Controllable Synthesis and Synergistic Antioxidation Mechanism of Poly(p-methoxyphenol-phenylamine) in Biodegradable Vegetable-Based Lubricating Oils

Poly(p-methoxyphenol-phenylamine) (P(MOP-PA)), a binary copolymer of a phenol and an aromatic amine, was synthesized by liquid-phase copolymerization. The tribological properties and antioxidation behavior of the as-synthesized P(MOP-PA) in castor oil and soybean oil were investigated, and its antioxidation mechanism was discussed based on theoretical calculations. The results show that the introduction of P(MOP-PA) into the two kinds of base stocks improves their antioxidation performance at elevated temperatures and reduces friction and wear under pin-on-disk and four-ball sliding tests. In addition, the intramolecular coordination of P(MOP-PA) is responsible for the reduction in the activation energy of hydrogen atom transfer and the stabilization of nitrogen free radicals, which contributes to improving the antioxidation ability of P(MOP-PA).