Viscoelastic mode distribution of moderately entangled linear polymers

Abstract

For monodisperse linear polymers, the steady state recoverable compliance J characterizing the terminal relaxation intensity/mode distribution is known to be (approximately) proportional to the molecular weight M in the light to moderately entangled regime, i.e., for M between the entanglement molecular weight Me and the characteristic molecular weight Mc' defined for J (Mc' = 4Me - 6Me). However, for those lightly to moderately entangled polymers, the so-called glassy relaxation and Rouse fluctuation processes have a non-negligible contribution to the complex modulus G* even in the terminal regime and thus to J. In other words, the G* and J data of those polymers do not exclusively refect the entanglement relaxation behavior of those polymers. For a test of this behavior, linear viscoelastic data were examined for entangled linear polystyrene (PS) and poly(p-tert-butyl styrene) (PtBS) in a wide range of M. The contribution of the glassy and Rouse fluctuation modes were subtracted from the G* data to evaluate the modulus Gent* exclusively refecting the entanglement relaxation. It turned out that the terminal mode distribution of Gent* and the corresponding compliance Jent were rather insensitive to M even for M < Mc' and close to those of well entangled high-M polymers, in particular for the case of PS. This result provides us with a clue for discussing the onset of entanglement. © 2010 The Society of Rheology, Japan.