Molecular Weight PEO Research Articles

The preparation, conductivity, viscosity and mechanical properties of polymer electrolytes and new hybrid ionic rubber electrolytes

The preparation and characterization of new ionic rubber electrolytes based on the ternary LiClO 4LiNO 3LiOAc and the high molecular weight PEO (m wt 8 × 10 6) is reported. The conductivity, viscosity and shear modulus have been measured. The decrease in conductivity due to incorporation of 9% PEO (m wt 8 × 10 6) in the salt mixture is small (factor of 5), but the increases in viscosity is enormous ( eg factor of ~5000 with only 5% PEO). 10% PEO (m wt 8 × 10 6) can give rise to a rubbery plateau above T g which extends to about 130 °C transition to liquid defined by the onset temperature of the varnishing of the shear modulus. These characteristics combined with the high Li cation transport number make this kind of material very promising. Results are compared with those of the conventional salts-in-polymer electrolytes and the crossover to the polymer-in-salts region is identified by a maximum in the rubbery modulus.

Polymer decoration study in chain folding behavior of solution‐grown poly(ethylene oxide) crystals

AbstractThe polymer decoration method based on the vaporization and condensation‐crystallization of polyethylene (PE) upon the fold surface of polymer crystals has been widely used to study the chain folding behavior of the crystals. When this method was utilized to study solution‐grown high molecular weight poly (ethylene oxide) (PEO) lamellar crystals, the highly anisotropic, low molecular weight fragment PE decorated become oriented parallel to the fold direction and form rods, which can be observed by transmission electron microscopy (TEM) and electron diffraction (ED). The growth sectors were clearly observed. From the ED patterns the {200} planes of the orthorhombic low molecular weight PE rod crystals can be observed, and the c‐axis of these crystals is aligned parallel to the {120} growth planes of the PEO crystals. The decoration results indicate that the major fold orientation of high molecular weight PEO single crystals grown from dilute solution is along the {120} planes. © 1995 John Wiley & Sons, Inc.

Ionic conductivity of poly(ethylene oxide) having charges on the chain end

Anionic charges are introduced in the chain end of a series of poly(ethylene oxide)s (PEO) with molecular weights from 350 to 4000. The ionic conductivities of PEO oligomers with a carboxylate chain end (PEOAc 2M 2) and of those with benzenesulfonate (PEOBsM and PEOBs 2M 2) were analyzed. The mechanical properties of these salts were greatly influenced not only by PEO molecular weight but also by the chain end structure. PEOAc 2M 2, which has charges on both chain ends, showed an amorphous phase, when the molecular weight of the PEO part was 400 and 600. These salts showed inherently high ionic conductivity, about 10 −4 S/cm at 323 K, because of the high mobility of carrier ions and the high ion concentration. The ionic conductivity increased with increasing the cation radius for all of the PEOAc 2M 2. Since PEO showed low diffusion coefficient values, these salts were expected to be the single-ion conductors. Furthermore, a series of PEOBs salts was prepared and their ionic conductivity was analyzed. A series of PEOBsM became viscous liquids at a moderate molecular weight range, such as from 350 to 750. These salts showed higher ionic conductivities than PEOAc 2M 2, reflecting lower dissociation energy of salt structure on the chain ends.

Investigation of Tb 3+ ion fluorescence properties in γ-irradiated poly(ethylene oxide)-TbCl 3 blended systems

Degradation of polymers by γ-irradiation using Tb 3+ ion as a fluorescence probe was investigated. When poly(ethylene oxide) blended with TbCl 3 films were γ-irradiated in air, the fluorescence intensity of Tb 3+ was found to be greatly increased and the molecular weights of PEO were decreased. These results suggest that radiolysis caused chain degradation of PEO and produced carbonyl groups at the end of the cleaved polymer chain. The chromophore moiety produced transfers energy to Tb 3+ ion located within the non-irradiative energy trasfer distance. It is suggested that blended films of PEO with Tb 3+ may be used as convenient and fast detectors of γ-irradiation doses.

Crystallization of carboxylic acid salts in poly(ethylene oxide) oligomers at higher temperatures

AbstractMany alkali metal carboxylates when dissolved in poly(ethylene oxide) (PEO) oligomers, are phaseseparated by heating. These were revealed to be the crystals of the initially dissolved corresponding salts from the X‐ray diffraction patterns. Some acetate salts achieve the lower limit of the lattice energy for phase separation of ordinary inorganic salts by heating in PEO oligomers. These carboxylate salts were therefore expected to show crystallization behavior in PEO oligomers by heating. The effects of cation size, alkyl chain length and molecular weight of PEO on the solubility are summarized. Negative temperature dependence of solubility of these acetate salts is seen in the PEO oligomers only when the salts have long alkyl chains. The salts containing larger cations needed a longer chain length of PEOs for crystallization by heating. These salts with longer alkyl chains showed positive temperautred dependence in lower molecular weight polyethers, but negative temperature dependence in solubility in PEO with molecular weights higher than 400. In PEO400, all the carboxylates with longer alkyl chains were phase separated by heating.

Drug Release from Compressed Hydrophilic POLYOX‐WSR Tablets

Drug release from compressed tablets manufactured with a powder mixture of poly(ethylene oxide) (PEO), a drug, and magnesium stearate is presented. Several factors such as molecular weight, drug loading, drug solubility, the pH of the dissolution medium, and stirring rate are investigated. The drug release from the high molecular weight PEO tablets (MW = 2×106and 4×106) is governed by the swelling of the polymer rather than by the erosion of the polymer, leading to anomalous release kinetics. However, the drug release from the low molecular weight PEO (MW = 0.9×106) is controlled primarily by the swelling/erosion of the polymer, resulting in front synchronization and a constant release rate. It is observed that drug loading and drug solubility do not influence the release of drugs from low molecular weight PEO tablets. The pH of the dissolution medium and the stirring rate do not affect the drug release regardless of the molecular weight of the PEO.

Thermal behavior of new polymer electrolytes

AbstractSolid polymer electrolytes (SPE) have been identified as a class of materials which could enable the fabrication of high energy density solid state lithium rechargeable batteries which could meet the performance requirements for advanced portable electronic and automotive applications. In order to achieve this goal, novel SPE systems having high ionic conductivity and good mechanical properties at or near ambient temperature must be developed. Novel lithium salts believed to be useful in realizing this objective have recently been proposed. The thermal behavior of SPE systems based on high molecular weight poly(ethylene oxide) (PEO) and on two novel salts, the lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and the lithium tris(trifluoromethylsulfonyl)‐methanide (LiTSFM) is reported and compared with the thermal behavior of the high molecular weight PEO–lithium trifluoromethane sulfonate (LiTFLT) SPE system. Phase diagrams for the PEO–LiTFSI and PEO–LiTFSM SPE systems have been established and are discussed in terms of their impact on SPE‐based rechargeable lithium battery technologies. The use of a novel plasticizer in conjunction with the PEO–LiTFSI‐based SPE system is reported and it is shown how this modifies the thermal behavior of the PEO–LiTFSI SPE system.

Permeability and blood compatibility properties of chitosan-poly(ethylene oxide) blend membranes for haemodialysis

Chitosan-poly(ethylene oxide) (PEO) blend membranes, using different molecular weights of PEO, were developed for improved permeability and blood compatibility. The equilibrium hydration increased from 44.7% for chitosan to 62.5% for chitosan-PEO blend membranes when the molecular weight of PEO was 10 000 (10K) or higher. An increase in the hydration of PEO blend membranes was due to intermolecular association between PEO and chitosan chains. Scanning electron microscopy showed that chitosan-PEO membranes were highly porous with size ranging from 50 to 80 nm in diameter observed in membranes made with PEO10K. Electron spectroscopy for chemical analysis suggested an increase in PEO on the membrane surface with increasing molecular weight in the blend. The permeability coefficient of urea increased from 5.47 × 10 −5 cm 2 min −1 in chitosan to 9.86 × 10 −5 cm 2 min −1 in chitosan-PEO10K membranes. The increase in permeability coefficient could be either due to an increase in the hydrophilicity or the high porosity of the membranes. Although chitosan-PEO membranes did not prevent serum complement activation, platelet adhesion and activation were significantly reduced. Chitosan-PEO blend membranes, therefore, appear to be beneficial in improving the permeability of toxic metabolites and in reducing the thrombogenicity for haemodialysis.

Thermal and structural analysis of heparin–PEO–PDMS–PEO–heparin pentablock copolymers

AbstractABCBA‐type amphiphilic block copolymers comprising polydimethylsiloxane (PDMS), poly(ethylene oxide) (PEO), and heparin segments were synthesized by coupling reactions between end‐functionalized oligomers. These multiblock copolymers were characterized to examine bulk properties using 1H‐NMR, FTIR, end‐group analysis, and sulfur elemental analysis. Block copolymers were further characterized in bulk using differential scanning calorimetry and X‐ray diffraction measurements. The PDMS glass transition remains unchanged with increasing PEO content, indicating coexistence of pure PDMS with mixed phases. Furthermore, endothermic melting of the block copolymers shifts to higher temperatures and becomes more intense with increasing PEO molecular weight. Additionally, the crystallinity of the PEO segment in the block copolymers increases with increasing PEO molecular weight. The PEO melting endotherm peak shifts from near 318 to 323 K with annealing. In the cooling thermogram, the block copolymers exhibit two crystallization exotherms, one near 303 K and the other near 193 K, attributed to PEO and PDMS recrystallization and nucleation, respectively. © 1994 John Wiley & Sons, Inc.

Viscoelastic Properties of Poly(ethylene oxide) Solution

The viscoelastic properties of poly(ethylene oxide) (PEO) solution were investigated using the dynamic oscillatory testing technique. With this technique, the effect of PEO molecular weight (MW), concentration, composition of mixed solvent systems consisting of propylene glycol, glycerol formal, and water, and the effect of NaCl salt on the viscoelastic properties of PEO solution were determined. Dynamic moduli (G1,G2), magnitude of complex viscosity (|η*|), and loss tangent (tan δ) were examined over a frequency range of 10−3–2.5 Hz at 30 °C. The results indicated that low MW PEOs show liquidlike behavior while high elasticity is exhibited by high MW PEOs due to entanglement formation. The complex viscosity, |η*|, exhibits shear thinning (power-law) characteristics under oscillatory measurements. The relationship between steady shear and complex viscosities follows the Cox–Merz rule over the shear rate and frequency region studied. Both the storage (G1) and loss (G2) modulus increase drastically as the proportion of water in the mixed solvent system increases. Similarly, bothG1andG2are found to increase while the tan δ decreases with increasing concentration of PEOs. The addition of up to 2% w/w NaCl in an aqueous solution of 10% w/w 2 million MW PEO has no observed detrimental effect on the viscoelastic behavior.

Dynamic light scattering of suspensions of PEO-coated latex particles

Photon correlation spectroscopy has been used in conjunction with electrophoresis to determine the hydrodynamic layer thickness (HLT) and surface properties of poly(ethylene oxide) (PEO) adsorbed onto carboxylated poly(styrene) and poly(styrene—butadiene) latexes from water. The effects of the surface charge density of the latex particle, the surface roughness of the latex particle, PEO molecular weight and concentration, the presence of PEO clusters in solution, and the manner in which PEO is added to the latex suspension on the HLT were studied. The properties and stability of brominated latex suspensions were also studied. The results indicate that the adsorption of PEO onto latex particles is kinetically controlled and that increased surface roughness and polarity of the latex particles decreases PEO adsorption. The molar mass exponent, a, was found to increase with decreasing surface roughness and surface charge density. The manner in which PEO is added to the latex suspension was found to be the most important factor affecting the value of a. A molar mass exponent of a = 0.36 ± 0.02 for all the latexes, regardless of surface roughness and surface charge density, was found for two-step PEO additions. PEO clusters in solution were found to increase the value of the effective diffusion constant, D eff, and thus decrease the calculated HLT. Bromination of the latexes allowed for an estimation of the “hairy” layer thickness of the latex particles.

Decreased solubility of alkali metal salts by heating in poly (ethylene oxide) oligomers

Several inorganic salts, homogeneously dissolved in poly (ethylene oxide) (PEO) oligomers, were crystallized by heating. The solubility of these salts (classified here as type 1) decreased considerably with increased temperature. However, an other group of inorganic salts (type 2) did not crystallize upon heating. The effect of terminal hydroxyl group fraction of PEO on the solubility of salt in the PEO was analyzed. It was concluded that the type 1 salts were solubilized mainly by the terminal hydroxyl groups of the PEOs. In contrast, type 2 salts are solubilized by not only terminal hydroxyl groups but also ether oxygens, and these salts are known to form complexes with high molecular weight PEO. The cation of the type 1 salts was solvated by both terminal hydroxyl groups in PEO oligomers. This negative temperature dependence of solubility of type 1 salts was attributed to the destabilization of the cation solvating structure by heating.

Chemical modification of butyl rubber. I. Synthesis and properties of poly(ethylene oxide)‐grafted butyl rubber

AbstractA new amphiphilic polymer, i.e., poly(ethylene oxide) (PEO)‐grafted butyl rubber (IIR‐g‐PEO), was synthesized by chemical modification of chlorinated butyl rubber (CIIR). This synthesis was based on the reaction between chlorine in CIIR and potassium salt of polyethylene glycol monomethyl ether (PEGM). PEGM's with molecular weights of 750 and 2000 were used. The maximum grafting percent of the resulted copolymers after the purification was ca. 45%, regardless of the molecular weight of PEGM. The microphase separated structure was observed in the films of IIR‐g‐PEOs. IIR‐g‐PEO, whose PEO molecular weight was 2000 and whose PEO content was 23.8 wt %, swelled 3.1% in water, and it was six times larger than the swelling of CIIR. The hydrophilicity of grafted polymers depended on the molecular weight of PEO side chains and PEO content. Even when the PEO contents were same in the polymers which were grafted PEGM‐750 and PEGM‐2000, their swellings in organic solvents were not equal. It was due to the difference of the microphase‐separated structures of the grafted polymers. IIR‐g‐PEO, whose PEO molecular weight was 750 and whose PEO content was 10.3 wt %, swelled 1.5% in water, but showed an excellent emulsifying ability, where an oil‐in‐water‐type emulsion was formed. © 1993 John Wiley & Sons, Inc.

Temperature-controlled ionic conductivity switching in poly[oligo(oxyethylene) methacrylate]/ poly (ethylene oxide) layered film

The present study is aimed to design the temperature-driven switching of the ionic conductivity in polymer electrolytes. First, thermotropic liquid crystalline molecule, 4'-ethoxybenzylidene-4-n-butylaniline (EBBA), was sandwiched with poly(oligo(oxyethylene) methacrylate)(PMEO) containing LiClO 4. A change in the ionic conductivity was observed by heating due to crystal/nematic phase change, but it was observed only in the first heating. On the other hand, the ionic conductivity of PEO sandwiched system showed drastic ionic conductivity jump which was attributed to the phase transition of the PEO. The temperature dependence of the ionic conductivity showed a good reproducibility in this system. The phase transition temperature was affected by the added salt concentration. This was comprehensible as freezing point depression of PEOs. The switching temperature was controllable in the range from −13°C to 52°C by the molecular weight of PEO and added salt concentration in the PEO. The formation of ion pair and aggregate ion was never observed by Raman spectroscopy in the range of salt concentration used in this experiment.

Effects of homopolymers on the gel formation in aqueous block copolymer solutions

The gel formation in aqueous EO 99 -PO 65 -EO 99 solutions has been studied (EO and PO being ethylene oxide and propylene oxide, respectively). The effects of the homopolymers (i.e., PEO and PPO) were investigated in detail. It was found that PEO of intermediate molecular weight causes the gel to «melt», at an amount of homopolymer which depends on the copolymer concentration. The efficiency of PEO in inducing the gel melting increases with its molecular weight, but at very high PEO molecular weights, phase separation, rather than gel melting, occurs. The gel melting bahavior was found also for a cationic polyelectrolyte (PDADMAC).

Cationic conductivity and relaxation processes in solid polymer electrolytes with lithium perfluoroalkyl sulfonate or sulfonato end-capped poly(ethylene oxide)

Blends of lithium perfluorinated sulfonate, C 8F 17SO 3Li, or sulfonato end-capped poly(ethylene oxide), PEO(SO 3Li) 2, with high molecular weight PEO have been used as solid polymer electrolytes. In these materials, either the anion is bulky enough or is anchored to a polymer backbone to expect the anionic transport number to be equal to zero, so that only the cation contributes to the current transport. In addition, the fluorine atoms in the first anion would decrease the ion pairing whereas the second structure may be seen as a self-solvating anion, bringing the oxygen atoms required for the solvation of the lithium cation. PEO(SO 3Li) 2 has been synthesized by reaction of PEO alcoholate with propane sultone. These solid polymer electrolytes have been characterized by d.s.c., X-ray diffraction and complex impedance spectroscopy. The conductivities at room temperature are around 10 −7 S cm −1, of the same order of magnitude as solid polymer electrolytes with only one mobile ion. Beside the resistances, some relevant parameters of the electrochemical behaviour (relaxation times, dispersive indexes) have been derived from analysis of complex impedance spectra and tentatively interpreted in the framework of charge carrier transport in heterogeneous electrolytic media in order to yield information about the morphological state of the materials.

Protein partitioning in two-phase aqueous polymer systems. 5. Decoupling of the effects of protein concentration, salt type, and polymer molecular weight

Measurements of the partitioning behavior of ovalbumin in the poly(ethylene oxide) (PEO)-dextran aqueous two-phase system reveal that experimental conditions can be found at which the effects of protein concentration, salt type, and PEO molecular weight can be decoupled. Specifically, the change in the logarithm of the ovalbumin partition coefficient, Δ(lnK p ) (where K p is the ratio of the protein concentrations in the top PEO-rich phase and the bottom dextran-rich phase), that accompanies a change in PEO molecular weight over the range 5000 to 35 000 Da was measured to be independent of the ovalbumin concentration and the type of salt (NaCl and Na 2 SO 4 ) present in the system

Poly(Ethylene oxide) (PEO) and different molecular weight PEO blends monolithic devices for drug release

An interpretation of the drug release from monolithic water-swellable and soluble polymer tablets is presented. A convenient parameter, a, which compares the drug-diffusive conductance in the gel layer with the swelling and dissolving characteristics of the unpenetrated polymer was used to describe the release behaviour of β-hydroxyethyl-theophylline (etofylline) from compression-moulded tablets of hydrophilic pure semicrystalline poly(ethylene oxides) of mol wt 600 000 and 4 000 000 and of two blends of the two molecular weights of poly(ethylene oxides). The water swelling and dissolution characteristics of two polymers and two blends were analysed, monitoring the thickness increase of the surface-dissolving layer and the rates of water swelling and penetration in the tablets. The drug diffusivities in the water-penetrated polymer gels were measured by carrying out permeation tests. Finally, drug release tests were performed to investigate the release kinetics of the different systems in an aqueous environment at 37°C. The drug release from the high molecular weight poly(ethylene oxide) is principally related to the material swelling rather than polymer dissolution, leading to a progressive decrease of the drug's diffusive conductance in the growing swollen layer, and hence to a nonconstant release induced by the prevailing diffusive control. Conversely, drug release from the low molecular weight poly(ethylene oxide) is strictly related to the polymer dissolution mechanism. The achievement of stationary conditions, in which the rate of swelling equals the rate of dissolution, ensures a constant release rate, even in the case of very low drug-diffusive conductance in the external gel layer. Intermediate behaviours were detected in the case of the two blends.

Polymer solid electrolytes-PEO and alkali halides: A modified preparative technique

Polymer solid electrolytes are prepared by a modified preparative technique without any additional solvent. By this technique the polymer solid electrolyte can be manufactured not in thin films but in a compact form, particularly disks or tablets. The conductivities of these PEO-based electrolytes are investigated depending on temperature, molecular weight of PEO and alkali halide content. For the system PEO/LiI the composition dependence of the lithium ion transport numbers are investigated. In the range of low salt content the results are similar to those obtained from thin film preparations.

PEO enhancement of platelet deposition, fibrinogen deposition, and complement C3 activation.

Whereas it has been commonly thought that adding polyethylene oxide PEO to a surface would diminish the capacity of the surface to cause deposition of platelets and of fibrinogen, and to activate complement C3, we present data showing exactly the opposite. These unexpected results are obtained with low molecular weight (2000) PEO, and are not found with higher molecular weight (20,000) PEO.