The phase behavior of blends of styrene/maleic anhydride copolymers (SMA) with styrene/methyl methacrylate copolymers (SMMA), styrene/acrylonitrile copolymers (SAN), tetramethyl bisphenol-A polycarbonate (TMPC), and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) have been determined. Tentative binary interaction energies were evaluated from mapping the copolymer composition miscibility boundaries using the Flory-Huggins theory combined with the binary interaction model. Data on phase-separation temperatures were too sparse for these systems to obtain refined estimates using the Sanchez-Lacombe theory. A negative interaction energy was obtained for the MA/AN pair; however, the MA unit showed strong repulsive interactions with all other monomer units examined here.