The rates and products of oxidation of styrene have been studied in the presence and absence of , '-azodiisobutyronitrile (ADEN) at 0.1 to 4 atmospheres of oxygen and at 35-85°. In the presence of initiator, the over-all rate of absorption of oxygen is proportional to [ADBN]Vi[CeHs]. In the absence of initiator, the rate is proportional to [C8H8]1,4[02]0•4. Oxygen therefore participates in the initiation of thermal oxidation, and the rate of this initiation at 50°is 38 times the rate of initiation of thermal polymerization in the absence of oxygen. The products of oxidation are polymeric peroxide, benzaldehyde and formaldehyde. The two aldehydes are formed in equivalent quantities and are primary oxidation products. The ratio of polyperoxide to aldehyde formed at 50°varies from about 17 at 760 mm. to about 1 at 25 mm., and decreases with increasing temperature. The average composition of the polyperoxide formed at 50°varies from (C8H8)i.502 at 10 mrn. pressure of oxygen to a limit of C8H802 at high pressure. The peroxide formed at 1 atmosphere and 50°closely approximates this limit and has a number-average molecular weight of 3,000-4,000. The molecular weight is controlled by an unknown chain transfer mechanism. The peroxide is a poor initiator of oxidation and polymerization. The direct formation of aldehydes is the result of some reaction of a polyperoxide radical ending in a styrene unit, probably a unimolecular reaction of this radical. An 18% conversion to polyperoxide was obtained by stirring a 0.02 M solution of ADEN in styrene at 50°f or 24 hours under an atmosphere of oxygen and precipitating the polymer with methanol.

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