Carbon fiber is a kind of material with outstanding properties and low density, which has tremendous applications such as aircraft, automobile industry, and so on. Polyacrylonitrile (PAN) is generally used as precursor to produce carbon fiber. From PAN to carbon fiber, several heat treatment processes including stabilization, carbonization and graphitization are involved, among which stabilization is the most important step. By heat treatment in air at 250oC – 400oC, linear polymeric structure is believed to be converted to ladder structure, which makes it more heat resistant in order to undergo further heat treatment at even higher temperature. For the past decades, several experimental approaches including FT-IR, Raman, TGA, etc, have been applied to characterize chemical and secondary structures of stabilized PAN. However, due to experimental limitations, stabilization structures and processes are still not well-understood at the molecular level.
In our research, we developed a novel strategy to characterize PAN stabilized at various temperatures. By applying two dimensional 13C-13C and 1H-13C correlation NMR techniques combined with 13C isotopic labeling, through-bond 13C-13C correlations of stabilized PAN was successfully obtained. Improved spectral resolutions of 1D and 2D NMR data for the first time reveals intramolecular reaction pathways for PAN stabilized under air and nitrogen, respectively.