Obtaining molecular-weight distribution information from the viscosity data of linear polymer melts

Based on the model of Bersted and Slee, and later Malkin and Teishev, both differential and integral methods were developed to determine the molecular-weight distribution (MWD) from viscosity data. The more sensitive differential method can detect small inflections in the viscosity data and convert these into MWD information. The integral method is, however, capable of handling moderately incomplete viscosity data. Combining self-consistent differential and integral approaches, we are able to resolve details of a MWD and quantify reasonably broad MWDs from many sets of limited viscosity data. These methods both have very short computation times. A reported overemphasis of the high-molecular-weight end of distribution is due to the excitation of Rouse modes during the rheological measurements at high frequencies, which masks the diffusive contributions of the low-molecular-weight components to the relaxation process. (C) 1998 The Society of Rheology.