Structure of Conducting Polymers

Besides synthesis, current basic research on conducting polymers is concentrated on structural analysis. Structural parameters — e.g. regularity and homogeneity of chain structures, but also chain length — play an important role in our understanding of the properties of such materials. Research on electropolymerized polymers has concentrated on polypyrrole and polythiophene in particular and, more recently, on polyaniline as well, while of the chemically produced materials polyacetylene stih attracts greatest interest. Spectroscopic methods have proved particularly suitable for characterizing structural properties These comprise surface techniques such as XPS, AES or ATR, on the one hand, and the usual methods of structural analysis, such as NMR, ESR and X-ray diffraction techniques, on the other hand. 

PPy was the first conducting polymer to be structurally analyzed. The discovery that a,a -disubstituted pyrroles did not electropolymerize led to the conclusion that the pyrrole units in PPy are a-linked Magic angle spinning C-NMR 

In contrast to the classic conducting polymers such as PPy, PTh, PP or PA, structural analyses of other systems are few and far between and limited for the most part to quantum mechanical model calculations on the formation of an ideal polymer structu- 

Chain length is another factor closely related to the structural characterization of conducting polymers. The importance of this parameter lies in its considerable influence on the electric as well as the electrochemical properties of conducting polymers. However, the molecular weight techniques normally used in polymer chemistry cannot be employed on account of the extreme insolubility of the materials. A comparison between spectroscopic findings (XPS, UPS, EES) for PPy and model calculations has led some researchers to conclude that 10 is the minimum number of monomeric units in a PPy chain, with the maximum within one order of magnitude n9- 27,i28) mechanical qualities of the electropolymerized films, 

The knowledge that conducting polymers can be charged, i.e. oxidized and reduced, raised early on the question of possible applications, such as the construction of a polymer battery. But basic research was long unable to explain the charge storage mechanism. 

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All these data show that only small changes of the polymerization parameters may lead to characteristic differences in the resulting structures of conducting polymers. Structural properties - for example, regularity and homogeneity of chain structures, but also chain length play an important role in our understanding of the properties of such materials. Spectroscopic methods have proved particularly... 

What are the structures of conductive polymers, and what is the mechanism for electronic transport in the solid-state ... 

B. Solid-state electropolymerization Structure of Conducting Polymers... 

Tourillon and co-workers have also carried out extensive ex-situ studies on the structure of conducting polymers following the features around the carbon edge. ... 

Several attempts have been made to discover the structure of conducting polymers. There were few successes in describing either the structure of isolated polymer chains on graphite substrate [81] or the packing of short oligomers [82], both using STM. 

The pristine conjugated polymers have been reported to contain electronic spins, presumably originating from inter-chain cross-linking in polyacetylene [25,26], formation of polynuclear structures in polypara-phenylene [27] and so on. The inter- and intra-chain reactions between these reactive sites can alter the chemical structure of conductive polymers even when they are pure, affecting their dopability and hence the electroactivity. 

T. Asmus and G.K. Wolf, Modification and structuring of conducting polymer films on insulating substrates by ion beam treatment, Nucl. Instrum. Meth. Phys. Res. B, 166-167, 732-736 (2000). 

So far, various structures of conductive-polymer containers have been produced by chemical or electrochemical approaches, including porous films, hollow spheres, tube-Uke... 

HGURE 5.2 (A) Structures of conducting polymers. (B) Representative high performance donor materials in polymer solar cell. (C) Representative fused aromatic ring building blocks for high performarxe donor materials. 

Umeda, T., et al. 2005. Fabrication of interpenetrating semilayered structure of conducting polymer and fullerene by solvent corrosion method and its photovoltaic properties. Jpn Appl Phys 44 4155. 

Hutchinson, G.R., Y.J. Zhao, B. Delley, A.J. Freeman, M. Ratner, and T. Marks. 2003. Electronic structure of conducting polymers Limitations of oligomer extrapolation approximations and effects of heteroatoms. Phys Rev B 68 035204. 

The foregoing is illustrative of the complexity of the electropolymerization process. There is obviously no universal mechanism determining what the surface structure of conducting polymers will be. However, from a practical standpoint these studies are very important to tailoring of the polymer surface to suit the application, be it electronic or electrochemical, since the needs for each application are unique. 

Figure 4-1. Chemical structures of conducting polymers, (a) Frans-polyacetylene (b) cw-polyacetylene (c) poIy(/i-phenylene) (d) polypyrrole (e) polythiophene (f) poly(/>-phenylenevinylene) (g) poly(2,5-thienylenevinylene) (h) polyaniline (leucoemeraldine base form) (i) polyisothianaphthene.

Fig. 114. Aromatic and quinoid structures of conducting polymers obtained by the introduction of heteroatoms (nitrogen, sulfur) in the isothianaphthene ring stem.

Figure 20.23 (A) Schematic of a typical oCVD reactor. (B) Chemical structures of conductive polymer deposited by oCVD. PEDOT PPy, polypyrrole PTAA, poly(3-thiopheneacetic acid) [147], (With permission from Elsevier).

F. Passivating Metal Oxide Layers and Electronic Structures of Conductive Polymers... 

Fig. 6.3 Chemical structures of conducting polymers and a fullerene derivative mostly used in organic polymer cells i.e., P3HT, MDMO-PPV, and PCBM...

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