COMPONENT PREDICTIONS AND THE RELAXATION SPECTRUM OF THE DOUBLE REPTATION MIXING RULE FOR POLYDISPERSE LINEAR FLEXIBLE POLYMERS

General, experimentally verifiable predictions;of individual component behavior of linear flexible polymers in arbitrary molecular weight di stributions are derived from the double reptation mixing rule. The dis tribution of stress/orientation among the different components of the molecular weight distribution during steady deformation and constraine d elastic recovery are developed for the case of a single exponential monodisperse relaxation function. The des Cloizeaux ''double reptation '' model and the Tsenoglou network model are shown to be equivalent an d the precise relationship between the model parameters is determined. Distinct contributions to the relaxation process from the separate me chanisms of reptation and matrix relaxation (constraint release) are i dentified. Experimental relaxation spectra of bidisperse blends of nea rly monodisperse polybutadienes reveal a cascade of discrete peaks in the terminal zone that are in qualitative agreement with theoretical p redictions from the double reptation mixing rule with a Doi-Edwards mo nodisperse relaxation function. The ability to accurately calculate ex perimental relaxation spectra for complex blends of nearly monodispers e materials is a powerful tool in developing, discriminating, and eval uating new mixing rules. (C) 1996 Society of Rheology.