Abstract
Structures of six p-phenylenediamine (PPD) antioxidants were optimized and their NMR shifts were evaluated by B3LYP calculations. The dependences of experimental values of Antioxidant Effectiveness (AEX) and Molar Antioxidant Effectiveness (AEM) in styrene-butadiene (SBR) and polyisoprene (PIR) rubber on the calculated NMR chemical shifts of nitrogens, tertiary carbons and hydrogens bonded to them were investigated by means of a multiple linear regression analysis. Based on regression parameter values, the significance of the N centers between aromatic rings (A) seems to be higher than of the N centers between aromatic rings and aliphatic chains (B) except AEM data in PIR. The extent of shielding the A center activity by the cumyl group in ortho-position was estimated. Regression parameters obtained for SBR are significantly higher than for PIR.
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