Doped polyphenylene

Doped polyphenylene sulfide Doped polythiophene Doped polyacetylene (Metallic) Conductors... 

Fig. 16a-c. Proposed crystal structures for a metal-ion doped polyacetylenes and fa metal-ion doped polyphenylene. Reproduced with permission from Ref. 4651... 

Yamaguchi I, Mizoguchi N, Sato M (2009) Self-doped polyphenylenes containing electron-accepting viologen side group. Macromolecules 42 4416-4425... 

Finally, just a few words dedicated to the synthesis of polyphenylenes, extremely important polymers, and in particular substituted polyphenylenes such as PPV, which exhibit superb thermal and chemical resihence, semiconduchng properties upon doping and applicahons such as OLEDs. Contrary to their linear acenes counterparts, long polyphenylenes can be obtained e.g., by Bergman s method consisting in the thermal cycloaromatization of enediynes (Lockhart et al, 1981). 

The deficiency of this model is the assumption of only light doping. However the soliton conductivity has also been established in highly doped material and not only for polyacetylene, but for polyphenylene too, in which the solitons cannot exist... 

Fig. 26. Photoconductivity spectra of polyphenylene sulfide initial (/), doped with tetra-cyanohinodimethene (2) and tetranitrilpiromel-lit add (3) [202]...

Kaeriyama et al.163) obtained insulating films of polyphenylene by electrochemical polymerization in nitromethane solution containing AlClj. Again, the films could be doped only to rather low conductivities and there was evidence of considerable structural irregularity. The first reports of a highly conducting film appear to be... 

Kovacic polyphenylene is brown with about 1 spin/chain detectable by ESR. Yamamoto polymer is yellow with a shorter chain length and fewer spins. In Kovacic polymer the spins and colour may both be due to polynuclear species. Polyphenylene produced from the poly(dihydrocatechol) precursor 249) is also yellow, but has a high molecular weight, of the order of 10s. It contains about 15% o-linkages, and the aromatization procedure may leave a high level of twists in the chain originating from the flexible precursor. This material dopes only to low levels of conductivity with sodium naphthalide (6x 10 3 Scm-1) and iron chloride (1.5 x 10-2 Scm-1) but reaches a level comparable to Kovacic and Yamamoto polyphenylenes with AsFs (102 S cm-1). 

Brown et al. 3S2) have recently emphasised the role of defect structures in heterocyclic polymers. They point out that the reported doped conductivities of these polymers may vary by as much as six orders of magnitude depending on the preparation procedure. They have applied the laser desorption method, discussed earlier for polyphenylene, to a range of polyheterocycles. Unlike polyphenylene, there was evidence for incomplete desorption and rearrangement of evaporated molecules. The results show that polymers prepared by Grignard coupling vary in their extent of bromination, the nature of the terminal species and the extent of formation of cyclic, polynuclear contaminants. 

Polyphenylene formed from simultaneously doped and polymerized crystals of terphenyl has the form of a macroscopic slab. The final conductivity with AsF5 doping is 60 S cm-1 along the chains and 40 S cm-1 perpendicular to the chains, less of a difference than would be expected on a simple chain conduction model61). 

Thin films of polyphenylene prepared under conditions of high shear are formed with the chains in the film plane481 , this is possibly the result of aggregation of particles which are elongated in the chain direction. These films were red with an absorption maximum at 500 nm which shifted to 380 nm on doping with SbF5 or on exposure to moisture. The authors suggest that the as-prepared polymer is doped with tetrachloroantimonate counterions. Fibres of polyphenylene have been prepared by extrusion of the powder at elevated temperature 482). A modest level of orientation was obtained (half-width of (110) peak of 37°). 

In general, doping tends to lead to a loss of x-ray order in polyacetylene and polyphenylene, suggesting that dopant ions may be distributed more or less at random. The structural models shown in Fig. 16 are clearly idealised as only limited order is seen even in cation-doped polymer. The anion dopants are much larger and apparently disrupt the structure too much for any sign of regularity to be seen, except in the case of iodine. 

The ionization potential of polyphenylene is around 8 eV and it is not surprising that oxidative degradation is not a problem the undoped polymer can withstand long periods at high temperatures in air with no change in its conductivity or its ability to dope 386). However, the high oxidation potential creates two problems. Firstly, the range of dopants with sufficient electron affinity to oxidize the polymer is limited, and there are few solvents in which the oxidation can take place without destruction of the solvent. Secondly, the doped polymer is expected to be reactive towards water and this is indeed the case 386). 

The origin of the conduction mechanism has been a source of controversy ever since conducting polymers were first discovered. At first, doping was assumed to simply remove electrons from the top of the valence band (oxidation) or add electrons to the bottom of the conduction band (reduction). This model associates charge carriers with free spins (unpaired electrons). However, the measured conductivity in doped polyacetylene (and other conducting polymers such as polyphenylene and polypyrrole) is r greater than what can be accounted for on the basis of free spin alone. 

Very few CPs are produced in bulk quantities. Polyphenylene sulfide, a member of the third generation of polymers, was produced in bulk quantities many years before CPs were established and its dopability was elucidated. Polyethylenedioxythiophene is commercially available as a water-based colloidal dispersion (Baytron P water dispersion), and presumably as dispersible powders. The powders with a conductivity of 5-10 S/cm can be dispersed in thermoplastic polymers and in organic solvents such as xylene. Polyaniline doped with dodecylbenzene sulfonic acid and complexed with zinc dodecylbenzene sulfonate is commercially available as a powder, which can be dispersed in polyolefins. The same polymer doped with p-toluenesulfonic acid is also available as a dispersible powder, Ormecon, and in a predispersed form for solution processing in polar and nonpolar media. Based on Ormecon PANi, there are many commercial products marketed for many different applications. 

Conductive polymers have been a goal of fundamental polymer research for many years, mainly because such materials would be lightweight and presumably moldable into any shape desired. Ten years ago, almost every polymer known displayed insulator properties, and research efforts to modify their character met with failure. Since that time, however, success has been reported in the literature, and a few conductive polymers do exist now, each with its merits and drawbacks. Various degrees of conductivity can be achieved principally by synthesizing an unsaturated, conjugated polymer and doping it in some fashion. Example polymers are polyphenylene,... 

It has been first demonstrated in 1977 by MacDiarmid et that films of polyacetylene can be chemically doped to semiconducting and metallic states. Shortly thereafter the possibility of electrochemical doping, resulting in highly conducting materials, had been shown not only for polyacetylene but also for a number of other polyenes, polyphenylenes and polychalcogenides. ... 

The electrochemical properties of conductive polymer systems are important with regard to understanding the electrochemical doping process and in applications of conductive polymers as battery electrodes. We have developed a computational method, based on the Valence Effective Hamiltonian technique, which is remarkably effective in the computation of oxidation and reduction potentials of a variety of conjugated polymers (polyacetylene, polyphenylene, polythiophene, polypyrrole) and their oligomers. 

To prepare new and inexpensive membranes, various trials have been made 196 sulfonated aromatic polyether membrane such as polyether ketones (PEEK),197 sulfonated polysulfone198 and membranes from sulfonated polyphenylene sulfide,199 phosphoric acid-doped polybenzimidazole, (PBI),200 polybenzimidazole having sulfonic acid groups,201 polybenzimidazole with phosphonic acid groups,202 a blend membrane of polybenzimidazole and sulfonated polysulfone,203 sulfonated phosphazene polymer.204... 

Polyphenylene sulfides doped with AsFs, I2, or SO3 could also provide electrically conductive materials [11 Id]. 

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