On the Rouse spectrum and the determination of the molecular weight distribution from rheological data

Maier er al. [Maier, D., et al., J. Rheol. 42, 1153-1173 (1998)] examined t he reconstruction of binary molecular weight distributions from rheological data for a series of polystyrene mixtures using a generalized mixing rule recently introduced [Anderssen, R. S. and D. W. Mead, J. Non-Newtonian Flui d Mech. 76, 299-306 (1998)]. They found an unexpected high value for beta(b eta = 3.84+/-0.1), the mixing parameter, which is 1 for the reptation and 2 for the double reptation or entanglement models. This result can be unders tood when the relaxation time spectrum is decomposed into a Rouse and an en tanglement part and only the latter is used for determination of the molecu lar weight distribution. Applying a procedure which separates the Rouse pro cesses from the spectrum determined from measured dynamic shear moduli, bet a values are found which are in accordance with the double reptation theory and which give very good agreement between molecular weight distributions determined by size-exclusion chromatography and by rheological data evaluat ion. (C) 2000 The Society of Rheology. [S0148-6055(00)01202-5].