Some evidence for the existence of the liquid-liquid transition: Melt rheology studies

Abstract

In 1963 Boyer proposed the existence of a liquid-liquid transition, T_ll, in polystyrene above the glass transition T_g. Since that time there has been considerable discussion and disagreement on the existence of this transition. Detailed shear modulus data as a function of temperature in the range 165–215°C will be presented for a series of polystyrenes of various molecular weights. In each case, as the temperature is increased, the modulus gradually decreases until a specific molecular weight dependent temperature is reached and then suddenly the modulus decreases rapidly over a few °C and then returns to its previous gradual decrease with increasing temperature. The response is reminiscent of the modulus behavior going through T_g. It is suggested that the temperature at which this sharp decreased in modulus takes place is T_ll. The molecular weight effects on T_ll will be discussed in terms of several rheological properties that measure the temperature of this transition.