Structure evolution mechanism of poly(acrylonitrile/itaconic acid/acrylamide) during thermal oxidative stabilization process

Polyacrylonitrile (PAN) polymers with different compositions were prepared by an efficient aqueous free-radical polymerization technique. Thermal properties of polyacrylonitrile homopolymer (PAN), poly(acrylonitrile/itaconic acid) [P(AN/IA)] and poly(acrylonitrile/itaconic acid/acrylamide) [P(AN/IA/AM)] were studied by Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry and thermogravimetry in detail. It was found that AM had the ability to initiate and accelerate thermal oxidative stabilization process, which was confirmed by the lower initiation temperature and broader exothermic peak in P(AN/IA/AM) as compared with that in P(AN/IA) and PAN. The intensity of heat releasing during the thermal treatment was relaxed due to the presence of two separated exothermic peaks. Accompanied by DSC analysis and calculation of the apparent activation energy of cyclization reaction, two peaks were assigned to the ionic and free radical induction mechanisms, respectively. The higher rate constant in P(AN/IA/AM) indicated that the ionic mechanism actually had a kinetic advantage at promoting thermal stability over the free radical mechanism. This study clearly show that the synthesized P(AN/IA/AM) terpolymers possess larger room to adjust manufacture parameters to fabricate high performance of PAN-based carbon fibers.