Chemical and electrochemical synthesis of polyaniline/platinum composites

The synthesis of polyaniline/platinum composites (PANI/Pt) has been achieved using both chemical and electrochemical methods. The direct chemical synthesis of PANI/Pt proceeds through the oxidation of aniline by PtCl₆²⁻ in the absence of a secondary oxidant. SEM images of these samples indicate that the Pt particles are on the order of ∼1 μm for the chemically prepared composite. Electrochemical PANI/Pt synthesis is initiated by the uptake and reduction of PtCl₆²⁻ into an a priori electrochemically deposited PANI film. This method produces a uniform dispersion of Pt particles with smaller particles with diameters ranging between 200 nm and 1 μm. The results indicate that electrochemical methods may be more suitable for controlling particle dimension. Both materials show reduced proton doping relative to PANI without Pt, indicating the metal particles directly influence proton doping and the oxidation state of the polymer. The electrochemical data indicate that the conductivity in solution is sufficient such that the normal acid doping is attainable for PANI/Pt produced using either synthetic method.     

EPR study of polyaniline highly doped by p-toluenesulfonic acid

Magnetic, relaxation and electronic dynamic parameters of paramagnetic centers in crystalline domains of polyaniline highly doped by p-toluenesulfonic acid (PANI-PTSA) as well as PANI-PTSA dispersed in poly(methyl methacrylate) (PANI-PTSA/PMMA) were studied by the 3-cm (9.7 GHz) and 2-mm (140 GHz) wavebands EPR. At both wavebands these polymers demonstrate the Lorentzian single line with the Dysonian contribution indicating intrinsic conductivity of metal-like domains ca. 1500-4000 S/cm at room temperature. Effective conductivity of the polymer is defined by Q3D delocalization of charge carriers within such domains and their Mott variable range hopping between the domains dominating its micro- and macroscopic conductivity. It was shown that the interaction of the charge carriers with the lattice phonons governs the intradomain charge transfer at high temperatures. Dimensionality of the system increases with the polymer dispersion in an insulating matrix. Dipole-dipole interaction of polarons with oxygen biradicals reversibly changes the relaxation of the spins in the initial and dispersed polymers. These paramagnetic centers strongly interact below and weakly above critical temperature T_c of the phase transition that leads to an extremal temperature dependence of the polymer linewidth. The dependence of T_c on electron precession frequency and/or on the PANI-PTSA dispersion in an insulating matrix was revealed. Spin relaxation and dynamics were analyzed to be non-correlated with charge transfer in PANI-PTSA that contradicts the “single conducting chain” model and justifies the formation of Q3D metal-like domains.     

Enzymatic synthesis of colloidal polyaniline particles

Polyaniline colloidal particles were enzymatically synthesized in aqueous media using poly(vinyl alcohol) as steric stabilizer. Hydrochloric acid, toluenesulfonic acid, and camphorsulfonic acid were used as doping agents during polymerization. Polyaniline showed chemical redox reversibility as demonstrated by changes in its electronic absorption spectra. Fourier transform infrared and UV-visible spectroscopic studies indicate a linear chemical structure of the synthesized polymer, whereas the results from X-ray photoelectron spectroscopy indicate the adsorption of poly(vinyl alcohol) at the surface of the particles. The doping agent used during the enzymatic polymerization of aniline influenced morphology and thermal stability of the synthesized particles. Polyaniline colloids prepared using p-toluenesulfonic acid showed spherical morphology and a narrow size distribution as shown by scanning electron microscopy and dynamic light scattering.     

Electrochemical synthesis and characterization of polyaniline thin film and polyaniline powder

The polyaniline thin film electrode and powder have been synthesized on graphite electrodes from 0.5 M hydrochloric acid solution under galvanostatic conditions. The water insoluble and acetone soluble polyaniline mass fractions of the powder, as well as the polymerization efficiency, based on the emeraldine salt have been determined. The morphology of the obtained emeraldine salt powder has been investigated by the optical microscopy.     

The reaction of polyaniline with iodine

Polyaniline (PANI) (emeraldine) base has been exposed to iodine in an ethanol-water suspension. The conductivity of PANI increased from 10⁻⁹ S cm⁻¹ to 10⁻⁴ S cm⁻¹ already at the molar ratio [I₂]/[PANI] = 1, and a higher content of iodine had only a marginal effect. This is the result of the protonation of PANI base with hydriodic acid, which is a by-product of the oxidation of the emeraldine form of PANI to pernigraniline constitutional units. The reaction is discussed on the basis of FTIR spectra. An alternative reaction, a ring-iodination of PANI, is marginal. Only one iodine atom substitutes a hydrogen atom in about 12 aniline units, even at high iodine concentration, [I₂]/[PANI] = 8. The film of polyaniline base can be used in sensing iodine; after exposure to the iodine vapor, the conductivity of the polyaniline film increased.     

Polymorphism of syndiotactic poly(p-fluoro-styrene)

Syndiotactic poly(p-fluoro-styrene) (s-PPFS) has been prepared with a polymerization procedure which allows reaching high average molecular masses and satisfactory yields. The polymorphic behavior of the polymer has been mainly studied by X-ray diffraction, calorimetric and infrared analyses. The main crystalline phase of s-PPFS, obtained by melt processing or cold-crystallization, exhibits trans-planar chains, is orthorhombic (a = 9.5 Å, b = 28.7 Å, c = 5.1 Å) and melts at nearly 320 °C. The X-ray analysis shows a strict analogy of this orthorhombic phase with the β phase of s-PS, also as for the occurrence of two limit ordered (β″) and disordered (β′) modifications, which differ for the intensity of reflections characterized by h + k = 2n + 1. A metastable crystalline phase, also exhibiting trans-planar chains, has been observed for as-polymerized samples as well as for amorphous samples crystallized by sorption of toluene or 1,4-difluoro-benzene. Mainly on the basis of solvent sorption and desorption experiments, it is suggested that this metastable phase is a co-crystalline phase with the low-molecular-mass guest molecules.     

A novel strategy for the synthesis of polyaniline nanostructures with controlled morphology

Polyaniline (PANI) nanostructures with sheets-, fiber- and spherical-like morphologies were synthesized from p-toluene sulfonic acid (p-TSA) aqueous solution. The results demonstrate that the morphology of PANI nanostructures was significantly influenced by the molar ratio of aniline to p-TSA. Other experimental parameters, such as polymerization temperature and the concentration of ammonium peroxydisulfate (APS), also have an influence on the morphology of PANI nanostructures. A rational mechanism based on the self-assembly of micelles is proposed for the formation of PANI nanostructures. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR), UV–visible spectroscopy (UV–vis) and X-ray diffraction (XRD) were applied to characterize the products.     

Hydrogen evolution performance of magnesium alanate prepared by a mechanochemical metathesis reaction method

Solvent-free magnesium alanates were prepared by a mechanochemical metathesis reaction method (ball milling method) with a variation of milling time. For the purpose of comparison, magnesium alanate was also prepared by metathesis reaction method in the presence of diethyl ether. The formation of magnesium alanate (Mg(AlH₄)₂) and magnesium alanate-diethyl ether (Mg(AlH₄)₂·Et₂O) adduct was confirmed by XRD measurements. In both magnesium alanates, hydrogen evolution occurred in the first step decomposition. The starting temperature for hydrogen evolution of the solvent-free magnesium alanates decreased with increasing milling time, whereas the amount of hydrogen evolution of the solvent-free magnesium alanates increased with increasing milling time. The maximum amount of hydrogen evolution of the Mg(AlH₄)₂·Et₂O adduct was slightly larger than that of the solvent-free Mg(AlH₄)₂, but the starting temperature for hydrogen evolution of the Mg(AlH₄)₂·Et₂O adduct was much higher than that of the solvent-free Mg(AlH₄)₂. The addition of a small amount of titanium to the solvent-free Mg(AlH₄)₂ greatly reduced the hydrogen evolution temperature of titanium-doped Mg(AlH₄)₂. However, the maximum amount of hydrogen evolution of the titanium-doped Mg(AlH₄)₂ was smaller than that of the solvent-free Mg(AlH₄)₂.     

Study on a novel catalytic reaction and its mechanism for CF3I synthesis

A novel vapor phase production process for CF₃I was successfully developed for the reaction between CHF₃ with I₂ in the presence of a unique catalyst. The most effective catalyst system for this reaction was found to be alkali metal salts which were supported on an activated carbon carrier. A consideration of the reaction mechanism suggests that the reaction proceeds via CF₂ carbenes formed on the catalyst surface as intermediates, followed by carbene disproportionation to CF₃ radicals, followed by reaction with I₂ to give CF₃I.     

硫酸氢钠掺杂聚苯胺催化合成环己酮缩乙二醇

以聚苯胺PAn和硫酸氢钠为原料,制备了硫酸氢钠掺杂率为20%(质量分数)的催化剂PAn-NaHSO4,并用于催化合成环己酮缩乙二醇,探讨了PAn-NaHSO4的催化活性,系统考察了醇酮摩尔比、催化剂用量、反应时间和带水剂用量对环己酮缩乙二醇收率的影响,并且用正交试验对反应条件进行了优化。在环己酮用量为0.1 mol,n(乙二醇)∶n(环己酮)=1.6∶1,催化剂用量占反应物总质量的1.2%,带水剂环己烷用量为9 mL,反应时间为2.5 h的条件下,产品收率可达96.79%,产品经红外光谱、气-质联用定性分析确定为环己酮缩乙二醇,经气相色谱检测纯度大于99.0%,催化剂重复使用5次后,产品收率仍大于90.0%。     

High capacitance properties of polyaniline by electrochemical deposition on a porous carbon substrate

Electrochemical deposition of polyaniline (PANI) is carried out on a porous carbon substrate for supercapacitor studies. The effect of substrate is studied by comparing the results obtained using platinum, stainless steel and porous carbon substrates. PANI deposited at 100 mV s⁻¹ sweep rate by potentiodynamic technique on porous carbon substrate is found to possess superior capacitance properties. Experimental variables, namely, concentrations of aniline monomer and H₂SO₄ supporting electrolyte are varied and arrived at the optimum concentrations to obtain a maximum capacitance of PANI. Low concentrations of both aniline and H₂SO₄, which produce PANI at low rates, are desirable. The PANI deposits prepared under these conditions possess network morphology of nanofibrils. Capacitance values as high as 1600 F g⁻¹ are obtained and PANI coated carbon electrodes facilitate charge-discharge current densities as high as 45 mA cm⁻² (19.8 A g⁻¹). Electrodes are found to be fairly stable over a long cycle-life, although there is some capacitance loss during the initial stages of cycling.     

Chemical synthesis of polyaniline in the presence of poly(amidosulfonic acids) with different rigidity of the polymer chain

Conducting polyaniline (PANI) was chemically synthesized in the presence of water-soluble aromatic polyamides containing sulfonic groups: poly-(p,p’-(2,2′-disulfonic acid)-diphenylene-tere-phthalamide) (t-PASA, rigid backbone), poly-(p,p’-(2,2′-disulfonic acid)-diphenylene-iso-phthalamide) (i-PASA, semi-rigid backbone) and their copolymer (co-PASA) with the monomers ratio 1:1, as well as in the presence of flexible-backbone polyacids: poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA) and poly(styrene sulfonic acid) (PSSA). In these conditions the matrix polymerization of aniline results in the formation of water-soluble interpolymer complexes of PANI with the above cited polyacids. The character of spectral changes in the UV, visible and near IR (UV-Vis-NIR) range during the synthesis and the polymerization rates depend strictly on the structure of polyacid matrix. Higher flexibility of the polyacid backbone (PAMPSA, PSSA) contributes to higher relative absorption of localized polarons (750 nm), while in the spectrum of interpolymer complexes with rigid-chain polyacid (t-PASA) the absorption of delocalized polarons (1300-1500 nm) prevails. The complexes with semi-flexible i-PASA and co-PASA exhibit intermediate behavior. The results are interpreted in terms of differences in the inter-chain interactions in the interpolymer complexes of different structure. Fourier transform infrared (FTIR) spectroscopy data support the assumption of the incorporation of the polyacids in the PANI through an interaction between sulfonic groups of the polyacids and nitrogen atoms of PANI. Spectroelectrochemical and electrochemical (cyclic voltammetry) studies of the films cast from the obtained solutions showed that the formation of quinoid units at high oxidation level is retarded in the interpolymer complexes of PANI with rigid- and semi-rigid-chain polyacids. Atomic force microscopy (AFM) and direct current (DC)-conductivity data are also presented.     

Solid-state NMR study of N labelled polyaniline upon reaction with DPPH

The quantitative investigation of the radical scavenging properties of polyaniline (PANI) upon reaction with excess of the stable DPPH radical (a 4:1 ratio of DPPH to aniline units in the polymer) was carried out using ¹⁵N and ¹³C solid state NMR spectroscopy. During the process the polyaniline was oxidised so that the imine content increased from 45 to 65%. The extent of oxidation measured by NMR was confirmed by N1s XPS analysis. However, within a 30 min reaction time, about 85% of the DPPH radicals were scavenged as monitored by the decay in its EPR signal. This is about 20 times greater than the fraction of DPPH required to oxidize PANI from an imine content of 45-65%. An identification of further redox processes is required to explain the high degree of radical scavenging. At the same time, there was no evidence of significant chemical binding or trapping of DPPH in the PANI structure.     

Controllable synthesis of MnO2/polyaniline nanocomposite and its electrochemical capacitive property

Polyaniline (PANI) and MnO₂/PANI composites are simply fabricated by one-step interfacial polymerization. The morphologies and components of MnO₂/PANI composites are modulated by changing the pH of the solution. Formation procedure and capacitive property of the products are investigated by XRD, FTIR, TEM, and electrochemical techniques. We demonstrate that MnO₂ as an intermedia material plays a key role in the formation of sample structures. The MnO₂/PANI composites exhibit good cycling stability as well as a high capacitance close to 207 F g⁻¹. Samples fabricated with the facile one-step method are also expected to be adopted in other field such as catalysis, lithium ion battery, and biosensor.     

Precise synthesis of polymers containing functional end groups by living ring-opening metathesis polymerization (ROMP): Efficient tools for synthesis of block/graft copolymers

This article summarizes recent examples for precise synthesis of (co)polymers containing functional end groups prepared by living ring-opening metathesis polymerization (ROMP) using molybdenum, ruthenium complex catalysts. In particular, this article reviews recent examples for synthesis of amphiphilic block/graft copolymers by adopting transition metal-catalyzed living ROMP technique. Unique characteristics of the living ROMP initiated by the molybdenum alkylidene complexes (so-called Schrock type catalyst), which accomplish precise control of the block segment (hydrophilic and hydrophobic) as well as exclusive introduction of functionalities at the polymer chain end, enable us to provide the synthesis of block copolymers varying different backbones by adopting the “grafting to” or the “grafting from” approach as well as “soluble” star shape polymers with controlled manner. The “grafting through” approach (polymerization of macromonomers) by the repetitive ROMP technique offers precise control of the amphiphilic block segments.     

Preparation,characterization and anticorrosive properties of a novel polyaniline/clinoptilolite nanocomposite

Nanocomposite of polyaniline (PANI) with natural clinoptilolite (Clino) was prepared. Formation of nanocomposite and incorporation of polyaniline in the clinoptilolite channels was confirmed and characterized using FTIR spectroscopy studies, X-ray diffraction (XRD) pattern, scanning electron microscopy (SEM) and cyclic voltammetry techniques. The anticorrosive properties of a 20 μm thickness coating of PANI/Clino nanocomposite with various weight ratios (1, 3 and 5%, w/w) of clinoptilolite content on iron coupons was evaluated and compared with pure polyaniline coating. According to the results in acidic environments PANI/Clino nanocomposite has enhanced corrosion protection effect in comparison to pure polyaniline coating. Comparative experiments revealed that PANI/Clino nanocomposite with 3% (w/w) clinoptilolite content has the best protective properties. Further experiments showed that the PANI/Clino nanocomposite has considerably different corrosion protection efficiencies in various corrosive environments.     

Rapid polymerization initiated by redox initiator for the synthesis of polyaniline nanofibers

High quality polyaniline nanofibers have been synthesized by a rapid polymerization of aniline using ammonium peroxydisulfate (APS)/Fe²⁺ redox initiator as the oxidant without any hard or soft templates. The addition of Fe²⁺ in conventional polymerization system plays an important role in changing the bulk morphologies of polyaniline from irregular particle agglomerates to nanofibers. Open-circuit potential measurements indicate that the rate of polymerization of aniline with the aid of Fe²⁺ ions has a substantial increase. The influences of synthetic parameters, such as the concentrations of aniline, dopant, and redox initiator, and reaction time, on the sizes and morphologies of polyaniline nanostructures have been investigated for elucidating the formation of polyaniline nanofibers. Fourier transform infrared spectrum, UV-vis spectrum, and cyclic voltammograms reveal that the molecular structures and electrochemical properties of polyaniline nanofibers do not differ significantly from that of conventional polyaniline.     

Electrochemical synthesis of polyaniline films on zinc-cobalt alloy deposited carbon steel surface in sodium oxalate

Polyaniline (PANI) coatings were electropolymerized on zinc-cobalt alloy deposited carbon steel (CS/ZnCo) electrode from an aqueous sodium oxalate solution using three different scan rates in cyclic voltammetric technique. Scanning electron microscopy (SEM) was used to analyze the surface morphology of the polymer film. The SEM images showed that the increase in scan rate induced an increase in grain size of the PANI film. The corrosion behavior of CS/ZnCo electrodes with and without PANI film in 3.5% NaCl solution were investigated through electrochemical impedance spectroscopy (EIS) and anodic polarization studies. The results of the study showed that the PANI coatings provided significant and effective protection for the CS/ZnCo electrode, in preventing corrosion. In addition, the PANI film that was synthesized at a high scan rate, exhibited the best anti-corrosive performance due to the formation of protective oxide layers through its catalytic efficiency.     

The synthesis of polymeric sulfides by reaction of dihaloalkanes with sodium sulfide

Several poly(alkylene sulfide)s have been synthesized in excellent yields from reactions of α,ω -dibromo- and/or α,ω-dichloroalkanes with sodium sulfide nonahydrate under reflux conditions. The procedure is general, simple and convenient for the production of various poly(alkylene sulfide)s and the way reaction parameters influence the properties of the polymers formed has been examined.

     

Electrochemical synthesis of polyaniline in the presence of poly(amidosulfonic acid)s with different rigidity of polymer backbone and characterization of the films obtained

We have studied electrochemical matrix polymerization of aniline in the presence of poly(amidosulfonic acid)s of different nature: poly(2-acrylamido-2-methyl-1-propanosulfonic acid) (PAMPSA, flexible backbone); poly(p,p′-(2,2′-disulfoacid)-diphenylene-iso-phthalamid) (i-PASA, semi-rigid backbone); poly(p,p′-(2,2′-disulfoacid)-diphelylene-tere-phthalamid) (t-PASA, rigid backbone). Also, we have investigated spectral and electrochemical properties of the films obtained, as well as their surface morphology. The matrix polymerization results in the formation of interpolymer complexes of polyaniline (PANI) and the above-cited polyacids. The acceleration of aniline electropolymerization in the presence of poly(amidosulfonic acid)s was observed due to association of aniline molecules to sulfonic groups of the polyacid and higher local concentration of protons near the polyacid backbone. The rigid-chain polyacids interfere with the normal course of the electropolymerization, which manifests itself in the changes of the shape of time dependences of absorbance and charge. Cyclic voltammetry and spectroelectrochemical experiments showed that the formation of interpolymer complex with rigid-chain polyacids distorts spectroelectrochemical characteristics of PANI. This evidently results from steric hindrances in the formation of quinoid units.