Study of Shear Stress Relaxation in Well-Characterized Polymer Liquids

Shear stress relaxation data were measured for a range of shear strains on several entangled polymer liquids in order to test time-strain factorability and the Doi-Edwards predictions about strain dependence. Undiluted samples and concentrated solutions of well-characterized linear and star poly butadienes with narrow molecular weight distributions were used. Some departures from time-strain factorability were found, but these appear to be nonsy sterna nonsystematic i.e., they do not correlate in any obvious way with the polymer structure. The strain dependence, however, follows the pattern observed by Osaki and Kurata for polystyrene solutions. The Doi-Edwards prediction gives a good account of the results at intermediate entanglement densities (35,000 < cM < 150,000 for linear and star polybutadienes), but systematic departures are found at higher values. The causes of the latter are unknown.