The name is absent

models, the polymer segments are allowed to vibrate around their equilibrium po-
sition, and the partition function of the polymer chain is written in terms of its
degrees of freedom. Prigogine [19] introduced an empirical c factor corresponding
to the degrees of freedom of the polymer chain. Using Prigogine-Flory cell theory,
Patterson [12] was able to explain the LCST type phase behavior in polymer systems.
However, an important issue regarding the individual roles of ‘excluded volume’ and
‘attractive’ interactions on these systems, remained unanswered. The perturbed hard
chain theory (PHCT) of Prausnitz and co-workers is also based Prigogine’s partition
function [20, 21]. Although, it has been successful in describing LCSTs in polyethylene
solutions in hydrocarbons [22], PHCT is not widely applied due to its great sensi-
tivity to the empirical c factor. The lattice hole approach was followed by Sanchez
and Lacombe [23, 24] in which the mixing-volume effects are incorporated via vacant
lattice sites. Thus, the description of polymer solutions with the Sanchez-Lacombe
equation of state can lead to both LCST and UCST behavior depending upon the
intermolecular interactions [25].

Continuum statistical mechanics models provide an effective route to include the
compressibility effects in the description of the phase behavior of polymer systems.
These equations of state (EOS) separate out the effects of ‘excluded volume’ and ‘at-
tractive’ interactions, which help understand the effects of each of them on the phase
behavior, individually. But the most important feature of these continuum models is
the accurate definition of density. In lattice models, the definition of density is rather

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