AbstractThe stereoregularity of poly(methoxystyrene)s was determined from the absorption of the aromatic C1carbon assuming a first‐order Markov statistics holds for the polymerization as well as polystyrenes. The stereoregularity of poly(p‐methoxystyrene)s prepared by sodium, potassium, or rubidium cations as catalysts in THF hardly varied and syndiotactic‐rich polymers were obtained, whereas a random polymer was formed with cesium‐naphthalene. In the polymerization ofp‐methoxystyrene in toluene, syndiotactic‐rich polymers were obtained with butyllithium and random polymers were prepared by sodium or potassium cations as catalysts. The stereoregularity of poly(o‐methoxystyrene)s prepared by sodium or potassium cations in tetrahydrofuran changed with the polymerization temperatures, and highly syndiotactic polymers were formed at−78°C. The structure of poly(o‐methoxystyrene)s obtained in toluene, markedly depended on the initiators; that is, with increasing the size of the ionic radius of the counterions, the isotacticity of the polymers decreased. The mechanism of the polymerization and the substituent effect of the stereoregula