ORIGINAL PAPER Effect of comonomer on the viscoelastic behavior of co-poly (acrylonitrile) solutions Reza Cheraghi 1 & S. Hajir Bahrami 1 & Mokhtar Arami 1 & Mojtaba Enayati 2 Received: 25 June 2016 /Accepted: 7 September 2016 # Springer Science+Business Media Dordrecht 2016 Abstract Three copolymers of acrylonitrile-methacrylic acid [P(AN-co-MAA)], acrylonitrile-ammonium salt of methacrylic acid [P(AN-co-AMA)], acrylonitrile- methacrylamide-itaconic acid [P(AN-MAM-IA)] and PAN homopolymer were synthesized by aqueous dispersion poly- merization technique. The polymerization conditions were ad- justed in such a way to produce polymers with similar com- position and molecular weight. The influence of comonomer nature on the viscoelastic behavior and spinnability of copolymer/dimethylsulfoxide (DMSO) solutions were inves- tigated. It was found that incorporation of these comonomers into PAN chains led to intense decrease in zero-shear viscosity to lower value as well as appearance of distinct plateau in comparison with PAN homopolymer. However, comparing the results of complex viscosity and shear viscosity of each PAN polymer showed different shear-thinning behavior, typ- ical deviation from Cox-Merz rule at high deformation rates. Amongst these copolymer solutions, P(AN-co-AMA) exhib- ited the longest relaxation time (λ) at low and medium fre- quencies. The lower values of frequency dependence of G′ (n′) and cross over frequency (ω c ) of storage modulus (G′) and loss modulus (G″) indicated that P(AN-co-AMA) was more elastic than other PAN copolymer solutions. The log-log plots of tan δ versus ω demonstrated that the comonomer nature affects the sol-gel transition behavior and elastic character of copolymer solutions. On average, based upon the slope of logGʹ versus logG data, the incorporation of comonomers inside PAN chains led to ~50 % increase in the homogeneity of solutions compared to PAN homopolymer. Keywords Polyacrylonitrile . Spinnability . Rheological behavior . Viscoelastic Introduction Since the industrial production of acrylic fibers, there has been an increased interest in using these fibers for textile and special applications. Special grade acrylic fiber (SAF) which is produced from polyacrylonitrile (PAN) copolymers, perhaps is the most suitable precursor for making high-performance carbon fibers (CFs) [1–4]. However, PAN homopolymer has never been used as a CF precursor due to its defective spinning and stabilization processing. Thus a small quantity of neutral comonomer e.g., methylacrylate (MA), methyl methacrylate (MMA) and acidic comonomers e.g., itaconic acid (IA), acrylic acid (AA), methacrylic acid (MAA), is usually incorporated into PAN poly- mer chains to improve the solubility, spinnability, drawability and thermal stability [5–8]. SAFs are regularly made by solution spinning methods such as wet spinning, dry-jet wet spinning or gel spinning [9, 10]. The spinnability and drawability of PAN solutions play important role to produce acrylic fibers with en- hanced properties. In solution spinning process specially in dry- jet wet spinning where high drawing ratios are possible, It is essential to have reduced shear-thinning and increased elasticity of PAN solutions for production of PAN-based CFs with high specific modulus and strength [11]. Therefore, focus on the rhe- ological behavior of spinning solution and understanding the solution properties is necessary to predict the solution extrusion performance and optimize the spinning process parameters [12–15]. Rheological characterizations were usually performed * S. Hajir Bahrami hajirb@aut.ac.ir 1 Department of Textile Engineering, Amirkabir University of Technology, Tehran 15875-4413, Iran 2 Department of Chemistry, Faculty of Science, University of Qom, Qom 37185359, Iran J Polym Res (2016) 23:207 DOI 10.1007/s10965-016-1104-4