Ratio Of PEO Research Articles

Saturation ratio of poly(ethylene oxide) to silicate in melt intercalated nanocomposites

Melt intercalation has been found to be a very successful approach for preparation of polymer–clay nanocomposites. An aspect of this area that has been little investigated is the amount of polymer required to fill the interlayer galleries of the clay. This paper reports experiments which determine the amount of poly(ethylene oxide) (PEO) required to saturate the spacing between montmorillonite (MMT) or organically-modified bentonite (B34) layers. Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were used to determine the saturation ratios of PEO to silicates, which are then compared to theoretical calculations. The deduced saturation ratio of PEO to MMT is 28:72, and PEO to B34 15:85 by XRD and DSC, whilst ratios of PEO to MMT of 21:79 and PEO to B34 10:90 were obtained via TGA. The density of intercalated PEO in the silicate galleries is estimated to be 0.82 g/cm 3, which suggests that PEO in the silicate galleries is far less efficiently packed than in the amorphous region of the bulk polymer.

Highly conductive polymer electrolytes supported by microporous membrane

Highly conductive polymer electrolytes supported by a microporous separator were prepared and characterized. These polymer electrolytes were prepared by coating poly(ethylene oxide) (PEO) and poly(ethylene glycol dimethacrylate) (PEGDMA) onto a microporous polyethylene membrane, and soaking them in an electrolyte solution. The relative weight ratio of PEO and PEGDMA coated on the microporous membrane proved to play a critical role in determining uptake of an electrolyte solution and ionic conductivity. The electrolyte optimized in this work displayed a high ionic conductivity and electrochemical stability, exhibiting no solvent leakage. An encapsulation of electrolyte solution within the porous membrane diminished the passivation of lithium electrodes. With these electrolytes, lithium-ion polymer cells composed of a carbon anode and LiCoO 2 cathode were assembled, and their electrochemical performances were evaluated.

Porous biodegradable polyesters. I. Preparation of porous poly(L-lactide) films by extraction of poly(ethylene oxide) from their blends

Porous poly(L-lactide) (PLLA) films were prepared by water extraction of poly(ethylene oxide) (PEO) from solution-cast PLLA and PEO blend films. The dependence of blend ratio and molecular weight of PEO on the porosity and pore size of films was investigated by gravimetry and scanning electron microscopy. The film porosity and extracted weight ratio were in good agreement with the expected for porous films prepared using PEO of low molecular weight (Mw = 1 × 103), but shifted to lower values than expected when high molecular weight PEO (Mw = 1 × 105) was utilized. The maximum pore size was larger for porous films prepared from PEO having higher molecular weight, when compared at the same blending ratio of PLLA and PEO before water extraction. Differential scanning calorimetry of as-cast PLLA and PEO blend films revealed that PLLA and PEO were phase-separated at least after solvent evaporation. On the other hand, comparison of blend films before and after extraction suggested that a small amount of PEO was trapped in the amorphous region between PLLA crystallites even after water extraction and hindered PLLA crystallization during solvent evaporation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 629–637, 2000

13C CP/MAS and 7Li NMR Study of Lithium Perchlorate/Poly(ethylene oxide)

To study compositional dependent conductivity of Li+-ions in lithium perchlorate/poly(ethylene oxide) (LiClO4/PEO) electrolytes, mobility of the Li+-ions and morphology of the electrolytes are investigated by examining the spin-lattice relaxation time (T1) of 7Li and by high-resolution solid-state 13C NMR methods. It is shown that the amount of the mobile Li+-ion estimated from the shorter 7Li-T1 component is not directly compared with the reported conductivity. The high-resolution solid-state 13C NMR spectra show that there exists five different CH2 carbons in the LiClO4/PEO electrolytes. The five peaks are assigned to (1) the crystalline phase of pure PEO, (2) the amorphous phase of PEO with the Li+-ions, and three complex phases of the following ratio of (3) PEO : Li+=3 : 1, (4) x : 1 (3<x<6), and (5) 6 : 1 . Furthermore, it is shown that the domain size of the PEO : Li+=6 : 1 phase in the LiClO4/PEO = 1/6 electrolyte is large and the mobility of the Li+-ions in the phase is so fast as to give a short 7Li-T1 comparable to that in the amorphous phase. The former ions are confined in the PEO : Li+=6 : 1 phase and do not contribute to conductivity while the latter does. Therefore, care should be taken in correlating the amount of the mobile Li+-ions obtained from the 7Li-T1 data to the Li+-ion conductivity.

Synthesis and characterization of oxymethylene-linked 2-vinylpyridine/oxyethylene multiblock copolymers

Oxymethylene-linked (2-vinylpyridine-oxyethylene) multiblock copolymers were prepared by coupling telechelic α,ω-dihydroxypoly(2-vinylpyridine) (THPVP) and poly(ethylene oxide) (PEO), using dichloromethane as coupling agent and KOH as catalyst. THPVP was synthesized by polymerization of 2-vinylpyridine in tetrahydrofuran/benzene using l-methylnaphthyllithium as anionic initiator, followed by capping with ethylene oxide and termination by methanol. The effects of charging weight ratio of PEO/ THPVP, copolymerization time and molecular weight of PEO or THPVP on the copolymerization were studied. The copolymers were characterized by IR, 'H NMR, membrane osmometry, transmission electron microscopy (TEM) and differential scanning calorimetry (DSC).

Structure and molecular motion of polystyrene chains adsorbed on a silica-tethered poly(ethylene oxide) by the spin-label method

The spin-label method was used to study the structure and molecular motion of polystyrene (PS) chains adsorbed on a silica-tethered poly(ethylene oxide) (PEO). Spin-labelled polystyrene with a narrow molecular weight distribution, having a weight-average molecular weight ( M w ) of 9.64 × 10 4, was adsorbed on the surface of the silica-tethered PEO with various grafting ratio lower than 2.1% in carbon tetrachloride solution at 35°C. Electron spin resonance (e.s.r.) spectra were observed at various temperatures after the samples had been dried completely. The e.s.r. spectra observed at − 196°C were composed of two spectra arising from spin labels attached to ‘train’ and ‘loop’ (or ‘tail’) segments, which were strongly and weakly interacted with the silica surface, respectively. The fractional amount of the ‘loop’ or ‘tail’ segments increases dramatically with grafting ratio of the PEO. The transition temperature of molecular motion estimated from the temperature dependence of the e.s.r. spectra decreases also dramatically with the grafting ratio of PEO. The ‘loop’ or ‘tail’ segments are attributed to PS chains protruding from the silica surface and/or embedded in the tethered PEO chains, whereas the ‘train’ segments are trapped near the silica surface.

Aqueous solution properties of oligo- and poly(ethylene oxide) by static light scattering and intrinsic viscosity

Conformational properties of ethylene glycol, oligo-, and poly(ethylene oxide) ranging in weight-average molecular weight ( M w) from 62 to 1.1 × 10 7 have been studied by static light scattering and viscometry in salt-free and 0.45 M K 2SO 4 water and in benzene. Above M w = 6 × 10 3, intrinsic viscosity ([η]) and z-average square radius of gyration (〈 S 2〉 2) of PEO in a salt-free solution at 25°C, [η] = 4.33 × 10 −4 M w 0.67 9 dl g −1 and 〈 S 2〉 z = 4.08 × 10 −18 M w 1.1 6 cm 2, respectively. The second virial coefficient is positive in water at 25°C but one order of magnitude smaller than reported by Devanand et al. ( Macromolecules, 1991, 24, 5943). A θ-temperature for PEO in 0.45 M K 2SO 4 aqueous solution is determined to be 34.5°C and above M w = 4 × 10 2, [η] and 〈 S 2〉 z follow the power laws for an unperturbed polymer chain. The characteristic ratio ( C ∞) of PEO is 5.2 ± 0.1. 9.3Åwas determined for the persistence length and 8.7Å −1 for the molar mass per unit contour length of a PEO chain, based on the helical wormlike touched-bead model. The PEO chain in water behaves as a flexible polymer with a relatively large hydrodynamic diameter (9Å) because of the hydration of the PEO chain.

Diode-Array UV Spectrometric Evidence for Cooperative Interactions in Binary Mixtures of Pluronics F77, F87, and F127

Iodine incorporation UV spectroscopy provides evidence that (PEOA−PPOB−PEOA) block copolymers (Pluronics) of related composition will aggregate either cooperatively or independently. Studying binary mixtures of Pluronics, selected from a series of Pluronics containing the same ratio of PEO:PPO (70% PEO, 30% PPO), allowed the effects of varying polymeric mass on the type of interaction observed to be investigated. Preliminary results indicate that the mass ratio of the PPO moieties determines the type of interaction observed.

Adsorption behaviour and conformation of selected poly(ethylene oxide) copolymers on the surface of a model colloidal drug carrier

The adsorption of some selected poly(ethylene oxide) containing copolymers onto a model colloidal drug carrier (polystyrene latex) was studied in terms of the adsorption isotherm and hydrodynamic thickness of the coating layer. The copolymers were selected on the basis of the biological effects that they produce when adsorbed onto polystyrene latex. Investigated were two tetrafunctional block copolymers of poly(ethylene oxide)-poly(propylene oxide) ethylene diamine (Poloxamine 908 and Poloxamine 904), and ABA triblock copolymer of poly(ethylene oxide)-poly(propylene oxide) (Poloxamer 407) and two AB polylactide-poly(ethylene glycol) copolymers (PLA:PEG) with ratios of 1.5:2 and 2:5 of polylactide to the poly(ethylene glycol) moiety. The dimensions of the poly(ethylene oxide) (PEO) chains on the surface (the PEO layer thickness and the surface area per one PEO chain) are found to be similar for the copolymers with relatively high ratio of PEO to hydrophobic moiety and with similar PEO size (Poloxamine 908, Poloxamer 407 and PLA:PEG 2:5), irrespective of the differences in the copolymer molecular composition and structure. A comparison between the dimensions of PEO free in a solution and in the adsorbed layer (the PEO layer thickness) of these polymers reveals that the most probable conformation of the higher molecular weight PEO chains at the surface is an elongated coil. A comparison of the biological performances of these systems shows a dramatically different in-vivo behaviour of the systems with significantly different dimensions of the adsorbed PEO (Poloxamine 908 and 904), while those with the similar PEO dimensions may exhibit comparable biological properties (Poloxamer 407 and Poloxamine 908) despite difference in the polymer molecular structure.

Electrochemical properties of lithium salt-poly(ethylene oxide)-ethylene carbonate polymer electrolyte and discharge characteristics of [formula omitted

Lithium salt-poly(ethylene oxide) polymer (PEO) electrolyte was prepared by solvent casting method. Ethylene carbonate (EC) was added to improve the ionic conductivity of the polymer electrolytes. The ionic conductivity of polymer electrolytes increased from 1.8 × 10 −7 S cm −1 to 2.7 × 10 −5 S cm −1 at 30 °C when the weight ratio of EC and PEO increased from 0 to 0.8. The activation energy of ionic conductivity obtained from log σ vs. 1/ T plot was 26.1 kJ mol −1 when the EC PEO weight ratio and [O] [Li + ] molar ratio were 0.8 and 25, respectively. The cyclic voltammetry results indicated that increasing the temperature resulted in the decrease of the peak potential difference of stripping of Li and deposition of Li + ( ΔE p). The discharge characteristic of lithium-manganese cell was significantly affected by the polymer electrolyte complexes, discharge temperature and current density.

Synthesis of nonionic flocculants by gamma irradiation of mixtures of polyacrylamide and poly(ethylene oxide)

AbstractThe synthesis of polyacrylamide (PAM) graft poly(ethylene oxide) (PEO) has been investigated and the reaction conditions were varied by gamma irradiation to optimize polystyrene latex flocculation by the copolymers. The effects of the gamma ray dosage, the PEO chain length, the ratio of PEO to PAM, and the crosslinking degree of copolymer were studied. The most effective flocculant was obtained by exposing a mixture of 1.2 wt % PAM (Mw = 5 × 106) and 0.94 wt % PEO (Mw = 5000) to 816 krad of gamma radiation. The resulting copolymer contained 24 wt % PEO. Crosslinking to give insoluble gels was an undesirable side reaction increased with γ‐ray dose and decreased with PEO addition. The most effective flocculants contained more than 15 wt % PEO with little crosslinking. The grafting behavior of triblock copolymer, poly(ethylene oxide)‐b‐poly(propylene oxide)‐b‐poly(ethylene oxide) (EmPnEm, where m and n are oxyethylene and oxypropylene unit, respectively), onto PAM by gamma radiation was also studied; grafting occurred but effective flocculants were not obtained. © 1994 John Wiley &amp; Sons, Inc.