Electrochemical synthesis of a polypyrrole thin film with supercritical carbon dioxide as a solvent

A conductive polypyrrole (PPy) film was successfully synthesized in a homogeneous supercritical carbon dioxide (scCO2)/acetonitrile (AN) system. The occurrence of a homogeneous supercritical state was confirmed by observations of the phase behavior of the system through a high-pressure cell with a viewing window. The concentration of a supporting electrolyte, tetrabutylammonium hexafluorophosphate (TBAPF6), significantly changed the phase behavior of the scCO2/AN system. The polymerization rate of the film in that system decreased with further addition of CO2. This result suggested that the low viscosity of scCO2 did not play an important role in improving the growth rate of the PPy film. The low polymerization rate might have been due to the electron-transfer resistance arising from the low dielectric constant of scCO2/AN mixture. The roughness of the film prepared in the homogeneous scCO2/AN system was 1/10 that synthesized in AN itself as a solvent. The slow growth of film and the high diffusion rate of the monomer seemed to account for the smooth flat film formation.     

聚吡咯薄膜在超临界CO_2与离子液体两相体系中的电化学合成

首次在超临界CO2与离子液体两相体系中实现了聚吡咯（PPyr）薄膜的电化学合成.与纯离子液体相比,该体系中合成的PPyr膜具有均匀平滑的表面.随着CO2压力的增加,膜的生长速度减慢,膜的表面变得更加均匀平滑.     

Pd(II) immobilized on mesoporous silica by N-heterocyclic carbene ionic liquids and catalysis for hydrogenation

In this work we synthesized Pd(II) immobilized on mesoporous silica by N-heterocyclic carbene (NHC) ionic liquids (ILs) with different alkyl chain lengths. The catalysts were characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), low-angle X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and nitrogen sorption. The catalysts were used for the hydrogenation of alkenes and allyl alcohol. The results indicated that the catalysts were very active, selective, and stable. The selectivity for the hydrogenation of allyl alcohol to 1-propanol increased with the increase of the alkyl chain length of the ILs. The effect of supercritical CO(2) (scCO(2)) on the hydrogenation of allyl alcohol was also studied, and it was demonstrated that scCO(2) could enhance the selectivity of the reaction considerably. The XPS study showed that the valence of Pd(II) remained unchanged under hydrogenation conditions.     

Electroactive Composite of FeCl3‐Doped P3HT/PLGA with Adjustable Electrical Conductivity for Potential Application in Neural Tissue Engineering

Conducting polymers (CPs) is one of intelligent biomaterials with the specific properties of reversible redox states, which have a significant effects on the cell behaviors and nerve tissue regeneration. However, the effects of CPs with different electrical conductivity on the behaviors of nerve cells are rarely reported. Therefore, a kind of Poly(3‐hexylthiophene) (P3HT) with certain molecular weight is synthesized by Kumada catalyst transfer polymerization (KCTP) method and employed to prepare bioabsorbable and electroactive intelligent composites of Poly(3‐hexylthiophene)/Poly(glycolide‐lactide) (P3HT/PLGA). FeCl₃ doping electroactive membranes with different electrical conductivities are prepared to investigate the cell behaviors. On the substrate with higher electrical conductivity, the proliferation of rat adrenal pheochromocytoma cells (PC12 cells) is significantly promoted and neurite length is increased obviously. In particular, the most significant improvements are the neuron gene expression of Synapsin 1 and microtubule‐associated protein 2 (MAP2) by the composites with high conductivity. These results suggest that P3HT/PLGA with suitable electrical conductivity have a positive role in promoting neural growth and differentiation, which is promising for advancing potential application of nerve repair and regeneration.     

Investigating the effect of the zwitterion/lactone equilibrium of rhodamine B on the cybotactic region of the acetonitrile/scCO2 cosolvent

We investigated the effect of adding acetonitrile to supercritical carbon dioxide (scCO(2)) in the presence of rhodamine B. This spectroscopic investigation of the scCO(2)/acetonitrile, rhodamine B/scCO(2), and rhodamine B/acetonitrile interactions revealed that rhodamine B, which possesses a temperature dependent equilibrium between a zwitterionic form and a neutral form, had a strong affect on the cybotactic region. To confirm that this effect was only dependent upon the rhodamine B/acetonitrile interactions and not merely due to the bulk-phase behavior of the scCO(2), we measured the compressibility of the scCO(2)/acetonitrile mixture and found it to be independent of the acetonitrile concentration to less than approximately 0.047 mol fraction. We fit the compressibility data using the Peng-Robinson equation of state because it is most appropriate for fluids in the region between 1.72 and 12.45 MPa and between 313 and 333 K.     

Synthesis and optical properties of π-conjugated polymers and oligomers bearing hexaphenylbenzene and tetraphenyl ethene units

π-Conjugated polymers (CPs) and oligomers (COs) bearing hexaphenylbenzene (HPB) and tetraphenyl ethene (TPE) units were synthesized by Sonogashira and Suzuki–Miyaura coupling reactions. The optical properties of the CPs and COs were investigated by UV–vis, photoluminescence (PL), and fluorescence lifetime (τ) measurements. The PL intensities of the solutions of the CPs and COs synthesized by Sonogashira coupling were reduced upon addition of poor solvent like water, which is attributed to aggregation-caused quenching. In contrast, the CP and COs bearing the TPE unit synthesized by Suzuki–Miyaura coupling exhibited aggregation-induced emission enhancement in solution. This difference in fluorescence behavior is discussed herein in terms of the molecular sizes, conformations in solution, and τ values of the CPs and COs.     

Vapour-adsorption and chromic behaviours of luminescent coordination polymers composed of a Pt(II)-diimine metalloligand and alkaline-earth metal ions

Four new bimetallic coordination polymers (CPs), {M[Pt(CN)(2)(5,5'-dcbpy)]·4H(2)O}(n) (M = Mg(2+), Ca(2+), Sr(2+), Ba(2+); 5,5'-H(2)dcbpy = 5,5'-dicarboxy-2,2'-bipyridine) were synthesized using four alkaline-earth metal ions and a Pt(II)-diimine metalloligand [Pt(CN)(2)(5,5'-H(2)dcbpy)]. All four CPs are isomorphous with the Zn complex, {Zn[Pt(CN)(2)(5,5'-dcbpy)]·4H(2)O}(n), which exhibits effective metallophilic interactions between Pt(II) ions. These CPs exhibited colourful thermochromic behaviour and solid-state solvatochromic-like behaviours when suspended in various solvents. Thermogravimetric analysis and vapour-adsorption measurements revealed that the CPs can reversibly adsorb water and MeOH vapours. The emission energy of the triplet metal-metal-to-ligand charge-transfer ((3)MMLCT) state varied markedly upon guest adsorption/desorption. The chromic and vapour-adsorption properties of these CPs depend strongly on the cross-linking M(2+) ions.     

Electrocatalytic hydrogen evolution of conducting coordination polymers based on 1,1,2,2-ethenetetrathiolate

Electrocatalysis based on metal–organic coordination polymers (CPs) catalyst, especially metal-1,1,2,2-ethenetetrathiolate (ett), has received increasing attention due to their high-electrical conductivity, unique morphology and excellent redox activity. Here, amorphous powder of CPs is synthesized and firmly coated on the surfaces of carbon fiber cloth (CFC), then serves as active electrocatalyst for hydrogen evolution reaction (HER). The operating overpotentials of the poly[K_x(M-ett)] (Co, Ni or Cu) are 0.43, 0.36, 0.45 V, respectively, at a current density of 10 mA cm⁻² with pH = 0, along with the Tafel plot of 144, 153, 329 mV dec⁻¹. Moreover, they show remarkable electrolysis stability under harsh acid conditions. This study extends the HER application of poly[K_x(M-ett)] coating on CFC surfaces.     

超临界二氧化碳中聚(丁二酸-丁二醇/乙二醇)酯(PBES)多孔聚合物的制备与表征

在超临界二氧化碳(scCO2)条件下,制备了可生物降解性的聚(丁二酸-丁二醇/乙二醇)酯(PBES)多孔材料,研究了scCO2的压力、温度对多孔材料的结构形貌和结晶度的影响。 结果表明,材料的孔洞分布、结构形态和结晶度与处理样品的压力、温度关系密切;经过scCO2处理后材料的结晶度有所降低。 孔径均匀分布,为50~200 μm,131 ℃处理样品的孔隙率为55.63%。     

Phase behavior in model homopolymer/CO2 and surfactant/CO2 systems: discontinuous molecular dynamics simulations

Discontinuous molecular dynamics simulations are performed on surfactant (HmTn)/solvent systems modeled as a mixture of single-sphere solvent molecules and freely jointed surfactant chains composed of m slightly solvent-philic head spheres (H) and n solvent-philic tail spheres (T), all of the same size. We use a square-well potential to account for the head-head, head-solvent, tail-tail, and tail-solvent interactions and a hard-sphere potential for the head-tail and solvent-solvent interactions. We first simulate homopolymer/supercritical CO2 (scCO2) systems to establish the appropriate interaction parameters for a surfactant/scCO2 system. Next, we simulate surfactant/scCO2 systems and explore the effect of the surfactant volume fraction, packing fraction, and temperature on the phase behavior. The transition from the two-phase region to the one-phase region is located by monitoring the contrast structure factor of the equilibrated surfactant/scCO2 system, and the micelle to unimer transition is located by monitoring the aggregate size distribution of the equilibrated surfactant/scCO2 system. We find a two-phase region, a micelle phase, and a unimer phase with increasing packing fraction at fixed temperature or with increasing temperature at fixed packing fraction. The phase diagram for the surfactant/scCO2 system in the surfactant volume fraction-packing fraction plane and the density dependence of the critical micelle concentration are in qualitative agreement with experimental observations. The phase behavior of a surfactant/scCO2 system can be directly related to the solubilities of the corresponding homopolymers that serve as the head and tail blocks for the surfactant. The influence of surfactant structure (head and tail lengths) on the phase transitions is explored.     

Solvophobic acceleration of Diels-Alder reactions in supercritical carbon dioxide

The rate of the Diels-Alder reaction between N-ethylmaleimide and 9-hydroxymethylanthracene in supercritical carbon dioxide (scCO(2)) was determined by following the disappearance of 9-hydroxymethylanthracene with in situ UV/vis absorption spectroscopy. The reaction conditions were 45-75 degrees C and 90-190 bar, which correspond to fluid densities (based on pure carbon dioxide) ranging between approximately 340 and 730 kg m(-3). The measured reaction rate at low scCO(2) fluid densities was nearly 25x faster than that reported in acetonitrile at the same temperature (45 degrees C). An inverse relationship between reaction rate and fluid density/pressure was observed at all temperatures in scCO(2). The apparent activation volumes were large and positive (350 cm(3) mol(-1)) and only a weak function of reduced temperature. A solvophobic mechanism analogous to those observed in conventional solvents is postulated to describe (a) the rate acceleration observed for this reaction in scCO(2) relative to that in acetonitrile, (b) the observed relationship between reaction rate and pressure/temperature/density, and (c) the large, positive activation volumes. Solubility measurements in scCO(2), rate measurements in conventional solvents, and an empirical correlation are used to support this theory. Our results advance the general understanding of reactivity in supercritical fluids and provide a rationale for selecting reactions which can be accelerated when conducted in scCO(2).     

Hydrogenation reactions using scCO2 as a solvent in microchannel reactors

We have developed an effective microfluidic system for hydrogenation reactions in scCO(2); the reactions proceeded very rapidly (within 1 second), by making the best use of scCO(2) and utilizing the large specific interfacial area of the microchannel reactor, and high reaction productivity was attained in each channel.     

Proton transfer from 2-naphthol to aliphatic amines in supercritical CO2

The proton transfer from 2-naphthol to aliphatic amines was studied in supercritical CO(2) (scCO(2)) and in cyclohexane as reference solvent, by absorption and fluorescence spectroscopy and by time-resolved emission. Irradiation of 2-naphthol in scCO(2) in the presence of ethyldiisopropylamine shows dynamic fluorescence quenching of the acidic form of 2-naphthol and emission from the basic form. Fluorescence excitation spectra show that the emission of the basic form is originated upon excitation of the acidic form. The interaction between 2-naphthol and the amines is described by the formation of a complex with proton donor-acceptor character in the ground and excited states of 2-naphthol. The acidity increase of 2-naphthol upon electronic excitation to the first excited singlet in scCO(2) is as high as in water. Proton transfer quantum yields of 0.6 can be easily achieved in scCO(2). The results have implications for carrying out acid-base catalyzed reactions in scCO(2).     

A New Dimension for Coordination Polymers and Metal–Organic Frameworks: Towards Functional Glasses and Liquids

There are two categories of coordination polymers (CPs): inorganic CPs (i‐CPs) and organic ligand bridged CPs (o‐CPs). Based on the successful crystal engineering of CPs, we here propose noncrystalline states and functionalities as a new research direction for CPs. Control over the liquid or glassy states in materials is essential to obtain specific properties and functions. Several studies suggest the feasibility of obtaining liquid/glassy states in o‐CPs by design principles. The combination of metal ions and organic bridging ligands, together with the liquid/glass phase transformation, offer the possibility to transform o‐CPs into ionic liquids and other ionic soft materials. Synchrotron measurements and computational approaches contribute to elucidating the structures and dynamics of the liquid/glassy states of o‐CPs. This offers the opportunity to tune the porosity, conductivity, transparency, and other material properties. The unique energy landscape of liquid/glass o‐CPs offers opportunities for properties and functions that are complementary to those of the crystalline state.     

Olefin metathesis in supercritical carbon dioxide

Liquid or supercritical carbon dioxide (scCO(2)) is a versatile reaction medium for ring-opening metathesis polymerization (ROMP) and ring-closing olefin metathesis (RCM) reactions using well-defined metal catalysts. The molybdenum alkylidene complex 1 and ruthenium carbenes 2 and 3 bearing PCy(3) or N-heterocyclic carbene ligands, respectively, can be used and are found to exhibit efficiency similar to that in chlorinated organic solvents. While compound 1 is readily soluble in scCO(2), complexes 2 and 3 behave like heterogeneous catalysts in this reaction medium. Importantly, however, the unique properties of scCO(2) provide significant advantages beyond simple solvent replacement. This pertains to highly convenient workup procedures both for polymeric and low molecular weight products, to catalyst immobilization, to reaction tuning by density control (RCM versus acyclic diene metathesis polymerization), and to applications of scCO(2) as a protective medium for basic amine functions. The latter phenomenon is explained by the reversible formation of the corresponding carbamic acid as evidenced by (1)H NMR data obtained in compressed CO(2). Together with its environmentally and toxicologically benign character, these unique physicochemical features sum up to a very attractive solvent profile of carbon dioxide for sustainable synthesis and production.     

Surfactant-mixing effects on the interfacial tension and the microemulsion formation in water/supercritical CO2 system

The effects of surfactant mixing on interfacial tension and on microemulsion formation were examined for systems of air/water and water/supercritical CO2 (scCO2) interfaces and for water/scCO2 microemulsions. A fluorinated surfactant, sodium bis(1H,1H,2H,2H-heptadecafluorodecyl)-2-sulfosuccinate (8FS(EO)2), was mixed with the three hydrocarbon surfactants, Pluronic L31, Tergitol TMN-6, and decyltrimethylammonium chloride (DeTAC), at equimolar ratio. For all the cases, the interfacial tension was significantly lowered by the mixing. The positive synergistic effect suggests that the mixed surfactants tend to pack more closely on the interface than the pure constituents. It was found, however, that the microemulsion formation in scCO2 was never facilitated by the mixing, except for the case of TMN-6. This is probably due to the segregation of the surfactants into hydrocarbon-rich and fluorocarbon-rich phases on the microemulsion surface.     

Nucleophilic displacements in supercritical carbon dioxide under phase-transfer catalysis conditions. 2. Effect of pressure and kinetics

The nucleophilic displacement on n-octylmesylate (n-C(8)H(17)OSO(2)CH(3), 1) with four different anions (I(-), Br(-), N(3)(-), and SCN(-)) is investigated under liquid-supercritical phase-transfer catalysis (LSc-PTC) conditions, i.e. in a biphase system of supercritical carbon dioxide (scCO(2)) and water, in the presence of both silica supported and conventional onium salts. The CO(2) pressure greatly affects the concentration of 1 in the sc-phase and plays a major role on its conversion. For example, at 50 degrees C and with a supported PT-catalyst, the conversion of 1 into n-octyl iodide drops by a factor of 5 as the CO(2) pressure is increased from 80 to 150 bar, while in the same pressure range, the solubility of n-octylmesylate in scCO(2) shows a 6-fold increase, indicating that the reagent is desorbed from the catalyst. Under LSc-PTC conditions, pseudo-first-order kinetic rate constants, evaluated for the investigated reactions, show that the performance of scCO(2) as a PTC solvent and the relative nucleophilicity order of the anions (N(3)(-) > I(-) > or = Br(-) > SCN(-)) are comparable to those of toluene and n-heptane. The behavior of conventional phosphonium salts in the scCO(2)/H(2)O biphase system suggests that the reaction may take place either within small droplets of PT-catalyst containing water or in a separate third liquid phase of the PT-catalyst itself.     

Formation of dispersed nanostructures from poly(ferrocenyldimethylsilane-b-dimethylsiloxane) nanotubes upon exposure to supercritical carbon dioxide

While incompatible block copolymers commonly assemble into several established classical or complex morphologies, highly asymmetric poly(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFS-b-PDMS) diblock copolymers can also self-organize into high-aspect-ratio nanotubes with PDMS corona in the presence of PDMS-selective organic solvents. Exposure of these nanotubes on a carbon substrate to supercritical carbon dioxide (scCO2), also a PDMS-selective solvent, appears to promote partial dissolution of the copolymer molecules. At sufficiently high copolymer concentrations, the dissolved molecules subsequently re-organize within the scCO2 environment to form new copolymer nanostructures that redeposit on the substrate upon scCO2 depressurization. Transmission electron microscopy reveals that micelles form under all the conditions examined here, whereas nanotubes coalesce and vesicles develop only at relatively high temperatures. The extent to which the copolymer nanotubes dissolve and the size distribution of the replacement micelles are sensitive to exposure conditions. These results suggest that the phase behavior of PFS-b-PDMS diblock copolymers in scCO2 may be remarkably rich and easily tunable.     

Surface activity of myristic acid in the poly(methyl methacrylate)/supercritical carbon dioxide system

To confirm the surface activity of myristic acid in the dispersion polymerization of vinyl monomers in scCO2, the interfacial tension (IFT) at the polymer/supercritical carbon dioxide (scCO2) interface has been measured. For the IFT measurements, a high-pressure pendant drop apparatus was constructed. The IFT data was obtained by the axisymmetric drop shape analysis of melt polymer droplets formed at the tip of a capillary. The reliability of the apparatus was confirmed by measuring the IFT of polystyrene (PS)/scCO2 and polypropylene (PP)/CO2 systems. The IFT of the poly(methyl methacrylate) (PMMA)/scCO2 system with and without myristic acid was also measured. The IFT decreased on addition of myristic acid. The magnitude of the IFT depression due to the myristic acid was comparable to that of PS/scCO2 systems with the block copolymer surfactant, PS-b-poly(fluorooctyl acrylate). The surface activity of the myristic acid was confirmed by the decrease of IFT.     

Peracetylated sugar derivatives show high solubility in liquid and supercritical carbon dioxide

[structure: see text] Acetylated sugars derivatives exhibit high solubility in liquid and supercritical carbon dioxide (scCO(2)). Peracetylated sorbitol and beta-D-galactose are soluble under mild conditions in scCO(2), high pressures are required to dissolve peracetylated beta-cyclodextrin, and peracetoxyalkyl chains impart CO(2)-solubility to amides.