Microstructural analysis and cis–trans isomerization of BR and SBR vulcanizates reinforced with silica and carbon black using NMR and IR

Abstract

SBR is composed of styrene, 1,2-unit, cis-1,4-unit, and trans-1,4-unit. Rubber chains were extracted from cured butadiene rubber (BR) and styrene-butadiene rubbers (SBRs) reinforced with silica and carbon black using o-dichlorobenzene, followed by coagulation to analyze their microstructures by nuclear magnetic resonance spectroscopy (NMR) and infrared spectroscopy (IR). Microstructures of the raw and cured samples were compared and their differences were discussed. The styrene contents of cured samples were greater than those of the raw samples because of a pendent group formed by a cure accelerator. The trans-1,4-unit contents of the cured samples were greater than those of the raw samples; whereas for the samples with high trans-1,4-unit content, the cis-1,4-units of cured samples were greater than those of the raw samples. This is because of cis–trans conversion, which is more favorable than the trans-to-cis conversion. By increasing the curatives content, the cis–trans conversion is activated. The 1,2-unit contents of cured samples were lower than those of the raw samples. The merits and demerits of the microstructural analyses using NMR and IR were also compared.