This study compared the impact of the natural antioxidant caffeic acid (CAF) with the synthetic antioxidants butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) on the thermal stability of propylene/ethylene copolymer (C-PP/PE), aiming to establish a theoretical framework for advances in polymeric antioxidant compounds. Theoretical calculations revealed that CAF had the lowest value of phenolic hydroxyl bond dissociation enthalpy (BDE) (325.6 kJ·mol-1), followed by BHT (328.2 kJ·mol-1) and then BHA (341.3 kJ·mol-1). BHA exhibited the lowest transition energy (TS) (49.3 kJ·mol–1), followed by CAF (56.03 kJ·mol–1) and BHT (75.57 kJ·mol–1), indicating higher efficiency in radical scavenging. Rate constants showed that BHA had the highest hydrogen extraction rate (k = 6.09×1012 M–1 s–1), followed by CAF (k = 6.08×1012 M–1 s–1) and BHT (k = 6.03×1012 M–1 s–1). Although BHA was slightly more effective, the difference with CAF was minimal (0.00164). In experimentation, C-PP/PE with BHA had a lower melt flow index (MFI) (8.51). Samples with CAF extracts showed a gradual decrease in MFI with increasing concentration (MFI from 9.4 to 5.98 for concentrations of 0.025 to 0.125 ppm). Decomposition occurred at 340°C in samples without additives and with 0.1 ppm of BHA, while different concentrations of CAF showed delayed degradation between 380-400°C. These results support the use of natural antioxidants like CAF to enhance the thermal properties of copolymers.