Bulk and Shear Rheology of a Symmetric Three-Arm Star Polystyrene

The bulk and shear rheological properties of a symmetric three-arm star polystyrene were measured using a selfbuilt pressurizable dilatometer and a commercial rheometer, respectively. The bulk properties investigated include the pressure–volume–temperature behavior, the pressure-dependent glass transition temperature (Tg), and the viscoelastic bulk modulus and Poisson’s ratio. Comparison with data for a linear polystyrene indicates that the star behaves similarly but with slightly higher Tgs at elevated pressures and slightly higher limiting bulk moduli in glass and rubbery states. The Poisson’s ratio shows a minimum at short times similar to what is observed for the linear chain. The horizontal shift factors above Tg obtained from reducing the bulk and shear viscoelastic responses are found to have similar temperature dependence when plotted using T Tg scaling; in addition, the shift factors also exhibit a similar temperature dependence to linear polystyrene. The retardation spectra