This paper discusses synthesis of novel antioxidant group from esterification of 3,5-di-tert-butyl-4-hydroxybenzoic acid and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid with unsaturated fatty alcohols. Esters were effectively synthesized and characterized using FTIR and NMR spectroscopy. The antioxidant activity was evaluated both in blending and radical grafting processes. Esters of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid showed significantly longer oxidation induction time than polymer samples stabilized with commercial antioxidant. Further, the effect of chain length and phenolic group were investigated on efficiency of antioxidants. The results of radical grafting reaction revealed that synthesized antioxidants were successfully grafted onto polymer chains and the phenolic moiety was functional after extraction process, while pure and commercially stabilized samples were degraded instantaneously. Also, different initiator systems were utilized to enhance the extent of grafting. Among MEK, DCP and DHBP peroxides, DHBP could be more effective in increasing the antioxidant grafted onto polymer. In addition, possibility of rising in graft content was investigated in presence of redox initiator. Findings suggest that these stabilizers could be used in radical grafting process to prolong the thermal stability of polymers. Keywords: unsaturated ester, sterically hindered phenol, antioxidant, radical grafting, polyolefin elastomer