Thiophene homopolymers

Light-Emitting Thiophene Homopolymers 2.4.2.1 Polythiophenes as Red-Light Emitters... 

Sotzing [2] prepared intrinsically conducting water-borne dispersions of poly (thieno[3,4-b]thiophene) homopolymer, (II), and copolymers of thieno[3,4-b] thiophene and 3,4-ethylenedioxythiophene, (111), for electroactive applications including electrochromic displays, optically transparent electrodes, and antistatic coatings. 

Huang s group has systematically studied the structure-property relationships of fluorene-thiophene-based conjugated polymers 57-60 [95, 96], In contrast to poly thiophene homopolymers, the regiochemistry of substitution in bithiophene fragments in the studied copolymers shows little effect on the optical bandgap (59 and 60, respectively Eg = 2.49 and 2.58 eV [96] or 2.57 and 2.60 eV [97, 98]) or the emission maxima, but the head-to-head copolymer 60 was significantly more thermally stable. 

A very efficient green-emitting fluorene copolymer 304 was synthesized by Shim and coworkers [390] via Suzuki coupling of dibromothieno[3,2-b]thiophene with dialkylfluorene-diboronic acid [390]. The authors compared the EL properties of this copolymer with PFO homopolymer 196 and PFO-bithiophene copolymer 295. Both the absorption and emission spectra of 304 are red-shifted compared with PFO 196 but slightly blue-shifted compared to bithiophene-based copolymer 295. PLEDs fabricated in the configuration ITO/ PEDOT/304/LiF/Al showed a pure green emission (CIE . v 0.29, r 0.63) close to the... 

Dithiyl radicals seem to be especially attractive because they can form extended homopolymer films. If one uses a simple compound that is capable of forming dithiyl radical, then that can open a way for formulation of a lubrication composition. For example, a poly(disulfide) was obtained as a result of a two-electron transfer to 2,5-di(thiocyanato)thiophene (Scheme 8.16) (Todres et al. 1979, Todres 1991). 

Because of the problems associated with copolymerizations of monomers of very different reactivity, many authors have looked at an alternative approach which is to synthesise appropriate sections of the desired polymer chain, then couple them electrochemically to get the final polymer. Naitoh et al.199) synthesised the dimer, 2,2 -thienylpyrrole and used this as a monomer to prepare the alternating pyrrole-thiophene copolymer. They claimed that the copolymer film obtained with HSO as the counter-ion is more conductive than either of the corresponding homopolymers by a factor of 10 to 20. McLeod et al. 200) synthesised 2,5-dithienylpyrrole and polymerized it electrochemically with silver p-toluenesulphonate as the electrolyte. They obtained films of polymer whose conductivity could be varied in the range 10 8 to 0.1 Scm-1. Surprisingly, some low conductivity films were soluble in acetone or acetonitrile and evaporation of the solvent gave a powder of similar conductivity. Based on the shift in the absorption maximum in the visible spectrum on polymerization, it was concluded that the soluble films were polymers with molecular weights of 4000. 

A combination of electron-rich thiophene units with relatively electron-deficient fluorene units should modify the bandgap of the material (and thus tune the emission) and improve the charge injection/transport balance compared to fluorene homopolymers. 

The main aim for FCC gasoline desulfurization is to remove thiophenic sulfur compounds. Membranes made from polar polymers with solubility parameter close to thiophenic sulfur are used for desulfurization of gasolines by PV It is evident that solubility parameter of primary sulfur components of gasolines, that is, thiophenic sulfur components, is 19-21 (J/cm )", while for other hydrocarbons, these values are 14-15 (J/cm )". This difference can be exploited for separation by PV. Solubility parameter values of most of the polymers used as membrane material lie in the range of 21-26 (J/cm )". Thus, membranes made from these polymers afford good selectivity for thiophenic sulfur. Apart from various homopolymers, chemically and physically modified polymers have also been used for per-vaporative desulfurization. Some of these modifications include using different types and amounts of cross-linkers, blending two polymers, and copolymerization. Composite and treated ionic membranes have also been tried for this separation. Polymer membranes tried for this separation include PDMS/PAN, PDMS/PEI, PDMS/PES, PDMS/ ceramic, polyetherimine (PI)/polyester, PEG/PES, and PU/PTEE. ... 

A copolymer of pyrrole and thiophene nano-fibrUs was electrochemically polymerized within the pores of microporous, anodic, aluminum oxide template membranes [105]. The copolymer nucleated and grew on the pore wall of the membrane since the polymers were cationic and the membrane had anionic sites on the pore wall. The length, thickness, and diameter of the copolymer nanofibrils could be controlled and with higher applied potential, more thiophene units were incorporated into the copolymer nanofibrUs [105]. Copolymer nanofibrils of pyrrole and aniline were also electrochemically polymerized within the pores of microporous, anodic, aluminum oxide template membranes [106]. Copolymer nanofibrils of PPy and poly(3-methylthiophene) prepared chemically in the microporous aluminum oxide template showed higher conductivity than the homopolymers did [107]. 

The combination of the repeat unit species typically used in electrochromic homopolymers such as the thiophene, furan, pyrrole, dioxythiophene and dioxypyrrole rings with one another and with other conjugated linkages (e.g., vinylenes, phenylenes, fluorenes, and carbazoles) provides color control through both the electronic character of the backbone and by steric interactions between repeat units (Table 20.6). 

Figure 9.14 shows band structures of homopolymers of pyrrole, thiophene and their derivatives. From this figure, type I and II heterostructure fabrication with organic conducting polymers are suggested for example, the type I heterostructure can be fabricated with polypyrrole and polythiophene and type II can be fabricated with polypyrrole and polyiso-thianaphthene (Figure 9.15). Recently, the photopolymerization of iso-thianaphthene has been reported [39]. By the combination of electropolymerization and photopolymerization, better heterostructures than those obtainable from electrocopolymerization are suggested.

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