Fourier transform infrared and wide‐angle X‐ray diffraction studies of the thermal cyclization reactions of high‐molar‐mass poly(acrylonitrile‐co‐itaconic acid)

Abstract

ABSTRACT:The stabilization reactions of a high-molarmass poly(acrylonitrile-co-itaconic acid) precursor in air at 200, 220, and 240°C were studied with Fourier transform infrared. Principally, the cyclization of nitrile groups leading to the ladder structures of tetrahydropyridine occurred. Evidence for oxidative reactions causing the conversion of the COC structure to CAC and generating groups such as OOH and CAO was also obtained. As the temperature of stabilization was increased, the rate of the reaction increased without causing great changes in the Fourier transform infrared spectral patterns. The maximum nitrile conversion achievable was limited by the temperature of stabilization. Although the reaction stagnated at 40 and 80% at 200 and 220°C, it was practically complete in about an hour at 240°C.Higher temperatures also favored the formation of extended conjugated structures. Wide-angle X-ray diffraction studies of the polymer stabilized at 300 and 400°C in argon confirmed that the aromatization index value and the crystallinity of the polymer increased proportionally to the temperature of pyrolysis. An analysis of the wide-angle X-ray diffraction pattern and the elemental composition of the stabilized polymer implied the formation of the tetrahydropyridine structure at 400°C. The higher pyrolysis temperature favored the formation of the lattice constituted by this group.

Effects of comonomer with carboxylic group on stabilization of high molecular weight polyacrylonitrile nanofibrous copolymers

“…After stabilization of the poly(AN-IA) copolymer fibers, the intensity of the main peak at 2θ = 17° nearly disappeared (data not shown). Similar observations have been reported in other studies [14]. On the other hand, poly(AN-CA) and poly(AN-IA-CA) copolymer fibers still showed weak diffraction, suggesting that the incorporated CA comonomers were able to sustain the crystal structure of the polymers.…”

“…Compared to the PAN homopolymer, the peak at 2θ = 17° in the case of the PAN copolymers was relatively weak. This indicates that there were fewer intermolecular nitrile group pairings in the PAN copolymers because of the random/irregular arrangement of the molecular chains [14]. After stabilization of the poly(AN-IA) copolymer fibers, the intensity of the main peak at 2θ = 17° nearly disappeared (data not shown).…”

“…(1) [10]. tion of a ladder structure [14]. As the stabilization proceeded, the 2245 cm -1 band of the nitrile groups decreased in intensity.…”

Simultaneous DSC/TG analysis on the thermal behavior of PAN polymers prepared by aqueous free-radical polymerization

“…The thermal stabilization conditions, including temperature, time and tension, must be optimized according to the thermal behavior of PAN polymers. The thermal behavior of PAN polymers have been investigated intensively in the last few decades [7][8][9][10][11][12][13][14][15]. However, because the thermal behavior depends closely on the nature and M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 3 content of comonomers as well as the polymerization techniques of PAN polymers [5,14,[16][17][18][19][20], there is still a lack of clarity about the thermo-chemical reactions hidden in the rear.…”

FTIR Study of the retardation effect of boric acid on the cyclization reaction of polyacrylonitrile

“…Among them, the cyclization reaction, which converts PAN into an infusible stable ladder polymer, is of most importance [7][8].…”