Synthesis and Properties of Polythiophenes

Polythiophenes (PTh s) (1 shown subsequently) have much in common with polypyrroles. They are formed from a cyclepenta-diene molecule, but which has an S heteroatom. Thiophene is oxidized to form a conducting electroactive polymer (CEP), with the greatest conductivity obtained from a-a linkages. There are some important differences between polythiophenes and polypyrroles, and these are discussed here. 

Polythiophene 1 can be synthesized either electrochemically or chemically using a 

This is particularly important because the development of systems utilizing thiophene have been thwarted by the polythiophene paradox. 2 It has been clearly shown that at potentials required to oxidize the thiophene monomer, the polymer itself becomes overoxidized. This overoxidation process proceeds according to Equation 6.2,3 and results in deterioration in the chemical and physical properties of the polymer. 

Therefore, if using constant-current or constant-potential polymerization, the product obtained will be a mixture of poly thiophene and overoxidized polythiophene. 

Various substituted thiophenes have been produced, the most common being 3-alkyl thiophenes. Sato and coworkers4 carried out a comprehensive study using thiophene (Th 2), 3-methylthiophene (MTh 3), and 3-ethylthiophene (ETh 4). 

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E. Zhou, J. Hon, C. Yang and Y. Li. Synthesis and properties of polythiophenes with conjugated side-chains containing carbon-carbon double and triple bonds. J. Polym. ScL, Part A Polym. Chem. 44(7), 2206-2214 (2006). 

Figure 12.1 Polarizing optical micrographs of PCBT (a) before and (b) after magnetically forced alignment. From I. Osaka, H. Goto, K. Itoh, K. Akagi, Synthesis and properties of polythiophene and polythienylenevinylene derivatives with liquid crystallinity, Mol. Cryst. Liq. Cryst, 365, 339 346 (2001), reprinted by permission of the publisher (Taylor Francis Ltd, http //www.tandfco.uk/journals)...

R. Toyoshima, M. Narita, K. Akagi, H. Shirakawa, Synthesis and properties of polythiophene derivatives with liquid crystalline substituents, Synth. Met., 69, 289-290 (1995). 

N. Koide, H. lida. Synthesis and properties of polythiophene containing mesogenic group at 3-position of thiophene ring. Mol. Cryst. Liq. Cryst., 261, 427-436 (1995). 

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