  High temperature approximation (HTA) is used to describe the phase behavior
of polydisperse multi-Yukawa hard-sphere chain fluid mixtures with chain length
polydispersity. It is demonstrated that in the frames of the HTA the model
belongs to the class of ``truncatable free energy models'', i.e. the models
with thermodynamical properties (Helmholtz free energy, chemical potential and
pressure) defined by the finite number of generalized moments. Using this
property we were able to calculate the complete phase diagram (i.e., cloud and
shadow curves as well as binodals) and chain length distribution functions of
the coexisting phases.
