Bekir Sari

Electrochemical copolymerization of pyrrole and aniline

Abstract This study covers the synthesis of homopolymers, copolymers and composites of aniline and pyrrole in nitrogen atmosphere using various solvent and supporting electrolytes. With the objective of examining the structure of the samples and analysing their properties, FT-IR spectra were taken, thermogravimetric analysis (TGA) was done and scanning electron microscopy (SEM) was used for microstructural analysis. The conductivity of each sample was determined through the four-probe method. Magnetic susceptibility measurements on the Gouy scale indicated that the polymers were diamagnetic. Hence, the synthesized polymers were found to contain no unpaired electrons. Homopolymerization and copolymerization reactions were carried out in an acetonitrile medium, using LiClO 4 as supporting electrolyte, in a perchloric acid medium and in a sulfuric acid medium separately, in order to analyse the effects of solvent and supporting electrolytes. As a result, the change of medium was observed to have a significant effect on the structure and properties of the resulting homopolymers. Similarly, in bilayer synthesis, changing the order of coating was observed to affect the structure and properties of samples, either partially or fully, based on the synthesis medium. For instance, coating polyaniline (PAn) over polypyrrole (PPy) in an acetonitrile + LiClO 4 medium or a water + H 2 SO 4 medium yielded composite samples, while coating PPy over PAn in the same media yielded copolymer samples. The resulting samples, however, turned out to be composites regardless of the order of coating, when the same synthesis was repeated in a HClO 4 medium.

Synthesis and Characterization of Polyindole/Poly(vinyl acetate) Conducting Composites

Composites of a polyindole (PIN) and poly(vinyl acetate) (PVAc) were prepared chemically using FeCl3 as an oxidant agent in anhydrous media. The composite compositions were altered by varying the indole monomer during preparation. The composites were characterized by FTIR and UV‐visible spectroscopies, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), stress‐strain experiments and conductivity measurements. Moreover, the film of PVAc and PIN/PVAc composites were prepared by casting on glass Petri dishes to examine their stress‐strain properties. PIN/PVAc composites are thermally more stable than PIN. It was found that the conductivities of PIN/PVAc composites depend on the indole content in the composites.

Electrochemical synthesis and characterization of homopolymers of polyfuran and polythiophene and bipolymer films polyfuran/polythiophene and polythiophene/polyfuran

In this study, conductive homopolymers and bipolymers of thiophene and furan were synthesized electrochemically in an anhydrous medium in a nitrogen atmosphere using LiClO4 as the supporting electrolyte and their properties (conductivities, surface structures, thermal properties) were analyzed. Homopolymers coated onto each other in different orders were also investigated. FTIR spectra were taken to analyze structural properties. Surface analyses of polymers were clarified by scanning electron microscopy (SEM). Electrochemical properties were determined using cyclic voltammetry (CV). We found that polythiophene/polyfuran (PT/PF) and PF/PT bipolymers formed a bilayer structure. To investigate the effect of the polymerization medium on the polymer structure, the conductivities of polymers were determined by the four-probe technique and magnetic properties were analyzed via Gouy scale measurements. PF and PT homopolymers and PF/PT and PT/PF bipolymers were found to have a bipolaron nature. As a result, and as shown by thermogravimetric analysis, bipolymers have higher decomposition temperatures than the homopolymers and are thermally stable.

Synthesis, Characterization and Electrorheological Properties of Polyindene/Kaolinite Composites

In this study, synthesis, characterization and electrorheological (ER) properties of polyindene (PIN) and polyindene/kaolinite composites were carried out by cationic radical polymerization using FeCl3 as the oxidizing agent. The homopolymer and composites, containing different amounts of PIN were characterized by FTIR spectroscopy, thermo‐gravimetric (TGA) analyses, scanning electron microscopy (SEM) and dynamic light scattering (DLS) methods. The conductivity and dielectric properties of PIN and PIN/kaolinite composites were determined. Suspensions of PIN and PIN/kaolinite composites were prepared in silicone oil (SO), at a series of concentrations (c=5–25 m/m %). The effects of concentration, shear rate, electric field strength, frequency, temperature and promoter on ER activities of suspensions were investigated.

Synthesis of Some Polymer‐Metal Complexes and Elucidation of their Structures

In this study, the nine coordination polymers of Fe(III), Co(II) and Ni(II) salts have been synthesized using polyacrylamide (PAA), polt(ethylene glycol) (PEG) and poly(vinyl alcohol) (PVA) and their structures were characterized by magnetic and conductivity measurements, ultraviolet‐visible (UV‐VIS), FTIR spectroscopy and thermogravimetric analysis (TGA). The structures of Fe(III) complexes in the all coordination polymers were found as tetrahedral. The structures of PAA‐Co(II) coordination polymer was determined as octahedral geometry whereas PEG‐Co(II) and PVA‐Co(II) complexes showed as tetrahedral structure. PAA‐Ni(II) and PEG‐Ni(II) complexes have octahedral geometry, whereas PVA‐Ni(II) has a square planar structure. Besides, the stress‐strain experiments of PVA‐metal coordination polymers obtained rubber‐like structure were carried out and the value of breaking‐strain of PVA‐Ni(II) complex was found to be about 17% of vulcanized natural rubber. The conductivities of the resulting polymer‐metal complexes were measured by four‐probe technique and were found in the range 10−5−10−6 Scm−1. Thus, it was suggested that they can be used in the field potential application of conducting polymers. TGA results revealed that among the complexes PEG‐Fe(III) and PVA‐Fe(III) complexes have the highest thermally stable.

Electrochemical Polymerization of Aniline at Low Supporting-Electrolyte Concentrations and Characterization of Obtained Films

Conductive polymers of aniline were synthesized in aqueous acidic media such as perchloric, sulfuric, hydrochloric, phosphoric, and trifluoroacetic acids and the effect of supporting electrolyte was investigated. The conductivity of each polyaniline (PAn) sample was determined by the four-probe technique. PAn (H2SO4) sample was shown to have the highest conductivity, specifically, 3.55 S cm–1. The effect of concentrations of monomers and acids on the conductivity of PAns was studied. It was observed that the conductivity decreased with increasing aniline concentration and increased with increasing sulfuric acid concentration. The conductivities of PAn (CF3COOH) were also investigated in different supporting electrolytes and highly good increments of its conductivities were obtained. Magnetic properties of the PAn salts were analyzed by Gouy balance measurements and it was found that their conducting mechanisms are of bipolaron nature. From the FTIR analysis it was found that polymerization occurs via the –NH2 group in a head-to-tail mechanism. The thermal analyses revealed that PAn (HCl) among the PAn salts studied shows the highest thermal stability. Surface analyses of polymers were clarified by scanning electron microscopy. From elemental analysis results, PAn salts were concluded to be in emeraldine structure.

Conducting Composites and Blends of Polythiophene and Polyoxymethylene

Abstract Conductive polyoxymethylene/polythiophene (POM/PT) composites and PT/POM blends were prepared by in situ chemical polymerization using FeCl3 oxidant and mixing in solutions, respectively. It was found that the properties of the composites and blends were different from those of homopolymers and also from each other. Formation of polymer and composites was supported by FT-IR analyses. According to the results of thermal analyses (TGA), it was shown that polymers and composites have good thermal stability. The thermal degradation temperature of POM/PT composite containing 88% PT is higher than those of the other composites. The thermal degradation temperature of PT/POM blend containing 27% POM was described as higher than that of the other blends. The morphological structures of polymers and composites were studied by scanning electron microscopy (SEM). It was found that morphological structures of composites were smoother than that of PT. The crystal structures of polymers and composites were investigated by X-ray diffraction analysis. It was found that the crystal regions increased with increasing amount of POM in the composites and blends.

Conducting Polyaniline Sensors for Some Organic and Inorganic Solvents

Abstract Polyaniline (PAn) emeraldine salts (PAn-Cl, PAn-Br, PAn-ClO4) were synthesized by the electrochemical method using different acids (HCl, HBr, HClO4). PAn salts in pellet form were used as sensors for organic (EtOH, CHCl3, C6H6) and inorganic (HCl, NH3) solvents. Electrical conductivity responses of PAns to five solvents were investigated. The change of electrical conductivity of PAns (Δσ), relative to the value measured before exposure, varied with the solvent used. The sensor properties of PAns varied depending on the nature of dopant anions such as the type and size. It was found that PAn-ClO4 has the highest sensing power on HCl, NH3, and CHCl3, and it has the lowest sensing power on C6H6.

Effect of synthetic route on structural and morphological properties of poly(thiophene- co -indole)

In this study, homopolymers of polythiophene (PT), polyindole (PIN) and their composites and copolymers were synthesized by chemical polymerization and were characterized by FTIR and UV-spectroscopy, and conductivity measurements. The conductivities of polymers, composites and copolymers were measured by a conventional four probe method at room temperature and different temperatures. Among the products, PT-PIN copolymer which was synthesized at polythiophene conditions revealed the highest conductivity with a value of 0.28 S cm−1. The thermal properties of the samples were investigated by using thermogravimetric analyses, and it was found that they have quite good thermal stability. X-ray diffraction spectra showed that the amorphous nature of the polymers. Morphological properties of the polymers, composites and copolymers have been investigated by scanning electron microscopy.

Electrorheology and creep-recovery behavior of conducting polythiophene/poly(oxymethylene)-blend suspensions

Electrorheological properties and creep-recovery behavior of polythiophene/polyoxymethylene-blend having PT(50%)/POM(50%) composition were investigated. Particle size, conductivity and dielectric values were measured to be 24.77 μm, 3.85 × 10−5 S·m−1 and 26.75, respectively. Sedimentation ratio was measured to be 64% at the end of 16 days. The effects of dispersed particle volume fraction, external electric field strength, shear rate, frequency and temperature on ER properties and storage modulus of PT/POM-blend/silicone oil (SO) suspensions were examined. Enhancement were observed in the electric field viscosities of the suspensions and thus they were classified as a smart material. Shear thinning non-Newtonian viscoelastic behavior was determined for PT/POM-blend/SO system. Further, time-dependent deformation was examined by creep-recovery tests and recoverable viscoelastic deformation established.