Abstract: The relaxation spectra of a set of star-shaped polystyrenes with the equal length of arms but different branching degree were determined by means of a stress relaxation instrument.The effect of branching structure on the rubbery plateau in the relaxation spectra was investigated,and the relaxation spectra were computer simulated using a"tube"model.The difference in viscoelastic properties of star-shaped polystyrenes were interpreted in terms of molecular motion.

Key words: Star-shaped polystyrene, Viscoelasticity, Mechanical relaxation