Stabilization of Atactic-Polyacrylonitrile under Nitrogen and Air As Studied by Solid-State NMR

Abstract

Solid-state (ss) NMR spectroscopy was applied to study the stabilization process of 30 wt % 13C-labeled atactic-polyacrylonitrile (a-PAN) heat-treated at various temperatures (Ts) under nitrogen and air. Direct polarization magic-angle spinning (DP/MAS) 13C NMR spectra provided quantitative information about the functional groups of stabilized a-PAN. Two dimensional (2D) refocused 13C–13C INADEQUATE and 1H–13C HETCOR NMR spectra gave through-bond and through-space correlations, respectively, of the complex intermediates and final structures of a-PAN stabilized at different Ts values. By comparing 1D and 2D NMR spectra, it was revealed that the stabilization process of a-PAN under nitrogen is initiated via cyclization, while the stabilization under air proceeds via dehydrogenation. Different initial processes lead to the isolated aromatic ring and ladder formation of the aromatic rings under nitrogen and air, respectively. Side reactions and intermediate structures are also discussed in detail. Through thi...