AbstractAttempts are reported to interprete quantitatively glass transition measurements for blends of poly(2,6‐dimethylphenylene oxide) (PPO) and poly(styrene‐co‐α‐methylstyrene) or poly(α‐methylstyrene). These blends are found to be miscible over the whole composition and molecular weight ranges. Furthermore, the influence of thermal annealing on the glass transition temperature is studied. It is shown that blends containing poly(α‐methylstyrene) or copolymers are in some cases very sensitive to thermal degradation. By employing FTIR spectroscopy the interactions in PPO/poly(α‐methylstyrene) b