Partially stereoregular poly(propylene oxide) (PPO) samples synthesized by Pruitt–Baggett catalyst (PBC) were dissolved in benzene, and Fe in the polymer was extracted with acidic aqueous solutions. The Fe in the polymer could be extracted gradually with 3 M HCl, but it could not be extracted with water and dilute HCl solutions. The Fe in the aqueous solutions was determined by ICP-AES (inductively coupled plasma–atomic emission spectrometry). It has been found that increasing the Fe in the aqueous solutions decreases the molecular weights of polymer samples.