3-methylthiophene/3-butylthiophene copolymers

Figure 11.13. Chemical structure of 3-methylthiophene/3-butylthiophene copolymer.

Closer reading of the published work, reveals that the polymers are not wholly soluble and that the extent of solubility is dependent on the solvent265). In the case of a butylthiophene-methylthiophene copolymer, hot THF solubilizes a fraction of low molecular weight which forms brittle films, while hot xylene extracts a higher molecular weight polymer which forms tough films. There remains an insoluble, and presumably cross-linked residue. The microstructure of the polymer is presumably quite dependent on the polymerization method and conditions. 

Elsenbaumer et aL 598> recently made a comparative study of stability of doped conducting polymers in air. They concluded that a combination of a stable polymer with a non-reactive dopant, such as butylthiophene-methylthiophene copolymer doped with FeClg, could give almost indefinite stability in air with an effective ceiling of 50 °C. 

A regiorandom copolymer of 3-methylthiophene and 3-butylthiophene possessed a conductivity of 50 S/cm, while a more regioregular copolymer with a 2 1 ratio of HT to HH couplings had a higher conductivity of 140 S/cm. Films of regioregular poly[3-(4-octylphenyl)thiophene] (POPT) with greater than 94% HT content possessed conductivities of 4 S/cm compared to 0.4 S/cm for regioirregular POPT. 

Reviewed below are random copolymerizations of thiophene, 3-methylthiophene, 3-butylthiophene, 3-hexylthiophene and 3-octylthiophene. The structure of polythiophene random copolymers is reviewed in Chapter 15 in a more comprehensive way. 

The conductivity of poly(3-butylthiophene) prepared electrochemically in PC containing Et4NPp6 is 110 S cm [42-4] and 40 S cm in nitrobenzene containing BU4NCIO4 [45-6]. In a significant and innovative contribution, researchers [46, 47] at Allied-Signal prepared copolymers of 3-methylthiophene and 3-butylthiophene (1 1) that are highly conductive, environmentally stable and solution-processable. The conductivity of a pellet of polymer doped with iodine is... 

Electrical conductivity of the iodine-doped copolymer prepared via the first route is 10 S cm and l Scm for the copolymer prepared by the second route. The conductivity of the 10 1 (3-MT/ MMA) copolymer after iodine doping is 0.2 S cm , indicating that conductivity increases with increasing concentration of thiophene units. Quantitative data on the solubility of doped poly(3-butylthiophene) and poly(3-methylthiophene-co-3-butylthiophene) are... 

Methylthiophene and 3-butylthiophene can be electrocopolymerized with 3-thienylacetic acid and its methyl ester [108-110] (cf. Table 8). The COOH group is covalently bound to the copolymer structure the carboxylic group does not take part in the electrochemical reaction. 

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