Conducting polymers poly-paraphenylene

An interesting copolymer of poly-p-phenylene and PA has also been produced as a conducting polymer. Poly(paraphenylene vinylene) (PPV) was made by a relatively new technique in which a soluble precursor polymer was prepared and processed prior to its conversion to the conjugated polymer [46]. Such a route allows variations to be made in the polymer morphology and hence the electrical conductivity. Before the development of this method, it was initially prepared as low-molecular-weight oligomeric powders [47] because of limitations in its solubility. 

All conducting polymers (and most of their derivatives), for example, poly(paraphenylene), poly(phenylene vinylene), polypyrrole, polythiophene (PT), polyfuran, poly(heteroaromatic vinylenes), and polyaniline (Fig. 29.1), undergo p- and/or n-redox doping. 

At the present time polyaniline is without doubt the most important conducting polymer from the point of view of large scale technological use however, derivatives of polythiophene and poly(phenylenevinylene) and indeed, polypyrrole, polyacetylene and poly-paraphenylene show considerable technological promise as specialty polymers, as described later. In view of the technological importance of polyaniline, its synthesis and properties will be emphasized in this review. 

To get a moderately high density of carriers per unit volume is relatively easy. For example in poly acetylene, a doping level of 10% per carbon can be achieved, corresponding to a carrier concentration of about 4x10 cm-. This is a typical number for conducting polymers such as polyacetylene, poly(paraphenylenevinylene), poly(paraphenylene), etc. The addition of side chains, as in the poly (3-alky Ithiophenes), reduces the maximum carrier density somewhat, simply because of the smaller fractional volume occupied by the conjugated backbones. For the emeraldine salt of polyaniline, there is one carrier per (B-NH-B-NH)+ repeat unit again n SxlO l. 

For well-known conducting polymers such as poly(p-phenylene), polythiophene, and poly(paraphenylene vinylene) (PPV), the influence of substituents has already been investigated on the experimental and theoretical levels [1097]. In the case of polyisothianaphthene, however, there is a lack of experimenttil data describing the influence of electron-donating and electron-withdrawing substituents. Therefore, only some earlier theoretical investigations will be discussed. 

Refs. [i] Gruber J Li RWC, Hummelgen IA (2001) Synthesis, properties and applications ofpoly(paraphenylene vinylene). In Nalwa HS (ed) Handbook of advanced electronic and photonic materials and devices. Academic Press, San Diego [ii] Kvarnstrom C, Ivaska A (1997) Characterization and applications of poly (p-phenylene) and poly(p-phenylene vinylene). In Nalwa HS (ed) Handbook of organic conductive molecules and polymers. Wiley, Chichester... 

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