Thermal and mechanical degradation of natural rubber (NR) mixed with N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), polymerized 1,2-dihydro-2,2,4-trimethyl-quinoline (TMQ), and 50/50 weight basis mixture under high temperature and shearing conditions were investigated using a moving die processability test and FTIR spectroscopy. Relationship between dynamic properties in terms of tan 8 value and chemical changes of NR molecules during degradation were correlated. The results indicated that the NR mixed with antioxidants caused decreased level of chain scission and oxidative degradation. The 6PPD provided better protection of NR against degradation at elevated temperature than TMQ. Furthermore, it was found that a prolonged mixing time caused more pronounced oxidative degradation on NR molecules than increased mixing temperature. The antioxidative capability of those antioxidants on NR was ordered based on their effectiveness as follows: 6PPD > 6PPD mixed with TMQ > TMQ. It was also found that the moving die processability test and FTIR spectroscopy are efficient routes to estimate the oxidative degradation of NR molecules. Therefore, the techniques could be applied to assess or compare antioxidative capability of various types and amounts of antioxidants used in the rubber formulation within a reasonable testing time. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 1702-1709, 2010