Poly oxidation rate

Hatano et aL U7) studied the poly(L-lysine)(PLL)- and poly(DL-lysine)-Cu(II) complexes as catalysts in the oxidation of 3,4-dihydroxyphenylalanine. The catalytic activity of PLL-Cu was found to be greater than that of ethylenediamine-Cu. The oxidation was asymmetrically catalyzed by PLL-Cu the D-isomer of the substrate coordinated to PLL-Cu more strongly and its oxidation rate was greater than that of the L-enantiomer. The asymmetrical oxidation was ascribed to the helical structure of PLL-Cu in an aqueous solution of pH 10.5118. ... 

The pronounced efficiency of EPDM (POLY) grafted with TPA on the photoageing of the parent polymer is reported on Figure 7. Similar experiment after vulcanisation (not shown) reduced the photo-oxidation rate by a factor 1.5 both for virgin and stabilized films. 

In oxidation reactions of ascorbic acid, homogentisic acid and hydroquinone by poly(l-histidine) — Cu(II) complex, the reaction profile shows a Michaelis-Menten type curve in the reaction condition of pH ranging from 5—6. These oxidation reaction rates are higher than the oxidation rates by the catalyst without poly(l-histidine). On the other hand, the rate of oxidation of a positively charged substrate, phenylenedi-... 

The materials analyzed were blends of polystyrene (PS) and poly(vinyl methyl ether) (PVME) in various ratios. The two components are miscible in all proportions at ambient temperature. The photooxidation mechanisms of the homo-polymers PS and PVME have been studied previously [4,7,8]. PVME has been shown to be much more sensitive to oxidation than PS and the rate of photooxidation of PVME was found to be approximately 10 times higher than that of PS. The photoproducts formed were identified by spectroscopy combined with chemical and physical treatments. The rate of oxidation of each component in the blend has been compared with the oxidation rate of the homopolymers studied separately. Because photooxidative aging induces modifications of the surface aspect of the material, the spectroscopic analysis of the photochemical behavior of the blend has been completed by an analysis of the surface of the samples by atomic force microscopy (AFM). A tentative correlation between the evolution of the roughness measured by AFM and the chemical changes occurring in the PVME-PS samples throughout irradiation is presented. 

Table 8. Michaelis constant (A ) and initial oxidation rate (Fd) in the oxidation of DOPA by poly(S-lysine) (PLL)-coppet(II) and poly(RS4ysine) (FDLL)-copper(ID complexes (29)...

Since poly(S-)ysine) — copper(II) complex at pH = 10.5 assumes aTielical conformation while it is random coiled at pH = 6.9, the selective catalysis towards the entantiomeric substrates is considered to be related to the a-helical conformation of the catalyst. This was confirmed also by the comparison of the oxidation rates of R-DOPA and S-DOPA at varkius temperatures in relation to the a-helical content of the catalyst as obtained by the circular diduroic analysis. From these and other (4>servations (SO), a schematic model of the intermediate of the oxidation reacticm has been proposed (Fig. 8) (SI). In this bifunctional coordination of DOPA, the... 

The utility of classical antioxidants such as hindered amines, phenols, and nitrones for the stabilization of pristine polyacetylene (29), poly(methyl acetylene) (30), and poly(l,6-heptadiyne) (31) has been examined. Poly(methyl acetylene), although dopable to only low conductivities (10" S/cm), has similar oxidative behavior to polyacetylene and serves as a good model for other polyenes. In general, the improvement in stability of poly(methyl acetylene) was limited, but combinations of hindered phenols and hydroperoxide scavengers resulted in a factor of 5 decrease in the oxidation rate (30) as monitored by the appearance of IR absorption bands attributable to carbonyl groups. These degradation rates are still too high for the use of these polyenes in an unprotected environment. The compatibility of such stabilizers with the dopants commonly used for polyacetylene was not studied. 

The oxidation rate in dry oxygen was found to be very similar to that of < 100 > silicon (see figure 9.8). This indicates that during oxidation silicon from the underlying poly-Si diffuses to the surface of the WSix where it becomes available for oxidation. It has been found [Saraswat et al.225] that for practical purposes the dry oxidation rate of CVD-WSix atop of poly-Si can be described by ... 

In Figure 1.69 an example of a conventional DT top-view is shown (oval shape) after collar oxide formation (black region) and DT fill with a highly doped poly-Si. The thermal oxide formed shows a strong dependence on the crystal orientation of the Si surface. This holds true for all oxidation modes, for example, dry and wet oxidation (in the wet -oxidation mode there is a carefully adjusted addition of FI2O as steam to the oxidation chamber resulting in an increased oxidation rate). This also holds true for... 

The interaction and subsequent oxidative behavior under UV light exposure of nanocomposite using poly(styrene) (PS) as polymer and LDH organomodified by a monomer surfactant as filler were recently investigated [115]. The photooxidation study revealed that the hybrid nanofiller did not modify the photooxidation mechanism of PS. The same products of oxidation were observed with the same proportions. A slightly higher oxidation rate was observed in the case of the sample with 5% of filler. The advantage of this system was its ability to be tailored in order to limit/ control eventual interactions with photostabilizers and antioxidants. 

Considerable potential is associated with the catalytic applications of Ag NPs, and there are several reports on the research in this field. The oxidation of ethylene, catalyzed by polyacrylic acid (PAA)-Ag nanoclusters, was performed in glycol under 1 atm of ethyleneioxygen. Products were identified as ethylene oxide by analysis with gas chromatography. Ag nanoclusters thus prepared had higher catalytic activity than a commercial silver catalyst. The oxidation rate catalyzed by the PAA-Ag nanoclusters remarkably inaeased with inaeasing reaction temperature. PAA-protected Ag nanoclusters had much higher activity than poly(A-vinyl-2-pyrrolidone)-protected particles at high temperatures. The addition of both caesium and rhenium ions eminently increased the catalytic activity of PAA-Ag nanoclusters (Shiraishi and Toshima 2000, Toshima et al. 2001). 

Polmer-snpported IBX Reagents. Two different phenoxide linked polymer-based IBX reagents have been developed. The silica supported reagent (Poly-IBX) is used in THE The oxidation rate increases relative to DMSO as solvent. The primary alcohol in the cyclohexanol may be oxidized preferentially, and thus avoid formation of the cyclohexanone expected from the secondary alcohol (eq 8). This selectively is retained even with a threefold... 

Blending methyl methacrylate-butadiene-styrene copolymer with poly(vinyl chloride) for instance was shown to decelerate the dehydrochlorination (leading to discoloration). The gel content, surface energy, and the spectroscopic characteristics of the blend was altered by the presence of the seccHid polymer [158]. In ethylene-propylene-diene rubber EPDM where the third monomer is ethylene-2-norbomene (NB), the photo-oxidation rate as measured by the accumulation of typical products such as hydroperoxides, varied linearly with the NB content [159]. The same held true for peroxide-crosslinked compounds of the same EPDM except that the linear relationship was found between the relative carbonyl absorbance on photoxidation and the amoiuit of peroxide used to crosslink the material... 

Membranes and Osmosis. Membranes based on PEI can be used for the dehydration of organic solvents such as 2-propanol, methyl ethyl ketone, and toluene (451), and for concentrating seawater (452—454). On exposure to ultrasound waves, aqueous PEI salt solutions and brominated poly(2,6-dimethylphenylene oxide) form stable emulsions from which it is possible to cast membranes in which submicrometer capsules of the salt solution ate embedded (455). The rate of release of the salt solution can be altered by surface—active substances. In membranes, PEI can act as a proton source in the generation of a photocurrent (456). The formation of a PEI coating on ion-exchange membranes modifies the transport properties and results in permanent selectivity of the membrane (457). The electrochemical testing of salts (458) is another possible appHcation of PEI. 

Concentration and Molecular Weight Effects. The viscosity of aqueous solutions of poly(ethylene oxide) depends on the concentration of the polymer solute, the molecular weight, the solution temperature, concentration of dissolved inorganic salts, and the shear rate. Viscosity increases with concentration and this dependence becomes more pronounced with increasing molecular weight. This combined effect is shown in Figure 3, in which solution viscosity is presented as a function of concentration for various molecular weight polymers. 

Effect of Shear. Concentrated aqueous solutions of poly(ethylene oxide) are pseudoplastic. The degree of pseudoplasticity increases as the molecular weight increases. Therefore, the viscosity of a given aqueous solution is a function of the shear rate used for the measurement. This relationship between viscosity and shear rate for solutions of various molecular weight poly(ethylene oxide) resins is presented in Figure 8. 

Further improvements in reaction rates and polymerization control have led to the commercial availabihty of poly(ethylene oxide) of varying molecular weights. 

Pyrotechnic mixtures may also contain additional components that are added to modify the bum rate, enhance the pyrotechnic effect, or serve as a binder to maintain the homogeneity of the blended mixture and provide mechanical strength when the composition is pressed or consoHdated into a tube or other container. These additional components may also function as oxidizers or fuels in the composition, and it can be anticipated that the heat output, bum rate, and ignition sensitivity may all be affected by the addition of another component to a pyrotechnic composition. An example of an additional component is the use of a catalyst, such as iron oxide, to enhance the decomposition rate of ammonium perchlorate. Diatomaceous earth or coarse sawdust may be used to slow up the bum rate of a composition, or magnesium carbonate (an acid neutralizer) may be added to help stabilize mixtures that contain an acid-sensitive component such as potassium chlorate. Binders include such materials as dextrin (partially hydrolyzed starch), various gums, and assorted polymers such as poly(vinyl alcohol), epoxies, and polyesters. Polybutadiene mbber binders are widely used as fuels and binders in the soHd propellant industry. The production of colored flames is enhanced by the presence of chlorine atoms in the pyrotechnic flame, so chlorine donors such as poly(vinyl chloride) or chlorinated mbber are often added to color-producing compositions, where they also serve as fuels. 

Poly(ethyl methacrylate) (PEMA) yields truly compatible blends with poly(vinyl acetate) up to 20% PEMA concentration (133). Synergistic improvement in material properties was observed. Poly(ethylene oxide) forms compatible homogeneous blends with poly(vinyl acetate) (134). The T of the blends and the crystaUizabiUty of the PEO depend on the composition. The miscibility window of poly(vinyl acetate) and its copolymers with alkyl acrylates can be broadened through the incorporation of acryUc acid as a third component (135). A description of compatible and incompatible blends of poly(vinyl acetate) and other copolymers has been compiled (136). Blends of poly(vinyl acetate) copolymers with urethanes can provide improved heat resistance to the product providing reduced creep rates in adhesives used for vinyl laminating (137). 

Unlike other water-soluble resins the poly(ethylene oxide)s may be injection moulded, extruded and calendered without difficulty. The viscosity is highly dependent on shear rate and to a lesser extent on temperature. Processing temperatures in the range 90-130°C may be used for polymers with an intrinsic viscosity of about 2.5. (The intrinsic viscosity is used as a measure of molecular weight.)... 

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