Poly(4,4′-diphenylsulfone terephthalamide) referred to as all para-position polysulfonamide (all para-position PSA) is a special kind of PSAs, copolymers of 3,3′-diaminodiphenylsulfone, 4,4′-diaminodiphenylsulfone, and terephthaloyl chloride. However, with the increasing para-structure content in the PSAs, the PSA shows very poor solubility in common amide-type polar aprotic solvents and cannot be used for wet spinning. In this article, it was found that all para-position PSA can be easily dissolved in N,N-Dimethylacetamide (DMAc)/LiCl system, and then the all para-position PSA fiber was prepared for the first time by wet spinning. The properties of all para-position PSA pulps and fibers were investigated via Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), scanning electron microscopy, thermal gravimetric analysis, dynamical mechanical analysis, X-ray diffraction (XRD), and tensile strength testing. The tensile strength, elongation at break, and crystallinity of the resulting fiber were 4.4 cN/dtex, 15.9%, and 33.53%, respectively. The results indicated that all para-position PSA fiber was a high-temperature resistance fiber with better mechanical properties than common PSA fiber. The improved tensile strength of the fiber will expand its applications and may take place of Nomex in certain fields and become a new generation of flame retardant and high-temperature resistant material. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Based on the constructed theoretical ternary phase diagrams of water/dimethyl sulfoxide (DMSO)/polyacrylonitrile (PAN) terpolymer system, the phase separation behavior for PAN fibers preparation was investigated. Theoretical ternary phase diagrams were determined by the extended Flory-Huggins theory. To investigate the temperature dependence of theoretical ternary phase diagrams, all binary interaction parameters at different temperatures were determined accurately and thoroughly revisited. From numerical calculations, it was found that a small quantity of water was needed to induce phase demixing. Meanwhile, the cloud point data of the system for more dilute PAN terpolymer solutions were determined by cloud point titration, and the cloud point data for more concentrated PAN terpolymer solutions were calculated by Boom's linearized cloud point (LCP) curve correlation. Furthermore, the morphology of PAN fibers was investigated by using scanning electron microscopy (SEM). With increasing the concentration of PAN terpolymer solutions as well as the quenching depth, the morphology of PAN fibers turns from large open channels to small bead-like structures, accompanying with a reduction of the porosity of PAN fibers. Judging from our investigation, it was clear that the final morphology of PAN fibers was mainly determined by phase separation in fiber-forming process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 261–275, 2009

The thermodynamics of polyacrylonitrile (PAN) terpolymer/dimethyl sulphoxide (DMSO)/water system was investigated by viscometric method. Fourier transform infrared (FTIR) measurement of the temperature dependence of polymer/solvent interaction was performed in the range of 25–80 °C, which was in good agreement with viscometric results. Meanwhile, the upper critical solution temperature (UCST) for PAN terpolymer/DMSO/water system, which is proved to be stable one, was determined from the temperature dependence of the expansion factor α_η3. The morphology of PAN precursor prepared by dry-jet-wet spinning with different fiber-forming conditions was examined with a scanning electron microscope (SEM). Judging from SEM photographs, not only the number and size of microvoids of PAN precursor gradually increase, with increasing the temperature of coagulation bath, but also the cross-section shape of PAN precursor changes from nephroid shape to elliptical shape or circular shape. Therefore, PAN precursor with different microstructures can be fabricated at different quenching-depths, suggesting that the final microstructure of the PAN precursor greatly depends on the phase separation in the fiber-forming process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1997–2011, 2008