Rheo-Dielectric Behavior of Oligostyrene and Polyisoprene

ICR Annual Report, Vol. 5, 199824 Flow effects were examined for dielectric behavior of oligostyrene (OS; M = 950) and cis-polyisoprene (PI; M = 8200). OS-1 has monomeric dipoles perpendicular to its backbone and the terminal dielectric relaxation results from the segmental motion, while for PI-8 having parallel dipoles this relaxation re-flects the global chain motion. The dielectric loss ε ” and viscosity η were measured for OS and PI at T well above respective Tg under steady shear flow at rates g << 1/τ1, with τ1 being the linear viscoelastic terminal relaxation time. The ε ” and η of PI were independent of g, as usually expected under such slow flow. In contrast, OS exhibited acceleration of the dielectric relaxation and the shear-thinning of η at g << 1/τ1. This thinning was related to flow-induced changes in some sort of dynamic structure, probably a cooperative domain structure, and the dielectric change detected acceleration of the segmen-tal motion due to this structural change