On the mechanism of ozone degradation of SBR

The reaction mechanism of the ozone attack of SBR copolymers was studied to obtain information for use in the development of elastomeric materials having improved resistance to deterioration in service. Techniques of ultracentrifugation and viscometry were utilized to follow molecular changes induced by ozone. Chemical changes were investigated by measuring variations in active oxygen group concentration. Results suggest that the autocatalytic degradation of uninhibited SBR was initiated by a random ozone attack at a double bond on the unozonized chain, producing an ozonide which decomposed spontaneously, forming small segments with activated chain‐ends. This primary reaction, in the presence of oxygen, activated an α‐methylenic chain cleavage process which was terminated when the molecules were degraded to a limiting size, where no more R. radicals were formed from α‐methylenic groups. The reaction was also terminated when oxygen was removed from the system.