The mechanism of multifunctional activity of N-1,3-dimethylbutyl-N'-phenyl quinone diimine (6QDI) has been investigated using squalene as a model substrate. It has been demonstrated that 6QDI reacts with squalene in the presence of sulfur and bound to the polymer as a paraphenylenediamine (PPD) antidegradant. The inhibitor as well as reinforcing activity is explained via experimental evidence. The size exclusion chromatography in combination with GC-Mass spectroscopy has been used to elucidate the mechanism.