The energy of activation is expected to be related to the latent heat of vaporization of the liquid, since the removal of a molecule from the surroundings of its neighbor forms a part of both processes. Such a relationship is indeed found and is taken as evidence that the particle that moves from site to site is probably a single molecule.
As chain length is increased in a homologous series of liquid up to a polymer range, the activation energy of flow does not increase proportionally with the heat of vaporization but levels off at a value which is independent of molecular size (the size of the chain).
It means that in long chain, the unit of flow is considerably smaller that the complete molecule.
It may be a segment of molecule that may contain 5-50 C-atoms.
Viscous flow occurs by successive jumps of the segments untill the whole chain is shifted.
But mind that, the chain segments of viscous flow are not necessarily the Same as the chain segment of high elasticity. The size of network segment is however larger than that of viscous Segment.