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. [ABSTRACT FROM AUTHOR]