Synergistic effect of comonomers on the thermal oxidative stabilization of polyacrylonitrile copolymers for carbon materials

Abstract

Thermal oxidative stabilization (TOS) behaviors of polyacrylonitrile (PAN) (co)polymers with different comonomers, such as itaconic acid (IA), methacrylic acid (MA), methyl methacrylate (MMA), vinyl acetate (VA), and VA/IA mixture, were investigated through Fourier transform infrared spectroscopy analysis to quantitatively determine the role of the comonomers. Poly(acrylonitrile-co-MMA) exhibited slow progress of TOS, indicating general radical mediated TOS processes. Facilitated stabilization behaviors of poly(acrylonitrile-co-IA) (PAIA) and poly(acrylonitrile-co-MA) (PAMA) were observed, indicating additional ionic initiating activity of the comonomer carboxylic units. Poly(acrylonitrile-co-VA) exhibited a certain induction period, followed by an accelerated TOS in the later stage, indicating effective in situ generation of acetic acid through the degradation of vinyl acetate units during the TOS. Interestingly, the PAN-based terpolymer containing both VA and IA exhibited not only the most efficient but also the fastest progress of cyclization among the (co)polymers. The results demonstrated a synergistic combination of VA and IA in terms of TOS characteristics, likely stemming from the cascade initiation activity of the carboxylic acid groups from IA and VA. The results suggested the importance of the type and combination of comonomers as a crucial factor to control the TOS processes, providing technical information to design an optimum precursor for better carbon materials.