Investigation of the Cyclization Mechanism of Poly(acrylonitrile-<i>co</i>-ethylenesulfonic acid) Copolymer during Thermal Oxidative Stabilization by <i>In Situ</i> Infrared Spectroscopy
Zhipeng He, Huichao Liu, Shuo Zhang, Jinglong Yang, Chi Jiang, Muwei Ji, Jiali Yu, Mingliang Wang, Caizhen Zhu, Jian Xu
Abstract
Cyclization reaction is a crucial step during the heat treatment process of polyacrylonitrile (PAN)-based carbon fibers (CFs). In this work, in situ infrared spectroscopy and two-dimensional (2D) correlation spectroscopy are employed for the investigation of the cyclization mechanisms of PAN and poly(acrylonitrile-co-ethylenesulfonic acid) [P(AN-co-ESA)] copolymer during different temperature treatments under air atmosphere. The cyclization reaction of PAN was promoted by an acknowledged free radical mechanism. The cyclization reaction of P(AN-co-ESA) copolymer was promoted by an autocatalytic cyclization mechanism. A key step during this process was that the association structures generated by the interaction of hydrogen bond under heat treatment and the bond of S═O change before the cyclization structures composed of C═C and C═N bonds. The new insight about the cyclization mechanism of P(AN-co-ESA) copolymer was verified by Fourier transform infrared spectroscopy and 2D correlation analysis. It is useful for further studies of the comonomer in PAN copolymers as a precursor of CFs.