Structural Identification of Polyacrylonitrile during Thermal Treatment by Selective 13 C Labeling and Solid-State 13 C NMR Spectroscopy

作者：Yusong Wang, Lianghua Xu, Mozhen Wang, Wenmin Pang, Xuewu Ge · 发表于：Macromolecules · 年份：2014 · DOI：10.1021/ma500727n · 被引用次数：82 · 研究领域：Fiber-reinforced polymer composites、Advancements in Battery Materials、Graphene research and applications

Four kinds of 13 C-labeled polyacrylonitrile (PAN) samples were prepared respectively by solution polymerization of acrylonitrile (AN) with selective 13 C labeling of different molecular sites. The composition and structure of the residues from the thermal treatment of PAN in argon at 250 and 350 °C were quantitatively analyzed in detail by one- and two-dimensional solid-state 13 C nuclear magnetic resonance (ssNMR) experiments. Compared with the NMR spectrum of each labeled carbon in AN monomer unit, nine chemical structures created during the heat treatment process have been identified accurately. On this basis, four reaction routes were proposed. It is noted that the main chemical change for PAN started from a cyclization reaction at a relatively low temperature, then experienced an aromazation reaction to form a molecular chain basically composed of isolated pyridine units, instead of the commonly reported ladder structure. This work also shows that the combination of selectively 13 C-labeled technique and a high spinning speed of 20 kHz in magic-angle spinning (MAS) NMR experiment could improve the detection sensitivity to nearly 2 orders of magnitude, and provide a clear ssNMR spectra with little peak overlaps, which will be helpful to discover the complex reaction mechanism in the manufacture of carbon fibers with high performance.