Processing of ICPs

The unique feature of ICPs is their electrical and mechanical properties. Due to the presence of the conjugated backbone, they tend to be insoluble and infusible, and this results in poor processabihty. To overcome this problem, extensive research has been carried out into the synthesis of ICPs that are easily processable. The different approaches that have been considered to improve processabihty of ICPs may be summarized as chain, particle, or core-sheU models (Fig. 6.10). 

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A characteristic feature of the parent polypyrroles, polythiophenes and polyanilines is their insolubility in water and common organic solvents (although the EB form of polyaniline is soluble in NMP, DMSO and several other solvents). This intractability and consequent difficulties in processing have until recently limited their exploitation. However, the introduction of substituents onto the aromatic rings of the polymers, the use of surfactant-like dopant anions and the generation of colloidal dispersions have markedly enhanced the processability of ICPs (see Section 8 below). 

With the help of similarities and differences between processing of conventional polymers and carbon-blackfilled compounds on one side and processing of ICP on the other side, the need for an integrated chemical, physical, and processing view on ICP is shown. In conclusion, the value of processing ICPs via dispersion into materials of well defined structure and morphology for basic research as well as its emerging industrial use, is pointed out. 

Right up to the present day, the processing of ICPs is regarded by most scientists as no more than a (perhaps not even) necessary evil that real researchers do not need to concern themselves with, because it is felt to be far too simple a problem affording little prospect of prestige. The preceding sub-section 3.3.1 and the subsections 3.6 and 3,7 are intended to show that this attitude is hampering basic research. This is all the more true in relation to commercial applications. 

At present it does not look as if the co-polymer approach will be able to make a useful contribution to the processing of ICPs or materials research. For several years now no significantly new and promising proposals have been published in this area. 

It should be noted that, besides high inherent EM properties of ICPs, their processability is of immense importance for techno-commercial applicability. Interestingly, it has been foimd that the processability of ICPs can be improved by copolymerization approach to obtain tradeoffbetween solubility, electrical properties and EM response [25]. 

Therefore, processing of ICP and OM can only be performed using dispersions, whereby the matrix or medium in which the ICP would have to be dispersed, can be a polymer (thermoplastic or thermoset), prepolymer, water, or organic solvent, and the technology has been improved in the last years with the effect that practically all kinds of dispersions in all kinds of media are accessible [2j. 

As far as processing of ICPs is concerned, various methods have been developed to prepare electrically conductive composites [139], among which melt processing is quite popular for thermoplastics [140, 141]. Martins and De Paoli [142] prepared polystyrene and polyaniline blends in a double-screw extruder, giving a conductive thermoplastic with electrical conductivity of 10 to 10 S cm . In most cases, conducting polymers are incompatible with thermoplastic, so a fimctional dopant is needed to improve compatibility. For example, dodecylbenzenosulfonic acid... 

Figure 6.10 Different strategies for improving the processability of ICPs. 6.4.1...

A general treatment of the redox processes of ICPs with special attention to PPP based on considerations of various conceivable processes and species involved therein was provided by Vorotynt-sev and Heinze [1110]. 

Last but not least, in spite of the triumphal procession of ICP-MS in modern anal5dical chemistry, an additional reference method which is based preferably on a different physical principle of signal generation is imperatively desirable to confirm or to disprove precarious results. From this point of view alone, HR-CS AAS, when its intrinsic potential is fully exploited, will, in the opinion of the authors, play an important role in future laboratory equipment. 

FIGURE 11.7 Flowsheet of formaldehyde production by the gas-phase oxidation of methane in the presence of nitrogen oxides (process of ICP RAS) [174]. (1) Air blower, (2) furnace, (3) receiver, (4) separator, (5,5 ) compressors, (6) contact apparatus for ammonia oxidation, (7) tubular heater, (8) reactor, (9) pipe cooler, (10) absorber, (11, 15) pumps, (12) receptacle for formalin, (13) scrubber, and (14) cooUng coil. 

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