Benzoquinone-hydroquinone polymers

The acceleration of grafting caused by hydroquinone increases the number of grafted chains but makes them shorter. The reaction rate and the yield of the graft polymer increase, however, since the former effect dominates the latter (Table 6). The chain shortening is due to the higher stationary concentration of OH radicals involved in chain termination and to the fact that hydroquinone and its oxidation products (semiquinone and benzoquinone) may also cause decomposition macroradicals. 

Cationic polymerisation (via initiation with sulfuric add or boron trifluoride) or anionic polymerization (in the presence of sodium ethoxide) were used for synthesis of polymers from 1,4-benzoquinone [124]. The number average molecular weight of products varied from 10 to 47 thousand, depending on the catalyst and its concentration. The polymerization product 101 contains hydroquinone and benzoqui-none moieties and has remarkable AO activity in stabilization of SBR at 100 °C. 

Phenolic ion exchangers derived from a phanol-formaIdehyde condensation reaction appeared in the first generation of ion-exchenge polymers. More recently, styrene-divinylbenzene copolymers incorporating azo-subslituied cresul and salicylic acid, catechol, hydroquinone. and benzoquinone bave been described, The quinone-type polymers selectively sorb Hg(lil) and the catechol reains sorb CtfVl). 

When dimethyl viologen dication is entrapped in DPPC vesicles and irradiated in the presence of external K4[Fe(CN)g], the viologen is reduced to the radical monocation and iron is oxidized. Light-induced membrane potential is thus built up (Calvin, 1978). Electrons can be stored and released in viologen-benzoquinone polymers on electrode surfaces. At first the quinone is reduced to the hydroquinone at low pH. Two electrons are entrapped per hydroquinone monomer. Upon raising the pH to 6-9, the viologen becomes reduced by the hydroquinone anions and delivers the electrons to the electrode (Smith et al., 1989)... 

Stabilization of the polymeric and monomeric components is required to avoid premature radical polymer formation of UP resin dissolved in styrene by heat, light, or metallic initiators. Insufficient stabilization causes an increase in viscosity that makes further processing impossible. Quinones and phenols in concentrations < 500 ppm are proven stabilizers for unsaturated polyester. The most important examples are hydroquinone, p-benzoquinone, tert-butyl-brenzcatechol and 2,6-di-tert-butyl-p-cresol [574]. For styrene, stabilization with 25 ppm p-tert-butyl-brenz-catechol is required [575]. Slight yellowing caused by the stabilizers is possible appropriate brighteners are recommended for optically demanding applications. 

Yamamoto T, Kimura T, Shiraishi K (1999) Preparation of pi-conjugated polymers composed of hydroquinone, p-benzoquinone, and p-diacetoxyphenylene units. Optical and redox properties of the polymers. Macromolecules 32 8886-8896... 

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