Alkyl EDOTs

With the first reports on EDOT s special polymerization behavior yielding conductive polymers, several simple derivatives also were published simultaneously. Short-chain alkyl substitution at the dioxane ring does not change the EDOT and PEDOT properties very much. As is possible with EDOT-CH2OH, EDOT-CH3 can be polymerized oxidatively with PSS as the counterion in water. Conductivity is decreased, compared to 

PEDOTrPSS. Medium- or long-chain alkyl EDOTs fail due to their very low water solubility. 

The synthesis of alkyl EDOTs and several special problems especially with longer alkyl chain educts have been described in Chapter 5. To give an overview here, too, a summary covering the most important methods is depicted in Eigure 12.19. 

Alkyl ether synthesis by Willamson ether synthesis is not very sufficient for longer chain alkylbromides like tetradecylbromide, due to strongly competing elimination reactions. For example, yields of the Williamson ether synthesis are reported to be as low as 24% (R = Ci4H29).i Here the transetherification has to be preferred. See also the corresponding references in Chapter 5. 

The conductivity of PEDOT-alkyl in the form of the in situ polymerizates is dependent on the alkyl group length, but the experimental results reported do not give a very clear picture. A good overview could be obtained by the special in situ measurement method described in detail by Aubert et al. Table 12.1 shows the data compiled in by Groenendaal et al.  

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Several alkyl-EDOT derivatives (synthesis via Williamson ether s)mthe-sis, transetherificahon,28 or Mitsunobu reaction, see Chapter 5) have been... 

Here the particular properties or sometimes advantages of alkyl-EDOTs shall be summarized, mainly following the systematic study published by Re5molds et al. ° The aryl-EDOT "EDOT-phenyl," see Figure 12.20, was included in this study. 

K. Zhang, B. Tieke, J. C. Forgie, and P. J. Skabara. 2009. Electrochemical polymerisation of N-arylated and N-alkylated EDOT-substituted pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) derivatives Influence of substitution pattern on optical and electronic properties. Macromol Rapid Commun 30(21) 1834-1840. 

Alkylation of Thiophene Poly(3,4-Ethylenedioxythiophene) and Sulfur Derivatives Reduced Bandgap Polymers Based on Chalcogen 3,4-Substituted Thiophenes Structural Modifications of EDOT Functionalized EDOT Derivatives... 

The EDOT system can be modified either by the substitution of ethylenedioxy bridge or by its replacement by another type of bridge. Both approaches involve a modification of the initial synthesis of EDOT [105]. Thus, alkylation of 3,4-dihydroxy-2,5-dicarboethoxythiophene [106] with 1-alkyl-1,2-dibromoethane or 2-alkyl-1,3-dibromobutane led to corresponding alkyl-EDOTand ProDOT derivatives [107]. 

EDOT monomers bearing w-iodo-alkyl and w-iodo-polyether side chains (80) have been electro-polymerized into corresponding polymers. These polymers can be rapidly and quantitatively converted into functionalized polymers under mild conditions by postpolymerization reaction with functional blocks bearing a thiolate group, as demonstrated in the case of tetrathiafulvalene (81) [ 151 ]. Application of the same procedure led to a modified electrode containing a tetrathiafulvalene core substituted by two polyether chains (82). It was shown that the binding of Pb by the polymer 82 could be electrochemicaUy driven [185]. 

Turbiez, M., P. Frere, and J. Roncali. 2003. Stable and soluble oligo-(3,4-ethylenedioxythiophene)s (EDOT) end-capped with alkyl chains. J Org Chem 68 5357-5360. 

Several reports related to PEDOT-coated particles and PEDOT hollow particles have been pronounced in the literature [359,360]. Dispersion polymerization has been applied for PEDOT-coated PS particles fabrication. 100 nm PS nanoparticle was used as the core material [359]. hi order to improve the stability of the PS particle, DBSA was used as the surfactant. It was presumed that hydrophobic alkyl chains of the surfactant were positioned towards the surface of PS particles and the sulfonic acid group toward the water phase. EDOT monomer was adsorbed on the surface of the PS nanosphere and polymerization was initiated by the addition of the APS oxidant. PS-PEDOT core-shell structure was distinctively visualized by TEM. The doped PEDOT shell had a higher electron density than the PS core and the thickness of the PEDOT shell was ca. 8 nm. 

Co-oligomers of EDOT and thienopyrazine 3.24 were synthesized by Berlin et al. (Chart 1.47) [337, 338]. Similarly to other thienopyrazine-based polymers, electrochemically generated polymers of 3.24 exhibited ambipolar electroactivity. P3.24a had an in situ conductivity of 0.5 Scm in the oxidized state and 0.01 S cm in the reduced state and corresponding values for alkylated derivative P3.24b were 15 and 0.03 Scm Both polymers had broad absorption bands peaking at 950 nm, suggesting small bandgaps [337]. 

Introduction of a hydroxymethyl group at the ethylene bridge of EDOT represents an alternative and practical approach for the functionalization of EDOT [79], After the introduction of functional groups was performed by Williamson alkylation or esterification reaction starting from 16 (Scheme 9.15), anodic oxidation led to the corresponding polymers. 

Many attempts have been made to synthesize doped, conductive PEDOT derivatives that are soluble in organic solvents. Some examples are EDOT materials that incorporate long- or medium-chain alkyl [82, 83], ether [84, 85] or urethane [86] groups. Unfortunately, many of these organosoluble examples refer to either neutral, undoped PEDOT or to materials that are far less conductive than aqueous-based PEDOT PSS and are therefore not generally useful for making highly conductive PEDOT films. 

The low oxidation (p-doping) potential of poly(oxythiophene)s along with high conductivity, transparency and stability of doped state make them ideal as a transparent conductor and as a hole-transport layer in various optoelectronic devices. On the other hand, alkyl-substituted EDOT and ProDOT derivatives are suitable for electrochromic applications. However, PEDOT remains one of the most extensively studied polymers in this class due to the easy commercial access of EDOT monomer and processable PEDOT polymers (Clevios-P). 

Another potential of nonfnnctionalized LLCs phases is related to the catalysis of polymerization reactions. For instance, hexagonal LLCs from poly(oxyethylene)-alkyl amphiphiles in water have been used to solubilize and to polymerize 3,4-ethyldioxythiophene (EDOT) within their 3 nm hydrophobic cores (Fignre 28). ... 

Several alternative routes have been suggested, which in some cases are especially useful to prepare alkyl derivatives of EDOT with substitution at the dioxane ring. The most important of these alternative pathways appears to be the acid catalyzed transetherification of 3,4-dimethoxythiophen (or other lower alkoxythiophenes) with vicinal diols. - ° The Williamson ether synthesis can lead to low yields particularly in the case of long chain 1,2-dibromoalkanes due to the competing elimination reactions instead of nucleophilic substitution, resulting in a-olefins or a-acetylenes. Although... 

Besides iron-III salts, special peroxides are the most important group of oxidants, which are able to polymerize EDOT and subsequently dope PEDOT to yield highly conductive PEDOT cations (bipolarons). There are a lot of peroxidic compounds—decomposed thermally or by the catalytic action of metal cations— which, by the reaction of intermediate free oxyradicals, produce typically blue dispersions of PEDOT in water. Most of them are not sufficient to achieve optimal high conductivity. Hydrogen peroxide, alkyl hydroperoxides like tBu-OOH, and diacyl peroxides like dibenzoyl peroxide have all been described as EDOT oxidants, without becoming technically importanD i EDOT is oxidized by m-chloroperbenzoic acid to a mixture of the corresponding sulfone and 3,4-ethylenedioxy-2(5H)-thiophenone in... 

Kudoh et al. have polymerized EDOT in the presence of sodium alkyl-naphthalenesulfonate with different alkyl chain lengths and an average... 

In Situ Polymerized EDOT Alkyl Eterivatives (Corresponds with Figure 8.10)... 

Similar circumstances are obvious are for R = Alkyl-NH-CO in the urethanes derived from EDOT-CH2OH (see formula A in Figure 8.11). A trend to lower conductivities with longer alkyl chains is observed. In contrast to the two examples for EDOT-CH20H-ethers in Figure 8.9, the conductivity of highly branched or cyclic urethane polymers is lower than that for open-chain derivatives with die same C number. 

Comparing the different groups of substituted EDOTs or even very similar compounds of the same group, another effect has to be kept in mind. For every compound there is an optimum temperature for in situ polymerization. This means that the best conductivity is achieved for EDOT and simple derivatives at room temperature or slightly elevated temperature, for example, at 40°C. EDOTs with longer alkyl chains tend to be less reactive and so need higher temperatures up to 80°C to achieve lowest surface resistances. 

Substitution of the EDOT moiety with a medium chain alkyl residue (-CH2-O-C10H21, stemming from EDOT-CH20H/etherification with n-decyl... 

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