Polyacrylonitrile Homopolymer Research Articles

Non-Coagulant Spinning of High-Strength Fibers from Homopolymer Polyacrylonitrile Synthesized via Anionic Polymerisation.

The rheological properties, spinnability, and thermal-oxidative stabilization of high-molecular-weight linear polyacrylonitrile (PAN) homopolymers (molecular weights Mη = 90-500 kg/mol), synthesized via a novel metal-free anionic polymerization method, were investigated to reduce coagulant use, enable solvent recycling, and increase the carbon yield of the resulting carbon fibers. This approach enabled the application of the mechanotropic (non-coagulating) spinning method for homopolymer PAN solutions in a wide range of molecular weights and demonstrated the possibility of achieving a high degree of fiber orientation and reasonable mechanical properties. Rheological analysis revealed a significant increase in solution elasticity (G') with increasing molecular weight, facilitating the choice of optimal deformation rates for effective chain stretching prior to strain-induced phase separation during the eco-friendly spinning of concentrated solutions without using coagulation baths. The possibility of collecting ~80 wt% of the solvent at the first stage of spinning from the as-spun fibers was shown. Transparent, defect-free fibers with a tensile strength of up to 800 MPa and elongation at break of about 20% were spun. Thermal treatment up to 1500 °C yielded carbon fibers with a carbon residue of ~50 wt%, in contrast to ~35 wt% for industrial radically polymerized PAN carbonized under the same conditions.

Acrylonitrile-Acrylic Acid Copolymer Ultrafiltration Membranes for Selective Asphaltene Removal from Crude Oil.

In this study, ultrafiltration membranes were developed via a nonsolvent-induced phase separation method for the removal of asphaltenes from crude oil. Polyacrylonitrile (PAN) and acrylonitrile copolymers with acrylic acid were used as membrane materials. Copolymerizing acrylonitrile with acrylic acid resulted in an improvement in the fouling resistance of the membranes. The addition of 10% of acrylic acid to the polymer chain decreases the water contact angle from 71° to 43°, reducing both the total fouling and irreversible fouling compared to membranes made from a PAN homopolymer. The obtained membranes with a pore size of 32-55 nm demonstrated a pure toluene permeance of 84.8-130.4 L/(m2·h·bar) and asphaltene rejection from oil/toluene solutions (100 g/L) of 33-95%. An analysis of the asphaltene rejection values revealed that the addition of acrylic acid increases the rejection values in comparison to PAN membranes with the same pore size. Our results suggest that the acrylonitrile-acrylic acid copolymer ultrafiltration membranes have promising potential for the efficient removal of asphaltenes from crude oil.

Synthesis of PAN-based carbon fiber precursors containing fumaric acid or maleic acid as novel comonomers

A series of Polyacrylonitrile (PAN) co- or terpolymers as PAN-based carbon fiber precursors was prepared using methyl acrylate (MA) as neutral comonomer and fumaric acid (fa) or maleic acid (ma) as acidic comonomer which is trans/cis isomer, respectively. In order to establish the optimized condition of polymerization, PAN polymers with different acrylonitrile weight ratios (92, 94, and 96 wt%) were synthesized with appropriate yield via stepwise solution polymerization system. The efficiency of cyclization reaction of PAN polymers containing fa or ma were dramatically improved as compared to PAN homopolymer, and initiation of cyclization showed a rapid progress at 210 °C despite short thermal treatment time during thermal oxidative stabilization (TOS). Additionally, the char yield of PAN co- or terpolymers was reasonable value which was similar to PAN homopolymer.

Constructing novel nanofibrous polyacrylonitrile (PAN)-based anion exchange membrane adsorber for protein separation

Purification of biopharmaceutical streams is essential for producing high quality therapeutic bioproducts. This work developed a novel polyacrylonitrile (PAN)-based nanofibrous membrane with strong anion exchange functionality via electrospinning. The key material functionality was obtained via RAFT copolymerization of acrylonitrile and dimethylaminoethyl acrylate (pAD), followed by quaternization to form quaternary amine (QA) ligands, namely pAQ, a series of nanofibrous PAN-pAQ membranes were electrospun by blending the pAQ copolymer with PAN homopolymer at varying ratios. The chemistry of the respective pAQ copolymer and resulting membranes was confirmed by NMR and FTIR, evidencing successful functionalization. As compared to the reference pure membrane PAN4 that was negatively charged, the resulting composite membranes showed a positive surface charge. The investigation on surface morphology revealed that the nanofiber diameter increased from 300 nm to 1 μm with an increasing blend ratio from 1:4 to 1:7 for the PAN-pAQ membranes. Such trend in surface micro/nano morphology changes strongly influenced other surface properties such as increased pore size, reduced specific surface area and increased hydrophobicity. The static binding of model protein BSA of PAN-pAQ membranes firstly increased with blend ratio from 1:4 to 1:5, and then decreased at 1:7, which was attributed to the complex trade-off relationship between surface micro/nano-structure and hence distribution/density of quaternary functional groups. The PAN-pAQ membranes showed about a 10-fold increase in static binding capacity compared to PAN4, up to 310–320 mg·g−1 at a blend ratio of 1:5. Thus through this study, we were able to demonstrate a facile route to incorporate pre-functionalized copolymers into conventional polymers to form chromatographic membranes, with many possibilities to tailor membrane functionality for a wide range of applications.

Thermal stabilization of poly(acrylonitrile-co-itaconic acid) nanofibers as carbon nanofiber precursor

The thermal treatment of poly (acrylonitrile-co-itaconic acid), (P (AN-co-IA)) and polyacrylonitrile (PAN) under the oxygen atmosphere has a complex mechanism which strongly affects the properties of final product carbon nanofiber. Not only precursor composition but also oxidation treatment parameters play a key role in the achievement of the desired properties of the end product; carbon nanofiber. PAN and P (AN-co-IA) based nanofibers were fabricated via electrospinning technique and later treated at different temperatures to investigate the oxidation procedure in the presence of itaconic acid as a copolymer form. Description of the oxidation (thermal stabilization) route of nanofibers is challenging thus powerful characterization tools such as electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and FTIR-ATR are used for characterization and evaluated dependently. All obtained results are pointed out that; IA addition has a positive effect on the oxidation process in nanoscale in terms of reduction of applied temperature and time compared to homopolymer PAN. Spectroscopic results were also correlated with the equivalent Circuit Parameters of Electrochemical Impedance Spectroscopic Measurements, where oxidation and carbonization stages can be followed easily due to the formation of heterocyclic and conjugated structures by thermal treatments.

Thermal Analysis and Crystal Structure of Poly(Acrylonitrile-Co-Itaconic Acid) Copolymers Synthesized in Water.

The composition and structure of polyacrylonitrile (PAN) precursors play an important role during thermal stabilization, which influences the properties of the resulting carbon fibers. In this paper, PAN homopolymer and PAN-itaconic (IA) copolymers with different IA contents were synthesized by aqueous phase precipitation polymerization. The effects of IA content on the structure and thermal properties were studied using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The morphology of PAN polymers showed that the average size of the PAN particles increased with the increase of IA content in the feed. The content of the IA comonomer on the copolymers was quantitatively characterized by the relative absorbance intensity (A1735/A2243) in FTIR spectrum. With the increase of IA content in the feed, PAN-IA copolymers exhibited lower degree of crystallinity and crystal size than the control PAN homopolymer. The results from DSC curves indicated that PAN-IA1.0 copolymers had lower initial exothermic temperature (192.4 °C) and velocity of evolving heat (6.33 J g−1 °C−1) in comparison with PAN homopolymer (Ti = 238.1 °C and ΔH/ΔT = 34.6 J g−1 °C−1) in an air atmosphere. TGA results suggested that PAN-IA1.0 copolymers had higher thermal stability than PAN homopolymer, which can form a ladder structure easier during thermal processing. Therefore, PAN-IA1.0 copolymers would be a suitable candidate for preparing high performance PAN based carbon fibers.

Carboxylate, nitrate, sulfonate, and phosphate catalysts for living radical polymerization via oxygen–iodine halogen bonding catalysis

Oxyanions, i.e., carboxylate, nitrate, phosphate, and sulfonate, were used for halogen-bonding-catalyzed living radial polymerization, giving low-dispersity polymethacrylates, polystyrene, and polyacrylonitrile homopolymers and block copolymers.

Influence of gas atmosphere on electron-induced reactions of polyacrylonitrile homopolymer powder at elevated temperature

The thermal stabilization of polyacrylonitrile precursor fibers is a highly exothermic and time-consuming process. In several investigations, the reduction of thermal stabilization time was demonstrated for an irradiation of polyacrylonitrile at room temperature in different atmospheres. Since electron induced chemical reactions strongly depend on the polymer chain segment mobility, the present investigation reports the electron treatment of polyacrylonitrile homopolymer (PAN) powder in air and nitrogen atmosphere at an average temperature of 125 °C. The irradiation temperature was precisely selected in order to study the electron induced reactions and changes of PAN structure at temperatures above the glass transition temperature, but below the initiation temperature of thermal induced reactions. Based on several analyses performed mainly at room temperature, the significant influence of gas atmosphere during the EB treatment of PAN powder at an average temperature of 125 °C on the number of trapped radicals, the ratio of chain scission density to density of crosslinked units, the level of fluorescence, the EB induced changes of constitution of PAN, the extent of cyclization and the residual mass at 800 °C under the conditions of TGA was shown.

Thermal Analysis on the Stabilization Behavior of Ternary Copolymers Based on Acrylonitrile, Methyl Acrylate and Itaconic Acid

Polyacrylonitrile (PAN)-based copolymers are widely used as a precursor for manufacturing high performance carbon fibers via a series of processes of thermal stabilization, carbonization, and graphitization. We have recently synthesized a series of copolymers with various compositions of acrylonitrile (AN), methyl acrylate (MA) and itaconic acid (IA) by using an efficient aqueous suspension polymerization. In this study, the influences of MA and IA units on thermal stabilization behavior of AN/MA/IA-based terpolymers has been investigated by thermal analyses using DSC and TGA. It was found that the glass transition temperatures (Tg) of AN/MA/IA-based terpolymers with a constant AN content increased with the IA content due to a specific interaction between carboxylic acid and nitrile groups, while the MA unit played a role of lowering Tg of the copolymers owing to the interruption of AN sequence with a strong dipole-dipole interaction. The exothermic peaks of DSC curves as well as the weight loss of TGA/DTG curves under air condition revealed that the IA unit in AN/MA/IA-based terpolymers contributed to accelerate the oxidation reaction especially under air condition and also to slow down the following cyclization and dehydrogenation reactions including isomerization, unlike PAN homopolymer and AN/MA-based bipolymers. On the other hand, the MA unit in AN/MA-based bipolymers and AN/MA/IA-based terpolymers served as a delaying agent on the overall thermal stabilization reactions of oxidation, cyclization and dehydrogenation.

Electrochemically mediated atom transfer radical polymerization of acrylonitrile and poly(acrylonitrile-b-butyl acrylate) copolymer as a precursor for N-doped mesoporous carbons

The synthesis of polyacrylonitrile (PAN) with precisely defined morphology is essential to obtain a polymer precursor for the preparation of high-value carbon-based materials. PAN homopolymers with very narrow molecular weight distribution were prepared by electrochemically mediated atom transfer radical polymerization (eATRP) of acrylonitrile. The redox properties of the Cu complexes used as eATRP catalysts were first investigated. Convenient polymerization conditions were identified by varying the applied potential, initiator nature, monomer and catalyst loading, and targeted molecular weight (MW). PAN with high MW, 9.1×104 g mol-1, was obtained in only 3 h. A shorter PAN was extended with butyl acrylate to prepare a well-defined PAN-b-PBA copolymer, which was subjected to annealing and pyrolysis. The obtained copolymer-templated nitrogen-enriched nanocarbon was characterized by BET, TEM and Raman spectroscopy. The material showed an exceptionally high nitrogen content, together with a remarkable activity toward O2 reduction and 40% selectivity for H2O2 production.

Detailed Cyclization Pathways Identification of Polyacrylonitrile and Poly(acrylonitrile-co-itaconic acid) by in Situ FTIR and Two-Dimensional Correlation analysis

In situ Fourier transform infrared spectroscopy (in situ FTIR) and two-dimensional (2D) correlation analysis were applied to investigate the cyclization pathways of polyacrylonitrile homopolymer (P...

Copolymer-Templated Synthesis of Nitrogen-Doped Mesoporous Carbons for Enhanced Adsorption of Hexavalent Chromium and Uranium

Polyacrylonitrile (PAN) homopolymer and polyacrylonitrile-block-poly(n-butyl acrylate) (PAN-b-PBA) block copolymer were synthesized via supplemental activator reducing agent atom transfer radical polymerization and used as precursors to nitrogen-doped nanocarbons. Carbonization was performed at two different temperatures (500 and 800 °C) to fabricate nanocarbons with different structural properties and nitrogen contents. Copolymer-templated nitrogen-doped carbons (CTNCs) had larger surface area and higher mesoporosity than PAN homopolymer-templated nanocarbons (PANCs), due to the presence of PBA block acting as a sacrificial porogen. Adsorption performances of PANCs and CTNCs for Cr(VI) and U(VI) species were systematically studied. Due to the well-defined structure and larger surface area, CTNCs showed stronger adsorption ability than PANCs. The nitrogen atoms incorporated into the carbon framework led to higher electrostatic attraction for Cr(VI) anions at low pH and complexation with U(VI) cations at h...

Separation and kinetic analysis of the thermo-oxidative reactions of polyacrylonitrile upon heat treatment

A polyacrylonitrile (PAN) homopolymer and a copolymer with methyl acrylate were analyzed by differential scanning calorimetry (DSC) in order to establish a method for the kinetic analysis of the stabilization reaction steps during heat treatment. The application of a program rarely used for the study of the chemical transformation of PAN and its copolymers resulted in five separate steps, which can be assigned with large probability to various cyclization and oxidation reactions. A more exact identification of the reactions needs further measurements and considerations. Overlapping peaks appearing in the DSC traces were deconvoluted and then quantitatively analyzed to obtain kinetic parameters. The kinetics of the processes were described by the Kissinger model. The model could be fitted well to four of the five processes that may indicate that these belong to individual reactions of the first order. The parameters obtained agree well with the few values of similar investigations published in the literature up to now. The results have large practical relevance, since the kinetic parameters obtained can be used in the preparation of intermediates and for the optimization of the stabilization process.

Investigation of the chemical changes during thermal treatment of polyacrylonitrile and 15N-labelled polyacrylonitrile by means of in-situ FTIR and 15N NMR spectroscopy

Fourier transform infrared (FTIR) spectroscopy is used to analyze in situ the temperature-dependent changes in homopolymer polyacrylonitrile (PAN) and 15N-labelled PAN during the thermal treatment between room temperature (RT) and 420 °C under a dinitrogen atmosphere. It is found that the nitrile peak at 2244 cm−1 (C≡N0) for the starting PAN disappears in favor of a new nitrile peak at 2199 cm−1 (C≡N1) which finally at higher temperatures is transformed into a yet unrecognized third nitrile peak at 2221 cm−1 (C≡N2). Additionally to the C≡N (nitrile) range, the C=C/C=N range and the C–H/N–H-range of the IR spectra are analyzed in detail, taking in particular into account for the first time the differences between 14N- and 15N-PAN and comparing the results for PAN with those of well-defined model compounds. Additionally, for the first time 15N NMR spectroscopy is performed on 15N-labelled model compounds as well as on 15N-labelled PAN and thermally treated 15N-labelled PAN. DFT calculations on relevant moieties are presented. Also, an investigation of the volatiles during the thermal treatment by Simultaneous Thermal Analysis (STA) is done providing for the first time quantitative data for the amounts of evolved ammonia and HCN. On the basis of these findings new aspects about the mechanism of the chemical transformations are explored.

Effects of Amino-Functionalized Carbon Nanotubes on the Crystal Structure and Thermal Properties of Polyacrylonitrile Homopolymer Microspheres.

Amino-functionalized multi-walled carbon nanotube (amino-CNT)/polyacrylonitrile (PAN) microspheres with diameter of about 300–400 nm were prepared by in situ polymerization under aqueous solution. The morphology, crystal structure, and thermal properties of amino-CNTs on a PAN homopolymer were investigated by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectra, X-ray diffraction, and differential scanning calorimetry. The results showed that the amino-CNTs had a significant influence on the morphology of microspheres, and the PAN matrix were grafted onto the surface of amino-CNTs with interfacial bonding between them. The XRD studies showed that the crystal size of amino-CNT/PAN microspheres with lower crystallinity was bigger than in the control PAN homopolymer. The analysis of thermal properties indicated that the amino-CNT/PAN microspheres with lower glass transition temperature had a lower initial temperature and velocity of evolving heat during the exothermic processing as compared with the PAN homopolymer. These results suggested that the incorporation of amino-CNTs into the PAN homopolymer matrix was beneficial for controlling the heat released during the stabilization processing.

Structure evolution mechanism of poly(acrylonitrile/itaconic acid/acrylamide) during thermal oxidative stabilization process

Polyacrylonitrile (PAN) polymers with different compositions were prepared by an efficient aqueous free-radical polymerization technique. Thermal properties of polyacrylonitrile homopolymer (PAN), poly(acrylonitrile/itaconic acid) [P(AN/IA)] and poly(acrylonitrile/itaconic acid/acrylamide) [P(AN/IA/AM)] were studied by Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry and thermogravimetry in detail. It was found that AM had the ability to initiate and accelerate thermal oxidative stabilization process, which was confirmed by the lower initiation temperature and broader exothermic peak in P(AN/IA/AM) as compared with that in P(AN/IA) and PAN. The intensity of heat releasing during the thermal treatment was relaxed due to the presence of two separated exothermic peaks. Accompanied by DSC analysis and calculation of the apparent activation energy of cyclization reaction, two peaks were assigned to the ionic and free radical induction mechanisms, respectively. The higher rate constant in P(AN/IA/AM) indicated that the ionic mechanism actually had a kinetic advantage at promoting thermal stability over the free radical mechanism. This study clearly show that the synthesized P(AN/IA/AM) terpolymers possess larger room to adjust manufacture parameters to fabricate high performance of PAN-based carbon fibers.

Preparation of hollow carbon submicro-fibers with controllable wall thicknesses from acrylonitrile copolymer

Most of the hollow carbon submicro-fibers (HCSFs) reported today are made from polyacrylonitrile (PAN) homopolymer. The obtained HCSFs are fragile due to the poor stabilization and spinnability of PAN. In this study, a bifunctional comonomer, β-methylhydrogen itaconate (MHI), was synthesized to prepare poly(acrylonitrile- co-β-methylhydrogen itaconate) [P(AN- co-MHI)] copolymer, which was used as a precursor to produce HCSF by coaxial electrospinning. The stabilization of P(AN- co-MHI) was studied by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR); the structure of HCSFs was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and field emission scanning electron microscopy (FE-SEM). The stabilization of P(AN- co-MHI) has been improved significantly by MHI with lower cyclization temperature, broadened peak and lower activation energy, which is beneficial to producing high-performance HCSFs. HCSFs with fine and uniform structures were obtained after stabilization and carbonization; the diameter of the HCSFs shrinks due to the elimination of N and the extra H. The diameter and wall thickness of HCSFs can be controlled simply by the feeding ratio of P(AN- co-MHI) solution/styrene- co-acrylonitrile solution. The resultant HCSFs can be bent more than 280° without breaking, which has potential applications in lithium-ion rechargeable batteries, supercapacitors, fuel cells, and catalyst.

Study on the thermal oxidative stabilization reactions and the formed structures in polyacrylonitrile during thermal treatment

The structural evolution of polyacrylonitrile (PAN) homopolymer during thermal oxidative stabilization (TOS) was tracked quantitatively by using fourier transform infrared spectroscopy (FTIR) and curve-fitting technology. The cyclization, dehydrogenation of linear PAN macromolecule chains, oxygen uptake reactions of linear PAN macromolecule chains and cyclic structures were discussed in detail through tracking quantitatively the evolution of some specific groups. The cyclization, dehydrogenation and oxygen uptake reactions were evolved synchronously at the initial stage of TOS processes, but dehydrogenation and oxygen uptake reactions became dominant as cyclization extent above 0.7. Based on the data from FTIR and curve-fitting, a new procedure was developed to calculate the formed cyclic structures. The cyclic structures formed at 250 °C possessed length about seven successive aromatic rings; however, the cyclic structures formed at 265 °C possessed length about six successive aromatic rings. The graphite-like structures of the carbonized PAN films which were stabilized at 250 °C possessed were better than that of the carbonized PAN films which were stabilized at 265 °C.

Thermal analysis and melt spinnability of poly(acrylonitrile-co-methyl acrylate) and poly(acrylonitrile-co-dimethyl itaconate) copolymers

This work investigated the cyclization possibility and melt spinnability of carbon fiber precursors, poly(acrylonitrile-co-methyl acrylate) (AN/MA) and poly(acrylonitrile-co-dimethyl itaconate) (AN/DMI). The onset temperature of cyclization of the AN/DMI copolymer is lower than that of the AN/MA copolymer and also the polyacrylonitrile (PAN) homopolymer. The enthalpy ( ΔH) of the AN/DMI copolymer is about 3–4 times that of the PAN homopolymer and about 1.8 times that of the AN/MA copolymer, indicating that the degree of cyclization of the AN/DMI copolymer is relatively higher. The melt dwell time of the AN/DMI copolymer is increased to about 3–5 times that of the AN/MA copolymer, especially when synthesized with a feed molar ratio of AN/DMI = 85/15. The AN/DMI copolymer (AN/DMI = 85/15) has the longest melt dwell time, 24.8 min, at the lowest melting temperature, 190oC, among all the PAN-related copolymers synthesized herein. Furthermore, the AN/DMI copolymer (AN/DMI = 85/15) can be rapidly cyclized at the cyclization temperature of 260℃, which is 25℃ lower than that of the AN/MA copolymer (AN/MA = 85/15). In short, this work demonstrates that the carbon fiber precursor made by the AN/DMI copolymer (AN/DMI = 85/15) will be superior to that of the AN/MA copolymer (AN/MA = 85/15) with respect to the melt spinnability and cyclization at low temperature.

Detailed examination of nitrile stretching vibrations relevant for understanding the behavior of thermally treated polyacrylonitrile

ABSTRACTThe influence of electronic and environmental effects on the wave number of nitrile stretching vibrations was examined with respect to moieties relevant for the polyacrylonitrile homopolymer and its assumed transformation products on thermal treatment in the course of carbon fiber production on the basis of four sources of information. Literature values were collected. Fourier transform infrared (FTIR) measurements on relevant commercially available compounds were performed. For the first time, model compounds were synthesized and examined, and for the first time, density functional theory calculations for unavailable important compounds were performed. The results place the interpretation of the FTIR data on much safer scientific ground than any other study before; in particular, they unequivocally disprove suggestions given in the previous literature and provide quantitative relative oscillation strengths for important peaks necessary for the quantitative kinetic evaluation of the changes, which will enable the systematic fine‐tuning of new proposals. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44936.