Structure-property relationships: phenolic antioxidants with high efficacy and low color contribution

Antioxidants can be divided into two broad classes, primary and secondary, depending upon their mode of action. The most broadly used primary antioxidants are hindered phenols. Phenolic antioxidants have traditionally been based on 2,6-di-t-butyl-4-methylphenol (BHT). This functional moiety has been incorporated into larger molecules affording products with lower volatility or greater polymer compatibility. More recently, molecules have been introduced which vary in steric hindrance about the phenol and also the way in which multiple phenol functional groups are linked to form larger molecules. This has led to structures which have lower color contribution. Surprisingly, in some cases these molecules have shown higher levels of efficacy relative to other antioxidants with similar phenol/molecular weight ratios. This has included enhanced levels of synergism with secondary antioxidants. An attempt is made to correlate structural features of these molecules to the enhanced performance and/or lower color.