Poly(acrylonitrile-co-2-methylenesuccinamic acid) as a potential carbon fiber precursor: preparation and stabilization

Abstract

A novel bifunctional comonomer 2-methylenesuccinamic acid (MLA) was synthesized to prepare poly(acrylonitrile-co-2-methylenesuccinamic acid) [P(AN-co-MLA)] copolymers, which can improve the stabilization of polyacrylonitrile significantly as a carbon fiber precursor. The structure and stabilization of P(AN-co-MLA) copolymers with different monomer feed ratios of AN/MLA were characterized by elemental analysis (EA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Reactivity ratio studies shows that MLA possesses higher reactivity than AN, resulting in higher MLA content in P(AN-co-MLA) copolymers than in the feed. The molecular weight and conversion of copolymer decrease gradually with the increase of MLA content in the feed. Comparing with PAN homopolymer, P(AN-co-MLA) copolymer has two or even three exothermic peaks, and the initial temperature of P(AN-co-MLA) copolymer is ca. 70 °C lower than that of PAN, which broadens the exothermic peak. The ΔH/ΔT reduces from 34.01 J g⁻¹ °C⁻¹ to less than 17.67 J g⁻¹ °C⁻¹, confirming that the incorporation of MLA can avoid centralized heat release effectively. In addition, the extent of stabilization increases as the MLA content in P(AN-co-MLA) copolymer increases under the same heat treatment conditions. The activation energy (E_a) calculation shows cyclization E_a of P(AN-co-MLA) reduces from ca. 168 kJ mol⁻¹ to ca. 110 kJ mol⁻¹, it is concluded that synthesized comonomer MLA can significantly improve stabilization of PAN, which is conducive to the preparation of high performance carbon fiber.