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

In order to replace terpolymers with bipolymers, three bifunctional comonomers were synthesized to prepare poly(acrylonitrile-co-beta-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 E-s = A(1610) (cm-1)/A(2244 cm-1) and SI = (I-0 - I-s)/I-0 were defined to evaluate the extent of stabilization, and the activation energy (E-a) 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 E-a. 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. (c) 2012 Elsevier Ltd. All rights reserved.