Abstract: Time sweep investigation ofthe static rheological behaviors of polypropylene(PP), polystyrene(PS)and their blends were carried out at low shear rates. The viscosity of neat PP and PS decreased linearly with time mainly due to thermal degradation. For the PP/PS alloy, the viscosity in-creased first and subsequently decreased. The first increase of the viscosity could be attributed to the in-terlockofthe phase structure and the later decrease was for the same reason of the homopolymers.

Key words: polymer alloy, static rheological behavior, time sweep, polypropylene, polystyrene