Sulfur‐containing azoinitiators and their properties

The thermolysis and photolysis of arylazosulfonates (1–3) and of arylazo phenyl sulfones (4–6) was studied. Compounds 1 to 3 are soluble in water. They are thermally stable up to 200°C; however, if they are irradiated with the light of a mercury-xenon high-pressure lamp, they decompose at room temperature. Their photolysis was studied either in water or in ethanol as solvent. For the photolysis in water an ionic mechanism of decomposition is suggested, while the results of the photolysis in ethanol can be explained on the basis of a competition of a radical with an ionic mechanism. Compounds 4 to 6 are thermally and photochemically instable. The thermal decomposition of 5 was studied in detail and found to be comparable to that of AIBN. Its decomposition follows first-order kinetics. The photolysis of 4–6 was carried out in ethanol or chloroform. The mechanism of photolysis depends on the solvent polarity. 5 was successfully used as initiator for the polymerization of methyl methacrylate.