Thus, polymer blends that are homogenous down to the molecular level, associated with a
negative value of the free energy of mixing and having a domain size comparable to the
domain size of the macromolecular statistical segment, can be considered as a miscible
polymer blend. The major factors that influence polymer miscibility are combinatorial
entropy of mixing, interaction energy, free volume, and specific interactions such as
hydrogen bonding [6]. For nonpolar polymer blends (ignoring the free volume term and
specific interactions term) the blend miscibility can be calculated by the FloryHuggins
equation: