The phase behavior of blends of polystyrene (PS) and a random copolymercarboxylated poly (2
6-dimethyl - 1
4-phenylene oalde) (CPPO) with 8.0mol%carboxyl content was studied by DSC. It was found that the blends showed acoexistence of an UCST an a LCST behavior. TEM was used to study the phase morphology of blends' It was found that the phase morphology of blends at lowarmealing temperature is different from that at high annealing temperature. Themechanism of phase transformation was discussed. It was found that the phase morphology of blends at low annealing temperature is different from that at high annealing temperature.The mechanism of phase transformation was discussed.It was found that the mechanism of phase separation of blends in UCST area is different from that in LCST.