Abstractp‐Isopropylstyrene was homopolymerized or copolymerized with styrene using AIBN as initiator in benzene at 50°C. The resulting polymers were easily oxidized by oxygen to produce polymers having hydroperoxy groups. The oxidized polymer was found to have considerably different solubility from the original polymer. Kinetic evaluation of the oxidation reactions of poly(p‐isopropylstyrene) showed that the tertiary hydrogen of the isopropyl group present at the pendant aromatic ring was more susceptible to the oxidation reaction than the main chain methine hydrogen. The rate constants of these two oxidation reactions were found to be 4,0 · 10−4mol−1/2· l1/2· sAutoxidation reactions of polystyrene derivatives1/2and 2,5 · 10−4mol−1/2· l1/2· s−1/2, respectively. These values were much smaller than that for the tertiary hydrogen atom of the isopropyl group of cumene (3,21 · 10−3mol−1/2· l1/2· s−1/2, at 68°C), a low m