Analog calorimetry is used as a tool to study the interaction of polystyrene, PS, with poly(2,6-dimethyl-1,4-phenylene oxide), PPO, and with poly(1,4-phenylene oxide). Electrostatic charge calculations were used as a guide to divide polymer repeat units and analogs into groups. A mean-field binary interaction model was used to evaluate group interaction energies. The enthalpic interaction energy for the blend of PS-PPO obtained from this study is -1.35 +/- 0.19 cal/cm(3), which is in good agreement with values obtained from neutron scattering. The results indicate that electronic rearrangements between the phenyl ring and substituted methyl groups in PPO have a large influence on the interaction with polystyrene.