In this brief review article some aspects of the thermodynamics of polymer mixtures are discussed

mainly based on the author's research. The studies of poly (methyl methacrylate)/chlorinated polyethylene (CPE)

poly (butyl acrylate)/CPE and CPE/CPE (different chlorine content) mixture verify the "dissimilarity" and "similarity" principles for predicting miscibility of polymer mixtures. The sign of heat of mixing of oligomeric analogues is not sufficient in predicting the miscibility. The Flory equation of state theory has been applied to simulate the phase boundaries of polymer mixtures.The empirical entropy parameter Q12 plays an important role in the calculation

this reduces the usefulness of the theory.With energy parameter X12 0 and Q12 0 the spinodals so calculated are reasonable compared to experiments.A hole model was suggested for the statistics of polymer mixtures.The new hole theory combines the features of both the Flory equation of state theory and the Sanchez lattice fluid theory and can be reduced to them under some conditions.