Formation of electrically conducting polymers

These questions are not just of academic interest as aryl azides have important application as photoresists in lithography, in the formation of electrically conducting polymers, organic synthesis, photoaffinity labeling, and in the covalent modification of polymer surfaces. 

KF Webb, J KowaUk, L Tolbert, AS Teja. The formation of electrically conducting polymer blends in supercritical carbon dioxide (to be published). 

In this chapter, we discussed possible methods for the formation of electrically conducting biocomposites using proteinaceous sohd biomasses arising from leather industries as wastes. The proteinaceous collagen wastes were blended with natural polymers (chitosan or GG) and different fillers such as GrC and nanotubes (ie, BCNTs and FWCNTs) to form hybrid-conducting biocomposite films. The formed biocomposife films were found fo exhibit promising mechanical, thermal, and electrical properties. The thermal properties of both of the hybrid composite materials increase moderately with the increase in the addition of nanocarbons. The mechanical... 

Fig. 1.11 Illustration of the process to fabricate morphologically controlled nanostructures of electrically conducting polymers on surfaces by using surfactant templates. This particular schematic draw represents the proposed scheme of wire formation on (a) chemically treated HOPG and (b) HOPG (Reprinted with permission from Carswell et al. [139]. Copyright 2009 American Chemical...

Processing with an environmentally benign supercritical fluid, such as carbon dioxide, is an attractive alternative to conventional processing of electrically conducting polymer blends. The advantages of supercritical carbon dioxide as a solvent for polymerization and blend formation have been outlined by many investigators (30,31). Carbon dioxide is inexpensive, nonflammable, offers high mass transport rates, and allows in situ removal of unreacted monomer and other impurities. It is also known to swell host polymers (32), which facilitates blend formation. 

Fig. 23-2 Procedure for the formation and transfer of electrically conductive polymer patterns onto insulating substrates. Step A application and development of patterned photoresist on the gold over mica substrate. Step B electrodeposition of electrically conductive polymer onto the exposed gold surface. Step C application of the adhesion promoter. Step D application of the insulator onto the adhesion promoting layer. Step E removal of the mica by immersion in dilute hydrofluoric acid solution. Step F etch removal of the gold layer by immersion in aqueous KI/I2 solution. Step G dissolution of residual photoresist in acetone. After Reference [955], reproduced with permission.

Another example of solid-state polymerisation is polymerisation of diacetylene derivatives which results in the formation of highly crystalline polymer that also conducts electricity. 

The electropolymerisation of the electrically conducting polymers thiophene (mentioned briefly aready in Chapter 5) and polypyrolle are thought to be produced by a scheme to that given in Fig. 6.22. (The scheme shows polypyrrole formation. Polythiophene is similar in that NH is replaced by S.)... 

Electrical conduction will occur by the hopping of either electrons or holes within these distributions of energy levels. Charge transport can be either of holes by transfer between the LUMO states or of electrons between the HOMO states. These correspond to the formation of either a radical cation by the removal of an electron to an adjacent electrode or an anion by the injection of an electron. The nature of the majority carriers will, therefore, be determined by the ionisation potentials and electron affinities of the conjugated moieties. A low ionisation potential will favour hole transport while a high electron affinity will favour electron transport. Most of the conductive polymers reported in the literature have low ionisation potentials and are hole, conductors. ... 

Electrically conducting polymers are quite different systems to the above elec-troinitiated chain polymerizations since they are formed by an unusual step-growth mechanism involving stoichiometric transfer of electrons. The polymers are obtained directly in a conductive polycationic form in which charge-compensating counter anions from the electrolyte system are intercalated into the polymer matrix [173], Exact mechanistic details remain the subject of discussion, but Scheme 4, which shows polypyrrole formation is plausible. Polythiophene is similar where S replaces NH in the ring. 

The technology of plasma formation of metal-containing polymers in the form of thin films dates from 1963, when Bradley and Hammes(15) prepared specimens from some forty different materials, and studied their electrical conductivities. Included in the study were organic compounds of iron, tin, titanium, mercury, selenium, and arsenic. The presence of a metal or transition element in the polymer did not lead to special electrical properties compared to the purely organic polymers studied. 

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