It was proposed earlier that the additional exothermic peak observed a
t 350-degrees-C in differential scanning calorimetry of PAN fibre is a
ssociated with certain intermolecular cross linking, as well as to the
aromatization of structure, which results in a better stabilized stru
cture. It has been further confirmed in the present study through infr
ared spectroscopy that these reactions take place in the fibre and occ
ur only in the presence of oxygen.