Self-doped polymers sulfonate

The related fully sulfonated, self-doped polymer poly(2-methoxyaniline-5-sulfonic acid) (PMAS 9) may be prepared under normal atmospheric pressure by the oxidation of 2-methoxyaniline-5-sulfonic acid (MAS) monomer with aqueous (NH4)2S208 in the presence of ammonia or pyridine (to permit dissolution of the MAS monomer).141 The polymerization pH was therefore >3.5. Subsequent studies showed that the product consisted of two fractions a major fraction with Mw of ca. 10,000 Da whose electrical conductivity and spectroscopic and redox switching properties were consistent with a PAn emeraldine salt, as well as a nonconducting, electroinactive oligomer (Mw ca. 2,000 Da).143 144 Pure samples of each of these materials can be obtained using cross-flow dialysis.145... 

The self-doped polymer, poly A-(4-sulfophenyl)aniline 10, bearing a sulfonated substituent on each of its N centers, has also been prepared by oxidizing the relevant monomer with (NH4)2S208 in aqueous HC1.146 147 Phosphonic acid substituents can also be utilized to generate self-doping PAn s, as illustrated by the oxidation using... 

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. 

In self-doped polyaniline, sulfonic groups induce changes in the geometry of the polyaniline backbone [152], affecting the physicochemical properties of the polymer. Comparative electronic absorption... 

While there are reports of making homopolymers of self-doped polymers (e.g., 2-methoxyaniline-5-sulfonic acid), many derivatized monomers do not polymerize alone to yield their respective homopolymers. For example, if the substituents are bulky (e.g., l-(2-amino)-pronane-3-sulfonic acid or l-(2-amino)-butane-3-sulfonic acid), the homopolymerization is not possible. In these cases, bulky substituent containing monomers need to be copolymerized... 

The majority of the sulfonated self-doped polymers are synthesized as copolymers since the presence of the electron-withdrawing sulfonic acid groups in the substituted monomers make it less suitable for oxidative polymerization. 

In self-doped polymers, the charge-compensating anion is covalently bound to the polymeric backbone, so that oxidative doping involves the expulsion of cationic species rather than anion insertion. Poly(3-thiophene-) -ethanesulfonate) and poly(3-thiophene-<5-butanesulfo-nate) (23) [171] were first prepared with the sulfonate group, which makes these polymers water-soluble. The polymers have been prepared by electropolymerization of the corresponding methyl esters, followed by hydrolysis to the polyelectrolytic form [171]. Films cast from water solution exhibited a rather short conjugation (maximum absorption at 425 nm, 3.6 eV) and conductivities of 1—10 S cm after doping [172]. 

Self-doped polymers are poly(thiophene)s bearing sufonic acid on the end of an alkyl substituent. These polymers are doped by their own sulfonic acid without any external dopants and are very stable in the doped state. Due to attached sulfonic acid, they are soluble in water. Anion-doping of the polymers is controlled by the motion of cations, thus quick responses are observed in anion-doping and undoping. The polymers are useful for dissipating charge on photoresists and other applications. 

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. 

Several water-soluble sulfonated polythiophenes such as 20 (x = 3 or 6) have been prepared by the FeClj oxidation of the corresponding monomers. " iR and NMR studies of these self-doped polymers in DjO/DMSO-dg or D20/acetonitrile-d3 showed a HT HH ratio of 4 1 in both cases. ... 

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). 

The range of soluble polythiophenes has been growing rapidly to include side chains up to docosane 267), ether and amide links in the side chains 268), and water-soluble polymers with sulfonated side chains (Table 1) which are claimed to be self-doping in that the sulphonate may act as the counterion to the delocalized chain cation 269,270). In principle, these polymers can be p-doped and undoped by the transport of a proton or a small cation rather than a large anion, and so may respond more rapidly. By treatment of an aqueous solution with NOPF6, a doped solution can be made, which slowly degrades. 

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.

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