Electrosyntheses of poly(neutral red), a polyaniline derivative

The electrochemical oxidation of neutral red in 0.5 mol dm⁻³ H₂SO₄ solution was carried out by using repeated potential cycling between −0.20 and 1.20 V (versus SCE). The polymer film was electrochemically deposited on a platinum anode and had an electrochemical activity in the solution of 0.5 mol dm⁻³ Na₂SO₄ with pH ≤ 4.0. The result from the X-ray photoelectron spectroscopy (XPS) experiment shows that the anions can be doped into the polymer film during the electropolymerization reaction of neutral red. The scanning electron microscopy (SEM) micrograph shows the surface of poly(neutral red) film deposited on the platinum foil is covered with a micro-structured network of mass interwoven fibers with a diameter of 2-4 μm. A straight fiber of the unsystematic micro-fibers is longer than 0.4 mm. The UV-vis spectrum and infrared spectrum (IR) of the polymer are different from those of the monomer.     

Electrosynthesis of poly(neutral red) incorporated with ferrocenesulfonic acid

The electrochemical oxidation of neutral red in 0.5 mol dm⁻³ sulfuric acid and 0.2 mol dm⁻³ ferrocenesulfonic acid solution was carried out using repeated potential cycling between −0.20 and 1.40 V (versus SCE). The polymer film was electrochemically deposited on a platinum anode and had an electrochemical activity in the solution of 0.5 mol dm⁻³ Na₂SO₄ with pH ≤ 7.0. The result from the X-ray photoelectron spectroscopy (XPS) experiment shows that the anions can be doped into the polymer film during the electrochemical polymerization reaction of neutral red. The scanning electron microscopy (SEM) micrograph shows that the surface of the resulting polymer film formed on the platinum foil is covered with a compact surface consisting of micro fibers. The visible spectrum and infrared spectrum (IR) of the polymer are different from those of the corresponding monomer. A possible chemical structure of the resulting polymer was also proposed.     

Preparation and characterisation of poly(3,4-ethylenedioxythiophene) and poly(3,4-ethylenedioxythiophene)/poly(neutral red) modified carbon film electrodes, and application as sensors for hydrogen peroxide

Poly(3,4-ethylenedioxythiophene) (PEDOT) films have been prepared for the first time on carbon-film electrodes (CFE) in aqueous solution using electropolymerisation by potential cycling, potentiostatically and galavanostatically. Characterisation of the modified electrodes was done by cyclic voltammetry and electrochemical impedance spectroscopy and the stability of the polymer films was probed. The coated electrodes were tested for application as hydrogen peroxide sensors, by oxidation and reduction. A novel polymer film was also formed by modification of CFE by co-electropolymerisation of EDOT and the phenazine dye neutral red (NR) – (PEDOT/PNR) with a view to enhancing the properties for sensor applications. It was found that hydrogen peroxide reduction at the PEDOT/PNR coated electrodes could be carried out at a less negative potential, the sensor performance comparing very favourably with that of other polymer-modified electrodes reported in the literature.     

Electrosynthesis and efficient electrocatalytic performance of poly(neutral red)/ordered mesoporous carbon composite

A novel composite film which contains ordered mesoporous carbon (OMC) along with the incorporation of poly(neutral red) (PNR) has been synthesized on glassy carbon electrode by potentiostatic method. This composite film was characterized by scanning electron microscope (SEM) and cyclic voltammetry (CV). Two pairs of the redox peaks appear at formal potential E^0′ = +0.045 V (peak I) and E^0′ = −0.49 V (peak II) at the PNR/OMC/GC electrode. And it is found that only the redox waves (peak I) exhibits good electrocatalytic activity towards nicotinamide adenine dinucleotide (NADH) and 2-mercaptoethanol (2-ME). Under a lower operation potential of +0.07 V, amperometry method was used to determine the concentration of NADH and 2-ME, respectively. In pH 7.0, sensors for two molecules under their corresponding optimized conditions were developed with acceptable sensitivity and low detection limits in large determination ranges. In addition, these sensors have good reproducibility and stability.     

Methanol electrooxidation on platinum microparticles electrodeposited on poly (o-methoxyaniline) films

In this paper we have studied the electrooxidation of methanol on electrodes obtained through the electrodeposition of platinum microparticles on poly (o-methoxyaniline) films. The dependence of the electroactivity on the electrodes preparation parameters has been detailed. It has been shown that the concentration of the monomer during the formation of the polymeric films influences the rate of polymer growth and the electrocatalytic activity. A maximum methanol electrooxidation peak current has been observed for polymers grown to an anodic voltammetric charge of approximately 75 mC cm⁻². It has been observed that the electroactivity increases when the platinum deposition is carried out in several steps instead of a single potential electrolysis. The conditions that favour a slower deposition process, i.e., smaller H₂PtCl₆ concentrations and smaller electrodeposition overpotential, lead to an enhancement of the methanol electrooxidation currents. This enhancement is attributed to an increase in the platinum surface area as a consequence of a decrease in the platinum particle size.     

Study by EQCM on the voltammetric electrogeneration of poly(neutral red). The effect of the pH and the nature of cations and anions on the electrochemistry of the films

Generation of poly(neutral red) films has been studied by means of the simultaneous measurements of current-potential and mass-potential curves during cyclic voltammetry (CV) experiments. It has been proved that the presence of molecular oxygen in the solution increases the amount of polymer deposited on the electrode. Otherwise, using the mass/charge ratio it is possible to obtain quantitative information about the electrodeposition by different procedures. It is observed that this ratio decreases when the amount of polymer electrogenerated increases, except when the polymer is not reduced and oxidised after its electrogeneration. The study of poly(neutral red) by CV and quartz crystal microbalance in solutions without monomer allows to discern between the role of different charged species which are present in the solution: salt cations (Cs⁺, Na⁺ and K⁺), salt anions (NO₃⁻, Cl⁻, I⁻ and Br⁻) and hydrated protons that can compensate electrical charge within the film during electrochemical processes.     

Synthesis and properties of polymer brush consisting of poly(phenylacetylene) main chain and poly(dimethylsiloxane) side chains

A novel polymer brush consisting of poly(phenylacetylene) (PPA) main chain and poly(dimethylsiloxane) (PDMS) side chains was synthesized by the polymerization of phenylacetylene-terminated PDMS macromonomer (M-PDMS). The macromonomer was prepared by the esterfication of monohydroxy-ended PDMS (PDMS-OH, degree of polymerization (DP) = 42) with p-ethynylbenzoic acid. The polymerization of M-PDMS using [(nbd)RhCl]₂/Et₃N catalyst led to polymer brush, poly(M-PDMS), with M_n up to 349?000 (DP of main chain 104). Poly(M-PDMS) with narrow molecular weight distribution (M_n = 39?900, M_w/M_n = 1.11) was obtained with a vinyl-Rh catalyst, [Rh{C(Ph)CPh₂}(nbd){P(4-FC₆H₄)₃}]/(4-FC₆H₄)₃P. Poly(M-PDMS)s were brown to orange viscous liquids and soluble in organic solvents such as toluene and CHCl₃. The UV-vis absorptions of poly(M-PDMS) were observed in the range of 350-525 nm, which are attributable to the PPA main chain.     

Poly(neutral red) as a NAD reduction catalyst and a NADH oxidation catalyst: Towards the development of a rechargeable biobattery

In this paper, we have established that poly(neutral red), PNR, functions as an electrocatalyst for the reduction and oxidation of NAD⁺/NADH in a rechargeable biobattery environment. The reversibility of this catalyst was possible only with the addition of Zn²⁺ for complexation to the redox polymer. The zinc ion complexation with the polymer facilitates electron and proton transfer to/from the substrate and the NAD⁺/NADH coenzyme without forming covalent bonds between the nicotinamide and the substrate surface. This research presents use of this reversible catalyst in a rechargeable biobattery. The rechargeable battery includes a Prussian blue cathode and a bioanode including NAD⁺-dependent alcohol dehydrogenase and zinc complexed PNR. This bioanode was coupled to the cathode with Nafion^® 212 acting as the ion exchange membrane separator between the two compartments. The biobattery has an open circuit potential of 0.545(±0.009) V when first assembled and 0.053(±0.005) V when fully discharged. However, when fully charged, the biobattery has an open circuit potential of 1.263(±0.051) V, a maximum power density of 16.3(±4.03) μW cm⁻³ and a maximum current density of 221(±13.2) μA cm⁻³. The efficiency and stability of the biobattery were studied by cycling continuously at a discharging rate of 1 C and the results obtained showed reasonable stability over 50 cycles.     

Thermal properties of poly(styrene-block-ε-caprolactone) in blends with poly(vinyl methyl ether)

The thermal characteristics of a styrene-ε-caprolactone diblock copolymer, P(S-b-CL), in blends with poly(vinyl methyl ether) (PVME) were studied by DSC. The glass transition temperatures show that PVME is only dissolved in the PCL block. It segregates from the PCL block at low temperatures. The addition of PVME leads to increasing crystallinity of the PCL block in a certain range of composition. However, degrees of crystallinity do not change significantly with crystallization temperature. Optical inspection revealed that the PCL block does not form spherulites. The crystallization kinetics of the PCL block has been systematically studied. The rate constants of crystallization for different blends decrease exponentially with crystallization temperature, whereas the rates of crystallization are scarcely affected by PVME content. The Avrami exponents were found close to two.     

Morphological study on three kinds of two-dimensional spherulites of poly(butylene terephthalate) (PBT)

Three kinds of thin film specimens, each of which containing one of the three types of two-dimensional poly(butylene terephthalate) (PBT) spherulites (i: usual-positive type, ii: usual-negative type, and iii: unusual type), were prepared and studied mainly by transmission electron microscopy. It was confirmed that all these kinds of spherulites are made up of only the α-modification crystals, and the growth directions for usual-positive type, usual-negative type, and unusual type are the [010]^∗, ^∗, and ^∗ directions in the reciprocal lattice, respectively. Furthermore, the arrangement of unit cell in each type of the spherulites was determined. The relationships between the arrangements of unit cell and the types of each resulting spherulite are discussed.     

Electrochemical synthesis of Pd particles on poly(vinylferrocenium)

Electrochemical synthesis of Pd particles on poly(vinylferrocenium) (PVF⁺) support was described. K₂PdCl₄ was used as the metal particle precursor. Pd particles were incorporated into the polymer matrix electrochemically either by cyclic voltammetric scans (between +1.0 V and −0.8 V vs. SCE) or by reduction at constant potential (at −0.8 V vs. SCE) from aqueous solution of K₂PdCl₄. Scanning electron microscopy (SEM) studies showed that the Pd particles were well dispersed in the polymer matrix. Experimental parameters such as polymer film thickness, number of cycles during cyclic voltammetric scans in K₂PdCl₄ and electrolysis time in K₂PdCl₄ were studied. The Pd/PVF⁺ system showed catalytic activity towards hydrazine oxidation and appreciable results were obtained when compared with the related studies.     

Electrocatalytic oxidation of methanol on carbon paste electrode modified by nickel ions dispersed into poly (1,5-diaminonaphthalene) film

Poly (1,5-diaminonaphthalene) film was prepared by using the repeated potential cycling technique in an acidic solution at the surface of carbon paste electrode. Then transition metal ions of Ni(II) were incorporated to the polymer by immersion of the modified electrode in a 1.0 M nickel chloride solution. The electrochemical characterization of this modified electrode exhibits stable redox behavior of the Ni(III)/Ni(II) couple. Also, cyclic voltammetric experiments showed that methanol electrooxidized at the surface of this Ni(II) dispersed polymeric modified carbon paste electrode [Ni/P-1,5-DAN/MCPE]. The mechanism of methanol oxidation changes from diffusion control at low concentration to a catalytic reaction at higher methanol concentration. The effects of both scan rate and methanol concentration on the anodic peak height of the methanol oxidation were discussed.     

Microstructural studies on BaCl2 doped poly(vinyl alcohol)

We have studied the effect of BaCl₂ dopant on the optical and microstructural properties of a polymer poly(vinyl alcohol) (PVA). Pure and BaCl₂ doped PVA films were prepared using solvent casting method. These films were characterized using FTIR, UV-visible, XRD and DSC techniques. The observed peaks around 3425 cm⁻¹, at 1733 cm⁻¹ and 1640 cm⁻¹ in the FTIR spectra were assigned to O-H, CC stretching and acetyle CO group vibrations, respectively. In the doped PVA shift in these bands can be understood on the basis of intra/inter molecular hydrogen bonding with the adjacent OH group of PVA. The UV-visible spectra shows the absorption bands around 196 nm and shoulders around 208 nm with different absorption intensities for doped PVA, which are assigned to n→π* transition. This indicates the presence of unsaturated bonds mainly in the tail-head of the polymer. Optical band energy gap is estimated using UV-visible spectra and it decreases with increasing dopant concentration. The powder XRD shows an increase in crystallinity in the doped PVA, which arises due to the interaction of dopant with PVA causing a molecular rearrangement within the amorphous phase of polymer. These modifications also influence the optical property of the doped polymer. The DSC study also supports increasing crystalline thickness and degree of crystallinity due to doping.     

Phase continuity and inversion in polystyrene/poly(methyl methacrylate) blends

Dual-phase continuity and phase inversion of polystyrene (PS)/poly(methyl methacrylate) (PMMA) blends processed in a twin-screw extruder was investigated using a selective extraction technique and scanning electron microscopy. Emphasis was placed on investigating the effects of viscosity ratio, blend composition, processing variables (mixing time and annealing) and diblock copolymer addition on the formation of bi-continuous phase structure (BPS) in PS/PMMA blends. The experimental results were compared with the volume fraction of phase inversion calculated with various semi-empirical models. The results showed that the formation of a BPS strongly depends on the blend composition and the viscosity ratio of the constituent components. Furthermore, BPS was found in a wide volume fraction interval. Increasing the mixing time and the addition of diblock copolymer, both led to a narrowing range of volume fraction in which BPS exists. Quiescent annealing coarsened the structure but indicated no qualitative changes. Some model predictions for phase inversion could predict qualitative aspects of the observed windows of co-continuity but none of the models could account quantitatively for the observed data.     

Photooxidative degradation of carboxylated poly(vinyl chloride)

Thin films of poly(vinyl chloride), PVC, and carboxylated poly(vinyl chloride), C-PVC, containing 1.8% of carboxyl groups were exposed to high energy ultraviolet radiation (λ = 254 nm) in laboratory conditions. The photochemical reactions in irradiated samples were studied by FTIR and UV–Vis spectroscopy, gel permeation chromatography and gravimetric estimation of insoluble gel. It was found that photodegradation and photocrosslinking in C-PVC is accelerated, whereas photodehydrochlorination is retarded comparing to these processes in PVC. Photooxidation investigated on the base of reaction leading to formation of hydroxyl groups is also more efficient in modified PVC. However, the total amount of carbonyl groups is much lower in UV-irradiated C-PVC than that in PVC. It indicates that competitive reactions (destruction of carboxyl groups and formation of new carbonyls) occur simultaneously in C-PVC chains. The influence of carbonyl groups on photochemical processes can be explained by an efficient Norrish I and II reactions as well as by energy transfer from absorbing species to weak chemical bonds.     

Polymer micelle-like aggregates of novel amphiphilic biodegradable poly(asparagine) grafted with poly(caprolactone)

Novel amphiphilic graft copolymers composed of poly(asparagine) (PAsn) as the hydrophilic backbone and poly(caprolactone) (PCL) as the hydrophobic segment were successfully synthesized by grafting PCL-HMDs to poly(succinimde). After tosylating PCL-diol with p-toluenesulfonylchloride (TsCl), tosylated poly(caprolactone) (PCL-OTs) was then reacted with hexamethylenediamine (HMD). The reaction of the amine terminated PCL with poly(succinimide) (PSI) and the following aminolysis resulted in poly(aspargine)-graft-poly(caprolactone) (PAsn-g-PCL). The degree of substitution (DS) and grafting reaction was confirmed by ¹³C NMR, FT-IR spectroscopy and elemental analysis. X-ray diffraction and DSC thermogram showed that the crystalline domain originated from PCL became apparent with an increase of DS. The amphiphilic comb-type graft polymer formed self-aggregates in aqueous solution when precipitated and dialysed against distilled water. Strong hydrophobic interaction of associated PCL grafts facilitated primary aggregate formation with DS, significantly reducing critical aggregation concentration and secondary aggregates also appeared in DLS measurements. Self-aggregates showed a bimodal size distribution originated from the self-aggregation and kinetically controlled particle aggregation, although the smaller primary aggregates was predominant. Spherical and dispersed aggregates of about 20 nm in diameter were observed by a transmission electron microscope.     

Different steps in the electrosynthesis of poly(3,4-ethylenedioxythiophene) on platinum

The initial stages of poly(3,4-ethylenedioxythiophene) (PEDOTh) film growth on platinum electrodes from TBAClO₄/acetonitrile solution are investigated by means of current-time transient measurements and tapping mode atomic force microscopy. It is shown that, for growth potentials in the range 1.17-1.29 V vs. SCE, the deposition process involves the formation of oligomers in the solution, progressive nucleation of centres of the new phase and three-dimensional growth of a first compact layer followed by a non-uniform distribution of granular-like clusters, whose number and size increase with the synthesis potential and charge. The obtained results reveal that PEDOTh films prepared at distinct potentials but with the same growth charge (Q_g) display similar electroactivities. They also depict that the electrochemical behaviour of the films is a function of the charge used for the synthesis, namely the reduction of tick PEDOTh layers (Q_g > 20 mC cm⁻²) includes more that one step, as a consequence of the formation of a two-layered polymer film.     

Crystallization, spherulite growth, and structure of blends of crystalline and amorphous poly(lactide)s

The effects of incorporated amorphous poly(dl-lactide) (PDLLA) on the isothermal crystallization and spherulite growth of crystalline poly(l-lactide) (PLLA) and the structure of the PLLA/PDLLA blends were investigated in the crystallization temperature (T_c) range of 90-150 °C. The differential scanning calorimetry results indicated that PLLA and PDLLA were phase-separated during crystallization. The small-angle X-ray scattering results revealed that for T_c of 130 °C, the long period associated with the lamellae stacks and the mean lamellar thickness values of pure PLLA and PLLA/PDLLA blend films did not depend on the PDLLA content. This finding is indicative of the fact that the coexisting PDLLA should have been excluded from the PLLA lamellae and inter-lamella regions during crystallization. The decrease in the spherulite growth rate and the increase in the disorder of spherulite morphology with an increase in PDLLA content strongly suggest that the presence of a very small amount of PDLLA chains in PLLA-rich phase disturbed the diffusion of PLLA chains to the growth sites of crystallites and the lamella orientation. However, the wide-angle X-ray scattering analysis indicated that the crystalline form of PLLA remained unvaried in the presence of PDLLA.     

Solid-state NMR studies on phase behavior and motional mobility in binary blends of polystyrene and poly(cyclohexyl methacrylate)

The phase behavior and motional mobility in binary blends of polystyrene (PS) and poly(cyclohexyl methacrylate) (PCHMA) have been investigated by solid state ¹³C NMR techniques. The blend miscibility has been studied by examining the ¹H spin-relaxation times in the laboratory frame (T₁^H) and in the rotating frame (T_1ρ^H) for the PCHMA/PS blends with various compositions and pure components. The T_1ρ^H results show that PCHMA and PS are intimately mixed at the molecular level within the blends at all compositions. In addition, according to the results of carbon T_1ρ relaxation time measurements, we conclude that mixing is intimate enough to cause a reduction in local chain mobility for PS, but an increase in side chain mobility for PCHMA.     

Epitaxial crystallization of poly(butylene adipate) on highly oriented isotactic polypropylene thin film

The crystallization behaviors of PBA on highly oriented iPP substrate both from solution and isotropic melt were studied by means of optical microscopy, AFM, X-ray and electron diffractions. The results clearly indicate the occurrence of heteroepitaxy of PBA on the iPP substrate in its β-form with both molecular chains ±50° apart from. This is based on the existence of perfect matching between the interchain distance of β-PBA along [100] direction and the distance of the out-sticking methyl side group arrays along the [101] direction of the (010) iPP plane. Electron diffraction pattern further confirms that the (010) lattice plane of the β-PBA is in contact with the iPP substrate.