Polymerization in liquid sulfur dioxide. Part XIII. Polymerization of styrene derivatives in liquid sulfur dioxide

Abstract p‐Bromostyrene, p‐methylstyrene and α‐methylstyrene were subjected to polymerization in liquid sulfur dioxide with α,α'‐azobisisobutyronitrile as an initiator at polymerization temperatures of 0–60°C. In case of polymerization of p‐bromostyrene, only polysulfones of 1:2 molar ratio between sulfur dioxide and p‐bromostyrene were obtained. No cationic polymerization was observed. In case of polymerization of p‐methylstyrene polysulfone having 1:2 composition, a radical polymerization product, as well as poly‐p‐methylstyrene, a cationic polymerization product, as obtained, revealing concurrent and competitive occurrence of both polymerizations. The cationic polymerization was explained as the result of the electron‐donating property of the para‐methyl substituent and the catalytic action of sulfur dioxide or sulfurous acid formed with a minute amount of water contained in liquid sulfur dioxide. In liquid sulfur dioxide, the cationic polymerization was perfectly inhibited by DMF and the radical polymerization was not affected by the presence of DMF. In a system in which the radical polymerization alone proceeded in liquid sulfur dioxide, the overall rate of the polymerization was proportional to the concentration of AIBN in the order of 0.7. This was interpreted to indicate that the strong solvation between sulfur dioxide and the terminal radical of the growing radical due to hyperconjugation of the p‐methyl group may stabilize the terminal radical, leading to a unimolecular termination. In the polymerization of α‐methylstyrene, the addition of AIBN did not give polysulfone, but gave poly‐α‐methylstyrene alone as a result of cationic polymerization.