Optimization of polymerization conditions of furan with aniline for variable conducting polymers

A high-throughput multiparameter optimization of chemical oxidative polymerization conditions has been developed for a facile synthesis of furan homopolymers and furan/aniline copolymers using a combinatorial method. The polymerization yield, molecular structure, and properties of the polymers would be optimized against typical polymerization parameters, including oxidant species, medium species, temperature, oxidant/monomer ratio, monomer concentration, dopant concentration, and furan/aniline comonomer ratio. The electrical conductivity, lead ion adsorptivity, chemical resistance, and thermal behavior of the polymers were also elaborated. It is found that only a combination of FeCl(3) and nitromethane as oxidant and medium, respectively, is appropriate for the furan homopolymerization. The homopolymerization yield increases consistently with an increase in the monomer concentration from 0.05 to 0.2 M and the FeCl(3)/furan molar ratio from 0.25 to 1.25. Although the as-prepared polyfuran exhibits very low conductivity, down to 10(-11) S cm(-1), the HCl- and HClO(4)-doped polyfurans possess much higher conductivities of 9.2 x 10(-8) and 2.38 x 10(-5) S cm(-1), respectively. In addition, the conductivity of the furan/aniline copolymer rises steadily with increasing aniline content, although the copolymerization yield shows a minimum at the furan/aniline molar ratio of 60/40, which is evidence of the occurrence of a real copolymerization between the furan and aniline monomers. The difficulty of synthesizing conducting polyfuran could be overcome to some extent by the polymerization in an appropriate condition optimized in this study. Particularly, the difficulty of synthesizing poly(furan-co-aniline) having much higher conductivity than the polyfuran would be largely conquered by chemical oxidative copolymerization of furan with aniline.     

Effect of electrolyte on the chemical polymerization of aniline

Chemical syntheses of polyaniline were performed in HCl (0.4-2.51 M) containing 0.1 M aniline and LiCl or MgCl₂, keeping the total amount of chloride in the reactional medium constant. This was done in order to investigate if the chloride ion, added as salt and not as acid, is incorporated from chloride containing solutions with lower total acid concentration. The synthesis processes were characterized by potentiometric and calorimetric measurements represented in curves containing kinetic parameters of the polymerization process. The analysis of the polymeric materials was performed by infrared spectroscopy, electric conductivity measurements and scanning electron microscopy. It was observed that both the acid and chloride concentration, have an influence on the polymerization rate and the properties of the polyaniline, however, the presence of monovalent (Li⁺) or divalent (Mg⁺²) cations does not seem to have a significant effect. Finally, the conductivity of PAni is lowered by high acid concentrations but high chloride concentrations seem to improve the conductivity.     

Effect of pyrolysis conditions on the properties of carbonaceous nanofibers obtained from freeze-dried cellulose nanofibers

Carbonaceous nanofibers (CsNFs) were produced by pyrolysis of cellulose nanofibers synthesised from wood pulp using a top-down approach. The effects of heat treatment conditions on the thermal, morphological, crystal and chemical properties of the CsNFs were investigated using TGA, SEM, XRD and FT-IR, respectively. The results showed that heat treatment conditions around the thermal decomposition temperature of cellulose greatly influence the morphology of resulting materials. Slow heating rates (1 °C/min) between 240 and 400 °C as well as prolonged isothermal heat treatment (17 h) at 240 °C were necessary to avoid destruction of the original fibrous morphology in carbonized nanofibers. On the other hand, such heat treatment had little effect on micron sized fibers. The optimized heat treatment conditions led to the release of oxygen and hydrogen from cellulose before thermal breakdown of glycosidic rings, which in turn prevented depolymerization and tar formation, resulting in the preservation of the fibrous morphology.     

Crosslinked fibrous composites based on cellulose nanofibers and collagen with in situ pH induced fibrillation

Collagen and cellulose nanofiber based composites were prepared by solution casting followed by pH induced in situ partial fibrillation of collagen phase and crosslinking of collagen phase using gluteraldehyde. Microscopy studies on the materials confirmed the presence of fibrous collagen and cellulose nanofibers embedded in the collagen matrix. The cellulose nanofiber addition as well as collagen crosslinking showed significant positive impact on the nanocomposite’s mechanical behaviour. The synergistic performance of the nanocomposites indicated stabilization and reinforcement through strong physical entanglement between collagen and cellulose fibres as well as chemical interaction between collagen matrix and collagen fibrils. The mechanical performance and stability in moist conditions showed the potential of these materials as implantable scaffolds in biomedical applications. The collagen-cellulose ratio, crosslinking agent and crosslinking level of collagen may be further optimised to tailor the mechanical properties and cytocompatibility of these composites for specific applications such as artificial ligament or tendon.     

Theoretical study of the oxidative polymerization of aniline with peroxydisulfate: Tetramer formation

Semi‐empirical quantum chemical study of the oxidative polymerization of aniline with ammonium peroxydisulfate, in aqueous solutions without added acid, has been based on the MNDO‐PM3 computations of thermodynamic, redox, and acid–base properties of reactive species and the intermediates, combined with the MM2 molecular mechanics force‐field method and conductor‐like screening model of solvation. The main reaction routes of aniline tetramerization are proposed. The regioselectivity of the formation of aniline tetramers by redox and electrophilic aromatic substitution reactions is analyzed. It was proved that the linear N? C4 coupled tetra‐aniline is formed as a dominant product by three different pathways: comproportionation redox reaction between N‐phenyl‐1,4‐benzoquinonediimine and 4‐aminodiphenylamine, the one‐electron oxidation of aniline with its half‐oxidized N? C4 coupled trimer, and the electrophilic aromatic substitution reaction of aniline with fully oxidized N? C4 coupled trianiline nitrenium cation. The electrophilic aromatic substitution reaction of the N? C4 coupled aniline trimer with aniline nitrenium cation, as well as the oxidation of aniline with half‐oxidized branched trimer, lead to the branched aniline tetramers. The competing character of different tetramerization routes is highlighted. The oxidative intramolecular cyclization of branched oligoanilines and polyaniline, leading to the generation of substituted phenazine units, has been predicted to accompany the classical routes of the polymerization of aniline. Various molecular (branched vs. linear) oligomeric structures produced at different level of acidity during the course of polymerization and their impact on the formation of supramolecular structures of conducting polyaniline (nanorods and nanotubes vs. granular morphology), are discussed. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Hydrodynamically induced formation of cellulose fibers. I. Observations on the formation of cellulose fibers from stirred solutions

Like synthetic polymers, a natural polymer such as cellulose may crystallize in fibrous form from stirred solutions. In the present work, it is demonstrated that cellulose fibers can be formed by precipitation from dimethyl sulfoxide/paraformaldehyde solutions by two methods that involve different mechanisms of fiber formation, viz., (A) precipitation of cellulose by addition of nonsolvent to the stirred cellulose solution, and (B) precipitation of cellulose by coagulation of droplets of cellulose solution in a stirred precipitant. Both processes yield fibers with properties depending on the stirring speed and the coagulant strength. The molecular orientation and tensile strength of the fibers produced by method A was low, but increased with the stirring speed, while some fibers formed by method B reached extremely high orientation, depending on the thickness of the fibers. The two mechanisms of fiber formation are discussed on the basis of the experimental observations.     

Clean and reactive nanostructured cellulose surface

A simple, solvent-free and low cost method to activate the surface of nanofibrillated cellulose films for further functionalization is presented. The method is based on the oxidative properties of UV radiation and ozone, to effectively remove contaminants from nanocellulosic surface, which remains clean and reactive for at least a week. The efficiency of the method is demonstrated by X-ray photoelectron spectroscopy (XPS) and contact angle measurements. In clear contrast to previous results on nanoscaled cellulose the relative atomic concentration of non-cellulosic carbon atoms was only 4 %, and water completely wetted the surface within seconds. After activation, neither chemical degradation nor morphological changes on cellulose were observed. This surface activation is essential for further functionalization of the film in dry state or nonpolar media. The surface activation was confirmed by silylation and a four times higher degree of substitution was achieved on the activated sample compared to non-activated reference film, as monitored with XPS.     

Graft polymerization of monomers onto cellulose and lignocelluloses by chemically induced initiator

The presence of a low percentage of lignin retards and inhibits the graft polymerization reaction of some vinyl monomers on lignocellulosic substrates. The retardation or inhibition effects of lignin in situ are discussed.     

Field effect conductance of conducting polymer nanofibers

We report on the electrical conductance of nanofibers of regioregular poly(3‐hexylthiophene) (RRP3HT) as a function of gate‐induced charge. Nanofibers of RRP3HT were deposited onto SiO₂/Si substrates by casting from dilute p‐xylene solutions. An analysis of the nanofibers by atomic force microscopy revealed fiber lengths of 0.2–5 μm, heights of 3–7 nm, and widths of approximately 15 nm. A field effect transistor geometry was used to probe the conductance of webs of nanofibers and single nanofibers; in these measurements, gold electrodes served as source and drain contacts, and the doped SiO₂/Si substrate served as the gate. Temperature‐dependent transport studies on webs of nanofibers revealed an activation energy of 108 meV at a gate‐induced hole density of 3.8 × 10¹² charges/cm². Pretreating SiO₂ with a hydrophobic hexamethyldisilazane (HMDS) layer reduced the activation energy to 65 meV at the same charge density. The turn‐on gate voltage on treated and untreated substrates increased in magnitude with decreasing temperature. Conductance measurements on single nanofibers on HMDS‐treated SiO₂ yielded hole mobilities as high as 0.06 cm²/Vs with on/off current ratios greater than 10³. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2674–2680, 2003     

Impedance change induced by varying polymerization temperature of conducting polymer thin films

In this study, we use a conducting polymer precursor to build layer-by-layer (LbL) films. Thermal conversion of the polymer precursor to conducting polymer makes the LbL films intractable, so the LbL films can be used as protective layers in salt solution. The conducting polymer LbL film shows stabilizing effect on top of another LbL thin film that contains nanoparticles. The LbL film prepared in this study shows a 35-fold increase of conductivity than the literature values obtained from non-conducting polymer films. The stabilization of the films is the result of the polymerization of the conducting polymer, so other anionic polymers or nanoparticles may be used to afford additional functionalities.     

Surface modification of TEMPO-oxidized cellulose nanofibers,and properties of their acrylate and epoxy resin composite films

Cellulose - The carboxy groups abundantly and densely present on 2,2,6,6-tetramehylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofibers (TEMPO-CNFs) have been chemically modified to...     

Plasma polymerization of aniline on different surface functionalized substrates

The plasma polymerization of aniline on different surface functionlized low-density polyethylene (LDPE) substrates was investigated, and the resulting polymer was characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and atomic force microscopy. The results showed that the structure of plasma-polymerized polyaniline was rather different from polyaniline synthesized by conventional chemical and electrochemical methods. This difference may be due to extensive coupling reactions and cross-linking reactions during the plasma polymerization process. The use of acrylic acid graft copolymerized LDPE substrate significantly enhanced the adhesion of the polyaniline to the substrate over that observed with pristine LDPE. The plasma polymerized polyaniline can be rendered electrically conductive if the polymerization is carried out on a polystyrenesulfonic acid-coated LDPE substrate. Conductivity can also be induced by acid protonation of the polyaniline by HClO(4). The reaction of the plasma-polymerized polyaniline with viologen grafted on the substrate under UV irradiation and with AuCl(3) and Pd(NO(3))(2) in acid solutions was also investigated.     

In situ polymerized polyaniline films. 4. Film formation in dispersion polymerization of aniline

Polyaniline films were grown on glass supports during dispersion polymerizations of aniline using poly(N-vinylpyrrolidone) and hydroxypropylcellulose as stabilizers. The initiation of polyaniline chains is proposed to be heterogeneously catalyzed by the surfaces immersed in the reaction mixture. Film formations in dispersion and precipitation polymerizations are compared. Surfometry and optical absorption were used to assess the submicrometer film thickness, and FTIR spectroscopy was used to analyze the chemical structure of films and prove the absence of stabilizer. The film thickness was proportional to the dimensions of simultaneously produced colloidal polyaniline particles. The conductivity of films increased with increasing film thickness.     

Effect of poly(ethylene oxide) on the kinetics of oxidative polymerization of aniline

The kinetics of polymerization of aniline hydrochloride in aqueous poly(ethylene oxide) solution in the presence of ammonium persulfate have been studied. The order of the catalytic step has been found to change from first to second when the molecular weight of poly(ethylene oxide) reaches a certain value. Adsorption equilibrium is rapidly established between the monomer and its oxidation products which give rise to a new phase and exert a catalytic effect.     

Electrochemical polymerization of aniline in SDS admicelles

The electrochemical polymerization of aniline was studied in sodium dodecyl sulfate (SDS) admicelles. The results demonstrate that electrochemical polymerization of aniline can be catalyzed by admicelles. The catalytic efficiency in SDS solutions increased slowly with SDS concentration when the SDS concentration was very low, but increased rapidly when SDS admicelles formed on the electrode surface. The catalytic efficiency decreased with the addition of n-pentanol. The polyaniline films formed in SDS admicelles were nanometer films and the size of particles in the films increased with SDS concentration, but decreased with the addition of n-pentanol. Therefore, n-C₅H₁₁OH can be used to regulate the electrochemical polymerization of aniline in SDS admicelles.     

Electrochemical polymerization of aniline in phosphoric acid

The electrochemical synthesis of common conductive polymers such as polyaniline in phosphoric acid is a little different from that in other acidic media such as sulfuric acid. Electropolymerization in phosphoric acid is difficult, and this electrolyte medium is not applicable for this purpose. However, it is possible to overcome this problem by the addition of a small amount of sulfuric acid. In this case, the electropolymerization process can be successfully performed when the phosphate ion is doped. For instance, polyaniline films electrodeposited from an electrolyte solution of phosphoric acid have good stabilities and useful morphologies. Interestingly, phosphate doping results in the formation of nanostructures, whereas the polymer surface is macroscopically smooth. In an appropriate ratio, a mixed electrolyte of H₃PO₄ and H₂SO₄ can be used for the electropolymerization of aniline; thus, H₂SO₄ acts as a required agent for successful polymer growth, and H₃PO₄ acts as a doping agent. In this case, a small amount of sulfate is incorporated into the polymer matrix, which does not participate in the electrochemical insertion/extraction process. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3304–3311, 2006     

Effect of pectin extraction method on properties of cellulose nanofibers isolated from sugar beet pulp

In this study, the effect of pectin extraction method on the properties of cellulose nanofibers (CNFs) isolated from sugar beet pulp (SBP) was studied. Pectin was extracted by the industrially practiced method by sulfuric acid hydrolysis or by enzymatic hydrolysis using a cellulase/xylanase enzymes mixture. The CNFs were then isolated by high-pressure homogenization and investigated in terms of their chemical composition, crystallinity, size, degree of polymerization, and re-dispersion in water after freeze-drying. The mechanical properties and surface characteristics of CNF films were also studied. The results showed that fibrillation of the de-pectinated SBP was more efficient for the acid hydrolyzed SBP. CNFs from the acid-hydrolyzed SBP had a slightly wider diameter, higher crystallinity, viscosity, and α-cellulose content but a lower degree of polymerization than CNFs from the enzyme-hydrolyzed SBP. Owing to the presence of more residual hemicelluloses in the CNFs from the enzyme-hydrolyzed SBP, the CNFs had higher re-dispersion ability in water. CNF films from enzyme-hydrolyzed SBP displayed slightly better mechanical properties and higher water contact angle than acid-hydrolyzed CNF films.

Graphic abstract