ORIENTATION OF POLYMER COILS IN DILUTE-SOLUTIONS UNDERGOING SHEAR-FLOW - BIREFRINGENCE EXPERIMENTS

Polymer orientation in dilute solutions undergoing shear flow is inves tigated by means of now birefringence using a quantity called ''orient ation resistance''. In the framework of theoretical models it was foun d that the intrinsic orientation resistance is strongly influenced by polydispersity (Bossart and Ottinger, 1985). Dilute solutions of two r adical polymerized polystyrene samples with different molecular weight s in both good and Theta solvents are investigated by flow birefringen ce. The experimentally obtained values for the intrinsic orientation r esistance are in very good agreement with the values calculated in the framework of kinetic polymer models. These experiments demonstrate th at the polydispersity effect is well understood and that flow birefrin gence constitutes an extremely precise method for determining molecula r weights. From our experiments it can be inferred that the number-ave rage molecular weight M-n of a polymer sample can be measured to withi n a relative error of Delta M-n/M-n = 3%. The use of the birefringence method for the determination of the molecular weight distribution of a polymer sample is suggested.