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

Maier et al. [Maier, D., et al., J. Rheol. 42, 1153–1173 (1998)] examined the 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 Fluid Mech. 76, 299–306 (1998)]. They found an unexpected high value for β(β=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 understood when the relaxation time spectrum is decomposed into a Rouse and an entanglement part and only the latter is used for determination of the molecular weight distribution. Applying a procedure which separates the Rouse processes from the spectrum determined from measured dynamic shear moduli, β 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 evaluation.