RHEOOPTICAL DETECTION OF SHEAR-INDUCED ORIENTATION OF HIGH MOLAR-MASSPOLYSTYRENE IN DILUTE-SOLUTION

The shear-induced orientation of high molar mass polystyrene (M(w) > 9 x 10(6) g mol-1) is investigated by means of rheooptical wide-angle l aser light scattering in dilute solution at 20-degrees-C in the near-t heta solvent trans-decalin and in thermodynamically good mixed solvent s consisting of oligostyrene in toluene. From these measurements the o rientation of the macromolecules with respect to the direction of flow is obtained as a function of shear rate and polymer concentration. Th e orientational behaviour is discussed with respect to the influence o f viscosity, solvent power and shear rate, and finally compared with t heoretical predictions and with literature data obtained by light scat tering and flow birefringence. The results obtained by the new rheoopt ical light scattering photometer are within the theoretical limits but differ in the degree of orientation, especially at very low shear rat es, from the experimental results given in the literature. This deviat ion is at least partly explained by means of polydispersity and chain stiffness.