Concentration Dependence of Viscoelastic Properties of a Mixture of Three- and Four-Branched Star Polystyrenes

Abstract

Viscoelastic properties of concentrated solutions of a mixture of three- and four-branched polystyrenes were measured by means of a concentric cylinder type rheometer. The Vogel parameters, αf and T0, were calculated from the temperature dependence of viscosity and the shift factor aT. From the frequency dependence of the storage shear modulus G′ and the loss modulus G″, the characteristic parameters in the terminal zone such as zero-shear viscosity η0 and steady-state compliance Je0 were evaluated. The dependence of these parameters on concentration was compared with that of concentrated solutions of linear polystyrenes. The concentration dependence of η0 for star polymers is very similar to that for linear ones. However, Je0 for the mixture of three-and four-branched polystyrenes showed unusual behavior that was quite different from that of linear polymer and monodisperse star polymer. The entanglement compliance is also discussed.