Study on the multiple cyclization reactions and the formed structures in poly(acrylonitrile‐co‐itaconic acid) copolymers during thermal treatment

Abstract

The present work provided some in‐depth understanding on the role of itaconic acid (IA) in the structural evolution of poly(acrylonitrile‐co‐itaconic acid) (PAI) polymers and the formed cyclic structures during thermal treatment. As the increasing content of IA, the cyclization initiated by the ionic mechanism increased with the less β‐amino nitrile formed and the higher extent of cyclization. The IA comonomer initiated multiple cyclization reactions, namely, the first ionic cyclization and the second ionic cyclization, by the jump transportation of activation species between different PAI chains during thermal treatment. The times of the jump transportation of activation species was about two or three at 250°C. The presence of IA comonomer promoted the formation of long sequence cyclic structures rather than isolated cyclic structure under non‐oxidative condition. The thermal stability of PAI was improved by the more and better cyclic structures and the crosslinking structures caused by the jump transportation of activation species, which reasonably resulted in a better graphitic lattice during the carbonization. Copyright © 2017 John Wiley & Sons, Ltd.

Detailed Cyclization Pathways Identification of Polyacrylonitrile and Poly(acrylonitrile-co-itaconic acid) by in Situ FTIR and Two-Dimensional Correlation analysis

“…Although the activity species of the ionic mechanism could jumped between different chains, such a large ratio of AN/IA will result in a very large value of the length of the formed cyclic structures. In our previous report, the jump times of activity species of the ionic mechanism is about three times between different chains . Based on this fact, the length of the cyclic structures formed by the ionic mechanism was calculated to be ca.…”

“…In our previous report, the jump times of activity species of the ionic mechanism is about three times between different chains. 58 Based on this fact, the length of the cyclic structures formed by the ionic mechanism was calculated to be ca. eight repeated six-membered rings.…”

Effects of oxygen on the structural evolution of polyacrylonitrile fibers during rapid thermal treatment

“…The chemical reactions involved in the stabilization of PAN bers are generally exothermic. 32 The above effects of oxygen on the evolution of the chemical and physical structures of PAN bers during the rapid thermal stabilization can be further investigated by their exothermic reaction behavior. The DSC curves of stabilized bers are shown in Fig.…”

Investigation of the Cyclization Mechanism of Poly(acrylonitrile-co-ethylenesulfonic acid) Copolymer during Thermal Oxidative Stabilization by In Situ Infrared Spectroscopy

“…Polyacrylonitrile (PAN)-based carbon fibers (CFs) have excellently comprehensive performance, such as anticorrosion and heat resistance, light weight, and ultrahigh tensile and Young’s moduli, − which arouse researchers’ attention in aerospace, architecture, vehicles, chemical equipment, sports products, and other fields. − The following processes including thermal oxidative stabilization (TOS), carbonization, and graphitization are used to prepare high-performance PAN-based CFs. ,,− During the TOS process, the linear PAN molecular chains are transformed into a thermostable and heteroaromatic cyclic structure by cyclization, dehydrogenation, and oxidation. , It has been generally accepted that the TOS process largely lies in the thermal treatment parameters, such as temperature, atmosphere, and time . Hence, to prepare ultra-high-performance PAN-based CFs, it is extremely important to comprehensively understand the cyclization mechanism during the process of TOS.…”