Monomeric antioxidants are widely used as effective antioxidants to protect polymers against thermal oxidation. Low molecular weight antioxidants are easily lost from polymer through migration, evaporation, and extraction. Physical loss of antioxidants is considered to be major concern in the environmental issues and safety regulation as well as long life time of polymers. The grafting copolymerization of natural rubber and o-aminophenol was carried out by using two-roll mill machine. The prepared natural rubber-graft-o-Aminophenol, NR-graft-o-AP, was analysed by using Infrared and 1 -NMR Spectroscopy techniques. The thermal stability, mechanical properties, and ultrasonic attenuation coefficient were evaluated for NBR vulcanizates containing the commercial antioxidant, N-phenyl- -naphthylamine (PBN), the prepared grafted antioxidant, NR-graft-o-AP, and the control vulcanizate. Results of the thermal stability showed that the prepared NR-graft-o-AP can protect NBR vulcanizate against thermal treatment much better than the commercial antioxidant, PBN, and control mix, respectively. The prepared grafted antioxidant improves the mechanical properties of NBR vulcanizate. 1. Introduction Polyolefin is one of the most widely used polymers and more susceptible to the oxidation. It well known that oxidation reactions increase at elevated temperatures during the processing of the polymer. All polymers will degrade when exposed to certain environmental conditions such as high temperatures, mechanical shear, and high-energy radiation (e.g., UV exposure). The presence of oxygen will often accelerate this degradation. The first step in the degradation process is usually the loss of hydrogen atom from the polymer chain due to this energy input. This polymer “free radical", [ ], can then react with an oxygen ( ) molecule to form peroxy radical [ ] which will in turn abstract hydrogen atom from another polymer chain to form hydroperoxide [ROOH]. The hydroperoxide can split into two new free radicals, [ ] + [ ], which continue to propagate the reaction to other polymer molecules. For certain polymers, such as acrylonitrile-butadiene copolymer, a polymer chain containing free radical is likely to split into two smaller chains [1–3]. One way to interrupt this process is to incorporate an antioxidant into the acrylonitrile-butadiene copolymer. There are different types of antioxidants that interrupt the degradation cycle: primary antioxidants, secondary antioxidants, multifunctional antioxidants, hydroxylamines, carbon-centered radical scavengers, and grafted antioxidants.
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