The glow curve obtained upon processing acrylonitrile-butadiene-styrene copolymers (ABS), through various machines, reaches a peak at 180°C. The proper assignment of that peak has required the study of the chemiluminescence (CL) shown by related polymers such as: polybutadiene (PB), styrene-acrylonitrile copolymer (SAN), and polyacrylonitrile (PAN). Three hydroperoxide types associated with the structural units, that is, 1, 2, and cis-and trans-1,4, exhibiting CL peaks at 180, 240, and 340°C, respectively, have been identified in the P B sample. The activation energy ( E , ) , recorded for the hydroperoxides thermal decomposition, was 15.0 2 1.0, 17.85 f 0.9, 20.7 f 0.8 kcal/mol. PAN shows a CL peak at 180°C. Its occurance is related to the color developed during the thermal treatment. That PAN peak has been attributed to the hydroperoxides generated on the acrylonitrile units neighboring the azomethinic structures. The corresponding E, is 23.3 f 1.0 kcall mol. The same peak (having an identical position and E,) has been identified with processed ABS and SAN copolymers. As is evident by CL studies, the processing induced oxidation mainly occurs within the SAN phase of the ABS copolymers, though it was also noted within 1,2 units of the P B phase.