Partially stereoregular poly(propylene oxide) (PPO), samples synthesized by the Pruitt-Baggett Catalyst (PBC) were fractionated at 25CEC and 50°C from acetone by adding small portions of water. At 25°C mainly solid-liquid phase separations took place. On the other hand, at 50°C, liquid-liquid phase separations were observed. Thus, it was possible to fractionate PPO on the basis of molecular weight. From the molecular weight measurements, it was concluded that 1 molecule of high PPO was formed for less than 10 Fe atoms.