Molecular mechanisms of thermo-oxidative stabilization in antioxidant-modified polyisoprene: bridging DFT calculations with macroscopic performance.

contextThermo-oxidative and ozone-induced degradation of natural rubber (NR) in modified asphalt necessitates the use of robust antidegradants, yet the precise quantum-mechanical prediction mechanisms underlying their action remain largely unexplored. This study integrates macroscopic experimental characterizations with density functional theory (DFT) simulations to evaluate the competitive efficacies and thermodynamic profiles of 6PPD, TMQ, and BHT. Theoretical evaluation reveals that hydrogen atom transfer (HAT) exclusively dominates radical scavenging, where the endergonic nature of TMQ (ΔG

methodsAll quantum chemical calculations were performed using density functional theory (DFT) at the B3LYP-D3(BJ)/def2-TZVP level of theory. The ORCA 6.1.1 software package was employed for all computational modeling, conducted in the gas phase under standard conditions (298.15 K, 1 atm) with unscaled zero-point energy (ZPE) corrections applied. Intrinsic molecular reactivities were extracted via conceptual DFT (CDFT) using frontier molecular orbital (FMO) energies. Transition-state (TS) geometries were approximated using relaxed surface scans (RSS) and subsequently subjected to rigorous saddle-point optimizations (OptTS), with authenticity verified by the presence of a single imaginary frequency in harmonic vibrational analysis. Theoretical infrared (IR) spectra were simulated via analytical frequency calculations. Experimentally, formulated NR compounds (F1-F4) were prepared via a two-roll open mill and vulcanized at 150 °C. Accelerated thermal aging was conducted in an air-circulating oven at 100 °C for 72 h. Macroscopic performance was evaluated using a moving die rheometer, universal testing machine (ISO 37:2017), durometer (ASTM D2240-15), SEM-EDX, and FTIR spectroscopy to validate the theoretical paradigms.