Electron structure variations in hindered phenolic antioxidant induced enhancement of thermo-oxidative aging performance in polyamide 6

Abstract

PA6 is widely used but vulnerable to thermo-oxidative aging, impacting its durability. Hindered phenols are key antioxidants that extend the service life of PA6 by slowing this aging process. However, the effect of molecular structural differences on their antioxidant activity is still elusive, impeding their development and application. Here, two antioxidants, 2-((3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)oxy)ethyl acrylate (PEA) and 2-((3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)oxy)propyl acrylate (PPA), were utilized to enhance the thermo-oxidative aging resistance of PA6. Their primary difference is that PPA possesses an electron-donating group in its molecular structure. The methyl functional group in the PPA molecule can increase the electron cloud density around the benzene ring, resulting in PPA having a higher free radical scavenging rate compared to PEA. In addition, in contrast to PEA, the low volatility and mobility of PPA ensure that its antioxidant activity can be fully utilized during aging. These factors collectively support the excellent antioxidant activity of PPA (PPA > PEA). As a result, the PA6/PPA composite maintains 88% of its original tensile strength after 12 days of continuous aging, whereas PA6/PEA and PA6/1010 (commercial antioxidant) composites retained 70% and methyl 30%, respectively. These encouraging findings provide a theoretical basis for the synthesis of antioxidants.