Self-doped conducting polymers solubility

The concept of self-doped conducting polymers was proposed some years ago with the synthesis of poly(3-thiophene-j8-ethanesulfonate) and poly(3-thiophene 5-butanesulfonate) (61) [278]. In these systems the charge-compensating anion is covalently bound to the polymeric backbone consequently, instead of anion incorporation, charge compensation upon doping involves the expulsion of cationic species. Furthermore, due to the presence of the sulfonate group, these polymers are the first examples of water-soluble PHCs. The polymers described in Ref. 278 were... 

Other 3-substituted thiophenes that have been polymerized include 3-methoxy [309-311], other 3-alkoxy [312], 3-phenyl [313,314], 3-(4-methoxyphenyl) [314], 3-(4-trifluoromethylphenyl) [314], 3-bromo [315], 3-alkylsulfonatethiophene [316-318], and others [319-323]. Poly-3-alkylsulfonate thiophenes are particularly interesting due to a striking property. Sodium poly-3-thiophene-j8-ethanesulfonate and sodium poly-3-thiophene-6-butanesulfonate and their conjugate acids are water soluble in both the doped and undoped states [317,318]. Ikenoue et al. [318] examined the conduction mechanism for this self-doped conducting polymer. 

Jung JW, Lee JU, Jo WH (2009) High-efficiency polymer solar cells with water-soluble and self-doped conducting polyaniline graft copolymer as hole transport layer. J Phys Chem C 114 633... 

Yin, W., and E. Ruckenstein. 2001. A water-soluble self-doped conducting polypyrrole-based copolymer. J Appl Polym Sci 79 86. 

Mainly sulphonate species have been chosen as internal dopant ions, because of their low reactivity in electrochemical redox processes. In this way, ionic transport in the conductive polypyrrole can be modulated by a high density of anionic sites, thus requiring the cation to be the mobile species. On the other hand, self-doped polymers can be electrochemically prepared without adding a salt to allow conduction [149]. Some of those self-doped materials are soluble in common solvents. 

Sulfonation of emeraldine base produces ring-substituted polyaniline. The ring-substituted polyaniline is self-doped and offers solubility in basic aqueous solutions [17,18]. The key feature of this self-doped polymer is its ability to maintain its conductivity up to pH 7, while the unsubstituted polyaniline is converted to an insulator at pH greater than about 4. 

Polyaniline (PANI) can be formed by electrochemical oxidation of aniline in aqueous acid, or by polymerization of aniline using an aqueous solution of ammonium thiosulfate and hydrochloric acid. This polymer is finding increasing use as a "transparent electrode" in semiconducting devices. To improve processibiHty, a large number of substituted polyanilines have been prepared. The sulfonated form of PANI is water soluble, and can be prepared by treatment of PANI with fuming sulfuric acid (31). A variety of other soluble substituted AJ-alkylsulfonic acid self-doped derivatives have been synthesized that possess moderate conductivity and allow facile preparation of spincoated thin films (32). 

Water-soluble derivatives of polythiophene have been made allowing counterions bound to the polymer backbone to self-dope with the protons (e.g., lithium and sodium ions) injecting electrons into the pi-system. Thus, combinations of sodium salts and proton salts (e.g., prepared from poly-3-(2-ethanesulfonate)thiophene) have been prepared that are both water-soluble and conducting. 

The mechanism for the SPAN layer changing the emission properties of the PPy VPV polymer is attributed to the formation of new emissive species due to protonation of the pyridyl units by SPAN. These species was identified by both absorption and PL experiments. Figure 9.15 shows the absorbance spectra of a PPy VPV layer, a SPAN layer, and a bilayer of PPy VPV/SPAN. SPAN is a self-doped, water-soluble conducting polymer with a room-temperature conductivity of 10-2 S/cm.18 It has a wide optical window from green to near infrared PPy VPV... 

Fig. 3.10. Some of the more commonly encountered organic conductor materials (a) polypyrrole, (b) polyaniline, and (c) poly(3,4-ethylenedioxythiophene) (PEDOT). When combined with water soluble organic acids (e.g. sulfonic acids like benzosul-fonic acid) many of these polymers can form doped complexes which are highly conductive and can be dispersed into suspension. Substituted versions of these polymers which are self-doped have also been developed.

The conducting and physical properties can be modified by the use of 3- and/or 4-substitutents, or A -substituents in the case of pyrrole. The counterions can be incorporated into a side-chain (self-doping) as in the polymer of 3-(thien-3-yl)propanesulfonic acid. Variation in the size of side-chains allows control of solubility. Mixed polymers with, for example, thiophenes and pyridines, are capable of both oxidative and reductive doping. 

Soluble conducting polymers can be solvent cast to form coatings. The addition of appropriate substituents to the polymer backbone or to the dopant ion can impart the necessary solubility to the polymer. For example, alkyl or alkoxy groups appended to the polymer backbone yield polypyrroles [117,118], polythiophenes [118], polyanilines [119,120], and poly(p-phenylenevinylenes) [97] that are soluble in common organic solvents. Alternatively, the attachment of ionizable functionalities (such as alkyl sulfonates or carboxylates) to the polymer backbone can impart water solubility to the polymer, and this approach has been used to form water-soluble polypyrroles [121], polythiophenes [122], and polyanilines [123]. These latter polymers are often referred to as self-doped polymers as the anionic dopant is covalently attached to the polymer backbone [9]. For use as a corrosion control coating, these water-soluble polymers must be cross-linked [124] or otherwise rendered insoluble. 

A distinctive property of self-doped polymers is their water solubility in the neutral (insulating) and doped (conducting) states. This solubility is due to the covalently attached negatively charged groups on the polymer backbone. Solubility allows a deposition of conductive and electroactive layers onto any, even a nonconducting, surface by a simple casting of self-doped polymers. Such layers could find numerous applications... 

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