The classical representation of the Gibbs free energy of mixing for the three-component system of PS, SM, and EVA is as follows:

3] represent for PS and EVA) are approximately of the same size, the Gibbs free energy of mixing becomes:

The necessary thermodynamic condition for the miscibility of components is that the Gibbs free energy of mixing, [delta][G.

As seen from this equation, the combinatorial entropy contribution is chain length dependent and thus, for high molecular weight polymers, it does not have an important effect on the Gibbs free energy of mixing.

It must be noted that the noncombinatorial entropy contribution that has not been taken into account in Eq 1 can also affect the Gibbs free energy of mixing (9), but for polymer mixtures it has been demonstrated that the heat of mixing contribution often dominates the other contributions (10, 11).