CONFIRMATION OF THE DOI-EDWARDS MODEL

We present simulation results for the Doi-Edwards model of entangled linear polymers and their stress relaxation, treating the chains as confined to Rouse-like motion within their entanglement tube. The viscosity is shown to reproduce the empirical M3.4 law with molecular weight provided the chain ends have Rouse character to their motion, irrespective of whether chain tension or contour length fluctuation effects are included. Fourier transform methods are used to generate realizations of the endbead motions, matching earlier results obtained by real time simulations by Ketzmerick and Ottinger. Absolute agreement with experimental viscosity-molecular weight data is obtained when tube renewal effects are incorporated, using the assumption that disengaged tube acts as plasticizer. The only parameters in fitting are directly and independently measured: the plateau modulus G(N)0 and how it dilutes upon plasticization, and the (Rouse) monomeric friction factor. Tube renewal is crucial to the value of Z(c) = M(c)/M(e). Using G(t) is-proportional-to (surviving tube fraction)a, our results match experiment for a almost-equal-to 2, but not for a = 1 or 3.