Rheological models based on the double reptation mixing rule:: The effects of a polydisperse environment

We present a comparison of various rheological models based on the double reptation concept, which relates linear viscoelastic data to molecular-weight distribution in order to determine the most efficient way to describe polydispersity effects. We have used for this study a two-step process. First, we have performed a systematic comparison of the predictions of various models with experimental data already published in the literature for binary blends of polystyrene (PS) and polymethylmethacrylate (PMMA). Then, we have compared the values of the complex shear modulus derived from these molecular models with rheological data obtained on commercial polydisperse polymers (PS, PMMA, and high-density polyethylene). It is shown that only the two models which explicitly take into account the effects of the polydisperse surrounding of a macromolecular chain through tube renewal effects are able to describe correctly the polydispersity effects on zero-shear viscosity and steady-state compliance. (C) 2000 The Society of Rheology. [S0148-6055(00)01303-1].