Oxidized Poly model compounds

Figure 5. Oxygen uptake of poly(phenylene oxide) and model compounds. Pyrex-filtered Hg lamp, 1-M benzene solution.

The linear polyethers are model compounds to show the effect of the insertion of one oxygen atom at different positions into the polyethylene -CH2-CH -repetitive unit. What will be the influence on the polymer XPS valence band spectrum, compared to the one of polyethylene (Figure 2) Our study was conducted on three materials poly(methylene oxide) or PMO, poly(ethylene oxide) or PEO, and poly(tetramethylene oxide) or PTMO, that are... 

The C-ls spectra of poly(ethylene terephthalate), poly(ethylene oxide), and anthraquinone are shown in Figure 7. All spectra were internally charge-referenced to an alkyl-like C-Is line at 284.0 eV. As shown in the figure, the oxygen-containing functional groups in these model compounds result in pronounced chemical shifts in the C-ls spectra. 

The rates and products of poly(vinyl alcohol) (PVA) photooxidation were measured over a temperature range of 30°-90°C. Oxidation was initiated with 253.7-nm light, and several model compounds were included. The PVA photooxidation rate was autocatalytic and relatively insensitive to temperature with the major products being carbon dioxide, acids, peroxides, polymeric p-hydroxyketone, and hydrogen peroxide. Acids were mostly formic acid and carboxylic acids at the polymer chain ends. Several molecules of carbon dioxide and acid were formed per statistical chain scission. The mechanism of the photooxidation of PVA is discussed. 

Poly(vinyl halides) (PVC etc.) and PoIy(vinyl alcohol) (PVA).—A series of papers has appeared concerned with the photo-dehydrochlorination, discoloration, and sensitized photolysis of model compounds of PVC,819 and its copolymers.220 The photolysis of poly(vinyl bromide)221 and a trifluorochloroethylene-vinylidene fluoride copolymer228 has been described. The photo-oxidative destruction of PVA has been reported in a series of papers.223... 

A recent study on similar lines using thermally oxidized poly(butadiene), in which the emitting chromophore is an oR-un-saturated carbonyl compound and model enones in poly(methylmethacrylate) and low-temperature glasses has shown that in addition to transitions expected on the basis of O2 diffusion rates, discontinuities in the Arrhenius plots due to intramolecular properties of the probes themselves through mechanisms 2 and particularly 3, above, appear (39,91). Thus in poly(methylmethacrylate) with the probes shown... 

Figure 9-5. Structures of complexes of a AgBF4 2-dimethoxy ethane complex, b AgBF4 , 2-dimethoxy ethane-ethylene adduct where 1,2-dimethoxy ethane is a model compound of poly(ethylene oxide) [15]. The silver ion is coordinated by two oxygen atoms from 1,2-dimethoxy ethane and two F atoms from the anion to make silver-polymer complexes, when AgBF4 is complexed with 1,2-dimethoxy ethane. One of the two F atoms bound to the silver ion is replaced by an ethylene molecule, when one ethylene molecule approaches the complex in an ethylene environment.

It was suspected that the low energy emission band results from keto defects that were introduced either during synthesis or by photo-oxidation during service. Experiments with poly(9,9-dioctylfluorene-co-fluo-renone) with 1% fluorenone as a model compound demonstrated that flu-orenone defects are generated by photo-oxidation and by thermal-oxidation. " Moreover, the formation of these defects is catalyzed by the metals with a low work function that are used as cathode materials in light-emitting diodes. 

Botelho and co-workers [25] made a comparative study of the thermo-oxidative degradation of poly(ethylene naphthalate) (PEN) and poly(butylene naphthalate) (PBN) The mechanism of the degradation of model compounds for these two polymers was similar in many ways to that noted for the terephthalate equivalents [13]. 

Techniques for chloromethylating polyarylether sulfones, polyphenylene oxide, phenolic resins, and model compounds were described recently [191]. When the subsequent products are cmiverted to quaternary amines, there is a decrease in the quatemization rate with increase in degree of substitutimi. This may be due to steric effects imposed by restricted rotation of the polymeric chains [191]. This phenomenon was not observed in quatemization of poly(chloromethyl styrene). The chloromethylation reaction of a polysulfone with chloromethyl ether, catalyzed by stannic chloride, can be illustrated as follows ... 

Polyanilines. Polyaniline was made nearly 140 years ago in 1862 by H. Letheby (183). At that time, polyaniline was known as aniline black. This material was prepared by the oxidation of aniline under mild conditions. The material found use in dyes and printing. Initial preparations of polyaniline (PANI) led to insoluble materials that had poor thermal processability and solvent solubility. Only recently has the structure of PANI been fully determined. This was accomplished by using model compounds and polymers for definitive structural analysis. Poly(p-phenylene amineimine) (PPAI) was synthesized directly to demonstrate that PANI is purely para-linked (184-186). 

Thermal and thermo-oxidative degradation have been studied as a function of chemical structure in poly(phenylquinoxaline) and poly(naphthylimido phenyl-quinoxaline). The introduction of the naphthalene units is claimed to decrease thermal stability, but to increase thermo-oxidative stability. The thermal degradation of polyhexazocyclanes and suitable model compounds has been... 

The stability, particularly the susceptibility to autooxidation, is the Achilles heel of the new materials as well as of organic polymers in general. The problem of oxidative damage has therefore been the object of intensive research. Poly(acetylene) (CH) . manufactured with Ziegler-Natta, Luttinger or other catalysts were used as model compounds. 

Model compounds for poly(acetylene) and oxidized poly(acetylene) are discussed with regard to the explanation of the spectral features observed in the conducting polymer. 

The predominant effect of flavonoid and isoflavonoid supplementation in ex vivo cell culture models appears to be one of promoting apoptosis [54—57]. This is repeatedly observed in studies witti transformed cancer cells, leading to the descriptions cytoprotective and/or chemopreventive [6,58]. Two poly-phenolic compounds that have been extensively studied in anticancer research are quercetin and genistein, a flavonoid and isoflavone, respectively. However, ex vivo studies with primary cultured cells in 2000 and 2001 showed that some flavonoids can prevent apoptosis promoted by agents that induce oxidative stress [7,8,59]. The outcome of flavonoid treatment is expected to show a complex dependence on a number of factors, including the type of flavonoid, its concentration, the type of cell (e.g., transformed versus nontransformed), the mechanisms of action of the flavonoid, the nature of the proapoptotic stimulus, and the specific apoptotic signaling pathway that is activated. 

The strueture of poly(ethylene-co-carbon oxide) (1.4 wt% CO) was studied by 50.3 MHz carbon-13 NMR spectroscopy [296]. With model compounds, assigments of new structures and previously undetected products of photodegradation and photo-oxidation in the solid state were made. Four per cent of the CO groups were aecounted for as ethyl ketones with the remainder being randomly distributed along the polymer backbone ehain. Evidence was presented for the formation of cis, trans-cyclobutanols. A novel a-branched ketonic structure was also found. The reactivity of ketonic groups is affected by polymer matrix morphology. 

---