The grafting of ADPEA onto natural rubber was executed with UV radiation. Benzoyl peroxide was used to initiate the free-radical grafting copolymerization. Natural rubber-graft-N-(4-aminodiphenylether) acrylamide (NR-g-ADPEA) was characterized with an IR technique. The paper aims interested to determine the crosslinking density by using the ultrasonic technique. The ultrasonic velocities of both longitudinal and shear waves were measured in thermoplastic discs of NBR vulcanizates as a function of aging time. Ultrasonic velocity measurements were taken at 2？MHz ultrasonic frequency using the pulse echo method. We studied the effect of aging on the mechanical properties, crosslinking density, and the swelling and extraction phenomena for acrylonitrile-butadiene copolymer (NBR) vulcanizates, which contained the prepared NR-g-ADPEA and a commercial antioxidant, N-isopropyl- -phenyl-p-phenylenediamine. The prepared antioxidant enhanced both the mechanical properties of the NBR vulcanizates and the permanence of the ingredients in these vulcanizates. 1. Introduction Recently attempts have been made to study the ultrasonic velocity and attenuation of polymers. When propagated in polymeric materials, acoustic waves are influenced by the polymer’s structure and by molecular relaxation processes. It is possible to estimate the viscoelastic properties of polymeric materials from the velocity and attenuation of longitudinal or shear waves. Furthermore, ultrasonic methods have been successfully used to monitor polymer processing, chemical reactions, film formation from aqueous polymer dispersions, glue processes, crosslinking density, and crystallization in polymers. Many industrial polymer products are exposed to various types of degradation by the subjection of polymer products to heat, various kinds of radiation, and mechanical stresses. Main-chain scission takes place, so their mechanical properties worsen. These degradation processes are considerably accelerated in the presence of oxygen. Degradation processes of polymers are influenced by the addition of various kinds of stabilizers, which should lower the rate of degradation via reactions with various radicals formed by polymer main-chain scission, isomerization, and free-radical transfer, as indicated by an inhibition of the oxidative degradation. The reaction of a peroxy radical with an inhibitor plays the main role in the retardation of polymer oxidation by antioxidants. The activity of antioxidants depends not only on their ability to trap peroxy and hydroperoxy radicals and the catalytic action in
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