Synthesis and characterization of poly (ethylene oxide) containing copolyimides for hydrogen purification

Reverse selective membranes comprising poly(ethylene oxide) (PEO) containing copolyimides (PEO-PI) with variations of acid dianhydrides and diamines have been synthesized for hydrogen purification. The reverse selectivity of the membranes decimate the energy required for hydrogen recompression process. Factors including PEO content, PEO molecular weight, and fractional free volume (FFV) that would affect the gas transport performance have been investigated and elucidated in terms of degree of crystallinity, phase separation in the PEO domain as well as inter-penetration between the hard and soft segments. In mixed gas tests of CO₂ and H₂ mixtures, a highly condensable CO₂ out compete H₂ for the sorption sites in hard segment and diminishes H₂ permeability. Thus the CO₂/H₂ selectivity in the mixed gas tests is much higher than that in pure gas tests. Mixed gas permeation tests at 35 °C and 2atm show that the best reverse selective membranes have a CO₂ permeability of 179.3 Barrers and a CO₂/H₂ permselectivity of 22.7. The physical properties of PEO-PIs have also been characterized by FTIR, DSC, GPC, WAXS, AFM and tensile strain tests.     

Miscibility of chitosan/poly(ethylene oxide) blends and effect of doping alkali and alkali earth metal ions on chitosan/PEO interaction

The miscibility of Chitosan (CS) and poly(ethylene oxide) (PEO) in their blends and the effect of K⁺ and Ca²⁺ doping on the CS/PEO interaction have been investigated in this work. CS and PEO appeared to be miscible and the DSC analysis suggested the Flory-Huggins interaction parameter χ_AB to be −0.21. Doping of K⁺ and Ca²⁺ into the CS/PEO blend matrix enhanced the cooperative interaction between CS and PEO and this enhancement was larger for Ca²⁺ than for K⁺. The difference between Ca²⁺ and K⁺ possibly reflects a stronger multi-valence interaction of Ca²⁺ with the amino and hydroxyl groups of CS as well as the ether groups of PEO to form a stable CS/Ca²⁺/PEO complex and a less significant interaction of K⁺, as suggested by DSC, WAXD and FTIR results. MD simulations clearly indicated the correlation between the dynamic behavior and the interaction of K⁺ and Ca²⁺ in the CS/PEO blend matrix.     

Synthesis and applications of heterobifunctional poly(ethylene oxide) oligomers

Poly(ethylene oxide) (PEO) oligomers are employed extensively in pharmaceutical and biomedical arenas mainly due to their excellent physical and biological properties, including solubility in water and organic solvents, lack of toxicity, and absence of immunogenicity. PEO can be chemically modified and reacted with, or adsorbed onto, other molecules and surfaces. Sophisticated applications for PEO have increased the demand for PEO oligomers with tailored functionalities, and heterobifunctional PEOs are often needed. This review discusses the synthesis and applications of heterobifunctional PEO oligomers possessing amine, carboxylate, thiol, and maleimide functional groups.     

Miscibility of C60-end-capped poly(ethylene oxide) with poly(vinyl chloride)

The miscibility of blends of single [60]fullerene (C₆₀)-end-capped poly(ethylene oxide) (FPEO) or double C₆₀-end-capped poly(ethylene oxide) (FPEOF) with poly(vinyl chloride) (PVC) has been studied. Similar to poly(ethylene oxide) (PEO), both FPEO and FPEOF are also miscible with PVC over the entire composition range. X-ray photoelectron spectroscopy showed the development of a new low-binding-energy Cl2p doublet and a new high-binding-energy O1s peak in FPEO/PVC blends. The results show that the miscibility between FPEO and PVC arises from hydrogen bonding interaction between the α-hydrogen of PVC and the ether oxygen of FPEO. From the melting point depression of PEO, FPEO or FPEOF in the blends, the Flory-Huggins interaction parameters were found to be −0.169, −0.142, −0.093 for PVC/PEO, PVC/FPEO and PVC/FPEOF, respectively, demonstrating that all the three blend systems are miscible in the melt. However, the incorporation of C₆₀ slightly impairs the interaction between PEO and PVC.     

Synthesis of functionalized multiarm poly(ethylene oxide) stars

Six arm poly(ethylene oxide) (PEO) stars carrying either 6 pyridyl or 12 hydroxyl groups at their periphery were synthesized using an arm-first approach. To this end, two novel α,ω-heterodifunctional PEO's, namely α-ketal,ω-hydroxy and α-pyridyl,ω-hydroxy PEO's were synthesized and, after the deprotonation of their hydroxyls, deactivated onto hexachlorocyclophosphazene which served to build the core. Quaternization of the stars containing six outer pyridyl groups created positive charges at their periphery while the acidic treatment of stars carrying terminal ketal rings afforded six arm PEO stars with 12 peripheral hydroxyls. The latter compound was subsequently deprotonated and used to polymerize ethylene oxide by a classical core-first approach. This resulted in the formation of highly branched PEO's also referred to as dendrimer-like PEO stars which consisted of a first generation of six PEO arms and a second generation of 12 hydroxy-ended PEO branches.     

Molecular dynamics simulation studies of binary blend miscibility of poly(3-hydroxybutyrate) and poly(ethylene oxide)

By means of full atomistic molecular dynamics simulation, the solubility parameters for pure poly(3-hydroxybutyrate) and poly(ethylene oxide) are calculated and the results are in agreement with the literature values. Furthermore, in order to reveal the blend property, the volume-temperature curve of the PHB/PEO blend system (1:2 blends in terms of repeated units) is simulated by employing the united atom approximation to obtain the glass transition temperature. From the volume-temperature curve, the glass transition temperature is about 258 K, which is compared well with the experimental results. It should be pointed out that the two simulated solubility parameters are similar and there is only one glass transition of the blend system, these indicate that the studied blend system is miscible.     

Synthesis of (ABCB)n type ternary amphiphilic multiblock copolymer via poly(ethylene oxide) macro-chain transfer agent

A novel (ABCB)_n type ternary amphiphilic multiblock copolymer was synthesized by stepwise insertion of monomers into the trithiocarbonate-embedded poly(ethylene oxide) (PEO) macro-chain transfer agent (PEO-CTA)_n. (PEO-CTA)_n was synthesized first by coupling of α,ω-dihydroxyl PEO with dicarboxylic trithiocarbonate, then styrene (St) and t-butyl acrylate (^tBA) were inserted into the (PEO-CTA)_n successively to yield (PEO-b-PS)_n and (PEO-b-PS-b-P^tBA-b-PS)_n, respectively. After hydrolysis of the (PEO-b-PS-b-P^tBA-b-PS)_n, the final product (PEO-b-PS-b-PAA-b-PS)_n was obtained.     

Aggregation behavior of two-arm fullerene-containing poly(ethylene oxide)

A water-soluble two-arm fullerene-containing poly(ethylene oxide) (PEO) was synthesized through isocyanate-hydroxy condensation reaction with fullerenol as a molecular core and characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetry, and matrix-assisted laser desorption ionization time of flight mass spectrometry. The aggregation behavior of the resulting amphiphilic polymer in water, THF, and DMF, was studied by gel permeation chromatography, laser light scattering, and transmission electron microscopy. The polymer forms spherical aggregates with an aggregation number around 540-1020.     

Formation of dendrite crystals in poly(ethylene oxide) interacting with bioresourceful tannin

A dendritic morphology, induced by miscibility with strong intermolecular interaction between poly(ethylene oxide) (PEO) and bioresourceful tannin [tannic acid (TA)]. Mechanism was investigated by differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy, wide-angle X-ray diffraction, and polarized optical microscopy. The cell crystallography preference in correlation to the intermolecular interaction in the dendrites in PEO/TA (70/30) blend was analyzed. Dendritic morphology was more distinct at PEO/TA = 70/30 composition, where the spherulitic growth rate showed a highly nonlinear relationship with respect to crystallization time (R α t ^1/2). Diffusion limitation mechanism caused by the crystallography preference attributed to the strong intermolecular interaction between PEO and TA was at work.     

Electrospinning of sodium alginate with poly(ethylene oxide)

Another natural biopolymer, sodium alginate, has been electrospun from aqueous solution by blending with a non-toxic, biocompatible, synthetic polymer poly(ethylene oxide) (PEO). The interaction between sodium alginate and PEO has been evidenced by FTIR and conductivity change, which is thought to be the main reason for the successful electrospinning. The solution properties of sodium alginate/PEO blends have been measured, including viscosity, conductivity and surface tension. The morphology and mechanical properties of the electrospun mats have been investigated. Smooth fibers with diameters around 250 nm are obtained from 3% solutions of varied alginate/PEO proportions ranging from 1:1 to 0:1. Tensile strength around 4 MPa is found with smooth fiber mats. The anti-water property of the electrospun mats has been improved by a combination of hexamethylene diisocyanate and aqueous calcium chloride cross-linkings.     

Orientation relaxation study on poly(ethylene oxide)-poly(vinyl phenol) blends by polarization modulation infrared linear dichroism

Orientation relaxation in miscible poly(vinyl phenol) (PVPh)-poly(ethylene oxide) (PEO) blends (from 25 to 40 wt% PEO) was investigated using polarization modulation infrared linear dichroism. This blend was selected to study the effect of strong hydrogen bonds on relaxation. The results show that PEO is more oriented than PVPh, and remains so throughout the experimental relaxation time. Relaxation proceeds in three stages. PVPh relaxation is systematically faster than that of PEO, while PEO relaxation times increase steadily with increasing PEO content. For PVPh, a maximum in relaxation times is observed around 30 wt% PEO. Relaxation coupling occurs for concentrations in PEO lower than 30 wt%, is marginal for the 35 wt% and clearly absent for the 40 wt% PEO blend. By comparison with previous rheology and near-infrared data, it can be concluded that hydrogen bonds do not automatically insure cooperativity during relaxation: for cooperativity to occur, the minor component of the blend must interact preferentially with the major component. This is the case of PVPh-rich compositions, but not for PEO-rich compositions (for 35 and 40 wt% PEO), for which the minor PVPh constituent interacts strongly with both PEO and other PVPh chains.     

Synthesis and characterization of amphiphilic graft copolymer poly(ethylene oxide)-graft-poly(methyl acrylate)

A novel well-defined amphiphilic graft copolymer of poly(ethylene oxide) as main chain and poly(methyl acrylate) as graft chains is successfully prepared by combination of anionic copolymerization with atom transfer radical polymerization (ATRP). The glycidol is protected by ethyl vinyl ether first, then obtained 2,3-epoxypropyl-1-ethoxyethyl ether (EPEE) is copolymerized with EO by initiation of mixture of diphenylmethyl potassium and triethylene glycol to give the well-defined poly(EO-co-EPEE), the latter is deprotected in the acidic conditions, then the recovered copolymer [(poly(EO-co-Gly)] with multi-pending hydroxyls is esterified with 2-bromoisobutyryl bromide to produce the ATRP macroinitiator with multi-pending activated bromides [poly(EO-co-Gly)_(ATRP)] to initiate the polymerization of methyl acrylate (MA). The object products and intermediates are characterized by NMR, MALDI-TOF-MS, FT-IR, and SEC in detail. In solution polymerization, the molecular weight distribution of the graft copolymers is rather narrow (M_w/M_n < 1.2), and the linear dependence of Ln [M₀]/[M] on time demonstrates that the MA polymerization is well controlled.     

Crystalline structures in ultrathin poly(ethylene oxide)/poly(methyl methacrylate) blend films

Amorphous poly(ethylene oxide)/poly(methyl methacrylate) (PEO/PMMA) blend films in extremely constrained states are meta-stable and phase separation of fractal-like branched patterns happens in them due to heterogeneously nucleated PEO crystallization by diffusion-limited aggregation. The crystalline branches are viewed flat-on with PEO chains oriented normal to the substrate surface, upon increasing PMMA content the branch width remains invariant but thickness increases. It is revealed that PMMA imposes different effects on PEO crystallization, i.e. the length and thickness of branches, depending on the film composition.     

Corona discharge from electrospinning jet of poly(ethylene oxide) solution

Corona discharges from electrospinning jets were observed and photographed at the tip of the Taylor cone, and in a cylindrical region around the jet, a few millimeters below the tip. The corona discharge was also faintly visible to a dark adapted eye. At the position at which the cylindrical corona discharge became apparent, typical conditions were a jet diameter of 30 μm, an applied potential of 12 kV, and a calculated radial electric field of 400 kV/cm, The calculated electric field required to create a corona in air around a metal wire of the same diameter, calculated from Peek's empirical formula, was only about 200 kV/cm. The cross sectional shape of some segments of the electrospun fibers had two or three lobes. The lobes often separated, and formed smaller fibers.     

Crystallization and unusual rheological behavior in poly(ethylene oxide)-clay nanocomposites

We report a systematic study of the crystallization and rheological behavior of poly(ethylene oxide) (PEO)-clay nanocomposites. To that end a series of nanocomposites based on PEOs of different molecular weight (10³ < MW < 10⁵ g/mol) and clay surface modifier was synthesized and characterized. Incorporation of organoclays with polar (MMT-OH) or aromatic groups (MMT-Ar) suppresses the crystallization of polymer chains in low MW PEO, but does not significantly affect the crystallization of high MW matrices. In addition, the relative complex viscosity of the nanocomposites based on low MW PEO increases significantly, but the effect is less pronounced at higher MWs. The viscosity increases in the series MMT-Alk < MMT-OH < MMT-Ar. In contrast to the neat PEO which exhibits a monotonic decrease of viscosity with temperature, all nanocomposites show an increase after a certain temperature. This is the first report of such dramatic enhancements in the viscoelasticity of nanocomposites, which are reversible, are based on a simple polymer matrix and are true in a wide temperature range.     

Conformational characteristics of poly(ethylene oxide) (PEO) in methanol

The conformational characteristics of poly(ethylene oxide) (PEO) in methanol at 25 °C were investigated by static light scattering and viscometry for high molar mass (M_w) PEO fractions covering M_w = 3.42 × 10⁵-5.05 × 10⁶ g mol⁻¹. No trace of downturn in the plot of angular dependence of Kc/R_θ at low angle was found. Experimental scaling laws for the second virial coefficient (A₂), the third virial coefficient (A₃), the radius of gyration and the intrinsic viscosity ([η]) were determined. The exponents characterizing these scaling laws confirmed that the PEO chain in methanol has a flexible conformation with relatively large excluded volume, but methanol is not as good solvent as water. On the other hand, the low value of interpenetration function (Ψ) and the relatively higher order of the dimensionless parameter Π are considered to be an indication of local chain stiffness. All the results obtained in this study allow us to conclude that the overall chain conformation of PEO assumed in methanol is basically a random coil, but is intermittently mixed with helical structure.     

Step-scan alternating DSC study of melting and crystallisation in poly(ethylene oxide)

Step-scan alternating differential scanning calorimetry (SSA-DSC) method was applied to investigate the phase behaviour of well-characterised poly(ethylene oxide) (PEO). Influence of the three main measurement's parameters of SSA-DSC method: length of the isothermal segment (t_iso/s), temperature jump between two subsequent isothermal segments (step/deg) and linear heating rate in dynamic segments (b/K/min), on the shape of reversing and non-reversing components during the melting and crystallisation of PEO, has been evaluated. It was found that the reversing component during melting of PEO is increasing with an increase of the isothermal segment length. This effect is due to the existence of defected polymer crystal structures that form metastable regions between crystal phase and already melted polymer. Reversible recrystallisation in the presence of still existing polymer crystals is facilitated by longer isothermal segments. By increasing the step, the equilibrium of reversible processes is shifted towards products and activation of rate-controlled processes takes place; molecular nucleation is hampered and partial melting and/or recrystallisation proceed slower—this effect can be observed as a decrease of reversing signal with increasing step.     

Mesogenic structures and charge-transfer reactions in poly(ethylene oxide) complexes

After discussion of a schematic model for the crystalline phases of some poly(ethylene oxide) (PEO)-Na⁺ complexes with organic anions, three types of material are discussed. (i) Complexes of sodium salts of organic acids substituted by hydrophobic groups are deposited from methanol as macrodomains of uniaxially oriented material; these rearrange to microdomain morphologies on heating above ca. 60°C. Similar anions substituted by polar groups form spherulitic complexes or they rearrange thermotropically to microdomain structures. (ii) The preparation of polythiocyanogen by a ‘canal’ polymerisation within a PEO-NaSCN lattice is described and its extraction to give a material of conductivity ca. 10^?1S cm^?1 after doping is discussed, (iii) Charge-transfer reactions with PEO-NaI and tetracyano-quinodimethan (TCNQ) to give films having conductivities of 10^?3-10Ω^?1 cm^?1 are also described.     

Blends of poly(ethylene oxide) and poly(4-vinylphenol-co-2-hydroxyethyl methacrylate): thermal analysis, morphological behaviour and specific interactions

DSC and optical microscopy were used to determine the miscibility and crystallinity of blends of poly(ethylene oxide) (PEO) with poly(4-vinylphenol-co-2-hydroxyethyl methacrylate) (PVPh-HEM). A single glass transition temperature was observed for all blends, indicating miscibility. A progressive decrease in the degree of crystallinity and in the size of the PEO spherullites is observed, as PVPh-HEM is added. FTIR was used to probe the intermolecular specific interactions of the blends and the miscibility of the blend is mainly attributed to PVPh-HEM/PEO intermolecular interactions via hydrogen bonding.