Polymerization reaction of styrene in liquid sulfur dioxide was carried out with α, α\u27 azo-bis (isobutyronitrile) as the initiator. Polymerization temperatures selected were 40°, 50°, and 60℃. The polymer thereby obtained were analyzed as styrene polysulfone but it was found that, irrespective of the polymerization temperature or polymerization rate, the polymers had a unit composition consisting of 2 moles of styrene and 1 mole of sulfur dioxide. From such an experimental fact, it was considered better to assume that a complex consisting of 2 moles of styrene and 1 mole of sulfur dioxide had formed prior to the initiation of polymerization, rather than treating this as the copolymerization of styrene and sulfur dioxide, and a kinetic treatment was made of the radical polymerization reation of this complex. As a result, the velocity of total polymerization reaction, Rp, was given as constant×[initiator]^_0[styrene+1/2SO_2]_0. Activation energy of the total reaction calculated on the basis of such hypothesis was 14.7 kcal/mole
