Effect of controlled tacticity of polyacrylonitrile (co)polymers on their thermal oxidative stabilization behaviors and the properties of resulting carbon films

Due to the spatial alignment of the nitrile groups and their involvement in the cyclization reactions during thermal oxidative stabilization (TOS) procedures, stereoregularity of polyacrylonitrile (PAN) precursors is one of the most important structural parameters to afford carbon materials. To elucidate this, PAN and poly(acrylonitrile-co-itaconic acid) with higher degree of isotacticity were prepared through template-assisted free-radical polymerization in the presence of MgCl2. Fourier-transform infrared spectroscopy was employed to quantitatively track the structural evolutions of the PAN (co)polymer precursors during their TOS procedures. The improved TOS efficiencies of the precursors were evidenced by high extents of cyclization, high concentrations of cyclized rings and enhanced oxygen uptakes of the isotactic PAN (co)polymers during the TOS procedures. The isotactic PAN (co)polymer precursors also exhibited relatively large heat evolutions with broad exothermic curves in differential scanning calorimetry observations, further suggesting efficient TOS procedures with safer processing conditions. The efficient TOS procedures of the isotactic PAN (co)polymer precursors resulted in carbon materials with high degrees of crystallinity and high amounts of sp2 clusters, affording much improved electrical conductivities. This study provided knowledge on the structural characteristics of the precursors for carbon materials with pre-designed properties, which is critical for their success in high-end applications.