Polyaniline Derivatives Research Articles

Development of a novel cyano group containing electrochemically deposited polymer film for ultrasensitive simultaneous detection of trace level cadmium and lead

Poly(diphenylamine-co-2-aminobenzonitrile) (P(DPA-co-2ABN)), a cyano group containing conducting polyaniline derivative, has been electrodeposited developed as the new material and utilized for the simultaneous electrochemical determination of trace levels of cadmium (Cd2+) and lead (Pb2+). P(DPA-co-2ABN) film preconcentrates effectively through cyano chelation and electrochemically strips the heavy metal ions with well separated potentials, which are beneficially utilized for ppb level simultaneous detection of Cd2+ and Pb2+. Differential pulse voltammetry studies revealed that Cd2+ and Pb2+ ions were simultaneously stripped with well-defined, separated and sharp peaks for Cd2+ and Pb2+. The influence of various operational parameters such as pulse amplitude, pulse time, scan rate, initial potential, end potential, accumulation potential and accumulation time on the electrochemical stripping of heavy metals were investigated in details. Under the optimal conditions, good linear correlations were obtained from 1.26 to 907.8ppm for Cd2+ and 0.26 to 58.73ppm for Pb2+, respectively. Low detection limits for Cd2+ and Pb2+, 0.255ppm and 0.165ppm, respectively, were observed. The practical utility of the new procedure was demonstrated in real samples.

Potential of magnetic nanoparticles for targeted drug delivery

Nanoparticles (NPs) play an important role in the molecular diagnosis, treatment, and monitoring of therapeutic outcomes in various diseases. Their nanoscale size, large surface area, unique capabilities, and negligible side effects make NPs highly effective for biomedical applications such as cancer therapy, thrombolysis, and molecular imaging. In particular, nontoxic superparamagnetic magnetic NPs (MNPs) with functionalized surface coatings can conjugate chemotherapeutic drugs or be used to target ligands/proteins, making them useful for drug delivery, targeted therapy, magnetic resonance imaging, transfection, and cell/protein/DNA separation. To optimize the therapeutic efficacy of MNPs for a specific application, three issues must be addressed. First, the efficacy of magnetic targeting/guidance is dependent on particle magnetization, which can be controlled by adjusting the reaction conditions during synthesis. Second, the tendency of MNPs to aggregate limits their therapeutic use in vivo; surface modifications to produce high positive or negative charges can reduce this tendency. Finally, the surface of MNPs can be coated with drugs which can be rapidly released after injection, resulting in targeting of low doses of the drug. Drugs therefore need to be conjugated to MNPs such that their release is delayed and their thermal stability enhanced. This chapter describes the creation of nanocarriers with a high drug-loading capacity comprised of a high-magnetization MNP core and a shell of aqueous, stable, conducting polyaniline derivatives and their applications in cancer therapy. It further summarizes some newly developed methods to synthesize and modify the surfaces of MNPs and their biomedical applications.

Influence of substituents in electrochemical and conducting properties of polyaniline derivatives and multi walled carbon nanotubes nanocomposites

Poly(o-methoxyaniline) and poly(o-methylaniline) were synthesized by oxidative polymerization in the presence of multi-walled carbon nanotubes (MWNT) for the fabrication of chloroform processable nanocomposites obtained by embedding MWNT in the polymer matrix without the formation of covalent bonds. The study of pressure–area isotherms highlighted different substituents along the aromatic rings affected the packing grade of macromolecules when spreading on different subphases in relation to the associated sterical hindrance. The presence of MWNT inside the polymer matrix showed to favor a more stretched conformation of macromolecules with a subsequent increment of area/molecule values with respect to the corresponding pure conducting polymers. Furthermore, the sterical hindrance affected the nanocomposite electrochemical properties and conducting polymers containing less hindering substituents along the aromatic rings turned out to be faster electrochemical systems. Less hindering substituents were also able to enhance the conducting properties of nanocomposite materials in association with MWNT.

Asymmetric hollow fibre membranes based on ring-substituted polyaniline and investigation towards its gas transport properties

A more soluble polyaniline derivative, i.e. poly(o-anisidine), (POAn), was synthesized in-house for this study by using an ortho substituted aniline monomer. It was observed that the prepared dope solution was more homogeneous with less visible agglomerates as compared to previously prepared polyaniline (PAni) solution. Integrally skinned hollow fibre membranes were successfully prepared by dry-jet wet spinning from POAn with N-methyl-2-pyrrolidone as a solvent and a more volatile tetrahydrofuran as a co-solvent for gas separation. The spinning air-gap lengths were varied to promote the formation of the membrane skin layer. POAn membranes prepared at higher air gap were more orientated with packed structure and good gas separation characteristics. They showed selectivities of O2/N2, CO2/N2, H2/N2 and H2/CO2 of about 13, 89, 370 and 4.2, respectively with permeation rates of H2, CO2 and O2 about 10.4, 2.5 and 0.37×10−6cm3 (STP)/cm2scmHg, respectively. Presence of methoxy group in POAn showed substantial enhancement in gas permeation properties compared to previously developed PAni membranes. The H2/N2 and CO2/N2 selectivities were improved by 3 and 7 times, respectively as compared to PAni membranes. Development of hollow fibre membranes using polyaniline derivative with improved processability and excellent gas separation performance depicts their potential for industrial gas separation applications.

Coordinative Layer-by-Layer Assembly of Electrochromic Thin Films based on Metal Ion Complexes of Terpyridine-Substituted Polyaniline Derivatives

Preparation, metal ion complexation, and coordinative assembly into organized electro-chromic films of a polyaniline derivative P1 substituted with tert-butyloxycarbonyl (boc) and terpyridine (tpy) substituent groups in alternating sequence are described. Cleavage of the boc groups after processing into thin films is also described. P1 is prepared upon Pd-catalyzed polycondensation of N-tert-butyloxycarbonyl-4,4'-dibromodiphenylamine and 4'(4-aminophenyl)-2,2':6,2''-terpyridine. The molecular weight is in the range of oligomers, the tetramer and pentamer being the most abundant species. P1 is soluble in common organic solvents. Solutions are pale yellow with blue or green fluorescence depending on the solvent. Fluorescence quantum yields up to 68% are found. P1 is able to complex divalent metal salts such as zinc(II) chloride, for example. Titration experiments indicate the formation of 2:1 tpy:metal ion complexes. Layer-by-layer (LbL) assembled films of metal ion complexes of P1 can be prepared, if negatively charged substrates are alternately dipped into solutions of metal(II) hexafluorophosphates and P1. Films of the zinc and nickel ion complex of P1 are lemon yellow in the neutral state and change color into greenish gray upon anodic oxidation, while Co-containing films are purple and change color into grayish blue upon oxidation. All color changes are reversible under ambient conditions. ATR-IR studies indicate that thermal treatment of the films at 180 °C, or acid treatment, e.g. with 5% aqueous trifluoroacetic acid solution, results in cleavage of the boc groups. P1 is transformed into the polyaniline derivative P2 with tpy substituent groups at every second N atom in the backbone. Films of metal ion complexes of P2 are also electrochromic albeit the colors differ slightly from those of P1. For example, the absorption maximum of the Zn-P2 film is at 456 nm, whereas it is at 446 nm for the corresponding Zn-P1 film. Prior to cleavage of the boc group, electrochromic switching times are 1.1 to 2.0 s for 30 to 40 nm thick films, while after the cleavage 0.5 to 1.2 s are found. The contrast is 13 to 19%, and not affected by the cleavage. Because of high stability, fast switching, and high contrast, the films might be useful as active materials in electrochromic devices.

Chemical synthesis and characterization of self-doped N-propanesulfonic acid polyaniline derivatives

In chemical oxidative homopolymerization of aniline-N-propanesulfonic acid, ammonium persulfate has been used as an oxidant to obtain water-soluble and self-acid-doped polyanilines. Copolymerization of aniline-N-propanesulfonic acid with aniline, using three feed molar ratios of comonomers has been studied, as well. The polymers and copolymers had moderate molecular weights and were soluble in water and polar solvents. They have been obtained in self-acid-doped form, as has been evidenced by UV–Vis spectroscopy, as green-colored materials, and can be de-doped with alkaline solutions. The propanesulfonic groups had not cleaved during the oxidative polymerization and the atomic ratio between nitrogen and sulfur atoms (N/S) was determined by X-ray photoelectron spectroscopy which was consistent with the chemical structure. The chemical structures and morphologies of the homo- and copolymers have been studied by FTIR, 1HNMR, UV–Vis, thermogravimetric analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction methods. The X-ray diffraction patterns of the homo- and copolymers have showed a high degree of crystallinity which can be explained by the ionic interaction between propanesulfonate anions and the amine nitrogen atoms of the main chain, resulting in the layering structure of the polyaniline chains. Electrical conductivity of the homopolymer determined at room temperature on pressed pellet was 0.0038 S/cm, while the copolymers show higher conductivities compared with homopolymer.

UV-induced modulation of the conductivity of polyaniline: towards a photo-patternable charge injection layer for structured organic light emitting diodes

In macromolecular electronics the organic material should offer—besides the desired electronic properties—the possibility of lateral patterning. Here, we report on a novel polyaniline derivative bearing photosensitive N-formamide groups. UV illumination of this polymeric material leads to a decarbonylation reaction resulting in polyaniline which can be subsequently protonated to yield the conductive emeraldine salt. Due to the fact that the conductivity depends on the conversion of the photoreaction, a selective adjustment of the conductivity by means of UV light is feasible. These photo-induced conductivity changes were corroborated in thin films by conductive AFM measurements. Further, we demonstrate the versatility of this polymer with respect to a patterned modification of the conductivity as well as its application as a photo-patternable charge injection layer for structured OLEDs. This makes the new polymer an interesting candidate for electrodes and interconnects in various organic electronic devices.

Microplates with Adaptive Surfaces

Here we present a new and versatile method for the modification of the well surfaces of polystyrene microtiter plates (microplates) with poly(N-phenylethylene diamine methacrylamide), (poly-NPEDMA). The chemical grafting of poly-NPEDMA to the surface of microplates resulted in the formation of thin layers of a polyaniline derivative bearing pendant methacrylamide double bonds. These were used as the attachment point for various functional polymers through photochemical grafting of various, for example, acrylate and methacrylate, polymers with different functionalities. In a model experiment, we have modified poly-NPEDMA-coated microplates with a small library of polymers containing different functional groups using a two-step approach. In the first step, double bonds were activated by UV irradiation in the presence of N,N-diethyldithiocarbamic acid benzyl ester (iniferter). This enabled grafting of the polymer library in the second step by UV irradiation of solutions of the corresponding monomers in the microplate wells. The uniformity of coatings was confirmed spectrophotometrically, by microscopic imaging and by contact angle measurements (CA). The feasibility of the current technology has been shown by the generation of a small library of polymers grafted to the microplate well surfaces and screening of their affinity to small molecules, such as atrazine, a trio of organic dyes, and a model protein, bovine serum albumin (BSA). The stability of the polymers, reproducibility of measurement, ease of preparation, and cost-effectiveness make this approach suitable for applications in high-throughput screening in the area of materials research.

Studies on Conductivity and Optical Properties of Poly(o-toluidine)-ferrous Sulfate Composites

Poly(o-toluidine) (POT), a derivative of polyaniline, has been synthesized by chemical oxidative polymerization. The synthesized POT is doped with ferrous sulfate. The dc conductivity of POT samples in pellet form is measured in the temperature range of 30°–100°C and is found to increase with temperature, showing the semiconductor nature of the samples. The samples are characterized by UV-visible and FT-IR spectroscopy, and X-ray diffraction pattern. UV-visible studies reveal that direct optical transitions exist in the samples. The X-ray diffraction pattern of powder POT shows semicrystalline nature. FT-IR studies provide information on structural changes in the backbone of POT with chemical doping.

Structural, Optical And Gas Evolution Studies Of 60 MeV Si5+ Ion Irradiated PoT-PVC Blends

Swift Heavy Ion (SHI) irradiation induces chemical and structural changes in polymers by evolving various gases and gaseous fragments. The evolution of gases as a result of chain scissoring and bond breaking leads to cross-linking and cluster formation. Study of the evolved gases helps in understanding the various chemical and structural changes occurring within the polymer under the effect of SHI irradiation. In the present work, Poly (o-toluidine) (PoT), a derivative of polyaniline, is prepared by chemical oxidation polymerization and is blended with polyvinylchloride (PVC) to achieve self supported films. These PoT-PVC blend films were irradiated by 60 MeV Si 5+ ions at different fluences and evolved gases were monitored on-line by Residual Gas Analyzer (RGA). Pre and post irradiation FTIR, UV-Visible absorption and XRD studies have been carried out on these films to observe the changes in chemical/structural and optical properties. An effort has been made to correlate the evolved gases and structural properties after irradiation.Copyright © 2011 VBRI press.

Alkyd coatings containing polyanilines for corrosion protection of mild steel

A study was carried out to investigate the performance of anti-corrosion coatings obtained from alkyd paints containing polyaniline and polyaniline derivatives applied on carbon steel. The polyaniline, the polyaniline derivates and the paints were characterized through FTIR and Raman spectroscopies and thermogravimetric analysis. Cyclic voltammetry studies showed that polyaniline and its derivates gave electroactive properties to the paints. Accelerated corrosion experiments (salt spray and humidity chamber) revealed a significant improvement in the performance of the coatings which contained the electroactive polymer compared to conventional coatings. These results were verified by evaluation of the electrical resistance and capacitance measurements of the films using electrochemical impedance spectroscopy. For some of the samples, the Raman spectra demonstrated the presence of an oxide layer at the coating/substrate interface composed basically of Fe2O3 and Fe3O4. The results of this study reinforce the possibility of protecting carbon steel against corrosion through the formation of a protective layer of oxides using coatings which contain electroactive polymers.

Design, synthesis and characterization of a novel self‐doped polyaniline derivative

AbstractA type of self‐doped polyaniline derivative was successfully synthesized using an oxidative coupling polymerization approach. The structure of the electroactive polymer was investigated using Fourier transform infrared and 1H NMR spectroscopy and gel permeation chromatography. Its thermal and spectral properties were characterized using thermogravimetric analysis and UV‐visible spectroscopy. The electrochemical activity of the polymer was studied using cyclic voltammetry (CV) in 1.0 mol L−1 H2SO4 solution with various scan rates. The peak current increases linearly with scan rate from 10 to 120 mV s−1, which indicates that the electrode reaction is controlled by a surface process. In addition, the self‐doped characteristic was investigated using CV in 1.0 mol L−1 KCl solution with pH value changing from 1 to 12, and the results indicate that the polymer has excellent electrochemical activity even in neutral and alkaline environments. Copyright © 2010 Society of Chemical Industry

Poly(o-anisidine)–polystyrene composite fibers via electrospinning process: Surface morphology and chemical vapor sensing

The electrospinning technique was utilized to produce camphorsulfonic acid (CSA) doped poly(o-anisidine) (POA)–polystyrene (PS) composite fibers in the non-woven mat form with different fiber characteristics, depending on the proportion of components in spinning solutions. CSA doped POA–PS composite fibers were fabricated onto interdigited gold substrates for use as chemical vapor sensors. The resultant composite fiber sensor responded to high polar volatile chemicals by showing a decrease in electrical resistance during the sensing measurement. The sensitivity of the composite fiber sensor when exposed to water vapor was higher than that of the composite fiber sensor subjected to ethanol vapor due to high polarity together with low vapor pressure of water compared with those of ethanol. The surface morphology of the non-woven composite fiber mat after chemical vapor sensing was unchanged. This work opens up the possibility of using the derivatives of polyaniline as a component in composite fibers for chemical sensing applications by taking advantages of their good solubility in common solvents as well as detectable electrical changes in terms of the relatively small amount of composite fibers needed.

Synthesis and characterization of polyaniline derivatives and related carbon nanotubes nanocomposites – Study of optical properties and band gap calculation

Poly(o-methylaniline) (POTO), poly(o-methoxyaniline) (POAS), poly(2,5-dimethylaniline) (PDMA), poly(2,5-dimethoxyaniline) (PDOA), and nanocomposite based on multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) embedded in these conducting polymers, were synthesized by oxidative polymerization. We used the Langmuir–Schaefer (LS) technique to fabricate films at the air–water interface and performed the doping process on the undoped films by dipping the substrates in 1 M hydrochloric acid (HCl) aqueous solution. We recorded UV–vis spectra for both the undoped and doped forms and calculated the related band gaps by using the Tauc equation. Experimental data showed the substituents affected the final oxidation ratio of the polymer chains and the presence of carbon nanotubes (CNTs) in the medium of reaction changed the properties in relation of the kind and number of substituents along the aromatic ring. The study of UV–vis spectra of the undoped nanocomposites and the calculated band gaps highlighted that the conducting polymer chains simply wrapped up around CNTs with no strong interaction. Both the kind and number of substituents along the aromatic rings strongly affected the protonation process, since their capability of “tuning” the formation of the polaronic state. The presence of CNTs in the polymer matrix showed no appreciable influence in the chemical properties of the doped nanocomposites with respect to the pure conducting polymers.

Helical opposition in poly(2-methoxyaniline) by tuning the concentration of salts in reaction solution

The synthesis and application of helical polyaniline derivatives (PANIs) have attracted much interest. However, most of these syntheses have been carried out in organic solutions. In our previous reports, helical PANIs were successfully realized in aqueous solution. Because helical architecture in the backbones of PANIs is an induced rather than the natural arrangement, it is significant to study the change in helicity in aqueous solution, especially opposition or reversion. One excess-handed helicity was induced in poly(2-methoxyaniline) (PMOA) by electrochemical polymerization of 2-methoxyaniline at pH = 2.5 in the presence of protonated β-cyclodextrin sulfate (CDS− H+). When 0.04 mol L−1 NaCl was added to the reaction solution, the PMOA backbone took on an opposite excess of one-handed helicity, which was confirmed by induced circular dichroism. Such a result originates from the dynamic switch between electrostatic and hydrogen-bonding interactions. The helix-inducing process in PMOA depends on the interaction between PMOA and chiral CDS. Due to the competition of Na+ Cl− with PMOA+ CDS−, the electrostatic interaction between PMOA and CDS is limited or weakened. Thus, the slightly preferred interaction between them switches from electrostatic to hydrogen bonding. Simultaneously, the interaction positions and distance are changed. The changed steric hindrance induces PMOA into adopting an opposite excess-handed helicity. Copyright © 2010 Society of Chemical Industry

Effect on Structure, Processability, and Conductivity of Poly(m-aminophenol) of the Initial Acidity/Basicity of the Polymerization Medium

Poly(m-aminophenol) was synthesized chemically from aqueous solutions of the monomer meta-aminophenol (mAP) in the initially acidic or basic medium by using ammonium persulfate as an oxidant. The polymer (PmAPA) synthesized in initially aqueous HCl medium was insoluble in organic solvents even after dedoping, while the polymer (PmAPB) synthesized in initially aqueous NaOH solution was found to be soluble in high pH water, dimethyl sulfoxide (DMSO), and dimethylformamide. It was possible to obtain a stable, free-standing film from the DMSO solution of PmAPB but, due to insolubility and infusibility, film casting was not possible for PmAPA. The synthesized polymers were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analyses, X-ray diffraction spectroscopy, and four-probe DC electrical conductivity. A ladder-type structure was formed during the chemical polymerization of mAP in aqueous HCl, while a hydroxyl derivative of polyaniline was obtained in aqueous NaOH. The conductivity of sulfuric acid-doped PmAPB was 104 times higher than that of in situ HCl-doped PmAPA. An explanation of the difference in properties of both polymers is given based on molecular modeling.

Self-dispersed polyaniline derivative extending electrochemical activity to neutral media

Self-dispersed poly-N-[5-(8-quinolinol)ylmethyl]aniline, which can be easily dispersed in some organic solvents without any dispersant, has been prepared by oxidative polymerization of 5-(anilinomethyl)-8-hydroxyquinoline. Although its conductivity only reaches 1.45 × 10 −3 S cm −1, it possesses good redox reversibility in aqueous electrolyte ranging from pH 1.0 to 7.0, and its cyclic voltammetry curves also show good cycling stability in the aqueous medium of pH 5.0. It will be a promising material for several applications such as biosensors due to increasing the operating pH window in aqueous media.

A comparative Raman spectroelectrochemical study of selected polyaniline derivatives in a pH-neutral solution

Selected conducting polymers (polyaniline and poly- N-methylaniline), and copolymers of aniline with o-, m-, and p-phenylenediamines, as well as with metanilic acid, have been electropolymerized at a gold electrode, and studied with Raman spectroscopy (532 nm excitation) in a pH-neutral solution. Characteristic Raman features have been obtained and analysed for (co)polymers within electrode potential range of −0.4 to 0.2 V vs. Ag/AgCl. Changes in Raman spectra depending on electrode potential have been analysed and assigned to different redox forms of (co)polymers. It has been shown that both oxidised and reduced forms of (co)polymers can exist, depending on electrode potential, even in a pH-neutral solution, where most of the polymers studied show no clearly defined electrochemical redox processes.

Electrosynthesis Thermodynamic Study of the Poly (o-methoxyaniline) POMA

Over the past 15 years, conducting polymers have been studied as additives with excellent potential for application in the processing of materials used in the areas of electromagnetic interference and microwave absorption, Members of this new class of materials called "synthetic metals", have one thing in common: long systems p conjugates, ie, shifting single and double bonds along the chain. The obvious interest is to combine in a single material the electrical properties of a semiconductor or metal with the advantages of a polymer. Poly-methoxianilyne, POMA is a group of derivatives of polyaniline obtained by the polymerization of aniline sulfonic. In these work we studied via electrochemical synthesis the thermodynamic parameters of polymerization reaction of POMA, the polymer obtained was characterized via Raman, DSC and UV-vis. The thermodynamic parameters involved in the electropolymerization as Gibbs free energy, entropy and equilibrium constant were determined

Methanol oxidation on the polymer coated and polymer-stabilized Pt nano-particles: A comparative study of permeability and catalyst particle distribution ability of the PANI and its derivatives

The electrosynthesis and characterization of poly (aniline and aniline derivatives) on the pretreated aluminum (Al/Pt) and platinum plated aluminum (Al–Pt) electrodes were investigated. The results show that the both of them are suitable substrates as well as smooth Pt and platinum plated Pt (Pt–Pt) for fabrication of polymer modified electrodes. Comparative study of permeability of the freshly deposited polyaniline and polyaniline derivatives on the smooth Pt and Al–Pt or Pt–Pt substrates towards the methanol were done. The electrooxidation of methanol was studied by cyclic voltammetry in 0.1 M sulfuric acid as supporting electrolyte. Enhanced electrocatalytic activity towards the methanol oxidation was noticed when the bulk Pt and Al–Pt or Pt–Pt were covered by polyaminoanilines and polyhydroxyanilines films due to the permeability of their films for methanol molecules. A high catalytic current related to oxidation of methanol was found for the polymer modified electrodes when Pt nano-particles were embedded into the polymer films referred to as polymers-stabilized Pt nano-particles. The enhanced electrocatalytic activity might be due to the dispersion of Pt nano-particles into the polymer matrixes and the synergistic effects between the dispersed Pt particles and their matrixes.