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.

Analytical considerations for determination of the microstructures of sulfur‐cured solution styrene − butadiene rubbers

“…The principal peaks related to the hydrogens bonded to the carbon − carbon double bond (C = C) are marked in the H NMR spectra. Three regions of 4.3 − 5.0 (1,2‐unit, H 2 C = C∼), 5.0 − 6.1 (∼C H = C H ∼ of 1,4‐unit and ∼ C = C H ∼ of 1,2‐unit) and 6.1 − 7.7 ppm (aromatic hydrogens of styrene and CHCl 3 ) were integrated for determination of the 1,2‐unit, 1,4‐unit and styrene contents . The peaks at 0.5 − 3.0 ppm correspond to hydrogens of saturated hydrocarbons such as ∼ CH 3 , ∼CH 2 ∼ and ∼ CH∼.…”

“…Figure shows the IR spectra of the raw and cured S‐SBR10 as representative. The peaks at 699, 724, 911 and 967 cm −1 were assigned to the styrene, cis ‐1,4‐unit, 1,2‐unit and trans ‐1,4‐unit, respectively …”

“…In general, the microstructures of raw SBRs are analyzed using liquid H NMR spectroscopy and transmission Fourier transform IR spectroscopy (FTIR) . Liquid H NMR analysis gives information on the styrene, 1,2‐unit and 1,4‐unit contents, while transmission FTIR analysis gives not only the styrene and 1,2‐unit contents but also the cis ‐ and trans ‐1,4‐unit contents . Liquid H NMR analysis is performed by dissolving a rubber sample in deuterated chloroform (CDCl 3 ), while transmission FTIR analysis is carried out by casting rubber solution on a KBr window.…”

“…Liquid H NMR analysis is performed by dissolving a rubber sample in deuterated chloroform (CDCl 3 ), while transmission FTIR analysis is carried out by casting rubber solution on a KBr window. In our previous work, a cured SBR sample was analyzed and reasons for the higher styrene content of the cured SBR and for differences in the cis ‐ and trans ‐1,4‐unit contents were discussed. The difference in the microstructures of cured and raw SBRs could be explained by the formation of a pendent group by the cure accelerator and cis − trans isomerization during the vulcanization process.…”

Analytical method for determination of microstructures of solution styrene-butadiene copolymers using 2-phenylpropene/styrene ratio of pyrolysis products

“…For cured SBRs (SBR vulcanizates), however, organic materials remaining in a sample must be eliminated, and crosslinked rubber chains have to be decrosslinked and extracted for NMR analysis. Also, NMR analysis results of cured SBRs show different microstructure from the raw SBRs because of formation of pendent groups and cis-trans conversion [18]. Pyrolysis techniques such as pyrolysis-gas chromatography (Py-GC) and prolysis-gas chromatography/mass spectrometry (Py-GC/MS) are also useful techniques for polymer analysis [19e26].…”