Precursor Routes to Poly p-Phenylene

PolyQj-Phenylene) is probably the most thermally and oxidatively stable conducting polymer known and has been of interest to polymer scientists both for its conducting properties and for its stability. Its synthesis by step-reaction polymerization or by chemical or electrochemical oxidation invariably gives powders or rather poor quality films, so that a precursor route would be very attractive. 

Marvel et al. 2471 attempted synthesis of poly(p-phenylene) from poly(l,3-cyclo-hexadiene), produced by Ziegler initiation  

Aromatization of the polycyclohexadiene by dehydrogenation with a range of reagents, including palladium, chloranil and N-bromosuccinimde, was only partially successful, partly because both the precursor and the product polymer are insoluble. Attempts to improve the aromatization by reaction of the polycyclohexadiene with Br2, followed by thermal elimination of HBr were also not very successful248 249) and there is the additional complication that the HBr produced may react with the polyene. 

Ballard et al. 250) have described synthesis of poly(p-phenylene) via the polymerization of esters of 5,6-m-dihydroxycyclohexadiene. The polymer, produced by free-radical initiation, is soluble in common solvents and smoothly eliminates in the temperature range 140 to 240 °C to give the aromatic polymer. 

Conventional synthetic chemistry needs a multi-step synthesis to give the cyclo-hexadiene diol in the tram-form, which is difficult to polymerize 251). A most ingenious feature of the work of Ballard et al. was the use of a bacterial fermentation route to prepare the diol in the m-form. A detailed account of the preparation, properties and transformation of the polymer has recently been published 252). In practice, the favoured esters are those of methylcarbonic acid, since the eliminated acid decomposes at transformation temperatures to yield methanol and C02. The main 

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V.P. Conticello, D.L. Gin, and R.H. Grubbs, Ring-opening metathesis polymerization of substituted bicyclo[2.2.2]octadienes a new precursor route to poly(p-phenylene vinylene), J. Am. Chem. Soc., 114 9708-9710, 1992. 

B. R. Hsieh, H. Antoniadis, D. C. Bland, and W. A. Feld. Chlorine precursor route to poly(p-phenylene vinylene)-based light emitting diodes, Adv. Mater. 7 36 (1995). 

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