Electrochemical synthesis and characterization of conducting polymers in supercritical carbon dioxide

This contribution reports the first synthesis of conducting polymers (CPs), specifically, polyaniline (PAn) and polypyrrole (PPy), in supercritical carbon dioxide (scCO2). CPs synthesized electrochemically in scCO2 were characterized with cyclic voltammetry (CV), four-point probe conductivity, scanning electron microscopy (SEM), and UV-vis spectroscopy. Preliminary data indicate that CPs synthesized by this method exhibit novel morphology and high conductivity comparable to that synthesized by traditional methods.     

Electrochemical growth of two-dimensional gold nanostructures on a thin polypyrrole film modified ITO electrode

Two-dimensional gold nanostructures have been fabricated by electrochemical deposition of gold nanoparticles onto indium tin oxide (ITO) glass substrate modified with thin polypyrrole film. By controlling the electrodeposition conditions, gold nanoparticles with dendritic rod, sheet, flower-like (consisting of staggered nanosheets), and pinecone-like structures were generated. The flower-like gold nanoparticles showed high catalytic activity on electrochemical reduction of oxygen, and its activity was measured to be approximately 25 times that of gold pinecones and 10(4) times that of gold nanosheets in terms of gold weight. The pinecone-like nanoparticles can form a compact film with nano-/microscale binary structure like a lotus leaf surface. After modification with n-dodecanethiol, the surface showed superhydrophobic properties with a water contact angle of 153.4 degrees and a tilt angle of 4.4 degrees (5 microL droplet).     

Efficient synthesis of isoindoles using supercritical carbon dioxide

Bicyclopyrroles were efficiently converted to the corresponding isoindoles by a retro Diels-Alder reaction in supercritical carbon dioxide. By adding ethylene gas as an oxygen scavenger, the isoindole yield was further improved.     

Preparation of conductive polypyrrole (PPy) composites under supercritical carbon dioxide conditions

Electrically conductive composites were prepared via the chemical oxidative polymerization of the pyrrole monomer in polystyrene (PS) and zinc neutralized sulfonated polystyrene (Zn-SPS) films under supercritical carbon dioxide (SC-CO₂) conditions. The strong swelling effect of SC-CO₂ made polypyrrole (PPy) particles not only form on the surface, but also become incorporated into the film, resulting in a homogeneous structure with a relatively higher conductivity. By comparison, the composite prepared in aqueous solutions shows a skin-core structure and a conductivity of 3 to 4 orders of magnitude lower than that of the former due to the diffusion-controlled process of the pyrrole monomer. The percolation thresholds of PS/PPy and Zn-SPS/PPy composites were 6.2% and 2.7% of the volume fraction of PPy, respectively, much lower than the theoretically predicted value of 16%. Moreover, the conductive composites prepared under SC-CO₂ conditions showed higher thermal stability, especially in the high-temperature region. Translated from Chemical Journal of Chinese Universities, 2006, 27(4): 771–774 (in Chinese)     

超临界二氧化碳中组氨酸催化合成环状碳酸酯

研究了超临界二氧化碳中α-氨基酸催化二氧化碳与环氧化物环加成反应合成环状碳酸酯,发现组氨酸的催化活性最高.在二氧化碳压力为8MPa、反应温度130℃、反应时间48h、组氨酸加入量为0.8mol%的条件下,二氧化物可以顺利的与各种环氧化物反应,以高的选择性和产率生成相应的环状碳酸酯.     

Novel chemical synthesis of polypyrrole thin film electrodes for supercapacitor application

Present investigation describes the cost-effective, novel and simple chemical synthesis of polypyrrole (PPy) thin films for supercapacitor application. These PPy films are characterized by different techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The XRD pattern reveals the amorphous nature of PPy thin film, which is highly feasible for supercapacitors. Further, FTIR study confirms the formation of PPy. The surface morphological study exhibit the coverage of uniform and smooth morphology on thin film. The electrochemical supercapacitive properties of PPy thin films are evaluated using cyclic voltammetry (CV) in 0.5 M H₂SO₄ electrolyte, which exhibits the maximum specific capacitance of 329 Fg⁻¹ at the scan rate of 5 mV s⁻¹. Additionally, an equivalent series resistance (ESR) of PPy thin films is found to be 1.08 Ω using electrochemical impedance measurement.     

The synthesis of polyacrylamide nanoparticles in supercritical carbon dioxide

Polyacrylamide nanoparticles, 50 to 200 nm, were created by inverse emulsion polymerization of acrylamide in supercritical carbon dioxide. The cross-linked polyacrylamide was produced by intermolecular imidization.     

Histidine-catalyzed synthesis of cyclic carbonates in supercritical carbon dioxide

The coupling reaction of carbon dioxide with epoxides was investigated using naturally occurring α-amino acids as the catalyst in supercritical carbon dioxide and it was found that L-histidine is the most active catalyst. In the presence of 0.8 mol% of L-histidine at 130 °C under 8 MPa of CO₂, the reaction of carbon dioxide with epoxides proceeded smoothly, affording corresponding cyclic carbonates in good to excellent yields.     

Liquid poly(ethylene glycol) and supercritical carbon dioxide as a biphasic solvent system for lipase-catalyzed esterification

The biphasic solvent system composed of poly(ethylene glycol)(PEG) and supercritical carbon dioxide (scCO2) is ideally suited for the lipase-catalyzed acylation of alcohols; batch or continuous flow acylations are possible, scCO2 being used to extract the products.     

Asymmetric synthesis using hydrolytic enzymes in supercritical carbon dioxide

The use of hydrolytic enzymes in supercritical carbon dioxide (scCO₂), an environmentally friendly solvent with many uses, is an attractive approach to asymmetric synthesis: several examples are reviewed here.     

Electrochemical carboxylation with carbon dioxide

Studies carried out in the past two years on electrochemical fixation of carbon dioxide with carbon-carbon bond formation, so-called electrochemical carboxylation or electrocarboxylation, are reviewed. Among about twenty papers on electrochemical carboxylation published from 2014 to the present, recent advances in electrochemical carboxylation regarding asymmetric carboxylation, sacrificial anode-free carboxylation, and carboxylation following aryl radical cyclization are focused on and discussed.     

Photoluminescent phenylated polyfluorenes synthesized in an organic solvent and supercritical carbon dioxide

A number of new phenylated polyfluorenes with blue emission are synthesized via the Diels-Alder reaction in chloronaphthalene and supercritical carbon dioxide. It is shown that these polymers are thermally stable. A comparative analysis of their properties shows that a ??green?? solvent is a suitable alternative to organic solvents for obtaining phenyl-substituted polyfluorenes via the Diels-Alder reaction.     

Lowering the dielectric constant of polyimide thin films by swelling with supercritical carbon dioxide

The swelling with supercritical carbon dioxide (sc‐CO₂) of thin films of polyimides having various structures was investigated. It was shown that the degree of swelling is significantly influenced by the solvent which was used for the synthesis of those polyimides, by the solvent which was used for the preparation of thin films and by the conformational rigidity of the polymers. The presence of hexafluoroisopropylidene groups in the main chain of a polymer prevents its swelling with sc‐CO₂. The best results were obtained for polyimide film ULTEM, based on m‐phenylene‐diamine and isopropylidene‐diphenoxy‐bis(phthalic anhydride), synthesized in benzoic acid, whose free volume increased twice and its dielectric constant decreased from 3.15 to 2.45 by swelling with sc‐CO₂. Copyright © 2013 John Wiley & Sons, Ltd.     

Atom transfer radical polymerization of MMA with a macromolecular ligand in a fluorinated solvent and in supercritical carbon dioxide

Macromolecular fluorinated ligands were prepared according to a three-step strategy that consists of the random copolymerization of heptadecafluorodecyl acrylate and 2-hydroxyethylacrylate, followed by the esterification of the pendant hydroxyl groups with acryloyl chloride and the Michael-type addition of tetraethyldiethylenetriamine onto the acrylic double bonds of the polymeric chains. These fluorinated macroligands were successfully used in the atom transfer radical polymerization of MMA catalyzed by a copper salt in a fluorinated solvent. The polymerization control was analyzed in relation to the copper salt, the initiator and the molecular weight and composition of the macroligand before being extended to the heterogeneous ATRP of MMA in scCO₂.     

Electrochemical synthesis of novel polypyrrole microstructures

Polypyrrole microstructures with unusual morphologies have been synthesized by direct electrochemical oxidation of pyrrole in beta-naphthalenesulfonic acid aqueous solution.     

Controlled electrochemical synthesis of polypyrrole nanoparticle thin film and its redox transition to a highly conductive and stable polypyrrole variant

We demonstrated here a unique method to produce a highly stable and conductive polypyrrole (PPY) nanoparticle film. The procedure entails controlling the redox switching and the electrochemical synthesis of PPY. PPY was synthesized at a very low forming potential or reaction rate in nonaqueous CH2Cl2 solvent to promote the PPY nanoparticle formation. Then its property was further optimized by first electrochemically reducing it at a hydrogen evolution potential in a neutral 0.1 M NaClO4, then in a slightly acidic 0.05 M asparagine electrolyte. The PPY nanoparticle thin film was characterized by AFM, UV-vis and EQCM. The procedures described here have proven to be reproducible. The data provided by the EQCM shows a reversible doping and undoping mechanism of asparagine indicating the presence of a highly conductive PPY variant. Both UV-vis and electrochemical characterization suggest that the PPY film made using our approach has excellent redox activity as well as high stability when characterized in asparagine solution. The reversible doping and undoping of asparagine during redox switching shows great potential of these PPY nanoparticle films as biological membranes for a broad range of biological applications.     

Electrochemical fabrication of nanoporous polypyrrole film on HOPG using nanobubbles as templates

A versatile method for preparing nanoporous polypyrrole (PPy) film using electrogenerated nanobubbles as templates on highly oriented pyrolytic graphite (HOPG) is presented using in situ electrochemical atomic force microscopy (EC-AFM).