Preparation and characterization of chemically synthesized poly(N-methylaniline)

Poly(N-methylaniline) (PNMA), a electrically conductive derivative of polyaniline was synthesized by chemical polymerization of N-methylaniline (NmANI) using ammoniumpersulfate (APS) as an oxidizing agent and studied by electrical conductivity measurement, UV–vis and FTIR spectroscopy. The observed electrical conductivity was found to have a dependence on some synthesis parameters. The oxidant/monomer molar ratio ∼1 and p-toluenesulfonic acid (PTSA)/monomer molar ratio ∼4 showed higher values of electrical conductivity for the polymer. The d.c. conductivities of PTSA doped poly(N-methylaniline) have been measured in the temperature range 298–373 K. The conductivity of the samples has been observed to show an increasing trend with increasing temperature. However, on increasing temperature from 298 K to 373 K, the conductivity rise was found to be more for the samples having lower dopant/monomer ratio. The observed d.c. conductivity data was described by Mott's three-dimensional variable range hopping (VRH) model.     

Onset of thermal degradation in poly(p-phenylene vinylene) films deposited by chemical vapor deposition

We report on the thermal degradation characteristics of heat treated poly(p-phenylene vinylene) (PPV) films deposited using chemical vapor deposition. It was found that no decrease in the thickness of the films (110 nm) occurred after isothermal heat treatment in vacuum at 450 °C for up to 1 h, while films treated at 500 °C for 1 h decreased to 70% of their original thickness. In situ mass spectrometry during heat treatment of the film at 500 °C showed the release of significant amounts of material including toluene and xylene ion fragments. However, Fourier transform infrared spectroscopy shows no significant change in bond structure, indicating that the decrease in film thickness after heat treatment is due to release of material and densification, not crosslinking or bond breaking.     

Insoluble poly(anthranilic acid) confined in Nafion membrane by chemical and electrochemical polymerization of anthranilic acid

Self-doped polyaniline (PANI) possesses superior electrochemical properties and processability in relation to the PANI due to an acid group substituted on the polymer backbone. However, the polar acid group causes the self-doped PANI to undergo dissolution in aqueous, in particular, acidic solutions. To prevent the solubility, poly(anthranilic acid), PANA, is confined in the cavities of the Nafion membrane by a novel electrochemical as well as a conventional chemical polymerization of anthranilic acid. The PANA is characterized by electrochemical, optical, spectroscopic and scanning electron microscopic studies.     

Preparation and characterization of graphene nanosheets/poly(3-hexylthiophene) thermoelectric composite materials

Graphene nanosheets/poly(3-hexylthiophene) (GNs/P3HT) composites were prepared by oxidative polymerization of 3-hexylthiophene in a GNs dispersed chloroform solution. The phase composition of the composite materials was analyzed by X-ray diffraction and Fourier transform infrared spectra. The thermoelectric properties of the cold pressed composite pellets with different GNs loadings were measured at room temperature. As the GNs loading increased from 0 to 30 wt.%, the electrical conductivity of the composites dramatically increased from ∼10⁻⁶ to ∼1.2 S/cm while the Seebeck coefficient slightly increased from 33.15 to 35.46 μV/K. The highest power factor (∼0.16 μW m⁻¹ K⁻²) was obtained in the 30 wt.% GNs/P3HT composite material.     

Design and synthesis of poly(p-phenylenevinylene) derivative with triphenylamine segments on polymer backbone

A new approach to the synthesis of conjugated polymer with triphenylamine (TPA) segments was presented. Electrochemical reversibility and thermal stability were found for this polymer. The introduction of TPA segments to the polymer backbone has modified its optical and electrochemical properties. The estimated highest occupied molecular orbital (HOMO) of 5.4 eV from electrochemical measurement suggested that it could be a low hole injection barrier when used as the active layer in the polymer LED. High brightness emission and improved efficiency were obtained in a double-layer device.     

Deposition of biodegradable poly (d,l-lactic acid) films using aerosol-assisted method

Biodegradable polymers have received increasing interests for biomedical applications. The surface morphology of biodegradable polymer films plays an important role for their applications in cell growth and tissue engineering. The conventional processes for the preparation of biodegradable polymer films are mainly based on solution-casting and melting methods, which are time-consuming and tend to be uncontrollable. For a better control of the surface morphology, an aerosol-assisted deposition process has been developed for the deposition of biodegradable poly (d,l-lactic acid) (PDLLA) films. It involves atomizing and transporting polymer fine droplets towards a heated substrate. With the evaporation of solvent, PDLLA films can be deposited rapidly on the substrate. In the aerosol-assisted deposition process, the thickness of the films can be controlled by the deposition time, and the surface morphology of the films is adjustable from highly porous to dense structure.     

Effect of alkyl side-chain length and solvent on the luminescent characteristics of poly(3-n-alkylthiophene)

In poly(3-n-alkylthiophene) (P3AT), the length of alkyl side chain as well as the solvent used for film casting affected the conformation and eventually the luminescent characteristics of the polymers. When the length of alkyl side chain was shorter than 12 carbon atoms, the electronic absorption and PL spectra of P3AT film showed red shift as the length of the alkyl side chain increased. This is because, when the length of the alkyl side chain is not too long, solvation is promoted with increase in the length of the alkyl side chain, leading to expanded chain structures with longer π-conjugation lengths. Conversely, when the length of the alkyl side chain was longer than 12 carbon atoms, the electronic absorption and PL spectra of P3AT film showed blue shift as the length of the alkyl side chain increased. This is because, when the length of the alkyl side chain is too long, the steric hindrance becomes predominant leading to highly distorted chain conformation with shorter π-conjugation lengths. The PL intensity of the film cast from THF was higher by an order of magnitude than that of the film cast from chloroform, toluene, or p-xylene. In the P3AT films cast from a poor solvent such as THF, the polymer chains are highly distorted leading to high PL intensity due to exciton localization. In the EL spectra of P3AT films cast from various solvents, λ_max shifted as much as 140 nm depending upon the solvent characteristics. This result demonstrates that the color of EL can be varied from blue to orange simply by casting the same polymer from a different solvent.     

Synthesis and characterization of efficient orange-red emitting poly(p-phenylenevinylene) derivatives with 1,3,4-oxadiazole unit

A series of the statistical copolymers of tetradecyloxy-3,5-bis-{2-(4-bromo-phenyl)-[1,3,4]oxadiazole}-benzene (4), 1,4-didecyloxy-2,5-diiodobenzene (5) and 1,4-dodecyloxy-2,5-divinylbenzene (6), for efficient light emitting diode were synthesized. As the feed ratio of compound 4 decreased, the absorption band at 320–360 nm decreased in the UV–vis spectra. In addition, as the composition of compound 4 decreased, the absorption intensity ratio at 1541 cm⁻¹ decreased in the FT-IR spectra. The photoluminescence and electroluminescence emission color of P showed green-yellow color (λ_max = 552 nm). However, the maximum wavelength of photoluminescence and electroluminescence of P1 and P2 were 581 and 583 nm, respectively, which were dramatically red-shifted than that of P. Moreover, these values were almost the same as the values of P3 (580 nm). It is concluded that the energy transfer from high energy oxadiazole segments to low energy alkoxy-PPV segments occurred completely. The efficiency of ITO/P2/Al was 0.0181%, which is the best efficiency among the device based on the copolymers. This is presumably due to that P2 has the best balanced hole- and electron-injection/transporting properties among the copolymers.     

The effect of the carbon nanotubes surface oxidation on the morphology and properties of poly(N-vinylcarbazole) coated multi-walled carbon nanotube nanocables

This article describes the effect of carbon nanotubes (CNTs) outer surface oxidation on the morphology and properties of poly(N-vinylcarbazole) (PNVC)-coated individual multi-walled CNT (MWCNT) nanocables. Surface oxidation of MWCNTs has been carried out by refluxing MWCNTs with 5 M nitric acid (HNO₃) at 80 °C for 1 h. The PNVC-coated MWCNT nanocables are synthesized by in situ solid-state polymerization of N-vinylcarbazole monomers in the presence of oxidised MWCNTs (o-MWCNTs) at an elevated temperature. The PNVC-coated MWCNT nanocables are characterized by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning and transmission electron microscopes, photo-luminescence spectroscopy, and direct-current conductivity measurements. Results show that the uniform nanolayer coating of PNVC decreases the inherent bulk conductivity of MWCNTs, but significantly increases the optical properties of MWCNTs.     

Enhanced chain order and dependence of the linear absorption of poly (p-phenylenevinylene) on the solution environment of its precursor polymer

A large change in the linear absorption spectrum of poly (p-phenylenevinylene) (PPV) occurs when it is prepared from freshly synthesized and undialysed poly(sulfonium chloride) salt. The red shift of the linear absorption maximum of the PPV is 30-50 nm compared to that obtained from dialysed prepolymer. Subsequent changes in the chain order, as monitored by the changes in the linear absorption spectrum of the converted PPV, have been investigated as a function of solvent, time and temperature. The use of water in the polysulfonium ion synthesis is critical for the attainment of high chain order. Water was also found to be better than methanol in preserving the chemical and conformational integrity of the precursor salts. The observed effects of water have been attributed to its high ionizing and solvating ability, and a lower nucleophilicity compared to methanol.