AbstractA mill‐mastication study of an EPDM polymer (DuPont, Nordel 1070) was conducted in the mill‐roll temperature range of 68–480°F. The extent of degradation was determined by dilute‐solution viscosity measurements. The role of oxygen in the polymer mastication was followed by infrared spectroscopy. The breakdown of the EPDM polymer on the mill is minimum in the temperature range of 185–315°F. Up to 315°F. the increase in temperature leads to a decreased amount of degradation. During cold mastication mechanical breakdown occurs. The use of a free‐radical acceptor shows that this type of breakdown is caused by the mechanical rupture of CC bonds in the polymer chain. At and above 350°F. thermooxidative degradation becomes dominant, the polymer degrading drastically, and the higher the temperature, the greater the extent of degradation for the same period of mastication. Infrared spectroscopy shows that hot mastication results in decreased double‐bond concentration and increased amounts of carbonyl and, possibly, anhydride and lactone groups. Of the carbonyl groups formed 30 are due to the oxidation of double bonds in terpolymer and 70 to the oxidation of the main chain. A mechanism is proposed to account for
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