Polyarylenes

Another important factor affecting the electronic properties is the steric barrier to planarity along the polymer chain. Since polyheterocycles and polyarylenes must adopt a planar geometry in the ionized state to form quinoid-like segments, steric factors that limit the ability of the polymer to adopt geometries which are planar with respect to adjacent rings have a detrimental effect on the electronic properties (181). 

L V. Krivoshei and V. M. Skorobogatov, Polyacetylene and Polyarylenes. Synthesis and Conductive Properties, Polymer Monographs Vol. 10, Gordon and Breach, Philadelphia, 1991. 

Poly(para-phenylene)s PPPs and other polyarylenes represent structure-classes of conjugated polyhydrocarbons which are currently under intensive investigation [7]. This, in turn, is the result of important advances that have been made in the chemistry of aromatic compounds in recent years. 

The strategy of Kaeriyama represents a so-called precursor route, and was developed in order to overcome the shortcomings (insolubility, lack of process-ability) of previous PPP syntheses. Accordingly, the condensation is performed with solubilized monomers, and a soluble polymeric intermediate is formed. This intermediate is then converted to PPP (or another polyarylene) in a final reaction step, preferentially carried out in the solid state, allowing the formation of homogeneous PPP films or layers. 

Based on the results of the synthesis of oligo- and poly(para-phenylene)s PPPs (see Sects. 2.1-2.3) several investigators have studied the generation of other oligo- and polyarylenes. 

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