On the blue-colored species,possibly assignable to a radical cation,formed by the aromatic hydrocarbon–sulfur dioxide–oxygen system: The polymerization of olefins initiated by aromatic hydrocarbons–oxygen in liquid sulfur dioxide

It was found that styrene in liquid sulfur dioxide polymerizes, giving polystyrene readily and quantitatively by addition of such aromatic hydrocarbons as anthracene and trans- or cis-stilbene in the presence of oxygen, and the polymerization proceeds via a cationic process. The observations on the electronic spectra and kinetics in the system suggested that the polymerization was initiated by an electron transfer from the aromatic hydrocarbon to oxygen, followed by the formation of styrene radical cation. Supporting evidence of the radical cation is that 1,1-diphenylethylene in liquid sulfur dioxide in the presence of oxygen shows a peak at λ_max = 605 mμ and reacts to give benzophenone and 1,1,3,3-tetraphenyl-butene-1, which are eliminated by addition of a radical or cation inhibitor.