Poly self-doped polymers

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... 

As the degradation of polyaniline occurs via an imine intermediate [281,284], Kim et al. [285] prepared self-doped polymer by alkylsulphonate substitution in the polymer backbone, Besides self-doping for a facile redox process, the perceived advantage of this bulky substituent includes the protection of nitrogen centres from nucleophiles responsible for irreversible degradation of polyaniline. Poly(aniline N-butylsulphonate) retained its reversible electrochromic response up to 150 000 cycles when scanned between its oxidized and reduced states (between 0.2 and 0.5 V) then started diminishing slowly. The excellent redox cyclability of poly(aniline N-butylsulphonate) over unsubstituted polyaniline was also confirmed by chronoabsorptom-etry by Kim et al. [285],... 

In an attempt to produce carbazole polymers soluble in aqueous solutions, oligoether groups have been attached to the carbazole unit at the iV-position (28d) and the polymer prepared by chemical polymerization and electrochemical polymerization [105]. Due to the oligoether substituents, electrochemical polymerization can occur in aqueous solutions without the need for a cosolvent. Polymer films switch between a highly transmissive state to deep green upon oxidation. The self-doped polymer, poly[3,6-carbaz-9-yl)propanesulfonate] (28e), has also been produced, which is water-soluble and switches from a transmissive neutral state to a dark green oxidized state [106]. 

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. 

Y. J. Qiu, J. R. Reynolds, Poly 3,6-(carbaz-9-yl)propanesulfonate —a self-doped polymer with both cation and anion-exchange properties, Journal of the Electrochemical Society 1990, 137, 900. 

Figure 2.39 Synthesis route of monomer, o-aminobenzylphosphonic acid (4) and self-doped polymer, poly(o-aminobenzylphosphonic acid) (5) (Reprinted with permission from Journal of the American Chemical Society, 117, 8517. Copyright (1995) American Chemical Society.)...

In this presentation we describe our work on self doped polymers (SDP) which were a natural evolution from the PAT discovery and more recent work on poly(arylenevinylenes), a series of polymers obtainable in very high molecular weight and high yield through a water soluble precursor polymer. 

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. 

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. 

It has been established that when polyelectrolytes are incorporated as dopants in PAn, the switch from conducting to nonconducting material is shifted to very-high-pH solutions, enabling electrochemistry to be carried out on PAn in neutral solutions.37 Poly(methoxyanilines) have been used as the basis of electromechanical actuating changes in dimensions in the thickness direction of more than 20% were reported as the polymers are doped and dedoped.38-39 Similar effects are observed if some level of self-doping is introduced into the PAn backbone.40... 

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