Study of melting and crystallization behavior of polyacrylonitrile using ultrafast differential scanning calorimetry

The thermal behavior of polyacrylonitrile (PAN) has been investigated using X-ray diffraction, differential scanning calorimetry (DSC), and ultrafast DSC. In conventional DSC, it is difficult to prevent the concurrent occurrence of the exothermic reactions of PAN with melting. However, in the ultrafast DSC curve, the exothermic peak due to these reactions disappears over the temperature range 0–400 °C at heating rates above 250 °C s⁻¹. Alternatively, the glass transition and the melting of PAN are observed over the temperature range 109–129 °C and 335–362 °C, respectively. Moreover, upon cooling from the molten state at a rate of −7500 °C s⁻¹, PAN crystallization is observed at 204 °C. These findings were observed repeatedly during heating and cooling measurements. From the extrapolation analysis, the zero-entropy-production melting temperature of PAN is found to lie in the temperature range 320–350 °C. Finally, the equilibrium melting temperature of PAN is estimated to be ca. 465 °C.