Molecular Dynamics Simulations of the Thermal Glass Transition in Polymer Melts: α-Relaxation Behaviour

We present Molecular Dynamics simulations of the thermal glass transition in a dense model polymer liquid. We performed a comparative study of both constant volume and constant pressure cooling of the polymer melt. Great emphasis was laid on a careful equilibration of the dense polymer melt at all studied temperatures. Our model introduces competing length scales in the interaction to prevent any crystallisation tendency. In this first manuscript we analyse the structural properties as a function of temperature and the long time or α-relaxation behaviour as observed in the dynamic structure factor and the self-diffusion of the polymer chains. The α-relaxation can be consistently analysed in terms of the mode coupling theory (MCT) of the glass transition. The mode coupling critical temperature, Tc, and the exponent, γ, defining the power law divergence of the α-relaxation timescale both depend on the thermodynamic ensemble employed in the simulation.