Polyethylene oxidative stability

Comparison of calculated values (present work) of the limiting volume fraction of free polymer 0, at which instability sets in, with experimental values. System Polyethylene oxide-stabilized polystyrene latex with polyethylene oxide as the free polymer at 298 K, with a = 85 nm, Xi = 0.466, xs = 0.31 and fi = 5 nm... 

Fluidized aqueous suspensions of 15% by weight or more of hydroxyethyl-cellulose, hydrophobically modified cellulose ether, hydrophobically modified hydroxyethylcellulose, methylcellulose, hydroxypropylmethylcellulose, and polyethylene oxide are prepared by adding the polymer to a concentrated sodium formate solution containing xanthan gum as a stabilizer [278]. The xanthan gum is dissolved in water before sodium formate is added. Then the polymer is added to the solution to form a fluid suspension of the polymers. The polymer suspension can serve as an aqueous concentrate for further use. 

As part of a multi-technique investigation (see also discussion under mid-infrared spectroscopy later), Corrales et al. [13] plotted the carbonyl index for films prepared from three grades of polyethylenes a high-density PE (HDPE), a linear low-density PE (LLDPE) and a metallocene PE (mPE) (see Figure 5). In this study, the data trend shown in Figure 5 correlated well with activation energies derived from the thermal analysis, which showed that the thermal-oxidative stability followed the order LLDPE > mPE > HDPE, whereas the trend... 

Novel thermally responsive polymeric nanoparticles that show high colloidal stability were prepared by Laukkanen et al. via emulsion polymerisation of VCL in the presence of the amphiphilic macromonomer cw-methoxy polyethylene oxide undecyl a-methacrylate (MAC11EO42) (Fig. 15) [177,178,182]. The macromonomer itself proved to be highly sur-... 

A new class of amphiphilic, surface-active graft copolymers, hydrophobically modified hydroxyethyl celluloses (HM-HEC s), are comprised of a cellulose backbone with short polyethylene oxide (PEO) and grafted alkyl side chains. They are excellent steric stabilizers of 0/W emulsions. 

Steric Stabilization. Steric stabilization was a term first introduced by Heller to explain how adsorbed polyethylene oxide polymers increased the salt concentration required for flocculation of negatively charged aqueous suspensions.(6) Heller s systems were stabilized by both mechanisms, as are most commercial dispersions today, aqueous and non-aqueous. Much of the more recent literature on steric stabilizers has been preoccupied with solubility requirements, for the solubility of polymers is a delicate matter and very sensitive to temperature and solvent... 

Capillary coating can also stabilize the migration times and resolutions. This is in particular necessary in the case of peptide and protein analysis, because proteins tend to stick to capillary walls. Often low-concentration polyethylene oxide solutions are recommended as well as dynamic bilayer coating formed by a non-covalent adsorption of polybrene and polyvinylsulfonate (PVS). Due to the stability of the EOF, the variation of intra- and intercapillary migration time was less than 1% relative standard deviation (RSD) with basic analytes and peptides. 

By contrast, Nal-doped polyethylene oxide membranes have permitted experimental research on tiny rechargeable Na/l2 batteries to be initiated (Figure 2). Chemical stability of the electrolyte, and the integrity of the mechanical contacts at the current collector/electrolyte interfaces, during repetitive cycling, must be improved. 

Polyethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) (Pluronic) block copolymer is a very efficient reducing agent and nanoparticle stabilizer. Au NPs of about 10 nm can be stabilized with PEO-PPO-PEO block copolymer solutions in water and at room temperature and using HAuC14 as precursor. The formation of gold nanoparticles is controlled by the overall molecular weight and relative block length of the block copolymer [118]. 

Citrate-capped Au NPs have been coated with a layer composed of the double hydrophilic block copolymer polyethylene oxide)-block-poly(2-(dimethylamino)eth-yl methacrylate)-SH (PEO-b-PDMA-SH) leading to core-shell, almost spherical, Au NPs of about 18 nm. The shell cross-linking of these hybrid Au NPs gives rise to high colloidal stability [122]. 

The addition of water-soluble polymers such as polyethylene oxide (PEO) or polyvinyl alcohol (PVA) into the synthetic mixture of the C TMAX-HN03-TE0S-H20 system (n = 16 or 18 X = Br or Cl) under shear flow is found to promote uniformity and elongation of rope-like mesoporous silica. The millimeter-scaled mesoporous silica ropes are found to possess a three-level hierarchical structure. The addition of water-soluble polymer does not affect the physical properties of the silica ropes. Moreover, further hydrothermal treatment of the acid-made material under basic ammonia conditions effectively promotes reconstruction of the silica nanochannels while maintaining the rope-like morphology. As a result, a notable enhancement in both thermal and hydrothermal stability is found. 

A second type of solid ionic conductors based around polyether compounds such as polyethylene oxide) (PEO) has been discovered and characterized. The polyethers can complex and stabilize lithium ions in organic media. They also dissolve salts such as L1CIO4 to produce conducting solid solutions. The use of these materials in rechargeable lithium-batteries has been proposed. 

A current hypothesis, which is receiving considerable attention, is that one can indeed produce a surface which actively repels proteins and other macromolecules123 124, 133). The basic idea is presented in Fig. 25, which shows that a neutral hydrophilic polymer, which exhibits considerable mobility or dynamics in the aqueous phase, can actively repel macromolecules from the interface by steric exclusion and interface entropy methods. This method has been well-known and applied in the field of colloid stability for many years 120). The most effective polymer appears to be polyethylene oxide, probably because of its very high chain mobility and only modest hydrogen bonding tendencies 121 123>. 

Fig. 25a and b. A protein resistant surface based on the steric repulsion argument commonly used in the colloid stability field U0). The interaction between a polyethylene oxide grafted surface and a protein solution is shown, a. suggests an excluded volume or steric repulsion mechanism b. the surface dynamics or polymer chain motion mechanism (from Ref., 33))... 

Using this novel solution-based method, we have been able to incorporate [C6H5CH2NH3][H2P04], BADP (77), an SHG-active material, into polymeric hosts such as poly(acrylamide) (PAA) and polyethylene oxide) (PEO) to produce transparent, colourless, low scattering SHG-active composites with excellent temporal stability. 

Pharmaceutical research on polymeric micelles has mainly focused on two kinds of block copolymers, namely, AB block copolymers or diblock copolymers and ABA or BAB block copolymers known as triblock copolymers (Bader et al., 1984 Yokoyama et al., 1990,1991 Kwon and Okano, 1996, 1999 Kwon, 1998, 2003 Alakahov and Kabanov, 1998). The most common hydrophilic block (A) of the block copolymers is polyethylene oxide (PEO). This polymer is highly hydrated through hydrogen bonding and sterically stabilizes surfaces of the polymeric micelles in aqueous systems. 

Hou Z, Theyssen N, Brinkmann A et al (2005) Biphasic aerobic oxidation of alcohols catalyzed by polyethylene glycol)-stabilized palladium nanoparticles in supercritical carbon dioxide. Angew Chem Int Ed 44(9) 1346—1349... 

Wang X, Yang H, Feng B et al (2009) Functionalized polyethylene glycol)-stabilized palladium nanoparticles as an efficient catalyst for aerobic oxidation of alcohols in supercritical carbon dioxide/poly(ethylene glycol) biphasic solvent system. Catal Lett 132 34-40... 

The second repulsive energy (referred to as steric repulsion) is produced by the presence of adsorbed surfactant layers of nonionic surfactants, such as alcohol ethoxylates or A-B, A-B-A block, or BA graft copolymers, where B is the anchor chain and A is the stabilizing chain [mostly based on polyethylene oxide (PEO) for aqueous systems]. When two droplets or particles with adsorbed PEO chains of thickness 5 approach a separation distance h such that h < 28, repulsion occurs as a result of two main effects. The first arises as a result of the unfavorable mixing of the PEO chains, when these are in good solvent conditions. This is referred to as Gm x and is given by the following expression ... 

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