Effect of comonomer structure on the stabilization and spinnability of polyacrylonitrile copolymers

Abstract

In order to replace terpolymers with bipolymers, three bifunctional comonomers were synthesized to prepare poly(acrylonitrile-co-β-methylhydrogen itaconate) [P(AN-co-MHI)], poly(acrylonitrile-co-3-aminocarbonyl-3-butenoic acid methyl ester) [P(AN-co-ABM)] and poly(acrylonitrile-co-3-ammoniumcarboxylate-3-butenoic acid methyl ester) [P(AN-co-ACBM)] which can be used as carbon fiber precursor. The stabilization mechanism and effect of comonomer structure on the stabilization of bipolymers were studied by Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry and thermogravimetry. Two parameters Es=A1610cm-1/A2244cm-1 and SI=(I0-Is)/I0 were defined to evaluate the extent of stabilization, and the activation energy (Ea) of the cyclization reactions were calculated by Kissinger method and Ozawa method. The results show that P(AN-co-MHI), P(AN-co-ACBM) and P(AN-co-ABM) exhibit better stabilization than terpolymers containing similar chemical composition, such as lower initiation temperature, larger extent of stabilization and smaller Ea. Furthermore, it is found that 3-ammoniumcarboxylate-3-butenoic acid methyl ester is the most effective one among the three comonomers for improving the stabilization of polyacrylonitrile (PAN) due to the strongest nucleophilicity of COO−NH4+ towards the carbon atom of adjacent nitrile groups. Simultaneously, the rheological analyses show that all the three bipolymers possess better spinnability than PAN homopolymer.