Polyaniline Oligomers Research Articles

Morphology studies of polyaniline lengthy nanofibers formed via dimers copolymerization approach

In this paper, two different aniline dimers, N-phenyl-1,2-phenylenediamine (2-PPD) and N-phenyl-1,4-phenylenediamine (4-PPD) were used as starting monomers in polyaniline (PANI) synthesis. It was found that 2-PPD dimer alone produced only an amorphous PANI oligomer with a flaky morphology, while the 4-PPD provided either linear nanofiber or a spaghetti-like hollow nanofiber structures comprising of worm-like fibril subunits. By adjusting the molar fed ratio of 4-PPD to 2-PPD in the copolymerization, long PANI nanofibers with length up to tens of microns, bundled together by single PANI fibrils with diameter ca. 3–5 nm, was formed. A possible formation mechanism was proposed taking account of the reactivity difference at positions 4 and 2 on the 4-PPD and 2-PPD, respectively.

Miscibility and physical properties of conducting poly(urea‐urethane) thermoplastic elastomers

AbstractA series of amine‐terminated polyaniline oligomer (OPA)‐based conducting poly(urea‐urethane) thermoplastic elastomers (PUUs) was synthesized by two‐stage solution polymerization and characterized by FTIR. Various percentages of OPA were introduced into PUUs as chain extenders to form hard segments of PUUs with urea‐linkages. Spectroscopic and differential scanning calorimetry, as well as dynamic mechanical analysis, were conducted to elucidate the interaction and degree of miscibility between hard and soft segments, which were related to the stress–strain properties of PUUs. The hydrogen bonding index (HBI) measured by FTIR was employed to show the degree of interchain hydrogen bonding. Copolymer films with higher OPA content exhibit higher HBI and the degree of miscibility is significantly improved. The resultant conducting copolymers have higher tensile strength, higher Young's modulus, and lower elongation at break, because of the long rigid structure of OPA and the increase in the number of hydrogen bonds among the copolymers blocks. Incorporating OPA in PUUs increases the mass of the residue at temperatures over 600°C, according to thermogravimetric analysis. The conductivity of PUUs is found to range from 0.83 S/cm for neat OPA to 6.11 × 10−5 S/cm for PUUs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3803–3810, 2007

X‐ray photoelectron and carbon Kα emission measurements and calculations of O‐, CO‐, N‐, and S‐containing substances

AbstractX‐ray fluorescence measurements for O‐containing [polyethylene oxide, polyvinyl alcohol, polyvinyl methyl ether], CO‐containing [polyvinyl methyl ketone, polyethylene terephthalate], N‐containing [poly‐4‐vinylpyridine (P4VP), polyaniline oligomer (PAO)], and S‐containing [polyphenylene sulfide] substances are presented. Carbon Kα X‐ray emission spectra (XES) and X‐ray photoelectron spectra (XPS) are compared with our DFT calculations performed with the Amsterdam density functional (ADF) program. The combined analysis of valence XPS and carbon Kα XES allows us to determine the individual contributions from pσ‐ and pπ‐bonding molecular orbitals of the polymers. The ΔSCF calculations yield the accurate C1s core‐electron binding energies (CEBEs) for all carbon sites of the organic compound. We calculate all CEBEs of the model molecules using the ΔEKS approach. Our simulated C1s photoelectron and C Kα emission spectra are in good agreement with our measurements. We also obtain WD (work function and the other energies) values for the polymers and PAO from the difference between calculated (gas‐phase) and measured (solid) CEBE values. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 162–172, 2007

DNA-Directed Assembly of Polyanilines: Modified Cytosine Nucleotides Transfer Sequence Programmability to a Conjoined Polymer

A series of polyaniline (PANI) oligomers was constructed from monomer units covalently linked to duplex DNA through N-(2-aminoethyl) groups bonded through cytosines. DNA oligomers containing the aniline monomers were treated with horseradish peroxidase (HRP) and H2O2 under conditions known to cause polymerization of aniline. No change in the absorption spectrum of the DNA was observed for samples containing fewer than four contiguous aniline groups. However, for oligomers containing four, five, or six aniline units, treatment with HRP and H2O2 led to the appearance of absorption features characteristic of the conducting "proton doped" emeraldine oxidation state of PANI. Molecular modeling shows that the DNA is distorted in the region of the PANI, but flanking regions of the DNA maintain their B-form structure. These findings provide a method to exploit the self-recognition, self-assembly, and sequence programmability of DNA for the formation of conducting polymers.

Theoretical Study of the Influence of Monomer Excess on the Structure and Properties of Polyaniline Oligomers

Polyaniline is among the most intensely investigated polymers because of its exceptional properties affording its current and potential applications. The structure and energy spectra of isolated oligomers and infinite chains in different oxidation states and degrees of protonation have been discussed at length from experimental and theoretical perspectives. The reaction environment effect, however, has received less attention and, particularly, the influence of monomer excess has been completely neglected in theoretical studies. Experimental measurements show that residual aniline is always detected in emeraldine samples obtained at low pH. Upon addition of oxidant to emeraldine PANI samples, post-polymerization due to the presence of excess monomers occurs. This is an indication of the formation of aniline-PANI complexes in the reaction medium. The presence of aniline monomers should affect the PANI chain arrangement and optical/conducting characteristics. Therefore, model clusters of aniline with neutral or singly protonated emeraldine tetramers in explicit water medium and periodic boundary conditions are addressed in this paper using a Monte Carlo/AMBER96/AM1 computational protocol to simulate the absorption spectra. The monomer impact on the structure, energy characteristics, and UV/vis spectra of the polymer are discussed.

Resolution of the binding configuration in nitrogen-doped carbon nanotubes

Nitrogen-doped carbon nanotubes ($\mathrm{N}$-doped $\mathrm{CNTs}$) were synthesized by exposing $\mathrm{CNTs}$ under high input power nitrogen plasma $(3.1\phantom{\rule{0.3em}{0ex}}\mathrm{kW})$, using a microwave plasma enhanced chemical vapor deposition system. In the analysis of high resolution transmission electron microscopy, it was found that graphene layers of the $\mathrm{N}$-doped $\mathrm{CNTs}$ became seriously curved, waved, or buckled, and even contained fullerene-like structures, in contrast to the parallel concentric graphene layers in the normal $\mathrm{CNTs}$. X-ray photoelectron spectroscopy $(\mathrm{XPS})$ and electron energy loss spectroscopy $(\mathrm{EELS})$ were combined to resolve the binding configurations of nitrogen and carbon in the $\mathrm{N}$-doped $\mathrm{CNTs}$. In the $\mathrm{XPS}$ study, it may be concluded that the $\mathrm{N}$-doped $\mathrm{CNTs}$ have three binding configuration types (poly 4-vinylpyridine, poly 9-vinylcarbazole, and poly aniline oligomer) using the method proposed by [F. L. Normand, J. Hommet, T. Sz\or\'enyi, C. Fuchs, and E. Fogarassy, Phys. Rev. B. 64, 235416 (2001)] $\mathrm{EELS}$ results showed that the incorporation of nitrogen into the $\mathrm{CNTs}$ would induce $s{p}^{2}$ binding for carbon atoms, similar to the results in amorphous carbon nitride films [J. Hu, P. Yang, and C. M. Leiber, C. Ronning, H. Feldermann, R. Merk, and H. Hofs\asPhys. Rev. B 57, 3185 (1998); , Phys. Rev. B 58, 2207 (1998)]. $\mathrm{N}\phantom{\rule{0.3em}{0ex}}1s$ core-level downshift of $\ensuremath{\sim}1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ in the $\mathrm{XPS}$ analyses was mainly caused by the screening effects of core holes in the $\ensuremath{\pi}$ bond around nitrogen atoms.

Analysis of polyaniline oligomers by laser desorption ionization and solventless MALDI

Analysis of polyaniline oligomers by laser desorption ionization and solventless MALDI

Analysis of polyaniline oligomers by laser desorption ionization and solventless MALDI

While direct laser desorption ionization of soluble polyaniline dried onto metal sample plates results in mass spectra that are similar to previously shown electrospray ionization data of similar samples, laser desorption of unsolubilized solid polyaniline results in major fragmentation of the phenyl rings. Solventless MALDI, a recently developed technique for insoluble or slightly soluble species, involves the use of only solid analyte and matrix during sample preparation. Solventless MALDI of solid polyaniline results in mass spectra that are similar to the direct laser desorption ionization spectra of the soluble oligomers with some larger molecular weight oligomers also being detected. Based on the matrix used, different series of polyaniline with dissimilar end groups are detected. The matrix also affects the percentages of benzenoid and quinoid units in the oligomers. Thus, solventless MALDI appears to be a promising new technique for the mass spectrometric analysis of low solubility, but industrially important, polyanilines.

Synthesis and characterization of low molecular weight oligomers of soluble polyaniline by electrospray ionization mass spectrometry

Mass spectrometry (MS) has not been utilized extensively for its ability to analyze the structure of polyaniline. This has been a result of polyaniline not being directly soluble in MS-“friendly” solvents. Here, low molecular weight oligomers of polyaniline are synthesized, using a modified room temperature synthesis of polyaniline, that are soluble in solvents that are better suited to electrospray MS analysis. Oligomers up to the 9-mer are identified from the mass spectra. Importantly, several different types of polyaniline oligomers that differ from one another based on their end groups were distinguished in the mass spectra. The use of tandem mass spectrometry (MS/MS) enabled identification of these various end groups.

An electronic tongue using polypyrrole and polyaniline

An electronic tongue composed of six different sensing units: a bare interdigitated electrode, and interdigitated electrodes coated with stearic acid (SA), a polyaniline oligomer (16-mer), polypyrrole (PPy) and mixtures (1:1, w/w) of 16-mer/SA and PPy/SA, was able to distinguish salt, sweet, bitter and acidic solutions. The films were deposited by the Langmuir–Blodgett (LB) technique onto interdigitated electrodes, and impedance studies were performed over the frequency range 20–10 5 Hz. The sensor is able to distinguish between different brands of mineral water, tea and coffee and can also differentiate tastants below the human detection threshold, proving that conducting polymers are useful sensing materials and transducers for this sort of application.

A comparative study of intermolecular interactions in the crystal structures of phenyl/phenyl end-capped oligoanilines.

Three crystal structures have been analysed from the point of view of intermolecular interactions: N,N'-diphenyl-1,4-benzoquinone diimine, C(18)H(14)N(2), (I), its reduced form N,N'-diphenyl-1,4-phenylenediamine, C(18)H(16)N(2), (II), and N,N'-diphenyl-1,4-phenylenediammonium bis(p-toluenesulfonate), C(18)H(18)N(2)(2+) x 2C(7)H(7)O(3)S(-), (III), which contains fully protonated (II) with p-toluenesulfonic acid. The local molecular C(i) symmetry is preserved in all three structures and the packing seems to be dominated by the mutual arrangement of the simple polyaniline oligomers in the different protonation states. In (I), the most significant molecular interactions are stacking forces, forming columns of molecules along [001]. Close packing of the columns results in C-centering of the structure. In (II), only van der Waals interactions can be observed. In the structure of (III), the p-toluenesulfonate ions serve as acceptors in relatively strong N[bond]H...O hydrogen bonds. The N,N'-diphenyl-1,4-phenylenediammonium cation intercalates between two anions related by a centre of symmetry.

Artificial Taste Sensor: Efficient Combination of Sensors Made from Langmuir−Blodgett Films of Conducting Polymers and a Ruthenium Complex and Self-Assembled Films of an Azobenzene-Containing Polymer

An artificial tongue composed of four sensors made from ultrathin films deposited onto gold interdigitated electrodes has been able to distinguish easily the four basic tastes (salty, sour, sweet, and bitter), in addition to detecting inorganic contaminants in ultrapure water and identifying different brands of coconut water. Some tastants were detected below the human threshold values, for example, 5 mM of NaCl or sucrose. Suppression of quinine by sucrose was also detected. The high sensitivity may be partially attributed to the ultrathin nature of the films as the sensors were produced with Langmuir−Blodgett films of the 16-mer polyaniline oligomer, polypyrrole, and a ruthenium complex and with self-assembled films of an azobenzene-containing polymer. The sensor response was evaluated with ac measurements taken at various frequencies, with the admittance being treated theoretically with an equivalent circuit representing the sensor immersed in a polyelectrolyte solution.

Theoretical study of protonation effects in polyaniline oligomers

We study the electronic properties of eight-ring, phenyl-capped oligomers of polyaniline, in different oxidation states. The study was conducted through the Quantum Chemistry technique AM1 and comprised unrestricted ground state geometry optimization, for reduced and oxidized oligomers, including simulation of protonation. We find that oxidation induces linearization and planarization of the backbone, as expected. The protonation and biprotonation processes induce a pronounced charge concentration (over ∼2-3 rings), which is accompanied by localized chain distortion and characterizes polaron defects.

Semi-empirical study of chain conformation and absorption spectra of polyanilines: size, solvent and disorder effects

In this paper, we present electronic structure calculations and conformational studies of polyaniline oligomers to investigate the influence of oligomer size, oxidation state and solvent effects in the UV–Vis absorption spectrum. Torsional barrier and solvent effect calculations are carried out within AM1 semi-empirical technique. Absorption spectra are simulated through ZINDO/S-CI calculations. Based on the analysis of the torsion potential curves, an interpretation is given for the diverse thermochromic behavior observed in insulating polyanilines as a function of oxidation state. Pernigraniline base, the fully oxidized form of polyaniline, has been reported to present an unusual redshift in its spectrum with increasing temperature. The potential energy associated to ring twisting calculated for pernigraniline exhibits a double well shape, which is different from the potentials obtained for the other forms. We concluded that the chain flexibility depends strongly on the oxidation state and is the source of the diverse chromic behavior.

From Polyaniline Oligomers to Conducting Organic Crystals

From Polyaniline Oligomers to Conducting Organic Crystals

Calculations of Band Gaps in Polyaniline from Theoretical Studies of Oligomers

Geometries and band gaps of polyaniline oligomers up to decamer have been systematically calculated and analyzed using various computational techniques such as molecular mechanics, semiempirical, and ab initio methods. On the basis of fully optimized geometries of neutral and charged forms of polyaniline oligomers, excitation energies are calculated at the semiempirical ZINDO (INDO/S) level and extrapolated to the band gap value of the infinite chain. Band gaps are also approximated by extrapolating the HOMO/LUMO difference calculated at the density functional level (B3LYP/6-31G*). The ZINDO//AM1 band gaps in the reduced and oxidized form of polyaniline (4.3 and 2.7 eV) are in good agreement with experimental values (3.8 ± 2 and 1.8 ± 3 eV, respectively). The doped form of polyaniline (two positive charges per four aniline units) has been computed with a spin-unrestricted method (UAM1) and the band gap approximated from an extrapolation of the tetramer and octamer. The calculated band gap of 1.3 eV (UZIND...

RRS characterization of selected oligomers of polyaniline in situ spectroelectrochemical study

Electrochemical, optical and vibrational properties of two oligomeric model compounds of emeraldine salt (ES), the only electrically conducting form of polyaniline, in nonaqueous solution are studied. The phenyl-end-capped dimer and tetramer of leucoemeraldine base are electrochemically oxidized in acetonitrile solution and the electrogenerated species are investigated using spectrophotometry and Resonance Raman Scattering (RRS). In situ resonance Raman study of the oligomers reveals the appearance of the vibrational bands characteristic of the semiquinoid units, and in particular of the CN bond intermediate between the single and double CN bonds which are strongly resonantly enhanced with a red excitation line. The vibrational assignments of the fundamental modes of the electrogenerated species are reported and compared with those of the corresponding polymeric form. Our Raman results provide very interesting information not only about the vibrational properties of emeraldine salt but also about its electronic configuration.

HREELS study of vapor-deposited polyaniline on Ag(110)

Ultra-thin films of polyaniline on Ag(110) were characterized using high-resolution electron energy loss spectroscopy (HREELS) in the vibrational and electronic loss regimes. The films were grown in situ by chemical vapor deposition using an emeraldine source. Initially, short polyaniline oligomers adsorb on the surface followed by polymerization to form longer polyaniline chains. The loss spectra in the far-infrared region indicate that the films become highly conducting upon protonation. In addition, the role of the substrate in the initial stages of polymer film growth is demonstrated by comparison with polyaniline on Cu and Au surfaces.

Polyaniline synthesis: influence of powder morphology on conductivity of solution cast blends with polystyrene

Synthesis of polyaniline (PANI) was performed under different conditions followed by dedoping, redoping with dodecyl benzene sulfonic acid (DBSA) and then blending with PS. The morphologies of the as-polymerized, doped and blended PANI were studied. The main polymerization stages seem to include: PANI oligomers assembling into nuclei, nuclei growing into primary particles (10 nm), primary particles assembling into aggregates (≈0.5 μm) and aggregates assembling into agglomerates (≈10 μm). The morphology of the as-polymerized PANI was found to be strongly related to the rate of oxidant addition, synthesis duration and synthesis temperature. This morphology dominates the effects of DBSA doping and dispersing the resulting PANI–DBSA in the matrix polymer. A fine PANI–DBSA powder with weakly bound aggregates is likely to disperse well in a solvent and hence promote the formation of the desired fine-network morphology and yield a low percolation threshold and high conductivity. Synthesis at a high oxidant addition rate, an excess of oxidant, a relatively high polymerization temperature and a short synthesis duration should diminish the tendency to form dense complex structures. These dense structures prevent efficient DBSA doping, deaggregation and the desired fine-network dispersion of PANI–DBSA in the blends.

Composite Langmuir Monolayers and Langmuir−Blodgett Films from 16-Mer Polyaniline

The formation of Langmuir monolayers and Langmuir−Blodgett films is reported for the first time for a polyaniline oligomer, 16-mer, that was mixed with cadmium stearate. The processibility of this oligomeric material was greatly improved as compared to the parent polyaniline, which allowed one to use common solvents like chloroform as the spreading solvent. Analogously to composite polyaniline monolayers, the stability and the transferability are found to depend on the 16-mer content in the composite film, with poor stability and low transfer ratios above 60% of 16-mer. Deposited Langmuir−Blodgett films were found to be undoped (or only weakly doped) since they were obtained from monolayers spread onto aqueous subphases (pH = 6.0). Uniform Langmuir−Blodgett (LB) deposition was confirmed by optical microscopy and UV−vis spectra whose intensity increased linearly with the number of layers deposited and also with the 16-mer content. Fourier transform infrared (FTIR) results revealed that cadmium stearate was...