WILLIAMS-LANDEL-FERRY VERSUS ARRHENIUS BEHAVIOR - POLYSTYRENE MELT VISCOELASTICITY REVISED

The dynamic melt viscoelasticity of polystyrene (PS) was carefully measured and critically revised for temperatures up to 290-degrees-C (about T(g) + 185-degrees-C). It has been found clearly that the Williams-Landel-Ferry (WLF) free-volume description is obeyed in the whole temperature range investigated here, whereas, rather surprisingly, no evidence was found for Arrhenius-like behaviour at the highest temperatures. The size of the PS jumping unit was quantitatively assessed to be about three skeletal bonds (i.e. one and a half monomer units). This size is large enough to cause the free volume to be the rate-limiting factor in such a wide temperature range.