VISCOSITY-TEMPERATURE RELATIONSHIPS OF A POLYCARBONATE MELT - WILLIAMS-LANDEL-FERRY VERSUS ARRHENIUS BEHAVIOR

The melt viscosity of polycarbonate from bisphenol-A a) was measured in a wide range of temperatures, from T(g) + 55-degrees-C up to about T(g) + 185-degrees-C. The experimental results are discussed in terms of the classical WLF (Williams-Landel-Ferry) and Arrhenius models. There are clear indications that the WLF approach holds over the entire temperature range investigated. This is rather unusual as the Arrhenius behaviour is reported to be the correct one for temperatures above approximately T(g) + 100-degrees-C. The most critical factor in our case seems to be the restricted number of bonds with rotational degree of freedom in the polycarbonate unit. The reduced number of virtual bonds with respect to real ones is discussed to be a possible reason for the large temperature range in which the free volume is the rate-limiting factor for the flow process.