer-specific effects. One can clearly distinguish two regimes: a r egime of small and one of large monomer displacements. The first regime cor responds to motion of a monomer in its local environment. It is dominated b y the cage effect and well described by the idealized mode-coupling theory. The second regime is governed by the late-beta/early-alpha process. In thi s regime the connectivity of the monomers begins to interfere with the cage dynamics and finally becomes dominant. The monomer displacement is compare d with simulation results for a binary Lennard-Jones mixture to highlight t he differences which are introduced by the connectivity of the particles.