(RSC Advances) New Understanding on the Reaction Pathways of the Polyacrylonitrile Copolymer Fiber Pre-Oxidation: Online Tracking by Two-Dimensional Correlation FTIR Spectroscopy
writer：Jing Zhao, Jihai Zhang, Tao Zhou,* Xifei Liu, Qiang Yuan, and Aiming Zhang
keywords：Polyacrylonitrile, pathway, two-dimensional correlation FTIR spectroscopy
source：期刊
specific source：RSC Advances, 2016, 6, 4397-4409
Issue time：2016年
Polyacrylonitrile (PAN) copolymer fiber pre-oxidation has an important influence on the final properties of carbon fibers. Understanding and tracking the reaction pathways of the pre-oxidation has a great significance for guarantee the quality of the resulting carbon fibers. In this study, the in situ FTIR spectroscopy combining the scaling moving-window two-dimensional correlation spectroscopy (scaling-MW2D) and 2D correlation analysis were used to study the reaction pathways. In addition, DSC and 13C solid-state NMR were used to assist the determination and to verify the chemical structure. Scaling-MW2D revealed that the pre-oxidation consisted of the initial process (A, 69?223 °C) and the main process (B, 223?309 °C). From the sequential order of 2D correlation analysis, the more detailed pathways were obtained. The induced reaction of comonomer units took place in process A (69?223 °C). In process B (223?309 °C), the initial cyclic structures were first generated from the induced structure formed in process A. Then, these initial cyclic structures underwent a series of the oxidation, the subsequent isomerization, and so on. After that, a large number of AN units were immediately involved in the main cyclization reaction, and some of β-amino nitriles was produced. One of new understandings obtained was that the initial cyclic structures after the oxidation, the isomerization, and so on were the real induced “nucleus” of the main cyclization reaction, and therefore, the oxygen in the air played a key role on the PAN main cyclization. The last step was the dehydrogenation reaction on the polycyclic structures at high temperature.