Synthesizing Hindered Structure Poly (p-Phenylenediamine) by Enzymatic Catalysis and Evaluating Its Antioxidation Mechanism in Biodegradable Castor Oils

In this study, poly( p- phenylenediamine) (PPDA) was synthesized by an enzymatic polymerization method using p- phenylenediamine as the monomer in the water phase. The PPDA structure was characterized by infrared (IR), gel permeation chromatography, and elemental analysis. The antioxidation behavior of the as-synthesized PPDA in biodegradable castor oil was investigated using a rotary oxygen bomb test and pressurized differential scanning calorimetry. A theoretical calculation was conducted to investigate its antioxidation mechanism. PPDA was found to exhibit excellent oxidation resistance in castor oil at 150 °C, which effectively prolonged the oxidation induction time of the oil. The results obtained herein suggest that as with phenolic antioxidants, PPDA with a hindered structure effectively improves the antioxidation performance of the oil by enhancing the stability of nitrogen free radicals.