Quinone polymers

Fig. 3.8. (a) A Structure of the hydroquinone-containing poly(siloxane). B Structure of the hydroquinone-containing poly(acrylonitrile-ethylene). The m n ratio is approximately 1 2 for both systems. Reprinted with permission from [10]. (b) Structure of the polyCether amine quinone) polymers. Reprinted with permission from [15], 1994 American Chemicad Society. 

Pullman and Pullman were the first to perform a calculation of the band structure for an idealized indole-5,6-quinone polymer, and their results enabled the prediction of an exceptional electron-accepting ability arising from extension of the lowest empty band in the bonding energy region... 

Quinone Cleavage and Resistance to Peroxide Treatment Hydrogen peroxide readily oxidizes o- and p-quinones via ring cleavage, forming colorless, open-chain carboxylic acids [21]. This is the predominant reaction, however, colored products may also be formed, particularly at high alkali concentrations. There is firm evidence for the formation of hydroxy-substituted quinones. In addition, the formation of quinone polymers has also been proposed. The hydroxy-quinones are probably formed... 

S Hosoya, K Seike, and 1 Nakano. Bleaching of high yield pulp Reactions of quino-nes and quinone polymers with some reducing agents. Mokuzai Gakkaishi 22 314-319, 1976. 

Figure S Typical response of the pofyetheramine quinone polymers / glucose oxidase / carbon paste electrodes to addition of glucose at = +200mV vs. SCE. Indicated under the response trace are the amounts (in ml) of O.IM ucose injected into die test solution (initial volume 10 ml).

Figure 6(a) Typical electrochemical Eadie-Hofstee plot for the polyetheramine quinone polymer (a) / ucose oxidase / carbon paste electrode at E = +200mV (vs. Ag/AgCl). 

Molecular weights of 1000-7000 have been reported (77) for some similar polymers from 1,4-dihydroxyanthraquinone. The zinc-1,4-dihydroxyanthra-quinone polymer was found to possess molecular weights of 1460-2220, determined by a sophisticated ultracentrifugation study 88). Differences in the preparative procedure that were used were slight, but could conceivably explain the variations. Insolubility of these products is the major reason that the molecular weight question cannot be answered by more conventional polymer techniques. 

Elastomers cured with two crosslinking systems such as sulphur and the polymerisation products of p-benzoquinone are shown to have much improved overall mechanical properties. Non-Gaussian behaviour of quinone polymer crosslinked elastomers viewed as bimodal networks was studied. The study focused on the effect of ageing time on the reduced stress values of the networks in relation to the elongation of the samples. The study is also extended to cover the possible effect of these bound antioxidants on the onset of the vulcanisation process and the hardness values of the elastomeric networks. 15 refs. 

Place 25 g. of methyl methacrylate polymer (G.B. Diakon (powder). Perspex (sheet) U.S.A. Lucite, Plexiglass) in a 100 ml. Claisen flask, attach an efficient condenser e.g., of the double smface type) and distil with a small luminous flame move the flame to and fro around the sides of the flask. At about 300° the polymer softens and undergoes rapid depolymerisation to the monomer, methyl methacrylate, which distils over into the receiver. Continue the distillation until only a small black residue (3-4 g.) remains. Redistil the hquid it passes over at 100-110°, mainly at 100-102°. The yield of methyl methacrylate (monomer) is 20 g. If the monomer is to be kept for any period, add 0 -1 g. of hydro quinone to act as a stabiUser or inhibitor of polymerisation. 

Oxidation of LLDPE starts at temperatures above 150°C. This reaction produces hydroxyl and carboxyl groups in polymer molecules as well as low molecular weight compounds such as water, aldehydes, ketones, and alcohols. Oxidation reactions can occur during LLDPE pelletization and processing to protect molten resins from oxygen attack during these operations, antioxidants (radical inhibitors) must be used. These antioxidants (qv) are added to LLDPE resins in concentrations of 0.1—0.5 wt %, and maybe naphthyl amines or phenylenediamines, substituted phenols, quinones, and alkyl phosphites (4), although inhibitors based on hindered phenols are preferred. 

Uses. About 35% of the isophthahc acid is used to prepare unsaturated polyester resins. These are condensation products of isophthahc acid, an unsaturated dibasic acid, most likely maleic anhydride, and a glycol such as propylene glycol. The polymer is dissolved in an inhibited vinyl monomer, usually styrene with a quinone inhibitor. When this viscous hquid is treated with a catalyst, heat or free-radical initiation causes cross-linking and sohdification. A range of properties is possible depending on the reactants used and their ratios (97). 

The free radicals initially formed are neutralized by the quinone stabilizers, temporarily delaying the cross-linking reaction between the styrene and the fumarate sites in the polyester polymer. This temporary induction period between catalysis and the change to a semisoHd gelatinous mass is referred to as gelation time and can be controUed precisely between 1—60 min by varying stabilizer and catalyst levels. 

An example of the Michael chemistry, typical of all quinones bearing a replaceable hydrogen, is the preparation of a sulfone (6) (in 55% yield), which was ultimately converted to a polystyrene redox polymer (11). 

Oxidizing agents, e.g., quinones, which were shown to be able to retard oxidation [13] can function as antioxidants (via a chain breaking acceptor process, CB—A) if they can compete with oxygen for the alkyl radicals (Scheme 4). In the case of polymers, reaction 4a can... 

An important problem encountered with polymer electrodes is that of overoxidation. It occurs after reversible charging of the electrode at high oxidation potentials and leads to polymer degeneration. The results of thorough studies show that such degenerative mechanisms are promoted by the nucleophilicity of the solvent. Especially the activity of water leads to the formation of quinone-type compounds, to the cleavage of C—C bonds, the liberation of CO2, and the formation of carboxylic acids Hence, there is a clear tendency to avoid both nucleophile solvents... 

Quinone diimines are capable of reacting rapidly with radicals formed during intensive mixing. The product, a polymer-bound PPD moiety, provides a polar functionality which is capable of improving polymer-filler interactions. In general the improvements can result in modest reductions in tangent delta (rolling resistance) and modest improvements in abrasion resistance. 

Humic acid and the corresponding fulvic acid are complex polymers whose structures are incompletely resolved. It is accepted that the structure of humic acid contains oxygenated structures, including quinones that can function as electron acceptors, while reduced humic acid may carry out reductions. These have been observed both in the presence of bacteria that provide the electron mediator and in the absence of bacteria in abiotic reactions, for example, reductive dehalogenation of hexachloroethane and tetrachloromethane by anthrahydroquininone-2,6-disulfonate (Curtis and Reinhard 1994). Reductions using sulfide as electron donor have been noted in Chapter 1. Some experimental aspects are worth noting ... 

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