Polymeric Antioxidants. I.

Abstract

Phenolic oligomers directly linked to aromatic rings were prepared by horseradish peroxidase catalyzed oxidation of phenol derivatives by hydrogen peroxide. The phenols used were p-cresol, p-ethylphenol, p-s-butylphenol, p-t-butylphenol, p-methoxyphenol, p-nonylphenol, m-cresol, m-t-butyl-phenol, m-methoxyphenol, and 3, 4-xylenol. p-Nonylphenol and m-t-butylphenol were not polymerized by oxidation. Number-average molecular weights (Mn) of para alkyl substituted phenolic oligomers were about 800 and bulky substituted groups prevented decrease in the number of hydroxyl groups during polymerization. Mn of p-methoxyphenol oligomer was almost 1700. Meta substituted oligomers had lower Mn and a greater number of remaining hydroxyl groups (D.R.H.) than the corresponding para substituted phenol oligomers. Antioxidant effects of the phenolic oligomers on the autoxidation of lard were evaluated. Improvement of this effect for lard could hardly be detected by polymerization. That of the oligomers on the autoxidation of tetralin was much more pronounced than for the corresponding monomers, except for p-methoxyphenol. Higher reactivity of phenolic oligomers toward peroxyl radicals and the formation of stable phenoxyl radicals may possibly have been the cause for this. Phenolic oligomers having higher D.R.H. exhibited the better antioxidant effect. The antioxidant effects of meta substituted oligomers were greater than those of the corresponding para substituted oligomers.