The copolymerization of styrene and sulphur dioxide II. The kinetics of polymerization

An apparatus has been developed for measuring the photochemical rate of uptake of sulphur dioxide by styrene solutions. A reaction vessel which permits the solution to be spread into a thin film to prevent excessive light absorption, and a capillary volume-change indicator for the gas-phase, are described. The photochemical catalyzed rate has been measured for a variety of conditions, and the various kinetic dependences are shown to be in accord with the reaction scheme postulated, which involves styrene and a 1 : 1 styrene/sulphur dioxide complex. The intensity exponent has been found to be one-half, and a rotating sector has been used for life-time determinations. Possible structures for the ‘complexyl ’ radical are examined and a likely one is shown to be that of a styryl radical with sulphur dioxide as the penultimate unit. Assuming this structure it is possible to compare velocity constants for the same type of radical with different penultimate units, and the results are examined from this point of view. The thermal reaction and uncatalyzed photo-reaction of the present system, and the behaviour of other vinyl monomers, are briefly discussed.