(4-Ethylphenyl)-3,5-ditertiarybutyl-4-hydroxybenzylamine, 1-phenyl-4-(3,5-ditertiarybutyl-4-hydroxybenzyl)piperazine, and 1-(3,5-ditertiarybutyl-4-hydroxybenzyl)piperidine were synthesized and characterized, and their performance in polypropylene copolymer (PPCP) was tested by multiple extrusions in a Brabender plasticorder. The thermooxidative stability of PPCP was assessed by the measurement of oxidative induction time at 200 +/- 1degreesC, and the thermal stability was assessed by observation of the change in the melt flow rate. A comparative study of the synthesized antioxidants with the commercially available antioxidant 2,6-ditertiarybutyl-4-methylphenol was made. The presence of phenolic and amino groups influenced the performance of the antioxiclants. The performance of the antioxidants influenced the thermal stability of the PPCP. (C) 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91:1097-1103, 2004.