AbstractPolymer blends can be either composed of mixtures of flexible components, of a stiff chain and a flexible macromolecule, or of two stiff‐chain polymers. All three cases may be dealt with in terms of the Flory lattice model. Special attention is paid to the influence of liquid crystalline order on the miscibility of the two polymers. For isotropic mixtures all three cases may be described in terms of the usual Flory–Huggins approximation. If a nematic phase is formed the miscibility of blends of rigid rods with flexible macromolecules (molecular composites) is strongly reduced because of entropic reasons. Highly ordered mixture of two stiff‐chain polymers in melt can be described in terms of the regular solution theory leading to the same miscibility criterion as is valid for two flexible polymers. All deductions are compared to recent experimental
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