The mechanism of thermal stabilization of polyacrylonitrile

Szepcsik, Balázs and Pukánszky, Béla (2019) The mechanism of thermal stabilization of polyacrylonitrile. THERMOCHIMICA ACTA, 671. pp. 200-208. ISSN 0040-6031

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Abstract

The two-step stabilization of a thoroughly characterized PAN homopolymer was studied by various methods including thermogravimetric analysis (TGA), evolved gas analysis (EGA), differential scanning calorimetry (DSC), Fourier transformed infrared spectroscopy (FTIR), oxygen microanalysis and theoretical energy calculations. Stabilization was carried out with pre-treatment in inert atmosphere, and the reactions taking place as well as the structure of the polymer formed were compared to those occurring in one-step (direct) oxidation. Five separate exothermic regions were detected in DSC measurements and they were assigned to seven reaction steps, for which appropriate mechanisms were proposed together with the relationship among individual reactions. The effect of stereoregularity on ring formation is discussed and a new scheme is suggested, which includes the cyclization of alternating nitrile groups in the gauche conformation. The number of successive rings formed during cyclization is determined with three independent methods and compared to previous concepts reported in the literature. The positive effect of pre-treatment in inert atmosphere on the structural stability of PAN during the subsequent pre-carbonization treatment is also demonstrated and explained by considering the mechanism of the reactions taking place during the process.

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