Abstract
Bifunctional comonomer 2-methylenesuccinamic acid (MLA) was designed and synthesized to prepare acrylonitrile copolymer P (AN-co-MLA) using mixed solvent polymerization as a carbon fiber precursor. The effect of monomer feed ratios on the structure and stabilization were characterized by elemental analysis (EA), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), X-ray diffraction (XRD), proton nuclear magnetic (1H NMR), and differential scanning calorimetry (DSC) for the P (AN-co-MLA) copolymers. The results indicated that both the conversion and molecular weight of polymerization reduce gradually when the MLA content is increased in the feed and that bifunctional comonomer MLA possesses a larger reactivity ratio than acrylonitrile (AN). P (AN-co-MLA) shows improved stabilization compared to the PAN homopolymer and poly (acrylonitrile-acrylic acid-methacrylic acid) [P (AN-AA-MA)], showing features such as lower initiation temperature, smaller cyclic activation energy, wider exothermic peak, and a larger stabilization degree, which are due to the ionic cyclization reaction initiated by MLA, confirming that the as-prepared P (AN-co-MLA) is the potential precursor for high-performance carbon fiber.
Highlights
Owing to their unique performance, such as high strength, high temperature resistance, good flexibility, and lightweight, carbon fibers are widely used in aerospace and other high-tech equipment
The nitrogen atom of the amide group can carry out a nucleophilic attack on the adjacent carbon atoms of the nitrile group, which can improve the solubility of PAN and can initiate the cyclization reaction of the nitrile group through an ion mechanism
Compared to the PAN homopolymer, the stabilization of P (AN-co-methylenesuccinamic acid (MLA)) was notably improved with a lower initiation temperature, smaller cyclic activation energy, and a higher stabilization degree due to the ionic cyclization reaction that was initiated by MLA
Summary
Owing to their unique performance, such as high strength, high temperature resistance, good flexibility, and lightweight, carbon fibers are widely used in aerospace and other high-tech equipment. The polymerization of the PAN homopolymer is only triggered through a radical mechanism that leads to a high cyclization temperature, centralized heat release, and poor carbon fiber performance [6,7]. To solve these problems, a small quantity of comonomers is usually introduced to the PAN polymer chains to reduce the intermolecular force and to improve the stabilization. In the polymerization process, the carboxyl groups in IA can trap free radicals and bind to them and release protons (H+ ), which is not conducive to the improvement of the molecular weight of the polymer, and it has a significant effect on promoting the tensile strength of the final carbon fiber. Compared to the PAN homopolymer, the stabilization of P (AN-co-MLA) was notably improved with a lower initiation temperature, smaller cyclic activation energy, and a higher stabilization degree due to the ionic cyclization reaction that was initiated by MLA
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