Oxygen with poly

Charge-transfer complexes of oxygen with poly(olefins) have been proposed as initiators of photodegradation (138), and it is of particular interest to note that recently oxygen-induced exci-mer fluorescence emission has been observed in poly(styrene) doped with aromatic compounds (139). 

The similarity of the contact potential hypothesis and the theory of boundary layer chemisorption on semiconductors cannot easily be dismissed. The concepts also apply to organic materials and the interaction of oxygen with poly-N-vinylcarbazole, for example, has been well established. 

Unlike most crystalline polymers, PVDF exhibits thermodynamic compatibiUty with other polymers (133). Blends of PVDF and poly(methyl methacrylate) (PMMA) are compatible over a wide range of blend composition (134,135). SoHd-state nmr studies showed that isotactic PMMA is more miscible with PVDF than atactic and syndiotactic PMMA (136). MiscibiUty of PVDF and poly(alkyl acrylates) depends on a specific interaction between PVDF and oxygen within the acrylate and the effect of this interaction is diminished as the hydrocarbon content of the ester is increased (137). Strong dipolar interactions are important to achieve miscibility with poly(vinyhdene fluoride) (138). PVDF blends are the object of many papers and patents specific blends of PVDF and acryflc copolymers have seen large commercial use. 

Figure 6. Partly assembled, 5-gallon, low density polyethylene liner in a corrugated carton. Liner is coated with poly(vinylidene chloride) (Saran) to block oxygen entry and prevent loss of aroma used for cola concentrate.

The epoxidation of enones with poly-D-leucine is complementary to other strategies. Enders et u/.[8] introduced a new method for the asymmetric epoxidation of a-enones using diethylzinc, oxygen and (1R, lR)-or (IS1, 2S)-N-methylpseudoephedrine as chiral auxiliary. 

A three-armed star polymer consisting of silane substituted with poly(vinyl chloride), poly(ethylene oxide) and polystyrene chains, the last of which is linked to the central unit through an oxygen atom. 

Photoionization at 193 nm in oxygenated solution of poly(C) causes strand breakage with high efficiency, half of which occurs at times < 4 ms, the other half with a half-life of 7 ms (Melvin et al. 1996 Table 11.8). This kinetic behavior is very different from what is seen after -OH-attack and points to the direct involvement of the Cyt radical cation. In poly(U), the (biphotonic) photoionization shows similar results (Table 11.8). With poly(A), the formation of strand breaks is 20-times less efficient as compared to poly(C) (Table 11.8), and this is in agreement with the above conclusion that the A-+ or A- do not cause strand breakage to any major extent. 

Michaels HB, Hunt JW (1977a) Radiolysis of the double-stranded polynucleotides poly(A+U) and DNA in the presence of oxygen. Radiat Res 72 32-47 Michaels HB, Hunt JW (1977b) Reaction of oxygen with radiation-induced free radicals on single-stranded polynucleotides. Radiat Res 72 18-31... 

A calibration curve for glucose at a UMB with poly( 1,3-DAB) is shown in Figure 3. The calibration curve is piece-linear. The linearity over the normal human clinical range for glucose (3-7 mM) is good (r=0.998), and the sensitivity is 9.2 pA/mM. The calibration curve levels off at about 15-20 mM glucose, due to oxygen limitation. 

Figure 3. Calibration curve for glucose at an ultramicrobiosensor with poly(l,3-DAB) film, showing oxygen limitation of glucose response above 20 mM glucose (E= +0.58 V vs Ag/AgCl).

Chigwada et al.36 have combined polyhedral oligosilsesquioxanes (POSS), which are cage-like hybrid molecules of silicon and oxygen, with TCP (tricresylphosphate) in poly(vinyl ester) resins (PVE). POSS molecule contains nonreactive organic functionalities allowing solubility and compatibility of the POSS with various polymers. POSS was incorporated alone (3-10 wt %) in PVE, and four compositions were made with TCP at 4wt % POSS + 4wt % TCP and 5wt % POSS + 5, 10, 15 wt % TCP. Fligh reductions in PHRR and THR were noticed. Nevertheless, the POSS/ TCP combination did not exhibit better performances than compositions with only 5 or 10 wt % of TCP alone. 

Figure 11-10 Solvation of the oxygen atoms of poly(vinyl alcohol), (a) Partial radial distribution functions of PVA oxygen with solvent oxygen and (b) solvent carbon atoms. The figure is taken from Miiller-Plathe and van Gunsteren [79]...

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