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 r eptation concept, which relates linear viscoelastic data to molecular-weigh t distribution in order to determine the most efficient way to describe pol ydispersity effects. We have used for this study a two-step process. First, we have performed a systematic comparison of the predictions of various mo dels 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 molecu lar models with rheological data obtained on "commercial" polydisperse poly mers (PS, PMMA, and high-density polyethylene). It is shown that only the t wo models which explicitly take into account the effects of the polydispers e surrounding of a macromolecular chain through "tube renewal" effects are able to describe correctly the polydispersity effects on zero-shear viscosi ty and steady-state compliance. (C) 2000 The Society of Rheology. [S0148-60 55(00)01303-1].