Polythiophene 3-methyl

Figure 5. Cyclic voltammograms of (a) 2,5"" -di-methyl-a-hexathiophene and (b) poly(2,2 -bithio-phene) films in acetonitrile containing 0.1 M E NCIO 103 (Reprinted from G. Zotti, G. Schia-von, A. Berlin, and G. Pagani, Electrochemistry of end-ca )ed oligothienyls-new insights into the polymerization mechanism and the charge storage, conduction and capacitive properties of polythiophene, Synth. Met. 61 (1-2) 81-87, 1993, with kind permission from Elsevier Science S.A.)...

Polythiophene films can be electrochemically cycled from the neutral to the conducting state with coulombic efficiencies in excess of 95% [443], with little evidence of decomposition of the material up to + 1.4 V vs. SCE in acetonitrile [37, 54, 56, 396,400] (the 3-methyl derivative being particularly stable [396]), but unlike polypyrrole, polythiophene can be both p- and n-doped, although the n-doped material has a lower maximum conductivity [444], Cyclic voltammetry shows two sets of peaks corresponding to the p- and n-doping reactions, with E° values at approximately + 1.1 V and — 1.4 V respectively (vs. an Ag+/Ag reference electrode)... 

Thus, many polymers with different conductivity were synthesized. To cite a few, these are polythiophene [158], 3-methylthiophene [159], polymers of 3-thiophene-acetic acid and methyl 3-thiophene-acetate [160], poly(2,5-thienylenevinylene) [161], poly(benzo[h]-thiophene) [162], poly(naphto[2,3-c]thio-phene) [163], poly(dithieno[3,2-h 2, 3 -fii]-thiophene) [164], poly(3- -hexylthiophene)... 

Polythiophene lends itself to the same routes to composites. A poly(3-methyl-thiophene)-poly(methylmethacrylate) composite has been made by electrochemical polymerization from a solution of thiophene and PMMA in methylene chloride and nitrobenzene. At high current densities the electrode side quickly became highly conducting while the outer side was less so 307). Similar composites have been prepared by chemical routes, using a Grignard reaction, firstly to couple the thiophene units in a step-reaction, then to initiate the polymerization of the methyl methacrylate 315). 

Against this background of infusible conducting polymers, the development of the soluble polythiophenes is most interesting. Glass transition temperatures have been reported as 48 °C for poly(3-butylthiophene) and 145 °C for poly(3-methyl-thiophene) 261). These polymers also show crystallinity in films and can be crystallized from solution. Solution studies indicate that there are two chain conformations 262) and the availability of a non-conjugated conformation may be a key to the low transition temperatures and solubility, when compared to the stiff-chain conjugated polymers. 

Burgmayer P and Murray R W 1984 Ion Gate Electrodes. Polypyrrole as a switchable ion conductor membrane J. Phys. Chem. 88 2515-21 Otero T F and de Larreta E 1988 Conductivity and capacity of polythiophene films impedance study J. Electroanal. Chem. 244 311-18 Sunde S, Hagen G and Odegird R 1993 Impedance analysis of the electrochemical doping of poly(3-methyl-thiophene) from aqueous nitrate solutions J. Electroanal. Chem. 345 59-82 Zaborsky O R 1973 Immobilized Enzymes (Cleveland, OH Chemical Rubber Company) (see especially pp 69,87)... 

The question about a helical configuration has often been raised, botli by theoi7 and experiment. The theoretical predictions for the most stable form of hithiopheiie is evidently dependent upon the set of basis functions used in the calculation, Wliereas Bredas et a . [9], and Cui and Kertesz [10] find that the planar form is stable, Samdal et a . [5] and Belletete et ai [11] find that twisted forms are most stable. For Unepolymeis Cui and Kertesz conclude that the planar fonn for unsubstituted polythiophene is slightly more stable than a twisted, helical form, and that the helical form is the most stable for the methyl-substituted polymer. 

Substituted-polythiophenes showed a remarkable effect on degradation and stability in electrochemical systems where poly(3-methylthiophene) was observed to be the most stable and poly(3,4-bis(ethylmercapto) thiophene) to be the least stable in the experiments conducted by Tsai et al. [272] on poly(3-ethyl-mercapto-thiophene), poly(3-hexylthiopliene), poly(3-methyl-thiophene) and poly(3,4-bis(ethylmercapto)thiophene). 

Keywords Water pollution, water purification, methylene blue, methyl orange, rhodamine B, heavy metal ions, Cr(VI), Hg(II), Pb(II), Cd(ll), Zn(II), Cu(II), adsorption, adsorbent, adsorbate, conducting polymers, polyaniline, polypyrrole, polythiophene, graphene, graphene oxide, carbon nanotubes (CNTs),... 

The molecular weights of substituted polymers are typically low compared with parent polymers due to the bulky nature of the ring substituents, which can hinder polymerization however, solubility in common organic solvent is increased. Dao et al. [193] have studied the effect of alkyl substituents on the molecular weight of polyaniline. The molecular weight of chemically prepared poly(2-methyl aniline) and poly(2-ethyl aniline) was reportedly 7000 and 5000g/mol, respectively, which is 15-times lower than polyaniline (80 000) prepared under identical conditions. A similar effect of alkyl substituents was observed on molecular weights of polythiophenes [207, 208]. 

Poly (thiophene)s are of particular interest as electfochromic materials owing to their chemical stability, ease of synthesis and processability. For the most part, current research has been focused on composites, blends and copolymer formations of several conjugated polyheterocyclics, polythiophene and its derivatives, especially PEIX)T. In one example, poly(3,4-ethylenedioxythiophene) (PEDOT)/poly(2-acrylamido-2-methyl-l-propanesulfonate) (PAMPS) composite films were prepared by Sonmez et al. for alternative electrochromic applications [50]. Thin composite films comprised of PEDOT/PAMPS were reported to switch rapidly between oxidized and neufial states, in less than 0.4 s, with an initial optical contrast of 76% at A.max. 615 nm. Nanostructured blends of electrochromic polymers such as polypyrrole and poly(3,4-ethylenedioxythiophene) were developed via self-assembly by Inganas etal. for application as an electrochromic window [26]. Uniir etal. developed a graft-type electrochromic copolymer of polythiophene and polytetrahydrofuran for use in elecfiochromic devices [51]. Two EDOT-based copolymers, poly[(3,4-ethylenedioxythiophene)-aZ/-(2,5-dioctyloxyphenylene)] and poly[(3,4-ethylenedioxythiophene)-aft-(9,9 -dioctylfluorene)] were developed by Aubert et al. as other candidates for electrochromic device development [52],... 

Due to the length of the alkoxy and alkyl substituents, substituted polythiophenes, such as poly(4,4 -dimethoxy-3 -methyl-2,2 5, 2 -terthiophene) (PDMTT) and poly(4,4 -dipentoxy-3 -dodecyl-2,2 5, 2 -terthiophene) (PDDTT), differ in their spectroelectrochemical and photoelectrochemical properties [56]. It was demonstrated that the maximum absorption wavelength of poly 3-[12-(jt -methoxyphenoxy) alkyljthiophene] also depends on the alkyl chain length of the substituted monomer [15],... 

Example 10 Polythiophene-Carboxylic Acid - Synthesis of Water-Soluble 2,5-Poly(thiophene-3-propionic Acid) and Poly(3-thiophene Methyl Acetate) (P3TMA)... 

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