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.     

Lewis acid catalysis in a supercritical carbon dioxide (scCO2)-poly(ethylene glycol) derivatives (PEGs) system: remarkable effect of PEGS as additives on reactivity of Ln(OTf)3-catalyzed Mannich and aldol reactions in scCO2

Use of poly(ethylene glycol) derivatives (PEGs) as additives in supercritical carbon dioxide (scCO2) was found to be effective for Mannich and aldol reactions of silyl enolates with aldehydes and imines, and formation of emulsions was observed in these systems.     

Solubilities of poly(ethylene glycol)s in the mixtures of supercritical carbon dioxide and cosolvent

The solubilities of poly(ethylene glycol) (PEG6000) (M.W.=7500) in the mixtures consisting of supercritical carbon dioxide (CO₂) and cosolvent have been measured by observing the cloud points at 313.15 K and 16 MPa. Ethanol and toluene were used as cosolvents. The solubility of PEG6000 is extremely low in either CO₂ or ethanol, but becomes about 20 wt.% in a mixture of the two. The maximum solubility is achieved at about 50 wt.% (polymer-free) ethanol. The solubilities of PEG6000 in the mixtures of supercritical CO₂ and the cosolvent have been correlated by a regular solution model using the local compositions of solvents around a solute molecule, and an expanded liquid equation of state model.     

Monte Carlo simulation of solute extraction via supercritical carbon dioxide from poly(ethylene glycol)

The partitioning of ethylbenzene between poly(ethylene glycol) (PEG) and supercritical carbon dioxide was studied at 308.15, 328.15 and 348.15 K and 10, 15.5 and 20 MPa with PEG-400, 600 and 900 using Monte Carlo molecular simulation. The effect of a cosolvent was also studied with either 5% ethane or 5% n-octane added. Ethylbenzene favored the supercritical phase most when the density was highest, and while ethane had little effect, the addition of n-octane increased the amount of solute dissolved in carbon dioxide. Increasing polymer molecular weight led to more solute in the PEG-rich phase. This coincides with a higher amount of dissolved carbon dioxide that preferentially solvates ethylbenzene.     

Conformational changes of poly(ethylene oxide) in poly(ethylene oxide)/poly(methyl methacrylate) blends by supercritical carbon dioxide

The effects of supercritical carbon dioxide (SC CO₂) fluids on the morphology and/or conformation of poly(ethylene oxide) (PEO) in PEO/poly(methyl methacrylate) (PMMA) blends were investigated by means of differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), and Fourier transform infrared (FTIR). According to DSC data for a given blend, the melting enthalpy and, therefore, degree of crystallinity of PEO were increased, whereas the melting temperature of PEO was decreased, with SC CO₂ treatment. The enhancement of PEO crystallization with SC CO₂ treatment, as demonstrated by DSC data, was supported by WAXD data. According to FTIR quantitative analyses, before SC CO₂ treatments, the conformation of PEO was transformed from helix to trans planar zigzag via blending with PMMA. This helix‐to‐trans transformation of PEO increased proportionally with increasing PMMA content, with around 0.7% helix‐to‐trans transformation per 1% PMMA incorporation into the blend. For a given blend upon SC CO₂ treatments, the conformation of PEO was transformed from trans to helix. This trans‐to‐helix transformation of PEO decreased with increasing PMMA contents in the blends because of the presence of interactions between the two polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2479–2489, 2004     

The influence of carbon dioxide cosolvent on solubility in poly(ethylene glycol)

Supercritical carbon dioxide (CO₂) and poly(ethylene glycol) (PEG) can be utilized as an environmentally friendly biphasic solvent system for catalysis reactions and subsequent product separation. To efficiently implement this technology, it is important to understand how solutes partition between these phases as well as how dissolved CO₂ in PEG affects the solvent properties. The work presented here explores the influence of CO₂ on the solubility of four different solutes in PEG. The transferable potentials for phase equilibria-united atom force field and configurational-bias Monte Carlo molecular simulation were employed to determine the solubilities of ethylbenzene, 1-octene, 1-pentanol, and 2-pentanone at 323.15 K and 15?MPa in PEG-600 using an ideal vapor phase with a Poynting-corrected vapor pressure. The effect of CO₂ concentration within the PEG phase was determined by varying the amount from no CO₂ to the saturation limit. The results indicate that while there is preferential solvation of CO₂ around the solutes, solubility of non-polar solutes is unchanged whereas there is a modest increase for polar solutes as the concentration of CO₂ increases. Increased solubility is analyzed in terms of both modified solvent structure and direct solute–CO₂ interactions.     

Synthesis of highly cross-linked poly(diethylene glycol dimethacrylate) microparticles in supercritical carbon dioxide

Herein we report the synthesis of poly(diethylene glycol dimethacrylate), poly(DEGDMA), by free-radical heterogeneous polymerization in supercritical carbon dioxide (scCO₂), using a commercially available carboxylic acid end-capped perfluoropolyether oil (Krytox 157FSL) as stabiliser. The effect of initial concentration of stabiliser, monomer and initiator on the yield and morphology of the resulting polymer has been investigated. Krytox worked effectively as a stabiliser and discrete poly(DEGDMA) particles with diameters ranging from 1.28 to 2.08 μm and narrow particle size distribution were produced in supercritical carbon dioxide, in high yield and in short reaction times, without making use of harmful organic solvents.     

Viscoelastic properties of single poly(ethylene glycol) molecules.

The viscoelastic properties of single poly(ethylene glycol) (PEG) molecules were measured by analysis of thermally and magnetically driven oscillations of an atomic force microscope (AFM) cantilever/molecule system. The molecular and monomer stiffness and friction of the PEG polymer were derived using a simple harmonic oscillator (SHO) model. Excellent agreement between the values of these two parameters obtained by the two approaches indicates the validity of the SHO model under the experimental regimes and the excellent reproducibility of the techniques. A sharp minimum in the monomeric friction is seen at around 180 pN applied force which we propose is due to a force induced change in the shape of the energy landscape describing the conformational transition of PEG from a helical to a planar state, which in turn affects the timescale of the transition and therefore modifies the measured internal friction. A knowledge of the viscoelastic response of PEG monomers is particularly important since PEG is widely used as a linker molecule for tethering groups of interest to the AFM tip in force spectroscopy experiments, and we show here that care must be exercised because of the force-dependent viscoelastic properties of these linkers.     

Synthesis and characterization of poly(ethylene glycol) derivatives

Five general routes for the preparation of polyoxyethylene [generally referred to as poly(ethylene glycol) or PEG] derivatives are described. These routes are (1) nucleophilic displacements with the alkoxide of PEG, (2) nucleophilic displacement on PEG–tosylate, –mesylate, or –bromide, (3) reductive amination of PEG–aldehyde, (4) reductive amination of PEG–amine, and (5) nucleophilic displacements on the s-triazine derivatives prepared from s-triazine trichloride (cyanuric chloride) and PEG. Eighteen derivatives are prepared and potential applications to catalysis, cell purifications, and other areas are discussed briefly.     

Liquid poly(ethylene glycol) and supercritical carbon dioxide: a benign biphasic solvent system for use and recycling of homogeneous catalysts

Poly(ethylene glycol) (PEG), having a molecular weight of 900 or 1500, is a solid at room temperature but a nonvolatile liquid at 40 degrees C under CO2 pressure. Homogeneously catalyzed hydrogenation can be performed in the molten PEG, followed by extraction of the product by supercritical CO2. The catalyst-containing PEG phase which remains in the vessel can be reused for hydrogenation without addition of further catalyst or PEG.     

Synthesis of poly(arylate-siloxane)s in supercritical carbon dioxide

The reaction between poly(4,4′-isopropylidene-2,2′-diphenylene (tere)isophthalate) copolymer and 3-aminopropyltriethoxysilane was investigated in supercritical carbon dioxide at 150 atm and 100° C. It was found that ester bonds in the copolyarylate undergo aminolysis under the above conditions to give rise to the formation of siloxane-containing amides, whose interaction with phenol groups of the macromolecules and moisture affords an insoluble poly(arylate-co-siloxane) fraction. Under the action of moisture, three-dimensional structures containing polyarylate and polysiloxane fragments are formed in the soluble fraction of the copolymer via the combined hydrolysis of ethoxysilane groups. The formation of the siloxane network affects the properties of the polymers. In particular, thermomechanical and thermal tests showed that sample deformation at 250°C decreases from 80 to 15%, while the carbon residue at 725°C increases twofold as compared to that of an initial polyarylate sample.     

Synthesis of associating poly(acrylic acid) in supercritical carbon dioxide and its solution properties

Hydrophobically associating polymers have been synthesized in supercritical carbon dioxide by copolymerization of acrylic acid with different amounts of acrylate with hydrocarbon or fluorocarbon groups. It was found that conversion of hydrocarbon comonomers was above 95% whereas that for fluorocarbon comonomers was only about 50%. In addition, large amounts of hydrophobic groups could be easily introduced to poly(acrylic acid) by reaction in supercritical carbon dioxide. The solution properties were investigated by rheology. The results indicated that intermolecular association of the copolymer was strong and viscosity was maximum under acidic conditions. In aqueous solutions fluorocarbon hydrophobes associated much more strongly than the hydrocarbon variety, but the viscosifying effect of PAAC-18 series copolymers in 2% (w/w) solution was more pronounced than that of the PAAF series, results which did not agree with the conclusions of Ravey and Stébé. It was also found that the thixotropy behavior of copolymer solution at pH 3.2 was more complex than that at pH 5.0, at which pseudoplasticity only was observed for solutions of all copolymers. Contact angles of copolymer solutions on a glass sheet were measured. The data indicated that contact angles of hydrocarbon-modified polymers were smaller than those of fluorocarbon analogues. As time passed the contact angle became smaller and smaller. Fluorocarbon analogues were better than hydrocarbon analogues, and longer hydrophobic chains were better than shorter chains, at maintaining the hydrophobic character of the surface.     

叶酸和聚乙二醇接枝作基因载体用壳聚糖的合成与表征

本研究将叶酸和聚乙二醇接枝到四种不同分子量的壳聚糖氨基侧链上,以改善壳聚糖的靶向性和水溶性作基因载体。用FTIE、1HNMR、UV-Vis、DSC和TEM对产物进行了表征,结果表明,叶酸和聚乙二醇被成功地接枝到壳聚糖上,所制得的载体有望作为潜在的肿瘤细胞靶向基因载体。     

Fiber-optic sensor for carbon dioxide with a ph indicator dispersed in a poly(ethylene glycol) membrane

A fiber-optic sensor for carbon dioxide gas is constructed, without an inner buffer solution, by using a dispersion of fluorescein in poly(ethylene glycol) deposited on the distal end of an optical fiber. Evaporation of the solvent is thus negligible. The response range is 0–28% (v/v) for carbon dioxide, with a detection limit of 0.1%. The response time achieved is 10 s. The membrane (ca. 10 μm thick) is composed of poly(ethylene glycol)s with molecular weights of 200 and 1540 dalton in a 20:80% (w/w) ratio. The best concentration of fluorescein is 5 × 10^?7 mol g^?1 of poly(ethylene glycol). The response mechanism of the sensor is discussed.     

Water-soluble hydrogen-bonding interpolymer complex formation between poly(ethylene glycol) and poly(acrylic acid) grafted with poly(2-acrylamido-2-methylpropanesulfonic acid)

Comb-type copolymers of poly(acrylic acid) grafted with poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPSA) side chains form with poly(ethylene glycol), at low pH, water-soluble hydrogen-bonding interpolymer complexes. Turbidimetry, viscometry, and dynamic light scattering measurements suggest that compact, negatively charged, colloidal nanoparticles are formed at pH<3.75. The influence of the structure of the graft copolymers and of the ionic strength of the solution on the size of these nanoparticles was investigated. It was found that their hydrodynamic radius decreases by increasing the molecular mass of the PAMPSA side chains of the graft copolymer and increases with increasing the ionic strength of the solution.     

Electron self-exchange reaction of viologen and its derivatives in poly(ethylene glycol)

The electron self-exchange rates (k_ex) of viologen and its derivatives are estimated by using microelectrode voltammetry in poly(ethylene glycol) films. The dependences of supporting electrolyte concentration and sizes of viologen and its derivatives on k_ex and diffusion coefficients (D) are discussed. Results show that k_ex increases with the decrease of supporting electrolyte concentration and sizes of reactants.     

Effects of surfactant micelles on viscosity and conductivity of poly(ethylene glycol) solutions

The neutral polymer-micelle interaction is investigated for various surfactants by viscometry and electrical conductometry. In order to exclude the well-known necklace scenario, we consider aqueous solutions of low molecular weight poly(ethylene glycol) (2-20)x10(3), whose radial size is comparable to or smaller than micelles. The single-tail surfactants consist of anionic, cationic, and nonionic head groups. It is found that the viscosity of the polymer solution may be increased several times by micelles if weak attraction between a polymer segment and a surfactant exists, epsilon相似文献   

Segmented block copolymers of poly(ethylene glycol) and poly(ethylene terephthalate)

A new series of segmented copolymers were synthesized from poly(ethylene terephthalate) (PET) oligomers and poly(ethylene glycol) (PEG) by a two‐step solution polymerization reaction. PET oligomers were obtained by glycolysis depolymerization. Structural features were defined by infrared and nuclear magnetic resonance (NMR) spectroscopy. The copolymer composition was calculated via ¹H NMR spectroscopy. The content of soft PEG segments was higher than that of hard PET segments. A single glass‐transition temperature was detected for all the synthesized segmented copolymers. This observation was found to be independent of the initial PET‐to‐PEG molar ratio. The molar masses of the copolymers were determined by gel permeation chromatography (GPC). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4448–4457, 2004     

An analysis of the complexation between poly(aspartic acid) and poly(ethylene glycol)

The compatibility between poly(aspartic acid) and poly(ethylene glycol) for the formation of an interpolymer complex (IPC) was investigated by dynamic rheology and evaluation of zeta potential values. The homogeneity of the realized IPC was observed by near infrared chemical imagistic (NIR-CI) technique. The data were sustained and underlined by the assessment of the compatibility between the polymeric compounds.