No abstract

Antioxidant properties of technical-grade mixtures containing 4, 6-methyl-substituted derivatives of isobornylphenol were studied. The antioxidant activity of samples was characterized by the inhibition rate constant k In . The effect of isobornylphenol on the kinetics of inhibition of the thermooxidative dehydrochlorination of poly(vinyl chloride) plasticized with dioctyl phthalate was examined.Isobornylphenols constitute a promising class of stabilizers primarily used to preclude oxidative transformations in medicinal materials, food packages, baby toys because of their low toxicity and high thermal stability. Therefore, studies of quantitative characteristics of the effi ciency of antioxidants are necessary for prediction of their application prospects [1][2][3][4][5][6][7].The goal of our study was to quantitatively examine the antioxidant activity of technical-grade mixtures based on 4, 6-substituted isobornylphenol derivatives and their effect on the thermooxidative destruction of poly(vinyl chloride). EXPERIMENTALThe chemical composition of terpene phenol (TP) samples and UV spectroscopic data obtained in 1,4-dioxane are listed in Table 1. It is known that TP1, TP2, TP4, and TP5 samples are technical-grade mixtures of dialkylated isobornylphenols, whereas sample TP3 is 99% pure [6]. All the samples are characterized by IR, UV, 1 H and 13 C NMR spectra [6].We studied the antioxidant activity (AOA) of TP1-TP5 mixtures of isobornylphenol in a model reaction of initiated oxidation of 1.4-dioxane by the method of kinetic photometry, as judged from the variation with time of the concentration of the antioxidants under study at a temperature of 348 K [2,8]. Azobisisobutyronitrile (AIBN) served to initiate the oxidation process [2].Experiments in which the AOA was studied were performed at an initiation rate V i = 2 × 10 -7 M s -1 in a thermostated cuvette placed in the cuvette compartment of a Shimadzu UV-2401 PC spectrophotometer. Kinetic curves of substance consumption were recorded by measuring the decrease in the optical density at the maximum absorption at λ max (nm) of 282 for TP1, 274 for TP2, 283 for TP3, 283 for TP4, and 289 for TP5. The numerical values of the consumption rate V in for compounds TP1-TP5 were calculated by the leastsquares method from the initial portion of the kinetic curve describing the consumption of the samples under study. 1,4-Dioxane was preliminarily purifi ed by the standard procedure [9]. The initiation rate V i was calculated by the equation V i = k i [AIBN], where k i is the initiation rate constant (s -1 ). When calculating the initiation rate, we assumed that k i = 2ek d , where k d is the rate constant of AIBN decomposition, and e is the probability of exit of radicals into the bulk. Calculations of k i were made