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TitleCarbon-13 solid state nuclear magnetic resonance spectroscopy of pitch
DownloadNot digitized. Availability
AuthorAxelson, D E
SourceCanada Centre for Mineral and Energy Technology, Energy Research Program, Coal Research Laboratories, Report 86-81(CF), 1986, 160 pages, Open Access logo Open Access
PublisherEnergy, Mines and Resources Canada
Mediapaper; on-line; digital
File formatpdf
Released1986 01 01
AbstractThe carbon-13 solid state cross polarization nuclear magnetic resonance analysis of eight pitch samples is reported. In order to elucidate the conditions for quantitative analysis, various relaxation parameters were measured , including : proton rotating frame spin -lattice relaxation, cross polarization relaxation times, and the carbon:13 spin-lattice relaxation times. From a combination of chemical shift considerations and dipolar dephasing experiments, the ratio of substituted to unsubstituted aromatic carbons and average aromatic cluster size were ascertained. Apparent aromaticity values were determined from both magic angle spinning experiments and static experiments. Unlike (the only) previously reported solid state nmr pitch study, there were no substantial differences in the aromaticity values derived from static spectra and magic angle spinning spectra. The aliphatic region consists almost exclusively of methyl groups attached to aromatic rings and methylene groups (-CH - , -CH :CH bridging 2 2 2 aromatic groups. The aromatic region comprises about 92 - 99% of the commercial and experimental Domtar pitches and only about 86% of the competitive commercial product. Average aromatic cluster sizes (including possible hydroaromatic rings) are in the range of 2 - 6 for the samples studied. The most noteworthy effect of structure versus relaxation times measured occurs for the carbon-13 spin:lattice relaxation time experiments. All three commercial samples exhibited longer relaxation times than the experimental samples, the differences being about a factor of two or more. This result indicates that there is a fundamental difference in either the molecular weight distribution, the nature of the bonding between the aromatic clusters (eg, aryl-aryl versus condensed ring versus methylene bridges), or the nature of the three dimensional organization of the aromatic rings in the solid state that results in significant differences in overall aromatic molecular mobility of the experimental samples compared with the commercial products. Part of the difference may be due to the nature and amount of the free radical species present, however.

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