Ferromagnetic-like Shift Observed in the Electron Magnetic Resonance of Porous Carbon Structures Prepared Using Low-temperature Isothermal Annealing of a Polyhydroxyamide Derivative

A poly(o-hydroxyamide) with oligo(oxy ethylene) pendants was synthesized to enhance its organic solubility and processibility. Isothermal annealing at 290 ˚C was then applied to the polymer films to remove the aliphatic chain groups at the 2 and the 5 position of the phenylene ring. Electron magnetic resonance (EMR) spectroscopy revealed a triplet-like EMR signal at g ∼ 2, reflecting the hyperfine structure caused by nitrogen nuclei in the pristine polymer. However, this triplet-like EMR signal transformed to a doublet EMR line shape after commencement of isothermal annealing. As the isothermal annealing time was increased further, the intensity of the EMR peaks at g ∼ 2 was relatively constant for up to 4 hours. Above 6 hours, the EMR peaks at g ∼ 2 split into two peaks, one at g ∼ 2 (3300 G) and the other at g ∼ 2.4 (3000 G). The intensity of these peaks increased in parallel. In particular, the EMR line of g ∼ 2.4 shifted to a lower magnetic field with decreasing temperature, which was interpreted as a typical ferromagnetic-like behavior. This anomalous phenomenon was explained by the formation of porous graphitic carbon structures, which was attributed to the ejection of gaseous components caused by thermal decomposition of the aliphatic chain groups. These porous graphitic carbon structures were confirmed by using Raman spectroscopy and scanning electron microscopy (SEM).