AbstractA radical mechanism is proposed for the formation of the 1,2‐polymer2in the “spontaneous” polymerization of 4‐vinylpyridinium salts 4‐VP.HX (X=NO3, ClO4, HSO4, I) in aqueous solution on the basis of strong inhibition by oxygen and other radical inhibitors.Quantitative investigation of the influence of oxygen on the formation of the 1,2‐polymer allowed the derivation of a formal kinetic scheme for the initiation and polymerization steps which is consistent with a free radical mechanism. Dependence of the average molecular weight of2on monomer concentration is in agreement with this model. Dependence of the inhibition time on the oxygen concentration as well as an acceleration of the final polymerization rate by prolonged treatment of the monomer solution with oxygen suggests the transitory involvement of polymeri